GCC 8.2 Manual

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Using the GNU Compiler Collection
For gcc version 8.2.0
(GCC)

Richard M. Stallman and the GCC Developer Community

Published by:
GNU Press
a division of the
Free Software Foundation
51 Franklin Street, Fifth Floor
Boston, MA 02110-1301 USA

Website: http://www.gnupress.org
General: press@gnu.org
Orders: sales@gnu.org
Tel 617-542-5942
Fax 617-542-2652

Last printed October 2003 for GCC 3.3.1.
Printed copies are available for $45 each.
Copyright c 1988-2018 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of
the GNU Free Documentation License, Version 1.3 or any later version published by the
Free Software Foundation; with the Invariant Sections being “Funding Free Software”, the
Front-Cover Texts being (a) (see below), and with the Back-Cover Texts being (b) (see
below). A copy of the license is included in the section entitled “GNU Free Documentation
License”.
(a) The FSF’s Front-Cover Text is:
A GNU Manual
(b) The FSF’s Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU software. Copies
published by the Free Software Foundation raise funds for GNU development.

i

Short Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1 Programming Languages Supported by GCC . . . . . . . . . . . . . . . 3
2 Language Standards Supported by GCC . . . . . . . . . . . . . . . . . . 5
3 GCC Command Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4 C Implementation-Defined Behavior . . . . . . . . . . . . . . . . . . . . 429
5 C++ Implementation-Defined Behavior . . . . . . . . . . . . . . . . . 437
6 Extensions to the C Language Family . . . . . . . . . . . . . . . . . . . 439
7 Extensions to the C++ Language . . . . . . . . . . . . . . . . . . . . . . 787
8 GNU Objective-C Features . . . . . . . . . . . . . . . . . . . . . . . . . . . 801
9 Binary Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817
10 gcov—a Test Coverage Program . . . . . . . . . . . . . . . . . . . . . . . 821
11 gcov-tool—an Offline Gcda Profile Processing Tool . . . . . . . 833
12 gcov-dump—an Offline Gcda and Gcno Profile Dump Tool . . 837
13 Known Causes of Trouble with GCC . . . . . . . . . . . . . . . . . . . . 839
14 Reporting Bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
15 How To Get Help with GCC . . . . . . . . . . . . . . . . . . . . . . . . . . 857
16 Contributing to GCC Development . . . . . . . . . . . . . . . . . . . . . 859
Funding Free Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
The GNU Project and GNU/Linux . . . . . . . . . . . . . . . . . . . . . . . . . 863
GNU General Public License . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865
GNU Free Documentation License . . . . . . . . . . . . . . . . . . . . . . . . . 877
Contributors to GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885
Option Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903
Keyword Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 927

iii

Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1

Programming Languages Supported by GCC
................................................. 3

2

Language Standards Supported by GCC . . . . . 5
2.1
2.2
2.3
2.4
2.5
2.6

3

C Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C++ Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Objective-C and Objective-C++ Languages . . . . . . . . . . . . . . . . . . . .
Go Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HSA Intermediate Language (HSAIL) . . . . . . . . . . . . . . . . . . . . . . . . . .
References for Other Languages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5
6
7
8
8
8

GCC Command Options . . . . . . . . . . . . . . . . . . . . . . . 9
3.1 Option Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 Options Controlling the Kind of Output . . . . . . . . . . . . . . . . . . . . . . . 29
3.3 Compiling C++ Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4 Options Controlling C Dialect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.5 Options Controlling C++ Dialect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.6 Options Controlling Objective-C and Objective-C++ Dialects . . 55
3.7 Options to Control Diagnostic Messages Formatting . . . . . . . . . . . 59
3.8 Options to Request or Suppress Warnings . . . . . . . . . . . . . . . . . . . . . 62
3.9 Options for Debugging Your Program . . . . . . . . . . . . . . . . . . . . . . . . 108
3.10 Options That Control Optimization . . . . . . . . . . . . . . . . . . . . . . . . . 114
3.11 Program Instrumentation Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
3.12 Options Controlling the Preprocessor. . . . . . . . . . . . . . . . . . . . . . . . 187
3.13 Passing Options to the Assembler . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
3.14 Options for Linking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
3.15 Options for Directory Search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
3.16 Options for Code Generation Conventions . . . . . . . . . . . . . . . . . . . 202
3.17 GCC Developer Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
3.18 Machine-Dependent Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
3.18.1 AArch64 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
3.18.1.1 ‘-march’ and ‘-mcpu’ Feature Modifiers . . . . . . . . . . . . 232
3.18.2 Adapteva Epiphany Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
3.18.3 ARC Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
3.18.4 ARM Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
3.18.5 AVR Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
3.18.5.1 EIND and Devices with More Than 128 Ki Bytes of
Flash. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
3.18.5.2 Handling of the RAMPD, RAMPX, RAMPY and RAMPZ Special
Function Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

iv

Using the GNU Compiler Collection (GCC)
3.18.5.3 AVR Built-in Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.6 Blackfin Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.7 C6X Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.8 CRIS Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.9 CR16 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.10 Darwin Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.11 DEC Alpha Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.12 FR30 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.13 FT32 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.14 FRV Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.15 GNU/Linux Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.16 H8/300 Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.17 HPPA Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.18 IA-64 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.19 LM32 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.20 M32C Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.21 M32R/D Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.22 M680x0 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.23 MCore Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.24 MeP Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.25 MicroBlaze Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.26 MIPS Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.27 MMIX Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.28 MN10300 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.29 Moxie Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.30 MSP430 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.31 NDS32 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.32 Nios II Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.33 Nvidia PTX Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.34 PDP-11 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.35 picoChip Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.36 PowerPC Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.37 PowerPC SPE Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.38 RISC-V Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.39 RL78 Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.40 IBM RS/6000 and PowerPC Options . . . . . . . . . . . . . . . . . .
3.18.41 RX Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.42 S/390 and zSeries Options . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.43 Score Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.44 SH Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.45 Solaris 2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.46 SPARC Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.47 SPU Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.48 Options for System V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.49 TILE-Gx Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.50 TILEPro Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.51 V850 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.52 VAX Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

264
267
270
270
272
272
276
280
281
281
285
285
286
289
292
293
293
295
300
301
302
304
318
319
320
320
322
323
328
329
330
331
331
342
344
345
361
364
368
369
375
375
381
383
384
384
384
387

v
3.18.53 Visium Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.54 VMS Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.55 VxWorks Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.56 x86 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.57 x86 Windows Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.58 Xstormy16 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.59 Xtensa Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.18.60 zSeries Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.19 Specifying Subprocesses and the Switches to Pass to Them . .
3.20 Environment Variables Affecting GCC . . . . . . . . . . . . . . . . . . . . . .
3.21 Using Precompiled Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

C Implementation-Defined Behavior . . . . . . . 429
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
4.13
4.14
4.15
4.16

5

Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Integers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Arrays and Pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Structures, Unions, Enumerations, and Bit-Fields . . . . . . . . . . . . .
Qualifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Declarators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Preprocessing Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Library Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Locale-Specific Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

429
429
429
430
431
431
432
433
433
434
435
435
435
436
436
436

C++ Implementation-Defined Behavior . . . 437
5.1
5.2

6

387
388
388
389
412
413
413
415
415
422
425

Conditionally-Supported Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437

Extensions to the C Language Family . . . . . . 439
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10
6.11
6.12

Statements and Declarations in Expressions . . . . . . . . . . . . . . . . . .
Locally Declared Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Labels as Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nested Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Constructing Function Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Referring to a Type with typeof . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conditionals with Omitted Operands . . . . . . . . . . . . . . . . . . . . . . . . .
128-bit Integers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Double-Word Integers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Complex Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Additional Floating Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Half-Precision Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

439
440
441
442
444
446
447
448
448
448
449
450

vi

Using the GNU Compiler Collection (GCC)
6.13 Decimal Floating Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.14 Hex Floats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.15 Fixed-Point Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.16 Named Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.16.1 AVR Named Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.16.2 M32C Named Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . .
6.16.3 RL78 Named Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.16.4 SPU Named Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.16.5 x86 Named Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.17 Arrays of Length Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.18 Structures with No Members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.19 Arrays of Variable Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.20 Macros with a Variable Number of Arguments. . . . . . . . . . . . . . .
6.21 Slightly Looser Rules for Escaped Newlines . . . . . . . . . . . . . . . . . .
6.22 Non-Lvalue Arrays May Have Subscripts . . . . . . . . . . . . . . . . . . . .
6.23 Arithmetic on void- and Function-Pointers . . . . . . . . . . . . . . . . . .
6.24 Pointers to Arrays with Qualifiers Work as Expected . . . . . . . .
6.25 Non-Constant Initializers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.26 Compound Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.27 Designated Initializers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.28 Case Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.29 Cast to a Union Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.30 Mixed Declarations and Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31 Declaring Attributes of Functions . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.1 Common Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.2 AArch64 Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.2.1 Inlining rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.3 ARC Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.4 ARM Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.5 AVR Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.6 Blackfin Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.7 CR16 Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.8 Epiphany Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.9 H8/300 Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.10 IA-64 Function Attributes. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.11 M32C Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.12 M32R/D Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.13 m68k Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.14 MCORE Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.15 MeP Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.16 MicroBlaze Function Attributes . . . . . . . . . . . . . . . . . . . . . . .
6.31.17 Microsoft Windows Function Attributes . . . . . . . . . . . . . . .
6.31.18 MIPS Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.19 MSP430 Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.20 NDS32 Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.21 Nios II Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.22 Nvidia PTX Function Attributes . . . . . . . . . . . . . . . . . . . . . .
6.31.23 PowerPC Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . .

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481
483
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vii
6.31.24 RISC-V Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.25 RL78 Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.26 RX Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.27 S/390 Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.28 SH Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.29 SPU Function Attributes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.30 Symbian OS Function Attributes . . . . . . . . . . . . . . . . . . . . . .
6.31.31 V850 Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.32 Visium Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.33 x86 Function Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.31.34 Xstormy16 Function Attributes . . . . . . . . . . . . . . . . . . . . . . .
6.32 Specifying Attributes of Variables . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.1 Common Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.2 ARC Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.3 AVR Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.4 Blackfin Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.5 H8/300 Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.6 IA-64 Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.7 M32R/D Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.8 MeP Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.9 Microsoft Windows Variable Attributes . . . . . . . . . . . . . . . . .
6.32.10 MSP430 Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.11 Nvidia PTX Variable Attributes . . . . . . . . . . . . . . . . . . . . . .
6.32.12 PowerPC Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.13 RL78 Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.14 SPU Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.15 V850 Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.16 x86 Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.32.17 Xstormy16 Variable Attributes . . . . . . . . . . . . . . . . . . . . . . . .
6.33 Specifying Attributes of Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.33.1 Common Type Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.33.2 ARC Type Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.33.3 ARM Type Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.33.4 MeP Type Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.33.5 PowerPC Type Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.33.6 SPU Type Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.33.7 x86 Type Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.34 Label Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.35 Enumerator Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.36 Statement Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.37 Attribute Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.38 Prototypes and Old-Style Function Definitions . . . . . . . . . . . . . .
6.39 C++ Style Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.40 Dollar Signs in Identifier Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.41 The Character ESC in Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.42 Inquiring on Alignment of Types or Variables . . . . . . . . . . . . . . .
6.43 An Inline Function is As Fast As a Macro . . . . . . . . . . . . . . . . . . .
6.44 When is a Volatile Object Accessed? . . . . . . . . . . . . . . . . . . . . . . . .

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viii

Using the GNU Compiler Collection (GCC)
6.45 How to Use Inline Assembly Language in C Code . . . . . . . . . . . 541
6.45.1 Basic Asm — Assembler Instructions Without Operands
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
6.45.2 Extended Asm - Assembler Instructions with C Expression
Operands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543
6.45.2.1 Volatile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
6.45.2.2 Assembler Template . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547
6.45.2.3 Output Operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548
6.45.2.4 Flag Output Operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
6.45.2.5 Input Operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
6.45.2.6 Clobbers and Scratch Registers . . . . . . . . . . . . . . . . . . . . 553
6.45.2.7 Goto Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556
6.45.2.8 x86 Operand Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 557
6.45.2.9 x86 Floating-Point asm Operands . . . . . . . . . . . . . . . . . . 558
6.45.3 Constraints for asm Operands . . . . . . . . . . . . . . . . . . . . . . . . . . 559
6.45.3.1 Simple Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
6.45.3.2 Multiple Alternative Constraints . . . . . . . . . . . . . . . . . . 562
6.45.3.3 Constraint Modifier Characters . . . . . . . . . . . . . . . . . . . . 562
6.45.3.4 Constraints for Particular Machines . . . . . . . . . . . . . . . 563
6.45.4 Controlling Names Used in Assembler Code . . . . . . . . . . . . 592
6.45.5 Variables in Specified Registers . . . . . . . . . . . . . . . . . . . . . . . . . 592
6.45.5.1 Defining Global Register Variables . . . . . . . . . . . . . . . . . 593
6.45.5.2 Specifying Registers for Local Variables. . . . . . . . . . . . 594
6.45.6 Size of an asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595
6.46 Alternate Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595
6.47 Incomplete enum Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596
6.48 Function Names as Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596
6.49 Getting the Return or Frame Address of a Function . . . . . . . . . 597
6.50 Using Vector Instructions through Built-in Functions . . . . . . . . 598
6.51 Support for offsetof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600
6.52 Legacy __sync Built-in Functions for Atomic Memory Access
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601
6.53 Built-in Functions for Memory Model Aware Atomic Operations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603
6.54 Built-in Functions to Perform Arithmetic with Overflow Checking
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607
6.55 x86-Specific Memory Model Extensions for Transactional Memory
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609
6.56 Object Size Checking Built-in Functions . . . . . . . . . . . . . . . . . . . . . 609
6.57 Pointer Bounds Checker Built-in Functions . . . . . . . . . . . . . . . . . . 611
6.58 Other Built-in Functions Provided by GCC . . . . . . . . . . . . . . . . . 613
6.59 Built-in Functions Specific to Particular Target Machines . . . . 626
6.59.1 AArch64 Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626
6.59.2 Alpha Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
6.59.3 Altera Nios II Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . 628
6.59.4 ARC Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 630
6.59.5 ARC SIMD Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . 632
6.59.6 ARM iWMMXt Built-in Functions . . . . . . . . . . . . . . . . . . . . . 636

ix
6.59.7 ARM C Language Extensions (ACLE) . . . . . . . . . . . . . . . . .
6.59.8 ARM Floating Point Status and Control Intrinsics . . . . . .
6.59.9 ARM ARMv8-M Security Extensions . . . . . . . . . . . . . . . . . . .
6.59.10 AVR Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.11 Blackfin Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.12 FR-V Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.12.1 Argument Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.12.2 Directly-Mapped Integer Functions . . . . . . . . . . . . . . .
6.59.12.3 Directly-Mapped Media Functions . . . . . . . . . . . . . . . .
6.59.12.4 Raw Read/Write Functions . . . . . . . . . . . . . . . . . . . . . .
6.59.12.5 Other Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.13 MIPS DSP Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.14 MIPS Paired-Single Support . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.15 MIPS Loongson Built-in Functions . . . . . . . . . . . . . . . . . . . .
6.59.15.1 Paired-Single Arithmetic . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.15.2 Paired-Single Built-in Functions . . . . . . . . . . . . . . . . . .
6.59.15.3 MIPS-3D Built-in Functions . . . . . . . . . . . . . . . . . . . . . .
6.59.16 MIPS SIMD Architecture (MSA) Support . . . . . . . . . . . . .
6.59.16.1 MIPS SIMD Architecture Built-in Functions . . . . . .
6.59.17 Other MIPS Built-in Functions. . . . . . . . . . . . . . . . . . . . . . . .
6.59.18 MSP430 Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.19 NDS32 Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.20 picoChip Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.21 PowerPC Built-in Functions. . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.22 PowerPC AltiVec Built-in Functions. . . . . . . . . . . . . . . . . . .
6.59.23 PowerPC Hardware Transactional Memory Built-in
Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.23.1 PowerPC HTM Low Level Built-in Functions . . . . .
6.59.23.2 PowerPC HTM High Level Inline Functions . . . . . .
6.59.24 PowerPC Atomic Memory Operation Functions . . . . . . .
6.59.25 RX Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.26 S/390 System z Built-in Functions . . . . . . . . . . . . . . . . . . . .
6.59.27 SH Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.28 SPARC VIS Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . .
6.59.29 SPU Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.30 TI C6X Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.31 TILE-Gx Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.32 TILEPro Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.33 x86 Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.59.34 x86 Transactional Memory Intrinsics . . . . . . . . . . . . . . . . . .
6.59.35 x86 Control-Flow Protection Intrinsics . . . . . . . . . . . . . . . .
6.60 Format Checks Specific to Particular Target Machines . . . . . . .
6.60.1 Solaris Format Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.60.2 Darwin Format Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61 Pragmas Accepted by GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.1 AArch64 Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.2 ARM Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.3 M32C Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

638
639
639
639
640
641
641
641
642
644
644
644
649
649
651
652
653
655
656
669
669
669
670
670
682
734
734
737
738
739
740
742
743
746
747
747
748
748
771
772
773
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x

Using the GNU Compiler Collection (GCC)
6.61.4 MeP Pragmas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.5 RS/6000 and PowerPC Pragmas . . . . . . . . . . . . . . . . . . . . . . .
6.61.6 S/390 Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.7 Darwin Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.8 Solaris Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.9 Symbol-Renaming Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.10 Structure-Layout Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.11 Weak Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.12 Diagnostic Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.13 Visibility Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.14 Push/Pop Macro Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.61.15 Function Specific Option Pragmas. . . . . . . . . . . . . . . . . . . . .
6.61.16 Loop-Specific Pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.62 Unnamed Structure and Union Fields . . . . . . . . . . . . . . . . . . . . . . .
6.63 Thread-Local Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.63.1 ISO/IEC 9899:1999 Edits for Thread-Local Storage . . . . .
6.63.2 ISO/IEC 14882:1998 Edits for Thread-Local Storage . . . .
6.64 Binary Constants using the ‘0b’ Prefix . . . . . . . . . . . . . . . . . . . . . .

7

774
775
775
775
776
776
777
778
778
779
779
780
780
781
782
782
783
785

Extensions to the C++ Language . . . . . . . . . . 787
7.1
7.2
7.3
7.4
7.5
7.6

When is a Volatile C++ Object Accessed? . . . . . . . . . . . . . . . . . . . 787
Restricting Pointer Aliasing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
Vague Linkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
C++ Interface and Implementation Pragmas . . . . . . . . . . . . . . . . . 789
Where’s the Template? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 790
Extracting the Function Pointer from a Bound Pointer to Member
Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
7.7 C++-Specific Variable, Function, and Type Attributes . . . . . . . 793
7.8 Function Multiversioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
7.9 Type Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
7.10 C++ Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798
7.11 Deprecated Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798
7.12 Backwards Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799

8

GNU Objective-C Features. . . . . . . . . . . . . . . . . . 801
8.1

GNU Objective-C Runtime API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.1 Modern GNU Objective-C Runtime API. . . . . . . . . . . . . . . . .
8.1.2 Traditional GNU Objective-C Runtime API . . . . . . . . . . . . .
8.2 +load: Executing Code before main . . . . . . . . . . . . . . . . . . . . . . . . . .
8.2.1 What You Can and Cannot Do in +load . . . . . . . . . . . . . . . .
8.3 Type Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.1 Legacy Type Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.2 @encode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.3 Method Signatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4 Garbage Collection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.5 Constant String Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6 compatibility_alias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.7 Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

801
801
802
802
803
804
806
806
807
807
808
809
809

xi
8.8
8.9

Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fast Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.9.1 Using Fast Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.9.2 C99-Like Fast Enumeration Syntax . . . . . . . . . . . . . . . . . . . . . .
8.9.3 Fast Enumeration Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.9.4 Fast Enumeration Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.10 Messaging with the GNU Objective-C Runtime. . . . . . . . . . . . . .
8.10.1 Dynamically Registering Methods . . . . . . . . . . . . . . . . . . . . . .
8.10.2 Forwarding Hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

811
811
811
811
812
813
814
814
814

9

Binary Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 817

10

gcov—a Test Coverage Program . . . . . . . . . . . 821

10.1
10.2
10.3
10.4
10.5

11

Introduction to gcov-tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833
Invoking gcov-tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833

gcov-dump—an Offline Gcda and Gcno Profile
Dump Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837

12.1
12.2

13

821
821
831
832
832

gcov-tool—an Offline Gcda Profile Processing
Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833

11.1
11.2

12

Introduction to gcov . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Invoking gcov . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using gcov with GCC Optimization . . . . . . . . . . . . . . . . . . . . . . . . .
Brief Description of gcov Data Files. . . . . . . . . . . . . . . . . . . . . . . . .
Data File Relocation to Support Cross-Profiling . . . . . . . . . . . . .

Introduction to gcov-dump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
Invoking gcov-dump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837

Known Causes of Trouble with GCC. . . . . . 839

13.1 Actual Bugs We Haven’t Fixed Yet . . . . . . . . . . . . . . . . . . . . . . . . . 839
13.2 Interoperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
13.3 Incompatibilities of GCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
13.4 Fixed Header Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
13.5 Standard Libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
13.6 Disappointments and Misunderstandings . . . . . . . . . . . . . . . . . . . . 845
13.7 Common Misunderstandings with GNU C++ . . . . . . . . . . . . . . . 846
13.7.1 Declare and Define Static Members . . . . . . . . . . . . . . . . . . . . 846
13.7.2 Name Lookup, Templates, and Accessing Members of Base
Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
13.7.3 Temporaries May Vanish Before You Expect. . . . . . . . . . . . 848
13.7.4 Implicit Copy-Assignment for Virtual Bases . . . . . . . . . . . . 849
13.8 Certain Changes We Don’t Want to Make . . . . . . . . . . . . . . . . . . . 850
13.9 Warning Messages and Error Messages . . . . . . . . . . . . . . . . . . . . . . 853

xii

Using the GNU Compiler Collection (GCC)

14

Reporting Bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855

14.1
14.2

Have You Found a Bug? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
How and Where to Report Bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855

15

How To Get Help with GCC . . . . . . . . . . . . . . 857

16

Contributing to GCC Development . . . . . . . 859

Funding Free Software . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
The GNU Project and GNU/Linux . . . . . . . . . . . . 863
GNU General Public License . . . . . . . . . . . . . . . . . . . 865
GNU Free Documentation License . . . . . . . . . . . . . 877
ADDENDUM: How to use this License for your documents . . . . . . . . 884

Contributors to GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885
Option Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903
Keyword Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 927

Introduction

1

Introduction
This manual documents how to use the GNU compilers, as well as their features and incompatibilities, and how to report bugs. It corresponds to the compilers (GCC) version 8.2.0.
The internals of the GNU compilers, including how to port them to new targets and some
information about how to write front ends for new languages, are documented in a separate
manual. See Section “Introduction” in GNU Compiler Collection (GCC) Internals.

Chapter 1: Programming Languages Supported by GCC

3

1 Programming Languages Supported by GCC
GCC stands for “GNU Compiler Collection”. GCC is an integrated distribution of compilers for several major programming languages. These languages currently include C, C++,
Objective-C, Objective-C++, Fortran, Ada, Go, and BRIG (HSAIL).
The abbreviation GCC has multiple meanings in common use. The current official meaning is “GNU Compiler Collection”, which refers generically to the complete suite of tools.
The name historically stood for “GNU C Compiler”, and this usage is still common when
the emphasis is on compiling C programs. Finally, the name is also used when speaking
of the language-independent component of GCC: code shared among the compilers for all
supported languages.
The language-independent component of GCC includes the majority of the optimizers,
as well as the “back ends” that generate machine code for various processors.
The part of a compiler that is specific to a particular language is called the “front end”.
In addition to the front ends that are integrated components of GCC, there are several
other front ends that are maintained separately. These support languages such as Pascal,
Mercury, and COBOL. To use these, they must be built together with GCC proper.
Most of the compilers for languages other than C have their own names. The C++ compiler
is G++, the Ada compiler is GNAT, and so on. When we talk about compiling one of those
languages, we might refer to that compiler by its own name, or as GCC. Either is correct.
Historically, compilers for many languages, including C++ and Fortran, have been implemented as “preprocessors” which emit another high level language such as C. None of
the compilers included in GCC are implemented this way; they all generate machine code
directly. This sort of preprocessor should not be confused with the C preprocessor, which
is an integral feature of the C, C++, Objective-C and Objective-C++ languages.

Chapter 2: Language Standards Supported by GCC

5

2 Language Standards Supported by GCC
For each language compiled by GCC for which there is a standard, GCC attempts to follow
one or more versions of that standard, possibly with some exceptions, and possibly with
some extensions.

2.1 C Language
The original ANSI C standard (X3.159-1989) was ratified in 1989 and published in 1990.
This standard was ratified as an ISO standard (ISO/IEC 9899:1990) later in 1990. There
were no technical differences between these publications, although the sections of the ANSI
standard were renumbered and became clauses in the ISO standard. The ANSI standard,
but not the ISO standard, also came with a Rationale document. This standard, in both
its forms, is commonly known as C89, or occasionally as C90, from the dates of ratification. To select this standard in GCC, use one of the options ‘-ansi’, ‘-std=c90’ or
‘-std=iso9899:1990’; to obtain all the diagnostics required by the standard, you should
also specify ‘-pedantic’ (or ‘-pedantic-errors’ if you want them to be errors rather than
warnings). See Section 3.4 [Options Controlling C Dialect], page 35.
Errors in the 1990 ISO C standard were corrected in two Technical Corrigenda published
in 1994 and 1996. GCC does not support the uncorrected version.
An amendment to the 1990 standard was published in 1995. This amendment added
digraphs and __STDC_VERSION__ to the language, but otherwise concerned the library. This
amendment is commonly known as AMD1; the amended standard is sometimes known as
C94 or C95. To select this standard in GCC, use the option ‘-std=iso9899:199409’ (with,
as for other standard versions, ‘-pedantic’ to receive all required diagnostics).
A new edition of the ISO C standard was published in 1999 as ISO/IEC 9899:1999, and
is commonly known as C99. (While in development, drafts of this standard version were
referred to as C9X.) GCC has substantially complete support for this standard version; see
http://gcc.gnu.org/c99status.html for details. To select this standard, use ‘-std=c99’
or ‘-std=iso9899:1999’.
Errors in the 1999 ISO C standard were corrected in three Technical Corrigenda published
in 2001, 2004 and 2007. GCC does not support the uncorrected version.
A fourth version of the C standard, known as C11, was published in 2011 as ISO/IEC
9899:2011. (While in development, drafts of this standard version were referred to as
C1X.) GCC has substantially complete support for this standard, enabled with ‘-std=c11’
or ‘-std=iso9899:2011’. A version with corrections integrated is known as C17 and is
supported with ‘-std=c17’ or ‘-std=iso9899:2017’; the corrections are also applied with
‘-std=c11’, and the only difference between the options is the value of __STDC_VERSION__.
By default, GCC provides some extensions to the C language that, on rare occasions conflict with the C standard. See Chapter 6 [Extensions to the C Language Family], page 439.
Some features that are part of the C99 standard are accepted as extensions in C90 mode,
and some features that are part of the C11 standard are accepted as extensions in C90 and
C99 modes. Use of the ‘-std’ options listed above disables these extensions where they
conflict with the C standard version selected. You may also select an extended version of
the C language explicitly with ‘-std=gnu90’ (for C90 with GNU extensions), ‘-std=gnu99’
(for C99 with GNU extensions) or ‘-std=gnu11’ (for C11 with GNU extensions).

6

Using the GNU Compiler Collection (GCC)

The default, if no C language dialect options are given, is ‘-std=gnu11’.
The ISO C standard defines (in clause 4) two classes of conforming implementation. A
conforming hosted implementation supports the whole standard including all the library
facilities; a conforming freestanding implementation is only required to provide certain
library facilities: those in , , , and ; since
AMD1, also those in ; since C99, also those in  and ;
and since C11, also those in  and . In addition, complex
types, added in C99, are not required for freestanding implementations.
The standard also defines two environments for programs, a freestanding environment,
required of all implementations and which may not have library facilities beyond those
required of freestanding implementations, where the handling of program startup and termination are implementation-defined; and a hosted environment, which is not required,
in which all the library facilities are provided and startup is through a function int main
(void) or int main (int, char *[]). An OS kernel is an example of a program running
in a freestanding environment; a program using the facilities of an operating system is an
example of a program running in a hosted environment.
GCC aims towards being usable as a conforming freestanding implementation, or as the
compiler for a conforming hosted implementation. By default, it acts as the compiler for a
hosted implementation, defining __STDC_HOSTED__ as 1 and presuming that when the names
of ISO C functions are used, they have the semantics defined in the standard. To make it act
as a conforming freestanding implementation for a freestanding environment, use the option
‘-ffreestanding’; it then defines __STDC_HOSTED__ to 0 and does not make assumptions
about the meanings of function names from the standard library, with exceptions noted
below. To build an OS kernel, you may well still need to make your own arrangements for
linking and startup. See Section 3.4 [Options Controlling C Dialect], page 35.
GCC does not provide the library facilities required only of hosted implementations, nor
yet all the facilities required by C99 of freestanding implementations on all platforms. To
use the facilities of a hosted environment, you need to find them elsewhere (for example, in
the GNU C library). See Section 13.5 [Standard Libraries], page 844.
Most of the compiler support routines used by GCC are present in ‘libgcc’, but there
are a few exceptions. GCC requires the freestanding environment provide memcpy, memmove,
memset and memcmp. Finally, if __builtin_trap is used, and the target does not implement
the trap pattern, then GCC emits a call to abort.
For references to Technical Corrigenda, Rationale documents and information concerning
the history of C that is available online, see http://gcc.gnu.org/readings.html

2.2 C++ Language
GCC supports the original ISO C++ standard published in 1998, and the 2011 and 2014
revisions.
The original ISO C++ standard was published as the ISO standard (ISO/IEC 14882:1998)
and amended by a Technical Corrigenda published in 2003 (ISO/IEC 14882:2003). These
standards are referred to as C++98 and C++03, respectively. GCC implements the majority
of C++98 (export is a notable exception) and most of the changes in C++03. To select
this standard in GCC, use one of the options ‘-ansi’, ‘-std=c++98’, or ‘-std=c++03’; to

Chapter 2: Language Standards Supported by GCC

7

obtain all the diagnostics required by the standard, you should also specify ‘-pedantic’ (or
‘-pedantic-errors’ if you want them to be errors rather than warnings).
A revised ISO C++ standard was published in 2011 as ISO/IEC 14882:2011, and is referred
to as C++11; before its publication it was commonly referred to as C++0x. C++11 contains
several changes to the C++ language, all of which have been implemented in GCC. For
details see https://gcc.gnu.org/projects/cxx-status.html#cxx11. To select this
standard in GCC, use the option ‘-std=c++11’.
Another revised ISO C++ standard was published in 2014 as ISO/IEC 14882:2014, and is
referred to as C++14; before its publication it was sometimes referred to as C++1y. C++14
contains several further changes to the C++ language, all of which have been implemented
in GCC. For details see https://gcc.gnu.org/projects/cxx-status.html#cxx14. To
select this standard in GCC, use the option ‘-std=c++14’.
The C++ language was further revised in 2017 and ISO/IEC 14882:2017 was published.
This is referred to as C++17, and before publication was often referred to as C++1z. GCC
supports all the changes in the new specification. For further details see https://gcc.
gnu.org/projects/cxx-status.html#cxx1z. Use the option ‘-std=c++17’ to select this
variant of C++.
More information about the C++ standards is available on the ISO C++ committee’s web
site at http://www.open-std.org/jtc1/sc22/wg21/.
To obtain all the diagnostics required by any of the standard versions described above
you should specify ‘-pedantic’ or ‘-pedantic-errors’, otherwise GCC will allow some
non-ISO C++ features as extensions. See Section 3.8 [Warning Options], page 62.
By default, GCC also provides some additional extensions to the C++ language that
on rare occasions conflict with the C++ standard. See Section 3.5 [C++ Dialect Options],
page 42. Use of the ‘-std’ options listed above disables these extensions where they they
conflict with the C++ standard version selected. You may also select an extended version
of the C++ language explicitly with ‘-std=gnu++98’ (for C++98 with GNU extensions), or
‘-std=gnu++11’ (for C++11 with GNU extensions), or ‘-std=gnu++14’ (for C++14 with GNU
extensions), or ‘-std=gnu++17’ (for C++17 with GNU extensions).
The default, if no C++ language dialect options are given, is ‘-std=gnu++14’.

2.3 Objective-C and Objective-C++ Languages
GCC supports “traditional” Objective-C (also known as “Objective-C 1.0”) and contains
support for the Objective-C exception and synchronization syntax. It has also support for
a number of “Objective-C 2.0” language extensions, including properties, fast enumeration
(only for Objective-C), method attributes and the @optional and @required keywords in
protocols. GCC supports Objective-C++ and features available in Objective-C are also
available in Objective-C++.
GCC by default uses the GNU Objective-C runtime library, which is part of GCC and
is not the same as the Apple/NeXT Objective-C runtime library used on Apple systems.
There are a number of differences documented in this manual. The options ‘-fgnu-runtime’
and ‘-fnext-runtime’ allow you to switch between producing output that works with the
GNU Objective-C runtime library and output that works with the Apple/NeXT ObjectiveC runtime library.

8

Using the GNU Compiler Collection (GCC)

There is no formal written standard for Objective-C or Objective-C++. The authoritative manual on traditional Objective-C (1.0) is “Object-Oriented Programming and
the Objective-C Language”: http: / / www . gnustep . org / resources / documentation /
ObjectivCBook.pdf is the original NeXTstep document.
The Objective-C exception and synchronization syntax (that is, the keywords @try,
@throw, @catch, @finally and @synchronized) is supported by GCC and is enabled with
the option ‘-fobjc-exceptions’. The syntax is briefly documented in this manual and in
the Objective-C 2.0 manuals from Apple.
The Objective-C 2.0 language extensions and features are automatically enabled;
they include properties (via the @property, @synthesize and @dynamic keywords),
fast enumeration (not available in Objective-C++), attributes for methods (such as
deprecated, noreturn, sentinel, format), the unused attribute for method arguments,
the @package keyword for instance variables and the @optional and @required keywords
in protocols. You can disable all these Objective-C 2.0 language extensions with the
option ‘-fobjc-std=objc1’, which causes the compiler to recognize the same Objective-C
language syntax recognized by GCC 4.0, and to produce an error if one of the new features
is used.
GCC has currently no support for non-fragile instance variables.
The authoritative manual on Objective-C 2.0 is available from Apple:
• https: / / developer . apple . com / library / content / documentation / Cocoa /
Conceptual/ProgrammingWithObjectiveC/Introduction/Introduction.html
For more information concerning the history of Objective-C that is available online, see
http://gcc.gnu.org/readings.html

2.4 Go Language
As of the GCC 4.7.1 release, GCC supports the Go 1 language standard, described at
https://golang.org/doc/go1.

2.5 HSA Intermediate Language (HSAIL)
GCC can compile the binary representation (BRIG) of the HSAIL text format as described
in HSA Programmer’s Reference Manual version 1.0.1. This capability is typically utilized to
implement the HSA runtime API’s HSAIL finalization extension for a gcc supported processor. HSA standards are freely available at http://www.hsafoundation.com/standards/
.

2.6 References for Other Languages
See Section “About This Guide” in GNAT Reference Manual, for information on standard
conformance and compatibility of the Ada compiler.
See Section “Standards” in The GNU Fortran Compiler, for details of standards supported by GNU Fortran.

Chapter 3: GCC Command Options

9

3 GCC Command Options
When you invoke GCC, it normally does preprocessing, compilation, assembly and linking.
The “overall options” allow you to stop this process at an intermediate stage. For example,
the ‘-c’ option says not to run the linker. Then the output consists of object files output
by the assembler. See Section 3.2 [Options Controlling the Kind of Output], page 29.
Other options are passed on to one or more stages of processing. Some options control
the preprocessor and others the compiler itself. Yet other options control the assembler and
linker; most of these are not documented here, since you rarely need to use any of them.
Most of the command-line options that you can use with GCC are useful for C programs;
when an option is only useful with another language (usually C++), the explanation says
so explicitly. If the description for a particular option does not mention a source language,
you can use that option with all supported languages.
The usual way to run GCC is to run the executable called gcc, or machine-gcc when
cross-compiling, or machine-gcc-version to run a specific version of GCC. When you
compile C++ programs, you should invoke GCC as g++ instead. See Section 3.3 [Compiling
C++ Programs], page 34, for information about the differences in behavior between gcc and
g++ when compiling C++ programs.
The gcc program accepts options and file names as operands. Many options have multiletter names; therefore multiple single-letter options may not be grouped: ‘-dv’ is very
different from ‘-d -v’.
You can mix options and other arguments. For the most part, the order you use doesn’t
matter. Order does matter when you use several options of the same kind; for example, if
you specify ‘-L’ more than once, the directories are searched in the order specified. Also,
the placement of the ‘-l’ option is significant.
Many options have long names starting with ‘-f’ or with ‘-W’—for example,
‘-fmove-loop-invariants’, ‘-Wformat’ and so on. Most of these have both positive and
negative forms; the negative form of ‘-ffoo’ is ‘-fno-foo’. This manual documents only
one of these two forms, whichever one is not the default.
See [Option Index], page 903, for an index to GCC’s options.

3.1 Option Summary
Here is a summary of all the options, grouped by type. Explanations are in the following
sections.
Overall Options
See Section 3.2 [Options Controlling the Kind of Output], page 29.
-c -S -E -o file -x language
-v -### --help[=class[,...]] --target-help --version
-pass-exit-codes -pipe -specs=file -wrapper
@file -ffile-prefix-map=old=new
-fplugin=file -fplugin-arg-name=arg
-fdump-ada-spec[-slim] -fada-spec-parent=unit -fdump-go-spec=file

C Language Options
See Section 3.4 [Options Controlling C Dialect], page 35.

10

Using the GNU Compiler Collection (GCC)

-ansi -std=standard -fgnu89-inline
-fpermitted-flt-eval-methods=standard
-aux-info filename -fallow-parameterless-variadic-functions
-fno-asm -fno-builtin -fno-builtin-function -fgimple
-fhosted -ffreestanding -fopenacc -fopenmp -fopenmp-simd
-fms-extensions -fplan9-extensions -fsso-struct=endianness
-fallow-single-precision -fcond-mismatch -flax-vector-conversions
-fsigned-bitfields -fsigned-char
-funsigned-bitfields -funsigned-char

C++ Language Options
See Section 3.5 [Options Controlling C++ Dialect], page 42.
-fabi-version=n -fno-access-control
-faligned-new=n -fargs-in-order=n -fcheck-new
-fconstexpr-depth=n -fconstexpr-loop-limit=n
-ffriend-injection
-fno-elide-constructors
-fno-enforce-eh-specs
-ffor-scope -fno-for-scope -fno-gnu-keywords
-fno-implicit-templates
-fno-implicit-inline-templates
-fno-implement-inlines -fms-extensions
-fnew-inheriting-ctors
-fnew-ttp-matching
-fno-nonansi-builtins -fnothrow-opt -fno-operator-names
-fno-optional-diags -fpermissive
-fno-pretty-templates
-frepo -fno-rtti -fsized-deallocation
-ftemplate-backtrace-limit=n
-ftemplate-depth=n
-fno-threadsafe-statics -fuse-cxa-atexit
-fno-weak -nostdinc++
-fvisibility-inlines-hidden
-fvisibility-ms-compat
-fext-numeric-literals
-Wabi=n -Wabi-tag -Wconversion-null -Wctor-dtor-privacy
-Wdelete-non-virtual-dtor -Wliteral-suffix -Wmultiple-inheritance
-Wnamespaces -Wnarrowing
-Wnoexcept -Wnoexcept-type -Wclass-memaccess
-Wnon-virtual-dtor -Wreorder -Wregister
-Weffc++ -Wstrict-null-sentinel -Wtemplates
-Wno-non-template-friend -Wold-style-cast
-Woverloaded-virtual -Wno-pmf-conversions
-Wsign-promo -Wvirtual-inheritance

Objective-C and Objective-C++ Language Options
See Section 3.6 [Options Controlling Objective-C and Objective-C++ Dialects],
page 55.
-fconstant-string-class=class-name
-fgnu-runtime -fnext-runtime
-fno-nil-receivers
-fobjc-abi-version=n
-fobjc-call-cxx-cdtors
-fobjc-direct-dispatch
-fobjc-exceptions
-fobjc-gc
-fobjc-nilcheck
-fobjc-std=objc1

Chapter 3: GCC Command Options

11

-fno-local-ivars
-fivar-visibility=[public|protected|private|package]
-freplace-objc-classes
-fzero-link
-gen-decls
-Wassign-intercept
-Wno-protocol -Wselector
-Wstrict-selector-match
-Wundeclared-selector

Diagnostic Message Formatting Options
See Section 3.7 [Options to Control Diagnostic Messages Formatting], page 59.
-fmessage-length=n
-fdiagnostics-show-location=[once|every-line]
-fdiagnostics-color=[auto|never|always]
-fno-diagnostics-show-option -fno-diagnostics-show-caret
-fdiagnostics-parseable-fixits -fdiagnostics-generate-patch
-fdiagnostics-show-template-tree -fno-elide-type
-fno-show-column

Warning Options
See Section 3.8 [Options to Request or Suppress Warnings], page 62.
-fsyntax-only -fmax-errors=n -Wpedantic
-pedantic-errors
-w -Wextra -Wall -Waddress -Waggregate-return
-Walloc-zero -Walloc-size-larger-than=n -Walloca -Walloca-larger-than=n
-Wno-aggressive-loop-optimizations -Warray-bounds -Warray-bounds=n
-Wno-attributes -Wbool-compare -Wbool-operation
-Wno-builtin-declaration-mismatch
-Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat
-Wc++-compat -Wc++11-compat -Wc++14-compat
-Wcast-align -Wcast-align=strict -Wcast-function-type -Wcast-qual
-Wchar-subscripts -Wchkp -Wcatch-value -Wcatch-value=n
-Wclobbered -Wcomment -Wconditionally-supported
-Wconversion -Wcoverage-mismatch -Wno-cpp -Wdangling-else -Wdate-time
-Wdelete-incomplete
-Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init
-Wdisabled-optimization
-Wno-discarded-qualifiers -Wno-discarded-array-qualifiers
-Wno-div-by-zero -Wdouble-promotion
-Wduplicated-branches -Wduplicated-cond
-Wempty-body -Wenum-compare -Wno-endif-labels -Wexpansion-to-defined
-Werror -Werror=* -Wextra-semi -Wfatal-errors
-Wfloat-equal -Wformat -Wformat=2
-Wno-format-contains-nul -Wno-format-extra-args
-Wformat-nonliteral -Wformat-overflow=n
-Wformat-security -Wformat-signedness -Wformat-truncation=n
-Wformat-y2k -Wframe-address
-Wframe-larger-than=len -Wno-free-nonheap-object -Wjump-misses-init
-Wif-not-aligned
-Wignored-qualifiers -Wignored-attributes -Wincompatible-pointer-types
-Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=n
-Wimplicit-function-declaration -Wimplicit-int
-Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context
-Wno-int-to-pointer-cast -Winvalid-memory-model -Wno-invalid-offsetof
-Winvalid-pch -Wlarger-than=len
-Wlogical-op -Wlogical-not-parentheses -Wlong-long
-Wmain -Wmaybe-uninitialized -Wmemset-elt-size -Wmemset-transposed-args

12

Using the GNU Compiler Collection (GCC)

-Wmisleading-indentation -Wmissing-attributes -Wmissing-braces
-Wmissing-field-initializers -Wmissing-include-dirs
-Wno-multichar -Wmultistatement-macros -Wnonnull -Wnonnull-compare
-Wnormalized=[none|id|nfc|nfkc]
-Wnull-dereference -Wodr -Wno-overflow -Wopenmp-simd
-Woverride-init-side-effects -Woverlength-strings
-Wpacked -Wpacked-bitfield-compat -Wpacked-not-aligned -Wpadded
-Wparentheses -Wno-pedantic-ms-format
-Wplacement-new -Wplacement-new=n
-Wpointer-arith -Wpointer-compare -Wno-pointer-to-int-cast
-Wno-pragmas -Wredundant-decls -Wrestrict -Wno-return-local-addr
-Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar
-Wshadow=global, -Wshadow=local, -Wshadow=compatible-local
-Wshift-overflow -Wshift-overflow=n
-Wshift-count-negative -Wshift-count-overflow -Wshift-negative-value
-Wsign-compare -Wsign-conversion -Wfloat-conversion
-Wno-scalar-storage-order -Wsizeof-pointer-div
-Wsizeof-pointer-memaccess -Wsizeof-array-argument
-Wstack-protector -Wstack-usage=len -Wstrict-aliasing
-Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=n
-Wstringop-overflow=n -Wstringop-truncation
-Wsuggest-attribute=[pure|const|noreturn|format|malloc]
-Wsuggest-final-types
-Wsuggest-final-methods -Wsuggest-override
-Wmissing-format-attribute -Wsubobject-linkage
-Wswitch -Wswitch-bool -Wswitch-default -Wswitch-enum
-Wswitch-unreachable -Wsync-nand
-Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs
-Wtype-limits -Wundef
-Wuninitialized -Wunknown-pragmas
-Wunsuffixed-float-constants -Wunused -Wunused-function
-Wunused-label -Wunused-local-typedefs -Wunused-macros
-Wunused-parameter -Wno-unused-result
-Wunused-value -Wunused-variable
-Wunused-const-variable -Wunused-const-variable=n
-Wunused-but-set-parameter -Wunused-but-set-variable
-Wuseless-cast -Wvariadic-macros -Wvector-operation-performance
-Wvla -Wvla-larger-than=n -Wvolatile-register-var -Wwrite-strings
-Wzero-as-null-pointer-constant -Whsa

C and Objective-C-only Warning Options
-Wbad-function-cast -Wmissing-declarations
-Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs
-Wold-style-declaration -Wold-style-definition
-Wstrict-prototypes -Wtraditional -Wtraditional-conversion
-Wdeclaration-after-statement -Wpointer-sign

Debugging Options
See Section 3.9 [Options for Debugging Your Program], page 108.
-g -glevel -gdwarf -gdwarf-version
-ggdb -grecord-gcc-switches -gno-record-gcc-switches
-gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf
-gas-loc-support -gno-as-loc-support
-gas-locview-support -gno-as-locview-support
-gcolumn-info -gno-column-info
-gstatement-frontiers -gno-statement-frontiers
-gvariable-location-views -gno-variable-location-views
-ginternal-reset-location-views -gno-internal-reset-location-views
-ginline-points -gno-inline-points

Chapter 3: GCC Command Options

13

-gvms -gxcoff -gxcoff+ -gz[=type]
-fdebug-prefix-map=old=new -fdebug-types-section
-fno-eliminate-unused-debug-types
-femit-struct-debug-baseonly -femit-struct-debug-reduced
-femit-struct-debug-detailed[=spec-list]
-feliminate-unused-debug-symbols -femit-class-debug-always
-fno-merge-debug-strings -fno-dwarf2-cfi-asm
-fvar-tracking -fvar-tracking-assignments

Optimization Options
See Section 3.10 [Options that Control Optimization], page 114.
-faggressive-loop-optimizations -falign-functions[=n]
-falign-jumps[=n]
-falign-labels[=n] -falign-loops[=n]
-fassociative-math -fauto-profile -fauto-profile[=path]
-fauto-inc-dec -fbranch-probabilities
-fbranch-target-load-optimize -fbranch-target-load-optimize2
-fbtr-bb-exclusive -fcaller-saves
-fcombine-stack-adjustments -fconserve-stack
-fcompare-elim -fcprop-registers -fcrossjumping
-fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules
-fcx-limited-range
-fdata-sections -fdce -fdelayed-branch
-fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively
-fdevirtualize-at-ltrans -fdse
-fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects
-ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=style
-fforward-propagate -ffp-contract=style -ffunction-sections
-fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity
-fgcse-sm -fhoist-adjacent-loads -fif-conversion
-fif-conversion2 -findirect-inlining
-finline-functions -finline-functions-called-once -finline-limit=n
-finline-small-functions -fipa-cp -fipa-cp-clone
-fipa-bit-cp -fipa-vrp
-fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-icf
-fira-algorithm=algorithm
-fira-region=region -fira-hoist-pressure
-fira-loop-pressure -fno-ira-share-save-slots
-fno-ira-share-spill-slots
-fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute
-fivopts -fkeep-inline-functions -fkeep-static-functions
-fkeep-static-consts -flimit-function-alignment -flive-range-shrinkage
-floop-block -floop-interchange -floop-strip-mine
-floop-unroll-and-jam -floop-nest-optimize
-floop-parallelize-all -flra-remat -flto -flto-compression-level
-flto-partition=alg -fmerge-all-constants
-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves
-fmove-loop-invariants -fno-branch-count-reg
-fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse
-fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole
-fno-peephole2 -fno-printf-return-value -fno-sched-interblock
-fno-sched-spec -fno-signed-zeros
-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss
-fomit-frame-pointer -foptimize-sibling-calls
-fpartial-inlining -fpeel-loops -fpredictive-commoning
-fprefetch-loop-arrays
-fprofile-correction
-fprofile-use -fprofile-use=path -fprofile-values

14

Using the GNU Compiler Collection (GCC)

-fprofile-reorder-functions
-freciprocal-math -free -frename-registers -freorder-blocks
-freorder-blocks-algorithm=algorithm
-freorder-blocks-and-partition -freorder-functions
-frerun-cse-after-loop -freschedule-modulo-scheduled-loops
-frounding-math -fsched2-use-superblocks -fsched-pressure
-fsched-spec-load -fsched-spec-load-dangerous
-fsched-stalled-insns-dep[=n] -fsched-stalled-insns[=n]
-fsched-group-heuristic -fsched-critical-path-heuristic
-fsched-spec-insn-heuristic -fsched-rank-heuristic
-fsched-last-insn-heuristic -fsched-dep-count-heuristic
-fschedule-fusion
-fschedule-insns -fschedule-insns2 -fsection-anchors
-fselective-scheduling -fselective-scheduling2
-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops
-fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate
-fsignaling-nans
-fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops
-fsplit-paths
-fsplit-wide-types -fssa-backprop -fssa-phiopt
-fstdarg-opt -fstore-merging -fstrict-aliasing
-fthread-jumps -ftracer -ftree-bit-ccp
-ftree-builtin-call-dce -ftree-ccp -ftree-ch
-ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts
-ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting
-ftree-loop-if-convert -ftree-loop-im
-ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns
-ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize
-ftree-loop-vectorize
-ftree-parallelize-loops=n -ftree-pre -ftree-partial-pre -ftree-pta
-ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra
-ftree-switch-conversion -ftree-tail-merge
-ftree-ter -ftree-vectorize -ftree-vrp -funconstrained-commons
-funit-at-a-time -funroll-all-loops -funroll-loops
-funsafe-math-optimizations -funswitch-loops
-fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt
-fweb -fwhole-program -fwpa -fuse-linker-plugin
--param name=value -O -O0 -O1 -O2 -O3 -Os -Ofast -Og

Program Instrumentation Options
See Section 3.11 [Program Instrumentation Options], page 172.
-p -pg -fprofile-arcs --coverage -ftest-coverage
-fprofile-abs-path
-fprofile-dir=path -fprofile-generate -fprofile-generate=path
-fsanitize=style -fsanitize-recover -fsanitize-recover=style
-fasan-shadow-offset=number -fsanitize-sections=s1,s2,...
-fsanitize-undefined-trap-on-error -fbounds-check
-fcheck-pointer-bounds -fchkp-check-incomplete-type
-fchkp-first-field-has-own-bounds -fchkp-narrow-bounds
-fchkp-narrow-to-innermost-array -fchkp-optimize
-fchkp-use-fast-string-functions -fchkp-use-nochk-string-functions
-fchkp-use-static-bounds -fchkp-use-static-const-bounds
-fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read
-fchkp-check-read -fchkp-check-write -fchkp-store-bounds
-fchkp-instrument-calls -fchkp-instrument-marked-only
-fchkp-use-wrappers -fchkp-flexible-struct-trailing-arrays
-fcf-protection=[full|branch|return|none]
-fstack-protector -fstack-protector-all -fstack-protector-strong

Chapter 3: GCC Command Options

-fstack-protector-explicit -fstack-check
-fstack-limit-register=reg -fstack-limit-symbol=sym
-fno-stack-limit -fsplit-stack
-fvtable-verify=[std|preinit|none]
-fvtv-counts -fvtv-debug
-finstrument-functions
-finstrument-functions-exclude-function-list=sym,sym,...
-finstrument-functions-exclude-file-list=file,file,...

Preprocessor Options
See Section 3.12 [Options Controlling the Preprocessor], page 187.
-Aquestion=answer
-A-question[=answer]
-C -CC -Dmacro[=defn]
-dD -dI -dM -dN -dU
-fdebug-cpp -fdirectives-only -fdollars-in-identifiers
-fexec-charset=charset -fextended-identifiers
-finput-charset=charset -fmacro-prefix-map=old=new
-fno-canonical-system-headers
-fpch-deps -fpch-preprocess
-fpreprocessed -ftabstop=width -ftrack-macro-expansion
-fwide-exec-charset=charset -fworking-directory
-H -imacros file -include file
-M -MD -MF -MG -MM -MMD -MP -MQ -MT
-no-integrated-cpp -P -pthread -remap
-traditional -traditional-cpp -trigraphs
-Umacro -undef
-Wp,option -Xpreprocessor option

Assembler Options
See Section 3.13 [Passing Options to the Assembler], page 194.
-Wa,option -Xassembler option

Linker Options
See Section 3.14 [Options for Linking], page 195.
object-file-name -fuse-ld=linker -llibrary
-nostartfiles -nodefaultlibs -nostdlib -pie -pthread -rdynamic
-s -static -static-pie -static-libgcc -static-libstdc++
-static-libasan -static-libtsan -static-liblsan -static-libubsan
-static-libmpx -static-libmpxwrappers
-shared -shared-libgcc -symbolic
-T script -Wl,option -Xlinker option
-u symbol -z keyword

Directory Options
See Section 3.15 [Options for Directory Search], page 199.
-Bprefix -Idir -I-idirafter dir
-imacros file -imultilib dir
-iplugindir=dir -iprefix file
-iquote dir -isysroot dir -isystem dir
-iwithprefix dir -iwithprefixbefore dir
-Ldir -no-canonical-prefixes --no-sysroot-suffix
-nostdinc -nostdinc++ --sysroot=dir

Code Generation Options
See Section 3.16 [Options for Code Generation Conventions], page 202.

15

16

Using the GNU Compiler Collection (GCC)

-fcall-saved-reg -fcall-used-reg
-ffixed-reg -fexceptions
-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables
-fasynchronous-unwind-tables
-fno-gnu-unique
-finhibit-size-directive -fno-common -fno-ident
-fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt
-fno-jump-tables
-frecord-gcc-switches
-freg-struct-return -fshort-enums -fshort-wchar
-fverbose-asm -fpack-struct[=n]
-fleading-underscore -ftls-model=model
-fstack-reuse=reuse_level
-ftrampolines -ftrapv -fwrapv
-fvisibility=[default|internal|hidden|protected]
-fstrict-volatile-bitfields -fsync-libcalls

Developer Options
See Section 3.17 [GCC Developer Options], page 212.
-dletters -dumpspecs -dumpmachine -dumpversion
-dumpfullversion -fchecking -fchecking=n -fdbg-cnt-list
-fdbg-cnt=counter-value-list
-fdisable-ipa-pass_name
-fdisable-rtl-pass_name
-fdisable-rtl-pass-name=range-list
-fdisable-tree-pass_name
-fdisable-tree-pass-name=range-list
-fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links
-fdump-class-hierarchy[-n]
-fdump-final-insns[=file]
-fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline
-fdump-lang-all
-fdump-lang-switch
-fdump-lang-switch-options
-fdump-lang-switch-options=filename
-fdump-passes
-fdump-rtl-pass -fdump-rtl-pass=filename
-fdump-statistics
-fdump-tree-all
-fdump-tree-switch
-fdump-tree-switch-options
-fdump-tree-switch-options=filename
-fcompare-debug[=opts] -fcompare-debug-second
-fenable-kind-pass
-fenable-kind-pass=range-list
-fira-verbose=n
-flto-report -flto-report-wpa -fmem-report-wpa
-fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report
-fopt-info -fopt-info-options[=file]
-fprofile-report
-frandom-seed=string -fsched-verbose=n
-fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose
-fstats -fstack-usage -ftime-report -ftime-report-details
-fvar-tracking-assignments-toggle -gtoggle
-print-file-name=library -print-libgcc-file-name
-print-multi-directory -print-multi-lib -print-multi-os-directory
-print-prog-name=program -print-search-dirs -Q

Chapter 3: GCC Command Options

-print-sysroot -print-sysroot-headers-suffix
-save-temps -save-temps=cwd -save-temps=obj -time[=file]

Machine-Dependent Options
See Section 3.18 [Machine-Dependent Options], page 228.
AArch64 Options
-mabi=name -mbig-endian -mlittle-endian
-mgeneral-regs-only
-mcmodel=tiny -mcmodel=small -mcmodel=large
-mstrict-align
-momit-leaf-frame-pointer
-mtls-dialect=desc -mtls-dialect=traditional
-mtls-size=size
-mfix-cortex-a53-835769 -mfix-cortex-a53-843419
-mlow-precision-recip-sqrt -mlow-precision-sqrt -mlow-precision-div
-mpc-relative-literal-loads
-msign-return-address=scope
-march=name -mcpu=name -mtune=name
-moverride=string -mverbose-cost-dump

Adapteva Epiphany Options
-mhalf-reg-file -mprefer-short-insn-regs
-mbranch-cost=num -mcmove -mnops=num -msoft-cmpsf
-msplit-lohi -mpost-inc -mpost-modify -mstack-offset=num
-mround-nearest -mlong-calls -mshort-calls -msmall16
-mfp-mode=mode -mvect-double -max-vect-align=num
-msplit-vecmove-early -m1reg-reg

ARC Options
-mbarrel-shifter -mjli-always
-mcpu=cpu -mA6 -mARC600 -mA7 -mARC700
-mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr
-mea -mno-mpy -mmul32x16 -mmul64 -matomic
-mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap
-mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape
-mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof
-mlong-calls -mmedium-calls -msdata -mirq-ctrl-saved
-mrgf-banked-regs -mlpc-width=width -G num
-mvolatile-cache -mtp-regno=regno
-malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc
-mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi
-mexpand-adddi -mindexed-loads -mlra -mlra-priority-none
-mlra-priority-compact mlra-priority-noncompact -mno-millicode
-mmixed-code -mq-class -mRcq -mRcw -msize-level=level
-mtune=cpu -mmultcost=num
-munalign-prob-threshold=probability -mmpy-option=multo
-mdiv-rem -mcode-density -mll64 -mfpu=fpu -mrf16

ARM Options
-mapcs-frame -mno-apcs-frame
-mabi=name
-mapcs-stack-check -mno-apcs-stack-check
-mapcs-reentrant -mno-apcs-reentrant
-msched-prolog -mno-sched-prolog
-mlittle-endian -mbig-endian
-mbe8 -mbe32
-mfloat-abi=name
-mfp16-format=name -mthumb-interwork -mno-thumb-interwork

17

18

Using the GNU Compiler Collection (GCC)

-mcpu=name -march=name -mfpu=name
-mtune=name -mprint-tune-info
-mstructure-size-boundary=n
-mabort-on-noreturn
-mlong-calls -mno-long-calls
-msingle-pic-base -mno-single-pic-base
-mpic-register=reg
-mnop-fun-dllimport
-mpoke-function-name
-mthumb -marm -mflip-thumb
-mtpcs-frame -mtpcs-leaf-frame
-mcaller-super-interworking -mcallee-super-interworking
-mtp=name -mtls-dialect=dialect
-mword-relocations
-mfix-cortex-m3-ldrd
-munaligned-access
-mneon-for-64bits
-mslow-flash-data
-masm-syntax-unified
-mrestrict-it
-mverbose-cost-dump
-mpure-code
-mcmse

AVR Options
-mmcu=mcu -mabsdata -maccumulate-args
-mbranch-cost=cost
-mcall-prologues -mgas-isr-prologues -mint8
-mn_flash=size -mno-interrupts
-mmain-is-OS_task -mrelax -mrmw -mstrict-X -mtiny-stack
-mfract-convert-truncate
-mshort-calls -nodevicelib
-Waddr-space-convert -Wmisspelled-isr

Blackfin Options
-mcpu=cpu[-sirevision]
-msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer
-mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly
-mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library
-mno-id-shared-library -mshared-library-id=n
-mleaf-id-shared-library -mno-leaf-id-shared-library
-msep-data -mno-sep-data -mlong-calls -mno-long-calls
-mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram
-micplb

C6X Options
-mbig-endian -mlittle-endian -march=cpu
-msim -msdata=sdata-type

CRIS Options
-mcpu=cpu -march=cpu -mtune=cpu
-mmax-stack-frame=n -melinux-stacksize=n
-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects
-mstack-align -mdata-align -mconst-align
-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt
-melf -maout -melinux -mlinux -sim -sim2
-mmul-bug-workaround -mno-mul-bug-workaround

CR16 Options

Chapter 3: GCC Command Options

-mmac
-mcr16cplus -mcr16c
-msim -mint32 -mbit-ops -mdata-model=model

Darwin Options
-all_load -allowable_client -arch -arch_errors_fatal
-arch_only -bind_at_load -bundle -bundle_loader
-client_name -compatibility_version -current_version
-dead_strip
-dependency-file -dylib_file -dylinker_install_name
-dynamic -dynamiclib -exported_symbols_list
-filelist -flat_namespace -force_cpusubtype_ALL
-force_flat_namespace -headerpad_max_install_names
-iframework
-image_base -init -install_name -keep_private_externs
-multi_module -multiply_defined -multiply_defined_unused
-noall_load -no_dead_strip_inits_and_terms
-nofixprebinding -nomultidefs -noprebind -noseglinkedit
-pagezero_size -prebind -prebind_all_twolevel_modules
-private_bundle -read_only_relocs -sectalign
-sectobjectsymbols -whyload -seg1addr
-sectcreate -sectobjectsymbols -sectorder
-segaddr -segs_read_only_addr -segs_read_write_addr
-seg_addr_table -seg_addr_table_filename -seglinkedit
-segprot -segs_read_only_addr -segs_read_write_addr
-single_module -static -sub_library -sub_umbrella
-twolevel_namespace -umbrella -undefined
-unexported_symbols_list -weak_reference_mismatches
-whatsloaded -F -gused -gfull -mmacosx-version-min=version
-mkernel -mone-byte-bool

DEC Alpha Options
-mno-fp-regs -msoft-float
-mieee -mieee-with-inexact -mieee-conformant
-mfp-trap-mode=mode -mfp-rounding-mode=mode
-mtrap-precision=mode -mbuild-constants
-mcpu=cpu-type -mtune=cpu-type
-mbwx -mmax -mfix -mcix
-mfloat-vax -mfloat-ieee
-mexplicit-relocs -msmall-data -mlarge-data
-msmall-text -mlarge-text
-mmemory-latency=time

FR30 Options
-msmall-model -mno-lsim

FT32 Options
-msim -mlra -mnodiv -mft32b -mcompress -mnopm

FRV Options
-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64
-mhard-float -msoft-float
-malloc-cc -mfixed-cc -mdword -mno-dword
-mdouble -mno-double
-mmedia -mno-media -mmuladd -mno-muladd
-mfdpic -minline-plt -mgprel-ro -multilib-library-pic
-mlinked-fp -mlong-calls -malign-labels
-mlibrary-pic -macc-4 -macc-8
-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move
-moptimize-membar -mno-optimize-membar

19

20

Using the GNU Compiler Collection (GCC)

-mscc -mno-scc -mcond-exec -mno-cond-exec
-mvliw-branch -mno-vliw-branch
-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec
-mno-nested-cond-exec -mtomcat-stats
-mTLS -mtls
-mcpu=cpu

GNU/Linux Options
-mglibc -muclibc -mmusl -mbionic -mandroid
-tno-android-cc -tno-android-ld

H8/300 Options
-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300

HPPA Options
-march=architecture-type
-mcaller-copies -mdisable-fpregs -mdisable-indexing
-mfast-indirect-calls -mgas -mgnu-ld -mhp-ld
-mfixed-range=register-range
-mjump-in-delay -mlinker-opt -mlong-calls
-mlong-load-store -mno-disable-fpregs
-mno-disable-indexing -mno-fast-indirect-calls -mno-gas
-mno-jump-in-delay -mno-long-load-store
-mno-portable-runtime -mno-soft-float
-mno-space-regs -msoft-float -mpa-risc-1-0
-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime
-mschedule=cpu-type -mspace-regs -msio -mwsio
-munix=unix-std -nolibdld -static -threads

IA-64 Options
-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic
-mvolatile-asm-stop -mregister-names -msdata -mno-sdata
-mconstant-gp -mauto-pic -mfused-madd
-minline-float-divide-min-latency
-minline-float-divide-max-throughput
-mno-inline-float-divide
-minline-int-divide-min-latency
-minline-int-divide-max-throughput
-mno-inline-int-divide
-minline-sqrt-min-latency -minline-sqrt-max-throughput
-mno-inline-sqrt
-mdwarf2-asm -mearly-stop-bits
-mfixed-range=register-range -mtls-size=tls-size
-mtune=cpu-type -milp32 -mlp64
-msched-br-data-spec -msched-ar-data-spec -msched-control-spec
-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec
-msched-spec-ldc -msched-spec-control-ldc
-msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns
-msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path
-msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost
-msched-max-memory-insns-hard-limit -msched-max-memory-insns=max-insns

LM32 Options
-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled
-msign-extend-enabled -muser-enabled

M32R/D Options
-m32r2 -m32rx -m32r
-mdebug
-malign-loops -mno-align-loops

Chapter 3: GCC Command Options

-missue-rate=number
-mbranch-cost=number
-mmodel=code-size-model-type
-msdata=sdata-type
-mno-flush-func -mflush-func=name
-mno-flush-trap -mflush-trap=number
-G num

M32C Options
-mcpu=cpu -msim -memregs=number

M680x0 Options
-march=arch -mcpu=cpu -mtune=tune
-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040
-m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407
-mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020
-mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort
-mno-short -mhard-float -m68881 -msoft-float -mpcrel
-malign-int -mstrict-align -msep-data -mno-sep-data
-mshared-library-id=n -mid-shared-library -mno-id-shared-library
-mxgot -mno-xgot -mlong-jump-table-offsets

MCore Options
-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates
-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields
-m4byte-functions -mno-4byte-functions -mcallgraph-data
-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim
-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment

MeP Options
-mabsdiff -mall-opts -maverage -mbased=n -mbitops
-mc=n -mclip -mconfig=name -mcop -mcop32 -mcop64 -mivc2
-mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax
-mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf
-mtiny=n

MicroBlaze Options
-msoft-float -mhard-float -msmall-divides -mcpu=cpu
-mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift
-mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss
-mxl-multiply-high -mxl-float-convert -mxl-float-sqrt
-mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-app-model

MIPS Options
-EL -EB -march=arch -mtune=arch
-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5
-mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6
-mips16 -mno-mips16 -mflip-mips16
-minterlink-compressed -mno-interlink-compressed
-minterlink-mips16 -mno-interlink-mips16
-mabi=abi -mabicalls -mno-abicalls
-mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot
-mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float
-mno-float -msingle-float -mdouble-float
-modd-spreg -mno-odd-spreg
-mabs=mode -mnan=encoding
-mdsp -mno-dsp -mdspr2 -mno-dspr2
-mmcu -mmno-mcu
-meva -mno-eva
-mvirt -mno-virt

21

22

Using the GNU Compiler Collection (GCC)

-mxpa -mno-xpa
-mmicromips -mno-micromips
-mmsa -mno-msa
-mfpu=fpu-type
-msmartmips -mno-smartmips
-mpaired-single -mno-paired-single -mdmx -mno-mdmx
-mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc
-mlong64 -mlong32 -msym32 -mno-sym32
-Gnum -mlocal-sdata -mno-local-sdata
-mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt
-membedded-data -mno-embedded-data
-muninit-const-in-rodata -mno-uninit-const-in-rodata
-mcode-readable=setting
-msplit-addresses -mno-split-addresses
-mexplicit-relocs -mno-explicit-relocs
-mcheck-zero-division -mno-check-zero-division
-mdivide-traps -mdivide-breaks
-mload-store-pairs -mno-load-store-pairs
-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls
-mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp
-mfix-24k -mno-fix-24k
-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400
-mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000
-mfix-vr4120 -mno-fix-vr4120
-mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1
-mflush-func=func -mno-flush-func
-mbranch-cost=num -mbranch-likely -mno-branch-likely
-mcompact-branches=policy
-mfp-exceptions -mno-fp-exceptions
-mvr4130-align -mno-vr4130-align -msynci -mno-synci
-mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4
-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address
-mframe-header-opt -mno-frame-header-opt

MMIX Options
-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu
-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols
-melf -mbranch-predict -mno-branch-predict -mbase-addresses
-mno-base-addresses -msingle-exit -mno-single-exit

MN10300 Options
-mmult-bug -mno-mult-bug
-mno-am33 -mam33 -mam33-2 -mam34
-mtune=cpu-type
-mreturn-pointer-on-d0
-mno-crt0 -mrelax -mliw -msetlb

Moxie Options
-meb -mel -mmul.x -mno-crt0

MSP430 Options
-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax
-mwarn-mcu
-mcode-region= -mdata-region=
-msilicon-errata= -msilicon-errata-warn=
-mhwmult= -minrt

NDS32 Options
-mbig-endian -mlittle-endian
-mreduced-regs -mfull-regs

Chapter 3: GCC Command Options

-mcmov -mno-cmov
-mext-perf -mno-ext-perf
-mext-perf2 -mno-ext-perf2
-mext-string -mno-ext-string
-mv3push -mno-v3push
-m16bit -mno-16bit
-misr-vector-size=num
-mcache-block-size=num
-march=arch
-mcmodel=code-model
-mctor-dtor -mrelax

Nios II Options
-G num -mgpopt=option -mgpopt -mno-gpopt
-mgprel-sec=regexp -mr0rel-sec=regexp
-mel -meb
-mno-bypass-cache -mbypass-cache
-mno-cache-volatile -mcache-volatile
-mno-fast-sw-div -mfast-sw-div
-mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div
-mcustom-insn=N -mno-custom-insn
-mcustom-fpu-cfg=name
-mhal -msmallc -msys-crt0=name -msys-lib=name
-march=arch -mbmx -mno-bmx -mcdx -mno-cdx

Nvidia PTX Options
-m32 -m64 -mmainkernel -moptimize

PDP-11 Options
-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10
-mbcopy -mbcopy-builtin -mint32 -mno-int16
-mint16 -mno-int32 -mfloat32 -mno-float64
-mfloat64 -mno-float32 -mabshi -mno-abshi
-mbranch-expensive -mbranch-cheap
-munix-asm -mdec-asm

picoChip Options
-mae=ae_type -mvliw-lookahead=N
-msymbol-as-address -mno-inefficient-warnings

PowerPC Options See RS/6000 and PowerPC Options.
PowerPC SPE Options
-mcpu=cpu-type
-mtune=cpu-type
-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb
-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc
-m32 -mxl-compat -mno-xl-compat
-malign-power -malign-natural
-msoft-float -mhard-float -mmultiple -mno-multiple
-msingle-float -mdouble-float
-mupdate -mno-update
-mavoid-indexed-addresses -mno-avoid-indexed-addresses
-mstrict-align -mno-strict-align -mrelocatable
-mno-relocatable -mrelocatable-lib -mno-relocatable-lib
-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian
-msingle-pic-base
-mprioritize-restricted-insns=priority
-msched-costly-dep=dependence_type
-minsert-sched-nops=scheme

23

24

Using the GNU Compiler Collection (GCC)

-mcall-sysv -mcall-netbsd
-maix-struct-return -msvr4-struct-return
-mabi=abi-type -msecure-plt -mbss-plt
-mblock-move-inline-limit=num
-misel -mno-isel
-misel=yes -misel=no
-mspe -mno-spe
-mspe=yes -mspe=no
-mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double
-mprototype -mno-prototype
-msim -mmvme -mads -myellowknife -memb -msdata
-msdata=opt -mvxworks -G num
-mrecip -mrecip=opt -mno-recip -mrecip-precision
-mno-recip-precision
-mpointers-to-nested-functions -mno-pointers-to-nested-functions
-msave-toc-indirect -mno-save-toc-indirect
-mcompat-align-parm -mno-compat-align-parm
-mfloat128 -mno-float128
-mgnu-attribute -mno-gnu-attribute
-mstack-protector-guard=guard -mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset

RISC-V Options
-mbranch-cost=N-instruction
-mplt -mno-plt
-mabi=ABI-string
-mfdiv -mno-fdiv
-mdiv -mno-div
-march=ISA-string
-mtune=processor-string
-mpreferred-stack-boundary=num
-msmall-data-limit=N-bytes
-msave-restore -mno-save-restore
-mstrict-align -mno-strict-align
-mcmodel=medlow -mcmodel=medany
-mexplicit-relocs -mno-explicit-relocs
-mrelax -mno-relax

RL78 Options
-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs
-mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14
-m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts

RS/6000 and PowerPC Options
-mcpu=cpu-type
-mtune=cpu-type
-mcmodel=code-model
-mpowerpc64
-maltivec -mno-altivec
-mpowerpc-gpopt -mno-powerpc-gpopt
-mpowerpc-gfxopt -mno-powerpc-gfxopt
-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd
-mfprnd -mno-fprnd
-mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp
-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc
-m64 -m32 -mxl-compat -mno-xl-compat -mpe
-malign-power -malign-natural
-msoft-float -mhard-float -mmultiple -mno-multiple

Chapter 3: GCC Command Options

-msingle-float -mdouble-float -msimple-fpu
-mupdate -mno-update
-mavoid-indexed-addresses -mno-avoid-indexed-addresses
-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align
-mstrict-align -mno-strict-align -mrelocatable
-mno-relocatable -mrelocatable-lib -mno-relocatable-lib
-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian
-mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base
-mprioritize-restricted-insns=priority
-msched-costly-dep=dependence_type
-minsert-sched-nops=scheme
-mcall-aixdesc -mcall-eabi -mcall-freebsd
-mcall-linux -mcall-netbsd -mcall-openbsd
-mcall-sysv -mcall-sysv-eabi -mcall-sysv-noeabi
-mtraceback=traceback_type
-maix-struct-return -msvr4-struct-return
-mabi=abi-type -msecure-plt -mbss-plt
-mblock-move-inline-limit=num
-mblock-compare-inline-limit=num
-mblock-compare-inline-loop-limit=num
-mstring-compare-inline-limit=num
-misel -mno-isel
-misel=yes -misel=no
-mpaired
-mvrsave -mno-vrsave
-mmulhw -mno-mulhw
-mdlmzb -mno-dlmzb
-mprototype -mno-prototype
-msim -mmvme -mads -myellowknife -memb -msdata
-msdata=opt -mreadonly-in-sdata -mvxworks -G num
-mrecip -mrecip=opt -mno-recip -mrecip-precision
-mno-recip-precision
-mveclibabi=type -mfriz -mno-friz
-mpointers-to-nested-functions -mno-pointers-to-nested-functions
-msave-toc-indirect -mno-save-toc-indirect
-mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector
-mcrypto -mno-crypto -mhtm -mno-htm
-mquad-memory -mno-quad-memory
-mquad-memory-atomic -mno-quad-memory-atomic
-mcompat-align-parm -mno-compat-align-parm
-mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware
-mgnu-attribute -mno-gnu-attribute
-mstack-protector-guard=guard -mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset

RX Options
-m64bit-doubles -m32bit-doubles -fpu -nofpu
-mcpu=
-mbig-endian-data -mlittle-endian-data
-msmall-data
-msim -mno-sim
-mas100-syntax -mno-as100-syntax
-mrelax
-mmax-constant-size=
-mint-register=
-mpid
-mallow-string-insns -mno-allow-string-insns
-mjsr

25

26

Using the GNU Compiler Collection (GCC)

-mno-warn-multiple-fast-interrupts
-msave-acc-in-interrupts

S/390 and zSeries Options
-mtune=cpu-type -march=cpu-type
-mhard-float -msoft-float -mhard-dfp -mno-hard-dfp
-mlong-double-64 -mlong-double-128
-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack
-msmall-exec -mno-small-exec -mmvcle -mno-mvcle
-m64 -m31 -mdebug -mno-debug -mesa -mzarch
-mhtm -mvx -mzvector
-mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd
-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard
-mhotpatch=halfwords,halfwords

Score Options
-meb -mel
-mnhwloop
-muls
-mmac
-mscore5 -mscore5u -mscore7 -mscore7d

SH Options
-m1 -m2 -m2e
-m2a-nofpu -m2a-single-only -m2a-single -m2a
-m3 -m3e
-m4-nofpu -m4-single-only -m4-single -m4
-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al
-mb -ml -mdalign -mrelax
-mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave
-mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct
-mprefergot -musermode -multcost=number -mdiv=strategy
-mdivsi3_libfunc=name -mfixed-range=register-range
-maccumulate-outgoing-args
-matomic-model=atomic-model
-mbranch-cost=num -mzdcbranch -mno-zdcbranch
-mcbranch-force-delay-slot
-mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra
-mpretend-cmove -mtas

Solaris 2 Options
-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text
-pthreads

SPARC Options
-mcpu=cpu-type
-mtune=cpu-type
-mcmodel=code-model
-mmemory-model=mem-model
-m32 -m64 -mapp-regs -mno-app-regs
-mfaster-structs -mno-faster-structs -mflat -mno-flat
-mfpu -mno-fpu -mhard-float -msoft-float
-mhard-quad-float -msoft-quad-float
-mstack-bias -mno-stack-bias
-mstd-struct-return -mno-std-struct-return
-munaligned-doubles -mno-unaligned-doubles
-muser-mode -mno-user-mode
-mv8plus -mno-v8plus -mvis -mno-vis
-mvis2 -mno-vis2 -mvis3 -mno-vis3
-mvis4 -mno-vis4 -mvis4b -mno-vis4b

Chapter 3: GCC Command Options

-mcbcond -mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld
-mpopc -mno-popc -msubxc -mno-subxc
-mfix-at697f -mfix-ut699 -mfix-ut700 -mfix-gr712rc
-mlra -mno-lra

SPU Options
-mwarn-reloc -merror-reloc
-msafe-dma -munsafe-dma
-mbranch-hints
-msmall-mem -mlarge-mem -mstdmain
-mfixed-range=register-range
-mea32 -mea64
-maddress-space-conversion -mno-address-space-conversion
-mcache-size=cache-size
-matomic-updates -mno-atomic-updates

System V Options
-Qy -Qn -YP,paths -Ym,dir

TILE-Gx Options
-mcpu=CPU -m32 -m64 -mbig-endian -mlittle-endian
-mcmodel=code-model

TILEPro Options
-mcpu=cpu -m32

V850 Options
-mlong-calls -mno-long-calls -mep -mno-ep
-mprolog-function -mno-prolog-function -mspace
-mtda=n -msda=n -mzda=n
-mapp-regs -mno-app-regs
-mdisable-callt -mno-disable-callt
-mv850e2v3 -mv850e2 -mv850e1 -mv850es
-mv850e -mv850 -mv850e3v5
-mloop
-mrelax
-mlong-jumps
-msoft-float
-mhard-float
-mgcc-abi
-mrh850-abi
-mbig-switch

VAX Options
-mg -mgnu -munix

Visium Options
-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float
-mcpu=cpu-type -mtune=cpu-type -msv-mode -muser-mode

VMS Options
-mvms-return-codes -mdebug-main=prefix -mmalloc64
-mpointer-size=size

VxWorks Options
-mrtp -non-static -Bstatic -Bdynamic
-Xbind-lazy -Xbind-now

x86 Options
-mtune=cpu-type -march=cpu-type
-mtune-ctrl=feature-list -mdump-tune-features -mno-default

27

28

Using the GNU Compiler Collection (GCC)

-mfpmath=unit
-masm=dialect -mno-fancy-math-387
-mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float
-mno-wide-multiply -mrtd -malign-double
-mpreferred-stack-boundary=num
-mincoming-stack-boundary=num
-mcld -mcx16 -msahf -mmovbe -mcrc32
-mrecip -mrecip=opt
-mvzeroupper -mprefer-avx128 -mprefer-vector-width=opt
-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx
-mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl
-mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes
-mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd
-mprefetchwt1 -mclflushopt -mxsavec -mxsaves
-msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop
-mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx
-mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes
-mshstk -mforce-indirect-call -mavx512vbmi2
-mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq
-mms-bitfields -mno-align-stringops -minline-all-stringops
-minline-stringops-dynamically -mstringop-strategy=alg
-mmemcpy-strategy=strategy -mmemset-strategy=strategy
-mpush-args -maccumulate-outgoing-args -m128bit-long-double
-m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128
-mregparm=num -msseregparm
-mveclibabi=type -mvect8-ret-in-mem
-mpc32 -mpc64 -mpc80 -mstackrealign
-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs
-mcmodel=code-model -mabi=name -maddress-mode=mode
-m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=num
-msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv
-mavx256-split-unaligned-load -mavx256-split-unaligned-store
-malign-data=type -mstack-protector-guard=guard
-mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset
-mstack-protector-guard-symbol=symbol -mmitigate-rop
-mgeneral-regs-only -mcall-ms2sysv-xlogues
-mindirect-branch=choice -mfunction-return=choice
-mindirect-branch-register

x86 Windows Options
-mconsole -mcygwin -mno-cygwin -mdll
-mnop-fun-dllimport -mthread
-municode -mwin32 -mwindows -fno-set-stack-executable

Xstormy16 Options
-msim

Xtensa Options
-mconst16 -mno-const16
-mfused-madd -mno-fused-madd
-mforce-no-pic
-mserialize-volatile -mno-serialize-volatile
-mtext-section-literals -mno-text-section-literals
-mauto-litpools -mno-auto-litpools
-mtarget-align -mno-target-align
-mlongcalls -mno-longcalls

zSeries Options See S/390 and zSeries Options.

Chapter 3: GCC Command Options

29

3.2 Options Controlling the Kind of Output
Compilation can involve up to four stages: preprocessing, compilation proper, assembly
and linking, always in that order. GCC is capable of preprocessing and compiling several
files either into several assembler input files, or into one assembler input file; then each
assembler input file produces an object file, and linking combines all the object files (those
newly compiled, and those specified as input) into an executable file.
For any given input file, the file name suffix determines what kind of compilation is done:
file.c

C source code that must be preprocessed.

file.i

C source code that should not be preprocessed.

file.ii

C++ source code that should not be preprocessed.

file.m

Objective-C source code. Note that you must link with the ‘libobjc’ library
to make an Objective-C program work.

file.mi

Objective-C source code that should not be preprocessed.

file.mm
file.M

Objective-C++ source code. Note that you must link with the ‘libobjc’ library
to make an Objective-C++ program work. Note that ‘.M’ refers to a literal
capital M.

file.mii

Objective-C++ source code that should not be preprocessed.

file.h

C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header (default), or C, C++ header file to be turned into an Ada spec (via
the ‘-fdump-ada-spec’ switch).

file.cc
file.cp
file.cxx
file.cpp
file.CPP
file.c++
file.C

C++ source code that must be preprocessed. Note that in ‘.cxx’, the last two
letters must both be literally ‘x’. Likewise, ‘.C’ refers to a literal capital C.

file.mm
file.M

Objective-C++ source code that must be preprocessed.

file.mii

Objective-C++ source code that should not be preprocessed.

file.hh
file.H
file.hp
file.hxx
file.hpp
file.HPP
file.h++
file.tcc

C++ header file to be turned into a precompiled header or Ada spec.

30

file.f
file.for
file.ftn
file.F
file.FOR
file.fpp
file.FPP
file.FTN
file.f90
file.f95
file.f03
file.f08
file.F90
file.F95
file.F03
file.F08
file.go

Using the GNU Compiler Collection (GCC)

Fixed form Fortran source code that should not be preprocessed.

Fixed form Fortran source code that must be preprocessed (with the traditional
preprocessor).

Free form Fortran source code that should not be preprocessed.

Free form Fortran source code that must be preprocessed (with the traditional
preprocessor).
Go source code.

file.brig
BRIG files (binary representation of HSAIL).
file.ads

Ada source code file that contains a library unit declaration (a declaration of a
package, subprogram, or generic, or a generic instantiation), or a library unit
renaming declaration (a package, generic, or subprogram renaming declaration).
Such files are also called specs.

file.adb

Ada source code file containing a library unit body (a subprogram or package
body). Such files are also called bodies.

file.s

Assembler code.

file.S
file.sx

Assembler code that must be preprocessed.

other

An object file to be fed straight into linking. Any file name with no recognized
suffix is treated this way.

You can specify the input language explicitly with the ‘-x’ option:
-x language
Specify explicitly the language for the following input files (rather than letting
the compiler choose a default based on the file name suffix). This option applies
to all following input files until the next ‘-x’ option. Possible values for language
are:
c c-header cpp-output
c++ c++-header c++-cpp-output
objective-c objective-c-header objective-c-cpp-output
objective-c++ objective-c++-header objective-c++-cpp-output

Chapter 3: GCC Command Options

31

assembler assembler-with-cpp
ada
f77 f77-cpp-input f95 f95-cpp-input
go
brig

-x none

Turn off any specification of a language, so that subsequent files are handled
according to their file name suffixes (as they are if ‘-x’ has not been used at
all).

If you only want some of the stages of compilation, you can use ‘-x’ (or filename suffixes)
to tell gcc where to start, and one of the options ‘-c’, ‘-S’, or ‘-E’ to say where gcc is to
stop. Note that some combinations (for example, ‘-x cpp-output -E’) instruct gcc to do
nothing at all.
-c

Compile or assemble the source files, but do not link. The linking stage simply
is not done. The ultimate output is in the form of an object file for each source
file.
By default, the object file name for a source file is made by replacing the suffix
‘.c’, ‘.i’, ‘.s’, etc., with ‘.o’.
Unrecognized input files, not requiring compilation or assembly, are ignored.

-S

Stop after the stage of compilation proper; do not assemble. The output is in
the form of an assembler code file for each non-assembler input file specified.
By default, the assembler file name for a source file is made by replacing the
suffix ‘.c’, ‘.i’, etc., with ‘.s’.
Input files that don’t require compilation are ignored.

-E

Stop after the preprocessing stage; do not run the compiler proper. The output
is in the form of preprocessed source code, which is sent to the standard output.
Input files that don’t require preprocessing are ignored.

-o file

Place output in file file. This applies to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or
preprocessed C code.
If ‘-o’ is not specified, the default is to put an executable file in ‘a.out’, the
object file for ‘source.suffix’ in ‘source.o’, its assembler file in ‘source.s’, a
precompiled header file in ‘source.suffix.gch’, and all preprocessed C source
on standard output.

-v

Print (on standard error output) the commands executed to run the stages of
compilation. Also print the version number of the compiler driver program and
of the preprocessor and the compiler proper.

-###

Like ‘-v’ except the commands are not executed and arguments are quoted
unless they contain only alphanumeric characters or ./-_. This is useful for
shell scripts to capture the driver-generated command lines.

--help

Print (on the standard output) a description of the command-line options understood by gcc. If the ‘-v’ option is also specified then ‘--help’ is also passed on
to the various processes invoked by gcc, so that they can display the commandline options they accept. If the ‘-Wextra’ option has also been specified (prior to

32

Using the GNU Compiler Collection (GCC)

the ‘--help’ option), then command-line options that have no documentation
associated with them are also displayed.
--target-help
Print (on the standard output) a description of target-specific command-line
options for each tool. For some targets extra target-specific information may
also be printed.
--help={class|[^]qualifier}[,...]
Print (on the standard output) a description of the command-line options understood by the compiler that fit into all specified classes and qualifiers. These
are the supported classes:
‘optimizers’
Display all of the optimization options supported by the compiler.
‘warnings’
Display all of the options controlling warning messages produced
by the compiler.
‘target’

Display target-specific options. Unlike the ‘--target-help’ option
however, target-specific options of the linker and assembler are not
displayed. This is because those tools do not currently support the
extended ‘--help=’ syntax.

‘params’

Display the values recognized by the ‘--param’ option.

language

Display the options supported for language, where language is the
name of one of the languages supported in this version of GCC.

‘common’

Display the options that are common to all languages.

These are the supported qualifiers:
‘undocumented’
Display only those options that are undocumented.
‘joined’

Display options taking an argument that appears after an equal sign
in the same continuous piece of text, such as: ‘--help=target’.

‘separate’
Display options taking an argument that appears as a separate word
following the original option, such as: ‘-o output-file’.
Thus for example to display all the undocumented target-specific switches supported by the compiler, use:
--help=target,undocumented

The sense of a qualifier can be inverted by prefixing it with the ‘^’ character,
so for example to display all binary warning options (i.e., ones that are either
on or off and that do not take an argument) that have a description, use:
--help=warnings,^joined,^undocumented

The argument to ‘--help=’ should not consist solely of inverted qualifiers.
Combining several classes is possible, although this usually restricts the output
so much that there is nothing to display. One case where it does work, however,

Chapter 3: GCC Command Options

33

is when one of the classes is target. For example, to display all the target-specific
optimization options, use:
--help=target,optimizers

The ‘--help=’ option can be repeated on the command line. Each successive
use displays its requested class of options, skipping those that have already been
displayed.
If the ‘-Q’ option appears on the command line before the ‘--help=’ option, then
the descriptive text displayed by ‘--help=’ is changed. Instead of describing
the displayed options, an indication is given as to whether the option is enabled,
disabled or set to a specific value (assuming that the compiler knows this at the
point where the ‘--help=’ option is used).
Here is a truncated example from the ARM port of gcc:
% gcc -Q -mabi=2 --help=target -c
The following options are target specific:
-mabi=
2
-mabort-on-noreturn
[disabled]
-mapcs
[disabled]

The output is sensitive to the effects of previous command-line options, so for
example it is possible to find out which optimizations are enabled at ‘-O2’ by
using:
-Q -O2 --help=optimizers

Alternatively you can discover which binary optimizations are enabled by ‘-O3’
by using:
gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
diff /tmp/O2-opts /tmp/O3-opts | grep enabled

--version
Display the version number and copyrights of the invoked GCC.
-pass-exit-codes
Normally the gcc program exits with the code of 1 if any phase of the compiler
returns a non-success return code. If you specify ‘-pass-exit-codes’, the gcc
program instead returns with the numerically highest error produced by any
phase returning an error indication. The C, C++, and Fortran front ends return
4 if an internal compiler error is encountered.
-pipe

Use pipes rather than temporary files for communication between the various
stages of compilation. This fails to work on some systems where the assembler
is unable to read from a pipe; but the GNU assembler has no trouble.

-specs=file
Process file after the compiler reads in the standard ‘specs’ file, in order to
override the defaults which the gcc driver program uses when determining what
switches to pass to cc1, cc1plus, as, ld, etc. More than one ‘-specs=file’
can be specified on the command line, and they are processed in order, from
left to right. See Section 3.19 [Spec Files], page 415, for information about the
format of the file.
-wrapper

Invoke all subcommands under a wrapper program. The name of the wrapper
program and its parameters are passed as a comma separated list.

34

Using the GNU Compiler Collection (GCC)

gcc -c t.c -wrapper gdb,--args

This invokes all subprograms of gcc under ‘gdb --args’, thus the invocation of
cc1 is ‘gdb --args cc1 ...’.
-ffile-prefix-map=old=new
When compiling files residing in directory ‘old’, record any references to
them in the result of the compilation as if the files resided in directory
‘new’ instead. Specifying this option is equivalent to specifying all the
individual ‘-f*-prefix-map’ options. This can be used to make reproducible
builds that are location independent. See also ‘-fmacro-prefix-map’ and
‘-fdebug-prefix-map’.
-fplugin=name.so
Load the plugin code in file name.so, assumed
be dlopen’d by the compiler. The base name
is used to identify the plugin for the purposes
‘-fplugin-arg-name-key=value’ below). Each
callback functions specified in the Plugins API.

to be a shared object to
of the shared object file
of argument parsing (See
plugin should define the

-fplugin-arg-name-key=value
Define an argument called key with a value of value for the plugin called name.
-fdump-ada-spec[-slim]
For C and C++ source and include files, generate corresponding Ada specs. See
Section “Generating Ada Bindings for C and C++ headers” in GNAT User’s
Guide, which provides detailed documentation on this feature.
-fada-spec-parent=unit
In conjunction with ‘-fdump-ada-spec[-slim]’ above, generate Ada specs as
child units of parent unit.
-fdump-go-spec=file
For input files in any language, generate corresponding Go declarations in file.
This generates Go const, type, var, and func declarations which may be
a useful way to start writing a Go interface to code written in some other
language.
@file

Read command-line options from file. The options read are inserted in place
of the original @file option. If file does not exist, or cannot be read, then the
option will be treated literally, and not removed.
Options in file are separated by whitespace. A whitespace character may be
included in an option by surrounding the entire option in either single or double
quotes. Any character (including a backslash) may be included by prefixing the
character to be included with a backslash. The file may itself contain additional
@file options; any such options will be processed recursively.

3.3 Compiling C++ Programs
C++ source files conventionally use one of the suffixes ‘.C’, ‘.cc’, ‘.cpp’, ‘.CPP’, ‘.c++’,
‘.cp’, or ‘.cxx’; C++ header files often use ‘.hh’, ‘.hpp’, ‘.H’, or (for shared template code)
‘.tcc’; and preprocessed C++ files use the suffix ‘.ii’. GCC recognizes files with these

Chapter 3: GCC Command Options

35

names and compiles them as C++ programs even if you call the compiler the same way as
for compiling C programs (usually with the name gcc).
However, the use of gcc does not add the C++ library. g++ is a program that calls GCC
and automatically specifies linking against the C++ library. It treats ‘.c’, ‘.h’ and ‘.i’ files
as C++ source files instead of C source files unless ‘-x’ is used. This program is also useful
when precompiling a C header file with a ‘.h’ extension for use in C++ compilations. On
many systems, g++ is also installed with the name c++.
When you compile C++ programs, you may specify many of the same command-line
options that you use for compiling programs in any language; or command-line options
meaningful for C and related languages; or options that are meaningful only for C++ programs. See Section 3.4 [Options Controlling C Dialect], page 35, for explanations of options
for languages related to C. See Section 3.5 [Options Controlling C++ Dialect], page 42, for
explanations of options that are meaningful only for C++ programs.

3.4 Options Controlling C Dialect
The following options control the dialect of C (or languages derived from C, such as C++,
Objective-C and Objective-C++) that the compiler accepts:
-ansi

In C mode, this is equivalent to ‘-std=c90’. In C++ mode, it is equivalent to
‘-std=c++98’.
This turns off certain features of GCC that are incompatible with ISO C90
(when compiling C code), or of standard C++ (when compiling C++ code), such
as the asm and typeof keywords, and predefined macros such as unix and vax
that identify the type of system you are using. It also enables the undesirable
and rarely used ISO trigraph feature. For the C compiler, it disables recognition
of C++ style ‘//’ comments as well as the inline keyword.
The alternate keywords __asm__, __extension__, __inline__ and __typeof_
_ continue to work despite ‘-ansi’. You would not want to use them in an ISO
C program, of course, but it is useful to put them in header files that might be
included in compilations done with ‘-ansi’. Alternate predefined macros such
as __unix__ and __vax__ are also available, with or without ‘-ansi’.
The ‘-ansi’ option does not cause non-ISO programs to be rejected
gratuitously. For that, ‘-Wpedantic’ is required in addition to ‘-ansi’. See
Section 3.8 [Warning Options], page 62.
The macro __STRICT_ANSI__ is predefined when the ‘-ansi’ option is used.
Some header files may notice this macro and refrain from declaring certain
functions or defining certain macros that the ISO standard doesn’t call for; this
is to avoid interfering with any programs that might use these names for other
things.
Functions that are normally built in but do not have semantics defined by ISO
C (such as alloca and ffs) are not built-in functions when ‘-ansi’ is used. See
Section 6.58 [Other built-in functions provided by GCC], page 613, for details
of the functions affected.

36

-std=

Using the GNU Compiler Collection (GCC)

Determine the language standard. See Chapter 2 [Language Standards Supported by GCC], page 5, for details of these standard versions. This option is
currently only supported when compiling C or C++.
The compiler can accept several base standards, such as ‘c90’ or ‘c++98’, and
GNU dialects of those standards, such as ‘gnu90’ or ‘gnu++98’. When a base
standard is specified, the compiler accepts all programs following that standard plus those using GNU extensions that do not contradict it. For example,
‘-std=c90’ turns off certain features of GCC that are incompatible with ISO
C90, such as the asm and typeof keywords, but not other GNU extensions that
do not have a meaning in ISO C90, such as omitting the middle term of a ?:
expression. On the other hand, when a GNU dialect of a standard is specified,
all features supported by the compiler are enabled, even when those features
change the meaning of the base standard. As a result, some strict-conforming
programs may be rejected. The particular standard is used by ‘-Wpedantic’ to
identify which features are GNU extensions given that version of the standard.
For example ‘-std=gnu90 -Wpedantic’ warns about C++ style ‘//’ comments,
while ‘-std=gnu99 -Wpedantic’ does not.
A value for this option must be provided; possible values are
‘c90’
‘c89’
‘iso9899:1990’
Support all ISO C90 programs (certain GNU extensions that conflict with ISO C90 are disabled). Same as ‘-ansi’ for C code.
‘iso9899:199409’
ISO C90 as modified in amendment 1.
‘c99’
‘c9x’
‘iso9899:1999’
‘iso9899:199x’
ISO C99. This standard is substantially completely supported,
modulo bugs and floating-point issues (mainly but not entirely
relating to optional C99 features from Annexes F and G). See
http://gcc.gnu.org/c99status.html for more information. The
names ‘c9x’ and ‘iso9899:199x’ are deprecated.
‘c11’
‘c1x’
‘iso9899:2011’
ISO C11, the 2011 revision of the ISO C standard. This standard is
substantially completely supported, modulo bugs, floating-point issues (mainly but not entirely relating to optional C11 features from
Annexes F and G) and the optional Annexes K (Bounds-checking
interfaces) and L (Analyzability). The name ‘c1x’ is deprecated.

Chapter 3: GCC Command Options

37

‘c17’
‘c18’
‘iso9899:2017’
‘iso9899:2018’
ISO C17, the 2017 revision of the ISO C standard (expected to
be published in 2018). This standard is same as C11 except for
corrections of defects (all of which are also applied with ‘-std=c11’)
and a new value of __STDC_VERSION__, and so is supported to the
same extent as C11.
‘gnu90’
‘gnu89’

GNU dialect of ISO C90 (including some C99 features).

‘gnu99’
‘gnu9x’

GNU dialect of ISO C99. The name ‘gnu9x’ is deprecated.

‘gnu11’
‘gnu1x’

GNU dialect of ISO C11. The name ‘gnu1x’ is deprecated.

‘gnu17’
‘gnu18’

GNU dialect of ISO C17. This is the default for C code.

‘c++98’
‘c++03’
‘gnu++98’
‘gnu++03’
‘c++11’
‘c++0x’
‘gnu++11’
‘gnu++0x’
‘c++14’
‘c++1y’
‘gnu++14’
‘gnu++1y’
‘c++17’
‘c++1z’
‘gnu++17’
‘gnu++1z’
‘c++2a’

The 1998 ISO C++ standard plus the 2003 technical corrigendum
and some additional defect reports. Same as ‘-ansi’ for C++ code.
GNU dialect of ‘-std=c++98’.
The 2011 ISO C++ standard plus amendments. The name ‘c++0x’
is deprecated.
GNU dialect of ‘-std=c++11’. The name ‘gnu++0x’ is deprecated.
The 2014 ISO C++ standard plus amendments. The name ‘c++1y’
is deprecated.
GNU dialect of ‘-std=c++14’. This is the default for C++ code.
The name ‘gnu++1y’ is deprecated.
The 2017 ISO C++ standard plus amendments. The name ‘c++1z’
is deprecated.
GNU dialect of ‘-std=c++17’. The name ‘gnu++1z’ is deprecated.
The next revision of the ISO C++ standard, tentatively planned
for 2020. Support is highly experimental, and will almost certainly
change in incompatible ways in future releases.

38

Using the GNU Compiler Collection (GCC)

‘gnu++2a’

GNU dialect of ‘-std=c++2a’. Support is highly experimental, and
will almost certainly change in incompatible ways in future releases.

-fgnu89-inline
The option ‘-fgnu89-inline’ tells GCC to use the traditional GNU semantics
for inline functions when in C99 mode. See Section 6.43 [An Inline Function is As Fast As a Macro], page 539. Using this option is roughly equivalent to adding the gnu_inline function attribute to all inline functions (see
Section 6.31 [Function Attributes], page 464).
The option ‘-fno-gnu89-inline’ explicitly tells GCC to use the C99 semantics
for inline when in C99 or gnu99 mode (i.e., it specifies the default behavior).
This option is not supported in ‘-std=c90’ or ‘-std=gnu90’ mode.
The preprocessor macros __GNUC_GNU_INLINE__ and __GNUC_STDC_INLINE__
may be used to check which semantics are in effect for inline functions. See
Section “Common Predefined Macros” in The C Preprocessor.
-fpermitted-flt-eval-methods=style
ISO/IEC TS 18661-3 defines new permissible values for FLT_EVAL_METHOD that
indicate that operations and constants with a semantic type that is an interchange or extended format should be evaluated to the precision and range of
that type. These new values are a superset of those permitted under C99/C11,
which does not specify the meaning of other positive values of FLT_EVAL_
METHOD. As such, code conforming to C11 may not have been written expecting
the possibility of the new values.
‘-fpermitted-flt-eval-methods’ specifies whether the compiler should allow
only the values of FLT_EVAL_METHOD specified in C99/C11, or the extended set
of values specified in ISO/IEC TS 18661-3.
style is either c11 or ts-18661-3 as appropriate.
The default when in a standards compliant mode (‘-std=c11’ or similar) is
‘-fpermitted-flt-eval-methods=c11’. The default when in a GNU dialect
(‘-std=gnu11’ or similar) is ‘-fpermitted-flt-eval-methods=ts-18661-3’.
-aux-info filename
Output to the given filename prototyped declarations for all functions declared
and/or defined in a translation unit, including those in header files. This option
is silently ignored in any language other than C.
Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or
unprototyped (‘I’, ‘N’ for new or ‘O’ for old, respectively, in the first character
after the line number and the colon), and whether it came from a declaration
or a definition (‘C’ or ‘F’, respectively, in the following character). In the case
of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration.
-fallow-parameterless-variadic-functions
Accept variadic functions without named parameters.

Chapter 3: GCC Command Options

39

Although it is possible to define such a function, this is not very useful as it
is not possible to read the arguments. This is only supported for C as this
construct is allowed by C++.
-fno-asm

Do not recognize asm, inline or typeof as a keyword, so that code can use
these words as identifiers. You can use the keywords __asm__, __inline__ and
__typeof__ instead. ‘-ansi’ implies ‘-fno-asm’.
In C++, this switch only affects the typeof keyword, since asm and inline
are standard keywords. You may want to use the ‘-fno-gnu-keywords’ flag
instead, which has the same effect. In C99 mode (‘-std=c99’ or ‘-std=gnu99’),
this switch only affects the asm and typeof keywords, since inline is a standard
keyword in ISO C99.

-fno-builtin
-fno-builtin-function
Don’t recognize built-in functions that do not begin with ‘__builtin_’ as prefix.
See Section 6.58 [Other built-in functions provided by GCC], page 613, for
details of the functions affected, including those which are not built-in functions
when ‘-ansi’ or ‘-std’ options for strict ISO C conformance are used because
they do not have an ISO standard meaning.
GCC normally generates special code to handle certain built-in functions more
efficiently; for instance, calls to alloca may become single instructions which
adjust the stack directly, and calls to memcpy may become inline copy loops.
The resulting code is often both smaller and faster, but since the function
calls no longer appear as such, you cannot set a breakpoint on those calls,
nor can you change the behavior of the functions by linking with a different
library. In addition, when a function is recognized as a built-in function, GCC
may use information about that function to warn about problems with calls to
that function, or to generate more efficient code, even if the resulting code still
contains calls to that function. For example, warnings are given with ‘-Wformat’
for bad calls to printf when printf is built in and strlen is known not to
modify global memory.
With the ‘-fno-builtin-function’ option only the built-in function function
is disabled. function must not begin with ‘__builtin_’. If a function is named
that is not built-in in this version of GCC, this option is ignored. There is
no corresponding ‘-fbuiltin-function’ option; if you wish to enable built-in
functions selectively when using ‘-fno-builtin’ or ‘-ffreestanding’, you may
define macros such as:
#define abs(n)
#define strcpy(d, s)

__builtin_abs ((n))
__builtin_strcpy ((d), (s))

-fgimple
Enable parsing of function definitions marked with __GIMPLE. This is an experimental feature that allows unit testing of GIMPLE passes.
-fhosted
Assert that compilation targets a hosted environment.
This implies
‘-fbuiltin’. A hosted environment is one in which the entire standard library

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Using the GNU Compiler Collection (GCC)

is available, and in which main has a return type of int. Examples are nearly
everything except a kernel. This is equivalent to ‘-fno-freestanding’.
-ffreestanding
Assert that compilation targets a freestanding environment. This implies
‘-fno-builtin’. A freestanding environment is one in which the standard
library may not exist, and program startup may not necessarily be at
main. The most obvious example is an OS kernel. This is equivalent to
‘-fno-hosted’.
See Chapter 2 [Language Standards Supported by GCC], page 5, for details of
freestanding and hosted environments.
-fopenacc
Enable handling of OpenACC directives #pragma acc in C/C++ and !$acc
in Fortran. When ‘-fopenacc’ is specified, the compiler generates accelerated code according to the OpenACC Application Programming Interface v2.0
https://www.openacc.org. This option implies ‘-pthread’, and thus is only
supported on targets that have support for ‘-pthread’.
-fopenacc-dim=geom
Specify default compute dimensions for parallel offload regions that do not
explicitly specify. The geom value is a triple of ’:’-separated sizes, in order
’gang’, ’worker’ and, ’vector’. A size can be omitted, to use a target-specific
default value.
-fopenmp

Enable handling of OpenMP directives #pragma omp in C/C++ and !$omp
in Fortran. When ‘-fopenmp’ is specified, the compiler generates parallel
code according to the OpenMP Application Program Interface v4.5
http://www.openmp.org/. This option implies ‘-pthread’, and thus is only
supported on targets that have support for ‘-pthread’. ‘-fopenmp’ implies
‘-fopenmp-simd’.

-fopenmp-simd
Enable handling of OpenMP’s SIMD directives with #pragma omp in C/C++
and !$omp in Fortran. Other OpenMP directives are ignored.
-fgnu-tm

When the option ‘-fgnu-tm’ is specified, the compiler generates code for the
Linux variant of Intel’s current Transactional Memory ABI specification document (Revision 1.1, May 6 2009). This is an experimental feature whose
interface may change in future versions of GCC, as the official specification
changes. Please note that not all architectures are supported for this feature.
For more information on GCC’s support for transactional memory, See Section
“The GNU Transactional Memory Library” in GNU Transactional Memory
Library.
Note that the transactional memory feature is not supported with non-call
exceptions (‘-fnon-call-exceptions’).

-fms-extensions
Accept some non-standard constructs used in Microsoft header files.
In C++ code, this allows member names in structures to be similar to previous
types declarations.

Chapter 3: GCC Command Options

41

typedef int UOW;
struct ABC {
UOW UOW;
};

Some cases of unnamed fields in structures and unions are only accepted
with this option. See Section 6.62 [Unnamed struct/union fields within
structs/unions], page 781, for details.
Note that this option is off for all targets but x86 targets using ms-abi.
-fplan9-extensions
Accept some non-standard constructs used in Plan 9 code.
This enables ‘-fms-extensions’, permits passing pointers to structures with
anonymous fields to functions that expect pointers to elements of the type of
the field, and permits referring to anonymous fields declared using a typedef.
See Section 6.62 [Unnamed struct/union fields within structs/unions], page 781,
for details. This is only supported for C, not C++.
-fcond-mismatch
Allow conditional expressions with mismatched types in the second and third
arguments. The value of such an expression is void. This option is not supported
for C++.
-flax-vector-conversions
Allow implicit conversions between vectors with differing numbers of elements
and/or incompatible element types. This option should not be used for new
code.
-funsigned-char
Let the type char be unsigned, like unsigned char.
Each kind of machine has a default for what char should be. It is either like
unsigned char by default or like signed char by default.
Ideally, a portable program should always use signed char or unsigned char
when it depends on the signedness of an object. But many programs have been
written to use plain char and expect it to be signed, or expect it to be unsigned,
depending on the machines they were written for. This option, and its inverse,
let you make such a program work with the opposite default.
The type char is always a distinct type from each of signed char or unsigned
char, even though its behavior is always just like one of those two.
-fsigned-char
Let the type char be signed, like signed char.
Note that this is equivalent to ‘-fno-unsigned-char’, which is the negative
form of ‘-funsigned-char’. Likewise, the option ‘-fno-signed-char’ is equivalent to ‘-funsigned-char’.

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Using the GNU Compiler Collection (GCC)

-fsigned-bitfields
-funsigned-bitfields
-fno-signed-bitfields
-fno-unsigned-bitfields
These options control whether a bit-field is signed or unsigned, when the declaration does not use either signed or unsigned. By default, such a bit-field is
signed, because this is consistent: the basic integer types such as int are signed
types.
-fsso-struct=endianness
Set the default scalar storage order of structures and unions to the specified endianness. The accepted values are ‘big-endian’, ‘little-endian’ and ‘native’
for the native endianness of the target (the default). This option is not supported for C++.
Warning: the ‘-fsso-struct’ switch causes GCC to generate code that is not
binary compatible with code generated without it if the specified endianness is
not the native endianness of the target.

3.5 Options Controlling C++ Dialect
This section describes the command-line options that are only meaningful for C++ programs.
You can also use most of the GNU compiler options regardless of what language your
program is in. For example, you might compile a file ‘firstClass.C’ like this:
g++ -g -fstrict-enums -O -c firstClass.C

In this example, only ‘-fstrict-enums’ is an option meant only for C++ programs; you can
use the other options with any language supported by GCC.
Some options for compiling C programs, such as ‘-std’, are also relevant for C++ programs. See Section 3.4 [Options Controlling C Dialect], page 35.
Here is a list of options that are only for compiling C++ programs:
-fabi-version=n
Use version n of the C++ ABI. The default is version 0.
Version 0 refers to the version conforming most closely to the C++ ABI specification. Therefore, the ABI obtained using version 0 will change in different
versions of G++ as ABI bugs are fixed.
Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.
Version 2 is the version of the C++ ABI that first appeared in G++ 3.4, and was
the default through G++ 4.9.
Version 3 corrects an error in mangling a constant address as a template argument.
Version 4, which first appeared in G++ 4.5, implements a standard mangling
for vector types.
Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute
const/volatile on function pointer types, decltype of a plain decl, and use of a
function parameter in the declaration of another parameter.

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43

Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of C++11 scoped enums and the mangling of template argument packs,
const/static cast, prefix ++ and –, and a class scope function used as a template argument.
Version 7, which first appeared in G++ 4.8, that treats nullptr t as a builtin
type and corrects the mangling of lambdas in default argument scope.
Version 8, which first appeared in G++ 4.9, corrects the substitution behavior
of function types with function-cv-qualifiers.
Version 9, which first appeared in G++ 5.2, corrects the alignment of nullptr_t.
Version 10, which first appeared in G++ 6.1, adds mangling of attributes that
affect type identity, such as ia32 calling convention attributes (e.g. ‘stdcall’).
Version 11, which first appeared in G++ 7, corrects the mangling of sizeof... expressions and operator names. For multiple entities with the same name within
a function, that are declared in different scopes, the mangling now changes starting with the twelfth occurrence. It also implies ‘-fnew-inheriting-ctors’.
Version 12, which first appeared in G++ 8, corrects the calling conventions for
empty classes on the x86 64 target and for classes with only deleted copy/move
constructors. It accidentally changes the calling convention for classes with a
deleted copy constructor and a trivial move constructor.
Version 13, which first appeared in G++ 8.2, fixes the accidental change in
version 12.
See also ‘-Wabi’.
-fabi-compat-version=n
On targets that support strong aliases, G++ works around mangling changes by
creating an alias with the correct mangled name when defining a symbol with
an incorrect mangled name. This switch specifies which ABI version to use for
the alias.
With ‘-fabi-version=0’ (the default), this defaults to 11 (GCC 7 compatibility). If another ABI version is explicitly selected, this defaults to 0. For compatibility with GCC versions 3.2 through 4.9, use ‘-fabi-compat-version=2’.
If this option is not provided but ‘-Wabi=n’ is, that version is used for compatibility aliases. If this option is provided along with ‘-Wabi’ (without the
version), the version from this option is used for the warning.
-fno-access-control
Turn off all access checking. This switch is mainly useful for working around
bugs in the access control code.
-faligned-new
Enable support for C++17 new of types that require more alignment than
void* ::operator new(std::size_t) provides. A numeric argument such as
-faligned-new=32 can be used to specify how much alignment (in bytes) is
provided by that function, but few users will need to override the default of
alignof(std::max_align_t).
This flag is enabled by default for ‘-std=c++17’.

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Using the GNU Compiler Collection (GCC)

-fcheck-new
Check that the pointer returned by operator new is non-null before attempting
to modify the storage allocated. This check is normally unnecessary because
the C++ standard specifies that operator new only returns 0 if it is declared
throw(), in which case the compiler always checks the return value even without
this option. In all other cases, when operator new has a non-empty exception
specification, memory exhaustion is signalled by throwing std::bad_alloc.
See also ‘new (nothrow)’.
-fconcepts
Enable support for the C++ Extensions for Concepts Technical Specification,
ISO 19217 (2015), which allows code like
template  concept bool Addable = requires (T t) { t + t; };
template  T add (T a, T b) { return a + b; }

-fconstexpr-depth=n
Set the maximum nested evaluation depth for C++11 constexpr functions to
n. A limit is needed to detect endless recursion during constant expression
evaluation. The minimum specified by the standard is 512.
-fconstexpr-loop-limit=n
Set the maximum number of iterations for a loop in C++14 constexpr functions
to n. A limit is needed to detect infinite loops during constant expression
evaluation. The default is 262144 (1<<18).
-fdeduce-init-list
Enable deduction of a template type parameter as std::initializer_list
from a brace-enclosed initializer list, i.e.
template  auto forward(T t) -> decltype (realfn (t))
{
return realfn (t);
}
void f()
{
forward({1,2}); // call forward>
}

This deduction was implemented as a possible extension to the originally proposed semantics for the C++11 standard, but was not part of the final standard,
so it is disabled by default. This option is deprecated, and may be removed in
a future version of G++.
-ffriend-injection
Inject friend functions into the enclosing namespace, so that they are visible
outside the scope of the class in which they are declared. Friend functions were
documented to work this way in the old Annotated C++ Reference Manual.
However, in ISO C++ a friend function that is not declared in an enclosing
scope can only be found using argument dependent lookup. GCC defaults to
the standard behavior.
This option is deprecated and will be removed.

Chapter 3: GCC Command Options

45

-fno-elide-constructors
The C++ standard allows an implementation to omit creating a temporary that
is only used to initialize another object of the same type. Specifying this option
disables that optimization, and forces G++ to call the copy constructor in all
cases. This option also causes G++ to call trivial member functions which
otherwise would be expanded inline.
In C++17, the compiler is required to omit these temporaries, but this option
still affects trivial member functions.
-fno-enforce-eh-specs
Don’t generate code to check for violation of exception specifications at run
time. This option violates the C++ standard, but may be useful for reducing
code size in production builds, much like defining NDEBUG. This does not give
user code permission to throw exceptions in violation of the exception specifications; the compiler still optimizes based on the specifications, so throwing an
unexpected exception results in undefined behavior at run time.
-fextern-tls-init
-fno-extern-tls-init
The C++11 and OpenMP standards allow thread_local and threadprivate
variables to have dynamic (runtime) initialization. To support this, any use of
such a variable goes through a wrapper function that performs any necessary
initialization. When the use and definition of the variable are in the same
translation unit, this overhead can be optimized away, but when the use is in a
different translation unit there is significant overhead even if the variable doesn’t
actually need dynamic initialization. If the programmer can be sure that no
use of the variable in a non-defining TU needs to trigger dynamic initialization
(either because the variable is statically initialized, or a use of the variable in
the defining TU will be executed before any uses in another TU), they can avoid
this overhead with the ‘-fno-extern-tls-init’ option.
On targets that support symbol aliases, the default is ‘-fextern-tls-init’.
On targets that do not support symbol aliases, the default is
‘-fno-extern-tls-init’.
-ffor-scope
-fno-for-scope
If ‘-ffor-scope’ is specified, the scope of variables declared in a for-initstatement is limited to the for loop itself, as specified by the C++ standard.
If ‘-fno-for-scope’ is specified, the scope of variables declared in a for-initstatement extends to the end of the enclosing scope, as was the case in old
versions of G++, and other (traditional) implementations of C++.
This option is deprecated and the associated non-standard functionality will be
removed.
-fno-gnu-keywords
Do not recognize typeof as a keyword, so that code can use this word as an
identifier. You can use the keyword __typeof__ instead. This option is implied
by the strict ISO C++ dialects: ‘-ansi’, ‘-std=c++98’, ‘-std=c++11’, etc.

46

Using the GNU Compiler Collection (GCC)

-fno-implicit-templates
Never emit code for non-inline templates that are instantiated implicitly (i.e.
by use); only emit code for explicit instantiations. See Section 7.5 [Template
Instantiation], page 790, for more information.
-fno-implicit-inline-templates
Don’t emit code for implicit instantiations of inline templates, either. The
default is to handle inlines differently so that compiles with and without optimization need the same set of explicit instantiations.
-fno-implement-inlines
To save space, do not emit out-of-line copies of inline functions controlled by
#pragma implementation. This causes linker errors if these functions are not
inlined everywhere they are called.
-fms-extensions
Disable Wpedantic warnings about constructs used in MFC, such as implicit
int and getting a pointer to member function via non-standard syntax.
-fnew-inheriting-ctors
Enable the P0136 adjustment to the semantics of C++11 constructor inheritance. This is part of C++17 but also considered to be a Defect Report against
C++11 and C++14. This flag is enabled by default unless ‘-fabi-version=10’
or lower is specified.
-fnew-ttp-matching
Enable the P0522 resolution to Core issue 150, template template parameters
and default arguments: this allows a template with default template arguments
as an argument for a template template parameter with fewer template parameters. This flag is enabled by default for ‘-std=c++17’.
-fno-nonansi-builtins
Disable built-in declarations of functions that are not mandated by ANSI/ISO
C. These include ffs, alloca, _exit, index, bzero, conjf, and other related
functions.
-fnothrow-opt
Treat a throw() exception specification as if it were a noexcept specification to
reduce or eliminate the text size overhead relative to a function with no exception specification. If the function has local variables of types with non-trivial
destructors, the exception specification actually makes the function smaller because the EH cleanups for those variables can be optimized away. The semantic
effect is that an exception thrown out of a function with such an exception specification results in a call to terminate rather than unexpected.
-fno-operator-names
Do not treat the operator name keywords and, bitand, bitor, compl, not, or
and xor as synonyms as keywords.
-fno-optional-diags
Disable diagnostics that the standard says a compiler does not need to issue.
Currently, the only such diagnostic issued by G++ is the one for a name having
multiple meanings within a class.

Chapter 3: GCC Command Options

47

-fpermissive
Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using ‘-fpermissive’ allows some nonconforming code to compile.
-fno-pretty-templates
When an error message refers to a specialization of a function template, the compiler normally prints the signature of the template followed by the template arguments and any typedefs or typenames in the signature (e.g. void f(T) [with
T = int] rather than void f(int)) so that it’s clear which template is involved.
When an error message refers to a specialization of a class template, the compiler omits any template arguments that match the default template arguments
for that template. If either of these behaviors make it harder to understand
the error message rather than easier, you can use ‘-fno-pretty-templates’ to
disable them.
-frepo

Enable automatic template instantiation at link time. This option also implies ‘-fno-implicit-templates’. See Section 7.5 [Template Instantiation],
page 790, for more information.

-fno-rtti
Disable generation of information about every class with virtual functions
for use by the C++ run-time type identification features (dynamic_cast and
typeid). If you don’t use those parts of the language, you can save some space
by using this flag. Note that exception handling uses the same information,
but G++ generates it as needed. The dynamic_cast operator can still be used
for casts that do not require run-time type information, i.e. casts to void * or
to unambiguous base classes.
-fsized-deallocation
Enable the built-in global declarations
void operator delete (void *, std::size_t) noexcept;
void operator delete[] (void *, std::size_t) noexcept;

as introduced in C++14. This is useful for user-defined replacement deallocation functions that, for example, use the size of the object to make deallocation faster. Enabled by default under ‘-std=c++14’ and above. The flag
‘-Wsized-deallocation’ warns about places that might want to add a definition.
-fstrict-enums
Allow the compiler to optimize using the assumption that a value of enumerated
type can only be one of the values of the enumeration (as defined in the C++
standard; basically, a value that can be represented in the minimum number
of bits needed to represent all the enumerators). This assumption may not be
valid if the program uses a cast to convert an arbitrary integer value to the
enumerated type.
-fstrong-eval-order
Evaluate member access, array subscripting, and shift expressions in left-toright order, and evaluate assignment in right-to-left order, as adopted for C++17.
Enabled by default with ‘-std=c++17’. ‘-fstrong-eval-order=some’ enables

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Using the GNU Compiler Collection (GCC)

just the ordering of member access and shift expressions, and is the default
without ‘-std=c++17’.
-ftemplate-backtrace-limit=n
Set the maximum number of template instantiation notes for a single warning
or error to n. The default value is 10.
-ftemplate-depth=n
Set the maximum instantiation depth for template classes to n. A limit on
the template instantiation depth is needed to detect endless recursions during
template class instantiation. ANSI/ISO C++ conforming programs must not
rely on a maximum depth greater than 17 (changed to 1024 in C++11). The
default value is 900, as the compiler can run out of stack space before hitting
1024 in some situations.
-fno-threadsafe-statics
Do not emit the extra code to use the routines specified in the C++ ABI for
thread-safe initialization of local statics. You can use this option to reduce code
size slightly in code that doesn’t need to be thread-safe.
-fuse-cxa-atexit
Register destructors for objects with static storage duration with the __cxa_
atexit function rather than the atexit function. This option is required for
fully standards-compliant handling of static destructors, but only works if your
C library supports __cxa_atexit.
-fno-use-cxa-get-exception-ptr
Don’t use the __cxa_get_exception_ptr runtime routine. This causes
std::uncaught_exception to be incorrect, but is necessary if the runtime
routine is not available.
-fvisibility-inlines-hidden
This switch declares that the user does not attempt to compare pointers to
inline functions or methods where the addresses of the two functions are taken
in different shared objects.
The effect of this is that GCC may, effectively, mark inline methods with __
attribute__ ((visibility ("hidden"))) so that they do not appear in the
export table of a DSO and do not require a PLT indirection when used within
the DSO. Enabling this option can have a dramatic effect on load and link
times of a DSO as it massively reduces the size of the dynamic export table
when the library makes heavy use of templates.
The behavior of this switch is not quite the same as marking the methods as
hidden directly, because it does not affect static variables local to the function
or cause the compiler to deduce that the function is defined in only one shared
object.
You may mark a method as having a visibility explicitly to negate the effect of
the switch for that method. For example, if you do want to compare pointers
to a particular inline method, you might mark it as having default visibility.
Marking the enclosing class with explicit visibility has no effect.

Chapter 3: GCC Command Options

49

Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. See Section 7.5 [Template
Instantiation], page 790.
-fvisibility-ms-compat
This flag attempts to use visibility settings to make GCC’s C++ linkage model
compatible with that of Microsoft Visual Studio.
The flag makes these changes to GCC’s linkage model:
1. It sets the default visibility to hidden, like ‘-fvisibility=hidden’.
2. Types, but not their members, are not hidden by default.
3. The One Definition Rule is relaxed for types without explicit visibility
specifications that are defined in more than one shared object: those declarations are permitted if they are permitted when this option is not used.
In new code it is better to use ‘-fvisibility=hidden’ and export those classes
that are intended to be externally visible. Unfortunately it is possible for code
to rely, perhaps accidentally, on the Visual Studio behavior.
Among the consequences of these changes are that static data members of
the same type with the same name but defined in different shared objects are
different, so changing one does not change the other; and that pointers to
function members defined in different shared objects may not compare equal.
When this flag is given, it is a violation of the ODR to define types with the
same name differently.
-fno-weak
Do not use weak symbol support, even if it is provided by the linker. By
default, G++ uses weak symbols if they are available. This option exists only
for testing, and should not be used by end-users; it results in inferior code and
has no benefits. This option may be removed in a future release of G++.
-nostdinc++
Do not search for header files in the standard directories specific to C++, but do
still search the other standard directories. (This option is used when building
the C++ library.)
In addition, these optimization, warning, and code generation options have meanings only
for C++ programs:
-Wabi (C, Objective-C, C++ and Objective-C++ only)
Warn when G++ it generates code that is probably not compatible with the
vendor-neutral C++ ABI. Since G++ now defaults to updating the ABI with
each major release, normally ‘-Wabi’ will warn only if there is a check added
later in a release series for an ABI issue discovered since the initial release.
‘-Wabi’ will warn about more things if an older ABI version is selected (with
‘-fabi-version=n’).
‘-Wabi’ can also be used with an explicit version number to warn about compatibility with a particular ‘-fabi-version’ level, e.g. ‘-Wabi=2’ to warn about
changes relative to ‘-fabi-version=2’.

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Using the GNU Compiler Collection (GCC)

If an explicit version number is provided and ‘-fabi-compat-version’ is
not specified, the version number from this option is used for compatibility
aliases. If no explicit version number is provided with this option, but
‘-fabi-compat-version’ is specified, that version number is used for ABI
warnings.
Although an effort has been made to warn about all such cases, there are
probably some cases that are not warned about, even though G++ is generating
incompatible code. There may also be cases where warnings are emitted even
though the code that is generated is compatible.
You should rewrite your code to avoid these warnings if you are concerned about
the fact that code generated by G++ may not be binary compatible with code
generated by other compilers.
Known incompatibilities in ‘-fabi-version=2’ (which was the default from
GCC 3.4 to 4.9) include:
• A template with a non-type template parameter of reference type was
mangled incorrectly:
extern int N;
template  struct S {};
void n (S) {2}

•

•

•

•

•

•

This was fixed in ‘-fabi-version=3’.
SIMD vector types declared using __attribute ((vector_size)) were
mangled in a non-standard way that does not allow for overloading of
functions taking vectors of different sizes.
The mangling was changed in ‘-fabi-version=4’.
__attribute ((const)) and noreturn were mangled as type qualifiers,
and decltype of a plain declaration was folded away.
These mangling issues were fixed in ‘-fabi-version=5’.
Scoped enumerators passed as arguments to a variadic function are promoted like unscoped enumerators, causing va_arg to complain. On most
targets this does not actually affect the parameter passing ABI, as there is
no way to pass an argument smaller than int.
Also, the ABI changed the mangling of template argument packs, const_
cast, static_cast, prefix increment/decrement, and a class scope function used as a template argument.
These issues were corrected in ‘-fabi-version=6’.
Lambdas in default argument scope were mangled incorrectly, and the ABI
changed the mangling of nullptr_t.
These issues were corrected in ‘-fabi-version=7’.
When mangling a function type with function-cv-qualifiers, the un-qualified
function type was incorrectly treated as a substitution candidate.
This was fixed in ‘-fabi-version=8’, the default for GCC 5.1.
decltype(nullptr) incorrectly had an alignment of 1, leading to unaligned accesses. Note that this did not affect the ABI of a function with
a nullptr_t parameter, as parameters have a minimum alignment.

Chapter 3: GCC Command Options

51

This was fixed in ‘-fabi-version=9’, the default for GCC 5.2.
• Target-specific attributes that affect the identity of a type, such as ia32
calling conventions on a function type (stdcall, regparm, etc.), did not
affect the mangled name, leading to name collisions when function pointers
were used as template arguments.
This was fixed in ‘-fabi-version=10’, the default for GCC 6.1.
It also warns about psABI-related changes. The known psABI changes at this
point include:
• For SysV/x86-64, unions with long double members are passed in memory
as specified in psABI. For example:
union U {
long double ld;
int i;
};

union U is always passed in memory.
-Wabi-tag (C++ and Objective-C++ only)
Warn when a type with an ABI tag is used in a context that does not have
that ABI tag. See Section 7.7 [C++ Attributes], page 793 for more information
about ABI tags.
-Wctor-dtor-privacy (C++ and Objective-C++ only)
Warn when a class seems unusable because all the constructors or destructors
in that class are private, and it has neither friends nor public static member
functions. Also warn if there are no non-private methods, and there’s at least
one private member function that isn’t a constructor or destructor.
-Wdelete-non-virtual-dtor (C++ and Objective-C++ only)
Warn when delete is used to destroy an instance of a class that has virtual
functions and non-virtual destructor. It is unsafe to delete an instance of a
derived class through a pointer to a base class if the base class does not have a
virtual destructor. This warning is enabled by ‘-Wall’.
-Wliteral-suffix (C++ and Objective-C++ only)
Warn when a string or character literal is followed by a ud-suffix which does not
begin with an underscore. As a conforming extension, GCC treats such suffixes
as separate preprocessing tokens in order to maintain backwards compatibility
with code that uses formatting macros from . For example:
#define __STDC_FORMAT_MACROS
#include 
#include 
int main() {
int64_t i64 = 123;
printf("My int64: %" PRId64"\n", i64);
}

In this case, PRId64 is treated as a separate preprocessing token.
Additionally, warn when a user-defined literal operator is declared with a literal
suffix identifier that doesn’t begin with an underscore. Literal suffix identifiers
that don’t begin with an underscore are reserved for future standardization.

52

Using the GNU Compiler Collection (GCC)

This warning is enabled by default.
-Wlto-type-mismatch
During the link-time optimization warn about type mismatches in global declarations from different compilation units. Requires ‘-flto’ to be enabled.
Enabled by default.
-Wno-narrowing (C++ and Objective-C++ only)
For C++11 and later standards, narrowing conversions are diagnosed by default,
as required by the standard. A narrowing conversion from a constant produces
an error, and a narrowing conversion from a non-constant produces a warning,
but ‘-Wno-narrowing’ suppresses the diagnostic. Note that this does not affect
the meaning of well-formed code; narrowing conversions are still considered
ill-formed in SFINAE contexts.
With ‘-Wnarrowing’ in C++98, warn when a narrowing conversion prohibited
by C++11 occurs within ‘{ }’, e.g.
int i = { 2.2 }; // error: narrowing from double to int

This flag is included in ‘-Wall’ and ‘-Wc++11-compat’.
-Wnoexcept (C++ and Objective-C++ only)
Warn when a noexcept-expression evaluates to false because of a call to a function that does not have a non-throwing exception specification (i.e. throw() or
noexcept) but is known by the compiler to never throw an exception.
-Wnoexcept-type (C++ and Objective-C++ only)
Warn if the C++17 feature making noexcept part of a function type changes
the mangled name of a symbol relative to C++14. Enabled by ‘-Wabi’ and
‘-Wc++17-compat’.
As an example:
template  void f(T t) { t(); };
void g() noexcept;
void h() { f(g); }

In C++14, f calls calls
f.

f,

but

in

C++17

it

calls

-Wclass-memaccess (C++ and Objective-C++ only)
Warn when the destination of a call to a raw memory function such as memset
or memcpy is an object of class type, and when writing into such an object might
bypass the class non-trivial or deleted constructor or copy assignment, violate
const-correctness or encapsulation, or corrupt virtual table pointers. Modifying
the representation of such objects may violate invariants maintained by member
functions of the class. For example, the call to memset below is undefined
because it modifies a non-trivial class object and is, therefore, diagnosed. The
safe way to either initialize or clear the storage of objects of such types is by
using the appropriate constructor or assignment operator, if one is available.
std::string str = "abc";
memset (&str, 0, sizeof str);

The ‘-Wclass-memaccess’ option is enabled by ‘-Wall’. Explicitly casting the
pointer to the class object to void * or to a type that can be safely accessed
by the raw memory function suppresses the warning.

Chapter 3: GCC Command Options

53

-Wnon-virtual-dtor (C++ and Objective-C++ only)
Warn when a class has virtual functions and an accessible non-virtual destructor
itself or in an accessible polymorphic base class, in which case it is possible but
unsafe to delete an instance of a derived class through a pointer to the class itself
or base class. This warning is automatically enabled if ‘-Weffc++’ is specified.
-Wregister (C++ and Objective-C++ only)
Warn on uses of the register storage class specifier, except when it is part of
the GNU Section 6.45.5 [Explicit Register Variables], page 592 extension. The
use of the register keyword as storage class specifier has been deprecated in
C++11 and removed in C++17. Enabled by default with ‘-std=c++17’.
-Wreorder (C++ and Objective-C++ only)
Warn when the order of member initializers given in the code does not match
the order in which they must be executed. For instance:
struct A {
int i;
int j;
A(): j (0), i (1) { }
};

The compiler rearranges the member initializers for i and j to match the declaration order of the members, emitting a warning to that effect. This warning
is enabled by ‘-Wall’.
-fext-numeric-literals (C++ and Objective-C++ only)
Accept imaginary, fixed-point, or machine-defined literal number suffixes as
GNU extensions. When this option is turned off these suffixes are treated
as C++11 user-defined literal numeric suffixes. This is on by default for all
pre-C++11 dialects and all GNU dialects: ‘-std=c++98’, ‘-std=gnu++98’,
‘-std=gnu++11’, ‘-std=gnu++14’. This option is off by default for ISO C++11
onwards (‘-std=c++11’, ...).
The following ‘-W...’ options are not affected by ‘-Wall’.
-Weffc++ (C++ and Objective-C++ only)
Warn about violations of the following style guidelines from Scott Meyers’ Effective C++ series of books:
• Define a copy constructor and an assignment operator for classes with
dynamically-allocated memory.
• Prefer initialization to assignment in constructors.
• Have operator= return a reference to *this.
• Don’t try to return a reference when you must return an object.
• Distinguish between prefix and postfix forms of increment and decrement
operators.
• Never overload &&, ||, or ,.
This option also enables ‘-Wnon-virtual-dtor’, which is also one of the effective C++ recommendations. However, the check is extended to warn about the
lack of virtual destructor in accessible non-polymorphic bases classes too.

54

Using the GNU Compiler Collection (GCC)

When selecting this option, be aware that the standard library headers do not
obey all of these guidelines; use ‘grep -v’ to filter out those warnings.
-Wstrict-null-sentinel (C++ and Objective-C++ only)
Warn about the use of an uncasted NULL as sentinel. When compiling only with
GCC this is a valid sentinel, as NULL is defined to __null. Although it is a null
pointer constant rather than a null pointer, it is guaranteed to be of the same
size as a pointer. But this use is not portable across different compilers.
-Wno-non-template-friend (C++ and Objective-C++ only)
Disable warnings when non-template friend functions are declared within a
template. In very old versions of GCC that predate implementation of the ISO
standard, declarations such as ‘friend int foo(int)’, where the name of the
friend is an unqualified-id, could be interpreted as a particular specialization
of a template function; the warning exists to diagnose compatibility problems,
and is enabled by default.
-Wold-style-cast (C++ and Objective-C++ only)
Warn if an old-style (C-style) cast to a non-void type is used within a C++
program. The new-style casts (dynamic_cast, static_cast, reinterpret_
cast, and const_cast) are less vulnerable to unintended effects and much
easier to search for.
-Woverloaded-virtual (C++ and Objective-C++ only)
Warn when a function declaration hides virtual functions from a base class. For
example, in:
struct A {
virtual void f();
};
struct B: public A {
void f(int);
};

the A class version of f is hidden in B, and code like:
B* b;
b->f();

fails to compile.
-Wno-pmf-conversions (C++ and Objective-C++ only)
Disable the diagnostic for converting a bound pointer to member function to a
plain pointer.
-Wsign-promo (C++ and Objective-C++ only)
Warn when overload resolution chooses a promotion from unsigned or enumerated type to a signed type, over a conversion to an unsigned type of the same
size. Previous versions of G++ tried to preserve unsignedness, but the standard
mandates the current behavior.
-Wtemplates (C++ and Objective-C++ only)
Warn when a primary template declaration is encountered. Some coding rules
disallow templates, and this may be used to enforce that rule. The warning is

Chapter 3: GCC Command Options

55

inactive inside a system header file, such as the STL, so one can still use the
STL. One may also instantiate or specialize templates.
-Wmultiple-inheritance (C++ and Objective-C++ only)
Warn when a class is defined with multiple direct base classes. Some coding
rules disallow multiple inheritance, and this may be used to enforce that rule.
The warning is inactive inside a system header file, such as the STL, so one
can still use the STL. One may also define classes that indirectly use multiple
inheritance.
-Wvirtual-inheritance
Warn when a class is defined with a virtual direct base class. Some coding rules
disallow multiple inheritance, and this may be used to enforce that rule. The
warning is inactive inside a system header file, such as the STL, so one can still
use the STL. One may also define classes that indirectly use virtual inheritance.
-Wnamespaces
Warn when a namespace definition is opened. Some coding rules disallow
namespaces, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL, so one can still use the STL.
One may also use using directives and qualified names.
-Wno-terminate (C++ and Objective-C++ only)
Disable the warning about a throw-expression that will immediately result in a
call to terminate.

3.6 Options Controlling Objective-C and Objective-C++
Dialects
(NOTE: This manual does not describe the Objective-C and Objective-C++ languages themselves. See Chapter 2 [Language Standards Supported by GCC], page 5, for references.)
This section describes the command-line options that are only meaningful for ObjectiveC and Objective-C++ programs. You can also use most of the language-independent GNU
compiler options. For example, you might compile a file ‘some_class.m’ like this:
gcc -g -fgnu-runtime -O -c some_class.m

In this example, ‘-fgnu-runtime’ is an option meant only for Objective-C and ObjectiveC++ programs; you can use the other options with any language supported by GCC.
Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front-end (e.g., ‘-Wtraditional’). Similarly,
Objective-C++ compilations may use C++-specific options (e.g., ‘-Wabi’).
Here is a list of options that are only for compiling Objective-C and Objective-C++
programs:
-fconstant-string-class=class-name
Use class-name as the name of the class to instantiate for each literal string
specified with the syntax @"...". The default class name is NXConstantString
if the GNU runtime is being used, and NSConstantString if the NeXT runtime
is being used (see below). The ‘-fconstant-cfstrings’ option, if also present,
overrides the ‘-fconstant-string-class’ setting and cause @"..." literals to
be laid out as constant CoreFoundation strings.

56

Using the GNU Compiler Collection (GCC)

-fgnu-runtime
Generate object code compatible with the standard GNU Objective-C runtime.
This is the default for most types of systems.
-fnext-runtime
Generate output compatible with the NeXT runtime. This is the default for
NeXT-based systems, including Darwin and Mac OS X. The macro __NEXT_
RUNTIME__ is predefined if (and only if) this option is used.
-fno-nil-receivers
Assume that all Objective-C message dispatches ([receiver message:arg]) in
this translation unit ensure that the receiver is not nil. This allows for more
efficient entry points in the runtime to be used. This option is only available in
conjunction with the NeXT runtime and ABI version 0 or 1.
-fobjc-abi-version=n
Use version n of the Objective-C ABI for the selected runtime. This option is
currently supported only for the NeXT runtime. In that case, Version 0 is the
traditional (32-bit) ABI without support for properties and other ObjectiveC 2.0 additions. Version 1 is the traditional (32-bit) ABI with support for
properties and other Objective-C 2.0 additions. Version 2 is the modern (64-bit)
ABI. If nothing is specified, the default is Version 0 on 32-bit target machines,
and Version 2 on 64-bit target machines.
-fobjc-call-cxx-cdtors
For each Objective-C class, check if any of its instance variables is a C++ object with a non-trivial default constructor. If so, synthesize a special - (id)
.cxx_construct instance method which runs non-trivial default constructors
on any such instance variables, in order, and then return self. Similarly, check
if any instance variable is a C++ object with a non-trivial destructor, and if
so, synthesize a special - (void) .cxx_destruct method which runs all such
default destructors, in reverse order.
The - (id) .cxx_construct and - (void) .cxx_destruct methods thusly
generated only operate on instance variables declared in the current
Objective-C class, and not those inherited from superclasses. It is the
responsibility of the Objective-C runtime to invoke all such methods in an
object’s inheritance hierarchy. The - (id) .cxx_construct methods are
invoked by the runtime immediately after a new object instance is allocated;
the - (void) .cxx_destruct methods are invoked immediately before the
runtime deallocates an object instance.
As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has support for invoking the - (id) .cxx_construct and - (void) .cxx_destruct
methods.
-fobjc-direct-dispatch
Allow fast jumps to the message dispatcher. On Darwin this is accomplished
via the comm page.

Chapter 3: GCC Command Options

57

-fobjc-exceptions
Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by C++. This option is required to use the Objective-C
keywords @try, @throw, @catch, @finally and @synchronized. This option is
available with both the GNU runtime and the NeXT runtime (but not available
in conjunction with the NeXT runtime on Mac OS X 10.2 and earlier).
-fobjc-gc
Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
This option is only available with the NeXT runtime; the GNU runtime has a
different garbage collection implementation that does not require special compiler flags.
-fobjc-nilcheck
For the NeXT runtime with version 2 of the ABI, check for a nil receiver in
method invocations before doing the actual method call. This is the default
and can be disabled using ‘-fno-objc-nilcheck’. Class methods and super
calls are never checked for nil in this way no matter what this flag is set to.
Currently this flag does nothing when the GNU runtime, or an older version of
the NeXT runtime ABI, is used.
-fobjc-std=objc1
Conform to the language syntax of Objective-C 1.0, the language recognized by
GCC 4.0. This only affects the Objective-C additions to the C/C++ language;
it does not affect conformance to C/C++ standards, which is controlled by
the separate C/C++ dialect option flags. When this option is used with the
Objective-C or Objective-C++ compiler, any Objective-C syntax that is not
recognized by GCC 4.0 is rejected. This is useful if you need to make sure that
your Objective-C code can be compiled with older versions of GCC.
-freplace-objc-classes
Emit a special marker instructing ld(1) not to statically link in the resulting
object file, and allow dyld(1) to load it in at run time instead. This is used
in conjunction with the Fix-and-Continue debugging mode, where the object
file in question may be recompiled and dynamically reloaded in the course of
program execution, without the need to restart the program itself. Currently,
Fix-and-Continue functionality is only available in conjunction with the NeXT
runtime on Mac OS X 10.3 and later.
-fzero-link
When compiling for the NeXT runtime, the compiler ordinarily replaces calls to
objc_getClass("...") (when the name of the class is known at compile time)
with static class references that get initialized at load time, which improves runtime performance. Specifying the ‘-fzero-link’ flag suppresses this behavior
and causes calls to objc_getClass("...") to be retained. This is useful in
Zero-Link debugging mode, since it allows for individual class implementations
to be modified during program execution. The GNU runtime currently always
retains calls to objc_get_class("...") regardless of command-line options.

58

Using the GNU Compiler Collection (GCC)

-fno-local-ivars
By default instance variables in Objective-C can be accessed as if they were
local variables from within the methods of the class they’re declared in. This
can lead to shadowing between instance variables and other variables declared
either locally inside a class method or globally with the same name. Specifying the ‘-fno-local-ivars’ flag disables this behavior thus avoiding variable
shadowing issues.
-fivar-visibility=[public|protected|private|package]
Set the default instance variable visibility to the specified option so that instance
variables declared outside the scope of any access modifier directives default to
the specified visibility.
-gen-decls
Dump interface declarations for all classes seen in the source file to a file named
‘sourcename.decl’.
-Wassign-intercept (Objective-C and Objective-C++ only)
Warn whenever an Objective-C assignment is being intercepted by the garbage
collector.
-Wno-protocol (Objective-C and Objective-C++ only)
If a class is declared to implement a protocol, a warning is issued for every
method in the protocol that is not implemented by the class. The default
behavior is to issue a warning for every method not explicitly implemented in the
class, even if a method implementation is inherited from the superclass. If you
use the ‘-Wno-protocol’ option, then methods inherited from the superclass
are considered to be implemented, and no warning is issued for them.
-Wselector (Objective-C and Objective-C++ only)
Warn if multiple methods of different types for the same selector are found
during compilation. The check is performed on the list of methods in the
final stage of compilation. Additionally, a check is performed for each selector
appearing in a @selector(...) expression, and a corresponding method for
that selector has been found during compilation. Because these checks scan the
method table only at the end of compilation, these warnings are not produced
if the final stage of compilation is not reached, for example because an error
is found during compilation, or because the ‘-fsyntax-only’ option is being
used.
-Wstrict-selector-match (Objective-C and Objective-C++ only)
Warn if multiple methods with differing argument and/or return types are found
for a given selector when attempting to send a message using this selector to
a receiver of type id or Class. When this flag is off (which is the default
behavior), the compiler omits such warnings if any differences found are confined
to types that share the same size and alignment.
-Wundeclared-selector (Objective-C and Objective-C++ only)
Warn if a @selector(...) expression referring to an undeclared selector is
found. A selector is considered undeclared if no method with that name has
been declared before the @selector(...) expression, either explicitly in an

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59

@interface or @protocol declaration, or implicitly in an @implementation
section. This option always performs its checks as soon as a @selector(...)
expression is found, while ‘-Wselector’ only performs its checks in the final
stage of compilation. This also enforces the coding style convention that methods and selectors must be declared before being used.
-print-objc-runtime-info
Generate C header describing the largest structure that is passed by value, if
any.

3.7 Options to Control Diagnostic Messages Formatting
Traditionally, diagnostic messages have been formatted irrespective of the output device’s
aspect (e.g. its width, . . . ). You can use the options described below to control the formatting algorithm for diagnostic messages, e.g. how many characters per line, how often
source location information should be reported. Note that some language front ends may
not honor these options.
-fmessage-length=n
Try to format error messages so that they fit on lines of about n characters. If
n is zero, then no line-wrapping is done; each error message appears on a single
line. This is the default for all front ends.
-fdiagnostics-show-location=once
Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit source location information once; that is, in case the message
is too long to fit on a single physical line and has to be wrapped, the source
location won’t be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior.
-fdiagnostics-show-location=every-line
Only meaningful in line-wrapping mode. Instructs the diagnostic messages
reporter to emit the same source location information (as prefix) for physical
lines that result from the process of breaking a message which is too long to fit
on a single line.
-fdiagnostics-color[=WHEN]
-fno-diagnostics-color
Use color in diagnostics. WHEN is ‘never’, ‘always’, or ‘auto’. The
default depends on how the compiler has been configured, it can be any
of the above WHEN options or also ‘never’ if GCC_COLORS environment
variable isn’t present in the environment, and ‘auto’ otherwise. ‘auto’
means to use color only when the standard error is a terminal. The
forms ‘-fdiagnostics-color’ and ‘-fno-diagnostics-color’ are aliases
for ‘-fdiagnostics-color=always’ and ‘-fdiagnostics-color=never’,
respectively.
The colors are defined by the environment variable GCC_COLORS. Its value is
a colon-separated list of capabilities and Select Graphic Rendition (SGR) substrings. SGR commands are interpreted by the terminal or terminal emulator.
(See the section in the documentation of your text terminal for permitted values

60

Using the GNU Compiler Collection (GCC)

and their meanings as character attributes.) These substring values are integers
in decimal representation and can be concatenated with semicolons. Common
values to concatenate include ‘1’ for bold, ‘4’ for underline, ‘5’ for blink, ‘7’ for
inverse, ‘39’ for default foreground color, ‘30’ to ‘37’ for foreground colors, ‘90’
to ‘97’ for 16-color mode foreground colors, ‘38;5;0’ to ‘38;5;255’ for 88-color
and 256-color modes foreground colors, ‘49’ for default background color, ‘40’
to ‘47’ for background colors, ‘100’ to ‘107’ for 16-color mode background colors, and ‘48;5;0’ to ‘48;5;255’ for 88-color and 256-color modes background
colors.
The default GCC_COLORS is
error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
quote=01:fixit-insert=32:fixit-delete=31:\
diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
type-diff=01;32

where ‘01;31’ is bold red, ‘01;35’ is bold magenta, ‘01;36’ is bold cyan, ‘32’
is green, ‘34’ is blue, ‘01’ is bold, and ‘31’ is red. Setting GCC_COLORS to the
empty string disables colors. Supported capabilities are as follows.
error=

SGR substring for error: markers.

warning=

SGR substring for warning: markers.

note=

SGR substring for note: markers.

range1=

SGR substring for first additional range.

range2=

SGR substring for second additional range.

locus=

SGR substring for location
‘file:line:column’ etc.

quote=

SGR substring for information printed within quotes.

information,

‘file:line’

or

fixit-insert=
SGR substring for fix-it hints suggesting text to be inserted or
replaced.
fixit-delete=
SGR substring for fix-it hints suggesting text to be deleted.
diff-filename=
SGR substring for filename headers within generated patches.
diff-hunk=
SGR substring for the starts of hunks within generated patches.
diff-delete=
SGR substring for deleted lines within generated patches.
diff-insert=
SGR substring for inserted lines within generated patches.
type-diff=
SGR substring for highlighting mismatching types within template
arguments in the C++ frontend.

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61

-fno-diagnostics-show-option
By default, each diagnostic emitted includes text indicating the command-line
option that directly controls the diagnostic (if such an option is known to the
diagnostic machinery). Specifying the ‘-fno-diagnostics-show-option’ flag
suppresses that behavior.
-fno-diagnostics-show-caret
By default, each diagnostic emitted includes the original source line and a caret
‘^’ indicating the column. This option suppresses this information. The source
line is truncated to n characters, if the ‘-fmessage-length=n’ option is given.
When the output is done to the terminal, the width is limited to the width
given by the COLUMNS environment variable or, if not set, to the terminal width.
-fdiagnostics-parseable-fixits
Emit fix-it hints in a machine-parseable format, suitable for consumption by
IDEs. For each fix-it, a line will be printed after the relevant diagnostic, starting
with the string “fix-it:”. For example:
fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"

The location is expressed as a half-open range, expressed as a count of bytes,
starting at byte 1 for the initial column. In the above example, bytes 3 through
20 of line 45 of “test.c” are to be replaced with the given string:
00000000011111111112222222222
12345678901234567890123456789
gtk_widget_showall (dlg);
^^^^^^^^^^^^^^^^^^
gtk_widget_show_all

The filename and replacement string escape backslash as “\\", tab as “\t”,
newline as “\n”, double quotes as “\"”, non-printable characters as octal (e.g.
vertical tab as “\013”).
An empty replacement string indicates that the given range is to be removed.
An empty range (e.g. “45:3-45:3”) indicates that the string is to be inserted at
the given position.
-fdiagnostics-generate-patch
Print fix-it hints to stderr in unified diff format, after any diagnostics are
printed. For example:
--- test.c
+++ test.c
@ -42,5 +42,5 @
void show_cb(GtkDialog *dlg)
{
- gtk_widget_showall(dlg);
+ gtk_widget_show_all(dlg);
}

The diff may or may not be colorized, following the same rules as for diagnostics
(see ‘-fdiagnostics-color’).
-fdiagnostics-show-template-tree
In the C++ frontend, when printing diagnostics showing mismatching template
types, such as:

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could not convert ’std::map >()’
from ’map<[...],vector>’ to ’map<[...],vector>

the ‘-fdiagnostics-show-template-tree’ flag enables printing a tree-like
structure showing the common and differing parts of the types, such as:
map<
[...],
vector<
[double != float]>>

The parts that differ are highlighted with color (“double” and “float” in this
case).
-fno-elide-type
By default when the C++ frontend prints diagnostics showing mismatching template types, common parts of the types are printed as “[...]” to simplify the
error message. For example:
could not convert ’std::map >()’
from ’map<[...],vector>’ to ’map<[...],vector>

Specifying the ‘-fno-elide-type’ flag suppresses that behavior. This flag also
affects the output of the ‘-fdiagnostics-show-template-tree’ flag.
-fno-show-column
Do not print column numbers in diagnostics. This may be necessary if diagnostics are being scanned by a program that does not understand the column
numbers, such as dejagnu.

3.8 Options to Request or Suppress Warnings
Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are risky or suggest there may have been an error.
The following language-independent options do not enable specific warnings but control
the kinds of diagnostics produced by GCC.
-fsyntax-only
Check the code for syntax errors, but don’t do anything beyond that.
-fmax-errors=n
Limits the maximum number of error messages to n, at which point GCC bails
out rather than attempting to continue processing the source code. If n is 0
(the default), there is no limit on the number of error messages produced. If
‘-Wfatal-errors’ is also specified, then ‘-Wfatal-errors’ takes precedence
over this option.
-w

Inhibit all warning messages.

-Werror

Make all warnings into errors.

-Werror=

Make the specified warning into an error. The specifier for a warning is
appended; for example ‘-Werror=switch’ turns the warnings controlled by
‘-Wswitch’ into errors. This switch takes a negative form, to be used to negate
‘-Werror’ for specific warnings; for example ‘-Wno-error=switch’ makes
‘-Wswitch’ warnings not be errors, even when ‘-Werror’ is in effect.

Chapter 3: GCC Command Options

63

The warning message for each controllable warning includes the option that
controls the warning. That option can then be used with ‘-Werror=’ and
‘-Wno-error=’ as described above. (Printing of the option in the warning message can be disabled using the ‘-fno-diagnostics-show-option’ flag.)
Note that specifying ‘-Werror=’foo automatically implies ‘-W’foo. However,
‘-Wno-error=’foo does not imply anything.
-Wfatal-errors
This option causes the compiler to abort compilation on the first error occurred
rather than trying to keep going and printing further error messages.
You can request many specific warnings with options beginning with ‘-W’, for example
‘-Wimplicit’ to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning ‘-Wno-’ to turn off warnings; for example,
‘-Wno-implicit’. This manual lists only one of the two forms, whichever is not the default.
For further language-specific options also refer to Section 3.5 [C++ Dialect Options], page 42
and Section 3.6 [Objective-C and Objective-C++ Dialect Options], page 55.
Some options, such as ‘-Wall’ and ‘-Wextra’, turn on other options, such as ‘-Wunused’,
which may turn on further options, such as ‘-Wunused-value’. The combined effect of
positive and negative forms is that more specific options have priority over less specific ones,
independently of their position in the command-line. For options of the same specificity,
the last one takes effect. Options enabled or disabled via pragmas (see Section 6.61.12
[Diagnostic Pragmas], page 778) take effect as if they appeared at the end of the commandline.
When an unrecognized warning option is requested (e.g., ‘-Wunknown-warning’),
GCC emits a diagnostic stating that the option is not recognized. However, if the
‘-Wno-’ form is used, the behavior is slightly different: no diagnostic is produced for
‘-Wno-unknown-warning’ unless other diagnostics are being produced. This allows the
use of new ‘-Wno-’ options with old compilers, but if something goes wrong, the compiler
warns that an unrecognized option is present.
-Wpedantic
-pedantic
Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that use forbidden extensions, and some other programs that do not
follow ISO C and ISO C++. For ISO C, follows the version of the ISO C standard specified by any ‘-std’ option used.
Valid ISO C and ISO C++ programs should compile properly with or without
this option (though a rare few require ‘-ansi’ or a ‘-std’ option specifying
the required version of ISO C). However, without this option, certain GNU
extensions and traditional C and C++ features are supported as well. With this
option, they are rejected.
‘-Wpedantic’ does not cause warning messages for use of the alternate keywords
whose names begin and end with ‘__’. Pedantic warnings are also disabled in
the expression that follows __extension__. However, only system header files
should use these escape routes; application programs should avoid them. See
Section 6.46 [Alternate Keywords], page 595.

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Using the GNU Compiler Collection (GCC)

Some users try to use ‘-Wpedantic’ to check programs for strict ISO C conformance. They soon find that it does not do quite what they want: it finds
some non-ISO practices, but not all—only those for which ISO C requires a
diagnostic, and some others for which diagnostics have been added.
A feature to report any failure to conform to ISO C might be useful in some
instances, but would require considerable additional work and would be quite
different from ‘-Wpedantic’. We don’t have plans to support such a feature in
the near future.
Where the standard specified with ‘-std’ represents a GNU extended dialect
of C, such as ‘gnu90’ or ‘gnu99’, there is a corresponding base standard, the
version of ISO C on which the GNU extended dialect is based. Warnings from
‘-Wpedantic’ are given where they are required by the base standard. (It
does not make sense for such warnings to be given only for features not in the
specified GNU C dialect, since by definition the GNU dialects of C include
all features the compiler supports with the given option, and there would be
nothing to warn about.)
-pedantic-errors
Give an error whenever the base standard (see ‘-Wpedantic’) requires a diagnostic, in some cases where there is undefined behavior at compile-time and in
some other cases that do not prevent compilation of programs that are valid
according to the standard. This is not equivalent to ‘-Werror=pedantic’, since
there are errors enabled by this option and not enabled by the latter and vice
versa.
-Wall

This enables all the warnings about constructions that some users consider
questionable, and that are easy to avoid (or modify to prevent the warning),
even in conjunction with macros. This also enables some language-specific
warnings described in Section 3.5 [C++ Dialect Options], page 42 and Section 3.6
[Objective-C and Objective-C++ Dialect Options], page 55.
‘-Wall’ turns on the following warning flags:
-Waddress
-Warray-bounds=1 (only with ‘-O2’)
-Wbool-compare
-Wbool-operation
-Wc++11-compat -Wc++14-compat
-Wcatch-value (C++ and Objective-C++ only)
-Wchar-subscripts
-Wcomment
-Wduplicate-decl-specifier (C and Objective-C only)
-Wenum-compare (in C/ObjC; this is on by default in C++)
-Wformat
-Wint-in-bool-context
-Wimplicit (C and Objective-C only)
-Wimplicit-int (C and Objective-C only)
-Wimplicit-function-declaration (C and Objective-C only)
-Winit-self (only for C++)
-Wlogical-not-parentheses
-Wmain (only for C/ObjC and unless ‘-ffreestanding’)
-Wmaybe-uninitialized
-Wmemset-elt-size

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65

-Wmemset-transposed-args
-Wmisleading-indentation (only for C/C++)
-Wmissing-attributes
-Wmissing-braces (only for C/ObjC)
-Wmultistatement-macros
-Wnarrowing (only for C++)
-Wnonnull
-Wnonnull-compare
-Wopenmp-simd
-Wparentheses
-Wpointer-sign
-Wreorder
-Wrestrict
-Wreturn-type
-Wsequence-point
-Wsign-compare (only in C++)
-Wsizeof-pointer-div
-Wsizeof-pointer-memaccess
-Wstrict-aliasing
-Wstrict-overflow=1
-Wstringop-truncation
-Wswitch
-Wtautological-compare
-Wtrigraphs
-Wuninitialized
-Wunknown-pragmas
-Wunused-function
-Wunused-label
-Wunused-value
-Wunused-variable
-Wvolatile-register-var

Note that some warning flags are not implied by ‘-Wall’. Some of them warn
about constructions that users generally do not consider questionable, but which
occasionally you might wish to check for; others warn about constructions that
are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled by ‘-Wextra’
but many of them must be enabled individually.
-Wextra

This enables some extra warning flags that are not enabled by ‘-Wall’. (This
option used to be called ‘-W’. The older name is still supported, but the newer
name is more descriptive.)
-Wclobbered
-Wcast-function-type
-Wempty-body
-Wignored-qualifiers
-Wimplicit-fallthrough=3
-Wmissing-field-initializers
-Wmissing-parameter-type (C only)
-Wold-style-declaration (C only)
-Woverride-init
-Wsign-compare (C only)
-Wtype-limits
-Wuninitialized
-Wshift-negative-value (in C++03 and in C99 and newer)
-Wunused-parameter (only with ‘-Wunused’ or ‘-Wall’)

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-Wunused-but-set-parameter (only with ‘-Wunused’ or ‘-Wall’)

The option ‘-Wextra’ also prints warning messages for the following cases:
• A pointer is compared against integer zero with <, <=, >, or >=.
• (C++ only) An enumerator and a non-enumerator both appear in a conditional expression.
• (C++ only) Ambiguous virtual bases.
• (C++ only) Subscripting an array that has been declared register.
• (C++ only) Taking the address of a variable that has been declared
register.
• (C++ only) A base class is not initialized in the copy constructor of a derived
class.
-Wchar-subscripts
Warn if an array subscript has type char. This is a common cause of error,
as programmers often forget that this type is signed on some machines. This
warning is enabled by ‘-Wall’.
-Wchkp

Warn about an invalid memory access that is found by Pointer Bounds Checker
(‘-fcheck-pointer-bounds’).

-Wno-coverage-mismatch
Warn if feedback profiles do not match when using the ‘-fprofile-use’ option.
If a source file is changed between compiling with ‘-fprofile-gen’ and with
‘-fprofile-use’, the files with the profile feedback can fail to match the source
file and GCC cannot use the profile feedback information. By default, this
warning is enabled and is treated as an error. ‘-Wno-coverage-mismatch’ can
be used to disable the warning or ‘-Wno-error=coverage-mismatch’ can be
used to disable the error. Disabling the error for this warning can result in
poorly optimized code and is useful only in the case of very minor changes such
as bug fixes to an existing code-base. Completely disabling the warning is not
recommended.
-Wno-cpp

(C, Objective-C, C++, Objective-C++ and Fortran only)
Suppress warning messages emitted by #warning directives.

-Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)
Give a warning when a value of type float is implicitly promoted to double.
CPUs with a 32-bit “single-precision” floating-point unit implement float in
hardware, but emulate double in software. On such a machine, doing computations using double values is much more expensive because of the overhead
required for software emulation.
It is easy to accidentally do computations with double because floating-point
literals are implicitly of type double. For example, in:
float area(float radius)
{
return 3.14159 * radius * radius;
}

Chapter 3: GCC Command Options

67

the compiler performs the entire computation with double because the floatingpoint literal is a double.
-Wduplicate-decl-specifier (C and Objective-C only)
Warn if a declaration has duplicate const, volatile, restrict or _Atomic
specifier. This warning is enabled by ‘-Wall’.
-Wformat
-Wformat=n
Check calls to printf and scanf, etc., to make sure that the arguments supplied
have types appropriate to the format string specified, and that the conversions
specified in the format string make sense. This includes standard functions, and
others specified by format attributes (see Section 6.31 [Function Attributes],
page 464), in the printf, scanf, strftime and strfmon (an X/Open extension, not in the C standard) families (or other target-specific families). Which
functions are checked without format attributes having been specified depends
on the standard version selected, and such checks of functions without the attribute specified are disabled by ‘-ffreestanding’ or ‘-fno-builtin’.
The formats are checked against the format features supported by GNU libc
version 2.2. These include all ISO C90 and C99 features, as well as features
from the Single Unix Specification and some BSD and GNU extensions. Other
library implementations may not support all these features; GCC does not support warning about features that go beyond a particular library’s limitations.
However, if ‘-Wpedantic’ is used with ‘-Wformat’, warnings are given about
format features not in the selected standard version (but not for strfmon formats, since those are not in any version of the C standard). See Section 3.4
[Options Controlling C Dialect], page 35.
-Wformat=1
-Wformat Option ‘-Wformat’ is equivalent to ‘-Wformat=1’, and
‘-Wno-format’ is equivalent to ‘-Wformat=0’. Since ‘-Wformat’
also checks for null format arguments for several functions,
‘-Wformat’ also implies ‘-Wnonnull’.
Some aspects of this
level of format checking can be disabled by the options:
‘-Wno-format-contains-nul’, ‘-Wno-format-extra-args’, and
‘-Wno-format-zero-length’. ‘-Wformat’ is enabled by ‘-Wall’.
-Wno-format-contains-nul
If ‘-Wformat’ is specified, do not warn about format strings that
contain NUL bytes.
-Wno-format-extra-args
If ‘-Wformat’ is specified, do not warn about excess arguments to
a printf or scanf format function. The C standard specifies that
such arguments are ignored.
Where the unused arguments lie between used arguments that are
specified with ‘$’ operand number specifications, normally warnings
are still given, since the implementation could not know what type
to pass to va_arg to skip the unused arguments. However, in the

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case of scanf formats, this option suppresses the warning if the unused arguments are all pointers, since the Single Unix Specification
says that such unused arguments are allowed.
-Wformat-overflow
-Wformat-overflow=level
Warn about calls to formatted input/output functions such as
sprintf and vsprintf that might overflow the destination buffer.
When the exact number of bytes written by a format directive
cannot be determined at compile-time it is estimated based on
heuristics that depend on the level argument and on optimization.
While enabling optimization will in most cases improve the
accuracy of the warning, it may also result in false positives.
-Wformat-overflow
-Wformat-overflow=1
Level 1 of ‘-Wformat-overflow’ enabled by ‘-Wformat’
employs a conservative approach that warns only about
calls that most likely overflow the buffer. At this level,
numeric arguments to format directives with unknown
values are assumed to have the value of one, and strings
of unknown length to be empty. Numeric arguments
that are known to be bounded to a subrange of their
type, or string arguments whose output is bounded either by their directive’s precision or by a finite set of
string literals, are assumed to take on the value within
the range that results in the most bytes on output.
For example, the call to sprintf below is diagnosed
because even with both a and b equal to zero, the terminating NUL character (’\0’) appended by the function to the destination buffer will be written past its
end. Increasing the size of the buffer by a single byte
is sufficient to avoid the warning, though it may not be
sufficient to avoid the overflow.
void f (int a, int b)
{
char buf [13];
sprintf (buf, "a = %i, b = %i\n", a, b);
}

-Wformat-overflow=2
Level 2 warns also about calls that might overflow
the destination buffer given an argument of sufficient
length or magnitude. At level 2, unknown numeric
arguments are assumed to have the minimum representable value for signed types with a precision greater
than 1, and the maximum representable value otherwise. Unknown string arguments whose length cannot
be assumed to be bounded either by the directive’s pre-

Chapter 3: GCC Command Options

69

cision, or by a finite set of string literals they may evaluate to, or the character array they may point to, are
assumed to be 1 character long.
At level 2, the call in the example above is again diagnosed, but this time because with a equal to a 32-bit
INT_MIN the first %i directive will write some of its digits beyond the end of the destination buffer. To make
the call safe regardless of the values of the two variables,
the size of the destination buffer must be increased to
at least 34 bytes. GCC includes the minimum size of
the buffer in an informational note following the warning.
An alternative to increasing the size of the destination buffer is to constrain the range of formatted values. The maximum length of string arguments can be
bounded by specifying the precision in the format directive. When numeric arguments of format directives can
be assumed to be bounded by less than the precision
of their type, choosing an appropriate length modifier
to the format specifier will reduce the required buffer
size. For example, if a and b in the example above
can be assumed to be within the precision of the short
int type then using either the %hi format directive or
casting the argument to short reduces the maximum
required size of the buffer to 24 bytes.
void f (int a, int b)
{
char buf [23];
sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
}

-Wno-format-zero-length
If ‘-Wformat’ is specified, do not warn about zero-length formats.
The C standard specifies that zero-length formats are allowed.
-Wformat=2
Enable ‘-Wformat’ plus additional format checks. Currently equivalent to ‘-Wformat -Wformat-nonliteral -Wformat-security
-Wformat-y2k’.
-Wformat-nonliteral
If ‘-Wformat’ is specified, also warn if the format string is not a
string literal and so cannot be checked, unless the format function
takes its format arguments as a va_list.
-Wformat-security
If ‘-Wformat’ is specified, also warn about uses of format functions
that represent possible security problems. At present, this warns
about calls to printf and scanf functions where the format string
is not a string literal and there are no format arguments, as in

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Using the GNU Compiler Collection (GCC)

printf (foo);. This may be a security hole if the format string
came from untrusted input and contains ‘%n’. (This is currently
a subset of what ‘-Wformat-nonliteral’ warns about, but in future warnings may be added to ‘-Wformat-security’ that are not
included in ‘-Wformat-nonliteral’.)
-Wformat-signedness
If ‘-Wformat’ is specified, also warn if the format string requires an
unsigned argument and the argument is signed and vice versa.
-Wformat-truncation
-Wformat-truncation=level
Warn about calls to formatted input/output functions such as
snprintf and vsnprintf that might result in output truncation.
When the exact number of bytes written by a format directive
cannot be determined at compile-time it is estimated based on
heuristics that depend on the level argument and on optimization.
While enabling optimization will in most cases improve the
accuracy of the warning, it may also result in false positives.
Except as noted otherwise, the option uses the same logic
‘-Wformat-overflow’.
-Wformat-truncation
-Wformat-truncation=1
Level 1 of ‘-Wformat-truncation’ enabled by
‘-Wformat’ employs a conservative approach that
warns only about calls to bounded functions whose
return value is unused and that will most likely result
in output truncation.
-Wformat-truncation=2
Level 2 warns also about calls to bounded functions
whose return value is used and that might result in
truncation given an argument of sufficient length or
magnitude.
-Wformat-y2k
If ‘-Wformat’ is specified, also warn about strftime formats that
may yield only a two-digit year.
-Wnonnull
Warn about passing a null pointer for arguments marked as requiring a non-null
value by the nonnull function attribute.
‘-Wnonnull’ is included in ‘-Wall’ and ‘-Wformat’. It can be disabled with the
‘-Wno-nonnull’ option.
-Wnonnull-compare
Warn when comparing an argument marked with the nonnull function attribute against null inside the function.
‘-Wnonnull-compare’ is included in ‘-Wall’. It can be disabled with the
‘-Wno-nonnull-compare’ option.

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71

-Wnull-dereference
Warn if the compiler detects paths that trigger erroneous or undefined behavior due to dereferencing a null pointer. This option is only active when
‘-fdelete-null-pointer-checks’ is active, which is enabled by optimizations
in most targets. The precision of the warnings depends on the optimization
options used.
-Winit-self (C, C++, Objective-C and Objective-C++ only)
Warn about uninitialized variables that are initialized with themselves. Note
this option can only be used with the ‘-Wuninitialized’ option.
For example, GCC warns about i being uninitialized in the following snippet
only when ‘-Winit-self’ has been specified:
int f()
{
int i = i;
return i;
}

This warning is enabled by ‘-Wall’ in C++.
-Wimplicit-int (C and Objective-C only)
Warn when a declaration does not specify a type. This warning is enabled by
‘-Wall’.
-Wimplicit-function-declaration (C and Objective-C only)
Give a warning whenever a function is used before being declared. In C99 mode
(‘-std=c99’ or ‘-std=gnu99’), this warning is enabled by default and it is made
into an error by ‘-pedantic-errors’. This warning is also enabled by ‘-Wall’.
-Wimplicit (C and Objective-C only)
Same as ‘-Wimplicit-int’ and ‘-Wimplicit-function-declaration’. This
warning is enabled by ‘-Wall’.
-Wimplicit-fallthrough
‘-Wimplicit-fallthrough’ is the same as ‘-Wimplicit-fallthrough=3’ and
‘-Wno-implicit-fallthrough’ is the same as ‘-Wimplicit-fallthrough=0’.
-Wimplicit-fallthrough=n
Warn when a switch case falls through. For example:
switch (cond)
{
case 1:
a = 1;
break;
case 2:
a = 2;
case 3:
a = 3;
break;
}

This warning does not warn when the last statement of a case cannot fall
through, e.g. when there is a return statement or a call to function declared with
the noreturn attribute. ‘-Wimplicit-fallthrough=’ also takes into account
control flow statements, such as ifs, and only warns when appropriate. E.g.

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Using the GNU Compiler Collection (GCC)

switch (cond)
{
case 1:
if (i > 3) {
bar (5);
break;
} else if (i < 1) {
bar (0);
} else
return;
default:
...
}

Since there are occasions where a switch case fall through is desirable, GCC
provides an attribute, __attribute__ ((fallthrough)), that is to be used
along with a null statement to suppress this warning that would normally occur:
switch (cond)
{
case 1:
bar (0);
__attribute__ ((fallthrough));
default:
...
}

C++17 provides a standard way to suppress the ‘-Wimplicit-fallthrough’
warning using [[fallthrough]]; instead of the GNU attribute. In C++11 or
C++14 users can use [[gnu::fallthrough]];, which is a GNU extension. Instead of these attributes, it is also possible to add a fallthrough comment to
silence the warning. The whole body of the C or C++ style comment should
match the given regular expressions listed below. The option argument n specifies what kind of comments are accepted:
• ‘-Wimplicit-fallthrough=0’ disables the warning altogether.
• ‘-Wimplicit-fallthrough=1’ matches .* regular expression, any comment is used as fallthrough comment.
• ‘-Wimplicit-fallthrough=2’ case insensitively matches .*falls?[ \t]*thr(ough|u).* regular expression.
• ‘-Wimplicit-fallthrough=3’ case sensitively matches one of the following
regular expressions:
• -fallthrough
• @fallthrough@
• lint -fallthrough[ \t]*
• [ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?
FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?
• [ \t.!]*(Else,? |Intentional(ly)? )?
Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?
• [ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?
fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?

Chapter 3: GCC Command Options

73

• ‘-Wimplicit-fallthrough=4’ case sensitively matches one of the following
regular expressions:
• -fallthrough
• @fallthrough@
• lint -fallthrough[ \t]*
• [ \t]*FALLTHR(OUGH|U)[ \t]*
• ‘-Wimplicit-fallthrough=5’ doesn’t recognize any comments as
fallthrough comments, only attributes disable the warning.
The comment needs to be followed after optional whitespace and other comments by case or default keywords or by a user label that precedes some case
or default label.
switch (cond)
{
case 1:
bar (0);
/* FALLTHRU */
default:
...
}

The ‘-Wimplicit-fallthrough=3’ warning is enabled by ‘-Wextra’.
-Wif-not-aligned (C, C++, Objective-C and Objective-C++ only)
Control if warning triggered by the warn_if_not_aligned attribute should be
issued. This is is enabled by default. Use ‘-Wno-if-not-aligned’ to disable it.
-Wignored-qualifiers (C and C++ only)
Warn if the return type of a function has a type qualifier such as const. For
ISO C such a type qualifier has no effect, since the value returned by a function
is not an lvalue. For C++, the warning is only emitted for scalar types or void.
ISO C prohibits qualified void return types on function definitions, so such
return types always receive a warning even without this option.
This warning is also enabled by ‘-Wextra’.
-Wignored-attributes (C and C++ only)
Warn when an attribute is ignored. This is different from the ‘-Wattributes’
option in that it warns whenever the compiler decides to drop an attribute, not
that the attribute is either unknown, used in a wrong place, etc. This warning
is enabled by default.
-Wmain

Warn if the type of main is suspicious. main should be a function with external
linkage, returning int, taking either zero arguments, two, or three arguments of
appropriate types. This warning is enabled by default in C++ and is enabled
by either ‘-Wall’ or ‘-Wpedantic’.

-Wmisleading-indentation (C and C++ only)
Warn when the indentation of the code does not reflect the block structure.
Specifically, a warning is issued for if, else, while, and for clauses with a
guarded statement that does not use braces, followed by an unguarded statement with the same indentation.

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Using the GNU Compiler Collection (GCC)

In the following example, the call to “bar” is misleadingly indented as if it were
guarded by the “if” conditional.
if (some_condition ())
foo ();
bar (); /* Gotcha: this is not guarded by the "if".

*/

In the case of mixed tabs and spaces, the warning uses the ‘-ftabstop=’ option
to determine if the statements line up (defaulting to 8).
The warning is not issued for code involving multiline preprocessor logic such
as the following example.
if (flagA)
foo (0);
#if SOME_CONDITION_THAT_DOES_NOT_HOLD
if (flagB)
#endif
foo (1);

The warning is not issued after a #line directive, since this typically indicates
autogenerated code, and no assumptions can be made about the layout of the
file that the directive references.
This warning is enabled by ‘-Wall’ in C and C++.
-Wmissing-attributes
Warn when a declaration of a function is missing one or more attributes that
a related function is declared with and whose absence may adversely affect the
correctness or efficiency of generated code. For example, in C++, the warning
is issued when an explicit specialization of a primary template declared with
attribute alloc_align, alloc_size, assume_aligned, format, format_arg,
malloc, or nonnull is declared without it. Attributes deprecated, error,
and warning suppress the warning. (see Section 6.31 [Function Attributes],
page 464).
‘-Wmissing-attributes’ is enabled by ‘-Wall’.
For example, since the declaration of the primary function template below
makes use of both attribute malloc and alloc_size the declaration of the
explicit specialization of the template is diagnosed because it is missing one of
the attributes.
template 
T* __attribute__ ((malloc, alloc_size (1)))
allocate (size_t);
template <>
void* __attribute__ ((malloc))
allocate (size_t);

// missing alloc_size

-Wmissing-braces
Warn if an aggregate or union initializer is not fully bracketed. In the following
example, the initializer for a is not fully bracketed, but that for b is fully
bracketed. This warning is enabled by ‘-Wall’ in C.
int a[2][2] = { 0, 1, 2, 3 };
int b[2][2] = { { 0, 1 }, { 2, 3 } };

This warning is enabled by ‘-Wall’.

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75

-Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)
Warn if a user-supplied include directory does not exist.
-Wmultistatement-macros
Warn about unsafe multiple statement macros that appear to be guarded by a
clause such as if, else, for, switch, or while, in which only the first statement
is actually guarded after the macro is expanded.
For example:
#define DOIT x++; y++
if (c)
DOIT;

will increment y unconditionally, not just when c holds. The can usually be
fixed by wrapping the macro in a do-while loop:
#define DOIT do { x++; y++; } while (0)
if (c)
DOIT;

This warning is enabled by ‘-Wall’ in C and C++.
-Wparentheses
Warn if parentheses are omitted in certain contexts, such as when there is an
assignment in a context where a truth value is expected, or when operators are
nested whose precedence people often get confused about.
Also warn if a comparison like x<=y<=z appears; this is equivalent to (x<=y ? 1
: 0) <= z, which is a different interpretation from that of ordinary mathematical notation.
Also warn for dangerous uses of the GNU extension to ?: with omitted middle
operand. When the condition in the ?: operator is a boolean expression, the
omitted value is always 1. Often programmers expect it to be a value computed
inside the conditional expression instead.
For C++ this also warns for some cases of unnecessary parentheses in declarations, which can indicate an attempt at a function call instead of a declaration:
{
// Declares a local variable called mymutex.
std::unique_lock (mymutex);
// User meant std::unique_lock lock (mymutex);
}

This warning is enabled by ‘-Wall’.
-Wsequence-point
Warn about code that may have undefined semantics because of violations of
sequence point rules in the C and C++ standards.
The C and C++ standards define the order in which expressions in a C/C++
program are evaluated in terms of sequence points, which represent a partial
ordering between the execution of parts of the program: those executed before
the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), after the
evaluation of the first operand of a &&, ||, ? : or , (comma) operator, before a
function is called (but after the evaluation of its arguments and the expression

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denoting the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions
of an expression is not specified. All these rules describe only a partial order
rather than a total order, since, for example, if two functions are called within
one expression with no sequence point between them, the order in which the
functions are called is not specified. However, the standards committee have
ruled that function calls do not overlap.
It is not specified when between sequence points modifications to the values of
objects take effect. Programs whose behavior depends on this have undefined
behavior; the C and C++ standards specify that “Between the previous and
next sequence point an object shall have its stored value modified at most once
by the evaluation of an expression. Furthermore, the prior value shall be read
only to determine the value to be stored.”. If a program breaks these rules, the
results on any particular implementation are entirely unpredictable.
Examples of code with undefined behavior are a = a++;, a[n] = b[n++] and
a[i++] = i;. Some more complicated cases are not diagnosed by this option,
and it may give an occasional false positive result, but in general it has been
found fairly effective at detecting this sort of problem in programs.
The C++17 standard will define the order of evaluation of operands in more
cases: in particular it requires that the right-hand side of an assignment be
evaluated before the left-hand side, so the above examples are no longer undefined. But this warning will still warn about them, to help people avoid writing
code that is undefined in C and earlier revisions of C++.
The standard is worded confusingly, therefore there is some debate over the
precise meaning of the sequence point rules in subtle cases. Links to discussions
of the problem, including proposed formal definitions, may be found on the GCC
readings page, at http://gcc.gnu.org/readings.html.
This warning is enabled by ‘-Wall’ for C and C++.
-Wno-return-local-addr
Do not warn about returning a pointer (or in C++, a reference) to a variable
that goes out of scope after the function returns.
-Wreturn-type
Warn whenever a function is defined with a return type that defaults to int.
Also warn about any return statement with no return value in a function whose
return type is not void (falling off the end of the function body is considered
returning without a value).
For C only, warn about a return statement with an expression in a function
whose return type is void, unless the expression type is also void. As a GNU
extension, the latter case is accepted without a warning unless ‘-Wpedantic’ is
used.
For C++, a function without return type always produces a diagnostic message,
even when ‘-Wno-return-type’ is specified. The only exceptions are main and
functions defined in system headers.
This warning is enabled by default for C++ and is enabled by ‘-Wall’.

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77

-Wshift-count-negative
Warn if shift count is negative. This warning is enabled by default.
-Wshift-count-overflow
Warn if shift count >= width of type. This warning is enabled by default.
-Wshift-negative-value
Warn if left shifting a negative value. This warning is enabled by ‘-Wextra’ in
C99 and C++11 modes (and newer).
-Wshift-overflow
-Wshift-overflow=n
Warn about left shift overflows. This warning is enabled by default in C99 and
C++11 modes (and newer).
-Wshift-overflow=1
This is the warning level of ‘-Wshift-overflow’ and is enabled by
default in C99 and C++11 modes (and newer). This warning level
does not warn about left-shifting 1 into the sign bit. (However, in
C, such an overflow is still rejected in contexts where an integer
constant expression is required.)
-Wshift-overflow=2
This warning level also warns about left-shifting 1 into the sign bit,
unless C++14 mode is active.
-Wswitch

Warn whenever a switch statement has an index of enumerated type and lacks
a case for one or more of the named codes of that enumeration. (The presence
of a default label prevents this warning.) case labels outside the enumeration
range also provoke warnings when this option is used (even if there is a default
label). This warning is enabled by ‘-Wall’.

-Wswitch-default
Warn whenever a switch statement does not have a default case.
-Wswitch-enum
Warn whenever a switch statement has an index of enumerated type and lacks
a case for one or more of the named codes of that enumeration. case labels
outside the enumeration range also provoke warnings when this option is used.
The only difference between ‘-Wswitch’ and this option is that this option gives
a warning about an omitted enumeration code even if there is a default label.
-Wswitch-bool
Warn whenever a switch statement has an index of boolean type and the case
values are outside the range of a boolean type. It is possible to suppress this
warning by casting the controlling expression to a type other than bool. For
example:
switch ((int) (a == 4))
{
...
}

This warning is enabled by default for C and C++ programs.

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-Wswitch-unreachable
Warn whenever a switch statement contains statements between the controlling
expression and the first case label, which will never be executed. For example:
switch (cond)
{
i = 15;
...
case 5:
...
}

‘-Wswitch-unreachable’ does not warn if the statement between the controlling expression and the first case label is just a declaration:
switch (cond)
{
int i;
...
case 5:
i = 5;
...
}

This warning is enabled by default for C and C++ programs.
-Wsync-nand (C and C++ only)
Warn when __sync_fetch_and_nand and __sync_nand_and_fetch built-in
functions are used. These functions changed semantics in GCC 4.4.
-Wunused-but-set-parameter
Warn whenever a function parameter is assigned to, but otherwise unused (aside
from its declaration).
To suppress this warning use the unused attribute (see Section 6.32 [Variable
Attributes], page 513).
This warning is also enabled by ‘-Wunused’ together with ‘-Wextra’.
-Wunused-but-set-variable
Warn whenever a local variable is assigned to, but otherwise unused (aside from
its declaration). This warning is enabled by ‘-Wall’.
To suppress this warning use the unused attribute (see Section 6.32 [Variable
Attributes], page 513).
This warning is also enabled by ‘-Wunused’, which is enabled by ‘-Wall’.
-Wunused-function
Warn whenever a static function is declared but not defined or a non-inline
static function is unused. This warning is enabled by ‘-Wall’.
-Wunused-label
Warn whenever a label is declared but not used. This warning is enabled by
‘-Wall’.
To suppress this warning use the unused attribute (see Section 6.32 [Variable
Attributes], page 513).

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79

-Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)
Warn when a typedef locally defined in a function is not used. This warning is
enabled by ‘-Wall’.
-Wunused-parameter
Warn whenever a function parameter is unused aside from its declaration.
To suppress this warning use the unused attribute (see Section 6.32 [Variable
Attributes], page 513).
-Wno-unused-result
Do not warn if a caller of a function marked with attribute warn_unused_
result (see Section 6.31 [Function Attributes], page 464) does not use its return
value. The default is ‘-Wunused-result’.
-Wunused-variable
Warn whenever a local or static variable is unused aside from its declaration.
This option implies ‘-Wunused-const-variable=1’ for C, but not for C++. This
warning is enabled by ‘-Wall’.
To suppress this warning use the unused attribute (see Section 6.32 [Variable
Attributes], page 513).
-Wunused-const-variable
-Wunused-const-variable=n
Warn whenever a constant static variable is unused aside from its declaration.
‘-Wunused-const-variable=1’ is enabled by ‘-Wunused-variable’ for C, but
not for C++. In C this declares variable storage, but in C++ this is not an error
since const variables take the place of #defines.
To suppress this warning use the unused attribute (see Section 6.32 [Variable
Attributes], page 513).
-Wunused-const-variable=1
This is the warning level that is enabled by ‘-Wunused-variable’
for C. It warns only about unused static const variables defined
in the main compilation unit, but not about static const variables
declared in any header included.
-Wunused-const-variable=2
This warning level also warns for unused constant static variables
in headers (excluding system headers). This is the warning level
of ‘-Wunused-const-variable’ and must be explicitly requested
since in C++ this isn’t an error and in C it might be harder to clean
up all headers included.
-Wunused-value
Warn whenever a statement computes a result that is explicitly not used. To
suppress this warning cast the unused expression to void. This includes an
expression-statement or the left-hand side of a comma expression that contains
no side effects. For example, an expression such as x[i,j] causes a warning,
while x[(void)i,j] does not.
This warning is enabled by ‘-Wall’.

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Using the GNU Compiler Collection (GCC)

All the above ‘-Wunused’ options combined.
In order to get a warning about an unused function parameter, you must either
specify ‘-Wextra -Wunused’ (note that ‘-Wall’ implies ‘-Wunused’), or separately specify ‘-Wunused-parameter’.

-Wuninitialized
Warn if an automatic variable is used without first being initialized or if a
variable may be clobbered by a setjmp call. In C++, warn if a non-static
reference or non-static const member appears in a class without constructors.
If you want to warn about code that uses the uninitialized value of the variable
in its own initializer, use the ‘-Winit-self’ option.
These warnings occur for individual uninitialized or clobbered elements of structure, union or array variables as well as for variables that are uninitialized or
clobbered as a whole. They do not occur for variables or elements declared
volatile. Because these warnings depend on optimization, the exact variables
or elements for which there are warnings depends on the precise optimization
options and version of GCC used.
Note that there may be no warning about a variable that is used only to compute
a value that itself is never used, because such computations may be deleted by
data flow analysis before the warnings are printed.
-Winvalid-memory-model
Warn for invocations of Section 6.53 [ atomic Builtins], page 603, Section 6.52
[ sync Builtins], page 601, and the C11 atomic generic functions with a memory
consistency argument that is either invalid for the operation or outside the range
of values of the memory_order enumeration. For example, since the __atomic_
store and __atomic_store_n built-ins are only defined for the relaxed, release,
and sequentially consistent memory orders the following code is diagnosed:
void store (int *i)
{
__atomic_store_n (i, 0, memory_order_consume);
}

‘-Winvalid-memory-model’ is enabled by default.
-Wmaybe-uninitialized
For an automatic (i.e. local) variable, if there exists a path from the function
entry to a use of the variable that is initialized, but there exist some other
paths for which the variable is not initialized, the compiler emits a warning if
it cannot prove the uninitialized paths are not executed at run time.
These warnings are only possible in optimizing compilation, because otherwise
GCC does not keep track of the state of variables.
These warnings are made optional because GCC may not be able to determine
when the code is correct in spite of appearing to have an error. Here is one
example of how this can happen:

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81

{
int x;
switch (y)
{
case 1: x = 1;
break;
case 2: x = 4;
break;
case 3: x = 5;
}
foo (x);
}

If the value of y is always 1, 2 or 3, then x is always initialized, but GCC doesn’t
know this. To suppress the warning, you need to provide a default case with
assert(0) or similar code.
This option also warns when a non-volatile automatic variable might be changed
by a call to longjmp. The compiler sees only the calls to setjmp. It cannot
know where longjmp will be called; in fact, a signal handler could call it at any
point in the code. As a result, you may get a warning even when there is in fact
no problem because longjmp cannot in fact be called at the place that would
cause a problem.
Some spurious warnings can be avoided if you declare all the functions you
use that never return as noreturn. See Section 6.31 [Function Attributes],
page 464.
This warning is enabled by ‘-Wall’ or ‘-Wextra’.
-Wunknown-pragmas
Warn when a #pragma directive is encountered that is not understood by GCC.
If this command-line option is used, warnings are even issued for unknown
pragmas in system header files. This is not the case if the warnings are only
enabled by the ‘-Wall’ command-line option.
-Wno-pragmas
Do not warn about misuses of pragmas, such as incorrect parameters, invalid
syntax, or conflicts between pragmas. See also ‘-Wunknown-pragmas’.
-Wstrict-aliasing
This option is only active when ‘-fstrict-aliasing’ is active. It warns about
code that might break the strict aliasing rules that the compiler is using for
optimization. The warning does not catch all cases, but does attempt to
catch the more common pitfalls. It is included in ‘-Wall’. It is equivalent
to ‘-Wstrict-aliasing=3’
-Wstrict-aliasing=n
This option is only active when ‘-fstrict-aliasing’ is active. It warns about
code that might break the strict aliasing rules that the compiler is using for optimization. Higher levels correspond to higher accuracy (fewer false positives).
Higher levels also correspond to more effort, similar to the way ‘-O’ works.
‘-Wstrict-aliasing’ is equivalent to ‘-Wstrict-aliasing=3’.
Level 1: Most aggressive, quick, least accurate. Possibly useful when higher
levels do not warn but ‘-fstrict-aliasing’ still breaks the code, as it has very

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Using the GNU Compiler Collection (GCC)

few false negatives. However, it has many false positives. Warns for all pointer
conversions between possibly incompatible types, even if never dereferenced.
Runs in the front end only.
Level 2: Aggressive, quick, not too precise. May still have many false positives
(not as many as level 1 though), and few false negatives (but possibly more
than level 1). Unlike level 1, it only warns when an address is taken. Warns
about incomplete types. Runs in the front end only.
Level 3 (default for ‘-Wstrict-aliasing’): Should have very few false positives
and few false negatives. Slightly slower than levels 1 or 2 when optimization
is enabled. Takes care of the common pun+dereference pattern in the front
end: *(int*)&some_float. If optimization is enabled, it also runs in the back
end, where it deals with multiple statement cases using flow-sensitive points-to
information. Only warns when the converted pointer is dereferenced. Does not
warn about incomplete types.
-Wstrict-overflow
-Wstrict-overflow=n
This option is only active when signed overflow is undefined. It warns about
cases where the compiler optimizes based on the assumption that signed overflow does not occur. Note that it does not warn about all cases where the code
might overflow: it only warns about cases where the compiler implements some
optimization. Thus this warning depends on the optimization level.
An optimization that assumes that signed overflow does not occur is perfectly
safe if the values of the variables involved are such that overflow never does, in
fact, occur. Therefore this warning can easily give a false positive: a warning
about code that is not actually a problem. To help focus on important issues,
several warning levels are defined. No warnings are issued for the use of undefined signed overflow when estimating how many iterations a loop requires, in
particular when determining whether a loop will be executed at all.
-Wstrict-overflow=1
Warn about cases that are both questionable and easy to avoid.
For example the compiler simplifies x + 1 > x to 1. This level of
‘-Wstrict-overflow’ is enabled by ‘-Wall’; higher levels are not,
and must be explicitly requested.
-Wstrict-overflow=2
Also warn about other cases where a comparison is simplified to a
constant. For example: abs (x) >= 0. This can only be simplified
when signed integer overflow is undefined, because abs (INT_MIN)
overflows to INT_MIN, which is less than zero. ‘-Wstrict-overflow’
(with no level) is the same as ‘-Wstrict-overflow=2’.
-Wstrict-overflow=3
Also warn about other cases where a comparison is simplified. For
example: x + 1 > 1 is simplified to x > 0.
-Wstrict-overflow=4
Also warn about other simplifications not covered by the above
cases. For example: (x * 10) / 5 is simplified to x * 2.

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83

-Wstrict-overflow=5
Also warn about cases where the compiler reduces the magnitude
of a constant involved in a comparison. For example: x + 2 > y is
simplified to x + 1 >= y. This is reported only at the highest warning level because this simplification applies to many comparisons,
so this warning level gives a very large number of false positives.
-Wstringop-overflow
-Wstringop-overflow=type
Warn for calls to string manipulation functions such as memcpy and strcpy
that are determined to overflow the destination buffer. The optional argument
is one greater than the type of Object Size Checking to perform to determine
the size of the destination. See Section 6.56 [Object Size Checking], page 609.
The argument is meaningful only for functions that operate on character arrays
but not for raw memory functions like memcpy which always make use of Object
Size type-0. The option also warns for calls that specify a size in excess of the
largest possible object or at most SIZE_MAX / 2 bytes. The option produces
the best results with optimization enabled but can detect a small subset of
simple buffer overflows even without optimization in calls to the GCC built-in
functions like __builtin_memcpy that correspond to the standard functions.
In any case, the option warns about just a subset of buffer overflows detected
by the corresponding overflow checking built-ins. For example, the option will
issue a warning for the strcpy call below because it copies at least 5 characters
(the string "blue" including the terminating NUL) into the buffer of size 4.
enum Color { blue, purple, yellow };
const char* f (enum Color clr)
{
static char buf [4];
const char *str;
switch (clr)
{
case blue: str = "blue"; break;
case purple: str = "purple"; break;
case yellow: str = "yellow"; break;
}
return strcpy (buf, str);

// warning here

}

Option ‘-Wstringop-overflow=2’ is enabled by default.
-Wstringop-overflow
-Wstringop-overflow=1
The ‘-Wstringop-overflow=1’ option uses type-zero Object Size
Checking to determine the sizes of destination objects. This is
the default setting of the option. At this setting the option will
not warn for writes past the end of subobjects of larger objects
accessed by pointers unless the size of the largest surrounding object
is known. When the destination may be one of several objects it is
assumed to be the largest one of them. On Linux systems, when
optimization is enabled at this setting the option warns for the same

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code as when the _FORTIFY_SOURCE macro is defined to a non-zero
value.
-Wstringop-overflow=2
The ‘-Wstringop-overflow=2’ option uses type-one Object Size
Checking to determine the sizes of destination objects. At this
setting the option will warn about overflows when writing to members of the largest complete objects whose exact size is known. It
will, however, not warn for excessive writes to the same members
of unknown objects referenced by pointers since they may point to
arrays containing unknown numbers of elements.
-Wstringop-overflow=3
The ‘-Wstringop-overflow=3’ option uses type-two Object Size
Checking to determine the sizes of destination objects. At this
setting the option warns about overflowing the smallest object or
data member. This is the most restrictive setting of the option that
may result in warnings for safe code.
-Wstringop-overflow=4
The ‘-Wstringop-overflow=4’ option uses type-three Object Size
Checking to determine the sizes of destination objects. At this
setting the option will warn about overflowing any data members,
and when the destination is one of several objects it uses the size of
the largest of them to decide whether to issue a warning. Similarly
to ‘-Wstringop-overflow=3’ this setting of the option may result
in warnings for benign code.
-Wstringop-truncation
Warn for calls to bounded string manipulation functions such as strncat,
strncpy, and stpncpy that may either truncate the copied string or leave the
destination unchanged.
In the following example, the call to strncat specifies a bound that is less
than the length of the source string. As a result, the copy of the source will
be truncated and so the call is diagnosed. To avoid the warning use bufsize strlen (buf) - 1) as the bound.
void append (char *buf, size_t bufsize)
{
strncat (buf, ".txt", 3);
}

As another example, the following call to strncpy results in copying to d just
the characters preceding the terminating NUL, without appending the NUL
to the end. Assuming the result of strncpy is necessarily a NUL-terminated
string is a common mistake, and so the call is diagnosed. To avoid the warning
when the result is not expected to be NUL-terminated, call memcpy instead.
void copy (char *d, const char *s)
{
strncpy (d, s, strlen (s));
}

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85

In the following example, the call to strncpy specifies the size of the destination
buffer as the bound. If the length of the source string is equal to or greater
than this size the result of the copy will not be NUL-terminated. Therefore,
the call is also diagnosed. To avoid the warning, specify sizeof buf - 1 as the
bound and set the last element of the buffer to NUL.
void copy (const char *s)
{
char buf[80];
strncpy (buf, s, sizeof buf);
...
}

In situations where a character array is intended to store a sequence of bytes
with no terminating NUL such an array may be annotated with attribute
nonstring to avoid this warning. Such arrays, however, are not suitable
arguments to functions that expect NUL-terminated strings. To help detect
accidental misuses of such arrays GCC issues warnings unless it can prove that
the use is safe. See Section 6.32.1 [Common Variable Attributes], page 513.
Option ‘-Wstringop-truncation’ is enabled by ‘-Wall’.
-Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]
Warn for cases where adding an attribute may be beneficial. The attributes
currently supported are listed below.
-Wsuggest-attribute=pure
-Wsuggest-attribute=const
-Wsuggest-attribute=noreturn
-Wsuggest-attribute=malloc
Warn about functions that might be candidates for attributes pure,
const or noreturn or malloc. The compiler only warns for functions visible in other compilation units or (in the case of pure and
const) if it cannot prove that the function returns normally. A
function returns normally if it doesn’t contain an infinite loop or
return abnormally by throwing, calling abort or trapping. This
analysis requires option ‘-fipa-pure-const’, which is enabled by
default at ‘-O’ and higher. Higher optimization levels improve the
accuracy of the analysis.
-Wsuggest-attribute=format
-Wmissing-format-attribute
Warn about function pointers that might be candidates for format
attributes. Note these are only possible candidates, not absolute
ones. GCC guesses that function pointers with format attributes
that are used in assignment, initialization, parameter passing or
return statements should have a corresponding format attribute
in the resulting type. I.e. the left-hand side of the assignment or
initialization, the type of the parameter variable, or the return type
of the containing function respectively should also have a format
attribute to avoid the warning.

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GCC also warns about function definitions that might be candidates for format attributes. Again, these are only possible candidates. GCC guesses that format attributes might be appropriate
for any function that calls a function like vprintf or vscanf, but
this might not always be the case, and some functions for which
format attributes are appropriate may not be detected.
-Wsuggest-attribute=cold
Warn about functions that might be candidates for cold attribute.
This is based on static detection and generally will only warn about
functions which always leads to a call to another cold function such
as wrappers of C++ throw or fatal error reporting functions leading
to abort.
-Wsuggest-final-types
Warn about types with virtual methods where code quality would be improved
if the type were declared with the C++11 final specifier, or, if possible, declared in an anonymous namespace. This allows GCC to more aggressively
devirtualize the polymorphic calls. This warning is more effective with link
time optimization, where the information about the class hierarchy graph is
more complete.
-Wsuggest-final-methods
Warn about virtual methods where code quality would be improved if the
method were declared with the C++11 final specifier, or, if possible, its type
were declared in an anonymous namespace or with the final specifier. This
warning is more effective with link-time optimization, where the information
about the class hierarchy graph is more complete. It is recommended to first
consider suggestions of ‘-Wsuggest-final-types’ and then rebuild with new
annotations.
-Wsuggest-override
Warn about overriding virtual functions that are not marked with the override
keyword.
-Walloc-zero
Warn about calls to allocation functions decorated with attribute alloc_size
that specify zero bytes, including those to the built-in forms of the functions
aligned_alloc, alloca, calloc, malloc, and realloc. Because the behavior
of these functions when called with a zero size differs among implementations
(and in the case of realloc has been deprecated) relying on it may result in
subtle portability bugs and should be avoided.
-Walloc-size-larger-than=n
Warn about calls to functions decorated with attribute alloc_size that attempt to allocate objects larger than the specified number of bytes, or where
the result of the size computation in an integer type with infinite precision
would exceed SIZE_MAX / 2. The option argument n may end in one of the
standard suffixes designating a multiple of bytes such as kB and KiB for kilobyte
and kibibyte, respectively, MB and MiB for megabyte and mebibyte, and so on.

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87

‘-Walloc-size-larger-than=’PTRDIFF MAX is enabled by default. Warnings controlled by the option can be disabled by specifying n of SIZE MAX or
more. See Section 6.31 [Function Attributes], page 464.
-Walloca

This option warns on all uses of alloca in the source.

-Walloca-larger-than=n
This option warns on calls to alloca that are not bounded by a controlling
predicate limiting its argument of integer type to at most n bytes, or calls
to alloca where the bound is unknown. Arguments of non-integer types are
considered unbounded even if they appear to be constrained to the expected
range.
For example, a bounded case of alloca could be:
void func (size_t n)
{
void *p;
if (n <= 1000)
p = alloca (n);
else
p = malloc (n);
f (p);
}

In the above example, passing -Walloca-larger-than=1000 would not issue a
warning because the call to alloca is known to be at most 1000 bytes. However,
if -Walloca-larger-than=500 were passed, the compiler would emit a warning.
Unbounded uses, on the other hand, are uses of alloca with no controlling
predicate constraining its integer argument. For example:
void func ()
{
void *p = alloca (n);
f (p);
}

If -Walloca-larger-than=500 were passed, the above would trigger a warning,
but this time because of the lack of bounds checking.
Note, that even seemingly correct code involving signed integers could cause a
warning:
void func (signed int n)
{
if (n < 500)
{
p = alloca (n);
f (p);
}
}

In the above example, n could be negative, causing a larger than expected
argument to be implicitly cast into the alloca call.
This option also warns when alloca is used in a loop.
This warning is not enabled by ‘-Wall’, and is only active when ‘-ftree-vrp’
is active (default for ‘-O2’ and above).
See also ‘-Wvla-larger-than=n’.

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-Warray-bounds
-Warray-bounds=n
This option is only active when ‘-ftree-vrp’ is active (default for ‘-O2’ and
above). It warns about subscripts to arrays that are always out of bounds. This
warning is enabled by ‘-Wall’.
-Warray-bounds=1
This is the warning level of ‘-Warray-bounds’ and is enabled by
‘-Wall’; higher levels are not, and must be explicitly requested.
-Warray-bounds=2
This warning level also warns about out of bounds access for arrays
at the end of a struct and for arrays accessed through pointers.
This warning level may give a larger number of false positives and
is deactivated by default.
-Wattribute-alias
Warn about declarations using the alias and similar attributes whose target is
incompatible with the type of the alias. See Section 6.31 [Declaring Attributes
of Functions], page 464.
-Wbool-compare
Warn about boolean expression compared with an integer value different from
true/false. For instance, the following comparison is always false:
int n = 5;
...
if ((n > 1) == 2) { ... }

This warning is enabled by ‘-Wall’.
-Wbool-operation
Warn about suspicious operations on expressions of a boolean type. For instance, bitwise negation of a boolean is very likely a bug in the program. For
C, this warning also warns about incrementing or decrementing a boolean,
which rarely makes sense. (In C++, decrementing a boolean is always invalid.
Incrementing a boolean is invalid in C++17, and deprecated otherwise.)
This warning is enabled by ‘-Wall’.
-Wduplicated-branches
Warn when an if-else has identical branches. This warning detects cases like
if (p != NULL)
return 0;
else
return 0;

It doesn’t warn when both branches contain just a null statement. This warning
also warn for conditional operators:
int i = x ? *p : *p;

-Wduplicated-cond
Warn about duplicated conditions in an if-else-if chain. For instance, warn for
the following code:
if (p->q != NULL) { ... }
else if (p->q != NULL) { ... }

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89

-Wframe-address
Warn when the ‘__builtin_frame_address’ or ‘__builtin_return_address’
is called with an argument greater than 0. Such calls may return indeterminate
values or crash the program. The warning is included in ‘-Wall’.
-Wno-discarded-qualifiers (C and Objective-C only)
Do not warn if type qualifiers on pointers are being discarded. Typically, the
compiler warns if a const char * variable is passed to a function that takes a
char * parameter. This option can be used to suppress such a warning.
-Wno-discarded-array-qualifiers (C and Objective-C only)
Do not warn if type qualifiers on arrays which are pointer targets are being
discarded. Typically, the compiler warns if a const int (*)[] variable is passed
to a function that takes a int (*)[] parameter. This option can be used to
suppress such a warning.
-Wno-incompatible-pointer-types (C and Objective-C only)
Do not warn when there is a conversion between pointers that have incompatible
types. This warning is for cases not covered by ‘-Wno-pointer-sign’, which
warns for pointer argument passing or assignment with different signedness.
-Wno-int-conversion (C and Objective-C only)
Do not warn about incompatible integer to pointer and pointer to integer conversions. This warning is about implicit conversions; for explicit conversions
the warnings ‘-Wno-int-to-pointer-cast’ and ‘-Wno-pointer-to-int-cast’
may be used.
-Wno-div-by-zero
Do not warn about compile-time integer division by zero. Floating-point division by zero is not warned about, as it can be a legitimate way of obtaining
infinities and NaNs.
-Wsystem-headers
Print warning messages for constructs found in system header files. Warnings
from system headers are normally suppressed, on the assumption that they
usually do not indicate real problems and would only make the compiler output
harder to read. Using this command-line option tells GCC to emit warnings
from system headers as if they occurred in user code. However, note that using
‘-Wall’ in conjunction with this option does not warn about unknown pragmas
in system headers—for that, ‘-Wunknown-pragmas’ must also be used.
-Wtautological-compare
Warn if a self-comparison always evaluates to true or false. This warning detects
various mistakes such as:
int i = 1;
...
if (i > i) { ... }

This warning also warns about bitwise comparisons that always evaluate to true
or false, for instance:
if ((a & 16) == 10) { ... }

will always be false.

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This warning is enabled by ‘-Wall’.
-Wtrampolines
Warn about trampolines generated for pointers to nested functions. A trampoline is a small piece of data or code that is created at run time on the stack
when the address of a nested function is taken, and is used to call the nested
function indirectly. For some targets, it is made up of data only and thus requires no special treatment. But, for most targets, it is made up of code and
thus requires the stack to be made executable in order for the program to work
properly.
-Wfloat-equal
Warn if floating-point values are used in equality comparisons.
The idea behind this is that sometimes it is convenient (for the programmer)
to consider floating-point values as approximations to infinitely precise real
numbers. If you are doing this, then you need to compute (by analyzing the
code, or in some other way) the maximum or likely maximum error that the
computation introduces, and allow for it when performing comparisons (and
when producing output, but that’s a different problem). In particular, instead
of testing for equality, you should check to see whether the two values have
ranges that overlap; and this is done with the relational operators, so equality
comparisons are probably mistaken.
-Wtraditional (C and Objective-C only)
Warn about certain constructs that behave differently in traditional and ISO
C. Also warn about ISO C constructs that have no traditional C equivalent,
and/or problematic constructs that should be avoided.
• Macro parameters that appear within string literals in the macro body. In
traditional C macro replacement takes place within string literals, but in
ISO C it does not.
• In traditional C, some preprocessor directives did not exist. Traditional
preprocessors only considered a line to be a directive if the ‘#’ appeared in
column 1 on the line. Therefore ‘-Wtraditional’ warns about directives
that traditional C understands but ignores because the ‘#’ does not appear
as the first character on the line. It also suggests you hide directives like
#pragma not understood by traditional C by indenting them. Some traditional implementations do not recognize #elif, so this option suggests
avoiding it altogether.
• A function-like macro that appears without arguments.
• The unary plus operator.
• The ‘U’ integer constant suffix, or the ‘F’ or ‘L’ floating-point constant
suffixes. (Traditional C does support the ‘L’ suffix on integer constants.)
Note, these suffixes appear in macros defined in the system headers of most
modern systems, e.g. the ‘_MIN’/‘_MAX’ macros in . Use of these
macros in user code might normally lead to spurious warnings, however
GCC’s integrated preprocessor has enough context to avoid warning in
these cases.

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91

• A function declared external in one block and then used after the end of
the block.
• A switch statement has an operand of type long.
• A non-static function declaration follows a static one. This construct
is not accepted by some traditional C compilers.
• The ISO type of an integer constant has a different width or signedness
from its traditional type. This warning is only issued if the base of the
constant is ten. I.e. hexadecimal or octal values, which typically represent
bit patterns, are not warned about.
• Usage of ISO string concatenation is detected.
• Initialization of automatic aggregates.
• Identifier conflicts with labels. Traditional C lacks a separate namespace
for labels.
• Initialization of unions. If the initializer is zero, the warning is omitted.
This is done under the assumption that the zero initializer in user code
appears conditioned on e.g. __STDC__ to avoid missing initializer warnings
and relies on default initialization to zero in the traditional C case.
• Conversions by prototypes between fixed/floating-point values and vice
versa. The absence of these prototypes when compiling with traditional
C causes serious problems. This is a subset of the possible conversion
warnings; for the full set use ‘-Wtraditional-conversion’.
• Use of ISO C style function definitions. This warning intentionally is not
issued for prototype declarations or variadic functions because these ISO
C features appear in your code when using libiberty’s traditional C compatibility macros, PARAMS and VPARAMS. This warning is also bypassed for
nested functions because that feature is already a GCC extension and thus
not relevant to traditional C compatibility.
-Wtraditional-conversion (C and Objective-C only)
Warn if a prototype causes a type conversion that is different from what would
happen to the same argument in the absence of a prototype. This includes
conversions of fixed point to floating and vice versa, and conversions changing
the width or signedness of a fixed-point argument except when the same as the
default promotion.
-Wdeclaration-after-statement (C and Objective-C only)
Warn when a declaration is found after a statement in a block. This construct,
known from C++, was introduced with ISO C99 and is by default allowed in
GCC. It is not supported by ISO C90. See Section 6.30 [Mixed Declarations],
page 463.
-Wshadow

Warn whenever a local variable or type declaration shadows another variable,
parameter, type, class member (in C++), or instance variable (in Objective-C)
or whenever a built-in function is shadowed. Note that in C++, the compiler
warns if a local variable shadows an explicit typedef, but not if it shadows a
struct/class/enum. Same as ‘-Wshadow=global’.

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-Wno-shadow-ivar (Objective-C only)
Do not warn whenever a local variable shadows an instance variable in an
Objective-C method.
-Wshadow=global
The default for ‘-Wshadow’. Warns for any (global) shadowing.
-Wshadow=local
Warn when a local variable shadows another local variable or parameter. This
warning is enabled by ‘-Wshadow=global’.
-Wshadow=compatible-local
Warn when a local variable shadows another local variable or parameter whose
type is compatible with that of the shadowing variable. In C++, type compatibility here means the type of the shadowing variable can be converted to that of the
shadowed variable. The creation of this flag (in addition to ‘-Wshadow=local’)
is based on the idea that when a local variable shadows another one of incompatible type, it is most likely intentional, not a bug or typo, as shown in the
following example:
for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
{
for (int i = 0; i < N; ++i)
{
...
}
...
}

Since the two variable i in the example above have incompatible types, enabling
only ‘-Wshadow=compatible-local’ will not emit a warning. Because their
types are incompatible, if a programmer accidentally uses one in place of the
other, type checking will catch that and emit an error or warning. So not
warning (about shadowing) in this case will not lead to undetected bugs. Use
of this flag instead of ‘-Wshadow=local’ can possibly reduce the number of
warnings triggered by intentional shadowing.
This warning is enabled by ‘-Wshadow=local’.
-Wlarger-than=len
Warn whenever an object of larger than len bytes is defined.
-Wframe-larger-than=len
Warn if the size of a function frame is larger than len bytes. The computation
done to determine the stack frame size is approximate and not conservative.
The actual requirements may be somewhat greater than len even if you do not
get a warning. In addition, any space allocated via alloca, variable-length
arrays, or related constructs is not included by the compiler when determining
whether or not to issue a warning.
-Wno-free-nonheap-object
Do not warn when attempting to free an object that was not allocated on the
heap.

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93

-Wstack-usage=len
Warn if the stack usage of a function might be larger than len bytes. The
computation done to determine the stack usage is conservative. Any space
allocated via alloca, variable-length arrays, or related constructs is included
by the compiler when determining whether or not to issue a warning.
The message is in keeping with the output of ‘-fstack-usage’.
• If the stack usage is fully static but exceeds the specified amount, it’s:
warning: stack usage is 1120 bytes

• If the stack usage is (partly) dynamic but bounded, it’s:
warning: stack usage might be 1648 bytes

• If the stack usage is (partly) dynamic and not bounded, it’s:
warning: stack usage might be unbounded

-Wno-pedantic-ms-format (MinGW targets only)
When used in combination with ‘-Wformat’ and ‘-pedantic’ without GNU
extensions, this option disables the warnings about non-ISO printf / scanf
format width specifiers I32, I64, and I used on Windows targets, which depend
on the MS runtime.
-Waligned-new
Warn about a new-expression of a type that requires greater alignment than
the alignof(std::max_align_t) but uses an allocation function without an
explicit alignment parameter. This option is enabled by ‘-Wall’.
Normally this only warns about global allocation functions, but
‘-Waligned-new=all’ also warns about class member allocation functions.
-Wplacement-new
-Wplacement-new=n
Warn about placement new expressions with undefined behavior, such as constructing an object in a buffer that is smaller than the type of the object. For
example, the placement new expression below is diagnosed because it attempts
to construct an array of 64 integers in a buffer only 64 bytes large.
char buf [64];
new (buf) int[64];

This warning is enabled by default.
-Wplacement-new=1
This is the default warning level of ‘-Wplacement-new’. At this
level the warning is not issued for some strictly undefined constructs
that GCC allows as extensions for compatibility with legacy code.
For example, the following new expression is not diagnosed at this
level even though it has undefined behavior according to the C++
standard because it writes past the end of the one-element array.
struct S { int n, a[1]; };
S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
new (s->a)int [32]();

-Wplacement-new=2
At this level, in addition to diagnosing all the same constructs as
at level 1, a diagnostic is also issued for placement new expressions

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Using the GNU Compiler Collection (GCC)

that construct an object in the last member of structure whose type
is an array of a single element and whose size is less than the size of
the object being constructed. While the previous example would be
diagnosed, the following construct makes use of the flexible member
array extension to avoid the warning at level 2.
struct S { int n, a[]; };
S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
new (s->a)int [32]();

-Wpointer-arith
Warn about anything that depends on the “size of” a function type or of void.
GNU C assigns these types a size of 1, for convenience in calculations with void
* pointers and pointers to functions. In C++, warn also when an arithmetic
operation involves NULL. This warning is also enabled by ‘-Wpedantic’.
-Wpointer-compare
Warn if a pointer is compared with a zero character constant. This usually
means that the pointer was meant to be dereferenced. For example:
const char *p = foo ();
if (p == ’\0’)
return 42;

Note that the code above is invalid in C++11.
This warning is enabled by default.
-Wtype-limits
Warn if a comparison is always true or always false due to the limited range of
the data type, but do not warn for constant expressions. For example, warn if
an unsigned variable is compared against zero with < or >=. This warning is
also enabled by ‘-Wextra’.
-Wcomment
-Wcomments
Warn whenever a comment-start sequence ‘/*’ appears in a ‘/*’ comment, or
whenever a backslash-newline appears in a ‘//’ comment. This warning is
enabled by ‘-Wall’.
-Wtrigraphs
Warn if any trigraphs are encountered that might change the meaning of the
program. Trigraphs within comments are not warned about, except those that
would form escaped newlines.
This option is implied by ‘-Wall’. If ‘-Wall’ is not given, this option
is still enabled unless trigraphs are enabled. To get trigraph conversion
without warnings, but get the other ‘-Wall’ warnings, use ‘-trigraphs -Wall
-Wno-trigraphs’.
-Wundef

Warn if an undefined identifier is evaluated in an #if directive. Such identifiers
are replaced with zero.

-Wexpansion-to-defined
Warn whenever ‘defined’ is encountered in the expansion of a macro (including
the case where the macro is expanded by an ‘#if’ directive). Such usage is not
portable. This warning is also enabled by ‘-Wpedantic’ and ‘-Wextra’.

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95

-Wunused-macros
Warn about macros defined in the main file that are unused. A macro is used
if it is expanded or tested for existence at least once. The preprocessor also
warns if the macro has not been used at the time it is redefined or undefined.
Built-in macros, macros defined on the command line, and macros defined in
include files are not warned about.
Note: If a macro is actually used, but only used in skipped conditional blocks,
then the preprocessor reports it as unused. To avoid the warning in such a case,
you might improve the scope of the macro’s definition by, for example, moving
it into the first skipped block. Alternatively, you could provide a dummy use
with something like:
#if defined the_macro_causing_the_warning
#endif

-Wno-endif-labels
Do not warn whenever an #else or an #endif are followed by text. This
sometimes happens in older programs with code of the form
#if FOO
...
#else FOO
...
#endif FOO

The second and third FOO should be in comments. This warning is on by default.
-Wbad-function-cast (C and Objective-C only)
Warn when a function call is cast to a non-matching type. For example, warn
if a call to a function returning an integer type is cast to a pointer type.
-Wc90-c99-compat (C and Objective-C only)
Warn about features not present in ISO C90, but present in ISO C99. For
instance, warn about use of variable length arrays, long long type, bool type,
compound literals, designated initializers, and so on. This option is independent
of the standards mode. Warnings are disabled in the expression that follows
__extension__.
-Wc99-c11-compat (C and Objective-C only)
Warn about features not present in ISO C99, but present in ISO C11. For instance, warn about use of anonymous structures and unions, _Atomic type qualifier, _Thread_local storage-class specifier, _Alignas specifier, Alignof operator, _Generic keyword, and so on. This option is independent of the standards
mode. Warnings are disabled in the expression that follows __extension__.
-Wc++-compat (C and Objective-C only)
Warn about ISO C constructs that are outside of the common subset of ISO C
and ISO C++, e.g. request for implicit conversion from void * to a pointer to
non-void type.
-Wc++11-compat (C++ and Objective-C++ only)
Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords in ISO C++
2011. This warning turns on ‘-Wnarrowing’ and is enabled by ‘-Wall’.

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Using the GNU Compiler Collection (GCC)

-Wc++14-compat (C++ and Objective-C++ only)
Warn about C++ constructs whose meaning differs between ISO C++ 2011 and
ISO C++ 2014. This warning is enabled by ‘-Wall’.
-Wc++17-compat (C++ and Objective-C++ only)
Warn about C++ constructs whose meaning differs between ISO C++ 2014 and
ISO C++ 2017. This warning is enabled by ‘-Wall’.
-Wcast-qual
Warn whenever a pointer is cast so as to remove a type qualifier from the target
type. For example, warn if a const char * is cast to an ordinary char *.
Also warn when making a cast that introduces a type qualifier in an unsafe way.
For example, casting char ** to const char ** is unsafe, as in this example:
/* p is char ** value. */
const char **q = (const char **) p;
/* Assignment of readonly string to const char * is OK.
*q = "string";
/* Now char** pointer points to read-only memory. */
**p = ’b’;

*/

-Wcast-align
Warn whenever a pointer is cast such that the required alignment of the target
is increased. For example, warn if a char * is cast to an int * on machines
where integers can only be accessed at two- or four-byte boundaries.
-Wcast-align=strict
Warn whenever a pointer is cast such that the required alignment of the target
is increased. For example, warn if a char * is cast to an int * regardless of the
target machine.
-Wcast-function-type
Warn when a function pointer is cast to an incompatible function pointer. In
a cast involving function types with a variable argument list only the types of
initial arguments that are provided are considered. Any parameter of pointertype matches any other pointer-type. Any benign differences in integral types
are ignored, like int vs. long on ILP32 targets. Likewise type qualifiers are
ignored. The function type void (*) (void) is special and matches everything,
which can be used to suppress this warning. In a cast involving pointer to
member types this warning warns whenever the type cast is changing the pointer
to member type. This warning is enabled by ‘-Wextra’.
-Wwrite-strings
When compiling C, give string constants the type const char[length] so that
copying the address of one into a non-const char * pointer produces a warning.
These warnings help you find at compile time code that can try to write into
a string constant, but only if you have been very careful about using const in
declarations and prototypes. Otherwise, it is just a nuisance. This is why we
did not make ‘-Wall’ request these warnings.
When compiling C++, warn about the deprecated conversion from string literals
to char *. This warning is enabled by default for C++ programs.

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97

-Wcatch-value
-Wcatch-value=n (C++ and Objective-C++ only)
Warn about catch handlers that do not catch via reference.
With
‘-Wcatch-value=1’ (or ‘-Wcatch-value’ for short) warn about polymorphic
class types that are caught by value. With ‘-Wcatch-value=2’ warn about all
class types that are caught by value. With ‘-Wcatch-value=3’ warn about all
types that are not caught by reference. ‘-Wcatch-value’ is enabled by ‘-Wall’.
-Wclobbered
Warn for variables that might be changed by longjmp or vfork. This warning
is also enabled by ‘-Wextra’.
-Wconditionally-supported (C++ and Objective-C++ only)
Warn for conditionally-supported (C++11 [intro.defs]) constructs.
-Wconversion
Warn for implicit conversions that may alter a value. This includes conversions
between real and integer, like abs (x) when x is double; conversions between
signed and unsigned, like unsigned ui = -1; and conversions to smaller types,
like sqrtf (M_PI). Do not warn for explicit casts like abs ((int) x) and ui
= (unsigned) -1, or if the value is not changed by the conversion like in abs
(2.0). Warnings about conversions between signed and unsigned integers can
be disabled by using ‘-Wno-sign-conversion’.
For C++, also warn for confusing overload resolution for user-defined conversions; and conversions that never use a type conversion operator: conversions
to void, the same type, a base class or a reference to them. Warnings about
conversions between signed and unsigned integers are disabled by default in
C++ unless ‘-Wsign-conversion’ is explicitly enabled.
-Wno-conversion-null (C++ and Objective-C++ only)
Do not warn for conversions between NULL and non-pointer types.
‘-Wconversion-null’ is enabled by default.
-Wzero-as-null-pointer-constant (C++ and Objective-C++ only)
Warn when a literal ‘0’ is used as null pointer constant. This can be useful to
facilitate the conversion to nullptr in C++11.
-Wsubobject-linkage (C++ and Objective-C++ only)
Warn if a class type has a base or a field whose type uses the anonymous
namespace or depends on a type with no linkage. If a type A depends on a type
B with no or internal linkage, defining it in multiple translation units would
be an ODR violation because the meaning of B is different in each translation
unit. If A only appears in a single translation unit, the best way to silence the
warning is to give it internal linkage by putting it in an anonymous namespace
as well. The compiler doesn’t give this warning for types defined in the main .C
file, as those are unlikely to have multiple definitions. ‘-Wsubobject-linkage’
is enabled by default.
-Wdangling-else
Warn about constructions where there may be confusion to which if statement
an else branch belongs. Here is an example of such a case:

98

Using the GNU Compiler Collection (GCC)

{
if (a)
if (b)
foo ();
else
bar ();
}

In C/C++, every else branch belongs to the innermost possible if statement,
which in this example is if (b). This is often not what the programmer expected, as illustrated in the above example by indentation the programmer
chose. When there is the potential for this confusion, GCC issues a warning when this flag is specified. To eliminate the warning, add explicit braces
around the innermost if statement so there is no way the else can belong to
the enclosing if. The resulting code looks like this:
{
if (a)
{
if (b)
foo ();
else
bar ();
}
}

This warning is enabled by ‘-Wparentheses’.
-Wdate-time
Warn when macros __TIME__, __DATE__ or __TIMESTAMP__ are encountered as
they might prevent bit-wise-identical reproducible compilations.
-Wdelete-incomplete (C++ and Objective-C++ only)
Warn when deleting a pointer to incomplete type, which may cause undefined
behavior at runtime. This warning is enabled by default.
-Wuseless-cast (C++ and Objective-C++ only)
Warn when an expression is casted to its own type.
-Wempty-body
Warn if an empty body occurs in an if, else or do while statement. This
warning is also enabled by ‘-Wextra’.
-Wenum-compare
Warn about a comparison between values of different enumerated types. In
C++ enumerated type mismatches in conditional expressions are also diagnosed
and the warning is enabled by default. In C this warning is enabled by ‘-Wall’.
-Wextra-semi (C++, Objective-C++ only)
Warn about redundant semicolon after in-class function definition.
-Wjump-misses-init (C, Objective-C only)
Warn if a goto statement or a switch statement jumps forward across the
initialization of a variable, or jumps backward to a label after the variable has
been initialized. This only warns about variables that are initialized when they
are declared. This warning is only supported for C and Objective-C; in C++
this sort of branch is an error in any case.

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99

‘-Wjump-misses-init’ is included in ‘-Wc++-compat’. It can be disabled with
the ‘-Wno-jump-misses-init’ option.
-Wsign-compare
Warn when a comparison between signed and unsigned values could produce
an incorrect result when the signed value is converted to unsigned. In C++, this
warning is also enabled by ‘-Wall’. In C, it is also enabled by ‘-Wextra’.
-Wsign-conversion
Warn for implicit conversions that may change the sign of an integer value, like
assigning a signed integer expression to an unsigned integer variable. An explicit
cast silences the warning. In C, this option is enabled also by ‘-Wconversion’.
-Wfloat-conversion
Warn for implicit conversions that reduce the precision of a real value. This
includes conversions from real to integer, and from higher precision real to lower
precision real values. This option is also enabled by ‘-Wconversion’.
-Wno-scalar-storage-order
Do not warn on suspicious constructs involving reverse scalar storage order.
-Wsized-deallocation (C++ and Objective-C++ only)
Warn about a definition of an unsized deallocation function
void operator delete (void *) noexcept;
void operator delete[] (void *) noexcept;

without a definition of the corresponding sized deallocation function
void operator delete (void *, std::size_t) noexcept;
void operator delete[] (void *, std::size_t) noexcept;

or vice versa. Enabled by ‘-Wextra’ along with ‘-fsized-deallocation’.
-Wsizeof-pointer-div
Warn for suspicious divisions of two sizeof expressions that divide the pointer
size by the element size, which is the usual way to compute the array size but
won’t work out correctly with pointers. This warning warns e.g. about sizeof
(ptr) / sizeof (ptr[0]) if ptr is not an array, but a pointer. This warning
is enabled by ‘-Wall’.
-Wsizeof-pointer-memaccess
Warn for suspicious length parameters to certain string and memory builtin functions if the argument uses sizeof. This warning triggers for example
for memset (ptr, 0, sizeof (ptr)); if ptr is not an array, but a pointer,
and suggests a possible fix, or about memcpy (&foo, ptr, sizeof (&foo));.
‘-Wsizeof-pointer-memaccess’ also warns about calls to bounded string copy
functions like strncat or strncpy that specify as the bound a sizeof expression of the source array. For example, in the following function the call to
strncat specifies the size of the source string as the bound. That is almost
certainly a mistake and so the call is diagnosed.
void make_file (const char *name)
{
char path[PATH_MAX];
strncpy (path, name, sizeof path - 1);

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Using the GNU Compiler Collection (GCC)

strncat (path, ".text", sizeof ".text");
...
}

The ‘-Wsizeof-pointer-memaccess’ option is enabled by ‘-Wall’.
-Wsizeof-array-argument
Warn when the sizeof operator is applied to a parameter that is declared as
an array in a function definition. This warning is enabled by default for C and
C++ programs.
-Wmemset-elt-size
Warn for suspicious calls to the memset built-in function, if the first argument
references an array, and the third argument is a number equal to the number
of elements, but not equal to the size of the array in memory. This indicates
that the user has omitted a multiplication by the element size. This warning is
enabled by ‘-Wall’.
-Wmemset-transposed-args
Warn for suspicious calls to the memset built-in function, if the second argument is not zero and the third argument is zero. This warns e.g. about
memset (buf, sizeof buf, 0) where most probably memset (buf, 0, sizeof
buf) was meant instead. The diagnostics is only emitted if the third argument
is literal zero. If it is some expression that is folded to zero, a cast of zero to
some type, etc., it is far less likely that the user has mistakenly exchanged the
arguments and no warning is emitted. This warning is enabled by ‘-Wall’.
-Waddress
Warn about suspicious uses of memory addresses. These include using the
address of a function in a conditional expression, such as void func(void);
if (func), and comparisons against the memory address of a string literal,
such as if (x == "abc"). Such uses typically indicate a programmer error: the
address of a function always evaluates to true, so their use in a conditional
usually indicate that the programmer forgot the parentheses in a function call;
and comparisons against string literals result in unspecified behavior and are
not portable in C, so they usually indicate that the programmer intended to
use strcmp. This warning is enabled by ‘-Wall’.
-Wlogical-op
Warn about suspicious uses of logical operators in expressions. This includes
using logical operators in contexts where a bit-wise operator is likely to be
expected. Also warns when the operands of a logical operator are the same:
extern int a;
if (a < 0 && a < 0) { ... }

-Wlogical-not-parentheses
Warn about logical not used on the left hand side operand of a comparison.
This option does not warn if the right operand is considered to be a boolean
expression. Its purpose is to detect suspicious code like the following:
int a;
...
if (!a > 1) { ... }

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101

It is possible to suppress the warning by wrapping the LHS into parentheses:
if ((!a) > 1) { ... }

This warning is enabled by ‘-Wall’.
-Waggregate-return
Warn if any functions that return structures or unions are defined or called. (In
languages where you can return an array, this also elicits a warning.)
-Wno-aggressive-loop-optimizations
Warn if in a loop with constant number of iterations the compiler detects undefined behavior in some statement during one or more of the iterations.
-Wno-attributes
Do not warn if an unexpected __attribute__ is used, such as unrecognized
attributes, function attributes applied to variables, etc. This does not stop
errors for incorrect use of supported attributes.
-Wno-builtin-declaration-mismatch
Warn if a built-in function is declared with the wrong signature or as nonfunction. This warning is enabled by default.
-Wno-builtin-macro-redefined
Do not warn if certain built-in macros are redefined. This suppresses warnings for redefinition of __TIMESTAMP__, __TIME__, __DATE__, __FILE__, and
__BASE_FILE__.
-Wstrict-prototypes (C and Objective-C only)
Warn if a function is declared or defined without specifying the argument types.
(An old-style function definition is permitted without a warning if preceded by
a declaration that specifies the argument types.)
-Wold-style-declaration (C and Objective-C only)
Warn for obsolescent usages, according to the C Standard, in a declaration. For
example, warn if storage-class specifiers like static are not the first things in
a declaration. This warning is also enabled by ‘-Wextra’.
-Wold-style-definition (C and Objective-C only)
Warn if an old-style function definition is used. A warning is given even if there
is a previous prototype.
-Wmissing-parameter-type (C and Objective-C only)
A function parameter is declared without a type specifier in K&R-style functions:
void foo(bar) { }

This warning is also enabled by ‘-Wextra’.
-Wmissing-prototypes (C and Objective-C only)
Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. Use this option to detect global functions that do not have a matching prototype declaration in a header file. This option is not valid for C++

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Using the GNU Compiler Collection (GCC)

because all function declarations provide prototypes and a non-matching declaration declares an overload rather than conflict with an earlier declaration.
Use ‘-Wmissing-declarations’ to detect missing declarations in C++.
-Wmissing-declarations
Warn if a global function is defined without a previous declaration. Do so even if
the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files. In C, no warnings are issued for functions with previous non-prototype declarations; use ‘-Wmissing-prototypes’
to detect missing prototypes. In C++, no warnings are issued for function templates, or for inline functions, or for functions in anonymous namespaces.
-Wmissing-field-initializers
Warn if a structure’s initializer has some fields missing. For example, the following code causes such a warning, because x.h is implicitly zero:
struct s { int f, g, h; };
struct s x = { 3, 4 };

This option does not warn about designated initializers, so the following modification does not trigger a warning:
struct s { int f, g, h; };
struct s x = { .f = 3, .g = 4 };

In C this option does not warn about the universal zero initializer ‘{ 0 }’:
struct s { int f, g, h; };
struct s x = { 0 };

Likewise, in C++ this option does not warn about the empty { } initializer, for
example:
struct s { int f, g, h; };
s x = { };

This warning is included in ‘-Wextra’. To get other ‘-Wextra’ warnings without
this one, use ‘-Wextra -Wno-missing-field-initializers’.
-Wno-multichar
Do not warn if a multicharacter constant (‘’FOOF’’) is used. Usually they
indicate a typo in the user’s code, as they have implementation-defined values,
and should not be used in portable code.
-Wnormalized=[none|id|nfc|nfkc]
In ISO C and ISO C++, two identifiers are different if they are different sequences
of characters. However, sometimes when characters outside the basic ASCII
character set are used, you can have two different character sequences that
look the same. To avoid confusion, the ISO 10646 standard sets out some
normalization rules which when applied ensure that two sequences that look the
same are turned into the same sequence. GCC can warn you if you are using
identifiers that have not been normalized; this option controls that warning.
There are four levels of warning supported by GCC.
The default is
‘-Wnormalized=nfc’, which warns about any identifier that is not in the ISO
10646 “C” normalized form, NFC. NFC is the recommended form for most
uses. It is equivalent to ‘-Wnormalized’.

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Unfortunately, there are some characters allowed in identifiers by ISO C and
ISO C++ that, when turned into NFC, are not allowed in identifiers. That is,
there’s no way to use these symbols in portable ISO C or C++ and have all
your identifiers in NFC. ‘-Wnormalized=id’ suppresses the warning for these
characters. It is hoped that future versions of the standards involved will correct
this, which is why this option is not the default.
You can switch the warning off for all characters by writing
‘-Wnormalized=none’ or ‘-Wno-normalized’.
You should only do
this if you are using some other normalization scheme (like “D”), because
otherwise you can easily create bugs that are literally impossible to see.
Some characters in ISO 10646 have distinct meanings but look identical in some
fonts or display methodologies, especially once formatting has been applied. For
instance \u207F, “SUPERSCRIPT LATIN SMALL LETTER N”, displays just
like a regular n that has been placed in a superscript. ISO 10646 defines the
NFKC normalization scheme to convert all these into a standard form as well,
and GCC warns if your code is not in NFKC if you use ‘-Wnormalized=nfkc’.
This warning is comparable to warning about every identifier that contains the
letter O because it might be confused with the digit 0, and so is not the default,
but may be useful as a local coding convention if the programming environment
cannot be fixed to display these characters distinctly.
-Wno-deprecated
Do not warn about usage of deprecated features. See Section 7.11 [Deprecated
Features], page 798.
-Wno-deprecated-declarations
Do not warn about uses of functions (see Section 6.31 [Function Attributes],
page 464), variables (see Section 6.32 [Variable Attributes], page 513), and types
(see Section 6.33 [Type Attributes], page 524) marked as deprecated by using
the deprecated attribute.
-Wno-overflow
Do not warn about compile-time overflow in constant expressions.
-Wno-odr

Warn about One Definition Rule violations during link-time optimization. Requires ‘-flto-odr-type-merging’ to be enabled. Enabled by default.

-Wopenmp-simd
Warn if the vectorizer cost model overrides the OpenMP simd directive set by
user. The ‘-fsimd-cost-model=unlimited’ option can be used to relax the
cost model.
-Woverride-init (C and Objective-C only)
Warn if an initialized field without side effects is overridden when using designated initializers (see Section 6.27 [Designated Initializers], page 461).
This warning is included in ‘-Wextra’. To get other ‘-Wextra’ warnings without
this one, use ‘-Wextra -Wno-override-init’.

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-Woverride-init-side-effects (C and Objective-C only)
Warn if an initialized field with side effects is overridden when using designated
initializers (see Section 6.27 [Designated Initializers], page 461). This warning
is enabled by default.
-Wpacked

Warn if a structure is given the packed attribute, but the packed attribute has no
effect on the layout or size of the structure. Such structures may be mis-aligned
for little benefit. For instance, in this code, the variable f.x in struct bar is
misaligned even though struct bar does not itself have the packed attribute:
struct foo {
int x;
char a, b, c, d;
} __attribute__((packed));
struct bar {
char z;
struct foo f;
};

-Wpacked-bitfield-compat
The 4.1, 4.2 and 4.3 series of GCC ignore the packed attribute on bit-fields
of type char. This has been fixed in GCC 4.4 but the change can lead to
differences in the structure layout. GCC informs you when the offset of such a
field has changed in GCC 4.4. For example there is no longer a 4-bit padding
between field a and b in this structure:
struct foo
{
char a:4;
char b:8;
} __attribute__ ((packed));

This warning is enabled by default. Use ‘-Wno-packed-bitfield-compat’ to
disable this warning.
-Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only)
Warn if a structure field with explicitly specified alignment in a packed struct
or union is misaligned. For example, a warning will be issued on struct S, like,
warning: alignment 1 of ’struct S’ is less than 8, in this code:
struct __attribute__ ((aligned (8))) S8 { char a[8]; };
struct __attribute__ ((packed)) S {
struct S8 s8;
};

This warning is enabled by ‘-Wall’.
-Wpadded

Warn if padding is included in a structure, either to align an element of the
structure or to align the whole structure. Sometimes when this happens it is
possible to rearrange the fields of the structure to reduce the padding and so
make the structure smaller.

-Wredundant-decls
Warn if anything is declared more than once in the same scope, even in cases
where multiple declaration is valid and changes nothing.

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105

-Wno-restrict
Warn when an object referenced by a restrict-qualified parameter (or, in
C++, a __restrict-qualified parameter) is aliased by another argument, or
when copies between such objects overlap. For example, the call to the strcpy
function below attempts to truncate the string by replacing its initial characters
with the last four. However, because the call writes the terminating NUL into
a[4], the copies overlap and the call is diagnosed.
void foo (void)
{
char a[] = "abcd1234";
strcpy (a, a + 4);
...
}

The ‘-Wrestrict’ option detects some instances of simple overlap even without
optimization but works best at ‘-O2’ and above. It is included in ‘-Wall’.
-Wnested-externs (C and Objective-C only)
Warn if an extern declaration is encountered within a function.
-Wno-inherited-variadic-ctor
Suppress warnings about use of C++11 inheriting constructors when the base
class inherited from has a C variadic constructor; the warning is on by default
because the ellipsis is not inherited.
-Winline

Warn if a function that is declared as inline cannot be inlined. Even with this
option, the compiler does not warn about failures to inline functions declared
in system headers.
The compiler uses a variety of heuristics to determine whether or not to inline a
function. For example, the compiler takes into account the size of the function
being inlined and the amount of inlining that has already been done in the current function. Therefore, seemingly insignificant changes in the source program
can cause the warnings produced by ‘-Winline’ to appear or disappear.

-Wno-invalid-offsetof (C++ and Objective-C++ only)
Suppress warnings from applying the offsetof macro to a non-POD type.
According to the 2014 ISO C++ standard, applying offsetof to a non-standardlayout type is undefined. In existing C++ implementations, however, offsetof
typically gives meaningful results. This flag is for users who are aware that
they are writing nonportable code and who have deliberately chosen to ignore
the warning about it.
The restrictions on offsetof may be relaxed in a future version of the C++
standard.
-Wint-in-bool-context
Warn for suspicious use of integer values where boolean values are expected,
such as conditional expressions (?:) using non-boolean integer constants in
boolean context, like if (a <= b ? 2 : 3). Or left shifting of signed integers
in boolean context, like for (a = 0; 1 << a; a++);. Likewise for all kinds of
multiplications regardless of the data type. This warning is enabled by ‘-Wall’.

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Using the GNU Compiler Collection (GCC)

-Wno-int-to-pointer-cast
Suppress warnings from casts to pointer type of an integer of a different
size.
In C++, casting to a pointer type of smaller size is an error.
‘Wint-to-pointer-cast’ is enabled by default.
-Wno-pointer-to-int-cast (C and Objective-C only)
Suppress warnings from casts from a pointer to an integer type of a different
size.
-Winvalid-pch
Warn if a precompiled header (see Section 3.21 [Precompiled Headers],
page 425) is found in the search path but cannot be used.
-Wlong-long
Warn if long long type is used. This is enabled by either ‘-Wpedantic’ or
‘-Wtraditional’ in ISO C90 and C++98 modes. To inhibit the warning messages, use ‘-Wno-long-long’.
-Wvariadic-macros
Warn if variadic macros are used in ISO C90 mode, or if the GNU
alternate syntax is used in ISO C99 mode. This is enabled by either
‘-Wpedantic’ or ‘-Wtraditional’. To inhibit the warning messages, use
‘-Wno-variadic-macros’.
-Wvarargs
Warn upon questionable usage of the macros used to handle variable arguments like va_start. This is default. To inhibit the warning messages, use
‘-Wno-varargs’.
-Wvector-operation-performance
Warn if vector operation is not implemented via SIMD capabilities of the architecture. Mainly useful for the performance tuning. Vector operation can be
implemented piecewise, which means that the scalar operation is performed
on every vector element; in parallel, which means that the vector operation
is implemented using scalars of wider type, which normally is more performance
efficient; and as a single scalar, which means that vector fits into a scalar
type.
-Wno-virtual-move-assign
Suppress warnings about inheriting from a virtual base with a non-trivial C++11
move assignment operator. This is dangerous because if the virtual base is
reachable along more than one path, it is moved multiple times, which can
mean both objects end up in the moved-from state. If the move assignment
operator is written to avoid moving from a moved-from object, this warning
can be disabled.
-Wvla

Warn if a variable-length array is used in the code. ‘-Wno-vla’ prevents the
‘-Wpedantic’ warning of the variable-length array.

-Wvla-larger-than=n
If this option is used, the compiler will warn on uses of variable-length arrays
where the size is either unbounded, or bounded by an argument that can be

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107

larger than n bytes. This is similar to how ‘-Walloca-larger-than=n’ works,
but with variable-length arrays.
Note that GCC may optimize small variable-length arrays of a known value
into plain arrays, so this warning may not get triggered for such arrays.
This warning is not enabled by ‘-Wall’, and is only active when ‘-ftree-vrp’
is active (default for ‘-O2’ and above).
See also ‘-Walloca-larger-than=n’.
-Wvolatile-register-var
Warn if a register variable is declared volatile. The volatile modifier does not
inhibit all optimizations that may eliminate reads and/or writes to register
variables. This warning is enabled by ‘-Wall’.
-Wdisabled-optimization
Warn if a requested optimization pass is disabled. This warning does not generally indicate that there is anything wrong with your code; it merely indicates
that GCC’s optimizers are unable to handle the code effectively. Often, the
problem is that your code is too big or too complex; GCC refuses to optimize
programs when the optimization itself is likely to take inordinate amounts of
time.
-Wpointer-sign (C and Objective-C only)
Warn for pointer argument passing or assignment with different signedness.
This option is only supported for C and Objective-C. It is implied by ‘-Wall’
and by ‘-Wpedantic’, which can be disabled with ‘-Wno-pointer-sign’.
-Wstack-protector
This option is only active when ‘-fstack-protector’ is active. It warns about
functions that are not protected against stack smashing.
-Woverlength-strings
Warn about string constants that are longer than the “minimum maximum”
length specified in the C standard. Modern compilers generally allow string
constants that are much longer than the standard’s minimum limit, but very
portable programs should avoid using longer strings.
The limit applies after string constant concatenation, and does not count the
trailing NUL. In C90, the limit was 509 characters; in C99, it was raised to
4095. C++98 does not specify a normative minimum maximum, so we do not
diagnose overlength strings in C++.
This option is implied by ‘-Wpedantic’, and can be disabled with
‘-Wno-overlength-strings’.
-Wunsuffixed-float-constants (C and Objective-C only)
Issue a warning for any floating constant that does not have a suffix. When
used together with ‘-Wsystem-headers’ it warns about such constants in system
header files. This can be useful when preparing code to use with the FLOAT_
CONST_DECIMAL64 pragma from the decimal floating-point extension to C99.
-Wno-designated-init (C and Objective-C only)
Suppress warnings when a positional initializer is used to initialize a structure
that has been marked with the designated_init attribute.

108

-Whsa

Using the GNU Compiler Collection (GCC)

Issue a warning when HSAIL cannot be emitted for the compiled function or
OpenMP construct.

3.9 Options for Debugging Your Program
To tell GCC to emit extra information for use by a debugger, in almost all cases you need
only to add ‘-g’ to your other options.
GCC allows you to use ‘-g’ with ‘-O’. The shortcuts taken by optimized code may
occasionally be surprising: some variables you declared may not exist at all; flow of control
may briefly move where you did not expect it; some statements may not be executed because
they compute constant results or their values are already at hand; some statements may
execute in different places because they have been moved out of loops. Nevertheless it
is possible to debug optimized output. This makes it reasonable to use the optimizer for
programs that might have bugs.
If you are not using some other optimization option, consider using ‘-Og’ (see Section 3.10
[Optimize Options], page 114) with ‘-g’. With no ‘-O’ option at all, some compiler passes
that collect information useful for debugging do not run at all, so that ‘-Og’ may result in
a better debugging experience.
-g

Produce debugging information in the operating system’s native format (stabs,
COFF, XCOFF, or DWARF). GDB can work with this debugging information.
On most systems that use stabs format, ‘-g’ enables use of extra debugging
information that only GDB can use; this extra information makes debugging
work better in GDB but probably makes other debuggers crash or refuse to read
the program. If you want to control for certain whether to generate the extra
information, use ‘-gstabs+’, ‘-gstabs’, ‘-gxcoff+’, ‘-gxcoff’, or ‘-gvms’ (see
below).

-ggdb

Produce debugging information for use by GDB. This means to use the most
expressive format available (DWARF, stabs, or the native format if neither of
those are supported), including GDB extensions if at all possible.

-gdwarf
-gdwarf-version
Produce debugging information in DWARF format (if that is supported). The
value of version may be either 2, 3, 4 or 5; the default version for most targets
is 4. DWARF Version 5 is only experimental.
Note that with DWARF Version 2, some ports require and always use some
non-conflicting DWARF 3 extensions in the unwind tables.
Version 4 may require GDB 7.0 and ‘-fvar-tracking-assignments’ for maximum benefit.
GCC no longer supports DWARF Version 1, which is substantially different
than Version 2 and later. For historical reasons, some other DWARF-related
options such as ‘-fno-dwarf2-cfi-asm’) retain a reference to DWARF Version
2 in their names, but apply to all currently-supported versions of DWARF.
-gstabs

Produce debugging information in stabs format (if that is supported), without
GDB extensions. This is the format used by DBX on most BSD systems.

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109

On MIPS, Alpha and System V Release 4 systems this option produces stabs
debugging output that is not understood by DBX. On System V Release 4
systems this option requires the GNU assembler.
-gstabs+

Produce debugging information in stabs format (if that is supported), using
GNU extensions understood only by the GNU debugger (GDB). The use of
these extensions is likely to make other debuggers crash or refuse to read the
program.

-gxcoff

Produce debugging information in XCOFF format (if that is supported). This
is the format used by the DBX debugger on IBM RS/6000 systems.

-gxcoff+

Produce debugging information in XCOFF format (if that is supported), using
GNU extensions understood only by the GNU debugger (GDB). The use of
these extensions is likely to make other debuggers crash or refuse to read the
program, and may cause assemblers other than the GNU assembler (GAS) to
fail with an error.

-gvms

Produce debugging information in Alpha/VMS debug format (if that is supported). This is the format used by DEBUG on Alpha/VMS systems.

-glevel
-ggdblevel
-gstabslevel
-gxcofflevel
-gvmslevel
Request debugging information and also use level to specify how much information. The default level is 2.
Level 0 produces no debug information at all. Thus, ‘-g0’ negates ‘-g’.
Level 1 produces minimal information, enough for making backtraces in parts
of the program that you don’t plan to debug. This includes descriptions of
functions and external variables, and line number tables, but no information
about local variables.
Level 3 includes extra information, such as all the macro definitions present in
the program. Some debuggers support macro expansion when you use ‘-g3’.
‘-gdwarf’ does not accept a concatenated debug level, to avoid confusion with
‘-gdwarf-level’. Instead use an additional ‘-glevel’ option to change the
debug level for DWARF.
-feliminate-unused-debug-symbols
Produce debugging information in stabs format (if that is supported), for only
symbols that are actually used.
-femit-class-debug-always
Instead of emitting debugging information for a C++ class in only one object file,
emit it in all object files using the class. This option should be used only with
debuggers that are unable to handle the way GCC normally emits debugging
information for classes because using this option increases the size of debugging
information by as much as a factor of two.

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Using the GNU Compiler Collection (GCC)

-fno-merge-debug-strings
Direct the linker to not merge together strings in the debugging information
that are identical in different object files. Merging is not supported by all
assemblers or linkers. Merging decreases the size of the debug information in
the output file at the cost of increasing link processing time. Merging is enabled
by default.
-fdebug-prefix-map=old=new
When compiling files residing in directory ‘old’, record debugging information
describing them as if the files resided in directory ‘new’ instead. This can be
used to replace a build-time path with an install-time path in the debug info.
It can also be used to change an absolute path to a relative path by using ‘.’ for
new. This can give more reproducible builds, which are location independent,
but may require an extra command to tell GDB where to find the source files.
See also ‘-ffile-prefix-map’.
-fvar-tracking
Run variable tracking pass. It computes where variables are stored at each position in code. Better debugging information is then generated (if the debugging
information format supports this information).
It is enabled by default when compiling with optimization (‘-Os’, ‘-O’, ‘-O2’,
. . . ), debugging information (‘-g’) and the debug info format supports it.
-fvar-tracking-assignments
Annotate assignments to user variables early in the compilation and attempt to
carry the annotations over throughout the compilation all the way to the end, in
an attempt to improve debug information while optimizing. Use of ‘-gdwarf-4’
is recommended along with it.
It can be enabled even if var-tracking is disabled, in which case annotations
are created and maintained, but discarded at the end. By default, this flag is
enabled together with ‘-fvar-tracking’, except when selective scheduling is
enabled.
-gsplit-dwarf
Separate as much DWARF debugging information as possible into a separate
output file with the extension ‘.dwo’. This option allows the build system to
avoid linking files with debug information. To be useful, this option requires a
debugger capable of reading ‘.dwo’ files.
-gpubnames
Generate DWARF .debug_pubnames and .debug_pubtypes sections.
-ggnu-pubnames
Generate .debug_pubnames and .debug_pubtypes sections in a format suitable
for conversion into a GDB index. This option is only useful with a linker that
can produce GDB index version 7.
-fdebug-types-section
When using DWARF Version 4 or higher, type DIEs can be put into their own
.debug_types section instead of making them part of the .debug_info section.

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111

It is more efficient to put them in a separate comdat sections since the linker
can then remove duplicates. But not all DWARF consumers support .debug_
types sections yet and on some objects .debug_types produces larger instead
of smaller debugging information.
-grecord-gcc-switches
-gno-record-gcc-switches
This switch causes the command-line options used to invoke the compiler that
may affect code generation to be appended to the DW AT producer attribute
in DWARF debugging information. The options are concatenated with spaces
separating them from each other and from the compiler version. It is enabled by
default. See also ‘-frecord-gcc-switches’ for another way of storing compiler
options into the object file.
-gstrict-dwarf
Disallow using extensions of later DWARF standard version than selected with
‘-gdwarf-version’. On most targets using non-conflicting DWARF extensions
from later standard versions is allowed.
-gno-strict-dwarf
Allow using extensions of later DWARF standard version than selected with
‘-gdwarf-version’.
-gas-loc-support
Inform the compiler that the assembler supports .loc directives. It may then
use them for the assembler to generate DWARF2+ line number tables.
This is generally desirable, because assembler-generated line-number tables are
a lot more compact than those the compiler can generate itself.
This option will be enabled by default if, at GCC configure time, the assembler
was found to support such directives.
-gno-as-loc-support
Force GCC to generate DWARF2+ line number tables internally, if DWARF2+
line number tables are to be generated.
gas-locview-support
Inform the compiler that the assembler supports view assignment and reset
assertion checking in .loc directives.
This option will be enabled by default if, at GCC configure time, the assembler
was found to support them.
gno-as-locview-support
Force GCC to assign view numbers internally, if ‘-gvariable-location-views’
are explicitly requested.
-gcolumn-info
-gno-column-info
Emit location column information into DWARF debugging information, rather
than just file and line. This option is enabled by default.

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-gstatement-frontiers
-gno-statement-frontiers
This option causes GCC to create markers in the internal representation at
the beginning of statements, and to keep them roughly in place throughout
compilation, using them to guide the output of is_stmt markers in the line
number table. This is enabled by default when compiling with optimization
(‘-Os’, ‘-O’, ‘-O2’, . . . ), and outputting DWARF 2 debug information at the
normal level.
-gvariable-location-views
-gvariable-location-views=incompat5
-gno-variable-location-views
Augment variable location lists with progressive view numbers implied from the
line number table. This enables debug information consumers to inspect state
at certain points of the program, even if no instructions associated with the
corresponding source locations are present at that point. If the assembler lacks
support for view numbers in line number tables, this will cause the compiler to
emit the line number table, which generally makes them somewhat less compact. The augmented line number tables and location lists are fully backwardcompatible, so they can be consumed by debug information consumers that are
not aware of these augmentations, but they won’t derive any benefit from them
either.
This is enabled by default when outputting DWARF 2 debug information at the normal level, as long as there is assembler support,
‘-fvar-tracking-assignments’ is enabled and ‘-gstrict-dwarf’ is
not. When assembler support is not available, this may still be enabled,
but it will force GCC to output internal line number tables, and if
‘-ginternal-reset-location-views’ is not enabled, that will most certainly
lead to silently mismatching location views.
There is a proposed representation for view numbers that is not backward
compatible with the location list format introduced in DWARF 5, that can be
enabled with ‘-gvariable-location-views=incompat5’. This option may be
removed in the future, is only provided as a reference implementation of the
proposed representation. Debug information consumers are not expected to
support this extended format, and they would be rendered unable to decode
location lists using it.
-ginternal-reset-location-views
-gnointernal-reset-location-views
Attempt to determine location views that can be omitted from location view
lists. This requires the compiler to have very accurate insn length estimates,
which isn’t always the case, and it may cause incorrect view lists to be generated
silently when using an assembler that does not support location view lists. The
GNU assembler will flag any such error as a view number mismatch. This is
only enabled on ports that define a reliable estimation function.

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-ginline-points
-gno-inline-points
Generate extended debug information for inlined functions. Location view
tracking markers are inserted at inlined entry points, so that address and view
numbers can be computed and output in debug information. This can be enabled independently of location views, in which case the view numbers won’t
be output, but it can only be enabled along with statement frontiers, and it is
only enabled by default if location views are enabled.
-gz[=type]
Produce compressed debug sections in DWARF format, if that is supported. If
type is not given, the default type depends on the capabilities of the assembler
and linker used. type may be one of ‘none’ (don’t compress debug sections),
‘zlib’ (use zlib compression in ELF gABI format), or ‘zlib-gnu’ (use zlib
compression in traditional GNU format). If the linker doesn’t support writing
compressed debug sections, the option is rejected. Otherwise, if the assembler
does not support them, ‘-gz’ is silently ignored when producing object files.
-femit-struct-debug-baseonly
Emit debug information for struct-like types only when the base name of the
compilation source file matches the base name of file in which the struct is
defined.
This option substantially reduces the size of debugging information,
but at significant potential loss in type information to the debugger.
See ‘-femit-struct-debug-reduced’ for a less aggressive option.
See
‘-femit-struct-debug-detailed’ for more detailed control.
This option works only with DWARF debug output.
-femit-struct-debug-reduced
Emit debug information for struct-like types only when the base name of the
compilation source file matches the base name of file in which the type is defined,
unless the struct is a template or defined in a system header.
This option significantly reduces the size of debugging information,
with some potential loss in type information to the debugger.
See
‘-femit-struct-debug-baseonly’ for a more aggressive option.
See
‘-femit-struct-debug-detailed’ for more detailed control.
This option works only with DWARF debug output.
-femit-struct-debug-detailed[=spec-list]
Specify the struct-like types for which the compiler generates debug information. The intent is to reduce duplicate struct debug information between different object files within the same program.
This option is a detailed version of ‘-femit-struct-debug-reduced’ and
‘-femit-struct-debug-baseonly’, which serves for most needs.
A specification has the syntax
[‘dir:’|‘ind:’][‘ord:’|‘gen:’](‘any’|‘sys’|‘base’|‘none’)
The optional first word limits the specification to structs that are used directly
(‘dir:’) or used indirectly (‘ind:’). A struct type is used directly when it is

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the type of a variable, member. Indirect uses arise through pointers to structs.
That is, when use of an incomplete struct is valid, the use is indirect. An
example is ‘struct one direct; struct two * indirect;’.
The optional second word limits the specification to ordinary structs (‘ord:’) or
generic structs (‘gen:’). Generic structs are a bit complicated to explain. For
C++, these are non-explicit specializations of template classes, or non-template
classes within the above. Other programming languages have generics, but
‘-femit-struct-debug-detailed’ does not yet implement them.
The third word specifies the source files for those structs for which the compiler
should emit debug information. The values ‘none’ and ‘any’ have the normal
meaning. The value ‘base’ means that the base of name of the file in which
the type declaration appears must match the base of the name of the main
compilation file. In practice, this means that when compiling ‘foo.c’, debug
information is generated for types declared in that file and ‘foo.h’, but not other
header files. The value ‘sys’ means those types satisfying ‘base’ or declared in
system or compiler headers.
You may need to experiment to determine the best settings for your application.
The default is ‘-femit-struct-debug-detailed=all’.
This option works only with DWARF debug output.
-fno-dwarf2-cfi-asm
Emit DWARF unwind info as compiler generated .eh_frame section instead of
using GAS .cfi_* directives.
-fno-eliminate-unused-debug-types
Normally, when producing DWARF output, GCC avoids producing debug symbol output for types that are nowhere used in the source file being compiled.
Sometimes it is useful to have GCC emit debugging information for all types
declared in a compilation unit, regardless of whether or not they are actually
used in that compilation unit, for example if, in the debugger, you want to cast
a value to a type that is not actually used in your program (but is declared).
More often, however, this results in a significant amount of wasted space.

3.10 Options That Control Optimization
These options control various sorts of optimizations.
Without any optimization option, the compiler’s goal is to reduce the cost of compilation
and to make debugging produce the expected results. Statements are independent: if you
stop the program with a breakpoint between statements, you can then assign a new value
to any variable or change the program counter to any other statement in the function and
get exactly the results you expect from the source code.
Turning on optimization flags makes the compiler attempt to improve the performance
and/or code size at the expense of compilation time and possibly the ability to debug the
program.
The compiler performs optimization based on the knowledge it has of the program. Compiling multiple files at once to a single output file mode allows the compiler to use information gained from all of the files when compiling each of them.

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Not all optimizations are controlled directly by a flag. Only optimizations that have a
flag are listed in this section.
Most optimizations are only enabled if an ‘-O’ level is set on the command line. Otherwise
they are disabled, even if individual optimization flags are specified.
Depending on the target and how GCC was configured, a slightly different set of optimizations may be enabled at each ‘-O’ level than those listed here. You can invoke GCC
with ‘-Q --help=optimizers’ to find out the exact set of optimizations that are enabled
at each level. See Section 3.2 [Overall Options], page 29, for examples.
-O
-O1

Optimize. Optimizing compilation takes somewhat more time, and a lot more
memory for a large function.
With ‘-O’, the compiler tries to reduce code size and execution time, without
performing any optimizations that take a great deal of compilation time.
‘-O’ turns on the following optimization flags:
-fauto-inc-dec
-fbranch-count-reg
-fcombine-stack-adjustments
-fcompare-elim
-fcprop-registers
-fdce
-fdefer-pop
-fdelayed-branch
-fdse
-fforward-propagate
-fguess-branch-probability
-fif-conversion2
-fif-conversion
-finline-functions-called-once
-fipa-pure-const
-fipa-profile
-fipa-reference
-fmerge-constants
-fmove-loop-invariants
-fomit-frame-pointer
-freorder-blocks
-fshrink-wrap
-fshrink-wrap-separate
-fsplit-wide-types
-fssa-backprop
-fssa-phiopt
-ftree-bit-ccp
-ftree-ccp
-ftree-ch
-ftree-coalesce-vars
-ftree-copy-prop
-ftree-dce
-ftree-dominator-opts
-ftree-dse
-ftree-forwprop
-ftree-fre
-ftree-phiprop
-ftree-sink
-ftree-slsr

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-ftree-sra
-ftree-pta
-ftree-ter
-funit-at-a-time

-O2

Optimize even more. GCC performs nearly all supported optimizations that do
not involve a space-speed tradeoff. As compared to ‘-O’, this option increases
both compilation time and the performance of the generated code.
‘-O2’ turns on all optimization flags specified by ‘-O’. It also turns on the
following optimization flags:
-fthread-jumps
-falign-functions -falign-jumps
-falign-loops -falign-labels
-fcaller-saves
-fcrossjumping
-fcse-follow-jumps -fcse-skip-blocks
-fdelete-null-pointer-checks
-fdevirtualize -fdevirtualize-speculatively
-fexpensive-optimizations
-fgcse -fgcse-lm
-fhoist-adjacent-loads
-finline-small-functions
-findirect-inlining
-fipa-cp
-fipa-bit-cp
-fipa-vrp
-fipa-sra
-fipa-icf
-fisolate-erroneous-paths-dereference
-flra-remat
-foptimize-sibling-calls
-foptimize-strlen
-fpartial-inlining
-fpeephole2
-freorder-blocks-algorithm=stc
-freorder-blocks-and-partition -freorder-functions
-frerun-cse-after-loop
-fsched-interblock -fsched-spec
-fschedule-insns -fschedule-insns2
-fstore-merging
-fstrict-aliasing
-ftree-builtin-call-dce
-ftree-switch-conversion -ftree-tail-merge
-fcode-hoisting
-ftree-pre
-ftree-vrp
-fipa-ra

Please note the warning under ‘-fgcse’ about invoking ‘-O2’ on programs that
use computed gotos.
-O3

Optimize yet more. ‘-O3’ turns on all optimizations specified by ‘-O2’ and also
turns on the following optimization flags:
-finline-functions
-funswitch-loops
-fpredictive-commoning
-fgcse-after-reload

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-ftree-loop-vectorize
-ftree-loop-distribution
-ftree-loop-distribute-patterns
-floop-interchange
-floop-unroll-and-jam
-fsplit-paths
-ftree-slp-vectorize
-fvect-cost-model
-ftree-partial-pre
-fpeel-loops
-fipa-cp-clone

-O0

Reduce compilation time and make debugging produce the expected results.
This is the default.

-Os

Optimize for size. ‘-Os’ enables all ‘-O2’ optimizations that do not typically
increase code size. It also performs further optimizations designed to reduce
code size.
‘-Os’ disables the following optimization flags:
-falign-functions -falign-jumps -falign-loops
-falign-labels -freorder-blocks -freorder-blocks-algorithm=stc
-freorder-blocks-and-partition -fprefetch-loop-arrays

-Ofast

Disregard strict standards compliance. ‘-Ofast’ enables all ‘-O3’ optimizations.
It also enables optimizations that are not valid for all standard-compliant programs. It turns on ‘-ffast-math’ and the Fortran-specific ‘-fstack-arrays’,
unless ‘-fmax-stack-var-size’ is specified, and ‘-fno-protect-parens’.

-Og

Optimize debugging experience. ‘-Og’ enables optimizations that do not interfere with debugging. It should be the optimization level of choice for the
standard edit-compile-debug cycle, offering a reasonable level of optimization
while maintaining fast compilation and a good debugging experience.

If you use multiple ‘-O’ options, with or without level numbers, the last such option is
the one that is effective.
Options of the form ‘-fflag’ specify machine-independent flags. Most flags have both
positive and negative forms; the negative form of ‘-ffoo’ is ‘-fno-foo’. In the table below,
only one of the forms is listed—the one you typically use. You can figure out the other form
by either removing ‘no-’ or adding it.
The following options control specific optimizations. They are either activated by ‘-O’
options or are related to ones that are. You can use the following flags in the rare cases
when “fine-tuning” of optimizations to be performed is desired.
-fno-defer-pop
Always pop the arguments to each function call as soon as that function returns. For machines that must pop arguments after a function call, the compiler
normally lets arguments accumulate on the stack for several function calls and
pops them all at once.
Disabled at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.

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-fforward-propagate
Perform a forward propagation pass on RTL. The pass tries to combine two
instructions and checks if the result can be simplified. If loop unrolling is active,
two passes are performed and the second is scheduled after loop unrolling.
This option is enabled by default at optimization levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.
-ffp-contract=style
‘-ffp-contract=off’ disables floating-point expression contraction.
‘-ffp-contract=fast’ enables floating-point expression contraction such as
forming of fused multiply-add operations if the target has native support for
them. ‘-ffp-contract=on’ enables floating-point expression contraction if
allowed by the language standard. This is currently not implemented and
treated equal to ‘-ffp-contract=off’.
The default is ‘-ffp-contract=fast’.
-fomit-frame-pointer
Omit the frame pointer in functions that don’t need one. This avoids the
instructions to save, set up and restore the frame pointer; on many targets it
also makes an extra register available.
On some targets this flag has no effect because the standard calling sequence
always uses a frame pointer, so it cannot be omitted.
Note that ‘-fno-omit-frame-pointer’ doesn’t guarantee the frame pointer is
used in all functions. Several targets always omit the frame pointer in leaf
functions.
Enabled by default at ‘-O’ and higher.
-foptimize-sibling-calls
Optimize sibling and tail recursive calls.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-foptimize-strlen
Optimize various standard C string functions (e.g. strlen, strchr or strcpy)
and their _FORTIFY_SOURCE counterparts into faster alternatives.
Enabled at levels ‘-O2’, ‘-O3’.
-fno-inline
Do not expand any functions inline apart from those marked with the always_
inline attribute. This is the default when not optimizing.
Single functions can be exempted from inlining by marking them with the
noinline attribute.
-finline-small-functions
Integrate functions into their callers when their body is smaller than expected
function call code (so overall size of program gets smaller). The compiler heuristically decides which functions are simple enough to be worth integrating in this
way. This inlining applies to all functions, even those not declared inline.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

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-findirect-inlining
Inline also indirect calls that are discovered to be known at compile time thanks
to previous inlining. This option has any effect only when inlining itself is turned
on by the ‘-finline-functions’ or ‘-finline-small-functions’ options.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-finline-functions
Consider all functions for inlining, even if they are not declared inline. The
compiler heuristically decides which functions are worth integrating in this way.
If all calls to a given function are integrated, and the function is declared
static, then the function is normally not output as assembler code in its own
right.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-finline-functions-called-once
Consider all static functions called once for inlining into their caller even if
they are not marked inline. If a call to a given function is integrated, then
the function is not output as assembler code in its own right.
Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’ and ‘-Os’.
-fearly-inlining
Inline functions marked by always_inline and functions whose body
seems smaller than the function call overhead early before doing
‘-fprofile-generate’ instrumentation and real inlining pass. Doing so makes
profiling significantly cheaper and usually inlining faster on programs having
large chains of nested wrapper functions.
Enabled by default.
-fipa-sra
Perform interprocedural scalar replacement of aggregates, removal of unused
parameters and replacement of parameters passed by reference by parameters
passed by value.
Enabled at levels ‘-O2’, ‘-O3’ and ‘-Os’.
-finline-limit=n
By default, GCC limits the size of functions that can be inlined. This flag
allows coarse control of this limit. n is the size of functions that can be inlined
in number of pseudo instructions.
Inlining is actually controlled by a number of parameters, which may be specified individually by using ‘--param name=value’. The ‘-finline-limit=n’
option sets some of these parameters as follows:
max-inline-insns-single
is set to n/2.
max-inline-insns-auto
is set to n/2.
See below for a documentation of the individual parameters controlling inlining
and for the defaults of these parameters.

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Note: there may be no value to ‘-finline-limit’ that results in default behavior.
Note: pseudo instruction represents, in this particular context, an abstract
measurement of function’s size. In no way does it represent a count of assembly
instructions and as such its exact meaning might change from one release to an
another.
-fno-keep-inline-dllexport
This is a more fine-grained version of ‘-fkeep-inline-functions’, which applies only to functions that are declared using the dllexport attribute or declspec. See Section 6.31 [Declaring Attributes of Functions], page 464.
-fkeep-inline-functions
In C, emit static functions that are declared inline into the object file, even
if the function has been inlined into all of its callers. This switch does not affect
functions using the extern inline extension in GNU C90. In C++, emit any
and all inline functions into the object file.
-fkeep-static-functions
Emit static functions into the object file, even if the function is never used.
-fkeep-static-consts
Emit variables declared static const when optimization isn’t turned on, even
if the variables aren’t referenced.
GCC enables this option by default. If you want to force the compiler to check
if a variable is referenced, regardless of whether or not optimization is turned
on, use the ‘-fno-keep-static-consts’ option.
-fmerge-constants
Attempt to merge identical constants (string constants and floating-point constants) across compilation units.
This option is the default for optimized compilation if the assembler and linker
support it. Use ‘-fno-merge-constants’ to inhibit this behavior.
Enabled at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.
-fmerge-all-constants
Attempt to merge identical constants and identical variables.
This option implies ‘-fmerge-constants’. In addition to ‘-fmerge-constants’
this considers e.g. even constant initialized arrays or initialized constant variables with integral or floating-point types. Languages like C or C++ require each
variable, including multiple instances of the same variable in recursive calls, to
have distinct locations, so using this option results in non-conforming behavior.
-fmodulo-sched
Perform swing modulo scheduling immediately before the first scheduling pass.
This pass looks at innermost loops and reorders their instructions by overlapping different iterations.
-fmodulo-sched-allow-regmoves
Perform more aggressive SMS-based modulo scheduling with register moves
allowed. By setting this flag certain anti-dependences edges are deleted, which

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triggers the generation of reg-moves based on the life-range analysis. This
option is effective only with ‘-fmodulo-sched’ enabled.
-fno-branch-count-reg
Avoid running a pass scanning for opportunities to use “decrement and branch”
instructions on a count register instead of generating sequences of instructions
that decrement a register, compare it against zero, and then branch based upon
the result. This option is only meaningful on architectures that support such
instructions, which include x86, PowerPC, IA-64 and S/390. Note that the
‘-fno-branch-count-reg’ option doesn’t remove the decrement and branch
instructions from the generated instruction stream introduced by other optimization passes.
Enabled by default at ‘-O1’ and higher.
The default is ‘-fbranch-count-reg’.
-fno-function-cse
Do not put function addresses in registers; make each instruction that calls a
constant function contain the function’s address explicitly.
This option results in less efficient code, but some strange hacks that alter the
assembler output may be confused by the optimizations performed when this
option is not used.
The default is ‘-ffunction-cse’
-fno-zero-initialized-in-bss
If the target supports a BSS section, GCC by default puts variables that are
initialized to zero into BSS. This can save space in the resulting code.
This option turns off this behavior because some programs explicitly rely on
variables going to the data section—e.g., so that the resulting executable can
find the beginning of that section and/or make assumptions based on that.
The default is ‘-fzero-initialized-in-bss’.
-fthread-jumps
Perform optimizations that check to see if a jump branches to a location where
another comparison subsumed by the first is found. If so, the first branch is
redirected to either the destination of the second branch or a point immediately
following it, depending on whether the condition is known to be true or false.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-fsplit-wide-types
When using a type that occupies multiple registers, such as long long on a
32-bit system, split the registers apart and allocate them independently. This
normally generates better code for those types, but may make debugging more
difficult.
Enabled at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.
-fcse-follow-jumps
In common subexpression elimination (CSE), scan through jump instructions
when the target of the jump is not reached by any other path. For example,

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when CSE encounters an if statement with an else clause, CSE follows the
jump when the condition tested is false.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-fcse-skip-blocks
This is similar to ‘-fcse-follow-jumps’, but causes CSE to follow jumps that
conditionally skip over blocks. When CSE encounters a simple if statement
with no else clause, ‘-fcse-skip-blocks’ causes CSE to follow the jump around
the body of the if.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-frerun-cse-after-loop
Re-run common subexpression elimination after loop optimizations are performed.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-fgcse

Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation.
Note: When compiling a program using computed gotos, a GCC extension,
you may get better run-time performance if you disable the global common
subexpression elimination pass by adding ‘-fno-gcse’ to the command line.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

-fgcse-lm
When ‘-fgcse-lm’ is enabled, global common subexpression elimination attempts to move loads that are only killed by stores into themselves. This
allows a loop containing a load/store sequence to be changed to a load outside
the loop, and a copy/store within the loop.
Enabled by default when ‘-fgcse’ is enabled.
-fgcse-sm
When ‘-fgcse-sm’ is enabled, a store motion pass is run after global common
subexpression elimination. This pass attempts to move stores out of loops.
When used in conjunction with ‘-fgcse-lm’, loops containing a load/store sequence can be changed to a load before the loop and a store after the loop.
Not enabled at any optimization level.
-fgcse-las
When ‘-fgcse-las’ is enabled, the global common subexpression elimination
pass eliminates redundant loads that come after stores to the same memory
location (both partial and full redundancies).
Not enabled at any optimization level.
-fgcse-after-reload
When ‘-fgcse-after-reload’ is enabled, a redundant load elimination pass
is performed after reload. The purpose of this pass is to clean up redundant
spilling.
-faggressive-loop-optimizations
This option tells the loop optimizer to use language constraints to derive bounds
for the number of iterations of a loop. This assumes that loop code does not

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invoke undefined behavior by for example causing signed integer overflows or
out-of-bound array accesses. The bounds for the number of iterations of a loop
are used to guide loop unrolling and peeling and loop exit test optimizations.
This option is enabled by default.
-funconstrained-commons
This option tells the compiler that variables declared in common blocks (e.g.
Fortran) may later be overridden with longer trailing arrays. This prevents
certain optimizations that depend on knowing the array bounds.
-fcrossjumping
Perform cross-jumping transformation. This transformation unifies equivalent
code and saves code size. The resulting code may or may not perform better
than without cross-jumping.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-fauto-inc-dec
Combine increments or decrements of addresses with memory accesses. This
pass is always skipped on architectures that do not have instructions to support
this. Enabled by default at ‘-O’ and higher on architectures that support this.
-fdce

Perform dead code elimination (DCE) on RTL. Enabled by default at ‘-O’ and
higher.

-fdse

Perform dead store elimination (DSE) on RTL. Enabled by default at ‘-O’ and
higher.

-fif-conversion
Attempt to transform conditional jumps into branch-less equivalents. This
includes use of conditional moves, min, max, set flags and abs instructions, and
some tricks doable by standard arithmetics. The use of conditional execution
on chips where it is available is controlled by ‘-fif-conversion2’.
Enabled at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.
-fif-conversion2
Use conditional execution (where available) to transform conditional jumps into
branch-less equivalents.
Enabled at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.
-fdeclone-ctor-dtor
The C++ ABI requires multiple entry points for constructors and destructors:
one for a base subobject, one for a complete object, and one for a virtual
destructor that calls operator delete afterwards. For a hierarchy with virtual
bases, the base and complete variants are clones, which means two copies of the
function. With this option, the base and complete variants are changed to be
thunks that call a common implementation.
Enabled by ‘-Os’.
-fdelete-null-pointer-checks
Assume that programs cannot safely dereference null pointers, and that no code
or data element resides at address zero. This option enables simple constant

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folding optimizations at all optimization levels. In addition, other optimization
passes in GCC use this flag to control global dataflow analyses that eliminate
useless checks for null pointers; these assume that a memory access to address
zero always results in a trap, so that if a pointer is checked after it has already
been dereferenced, it cannot be null.
Note however that in some environments this assumption is not true.
Use ‘-fno-delete-null-pointer-checks’ to disable this optimization for
programs that depend on that behavior.
This option is enabled by default on most targets. On Nios II ELF, it defaults
to off. On AVR, CR16, and MSP430, this option is completely disabled.
Passes that use the dataflow information are enabled independently at different
optimization levels.
-fdevirtualize
Attempt to convert calls to virtual functions to direct calls.
This is
done both within a procedure and interprocedurally as part of indirect
inlining (‘-findirect-inlining’) and interprocedural constant propagation
(‘-fipa-cp’). Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-fdevirtualize-speculatively
Attempt to convert calls to virtual functions to speculative direct calls. Based
on the analysis of the type inheritance graph, determine for a given call the
set of likely targets. If the set is small, preferably of size 1, change the call
into a conditional deciding between direct and indirect calls. The speculative
calls enable more optimizations, such as inlining. When they seem useless after
further optimization, they are converted back into original form.
-fdevirtualize-at-ltrans
Stream extra information needed for aggressive devirtualization when running
the link-time optimizer in local transformation mode. This option enables more
devirtualization but significantly increases the size of streamed data. For this
reason it is disabled by default.
-fexpensive-optimizations
Perform a number of minor optimizations that are relatively expensive.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-free

Attempt to remove redundant extension instructions. This is especially helpful
for the x86-64 architecture, which implicitly zero-extends in 64-bit registers
after writing to their lower 32-bit half.
Enabled for Alpha, AArch64 and x86 at levels ‘-O2’, ‘-O3’, ‘-Os’.

-fno-lifetime-dse
In C++ the value of an object is only affected by changes within its lifetime:
when the constructor begins, the object has an indeterminate value, and any
changes during the lifetime of the object are dead when the object is destroyed. Normally dead store elimination will take advantage of this; if your
code relies on the value of the object storage persisting beyond the lifetime
of the object, you can use this flag to disable this optimization. To preserve stores before the constructor starts (e.g. because your operator new

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clears the object storage) but still treat the object as dead after the destructor you, can use ‘-flifetime-dse=1’. The default behavior can be explicitly selected with ‘-flifetime-dse=2’. ‘-flifetime-dse=0’ is equivalent to
‘-fno-lifetime-dse’.
-flive-range-shrinkage
Attempt to decrease register pressure through register live range shrinkage.
This is helpful for fast processors with small or moderate size register sets.
-fira-algorithm=algorithm
Use the specified coloring algorithm for the integrated register allocator. The
algorithm argument can be ‘priority’, which specifies Chow’s priority coloring,
or ‘CB’, which specifies Chaitin-Briggs coloring. Chaitin-Briggs coloring is not
implemented for all architectures, but for those targets that do support it, it is
the default because it generates better code.
-fira-region=region
Use specified regions for the integrated register allocator. The region argument
should be one of the following:
‘all’

Use all loops as register allocation regions. This can give the best
results for machines with a small and/or irregular register set.

‘mixed’

Use all loops except for loops with small register pressure as the
regions. This value usually gives the best results in most cases and
for most architectures, and is enabled by default when compiling
with optimization for speed (‘-O’, ‘-O2’, . . . ).

‘one’

Use all functions as a single region. This typically results in the
smallest code size, and is enabled by default for ‘-Os’ or ‘-O0’.

-fira-hoist-pressure
Use IRA to evaluate register pressure in the code hoisting pass for decisions to
hoist expressions. This option usually results in smaller code, but it can slow
the compiler down.
This option is enabled at level ‘-Os’ for all targets.
-fira-loop-pressure
Use IRA to evaluate register pressure in loops for decisions to move loop invariants. This option usually results in generation of faster and smaller code on
machines with large register files (>= 32 registers), but it can slow the compiler
down.
This option is enabled at level ‘-O3’ for some targets.
-fno-ira-share-save-slots
Disable sharing of stack slots used for saving call-used hard registers living
through a call. Each hard register gets a separate stack slot, and as a result
function stack frames are larger.
-fno-ira-share-spill-slots
Disable sharing of stack slots allocated for pseudo-registers. Each pseudoregister that does not get a hard register gets a separate stack slot, and as
a result function stack frames are larger.

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-flra-remat
Enable CFG-sensitive rematerialization in LRA. Instead of loading values of
spilled pseudos, LRA tries to rematerialize (recalculate) values if it is profitable.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-fdelayed-branch
If supported for the target machine, attempt to reorder instructions to exploit
instruction slots available after delayed branch instructions.
Enabled at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.
-fschedule-insns
If supported for the target machine, attempt to reorder instructions to eliminate
execution stalls due to required data being unavailable. This helps machines
that have slow floating point or memory load instructions by allowing other
instructions to be issued until the result of the load or floating-point instruction
is required.
Enabled at levels ‘-O2’, ‘-O3’.
-fschedule-insns2
Similar to ‘-fschedule-insns’, but requests an additional pass of instruction
scheduling after register allocation has been done. This is especially useful on
machines with a relatively small number of registers and where memory load
instructions take more than one cycle.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-fno-sched-interblock
Don’t schedule instructions across basic blocks. This is normally enabled by
default when scheduling before register allocation, i.e. with ‘-fschedule-insns’
or at ‘-O2’ or higher.
-fno-sched-spec
Don’t allow speculative motion of non-load instructions. This is normally
enabled by default when scheduling before register allocation, i.e. with
‘-fschedule-insns’ or at ‘-O2’ or higher.
-fsched-pressure
Enable register pressure sensitive insn scheduling before register allocation.
This only makes sense when scheduling before register allocation is enabled,
i.e. with ‘-fschedule-insns’ or at ‘-O2’ or higher. Usage of this option can
improve the generated code and decrease its size by preventing register pressure
increase above the number of available hard registers and subsequent spills in
register allocation.
-fsched-spec-load
Allow speculative motion of some load instructions. This only makes sense
when scheduling before register allocation, i.e. with ‘-fschedule-insns’ or at
‘-O2’ or higher.

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-fsched-spec-load-dangerous
Allow speculative motion of more load instructions. This only makes sense
when scheduling before register allocation, i.e. with ‘-fschedule-insns’ or at
‘-O2’ or higher.
-fsched-stalled-insns
-fsched-stalled-insns=n
Define how many insns (if any) can be moved prematurely from the queue
of stalled insns into the ready list during the second scheduling pass.
‘-fno-sched-stalled-insns’ means that no insns are moved prematurely,
‘-fsched-stalled-insns=0’ means there is no limit on how many queued
insns can be moved prematurely. ‘-fsched-stalled-insns’ without a value
is equivalent to ‘-fsched-stalled-insns=1’.
-fsched-stalled-insns-dep
-fsched-stalled-insns-dep=n
Define how many insn groups (cycles) are examined for a dependency on a stalled insn that is a candidate for premature removal
from the queue of stalled insns.
This has an effect only during
the second scheduling pass, and only if ‘-fsched-stalled-insns’
is
used.
‘-fno-sched-stalled-insns-dep’
is
equivalent
to
‘-fsched-stalled-insns-dep=0’.
‘-fsched-stalled-insns-dep’
without a value is equivalent to ‘-fsched-stalled-insns-dep=1’.
-fsched2-use-superblocks
When scheduling after register allocation, use superblock scheduling. This allows motion across basic block boundaries, resulting in faster schedules. This
option is experimental, as not all machine descriptions used by GCC model the
CPU closely enough to avoid unreliable results from the algorithm.
This only makes sense when scheduling after register allocation, i.e. with
‘-fschedule-insns2’ or at ‘-O2’ or higher.
-fsched-group-heuristic
Enable the group heuristic in the scheduler. This heuristic favors the instruction
that belongs to a schedule group. This is enabled by default when scheduling
is enabled, i.e. with ‘-fschedule-insns’ or ‘-fschedule-insns2’ or at ‘-O2’
or higher.
-fsched-critical-path-heuristic
Enable the critical-path heuristic in the scheduler. This heuristic favors instructions on the critical path. This is enabled by default when scheduling is
enabled, i.e. with ‘-fschedule-insns’ or ‘-fschedule-insns2’ or at ‘-O2’ or
higher.
-fsched-spec-insn-heuristic
Enable the speculative instruction heuristic in the scheduler. This heuristic
favors speculative instructions with greater dependency weakness. This is enabled by default when scheduling is enabled, i.e. with ‘-fschedule-insns’ or
‘-fschedule-insns2’ or at ‘-O2’ or higher.

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-fsched-rank-heuristic
Enable the rank heuristic in the scheduler. This heuristic favors the instruction belonging to a basic block with greater size or frequency. This is enabled by default when scheduling is enabled, i.e. with ‘-fschedule-insns’ or
‘-fschedule-insns2’ or at ‘-O2’ or higher.
-fsched-last-insn-heuristic
Enable the last-instruction heuristic in the scheduler. This heuristic favors the
instruction that is less dependent on the last instruction scheduled. This is
enabled by default when scheduling is enabled, i.e. with ‘-fschedule-insns’
or ‘-fschedule-insns2’ or at ‘-O2’ or higher.
-fsched-dep-count-heuristic
Enable the dependent-count heuristic in the scheduler. This heuristic favors
the instruction that has more instructions depending on it. This is enabled
by default when scheduling is enabled, i.e. with ‘-fschedule-insns’ or
‘-fschedule-insns2’ or at ‘-O2’ or higher.
-freschedule-modulo-scheduled-loops
Modulo scheduling is performed before traditional scheduling. If a loop is modulo scheduled, later scheduling passes may change its schedule. Use this option
to control that behavior.
-fselective-scheduling
Schedule instructions using selective scheduling algorithm. Selective scheduling
runs instead of the first scheduler pass.
-fselective-scheduling2
Schedule instructions using selective scheduling algorithm. Selective scheduling
runs instead of the second scheduler pass.
-fsel-sched-pipelining
Enable software pipelining of innermost loops during selective scheduling.
This option has no effect unless one of ‘-fselective-scheduling’ or
‘-fselective-scheduling2’ is turned on.
-fsel-sched-pipelining-outer-loops
When pipelining loops during selective scheduling, also pipeline outer loops.
This option has no effect unless ‘-fsel-sched-pipelining’ is turned on.
-fsemantic-interposition
Some object formats, like ELF, allow interposing of symbols by the dynamic
linker. This means that for symbols exported from the DSO, the compiler cannot perform interprocedural propagation, inlining and other optimizations in
anticipation that the function or variable in question may change. While this
feature is useful, for example, to rewrite memory allocation functions by a debugging implementation, it is expensive in the terms of code quality. With
‘-fno-semantic-interposition’ the compiler assumes that if interposition
happens for functions the overwriting function will have precisely the same
semantics (and side effects). Similarly if interposition happens for variables,
the constructor of the variable will be the same. The flag has no effect for

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functions explicitly declared inline (where it is never allowed for interposition
to change semantics) and for symbols explicitly declared weak.
-fshrink-wrap
Emit function prologues only before parts of the function that need it, rather
than at the top of the function. This flag is enabled by default at ‘-O’ and
higher.
-fshrink-wrap-separate
Shrink-wrap separate parts of the prologue and epilogue separately, so that
those parts are only executed when needed. This option is on by default, but
has no effect unless ‘-fshrink-wrap’ is also turned on and the target supports
this.
-fcaller-saves
Enable allocation of values to registers that are clobbered by function calls, by
emitting extra instructions to save and restore the registers around such calls.
Such allocation is done only when it seems to result in better code.
This option is always enabled by default on certain machines, usually those
which have no call-preserved registers to use instead.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-fcombine-stack-adjustments
Tracks stack adjustments (pushes and pops) and stack memory references and
then tries to find ways to combine them.
Enabled by default at ‘-O1’ and higher.
-fipa-ra

Use caller save registers for allocation if those registers are not used by any called
function. In that case it is not necessary to save and restore them around calls.
This is only possible if called functions are part of same compilation unit as
current function and they are compiled before it.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’, however the option is disabled if generated
code will be instrumented for profiling (‘-p’, or ‘-pg’) or if callee’s register usage
cannot be known exactly (this happens on targets that do not expose prologues
and epilogues in RTL).

-fconserve-stack
Attempt to minimize stack usage. The compiler attempts to use less stack
space, even if that makes the program slower. This option implies setting the
‘large-stack-frame’ parameter to 100 and the ‘large-stack-frame-growth’
parameter to 400.
-ftree-reassoc
Perform reassociation on trees. This flag is enabled by default at ‘-O’ and
higher.
-fcode-hoisting
Perform code hoisting. Code hoisting tries to move the evaluation of expressions
executed on all paths to the function exit as early as possible. This is especially
useful as a code size optimization, but it often helps for code speed as well.
This flag is enabled by default at ‘-O2’ and higher.

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-ftree-pre
Perform partial redundancy elimination (PRE) on trees. This flag is enabled
by default at ‘-O2’ and ‘-O3’.
-ftree-partial-pre
Make partial redundancy elimination (PRE) more aggressive. This flag is enabled by default at ‘-O3’.
-ftree-forwprop
Perform forward propagation on trees. This flag is enabled by default at ‘-O’
and higher.
-ftree-fre
Perform full redundancy elimination (FRE) on trees. The difference between
FRE and PRE is that FRE only considers expressions that are computed on
all paths leading to the redundant computation. This analysis is faster than
PRE, though it exposes fewer redundancies. This flag is enabled by default at
‘-O’ and higher.
-ftree-phiprop
Perform hoisting of loads from conditional pointers on trees. This pass is enabled by default at ‘-O’ and higher.
-fhoist-adjacent-loads
Speculatively hoist loads from both branches of an if-then-else if the loads are
from adjacent locations in the same structure and the target architecture has
a conditional move instruction. This flag is enabled by default at ‘-O2’ and
higher.
-ftree-copy-prop
Perform copy propagation on trees. This pass eliminates unnecessary copy
operations. This flag is enabled by default at ‘-O’ and higher.
-fipa-pure-const
Discover which functions are pure or constant. Enabled by default at ‘-O’ and
higher.
-fipa-reference
Discover which static variables do not escape the compilation unit. Enabled by
default at ‘-O’ and higher.
-fipa-pta
Perform interprocedural pointer analysis and interprocedural modification and
reference analysis. This option can cause excessive memory and compile-time
usage on large compilation units. It is not enabled by default at any optimization level.
-fipa-profile
Perform interprocedural profile propagation. The functions called only from
cold functions are marked as cold. Also functions executed once (such as cold,
noreturn, static constructors or destructors) are identified. Cold functions and
loop less parts of functions executed once are then optimized for size. Enabled
by default at ‘-O’ and higher.

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-fipa-cp

131

Perform interprocedural constant propagation. This optimization analyzes the
program to determine when values passed to functions are constants and then
optimizes accordingly. This optimization can substantially increase performance if the application has constants passed to functions. This flag is enabled
by default at ‘-O2’, ‘-Os’ and ‘-O3’.

-fipa-cp-clone
Perform function cloning to make interprocedural constant propagation
stronger. When enabled, interprocedural constant propagation performs
function cloning when externally visible function can be called with constant
arguments. Because this optimization can create multiple copies of functions, it
may significantly increase code size (see ‘--param ipcp-unit-growth=value’).
This flag is enabled by default at ‘-O3’.
-fipa-bit-cp
When enabled, perform interprocedural bitwise constant propagation. This flag
is enabled by default at ‘-O2’. It requires that ‘-fipa-cp’ is enabled.
-fipa-vrp
When enabled, perform interprocedural propagation of value ranges. This flag
is enabled by default at ‘-O2’. It requires that ‘-fipa-cp’ is enabled.
-fipa-icf
Perform Identical Code Folding for functions and read-only variables. The
optimization reduces code size and may disturb unwind stacks by replacing a
function by equivalent one with a different name. The optimization works more
effectively with link-time optimization enabled.
Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF
works on different levels and thus the optimizations are not same - there are
equivalences that are found only by GCC and equivalences found only by Gold.
This flag is enabled by default at ‘-O2’ and ‘-Os’.
-fisolate-erroneous-paths-dereference
Detect paths that trigger erroneous or undefined behavior due to dereferencing
a null pointer. Isolate those paths from the main control flow and turn the statement with erroneous or undefined behavior into a trap. This flag is enabled by
default at ‘-O2’ and higher and depends on ‘-fdelete-null-pointer-checks’
also being enabled.
-fisolate-erroneous-paths-attribute
Detect paths that trigger erroneous or undefined behavior due to a null value
being used in a way forbidden by a returns_nonnull or nonnull attribute.
Isolate those paths from the main control flow and turn the statement with
erroneous or undefined behavior into a trap. This is not currently enabled, but
may be enabled by ‘-O2’ in the future.
-ftree-sink
Perform forward store motion on trees. This flag is enabled by default at ‘-O’
and higher.

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-ftree-bit-ccp
Perform sparse conditional bit constant propagation on trees and propagate
pointer alignment information. This pass only operates on local scalar variables
and is enabled by default at ‘-O’ and higher. It requires that ‘-ftree-ccp’ is
enabled.
-ftree-ccp
Perform sparse conditional constant propagation (CCP) on trees. This pass
only operates on local scalar variables and is enabled by default at ‘-O’ and
higher.
-fssa-backprop
Propagate information about uses of a value up the definition chain in order to
simplify the definitions. For example, this pass strips sign operations if the sign
of a value never matters. The flag is enabled by default at ‘-O’ and higher.
-fssa-phiopt
Perform pattern matching on SSA PHI nodes to optimize conditional code.
This pass is enabled by default at ‘-O’ and higher.
-ftree-switch-conversion
Perform conversion of simple initializations in a switch to initializations from a
scalar array. This flag is enabled by default at ‘-O2’ and higher.
-ftree-tail-merge
Look for identical code sequences. When found, replace one with a jump
to the other. This optimization is known as tail merging or cross jumping.
This flag is enabled by default at ‘-O2’ and higher. The compilation time in
this pass can be limited using ‘max-tail-merge-comparisons’ parameter and
‘max-tail-merge-iterations’ parameter.
-ftree-dce
Perform dead code elimination (DCE) on trees. This flag is enabled by default
at ‘-O’ and higher.
-ftree-builtin-call-dce
Perform conditional dead code elimination (DCE) for calls to built-in functions
that may set errno but are otherwise free of side effects. This flag is enabled
by default at ‘-O2’ and higher if ‘-Os’ is not also specified.
-ftree-dominator-opts
Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy elimination, range propagation and expression simplification) based on a
dominator tree traversal. This also performs jump threading (to reduce jumps
to jumps). This flag is enabled by default at ‘-O’ and higher.
-ftree-dse
Perform dead store elimination (DSE) on trees. A dead store is a store into a
memory location that is later overwritten by another store without any intervening loads. In this case the earlier store can be deleted. This flag is enabled
by default at ‘-O’ and higher.

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-ftree-ch
Perform loop header copying on trees. This is beneficial since it increases effectiveness of code motion optimizations. It also saves one jump. This flag is
enabled by default at ‘-O’ and higher. It is not enabled for ‘-Os’, since it usually
increases code size.
-ftree-loop-optimize
Perform loop optimizations on trees. This flag is enabled by default at ‘-O’ and
higher.
-ftree-loop-linear
-floop-strip-mine
-floop-block
Perform loop nest optimizations. Same as ‘-floop-nest-optimize’. To use
this code transformation, GCC has to be configured with ‘--with-isl’ to enable the Graphite loop transformation infrastructure.
-fgraphite-identity
Enable the identity transformation for graphite. For every SCoP we generate the polyhedral representation and transform it back to gimple. Using
‘-fgraphite-identity’ we can check the costs or benefits of the GIMPLE
-> GRAPHITE -> GIMPLE transformation. Some minimal optimizations are
also performed by the code generator isl, like index splitting and dead code
elimination in loops.
-floop-nest-optimize
Enable the isl based loop nest optimizer. This is a generic loop nest optimizer
based on the Pluto optimization algorithms. It calculates a loop structure
optimized for data-locality and parallelism. This option is experimental.
-floop-parallelize-all
Use the Graphite data dependence analysis to identify loops that can be parallelized. Parallelize all the loops that can be analyzed to not contain loop carried
dependences without checking that it is profitable to parallelize the loops.
-ftree-coalesce-vars
While transforming the program out of the SSA representation, attempt to
reduce copying by coalescing versions of different user-defined variables, instead
of just compiler temporaries. This may severely limit the ability to debug an
optimized program compiled with ‘-fno-var-tracking-assignments’. In the
negated form, this flag prevents SSA coalescing of user variables. This option is
enabled by default if optimization is enabled, and it does very little otherwise.
-ftree-loop-if-convert
Attempt to transform conditional jumps in the innermost loops to branch-less
equivalents. The intent is to remove control-flow from the innermost loops in
order to improve the ability of the vectorization pass to handle these loops.
This is enabled by default if vectorization is enabled.

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Using the GNU Compiler Collection (GCC)

-ftree-loop-distribution
Perform loop distribution. This flag can improve cache performance on big loop
bodies and allow further loop optimizations, like parallelization or vectorization,
to take place. For example, the loop
DO I = 1, N
A(I) = B(I) + C
D(I) = E(I) * F
ENDDO

is transformed to
DO I = 1,
A(I) =
ENDDO
DO I = 1,
D(I) =
ENDDO

N
B(I) + C
N
E(I) * F

-ftree-loop-distribute-patterns
Perform loop distribution of patterns that can be code generated with calls to
a library. This flag is enabled by default at ‘-O3’.
This pass distributes the initialization loops and generates a call to memset
zero. For example, the loop
DO I = 1, N
A(I) = 0
B(I) = A(I) + I
ENDDO

is transformed to
DO I = 1,
A(I) =
ENDDO
DO I = 1,
B(I) =
ENDDO

N
0
N
A(I) + I

and the initialization loop is transformed into a call to memset zero.
-floop-interchange
Perform loop interchange outside of graphite. This flag can improve cache performance on loop nest and allow further loop optimizations, like vectorization,
to take place. For example, the loop
for (int i = 0; i < N; i++)
for (int j = 0; j < N; j++)
for (int k = 0; k < N; k++)
c[i][j] = c[i][j] + a[i][k]*b[k][j];

is transformed to
for (int i = 0; i < N; i++)
for (int k = 0; k < N; k++)
for (int j = 0; j < N; j++)
c[i][j] = c[i][j] + a[i][k]*b[k][j];

This flag is enabled by default at ‘-O3’.
-floop-unroll-and-jam
Apply unroll and jam transformations on feasible loops. In a loop nest this
unrolls the outer loop by some factor and fuses the resulting multiple inner
loops. This flag is enabled by default at ‘-O3’.

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-ftree-loop-im
Perform loop invariant motion on trees. This pass moves only invariants that
are hard to handle at RTL level (function calls, operations that expand to nontrivial sequences of insns). With ‘-funswitch-loops’ it also moves operands
of conditions that are invariant out of the loop, so that we can use just trivial
invariantness analysis in loop unswitching. The pass also includes store motion.
-ftree-loop-ivcanon
Create a canonical counter for number of iterations in loops for which determining number of iterations requires complicated analysis. Later optimizations
then may determine the number easily. Useful especially in connection with
unrolling.
-fivopts

Perform induction variable optimizations (strength reduction, induction variable merging and induction variable elimination) on trees.

-ftree-parallelize-loops=n
Parallelize loops, i.e., split their iteration space to run in n threads. This is
only possible for loops whose iterations are independent and can be arbitrarily
reordered. The optimization is only profitable on multiprocessor machines, for
loops that are CPU-intensive, rather than constrained e.g. by memory bandwidth. This option implies ‘-pthread’, and thus is only supported on targets
that have support for ‘-pthread’.
-ftree-pta
Perform function-local points-to analysis on trees. This flag is enabled by default at ‘-O’ and higher.
-ftree-sra
Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early. This
flag is enabled by default at ‘-O’ and higher.
-fstore-merging
Perform merging of narrow stores to consecutive memory addresses. This pass
merges contiguous stores of immediate values narrower than a word into fewer
wider stores to reduce the number of instructions. This is enabled by default
at ‘-O2’ and higher as well as ‘-Os’.
-ftree-ter
Perform temporary expression replacement during the SSA->normal phase. Single use/single def temporaries are replaced at their use location with their defining expression. This results in non-GIMPLE code, but gives the expanders
much more complex trees to work on resulting in better RTL generation. This
is enabled by default at ‘-O’ and higher.
-ftree-slsr
Perform straight-line strength reduction on trees. This recognizes related expressions involving multiplications and replaces them by less expensive calculations when possible. This is enabled by default at ‘-O’ and higher.

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Using the GNU Compiler Collection (GCC)

-ftree-vectorize
Perform vectorization on trees. This flag enables ‘-ftree-loop-vectorize’
and ‘-ftree-slp-vectorize’ if not explicitly specified.
-ftree-loop-vectorize
Perform loop vectorization on trees. This flag is enabled by default at ‘-O3’
and when ‘-ftree-vectorize’ is enabled.
-ftree-slp-vectorize
Perform basic block vectorization on trees. This flag is enabled by default at
‘-O3’ and when ‘-ftree-vectorize’ is enabled.
-fvect-cost-model=model
Alter the cost model used for vectorization. The model argument should be
one of ‘unlimited’, ‘dynamic’ or ‘cheap’. With the ‘unlimited’ model the
vectorized code-path is assumed to be profitable while with the ‘dynamic’ model
a runtime check guards the vectorized code-path to enable it only for iteration
counts that will likely execute faster than when executing the original scalar
loop. The ‘cheap’ model disables vectorization of loops where doing so would be
cost prohibitive for example due to required runtime checks for data dependence
or alignment but otherwise is equal to the ‘dynamic’ model. The default cost
model depends on other optimization flags and is either ‘dynamic’ or ‘cheap’.
-fsimd-cost-model=model
Alter the cost model used for vectorization of loops marked with the
OpenMP simd directive. The model argument should be one of ‘unlimited’,
‘dynamic’, ‘cheap’.
All values of model have the same meaning as
described in ‘-fvect-cost-model’ and by default a cost model defined with
‘-fvect-cost-model’ is used.
-ftree-vrp
Perform Value Range Propagation on trees. This is similar to the constant propagation pass, but instead of values, ranges of values are propagated. This allows
the optimizers to remove unnecessary range checks like array bound checks and
null pointer checks. This is enabled by default at ‘-O2’ and higher. Null pointer
check elimination is only done if ‘-fdelete-null-pointer-checks’ is enabled.
-fsplit-paths
Split paths leading to loop backedges. This can improve dead code elimination
and common subexpression elimination. This is enabled by default at ‘-O2’ and
above.
-fsplit-ivs-in-unroller
Enables expression of values of induction variables in later iterations of the
unrolled loop using the value in the first iteration. This breaks long dependency
chains, thus improving efficiency of the scheduling passes.
A combination of ‘-fweb’ and CSE is often sufficient to obtain the same effect.
However, that is not reliable in cases where the loop body is more complicated
than a single basic block. It also does not work at all on some architectures
due to restrictions in the CSE pass.
This optimization is enabled by default.

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-fvariable-expansion-in-unroller
With this option, the compiler creates multiple copies of some local variables
when unrolling a loop, which can result in superior code.
-fpartial-inlining
Inline parts of functions. This option has any effect only when inlining itself
is turned on by the ‘-finline-functions’ or ‘-finline-small-functions’
options.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-fpredictive-commoning
Perform predictive commoning optimization, i.e., reusing computations (especially memory loads and stores) performed in previous iterations of loops.
This option is enabled at level ‘-O3’.
-fprefetch-loop-arrays
If supported by the target machine, generate instructions to prefetch memory
to improve the performance of loops that access large arrays.
This option may generate better or worse code; results are highly dependent on
the structure of loops within the source code.
Disabled at level ‘-Os’.
-fno-printf-return-value
Do not substitute constants for known return value of formatted output functions such as sprintf, snprintf, vsprintf, and vsnprintf (but not printf
of fprintf). This transformation allows GCC to optimize or even eliminate
branches based on the known return value of these functions called with arguments that are either constant, or whose values are known to be in a range
that makes determining the exact return value possible. For example, when
‘-fprintf-return-value’ is in effect, both the branch and the body of the if
statement (but not the call to snprint) can be optimized away when i is a
32-bit or smaller integer because the return value is guaranteed to be at most
8.
char buf[9];
if (snprintf (buf, "%08x", i) >= sizeof buf)
...

The ‘-fprintf-return-value’ option relies on other optimizations and
yields best results with ‘-O2’ and above.
It works in tandem with
the ‘-Wformat-overflow’ and ‘-Wformat-truncation’ options.
The
‘-fprintf-return-value’ option is enabled by default.
-fno-peephole
-fno-peephole2
Disable any machine-specific peephole optimizations. The difference between
‘-fno-peephole’ and ‘-fno-peephole2’ is in how they are implemented in the
compiler; some targets use one, some use the other, a few use both.
‘-fpeephole’ is enabled by default. ‘-fpeephole2’ enabled at levels ‘-O2’,
‘-O3’, ‘-Os’.

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-fno-guess-branch-probability
Do not guess branch probabilities using heuristics.
GCC uses heuristics to guess branch probabilities if they are not provided
by profiling feedback (‘-fprofile-arcs’). These heuristics are based on the
control flow graph. If some branch probabilities are specified by __builtin_
expect, then the heuristics are used to guess branch probabilities for the rest
of the control flow graph, taking the __builtin_expect info into account. The
interactions between the heuristics and __builtin_expect can be complex,
and in some cases, it may be useful to disable the heuristics so that the effects
of __builtin_expect are easier to understand.
The default is ‘-fguess-branch-probability’ at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.
-freorder-blocks
Reorder basic blocks in the compiled function in order to reduce number of
taken branches and improve code locality.
Enabled at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.
-freorder-blocks-algorithm=algorithm
Use the specified algorithm for basic block reordering. The algorithm argument
can be ‘simple’, which does not increase code size (except sometimes due to
secondary effects like alignment), or ‘stc’, the “software trace cache” algorithm,
which tries to put all often executed code together, minimizing the number of
branches executed by making extra copies of code.
The default is ‘simple’ at levels ‘-O’, ‘-Os’, and ‘stc’ at levels ‘-O2’, ‘-O3’.
-freorder-blocks-and-partition
In addition to reordering basic blocks in the compiled function, in order to
reduce number of taken branches, partitions hot and cold basic blocks into
separate sections of the assembly and ‘.o’ files, to improve paging and cache
locality performance.
This optimization is automatically turned off in the presence of exception handling or unwind tables (on targets using setjump/longjump or target specific
scheme), for linkonce sections, for functions with a user-defined section attribute and on any architecture that does not support named sections. When
‘-fsplit-stack’ is used this option is not enabled by default (to avoid linker
errors), but may be enabled explicitly (if using a working linker).
Enabled for x86 at levels ‘-O2’, ‘-O3’, ‘-Os’.
-freorder-functions
Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections .text.hot for most frequently executed
functions and .text.unlikely for unlikely executed functions. Reordering is
done by the linker so object file format must support named sections and linker
must place them in a reasonable way.
Also profile feedback must be available to make this option effective. See
‘-fprofile-arcs’ for details.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

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-fstrict-aliasing
Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and C++), this activates optimizations based on
the type of expressions. In particular, an object of one type is assumed never
to reside at the same address as an object of a different type, unless the types
are almost the same. For example, an unsigned int can alias an int, but not
a void* or a double. A character type may alias any other type.
Pay special attention to code like this:
union a_union {
int i;
double d;
};
int f() {
union a_union t;
t.d = 3.0;
return t.i;
}

The practice of reading from a different union member than the one
most recently written to (called “type-punning”) is common. Even with
‘-fstrict-aliasing’, type-punning is allowed, provided the memory is
accessed through the union type. So, the code above works as expected. See
Section 4.9 [Structures unions enumerations and bit-fields implementation],
page 433. However, this code might not:
int f() {
union a_union t;
int* ip;
t.d = 3.0;
ip = &t.i;
return *ip;
}

Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior, even if the cast uses a union type,
e.g.:
int f() {
double d = 3.0;
return ((union a_union *) &d)->i;
}

The ‘-fstrict-aliasing’ option is enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-falign-functions
-falign-functions=n
Align the start of functions to the next power-of-two greater than n, skipping
up to n bytes. For instance, ‘-falign-functions=32’ aligns functions to the
next 32-byte boundary, but ‘-falign-functions=24’ aligns to the next 32-byte
boundary only if this can be done by skipping 23 bytes or less.
‘-fno-align-functions’ and ‘-falign-functions=1’ are equivalent and mean
that functions are not aligned.
Some assemblers only support this flag when n is a power of two; in that case,
it is rounded up.

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If n is not specified or is zero, use a machine-dependent default. The maximum
allowed n option value is 65536.
Enabled at levels ‘-O2’, ‘-O3’.
-flimit-function-alignment
If this option is enabled, the compiler tries to avoid unnecessarily overaligning
functions. It attempts to instruct the assembler to align by the amount specified by ‘-falign-functions’, but not to skip more bytes than the size of the
function.
-falign-labels
-falign-labels=n
Align all branch targets to a power-of-two boundary, skipping up to n bytes
like ‘-falign-functions’. This option can easily make code slower, because
it must insert dummy operations for when the branch target is reached in the
usual flow of the code.
‘-fno-align-labels’ and ‘-falign-labels=1’ are equivalent and mean that
labels are not aligned.
If ‘-falign-loops’ or ‘-falign-jumps’ are applicable and are greater than this
value, then their values are used instead.
If n is not specified or is zero, use a machine-dependent default which is very
likely to be ‘1’, meaning no alignment. The maximum allowed n option value
is 65536.
Enabled at levels ‘-O2’, ‘-O3’.
-falign-loops
-falign-loops=n
Align loops to a power-of-two boundary, skipping up to n bytes like
‘-falign-functions’. If the loops are executed many times, this makes up
for any execution of the dummy operations.
‘-fno-align-loops’ and ‘-falign-loops=1’ are equivalent and mean that
loops are not aligned. The maximum allowed n option value is 65536.
If n is not specified or is zero, use a machine-dependent default.
Enabled at levels ‘-O2’, ‘-O3’.
-falign-jumps
-falign-jumps=n
Align branch targets to a power-of-two boundary, for branch targets where
the targets can only be reached by jumping, skipping up to n bytes like
‘-falign-functions’. In this case, no dummy operations need be executed.
‘-fno-align-jumps’ and ‘-falign-jumps=1’ are equivalent and mean that
loops are not aligned.
If n is not specified or is zero, use a machine-dependent default. The maximum
allowed n option value is 65536.
Enabled at levels ‘-O2’, ‘-O3’.

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-funit-at-a-time
This option is left for compatibility reasons. ‘-funit-at-a-time’ has no
effect, while ‘-fno-unit-at-a-time’ implies ‘-fno-toplevel-reorder’ and
‘-fno-section-anchors’.
Enabled by default.
-fno-toplevel-reorder
Do not reorder top-level functions, variables, and asm statements. Output them
in the same order that they appear in the input file. When this option is
used, unreferenced static variables are not removed. This option is intended to
support existing code that relies on a particular ordering. For new code, it is
better to use attributes when possible.
Enabled at level ‘-O0’.
When disabled explicitly, it also implies
‘-fno-section-anchors’, which is otherwise enabled at ‘-O0’ on some targets.
-fweb

Constructs webs as commonly used for register allocation purposes and assign
each web individual pseudo register. This allows the register allocation pass
to operate on pseudos directly, but also strengthens several other optimization
passes, such as CSE, loop optimizer and trivial dead code remover. It can,
however, make debugging impossible, since variables no longer stay in a “home
register”.
Enabled by default with ‘-funroll-loops’.

-fwhole-program
Assume that the current compilation unit represents the whole program being
compiled. All public functions and variables with the exception of main and
those merged by attribute externally_visible become static functions and
in effect are optimized more aggressively by interprocedural optimizers.
This option should not be used in combination with ‘-flto’. Instead relying
on a linker plugin should provide safer and more precise information.
-flto[=n]
This option runs the standard link-time optimizer. When invoked with source
code, it generates GIMPLE (one of GCC’s internal representations) and writes
it to special ELF sections in the object file. When the object files are linked
together, all the function bodies are read from these ELF sections and instantiated as if they had been part of the same translation unit.
To use the link-time optimizer, ‘-flto’ and optimization options should be
specified at compile time and during the final link. It is recommended that you
compile all the files participating in the same link with the same options and
also specify those options at link time. For example:
gcc -c -O2 -flto foo.c
gcc -c -O2 -flto bar.c
gcc -o myprog -flto -O2 foo.o bar.o

The first two invocations to GCC save a bytecode representation of GIMPLE
into special ELF sections inside ‘foo.o’ and ‘bar.o’. The final invocation reads
the GIMPLE bytecode from ‘foo.o’ and ‘bar.o’, merges the two files into a
single internal image, and compiles the result as usual. Since both ‘foo.o’

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and ‘bar.o’ are merged into a single image, this causes all the interprocedural
analyses and optimizations in GCC to work across the two files as if they were a
single one. This means, for example, that the inliner is able to inline functions
in ‘bar.o’ into functions in ‘foo.o’ and vice-versa.
Another (simpler) way to enable link-time optimization is:
gcc -o myprog -flto -O2 foo.c bar.c

The above generates bytecode for ‘foo.c’ and ‘bar.c’, merges them together
into a single GIMPLE representation and optimizes them as usual to produce
‘myprog’.
The only important thing to keep in mind is that to enable link-time optimizations you need to use the GCC driver to perform the link step. GCC then
automatically performs link-time optimization if any of the objects involved
were compiled with the ‘-flto’ command-line option. You generally should
specify the optimization options to be used for link-time optimization though
GCC tries to be clever at guessing an optimization level to use from the options
used at compile time if you fail to specify one at link time. You can always override the automatic decision to do link-time optimization by passing ‘-fno-lto’
to the link command.
To make whole program optimization effective, it is necessary to make
certain whole program assumptions. The compiler needs to know what
functions and variables can be accessed by libraries and runtime outside
of the link-time optimized unit. When supported by the linker, the linker
plugin (see ‘-fuse-linker-plugin’) passes information to the compiler about
used and externally visible symbols. When the linker plugin is not available,
‘-fwhole-program’ should be used to allow the compiler to make these
assumptions, which leads to more aggressive optimization decisions.
When ‘-fuse-linker-plugin’ is not enabled, when a file is compiled
with ‘-flto’, the generated object file is larger than a regular object
file because it contains GIMPLE bytecodes and the usual final code (see
‘-ffat-lto-objects’. This means that object files with LTO information
can be linked as normal object files; if ‘-fno-lto’ is passed to the
linker, no interprocedural optimizations are applied.
Note that when
‘-fno-fat-lto-objects’ is enabled the compile stage is faster but you cannot
perform a regular, non-LTO link on them.
Additionally, the optimization flags used to compile individual files are not
necessarily related to those used at link time. For instance,
gcc -c -O0 -ffat-lto-objects -flto foo.c
gcc -c -O0 -ffat-lto-objects -flto bar.c
gcc -o myprog -O3 foo.o bar.o

This produces individual object files with unoptimized assembler code, but the
resulting binary ‘myprog’ is optimized at ‘-O3’. If, instead, the final binary is
generated with ‘-fno-lto’, then ‘myprog’ is not optimized.
When producing the final binary, GCC only applies link-time optimizations to
those files that contain bytecode. Therefore, you can mix and match object
files and libraries with GIMPLE bytecodes and final object code. GCC auto-

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matically selects which files to optimize in LTO mode and which files to link
without further processing.
There are some code generation flags preserved by GCC when generating bytecodes, as they need to be used during the final link stage. Generally options
specified at link time override those specified at compile time.
If you do not specify an optimization level option ‘-O’ at link time, then GCC
uses the highest optimization level used when compiling the object files.
Currently, the following options and their settings are taken from the first object file that explicitly specifies them: ‘-fPIC’, ‘-fpic’, ‘-fpie’, ‘-fcommon’,
‘-fexceptions’, ‘-fnon-call-exceptions’, ‘-fgnu-tm’ and all the ‘-m’ target
flags.
Certain ABI-changing flags are required to match in all compilation units, and
trying to override this at link time with a conflicting value is ignored. This
includes options such as ‘-freg-struct-return’ and ‘-fpcc-struct-return’.
Other options such as ‘-ffp-contract’, ‘-fno-strict-overflow’, ‘-fwrapv’,
‘-fno-trapv’ or ‘-fno-strict-aliasing’ are passed through to the
link stage and merged conservatively for conflicting translation units.
Specifically ‘-fno-strict-overflow’, ‘-fwrapv’ and ‘-fno-trapv’ take
precedence; and for example ‘-ffp-contract=off’ takes precedence over
‘-ffp-contract=fast’. You can override them at link time.
If LTO encounters objects with C linkage declared with incompatible types in
separate translation units to be linked together (undefined behavior according
to ISO C99 6.2.7), a non-fatal diagnostic may be issued. The behavior is still
undefined at run time. Similar diagnostics may be raised for other languages.
Another feature of LTO is that it is possible to apply interprocedural optimizations on files written in different languages:
gcc -c -flto foo.c
g++ -c -flto bar.cc
gfortran -c -flto baz.f90
g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran

Notice that the final link is done with g++ to get the C++ runtime libraries and
‘-lgfortran’ is added to get the Fortran runtime libraries. In general, when
mixing languages in LTO mode, you should use the same link command options
as when mixing languages in a regular (non-LTO) compilation.
If object files containing GIMPLE bytecode are stored in a library archive, say
‘libfoo.a’, it is possible to extract and use them in an LTO link if you are
using a linker with plugin support. To create static libraries suitable for LTO,
use gcc-ar and gcc-ranlib instead of ar and ranlib; to show the symbols
of object files with GIMPLE bytecode, use gcc-nm. Those commands require
that ar, ranlib and nm have been compiled with plugin support. At link time,
use the the flag ‘-fuse-linker-plugin’ to ensure that the library participates
in the LTO optimization process:
gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo

With the linker plugin enabled, the linker extracts the needed GIMPLE files
from ‘libfoo.a’ and passes them on to the running GCC to make them part
of the aggregated GIMPLE image to be optimized.

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If you are not using a linker with plugin support and/or do not enable the linker
plugin, then the objects inside ‘libfoo.a’ are extracted and linked as usual,
but they do not participate in the LTO optimization process. In order to make
a static library suitable for both LTO optimization and usual linkage, compile
its object files with ‘-flto’ ‘-ffat-lto-objects’.
Link-time optimizations do not require the presence of the whole program to
operate. If the program does not require any symbols to be exported, it is possible to combine ‘-flto’ and ‘-fwhole-program’ to allow the interprocedural
optimizers to use more aggressive assumptions which may lead to improved optimization opportunities. Use of ‘-fwhole-program’ is not needed when linker
plugin is active (see ‘-fuse-linker-plugin’).
The current implementation of LTO makes no attempt to generate bytecode
that is portable between different types of hosts. The bytecode files are versioned and there is a strict version check, so bytecode files generated in one
version of GCC do not work with an older or newer version of GCC.
Link-time optimization does not work well with generation of debugging information on systems other than those using a combination of ELF and DWARF.
If you specify the optional n, the optimization and code generation done at link
time is executed in parallel using n parallel jobs by utilizing an installed make
program. The environment variable MAKE may be used to override the program
used. The default value for n is 1.
You can also specify ‘-flto=jobserver’ to use GNU make’s job server mode to
determine the number of parallel jobs. This is useful when the Makefile calling
GCC is already executing in parallel. You must prepend a ‘+’ to the command
recipe in the parent Makefile for this to work. This option likely only works if
MAKE is GNU make.
-flto-partition=alg
Specify the partitioning algorithm used by the link-time optimizer. The value
is either ‘1to1’ to specify a partitioning mirroring the original source files or
‘balanced’ to specify partitioning into equally sized chunks (whenever possible) or ‘max’ to create new partition for every symbol where possible. Specifying
‘none’ as an algorithm disables partitioning and streaming completely. The default value is ‘balanced’. While ‘1to1’ can be used as an workaround for various
code ordering issues, the ‘max’ partitioning is intended for internal testing only.
The value ‘one’ specifies that exactly one partition should be used while the
value ‘none’ bypasses partitioning and executes the link-time optimization step
directly from the WPA phase.
-flto-odr-type-merging
Enable streaming of mangled types names of C++ types and their unification at
link time. This increases size of LTO object files, but enables diagnostics about
One Definition Rule violations.
-flto-compression-level=n
This option specifies the level of compression used for intermediate language
written to LTO object files, and is only meaningful in conjunction with LTO

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mode (‘-flto’). Valid values are 0 (no compression) to 9 (maximum compression). Values outside this range are clamped to either 0 or 9. If the option is
not given, a default balanced compression setting is used.
-fuse-linker-plugin
Enables the use of a linker plugin during link-time optimization. This option
relies on plugin support in the linker, which is available in gold or in GNU ld
2.21 or newer.
This option enables the extraction of object files with GIMPLE bytecode out
of library archives. This improves the quality of optimization by exposing more
code to the link-time optimizer. This information specifies what symbols can be
accessed externally (by non-LTO object or during dynamic linking). Resulting
code quality improvements on binaries (and shared libraries that use hidden
visibility) are similar to ‘-fwhole-program’. See ‘-flto’ for a description of
the effect of this flag and how to use it.
This option is enabled by default when LTO support in GCC is enabled and
GCC was configured for use with a linker supporting plugins (GNU ld 2.21 or
newer or gold).
-ffat-lto-objects
Fat LTO objects are object files that contain both the intermediate language
and the object code. This makes them usable for both LTO linking and normal
linking. This option is effective only when compiling with ‘-flto’ and is ignored
at link time.
‘-fno-fat-lto-objects’ improves compilation time over plain LTO, but requires the complete toolchain to be aware of LTO. It requires a linker with linker
plugin support for basic functionality. Additionally, nm, ar and ranlib need
to support linker plugins to allow a full-featured build environment (capable of
building static libraries etc). GCC provides the gcc-ar, gcc-nm, gcc-ranlib
wrappers to pass the right options to these tools. With non fat LTO makefiles
need to be modified to use them.
Note that modern binutils provide plugin auto-load mechanism. Installing the
linker plugin into ‘$libdir/bfd-plugins’ has the same effect as usage of the
command wrappers (gcc-ar, gcc-nm and gcc-ranlib).
The default is ‘-fno-fat-lto-objects’ on targets with linker plugin support.
-fcompare-elim
After register allocation and post-register allocation instruction splitting, identify arithmetic instructions that compute processor flags similar to a comparison
operation based on that arithmetic. If possible, eliminate the explicit comparison operation.
This pass only applies to certain targets that cannot explicitly represent the
comparison operation before register allocation is complete.
Enabled at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.

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-fcprop-registers
After register allocation and post-register allocation instruction splitting, perform a copy-propagation pass to try to reduce scheduling dependencies and
occasionally eliminate the copy.
Enabled at levels ‘-O’, ‘-O2’, ‘-O3’, ‘-Os’.
-fprofile-correction
Profiles collected using an instrumented binary for multi-threaded programs
may be inconsistent due to missed counter updates. When this option is specified, GCC uses heuristics to correct or smooth out such inconsistencies. By
default, GCC emits an error message when an inconsistent profile is detected.
-fprofile-use
-fprofile-use=path
Enable profile feedback-directed optimizations, and the following optimizations
which are generally profitable only with profile feedback available:
‘-fbranch-probabilities’, ‘-fvpt’, ‘-funroll-loops’, ‘-fpeel-loops’,
‘-ftracer’, ‘-ftree-vectorize’, and ‘ftree-loop-distribute-patterns’.
Before you can use this option, you must first generate profiling information.
See Section 3.11 [Instrumentation Options], page 172, for information about
the ‘-fprofile-generate’ option.
By default, GCC emits an error message if the feedback profiles do not
match the source code. This error can be turned into a warning by using
‘-Wcoverage-mismatch’. Note this may result in poorly optimized code.
If path is specified, GCC looks at the path to find the profile feedback data
files. See ‘-fprofile-dir’.
-fauto-profile
-fauto-profile=path
Enable sampling-based feedback-directed optimizations, and the following optimizations which are generally profitable only with profile feedback available:
‘-fbranch-probabilities’, ‘-fvpt’, ‘-funroll-loops’, ‘-fpeel-loops’,
‘-ftracer’,
‘-ftree-vectorize’,
‘-finline-functions’,
‘-fipa-cp’,
‘-fipa-cp-clone’,
‘-fpredictive-commoning’,
‘-funswitch-loops’,
‘-fgcse-after-reload’, and ‘-ftree-loop-distribute-patterns’.
path is the name of a file containing AutoFDO profile information. If omitted,
it defaults to ‘fbdata.afdo’ in the current directory.
Producing an AutoFDO profile data file requires running your program with the
perf utility on a supported GNU/Linux target system. For more information,
see https://perf.wiki.kernel.org/.
E.g.
perf record -e br_inst_retired:near_taken -b -o perf.data \
-- your_program

Then use the create_gcov tool to convert the raw profile data to a format
that can be used by GCC. You must also supply the unstripped binary for your
program to this tool. See https://github.com/google/autofdo.
E.g.

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147

create_gcov --binary=your_program.unstripped --profile=perf.data \
--gcov=profile.afdo

The following options control compiler behavior regarding floating-point arithmetic.
These options trade off between speed and correctness. All must be specifically enabled.
-ffloat-store
Do not store floating-point variables in registers, and inhibit other options that
might change whether a floating-point value is taken from a register or memory.
This option prevents undesirable excess precision on machines such as the 68000
where the floating registers (of the 68881) keep more precision than a double
is supposed to have. Similarly for the x86 architecture. For most programs,
the excess precision does only good, but a few programs rely on the precise
definition of IEEE floating point. Use ‘-ffloat-store’ for such programs, after
modifying them to store all pertinent intermediate computations into variables.
-fexcess-precision=style
This option allows further control over excess precision on machines where
floating-point operations occur in a format with more precision or range
than the IEEE standard and interchange floating-point types. By default,
‘-fexcess-precision=fast’ is in effect; this means that operations may
be carried out in a wider precision than the types specified in the source
if that would result in faster code, and it is unpredictable when rounding
to the types specified in the source code takes place. When compiling C, if
‘-fexcess-precision=standard’ is specified then excess precision follows
the rules specified in ISO C99; in particular, both casts and assignments
cause values to be rounded to their semantic types (whereas ‘-ffloat-store’
only affects assignments). This option is enabled by default for C if a strict
conformance option such as ‘-std=c99’ is used. ‘-ffast-math’ enables
‘-fexcess-precision=fast’ by default regardless of whether a strict
conformance option is used.
‘-fexcess-precision=standard’ is not implemented for languages other than
C. On the x86, it has no effect if ‘-mfpmath=sse’ or ‘-mfpmath=sse+387’ is
specified; in the former case, IEEE semantics apply without excess precision,
and in the latter, rounding is unpredictable.
-ffast-math
Sets the options ‘-fno-math-errno’, ‘-funsafe-math-optimizations’,
‘-ffinite-math-only’, ‘-fno-rounding-math’, ‘-fno-signaling-nans’,
‘-fcx-limited-range’ and ‘-fexcess-precision=fast’.
This option causes the preprocessor macro __FAST_MATH__ to be defined.
This option is not turned on by any ‘-O’ option besides ‘-Ofast’ since it can
result in incorrect output for programs that depend on an exact implementation
of IEEE or ISO rules/specifications for math functions. It may, however, yield
faster code for programs that do not require the guarantees of these specifications.
-fno-math-errno
Do not set errno after calling math functions that are executed with a single
instruction, e.g., sqrt. A program that relies on IEEE exceptions for math

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error handling may want to use this flag for speed while maintaining IEEE
arithmetic compatibility.
This option is not turned on by any ‘-O’ option since it can result in incorrect
output for programs that depend on an exact implementation of IEEE or ISO
rules/specifications for math functions. It may, however, yield faster code for
programs that do not require the guarantees of these specifications.
The default is ‘-fmath-errno’.
On Darwin systems, the math library never sets errno. There is therefore
no reason for the compiler to consider the possibility that it might, and
‘-fno-math-errno’ is the default.
-funsafe-math-optimizations
Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate IEEE or ANSI standards.
When used at link time, it may include libraries or startup files that change the
default FPU control word or other similar optimizations.
This option is not turned on by any ‘-O’ option since it can result in incorrect output for programs that depend on an exact implementation of IEEE
or ISO rules/specifications for math functions. It may, however, yield faster
code for programs that do not require the guarantees of these specifications.
Enables ‘-fno-signed-zeros’, ‘-fno-trapping-math’, ‘-fassociative-math’
and ‘-freciprocal-math’.
The default is ‘-fno-unsafe-math-optimizations’.
-fassociative-math
Allow re-association of operands in series of floating-point operations. This violates the ISO C and C++ language standard by possibly changing computation
result. NOTE: re-ordering may change the sign of zero as well as ignore NaNs
and inhibit or create underflow or overflow (and thus cannot be used on code
that relies on rounding behavior like (x + 2**52) - 2**52. May also reorder
floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both ‘-fno-signed-zeros’ and
‘-fno-trapping-math’ be in effect. Moreover, it doesn’t make much sense with
‘-frounding-math’. For Fortran the option is automatically enabled when both
‘-fno-signed-zeros’ and ‘-fno-trapping-math’ are in effect.
The default is ‘-fno-associative-math’.
-freciprocal-math
Allow the reciprocal of a value to be used instead of dividing by the value if
this enables optimizations. For example x / y can be replaced with x * (1/y),
which is useful if (1/y) is subject to common subexpression elimination. Note
that this loses precision and increases the number of flops operating on the
value.
The default is ‘-fno-reciprocal-math’.
-ffinite-math-only
Allow optimizations for floating-point arithmetic that assume that arguments
and results are not NaNs or +-Infs.

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This option is not turned on by any ‘-O’ option since it can result in incorrect
output for programs that depend on an exact implementation of IEEE or ISO
rules/specifications for math functions. It may, however, yield faster code for
programs that do not require the guarantees of these specifications.
The default is ‘-fno-finite-math-only’.
-fno-signed-zeros
Allow optimizations for floating-point arithmetic that ignore the signedness of
zero. IEEE arithmetic specifies the behavior of distinct +0.0 and −0.0 values,
which then prohibits simplification of expressions such as x+0.0 or 0.0*x (even
with ‘-ffinite-math-only’). This option implies that the sign of a zero result
isn’t significant.
The default is ‘-fsigned-zeros’.
-fno-trapping-math
Compile code assuming that floating-point operations cannot generate uservisible traps. These traps include division by zero, overflow, underflow, inexact
result and invalid operation. This option requires that ‘-fno-signaling-nans’
be in effect. Setting this option may allow faster code if one relies on “non-stop”
IEEE arithmetic, for example.
This option should never be turned on by any ‘-O’ option since it can result
in incorrect output for programs that depend on an exact implementation of
IEEE or ISO rules/specifications for math functions.
The default is ‘-ftrapping-math’.
-frounding-math
Disable transformations and optimizations that assume default floating-point
rounding behavior. This is round-to-zero for all floating point to integer conversions, and round-to-nearest for all other arithmetic truncations. This option
should be specified for programs that change the FP rounding mode dynamically, or that may be executed with a non-default rounding mode. This option
disables constant folding of floating-point expressions at compile time (which
may be affected by rounding mode) and arithmetic transformations that are
unsafe in the presence of sign-dependent rounding modes.
The default is ‘-fno-rounding-math’.
This option is experimental and does not currently guarantee to disable all GCC
optimizations that are affected by rounding mode. Future versions of GCC may
provide finer control of this setting using C99’s FENV_ACCESS pragma. This
command-line option will be used to specify the default state for FENV_ACCESS.
-fsignaling-nans
Compile code assuming that IEEE signaling NaNs may generate user-visible
traps during floating-point operations. Setting this option disables optimizations that may change the number of exceptions visible with signaling NaNs.
This option implies ‘-ftrapping-math’.
This option causes the preprocessor macro __SUPPORT_SNAN__ to be defined.
The default is ‘-fno-signaling-nans’.

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This option is experimental and does not currently guarantee to disable all
GCC optimizations that affect signaling NaN behavior.
-fno-fp-int-builtin-inexact
Do not allow the built-in functions ceil, floor, round and trunc, and their
float and long double variants, to generate code that raises the “inexact”
floating-point exception for noninteger arguments. ISO C99 and C11 allow
these functions to raise the “inexact” exception, but ISO/IEC TS 18661-1:2014,
the C bindings to IEEE 754-2008, does not allow these functions to do so.
The default is ‘-ffp-int-builtin-inexact’, allowing the exception to be
raised. This option does nothing unless ‘-ftrapping-math’ is in effect.
Even if ‘-fno-fp-int-builtin-inexact’ is used, if the functions generate a
call to a library function then the “inexact” exception may be raised if the
library implementation does not follow TS 18661.
-fsingle-precision-constant
Treat floating-point constants as single precision instead of implicitly converting
them to double-precision constants.
-fcx-limited-range
When enabled, this option states that a range reduction step is not needed when
performing complex division. Also, there is no checking whether the result of
a complex multiplication or division is NaN + I*NaN, with an attempt to rescue
the situation in that case. The default is ‘-fno-cx-limited-range’, but is
enabled by ‘-ffast-math’.
This option controls the default setting of the ISO C99 CX_LIMITED_RANGE
pragma. Nevertheless, the option applies to all languages.
-fcx-fortran-rules
Complex multiplication and division follow Fortran rules. Range reduction is
done as part of complex division, but there is no checking whether the result of
a complex multiplication or division is NaN + I*NaN, with an attempt to rescue
the situation in that case.
The default is ‘-fno-cx-fortran-rules’.
The following options control optimizations that may improve performance, but are not
enabled by any ‘-O’ options. This section includes experimental options that may produce
broken code.
-fbranch-probabilities
After running a program compiled with ‘-fprofile-arcs’ (see Section 3.11
[Instrumentation Options], page 172), you can compile it a second time
using ‘-fbranch-probabilities’, to improve optimizations based on
the number of times each branch was taken. When a program compiled
with ‘-fprofile-arcs’ exits, it saves arc execution counts to a file called
‘sourcename.gcda’ for each source file. The information in this data file is
very dependent on the structure of the generated code, so you must use the
same source code and the same optimization options for both compilations.
With ‘-fbranch-probabilities’, GCC puts a ‘REG_BR_PROB’ note on each
‘JUMP_INSN’ and ‘CALL_INSN’. These can be used to improve optimization.

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Currently, they are only used in one place: in ‘reorg.c’, instead of guessing
which path a branch is most likely to take, the ‘REG_BR_PROB’ values are used
to exactly determine which path is taken more often.
-fprofile-values
If combined with ‘-fprofile-arcs’, it adds code so that some data about
values of expressions in the program is gathered.
With ‘-fbranch-probabilities’, it reads back the data gathered from profiling values of expressions for usage in optimizations.
Enabled with ‘-fprofile-generate’ and ‘-fprofile-use’.
-fprofile-reorder-functions
Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions in ascending order.
Enabled with ‘-fprofile-use’.
-fvpt

If combined with ‘-fprofile-arcs’, this option instructs the compiler to add
code to gather information about values of expressions.
With ‘-fbranch-probabilities’, it reads back the data gathered and actually
performs the optimizations based on them. Currently the optimizations include
specialization of division operations using the knowledge about the value of the
denominator.

-frename-registers
Attempt to avoid false dependencies in scheduled code by making use of registers
left over after register allocation. This optimization most benefits processors
with lots of registers. Depending on the debug information format adopted by
the target, however, it can make debugging impossible, since variables no longer
stay in a “home register”.
Enabled by default with ‘-funroll-loops’.
-fschedule-fusion
Performs a target dependent pass over the instruction stream to schedule instructions of same type together because target machine can execute them more
efficiently if they are adjacent to each other in the instruction flow.
Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.
-ftracer

Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better
job.
Enabled with ‘-fprofile-use’.

-funroll-loops
Unroll loops whose number of iterations can be determined at compile time or
upon entry to the loop. ‘-funroll-loops’ implies ‘-frerun-cse-after-loop’,
‘-fweb’ and ‘-frename-registers’. It also turns on complete loop peeling (i.e.
complete removal of loops with a small constant number of iterations). This
option makes code larger, and may or may not make it run faster.
Enabled with ‘-fprofile-use’.

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-funroll-all-loops
Unroll all loops, even if their number of iterations is uncertain when the loop is
entered. This usually makes programs run more slowly. ‘-funroll-all-loops’
implies the same options as ‘-funroll-loops’.
-fpeel-loops
Peels loops for which there is enough information that they do not roll much
(from profile feedback or static analysis). It also turns on complete loop peeling
(i.e. complete removal of loops with small constant number of iterations).
Enabled with ‘-O3’ and/or ‘-fprofile-use’.
-fmove-loop-invariants
Enables the loop invariant motion pass in the RTL loop optimizer. Enabled at
level ‘-O1’
-fsplit-loops
Split a loop into two if it contains a condition that’s always true for one side of
the iteration space and false for the other.
-funswitch-loops
Move branches with loop invariant conditions out of the loop, with duplicates
of the loop on both branches (modified according to result of the condition).
-ffunction-sections
-fdata-sections
Place each function or data item into its own section in the output file if the
target supports arbitrary sections. The name of the function or the name of
the data item determines the section’s name in the output file.
Use these options on systems where the linker can perform optimizations to
improve locality of reference in the instruction space. Most systems using the
ELF object format have linkers with such optimizations. On AIX, the linker
rearranges sections (CSECTs) based on the call graph. The performance impact
varies.
Together with a linker garbage collection (linker ‘--gc-sections’ option) these
options may lead to smaller statically-linked executables (after stripping).
On ELF/DWARF systems these options do not degenerate the quality of the
debug information. There could be issues with other object files/debug info
formats.
Only use these options when there are significant benefits from doing so. When
you specify these options, the assembler and linker create larger object and
executable files and are also slower. These options affect code generation. They
prevent optimizations by the compiler and assembler using relative locations
inside a translation unit since the locations are unknown until link time. An
example of such an optimization is relaxing calls to short call instructions.
-fbranch-target-load-optimize
Perform branch target register load optimization before prologue / epilogue
threading. The use of target registers can typically be exposed only during
reload, thus hoisting loads out of loops and doing inter-block scheduling needs
a separate optimization pass.

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-fbranch-target-load-optimize2
Perform branch target register load optimization after prologue / epilogue
threading.
-fbtr-bb-exclusive
When performing branch target register load optimization, don’t reuse branch
target registers within any basic block.
-fstdarg-opt
Optimize the prologue of variadic argument functions with respect to usage of
those arguments.
-fsection-anchors
Try to reduce the number of symbolic address calculations by using shared
“anchor” symbols to address nearby objects. This transformation can help to
reduce the number of GOT entries and GOT accesses on some targets.
For example, the implementation of the following function foo:
static int a, b, c;
int foo (void) { return a + b + c; }

usually calculates the addresses of all three variables, but if you compile it with
‘-fsection-anchors’, it accesses the variables from a common anchor point
instead. The effect is similar to the following pseudocode (which isn’t valid C):
int foo (void)
{
register int *xr = &x;
return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
}

Not all targets support this option.
--param name=value
In some places, GCC uses various constants to control the amount of optimization that is done. For example, GCC does not inline functions that contain
more than a certain number of instructions. You can control some of these
constants on the command line using the ‘--param’ option.
The names of specific parameters, and the meaning of the values, are tied to
the internals of the compiler, and are subject to change without notice in future
releases.
In each case, the value is an integer. The allowable choices for name are:
predictable-branch-outcome
When branch is predicted to be taken with probability lower than
this threshold (in percent), then it is considered well predictable.
The default is 10.
max-rtl-if-conversion-insns
RTL if-conversion tries to remove conditional branches around a
block and replace them with conditionally executed instructions.
This parameter gives the maximum number of instructions in a
block which should be considered for if-conversion. The default
is 10, though the compiler will also use other heuristics to decide
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max-rtl-if-conversion-predictable-cost
max-rtl-if-conversion-unpredictable-cost
RTL if-conversion will try to remove conditional branches around
a block and replace them with conditionally executed instructions.
These parameters give the maximum permissible cost for the
sequence that would be generated by if-conversion depending on
whether the branch is statically determined to be predictable or
not. The units for this parameter are the same as those for the
GCC internal seq cost metric. The compiler will try to provide a
reasonable default for this parameter using the BRANCH COST
target macro.
max-crossjump-edges
The maximum number of incoming edges to consider for crossjumping. The algorithm used by ‘-fcrossjumping’ is O(N 2 ) in
the number of edges incoming to each block. Increasing values
mean more aggressive optimization, making the compilation time
increase with probably small improvement in executable size.
min-crossjump-insns
The minimum number of instructions that must be matched at the
end of two blocks before cross-jumping is performed on them. This
value is ignored in the case where all instructions in the block being
cross-jumped from are matched. The default value is 5.
max-grow-copy-bb-insns
The maximum code size expansion factor when copying basic blocks
instead of jumping. The expansion is relative to a jump instruction.
The default value is 8.
max-goto-duplication-insns
The maximum number of instructions to duplicate to a block that
jumps to a computed goto. To avoid O(N 2 ) behavior in a number
of passes, GCC factors computed gotos early in the compilation
process, and unfactors them as late as possible. Only computed
jumps at the end of a basic blocks with no more than max-gotoduplication-insns are unfactored. The default value is 8.
max-delay-slot-insn-search
The maximum number of instructions to consider when looking for
an instruction to fill a delay slot. If more than this arbitrary number
of instructions are searched, the time savings from filling the delay
slot are minimal, so stop searching. Increasing values mean more
aggressive optimization, making the compilation time increase with
probably small improvement in execution time.
max-delay-slot-live-search
When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register
information. Increasing this arbitrarily chosen value means more

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aggressive optimization, increasing the compilation time. This parameter should be removed when the delay slot code is rewritten
to maintain the control-flow graph.
max-gcse-memory
The approximate maximum amount of memory that can be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required,
the optimization is not done.
max-gcse-insertion-ratio
If the ratio of expression insertions to deletions is larger than this
value for any expression, then RTL PRE inserts or removes the
expression and thus leaves partially redundant computations in the
instruction stream. The default value is 20.
max-pending-list-length
The maximum number of pending dependencies scheduling allows
before flushing the current state and starting over. Large functions
with few branches or calls can create excessively large lists which
needlessly consume memory and resources.
max-modulo-backtrack-attempts
The maximum number of backtrack attempts the scheduler should
make when modulo scheduling a loop. Larger values can exponentially increase compilation time.
max-inline-insns-single
Several parameters control the tree inliner used in GCC. This number sets the maximum number of instructions (counted in GCC’s
internal representation) in a single function that the tree inliner
considers for inlining. This only affects functions declared inline
and methods implemented in a class declaration (C++). The default value is 400.
max-inline-insns-auto
When you use ‘-finline-functions’ (included in ‘-O3’), a lot of
functions that would otherwise not be considered for inlining by
the compiler are investigated. To those functions, a different (more
restrictive) limit compared to functions declared inline can be applied. The default value is 30.
inline-min-speedup
When estimated performance improvement of caller + callee runtime exceeds this threshold (in percent), the function can be inlined
regardless of the limit on ‘--param max-inline-insns-single’
and ‘--param max-inline-insns-auto’. The default value is 15.
large-function-insns
The limit specifying really large functions. For functions larger
than this limit after inlining, inlining is constrained by ‘--param

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large-function-growth’. This parameter is useful primarily to
avoid extreme compilation time caused by non-linear algorithms
used by the back end. The default value is 2700.
large-function-growth
Specifies maximal growth of large function caused by inlining in percents. The default value is 100 which limits large function growth
to 2.0 times the original size.
large-unit-insns
The limit specifying large translation unit. Growth caused by
inlining of units larger than this limit is limited by ‘--param
inline-unit-growth’. For small units this might be too tight.
For example, consider a unit consisting of function A that is
inline and B that just calls A three times. If B is small relative
to A, the growth of unit is 300\% and yet such inlining is
very sane. For very large units consisting of small inlineable
functions, however, the overall unit growth limit is needed to avoid
exponential explosion of code size. Thus for smaller units, the
size is increased to ‘--param large-unit-insns’ before applying
‘--param inline-unit-growth’. The default is 10000.
inline-unit-growth
Specifies maximal overall growth of the compilation unit caused by
inlining. The default value is 20 which limits unit growth to 1.2
times the original size. Cold functions (either marked cold via an
attribute or by profile feedback) are not accounted into the unit
size.
ipcp-unit-growth
Specifies maximal overall growth of the compilation unit caused
by interprocedural constant propagation. The default value is 10
which limits unit growth to 1.1 times the original size.
large-stack-frame
The limit specifying large stack frames. While inlining the algorithm is trying to not grow past this limit too much. The default
value is 256 bytes.
large-stack-frame-growth
Specifies maximal growth of large stack frames caused by inlining in
percents. The default value is 1000 which limits large stack frame
growth to 11 times the original size.
max-inline-insns-recursive
max-inline-insns-recursive-auto
Specifies the maximum number of instructions an out-of-line copy of
a self-recursive inline function can grow into by performing recursive
inlining.
‘--param max-inline-insns-recursive’ applies to functions declared inline. For functions not declared inline, recursive inlin-

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ing happens only when ‘-finline-functions’ (included in ‘-O3’)
is enabled; ‘--param max-inline-insns-recursive-auto’ applies
instead. The default value is 450.
max-inline-recursive-depth
max-inline-recursive-depth-auto
Specifies the maximum recursion depth used for recursive inlining.
‘--param max-inline-recursive-depth’ applies to functions declared inline. For functions not declared inline, recursive inlining happens only when ‘-finline-functions’ (included in ‘-O3’)
is enabled; ‘--param max-inline-recursive-depth-auto’ applies
instead. The default value is 8.
min-inline-recursive-probability
Recursive inlining is profitable only for function having deep recursion in average and can hurt for function having little recursion
depth by increasing the prologue size or complexity of function
body to other optimizers.
When profile feedback is available (see ‘-fprofile-generate’) the
actual recursion depth can be guessed from the probability that
function recurses via a given call expression. This parameter limits
inlining only to call expressions whose probability exceeds the given
threshold (in percents). The default value is 10.
early-inlining-insns
Specify growth that the early inliner can make. In effect it increases
the amount of inlining for code having a large abstraction penalty.
The default value is 14.
max-early-inliner-iterations
Limit of iterations of the early inliner. This basically bounds the
number of nested indirect calls the early inliner can resolve. Deeper
chains are still handled by late inlining.
comdat-sharing-probability
Probability (in percent) that C++ inline function with comdat visibility are shared across multiple compilation units. The default
value is 20.
profile-func-internal-id
A parameter to control whether to use function internal id in profile
database lookup. If the value is 0, the compiler uses an id that
is based on function assembler name and filename, which makes
old profile data more tolerant to source changes such as function
reordering etc. The default value is 0.
min-vect-loop-bound
The minimum number of iterations under which loops are not vectorized when ‘-ftree-vectorize’ is used. The number of iterations after vectorization needs to be greater than the value specified
by this option to allow vectorization. The default value is 0.

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gcse-cost-distance-ratio
Scaling factor in calculation of maximum distance an expression can
be moved by GCSE optimizations. This is currently supported only
in the code hoisting pass. The bigger the ratio, the more aggressive code hoisting is with simple expressions, i.e., the expressions
that have cost less than ‘gcse-unrestricted-cost’. Specifying 0
disables hoisting of simple expressions. The default value is 10.
gcse-unrestricted-cost
Cost, roughly measured as the cost of a single typical machine
instruction, at which GCSE optimizations do not constrain the distance an expression can travel. This is currently supported only
in the code hoisting pass. The lesser the cost, the more aggressive code hoisting is. Specifying 0 allows all expressions to travel
unrestricted distances. The default value is 3.
max-hoist-depth
The depth of search in the dominator tree for expressions to hoist.
This is used to avoid quadratic behavior in hoisting algorithm. The
value of 0 does not limit on the search, but may slow down compilation of huge functions. The default value is 30.
max-tail-merge-comparisons
The maximum amount of similar bbs to compare a bb with. This is
used to avoid quadratic behavior in tree tail merging. The default
value is 10.
max-tail-merge-iterations
The maximum amount of iterations of the pass over the function.
This is used to limit compilation time in tree tail merging. The
default value is 2.
store-merging-allow-unaligned
Allow the store merging pass to introduce unaligned stores if it is
legal to do so. The default value is 1.
max-stores-to-merge
The maximum number of stores to attempt to merge into wider
stores in the store merging pass. The minimum value is 2 and the
default is 64.
max-unrolled-insns
The maximum number of instructions that a loop may have to be
unrolled. If a loop is unrolled, this parameter also determines how
many times the loop code is unrolled.
max-average-unrolled-insns
The maximum number of instructions biased by probabilities of
their execution that a loop may have to be unrolled. If a loop is
unrolled, this parameter also determines how many times the loop
code is unrolled.

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max-unroll-times
The maximum number of unrollings of a single loop.
max-peeled-insns
The maximum number of instructions that a loop may have to be
peeled. If a loop is peeled, this parameter also determines how
many times the loop code is peeled.
max-peel-times
The maximum number of peelings of a single loop.
max-peel-branches
The maximum number of branches on the hot path through the
peeled sequence.
max-completely-peeled-insns
The maximum number of insns of a completely peeled loop.
max-completely-peel-times
The maximum number of iterations of a loop to be suitable for
complete peeling.
max-completely-peel-loop-nest-depth
The maximum depth of a loop nest suitable for complete peeling.
max-unswitch-insns
The maximum number of insns of an unswitched loop.
max-unswitch-level
The maximum number of branches unswitched in a single loop.
max-loop-headers-insns
The maximum number of insns in loop header duplicated by the
copy loop headers pass.
lim-expensive
The minimum cost of an expensive expression in the loop invariant
motion.
iv-consider-all-candidates-bound
Bound on number of candidates for induction variables, below
which all candidates are considered for each use in induction
variable optimizations. If there are more candidates than this,
only the most relevant ones are considered to avoid quadratic time
complexity.
iv-max-considered-uses
The induction variable optimizations give up on loops that contain
more induction variable uses.
iv-always-prune-cand-set-bound
If the number of candidates in the set is smaller than this value,
always try to remove unnecessary ivs from the set when adding a
new one.

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avg-loop-niter
Average number of iterations of a loop.
dse-max-object-size
Maximum size (in bytes) of objects tracked bytewise by dead store
elimination. Larger values may result in larger compilation times.
scev-max-expr-size
Bound on size of expressions used in the scalar evolutions analyzer.
Large expressions slow the analyzer.
scev-max-expr-complexity
Bound on the complexity of the expressions in the scalar evolutions
analyzer. Complex expressions slow the analyzer.
max-tree-if-conversion-phi-args
Maximum number of arguments in a PHI supported by TREE if
conversion unless the loop is marked with simd pragma.
vect-max-version-for-alignment-checks
The maximum number of run-time checks that can be performed
when doing loop versioning for alignment in the vectorizer.
vect-max-version-for-alias-checks
The maximum number of run-time checks that can be performed
when doing loop versioning for alias in the vectorizer.
vect-max-peeling-for-alignment
The maximum number of loop peels to enhance access alignment
for vectorizer. Value -1 means no limit.
max-iterations-to-track
The maximum number of iterations of a loop the brute-force algorithm for analysis of the number of iterations of the loop tries to
evaluate.
hot-bb-count-ws-permille
A basic block profile count is considered hot if it contributes to the
given permillage (i.e. 0...1000) of the entire profiled execution.
hot-bb-frequency-fraction
Select fraction of the entry block frequency of executions of basic
block in function given basic block needs to have to be considered
hot.
max-predicted-iterations
The maximum number of loop iterations we predict statically. This
is useful in cases where a function contains a single loop with known
bound and another loop with unknown bound. The known number
of iterations is predicted correctly, while the unknown number of
iterations average to roughly 10. This means that the loop without
bounds appears artificially cold relative to the other one.

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builtin-expect-probability
Control the probability of the expression having the specified value.
This parameter takes a percentage (i.e. 0 ... 100) as input. The
default probability of 90 is obtained empirically.
align-threshold
Select fraction of the maximal frequency of executions of a basic
block in a function to align the basic block.
align-loop-iterations
A loop expected to iterate at least the selected number of iterations
is aligned.
tracer-dynamic-coverage
tracer-dynamic-coverage-feedback
This value is used to limit superblock formation once the given percentage of executed instructions is covered. This limits unnecessary
code size expansion.
The ‘tracer-dynamic-coverage-feedback’ parameter is used
only when profile feedback is available. The real profiles (as
opposed to statically estimated ones) are much less balanced
allowing the threshold to be larger value.
tracer-max-code-growth
Stop tail duplication once code growth has reached given percentage. This is a rather artificial limit, as most of the duplicates are
eliminated later in cross jumping, so it may be set to much higher
values than is the desired code growth.
tracer-min-branch-ratio
Stop reverse growth when the reverse probability of best edge is
less than this threshold (in percent).
tracer-min-branch-probability
tracer-min-branch-probability-feedback
Stop forward growth if the best edge has probability lower than
this threshold.
Similarly to ‘tracer-dynamic-coverage’ two parameters are
provided.
‘tracer-min-branch-probability-feedback’
is used for compilation with profile feedback and
‘tracer-min-branch-probability’
compilation
without.
The value for compilation with profile feedback needs to be more
conservative (higher) in order to make tracer effective.
stack-clash-protection-guard-size
Specify the size of the operating system provided stack guard as
2 raised to num bytes. The default value is 12 (4096 bytes). Acceptable values are between 12 and 30. Higher values may reduce
the number of explicit probes, but a value larger than the operating system provided guard will leave code vulnerable to stack clash
style attacks.

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stack-clash-protection-probe-interval
Stack clash protection involves probing stack space as it is allocated. This param controls the maximum distance between probes
into the stack as 2 raised to num bytes. Acceptable values are
between 10 and 16 and defaults to 12. Higher values may reduce
the number of explicit probes, but a value larger than the operating system provided guard will leave code vulnerable to stack clash
style attacks.
max-cse-path-length
The maximum number of basic blocks on path that CSE considers.
The default is 10.
max-cse-insns
The maximum number of instructions CSE processes before flushing. The default is 1000.
ggc-min-expand
GCC uses a garbage collector to manage its own memory allocation. This parameter specifies the minimum percentage by which
the garbage collector’s heap should be allowed to expand between
collections. Tuning this may improve compilation speed; it has no
effect on code generation.
The default is 30% + 70% * (RAM/1GB) with an upper bound
of 100% when RAM >= 1GB. If getrlimit is available, the notion of “RAM” is the smallest of actual RAM and RLIMIT_DATA or
RLIMIT_AS. If GCC is not able to calculate RAM on a particular
platform, the lower bound of 30% is used. Setting this parameter
and ‘ggc-min-heapsize’ to zero causes a full collection to occur
at every opportunity. This is extremely slow, but can be useful for
debugging.
ggc-min-heapsize
Minimum size of the garbage collector’s heap before it begins
bothering to collect garbage. The first collection occurs after the
heap expands by ‘ggc-min-expand’% beyond ‘ggc-min-heapsize’.
Again, tuning this may improve compilation speed, and has no
effect on code generation.
The default is the smaller of RAM/8, RLIMIT RSS, or a limit
that tries to ensure that RLIMIT DATA or RLIMIT AS are not
exceeded, but with a lower bound of 4096 (four megabytes) and
an upper bound of 131072 (128 megabytes). If GCC is not able
to calculate RAM on a particular platform, the lower bound is
used. Setting this parameter very large effectively disables garbage
collection. Setting this parameter and ‘ggc-min-expand’ to zero
causes a full collection to occur at every opportunity.
max-reload-search-insns
The maximum number of instruction reload should look backward
for equivalent register. Increasing values mean more aggressive op-

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timization, making the compilation time increase with probably
slightly better performance. The default value is 100.
max-cselib-memory-locations
The maximum number of memory locations cselib should take into
account. Increasing values mean more aggressive optimization,
making the compilation time increase with probably slightly better
performance. The default value is 500.
max-sched-ready-insns
The maximum number of instructions ready to be issued the scheduler should consider at any given time during the first scheduling
pass. Increasing values mean more thorough searches, making the
compilation time increase with probably little benefit. The default
value is 100.
max-sched-region-blocks
The maximum number of blocks in a region to be considered for
interblock scheduling. The default value is 10.
max-pipeline-region-blocks
The maximum number of blocks in a region to be considered for
pipelining in the selective scheduler. The default value is 15.
max-sched-region-insns
The maximum number of insns in a region to be considered for
interblock scheduling. The default value is 100.
max-pipeline-region-insns
The maximum number of insns in a region to be considered for
pipelining in the selective scheduler. The default value is 200.
min-spec-prob
The minimum probability (in percents) of reaching a source block
for interblock speculative scheduling. The default value is 40.
max-sched-extend-regions-iters
The maximum number of iterations through CFG to extend regions.
A value of 0 (the default) disables region extensions.
max-sched-insn-conflict-delay
The maximum conflict delay for an insn to be considered for speculative motion. The default value is 3.
sched-spec-prob-cutoff
The minimal probability of speculation success (in percents), so
that speculative insns are scheduled. The default value is 40.
sched-state-edge-prob-cutoff
The minimum probability an edge must have for the scheduler to
save its state across it. The default value is 10.
sched-mem-true-dep-cost
Minimal distance (in CPU cycles) between store and load targeting
same memory locations. The default value is 1.

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selsched-max-lookahead
The maximum size of the lookahead window of selective scheduling.
It is a depth of search for available instructions. The default value
is 50.
selsched-max-sched-times
The maximum number of times that an instruction is scheduled
during selective scheduling. This is the limit on the number of
iterations through which the instruction may be pipelined. The
default value is 2.
selsched-insns-to-rename
The maximum number of best instructions in the ready list that
are considered for renaming in the selective scheduler. The default
value is 2.
sms-min-sc
The minimum value of stage count that swing modulo scheduler
generates. The default value is 2.
max-last-value-rtl
The maximum size measured as number of RTLs that can be
recorded in an expression in combiner for a pseudo register as last
known value of that register. The default is 10000.
max-combine-insns
The maximum number of instructions the RTL combiner tries to
combine. The default value is 2 at ‘-Og’ and 4 otherwise.
integer-share-limit
Small integer constants can use a shared data structure, reducing
the compiler’s memory usage and increasing its speed. This sets
the maximum value of a shared integer constant. The default value
is 256.
ssp-buffer-size
The minimum size of buffers (i.e. arrays) that receive stack smashing protection when ‘-fstack-protection’ is used.
min-size-for-stack-sharing
The minimum size of variables taking part in stack slot sharing
when not optimizing. The default value is 32.
max-jump-thread-duplication-stmts
Maximum number of statements allowed in a block that needs to
be duplicated when threading jumps.
max-fields-for-field-sensitive
Maximum number of fields in a structure treated in a field sensitive
manner during pointer analysis. The default is zero for ‘-O0’ and
‘-O1’, and 100 for ‘-Os’, ‘-O2’, and ‘-O3’.

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prefetch-latency
Estimate on average number of instructions that are executed before prefetch finishes. The distance prefetched ahead is proportional to this constant. Increasing this number may also lead to
less streams being prefetched (see ‘simultaneous-prefetches’).
simultaneous-prefetches
Maximum number of prefetches that can run at the same time.
l1-cache-line-size
The size of cache line in L1 cache, in bytes.
l1-cache-size
The size of L1 cache, in kilobytes.
l2-cache-size
The size of L2 cache, in kilobytes.
loop-interchange-max-num-stmts
The maximum number of stmts in a loop to be interchanged.
loop-interchange-stride-ratio
The minimum ratio between stride of two loops for interchange to
be profitable.
min-insn-to-prefetch-ratio
The minimum ratio between the number of instructions and the
number of prefetches to enable prefetching in a loop.
prefetch-min-insn-to-mem-ratio
The minimum ratio between the number of instructions and the
number of memory references to enable prefetching in a loop.
use-canonical-types
Whether the compiler should use the “canonical” type system. By
default, this should always be 1, which uses a more efficient internal
mechanism for comparing types in C++ and Objective-C++. However, if bugs in the canonical type system are causing compilation
failures, set this value to 0 to disable canonical types.
switch-conversion-max-branch-ratio
Switch initialization conversion refuses to create arrays that are bigger than ‘switch-conversion-max-branch-ratio’ times the number of branches in the switch.
max-partial-antic-length
Maximum length of the partial antic set computed during the tree
partial redundancy elimination optimization (‘-ftree-pre’) when
optimizing at ‘-O3’ and above. For some sorts of source code the enhanced partial redundancy elimination optimization can run away,
consuming all of the memory available on the host machine. This
parameter sets a limit on the length of the sets that are computed,
which prevents the runaway behavior. Setting a value of 0 for this
parameter allows an unlimited set length.

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sccvn-max-scc-size
Maximum size of a strongly connected component (SCC) during
SCCVN processing. If this limit is hit, SCCVN processing for the
whole function is not done and optimizations depending on it are
disabled. The default maximum SCC size is 10000.
sccvn-max-alias-queries-per-access
Maximum number of alias-oracle queries we perform when looking
for redundancies for loads and stores. If this limit is hit the search
is aborted and the load or store is not considered redundant. The
number of queries is algorithmically limited to the number of stores
on all paths from the load to the function entry. The default maximum number of queries is 1000.
ira-max-loops-num
IRA uses regional register allocation by default. If a function contains more loops than the number given by this parameter, only at
most the given number of the most frequently-executed loops form
regions for regional register allocation. The default value of the
parameter is 100.
ira-max-conflict-table-size
Although IRA uses a sophisticated algorithm to compress the conflict table, the table can still require excessive amounts of memory
for huge functions. If the conflict table for a function could be more
than the size in MB given by this parameter, the register allocator
instead uses a faster, simpler, and lower-quality algorithm that does
not require building a pseudo-register conflict table. The default
value of the parameter is 2000.
ira-loop-reserved-regs
IRA can be used to evaluate more accurate register pressure in
loops for decisions to move loop invariants (see ‘-O3’). The number
of available registers reserved for some other purposes is given by
this parameter. The default value of the parameter is 2, which
is the minimal number of registers needed by typical instructions.
This value is the best found from numerous experiments.
lra-inheritance-ebb-probability-cutoff
LRA tries to reuse values reloaded in registers in subsequent insns.
This optimization is called inheritance. EBB is used as a region to
do this optimization. The parameter defines a minimal fall-through
edge probability in percentage used to add BB to inheritance EBB
in LRA. The default value of the parameter is 40. The value was
chosen from numerous runs of SPEC2000 on x86-64.
loop-invariant-max-bbs-in-loop
Loop invariant motion can be very expensive, both in compilation
time and in amount of needed compile-time memory, with very
large loops. Loops with more basic blocks than this parameter

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won’t have loop invariant motion optimization performed on them.
The default value of the parameter is 1000 for ‘-O1’ and 10000 for
‘-O2’ and above.
loop-max-datarefs-for-datadeps
Building data dependencies is expensive for very large loops. This
parameter limits the number of data references in loops that are
considered for data dependence analysis. These large loops are no
handled by the optimizations using loop data dependencies. The
default value is 1000.
max-vartrack-size
Sets a maximum number of hash table slots to use during variable
tracking dataflow analysis of any function. If this limit is exceeded
with variable tracking at assignments enabled, analysis for that
function is retried without it, after removing all debug insns from
the function. If the limit is exceeded even without debug insns, var
tracking analysis is completely disabled for the function. Setting
the parameter to zero makes it unlimited.
max-vartrack-expr-depth
Sets a maximum number of recursion levels when attempting to
map variable names or debug temporaries to value expressions.
This trades compilation time for more complete debug information.
If this is set too low, value expressions that are available and could
be represented in debug information may end up not being used;
setting this higher may enable the compiler to find more complex
debug expressions, but compile time and memory use may grow.
The default is 12.
max-debug-marker-count
Sets a threshold on the number of debug markers (e.g. begin stmt
markers) to avoid complexity explosion at inlining or expanding to
RTL. If a function has more such gimple stmts than the set limit,
such stmts will be dropped from the inlined copy of a function, and
from its RTL expansion. The default is 100000.
min-nondebug-insn-uid
Use uids starting at this parameter for nondebug insns. The range
below the parameter is reserved exclusively for debug insns created
by ‘-fvar-tracking-assignments’, but debug insns may get (nonoverlapping) uids above it if the reserved range is exhausted.
ipa-sra-ptr-growth-factor
IPA-SRA replaces a pointer to an aggregate with one or more
new parameters only when their cumulative size is less or equal
to ‘ipa-sra-ptr-growth-factor’ times the size of the original
pointer parameter.

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sra-max-scalarization-size-Ospeed
sra-max-scalarization-size-Osize
The two Scalar Reduction of Aggregates passes (SRA and
IPA-SRA) aim to replace scalar parts of aggregates with
uses of independent scalar variables.
These parameters
control the maximum size, in storage units, of aggregate
which is considered for replacement when compiling for
speed
(‘sra-max-scalarization-size-Ospeed’)
or
size
(‘sra-max-scalarization-size-Osize’) respectively.
tm-max-aggregate-size
When making copies of thread-local variables in a transaction, this
parameter specifies the size in bytes after which variables are saved
with the logging functions as opposed to save/restore code sequence
pairs. This option only applies when using ‘-fgnu-tm’.
graphite-max-nb-scop-params
To avoid exponential effects in the Graphite loop transforms, the
number of parameters in a Static Control Part (SCoP) is bounded.
The default value is 10 parameters, a value of zero can be used to
lift the bound. A variable whose value is unknown at compilation
time and defined outside a SCoP is a parameter of the SCoP.
loop-block-tile-size
Loop blocking or strip mining transforms, enabled with
‘-floop-block’ or ‘-floop-strip-mine’, strip mine each loop in
the loop nest by a given number of iterations. The strip length
can be changed using the ‘loop-block-tile-size’ parameter.
The default value is 51 iterations.
loop-unroll-jam-size
Specify the unroll factor for the ‘-floop-unroll-and-jam’ option.
The default value is 4.
loop-unroll-jam-depth
Specify the dimension to be unrolled (counting from the most inner
loop) for the ‘-floop-unroll-and-jam’. The default value is 2.
ipa-cp-value-list-size
IPA-CP attempts to track all possible values and types passed to a
function’s parameter in order to propagate them and perform devirtualization. ‘ipa-cp-value-list-size’ is the maximum number
of values and types it stores per one formal parameter of a function.
ipa-cp-eval-threshold
IPA-CP calculates its own score of cloning profitability heuristics
and performs those cloning opportunities with scores that exceed
‘ipa-cp-eval-threshold’.
ipa-cp-recursion-penalty
Percentage penalty the recursive functions will receive when they
are evaluated for cloning.

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ipa-cp-single-call-penalty
Percentage penalty functions containing a single call to another
function will receive when they are evaluated for cloning.
ipa-max-agg-items
IPA-CP is also capable to propagate a number of scalar values
passed in an aggregate. ‘ipa-max-agg-items’ controls the maximum number of such values per one parameter.
ipa-cp-loop-hint-bonus
When IPA-CP determines that a cloning candidate would make
the number of iterations of a loop known, it adds a bonus of
‘ipa-cp-loop-hint-bonus’ to the profitability score of the
candidate.
ipa-cp-array-index-hint-bonus
When IPA-CP determines that a cloning candidate would
make the index of an array access known, it adds a bonus of
‘ipa-cp-array-index-hint-bonus’ to the profitability score of
the candidate.
ipa-max-aa-steps
During its analysis of function bodies, IPA-CP employs alias
analysis in order to track values pointed to by function parameters.
In order not spend too much time analyzing huge functions, it
gives up and consider all memory clobbered after examining
‘ipa-max-aa-steps’ statements modifying memory.
lto-partitions
Specify desired number of partitions produced during WHOPR
compilation. The number of partitions should exceed the number
of CPUs used for compilation. The default value is 32.
lto-min-partition
Size of minimal partition for WHOPR (in estimated instructions).
This prevents expenses of splitting very small programs into too
many partitions.
lto-max-partition
Size of max partition for WHOPR (in estimated instructions). to
provide an upper bound for individual size of partition. Meant to
be used only with balanced partitioning.
cxx-max-namespaces-for-diagnostic-help
The maximum number of namespaces to consult for suggestions
when C++ name lookup fails for an identifier. The default is 1000.
sink-frequency-threshold
The maximum relative execution frequency (in percents) of the target block relative to a statement’s original block to allow statement
sinking of a statement. Larger numbers result in more aggressive

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statement sinking. The default value is 75. A small positive adjustment is applied for statements with memory operands as those
are even more profitable so sink.
max-stores-to-sink
The maximum number of conditional store pairs that can be
sunk. Set to 0 if either vectorization (‘-ftree-vectorize’)
or if-conversion (‘-ftree-loop-if-convert’) is disabled. The
default is 2.
allow-store-data-races
Allow optimizers to introduce new data races on stores. Set to
1 to allow, otherwise to 0. This option is enabled by default at
optimization level ‘-Ofast’.
case-values-threshold
The smallest number of different values for which it is best to use
a jump-table instead of a tree of conditional branches. If the value
is 0, use the default for the machine. The default is 0.
tree-reassoc-width
Set the maximum number of instructions executed in parallel in reassociated tree. This parameter overrides target dependent heuristics used by default if has non zero value.
sched-pressure-algorithm
Choose between the two available implementations of
‘-fsched-pressure’. Algorithm 1 is the original implementation
and is the more likely to prevent instructions from being reordered.
Algorithm 2 was designed to be a compromise between the
relatively conservative approach taken by algorithm 1 and the
rather aggressive approach taken by the default scheduler. It relies
more heavily on having a regular register file and accurate register
pressure classes. See ‘haifa-sched.c’ in the GCC sources for
more details.
The default choice depends on the target.
max-slsr-cand-scan
Set the maximum number of existing candidates that are considered when seeking a basis for a new straight-line strength reduction
candidate.
asan-globals
Enable buffer overflow detection for global objects.
This
kind of protection is enabled by default if you are using
‘-fsanitize=address’ option.
To disable global objects
protection use ‘--param asan-globals=0’.
asan-stack
Enable buffer overflow detection for stack objects. This kind of
protection is enabled by default when using ‘-fsanitize=address’.
To disable stack protection use ‘--param asan-stack=0’ option.

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asan-instrument-reads
Enable buffer overflow detection for memory reads.
This
kind of protection is enabled by default when using
‘-fsanitize=address’. To disable memory reads protection use
‘--param asan-instrument-reads=0’.
asan-instrument-writes
Enable buffer overflow detection for memory writes.
This
kind of protection is enabled by default when using
‘-fsanitize=address’. To disable memory writes protection use
‘--param asan-instrument-writes=0’ option.
asan-memintrin
Enable detection for built-in functions. This kind of protection is
enabled by default when using ‘-fsanitize=address’. To disable
built-in functions protection use ‘--param asan-memintrin=0’.
asan-use-after-return
Enable detection of use-after-return. This kind of protection is
enabled by default when using the ‘-fsanitize=address’ option.
To disable it use ‘--param asan-use-after-return=0’.
Note: By default the check is disabled at run time. To enable it, add
detect_stack_use_after_return=1 to the environment variable
ASAN_OPTIONS.
asan-instrumentation-with-call-threshold
If number of memory accesses in function being instrumented
is greater or equal to this number, use callbacks instead
of inline checks. E.g. to disable inline code use ‘--param
asan-instrumentation-with-call-threshold=0’.
use-after-scope-direct-emission-threshold
If the size of a local variable in bytes is smaller or equal to this
number, directly poison (or unpoison) shadow memory instead of
using run-time callbacks. The default value is 256.
chkp-max-ctor-size
Static constructors generated by Pointer Bounds Checker may become very large and significantly increase compile time at optimization level ‘-O1’ and higher. This parameter is a maximum number
of statements in a single generated constructor. Default value is
5000.
max-fsm-thread-path-insns
Maximum number of instructions to copy when duplicating blocks
on a finite state automaton jump thread path. The default is 100.
max-fsm-thread-length
Maximum number of basic blocks on a finite state automaton jump
thread path. The default is 10.

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max-fsm-thread-paths
Maximum number of new jump thread paths to create for a finite
state automaton. The default is 50.
parloops-chunk-size
Chunk size of omp schedule for loops parallelized by parloops. The
default is 0.
parloops-schedule
Schedule type of omp schedule for loops parallelized by parloops
(static, dynamic, guided, auto, runtime). The default is static.
parloops-min-per-thread
The minimum number of iterations per thread of an innermost parallelized loop for which the parallelized variant is prefered over the
single threaded one. The default is 100. Note that for a parallelized
loop nest the minimum number of iterations of the outermost loop
per thread is two.
max-ssa-name-query-depth
Maximum depth of recursion when querying properties of SSA
names in things like fold routines. One level of recursion corresponds to following a use-def chain.
hsa-gen-debug-stores
Enable emission of special debug stores within HSA kernels
which are then read and reported by libgomp plugin. Generation of these stores is disabled by default, use ‘--param
hsa-gen-debug-stores=1’ to enable it.
max-speculative-devirt-maydefs
The maximum number of may-defs we analyze when looking for a
must-def specifying the dynamic type of an object that invokes a
virtual call we may be able to devirtualize speculatively.
max-vrp-switch-assertions
The maximum number of assertions to add along the default edge
of a switch statement during VRP. The default is 10.
unroll-jam-min-percent
The minimum percentage of memory references that must be optimized away for the unroll-and-jam transformation to be considered
profitable.
unroll-jam-max-unroll
The maximum number of times the outer loop should be unrolled
by the unroll-and-jam transformation.

3.11 Program Instrumentation Options
GCC supports a number of command-line options that control adding run-time instrumentation to the code it normally generates. For example, one purpose of instrumentation is

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collect profiling statistics for use in finding program hot spots, code coverage analysis, or
profile-guided optimizations. Another class of program instrumentation is adding run-time
checking to detect programming errors like invalid pointer dereferences or out-of-bounds
array accesses, as well as deliberately hostile attacks such as stack smashing or C++ vtable
hijacking. There is also a general hook which can be used to implement other forms of
tracing or function-level instrumentation for debug or program analysis purposes.
-p

Generate extra code to write profile information suitable for the analysis program prof. You must use this option when compiling the source files you want
data about, and you must also use it when linking.

-pg

Generate extra code to write profile information suitable for the analysis program gprof. You must use this option when compiling the source files you want
data about, and you must also use it when linking.

-fprofile-arcs
Add code so that program flow arcs are instrumented. During execution the
program records how many times each branch and call is executed and how
many times it is taken or returns. On targets that support constructors with
priority support, profiling properly handles constructors, destructors and C++
constructors (and destructors) of classes which are used as a type of a global
variable.
When the compiled program exits it saves this data to a file called
‘auxname.gcda’ for each source file. The data may be used for profile-directed
optimizations (‘-fbranch-probabilities’), or for test coverage analysis
(‘-ftest-coverage’). Each object file’s auxname is generated from the name
of the output file, if explicitly specified and it is not the final executable,
otherwise it is the basename of the source file. In both cases any suffix is
removed (e.g. ‘foo.gcda’ for input file ‘dir/foo.c’, or ‘dir/foo.gcda’ for
output file specified as ‘-o dir/foo.o’). See Section 10.5 [Cross-profiling],
page 832.
--coverage
This option is used to compile and link code instrumented for coverage analysis.
The option is a synonym for ‘-fprofile-arcs’ ‘-ftest-coverage’ (when compiling) and ‘-lgcov’ (when linking). See the documentation for those options
for more details.
• Compile the source files with ‘-fprofile-arcs’ plus optimization and
code generation options. For test coverage analysis, use the additional
‘-ftest-coverage’ option. You do not need to profile every source file in
a program.
• Compile the source files additionally with ‘-fprofile-abs-path’ to create
absolute path names in the ‘.gcno’ files. This allows gcov to find the
correct sources in projects where compilations occur with different working
directories.
• Link your object files with ‘-lgcov’ or ‘-fprofile-arcs’ (the latter implies
the former).
• Run the program on a representative workload to generate the arc profile
information. This may be repeated any number of times. You can run

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concurrent instances of your program, and provided that the file system
supports locking, the data files will be correctly updated. Unless a strict
ISO C dialect option is in effect, fork calls are detected and correctly
handled without double counting.
• For profile-directed optimizations, compile the source files again
with the same optimization and code generation options plus
‘-fbranch-probabilities’ (see Section 3.10 [Options that Control
Optimization], page 114).
• For test coverage analysis, use gcov to produce human readable information
from the ‘.gcno’ and ‘.gcda’ files. Refer to the gcov documentation for
further information.
With ‘-fprofile-arcs’, for each function of your program GCC creates a
program flow graph, then finds a spanning tree for the graph. Only arcs that
are not on the spanning tree have to be instrumented: the compiler adds code
to count the number of times that these arcs are executed. When an arc is
the only exit or only entrance to a block, the instrumentation code can be
added to the block; otherwise, a new basic block must be created to hold the
instrumentation code.
-ftest-coverage
Produce a notes file that the gcov code-coverage utility (see Chapter 10 [gcov—
a Test Coverage Program], page 821) can use to show program coverage. Each
source file’s note file is called ‘auxname.gcno’. Refer to the ‘-fprofile-arcs’
option above for a description of auxname and instructions on how to generate
test coverage data. Coverage data matches the source files more closely if you
do not optimize.
-fprofile-abs-path
Automatically convert relative source file names to absolute path names in the
‘.gcno’ files. This allows gcov to find the correct sources in projects where
compilations occur with different working directories.
-fprofile-dir=path
Set the directory to search for the profile data files in to path. This
option affects only the profile data generated by ‘-fprofile-generate’,
‘-ftest-coverage’, ‘-fprofile-arcs’ and used by ‘-fprofile-use’ and
‘-fbranch-probabilities’ and its related options. Both absolute and relative
paths can be used. By default, GCC uses the current directory as path, thus
the profile data file appears in the same directory as the object file.
-fprofile-generate
-fprofile-generate=path
Enable options usually used for instrumenting application to produce profile
useful for later recompilation with profile feedback based optimization. You
must use ‘-fprofile-generate’ both when compiling and when linking your
program.
The following options are enabled: ‘-fprofile-arcs’, ‘-fprofile-values’,
‘-fvpt’.

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If path is specified, GCC looks at the path to find the profile feedback data
files. See ‘-fprofile-dir’.
To optimize the program based on the collected profile information, use
‘-fprofile-use’. See Section 3.10 [Optimize Options], page 114, for more
information.
-fprofile-update=method
Alter the update method for an application instrumented for profile feedback
based optimization. The method argument should be one of ‘single’, ‘atomic’
or ‘prefer-atomic’. The first one is useful for single-threaded applications,
while the second one prevents profile corruption by emitting thread-safe code.
Warning: When an application does not properly join all threads (or creates
an detached thread), a profile file can be still corrupted.
Using ‘prefer-atomic’ would be transformed either to ‘atomic’, when supported by a target, or to ‘single’ otherwise. The GCC driver automatically
selects ‘prefer-atomic’ when ‘-pthread’ is present in the command line.
-fsanitize=address
Enable AddressSanitizer, a fast memory error detector. Memory access
instructions are instrumented to detect out-of-bounds and use-after-free bugs.
The option enables ‘-fsanitize-address-use-after-scope’. See https://
github.com/google/sanitizers/wiki/AddressSanitizer for more details.
The run-time behavior can be influenced using the ASAN_OPTIONS environment
variable. When set to help=1, the available options are shown at startup of
the instrumented program. See https://github.com/google/sanitizers/
wiki / AddressSanitizerFlags # run-time-flags for a list of supported
options. The option cannot be combined with ‘-fsanitize=thread’ and/or
‘-fcheck-pointer-bounds’.
-fsanitize=kernel-address
Enable AddressSanitizer for Linux kernel. See https: / / github . com /
google/kasan/wiki for more details. The option cannot be combined with
‘-fcheck-pointer-bounds’.
-fsanitize=pointer-compare
Instrument comparison operation (<, <=, >, >=) with pointer operands.
The option must be combined with either ‘-fsanitize=kernel-address’
or ‘-fsanitize=address’ The option cannot be combined with
‘-fsanitize=thread’ and/or ‘-fcheck-pointer-bounds’. Note: By default
the check is disabled at run time. To enable it, add detect_invalid_
pointer_pairs=2 to the environment variable ASAN_OPTIONS.
Using
detect_invalid_pointer_pairs=1 detects invalid operation only when both
pointers are non-null.
-fsanitize=pointer-subtract
Instrument subtraction with pointer operands. The option must be combined
with either ‘-fsanitize=kernel-address’ or ‘-fsanitize=address’
The option cannot be combined with ‘-fsanitize=thread’ and/or
‘-fcheck-pointer-bounds’. Note: By default the check is disabled at run

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time. To enable it, add detect_invalid_pointer_pairs=2 to the environment variable ASAN_OPTIONS.
Using detect_invalid_pointer_pairs=1
detects invalid operation only when both pointers are non-null.
-fsanitize=thread
Enable ThreadSanitizer, a fast data race detector.
Memory access
instructions are instrumented to detect data race bugs. See https: / /
github . com / google / sanitizers / wiki # threadsanitizer for more
details. The run-time behavior can be influenced using the TSAN_OPTIONS
environment variable; see https: / / github . com / google / sanitizers /
wiki / ThreadSanitizerFlags for a list of supported options. The option
cannot be combined with ‘-fsanitize=address’, ‘-fsanitize=leak’ and/or
‘-fcheck-pointer-bounds’.
Note that sanitized atomic builtins cannot throw exceptions when
operating on invalid memory addresses with non-call exceptions
(‘-fnon-call-exceptions’).
-fsanitize=leak
Enable LeakSanitizer, a memory leak detector. This option only matters for
linking of executables and the executable is linked against a library that overrides malloc and other allocator functions. See https://github.com/google/
sanitizers/wiki/AddressSanitizerLeakSanitizer for more details. The
run-time behavior can be influenced using the LSAN_OPTIONS environment variable. The option cannot be combined with ‘-fsanitize=thread’.
-fsanitize=undefined
Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector. Various computations are instrumented to detect undefined behavior at runtime.
Current suboptions are:
-fsanitize=shift
This option enables checking that the result of a shift operation
is not undefined.
Note that what exactly is considered
undefined differs slightly between C and C++, as well as between
ISO C90 and C99, etc.
This option has two suboptions,
‘-fsanitize=shift-base’ and ‘-fsanitize=shift-exponent’.
-fsanitize=shift-exponent
This option enables checking that the second argument of a shift
operation is not negative and is smaller than the precision of the
promoted first argument.
-fsanitize=shift-base
If the second argument of a shift operation is within range, check
that the result of a shift operation is not undefined. Note that what
exactly is considered undefined differs slightly between C and C++,
as well as between ISO C90 and C99, etc.
-fsanitize=integer-divide-by-zero
Detect integer division by zero as well as INT_MIN / -1 division.

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177

-fsanitize=unreachable
With this option, the compiler turns the __builtin_unreachable
call into a diagnostics message call instead. When reaching the
__builtin_unreachable call, the behavior is undefined.
-fsanitize=vla-bound
This option instructs the compiler to check that the size of a variable length array is positive.
-fsanitize=null
This option enables pointer checking. Particularly, the application
built with this option turned on will issue an error message when
it tries to dereference a NULL pointer, or if a reference (possibly
an rvalue reference) is bound to a NULL pointer, or if a method is
invoked on an object pointed by a NULL pointer.
-fsanitize=return
This option enables return statement checking. Programs built
with this option turned on will issue an error message when the
end of a non-void function is reached without actually returning a
value. This option works in C++ only.
-fsanitize=signed-integer-overflow
This option enables signed integer overflow checking. We check that
the result of +, *, and both unary and binary - does not overflow
in the signed arithmetics. Note, integer promotion rules must be
taken into account. That is, the following is not an overflow:
signed char a = SCHAR_MAX;
a++;

-fsanitize=bounds
This option enables instrumentation of array bounds. Various out
of bounds accesses are detected. Flexible array members, flexible
array member-like arrays, and initializers of variables with static
storage are not instrumented. The option cannot be combined with
‘-fcheck-pointer-bounds’.
-fsanitize=bounds-strict
This option enables strict instrumentation of array bounds. Most
out of bounds accesses are detected, including flexible array members and flexible array member-like arrays. Initializers of variables
with static storage are not instrumented. The option cannot be
combined with ‘-fcheck-pointer-bounds’.
-fsanitize=alignment
This option enables checking of alignment of pointers when they are
dereferenced, or when a reference is bound to insufficiently aligned
target, or when a method or constructor is invoked on insufficiently
aligned object.

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Using the GNU Compiler Collection (GCC)

-fsanitize=object-size
This option enables instrumentation of memory references using the
__builtin_object_size function. Various out of bounds pointer
accesses are detected.
-fsanitize=float-divide-by-zero
Detect floating-point division by zero.
Unlike other similar
options, ‘-fsanitize=float-divide-by-zero’ is not enabled by
‘-fsanitize=undefined’, since floating-point division by zero can
be a legitimate way of obtaining infinities and NaNs.
-fsanitize=float-cast-overflow
This option enables floating-point type to integer conversion checking. We check that the result of the conversion does not overflow.
Unlike other similar options, ‘-fsanitize=float-cast-overflow’
is not enabled by ‘-fsanitize=undefined’. This option does not
work well with FE_INVALID exceptions enabled.
-fsanitize=nonnull-attribute
This option enables instrumentation of calls, checking whether null
values are not passed to arguments marked as requiring a non-null
value by the nonnull function attribute.
-fsanitize=returns-nonnull-attribute
This option enables instrumentation of return statements in functions marked with returns_nonnull function attribute, to detect
returning of null values from such functions.
-fsanitize=bool
This option enables instrumentation of loads from bool. If a value
other than 0/1 is loaded, a run-time error is issued.
-fsanitize=enum
This option enables instrumentation of loads from an enum type.
If a value outside the range of values for the enum type is loaded,
a run-time error is issued.
-fsanitize=vptr
This option enables instrumentation of C++ member function calls,
member accesses and some conversions between pointers to base
and derived classes, to verify the referenced object has the correct
dynamic type.
-fsanitize=pointer-overflow
This option enables instrumentation of pointer arithmetics. If the
pointer arithmetics overflows, a run-time error is issued.
-fsanitize=builtin
This option enables instrumentation of arguments to selected
builtin functions. If an invalid value is passed to such arguments,
a run-time error is issued. E.g. passing 0 as the argument to
__builtin_ctz or __builtin_clz invokes undefined behavior
and is diagnosed by this option.

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While ‘-ftrapv’ causes traps for signed overflows to be emitted,
‘-fsanitize=undefined’ gives a diagnostic message. This currently works
only for the C family of languages.
-fno-sanitize=all
This option disables all previously enabled sanitizers. ‘-fsanitize=all’ is not
allowed, as some sanitizers cannot be used together.
-fasan-shadow-offset=number
This option forces GCC to use custom shadow offset in AddressSanitizer checks.
It is useful for experimenting with different shadow memory layouts in Kernel
AddressSanitizer.
-fsanitize-sections=s1,s2,...
Sanitize global variables in selected user-defined sections. si may contain wildcards.
-fsanitize-recover[=opts]
‘-fsanitize-recover=’ controls error recovery mode for sanitizers mentioned
in comma-separated list of opts. Enabling this option for a sanitizer component
causes it to attempt to continue running the program as if no error happened.
This means multiple runtime errors can be reported in a single program run,
and the exit code of the program may indicate success even when errors have
been reported. The ‘-fno-sanitize-recover=’ option can be used to alter
this behavior: only the first detected error is reported and program then exits
with a non-zero exit code.
Currently this feature only works for ‘-fsanitize=undefined’ (and its
suboptions except for ‘-fsanitize=unreachable’ and ‘-fsanitize=return’),
‘-fsanitize=float-cast-overflow’, ‘-fsanitize=float-divide-by-zero’,
‘-fsanitize=bounds-strict’,
‘-fsanitize=kernel-address’
and
‘-fsanitize=address’. For these sanitizers error recovery is turned on by
default, except ‘-fsanitize=address’, for which this feature is experimental.
‘-fsanitize-recover=all’ and ‘-fno-sanitize-recover=all’ is also
accepted, the former enables recovery for all sanitizers that support it, the
latter disables recovery for all sanitizers that support it.
Even if a recovery mode is turned on the compiler side, it needs to be also
enabled on the runtime library side, otherwise the failures are still fatal. The
runtime library defaults to halt_on_error=0 for ThreadSanitizer and UndefinedBehaviorSanitizer, while default value for AddressSanitizer is halt_on_
error=1. This can be overridden through setting the halt_on_error flag in
the corresponding environment variable.
Syntax without an explicit opts parameter is deprecated. It is equivalent to
specifying an opts list of:
undefined,float-cast-overflow,float-divide-by-zero,bounds-strict

-fsanitize-address-use-after-scope
Enable sanitization of local variables to detect use-after-scope bugs. The option
sets ‘-fstack-reuse’ to ‘none’.

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Using the GNU Compiler Collection (GCC)

-fsanitize-undefined-trap-on-error
The ‘-fsanitize-undefined-trap-on-error’ option instructs the compiler to
report undefined behavior using __builtin_trap rather than a libubsan library routine. The advantage of this is that the libubsan library is not needed
and is not linked in, so this is usable even in freestanding environments.
-fsanitize-coverage=trace-pc
Enable coverage-guided fuzzing code instrumentation.
sanitizer_cov_trace_pc into every basic block.

Inserts a call to __

-fsanitize-coverage=trace-cmp
Enable dataflow guided fuzzing code instrumentation.
Inserts a call
to
__sanitizer_cov_trace_cmp1,
__sanitizer_cov_trace_cmp2,
__sanitizer_cov_trace_cmp4 or __sanitizer_cov_trace_cmp8 for integral
comparison with both operands variable or __sanitizer_cov_trace_
const_cmp1,
__sanitizer_cov_trace_const_cmp2,
__sanitizer_cov_
trace_const_cmp4 or __sanitizer_cov_trace_const_cmp8 for integral
comparison with one operand constant, __sanitizer_cov_trace_cmpf
or __sanitizer_cov_trace_cmpd for float or double comparisons and
__sanitizer_cov_trace_switch for switch statements.
-fbounds-check
For front ends that support it, generate additional code to check that indices
used to access arrays are within the declared range. This is currently only
supported by the Fortran front end, where this option defaults to false.
-fcheck-pointer-bounds
Enable Pointer Bounds Checker instrumentation. Each memory reference is
instrumented with checks of the pointer used for memory access against bounds
associated with that pointer.
Currently there is only an implementation for Intel MPX available, thus x86
GNU/Linux target and ‘-mmpx’ are required to enable this feature. MPX-based
instrumentation requires a runtime library to enable MPX in hardware and
handle bounds violation signals. By default when ‘-fcheck-pointer-bounds’
and ‘-mmpx’ options are used to link a program, the GCC driver links against the
‘libmpx’ and ‘libmpxwrappers’ libraries. Bounds checking on calls to dynamic
libraries requires a linker with ‘-z bndplt’ support; if GCC was configured with
a linker without support for this option (including the Gold linker and older
versions of ld), a warning is given if you link with ‘-mmpx’ without also specifying
‘-static’, since the overall effectiveness of the bounds checking protection is
reduced. See also ‘-static-libmpxwrappers’.
MPX-based instrumentation may be used for debugging and also may be
included in production code to increase program security. Depending on
usage, you may have different requirements for the runtime library. The
current version of the MPX runtime library is more oriented for use as a
debugging tool. MPX runtime library usage implies ‘-lpthread’. See also
‘-static-libmpx’. The runtime library behavior can be influenced using
various CHKP_RT_* environment variables. See https://gcc.gnu.org/wiki/
Intel%20MPX%20support%20in%20the%20GCC%20compiler for more details.

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Generated instrumentation may be controlled by various ‘-fchkp-*’ options
and by the bnd_variable_size structure field attribute (see Section 6.33
[Type Attributes], page 524) and bnd_legacy, and bnd_instrument function
attributes (see Section 6.31 [Function Attributes], page 464). GCC also
provides a number of built-in functions for controlling the Pointer Bounds
Checker. See Section 6.57 [Pointer Bounds Checker builtins], page 611, for
more information.
-fchkp-check-incomplete-type
Generate pointer bounds checks for variables with incomplete type. Enabled
by default.
-fchkp-narrow-bounds
Controls bounds used by Pointer Bounds Checker for pointers to object
fields. If narrowing is enabled then field bounds are used. Otherwise object
bounds are used.
See also ‘-fchkp-narrow-to-innermost-array’ and
‘-fchkp-first-field-has-own-bounds’. Enabled by default.
-fchkp-first-field-has-own-bounds
Forces Pointer Bounds Checker to use narrowed bounds for the address of the
first field in the structure. By default a pointer to the first field has the same
bounds as a pointer to the whole structure.
-fchkp-flexible-struct-trailing-arrays
Forces Pointer Bounds Checker to treat all trailing arrays in structures as possibly flexible. By default only array fields with zero length or that are marked
with attribute bnd variable size are treated as flexible.
-fchkp-narrow-to-innermost-array
Forces Pointer Bounds Checker to use bounds of the innermost arrays in case
of nested static array access. By default this option is disabled and bounds of
the outermost array are used.
-fchkp-optimize
Enables Pointer Bounds Checker optimizations. Enabled by default at optimization levels ‘-O’, ‘-O2’, ‘-O3’.
-fchkp-use-fast-string-functions
Enables use of *_nobnd versions of string functions (not copying bounds) by
Pointer Bounds Checker. Disabled by default.
-fchkp-use-nochk-string-functions
Enables use of *_nochk versions of string functions (not checking bounds) by
Pointer Bounds Checker. Disabled by default.
-fchkp-use-static-bounds
Allow Pointer Bounds Checker to generate static bounds holding bounds of
static variables. Enabled by default.
-fchkp-use-static-const-bounds
Use statically-initialized bounds for constant bounds instead of generating them each time they are required.
By default enabled when
‘-fchkp-use-static-bounds’ is enabled.

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Using the GNU Compiler Collection (GCC)

-fchkp-treat-zero-dynamic-size-as-infinite
With this option, objects with incomplete type whose dynamically-obtained size
is zero are treated as having infinite size instead by Pointer Bounds Checker.
This option may be helpful if a program is linked with a library missing size
information for some symbols. Disabled by default.
-fchkp-check-read
Instructs Pointer Bounds Checker to generate checks for all read accesses to
memory. Enabled by default.
-fchkp-check-write
Instructs Pointer Bounds Checker to generate checks for all write accesses to
memory. Enabled by default.
-fchkp-store-bounds
Instructs Pointer Bounds Checker to generate bounds stores for pointer writes.
Enabled by default.
-fchkp-instrument-calls
Instructs Pointer Bounds Checker to pass pointer bounds to calls. Enabled by
default.
-fchkp-instrument-marked-only
Instructs Pointer Bounds Checker to instrument only functions marked with the
bnd_instrument attribute (see Section 6.31 [Function Attributes], page 464).
Disabled by default.
-fchkp-use-wrappers
Allows Pointer Bounds Checker to replace calls to built-in functions with calls
to wrapper functions. When ‘-fchkp-use-wrappers’ is used to link a program, the GCC driver automatically links against ‘libmpxwrappers’. See also
‘-static-libmpxwrappers’. Enabled by default.
-fcf-protection=[full|branch|return|none]
Enable code instrumentation of control-flow transfers to increase program security by checking that target addresses of control-flow transfer instructions
(such as indirect function call, function return, indirect jump) are valid. This
prevents diverting the flow of control to an unexpected target. This is intended
to protect against such threats as Return-oriented Programming (ROP), and
similarly call/jmp-oriented programming (COP/JOP).
The value branch tells the compiler to implement checking of validity of controlflow transfer at the point of indirect branch instructions, i.e. call/jmp instructions. The value return implements checking of validity at the point of returning from a function. The value full is an alias for specifying both branch and
return. The value none turns off instrumentation.
The macro __CET__ is defined when ‘-fcf-protection’ is used. The first bit
of __CET__ is set to 1 for the value branch and the second bit of __CET__ is set
to 1 for the return.
You can also use the nocf_check attribute to identify which functions and calls
should be skipped from instrumentation (see Section 6.31 [Function Attributes],
page 464).

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Currently the x86 GNU/Linux target provides an implementation based on
Intel Control-flow Enforcement Technology (CET).
-fstack-protector
Emit extra code to check for buffer overflows, such as stack smashing attacks.
This is done by adding a guard variable to functions with vulnerable objects.
This includes functions that call alloca, and functions with buffers larger than
8 bytes. The guards are initialized when a function is entered and then checked
when the function exits. If a guard check fails, an error message is printed and
the program exits.
-fstack-protector-all
Like ‘-fstack-protector’ except that all functions are protected.
-fstack-protector-strong
Like ‘-fstack-protector’ but includes additional functions to be protected
— those that have local array definitions, or have references to local frame
addresses.
-fstack-protector-explicit
Like ‘-fstack-protector’ but only protects those functions which have the
stack_protect attribute.
-fstack-check
Generate code to verify that you do not go beyond the boundary of the stack.
You should specify this flag if you are running in an environment with multiple
threads, but you only rarely need to specify it in a single-threaded environment
since stack overflow is automatically detected on nearly all systems if there is
only one stack.
Note that this switch does not actually cause checking to be done; the operating
system or the language runtime must do that. The switch causes generation of
code to ensure that they see the stack being extended.
You can additionally specify a string parameter: ‘no’ means no checking,
‘generic’ means force the use of old-style checking, ‘specific’ means use the
best checking method and is equivalent to bare ‘-fstack-check’.
Old-style checking is a generic mechanism that requires no specific target support in the compiler but comes with the following drawbacks:
1. Modified allocation strategy for large objects: they are always allocated
dynamically if their size exceeds a fixed threshold. Note this may change
the semantics of some code.
2. Fixed limit on the size of the static frame of functions: when it is topped
by a particular function, stack checking is not reliable and a warning is
issued by the compiler.
3. Inefficiency: because of both the modified allocation strategy and the
generic implementation, code performance is hampered.
Note that old-style stack checking is also the fallback method for ‘specific’ if
no target support has been added in the compiler.

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‘-fstack-check=’ is designed for Ada’s needs to detect infinite recursion and
stack overflows. ‘specific’ is an excellent choice when compiling Ada code.
It is not generally sufficient to protect against stack-clash attacks. To protect
against those you want ‘-fstack-clash-protection’.
-fstack-clash-protection
Generate code to prevent stack clash style attacks. When this option is enabled,
the compiler will only allocate one page of stack space at a time and each page
is accessed immediately after allocation. Thus, it prevents allocations from
jumping over any stack guard page provided by the operating system.
Most targets do not fully support stack clash protection. However, on those
targets ‘-fstack-clash-protection’ will protect dynamic stack allocations.
‘-fstack-clash-protection’ may also provide limited protection for static
stack allocations if the target supports ‘-fstack-check=specific’.
-fstack-limit-register=reg
-fstack-limit-symbol=sym
-fno-stack-limit
Generate code to ensure that the stack does not grow beyond a certain value,
either the value of a register or the address of a symbol. If a larger stack is
required, a signal is raised at run time. For most targets, the signal is raised
before the stack overruns the boundary, so it is possible to catch the signal
without taking special precautions.
For instance, if the stack starts at absolute address ‘0x80000000’ and grows
downwards, you can use the flags ‘-fstack-limit-symbol=__stack_limit’
and ‘-Wl,--defsym,__stack_limit=0x7ffe0000’ to enforce a stack limit of
128KB. Note that this may only work with the GNU linker.
You can locally override stack limit checking by using the no_stack_limit
function attribute (see Section 6.31 [Function Attributes], page 464).
-fsplit-stack
Generate code to automatically split the stack before it overflows. The resulting
program has a discontiguous stack which can only overflow if the program is
unable to allocate any more memory. This is most useful when running threaded
programs, as it is no longer necessary to calculate a good stack size to use for
each thread. This is currently only implemented for the x86 targets running
GNU/Linux.
When code compiled with ‘-fsplit-stack’ calls code compiled without
‘-fsplit-stack’, there may not be much stack space available for the
latter code to run. If compiling all code, including library code, with
‘-fsplit-stack’ is not an option, then the linker can fix up these calls so that
the code compiled without ‘-fsplit-stack’ always has a large stack. Support
for this is implemented in the gold linker in GNU binutils release 2.21 and
later.
-fvtable-verify=[std|preinit|none]
This option is only available when compiling C++ code. It turns on (or off, if
using ‘-fvtable-verify=none’) the security feature that verifies at run time,

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185

for every virtual call, that the vtable pointer through which the call is made
is valid for the type of the object, and has not been corrupted or overwritten.
If an invalid vtable pointer is detected at run time, an error is reported and
execution of the program is immediately halted.
This option causes run-time data structures to be built at program startup,
which are used for verifying the vtable pointers. The options ‘std’ and
‘preinit’ control the timing of when these data structures are built. In both
cases the data structures are built before execution reaches main. Using
‘-fvtable-verify=std’ causes the data structures to be built after shared
libraries have been loaded and initialized. ‘-fvtable-verify=preinit’ causes
them to be built before shared libraries have been loaded and initialized.
If this option appears multiple times in the command line with different values
specified, ‘none’ takes highest priority over both ‘std’ and ‘preinit’; ‘preinit’
takes priority over ‘std’.
-fvtv-debug
When
used
in
conjunction
with
‘-fvtable-verify=std’
or
‘-fvtable-verify=preinit’, causes debug versions of the runtime
functions for the vtable verification feature to be called. This flag also causes
the compiler to log information about which vtable pointers it finds for each
class. This information is written to a file named ‘vtv_set_ptr_data.log’
in the directory named by the environment variable VTV_LOGS_DIR if that is
defined or the current working directory otherwise.
Note: This feature appends data to the log file. If you want a fresh log file, be
sure to delete any existing one.
-fvtv-counts
This is a debugging flag.
When used in conjunction with
‘-fvtable-verify=std’ or ‘-fvtable-verify=preinit’,
this causes
the compiler to keep track of the total number of virtual calls it encounters
and the number of verifications it inserts. It also counts the number of calls to
certain run-time library functions that it inserts and logs this information for
each compilation unit. The compiler writes this information to a file named
‘vtv_count_data.log’ in the directory named by the environment variable
VTV_LOGS_DIR if that is defined or the current working directory otherwise. It
also counts the size of the vtable pointer sets for each class, and writes this
information to ‘vtv_class_set_sizes.log’ in the same directory.
Note: This feature appends data to the log files. To get fresh log files, be sure
to delete any existing ones.
-finstrument-functions
Generate instrumentation calls for entry and exit to functions. Just after function entry and just before function exit, the following profiling functions are
called with the address of the current function and its call site. (On some platforms, __builtin_return_address does not work beyond the current function,
so the call site information may not be available to the profiling functions otherwise.)
void __cyg_profile_func_enter (void *this_fn,

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void __cyg_profile_func_exit

void *call_site);
(void *this_fn,
void *call_site);

The first argument is the address of the start of the current function, which
may be looked up exactly in the symbol table.
This instrumentation is also done for functions expanded inline in other functions. The profiling calls indicate where, conceptually, the inline function is
entered and exited. This means that addressable versions of such functions
must be available. If all your uses of a function are expanded inline, this may
mean an additional expansion of code size. If you use extern inline in your
C code, an addressable version of such functions must be provided. (This is
normally the case anyway, but if you get lucky and the optimizer always expands the functions inline, you might have gotten away without providing static
copies.)
A function may be given the attribute no_instrument_function, in which case
this instrumentation is not done. This can be used, for example, for the profiling
functions listed above, high-priority interrupt routines, and any functions from
which the profiling functions cannot safely be called (perhaps signal handlers,
if the profiling routines generate output or allocate memory).
-finstrument-functions-exclude-file-list=file,file,...
Set the list of functions that are excluded from instrumentation (see the description of ‘-finstrument-functions’). If the file that contains a function
definition matches with one of file, then that function is not instrumented. The
match is done on substrings: if the file parameter is a substring of the file name,
it is considered to be a match.
For example:
-finstrument-functions-exclude-file-list=/bits/stl,include/sys

excludes any inline function defined in files whose pathnames contain
‘/bits/stl’ or ‘include/sys’.
If, for some reason, you want to include letter ‘,’ in one of sym, write ‘\,’. For
example, ‘-finstrument-functions-exclude-file-list=’\,\,tmp’’ (note
the single quote surrounding the option).
-finstrument-functions-exclude-function-list=sym,sym,...
This is similar to ‘-finstrument-functions-exclude-file-list’, but this
option sets the list of function names to be excluded from instrumentation.
The function name to be matched is its user-visible name, such as
vector blah(const vector &), not the internal mangled name
(e.g., _Z4blahRSt6vectorIiSaIiEE). The match is done on substrings: if the
sym parameter is a substring of the function name, it is considered to be
a match. For C99 and C++ extended identifiers, the function name must be
given in UTF-8, not using universal character names.
-fpatchable-function-entry=N[,M]
Generate N NOPs right at the beginning of each function, with the function
entry point before the M th NOP. If M is omitted, it defaults to 0 so the function entry points to the address just at the first NOP. The NOP instructions

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reserve extra space which can be used to patch in any desired instrumentation at run time, provided that the code segment is writable. The amount of
space is controllable indirectly via the number of NOPs; the NOP instruction
used corresponds to the instruction emitted by the internal GCC back-end interface gen_nop. This behavior is target-specific and may also depend on the
architecture variant and/or other compilation options.
For run-time identification, the starting addresses of these areas, which correspond to their respective function entries minus M, are additionally collected
in the __patchable_function_entries section of the resulting binary.
Note
that
the
value
of
__attribute__ ((patchable_function_
entry (N,M)))
takes
precedence
over
command-line
option
‘-fpatchable-function-entry=N,M’.
This can be used to increase
the area size or to remove it completely on a single function. If N=0, no pad
location is recorded.
The NOP instructions are inserted at—and maybe before, depending on M—the
function entry address, even before the prologue.

3.12 Options Controlling the Preprocessor
These options control the C preprocessor, which is run on each C source file before actual
compilation.
If you use the ‘-E’ option, nothing is done except preprocessing. Some of these options
make sense only together with ‘-E’ because they cause the preprocessor output to be unsuitable for actual compilation.
In addition to the options listed here, there are a number of options to control search
paths for include files documented in Section 3.15 [Directory Options], page 199. Options
to control preprocessor diagnostics are listed in Section 3.8 [Warning Options], page 62.
-D name

Predefine name as a macro, with definition 1.

-D name=definition
The contents of definition are tokenized and processed as if they appeared during translation phase three in a ‘#define’ directive. In particular, the definition
is truncated by embedded newline characters.
If you are invoking the preprocessor from a shell or shell-like program you may
need to use the shell’s quoting syntax to protect characters such as spaces that
have a meaning in the shell syntax.
If you wish to define a function-like macro on the command line, write its
argument list with surrounding parentheses before the equals sign (if any).
Parentheses are meaningful to most shells, so you should quote the option.
With sh and csh, ‘-D’name(args...)=definition’’ works.
‘-D’ and ‘-U’ options are processed in the order they are given on the command
line. All ‘-imacros file’ and ‘-include file’ options are processed after all
‘-D’ and ‘-U’ options.
-U name

Cancel any previous definition of name, either built in or provided with a ‘-D’
option.

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-include file
Process file as if #include "file" appeared as the first line of the primary
source file. However, the first directory searched for file is the preprocessor’s
working directory instead of the directory containing the main source file. If
not found there, it is searched for in the remainder of the #include "..."
search chain as normal.
If multiple ‘-include’ options are given, the files are included in the order they
appear on the command line.
-imacros file
Exactly like ‘-include’, except that any output produced by scanning file is
thrown away. Macros it defines remain defined. This allows you to acquire all
the macros from a header without also processing its declarations.
All files specified by ‘-imacros’ are processed before all files specified by
‘-include’.
-undef

Do not predefine any system-specific or GCC-specific macros. The standard
predefined macros remain defined.

-pthread

Define additional macros required for using the POSIX threads library. You
should use this option consistently for both compilation and linking. This
option is supported on GNU/Linux targets, most other Unix derivatives, and
also on x86 Cygwin and MinGW targets.

-M

Instead of outputting the result of preprocessing, output a rule suitable for make
describing the dependencies of the main source file. The preprocessor outputs
one make rule containing the object file name for that source file, a colon, and
the names of all the included files, including those coming from ‘-include’ or
‘-imacros’ command-line options.
Unless specified explicitly (with ‘-MT’ or ‘-MQ’), the object file name consists of
the name of the source file with any suffix replaced with object file suffix and
with any leading directory parts removed. If there are many included files then
the rule is split into several lines using ‘\’-newline. The rule has no commands.
This option does not suppress the preprocessor’s debug output, such as ‘-dM’.
To avoid mixing such debug output with the dependency rules you should explicitly specify the dependency output file with ‘-MF’, or use an environment
variable like DEPENDENCIES_OUTPUT (see Section 3.20 [Environment Variables],
page 422). Debug output is still sent to the regular output stream as normal.
Passing ‘-M’ to the driver implies ‘-E’, and suppresses warnings with an implicit
‘-w’.

-MM

Like ‘-M’ but do not mention header files that are found in system header
directories, nor header files that are included, directly or indirectly, from such
a header.
This implies that the choice of angle brackets or double quotes in an ‘#include’
directive does not in itself determine whether that header appears in ‘-MM’
dependency output.

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-MF file

When used with ‘-M’ or ‘-MM’, specifies a file to write the dependencies to. If
no ‘-MF’ switch is given the preprocessor sends the rules to the same place it
would send preprocessed output.
When used with the driver options ‘-MD’ or ‘-MMD’, ‘-MF’ overrides the default
dependency output file.
If file is ‘-’, then the dependencies are written to ‘stdout’.

-MG

In conjunction with an option such as ‘-M’ requesting dependency generation,
‘-MG’ assumes missing header files are generated files and adds them to the
dependency list without raising an error. The dependency filename is taken
directly from the #include directive without prepending any path. ‘-MG’ also
suppresses preprocessed output, as a missing header file renders this useless.
This feature is used in automatic updating of makefiles.

-MP

This option instructs CPP to add a phony target for each dependency other
than the main file, causing each to depend on nothing. These dummy rules
work around errors make gives if you remove header files without updating the
‘Makefile’ to match.
This is typical output:
test.o: test.c test.h
test.h:

-MT target
Change the target of the rule emitted by dependency generation. By default
CPP takes the name of the main input file, deletes any directory components
and any file suffix such as ‘.c’, and appends the platform’s usual object suffix.
The result is the target.
An ‘-MT’ option sets the target to be exactly the string you specify. If you want
multiple targets, you can specify them as a single argument to ‘-MT’, or use
multiple ‘-MT’ options.
For example, ‘-MT ’$(objpfx)foo.o’’ might give
$(objpfx)foo.o: foo.c

-MQ target
Same as ‘-MT’, but it quotes any characters which are special to Make.
‘-MQ ’$(objpfx)foo.o’’ gives
$$(objpfx)foo.o: foo.c

The default target is automatically quoted, as if it were given with ‘-MQ’.
-MD

‘-MD’ is equivalent to ‘-M -MF file’, except that ‘-E’ is not implied. The driver
determines file based on whether an ‘-o’ option is given. If it is, the driver uses
its argument but with a suffix of ‘.d’, otherwise it takes the name of the input
file, removes any directory components and suffix, and applies a ‘.d’ suffix.
If ‘-MD’ is used in conjunction with ‘-E’, any ‘-o’ switch is understood to specify
the dependency output file (see [-MF], page 188), but if used without ‘-E’, each
‘-o’ is understood to specify a target object file.
Since ‘-E’ is not implied, ‘-MD’ can be used to generate a dependency output
file as a side effect of the compilation process.

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-MMD

Using the GNU Compiler Collection (GCC)

Like ‘-MD’ except mention only user header files, not system header files.

-fpreprocessed
Indicate to the preprocessor that the input file has already been preprocessed.
This suppresses things like macro expansion, trigraph conversion, escaped newline splicing, and processing of most directives. The preprocessor still recognizes
and removes comments, so that you can pass a file preprocessed with ‘-C’ to the
compiler without problems. In this mode the integrated preprocessor is little
more than a tokenizer for the front ends.
‘-fpreprocessed’ is implicit if the input file has one of the extensions ‘.i’,
‘.ii’ or ‘.mi’. These are the extensions that GCC uses for preprocessed files
created by ‘-save-temps’.
-fdirectives-only
When preprocessing, handle directives, but do not expand macros.
The option’s behavior depends on the ‘-E’ and ‘-fpreprocessed’ options.
With ‘-E’, preprocessing is limited to the handling of directives such as #define,
#ifdef, and #error. Other preprocessor operations, such as macro expansion
and trigraph conversion are not performed. In addition, the ‘-dD’ option is
implicitly enabled.
With ‘-fpreprocessed’, predefinition of command line and most builtin macros
is disabled. Macros such as __LINE__, which are contextually dependent, are
handled normally. This enables compilation of files previously preprocessed
with -E -fdirectives-only.
With both ‘-E’ and ‘-fpreprocessed’, the rules for ‘-fpreprocessed’ take
precedence. This enables full preprocessing of files previously preprocessed
with -E -fdirectives-only.
-fdollars-in-identifiers
Accept ‘$’ in identifiers.
-fextended-identifiers
Accept universal character names in identifiers. This option is enabled by default for C99 (and later C standard versions) and C++.
-fno-canonical-system-headers
When preprocessing, do not shorten system header paths with canonicalization.
-ftabstop=width
Set the distance between tab stops. This helps the preprocessor report correct
column numbers in warnings or errors, even if tabs appear on the line. If the
value is less than 1 or greater than 100, the option is ignored. The default is 8.
-ftrack-macro-expansion[=level]
Track locations of tokens across macro expansions. This allows the compiler to
emit diagnostic about the current macro expansion stack when a compilation
error occurs in a macro expansion. Using this option makes the preprocessor
and the compiler consume more memory. The level parameter can be used
to choose the level of precision of token location tracking thus decreasing the
memory consumption if necessary. Value ‘0’ of level de-activates this option.

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Value ‘1’ tracks tokens locations in a degraded mode for the sake of minimal
memory overhead. In this mode all tokens resulting from the expansion of an
argument of a function-like macro have the same location. Value ‘2’ tracks
tokens locations completely. This value is the most memory hungry. When this
option is given no argument, the default parameter value is ‘2’.
Note that -ftrack-macro-expansion=2 is activated by default.
-fmacro-prefix-map=old=new
When preprocessing files residing in directory ‘old’, expand the __FILE__ and
__BASE_FILE__ macros as if the files resided in directory ‘new’ instead. This
can be used to change an absolute path to a relative path by using ‘.’ for
new which can result in more reproducible builds that are location independent. This option also affects __builtin_FILE() during compilation. See also
‘-ffile-prefix-map’.
-fexec-charset=charset
Set the execution character set, used for string and character constants. The
default is UTF-8. charset can be any encoding supported by the system’s iconv
library routine.
-fwide-exec-charset=charset
Set the wide execution character set, used for wide string and character constants. The default is UTF-32 or UTF-16, whichever corresponds to the width
of wchar_t. As with ‘-fexec-charset’, charset can be any encoding supported
by the system’s iconv library routine; however, you will have problems with
encodings that do not fit exactly in wchar_t.
-finput-charset=charset
Set the input character set, used for translation from the character set of the
input file to the source character set used by GCC. If the locale does not specify,
or GCC cannot get this information from the locale, the default is UTF-8. This
can be overridden by either the locale or this command-line option. Currently
the command-line option takes precedence if there’s a conflict. charset can be
any encoding supported by the system’s iconv library routine.
-fpch-deps
When using precompiled headers (see Section 3.21 [Precompiled Headers],
page 425), this flag causes the dependency-output flags to also list the
files from the precompiled header’s dependencies. If not specified, only the
precompiled header are listed and not the files that were used to create it,
because those files are not consulted when a precompiled header is used.
-fpch-preprocess
This option allows use of a precompiled header (see Section 3.21 [Precompiled
Headers], page 425) together with ‘-E’. It inserts a special #pragma, #pragma
GCC pch_preprocess "filename" in the output to mark the place where the
precompiled header was found, and its filename. When ‘-fpreprocessed’ is in
use, GCC recognizes this #pragma and loads the PCH.
This option is off by default, because the resulting preprocessed output is only
really suitable as input to GCC. It is switched on by ‘-save-temps’.

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You should not write this #pragma in your own code, but it is safe to edit the
filename if the PCH file is available in a different location. The filename may
be absolute or it may be relative to GCC’s current directory.
-fworking-directory
Enable generation of linemarkers in the preprocessor output that let the compiler know the current working directory at the time of preprocessing. When
this option is enabled, the preprocessor emits, after the initial linemarker, a
second linemarker with the current working directory followed by two slashes.
GCC uses this directory, when it’s present in the preprocessed input, as the directory emitted as the current working directory in some debugging information
formats. This option is implicitly enabled if debugging information is enabled,
but this can be inhibited with the negated form ‘-fno-working-directory’.
If the ‘-P’ flag is present in the command line, this option has no effect, since
no #line directives are emitted whatsoever.
-A predicate=answer
Make an assertion with the predicate predicate and answer answer. This form
is preferred to the older form ‘-A predicate(answer)’, which is still supported,
because it does not use shell special characters.
-A -predicate=answer
Cancel an assertion with the predicate predicate and answer answer.
-C

Do not discard comments. All comments are passed through to the output file,
except for comments in processed directives, which are deleted along with the
directive.
You should be prepared for side effects when using ‘-C’; it causes the preprocessor to treat comments as tokens in their own right. For example, comments
appearing at the start of what would be a directive line have the effect of turning that line into an ordinary source line, since the first token on the line is no
longer a ‘#’.

-CC

Do not discard comments, including during macro expansion. This is like ‘-C’,
except that comments contained within macros are also passed through to the
output file where the macro is expanded.
In addition to the side effects of the ‘-C’ option, the ‘-CC’ option causes all
C++-style comments inside a macro to be converted to C-style comments. This
is to prevent later use of that macro from inadvertently commenting out the
remainder of the source line.
The ‘-CC’ option is generally used to support lint comments.

-P

Inhibit generation of linemarkers in the output from the preprocessor. This
might be useful when running the preprocessor on something that is not C code,
and will be sent to a program which might be confused by the linemarkers.

-traditional
-traditional-cpp
Try to imitate the behavior of pre-standard C preprocessors, as opposed to ISO
C preprocessors. See the GNU CPP manual for details.

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Note that GCC does not otherwise attempt to emulate a pre-standard C compiler, and these options are only supported with the ‘-E’ switch, or when invoking CPP explicitly.
-trigraphs
Support ISO C trigraphs. These are three-character sequences, all starting with
‘??’, that are defined by ISO C to stand for single characters. For example, ‘??/’
stands for ‘\’, so ‘’??/n’’ is a character constant for a newline.
The nine trigraphs and their replacements are
Trigraph:
Replacement:

??(
[

??)
]

??<
{

??>
}

??=
#

??/
\

??’
^

??!
|

??~

By default, GCC ignores trigraphs, but in standard-conforming modes it converts them. See the ‘-std’ and ‘-ansi’ options.
-remap

Enable special code to work around file systems which only permit very short
file names, such as MS-DOS.

-H

Print the name of each header file used, in addition to other normal activities.
Each name is indented to show how deep in the ‘#include’ stack it is. Precompiled header files are also printed, even if they are found to be invalid; an invalid
precompiled header file is printed with ‘...x’ and a valid one with ‘...!’ .

-dletters
Says to make debugging dumps during compilation as specified by letters. The
flags documented here are those relevant to the preprocessor. Other letters
are interpreted by the compiler proper, or reserved for future versions of GCC,
and so are silently ignored. If you specify letters whose behavior conflicts, the
result is undefined. See Section 3.17 [Developer Options], page 212, for more
information.
-dM

Instead of the normal output, generate a list of ‘#define’ directives
for all the macros defined during the execution of the preprocessor,
including predefined macros. This gives you a way of finding out
what is predefined in your version of the preprocessor. Assuming
you have no file ‘foo.h’, the command
touch foo.h; cpp -dM foo.h

shows all the predefined macros.
If you use ‘-dM’ without the ‘-E’ option, ‘-dM’ is interpreted as a
synonym for ‘-fdump-rtl-mach’. See Section “Developer Options”
in gcc.
-dD

Like ‘-dM’ except in two respects: it does not include the predefined
macros, and it outputs both the ‘#define’ directives and the result
of preprocessing. Both kinds of output go to the standard output
file.

-dN

Like ‘-dD’, but emit only the macro names, not their expansions.

-dI

Output ‘#include’ directives in addition to the result of preprocessing.

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Using the GNU Compiler Collection (GCC)

-dU

Like ‘-dD’ except that only macros that are expanded, or whose definedness is tested in preprocessor directives, are output; the output
is delayed until the use or test of the macro; and ‘#undef’ directives
are also output for macros tested but undefined at the time.

-fdebug-cpp
This option is only useful for debugging GCC. When used from CPP or with
‘-E’, it dumps debugging information about location maps. Every token in the
output is preceded by the dump of the map its location belongs to.
When used from GCC without ‘-E’, this option has no effect.
-Wp,option
You can use ‘-Wp,option’ to bypass the compiler driver and pass option directly
through to the preprocessor. If option contains commas, it is split into multiple
options at the commas. However, many options are modified, translated or
interpreted by the compiler driver before being passed to the preprocessor,
and ‘-Wp’ forcibly bypasses this phase. The preprocessor’s direct interface is
undocumented and subject to change, so whenever possible you should avoid
using ‘-Wp’ and let the driver handle the options instead.
-Xpreprocessor option
Pass option as an option to the preprocessor. You can use this to supply
system-specific preprocessor options that GCC does not recognize.
If you want to pass an option that takes an argument, you must use
‘-Xpreprocessor’ twice, once for the option and once for the argument.
-no-integrated-cpp
Perform preprocessing as a separate pass before compilation. By default, GCC
performs preprocessing as an integrated part of input tokenization and parsing.
If this option is provided, the appropriate language front end (cc1, cc1plus,
or cc1obj for C, C++, and Objective-C, respectively) is instead invoked twice,
once for preprocessing only and once for actual compilation of the preprocessed
input. This option may be useful in conjunction with the ‘-B’ or ‘-wrapper’
options to specify an alternate preprocessor or perform additional processing of
the program source between normal preprocessing and compilation.

3.13 Passing Options to the Assembler
You can pass options to the assembler.
-Wa,option
Pass option as an option to the assembler. If option contains commas, it is split
into multiple options at the commas.
-Xassembler option
Pass option as an option to the assembler. You can use this to supply systemspecific assembler options that GCC does not recognize.
If you want to pass an option that takes an argument, you must use
‘-Xassembler’ twice, once for the option and once for the argument.

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3.14 Options for Linking
These options come into play when the compiler links object files into an executable output
file. They are meaningless if the compiler is not doing a link step.
object-file-name
A file name that does not end in a special recognized suffix is considered to
name an object file or library. (Object files are distinguished from libraries by
the linker according to the file contents.) If linking is done, these object files
are used as input to the linker.
-c
-S
-E

If any of these options is used, then the linker is not run, and object file names
should not be used as arguments. See Section 3.2 [Overall Options], page 29.

-fuse-ld=bfd
Use the bfd linker instead of the default linker.
-fuse-ld=gold
Use the gold linker instead of the default linker.
-llibrary
-l library
Search the library named library when linking. (The second alternative with
the library as a separate argument is only for POSIX compliance and is not
recommended.)
It makes a difference where in the command you write this option; the linker
searches and processes libraries and object files in the order they are specified. Thus, ‘foo.o -lz bar.o’ searches library ‘z’ after file ‘foo.o’ but before
‘bar.o’. If ‘bar.o’ refers to functions in ‘z’, those functions may not be loaded.
The linker searches a standard list of directories for the library, which is actually
a file named ‘liblibrary.a’. The linker then uses this file as if it had been
specified precisely by name.
The directories searched include several standard system directories plus any
that you specify with ‘-L’.
Normally the files found this way are library files—archive files whose members
are object files. The linker handles an archive file by scanning through it for
members which define symbols that have so far been referenced but not defined.
But if the file that is found is an ordinary object file, it is linked in the usual
fashion. The only difference between using an ‘-l’ option and specifying a file
name is that ‘-l’ surrounds library with ‘lib’ and ‘.a’ and searches several
directories.
-lobjc

You need this special case of the ‘-l’ option in order to link an Objective-C or
Objective-C++ program.

-nostartfiles
Do not use the standard system startup files when linking. The standard system
libraries are used normally, unless ‘-nostdlib’ or ‘-nodefaultlibs’ is used.

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-nodefaultlibs
Do not use the standard system libraries when linking. Only the libraries you
specify are passed to the linker, and options specifying linkage of the system
libraries, such as ‘-static-libgcc’ or ‘-shared-libgcc’, are ignored. The
standard startup files are used normally, unless ‘-nostartfiles’ is used.
The compiler may generate calls to memcmp, memset, memcpy and memmove.
These entries are usually resolved by entries in libc. These entry points should
be supplied through some other mechanism when this option is specified.
-nostdlib
Do not use the standard system startup files or libraries when linking. No
startup files and only the libraries you specify are passed to the linker, and
options specifying linkage of the system libraries, such as ‘-static-libgcc’ or
‘-shared-libgcc’, are ignored.
The compiler may generate calls to memcmp, memset, memcpy and memmove.
These entries are usually resolved by entries in libc. These entry points should
be supplied through some other mechanism when this option is specified.
One of the standard libraries bypassed by ‘-nostdlib’ and ‘-nodefaultlibs’
is ‘libgcc.a’, a library of internal subroutines which GCC uses to overcome
shortcomings of particular machines, or special needs for some languages. (See
Section “Interfacing to GCC Output” in GNU Compiler Collection (GCC) Internals, for more discussion of ‘libgcc.a’.) In most cases, you need ‘libgcc.a’
even when you want to avoid other standard libraries. In other words, when you
specify ‘-nostdlib’ or ‘-nodefaultlibs’ you should usually specify ‘-lgcc’ as
well. This ensures that you have no unresolved references to internal GCC
library subroutines. (An example of such an internal subroutine is __main,
used to ensure C++ constructors are called; see Section “collect2” in GNU
Compiler Collection (GCC) Internals.)
-pie

Produce a dynamically linked position independent executable on targets that
support it. For predictable results, you must also specify the same set of options
used for compilation (‘-fpie’, ‘-fPIE’, or model suboptions) when you specify
this linker option.

-no-pie

Don’t produce a dynamically linked position independent executable.

-static-pie
Produce a static position independent executable on targets that support it.
A static position independent executable is similar to a static executable, but
can be loaded at any address without a dynamic linker. For predictable results,
you must also specify the same set of options used for compilation (‘-fpie’,
‘-fPIE’, or model suboptions) when you specify this linker option.
-pthread

Link with the POSIX threads library. This option is supported on GNU/Linux
targets, most other Unix derivatives, and also on x86 Cygwin and MinGW
targets. On some targets this option also sets flags for the preprocessor, so it
should be used consistently for both compilation and linking.

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-rdynamic
Pass the flag ‘-export-dynamic’ to the ELF linker, on targets that support
it. This instructs the linker to add all symbols, not only used ones, to the
dynamic symbol table. This option is needed for some uses of dlopen or to
allow obtaining backtraces from within a program.
-s

Remove all symbol table and relocation information from the executable.

-static

On systems that support dynamic linking, this overrides ‘-pie’ and prevents
linking with the shared libraries. On other systems, this option has no effect.

-shared

Produce a shared object which can then be linked with other objects to form
an executable. Not all systems support this option. For predictable results,
you must also specify the same set of options used for compilation (‘-fpic’,
‘-fPIC’, or model suboptions) when you specify this linker option.1

-shared-libgcc
-static-libgcc
On systems that provide ‘libgcc’ as a shared library, these options force the
use of either the shared or static version, respectively. If no shared version of
‘libgcc’ was built when the compiler was configured, these options have no
effect.
There are several situations in which an application should use the shared
‘libgcc’ instead of the static version. The most common of these is when
the application wishes to throw and catch exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should
use the shared ‘libgcc’.
Therefore, the G++ and driver automatically adds ‘-shared-libgcc’ whenever
you build a shared library or a main executable, because C++ programs typically
use exceptions, so this is the right thing to do.
If, instead, you use the GCC driver to create shared libraries, you may find
that they are not always linked with the shared ‘libgcc’. If GCC finds, at its
configuration time, that you have a non-GNU linker or a GNU linker that does
not support option ‘--eh-frame-hdr’, it links the shared version of ‘libgcc’
into shared libraries by default. Otherwise, it takes advantage of the linker and
optimizes away the linking with the shared version of ‘libgcc’, linking with the
static version of libgcc by default. This allows exceptions to propagate through
such shared libraries, without incurring relocation costs at library load time.
However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ driver, as appropriate for the languages
used in the program, or using the option ‘-shared-libgcc’, such that it is
linked with the shared ‘libgcc’.
1

On some systems, ‘gcc -shared’ needs to build supplementary stub code for constructors to work. On
multi-libbed systems, ‘gcc -shared’ must select the correct support libraries to link against. Failing to
supply the correct flags may lead to subtle defects. Supplying them in cases where they are not necessary
is innocuous.

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-static-libasan
When the ‘-fsanitize=address’ option is used to link a program, the GCC
driver automatically links against ‘libasan’. If ‘libasan’ is available as a
shared library, and the ‘-static’ option is not used, then this links against the
shared version of ‘libasan’. The ‘-static-libasan’ option directs the GCC
driver to link ‘libasan’ statically, without necessarily linking other libraries
statically.
-static-libtsan
When the ‘-fsanitize=thread’ option is used to link a program, the GCC
driver automatically links against ‘libtsan’. If ‘libtsan’ is available as a
shared library, and the ‘-static’ option is not used, then this links against the
shared version of ‘libtsan’. The ‘-static-libtsan’ option directs the GCC
driver to link ‘libtsan’ statically, without necessarily linking other libraries
statically.
-static-liblsan
When the ‘-fsanitize=leak’ option is used to link a program, the GCC driver
automatically links against ‘liblsan’. If ‘liblsan’ is available as a shared
library, and the ‘-static’ option is not used, then this links against the shared
version of ‘liblsan’. The ‘-static-liblsan’ option directs the GCC driver to
link ‘liblsan’ statically, without necessarily linking other libraries statically.
-static-libubsan
When the ‘-fsanitize=undefined’ option is used to link a program, the GCC
driver automatically links against ‘libubsan’. If ‘libubsan’ is available as a
shared library, and the ‘-static’ option is not used, then this links against the
shared version of ‘libubsan’. The ‘-static-libubsan’ option directs the GCC
driver to link ‘libubsan’ statically, without necessarily linking other libraries
statically.
-static-libmpx
When the ‘-fcheck-pointer bounds’ and ‘-mmpx’ options are used to link a
program, the GCC driver automatically links against ‘libmpx’. If ‘libmpx’ is
available as a shared library, and the ‘-static’ option is not used, then this
links against the shared version of ‘libmpx’. The ‘-static-libmpx’ option
directs the GCC driver to link ‘libmpx’ statically, without necessarily linking
other libraries statically.
-static-libmpxwrappers
When the ‘-fcheck-pointer bounds’ and ‘-mmpx’ options are used to link a
program without also using ‘-fno-chkp-use-wrappers’, the GCC driver automatically links against ‘libmpxwrappers’. If ‘libmpxwrappers’ is available as a
shared library, and the ‘-static’ option is not used, then this links against the
shared version of ‘libmpxwrappers’. The ‘-static-libmpxwrappers’ option
directs the GCC driver to link ‘libmpxwrappers’ statically, without necessarily
linking other libraries statically.
-static-libstdc++
When the g++ program is used to link a C++ program, it normally automatically
links against ‘libstdc++’. If ‘libstdc++’ is available as a shared library, and

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the ‘-static’ option is not used, then this links against the shared version of
‘libstdc++’. That is normally fine. However, it is sometimes useful to freeze
the version of ‘libstdc++’ used by the program without going all the way to
a fully static link. The ‘-static-libstdc++’ option directs the g++ driver to
link ‘libstdc++’ statically, without necessarily linking other libraries statically.
-symbolic
Bind references to global symbols when building a shared object. Warn about
any unresolved references (unless overridden by the link editor option ‘-Xlinker
-z -Xlinker defs’). Only a few systems support this option.
-T script Use script as the linker script. This option is supported by most systems using
the GNU linker. On some targets, such as bare-board targets without an operating system, the ‘-T’ option may be required when linking to avoid references
to undefined symbols.
-Xlinker option
Pass option as an option to the linker. You can use this to supply system-specific
linker options that GCC does not recognize.
If you want to pass an option that takes a separate argument, you must use
‘-Xlinker’ twice, once for the option and once for the argument. For example,
to pass ‘-assert definitions’, you must write ‘-Xlinker -assert -Xlinker
definitions’. It does not work to write ‘-Xlinker "-assert definitions"’,
because this passes the entire string as a single argument, which is not what
the linker expects.
When using the GNU linker, it is usually more convenient to pass arguments to
linker options using the ‘option=value’ syntax than as separate arguments. For
example, you can specify ‘-Xlinker -Map=output.map’ rather than ‘-Xlinker
-Map -Xlinker output.map’. Other linkers may not support this syntax for
command-line options.
-Wl,option
Pass option as an option to the linker. If option contains commas, it is split into
multiple options at the commas. You can use this syntax to pass an argument
to the option. For example, ‘-Wl,-Map,output.map’ passes ‘-Map output.map’
to the linker. When using the GNU linker, you can also get the same effect
with ‘-Wl,-Map=output.map’.
-u symbol Pretend the symbol symbol is undefined, to force linking of library modules
to define it. You can use ‘-u’ multiple times with different symbols to force
loading of additional library modules.
-z keyword
‘-z’ is passed directly on to the linker along with the keyword keyword. See
the section in the documentation of your linker for permitted values and their
meanings.

3.15 Options for Directory Search
These options specify directories to search for header files, for libraries and for parts of the
compiler:

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-I dir
-iquote dir
-isystem dir
-idirafter dir
Add the directory dir to the list of directories to be searched for header files during preprocessing. If dir begins with ‘=’ or $SYSROOT, then the ‘=’ or $SYSROOT
is replaced by the sysroot prefix; see ‘--sysroot’ and ‘-isysroot’.
Directories specified with ‘-iquote’ apply only to the quote form of the
directive, #include "file". Directories specified with ‘-I’, ‘-isystem’,
or ‘-idirafter’ apply to lookup for both the #include "file" and
#include  directives.
You can specify any number or combination of these options on the command
line to search for header files in several directories. The lookup order is as
follows:
1. For the quote form of the include directive, the directory of the current file
is searched first.
2. For the quote form of the include directive, the directories specified by
‘-iquote’ options are searched in left-to-right order, as they appear on the
command line.
3. Directories specified with ‘-I’ options are scanned in left-to-right order.
4. Directories specified with ‘-isystem’ options are scanned in left-to-right
order.
5. Standard system directories are scanned.
6. Directories specified with ‘-idirafter’ options are scanned in left-to-right
order.
You can use ‘-I’ to override a system header file, substituting your own version, since these directories are searched before the standard system header file
directories. However, you should not use this option to add directories that
contain vendor-supplied system header files; use ‘-isystem’ for that.
The ‘-isystem’ and ‘-idirafter’ options also mark the directory as a system
directory, so that it gets the same special treatment that is applied to the
standard system directories.
If a standard system include directory, or a directory specified with ‘-isystem’,
is also specified with ‘-I’, the ‘-I’ option is ignored. The directory is still
searched but as a system directory at its normal position in the system include
chain. This is to ensure that GCC’s procedure to fix buggy system headers and
the ordering for the #include_next directive are not inadvertently changed.
If you really need to change the search order for system directories, use the
‘-nostdinc’ and/or ‘-isystem’ options.
-I-

Split the include path. This option has been deprecated. Please use ‘-iquote’
instead for ‘-I’ directories before the ‘-I-’ and remove the ‘-I-’ option.
Any directories specified with ‘-I’ options before ‘-I-’ are searched only
for headers requested with #include "file"; they are not searched for

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#include . If additional directories are specified with ‘-I’ options after
the ‘-I-’, those directories are searched for all ‘#include’ directives.
In addition, ‘-I-’ inhibits the use of the directory of the current file directory
as the first search directory for #include "file". There is no way to override
this effect of ‘-I-’.
-iprefix prefix
Specify prefix as the prefix for subsequent ‘-iwithprefix’ options. If the prefix
represents a directory, you should include the final ‘/’.
-iwithprefix dir
-iwithprefixbefore dir
Append dir to the prefix specified previously with ‘-iprefix’, and add the
resulting directory to the include search path. ‘-iwithprefixbefore’ puts it
in the same place ‘-I’ would; ‘-iwithprefix’ puts it where ‘-idirafter’ would.
-isysroot dir
This option is like the ‘--sysroot’ option, but applies only to header files
(except for Darwin targets, where it applies to both header files and libraries).
See the ‘--sysroot’ option for more information.
-imultilib dir
Use dir as a subdirectory of the directory containing target-specific C++ headers.
-nostdinc
Do not search the standard system directories for header files. Only the directories explicitly specified with ‘-I’, ‘-iquote’, ‘-isystem’, and/or ‘-idirafter’
options (and the directory of the current file, if appropriate) are searched.
-nostdinc++
Do not search for header files in the C++-specific standard directories, but do
still search the other standard directories. (This option is used when building
the C++ library.)
-iplugindir=dir
Set the directory to search for plugins that are passed by ‘-fplugin=name’
instead of ‘-fplugin=path/name.so’. This option is not meant to be used by
the user, but only passed by the driver.
-Ldir

Add directory dir to the list of directories to be searched for ‘-l’.

-Bprefix

This option specifies where to find the executables, libraries, include files, and
data files of the compiler itself.
The compiler driver program runs one or more of the subprograms cpp, cc1,
as and ld. It tries prefix as a prefix for each program it tries to run, both
with and without ‘machine/version/’ for the corresponding target machine
and compiler version.
For each subprogram to be run, the compiler driver first tries the ‘-B’ prefix, if
any. If that name is not found, or if ‘-B’ is not specified, the driver tries two
standard prefixes, ‘/usr/lib/gcc/’ and ‘/usr/local/lib/gcc/’. If neither of
those results in a file name that is found, the unmodified program name is
searched for using the directories specified in your PATH environment variable.

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The compiler checks to see if the path provided by ‘-B’ refers to a directory,
and if necessary it adds a directory separator character at the end of the path.
‘-B’ prefixes that effectively specify directory names also apply to libraries in
the linker, because the compiler translates these options into ‘-L’ options for
the linker. They also apply to include files in the preprocessor, because the
compiler translates these options into ‘-isystem’ options for the preprocessor.
In this case, the compiler appends ‘include’ to the prefix.
The runtime support file ‘libgcc.a’ can also be searched for using the ‘-B’
prefix, if needed. If it is not found there, the two standard prefixes above are
tried, and that is all. The file is left out of the link if it is not found by those
means.
Another way to specify a prefix much like the ‘-B’ prefix is to use the environment variable GCC_EXEC_PREFIX. See Section 3.20 [Environment Variables],
page 422.
As a special kludge, if the path provided by ‘-B’ is ‘[dir/]stageN/’, where N
is a number in the range 0 to 9, then it is replaced by ‘[dir/]include’. This
is to help with boot-strapping the compiler.
-no-canonical-prefixes
Do not expand any symbolic links, resolve references to ‘/../’ or ‘/./’, or make
the path absolute when generating a relative prefix.
--sysroot=dir
Use dir as the logical root directory for headers and libraries. For example, if
the compiler normally searches for headers in ‘/usr/include’ and libraries in
‘/usr/lib’, it instead searches ‘dir/usr/include’ and ‘dir/usr/lib’.
If you use both this option and the ‘-isysroot’ option, then the ‘--sysroot’
option applies to libraries, but the ‘-isysroot’ option applies to header files.
The GNU linker (beginning with version 2.16) has the necessary support for
this option. If your linker does not support this option, the header file aspect
of ‘--sysroot’ still works, but the library aspect does not.
--no-sysroot-suffix
For some targets, a suffix is added to the root directory specified with
‘--sysroot’, depending on the other options used, so that headers may for example be found in ‘dir/suffix/usr/include’ instead of ‘dir/usr/include’.
This option disables the addition of such a suffix.

3.16 Options for Code Generation Conventions
These machine-independent options control the interface conventions used in code generation.
Most of them have both positive and negative forms; the negative form of ‘-ffoo’ is
‘-fno-foo’. In the table below, only one of the forms is listed—the one that is not the
default. You can figure out the other form by either removing ‘no-’ or adding it.
-fstack-reuse=reuse-level
This option controls stack space reuse for user declared local/auto variables
and compiler generated temporaries. reuse level can be ‘all’, ‘named_vars’,

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203

or ‘none’. ‘all’ enables stack reuse for all local variables and temporaries,
‘named_vars’ enables the reuse only for user defined local variables with names,
and ‘none’ disables stack reuse completely. The default value is ‘all’. The option is needed when the program extends the lifetime of a scoped local variable
or a compiler generated temporary beyond the end point defined by the language. When a lifetime of a variable ends, and if the variable lives in memory,
the optimizing compiler has the freedom to reuse its stack space with other
temporaries or scoped local variables whose live range does not overlap with
it. Legacy code extending local lifetime is likely to break with the stack reuse
optimization.
For example,
int *p;
{
int local1;
p = &local1;
local1 = 10;
....
}
{
int local2;
local2 = 20;
...
}
if (*p == 10)
{

// out of scope use of local1

}

Another example:
struct A
{
A(int k) : i(k), j(k) { }
int i;
int j;
};
A *ap;
void foo(const A& ar)
{
ap = &ar;
}
void bar()
{
foo(A(10)); // temp object’s lifetime ends when foo returns
{
A a(20);
....
}
ap->i+= 10;

// ap references out of scope temp whose space
// is reused with a. What is the value of ap->i?

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}

The lifetime of a compiler generated temporary is well defined by the C++
standard. When a lifetime of a temporary ends, and if the temporary lives
in memory, the optimizing compiler has the freedom to reuse its stack space
with other temporaries or scoped local variables whose live range does not
overlap with it. However some of the legacy code relies on the behavior of older
compilers in which temporaries’ stack space is not reused, the aggressive stack
reuse can lead to runtime errors. This option is used to control the temporary
stack reuse optimization.
-ftrapv

This option generates traps for signed overflow on addition, subtraction, multiplication operations. The options ‘-ftrapv’ and ‘-fwrapv’ override each other,
so using ‘-ftrapv’ ‘-fwrapv’ on the command-line results in ‘-fwrapv’ being
effective. Note that only active options override, so using ‘-ftrapv’ ‘-fwrapv’
‘-fno-wrapv’ on the command-line results in ‘-ftrapv’ being effective.

-fwrapv

This option instructs the compiler to assume that signed arithmetic overflow of
addition, subtraction and multiplication wraps around using twos-complement
representation. This flag enables some optimizations and disables others.
The options ‘-ftrapv’ and ‘-fwrapv’ override each other, so using ‘-ftrapv’
‘-fwrapv’ on the command-line results in ‘-fwrapv’ being effective. Note that
only active options override, so using ‘-ftrapv’ ‘-fwrapv’ ‘-fno-wrapv’ on the
command-line results in ‘-ftrapv’ being effective.

-fwrapv-pointer
This option instructs the compiler to assume that pointer arithmetic overflow on
addition and subtraction wraps around using twos-complement representation.
This flag disables some optimizations which assume pointer overflow is invalid.
-fstrict-overflow
This option implies ‘-fno-wrapv’ ‘-fno-wrapv-pointer’ and when negated
implies ‘-fwrapv’ ‘-fwrapv-pointer’.
-fexceptions
Enable exception handling. Generates extra code needed to propagate exceptions. For some targets, this implies GCC generates frame unwind information
for all functions, which can produce significant data size overhead, although
it does not affect execution. If you do not specify this option, GCC enables
it by default for languages like C++ that normally require exception handling,
and disables it for languages like C that do not normally require it. However,
you may need to enable this option when compiling C code that needs to interoperate properly with exception handlers written in C++. You may also wish
to disable this option if you are compiling older C++ programs that don’t use
exception handling.
-fnon-call-exceptions
Generate code that allows trapping instructions to throw exceptions. Note that
this requires platform-specific runtime support that does not exist everywhere.
Moreover, it only allows trapping instructions to throw exceptions, i.e. memory

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references or floating-point instructions. It does not allow exceptions to be
thrown from arbitrary signal handlers such as SIGALRM.
-fdelete-dead-exceptions
Consider that instructions that may throw exceptions but don’t otherwise contribute to the execution of the program can be optimized away. This option is
enabled by default for the Ada front end, as permitted by the Ada language
specification. Optimization passes that cause dead exceptions to be removed
are enabled independently at different optimization levels.
-funwind-tables
Similar to ‘-fexceptions’, except that it just generates any needed static data,
but does not affect the generated code in any other way. You normally do
not need to enable this option; instead, a language processor that needs this
handling enables it on your behalf.
-fasynchronous-unwind-tables
Generate unwind table in DWARF format, if supported by target machine.
The table is exact at each instruction boundary, so it can be used for stack
unwinding from asynchronous events (such as debugger or garbage collector).
-fno-gnu-unique
On systems with recent GNU assembler and C library, the C++ compiler uses
the STB_GNU_UNIQUE binding to make sure that definitions of template static
data members and static local variables in inline functions are unique even in
the presence of RTLD_LOCAL; this is necessary to avoid problems with a library
used by two different RTLD_LOCAL plugins depending on a definition in one of
them and therefore disagreeing with the other one about the binding of the
symbol. But this causes dlclose to be ignored for affected DSOs; if your
program relies on reinitialization of a DSO via dlclose and dlopen, you can
use ‘-fno-gnu-unique’.
-fpcc-struct-return
Return “short” struct and union values in memory like longer ones, rather
than in registers. This convention is less efficient, but it has the advantage
of allowing intercallability between GCC-compiled files and files compiled with
other compilers, particularly the Portable C Compiler (pcc).
The precise convention for returning structures in memory depends on the target configuration macros.
Short structures and unions are those whose size and alignment match that of
some integer type.
Warning: code compiled with the ‘-fpcc-struct-return’ switch is not binary
compatible with code compiled with the ‘-freg-struct-return’ switch. Use
it to conform to a non-default application binary interface.
-freg-struct-return
Return struct and union values in registers when possible. This is more efficient for small structures than ‘-fpcc-struct-return’.
If you specify neither ‘-fpcc-struct-return’ nor ‘-freg-struct-return’,
GCC defaults to whichever convention is standard for the target. If there is

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no standard convention, GCC defaults to ‘-fpcc-struct-return’, except on
targets where GCC is the principal compiler. In those cases, we can choose
the standard, and we chose the more efficient register return alternative.
Warning: code compiled with the ‘-freg-struct-return’ switch is not binary
compatible with code compiled with the ‘-fpcc-struct-return’ switch. Use
it to conform to a non-default application binary interface.
-fshort-enums
Allocate to an enum type only as many bytes as it needs for the declared range of
possible values. Specifically, the enum type is equivalent to the smallest integer
type that has enough room.
Warning: the ‘-fshort-enums’ switch causes GCC to generate code that is not
binary compatible with code generated without that switch. Use it to conform
to a non-default application binary interface.
-fshort-wchar
Override the underlying type for wchar_t to be short unsigned int instead
of the default for the target. This option is useful for building programs to run
under WINE.
Warning: the ‘-fshort-wchar’ switch causes GCC to generate code that is not
binary compatible with code generated without that switch. Use it to conform
to a non-default application binary interface.
-fno-common
In C code, this option controls the placement of global variables defined without an initializer, known as tentative definitions in the C standard. Tentative
definitions are distinct from declarations of a variable with the extern keyword,
which do not allocate storage.
Unix C compilers have traditionally allocated storage for uninitialized global
variables in a common block. This allows the linker to resolve all tentative
definitions of the same variable in different compilation units to the same object,
or to a non-tentative definition. This is the behavior specified by ‘-fcommon’,
and is the default for GCC on most targets. On the other hand, this behavior
is not required by ISO C, and on some targets may carry a speed or code size
penalty on variable references.
The ‘-fno-common’ option specifies that the compiler should instead place uninitialized global variables in the data section of the object file. This inhibits the
merging of tentative definitions by the linker so you get a multiple-definition
error if the same variable is defined in more than one compilation unit. Compiling with ‘-fno-common’ is useful on targets for which it provides better performance, or if you wish to verify that the program will work on other systems
that always treat uninitialized variable definitions this way.
-fno-ident
Ignore the #ident directive.
-finhibit-size-directive
Don’t output a .size assembler directive, or anything else that would cause
trouble if the function is split in the middle, and the two halves are placed at lo-

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207

cations far apart in memory. This option is used when compiling ‘crtstuff.c’;
you should not need to use it for anything else.
-fverbose-asm
Put extra commentary information in the generated assembly code to make it
more readable. This option is generally only of use to those who actually need
to read the generated assembly code (perhaps while debugging the compiler
itself).
‘-fno-verbose-asm’, the default, causes the extra information to be omitted
and is useful when comparing two assembler files.
The added comments include:
• information on the compiler version and command-line options,
• the source code lines associated with the assembly instructions, in the form
FILENAME:LINENUMBER:CONTENT OF LINE,
• hints on which high-level expressions correspond to the various assembly
instruction operands.
For example, given this C source file:
int test (int n)
{
int i;
int total = 0;
for (i = 0; i < n; i++)
total += i * i;
return total;
}

compiling to (x86 64) assembly via ‘-S’ and emitting the result direct to stdout
via ‘-o’ ‘-’
gcc -S test.c -fverbose-asm -Os -o -

gives output similar to this:
.file "test.c"
# GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
[...snip...]
# options passed:
[...snip...]
.text
.globl test
.type test, @function
test:
.LFB0:
.cfi_startproc
# test.c:4:
int total = 0;
xorl %eax, %eax # 
# test.c:6:
for (i = 0; i < n; i++)
xorl %edx, %edx # i
.L2:
# test.c:6:
for (i = 0; i < n; i++)
cmpl %edi, %edx # n, i
jge .L5 #,

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# test.c:7:
total += i * i;
movl %edx, %ecx # i, tmp92
imull %edx, %ecx # i, tmp92
# test.c:6:
for (i = 0; i < n; i++)
incl %edx # i
# test.c:7:
total += i * i;
addl %ecx, %eax # tmp92, 
jmp .L2 #
.L5:
# test.c:10: }
ret
.cfi_endproc
.LFE0:
.size test, .-test
.ident "GCC: (GNU) 7.0.0 20160809 (experimental)"
.section .note.GNU-stack,"",@progbits

The comments are intended for humans rather than machines and hence the
precise format of the comments is subject to change.
-frecord-gcc-switches
This switch causes the command line used to invoke the compiler to be recorded
into the object file that is being created. This switch is only implemented on
some targets and the exact format of the recording is target and binary file
format dependent, but it usually takes the form of a section containing ASCII
text. This switch is related to the ‘-fverbose-asm’ switch, but that switch
only records information in the assembler output file as comments, so it never
reaches the object file. See also ‘-grecord-gcc-switches’ for another way of
storing compiler options into the object file.
-fpic

Generate position-independent code (PIC) suitable for use in a shared library,
if supported for the target machine. Such code accesses all constant addresses
through a global offset table (GOT). The dynamic loader resolves the GOT
entries when the program starts (the dynamic loader is not part of GCC; it
is part of the operating system). If the GOT size for the linked executable
exceeds a machine-specific maximum size, you get an error message from the
linker indicating that ‘-fpic’ does not work; in that case, recompile with ‘-fPIC’
instead. (These maximums are 8k on the SPARC, 28k on AArch64 and 32k on
the m68k and RS/6000. The x86 has no such limit.)
Position-independent code requires special support, and therefore works only on
certain machines. For the x86, GCC supports PIC for System V but not for the
Sun 386i. Code generated for the IBM RS/6000 is always position-independent.
When this flag is set, the macros __pic__ and __PIC__ are defined to 1.

-fPIC

If supported for the target machine, emit position-independent code, suitable
for dynamic linking and avoiding any limit on the size of the global offset table.
This option makes a difference on AArch64, m68k, PowerPC and SPARC.
Position-independent code requires special support, and therefore works only
on certain machines.
When this flag is set, the macros __pic__ and __PIC__ are defined to 2.

Chapter 3: GCC Command Options

-fpie
-fPIE

-fno-plt

209

These options are similar to ‘-fpic’ and ‘-fPIC’, but generated position independent code can be only linked into executables. Usually these options are
used when ‘-pie’ GCC option is used during linking.
‘-fpie’ and ‘-fPIE’ both define the macros __pie__ and __PIE__. The macros
have the value 1 for ‘-fpie’ and 2 for ‘-fPIE’.
Do not use the PLT for external function calls in position-independent code.
Instead, load the callee address at call sites from the GOT and branch to it.
This leads to more efficient code by eliminating PLT stubs and exposing GOT
loads to optimizations. On architectures such as 32-bit x86 where PLT stubs
expect the GOT pointer in a specific register, this gives more register allocation
freedom to the compiler. Lazy binding requires use of the PLT; with ‘-fno-plt’
all external symbols are resolved at load time.
Alternatively, the function attribute noplt can be used to avoid calls through
the PLT for specific external functions.
In position-dependent code, a few targets also convert calls to functions that
are marked to not use the PLT to use the GOT instead.

-fno-jump-tables
Do not use jump tables for switch statements even where it would be more efficient than other code generation strategies. This option is of use in conjunction
with ‘-fpic’ or ‘-fPIC’ for building code that forms part of a dynamic linker
and cannot reference the address of a jump table. On some targets, jump tables
do not require a GOT and this option is not needed.
-ffixed-reg
Treat the register named reg as a fixed register; generated code should never
refer to it (except perhaps as a stack pointer, frame pointer or in some other
fixed role).
reg must be the name of a register. The register names accepted are machinespecific and are defined in the REGISTER_NAMES macro in the machine description macro file.
This flag does not have a negative form, because it specifies a three-way choice.
-fcall-used-reg
Treat the register named reg as an allocable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live
across a call. Functions compiled this way do not save and restore the register
reg.
It is an error to use this flag with the frame pointer or stack pointer. Use of this
flag for other registers that have fixed pervasive roles in the machine’s execution
model produces disastrous results.
This flag does not have a negative form, because it specifies a three-way choice.
-fcall-saved-reg
Treat the register named reg as an allocable register saved by functions. It may
be allocated even for temporaries or variables that live across a call. Functions
compiled this way save and restore the register reg if they use it.

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It is an error to use this flag with the frame pointer or stack pointer. Use of this
flag for other registers that have fixed pervasive roles in the machine’s execution
model produces disastrous results.
A different sort of disaster results from the use of this flag for a register in which
function values may be returned.
This flag does not have a negative form, because it specifies a three-way choice.
-fpack-struct[=n]
Without a value specified, pack all structure members together without holes.
When a value is specified (which must be a small power of two), pack structure
members according to this value, representing the maximum alignment (that
is, objects with default alignment requirements larger than this are output
potentially unaligned at the next fitting location.
Warning: the ‘-fpack-struct’ switch causes GCC to generate code that is
not binary compatible with code generated without that switch. Additionally,
it makes the code suboptimal. Use it to conform to a non-default application
binary interface.
-fleading-underscore
This option and its counterpart, ‘-fno-leading-underscore’, forcibly change
the way C symbols are represented in the object file. One use is to help link
with legacy assembly code.
Warning: the ‘-fleading-underscore’ switch causes GCC to generate code
that is not binary compatible with code generated without that switch. Use it
to conform to a non-default application binary interface. Not all targets provide
complete support for this switch.
-ftls-model=model
Alter the thread-local storage model to be used (see Section 6.63 [ThreadLocal], page 782). The model argument should be one of ‘global-dynamic’,
‘local-dynamic’, ‘initial-exec’ or ‘local-exec’. Note that the choice is
subject to optimization: the compiler may use a more efficient model for symbols not visible outside of the translation unit, or if ‘-fpic’ is not given on the
command line.
The default without ‘-fpic’ is ‘initial-exec’; with ‘-fpic’ the default is
‘global-dynamic’.
-ftrampolines
For targets that normally need trampolines for nested functions, always generate them instead of using descriptors. Otherwise, for targets that do not need
them, like for example HP-PA or IA-64, do nothing.
A trampoline is a small piece of code that is created at run time on the stack
when the address of a nested function is taken, and is used to call the nested
function indirectly. Therefore, it requires the stack to be made executable in
order for the program to work properly.
‘-fno-trampolines’ is enabled by default on a language by language basis
to let the compiler avoid generating them, if it computes that this is safe,
and replace them with descriptors. Descriptors are made up of data only, but

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the generated code must be prepared to deal with them. As of this writing,
‘-fno-trampolines’ is enabled by default only for Ada.
Moreover, code compiled with ‘-ftrampolines’ and code compiled with
‘-fno-trampolines’ are not binary compatible if nested functions are
present. This option must therefore be used on a program-wide basis and be
manipulated with extreme care.
-fvisibility=[default|internal|hidden|protected]
Set the default ELF image symbol visibility to the specified option—all symbols
are marked with this unless overridden within the code. Using this feature can
very substantially improve linking and load times of shared object libraries,
produce more optimized code, provide near-perfect API export and prevent
symbol clashes. It is strongly recommended that you use this in any shared
objects you distribute.
Despite the nomenclature, ‘default’ always means public; i.e., available to be
linked against from outside the shared object. ‘protected’ and ‘internal’ are
pretty useless in real-world usage so the only other commonly used option is
‘hidden’. The default if ‘-fvisibility’ isn’t specified is ‘default’, i.e., make
every symbol public.
A good explanation of the benefits offered by ensuring ELF symbols have
the correct visibility is given by “How To Write Shared Libraries” by Ulrich
Drepper (which can be found at https://www.akkadia.org/drepper/)—
however a superior solution made possible by this option to marking things
hidden when the default is public is to make the default hidden and
mark things public. This is the norm with DLLs on Windows and with
‘-fvisibility=hidden’ and __attribute__ ((visibility("default")))
instead of __declspec(dllexport) you get almost identical semantics with
identical syntax. This is a great boon to those working with cross-platform
projects.
For those adding visibility support to existing code, you may find #pragma GCC
visibility of use. This works by you enclosing the declarations you wish
to set visibility for with (for example) #pragma GCC visibility push(hidden)
and #pragma GCC visibility pop. Bear in mind that symbol visibility should
be viewed as part of the API interface contract and thus all new code should
always specify visibility when it is not the default; i.e., declarations only for
use within the local DSO should always be marked explicitly as hidden as so
to avoid PLT indirection overheads—making this abundantly clear also aids
readability and self-documentation of the code. Note that due to ISO C++
specification requirements, operator new and operator delete must always
be of default visibility.
Be aware that headers from outside your project, in particular system headers and headers from any other library you use, may not be expecting to be
compiled with visibility other than the default. You may need to explicitly say
#pragma GCC visibility push(default) before including any such headers.
extern declarations are not affected by ‘-fvisibility’, so a lot of code can be
recompiled with ‘-fvisibility=hidden’ with no modifications. However, this

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means that calls to extern functions with no explicit visibility use the PLT, so
it is more effective to use __attribute ((visibility)) and/or #pragma GCC
visibility to tell the compiler which extern declarations should be treated
as hidden.
Note that ‘-fvisibility’ does affect C++ vague linkage entities. This means
that, for instance, an exception class that is be thrown between DSOs must
be explicitly marked with default visibility so that the ‘type_info’ nodes are
unified between the DSOs.
An overview of these techniques, their benefits and how to use them is at
http://gcc.gnu.org/wiki/Visibility.
-fstrict-volatile-bitfields
This option should be used if accesses to volatile bit-fields (or other structure
fields, although the compiler usually honors those types anyway) should use a
single access of the width of the field’s type, aligned to a natural alignment if
possible. For example, targets with memory-mapped peripheral registers might
require all such accesses to be 16 bits wide; with this flag you can declare
all peripheral bit-fields as unsigned short (assuming short is 16 bits on these
targets) to force GCC to use 16-bit accesses instead of, perhaps, a more efficient
32-bit access.
If this option is disabled, the compiler uses the most efficient instruction. In
the previous example, that might be a 32-bit load instruction, even though
that accesses bytes that do not contain any portion of the bit-field, or memorymapped registers unrelated to the one being updated.
In some cases, such as when the packed attribute is applied to a structure
field, it may not be possible to access the field with a single read or write that
is correctly aligned for the target machine. In this case GCC falls back to
generating multiple accesses rather than code that will fault or truncate the
result at run time.
Note: Due to restrictions of the C/C++11 memory model, write accesses are not
allowed to touch non bit-field members. It is therefore recommended to define
all bits of the field’s type as bit-field members.
The default value of this option is determined by the application binary interface
for the target processor.
-fsync-libcalls
This option controls whether any out-of-line instance of the __sync family of
functions may be used to implement the C++11 __atomic family of functions.
The default value of this option is enabled, thus the only useful form of the
option is ‘-fno-sync-libcalls’. This option is used in the implementation of
the ‘libatomic’ runtime library.

3.17 GCC Developer Options
This section describes command-line options that are primarily of interest to GCC developers, including options to support compiler testing and investigation of compiler bugs and
compile-time performance problems. This includes options that produce debug dumps at

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various points in the compilation; that print statistics such as memory use and execution
time; and that print information about GCC’s configuration, such as where it searches for
libraries. You should rarely need to use any of these options for ordinary compilation and
linking tasks.
-dletters
-fdump-rtl-pass
-fdump-rtl-pass=filename
Says to make debugging dumps during compilation at times specified by letters.
This is used for debugging the RTL-based passes of the compiler. The file names
for most of the dumps are made by appending a pass number and a word to
the dumpname, and the files are created in the directory of the output file.
In case of ‘=filename’ option, the dump is output on the given file instead
of the pass numbered dump files. Note that the pass number is assigned as
passes are registered into the pass manager. Most passes are registered in the
order that they will execute and for these passes the number corresponds to the
pass execution order. However, passes registered by plugins, passes specific to
compilation targets, or passes that are otherwise registered after all the other
passes are numbered higher than a pass named "final", even if they are executed
earlier. dumpname is generated from the name of the output file if explicitly
specified and not an executable, otherwise it is the basename of the source file.
Some ‘-dletters’ switches have different meaning when ‘-E’ is used for preprocessing. See Section 3.12 [Preprocessor Options], page 187, for information
about preprocessor-specific dump options.
Debug dumps can be enabled with a ‘-fdump-rtl’ switch or some ‘-d’ option
letters. Here are the possible letters for use in pass and letters, and their
meanings:
-fdump-rtl-alignments
Dump after branch alignments have been computed.
-fdump-rtl-asmcons
Dump after fixing rtl statements that have unsatisfied in/out constraints.
-fdump-rtl-auto_inc_dec
Dump after auto-inc-dec discovery. This pass is only run on architectures that have auto inc or auto dec instructions.
-fdump-rtl-barriers
Dump after cleaning up the barrier instructions.
-fdump-rtl-bbpart
Dump after partitioning hot and cold basic blocks.
-fdump-rtl-bbro
Dump after block reordering.
-fdump-rtl-btl1
-fdump-rtl-btl2
‘-fdump-rtl-btl1’ and ‘-fdump-rtl-btl2’ enable dumping after
the two branch target load optimization passes.

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-fdump-rtl-bypass
Dump after jump bypassing and control flow optimizations.
-fdump-rtl-combine
Dump after the RTL instruction combination pass.
-fdump-rtl-compgotos
Dump after duplicating the computed gotos.
-fdump-rtl-ce1
-fdump-rtl-ce2
-fdump-rtl-ce3
‘-fdump-rtl-ce1’, ‘-fdump-rtl-ce2’, and ‘-fdump-rtl-ce3’ enable dumping after the three if conversion passes.
-fdump-rtl-cprop_hardreg
Dump after hard register copy propagation.
-fdump-rtl-csa
Dump after combining stack adjustments.
-fdump-rtl-cse1
-fdump-rtl-cse2
‘-fdump-rtl-cse1’ and ‘-fdump-rtl-cse2’ enable dumping after
the two common subexpression elimination passes.
-fdump-rtl-dce
Dump after the standalone dead code elimination passes.
-fdump-rtl-dbr
Dump after delayed branch scheduling.
-fdump-rtl-dce1
-fdump-rtl-dce2
‘-fdump-rtl-dce1’ and ‘-fdump-rtl-dce2’ enable dumping after
the two dead store elimination passes.
-fdump-rtl-eh
Dump after finalization of EH handling code.
-fdump-rtl-eh_ranges
Dump after conversion of EH handling range regions.
-fdump-rtl-expand
Dump after RTL generation.
-fdump-rtl-fwprop1
-fdump-rtl-fwprop2
‘-fdump-rtl-fwprop1’ and ‘-fdump-rtl-fwprop2’ enable dumping after the two forward propagation passes.
-fdump-rtl-gcse1
-fdump-rtl-gcse2
‘-fdump-rtl-gcse1’ and ‘-fdump-rtl-gcse2’ enable dumping after global common subexpression elimination.

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-fdump-rtl-init-regs
Dump after the initialization of the registers.
-fdump-rtl-initvals
Dump after the computation of the initial value sets.
-fdump-rtl-into_cfglayout
Dump after converting to cfglayout mode.
-fdump-rtl-ira
Dump after iterated register allocation.
-fdump-rtl-jump
Dump after the second jump optimization.
-fdump-rtl-loop2
‘-fdump-rtl-loop2’ enables dumping after the rtl loop optimization passes.
-fdump-rtl-mach
Dump after performing the machine dependent reorganization pass,
if that pass exists.
-fdump-rtl-mode_sw
Dump after removing redundant mode switches.
-fdump-rtl-rnreg
Dump after register renumbering.
-fdump-rtl-outof_cfglayout
Dump after converting from cfglayout mode.
-fdump-rtl-peephole2
Dump after the peephole pass.
-fdump-rtl-postreload
Dump after post-reload optimizations.
-fdump-rtl-pro_and_epilogue
Dump after generating the function prologues and epilogues.
-fdump-rtl-sched1
-fdump-rtl-sched2
‘-fdump-rtl-sched1’ and ‘-fdump-rtl-sched2’ enable dumping
after the basic block scheduling passes.
-fdump-rtl-ree
Dump after sign/zero extension elimination.
-fdump-rtl-seqabstr
Dump after common sequence discovery.
-fdump-rtl-shorten
Dump after shortening branches.
-fdump-rtl-sibling
Dump after sibling call optimizations.

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-fdump-rtl-split1
-fdump-rtl-split2
-fdump-rtl-split3
-fdump-rtl-split4
-fdump-rtl-split5
These options enable dumping after five rounds of instruction splitting.
-fdump-rtl-sms
Dump after modulo scheduling. This pass is only run on some
architectures.
-fdump-rtl-stack
Dump after conversion from GCC’s “flat register file” registers to
the x87’s stack-like registers. This pass is only run on x86 variants.
-fdump-rtl-subreg1
-fdump-rtl-subreg2
‘-fdump-rtl-subreg1’ and ‘-fdump-rtl-subreg2’ enable dumping after the two subreg expansion passes.
-fdump-rtl-unshare
Dump after all rtl has been unshared.
-fdump-rtl-vartrack
Dump after variable tracking.
-fdump-rtl-vregs
Dump after converting virtual registers to hard registers.
-fdump-rtl-web
Dump after live range splitting.
-fdump-rtl-regclass
-fdump-rtl-subregs_of_mode_init
-fdump-rtl-subregs_of_mode_finish
-fdump-rtl-dfinit
-fdump-rtl-dfinish
These dumps are defined but always produce empty files.
-da
-fdump-rtl-all
Produce all the dumps listed above.
-dA

Annotate the assembler output with miscellaneous debugging information.

-dD

Dump all macro definitions, at the end of preprocessing, in addition
to normal output.

-dH

Produce a core dump whenever an error occurs.

-dp

Annotate the assembler output with a comment indicating which
pattern and alternative is used. The length and cost of each instruction are also printed.

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-dP

Dump the RTL in the assembler output as a comment before each
instruction. Also turns on ‘-dp’ annotation.

-dx

Just generate RTL for a function instead of compiling it. Usually
used with ‘-fdump-rtl-expand’.

-fdump-noaddr
When doing debugging dumps, suppress address output. This makes it more
feasible to use diff on debugging dumps for compiler invocations with different
compiler binaries and/or different text / bss / data / heap / stack / dso start
locations.
-freport-bug
Collect and dump debug information into a temporary file if an internal compiler
error (ICE) occurs.
-fdump-unnumbered
When doing debugging dumps, suppress instruction numbers and address output. This makes it more feasible to use diff on debugging dumps for compiler
invocations with different options, in particular with and without ‘-g’.
-fdump-unnumbered-links
When doing debugging dumps (see ‘-d’ option above), suppress instruction
numbers for the links to the previous and next instructions in a sequence.
-fdump-ipa-switch
Control the dumping at various stages of inter-procedural analysis language tree
to a file. The file name is generated by appending a switch specific suffix to the
source file name, and the file is created in the same directory as the output file.
The following dumps are possible:
‘all’

Enables all inter-procedural analysis dumps.

‘cgraph’

Dumps information about call-graph optimization, unused function
removal, and inlining decisions.

‘inline’

Dump after function inlining.

-fdump-lang-all
-fdump-lang-switch
-fdump-lang-switch-options
-fdump-lang-switch-options=filename
Control the dumping of language-specific information. The options and filename portions behave as described in the ‘-fdump-tree’ option. The following
switch values are accepted:
‘all’
Enable all language-specific dumps.
‘class’

Dump class hierarchy information. Virtual table information is
emitted unless ’‘slim’’ is specified. This option is applicable to
C++ only.

‘raw’

Dump the raw internal tree data. This option is applicable to C++
only.

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-fdump-passes
Print on ‘stderr’ the list of optimization passes that are turned on and off by
the current command-line options.
-fdump-statistics-option
Enable and control dumping of pass statistics in a separate file. The file name
is generated by appending a suffix ending in ‘.statistics’ to the source file
name, and the file is created in the same directory as the output file. If the
‘-option’ form is used, ‘-stats’ causes counters to be summed over the whole
compilation unit while ‘-details’ dumps every event as the passes generate
them. The default with no option is to sum counters for each function compiled.
-fdump-tree-all
-fdump-tree-switch
-fdump-tree-switch-options
-fdump-tree-switch-options=filename
Control the dumping at various stages of processing the intermediate language
tree to a file. The file name is generated by appending a switch-specific suffix to
the source file name, and the file is created in the same directory as the output
file. In case of ‘=filename’ option, the dump is output on the given file instead
of the auto named dump files. If the ‘-options’ form is used, options is a list
of ‘-’ separated options which control the details of the dump. Not all options
are applicable to all dumps; those that are not meaningful are ignored. The
following options are available
‘address’

Print the address of each node. Usually this is not meaningful as it
changes according to the environment and source file. Its primary
use is for tying up a dump file with a debug environment.

‘asmname’

If DECL_ASSEMBLER_NAME has been set for a given decl, use that
in the dump instead of DECL_NAME. Its primary use is ease of use
working backward from mangled names in the assembly file.

‘slim’

When dumping front-end intermediate representations, inhibit
dumping of members of a scope or body of a function merely
because that scope has been reached. Only dump such items when
they are directly reachable by some other path.
When dumping pretty-printed trees, this option inhibits dumping
the bodies of control structures.
When dumping RTL, print the RTL in slim (condensed) form instead of the default LISP-like representation.

‘raw’

Print a raw representation of the tree. By default, trees are prettyprinted into a C-like representation.

‘details’

Enable more detailed dumps (not honored by every dump option).
Also include information from the optimization passes.

‘stats’

Enable dumping various statistics about the pass (not honored by
every dump option).

‘blocks’

Enable showing basic block boundaries (disabled in raw dumps).

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219

For each of the other indicated dump files (‘-fdump-rtl-pass’),
dump a representation of the control flow graph suitable for viewing
with GraphViz to ‘file.passid.pass.dot’. Each function in the
file is pretty-printed as a subgraph, so that GraphViz can render
them all in a single plot.
This option currently only works for RTL dumps, and the RTL is
always dumped in slim form.

‘vops’

Enable showing virtual operands for every statement.

‘lineno’

Enable showing line numbers for statements.

‘uid’

Enable showing the unique ID (DECL_UID) for each variable.

‘verbose’

Enable showing the tree dump for each statement.

‘eh’

Enable showing the EH region number holding each statement.

‘scev’

Enable showing scalar evolution analysis details.

‘optimized’
Enable showing optimization information (only available in certain
passes).
‘missed’

Enable showing missed optimization information (only available in
certain passes).

‘note’

Enable other detailed optimization information (only available in
certain passes).

‘=filename’
Instead of an auto named dump file, output into the given file name.
The file names ‘stdout’ and ‘stderr’ are treated specially and are
considered already open standard streams. For example,
gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
-fdump-tree-pre=/dev/stderr file.c

outputs vectorizer dump into ‘foo.dump’, while the PRE dump is
output on to ‘stderr’. If two conflicting dump filenames are given
for the same pass, then the latter option overrides the earlier one.
‘all’

Turn on all options, except ‘raw’, ‘slim’, ‘verbose’ and ‘lineno’.

‘optall’

Turn on all optimization options, i.e., ‘optimized’, ‘missed’, and
‘note’.

To determine what tree dumps are available or find the dump for a pass of
interest follow the steps below.
1. Invoke GCC with ‘-fdump-passes’ and in the ‘stderr’ output look for
a code that corresponds to the pass you are interested in. For example,
the codes tree-evrp, tree-vrp1, and tree-vrp2 correspond to the three
Value Range Propagation passes. The number at the end distinguishes
distinct invocations of the same pass.

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2. To enable the creation of the dump file, append the pass code to the
‘-fdump-’ option prefix and invoke GCC with it. For example, to enable
the dump from the Early Value Range Propagation pass, invoke GCC with
the ‘-fdump-tree-evrp’ option. Optionally, you may specify the name of
the dump file. If you don’t specify one, GCC creates as described below.
3. Find the pass dump in a file whose name is composed of three components
separated by a period: the name of the source file GCC was invoked to
compile, a numeric suffix indicating the pass number followed by the letter
‘t’ for tree passes (and the letter ‘r’ for RTL passes), and finally the pass
code. For example, the Early VRP pass dump might be in a file named
‘myfile.c.038t.evrp’ in the current working directory. Note that the
numeric codes are not stable and may change from one version of GCC to
another.
-fopt-info
-fopt-info-options
-fopt-info-options=filename
Controls optimization dumps from various optimization passes.
If the
‘-options’ form is used, options is a list of ‘-’ separated option keywords to
select the dump details and optimizations.
The options can be divided into two groups: options describing the verbosity of
the dump, and options describing which optimizations should be included. The
options from both the groups can be freely mixed as they are non-overlapping.
However, in case of any conflicts, the later options override the earlier options
on the command line.
The following options control the dump verbosity:
‘optimized’
Print information when an optimization is successfully applied. It
is up to a pass to decide which information is relevant. For example,
the vectorizer passes print the source location of loops which are
successfully vectorized.
‘missed’

Print information about missed optimizations. Individual passes
control which information to include in the output.

‘note’

Print verbose information about optimizations, such as certain
transformations, more detailed messages about decisions etc.

‘all’

Print detailed optimization information.
‘optimized’, ‘missed’, and ‘note’.

This

includes

One or more of the following option keywords can be used to describe a group
of optimizations:
‘ipa’

Enable dumps from all interprocedural optimizations.

‘loop’

Enable dumps from all loop optimizations.

‘inline’

Enable dumps from all inlining optimizations.

‘omp’

Enable dumps from all OMP (Offloading and Multi Processing)
optimizations.

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‘vec’

Enable dumps from all vectorization optimizations.

‘optall’

Enable dumps from all optimizations. This is a superset of the
optimization groups listed above.

If options is omitted, it defaults to ‘optimized-optall’, which means to dump
all info about successful optimizations from all the passes.
If the filename is provided, then the dumps from all the applicable optimizations are concatenated into the filename. Otherwise the dump is output onto
‘stderr’. Though multiple ‘-fopt-info’ options are accepted, only one of them
can include a filename. If other filenames are provided then all but the first
such option are ignored.
Note that the output filename is overwritten in case of multiple translation
units. If a combined output from multiple translation units is desired, ‘stderr’
should be used instead.
In the following example, the optimization info is output to ‘stderr’:
gcc -O3 -fopt-info

This example:
gcc -O3 -fopt-info-missed=missed.all

outputs missed optimization report from all the passes into ‘missed.all’, and
this one:
gcc -O2 -ftree-vectorize -fopt-info-vec-missed

prints information about missed optimization opportunities from vectorization passes on ‘stderr’. Note that ‘-fopt-info-vec-missed’ is equivalent
to ‘-fopt-info-missed-vec’. The order of the optimization group names and
message types listed after ‘-fopt-info’ does not matter.
As another example,
gcc -O3 -fopt-info-inline-optimized-missed=inline.txt

outputs information about missed optimizations as well as optimized locations
from all the inlining passes into ‘inline.txt’.
Finally, consider:
gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt

Here the two output filenames ‘vec.miss’ and ‘loop.opt’ are in conflict since
only one output file is allowed. In this case, only the first option takes effect and
the subsequent options are ignored. Thus only ‘vec.miss’ is produced which
contains dumps from the vectorizer about missed opportunities.
-fsched-verbose=n
On targets that use instruction scheduling, this option controls the amount of
debugging output the scheduler prints to the dump files.
For n greater than zero, ‘-fsched-verbose’ outputs the same information as
‘-fdump-rtl-sched1’ and ‘-fdump-rtl-sched2’. For n greater than one, it also
output basic block probabilities, detailed ready list information and unit/insn
info. For n greater than two, it includes RTL at abort point, control-flow and
regions info. And for n over four, ‘-fsched-verbose’ also includes dependence
info.

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-fenable-kind-pass
-fdisable-kind-pass=range-list
This is a set of options that are used to explicitly disable/enable optimization
passes. These options are intended for use for debugging GCC. Compiler users
should use regular options for enabling/disabling passes instead.
-fdisable-ipa-pass
Disable IPA pass pass. pass is the pass name. If the same pass
is statically invoked in the compiler multiple times, the pass name
should be appended with a sequential number starting from 1.
-fdisable-rtl-pass
-fdisable-rtl-pass=range-list
Disable RTL pass pass. pass is the pass name. If the same pass is
statically invoked in the compiler multiple times, the pass name
should be appended with a sequential number starting from 1.
range-list is a comma-separated list of function ranges or assembler names. Each range is a number pair separated by a colon.
The range is inclusive in both ends. If the range is trivial, the
number pair can be simplified as a single number. If the function’s
call graph node’s uid falls within one of the specified ranges, the
pass is disabled for that function. The uid is shown in the function
header of a dump file, and the pass names can be dumped by using
option ‘-fdump-passes’.
-fdisable-tree-pass
-fdisable-tree-pass=range-list
Disable tree pass pass. See ‘-fdisable-rtl’ for the description of
option arguments.
-fenable-ipa-pass
Enable IPA pass pass. pass is the pass name. If the same pass
is statically invoked in the compiler multiple times, the pass name
should be appended with a sequential number starting from 1.
-fenable-rtl-pass
-fenable-rtl-pass=range-list
Enable RTL pass pass. See ‘-fdisable-rtl’ for option argument
description and examples.
-fenable-tree-pass
-fenable-tree-pass=range-list
Enable tree pass pass. See ‘-fdisable-rtl’ for the description of
option arguments.
Here are some examples showing uses of these options.
# disable ccp1 for all functions
-fdisable-tree-ccp1
# disable complete unroll for function whose cgraph node uid is 1
-fenable-tree-cunroll=1
# disable gcse2 for functions at the following ranges [1,1],

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# [300,400], and [400,1000]
# disable gcse2 for functions foo and foo2
-fdisable-rtl-gcse2=foo,foo2
# disable early inlining
-fdisable-tree-einline
# disable ipa inlining
-fdisable-ipa-inline
# enable tree full unroll
-fenable-tree-unroll

-fchecking
-fchecking=n
Enable internal consistency checking. The default depends on the compiler
configuration. ‘-fchecking=2’ enables further internal consistency checking
that might affect code generation.
-frandom-seed=string
This option provides a seed that GCC uses in place of random numbers in
generating certain symbol names that have to be different in every compiled
file. It is also used to place unique stamps in coverage data files and the object
files that produce them. You can use the ‘-frandom-seed’ option to produce
reproducibly identical object files.
The string can either be a number (decimal, octal or hex) or an arbitrary string
(in which case it’s converted to a number by computing CRC32).
The string should be different for every file you compile.
-save-temps
-save-temps=cwd
Store the usual “temporary” intermediate files permanently; place them in the
current directory and name them based on the source file. Thus, compiling
‘foo.c’ with ‘-c -save-temps’ produces files ‘foo.i’ and ‘foo.s’, as well as
‘foo.o’. This creates a preprocessed ‘foo.i’ output file even though the compiler now normally uses an integrated preprocessor.
When used in combination with the ‘-x’ command-line option, ‘-save-temps’
is sensible enough to avoid over writing an input source file with the same
extension as an intermediate file. The corresponding intermediate file may be
obtained by renaming the source file before using ‘-save-temps’.
If you invoke GCC in parallel, compiling several different source files that share
a common base name in different subdirectories or the same source file compiled
for multiple output destinations, it is likely that the different parallel compilers
will interfere with each other, and overwrite the temporary files. For instance:
gcc -save-temps -o outdir1/foo.o indir1/foo.c&
gcc -save-temps -o outdir2/foo.o indir2/foo.c&

may result in ‘foo.i’ and ‘foo.o’ being written to simultaneously by both
compilers.
-save-temps=obj
Store the usual “temporary” intermediate files permanently. If the ‘-o’ option
is used, the temporary files are based on the object file. If the ‘-o’ option is
not used, the ‘-save-temps=obj’ switch behaves like ‘-save-temps’.

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For example:
gcc -save-temps=obj -c foo.c
gcc -save-temps=obj -c bar.c -o dir/xbar.o
gcc -save-temps=obj foobar.c -o dir2/yfoobar

creates ‘foo.i’, ‘foo.s’, ‘dir/xbar.i’, ‘dir/xbar.s’, ‘dir2/yfoobar.i’,
‘dir2/yfoobar.s’, and ‘dir2/yfoobar.o’.
-time[=file]
Report the CPU time taken by each subprocess in the compilation sequence.
For C source files, this is the compiler proper and assembler (plus the linker if
linking is done).
Without the specification of an output file, the output looks like this:
# cc1 0.12 0.01
# as 0.00 0.01

The first number on each line is the “user time”, that is time spent executing
the program itself. The second number is “system time”, time spent executing
operating system routines on behalf of the program. Both numbers are in
seconds.
With the specification of an output file, the output is appended to the named
file, and it looks like this:
0.12 0.01 cc1 options
0.00 0.01 as options

The “user time” and the “system time” are moved before the program name,
and the options passed to the program are displayed, so that one can later tell
what file was being compiled, and with which options.
-fdump-final-insns[=file]
Dump the final internal representation (RTL) to file. If the optional argument
is omitted (or if file is .), the name of the dump file is determined by appending
.gkd to the compilation output file name.
-fcompare-debug[=opts]
If no error occurs during compilation, run the compiler a second time, adding
opts and ‘-fcompare-debug-second’ to the arguments passed to the second
compilation. Dump the final internal representation in both compilations, and
print an error if they differ.
If the equal sign is omitted, the default ‘-gtoggle’ is used.
The environment variable GCC_COMPARE_DEBUG, if defined, non-empty and
nonzero, implicitly enables ‘-fcompare-debug’. If GCC_COMPARE_DEBUG is
defined to a string starting with a dash, then it is used for opts, otherwise the
default ‘-gtoggle’ is used.
‘-fcompare-debug=’, with the equal sign but without opts, is equivalent to
‘-fno-compare-debug’, which disables the dumping of the final representation
and the second compilation, preventing even GCC_COMPARE_DEBUG from taking
effect.
To verify full coverage during ‘-fcompare-debug’ testing, set GCC_COMPARE_
DEBUG to say ‘-fcompare-debug-not-overridden’, which GCC rejects as

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an invalid option in any actual compilation (rather than preprocessing,
assembly or linking). To get just a warning, setting GCC_COMPARE_DEBUG to
‘-w%n-fcompare-debug not overridden’ will do.
-fcompare-debug-second
This option is implicitly passed to the compiler for the second compilation
requested by ‘-fcompare-debug’, along with options to silence warnings, and
omitting other options that would cause the compiler to produce output to files
or to standard output as a side effect. Dump files and preserved temporary files
are renamed so as to contain the .gk additional extension during the second
compilation, to avoid overwriting those generated by the first.
When this option is passed to the compiler driver, it causes the first compilation
to be skipped, which makes it useful for little other than debugging the compiler
proper.
-gtoggle

Turn off generation of debug info, if leaving out this option generates it, or turn
it on at level 2 otherwise. The position of this argument in the command line
does not matter; it takes effect after all other options are processed, and it does
so only once, no matter how many times it is given. This is mainly intended to
be used with ‘-fcompare-debug’.

-fvar-tracking-assignments-toggle
Toggle ‘-fvar-tracking-assignments’, in the same way that ‘-gtoggle’ toggles ‘-g’.
-Q

Makes the compiler print out each function name as it is compiled, and print
some statistics about each pass when it finishes.

-ftime-report
Makes the compiler print some statistics about the time consumed by each pass
when it finishes.
-ftime-report-details
Record the time consumed by infrastructure parts separately for each pass.
-fira-verbose=n
Control the verbosity of the dump file for the integrated register allocator. The
default value is 5. If the value n is greater or equal to 10, the dump output is
sent to stderr using the same format as n minus 10.
-flto-report
Prints a report with internal details on the workings of the link-time optimizer.
The contents of this report vary from version to version. It is meant to be useful
to GCC developers when processing object files in LTO mode (via ‘-flto’).
Disabled by default.
-flto-report-wpa
Like ‘-flto-report’, but only print for the WPA phase of Link Time Optimization.
-fmem-report
Makes the compiler print some statistics about permanent memory allocation
when it finishes.

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-fmem-report-wpa
Makes the compiler print some statistics about permanent memory allocation
for the WPA phase only.
-fpre-ipa-mem-report
-fpost-ipa-mem-report
Makes the compiler print some statistics about permanent memory allocation
before or after interprocedural optimization.
-fprofile-report
Makes the compiler print some statistics about consistency of the (estimated)
profile and effect of individual passes.
-fstack-usage
Makes the compiler output stack usage information for the program, on a perfunction basis. The filename for the dump is made by appending ‘.su’ to the
auxname. auxname is generated from the name of the output file, if explicitly
specified and it is not an executable, otherwise it is the basename of the source
file. An entry is made up of three fields:
• The name of the function.
• A number of bytes.
• One or more qualifiers: static, dynamic, bounded.
The qualifier static means that the function manipulates the stack statically: a
fixed number of bytes are allocated for the frame on function entry and released
on function exit; no stack adjustments are otherwise made in the function. The
second field is this fixed number of bytes.
The qualifier dynamic means that the function manipulates the stack dynamically: in addition to the static allocation described above, stack adjustments are
made in the body of the function, for example to push/pop arguments around
function calls. If the qualifier bounded is also present, the amount of these adjustments is bounded at compile time and the second field is an upper bound of
the total amount of stack used by the function. If it is not present, the amount
of these adjustments is not bounded at compile time and the second field only
represents the bounded part.
-fstats

Emit statistics about front-end processing at the end of the compilation. This
option is supported only by the C++ front end, and the information is generally
only useful to the G++ development team.

-fdbg-cnt-list
Print the name and the counter upper bound for all debug counters.
-fdbg-cnt=counter-value-list
Set the internal debug counter upper bound. counter-value-list is a commaseparated list of name:value pairs which sets the upper bound of each debug
counter name to value. All debug counters have the initial upper bound of
UINT_MAX; thus dbg_cnt returns true always unless the upper bound is set
by this option. For example, with ‘-fdbg-cnt=dce:10,tail_call:0’, dbg_
cnt(dce) returns true only for first 10 invocations.

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-print-file-name=library
Print the full absolute name of the library file library that would be used when
linking—and don’t do anything else. With this option, GCC does not compile
or link anything; it just prints the file name.
-print-multi-directory
Print the directory name corresponding to the multilib selected by any other
switches present in the command line. This directory is supposed to exist in
GCC_EXEC_PREFIX.
-print-multi-lib
Print the mapping from multilib directory names to compiler switches that
enable them. The directory name is separated from the switches by ‘;’, and
each switch starts with an ‘@’ instead of the ‘-’, without spaces between multiple
switches. This is supposed to ease shell processing.
-print-multi-os-directory
Print the path to OS libraries for the selected multilib, relative to some ‘lib’
subdirectory. If OS libraries are present in the ‘lib’ subdirectory and no multilibs are used, this is usually just ‘.’, if OS libraries are present in ‘libsuffix’
sibling directories this prints e.g. ‘../lib64’, ‘../lib’ or ‘../lib32’, or if
OS libraries are present in ‘lib/subdir’ subdirectories it prints e.g. ‘amd64’,
‘sparcv9’ or ‘ev6’.
-print-multiarch
Print the path to OS libraries for the selected multiarch, relative to some ‘lib’
subdirectory.
-print-prog-name=program
Like ‘-print-file-name’, but searches for a program such as cpp.
-print-libgcc-file-name
Same as ‘-print-file-name=libgcc.a’.
This is useful when you use ‘-nostdlib’ or ‘-nodefaultlibs’ but you do want
to link with ‘libgcc.a’. You can do:
gcc -nostdlib files... ‘gcc -print-libgcc-file-name‘

-print-search-dirs
Print the name of the configured installation directory and a list of program
and library directories gcc searches—and don’t do anything else.
This is useful when gcc prints the error message ‘installation problem,
cannot exec cpp0: No such file or directory’. To resolve this you either
need to put ‘cpp0’ and the other compiler components where gcc expects to
find them, or you can set the environment variable GCC_EXEC_PREFIX to the directory where you installed them. Don’t forget the trailing ‘/’. See Section 3.20
[Environment Variables], page 422.
-print-sysroot
Print the target sysroot directory that is used during compilation. This is the
target sysroot specified either at configure time or using the ‘--sysroot’ option,
possibly with an extra suffix that depends on compilation options. If no target
sysroot is specified, the option prints nothing.

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-print-sysroot-headers-suffix
Print the suffix added to the target sysroot when searching for headers, or
give an error if the compiler is not configured with such a suffix—and don’t do
anything else.
-dumpmachine
Print the compiler’s target machine (for example, ‘i686-pc-linux-gnu’)—and
don’t do anything else.
-dumpversion
Print the compiler version (for example, 3.0, 6.3.0 or 7)—and don’t do anything else. This is the compiler version used in filesystem paths, specs, can
be depending on how the compiler has been configured just a single number
(major version), two numbers separated by dot (major and minor version) or
three numbers separated by dots (major, minor and patchlevel version).
-dumpfullversion
Print the full compiler version, always 3 numbers separated by dots, major,
minor and patchlevel version.
-dumpspecs
Print the compiler’s built-in specs—and don’t do anything else. (This is used
when GCC itself is being built.) See Section 3.19 [Spec Files], page 415.

3.18 Machine-Dependent Options
Each target machine supported by GCC can have its own options—for example, to allow
you to compile for a particular processor variant or ABI, or to control optimizations specific
to that machine. By convention, the names of machine-specific options start with ‘-m’.
Some configurations of the compiler also support additional target-specific options, usually for compatibility with other compilers on the same platform.

3.18.1 AArch64 Options
These options are defined for AArch64 implementations:
-mabi=name
Generate code for the specified data model. Permissible values are ‘ilp32’ for
SysV-like data model where int, long int and pointers are 32 bits, and ‘lp64’
for SysV-like data model where int is 32 bits, but long int and pointers are 64
bits.
The default depends on the specific target configuration. Note that the LP64
and ILP32 ABIs are not link-compatible; you must compile your entire program
with the same ABI, and link with a compatible set of libraries.
-mbig-endian
Generate big-endian code. This is the default when GCC is configured for an
‘aarch64_be-*-*’ target.
-mgeneral-regs-only
Generate code which uses only the general-purpose registers. This will prevent
the compiler from using floating-point and Advanced SIMD registers but will
not impose any restrictions on the assembler.

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-mlittle-endian
Generate little-endian code. This is the default when GCC is configured for an
‘aarch64-*-*’ but not an ‘aarch64_be-*-*’ target.
-mcmodel=tiny
Generate code for the tiny code model. The program and its statically defined
symbols must be within 1MB of each other. Programs can be statically or
dynamically linked.
-mcmodel=small
Generate code for the small code model. The program and its statically defined
symbols must be within 4GB of each other. Programs can be statically or
dynamically linked. This is the default code model.
-mcmodel=large
Generate code for the large code model. This makes no assumptions about
addresses and sizes of sections. Programs can be statically linked only.
-mstrict-align
Avoid generating memory accesses that may not be aligned on a natural object
boundary as described in the architecture specification.
-momit-leaf-frame-pointer
-mno-omit-leaf-frame-pointer
Omit or keep the frame pointer in leaf functions. The former behavior is the
default.
-mtls-dialect=desc
Use TLS descriptors as the thread-local storage mechanism for dynamic accesses
of TLS variables. This is the default.
-mtls-dialect=traditional
Use traditional TLS as the thread-local storage mechanism for dynamic accesses
of TLS variables.
-mtls-size=size
Specify bit size of immediate TLS offsets. Valid values are 12, 24, 32, 48. This
option requires binutils 2.26 or newer.
-mfix-cortex-a53-835769
-mno-fix-cortex-a53-835769
Enable or disable the workaround for the ARM Cortex-A53 erratum number
835769. This involves inserting a NOP instruction between memory instructions
and 64-bit integer multiply-accumulate instructions.
-mfix-cortex-a53-843419
-mno-fix-cortex-a53-843419
Enable or disable the workaround for the ARM Cortex-A53 erratum number
843419. This erratum workaround is made at link time and this will only pass
the corresponding flag to the linker.

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-mlow-precision-recip-sqrt
-mno-low-precision-recip-sqrt
Enable or disable the reciprocal square root approximation. This option only
has an effect if ‘-ffast-math’ or ‘-funsafe-math-optimizations’ is used as
well. Enabling this reduces precision of reciprocal square root results to about
16 bits for single precision and to 32 bits for double precision.
-mlow-precision-sqrt
-mno-low-precision-sqrt
Enable or disable the square root approximation. This option only has an
effect if ‘-ffast-math’ or ‘-funsafe-math-optimizations’ is used as well.
Enabling this reduces precision of square root results to about 16 bits for
single precision and to 32 bits for double precision. If enabled, it implies
‘-mlow-precision-recip-sqrt’.
-mlow-precision-div
-mno-low-precision-div
Enable or disable the division approximation. This option only has an effect if
‘-ffast-math’ or ‘-funsafe-math-optimizations’ is used as well. Enabling
this reduces precision of division results to about 16 bits for single precision
and to 32 bits for double precision.
-march=name
Specify the name of the target architecture and, optionally, one or more feature
modifiers. This option has the form ‘-march=arch{+[no]feature}*’.
The permissible values for arch are ‘armv8-a’, ‘armv8.1-a’, ‘armv8.2-a’,
‘armv8.3-a’ or ‘armv8.4-a’ or native.
The value ‘armv8.4-a’ implies ‘armv8.3-a’ and enables compiler support for
the ARMv8.4-A architecture extensions.
The value ‘armv8.3-a’ implies ‘armv8.2-a’ and enables compiler support for
the ARMv8.3-A architecture extensions.
The value ‘armv8.2-a’ implies ‘armv8.1-a’ and enables compiler support for
the ARMv8.2-A architecture extensions.
The value ‘armv8.1-a’ implies ‘armv8-a’ and enables compiler support for the
ARMv8.1-A architecture extension. In particular, it enables the ‘+crc’, ‘+lse’,
and ‘+rdma’ features.
The value ‘native’ is available on native AArch64 GNU/Linux and causes the
compiler to pick the architecture of the host system. This option has no effect
if the compiler is unable to recognize the architecture of the host system,
The permissible values for feature are listed in the sub-section on [‘-march’ and
‘-mcpu’ Feature Modifiers], page 232. Where conflicting feature modifiers are
specified, the right-most feature is used.
GCC uses name to determine what kind of instructions it can emit when generating assembly code. If ‘-march’ is specified without either of ‘-mtune’ or
‘-mcpu’ also being specified, the code is tuned to perform well across a range of
target processors implementing the target architecture.

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-mtune=name
Specify the name of the target processor for which GCC should
tune the performance of the code.
Permissible values for this option are:
‘generic’,
‘cortex-a35’,
‘cortex-a53’,
‘cortex-a55’,
‘cortex-a57’, ‘cortex-a72’, ‘cortex-a73’, ‘cortex-a75’, ‘exynos-m1’,
‘falkor’,
‘qdf24xx’,
‘saphira’,
‘xgene1’,
‘vulcan’,
‘thunderx’,
‘thunderxt88’,
‘thunderxt88p1’,
‘thunderxt81’,
‘thunderxt83’,
‘thunderx2t99’,
‘cortex-a57.cortex-a53’,
‘cortex-a72.cortex-a53’,
‘cortex-a73.cortex-a35’, ‘cortex-a73.cortex-a53’, ‘cortex-a75.cortex-a55’,
‘native’.
The
values
‘cortex-a57.cortex-a53’,
‘cortex-a72.cortex-a53’,
‘cortex-a73.cortex-a35’, ‘cortex-a73.cortex-a53’, ‘cortex-a75.cortex-a55’
specify that GCC should tune for a big.LITTLE system.
Additionally on native AArch64 GNU/Linux systems the value ‘native’ tunes
performance to the host system. This option has no effect if the compiler is
unable to recognize the processor of the host system.
Where none of ‘-mtune=’, ‘-mcpu=’ or ‘-march=’ are specified, the code is tuned
to perform well across a range of target processors.
This option cannot be suffixed by feature modifiers.
-mcpu=name
Specify the name of the target processor, optionally suffixed by one or more
feature modifiers. This option has the form ‘-mcpu=cpu{+[no]feature}*’, where
the permissible values for cpu are the same as those available for ‘-mtune’. The
permissible values for feature are documented in the sub-section on [‘-march’
and ‘-mcpu’ Feature Modifiers], page 232. Where conflicting feature modifiers
are specified, the right-most feature is used.
GCC uses name to determine what kind of instructions it can emit when generating assembly code (as if by ‘-march’) and to determine the target processor
for which to tune for performance (as if by ‘-mtune’). Where this option is used
in conjunction with ‘-march’ or ‘-mtune’, those options take precedence over
the appropriate part of this option.
-moverride=string
Override tuning decisions made by the back-end in response to a ‘-mtune=’
switch. The syntax, semantics, and accepted values for string in this option are
not guaranteed to be consistent across releases.
This option is only intended to be useful when developing GCC.
-mverbose-cost-dump
Enable verbose cost model dumping in the debug dump files. This option is
provided for use in debugging the compiler.
-mpc-relative-literal-loads
-mno-pc-relative-literal-loads
Enable or disable PC-relative literal loads. With this option literal pools are
accessed using a single instruction and emitted after each function. This lim-

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its the maximum size of functions to 1MB. This is enabled by default for
‘-mcmodel=tiny’.
-msign-return-address=scope
Select the function scope on which return address signing will be applied. Permissible values are ‘none’, which disables return address signing, ‘non-leaf’,
which enables pointer signing for functions which are not leaf functions, and
‘all’, which enables pointer signing for all functions. The default value is
‘none’.
-msve-vector-bits=bits
Specify the number of bits in an SVE vector register. This option only has an
effect when SVE is enabled.
GCC supports two forms of SVE code generation: “vector-length agnostic”
output that works with any size of vector register and “vector-length specific”
output that only works when the vector registers are a particular size. Replacing
bits with ‘scalable’ selects vector-length agnostic output while replacing it
with a number selects vector-length specific output. The possible lengths in
the latter case are: 128, 256, 512, 1024 and 2048. ‘scalable’ is the default.
At present, ‘-msve-vector-bits=128’ produces the same output as
‘-msve-vector-bits=scalable’.

3.18.1.1 ‘-march’ and ‘-mcpu’ Feature Modifiers
Feature modifiers used with ‘-march’ and ‘-mcpu’ can be any of the following and their
inverses ‘nofeature’:
‘crc’

Enable CRC extension. This is on by default for ‘-march=armv8.1-a’.

‘crypto’

Enable Crypto extension. This also enables Advanced SIMD and floating-point
instructions.

‘fp’

Enable floating-point instructions. This is on by default for all possible values
for options ‘-march’ and ‘-mcpu’.

‘simd’

Enable Advanced SIMD instructions. This also enables floating-point instructions. This is on by default for all possible values for options ‘-march’ and
‘-mcpu’.

‘sve’

Enable Scalable Vector Extension instructions. This also enables Advanced
SIMD and floating-point instructions.

‘lse’

Enable Large System Extension instructions.
‘-march=armv8.1-a’.

‘rdma’

Enable Round Double Multiply Accumulate instructions. This is on by default
for ‘-march=armv8.1-a’.

‘fp16’

Enable FP16 extension. This also enables floating-point instructions.

‘fp16fml’

Enable FP16 fmla extension. This also enables FP16 extensions and floatingpoint instructions. This option is enabled by default for ‘-march=armv8.4-a’.
Use of this option with architectures prior to Armv8.2-A is not supported.

This is on by default for

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‘rcpc’

Enable the RcPc extension. This does not change code generation from GCC,
but is passed on to the assembler, enabling inline asm statements to use instructions from the RcPc extension.

‘dotprod’

Enable the Dot Product extension. This also enables Advanced SIMD instructions.

‘aes’

Enable the Armv8-a aes and pmull crypto extension. This also enables Advanced SIMD instructions.

‘sha2’

Enable the Armv8-a sha2 crypto extension. This also enables Advanced SIMD
instructions.

‘sha3’

Enable the sha512 and sha3 crypto extension. This also enables Advanced
SIMD instructions. Use of this option with architectures prior to Armv8.2-A is
not supported.

‘sm4’

Enable the sm3 and sm4 crypto extension. This also enables Advanced SIMD
instructions. Use of this option with architectures prior to Armv8.2-A is not
supported.

Feature ‘crypto’ implies ‘aes’, ‘sha2’, and ‘simd’, which implies ‘fp’. Conversely, ‘nofp’
implies ‘nosimd’, which implies ‘nocrypto’, ‘noaes’ and ‘nosha2’.

3.18.2 Adapteva Epiphany Options
These ‘-m’ options are defined for Adapteva Epiphany:
-mhalf-reg-file
Don’t allocate any register in the range r32. . . r63. That allows code to run
on hardware variants that lack these registers.
-mprefer-short-insn-regs
Preferentially allocate registers that allow short instruction generation. This
can result in increased instruction count, so this may either reduce or increase
overall code size.
-mbranch-cost=num
Set the cost of branches to roughly num “simple” instructions. This cost is only
a heuristic and is not guaranteed to produce consistent results across releases.
-mcmove

Enable the generation of conditional moves.

-mnops=num
Emit num NOPs before every other generated instruction.
-mno-soft-cmpsf
For single-precision floating-point comparisons, emit an fsub instruction and
test the flags. This is faster than a software comparison, but can get incorrect results in the presence of NaNs, or when two different small numbers are compared
such that their difference is calculated as zero. The default is ‘-msoft-cmpsf’,
which uses slower, but IEEE-compliant, software comparisons.
-mstack-offset=num
Set the offset between the top of the stack and the stack pointer. E.g., a value
of 8 means that the eight bytes in the range sp+0...sp+7 can be used by leaf

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functions without stack allocation. Values other than ‘8’ or ‘16’ are untested
and unlikely to work. Note also that this option changes the ABI; compiling
a program with a different stack offset than the libraries have been compiled
with generally does not work. This option can be useful if you want to evaluate
if a different stack offset would give you better code, but to actually use a
different stack offset to build working programs, it is recommended to configure
the toolchain with the appropriate ‘--with-stack-offset=num’ option.
-mno-round-nearest
Make the scheduler assume that the rounding mode has been set to truncating.
The default is ‘-mround-nearest’.
-mlong-calls
If not otherwise specified by an attribute, assume all calls might be beyond the
offset range of the b / bl instructions, and therefore load the function address
into a register before performing a (otherwise direct) call. This is the default.
-mshort-calls
If not otherwise specified by an attribute, assume all direct calls are in the range
of the b / bl instructions, so use these instructions for direct calls. The default
is ‘-mlong-calls’.
-msmall16
Assume addresses can be loaded as 16-bit unsigned values. This does not apply
to function addresses for which ‘-mlong-calls’ semantics are in effect.
-mfp-mode=mode
Set the prevailing mode of the floating-point unit. This determines the floatingpoint mode that is provided and expected at function call and return time.
Making this mode match the mode you predominantly need at function start can
make your programs smaller and faster by avoiding unnecessary mode switches.
mode can be set to one the following values:
‘caller’

Any mode at function entry is valid, and retained or restored when
the function returns, and when it calls other functions. This mode
is useful for compiling libraries or other compilation units you might
want to incorporate into different programs with different prevailing FPU modes, and the convenience of being able to use a single
object file outweighs the size and speed overhead for any extra
mode switching that might be needed, compared with what would
be needed with a more specific choice of prevailing FPU mode.

‘truncate’
This is the mode used for floating-point calculations with truncating
(i.e. round towards zero) rounding mode. That includes conversion
from floating point to integer.
‘round-nearest’
This is the mode used for floating-point calculations with roundto-nearest-or-even rounding mode.

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235

This is the mode used to perform integer calculations in the FPU,
e.g. integer multiply, or integer multiply-and-accumulate.

The default is ‘-mfp-mode=caller’
-mnosplit-lohi
-mno-postinc
-mno-postmodify
Code generation tweaks that disable, respectively, splitting of 32-bit loads, generation of post-increment addresses, and generation of post-modify addresses.
The defaults are ‘msplit-lohi’, ‘-mpost-inc’, and ‘-mpost-modify’.
-mnovect-double
Change the preferred SIMD mode to SImode. The default is ‘-mvect-double’,
which uses DImode as preferred SIMD mode.
-max-vect-align=num
The maximum alignment for SIMD vector mode types. num may be 4 or 8.
The default is 8. Note that this is an ABI change, even though many library
function interfaces are unaffected if they don’t use SIMD vector modes in places
that affect size and/or alignment of relevant types.
-msplit-vecmove-early
Split vector moves into single word moves before reload. In theory this can give
better register allocation, but so far the reverse seems to be generally the case.
-m1reg-reg
Specify a register to hold the constant −1, which makes loading small negative
constants and certain bitmasks faster. Allowable values for reg are ‘r43’ and
‘r63’, which specify use of that register as a fixed register, and ‘none’, which
means that no register is used for this purpose. The default is ‘-m1reg-none’.

3.18.3 ARC Options
The following options control the architecture variant for which code is being compiled:
-mbarrel-shifter
Generate instructions supported by barrel shifter. This is the default unless
‘-mcpu=ARC601’ or ‘-mcpu=ARCEM’ is in effect.
-mjli-always
Force to call a function using jli s instruction. This option is valid only for
ARCv2 architecture.
-mcpu=cpu
Set architecture type, register usage, and instruction scheduling parameters for
cpu. There are also shortcut alias options available for backward compatibility
and convenience. Supported values for cpu are
‘arc600’

Compile for ARC600. Aliases: ‘-mA6’, ‘-mARC600’.

‘arc601’

Compile for ARC601. Alias: ‘-mARC601’.

‘arc700’

Compile for ARC700. Aliases: ‘-mA7’, ‘-mARC700’. This is the
default when configured with ‘--with-cpu=arc700’.

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‘arcem’

Compile for ARC EM.

‘archs’

Compile for ARC HS.

‘em’

Compile for ARC EM CPU with no hardware extensions.

‘em4’

Compile for ARC EM4 CPU.

‘em4_dmips’
Compile for ARC EM4 DMIPS CPU.
‘em4_fpus’
Compile for ARC EM4 DMIPS CPU with the single-precision
floating-point extension.
‘em4_fpuda’
Compile for ARC EM4 DMIPS CPU with single-precision floatingpoint and double assist instructions.
‘hs’

Compile for ARC HS CPU with no hardware extensions except the
atomic instructions.

‘hs34’

Compile for ARC HS34 CPU.

‘hs38’

Compile for ARC HS38 CPU.

‘hs38_linux’
Compile for ARC HS38 CPU with all hardware extensions on.
‘arc600_norm’
Compile for ARC 600 CPU with norm instructions enabled.
‘arc600_mul32x16’
Compile for ARC 600 CPU with norm and 32x16-bit multiply instructions enabled.
‘arc600_mul64’
Compile for ARC 600 CPU with norm and mul64-family instructions enabled.
‘arc601_norm’
Compile for ARC 601 CPU with norm instructions enabled.
‘arc601_mul32x16’
Compile for ARC 601 CPU with norm and 32x16-bit multiply instructions enabled.
‘arc601_mul64’
Compile for ARC 601 CPU with norm and mul64-family instructions enabled.
‘nps400’

Compile for ARC 700 on NPS400 chip.

‘em_mini’

Compile for ARC EM minimalist configuration featuring reduced
register set.

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-mdpfp
-mdpfp-compact
Generate double-precision FPX instructions, tuned for the compact implementation.
-mdpfp-fast
Generate double-precision FPX instructions, tuned for the fast implementation.
-mno-dpfp-lrsr
Disable lr and sr instructions from using FPX extension aux registers.
-mea

Generate extended arithmetic instructions. Currently only divaw, adds, subs,
and sat16 are supported. This is always enabled for ‘-mcpu=ARC700’.

-mno-mpy

Do not generate mpy-family instructions for ARC700. This option is deprecated.

-mmul32x16
Generate 32x16-bit multiply and multiply-accumulate instructions.
-mmul64

Generate mul64 and mulu64 instructions. Only valid for ‘-mcpu=ARC600’.

-mnorm

Generate norm instructions. This is the default if ‘-mcpu=ARC700’ is in effect.

-mspfp
-mspfp-compact
Generate single-precision FPX instructions, tuned for the compact implementation.
-mspfp-fast
Generate single-precision FPX instructions, tuned for the fast implementation.
-msimd

Enable generation of ARC SIMD instructions via target-specific builtins. Only
valid for ‘-mcpu=ARC700’.

-msoft-float
This option ignored; it is provided for compatibility purposes only. Software
floating-point code is emitted by default, and this default can overridden by
FPX options; ‘-mspfp’, ‘-mspfp-compact’, or ‘-mspfp-fast’ for single precision, and ‘-mdpfp’, ‘-mdpfp-compact’, or ‘-mdpfp-fast’ for double precision.
-mswap

Generate swap instructions.

-matomic

This enables use of the locked load/store conditional extension to implement
atomic memory built-in functions. Not available for ARC 6xx or ARC EM
cores.

-mdiv-rem
Enable div and rem instructions for ARCv2 cores.
-mcode-density
Enable code density instructions for ARC EM. This option is on by default for
ARC HS.
-mll64

Enable double load/store operations for ARC HS cores.

-mtp-regno=regno
Specify thread pointer register number.

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-mmpy-option=multo
Compile ARCv2 code with a multiplier design option. You can specify the
option using either a string or numeric value for multo. ‘wlh1’ is the default
value. The recognized values are:
‘0’
‘none’
‘1’
‘w’
‘2’
‘wlh1’
‘3’
‘wlh2’
‘4’
‘wlh3’
‘5’
‘wlh4’
‘6’
‘wlh5’

No multiplier available.
16x16 multiplier, fully pipelined. The following instructions are
enabled: mpyw and mpyuw.
32x32 multiplier, fully pipelined (1 stage). The following instructions are additionally enabled: mpy, mpyu, mpym, mpymu, and mpy_s.
32x32 multiplier, fully pipelined (2 stages). The following instructions are additionally enabled: mpy, mpyu, mpym, mpymu, and mpy_s.
Two 16x16 multipliers, blocking, sequential. The following instructions are additionally enabled: mpy, mpyu, mpym, mpymu, and mpy_s.
One 16x16 multiplier, blocking, sequential. The following instructions are additionally enabled: mpy, mpyu, mpym, mpymu, and mpy_s.
One 32x4 multiplier, blocking, sequential. The following instructions are additionally enabled: mpy, mpyu, mpym, mpymu, and mpy_s.

‘7’
‘plus_dmpy’
ARC HS SIMD support.
‘8’
‘plus_macd’
ARC HS SIMD support.
‘9’
‘plus_qmacw’
ARC HS SIMD support.
This option is only available for ARCv2 cores.
-mfpu=fpu
Enables support for specific floating-point hardware extensions for ARCv2
cores. Supported values for fpu are:
‘fpus’

Enables support for single-precision floating-point hardware extensions.

‘fpud’

Enables support for double-precision floating-point hardware extensions. The single-precision floating-point extension is also enabled.
Not available for ARC EM.

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‘fpuda’

239

Enables support for double-precision floating-point hardware
extensions using double-precision assist instructions.
The
single-precision floating-point extension is also enabled. This
option is only available for ARC EM.

‘fpuda_div’
Enables support for double-precision floating-point hardware
extensions using double-precision assist instructions.
The
single-precision floating-point, square-root, and divide extensions
are also enabled. This option is only available for ARC EM.
‘fpuda_fma’
Enables support for double-precision floating-point hardware
extensions using double-precision assist instructions.
The
single-precision floating-point and fused multiply and add
hardware extensions are also enabled. This option is only available
for ARC EM.
‘fpuda_all’
Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. All single-precision
floating-point hardware extensions are also enabled. This option is
only available for ARC EM.
‘fpus_div’
Enables support for single-precision floating-point, square-root and
divide hardware extensions.
‘fpud_div’
Enables support for double-precision floating-point, square-root
and divide hardware extensions. This option includes option
‘fpus_div’. Not available for ARC EM.
‘fpus_fma’
Enables support for single-precision floating-point and fused multiply and add hardware extensions.
‘fpud_fma’
Enables support for double-precision floating-point and fused multiply and add hardware extensions. This option includes option
‘fpus_fma’. Not available for ARC EM.
‘fpus_all’
Enables support for all single-precision floating-point hardware extensions.
‘fpud_all’
Enables support for all single- and double-precision floating-point
hardware extensions. Not available for ARC EM.
-mirq-ctrl-saved=register-range, blink, lp_count
Specifies general-purposes registers that the processor automatically
saves/restores on interrupt entry and exit. register-range is specified as two

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registers separated by a dash. The register range always starts with r0, the
upper limit is fp register. blink and lp count are optional. This option is only
valid for ARC EM and ARC HS cores.
-mrgf-banked-regs=number
Specifies the number of registers replicated in second register bank on entry
to fast interrupt. Fast interrupts are interrupts with the highest priority level
P0. These interrupts save only PC and STATUS32 registers to avoid memory
transactions during interrupt entry and exit sequences. Use this option when
you are using fast interrupts in an ARC V2 family processor. Permitted values
are 4, 8, 16, and 32.
-mlpc-width=width
Specify the width of the lp_count register. Valid values for width are 8, 16, 20,
24, 28 and 32 bits. The default width is fixed to 32 bits. If the width is less than
32, the compiler does not attempt to transform loops in your program to use
the zero-delay loop mechanism unless it is known that the lp_count register
can hold the required loop-counter value. Depending on the width specified,
the compiler and run-time library might continue to use the loop mechanism for
various needs. This option defines macro __ARC_LPC_WIDTH__ with the value
of width.
-mrf16

This option instructs the compiler to generate code for a 16-entry register file.
This option defines the __ARC_RF16__ preprocessor macro.

The following options are passed through to the assembler, and also define preprocessor
macro symbols.
-mdsp-packa
Passed down to the assembler to enable the DSP Pack A extensions. Also sets
the preprocessor symbol __Xdsp_packa. This option is deprecated.
-mdvbf

Passed down to the assembler to enable the dual Viterbi butterfly extension.
Also sets the preprocessor symbol __Xdvbf. This option is deprecated.

-mlock

Passed down to the assembler to enable the locked load/store conditional extension. Also sets the preprocessor symbol __Xlock.

-mmac-d16
Passed down to the assembler. Also sets the preprocessor symbol __Xxmac_d16.
This option is deprecated.
-mmac-24

Passed down to the assembler. Also sets the preprocessor symbol __Xxmac_24.
This option is deprecated.

-mrtsc

Passed down to the assembler to enable the 64-bit time-stamp counter extension instruction. Also sets the preprocessor symbol __Xrtsc. This option is
deprecated.

-mswape

Passed down to the assembler to enable the swap byte ordering extension instruction. Also sets the preprocessor symbol __Xswape.

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-mtelephony
Passed down to the assembler to enable dual- and single-operand instructions
for telephony. Also sets the preprocessor symbol __Xtelephony. This option is
deprecated.
-mxy

Passed down to the assembler to enable the XY memory extension. Also sets
the preprocessor symbol __Xxy.

The following options control how the assembly code is annotated:
-misize

Annotate assembler instructions with estimated addresses.

-mannotate-align
Explain what alignment considerations lead to the decision to make an instruction short or long.
The following options are passed through to the linker:
-marclinux
Passed through to the linker, to specify use of the arclinux emulation. This
option is enabled by default in tool chains built for arc-linux-uclibc and
arceb-linux-uclibc targets when profiling is not requested.
-marclinux_prof
Passed through to the linker, to specify use of the arclinux_prof emulation.
This option is enabled by default in tool chains built for arc-linux-uclibc
and arceb-linux-uclibc targets when profiling is requested.
The following options control the semantics of generated code:
-mlong-calls
Generate calls as register indirect calls, thus providing access to the full 32-bit
address range.
-mmedium-calls
Don’t use less than 25-bit addressing range for calls, which is the offset available for an unconditional branch-and-link instruction. Conditional execution
of function calls is suppressed, to allow use of the 25-bit range, rather than
the 21-bit range with conditional branch-and-link. This is the default for tool
chains built for arc-linux-uclibc and arceb-linux-uclibc targets.
-G num

Put definitions of externally-visible data in a small data section if that data
is no bigger than num bytes. The default value of num is 4 for any ARC
configuration, or 8 when we have double load/store operations.

-mno-sdata
Do not generate sdata references. This is the default for tool chains built for
arc-linux-uclibc and arceb-linux-uclibc targets.
-mvolatile-cache
Use ordinarily cached memory accesses for volatile references. This is the default.
-mno-volatile-cache
Enable cache bypass for volatile references.

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The following options fine tune code generation:
-malign-call
Do alignment optimizations for call instructions.
-mauto-modify-reg
Enable the use of pre/post modify with register displacement.
-mbbit-peephole
Enable bbit peephole2.
-mno-brcc
This option disables a target-specific pass in ‘arc_reorg’ to generate compareand-branch (brcc) instructions. It has no effect on generation of these instructions driven by the combiner pass.
-mcase-vector-pcrel
Use PC-relative switch case tables to enable case table shortening. This is the
default for ‘-Os’.
-mcompact-casesi
Enable compact casesi pattern. This is the default for ‘-Os’, and only available
for ARCv1 cores.
-mno-cond-exec
Disable the ARCompact-specific pass to generate conditional execution instructions.
Due to delay slot scheduling and interactions between operand numbers, literal
sizes, instruction lengths, and the support for conditional execution, the targetindependent pass to generate conditional execution is often lacking, so the ARC
port has kept a special pass around that tries to find more conditional execution
generation opportunities after register allocation, branch shortening, and delay
slot scheduling have been done. This pass generally, but not always, improves
performance and code size, at the cost of extra compilation time, which is why
there is an option to switch it off. If you have a problem with call instructions
exceeding their allowable offset range because they are conditionalized, you
should consider using ‘-mmedium-calls’ instead.
-mearly-cbranchsi
Enable pre-reload use of the cbranchsi pattern.
-mexpand-adddi
Expand adddi3 and subdi3 at RTL generation time into add.f, adc etc. This
option is deprecated.
-mindexed-loads
Enable the use of indexed loads. This can be problematic because some optimizers then assume that indexed stores exist, which is not the case.
-mlra

Enable Local Register Allocation. This is still experimental for ARC, so by
default the compiler uses standard reload (i.e. ‘-mno-lra’).

-mlra-priority-none
Don’t indicate any priority for target registers.

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-mlra-priority-compact
Indicate target register priority for r0..r3 / r12..r15.
-mlra-priority-noncompact
Reduce target register priority for r0..r3 / r12..r15.
-mno-millicode
When optimizing for size (using ‘-Os’), prologues and epilogues that have to
save or restore a large number of registers are often shortened by using call
to a special function in libgcc; this is referred to as a millicode call. As these
calls can pose performance issues, and/or cause linking issues when linking in a
nonstandard way, this option is provided to turn off millicode call generation.
-mmixed-code
Tweak register allocation to help 16-bit instruction generation. This generally
has the effect of decreasing the average instruction size while increasing the
instruction count.
-mq-class
Enable ‘q’ instruction alternatives. This is the default for ‘-Os’.
-mRcq

Enable ‘Rcq’ constraint handling. Most short code generation depends on this.
This is the default.

-mRcw

Enable ‘Rcw’ constraint handling. Most ccfsm condexec mostly depends on this.
This is the default.

-msize-level=level
Fine-tune size optimization with regards to instruction lengths and alignment.
The recognized values for level are:
‘0’

No size optimization. This level is deprecated and treated like ‘1’.

‘1’

Short instructions are used opportunistically.

‘2’

In addition, alignment of loops and of code after barriers are
dropped.

‘3’

In addition, optional data alignment is dropped, and the option
‘Os’ is enabled.

This defaults to ‘3’ when ‘-Os’ is in effect. Otherwise, the behavior when this
is not set is equivalent to level ‘1’.
-mtune=cpu
Set instruction scheduling parameters for cpu, overriding any implied by
‘-mcpu=’.
Supported values for cpu are
‘ARC600’

Tune for ARC600 CPU.

‘ARC601’

Tune for ARC601 CPU.

‘ARC700’

Tune for ARC700 CPU with standard multiplier block.

‘ARC700-xmac’
Tune for ARC700 CPU with XMAC block.

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‘ARC725D’

Tune for ARC725D CPU.

‘ARC750D’

Tune for ARC750D CPU.

-mmultcost=num
Cost to assume for a multiply instruction, with ‘4’ being equal to a normal
instruction.
-munalign-prob-threshold=probability
Set probability threshold for unaligning branches. When tuning for ‘ARC700’
and optimizing for speed, branches without filled delay slot are preferably emitted unaligned and long, unless profiling indicates that the probability for the
branch to be taken is below probability. See Section 10.5 [Cross-profiling],
page 832. The default is (REG BR PROB BASE/2), i.e. 5000.
The following options are maintained for backward compatibility, but are now deprecated
and will be removed in a future release:
-margonaut
Obsolete FPX.
-mbig-endian
-EB
Compile code for big-endian targets. Use of these options is now deprecated.
Big-endian code is supported by configuring GCC to build arceb-elf32 and
arceb-linux-uclibc targets, for which big endian is the default.
-mlittle-endian
-EL
Compile code for little-endian targets. Use of these options is now deprecated.
Little-endian code is supported by configuring GCC to build arc-elf32 and
arc-linux-uclibc targets, for which little endian is the default.
-mbarrel_shifter
Replaced by ‘-mbarrel-shifter’.
-mdpfp_compact
Replaced by ‘-mdpfp-compact’.
-mdpfp_fast
Replaced by ‘-mdpfp-fast’.
-mdsp_packa
Replaced by ‘-mdsp-packa’.
-mEA

Replaced by ‘-mea’.

-mmac_24

Replaced by ‘-mmac-24’.

-mmac_d16
Replaced by ‘-mmac-d16’.
-mspfp_compact
Replaced by ‘-mspfp-compact’.
-mspfp_fast
Replaced by ‘-mspfp-fast’.

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245

-mtune=cpu
Values ‘arc600’, ‘arc601’, ‘arc700’ and ‘arc700-xmac’ for cpu are replaced by
‘ARC600’, ‘ARC601’, ‘ARC700’ and ‘ARC700-xmac’ respectively.
-multcost=num
Replaced by ‘-mmultcost’.

3.18.4 ARM Options
These ‘-m’ options are defined for the ARM port:
-mabi=name
Generate code for the specified ABI. Permissible values are: ‘apcs-gnu’,
‘atpcs’, ‘aapcs’, ‘aapcs-linux’ and ‘iwmmxt’.
-mapcs-frame
Generate a stack frame that is compliant with the ARM Procedure Call Standard for all functions, even if this is not strictly necessary for correct execution of
the code. Specifying ‘-fomit-frame-pointer’ with this option causes the stack
frames not to be generated for leaf functions. The default is ‘-mno-apcs-frame’.
This option is deprecated.
-mapcs

This is a synonym for ‘-mapcs-frame’ and is deprecated.

-mthumb-interwork
Generate code that supports calling between the ARM and Thumb
instruction sets. Without this option, on pre-v5 architectures, the two
instruction sets cannot be reliably used inside one program. The default
is ‘-mno-thumb-interwork’, since slightly larger code is generated when
‘-mthumb-interwork’ is specified. In AAPCS configurations this option is
meaningless.
-mno-sched-prolog
Prevent the reordering of instructions in the function prologue, or the merging
of those instruction with the instructions in the function’s body. This means
that all functions start with a recognizable set of instructions (or in fact one of
a choice from a small set of different function prologues), and this information
can be used to locate the start of functions inside an executable piece of code.
The default is ‘-msched-prolog’.
-mfloat-abi=name
Specifies which floating-point ABI to use. Permissible values are: ‘soft’,
‘softfp’ and ‘hard’.
Specifying ‘soft’ causes GCC to generate output containing library calls for
floating-point operations. ‘softfp’ allows the generation of code using hardware floating-point instructions, but still uses the soft-float calling conventions.
‘hard’ allows generation of floating-point instructions and uses FPU-specific
calling conventions.
The default depends on the specific target configuration. Note that the hardfloat and soft-float ABIs are not link-compatible; you must compile your entire
program with the same ABI, and link with a compatible set of libraries.

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-mlittle-endian
Generate code for a processor running in little-endian mode. This is the default
for all standard configurations.
-mbig-endian
Generate code for a processor running in big-endian mode; the default is to
compile code for a little-endian processor.
-mbe8
-mbe32

When linking a big-endian image select between BE8 and BE32 formats. The
option has no effect for little-endian images and is ignored. The default is dependent on the selected target architecture. For ARMv6 and later architectures
the default is BE8, for older architectures the default is BE32. BE32 format
has been deprecated by ARM.

-march=name[+extension...]
This specifies the name of the target ARM architecture. GCC uses this name
to determine what kind of instructions it can emit when generating assembly
code. This option can be used in conjunction with or instead of the ‘-mcpu=’
option.
Permissible names are: ‘armv4t’, ‘armv5t’, ‘armv5te’, ‘armv6’, ‘armv6j’,
‘armv6k’, ‘armv6kz’, ‘armv6t2’, ‘armv6z’, ‘armv6zk’, ‘armv7’, ‘armv7-a’,
‘armv7ve’, ‘armv8-a’, ‘armv8.1-a’, ‘armv8.2-a’, ‘armv8.3-a’, ‘armv8.4-a’,
‘armv7-r’, ‘armv8-r’, ‘armv6-m’, ‘armv6s-m’, ‘armv7-m’, ‘armv7e-m’,
‘armv8-m.base’, ‘armv8-m.main’, ‘iwmmxt’ and ‘iwmmxt2’.
Additionally, the following architectures, which lack support for the Thumb
execution state, are recognized but support is deprecated: ‘armv2’, ‘armv2a’,
‘armv3’, ‘armv3m’, ‘armv4’, ‘armv5’ and ‘armv5e’.
Many of the architectures support extensions. These can be added by appending ‘+extension’ to the architecture name. Extension options are processed in
order and capabilities accumulate. An extension will also enable any necessary
base extensions upon which it depends. For example, the ‘+crypto’ extension
will always enable the ‘+simd’ extension. The exception to the additive construction is for extensions that are prefixed with ‘+no...’: these extensions
disable the specified option and any other extensions that may depend on the
presence of that extension.
For example, ‘-march=armv7-a+simd+nofp+vfpv4’ is equivalent to writing
‘-march=armv7-a+vfpv4’ since the ‘+simd’ option is entirely disabled by the
‘+nofp’ option that follows it.
Most extension names are generically named, but have an effect that is dependent upon the architecture to which it is applied. For example, the ‘+simd’
option can be applied to both ‘armv7-a’ and ‘armv8-a’ architectures, but will
enable the original ARMv7-A Advanced SIMD (Neon) extensions for ‘armv7-a’
and the ARMv8-A variant for ‘armv8-a’.
The table below lists the supported extensions for each architecture. Architectures not mentioned do not support any extensions.

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‘armv5e’
‘armv5te’
‘armv6’
‘armv6j’
‘armv6k’
‘armv6kz’
‘armv6t2’
‘armv6z’
‘armv6zk’

‘armv7’

‘+fp’

The VFPv2 floating-point instructions. The extension
‘+vfpv2’ can be used as an alias for this extension.

‘+nofp’

Disable the floating-point instructions.

The common subset of the ARMv7-A, ARMv7-R and ARMv7-M
architectures.
‘+fp’

The VFPv3 floating-point instructions, with 16 doubleprecision registers. The extension ‘+vfpv3-d16’ can be
used as an alias for this extension. Note that floatingpoint is not supported by the base ARMv7-M architecture, but is compatible with both the ARMv7-A and
ARMv7-R architectures.

‘+nofp’

Disable the floating-point instructions.

‘+fp’

The VFPv3 floating-point instructions, with 16 doubleprecision registers. The extension ‘+vfpv3-d16’ can be
used as an alias for this extension.

‘+simd’

The Advanced SIMD (Neon) v1 and the VFPv3
floating-point instructions. The extensions ‘+neon’
and ‘+neon-vfpv3’ can be used as aliases for this
extension.

‘+vfpv3’

The VFPv3 floating-point instructions, with 32 doubleprecision registers.

‘armv7-a’

‘+vfpv3-d16-fp16’
The VFPv3 floating-point instructions, with 16 doubleprecision registers and the half-precision floating-point
conversion operations.
‘+vfpv3-fp16’
The VFPv3 floating-point instructions, with 32 doubleprecision registers and the half-precision floating-point
conversion operations.
‘+vfpv4-d16’
The VFPv4 floating-point instructions, with 16 doubleprecision registers.

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‘+vfpv4’

The VFPv4 floating-point instructions, with 32 doubleprecision registers.

‘+neon-fp16’
The Advanced SIMD (Neon) v1 and the VFPv3
floating-point instructions, with the half-precision
floating-point conversion operations.
‘+neon-vfpv4’
The Advanced SIMD (Neon) v2 and the VFPv4
floating-point instructions.

‘armv7ve’

‘+nosimd’

Disable the Advanced SIMD instructions (does not disable floating point).

‘+nofp’

Disable the floating-point and Advanced SIMD instructions.

The extended version of the ARMv7-A architecture with support
for virtualization.
‘+fp’

The VFPv4 floating-point instructions, with 16 doubleprecision registers. The extension ‘+vfpv4-d16’ can be
used as an alias for this extension.

‘+simd’

The Advanced SIMD (Neon) v2 and the VFPv4
floating-point instructions.
The extension
‘+neon-vfpv4’ can be used as an alias for this
extension.

‘+vfpv3-d16’
The VFPv3 floating-point instructions, with 16 doubleprecision registers.
‘+vfpv3’

The VFPv3 floating-point instructions, with 32 doubleprecision registers.

‘+vfpv3-d16-fp16’
The VFPv3 floating-point instructions, with 16 doubleprecision registers and the half-precision floating-point
conversion operations.
‘+vfpv3-fp16’
The VFPv3 floating-point instructions, with 32 doubleprecision registers and the half-precision floating-point
conversion operations.
‘+vfpv4-d16’
The VFPv4 floating-point instructions, with 16 doubleprecision registers.
‘+vfpv4’

The VFPv4 floating-point instructions, with 32 doubleprecision registers.

Chapter 3: GCC Command Options

‘+neon’

249

The Advanced SIMD (Neon) v1 and the VFPv3
floating-point instructions.
The extension
‘+neon-vfpv3’ can be used as an alias for this
extension.

‘+neon-fp16’
The Advanced SIMD (Neon) v1 and the VFPv3
floating-point instructions, with the half-precision
floating-point conversion operations.
‘+nosimd’

Disable the Advanced SIMD instructions (does not disable floating point).

‘+nofp’

Disable the floating-point and Advanced SIMD instructions.

‘+crc’

The Cyclic Redundancy Check (CRC) instructions.

‘+simd’

The ARMv8-A Advanced SIMD and floating-point instructions.

‘+crypto’

The cryptographic instructions.

‘armv8-a’

‘+nocrypto’
Disable the cryptographic instructions.
‘+nofp’

Disable the floating-point, Advanced SIMD and cryptographic instructions.

‘armv8.1-a’
‘+simd’

The ARMv8.1-A Advanced SIMD and floating-point
instructions.

‘+crypto’

The cryptographic instructions. This also enables the
Advanced SIMD and floating-point instructions.

‘+nocrypto’
Disable the cryptographic instructions.
‘+nofp’

Disable the floating-point, Advanced SIMD and cryptographic instructions.

‘armv8.2-a’
‘armv8.3-a’
‘+fp16’

The half-precision floating-point data processing
instructions. This also enables the Advanced SIMD
and floating-point instructions.

‘+fp16fml’
The half-precision floating-point fmla extension. This
also enables the half-precision floating-point extension
and Advanced SIMD and floating-point instructions.

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Using the GNU Compiler Collection (GCC)

‘+simd’

The ARMv8.1-A Advanced SIMD and floating-point
instructions.

‘+crypto’

The cryptographic instructions. This also enables the
Advanced SIMD and floating-point instructions.

‘+dotprod’
Enable the Dot Product extension. This also enables
Advanced SIMD instructions.
‘+nocrypto’
Disable the cryptographic extension.
‘+nofp’
‘armv8.4-a’
‘+fp16’

Disable the floating-point, Advanced SIMD and cryptographic instructions.
The half-precision floating-point data processing
instructions. This also enables the Advanced SIMD
and floating-point instructions as well as the Dot
Product extension and the half-precision floating-point
fmla extension.

‘+simd’

The ARMv8.3-A Advanced SIMD and floating-point
instructions as well as the Dot Product extension.

‘+crypto’

The cryptographic instructions. This also enables the
Advanced SIMD and floating-point instructions as well
as the Dot Product extension.

‘+nocrypto’
Disable the cryptographic extension.
‘+nofp’

Disable the floating-point, Advanced SIMD and cryptographic instructions.

‘+fp.sp’

The single-precision VFPv3 floating-point instructions.
The extension ‘+vfpv3xd’ can be used as an alias for
this extension.

‘+fp’

The VFPv3 floating-point instructions with 16 doubleprecision registers. The extension +vfpv3-d16 can be
used as an alias for this extension.

‘+nofp’

Disable the floating-point extension.

‘+idiv’

The ARM-state integer division instructions.

‘+noidiv’

Disable the ARM-state integer division extension.

‘+fp’

The single-precision VFPv4 floating-point instructions.

‘+fpv5’

The single-precision FPv5 floating-point instructions.

‘armv7-r’

‘armv7e-m’

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251

‘+fp.dp’

The single- and double-precision FPv5 floating-point
instructions.

‘+nofp’

Disable the floating-point extensions.

‘armv8-m.main’
‘+dsp’

The DSP instructions.

‘+nodsp’

Disable the DSP extension.

‘+fp’

The single-precision floating-point instructions.

‘+fp.dp’

The single- and double-precision floating-point instructions.

‘+nofp’

Disable the floating-point extension.

‘+crc’

The Cyclic Redundancy Check (CRC) instructions.

‘+fp.sp’

The single-precision FPv5 floating-point instructions.

‘+simd’

The ARMv8-A Advanced SIMD and floating-point instructions.

‘+crypto’

The cryptographic instructions.

‘armv8-r’

‘+nocrypto’
Disable the cryptographic instructions.
‘+nofp’

Disable the floating-point, Advanced SIMD and cryptographic instructions.

‘-march=native’ causes the compiler to auto-detect the architecture of the build
computer. At present, this feature is only supported on GNU/Linux, and not
all architectures are recognized. If the auto-detect is unsuccessful the option
has no effect.
-mtune=name
This option specifies the name of the target ARM processor for which GCC
should tune the performance of the code. For some ARM implementations
better performance can be obtained by using this option.
Permissible
names are: ‘arm2’, ‘arm250’, ‘arm3’, ‘arm6’, ‘arm60’, ‘arm600’, ‘arm610’,
‘arm620’, ‘arm7’, ‘arm7m’, ‘arm7d’, ‘arm7dm’, ‘arm7di’, ‘arm7dmi’, ‘arm70’,
‘arm700’, ‘arm700i’, ‘arm710’, ‘arm710c’, ‘arm7100’, ‘arm720’, ‘arm7500’,
‘arm7500fe’, ‘arm7tdmi’, ‘arm7tdmi-s’, ‘arm710t’, ‘arm720t’, ‘arm740t’,
‘strongarm’, ‘strongarm110’, ‘strongarm1100’, ‘strongarm1110’, ‘arm8’,
‘arm810’, ‘arm9’, ‘arm9e’, ‘arm920’, ‘arm920t’, ‘arm922t’, ‘arm946e-s’,
‘arm966e-s’, ‘arm968e-s’, ‘arm926ej-s’, ‘arm940t’, ‘arm9tdmi’, ‘arm10tdmi’,
‘arm1020t’, ‘arm1026ej-s’, ‘arm10e’, ‘arm1020e’, ‘arm1022e’, ‘arm1136j-s’,
‘arm1136jf-s’, ‘mpcore’, ‘mpcorenovfp’, ‘arm1156t2-s’, ‘arm1156t2f-s’,
‘arm1176jz-s’,
‘arm1176jzf-s’,
‘generic-armv7-a’,
‘cortex-a5’,
‘cortex-a7’, ‘cortex-a8’, ‘cortex-a9’, ‘cortex-a12’, ‘cortex-a15’,
‘cortex-a17’, ‘cortex-a32’, ‘cortex-a35’, ‘cortex-a53’, ‘cortex-a55’,

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Using the GNU Compiler Collection (GCC)

‘cortex-a57’, ‘cortex-a72’, ‘cortex-a73’, ‘cortex-a75’, ‘cortex-r4’,
‘cortex-r4f’, ‘cortex-r5’, ‘cortex-r7’, ‘cortex-r8’, ‘cortex-r52’,
‘cortex-m33’, ‘cortex-m23’, ‘cortex-m7’, ‘cortex-m4’, ‘cortex-m3’,
‘cortex-m1’, ‘cortex-m0’, ‘cortex-m0plus’, ‘cortex-m1.small-multiply’,
‘cortex-m0.small-multiply’,
‘cortex-m0plus.small-multiply’,
‘exynos-m1’, ‘marvell-pj4’, ‘xscale’, ‘iwmmxt’, ‘iwmmxt2’, ‘ep9312’, ‘fa526’,
‘fa626’, ‘fa606te’, ‘fa626te’, ‘fmp626’, ‘fa726te’, ‘xgene1’.
Additionally, this option can specify that GCC should tune the
performance of the code for a big.LITTLE system.
Permissible
names
are:
‘cortex-a15.cortex-a7’,
‘cortex-a17.cortex-a7’,
‘cortex-a57.cortex-a53’, ‘cortex-a72.cortex-a53’, ‘cortex-a72.cortex-a35’,
‘cortex-a73.cortex-a53’, ‘cortex-a75.cortex-a55’.
‘-mtune=generic-arch’ specifies that GCC should tune the performance for a
blend of processors within architecture arch. The aim is to generate code that
run well on the current most popular processors, balancing between optimizations that benefit some CPUs in the range, and avoiding performance pitfalls
of other CPUs. The effects of this option may change in future GCC versions
as CPU models come and go.
‘-mtune’ permits the same extension options as ‘-mcpu’, but the extension options do not affect the tuning of the generated code.
‘-mtune=native’ causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all
architectures are recognized. If the auto-detect is unsuccessful the option has
no effect.
-mcpu=name[+extension...]
This specifies the name of the target ARM processor. GCC uses this name to
derive the name of the target ARM architecture (as if specified by ‘-march’) and
the ARM processor type for which to tune for performance (as if specified by
‘-mtune’). Where this option is used in conjunction with ‘-march’ or ‘-mtune’,
those options take precedence over the appropriate part of this option.
Many of the supported CPUs implement optional architectural extensions.
Where this is so the architectural extensions are normally enabled by default. If
implementations that lack the extension exist, then the extension syntax can be
used to disable those extensions that have been omitted. For floating-point and
Advanced SIMD (Neon) instructions, the settings of the options ‘-mfloat-abi’
and ‘-mfpu’ must also be considered: floating-point and Advanced SIMD instructions will only be used if ‘-mfloat-abi’ is not set to ‘soft’; and any setting
of ‘-mfpu’ other than ‘auto’ will override the available floating-point and SIMD
extension instructions.
For example, ‘cortex-a9’ can be found in three major configurations: integer
only, with just a floating-point unit or with floating-point and Advanced SIMD.
The default is to enable all the instructions, but the extensions ‘+nosimd’ and
‘+nofp’ can be used to disable just the SIMD or both the SIMD and floatingpoint instructions respectively.
Permissible names for this option are the same as those for ‘-mtune’.

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253

The following extension options are common to the listed CPUs:
‘+nodsp’

Disable the DSP instructions on ‘cortex-m33’.

‘+nofp’

Disables the floating-point instructions on ‘arm9e’, ‘arm946e-s’,
‘arm966e-s’, ‘arm968e-s’, ‘arm10e’, ‘arm1020e’, ‘arm1022e’,
‘arm926ej-s’,
‘arm1026ej-s’,
‘cortex-r5’,
‘cortex-r7’,
‘cortex-r8’, ‘cortex-m4’, ‘cortex-m7’ and ‘cortex-m33’.
Disables the floating-point and SIMD instructions on
‘generic-armv7-a’, ‘cortex-a5’, ‘cortex-a7’, ‘cortex-a8’,
‘cortex-a9’,
‘cortex-a12’,
‘cortex-a15’,
‘cortex-a17’,
‘cortex-a15.cortex-a7’,
‘cortex-a17.cortex-a7’,
‘cortex-a32’, ‘cortex-a35’, ‘cortex-a53’ and ‘cortex-a55’.

‘+nofp.dp’
Disables the double-precision component of the floating-point instructions on ‘cortex-r5’, ‘cortex-r52’ and ‘cortex-m7’.
‘+nosimd’

Disables the SIMD (but not floating-point) instructions on
‘generic-armv7-a’, ‘cortex-a5’, ‘cortex-a7’ and ‘cortex-a9’.

‘+crypto’

Enables the cryptographic instructions on ‘cortex-a32’,
‘cortex-a35’,
‘cortex-a53’,
‘cortex-a55’,
‘cortex-a57’,
‘cortex-a72’,
‘cortex-a73’,
‘cortex-a75’,
‘exynos-m1’,
‘xgene1’, ‘cortex-a57.cortex-a53’, ‘cortex-a72.cortex-a53’,
‘cortex-a73.cortex-a35’,
‘cortex-a73.cortex-a53’
and
‘cortex-a75.cortex-a55’.

Additionally the ‘generic-armv7-a’ pseudo target defaults to VFPv3 with
16 double-precision registers. It supports the following extension options:
‘vfpv3-d16’, ‘vfpv3’, ‘vfpv3-d16-fp16’, ‘vfpv3-fp16’, ‘vfpv4-d16’, ‘vfpv4’,
‘neon’, ‘neon-vfpv3’, ‘neon-fp16’, ‘neon-vfpv4’. The meanings are the same
as for the extensions to ‘-march=armv7-a’.
‘-mcpu=generic-arch’ is also permissible, and is equivalent to ‘-march=arch
-mtune=generic-arch’. See ‘-mtune’ for more information.
‘-mcpu=native’ causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all
architectures are recognized. If the auto-detect is unsuccessful the option has
no effect.
-mfpu=name
This specifies what floating-point hardware (or hardware emulation) is available
on the target. Permissible names are: ‘auto’, ‘vfpv2’, ‘vfpv3’, ‘vfpv3-fp16’,
‘vfpv3-d16’, ‘vfpv3-d16-fp16’, ‘vfpv3xd’, ‘vfpv3xd-fp16’, ‘neon-vfpv3’,
‘neon-fp16’, ‘vfpv4’, ‘vfpv4-d16’, ‘fpv4-sp-d16’, ‘neon-vfpv4’, ‘fpv5-d16’,
‘fpv5-sp-d16’, ‘fp-armv8’, ‘neon-fp-armv8’ and ‘crypto-neon-fp-armv8’.
Note that ‘neon’ is an alias for ‘neon-vfpv3’ and ‘vfp’ is an alias for ‘vfpv2’.
The setting ‘auto’ is the default and is special. It causes the compiler to select
the floating-point and Advanced SIMD instructions based on the settings of
‘-mcpu’ and ‘-march’.

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Using the GNU Compiler Collection (GCC)

If the selected floating-point hardware includes the NEON extension (e.g.
‘-mfpu=neon’), note that floating-point operations are not generated by
GCC’s auto-vectorization pass unless ‘-funsafe-math-optimizations’ is
also specified. This is because NEON hardware does not fully implement the
IEEE 754 standard for floating-point arithmetic (in particular denormal values
are treated as zero), so the use of NEON instructions may lead to a loss of
precision.
You can also set the fpu name at function level by using the target("fpu=")
function attributes (see Section 6.31.4 [ARM Function Attributes], page 484)
or pragmas (see Section 6.61.15 [Function Specific Option Pragmas], page 780).
-mfp16-format=name
Specify the format of the __fp16 half-precision floating-point type. Permissible
names are ‘none’, ‘ieee’, and ‘alternative’; the default is ‘none’, in which case
the __fp16 type is not defined. See Section 6.12 [Half-Precision], page 450, for
more information.
-mstructure-size-boundary=n
The sizes of all structures and unions are rounded up to a multiple of the
number of bits set by this option. Permissible values are 8, 32 and 64. The
default value varies for different toolchains. For the COFF targeted toolchain
the default value is 8. A value of 64 is only allowed if the underlying ABI
supports it.
Specifying a larger number can produce faster, more efficient code, but can also
increase the size of the program. Different values are potentially incompatible.
Code compiled with one value cannot necessarily expect to work with code
or libraries compiled with another value, if they exchange information using
structures or unions.
This option is deprecated.
-mabort-on-noreturn
Generate a call to the function abort at the end of a noreturn function. It is
executed if the function tries to return.
-mlong-calls
-mno-long-calls
Tells the compiler to perform function calls by first loading the address of the
function into a register and then performing a subroutine call on this register.
This switch is needed if the target function lies outside of the 64-megabyte
addressing range of the offset-based version of subroutine call instruction.
Even if this switch is enabled, not all function calls are turned into long calls.
The heuristic is that static functions, functions that have the short_call attribute, functions that are inside the scope of a #pragma no_long_calls directive, and functions whose definitions have already been compiled within the
current compilation unit are not turned into long calls. The exceptions to this
rule are that weak function definitions, functions with the long_call attribute
or the section attribute, and functions that are within the scope of a #pragma
long_calls directive are always turned into long calls.

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255

This feature is not enabled by default. Specifying ‘-mno-long-calls’ restores
the default behavior, as does placing the function calls within the scope of a
#pragma long_calls_off directive. Note these switches have no effect on how
the compiler generates code to handle function calls via function pointers.
-msingle-pic-base
Treat the register used for PIC addressing as read-only, rather than loading
it in the prologue for each function. The runtime system is responsible for
initializing this register with an appropriate value before execution begins.
-mpic-register=reg
Specify the register to be used for PIC addressing. For standard PIC base case,
the default is any suitable register determined by compiler. For single PIC base
case, the default is ‘R9’ if target is EABI based or stack-checking is enabled,
otherwise the default is ‘R10’.
-mpic-data-is-text-relative
Assume that the displacement between the text and data segments is fixed at
static link time. This permits using PC-relative addressing operations to access
data known to be in the data segment. For non-VxWorks RTP targets, this
option is enabled by default. When disabled on such targets, it will enable
‘-msingle-pic-base’ by default.
-mpoke-function-name
Write the name of each function into the text section, directly preceding the
function prologue. The generated code is similar to this:
t0
.ascii "arm_poke_function_name", 0
.align
t1
.word 0xff000000 + (t1 - t0)
arm_poke_function_name
mov
ip, sp
stmfd
sp!, {fp, ip, lr, pc}
sub
fp, ip, #4

When performing a stack backtrace, code can inspect the value of pc stored at
fp + 0. If the trace function then looks at location pc - 12 and the top 8 bits
are set, then we know that there is a function name embedded immediately
preceding this location and has length ((pc[-3]) & 0xff000000).
-mthumb
-marm
Select between generating code that executes in ARM and Thumb states.
The default for most configurations is to generate code that executes in
ARM state, but the default can be changed by configuring GCC with the
‘--with-mode=’state configure option.
You can also override the ARM and Thumb mode for each function by using the
target("thumb") and target("arm") function attributes (see Section 6.31.4
[ARM Function Attributes], page 484) or pragmas (see Section 6.61.15 [Function
Specific Option Pragmas], page 780).

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Using the GNU Compiler Collection (GCC)

-mflip-thumb
Switch ARM/Thumb modes on alternating functions. This option is provided
for regression testing of mixed Thumb/ARM code generation, and is not intended for ordinary use in compiling code.
-mtpcs-frame
Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all non-leaf functions. (A leaf function is one that does not call any
other functions.) The default is ‘-mno-tpcs-frame’.
-mtpcs-leaf-frame
Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all leaf functions. (A leaf function is one that does not call any other
functions.) The default is ‘-mno-apcs-leaf-frame’.
-mcallee-super-interworking
Gives all externally visible functions in the file being compiled an ARM instruction set header which switches to Thumb mode before executing the rest
of the function. This allows these functions to be called from non-interworking
code. This option is not valid in AAPCS configurations because interworking
is enabled by default.
-mcaller-super-interworking
Allows calls via function pointers (including virtual functions) to execute correctly regardless of whether the target code has been compiled for interworking
or not. There is a small overhead in the cost of executing a function pointer
if this option is enabled. This option is not valid in AAPCS configurations
because interworking is enabled by default.
-mtp=name
Specify the access model for the thread local storage pointer. The valid models
are ‘soft’, which generates calls to __aeabi_read_tp, ‘cp15’, which fetches the
thread pointer from cp15 directly (supported in the arm6k architecture), and
‘auto’, which uses the best available method for the selected processor. The
default setting is ‘auto’.
-mtls-dialect=dialect
Specify the dialect to use for accessing thread local storage. Two dialects are
supported—‘gnu’ and ‘gnu2’. The ‘gnu’ dialect selects the original GNU scheme
for supporting local and global dynamic TLS models. The ‘gnu2’ dialect selects
the GNU descriptor scheme, which provides better performance for shared libraries. The GNU descriptor scheme is compatible with the original scheme,
but does require new assembler, linker and library support. Initial and local
exec TLS models are unaffected by this option and always use the original
scheme.
-mword-relocations
Only generate absolute relocations on word-sized values (i.e. R ARM ABS32).
This is enabled by default on targets (uClinux, SymbianOS) where the runtime
loader imposes this restriction, and when ‘-fpic’ or ‘-fPIC’ is specified.

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257

-mfix-cortex-m3-ldrd
Some Cortex-M3 cores can cause data corruption when ldrd instructions
with overlapping destination and base registers are used.
This option
avoids generating these instructions. This option is enabled by default when
‘-mcpu=cortex-m3’ is specified.
-munaligned-access
-mno-unaligned-access
Enables (or disables) reading and writing of 16- and 32- bit values from addresses that are not 16- or 32- bit aligned. By default unaligned access is
disabled for all pre-ARMv6, all ARMv6-M and for ARMv8-M Baseline architectures, and enabled for all other architectures. If unaligned access is not
enabled then words in packed data structures are accessed a byte at a time.
The ARM attribute Tag_CPU_unaligned_access is set in the generated object
file to either true or false, depending upon the setting of this option. If unaligned
access is enabled then the preprocessor symbol __ARM_FEATURE_UNALIGNED is
also defined.
-mneon-for-64bits
Enables using Neon to handle scalar 64-bits operations. This is disabled by
default since the cost of moving data from core registers to Neon is high.
-mslow-flash-data
Assume loading data from flash is slower than fetching instruction. Therefore
literal load is minimized for better performance. This option is only supported
when compiling for ARMv7 M-profile and off by default.
-masm-syntax-unified
Assume inline assembler is using unified asm syntax. The default is currently off
which implies divided syntax. This option has no impact on Thumb2. However,
this may change in future releases of GCC. Divided syntax should be considered
deprecated.
-mrestrict-it
Restricts generation of IT blocks to conform to the rules of ARMv8-A. IT blocks
can only contain a single 16-bit instruction from a select set of instructions. This
option is on by default for ARMv8-A Thumb mode.
-mprint-tune-info
Print CPU tuning information as comment in assembler file. This is an option
used only for regression testing of the compiler and not intended for ordinary
use in compiling code. This option is disabled by default.
-mverbose-cost-dump
Enable verbose cost model dumping in the debug dump files. This option is
provided for use in debugging the compiler.
-mpure-code
Do not allow constant data to be placed in code sections. Additionally, when
compiling for ELF object format give all text sections the ELF processor-specific
section attribute SHF_ARM_PURECODE. This option is only available when generating non-pic code for M-profile targets with the MOVT instruction.

258

-mcmse

Using the GNU Compiler Collection (GCC)

Generate secure code as per the "ARMv8-M Security Extensions: Requirements on Development Tools Engineering Specification", which can be found
on http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/
ECM0359818_armv8m_security_extensions_reqs_on_dev_tools_1_0.pdf.

3.18.5 AVR Options
These options are defined for AVR implementations:
-mmcu=mcu
Specify Atmel AVR instruction set architectures (ISA) or MCU type.
The default for this option is ‘avr2’.
GCC supports the following AVR devices and ISAs:
avr2

“Classic” devices with up to 8 KiB of program memory.
mcu = attiny22, attiny26, at90c8534, at90s2313, at90s2323,
at90s2333, at90s2343, at90s4414, at90s4433, at90s4434,
at90s8515, at90s8535.

avr25

“Classic” devices with up to 8 KiB of program memory and with
the MOVW instruction.
mcu = ata5272, ata6616c, attiny13, attiny13a, attiny2313,
attiny2313a, attiny24, attiny24a, attiny25, attiny261,
attiny261a, attiny43u, attiny4313, attiny44, attiny44a,
attiny441, attiny45, attiny461, attiny461a, attiny48,
attiny828, attiny84, attiny84a, attiny841, attiny85,
attiny861, attiny861a, attiny87, attiny88, at86rf401.

avr3

“Classic” devices with 16 KiB up to 64 KiB of program memory.
mcu = at43usb355, at76c711.

avr31

“Classic” devices with 128 KiB of program memory.
mcu = atmega103, at43usb320.

avr35

“Classic” devices with 16 KiB up to 64 KiB of program memory
and with the MOVW instruction.
mcu = ata5505, ata6617c, ata664251, atmega16u2, atmega32u2,
atmega8u2, attiny1634, attiny167, at90usb162, at90usb82.

avr4

“Enhanced” devices with up to 8 KiB of program memory.
mcu = ata6285, ata6286, ata6289, ata6612c, atmega48,
atmega48a, atmega48p, atmega48pa, atmega48pb, atmega8,
atmega8a, atmega8hva, atmega8515, atmega8535, atmega88,
atmega88a, atmega88p, atmega88pa, atmega88pb, at90pwm1,
at90pwm2, at90pwm2b, at90pwm3, at90pwm3b, at90pwm81.

avr5

“Enhanced” devices with 16 KiB up to 64 KiB of program
memory.
mcu = ata5702m322, ata5782, ata5790, ata5790n, ata5791,
ata5795, ata5831, ata6613c, ata6614q, ata8210, ata8510,
atmega16,
atmega16a,
atmega16hva,
atmega16hva2,
atmega16hvb, atmega16hvbrevb, atmega16m1, atmega16u4,

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atmega161, atmega162, atmega163, atmega164a, atmega164p,
atmega164pa,
atmega165,
atmega165a,
atmega165p,
atmega165pa,
atmega168,
atmega168a,
atmega168p,
atmega168pa,
atmega168pb,
atmega169,
atmega169a,
atmega169p, atmega169pa, atmega32, atmega32a, atmega32c1,
atmega32hvb, atmega32hvbrevb, atmega32m1, atmega32u4,
atmega32u6, atmega323, atmega324a, atmega324p, atmega324pa,
atmega325, atmega325a, atmega325p, atmega325pa, atmega3250,
atmega3250a,
atmega3250p,
atmega3250pa,
atmega328,
atmega328p, atmega328pb, atmega329, atmega329a, atmega329p,
atmega329pa,
atmega3290,
atmega3290a,
atmega3290p,
atmega3290pa, atmega406, atmega64, atmega64a, atmega64c1,
atmega64hve, atmega64hve2, atmega64m1, atmega64rfr2,
atmega640, atmega644, atmega644a, atmega644p, atmega644pa,
atmega644rfr2,
atmega645,
atmega645a,
atmega645p,
atmega6450,
atmega6450a,
atmega6450p,
atmega649,
atmega649a,
atmega649p,
atmega6490,
atmega6490a,
atmega6490p, at90can32, at90can64, at90pwm161, at90pwm216,
at90pwm316, at90scr100, at90usb646, at90usb647, at94k,
m3000.
avr51

“Enhanced” devices with 128 KiB of program memory.
mcu = atmega128, atmega128a, atmega128rfa1, atmega128rfr2,
atmega1280,
atmega1281,
atmega1284,
atmega1284p,
atmega1284rfr2, at90can128, at90usb1286, at90usb1287.

avr6

“Enhanced” devices with 3-byte PC, i.e. with more than 128 KiB
of program memory.
mcu
=
atmega256rfr2,
atmega2560,
atmega2561,
atmega2564rfr2.

avrxmega2
“XMEGA” devices with more than 8 KiB and up to 64 KiB of
program memory.
mcu = atxmega16a4, atxmega16a4u, atxmega16c4, atxmega16d4,
atxmega16e5, atxmega32a4, atxmega32a4u, atxmega32c3,
atxmega32c4,
atxmega32d3,
atxmega32d4,
atxmega32e5,
atxmega8e5.
avrxmega3
“XMEGA” devices with up to 64 KiB of combined program
memory and RAM, and with program memory visible in the RAM
address space.
mcu = attiny1614, attiny1616, attiny1617, attiny212,
attiny214, attiny3214, attiny3216, attiny3217, attiny412,
attiny414, attiny416, attiny417, attiny814, attiny816,
attiny817.

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avrxmega4
“XMEGA” devices with more than 64 KiB and up to 128 KiB of
program memory.
mcu
=
atxmega64a3,
atxmega64a3u,
atxmega64a4u,
atxmega64b1,
atxmega64b3,
atxmega64c3,
atxmega64d3,
atxmega64d4.
avrxmega5
“XMEGA” devices with more than 64 KiB and up to 128 KiB of
program memory and more than 64 KiB of RAM.
mcu = atxmega64a1, atxmega64a1u.
avrxmega6
“XMEGA” devices with more than 128 KiB of program memory.
mcu = atxmega128a3,
atxmega128a3u,
atxmega128b1,
atxmega128b3, atxmega128c3, atxmega128d3, atxmega128d4,
atxmega192a3, atxmega192a3u, atxmega192c3, atxmega192d3,
atxmega256a3,
atxmega256a3b,
atxmega256a3bu,
atxmega256a3u, atxmega256c3, atxmega256d3, atxmega384c3,
atxmega384d3.
avrxmega7
“XMEGA” devices with more than 128 KiB of program memory
and more than 64 KiB of RAM.
mcu = atxmega128a1, atxmega128a1u, atxmega128a4u.
avrtiny

“TINY” Tiny core devices with 512 B up to 4 KiB of program
memory.
mcu = attiny10, attiny20, attiny4, attiny40, attiny5,
attiny9.

avr1

This ISA is implemented by the minimal AVR core and supported
for assembler only.
mcu = attiny11, attiny12, attiny15, attiny28, at90s1200.

-mabsdata
Assume that all data in static storage can be accessed by LDS / STS instructions. This option has only an effect on reduced Tiny devices like ATtiny40.
See also the absdata Section 6.32.3 [AVR Variable Attributes], page 518.
-maccumulate-args
Accumulate outgoing function arguments and acquire/release the needed stack
space for outgoing function arguments once in function prologue/epilogue.
Without this option, outgoing arguments are pushed before calling a function
and popped afterwards.
Popping the arguments after the function call can be expensive on AVR so
that accumulating the stack space might lead to smaller executables because
arguments need not be removed from the stack after such a function call.
This option can lead to reduced code size for functions that perform several
calls to functions that get their arguments on the stack like calls to printf-like
functions.

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-mbranch-cost=cost
Set the branch costs for conditional branch instructions to cost. Reasonable
values for cost are small, non-negative integers. The default branch cost is 0.
-mcall-prologues
Functions prologues/epilogues are expanded as calls to appropriate subroutines.
Code size is smaller.
-mgas-isr-prologues
Interrupt service routines (ISRs) may use the __gcc_isr pseudo instruction
supported by GNU Binutils. If this option is on, the feature can still be disabled for individual ISRs by means of the Section 6.31.5 [no_gccisr], page 486
function attribute. This feature is activated per default if optimization is on
(but not with ‘-Og’, see Section 3.10 [Optimize Options], page 114), and if GNU
Binutils support PR21683.
-mint8

Assume int to be 8-bit integer. This affects the sizes of all types: a char is 1
byte, an int is 1 byte, a long is 2 bytes, and long long is 4 bytes. Please note
that this option does not conform to the C standards, but it results in smaller
code size.

-mmain-is-OS_task
Do not save registers in main. The effect is the same like attaching attribute
Section 6.31.5 [OS_task], page 486 to main. It is activated per default if optimization is on.
-mn-flash=num
Assume that the flash memory has a size of num times 64 KiB.
-mno-interrupts
Generated code is not compatible with hardware interrupts.
smaller.

Code size is

-mrelax

Try to replace CALL resp. JMP instruction by the shorter RCALL resp. RJMP instruction if applicable. Setting ‘-mrelax’ just adds the ‘--mlink-relax’ option
to the assembler’s command line and the ‘--relax’ option to the linker’s command line.
Jump relaxing is performed by the linker because jump offsets are not known
before code is located. Therefore, the assembler code generated by the compiler
is the same, but the instructions in the executable may differ from instructions
in the assembler code.
Relaxing must be turned on if linker stubs are needed, see the section on EIND
and linker stubs below.

-mrmw

Assume that the device supports the Read-Modify-Write instructions XCH, LAC,
LAS and LAT.

-mshort-calls
Assume that RJMP and RCALL can target the whole program memory.
This option is used internally for multilib selection. It is not an optimization
option, and you don’t need to set it by hand.

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-msp8

Using the GNU Compiler Collection (GCC)

Treat the stack pointer register as an 8-bit register, i.e. assume the high byte of
the stack pointer is zero. In general, you don’t need to set this option by hand.
This option is used internally by the compiler to select and build multilibs
for architectures avr2 and avr25. These architectures mix devices with and
without SPH. For any setting other than ‘-mmcu=avr2’ or ‘-mmcu=avr25’ the
compiler driver adds or removes this option from the compiler proper’s command line, because the compiler then knows if the device or architecture has
an 8-bit stack pointer and thus no SPH register or not.

-mstrict-X
Use address register X in a way proposed by the hardware. This means that X
is only used in indirect, post-increment or pre-decrement addressing.
Without this option, the X register may be used in the same way as Y or Z which
then is emulated by additional instructions. For example, loading a value with
X+const addressing with a small non-negative const < 64 to a register Rn is
performed as
adiw r26, const
; X += const
ld
Rn, X
; Rn = *X
sbiw r26, const
; X -= const
-mtiny-stack
Only change the lower 8 bits of the stack pointer.
-mfract-convert-truncate
Allow to use truncation instead of rounding towards zero for fractional fixedpoint types.
-nodevicelib
Don’t link against AVR-LibC’s device specific library lib.a.
-Waddr-space-convert
Warn about conversions between address spaces in the case where the resulting
address space is not contained in the incoming address space.
-Wmisspelled-isr
Warn if the ISR is misspelled, i.e. without

vector prefix. Enabled by default.

3.18.5.1 EIND and Devices with More Than 128 Ki Bytes of Flash
Pointers in the implementation are 16 bits wide. The address of a function or label is
represented as word address so that indirect jumps and calls can target any code address
in the range of 64 Ki words.
In order to facilitate indirect jump on devices with more than 128 Ki bytes of program
memory space, there is a special function register called EIND that serves as most significant
part of the target address when EICALL or EIJMP instructions are used.
Indirect jumps and calls on these devices are handled as follows by the compiler and are
subject to some limitations:
• The compiler never sets EIND.
• The compiler uses EIND implicitly in EICALL/EIJMP instructions or might read EIND
directly in order to emulate an indirect call/jump by means of a RET instruction.

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• The compiler assumes that EIND never changes during the startup code or during the
application. In particular, EIND is not saved/restored in function or interrupt service
routine prologue/epilogue.
• For indirect calls to functions and computed goto, the linker generates stubs. Stubs are
jump pads sometimes also called trampolines. Thus, the indirect call/jump jumps to
such a stub. The stub contains a direct jump to the desired address.
• Linker relaxation must be turned on so that the linker generates the stubs correctly
in all situations. See the compiler option ‘-mrelax’ and the linker option ‘--relax’.
There are corner cases where the linker is supposed to generate stubs but aborts without
relaxation and without a helpful error message.
• The default linker script is arranged for code with EIND = 0. If code is supposed to
work for a setup with EIND != 0, a custom linker script has to be used in order to place
the sections whose name start with .trampolines into the segment where EIND points
to.
• The startup code from libgcc never sets EIND. Notice that startup code is a blend
of code from libgcc and AVR-LibC. For the impact of AVR-LibC on EIND, see the
AVR-LibC user manual.
• It is legitimate for user-specific startup code to set up EIND early, for example by means
of initialization code located in section .init3. Such code runs prior to general startup
code that initializes RAM and calls constructors, but after the bit of startup code from
AVR-LibC that sets EIND to the segment where the vector table is located.
#include 
static void
__attribute__((section(".init3"),naked,used,no_instrument_function))
init3_set_eind (void)
{
__asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
"out %i0,r24" :: "n" (&EIND) : "r24","memory");
}
The __trampolines_start symbol is defined in the linker script.
• Stubs are generated automatically by the linker if the following two conditions are met:
− The address of a label is taken by means of the gs modifier (short for generate
stubs) like so:
LDI r24, lo8(gs(func))
LDI r25, hi8(gs(func))
− The final location of that label is in a code segment outside the segment where the
stubs are located.
• The compiler emits such gs modifiers for code labels in the following situations:
− Taking address of a function or code label.
− Computed goto.
− If prologue-save function is used, see ‘-mcall-prologues’ command-line option.
− Switch/case dispatch tables. If you do not want such dispatch tables you can
specify the ‘-fno-jump-tables’ command-line option.

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− C and C++ constructors/destructors called during startup/shutdown.
− If the tools hit a gs() modifier explained above.
• Jumping to non-symbolic addresses like so is not supported:
int main (void)
{
/* Call function at word address 0x2 */
return ((int(*)(void)) 0x2)();
}
Instead, a stub has to be set up, i.e. the function has to be called through a symbol
(func_4 in the example):
int main (void)
{
extern int func_4 (void);
/* Call function at byte address 0x4 */
return func_4();
}
and the application be linked with ‘-Wl,--defsym,func_4=0x4’. Alternatively, func_4
can be defined in the linker script.

3.18.5.2 Handling of the RAMPD, RAMPX, RAMPY and RAMPZ Special
Function Registers
Some AVR devices support memories larger than the 64 KiB range that can be accessed
with 16-bit pointers. To access memory locations outside this 64 KiB range, the content of a
RAMP register is used as high part of the address: The X, Y, Z address register is concatenated
with the RAMPX, RAMPY, RAMPZ special function register, respectively, to get a wide address.
Similarly, RAMPD is used together with direct addressing.
• The startup code initializes the RAMP special function registers with zero.
• If a [AVR Named Address Spaces], page 453 other than generic or __flash is used,
then RAMPZ is set as needed before the operation.
• If the device supports RAM larger than 64 KiB and the compiler needs to change RAMPZ
to accomplish an operation, RAMPZ is reset to zero after the operation.
• If the device comes with a specific RAMP register, the ISR prologue/epilogue
saves/restores that SFR and initializes it with zero in case the ISR code might
(implicitly) use it.
• RAM larger than 64 KiB is not supported by GCC for AVR targets. If you use inline
assembler to read from locations outside the 16-bit address range and change one of
the RAMP registers, you must reset it to zero after the access.

3.18.5.3 AVR Built-in Macros
GCC defines several built-in macros so that the user code can test for the presence or
absence of features. Almost any of the following built-in macros are deduced from device
capabilities and thus triggered by the ‘-mmcu=’ command-line option.
For even more AVR-specific built-in macros see [AVR Named Address Spaces], page 453
and Section 6.59.10 [AVR Built-in Functions], page 639.

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__AVR_ARCH__
Build-in macro that resolves to a decimal number that identifies the architecture
and depends on the ‘-mmcu=mcu’ option. Possible values are:
2, 25, 3, 31, 35, 4, 5, 51, 6
for mcu=avr2, avr25, avr3, avr31, avr35, avr4, avr5, avr51, avr6,
respectively and
100, 102, 103, 104, 105, 106, 107
for mcu=avrtiny, avrxmega2, avrxmega3, avrxmega4, avrxmega5, avrxmega6,
avrxmega7, respectively. If mcu specifies a device, this built-in macro is set
accordingly. For example, with ‘-mmcu=atmega8’ the macro is defined to 4.
__AVR_Device__
Setting ‘-mmcu=device’ defines this built-in macro which reflects the
device’s name. For example, ‘-mmcu=atmega8’ defines the built-in macro
__AVR_ATmega8__, ‘-mmcu=attiny261a’ defines __AVR_ATtiny261A__, etc.
The built-in macros’ names follow the scheme __AVR_Device__ where Device is
the device name as from the AVR user manual. The difference between Device
in the built-in macro and device in ‘-mmcu=device’ is that the latter is always
lowercase.
If device is not a device but only a core architecture like ‘avr51’, this macro is
not defined.
__AVR_DEVICE_NAME__
Setting ‘-mmcu=device’ defines this built-in macro to the device’s name. For
example, with ‘-mmcu=atmega8’ the macro is defined to atmega8.
If device is not a device but only a core architecture like ‘avr51’, this macro is
not defined.
__AVR_XMEGA__
The device / architecture belongs to the XMEGA family of devices.
__AVR_HAVE_ELPM__
The device has the ELPM instruction.
__AVR_HAVE_ELPMX__
The device has the ELPM Rn,Z and ELPM Rn,Z+ instructions.
__AVR_HAVE_MOVW__
The device has the MOVW instruction to perform 16-bit register-register moves.
__AVR_HAVE_LPMX__
The device has the LPM Rn,Z and LPM Rn,Z+ instructions.
__AVR_HAVE_MUL__
The device has a hardware multiplier.
__AVR_HAVE_JMP_CALL__
The device has the JMP and CALL instructions. This is the case for devices with
more than 8 KiB of program memory.

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__AVR_HAVE_EIJMP_EICALL__
__AVR_3_BYTE_PC__
The device has the EIJMP and EICALL instructions. This is the case for devices
with more than 128 KiB of program memory. This also means that the program
counter (PC) is 3 bytes wide.
__AVR_2_BYTE_PC__
The program counter (PC) is 2 bytes wide. This is the case for devices with up
to 128 KiB of program memory.
__AVR_HAVE_8BIT_SP__
__AVR_HAVE_16BIT_SP__
The stack pointer (SP) register is treated as 8-bit respectively 16-bit register
by the compiler. The definition of these macros is affected by ‘-mtiny-stack’.
__AVR_HAVE_SPH__
__AVR_SP8__
The device has the SPH (high part of stack pointer) special function register
or has an 8-bit stack pointer, respectively. The definition of these macros is
affected by ‘-mmcu=’ and in the cases of ‘-mmcu=avr2’ and ‘-mmcu=avr25’ also
by ‘-msp8’.
__AVR_HAVE_RAMPD__
__AVR_HAVE_RAMPX__
__AVR_HAVE_RAMPY__
__AVR_HAVE_RAMPZ__
The device has the RAMPD, RAMPX, RAMPY, RAMPZ special function register, respectively.
__NO_INTERRUPTS__
This macro reflects the ‘-mno-interrupts’ command-line option.
__AVR_ERRATA_SKIP__
__AVR_ERRATA_SKIP_JMP_CALL__
Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit instructions
because of a hardware erratum. Skip instructions are SBRS, SBRC, SBIS, SBIC
and CPSE. The second macro is only defined if __AVR_HAVE_JMP_CALL__ is also
set.
__AVR_ISA_RMW__
The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT).
__AVR_SFR_OFFSET__=offset
Instructions that can address I/O special function registers directly like IN, OUT,
SBI, etc. may use a different address as if addressed by an instruction to access
RAM like LD or STS. This offset depends on the device architecture and has to
be subtracted from the RAM address in order to get the respective I/O address.
__AVR_SHORT_CALLS__
The ‘-mshort-calls’ command line option is set.

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__AVR_PM_BASE_ADDRESS__=addr
Some devices support reading from flash memory by means of LD* instructions.
The flash memory is seen in the data address space at an offset of __AVR_PM_
BASE_ADDRESS__. If this macro is not defined, this feature is not available. If
defined, the address space is linear and there is no need to put .rodata into
RAM. This is handled by the default linker description file, and is currently
available for avrtiny and avrxmega3. Even more convenient, there is no need
to use address spaces like __flash or features like attribute progmem and pgm_
read_*.
__WITH_AVRLIBC__
The compiler is configured to be used together with AVR-Libc.
‘--with-avrlibc’ configure option.

See the

3.18.6 Blackfin Options
-mcpu=cpu[-sirevision]
Specifies the name of the target Blackfin processor. Currently, cpu can be
one of ‘bf512’, ‘bf514’, ‘bf516’, ‘bf518’, ‘bf522’, ‘bf523’, ‘bf524’, ‘bf525’,
‘bf526’, ‘bf527’, ‘bf531’, ‘bf532’, ‘bf533’, ‘bf534’, ‘bf536’, ‘bf537’, ‘bf538’,
‘bf539’, ‘bf542’, ‘bf544’, ‘bf547’, ‘bf548’, ‘bf549’, ‘bf542m’, ‘bf544m’,
‘bf547m’, ‘bf548m’, ‘bf549m’, ‘bf561’, ‘bf592’.
The optional sirevision specifies the silicon revision of the target Blackfin processor. Any workarounds available for the targeted silicon revision are enabled. If sirevision is ‘none’, no workarounds are enabled. If sirevision is
‘any’, all workarounds for the targeted processor are enabled. The __SILICON_
REVISION__ macro is defined to two hexadecimal digits representing the major
and minor numbers in the silicon revision. If sirevision is ‘none’, the __SILICON_
REVISION__ is not defined. If sirevision is ‘any’, the __SILICON_REVISION__ is
defined to be 0xffff. If this optional sirevision is not used, GCC assumes the
latest known silicon revision of the targeted Blackfin processor.
GCC defines a preprocessor macro for the specified cpu. For the ‘bfin-elf’
toolchain, this option causes the hardware BSP provided by libgloss to be linked
in if ‘-msim’ is not given.
Without this option, ‘bf532’ is used as the processor by default.
Note that support for ‘bf561’ is incomplete. For ‘bf561’, only the preprocessor
macro is defined.
-msim

Specifies that the program will be run on the simulator. This causes the simulator BSP provided by libgloss to be linked in. This option has effect only for
‘bfin-elf’ toolchain. Certain other options, such as ‘-mid-shared-library’
and ‘-mfdpic’, imply ‘-msim’.

-momit-leaf-frame-pointer
Don’t keep the frame pointer in a register for leaf functions. This avoids the
instructions to save, set up and restore frame pointers and makes an extra
register available in leaf functions.

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-mspecld-anomaly
When enabled, the compiler ensures that the generated code does not contain
speculative loads after jump instructions. If this option is used, __WORKAROUND_
SPECULATIVE_LOADS is defined.
-mno-specld-anomaly
Don’t generate extra code to prevent speculative loads from occurring.
-mcsync-anomaly
When enabled, the compiler ensures that the generated code does not contain
CSYNC or SSYNC instructions too soon after conditional branches. If this
option is used, __WORKAROUND_SPECULATIVE_SYNCS is defined.
-mno-csync-anomaly
Don’t generate extra code to prevent CSYNC or SSYNC instructions from
occurring too soon after a conditional branch.
-mlow-64k
When enabled, the compiler is free to take advantage of the knowledge that the
entire program fits into the low 64k of memory.
-mno-low-64k
Assume that the program is arbitrarily large. This is the default.
-mstack-check-l1
Do stack checking using information placed into L1 scratchpad memory by the
uClinux kernel.
-mid-shared-library
Generate code that supports shared libraries via the library ID method. This
allows for execute in place and shared libraries in an environment without virtual memory management. This option implies ‘-fPIC’. With a ‘bfin-elf’
target, this option implies ‘-msim’.
-mno-id-shared-library
Generate code that doesn’t assume ID-based shared libraries are being used.
This is the default.
-mleaf-id-shared-library
Generate code that supports shared libraries via the library ID method, but
assumes that this library or executable won’t link against any other ID shared
libraries. That allows the compiler to use faster code for jumps and calls.
-mno-leaf-id-shared-library
Do not assume that the code being compiled won’t link against any ID shared
libraries. Slower code is generated for jump and call insns.
-mshared-library-id=n
Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other
values forces the allocation of that number to the current library but is no more
space- or time-efficient than omitting this option.

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-msep-data
Generate code that allows the data segment to be located in a different area of
memory from the text segment. This allows for execute in place in an environment without virtual memory management by eliminating relocations against
the text section.
-mno-sep-data
Generate code that assumes that the data segment follows the text segment.
This is the default.
-mlong-calls
-mno-long-calls
Tells the compiler to perform function calls by first loading the address of the
function into a register and then performing a subroutine call on this register.
This switch is needed if the target function lies outside of the 24-bit addressing
range of the offset-based version of subroutine call instruction.
This feature is not enabled by default. Specifying ‘-mno-long-calls’ restores
the default behavior. Note these switches have no effect on how the compiler
generates code to handle function calls via function pointers.
-mfast-fp
Link with the fast floating-point library. This library relaxes some of the
IEEE floating-point standard’s rules for checking inputs against Not-a-Number
(NAN), in the interest of performance.
-minline-plt
Enable inlining of PLT entries in function calls to functions that are not known
to bind locally. It has no effect without ‘-mfdpic’.
-mmulticore
Build a standalone application for multicore Blackfin processors.
This
option causes proper start files and link scripts supporting multicore to be
used, and defines the macro __BFIN_MULTICORE. It can only be used with
‘-mcpu=bf561[-sirevision]’.
This option can be used with ‘-mcorea’ or ‘-mcoreb’, which selects the oneapplication-per-core programming model. Without ‘-mcorea’ or ‘-mcoreb’, the
single-application/dual-core programming model is used. In this model, the
main function of Core B should be named as coreb_main.
If this option is not used, the single-core application programming model is
used.
-mcorea

Build a standalone application for Core A of BF561 when using the oneapplication-per-core programming model. Proper start files and link scripts
are used to support Core A, and the macro __BFIN_COREA is defined. This
option can only be used in conjunction with ‘-mmulticore’.

-mcoreb

Build a standalone application for Core B of BF561 when using the
one-application-per-core programming model. Proper start files and link
scripts are used to support Core B, and the macro __BFIN_COREB is defined.
When this option is used, coreb_main should be used instead of main. This
option can only be used in conjunction with ‘-mmulticore’.

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-msdram

Build a standalone application for SDRAM. Proper start files and link scripts
are used to put the application into SDRAM, and the macro __BFIN_SDRAM is
defined. The loader should initialize SDRAM before loading the application.

-micplb

Assume that ICPLBs are enabled at run time. This has an effect on certain
anomaly workarounds. For Linux targets, the default is to assume ICPLBs are
enabled; for standalone applications the default is off.

3.18.7 C6X Options
-march=name
This specifies the name of the target architecture. GCC uses this name to
determine what kind of instructions it can emit when generating assembly code.
Permissible names are: ‘c62x’, ‘c64x’, ‘c64x+’, ‘c67x’, ‘c67x+’, ‘c674x’.
-mbig-endian
Generate code for a big-endian target.
-mlittle-endian
Generate code for a little-endian target. This is the default.
-msim

Choose startup files and linker script suitable for the simulator.

-msdata=default
Put small global and static data in the .neardata section, which is pointed
to by register B14. Put small uninitialized global and static data in the .bss
section, which is adjacent to the .neardata section. Put small read-only data
into the .rodata section. The corresponding sections used for large pieces of
data are .fardata, .far and .const.
-msdata=all
Put all data, not just small objects, into the sections reserved for small data,
and use addressing relative to the B14 register to access them.
-msdata=none
Make no use of the sections reserved for small data, and use absolute addresses
to access all data. Put all initialized global and static data in the .fardata
section, and all uninitialized data in the .far section. Put all constant data
into the .const section.

3.18.8 CRIS Options
These options are defined specifically for the CRIS ports.
-march=architecture-type
-mcpu=architecture-type
Generate code for the specified architecture. The choices for architecturetype are ‘v3’, ‘v8’ and ‘v10’ for respectively ETRAX 4, ETRAX 100, and
ETRAX 100 LX. Default is ‘v0’ except for cris-axis-linux-gnu, where the default is ‘v10’.
-mtune=architecture-type
Tune to architecture-type everything applicable about the generated code,
except for the ABI and the set of available instructions. The choices for
architecture-type are the same as for ‘-march=architecture-type’.

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-mmax-stack-frame=n
Warn when the stack frame of a function exceeds n bytes.
-metrax4
-metrax100
The options ‘-metrax4’ and ‘-metrax100’ are synonyms for ‘-march=v3’ and
‘-march=v8’ respectively.
-mmul-bug-workaround
-mno-mul-bug-workaround
Work around a bug in the muls and mulu instructions for CPU models where
it applies. This option is active by default.
-mpdebug

Enable CRIS-specific verbose debug-related information in the assembly code.
This option also has the effect of turning off the ‘#NO_APP’ formatted-code
indicator to the assembler at the beginning of the assembly file.

-mcc-init
Do not use condition-code results from previous instruction; always emit compare and test instructions before use of condition codes.
-mno-side-effects
Do not emit instructions with side effects in addressing modes other than postincrement.
-mstack-align
-mno-stack-align
-mdata-align
-mno-data-align
-mconst-align
-mno-const-align
These options (‘no-’ options) arrange (eliminate arrangements) for the stack
frame, individual data and constants to be aligned for the maximum single
data access size for the chosen CPU model. The default is to arrange for 32bit alignment. ABI details such as structure layout are not affected by these
options.
-m32-bit
-m16-bit
-m8-bit

Similar to the stack- data- and const-align options above, these options arrange
for stack frame, writable data and constants to all be 32-bit, 16-bit or 8-bit
aligned. The default is 32-bit alignment.

-mno-prologue-epilogue
-mprologue-epilogue
With ‘-mno-prologue-epilogue’, the normal function prologue and epilogue
which set up the stack frame are omitted and no return instructions or return
sequences are generated in the code. Use this option only together with visual
inspection of the compiled code: no warnings or errors are generated when
call-saved registers must be saved, or storage for local variables needs to be
allocated.

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-mno-gotplt
-mgotplt With ‘-fpic’ and ‘-fPIC’, don’t generate (do generate) instruction sequences
that load addresses for functions from the PLT part of the GOT rather than
(traditional on other architectures) calls to the PLT. The default is ‘-mgotplt’.
-melf

Legacy no-op option only recognized with the cris-axis-elf and cris-axis-linuxgnu targets.

-mlinux

Legacy no-op option only recognized with the cris-axis-linux-gnu target.

-sim

This option, recognized for the cris-axis-elf, arranges to link with input-output
functions from a simulator library. Code, initialized data and zero-initialized
data are allocated consecutively.

-sim2

Like ‘-sim’, but pass linker options to locate initialized data at 0x40000000 and
zero-initialized data at 0x80000000.

3.18.9 CR16 Options
These options are defined specifically for the CR16 ports.
-mmac

Enable the use of multiply-accumulate instructions. Disabled by default.

-mcr16cplus
-mcr16c
Generate code for CR16C or CR16C+ architecture. CR16C+ architecture is
default.
-msim

Links the library libsim.a which is in compatible with simulator. Applicable to
ELF compiler only.

-mint32

Choose integer type as 32-bit wide.

-mbit-ops
Generates sbit/cbit instructions for bit manipulations.
-mdata-model=model
Choose a data model. The choices for model are ‘near’, ‘far’ or ‘medium’.
‘medium’ is default. However, ‘far’ is not valid with ‘-mcr16c’, as the CR16C
architecture does not support the far data model.

3.18.10 Darwin Options
These options are defined for all architectures running the Darwin operating system.
FSF GCC on Darwin does not create “fat” object files; it creates an object file for the
single architecture that GCC was built to target. Apple’s GCC on Darwin does create
“fat” files if multiple ‘-arch’ options are used; it does so by running the compiler or linker
multiple times and joining the results together with ‘lipo’.
The subtype of the file created (like ‘ppc7400’ or ‘ppc970’ or ‘i686’) is determined
by the flags that specify the ISA that GCC is targeting, like ‘-mcpu’ or ‘-march’. The
‘-force_cpusubtype_ALL’ option can be used to override this.
The Darwin tools vary in their behavior when presented with an ISA mismatch. The
assembler, ‘as’, only permits instructions to be used that are valid for the subtype of the
file it is generating, so you cannot put 64-bit instructions in a ‘ppc750’ object file. The

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linker for shared libraries, ‘/usr/bin/libtool’, fails and prints an error if asked to create
a shared library with a less restrictive subtype than its input files (for instance, trying to
put a ‘ppc970’ object file in a ‘ppc7400’ library). The linker for executables, ld, quietly
gives the executable the most restrictive subtype of any of its input files.
-Fdir

Add the framework directory dir to the head of the list of directories to be
searched for header files. These directories are interleaved with those specified
by ‘-I’ options and are scanned in a left-to-right order.
A framework directory is a directory with frameworks in it. A framework is
a directory with a ‘Headers’ and/or ‘PrivateHeaders’ directory contained
directly in it that ends in ‘.framework’. The name of a framework is the
name of this directory excluding the ‘.framework’. Headers associated with
the framework are found in one of those two directories, with ‘Headers’
being searched first. A subframework is a framework directory that is in a
framework’s ‘Frameworks’ directory. Includes of subframework headers can
only appear in a header of a framework that contains the subframework,
or in a sibling subframework header.
Two subframeworks are siblings
if they occur in the same framework. A subframework should not have
the same name as a framework; a warning is issued if this is violated.
Currently a subframework cannot have subframeworks; in the future, the
mechanism may be extended to support this. The standard frameworks can
be found in ‘/System/Library/Frameworks’ and ‘/Library/Frameworks’.
An example include looks like #include , where
‘Framework’ denotes the name of the framework and ‘header.h’ is found in
the ‘PrivateHeaders’ or ‘Headers’ directory.

-iframeworkdir
Like ‘-F’ except the directory is a treated as a system directory. The main
difference between this ‘-iframework’ and ‘-F’ is that with ‘-iframework’ the
compiler does not warn about constructs contained within header files found
via dir. This option is valid only for the C family of languages.
-gused

Emit debugging information for symbols that are used. For stabs debugging
format, this enables ‘-feliminate-unused-debug-symbols’. This is by default
ON.

-gfull

Emit debugging information for all symbols and types.

-mmacosx-version-min=version
The earliest version of MacOS X that this executable will run on is version.
Typical values of version include 10.1, 10.2, and 10.3.9.
If the compiler was built to use the system’s headers by default, then the default
for this option is the system version on which the compiler is running, otherwise
the default is to make choices that are compatible with as many systems and
code bases as possible.
-mkernel

Enable kernel development mode.
The ‘-mkernel’ option sets
‘-static’, ‘-fno-common’, ‘-fno-use-cxa-atexit’, ‘-fno-exceptions’,
‘-fno-non-call-exceptions’, ‘-fapple-kext’, ‘-fno-weak’ and ‘-fno-rtti’

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where applicable. This mode also sets ‘-mno-altivec’, ‘-msoft-float’,
‘-fno-builtin’ and ‘-mlong-branch’ for PowerPC targets.
-mone-byte-bool
Override the defaults for bool so that sizeof(bool)==1.
By default
sizeof(bool) is 4 when compiling for Darwin/PowerPC and 1 when
compiling for Darwin/x86, so this option has no effect on x86.
Warning: The ‘-mone-byte-bool’ switch causes GCC to generate code that
is not binary compatible with code generated without that switch. Using this
switch may require recompiling all other modules in a program, including system libraries. Use this switch to conform to a non-default data model.
-mfix-and-continue
-ffix-and-continue
-findirect-data
Generate code suitable for fast turnaround development, such as to
allow GDB to dynamically load ‘.o’ files into already-running programs.
‘-findirect-data’ and ‘-ffix-and-continue’ are provided for backwards
compatibility.
-all_load
Loads all members of static archive libraries. See man ld(1) for more information.
-arch_errors_fatal
Cause the errors having to do with files that have the wrong architecture to be
fatal.
-bind_at_load
Causes the output file to be marked such that the dynamic linker will bind all
undefined references when the file is loaded or launched.
-bundle

Produce a Mach-o bundle format file. See man ld(1) for more information.

-bundle_loader executable
This option specifies the executable that will load the build output file being
linked. See man ld(1) for more information.
-dynamiclib
When passed this option, GCC produces a dynamic library instead of an executable when linking, using the Darwin ‘libtool’ command.
-force_cpusubtype_ALL
This causes GCC’s output file to have the ‘ALL’ subtype, instead of one controlled by the ‘-mcpu’ or ‘-march’ option.

Chapter 3: GCC Command Options

-allowable_client client_name
-client_name
-compatibility_version
-current_version
-dead_strip
-dependency-file
-dylib_file
-dylinker_install_name
-dynamic
-exported_symbols_list
-filelist
-flat_namespace
-force_flat_namespace
-headerpad_max_install_names
-image_base
-init
-install_name
-keep_private_externs
-multi_module
-multiply_defined
-multiply_defined_unused
-noall_load
-no_dead_strip_inits_and_terms
-nofixprebinding
-nomultidefs
-noprebind
-noseglinkedit
-pagezero_size
-prebind
-prebind_all_twolevel_modules
-private_bundle
-read_only_relocs
-sectalign
-sectobjectsymbols
-whyload
-seg1addr
-sectcreate
-sectobjectsymbols
-sectorder
-segaddr
-segs_read_only_addr

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-segs_read_write_addr
-seg_addr_table
-seg_addr_table_filename
-seglinkedit
-segprot
-segs_read_only_addr
-segs_read_write_addr
-single_module
-static
-sub_library
-sub_umbrella
-twolevel_namespace
-umbrella
-undefined
-unexported_symbols_list
-weak_reference_mismatches
-whatsloaded
These options are passed to the Darwin linker. The Darwin linker man page
describes them in detail.

3.18.11 DEC Alpha Options
These ‘-m’ options are defined for the DEC Alpha implementations:
-mno-soft-float
-msoft-float
Use (do not use) the hardware floating-point instructions for floating-point operations. When ‘-msoft-float’ is specified, functions in ‘libgcc.a’ are used
to perform floating-point operations. Unless they are replaced by routines that
emulate the floating-point operations, or compiled in such a way as to call such
emulations routines, these routines issue floating-point operations. If you are
compiling for an Alpha without floating-point operations, you must ensure that
the library is built so as not to call them.
Note that Alpha implementations without floating-point operations are required
to have floating-point registers.
-mfp-reg
-mno-fp-regs
Generate code that uses (does not use) the floating-point register set.
‘-mno-fp-regs’ implies ‘-msoft-float’. If the floating-point register set is
not used, floating-point operands are passed in integer registers as if they were
integers and floating-point results are passed in $0 instead of $f0. This is a
non-standard calling sequence, so any function with a floating-point argument
or return value called by code compiled with ‘-mno-fp-regs’ must also be
compiled with that option.
A typical use of this option is building a kernel that does not use, and hence
need not save and restore, any floating-point registers.

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-mieee

277

The Alpha architecture implements floating-point hardware optimized for maximum performance. It is mostly compliant with the IEEE floating-point standard. However, for full compliance, software assistance is required. This option
generates code fully IEEE-compliant code except that the inexact-flag is not
maintained (see below). If this option is turned on, the preprocessor macro
_IEEE_FP is defined during compilation. The resulting code is less efficient but
is able to correctly support denormalized numbers and exceptional IEEE values
such as not-a-number and plus/minus infinity. Other Alpha compilers call this
option ‘-ieee_with_no_inexact’.

-mieee-with-inexact
This is like ‘-mieee’ except the generated code also maintains the IEEE inexactflag. Turning on this option causes the generated code to implement fullycompliant IEEE math. In addition to _IEEE_FP, _IEEE_FP_EXACT is defined as
a preprocessor macro. On some Alpha implementations the resulting code may
execute significantly slower than the code generated by default. Since there is
very little code that depends on the inexact-flag, you should normally not specify this option. Other Alpha compilers call this option ‘-ieee_with_inexact’.
-mfp-trap-mode=trap-mode
This option controls what floating-point related traps are enabled. Other Alpha
compilers call this option ‘-fptm trap-mode’. The trap mode can be set to one
of four values:
‘n’

This is the default (normal) setting. The only traps that are enabled are the ones that cannot be disabled in software (e.g., division
by zero trap).

‘u’

In addition to the traps enabled by ‘n’, underflow traps are enabled
as well.

‘su’

Like ‘u’, but the instructions are marked to be safe for software
completion (see Alpha architecture manual for details).

‘sui’

Like ‘su’, but inexact traps are enabled as well.

-mfp-rounding-mode=rounding-mode
Selects the IEEE rounding mode. Other Alpha compilers call this option ‘-fprm
rounding-mode’. The rounding-mode can be one of:
‘n’

Normal IEEE rounding mode. Floating-point numbers are rounded
towards the nearest machine number or towards the even machine
number in case of a tie.

‘m’

Round towards minus infinity.

‘c’

Chopped rounding mode. Floating-point numbers are rounded towards zero.

‘d’

Dynamic rounding mode. A field in the floating-point control register (fpcr, see Alpha architecture reference manual) controls the
rounding mode in effect. The C library initializes this register for
rounding towards plus infinity. Thus, unless your program modifies
the fpcr, ‘d’ corresponds to round towards plus infinity.

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-mtrap-precision=trap-precision
In the Alpha architecture, floating-point traps are imprecise. This means without software assistance it is impossible to recover from a floating trap and
program execution normally needs to be terminated. GCC can generate code
that can assist operating system trap handlers in determining the exact location that caused a floating-point trap. Depending on the requirements of an
application, different levels of precisions can be selected:
‘p’

Program precision. This option is the default and means a trap
handler can only identify which program caused a floating-point
exception.

‘f’

Function precision. The trap handler can determine the function
that caused a floating-point exception.

‘i’

Instruction precision. The trap handler can determine the exact
instruction that caused a floating-point exception.

Other Alpha compilers provide the equivalent options called ‘-scope_safe’ and
‘-resumption_safe’.
-mieee-conformant
This option marks the generated code as IEEE conformant. You must not
use this option unless you also specify ‘-mtrap-precision=i’ and either
‘-mfp-trap-mode=su’ or ‘-mfp-trap-mode=sui’. Its only effect is to emit the
line ‘.eflag 48’ in the function prologue of the generated assembly file.
-mbuild-constants
Normally GCC examines a 32- or 64-bit integer constant to see if it can construct
it from smaller constants in two or three instructions. If it cannot, it outputs
the constant as a literal and generates code to load it from the data segment
at run time.
Use this option to require GCC to construct all integer constants using code,
even if it takes more instructions (the maximum is six).
You typically use this option to build a shared library dynamic loader. Itself a
shared library, it must relocate itself in memory before it can find the variables
and constants in its own data segment.
-mbwx
-mno-bwx
-mcix
-mno-cix
-mfix
-mno-fix
-mmax
-mno-max

Indicate whether GCC should generate code to use the optional BWX, CIX, FIX
and MAX instruction sets. The default is to use the instruction sets supported
by the CPU type specified via ‘-mcpu=’ option or that of the CPU on which
GCC was built if none is specified.

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-mfloat-vax
-mfloat-ieee
Generate code that uses (does not use) VAX F and G floating-point arithmetic
instead of IEEE single and double precision.
-mexplicit-relocs
-mno-explicit-relocs
Older Alpha assemblers provided no way to generate symbol relocations except
via assembler macros. Use of these macros does not allow optimal instruction
scheduling. GNU binutils as of version 2.12 supports a new syntax that allows the compiler to explicitly mark which relocations should apply to which
instructions. This option is mostly useful for debugging, as GCC detects the
capabilities of the assembler when it is built and sets the default accordingly.
-msmall-data
-mlarge-data
When ‘-mexplicit-relocs’ is in effect, static data is accessed via gp-relative
relocations. When ‘-msmall-data’ is used, objects 8 bytes long or smaller are
placed in a small data area (the .sdata and .sbss sections) and are accessed
via 16-bit relocations off of the $gp register. This limits the size of the small
data area to 64KB, but allows the variables to be directly accessed via a single
instruction.
The default is ‘-mlarge-data’. With this option the data area is limited to just
below 2GB. Programs that require more than 2GB of data must use malloc or
mmap to allocate the data in the heap instead of in the program’s data segment.
When generating code for shared libraries, ‘-fpic’ implies ‘-msmall-data’ and
‘-fPIC’ implies ‘-mlarge-data’.
-msmall-text
-mlarge-text
When ‘-msmall-text’ is used, the compiler assumes that the code of the entire
program (or shared library) fits in 4MB, and is thus reachable with a branch instruction. When ‘-msmall-data’ is used, the compiler can assume that all local
symbols share the same $gp value, and thus reduce the number of instructions
required for a function call from 4 to 1.
The default is ‘-mlarge-text’.
-mcpu=cpu_type
Set the instruction set and instruction scheduling parameters for machine type
cpu type. You can specify either the ‘EV’ style name or the corresponding chip
number. GCC supports scheduling parameters for the EV4, EV5 and EV6
family of processors and chooses the default values for the instruction set from
the processor you specify. If you do not specify a processor type, GCC defaults
to the processor on which the compiler was built.
Supported values for cpu type are
‘ev4’
‘ev45’
‘21064’

Schedules as an EV4 and has no instruction set extensions.

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‘ev5’
‘21164’

Schedules as an EV5 and has no instruction set extensions.

‘ev56’
‘21164a’

Schedules as an EV5 and supports the BWX extension.

‘pca56’
‘21164pc’
‘21164PC’

Schedules as an EV5 and supports the BWX and MAX extensions.

‘ev6’
‘21264’
‘ev67’
‘21264a’

Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
extensions.

Native toolchains also support the value ‘native’, which selects the best architecture option for the host processor. ‘-mcpu=native’ has no effect if GCC
does not recognize the processor.
-mtune=cpu_type
Set only the instruction scheduling parameters for machine type cpu type. The
instruction set is not changed.
Native toolchains also support the value ‘native’, which selects the best architecture option for the host processor. ‘-mtune=native’ has no effect if GCC
does not recognize the processor.
-mmemory-latency=time
Sets the latency the scheduler should assume for typical memory references
as seen by the application. This number is highly dependent on the memory
access patterns used by the application and the size of the external cache on
the machine.
Valid options for time are
‘number’
‘L1’
‘L2’
‘L3’
‘main’

A decimal number representing clock cycles.

The compiler contains estimates of the number of clock cycles for
“typical” EV4 & EV5 hardware for the Level 1, 2 & 3 caches (also
called Dcache, Scache, and Bcache), as well as to main memory.
Note that L3 is only valid for EV5.

3.18.12 FR30 Options
These options are defined specifically for the FR30 port.
-msmall-model
Use the small address space model. This can produce smaller code, but it does
assume that all symbolic values and addresses fit into a 20-bit range.

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-mno-lsim
Assume that runtime support has been provided and so there is no need to
include the simulator library (‘libsim.a’) on the linker command line.

3.18.13 FT32 Options
These options are defined specifically for the FT32 port.
-msim

Specifies that the program will be run on the simulator. This causes an alternate
runtime startup and library to be linked. You must not use this option when
generating programs that will run on real hardware; you must provide your own
runtime library for whatever I/O functions are needed.

-mlra

Enable Local Register Allocation. This is still experimental for FT32, so by
default the compiler uses standard reload.

-mnodiv

Do not use div and mod instructions.

-mft32b

Enable use of the extended instructions of the FT32B processor.

-mcompress
Compress all code using the Ft32B code compression scheme.
-mnopm

Do not generate code that reads program memory.

3.18.14 FRV Options
-mgpr-32
Only use the first 32 general-purpose registers.
-mgpr-64
Use all 64 general-purpose registers.
-mfpr-32
Use only the first 32 floating-point registers.
-mfpr-64
Use all 64 floating-point registers.
-mhard-float
Use hardware instructions for floating-point operations.
-msoft-float
Use library routines for floating-point operations.
-malloc-cc
Dynamically allocate condition code registers.
-mfixed-cc
Do not try to dynamically allocate condition code registers, only use icc0 and
fcc0.
-mdword
Change ABI to use double word insns.

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-mno-dword
Do not use double word instructions.
-mdouble
Use floating-point double instructions.
-mno-double
Do not use floating-point double instructions.
-mmedia
Use media instructions.
-mno-media
Do not use media instructions.
-mmuladd
Use multiply and add/subtract instructions.
-mno-muladd
Do not use multiply and add/subtract instructions.
-mfdpic
Select the FDPIC ABI, which uses function descriptors to represent pointers
to functions. Without any PIC/PIE-related options, it implies ‘-fPIE’. With
‘-fpic’ or ‘-fpie’, it assumes GOT entries and small data are within a 12-bit
range from the GOT base address; with ‘-fPIC’ or ‘-fPIE’, GOT offsets are
computed with 32 bits. With a ‘bfin-elf’ target, this option implies ‘-msim’.
-minline-plt
Enable inlining of PLT entries in function calls to functions that are not known
to bind locally. It has no effect without ‘-mfdpic’. It’s enabled by default if
optimizing for speed and compiling for shared libraries (i.e., ‘-fPIC’ or ‘-fpic’),
or when an optimization option such as ‘-O3’ or above is present in the command
line.
-mTLS
Assume a large TLS segment when generating thread-local code.
-mtls
Do not assume a large TLS segment when generating thread-local code.
-mgprel-ro
Enable the use of GPREL relocations in the FDPIC ABI for data that is known to
be in read-only sections. It’s enabled by default, except for ‘-fpic’ or ‘-fpie’:
even though it may help make the global offset table smaller, it trades 1 instruction for 4. With ‘-fPIC’ or ‘-fPIE’, it trades 3 instructions for 4, one of
which may be shared by multiple symbols, and it avoids the need for a GOT
entry for the referenced symbol, so it’s more likely to be a win. If it is not,
‘-mno-gprel-ro’ can be used to disable it.
-multilib-library-pic
Link with the (library, not FD) pic libraries. It’s implied by ‘-mlibrary-pic’,
as well as by ‘-fPIC’ and ‘-fpic’ without ‘-mfdpic’. You should never have to
use it explicitly.

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-mlinked-fp
Follow the EABI requirement of always creating a frame pointer whenever a
stack frame is allocated. This option is enabled by default and can be disabled
with ‘-mno-linked-fp’.
-mlong-calls
Use indirect addressing to call functions outside the current compilation unit.
This allows the functions to be placed anywhere within the 32-bit address space.
-malign-labels
Try to align labels to an 8-byte boundary by inserting NOPs into the previous
packet. This option only has an effect when VLIW packing is enabled. It
doesn’t create new packets; it merely adds NOPs to existing ones.
-mlibrary-pic
Generate position-independent EABI code.
-macc-4
Use only the first four media accumulator registers.
-macc-8
Use all eight media accumulator registers.
-mpack
Pack VLIW instructions.
-mno-pack
Do not pack VLIW instructions.
-mno-eflags
Do not mark ABI switches in e flags.
-mcond-move
Enable the use of conditional-move instructions (default).
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mno-cond-move
Disable the use of conditional-move instructions.
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mscc
Enable the use of conditional set instructions (default).
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mno-scc
Disable the use of conditional set instructions.
This switch is mainly for debugging the compiler and will likely be removed in
a future version.

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-mcond-exec
Enable the use of conditional execution (default).
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mno-cond-exec
Disable the use of conditional execution.
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mvliw-branch
Run a pass to pack branches into VLIW instructions (default).
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mno-vliw-branch
Do not run a pass to pack branches into VLIW instructions.
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mmulti-cond-exec
Enable optimization of && and || in conditional execution (default).
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mno-multi-cond-exec
Disable optimization of && and || in conditional execution.
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mnested-cond-exec
Enable nested conditional execution optimizations (default).
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-mno-nested-cond-exec
Disable nested conditional execution optimizations.
This switch is mainly for debugging the compiler and will likely be removed in
a future version.
-moptimize-membar
This switch removes redundant membar instructions from the compilergenerated code. It is enabled by default.
-mno-optimize-membar
This switch disables the automatic removal of redundant membar instructions
from the generated code.
-mtomcat-stats
Cause gas to print out tomcat statistics.

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-mcpu=cpu
Select the processor type for which to generate code. Possible values are ‘frv’,
‘fr550’, ‘tomcat’, ‘fr500’, ‘fr450’, ‘fr405’, ‘fr400’, ‘fr300’ and ‘simple’.

3.18.15 GNU/Linux Options
These ‘-m’ options are defined for GNU/Linux targets:
-mglibc

Use the GNU C library. This is the default except on ‘*-*-linux-*uclibc*’,
‘*-*-linux-*musl*’ and ‘*-*-linux-*android*’ targets.

-muclibc

Use uClibc C library. This is the default on ‘*-*-linux-*uclibc*’ targets.

-mmusl

Use the musl C library. This is the default on ‘*-*-linux-*musl*’ targets.

-mbionic

Use Bionic C library. This is the default on ‘*-*-linux-*android*’ targets.

-mandroid
Compile code compatible with Android platform. This is the default on
‘*-*-linux-*android*’ targets.
When compiling, this option enables ‘-mbionic’, ‘-fPIC’, ‘-fno-exceptions’
and ‘-fno-rtti’ by default. When linking, this option makes the GCC driver
pass Android-specific options to the linker. Finally, this option causes the
preprocessor macro __ANDROID__ to be defined.
-tno-android-cc
Disable compilation effects of ‘-mandroid’, i.e., do not enable ‘-mbionic’,
‘-fPIC’, ‘-fno-exceptions’ and ‘-fno-rtti’ by default.
-tno-android-ld
Disable linking effects of ‘-mandroid’, i.e., pass standard Linux linking options
to the linker.

3.18.16 H8/300 Options
These ‘-m’ options are defined for the H8/300 implementations:
-mrelax

Shorten some address references at link time, when possible; uses the linker
option ‘-relax’. See Section “ld and the H8/300” in Using ld, for a fuller
description.

-mh

Generate code for the H8/300H.

-ms

Generate code for the H8S.

-mn

Generate code for the H8S and H8/300H in the normal mode. This switch must
be used either with ‘-mh’ or ‘-ms’.

-ms2600

Generate code for the H8S/2600. This switch must be used with ‘-ms’.

-mexr

Extended registers are stored on stack before execution of function with monitor
attribute. Default option is ‘-mexr’. This option is valid only for H8S targets.

-mno-exr

Extended registers are not stored on stack before execution of function with
monitor attribute. Default option is ‘-mno-exr’. This option is valid only for
H8S targets.

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-mint32

Using the GNU Compiler Collection (GCC)

Make int data 32 bits by default.

-malign-300
On the H8/300H and H8S, use the same alignment rules as for the H8/300.
The default for the H8/300H and H8S is to align longs and floats on 4-byte
boundaries. ‘-malign-300’ causes them to be aligned on 2-byte boundaries.
This option has no effect on the H8/300.

3.18.17 HPPA Options
These ‘-m’ options are defined for the HPPA family of computers:
-march=architecture-type
Generate code for the specified architecture. The choices for architecture-type
are ‘1.0’ for PA 1.0, ‘1.1’ for PA 1.1, and ‘2.0’ for PA 2.0 processors. Refer
to ‘/usr/lib/sched.models’ on an HP-UX system to determine the proper
architecture option for your machine. Code compiled for lower numbered architectures runs on higher numbered architectures, but not the other way around.
-mpa-risc-1-0
-mpa-risc-1-1
-mpa-risc-2-0
Synonyms for ‘-march=1.0’, ‘-march=1.1’, and ‘-march=2.0’ respectively.
-mcaller-copies
The caller copies function arguments passed by hidden reference. This option
should be used with care as it is not compatible with the default 32-bit runtime.
However, only aggregates larger than eight bytes are passed by hidden reference
and the option provides better compatibility with OpenMP.
-mjump-in-delay
This option is ignored and provided for compatibility purposes only.
-mdisable-fpregs
Prevent floating-point registers from being used in any manner. This is necessary for compiling kernels that perform lazy context switching of floating-point
registers. If you use this option and attempt to perform floating-point operations, the compiler aborts.
-mdisable-indexing
Prevent the compiler from using indexing address modes. This avoids some
rather obscure problems when compiling MIG generated code under MACH.
-mno-space-regs
Generate code that assumes the target has no space registers. This allows GCC
to generate faster indirect calls and use unscaled index address modes.
Such code is suitable for level 0 PA systems and kernels.
-mfast-indirect-calls
Generate code that assumes calls never cross space boundaries. This allows
GCC to emit code that performs faster indirect calls.
This option does not work in the presence of shared libraries or nested functions.

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-mfixed-range=register-range
Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling
kernel code. A register range is specified as two registers separated by a dash.
Multiple register ranges can be specified separated by a comma.
-mlong-load-store
Generate 3-instruction load and store sequences as sometimes required by the
HP-UX 10 linker. This is equivalent to the ‘+k’ option to the HP compilers.
-mportable-runtime
Use the portable calling conventions proposed by HP for ELF systems.
-mgas

Enable the use of assembler directives only GAS understands.

-mschedule=cpu-type
Schedule code according to the constraints for the machine type cpu-type. The
choices for cpu-type are ‘700’ ‘7100’, ‘7100LC’, ‘7200’, ‘7300’ and ‘8000’. Refer
to ‘/usr/lib/sched.models’ on an HP-UX system to determine the proper
scheduling option for your machine. The default scheduling is ‘8000’.
-mlinker-opt
Enable the optimization pass in the HP-UX linker. Note this makes symbolic
debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
linkers in which they give bogus error messages when linking some programs.
-msoft-float
Generate output containing library calls for floating point. Warning: the requisite libraries are not available for all HPPA targets. Normally the facilities of
the machine’s usual C compiler are used, but this cannot be done directly in
cross-compilation. You must make your own arrangements to provide suitable
library functions for cross-compilation.
‘-msoft-float’ changes the calling convention in the output file; therefore, it
is only useful if you compile all of a program with this option. In particular, you need to compile ‘libgcc.a’, the library that comes with GCC, with
‘-msoft-float’ in order for this to work.
-msio

Generate the predefine, _SIO, for server IO. The default is ‘-mwsio’. This generates the predefines, __hp9000s700, __hp9000s700__ and _WSIO, for workstation IO. These options are available under HP-UX and HI-UX.

-mgnu-ld

Use options specific to GNU ld. This passes ‘-shared’ to ld when building a
shared library. It is the default when GCC is configured, explicitly or implicitly, with the GNU linker. This option does not affect which ld is called; it
only changes what parameters are passed to that ld. The ld that is called is
determined by the ‘--with-ld’ configure option, GCC’s program search path,
and finally by the user’s PATH. The linker used by GCC can be printed using ‘which ‘gcc -print-prog-name=ld‘’. This option is only available on the
64-bit HP-UX GCC, i.e. configured with ‘hppa*64*-*-hpux*’.

-mhp-ld

Use options specific to HP ld. This passes ‘-b’ to ld when building a shared
library and passes ‘+Accept TypeMismatch’ to ld on all links. It is the default

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when GCC is configured, explicitly or implicitly, with the HP linker. This option does not affect which ld is called; it only changes what parameters are
passed to that ld. The ld that is called is determined by the ‘--with-ld’ configure option, GCC’s program search path, and finally by the user’s PATH. The
linker used by GCC can be printed using ‘which ‘gcc -print-prog-name=ld‘’.
This option is only available on the 64-bit HP-UX GCC, i.e. configured with
‘hppa*64*-*-hpux*’.
-mlong-calls
Generate code that uses long call sequences. This ensures that a call is always
able to reach linker generated stubs. The default is to generate long calls
only when the distance from the call site to the beginning of the function or
translation unit, as the case may be, exceeds a predefined limit set by the
branch type being used. The limits for normal calls are 7,600,000 and 240,000
bytes, respectively for the PA 2.0 and PA 1.X architectures. Sibcalls are always
limited at 240,000 bytes.
Distances are measured from the beginning of functions when using
the ‘-ffunction-sections’ option, or when using the ‘-mgas’ and
‘-mno-portable-runtime’ options together under HP-UX with the SOM
linker.
It is normally not desirable to use this option as it degrades performance. However, it may be useful in large applications, particularly when partial linking is
used to build the application.
The types of long calls used depends on the capabilities of the assembler and
linker, and the type of code being generated. The impact on systems that
support long absolute calls, and long pic symbol-difference or pc-relative calls
should be relatively small. However, an indirect call is used on 32-bit ELF
systems in pic code and it is quite long.
-munix=unix-std
Generate compiler predefines and select a startfile for the specified UNIX standard. The choices for unix-std are ‘93’, ‘95’ and ‘98’. ‘93’ is supported on all
HP-UX versions. ‘95’ is available on HP-UX 10.10 and later. ‘98’ is available
on HP-UX 11.11 and later. The default values are ‘93’ for HP-UX 10.00, ‘95’
for HP-UX 10.10 though to 11.00, and ‘98’ for HP-UX 11.11 and later.
‘-munix=93’ provides the same predefines as GCC 3.3 and 3.4. ‘-munix=95’
provides additional predefines for XOPEN_UNIX and _XOPEN_SOURCE_EXTENDED,
and the startfile ‘unix95.o’. ‘-munix=98’ provides additional predefines for
_XOPEN_UNIX, _XOPEN_SOURCE_EXTENDED, _INCLUDE__STDC_A1_SOURCE and _
INCLUDE_XOPEN_SOURCE_500, and the startfile ‘unix98.o’.
It is important to note that this option changes the interfaces for various library
routines. It also affects the operational behavior of the C library. Thus, extreme
care is needed in using this option.
Library code that is intended to operate with more than one UNIX standard
must test, set and restore the variable __xpg4_extended_mask as appropriate.
Most GNU software doesn’t provide this capability.

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-nolibdld
Suppress the generation of link options to search libdld.sl when the ‘-static’
option is specified on HP-UX 10 and later.
-static

The HP-UX implementation of setlocale in libc has a dependency on libdld.sl.
There isn’t an archive version of libdld.sl. Thus, when the ‘-static’ option is
specified, special link options are needed to resolve this dependency.
On HP-UX 10 and later, the GCC driver adds the necessary options to link
with libdld.sl when the ‘-static’ option is specified. This causes the resulting
binary to be dynamic. On the 64-bit port, the linkers generate dynamic binaries
by default in any case. The ‘-nolibdld’ option can be used to prevent the GCC
driver from adding these link options.

-threads

Add support for multithreading with the dce thread library under HP-UX. This
option sets flags for both the preprocessor and linker.

3.18.18 IA-64 Options
These are the ‘-m’ options defined for the Intel IA-64 architecture.
-mbig-endian
Generate code for a big-endian target. This is the default for HP-UX.
-mlittle-endian
Generate code for a little-endian target. This is the default for AIX5 and
GNU/Linux.
-mgnu-as
-mno-gnu-as
Generate (or don’t) code for the GNU assembler. This is the default.
-mgnu-ld
-mno-gnu-ld
Generate (or don’t) code for the GNU linker. This is the default.
-mno-pic

Generate code that does not use a global pointer register. The result is not
position independent code, and violates the IA-64 ABI.

-mvolatile-asm-stop
-mno-volatile-asm-stop
Generate (or don’t) a stop bit immediately before and after volatile asm statements.
-mregister-names
-mno-register-names
Generate (or don’t) ‘in’, ‘loc’, and ‘out’ register names for the stacked registers.
This may make assembler output more readable.
-mno-sdata
-msdata
Disable (or enable) optimizations that use the small data section. This may be
useful for working around optimizer bugs.
-mconstant-gp
Generate code that uses a single constant global pointer value. This is useful
when compiling kernel code.

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-mauto-pic
Generate code that is self-relocatable. This implies ‘-mconstant-gp’. This is
useful when compiling firmware code.
-minline-float-divide-min-latency
Generate code for inline divides of floating-point values using the minimum
latency algorithm.
-minline-float-divide-max-throughput
Generate code for inline divides of floating-point values using the maximum
throughput algorithm.
-mno-inline-float-divide
Do not generate inline code for divides of floating-point values.
-minline-int-divide-min-latency
Generate code for inline divides of integer values using the minimum latency
algorithm.
-minline-int-divide-max-throughput
Generate code for inline divides of integer values using the maximum throughput algorithm.
-mno-inline-int-divide
Do not generate inline code for divides of integer values.
-minline-sqrt-min-latency
Generate code for inline square roots using the minimum latency algorithm.
-minline-sqrt-max-throughput
Generate code for inline square roots using the maximum throughput algorithm.
-mno-inline-sqrt
Do not generate inline code for sqrt.
-mfused-madd
-mno-fused-madd
Do (don’t) generate code that uses the fused multiply/add or multiply/subtract
instructions. The default is to use these instructions.
-mno-dwarf2-asm
-mdwarf2-asm
Don’t (or do) generate assembler code for the DWARF line number debugging
info. This may be useful when not using the GNU assembler.
-mearly-stop-bits
-mno-early-stop-bits
Allow stop bits to be placed earlier than immediately preceding the instruction
that triggered the stop bit. This can improve instruction scheduling, but does
not always do so.
-mfixed-range=register-range
Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling

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kernel code. A register range is specified as two registers separated by a dash.
Multiple register ranges can be specified separated by a comma.
-mtls-size=tls-size
Specify bit size of immediate TLS offsets. Valid values are 14, 22, and 64.
-mtune=cpu-type
Tune the instruction scheduling for a particular CPU, Valid values are
‘itanium’, ‘itanium1’, ‘merced’, ‘itanium2’, and ‘mckinley’.
-milp32
-mlp64

Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets
int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and
long and pointer to 64 bits. These are HP-UX specific flags.

-mno-sched-br-data-spec
-msched-br-data-spec
(Dis/En)able data speculative scheduling before reload. This results in generation of ld.a instructions and the corresponding check instructions (ld.c /
chk.a). The default setting is disabled.
-msched-ar-data-spec
-mno-sched-ar-data-spec
(En/Dis)able data speculative scheduling after reload. This results in generation of ld.a instructions and the corresponding check instructions (ld.c /
chk.a). The default setting is enabled.
-mno-sched-control-spec
-msched-control-spec
(Dis/En)able control speculative scheduling. This feature is available only during region scheduling (i.e. before reload). This results in generation of the
ld.s instructions and the corresponding check instructions chk.s. The default
setting is disabled.
-msched-br-in-data-spec
-mno-sched-br-in-data-spec
(En/Dis)able speculative scheduling of the instructions that are dependent
on the data speculative loads before reload. This is effective only with
‘-msched-br-data-spec’ enabled. The default setting is enabled.
-msched-ar-in-data-spec
-mno-sched-ar-in-data-spec
(En/Dis)able speculative scheduling of the instructions that are dependent
on the data speculative loads after reload. This is effective only with
‘-msched-ar-data-spec’ enabled. The default setting is enabled.
-msched-in-control-spec
-mno-sched-in-control-spec
(En/Dis)able speculative scheduling of the instructions that are dependent on the control speculative loads.
This is effective only with
‘-msched-control-spec’ enabled. The default setting is enabled.

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-mno-sched-prefer-non-data-spec-insns
-msched-prefer-non-data-spec-insns
If enabled, data-speculative instructions are chosen for schedule only if there
are no other choices at the moment. This makes the use of the data speculation
much more conservative. The default setting is disabled.
-mno-sched-prefer-non-control-spec-insns
-msched-prefer-non-control-spec-insns
If enabled, control-speculative instructions are chosen for schedule only if there
are no other choices at the moment. This makes the use of the control speculation much more conservative. The default setting is disabled.
-mno-sched-count-spec-in-critical-path
-msched-count-spec-in-critical-path
If enabled, speculative dependencies are considered during computation of the
instructions priorities. This makes the use of the speculation a bit more conservative. The default setting is disabled.
-msched-spec-ldc
Use a simple data speculation check. This option is on by default.
-msched-control-spec-ldc
Use a simple check for control speculation. This option is on by default.
-msched-stop-bits-after-every-cycle
Place a stop bit after every cycle when scheduling. This option is on by default.
-msched-fp-mem-deps-zero-cost
Assume that floating-point stores and loads are not likely to cause a conflict
when placed into the same instruction group. This option is disabled by default.
-msel-sched-dont-check-control-spec
Generate checks for control speculation in selective scheduling. This flag is
disabled by default.
-msched-max-memory-insns=max-insns
Limit on the number of memory insns per instruction group, giving lower priority to subsequent memory insns attempting to schedule in the same instruction
group. Frequently useful to prevent cache bank conflicts. The default value is
1.
-msched-max-memory-insns-hard-limit
Makes the limit specified by ‘msched-max-memory-insns’ a hard limit, disallowing more than that number in an instruction group. Otherwise, the limit
is “soft”, meaning that non-memory operations are preferred when the limit is
reached, but memory operations may still be scheduled.

3.18.19 LM32 Options
These ‘-m’ options are defined for the LatticeMico32 architecture:
-mbarrel-shift-enabled
Enable barrel-shift instructions.

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-mdivide-enabled
Enable divide and modulus instructions.
-mmultiply-enabled
Enable multiply instructions.
-msign-extend-enabled
Enable sign extend instructions.
-muser-enabled
Enable user-defined instructions.

3.18.20 M32C Options
-mcpu=name
Select the CPU for which code is generated. name may be one of ‘r8c’ for
the R8C/Tiny series, ‘m16c’ for the M16C (up to /60) series, ‘m32cm’ for the
M16C/80 series, or ‘m32c’ for the M32C/80 series.
-msim

Specifies that the program will be run on the simulator. This causes an alternate
runtime library to be linked in which supports, for example, file I/O. You must
not use this option when generating programs that will run on real hardware;
you must provide your own runtime library for whatever I/O functions are
needed.

-memregs=number
Specifies the number of memory-based pseudo-registers GCC uses during code
generation. These pseudo-registers are used like real registers, so there is a
tradeoff between GCC’s ability to fit the code into available registers, and the
performance penalty of using memory instead of registers. Note that all modules
in a program must be compiled with the same value for this option. Because
of that, you must not use this option with GCC’s default runtime libraries.

3.18.21 M32R/D Options
These ‘-m’ options are defined for Renesas M32R/D architectures:
-m32r2

Generate code for the M32R/2.

-m32rx

Generate code for the M32R/X.

-m32r

Generate code for the M32R. This is the default.

-mmodel=small
Assume all objects live in the lower 16MB of memory (so that their addresses
can be loaded with the ld24 instruction), and assume all subroutines are reachable with the bl instruction. This is the default.
The addressability of a particular object can be set with the model attribute.
-mmodel=medium
Assume objects may be anywhere in the 32-bit address space (the compiler
generates seth/add3 instructions to load their addresses), and assume all subroutines are reachable with the bl instruction.

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-mmodel=large
Assume objects may be anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses), and assume subroutines
may not be reachable with the bl instruction (the compiler generates the much
slower seth/add3/jl instruction sequence).
-msdata=none
Disable use of the small data area. Variables are put into one of .data, .bss, or
.rodata (unless the section attribute has been specified). This is the default.
The small data area consists of sections .sdata and .sbss. Objects may be
explicitly put in the small data area with the section attribute using one of
these sections.
-msdata=sdata
Put small global and static data in the small data area, but do not generate
special code to reference them.
-msdata=use
Put small global and static data in the small data area, and generate special
instructions to reference them.
-G num

Put global and static objects less than or equal to num bytes into the small
data or BSS sections instead of the normal data or BSS sections. The default
value of num is 8. The ‘-msdata’ option must be set to one of ‘sdata’ or ‘use’
for this option to have any effect.
All modules should be compiled with the same ‘-G num’ value. Compiling with
different values of num may or may not work; if it doesn’t the linker gives an
error message—incorrect code is not generated.

-mdebug

Makes the M32R-specific code in the compiler display some statistics that might
help in debugging programs.

-malign-loops
Align all loops to a 32-byte boundary.
-mno-align-loops
Do not enforce a 32-byte alignment for loops. This is the default.
-missue-rate=number
Issue number instructions per cycle. number can only be 1 or 2.
-mbranch-cost=number
number can only be 1 or 2. If it is 1 then branches are preferred over conditional
code, if it is 2, then the opposite applies.
-mflush-trap=number
Specifies the trap number to use to flush the cache. The default is 12. Valid
numbers are between 0 and 15 inclusive.
-mno-flush-trap
Specifies that the cache cannot be flushed by using a trap.

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-mflush-func=name
Specifies the name of the operating system function to call to flush the cache.
The default is ‘_flush_cache’, but a function call is only used if a trap is not
available.
-mno-flush-func
Indicates that there is no OS function for flushing the cache.

3.18.22 M680x0 Options
These are the ‘-m’ options defined for M680x0 and ColdFire processors. The default settings
depend on which architecture was selected when the compiler was configured; the defaults
for the most common choices are given below.
-march=arch
Generate code for a specific M680x0 or ColdFire instruction set architecture.
Permissible values of arch for M680x0 architectures are: ‘68000’, ‘68010’,
‘68020’, ‘68030’, ‘68040’, ‘68060’ and ‘cpu32’. ColdFire architectures are
selected according to Freescale’s ISA classification and the permissible values
are: ‘isaa’, ‘isaaplus’, ‘isab’ and ‘isac’.
GCC defines a macro __mcfarch__ whenever it is generating code for a ColdFire
target. The arch in this macro is one of the ‘-march’ arguments given above.
When used together, ‘-march’ and ‘-mtune’ select code that runs on a family
of similar processors but that is optimized for a particular microarchitecture.
-mcpu=cpu
Generate code for a specific M680x0 or ColdFire processor. The M680x0 cpus
are: ‘68000’, ‘68010’, ‘68020’, ‘68030’, ‘68040’, ‘68060’, ‘68302’, ‘68332’ and
‘cpu32’. The ColdFire cpus are given by the table below, which also classifies
the CPUs into families:
Family
‘-mcpu’ arguments
‘51’
‘51’ ‘51ac’ ‘51ag’ ‘51cn’ ‘51em’ ‘51je’ ‘51jf’ ‘51jg’ ‘51jm’ ‘51mm’ ‘51qe’
‘51qm’
‘5206’
‘5202’ ‘5204’ ‘5206’
‘5206e’
‘5206e’
‘5208’
‘5207’ ‘5208’
‘5211a’
‘5210a’ ‘5211a’
‘5213’
‘5211’ ‘5212’ ‘5213’
‘5216’
‘5214’ ‘5216’
‘52235’
‘52230’ ‘52231’ ‘52232’ ‘52233’ ‘52234’ ‘52235’
‘5225’
‘5224’ ‘5225’
‘52259’
‘52252’ ‘52254’ ‘52255’ ‘52256’ ‘52258’ ‘52259’
‘5235’
‘5232’ ‘5233’ ‘5234’ ‘5235’ ‘523x’
‘5249’
‘5249’
‘5250’
‘5250’
‘5271’
‘5270’ ‘5271’
‘5272’
‘5272’
‘5275’
‘5274’ ‘5275’
‘5282’
‘5280’ ‘5281’ ‘5282’ ‘528x’

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‘53017’
‘5307’
‘5329’
‘5373’
‘5407’
‘5475’

‘53011’ ‘53012’ ‘53013’ ‘53014’ ‘53015’ ‘53016’ ‘53017’
‘5307’
‘5327’ ‘5328’ ‘5329’ ‘532x’
‘5372’ ‘5373’ ‘537x’
‘5407’
‘5470’ ‘5471’ ‘5472’ ‘5473’ ‘5474’ ‘5475’ ‘547x’ ‘5480’ ‘5481’ ‘5482’
‘5483’ ‘5484’ ‘5485’
‘-mcpu=cpu’ overrides ‘-march=arch’ if arch is compatible with cpu. Other
combinations of ‘-mcpu’ and ‘-march’ are rejected.
GCC defines the macro __mcf_cpu_cpu when ColdFire target cpu is selected.
It also defines __mcf_family_family, where the value of family is given by the
table above.

-mtune=tune
Tune the code for a particular microarchitecture within the constraints set by
‘-march’ and ‘-mcpu’. The M680x0 microarchitectures are: ‘68000’, ‘68010’,
‘68020’, ‘68030’, ‘68040’, ‘68060’ and ‘cpu32’. The ColdFire microarchitectures
are: ‘cfv1’, ‘cfv2’, ‘cfv3’, ‘cfv4’ and ‘cfv4e’.
You can also use ‘-mtune=68020-40’ for code that needs to run relatively well
on 68020, 68030 and 68040 targets. ‘-mtune=68020-60’ is similar but includes
68060 targets as well. These two options select the same tuning decisions as
‘-m68020-40’ and ‘-m68020-60’ respectively.
GCC defines the macros __mcarch and __mcarch__ when tuning for 680x0
architecture arch. It also defines mcarch unless either ‘-ansi’ or a non-GNU
‘-std’ option is used. If GCC is tuning for a range of architectures, as selected
by ‘-mtune=68020-40’ or ‘-mtune=68020-60’, it defines the macros for every
architecture in the range.
GCC also defines the macro __muarch__ when tuning for ColdFire microarchitecture uarch, where uarch is one of the arguments given above.
-m68000
-mc68000

Generate output for a 68000. This is the default when the compiler is configured
for 68000-based systems. It is equivalent to ‘-march=68000’.
Use this option for microcontrollers with a 68000 or EC000 core, including the
68008, 68302, 68306, 68307, 68322, 68328 and 68356.

-m68010
-m68020
-mc68020

Generate output for a 68010. This is the default when the compiler is configured
for 68010-based systems. It is equivalent to ‘-march=68010’.
Generate output for a 68020. This is the default when the compiler is configured
for 68020-based systems. It is equivalent to ‘-march=68020’.

-m68030

Generate output for a 68030. This is the default when the compiler is configured
for 68030-based systems. It is equivalent to ‘-march=68030’.

-m68040

Generate output for a 68040. This is the default when the compiler is configured
for 68040-based systems. It is equivalent to ‘-march=68040’.

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This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. Use this option if your 68040 does not have
code to emulate those instructions.
-m68060

Generate output for a 68060. This is the default when the compiler is configured
for 68060-based systems. It is equivalent to ‘-march=68060’.
This option inhibits the use of 68020 and 68881/68882 instructions that have
to be emulated by software on the 68060. Use this option if your 68060 does
not have code to emulate those instructions.

-mcpu32

Generate output for a CPU32. This is the default when the compiler is configured for CPU32-based systems. It is equivalent to ‘-march=cpu32’.
Use this option for microcontrollers with a CPU32 or CPU32+ core, including
the 68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360.

-m5200

Generate output for a 520X ColdFire CPU. This is the default when the compiler is configured for 520X-based systems. It is equivalent to ‘-mcpu=5206’,
and is now deprecated in favor of that option.
Use this option for microcontroller with a 5200 core, including the MCF5202,
MCF5203, MCF5204 and MCF5206.

-m5206e

Generate output for a 5206e ColdFire CPU. The option is now deprecated in
favor of the equivalent ‘-mcpu=5206e’.

-m528x

Generate output for a member of the ColdFire 528X family. The option is now
deprecated in favor of the equivalent ‘-mcpu=528x’.

-m5307

Generate output for a ColdFire 5307 CPU. The option is now deprecated in
favor of the equivalent ‘-mcpu=5307’.

-m5407

Generate output for a ColdFire 5407 CPU. The option is now deprecated in
favor of the equivalent ‘-mcpu=5407’.

-mcfv4e

Generate output for a ColdFire V4e family CPU (e.g. 547x/548x). This includes use of hardware floating-point instructions. The option is equivalent to
‘-mcpu=547x’, and is now deprecated in favor of that option.

-m68020-40
Generate output for a 68040, without using any of the new instructions. This
results in code that can run relatively efficiently on either a 68020/68881 or a
68030 or a 68040. The generated code does use the 68881 instructions that are
emulated on the 68040.
The option is equivalent to ‘-march=68020’ ‘-mtune=68020-40’.
-m68020-60
Generate output for a 68060, without using any of the new instructions. This
results in code that can run relatively efficiently on either a 68020/68881 or a
68030 or a 68040. The generated code does use the 68881 instructions that are
emulated on the 68060.
The option is equivalent to ‘-march=68020’ ‘-mtune=68020-60’.

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-mhard-float
-m68881
Generate floating-point instructions. This is the default for 68020 and above,
and for ColdFire devices that have an FPU. It defines the macro __HAVE_
68881__ on M680x0 targets and __mcffpu__ on ColdFire targets.
-msoft-float
Do not generate floating-point instructions; use library calls instead. This is the
default for 68000, 68010, and 68832 targets. It is also the default for ColdFire
devices that have no FPU.
-mdiv
-mno-div

Generate (do not generate) ColdFire hardware divide and remainder instructions. If ‘-march’ is used without ‘-mcpu’, the default is “on” for ColdFire architectures and “off” for M680x0 architectures. Otherwise, the default is taken
from the target CPU (either the default CPU, or the one specified by ‘-mcpu’).
For example, the default is “off” for ‘-mcpu=5206’ and “on” for ‘-mcpu=5206e’.
GCC defines the macro __mcfhwdiv__ when this option is enabled.

-mshort

Consider type int to be 16 bits wide, like short int. Additionally, parameters
passed on the stack are also aligned to a 16-bit boundary even on targets whose
API mandates promotion to 32-bit.

-mno-short
Do not consider type int to be 16 bits wide. This is the default.
-mnobitfield
-mno-bitfield
Do not use the bit-field instructions. The ‘-m68000’, ‘-mcpu32’ and ‘-m5200’
options imply ‘-mnobitfield’.
-mbitfield
Do use the bit-field instructions. The ‘-m68020’ option implies ‘-mbitfield’.
This is the default if you use a configuration designed for a 68020.
-mrtd

Use a different function-calling convention, in which functions that take a fixed
number of arguments return with the rtd instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no
need to pop the arguments there.
This calling convention is incompatible with the one normally used on Unix, so
you cannot use it if you need to call libraries compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that take variable
numbers of arguments (including printf); otherwise incorrect code is generated
for calls to those functions.
In addition, seriously incorrect code results if you call a function with too many
arguments. (Normally, extra arguments are harmlessly ignored.)
The rtd instruction is supported by the 68010, 68020, 68030, 68040, 68060 and
CPU32 processors, but not by the 68000 or 5200.

-mno-rtd

Do not use the calling conventions selected by ‘-mrtd’. This is the default.

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-malign-int
-mno-align-int
Control whether GCC aligns int, long, long long, float, double, and long
double variables on a 32-bit boundary (‘-malign-int’) or a 16-bit boundary
(‘-mno-align-int’). Aligning variables on 32-bit boundaries produces code
that runs somewhat faster on processors with 32-bit busses at the expense of
more memory.
Warning: if you use the ‘-malign-int’ switch, GCC aligns structures containing the above types differently than most published application binary interface
specifications for the m68k.
-mpcrel

Use the pc-relative addressing mode of the 68000 directly, instead of using a
global offset table. At present, this option implies ‘-fpic’, allowing at most a
16-bit offset for pc-relative addressing. ‘-fPIC’ is not presently supported with
‘-mpcrel’, though this could be supported for 68020 and higher processors.

-mno-strict-align
-mstrict-align
Do not (do) assume that unaligned memory references are handled by the system.
-msep-data
Generate code that allows the data segment to be located in a different area of
memory from the text segment. This allows for execute-in-place in an environment without virtual memory management. This option implies ‘-fPIC’.
-mno-sep-data
Generate code that assumes that the data segment follows the text segment.
This is the default.
-mid-shared-library
Generate code that supports shared libraries via the library ID method. This
allows for execute-in-place and shared libraries in an environment without virtual memory management. This option implies ‘-fPIC’.
-mno-id-shared-library
Generate code that doesn’t assume ID-based shared libraries are being used.
This is the default.
-mshared-library-id=n
Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other
values forces the allocation of that number to the current library, but is no more
space- or time-efficient than omitting this option.
-mxgot
-mno-xgot
When generating position-independent code for ColdFire, generate code that
works if the GOT has more than 8192 entries. This code is larger and slower
than code generated without this option. On M680x0 processors, this option is
not needed; ‘-fPIC’ suffices.

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GCC normally uses a single instruction to load values from the GOT. While
this is relatively efficient, it only works if the GOT is smaller than about 64k.
Anything larger causes the linker to report an error such as:
relocation truncated to fit: R_68K_GOT16O foobar

If this happens, you should recompile your code with ‘-mxgot’. It should then
work with very large GOTs. However, code generated with ‘-mxgot’ is less
efficient, since it takes 4 instructions to fetch the value of a global symbol.
Note that some linkers, including newer versions of the GNU linker, can create
multiple GOTs and sort GOT entries. If you have such a linker, you should
only need to use ‘-mxgot’ when compiling a single object file that accesses more
than 8192 GOT entries. Very few do.
These options have no effect unless GCC is generating position-independent
code.
-mlong-jump-table-offsets
Use 32-bit offsets in switch tables. The default is to use 16-bit offsets.

3.18.23 MCore Options
These are the ‘-m’ options defined for the Motorola M*Core processors.
-mhardlit
-mno-hardlit
Inline constants into the code stream if it can be done in two instructions or
less.
-mdiv
-mno-div

Use the divide instruction. (Enabled by default).

-mrelax-immediate
-mno-relax-immediate
Allow arbitrary-sized immediates in bit operations.
-mwide-bitfields
-mno-wide-bitfields
Always treat bit-fields as int-sized.
-m4byte-functions
-mno-4byte-functions
Force all functions to be aligned to a 4-byte boundary.
-mcallgraph-data
-mno-callgraph-data
Emit callgraph information.
-mslow-bytes
-mno-slow-bytes
Prefer word access when reading byte quantities.
-mlittle-endian
-mbig-endian
Generate code for a little-endian target.

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-m210
-m340

301

Generate code for the 210 processor.

-mno-lsim
Assume that runtime support has been provided and so omit the simulator
library (‘libsim.a)’ from the linker command line.
-mstack-increment=size
Set the maximum amount for a single stack increment operation. Large values
can increase the speed of programs that contain functions that need a large
amount of stack space, but they can also trigger a segmentation fault if the
stack is extended too much. The default value is 0x1000.

3.18.24 MeP Options
-mabsdiff
Enables the abs instruction, which is the absolute difference between two registers.
-mall-opts
Enables all the optional instructions—average, multiply, divide, bit operations,
leading zero, absolute difference, min/max, clip, and saturation.
-maverage
Enables the ave instruction, which computes the average of two registers.
-mbased=n
Variables of size n bytes or smaller are placed in the .based section by default.
Based variables use the $tp register as a base register, and there is a 128-byte
limit to the .based section.
-mbitops

Enables the bit operation instructions—bit test (btstm), set (bsetm), clear
(bclrm), invert (bnotm), and test-and-set (tas).

-mc=name

Selects which section constant data is placed in. name may be ‘tiny’, ‘near’,
or ‘far’.

-mclip

Enables the clip instruction. Note that ‘-mclip’ is not useful unless you also
provide ‘-mminmax’.

-mconfig=name
Selects one of the built-in core configurations. Each MeP chip has one or more
modules in it; each module has a core CPU and a variety of coprocessors,
optional instructions, and peripherals. The MeP-Integrator tool, not part of
GCC, provides these configurations through this option; using this option is
the same as using all the corresponding command-line options. The default
configuration is ‘default’.
-mcop

Enables the coprocessor instructions. By default, this is a 32-bit coprocessor.
Note that the coprocessor is normally enabled via the ‘-mconfig=’ option.

-mcop32

Enables the 32-bit coprocessor’s instructions.

-mcop64

Enables the 64-bit coprocessor’s instructions.

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-mivc2

Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor.

-mdc

Causes constant variables to be placed in the .near section.

-mdiv

Enables the div and divu instructions.

-meb

Generate big-endian code.

-mel

Generate little-endian code.

-mio-volatile
Tells the compiler that any variable marked with the io attribute is to be
considered volatile.
-ml

Causes variables to be assigned to the .far section by default.

-mleadz

Enables the leadz (leading zero) instruction.

-mm

Causes variables to be assigned to the .near section by default.

-mminmax

Enables the min and max instructions.

-mmult

Enables the multiplication and multiply-accumulate instructions.

-mno-opts
Disables all the optional instructions enabled by ‘-mall-opts’.
-mrepeat

Enables the repeat and erepeat instructions, used for low-overhead looping.

-ms

Causes all variables to default to the .tiny section. Note that there is a 65536byte limit to this section. Accesses to these variables use the %gp base register.

-msatur

Enables the saturation instructions. Note that the compiler does not currently
generate these itself, but this option is included for compatibility with other
tools, like as.

-msdram

Link the SDRAM-based runtime instead of the default ROM-based runtime.

-msim

Link the simulator run-time libraries.

-msimnovec
Link the simulator runtime libraries, excluding built-in support for reset and
exception vectors and tables.
-mtf

Causes all functions to default to the .far section. Without this option, functions default to the .near section.

-mtiny=n

Variables that are n bytes or smaller are allocated to the .tiny section. These
variables use the $gp base register. The default for this option is 4, but note
that there’s a 65536-byte limit to the .tiny section.

3.18.25 MicroBlaze Options
-msoft-float
Use software emulation for floating point (default).
-mhard-float
Use hardware floating-point instructions.

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-mmemcpy

303

Do not optimize block moves, use memcpy.

-mno-clearbss
This option is deprecated. Use ‘-fno-zero-initialized-in-bss’ instead.
-mcpu=cpu-type
Use features of, and schedule code for, the given CPU. Supported values are in
the format ‘vX.YY.Z’, where X is a major version, YY is the minor version, and
Z is compatibility code. Example values are ‘v3.00.a’, ‘v4.00.b’, ‘v5.00.a’,
‘v5.00.b’, ‘v5.00.b’, ‘v6.00.a’.
-mxl-soft-mul
Use software multiply emulation (default).
-mxl-soft-div
Use software emulation for divides (default).
-mxl-barrel-shift
Use the hardware barrel shifter.
-mxl-pattern-compare
Use pattern compare instructions.
-msmall-divides
Use table lookup optimization for small signed integer divisions.
-mxl-stack-check
This option is deprecated. Use ‘-fstack-check’ instead.
-mxl-gp-opt
Use GP-relative .sdata/.sbss sections.
-mxl-multiply-high
Use multiply high instructions for high part of 32x32 multiply.
-mxl-float-convert
Use hardware floating-point conversion instructions.
-mxl-float-sqrt
Use hardware floating-point square root instruction.
-mbig-endian
Generate code for a big-endian target.
-mlittle-endian
Generate code for a little-endian target.
-mxl-reorder
Use reorder instructions (swap and byte reversed load/store).
-mxl-mode-app-model
Select application model app-model. Valid models are
‘executable’
normal executable (default), uses startup code ‘crt0.o’.

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‘xmdstub’

for use with Xilinx Microprocessor Debugger (XMD) based software intrusive debug agent called xmdstub. This uses startup file
‘crt1.o’ and sets the start address of the program to 0x800.

‘bootstrap’
for applications that are loaded using a bootloader. This model uses
startup file ‘crt2.o’ which does not contain a processor reset vector
handler. This is suitable for transferring control on a processor reset
to the bootloader rather than the application.
‘novectors’
for applications that do not require any of the MicroBlaze vectors.
This option may be useful for applications running within a monitoring application. This model uses ‘crt3.o’ as a startup file.
Option ‘-xl-mode-app-model’ is a deprecated alias for ‘-mxl-mode-appmodel’.

3.18.26 MIPS Options
-EB

Generate big-endian code.

-EL

Generate little-endian code. This is the default for ‘mips*el-*-*’ configurations.

-march=arch
Generate code that runs on arch, which can be the name of a generic MIPS
ISA, or the name of a particular processor. The ISA names are: ‘mips1’,
‘mips2’, ‘mips3’, ‘mips4’, ‘mips32’, ‘mips32r2’, ‘mips32r3’, ‘mips32r5’,
‘mips32r6’, ‘mips64’, ‘mips64r2’, ‘mips64r3’, ‘mips64r5’ and ‘mips64r6’.
The processor names are: ‘4kc’, ‘4km’, ‘4kp’, ‘4ksc’, ‘4kec’, ‘4kem’, ‘4kep’,
‘4ksd’, ‘5kc’, ‘5kf’, ‘20kc’, ‘24kc’, ‘24kf2_1’, ‘24kf1_1’, ‘24kec’, ‘24kef2_1’,
‘24kef1_1’, ‘34kc’, ‘34kf2_1’, ‘34kf1_1’, ‘34kn’, ‘74kc’, ‘74kf2_1’, ‘74kf1_1’,
‘74kf3_2’, ‘1004kc’, ‘1004kf2_1’, ‘1004kf1_1’, ‘i6400’, ‘interaptiv’,
‘loongson2e’, ‘loongson2f’, ‘loongson3a’, ‘m4k’, ‘m14k’, ‘m14kc’, ‘m14ke’,
‘m14kec’, ‘m5100’, ‘m5101’, ‘octeon’, ‘octeon+’, ‘octeon2’, ‘octeon3’, ‘orion’,
‘p5600’, ‘r2000’, ‘r3000’, ‘r3900’, ‘r4000’, ‘r4400’, ‘r4600’, ‘r4650’, ‘r4700’,
‘r6000’, ‘r8000’, ‘rm7000’, ‘rm9000’, ‘r10000’, ‘r12000’, ‘r14000’, ‘r16000’,
‘sb1’, ‘sr71000’, ‘vr4100’, ‘vr4111’, ‘vr4120’, ‘vr4130’, ‘vr4300’, ‘vr5000’,
‘vr5400’, ‘vr5500’, ‘xlr’ and ‘xlp’. The special value ‘from-abi’ selects the
most compatible architecture for the selected ABI (that is, ‘mips1’ for 32-bit
ABIs and ‘mips3’ for 64-bit ABIs).
The native Linux/GNU toolchain also supports the value ‘native’, which selects
the best architecture option for the host processor. ‘-march=native’ has no
effect if GCC does not recognize the processor.
In processor names, a final ‘000’ can be abbreviated as ‘k’ (for example,
‘-march=r2k’). Prefixes are optional, and ‘vr’ may be written ‘r’.
Names of the form ‘nf2_1’ refer to processors with FPUs clocked at half the rate
of the core, names of the form ‘nf1_1’ refer to processors with FPUs clocked at
the same rate as the core, and names of the form ‘nf3_2’ refer to processors with

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FPUs clocked a ratio of 3:2 with respect to the core. For compatibility reasons,
‘nf’ is accepted as a synonym for ‘nf2_1’ while ‘nx’ and ‘bfx’ are accepted as
synonyms for ‘nf1_1’.
GCC defines two macros based on the value of this option. The first is _MIPS_
ARCH, which gives the name of target architecture, as a string. The second
has the form _MIPS_ARCH_foo, where foo is the capitalized value of _MIPS_
ARCH. For example, ‘-march=r2000’ sets _MIPS_ARCH to "r2000" and defines
the macro _MIPS_ARCH_R2000.
Note that the _MIPS_ARCH macro uses the processor names given above. In
other words, it has the full prefix and does not abbreviate ‘000’ as ‘k’. In the
case of ‘from-abi’, the macro names the resolved architecture (either "mips1"
or "mips3"). It names the default architecture when no ‘-march’ option is
given.
-mtune=arch
Optimize for arch. Among other things, this option controls the way instructions are scheduled, and the perceived cost of arithmetic operations. The list
of arch values is the same as for ‘-march’.
When this option is not used, GCC optimizes for the processor specified by
‘-march’. By using ‘-march’ and ‘-mtune’ together, it is possible to generate
code that runs on a family of processors, but optimize the code for one particular
member of that family.
‘-mtune’ defines the macros _MIPS_TUNE and _MIPS_TUNE_foo, which work in
the same way as the ‘-march’ ones described above.
-mips1

Equivalent to ‘-march=mips1’.

-mips2

Equivalent to ‘-march=mips2’.

-mips3

Equivalent to ‘-march=mips3’.

-mips4

Equivalent to ‘-march=mips4’.

-mips32

Equivalent to ‘-march=mips32’.

-mips32r3
Equivalent to ‘-march=mips32r3’.
-mips32r5
Equivalent to ‘-march=mips32r5’.
-mips32r6
Equivalent to ‘-march=mips32r6’.
-mips64

Equivalent to ‘-march=mips64’.

-mips64r2
Equivalent to ‘-march=mips64r2’.
-mips64r3
Equivalent to ‘-march=mips64r3’.
-mips64r5
Equivalent to ‘-march=mips64r5’.

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-mips64r6
Equivalent to ‘-march=mips64r6’.
-mips16
-mno-mips16
Generate (do not generate) MIPS16 code. If GCC is targeting a MIPS32 or
MIPS64 architecture, it makes use of the MIPS16e ASE.
MIPS16 code generation can also be controlled on a per-function basis by means
of mips16 and nomips16 attributes. See Section 6.31 [Function Attributes],
page 464, for more information.
-mflip-mips16
Generate MIPS16 code on alternating functions. This option is provided for
regression testing of mixed MIPS16/non-MIPS16 code generation, and is not
intended for ordinary use in compiling user code.
-minterlink-compressed
-mno-interlink-compressed
Require (do not require) that code using the standard (uncompressed) MIPS
ISA be link-compatible with MIPS16 and microMIPS code, and vice versa.
For example, code using the standard ISA encoding cannot jump directly to
MIPS16 or microMIPS code; it must either use a call or an indirect jump.
‘-minterlink-compressed’ therefore disables direct jumps unless GCC knows
that the target of the jump is not compressed.
-minterlink-mips16
-mno-interlink-mips16
Aliases of ‘-minterlink-compressed’ and ‘-mno-interlink-compressed’.
These options predate the microMIPS ASE and are retained for backwards
compatibility.
-mabi=32
-mabi=o64
-mabi=n32
-mabi=64
-mabi=eabi
Generate code for the given ABI.
Note that the EABI has a 32-bit and a 64-bit variant. GCC normally generates
64-bit code when you select a 64-bit architecture, but you can use ‘-mgp32’ to
get 32-bit code instead.
For information about the O64 ABI, see http://gcc.gnu.org/projects/
mipso64-abi.html.
GCC supports a variant of the o32 ABI in which floating-point registers are
64 rather than 32 bits wide. You can select this combination with ‘-mabi=32’
‘-mfp64’. This ABI relies on the mthc1 and mfhc1 instructions and is therefore
only supported for MIPS32R2, MIPS32R3 and MIPS32R5 processors.
The register assignments for arguments and return values remain the same, but
each scalar value is passed in a single 64-bit register rather than a pair of 32-bit

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registers. For example, scalar floating-point values are returned in ‘$f0’ only,
not a ‘$f0’/‘$f1’ pair. The set of call-saved registers also remains the same in
that the even-numbered double-precision registers are saved.
Two additional variants of the o32 ABI are supported to enable a transition from
32-bit to 64-bit registers. These are FPXX (‘-mfpxx’) and FP64A (‘-mfp64’
‘-mno-odd-spreg’). The FPXX extension mandates that all code must execute
correctly when run using 32-bit or 64-bit registers. The code can be interlinked
with either FP32 or FP64, but not both. The FP64A extension is similar to the
FP64 extension but forbids the use of odd-numbered single-precision registers.
This can be used in conjunction with the FRE mode of FPUs in MIPS32R5
processors and allows both FP32 and FP64A code to interlink and run in the
same process without changing FPU modes.
-mabicalls
-mno-abicalls
Generate (do not generate) code that is suitable for SVR4-style dynamic objects. ‘-mabicalls’ is the default for SVR4-based systems.
-mshared
-mno-shared
Generate (do not generate) code that is fully position-independent, and that can
therefore be linked into shared libraries. This option only affects ‘-mabicalls’.
All ‘-mabicalls’ code has traditionally been position-independent, regardless of
options like ‘-fPIC’ and ‘-fpic’. However, as an extension, the GNU toolchain
allows executables to use absolute accesses for locally-binding symbols. It can
also use shorter GP initialization sequences and generate direct calls to locallydefined functions. This mode is selected by ‘-mno-shared’.
‘-mno-shared’ depends on binutils 2.16 or higher and generates objects that
can only be linked by the GNU linker. However, the option does not affect the
ABI of the final executable; it only affects the ABI of relocatable objects. Using
‘-mno-shared’ generally makes executables both smaller and quicker.
‘-mshared’ is the default.
-mplt
-mno-plt

Assume (do not assume) that the static and dynamic linkers support PLTs and
copy relocations. This option only affects ‘-mno-shared -mabicalls’. For the
n64 ABI, this option has no effect without ‘-msym32’.
You can make ‘-mplt’ the default by configuring GCC with ‘--with-mips-plt’.
The default is ‘-mno-plt’ otherwise.

-mxgot
-mno-xgot
Lift (do not lift) the usual restrictions on the size of the global offset table.
GCC normally uses a single instruction to load values from the GOT. While
this is relatively efficient, it only works if the GOT is smaller than about 64k.
Anything larger causes the linker to report an error such as:
relocation truncated to fit: R_MIPS_GOT16 foobar

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If this happens, you should recompile your code with ‘-mxgot’. This works with
very large GOTs, although the code is also less efficient, since it takes three
instructions to fetch the value of a global symbol.
Note that some linkers can create multiple GOTs. If you have such a linker,
you should only need to use ‘-mxgot’ when a single object file accesses more
than 64k’s worth of GOT entries. Very few do.
These options have no effect unless GCC is generating position independent
code.
-mgp32

Assume that general-purpose registers are 32 bits wide.

-mgp64

Assume that general-purpose registers are 64 bits wide.

-mfp32

Assume that floating-point registers are 32 bits wide.

-mfp64

Assume that floating-point registers are 64 bits wide.

-mfpxx

Do not assume the width of floating-point registers.

-mhard-float
Use floating-point coprocessor instructions.
-msoft-float
Do not use floating-point coprocessor instructions. Implement floating-point
calculations using library calls instead.
-mno-float
Equivalent to ‘-msoft-float’, but additionally asserts that the program being compiled does not perform any floating-point operations. This option is
presently supported only by some bare-metal MIPS configurations, where it
may select a special set of libraries that lack all floating-point support (including, for example, the floating-point printf formats). If code compiled with
‘-mno-float’ accidentally contains floating-point operations, it is likely to suffer a link-time or run-time failure.
-msingle-float
Assume that the floating-point coprocessor only supports single-precision operations.
-mdouble-float
Assume that the floating-point coprocessor supports double-precision operations. This is the default.
-modd-spreg
-mno-odd-spreg
Enable the use of odd-numbered single-precision floating-point registers for the
o32 ABI. This is the default for processors that are known to support these
registers. When using the o32 FPXX ABI, ‘-mno-odd-spreg’ is set by default.
-mabs=2008
-mabs=legacy
These options control the treatment of the special not-a-number (NaN) IEEE
754 floating-point data with the abs.fmt and neg.fmt machine instructions.

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By default or when ‘-mabs=legacy’ is used the legacy treatment is selected. In
this case these instructions are considered arithmetic and avoided where correct
operation is required and the input operand might be a NaN. A longer sequence
of instructions that manipulate the sign bit of floating-point datum manually is
used instead unless the ‘-ffinite-math-only’ option has also been specified.
The ‘-mabs=2008’ option selects the IEEE 754-2008 treatment. In this case
these instructions are considered non-arithmetic and therefore operating correctly in all cases, including in particular where the input operand is a NaN.
These instructions are therefore always used for the respective operations.
-mnan=2008
-mnan=legacy
These options control the encoding of the special not-a-number (NaN) IEEE
754 floating-point data.
The ‘-mnan=legacy’ option selects the legacy encoding. In this case quiet NaNs
(qNaNs) are denoted by the first bit of their trailing significand field being 0,
whereas signaling NaNs (sNaNs) are denoted by the first bit of their trailing
significand field being 1.
The ‘-mnan=2008’ option selects the IEEE 754-2008 encoding. In this case
qNaNs are denoted by the first bit of their trailing significand field being 1,
whereas sNaNs are denoted by the first bit of their trailing significand field
being 0.
The default is ‘-mnan=legacy’ unless GCC has been configured with
‘--with-nan=2008’.
-mllsc
-mno-llsc
Use (do not use) ‘ll’, ‘sc’, and ‘sync’ instructions to implement atomic memory
built-in functions. When neither option is specified, GCC uses the instructions
if the target architecture supports them.
‘-mllsc’ is useful if the runtime environment can emulate the instructions and
‘-mno-llsc’ can be useful when compiling for nonstandard ISAs. You can
make either option the default by configuring GCC with ‘--with-llsc’ and
‘--without-llsc’ respectively. ‘--with-llsc’ is the default for some configurations; see the installation documentation for details.
-mdsp
-mno-dsp

Use (do not use) revision 1 of the MIPS DSP ASE. See Section 6.59.13 [MIPS
DSP Built-in Functions], page 644. This option defines the preprocessor macro
__mips_dsp. It also defines __mips_dsp_rev to 1.

-mdspr2
-mno-dspr2
Use (do not use) revision 2 of the MIPS DSP ASE. See Section 6.59.13 [MIPS
DSP Built-in Functions], page 644. This option defines the preprocessor macros
__mips_dsp and __mips_dspr2. It also defines __mips_dsp_rev to 2.

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-msmartmips
-mno-smartmips
Use (do not use) the MIPS SmartMIPS ASE.
-mpaired-single
-mno-paired-single
Use (do not use) paired-single floating-point instructions. See Section 6.59.14
[MIPS Paired-Single Support], page 649. This option requires hardware
floating-point support to be enabled.
-mdmx
-mno-mdmx
Use (do not use) MIPS Digital Media Extension instructions. This option can
only be used when generating 64-bit code and requires hardware floating-point
support to be enabled.
-mips3d
-mno-mips3d
Use (do not use) the MIPS-3D ASE. See Section 6.59.15.3 [MIPS-3D Built-in
Functions], page 653. The option ‘-mips3d’ implies ‘-mpaired-single’.
-mmicromips
-mno-micromips
Generate (do not generate) microMIPS code.
MicroMIPS code generation can also be controlled on a per-function basis by
means of micromips and nomicromips attributes. See Section 6.31 [Function
Attributes], page 464, for more information.
-mmt
-mno-mt

Use (do not use) MT Multithreading instructions.

-mmcu
-mno-mcu

Use (do not use) the MIPS MCU ASE instructions.

-meva
-mno-eva

Use (do not use) the MIPS Enhanced Virtual Addressing instructions.

-mvirt
-mno-virt
Use (do not use) the MIPS Virtualization (VZ) instructions.
-mxpa
-mno-xpa

Use (do not use) the MIPS eXtended Physical Address (XPA) instructions.

-mlong64

Force long types to be 64 bits wide. See ‘-mlong32’ for an explanation of the
default and the way that the pointer size is determined.

-mlong32

Force long, int, and pointer types to be 32 bits wide.
The default size of ints, longs and pointers depends on the ABI. All the
supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as does the
64-bit EABI; the others use 32-bit longs. Pointers are the same size as longs,
or the same size as integer registers, whichever is smaller.

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-msym32
-mno-sym32
Assume (do not assume) that all symbols have 32-bit values, regardless of
the selected ABI. This option is useful in combination with ‘-mabi=64’ and
‘-mno-abicalls’ because it allows GCC to generate shorter and faster references to symbolic addresses.
-G num

Put definitions of externally-visible data in a small data section if that data is
no bigger than num bytes. GCC can then generate more efficient accesses to
the data; see ‘-mgpopt’ for details.
The default ‘-G’ option depends on the configuration.

-mlocal-sdata
-mno-local-sdata
Extend (do not extend) the ‘-G’ behavior to local data too, such as to static
variables in C. ‘-mlocal-sdata’ is the default for all configurations.
If the linker complains that an application is using too much small data,
you might want to try rebuilding the less performance-critical parts with
‘-mno-local-sdata’. You might also want to build large libraries with
‘-mno-local-sdata’, so that the libraries leave more room for the main
program.
-mextern-sdata
-mno-extern-sdata
Assume (do not assume) that externally-defined data is in a small data section
if the size of that data is within the ‘-G’ limit. ‘-mextern-sdata’ is the default
for all configurations.
If you compile a module Mod with ‘-mextern-sdata’ ‘-G num’ ‘-mgpopt’, and
Mod references a variable Var that is no bigger than num bytes, you must make
sure that Var is placed in a small data section. If Var is defined by another
module, you must either compile that module with a high-enough ‘-G’ setting
or attach a section attribute to Var’s definition. If Var is common, you must
link the application with a high-enough ‘-G’ setting.
The easiest way of satisfying these restrictions is to compile and link every
module with the same ‘-G’ option. However, you may wish to build a library
that supports several different small data limits. You can do this by compiling the library with the highest supported ‘-G’ setting and additionally using ‘-mno-extern-sdata’ to stop the library from making assumptions about
externally-defined data.
-mgpopt
-mno-gpopt
Use (do not use) GP-relative accesses for symbols that are known to be in a
small data section; see ‘-G’, ‘-mlocal-sdata’ and ‘-mextern-sdata’. ‘-mgpopt’
is the default for all configurations.
‘-mno-gpopt’ is useful for cases where the $gp register might not hold the value
of _gp. For example, if the code is part of a library that might be used in a
boot monitor, programs that call boot monitor routines pass an unknown value

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in $gp. (In such situations, the boot monitor itself is usually compiled with
‘-G0’.)
‘-mno-gpopt’ implies ‘-mno-local-sdata’ and ‘-mno-extern-sdata’.
-membedded-data
-mno-embedded-data
Allocate variables to the read-only data section first if possible, then next in the
small data section if possible, otherwise in data. This gives slightly slower code
than the default, but reduces the amount of RAM required when executing,
and thus may be preferred for some embedded systems.
-muninit-const-in-rodata
-mno-uninit-const-in-rodata
Put uninitialized const variables in the read-only data section. This option is
only meaningful in conjunction with ‘-membedded-data’.
-mcode-readable=setting
Specify whether GCC may generate code that reads from executable sections.
There are three possible settings:
-mcode-readable=yes
Instructions may freely access executable sections. This is the default setting.
-mcode-readable=pcrel
MIPS16 PC-relative load instructions can access executable sections, but other instructions must not do so. This option is useful
on 4KSc and 4KSd processors when the code TLBs have the Read
Inhibit bit set. It is also useful on processors that can be configured
to have a dual instruction/data SRAM interface and that, like the
M4K, automatically redirect PC-relative loads to the instruction
RAM.
-mcode-readable=no
Instructions must not access executable sections. This option can
be useful on targets that are configured to have a dual instruction/data SRAM interface but that (unlike the M4K) do not automatically redirect PC-relative loads to the instruction RAM.
-msplit-addresses
-mno-split-addresses
Enable (disable) use of the %hi() and %lo() assembler relocation operators.
This option has been superseded by ‘-mexplicit-relocs’ but is retained for
backwards compatibility.
-mexplicit-relocs
-mno-explicit-relocs
Use (do not use) assembler relocation operators when dealing with symbolic
addresses. The alternative, selected by ‘-mno-explicit-relocs’, is to use assembler macros instead.
‘-mexplicit-relocs’ is the default if GCC was configured to use an assembler
that supports relocation operators.

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-mcheck-zero-division
-mno-check-zero-division
Trap (do not trap) on integer division by zero.
The default is ‘-mcheck-zero-division’.
-mdivide-traps
-mdivide-breaks
MIPS systems check for division by zero by generating either a conditional
trap or a break instruction. Using traps results in smaller code, but is only
supported on MIPS II and later. Also, some versions of the Linux kernel have
a bug that prevents trap from generating the proper signal (SIGFPE). Use
‘-mdivide-traps’ to allow conditional traps on architectures that support them
and ‘-mdivide-breaks’ to force the use of breaks.
The default is usually ‘-mdivide-traps’, but this can be overridden at configure
time using ‘--with-divide=breaks’. Divide-by-zero checks can be completely
disabled using ‘-mno-check-zero-division’.
-mload-store-pairs
-mno-load-store-pairs
Enable (disable) an optimization that pairs consecutive load or store instructions to enable load/store bonding. This option is enabled by default but only
takes effect when the selected architecture is known to support bonding.
-mmemcpy
-mno-memcpy
Force (do not force) the use of memcpy for non-trivial block moves. The default
is ‘-mno-memcpy’, which allows GCC to inline most constant-sized copies.
-mlong-calls
-mno-long-calls
Disable (do not disable) use of the jal instruction. Calling functions using
jal is more efficient but requires the caller and callee to be in the same 256
megabyte segment.
This option has no effect on abicalls code. The default is ‘-mno-long-calls’.
-mmad
-mno-mad

Enable (disable) use of the mad, madu and mul instructions, as provided by the
R4650 ISA.

-mimadd
-mno-imadd
Enable (disable) use of the madd and msub integer instructions. The default
is ‘-mimadd’ on architectures that support madd and msub except for the 74k
architecture where it was found to generate slower code.
-mfused-madd
-mno-fused-madd
Enable (disable) use of the floating-point multiply-accumulate instructions,
when they are available. The default is ‘-mfused-madd’.
On the R8000 CPU when multiply-accumulate instructions are used, the intermediate product is calculated to infinite precision and is not subject to the

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FCSR Flush to Zero bit. This may be undesirable in some circumstances. On
other processors the result is numerically identical to the equivalent computation using separate multiply, add, subtract and negate instructions.
-nocpp

Tell the MIPS assembler to not run its preprocessor over user assembler files
(with a ‘.s’ suffix) when assembling them.

-mfix-24k
-mno-fix-24k
Work around the 24K E48 (lost data on stores during refill) errata.
workarounds are implemented by the assembler rather than by GCC.

The

-mfix-r4000
-mno-fix-r4000
Work around certain R4000 CPU errata:
− A double-word or a variable shift may give an incorrect result if executed
immediately after starting an integer division.
− A double-word or a variable shift may give an incorrect result if executed
while an integer multiplication is in progress.
− An integer division may give an incorrect result if started in a delay slot of
a taken branch or a jump.
-mfix-r4400
-mno-fix-r4400
Work around certain R4400 CPU errata:
− A double-word or a variable shift may give an incorrect result if executed
immediately after starting an integer division.
-mfix-r10000
-mno-fix-r10000
Work around certain R10000 errata:
− ll/sc sequences may not behave atomically on revisions prior to 3.0. They
may deadlock on revisions 2.6 and earlier.
This option can only be used if the target architecture supports branch-likely
instructions. ‘-mfix-r10000’ is the default when ‘-march=r10000’ is used;
‘-mno-fix-r10000’ is the default otherwise.
-mfix-rm7000
-mno-fix-rm7000
Work around the RM7000 dmult/dmultu errata. The workarounds are implemented by the assembler rather than by GCC.
-mfix-vr4120
-mno-fix-vr4120
Work around certain VR4120 errata:
− dmultu does not always produce the correct result.
− div and ddiv do not always produce the correct result if one of the operands
is negative.

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The workarounds for the division errata rely on special functions in ‘libgcc.a’.
At present, these functions are only provided by the mips64vr*-elf configurations.
Other VR4120 errata require a NOP to be inserted between certain pairs of
instructions. These errata are handled by the assembler, not by GCC itself.
-mfix-vr4130
Work around the VR4130 mflo/mfhi errata. The workarounds are implemented
by the assembler rather than by GCC, although GCC avoids using mflo and
mfhi if the VR4130 macc, macchi, dmacc and dmacchi instructions are available
instead.
-mfix-sb1
-mno-fix-sb1
Work around certain SB-1 CPU core errata. (This flag currently works around
the SB-1 revision 2 “F1” and “F2” floating-point errata.)
-mr10k-cache-barrier=setting
Specify whether GCC should insert cache barriers to avoid the side effects of
speculation on R10K processors.
In common with many processors, the R10K tries to predict the outcome of
a conditional branch and speculatively executes instructions from the “taken”
branch. It later aborts these instructions if the predicted outcome is wrong.
However, on the R10K, even aborted instructions can have side effects.
This problem only affects kernel stores and, depending on the system, kernel
loads. As an example, a speculatively-executed store may load the target memory into cache and mark the cache line as dirty, even if the store itself is later
aborted. If a DMA operation writes to the same area of memory before the
“dirty” line is flushed, the cached data overwrites the DMA-ed data. See the
R10K processor manual for a full description, including other potential problems.
One workaround is to insert cache barrier instructions before every memory
access that might be speculatively executed and that might have side effects
even if aborted. ‘-mr10k-cache-barrier=setting’ controls GCC’s implementation of this workaround. It assumes that aborted accesses to any byte in the
following regions does not have side effects:
1. the memory occupied by the current function’s stack frame;
2. the memory occupied by an incoming stack argument;
3. the memory occupied by an object with a link-time-constant address.
It is the kernel’s responsibility to ensure that speculative accesses to these
regions are indeed safe.
If the input program contains a function declaration such as:
void foo (void);

then the implementation of foo must allow j foo and jal foo to be executed
speculatively. GCC honors this restriction for functions it compiles itself. It
expects non-GCC functions (such as hand-written assembly code) to do the
same.

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The option has three forms:
-mr10k-cache-barrier=load-store
Insert a cache barrier before a load or store that might be speculatively executed and that might have side effects even if aborted.
-mr10k-cache-barrier=store
Insert a cache barrier before a store that might be speculatively
executed and that might have side effects even if aborted.
-mr10k-cache-barrier=none
Disable the insertion of cache barriers. This is the default setting.
-mflush-func=func
-mno-flush-func
Specifies the function to call to flush the I and D caches, or to not call any
such function. If called, the function must take the same arguments as the
common _flush_func, that is, the address of the memory range for which the
cache is being flushed, the size of the memory range, and the number 3 (to flush
both caches). The default depends on the target GCC was configured for, but
commonly is either _flush_func or __cpu_flush.
mbranch-cost=num
Set the cost of branches to roughly num “simple” instructions. This cost is only
a heuristic and is not guaranteed to produce consistent results across releases.
A zero cost redundantly selects the default, which is based on the ‘-mtune’
setting.
-mbranch-likely
-mno-branch-likely
Enable or disable use of Branch Likely instructions, regardless of the default
for the selected architecture. By default, Branch Likely instructions may be
generated if they are supported by the selected architecture. An exception
is for the MIPS32 and MIPS64 architectures and processors that implement
those architectures; for those, Branch Likely instructions are not be generated
by default because the MIPS32 and MIPS64 architectures specifically deprecate
their use.
-mcompact-branches=never
-mcompact-branches=optimal
-mcompact-branches=always
These options control which form of branches will be generated. The default is
‘-mcompact-branches=optimal’.
The ‘-mcompact-branches=never’ option ensures that compact branch instructions will never be generated.
The ‘-mcompact-branches=always’ option ensures that a compact branch instruction will be generated if available. If a compact branch instruction is not
available, a delay slot form of the branch will be used instead.
This option is supported from MIPS Release 6 onwards.
The ‘-mcompact-branches=optimal’ option will cause a delay slot branch to
be used if one is available in the current ISA and the delay slot is successfully

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317

filled. If the delay slot is not filled, a compact branch will be chosen if one is
available.
-mfp-exceptions
-mno-fp-exceptions
Specifies whether FP exceptions are enabled. This affects how FP instructions
are scheduled for some processors. The default is that FP exceptions are enabled.
For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
64-bit code, then we can use both FP pipes. Otherwise, we can only use one
FP pipe.
-mvr4130-align
-mno-vr4130-align
The VR4130 pipeline is two-way superscalar, but can only issue two instructions
together if the first one is 8-byte aligned. When this option is enabled, GCC
aligns pairs of instructions that it thinks should execute in parallel.
This option only has an effect when optimizing for the VR4130. It normally
makes code faster, but at the expense of making it bigger. It is enabled by
default at optimization level ‘-O3’.
-msynci
-mno-synci
Enable (disable) generation of synci instructions on architectures that support it. The synci instructions (if enabled) are generated when __builtin__
_clear_cache is compiled.
This option defaults to ‘-mno-synci’, but the default can be overridden by
configuring GCC with ‘--with-synci’.
When compiling code for single processor systems, it is generally safe to use
synci. However, on many multi-core (SMP) systems, it does not invalidate the
instruction caches on all cores and may lead to undefined behavior.
-mrelax-pic-calls
-mno-relax-pic-calls
Try to turn PIC calls that are normally dispatched via register $25 into direct
calls. This is only possible if the linker can resolve the destination at link time
and if the destination is within range for a direct call.
‘-mrelax-pic-calls’ is the default if GCC was configured to use an
assembler and a linker that support the .reloc assembly directive and
‘-mexplicit-relocs’ is in effect.
With ‘-mno-explicit-relocs’, this
optimization can be performed by the assembler and the linker alone without
help from the compiler.
-mmcount-ra-address
-mno-mcount-ra-address
Emit (do not emit) code that allows _mcount to modify the calling function’s
return address. When enabled, this option extends the usual _mcount interface
with a new ra-address parameter, which has type intptr_t * and is passed in

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register $12. _mcount can then modify the return address by doing both of the
following:
• Returning the new address in register $31.
• Storing the new address in *ra-address, if ra-address is nonnull.
The default is ‘-mno-mcount-ra-address’.
-mframe-header-opt
-mno-frame-header-opt
Enable (disable) frame header optimization in the o32 ABI. When using the o32
ABI, calling functions will allocate 16 bytes on the stack for the called function
to write out register arguments. When enabled, this optimization will suppress
the allocation of the frame header if it can be determined that it is unused.
This optimization is off by default at all optimization levels.
-mlxc1-sxc1
-mno-lxc1-sxc1
When applicable, enable (disable) the generation of lwxc1, swxc1, ldxc1, sdxc1
instructions. Enabled by default.
-mmadd4
-mno-madd4
When applicable, enable (disable) the generation of 4-operand madd.s, madd.d
and related instructions. Enabled by default.

3.18.27 MMIX Options
These options are defined for the MMIX:
-mlibfuncs
-mno-libfuncs
Specify that intrinsic library functions are being compiled, passing all values in
registers, no matter the size.
-mepsilon
-mno-epsilon
Generate floating-point comparison instructions that compare with respect to
the rE epsilon register.
-mabi=mmixware
-mabi=gnu
Generate code that passes function parameters and return values that (in the
called function) are seen as registers $0 and up, as opposed to the GNU ABI
which uses global registers $231 and up.
-mzero-extend
-mno-zero-extend
When reading data from memory in sizes shorter than 64 bits, use (do not use)
zero-extending load instructions by default, rather than sign-extending ones.

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-mknuthdiv
-mno-knuthdiv
Make the result of a division yielding a remainder have the same sign as the
divisor. With the default, ‘-mno-knuthdiv’, the sign of the remainder follows
the sign of the dividend. Both methods are arithmetically valid, the latter being
almost exclusively used.
-mtoplevel-symbols
-mno-toplevel-symbols
Prepend (do not prepend) a ‘:’ to all global symbols, so the assembly code can
be used with the PREFIX assembly directive.
-melf

Generate an executable in the ELF format, rather than the default ‘mmo’ format
used by the mmix simulator.

-mbranch-predict
-mno-branch-predict
Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable branch.
-mbase-addresses
-mno-base-addresses
Generate (do not generate) code that uses base addresses. Using a base address
automatically generates a request (handled by the assembler and the linker)
for a constant to be set up in a global register. The register is used for one or
more base address requests within the range 0 to 255 from the value held in the
register. The generally leads to short and fast code, but the number of different
data items that can be addressed is limited. This means that a program that
uses lots of static data may require ‘-mno-base-addresses’.
-msingle-exit
-mno-single-exit
Force (do not force) generated code to have a single exit point in each function.

3.18.28 MN10300 Options
These ‘-m’ options are defined for Matsushita MN10300 architectures:
-mmult-bug
Generate code to avoid bugs in the multiply instructions for the MN10300
processors. This is the default.
-mno-mult-bug
Do not generate code to avoid bugs in the multiply instructions for the MN10300
processors.
-mam33

Generate code using features specific to the AM33 processor.

-mno-am33
Do not generate code using features specific to the AM33 processor. This is the
default.
-mam33-2

Generate code using features specific to the AM33/2.0 processor.

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Generate code using features specific to the AM34 processor.

-mtune=cpu-type
Use the timing characteristics of the indicated CPU type when scheduling instructions. This does not change the targeted processor type. The CPU type
must be one of ‘mn10300’, ‘am33’, ‘am33-2’ or ‘am34’.
-mreturn-pointer-on-d0
When generating a function that returns a pointer, return the pointer in both
a0 and d0. Otherwise, the pointer is returned only in a0, and attempts to call
such functions without a prototype result in errors. Note that this option is on
by default; use ‘-mno-return-pointer-on-d0’ to disable it.
-mno-crt0
Do not link in the C run-time initialization object file.
-mrelax

Indicate to the linker that it should perform a relaxation optimization pass to
shorten branches, calls and absolute memory addresses. This option only has
an effect when used on the command line for the final link step.
This option makes symbolic debugging impossible.

-mliw

Allow the compiler to generate Long Instruction Word instructions if the target
is the ‘AM33’ or later. This is the default. This option defines the preprocessor
macro __LIW__.

-mnoliw

Do not allow the compiler to generate Long Instruction Word instructions. This
option defines the preprocessor macro __NO_LIW__.

-msetlb

Allow the compiler to generate the SETLB and Lcc instructions if the target
is the ‘AM33’ or later. This is the default. This option defines the preprocessor
macro __SETLB__.

-mnosetlb
Do not allow the compiler to generate SETLB or Lcc instructions. This option
defines the preprocessor macro __NO_SETLB__.

3.18.29 Moxie Options
-meb

Generate big-endian code. This is the default for ‘moxie-*-*’ configurations.

-mel

Generate little-endian code.

-mmul.x

Generate mul.x and umul.x instructions. This is the default for ‘moxiebox-*-*’
configurations.

-mno-crt0
Do not link in the C run-time initialization object file.

3.18.30 MSP430 Options
These options are defined for the MSP430:
-masm-hex
Force assembly output to always use hex constants. Normally such constants
are signed decimals, but this option is available for testsuite and/or aesthetic
purposes.

Chapter 3: GCC Command Options

-mmcu=

321

Select the MCU to target. This is used to create a C preprocessor symbol
based upon the MCU name, converted to upper case and pre- and post-fixed
with ‘__’. This in turn is used by the ‘msp430.h’ header file to select an MCUspecific supplementary header file.
The option also sets the ISA to use. If the MCU name is one that is known
to only support the 430 ISA then that is selected, otherwise the 430X ISA is
selected. A generic MCU name of ‘msp430’ can also be used to select the 430
ISA. Similarly the generic ‘msp430x’ MCU name selects the 430X ISA.
In addition an MCU-specific linker script is added to the linker command line.
The script’s name is the name of the MCU with ‘.ld’ appended. Thus specifying
‘-mmcu=xxx’ on the gcc command line defines the C preprocessor symbol __XXX_
_ and cause the linker to search for a script called ‘xxx.ld’.
This option is also passed on to the assembler.

-mwarn-mcu
-mno-warn-mcu
This option enables or disables warnings about conflicts between the MCU name
specified by the ‘-mmcu’ option and the ISA set by the ‘-mcpu’ option and/or
the hardware multiply support set by the ‘-mhwmult’ option. It also toggles
warnings about unrecognized MCU names. This option is on by default.
-mcpu=

Specifies the ISA to use. Accepted values are ‘msp430’, ‘msp430x’ and
‘msp430xv2’. This option is deprecated. The ‘-mmcu=’ option should be used
to select the ISA.

-msim

Link to the simulator runtime libraries and linker script. Overrides any scripts
that would be selected by the ‘-mmcu=’ option.

-mlarge

Use large-model addressing (20-bit pointers, 32-bit size_t).

-msmall

Use small-model addressing (16-bit pointers, 16-bit size_t).

-mrelax

This option is passed to the assembler and linker, and allows the linker to
perform certain optimizations that cannot be done until the final link.

mhwmult=

Describes the type of hardware multiply supported by the target. Accepted
values are ‘none’ for no hardware multiply, ‘16bit’ for the original 16-bit-only
multiply supported by early MCUs. ‘32bit’ for the 16/32-bit multiply supported by later MCUs and ‘f5series’ for the 16/32-bit multiply supported by
F5-series MCUs. A value of ‘auto’ can also be given. This tells GCC to deduce
the hardware multiply support based upon the MCU name provided by the
‘-mmcu’ option. If no ‘-mmcu’ option is specified or if the MCU name is not
recognized then no hardware multiply support is assumed. auto is the default
setting.
Hardware multiplies are normally performed by calling a library routine. This
saves space in the generated code. When compiling at ‘-O3’ or higher however
the hardware multiplier is invoked inline. This makes for bigger, but faster
code.
The hardware multiply routines disable interrupts whilst running and restore
the previous interrupt state when they finish. This makes them safe to use
inside interrupt handlers as well as in normal code.

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-minrt

Using the GNU Compiler Collection (GCC)

Enable the use of a minimum runtime environment - no static initializers or
constructors. This is intended for memory-constrained devices. The compiler
includes special symbols in some objects that tell the linker and runtime which
code fragments are required.

-mcode-region=
-mdata-region=
These options tell the compiler where to place functions and data that do not
have one of the lower, upper, either or section attributes. Possible values
are lower, upper, either or any. The first three behave like the corresponding
attribute. The fourth possible value - any - is the default. It leaves placement
entirely up to the linker script and how it assigns the standard sections (.text,
.data, etc) to the memory regions.
-msilicon-errata=
This option passes on a request to assembler to enable the fixes for the named
silicon errata.
-msilicon-errata-warn=
This option passes on a request to the assembler to enable warning messages
when a silicon errata might need to be applied.

3.18.31 NDS32 Options
These options are defined for NDS32 implementations:
-mbig-endian
Generate code in big-endian mode.
-mlittle-endian
Generate code in little-endian mode.
-mreduced-regs
Use reduced-set registers for register allocation.
-mfull-regs
Use full-set registers for register allocation.
-mcmov

Generate conditional move instructions.

-mno-cmov
Do not generate conditional move instructions.
-mext-perf
Generate performance extension instructions.
-mno-ext-perf
Do not generate performance extension instructions.
-mext-perf2
Generate performance extension 2 instructions.
-mno-ext-perf2
Do not generate performance extension 2 instructions.

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-mext-string
Generate string extension instructions.
-mno-ext-string
Do not generate string extension instructions.
-mv3push

Generate v3 push25/pop25 instructions.

-mno-v3push
Do not generate v3 push25/pop25 instructions.
-m16-bit

Generate 16-bit instructions.

-mno-16-bit
Do not generate 16-bit instructions.
-misr-vector-size=num
Specify the size of each interrupt vector, which must be 4 or 16.
-mcache-block-size=num
Specify the size of each cache block, which must be a power of 2 between 4 and
512.
-march=arch
Specify the name of the target architecture.
-mcmodel=code-model
Set the code model to one of
‘small’

All the data and read-only data segments must be within 512KB
addressing space. The text segment must be within 16MB addressing space.

‘medium’

The data segment must be within 512KB while the read-only data
segment can be within 4GB addressing space. The text segment
should be still within 16MB addressing space.

‘large’

All the text and data segments can be within 4GB addressing space.

-mctor-dtor
Enable constructor/destructor feature.
-mrelax

Guide linker to relax instructions.

3.18.32 Nios II Options
These are the options defined for the Altera Nios II processor.
-G num

Put global and static objects less than or equal to num bytes into the small
data or BSS sections instead of the normal data or BSS sections. The default
value of num is 8.

-mgpopt=option
-mgpopt
-mno-gpopt
Generate (do not generate) GP-relative accesses. The following option names
are recognized:

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‘none’

Do not generate GP-relative accesses.

‘local’

Generate GP-relative accesses for small data objects that are not
external, weak, or uninitialized common symbols. Also use GPrelative addressing for objects that have been explicitly placed in a
small data section via a section attribute.

‘global’

As for ‘local’, but also generate GP-relative accesses for small data
objects that are external, weak, or common. If you use this option,
you must ensure that all parts of your program (including libraries)
are compiled with the same ‘-G’ setting.

‘data’

Generate GP-relative accesses for all data objects in the program.
If you use this option, the entire data and BSS segments of your
program must fit in 64K of memory and you must use an appropriate linker script to allocate them within the addressable range of
the global pointer.

‘all’

Generate GP-relative addresses for function pointers as well as data
pointers. If you use this option, the entire text, data, and BSS
segments of your program must fit in 64K of memory and you
must use an appropriate linker script to allocate them within the
addressable range of the global pointer.

‘-mgpopt’ is equivalent to ‘-mgpopt=local’, and ‘-mno-gpopt’ is equivalent to
‘-mgpopt=none’.
The default is ‘-mgpopt’ except when ‘-fpic’ or ‘-fPIC’ is specified to generate
position-independent code. Note that the Nios II ABI does not permit GPrelative accesses from shared libraries.
You may need to specify ‘-mno-gpopt’ explicitly when building programs that
include large amounts of small data, including large GOT data sections. In this
case, the 16-bit offset for GP-relative addressing may not be large enough to
allow access to the entire small data section.
-mgprel-sec=regexp
This option specifies additional section names that can be accessed via GPrelative addressing. It is most useful in conjunction with section attributes
on variable declarations (see Section 6.32.1 [Common Variable Attributes],
page 513) and a custom linker script. The regexp is a POSIX Extended Regular
Expression.
This option does not affect the behavior of the ‘-G’ option, and and the specified
sections are in addition to the standard .sdata and .sbss small-data sections
that are recognized by ‘-mgpopt’.
-mr0rel-sec=regexp
This option specifies names of sections that can be accessed via a 16-bit offset
from r0; that is, in the low 32K or high 32K of the 32-bit address space. It is
most useful in conjunction with section attributes on variable declarations (see
Section 6.32.1 [Common Variable Attributes], page 513) and a custom linker
script. The regexp is a POSIX Extended Regular Expression.

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In contrast to the use of GP-relative addressing for small data, zero-based
addressing is never generated by default and there are no conventional section
names used in standard linker scripts for sections in the low or high areas of
memory.
-mel
-meb

Generate little-endian (default) or big-endian (experimental) code, respectively.

-march=arch
This specifies the name of the target Nios II architecture. GCC uses this name
to determine what kind of instructions it can emit when generating assembly
code. Permissible names are: ‘r1’, ‘r2’.
The preprocessor macro __nios2_arch__ is available to programs, with value
1 or 2, indicating the targeted ISA level.
-mbypass-cache
-mno-bypass-cache
Force all load and store instructions to always bypass cache by using I/O variants of the instructions. The default is not to bypass the cache.
-mno-cache-volatile
-mcache-volatile
Volatile memory access bypass the cache using the I/O variants of the load and
store instructions. The default is not to bypass the cache.
-mno-fast-sw-div
-mfast-sw-div
Do not use table-based fast divide for small numbers. The default is to use the
fast divide at ‘-O3’ and above.
-mno-hw-mul
-mhw-mul
-mno-hw-mulx
-mhw-mulx
-mno-hw-div
-mhw-div Enable or disable emitting mul, mulx and div family of instructions by the
compiler. The default is to emit mul and not emit div and mulx.
-mbmx
-mno-bmx
-mcdx
-mno-cdx

Enable or disable generation of Nios II R2 BMX (bit manipulation) and
CDX (code density) instructions. Enabling these instructions also requires
‘-march=r2’. Since these instructions are optional extensions to the R2
architecture, the default is not to emit them.

-mcustom-insn=N
-mno-custom-insn
Each ‘-mcustom-insn=N’ option enables use of a custom instruction
with encoding N when generating code that uses insn.
For example,
‘-mcustom-fadds=253’ generates custom instruction 253 for single-precision

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floating-point add operations instead of the default behavior of using a library
call.
The following values of insn are supported. Except as otherwise noted, floatingpoint operations are expected to be implemented with normal IEEE 754 semantics and correspond directly to the C operators or the equivalent GCC built-in
functions (see Section 6.58 [Other Builtins], page 613).
Single-precision floating point:
‘fadds’, ‘fsubs’, ‘fdivs’, ‘fmuls’
Binary arithmetic operations.
‘fnegs’

Unary negation.

‘fabss’

Unary absolute value.

‘fcmpeqs’, ‘fcmpges’, ‘fcmpgts’, ‘fcmples’, ‘fcmplts’, ‘fcmpnes’
Comparison operations.
‘fmins’, ‘fmaxs’
Floating-point minimum and maximum. These instructions are
only generated if ‘-ffinite-math-only’ is specified.
‘fsqrts’

Unary square root operation.

‘fcoss’, ‘fsins’, ‘ftans’, ‘fatans’, ‘fexps’, ‘flogs’
Floating-point trigonometric and exponential functions. These instructions are only generated if ‘-funsafe-math-optimizations’
is also specified.
Double-precision floating point:
‘faddd’, ‘fsubd’, ‘fdivd’, ‘fmuld’
Binary arithmetic operations.
‘fnegd’

Unary negation.

‘fabsd’

Unary absolute value.

‘fcmpeqd’, ‘fcmpged’, ‘fcmpgtd’, ‘fcmpled’, ‘fcmpltd’, ‘fcmpned’
Comparison operations.
‘fmind’, ‘fmaxd’
Double-precision minimum and maximum. These instructions are
only generated if ‘-ffinite-math-only’ is specified.
‘fsqrtd’

Unary square root operation.

‘fcosd’, ‘fsind’, ‘ftand’, ‘fatand’, ‘fexpd’, ‘flogd’
Double-precision trigonometric and exponential functions. These
instructions are only generated if ‘-funsafe-math-optimizations’
is also specified.
Conversions:
‘fextsd’

Conversion from single precision to double precision.

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327

‘ftruncds’
Conversion from double precision to single precision.
‘fixsi’, ‘fixsu’, ‘fixdi’, ‘fixdu’
Conversion from floating point to signed or unsigned integer types,
with truncation towards zero.
‘round’

Conversion from single-precision floating point to signed integer,
rounding to the nearest integer and ties away from zero.
This corresponds to the __builtin_lroundf function when
‘-fno-math-errno’ is used.

‘floatis’, ‘floatus’, ‘floatid’, ‘floatud’
Conversion from signed or unsigned integer types to floating-point
types.
In addition, all of the following transfer instructions for internal registers X and
Y must be provided to use any of the double-precision floating-point instructions. Custom instructions taking two double-precision source operands expect
the first operand in the 64-bit register X. The other operand (or only operand
of a unary operation) is given to the custom arithmetic instruction with the
least significant half in source register src1 and the most significant half in src2.
A custom instruction that returns a double-precision result returns the most
significant 32 bits in the destination register and the other half in 32-bit register
Y. GCC automatically generates the necessary code sequences to write register
X and/or read register Y when double-precision floating-point instructions are
used.
‘fwrx’

Write src1 into the least significant half of X and src2 into the most
significant half of X.

‘fwry’

Write src1 into Y.

‘frdxhi’, ‘frdxlo’
Read the most or least (respectively) significant half of X and store
it in dest.
‘frdy’

Read the value of Y and store it into dest.

Note that you can gain more local control over generation of Nios II custom instructions by using the target("custom-insn=N") and target("no-custominsn") function attributes (see Section 6.31 [Function Attributes], page 464)
or pragmas (see Section 6.61.15 [Function Specific Option Pragmas], page 780).
-mcustom-fpu-cfg=name
This option enables a predefined, named set of custom instruction encodings
(see ‘-mcustom-insn’ above). Currently, the following sets are defined:
‘-mcustom-fpu-cfg=60-1’ is equivalent to:
-mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-fsingle-precision-constant

‘-mcustom-fpu-cfg=60-2’ is equivalent to:

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-mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-mcustom-fdivs=255
-fsingle-precision-constant

‘-mcustom-fpu-cfg=72-3’ is equivalent to:
-mcustom-floatus=243
-mcustom-fixsi=244
-mcustom-floatis=245
-mcustom-fcmpgts=246
-mcustom-fcmples=249
-mcustom-fcmpeqs=250
-mcustom-fcmpnes=251
-mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-mcustom-fdivs=255
-fsingle-precision-constant

Custom instruction assignments given by individual ‘-mcustom-insn=’ options
override those given by ‘-mcustom-fpu-cfg=’, regardless of the order of the
options on the command line.
Note that you can gain more local control over selection of a FPU configuration by using the target("custom-fpu-cfg=name") function attribute (see
Section 6.31 [Function Attributes], page 464) or pragma (see Section 6.61.15
[Function Specific Option Pragmas], page 780).
These additional ‘-m’ options are available for the Altera Nios II ELF (bare-metal) target:
-mhal

Link with HAL BSP. This suppresses linking with the GCC-provided C runtime startup and termination code, and is typically used in conjunction with
‘-msys-crt0=’ to specify the location of the alternate startup code provided by
the HAL BSP.

-msmallc

Link with a limited version of the C library, ‘-lsmallc’, rather than Newlib.

-msys-crt0=startfile
startfile is the file name of the startfile (crt0) to use when linking. This option
is only useful in conjunction with ‘-mhal’.
-msys-lib=systemlib
systemlib is the library name of the library that provides low-level system calls
required by the C library, e.g. read and write. This option is typically used
to link with a library provided by a HAL BSP.

3.18.33 Nvidia PTX Options
These options are defined for Nvidia PTX:
-m32
-m64

Generate code for 32-bit or 64-bit ABI.

-mmainkernel
Link in code for a
execution.

main kernel. This is for stand-alone instead of offloading

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329

-moptimize
Apply partitioned execution optimizations. This is the default when any level
of optimization is selected.
-msoft-stack
Generate code that does not use .local memory directly for stack storage.
Instead, a per-warp stack pointer is maintained explicitly. This enables variablelength stack allocation (with variable-length arrays or alloca), and when global
memory is used for underlying storage, makes it possible to access automatic
variables from other threads, or with atomic instructions. This code generation
variant is used for OpenMP offloading, but the option is exposed on its own for
the purpose of testing the compiler; to generate code suitable for linking into
programs using OpenMP offloading, use option ‘-mgomp’.
-muniform-simt
Switch to code generation variant that allows to execute all threads in each
warp, while maintaining memory state and side effects as if only one thread in
each warp was active outside of OpenMP SIMD regions. All atomic operations
and calls to runtime (malloc, free, vprintf) are conditionally executed (iff current
lane index equals the master lane index), and the register being assigned is
copied via a shuffle instruction from the master lane. Outside of SIMD regions
lane 0 is the master; inside, each thread sees itself as the master. Shared
memory array int __nvptx_uni[] stores all-zeros or all-ones bitmasks for each
warp, indicating current mode (0 outside of SIMD regions). Each thread can
bitwise-and the bitmask at position tid.y with current lane index to compute
the master lane index.
-mgomp

Generate code for use in OpenMP offloading: enables ‘-msoft-stack’ and
‘-muniform-simt’ options, and selects corresponding multilib variant.

3.18.34 PDP-11 Options
These options are defined for the PDP-11:
-mfpu

Use hardware FPP floating point. This is the default. (FIS floating point on
the PDP-11/40 is not supported.)

-msoft-float
Do not use hardware floating point.
-mac0

Return floating-point results in ac0 (fr0 in Unix assembler syntax).

-mno-ac0

Return floating-point results in memory. This is the default.

-m40

Generate code for a PDP-11/40.

-m45

Generate code for a PDP-11/45. This is the default.

-m10

Generate code for a PDP-11/10.

-mbcopy-builtin
Use inline movmemhi patterns for copying memory. This is the default.
-mbcopy

Do not use inline movmemhi patterns for copying memory.

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-mint16
-mno-int32
Use 16-bit int. This is the default.
-mint32
-mno-int16
Use 32-bit int.
-mfloat64
-mno-float32
Use 64-bit float. This is the default.
-mfloat32
-mno-float64
Use 32-bit float.
-mabshi

Use abshi2 pattern. This is the default.

-mno-abshi
Do not use abshi2 pattern.
-mbranch-expensive
Pretend that branches are expensive. This is for experimenting with code generation only.
-mbranch-cheap
Do not pretend that branches are expensive. This is the default.
-munix-asm
Use Unix assembler syntax.
‘pdp11-*-bsd’.

This is the default when configured for

-mdec-asm
Use DEC assembler syntax. This is the default when configured for any PDP-11
target other than ‘pdp11-*-bsd’.

3.18.35 picoChip Options
These ‘-m’ options are defined for picoChip implementations:
-mae=ae_type
Set the instruction set, register set, and instruction scheduling parameters for
array element type ae type. Supported values for ae type are ‘ANY’, ‘MUL’, and
‘MAC’.
‘-mae=ANY’ selects a completely generic AE type. Code generated with this
option runs on any of the other AE types. The code is not as efficient as it
would be if compiled for a specific AE type, and some types of operation (e.g.,
multiplication) do not work properly on all types of AE.
‘-mae=MUL’ selects a MUL AE type. This is the most useful AE type for compiled code, and is the default.
‘-mae=MAC’ selects a DSP-style MAC AE. Code compiled with this option may
suffer from poor performance of byte (char) manipulation, since the DSP AE
does not provide hardware support for byte load/stores.

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-msymbol-as-address
Enable the compiler to directly use a symbol name as an address in a load/store
instruction, without first loading it into a register. Typically, the use of this
option generates larger programs, which run faster than when the option isn’t
used. However, the results vary from program to program, so it is left as a user
option, rather than being permanently enabled.
-mno-inefficient-warnings
Disables warnings about the generation of inefficient code. These warnings can
be generated, for example, when compiling code that performs byte-level memory operations on the MAC AE type. The MAC AE has no hardware support
for byte-level memory operations, so all byte load/stores must be synthesized
from word load/store operations. This is inefficient and a warning is generated
to indicate that you should rewrite the code to avoid byte operations, or to target an AE type that has the necessary hardware support. This option disables
these warnings.

3.18.36 PowerPC Options
These are listed under See Section 3.18.40 [RS/6000 and PowerPC Options], page 345.

3.18.37 PowerPC SPE Options
These ‘-m’ options are defined for PowerPC SPE:
-mmfcrf
-mno-mfcrf
-mpopcntb
-mno-popcntb
You use these options to specify which instructions are available on the processor
you are using. The default value of these options is determined when configuring
GCC. Specifying the ‘-mcpu=cpu_type’ overrides the specification of these
options. We recommend you use the ‘-mcpu=cpu_type’ option rather than the
options listed above.
The ‘-mmfcrf’ option allows GCC to generate the move from condition register
field instruction implemented on the POWER4 processor and other processors
that support the PowerPC V2.01 architecture. The ‘-mpopcntb’ option allows
GCC to generate the popcount and double-precision FP reciprocal estimate
instruction implemented on the POWER5 processor and other processors that
support the PowerPC V2.02 architecture.
-mcpu=cpu_type
Set architecture type, register usage, and instruction scheduling parameters for
machine type cpu type. Supported values for cpu type are ‘8540’, ‘8548’, and
‘native’.
‘-mcpu=powerpc’ specifies pure 32-bit PowerPC (either endian), with an appropriate, generic processor model assumed for scheduling purposes.
Specifying ‘native’ as cpu type detects and selects the architecture option that
corresponds to the host processor of the system performing the compilation.
‘-mcpu=native’ has no effect if GCC does not recognize the processor.

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The other options specify a specific processor. Code generated under those
options runs best on that processor, and may not run at all on others.
The ‘-mcpu’ options automatically enable or disable the following options:
-mhard-float -mmfcrf -mmultiple
-mpopcntb -mpopcntd
-msingle-float -mdouble-float
-mfloat128

The particular options set for any particular CPU varies between compiler
versions, depending on what setting seems to produce optimal code for that
CPU; it doesn’t necessarily reflect the actual hardware’s capabilities. If you
wish to set an individual option to a particular value, you may specify it after
the ‘-mcpu’ option, like ‘-mcpu=8548’.
-mtune=cpu_type
Set the instruction scheduling parameters for machine type cpu type, but do
not set the architecture type or register usage, as ‘-mcpu=cpu_type’ does. The
same values for cpu type are used for ‘-mtune’ as for ‘-mcpu’. If both are
specified, the code generated uses the architecture and registers set by ‘-mcpu’,
but the scheduling parameters set by ‘-mtune’.
-msecure-plt
Generate code that allows ld and ld.so to build executables and shared libraries with non-executable .plt and .got sections. This is a PowerPC 32-bit
SYSV ABI option.
-mbss-plt
Generate code that uses a BSS .plt section that ld.so fills in, and requires
.plt and .got sections that are both writable and executable. This is a PowerPC 32-bit SYSV ABI option.
-misel
-mno-isel
This switch enables or disables the generation of ISEL instructions.
-misel=yes/no
This switch has been deprecated. Use ‘-misel’ and ‘-mno-isel’ instead.
-mspe
-mno-spe

This switch enables or disables the generation of SPE simd instructions.

-mspe=yes/no
This option has been deprecated. Use ‘-mspe’ and ‘-mno-spe’ instead.
-mfloat128
-mno-float128
Enable/disable the float128 keyword for IEEE 128-bit floating point and use
either software emulation for IEEE 128-bit floating point or hardware instructions.
-mfloat-gprs=yes/single/double/no
-mfloat-gprs
This switch enables or disables the generation of floating-point operations on
the general-purpose registers for architectures that support it.

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The argument ‘yes’ or ‘single’ enables the use of single-precision floating-point
operations.
The argument ‘double’ enables the use of single and double-precision floatingpoint operations.
The argument ‘no’ disables floating-point operations on the general-purpose
registers.
This option is currently only available on the MPC854x.
-mfull-toc
-mno-fp-in-toc
-mno-sum-in-toc
-mminimal-toc
Modify generation of the TOC (Table Of Contents), which is created for every
executable file. The ‘-mfull-toc’ option is selected by default. In that case,
GCC allocates at least one TOC entry for each unique non-automatic variable
reference in your program. GCC also places floating-point constants in the
TOC. However, only 16,384 entries are available in the TOC.
If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the
‘-mno-fp-in-toc’ and ‘-mno-sum-in-toc’ options. ‘-mno-fp-in-toc’ prevents
GCC from putting floating-point constants in the TOC and ‘-mno-sum-in-toc’
forces GCC to generate code to calculate the sum of an address and a constant
at run time instead of putting that sum into the TOC. You may specify one
or both of these options. Each causes GCC to produce very slightly slower and
larger code at the expense of conserving TOC space.
If you still run out of space in the TOC even when you specify both of these
options, specify ‘-mminimal-toc’ instead. This option causes GCC to make
only one TOC entry for every file. When you specify this option, GCC produces
code that is slower and larger but which uses extremely little TOC space. You
may wish to use this option only on files that contain less frequently-executed
code.
-maix32

Disables the 64-bit ABI. GCC defaults to ‘-maix32’.

-mxl-compat
-mno-xl-compat
Produce code that conforms more closely to IBM XL compiler semantics when
using AIX-compatible ABI. Pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument
FPRs. Do not assume that most significant double in 128-bit long double value
is properly rounded when comparing values and converting to double. Use XL
symbol names for long double support routines.
The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of
its arguments with fewer arguments than declared. IBM XL compilers access
floating-point arguments that do not fit in the RSA from the stack when a
subroutine is compiled without optimization. Because always storing floatingpoint arguments on the stack is inefficient and rarely needed, this option is not

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enabled by default and only is necessary when calling subroutines compiled by
IBM XL compilers without optimization.
-malign-natural
-malign-power
On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
‘-malign-natural’ overrides the ABI-defined alignment of larger types, such
as floating-point doubles, on their natural size-based boundary. The option
‘-malign-power’ instructs GCC to follow the ABI-specified alignment rules.
GCC defaults to the standard alignment defined in the ABI.
On 64-bit Darwin, natural alignment is the default, and ‘-malign-power’ is not
supported.
-msoft-float
-mhard-float
Generate code that does not use (uses) the floating-point register set. Software
floating-point emulation is provided if you use the ‘-msoft-float’ option, and
pass the option to GCC when linking.
-msingle-float
-mdouble-float
Generate code for single- or double-precision floating-point operations.
‘-mdouble-float’ implies ‘-msingle-float’.
-mmultiple
-mno-multiple
Generate code that uses (does not use) the load multiple word instructions
and the store multiple word instructions. These instructions are generated by
default on POWER systems, and not generated on PowerPC systems. Do not
use ‘-mmultiple’ on little-endian PowerPC systems, since those instructions
do not work when the processor is in little-endian mode. The exceptions are
PPC740 and PPC750 which permit these instructions in little-endian mode.
-mupdate
-mno-update
Generate code that uses (does not use) the load or store instructions that update
the base register to the address of the calculated memory location. These
instructions are generated by default. If you use ‘-mno-update’, there is a small
window between the time that the stack pointer is updated and the address of
the previous frame is stored, which means code that walks the stack frame
across interrupts or signals may get corrupted data.
-mavoid-indexed-addresses
-mno-avoid-indexed-addresses
Generate code that tries to avoid (not avoid) the use of indexed load or store
instructions. These instructions can incur a performance penalty on Power6
processors in certain situations, such as when stepping through large arrays
that cross a 16M boundary. This option is enabled by default when targeting
Power6 and disabled otherwise.

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-mfused-madd
-mno-fused-madd
Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent ‘-mfused-madd’ option is
now mapped to the machine-independent ‘-ffp-contract=fast’ option, and
‘-mno-fused-madd’ is mapped to ‘-ffp-contract=off’.
-mno-strict-align
-mstrict-align
On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references are handled by the system.
-mrelocatable
-mno-relocatable
Generate code that allows (does not allow) a static executable to be relocated
to a different address at run time. A simple embedded PowerPC system loader
should relocate the entire contents of .got2 and 4-byte locations listed in the
.fixup section, a table of 32-bit addresses generated by this option. For this
to work, all objects linked together must be compiled with ‘-mrelocatable’
or ‘-mrelocatable-lib’. ‘-mrelocatable’ code aligns the stack to an 8-byte
boundary.
-mrelocatable-lib
-mno-relocatable-lib
Like ‘-mrelocatable’, ‘-mrelocatable-lib’ generates a .fixup section to allow static executables to be relocated at run time, but ‘-mrelocatable-lib’
does not use the smaller stack alignment of ‘-mrelocatable’. Objects compiled with ‘-mrelocatable-lib’ may be linked with objects compiled with any
combination of the ‘-mrelocatable’ options.
-mno-toc
-mtoc

On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the
program.

-mlittle
-mlittle-endian
On System V.4 and embedded PowerPC systems compile code for the processor
in little-endian mode. The ‘-mlittle-endian’ option is the same as ‘-mlittle’.
-mbig
-mbig-endian
On System V.4 and embedded PowerPC systems compile code for the processor
in big-endian mode. The ‘-mbig-endian’ option is the same as ‘-mbig’.
-mdynamic-no-pic
On Darwin and Mac OS X systems, compile code so that it is not relocatable,
but that its external references are relocatable. The resulting code is suitable
for applications, but not shared libraries.

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-msingle-pic-base
Treat the register used for PIC addressing as read-only, rather than loading
it in the prologue for each function. The runtime system is responsible for
initializing this register with an appropriate value before execution begins.
-mprioritize-restricted-insns=priority
This option controls the priority that is assigned to dispatch-slot restricted
instructions during the second scheduling pass. The argument priority takes
the value ‘0’, ‘1’, or ‘2’ to assign no, highest, or second-highest (respectively)
priority to dispatch-slot restricted instructions.
-msched-costly-dep=dependence_type
This option controls which dependences are considered costly by the target
during instruction scheduling. The argument dependence type takes one of the
following values:
‘no’

No dependence is costly.

‘all’

All dependences are costly.

‘true_store_to_load’
A true dependence from store to load is costly.
‘store_to_load’
Any dependence from store to load is costly.
number

Any dependence for which the latency is greater than or equal to
number is costly.

-minsert-sched-nops=scheme
This option controls which NOP insertion scheme is used during the second
scheduling pass. The argument scheme takes one of the following values:
‘no’

Don’t insert NOPs.

‘pad’

Pad with NOPs any dispatch group that has vacant issue slots,
according to the scheduler’s grouping.

‘regroup_exact’
Insert NOPs to force costly dependent insns into separate groups.
Insert exactly as many NOPs as needed to force an insn to a new
group, according to the estimated processor grouping.
number

Insert NOPs to force costly dependent insns into separate groups.
Insert number NOPs to force an insn to a new group.

-mcall-sysv
On System V.4 and embedded PowerPC systems compile code using calling
conventions that adhere to the March 1995 draft of the System V Application
Binary Interface, PowerPC processor supplement. This is the default unless
you configured GCC using ‘powerpc-*-eabiaix’.
-mcall-sysv-eabi
-mcall-eabi
Specify both ‘-mcall-sysv’ and ‘-meabi’ options.

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-mcall-sysv-noeabi
Specify both ‘-mcall-sysv’ and ‘-mno-eabi’ options.
-mcall-aixdesc
On System V.4 and embedded PowerPC systems compile code for the AIX
operating system.
-mcall-linux
On System V.4 and embedded PowerPC systems compile code for the Linuxbased GNU system.
-mcall-freebsd
On System V.4 and embedded PowerPC systems compile code for the FreeBSD
operating system.
-mcall-netbsd
On System V.4 and embedded PowerPC systems compile code for the NetBSD
operating system.
-mcall-openbsd
On System V.4 and embedded PowerPC systems compile code for the OpenBSD
operating system.
-maix-struct-return
Return all structures in memory (as specified by the AIX ABI).
-msvr4-struct-return
Return structures smaller than 8 bytes in registers (as specified by the SVR4
ABI).
-mabi=abi-type
Extend the current ABI with a particular extension, or remove such extension.
Valid values are ‘altivec’, ‘no-altivec’, ‘spe’, ‘no-spe’, ‘ibmlongdouble’,
‘ieeelongdouble’, ‘elfv1’, ‘elfv2’.
-mabi=spe
Extend the current ABI with SPE ABI extensions. This does not change the
default ABI, instead it adds the SPE ABI extensions to the current ABI.
-mabi=no-spe
Disable Book-E SPE ABI extensions for the current ABI.
-mabi=ibmlongdouble
Change the current ABI to use IBM extended-precision long double. This is
not likely to work if your system defaults to using IEEE extended-precision long
double. If you change the long double type from IEEE extended-precision, the
compiler will issue a warning unless you use the ‘-Wno-psabi’ option.
-mabi=ieeelongdouble
Change the current ABI to use IEEE extended-precision long double. This is
not likely to work if your system defaults to using IBM extended-precision long
double. If you change the long double type from IBM extended-precision, the
compiler will issue a warning unless you use the ‘-Wno-psabi’ option.

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-mabi=elfv1
Change the current ABI to use the ELFv1 ABI. This is the default ABI for
big-endian PowerPC 64-bit Linux. Overriding the default ABI requires special
system support and is likely to fail in spectacular ways.
-mabi=elfv2
Change the current ABI to use the ELFv2 ABI. This is the default ABI for
little-endian PowerPC 64-bit Linux. Overriding the default ABI requires special
system support and is likely to fail in spectacular ways.
-mgnu-attribute
-mno-gnu-attribute
Emit .gnu attribute assembly directives to set tag/value pairs in a
.gnu.attributes section that specify ABI variations in function parameters or
return values.
-mprototype
-mno-prototype
On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must
insert an instruction before every non-prototyped call to set or clear bit 6 of the
condition code register (CR) to indicate whether floating-point values are passed
in the floating-point registers in case the function takes variable arguments.
With ‘-mprototype’, only calls to prototyped variable argument functions set
or clear the bit.
-msim

On embedded PowerPC systems, assume that the startup module is called
‘sim-crt0.o’ and that the standard C libraries are ‘libsim.a’ and ‘libc.a’.
This is the default for ‘powerpc-*-eabisim’ configurations.

-mmvme

On embedded PowerPC systems, assume that the startup module is called
‘crt0.o’ and the standard C libraries are ‘libmvme.a’ and ‘libc.a’.

-mads

On embedded PowerPC systems, assume that the startup module is called
‘crt0.o’ and the standard C libraries are ‘libads.a’ and ‘libc.a’.

-myellowknife
On embedded PowerPC systems, assume that the startup module is called
‘crt0.o’ and the standard C libraries are ‘libyk.a’ and ‘libc.a’.
-mvxworks
On System V.4 and embedded PowerPC systems, specify that you are compiling
for a VxWorks system.
-memb

On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags header
to indicate that ‘eabi’ extended relocations are used.

-meabi
-mno-eabi
On System V.4 and embedded PowerPC systems do (do not) adhere to the
Embedded Applications Binary Interface (EABI), which is a set of modifications
to the System V.4 specifications. Selecting ‘-meabi’ means that the stack is

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aligned to an 8-byte boundary, a function __eabi is called from main to set up
the EABI environment, and the ‘-msdata’ option can use both r2 and r13 to
point to two separate small data areas. Selecting ‘-mno-eabi’ means that the
stack is aligned to a 16-byte boundary, no EABI initialization function is called
from main, and the ‘-msdata’ option only uses r13 to point to a single small
data area. The ‘-meabi’ option is on by default if you configured GCC using
one of the ‘powerpc*-*-eabi*’ options.
-msdata=eabi
On System V.4 and embedded PowerPC systems, put small initialized const
global and static data in the .sdata2 section, which is pointed to by register
r2. Put small initialized non-const global and static data in the .sdata section, which is pointed to by register r13. Put small uninitialized global and
static data in the .sbss section, which is adjacent to the .sdata section. The
‘-msdata=eabi’ option is incompatible with the ‘-mrelocatable’ option. The
‘-msdata=eabi’ option also sets the ‘-memb’ option.
-msdata=sysv
On System V.4 and embedded PowerPC systems, put small global and static
data in the .sdata section, which is pointed to by register r13. Put small
uninitialized global and static data in the .sbss section, which is adjacent
to the .sdata section. The ‘-msdata=sysv’ option is incompatible with the
‘-mrelocatable’ option.
-msdata=default
-msdata
On System V.4 and embedded PowerPC systems, if ‘-meabi’ is used, compile code the same as ‘-msdata=eabi’, otherwise compile code the same as
‘-msdata=sysv’.
-msdata=data
On System V.4 and embedded PowerPC systems, put small global data in the
.sdata section. Put small uninitialized global data in the .sbss section. Do
not use register r13 to address small data however. This is the default behavior
unless other ‘-msdata’ options are used.
-msdata=none
-mno-sdata
On embedded PowerPC systems, put all initialized global and static data in
the .data section, and all uninitialized data in the .bss section.
-mblock-move-inline-limit=num
Inline all block moves (such as calls to memcpy or structure copies) less than or
equal to num bytes. The minimum value for num is 32 bytes on 32-bit targets
and 64 bytes on 64-bit targets. The default value is target-specific.
-G num

On embedded PowerPC systems, put global and static items less than or equal
to num bytes into the small data or BSS sections instead of the normal data or
BSS section. By default, num is 8. The ‘-G num’ switch is also passed to the
linker. All modules should be compiled with the same ‘-G num’ value.

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-mregnames
-mno-regnames
On System V.4 and embedded PowerPC systems do (do not) emit register
names in the assembly language output using symbolic forms.
-mlongcall
-mno-longcall
By default assume that all calls are far away so that a longer and more expensive
calling sequence is required. This is required for calls farther than 32 megabytes
(33,554,432 bytes) from the current location. A short call is generated if the
compiler knows the call cannot be that far away. This setting can be overridden
by the shortcall function attribute, or by #pragma longcall(0).
Some linkers are capable of detecting out-of-range calls and generating glue
code on the fly. On these systems, long calls are unnecessary and generate
slower code. As of this writing, the AIX linker can do this, as can the GNU
linker for PowerPC/64. It is planned to add this feature to the GNU linker for
32-bit PowerPC systems as well.
In the future, GCC may ignore all longcall specifications when the linker is
known to generate glue.
-mtls-markers
-mno-tls-markers
Mark (do not mark) calls to __tls_get_addr with a relocation specifying the
function argument. The relocation allows the linker to reliably associate function call with argument setup instructions for TLS optimization, which in turn
allows GCC to better schedule the sequence.
-mrecip
-mno-recip
This option enables use of the reciprocal estimate and reciprocal square
root estimate instructions with additional Newton-Raphson steps to increase
precision instead of doing a divide or square root and divide for floating-point
arguments. You should use the ‘-ffast-math’ option when using ‘-mrecip’
(or at least ‘-funsafe-math-optimizations’, ‘-ffinite-math-only’,
‘-freciprocal-math’ and ‘-fno-trapping-math’).
Note that while the
throughput of the sequence is generally higher than the throughput of the
non-reciprocal instruction, the precision of the sequence can be decreased by
up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square
roots.
-mrecip=opt
This option controls which reciprocal estimate instructions may be used. opt
is a comma-separated list of options, which may be preceded by a ! to invert
the option:
‘all’

Enable all estimate instructions.

‘default’

Enable the default instructions, equivalent to ‘-mrecip’.

‘none’

Disable all estimate instructions, equivalent to ‘-mno-recip’.

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‘div’

Enable the reciprocal approximation instructions for both single
and double precision.

‘divf’

Enable the single-precision reciprocal approximation instructions.

‘divd’

Enable the double-precision reciprocal approximation instructions.

‘rsqrt’

Enable the reciprocal square root approximation instructions for
both single and double precision.

‘rsqrtf’

Enable the single-precision reciprocal square root approximation
instructions.

‘rsqrtd’

Enable the double-precision reciprocal square root approximation
instructions.

So, for example, ‘-mrecip=all,!rsqrtd’ enables all of the reciprocal estimate
instructions, except for the FRSQRTE, XSRSQRTEDP, and XVRSQRTEDP instructions
which handle the double-precision reciprocal square root calculations.
-mrecip-precision
-mno-recip-precision
Assume (do not assume) that the reciprocal estimate instructions provide
higher-precision estimates than is mandated by the PowerPC ABI. Selecting
‘-mcpu=power6’, ‘-mcpu=power7’ or ‘-mcpu=power8’ automatically selects
‘-mrecip-precision’. The double-precision square root estimate instructions
are not generated by default on low-precision machines, since they do not
provide an estimate that converges after three steps.
-mpointers-to-nested-functions
-mno-pointers-to-nested-functions
Generate (do not generate) code to load up the static chain register (r11) when
calling through a pointer on AIX and 64-bit Linux systems where a function
pointer points to a 3-word descriptor giving the function address, TOC value to
be loaded in register r2, and static chain value to be loaded in register r11. The
‘-mpointers-to-nested-functions’ is on by default. You cannot call through
pointers to nested functions or pointers to functions compiled in other languages
that use the static chain if you use ‘-mno-pointers-to-nested-functions’.
-msave-toc-indirect
-mno-save-toc-indirect
Generate (do not generate) code to save the TOC value in the reserved stack
location in the function prologue if the function calls through a pointer on AIX
and 64-bit Linux systems. If the TOC value is not saved in the prologue, it is
saved just before the call through the pointer. The ‘-mno-save-toc-indirect’
option is the default.
-mcompat-align-parm
-mno-compat-align-parm
Generate (do not generate) code to pass structure parameters with a maximum
alignment of 64 bits, for compatibility with older versions of GCC.
Older versions of GCC (prior to 4.9.0) incorrectly did not align a structure
parameter on a 128-bit boundary when that structure contained a member

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requiring 128-bit alignment. This is corrected in more recent versions of GCC.
This option may be used to generate code that is compatible with functions
compiled with older versions of GCC.
The ‘-mno-compat-align-parm’ option is the default.
-mstack-protector-guard=guard
-mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset
-mstack-protector-guard-symbol=symbol
Generate stack protection code using canary at guard. Supported locations are
‘global’ for global canary or ‘tls’ for per-thread canary in the TLS block (the
default with GNU libc version 2.4 or later).
With the latter choice the options ‘-mstack-protector-guard-reg=reg’ and
‘-mstack-protector-guard-offset=offset’ furthermore specify which register to use as base register for reading the canary, and from what offset from
that base register. The default for those is as specified in the relevant ABI.
‘-mstack-protector-guard-symbol=symbol’ overrides the offset with a symbol reference to a canary in the TLS block.

3.18.38 RISC-V Options
These command-line options are defined for RISC-V targets:
-mbranch-cost=n
Set the cost of branches to roughly n instructions.
-mplt
-mno-plt

When generating PIC code, do or don’t allow the use of PLTs. Ignored for
non-PIC. The default is ‘-mplt’.

-mabi=ABI-string
Specify integer and floating-point calling convention. ABI-string contains two
parts: the size of integer types and the registers used for floating-point types.
For example ‘-march=rv64ifd -mabi=lp64d’ means that ‘long’ and pointers
are 64-bit (implicitly defining ‘int’ to be 32-bit), and that floating-point values
up to 64 bits wide are passed in F registers. Contrast this with ‘-march=rv64ifd
-mabi=lp64f’, which still allows the compiler to generate code that uses the
F and D extensions but only allows floating-point values up to 32 bits long to
be passed in registers; or ‘-march=rv64ifd -mabi=lp64’, in which no floatingpoint arguments will be passed in registers.
The default for this argument is system dependent, users who want a specific calling convention should specify one explicitly. The valid calling conventions are: ‘ilp32’, ‘ilp32f’, ‘ilp32d’, ‘lp64’, ‘lp64f’, and ‘lp64d’. Some
calling conventions are impossible to implement on some ISAs: for example,
‘-march=rv32if -mabi=ilp32d’ is invalid because the ABI requires 64-bit values be passed in F registers, but F registers are only 32 bits wide.

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-mfdiv
-mno-fdiv
Do or don’t use hardware floating-point divide and square root instructions.
This requires the F or D extensions for floating-point registers. The default is
to use them if the specified architecture has these instructions.
-mdiv
-mno-div

Do or don’t use hardware instructions for integer division. This requires the
M extension. The default is to use them if the specified architecture has these
instructions.

-march=ISA-string
Generate code for given RISC-V ISA (e.g. ‘rv64im’). ISA strings must be
lower-case. Examples include ‘rv64i’, ‘rv32g’, and ‘rv32imaf’.
-mtune=processor-string
Optimize the output for the given processor, specified by microarchitecture
name.
-mpreferred-stack-boundary=num
Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary.
If ‘-mpreferred-stack-boundary’ is not specified, the default is 4 (16 bytes or
128-bits).
Warning: If you use this switch, then you must build all modules with the same
value, including any libraries. This includes the system libraries and startup
modules.
-msmall-data-limit=n
Put global and static data smaller than n bytes into a special section (on some
targets).
-msave-restore
-mno-save-restore
Do or don’t use smaller but slower prologue and epilogue code that uses library
function calls. The default is to use fast inline prologues and epilogues.
-mstrict-align
-mno-strict-align
Do not or do generate unaligned memory accesses. The default is set depending
on whether the processor we are optimizing for supports fast unaligned access
or not.
-mcmodel=medlow
Generate code for the medium-low code model. The program and its statically
defined symbols must lie within a single 2 GiB address range and must lie
between absolute addresses −2 GiB and +2 GiB. Programs can be statically or
dynamically linked. This is the default code model.
-mcmodel=medany
Generate code for the medium-any code model. The program and its statically
defined symbols must be within any single 2 GiB address range. Programs can
be statically or dynamically linked.

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-mexplicit-relocs
-mno-exlicit-relocs
Use or do not use assembler relocation operators when dealing with symbolic
addresses. The alternative is to use assembler macros instead, which may limit
optimization.
-mrelax
-mno-relax
Take advantage of linker relaxations to reduce the number of instructions required to materialize symbol addresses. The default is to take advantage of
linker relaxations.

3.18.39 RL78 Options
-msim

Links in additional target libraries to support operation within a simulator.

-mmul=none
-mmul=g10
-mmul=g13
-mmul=g14
-mmul=rl78
Specifies the type of hardware multiplication and division support to be used.
The simplest is none, which uses software for both multiplication and division.
This is the default. The g13 value is for the hardware multiply/divide peripheral
found on the RL78/G13 (S2 core) targets. The g14 value selects the use of the
multiplication and division instructions supported by the RL78/G14 (S3 core)
parts. The value rl78 is an alias for g14 and the value mg10 is an alias for
none.
In addition a C preprocessor macro is defined, based upon the setting of this
option. Possible values are: __RL78_MUL_NONE__, __RL78_MUL_G13__ or __
RL78_MUL_G14__.
-mcpu=g10
-mcpu=g13
-mcpu=g14
-mcpu=rl78
Specifies the RL78 core to target. The default is the G14 core, also known
as an S3 core or just RL78. The G13 or S2 core does not have multiply or
divide instructions, instead it uses a hardware peripheral for these operations.
The G10 or S1 core does not have register banks, so it uses a different calling
convention.
If this option is set it also selects the type of hardware multiply support to
use, unless this is overridden by an explicit ‘-mmul=none’ option on the command line. Thus specifying ‘-mcpu=g13’ enables the use of the G13 hardware
multiply peripheral and specifying ‘-mcpu=g10’ disables the use of hardware
multiplications altogether.
Note, although the RL78/G14 core is the default target, specifying ‘-mcpu=g14’
or ‘-mcpu=rl78’ on the command line does change the behavior of the toolchain
since it also enables G14 hardware multiply support. If these options are not

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specified on the command line then software multiplication routines will be used
even though the code targets the RL78 core. This is for backwards compatibility
with older toolchains which did not have hardware multiply and divide support.
In addition a C preprocessor macro is defined, based upon the setting of this
option. Possible values are: __RL78_G10__, __RL78_G13__ or __RL78_G14__.
-mg10
-mg13
-mg14
-mrl78

These are aliases for the corresponding ‘-mcpu=’ option. They are provided for
backwards compatibility.

-mallregs
Allow the compiler to use all of the available registers. By default registers
r24..r31 are reserved for use in interrupt handlers. With this option enabled
these registers can be used in ordinary functions as well.
-m64bit-doubles
-m32bit-doubles
Make the double data type be 64 bits (‘-m64bit-doubles’) or 32 bits
(‘-m32bit-doubles’) in size. The default is ‘-m32bit-doubles’.
-msave-mduc-in-interrupts
-mno-save-mduc-in-interrupts
Specifies that interrupt handler functions should preserve the MDUC registers.
This is only necessary if normal code might use the MDUC registers, for example
because it performs multiplication and division operations. The default is to
ignore the MDUC registers as this makes the interrupt handlers faster. The
target option -mg13 needs to be passed for this to work as this feature is only
available on the G13 target (S2 core). The MDUC registers will only be saved if
the interrupt handler performs a multiplication or division operation or it calls
another function.

3.18.40 IBM RS/6000 and PowerPC Options
These ‘-m’ options are defined for the IBM RS/6000 and PowerPC:
-mpowerpc-gpopt
-mno-powerpc-gpopt
-mpowerpc-gfxopt
-mno-powerpc-gfxopt

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-mpowerpc64
-mno-powerpc64
-mmfcrf
-mno-mfcrf
-mpopcntb
-mno-popcntb
-mpopcntd
-mno-popcntd
-mfprnd
-mno-fprnd
-mcmpb
-mno-cmpb
-mmfpgpr
-mno-mfpgpr
-mhard-dfp
-mno-hard-dfp
You use these options to specify which instructions are available on the processor
you are using. The default value of these options is determined when configuring
GCC. Specifying the ‘-mcpu=cpu_type’ overrides the specification of these
options. We recommend you use the ‘-mcpu=cpu_type’ option rather than the
options listed above.
Specifying ‘-mpowerpc-gpopt’ allows GCC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point
square root. Specifying ‘-mpowerpc-gfxopt’ allows GCC to use the optional
PowerPC architecture instructions in the Graphics group, including floatingpoint select.
The ‘-mmfcrf’ option allows GCC to generate the move from condition register
field instruction implemented on the POWER4 processor and other processors
that support the PowerPC V2.01 architecture. The ‘-mpopcntb’ option allows
GCC to generate the popcount and double-precision FP reciprocal estimate
instruction implemented on the POWER5 processor and other processors that
support the PowerPC V2.02 architecture. The ‘-mpopcntd’ option allows GCC
to generate the popcount instruction implemented on the POWER7 processor and other processors that support the PowerPC V2.06 architecture. The
‘-mfprnd’ option allows GCC to generate the FP round to integer instructions
implemented on the POWER5+ processor and other processors that support the
PowerPC V2.03 architecture. The ‘-mcmpb’ option allows GCC to generate the
compare bytes instruction implemented on the POWER6 processor and other
processors that support the PowerPC V2.05 architecture. The ‘-mmfpgpr’ option allows GCC to generate the FP move to/from general-purpose register instructions implemented on the POWER6X processor and other processors that
support the extended PowerPC V2.05 architecture. The ‘-mhard-dfp’ option
allows GCC to generate the decimal floating-point instructions implemented on
some POWER processors.

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The ‘-mpowerpc64’ option allows GCC to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as
64-bit, doubleword quantities. GCC defaults to ‘-mno-powerpc64’.
-mcpu=cpu_type
Set architecture type, register usage, and instruction scheduling parameters for
machine type cpu type. Supported values for cpu type are ‘401’, ‘403’, ‘405’,
‘405fp’, ‘440’, ‘440fp’, ‘464’, ‘464fp’, ‘476’, ‘476fp’, ‘505’, ‘601’, ‘602’, ‘603’,
‘603e’, ‘604’, ‘604e’, ‘620’, ‘630’, ‘740’, ‘7400’, ‘7450’, ‘750’, ‘801’, ‘821’, ‘823’,
‘860’, ‘970’, ‘8540’, ‘a2’, ‘e300c2’, ‘e300c3’, ‘e500mc’, ‘e500mc64’, ‘e5500’,
‘e6500’, ‘ec603e’, ‘G3’, ‘G4’, ‘G5’, ‘titan’, ‘power3’, ‘power4’, ‘power5’,
‘power5+’, ‘power6’, ‘power6x’, ‘power7’, ‘power8’, ‘power9’, ‘powerpc’,
‘powerpc64’, ‘powerpc64le’, ‘rs64’, and ‘native’.
‘-mcpu=powerpc’, ‘-mcpu=powerpc64’, and ‘-mcpu=powerpc64le’ specify pure
32-bit PowerPC (either endian), 64-bit big endian PowerPC and 64-bit little
endian PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes.
Specifying ‘native’ as cpu type detects and selects the architecture option that
corresponds to the host processor of the system performing the compilation.
‘-mcpu=native’ has no effect if GCC does not recognize the processor.
The other options specify a specific processor. Code generated under those
options runs best on that processor, and may not run at all on others.
The ‘-mcpu’ options automatically enable or disable the following options:
-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple
-mpopcntb -mpopcntd -mpowerpc64
-mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float
-msimple-fpu -mmulhw -mdlmzb -mmfpgpr -mvsx
-mcrypto -mhtm -mpower8-fusion -mpower8-vector
-mquad-memory -mquad-memory-atomic -mfloat128 -mfloat128-hardware

The particular options set for any particular CPU varies between compiler
versions, depending on what setting seems to produce optimal code for that
CPU; it doesn’t necessarily reflect the actual hardware’s capabilities. If you
wish to set an individual option to a particular value, you may specify it after
the ‘-mcpu’ option, like ‘-mcpu=970 -mno-altivec’.
On AIX, the ‘-maltivec’ and ‘-mpowerpc64’ options are not enabled or disabled
by the ‘-mcpu’ option at present because AIX does not have full support for
these options. You may still enable or disable them individually if you’re sure
it’ll work in your environment.
-mtune=cpu_type
Set the instruction scheduling parameters for machine type cpu type, but do
not set the architecture type or register usage, as ‘-mcpu=cpu_type’ does. The
same values for cpu type are used for ‘-mtune’ as for ‘-mcpu’. If both are
specified, the code generated uses the architecture and registers set by ‘-mcpu’,
but the scheduling parameters set by ‘-mtune’.
-mcmodel=small
Generate PowerPC64 code for the small model: The TOC is limited to 64k.

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-mcmodel=medium
Generate PowerPC64 code for the medium model: The TOC and other static
data may be up to a total of 4G in size. This is the default for 64-bit Linux.
-mcmodel=large
Generate PowerPC64 code for the large model: The TOC may be up to 4G in
size. Other data and code is only limited by the 64-bit address space.
-maltivec
-mno-altivec
Generate code that uses (does not use) AltiVec instructions, and also enable the
use of built-in functions that allow more direct access to the AltiVec instruction
set. You may also need to set ‘-mabi=altivec’ to adjust the current ABI with
AltiVec ABI enhancements.
When ‘-maltivec’ is used, rather than ‘-maltivec=le’ or ‘-maltivec=be’,
the element order for AltiVec intrinsics such as vec_splat, vec_extract, and
vec_insert match array element order corresponding to the endianness of the
target. That is, element zero identifies the leftmost element in a vector register
when targeting a big-endian platform, and identifies the rightmost element in
a vector register when targeting a little-endian platform.
-maltivec=be
Generate AltiVec instructions using big-endian element order, regardless of
whether the target is big- or little-endian. This is the default when targeting a big-endian platform. Using this option is currently deprecated. Support
for this feature will be removed in GCC 9.
The element order is used to interpret element numbers in AltiVec intrinsics
such as vec_splat, vec_extract, and vec_insert. By default, these match
array element order corresponding to the endianness for the target.
-maltivec=le
Generate AltiVec instructions using little-endian element order, regardless of
whether the target is big- or little-endian. This is the default when targeting
a little-endian platform. This option is currently ignored when targeting a
big-endian platform.
The element order is used to interpret element numbers in AltiVec intrinsics
such as vec_splat, vec_extract, and vec_insert. By default, these match
array element order corresponding to the endianness for the target.
-mvrsave
-mno-vrsave
Generate VRSAVE instructions when generating AltiVec code.
-msecure-plt
Generate code that allows ld and ld.so to build executables and shared libraries with non-executable .plt and .got sections. This is a PowerPC 32-bit
SYSV ABI option.

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-mbss-plt
Generate code that uses a BSS .plt section that ld.so fills in, and requires
.plt and .got sections that are both writable and executable. This is a PowerPC 32-bit SYSV ABI option.
-misel
-mno-isel
This switch enables or disables the generation of ISEL instructions.
-misel=yes/no
This switch has been deprecated. Use ‘-misel’ and ‘-mno-isel’ instead.
-mpaired
-mno-paired
This switch enables or disables the generation of PAIRED simd instructions.
-mvsx
-mno-vsx

Generate code that uses (does not use) vector/scalar (VSX) instructions, and
also enable the use of built-in functions that allow more direct access to the
VSX instruction set.

-mcrypto
-mno-crypto
Enable the use (disable) of the built-in functions that allow direct access to
the cryptographic instructions that were added in version 2.07 of the PowerPC
ISA.
-mhtm
-mno-htm

Enable (disable) the use of the built-in functions that allow direct access to
the Hardware Transactional Memory (HTM) instructions that were added in
version 2.07 of the PowerPC ISA.

-mpower8-fusion
-mno-power8-fusion
Generate code that keeps (does not keeps) some integer operations adjacent so
that the instructions can be fused together on power8 and later processors.
-mpower8-vector
-mno-power8-vector
Generate code that uses (does not use) the vector and scalar instructions that
were added in version 2.07 of the PowerPC ISA. Also enable the use of built-in
functions that allow more direct access to the vector instructions.
-mquad-memory
-mno-quad-memory
Generate code that uses (does not use) the non-atomic quad word memory
instructions. The ‘-mquad-memory’ option requires use of 64-bit mode.
-mquad-memory-atomic
-mno-quad-memory-atomic
Generate code that uses (does not use) the atomic quad word memory instructions. The ‘-mquad-memory-atomic’ option requires use of 64-bit mode.

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Using the GNU Compiler Collection (GCC)

-mfloat128
-mno-float128
Enable/disable the float128 keyword for IEEE 128-bit floating point and use
either software emulation for IEEE 128-bit floating point or hardware instructions.
The VSX instruction set (‘-mvsx’, ‘-mcpu=power7’, ‘-mcpu=power8’), or
‘-mcpu=power9’ must be enabled to use the IEEE 128-bit floating point
support. The IEEE 128-bit floating point support only works on PowerPC
Linux systems.
The default for ‘-mfloat128’ is enabled on PowerPC Linux systems using the
VSX instruction set, and disabled on other systems.
If you use the ISA 3.0 instruction set (‘-mpower9-vector’ or ‘-mcpu=power9’)
on a 64-bit system, the IEEE 128-bit floating point support will also enable the
generation of ISA 3.0 IEEE 128-bit floating point instructions. Otherwise, if
you do not specify to generate ISA 3.0 instructions or you are targeting a 32bit big endian system, IEEE 128-bit floating point will be done with software
emulation.
-mfloat128-hardware
-mno-float128-hardware
Enable/disable using ISA 3.0 hardware instructions to support the
data type.

float128

The default for ‘-mfloat128-hardware’ is enabled on PowerPC Linux systems
using the ISA 3.0 instruction set, and disabled on other systems.
-m32
-m64

Generate code for 32-bit or 64-bit environments of Darwin and SVR4 targets
(including GNU/Linux). The 32-bit environment sets int, long and pointer
to 32 bits and generates code that runs on any PowerPC variant. The 64-bit
environment sets int to 32 bits and long and pointer to 64 bits, and generates
code for PowerPC64, as for ‘-mpowerpc64’.

-mfull-toc
-mno-fp-in-toc
-mno-sum-in-toc
-mminimal-toc
Modify generation of the TOC (Table Of Contents), which is created for every
executable file. The ‘-mfull-toc’ option is selected by default. In that case,
GCC allocates at least one TOC entry for each unique non-automatic variable
reference in your program. GCC also places floating-point constants in the
TOC. However, only 16,384 entries are available in the TOC.
If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the
‘-mno-fp-in-toc’ and ‘-mno-sum-in-toc’ options. ‘-mno-fp-in-toc’ prevents
GCC from putting floating-point constants in the TOC and ‘-mno-sum-in-toc’
forces GCC to generate code to calculate the sum of an address and a constant
at run time instead of putting that sum into the TOC. You may specify one

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351

or both of these options. Each causes GCC to produce very slightly slower and
larger code at the expense of conserving TOC space.
If you still run out of space in the TOC even when you specify both of these
options, specify ‘-mminimal-toc’ instead. This option causes GCC to make
only one TOC entry for every file. When you specify this option, GCC produces
code that is slower and larger but which uses extremely little TOC space. You
may wish to use this option only on files that contain less frequently-executed
code.
-maix64
-maix32

Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit long
type, and the infrastructure needed to support them. Specifying ‘-maix64’
implies ‘-mpowerpc64’, while ‘-maix32’ disables the 64-bit ABI and implies
‘-mno-powerpc64’. GCC defaults to ‘-maix32’.

-mxl-compat
-mno-xl-compat
Produce code that conforms more closely to IBM XL compiler semantics when
using AIX-compatible ABI. Pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument
FPRs. Do not assume that most significant double in 128-bit long double value
is properly rounded when comparing values and converting to double. Use XL
symbol names for long double support routines.
The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of
its arguments with fewer arguments than declared. IBM XL compilers access
floating-point arguments that do not fit in the RSA from the stack when a
subroutine is compiled without optimization. Because always storing floatingpoint arguments on the stack is inefficient and rarely needed, this option is not
enabled by default and only is necessary when calling subroutines compiled by
IBM XL compilers without optimization.
-mpe

Support IBM RS/6000 SP Parallel Environment (PE). Link an application
written to use message passing with special startup code to enable the application to run. The system must have PE installed in the standard location (‘/usr/lpp/ppe.poe/’), or the ‘specs’ file must be overridden with the
‘-specs=’ option to specify the appropriate directory location. The Parallel
Environment does not support threads, so the ‘-mpe’ option and the ‘-pthread’
option are incompatible.

-malign-natural
-malign-power
On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
‘-malign-natural’ overrides the ABI-defined alignment of larger types, such
as floating-point doubles, on their natural size-based boundary. The option
‘-malign-power’ instructs GCC to follow the ABI-specified alignment rules.
GCC defaults to the standard alignment defined in the ABI.
On 64-bit Darwin, natural alignment is the default, and ‘-malign-power’ is not
supported.

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-msoft-float
-mhard-float
Generate code that does not use (uses) the floating-point register set. Software
floating-point emulation is provided if you use the ‘-msoft-float’ option, and
pass the option to GCC when linking.
-msingle-float
-mdouble-float
Generate code for single- or double-precision floating-point operations.
‘-mdouble-float’ implies ‘-msingle-float’.
-msimple-fpu
Do not generate sqrt and div instructions for hardware floating-point unit.
-mfpu=name
Specify type of floating-point unit. Valid values for name are ‘sp_lite’
(equivalent to ‘-msingle-float -msimple-fpu’),
‘dp_lite’ (equivalent to ‘-mdouble-float -msimple-fpu’), ‘sp_full’ (equivalent to
‘-msingle-float’), and ‘dp_full’ (equivalent to ‘-mdouble-float’).
-mxilinx-fpu
Perform optimizations for the floating-point unit on Xilinx PPC 405/440.
-mmultiple
-mno-multiple
Generate code that uses (does not use) the load multiple word instructions
and the store multiple word instructions. These instructions are generated by
default on POWER systems, and not generated on PowerPC systems. Do not
use ‘-mmultiple’ on little-endian PowerPC systems, since those instructions
do not work when the processor is in little-endian mode. The exceptions are
PPC740 and PPC750 which permit these instructions in little-endian mode.
-mupdate
-mno-update
Generate code that uses (does not use) the load or store instructions that update
the base register to the address of the calculated memory location. These
instructions are generated by default. If you use ‘-mno-update’, there is a small
window between the time that the stack pointer is updated and the address of
the previous frame is stored, which means code that walks the stack frame
across interrupts or signals may get corrupted data.
-mavoid-indexed-addresses
-mno-avoid-indexed-addresses
Generate code that tries to avoid (not avoid) the use of indexed load or store
instructions. These instructions can incur a performance penalty on Power6
processors in certain situations, such as when stepping through large arrays
that cross a 16M boundary. This option is enabled by default when targeting
Power6 and disabled otherwise.

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-mfused-madd
-mno-fused-madd
Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent ‘-mfused-madd’ option is
now mapped to the machine-independent ‘-ffp-contract=fast’ option, and
‘-mno-fused-madd’ is mapped to ‘-ffp-contract=off’.
-mmulhw
-mno-mulhw
Generate code that uses (does not use) the half-word multiply and multiplyaccumulate instructions on the IBM 405, 440, 464 and 476 processors. These
instructions are generated by default when targeting those processors.
-mdlmzb
-mno-dlmzb
Generate code that uses (does not use) the string-search ‘dlmzb’ instruction on
the IBM 405, 440, 464 and 476 processors. This instruction is generated by
default when targeting those processors.
-mno-bit-align
-mbit-align
On System V.4 and embedded PowerPC systems do not (do) force structures
and unions that contain bit-fields to be aligned to the base type of the bit-field.
For example, by default a structure containing nothing but 8 unsigned bitfields of length 1 is aligned to a 4-byte boundary and has a size of 4 bytes. By
using ‘-mno-bit-align’, the structure is aligned to a 1-byte boundary and is 1
byte in size.
-mno-strict-align
-mstrict-align
On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references are handled by the system.
-mrelocatable
-mno-relocatable
Generate code that allows (does not allow) a static executable to be relocated
to a different address at run time. A simple embedded PowerPC system loader
should relocate the entire contents of .got2 and 4-byte locations listed in the
.fixup section, a table of 32-bit addresses generated by this option. For this
to work, all objects linked together must be compiled with ‘-mrelocatable’
or ‘-mrelocatable-lib’. ‘-mrelocatable’ code aligns the stack to an 8-byte
boundary.
-mrelocatable-lib
-mno-relocatable-lib
Like ‘-mrelocatable’, ‘-mrelocatable-lib’ generates a .fixup section to allow static executables to be relocated at run time, but ‘-mrelocatable-lib’
does not use the smaller stack alignment of ‘-mrelocatable’. Objects compiled with ‘-mrelocatable-lib’ may be linked with objects compiled with any
combination of the ‘-mrelocatable’ options.

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-mno-toc
-mtoc

Using the GNU Compiler Collection (GCC)

On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the
program.

-mlittle
-mlittle-endian
On System V.4 and embedded PowerPC systems compile code for the processor
in little-endian mode. The ‘-mlittle-endian’ option is the same as ‘-mlittle’.
-mbig
-mbig-endian
On System V.4 and embedded PowerPC systems compile code for the processor
in big-endian mode. The ‘-mbig-endian’ option is the same as ‘-mbig’.
-mdynamic-no-pic
On Darwin and Mac OS X systems, compile code so that it is not relocatable,
but that its external references are relocatable. The resulting code is suitable
for applications, but not shared libraries.
-msingle-pic-base
Treat the register used for PIC addressing as read-only, rather than loading
it in the prologue for each function. The runtime system is responsible for
initializing this register with an appropriate value before execution begins.
-mprioritize-restricted-insns=priority
This option controls the priority that is assigned to dispatch-slot restricted
instructions during the second scheduling pass. The argument priority takes
the value ‘0’, ‘1’, or ‘2’ to assign no, highest, or second-highest (respectively)
priority to dispatch-slot restricted instructions.
-msched-costly-dep=dependence_type
This option controls which dependences are considered costly by the target
during instruction scheduling. The argument dependence type takes one of the
following values:
‘no’

No dependence is costly.

‘all’

All dependences are costly.

‘true_store_to_load’
A true dependence from store to load is costly.
‘store_to_load’
Any dependence from store to load is costly.
number

Any dependence for which the latency is greater than or equal to
number is costly.

-minsert-sched-nops=scheme
This option controls which NOP insertion scheme is used during the second
scheduling pass. The argument scheme takes one of the following values:
‘no’

Don’t insert NOPs.

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‘pad’

355

Pad with NOPs any dispatch group that has vacant issue slots,
according to the scheduler’s grouping.

‘regroup_exact’
Insert NOPs to force costly dependent insns into separate groups.
Insert exactly as many NOPs as needed to force an insn to a new
group, according to the estimated processor grouping.
number

Insert NOPs to force costly dependent insns into separate groups.
Insert number NOPs to force an insn to a new group.

-mcall-sysv
On System V.4 and embedded PowerPC systems compile code using calling
conventions that adhere to the March 1995 draft of the System V Application
Binary Interface, PowerPC processor supplement. This is the default unless
you configured GCC using ‘powerpc-*-eabiaix’.
-mcall-sysv-eabi
-mcall-eabi
Specify both ‘-mcall-sysv’ and ‘-meabi’ options.
-mcall-sysv-noeabi
Specify both ‘-mcall-sysv’ and ‘-mno-eabi’ options.
-mcall-aixdesc
On System V.4 and embedded PowerPC systems compile code for the AIX
operating system.
-mcall-linux
On System V.4 and embedded PowerPC systems compile code for the Linuxbased GNU system.
-mcall-freebsd
On System V.4 and embedded PowerPC systems compile code for the FreeBSD
operating system.
-mcall-netbsd
On System V.4 and embedded PowerPC systems compile code for the NetBSD
operating system.
-mcall-openbsd
On System V.4 and embedded PowerPC systems compile code for the OpenBSD
operating system.
-mtraceback=traceback_type
Select the type of traceback table. Valid values for traceback type are ‘full’,
‘part’, and ‘no’.
-maix-struct-return
Return all structures in memory (as specified by the AIX ABI).
-msvr4-struct-return
Return structures smaller than 8 bytes in registers (as specified by the SVR4
ABI).

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-mabi=abi-type
Extend the current ABI with a particular extension, or remove such extension.
Valid values are ‘altivec’, ‘no-altivec’, ‘spe’, ‘no-spe’, ‘ibmlongdouble’,
‘ieeelongdouble’, ‘elfv1’, ‘elfv2’.
-mabi=ibmlongdouble
Change the current ABI to use IBM extended-precision long double. This is
not likely to work if your system defaults to using IEEE extended-precision long
double. If you change the long double type from IEEE extended-precision, the
compiler will issue a warning unless you use the ‘-Wno-psabi’ option.
-mabi=ieeelongdouble
Change the current ABI to use IEEE extended-precision long double. This is
not likely to work if your system defaults to using IBM extended-precision long
double. If you change the long double type from IBM extended-precision, the
compiler will issue a warning unless you use the ‘-Wno-psabi’ option.
-mabi=elfv1
Change the current ABI to use the ELFv1 ABI. This is the default ABI for
big-endian PowerPC 64-bit Linux. Overriding the default ABI requires special
system support and is likely to fail in spectacular ways.
-mabi=elfv2
Change the current ABI to use the ELFv2 ABI. This is the default ABI for
little-endian PowerPC 64-bit Linux. Overriding the default ABI requires special
system support and is likely to fail in spectacular ways.
-mgnu-attribute
-mno-gnu-attribute
Emit .gnu attribute assembly directives to set tag/value pairs in a
.gnu.attributes section that specify ABI variations in function parameters or
return values.
-mprototype
-mno-prototype
On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must
insert an instruction before every non-prototyped call to set or clear bit 6 of the
condition code register (CR) to indicate whether floating-point values are passed
in the floating-point registers in case the function takes variable arguments.
With ‘-mprototype’, only calls to prototyped variable argument functions set
or clear the bit.
-msim

On embedded PowerPC systems, assume that the startup module is called
‘sim-crt0.o’ and that the standard C libraries are ‘libsim.a’ and ‘libc.a’.
This is the default for ‘powerpc-*-eabisim’ configurations.

-mmvme

On embedded PowerPC systems, assume that the startup module is called
‘crt0.o’ and the standard C libraries are ‘libmvme.a’ and ‘libc.a’.

-mads

On embedded PowerPC systems, assume that the startup module is called
‘crt0.o’ and the standard C libraries are ‘libads.a’ and ‘libc.a’.

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-myellowknife
On embedded PowerPC systems, assume that the startup module is called
‘crt0.o’ and the standard C libraries are ‘libyk.a’ and ‘libc.a’.
-mvxworks
On System V.4 and embedded PowerPC systems, specify that you are compiling
for a VxWorks system.
-memb

On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags header
to indicate that ‘eabi’ extended relocations are used.

-meabi
-mno-eabi
On System V.4 and embedded PowerPC systems do (do not) adhere to the
Embedded Applications Binary Interface (EABI), which is a set of modifications
to the System V.4 specifications. Selecting ‘-meabi’ means that the stack is
aligned to an 8-byte boundary, a function __eabi is called from main to set up
the EABI environment, and the ‘-msdata’ option can use both r2 and r13 to
point to two separate small data areas. Selecting ‘-mno-eabi’ means that the
stack is aligned to a 16-byte boundary, no EABI initialization function is called
from main, and the ‘-msdata’ option only uses r13 to point to a single small
data area. The ‘-meabi’ option is on by default if you configured GCC using
one of the ‘powerpc*-*-eabi*’ options.
-msdata=eabi
On System V.4 and embedded PowerPC systems, put small initialized const
global and static data in the .sdata2 section, which is pointed to by register
r2. Put small initialized non-const global and static data in the .sdata section, which is pointed to by register r13. Put small uninitialized global and
static data in the .sbss section, which is adjacent to the .sdata section. The
‘-msdata=eabi’ option is incompatible with the ‘-mrelocatable’ option. The
‘-msdata=eabi’ option also sets the ‘-memb’ option.
-msdata=sysv
On System V.4 and embedded PowerPC systems, put small global and static
data in the .sdata section, which is pointed to by register r13. Put small
uninitialized global and static data in the .sbss section, which is adjacent
to the .sdata section. The ‘-msdata=sysv’ option is incompatible with the
‘-mrelocatable’ option.
-msdata=default
-msdata
On System V.4 and embedded PowerPC systems, if ‘-meabi’ is used, compile code the same as ‘-msdata=eabi’, otherwise compile code the same as
‘-msdata=sysv’.
-msdata=data
On System V.4 and embedded PowerPC systems, put small global data in the
.sdata section. Put small uninitialized global data in the .sbss section. Do
not use register r13 to address small data however. This is the default behavior
unless other ‘-msdata’ options are used.

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Using the GNU Compiler Collection (GCC)

-msdata=none
-mno-sdata
On embedded PowerPC systems, put all initialized global and static data in
the .data section, and all uninitialized data in the .bss section.
-mreadonly-in-sdata
-mreadonly-in-sdata
Put read-only objects in the .sdata section as well. This is the default.
-mblock-move-inline-limit=num
Inline all block moves (such as calls to memcpy or structure copies) less than or
equal to num bytes. The minimum value for num is 32 bytes on 32-bit targets
and 64 bytes on 64-bit targets. The default value is target-specific.
-mblock-compare-inline-limit=num
Generate non-looping inline code for all block compares (such as calls to memcmp
or structure compares) less than or equal to num bytes. If num is 0, all inline
expansion (non-loop and loop) of block compare is disabled. The default value
is target-specific.
-mblock-compare-inline-loop-limit=num
Generate an inline expansion using loop code for all block compares that are
less than or equal to num bytes, but greater than the limit for non-loop inline
block compare expansion. If the block length is not constant, at most num
bytes will be compared before memcmp is called to compare the remainder of the
block. The default value is target-specific.
-mstring-compare-inline-limit=num
Generate at most num pairs of load instructions to compare the string inline.
If the difference or end of string is not found at the end of the inline compare
a call to strcmp or strncmp will take care of the rest of the comparison. The
default is 8 pairs of loads, which will compare 64 bytes on a 64-bit target and
32 bytes on a 32-bit target.
-G num

On embedded PowerPC systems, put global and static items less than or equal
to num bytes into the small data or BSS sections instead of the normal data or
BSS section. By default, num is 8. The ‘-G num’ switch is also passed to the
linker. All modules should be compiled with the same ‘-G num’ value.

-mregnames
-mno-regnames
On System V.4 and embedded PowerPC systems do (do not) emit register
names in the assembly language output using symbolic forms.
-mlongcall
-mno-longcall
By default assume that all calls are far away so that a longer and more expensive
calling sequence is required. This is required for calls farther than 32 megabytes
(33,554,432 bytes) from the current location. A short call is generated if the
compiler knows the call cannot be that far away. This setting can be overridden
by the shortcall function attribute, or by #pragma longcall(0).

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Some linkers are capable of detecting out-of-range calls and generating glue
code on the fly. On these systems, long calls are unnecessary and generate
slower code. As of this writing, the AIX linker can do this, as can the GNU
linker for PowerPC/64. It is planned to add this feature to the GNU linker for
32-bit PowerPC systems as well.
On Darwin/PPC systems, #pragma longcall generates jbsr callee, L42,
plus a branch island (glue code). The two target addresses represent the callee
and the branch island. The Darwin/PPC linker prefers the first address and
generates a bl callee if the PPC bl instruction reaches the callee directly;
otherwise, the linker generates bl L42 to call the branch island. The branch
island is appended to the body of the calling function; it computes the full
32-bit address of the callee and jumps to it.
On Mach-O (Darwin) systems, this option directs the compiler emit to the glue
for every direct call, and the Darwin linker decides whether to use or discard
it.
In the future, GCC may ignore all longcall specifications when the linker is
known to generate glue.
-mtls-markers
-mno-tls-markers
Mark (do not mark) calls to __tls_get_addr with a relocation specifying the
function argument. The relocation allows the linker to reliably associate function call with argument setup instructions for TLS optimization, which in turn
allows GCC to better schedule the sequence.
-mrecip
-mno-recip
This option enables use of the reciprocal estimate and reciprocal square
root estimate instructions with additional Newton-Raphson steps to increase
precision instead of doing a divide or square root and divide for floating-point
arguments. You should use the ‘-ffast-math’ option when using ‘-mrecip’
(or at least ‘-funsafe-math-optimizations’, ‘-ffinite-math-only’,
‘-freciprocal-math’ and ‘-fno-trapping-math’).
Note that while the
throughput of the sequence is generally higher than the throughput of the
non-reciprocal instruction, the precision of the sequence can be decreased by
up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square
roots.
-mrecip=opt
This option controls which reciprocal estimate instructions may be used. opt
is a comma-separated list of options, which may be preceded by a ! to invert
the option:
‘all’

Enable all estimate instructions.

‘default’

Enable the default instructions, equivalent to ‘-mrecip’.

‘none’

Disable all estimate instructions, equivalent to ‘-mno-recip’.

‘div’

Enable the reciprocal approximation instructions for both single
and double precision.

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‘divf’

Enable the single-precision reciprocal approximation instructions.

‘divd’

Enable the double-precision reciprocal approximation instructions.

‘rsqrt’

Enable the reciprocal square root approximation instructions for
both single and double precision.

‘rsqrtf’

Enable the single-precision reciprocal square root approximation
instructions.

‘rsqrtd’

Enable the double-precision reciprocal square root approximation
instructions.

So, for example, ‘-mrecip=all,!rsqrtd’ enables all of the reciprocal estimate
instructions, except for the FRSQRTE, XSRSQRTEDP, and XVRSQRTEDP instructions
which handle the double-precision reciprocal square root calculations.
-mrecip-precision
-mno-recip-precision
Assume (do not assume) that the reciprocal estimate instructions provide
higher-precision estimates than is mandated by the PowerPC ABI. Selecting
‘-mcpu=power6’, ‘-mcpu=power7’ or ‘-mcpu=power8’ automatically selects
‘-mrecip-precision’. The double-precision square root estimate instructions
are not generated by default on low-precision machines, since they do not
provide an estimate that converges after three steps.
-mveclibabi=type
Specifies the ABI type to use for vectorizing intrinsics using an external
library. The only type supported at present is ‘mass’, which specifies to use
IBM’s Mathematical Acceleration Subsystem (MASS) libraries for vectorizing
intrinsics using external libraries. GCC currently emits calls to acosd2,
acosf4, acoshd2, acoshf4, asind2, asinf4, asinhd2, asinhf4, atan2d2,
atan2f4, atand2, atanf4, atanhd2, atanhf4, cbrtd2, cbrtf4, cosd2, cosf4,
coshd2, coshf4, erfcd2, erfcf4, erfd2, erff4, exp2d2, exp2f4, expd2,
expf4, expm1d2, expm1f4, hypotd2, hypotf4, lgammad2, lgammaf4, log10d2,
log10f4, log1pd2, log1pf4, log2d2, log2f4, logd2, logf4, powd2, powf4,
sind2, sinf4, sinhd2, sinhf4, sqrtd2, sqrtf4, tand2, tanf4, tanhd2, and
tanhf4 when generating code for power7. Both ‘-ftree-vectorize’ and
‘-funsafe-math-optimizations’ must also be enabled. The MASS libraries
must be specified at link time.
-mfriz
-mno-friz
Generate (do not generate) the friz instruction when the
‘-funsafe-math-optimizations’ option is used to optimize rounding
of floating-point values to 64-bit integer and back to floating point. The friz
instruction does not return the same value if the floating-point number is too
large to fit in an integer.
-mpointers-to-nested-functions
-mno-pointers-to-nested-functions
Generate (do not generate) code to load up the static chain register (r11) when
calling through a pointer on AIX and 64-bit Linux systems where a function

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pointer points to a 3-word descriptor giving the function address, TOC value to
be loaded in register r2, and static chain value to be loaded in register r11. The
‘-mpointers-to-nested-functions’ is on by default. You cannot call through
pointers to nested functions or pointers to functions compiled in other languages
that use the static chain if you use ‘-mno-pointers-to-nested-functions’.
-msave-toc-indirect
-mno-save-toc-indirect
Generate (do not generate) code to save the TOC value in the reserved stack
location in the function prologue if the function calls through a pointer on AIX
and 64-bit Linux systems. If the TOC value is not saved in the prologue, it is
saved just before the call through the pointer. The ‘-mno-save-toc-indirect’
option is the default.
-mcompat-align-parm
-mno-compat-align-parm
Generate (do not generate) code to pass structure parameters with a maximum
alignment of 64 bits, for compatibility with older versions of GCC.
Older versions of GCC (prior to 4.9.0) incorrectly did not align a structure
parameter on a 128-bit boundary when that structure contained a member
requiring 128-bit alignment. This is corrected in more recent versions of GCC.
This option may be used to generate code that is compatible with functions
compiled with older versions of GCC.
The ‘-mno-compat-align-parm’ option is the default.
-mstack-protector-guard=guard
-mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset
-mstack-protector-guard-symbol=symbol
Generate stack protection code using canary at guard. Supported locations are
‘global’ for global canary or ‘tls’ for per-thread canary in the TLS block (the
default with GNU libc version 2.4 or later).
With the latter choice the options ‘-mstack-protector-guard-reg=reg’ and
‘-mstack-protector-guard-offset=offset’ furthermore specify which register to use as base register for reading the canary, and from what offset from
that base register. The default for those is as specified in the relevant ABI.
‘-mstack-protector-guard-symbol=symbol’ overrides the offset with a symbol reference to a canary in the TLS block.

3.18.41 RX Options
These command-line options are defined for RX targets:
-m64bit-doubles
-m32bit-doubles
Make the double data type be 64 bits (‘-m64bit-doubles’) or 32 bits
(‘-m32bit-doubles’) in size. The default is ‘-m32bit-doubles’. Note RX
floating-point hardware only works on 32-bit values, which is why the default
is ‘-m32bit-doubles’.

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-fpu
-nofpu

Using the GNU Compiler Collection (GCC)

Enables (‘-fpu’) or disables (‘-nofpu’) the use of RX floating-point hardware.
The default is enabled for the RX600 series and disabled for the RX200 series.
Floating-point instructions are only generated for 32-bit floating-point values,
however, so the FPU hardware is not used for doubles if the ‘-m64bit-doubles’
option is used.
Note If the ‘-fpu’ option is enabled then ‘-funsafe-math-optimizations’ is
also enabled automatically. This is because the RX FPU instructions are themselves unsafe.

-mcpu=name
Selects the type of RX CPU to be targeted. Currently three types are supported, the generic ‘RX600’ and ‘RX200’ series hardware and the specific ‘RX610’
CPU. The default is ‘RX600’.
The only difference between ‘RX600’ and ‘RX610’ is that the ‘RX610’ does not
support the MVTIPL instruction.
The ‘RX200’ series does not have a hardware floating-point unit and so ‘-nofpu’
is enabled by default when this type is selected.
-mbig-endian-data
-mlittle-endian-data
Store data (but not code) in the big-endian format.
The default is
‘-mlittle-endian-data’, i.e. to store data in the little-endian format.
-msmall-data-limit=N
Specifies the maximum size in bytes of global and static variables which can be
placed into the small data area. Using the small data area can lead to smaller
and faster code, but the size of area is limited and it is up to the programmer to
ensure that the area does not overflow. Also when the small data area is used
one of the RX’s registers (usually r13) is reserved for use pointing to this area,
so it is no longer available for use by the compiler. This could result in slower
and/or larger code if variables are pushed onto the stack instead of being held
in this register.
Note, common variables (variables that have not been initialized) and constants
are not placed into the small data area as they are assigned to other sections
in the output executable.
The default value is zero, which disables this feature. Note, this feature is not
enabled by default with higher optimization levels (‘-O2’ etc) because of the
potentially detrimental effects of reserving a register. It is up to the programmer
to experiment and discover whether this feature is of benefit to their program.
See the description of the ‘-mpid’ option for a description of how the actual
register to hold the small data area pointer is chosen.
-msim
-mno-sim

Use the simulator runtime. The default is to use the libgloss board-specific
runtime.

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-mas100-syntax
-mno-as100-syntax
When generating assembler output use a syntax that is compatible with Renesas’s AS100 assembler. This syntax can also be handled by the GAS assembler,
but it has some restrictions so it is not generated by default.
-mmax-constant-size=N
Specifies the maximum size, in bytes, of a constant that can be used as an
operand in a RX instruction. Although the RX instruction set does allow
constants of up to 4 bytes in length to be used in instructions, a longer value
equates to a longer instruction. Thus in some circumstances it can be beneficial
to restrict the size of constants that are used in instructions. Constants that
are too big are instead placed into a constant pool and referenced via register
indirection.
The value N can be between 0 and 4. A value of 0 (the default) or 4 means
that constants of any size are allowed.
-mrelax

Enable linker relaxation. Linker relaxation is a process whereby the linker
attempts to reduce the size of a program by finding shorter versions of various
instructions. Disabled by default.

-mint-register=N
Specify the number of registers to reserve for fast interrupt handler functions.
The value N can be between 0 and 4. A value of 1 means that register r13 is
reserved for the exclusive use of fast interrupt handlers. A value of 2 reserves
r13 and r12. A value of 3 reserves r13, r12 and r11, and a value of 4 reserves
r13 through r10. A value of 0, the default, does not reserve any registers.
-msave-acc-in-interrupts
Specifies that interrupt handler functions should preserve the accumulator register. This is only necessary if normal code might use the accumulator register,
for example because it performs 64-bit multiplications. The default is to ignore
the accumulator as this makes the interrupt handlers faster.
-mpid
-mno-pid

Enables the generation of position independent data. When enabled any access
to constant data is done via an offset from a base address held in a register.
This allows the location of constant data to be determined at run time without requiring the executable to be relocated, which is a benefit to embedded
applications with tight memory constraints. Data that can be modified is not
affected by this option.
Note, using this feature reserves a register, usually r13, for the constant data
base address. This can result in slower and/or larger code, especially in complicated functions.
The actual register chosen to hold the constant data base address depends upon
whether the ‘-msmall-data-limit’ and/or the ‘-mint-register’ commandline options are enabled. Starting with register r13 and proceeding downwards,
registers are allocated first to satisfy the requirements of ‘-mint-register’,
then ‘-mpid’ and finally ‘-msmall-data-limit’. Thus it is possible for the

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small data area register to be r8 if both ‘-mint-register=4’ and ‘-mpid’ are
specified on the command line.
By default this feature is not enabled. The default can be restored via the
‘-mno-pid’ command-line option.
-mno-warn-multiple-fast-interrupts
-mwarn-multiple-fast-interrupts
Prevents GCC from issuing a warning message if it finds more than one fast
interrupt handler when it is compiling a file. The default is to issue a warning
for each extra fast interrupt handler found, as the RX only supports one such
interrupt.
-mallow-string-insns
-mno-allow-string-insns
Enables or disables the use of the string manipulation instructions SMOVF,
SCMPU, SMOVB, SMOVU, SUNTIL SWHILE and also the RMPA instruction. These
instructions may prefetch data, which is not safe to do if accessing an I/O
register. (See section 12.2.7 of the RX62N Group User’s Manual for more information).
The default is to allow these instructions, but it is not possible for GCC to
reliably detect all circumstances where a string instruction might be used to
access an I/O register, so their use cannot be disabled automatically. Instead it
is reliant upon the programmer to use the ‘-mno-allow-string-insns’ option
if their program accesses I/O space.
When the instructions are enabled GCC defines the C preprocessor symbol _
_RX_ALLOW_STRING_INSNS__, otherwise it defines the symbol __RX_DISALLOW_
STRING_INSNS__.
-mjsr
-mno-jsr

Use only (or not only) JSR instructions to access functions. This option can be
used when code size exceeds the range of BSR instructions. Note that ‘-mno-jsr’
does not mean to not use JSR but instead means that any type of branch may
be used.

Note: The generic GCC command-line option ‘-ffixed-reg’ has special significance to
the RX port when used with the interrupt function attribute. This attribute indicates a
function intended to process fast interrupts. GCC ensures that it only uses the registers r10,
r11, r12 and/or r13 and only provided that the normal use of the corresponding registers
have been restricted via the ‘-ffixed-reg’ or ‘-mint-register’ command-line options.

3.18.42 S/390 and zSeries Options
These are the ‘-m’ options defined for the S/390 and zSeries architecture.
-mhard-float
-msoft-float
Use (do not use) the hardware floating-point instructions and registers
for floating-point operations. When ‘-msoft-float’ is specified, functions
in ‘libgcc.a’ are used to perform floating-point operations.
When

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‘-mhard-float’ is specified, the compiler generates IEEE floating-point
instructions. This is the default.
-mhard-dfp
-mno-hard-dfp
Use (do not use) the hardware decimal-floating-point instructions for
decimal-floating-point operations.
When ‘-mno-hard-dfp’ is specified,
functions in ‘libgcc.a’ are used to perform decimal-floating-point operations.
When ‘-mhard-dfp’ is specified, the compiler generates decimal-floating-point
hardware instructions. This is the default for ‘-march=z9-ec’ or higher.
-mlong-double-64
-mlong-double-128
These switches control the size of long double type. A size of 64 bits makes
the long double type equivalent to the double type. This is the default.
-mbackchain
-mno-backchain
Store (do not store) the address of the caller’s frame as backchain pointer
into the callee’s stack frame. A backchain may be needed to allow debugging
using tools that do not understand DWARF call frame information. When
‘-mno-packed-stack’ is in effect, the backchain pointer is stored at the bottom
of the stack frame; when ‘-mpacked-stack’ is in effect, the backchain is placed
into the topmost word of the 96/160 byte register save area.
In general, code compiled with ‘-mbackchain’ is call-compatible with code compiled with ‘-mmo-backchain’; however, use of the backchain for debugging purposes usually requires that the whole binary is built with ‘-mbackchain’. Note
that the combination of ‘-mbackchain’, ‘-mpacked-stack’ and ‘-mhard-float’
is not supported. In order to build a linux kernel use ‘-msoft-float’.
The default is to not maintain the backchain.
-mpacked-stack
-mno-packed-stack
Use (do not use) the packed stack layout. When ‘-mno-packed-stack’ is specified, the compiler uses the all fields of the 96/160 byte register save area
only for their default purpose; unused fields still take up stack space. When
‘-mpacked-stack’ is specified, register save slots are densely packed at the top
of the register save area; unused space is reused for other purposes, allowing for
more efficient use of the available stack space. However, when ‘-mbackchain’
is also in effect, the topmost word of the save area is always used to store the
backchain, and the return address register is always saved two words below the
backchain.
As long as the stack frame backchain is not used, code generated
with ‘-mpacked-stack’ is call-compatible with code generated with
‘-mno-packed-stack’. Note that some non-FSF releases of GCC 2.95 for
S/390 or zSeries generated code that uses the stack frame backchain at run
time, not just for debugging purposes. Such code is not call-compatible with
code compiled with ‘-mpacked-stack’. Also, note that the combination of

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Using the GNU Compiler Collection (GCC)

‘-mbackchain’, ‘-mpacked-stack’ and ‘-mhard-float’ is not supported. In
order to build a linux kernel use ‘-msoft-float’.
The default is to not use the packed stack layout.
-msmall-exec
-mno-small-exec
Generate (or do not generate) code using the bras instruction to do subroutine
calls. This only works reliably if the total executable size does not exceed 64k.
The default is to use the basr instruction instead, which does not have this
limitation.
-m64
-m31

-mzarch
-mesa

-mhtm
-mno-htm

-mvx
-mno-vx

When ‘-m31’ is specified, generate code compliant to the GNU/Linux for S/390
ABI. When ‘-m64’ is specified, generate code compliant to the GNU/Linux for
zSeries ABI. This allows GCC in particular to generate 64-bit instructions. For
the ‘s390’ targets, the default is ‘-m31’, while the ‘s390x’ targets default to
‘-m64’.
When ‘-mzarch’ is specified, generate code using the instructions available on
z/Architecture. When ‘-mesa’ is specified, generate code using the instructions
available on ESA/390. Note that ‘-mesa’ is not possible with ‘-m64’. When
generating code compliant to the GNU/Linux for S/390 ABI, the default is
‘-mesa’. When generating code compliant to the GNU/Linux for zSeries ABI,
the default is ‘-mzarch’.
The ‘-mhtm’ option enables a set of builtins making use of instructions available
with the transactional execution facility introduced with the IBM zEnterprise
EC12 machine generation Section 6.59.26 [S/390 System z Built-in Functions],
page 740. ‘-mhtm’ is enabled by default when using ‘-march=zEC12’.
When ‘-mvx’ is specified, generate code using the instructions available with the
vector extension facility introduced with the IBM z13 machine generation. This
option changes the ABI for some vector type values with regard to alignment
and calling conventions. In case vector type values are being used in an ABIrelevant context a GAS ‘.gnu_attribute’ command will be added to mark the
resulting binary with the ABI used. ‘-mvx’ is enabled by default when using
‘-march=z13’.

-mzvector
-mno-zvector
The ‘-mzvector’ option enables vector language extensions and builtins using
instructions available with the vector extension facility introduced with the
IBM z13 machine generation. This option adds support for ‘vector’ to be
used as a keyword to define vector type variables and arguments. ‘vector’
is only available when GNU extensions are enabled. It will not be expanded
when requesting strict standard compliance e.g. with ‘-std=c99’. In addition
to the GCC low-level builtins ‘-mzvector’ enables a set of builtins added for

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compatibility with AltiVec-style implementations like Power and Cell. In order
to make use of these builtins the header file ‘vecintrin.h’ needs to be included.
‘-mzvector’ is disabled by default.
-mmvcle
-mno-mvcle
Generate (or do not generate) code using the mvcle instruction to perform
block moves. When ‘-mno-mvcle’ is specified, use a mvc loop instead. This is
the default unless optimizing for size.
-mdebug
-mno-debug
Print (or do not print) additional debug information when compiling. The
default is to not print debug information.
-march=cpu-type
Generate code
representing a
‘z900’/‘arch5’,
‘z196’/‘arch9’,

that runs on cpu-type, which is the name of a system
certain processor type. Possible values for cpu-type are
‘z990’/‘arch6’, ‘z9-109’, ‘z9-ec’/‘arch7’, ‘z10’/‘arch8’,
‘zEC12’, ‘z13’/‘arch11’, and ‘native’.

The default is ‘-march=z900’. ‘g5’/‘arch3’ and ‘g6’ are deprecated and will be
removed with future releases.
Specifying ‘native’ as cpu type can be used to select the best architecture
option for the host processor. ‘-march=native’ has no effect if GCC does not
recognize the processor.
-mtune=cpu-type
Tune to cpu-type everything applicable about the generated code, except for
the ABI and the set of available instructions. The list of cpu-type values is the
same as for ‘-march’. The default is the value used for ‘-march’.
-mtpf-trace
-mno-tpf-trace
Generate code that adds (does not add) in TPF OS specific branches to trace
routines in the operating system. This option is off by default, even when
compiling for the TPF OS.
-mfused-madd
-mno-fused-madd
Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware
floating point is used.
-mwarn-framesize=framesize
Emit a warning if the current function exceeds the given frame size. Because
this is a compile-time check it doesn’t need to be a real problem when the
program runs. It is intended to identify functions that most probably cause a
stack overflow. It is useful to be used in an environment with limited stack size
e.g. the linux kernel.

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-mwarn-dynamicstack
Emit a warning if the function calls alloca or uses dynamically-sized arrays.
This is generally a bad idea with a limited stack size.
-mstack-guard=stack-guard
-mstack-size=stack-size
If these options are provided the S/390 back end emits additional instructions
in the function prologue that trigger a trap if the stack size is stack-guard bytes
above the stack-size (remember that the stack on S/390 grows downward).
If the stack-guard option is omitted the smallest power of 2 larger than the
frame size of the compiled function is chosen. These options are intended to
be used to help debugging stack overflow problems. The additionally emitted
code causes only little overhead and hence can also be used in production-like
systems without greater performance degradation. The given values have to be
exact powers of 2 and stack-size has to be greater than stack-guard without
exceeding 64k. In order to be efficient the extra code makes the assumption
that the stack starts at an address aligned to the value given by stack-size. The
stack-guard option can only be used in conjunction with stack-size.
-mhotpatch=pre-halfwords,post-halfwords
If the hotpatch option is enabled, a “hot-patching” function prologue is generated for all functions in the compilation unit. The funtion label is prepended
with the given number of two-byte NOP instructions (pre-halfwords, maximum
1000000). After the label, 2 * post-halfwords bytes are appended, using the
largest NOP like instructions the architecture allows (maximum 1000000).
If both arguments are zero, hotpatching is disabled.
This option can be overridden for individual functions with the hotpatch attribute.

3.18.43 Score Options
These options are defined for Score implementations:
-meb

Compile code for big-endian mode. This is the default.

-mel

Compile code for little-endian mode.

-mnhwloop
Disable generation of bcnz instructions.
-muls

Enable generation of unaligned load and store instructions.

-mmac

Enable the use of multiply-accumulate instructions. Disabled by default.

-mscore5

Specify the SCORE5 as the target architecture.

-mscore5u
Specify the SCORE5U of the target architecture.
-mscore7

Specify the SCORE7 as the target architecture. This is the default.

-mscore7d
Specify the SCORE7D as the target architecture.

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3.18.44 SH Options
These ‘-m’ options are defined for the SH implementations:
-m1

Generate code for the SH1.

-m2

Generate code for the SH2.

-m2e

Generate code for the SH2e.

-m2a-nofpu
Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way
that the floating-point unit is not used.
-m2a-single-only
Generate code for the SH2a-FPU, in such a way that no double-precision
floating-point operations are used.
-m2a-single
Generate code for the SH2a-FPU assuming the floating-point unit is in singleprecision mode by default.
-m2a

Generate code for the SH2a-FPU assuming the floating-point unit is in doubleprecision mode by default.

-m3

Generate code for the SH3.

-m3e

Generate code for the SH3e.

-m4-nofpu
Generate code for the SH4 without a floating-point unit.
-m4-single-only
Generate code for the SH4 with a floating-point unit that only supports singleprecision arithmetic.
-m4-single
Generate code for the SH4 assuming the floating-point unit is in single-precision
mode by default.
-m4

Generate code for the SH4.

-m4-100

Generate code for SH4-100.

-m4-100-nofpu
Generate code for SH4-100 in such a way that the floating-point unit is not
used.
-m4-100-single
Generate code for SH4-100 assuming the floating-point unit is in single-precision
mode by default.
-m4-100-single-only
Generate code for SH4-100 in such a way that no double-precision floating-point
operations are used.
-m4-200

Generate code for SH4-200.

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-m4-200-nofpu
Generate code for SH4-200 without in such a way that the floating-point unit
is not used.
-m4-200-single
Generate code for SH4-200 assuming the floating-point unit is in single-precision
mode by default.
-m4-200-single-only
Generate code for SH4-200 in such a way that no double-precision floating-point
operations are used.
-m4-300

Generate code for SH4-300.

-m4-300-nofpu
Generate code for SH4-300 without in such a way that the floating-point unit
is not used.
-m4-300-single
Generate code for SH4-300 in such a way that no double-precision floating-point
operations are used.
-m4-300-single-only
Generate code for SH4-300 in such a way that no double-precision floating-point
operations are used.
-m4-340

Generate code for SH4-340 (no MMU, no FPU).

-m4-500

Generate code for SH4-500 (no FPU). Passes ‘-isa=sh4-nofpu’ to the assembler.

-m4a-nofpu
Generate code for the SH4al-dsp, or for a SH4a in such a way that the floatingpoint unit is not used.
-m4a-single-only
Generate code for the SH4a, in such a way that no double-precision floatingpoint operations are used.
-m4a-single
Generate code for the SH4a assuming the floating-point unit is in
single-precision mode by default.
-m4a

Generate code for the SH4a.

-m4al

Same as ‘-m4a-nofpu’, except that it implicitly passes ‘-dsp’ to the assembler.
GCC doesn’t generate any DSP instructions at the moment.

-mb

Compile code for the processor in big-endian mode.

-ml

Compile code for the processor in little-endian mode.

-mdalign

Align doubles at 64-bit boundaries. Note that this changes the calling conventions, and thus some functions from the standard C library do not work unless
you recompile it first with ‘-mdalign’.

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-mrelax

371

Shorten some address references at link time, when possible; uses the linker
option ‘-relax’.

-mbigtable
Use 32-bit offsets in switch tables. The default is to use 16-bit offsets.
-mbitops

Enable the use of bit manipulation instructions on SH2A.

-mfmovd

Enable the use of the instruction fmovd. Check ‘-mdalign’ for alignment constraints.

-mrenesas
Comply with the calling conventions defined by Renesas.
-mno-renesas
Comply with the calling conventions defined for GCC before the Renesas conventions were available. This option is the default for all targets of the SH
toolchain.
-mnomacsave
Mark the MAC register as call-clobbered, even if ‘-mrenesas’ is given.
-mieee
-mno-ieee
Control the IEEE compliance of floating-point comparisons, which affects the
handling of cases where the result of a comparison is unordered. By default
‘-mieee’ is implicitly enabled. If ‘-ffinite-math-only’ is enabled ‘-mno-ieee’
is implicitly set, which results in faster floating-point greater-equal and lessequal comparisons. The implicit settings can be overridden by specifying either
‘-mieee’ or ‘-mno-ieee’.
-minline-ic_invalidate
Inline code to invalidate instruction cache entries after setting up nested function trampolines. This option has no effect if ‘-musermode’ is in effect and the
selected code generation option (e.g. ‘-m4’) does not allow the use of the icbi
instruction. If the selected code generation option does not allow the use of
the icbi instruction, and ‘-musermode’ is not in effect, the inlined code manipulates the instruction cache address array directly with an associative write.
This not only requires privileged mode at run time, but it also fails if the cache
line had been mapped via the TLB and has become unmapped.
-misize

Dump instruction size and location in the assembly code.

-mpadstruct
This option is deprecated. It pads structures to multiple of 4 bytes, which is
incompatible with the SH ABI.
-matomic-model=model
Sets the model of atomic operations and additional parameters as a comma
separated list. For details on the atomic built-in functions see Section 6.53
[ atomic Builtins], page 603. The following models and parameters are supported:

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‘none’

Disable compiler generated atomic sequences and emit library calls
for atomic operations. This is the default if the target is not sh**-linux*.

‘soft-gusa’
Generate GNU/Linux compatible gUSA software atomic sequences
for the atomic built-in functions. The generated atomic sequences
require additional support from the interrupt/exception handling
code of the system and are only suitable for SH3* and SH4* singlecore systems. This option is enabled by default when the target
is sh*-*-linux* and SH3* or SH4*. When the target is SH4A,
this option also partially utilizes the hardware atomic instructions
movli.l and movco.l to create more efficient code, unless ‘strict’
is specified.
‘soft-tcb’
Generate software atomic sequences that use a variable in the
thread control block. This is a variation of the gUSA sequences
which can also be used on SH1* and SH2* targets.
The
generated atomic sequences require additional support from the
interrupt/exception handling code of the system and are only
suitable for single-core systems. When using this model, the
‘gbr-offset=’ parameter has to be specified as well.
‘soft-imask’
Generate software atomic sequences that temporarily disable interrupts by setting SR.IMASK = 1111. This model works only when the
program runs in privileged mode and is only suitable for single-core
systems. Additional support from the interrupt/exception handling
code of the system is not required. This model is enabled by default
when the target is sh*-*-linux* and SH1* or SH2*.
‘hard-llcs’
Generate hardware atomic sequences using the movli.l and
movco.l instructions only. This is only available on SH4A and is
suitable for multi-core systems. Since the hardware instructions
support only 32 bit atomic variables access to 8 or 16 bit variables
is emulated with 32 bit accesses. Code compiled with this
option is also compatible with other software atomic model
interrupt/exception handling systems if executed on an SH4A
system. Additional support from the interrupt/exception handling
code of the system is not required for this model.
‘gbr-offset=’
This parameter specifies the offset in bytes of the variable in the
thread control block structure that should be used by the generated
atomic sequences when the ‘soft-tcb’ model has been selected. For
other models this parameter is ignored. The specified value must
be an integer multiple of four and in the range 0-1020.

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‘strict’

-mtas

373

This parameter prevents mixed usage of multiple atomic models,
even if they are compatible, and makes the compiler generate
atomic sequences of the specified model only.

Generate the tas.b opcode for __atomic_test_and_set. Notice that depending on the particular hardware and software configuration this can degrade
overall performance due to the operand cache line flushes that are implied by
the tas.b instruction. On multi-core SH4A processors the tas.b instruction
must be used with caution since it can result in data corruption for certain
cache configurations.

-mprefergot
When generating position-independent code, emit function calls using the
Global Offset Table instead of the Procedure Linkage Table.
-musermode
-mno-usermode
Don’t allow (allow) the compiler generating privileged mode code. Specifying
‘-musermode’ also implies ‘-mno-inline-ic_invalidate’ if the inlined code
would not work in user mode. ‘-musermode’ is the default when the target is
sh*-*-linux*. If the target is SH1* or SH2* ‘-musermode’ has no effect, since
there is no user mode.
-multcost=number
Set the cost to assume for a multiply insn.
-mdiv=strategy
Set the division strategy to be used for integer division operations. strategy
can be one of:
‘call-div1’
Calls a library function that uses the single-step division instruction div1 to perform the operation. Division by zero calculates an
unspecified result and does not trap. This is the default except for
SH4, SH2A and SHcompact.
‘call-fp’

Calls a library function that performs the operation in double precision floating point. Division by zero causes a floating-point exception. This is the default for SHcompact with FPU. Specifying
this for targets that do not have a double precision FPU defaults
to call-div1.

‘call-table’
Calls a library function that uses a lookup table for small divisors
and the div1 instruction with case distinction for larger divisors.
Division by zero calculates an unspecified result and does not trap.
This is the default for SH4. Specifying this for targets that do not
have dynamic shift instructions defaults to call-div1.
When a division strategy has not been specified the default strategy is selected
based on the current target. For SH2A the default strategy is to use the divs
and divu instructions instead of library function calls.

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-maccumulate-outgoing-args
Reserve space once for outgoing arguments in the function prologue rather than
around each call. Generally beneficial for performance and size. Also needed
for unwinding to avoid changing the stack frame around conditional code.
-mdivsi3_libfunc=name
Set the name of the library function used for 32-bit signed division to name.
This only affects the name used in the ‘call’ division strategies, and the compiler still expects the same sets of input/output/clobbered registers as if this
option were not present.
-mfixed-range=register-range
Generate code treating the given register range as fixed registers. A fixed
register is one that the register allocator can not use. This is useful when
compiling kernel code. A register range is specified as two registers separated
by a dash. Multiple register ranges can be specified separated by a comma.
-mbranch-cost=num
Assume num to be the cost for a branch instruction. Higher numbers make the
compiler try to generate more branch-free code if possible. If not specified the
value is selected depending on the processor type that is being compiled for.
-mzdcbranch
-mno-zdcbranch
Assume (do not assume) that zero displacement conditional branch instructions bt and bf are fast. If ‘-mzdcbranch’ is specified, the compiler prefers
zero displacement branch code sequences. This is enabled by default when
generating code for SH4 and SH4A. It can be explicitly disabled by specifying
‘-mno-zdcbranch’.
-mcbranch-force-delay-slot
Force the usage of delay slots for conditional branches, which stuffs the delay
slot with a nop if a suitable instruction cannot be found. By default this option
is disabled. It can be enabled to work around hardware bugs as found in the
original SH7055.
-mfused-madd
-mno-fused-madd
Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent ‘-mfused-madd’ option is
now mapped to the machine-independent ‘-ffp-contract=fast’ option, and
‘-mno-fused-madd’ is mapped to ‘-ffp-contract=off’.
-mfsca
-mno-fsca
Allow or disallow the compiler to emit the fsca instruction for sine and cosine approximations. The option ‘-mfsca’ must be used in combination with
‘-funsafe-math-optimizations’. It is enabled by default when generating
code for SH4A. Using ‘-mno-fsca’ disables sine and cosine approximations even
if ‘-funsafe-math-optimizations’ is in effect.

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-mfsrra
-mno-fsrra
Allow or disallow the compiler to emit the fsrra instruction for reciprocal
square root approximations. The option ‘-mfsrra’ must be used in combination with ‘-funsafe-math-optimizations’ and ‘-ffinite-math-only’. It is
enabled by default when generating code for SH4A. Using ‘-mno-fsrra’ disables
reciprocal square root approximations even if ‘-funsafe-math-optimizations’
and ‘-ffinite-math-only’ are in effect.
-mpretend-cmove
Prefer zero-displacement conditional branches for conditional move instruction
patterns. This can result in faster code on the SH4 processor.
-mfdpic

Generate code using the FDPIC ABI.

3.18.45 Solaris 2 Options
These ‘-m’ options are supported on Solaris 2:
-mclear-hwcap
‘-mclear-hwcap’ tells the compiler to remove the hardware capabilities generated by the Solaris assembler. This is only necessary when object files use ISA
extensions not supported by the current machine, but check at runtime whether
or not to use them.
-mimpure-text
‘-mimpure-text’, used in addition to ‘-shared’, tells the compiler to not pass
‘-z text’ to the linker when linking a shared object. Using this option, you can
link position-dependent code into a shared object.
‘-mimpure-text’ suppresses the “relocations remain against allocatable but
non-writable sections” linker error message. However, the necessary relocations trigger copy-on-write, and the shared object is not actually shared across
processes. Instead of using ‘-mimpure-text’, you should compile all source
code with ‘-fpic’ or ‘-fPIC’.
These switches are supported in addition to the above on Solaris 2:
-pthreads
This is a synonym for ‘-pthread’.

3.18.46 SPARC Options
These ‘-m’ options are supported on the SPARC:
-mno-app-regs
-mapp-regs
Specify ‘-mapp-regs’ to generate output using the global registers 2 through 4,
which the SPARC SVR4 ABI reserves for applications. Like the global register
1, each global register 2 through 4 is then treated as an allocable register that
is clobbered by function calls. This is the default.
To be fully SVR4 ABI-compliant at the cost of some performance loss, specify
‘-mno-app-regs’. You should compile libraries and system software with this
option.

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-mflat
-mno-flat
With ‘-mflat’, the compiler does not generate save/restore instructions and
uses a “flat” or single register window model. This model is compatible with
the regular register window model. The local registers and the input registers
(0–5) are still treated as “call-saved” registers and are saved on the stack as
needed.
With ‘-mno-flat’ (the default), the compiler generates save/restore instructions (except for leaf functions). This is the normal operating mode.
-mfpu
-mhard-float
Generate output containing floating-point instructions. This is the default.
-mno-fpu
-msoft-float
Generate output containing library calls for floating point. Warning: the requisite libraries are not available for all SPARC targets. Normally the facilities
of the machine’s usual C compiler are used, but this cannot be done directly in
cross-compilation. You must make your own arrangements to provide suitable
library functions for cross-compilation. The embedded targets ‘sparc-*-aout’
and ‘sparclite-*-*’ do provide software floating-point support.
‘-msoft-float’ changes the calling convention in the output file; therefore, it
is only useful if you compile all of a program with this option. In particular, you need to compile ‘libgcc.a’, the library that comes with GCC, with
‘-msoft-float’ in order for this to work.
-mhard-quad-float
Generate output containing quad-word (long double) floating-point instructions.
-msoft-quad-float
Generate output containing library calls for quad-word (long double) floatingpoint instructions. The functions called are those specified in the SPARC ABI.
This is the default.
As of this writing, there are no SPARC implementations that have hardware
support for the quad-word floating-point instructions. They all invoke a trap
handler for one of these instructions, and then the trap handler emulates the
effect of the instruction. Because of the trap handler overhead, this is much
slower than calling the ABI library routines. Thus the ‘-msoft-quad-float’
option is the default.
-mno-unaligned-doubles
-munaligned-doubles
Assume that doubles have 8-byte alignment. This is the default.
With ‘-munaligned-doubles’, GCC assumes that doubles have 8-byte alignment only if they are contained in another type, or if they have an absolute
address. Otherwise, it assumes they have 4-byte alignment. Specifying this
option avoids some rare compatibility problems with code generated by other

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compilers. It is not the default because it results in a performance loss, especially for floating-point code.
-muser-mode
-mno-user-mode
Do not generate code that can only run in supervisor mode. This is relevant
only for the casa instruction emitted for the LEON3 processor. This is the
default.
-mfaster-structs
-mno-faster-structs
With ‘-mfaster-structs’, the compiler assumes that structures should have
8-byte alignment. This enables the use of pairs of ldd and std instructions
for copies in structure assignment, in place of twice as many ld and st pairs.
However, the use of this changed alignment directly violates the SPARC ABI.
Thus, it’s intended only for use on targets where the developer acknowledges
that their resulting code is not directly in line with the rules of the ABI.
-mstd-struct-return
-mno-std-struct-return
With ‘-mstd-struct-return’, the compiler generates checking code in functions returning structures or unions to detect size mismatches between the two
sides of function calls, as per the 32-bit ABI.
The default is ‘-mno-std-struct-return’. This option has no effect in 64-bit
mode.
-mlra
-mno-lra

Enable Local Register Allocation. This is the default for SPARC since GCC 7
so ‘-mno-lra’ needs to be passed to get old Reload.

-mcpu=cpu_type
Set the instruction set, register set, and instruction scheduling parameters for
machine type cpu type. Supported values for cpu type are ‘v7’, ‘cypress’,
‘v8’, ‘supersparc’, ‘hypersparc’, ‘leon’, ‘leon3’, ‘leon3v7’, ‘sparclite’,
‘f930’, ‘f934’, ‘sparclite86x’, ‘sparclet’, ‘tsc701’, ‘v9’, ‘ultrasparc’,
‘ultrasparc3’, ‘niagara’, ‘niagara2’, ‘niagara3’, ‘niagara4’, ‘niagara7’
and ‘m8’.
Native Solaris and GNU/Linux toolchains also support the value
‘native’, which selects the best architecture option for the host processor.
‘-mcpu=native’ has no effect if GCC does not recognize the processor.
Default instruction scheduling parameters are used for values that select an
architecture and not an implementation. These are ‘v7’, ‘v8’, ‘sparclite’,
‘sparclet’, ‘v9’.
Here is a list of each supported architecture and their supported implementations.
v7

cypress, leon3v7

v8

supersparc, hypersparc, leon, leon3

sparclite

f930, f934, sparclite86x

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sparclet

tsc701

v9

ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4, niagara7, m8

By default (unless configured otherwise), GCC generates code for the V7 variant of the SPARC architecture. With ‘-mcpu=cypress’, the compiler additionally optimizes it for the Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series. This is also appropriate for the older SPARCStation 1, 2, IPX etc.
With ‘-mcpu=v8’, GCC generates code for the V8 variant of the SPARC architecture. The only difference from V7 code is that the compiler emits the integer
multiply and integer divide instructions which exist in SPARC-V8 but not in
SPARC-V7. With ‘-mcpu=supersparc’, the compiler additionally optimizes it
for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
series.
With ‘-mcpu=sparclite’, GCC generates code for the SPARClite variant of the
SPARC architecture. This adds the integer multiply, integer divide step and
scan (ffs) instructions which exist in SPARClite but not in SPARC-V7. With
‘-mcpu=f930’, the compiler additionally optimizes it for the Fujitsu MB86930
chip, which is the original SPARClite, with no FPU. With ‘-mcpu=f934’, the
compiler additionally optimizes it for the Fujitsu MB86934 chip, which is the
more recent SPARClite with FPU.
With ‘-mcpu=sparclet’, GCC generates code for the SPARClet variant of the
SPARC architecture. This adds the integer multiply, multiply/accumulate,
integer divide step and scan (ffs) instructions which exist in SPARClet but
not in SPARC-V7. With ‘-mcpu=tsc701’, the compiler additionally optimizes
it for the TEMIC SPARClet chip.
With ‘-mcpu=v9’, GCC generates code for the V9 variant of the SPARC architecture. This adds 64-bit integer and floating-point move instructions, 3
additional floating-point condition code registers and conditional move instructions. With ‘-mcpu=ultrasparc’, the compiler additionally optimizes it for the
Sun UltraSPARC I/II/IIi chips. With ‘-mcpu=ultrasparc3’, the compiler additionally optimizes it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips.
With ‘-mcpu=niagara’, the compiler additionally optimizes it for Sun UltraSPARC T1 chips. With ‘-mcpu=niagara2’, the compiler additionally optimizes
it for Sun UltraSPARC T2 chips. With ‘-mcpu=niagara3’, the compiler additionally optimizes it for Sun UltraSPARC T3 chips. With ‘-mcpu=niagara4’,
the compiler additionally optimizes it for Sun UltraSPARC T4 chips. With
‘-mcpu=niagara7’, the compiler additionally optimizes it for Oracle SPARC
M7 chips. With ‘-mcpu=m8’, the compiler additionally optimizes it for Oracle
M8 chips.
-mtune=cpu_type
Set the instruction scheduling parameters for machine type cpu type, but do
not set the instruction set or register set that the option ‘-mcpu=cpu_type’
does.

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The same values for ‘-mcpu=cpu_type’ can be used for ‘-mtune=cpu_type’, but
the only useful values are those that select a particular CPU implementation.
Those are ‘cypress’, ‘supersparc’, ‘hypersparc’, ‘leon’, ‘leon3’, ‘leon3v7’,
‘f930’, ‘f934’, ‘sparclite86x’, ‘tsc701’, ‘ultrasparc’, ‘ultrasparc3’,
‘niagara’, ‘niagara2’, ‘niagara3’, ‘niagara4’, ‘niagara7’ and ‘m8’. With
native Solaris and GNU/Linux toolchains, ‘native’ can also be used.
-mv8plus
-mno-v8plus
With ‘-mv8plus’, GCC generates code for the SPARC-V8+ ABI. The difference
from the V8 ABI is that the global and out registers are considered 64 bits
wide. This is enabled by default on Solaris in 32-bit mode for all SPARC-V9
processors.
-mvis
-mno-vis

With ‘-mvis’, GCC generates code that takes advantage of the UltraSPARC
Visual Instruction Set extensions. The default is ‘-mno-vis’.

-mvis2
-mno-vis2
With ‘-mvis2’, GCC generates code that takes advantage of version 2.0 of the
UltraSPARC Visual Instruction Set extensions. The default is ‘-mvis2’ when
targeting a cpu that supports such instructions, such as UltraSPARC-III and
later. Setting ‘-mvis2’ also sets ‘-mvis’.
-mvis3
-mno-vis3
With ‘-mvis3’, GCC generates code that takes advantage of version 3.0 of the
UltraSPARC Visual Instruction Set extensions. The default is ‘-mvis3’ when
targeting a cpu that supports such instructions, such as niagara-3 and later.
Setting ‘-mvis3’ also sets ‘-mvis2’ and ‘-mvis’.
-mvis4
-mno-vis4
With ‘-mvis4’, GCC generates code that takes advantage of version 4.0 of the
UltraSPARC Visual Instruction Set extensions. The default is ‘-mvis4’ when
targeting a cpu that supports such instructions, such as niagara-7 and later.
Setting ‘-mvis4’ also sets ‘-mvis3’, ‘-mvis2’ and ‘-mvis’.
-mvis4b
-mno-vis4b
With ‘-mvis4b’, GCC generates code that takes advantage of version 4.0 of
the UltraSPARC Visual Instruction Set extensions, plus the additional VIS
instructions introduced in the Oracle SPARC Architecture 2017. The default
is ‘-mvis4b’ when targeting a cpu that supports such instructions, such as m8
and later. Setting ‘-mvis4b’ also sets ‘-mvis4’, ‘-mvis3’, ‘-mvis2’ and ‘-mvis’.
-mcbcond
-mno-cbcond
With ‘-mcbcond’, GCC generates code that takes advantage of the
UltraSPARC Compare-and-Branch-on-Condition instructions. The default is

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‘-mcbcond’ when targeting a CPU that supports such instructions, such as
Niagara-4 and later.
-mfmaf
-mno-fmaf
With ‘-mfmaf’, GCC generates code that takes advantage of the UltraSPARC
Fused Multiply-Add Floating-point instructions. The default is ‘-mfmaf’ when
targeting a CPU that supports such instructions, such as Niagara-3 and later.
-mfsmuld
-mno-fsmuld
With ‘-mfsmuld’, GCC generates code that takes advantage of the
Floating-point Multiply Single to Double (FsMULd) instruction. The default
is ‘-mfsmuld’ when targeting a CPU supporting the architecture versions V8
or V9 with FPU except ‘-mcpu=leon’.
-mpopc
-mno-popc
With ‘-mpopc’, GCC generates code that takes advantage of the UltraSPARC
Population Count instruction. The default is ‘-mpopc’ when targeting a CPU
that supports such an instruction, such as Niagara-2 and later.
-msubxc
-mno-subxc
With ‘-msubxc’, GCC generates code that takes advantage of the UltraSPARC
Subtract-Extended-with-Carry instruction. The default is ‘-msubxc’ when targeting a CPU that supports such an instruction, such as Niagara-7 and later.
-mfix-at697f
Enable the documented workaround for the single erratum of the Atmel AT697F
processor (which corresponds to erratum #13 of the AT697E processor).
-mfix-ut699
Enable the documented workarounds for the floating-point errata and the data
cache nullify errata of the UT699 processor.
-mfix-ut700
Enable the documented workaround for the back-to-back store errata of the
UT699E/UT700 processor.
-mfix-gr712rc
Enable the documented workaround for the back-to-back store errata of the
GR712RC processor.
These ‘-m’ options are supported in addition to the above on SPARC-V9 processors in
64-bit environments:
-m32
-m64

Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets
int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and
long and pointer to 64 bits.

-mcmodel=which
Set the code model to one of

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‘medlow’

The Medium/Low code model: 64-bit addresses, programs must be
linked in the low 32 bits of memory. Programs can be statically or
dynamically linked.

‘medmid’

The Medium/Middle code model: 64-bit addresses, programs must
be linked in the low 44 bits of memory, the text and data segments
must be less than 2GB in size and the data segment must be located
within 2GB of the text segment.

‘medany’

The Medium/Anywhere code model: 64-bit addresses, programs
may be linked anywhere in memory, the text and data segments
must be less than 2GB in size and the data segment must be located
within 2GB of the text segment.

‘embmedany’
The Medium/Anywhere code model for embedded systems: 64-bit
addresses, the text and data segments must be less than 2GB in
size, both starting anywhere in memory (determined at link time).
The global register %g4 points to the base of the data segment.
Programs are statically linked and PIC is not supported.
-mmemory-model=mem-model
Set the memory model in force on the processor to one of
‘default’

The default memory model for the processor and operating system.

‘rmo’

Relaxed Memory Order

‘pso’

Partial Store Order

‘tso’

Total Store Order

‘sc’

Sequential Consistency

These memory models are formally defined in Appendix D of the SPARC-V9
architecture manual, as set in the processor’s PSTATE.MM field.
-mstack-bias
-mno-stack-bias
With ‘-mstack-bias’, GCC assumes that the stack pointer, and frame pointer
if present, are offset by −2047 which must be added back when making stack
frame references. This is the default in 64-bit mode. Otherwise, assume no
such offset is present.

3.18.47 SPU Options
These ‘-m’ options are supported on the SPU:
-mwarn-reloc
-merror-reloc
The loader for SPU does not handle dynamic relocations. By default, GCC
gives an error when it generates code that requires a dynamic relocation.
‘-mno-error-reloc’ disables the error, ‘-mwarn-reloc’ generates a warning
instead.

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-msafe-dma
-munsafe-dma
Instructions that initiate or test completion of DMA must not be reordered
with respect to loads and stores of the memory that is being accessed. With
‘-munsafe-dma’ you must use the volatile keyword to protect memory accesses, but that can lead to inefficient code in places where the memory is
known to not change. Rather than mark the memory as volatile, you can use
‘-msafe-dma’ to tell the compiler to treat the DMA instructions as potentially
affecting all memory.
-mbranch-hints
By default, GCC generates a branch hint instruction to avoid pipeline stalls for
always-taken or probably-taken branches. A hint is not generated closer than 8
instructions away from its branch. There is little reason to disable them, except
for debugging purposes, or to make an object a little bit smaller.
-msmall-mem
-mlarge-mem
By default, GCC generates code assuming that addresses are never larger than
18 bits. With ‘-mlarge-mem’ code is generated that assumes a full 32-bit address.
-mstdmain
By default, GCC links against startup code that assumes the SPU-style
main function interface (which has an unconventional parameter list). With
‘-mstdmain’, GCC links your program against startup code that assumes a
C99-style interface to main, including a local copy of argv strings.
-mfixed-range=register-range
Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling
kernel code. A register range is specified as two registers separated by a dash.
Multiple register ranges can be specified separated by a comma.
-mea32
-mea64

Compile code assuming that pointers to the PPU address space accessed via the
__ea named address space qualifier are either 32 or 64 bits wide. The default
is 32 bits. As this is an ABI-changing option, all object code in an executable
must be compiled with the same setting.

-maddress-space-conversion
-mno-address-space-conversion
Allow/disallow treating the __ea address space as superset of the generic address space. This enables explicit type casts between __ea and generic pointer
as well as implicit conversions of generic pointers to __ea pointers. The default
is to allow address space pointer conversions.
-mcache-size=cache-size
This option controls the version of libgcc that the compiler links to an executable
and selects a software-managed cache for accessing variables in the __ea address

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space with a particular cache size. Possible options for cache-size are ‘8’, ‘16’,
‘32’, ‘64’ and ‘128’. The default cache size is 64KB.
-matomic-updates
-mno-atomic-updates
This option controls the version of libgcc that the compiler links to an executable
and selects whether atomic updates to the software-managed cache of PPU-side
variables are used. If you use atomic updates, changes to a PPU variable from
SPU code using the __ea named address space qualifier do not interfere with
changes to other PPU variables residing in the same cache line from PPU code.
If you do not use atomic updates, such interference may occur; however, writing
back cache lines is more efficient. The default behavior is to use atomic updates.
-mdual-nops
-mdual-nops=n
By default, GCC inserts NOPs to increase dual issue when it expects it to
increase performance. n can be a value from 0 to 10. A smaller n inserts fewer
NOPs. 10 is the default, 0 is the same as ‘-mno-dual-nops’. Disabled with
‘-Os’.
-mhint-max-nops=n
Maximum number of NOPs to insert for a branch hint. A branch hint must be
at least 8 instructions away from the branch it is affecting. GCC inserts up to
n NOPs to enforce this, otherwise it does not generate the branch hint.
-mhint-max-distance=n
The encoding of the branch hint instruction limits the hint to be within 256
instructions of the branch it is affecting. By default, GCC makes sure it is
within 125.
-msafe-hints
Work around a hardware bug that causes the SPU to stall indefinitely. By
default, GCC inserts the hbrp instruction to make sure this stall won’t happen.

3.18.48 Options for System V
These additional options are available on System V Release 4 for compatibility with other
compilers on those systems:
-G

Create a shared object. It is recommended that ‘-symbolic’ or ‘-shared’ be
used instead.

-Qy

Identify the versions of each tool used by the compiler, in a .ident assembler
directive in the output.

-Qn

Refrain from adding .ident directives to the output file (this is the default).

-YP,dirs

Search the directories dirs, and no others, for libraries specified with ‘-l’.

-Ym,dir

Look in the directory dir to find the M4 preprocessor. The assembler uses this
option.

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3.18.49 TILE-Gx Options
These ‘-m’ options are supported on the TILE-Gx:
-mcmodel=small
Generate code for the small model. The distance for direct calls is limited to
500M in either direction. PC-relative addresses are 32 bits. Absolute addresses
support the full address range.
-mcmodel=large
Generate code for the large model. There is no limitation on call distance,
pc-relative addresses, or absolute addresses.
-mcpu=name
Selects the type of CPU to be targeted. Currently the only supported type is
‘tilegx’.
-m32
-m64

Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets
int, long, and pointer to 32 bits. The 64-bit environment sets int to 32 bits and
long and pointer to 64 bits.

-mbig-endian
-mlittle-endian
Generate code in big/little endian mode, respectively.

3.18.50 TILEPro Options
These ‘-m’ options are supported on the TILEPro:
-mcpu=name
Selects the type of CPU to be targeted. Currently the only supported type is
‘tilepro’.
-m32

Generate code for a 32-bit environment, which sets int, long, and pointer to 32
bits. This is the only supported behavior so the flag is essentially ignored.

3.18.51 V850 Options
These ‘-m’ options are defined for V850 implementations:
-mlong-calls
-mno-long-calls
Treat all calls as being far away (near). If calls are assumed to be far away, the
compiler always loads the function’s address into a register, and calls indirect
through the pointer.
-mno-ep
-mep

Do not optimize (do optimize) basic blocks that use the same index pointer 4
or more times to copy pointer into the ep register, and use the shorter sld and
sst instructions. The ‘-mep’ option is on by default if you optimize.

-mno-prolog-function
-mprolog-function
Do not use (do use) external functions to save and restore registers at the
prologue and epilogue of a function. The external functions are slower, but use

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less code space if more than one function saves the same number of registers.
The ‘-mprolog-function’ option is on by default if you optimize.
-mspace

Try to make the code as small as possible. At present, this just turns on the
‘-mep’ and ‘-mprolog-function’ options.

-mtda=n

Put static or global variables whose size is n bytes or less into the tiny data
area that register ep points to. The tiny data area can hold up to 256 bytes in
total (128 bytes for byte references).

-msda=n

Put static or global variables whose size is n bytes or less into the small data
area that register gp points to. The small data area can hold up to 64 kilobytes.

-mzda=n

Put static or global variables whose size is n bytes or less into the first 32
kilobytes of memory.

-mv850

Specify that the target processor is the V850.

-mv850e3v5
Specify that the target processor is the V850E3V5. The preprocessor constant
__v850e3v5__ is defined if this option is used.
-mv850e2v4
Specify that the target processor is the V850E3V5. This is an alias for the
‘-mv850e3v5’ option.
-mv850e2v3
Specify that the target processor is the V850E2V3. The preprocessor constant
__v850e2v3__ is defined if this option is used.
-mv850e2

Specify that the target processor is the V850E2. The preprocessor constant
__v850e2__ is defined if this option is used.

-mv850e1

Specify that the target processor is the V850E1. The preprocessor constants
__v850e1__ and __v850e__ are defined if this option is used.

-mv850es

Specify that the target processor is the V850ES. This is an alias for the
‘-mv850e1’ option.

-mv850e

Specify that the target processor is the V850E. The preprocessor constant
__v850e__ is defined if this option is used.
If neither ‘-mv850’ nor ‘-mv850e’ nor ‘-mv850e1’ nor ‘-mv850e2’ nor
‘-mv850e2v3’ nor ‘-mv850e3v5’ are defined then a default target processor is
chosen and the relevant ‘__v850*__’ preprocessor constant is defined.
The preprocessor constants __v850 and __v851__ are always defined, regardless
of which processor variant is the target.

-mdisable-callt
-mno-disable-callt
This option suppresses generation of the CALLT instruction for the v850e,
v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850 architecture.
This option is enabled by default when the RH850 ABI is in use (see
‘-mrh850-abi’), and disabled by default when the GCC ABI is in use. If
CALLT instructions are being generated then the C preprocessor symbol
__V850_CALLT__ is defined.

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-mrelax
-mno-relax
Pass on (or do not pass on) the ‘-mrelax’ command-line option to the assembler.
-mlong-jumps
-mno-long-jumps
Disable (or re-enable) the generation of PC-relative jump instructions.
-msoft-float
-mhard-float
Disable (or re-enable) the generation of hardware floating point instructions.
This option is only significant when the target architecture is ‘V850E2V3’ or
higher. If hardware floating point instructions are being generated then the C
preprocessor symbol __FPU_OK__ is defined, otherwise the symbol __NO_FPU__
is defined.
-mloop

Enables the use of the e3v5 LOOP instruction. The use of this instruction is
not enabled by default when the e3v5 architecture is selected because its use is
still experimental.

-mrh850-abi
-mghs
Enables support for the RH850 version of the V850 ABI. This is the default.
With this version of the ABI the following rules apply:
• Integer sized structures and unions are returned via a memory pointer
rather than a register.
• Large structures and unions (more than 8 bytes in size) are passed by value.
• Functions are aligned to 16-bit boundaries.
• The ‘-m8byte-align’ command-line option is supported.
• The ‘-mdisable-callt’ command-line option is enabled by default. The
‘-mno-disable-callt’ command-line option is not supported.
When this version of the ABI is enabled the C preprocessor symbol __V850_
RH850_ABI__ is defined.
-mgcc-abi
Enables support for the old GCC version of the V850 ABI. With this version
of the ABI the following rules apply:
• Integer sized structures and unions are returned in register r10.
• Large structures and unions (more than 8 bytes in size) are passed by
reference.
• Functions are aligned to 32-bit boundaries, unless optimizing for size.
• The ‘-m8byte-align’ command-line option is not supported.
• The ‘-mdisable-callt’ command-line option is supported but not enabled
by default.
When this version of the ABI is enabled the C preprocessor symbol __V850_
GCC_ABI__ is defined.

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-m8byte-align
-mno-8byte-align
Enables support for double and long long types to be aligned on 8-byte boundaries. The default is to restrict the alignment of all objects to at most 4-bytes.
When ‘-m8byte-align’ is in effect the C preprocessor symbol __V850_8BYTE_
ALIGN__ is defined.
-mbig-switch
Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table.
-mapp-regs
This option causes r2 and r5 to be used in the code generated by the compiler.
This setting is the default.
-mno-app-regs
This option causes r2 and r5 to be treated as fixed registers.

3.18.52 VAX Options
These ‘-m’ options are defined for the VAX:
-munix

Do not output certain jump instructions (aobleq and so on) that the Unix
assembler for the VAX cannot handle across long ranges.

-mgnu

Do output those jump instructions, on the assumption that the GNU assembler
is being used.

-mg

Output code for G-format floating-point numbers instead of D-format.

3.18.53 Visium Options
-mdebug

A program which performs file I/O and is destined to run on an MCM target
should be linked with this option. It causes the libraries libc.a and libdebug.a
to be linked. The program should be run on the target under the control of the
GDB remote debugging stub.

-msim

A program which performs file I/O and is destined to run on the simulator
should be linked with option. This causes libraries libc.a and libsim.a to be
linked.

-mfpu
-mhard-float
Generate code containing floating-point instructions. This is the default.
-mno-fpu
-msoft-float
Generate code containing library calls for floating-point.
‘-msoft-float’ changes the calling convention in the output file; therefore, it
is only useful if you compile all of a program with this option. In particular, you need to compile ‘libgcc.a’, the library that comes with GCC, with
‘-msoft-float’ in order for this to work.

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Using the GNU Compiler Collection (GCC)

-mcpu=cpu_type
Set the instruction set, register set, and instruction scheduling parameters for
machine type cpu type. Supported values for cpu type are ‘mcm’, ‘gr5’ and
‘gr6’.
‘mcm’ is a synonym of ‘gr5’ present for backward compatibility.
By default (unless configured otherwise), GCC generates code for the GR5
variant of the Visium architecture.
With ‘-mcpu=gr6’, GCC generates code for the GR6 variant of the Visium
architecture. The only difference from GR5 code is that the compiler will
generate block move instructions.
-mtune=cpu_type
Set the instruction scheduling parameters for machine type cpu type, but do
not set the instruction set or register set that the option ‘-mcpu=cpu_type’
would.
-msv-mode
Generate code for the supervisor mode, where there are no restrictions on the
access to general registers. This is the default.
-muser-mode
Generate code for the user mode, where the access to some general registers is
forbidden: on the GR5, registers r24 to r31 cannot be accessed in this mode;
on the GR6, only registers r29 to r31 are affected.

3.18.54 VMS Options
These ‘-m’ options are defined for the VMS implementations:
-mvms-return-codes
Return VMS condition codes from main. The default is to return POSIX-style
condition (e.g. error) codes.
-mdebug-main=prefix
Flag the first routine whose name starts with prefix as the main routine for the
debugger.
-mmalloc64
Default to 64-bit memory allocation routines.
-mpointer-size=size
Set the default size of pointers. Possible options for size are ‘32’ or ‘short’ for
32 bit pointers, ‘64’ or ‘long’ for 64 bit pointers, and ‘no’ for supporting only
32 bit pointers. The later option disables pragma pointer_size.

3.18.55 VxWorks Options
The options in this section are defined for all VxWorks targets. Options specific to the
target hardware are listed with the other options for that target.
-mrtp

GCC can generate code for both VxWorks kernels and real time processes
(RTPs). This option switches from the former to the latter. It also defines
the preprocessor macro __RTP__.

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-non-static
Link an RTP executable against shared libraries rather than static libraries.
The options ‘-static’ and ‘-shared’ can also be used for RTPs (see Section 3.14
[Link Options], page 195); ‘-static’ is the default.
-Bstatic
-Bdynamic
These options are passed down to the linker. They are defined for compatibility
with Diab.
-Xbind-lazy
Enable lazy binding of function calls. This option is equivalent to ‘-Wl,-z,now’
and is defined for compatibility with Diab.
-Xbind-now
Disable lazy binding of function calls. This option is the default and is defined
for compatibility with Diab.

3.18.56 x86 Options
These ‘-m’ options are defined for the x86 family of computers.
-march=cpu-type
Generate instructions for the machine type cpu-type.
In contrast to
‘-mtune=cpu-type’, which merely tunes the generated code for the specified
cpu-type, ‘-march=cpu-type’ allows GCC to generate code that may
not run at all on processors other than the one indicated. Specifying
‘-march=cpu-type’ implies ‘-mtune=cpu-type’.
The choices for cpu-type are:
‘native’

This selects the CPU to generate code for at compilation time by
determining the processor type of the compiling machine. Using
‘-march=native’ enables all instruction subsets supported by the
local machine (hence the result might not run on different machines). Using ‘-mtune=native’ produces code optimized for the
local machine under the constraints of the selected instruction set.

‘x86-64’

A generic CPU with 64-bit extensions.

‘i386’

Original Intel i386 CPU.

‘i486’

Intel i486 CPU. (No scheduling is implemented for this chip.)

‘i586’
‘pentium’

Intel Pentium CPU with no MMX support.

‘lakemont’
Intel Lakemont MCU, based on Intel Pentium CPU.
‘pentium-mmx’
Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support.
‘pentiumpro’
Intel Pentium Pro CPU.

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Using the GNU Compiler Collection (GCC)

‘i686’

When used with ‘-march’, the Pentium Pro instruction set is used,
so the code runs on all i686 family chips. When used with ‘-mtune’,
it has the same meaning as ‘generic’.

‘pentium2’
Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set support.
‘pentium3’
‘pentium3m’
Intel Pentium III CPU, based on Pentium Pro core with MMX and
SSE instruction set support.
‘pentium-m’
Intel Pentium M; low-power version of Intel Pentium III CPU with
MMX, SSE and SSE2 instruction set support. Used by Centrino
notebooks.
‘pentium4’
‘pentium4m’
Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set
support.
‘prescott’
Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2
and SSE3 instruction set support.
‘nocona’

Improved version of Intel Pentium 4 CPU with 64-bit extensions,
MMX, SSE, SSE2 and SSE3 instruction set support.

‘core2’

Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3
and SSSE3 instruction set support.

‘nehalem’

Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2,
SSE3, SSSE3, SSE4.1, SSE4.2 and POPCNT instruction set support.

‘westmere’
Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2,
SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction set support.
‘sandybridge’
Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE,
SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES and
PCLMUL instruction set support.
‘ivybridge’
Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL,
FSGSBASE, RDRND and F16C instruction set support.
‘haswell’

Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE,
SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2,

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AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2 and
F16C instruction set support.
‘broadwell’
Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE,
SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2,
AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C,
RDSEED, ADCX and PREFETCHW instruction set support.
‘skylake’

Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE,
SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2,
AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C,
RDSEED, ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC and
XSAVES instruction set support.

‘bonnell’

Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE,
SSE2, SSE3 and SSSE3 instruction set support.

‘silvermont’
Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE,
SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PCLMUL
and RDRND instruction set support.
‘knl’

Intel Knight’s Landing CPU with 64-bit extensions, MOVBE,
MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT,
AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI,
BMI2, F16C, RDSEED, ADCX, PREFETCHW, AVX512F,
AVX512PF, AVX512ER and AVX512CD instruction set support.

‘knm’

Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX,
SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX,
AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2,
F16C, RDSEED, ADCX, PREFETCHW, AVX512F, AVX512PF,
AVX512ER, AVX512CD, AVX5124VNNIW, AVX5124FMAPS
and AVX512VPOPCNTDQ instruction set support.

‘skylake-avx512’
Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX,
SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU,
AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI,
BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT,
XSAVEC, XSAVES, AVX512F, CLWB, AVX512VL, AVX512BW,
AVX512DQ and AVX512CD instruction set support.
‘cannonlake’
Intel Cannonlake Server CPU with 64-bit extensions, MOVBE,
MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT,
PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND,
FMA, BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW,
CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
AVX512BW,
AVX512DQ,
AVX512CD,
AVX512VBMI,
AVX512IFMA, SHA and UMIP instruction set support.

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‘icelake-client’
Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX,
SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU,
AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI,
BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT,
XSAVEC, XSAVES, AVX512F, AVX512VL, AVX512BW,
AVX512DQ,
AVX512CD,
AVX512VBMI,
AVX512IFMA,
SHA, CLWB, UMIP, RDPID, GFNI, AVX512VBMI2,
AVX512VPOPCNTDQ,
AVX512BITALG,
AVX512VNNI,
VPCLMULQDQ, VAES instruction set support.
‘icelake-server’
Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX,
SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU,
AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI,
BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT,
XSAVEC, XSAVES, AVX512F, AVX512VL, AVX512BW,
AVX512DQ,
AVX512CD,
AVX512VBMI,
AVX512IFMA,
SHA, CLWB, UMIP, RDPID, GFNI, AVX512VBMI2,
AVX512VPOPCNTDQ,
AVX512BITALG,
AVX512VNNI,
VPCLMULQDQ, VAES, PCONFIG and WBNOINVD instruction
set support.
‘k6’
‘k6-2’
‘k6-3’

AMD K6 CPU with MMX instruction set support.

Improved versions of AMD K6 CPU with MMX and 3DNow! instruction set support.

‘athlon’
‘athlon-tbird’
AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and
SSE prefetch instructions support.
‘athlon-4’
‘athlon-xp’
‘athlon-mp’
Improved AMD Athlon CPU with MMX, 3DNow!, enhanced
3DNow! and full SSE instruction set support.
‘k8’
‘opteron’
‘athlon64’
‘athlon-fx’
Processors based on the AMD K8 core with x86-64 instruction set
support, including the AMD Opteron, Athlon 64, and Athlon 64 FX
processors. (This supersets MMX, SSE, SSE2, 3DNow!, enhanced
3DNow! and 64-bit instruction set extensions.)

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‘k8-sse3’
‘opteron-sse3’
‘athlon64-sse3’
Improved versions of AMD K8 cores with SSE3 instruction set support.
‘amdfam10’
‘barcelona’
CPUs based on AMD Family 10h cores with x86-64 instruction
set support. (This supersets MMX, SSE, SSE2, SSE3, SSE4A,
3DNow!, enhanced 3DNow!, ABM and 64-bit instruction set extensions.)
‘bdver1’

CPUs based on AMD Family 15h cores with x86-64 instruction
set support. (This supersets FMA4, AVX, XOP, LWP, AES,
PCL MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)

‘bdver2’

AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP,
LWP, AES, PCL MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,
SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)

‘bdver3’

AMD Family 15h core based CPUs with x86-64 instruction set
support. (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES, PCL MUL, CX16, MMX, SSE,
SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.

‘bdver4’

AMD Family 15h core based CPUs with x86-64 instruction set
support. (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4,
FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCL MUL, CX16,
MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
SSE4.2, ABM and 64-bit instruction set extensions.

‘znver1’

AMD Family 17h core based CPUs with x86-64 instruction set
support. (This supersets BMI, BMI2, F16C, FMA, FSGSBASE,
AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO,
AES, PCL MUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3,
SSE4A, SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES,
CLFLUSHOPT, POPCNT, and 64-bit instruction set extensions.

‘btver1’

CPUs based on AMD Family 14h cores with x86-64 instruction set
support. (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A,
CX16, ABM and 64-bit instruction set extensions.)

‘btver2’

CPUs based on AMD Family 16h cores with x86-64 instruction set
support. This includes MOVBE, F16C, BMI, AVX, PCL MUL,
AES, SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2,
SSE, MMX and 64-bit instruction set extensions.

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‘winchip-c6’
IDT WinChip C6 CPU, dealt in same way as i486 with additional
MMX instruction set support.
‘winchip2’
IDT WinChip 2 CPU, dealt in same way as i486 with additional
MMX and 3DNow! instruction set support.
‘c3’

VIA C3 CPU with MMX and 3DNow! instruction set support. (No
scheduling is implemented for this chip.)

‘c3-2’

VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction
set support. (No scheduling is implemented for this chip.)

‘c7’

VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction
set support. (No scheduling is implemented for this chip.)

‘samuel-2’
VIA Eden Samuel 2 CPU with MMX and 3DNow! instruction set
support. (No scheduling is implemented for this chip.)
‘nehemiah’
VIA Eden Nehemiah CPU with MMX and SSE instruction set support. (No scheduling is implemented for this chip.)
‘esther’

VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction set support. (No scheduling is implemented for this chip.)

‘eden-x2’

VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3 instruction set support. (No scheduling is implemented for this chip.)

‘eden-x4’

VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3,
SSE4.1, SSE4.2, AVX and AVX2 instruction set support. (No
scheduling is implemented for this chip.)

‘nano’

Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and
SSSE3 instruction set support. (No scheduling is implemented for
this chip.)

‘nano-1000’
VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and
SSSE3 instruction set support. (No scheduling is implemented for
this chip.)
‘nano-2000’
VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and
SSSE3 instruction set support. (No scheduling is implemented for
this chip.)
‘nano-3000’
VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3
and SSE4.1 instruction set support. (No scheduling is implemented
for this chip.)

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‘nano-x2’

VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3,
SSSE3 and SSE4.1 instruction set support. (No scheduling is implemented for this chip.)

‘nano-x4’

VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3,
SSSE3 and SSE4.1 instruction set support. (No scheduling is implemented for this chip.)

‘geode’

AMD Geode embedded processor with MMX and 3DNow! instruction set support.

-mtune=cpu-type
Tune to cpu-type everything applicable about the generated code, except for
the ABI and the set of available instructions. While picking a specific cpu-type
schedules things appropriately for that particular chip, the compiler does not
generate any code that cannot run on the default machine type unless you use
a ‘-march=cpu-type’ option. For example, if GCC is configured for i686-pclinux-gnu then ‘-mtune=pentium4’ generates code that is tuned for Pentium 4
but still runs on i686 machines.
The choices for cpu-type are the same as for ‘-march’. In addition, ‘-mtune’
supports 2 extra choices for cpu-type:
‘generic’

Produce code optimized for the most common IA32/AMD64/
EM64T processors. If you know the CPU on which your code will
run, then you should use the corresponding ‘-mtune’ or ‘-march’
option instead of ‘-mtune=generic’. But, if you do not know
exactly what CPU users of your application will have, then you
should use this option.
As new processors are deployed in the marketplace, the behavior of
this option will change. Therefore, if you upgrade to a newer version
of GCC, code generation controlled by this option will change to
reflect the processors that are most common at the time that version
of GCC is released.
There is no ‘-march=generic’ option because ‘-march’ indicates
the instruction set the compiler can use, and there is no generic
instruction set applicable to all processors. In contrast, ‘-mtune’
indicates the processor (or, in this case, collection of processors) for
which the code is optimized.

‘intel’

Produce code optimized for the most current Intel processors, which
are Haswell and Silvermont for this version of GCC. If you know
the CPU on which your code will run, then you should use the corresponding ‘-mtune’ or ‘-march’ option instead of ‘-mtune=intel’.
But, if you want your application performs better on both Haswell
and Silvermont, then you should use this option.
As new Intel processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a
newer version of GCC, code generation controlled by this option

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will change to reflect the most current Intel processors at the time
that version of GCC is released.
There is no ‘-march=intel’ option because ‘-march’ indicates the
instruction set the compiler can use, and there is no common instruction set applicable to all processors. In contrast, ‘-mtune’
indicates the processor (or, in this case, collection of processors)
for which the code is optimized.
-mcpu=cpu-type
A deprecated synonym for ‘-mtune’.
-mfpmath=unit
Generate floating-point arithmetic for selected unit unit. The choices for unit
are:
‘387’

Use the standard 387 floating-point coprocessor present on the majority of chips and emulated otherwise. Code compiled with this
option runs almost everywhere. The temporary results are computed in 80-bit precision instead of the precision specified by the
type, resulting in slightly different results compared to most of other
chips. See ‘-ffloat-store’ for more detailed description.
This is the default choice for non-Darwin x86-32 targets.

‘sse’

Use scalar floating-point instructions present in the SSE instruction
set. This instruction set is supported by Pentium III and newer
chips, and in the AMD line by Athlon-4, Athlon XP and Athlon MP
chips. The earlier version of the SSE instruction set supports only
single-precision arithmetic, thus the double and extended-precision
arithmetic are still done using 387. A later version, present only
in Pentium 4 and AMD x86-64 chips, supports double-precision
arithmetic too.
For the x86-32 compiler, you must use ‘-march=cpu-type’, ‘-msse’
or ‘-msse2’ switches to enable SSE extensions and make this option
effective. For the x86-64 compiler, these extensions are enabled by
default.
The resulting code should be considerably faster in the majority of
cases and avoid the numerical instability problems of 387 code, but
may break some existing code that expects temporaries to be 80
bits.
This is the default choice for the x86-64 compiler, Darwin x86-32
targets, and the default choice for x86-32 targets with the SSE2
instruction set when ‘-ffast-math’ is enabled.

‘sse,387’
‘sse+387’
‘both’

Attempt to utilize both instruction sets at once. This effectively
doubles the amount of available registers, and on chips with separate execution units for 387 and SSE the execution resources too.
Use this option with care, as it is still experimental, because the

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GCC register allocator does not model separate functional units
well, resulting in unstable performance.
-masm=dialect
Output assembly instructions using selected dialect. Also affects which dialect
is used for basic asm (see Section 6.45.1 [Basic Asm], page 542) and extended asm
(see Section 6.45.2 [Extended Asm], page 543). Supported choices (in dialect
order) are ‘att’ or ‘intel’. The default is ‘att’. Darwin does not support
‘intel’.
-mieee-fp
-mno-ieee-fp
Control whether or not the compiler uses IEEE floating-point comparisons.
These correctly handle the case where the result of a comparison is unordered.
-m80387
-mhard-float
Generate output containing 80387 instructions for floating point.
-mno-80387
-msoft-float
Generate output containing library calls for floating point.
Warning: the requisite libraries are not part of GCC. Normally the facilities
of the machine’s usual C compiler are used, but this cannot be done directly in
cross-compilation. You must make your own arrangements to provide suitable
library functions for cross-compilation.
On machines where a function returns floating-point results in the 80387 register
stack, some floating-point opcodes may be emitted even if ‘-msoft-float’ is
used.
-mno-fp-ret-in-387
Do not use the FPU registers for return values of functions.
The usual calling convention has functions return values of types float and
double in an FPU register, even if there is no FPU. The idea is that the
operating system should emulate an FPU.
The option ‘-mno-fp-ret-in-387’ causes such values to be returned in ordinary
CPU registers instead.
-mno-fancy-math-387
Some 387 emulators do not support the sin, cos and sqrt instructions for the
387. Specify this option to avoid generating those instructions. This option is
the default on OpenBSD and NetBSD. This option is overridden when ‘-march’
indicates that the target CPU always has an FPU and so the instruction does
not need emulation. These instructions are not generated unless you also use
the ‘-funsafe-math-optimizations’ switch.
-malign-double
-mno-align-double
Control whether GCC aligns double, long double, and long long variables on
a two-word boundary or a one-word boundary. Aligning double variables on a

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two-word boundary produces code that runs somewhat faster on a Pentium at
the expense of more memory.
On x86-64, ‘-malign-double’ is enabled by default.
Warning: if you use the ‘-malign-double’ switch, structures containing the
above types are aligned differently than the published application binary interface specifications for the x86-32 and are not binary compatible with structures
in code compiled without that switch.
-m96bit-long-double
-m128bit-long-double
These switches control the size of long double type. The x86-32 application
binary interface specifies the size to be 96 bits, so ‘-m96bit-long-double’ is
the default in 32-bit mode.
Modern architectures (Pentium and newer) prefer long double to be aligned
to an 8- or 16-byte boundary. In arrays or structures conforming to the ABI,
this is not possible. So specifying ‘-m128bit-long-double’ aligns long double
to a 16-byte boundary by padding the long double with an additional 32-bit
zero.
In the x86-64 compiler, ‘-m128bit-long-double’ is the default choice as its
ABI specifies that long double is aligned on 16-byte boundary.
Notice that neither of these options enable any extra precision over the x87
standard of 80 bits for a long double.
Warning: if you override the default value for your target ABI, this changes
the size of structures and arrays containing long double variables, as well as
modifying the function calling convention for functions taking long double.
Hence they are not binary-compatible with code compiled without that switch.
-mlong-double-64
-mlong-double-80
-mlong-double-128
These switches control the size of long double type. A size of 64 bits makes the
long double type equivalent to the double type. This is the default for 32-bit
Bionic C library. A size of 128 bits makes the long double type equivalent to
the __float128 type. This is the default for 64-bit Bionic C library.
Warning: if you override the default value for your target ABI, this changes
the size of structures and arrays containing long double variables, as well as
modifying the function calling convention for functions taking long double.
Hence they are not binary-compatible with code compiled without that switch.
-malign-data=type
Control how GCC aligns variables. Supported values for type are ‘compat’
uses increased alignment value compatible uses GCC 4.8 and earlier, ‘abi’ uses
alignment value as specified by the psABI, and ‘cacheline’ uses increased
alignment value to match the cache line size. ‘compat’ is the default.

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-mlarge-data-threshold=threshold
When ‘-mcmodel=medium’ is specified, data objects larger than threshold are
placed in the large data section. This value must be the same across all objects
linked into the binary, and defaults to 65535.
-mrtd

Use a different function-calling convention, in which functions that take a fixed
number of arguments return with the ret num instruction, which pops their
arguments while returning. This saves one instruction in the caller since there
is no need to pop the arguments there.
You can specify that an individual function is called with this calling sequence
with the function attribute stdcall. You can also override the ‘-mrtd’ option
by using the function attribute cdecl. See Section 6.31 [Function Attributes],
page 464.
Warning: this calling convention is incompatible with the one normally used on
Unix, so you cannot use it if you need to call libraries compiled with the Unix
compiler.
Also, you must provide function prototypes for all functions that take variable
numbers of arguments (including printf); otherwise incorrect code is generated
for calls to those functions.
In addition, seriously incorrect code results if you call a function with too many
arguments. (Normally, extra arguments are harmlessly ignored.)

-mregparm=num
Control how many registers are used to pass integer arguments. By default, no
registers are used to pass arguments, and at most 3 registers can be used. You
can control this behavior for a specific function by using the function attribute
regparm. See Section 6.31 [Function Attributes], page 464.
Warning: if you use this switch, and num is nonzero, then you must build all
modules with the same value, including any libraries. This includes the system
libraries and startup modules.
-msseregparm
Use SSE register passing conventions for float and double arguments and return
values. You can control this behavior for a specific function by using the function attribute sseregparm. See Section 6.31 [Function Attributes], page 464.
Warning: if you use this switch then you must build all modules with the same
value, including any libraries. This includes the system libraries and startup
modules.
-mvect8-ret-in-mem
Return 8-byte vectors in memory instead of MMX registers. This is the default
on Solaris 8 and 9 and VxWorks to match the ABI of the Sun Studio compilers
until version 12. Later compiler versions (starting with Studio 12 Update 1)
follow the ABI used by other x86 targets, which is the default on Solaris 10 and
later. Only use this option if you need to remain compatible with existing code
produced by those previous compiler versions or older versions of GCC.

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-mpc32
-mpc64
-mpc80
Set 80387 floating-point precision to 32, 64 or 80 bits. When ‘-mpc32’ is specified, the significands of results of floating-point operations are rounded to 24 bits
(single precision); ‘-mpc64’ rounds the significands of results of floating-point
operations to 53 bits (double precision) and ‘-mpc80’ rounds the significands
of results of floating-point operations to 64 bits (extended double precision),
which is the default. When this option is used, floating-point operations in
higher precisions are not available to the programmer without setting the FPU
control word explicitly.
Setting the rounding of floating-point operations to less than the default 80 bits
can speed some programs by 2% or more. Note that some mathematical libraries
assume that extended-precision (80-bit) floating-point operations are enabled
by default; routines in such libraries could suffer significant loss of accuracy,
typically through so-called “catastrophic cancellation”, when this option is used
to set the precision to less than extended precision.
-mstackrealign
Realign the stack at entry. On the x86, the ‘-mstackrealign’ option generates
an alternate prologue and epilogue that realigns the run-time stack if necessary.
This supports mixing legacy codes that keep 4-byte stack alignment with modern codes that keep 16-byte stack alignment for SSE compatibility. See also the
attribute force_align_arg_pointer, applicable to individual functions.
-mpreferred-stack-boundary=num
Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary.
If ‘-mpreferred-stack-boundary’ is not specified, the default is 4 (16 bytes or
128 bits).
Warning: When generating code for the x86-64 architecture with SSE extensions disabled, ‘-mpreferred-stack-boundary=3’ can be used to keep the stack
boundary aligned to 8 byte boundary. Since x86-64 ABI require 16 byte stack
alignment, this is ABI incompatible and intended to be used in controlled environment where stack space is important limitation. This option leads to wrong
code when functions compiled with 16 byte stack alignment (such as functions
from a standard library) are called with misaligned stack. In this case, SSE
instructions may lead to misaligned memory access traps. In addition, variable
arguments are handled incorrectly for 16 byte aligned objects (including x87
long double and int128), leading to wrong results. You must build all modules
with ‘-mpreferred-stack-boundary=3’, including any libraries. This includes
the system libraries and startup modules.
-mincoming-stack-boundary=num
Assume the incoming stack is aligned to a 2 raised to num byte boundary.
If ‘-mincoming-stack-boundary’ is not specified, the one specified by
‘-mpreferred-stack-boundary’ is used.
On Pentium and Pentium Pro, double and long double values should be
aligned to an 8-byte boundary (see ‘-malign-double’) or suffer significant run

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401

time performance penalties. On Pentium III, the Streaming SIMD Extension
(SSE) data type __m128 may not work properly if it is not 16-byte aligned.
To ensure proper alignment of this values on the stack, the stack boundary
must be as aligned as that required by any value stored on the stack. Further,
every function must be generated such that it keeps the stack aligned. Thus
calling a function compiled with a higher preferred stack boundary from a
function compiled with a lower preferred stack boundary most likely misaligns
the stack. It is recommended that libraries that use callbacks always use the
default setting.
This extra alignment does consume extra stack space, and generally increases
code size. Code that is sensitive to stack space usage, such as embedded systems
and operating system kernels, may want to reduce the preferred alignment to
‘-mpreferred-stack-boundary=2’.
-mmmx
-msse
-msse2
-msse3
-mssse3
-msse4
-msse4a
-msse4.1
-msse4.2
-mavx
-mavx2
-mavx512f
-mavx512pf
-mavx512er
-mavx512cd
-mavx512vl
-mavx512bw
-mavx512dq
-mavx512ifma
-mavx512vbmi
-msha
-maes
-mpclmul
-mclflushopt
-mfsgsbase
-mrdrnd
-mf16c
-mfma
-mpconfig
-mwbnoinvd
-mfma4
-mprefetchwt1
-mxop
-mlwp
-m3dnow
-m3dnowa
-mpopcnt

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Using the GNU Compiler Collection (GCC)

-mabm
-mbmi
-mbmi2
-mlzcnt
-mfxsr
-mxsave
-mxsaveopt
-mxsavec
-mxsaves
-mrtm
-mtbm
-mmpx
-mmwaitx
-mclzero
-mpku
-mavx512vbmi2
-mgfni
-mvaes
-mvpclmulqdq
-mavx512bitalg
-mmovdiri
-mmovdir64b
-mavx512vpopcntdq
These switches enable the use of instructions in the MMX, SSE, SSE2,
SSE3, SSSE3, SSE4.1, AVX, AVX2, AVX512F, AVX512PF, AVX512ER,
AVX512CD, SHA, AES, PCLMUL, FSGSBASE, RDRND, F16C, FMA,
SSE4A, FMA4, XOP, LWP, ABM, AVX512VL, AVX512BW, AVX512DQ,
AVX512IFMA, AVX512VBMI, BMI, BMI2, VAES, FXSR, XSAVE,
XSAVEOPT, LZCNT, RTM, MPX, MWAITX, PKU, IBT, SHSTK,
AVX512VBMI2, GFNI, VPCLMULQDQ, AVX512BITALG, MOVDIRI,
MOVDIR64B, AVX512VPOPCNTDQ3DNow! or enhanced 3DNow! extended
instruction sets. Each has a corresponding ‘-mno-’ option to disable use of
these instructions.
These extensions are also available as built-in functions: see Section 6.59.33 [x86
Built-in Functions], page 748, for details of the functions enabled and disabled
by these switches.
To generate SSE/SSE2 instructions automatically from floating-point code (as
opposed to 387 instructions), see ‘-mfpmath=sse’.
GCC depresses SSEx instructions when ‘-mavx’ is used. Instead, it generates new AVX instructions or AVX equivalence for all SSEx instructions when
needed.
These options enable GCC to use these extended instructions in generated
code, even without ‘-mfpmath=sse’. Applications that perform run-time CPU
detection must compile separate files for each supported architecture, using the
appropriate flags. In particular, the file containing the CPU detection code
should be compiled without these options.

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403

-mdump-tune-features
This option instructs GCC to dump the names of the x86 performance
tuning features and default settings.
The names can be used in
‘-mtune-ctrl=feature-list’.
-mtune-ctrl=feature-list
This option is used to do fine grain control of x86 code generation
features. feature-list is a comma separated list of feature names. See also
‘-mdump-tune-features’. When specified, the feature is turned on if it is not
preceded with ‘^’, otherwise, it is turned off. ‘-mtune-ctrl=feature-list’
is intended to be used by GCC developers. Using it may lead to code paths
not covered by testing and can potentially result in compiler ICEs or runtime
errors.
-mno-default
This option instructs GCC to turn off all tunable features.
‘-mtune-ctrl=feature-list’ and ‘-mdump-tune-features’.
-mcld

See also

This option instructs GCC to emit a cld instruction in the prologue of functions
that use string instructions. String instructions depend on the DF flag to select
between autoincrement or autodecrement mode. While the ABI specifies the
DF flag to be cleared on function entry, some operating systems violate this
specification by not clearing the DF flag in their exception dispatchers. The
exception handler can be invoked with the DF flag set, which leads to wrong
direction mode when string instructions are used. This option can be enabled
by default on 32-bit x86 targets by configuring GCC with the ‘--enable-cld’
configure option. Generation of cld instructions can be suppressed with the
‘-mno-cld’ compiler option in this case.

-mvzeroupper
This option instructs GCC to emit a vzeroupper instruction before a transfer of
control flow out of the function to minimize the AVX to SSE transition penalty
as well as remove unnecessary zeroupper intrinsics.
-mprefer-avx128
This option instructs GCC to use 128-bit AVX instructions instead of 256-bit
AVX instructions in the auto-vectorizer.
-mprefer-vector-width=opt
This option instructs GCC to use opt-bit vector width in instructions instead
of default on the selected platform.

-mcx16

‘none’

No extra limitations applied to GCC other than defined by the
selected platform.

‘128’

Prefer 128-bit vector width for instructions.

‘256’

Prefer 256-bit vector width for instructions.

‘512’

Prefer 512-bit vector width for instructions.

This option enables GCC to generate CMPXCHG16B instructions in 64-bit code
to implement compare-and-exchange operations on 16-byte aligned 128-bit objects. This is useful for atomic updates of data structures exceeding one machine

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word in size. The compiler uses this instruction to implement Section 6.52
[ sync Builtins], page 601. However, for Section 6.53 [ atomic Builtins],
page 603 operating on 128-bit integers, a library call is always used.
-msahf

This option enables generation of SAHF instructions in 64-bit code. Early Intel
Pentium 4 CPUs with Intel 64 support, prior to the introduction of Pentium
4 G1 step in December 2005, lacked the LAHF and SAHF instructions which are
supported by AMD64. These are load and store instructions, respectively, for
certain status flags. In 64-bit mode, the SAHF instruction is used to optimize
fmod, drem, and remainder built-in functions; see Section 6.58 [Other Builtins],
page 613 for details.

-mmovbe

This option enables use of the movbe instruction to implement __builtin_
bswap32 and __builtin_bswap64.

-mshstk

The ‘-mshstk’ option enables shadow stack built-in functions from x86 Controlflow Enforcement Technology (CET).

-mcrc32

This option enables built-in functions __builtin_ia32_crc32qi, __builtin_
ia32_crc32hi, __builtin_ia32_crc32si and __builtin_ia32_crc32di to
generate the crc32 machine instruction.

-mrecip

This option enables use of RCPSS and RSQRTSS instructions (and their
vectorized variants RCPPS and RSQRTPS) with an additional Newton-Raphson
step to increase precision instead of DIVSS and SQRTSS (and their vectorized
variants) for single-precision floating-point arguments. These instructions are
generated only when ‘-funsafe-math-optimizations’ is enabled together
with ‘-ffinite-math-only’ and ‘-fno-trapping-math’. Note that while the
throughput of the sequence is higher than the throughput of the non-reciprocal
instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e.
the inverse of 1.0 equals 0.99999994).
Note that GCC implements 1.0f/sqrtf(x) in terms of RSQRTSS (or RSQRTPS)
already with ‘-ffast-math’ (or the above option combination), and doesn’t
need ‘-mrecip’.
Also note that GCC emits the above sequence with additional Newton-Raphson
step for vectorized single-float division and vectorized sqrtf(x) already with
‘-ffast-math’ (or the above option combination), and doesn’t need ‘-mrecip’.

-mrecip=opt
This option controls which reciprocal estimate instructions may be used. opt
is a comma-separated list of options, which may be preceded by a ‘!’ to invert
the option:
‘all’

Enable all estimate instructions.

‘default’

Enable the default instructions, equivalent to ‘-mrecip’.

‘none’

Disable all estimate instructions, equivalent to ‘-mno-recip’.

‘div’

Enable the approximation for scalar division.

‘vec-div’

Enable the approximation for vectorized division.

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‘sqrt’

405

Enable the approximation for scalar square root.

‘vec-sqrt’
Enable the approximation for vectorized square root.
So, for example, ‘-mrecip=all,!sqrt’ enables all of the reciprocal approximations, except for square root.
-mveclibabi=type
Specifies the ABI type to use for vectorizing intrinsics using an external library. Supported values for type are ‘svml’ for the Intel short vector math
library and ‘acml’ for the AMD math core library. To use this option, both
‘-ftree-vectorize’ and ‘-funsafe-math-optimizations’ have to be enabled,
and an SVML or ACML ABI-compatible library must be specified at link time.
GCC currently emits calls to vmldExp2, vmldLn2, vmldLog102, vmldLog102,
vmldPow2, vmldTanh2, vmldTan2, vmldAtan2, vmldAtanh2, vmldCbrt2,
vmldSinh2, vmldSin2, vmldAsinh2, vmldAsin2, vmldCosh2, vmldCos2,
vmldAcosh2, vmldAcos2, vmlsExp4, vmlsLn4, vmlsLog104, vmlsLog104,
vmlsPow4, vmlsTanh4, vmlsTan4, vmlsAtan4, vmlsAtanh4, vmlsCbrt4,
vmlsSinh4, vmlsSin4, vmlsAsinh4, vmlsAsin4, vmlsCosh4, vmlsCos4,
vmlsAcosh4 and vmlsAcos4 for corresponding function type when
‘-mveclibabi=svml’ is used, and __vrd2_sin, __vrd2_cos, __vrd2_exp,
__vrd2_log, __vrd2_log2, __vrd2_log10, __vrs4_sinf, __vrs4_cosf,
__vrs4_expf, __vrs4_logf, __vrs4_log2f, __vrs4_log10f and __vrs4_powf
for the corresponding function type when ‘-mveclibabi=acml’ is used.
-mabi=name
Generate code for the specified calling convention. Permissible values are ‘sysv’
for the ABI used on GNU/Linux and other systems, and ‘ms’ for the Microsoft
ABI. The default is to use the Microsoft ABI when targeting Microsoft Windows
and the SysV ABI on all other systems. You can control this behavior for
specific functions by using the function attributes ms_abi and sysv_abi. See
Section 6.31 [Function Attributes], page 464.
-mforce-indirect-call
Force all calls to functions to be indirect. This is useful when using Intel
Processor Trace where it generates more precise timing information for function
calls.
-mcall-ms2sysv-xlogues
Due to differences in 64-bit ABIs, any Microsoft ABI function that calls a System V ABI function must consider RSI, RDI and XMM6-15 as clobbered. By
default, the code for saving and restoring these registers is emitted inline, resulting in fairly lengthy prologues and epilogues. Using ‘-mcall-ms2sysv-xlogues’
emits prologues and epilogues that use stubs in the static portion of libgcc to
perform these saves and restores, thus reducing function size at the cost of a
few extra instructions.

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-mtls-dialect=type
Generate code to access thread-local storage using the ‘gnu’ or ‘gnu2’ conventions. ‘gnu’ is the conservative default; ‘gnu2’ is more efficient, but it may add
compile- and run-time requirements that cannot be satisfied on all systems.
-mpush-args
-mno-push-args
Use PUSH operations to store outgoing parameters. This method is shorter
and usually equally fast as method using SUB/MOV operations and is enabled
by default. In some cases disabling it may improve performance because of
improved scheduling and reduced dependencies.
-maccumulate-outgoing-args
If enabled, the maximum amount of space required for outgoing arguments
is computed in the function prologue. This is faster on most modern CPUs
because of reduced dependencies, improved scheduling and reduced stack usage
when the preferred stack boundary is not equal to 2. The drawback is a notable
increase in code size. This switch implies ‘-mno-push-args’.
-mthreads
Support thread-safe exception handling on MinGW. Programs that rely
on thread-safe exception handling must compile and link all code with the
‘-mthreads’ option. When compiling, ‘-mthreads’ defines ‘-D_MT’; when
linking, it links in a special thread helper library ‘-lmingwthrd’ which cleans
up per-thread exception-handling data.
-mms-bitfields
-mno-ms-bitfields
Enable/disable bit-field layout compatible with the native Microsoft Windows
compiler.
If packed is used on a structure, or if bit-fields are used, it may be that the
Microsoft ABI lays out the structure differently than the way GCC normally
does. Particularly when moving packed data between functions compiled with
GCC and the native Microsoft compiler (either via function call or as data in
a file), it may be necessary to access either format.
This option is enabled by default for Microsoft Windows targets. This behavior can also be controlled locally by use of variable or type attributes. For
more information, see Section 6.32.16 [x86 Variable Attributes], page 524 and
Section 6.33.7 [x86 Type Attributes], page 532.
The Microsoft structure layout algorithm is fairly simple with the exception of
the bit-field packing. The padding and alignment of members of structures and
whether a bit-field can straddle a storage-unit boundary are determine by these
rules:
1. Structure members are stored sequentially in the order in which they are
declared: the first member has the lowest memory address and the last
member the highest.
2. Every data object has an alignment requirement. The alignment requirement for all data except structures, unions, and arrays is either the size of

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the object or the current packing size (specified with either the aligned
attribute or the pack pragma), whichever is less. For structures, unions,
and arrays, the alignment requirement is the largest alignment requirement
of its members. Every object is allocated an offset so that:
offset % alignment_requirement == 0

3. Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation
unit if the integral types are the same size and if the next bit-field fits into
the current allocation unit without crossing the boundary imposed by the
common alignment requirements of the bit-fields.
MSVC interprets zero-length bit-fields in the following ways:
1. If a zero-length bit-field is inserted between two bit-fields that are normally
coalesced, the bit-fields are not coalesced.
For example:
struct
{
unsigned long bf_1 : 12;
unsigned long : 0;
unsigned long bf_2 : 12;
} t1;

The size of t1 is 8 bytes with the zero-length bit-field. If the zero-length
bit-field were removed, t1’s size would be 4 bytes.
2. If a zero-length bit-field is inserted after a bit-field, foo, and the alignment
of the zero-length bit-field is greater than the member that follows it, bar,
bar is aligned as the type of the zero-length bit-field.
For example:
struct
{
char foo : 4;
short : 0;
char bar;
} t2;
struct
{
char foo : 4;
short : 0;
double bar;
} t3;

For t2, bar is placed at offset 2, rather than offset 1. Accordingly, the size
of t2 is 4. For t3, the zero-length bit-field does not affect the alignment of
bar or, as a result, the size of the structure.
Taking this into account, it is important to note the following:
1. If a zero-length bit-field follows a normal bit-field, the type of the zerolength bit-field may affect the alignment of the structure as whole. For
example, t2 has a size of 4 bytes, since the zero-length bit-field follows
a normal bit-field, and is of type short.
2. Even if a zero-length bit-field is not followed by a normal bit-field, it
may still affect the alignment of the structure:

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struct
{
char foo : 6;
long : 0;
} t4;

Here, t4 takes up 4 bytes.
3. Zero-length bit-fields following non-bit-field members are ignored:
struct
{
char foo;
long : 0;
char bar;
} t5;

Here, t5 takes up 2 bytes.
-mno-align-stringops
Do not align the destination of inlined string operations. This switch reduces
code size and improves performance in case the destination is already aligned,
but GCC doesn’t know about it.
-minline-all-stringops
By default GCC inlines string operations only when the destination is known to
be aligned to least a 4-byte boundary. This enables more inlining and increases
code size, but may improve performance of code that depends on fast memcpy,
strlen, and memset for short lengths.
-minline-stringops-dynamically
For string operations of unknown size, use run-time checks with inline code for
small blocks and a library call for large blocks.
-mstringop-strategy=alg
Override the internal decision heuristic for the particular algorithm to use for
inlining string operations. The allowed values for alg are:
‘rep_byte’
‘rep_4byte’
‘rep_8byte’
Expand using i386 rep prefix of the specified size.
‘byte_loop’
‘loop’
‘unrolled_loop’
Expand into an inline loop.
‘libcall’

Always use a library call.

-mmemcpy-strategy=strategy
Override the internal decision heuristic to decide if __builtin_memcpy
should be inlined and what inline algorithm to use when the expected
size of the copy operation is known. strategy is a comma-separated list of
alg:max size:dest align triplets. alg is specified in ‘-mstringop-strategy’,
max size specifies the max byte size with which inline algorithm alg is allowed.
For the last triplet, the max size must be -1. The max size of the triplets in

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409

the list must be specified in increasing order. The minimal byte size for alg is
0 for the first triplet and max_size + 1 of the preceding range.
-mmemset-strategy=strategy
The option is similar to ‘-mmemcpy-strategy=’ except that it is to control __
builtin_memset expansion.
-momit-leaf-frame-pointer
Don’t keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up, and restore frame pointers and makes an extra register
available in leaf functions. The option ‘-fomit-leaf-frame-pointer’ removes
the frame pointer for leaf functions, which might make debugging harder.
-mtls-direct-seg-refs
-mno-tls-direct-seg-refs
Controls whether TLS variables may be accessed with offsets from the TLS
segment register (%gs for 32-bit, %fs for 64-bit), or whether the thread base
pointer must be added. Whether or not this is valid depends on the operating
system, and whether it maps the segment to cover the entire TLS area.
For systems that use the GNU C Library, the default is on.
-msse2avx
-mno-sse2avx
Specify that the assembler should encode SSE instructions with VEX prefix.
The option ‘-mavx’ turns this on by default.
-mfentry
-mno-fentry
If profiling is active (‘-pg’), put the profiling counter call before the prologue.
Note: On x86 architectures the attribute ms_hook_prologue isn’t possible at
the moment for ‘-mfentry’ and ‘-pg’.
-mrecord-mcount
-mno-record-mcount
If profiling is active (‘-pg’), generate a mcount loc section that contains pointers to each profiling call. This is useful for automatically patching and out calls.
-mnop-mcount
-mno-nop-mcount
If profiling is active (‘-pg’), generate the calls to the profiling functions as NOPs.
This is useful when they should be patched in later dynamically. This is likely
only useful together with ‘-mrecord-mcount’.
-mskip-rax-setup
-mno-skip-rax-setup
When generating code for the x86-64 architecture with SSE extensions disabled,
‘-mskip-rax-setup’ can be used to skip setting up RAX register when there
are no variable arguments passed in vector registers.
Warning: Since RAX register is used to avoid unnecessarily saving vector registers on stack when passing variable arguments, the impacts of this option are
callees may waste some stack space, misbehave or jump to a random location.
GCC 4.4 or newer don’t have those issues, regardless the RAX register value.

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-m8bit-idiv
-mno-8bit-idiv
On some processors, like Intel Atom, 8-bit unsigned integer divide is much faster
than 32-bit/64-bit integer divide. This option generates a run-time check. If
both dividend and divisor are within range of 0 to 255, 8-bit unsigned integer
divide is used instead of 32-bit/64-bit integer divide.
-mavx256-split-unaligned-load
-mavx256-split-unaligned-store
Split 32-byte AVX unaligned load and store.
-mstack-protector-guard=guard
-mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset
Generate stack protection code using canary at guard. Supported locations
are ‘global’ for global canary or ‘tls’ for per-thread canary in the TLS block
(the default). This option has effect only when ‘-fstack-protector’ or
‘-fstack-protector-all’ is specified.
With the latter choice the options ‘-mstack-protector-guard-reg=reg’ and
‘-mstack-protector-guard-offset=offset’ furthermore specify which segment register (%fs or %gs) to use as base register for reading the canary, and
from what offset from that base register. The default for those is as specified
in the relevant ABI.
-mmitigate-rop
Try to avoid generating code sequences that contain unintended return opcodes,
to mitigate against certain forms of attack. At the moment, this option is limited in what it can do and should not be relied on to provide serious protection.
-mgeneral-regs-only
Generate code that uses only the general-purpose registers. This prevents the
compiler from using floating-point, vector, mask and bound registers.
-mindirect-branch=choice
Convert indirect call and jump with choice. The default is ‘keep’, which keeps
indirect call and jump unmodified. ‘thunk’ converts indirect call and jump
to call and return thunk. ‘thunk-inline’ converts indirect call and jump to
inlined call and return thunk. ‘thunk-extern’ converts indirect call and jump
to external call and return thunk provided in a separate object file. You can
control this behavior for a specific function by using the function attribute
indirect_branch. See Section 6.31 [Function Attributes], page 464.
Note that ‘-mcmodel=large’ is incompatible with ‘-mindirect-branch=thunk’
and ‘-mindirect-branch=thunk-extern’ since the thunk function may not be
reachable in the large code model.
Note that ‘-mindirect-branch=thunk-extern’ is incompatible with
‘-fcf-protection=branch’ and ‘-fcheck-pointer-bounds’ since the external
thunk can not be modified to disable control-flow check.

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-mfunction-return=choice
Convert function return with choice. The default is ‘keep’, which keeps function return unmodified. ‘thunk’ converts function return to call and return
thunk. ‘thunk-inline’ converts function return to inlined call and return
thunk. ‘thunk-extern’ converts function return to external call and return
thunk provided in a separate object file. You can control this behavior for
a specific function by using the function attribute function_return. See
Section 6.31 [Function Attributes], page 464.
Note that ‘-mcmodel=large’ is incompatible with ‘-mfunction-return=thunk’
and ‘-mfunction-return=thunk-extern’ since the thunk function may not be
reachable in the large code model.
-mindirect-branch-register
Force indirect call and jump via register.
These ‘-m’ switches are supported in addition to the above on x86-64 processors in 64-bit
environments.
-m32
-m64
-mx32
-m16
-miamcu

Generate code for a 16-bit, 32-bit or 64-bit environment. The ‘-m32’ option
sets int, long, and pointer types to 32 bits, and generates code that runs on
any i386 system.
The ‘-m64’ option sets int to 32 bits and long and pointer types to 64 bits, and
generates code for the x86-64 architecture. For Darwin only the ‘-m64’ option
also turns off the ‘-fno-pic’ and ‘-mdynamic-no-pic’ options.
The ‘-mx32’ option sets int, long, and pointer types to 32 bits, and generates
code for the x86-64 architecture.
The ‘-m16’ option is the same as ‘-m32’, except for that it outputs the
.code16gcc assembly directive at the beginning of the assembly output so
that the binary can run in 16-bit mode.
The ‘-miamcu’ option generates code which conforms to Intel MCU psABI. It
requires the ‘-m32’ option to be turned on.

-mno-red-zone
Do not use a so-called “red zone” for x86-64 code. The red zone is mandated by
the x86-64 ABI; it is a 128-byte area beyond the location of the stack pointer
that is not modified by signal or interrupt handlers and therefore can be used for
temporary data without adjusting the stack pointer. The flag ‘-mno-red-zone’
disables this red zone.
-mcmodel=small
Generate code for the small code model: the program and its symbols must be
linked in the lower 2 GB of the address space. Pointers are 64 bits. Programs
can be statically or dynamically linked. This is the default code model.

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-mcmodel=kernel
Generate code for the kernel code model. The kernel runs in the negative 2 GB
of the address space. This model has to be used for Linux kernel code.
-mcmodel=medium
Generate code for the medium model: the program is linked in the lower 2 GB
of the address space. Small symbols are also placed there. Symbols with sizes
larger than ‘-mlarge-data-threshold’ are put into large data or BSS sections
and can be located above 2GB. Programs can be statically or dynamically
linked.
-mcmodel=large
Generate code for the large model. This model makes no assumptions about
addresses and sizes of sections.
-maddress-mode=long
Generate code for long address mode. This is only supported for 64-bit and
x32 environments. It is the default address mode for 64-bit environments.
-maddress-mode=short
Generate code for short address mode. This is only supported for 32-bit and x32
environments. It is the default address mode for 32-bit and x32 environments.

3.18.57 x86 Windows Options
These additional options are available for Microsoft Windows targets:
-mconsole
This option specifies that a console application is to be generated, by instructing
the linker to set the PE header subsystem type required for console applications.
This option is available for Cygwin and MinGW targets and is enabled by
default on those targets.
-mdll

This option is available for Cygwin and MinGW targets. It specifies that a
DLL—a dynamic link library—is to be generated, enabling the selection of the
required runtime startup object and entry point.

-mnop-fun-dllimport
This option is available for Cygwin and MinGW targets. It specifies that the
dllimport attribute should be ignored.
-mthread

This option is available for MinGW targets. It specifies that MinGW-specific
thread support is to be used.

-municode
This option is available for MinGW-w64 targets. It causes the UNICODE preprocessor macro to be predefined, and chooses Unicode-capable runtime startup
code.
-mwin32

This option is available for Cygwin and MinGW targets. It specifies that the
typical Microsoft Windows predefined macros are to be set in the pre-processor,
but does not influence the choice of runtime library/startup code.

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413

-mwindows
This option is available for Cygwin and MinGW targets. It specifies that a GUI
application is to be generated by instructing the linker to set the PE header
subsystem type appropriately.
-fno-set-stack-executable
This option is available for MinGW targets. It specifies that the executable flag
for the stack used by nested functions isn’t set. This is necessary for binaries
running in kernel mode of Microsoft Windows, as there the User32 API, which
is used to set executable privileges, isn’t available.
-fwritable-relocated-rdata
This option is available for MinGW and Cygwin targets. It specifies that
relocated-data in read-only section is put into the .data section. This is a
necessary for older runtimes not supporting modification of .rdata sections for
pseudo-relocation.
-mpe-aligned-commons
This option is available for Cygwin and MinGW targets. It specifies that the
GNU extension to the PE file format that permits the correct alignment of
COMMON variables should be used when generating code. It is enabled by
default if GCC detects that the target assembler found during configuration
supports the feature.
See also under Section 3.18.56 [x86 Options], page 389 for standard options.

3.18.58 Xstormy16 Options
These options are defined for Xstormy16:
-msim

Choose startup files and linker script suitable for the simulator.

3.18.59 Xtensa Options
These options are supported for Xtensa targets:
-mconst16
-mno-const16
Enable or disable use of CONST16 instructions for loading constant values. The
CONST16 instruction is currently not a standard option from Tensilica. When
enabled, CONST16 instructions are always used in place of the standard L32R instructions. The use of CONST16 is enabled by default only if the L32R instruction
is not available.
-mfused-madd
-mno-fused-madd
Enable or disable use of fused multiply/add and multiply/subtract instructions
in the floating-point option. This has no effect if the floating-point option
is not also enabled. Disabling fused multiply/add and multiply/subtract instructions forces the compiler to use separate instructions for the multiply and
add/subtract operations. This may be desirable in some cases where strict
IEEE 754-compliant results are required: the fused multiply add/subtract instructions do not round the intermediate result, thereby producing results with

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more bits of precision than specified by the IEEE standard. Disabling fused
multiply add/subtract instructions also ensures that the program output is not
sensitive to the compiler’s ability to combine multiply and add/subtract operations.
-mserialize-volatile
-mno-serialize-volatile
When this option is enabled, GCC inserts MEMW instructions before volatile
memory references to guarantee sequential consistency.
The default is
‘-mserialize-volatile’. Use ‘-mno-serialize-volatile’ to omit the MEMW
instructions.
-mforce-no-pic
For targets, like GNU/Linux, where all user-mode Xtensa code must be
position-independent code (PIC), this option disables PIC for compiling kernel
code.
-mtext-section-literals
-mno-text-section-literals
These options control the treatment of literal pools.
The default is
‘-mno-text-section-literals’, which places literals in a separate section
in the output file. This allows the literal pool to be placed in a data
RAM/ROM, and it also allows the linker to combine literal pools from
separate object files to remove redundant literals and improve code size. With
‘-mtext-section-literals’, the literals are interspersed in the text section
in order to keep them as close as possible to their references. This may be
necessary for large assembly files. Literals for each function are placed right
before that function.
-mauto-litpools
-mno-auto-litpools
These options control the treatment of literal pools.
The default is
‘-mno-auto-litpools’, which places literals in a separate section in the output
file unless ‘-mtext-section-literals’ is used. With ‘-mauto-litpools’ the
literals are interspersed in the text section by the assembler. Compiler does
not produce explicit .literal directives and loads literals into registers with
MOVI instructions instead of L32R to let the assembler do relaxation and place
literals as necessary. This option allows assembler to create several literal
pools per function and assemble very big functions, which may not be possible
with ‘-mtext-section-literals’.
-mtarget-align
-mno-target-align
When this option is enabled, GCC instructs the assembler to automatically align
instructions to reduce branch penalties at the expense of some code density. The
assembler attempts to widen density instructions to align branch targets and the
instructions following call instructions. If there are not enough preceding safe
density instructions to align a target, no widening is performed. The default is
‘-mtarget-align’. These options do not affect the treatment of auto-aligned

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415

instructions like LOOP, which the assembler always aligns, either by widening
density instructions or by inserting NOP instructions.
-mlongcalls
-mno-longcalls
When this option is enabled, GCC instructs the assembler to translate direct
calls to indirect calls unless it can determine that the target of a direct call is
in the range allowed by the call instruction. This translation typically occurs
for calls to functions in other source files. Specifically, the assembler translates
a direct CALL instruction into an L32R followed by a CALLX instruction. The
default is ‘-mno-longcalls’. This option should be used in programs where the
call target can potentially be out of range. This option is implemented in the
assembler, not the compiler, so the assembly code generated by GCC still shows
direct call instructions—look at the disassembled object code to see the actual
instructions. Note that the assembler uses an indirect call for every cross-file
call, not just those that really are out of range.

3.18.60 zSeries Options
These are listed under See Section 3.18.42 [S/390 and zSeries Options], page 364.

3.19 Specifying Subprocesses and the Switches to Pass to
Them
gcc is a driver program. It performs its job by invoking a sequence of other programs to do
the work of compiling, assembling and linking. GCC interprets its command-line parameters
and uses these to deduce which programs it should invoke, and which command-line options
it ought to place on their command lines. This behavior is controlled by spec strings. In
most cases there is one spec string for each program that GCC can invoke, but a few
programs have multiple spec strings to control their behavior. The spec strings built into
GCC can be overridden by using the ‘-specs=’ command-line switch to specify a spec file.
Spec files are plain-text files that are used to construct spec strings. They consist of a
sequence of directives separated by blank lines. The type of directive is determined by the
first non-whitespace character on the line, which can be one of the following:
%command

Issues a command to the spec file processor. The commands that can appear
here are:
%include 
Search for file and insert its text at the current point in the specs
file.
%include_noerr 
Just like ‘%include’, but do not generate an error message if the
include file cannot be found.
%rename old_name new_name
Rename the spec string old name to new name.

*[spec_name]:
This tells the compiler to create, override or delete the named spec string. All
lines after this directive up to the next directive or blank line are considered to

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be the text for the spec string. If this results in an empty string then the spec
is deleted. (Or, if the spec did not exist, then nothing happens.) Otherwise, if
the spec does not currently exist a new spec is created. If the spec does exist
then its contents are overridden by the text of this directive, unless the first
character of that text is the ‘+’ character, in which case the text is appended
to the spec.
[suffix]:
Creates a new ‘[suffix] spec’ pair. All lines after this directive and up to the
next directive or blank line are considered to make up the spec string for the
indicated suffix. When the compiler encounters an input file with the named
suffix, it processes the spec string in order to work out how to compile that file.
For example:
.ZZ:
z-compile -input %i

This says that any input file whose name ends in ‘.ZZ’ should be passed to the
program ‘z-compile’, which should be invoked with the command-line switch
‘-input’ and with the result of performing the ‘%i’ substitution. (See below.)
As an alternative to providing a spec string, the text following a suffix directive
can be one of the following:
@language
This says that the suffix is an alias for a known language. This is
similar to using the ‘-x’ command-line switch to GCC to specify a
language explicitly. For example:
.ZZ:
@c++

Says that .ZZ files are, in fact, C++ source files.
#name

This causes an error messages saying:
name compiler not installed on this system.

GCC already has an extensive list of suffixes built into it. This directive adds
an entry to the end of the list of suffixes, but since the list is searched from
the end backwards, it is effectively possible to override earlier entries using this
technique.
GCC has the following spec strings built into it. Spec files can override these strings or
create their own. Note that individual targets can also add their own spec strings to this
list.
asm
asm_final
cpp
cc1
cc1plus
endfile
link
lib
libgcc
linker
predefines

Options to pass to the assembler
Options to pass to the assembler post-processor
Options to pass to the C preprocessor
Options to pass to the C compiler
Options to pass to the C++ compiler
Object files to include at the end of the link
Options to pass to the linker
Libraries to include on the command line to the linker
Decides which GCC support library to pass to the linker
Sets the name of the linker
Defines to be passed to the C preprocessor

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signed_char
startfile

417

Defines to pass to CPP to say whether char is signed
by default
Object files to include at the start of the link

Here is a small example of a spec file:
%rename lib

old_lib

*lib:
--start-group -lgcc -lc -leval1 --end-group %(old_lib)

This example renames the spec called ‘lib’ to ‘old_lib’ and then overrides the previous
definition of ‘lib’ with a new one. The new definition adds in some extra command-line
options before including the text of the old definition.
Spec strings are a list of command-line options to be passed to their corresponding program. In addition, the spec strings can contain ‘%’-prefixed sequences to substitute variable
text or to conditionally insert text into the command line. Using these constructs it is
possible to generate quite complex command lines.
Here is a table of all defined ‘%’-sequences for spec strings. Note that spaces are not
generated automatically around the results of expanding these sequences. Therefore you
can concatenate them together or combine them with constant text in a single argument.
%%

Substitute one ‘%’ into the program name or argument.

%i

Substitute the name of the input file being processed.

%b

Substitute the basename of the input file being processed. This is the substring
up to (and not including) the last period and not including the directory.

%B

This is the same as ‘%b’, but include the file suffix (text after the last period).

%d

Marks the argument containing or following the ‘%d’ as a temporary file name,
so that that file is deleted if GCC exits successfully. Unlike ‘%g’, this contributes
no text to the argument.

%gsuffix

Substitute a file name that has suffix suffix and is chosen once per compilation,
and mark the argument in the same way as ‘%d’. To reduce exposure to denialof-service attacks, the file name is now chosen in a way that is hard to predict
even when previously chosen file names are known. For example, ‘%g.s ...
%g.o ... %g.s’ might turn into ‘ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s’. suffix
matches the regexp ‘[.A-Za-z]*’ or the special string ‘%O’, which is treated
exactly as if ‘%O’ had been preprocessed. Previously, ‘%g’ was simply substituted
with a file name chosen once per compilation, without regard to any appended
suffix (which was therefore treated just like ordinary text), making such attacks
more likely to succeed.

%usuffix

Like ‘%g’, but generates a new temporary file name each time it appears instead
of once per compilation.

%Usuffix

Substitutes the last file name generated with ‘%usuffix’, generating a new
one if there is no such last file name. In the absence of any ‘%usuffix’, this
is just like ‘%gsuffix’, except they don’t share the same suffix space, so ‘%g.s
... %U.s ... %g.s ... %U.s’ involves the generation of two distinct file names,
one for each ‘%g.s’ and another for each ‘%U.s’. Previously, ‘%U’ was simply

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substituted with a file name chosen for the previous ‘%u’, without regard to any
appended suffix.
%jsuffix

%|suffix
%msuffix

Substitutes the name of the HOST_BIT_BUCKET, if any, and if it is writable, and
if ‘-save-temps’ is not used; otherwise, substitute the name of a temporary
file, just like ‘%u’. This temporary file is not meant for communication between
processes, but rather as a junk disposal mechanism.
Like ‘%g’, except if ‘-pipe’ is in effect. In that case ‘%|’ substitutes a single
dash and ‘%m’ substitutes nothing at all. These are the two most common
ways to instruct a program that it should read from standard input or write
to standard output. If you need something more elaborate you can use an
‘%{pipe:X}’ construct: see for example ‘f/lang-specs.h’.

%.SUFFIX

Substitutes .SUFFIX for the suffixes of a matched switch’s args when it is
subsequently output with ‘%*’. SUFFIX is terminated by the next space or %.

%w

Marks the argument containing or following the ‘%w’ as the designated output
file of this compilation. This puts the argument into the sequence of arguments
that ‘%o’ substitutes.

%o

Substitutes the names of all the output files, with spaces automatically placed
around them. You should write spaces around the ‘%o’ as well or the results are
undefined. ‘%o’ is for use in the specs for running the linker. Input files whose
names have no recognized suffix are not compiled at all, but they are included
among the output files, so they are linked.

%O

Substitutes the suffix for object files. Note that this is handled specially when
it immediately follows ‘%g, %u, or %U’, because of the need for those to form
complete file names. The handling is such that ‘%O’ is treated exactly as if it
had already been substituted, except that ‘%g, %u, and %U’ do not currently
support additional suffix characters following ‘%O’ as they do following, for
example, ‘.o’.

%p

Substitutes the standard macro predefinitions for the current target machine.
Use this when running cpp.

%P

Like ‘%p’, but puts ‘__’ before and after the name of each predefined macro,
except for macros that start with ‘__’ or with ‘_L’, where L is an uppercase
letter. This is for ISO C.

%I

Substitute any of ‘-iprefix’ (made from GCC_EXEC_PREFIX), ‘-isysroot’
(made from TARGET_SYSTEM_ROOT), ‘-isystem’ (made from COMPILER_PATH
and ‘-B’ options) and ‘-imultilib’ as necessary.

%s

Current argument is the name of a library or startup file of some sort. Search
for that file in a standard list of directories and substitute the full name found.
The current working directory is included in the list of directories scanned.

%T

Current argument is the name of a linker script. Search for that file in the
current list of directories to scan for libraries. If the file is located insert a
‘--script’ option into the command line followed by the full path name found.

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419

If the file is not found then generate an error message. Note: the current
working directory is not searched.
%estr

Print str as an error message. str is terminated by a newline. Use this when
inconsistent options are detected.

%(name)

Substitute the contents of spec string name at this point.

%x{option}
Accumulate an option for ‘%X’.
%X

Output the accumulated linker options specified by ‘-Wl’ or a ‘%x’ spec string.

%Y

Output the accumulated assembler options specified by ‘-Wa’.

%Z

Output the accumulated preprocessor options specified by ‘-Wp’.

%a

Process the asm spec. This is used to compute the switches to be passed to the
assembler.

%A

Process the asm_final spec. This is a spec string for passing switches to an
assembler post-processor, if such a program is needed.

%l

Process the link spec. This is the spec for computing the command line passed
to the linker. Typically it makes use of the ‘%L %G %S %D and %E’ sequences.

%D

Dump out a ‘-L’ option for each directory that GCC believes might contain
startup files. If the target supports multilibs then the current multilib directory
is prepended to each of these paths.

%L

Process the lib spec. This is a spec string for deciding which libraries are
included on the command line to the linker.

%G

Process the libgcc spec. This is a spec string for deciding which GCC support
library is included on the command line to the linker.

%S

Process the startfile spec. This is a spec for deciding which object files are
the first ones passed to the linker. Typically this might be a file named ‘crt0.o’.

%E

Process the endfile spec. This is a spec string that specifies the last object
files that are passed to the linker.

%C

Process the cpp spec. This is used to construct the arguments to be passed to
the C preprocessor.

%1

Process the cc1 spec. This is used to construct the options to be passed to the
actual C compiler (cc1).

%2

Process the cc1plus spec. This is used to construct the options to be passed
to the actual C++ compiler (cc1plus).

%*

Substitute the variable part of a matched option. See below. Note that each
comma in the substituted string is replaced by a single space.

%>’ acts on negative numbers by sign extension.
As an extension to the C language, GCC does not use the latitude given in C99 and C11
only to treat certain aspects of signed ‘<<’ as undefined. However, ‘-fsanitize=shift’
(and ‘-fsanitize=undefined’) will diagnose such cases. They are also diagnosed where
constant expressions are required.
• The sign of the remainder on integer division (C90 6.3.5).
GCC always follows the C99 and C11 requirement that the result of division is truncated
towards zero.

4.6 Floating Point
• The accuracy of the floating-point operations and of the library functions in 
and  that return floating-point results (C90, C99 and C11 5.2.4.2.2).
The accuracy is unknown.
• The rounding behaviors characterized by non-standard values of FLT_ROUNDS
(C90, C99 and C11 5.2.4.2.2).
GCC does not use such values.

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Using the GNU Compiler Collection (GCC)

• The evaluation methods characterized by non-standard negative values of FLT_EVAL_
METHOD (C99 and C11 5.2.4.2.2).
GCC does not use such values.
• The direction of rounding when an integer is converted to a floating-point number that
cannot exactly represent the original value (C90 6.2.1.3, C99 and C11 6.3.1.4).
C99 Annex F is followed.
• The direction of rounding when a floating-point number is converted to a narrower
floating-point number (C90 6.2.1.4, C99 and C11 6.3.1.5).
C99 Annex F is followed.
• How the nearest representable value or the larger or smaller representable value immediately adjacent to the nearest representable value is chosen for certain floating
constants (C90 6.1.3.1, C99 and C11 6.4.4.2).
C99 Annex F is followed.
• Whether and how floating expressions are contracted when not disallowed by the FP_
CONTRACT pragma (C99 and C11 6.5).
Expressions
are
currently
only
contracted
if
‘-ffp-contract=fast’,
‘-funsafe-math-optimizations’ or ‘-ffast-math’ are used.
This is subject
to change.
• The default state for the FENV_ACCESS pragma (C99 and C11 7.6.1).
This pragma is not implemented, but the default is to “off” unless ‘-frounding-math’
is used in which case it is “on”.
• Additional floating-point exceptions, rounding modes, environments, and classifications, and their macro names (C99 and C11 7.6, C99 and C11 7.12).
This is dependent on the implementation of the C library, and is not defined by GCC
itself.
• The default state for the FP_CONTRACT pragma (C99 and C11 7.12.2).
This pragma is not implemented. Expressions are currently only contracted if
‘-ffp-contract=fast’, ‘-funsafe-math-optimizations’ or ‘-ffast-math’ are used.
This is subject to change.
• Whether the “inexact” floating-point exception can be raised when the rounded result
actually does equal the mathematical result in an IEC 60559 conformant implementation (C99 F.9).
This is dependent on the implementation of the C library, and is not defined by GCC
itself.
• Whether the “underflow” (and “inexact”) floating-point exception can be raised when
a result is tiny but not inexact in an IEC 60559 conformant implementation (C99 F.9).
This is dependent on the implementation of the C library, and is not defined by GCC
itself.

4.7 Arrays and Pointers
• The result of converting a pointer to an integer or vice versa (C90 6.3.4, C99 and C11
6.3.2.3).

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A cast from pointer to integer discards most-significant bits if the pointer representation
is larger than the integer type, sign-extends1 if the pointer representation is smaller
than the integer type, otherwise the bits are unchanged.
A cast from integer to pointer discards most-significant bits if the pointer representation
is smaller than the integer type, extends according to the signedness of the integer type
if the pointer representation is larger than the integer type, otherwise the bits are
unchanged.
When casting from pointer to integer and back again, the resulting pointer must reference the same object as the original pointer, otherwise the behavior is undefined.
That is, one may not use integer arithmetic to avoid the undefined behavior of pointer
arithmetic as proscribed in C99 and C11 6.5.6/8.
• The size of the result of subtracting two pointers to elements of the same array (C90
6.3.6, C99 and C11 6.5.6).
The value is as specified in the standard and the type is determined by the ABI.

4.8 Hints
• The extent to which suggestions made by using the register storage-class specifier
are effective (C90 6.5.1, C99 and C11 6.7.1).
The register specifier affects code generation only in these ways:
• When used as part of the register variable extension, see Section 6.45.5 [Explicit
Register Variables], page 592.
• When ‘-O0’ is in use, the compiler allocates distinct stack memory for all variables
that do not have the register storage-class specifier; if register is specified, the
variable may have a shorter lifespan than the code would indicate and may never
be placed in memory.
• On some rare x86 targets, setjmp doesn’t save the registers in all circumstances.
In those cases, GCC doesn’t allocate any variables in registers unless they are
marked register.
• The extent to which suggestions made by using the inline function specifier are effective
(C99 and C11 6.7.4).
GCC will not inline any functions if the ‘-fno-inline’ option is used or if ‘-O0’ is
used. Otherwise, GCC may still be unable to inline a function for many reasons; the
‘-Winline’ option may be used to determine if a function has not been inlined and why
not.

4.9 Structures, Unions, Enumerations, and Bit-Fields
• A member of a union object is accessed using a member of a different type (C90 6.3.2.3).
The relevant bytes of the representation of the object are treated as an object of the type
used for the access. See [Type-punning], page 139. This may be a trap representation.
• Whether a “plain” int bit-field is treated as a signed int bit-field or as an unsigned
int bit-field (C90 6.5.2, C90 6.5.2.1, C99 and C11 6.7.2, C99 and C11 6.7.2.1).
1

Future versions of GCC may zero-extend, or use a target-defined ptr_extend pattern. Do not rely on
sign extension.

434

•

•
•

•
•

•

Using the GNU Compiler Collection (GCC)

By default it is treated as signed int but this may be changed by the
‘-funsigned-bitfields’ option.
Allowable bit-field types other than _Bool, signed int, and unsigned int (C99 and
C11 6.7.2.1).
Other integer types, such as long int, and enumerated types are permitted even in
strictly conforming mode.
Whether atomic types are permitted for bit-fields (C11 6.7.2.1).
Atomic types are not permitted for bit-fields.
Whether a bit-field can straddle a storage-unit boundary (C90 6.5.2.1, C99 and C11
6.7.2.1).
Determined by ABI.
The order of allocation of bit-fields within a unit (C90 6.5.2.1, C99 and C11 6.7.2.1).
Determined by ABI.
The alignment of non-bit-field members of structures (C90 6.5.2.1, C99 and C11
6.7.2.1).
Determined by ABI.
The integer type compatible with each enumerated type (C90 6.5.2.2, C99 and C11
6.7.2.2).
Normally, the type is unsigned int if there are no negative values in the enumeration,
otherwise int. If ‘-fshort-enums’ is specified, then if there are negative values it is
the first of signed char, short and int that can represent all the values, otherwise it
is the first of unsigned char, unsigned short and unsigned int that can represent
all the values.
On some targets, ‘-fshort-enums’ is the default; this is determined by the ABI.

4.10 Qualifiers
• What constitutes an access to an object that has volatile-qualified type (C90 6.5.3, C99
and C11 6.7.3).
Such an object is normally accessed by pointers and used for accessing hardware. In
most expressions, it is intuitively obvious what is a read and what is a write. For
example
volatile int *dst = somevalue;
volatile int *src = someothervalue;
*dst = *src;

will cause a read of the volatile object pointed to by src and store the value into the
volatile object pointed to by dst. There is no guarantee that these reads and writes
are atomic, especially for objects larger than int.
However, if the volatile storage is not being modified, and the value of the volatile
storage is not used, then the situation is less obvious. For example
volatile int *src = somevalue;
*src;

According to the C standard, such an expression is an rvalue whose type is the unqualified version of its original type, i.e. int. Whether GCC interprets this as a read of

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435

the volatile object being pointed to or only as a request to evaluate the expression for
its side effects depends on this type.
If it is a scalar type, or on most targets an aggregate type whose only member object
is of a scalar type, or a union type whose member objects are of scalar types, the
expression is interpreted by GCC as a read of the volatile object; in the other cases,
the expression is only evaluated for its side effects.

4.11 Declarators
• The maximum number of declarators that may modify an arithmetic, structure or
union type (C90 6.5.4).
GCC is only limited by available memory.

4.12 Statements
• The maximum number of case values in a switch statement (C90 6.6.4.2).
GCC is only limited by available memory.

4.13 Preprocessing Directives
See Section “Implementation-defined behavior” in The C Preprocessor, for details of these
aspects of implementation-defined behavior.
• The locations within #pragma directives where header name preprocessing tokens are
recognized (C11 6.4, C11 6.4.7).
• How sequences in both forms of header names are mapped to headers or external source
file names (C90 6.1.7, C99 and C11 6.4.7).
• Whether the value of a character constant in a constant expression that controls conditional inclusion matches the value of the same character constant in the execution
character set (C90 6.8.1, C99 and C11 6.10.1).
• Whether the value of a single-character character constant in a constant expression
that controls conditional inclusion may have a negative value (C90 6.8.1, C99 and C11
6.10.1).
• The places that are searched for an included ‘<>’ delimited header, and how the places
are specified or the header is identified (C90 6.8.2, C99 and C11 6.10.2).
• How the named source file is searched for in an included ‘""’ delimited header (C90
6.8.2, C99 and C11 6.10.2).
• The method by which preprocessing tokens (possibly resulting from macro expansion)
in a #include directive are combined into a header name (C90 6.8.2, C99 and C11
6.10.2).
• The nesting limit for #include processing (C90 6.8.2, C99 and C11 6.10.2).
• Whether the ‘#’ operator inserts a ‘\’ character before the ‘\’ character that begins
a universal character name in a character constant or string literal (C99 and C11
6.10.3.2).
• The behavior on each recognized non-STDC #pragma directive (C90 6.8.6, C99 and C11
6.10.6).

436

Using the GNU Compiler Collection (GCC)

See Section “Pragmas” in The C Preprocessor, for details of pragmas accepted by GCC
on all targets. See Section 6.61 [Pragmas Accepted by GCC], page 773, for details of
target-specific pragmas.
• The definitions for __DATE__ and __TIME__ when respectively, the date and time of
translation are not available (C90 6.8.8, C99 6.10.8, C11 6.10.8.1).

4.14 Library Functions
The behavior of most of these points are dependent on the implementation of the C library,
and are not defined by GCC itself.
• The null pointer constant to which the macro NULL expands (C90 7.1.6, C99 7.17, C11
7.19).
In , NULL expands to ((void *)0). GCC does not provide the other headers
which define NULL and some library implementations may use other definitions in those
headers.

4.15 Architecture
• The values or expressions assigned to the macros specified in the headers ,
, and  (C90, C99 and C11 5.2.4.2, C99 7.18.2, C99 7.18.3, C11
7.20.2, C11 7.20.3).
Determined by ABI.
• The result of attempting to indirectly access an object with automatic or thread storage
duration from a thread other than the one with which it is associated (C11 6.2.4).
Such accesses are supported, subject to the same requirements for synchronization for
concurrent accesses as for concurrent accesses to any object.
• The number, order, and encoding of bytes in any object (when not explicitly specified
in this International Standard) (C99 and C11 6.2.6.1).
Determined by ABI.
• Whether any extended alignments are supported and the contexts in which they are
supported (C11 6.2.8).
Extended alignments up to 228 (bytes) are supported for objects of automatic storage
duration. Alignments supported for objects of static and thread storage duration are
determined by the ABI.
• Valid alignment values other than those returned by an Alignof expression for fundamental types, if any (C11 6.2.8).
Valid alignments are powers of 2 up to and including 228 .
• The value of the result of the sizeof and _Alignof operators (C90 6.3.3.4, C99 and
C11 6.5.3.4).
Determined by ABI.

4.16 Locale-Specific Behavior
The behavior of these points are dependent on the implementation of the C library, and are
not defined by GCC itself.

Chapter 5: C++ Implementation-Defined Behavior

437

5 C++ Implementation-Defined Behavior
A conforming implementation of ISO C++ is required to document its choice of behavior
in each of the areas that are designated “implementation defined”. The following lists all
such areas, along with the section numbers from the ISO/IEC 14882:1998 and ISO/IEC
14882:2003 standards. Some areas are only implementation-defined in one version of the
standard.
Some choices depend on the externally determined ABI for the platform (including standard character encodings) which GCC follows; these are listed as “determined by ABI”
below. See Chapter 9 [Binary Compatibility], page 817, and http: / / gcc . gnu . org /
readings.html. Some choices are documented in the preprocessor manual. See Section
“Implementation-defined behavior” in The C Preprocessor. Some choices are documented
in the corresponding document for the C language. See Chapter 4 [C Implementation],
page 429. Some choices are made by the library and operating system (or other environment when compiling for a freestanding environment); refer to their documentation for
details.

5.1 Conditionally-Supported Behavior
Each implementation shall include documentation that identifies all conditionally-supported
constructs that it does not support (C++0x 1.4).
• Whether an argument of class type with a non-trivial copy constructor or destructor
can be passed to ... (C++0x 5.2.2).
Such argument passing is supported, using the same pass-by-invisible-reference approach used for normal function arguments of such types.

5.2 Exception Handling
• In the situation where no matching handler is found, it is implementation-defined
whether or not the stack is unwound before std::terminate() is called (C++98 15.5.1).
The stack is not unwound before std::terminate is called.
c Copyright (C) 1988-2018 Free Software Foundation, Inc.

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439

6 Extensions to the C Language Family
GNU C provides several language features not found in ISO standard C. (The ‘-pedantic’
option directs GCC to print a warning message if any of these features is used.) To test for
the availability of these features in conditional compilation, check for a predefined macro
__GNUC__, which is always defined under GCC.
These extensions are available in C and Objective-C. Most of them are also available in
C++. See Chapter 7 [Extensions to the C++ Language], page 787, for extensions that apply
only to C++.
Some features that are in ISO C99 but not C90 or C++ are also, as extensions, accepted
by GCC in C90 mode and in C++.

6.1 Statements and Declarations in Expressions
A compound statement enclosed in parentheses may appear as an expression in GNU C.
This allows you to use loops, switches, and local variables within an expression.
Recall that a compound statement is a sequence of statements surrounded by braces; in
this construct, parentheses go around the braces. For example:
({ int y = foo (); int z;
if (y > 0) z = y;
else z = - y;
z; })

is a valid (though slightly more complex than necessary) expression for the absolute value
of foo ().
The last thing in the compound statement should be an expression followed by a semicolon; the value of this subexpression serves as the value of the entire construct. (If you use
some other kind of statement last within the braces, the construct has type void, and thus
effectively no value.)
This feature is especially useful in making macro definitions “safe” (so that they evaluate
each operand exactly once). For example, the “maximum” function is commonly defined
as a macro in standard C as follows:
#define max(a,b) ((a) > (b) ? (a) : (b))

But this definition computes either a or b twice, with bad results if the operand has side
effects. In GNU C, if you know the type of the operands (here taken as int), you can define
the macro safely as follows:
#define maxint(a,b) \
({int _a = (a), _b = (b); _a > _b ? _a : _b; })

Embedded statements are not allowed in constant expressions, such as the value of an
enumeration constant, the width of a bit-field, or the initial value of a static variable.
If you don’t know the type of the operand, you can still do this, but you must use typeof
or __auto_type (see Section 6.6 [Typeof], page 446).
In G++, the result value of a statement expression undergoes array and function pointer
decay, and is returned by value to the enclosing expression. For instance, if A is a class,
then

440

Using the GNU Compiler Collection (GCC)

A a;
({a;}).Foo ()

constructs a temporary A object to hold the result of the statement expression, and that is
used to invoke Foo. Therefore the this pointer observed by Foo is not the address of a.
In a statement expression, any temporaries created within a statement are destroyed at
that statement’s end. This makes statement expressions inside macros slightly different
from function calls. In the latter case temporaries introduced during argument evaluation
are destroyed at the end of the statement that includes the function call. In the statement
expression case they are destroyed during the statement expression. For instance,
#define macro(a) ({__typeof__(a) b = (a); b + 3; })
template T function(T a) { T b = a; return b + 3; }
void foo ()
{
macro (X ());
function (X ());
}

has different places where temporaries are destroyed. For the macro case, the temporary
X is destroyed just after the initialization of b. In the function case that temporary is
destroyed when the function returns.
These considerations mean that it is probably a bad idea to use statement expressions of
this form in header files that are designed to work with C++. (Note that some versions of
the GNU C Library contained header files using statement expressions that lead to precisely
this bug.)
Jumping into a statement expression with goto or using a switch statement outside the
statement expression with a case or default label inside the statement expression is not
permitted. Jumping into a statement expression with a computed goto (see Section 6.3
[Labels as Values], page 441) has undefined behavior. Jumping out of a statement expression is permitted, but if the statement expression is part of a larger expression then it is
unspecified which other subexpressions of that expression have been evaluated except where
the language definition requires certain subexpressions to be evaluated before or after the
statement expression. In any case, as with a function call, the evaluation of a statement
expression is not interleaved with the evaluation of other parts of the containing expression.
For example,
foo (), (({ bar1 (); goto a; 0; }) + bar2 ()), baz();

calls foo and bar1 and does not call baz but may or may not call bar2. If bar2 is called,
it is called after foo and before bar1.

6.2 Locally Declared Labels
GCC allows you to declare local labels in any nested block scope. A local label is just like
an ordinary label, but you can only reference it (with a goto statement, or by taking its
address) within the block in which it is declared.
A local label declaration looks like this:
__label__ label;

or

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441

__label__ label1, label2, /* . . . */;

Local label declarations must come at the beginning of the block, before any ordinary
declarations or statements.
The label declaration defines the label name, but does not define the label itself. You must
do this in the usual way, with label:, within the statements of the statement expression.
The local label feature is useful for complex macros. If a macro contains nested loops,
a goto can be useful for breaking out of them. However, an ordinary label whose scope
is the whole function cannot be used: if the macro can be expanded several times in one
function, the label is multiply defined in that function. A local label avoids this problem.
For example:
#define SEARCH(value, array, target)
do {
__label__ found;
typeof (target) _SEARCH_target = (target);
typeof (*(array)) *_SEARCH_array = (array);
int i, j;
int value;
for (i = 0; i < max; i++)
for (j = 0; j < max; j++)
if (_SEARCH_array[i][j] == _SEARCH_target)
{ (value) = i; goto found; }
(value) = -1;
found:;
} while (0)

\
\
\
\
\
\
\
\
\
\
\
\
\

This could also be written using a statement expression:
#define SEARCH(array, target)
({
__label__ found;
typeof (target) _SEARCH_target = (target);
typeof (*(array)) *_SEARCH_array = (array);
int i, j;
int value;
for (i = 0; i < max; i++)
for (j = 0; j < max; j++)
if (_SEARCH_array[i][j] == _SEARCH_target)
{ value = i; goto found; }
value = -1;
found:
value;
})

\
\
\
\
\
\
\
\
\
\
\
\
\
\

Local label declarations also make the labels they declare visible to nested functions, if
there are any. See Section 6.4 [Nested Functions], page 442, for details.

6.3 Labels as Values
You can get the address of a label defined in the current function (or a containing function)
with the unary operator ‘&&’. The value has type void *. This value is a constant and can
be used wherever a constant of that type is valid. For example:
void *ptr;
/* . . . */
ptr = &&foo;

442

Using the GNU Compiler Collection (GCC)

To use these values, you need to be able to jump to one. This is done with the computed
goto statement1 , goto *exp;. For example,
goto *ptr;

Any expression of type void * is allowed.
One way of using these constants is in initializing a static array that serves as a jump
table:
static void *array[] = { &&foo, &&bar, &&hack };

Then you can select a label with indexing, like this:
goto *array[i];

Note that this does not check whether the subscript is in bounds—array indexing in C never
does that.
Such an array of label values serves a purpose much like that of the switch statement.
The switch statement is cleaner, so use that rather than an array unless the problem does
not fit a switch statement very well.
Another use of label values is in an interpreter for threaded code. The labels within the
interpreter function can be stored in the threaded code for super-fast dispatching.
You may not use this mechanism to jump to code in a different function. If you do that,
totally unpredictable things happen. The best way to avoid this is to store the label address
only in automatic variables and never pass it as an argument.
An alternate way to write the above example is
static const int array[] = { &&foo - &&foo, &&bar - &&foo,
&&hack - &&foo };
goto *(&&foo + array[i]);

This is more friendly to code living in shared libraries, as it reduces the number of dynamic
relocations that are needed, and by consequence, allows the data to be read-only. This
alternative with label differences is not supported for the AVR target, please use the first
approach for AVR programs.
The &&foo expressions for the same label might have different values if the containing function is inlined or cloned. If a program relies on them being always the same,
__attribute__((__noinline__,__noclone__)) should be used to prevent inlining and
cloning. If &&foo is used in a static variable initializer, inlining and cloning is forbidden.

6.4 Nested Functions
A nested function is a function defined inside another function. Nested functions are supported as an extension in GNU C, but are not supported by GNU C++.
The nested function’s name is local to the block where it is defined. For example, here
we define a nested function named square, and call it twice:
foo (double a, double b)
{
double square (double z) { return z * z; }
return square (a) + square (b);
}
1

The analogous feature in Fortran is called an assigned goto, but that name seems inappropriate in C,
where one can do more than simply store label addresses in label variables.

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443

The nested function can access all the variables of the containing function that are visible
at the point of its definition. This is called lexical scoping. For example, here we show a
nested function which uses an inherited variable named offset:
bar (int *array, int offset, int size)
{
int access (int *array, int index)
{ return array[index + offset]; }
int i;
/* . . . */
for (i = 0; i < size; i++)
/* . . . */ access (array, i) /* . . . */
}

Nested function definitions are permitted within functions in the places where variable
definitions are allowed; that is, in any block, mixed with the other declarations and statements in the block.
It is possible to call the nested function from outside the scope of its name by storing its
address or passing the address to another function:
hack (int *array, int size)
{
void store (int index, int value)
{ array[index] = value; }
intermediate (store, size);
}

Here, the function intermediate receives the address of store as an argument. If
intermediate calls store, the arguments given to store are used to store into array.
But this technique works only so long as the containing function (hack, in this example)
does not exit.
If you try to call the nested function through its address after the containing function
exits, all hell breaks loose. If you try to call it after a containing scope level exits, and if it
refers to some of the variables that are no longer in scope, you may be lucky, but it’s not
wise to take the risk. If, however, the nested function does not refer to anything that has
gone out of scope, you should be safe.
GCC implements taking the address of a nested function using a technique called trampolines. This technique was described in Lexical Closures for C++ (Thomas M. Breuel,
USENIX C++ Conference Proceedings, October 17-21, 1988).
A nested function can jump to a label inherited from a containing function, provided
the label is explicitly declared in the containing function (see Section 6.2 [Local Labels],
page 440). Such a jump returns instantly to the containing function, exiting the nested
function that did the goto and any intermediate functions as well. Here is an example:

444

Using the GNU Compiler Collection (GCC)

bar (int *array, int offset, int size)
{
__label__ failure;
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
int i;
/* . . . */
for (i = 0; i < size; i++)
/* . . . */ access (array, i) /* . . . */
/* . . . */
return 0;
/* Control comes here from access
if it detects an error. */
failure:
return -1;
}

A nested function always has no linkage. Declaring one with extern or static is erroneous. If you need to declare the nested function before its definition, use auto (which is
otherwise meaningless for function declarations).
bar (int *array, int offset, int size)
{
__label__ failure;
auto int access (int *, int);
/* . . . */
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
/* . . . */
}

6.5 Constructing Function Calls
Using the built-in functions described below, you can record the arguments a function
received, and call another function with the same arguments, without knowing the number
or types of the arguments.
You can also record the return value of that function call, and later return that value,
without knowing what data type the function tried to return (as long as your caller expects
that data type).
However, these built-in functions may interact badly with some sophisticated features or
other extensions of the language. It is, therefore, not recommended to use them outside
very simple functions acting as mere forwarders for their arguments.

void * __builtin_apply_args ()

[Built-in Function]
This built-in function returns a pointer to data describing how to perform a call with
the same arguments as are passed to the current function.

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The function saves the arg pointer register, structure value address, and all registers
that might be used to pass arguments to a function into a block of memory allocated
on the stack. Then it returns the address of that block.

void * __builtin_apply (void (*function)(), void
*arguments, size t size)

[Built-in Function]

This built-in function invokes function with a copy of the parameters described by
arguments and size.
The value of arguments should be the value returned by __builtin_apply_args.
The argument size specifies the size of the stack argument data, in bytes.
This function returns a pointer to data describing how to return whatever value is
returned by function. The data is saved in a block of memory allocated on the stack.
It is not always simple to compute the proper value for size. The value is used by
__builtin_apply to compute the amount of data that should be pushed on the stack
and copied from the incoming argument area.

void __builtin_return (void *result)

[Built-in Function]
This built-in function returns the value described by result from the containing function. You should specify, for result, a value returned by __builtin_apply.

__builtin_va_arg_pack ()

[Built-in Function]
This built-in function represents all anonymous arguments of an inline function. It
can be used only in inline functions that are always inlined, never compiled as a
separate function, such as those using __attribute__ ((__always_inline__)) or _
_attribute__ ((__gnu_inline__)) extern inline functions. It must be only passed
as last argument to some other function with variable arguments. This is useful for
writing small wrapper inlines for variable argument functions, when using preprocessor macros is undesirable. For example:
extern int myprintf (FILE *f, const char *format, ...);
extern inline __attribute__ ((__gnu_inline__)) int
myprintf (FILE *f, const char *format, ...)
{
int r = fprintf (f, "myprintf: ");
if (r < 0)
return r;
int s = fprintf (f, format, __builtin_va_arg_pack ());
if (s < 0)
return s;
return r + s;
}

size_t __builtin_va_arg_pack_len ()

[Built-in Function]
This built-in function returns the number of anonymous arguments of an inline function. It can be used only in inline functions that are always inlined, never compiled as
a separate function, such as those using __attribute__ ((__always_inline__)) or
__attribute__ ((__gnu_inline__)) extern inline functions. For example following
does link- or run-time checking of open arguments for optimized code:
#ifdef __OPTIMIZE__
extern inline __attribute__((__gnu_inline__)) int
myopen (const char *path, int oflag, ...)

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{
if (__builtin_va_arg_pack_len () > 1)
warn_open_too_many_arguments ();
if (__builtin_constant_p (oflag))
{
if ((oflag & O_CREAT) != 0 && __builtin_va_arg_pack_len () < 1)
{
warn_open_missing_mode ();
return __open_2 (path, oflag);
}
return open (path, oflag, __builtin_va_arg_pack ());
}
if (__builtin_va_arg_pack_len () < 1)
return __open_2 (path, oflag);
return open (path, oflag, __builtin_va_arg_pack ());
}
#endif

6.6 Referring to a Type with typeof
Another way to refer to the type of an expression is with typeof. The syntax of using of
this keyword looks like sizeof, but the construct acts semantically like a type name defined
with typedef.
There are two ways of writing the argument to typeof: with an expression or with a
type. Here is an example with an expression:
typeof (x[0](1))

This assumes that x is an array of pointers to functions; the type described is that of the
values of the functions.
Here is an example with a typename as the argument:
typeof (int *)

Here the type described is that of pointers to int.
If you are writing a header file that must work when included in ISO C programs, write
__typeof__ instead of typeof. See Section 6.46 [Alternate Keywords], page 595.
A typeof construct can be used anywhere a typedef name can be used. For example,
you can use it in a declaration, in a cast, or inside of sizeof or typeof.
The operand of typeof is evaluated for its side effects if and only if it is an expression of
variably modified type or the name of such a type.
typeof is often useful in conjunction with statement expressions (see Section 6.1 [Statement Exprs], page 439). Here is how the two together can be used to define a safe “maximum” macro which operates on any arithmetic type and evaluates each of its arguments
exactly once:
#define max(a,b) \
({ typeof (a) _a = (a); \
typeof (b) _b = (b); \
_a > _b ? _a : _b; })

The reason for using names that start with underscores for the local variables is to avoid
conflicts with variable names that occur within the expressions that are substituted for a

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and b. Eventually we hope to design a new form of declaration syntax that allows you to
declare variables whose scopes start only after their initializers; this will be a more reliable
way to prevent such conflicts.
Some more examples of the use of typeof:
• This declares y with the type of what x points to.
typeof (*x) y;

• This declares y as an array of such values.
typeof (*x) y[4];

• This declares y as an array of pointers to characters:
typeof (typeof (char *)[4]) y;

It is equivalent to the following traditional C declaration:
char *y[4];

To see the meaning of the declaration using typeof, and why it might be a useful way
to write, rewrite it with these macros:
#define pointer(T) typeof(T *)
#define array(T, N) typeof(T [N])

Now the declaration can be rewritten this way:
array (pointer (char), 4) y;

Thus, array (pointer (char), 4) is the type of arrays of 4 pointers to char.
In GNU C, but not GNU C++, you may also declare the type of a variable as __auto_type.
In that case, the declaration must declare only one variable, whose declarator must just be
an identifier, the declaration must be initialized, and the type of the variable is determined
by the initializer; the name of the variable is not in scope until after the initializer. (In C++,
you should use C++11 auto for this purpose.) Using __auto_type, the “maximum” macro
above could be written as:
#define max(a,b) \
({ __auto_type _a = (a); \
__auto_type _b = (b); \
_a > _b ? _a : _b; })

Using __auto_type instead of typeof has two advantages:
• Each argument to the macro appears only once in the expansion of the macro. This
prevents the size of the macro expansion growing exponentially when calls to such
macros are nested inside arguments of such macros.
• If the argument to the macro has variably modified type, it is evaluated only once when
using __auto_type, but twice if typeof is used.

6.7 Conditionals with Omitted Operands
The middle operand in a conditional expression may be omitted. Then if the first operand
is nonzero, its value is the value of the conditional expression.
Therefore, the expression
x ? : y

has the value of x if that is nonzero; otherwise, the value of y.
This example is perfectly equivalent to

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x ? x : y

In this simple case, the ability to omit the middle operand is not especially useful. When it
becomes useful is when the first operand does, or may (if it is a macro argument), contain a
side effect. Then repeating the operand in the middle would perform the side effect twice.
Omitting the middle operand uses the value already computed without the undesirable
effects of recomputing it.

6.8 128-bit Integers
As an extension the integer scalar type __int128 is supported for targets which have an
integer mode wide enough to hold 128 bits. Simply write __int128 for a signed 128-bit
integer, or unsigned __int128 for an unsigned 128-bit integer. There is no support in GCC
for expressing an integer constant of type __int128 for targets with long long integer less
than 128 bits wide.

6.9 Double-Word Integers
ISO C99 supports data types for integers that are at least 64 bits wide, and as an extension
GCC supports them in C90 mode and in C++. Simply write long long int for a signed
integer, or unsigned long long int for an unsigned integer. To make an integer constant
of type long long int, add the suffix ‘LL’ to the integer. To make an integer constant of
type unsigned long long int, add the suffix ‘ULL’ to the integer.
You can use these types in arithmetic like any other integer types. Addition, subtraction,
and bitwise boolean operations on these types are open-coded on all types of machines.
Multiplication is open-coded if the machine supports a fullword-to-doubleword widening
multiply instruction. Division and shifts are open-coded only on machines that provide
special support. The operations that are not open-coded use special library routines that
come with GCC.
There may be pitfalls when you use long long types for function arguments without
function prototypes. If a function expects type int for its argument, and you pass a value
of type long long int, confusion results because the caller and the subroutine disagree
about the number of bytes for the argument. Likewise, if the function expects long long
int and you pass int. The best way to avoid such problems is to use prototypes.

6.10 Complex Numbers
ISO C99 supports complex floating data types, and as an extension GCC supports them in
C90 mode and in C++. GCC also supports complex integer data types which are not part
of ISO C99. You can declare complex types using the keyword _Complex. As an extension,
the older GNU keyword __complex__ is also supported.
For example, ‘_Complex double x;’ declares x as a variable whose real part and imaginary part are both of type double. ‘_Complex short int y;’ declares y to have real and
imaginary parts of type short int; this is not likely to be useful, but it shows that the set
of complex types is complete.
To write a constant with a complex data type, use the suffix ‘i’ or ‘j’ (either one; they
are equivalent). For example, 2.5fi has type _Complex float and 3i has type _Complex
int. Such a constant always has a pure imaginary value, but you can form any complex

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value you like by adding one to a real constant. This is a GNU extension; if you have
an ISO C99 conforming C library (such as the GNU C Library), and want to construct
complex constants of floating type, you should include  and use the macros I
or _Complex_I instead.
The ISO C++14 library also defines the ‘i’ suffix, so C++14 code that includes the
‘’ header cannot use ‘i’ for the GNU extension. The ‘j’ suffix still has the
GNU meaning.
To extract the real part of a complex-valued expression exp, write __real__ exp. Likewise, use __imag__ to extract the imaginary part. This is a GNU extension; for values of
floating type, you should use the ISO C99 functions crealf, creal, creall, cimagf, cimag
and cimagl, declared in  and also provided as built-in functions by GCC.
The operator ‘~’ performs complex conjugation when used on a value with a complex
type. This is a GNU extension; for values of floating type, you should use the ISO C99
functions conjf, conj and conjl, declared in  and also provided as built-in
functions by GCC.
GCC can allocate complex automatic variables in a noncontiguous fashion; it’s even
possible for the real part to be in a register while the imaginary part is on the stack (or
vice versa). Only the DWARF debug info format can represent this, so use of DWARF is
recommended. If you are using the stabs debug info format, GCC describes a noncontiguous
complex variable as if it were two separate variables of noncomplex type. If the variable’s
actual name is foo, the two fictitious variables are named foo$real and foo$imag. You
can examine and set these two fictitious variables with your debugger.

6.11 Additional Floating Types
ISO/IEC TS 18661-3:2015 defines C support for additional floating types _Floatn and _
Floatnx, and GCC supports these type names; the set of types supported depends on the
target architecture. These types are not supported when compiling C++. Constants with
these types use suffixes fn or Fn and fnx or Fnx. These type names can be used together
with _Complex to declare complex types.
As an extension, GNU C and GNU C++ support additional floating types, which are not
supported by all targets.
• __float128 is available on i386, x86 64, IA-64, and hppa HP-UX, as well as on PowerPC GNU/Linux targets that enable the vector scalar (VSX) instruction set. __
float128 supports the 128-bit floating type. On i386, x86 64, PowerPC, and IA-64
other than HP-UX, __float128 is an alias for _Float128. On hppa and IA-64 HP-UX,
__float128 is an alias for long double.
• __float80 is available on the i386, x86 64, and IA-64 targets, and supports the 80-bit
(XFmode) floating type. It is an alias for the type name _Float64x on these targets.
• __ibm128 is available on PowerPC targets, and provides access to the IBM extended
double format which is the current format used for long double. When long double
transitions to __float128 on PowerPC in the future, __ibm128 will remain for use in
conversions between the two types.
Support for these additional types includes the arithmetic operators: add, subtract, multiply, divide; unary arithmetic operators; relational operators; equality operators; and con-

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versions to and from integer and other floating types. Use a suffix ‘w’ or ‘W’ in a literal
constant of type __float80 or type __ibm128. Use a suffix ‘q’ or ‘Q’ for _float128.
In order to use _Float128, __float128, and __ibm128 on PowerPC Linux systems, you
must use the ‘-mfloat128’ option. It is expected in future versions of GCC that _Float128
and __float128 will be enabled automatically.
The _Float128 type is supported on all systems where __float128 is supported or
where long double has the IEEE binary128 format. The _Float64x type is supported on
all systems where __float128 is supported. The _Float32 type is supported on all systems
supporting IEEE binary32; the _Float64 and _Float32x types are supported on all systems
supporting IEEE binary64. The _Float16 type is supported on AArch64 systems by default,
and on ARM systems when the IEEE format for 16-bit floating-point types is selected with
‘-mfp16-format=ieee’. GCC does not currently support _Float128x on any systems.
On the i386, x86 64, IA-64, and HP-UX targets, you can declare complex types using
the corresponding internal complex type, XCmode for __float80 type and TCmode for __
float128 type:
typedef _Complex float __attribute__((mode(TC))) _Complex128;
typedef _Complex float __attribute__((mode(XC))) _Complex80;

On the PowerPC Linux VSX targets, you can declare complex types using the corresponding internal complex type, KCmode for __float128 type and ICmode for __ibm128
type:
typedef _Complex float __attribute__((mode(KC))) _Complex_float128;
typedef _Complex float __attribute__((mode(IC))) _Complex_ibm128;

6.12 Half-Precision Floating Point
On ARM and AArch64 targets, GCC supports half-precision (16-bit) floating point via the
__fp16 type defined in the ARM C Language Extensions. On ARM systems, you must
enable this type explicitly with the ‘-mfp16-format’ command-line option in order to use
it.
ARM targets support two incompatible representations for half-precision floating-point
values. You must choose one of the representations and use it consistently in your program.
Specifying ‘-mfp16-format=ieee’ selects the IEEE 754-2008 format. This format can
represent normalized values in the range of 2−14 to 65504. There are 11 bits of significand
precision, approximately 3 decimal digits.
Specifying ‘-mfp16-format=alternative’ selects the ARM alternative format. This representation is similar to the IEEE format, but does not support infinities or NaNs. Instead,
the range of exponents is extended, so that this format can represent normalized values in
the range of 2−14 to 131008.
The GCC port for AArch64 only supports the IEEE 754-2008 format, and does not
require use of the ‘-mfp16-format’ command-line option.
The __fp16 type may only be used as an argument to intrinsics defined in ,
or as a storage format. For purposes of arithmetic and other operations, __fp16 values in
C or C++ expressions are automatically promoted to float.
The ARM target provides hardware support for conversions between __fp16 and float
values as an extension to VFP and NEON (Advanced SIMD), and from ARMv8-A provides

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hardware support for conversions between __fp16 and double values. GCC generates
code using these hardware instructions if you compile with options to select an FPU that
provides them; for example, ‘-mfpu=neon-fp16 -mfloat-abi=softfp’, in addition to the
‘-mfp16-format’ option to select a half-precision format.
Language-level support for the __fp16 data type is independent of whether GCC generates code using hardware floating-point instructions. In cases where hardware support
is not specified, GCC implements conversions between __fp16 and other types as library
calls.
It is recommended that portable code use the _Float16 type defined by ISO/IEC TS
18661-3:2015. See Section 6.11 [Floating Types], page 449.

6.13 Decimal Floating Types
As an extension, GNU C supports decimal floating types as defined in the N1312 draft of
ISO/IEC WDTR24732. Support for decimal floating types in GCC will evolve as the draft
technical report changes. Calling conventions for any target might also change. Not all
targets support decimal floating types.
The decimal floating types are _Decimal32, _Decimal64, and _Decimal128. They use a
radix of ten, unlike the floating types float, double, and long double whose radix is not
specified by the C standard but is usually two.
Support for decimal floating types includes the arithmetic operators add, subtract, multiply, divide; unary arithmetic operators; relational operators; equality operators; and conversions to and from integer and other floating types. Use a suffix ‘df’ or ‘DF’ in a literal
constant of type _Decimal32, ‘dd’ or ‘DD’ for _Decimal64, and ‘dl’ or ‘DL’ for _Decimal128.
GCC support of decimal float as specified by the draft technical report is incomplete:
• When the value of a decimal floating type cannot be represented in the integer type to
which it is being converted, the result is undefined rather than the result value specified
by the draft technical report.
• GCC does not provide the C library functionality associated with ‘math.h’, ‘fenv.h’,
‘stdio.h’, ‘stdlib.h’, and ‘wchar.h’, which must come from a separate C library
implementation. Because of this the GNU C compiler does not define macro __STDC_
DEC_FP__ to indicate that the implementation conforms to the technical report.
Types _Decimal32, _Decimal64, and _Decimal128 are supported by the DWARF debug
information format.

6.14 Hex Floats
ISO C99 supports floating-point numbers written not only in the usual decimal notation,
such as 1.55e1, but also numbers such as 0x1.fp3 written in hexadecimal format. As
a GNU extension, GCC supports this in C90 mode (except in some cases when strictly
conforming) and in C++. In that format the ‘0x’ hex introducer and the ‘p’ or ‘P’ exponent
field are mandatory. The exponent is a decimal number that indicates the power of 2 by
15
which the significant part is multiplied. Thus ‘0x1.f’ is 1 16
, ‘p3’ multiplies it by 8, and the
value of 0x1.fp3 is the same as 1.55e1.
Unlike for floating-point numbers in the decimal notation the exponent is always required
in the hexadecimal notation. Otherwise the compiler would not be able to resolve the

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ambiguity of, e.g., 0x1.f. This could mean 1.0f or 1.9375 since ‘f’ is also the extension
for floating-point constants of type float.

6.15 Fixed-Point Types
As an extension, GNU C supports fixed-point types as defined in the N1169 draft of ISO/IEC
DTR 18037. Support for fixed-point types in GCC will evolve as the draft technical report
changes. Calling conventions for any target might also change. Not all targets support
fixed-point types.
The fixed-point types are short _Fract, _Fract, long _Fract, long long _Fract,
unsigned short _Fract, unsigned _Fract, unsigned long _Fract, unsigned long long
_Fract, _Sat short _Fract, _Sat _Fract, _Sat long _Fract, _Sat long long _Fract,
_Sat unsigned short _Fract, _Sat unsigned _Fract, _Sat unsigned long _Fract, _Sat
unsigned long long _Fract, short _Accum, _Accum, long _Accum, long long _Accum,
unsigned short _Accum, unsigned _Accum, unsigned long _Accum, unsigned long long
_Accum, _Sat short _Accum, _Sat _Accum, _Sat long _Accum, _Sat long long _Accum,
_Sat unsigned short _Accum, _Sat unsigned _Accum, _Sat unsigned long _Accum, _Sat
unsigned long long _Accum.
Fixed-point data values contain fractional and optional integral parts. The format of
fixed-point data varies and depends on the target machine.
Support for fixed-point types includes:
• prefix and postfix increment and decrement operators (++, --)
• unary arithmetic operators (+, -, !)
• binary arithmetic operators (+, -, *, /)
• binary shift operators (<<, >>)
• relational operators (<, <=, >=, >)
• equality operators (==, !=)
• assignment operators (+=, -=, *=, /=, <<=, >>=)
• conversions to and from integer, floating-point, or fixed-point types
Use a suffix in a fixed-point literal constant:
• ‘hr’ or ‘HR’ for short _Fract and _Sat short _Fract
• ‘r’ or ‘R’ for _Fract and _Sat _Fract
• ‘lr’ or ‘LR’ for long _Fract and _Sat long _Fract
• ‘llr’ or ‘LLR’ for long long _Fract and _Sat long long _Fract
• ‘uhr’ or ‘UHR’ for unsigned short _Fract and _Sat unsigned short _Fract
• ‘ur’ or ‘UR’ for unsigned _Fract and _Sat unsigned _Fract
• ‘ulr’ or ‘ULR’ for unsigned long _Fract and _Sat unsigned long _Fract
• ‘ullr’ or ‘ULLR’ for unsigned long long _Fract and _Sat unsigned long long
_Fract
• ‘hk’ or ‘HK’ for short _Accum and _Sat short _Accum
• ‘k’ or ‘K’ for _Accum and _Sat _Accum
• ‘lk’ or ‘LK’ for long _Accum and _Sat long _Accum

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• ‘llk’ or ‘LLK’ for long long _Accum and _Sat long long _Accum
• ‘uhk’ or ‘UHK’ for unsigned short _Accum and _Sat unsigned short _Accum
• ‘uk’ or ‘UK’ for unsigned _Accum and _Sat unsigned _Accum
• ‘ulk’ or ‘ULK’ for unsigned long _Accum and _Sat unsigned long _Accum
• ‘ullk’ or ‘ULLK’ for unsigned long long _Accum and _Sat unsigned long long
_Accum
GCC support of fixed-point types as specified by the draft technical report is incomplete:
• Pragmas to control overflow and rounding behaviors are not implemented.
Fixed-point types are supported by the DWARF debug information format.

6.16 Named Address Spaces
As an extension, GNU C supports named address spaces as defined in the N1275 draft of
ISO/IEC DTR 18037. Support for named address spaces in GCC will evolve as the draft
technical report changes. Calling conventions for any target might also change. At present,
only the AVR, SPU, M32C, RL78, and x86 targets support address spaces other than the
generic address space.
Address space identifiers may be used exactly like any other C type qualifier (e.g., const
or volatile). See the N1275 document for more details.

6.16.1 AVR Named Address Spaces
On the AVR target, there are several address spaces that can be used in order to put readonly data into the flash memory and access that data by means of the special instructions
LPM or ELPM needed to read from flash.
Devices belonging to avrtiny and avrxmega3 can access flash memory by means of LD*
instructions because the flash memory is mapped into the RAM address space. There is no
need for language extensions like __flash or attribute Section 6.32.3 [progmem], page 518.
The default linker description files for these devices cater for that feature and .rodata
stays in flash: The compiler just generates LD* instructions, and the linker script adds core
specific offsets to all .rodata symbols: 0x4000 in the case of avrtiny and 0x8000 in the
case of avrxmega3. See Section 3.18.5 [AVR Options], page 258 for a list of respective
devices.
For devices not in avrtiny or avrxmega3, any data including read-only data is located in
RAM (the generic address space) because flash memory is not visible in the RAM address
space. In order to locate read-only data in flash memory and to generate the right instructions to access this data without using (inline) assembler code, special address spaces are
needed.
__flash

The __flash qualifier locates data in the .progmem.data section. Data is read
using the LPM instruction. Pointers to this address space are 16 bits wide.

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__flash1
__flash2
__flash3
__flash4
__flash5

These are 16-bit address spaces locating data in section .progmemN.data where
N refers to address space __flashN. The compiler sets the RAMPZ segment
register appropriately before reading data by means of the ELPM instruction.
This is a 24-bit address space that linearizes flash and RAM: If the high bit
of the address is set, data is read from RAM using the lower two bytes as
RAM address. If the high bit of the address is clear, data is read from flash
with RAMPZ set according to the high byte of the address. See Section 6.59.10
[__builtin_avr_flash_segment], page 639.

__memx

Objects in this address space are located in .progmemx.data.
Example
char my_read (const __flash char ** p)
{
/* p is a pointer to RAM that points to a pointer to flash.
The first indirection of p reads that flash pointer
from RAM and the second indirection reads a char from this
flash address. */
return **p;
}
/* Locate array[] in flash memory */
const __flash int array[] = { 3, 5, 7, 11, 13, 17, 19 };
int i = 1;
int main (void)
{
/* Return 17 by reading from flash memory */
return array[array[i]];
}

For each named address space supported by avr-gcc there is an equally named but uppercase
built-in macro defined. The purpose is to facilitate testing if respective address space
support is available or not:
#ifdef __FLASH
const __flash int var = 1;
int read_var (void)
{
return var;
}
#else
#include  /* From AVR-LibC */
const int var PROGMEM = 1;
int read_var (void)
{
return (int) pgm_read_word (&var);

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}
#endif /* __FLASH */

Notice that attribute Section 6.32.3 [progmem], page 518 locates data in flash but accesses
to these data read from generic address space, i.e. from RAM, so that you need special
accessors like pgm_read_byte from AVR-LibC together with attribute progmem.
Limitations and caveats
• Reading across the 64 KiB section boundary of the __flash or __flashN address spaces
shows undefined behavior. The only address space that supports reading across the
64 KiB flash segment boundaries is __memx.
• If you use one of the __flashN address spaces you must arrange your linker script to
locate the .progmemN.data sections according to your needs.
• Any data or pointers to the non-generic address spaces must be qualified as const,
i.e. as read-only data. This still applies if the data in one of these address spaces like
software version number or calibration lookup table are intended to be changed after
load time by, say, a boot loader. In this case the right qualification is const volatile
so that the compiler must not optimize away known values or insert them as immediates
into operands of instructions.
• The following code initializes a variable pfoo located in static storage with a 24-bit
address:
extern const __memx char foo;
const __memx void *pfoo = &foo;

• On the reduced Tiny devices like ATtiny40, no address spaces are supported. Just
use vanilla C / C++ code without overhead as outlined above. Attribute progmem is
supported but works differently, see Section 6.32.3 [AVR Variable Attributes], page 518.

6.16.2 M32C Named Address Spaces
On the M32C target, with the R8C and M16C CPU variants, variables qualified with __far
are accessed using 32-bit addresses in order to access memory beyond the first 64 Ki bytes.
If __far is used with the M32CM or M32C CPU variants, it has no effect.

6.16.3 RL78 Named Address Spaces
On the RL78 target, variables qualified with __far are accessed with 32-bit pointers (20bit addresses) rather than the default 16-bit addresses. Non-far variables are assumed to
appear in the topmost 64 KiB of the address space.

6.16.4 SPU Named Address Spaces
On the SPU target variables may be declared as belonging to another address space by
qualifying the type with the __ea address space identifier:
extern int __ea i;

The compiler generates special code to access the variable i. It may use runtime library
support, or generate special machine instructions to access that address space.

6.16.5 x86 Named Address Spaces
On the x86 target, variables may be declared as being relative to the %fs or %gs segments.

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__seg_fs
__seg_gs

The object is accessed with the respective segment override prefix.
The respective segment base must be set via some method specific to the operating system. Rather than require an expensive system call to retrieve the
segment base, these address spaces are not considered to be subspaces of the
generic (flat) address space. This means that explicit casts are required to convert pointers between these address spaces and the generic address space. In
practice the application should cast to uintptr_t and apply the segment base
offset that it installed previously.
The preprocessor symbols __SEG_FS and __SEG_GS are defined when these address spaces are supported.

6.17 Arrays of Length Zero
Zero-length arrays are allowed in GNU C. They are very useful as the last element of a
structure that is really a header for a variable-length object:
struct line {
int length;
char contents[0];
};
struct line *thisline = (struct line *)
malloc (sizeof (struct line) + this_length);
thisline->length = this_length;

In ISO C90, you would have to give contents a length of 1, which means either you
waste space or complicate the argument to malloc.
In ISO C99, you would use a flexible array member, which is slightly different in syntax
and semantics:
• Flexible array members are written as contents[] without the 0.
• Flexible array members have incomplete type, and so the sizeof operator may not
be applied. As a quirk of the original implementation of zero-length arrays, sizeof
evaluates to zero.
• Flexible array members may only appear as the last member of a struct that is
otherwise non-empty.
• A structure containing a flexible array member, or a union containing such a structure
(possibly recursively), may not be a member of a structure or an element of an array.
(However, these uses are permitted by GCC as extensions.)
Non-empty initialization of zero-length arrays is treated like any case where there are
more initializer elements than the array holds, in that a suitable warning about “excess
elements in array” is given, and the excess elements (all of them, in this case) are ignored.
GCC allows static initialization of flexible array members. This is equivalent to defining
a new structure containing the original structure followed by an array of sufficient size to
contain the data. E.g. in the following, f1 is constructed as if it were declared like f2.
struct f1 {
int x; int y[];
} f1 = { 1, { 2, 3, 4 } };

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struct f2 {
struct f1 f1; int data[3];
} f2 = { { 1 }, { 2, 3, 4 } };

The convenience of this extension is that f1 has the desired type, eliminating the need to
consistently refer to f2.f1.
This has symmetry with normal static arrays, in that an array of unknown size is also
written with [].
Of course, this extension only makes sense if the extra data comes at the end of a top-level
object, as otherwise we would be overwriting data at subsequent offsets. To avoid undue
complication and confusion with initialization of deeply nested arrays, we simply disallow
any non-empty initialization except when the structure is the top-level object. For example:
struct foo { int x; int y[]; };
struct bar { struct foo z; };
struct
struct
struct
struct

foo
bar
bar
foo

a = { 1, {
b = { { 1,
c = { { 1,
d[1] = { {

2, 3, 4 } };
// Valid.
{ 2, 3, 4 } } };
// Invalid.
{ } } };
// Valid.
1, { 2, 3, 4 } } }; // Invalid.

6.18 Structures with No Members
GCC permits a C structure to have no members:
struct empty {
};

The structure has size zero. In C++, empty structures are part of the language. G++
treats empty structures as if they had a single member of type char.

6.19 Arrays of Variable Length
Variable-length automatic arrays are allowed in ISO C99, and as an extension GCC accepts
them in C90 mode and in C++. These arrays are declared like any other automatic arrays,
but with a length that is not a constant expression. The storage is allocated at the point
of declaration and deallocated when the block scope containing the declaration exits. For
example:
FILE *
concat_fopen (char *s1, char *s2, char *mode)
{
char str[strlen (s1) + strlen (s2) + 1];
strcpy (str, s1);
strcat (str, s2);
return fopen (str, mode);
}

Jumping or breaking out of the scope of the array name deallocates the storage. Jumping
into the scope is not allowed; you get an error message for it.
As an extension, GCC accepts variable-length arrays as a member of a structure or a
union. For example:
void
foo (int n)
{
struct S { int x[n]; };

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}

You can use the function alloca to get an effect much like variable-length arrays. The
function alloca is available in many other C implementations (but not in all). On the
other hand, variable-length arrays are more elegant.
There are other differences between these two methods. Space allocated with alloca
exists until the containing function returns. The space for a variable-length array is deallocated as soon as the array name’s scope ends, unless you also use alloca in this scope.
You can also use variable-length arrays as arguments to functions:
struct entry
tester (int len, char data[len][len])
{
/* . . . */
}

The length of an array is computed once when the storage is allocated and is remembered
for the scope of the array in case you access it with sizeof.
If you want to pass the array first and the length afterward, you can use a forward
declaration in the parameter list—another GNU extension.
struct entry
tester (int len; char data[len][len], int len)
{
/* . . . */
}

The ‘int len’ before the semicolon is a parameter forward declaration, and it serves the
purpose of making the name len known when the declaration of data is parsed.
You can write any number of such parameter forward declarations in the parameter list.
They can be separated by commas or semicolons, but the last one must end with a semicolon,
which is followed by the “real” parameter declarations. Each forward declaration must
match a “real” declaration in parameter name and data type. ISO C99 does not support
parameter forward declarations.

6.20 Macros with a Variable Number of Arguments.
In the ISO C standard of 1999, a macro can be declared to accept a variable number of
arguments much as a function can. The syntax for defining the macro is similar to that of
a function. Here is an example:
#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)

Here ‘...’ is a variable argument. In the invocation of such a macro, it represents the
zero or more tokens until the closing parenthesis that ends the invocation, including any
commas. This set of tokens replaces the identifier __VA_ARGS__ in the macro body wherever
it appears. See the CPP manual for more information.
GCC has long supported variadic macros, and used a different syntax that allowed you
to give a name to the variable arguments just like any other argument. Here is an example:
#define debug(format, args...) fprintf (stderr, format, args)

This is in all ways equivalent to the ISO C example above, but arguably more readable and
descriptive.
GNU CPP has two further variadic macro extensions, and permits them to be used with
either of the above forms of macro definition.

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In standard C, you are not allowed to leave the variable argument out entirely; but you
are allowed to pass an empty argument. For example, this invocation is invalid in ISO C,
because there is no comma after the string:
debug ("A message")

GNU CPP permits you to completely omit the variable arguments in this way. In the
above examples, the compiler would complain, though since the expansion of the macro still
has the extra comma after the format string.
To help solve this problem, CPP behaves specially for variable arguments used with the
token paste operator, ‘##’. If instead you write
#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)

and if the variable arguments are omitted or empty, the ‘##’ operator causes the preprocessor
to remove the comma before it. If you do provide some variable arguments in your macro
invocation, GNU CPP does not complain about the paste operation and instead places the
variable arguments after the comma. Just like any other pasted macro argument, these
arguments are not macro expanded.

6.21 Slightly Looser Rules for Escaped Newlines
The preprocessor treatment of escaped newlines is more relaxed than that specified by
the C90 standard, which requires the newline to immediately follow a backslash. GCC’s
implementation allows whitespace in the form of spaces, horizontal and vertical tabs, and
form feeds between the backslash and the subsequent newline. The preprocessor issues a
warning, but treats it as a valid escaped newline and combines the two lines to form a single
logical line. This works within comments and tokens, as well as between tokens. Comments
are not treated as whitespace for the purposes of this relaxation, since they have not yet
been replaced with spaces.

6.22 Non-Lvalue Arrays May Have Subscripts
In ISO C99, arrays that are not lvalues still decay to pointers, and may be subscripted,
although they may not be modified or used after the next sequence point and the unary
‘&’ operator may not be applied to them. As an extension, GNU C allows such arrays to
be subscripted in C90 mode, though otherwise they do not decay to pointers outside C99
mode. For example, this is valid in GNU C though not valid in C90:
struct foo {int a[4];};
struct foo f();
bar (int index)
{
return f().a[index];
}

6.23 Arithmetic on void- and Function-Pointers
In GNU C, addition and subtraction operations are supported on pointers to void and on
pointers to functions. This is done by treating the size of a void or of a function as 1.
A consequence of this is that sizeof is also allowed on void and on function types, and
returns 1.

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The option ‘-Wpointer-arith’ requests a warning if these extensions are used.

6.24 Pointers to Arrays with Qualifiers Work as Expected
In GNU C, pointers to arrays with qualifiers work similar to pointers to other qualified
types. For example, a value of type int (*)[5] can be used to initialize a variable of type
const int (*)[5]. These types are incompatible in ISO C because the const qualifier is
formally attached to the element type of the array and not the array itself.
extern void
transpose (int N, int M, double out[M][N], const double in[N][M]);
double x[3][2];
double y[2][3];
...
transpose(3, 2, y, x);

6.25 Non-Constant Initializers
As in standard C++ and ISO C99, the elements of an aggregate initializer for an automatic
variable are not required to be constant expressions in GNU C. Here is an example of an
initializer with run-time varying elements:
foo (float f, float g)
{
float beat_freqs[2] = { f-g, f+g };
/* . . . */
}

6.26 Compound Literals
A compound literal looks like a cast of a brace-enclosed aggregate initializer list. Its value is
an object of the type specified in the cast, containing the elements specified in the initializer.
Unlike the result of a cast, a compound literal is an lvalue. ISO C99 and later support
compound literals. As an extension, GCC supports compound literals also in C90 mode
and in C++, although as explained below, the C++ semantics are somewhat different.
Usually, the specified type of a compound literal is a structure. Assume that struct foo
and structure are declared as shown:
struct foo {int a; char b[2];} structure;

Here is an example of constructing a struct foo with a compound literal:
structure = ((struct foo) {x + y, ’a’, 0});

This is equivalent to writing the following:
{
struct foo temp = {x + y, ’a’, 0};
structure = temp;
}

You can also construct an array, though this is dangerous in C++, as explained below.
If all the elements of the compound literal are (made up of) simple constant expressions
suitable for use in initializers of objects of static storage duration, then the compound literal
can be coerced to a pointer to its first element and used in such an initializer, as shown
here:
char **foo = (char *[]) { "x", "y", "z" };

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Compound literals for scalar types and union types are also allowed. In the following
example the variable i is initialized to the value 2, the result of incrementing the unnamed
object created by the compound literal.
int i = ++(int) { 1 };

As a GNU extension, GCC allows initialization of objects with static storage duration
by compound literals (which is not possible in ISO C99 because the initializer is not a
constant). It is handled as if the object were initialized only with the brace-enclosed list if
the types of the compound literal and the object match. The elements of the compound
literal must be constant. If the object being initialized has array type of unknown size, the
size is determined by the size of the compound literal.
static struct foo x = (struct foo) {1, ’a’, ’b’};
static int y[] = (int []) {1, 2, 3};
static int z[] = (int [3]) {1};

The above lines are equivalent to the following:
static struct foo x = {1, ’a’, ’b’};
static int y[] = {1, 2, 3};
static int z[] = {1, 0, 0};

In C, a compound literal designates an unnamed object with static or automatic storage
duration. In C++, a compound literal designates a temporary object that only lives until
the end of its full-expression. As a result, well-defined C code that takes the address of
a subobject of a compound literal can be undefined in C++, so G++ rejects the conversion
of a temporary array to a pointer. For instance, if the array compound literal example
above appeared inside a function, any subsequent use of foo in C++ would have undefined
behavior because the lifetime of the array ends after the declaration of foo.
As an optimization, G++ sometimes gives array compound literals longer lifetimes: when
the array either appears outside a function or has a const-qualified type. If foo and its
initializer had elements of type char *const rather than char *, or if foo were a global
variable, the array would have static storage duration. But it is probably safest just to
avoid the use of array compound literals in C++ code.

6.27 Designated Initializers
Standard C90 requires the elements of an initializer to appear in a fixed order, the same as
the order of the elements in the array or structure being initialized.
In ISO C99 you can give the elements in any order, specifying the array indices or structure
field names they apply to, and GNU C allows this as an extension in C90 mode as well.
This extension is not implemented in GNU C++.
To specify an array index, write ‘[index] =’ before the element value. For example,
int a[6] = { [4] = 29, [2] = 15 };

is equivalent to
int a[6] = { 0, 0, 15, 0, 29, 0 };

The index values must be constant expressions, even if the array being initialized is automatic.
An alternative syntax for this that has been obsolete since GCC 2.5 but GCC still accepts
is to write ‘[index]’ before the element value, with no ‘=’.

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To initialize a range of elements to the same value, write ‘[first ... last] = value’.
This is a GNU extension. For example,
int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

If the value in it has side effects, the side effects happen only once, not for each initialized
field by the range initializer.
Note that the length of the array is the highest value specified plus one.
In a structure initializer, specify the name of a field to initialize with ‘.fieldname =’
before the element value. For example, given the following structure,
struct point { int x, y; };

the following initialization
struct point p = { .y = yvalue, .x = xvalue };

is equivalent to
struct point p = { xvalue, yvalue };

Another syntax that has the same meaning, obsolete since GCC 2.5, is ‘fieldname:’, as
shown here:
struct point p = { y: yvalue, x: xvalue };

Omitted field members are implicitly initialized the same as objects that have static
storage duration.
The ‘[index]’ or ‘.fieldname’ is known as a designator. You can also use a designator
(or the obsolete colon syntax) when initializing a union, to specify which element of the
union should be used. For example,
union foo { int i; double d; };
union foo f = { .d = 4 };

converts 4 to a double to store it in the union using the second element. By contrast,
casting 4 to type union foo stores it into the union as the integer i, since it is an integer.
See Section 6.29 [Cast to Union], page 463.
You can combine this technique of naming elements with ordinary C initialization of
successive elements. Each initializer element that does not have a designator applies to the
next consecutive element of the array or structure. For example,
int a[6] = { [1] = v1, v2, [4] = v4 };

is equivalent to
int a[6] = { 0, v1, v2, 0, v4, 0 };

Labeling the elements of an array initializer is especially useful when the indices are
characters or belong to an enum type. For example:
int whitespace[256]
= { [’ ’] = 1, [’\t’] = 1, [’\h’] = 1,
[’\f’] = 1, [’\n’] = 1, [’\r’] = 1 };

You can also write a series of ‘.fieldname’ and ‘[index]’ designators before an ‘=’ to
specify a nested subobject to initialize; the list is taken relative to the subobject corresponding to the closest surrounding brace pair. For example, with the ‘struct point’ declaration
above:
struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };

If the same field is initialized multiple times, it has the value from the last initialization.
If any such overridden initialization has side effect, it is unspecified whether the side effect
happens or not. Currently, GCC discards them and issues a warning.

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6.28 Case Ranges
You can specify a range of consecutive values in a single case label, like this:
case low ... high:

This has the same effect as the proper number of individual case labels, one for each integer
value from low to high, inclusive.
This feature is especially useful for ranges of ASCII character codes:
case ’A’ ... ’Z’:

Be careful: Write spaces around the ..., for otherwise it may be parsed wrong when you
use it with integer values. For example, write this:
case 1 ... 5:

rather than this:
case 1...5:

6.29 Cast to a Union Type
A cast to union type looks similar to other casts, except that the type specified is a union
type. You can specify the type either with the union keyword or with a typedef name
that refers to a union. A cast to a union actually creates a compound literal and yields an
lvalue, not an rvalue like true casts do. See Section 6.26 [Compound Literals], page 460.
The types that may be cast to the union type are those of the members of the union.
Thus, given the following union and variables:
union foo { int i; double d; };
int x;
double y;

both x and y can be cast to type union foo.
Using the cast as the right-hand side of an assignment to a variable of union type is
equivalent to storing in a member of the union:
union foo u;
/* . . . */
u = (union foo) x
u = (union foo) y

≡
≡

u.i = x
u.d = y

You can also use the union cast as a function argument:
void hack (union foo);
/* . . . */
hack ((union foo) x);

6.30 Mixed Declarations and Code
ISO C99 and ISO C++ allow declarations and code to be freely mixed within compound
statements. As an extension, GNU C also allows this in C90 mode. For example, you could
do:
int i;
/* . . . */
i++;
int j = i + 2;

Each identifier is visible from where it is declared until the end of the enclosing block.

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6.31 Declaring Attributes of Functions
In GNU C, you can use function attributes to declare certain things about functions called
in your program which help the compiler optimize calls and check your code more carefully.
For example, you can use attributes to declare that a function never returns (noreturn),
returns a value depending only on its arguments (pure), or has printf-style arguments
(format).
You can also use attributes to control memory placement, code generation options or
call/return conventions within the function being annotated. Many of these attributes are
target-specific. For example, many targets support attributes for defining interrupt handler
functions, which typically must follow special register usage and return conventions.
Function attributes are introduced by the __attribute__ keyword on a declaration,
followed by an attribute specification inside double parentheses. You can specify multiple
attributes in a declaration by separating them by commas within the double parentheses
or by immediately following an attribute declaration with another attribute declaration.
See Section 6.37 [Attribute Syntax], page 534, for the exact rules on attribute syntax and
placement. Compatible attribute specifications on distinct declarations of the same function
are merged. An attribute specification that is not compatible with attributes already applied
to a declaration of the same function is ignored with a warning.
GCC also supports attributes on variable declarations (see Section 6.32 [Variable Attributes], page 513), labels (see Section 6.34 [Label Attributes], page 532), enumerators (see
Section 6.35 [Enumerator Attributes], page 533), statements (see Section 6.36 [Statement
Attributes], page 533), and types (see Section 6.33 [Type Attributes], page 524).
There is some overlap between the purposes of attributes and pragmas (see Section 6.61
[Pragmas Accepted by GCC], page 773). It has been found convenient to use __attribute_
_ to achieve a natural attachment of attributes to their corresponding declarations, whereas
#pragma is of use for compatibility with other compilers or constructs that do not naturally
form part of the grammar.
In addition to the attributes documented here, GCC plugins may provide their own
attributes.

6.31.1 Common Function Attributes
The following attributes are supported on most targets.
alias ("target")
The alias attribute causes the declaration to be emitted as an alias for another
symbol, which must be specified. For instance,
void __f () { /* Do something. */; }
void f () __attribute__ ((weak, alias ("__f")));

defines ‘f’ to be a weak alias for ‘__f’. In C++, the mangled name for the target
must be used. It is an error if ‘__f’ is not defined in the same translation unit.
This attribute requires assembler and object file support, and may not be available on all targets.
aligned (alignment)
This attribute specifies a minimum alignment for the function, measured in
bytes.

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You cannot use this attribute to decrease the alignment of a function, only
to increase it. However, when you explicitly specify a function alignment this
overrides the effect of the ‘-falign-functions’ (see Section 3.10 [Optimize
Options], page 114) option for this function.
Note that the effectiveness of aligned attributes may be limited by inherent
limitations in your linker. On many systems, the linker is only able to arrange
for functions to be aligned up to a certain maximum alignment. (For some
linkers, the maximum supported alignment may be very very small.) See your
linker documentation for further information.
The aligned attribute can also be used for variables and fields (see Section 6.32
[Variable Attributes], page 513.)
alloc_align
The alloc_align attribute is used to tell the compiler that the function return
value points to memory, where the returned pointer minimum alignment is given
by one of the functions parameters. GCC uses this information to improve
pointer alignment analysis.
The function parameter denoting the allocated alignment is specified by one
integer argument, whose number is the argument of the attribute. Argument
numbering starts at one.
For instance,
void* my_memalign(size_t, size_t) __attribute__((alloc_align(1)))

declares that my_memalign returns memory with minimum alignment given by
parameter 1.
alloc_size
The alloc_size attribute is used to tell the compiler that the function return
value points to memory, where the size is given by one or two of the functions parameters. GCC uses this information to improve the correctness of
__builtin_object_size.
The function parameter(s) denoting the allocated size are specified by one or
two integer arguments supplied to the attribute. The allocated size is either
the value of the single function argument specified or the product of the two
function arguments specified. Argument numbering starts at one.
For instance,
void* my_calloc(size_t, size_t) __attribute__((alloc_size(1,2)))
void* my_realloc(void*, size_t) __attribute__((alloc_size(2)))

declares that my_calloc returns memory of the size given by the product of
parameter 1 and 2 and that my_realloc returns memory of the size given by
parameter 2.
always_inline
Generally, functions are not inlined unless optimization is specified. For functions declared inline, this attribute inlines the function independent of any
restrictions that otherwise apply to inlining. Failure to inline such a function
is diagnosed as an error. Note that if such a function is called indirectly the
compiler may or may not inline it depending on optimization level and a failure
to inline an indirect call may or may not be diagnosed.

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artificial
This attribute is useful for small inline wrappers that if possible should appear
during debugging as a unit. Depending on the debug info format it either means
marking the function as artificial or using the caller location for all instructions
within the inlined body.
assume_aligned
The assume_aligned attribute is used to tell the compiler that the function
return value points to memory, where the returned pointer minimum alignment
is given by the first argument. If the attribute has two arguments, the second
argument is misalignment offset.
For instance
void* my_alloc1(size_t) __attribute__((assume_aligned(16)))
void* my_alloc2(size_t) __attribute__((assume_aligned(32, 8)))

declares that my_alloc1 returns 16-byte aligned pointer and that my_alloc2
returns a pointer whose value modulo 32 is equal to 8.
bnd_instrument
The bnd_instrument attribute on functions is used to inform the compiler
that the function should be instrumented when compiled with the
‘-fchkp-instrument-marked-only’ option.
bnd_legacy
The bnd_legacy attribute on functions is used to inform the compiler
that the function should not be instrumented when compiled with the
‘-fcheck-pointer-bounds’ option.
cold

The cold attribute on functions is used to inform the compiler that the function
is unlikely to be executed. The function is optimized for size rather than speed
and on many targets it is placed into a special subsection of the text section
so all cold functions appear close together, improving code locality of non-cold
parts of program. The paths leading to calls of cold functions within code are
marked as unlikely by the branch prediction mechanism. It is thus useful to
mark functions used to handle unlikely conditions, such as perror, as cold to
improve optimization of hot functions that do call marked functions in rare
occasions.
When profile feedback is available, via ‘-fprofile-use’, cold functions are
automatically detected and this attribute is ignored.

const

Many functions do not examine any values except their arguments, and have
no effects except to return a value. Calls to such functions lend themselves to
optimization such as common subexpression elimination. The const attribute
imposes greater restrictions on a function’s definition than the similar pure
attribute below because it prohibits the function from reading global variables.
Consequently, the presence of the attribute on a function declaration allows
GCC to emit more efficient code for some calls to the function. Decorating the
same function with both the const and the pure attribute is diagnosed.
Note that a function that has pointer arguments and examines the data pointed
to must not be declared const. Likewise, a function that calls a non-const

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function usually must not be const. Because a const function cannot have
any side effects it does not make sense for such a function to return void.
Declaring such a function is diagnosed.
constructor
destructor
constructor (priority)
destructor (priority)
The constructor attribute causes the function to be called automatically before execution enters main (). Similarly, the destructor attribute causes the
function to be called automatically after main () completes or exit () is called.
Functions with these attributes are useful for initializing data that is used implicitly during the execution of the program.
You may provide an optional integer priority to control the order in which
constructor and destructor functions are run. A constructor with a smaller
priority number runs before a constructor with a larger priority number; the
opposite relationship holds for destructors. So, if you have a constructor that
allocates a resource and a destructor that deallocates the same resource, both
functions typically have the same priority. The priorities for constructor and
destructor functions are the same as those specified for namespace-scope C++
objects (see Section 7.7 [C++ Attributes], page 793). However, at present, the
order in which constructors for C++ objects with static storage duration and
functions decorated with attribute constructor are invoked is unspecified. In
mixed declarations, attribute init_priority can be used to impose a specific
ordering.
deprecated
deprecated (msg)
The deprecated attribute results in a warning if the function is used anywhere
in the source file. This is useful when identifying functions that are expected
to be removed in a future version of a program. The warning also includes the
location of the declaration of the deprecated function, to enable users to easily
find further information about why the function is deprecated, or what they
should do instead. Note that the warnings only occurs for uses:
int old_fn () __attribute__ ((deprecated));
int old_fn ();
int (*fn_ptr)() = old_fn;

results in a warning on line 3 but not line 2. The optional msg argument, which
must be a string, is printed in the warning if present.
The deprecated attribute can also be used for variables and types (see
Section 6.32 [Variable Attributes], page 513, see Section 6.33 [Type Attributes],
page 524.)
error ("message")
warning ("message")
If the error or warning attribute is used on a function declaration and a call to
such a function is not eliminated through dead code elimination or other optimizations, an error or warning (respectively) that includes message is diagnosed.

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This is useful for compile-time checking, especially together with __builtin_
constant_p and inline functions where checking the inline function arguments
is not possible through extern char [(condition) ? 1 : -1]; tricks.
While it is possible to leave the function undefined and thus invoke a link failure
(to define the function with a message in .gnu.warning* section), when using
these attributes the problem is diagnosed earlier and with exact location of
the call even in presence of inline functions or when not emitting debugging
information.
externally_visible
This attribute, attached to a global variable or function, nullifies the effect
of the ‘-fwhole-program’ command-line option, so the object remains visible
outside the current compilation unit.
If ‘-fwhole-program’ is used together with ‘-flto’ and gold is used as the
linker plugin, externally_visible attributes are automatically added to functions (not variable yet due to a current gold issue) that are accessed outside of
LTO objects according to resolution file produced by gold. For other linkers
that cannot generate resolution file, explicit externally_visible attributes
are still necessary.
flatten

Generally, inlining into a function is limited. For a function marked with this
attribute, every call inside this function is inlined, if possible. Whether the
function itself is considered for inlining depends on its size and the current
inlining parameters.

format (archetype, string-index, first-to-check)
The format attribute specifies that a function takes printf, scanf, strftime
or strfmon style arguments that should be type-checked against a format string.
For example, the declaration:
extern int
my_printf (void *my_object, const char *my_format, ...)
__attribute__ ((format (printf, 2, 3)));

causes the compiler to check the arguments in calls to my_printf for consistency
with the printf style format string argument my_format.
The parameter archetype determines how the format string is interpreted, and
should be printf, scanf, strftime, gnu_printf, gnu_scanf, gnu_strftime
or strfmon. (You can also use __printf__, __scanf__, __strftime__ or __
strfmon__.) On MinGW targets, ms_printf, ms_scanf, and ms_strftime are
also present. archetype values such as printf refer to the formats accepted by
the system’s C runtime library, while values prefixed with ‘gnu_’ always refer to
the formats accepted by the GNU C Library. On Microsoft Windows targets,
values prefixed with ‘ms_’ refer to the formats accepted by the ‘msvcrt.dll’
library. The parameter string-index specifies which argument is the format
string argument (starting from 1), while first-to-check is the number of the
first argument to check against the format string. For functions where the
arguments are not available to be checked (such as vprintf), specify the third
parameter as zero. In this case the compiler only checks the format string for
consistency. For strftime formats, the third parameter is required to be zero.

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Since non-static C++ methods have an implicit this argument, the arguments
of such methods should be counted from two, not one, when giving values for
string-index and first-to-check.
In the example above, the format string (my_format) is the second argument
of the function my_print, and the arguments to check start with the third
argument, so the correct parameters for the format attribute are 2 and 3.
The format attribute allows you to identify your own functions that take format strings as arguments, so that GCC can check the calls to these functions
for errors. The compiler always (unless ‘-ffreestanding’ or ‘-fno-builtin’
is used) checks formats for the standard library functions printf, fprintf,
sprintf, scanf, fscanf, sscanf, strftime, vprintf, vfprintf and vsprintf
whenever such warnings are requested (using ‘-Wformat’), so there is no need
to modify the header file ‘stdio.h’. In C99 mode, the functions snprintf,
vsnprintf, vscanf, vfscanf and vsscanf are also checked. Except in strictly
conforming C standard modes, the X/Open function strfmon is also checked
as are printf_unlocked and fprintf_unlocked. See Section 3.4 [Options
Controlling C Dialect], page 35.
For Objective-C dialects, NSString (or __NSString__) is recognized in the
same context. Declarations including these format attributes are parsed for
correct syntax, however the result of checking of such format strings is not yet
defined, and is not carried out by this version of the compiler.
The target may also provide additional types of format checks. See Section 6.60
[Format Checks Specific to Particular Target Machines], page 773.
format_arg (string-index)
The format_arg attribute specifies that a function takes a format string for
a printf, scanf, strftime or strfmon style function and modifies it (for example, to translate it into another language), so the result can be passed to
a printf, scanf, strftime or strfmon style function (with the remaining arguments to the format function the same as they would have been for the
unmodified string). For example, the declaration:
extern char *
my_dgettext (char *my_domain, const char *my_format)
__attribute__ ((format_arg (2)));

causes the compiler to check the arguments in calls to a printf, scanf,
strftime or strfmon type function, whose format string argument is a
call to the my_dgettext function, for consistency with the format string
argument my_format. If the format_arg attribute had not been specified, all
the compiler could tell in such calls to format functions would be that the
format string argument is not constant; this would generate a warning when
‘-Wformat-nonliteral’ is used, but the calls could not be checked without
the attribute.
The parameter string-index specifies which argument is the format string argument (starting from one). Since non-static C++ methods have an implicit this
argument, the arguments of such methods should be counted from two.
The format_arg attribute allows you to identify your own functions that modify
format strings, so that GCC can check the calls to printf, scanf, strftime or

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strfmon type function whose operands are a call to one of your own function.
The compiler always treats gettext, dgettext, and dcgettext in this manner
except when strict ISO C support is requested by ‘-ansi’ or an appropriate
‘-std’ option, or ‘-ffreestanding’ or ‘-fno-builtin’ is used. See Section 3.4
[Options Controlling C Dialect], page 35.
For Objective-C dialects, the format-arg attribute may refer to an NSString
reference for compatibility with the format attribute above.
The target may also allow additional types in format-arg attributes. See
Section 6.60 [Format Checks Specific to Particular Target Machines], page 773.
gnu_inline
This attribute should be used with a function that is also declared with the
inline keyword. It directs GCC to treat the function as if it were defined in
gnu90 mode even when compiling in C99 or gnu99 mode.
If the function is declared extern, then this definition of the function is used
only for inlining. In no case is the function compiled as a standalone function,
not even if you take its address explicitly. Such an address becomes an external
reference, as if you had only declared the function, and had not defined it. This
has almost the effect of a macro. The way to use this is to put a function
definition in a header file with this attribute, and put another copy of the
function, without extern, in a library file. The definition in the header file
causes most calls to the function to be inlined. If any uses of the function
remain, they refer to the single copy in the library. Note that the two definitions
of the functions need not be precisely the same, although if they do not have
the same effect your program may behave oddly.
In C, if the function is neither extern nor static, then the function is compiled
as a standalone function, as well as being inlined where possible.
This is how GCC traditionally handled functions declared inline. Since ISO
C99 specifies a different semantics for inline, this function attribute is provided
as a transition measure and as a useful feature in its own right. This attribute
is available in GCC 4.1.3 and later. It is available if either of the preprocessor macros __GNUC_GNU_INLINE__ or __GNUC_STDC_INLINE__ are defined. See
Section 6.43 [An Inline Function is As Fast As a Macro], page 539.
In C++, this attribute does not depend on extern in any way, but it still requires
the inline keyword to enable its special behavior.
hot

The hot attribute on a function is used to inform the compiler that the function is a hot spot of the compiled program. The function is optimized more
aggressively and on many targets it is placed into a special subsection of the
text section so all hot functions appear close together, improving locality.
When profile feedback is available, via ‘-fprofile-use’, hot functions are automatically detected and this attribute is ignored.

ifunc ("resolver")
The ifunc attribute is used to mark a function as an indirect function using the
STT GNU IFUNC symbol type extension to the ELF standard. This allows the
resolution of the symbol value to be determined dynamically at load time, and

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an optimized version of the routine to be selected for the particular processor or
other system characteristics determined then. To use this attribute, first define
the implementation functions available, and a resolver function that returns a
pointer to the selected implementation function. The implementation functions’
declarations must match the API of the function being implemented. The
resolver should be declared to be a function taking no arguments and returning
a pointer to a function of the same type as the implementation. For example:
void *my_memcpy (void *dst, const void *src, size_t len)
{
...
return dst;
}
static void * (*resolve_memcpy (void))(void *, const void *, size_t)
{
return my_memcpy; // we will just always select this routine
}

The exported header file declaring the function the user calls would contain:
extern void *memcpy (void *, const void *, size_t);

allowing the user to call memcpy as a regular function, unaware of the actual
implementation. Finally, the indirect function needs to be defined in the same
translation unit as the resolver function:
void *memcpy (void *, const void *, size_t)
__attribute__ ((ifunc ("resolve_memcpy")));

In C++, the ifunc attribute takes a string that is the mangled name of the
resolver function. A C++ resolver for a non-static member function of class
C should be declared to return a pointer to a non-member function taking
pointer to C as the first argument, followed by the same arguments as of
the implementation function. G++ checks the signatures of the two functions
and issues a ‘-Wattribute-alias’ warning for mismatches. To suppress a
warning for the necessary cast from a pointer to the implementation member function to the type of the corresponding non-member function use the
‘-Wno-pmf-conversions’ option. For example:
class S
{
private:
int debug_impl (int);
int optimized_impl (int);
typedef int Func (S*, int);
static Func* resolver ();
public:
int interface (int);
};
int S::debug_impl (int) { /* . . . */ }
int S::optimized_impl (int) { /* . . . */ }
S::Func* S::resolver ()
{

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Using the GNU Compiler Collection (GCC)

int (S::*pimpl) (int)
= getenv ("DEBUG") ? &S::debug_impl : &S::optimized_impl;
// Cast triggers -Wno-pmf-conversions.
return reinterpret_cast(pimpl);
}
int S::interface (int) __attribute__ ((ifunc ("_ZN1S8resolverEv")));

Indirect functions cannot be weak. Binutils version 2.20.1 or higher and GNU
C Library version 2.11.1 are required to use this feature.
interrupt
interrupt_handler
Many GCC back ends support attributes to indicate that a function is an interrupt handler, which tells the compiler to generate function entry and exit
sequences that differ from those from regular functions. The exact syntax and
behavior are target-specific; refer to the following subsections for details.
leaf

Calls to external functions with this attribute must return to the current compilation unit only by return or by exception handling. In particular, a leaf
function is not allowed to invoke callback functions passed to it from the current compilation unit, directly call functions exported by the unit, or longjmp
into the unit. Leaf functions might still call functions from other compilation
units and thus they are not necessarily leaf in the sense that they contain no
function calls at all.
The attribute is intended for library functions to improve dataflow analysis.
The compiler takes the hint that any data not escaping the current compilation
unit cannot be used or modified by the leaf function. For example, the sin
function is a leaf function, but qsort is not.
Note that leaf functions might indirectly run a signal handler defined in the
current compilation unit that uses static variables. Similarly, when lazy symbol
resolution is in effect, leaf functions might invoke indirect functions whose resolver function or implementation function is defined in the current compilation
unit and uses static variables. There is no standard-compliant way to write such
a signal handler, resolver function, or implementation function, and the best
that you can do is to remove the leaf attribute or mark all such static variables
volatile. Lastly, for ELF-based systems that support symbol interposition,
care should be taken that functions defined in the current compilation unit do
not unexpectedly interpose other symbols based on the defined standards mode
and defined feature test macros; otherwise an inadvertent callback would be
added.
The attribute has no effect on functions defined within the current compilation
unit. This is to allow easy merging of multiple compilation units into one, for
example, by using the link-time optimization. For this reason the attribute is
not allowed on types to annotate indirect calls.

malloc

This tells the compiler that a function is malloc-like, i.e., that the pointer P
returned by the function cannot alias any other pointer valid when the func-

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473

tion returns, and moreover no pointers to valid objects occur in any storage
addressed by P.
Using this attribute can improve optimization. Functions like malloc and
calloc have this property because they return a pointer to uninitialized or
zeroed-out storage. However, functions like realloc do not have this property,
as they can return a pointer to storage containing pointers.
no_icf

This function attribute prevents a functions from being merged with another
semantically equivalent function.

no_instrument_function
If ‘-finstrument-functions’ is given, profiling function calls are generated at
entry and exit of most user-compiled functions. Functions with this attribute
are not so instrumented.
no_profile_instrument_function
The no_profile_instrument_function attribute on functions is used to inform the compiler that it should not process any profile feedback based optimization code instrumentation.
no_reorder
Do not reorder functions or variables marked no_reorder against each other or
top level assembler statements the executable. The actual order in the program
will depend on the linker command line. Static variables marked like this are
also not removed. This has a similar effect as the ‘-fno-toplevel-reorder’
option, but only applies to the marked symbols.
no_sanitize ("sanitize_option")
The no_sanitize attribute on functions is used to inform the compiler that it
should not do sanitization of all options mentioned in sanitize option. A list of
values acceptable by ‘-fsanitize’ option can be provided.
void
f ()
void
g ()

__attribute__ ((no_sanitize ("alignment", "object-size")))
{ /* Do something. */; }
__attribute__ ((no_sanitize ("alignment,object-size")))
{ /* Do something. */; }

no_sanitize_address
no_address_safety_analysis
The no_sanitize_address attribute on functions is used to inform the compiler that it should not instrument memory accesses in the function when
compiling with the ‘-fsanitize=address’ option. The no_address_safety_
analysis is a deprecated alias of the no_sanitize_address attribute, new
code should use no_sanitize_address.
no_sanitize_thread
The no_sanitize_thread attribute on functions is used to inform the compiler
that it should not instrument memory accesses in the function when compiling
with the ‘-fsanitize=thread’ option.
no_sanitize_undefined
The no_sanitize_undefined attribute on functions is used to inform the compiler that it should not check for undefined behavior in the function when compiling with the ‘-fsanitize=undefined’ option.

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no_split_stack
If ‘-fsplit-stack’ is given, functions have a small prologue which decides
whether to split the stack. Functions with the no_split_stack attribute do
not have that prologue, and thus may run with only a small amount of stack
space available.
no_stack_limit
This attribute locally overrides the ‘-fstack-limit-register’ and
‘-fstack-limit-symbol’ command-line options; it has the effect of disabling
stack limit checking in the function it applies to.
noclone

This function attribute prevents a function from being considered for cloning—a
mechanism that produces specialized copies of functions and which is (currently)
performed by interprocedural constant propagation.

noinline

This function attribute prevents a function from being considered for inlining.
If the function does not have side effects, there are optimizations other than
inlining that cause function calls to be optimized away, although the function
call is live. To keep such calls from being optimized away, put
asm ("");

(see Section 6.45.2 [Extended Asm], page 543) in the called function, to serve
as a special side effect.
noipa

Disable interprocedural optimizations between the function with this attribute
and its callers, as if the body of the function is not available when optimizing
callers and the callers are unavailable when optimizing the body. This attribute
implies noinline, noclone and no_icf attributes. However, this attribute is
not equivalent to a combination of other attributes, because its purpose is to
suppress existing and future optimizations employing interprocedural analysis,
including those that do not have an attribute suitable for disabling them individually. This attribute is supported mainly for the purpose of testing the
compiler.

nonnull (arg-index, ...)
The nonnull attribute specifies that some function parameters should be nonnull pointers. For instance, the declaration:
extern void *
my_memcpy (void *dest, const void *src, size_t len)
__attribute__((nonnull (1, 2)));

causes the compiler to check that, in calls to my_memcpy, arguments dest and
src are non-null. If the compiler determines that a null pointer is passed in
an argument slot marked as non-null, and the ‘-Wnonnull’ option is enabled, a
warning is issued. The compiler may also choose to make optimizations based
on the knowledge that certain function arguments will never be null.
If no argument index list is given to the nonnull attribute, all pointer arguments
are marked as non-null. To illustrate, the following declaration is equivalent to
the previous example:
extern void *
my_memcpy (void *dest, const void *src, size_t len)
__attribute__((nonnull));

Chapter 6: Extensions to the C Language Family

noplt

475

The noplt attribute is the counterpart to option ‘-fno-plt’. Calls to functions
marked with this attribute in position-independent code do not use the PLT.
/* Externally defined function foo.
int foo () __attribute__ ((noplt));

*/

int
main (/* . . . */)
{
/* . . . */
foo ();
/* . . . */
}

The noplt attribute on function foo tells the compiler to assume that the
function foo is externally defined and that the call to foo must avoid the PLT
in position-independent code.
In position-dependent code, a few targets also convert calls to functions that
are marked to not use the PLT to use the GOT instead.
noreturn

A few standard library functions, such as abort and exit, cannot return. GCC
knows this automatically. Some programs define their own functions that never
return. You can declare them noreturn to tell the compiler this fact. For
example,
void fatal () __attribute__ ((noreturn));
void
fatal (/* . . . */)
{
/* . . . */ /* Print error message. */ /* . . . */
exit (1);
}

The noreturn keyword tells the compiler to assume that fatal cannot return.
It can then optimize without regard to what would happen if fatal ever did
return. This makes slightly better code. More importantly, it helps avoid
spurious warnings of uninitialized variables.
The noreturn keyword does not affect the exceptional path when that applies:
a noreturn-marked function may still return to the caller by throwing an exception or calling longjmp.
Do not assume that registers saved by the calling function are restored before
calling the noreturn function.
It does not make sense for a noreturn function to have a return type other
than void.
nothrow

The nothrow attribute is used to inform the compiler that a function cannot
throw an exception. For example, most functions in the standard C library can
be guaranteed not to throw an exception with the notable exceptions of qsort
and bsearch that take function pointer arguments.

optimize

The optimize attribute is used to specify that a function is to be compiled with
different optimization options than specified on the command line. Arguments
can either be numbers or strings. Numbers are assumed to be an optimization
level. Strings that begin with O are assumed to be an optimization option,

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while other options are assumed to be used with a -f prefix. You can also
use the ‘#pragma GCC optimize’ pragma to set the optimization options that
affect more than one function. See Section 6.61.15 [Function Specific Option
Pragmas], page 780, for details about the ‘#pragma GCC optimize’ pragma.
This attribute should be used for debugging purposes only. It is not suitable in
production code.
patchable_function_entry
In case the target’s text segment can be made writable at run time by any
means, padding the function entry with a number of NOPs can be used to
provide a universal tool for instrumentation.
The patchable_function_entry function attribute can be used to change the
number of NOPs to any desired value. The two-value syntax is the same as
for the command-line switch ‘-fpatchable-function-entry=N,M’, generating
N NOPs, with the function entry point before the M th NOP instruction. M
defaults to 0 if omitted e.g. function entry point is before the first NOP.
If patchable function entries are enabled globally using the command-line option ‘-fpatchable-function-entry=N,M’, then you must disable instrumentation on all functions that are part of the instrumentation framework with the
attribute patchable_function_entry (0) to prevent recursion.
pure

Many functions have no effects except the return value and their return value
depends only on the parameters and/or global variables. Calls to such functions
can be subject to common subexpression elimination and loop optimization just
as an arithmetic operator would be. These functions should be declared with
the attribute pure. For example,
int square (int) __attribute__ ((pure));

says that the hypothetical function square is safe to call fewer times than the
program says.
Some common examples of pure functions are strlen or memcmp. Interesting non-pure functions are functions with infinite loops or those depending on
volatile memory or other system resource, that may change between two consecutive calls (such as feof in a multithreading environment).
The pure attribute imposes similar but looser restrictions on a function’s defintion than the const attribute: it allows the function to read global variables.
Decorating the same function with both the pure and the const attribute is
diagnosed. Because a pure function cannot have any side effects it does not
make sense for such a function to return void. Declaring such a function is
diagnosed.
returns_nonnull
The returns_nonnull attribute specifies that the function return value should
be a non-null pointer. For instance, the declaration:
extern void *
mymalloc (size_t len) __attribute__((returns_nonnull));

lets the compiler optimize callers based on the knowledge that the return value
will never be null.

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477

returns_twice
The returns_twice attribute tells the compiler that a function may return
more than one time. The compiler ensures that all registers are dead before
calling such a function and emits a warning about the variables that may be
clobbered after the second return from the function. Examples of such functions
are setjmp and vfork. The longjmp-like counterpart of such function, if any,
might need to be marked with the noreturn attribute.
section ("section-name")
Normally, the compiler places the code it generates in the text section. Sometimes, however, you need additional sections, or you need certain particular
functions to appear in special sections. The section attribute specifies that a
function lives in a particular section. For example, the declaration:
extern void foobar (void) __attribute__ ((section ("bar")));

puts the function foobar in the bar section.
Some file formats do not support arbitrary sections so the section attribute
is not available on all platforms. If you need to map the entire contents of a
module to a particular section, consider using the facilities of the linker instead.
sentinel

This function attribute ensures that a parameter in a function call is an explicit
NULL. The attribute is only valid on variadic functions. By default, the sentinel
is located at position zero, the last parameter of the function call. If an optional
integer position argument P is supplied to the attribute, the sentinel must be
located at position P counting backwards from the end of the argument list.
__attribute__ ((sentinel))
is equivalent to
__attribute__ ((sentinel(0)))

The attribute is automatically set with a position of 0 for the built-in functions
execl and execlp. The built-in function execle has the attribute set with a
position of 1.
A valid NULL in this context is defined as zero with any pointer type. If your
system defines the NULL macro with an integer type then you need to add
an explicit cast. GCC replaces stddef.h with a copy that redefines NULL
appropriately.
The warnings for missing or incorrect sentinels are enabled with ‘-Wformat’.
simd
simd("mask")
This attribute enables creation of one or more function versions that can process
multiple arguments using SIMD instructions from a single invocation. Specifying this attribute allows compiler to assume that such versions are available
at link time (provided in the same or another translation unit). Generated
versions are target-dependent and described in the corresponding Vector ABI
document. For x86 64 target this document can be found here.
The optional argument mask may have the value notinbranch or inbranch,
and instructs the compiler to generate non-masked or masked clones correspondingly. By default, all clones are generated.

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If the attribute is specified and #pragma omp declare simd is present on a
declaration and the ‘-fopenmp’ or ‘-fopenmp-simd’ switch is specified, then
the attribute is ignored.
stack_protect
This attribute adds stack protection code to the function if
flags
‘-fstack-protector’,
‘-fstack-protector-strong’
or
‘-fstack-protector-explicit’ are set.
target (options)
Multiple target back ends implement the target attribute to specify that a
function is to be compiled with different target options than specified on the
command line. This can be used for instance to have functions compiled with a
different ISA (instruction set architecture) than the default. You can also use
the ‘#pragma GCC target’ pragma to set more than one function to be compiled
with specific target options. See Section 6.61.15 [Function Specific Option Pragmas], page 780, for details about the ‘#pragma GCC target’ pragma.
For instance, on an x86, you could declare one function with
the
target("sse4.1,arch=core2")
attribute
and
another
with
target("sse4a,arch=amdfam10"). This is equivalent to compiling the first
function with ‘-msse4.1’ and ‘-march=core2’ options, and the second function
with ‘-msse4a’ and ‘-march=amdfam10’ options. It is up to you to make sure
that a function is only invoked on a machine that supports the particular
ISA it is compiled for (for example by using cpuid on x86 to determine what
feature bits and architecture family are used).
int core2_func (void) __attribute__ ((__target__ ("arch=core2")));
int sse3_func (void) __attribute__ ((__target__ ("sse3")));

You can either use multiple strings separated by commas to specify multiple
options, or separate the options with a comma (‘,’) within a single string.
The options supported are specific to each target; refer to Section 6.31.33 [x86
Function Attributes], page 506, Section 6.31.23 [PowerPC Function Attributes],
page 499, Section 6.31.4 [ARM Function Attributes], page 484, Section 6.31.2
[AArch64 Function Attributes], page 481, Section 6.31.21 [Nios II Function
Attributes], page 498, and Section 6.31.27 [S/390 Function Attributes], page 504
for details.
target_clones (options)
The target_clones attribute is used to specify that a function be cloned into
multiple versions compiled with different target options than specified on the
command line. The supported options and restrictions are the same as for
target attribute.
For instance, on an x86, you could compile a function with target_
clones("sse4.1,avx"). GCC creates two function clones, one compiled with
‘-msse4.1’ and another with ‘-mavx’.
On a PowerPC, you can compile a function with target_
clones("cpu=power9,default").
GCC will create two function
clones, one compiled with ‘-mcpu=power9’ and another with the default

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options. GCC must be configured to use GLIBC 2.23 or newer in order to use
the target_clones attribute.
It also creates a resolver function (see the ifunc attribute above) that dynamically selects a clone suitable for current architecture. The resolver is created
only if there is a usage of a function with target_clones attribute.
unused

This attribute, attached to a function, means that the function is meant to be
possibly unused. GCC does not produce a warning for this function.

used

This attribute, attached to a function, means that code must be emitted for the
function even if it appears that the function is not referenced. This is useful,
for example, when the function is referenced only in inline assembly.
When applied to a member function of a C++ class template, the attribute also
means that the function is instantiated if the class itself is instantiated.

visibility ("visibility_type")
This attribute affects the linkage of the declaration to which it is attached. It
can be applied to variables (see Section 6.32.1 [Common Variable Attributes],
page 513) and types (see Section 6.33.1 [Common Type Attributes], page 524)
as well as functions.
There are four supported visibility type values: default, hidden, protected or
internal visibility.
void __attribute__ ((visibility ("protected")))
f () { /* Do something. */; }
int i __attribute__ ((visibility ("hidden")));

The possible values of visibility type correspond to the visibility settings in the
ELF gABI.
default

Default visibility is the normal case for the object file format. This
value is available for the visibility attribute to override other options
that may change the assumed visibility of entities.
On ELF, default visibility means that the declaration is visible to
other modules and, in shared libraries, means that the declared
entity may be overridden.
On Darwin, default visibility means that the declaration is visible
to other modules.
Default visibility corresponds to “external linkage” in the language.

hidden

Hidden visibility indicates that the entity declared has a new form
of linkage, which we call “hidden linkage”. Two declarations of an
object with hidden linkage refer to the same object if they are in
the same shared object.

internal

Internal visibility is like hidden visibility, but with additional processor specific semantics. Unless otherwise specified by the psABI,
GCC defines internal visibility to mean that a function is never
called from another module. Compare this with hidden functions
which, while they cannot be referenced directly by other modules,
can be referenced indirectly via function pointers. By indicating

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that a function cannot be called from outside the module, GCC
may for instance omit the load of a PIC register since it is known
that the calling function loaded the correct value.
protected
Protected visibility is like default visibility except that it indicates
that references within the defining module bind to the definition in
that module. That is, the declared entity cannot be overridden by
another module.
All visibilities are supported on many, but not all, ELF targets (supported
when the assembler supports the ‘.visibility’ pseudo-op). Default visibility
is supported everywhere. Hidden visibility is supported on Darwin targets.
The visibility attribute should be applied only to declarations that would otherwise have external linkage. The attribute should be applied consistently, so that
the same entity should not be declared with different settings of the attribute.
In C++, the visibility attribute applies to types as well as functions and objects,
because in C++ types have linkage. A class must not have greater visibility than
its non-static data member types and bases, and class members default to the
visibility of their class. Also, a declaration without explicit visibility is limited
to the visibility of its type.
In C++, you can mark member functions and static member variables of a class
with the visibility attribute. This is useful if you know a particular method or
static member variable should only be used from one shared object; then you
can mark it hidden while the rest of the class has default visibility. Care must
be taken to avoid breaking the One Definition Rule; for example, it is usually
not useful to mark an inline method as hidden without marking the whole class
as hidden.
A C++ namespace declaration can also have the visibility attribute.
namespace nspace1 __attribute__ ((visibility ("protected")))
{ /* Do something. */; }

This attribute applies only to the particular namespace body, not to other
definitions of the same namespace; it is equivalent to using ‘#pragma GCC
visibility’ before and after the namespace definition (see Section 6.61.13
[Visibility Pragmas], page 779).
In C++, if a template argument has limited visibility, this restriction is implicitly
propagated to the template instantiation. Otherwise, template instantiations
and specializations default to the visibility of their template.
If both the template and enclosing class have explicit visibility, the visibility
from the template is used.
warn_unused_result
The warn_unused_result attribute causes a warning to be emitted if a caller of
the function with this attribute does not use its return value. This is useful for
functions where not checking the result is either a security problem or always
a bug, such as realloc.
int fn () __attribute__ ((warn_unused_result));

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int foo ()
{
if (fn () < 0) return -1;
fn ();
return 0;
}

results in warning on line 5.
weak

The weak attribute causes the declaration to be emitted as a weak symbol
rather than a global. This is primarily useful in defining library functions that
can be overridden in user code, though it can also be used with non-function
declarations. Weak symbols are supported for ELF targets, and also for a.out
targets when using the GNU assembler and linker.

weakref
weakref ("target")
The weakref attribute marks a declaration as a weak reference. Without arguments, it should be accompanied by an alias attribute naming the target
symbol. Optionally, the target may be given as an argument to weakref itself.
In either case, weakref implicitly marks the declaration as weak. Without a
target, given as an argument to weakref or to alias, weakref is equivalent to
weak.
static int x() __attribute__
/* is equivalent to... */
static int x() __attribute__
/* and to... */
static int x() __attribute__
static int x() __attribute__

((weakref ("y")));
((weak, weakref, alias ("y")));
((weakref));
((alias ("y")));

A weak reference is an alias that does not by itself require a definition to be
given for the target symbol. If the target symbol is only referenced through
weak references, then it becomes a weak undefined symbol. If it is directly
referenced, however, then such strong references prevail, and a definition is
required for the symbol, not necessarily in the same translation unit.
The effect is equivalent to moving all references to the alias to a separate translation unit, renaming the alias to the aliased symbol, declaring it as weak,
compiling the two separate translation units and performing a reloadable link
on them.
At present, a declaration to which weakref is attached can only be static.

6.31.2 AArch64 Function Attributes
The following target-specific function attributes are available for the AArch64 target. For
the most part, these options mirror the behavior of similar command-line options (see
Section 3.18.1 [AArch64 Options], page 228), but on a per-function basis.
general-regs-only
Indicates that no floating-point or Advanced SIMD registers should be used
when generating code for this function. If the function explicitly uses floatingpoint code, then the compiler gives an error. This is the same behavior as that
of the command-line option ‘-mgeneral-regs-only’.

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fix-cortex-a53-835769
Indicates that the workaround for the Cortex-A53 erratum 835769 should be
applied to this function. To explicitly disable the workaround for this function
specify the negated form: no-fix-cortex-a53-835769. This corresponds to
the behavior of the command line options ‘-mfix-cortex-a53-835769’ and
‘-mno-fix-cortex-a53-835769’.
cmodel=

Indicates that code should be generated for a particular code model for this
function. The behavior and permissible arguments are the same as for the
command line option ‘-mcmodel=’.

strict-align
Indicates that the compiler should not assume that unaligned memory references are handled by the system. The behavior is the same as for the commandline option ‘-mstrict-align’.
omit-leaf-frame-pointer
Indicates that the frame pointer should be omitted for a leaf function
call.
To keep the frame pointer, the inverse attribute no-omit-leafframe-pointer can be specified.
These attributes have the same
behavior as the command-line options ‘-momit-leaf-frame-pointer’ and
‘-mno-omit-leaf-frame-pointer’.
tls-dialect=
Specifies the TLS dialect to use for this function. The behavior and permissible
arguments are the same as for the command-line option ‘-mtls-dialect=’.
arch=

Specifies the architecture version and architectural extensions to use for this
function. The behavior and permissible arguments are the same as for the
‘-march=’ command-line option.

tune=

Specifies the core for which to tune the performance of this function. The behavior and permissible arguments are the same as for the ‘-mtune=’ command-line
option.

cpu=

Specifies the core for which to tune the performance of this function and also
whose architectural features to use. The behavior and valid arguments are the
same as for the ‘-mcpu=’ command-line option.

sign-return-address
Select the function scope on which return address signing will be applied. The
behavior and permissible arguments are the same as for the command-line option ‘-msign-return-address=’. The default value is none.
The above target attributes can be specified as follows:
__attribute__((target("attr-string")))
int
f (int a)
{
return a + 5;
}

where attr-string is one of the attribute strings specified above.

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Additionally, the architectural extension string may be specified on its own. This can
be used to turn on and off particular architectural extensions without having to specify a
particular architecture version or core. Example:
__attribute__((target("+crc+nocrypto")))
int
foo (int a)
{
return a + 5;
}

In this example target("+crc+nocrypto") enables the crc extension and disables the
crypto extension for the function foo without modifying an existing ‘-march=’ or ‘-mcpu’
option.
Multiple target function attributes can be specified by separating them with a comma.
For example:
__attribute__((target("arch=armv8-a+crc+crypto,tune=cortex-a53")))
int
foo (int a)
{
return a + 5;
}

is valid and compiles function foo for ARMv8-A with crc and crypto extensions and
tunes it for cortex-a53.

6.31.2.1 Inlining rules
Specifying target attributes on individual functions or performing link-time optimization
across translation units compiled with different target options can affect function inlining
rules:
In particular, a caller function can inline a callee function only if the architectural
features available to the callee are a subset of the features available to the caller.
For example: A function foo compiled with ‘-march=armv8-a+crc’, or tagged with
the equivalent arch=armv8-a+crc attribute, can inline a function bar compiled with
‘-march=armv8-a+nocrc’ because the all the architectural features that function bar
requires are available to function foo. Conversely, function bar cannot inline function foo.
Additionally inlining a function compiled with ‘-mstrict-align’ into a function compiled
without -mstrict-align is not allowed. However, inlining a function compiled without
‘-mstrict-align’ into a function compiled with ‘-mstrict-align’ is allowed.
Note that CPU tuning options and attributes such as the ‘-mcpu=’, ‘-mtune=’ do not
inhibit inlining unless the CPU specified by the ‘-mcpu=’ option or the cpu= attribute
conflicts with the architectural feature rules specified above.

6.31.3 ARC Function Attributes
These function attributes are supported by the ARC back end:
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.

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On the ARC, you must specify the kind of interrupt to be handled in a parameter to the interrupt attribute like this:
void f () __attribute__ ((interrupt ("ilink1")));

Permissible values for this parameter are: ilink1 and ilink2.
long_call
medium_call
short_call
These attributes specify how a particular function is called. These attributes
override the ‘-mlong-calls’ and ‘-mmedium-calls’ (see Section 3.18.3 [ARC
Options], page 235) command-line switches and #pragma long_calls settings.
For ARC, a function marked with the long_call attribute is always called
using register-indirect jump-and-link instructions, thereby enabling the called
function to be placed anywhere within the 32-bit address space. A function
marked with the medium_call attribute will always be close enough to be called
with an unconditional branch-and-link instruction, which has a 25-bit offset
from the call site. A function marked with the short_call attribute will always
be close enough to be called with a conditional branch-and-link instruction,
which has a 21-bit offset from the call site.
jli_always
Forces a particular function to be called using jli instruction. The jli instruction makes use of a table stored into .jlitab section, which holds the location
of the functions which are addressed using this instruction.
jli_fixed
Identical like the above one, but the location of the function in the jli table is
known and given as an attribute parameter.
secure_call
This attribute allows one to mark secure-code functions that are callable from
normal mode. The location of the secure call function into the sjli table needs
to be passed as argument.

6.31.4 ARM Function Attributes
These function attributes are supported for ARM targets:
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
You can specify the kind of interrupt to be handled by adding an optional
parameter to the interrupt attribute like this:
void f () __attribute__ ((interrupt ("IRQ")));

Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF.
On ARMv7-M the interrupt type is ignored, and the attribute means the function may be called with a word-aligned stack pointer.
isr

Use this attribute on ARM to write Interrupt Service Routines. This is an alias
to the interrupt attribute above.

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long_call
short_call
These attributes specify how a particular function is called. These attributes
override the ‘-mlong-calls’ (see Section 3.18.4 [ARM Options], page 245)
command-line switch and #pragma long_calls settings. For ARM, the long_
call attribute indicates that the function might be far away from the call site
and require a different (more expensive) calling sequence. The short_call attribute always places the offset to the function from the call site into the ‘BL’
instruction directly.
naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

pcs
The pcs attribute can be used to control the calling convention used for a
function on ARM. The attribute takes an argument that specifies the calling
convention to use.
When compiling using the AAPCS ABI (or a variant of it) then valid values for
the argument are "aapcs" and "aapcs-vfp". In order to use a variant other
than "aapcs" then the compiler must be permitted to use the appropriate coprocessor registers (i.e., the VFP registers must be available in order to use
"aapcs-vfp"). For example,
/* Argument passed in r0, and result returned in r0+r1.
double f2d (float) __attribute__((pcs("aapcs")));

*/

Variadic functions always use the "aapcs" calling convention and the compiler
rejects attempts to specify an alternative.
target (options)
As discussed in Section 6.31.1 [Common Function Attributes], page 464, this
attribute allows specification of target-specific compilation options.
On ARM, the following options are allowed:
‘thumb’

Force code generation in the Thumb (T16/T32) ISA, depending on
the architecture level.

‘arm’

Force code generation in the ARM (A32) ISA.
Functions from different modes can be inlined in the caller’s mode.

‘fpu=’

Specifies the fpu for which to tune the performance of this function.
The behavior and permissible arguments are the same as for the
‘-mfpu=’ command-line option.

‘arch=’

Specifies the architecture version and architectural extensions to
use for this function. The behavior and permissible arguments are
the same as for the ‘-march=’ command-line option.

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The above target attributes can be specified as follows:
__attribute__((target("arch=armv8-a+crc")))
int
f (int a)
{
return a + 5;
}

Additionally, the architectural extension string may be specified on
its own. This can be used to turn on and off particular architectural extensions without having to specify a particular architecture
version or core. Example:
__attribute__((target("+crc+nocrypto")))
int
foo (int a)
{
return a + 5;
}

In this example target("+crc+nocrypto") enables the crc extension and disables the crypto extension for the function foo without
modifying an existing ‘-march=’ or ‘-mcpu’ option.

6.31.5 AVR Function Attributes
These function attributes are supported by the AVR back end:
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
On the AVR, the hardware globally disables interrupts when an interrupt is
executed. The first instruction of an interrupt handler declared with this attribute is a SEI instruction to re-enable interrupts. See also the signal function
attribute that does not insert a SEI instruction. If both signal and interrupt
are specified for the same function, signal is silently ignored.
naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

no_gccisr
Do not use __gcc_isr pseudo instructions in a function with the interrupt or
signal attribute aka. interrupt service routine (ISR). Use this attribute if the
preamble of the ISR prologue should always read
push __zero_reg__
push __tmp_reg__
in
__tmp_reg__, __SREG__
push __tmp_reg__

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clr
__zero_reg__
and accordingly for the postamble of the epilogue — no matter whether the
mentioned registers are actually used in the ISR or not. Situations where you
might want to use this attribute include:
• Code that (effectively) clobbers bits of SREG other than the I-flag by writing
to the memory location of SREG.
• Code that uses inline assembler to jump to a different function which expects (parts of) the prologue code as outlined above to be present.
To disable __gcc_isr generation for the whole compilation unit, there is option
‘-mno-gas-isr-prologues’, see Section 3.18.5 [AVR Options], page 258.
OS_main
OS_task

signal

On AVR, functions with the OS_main or OS_task attribute do not save/restore
any call-saved register in their prologue/epilogue.
The OS_main attribute can be used when there is guarantee that interrupts are
disabled at the time when the function is entered. This saves resources when
the stack pointer has to be changed to set up a frame for local variables.
The OS_task attribute can be used when there is no guarantee that interrupts
are disabled at that time when the function is entered like for, e.g. task functions
in a multi-threading operating system. In that case, changing the stack pointer
register is guarded by save/clear/restore of the global interrupt enable flag.
The differences to the naked function attribute are:
• naked functions do not have a return instruction whereas OS_main and
OS_task functions have a RET or RETI return instruction.
• naked functions do not set up a frame for local variables or a frame pointer
whereas OS_main and OS_task do this as needed.
Use this attribute on the AVR to indicate that the specified function is an
interrupt handler. The compiler generates function entry and exit sequences
suitable for use in an interrupt handler when this attribute is present.
See also the interrupt function attribute.
The AVR hardware globally disables interrupts when an interrupt is executed.
Interrupt handler functions defined with the signal attribute do not re-enable
interrupts. It is save to enable interrupts in a signal handler. This “save” only
applies to the code generated by the compiler and not to the IRQ layout of the
application which is responsibility of the application.
If both signal and interrupt are specified for the same function, signal is
silently ignored.

6.31.6 Blackfin Function Attributes
These function attributes are supported by the Blackfin back end:
exception_handler
Use this attribute on the Blackfin to indicate that the specified function is an
exception handler. The compiler generates function entry and exit sequences
suitable for use in an exception handler when this attribute is present.

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interrupt_handler
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
kspisusp

When used together with interrupt_handler, exception_handler or nmi_
handler, code is generated to load the stack pointer from the USP register in
the function prologue.

l1_text

This attribute specifies a function to be placed into L1 Instruction SRAM.
The function is put into a specific section named .l1.text. With ‘-mfdpic’,
function calls with a such function as the callee or caller uses inlined PLT.

l2

This attribute specifies a function to be placed into L2 SRAM. The function
is put into a specific section named .l2.text. With ‘-mfdpic’, callers of such
functions use an inlined PLT.

longcall
shortcall
The longcall attribute indicates that the function might be far away from
the call site and require a different (more expensive) calling sequence. The
shortcall attribute indicates that the function is always close enough for the
shorter calling sequence to be used. These attributes override the ‘-mlongcall’
switch.
nesting

Use this attribute together with interrupt_handler, exception_handler or
nmi_handler to indicate that the function entry code should enable nested
interrupts or exceptions.

nmi_handler
Use this attribute on the Blackfin to indicate that the specified function is an
NMI handler. The compiler generates function entry and exit sequences suitable
for use in an NMI handler when this attribute is present.
saveall

Use this attribute to indicate that all registers except the stack pointer should
be saved in the prologue regardless of whether they are used or not.

6.31.7 CR16 Function Attributes
These function attributes are supported by the CR16 back end:
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.

6.31.8 Epiphany Function Attributes
These function attributes are supported by the Epiphany back end:
disinterrupt
This attribute causes the compiler to emit instructions to disable interrupts for
the duration of the given function.

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forwarder_section
This attribute modifies the behavior of an interrupt handler. The interrupt
handler may be in external memory which cannot be reached by a branch
instruction, so generate a local memory trampoline to transfer control. The
single parameter identifies the section where the trampoline is placed.
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present. It may also generate a special
section with code to initialize the interrupt vector table.
On Epiphany targets one or more optional parameters can be added like this:
void __attribute__ ((interrupt ("dma0, dma1"))) universal_dma_handler ();

Permissible values for these parameters are: reset, software_exception,
page_miss, timer0, timer1, message, dma0, dma1, wand and swi. Multiple
parameters indicate that multiple entries in the interrupt vector table should
be initialized for this function, i.e. for each parameter name, a jump to the
function is emitted in the section ivt entry name. The parameter(s) may be
omitted entirely, in which case no interrupt vector table entry is provided.
Note that interrupts are enabled inside the function unless the disinterrupt
attribute is also specified.
The following examples are all valid uses of these attributes on Epiphany targets:
void __attribute__ ((interrupt)) universal_handler ();
void __attribute__ ((interrupt ("dma1"))) dma1_handler ();
void __attribute__ ((interrupt ("dma0, dma1")))
universal_dma_handler ();
void __attribute__ ((interrupt ("timer0"), disinterrupt))
fast_timer_handler ();
void __attribute__ ((interrupt ("dma0, dma1"),
forwarder_section ("tramp")))
external_dma_handler ();

long_call
short_call
These attributes specify how a particular function is called. These attributes
override the ‘-mlong-calls’ (see Section 3.18.2 [Adapteva Epiphany Options],
page 233) command-line switch and #pragma long_calls settings.

6.31.9 H8/300 Function Attributes
These function attributes are available for H8/300 targets:
function_vector
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified function should be called through the function vector. Calling a function
through the function vector reduces code size; however, the function vector
has a limited size (maximum 128 entries on the H8/300 and 64 entries on the
H8/300H and H8S) and shares space with the interrupt vector.

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interrupt_handler
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the
specified function is an interrupt handler. The compiler generates function
entry and exit sequences suitable for use in an interrupt handler when this
attribute is present.
saveall

Use this attribute on the H8/300, H8/300H, and H8S to indicate that all registers except the stack pointer should be saved in the prologue regardless of
whether they are used or not.

6.31.10 IA-64 Function Attributes
These function attributes are supported on IA-64 targets:
syscall_linkage
This attribute is used to modify the IA-64 calling convention by marking all
input registers as live at all function exits. This makes it possible to restart a
system call after an interrupt without having to save/restore the input registers.
This also prevents kernel data from leaking into application code.
version_id
This IA-64 HP-UX attribute, attached to a global variable or function, renames
a symbol to contain a version string, thus allowing for function level versioning.
HP-UX system header files may use function level versioning for some system
calls.
extern int foo () __attribute__((version_id ("20040821")));

Calls to foo are mapped to calls to foo{20040821}.

6.31.11 M32C Function Attributes
These function attributes are supported by the M32C back end:
bank_switch
When added to an interrupt handler with the M32C port, causes the prologue
and epilogue to use bank switching to preserve the registers rather than saving
them on the stack.
fast_interrupt
Use this attribute on the M32C port to indicate that the specified function is
a fast interrupt handler. This is just like the interrupt attribute, except that
freit is used to return instead of reit.
function_vector
On M16C/M32C targets, the function_vector attribute declares a special
page subroutine call function. Use of this attribute reduces the code size by 2
bytes for each call generated to the subroutine. The argument to the attribute is
the vector number entry from the special page vector table which contains the 16
low-order bits of the subroutine’s entry address. Each vector table has special
page number (18 to 255) that is used in jsrs instructions. Jump addresses
of the routines are generated by adding 0x0F0000 (in case of M16C targets)
or 0xFF0000 (in case of M32C targets), to the 2-byte addresses set in the
vector table. Therefore you need to ensure that all the special page vector

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routines should get mapped within the address range 0x0F0000 to 0x0FFFFF
(for M16C) and 0xFF0000 to 0xFFFFFF (for M32C).
In the following example 2 bytes are saved for each call to function foo.
void foo (void) __attribute__((function_vector(0x18)));
void foo (void)
{
}
void bar (void)
{
foo();
}

If functions are defined in one file and are called in another file, then be sure
to write this declaration in both files.
This attribute is ignored for R8C target.
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.

6.31.12 M32R/D Function Attributes
These function attributes are supported by the M32R/D back end:
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
model (model-name)
On the M32R/D, use this attribute to set the addressability of an object, and of
the code generated for a function. The identifier model-name is one of small,
medium, or large, representing each of the code models.
Small model objects live in the lower 16MB of memory (so that their addresses
can be loaded with the ld24 instruction), and are callable with the bl instruction.
Medium model objects may live anywhere in the 32-bit address space (the
compiler generates seth/add3 instructions to load their addresses), and are
callable with the bl instruction.
Large model objects may live anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses), and may not
be reachable with the bl instruction (the compiler generates the much slower
seth/add3/jl instruction sequence).

6.31.13 m68k Function Attributes
These function attributes are supported by the m68k back end:

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interrupt
interrupt_handler
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present. Either name may be used.
interrupt_thread
Use this attribute on fido, a subarchitecture of the m68k, to indicate that the
specified function is an interrupt handler that is designed to run as a thread.
The compiler omits generate prologue/epilogue sequences and replaces the return instruction with a sleep instruction. This attribute is available only on
fido.

6.31.14 MCORE Function Attributes
These function attributes are supported by the MCORE back end:
naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

6.31.15 MeP Function Attributes
These function attributes are supported by the MeP back end:
disinterrupt
On MeP targets, this attribute causes the compiler to emit instructions to
disable interrupts for the duration of the given function.
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
near

This attribute causes the compiler to assume the called function is close enough
to use the normal calling convention, overriding the ‘-mtf’ command-line option.

far

On MeP targets this causes the compiler to use a calling convention that assumes the called function is too far away for the built-in addressing modes.

vliw

The vliw attribute tells the compiler to emit instructions in VLIW mode instead
of core mode. Note that this attribute is not allowed unless a VLIW coprocessor
has been configured and enabled through command-line options.

6.31.16 MicroBlaze Function Attributes
These function attributes are supported on MicroBlaze targets:

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save_volatiles
Use this attribute to indicate that the function is an interrupt handler. All
volatile registers (in addition to non-volatile registers) are saved in the function
prologue. If the function is a leaf function, only volatiles used by the function
are saved. A normal function return is generated instead of a return from
interrupt.
break_handler
Use this attribute to indicate that the specified function is a break handler.
The compiler generates function entry and exit sequences suitable for use in an
break handler when this attribute is present. The return from break_handler
is done through the rtbd instead of rtsd.
void f () __attribute__ ((break_handler));

interrupt_handler
fast_interrupt
These attributes indicate that the specified function is an interrupt handler.
Use the fast_interrupt attribute to indicate handlers used in low-latency
interrupt mode, and interrupt_handler for interrupts that do not use lowlatency handlers. In both cases, GCC emits appropriate prologue code and
generates a return from the handler using rtid instead of rtsd.

6.31.17 Microsoft Windows Function Attributes
The following attributes are available on Microsoft Windows and Symbian OS targets.
dllexport
On Microsoft Windows targets and Symbian OS targets the dllexport attribute causes the compiler to provide a global pointer to a pointer in a DLL,
so that it can be referenced with the dllimport attribute. On Microsoft Windows targets, the pointer name is formed by combining _imp__ and the function
or variable name.
You can use __declspec(dllexport) as a synonym for __attribute__
((dllexport)) for compatibility with other compilers.
On systems that support the visibility attribute, this attribute also implies
“default” visibility. It is an error to explicitly specify any other visibility.
GCC’s default behavior is to emit all inline functions with the dllexport
attribute.
Since this can cause object file-size bloat, you can use
‘-fno-keep-inline-dllexport’, which tells GCC to ignore the attribute for
inlined functions unless the ‘-fkeep-inline-functions’ flag is used instead.
The attribute is ignored for undefined symbols.
When applied to C++ classes, the attribute marks defined non-inlined member
functions and static data members as exports. Static consts initialized in-class
are not marked unless they are also defined out-of-class.
For Microsoft Windows targets there are alternative methods for including the
symbol in the DLL’s export table such as using a ‘.def’ file with an EXPORTS
section or, with GNU ld, using the ‘--export-all’ linker flag.

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dllimport
On Microsoft Windows and Symbian OS targets, the dllimport attribute
causes the compiler to reference a function or variable via a global pointer
to a pointer that is set up by the DLL exporting the symbol. The attribute
implies extern. On Microsoft Windows targets, the pointer name is formed by
combining _imp__ and the function or variable name.
You can use __declspec(dllimport) as a synonym for __attribute__
((dllimport)) for compatibility with other compilers.
On systems that support the visibility attribute, this attribute also implies
“default” visibility. It is an error to explicitly specify any other visibility.
Currently, the attribute is ignored for inlined functions. If the attribute is applied to a symbol definition, an error is reported. If a symbol previously declared
dllimport is later defined, the attribute is ignored in subsequent references,
and a warning is emitted. The attribute is also overridden by a subsequent
declaration as dllexport.
When applied to C++ classes, the attribute marks non-inlined member functions
and static data members as imports. However, the attribute is ignored for
virtual methods to allow creation of vtables using thunks.
On the SH Symbian OS target the dllimport attribute also has another affect—
it can cause the vtable and run-time type information for a class to be exported.
This happens when the class has a dllimported constructor or a non-inline, nonpure virtual function and, for either of those two conditions, the class also has
an inline constructor or destructor and has a key function that is defined in the
current translation unit.
For Microsoft Windows targets the use of the dllimport attribute on functions
is not necessary, but provides a small performance benefit by eliminating a
thunk in the DLL. The use of the dllimport attribute on imported variables
can be avoided by passing the ‘--enable-auto-import’ switch to the GNU
linker. As with functions, using the attribute for a variable eliminates a thunk
in the DLL.
One drawback to using this attribute is that a pointer to a variable marked
as dllimport cannot be used as a constant address. However, a pointer to a
function with the dllimport attribute can be used as a constant initializer;
in this case, the address of a stub function in the import lib is referenced.
On Microsoft Windows targets, the attribute can be disabled for functions by
setting the ‘-mnop-fun-dllimport’ flag.

6.31.18 MIPS Function Attributes
These function attributes are supported by the MIPS back end:
interrupt
Use this attribute to indicate that the specified function is an interrupt
handler. The compiler generates function entry and exit sequences suitable
for use in an interrupt handler when this attribute is present. An optional
argument is supported for the interrupt attribute which allows the interrupt
mode to be described. By default GCC assumes the external interrupt

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controller (EIC) mode is in use, this can be explicitly set using eic. When
interrupts are non-masked then the requested Interrupt Priority Level
(IPL) is copied to the current IPL which has the effect of only enabling
higher priority interrupts. To use vectored interrupt mode use the argument
vector=[sw0|sw1|hw0|hw1|hw2|hw3|hw4|hw5], this will change the behavior
of the non-masked interrupt support and GCC will arrange to mask all
interrupts from sw0 up to and including the specified interrupt vector.
You can use the following attributes to modify the behavior of an interrupt
handler:
use_shadow_register_set
Assume that the handler uses a shadow register set, instead of the
main general-purpose registers. An optional argument intstack is
supported to indicate that the shadow register set contains a valid
stack pointer.
keep_interrupts_masked
Keep interrupts masked for the whole function. Without this attribute, GCC tries to reenable interrupts for as much of the function
as it can.
use_debug_exception_return
Return using the deret instruction. Interrupt handlers that don’t
have this attribute return using eret instead.
You can use any combination of these attributes, as shown below:
void
void
void
void
void

__attribute__
__attribute__
__attribute__
__attribute__
__attribute__

void __attribute__
void __attribute__
void __attribute__

void __attribute__
void __attribute__

((interrupt)) v0 ();
((interrupt, use_shadow_register_set)) v1 ();
((interrupt, keep_interrupts_masked)) v2 ();
((interrupt, use_debug_exception_return)) v3 ();
((interrupt, use_shadow_register_set,
keep_interrupts_masked)) v4 ();
((interrupt, use_shadow_register_set,
use_debug_exception_return)) v5 ();
((interrupt, keep_interrupts_masked,
use_debug_exception_return)) v6 ();
((interrupt, use_shadow_register_set,
keep_interrupts_masked,
use_debug_exception_return)) v7 ();
((interrupt("eic"))) v8 ();
((interrupt("vector=hw3"))) v9 ();

long_call
short_call
near
far
These attributes specify how a particular function is called on MIPS. The
attributes override the ‘-mlong-calls’ (see Section 3.18.26 [MIPS Options],
page 304) command-line switch. The long_call and far attributes are synonyms, and cause the compiler to always call the function by first loading
its address into a register, and then using the contents of that register. The
short_call and near attributes are synonyms, and have the opposite effect;
they specify that non-PIC calls should be made using the more efficient jal
instruction.

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mips16
nomips16
On MIPS targets, you can use the mips16 and nomips16 function attributes to
locally select or turn off MIPS16 code generation. A function with the mips16
attribute is emitted as MIPS16 code, while MIPS16 code generation is disabled for functions with the nomips16 attribute. These attributes override the
‘-mips16’ and ‘-mno-mips16’ options on the command line (see Section 3.18.26
[MIPS Options], page 304).
When compiling files containing mixed MIPS16 and non-MIPS16 code, the preprocessor symbol __mips16 reflects the setting on the command line, not that
within individual functions. Mixed MIPS16 and non-MIPS16 code may interact badly with some GCC extensions such as __builtin_apply (see Section 6.5
[Constructing Calls], page 444).
micromips, MIPS
nomicromips, MIPS
On MIPS targets, you can use the micromips and nomicromips function attributes to locally select or turn off microMIPS code generation. A function with
the micromips attribute is emitted as microMIPS code, while microMIPS code
generation is disabled for functions with the nomicromips attribute. These
attributes override the ‘-mmicromips’ and ‘-mno-micromips’ options on the
command line (see Section 3.18.26 [MIPS Options], page 304).
When compiling files containing mixed microMIPS and non-microMIPS code,
the preprocessor symbol __mips_micromips reflects the setting on the command line, not that within individual functions. Mixed microMIPS and nonmicroMIPS code may interact badly with some GCC extensions such as __
builtin_apply (see Section 6.5 [Constructing Calls], page 444).
nocompression
On MIPS targets, you can use the nocompression function attribute to locally
turn off MIPS16 and microMIPS code generation. This attribute overrides the
‘-mips16’ and ‘-mmicromips’ options on the command line (see Section 3.18.26
[MIPS Options], page 304).

6.31.19 MSP430 Function Attributes
These function attributes are supported by the MSP430 back end:
critical

Critical functions disable interrupts upon entry and restore the previous interrupt state upon exit. Critical functions cannot also have the naked or
reentrant attributes. They can have the interrupt attribute.

interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
You can provide an argument to the interrupt attribute which specifies a name
or number. If the argument is a number it indicates the slot in the interrupt
vector table (0 - 31) to which this handler should be assigned. If the argument

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is a name it is treated as a symbolic name for the vector slot. These names
should match up with appropriate entries in the linker script. By default the
names watchdog for vector 26, nmi for vector 30 and reset for vector 31 are
recognized.
naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

reentrant
Reentrant functions disable interrupts upon entry and enable them upon exit.
Reentrant functions cannot also have the naked or critical attributes. They
can have the interrupt attribute.
wakeup

lower
upper
either

This attribute only applies to interrupt functions. It is silently ignored if applied to a non-interrupt function. A wakeup interrupt function will rouse the
processor from any low-power state that it might be in when the function exits.

On the MSP430 target these attributes can be used to specify whether the
function or variable should be placed into low memory, high memory, or the
placement should be left to the linker to decide. The attributes are only significant if compiling for the MSP430X architecture.
The attributes work in conjunction with a linker script that has been augmented
to specify where to place sections with a .lower and a .upper prefix. So,
for example, as well as placing the .data section, the script also specifies the
placement of a .lower.data and a .upper.data section. The intention is that
lower sections are placed into a small but easier to access memory region and
the upper sections are placed into a larger, but slower to access, region.
The either attribute is special. It tells the linker to place the object into the
corresponding lower section if there is room for it. If there is insufficient room
then the object is placed into the corresponding upper section instead. Note
that the placement algorithm is not very sophisticated. It does not attempt to
find an optimal packing of the lower sections. It just makes one pass over the
objects and does the best that it can. Using the ‘-ffunction-sections’ and
‘-fdata-sections’ command-line options can help the packing, however, since
they produce smaller, easier to pack regions.

6.31.20 NDS32 Function Attributes
These function attributes are supported by the NDS32 back end:
exception
Use this attribute on the NDS32 target to indicate that the specified function
is an exception handler. The compiler will generate corresponding sections for
use in an exception handler.

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interrupt
On NDS32 target, this attribute indicates that the specified function is an
interrupt handler. The compiler generates corresponding sections for use in an
interrupt handler. You can use the following attributes to modify the behavior:
nested

This interrupt service routine is interruptible.

not_nested
This interrupt service routine is not interruptible.
nested_ready
This interrupt service routine is interruptible after PSW.GIE (global
interrupt enable) is set. This allows interrupt service routine to
finish some short critical code before enabling interrupts.
save_all

The system will help save all registers into stack before entering
interrupt handler.

partial_save
The system will help save caller registers into stack before entering
interrupt handler.
naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

reset

Use this attribute on the NDS32 target to indicate that the specified function
is a reset handler. The compiler will generate corresponding sections for use in
a reset handler. You can use the following attributes to provide extra exception
handling:
nmi

Provide a user-defined function to handle NMI exception.

warm

Provide a user-defined function to handle warm reset exception.

6.31.21 Nios II Function Attributes
These function attributes are supported by the Nios II back end:
target (options)
As discussed in Section 6.31.1 [Common Function Attributes], page 464, this
attribute allows specification of target-specific compilation options.
When compiling for Nios II, the following options are allowed:
‘custom-insn=N’
‘no-custom-insn’
Each ‘custom-insn=N’ attribute locally enables use of a custom
instruction with encoding N when generating code that uses
insn. Similarly, ‘no-custom-insn’ locally inhibits use of the
custom instruction insn. These target attributes correspond to

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the ‘-mcustom-insn=N’ and ‘-mno-custom-insn’ command-line
options, and support the same set of insn keywords.
See
Section 3.18.32 [Nios II Options], page 323, for more information.
‘custom-fpu-cfg=name’
This attribute corresponds to the ‘-mcustom-fpu-cfg=name’
command-line option, to select a predefined set of custom
instructions named name. See Section 3.18.32 [Nios II Options],
page 323, for more information.

6.31.22 Nvidia PTX Function Attributes
These function attributes are supported by the Nvidia PTX back end:
kernel

This attribute indicates that the corresponding function should be compiled
as a kernel function, which can be invoked from the host via the CUDA RT
library. By default functions are only callable only from other PTX functions.
Kernel functions must have void return type.

6.31.23 PowerPC Function Attributes
These function attributes are supported by the PowerPC back end:
longcall
shortcall
The longcall attribute indicates that the function might be far away from
the call site and require a different (more expensive) calling sequence. The
shortcall attribute indicates that the function is always close enough for
the shorter calling sequence to be used. These attributes override both the
‘-mlongcall’ switch and the #pragma longcall setting.
See Section 3.18.40 [RS/6000 and PowerPC Options], page 345, for more information on whether long calls are necessary.
target (options)
As discussed in Section 6.31.1 [Common Function Attributes], page 464, this
attribute allows specification of target-specific compilation options.
On the PowerPC, the following options are allowed:
‘altivec’
‘no-altivec’
Generate code that uses (does not use) AltiVec instructions.
In 32-bit code, you cannot enable AltiVec instructions unless
‘-mabi=altivec’ is used on the command line.
‘cmpb’
‘no-cmpb’

Generate code that uses (does not use) the compare bytes instruction implemented on the POWER6 processor and other processors
that support the PowerPC V2.05 architecture.

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‘dlmzb’
‘no-dlmzb’
Generate code that uses (does not use) the string-search ‘dlmzb’
instruction on the IBM 405, 440, 464 and 476 processors. This
instruction is generated by default when targeting those processors.
‘fprnd’
‘no-fprnd’
Generate code that uses (does not use) the FP round to integer
instructions implemented on the POWER5+ processor and other
processors that support the PowerPC V2.03 architecture.
‘hard-dfp’
‘no-hard-dfp’
Generate code that uses (does not use) the decimal floating-point
instructions implemented on some POWER processors.
‘isel’
‘no-isel’

Generate code that uses (does not use) ISEL instruction.

‘mfcrf’
‘no-mfcrf’
Generate code that uses (does not use) the move from condition
register field instruction implemented on the POWER4 processor
and other processors that support the PowerPC V2.01 architecture.
‘mfpgpr’
‘no-mfpgpr’
Generate code that uses (does not use) the FP move to/from general purpose register instructions implemented on the POWER6X
processor and other processors that support the extended PowerPC
V2.05 architecture.
‘mulhw’
‘no-mulhw’
Generate code that uses (does not use) the half-word multiply and
multiply-accumulate instructions on the IBM 405, 440, 464 and
476 processors. These instructions are generated by default when
targeting those processors.
‘multiple’
‘no-multiple’
Generate code that uses (does not use) the load multiple word
instructions and the store multiple word instructions.
‘update’
‘no-update’
Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated
memory location.

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‘popcntb’
‘no-popcntb’
Generate code that uses (does not use) the popcount and doubleprecision FP reciprocal estimate instruction implemented on the
POWER5 processor and other processors that support the PowerPC V2.02 architecture.
‘popcntd’
‘no-popcntd’
Generate code that uses (does not use) the popcount instruction
implemented on the POWER7 processor and other processors that
support the PowerPC V2.06 architecture.
‘powerpc-gfxopt’
‘no-powerpc-gfxopt’
Generate code that uses (does not use) the optional PowerPC architecture instructions in the Graphics group, including floating-point
select.
‘powerpc-gpopt’
‘no-powerpc-gpopt’
Generate code that uses (does not use) the optional PowerPC architecture instructions in the General Purpose group, including
floating-point square root.
‘recip-precision’
‘no-recip-precision’
Assume (do not assume) that the reciprocal estimate instructions
provide higher-precision estimates than is mandated by the PowerPC ABI.
‘string’
‘no-string’
Generate code that uses (does not use) the load string instructions
and the store string word instructions to save multiple registers and
do small block moves.
‘vsx’
‘no-vsx’

‘friz’
‘no-friz’

Generate code that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of built-in functions that allow
more direct access to the VSX instruction set. In 32-bit code, you
cannot enable VSX or AltiVec instructions unless ‘-mabi=altivec’
is used on the command line.
Generate (do not generate) the friz instruction when the
‘-funsafe-math-optimizations’ option is used to optimize
rounding a floating-point value to 64-bit integer and back to
floating point. The friz instruction does not return the same
value if the floating-point number is too large to fit in an integer.

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‘avoid-indexed-addresses’
‘no-avoid-indexed-addresses’
Generate code that tries to avoid (not avoid) the use of indexed
load or store instructions.
‘paired’
‘no-paired’
Generate code that uses (does not use) the generation of PAIRED
simd instructions.
‘longcall’
‘no-longcall’
Generate code that assumes (does not assume) that all calls are far
away so that a longer more expensive calling sequence is required.
‘cpu=CPU’

Specify the architecture to generate code for when compiling the
function. If you select the target("cpu=power7") attribute when
generating 32-bit code, VSX and AltiVec instructions are not generated unless you use the ‘-mabi=altivec’ option on the command
line.

‘tune=TUNE’
Specify the architecture to tune for when compiling the function.
If you do not specify the target("tune=TUNE") attribute and you
do specify the target("cpu=CPU") attribute, compilation tunes for
the CPU architecture, and not the default tuning specified on the
command line.
On the PowerPC, the inliner does not inline a function that has different target
options than the caller, unless the callee has a subset of the target options of
the caller.

6.31.24 RISC-V Function Attributes
These function attributes are supported by the RISC-V back end:
naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

6.31.25 RL78 Function Attributes
These function attributes are supported by the RL78 back end:
interrupt
brk_interrupt
These attributes indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.

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Use brk_interrupt instead of interrupt for handlers intended to be used with
the BRK opcode (i.e. those that must end with RETB instead of RETI).
naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

6.31.26 RX Function Attributes
These function attributes are supported by the RX back end:
fast_interrupt
Use this attribute on the RX port to indicate that the specified function is a
fast interrupt handler. This is just like the interrupt attribute, except that
freit is used to return instead of reit.
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
On RX and RL78 targets, you may specify one or more vector numbers as arguments to the attribute, as well as naming an alternate table name. Parameters
are handled sequentially, so one handler can be assigned to multiple entries in
multiple tables. One may also pass the magic string "$default" which causes
the function to be used for any unfilled slots in the current table.
This example shows a simple assignment of a function to one vector in the
default table (note that preprocessor macros may be used for chip-specific symbolic vector names):
void __attribute__ ((interrupt (5))) txd1_handler ();

This example assigns a function to two slots in the default table (using preprocessor macros defined elsewhere) and makes it the default for the dct table:
void __attribute__ ((interrupt (RXD1_VECT,RXD2_VECT,"dct","$default")))
txd1_handler ();

naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

vector

This RX attribute is similar to the interrupt attribute, including its parameters, but does not make the function an interrupt-handler type function (i.e. it
retains the normal C function calling ABI). See the interrupt attribute for a
description of its arguments.

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6.31.27 S/390 Function Attributes
These function attributes are supported on the S/390:
hotpatch (halfwords-before-function-label,halfwords-after-function-label)
On S/390 System z targets, you can use this function attribute to make GCC
generate a “hot-patching” function prologue. If the ‘-mhotpatch=’ commandline option is used at the same time, the hotpatch attribute takes precedence.
The first of the two arguments specifies the number of halfwords to be added
before the function label. A second argument can be used to specify the number
of halfwords to be added after the function label. For both arguments the
maximum allowed value is 1000000.
If both arguments are zero, hotpatching is disabled.
target (options)
As discussed in Section 6.31.1 [Common Function Attributes], page 464, this
attribute allows specification of target-specific compilation options.
On S/390, the following options are supported:
‘arch=’
‘tune=’
‘stack-guard=’
‘stack-size=’
‘branch-cost=’
‘warn-framesize=’
‘backchain’
‘no-backchain’
‘hard-dfp’
‘no-hard-dfp’
‘hard-float’
‘soft-float’
‘htm’
‘no-htm’
‘vx’
‘no-vx’
‘packed-stack’
‘no-packed-stack’
‘small-exec’
‘no-small-exec’
‘mvcle’
‘no-mvcle’
‘warn-dynamicstack’
‘no-warn-dynamicstack’
The options work exactly like the S/390 specific command line options (without
the prefix ‘-m’) except that they do not change any feature macros. For example,
target("no-vx")

does not undefine the __VEC__ macro.

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6.31.28 SH Function Attributes
These function attributes are supported on the SH family of processors:
function_vector
On SH2A targets, this attribute declares a function to be called using the TBR
relative addressing mode. The argument to this attribute is the entry number of
the same function in a vector table containing all the TBR relative addressable
functions. For correct operation the TBR must be setup accordingly to point to
the start of the vector table before any functions with this attribute are invoked.
Usually a good place to do the initialization is the startup routine. The TBR
relative vector table can have at max 256 function entries. The jumps to these
functions are generated using a SH2A specific, non delayed branch instruction
JSR/N @(disp8,TBR). You must use GAS and GLD from GNU binutils version
2.7 or later for this attribute to work correctly.
In an application, for a function being called once, this attribute saves at least 8
bytes of code; and if other successive calls are being made to the same function,
it saves 2 bytes of code per each of these calls.
interrupt_handler
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
nosave_low_regs
Use this attribute on SH targets to indicate that an interrupt_handler function should not save and restore registers R0..R7. This can be used on SH3*
and SH4* targets that have a second R0..R7 register bank for non-reentrant
interrupt handlers.
renesas

On SH targets this attribute specifies that the function or struct follows the
Renesas ABI.

resbank

On the SH2A target, this attribute enables the high-speed register saving and
restoration using a register bank for interrupt_handler routines. Saving to
the bank is performed automatically after the CPU accepts an interrupt that
uses a register bank.
The nineteen 32-bit registers comprising general register R0 to R14, control
register GBR, and system registers MACH, MACL, and PR and the vector
table address offset are saved into a register bank. Register banks are stacked
in first-in last-out (FILO) sequence. Restoration from the bank is executed by
issuing a RESBANK instruction.

sp_switch
Use this attribute on the SH to indicate an interrupt_handler function should
switch to an alternate stack. It expects a string argument that names a global
variable holding the address of the alternate stack.
void *alt_stack;
void f () __attribute__ ((interrupt_handler,
sp_switch ("alt_stack")));

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trap_exit
Use this attribute on the SH for an interrupt_handler to return using trapa
instead of rte. This attribute expects an integer argument specifying the trap
number to be used.
trapa_handler
On SH targets this function attribute is similar to interrupt_handler but it
does not save and restore all registers.

6.31.29 SPU Function Attributes
These function attributes are supported by the SPU back end:
naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

6.31.30 Symbian OS Function Attributes
See Section 6.31.17 [Microsoft Windows Function Attributes], page 493, for discussion of
the dllexport and dllimport attributes.

6.31.31 V850 Function Attributes
The V850 back end supports these function attributes:
interrupt
interrupt_handler
Use these attributes to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use
in an interrupt handler when either attribute is present.

6.31.32 Visium Function Attributes
These function attributes are supported by the Visium back end:
interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.

6.31.33 x86 Function Attributes
These function attributes are supported by the x86 back end:
cdecl

On the x86-32 targets, the cdecl attribute causes the compiler to assume that
the calling function pops off the stack space used to pass arguments. This is
useful to override the effects of the ‘-mrtd’ switch.

fastcall

On x86-32 targets, the fastcall attribute causes the compiler to pass the first
argument (if of integral type) in the register ECX and the second argument (if

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of integral type) in the register EDX. Subsequent and other typed arguments
are passed on the stack. The called function pops the arguments off the stack.
If the number of arguments is variable all arguments are pushed on the stack.
thiscall

On x86-32 targets, the thiscall attribute causes the compiler to pass the first
argument (if of integral type) in the register ECX. Subsequent and other typed
arguments are passed on the stack. The called function pops the arguments
off the stack. If the number of arguments is variable all arguments are pushed
on the stack. The thiscall attribute is intended for C++ non-static member
functions. As a GCC extension, this calling convention can be used for C
functions and for static member methods.

ms_abi
sysv_abi
On 32-bit and 64-bit x86 targets, you can use an ABI attribute to indicate
which calling convention should be used for a function. The ms_abi attribute
tells the compiler to use the Microsoft ABI, while the sysv_abi attribute tells
the compiler to use the ABI used on GNU/Linux and other systems. The
default is to use the Microsoft ABI when targeting Windows. On all other
systems, the default is the x86/AMD ABI.
Note, the ms_abi attribute for Microsoft Windows 64-bit targets currently requires the ‘-maccumulate-outgoing-args’ option.
callee_pop_aggregate_return (number)
On x86-32 targets, you can use this attribute to control how aggregates are
returned in memory. If the caller is responsible for popping the hidden pointer
together with the rest of the arguments, specify number equal to zero. If callee
is responsible for popping the hidden pointer, specify number equal to one.
The default x86-32 ABI assumes that the callee pops the stack for hidden
pointer. However, on x86-32 Microsoft Windows targets, the compiler assumes
that the caller pops the stack for hidden pointer.
ms_hook_prologue
On 32-bit and 64-bit x86 targets, you can use this function attribute to make
GCC generate the “hot-patching” function prologue used in Win32 API functions in Microsoft Windows XP Service Pack 2 and newer.
naked

This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The
specified function will not have prologue/epilogue sequences generated by the
compiler. Only basic asm statements can safely be included in naked functions
(see Section 6.45.1 [Basic Asm], page 542). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended
upon to work reliably and are not supported.

regparm (number)
On x86-32 targets, the regparm attribute causes the compiler to pass arguments
number one to number if they are of integral type in registers EAX, EDX,
and ECX instead of on the stack. Functions that take a variable number of
arguments continue to be passed all of their arguments on the stack.

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Beware that on some ELF systems this attribute is unsuitable for global functions in shared libraries with lazy binding (which is the default). Lazy binding
sends the first call via resolving code in the loader, which might assume EAX,
EDX and ECX can be clobbered, as per the standard calling conventions. Solaris 8 is affected by this. Systems with the GNU C Library version 2.1 or
higher and FreeBSD are believed to be safe since the loaders there save EAX,
EDX and ECX. (Lazy binding can be disabled with the linker or the loader if
desired, to avoid the problem.)
sseregparm
On x86-32 targets with SSE support, the sseregparm attribute causes the compiler to pass up to 3 floating-point arguments in SSE registers instead of on the
stack. Functions that take a variable number of arguments continue to pass all
of their floating-point arguments on the stack.
force_align_arg_pointer
On x86 targets, the force_align_arg_pointer attribute may be applied to
individual function definitions, generating an alternate prologue and epilogue
that realigns the run-time stack if necessary. This supports mixing legacy codes
that run with a 4-byte aligned stack with modern codes that keep a 16-byte
stack for SSE compatibility.
stdcall

On x86-32 targets, the stdcall attribute causes the compiler to assume that
the called function pops off the stack space used to pass arguments, unless it
takes a variable number of arguments.

no_caller_saved_registers
Use this attribute to indicate that the specified function has no caller-saved
registers. That is, all registers are callee-saved. For example, this attribute can
be used for a function called from an interrupt handler. The compiler generates proper function entry and exit sequences to save and restore any modified
registers, except for the EFLAGS register. Since GCC doesn’t preserve MPX,
SSE, MMX nor x87 states, the GCC option ‘-mgeneral-regs-only’ should be
used to compile functions with no_caller_saved_registers attribute.
interrupt
Use this attribute to indicate that the specified function is an interrupt handler or an exception handler (depending on parameters passed to the function,
explained further). The compiler generates function entry and exit sequences
suitable for use in an interrupt handler when this attribute is present. The IRET
instruction, instead of the RET instruction, is used to return from interrupt handlers. All registers, except for the EFLAGS register which is restored by the
IRET instruction, are preserved by the compiler. Since GCC doesn’t preserve
MPX, SSE, MMX nor x87 states, the GCC option ‘-mgeneral-regs-only’
should be used to compile interrupt and exception handlers.
Any interruptible-without-stack-switch code must be compiled with
‘-mno-red-zone’ since interrupt handlers can and will, because of the
hardware design, touch the red zone.
An interrupt handler must be declared with a mandatory pointer argument:

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struct interrupt_frame;
__attribute__ ((interrupt))
void
f (struct interrupt_frame *frame)
{
}

and you must define struct interrupt_frame as described in the processor’s
manual.
Exception handlers differ from interrupt handlers because the system pushes an
error code on the stack. An exception handler declaration is similar to that for
an interrupt handler, but with a different mandatory function signature. The
compiler arranges to pop the error code off the stack before the IRET instruction.
#ifdef __x86_64__
typedef unsigned long long int uword_t;
#else
typedef unsigned int uword_t;
#endif
struct interrupt_frame;
__attribute__ ((interrupt))
void
f (struct interrupt_frame *frame, uword_t error_code)
{
...
}

Exception handlers should only be used for exceptions that push an error code;
you should use an interrupt handler in other cases. The system will crash if the
wrong kind of handler is used.
target (options)
As discussed in Section 6.31.1 [Common Function Attributes], page 464, this
attribute allows specification of target-specific compilation options.
On the x86, the following options are allowed:
‘abm’
‘no-abm’

Enable/disable the generation of the advanced bit instructions.

‘aes’
‘no-aes’

Enable/disable the generation of the AES instructions.

‘default’
‘mmx’
‘no-mmx’

See Section 7.8 [Function Multiversioning], page 794, where it is
used to specify the default function version.
Enable/disable the generation of the MMX instructions.

‘pclmul’
‘no-pclmul’
Enable/disable the generation of the PCLMUL instructions.
‘popcnt’
‘no-popcnt’
Enable/disable the generation of the POPCNT instruction.

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‘sse’
‘no-sse’

Enable/disable the generation of the SSE instructions.

‘sse2’
‘no-sse2’

Enable/disable the generation of the SSE2 instructions.

‘sse3’
‘no-sse3’

Enable/disable the generation of the SSE3 instructions.

‘sse4’
‘no-sse4’

Enable/disable the generation of the SSE4 instructions (both
SSE4.1 and SSE4.2).

‘sse4.1’
‘no-sse4.1’
Enable/disable the generation of the sse4.1 instructions.
‘sse4.2’
‘no-sse4.2’
Enable/disable the generation of the sse4.2 instructions.
‘sse4a’
‘no-sse4a’
Enable/disable the generation of the SSE4A instructions.
‘fma4’
‘no-fma4’

Enable/disable the generation of the FMA4 instructions.

‘xop’
‘no-xop’

Enable/disable the generation of the XOP instructions.

‘lwp’
‘no-lwp’

Enable/disable the generation of the LWP instructions.

‘ssse3’
‘no-ssse3’
Enable/disable the generation of the SSSE3 instructions.
‘cld’
‘no-cld’

Enable/disable the generation of the CLD before string moves.

‘fancy-math-387’
‘no-fancy-math-387’
Enable/disable the generation of the sin, cos, and sqrt instructions on the 387 floating-point unit.
‘ieee-fp’
‘no-ieee-fp’
Enable/disable the generation of floating point that depends on
IEEE arithmetic.
‘inline-all-stringops’
‘no-inline-all-stringops’
Enable/disable inlining of string operations.

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‘inline-stringops-dynamically’
‘no-inline-stringops-dynamically’
Enable/disable the generation of the inline code to do small string
operations and calling the library routines for large operations.
‘align-stringops’
‘no-align-stringops’
Do/do not align destination of inlined string operations.
‘recip’
‘no-recip’
Enable/disable the generation of RCPSS, RCPPS, RSQRTSS and
RSQRTPS instructions followed an additional Newton-Raphson
step instead of doing a floating-point division.
‘arch=ARCH’
Specify the architecture to generate code for in compiling the function.
‘tune=TUNE’
Specify the architecture to tune for in compiling the function.
‘fpmath=FPMATH’
Specify which floating-point unit to use.
You must
specify
the
target("fpmath=sse,387")
option
as
target("fpmath=sse+387") because the comma would
separate different options.
‘indirect_branch("choice")’
On x86 targets, the indirect_branch attribute causes the compiler
to convert indirect call and jump with choice. ‘keep’ keeps indirect
call and jump unmodified. ‘thunk’ converts indirect call and jump
to call and return thunk. ‘thunk-inline’ converts indirect call and
jump to inlined call and return thunk. ‘thunk-extern’ converts
indirect call and jump to external call and return thunk provided
in a separate object file.
‘function_return("choice")’
On x86 targets, the function_return attribute causes the compiler
to convert function return with choice. ‘keep’ keeps function return
unmodified. ‘thunk’ converts function return to call and return
thunk. ‘thunk-inline’ converts function return to inlined call and
return thunk. ‘thunk-extern’ converts function return to external
call and return thunk provided in a separate object file.
‘nocf_check’
The nocf_check attribute on a function is used to inform the compiler that the function’s prologue should not be instrumented when
compiled with the ‘-fcf-protection=branch’ option. The compiler assumes that the function’s address is a valid target for a
control-flow transfer.

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The nocf_check attribute on a type of pointer to function is used
to inform the compiler that a call through the pointer should not be
instrumented when compiled with the ‘-fcf-protection=branch’
option. The compiler assumes that the function’s address from
the pointer is a valid target for a control-flow transfer. A direct
function call through a function name is assumed to be a safe call
thus direct calls are not instrumented by the compiler.
The nocf_check attribute is applied to an object’s type. In case
of assignment of a function address or a function pointer to another pointer, the attribute is not carried over from the right-hand
object’s type; the type of left-hand object stays unchanged. The
compiler checks for nocf_check attribute mismatch and reports a
warning in case of mismatch.
{
int foo (void) __attribute__(nocf_check);
void (*foo1)(void) __attribute__(nocf_check);
void (*foo2)(void);
/* foo’s address is assumed to be valid.
int
foo (void)

*/

/* This call site is not checked for control-flow
validity. */
(*foo1)();
/* A warning is issued about attribute mismatch.
foo1 = foo2;
/* This call site is still not checked.
(*foo1)();
/* This call site is checked.
(*foo2)();

*/

*/

*/

/* A warning is issued about attribute mismatch.
foo2 = foo1;
/* This call site is still checked.
(*foo2)();

*/

*/

return 0;
}

On the x86, the inliner does not inline a function that has different target
options than the caller, unless the callee has a subset of the target options of
the caller. For example a function declared with target("sse3") can inline a
function with target("sse2"), since -msse3 implies -msse2.

6.31.34 Xstormy16 Function Attributes
These function attributes are supported by the Xstormy16 back end:

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interrupt
Use this attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.

6.32 Specifying Attributes of Variables
The keyword __attribute__ allows you to specify special attributes of variables or structure
fields. This keyword is followed by an attribute specification inside double parentheses.
Some attributes are currently defined generically for variables. Other attributes are defined
for variables on particular target systems. Other attributes are available for functions (see
Section 6.31 [Function Attributes], page 464), labels (see Section 6.34 [Label Attributes],
page 532), enumerators (see Section 6.35 [Enumerator Attributes], page 533), statements
(see Section 6.36 [Statement Attributes], page 533), and for types (see Section 6.33 [Type
Attributes], page 524). Other front ends might define more attributes (see Chapter 7
[Extensions to the C++ Language], page 787).
See Section 6.37 [Attribute Syntax], page 534, for details of the exact syntax for using
attributes.

6.32.1 Common Variable Attributes
The following attributes are supported on most targets.
aligned (alignment)
This attribute specifies a minimum alignment for the variable or structure field,
measured in bytes. For example, the declaration:
int x __attribute__ ((aligned (16))) = 0;

causes the compiler to allocate the global variable x on a 16-byte boundary. On
a 68040, this could be used in conjunction with an asm expression to access the
move16 instruction which requires 16-byte aligned operands.
You can also specify the alignment of structure fields. For example, to create a
double-word aligned int pair, you could write:
struct foo { int x[2] __attribute__ ((aligned (8))); };

This is an alternative to creating a union with a double member, which forces
the union to be double-word aligned.
As in the preceding examples, you can explicitly specify the alignment (in bytes)
that you wish the compiler to use for a given variable or structure field. Alternatively, you can leave out the alignment factor and just ask the compiler
to align a variable or field to the default alignment for the target architecture
you are compiling for. The default alignment is sufficient for all scalar types,
but may not be enough for all vector types on a target that supports vector
operations. The default alignment is fixed for a particular target ABI.
GCC also provides a target specific macro __BIGGEST_ALIGNMENT__, which is
the largest alignment ever used for any data type on the target machine you
are compiling for. For example, you could write:
short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__)));

The compiler automatically sets the alignment for the declared variable or field
to __BIGGEST_ALIGNMENT__. Doing this can often make copy operations more

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efficient, because the compiler can use whatever instructions copy the biggest
chunks of memory when performing copies to or from the variables or fields that
you have aligned this way. Note that the value of __BIGGEST_ALIGNMENT__ may
change depending on command-line options.
When used on a struct, or struct member, the aligned attribute can only increase the alignment; in order to decrease it, the packed attribute must be
specified as well. When used as part of a typedef, the aligned attribute can
both increase and decrease alignment, and specifying the packed attribute generates a warning.
Note that the effectiveness of aligned attributes may be limited by inherent
limitations in your linker. On many systems, the linker is only able to arrange
for variables to be aligned up to a certain maximum alignment. (For some
linkers, the maximum supported alignment may be very very small.) If your
linker is only able to align variables up to a maximum of 8-byte alignment,
then specifying aligned(16) in an __attribute__ still only provides you with
8-byte alignment. See your linker documentation for further information.
The aligned attribute can also be used for functions (see Section 6.31.1 [Common Function Attributes], page 464.)
warn_if_not_aligned (alignment)
This attribute specifies a threshold for the structure field, measured in bytes.
If the structure field is aligned below the threshold, a warning will be issued.
For example, the declaration:
struct foo
{
int i1;
int i2;
unsigned long long x __attribute__((warn_if_not_aligned(16)));
};

causes the compiler to issue an warning on struct foo, like ‘warning:
alignment 8 of ’struct foo’ is less than 16’. The compiler also issues a
warning, like ‘warning: ’x’ offset 8 in ’struct foo’ isn’t aligned to
16’, when the structure field has the misaligned offset:
struct foo
{
int i1;
int i2;
unsigned long long x __attribute__((warn_if_not_aligned(16)));
} __attribute__((aligned(16)));

This warning can be disabled by ‘-Wno-if-not-aligned’. The warn_if_not_
aligned attribute can also be used for types (see Section 6.33.1 [Common Type
Attributes], page 524.)
cleanup (cleanup_function)
The cleanup attribute runs a function when the variable goes out of scope.
This attribute can only be applied to auto function scope variables; it may not
be applied to parameters or variables with static storage duration. The function
must take one parameter, a pointer to a type compatible with the variable. The
return value of the function (if any) is ignored.

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If ‘-fexceptions’ is enabled, then cleanup function is run during the stack
unwinding that happens during the processing of the exception. Note that the
cleanup attribute does not allow the exception to be caught, only to perform
an action. It is undefined what happens if cleanup function does not return
normally.
common
nocommon

The common attribute requests GCC to place a variable in “common” storage.
The nocommon attribute requests the opposite—to allocate space for it directly.
These attributes override the default chosen by the ‘-fno-common’ and
‘-fcommon’ flags respectively.

deprecated
deprecated (msg)
The deprecated attribute results in a warning if the variable is used anywhere
in the source file. This is useful when identifying variables that are expected
to be removed in a future version of a program. The warning also includes the
location of the declaration of the deprecated variable, to enable users to easily
find further information about why the variable is deprecated, or what they
should do instead. Note that the warning only occurs for uses:
extern int old_var __attribute__ ((deprecated));
extern int old_var;
int new_fn () { return old_var; }

results in a warning on line 3 but not line 2. The optional msg argument, which
must be a string, is printed in the warning if present.
The deprecated attribute can also be used for functions and types (see
Section 6.31.1 [Common Function Attributes], page 464, see Section 6.33.1
[Common Type Attributes], page 524).
nonstring
The nonstring variable attribute specifies that an object or member declaration with type array of char, signed char, or unsigned char, or pointer to
such a type is intended to store character arrays that do not necessarily contain
a terminating NUL. This is useful in detecting uses of such arrays or pointers
with functions that expect NUL-terminated strings, and to avoid warnings when
such an array or pointer is used as an argument to a bounded string manipulation function such as strncpy. For example, without the attribute, GCC will
issue a warning for the strncpy call below because it may truncate the copy
without appending the terminating NUL character. Using the attribute makes
it possible to suppress the warning. However, when the array is declared with
the attribute the call to strlen is diagnosed because when the array doesn’t
contain a NUL-terminated string the call is undefined. To copy, compare, of
search non-string character arrays use the memcpy, memcmp, memchr, and other
functions that operate on arrays of bytes. In addition, calling strnlen and
strndup with such arrays is safe provided a suitable bound is specified, and not
diagnosed.
struct Data
{
char name [32] __attribute__ ((nonstring));

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};
int f (struct Data *pd, const char *s)
{
strncpy (pd->name, s, sizeof pd->name);
...
return strlen (pd->name);
// unsafe, gets a warning
}

mode (mode)
This attribute specifies the data type for the declaration—whichever type corresponds to the mode mode. This in effect lets you request an integer or floatingpoint type according to its width.
See Section “Machine Modes” in GNU Compiler Collection (GCC) Internals, for
a list of the possible keywords for mode. You may also specify a mode of byte
or __byte__ to indicate the mode corresponding to a one-byte integer, word or
__word__ for the mode of a one-word integer, and pointer or __pointer__ for
the mode used to represent pointers.
packed

The packed attribute specifies that a variable or structure field should have the
smallest possible alignment—one byte for a variable, and one bit for a field,
unless you specify a larger value with the aligned attribute.
Here is a structure in which the field x is packed, so that it immediately follows
a:
struct foo
{
char a;
int x[2] __attribute__ ((packed));
};

Note: The 4.1, 4.2 and 4.3 series of GCC ignore the packed attribute on
bit-fields of type char. This has been fixed in GCC 4.4 but the change
can lead to differences in the structure layout. See the documentation of
‘-Wpacked-bitfield-compat’ for more information.
section ("section-name")
Normally, the compiler places the objects it generates in sections like data and
bss. Sometimes, however, you need additional sections, or you need certain
particular variables to appear in special sections, for example to map to special
hardware. The section attribute specifies that a variable (or function) lives
in a particular section. For example, this small program uses several specific
section names:
struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
int init_data __attribute__ ((section ("INITDATA")));
main()
{
/* Initialize stack pointer */
init_sp (stack + sizeof (stack));
/* Initialize initialized data */

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memcpy (&init_data, &data, &edata - &data);
/* Turn on the serial ports */
init_duart (&a);
init_duart (&b);
}

Use the section attribute with global variables and not local variables, as shown
in the example.
You may use the section attribute with initialized or uninitialized global variables but the linker requires each object be defined once, with the exception
that uninitialized variables tentatively go in the common (or bss) section and
can be multiply “defined”. Using the section attribute changes what section
the variable goes into and may cause the linker to issue an error if an uninitialized variable has multiple definitions. You can force a variable to be initialized
with the ‘-fno-common’ flag or the nocommon attribute.
Some file formats do not support arbitrary sections so the section attribute
is not available on all platforms. If you need to map the entire contents of a
module to a particular section, consider using the facilities of the linker instead.
tls_model ("tls_model")
The tls_model attribute sets thread-local storage model (see Section 6.63
[Thread-Local], page 782) of a particular __thread variable, overriding
‘-ftls-model=’ command-line switch on a per-variable basis. The tls model
argument should be one of global-dynamic, local-dynamic, initial-exec
or local-exec.
Not all targets support this attribute.
unused

This attribute, attached to a variable, means that the variable is meant to be
possibly unused. GCC does not produce a warning for this variable.

used

This attribute, attached to a variable with static storage, means that the variable must be emitted even if it appears that the variable is not referenced.
When applied to a static data member of a C++ class template, the attribute
also means that the member is instantiated if the class itself is instantiated.

vector_size (bytes)
This attribute specifies the vector size for the variable, measured in bytes. For
example, the declaration:
int foo __attribute__ ((vector_size (16)));

causes the compiler to set the mode for foo, to be 16 bytes, divided into int
sized units. Assuming a 32-bit int (a vector of 4 units of 4 bytes), the corresponding mode of foo is V4SI.
This attribute is only applicable to integral and float scalars, although arrays,
pointers, and function return values are allowed in conjunction with this construct.
Aggregates with this attribute are invalid, even if they are of the same size as
a corresponding scalar. For example, the declaration:
struct S { int a; };

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struct S

__attribute__ ((vector_size (16))) foo;

is invalid even if the size of the structure is the same as the size of the int.
visibility ("visibility_type")
This attribute affects the linkage of the declaration to which it is attached.
The visibility attribute is described in Section 6.31.1 [Common Function
Attributes], page 464.
weak

The weak attribute is described in Section 6.31.1 [Common Function
Attributes], page 464.

6.32.2 ARC Variable Attributes
aux

The aux attribute is used to directly access the ARC’s auxiliary register space
from C. The auxilirary register number is given via attribute argument.

6.32.3 AVR Variable Attributes
progmem

The progmem attribute is used on the AVR to place read-only data in the nonvolatile program memory (flash). The progmem attribute accomplishes this by
putting respective variables into a section whose name starts with .progmem.
This attribute works similar to the section attribute but adds additional checking.
• Ordinary AVR cores with 32 general purpose registers:
progmem affects the location of the data but not how this data is
accessed. In order to read data located with the progmem attribute
(inline) assembler must be used.
/* Use custom macros from AVR-LibC */
#include 
/* Locate var in flash memory */
const int var[2] PROGMEM = { 1, 2 };
int read_var (int i)
{
/* Access var[] by accessor macro from avr/pgmspace.h */
return (int) pgm_read_word (& var[i]);
}

AVR is a Harvard architecture processor and data and read-only
data normally resides in the data memory (RAM).
See also the [AVR Named Address Spaces], page 453 section for an
alternate way to locate and access data in flash memory.
• AVR cores with flash memory visible in the RAM address range:
On such devices, there is no need for attribute progmem or [__
flash], page 453 qualifier at all. Just use standard C / C++. The
compiler will generate LD* instructions. As flash memory is visible
in the RAM address range, and the default linker script does not
locate .rodata in RAM, no special features are needed in order
not to waste RAM for read-only data or to read from flash. You
might even get slightly better performance by avoiding progmem

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and __flash. This applies to devices from families avrtiny and
avrxmega3, see Section 3.18.5 [AVR Options], page 258 for an overview.
• Reduced AVR Tiny cores like ATtiny40:
The compiler adds 0x4000 to the addresses of objects and declarations in progmem and locates the objects in flash memory, namely
in section .progmem.data. The offset is needed because the flash
memory is visible in the RAM address space starting at address
0x4000.
Data in progmem can be accessed by means of ordinary C code, no
special functions or macros are needed.
/* var is located in flash memory */
extern const int var[2] __attribute__((progmem));
int read_var (int i)
{
return var[i];
}

Please notice that on these devices, there is no need for progmem
at all.
io
io (addr) Variables with the io attribute are used to address memory-mapped peripherals
in the io address range. If an address is specified, the variable is assigned that
address, and the value is interpreted as an address in the data address space.
Example:
volatile int porta __attribute__((io (0x22)));

The address specified in the address in the data address range.
Otherwise, the variable it is not assigned an address, but the compiler will still
use in/out instructions where applicable, assuming some other module assigns
an address in the io address range. Example:
extern volatile int porta __attribute__((io));

io_low
io_low (addr)
This is like the io attribute, but additionally it informs the compiler that the
object lies in the lower half of the I/O area, allowing the use of cbi, sbi, sbic
and sbis instructions.
address
address (addr)
Variables with the address attribute are used to address memory-mapped peripherals that may lie outside the io address range.
volatile int porta __attribute__((address (0x600)));

absdata

Variables in static storage and with the absdata attribute can be accessed by
the LDS and STS instructions which take absolute addresses.
• This attribute is only supported for the reduced AVR Tiny core like ATtiny40.

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• You must make sure that respective data is located in the address range
0x40. . . 0xbf accessible by LDS and STS. One way to achieve this as an
appropriate linker description file.
• If the location does not fit the address range of LDS and STS, there is
currently (Binutils 2.26) just an unspecific warning like
module.c:(.text+0x1c): warning: internal error: out
of range error
See also the ‘-mabsdata’ Section 3.18.5 [AVR Options], page 258.

6.32.4 Blackfin Variable Attributes
Three attributes are currently defined for the Blackfin.
l1_data
l1_data_A
l1_data_B
Use these attributes on the Blackfin to place the variable into L1 Data SRAM.
Variables with l1_data attribute are put into the specific section named
.l1.data. Those with l1_data_A attribute are put into the specific section
named .l1.data.A. Those with l1_data_B attribute are put into the specific
section named .l1.data.B.
l2

Use this attribute on the Blackfin to place the variable into L2 SRAM. Variables
with l2 attribute are put into the specific section named .l2.data.

6.32.5 H8/300 Variable Attributes
These variable attributes are available for H8/300 targets:
eightbit_data
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the
specified variable should be placed into the eight-bit data section. The compiler
generates more efficient code for certain operations on data in the eight-bit data
area. Note the eight-bit data area is limited to 256 bytes of data.
You must use GAS and GLD from GNU binutils version 2.7 or later for this
attribute to work correctly.
tiny_data
Use this attribute on the H8/300H and H8S to indicate that the specified variable should be placed into the tiny data section. The compiler generates more
efficient code for loads and stores on data in the tiny data section. Note the
tiny data area is limited to slightly under 32KB of data.

6.32.6 IA-64 Variable Attributes
The IA-64 back end supports the following variable attribute:
model (model-name)
On IA-64, use this attribute to set the addressability of an object. At present,
the only supported identifier for model-name is small, indicating addressability via “small” (22-bit) addresses (so that their addresses can be loaded with

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the addl instruction). Caveat: such addressing is by definition not position
independent and hence this attribute must not be used for objects defined by
shared libraries.

6.32.7 M32R/D Variable Attributes
One attribute is currently defined for the M32R/D.
model (model-name)
Use this attribute on the M32R/D to set the addressability of an object. The
identifier model-name is one of small, medium, or large, representing each of
the code models.
Small model objects live in the lower 16MB of memory (so that their addresses
can be loaded with the ld24 instruction).
Medium and large model objects may live anywhere in the 32-bit address space
(the compiler generates seth/add3 instructions to load their addresses).

6.32.8 MeP Variable Attributes
The MeP target has a number of addressing modes and busses. The near space spans
the standard memory space’s first 16 megabytes (24 bits). The far space spans the entire
32-bit memory space. The based space is a 128-byte region in the memory space that is
addressed relative to the $tp register. The tiny space is a 65536-byte region relative to the
$gp register. In addition to these memory regions, the MeP target has a separate 16-bit
control bus which is specified with cb attributes.
based

Any variable with the based attribute is assigned to the .based section, and is
accessed with relative to the $tp register.

tiny

Likewise, the tiny attribute assigned variables to the .tiny section, relative to
the $gp register.

near

Variables with the near attribute are assumed to have addresses that fit in a
24-bit addressing mode. This is the default for large variables (-mtiny=4 is the
default) but this attribute can override -mtiny= for small variables, or override
-ml.

far

Variables with the far attribute are addressed using a full 32-bit address. Since
this covers the entire memory space, this allows modules to make no assumptions about where variables might be stored.

io
io (addr) Variables with the io attribute are used to address memory-mapped peripherals. If an address is specified, the variable is assigned that address, else it is
not assigned an address (it is assumed some other module assigns an address).
Example:
int timer_count __attribute__((io(0x123)));

cb
cb (addr) Variables with the cb attribute are used to access the control bus, using special
instructions. addr indicates the control bus address. Example:
int cpu_clock __attribute__((cb(0x123)));

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6.32.9 Microsoft Windows Variable Attributes
You can use these attributes on Microsoft Windows targets. Section 6.32.16 [x86 Variable
Attributes], page 524 for additional Windows compatibility attributes available on all x86
targets.
dllimport
dllexport
The dllimport and dllexport attributes are described in Section 6.31.17 [Microsoft Windows Function Attributes], page 493.
selectany
The selectany attribute causes an initialized global variable to have link-once
semantics. When multiple definitions of the variable are encountered by the
linker, the first is selected and the remainder are discarded. Following usage
by the Microsoft compiler, the linker is told not to warn about size or content
differences of the multiple definitions.
Although the primary usage of this attribute is for POD types, the attribute can
also be applied to global C++ objects that are initialized by a constructor. In
this case, the static initialization and destruction code for the object is emitted
in each translation defining the object, but the calls to the constructor and
destructor are protected by a link-once guard variable.
The selectany attribute is only available on Microsoft Windows targets.
You can use __declspec (selectany) as a synonym for __attribute__
((selectany)) for compatibility with other compilers.
shared

On Microsoft Windows, in addition to putting variable definitions in a named
section, the section can also be shared among all running copies of an executable
or DLL. For example, this small program defines shared data by putting it in
a named section shared and marking the section shareable:
int foo __attribute__((section ("shared"), shared)) = 0;
int
main()
{
/* Read and write foo. All running
copies see the same value. */
return 0;
}

You may only use the shared attribute along with section attribute with a
fully-initialized global definition because of the way linkers work. See section
attribute for more information.
The shared attribute is only available on Microsoft Windows.

6.32.10 MSP430 Variable Attributes
noinit

Any data with the noinit attribute will not be initialised by the C runtime
startup code, or the program loader. Not initialising data in this way can reduce
program startup times.

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persistent
Any variable with the persistent attribute will not be initialised by the C
runtime startup code. Instead its value will be set once, when the application
is loaded, and then never initialised again, even if the processor is reset or the
program restarts. Persistent data is intended to be placed into FLASH RAM,
where its value will be retained across resets. The linker script being used to
create the application should ensure that persistent data is correctly placed.
lower
upper
either

These attributes are the same as the MSP430 function attributes of the same
name (see Section 6.31.19 [MSP430 Function Attributes], page 496). These
attributes can be applied to both functions and variables.

6.32.11 Nvidia PTX Variable Attributes
These variable attributes are supported by the Nvidia PTX back end:
shared

Use this attribute to place a variable in the .shared memory space. This
memory space is private to each cooperative thread array; only threads within
one thread block refer to the same instance of the variable. The runtime does
not initialize variables in this memory space.

6.32.12 PowerPC Variable Attributes
Three attributes currently are defined for PowerPC configurations: altivec, ms_struct
and gcc_struct.
For full documentation of the struct attributes please see the documentation in
Section 6.32.16 [x86 Variable Attributes], page 524.
For documentation of altivec attribute please see the documentation in Section 6.33.5
[PowerPC Type Attributes], page 531.

6.32.13 RL78 Variable Attributes
The RL78 back end supports the saddr variable attribute. This specifies placement of the
corresponding variable in the SADDR area, which can be accessed more efficiently than the
default memory region.

6.32.14 SPU Variable Attributes
The SPU supports the spu_vector attribute for variables. For documentation of this
attribute please see the documentation in Section 6.33.6 [SPU Type Attributes], page 531.

6.32.15 V850 Variable Attributes
These variable attributes are supported by the V850 back end:
sda

Use this attribute to explicitly place a variable in the small data area, which
can hold up to 64 kilobytes.

tda

Use this attribute to explicitly place a variable in the tiny data area, which can
hold up to 256 bytes in total.

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zda

Use this attribute to explicitly place a variable in the first 32 kilobytes of memory.

6.32.16 x86 Variable Attributes
Two attributes are currently defined for x86 configurations: ms_struct and gcc_struct.
ms_struct
gcc_struct
If packed is used on a structure, or if bit-fields are used, it may be that the
Microsoft ABI lays out the structure differently than the way GCC normally
does. Particularly when moving packed data between functions compiled with
GCC and the native Microsoft compiler (either via function call or as data in
a file), it may be necessary to access either format.
The ms_struct and gcc_struct attributes correspond to the ‘-mms-bitfields’
and ‘-mno-ms-bitfields’ command-line options, respectively;
see
Section 3.18.56 [x86 Options], page 389, for details of how structure layout is
affected. See Section 6.33.7 [x86 Type Attributes], page 532, for information
about the corresponding attributes on types.

6.32.17 Xstormy16 Variable Attributes
One attribute is currently defined for xstormy16 configurations: below100.
below100
If a variable has the below100 attribute (BELOW100 is allowed also), GCC places
the variable in the first 0x100 bytes of memory and use special opcodes to access
it. Such variables are placed in either the .bss_below100 section or the .data_
below100 section.

6.33 Specifying Attributes of Types
The keyword __attribute__ allows you to specify special attributes of types. Some type
attributes apply only to struct and union types, while others can apply to any type defined via a typedef declaration. Other attributes are defined for functions (see Section 6.31
[Function Attributes], page 464), labels (see Section 6.34 [Label Attributes], page 532), enumerators (see Section 6.35 [Enumerator Attributes], page 533), statements (see Section 6.36
[Statement Attributes], page 533), and for variables (see Section 6.32 [Variable Attributes],
page 513).
The __attribute__ keyword is followed by an attribute specification inside double parentheses.
You may specify type attributes in an enum, struct or union type declaration or definition
by placing them immediately after the struct, union or enum keyword. A less preferred
syntax is to place them just past the closing curly brace of the definition.
You can also include type attributes in a typedef declaration. See Section 6.37 [Attribute
Syntax], page 534, for details of the exact syntax for using attributes.

6.33.1 Common Type Attributes
The following type attributes are supported on most targets.

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aligned (alignment)
This attribute specifies a minimum alignment (in bytes) for variables of the
specified type. For example, the declarations:
struct S { short f[3]; } __attribute__ ((aligned (8)));
typedef int more_aligned_int __attribute__ ((aligned (8)));

force the compiler to ensure (as far as it can) that each variable whose type is
struct S or more_aligned_int is allocated and aligned at least on a 8-byte
boundary. On a SPARC, having all variables of type struct S aligned to 8-byte
boundaries allows the compiler to use the ldd and std (doubleword load and
store) instructions when copying one variable of type struct S to another, thus
improving run-time efficiency.
Note that the alignment of any given struct or union type is required by the
ISO C standard to be at least a perfect multiple of the lowest common multiple
of the alignments of all of the members of the struct or union in question. This
means that you can effectively adjust the alignment of a struct or union type
by attaching an aligned attribute to any one of the members of such a type,
but the notation illustrated in the example above is a more obvious, intuitive,
and readable way to request the compiler to adjust the alignment of an entire
struct or union type.
As in the preceding example, you can explicitly specify the alignment (in bytes)
that you wish the compiler to use for a given struct or union type. Alternatively, you can leave out the alignment factor and just ask the compiler to
align a type to the maximum useful alignment for the target machine you are
compiling for. For example, you could write:
struct S { short f[3]; } __attribute__ ((aligned));

Whenever you leave out the alignment factor in an aligned attribute specification, the compiler automatically sets the alignment for the type to the largest
alignment that is ever used for any data type on the target machine you are
compiling for. Doing this can often make copy operations more efficient, because the compiler can use whatever instructions copy the biggest chunks of
memory when performing copies to or from the variables that have types that
you have aligned this way.
In the example above, if the size of each short is 2 bytes, then the size of the
entire struct S type is 6 bytes. The smallest power of two that is greater than
or equal to that is 8, so the compiler sets the alignment for the entire struct
S type to 8 bytes.
Note that although you can ask the compiler to select a time-efficient alignment
for a given type and then declare only individual stand-alone objects of that
type, the compiler’s ability to select a time-efficient alignment is primarily useful
only when you plan to create arrays of variables having the relevant (efficiently
aligned) type. If you declare or use arrays of variables of an efficiently-aligned
type, then it is likely that your program also does pointer arithmetic (or subscripting, which amounts to the same thing) on pointers to the relevant type,
and the code that the compiler generates for these pointer arithmetic operations
is often more efficient for efficiently-aligned types than for other types.

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Note that the effectiveness of aligned attributes may be limited by inherent
limitations in your linker. On many systems, the linker is only able to arrange
for variables to be aligned up to a certain maximum alignment. (For some
linkers, the maximum supported alignment may be very very small.) If your
linker is only able to align variables up to a maximum of 8-byte alignment,
then specifying aligned(16) in an __attribute__ still only provides you with
8-byte alignment. See your linker documentation for further information.
The aligned attribute can only increase alignment. Alignment can be decreased by specifying the packed attribute. See below.
warn_if_not_aligned (alignment)
This attribute specifies a threshold for the structure field, measured in bytes.
If the structure field is aligned below the threshold, a warning will be issued.
For example, the declaration:
typedef unsigned long long __u64
__attribute__((aligned(4),warn_if_not_aligned(8)));
struct foo
{
int i1;
int i2;
__u64 x;
};

causes the compiler to issue an warning on struct foo, like ‘warning:
alignment 4 of ’struct foo’ is less than 8’. It is used to define struct
foo in such a way that struct foo has the same layout and the structure field
x has the same alignment when __u64 is aligned at either 4 or 8 bytes. Align
struct foo to 8 bytes:
struct foo
{
int i1;
int i2;
__u64 x;
} __attribute__((aligned(8)));

silences the warning. The compiler also issues a warning, like ‘warning: ’x’
offset 12 in ’struct foo’ isn’t aligned to 8’, when the structure field has
the misaligned offset:
struct foo
{
int i1;
int i2;
int i3;
__u64 x;
} __attribute__((aligned(8)));

This warning can be disabled by ‘-Wno-if-not-aligned’.
bnd_variable_size
When applied to a structure field, this attribute tells Pointer Bounds Checker
that the size of this field should not be computed using static type information.
It may be used to mark variably-sized static array fields placed at the end of a
structure.

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struct S
{
int size;
char data[1];
}
S *p = (S *)malloc (sizeof(S) + 100);
p->data[10] = 0; //Bounds violation

By using an attribute for the field we may avoid unwanted bound violation
checks:
struct S
{
int size;
char data[1] __attribute__((bnd_variable_size));
}
S *p = (S *)malloc (sizeof(S) + 100);
p->data[10] = 0; //OK

deprecated
deprecated (msg)
The deprecated attribute results in a warning if the type is used anywhere in
the source file. This is useful when identifying types that are expected to be
removed in a future version of a program. If possible, the warning also includes
the location of the declaration of the deprecated type, to enable users to easily
find further information about why the type is deprecated, or what they should
do instead. Note that the warnings only occur for uses and then only if the type
is being applied to an identifier that itself is not being declared as deprecated.
typedef int T1 __attribute__ ((deprecated));
T1 x;
typedef T1 T2;
T2 y;
typedef T1 T3 __attribute__ ((deprecated));
T3 z __attribute__ ((deprecated));

results in a warning on line 2 and 3 but not lines 4, 5, or 6. No warning is
issued for line 4 because T2 is not explicitly deprecated. Line 5 has no warning
because T3 is explicitly deprecated. Similarly for line 6. The optional msg
argument, which must be a string, is printed in the warning if present.
The deprecated attribute can also be used for functions and variables (see
Section 6.31 [Function Attributes], page 464, see Section 6.32 [Variable Attributes], page 513.)
designated_init
This attribute may only be applied to structure types. It indicates that any initialization of an object of this type must use designated initializers rather than
positional initializers. The intent of this attribute is to allow the programmer
to indicate that a structure’s layout may change, and that therefore relying on
positional initialization will result in future breakage.
GCC emits warnings based on this attribute by default;
use
‘-Wno-designated-init’ to suppress them.
may_alias
Accesses through pointers to types with this attribute are not subject to typebased alias analysis, but are instead assumed to be able to alias any other type

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of objects. In the context of section 6.5 paragraph 7 of the C99 standard, an
lvalue expression dereferencing such a pointer is treated like having a character
type. See ‘-fstrict-aliasing’ for more information on aliasing issues. This
extension exists to support some vector APIs, in which pointers to one vector
type are permitted to alias pointers to a different vector type.
Note that an object of a type with this attribute does not have any special
semantics.
Example of use:
typedef short __attribute__((__may_alias__)) short_a;
int
main (void)
{
int a = 0x12345678;
short_a *b = (short_a *) &a;
b[1] = 0;
if (a == 0x12345678)
abort();
exit(0);
}

If you replaced short_a with short in the variable declaration, the above program would abort when compiled with ‘-fstrict-aliasing’, which is on by
default at ‘-O2’ or above.
packed

This attribute, attached to struct or union type definition, specifies that each
member (other than zero-width bit-fields) of the structure or union is placed
to minimize the memory required. When attached to an enum definition, it
indicates that the smallest integral type should be used.
Specifying the packed attribute for struct and union types is equivalent to
specifying the packed attribute on each of the structure or union members.
Specifying the ‘-fshort-enums’ flag on the command line is equivalent to specifying the packed attribute on all enum definitions.
In the following example struct my_packed_struct’s members are packed
closely together, but the internal layout of its s member is not packed—to
do that, struct my_unpacked_struct needs to be packed too.
struct my_unpacked_struct
{
char c;
int i;
};
struct __attribute__ ((__packed__)) my_packed_struct
{
char c;
int i;
struct my_unpacked_struct s;
};

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You may only specify the packed attribute attribute on the definition of an
enum, struct or union, not on a typedef that does not also define the enumerated type, structure or union.
scalar_storage_order ("endianness")
When attached to a union or a struct, this attribute sets the storage order,
aka endianness, of the scalar fields of the type, as well as the array fields whose
component is scalar. The supported endiannesses are big-endian and littleendian. The attribute has no effects on fields which are themselves a union, a
struct or an array whose component is a union or a struct, and it is possible
for these fields to have a different scalar storage order than the enclosing type.
This attribute is supported only for targets that use a uniform default scalar
storage order (fortunately, most of them), i.e. targets that store the scalars
either all in big-endian or all in little-endian.
Additional restrictions are enforced for types with the reverse scalar storage
order with regard to the scalar storage order of the target:
• Taking the address of a scalar field of a union or a struct with reverse
scalar storage order is not permitted and yields an error.
• Taking the address of an array field, whose component is scalar, of a union
or a struct with reverse scalar storage order is permitted but yields a
warning, unless ‘-Wno-scalar-storage-order’ is specified.
• Taking the address of a union or a struct with reverse scalar storage order
is permitted.
These restrictions exist because the storage order attribute is lost when the
address of a scalar or the address of an array with scalar component is taken,
so storing indirectly through this address generally does not work. The second
case is nevertheless allowed to be able to perform a block copy from or to the
array.
Moreover, the use of type punning or aliasing to toggle the storage order is
not supported; that is to say, a given scalar object cannot be accessed through
distinct types that assign a different storage order to it.
transparent_union
This attribute, attached to a union type definition, indicates that any function
parameter having that union type causes calls to that function to be treated in
a special way.
First, the argument corresponding to a transparent union type can be of any
type in the union; no cast is required. Also, if the union contains a pointer type,
the corresponding argument can be a null pointer constant or a void pointer
expression; and if the union contains a void pointer type, the corresponding
argument can be any pointer expression. If the union member type is a pointer,
qualifiers like const on the referenced type must be respected, just as with
normal pointer conversions.
Second, the argument is passed to the function using the calling conventions of
the first member of the transparent union, not the calling conventions of the

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union itself. All members of the union must have the same machine representation; this is necessary for this argument passing to work properly.
Transparent unions are designed for library functions that have multiple interfaces for compatibility reasons. For example, suppose the wait function must
accept either a value of type int * to comply with POSIX, or a value of type
union wait * to comply with the 4.1BSD interface. If wait’s parameter were
void *, wait would accept both kinds of arguments, but it would also accept
any other pointer type and this would make argument type checking less useful.
Instead,  might define the interface as follows:
typedef union __attribute__ ((__transparent_union__))
{
int *__ip;
union wait *__up;
} wait_status_ptr_t;
pid_t wait (wait_status_ptr_t);

This interface allows either int * or union wait * arguments to be passed,
using the int * calling convention. The program can call wait with arguments
of either type:
int w1 () { int w; return wait (&w); }
int w2 () { union wait w; return wait (&w); }

With this interface, wait’s implementation might look like this:
pid_t wait (wait_status_ptr_t p)
{
return waitpid (-1, p.__ip, 0);
}

unused

When attached to a type (including a union or a struct), this attribute means
that variables of that type are meant to appear possibly unused. GCC does not
produce a warning for any variables of that type, even if the variable appears to
do nothing. This is often the case with lock or thread classes, which are usually
defined and then not referenced, but contain constructors and destructors that
have nontrivial bookkeeping functions.

visibility
In C++, attribute visibility (see Section 6.31 [Function Attributes], page 464)
can also be applied to class, struct, union and enum types. Unlike other type
attributes, the attribute must appear between the initial keyword and the name
of the type; it cannot appear after the body of the type.
Note that the type visibility is applied to vague linkage entities associated with
the class (vtable, typeinfo node, etc.). In particular, if a class is thrown as
an exception in one shared object and caught in another, the class must have
default visibility. Otherwise the two shared objects are unable to use the same
typeinfo node and exception handling will break.
To specify multiple attributes, separate them by commas within the double parentheses:
for example, ‘__attribute__ ((aligned (16), packed))’.

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6.33.2 ARC Type Attributes
Declaring objects with uncached allows you to exclude data-cache participation in load and
store operations on those objects without involving the additional semantic implications
of volatile. The .di instruction suffix is used for all loads and stores of data declared
uncached.

6.33.3 ARM Type Attributes
On those ARM targets that support dllimport (such as Symbian OS), you can use the
notshared attribute to indicate that the virtual table and other similar data for a class
should not be exported from a DLL. For example:
class __declspec(notshared) C {
public:
__declspec(dllimport) C();
virtual void f();
}
__declspec(dllexport)
C::C() {}

In this code, C::C is exported from the current DLL, but the virtual table for C is not
exported. (You can use __attribute__ instead of __declspec if you prefer, but most
Symbian OS code uses __declspec.)

6.33.4 MeP Type Attributes
Many of the MeP variable attributes may be applied to types as well. Specifically, the
based, tiny, near, and far attributes may be applied to either. The io and cb attributes
may not be applied to types.

6.33.5 PowerPC Type Attributes
Three attributes currently are defined for PowerPC configurations: altivec, ms_struct
and gcc_struct.
For full documentation of the ms_struct and gcc_struct attributes please see the documentation in Section 6.33.7 [x86 Type Attributes], page 532.
The altivec attribute allows one to declare AltiVec vector data types supported by the
AltiVec Programming Interface Manual. The attribute requires an argument to specify one
of three vector types: vector__, pixel__ (always followed by unsigned short), and bool__
(always followed by unsigned).
__attribute__((altivec(vector__)))
__attribute__((altivec(pixel__))) unsigned short
__attribute__((altivec(bool__))) unsigned

These attributes mainly are intended to support the __vector, __pixel, and __bool
AltiVec keywords.

6.33.6 SPU Type Attributes
The SPU supports the spu_vector attribute for types. This attribute allows one to declare vector data types supported by the Sony/Toshiba/IBM SPU Language Extensions
Specification. It is intended to support the __vector keyword.

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6.33.7 x86 Type Attributes
Two attributes are currently defined for x86 configurations: ms_struct and gcc_struct.
ms_struct
gcc_struct
If packed is used on a structure, or if bit-fields are used it may be that the
Microsoft ABI packs them differently than GCC normally packs them. Particularly when moving packed data between functions compiled with GCC and
the native Microsoft compiler (either via function call or as data in a file), it
may be necessary to access either format.
The ms_struct and gcc_struct attributes correspond to the ‘-mms-bitfields’
and ‘-mno-ms-bitfields’ command-line options, respectively;
see
Section 3.18.56 [x86 Options], page 389, for details of how structure layout
is affected. See Section 6.32.16 [x86 Variable Attributes], page 524, for
information about the corresponding attributes on variables.

6.34 Label Attributes
GCC allows attributes to be set on C labels. See Section 6.37 [Attribute Syntax], page 534,
for details of the exact syntax for using attributes. Other attributes are available for
functions (see Section 6.31 [Function Attributes], page 464), variables (see Section 6.32
[Variable Attributes], page 513), enumerators (see Section 6.35 [Enumerator Attributes],
page 533), statements (see Section 6.36 [Statement Attributes], page 533), and for types
(see Section 6.33 [Type Attributes], page 524).
This example uses the cold label attribute to indicate the ErrorHandling branch is
unlikely to be taken and that the ErrorHandling label is unused:
asm goto ("some asm" : : : : NoError);
/* This branch (the fall-through from the asm) is less commonly used */
ErrorHandling:
__attribute__((cold, unused)); /* Semi-colon is required here */
printf("error\n");
return 0;
NoError:
printf("no error\n");
return 1;

unused

This feature is intended for program-generated code that may contain unused
labels, but which is compiled with ‘-Wall’. It is not normally appropriate to
use in it human-written code, though it could be useful in cases where the code
that jumps to the label is contained within an #ifdef conditional.

hot

The hot attribute on a label is used to inform the compiler that the path
following the label is more likely than paths that are not so annotated. This
attribute is used in cases where __builtin_expect cannot be used, for instance
with computed goto or asm goto.

cold

The cold attribute on labels is used to inform the compiler that the path
following the label is unlikely to be executed. This attribute is used in cases

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where __builtin_expect cannot be used, for instance with computed goto or
asm goto.

6.35 Enumerator Attributes
GCC allows attributes to be set on enumerators. See Section 6.37 [Attribute Syntax],
page 534, for details of the exact syntax for using attributes. Other attributes are available
for functions (see Section 6.31 [Function Attributes], page 464), variables (see Section 6.32
[Variable Attributes], page 513), labels (see Section 6.34 [Label Attributes], page 532), statements (see Section 6.36 [Statement Attributes], page 533), and for types (see Section 6.33
[Type Attributes], page 524).
This example uses the deprecated enumerator attribute to indicate the oldval enumerator is deprecated:
enum E {
oldval __attribute__((deprecated)),
newval
};
int
fn (void)
{
return oldval;
}

deprecated
The deprecated attribute results in a warning if the enumerator is used anywhere in the source file. This is useful when identifying enumerators that are
expected to be removed in a future version of a program. The warning also
includes the location of the declaration of the deprecated enumerator, to enable
users to easily find further information about why the enumerator is deprecated,
or what they should do instead. Note that the warnings only occurs for uses.

6.36 Statement Attributes
GCC allows attributes to be set on null statements. See Section 6.37 [Attribute Syntax], page 534, for details of the exact syntax for using attributes. Other attributes are
available for functions (see Section 6.31 [Function Attributes], page 464), variables (see
Section 6.32 [Variable Attributes], page 513), labels (see Section 6.34 [Label Attributes],
page 532), enumerators (see Section 6.35 [Enumerator Attributes], page 533), and for types
(see Section 6.33 [Type Attributes], page 524).
This example uses the fallthrough statement attribute to indicate that the
‘-Wimplicit-fallthrough’ warning should not be emitted:
switch (cond)
{
case 1:
bar (1);
__attribute__((fallthrough));
case 2:
...
}

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fallthrough
The fallthrough attribute with a null statement serves as a fallthrough statement. It hints to the compiler that a statement that falls through to another
case label, or user-defined label in a switch statement is intentional and thus
the ‘-Wimplicit-fallthrough’ warning must not trigger. The fallthrough attribute may appear at most once in each attribute list, and may not be mixed
with other attributes. It can only be used in a switch statement (the compiler
will issue an error otherwise), after a preceding statement and before a logically
succeeding case label, or user-defined label.

6.37 Attribute Syntax
This section describes the syntax with which __attribute__ may be used, and the constructs to which attribute specifiers bind, for the C language. Some details may vary for
C++ and Objective-C. Because of infelicities in the grammar for attributes, some forms
described here may not be successfully parsed in all cases.
There are some problems with the semantics of attributes in C++. For example, there
are no manglings for attributes, although they may affect code generation, so problems
may arise when attributed types are used in conjunction with templates or overloading.
Similarly, typeid does not distinguish between types with different attributes. Support for
attributes in C++ may be restricted in future to attributes on declarations only, but not on
nested declarators.
See Section 6.31 [Function Attributes], page 464, for details of the semantics of attributes
applying to functions. See Section 6.32 [Variable Attributes], page 513, for details of the
semantics of attributes applying to variables. See Section 6.33 [Type Attributes], page 524,
for details of the semantics of attributes applying to structure, union and enumerated types.
See Section 6.34 [Label Attributes], page 532, for details of the semantics of attributes
applying to labels. See Section 6.35 [Enumerator Attributes], page 533, for details of the
semantics of attributes applying to enumerators. See Section 6.36 [Statement Attributes],
page 533, for details of the semantics of attributes applying to statements.
An attribute specifier is of the form __attribute__ ((attribute-list)). An attribute
list is a possibly empty comma-separated sequence of attributes, where each attribute is
one of the following:
• Empty. Empty attributes are ignored.
• An attribute name (which may be an identifier such as unused, or a reserved word such
as const).
• An attribute name followed by a parenthesized list of parameters for the attribute.
These parameters take one of the following forms:
• An identifier. For example, mode attributes use this form.
• An identifier followed by a comma and a non-empty comma-separated list of expressions. For example, format attributes use this form.
• A possibly empty comma-separated list of expressions. For example, format_arg
attributes use this form with the list being a single integer constant expression,
and alias attributes use this form with the list being a single string constant.

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An attribute specifier list is a sequence of one or more attribute specifiers, not separated
by any other tokens.
You may optionally specify attribute names with ‘__’ preceding and following the name.
This allows you to use them in header files without being concerned about a possible macro
of the same name. For example, you may use the attribute name __noreturn__ instead of
noreturn.

Label Attributes
In GNU C, an attribute specifier list may appear after the colon following a label, other than
a case or default label. GNU C++ only permits attributes on labels if the attribute specifier
is immediately followed by a semicolon (i.e., the label applies to an empty statement). If
the semicolon is missing, C++ label attributes are ambiguous, as it is permissible for a
declaration, which could begin with an attribute list, to be labelled in C++. Declarations
cannot be labelled in C90 or C99, so the ambiguity does not arise there.

Enumerator Attributes
In GNU C, an attribute specifier list may appear as part of an enumerator. The attribute
goes after the enumeration constant, before =, if present. The optional attribute in the
enumerator appertains to the enumeration constant. It is not possible to place the attribute
after the constant expression, if present.

Statement Attributes
In GNU C, an attribute specifier list may appear as part of a null statement. The attribute
goes before the semicolon.

Type Attributes
An attribute specifier list may appear as part of a struct, union or enum specifier. It may
go either immediately after the struct, union or enum keyword, or after the closing brace.
The former syntax is preferred. Where attribute specifiers follow the closing brace, they
are considered to relate to the structure, union or enumerated type defined, not to any
enclosing declaration the type specifier appears in, and the type defined is not complete
until after the attribute specifiers.

All other attributes
Otherwise, an attribute specifier appears as part of a declaration, counting declarations
of unnamed parameters and type names, and relates to that declaration (which may be
nested in another declaration, for example in the case of a parameter declaration), or to
a particular declarator within a declaration. Where an attribute specifier is applied to a
parameter declared as a function or an array, it should apply to the function or array rather
than the pointer to which the parameter is implicitly converted, but this is not yet correctly
implemented.
Any list of specifiers and qualifiers at the start of a declaration may contain attribute
specifiers, whether or not such a list may in that context contain storage class specifiers.
(Some attributes, however, are essentially in the nature of storage class specifiers, and only
make sense where storage class specifiers may be used; for example, section.) There is one
necessary limitation to this syntax: the first old-style parameter declaration in a function

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definition cannot begin with an attribute specifier, because such an attribute applies to the
function instead by syntax described below (which, however, is not yet implemented in this
case). In some other cases, attribute specifiers are permitted by this grammar but not yet
supported by the compiler. All attribute specifiers in this place relate to the declaration as
a whole. In the obsolescent usage where a type of int is implied by the absence of type
specifiers, such a list of specifiers and qualifiers may be an attribute specifier list with no
other specifiers or qualifiers.
At present, the first parameter in a function prototype must have some type specifier that
is not an attribute specifier; this resolves an ambiguity in the interpretation of void f(int
(__attribute__((foo)) x)), but is subject to change. At present, if the parentheses of a
function declarator contain only attributes then those attributes are ignored, rather than
yielding an error or warning or implying a single parameter of type int, but this is subject
to change.
An attribute specifier list may appear immediately before a declarator (other than the
first) in a comma-separated list of declarators in a declaration of more than one identifier
using a single list of specifiers and qualifiers. Such attribute specifiers apply only to the
identifier before whose declarator they appear. For example, in
__attribute__((noreturn)) void d0 (void),
__attribute__((format(printf, 1, 2))) d1 (const char *, ...),
d2 (void);

the noreturn attribute applies to all the functions declared; the format attribute only
applies to d1.
An attribute specifier list may appear immediately before the comma, = or semicolon
terminating the declaration of an identifier other than a function definition. Such attribute
specifiers apply to the declared object or function. Where an assembler name for an object
or function is specified (see Section 6.45.4 [Asm Labels], page 592), the attribute must follow
the asm specification.
An attribute specifier list may, in future, be permitted to appear after the declarator in
a function definition (before any old-style parameter declarations or the function body).
Attribute specifiers may be mixed with type qualifiers appearing inside the [] of a parameter array declarator, in the C99 construct by which such qualifiers are applied to the
pointer to which the array is implicitly converted. Such attribute specifiers apply to the
pointer, not to the array, but at present this is not implemented and they are ignored.
An attribute specifier list may appear at the start of a nested declarator. At present,
there are some limitations in this usage: the attributes correctly apply to the declarator,
but for most individual attributes the semantics this implies are not implemented. When
attribute specifiers follow the * of a pointer declarator, they may be mixed with any type
qualifiers present. The following describes the formal semantics of this syntax. It makes
the most sense if you are familiar with the formal specification of declarators in the ISO C
standard.
Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration T D1, where T contains
declaration specifiers that specify a type Type (such as int) and D1 is a declarator that
contains an identifier ident. The type specified for ident for derived declarators whose type
does not include an attribute specifier is as in the ISO C standard.

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If D1 has the form ( attribute-specifier-list D ), and the declaration T D specifies
the type “derived-declarator-type-list Type” for ident, then T D1 specifies the type “deriveddeclarator-type-list attribute-specifier-list Type” for ident.
If D1 has the form * type-qualifier-and-attribute-specifier-list D, and the declaration T D specifies the type “derived-declarator-type-list Type” for ident, then T D1 specifies the type “derived-declarator-type-list type-qualifier-and-attribute-specifier-list pointer
to Type” for ident.
For example,
void (__attribute__((noreturn)) ****f) (void);

specifies the type “pointer to pointer to pointer to pointer to non-returning function returning void”. As another example,
char *__attribute__((aligned(8))) *f;

specifies the type “pointer to 8-byte-aligned pointer to char”. Note again that this does not
work with most attributes; for example, the usage of ‘aligned’ and ‘noreturn’ attributes
given above is not yet supported.
For compatibility with existing code written for compiler versions that did not implement
attributes on nested declarators, some laxity is allowed in the placing of attributes. If an
attribute that only applies to types is applied to a declaration, it is treated as applying to
the type of that declaration. If an attribute that only applies to declarations is applied to
the type of a declaration, it is treated as applying to that declaration; and, for compatibility
with code placing the attributes immediately before the identifier declared, such an attribute
applied to a function return type is treated as applying to the function type, and such an
attribute applied to an array element type is treated as applying to the array type. If an
attribute that only applies to function types is applied to a pointer-to-function type, it is
treated as applying to the pointer target type; if such an attribute is applied to a function
return type that is not a pointer-to-function type, it is treated as applying to the function
type.

6.38 Prototypes and Old-Style Function Definitions
GNU C extends ISO C to allow a function prototype to override a later old-style nonprototype definition. Consider the following example:
/* Use prototypes unless the compiler is old-fashioned.
#ifdef __STDC__
#define P(x) x
#else
#define P(x) ()
#endif
/* Prototype function declaration.
int isroot P((uid_t));

*/

/* Old-style function definition. */
int
isroot (x)
/* ??? lossage here ??? */
uid_t x;
{
return x == 0;
}

*/

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Suppose the type uid_t happens to be short. ISO C does not allow this example,
because subword arguments in old-style non-prototype definitions are promoted. Therefore
in this example the function definition’s argument is really an int, which does not match
the prototype argument type of short.
This restriction of ISO C makes it hard to write code that is portable to traditional C
compilers, because the programmer does not know whether the uid_t type is short, int,
or long. Therefore, in cases like these GNU C allows a prototype to override a later oldstyle definition. More precisely, in GNU C, a function prototype argument type overrides
the argument type specified by a later old-style definition if the former type is the same as
the latter type before promotion. Thus in GNU C the above example is equivalent to the
following:
int isroot (uid_t);
int
isroot (uid_t x)
{
return x == 0;
}

GNU C++ does not support old-style function definitions, so this extension is irrelevant.

6.39 C++ Style Comments
In GNU C, you may use C++ style comments, which start with ‘//’ and continue until
the end of the line. Many other C implementations allow such comments, and they are
included in the 1999 C standard. However, C++ style comments are not recognized if you
specify an ‘-std’ option specifying a version of ISO C before C99, or ‘-ansi’ (equivalent to
‘-std=c90’).

6.40 Dollar Signs in Identifier Names
In GNU C, you may normally use dollar signs in identifier names. This is because many
traditional C implementations allow such identifiers. However, dollar signs in identifiers are
not supported on a few target machines, typically because the target assembler does not
allow them.

6.41 The Character ESC in Constants
You can use the sequence ‘\e’ in a string or character constant to stand for the ASCII
character ESC.

6.42 Inquiring on Alignment of Types or Variables
The keyword __alignof__ allows you to inquire about how an object is aligned, or the
minimum alignment usually required by a type. Its syntax is just like sizeof.
For example, if the target machine requires a double value to be aligned on an 8-byte
boundary, then __alignof__ (double) is 8. This is true on many RISC machines. On
more traditional machine designs, __alignof__ (double) is 4 or even 2.

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Some machines never actually require alignment; they allow reference to any data type
even at an odd address. For these machines, __alignof__ reports the smallest alignment
that GCC gives the data type, usually as mandated by the target ABI.
If the operand of __alignof__ is an lvalue rather than a type, its value is the required
alignment for its type, taking into account any minimum alignment specified with GCC’s
__attribute__ extension (see Section 6.32 [Variable Attributes], page 513). For example,
after this declaration:
struct foo { int x; char y; } foo1;

the value of __alignof__ (foo1.y) is 1, even though its actual alignment is probably 2 or
4, the same as __alignof__ (int).
It is an error to ask for the alignment of an incomplete type.

6.43 An Inline Function is As Fast As a Macro
By declaring a function inline, you can direct GCC to make calls to that function faster. One
way GCC can achieve this is to integrate that function’s code into the code for its callers.
This makes execution faster by eliminating the function-call overhead; in addition, if any of
the actual argument values are constant, their known values may permit simplifications at
compile time so that not all of the inline function’s code needs to be included. The effect
on code size is less predictable; object code may be larger or smaller with function inlining,
depending on the particular case. You can also direct GCC to try to integrate all “simple
enough” functions into their callers with the option ‘-finline-functions’.
GCC implements three different semantics of declaring a function inline. One is available
with ‘-std=gnu89’ or ‘-fgnu89-inline’ or when gnu_inline attribute is present on all
inline declarations, another when ‘-std=c99’, ‘-std=gnu99’ or an option for a later C version
is used (without ‘-fgnu89-inline’), and the third is used when compiling C++.
To declare a function inline, use the inline keyword in its declaration, like this:
static inline int
inc (int *a)
{
return (*a)++;
}

If you are writing a header file to be included in ISO C90 programs, write __inline__
instead of inline. See Section 6.46 [Alternate Keywords], page 595.
The three types of inlining behave similarly in two important cases: when the inline
keyword is used on a static function, like the example above, and when a function is first
declared without using the inline keyword and then is defined with inline, like this:
extern int inc (int *a);
inline int
inc (int *a)
{
return (*a)++;
}

In both of these common cases, the program behaves the same as if you had not used the
inline keyword, except for its speed.
When a function is both inline and static, if all calls to the function are integrated into
the caller, and the function’s address is never used, then the function’s own assembler code is

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never referenced. In this case, GCC does not actually output assembler code for the function,
unless you specify the option ‘-fkeep-inline-functions’. If there is a nonintegrated call,
then the function is compiled to assembler code as usual. The function must also be compiled
as usual if the program refers to its address, because that cannot be inlined.
Note that certain usages in a function definition can make it unsuitable for inline substitution. Among these usages are: variadic functions, use of alloca, use of computed goto (see
Section 6.3 [Labels as Values], page 441), use of nonlocal goto, use of nested functions, use
of setjmp, use of __builtin_longjmp and use of __builtin_return or __builtin_apply_
args. Using ‘-Winline’ warns when a function marked inline could not be substituted,
and gives the reason for the failure.
As required by ISO C++, GCC considers member functions defined within the body of a
class to be marked inline even if they are not explicitly declared with the inline keyword.
You can override this with ‘-fno-default-inline’; see Section 3.5 [Options Controlling
C++ Dialect], page 42.
GCC does not inline any functions when not optimizing unless you specify the
‘always_inline’ attribute for the function, like this:
/* Prototype. */
inline void foo (const char) __attribute__((always_inline));

The remainder of this section is specific to GNU C90 inlining.
When an inline function is not static, then the compiler must assume that there may be
calls from other source files; since a global symbol can be defined only once in any program,
the function must not be defined in the other source files, so the calls therein cannot be
integrated. Therefore, a non-static inline function is always compiled on its own in the
usual fashion.
If you specify both inline and extern in the function definition, then the definition is
used only for inlining. In no case is the function compiled on its own, not even if you refer
to its address explicitly. Such an address becomes an external reference, as if you had only
declared the function, and had not defined it.
This combination of inline and extern has almost the effect of a macro. The way to use
it is to put a function definition in a header file with these keywords, and put another copy
of the definition (lacking inline and extern) in a library file. The definition in the header
file causes most calls to the function to be inlined. If any uses of the function remain, they
refer to the single copy in the library.

6.44 When is a Volatile Object Accessed?
C has the concept of volatile objects. These are normally accessed by pointers and used
for accessing hardware or inter-thread communication. The standard encourages compilers
to refrain from optimizations concerning accesses to volatile objects, but leaves it implementation defined as to what constitutes a volatile access. The minimum requirement is
that at a sequence point all previous accesses to volatile objects have stabilized and no
subsequent accesses have occurred. Thus an implementation is free to reorder and combine
volatile accesses that occur between sequence points, but cannot do so for accesses across a
sequence point. The use of volatile does not allow you to violate the restriction on updating
objects multiple times between two sequence points.

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Accesses to non-volatile objects are not ordered with respect to volatile accesses. You
cannot use a volatile object as a memory barrier to order a sequence of writes to non-volatile
memory. For instance:
int *ptr = something;
volatile int vobj;
*ptr = something;
vobj = 1;

Unless *ptr and vobj can be aliased, it is not guaranteed that the write to *ptr occurs by
the time the update of vobj happens. If you need this guarantee, you must use a stronger
memory barrier such as:
int *ptr = something;
volatile int vobj;
*ptr = something;
asm volatile ("" : : : "memory");
vobj = 1;

A scalar volatile object is read when it is accessed in a void context:
volatile int *src = somevalue;
*src;

Such expressions are rvalues, and GCC implements this as a read of the volatile object
being pointed to.
Assignments are also expressions and have an rvalue. However when assigning to a scalar
volatile, the volatile object is not reread, regardless of whether the assignment expression’s
rvalue is used or not. If the assignment’s rvalue is used, the value is that assigned to the
volatile object. For instance, there is no read of vobj in all the following cases:
int obj;
volatile int vobj;
vobj = something;
obj = vobj = something;
obj ? vobj = onething : vobj = anotherthing;
obj = (something, vobj = anotherthing);

If you need to read the volatile object after an assignment has occurred, you must use a
separate expression with an intervening sequence point.
As bit-fields are not individually addressable, volatile bit-fields may be implicitly read
when written to, or when adjacent bit-fields are accessed. Bit-field operations may be
optimized such that adjacent bit-fields are only partially accessed, if they straddle a storage
unit boundary. For these reasons it is unwise to use volatile bit-fields to access hardware.

6.45 How to Use Inline Assembly Language in C Code
The asm keyword allows you to embed assembler instructions within C code. GCC provides
two forms of inline asm statements. A basic asm statement is one with no operands (see
Section 6.45.1 [Basic Asm], page 542), while an extended asm statement (see Section 6.45.2
[Extended Asm], page 543) includes one or more operands. The extended form is preferred
for mixing C and assembly language within a function, but to include assembly language
at top level you must use basic asm.
You can also use the asm keyword to override the assembler name for a C symbol, or to
place a C variable in a specific register.

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6.45.1 Basic Asm — Assembler Instructions Without Operands
A basic asm statement has the following syntax:
asm [ volatile ] ( AssemblerInstructions )
The asm keyword is a GNU extension. When writing code that can be compiled with
‘-ansi’ and the various ‘-std’ options, use __asm__ instead of asm (see Section 6.46 [Alternate Keywords], page 595).

Qualifiers
volatile

The optional volatile qualifier has no effect. All basic asm blocks are implicitly
volatile.

Parameters
AssemblerInstructions
This is a literal string that specifies the assembler code. The string can contain
any instructions recognized by the assembler, including directives. GCC does
not parse the assembler instructions themselves and does not know what they
mean or even whether they are valid assembler input.
You may place multiple assembler instructions together in a single asm string,
separated by the characters normally used in assembly code for the system. A
combination that works in most places is a newline to break the line, plus a
tab character (written as ‘\n\t’). Some assemblers allow semicolons as a line
separator. However, note that some assembler dialects use semicolons to start
a comment.

Remarks
Using extended asm (see Section 6.45.2 [Extended Asm], page 543) typically produces
smaller, safer, and more efficient code, and in most cases it is a better solution than basic
asm. However, there are two situations where only basic asm can be used:
• Extended asm statements have to be inside a C function, so to write inline assembly
language at file scope (“top-level”), outside of C functions, you must use basic asm. You
can use this technique to emit assembler directives, define assembly language macros
that can be invoked elsewhere in the file, or write entire functions in assembly language.
• Functions declared with the naked attribute also require basic asm (see Section 6.31
[Function Attributes], page 464).
Safely accessing C data and calling functions from basic asm is more complex than it may
appear. To access C data, it is better to use extended asm.
Do not expect a sequence of asm statements to remain perfectly consecutive after compilation. If certain instructions need to remain consecutive in the output, put them in a single
multi-instruction asm statement. Note that GCC’s optimizers can move asm statements
relative to other code, including across jumps.
asm statements may not perform jumps into other asm statements. GCC does not know
about these jumps, and therefore cannot take account of them when deciding how to optimize. Jumps from asm to C labels are only supported in extended asm.

Chapter 6: Extensions to the C Language Family

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Under certain circumstances, GCC may duplicate (or remove duplicates of) your assembly code when optimizing. This can lead to unexpected duplicate symbol errors during
compilation if your assembly code defines symbols or labels.
Warning: The C standards do not specify semantics for asm, making it a potential source
of incompatibilities between compilers. These incompatibilities may not produce compiler
warnings/errors.
GCC does not parse basic asm’s AssemblerInstructions, which means there is no way to
communicate to the compiler what is happening inside them. GCC has no visibility of
symbols in the asm and may discard them as unreferenced. It also does not know about
side effects of the assembler code, such as modifications to memory or registers. Unlike
some compilers, GCC assumes that no changes to general purpose registers occur. This
assumption may change in a future release.
To avoid complications from future changes to the semantics and the compatibility issues
between compilers, consider replacing basic asm with extended asm. See How to convert
from basic asm to extended asm for information about how to perform this conversion.
The compiler copies the assembler instructions in a basic asm verbatim to the assembly
language output file, without processing dialects or any of the ‘%’ operators that are available
with extended asm. This results in minor differences between basic asm strings and extended
asm templates. For example, to refer to registers you might use ‘%eax’ in basic asm and
‘%%eax’ in extended asm.
On targets such as x86 that support multiple assembler dialects, all basic asm blocks
use the assembler dialect specified by the ‘-masm’ command-line option (see Section 3.18.56
[x86 Options], page 389). Basic asm provides no mechanism to provide different assembler
strings for different dialects.
For basic asm with non-empty assembler string GCC assumes the assembler block does
not change any general purpose registers, but it may read or write any globally accessible
variable.
Here is an example of basic asm for i386:
/* Note that this code will not compile with -masm=intel */
#define DebugBreak() asm("int $3")

6.45.2 Extended Asm - Assembler Instructions with C Expression
Operands
With extended asm you can read and write C variables from assembler and perform jumps
from assembler code to C labels. Extended asm syntax uses colons (‘:’) to delimit the
operand parameters after the assembler template:
asm [volatile] ( AssemblerTemplate
: OutputOperands
[ : InputOperands
[ : Clobbers ] ])
asm [volatile] goto ( AssemblerTemplate
:
: InputOperands
: Clobbers

544

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: GotoLabels)
The asm keyword is a GNU extension. When writing code that can be compiled with
‘-ansi’ and the various ‘-std’ options, use __asm__ instead of asm (see Section 6.46 [Alternate Keywords], page 595).

Qualifiers
volatile

The typical use of extended asm statements is to manipulate input values to
produce output values. However, your asm statements may also produce side
effects. If so, you may need to use the volatile qualifier to disable certain
optimizations. See [Volatile], page 545.

goto

This qualifier informs the compiler that the asm statement may perform a jump
to one of the labels listed in the GotoLabels. See [GotoLabels], page 556.

Parameters
AssemblerTemplate
This is a literal string that is the template for the assembler code. It is a
combination of fixed text and tokens that refer to the input, output, and goto
parameters. See [AssemblerTemplate], page 547.
OutputOperands
A comma-separated list of the C variables modified by the instructions in
the AssemblerTemplate. An empty list is permitted. See [OutputOperands],
page 548.
InputOperands
A comma-separated list of C expressions read by the instructions in the
AssemblerTemplate. An empty list is permitted. See [InputOperands],
page 552.
Clobbers

A comma-separated list of registers or other values changed by the
AssemblerTemplate, beyond those listed as outputs.
An empty list is
permitted. See [Clobbers and Scratch Registers], page 553.

GotoLabels
When you are using the goto form of asm, this section contains the list of
all C labels to which the code in the AssemblerTemplate may jump. See
[GotoLabels], page 556.
asm statements may not perform jumps into other asm statements, only to the
listed GotoLabels. GCC’s optimizers do not know about other jumps; therefore
they cannot take account of them when deciding how to optimize.
The total number of input + output + goto operands is limited to 30.

Remarks
The asm statement allows you to include assembly instructions directly within C code.
This may help you to maximize performance in time-sensitive code or to access assembly
instructions that are not readily available to C programs.

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545

Note that extended asm statements must be inside a function. Only basic asm may be
outside functions (see Section 6.45.1 [Basic Asm], page 542). Functions declared with the
naked attribute also require basic asm (see Section 6.31 [Function Attributes], page 464).
While the uses of asm are many and varied, it may help to think of an asm statement as
a series of low-level instructions that convert input parameters to output parameters. So a
simple (if not particularly useful) example for i386 using asm might look like this:
int src = 1;
int dst;
asm ("mov %1, %0\n\t"
"add $1, %0"
: "=r" (dst)
: "r" (src));
printf("%d\n", dst);
This code copies src to dst and add 1 to dst.

6.45.2.1 Volatile
GCC’s optimizers sometimes discard asm statements if they determine there is no need for
the output variables. Also, the optimizers may move code out of loops if they believe that
the code will always return the same result (i.e. none of its input values change between
calls). Using the volatile qualifier disables these optimizations. asm statements that have
no output operands, including asm goto statements, are implicitly volatile.
This i386 code demonstrates a case that does not use (or require) the volatile qualifier. If it is performing assertion checking, this code uses asm to perform the validation.
Otherwise, dwRes is unreferenced by any code. As a result, the optimizers can discard the
asm statement, which in turn removes the need for the entire DoCheck routine. By omitting
the volatile qualifier when it isn’t needed you allow the optimizers to produce the most
efficient code possible.
void DoCheck(uint32_t dwSomeValue)
{
uint32_t dwRes;
// Assumes dwSomeValue is not zero.
asm ("bsfl %1,%0"
: "=r" (dwRes)
: "r" (dwSomeValue)
: "cc");
assert(dwRes > 3);
}
The next example shows a case where the optimizers can recognize that the input
(dwSomeValue) never changes during the execution of the function and can therefore move
the asm outside the loop to produce more efficient code. Again, using volatile disables
this type of optimization.

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void do_print(uint32_t dwSomeValue)
{
uint32_t dwRes;
for (uint32_t x=0; x < 5; x++)
{
// Assumes dwSomeValue is not zero.
asm ("bsfl %1,%0"
: "=r" (dwRes)
: "r" (dwSomeValue)
: "cc");
printf("%u: %u %u\n", x, dwSomeValue, dwRes);
}
}
The following example demonstrates a case where you need to use the volatile qualifier.
It uses the x86 rdtsc instruction, which reads the computer’s time-stamp counter. Without
the volatile qualifier, the optimizers might assume that the asm block will always return
the same value and therefore optimize away the second call.
uint64_t msr;
asm volatile ( "rdtsc\n\t"
"shl $32, %%rdx\n\t"
"or %%rdx, %0"
: "=a" (msr)
:
: "rdx");

// Returns the time in EDX:EAX.
// Shift the upper bits left.
// ’Or’ in the lower bits.

printf("msr: %llx\n", msr);
// Do other work...
// Reprint the timestamp
asm volatile ( "rdtsc\n\t"
"shl $32, %%rdx\n\t"
"or %%rdx, %0"
: "=a" (msr)
:
: "rdx");

// Returns the time in EDX:EAX.
// Shift the upper bits left.
// ’Or’ in the lower bits.

printf("msr: %llx\n", msr);
GCC’s optimizers do not treat this code like the non-volatile code in the earlier examples.
They do not move it out of loops or omit it on the assumption that the result from a previous
call is still valid.
Note that the compiler can move even volatile asm instructions relative to other code,
including across jump instructions. For example, on many targets there is a system register

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547

that controls the rounding mode of floating-point operations. Setting it with a volatile asm,
as in the following PowerPC example, does not work reliably.
asm volatile("mtfsf 255, %0" : : "f" (fpenv));
sum = x + y;
The compiler may move the addition back before the volatile asm. To make it work as
expected, add an artificial dependency to the asm by referencing a variable in the subsequent
code, for example:
asm volatile ("mtfsf 255,%1" : "=X" (sum) : "f" (fpenv));
sum = x + y;
Under certain circumstances, GCC may duplicate (or remove duplicates of) your assembly
code when optimizing. This can lead to unexpected duplicate symbol errors during compilation if your asm code defines symbols or labels. Using ‘%=’ (see [AssemblerTemplate],
page 547) may help resolve this problem.

6.45.2.2 Assembler Template
An assembler template is a literal string containing assembler instructions. The compiler
replaces tokens in the template that refer to inputs, outputs, and goto labels, and then
outputs the resulting string to the assembler. The string can contain any instructions
recognized by the assembler, including directives. GCC does not parse the assembler instructions themselves and does not know what they mean or even whether they are valid
assembler input. However, it does count the statements (see Section 6.45.6 [Size of an asm],
page 595).
You may place multiple assembler instructions together in a single asm string, separated
by the characters normally used in assembly code for the system. A combination that works
in most places is a newline to break the line, plus a tab character to move to the instruction
field (written as ‘\n\t’). Some assemblers allow semicolons as a line separator. However,
note that some assembler dialects use semicolons to start a comment.
Do not expect a sequence of asm statements to remain perfectly consecutive after compilation, even when you are using the volatile qualifier. If certain instructions need to
remain consecutive in the output, put them in a single multi-instruction asm statement.
Accessing data from C programs without using input/output operands (such as by using
global symbols directly from the assembler template) may not work as expected. Similarly,
calling functions directly from an assembler template requires a detailed understanding of
the target assembler and ABI.
Since GCC does not parse the assembler template, it has no visibility of any symbols it
references. This may result in GCC discarding those symbols as unreferenced unless they
are also listed as input, output, or goto operands.

Special format strings
In addition to the tokens described by the input, output, and goto operands, these tokens
have special meanings in the assembler template:
‘%%’

Outputs a single ‘%’ into the assembler code.

‘%=’

Outputs a number that is unique to each instance of the asm statement in the
entire compilation. This option is useful when creating local labels and referring

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to them multiple times in a single template that generates multiple assembler
instructions.
‘%{’
‘%|’
‘%}’

Outputs ‘{’, ‘|’, and ‘}’ characters (respectively) into the assembler code. When
unescaped, these characters have special meaning to indicate multiple assembler
dialects, as described below.

Multiple assembler dialects in asm templates
On targets such as x86, GCC supports multiple assembler dialects. The ‘-masm’ option
controls which dialect GCC uses as its default for inline assembler. The target-specific
documentation for the ‘-masm’ option contains the list of supported dialects, as well as
the default dialect if the option is not specified. This information may be important to
understand, since assembler code that works correctly when compiled using one dialect will
likely fail if compiled using another. See Section 3.18.56 [x86 Options], page 389.
If your code needs to support multiple assembler dialects (for example, if you are writing
public headers that need to support a variety of compilation options), use constructs of this
form:
{ dialect0 | dialect1 | dialect2... }
This construct outputs dialect0 when using dialect #0 to compile the code, dialect1
for dialect #1, etc. If there are fewer alternatives within the braces than the number of
dialects the compiler supports, the construct outputs nothing.
For example, if an x86 compiler supports two dialects (‘att’, ‘intel’), an assembler
template such as this:
"bt{l %[Offset],%[Base] | %[Base],%[Offset]}; jc %l2"
is equivalent to one of
"btl %[Offset],%[Base] ; jc %l2"
/* att dialect */
"bt %[Base],%[Offset]; jc %l2"
/* intel dialect */
Using that same compiler, this code:
"xchg{l}\t{%%}ebx, %1"
corresponds to either
"xchgl\t%%ebx, %1"
/* att dialect */
"xchg\tebx, %1"
/* intel dialect */
There is no support for nesting dialect alternatives.

6.45.2.3 Output Operands
An asm statement has zero or more output operands indicating the names of C variables
modified by the assembler code.
In this i386 example, old (referred to in the template string as %0) and *Base (as %1) are
outputs and Offset (%2) is an input:
bool old;
__asm__ ("btsl %2,%1\n\t" // Turn on zero-based bit #Offset in Base.

Chapter 6: Extensions to the C Language Family

549

"sbb %0,%0"
// Use the CF to calculate old.
: "=r" (old), "+rm" (*Base)
: "Ir" (Offset)
: "cc");
return old;
Operands are separated by commas. Each operand has this format:
[ [asmSymbolicName] ] constraint (cvariablename)
asmSymbolicName
Specifies a symbolic name for the operand. Reference the name in the assembler
template by enclosing it in square brackets (i.e. ‘%[Value]’). The scope of the
name is the asm statement that contains the definition. Any valid C variable
name is acceptable, including names already defined in the surrounding code.
No two operands within the same asm statement can use the same symbolic
name.
When not using an asmSymbolicName, use the (zero-based) position of the
operand in the list of operands in the assembler template. For example if there
are three output operands, use ‘%0’ in the template to refer to the first, ‘%1’ for
the second, and ‘%2’ for the third.
constraint A string constant specifying constraints on the placement of the operand; See
Section 6.45.3 [Constraints], page 559, for details.
Output constraints must begin with either ‘=’ (a variable overwriting an existing value) or ‘+’ (when reading and writing). When using ‘=’, do not assume
the location contains the existing value on entry to the asm, except when the
operand is tied to an input; see [Input Operands], page 552.
After the prefix, there must be one or more additional constraints (see
Section 6.45.3 [Constraints], page 559) that describe where the value resides.
Common constraints include ‘r’ for register and ‘m’ for memory. When you list
more than one possible location (for example, "=rm"), the compiler chooses
the most efficient one based on the current context. If you list as many
alternates as the asm statement allows, you permit the optimizers to produce
the best possible code. If you must use a specific register, but your Machine
Constraints do not provide sufficient control to select the specific register you
want, local register variables may provide a solution (see Section 6.45.5.2
[Local Register Variables], page 594).
cvariablename
Specifies a C lvalue expression to hold the output, typically a variable name.
The enclosing parentheses are a required part of the syntax.
When the compiler selects the registers to use to represent the output operands, it does
not use any of the clobbered registers (see [Clobbers and Scratch Registers], page 553).
Output operand expressions must be lvalues. The compiler cannot check whether the
operands have data types that are reasonable for the instruction being executed. For output
expressions that are not directly addressable (for example a bit-field), the constraint must

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allow a register. In that case, GCC uses the register as the output of the asm, and then
stores that register into the output.
Operands using the ‘+’ constraint modifier count as two operands (that is, both as input
and output) towards the total maximum of 30 operands per asm statement.
Use the ‘&’ constraint modifier (see Section 6.45.3.3 [Modifiers], page 562) on all output
operands that must not overlap an input. Otherwise, GCC may allocate the output operand
in the same register as an unrelated input operand, on the assumption that the assembler
code consumes its inputs before producing outputs. This assumption may be false if the
assembler code actually consists of more than one instruction.
The same problem can occur if one output parameter (a) allows a register constraint and
another output parameter (b) allows a memory constraint. The code generated by GCC
to access the memory address in b can contain registers which might be shared by a, and
GCC considers those registers to be inputs to the asm. As above, GCC assumes that such
input registers are consumed before any outputs are written. This assumption may result
in incorrect behavior if the asm writes to a before using b. Combining the ‘&’ modifier with
the register constraint on a ensures that modifying a does not affect the address referenced
by b. Otherwise, the location of b is undefined if a is modified before using b.
asm supports operand modifiers on operands (for example ‘%k2’ instead of simply ‘%2’).
Typically these qualifiers are hardware dependent. The list of supported modifiers for x86
is found at [x86Operandmodifiers], page 557.
If the C code that follows the asm makes no use of any of the output operands, use
volatile for the asm statement to prevent the optimizers from discarding the asm statement
as unneeded (see [Volatile], page 545).
This code makes no use of the optional asmSymbolicName. Therefore it references the
first output operand as %0 (were there a second, it would be %1, etc). The number of the
first input operand is one greater than that of the last output operand. In this i386 example,
that makes Mask referenced as %1:
uint32_t Mask = 1234;
uint32_t Index;
asm ("bsfl %1, %0"
: "=r" (Index)
: "r" (Mask)
: "cc");
That code overwrites the variable Index (‘=’), placing the value in a register (‘r’). Using
the generic ‘r’ constraint instead of a constraint for a specific register allows the compiler
to pick the register to use, which can result in more efficient code. This may not be possible
if an assembler instruction requires a specific register.
The following i386 example uses the asmSymbolicName syntax. It produces the same
result as the code above, but some may consider it more readable or more maintainable
since reordering index numbers is not necessary when adding or removing operands. The
names aIndex and aMask are only used in this example to emphasize which names get used
where. It is acceptable to reuse the names Index and Mask.
uint32_t Mask = 1234;
uint32_t Index;

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551

asm ("bsfl %[aMask], %[aIndex]"
: [aIndex] "=r" (Index)
: [aMask] "r" (Mask)
: "cc");
Here are some more examples of output operands.
uint32_t c = 1;
uint32_t d;
uint32_t *e = &c;
asm ("mov %[e], %[d]"
: [d] "=rm" (d)
: [e] "rm" (*e));
Here, d may either be in a register or in memory. Since the compiler might already have
the current value of the uint32_t location pointed to by e in a register, you can enable it
to choose the best location for d by specifying both constraints.

6.45.2.4 Flag Output Operands
Some targets have a special register that holds the “flags” for the result of an operation or
comparison. Normally, the contents of that register are either unmodifed by the asm, or
the asm is considered to clobber the contents.
On some targets, a special form of output operand exists by which conditions in the flags
register may be outputs of the asm. The set of conditions supported are target specific, but
the general rule is that the output variable must be a scalar integer, and the value is boolean.
When supported, the target defines the preprocessor symbol __GCC_ASM_FLAG_OUTPUTS__.
Because of the special nature of the flag output operands, the constraint may not include
alternatives.
Most often, the target has only one flags register, and thus is an implied operand of
many instructions. In this case, the operand should not be referenced within the assembler
template via %0 etc, as there’s no corresponding text in the assembly language.
x86 family The flag output constraints for the x86 family are of the form ‘=@cccond’ where
cond is one of the standard conditions defined in the ISA manual for jcc or
setcc.
a

“above” or unsigned greater than

ae

“above or equal” or unsigned greater than or equal

b

“below” or unsigned less than

be

“below or equal” or unsigned less than or equal

c

carry flag set

e
z

“equal” or zero flag set

g

signed greater than

ge

signed greater than or equal

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l

signed less than

le

signed less than or equal

o

overflow flag set

p

parity flag set

s

sign flag set

na
nae
nb
nbe
nc
ne
ng
nge
nl
nle
no
np
ns
nz

“not” flag, or inverted versions of those above

6.45.2.5 Input Operands
Input operands make values from C variables and expressions available to the assembly
code.
Operands are separated by commas. Each operand has this format:
[ [asmSymbolicName] ] constraint (cexpression)
asmSymbolicName
Specifies a symbolic name for the operand. Reference the name in the assembler
template by enclosing it in square brackets (i.e. ‘%[Value]’). The scope of the
name is the asm statement that contains the definition. Any valid C variable
name is acceptable, including names already defined in the surrounding code.
No two operands within the same asm statement can use the same symbolic
name.
When not using an asmSymbolicName, use the (zero-based) position of the
operand in the list of operands in the assembler template. For example if there
are two output operands and three inputs, use ‘%2’ in the template to refer to
the first input operand, ‘%3’ for the second, and ‘%4’ for the third.
constraint A string constant specifying constraints on the placement of the operand; See
Section 6.45.3 [Constraints], page 559, for details.
Input constraint strings may not begin with either ‘=’ or ‘+’. When you list
more than one possible location (for example, ‘"irm"’), the compiler chooses
the most efficient one based on the current context. If you must use a specific
register, but your Machine Constraints do not provide sufficient control to select

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the specific register you want, local register variables may provide a solution
(see Section 6.45.5.2 [Local Register Variables], page 594).
Input constraints can also be digits (for example, "0"). This indicates that
the specified input must be in the same place as the output constraint at the
(zero-based) index in the output constraint list. When using asmSymbolicName
syntax for the output operands, you may use these names (enclosed in brackets
‘[]’) instead of digits.
cexpression
This is the C variable or expression being passed to the asm statement as input.
The enclosing parentheses are a required part of the syntax.
When the compiler selects the registers to use to represent the input operands, it does
not use any of the clobbered registers (see [Clobbers and Scratch Registers], page 553).
If there are no output operands but there are input operands, place two consecutive colons
where the output operands would go:
__asm__ ("some instructions"
: /* No outputs. */
: "r" (Offset / 8));
Warning: Do not modify the contents of input-only operands (except for inputs tied
to outputs). The compiler assumes that on exit from the asm statement these operands
contain the same values as they had before executing the statement. It is not possible
to use clobbers to inform the compiler that the values in these inputs are changing. One
common work-around is to tie the changing input variable to an output variable that never
gets used. Note, however, that if the code that follows the asm statement makes no use
of any of the output operands, the GCC optimizers may discard the asm statement as
unneeded (see [Volatile], page 545).
asm supports operand modifiers on operands (for example ‘%k2’ instead of simply ‘%2’).
Typically these qualifiers are hardware dependent. The list of supported modifiers for x86
is found at [x86Operandmodifiers], page 557.
In this example using the fictitious combine instruction, the constraint "0" for input
operand 1 says that it must occupy the same location as output operand 0. Only input
operands may use numbers in constraints, and they must each refer to an output operand.
Only a number (or the symbolic assembler name) in the constraint can guarantee that one
operand is in the same place as another. The mere fact that foo is the value of both operands
is not enough to guarantee that they are in the same place in the generated assembler code.
asm ("combine %2, %0"
: "=r" (foo)
: "0" (foo), "g" (bar));
Here is an example using symbolic names.
asm ("cmoveq %1, %2, %[result]"
: [result] "=r"(result)
: "r" (test), "r" (new), "[result]" (old));

6.45.2.6 Clobbers and Scratch Registers
While the compiler is aware of changes to entries listed in the output operands, the inline
asm code may modify more than just the outputs. For example, calculations may require

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additional registers, or the processor may overwrite a register as a side effect of a particular
assembler instruction. In order to inform the compiler of these changes, list them in the
clobber list. Clobber list items are either register names or the special clobbers (listed
below). Each clobber list item is a string constant enclosed in double quotes and separated
by commas.
Clobber descriptions may not in any way overlap with an input or output operand. For
example, you may not have an operand describing a register class with one member when
listing that register in the clobber list. Variables declared to live in specific registers (see
Section 6.45.5 [Explicit Register Variables], page 592) and used as asm input or output
operands must have no part mentioned in the clobber description. In particular, there is
no way to specify that input operands get modified without also specifying them as output
operands.
When the compiler selects which registers to use to represent input and output operands,
it does not use any of the clobbered registers. As a result, clobbered registers are available
for any use in the assembler code.
Here is a realistic example for the VAX showing the use of clobbered registers:
asm volatile ("movc3 %0, %1, %2"
: /* No outputs. */
: "g" (from), "g" (to), "g" (count)
: "r0", "r1", "r2", "r3", "r4", "r5", "memory");
Also, there are two special clobber arguments:
"cc"

The "cc" clobber indicates that the assembler code modifies the flags register.
On some machines, GCC represents the condition codes as a specific hardware
register; "cc" serves to name this register. On other machines, condition code
handling is different, and specifying "cc" has no effect. But it is valid no matter
what the target.

"memory"

The "memory" clobber tells the compiler that the assembly code performs memory reads or writes to items other than those listed in the input and output
operands (for example, accessing the memory pointed to by one of the input
parameters). To ensure memory contains correct values, GCC may need to
flush specific register values to memory before executing the asm. Further, the
compiler does not assume that any values read from memory before an asm remain unchanged after that asm; it reloads them as needed. Using the "memory"
clobber effectively forms a read/write memory barrier for the compiler.
Note that this clobber does not prevent the processor from doing speculative
reads past the asm statement. To prevent that, you need processor-specific
fence instructions.

Flushing registers to memory has performance implications and may be an issue for timesensitive code. You can provide better information to GCC to avoid this, as shown in the
following examples. At a minimum, aliasing rules allow GCC to know what memory doesn’t
need to be flushed.
Here is a fictitious sum of squares instruction, that takes two pointers to floating point
values in memory and produces a floating point register output. Notice that x, and y both
appear twice in the asm parameters, once to specify memory accessed, and once to specify

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555

a base register used by the asm. You won’t normally be wasting a register by doing this as
GCC can use the same register for both purposes. However, it would be foolish to use both
%1 and %3 for x in this asm and expect them to be the same. In fact, %3 may well not be a
register. It might be a symbolic memory reference to the object pointed to by x.
asm ("sumsq %0, %1, %2"
: "+f" (result)
: "r" (x), "r" (y), "m" (*x), "m" (*y));

Here is a fictitious *z++ = *x++ * *y++ instruction. Notice that the x, y and z pointer
registers must be specified as input/output because the asm modifies them.
asm ("vecmul %0, %1, %2"
: "+r" (z), "+r" (x), "+r" (y), "=m" (*z)
: "m" (*x), "m" (*y));

An x86 example where the string memory argument is of unknown length.
asm("repne scasb"
: "=c" (count), "+D" (p)
: "m" (*(const char (*)[]) p), "0" (-1), "a" (0));

If you know the above will only be reading a ten byte array then you could instead use
a memory input like: "m" (*(const char (*)[10]) p).
Here is an example of a PowerPC vector scale implemented in assembly, complete with
vector and condition code clobbers, and some initialized offset registers that are unchanged
by the asm.
void
dscal (size_t n, double *x, double alpha)
{
asm ("/* lots of asm here */"
: "+m" (*(double (*)[n]) x), "+&r" (n), "+b" (x)
: "d" (alpha), "b" (32), "b" (48), "b" (64),
"b" (80), "b" (96), "b" (112)
: "cr0",
"vs32","vs33","vs34","vs35","vs36","vs37","vs38","vs39",
"vs40","vs41","vs42","vs43","vs44","vs45","vs46","vs47");
}

Rather than allocating fixed registers via clobbers to provide scratch registers for an asm
statement, an alternative is to define a variable and make it an early-clobber output as with
a2 and a3 in the example below. This gives the compiler register allocator more freedom.
You can also define a variable and make it an output tied to an input as with a0 and a1,
tied respectively to ap and lda. Of course, with tied outputs your asm can’t use the input
value after modifying the output register since they are one and the same register. What’s
more, if you omit the early-clobber on the output, it is possible that GCC might allocate
the same register to another of the inputs if GCC could prove they had the same value on
entry to the asm. This is why a1 has an early-clobber. Its tied input, lda might conceivably
be known to have the value 16 and without an early-clobber share the same register as %11.
On the other hand, ap can’t be the same as any of the other inputs, so an early-clobber
on a0 is not needed. It is also not desirable in this case. An early-clobber on a0 would
cause GCC to allocate a separate register for the "m" (*(const double (*)[]) ap) input.
Note that tying an input to an output is the way to set up an initialized temporary register
modified by an asm statement. An input not tied to an output is assumed by GCC to be
unchanged, for example "b" (16) below sets up %11 to 16, and GCC might use that register
in following code if the value 16 happened to be needed. You can even use a normal asm

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output for a scratch if all inputs that might share the same register are consumed before
the scratch is used. The VSX registers clobbered by the asm statement could have used this
technique except for GCC’s limit on the number of asm parameters.
static void
dgemv_kernel_4x4 (long n, const double *ap, long lda,
const double *x, double *y, double alpha)
{
double *a0;
double *a1;
double *a2;
double *a3;
__asm__
(
/* lots of asm here */
"#n=%1 ap=%8=%12 lda=%13 x=%7=%10 y=%0=%2 alpha=%9 o16=%11\n"
"#a0=%3 a1=%4 a2=%5 a3=%6"
:
"+m" (*(double (*)[n]) y),
"+&r" (n), // 1
"+b" (y), // 2
"=b" (a0), // 3
"=&b" (a1), // 4
"=&b" (a2), // 5
"=&b" (a3) // 6
:
"m" (*(const double (*)[n]) x),
"m" (*(const double (*)[]) ap),
"d" (alpha), // 9
"r" (x), // 10
"b" (16), // 11
"3" (ap), // 12
"4" (lda) // 13
:
"cr0",
"vs32","vs33","vs34","vs35","vs36","vs37",
"vs40","vs41","vs42","vs43","vs44","vs45","vs46","vs47"
);
}

6.45.2.7 Goto Labels
asm goto allows assembly code to jump to one or more C labels. The GotoLabels section
in an asm goto statement contains a comma-separated list of all C labels to which the
assembler code may jump. GCC assumes that asm execution falls through to the next
statement (if this is not the case, consider using the __builtin_unreachable intrinsic
after the asm statement). Optimization of asm goto may be improved by using the hot and
cold label attributes (see Section 6.34 [Label Attributes], page 532).
An asm goto statement cannot have outputs. This is due to an internal restriction of
the compiler: control transfer instructions cannot have outputs. If the assembler code does
modify anything, use the "memory" clobber to force the optimizers to flush all register values
to memory and reload them if necessary after the asm statement.
Also note that an asm goto statement is always implicitly considered volatile.

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To reference a label in the assembler template, prefix it with ‘%l’ (lowercase ‘L’) followed
by its (zero-based) position in GotoLabels plus the number of input operands. For example,
if the asm has three inputs and references two labels, refer to the first label as ‘%l3’ and the
second as ‘%l4’).
Alternately, you can reference labels using the actual C label name enclosed in brackets.
For example, to reference a label named carry, you can use ‘%l[carry]’. The label must
still be listed in the GotoLabels section when using this approach.
Here is an example of asm goto for i386:
asm goto (
"btl %1, %0\n\t"
"jc %l2"
: /* No outputs. */
: "r" (p1), "r" (p2)
: "cc"
: carry);
return 0;
carry:
return 1;
The following example shows an asm goto that uses a memory clobber.
int frob(int x)
{
int y;
asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
: /* No outputs. */
: "r"(x), "r"(&y)
: "r5", "memory"
: error);
return y;
error:
return -1;
}

6.45.2.8 x86 Operand Modifiers
References to input, output, and goto operands in the assembler template of extended asm
statements can use modifiers to affect the way the operands are formatted in the code
output to the assembler. For example, the following code uses the ‘h’ and ‘b’ modifiers for
x86:
uint16_t num;
asm volatile ("xchg %h0, %b0" : "+a" (num) );
These modifiers generate this assembler code:
xchg %ah, %al
The rest of this discussion uses the following code for illustrative purposes.

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Using the GNU Compiler Collection (GCC)

int main()
{
int iInt = 1;
top:
asm volatile goto ("some assembler instructions here"
: /* No outputs. */
: "q" (iInt), "X" (sizeof(unsigned char) + 1)
: /* No clobbers. */
: top);
}
With no modifiers, this is what the output from the operands would be for the ‘att’ and
‘intel’ dialects of assembler:
Operand ‘att’
%0
%eax
%1
$2
%2
$.L2
The table below

‘intel’
eax
2
OFFSET FLAT:.L2
shows the list of supported modifiers and their effects.

Modifier
z

Operand
%z0

‘att’
l

‘intel’

b
h

%b0
%h0

%al
%ah

al
ah

%w0
%k0
%q0
%l2

%ax
%eax
%rax
.L2

ax
eax
rax
.L2

%c1

2

2

w
k
q
l
c

Description
Print the opcode suffix for the size of the
current integer operand (one of b/w/l/q).
Print the QImode name of the register.
Print the QImode name for a “high”
register.
Print the HImode name of the register.
Print the SImode name of the register.
Print the DImode name of the register.
Print the label name with no
punctuation.
Require a constant operand and print the
constant expression with no punctuation.
V is a special modifier which prints the name of the

full integer register without %.

6.45.2.9 x86 Floating-Point asm Operands
On x86 targets, there are several rules on the usage of stack-like registers in the operands
of an asm. These rules apply only to the operands that are stack-like registers:
1. Given a set of input registers that die in an asm, it is necessary to know which are
implicitly popped by the asm, and which must be explicitly popped by GCC.
An input register that is implicitly popped by the asm must be explicitly clobbered,
unless it is constrained to match an output operand.
2. For any input register that is implicitly popped by an asm, it is necessary to know how
to adjust the stack to compensate for the pop. If any non-popped input is closer to

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559

the top of the reg-stack than the implicitly popped register, it would not be possible to
know what the stack looked like—it’s not clear how the rest of the stack “slides up”.
All implicitly popped input registers must be closer to the top of the reg-stack than
any input that is not implicitly popped.
It is possible that if an input dies in an asm, the compiler might use the input register
for an output reload. Consider this example:
asm ("foo" : "=t" (a) : "f" (b));

This code says that input b is not popped by the asm, and that the asm pushes a result
onto the reg-stack, i.e., the stack is one deeper after the asm than it was before. But,
it is possible that reload may think that it can use the same register for both the input
and the output.
To prevent this from happening, if any input operand uses the ‘f’ constraint, all output
register constraints must use the ‘&’ early-clobber modifier.
The example above is correctly written as:
asm ("foo" : "=&t" (a) : "f" (b));

3. Some operands need to be in particular places on the stack. All output operands fall
in this category—GCC has no other way to know which registers the outputs appear
in unless you indicate this in the constraints.
Output operands must specifically indicate which register an output appears in after
an asm. ‘=f’ is not allowed: the operand constraints must select a class with a single
register.
4. Output operands may not be “inserted” between existing stack registers. Since no 387
opcode uses a read/write operand, all output operands are dead before the asm, and are
pushed by the asm. It makes no sense to push anywhere but the top of the reg-stack.
Output operands must start at the top of the reg-stack: output operands may not
“skip” a register.
5. Some asm statements may need extra stack space for internal calculations. This can
be guaranteed by clobbering stack registers unrelated to the inputs and outputs.
This asm takes one input, which is internally popped, and produces two outputs.
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));

This asm takes two inputs, which are popped by the fyl2xp1 opcode, and replaces them
with one output. The st(1) clobber is necessary for the compiler to know that fyl2xp1
pops both inputs.
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");

6.45.3 Constraints for asm Operands
Here are specific details on what constraint letters you can use with asm operands. Constraints can say whether an operand may be in a register, and which kinds of register;
whether the operand can be a memory reference, and which kinds of address; whether the
operand may be an immediate constant, and which possible values it may have. Constraints
can also require two operands to match. Side-effects aren’t allowed in operands of inline
asm, unless ‘<’ or ‘>’ constraints are used, because there is no guarantee that the side effects
will happen exactly once in an instruction that can update the addressing register.

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Using the GNU Compiler Collection (GCC)

6.45.3.1 Simple Constraints
The simplest kind of constraint is a string full of letters, each of which describes one kind
of operand that is permitted. Here are the letters that are allowed:
whitespace
Whitespace characters are ignored and can be inserted at any position except
the first. This enables each alternative for different operands to be visually
aligned in the machine description even if they have different number of constraints and modifiers.
‘m’

A memory operand is allowed, with any kind of address that the machine supports in general. Note that the letter used for the general memory constraint
can be re-defined by a back end using the TARGET_MEM_CONSTRAINT macro.

‘o’

A memory operand is allowed, but only if the address is offsettable. This
means that adding a small integer (actually, the width in bytes of the operand,
as determined by its machine mode) may be added to the address and the result
is also a valid memory address.
For example, an address which is constant is offsettable; so is an address that
is the sum of a register and a constant (as long as a slightly larger constant
is also within the range of address-offsets supported by the machine); but an
autoincrement or autodecrement address is not offsettable. More complicated
indirect/indexed addresses may or may not be offsettable depending on the
other addressing modes that the machine supports.
Note that in an output operand which can be matched by another operand,
the constraint letter ‘o’ is valid only when accompanied by both ‘<’ (if the
target machine has predecrement addressing) and ‘>’ (if the target machine has
preincrement addressing).

‘V’

A memory operand that is not offsettable. In other words, anything that would
fit the ‘m’ constraint but not the ‘o’ constraint.

‘<’

A memory operand with autodecrement addressing (either predecrement or
postdecrement) is allowed. In inline asm this constraint is only allowed if the
operand is used exactly once in an instruction that can handle the side effects.
Not using an operand with ‘<’ in constraint string in the inline asm pattern
at all or using it in multiple instructions isn’t valid, because the side effects
wouldn’t be performed or would be performed more than once. Furthermore,
on some targets the operand with ‘<’ in constraint string must be accompanied
by special instruction suffixes like %U0 instruction suffix on PowerPC or %P0 on
IA-64.

‘>’

A memory operand with autoincrement addressing (either preincrement or
postincrement) is allowed. In inline asm the same restrictions as for ‘<’ apply.

‘r’

A register operand is allowed provided that it is in a general register.

‘i’

An immediate integer operand (one with constant value) is allowed. This includes symbolic constants whose values will be known only at assembly time or
later.

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‘n’

561

An immediate integer operand with a known numeric value is allowed. Many
systems cannot support assembly-time constants for operands less than a word
wide. Constraints for these operands should use ‘n’ rather than ‘i’.

‘I’, ‘J’, ‘K’, . . . ‘P’
Other letters in the range ‘I’ through ‘P’ may be defined in a machine-dependent
fashion to permit immediate integer operands with explicit integer values in
specified ranges. For example, on the 68000, ‘I’ is defined to stand for the
range of values 1 to 8. This is the range permitted as a shift count in the shift
instructions.
‘E’

An immediate floating operand (expression code const_double) is allowed, but
only if the target floating point format is the same as that of the host machine
(on which the compiler is running).

‘F’

An immediate floating operand
const_vector) is allowed.

‘G’, ‘H’

‘G’ and ‘H’ may be defined in a machine-dependent fashion to permit immediate
floating operands in particular ranges of values.

‘s’

An immediate integer operand whose value is not an explicit integer is allowed.
This might appear strange; if an insn allows a constant operand with a value
not known at compile time, it certainly must allow any known value. So why
use ‘s’ instead of ‘i’? Sometimes it allows better code to be generated.
For example, on the 68000 in a fullword instruction it is possible to use an
immediate operand; but if the immediate value is between −128 and 127, better
code results from loading the value into a register and using the register. This
is because the load into the register can be done with a ‘moveq’ instruction. We
arrange for this to happen by defining the letter ‘K’ to mean “any integer outside
the range −128 to 127”, and then specifying ‘Ks’ in the operand constraints.

‘g’

Any register, memory or immediate integer operand is allowed, except for registers that are not general registers.

‘X’

Any operand whatsoever is allowed.

(expression

code

const_double

or

‘0’, ‘1’, ‘2’, . . . ‘9’
An operand that matches the specified operand number is allowed. If a digit
is used together with letters within the same alternative, the digit should come
last.
This number is allowed to be more than a single digit. If multiple digits are encountered consecutively, they are interpreted as a single decimal integer. There
is scant chance for ambiguity, since to-date it has never been desirable that
‘10’ be interpreted as matching either operand 1 or operand 0. Should this be
desired, one can use multiple alternatives instead.
This is called a matching constraint and what it really means is that the assembler has only a single operand that fills two roles which asm distinguishes. For
example, an add instruction uses two input operands and an output operand,
but on most CISC machines an add instruction really has only two operands,
one of them an input-output operand:

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Using the GNU Compiler Collection (GCC)

addl #35,r12

Matching constraints are used in these circumstances. More precisely, the two
operands that match must include one input-only operand and one output-only
operand. Moreover, the digit must be a smaller number than the number of
the operand that uses it in the constraint.
‘p’

An operand that is a valid memory address is allowed. This is for “load address”
and “push address” instructions.
‘p’ in the constraint must be accompanied by address_operand as the predicate
in the match_operand. This predicate interprets the mode specified in the
match_operand as the mode of the memory reference for which the address
would be valid.

other-letters
Other letters can be defined in machine-dependent fashion to stand for particular classes of registers or other arbitrary operand types. ‘d’, ‘a’ and ‘f’
are defined on the 68000/68020 to stand for data, address and floating point
registers.

6.45.3.2 Multiple Alternative Constraints
Sometimes a single instruction has multiple alternative sets of possible operands. For example, on the 68000, a logical-or instruction can combine register or an immediate value
into memory, or it can combine any kind of operand into a register; but it cannot combine
one memory location into another.
These constraints are represented as multiple alternatives. An alternative can be described by a series of letters for each operand. The overall constraint for an operand is
made from the letters for this operand from the first alternative, a comma, the letters for
this operand from the second alternative, a comma, and so on until the last alternative. All
operands for a single instruction must have the same number of alternatives.
So the first alternative for the 68000’s logical-or could be written as "+m" (output)
: "ir" (input). The second could be "+r" (output): "irm" (input). However, the
fact that two memory locations cannot be used in a single instruction prevents simply
using "+rm" (output) : "irm" (input). Using multi-alternatives, this might be written
as "+m,r" (output) : "ir,irm" (input). This describes all the available alternatives to
the compiler, allowing it to choose the most efficient one for the current conditions.
There is no way within the template to determine which alternative was chosen. However
you may be able to wrap your asm statements with builtins such as __builtin_constant_p
to achieve the desired results.

6.45.3.3 Constraint Modifier Characters
Here are constraint modifier characters.
‘=’

Means that this operand is written to by this instruction: the previous value is
discarded and replaced by new data.

‘+’

Means that this operand is both read and written by the instruction.
When the compiler fixes up the operands to satisfy the constraints, it needs to
know which operands are read by the instruction and which are written by it.

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‘=’ identifies an operand which is only written; ‘+’ identifies an operand that is
both read and written; all other operands are assumed to only be read.
If you specify ‘=’ or ‘+’ in a constraint, you put it in the first character of the
constraint string.
‘&’

Means (in a particular alternative) that this operand is an earlyclobber operand,
which is written before the instruction is finished using the input operands.
Therefore, this operand may not lie in a register that is read by the instruction
or as part of any memory address.
‘&’ applies only to the alternative in which it is written. In constraints with
multiple alternatives, sometimes one alternative requires ‘&’ while others do
not. See, for example, the ‘movdf’ insn of the 68000.
A operand which is read by the instruction can be tied to an earlyclobber
operand if its only use as an input occurs before the early result is written.
Adding alternatives of this form often allows GCC to produce better code when
only some of the read operands can be affected by the earlyclobber. See, for
example, the ‘mulsi3’ insn of the ARM.
Furthermore, if the earlyclobber operand is also a read/write operand, then
that operand is written only after it’s used.
‘&’ does not obviate the need to write ‘=’ or ‘+’. As earlyclobber operands
are always written, a read-only earlyclobber operand is ill-formed and will be
rejected by the compiler.

‘%’

Declares the instruction to be commutative for this operand and the following
operand. This means that the compiler may interchange the two operands if
that is the cheapest way to make all operands fit the constraints. ‘%’ applies to
all alternatives and must appear as the first character in the constraint. Only
read-only operands can use ‘%’.
GCC can only handle one commutative pair in an asm; if you use more, the
compiler may fail. Note that you need not use the modifier if the two alternatives are strictly identical; this would only waste time in the reload pass.

6.45.3.4 Constraints for Particular Machines
Whenever possible, you should use the general-purpose constraint letters in asm arguments,
since they will convey meaning more readily to people reading your code. Failing that, use
the constraint letters that usually have very similar meanings across architectures. The
most commonly used constraints are ‘m’ and ‘r’ (for memory and general-purpose registers
respectively; see Section 6.45.3.1 [Simple Constraints], page 560), and ‘I’, usually the letter
indicating the most common immediate-constant format.
Each architecture defines additional constraints. These constraints are used by the compiler itself for instruction generation, as well as for asm statements; therefore, some of the
constraints are not particularly useful for asm. Here is a summary of some of the machinedependent constraints available on some particular machines; it includes both constraints
that are useful for asm and constraints that aren’t. The compiler source file mentioned in
the table heading for each architecture is the definitive reference for the meanings of that
architecture’s constraints.

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Using the GNU Compiler Collection (GCC)

AArch64 family—‘config/aarch64/constraints.md’
k
The stack pointer register (SP)
w

Floating point register, Advanced SIMD vector register or SVE
vector register

Upl

One of the low eight SVE predicate registers (P0 to P7)

Upa

Any of the SVE predicate registers (P0 to P15)

I

Integer constant that is valid as an immediate operand in an ADD
instruction

J

Integer constant that is valid as an immediate operand in a SUB
instruction (once negated)

K

Integer constant that can be used with a 32-bit logical instruction

L

Integer constant that can be used with a 64-bit logical instruction

M

Integer constant that is valid as an immediate operand in a 32bit MOV pseudo instruction. The MOV may be assembled to one of
several different machine instructions depending on the value

N

Integer constant that is valid as an immediate operand in a 64-bit
MOV pseudo instruction

S

An absolute symbolic address or a label reference

Y

Floating point constant zero

Z

Integer constant zero

Ush

The high part (bits 12 and upwards) of the pc-relative address of a
symbol within 4GB of the instruction

Q

A memory address which uses a single base register with no offset

Ump

A memory address suitable for a load/store pair instruction in SI,
DI, SF and DF modes

ARC —‘config/arc/constraints.md’
q
Registers usable in ARCompact 16-bit instructions: r0-r3, r12r15. This constraint can only match when the ‘-mq’ option is in
effect.
e

Registers usable as base-regs of memory addresses in ARCompact
16-bit memory instructions: r0-r3, r12-r15, sp. This constraint
can only match when the ‘-mq’ option is in effect.

D

ARC FPX (dpfp) 64-bit registers. D0, D1.

I

A signed 12-bit integer constant.

Cal

constant for arithmetic/logical operations. This might be any constant that can be put into a long immediate by the assmbler or
linker without involving a PIC relocation.

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565

K

A 3-bit unsigned integer constant.

L

A 6-bit unsigned integer constant.

CnL

One’s complement of a 6-bit unsigned integer constant.

CmL

Two’s complement of a 6-bit unsigned integer constant.

M

A 5-bit unsigned integer constant.

O

A 7-bit unsigned integer constant.

P

A 8-bit unsigned integer constant.

H

Any const double value.

ARM family—‘config/arm/constraints.md’
h
In Thumb state, the core registers r8-r15.
k

The stack pointer register.

l

In Thumb State the core registers r0-r7. In ARM state this is an
alias for the r constraint.

t

VFP floating-point registers s0-s31. Used for 32 bit values.

w

VFP floating-point registers d0-d31 and the appropriate subset d0d15 based on command line options. Used for 64 bit values only.
Not valid for Thumb1.

y

The iWMMX co-processor registers.

z

The iWMMX GR registers.

G

The floating-point constant 0.0

I

Integer that is valid as an immediate operand in a data processing
instruction. That is, an integer in the range 0 to 255 rotated by a
multiple of 2

J

Integer in the range −4095 to 4095

K

Integer that satisfies constraint ‘I’ when inverted (ones complement)

L

Integer that satisfies constraint ‘I’ when negated (twos complement)

M

Integer in the range 0 to 32

Q

A memory reference where the exact address is in a single register
(‘‘m’’ is preferable for asm statements)

R

An item in the constant pool

S

A symbol in the text segment of the current file

Uv

A memory reference
(reg+constant offset)

Uy

A memory reference suitable for iWMMXt load/store instructions.

suitable

for

VFP

load/store

insns

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Using the GNU Compiler Collection (GCC)

Uq

A memory reference suitable for the ARMv4 ldrsb instruction.

AVR family—‘config/avr/constraints.md’
l
Registers from r0 to r15
a

Registers from r16 to r23

d

Registers from r16 to r31

w

Registers from r24 to r31. These registers can be used in ‘adiw’
command

e

Pointer register (r26–r31)

b

Base pointer register (r28–r31)

q

Stack pointer register (SPH:SPL)

t

Temporary register r0

x

Register pair X (r27:r26)

y

Register pair Y (r29:r28)

z

Register pair Z (r31:r30)

I

Constant greater than −1, less than 64

J

Constant greater than −64, less than 1

K

Constant integer 2

L

Constant integer 0

M

Constant that fits in 8 bits

N

Constant integer −1

O

Constant integer 8, 16, or 24

P

Constant integer 1

G

A floating point constant 0.0

Q

A memory address based on Y or Z pointer with displacement.

Blackfin family—‘config/bfin/constraints.md’
a
P register
d

D register

z

A call clobbered P register.

qn

A single register. If n is in the range 0 to 7, the corresponding D
register. If it is A, then the register P0.

D

Even-numbered D register

W

Odd-numbered D register

e

Accumulator register.

A

Even-numbered accumulator register.

Chapter 6: Extensions to the C Language Family

567

B

Odd-numbered accumulator register.

b

I register

v

B register

f

M register

c

Registers used for circular buffering, i.e. I, B, or L registers.

C

The CC register.

t

LT0 or LT1.

k

LC0 or LC1.

u

LB0 or LB1.

x

Any D, P, B, M, I or L register.

y

Additional registers typically used only in prologues and epilogues:
RETS, RETN, RETI, RETX, RETE, ASTAT, SEQSTAT and USP.

w

Any register except accumulators or CC.

Ksh

Signed 16 bit integer (in the range −32768 to 32767)

Kuh

Unsigned 16 bit integer (in the range 0 to 65535)

Ks7

Signed 7 bit integer (in the range −64 to 63)

Ku7

Unsigned 7 bit integer (in the range 0 to 127)

Ku5

Unsigned 5 bit integer (in the range 0 to 31)

Ks4

Signed 4 bit integer (in the range −8 to 7)

Ks3

Signed 3 bit integer (in the range −3 to 4)

Ku3

Unsigned 3 bit integer (in the range 0 to 7)

Pn

Constant n, where n is a single-digit constant in the range 0 to 4.

PA

An integer equal to one of the MACFLAG XXX constants that is
suitable for use with either accumulator.

PB

An integer equal to one of the MACFLAG XXX constants that is
suitable for use only with accumulator A1.

M1

Constant 255.

M2

Constant 65535.

J

An integer constant with exactly a single bit set.

L

An integer constant with all bits set except exactly one.

H
Q

Any SYMBOL REF.

CR16 Architecture—‘config/cr16/cr16.h’
b
Registers from r0 to r14 (registers without stack pointer)

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Using the GNU Compiler Collection (GCC)

t

Register from r0 to r11 (all 16-bit registers)

p

Register from r12 to r15 (all 32-bit registers)

I

Signed constant that fits in 4 bits

J

Signed constant that fits in 5 bits

K

Signed constant that fits in 6 bits

L

Unsigned constant that fits in 4 bits

M

Signed constant that fits in 32 bits

N

Check for 64 bits wide constants for add/sub instructions

G

Floating point constant that is legal for store immediate

Epiphany—‘config/epiphany/constraints.md’
U16
An unsigned 16-bit constant.
K

An unsigned 5-bit constant.

L

A signed 11-bit constant.

Cm1

A signed 11-bit constant added to −1. Can only match when the
‘-m1reg-reg’ option is active.

Cl1

Left-shift of −1, i.e., a bit mask with a block of leading ones, the
rest being a block of trailing zeroes. Can only match when the
‘-m1reg-reg’ option is active.

Cr1

Right-shift of −1, i.e., a bit mask with a trailing block of ones, the
rest being zeroes. Or to put it another way, one less than a power
of two. Can only match when the ‘-m1reg-reg’ option is active.

Cal

Constant for arithmetic/logical operations. This is like i, except
that for position independent code, no symbols / expressions needing relocations are allowed.

Csy

Symbolic constant for call/jump instruction.

Rcs

The register class usable in short insns. This is a register class
constraint, and can thus drive register allocation. This constraint
won’t match unless ‘-mprefer-short-insn-regs’ is in effect.

Rsc

The the register class of registers that can be used to hold a sibcall
call address. I.e., a caller-saved register.

Rct

Core control register class.

Rgs

The register group usable in short insns. This constraint does not
use a register class, so that it only passively matches suitable registers, and doesn’t drive register allocation.

Rra

Matches the return address if it can be replaced with the link register.

Rcc

Matches the integer condition code register.

Chapter 6: Extensions to the C Language Family

569

Sra

Matches the return address if it is in a stack slot.

Cfm

Matches control register values to switch fp mode, which are encapsulated in UNSPEC_FP_MODE.

FRV—‘config/frv/frv.h’
a

Register in the class ACC_REGS (acc0 to acc7).

b

Register in the class EVEN_ACC_REGS (acc0 to acc7).

c

Register in the class CC_REGS (fcc0 to fcc3 and icc0 to icc3).

d

Register in the class GPR_REGS (gr0 to gr63).

e

Register in the class EVEN_REGS (gr0 to gr63). Odd registers are
excluded not in the class but through the use of a machine mode
larger than 4 bytes.

f

Register in the class FPR_REGS (fr0 to fr63).

h

Register in the class FEVEN_REGS (fr0 to fr63). Odd registers are
excluded not in the class but through the use of a machine mode
larger than 4 bytes.

l

Register in the class LR_REG (the lr register).

q

Register in the class QUAD_REGS (gr2 to gr63). Register numbers
not divisible by 4 are excluded not in the class but through the use
of a machine mode larger than 8 bytes.

t

Register in the class ICC_REGS (icc0 to icc3).

u

Register in the class FCC_REGS (fcc0 to fcc3).

v

Register in the class ICR_REGS (cc4 to cc7).

w

Register in the class FCR_REGS (cc0 to cc3).

x

Register in the class QUAD_FPR_REGS (fr0 to fr63). Register numbers not divisible by 4 are excluded not in the class but through
the use of a machine mode larger than 8 bytes.

z

Register in the class SPR_REGS (lcr and lr).

A

Register in the class QUAD_ACC_REGS (acc0 to acc7).

B

Register in the class ACCG_REGS (accg0 to accg7).

C

Register in the class CR_REGS (cc0 to cc7).

G

Floating point constant zero

I

6-bit signed integer constant

J

10-bit signed integer constant

L

16-bit signed integer constant

M

16-bit unsigned integer constant

570

Using the GNU Compiler Collection (GCC)

N

12-bit signed integer constant that is negative—i.e. in the range of
−2048 to −1

O

Constant zero

P

12-bit signed integer constant that is greater than zero—i.e. in the
range of 1 to 2047.

FT32—‘config/ft32/constraints.md’
A
An absolute address
B

An offset address

W

A register indirect memory operand

e

An offset address.

f

An offset address.

O

The constant zero or one

I

A 16-bit signed constant (−32768 . . . 32767)

w

A bitfield mask suitable for bext or bins

x

An inverted bitfield mask suitable for bext or bins

L

A 16-bit unsigned constant, multiple of 4 (0 . . . 65532)

S

A 20-bit signed constant (−524288 . . . 524287)

b

A constant for a bitfield width (1 . . . 16)

KA

A 10-bit signed constant (−512 . . . 511)

Hewlett-Packard PA-RISC—‘config/pa/pa.h’
a
General register 1
f

Floating point register

q

Shift amount register

x

Floating point register (deprecated)

y

Upper floating point register (32-bit), floating point register (64bit)

Z

Any register

I

Signed 11-bit integer constant

J

Signed 14-bit integer constant

K

Integer constant that can be deposited with a zdepi instruction

L

Signed 5-bit integer constant

M

Integer constant 0

N

Integer constant that can be loaded with a ldil instruction

O

Integer constant whose value plus one is a power of 2

Chapter 6: Extensions to the C Language Family

571

P

Integer constant that can be used for and operations in depi and
extru instructions

S

Integer constant 31

U

Integer constant 63

G

Floating-point constant 0.0

A

A lo_sum data-linkage-table memory operand

Q

A memory operand that can be used as the destination operand of
an integer store instruction

R

A scaled or unscaled indexed memory operand

T

A memory operand for floating-point loads and stores

W

A register indirect memory operand

Intel IA-64—‘config/ia64/ia64.h’
a
General register r0 to r3 for addl instruction
b

Branch register

c

Predicate register (‘c’ as in “conditional”)

d

Application register residing in M-unit

e

Application register residing in I-unit

f

Floating-point register

m

Memory operand. If used together with ‘<’ or ‘>’, the operand can
have postincrement and postdecrement which require printing with
‘%Pn’ on IA-64.

G

Floating-point constant 0.0 or 1.0

I

14-bit signed integer constant

J

22-bit signed integer constant

K

8-bit signed integer constant for logical instructions

L

8-bit adjusted signed integer constant for compare pseudo-ops

M

6-bit unsigned integer constant for shift counts

N

9-bit signed integer constant for load and store postincrements

O

The constant zero

P

0 or −1 for dep instruction

Q

Non-volatile memory for floating-point loads and stores

R

Integer constant in the range 1 to 4 for shladd instruction

S

Memory operand except postincrement and postdecrement. This
is now roughly the same as ‘m’ when not used together with ‘<’ or
‘>’.

572

Using the GNU Compiler Collection (GCC)

M32C—‘config/m32c/m32c.c’
Rsp
Rfb
Rsb
‘$sp’, ‘$fb’, ‘$sb’.
Rcr

Any control register, when they’re 16 bits wide (nothing if control
registers are 24 bits wide)

Rcl

Any control register, when they’re 24 bits wide.

R0w
R1w
R2w
R3w

$r0, $r1, $r2, $r3.

R02

$r0 or $r2, or $r2r0 for 32 bit values.

R13

$r1 or $r3, or $r3r1 for 32 bit values.

Rdi

A register that can hold a 64 bit value.

Rhl

$r0 or $r1 (registers with addressable high/low bytes)

R23

$r2 or $r3

Raa

Address registers

Raw

Address registers when they’re 16 bits wide.

Ral

Address registers when they’re 24 bits wide.

Rqi

Registers that can hold QI values.

Rad

Registers that can be used with displacements ($a0, $a1, $sb).

Rsi

Registers that can hold 32 bit values.

Rhi

Registers that can hold 16 bit values.

Rhc

Registers chat can hold 16 bit values, including all control registers.

Rra

$r0 through R1, plus $a0 and $a1.

Rfl

The flags register.

Rmm

The memory-based pseudo-registers $mem0 through $mem15.

Rpi

Registers that can hold pointers (16 bit registers for r8c, m16c; 24
bit registers for m32cm, m32c).

Rpa

Matches multiple registers in a PARALLEL to form a larger register. Used to match function return values.

Is3

−8 . . . 7

IS1

−128 . . . 127

IS2

−32768 . . . 32767

IU2

0 . . . 65535

Chapter 6: Extensions to the C Language Family

In4

−8 . . . −1 or 1 . . . 8

In5

−16 . . . −1 or 1 . . . 16

In6

−32 . . . −1 or 1 . . . 32

IM2

−65536 . . . −1

Ilb

An 8 bit value with exactly one bit set.

Ilw

A 16 bit value with exactly one bit set.

Sd

The common src/dest memory addressing modes.

Sa

Memory addressed using $a0 or $a1.

Si

Memory addressed with immediate addresses.

Ss

Memory addressed using the stack pointer ($sp).

Sf

Memory addressed using the frame base register ($fb).

Ss

Memory addressed using the small base register ($sb).

S1

$r1h

573

MicroBlaze—‘config/microblaze/constraints.md’
d
A general register (r0 to r31).
z

A status register (rmsr, $fcc1 to $fcc7).

MIPS—‘config/mips/constraints.md’
d
A general-purpose register. This is equivalent to r unless generating
MIPS16 code, in which case the MIPS16 register set is used.
f

A floating-point register (if available).

h

Formerly the hi register. This constraint is no longer supported.

l

The lo register. Use this register to store values that are no bigger
than a word.

x

The concatenated hi and lo registers. Use this register to store
doubleword values.

c

A register suitable for use in an indirect jump. This will always be
$25 for ‘-mabicalls’.

v

Register $3. Do not use this constraint in new code; it is retained
only for compatibility with glibc.

y

Equivalent to r; retained for backwards compatibility.

z

A floating-point condition code register.

I

A signed 16-bit constant (for arithmetic instructions).

J

Integer zero.

K

An unsigned 16-bit constant (for logic instructions).

574

Using the GNU Compiler Collection (GCC)

L

A signed 32-bit constant in which the lower 16 bits are zero. Such
constants can be loaded using lui.

M

A constant that cannot be loaded using lui, addiu or ori.

N

A constant in the range −65535 to −1 (inclusive).

O

A signed 15-bit constant.

P

A constant in the range 1 to 65535 (inclusive).

G

Floating-point zero.

R

An address that can be used in a non-macro load or store.

ZC

A memory operand whose address is formed by a base register
and offset that is suitable for use in instructions with the same
addressing mode as ll and sc.

ZD

An address suitable for a prefetch instruction, or for any other
instruction with the same addressing mode as prefetch.

Motorola 680x0—‘config/m68k/constraints.md’
a
Address register
d

Data register

f

68881 floating-point register, if available

I

Integer in the range 1 to 8

J

16-bit signed number

K

Signed number whose magnitude is greater than 0x80

L

Integer in the range −8 to −1

M

Signed number whose magnitude is greater than 0x100

N

Range 24 to 31, rotatert:SI 8 to 1 expressed as rotate

O

16 (for rotate using swap)

P

Range 8 to 15, rotatert:HI 8 to 1 expressed as rotate

R

Numbers that mov3q can handle

G

Floating point constant that is not a 68881 constant

S

Operands that satisfy ’m’ when -mpcrel is in effect

T

Operands that satisfy ’s’ when -mpcrel is not in effect

Q

Address register indirect addressing mode

U

Register offset addressing

W

const call operand

Cs

symbol ref or const

Ci

const int

Chapter 6: Extensions to the C Language Family

C0

const int 0

Cj

Range of signed numbers that don’t fit in 16 bits

Cmvq

Integers valid for mvq

Capsw

Integers valid for a moveq followed by a swap

Cmvz

Integers valid for mvz

Cmvs

Integers valid for mvs

Ap

push operand

Ac

Non-register operands allowed in clr

575

Moxie—‘config/moxie/constraints.md’
A
An absolute address
B

An offset address

W

A register indirect memory operand

I

A constant in the range of 0 to 255.

N

A constant in the range of 0 to −255.

MSP430–‘config/msp430/constraints.md’
R12
Register R12.
R13

Register R13.

K

Integer constant 1.

L

Integer constant -1^20..1^19.

M

Integer constant 1-4.

Ya

Memory references which do not require an extended MOVX instruction.

Yl

Memory reference, labels only.

Ys

Memory reference, stack only.

NDS32—‘config/nds32/constraints.md’
w
LOW register class $r0 to $r7 constraint for V3/V3M ISA.
l

LOW register class $r0 to $r7.

d

MIDDLE register class $r0 to $r11, $r16 to $r19.

h

HIGH register class $r12 to $r14, $r20 to $r31.

t

Temporary assist register $ta (i.e. $r15).

k

Stack register $sp.

Iu03

Unsigned immediate 3-bit value.

In03

Negative immediate 3-bit value in the range of −7–0.

576

Using the GNU Compiler Collection (GCC)

Iu04

Unsigned immediate 4-bit value.

Is05

Signed immediate 5-bit value.

Iu05

Unsigned immediate 5-bit value.

In05

Negative immediate 5-bit value in the range of −31–0.

Ip05

Unsigned immediate 5-bit value for movpi45 instruction with range
16–47.

Iu06

Unsigned immediate 6-bit value constraint for addri36.sp instruction.

Iu08

Unsigned immediate 8-bit value.

Iu09

Unsigned immediate 9-bit value.

Is10

Signed immediate 10-bit value.

Is11

Signed immediate 11-bit value.

Is15

Signed immediate 15-bit value.

Iu15

Unsigned immediate 15-bit value.

Ic15

A constant which is not in the range of imm15u but ok for bclr
instruction.

Ie15

A constant which is not in the range of imm15u but ok for bset
instruction.

It15

A constant which is not in the range of imm15u but ok for btgl
instruction.

Ii15

A constant whose compliment value is in the range of imm15u and
ok for bitci instruction.

Is16

Signed immediate 16-bit value.

Is17

Signed immediate 17-bit value.

Is19

Signed immediate 19-bit value.

Is20

Signed immediate 20-bit value.

Ihig

The immediate value that can be simply set high 20-bit.

Izeb

The immediate value 0xff.

Izeh

The immediate value 0xffff.

Ixls

The immediate value 0x01.

Ix11

The immediate value 0x7ff.

Ibms

The immediate value with power of 2.

Ifex

The immediate value with power of 2 minus 1.

U33

Memory constraint for 333 format.

U45

Memory constraint for 45 format.

Chapter 6: Extensions to the C Language Family

U37

577

Memory constraint for 37 format.

Nios II family—‘config/nios2/constraints.md’
I
Integer that is valid as an immediate operand in an instruction
taking a signed 16-bit number. Range −32768 to 32767.
J

Integer that is valid as an immediate operand in an instruction
taking an unsigned 16-bit number. Range 0 to 65535.

K

Integer that is valid as an immediate operand in an instruction
taking only the upper 16-bits of a 32-bit number. Range 32-bit
numbers with the lower 16-bits being 0.

L

Integer that is valid as an immediate operand for a shift instruction.
Range 0 to 31.

M

Integer that is valid as an immediate operand for only the value 0.
Can be used in conjunction with the format modifier z to use r0
instead of 0 in the assembly output.

N

Integer that is valid as an immediate operand for a custom instruction opcode. Range 0 to 255.

P

An immediate operand for R2 andchi/andci instructions.

S

Matches immediates which are addresses in the small data section
and therefore can be added to gp as a 16-bit immediate to re-create
their 32-bit value.

U

Matches constants suitable as an operand for the rdprs and cache
instructions.

v

A memory operand suitable for Nios II R2 load/store exclusive
instructions.

w

A memory operand suitable for load/store IO and cache instructions.

PDP-11—‘config/pdp11/constraints.md’
a
Floating point registers AC0 through AC3. These can be loaded
from/to memory with a single instruction.
d

Odd numbered general registers (R1, R3, R5). These are used for
16-bit multiply operations.

f

Any of the floating point registers (AC0 through AC5).

G

Floating point constant 0.

I

An integer constant that fits in 16 bits.

J

An integer constant whose low order 16 bits are zero.

K

An integer constant that does not meet the constraints for codes
‘I’ or ‘J’.

L

The integer constant 1.

578

Using the GNU Compiler Collection (GCC)

M

The integer constant −1.

N

The integer constant 0.

O

Integer constants −4 through −1 and 1 through 4; shifts by these
amounts are handled as multiple single-bit shifts rather than a single variable-length shift.

Q

A memory reference which requires an additional word (address or
offset) after the opcode.

R

A memory reference that is encoded within the opcode.

PowerPC and IBM RS6000—‘config/rs6000/constraints.md’
b

Address base register

d

Floating point register (containing 64-bit value)

f

Floating point register (containing 32-bit value)

v

Altivec vector register

wa

Any VSX register if the ‘-mvsx’ option was used or NO REGS.
When using any of the register constraints (wa, wd, wf, wg, wh, wi,
wj, wk, wl, wm, wo, wp, wq, ws, wt, wu, wv, ww, or wy) that take
VSX registers, you must use %x in the template so that the
correct register is used. Otherwise the register number output in
the assembly file will be incorrect if an Altivec register is an operand
of a VSX instruction that expects VSX register numbering.
asm ("xvadddp %x0,%x1,%x2"
: "=wa" (v1)
: "wa" (v2), "wa" (v3));

is correct, but:
asm ("xvadddp %0,%1,%2"
: "=wa" (v1)
: "wa" (v2), "wa" (v3));

is not correct.
If an instruction only takes Altivec registers, you do not want to
use %x.
asm ("xsaddqp %0,%1,%2"
: "=v" (v1)
: "v" (v2), "v" (v3));

is correct because the xsaddqp instruction only takes Altivec registers, while:
asm ("xsaddqp %x0,%x1,%x2"
: "=v" (v1)
: "v" (v2), "v" (v3));

is incorrect.
wb

Altivec register if ‘-mcpu=power9’ is used or NO REGS.

wd

VSX vector register to hold vector double data or NO REGS.

Chapter 6: Extensions to the C Language Family

579

we

VSX register if the ‘-mcpu=power9’ and ‘-m64’ options were used
or NO REGS.

wf

VSX vector register to hold vector float data or NO REGS.

wg

If ‘-mmfpgpr’ was used, a floating point register or NO REGS.

wh

Floating point register if direct moves are available, or NO REGS.

wi

FP or VSX register to hold 64-bit integers for VSX insns or
NO REGS.

wj

FP or VSX register to hold 64-bit integers for direct moves or
NO REGS.

wk

FP or VSX register to hold 64-bit doubles for direct moves or
NO REGS.

wl

Floating point register if the LFIWAX instruction is enabled or
NO REGS.

wm

VSX register if direct move instructions are enabled, or NO REGS.

wn

No register (NO REGS).

wo

VSX register to use for ISA 3.0 vector instructions, or NO REGS.

wp

VSX register to use for IEEE 128-bit floating point TFmode, or
NO REGS.

wq

VSX register to use for IEEE 128-bit floating point, or NO REGS.

wr

General purpose register if 64-bit instructions are enabled or
NO REGS.

ws

VSX vector register to hold scalar double values or NO REGS.

wt

VSX vector register to hold 128 bit integer or NO REGS.

wu

Altivec register to use for float/32-bit int loads/stores or
NO REGS.

wv

Altivec register to use for double loads/stores or NO REGS.

ww

FP or VSX register to perform float operations under ‘-mvsx’ or
NO REGS.

wx

Floating point register if the STFIWX instruction is enabled or
NO REGS.

wy

FP or VSX register to perform ISA 2.07 float ops or NO REGS.

wz

Floating point register if the LFIWZX instruction is enabled or
NO REGS.

wA

Address base register if 64-bit instructions are enabled or
NO REGS.

wB

Signed 5-bit constant integer that can be loaded into an altivec
register.

580

Using the GNU Compiler Collection (GCC)

wD

Int constant that is the element number of the 64-bit scalar in a
vector.

wE

Vector constant that can be loaded with the XXSPLTIB instruction.

wF

Memory operand suitable for power9 fusion load/stores.

wG

Memory operand suitable for TOC fusion memory references.

wH

Altivec register if ‘-mvsx-small-integer’.

wI

Floating point register if ‘-mvsx-small-integer’.

wJ

FP register if ‘-mvsx-small-integer’ and ‘-mpower9-vector’.

wK

Altivec register if ‘-mvsx-small-integer’ and ‘-mpower9-vector’.

wL

Int constant that is the element number that the MFVSRLD instruction. targets.

wM

Match vector constant with all 1’s if the XXLORC instruction is
available.

wO

A memory operand suitable for the ISA 3.0 vector d-form instructions.

wQ

A memory address that will work with the lq and stq instructions.

wS

Vector constant that can be loaded with XXSPLTIB & sign extension.

h

‘MQ’, ‘CTR’, or ‘LINK’ register

c

‘CTR’ register

l

‘LINK’ register

x

‘CR’ register (condition register) number 0

y

‘CR’ register (condition register)

z

‘XER[CA]’ carry bit (part of the XER register)

I

Signed 16-bit constant

J

Unsigned 16-bit constant shifted left 16 bits (use ‘L’ instead for
SImode constants)

K

Unsigned 16-bit constant

L

Signed 16-bit constant shifted left 16 bits

M

Constant larger than 31

N

Exact power of 2

O

Zero

P

Constant whose negation is a signed 16-bit constant

G

Floating point constant that can be loaded into a register with one
instruction per word

Chapter 6: Extensions to the C Language Family

581

H

Integer/Floating point constant that can be loaded into a register
using three instructions

m

Memory operand. Normally, m does not allow addresses that update
the base register. If ‘<’ or ‘>’ constraint is also used, they are
allowed and therefore on PowerPC targets in that case it is only safe
to use ‘m<>’ in an asm statement if that asm statement accesses the
operand exactly once. The asm statement must also use ‘%U’
as a placeholder for the “update” flag in the corresponding load or
store instruction. For example:
asm ("st%U0 %1,%0" : "=m<>" (mem) : "r" (val));

is correct but:
asm ("st %1,%0" : "=m<>" (mem) : "r" (val));

is not.
es

A “stable” memory operand; that is, one which does not include
any automodification of the base register. This used to be useful
when ‘m’ allowed automodification of the base register, but as those
are now only allowed when ‘<’ or ‘>’ is used, ‘es’ is basically the
same as ‘m’ without ‘<’ and ‘>’.

Q

Memory operand that is an offset from a register (it is usually better
to use ‘m’ or ‘es’ in asm statements)

Z

Memory operand that is an indexed or indirect from a register (it
is usually better to use ‘m’ or ‘es’ in asm statements)

R

AIX TOC entry

a

Address operand that is an indexed or indirect from a register (‘p’
is preferable for asm statements)

U

System V Release 4 small data area reference

W

Vector constant that does not require memory

j

Vector constant that is all zeros.

RL78—‘config/rl78/constraints.md’
Int3
An integer constant in the range 1 . . . 7.
Int8

An integer constant in the range 0 . . . 255.

J

An integer constant in the range −255 . . . 0

K

The integer constant 1.

L

The integer constant -1.

M

The integer constant 0.

N

The integer constant 2.

O

The integer constant -2.

P

An integer constant in the range 1 . . . 15.

582

Using the GNU Compiler Collection (GCC)

Qbi

The built-in compare types–eq, ne, gtu, ltu, geu, and leu.

Qsc

The synthetic compare types–gt, lt, ge, and le.

Wab

A memory reference with an absolute address.

Wbc

A memory reference using BC as a base register, with an optional
offset.

Wca

A memory reference using AX, BC, DE, or HL for the address, for
calls.

Wcv

A memory reference using any 16-bit register pair for the address,
for calls.

Wd2

A memory reference using DE as a base register, with an optional
offset.

Wde

A memory reference using DE as a base register, without any offset.

Wfr

Any memory reference to an address in the far address space.

Wh1

A memory reference using HL as a base register, with an optional
one-byte offset.

Whb

A memory reference using HL as a base register, with B or C as the
index register.

Whl

A memory reference using HL as a base register, without any offset.

Ws1

A memory reference using SP as a base register, with an optional
one-byte offset.

Y

Any memory reference to an address in the near address space.

A

The AX register.

B

The BC register.

D

The DE register.

R

A through L registers.

S

The SP register.

T

The HL register.

Z08W

The 16-bit R8 register.

Z10W

The 16-bit R10 register.

Zint

The registers reserved for interrupts (R24 to R31).

a

The A register.

b

The B register.

c

The C register.

d

The D register.

e

The E register.

Chapter 6: Extensions to the C Language Family

h

The H register.

l

The L register.

v

The virtual registers.

w

The PSW register.

x

The X register.

583

RISC-V—‘config/riscv/constraints.md’
f
A floating-point register (if availiable).
I

An I-type 12-bit signed immediate.

J

Integer zero.

K

A 5-bit unsigned immediate for CSR access instructions.

A

An address that is held in a general-purpose register.

RX—‘config/rx/constraints.md’
Q
An address which does not involve register indirect addressing or
pre/post increment/decrement addressing.
Symbol

A symbol reference.

Int08

A constant in the range −256 to 255, inclusive.

Sint08

A constant in the range −128 to 127, inclusive.

Sint16

A constant in the range −32768 to 32767, inclusive.

Sint24

A constant in the range −8388608 to 8388607, inclusive.

Uint04

A constant in the range 0 to 15, inclusive.

S/390 and zSeries—‘config/s390/s390.h’
a
Address register (general purpose register except r0)
c

Condition code register

d

Data register (arbitrary general purpose register)

f

Floating-point register

I

Unsigned 8-bit constant (0–255)

J

Unsigned 12-bit constant (0–4095)

K

Signed 16-bit constant (−32768–32767)

L

Value appropriate as displacement.
(0..4095)
for short displacement
(−524288..524287)
for long displacement

M

Constant integer with a value of 0x7fffffff.

584

Using the GNU Compiler Collection (GCC)

N

Multiple letter constraint followed by 4 parameter letters.
0..9:

number of the part counting from most to least significant

H,Q:

mode of the part

D,S,H:

mode of the containing operand

0,F:

value of the other parts (F—all bits set)

The constraint matches if the specified part of a constant has a
value different from its other parts.
Q

Memory reference without index register and with short displacement.

R

Memory reference with index register and short displacement.

S

Memory reference without index register but with long displacement.

T

Memory reference with index register and long displacement.

U

Pointer with short displacement.

W

Pointer with long displacement.

Y

Shift count operand.

SPARC—‘config/sparc/sparc.h’
f
Floating-point register on the SPARC-V8 architecture and lower
floating-point register on the SPARC-V9 architecture.
e

Floating-point register. It is equivalent to ‘f’ on the SPARC-V8
architecture and contains both lower and upper floating-point registers on the SPARC-V9 architecture.

c

Floating-point condition code register.

d

Lower floating-point register. It is only valid on the SPARC-V9
architecture when the Visual Instruction Set is available.

b

Floating-point register. It is only valid on the SPARC-V9 architecture when the Visual Instruction Set is available.

h

64-bit global or out register for the SPARC-V8+ architecture.

C

The constant all-ones, for floating-point.

A

Signed 5-bit constant

D

A vector constant

I

Signed 13-bit constant

J

Zero

K

32-bit constant with the low 12 bits clear (a constant that can be
loaded with the sethi instruction)

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585

L

A constant in the range supported by movcc instructions (11-bit
signed immediate)

M

A constant in the range supported by movrcc instructions (10-bit
signed immediate)

N

Same as ‘K’, except that it verifies that bits that are not in the
lower 32-bit range are all zero. Must be used instead of ‘K’ for
modes wider than SImode

O

The constant 4096

G

Floating-point zero

H

Signed 13-bit constant, sign-extended to 32 or 64 bits

P

The constant -1

Q

Floating-point constant whose integral representation can be moved
into an integer register using a single sethi instruction

R

Floating-point constant whose integral representation can be moved
into an integer register using a single mov instruction

S

Floating-point constant whose integral representation can be moved
into an integer register using a high/lo sum instruction sequence

T

Memory address aligned to an 8-byte boundary

U

Even register

W

Memory address for ‘e’ constraint registers

w

Memory address with only a base register

Y

Vector zero

SPU—‘config/spu/spu.h’
a
An immediate which can be loaded with the il/ila/ilh/ilhu instructions. const int is treated as a 64 bit value.
c

An immediate for and/xor/or instructions. const int is treated as
a 64 bit value.

d

An immediate for the iohl instruction. const int is treated as a 64
bit value.

f

An immediate which can be loaded with fsmbi.

A

An immediate which can be loaded with the il/ila/ilh/ilhu instructions. const int is treated as a 32 bit value.

B

An immediate for most arithmetic instructions. const int is treated
as a 32 bit value.

C

An immediate for and/xor/or instructions. const int is treated as
a 32 bit value.

D

An immediate for the iohl instruction. const int is treated as a 32
bit value.

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Using the GNU Compiler Collection (GCC)

I

A constant in the range [−64, 63] for shift/rotate instructions.

J

An unsigned 7-bit constant for conversion/nop/channel instructions.

K

A signed 10-bit constant for most arithmetic instructions.

M

A signed 16 bit immediate for stop.

N

An unsigned 16-bit constant for iohl and fsmbi.

O

An unsigned 7-bit constant whose 3 least significant bits are 0.

P

An unsigned 3-bit constant for 16-byte rotates and shifts

R

Call operand, reg, for indirect calls

S

Call operand, symbol, for relative calls.

T

Call operand, const int, for absolute calls.

U

An immediate which can be loaded with the il/ila/ilh/ilhu instructions. const int is sign extended to 128 bit.

W

An immediate for shift and rotate instructions. const int is treated
as a 32 bit value.

Y

An immediate for and/xor/or instructions. const int is sign extended as a 128 bit.

Z

An immediate for the iohl instruction. const int is sign extended
to 128 bit.

TI C6X family—‘config/c6x/constraints.md’
a
Register file A (A0–A31).
b

Register file B (B0–B31).

A

Predicate registers in register file A (A0–A2 on C64X and higher,
A1 and A2 otherwise).

B

Predicate registers in register file B (B0–B2).

C

A call-used register in register file B (B0–B9, B16–B31).

Da

Register file A, excluding predicate registers (A3–A31, plus A0 if
not C64X or higher).

Db

Register file B, excluding predicate registers (B3–B31).

Iu4

Integer constant in the range 0 . . . 15.

Iu5

Integer constant in the range 0 . . . 31.

In5

Integer constant in the range −31 . . . 0.

Is5

Integer constant in the range −16 . . . 15.

I5x

Integer constant that can be the operand of an ADDA or a SUBA
insn.

Chapter 6: Extensions to the C Language Family

IuB

Integer constant in the range 0 . . . 65535.

IsB

Integer constant in the range −32768 . . . 32767.

IsC

Integer constant in the range −220 . . . 220 − 1.

Jc

Integer constant that is a valid mask for the clr instruction.

Js

Integer constant that is a valid mask for the set instruction.

Q

Memory location with A base register.

R

Memory location with B base register.

Z

Register B14 (aka DP).

587

TILE-Gx—‘config/tilegx/constraints.md’
R00
R01
R02
R03
R04
R05
R06
R07
R08
R09
R10
Each of these represents a register constraint for an individual register, from r0 to r10.
I

Signed 8-bit integer constant.

J

Signed 16-bit integer constant.

K

Unsigned 16-bit integer constant.

L

Integer constant that fits in one signed byte when incremented by
one (−129 . . . 126).

m

Memory operand. If used together with ‘<’ or ‘>’, the operand can
have postincrement which requires printing with ‘%In’ and ‘%in’ on
TILE-Gx. For example:
asm ("st_add %I0,%1,%i0" : "=m<>" (*mem) : "r" (val));

M

A bit mask suitable for the BFINS instruction.

N

Integer constant that is a byte tiled out eight times.

O

The integer zero constant.

P

Integer constant that is a sign-extended byte tiled out as four shorts.

Q

Integer constant that fits in one signed byte when incremented
(−129 . . . 126), but excluding -1.

S

Integer constant that has all 1 bits consecutive and starting at bit
0.

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Using the GNU Compiler Collection (GCC)

T

A 16-bit fragment of a got, tls, or pc-relative reference.

U

Memory operand except postincrement. This is roughly the same
as ‘m’ when not used together with ‘<’ or ‘>’.

W

An 8-element vector constant with identical elements.

Y

A 4-element vector constant with identical elements.

Z0

The integer constant 0xffffffff.

Z1

The integer constant 0xffffffff00000000.

TILEPro—‘config/tilepro/constraints.md’
R00
R01
R02
R03
R04
R05
R06
R07
R08
R09
R10
Each of these represents a register constraint for an individual register, from r0 to r10.
I

Signed 8-bit integer constant.

J

Signed 16-bit integer constant.

K

Nonzero integer constant with low 16 bits zero.

L

Integer constant that fits in one signed byte when incremented by
one (−129 . . . 126).

m

Memory operand. If used together with ‘<’ or ‘>’, the operand can
have postincrement which requires printing with ‘%In’ and ‘%in’ on
TILEPro. For example:
asm ("swadd %I0,%1,%i0" : "=m<>" (mem) : "r" (val));

M

A bit mask suitable for the MM instruction.

N

Integer constant that is a byte tiled out four times.

O

The integer zero constant.

P

Integer constant that is a sign-extended byte tiled out as two shorts.

Q

Integer constant that fits in one signed byte when incremented
(−129 . . . 126), but excluding -1.

T

A symbolic operand, or a 16-bit fragment of a got, tls, or pc-relative
reference.

U

Memory operand except postincrement. This is roughly the same
as ‘m’ when not used together with ‘<’ or ‘>’.

Chapter 6: Extensions to the C Language Family

W

A 4-element vector constant with identical elements.

Y

A 2-element vector constant with identical elements.

589

Visium—‘config/visium/constraints.md’
b

EAM register mdb

c

EAM register mdc

f

Floating point register

l

General register, but not r29, r30 and r31

t

Register r1

u

Register r2

v

Register r3

G

Floating-point constant 0.0

J

Integer constant in the range 0 .. 65535 (16-bit immediate)

K

Integer constant in the range 1 .. 31 (5-bit immediate)

L

Integer constant in the range −65535 .. −1 (16-bit negative immediate)

M

Integer constant −1

O

Integer constant 0

P

Integer constant 32

x86 family—‘config/i386/constraints.md’
R

Legacy register—the eight integer registers available on all i386
processors (a, b, c, d, si, di, bp, sp).

q

Any register accessible as rl. In 32-bit mode, a, b, c, and d; in
64-bit mode, any integer register.

Q

Any register accessible as rh: a, b, c, and d.

a

The a register.

b

The b register.

c

The c register.

d

The d register.

S

The si register.

D

The di register.

A

The a and d registers. This class is used for instructions that return double word results in the ax:dx register pair. Single word
values will be allocated either in ax or dx. For example on i386 the
following implements rdtsc:

590

Using the GNU Compiler Collection (GCC)

unsigned long long rdtsc (void)
{
unsigned long long tick;
__asm__ __volatile__("rdtsc":"=A"(tick));
return tick;
}

This is not correct on x86-64 as it would allocate tick in either ax
or dx. You have to use the following variant instead:
unsigned long long rdtsc (void)
{
unsigned int tickl, tickh;
__asm__ __volatile__("rdtsc":"=a"(tickl),"=d"(tickh));
return ((unsigned long long)tickh << 32)|tickl;
}

U

The call-clobbered integer registers.

f

Any 80387 floating-point (stack) register.

t

Top of 80387 floating-point stack (%st(0)).

u

Second from top of 80387 floating-point stack (%st(1)).

y

Any MMX register.

x

Any SSE register.

v

Any EVEX encodable SSE register (%xmm0-%xmm31).

Yz

First SSE register (%xmm0).

I

Integer constant in the range 0 . . . 31, for 32-bit shifts.

J

Integer constant in the range 0 . . . 63, for 64-bit shifts.

K

Signed 8-bit integer constant.

L

0xFF or 0xFFFF, for andsi as a zero-extending move.

M

0, 1, 2, or 3 (shifts for the lea instruction).

N

Unsigned 8-bit integer constant (for in and out instructions).

G

Standard 80387 floating point constant.

C

SSE constant zero operand.

e

32-bit signed integer constant, or a symbolic reference known to
fit that range (for immediate operands in sign-extending x86-64
instructions).

We

32-bit signed integer constant, or a symbolic reference known to fit
that range (for sign-extending conversion operations that require
non-VOIDmode immediate operands).

Wz

32-bit unsigned integer constant, or a symbolic reference known to
fit that range (for zero-extending conversion operations that require
non-VOIDmode immediate operands).

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591

Wd

128-bit integer constant where both the high and low 64-bit word
satisfy the e constraint.

Z

32-bit unsigned integer constant, or a symbolic reference known to
fit that range (for immediate operands in zero-extending x86-64
instructions).

Tv

VSIB address operand.

Ts

Address operand without segment register.

Ti

MPX address operand without index.

Tb

MPX address operand without base.

Xstormy16—‘config/stormy16/stormy16.h’
a
Register r0.
b

Register r1.

c

Register r2.

d

Register r8.

e

Registers r0 through r7.

t

Registers r0 and r1.

y

The carry register.

z

Registers r8 and r9.

I

A constant between 0 and 3 inclusive.

J

A constant that has exactly one bit set.

K

A constant that has exactly one bit clear.

L

A constant between 0 and 255 inclusive.

M

A constant between −255 and 0 inclusive.

N

A constant between −3 and 0 inclusive.

O

A constant between 1 and 4 inclusive.

P

A constant between −4 and −1 inclusive.

Q

A memory reference that is a stack push.

R

A memory reference that is a stack pop.

S

A memory reference that refers to a constant address of known
value.

T

The register indicated by Rx (not implemented yet).

U

A constant that is not between 2 and 15 inclusive.

Z

The constant 0.

Xtensa—‘config/xtensa/constraints.md’
a
General-purpose 32-bit register

592

Using the GNU Compiler Collection (GCC)

b

One-bit boolean register

A

MAC16 40-bit accumulator register

I

Signed 12-bit integer constant, for use in MOVI instructions

J

Signed 8-bit integer constant, for use in ADDI instructions

K

Integer constant valid for BccI instructions

L

Unsigned constant valid for BccUI instructions

6.45.4 Controlling Names Used in Assembler Code
You can specify the name to be used in the assembler code for a C function or variable by
writing the asm (or __asm__) keyword after the declarator. It is up to you to make sure
that the assembler names you choose do not conflict with any other assembler symbols, or
reference registers.

Assembler names for data:
This sample shows how to specify the assembler name for data:
int foo asm ("myfoo") = 2;

This specifies that the name to be used for the variable foo in the assembler code should
be ‘myfoo’ rather than the usual ‘_foo’.
On systems where an underscore is normally prepended to the name of a C variable, this
feature allows you to define names for the linker that do not start with an underscore.
GCC does not support using this feature with a non-static local variable since such
variables do not have assembler names. If you are trying to put the variable in a particular
register, see Section 6.45.5 [Explicit Register Variables], page 592.

Assembler names for functions:
To specify the assembler name for functions, write a declaration for the function before its
definition and put asm there, like this:
int func (int x, int y) asm ("MYFUNC");
int func (int x, int y)
{
/* . . . */

This specifies that the name to be used for the function func in the assembler code should
be MYFUNC.

6.45.5 Variables in Specified Registers
GNU C allows you to associate specific hardware registers with C variables. In almost all
cases, allowing the compiler to assign registers produces the best code. However under
certain unusual circumstances, more precise control over the variable storage is required.
Both global and local variables can be associated with a register. The consequences of
performing this association are very different between the two, as explained in the sections
below.

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6.45.5.1 Defining Global Register Variables
You can define a global register variable and associate it with a specified register like this:
register int *foo asm ("r12");

Here r12 is the name of the register that should be used. Note that this is the same
syntax used for defining local register variables, but for a global variable the declaration
appears outside a function. The register keyword is required, and cannot be combined
with static. The register name must be a valid register name for the target platform.
Registers are a scarce resource on most systems and allowing the compiler to manage
their usage usually results in the best code. However, under special circumstances it can
make sense to reserve some globally. For example this may be useful in programs such as
programming language interpreters that have a couple of global variables that are accessed
very often.
After defining a global register variable, for the current compilation unit:
• The register is reserved entirely for this use, and will not be allocated for any other
purpose.
• The register is not saved and restored by any functions.
• Stores into this register are never deleted even if they appear to be dead, but references
may be deleted, moved or simplified.
Note that these points only apply to code that is compiled with the definition. The
behavior of code that is merely linked in (for example code from libraries) is not affected.
If you want to recompile source files that do not actually use your global register variable
so they do not use the specified register for any other purpose, you need not actually add
the global register declaration to their source code. It suffices to specify the compiler option
‘-ffixed-reg’ (see Section 3.16 [Code Gen Options], page 202) to reserve the register.

Declaring the variable
Global register variables can not have initial values, because an executable file has no means
to supply initial contents for a register.
When selecting a register, choose one that is normally saved and restored by function
calls on your machine. This ensures that code which is unaware of this reservation (such as
library routines) will restore it before returning.
On machines with register windows, be sure to choose a global register that is not affected
magically by the function call mechanism.

Using the variable
When calling routines that are not aware of the reservation, be cautious if those routines
call back into code which uses them. As an example, if you call the system library version of
qsort, it may clobber your registers during execution, but (if you have selected appropriate
registers) it will restore them before returning. However it will not restore them before
calling qsort’s comparison function. As a result, global values will not reliably be available
to the comparison function unless the qsort function itself is rebuilt.
Similarly, it is not safe to access the global register variables from signal handlers or from
more than one thread of control. Unless you recompile them specially for the task at hand,
the system library routines may temporarily use the register for other things.

594

Using the GNU Compiler Collection (GCC)

On most machines, longjmp restores to each global register variable the value it had at
the time of the setjmp. On some machines, however, longjmp does not change the value
of global register variables. To be portable, the function that called setjmp should make
other arrangements to save the values of the global register variables, and to restore them
in a longjmp. This way, the same thing happens regardless of what longjmp does.
Eventually there may be a way of asking the compiler to choose a register automatically,
but first we need to figure out how it should choose and how to enable you to guide the
choice. No solution is evident.

6.45.5.2 Specifying Registers for Local Variables
You can define a local register variable and associate it with a specified register like this:
register int *foo asm ("r12");

Here r12 is the name of the register that should be used. Note that this is the same syntax
used for defining global register variables, but for a local variable the declaration appears
within a function. The register keyword is required, and cannot be combined with static.
The register name must be a valid register name for the target platform.
As with global register variables, it is recommended that you choose a register that is
normally saved and restored by function calls on your machine, so that calls to library
routines will not clobber it.
The only supported use for this feature is to specify registers for input and output
operands when calling Extended asm (see Section 6.45.2 [Extended Asm], page 543). This
may be necessary if the constraints for a particular machine don’t provide sufficient control
to select the desired register. To force an operand into a register, create a local variable
and specify the register name after the variable’s declaration. Then use the local variable
for the asm operand and specify any constraint letter that matches the register:
register int *p1 asm
register int *p2 asm
register int *result
asm ("sysint" : "=r"

("r0") = ...;
("r1") = ...;
asm ("r0");
(result) : "0" (p1), "r" (p2));

Warning: In the above example, be aware that a register (for example r0) can be callclobbered by subsequent code, including function calls and library calls for arithmetic operators on other variables (for example the initialization of p2). In this case, use temporary
variables for expressions between the register assignments:
int t1 = ...;
register int *p1 asm
register int *p2 asm
register int *result
asm ("sysint" : "=r"

("r0") = ...;
("r1") = t1;
asm ("r0");
(result) : "0" (p1), "r" (p2));

Defining a register variable does not reserve the register. Other than when invoking the
Extended asm, the contents of the specified register are not guaranteed. For this reason, the
following uses are explicitly not supported. If they appear to work, it is only happenstance,
and may stop working as intended due to (seemingly) unrelated changes in surrounding
code, or even minor changes in the optimization of a future version of gcc:
• Passing parameters to or from Basic asm
• Passing parameters to or from Extended asm without using input or output operands.
• Passing parameters to or from routines written in assembler (or other languages) using
non-standard calling conventions.

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595

Some developers use Local Register Variables in an attempt to improve gcc’s allocation of
registers, especially in large functions. In this case the register name is essentially a hint to
the register allocator. While in some instances this can generate better code, improvements
are subject to the whims of the allocator/optimizers. Since there are no guarantees that
your improvements won’t be lost, this usage of Local Register Variables is discouraged.
On the MIPS platform, there is related use for local register variables with slightly different characteristics (see Section “Defining coprocessor specifics for MIPS targets” in GNU
Compiler Collection (GCC) Internals).

6.45.6 Size of an asm
Some targets require that GCC track the size of each instruction used in order to generate
correct code. Because the final length of the code produced by an asm statement is only
known by the assembler, GCC must make an estimate as to how big it will be. It does
this by counting the number of instructions in the pattern of the asm and multiplying that
by the length of the longest instruction supported by that processor. (When working out
the number of instructions, it assumes that any occurrence of a newline or of whatever
statement separator character is supported by the assembler – typically ‘;’ — indicates the
end of an instruction.)
Normally, GCC’s estimate is adequate to ensure that correct code is generated, but it is
possible to confuse the compiler if you use pseudo instructions or assembler macros that
expand into multiple real instructions, or if you use assembler directives that expand to
more space in the object file than is needed for a single instruction. If this happens then
the assembler may produce a diagnostic saying that a label is unreachable.

6.46 Alternate Keywords
‘-ansi’ and the various ‘-std’ options disable certain keywords. This causes trouble when
you want to use GNU C extensions, or a general-purpose header file that should be usable
by all programs, including ISO C programs. The keywords asm, typeof and inline are
not available in programs compiled with ‘-ansi’ or ‘-std’ (although inline can be used in
a program compiled with ‘-std=c99’ or ‘-std=c11’). The ISO C99 keyword restrict is
only available when ‘-std=gnu99’ (which will eventually be the default) or ‘-std=c99’ (or
the equivalent ‘-std=iso9899:1999’), or an option for a later standard version, is used.
The way to solve these problems is to put ‘__’ at the beginning and end of each problematical keyword. For example, use __asm__ instead of asm, and __inline__ instead of
inline.
Other C compilers won’t accept these alternative keywords; if you want to compile with
another compiler, you can define the alternate keywords as macros to replace them with
the customary keywords. It looks like this:
#ifndef __GNUC__
#define __asm__ asm
#endif

‘-pedantic’ and other options cause warnings for many GNU C extensions. You can prevent such warnings within one expression by writing __extension__ before the expression.
__extension__ has no effect aside from this.

596

Using the GNU Compiler Collection (GCC)

6.47 Incomplete enum Types
You can define an enum tag without specifying its possible values. This results in an incomplete type, much like what you get if you write struct foo without describing the elements.
A later declaration that does specify the possible values completes the type.
You cannot allocate variables or storage using the type while it is incomplete. However,
you can work with pointers to that type.
This extension may not be very useful, but it makes the handling of enum more consistent
with the way struct and union are handled.
This extension is not supported by GNU C++.

6.48 Function Names as Strings
GCC provides three magic constants that hold the name of the current function as a string.
In C++11 and later modes, all three are treated as constant expressions and can be used
in constexpr constexts. The first of these constants is __func__, which is part of the C99
standard:
The identifier __func__ is implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration
static const char __func__[] = "function-name";

appeared, where function-name is the name of the lexically-enclosing function. This name
is the unadorned name of the function. As an extension, at file (or, in C++, namespace
scope), __func__ evaluates to the empty string.
__FUNCTION__ is another name for __func__, provided for backward compatibility with
old versions of GCC.
In C, __PRETTY_FUNCTION__ is yet another name for __func__, except that at file (or,
in C++, namespace scope), it evaluates to the string "top level". In addition, in C++,
__PRETTY_FUNCTION__ contains the signature of the function as well as its bare name. For
example, this program:
extern "C" int printf (const char *, ...);
class a {
public:
void sub (int i)
{
printf ("__FUNCTION__ = %s\n", __FUNCTION__);
printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
}
};
int
main (void)
{
a ax;
ax.sub (0);
return 0;
}

gives this output:
__FUNCTION__ = sub
__PRETTY_FUNCTION__ = void a::sub(int)

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597

These identifiers are variables, not preprocessor macros, and may not be used to initialize
char arrays or be concatenated with string literals.

6.49 Getting the Return or Frame Address of a Function
These functions may be used to get information about the callers of a function.

void * __builtin_return_address (unsigned int level)

[Built-in Function]
This function returns the return address of the current function, or of one of its callers.
The level argument is number of frames to scan up the call stack. A value of 0 yields
the return address of the current function, a value of 1 yields the return address of
the caller of the current function, and so forth. When inlining the expected behavior
is that the function returns the address of the function that is returned to. To work
around this behavior use the noinline function attribute.
The level argument must be a constant integer.
On some machines it may be impossible to determine the return address of any
function other than the current one; in such cases, or when the top of the stack has
been reached, this function returns 0 or a random value. In addition, __builtin_
frame_address may be used to determine if the top of the stack has been reached.
Additional post-processing of the returned value may be needed, see __builtin_
extract_return_addr.
Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program. As a result, calls that are considered unsafe are
diagnosed when the ‘-Wframe-address’ option is in effect. Such calls should only be
made in debugging situations.

void * __builtin_extract_return_addr (void *addr)

[Built-in Function]
The address as returned by __builtin_return_address may have to be fed through
this function to get the actual encoded address. For example, on the 31-bit S/390
platform the highest bit has to be masked out, or on SPARC platforms an offset has
to be added for the true next instruction to be executed.
If no fixup is needed, this function simply passes through addr.

void * __builtin_frob_return_address (void *addr)

[Built-in Function]
This function does the reverse of __builtin_extract_return_addr.

void * __builtin_frame_address (unsigned int level)

[Built-in Function]
This function is similar to __builtin_return_address, but it returns the address of
the function frame rather than the return address of the function. Calling __builtin_
frame_address with a value of 0 yields the frame address of the current function, a
value of 1 yields the frame address of the caller of the current function, and so forth.
The frame is the area on the stack that holds local variables and saved registers. The
frame address is normally the address of the first word pushed on to the stack by the
function. However, the exact definition depends upon the processor and the calling
convention. If the processor has a dedicated frame pointer register, and the function
has a frame, then __builtin_frame_address returns the value of the frame pointer
register.

598

Using the GNU Compiler Collection (GCC)

On some machines it may be impossible to determine the frame address of any function
other than the current one; in such cases, or when the top of the stack has been
reached, this function returns 0 if the first frame pointer is properly initialized by the
startup code.
Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program. As a result, calls that are considered unsafe are
diagnosed when the ‘-Wframe-address’ option is in effect. Such calls should only be
made in debugging situations.

6.50 Using Vector Instructions through Built-in Functions
On some targets, the instruction set contains SIMD vector instructions which operate on
multiple values contained in one large register at the same time. For example, on the x86
the MMX, 3DNow! and SSE extensions can be used this way.
The first step in using these extensions is to provide the necessary data types. This should
be done using an appropriate typedef:
typedef int v4si __attribute__ ((vector_size (16)));

The int type specifies the base type, while the attribute specifies the vector size for the
variable, measured in bytes. For example, the declaration above causes the compiler to set
the mode for the v4si type to be 16 bytes wide and divided into int sized units. For a
32-bit int this means a vector of 4 units of 4 bytes, and the corresponding mode of foo is
V4SI.
The vector_size attribute is only applicable to integral and float scalars, although
arrays, pointers, and function return values are allowed in conjunction with this construct.
Only sizes that are a power of two are currently allowed.
All the basic integer types can be used as base types, both as signed and as unsigned:
char, short, int, long, long long. In addition, float and double can be used to build
floating-point vector types.
Specifying a combination that is not valid for the current architecture causes GCC to
synthesize the instructions using a narrower mode. For example, if you specify a variable of
type V4SI and your architecture does not allow for this specific SIMD type, GCC produces
code that uses 4 SIs.
The types defined in this manner can be used with a subset of normal C operations.
Currently, GCC allows using the following operators on these types: +, -, *, /, unary
minus, ^, |, &, ~, %.
The operations behave like C++ valarrays. Addition is defined as the addition of the
corresponding elements of the operands. For example, in the code below, each of the 4
elements in a is added to the corresponding 4 elements in b and the resulting vector is
stored in c.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a, b, c;
c = a + b;

Subtraction, multiplication, division, and the logical operations operate in a similar manner. Likewise, the result of using the unary minus or complement operators on a vector type

Chapter 6: Extensions to the C Language Family

599

is a vector whose elements are the negative or complemented values of the corresponding
elements in the operand.
It is possible to use shifting operators <<, >> on integer-type vectors. The operation is
defined as following: {a0, a1, ..., an} >> {b0, b1, ..., bn} == {a0 >> b0, a1 >> b1,
..., an >> bn}. Vector operands must have the same number of elements.
For convenience, it is allowed to use a binary vector operation where one operand is a
scalar. In that case the compiler transforms the scalar operand into a vector where each
element is the scalar from the operation. The transformation happens only if the scalar
could be safely converted to the vector-element type. Consider the following code.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a, b, c;
long l;
a = b + 1;
a = 2 * b;

/* a = b + {1,1,1,1}; */
/* a = {2,2,2,2} * b; */

a = l + a;

/* Error, cannot convert long to int. */

Vectors can be subscripted as if the vector were an array with the same number of elements
and base type. Out of bound accesses invoke undefined behavior at run time. Warnings for
out of bound accesses for vector subscription can be enabled with ‘-Warray-bounds’.
Vector comparison is supported with standard comparison operators: ==, !=, <, <=, >,
>=. Comparison operands can be vector expressions of integer-type or real-type. Comparison between integer-type vectors and real-type vectors are not supported. The result of
the comparison is a vector of the same width and number of elements as the comparison
operands with a signed integral element type.
Vectors are compared element-wise producing 0 when comparison is false and -1 (constant
of the appropriate type where all bits are set) otherwise. Consider the following example.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a = {1,2,3,4};
v4si b = {3,2,1,4};
v4si c;
c = a > b;
c = a == b;

/* The result would be {0, 0,-1, 0}
/* The result would be {0,-1, 0,-1}

*/
*/

In C++, the ternary operator ?: is available. a?b:c, where b and c are vectors of the same
type and a is an integer vector with the same number of elements of the same size as b and
c, computes all three arguments and creates a vector {a[0]?b[0]:c[0], a[1]?b[1]:c[1],
...}. Note that unlike in OpenCL, a is thus interpreted as a != 0 and not a < 0. As in the
case of binary operations, this syntax is also accepted when one of b or c is a scalar that is
then transformed into a vector. If both b and c are scalars and the type of true?b:c has
the same size as the element type of a, then b and c are converted to a vector type whose
elements have this type and with the same number of elements as a.
In C++, the logic operators !, &&, || are available for vectors. !v is equivalent to v
== 0, a && b is equivalent to a!=0 & b!=0 and a || b is equivalent to a!=0 | b!=0. For
mixed operations between a scalar s and a vector v, s && v is equivalent to s?v!=0:0 (the
evaluation is short-circuit) and v && s is equivalent to v!=0 & (s?-1:0).

600

Using the GNU Compiler Collection (GCC)

Vector shuffling is available using functions __builtin_shuffle (vec, mask) and __
builtin_shuffle (vec0, vec1, mask). Both functions construct a permutation of elements from one or two vectors and return a vector of the same type as the input vector(s).
The mask is an integral vector with the same width (W ) and element count (N ) as the
output vector.
The elements of the input vectors are numbered in memory ordering of vec0 beginning
at 0 and vec1 beginning at N. The elements of mask are considered modulo N in the
single-operand case and modulo 2 ∗ N in the two-operand case.
Consider the following example,
typedef int v4si __attribute__ ((vector_size (16)));
v4si
v4si
v4si
v4si
v4si

a = {1,2,3,4};
b = {5,6,7,8};
mask1 = {0,1,1,3};
mask2 = {0,4,2,5};
res;

res = __builtin_shuffle (a, mask1);
res = __builtin_shuffle (a, b, mask2);

/* res is {1,2,2,4}
/* res is {1,5,3,6}

*/
*/

Note that __builtin_shuffle is intentionally semantically compatible with the OpenCL
shuffle and shuffle2 functions.
You can declare variables and use them in function calls and returns, as well as in assignments and some casts. You can specify a vector type as a return type for a function.
Vector types can also be used as function arguments. It is possible to cast from one vector
type to another, provided they are of the same size (in fact, you can also cast vectors to
and from other datatypes of the same size).
You cannot operate between vectors of different lengths or different signedness without a
cast.

6.51 Support for offsetof
GCC implements for both C and C++ a syntactic extension to implement the offsetof
macro.
primary:
"__builtin_offsetof" "(" typename "," offsetof_member_designator ")"
offsetof_member_designator:
identifier
| offsetof_member_designator "." identifier
| offsetof_member_designator "[" expr "]"

This extension is sufficient such that
#define offsetof(type, member)

__builtin_offsetof (type, member)

is a suitable definition of the offsetof macro. In C++, type may be dependent. In either
case, member may consist of a single identifier, or a sequence of member accesses and array
references.

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6.52 Legacy __sync Built-in Functions for Atomic Memory
Access
The following built-in functions are intended to be compatible with those described in the
Intel Itanium Processor-specific Application Binary Interface, section 7.4. As such, they
depart from normal GCC practice by not using the ‘__builtin_’ prefix and also by being
overloaded so that they work on multiple types.
The definition given in the Intel documentation allows only for the use of the types int,
long, long long or their unsigned counterparts. GCC allows any scalar type that is 1, 2, 4
or 8 bytes in size other than the C type _Bool or the C++ type bool. Operations on pointer
arguments are performed as if the operands were of the uintptr_t type. That is, they are
not scaled by the size of the type to which the pointer points.
These functions are implemented in terms of the ‘__atomic’ builtins (see Section 6.53
[ atomic Builtins], page 603). They should not be used for new code which should use the
‘__atomic’ builtins instead.
Not all operations are supported by all target processors. If a particular operation cannot
be implemented on the target processor, a warning is generated and a call to an external
function is generated. The external function carries the same name as the built-in version,
with an additional suffix ‘_n’ where n is the size of the data type.
In most cases, these built-in functions are considered a full barrier. That is, no memory
operand is moved across the operation, either forward or backward. Further, instructions
are issued as necessary to prevent the processor from speculating loads across the operation
and from queuing stores after the operation.
All of the routines are described in the Intel documentation to take “an optional list
of variables protected by the memory barrier”. It’s not clear what is meant by that; it
could mean that only the listed variables are protected, or it could mean a list of additional
variables to be protected. The list is ignored by GCC which treats it as empty. GCC
interprets an empty list as meaning that all globally accessible variables should be protected.
type
type
type
type
type
type

__sync_fetch_and_add (type *ptr, type value, ...)
__sync_fetch_and_sub (type *ptr, type value, ...)
__sync_fetch_and_or (type *ptr, type value, ...)
__sync_fetch_and_and (type *ptr, type value, ...)
__sync_fetch_and_xor (type *ptr, type value, ...)
__sync_fetch_and_nand (type *ptr, type value, ...)
These built-in functions perform the operation suggested by the name, and returns the value that had previously been in memory. That is, operations on
integer operands have the following semantics. Operations on pointer arguments are performed as if the operands were of the uintptr_t type. That is,
they are not scaled by the size of the type to which the pointer points.
{ tmp = *ptr; *ptr op= value; return tmp; }
{ tmp = *ptr; *ptr = ~(tmp & value); return tmp; }

// nand

The object pointed to by the first argument must be of integer or pointer type.
It must not be a boolean type.
Note: GCC 4.4 and later implement __sync_fetch_and_nand as *ptr = ~(tmp
& value) instead of *ptr = ~tmp & value.

602

type
type
type
type
type
type

Using the GNU Compiler Collection (GCC)

__sync_add_and_fetch (type *ptr, type value, ...)
__sync_sub_and_fetch (type *ptr, type value, ...)
__sync_or_and_fetch (type *ptr, type value, ...)
__sync_and_and_fetch (type *ptr, type value, ...)
__sync_xor_and_fetch (type *ptr, type value, ...)
__sync_nand_and_fetch (type *ptr, type value, ...)
These built-in functions perform the operation suggested by the name, and
return the new value. That is, operations on integer operands have the following
semantics. Operations on pointer operands are performed as if the operand’s
type were uintptr_t.
{ *ptr op= value; return *ptr; }
{ *ptr = ~(*ptr & value); return *ptr; }

// nand

The same constraints on arguments apply as for the corresponding __sync_op_
and_fetch built-in functions.
Note: GCC 4.4 and later implement __sync_nand_and_fetch as *ptr =
~(*ptr & value) instead of *ptr = ~*ptr & value.
bool __sync_bool_compare_and_swap (type *ptr, type oldval, type newval, ...)
type __sync_val_compare_and_swap (type *ptr, type oldval, type newval, ...)
These built-in functions perform an atomic compare and swap. That is, if the
current value of *ptr is oldval, then write newval into *ptr.
The “bool” version returns true if the comparison is successful and newval is
written. The “val” version returns the contents of *ptr before the operation.
__sync_synchronize (...)
This built-in function issues a full memory barrier.
type __sync_lock_test_and_set (type *ptr, type value, ...)
This built-in function, as described by Intel, is not a traditional test-and-set
operation, but rather an atomic exchange operation. It writes value into *ptr,
and returns the previous contents of *ptr.
Many targets have only minimal support for such locks, and do not support a
full exchange operation. In this case, a target may support reduced functionality
here by which the only valid value to store is the immediate constant 1. The
exact value actually stored in *ptr is implementation defined.
This built-in function is not a full barrier, but rather an acquire barrier. This
means that references after the operation cannot move to (or be speculated to)
before the operation, but previous memory stores may not be globally visible
yet, and previous memory loads may not yet be satisfied.
void __sync_lock_release (type *ptr, ...)
This built-in function releases the lock acquired by __sync_lock_test_and_
set. Normally this means writing the constant 0 to *ptr.
This built-in function is not a full barrier, but rather a release barrier. This
means that all previous memory stores are globally visible, and all previous
memory loads have been satisfied, but following memory reads are not prevented
from being speculated to before the barrier.

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603

6.53 Built-in Functions for Memory Model Aware Atomic
Operations
The following built-in functions approximately match the requirements for the C++11 memory model. They are all identified by being prefixed with ‘__atomic’ and most are overloaded
so that they work with multiple types.
These functions are intended to replace the legacy ‘__sync’ builtins. The main difference
is that the memory order that is requested is a parameter to the functions. New code should
always use the ‘__atomic’ builtins rather than the ‘__sync’ builtins.
Note that the ‘__atomic’ builtins assume that programs will conform to the C++11 memory model. In particular, they assume that programs are free of data races. See the C++11
standard for detailed requirements.
The ‘__atomic’ builtins can be used with any integral scalar or pointer type that is 1, 2,
4, or 8 bytes in length. 16-byte integral types are also allowed if ‘__int128’ (see Section 6.8
[ int128], page 448) is supported by the architecture.
The four non-arithmetic functions (load, store, exchange, and compare exchange) all have
a generic version as well. This generic version works on any data type. It uses the lock-free
built-in function if the specific data type size makes that possible; otherwise, an external call
is left to be resolved at run time. This external call is the same format with the addition of
a ‘size_t’ parameter inserted as the first parameter indicating the size of the object being
pointed to. All objects must be the same size.
There are 6 different memory orders that can be specified. These map to the C++11
memory orders with the same names, see the C++11 standard or the GCC wiki on atomic
synchronization for detailed definitions. Individual targets may also support additional
memory orders for use on specific architectures. Refer to the target documentation for
details of these.
An atomic operation can both constrain code motion and be mapped to hardware instructions for synchronization between threads (e.g., a fence). To which extent this happens is
controlled by the memory orders, which are listed here in approximately ascending order
of strength. The description of each memory order is only meant to roughly illustrate the
effects and is not a specification; see the C++11 memory model for precise semantics.
__ATOMIC_RELAXED
Implies no inter-thread ordering constraints.
__ATOMIC_CONSUME
This is currently implemented using the stronger __ATOMIC_ACQUIRE memory
order because of a deficiency in C++11’s semantics for memory_order_consume.
__ATOMIC_ACQUIRE
Creates an inter-thread happens-before constraint from the release (or stronger)
semantic store to this acquire load. Can prevent hoisting of code to before the
operation.
__ATOMIC_RELEASE
Creates an inter-thread happens-before constraint to acquire (or stronger) semantic loads that read from this release store. Can prevent sinking of code to
after the operation.

604

Using the GNU Compiler Collection (GCC)

__ATOMIC_ACQ_REL
Combines the effects of both __ATOMIC_ACQUIRE and __ATOMIC_RELEASE.
__ATOMIC_SEQ_CST
Enforces total ordering with all other __ATOMIC_SEQ_CST operations.
Note that in the C++11 memory model, fences (e.g., ‘__atomic_thread_fence’) take effect in combination with other atomic operations on specific memory locations (e.g., atomic
loads); operations on specific memory locations do not necessarily affect other operations
in the same way.
Target architectures are encouraged to provide their own patterns for each of the atomic
built-in functions. If no target is provided, the original non-memory model set of ‘__sync’
atomic built-in functions are used, along with any required synchronization fences surrounding it in order to achieve the proper behavior. Execution in this case is subject to the same
restrictions as those built-in functions.
If there is no pattern or mechanism to provide a lock-free instruction sequence, a call is
made to an external routine with the same parameters to be resolved at run time.
When implementing patterns for these built-in functions, the memory order parameter
can be ignored as long as the pattern implements the most restrictive __ATOMIC_SEQ_CST
memory order. Any of the other memory orders execute correctly with this memory order
but they may not execute as efficiently as they could with a more appropriate implementation of the relaxed requirements.
Note that the C++11 standard allows for the memory order parameter to be determined
at run time rather than at compile time. These built-in functions map any run-time value
to __ATOMIC_SEQ_CST rather than invoke a runtime library call or inline a switch statement.
This is standard compliant, safe, and the simplest approach for now.
The memory order parameter is a signed int, but only the lower 16 bits are reserved for
the memory order. The remainder of the signed int is reserved for target use and should be
0. Use of the predefined atomic values ensures proper usage.

type __atomic_load_n (type *ptr, int memorder)

[Built-in Function]
This built-in function implements an atomic load operation. It returns the contents
of *ptr.

The valid memory order variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, __
ATOMIC_ACQUIRE, and __ATOMIC_CONSUME.

void __atomic_load (type *ptr, type *ret, int memorder)

[Built-in Function]
This is the generic version of an atomic load. It returns the contents of *ptr in *ret.

void __atomic_store_n (type *ptr, type val, int memorder)

[Built-in Function]
This built-in function implements an atomic store operation. It writes val into *ptr.
The valid memory order variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, and
__ATOMIC_RELEASE.

void __atomic_store (type *ptr, type *val, int memorder)

[Built-in Function]
This is the generic version of an atomic store. It stores the value of *val into *ptr.

Chapter 6: Extensions to the C Language Family

type __atomic_exchange_n (type *ptr, type val, int

605

[Built-in Function]

memorder)
This built-in function implements an atomic exchange operation. It writes val into
*ptr, and returns the previous contents of *ptr.
The valid memory order variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, __
ATOMIC_ACQUIRE, __ATOMIC_RELEASE, and __ATOMIC_ACQ_REL.

void __atomic_exchange (type *ptr, type *val, type *ret, int

[Built-in Function]
memorder)
This is the generic version of an atomic exchange. It stores the contents of *val into
*ptr. The original value of *ptr is copied into *ret.

bool __atomic_compare_exchange_n (type *ptr, type
[Built-in Function]
*expected, type desired, bool weak, int success memorder, int
failure memorder)
This built-in function implements an atomic compare and exchange operation. This
compares the contents of *ptr with the contents of *expected. If equal, the operation
is a read-modify-write operation that writes desired into *ptr. If they are not equal,
the operation is a read and the current contents of *ptr are written into *expected.
weak is true for weak compare exchange, which may fail spuriously, and false for
the strong variation, which never fails spuriously. Many targets only offer the strong
variation and ignore the parameter. When in doubt, use the strong variation.
If desired is written into *ptr then true is returned and memory is affected according
to the memory order specified by success memorder. There are no restrictions on
what memory order can be used here.
Otherwise, false is returned and memory is affected according to failure memorder.
This memory order cannot be __ATOMIC_RELEASE nor __ATOMIC_ACQ_REL. It also
cannot be a stronger order than that specified by success memorder.

bool __atomic_compare_exchange (type *ptr, type
[Built-in Function]
*expected, type *desired, bool weak, int success memorder, int
failure memorder)
This built-in function implements the generic version of __atomic_compare_
exchange. The function is virtually identical to __atomic_compare_exchange_n,
except the desired value is also a pointer.

type
type
type
type
type
type

__atomic_add_fetch (type *ptr, type val, int memorder)
__atomic_sub_fetch (type *ptr, type val, int memorder)
__atomic_and_fetch (type *ptr, type val, int memorder)
__atomic_xor_fetch (type *ptr, type val, int memorder)
__atomic_or_fetch (type *ptr, type val, int memorder)
__atomic_nand_fetch (type *ptr, type val, int

[Built-in
[Built-in
[Built-in
[Built-in
[Built-in
[Built-in

Function]
Function]
Function]
Function]
Function]
Function]

memorder)
These built-in functions perform the operation suggested by the name, and return
the result of the operation. Operations on pointer arguments are performed as if the
operands were of the uintptr_t type. That is, they are not scaled by the size of the
type to which the pointer points.

606

Using the GNU Compiler Collection (GCC)

{ *ptr op= val; return *ptr; }

The object pointed to by the first argument must be of integer or pointer type. It
must not be a boolean type. All memory orders are valid.

type
type
type
type
type
type

__atomic_fetch_add (type *ptr, type val, int memorder)
__atomic_fetch_sub (type *ptr, type val, int memorder)
__atomic_fetch_and (type *ptr, type val, int memorder)
__atomic_fetch_xor (type *ptr, type val, int memorder)
__atomic_fetch_or (type *ptr, type val, int memorder)
__atomic_fetch_nand (type *ptr, type val, int

[Built-in
[Built-in
[Built-in
[Built-in
[Built-in
[Built-in

Function]
Function]
Function]
Function]
Function]
Function]

memorder)
These built-in functions perform the operation suggested by the name, and return
the value that had previously been in *ptr. Operations on pointer arguments are
performed as if the operands were of the uintptr_t type. That is, they are not
scaled by the size of the type to which the pointer points.
{ tmp = *ptr; *ptr op= val; return tmp; }

The same constraints on arguments apply as for the corresponding __atomic_op_
fetch built-in functions. All memory orders are valid.

bool __atomic_test_and_set (void *ptr, int memorder)

[Built-in Function]
This built-in function performs an atomic test-and-set operation on the byte at *ptr.
The byte is set to some implementation defined nonzero “set” value and the return
value is true if and only if the previous contents were “set”. It should be only used
for operands of type bool or char. For other types only part of the value may be set.
All memory orders are valid.

void __atomic_clear (bool *ptr, int memorder)

[Built-in Function]
This built-in function performs an atomic clear operation on *ptr. After the operation, *ptr contains 0. It should be only used for operands of type bool or char
and in conjunction with __atomic_test_and_set. For other types it may only clear
partially. If the type is not bool prefer using __atomic_store.
The valid memory order variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, and
__ATOMIC_RELEASE.

void __atomic_thread_fence (int memorder)

[Built-in Function]
This built-in function acts as a synchronization fence between threads based on the
specified memory order.
All memory orders are valid.

void __atomic_signal_fence (int memorder)

[Built-in Function]
This built-in function acts as a synchronization fence between a thread and signal
handlers based in the same thread.
All memory orders are valid.

bool __atomic_always_lock_free (size t size, void *ptr)

[Built-in Function]
This built-in function returns true if objects of size bytes always generate lock-free
atomic instructions for the target architecture. size must resolve to a compile-time
constant and the result also resolves to a compile-time constant.

Chapter 6: Extensions to the C Language Family

607

ptr is an optional pointer to the object that may be used to determine alignment. A
value of 0 indicates typical alignment should be used. The compiler may also ignore
this parameter.
if (__atomic_always_lock_free (sizeof (long long), 0))

bool __atomic_is_lock_free (size t size, void *ptr)

[Built-in Function]
This built-in function returns true if objects of size bytes always generate lock-free
atomic instructions for the target architecture. If the built-in function is not known
to be lock-free, a call is made to a runtime routine named __atomic_is_lock_free.
ptr is an optional pointer to the object that may be used to determine alignment. A
value of 0 indicates typical alignment should be used. The compiler may also ignore
this parameter.

6.54 Built-in Functions to Perform Arithmetic with
Overflow Checking
The following built-in functions allow performing simple arithmetic operations together with
checking whether the operations overflowed.

bool __builtin_add_overflow (type1 a, type2 b, type3

[Built-in Function]

*res)

bool __builtin_sadd_overflow (int a, int b, int *res)
bool __builtin_saddl_overflow (long int a, long int b, long

[Built-in Function]
[Built-in Function]

int *res)

bool __builtin_saddll_overflow (long long int a, long long

[Built-in Function]

int b, long long int *res)

bool __builtin_uadd_overflow (unsigned int a, unsigned int

[Built-in Function]

b, unsigned int *res)

bool __builtin_uaddl_overflow (unsigned long int a,

[Built-in Function]
unsigned long int b, unsigned long int *res)
bool __builtin_uaddll_overflow (unsigned long long int a,
[Built-in Function]
unsigned long long int b, unsigned long long int *res)
These built-in functions promote the first two operands into infinite precision signed
type and perform addition on those promoted operands. The result is then cast to
the type the third pointer argument points to and stored there. If the stored result is
equal to the infinite precision result, the built-in functions return false, otherwise they
return true. As the addition is performed in infinite signed precision, these built-in
functions have fully defined behavior for all argument values.
The first built-in function allows arbitrary integral types for operands and the result
type must be pointer to some integral type other than enumerated or boolean type,
the rest of the built-in functions have explicit integer types.
The compiler will attempt to use hardware instructions to implement these built-in
functions where possible, like conditional jump on overflow after addition, conditional
jump on carry etc.

bool __builtin_sub_overflow (type1 a, type2 b, type3

[Built-in Function]

*res)

bool __builtin_ssub_overflow (int a, int b, int *res)

[Built-in Function]

608

Using the GNU Compiler Collection (GCC)

bool __builtin_ssubl_overflow (long int a, long int b, long

[Built-in Function]

int *res)

bool __builtin_ssubll_overflow (long long int a, long long

[Built-in Function]

int b, long long int *res)

bool __builtin_usub_overflow (unsigned int a, unsigned int

[Built-in Function]

b, unsigned int *res)

bool __builtin_usubl_overflow (unsigned long int a,

[Built-in Function]
unsigned long int b, unsigned long int *res)
bool __builtin_usubll_overflow (unsigned long long int a,
[Built-in Function]
unsigned long long int b, unsigned long long int *res)
These built-in functions are similar to the add overflow checking built-in functions
above, except they perform subtraction, subtract the second argument from the first
one, instead of addition.

bool __builtin_mul_overflow (type1 a, type2 b, type3

[Built-in Function]

*res)

bool __builtin_smul_overflow (int a, int b, int *res)
bool __builtin_smull_overflow (long int a, long int b, long

[Built-in Function]
[Built-in Function]

int *res)

bool __builtin_smulll_overflow (long long int a, long long

[Built-in Function]

int b, long long int *res)

bool __builtin_umul_overflow (unsigned int a, unsigned int

[Built-in Function]

b, unsigned int *res)

bool __builtin_umull_overflow (unsigned long int a,

[Built-in Function]
unsigned long int b, unsigned long int *res)
bool __builtin_umulll_overflow (unsigned long long int a,
[Built-in Function]
unsigned long long int b, unsigned long long int *res)
These built-in functions are similar to the add overflow checking built-in functions
above, except they perform multiplication, instead of addition.
The following built-in functions allow checking if simple arithmetic operation would overflow.

bool __builtin_add_overflow_p (type1 a, type2 b, type3

[Built-in Function]

c)

bool __builtin_sub_overflow_p (type1 a, type2 b, type3

[Built-in Function]

c)

bool __builtin_mul_overflow_p (type1 a, type2 b, type3

[Built-in Function]
c)
These built-in functions are similar to __builtin_add_overflow, __builtin_sub_
overflow, or __builtin_mul_overflow, except that they don’t store the result of
the arithmetic operation anywhere and the last argument is not a pointer, but some
expression with integral type other than enumerated or boolean type.
The built-in functions promote the first two operands into infinite precision signed
type and perform addition on those promoted operands. The result is then cast to
the type of the third argument. If the cast result is equal to the infinite precision
result, the built-in functions return false, otherwise they return true. The value of the
third argument is ignored, just the side effects in the third argument are evaluated,

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and no integral argument promotions are performed on the last argument. If the
third argument is a bit-field, the type used for the result cast has the precision and
signedness of the given bit-field, rather than precision and signedness of the underlying
type.
For example, the following macro can be used to portably check, at compile-time,
whether or not adding two constant integers will overflow, and perform the addition
only when it is known to be safe and not to trigger a ‘-Woverflow’ warning.
#define INT_ADD_OVERFLOW_P(a, b) \
__builtin_add_overflow_p (a, b, (__typeof__ ((a) + (b))) 0)
enum {
A = INT_MAX, B = 3,
C = INT_ADD_OVERFLOW_P (A, B) ? 0 : A + B,
D = __builtin_add_overflow_p (1, SCHAR_MAX, (signed char) 0)
};

The compiler will attempt to use hardware instructions to implement these built-in
functions where possible, like conditional jump on overflow after addition, conditional
jump on carry etc.

6.55 x86-Specific Memory Model Extensions for
Transactional Memory
The x86 architecture supports additional memory ordering flags to mark critical sections
for hardware lock elision. These must be specified in addition to an existing memory order
to atomic intrinsics.
__ATOMIC_HLE_ACQUIRE
Start lock elision on a lock variable. Memory order must be __ATOMIC_ACQUIRE
or stronger.
__ATOMIC_HLE_RELEASE
End lock elision on a lock variable. Memory order must be __ATOMIC_RELEASE
or stronger.
When a lock acquire fails, it is required for good performance to abort the transaction
quickly. This can be done with a _mm_pause.
#include  // For _mm_pause
int lockvar;
/* Acquire lock with lock elision */
while (__atomic_exchange_n(&lockvar, 1, __ATOMIC_ACQUIRE|__ATOMIC_HLE_ACQUIRE))
_mm_pause(); /* Abort failed transaction */
...
/* Free lock with lock elision */
__atomic_store_n(&lockvar, 0, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE);

6.56 Object Size Checking Built-in Functions
GCC implements a limited buffer overflow protection mechanism that can prevent some
buffer overflow attacks by determining the sizes of objects into which data is about to be
written and preventing the writes when the size isn’t sufficient. The built-in functions described below yield the best results when used together and when optimization is enabled.

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For example, to detect object sizes across function boundaries or to follow pointer assignments through non-trivial control flow they rely on various optimization passes enabled
with ‘-O2’. However, to a limited extent, they can be used without optimization as well.

size_t __builtin_object_size (const void * ptr, int type)

[Built-in Function]
is a built-in construct that returns a constant number of bytes from ptr to the end of
the object ptr pointer points to (if known at compile time). __builtin_object_size
never evaluates its arguments for side effects. If there are any side effects in them,
it returns (size_t) -1 for type 0 or 1 and (size_t) 0 for type 2 or 3. If there are
multiple objects ptr can point to and all of them are known at compile time, the
returned number is the maximum of remaining byte counts in those objects if type
& 2 is 0 and minimum if nonzero. If it is not possible to determine which objects ptr
points to at compile time, __builtin_object_size should return (size_t) -1 for
type 0 or 1 and (size_t) 0 for type 2 or 3.
type is an integer constant from 0 to 3. If the least significant bit is clear, objects are
whole variables, if it is set, a closest surrounding subobject is considered the object a
pointer points to. The second bit determines if maximum or minimum of remaining
bytes is computed.
struct V { char buf1[10]; int b; char buf2[10]; } var;
char *p = &var.buf1[1], *q = &var.b;
/* Here the object p points to is var. */
assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
/* The subobject p points to is var.buf1. */
assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
/* The object q points to is var. */
assert (__builtin_object_size (q, 0)
== (char *) (&var + 1) - (char *) &var.b);
/* The subobject q points to is var.b. */
assert (__builtin_object_size (q, 1) == sizeof (var.b));

There are built-in functions added for many common string operation functions, e.g., for
memcpy __builtin___memcpy_chk built-in is provided. This built-in has an additional last
argument, which is the number of bytes remaining in the object the dest argument points
to or (size_t) -1 if the size is not known.
The built-in functions are optimized into the normal string functions like memcpy if the
last argument is (size_t) -1 or if it is known at compile time that the destination object
will not be overflowed. If the compiler can determine at compile time that the object will
always be overflowed, it issues a warning.
The intended use can be e.g.
#undef memcpy
#define bos0(dest) __builtin_object_size (dest, 0)
#define memcpy(dest, src, n) \
__builtin___memcpy_chk (dest, src, n, bos0 (dest))
char *volatile p;
char buf[10];
/* It is unknown what object p points to, so this is optimized
into plain memcpy - no checking is possible. */
memcpy (p, "abcde", n);
/* Destination is known and length too. It is known at compile

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time there will be no overflow. */
memcpy (&buf[5], "abcde", 5);
/* Destination is known, but the length is not known at compile time.
This will result in __memcpy_chk call that can check for overflow
at run time. */
memcpy (&buf[5], "abcde", n);
/* Destination is known and it is known at compile time there will
be overflow. There will be a warning and __memcpy_chk call that
will abort the program at run time. */
memcpy (&buf[6], "abcde", 5);

Such built-in functions are provided for memcpy, mempcpy, memmove, memset, strcpy,
stpcpy, strncpy, strcat and strncat.
There are also checking built-in functions for formatted output functions.
int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
const char *fmt, ...);
int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
va_list ap);
int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
const char *fmt, va_list ap);

The added flag argument is passed unchanged to __sprintf_chk etc. functions and can
contain implementation specific flags on what additional security measures the checking
function might take, such as handling %n differently.
The os argument is the object size s points to, like in the other built-in functions. There
is a small difference in the behavior though, if os is (size_t) -1, the built-in functions are
optimized into the non-checking functions only if flag is 0, otherwise the checking function
is called with os argument set to (size_t) -1.
In addition to this, there are checking built-in functions __builtin___printf_chk, _
_builtin___vprintf_chk, __builtin___fprintf_chk and __builtin___vfprintf_chk.
These have just one additional argument, flag, right before format string fmt. If the compiler
is able to optimize them to fputc etc. functions, it does, otherwise the checking function is
called and the flag argument passed to it.

6.57 Pointer Bounds Checker Built-in Functions
GCC provides a set of built-in functions to control Pointer Bounds Checker instrumentation.
Note that all Pointer Bounds Checker builtins can be used even if you compile with Pointer
Bounds Checker off (‘-fno-check-pointer-bounds’). The behavior may differ in such case
as documented below.

void * __builtin___bnd_set_ptr_bounds (const void *q,
size t size)

[Built-in Function]

This built-in function returns a new pointer with the value of q, and associate it with
the bounds [q, q+size-1]. With Pointer Bounds Checker off, the built-in function just
returns the first argument.
extern void *__wrap_malloc (size_t n)
{
void *p = (void *)__real_malloc (n);
if (!p) return __builtin___bnd_null_ptr_bounds (p);
return __builtin___bnd_set_ptr_bounds (p, n);
}

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Using the GNU Compiler Collection (GCC)

void * __builtin___bnd_narrow_ptr_bounds (const void
*p, const void *q, size t size)

[Built-in Function]

This built-in function returns a new pointer with the value of p and associates it with
the narrowed bounds formed by the intersection of bounds associated with q and the
bounds [p, p + size - 1]. With Pointer Bounds Checker off, the built-in function just
returns the first argument.
void init_objects (object *objs, size_t size)
{
size_t i;
/* Initialize objects one-by-one passing pointers with bounds of
an object, not the full array of objects. */
for (i = 0; i < size; i++)
init_object (__builtin___bnd_narrow_ptr_bounds (objs + i, objs,
sizeof(object)));
}

void * __builtin___bnd_copy_ptr_bounds (const void *q,
const void *r)

[Built-in Function]

This built-in function returns a new pointer with the value of q, and associates it with
the bounds already associated with pointer r. With Pointer Bounds Checker off, the
built-in function just returns the first argument.
/* Here is a way to get pointer to object’s field but
still with the full object’s bounds. */
int *field_ptr = __builtin___bnd_copy_ptr_bounds (&objptr->int_field,
objptr);

void * __builtin___bnd_init_ptr_bounds (const void *q)

[Built-in Function]
This built-in function returns a new pointer with the value of q, and associates it
with INIT (allowing full memory access) bounds. With Pointer Bounds Checker off,
the built-in function just returns the first argument.

void * __builtin___bnd_null_ptr_bounds (const void *q)

[Built-in Function]
This built-in function returns a new pointer with the value of q, and associates it
with NULL (allowing no memory access) bounds. With Pointer Bounds Checker off,
the built-in function just returns the first argument.

void __builtin___bnd_store_ptr_bounds (const void
**ptr_addr, const void *ptr_val)

[Built-in Function]

This built-in function stores the bounds associated with pointer ptr val and location
ptr addr into Bounds Table. This can be useful to propagate bounds from legacy
code without touching the associated pointer’s memory when pointers are copied as
integers. With Pointer Bounds Checker off, the built-in function call is ignored.

void __builtin___bnd_chk_ptr_lbounds (const void *q)

[Built-in Function]
This built-in function checks if the pointer q is within the lower bound of its associated
bounds. With Pointer Bounds Checker off, the built-in function call is ignored.
extern void *__wrap_memset (void *dst, int c, size_t len)
{
if (len > 0)
{
__builtin___bnd_chk_ptr_lbounds (dst);
__builtin___bnd_chk_ptr_ubounds ((char *)dst + len - 1);

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__real_memset (dst, c, len);
}
return dst;
}

void __builtin___bnd_chk_ptr_ubounds (const void *q)

[Built-in Function]
This built-in function checks if the pointer q is within the upper bound of its associated
bounds. With Pointer Bounds Checker off, the built-in function call is ignored.

void __builtin___bnd_chk_ptr_bounds (const void *q, size t
size)

[Built-in Function]

This built-in function checks if [q, q + size - 1] is within the lower and upper bounds
associated with q. With Pointer Bounds Checker off, the built-in function call is
ignored.
extern void *__wrap_memcpy (void *dst, const void *src, size_t n)
{
if (n > 0)
{
__bnd_chk_ptr_bounds (dst, n);
__bnd_chk_ptr_bounds (src, n);
__real_memcpy (dst, src, n);
}
return dst;
}

const void * __builtin___bnd_get_ptr_lbound (const
void *q)

[Built-in Function]

This built-in function returns the lower bound associated with the pointer q, as a
pointer value. This is useful for debugging using printf. With Pointer Bounds
Checker off, the built-in function returns 0.
void *lb = __builtin___bnd_get_ptr_lbound (q);
void *ub = __builtin___bnd_get_ptr_ubound (q);
printf ("q = %p lb(q) = %p ub(q) = %p", q, lb, ub);

const void * __builtin___bnd_get_ptr_ubound (const
void *q)

[Built-in Function]

This built-in function returns the upper bound (which is a pointer) associated with
the pointer q. With Pointer Bounds Checker off, the built-in function returns -1.

6.58 Other Built-in Functions Provided by GCC
GCC provides a large number of built-in functions other than the ones mentioned above.
Some of these are for internal use in the processing of exceptions or variable-length argument
lists and are not documented here because they may change from time to time; we do not
recommend general use of these functions.
The remaining functions are provided for optimization purposes.
With the exception of built-ins that have library equivalents such as the standard C
library functions discussed below, or that expand to library calls, GCC built-in functions
are always expanded inline and thus do not have corresponding entry points and their
address cannot be obtained. Attempting to use them in an expression other than a function
call results in a compile-time error.

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GCC includes built-in versions of many of the functions in the standard C library. These
functions come in two forms: one whose names start with the __builtin_ prefix, and the
other without. Both forms have the same type (including prototype), the same address
(when their address is taken), and the same meaning as the C library functions even if you
specify the ‘-fno-builtin’ option see Section 3.4 [C Dialect Options], page 35). Many of
these functions are only optimized in certain cases; if they are not optimized in a particular
case, a call to the library function is emitted.
Outside strict ISO C mode (‘-ansi’, ‘-std=c90’, ‘-std=c99’ or ‘-std=c11’), the
functions _exit, alloca, bcmp, bzero, dcgettext, dgettext, dremf, dreml, drem,
exp10f, exp10l, exp10, ffsll, ffsl, ffs, fprintf_unlocked, fputs_unlocked, gammaf,
gammal, gamma, gammaf_r, gammal_r, gamma_r, gettext, index, isascii, j0f, j0l,
j0, j1f, j1l, j1, jnf, jnl, jn, lgammaf_r, lgammal_r, lgamma_r, mempcpy, pow10f,
pow10l, pow10, printf_unlocked, rindex, scalbf, scalbl, scalb, signbit, signbitf,
signbitl, signbitd32, signbitd64, signbitd128, significandf, significandl,
significand, sincosf, sincosl, sincos, stpcpy, stpncpy, strcasecmp, strdup,
strfmon, strncasecmp, strndup, toascii, y0f, y0l, y0, y1f, y1l, y1, ynf, ynl and yn
may be handled as built-in functions. All these functions have corresponding versions
prefixed with __builtin_, which may be used even in strict C90 mode.
The ISO C99 functions _Exit, acoshf, acoshl, acosh, asinhf, asinhl, asinh,
atanhf, atanhl, atanh, cabsf, cabsl, cabs, cacosf, cacoshf, cacoshl, cacosh, cacosl,
cacos, cargf, cargl, carg, casinf, casinhf, casinhl, casinh, casinl, casin, catanf,
catanhf, catanhl, catanh, catanl, catan, cbrtf, cbrtl, cbrt, ccosf, ccoshf, ccoshl,
ccosh, ccosl, ccos, cexpf, cexpl, cexp, cimagf, cimagl, cimag, clogf, clogl, clog,
conjf, conjl, conj, copysignf, copysignl, copysign, cpowf, cpowl, cpow, cprojf,
cprojl, cproj, crealf, creall, creal, csinf, csinhf, csinhl, csinh, csinl, csin,
csqrtf, csqrtl, csqrt, ctanf, ctanhf, ctanhl, ctanh, ctanl, ctan, erfcf, erfcl,
erfc, erff, erfl, erf, exp2f, exp2l, exp2, expm1f, expm1l, expm1, fdimf, fdiml, fdim,
fmaf, fmal, fmaxf, fmaxl, fmax, fma, fminf, fminl, fmin, hypotf, hypotl, hypot,
ilogbf, ilogbl, ilogb, imaxabs, isblank, iswblank, lgammaf, lgammal, lgamma, llabs,
llrintf, llrintl, llrint, llroundf, llroundl, llround, log1pf, log1pl, log1p,
log2f, log2l, log2, logbf, logbl, logb, lrintf, lrintl, lrint, lroundf, lroundl,
lround, nearbyintf, nearbyintl, nearbyint, nextafterf, nextafterl, nextafter,
nexttowardf, nexttowardl, nexttoward, remainderf, remainderl, remainder, remquof,
remquol, remquo, rintf, rintl, rint, roundf, roundl, round, scalblnf, scalblnl,
scalbln, scalbnf, scalbnl, scalbn, snprintf, tgammaf, tgammal, tgamma, truncf,
truncl, trunc, vfscanf, vscanf, vsnprintf and vsscanf are handled as built-in
functions except in strict ISO C90 mode (‘-ansi’ or ‘-std=c90’).
There are also built-in versions of the ISO C99 functions acosf, acosl, asinf, asinl,
atan2f, atan2l, atanf, atanl, ceilf, ceill, cosf, coshf, coshl, cosl, expf, expl,
fabsf, fabsl, floorf, floorl, fmodf, fmodl, frexpf, frexpl, ldexpf, ldexpl, log10f,
log10l, logf, logl, modfl, modf, powf, powl, sinf, sinhf, sinhl, sinl, sqrtf, sqrtl,
tanf, tanhf, tanhl and tanl that are recognized in any mode since ISO C90 reserves these
names for the purpose to which ISO C99 puts them. All these functions have corresponding
versions prefixed with __builtin_.
There are also built-in functions __builtin_fabsfn, __builtin_fabsfnx, __builtin_
copysignfn and __builtin_copysignfnx, corresponding to the TS 18661-3 functions

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fabsfn, fabsfnx, copysignfn and copysignfnx, for supported types _Floatn and
_Floatnx.
There are also GNU extension functions clog10, clog10f and clog10l which names
are reserved by ISO C99 for future use. All these functions have versions prefixed with
__builtin_.
The ISO C94 functions iswalnum, iswalpha, iswcntrl, iswdigit, iswgraph, iswlower,
iswprint, iswpunct, iswspace, iswupper, iswxdigit, towlower and towupper are handled as built-in functions except in strict ISO C90 mode (‘-ansi’ or ‘-std=c90’).
The ISO C90 functions abort, abs, acos, asin, atan2, atan, calloc, ceil, cosh,
cos, exit, exp, fabs, floor, fmod, fprintf, fputs, frexp, fscanf, isalnum, isalpha,
iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit,
tolower, toupper, labs, ldexp, log10, log, malloc, memchr, memcmp, memcpy, memset,
modf, pow, printf, putchar, puts, scanf, sinh, sin, snprintf, sprintf, sqrt, sscanf,
strcat, strchr, strcmp, strcpy, strcspn, strlen, strncat, strncmp, strncpy, strpbrk,
strrchr, strspn, strstr, tanh, tan, vfprintf, vprintf and vsprintf are all recognized
as built-in functions unless ‘-fno-builtin’ is specified (or ‘-fno-builtin-function’ is
specified for an individual function). All of these functions have corresponding versions
prefixed with __builtin_.
GCC provides built-in versions of the ISO C99 floating-point comparison macros that
avoid raising exceptions for unordered operands. They have the same names as the standard macros ( isgreater, isgreaterequal, isless, islessequal, islessgreater, and
isunordered) , with __builtin_ prefixed. We intend for a library implementor to be able
to simply #define each standard macro to its built-in equivalent. In the same fashion,
GCC provides fpclassify, isfinite, isinf_sign, isnormal and signbit built-ins used
with __builtin_ prefixed. The isinf and isnan built-in functions appear both with and
without the __builtin_ prefix.

void *__builtin_alloca (size t size)

[Built-in Function]
The __builtin_alloca function must be called at block scope. The function allocates
an object size bytes large on the stack of the calling function. The object is aligned on
the default stack alignment boundary for the target determined by the __BIGGEST_
ALIGNMENT__ macro. The __builtin_alloca function returns a pointer to the first
byte of the allocated object. The lifetime of the allocated object ends just before
the calling function returns to its caller. This is so even when __builtin_alloca is
called within a nested block.
For example, the following function allocates eight objects of n bytes each on the
stack, storing a pointer to each in consecutive elements of the array a. It then passes
the array to function g which can safely use the storage pointed to by each of the
array elements.
void f (unsigned n)
{
void *a [8];
for (int i = 0; i != 8; ++i)
a [i] = __builtin_alloca (n);
g (a, n);
}

// safe

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Since the __builtin_alloca function doesn’t validate its argument it is the responsibility of its caller to make sure the argument doesn’t cause it to exceed the stack
size limit. The __builtin_alloca function is provided to make it possible to allocate on the stack arrays of bytes with an upper bound that may be computed at run
time. Since C99 Variable Length Arrays offer similar functionality under a portable,
more convenient, and safer interface they are recommended instead, in both C99 and
C++ programs where GCC provides them as an extension. See Section 6.19 [Variable
Length], page 457, for details.

void *__builtin_alloca_with_align (size t size, size t

[Built-in Function]
alignment)
The __builtin_alloca_with_align function must be called at block scope. The
function allocates an object size bytes large on the stack of the calling function.
The allocated object is aligned on the boundary specified by the argument alignment
whose unit is given in bits (not bytes). The size argument must be positive and
not exceed the stack size limit. The alignment argument must be a constant integer
expression that evaluates to a power of 2 greater than or equal to CHAR_BIT and less
than some unspecified maximum. Invocations with other values are rejected with an
error indicating the valid bounds. The function returns a pointer to the first byte of
the allocated object. The lifetime of the allocated object ends at the end of the block
in which the function was called. The allocated storage is released no later than just
before the calling function returns to its caller, but may be released at the end of the
block in which the function was called.
For example, in the following function the call to g is unsafe because when overalign
is non-zero, the space allocated by __builtin_alloca_with_align may have been
released at the end of the if statement in which it was called.
void f (unsigned n, bool overalign)
{
void *p;
if (overalign)
p = __builtin_alloca_with_align (n, 64 /* bits */);
else
p = __builtin_alloc (n);
g (p, n);

// unsafe

}

Since the __builtin_alloca_with_align function doesn’t validate its size argument
it is the responsibility of its caller to make sure the argument doesn’t cause it to
exceed the stack size limit. The __builtin_alloca_with_align function is provided
to make it possible to allocate on the stack overaligned arrays of bytes with an upper
bound that may be computed at run time. Since C99 Variable Length Arrays offer
the same functionality under a portable, more convenient, and safer interface they
are recommended instead, in both C99 and C++ programs where GCC provides them
as an extension. See Section 6.19 [Variable Length], page 457, for details.

void *__builtin_alloca_with_align_and_max (size t size,

[Built-in Function]
size t alignment, size t max size)
Similar to __builtin_alloca_with_align but takes an extra argument specifying
an upper bound for size in case its value cannot be computed at compile time, for use

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by ‘-fstack-usage’, ‘-Wstack-usage’ and ‘-Walloca-larger-than’. max size must
be a constant integer expression, it has no effect on code generation and no attempt
is made to check its compatibility with size.

int __builtin_types_compatible_p (type1, type2)

[Built-in Function]
You can use the built-in function __builtin_types_compatible_p to determine
whether two types are the same.

This built-in function returns 1 if the unqualified versions of the types type1 and
type2 (which are types, not expressions) are compatible, 0 otherwise. The result of
this built-in function can be used in integer constant expressions.
This built-in function ignores top level qualifiers (e.g., const, volatile). For example, int is equivalent to const int.
The type int[] and int[5] are compatible. On the other hand, int and char * are
not compatible, even if the size of their types, on the particular architecture are the
same. Also, the amount of pointer indirection is taken into account when determining
similarity. Consequently, short * is not similar to short **. Furthermore, two types
that are typedefed are considered compatible if their underlying types are compatible.
An enum type is not considered to be compatible with another enum type even if both
are compatible with the same integer type; this is what the C standard specifies. For
example, enum {foo, bar} is not similar to enum {hot, dog}.
You typically use this function in code whose execution varies depending on the
arguments’ types. For example:
#define foo(x)
\
({
\
typeof (x) tmp = (x);
\
if (__builtin_types_compatible_p (typeof (x), long double)) \
tmp = foo_long_double (tmp);
\
else if (__builtin_types_compatible_p (typeof (x), double)) \
tmp = foo_double (tmp);
\
else if (__builtin_types_compatible_p (typeof (x), float)) \
tmp = foo_float (tmp);
\
else
\
abort ();
\
tmp;
\
})

Note: This construct is only available for C.

type __builtin_call_with_static_chain (call_exp,
pointer_exp)

[Built-in Function]

The call exp expression must be a function call, and the pointer exp expression must
be a pointer. The pointer exp is passed to the function call in the target’s static
chain location. The result of builtin is the result of the function call.
Note: This builtin is only available for C. This builtin can be used to call Go closures
from C.

type __builtin_choose_expr (const_exp, exp1, exp2)

[Built-in Function]
You can use the built-in function __builtin_choose_expr to evaluate code depending on the value of a constant expression. This built-in function returns exp1 if

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const exp, which is an integer constant expression, is nonzero. Otherwise it returns
exp2.
This built-in function is analogous to the ‘? :’ operator in C, except that the expression returned has its type unaltered by promotion rules. Also, the built-in function
does not evaluate the expression that is not chosen. For example, if const exp evaluates to true, exp2 is not evaluated even if it has side effects.
This built-in function can return an lvalue if the chosen argument is an lvalue.
If exp1 is returned, the return type is the same as exp1’s type. Similarly, if exp2 is
returned, its return type is the same as exp2.
Example:
#define foo(x)
__builtin_choose_expr (
__builtin_types_compatible_p (typeof (x), double),
foo_double (x),
__builtin_choose_expr (
__builtin_types_compatible_p (typeof (x), float),
foo_float (x),
/* The void expression results in a compile-time error \
when assigning the result to something. */
\
(void)0))

\
\
\
\
\
\
\

Note: This construct is only available for C. Furthermore, the unused expression
(exp1 or exp2 depending on the value of const exp) may still generate syntax errors.
This may change in future revisions.

type __builtin_tgmath (functions, arguments)

[Built-in Function]
The built-in function __builtin_tgmath, available only for C and Objective-C, calls
a function determined according to the rules of  macros. It is intended
to be used in implementations of that header, so that expansions of macros from
that header only expand each of their arguments once, to avoid problems when calls
to such macros are nested inside the arguments of other calls to such macros; in
addition, it results in better diagnostics for invalid calls to  macros than
implementations using other GNU C language features. For example, the pow typegeneric macro might be defined as:
#define pow(a, b) __builtin_tgmath (powf, pow, powl, \
cpowf, cpow, cpowl, a, b)

The arguments to __builtin_tgmath are at least two pointers to functions, followed
by the arguments to the type-generic macro (which will be passed as arguments to
the selected function). All the pointers to functions must be pointers to prototyped
functions, none of which may have variable arguments, and all of which must have the
same number of parameters; the number of parameters of the first function determines
how many arguments to __builtin_tgmath are interpreted as function pointers, and
how many as the arguments to the called function.
The types of the specified functions must all be different, but related to each other
in the same way as a set of functions that may be selected between by a macro
in . This means that the functions are parameterized by a floating-point
type t, different for each such function. The function return types may all be the same
type, or they may be t for each function, or they may be the real type corresponding to
t for each function (if some of the types t are complex). Likewise, for each parameter

Chapter 6: Extensions to the C Language Family

619

position, the type of the parameter in that position may always be the same type, or
may be t for each function (this case must apply for at least one parameter position),
or may be the real type corresponding to t for each function.
The standard rules for  macros are used to find a common type u from
the types of the arguments for parameters whose types vary between the functions;
complex integer types (a GNU extension) are treated like _Complex double for this
purpose (or _Complex _Float64 if all the function return types are the same _Floatn
or _Floatnx type). If the function return types vary, or are all the same integer type,
the function called is the one for which t is u, and it is an error if there is no such
function. If the function return types are all the same floating-point type, the typegeneric macro is taken to be one of those from TS 18661 that rounds the result to a
narrower type; if there is a function for which t is u, it is called, and otherwise the
first function, if any, for which t has at least the range and precision of u is called,
and it is an error if there is no such function.

type __builtin_complex (real, imag)

[Built-in Function]
The built-in function __builtin_complex is provided for use in implementing the
ISO C11 macros CMPLXF, CMPLX and CMPLXL. real and imag must have the same type,
a real binary floating-point type, and the result has the corresponding complex type
with real and imaginary parts real and imag. Unlike ‘real + I * imag’, this works
even when infinities, NaNs and negative zeros are involved.

int __builtin_constant_p (exp)

[Built-in Function]
You can use the built-in function __builtin_constant_p to determine if a value is
known to be constant at compile time and hence that GCC can perform constantfolding on expressions involving that value. The argument of the function is the value
to test. The function returns the integer 1 if the argument is known to be a compiletime constant and 0 if it is not known to be a compile-time constant. A return of 0
does not indicate that the value is not a constant, but merely that GCC cannot prove
it is a constant with the specified value of the ‘-O’ option.
You typically use this function in an embedded application where memory is a critical
resource. If you have some complex calculation, you may want it to be folded if it
involves constants, but need to call a function if it does not. For example:
#define Scale_Value(X)
\
(__builtin_constant_p (X) \
? ((X) * SCALE + OFFSET) : Scale (X))

You may use this built-in function in either a macro or an inline function. However, if
you use it in an inlined function and pass an argument of the function as the argument
to the built-in, GCC never returns 1 when you call the inline function with a string
constant or compound literal (see Section 6.26 [Compound Literals], page 460) and
does not return 1 when you pass a constant numeric value to the inline function unless
you specify the ‘-O’ option.
You may also use __builtin_constant_p in initializers for static data. For instance,
you can write
static const int table[] = {
__builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
/* . . . */
};

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This is an acceptable initializer even if EXPRESSION is not a constant expression,
including the case where __builtin_constant_p returns 1 because EXPRESSION
can be folded to a constant but EXPRESSION contains operands that are not otherwise permitted in a static initializer (for example, 0 && foo ()). GCC must be more
conservative about evaluating the built-in in this case, because it has no opportunity
to perform optimization.

long __builtin_expect (long exp, long c)

[Built-in Function]
You may use __builtin_expect to provide the compiler with branch prediction
information. In general, you should prefer to use actual profile feedback for this
(‘-fprofile-arcs’), as programmers are notoriously bad at predicting how their
programs actually perform. However, there are applications in which this data is
hard to collect.
The return value is the value of exp, which should be an integral expression. The
semantics of the built-in are that it is expected that exp == c. For example:
if (__builtin_expect (x, 0))
foo ();

indicates that we do not expect to call foo, since we expect x to be zero. Since you
are limited to integral expressions for exp, you should use constructions such as
if (__builtin_expect (ptr != NULL, 1))
foo (*ptr);

when testing pointer or floating-point values.

void __builtin_trap (void)

[Built-in Function]
This function causes the program to exit abnormally. GCC implements this function
by using a target-dependent mechanism (such as intentionally executing an illegal
instruction) or by calling abort. The mechanism used may vary from release to
release so you should not rely on any particular implementation.

void __builtin_unreachable (void)

[Built-in Function]
If control flow reaches the point of the __builtin_unreachable, the program is undefined. It is useful in situations where the compiler cannot deduce the unreachability
of the code.
One such case is immediately following an asm statement that either never terminates,
or one that transfers control elsewhere and never returns. In this example, without
the __builtin_unreachable, GCC issues a warning that control reaches the end of
a non-void function. It also generates code to return after the asm.
int f (int c, int v)
{
if (c)
{
return v;
}
else
{
asm("jmp error_handler");
__builtin_unreachable ();
}
}

Chapter 6: Extensions to the C Language Family

621

Because the asm statement unconditionally transfers control out of the function, control never reaches the end of the function body. The __builtin_unreachable is in
fact unreachable and communicates this fact to the compiler.
Another use for __builtin_unreachable is following a call a function that never
returns but that is not declared __attribute__((noreturn)), as in this example:
void function_that_never_returns (void);
int g (int c)
{
if (c)
{
return 1;
}
else
{
function_that_never_returns ();
__builtin_unreachable ();
}
}

void * __builtin_assume_aligned (const void *exp, size t
align, ...)

[Built-in Function]

This function returns its first argument, and allows the compiler to assume that the
returned pointer is at least align bytes aligned. This built-in can have either two or
three arguments, if it has three, the third argument should have integer type, and if
it is nonzero means misalignment offset. For example:
void *x = __builtin_assume_aligned (arg, 16);

means that the compiler can assume x, set to arg, is at least 16-byte aligned, while:
void *x = __builtin_assume_aligned (arg, 32, 8);

means that the compiler can assume for x, set to arg, that (char *) x - 8 is 32-byte
aligned.

int __builtin_LINE ()

[Built-in Function]
This function is the equivalent of the preprocessor __LINE__ macro and returns a
constant integer expression that evaluates to the line number of the invocation of the
built-in. When used as a C++ default argument for a function F, it returns the line
number of the call to F.

const char * __builtin_FUNCTION ()

[Built-in Function]
This function is the equivalent of the __FUNCTION__ symbol and returns an address
constant pointing to the name of the function from which the built-in was invoked,
or the empty string if the invocation is not at function scope. When used as a C++
default argument for a function F, it returns the name of F’s caller or the empty
string if the call was not made at function scope.

const char * __builtin_FILE ()

[Built-in Function]
This function is the equivalent of the preprocessor __FILE__ macro and returns an
address constant pointing to the file name containing the invocation of the built-in,
or the empty string if the invocation is not at function scope. When used as a C++

622

Using the GNU Compiler Collection (GCC)

default argument for a function F, it returns the file name of the call to F or the
empty string if the call was not made at function scope.
For example, in the following, each call to function foo will print a line similar to
"file.c:123: foo: message" with the name of the file and the line number of the
printf call, the name of the function foo, followed by the word message.
const char*
function (const char *func = __builtin_FUNCTION ())
{
return func;
}
void foo (void)
{
printf ("%s:%i: %s: message\n", file (), line (), function ());
}

void __builtin___clear_cache (char *begin, char *end)

[Built-in Function]
This function is used to flush the processor’s instruction cache for the region of memory between begin inclusive and end exclusive. Some targets require that the instruction cache be flushed, after modifying memory containing code, in order to obtain
deterministic behavior.
If the target does not require instruction cache flushes, __builtin___clear_cache
has no effect. Otherwise either instructions are emitted in-line to clear the instruction
cache or a call to the __clear_cache function in libgcc is made.

void __builtin_prefetch (const void *addr, ...)

[Built-in Function]
This function is used to minimize cache-miss latency by moving data into a cache
before it is accessed. You can insert calls to __builtin_prefetch into code for
which you know addresses of data in memory that is likely to be accessed soon. If
the target supports them, data prefetch instructions are generated. If the prefetch is
done early enough before the access then the data will be in the cache by the time it
is accessed.
The value of addr is the address of the memory to prefetch. There are two optional
arguments, rw and locality. The value of rw is a compile-time constant one or zero;
one means that the prefetch is preparing for a write to the memory address and zero,
the default, means that the prefetch is preparing for a read. The value locality must
be a compile-time constant integer between zero and three. A value of zero means
that the data has no temporal locality, so it need not be left in the cache after the
access. A value of three means that the data has a high degree of temporal locality and
should be left in all levels of cache possible. Values of one and two mean, respectively,
a low or moderate degree of temporal locality. The default is three.
for (i = 0; i < n; i++)
{
a[i] = a[i] + b[i];
__builtin_prefetch (&a[i+j], 1, 1);
__builtin_prefetch (&b[i+j], 0, 1);
/* . . . */
}

Chapter 6: Extensions to the C Language Family

623

Data prefetch does not generate faults if addr is invalid, but the address expression
itself must be valid. For example, a prefetch of p->next does not fault if p->next is
not a valid address, but evaluation faults if p is not a valid address.
If the target does not support data prefetch, the address expression is evaluated if it
includes side effects but no other code is generated and GCC does not issue a warning.

double __builtin_huge_val (void)

[Built-in Function]
Returns a positive infinity, if supported by the floating-point format, else DBL_MAX.
This function is suitable for implementing the ISO C macro HUGE_VAL.

float __builtin_huge_valf (void)

[Built-in Function]

Similar to __builtin_huge_val, except the return type is float.

long double __builtin_huge_vall (void)

[Built-in Function]
Similar to __builtin_huge_val, except the return type is long double.

_Floatn __builtin_huge_valfn (void)

[Built-in Function]
Similar to __builtin_huge_val, except the return type is _Floatn.

_Floatnx __builtin_huge_valfnx (void)

[Built-in Function]
Similar to __builtin_huge_val, except the return type is _Floatnx.

int __builtin_fpclassify (int, int, int, int, int, ...)

[Built-in Function]
This built-in implements the C99 fpclassify functionality. The first five int arguments
should be the target library’s notion of the possible FP classes and are used for return
values. They must be constant values and they must appear in this order: FP_NAN,
FP_INFINITE, FP_NORMAL, FP_SUBNORMAL and FP_ZERO. The ellipsis is for exactly one
floating-point value to classify. GCC treats the last argument as type-generic, which
means it does not do default promotion from float to double.

double __builtin_inf (void)

[Built-in Function]
Similar to __builtin_huge_val, except a warning is generated if the target floatingpoint format does not support infinities.

_Decimal32 __builtin_infd32 (void)

[Built-in Function]

Similar to __builtin_inf, except the return type is _Decimal32.

_Decimal64 __builtin_infd64 (void)

[Built-in Function]

Similar to __builtin_inf, except the return type is _Decimal64.

_Decimal128 __builtin_infd128 (void)

[Built-in Function]
Similar to __builtin_inf, except the return type is _Decimal128.

float __builtin_inff (void)

[Built-in Function]
Similar to __builtin_inf, except the return type is float. This function is suitable
for implementing the ISO C99 macro INFINITY.

long double __builtin_infl (void)

[Built-in Function]
Similar to __builtin_inf, except the return type is long double.

_Floatn __builtin_inffn (void)
Similar to __builtin_inf, except the return type is _Floatn.

[Built-in Function]

624

Using the GNU Compiler Collection (GCC)

_Floatn __builtin_inffnx (void)

[Built-in Function]

Similar to __builtin_inf, except the return type is _Floatnx.

int __builtin_isinf_sign (...)

[Built-in Function]
Similar to isinf, except the return value is -1 for an argument of -Inf and 1 for
an argument of +Inf. Note while the parameter list is an ellipsis, this function only
accepts exactly one floating-point argument. GCC treats this parameter as typegeneric, which means it does not do default promotion from float to double.

double __builtin_nan (const char *str)

[Built-in Function]
This is an implementation of the ISO C99 function nan.
Since ISO C99 defines this function in terms of strtod, which we do not implement,
a description of the parsing is in order. The string is parsed as by strtol; that is, the
base is recognized by leading ‘0’ or ‘0x’ prefixes. The number parsed is placed in the
significand such that the least significant bit of the number is at the least significant
bit of the significand. The number is truncated to fit the significand field provided.
The significand is forced to be a quiet NaN.
This function, if given a string literal all of which would have been consumed by
strtol, is evaluated early enough that it is considered a compile-time constant.

_Decimal32 __builtin_nand32 (const char *str)

[Built-in Function]

Similar to __builtin_nan, except the return type is _Decimal32.

_Decimal64 __builtin_nand64 (const char *str)

[Built-in Function]

Similar to __builtin_nan, except the return type is _Decimal64.

_Decimal128 __builtin_nand128 (const char *str)

[Built-in Function]
Similar to __builtin_nan, except the return type is _Decimal128.

float __builtin_nanf (const char *str)

[Built-in Function]

Similar to __builtin_nan, except the return type is float.

long double __builtin_nanl (const char *str)

[Built-in Function]
Similar to __builtin_nan, except the return type is long double.

_Floatn __builtin_nanfn (const char *str)

[Built-in Function]

Similar to __builtin_nan, except the return type is _Floatn.

_Floatnx __builtin_nanfnx (const char *str)

[Built-in Function]

Similar to __builtin_nan, except the return type is _Floatnx.

double __builtin_nans (const char *str)

[Built-in Function]
Similar to __builtin_nan, except the significand is forced to be a signaling NaN.
The nans function is proposed by WG14 N965.

float __builtin_nansf (const char *str)

[Built-in Function]

Similar to __builtin_nans, except the return type is float.

long double __builtin_nansl (const char *str)

[Built-in Function]
Similar to __builtin_nans, except the return type is long double.

Chapter 6: Extensions to the C Language Family

625

_Floatn __builtin_nansfn (const char *str)

[Built-in Function]

Similar to __builtin_nans, except the return type is _Floatn.

_Floatnx __builtin_nansfnx (const char *str)

[Built-in Function]

Similar to __builtin_nans, except the return type is _Floatnx.

int __builtin_ffs (int x)

[Built-in Function]
Returns one plus the index of the least significant 1-bit of x, or if x is zero, returns
zero.

int __builtin_clz (unsigned int x)

[Built-in Function]
Returns the number of leading 0-bits in x, starting at the most significant bit position.
If x is 0, the result is undefined.

int __builtin_ctz (unsigned int x)

[Built-in Function]
Returns the number of trailing 0-bits in x, starting at the least significant bit position.
If x is 0, the result is undefined.

int __builtin_clrsb (int x)

[Built-in Function]
Returns the number of leading redundant sign bits in x, i.e. the number of bits
following the most significant bit that are identical to it. There are no special cases
for 0 or other values.

int __builtin_popcount (unsigned int x)

[Built-in Function]

Returns the number of 1-bits in x.

int __builtin_parity (unsigned int x)

[Built-in Function]

Returns the parity of x, i.e. the number of 1-bits in x modulo 2.

int __builtin_ffsl (long)

[Built-in Function]

Similar to __builtin_ffs, except the argument type is long.

int __builtin_clzl (unsigned long)

[Built-in Function]
Similar to __builtin_clz, except the argument type is unsigned long.

int __builtin_ctzl (unsigned long)

[Built-in Function]
Similar to __builtin_ctz, except the argument type is unsigned long.

int __builtin_clrsbl (long)

[Built-in Function]

Similar to __builtin_clrsb, except the argument type is long.

int __builtin_popcountl (unsigned long)

[Built-in Function]
Similar to __builtin_popcount, except the argument type is unsigned long.

int __builtin_parityl (unsigned long)

[Built-in Function]
Similar to __builtin_parity, except the argument type is unsigned long.

int __builtin_ffsll (long long)

[Built-in Function]
Similar to __builtin_ffs, except the argument type is long long.

int __builtin_clzll (unsigned long long)

[Built-in Function]
Similar to __builtin_clz, except the argument type is unsigned long long.

626

Using the GNU Compiler Collection (GCC)

int __builtin_ctzll (unsigned long long)

[Built-in Function]
Similar to __builtin_ctz, except the argument type is unsigned long long.

int __builtin_clrsbll (long long)

[Built-in Function]
Similar to __builtin_clrsb, except the argument type is long long.

int __builtin_popcountll (unsigned long long)

[Built-in Function]
Similar to __builtin_popcount, except the argument type is unsigned long long.

int __builtin_parityll (unsigned long long)

[Built-in Function]
Similar to __builtin_parity, except the argument type is unsigned long long.

double __builtin_powi (double, int)

[Built-in Function]
Returns the first argument raised to the power of the second. Unlike the pow function
no guarantees about precision and rounding are made.

float __builtin_powif (float, int)

[Built-in Function]
Similar to __builtin_powi, except the argument and return types are float.

long double __builtin_powil (long double, int)

[Built-in Function]
Similar to __builtin_powi, except the argument and return types are long double.

uint16_t __builtin_bswap16 (uint16 t x)

[Built-in Function]
Returns x with the order of the bytes reversed; for example, 0xaabb becomes 0xbbaa.
Byte here always means exactly 8 bits.

uint32_t __builtin_bswap32 (uint32 t x)

[Built-in Function]
Similar to __builtin_bswap16, except the argument and return types are 32 bit.

uint64_t __builtin_bswap64 (uint64 t x)

[Built-in Function]
Similar to __builtin_bswap32, except the argument and return types are 64 bit.

Pmode __builtin_extend_pointer (void * x)

[Built-in Function]
On targets where the user visible pointer size is smaller than the size of an actual
hardware address this function returns the extended user pointer. Targets where this
is true included ILP32 mode on x86 64 or Aarch64. This function is mainly useful
when writing inline assembly code.

6.59 Built-in Functions Specific to Particular Target
Machines
On some target machines, GCC supports many built-in functions specific to those machines.
Generally these generate calls to specific machine instructions, but allow the compiler to
schedule those calls.

6.59.1 AArch64 Built-in Functions
These built-in functions are available for the AArch64 family of processors.
unsigned int __builtin_aarch64_get_fpcr ()
void __builtin_aarch64_set_fpcr (unsigned int)
unsigned int __builtin_aarch64_get_fpsr ()
void __builtin_aarch64_set_fpsr (unsigned int)

Chapter 6: Extensions to the C Language Family

627

6.59.2 Alpha Built-in Functions
These built-in functions are available for the Alpha family of processors, depending on the
command-line switches used.
The following built-in functions are always available. They all generate the machine
instruction that is part of the name.
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long
long

__builtin_alpha_implver (void)
__builtin_alpha_rpcc (void)
__builtin_alpha_amask (long)
__builtin_alpha_cmpbge (long, long)
__builtin_alpha_extbl (long, long)
__builtin_alpha_extwl (long, long)
__builtin_alpha_extll (long, long)
__builtin_alpha_extql (long, long)
__builtin_alpha_extwh (long, long)
__builtin_alpha_extlh (long, long)
__builtin_alpha_extqh (long, long)
__builtin_alpha_insbl (long, long)
__builtin_alpha_inswl (long, long)
__builtin_alpha_insll (long, long)
__builtin_alpha_insql (long, long)
__builtin_alpha_inswh (long, long)
__builtin_alpha_inslh (long, long)
__builtin_alpha_insqh (long, long)
__builtin_alpha_mskbl (long, long)
__builtin_alpha_mskwl (long, long)
__builtin_alpha_mskll (long, long)
__builtin_alpha_mskql (long, long)
__builtin_alpha_mskwh (long, long)
__builtin_alpha_msklh (long, long)
__builtin_alpha_mskqh (long, long)
__builtin_alpha_umulh (long, long)
__builtin_alpha_zap (long, long)
__builtin_alpha_zapnot (long, long)

The following built-in functions are always with ‘-mmax’ or ‘-mcpu=cpu’ where cpu is
pca56 or later. They all generate the machine instruction that is part of the name.
long
long
long
long
long
long
long
long
long
long
long
long
long

__builtin_alpha_pklb (long)
__builtin_alpha_pkwb (long)
__builtin_alpha_unpkbl (long)
__builtin_alpha_unpkbw (long)
__builtin_alpha_minub8 (long, long)
__builtin_alpha_minsb8 (long, long)
__builtin_alpha_minuw4 (long, long)
__builtin_alpha_minsw4 (long, long)
__builtin_alpha_maxub8 (long, long)
__builtin_alpha_maxsb8 (long, long)
__builtin_alpha_maxuw4 (long, long)
__builtin_alpha_maxsw4 (long, long)
__builtin_alpha_perr (long, long)

The following built-in functions are always with ‘-mcix’ or ‘-mcpu=cpu’ where cpu is ev67
or later. They all generate the machine instruction that is part of the name.
long __builtin_alpha_cttz (long)
long __builtin_alpha_ctlz (long)
long __builtin_alpha_ctpop (long)

628

Using the GNU Compiler Collection (GCC)

The following built-in functions are available on systems that use the OSF/1 PALcode. Normally they invoke the rduniq and wruniq PAL calls, but when invoked with
‘-mtls-kernel’, they invoke rdval and wrval.
void *__builtin_thread_pointer (void)
void __builtin_set_thread_pointer (void *)

6.59.3 Altera Nios II Built-in Functions
These built-in functions are available for the Altera Nios II family of processors.
The following built-in functions are always available. They all generate the machine
instruction that is part of the name.
int __builtin_ldbio (volatile const void *)
int __builtin_ldbuio (volatile const void *)
int __builtin_ldhio (volatile const void *)
int __builtin_ldhuio (volatile const void *)
int __builtin_ldwio (volatile const void *)
void __builtin_stbio (volatile void *, int)
void __builtin_sthio (volatile void *, int)
void __builtin_stwio (volatile void *, int)
void __builtin_sync (void)
int __builtin_rdctl (int)
int __builtin_rdprs (int, int)
void __builtin_wrctl (int, int)
void __builtin_flushd (volatile void *)
void __builtin_flushda (volatile void *)
int __builtin_wrpie (int);
void __builtin_eni (int);
int __builtin_ldex (volatile const void *)
int __builtin_stex (volatile void *, int)
int __builtin_ldsex (volatile const void *)
int __builtin_stsex (volatile void *, int)
The following built-in functions are always available. They all generate a Nios II Custom
Instruction. The name of the function represents the types that the function takes and
returns. The letter before the n is the return type or void if absent. The n represents the
first parameter to all the custom instructions, the custom instruction number. The two
letters after the n represent the up to two parameters to the function.
The letters represent the following data types:

void for return type and no parameter for parameter types.
i

int for return type and parameter type

f

float for return type and parameter type

p

void * for return type and parameter type
And the function names are:
void __builtin_custom_n (void)
void __builtin_custom_ni (int)

Chapter 6: Extensions to the C Language Family

void __builtin_custom_nf (float)
void __builtin_custom_np (void *)
void __builtin_custom_nii (int, int)
void __builtin_custom_nif (int, float)
void __builtin_custom_nip (int, void *)
void __builtin_custom_nfi (float, int)
void __builtin_custom_nff (float, float)
void __builtin_custom_nfp (float, void *)
void __builtin_custom_npi (void *, int)
void __builtin_custom_npf (void *, float)
void __builtin_custom_npp (void *, void *)
int __builtin_custom_in (void)
int __builtin_custom_ini (int)
int __builtin_custom_inf (float)
int __builtin_custom_inp (void *)
int __builtin_custom_inii (int, int)
int __builtin_custom_inif (int, float)
int __builtin_custom_inip (int, void *)
int __builtin_custom_infi (float, int)
int __builtin_custom_inff (float, float)
int __builtin_custom_infp (float, void *)
int __builtin_custom_inpi (void *, int)
int __builtin_custom_inpf (void *, float)
int __builtin_custom_inpp (void *, void *)
float __builtin_custom_fn (void)
float __builtin_custom_fni (int)
float __builtin_custom_fnf (float)
float __builtin_custom_fnp (void *)
float __builtin_custom_fnii (int, int)
float __builtin_custom_fnif (int, float)
float __builtin_custom_fnip (int, void *)
float __builtin_custom_fnfi (float, int)
float __builtin_custom_fnff (float, float)
float __builtin_custom_fnfp (float, void *)
float __builtin_custom_fnpi (void *, int)
float __builtin_custom_fnpf (void *, float)
float __builtin_custom_fnpp (void *, void *)
void * __builtin_custom_pn (void)
void * __builtin_custom_pni (int)
void * __builtin_custom_pnf (float)
void * __builtin_custom_pnp (void *)
void * __builtin_custom_pnii (int, int)
void * __builtin_custom_pnif (int, float)
void * __builtin_custom_pnip (int, void *)
void * __builtin_custom_pnfi (float, int)
void * __builtin_custom_pnff (float, float)
void * __builtin_custom_pnfp (float, void *)

629

630

Using the GNU Compiler Collection (GCC)

void * __builtin_custom_pnpi (void *, int)
void * __builtin_custom_pnpf (void *, float)
void * __builtin_custom_pnpp (void *, void *)

6.59.4 ARC Built-in Functions
The following built-in functions are provided for ARC targets. The built-ins generate the
corresponding assembly instructions. In the examples given below, the generated code
often requires an operand or result to be in a register. Where necessary further code will
be generated to ensure this is true, but for brevity this is not described in each case.
Note: Using a built-in to generate an instruction not supported by a target may cause
problems. At present the compiler is not guaranteed to detect such misuse, and as a result
an internal compiler error may be generated.

int __builtin_arc_aligned (void *val, int alignval)

[Built-in Function]
Return 1 if val is known to have the byte alignment given by alignval, otherwise return
0. Note that this is different from
__alignof__(*(char *)val) >= alignval

because alignof sees only the type of the dereference, whereas builtin arc align
uses alignment information from the pointer as well as from the pointed-to type. The
information available will depend on optimization level.

void __builtin_arc_brk (void)

[Built-in Function]

Generates
brk

unsigned int __builtin_arc_core_read (unsigned int
regno)

[Built-in Function]

The operand is the number of a register to be read. Generates:
mov

dest, rregno

where the value in dest will be the result returned from the built-in.

void __builtin_arc_core_write (unsigned int regno,
unsigned int val)

[Built-in Function]

The first operand is the number of a register to be written, the second operand is a
compile time constant to write into that register. Generates:
mov

rregno, val

int __builtin_arc_divaw (int a, int b)

[Built-in Function]
Only available if either ‘-mcpu=ARC700’ or ‘-meA’ is set. Generates:
divaw

dest, a, b

where the value in dest will be the result returned from the built-in.

void __builtin_arc_flag (unsigned int a)
Generates
flag

a

[Built-in Function]

Chapter 6: Extensions to the C Language Family

631

unsigned int __builtin_arc_lr (unsigned int auxr)

[Built-in Function]
The operand, auxv, is the address of an auxiliary register and must be a compile time
constant. Generates:
lr dest, [auxr]
Where the value in dest will be the result returned from the built-in.

void __builtin_arc_mul64 (int a, int b)

[Built-in Function]

Only available with ‘-mmul64’. Generates:
mul64 a, b

void __builtin_arc_mulu64 (unsigned int a, unsigned int b)

[Built-in Function]

Only available with ‘-mmul64’. Generates:
mulu64 a, b

void __builtin_arc_nop (void)

[Built-in Function]

Generates:
nop

int __builtin_arc_norm (int src)

[Built-in Function]
Only valid if the ‘norm’ instruction is available through the ‘-mnorm’ option or by
default with ‘-mcpu=ARC700’. Generates:
norm dest, src
Where the value in dest will be the result returned from the built-in.

short int __builtin_arc_normw (short int src)

[Built-in Function]
Only valid if the ‘normw’ instruction is available through the ‘-mnorm’ option or by
default with ‘-mcpu=ARC700’. Generates:
normw dest, src
Where the value in dest will be the result returned from the built-in.

void __builtin_arc_rtie (void)

[Built-in Function]

Generates:
rtie

void __builtin_arc_sleep (int a
Generates:
sleep

[Built-in Function]

a

void __builtin_arc_sr (unsigned int auxr, unsigned int val)

[Built-in Function]
The first argument, auxv, is the address of an auxiliary register, the second argument,
val, is a compile time constant to be written to the register. Generates:
sr auxr, [val]

int __builtin_arc_swap (int src)

[Built-in Function]

Only valid with ‘-mswap’. Generates:
swap dest, src
Where the value in dest will be the result returned from the built-in.

632

Using the GNU Compiler Collection (GCC)

void __builtin_arc_swi (void)

[Built-in Function]

Generates:
swi

void __builtin_arc_sync (void)

[Built-in Function]

Only available with ‘-mcpu=ARC700’. Generates:
sync

void __builtin_arc_trap_s (unsigned int c)

[Built-in Function]

Only available with ‘-mcpu=ARC700’. Generates:
trap_s c

void __builtin_arc_unimp_s (void)

[Built-in Function]

Only available with ‘-mcpu=ARC700’. Generates:
unimp_s
The instructions generated by the following builtins are not considered as candidates for
scheduling. They are not moved around by the compiler during scheduling, and thus can
be expected to appear where they are put in the C code:
__builtin_arc_brk()
__builtin_arc_core_read()
__builtin_arc_core_write()
__builtin_arc_flag()
__builtin_arc_lr()
__builtin_arc_sleep()
__builtin_arc_sr()
__builtin_arc_swi()

6.59.5 ARC SIMD Built-in Functions
SIMD builtins provided by the compiler can be used to generate the vector instructions.
This section describes the available builtins and their usage in programs. With the ‘-msimd’
option, the compiler provides 128-bit vector types, which can be specified using the vector_
size attribute. The header file ‘arc-simd.h’ can be included to use the following predefined
types:
typedef int __v4si
__attribute__((vector_size(16)));
typedef short __v8hi __attribute__((vector_size(16)));
These types can be used to define 128-bit variables. The built-in functions listed in the
following section can be used on these variables to generate the vector operations.
For all builtins, __builtin_arc_someinsn, the header file ‘arc-simd.h’ also provides
equivalent macros called _someinsn that can be used for programming ease and improved
readability. The following macros for DMA control are also provided:
#define _setup_dma_in_channel_reg _vdiwr
#define _setup_dma_out_channel_reg _vdowr
The following is a complete list of all the SIMD built-ins provided for ARC, grouped by
calling signature.
The following take two __v8hi arguments and return a __v8hi result:

Chapter 6: Extensions to the C Language Family

__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi

__builtin_arc_vaddaw (__v8hi, __v8hi)
__builtin_arc_vaddw (__v8hi, __v8hi)
__builtin_arc_vand (__v8hi, __v8hi)
__builtin_arc_vandaw (__v8hi, __v8hi)
__builtin_arc_vavb (__v8hi, __v8hi)
__builtin_arc_vavrb (__v8hi, __v8hi)
__builtin_arc_vbic (__v8hi, __v8hi)
__builtin_arc_vbicaw (__v8hi, __v8hi)
__builtin_arc_vdifaw (__v8hi, __v8hi)
__builtin_arc_vdifw (__v8hi, __v8hi)
__builtin_arc_veqw (__v8hi, __v8hi)
__builtin_arc_vh264f (__v8hi, __v8hi)
__builtin_arc_vh264ft (__v8hi, __v8hi)
__builtin_arc_vh264fw (__v8hi, __v8hi)
__builtin_arc_vlew (__v8hi, __v8hi)
__builtin_arc_vltw (__v8hi, __v8hi)
__builtin_arc_vmaxaw (__v8hi, __v8hi)
__builtin_arc_vmaxw (__v8hi, __v8hi)
__builtin_arc_vminaw (__v8hi, __v8hi)
__builtin_arc_vminw (__v8hi, __v8hi)
__builtin_arc_vmr1aw (__v8hi, __v8hi)
__builtin_arc_vmr1w (__v8hi, __v8hi)
__builtin_arc_vmr2aw (__v8hi, __v8hi)
__builtin_arc_vmr2w (__v8hi, __v8hi)
__builtin_arc_vmr3aw (__v8hi, __v8hi)
__builtin_arc_vmr3w (__v8hi, __v8hi)
__builtin_arc_vmr4aw (__v8hi, __v8hi)
__builtin_arc_vmr4w (__v8hi, __v8hi)
__builtin_arc_vmr5aw (__v8hi, __v8hi)
__builtin_arc_vmr5w (__v8hi, __v8hi)
__builtin_arc_vmr6aw (__v8hi, __v8hi)
__builtin_arc_vmr6w (__v8hi, __v8hi)
__builtin_arc_vmr7aw (__v8hi, __v8hi)
__builtin_arc_vmr7w (__v8hi, __v8hi)
__builtin_arc_vmrb (__v8hi, __v8hi)
__builtin_arc_vmulaw (__v8hi, __v8hi)
__builtin_arc_vmulfaw (__v8hi, __v8hi)
__builtin_arc_vmulfw (__v8hi, __v8hi)
__builtin_arc_vmulw (__v8hi, __v8hi)
__builtin_arc_vnew (__v8hi, __v8hi)
__builtin_arc_vor (__v8hi, __v8hi)
__builtin_arc_vsubaw (__v8hi, __v8hi)
__builtin_arc_vsubw (__v8hi, __v8hi)
__builtin_arc_vsummw (__v8hi, __v8hi)
__builtin_arc_vvc1f (__v8hi, __v8hi)
__builtin_arc_vvc1ft (__v8hi, __v8hi)
__builtin_arc_vxor (__v8hi, __v8hi)

633

634

Using the GNU Compiler Collection (GCC)

__v8hi __builtin_arc_vxoraw (__v8hi, __v8hi)
The following take one __v8hi and one int argument and return a __v8hi result:
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi

__builtin_arc_vbaddw (__v8hi, int)
__builtin_arc_vbmaxw (__v8hi, int)
__builtin_arc_vbminw (__v8hi, int)
__builtin_arc_vbmulaw (__v8hi, int)
__builtin_arc_vbmulfw (__v8hi, int)
__builtin_arc_vbmulw (__v8hi, int)
__builtin_arc_vbrsubw (__v8hi, int)
__builtin_arc_vbsubw (__v8hi, int)

The following take one __v8hi argument and one int argument which must be a 3-bit
compile time constant indicating a register number I0-I7. They return a __v8hi result.
__v8hi __builtin_arc_vasrw (__v8hi, const int)
__v8hi __builtin_arc_vsr8 (__v8hi, const int)
__v8hi __builtin_arc_vsr8aw (__v8hi, const int)
The following take one __v8hi argument and one int argument which must be a 6-bit
compile time constant. They return a __v8hi result.
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi

__builtin_arc_vasrpwbi (__v8hi, const int)
__builtin_arc_vasrrpwbi (__v8hi, const int)
__builtin_arc_vasrrwi (__v8hi, const int)
__builtin_arc_vasrsrwi (__v8hi, const int)
__builtin_arc_vasrwi (__v8hi, const int)
__builtin_arc_vsr8awi (__v8hi, const int)
__builtin_arc_vsr8i (__v8hi, const int)

The following take one __v8hi argument and one int argument which must be a 8-bit
compile time constant. They return a __v8hi result.
__v8hi
__v8hi
__v8hi
__v8hi

__builtin_arc_vd6tapf (__v8hi, const int)
__builtin_arc_vmvaw (__v8hi, const int)
__builtin_arc_vmvw (__v8hi, const int)
__builtin_arc_vmvzw (__v8hi, const int)

The following take two int arguments, the second of which which must be a 8-bit compile
time constant. They return a __v8hi result:
__v8hi __builtin_arc_vmovaw (int, const int)
__v8hi __builtin_arc_vmovw (int, const int)
__v8hi __builtin_arc_vmovzw (int, const int)
The following take a single __v8hi argument and return a __v8hi result:
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi
__v8hi

__builtin_arc_vabsaw (__v8hi)
__builtin_arc_vabsw (__v8hi)
__builtin_arc_vaddsuw (__v8hi)
__builtin_arc_vexch1 (__v8hi)
__builtin_arc_vexch2 (__v8hi)
__builtin_arc_vexch4 (__v8hi)
__builtin_arc_vsignw (__v8hi)
__builtin_arc_vupbaw (__v8hi)

Chapter 6: Extensions to the C Language Family

635

__v8hi __builtin_arc_vupbw (__v8hi)
__v8hi __builtin_arc_vupsbaw (__v8hi)
__v8hi __builtin_arc_vupsbw (__v8hi)
The following take two int arguments and return no result:
void __builtin_arc_vdirun (int, int)
void __builtin_arc_vdorun (int, int)
The following take two int arguments and return no result. The first argument must a
3-bit compile time constant indicating one of the DR0-DR7 DMA setup channels:
void __builtin_arc_vdiwr (const int, int)
void __builtin_arc_vdowr (const int, int)
The following take an int argument and return no result:
void
void
void
void

__builtin_arc_vendrec (int)
__builtin_arc_vrec (int)
__builtin_arc_vrecrun (int)
__builtin_arc_vrun (int)

The following take a __v8hi argument and two int arguments and return a __v8hi
result. The second argument must be a 3-bit compile time constants, indicating one the
registers I0-I7, and the third argument must be an 8-bit compile time constant.
Note: Although the equivalent hardware instructions do not take an SIMD register as an
operand, these builtins overwrite the relevant bits of the __v8hi register provided as the
first argument with the value loaded from the [Ib, u8] location in the SDM.
__v8hi
__v8hi
__v8hi
__v8hi

__builtin_arc_vld32 (__v8hi, const int, const int)
__builtin_arc_vld32wh (__v8hi, const int, const int)
__builtin_arc_vld32wl (__v8hi, const int, const int)
__builtin_arc_vld64 (__v8hi, const int, const int)

The following take two int arguments and return a __v8hi result. The first argument
must be a 3-bit compile time constants, indicating one the registers I0-I7, and the second
argument must be an 8-bit compile time constant.
__v8hi __builtin_arc_vld128 (const int, const int)
__v8hi __builtin_arc_vld64w (const int, const int)
The following take a __v8hi argument and two int arguments and return no result. The
second argument must be a 3-bit compile time constants, indicating one the registers I0-I7,
and the third argument must be an 8-bit compile time constant.
void __builtin_arc_vst128 (__v8hi, const int, const int)
void __builtin_arc_vst64 (__v8hi, const int, const int)
The following take a __v8hi argument and three int arguments and return no result.
The second argument must be a 3-bit compile-time constant, identifying the 16-bit subregister to be stored, the third argument must be a 3-bit compile time constants, indicating
one the registers I0-I7, and the fourth argument must be an 8-bit compile time constant.
void __builtin_arc_vst16_n (__v8hi, const int, const int, const int)
void __builtin_arc_vst32_n (__v8hi, const int, const int, const int)

636

Using the GNU Compiler Collection (GCC)

6.59.6 ARM iWMMXt Built-in Functions
These built-in functions are available for the ARM family of processors when the
‘-mcpu=iwmmxt’ switch is used:
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef char v8qi __attribute__ ((vector_size (8)));
int __builtin_arm_getwcgr0 (void)
void __builtin_arm_setwcgr0 (int)
int __builtin_arm_getwcgr1 (void)
void __builtin_arm_setwcgr1 (int)
int __builtin_arm_getwcgr2 (void)
void __builtin_arm_setwcgr2 (int)
int __builtin_arm_getwcgr3 (void)
void __builtin_arm_setwcgr3 (int)
int __builtin_arm_textrmsb (v8qi, int)
int __builtin_arm_textrmsh (v4hi, int)
int __builtin_arm_textrmsw (v2si, int)
int __builtin_arm_textrmub (v8qi, int)
int __builtin_arm_textrmuh (v4hi, int)
int __builtin_arm_textrmuw (v2si, int)
v8qi __builtin_arm_tinsrb (v8qi, int, int)
v4hi __builtin_arm_tinsrh (v4hi, int, int)
v2si __builtin_arm_tinsrw (v2si, int, int)
long long __builtin_arm_tmia (long long, int, int)
long long __builtin_arm_tmiabb (long long, int, int)
long long __builtin_arm_tmiabt (long long, int, int)
long long __builtin_arm_tmiaph (long long, int, int)
long long __builtin_arm_tmiatb (long long, int, int)
long long __builtin_arm_tmiatt (long long, int, int)
int __builtin_arm_tmovmskb (v8qi)
int __builtin_arm_tmovmskh (v4hi)
int __builtin_arm_tmovmskw (v2si)
long long __builtin_arm_waccb (v8qi)
long long __builtin_arm_wacch (v4hi)
long long __builtin_arm_waccw (v2si)
v8qi __builtin_arm_waddb (v8qi, v8qi)
v8qi __builtin_arm_waddbss (v8qi, v8qi)
v8qi __builtin_arm_waddbus (v8qi, v8qi)
v4hi __builtin_arm_waddh (v4hi, v4hi)
v4hi __builtin_arm_waddhss (v4hi, v4hi)
v4hi __builtin_arm_waddhus (v4hi, v4hi)
v2si __builtin_arm_waddw (v2si, v2si)
v2si __builtin_arm_waddwss (v2si, v2si)
v2si __builtin_arm_waddwus (v2si, v2si)
v8qi __builtin_arm_walign (v8qi, v8qi, int)
long long __builtin_arm_wand(long long, long long)
long long __builtin_arm_wandn (long long, long long)
v8qi __builtin_arm_wavg2b (v8qi, v8qi)
v8qi __builtin_arm_wavg2br (v8qi, v8qi)
v4hi __builtin_arm_wavg2h (v4hi, v4hi)
v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
v2si __builtin_arm_wcmpeqw (v2si, v2si)
v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)

Chapter 6: Extensions to the C Language Family

v2si
v8qi
v4hi
v2si
long
long
long
long
v4hi
v4hi
v8qi
v4hi
v2si
v8qi
v4hi
v2si
v8qi
v4hi
v2si
v8qi
v4hi
v2si
v4hi
v4hi
v4hi
long
v2si
v2si
v8qi
v8qi
v4hi
v4hi
long
long
v4hi
v4hi
v2si
v2si
v2si
v2si
v2si
v2si
v4hi
long
long
v4hi
v4hi
v2si
v2si
long
long
v4hi
v4hi
v2si
v2si
long
long
v4hi

__builtin_arm_wcmpgtsw (v2si, v2si)
__builtin_arm_wcmpgtub (v8qi, v8qi)
__builtin_arm_wcmpgtuh (v4hi, v4hi)
__builtin_arm_wcmpgtuw (v2si, v2si)
long __builtin_arm_wmacs (long long, v4hi, v4hi)
long __builtin_arm_wmacsz (v4hi, v4hi)
long __builtin_arm_wmacu (long long, v4hi, v4hi)
long __builtin_arm_wmacuz (v4hi, v4hi)
__builtin_arm_wmadds (v4hi, v4hi)
__builtin_arm_wmaddu (v4hi, v4hi)
__builtin_arm_wmaxsb (v8qi, v8qi)
__builtin_arm_wmaxsh (v4hi, v4hi)
__builtin_arm_wmaxsw (v2si, v2si)
__builtin_arm_wmaxub (v8qi, v8qi)
__builtin_arm_wmaxuh (v4hi, v4hi)
__builtin_arm_wmaxuw (v2si, v2si)
__builtin_arm_wminsb (v8qi, v8qi)
__builtin_arm_wminsh (v4hi, v4hi)
__builtin_arm_wminsw (v2si, v2si)
__builtin_arm_wminub (v8qi, v8qi)
__builtin_arm_wminuh (v4hi, v4hi)
__builtin_arm_wminuw (v2si, v2si)
__builtin_arm_wmulsm (v4hi, v4hi)
__builtin_arm_wmulul (v4hi, v4hi)
__builtin_arm_wmulum (v4hi, v4hi)
long __builtin_arm_wor (long long, long long)
__builtin_arm_wpackdss (long long, long long)
__builtin_arm_wpackdus (long long, long long)
__builtin_arm_wpackhss (v4hi, v4hi)
__builtin_arm_wpackhus (v4hi, v4hi)
__builtin_arm_wpackwss (v2si, v2si)
__builtin_arm_wpackwus (v2si, v2si)
long __builtin_arm_wrord (long long, long long)
long __builtin_arm_wrordi (long long, int)
__builtin_arm_wrorh (v4hi, long long)
__builtin_arm_wrorhi (v4hi, int)
__builtin_arm_wrorw (v2si, long long)
__builtin_arm_wrorwi (v2si, int)
__builtin_arm_wsadb (v2si, v8qi, v8qi)
__builtin_arm_wsadbz (v8qi, v8qi)
__builtin_arm_wsadh (v2si, v4hi, v4hi)
__builtin_arm_wsadhz (v4hi, v4hi)
__builtin_arm_wshufh (v4hi, int)
long __builtin_arm_wslld (long long, long long)
long __builtin_arm_wslldi (long long, int)
__builtin_arm_wsllh (v4hi, long long)
__builtin_arm_wsllhi (v4hi, int)
__builtin_arm_wsllw (v2si, long long)
__builtin_arm_wsllwi (v2si, int)
long __builtin_arm_wsrad (long long, long long)
long __builtin_arm_wsradi (long long, int)
__builtin_arm_wsrah (v4hi, long long)
__builtin_arm_wsrahi (v4hi, int)
__builtin_arm_wsraw (v2si, long long)
__builtin_arm_wsrawi (v2si, int)
long __builtin_arm_wsrld (long long, long long)
long __builtin_arm_wsrldi (long long, int)
__builtin_arm_wsrlh (v4hi, long long)

637

638

Using the GNU Compiler Collection (GCC)

v4hi
v2si
v2si
v8qi
v8qi
v8qi
v4hi
v4hi
v4hi
v2si
v2si
v2si
v4hi
v2si
long
v4hi
v2si
long
v4hi
v2si
long
v4hi
v2si
long
v8qi
v4hi
v2si
v8qi
v4hi
v2si
long
long

__builtin_arm_wsrlhi (v4hi, int)
__builtin_arm_wsrlw (v2si, long long)
__builtin_arm_wsrlwi (v2si, int)
__builtin_arm_wsubb (v8qi, v8qi)
__builtin_arm_wsubbss (v8qi, v8qi)
__builtin_arm_wsubbus (v8qi, v8qi)
__builtin_arm_wsubh (v4hi, v4hi)
__builtin_arm_wsubhss (v4hi, v4hi)
__builtin_arm_wsubhus (v4hi, v4hi)
__builtin_arm_wsubw (v2si, v2si)
__builtin_arm_wsubwss (v2si, v2si)
__builtin_arm_wsubwus (v2si, v2si)
__builtin_arm_wunpckehsb (v8qi)
__builtin_arm_wunpckehsh (v4hi)
long __builtin_arm_wunpckehsw (v2si)
__builtin_arm_wunpckehub (v8qi)
__builtin_arm_wunpckehuh (v4hi)
long __builtin_arm_wunpckehuw (v2si)
__builtin_arm_wunpckelsb (v8qi)
__builtin_arm_wunpckelsh (v4hi)
long __builtin_arm_wunpckelsw (v2si)
__builtin_arm_wunpckelub (v8qi)
__builtin_arm_wunpckeluh (v4hi)
long __builtin_arm_wunpckeluw (v2si)
__builtin_arm_wunpckihb (v8qi, v8qi)
__builtin_arm_wunpckihh (v4hi, v4hi)
__builtin_arm_wunpckihw (v2si, v2si)
__builtin_arm_wunpckilb (v8qi, v8qi)
__builtin_arm_wunpckilh (v4hi, v4hi)
__builtin_arm_wunpckilw (v2si, v2si)
long __builtin_arm_wxor (long long, long long)
long __builtin_arm_wzero ()

6.59.7 ARM C Language Extensions (ACLE)
GCC implements extensions for C as described in the ARM C Language Extensions (ACLE)
specification, which can be found at http://infocenter.arm.com/help/topic/com.arm.
doc.ihi0053c/IHI0053C_acle_2_0.pdf.
As a part of ACLE, GCC implements extensions for Advanced SIMD as described in the
ARM C Language Extensions Specification. The complete list of Advanced SIMD intrinsics
can be found at http://infocenter.arm.com/help/topic/com.arm.doc.ihi0073a/
IHI0073A_arm_neon_intrinsics_ref.pdf. The built-in intrinsics for the Advanced SIMD
extension are available when NEON is enabled.
Currently, ARM and AArch64 back ends do not support ACLE 2.0 fully. Both back ends
support CRC32 intrinsics and the ARM back end supports the Coprocessor intrinsics, all
from ‘arm_acle.h’. The ARM back end’s 16-bit floating-point Advanced SIMD intrinsics
currently comply to ACLE v1.1. AArch64’s back end does not have support for 16-bit
floating point Advanced SIMD intrinsics yet.
See Section 3.18.4 [ARM Options], page 245 and Section 3.18.1 [AArch64 Options],
page 228 for more information on the availability of extensions.

Chapter 6: Extensions to the C Language Family

639

6.59.8 ARM Floating Point Status and Control Intrinsics
These built-in functions are available for the ARM family of processors with floating-point
unit.
unsigned int __builtin_arm_get_fpscr ()
void __builtin_arm_set_fpscr (unsigned int)

6.59.9 ARM ARMv8-M Security Extensions
GCC implements the ARMv8-M Security Extensions as described in the ARMv8-M Security Extensions: Requirements on Development Tools Engineering Specification, which
can be found at http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/
ECM0359818_armv8m_security_extensions_reqs_on_dev_tools_1_0.pdf.
As part of the Security Extensions GCC implements two new function attributes: cmse_
nonsecure_entry and cmse_nonsecure_call.
As part of the Security Extensions GCC implements the intrinsics below. FPTR is used
here to mean any function pointer type.
cmse_address_info_t cmse_TT (void *)
cmse_address_info_t cmse_TT_fptr (FPTR)
cmse_address_info_t cmse_TTT (void *)
cmse_address_info_t cmse_TTT_fptr (FPTR)
cmse_address_info_t cmse_TTA (void *)
cmse_address_info_t cmse_TTA_fptr (FPTR)
cmse_address_info_t cmse_TTAT (void *)
cmse_address_info_t cmse_TTAT_fptr (FPTR)
void * cmse_check_address_range (void *, size_t, int)
typeof(p) cmse_nsfptr_create (FPTR p)
intptr_t cmse_is_nsfptr (FPTR)
int cmse_nonsecure_caller (void)

6.59.10 AVR Built-in Functions
For each built-in function for AVR, there is an equally named, uppercase built-in macro
defined. That way users can easily query if or if not a specific built-in is implemented or not.
For example, if __builtin_avr_nop is available the macro __BUILTIN_AVR_NOP is defined
to 1 and undefined otherwise.
void __builtin_avr_nop (void)
void __builtin_avr_sei (void)
void __builtin_avr_cli (void)
void __builtin_avr_sleep (void)
void __builtin_avr_wdr (void)
unsigned char __builtin_avr_swap (unsigned char)
unsigned int __builtin_avr_fmul (unsigned char, unsigned char)
int __builtin_avr_fmuls (char, char)
int __builtin_avr_fmulsu (char, unsigned char)
These built-in functions map to the respective machine instruction, i.e. nop,
sei, cli, sleep, wdr, swap, fmul, fmuls resp. fmulsu. The three fmul*
built-ins are implemented as library call if no hardware multiplier is available.
void __builtin_avr_delay_cycles (unsigned long ticks)
Delay execution for ticks cycles. Note that this built-in does not take into
account the effect of interrupts that might increase delay time. ticks must be a

640

Using the GNU Compiler Collection (GCC)

compile-time integer constant; delays with a variable number of cycles are not
supported.
char __builtin_avr_flash_segment (const __memx void*)
This built-in takes a byte address to the 24-bit [AVR Named Address Spaces],
page 453 __memx and returns the number of the flash segment (the 64 KiB
chunk) where the address points to. Counting starts at 0. If the address does
not point to flash memory, return -1.
uint8_t __builtin_avr_insert_bits (uint32_t map, uint8_t bits, uint8_t val)
Insert bits from bits into val and return the resulting value. The nibbles of map
determine how the insertion is performed: Let X be the n-th nibble of map
1. If X is 0xf, then the n-th bit of val is returned unaltered.
2. If X is in the range 0. . . 7, then the n-th result bit is set to the X-th bit of
bits
3. If X is in the range 8. . . 0xe, then the n-th result bit is undefined.
One typical use case for this built-in is adjusting input and output values to
non-contiguous port layouts. Some examples:
// same as val, bits is unused
__builtin_avr_insert_bits (0xffffffff, bits, val)
// same as bits, val is unused
__builtin_avr_insert_bits (0x76543210, bits, val)
// same as rotating bits by 4
__builtin_avr_insert_bits (0x32107654, bits, 0)
// high nibble of result is the high nibble of val
// low nibble of result is the low nibble of bits
__builtin_avr_insert_bits (0xffff3210, bits, val)
// reverse the bit order of bits
__builtin_avr_insert_bits (0x01234567, bits, 0)

void __builtin_avr_nops (unsigned count)
Insert count NOP instructions. The number of instructions must be a compiletime integer constant.
There are many more AVR-specific built-in functions that are used to implement the
ISO/IEC TR 18037 “Embedded C” fixed-point functions of section 7.18a.6. You don’t need
to use these built-ins directly. Instead, use the declarations as supplied by the stdfix.h
header with GNU-C99:
#include 
// Re-interpret the bit representation of unsigned 16-bit
// integer uval as Q-format 0.16 value.
unsigned fract get_bits (uint_ur_t uval)
{
return urbits (uval);
}

6.59.11 Blackfin Built-in Functions
Currently, there are two Blackfin-specific built-in functions. These are used for generating
CSYNC and SSYNC machine insns without using inline assembly; by using these built-in

Chapter 6: Extensions to the C Language Family

641

functions the compiler can automatically add workarounds for hardware errata involving
these instructions. These functions are named as follows:
void __builtin_bfin_csync (void)
void __builtin_bfin_ssync (void)

6.59.12 FR-V Built-in Functions
GCC provides many FR-V-specific built-in functions. In general, these functions are intended to be compatible with those described by FR-V Family, Softune C/C++ Compiler
Manual (V6), Fujitsu Semiconductor. The two exceptions are __MDUNPACKH and __MBTOHE,
the GCC forms of which pass 128-bit values by pointer rather than by value.
Most of the functions are named after specific FR-V instructions. Such functions are said
to be “directly mapped” and are summarized here in tabular form.

6.59.12.1 Argument Types
The arguments to the built-in functions can be divided into three groups: register numbers,
compile-time constants and run-time values. In order to make this classification clear at a
glance, the arguments and return values are given the following pseudo types:
Pseudo type
Real C type
Constant? Description
uh
unsigned short
No
an unsigned halfword
uw1
unsigned int
No
an unsigned word
sw1
int
No
a signed word
uw2
unsigned long long
No
an unsigned doubleword
sw2
long long
No
a signed doubleword
const
int
Yes
an integer constant
acc
int
Yes
an ACC register number
iacc
int
Yes
an IACC register number
These pseudo types are not defined by GCC, they are simply a notational convenience
used in this manual.
Arguments of type uh, uw1, sw1, uw2 and sw2 are evaluated at run time. They correspond
to register operands in the underlying FR-V instructions.
const arguments represent immediate operands in the underlying FR-V instructions.
They must be compile-time constants.
acc arguments are evaluated at compile time and specify the number of an accumulator
register. For example, an acc argument of 2 selects the ACC2 register.
iacc arguments are similar to acc arguments but specify the number of an IACC register.
See see Section 6.59.12.5 [Other Built-in Functions], page 644 for more details.

6.59.12.2 Directly-Mapped Integer Functions
The functions listed below map directly to FR-V I-type instructions.
Function prototype
Example usage
sw1 __ADDSS (sw1, sw1)
c = __ADDSS (a, b)
sw1 __SCAN (sw1, sw1)
c = __SCAN (a, b)
sw1 __SCUTSS (sw1)
b = __SCUTSS (a)
sw1 __SLASS (sw1, sw1)
c = __SLASS (a, b)
void __SMASS (sw1, sw1)
__SMASS (a, b)

Assembly output
ADDSS a,b,c
SCAN a,b,c
SCUTSS a,b
SLASS a,b,c
SMASS a,b

642

void __SMSSS (sw1, sw1)
void __SMU (sw1, sw1)
sw2 __SMUL (sw1, sw1)
sw1 __SUBSS (sw1, sw1)
uw2 __UMUL (uw1, uw1)

Using the GNU Compiler Collection (GCC)

__SMSSS (a, b)
__SMU (a, b)
c = __SMUL (a, b)
c = __SUBSS (a, b)
c = __UMUL (a, b)

SMSSS a,b
SMU a,b
SMUL a,b,c
SUBSS a,b,c
UMUL a,b,c

6.59.12.3 Directly-Mapped Media Functions
The functions listed below map directly to FR-V M-type instructions.
Function prototype
uw1 __MABSHS (sw1)
void __MADDACCS (acc, acc)
sw1 __MADDHSS (sw1, sw1)
uw1 __MADDHUS (uw1, uw1)
uw1 __MAND (uw1, uw1)
void __MASACCS (acc, acc)
uw1 __MAVEH (uw1, uw1)
uw2 __MBTOH (uw1)
void __MBTOHE (uw1 *, uw1)
void __MCLRACC (acc)
void __MCLRACCA (void)
uw1 __Mcop1 (uw1, uw1)
uw1 __Mcop2 (uw1, uw1)
uw1 __MCPLHI (uw2, const)
uw1 __MCPLI (uw2, const)
void __MCPXIS (acc, sw1, sw1)
void __MCPXIU (acc, uw1, uw1)
void __MCPXRS (acc, sw1, sw1)
void __MCPXRU (acc, uw1, uw1)
uw1 __MCUT (acc, uw1)
uw1 __MCUTSS (acc, sw1)
void __MDADDACCS (acc, acc)
void __MDASACCS (acc, acc)
uw2 __MDCUTSSI (acc, const)
uw2 __MDPACKH (uw2, uw2)
uw2 __MDROTLI (uw2, const)
void __MDSUBACCS (acc, acc)
void __MDUNPACKH (uw1 *, uw2)
uw2 __MEXPDHD (uw1, const)
uw1 __MEXPDHW (uw1, const)
uw1 __MHDSETH (uw1, const)
sw1 __MHDSETS (const)
uw1 __MHSETHIH (uw1, const)
sw1 __MHSETHIS (sw1, const)
uw1 __MHSETLOH (uw1, const)
sw1 __MHSETLOS (sw1, const)
uw1 __MHTOB (uw2)

Example usage
b = __MABSHS (a)
__MADDACCS (b, a)
c = __MADDHSS (a, b)
c = __MADDHUS (a, b)
c = __MAND (a, b)
__MASACCS (b, a)
c = __MAVEH (a, b)
b = __MBTOH (a)
__MBTOHE (&b, a)
__MCLRACC (a)
__MCLRACCA ()
c = __Mcop1 (a, b)
c = __Mcop2 (a, b)
c = __MCPLHI (a, b)
c = __MCPLI (a, b)
__MCPXIS (c, a, b)
__MCPXIU (c, a, b)
__MCPXRS (c, a, b)
__MCPXRU (c, a, b)
c = __MCUT (a, b)
c = __MCUTSS (a, b)
__MDADDACCS (b, a)
__MDASACCS (b, a)
c = __MDCUTSSI (a, b)
c = __MDPACKH (a, b)
c = __MDROTLI (a, b)
__MDSUBACCS (b, a)
__MDUNPACKH (&b, a)
c = __MEXPDHD (a, b)
c = __MEXPDHW (a, b)
c = __MHDSETH (a, b)
b = __MHDSETS (a)
b = __MHSETHIH (b, a)
b = __MHSETHIS (b, a)
b = __MHSETLOH (b, a)
b = __MHSETLOS (b, a)
b = __MHTOB (a)

Assembly output
MABSHS a,b
MADDACCS a,b
MADDHSS a,b,c
MADDHUS a,b,c
MAND a,b,c
MASACCS a,b
MAVEH a,b,c
MBTOH a,b
MBTOHE a,b
MCLRACC a
MCLRACCA
Mcop1 a,b,c
Mcop2 a,b,c
MCPLHI a,#b,c
MCPLI a,#b,c
MCPXIS a,b,c
MCPXIU a,b,c
MCPXRS a,b,c
MCPXRU a,b,c
MCUT a,b,c
MCUTSS a,b,c
MDADDACCS a,b
MDASACCS a,b
MDCUTSSI a,#b,c
MDPACKH a,b,c
MDROTLI a,#b,c
MDSUBACCS a,b
MDUNPACKH a,b
MEXPDHD a,#b,c
MEXPDHW a,#b,c
MHDSETH a,#b,c
MHDSETS #a,b
MHSETHIH #a,b
MHSETHIS #a,b
MHSETLOH #a,b
MHSETLOS #a,b
MHTOB a,b

Chapter 6: Extensions to the C Language Family

void __MMACHS (acc, sw1, sw1)
void __MMACHU (acc, uw1, uw1)
void __MMRDHS (acc, sw1, sw1)
void __MMRDHU (acc, uw1, uw1)
void __MMULHS (acc, sw1, sw1)
void __MMULHU (acc, uw1, uw1)
void __MMULXHS (acc, sw1, sw1)
void __MMULXHU (acc, uw1, uw1)
uw1 __MNOT (uw1)
uw1 __MOR (uw1, uw1)
uw1 __MPACKH (uh, uh)
sw2 __MQADDHSS (sw2, sw2)
uw2 __MQADDHUS (uw2, uw2)
void __MQCPXIS (acc, sw2, sw2)
void __MQCPXIU (acc, uw2, uw2)
void __MQCPXRS (acc, sw2, sw2)
void __MQCPXRU (acc, uw2, uw2)
sw2 __MQLCLRHS (sw2, sw2)
sw2 __MQLMTHS (sw2, sw2)
void __MQMACHS (acc, sw2, sw2)
void __MQMACHU (acc, uw2, uw2)
void __MQMACXHS (acc, sw2, sw2)
void __MQMULHS (acc, sw2, sw2)
void __MQMULHU (acc, uw2, uw2)
void __MQMULXHS (acc, sw2, sw2)
void __MQMULXHU (acc, uw2, uw2)
sw2 __MQSATHS (sw2, sw2)
uw2 __MQSLLHI (uw2, int)
sw2 __MQSRAHI (sw2, int)
sw2 __MQSUBHSS (sw2, sw2)
uw2 __MQSUBHUS (uw2, uw2)
void __MQXMACHS (acc, sw2, sw2)
void __MQXMACXHS (acc, sw2, sw2)
uw1 __MRDACC (acc)
uw1 __MRDACCG (acc)
uw1 __MROTLI (uw1, const)
uw1 __MROTRI (uw1, const)
sw1 __MSATHS (sw1, sw1)
uw1 __MSATHU (uw1, uw1)
uw1 __MSLLHI (uw1, const)
sw1 __MSRAHI (sw1, const)
uw1 __MSRLHI (uw1, const)
void __MSUBACCS (acc, acc)
sw1 __MSUBHSS (sw1, sw1)
uw1 __MSUBHUS (uw1, uw1)
void __MTRAP (void)
uw2 __MUNPACKH (uw1)

__MMACHS (c, a, b)
__MMACHU (c, a, b)
__MMRDHS (c, a, b)
__MMRDHU (c, a, b)
__MMULHS (c, a, b)
__MMULHU (c, a, b)
__MMULXHS (c, a, b)
__MMULXHU (c, a, b)
b = __MNOT (a)
c = __MOR (a, b)
c = __MPACKH (a, b)
c = __MQADDHSS (a, b)
c = __MQADDHUS (a, b)
__MQCPXIS (c, a, b)
__MQCPXIU (c, a, b)
__MQCPXRS (c, a, b)
__MQCPXRU (c, a, b)
c = __MQLCLRHS (a, b)
c = __MQLMTHS (a, b)
__MQMACHS (c, a, b)
__MQMACHU (c, a, b)
__MQMACXHS (c, a, b)
__MQMULHS (c, a, b)
__MQMULHU (c, a, b)
__MQMULXHS (c, a, b)
__MQMULXHU (c, a, b)
c = __MQSATHS (a, b)
c = __MQSLLHI (a, b)
c = __MQSRAHI (a, b)
c = __MQSUBHSS (a, b)
c = __MQSUBHUS (a, b)
__MQXMACHS (c, a, b)
__MQXMACXHS (c, a, b)
b = __MRDACC (a)
b = __MRDACCG (a)
c = __MROTLI (a, b)
c = __MROTRI (a, b)
c = __MSATHS (a, b)
c = __MSATHU (a, b)
c = __MSLLHI (a, b)
c = __MSRAHI (a, b)
c = __MSRLHI (a, b)
__MSUBACCS (b, a)
c = __MSUBHSS (a, b)
c = __MSUBHUS (a, b)
__MTRAP ()
b = __MUNPACKH (a)

643

MMACHS a,b,c
MMACHU a,b,c
MMRDHS a,b,c
MMRDHU a,b,c
MMULHS a,b,c
MMULHU a,b,c
MMULXHS a,b,c
MMULXHU a,b,c
MNOT a,b
MOR a,b,c
MPACKH a,b,c
MQADDHSS a,b,c
MQADDHUS a,b,c
MQCPXIS a,b,c
MQCPXIU a,b,c
MQCPXRS a,b,c
MQCPXRU a,b,c
MQLCLRHS a,b,c
MQLMTHS a,b,c
MQMACHS a,b,c
MQMACHU a,b,c
MQMACXHS a,b,c
MQMULHS a,b,c
MQMULHU a,b,c
MQMULXHS a,b,c
MQMULXHU a,b,c
MQSATHS a,b,c
MQSLLHI a,b,c
MQSRAHI a,b,c
MQSUBHSS a,b,c
MQSUBHUS a,b,c
MQXMACHS a,b,c
MQXMACXHS a,b,c
MRDACC a,b
MRDACCG a,b
MROTLI a,#b,c
MROTRI a,#b,c
MSATHS a,b,c
MSATHU a,b,c
MSLLHI a,#b,c
MSRAHI a,#b,c
MSRLHI a,#b,c
MSUBACCS a,b
MSUBHSS a,b,c
MSUBHUS a,b,c
MTRAP
MUNPACKH a,b

644

uw1 __MWCUT (uw2, uw1)
void __MWTACC (acc, uw1)
void __MWTACCG (acc, uw1)
uw1 __MXOR (uw1, uw1)

Using the GNU Compiler Collection (GCC)

c = __MWCUT (a, b)
__MWTACC (b, a)
__MWTACCG (b, a)
c = __MXOR (a, b)

MWCUT a,b,c
MWTACC a,b
MWTACCG a,b
MXOR a,b,c

6.59.12.4 Raw Read/Write Functions
This sections describes built-in functions related to read and write instructions to access
memory. These functions generate membar instructions to flush the I/O load and stores
where appropriate, as described in Fujitsu’s manual described above.
unsigned char __builtin_read8 (void *data)
unsigned short __builtin_read16 (void *data)
unsigned long __builtin_read32 (void *data)
unsigned long long __builtin_read64 (void *data)
void __builtin_write8 (void *data, unsigned char datum)
void __builtin_write16 (void *data, unsigned short datum)
void __builtin_write32 (void *data, unsigned long datum)
void __builtin_write64 (void *data, unsigned long long datum)

6.59.12.5 Other Built-in Functions
This section describes built-in functions that are not named after a specific FR-V instruction.
sw2 __IACCreadll (iacc reg)
Return the full 64-bit value of IACC0. The reg argument is reserved for future
expansion and must be 0.
sw1 __IACCreadl (iacc reg)
Return the value of IACC0H if reg is 0 and IACC0L if reg is 1. Other values
of reg are rejected as invalid.
void __IACCsetll (iacc reg, sw2 x)
Set the full 64-bit value of IACC0 to x. The reg argument is reserved for future
expansion and must be 0.
void __IACCsetl (iacc reg, sw1 x)
Set IACC0H to x if reg is 0 and IACC0L to x if reg is 1. Other values of reg
are rejected as invalid.
void __data_prefetch0 (const void *x)
Use the dcpl instruction to load the contents of address x into the data cache.
void __data_prefetch (const void *x)
Use the nldub instruction to load the contents of address x into the data cache.
The instruction is issued in slot I1.

6.59.13 MIPS DSP Built-in Functions
The MIPS DSP Application-Specific Extension (ASE) includes new instructions that are designed to improve the performance of DSP and media applications. It provides instructions
that operate on packed 8-bit/16-bit integer data, Q7, Q15 and Q31 fractional data.

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GCC supports MIPS DSP operations using both the generic vector extensions (see
Section 6.50 [Vector Extensions], page 598) and a collection of MIPS-specific built-in functions. Both kinds of support are enabled by the ‘-mdsp’ command-line option.
Revision 2 of the ASE was introduced in the second half of 2006. This revision adds extra
instructions to the original ASE, but is otherwise backwards-compatible with it. You can
select revision 2 using the command-line option ‘-mdspr2’; this option implies ‘-mdsp’.
The SCOUNT and POS bits of the DSP control register are global. The WRDSP,
EXTPDP, EXTPDPV and MTHLIP instructions modify the SCOUNT and POS bits. During optimization, the compiler does not delete these instructions and it does not delete calls
to functions containing these instructions.
At present, GCC only provides support for operations on 32-bit vectors. The vector type
associated with 8-bit integer data is usually called v4i8, the vector type associated with
Q7 is usually called v4q7, the vector type associated with 16-bit integer data is usually
called v2i16, and the vector type associated with Q15 is usually called v2q15. They can
be defined in C as follows:
typedef
typedef
typedef
typedef

signed char
signed char
short v2i16
short v2q15

v4i8 __attribute__ ((vector_size(4)));
v4q7 __attribute__ ((vector_size(4)));
__attribute__ ((vector_size(4)));
__attribute__ ((vector_size(4)));

v4i8, v4q7, v2i16 and v2q15 values are initialized in the same way as aggregates. For
example:
v4i8 a = {1, 2, 3, 4};
v4i8 b;
b = (v4i8) {5, 6, 7, 8};
v2q15 c = {0x0fcb, 0x3a75};
v2q15 d;
d = (v2q15) {0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15};

Note: The CPU’s endianness determines the order in which values are packed. On
little-endian targets, the first value is the least significant and the last value is the most
significant. The opposite order applies to big-endian targets. For example, the code above
sets the lowest byte of a to 1 on little-endian targets and 4 on big-endian targets.
Note: Q7, Q15 and Q31 values must be initialized with their integer representation.
As shown in this example, the integer representation of a Q7 value can be obtained by
multiplying the fractional value by 0x1.0p7. The equivalent for Q15 values is to multiply
by 0x1.0p15. The equivalent for Q31 values is to multiply by 0x1.0p31.
The table below lists the v4i8 and v2q15 operations for which hardware support exists.
a and b are v4i8 values, and c and d are v2q15 values.
C code
a+b
c+d
a-b
c-d

MIPS instruction
addu.qb
addq.ph
subu.qb
subq.ph

The table below lists the v2i16 operation for which hardware support exists for the DSP
ASE REV 2. e and f are v2i16 values.
C code

MIPS instruction

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e*f

mul.ph

It is easier to describe the DSP built-in functions if we first define the following types:
typedef
typedef
typedef
typedef

int q31;
int i32;
unsigned int ui32;
long long a64;

q31 and i32 are actually the same as int, but we use q31 to indicate a Q31 fractional
value and i32 to indicate a 32-bit integer value. Similarly, a64 is the same as long long,
but we use a64 to indicate values that are placed in one of the four DSP accumulators
($ac0, $ac1, $ac2 or $ac3).
Also, some built-in functions prefer or require immediate numbers as parameters, because
the corresponding DSP instructions accept both immediate numbers and register operands,
or accept immediate numbers only. The immediate parameters are listed as follows.
imm0_3: 0 to 3.
imm0_7: 0 to 7.
imm0_15: 0 to 15.
imm0_31: 0 to 31.
imm0_63: 0 to 63.
imm0_255: 0 to 255.
imm_n32_31: -32 to 31.
imm_n512_511: -512 to 511.

The following built-in functions map directly to a particular MIPS DSP instruction.
Please refer to the architecture specification for details on what each instruction does.
v2q15 __builtin_mips_addq_ph (v2q15, v2q15)
v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15)
q31 __builtin_mips_addq_s_w (q31, q31)
v4i8 __builtin_mips_addu_qb (v4i8, v4i8)
v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8)
v2q15 __builtin_mips_subq_ph (v2q15, v2q15)
v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15)
q31 __builtin_mips_subq_s_w (q31, q31)
v4i8 __builtin_mips_subu_qb (v4i8, v4i8)
v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8)
i32 __builtin_mips_addsc (i32, i32)
i32 __builtin_mips_addwc (i32, i32)
i32 __builtin_mips_modsub (i32, i32)
i32 __builtin_mips_raddu_w_qb (v4i8)
v2q15 __builtin_mips_absq_s_ph (v2q15)
q31 __builtin_mips_absq_s_w (q31)
v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15)
v2q15 __builtin_mips_precrq_ph_w (q31, q31)
v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31)
v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15)
q31 __builtin_mips_preceq_w_phl (v2q15)
q31 __builtin_mips_preceq_w_phr (v2q15)
v2q15 __builtin_mips_precequ_ph_qbl (v4i8)
v2q15 __builtin_mips_precequ_ph_qbr (v4i8)
v2q15 __builtin_mips_precequ_ph_qbla (v4i8)
v2q15 __builtin_mips_precequ_ph_qbra (v4i8)
v2q15 __builtin_mips_preceu_ph_qbl (v4i8)
v2q15 __builtin_mips_preceu_ph_qbr (v4i8)
v2q15 __builtin_mips_preceu_ph_qbla (v4i8)
v2q15 __builtin_mips_preceu_ph_qbra (v4i8)
v4i8 __builtin_mips_shll_qb (v4i8, imm0_7)

Chapter 6: Extensions to the C Language Family

v4i8 __builtin_mips_shll_qb (v4i8, i32)
v2q15 __builtin_mips_shll_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_ph (v2q15, i32)
v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_s_ph (v2q15, i32)
q31 __builtin_mips_shll_s_w (q31, imm0_31)
q31 __builtin_mips_shll_s_w (q31, i32)
v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7)
v4i8 __builtin_mips_shrl_qb (v4i8, i32)
v2q15 __builtin_mips_shra_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_ph (v2q15, i32)
v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_r_ph (v2q15, i32)
q31 __builtin_mips_shra_r_w (q31, imm0_31)
q31 __builtin_mips_shra_r_w (q31, i32)
v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15)
v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15)
v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15)
a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15)
i32 __builtin_mips_bitrev (i32)
i32 __builtin_mips_insv (i32, i32)
v4i8 __builtin_mips_repl_qb (imm0_255)
v4i8 __builtin_mips_repl_qb (i32)
v2q15 __builtin_mips_repl_ph (imm_n512_511)
v2q15 __builtin_mips_repl_ph (i32)
void __builtin_mips_cmpu_eq_qb (v4i8, v4i8)
void __builtin_mips_cmpu_lt_qb (v4i8, v4i8)
void __builtin_mips_cmpu_le_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8)
void __builtin_mips_cmp_eq_ph (v2q15, v2q15)
void __builtin_mips_cmp_lt_ph (v2q15, v2q15)
void __builtin_mips_cmp_le_ph (v2q15, v2q15)
v4i8 __builtin_mips_pick_qb (v4i8, v4i8)
v2q15 __builtin_mips_pick_ph (v2q15, v2q15)
v2q15 __builtin_mips_packrl_ph (v2q15, v2q15)
i32 __builtin_mips_extr_w (a64, imm0_31)
i32 __builtin_mips_extr_w (a64, i32)
i32 __builtin_mips_extr_r_w (a64, imm0_31)
i32 __builtin_mips_extr_s_h (a64, i32)
i32 __builtin_mips_extr_rs_w (a64, imm0_31)
i32 __builtin_mips_extr_rs_w (a64, i32)
i32 __builtin_mips_extr_s_h (a64, imm0_31)

647

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i32 __builtin_mips_extr_r_w (a64, i32)
i32 __builtin_mips_extp (a64, imm0_31)
i32 __builtin_mips_extp (a64, i32)
i32 __builtin_mips_extpdp (a64, imm0_31)
i32 __builtin_mips_extpdp (a64, i32)
a64 __builtin_mips_shilo (a64, imm_n32_31)
a64 __builtin_mips_shilo (a64, i32)
a64 __builtin_mips_mthlip (a64, i32)
void __builtin_mips_wrdsp (i32, imm0_63)
i32 __builtin_mips_rddsp (imm0_63)
i32 __builtin_mips_lbux (void *, i32)
i32 __builtin_mips_lhx (void *, i32)
i32 __builtin_mips_lwx (void *, i32)
a64 __builtin_mips_ldx (void *, i32) [MIPS64 only]
i32 __builtin_mips_bposge32 (void)
a64 __builtin_mips_madd (a64, i32, i32);
a64 __builtin_mips_maddu (a64, ui32, ui32);
a64 __builtin_mips_msub (a64, i32, i32);
a64 __builtin_mips_msubu (a64, ui32, ui32);
a64 __builtin_mips_mult (i32, i32);
a64 __builtin_mips_multu (ui32, ui32);

The following built-in functions map directly to a particular MIPS DSP REV 2 instruction. Please refer to the architecture specification for details on what each instruction does.
v4q7 __builtin_mips_absq_s_qb (v4q7);
v2i16 __builtin_mips_addu_ph (v2i16, v2i16);
v2i16 __builtin_mips_addu_s_ph (v2i16, v2i16);
v4i8 __builtin_mips_adduh_qb (v4i8, v4i8);
v4i8 __builtin_mips_adduh_r_qb (v4i8, v4i8);
i32 __builtin_mips_append (i32, i32, imm0_31);
i32 __builtin_mips_balign (i32, i32, imm0_3);
i32 __builtin_mips_cmpgdu_eq_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgdu_lt_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgdu_le_qb (v4i8, v4i8);
a64 __builtin_mips_dpa_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dps_w_ph (a64, v2i16, v2i16);
v2i16 __builtin_mips_mul_ph (v2i16, v2i16);
v2i16 __builtin_mips_mul_s_ph (v2i16, v2i16);
q31 __builtin_mips_mulq_rs_w (q31, q31);
v2q15 __builtin_mips_mulq_s_ph (v2q15, v2q15);
q31 __builtin_mips_mulq_s_w (q31, q31);
a64 __builtin_mips_mulsa_w_ph (a64, v2i16, v2i16);
v4i8 __builtin_mips_precr_qb_ph (v2i16, v2i16);
v2i16 __builtin_mips_precr_sra_ph_w (i32, i32, imm0_31);
v2i16 __builtin_mips_precr_sra_r_ph_w (i32, i32, imm0_31);
i32 __builtin_mips_prepend (i32, i32, imm0_31);
v4i8 __builtin_mips_shra_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shra_r_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shra_qb (v4i8, i32);
v4i8 __builtin_mips_shra_r_qb (v4i8, i32);
v2i16 __builtin_mips_shrl_ph (v2i16, imm0_15);
v2i16 __builtin_mips_shrl_ph (v2i16, i32);
v2i16 __builtin_mips_subu_ph (v2i16, v2i16);
v2i16 __builtin_mips_subu_s_ph (v2i16, v2i16);
v4i8 __builtin_mips_subuh_qb (v4i8, v4i8);
v4i8 __builtin_mips_subuh_r_qb (v4i8, v4i8);
v2q15 __builtin_mips_addqh_ph (v2q15, v2q15);
v2q15 __builtin_mips_addqh_r_ph (v2q15, v2q15);

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q31 __builtin_mips_addqh_w (q31, q31);
q31 __builtin_mips_addqh_r_w (q31, q31);
v2q15 __builtin_mips_subqh_ph (v2q15, v2q15);
v2q15 __builtin_mips_subqh_r_ph (v2q15, v2q15);
q31 __builtin_mips_subqh_w (q31, q31);
q31 __builtin_mips_subqh_r_w (q31, q31);
a64 __builtin_mips_dpax_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dpsx_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dpaqx_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpaqx_sa_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpsqx_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpsqx_sa_w_ph (a64, v2q15, v2q15);

6.59.14 MIPS Paired-Single Support
The MIPS64 architecture includes a number of instructions that operate on pairs of singleprecision floating-point values. Each pair is packed into a 64-bit floating-point register, with
one element being designated the “upper half” and the other being designated the “lower
half”.
GCC supports paired-single operations using both the generic vector extensions (see
Section 6.50 [Vector Extensions], page 598) and a collection of MIPS-specific built-in functions. Both kinds of support are enabled by the ‘-mpaired-single’ command-line option.
The vector type associated with paired-single values is usually called v2sf. It can be
defined in C as follows:
typedef float v2sf __attribute__ ((vector_size (8)));

v2sf values are initialized in the same way as aggregates. For example:
v2sf a = {1.5, 9.1};
v2sf b;
float e, f;
b = (v2sf) {e, f};

Note: The CPU’s endianness determines which value is stored in the upper half of a
register and which value is stored in the lower half. On little-endian targets, the first value
is the lower one and the second value is the upper one. The opposite order applies to bigendian targets. For example, the code above sets the lower half of a to 1.5 on little-endian
targets and 9.1 on big-endian targets.

6.59.15 MIPS Loongson Built-in Functions
GCC provides intrinsics to access the SIMD instructions provided by the ST Microelectronics Loongson-2E and -2F processors. These intrinsics, available after inclusion of the
loongson.h header file, operate on the following 64-bit vector types:
• uint8x8_t, a vector of eight unsigned 8-bit integers;
• uint16x4_t, a vector of four unsigned 16-bit integers;
• uint32x2_t, a vector of two unsigned 32-bit integers;
• int8x8_t, a vector of eight signed 8-bit integers;
• int16x4_t, a vector of four signed 16-bit integers;
• int32x2_t, a vector of two signed 32-bit integers.
The intrinsics provided are listed below; each is named after the machine instruction
to which it corresponds, with suffixes added as appropriate to distinguish intrinsics that

650

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expand to the same machine instruction yet have different argument types. Refer to the
architecture documentation for a description of the functionality of each instruction.
int16x4_t packsswh (int32x2_t s, int32x2_t t);
int8x8_t packsshb (int16x4_t s, int16x4_t t);
uint8x8_t packushb (uint16x4_t s, uint16x4_t t);
uint32x2_t paddw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t paddh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t paddb_u (uint8x8_t s, uint8x8_t t);
int32x2_t paddw_s (int32x2_t s, int32x2_t t);
int16x4_t paddh_s (int16x4_t s, int16x4_t t);
int8x8_t paddb_s (int8x8_t s, int8x8_t t);
uint64_t paddd_u (uint64_t s, uint64_t t);
int64_t paddd_s (int64_t s, int64_t t);
int16x4_t paddsh (int16x4_t s, int16x4_t t);
int8x8_t paddsb (int8x8_t s, int8x8_t t);
uint16x4_t paddush (uint16x4_t s, uint16x4_t t);
uint8x8_t paddusb (uint8x8_t s, uint8x8_t t);
uint64_t pandn_ud (uint64_t s, uint64_t t);
uint32x2_t pandn_uw (uint32x2_t s, uint32x2_t t);
uint16x4_t pandn_uh (uint16x4_t s, uint16x4_t t);
uint8x8_t pandn_ub (uint8x8_t s, uint8x8_t t);
int64_t pandn_sd (int64_t s, int64_t t);
int32x2_t pandn_sw (int32x2_t s, int32x2_t t);
int16x4_t pandn_sh (int16x4_t s, int16x4_t t);
int8x8_t pandn_sb (int8x8_t s, int8x8_t t);
uint16x4_t pavgh (uint16x4_t s, uint16x4_t t);
uint8x8_t pavgb (uint8x8_t s, uint8x8_t t);
uint32x2_t pcmpeqw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t pcmpeqh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t pcmpeqb_u (uint8x8_t s, uint8x8_t t);
int32x2_t pcmpeqw_s (int32x2_t s, int32x2_t t);
int16x4_t pcmpeqh_s (int16x4_t s, int16x4_t t);
int8x8_t pcmpeqb_s (int8x8_t s, int8x8_t t);
uint32x2_t pcmpgtw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t pcmpgth_u (uint16x4_t s, uint16x4_t t);
uint8x8_t pcmpgtb_u (uint8x8_t s, uint8x8_t t);
int32x2_t pcmpgtw_s (int32x2_t s, int32x2_t t);
int16x4_t pcmpgth_s (int16x4_t s, int16x4_t t);
int8x8_t pcmpgtb_s (int8x8_t s, int8x8_t t);
uint16x4_t pextrh_u (uint16x4_t s, int field);
int16x4_t pextrh_s (int16x4_t s, int field);
uint16x4_t pinsrh_0_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_1_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_2_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_3_u (uint16x4_t s, uint16x4_t t);
int16x4_t pinsrh_0_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_1_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_2_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_3_s (int16x4_t s, int16x4_t t);
int32x2_t pmaddhw (int16x4_t s, int16x4_t t);
int16x4_t pmaxsh (int16x4_t s, int16x4_t t);
uint8x8_t pmaxub (uint8x8_t s, uint8x8_t t);
int16x4_t pminsh (int16x4_t s, int16x4_t t);
uint8x8_t pminub (uint8x8_t s, uint8x8_t t);
uint8x8_t pmovmskb_u (uint8x8_t s);
int8x8_t pmovmskb_s (int8x8_t s);
uint16x4_t pmulhuh (uint16x4_t s, uint16x4_t t);
int16x4_t pmulhh (int16x4_t s, int16x4_t t);

Chapter 6: Extensions to the C Language Family

651

int16x4_t pmullh (int16x4_t s, int16x4_t t);
int64_t pmuluw (uint32x2_t s, uint32x2_t t);
uint8x8_t pasubub (uint8x8_t s, uint8x8_t t);
uint16x4_t biadd (uint8x8_t s);
uint16x4_t psadbh (uint8x8_t s, uint8x8_t t);
uint16x4_t pshufh_u (uint16x4_t dest, uint16x4_t s, uint8_t order);
int16x4_t pshufh_s (int16x4_t dest, int16x4_t s, uint8_t order);
uint16x4_t psllh_u (uint16x4_t s, uint8_t amount);
int16x4_t psllh_s (int16x4_t s, uint8_t amount);
uint32x2_t psllw_u (uint32x2_t s, uint8_t amount);
int32x2_t psllw_s (int32x2_t s, uint8_t amount);
uint16x4_t psrlh_u (uint16x4_t s, uint8_t amount);
int16x4_t psrlh_s (int16x4_t s, uint8_t amount);
uint32x2_t psrlw_u (uint32x2_t s, uint8_t amount);
int32x2_t psrlw_s (int32x2_t s, uint8_t amount);
uint16x4_t psrah_u (uint16x4_t s, uint8_t amount);
int16x4_t psrah_s (int16x4_t s, uint8_t amount);
uint32x2_t psraw_u (uint32x2_t s, uint8_t amount);
int32x2_t psraw_s (int32x2_t s, uint8_t amount);
uint32x2_t psubw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t psubh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t psubb_u (uint8x8_t s, uint8x8_t t);
int32x2_t psubw_s (int32x2_t s, int32x2_t t);
int16x4_t psubh_s (int16x4_t s, int16x4_t t);
int8x8_t psubb_s (int8x8_t s, int8x8_t t);
uint64_t psubd_u (uint64_t s, uint64_t t);
int64_t psubd_s (int64_t s, int64_t t);
int16x4_t psubsh (int16x4_t s, int16x4_t t);
int8x8_t psubsb (int8x8_t s, int8x8_t t);
uint16x4_t psubush (uint16x4_t s, uint16x4_t t);
uint8x8_t psubusb (uint8x8_t s, uint8x8_t t);
uint32x2_t punpckhwd_u (uint32x2_t s, uint32x2_t t);
uint16x4_t punpckhhw_u (uint16x4_t s, uint16x4_t t);
uint8x8_t punpckhbh_u (uint8x8_t s, uint8x8_t t);
int32x2_t punpckhwd_s (int32x2_t s, int32x2_t t);
int16x4_t punpckhhw_s (int16x4_t s, int16x4_t t);
int8x8_t punpckhbh_s (int8x8_t s, int8x8_t t);
uint32x2_t punpcklwd_u (uint32x2_t s, uint32x2_t t);
uint16x4_t punpcklhw_u (uint16x4_t s, uint16x4_t t);
uint8x8_t punpcklbh_u (uint8x8_t s, uint8x8_t t);
int32x2_t punpcklwd_s (int32x2_t s, int32x2_t t);
int16x4_t punpcklhw_s (int16x4_t s, int16x4_t t);
int8x8_t punpcklbh_s (int8x8_t s, int8x8_t t);

6.59.15.1 Paired-Single Arithmetic
The table below lists the v2sf operations for which hardware support exists. a, b and c are
v2sf values and x is an integral value.
C code
a+b
a-b
-a
a*b
a*b+c
a*b-c
-(a * b + c)

MIPS instruction
add.ps
sub.ps
neg.ps
mul.ps
madd.ps
msub.ps
nmadd.ps

652

Using the GNU Compiler Collection (GCC)

-(a * b - c)
x?a:b

nmsub.ps
movn.ps/movz.ps

Note that the multiply-accumulate instructions can be disabled using the command-line
option -mno-fused-madd.

6.59.15.2 Paired-Single Built-in Functions
The following paired-single functions map directly to a particular MIPS instruction. Please
refer to the architecture specification for details on what each instruction does.
v2sf __builtin_mips_pll_ps (v2sf, v2sf)
Pair lower lower (pll.ps).
v2sf __builtin_mips_pul_ps (v2sf, v2sf)
Pair upper lower (pul.ps).
v2sf __builtin_mips_plu_ps (v2sf, v2sf)
Pair lower upper (plu.ps).
v2sf __builtin_mips_puu_ps (v2sf, v2sf)
Pair upper upper (puu.ps).
v2sf __builtin_mips_cvt_ps_s (float, float)
Convert pair to paired single (cvt.ps.s).
float __builtin_mips_cvt_s_pl (v2sf)
Convert pair lower to single (cvt.s.pl).
float __builtin_mips_cvt_s_pu (v2sf)
Convert pair upper to single (cvt.s.pu).
v2sf __builtin_mips_abs_ps (v2sf)
Absolute value (abs.ps).
v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int)
Align variable (alnv.ps).
Note: The value of the third parameter must be 0 or 4 modulo 8, otherwise the
result is unpredictable. Please read the instruction description for details.
The following multi-instruction functions are also available. In each case, cond can be
any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq,
ngl, lt, nge, le or ngt.
v2sf __builtin_mips_movt_c_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)
v2sf __builtin_mips_movf_c_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)
Conditional move based on floating-point comparison (c.cond.ps,
movt.ps/movf.ps).
The movt functions return the value x computed by:
c.cond.ps cc,a,b
mov.ps x,c
movt.ps x,d,cc

The movf functions are similar but use movf.ps instead of movt.ps.

Chapter 6: Extensions to the C Language Family

653

int __builtin_mips_upper_c_cond_ps (v2sf a, v2sf b)
int __builtin_mips_lower_c_cond_ps (v2sf a, v2sf b)
Comparison of two paired-single values (c.cond.ps, bc1t/bc1f).
These functions compare a and b using c.cond.ps and return either the upper
or lower half of the result. For example:
v2sf a, b;
if (__builtin_mips_upper_c_eq_ps (a, b))
upper_halves_are_equal ();
else
upper_halves_are_unequal ();
if (__builtin_mips_lower_c_eq_ps (a, b))
lower_halves_are_equal ();
else
lower_halves_are_unequal ();

6.59.15.3 MIPS-3D Built-in Functions
The MIPS-3D Application-Specific Extension (ASE) includes additional paired-single instructions that are designed to improve the performance of 3D graphics operations. Support
for these instructions is controlled by the ‘-mips3d’ command-line option.
The functions listed below map directly to a particular MIPS-3D instruction. Please refer
to the architecture specification for more details on what each instruction does.
v2sf __builtin_mips_addr_ps (v2sf, v2sf)
Reduction add (addr.ps).
v2sf __builtin_mips_mulr_ps (v2sf, v2sf)
Reduction multiply (mulr.ps).
v2sf __builtin_mips_cvt_pw_ps (v2sf)
Convert paired single to paired word (cvt.pw.ps).
v2sf __builtin_mips_cvt_ps_pw (v2sf)
Convert paired word to paired single (cvt.ps.pw).
float __builtin_mips_recip1_s (float)
double __builtin_mips_recip1_d (double)
v2sf __builtin_mips_recip1_ps (v2sf)
Reduced-precision reciprocal (sequence step 1) (recip1.fmt).
float __builtin_mips_recip2_s (float, float)
double __builtin_mips_recip2_d (double, double)
v2sf __builtin_mips_recip2_ps (v2sf, v2sf)
Reduced-precision reciprocal (sequence step 2) (recip2.fmt).
float __builtin_mips_rsqrt1_s (float)
double __builtin_mips_rsqrt1_d (double)
v2sf __builtin_mips_rsqrt1_ps (v2sf)
Reduced-precision reciprocal square root (sequence step 1) (rsqrt1.fmt).
float __builtin_mips_rsqrt2_s (float, float)
double __builtin_mips_rsqrt2_d (double, double)
v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf)
Reduced-precision reciprocal square root (sequence step 2) (rsqrt2.fmt).

654

Using the GNU Compiler Collection (GCC)

The following multi-instruction functions are also available. In each case, cond can be
any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq,
ngl, lt, nge, le or ngt.
int __builtin_mips_cabs_cond_s (float a, float b)
int __builtin_mips_cabs_cond_d (double a, double b)
Absolute comparison of two scalar values (cabs.cond.fmt, bc1t/bc1f).
These functions compare a and b using cabs.cond.s or cabs.cond.d and return the result as a boolean value. For example:
float a, b;
if (__builtin_mips_cabs_eq_s (a, b))
true ();
else
false ();

int __builtin_mips_upper_cabs_cond_ps (v2sf a, v2sf b)
int __builtin_mips_lower_cabs_cond_ps (v2sf a, v2sf b)
Absolute comparison of two paired-single values (cabs.cond.ps, bc1t/bc1f).
These functions compare a and b using cabs.cond.ps and return either the
upper or lower half of the result. For example:
v2sf a, b;
if (__builtin_mips_upper_cabs_eq_ps (a, b))
upper_halves_are_equal ();
else
upper_halves_are_unequal ();
if (__builtin_mips_lower_cabs_eq_ps (a, b))
lower_halves_are_equal ();
else
lower_halves_are_unequal ();

v2sf __builtin_mips_movt_cabs_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)
v2sf __builtin_mips_movf_cabs_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)
Conditional move based on absolute comparison (cabs.cond.ps,
movt.ps/movf.ps).
The movt functions return the value x computed by:
cabs.cond.ps cc,a,b
mov.ps x,c
movt.ps x,d,cc

The movf functions are similar but use movf.ps instead of movt.ps.
int
int
int
int

__builtin_mips_any_c_cond_ps (v2sf a, v2sf b)
__builtin_mips_all_c_cond_ps (v2sf a, v2sf b)
__builtin_mips_any_cabs_cond_ps (v2sf a, v2sf b)
__builtin_mips_all_cabs_cond_ps (v2sf a, v2sf b)
Comparison of two paired-single values (c.cond.ps/cabs.cond.ps,
bc1any2t/bc1any2f).
These functions compare a and b using c.cond.ps or cabs.cond.ps. The any
forms return true if either result is true and the all forms return true if both
results are true. For example:
v2sf a, b;

Chapter 6: Extensions to the C Language Family

655

if (__builtin_mips_any_c_eq_ps (a, b))
one_is_true ();
else
both_are_false ();
if (__builtin_mips_all_c_eq_ps (a, b))
both_are_true ();
else
one_is_false ();

int
int
int
int

__builtin_mips_any_c_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)
__builtin_mips_all_c_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)
__builtin_mips_any_cabs_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)
__builtin_mips_all_cabs_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)
Comparison of four paired-single values (c.cond.ps/cabs.cond.ps,
bc1any4t/bc1any4f).
These functions use c.cond.ps or cabs.cond.ps to compare a with b and to
compare c with d. The any forms return true if any of the four results are true
and the all forms return true if all four results are true. For example:
v2sf a, b, c, d;
if (__builtin_mips_any_c_eq_4s (a, b, c, d))
some_are_true ();
else
all_are_false ();
if (__builtin_mips_all_c_eq_4s (a, b, c, d))
all_are_true ();
else
some_are_false ();

6.59.16 MIPS SIMD Architecture (MSA) Support
GCC provides intrinsics to access the SIMD instructions provided by the MSA MIPS SIMD
Architecture. The interface is made available by including  and using ‘-mmsa
-mhard-float -mfp64 -mnan=2008’. For each __builtin_msa_*, there is a shortened name
of the intrinsic, __msa_*.
MSA implements 128-bit wide vector registers, operating on 8-, 16-, 32- and 64-bit integer,
16- and 32-bit fixed-point, or 32- and 64-bit floating point data elements. The following
vectors typedefs are included in msa.h:
• v16i8, a vector of sixteen signed 8-bit integers;
• v16u8, a vector of sixteen unsigned 8-bit integers;
• v8i16, a vector of eight signed 16-bit integers;
• v8u16, a vector of eight unsigned 16-bit integers;
• v4i32, a vector of four signed 32-bit integers;
• v4u32, a vector of four unsigned 32-bit integers;
• v2i64, a vector of two signed 64-bit integers;
• v2u64, a vector of two unsigned 64-bit integers;
• v4f32, a vector of four 32-bit floats;
• v2f64, a vector of two 64-bit doubles.

656

Using the GNU Compiler Collection (GCC)

Instructions and corresponding built-ins may have additional restrictions and/or input/output values manipulated:
• imm0_1, an integer literal in range 0 to 1;
• imm0_3, an integer literal in range 0 to 3;
• imm0_7, an integer literal in range 0 to 7;
• imm0_15, an integer literal in range 0 to 15;
• imm0_31, an integer literal in range 0 to 31;
• imm0_63, an integer literal in range 0 to 63;
• imm0_255, an integer literal in range 0 to 255;
• imm_n16_15, an integer literal in range -16 to 15;
• imm_n512_511, an integer literal in range -512 to 511;
• imm_n1024_1022, an integer literal in range -512 to 511 left shifted by 1 bit, i.e., -1024,
-1022, . . . , 1020, 1022;
• imm_n2048_2044, an integer literal in range -512 to 511 left shifted by 2 bits, i.e., -2048,
-2044, . . . , 2040, 2044;
• imm_n4096_4088, an integer literal in range -512 to 511 left shifted by 3 bits, i.e., -4096,
-4088, . . . , 4080, 4088;
• imm1_4, an integer literal in range 1 to 4;
• i32, i64, u32, u64, f32, f64, defined as follows:
{
typedef int i32;
#if __LONG_MAX__ == __LONG_LONG_MAX__
typedef long i64;
#else
typedef long long i64;
#endif
typedef unsigned
#if __LONG_MAX__
typedef unsigned
#else
typedef unsigned
#endif

int u32;
== __LONG_LONG_MAX__
long u64;
long long u64;

typedef double f64;
typedef float f32;
}

6.59.16.1 MIPS SIMD Architecture Built-in Functions
The intrinsics provided are listed below; each is named after the machine instruction.
v16i8
v8i16
v4i32
v2i64

__builtin_msa_add_a_b
__builtin_msa_add_a_h
__builtin_msa_add_a_w
__builtin_msa_add_a_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_adds_a_b
__builtin_msa_adds_a_h
__builtin_msa_adds_a_w
__builtin_msa_adds_a_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,
(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);
v16i8);
v8i16);
v4i32);
v2i64);

Chapter 6: Extensions to the C Language Family

v16i8
v8i16
v4i32
v2i64

__builtin_msa_adds_s_b
__builtin_msa_adds_s_h
__builtin_msa_adds_s_w
__builtin_msa_adds_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_adds_u_b
__builtin_msa_adds_u_h
__builtin_msa_adds_u_w
__builtin_msa_adds_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_addv_b
__builtin_msa_addv_h
__builtin_msa_addv_w
__builtin_msa_addv_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_addvi_b
__builtin_msa_addvi_h
__builtin_msa_addvi_w
__builtin_msa_addvi_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_31);
imm0_31);
imm0_31);
imm0_31);

v16u8 __builtin_msa_and_v (v16u8, v16u8);
v16u8 __builtin_msa_andi_b (v16u8, imm0_255);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_asub_s_b
__builtin_msa_asub_s_h
__builtin_msa_asub_s_w
__builtin_msa_asub_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_asub_u_b
__builtin_msa_asub_u_h
__builtin_msa_asub_u_w
__builtin_msa_asub_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_ave_s_b
__builtin_msa_ave_s_h
__builtin_msa_ave_s_w
__builtin_msa_ave_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_ave_u_b
__builtin_msa_ave_u_h
__builtin_msa_ave_u_w
__builtin_msa_ave_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_aver_s_b
__builtin_msa_aver_s_h
__builtin_msa_aver_s_w
__builtin_msa_aver_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_aver_u_b
__builtin_msa_aver_u_h
__builtin_msa_aver_u_w
__builtin_msa_aver_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16u8 __builtin_msa_bclr_b (v16u8, v16u8);
v8u16 __builtin_msa_bclr_h (v8u16, v8u16);
v4u32 __builtin_msa_bclr_w (v4u32, v4u32);

657

658

Using the GNU Compiler Collection (GCC)

v2u64 __builtin_msa_bclr_d (v2u64, v2u64);
v16u8
v8u16
v4u32
v2u64

__builtin_msa_bclri_b
__builtin_msa_bclri_h
__builtin_msa_bclri_w
__builtin_msa_bclri_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_binsl_b
__builtin_msa_binsl_h
__builtin_msa_binsl_w
__builtin_msa_binsl_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8,
v8u16,
v4u32,
v2u64,

v16u8
v8u16
v4u32
v2u64

__builtin_msa_binsli_b
__builtin_msa_binsli_h
__builtin_msa_binsli_w
__builtin_msa_binsli_d

v16u8
v8u16
v4u32
v2u64

__builtin_msa_binsr_b
__builtin_msa_binsr_h
__builtin_msa_binsr_w
__builtin_msa_binsr_d

v16u8
v8u16
v4u32
v2u64

__builtin_msa_binsri_b
__builtin_msa_binsri_h
__builtin_msa_binsri_w
__builtin_msa_binsri_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,
(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8,
v8u16,
v4u32,
v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16u8,
v8u16,
v4u32,
v2u64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8,
v8u16,
v4u32,
v2u64,

v16u8);
v8u16);
v4u32);
v2u64);
imm0_7);
imm0_15);
imm0_31);
imm0_63);

v16u8 __builtin_msa_bmnz_v (v16u8, v16u8, v16u8);
v16u8 __builtin_msa_bmnzi_b (v16u8, v16u8, imm0_255);
v16u8 __builtin_msa_bmz_v (v16u8, v16u8, v16u8);
v16u8 __builtin_msa_bmzi_b (v16u8, v16u8, imm0_255);
v16u8
v8u16
v4u32
v2u64

__builtin_msa_bneg_b
__builtin_msa_bneg_h
__builtin_msa_bneg_w
__builtin_msa_bneg_d

v16u8
v8u16
v4u32
v2u64

__builtin_msa_bnegi_b
__builtin_msa_bnegi_h
__builtin_msa_bnegi_w
__builtin_msa_bnegi_d

i32
i32
i32
i32

__builtin_msa_bnz_b
__builtin_msa_bnz_h
__builtin_msa_bnz_w
__builtin_msa_bnz_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,
(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);
imm0_7);
imm0_15);
imm0_31);
imm0_63);

(v16u8);
(v8u16);
(v4u32);
(v2u64);

i32 __builtin_msa_bnz_v (v16u8);
v16u8 __builtin_msa_bsel_v (v16u8, v16u8, v16u8);
v16u8 __builtin_msa_bseli_b (v16u8, v16u8, imm0_255);
v16u8 __builtin_msa_bset_b (v16u8, v16u8);
v8u16 __builtin_msa_bset_h (v8u16, v8u16);

Chapter 6: Extensions to the C Language Family

v4u32 __builtin_msa_bset_w (v4u32, v4u32);
v2u64 __builtin_msa_bset_d (v2u64, v2u64);
v16u8
v8u16
v4u32
v2u64
i32
i32
i32
i32

__builtin_msa_bseti_b
__builtin_msa_bseti_h
__builtin_msa_bseti_w
__builtin_msa_bseti_d

__builtin_msa_bz_b
__builtin_msa_bz_h
__builtin_msa_bz_w
__builtin_msa_bz_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

(v16u8);
(v8u16);
(v4u32);
(v2u64);

i32 __builtin_msa_bz_v (v16u8);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_ceq_b
__builtin_msa_ceq_h
__builtin_msa_ceq_w
__builtin_msa_ceq_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_ceqi_b
__builtin_msa_ceqi_h
__builtin_msa_ceqi_w
__builtin_msa_ceqi_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm_n16_15);
imm_n16_15);
imm_n16_15);
imm_n16_15);

i32 __builtin_msa_cfcmsa (imm0_31);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_cle_s_b
__builtin_msa_cle_s_h
__builtin_msa_cle_s_w
__builtin_msa_cle_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_cle_u_b
__builtin_msa_cle_u_h
__builtin_msa_cle_u_w
__builtin_msa_cle_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_clei_s_b
__builtin_msa_clei_s_h
__builtin_msa_clei_s_w
__builtin_msa_clei_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm_n16_15);
imm_n16_15);
imm_n16_15);
imm_n16_15);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_clei_u_b
__builtin_msa_clei_u_h
__builtin_msa_clei_u_w
__builtin_msa_clei_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

imm0_31);
imm0_31);
imm0_31);
imm0_31);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_clt_s_b
__builtin_msa_clt_s_h
__builtin_msa_clt_s_w
__builtin_msa_clt_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_clt_u_b
__builtin_msa_clt_u_h
__builtin_msa_clt_u_w
__builtin_msa_clt_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16i8 __builtin_msa_clti_s_b (v16i8, imm_n16_15);

659

660

Using the GNU Compiler Collection (GCC)

v8i16 __builtin_msa_clti_s_h (v8i16, imm_n16_15);
v4i32 __builtin_msa_clti_s_w (v4i32, imm_n16_15);
v2i64 __builtin_msa_clti_s_d (v2i64, imm_n16_15);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_clti_u_b
__builtin_msa_clti_u_h
__builtin_msa_clti_u_w
__builtin_msa_clti_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

imm0_31);
imm0_31);
imm0_31);
imm0_31);

i32
i32
i32
i64

__builtin_msa_copy_s_b
__builtin_msa_copy_s_h
__builtin_msa_copy_s_w
__builtin_msa_copy_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_15);
imm0_7);
imm0_3);
imm0_1);

u32
u32
u32
u64

__builtin_msa_copy_u_b
__builtin_msa_copy_u_h
__builtin_msa_copy_u_w
__builtin_msa_copy_u_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_15);
imm0_7);
imm0_3);
imm0_1);

void __builtin_msa_ctcmsa (imm0_31, i32);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_div_s_b
__builtin_msa_div_s_h
__builtin_msa_div_s_w
__builtin_msa_div_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_div_u_b
__builtin_msa_div_u_h
__builtin_msa_div_u_w
__builtin_msa_div_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v8i16 __builtin_msa_dotp_s_h (v16i8, v16i8);
v4i32 __builtin_msa_dotp_s_w (v8i16, v8i16);
v2i64 __builtin_msa_dotp_s_d (v4i32, v4i32);
v8u16 __builtin_msa_dotp_u_h (v16u8, v16u8);
v4u32 __builtin_msa_dotp_u_w (v8u16, v8u16);
v2u64 __builtin_msa_dotp_u_d (v4u32, v4u32);
v8i16 __builtin_msa_dpadd_s_h (v8i16, v16i8, v16i8);
v4i32 __builtin_msa_dpadd_s_w (v4i32, v8i16, v8i16);
v2i64 __builtin_msa_dpadd_s_d (v2i64, v4i32, v4i32);
v8u16 __builtin_msa_dpadd_u_h (v8u16, v16u8, v16u8);
v4u32 __builtin_msa_dpadd_u_w (v4u32, v8u16, v8u16);
v2u64 __builtin_msa_dpadd_u_d (v2u64, v4u32, v4u32);
v8i16 __builtin_msa_dpsub_s_h (v8i16, v16i8, v16i8);
v4i32 __builtin_msa_dpsub_s_w (v4i32, v8i16, v8i16);
v2i64 __builtin_msa_dpsub_s_d (v2i64, v4i32, v4i32);
v8i16 __builtin_msa_dpsub_u_h (v8i16, v16u8, v16u8);
v4i32 __builtin_msa_dpsub_u_w (v4i32, v8u16, v8u16);
v2i64 __builtin_msa_dpsub_u_d (v2i64, v4u32, v4u32);
v4f32 __builtin_msa_fadd_w (v4f32, v4f32);
v2f64 __builtin_msa_fadd_d (v2f64, v2f64);

Chapter 6: Extensions to the C Language Family

v4i32 __builtin_msa_fcaf_w (v4f32, v4f32);
v2i64 __builtin_msa_fcaf_d (v2f64, v2f64);
v4i32 __builtin_msa_fceq_w (v4f32, v4f32);
v2i64 __builtin_msa_fceq_d (v2f64, v2f64);
v4i32 __builtin_msa_fclass_w (v4f32);
v2i64 __builtin_msa_fclass_d (v2f64);
v4i32 __builtin_msa_fcle_w (v4f32, v4f32);
v2i64 __builtin_msa_fcle_d (v2f64, v2f64);
v4i32 __builtin_msa_fclt_w (v4f32, v4f32);
v2i64 __builtin_msa_fclt_d (v2f64, v2f64);
v4i32 __builtin_msa_fcne_w (v4f32, v4f32);
v2i64 __builtin_msa_fcne_d (v2f64, v2f64);
v4i32 __builtin_msa_fcor_w (v4f32, v4f32);
v2i64 __builtin_msa_fcor_d (v2f64, v2f64);
v4i32 __builtin_msa_fcueq_w (v4f32, v4f32);
v2i64 __builtin_msa_fcueq_d (v2f64, v2f64);
v4i32 __builtin_msa_fcule_w (v4f32, v4f32);
v2i64 __builtin_msa_fcule_d (v2f64, v2f64);
v4i32 __builtin_msa_fcult_w (v4f32, v4f32);
v2i64 __builtin_msa_fcult_d (v2f64, v2f64);
v4i32 __builtin_msa_fcun_w (v4f32, v4f32);
v2i64 __builtin_msa_fcun_d (v2f64, v2f64);
v4i32 __builtin_msa_fcune_w (v4f32, v4f32);
v2i64 __builtin_msa_fcune_d (v2f64, v2f64);
v4f32 __builtin_msa_fdiv_w (v4f32, v4f32);
v2f64 __builtin_msa_fdiv_d (v2f64, v2f64);
v8i16 __builtin_msa_fexdo_h (v4f32, v4f32);
v4f32 __builtin_msa_fexdo_w (v2f64, v2f64);
v4f32 __builtin_msa_fexp2_w (v4f32, v4i32);
v2f64 __builtin_msa_fexp2_d (v2f64, v2i64);
v4f32 __builtin_msa_fexupl_w (v8i16);
v2f64 __builtin_msa_fexupl_d (v4f32);
v4f32 __builtin_msa_fexupr_w (v8i16);
v2f64 __builtin_msa_fexupr_d (v4f32);
v4f32 __builtin_msa_ffint_s_w (v4i32);
v2f64 __builtin_msa_ffint_s_d (v2i64);
v4f32 __builtin_msa_ffint_u_w (v4u32);
v2f64 __builtin_msa_ffint_u_d (v2u64);
v4f32 __builtin_msa_ffql_w (v8i16);

661

662

Using the GNU Compiler Collection (GCC)

v2f64 __builtin_msa_ffql_d (v4i32);
v4f32 __builtin_msa_ffqr_w (v8i16);
v2f64 __builtin_msa_ffqr_d (v4i32);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_fill_b
__builtin_msa_fill_h
__builtin_msa_fill_w
__builtin_msa_fill_d

(i32);
(i32);
(i32);
(i64);

v4f32 __builtin_msa_flog2_w (v4f32);
v2f64 __builtin_msa_flog2_d (v2f64);
v4f32 __builtin_msa_fmadd_w (v4f32, v4f32, v4f32);
v2f64 __builtin_msa_fmadd_d (v2f64, v2f64, v2f64);
v4f32 __builtin_msa_fmax_w (v4f32, v4f32);
v2f64 __builtin_msa_fmax_d (v2f64, v2f64);
v4f32 __builtin_msa_fmax_a_w (v4f32, v4f32);
v2f64 __builtin_msa_fmax_a_d (v2f64, v2f64);
v4f32 __builtin_msa_fmin_w (v4f32, v4f32);
v2f64 __builtin_msa_fmin_d (v2f64, v2f64);
v4f32 __builtin_msa_fmin_a_w (v4f32, v4f32);
v2f64 __builtin_msa_fmin_a_d (v2f64, v2f64);
v4f32 __builtin_msa_fmsub_w (v4f32, v4f32, v4f32);
v2f64 __builtin_msa_fmsub_d (v2f64, v2f64, v2f64);
v4f32 __builtin_msa_fmul_w (v4f32, v4f32);
v2f64 __builtin_msa_fmul_d (v2f64, v2f64);
v4f32 __builtin_msa_frint_w (v4f32);
v2f64 __builtin_msa_frint_d (v2f64);
v4f32 __builtin_msa_frcp_w (v4f32);
v2f64 __builtin_msa_frcp_d (v2f64);
v4f32 __builtin_msa_frsqrt_w (v4f32);
v2f64 __builtin_msa_frsqrt_d (v2f64);
v4i32 __builtin_msa_fsaf_w (v4f32, v4f32);
v2i64 __builtin_msa_fsaf_d (v2f64, v2f64);
v4i32 __builtin_msa_fseq_w (v4f32, v4f32);
v2i64 __builtin_msa_fseq_d (v2f64, v2f64);
v4i32 __builtin_msa_fsle_w (v4f32, v4f32);
v2i64 __builtin_msa_fsle_d (v2f64, v2f64);
v4i32 __builtin_msa_fslt_w (v4f32, v4f32);
v2i64 __builtin_msa_fslt_d (v2f64, v2f64);
v4i32 __builtin_msa_fsne_w (v4f32, v4f32);
v2i64 __builtin_msa_fsne_d (v2f64, v2f64);

Chapter 6: Extensions to the C Language Family

v4i32 __builtin_msa_fsor_w (v4f32, v4f32);
v2i64 __builtin_msa_fsor_d (v2f64, v2f64);
v4f32 __builtin_msa_fsqrt_w (v4f32);
v2f64 __builtin_msa_fsqrt_d (v2f64);
v4f32 __builtin_msa_fsub_w (v4f32, v4f32);
v2f64 __builtin_msa_fsub_d (v2f64, v2f64);
v4i32 __builtin_msa_fsueq_w (v4f32, v4f32);
v2i64 __builtin_msa_fsueq_d (v2f64, v2f64);
v4i32 __builtin_msa_fsule_w (v4f32, v4f32);
v2i64 __builtin_msa_fsule_d (v2f64, v2f64);
v4i32 __builtin_msa_fsult_w (v4f32, v4f32);
v2i64 __builtin_msa_fsult_d (v2f64, v2f64);
v4i32 __builtin_msa_fsun_w (v4f32, v4f32);
v2i64 __builtin_msa_fsun_d (v2f64, v2f64);
v4i32 __builtin_msa_fsune_w (v4f32, v4f32);
v2i64 __builtin_msa_fsune_d (v2f64, v2f64);
v4i32 __builtin_msa_ftint_s_w (v4f32);
v2i64 __builtin_msa_ftint_s_d (v2f64);
v4u32 __builtin_msa_ftint_u_w (v4f32);
v2u64 __builtin_msa_ftint_u_d (v2f64);
v8i16 __builtin_msa_ftq_h (v4f32, v4f32);
v4i32 __builtin_msa_ftq_w (v2f64, v2f64);
v4i32 __builtin_msa_ftrunc_s_w (v4f32);
v2i64 __builtin_msa_ftrunc_s_d (v2f64);
v4u32 __builtin_msa_ftrunc_u_w (v4f32);
v2u64 __builtin_msa_ftrunc_u_d (v2f64);
v8i16 __builtin_msa_hadd_s_h (v16i8, v16i8);
v4i32 __builtin_msa_hadd_s_w (v8i16, v8i16);
v2i64 __builtin_msa_hadd_s_d (v4i32, v4i32);
v8u16 __builtin_msa_hadd_u_h (v16u8, v16u8);
v4u32 __builtin_msa_hadd_u_w (v8u16, v8u16);
v2u64 __builtin_msa_hadd_u_d (v4u32, v4u32);
v8i16 __builtin_msa_hsub_s_h (v16i8, v16i8);
v4i32 __builtin_msa_hsub_s_w (v8i16, v8i16);
v2i64 __builtin_msa_hsub_s_d (v4i32, v4i32);
v8i16 __builtin_msa_hsub_u_h (v16u8, v16u8);
v4i32 __builtin_msa_hsub_u_w (v8u16, v8u16);
v2i64 __builtin_msa_hsub_u_d (v4u32, v4u32);
v16i8 __builtin_msa_ilvev_b (v16i8, v16i8);
v8i16 __builtin_msa_ilvev_h (v8i16, v8i16);
v4i32 __builtin_msa_ilvev_w (v4i32, v4i32);

663

664

Using the GNU Compiler Collection (GCC)

v2i64 __builtin_msa_ilvev_d (v2i64, v2i64);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_ilvl_b
__builtin_msa_ilvl_h
__builtin_msa_ilvl_w
__builtin_msa_ilvl_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8
v8i16
v4i32
v2i64

__builtin_msa_ilvod_b
__builtin_msa_ilvod_h
__builtin_msa_ilvod_w
__builtin_msa_ilvod_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_ilvr_b
__builtin_msa_ilvr_h
__builtin_msa_ilvr_w
__builtin_msa_ilvr_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_insert_b
__builtin_msa_insert_h
__builtin_msa_insert_w
__builtin_msa_insert_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_insve_b
__builtin_msa_insve_h
__builtin_msa_insve_w
__builtin_msa_insve_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_ld_b
__builtin_msa_ld_h
__builtin_msa_ld_w
__builtin_msa_ld_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_ldi_b
__builtin_msa_ldi_h
__builtin_msa_ldi_w
__builtin_msa_ldi_d

v16i8);
v8i16);
v4i32);
v2i64);

(v16i8,
(v8i16,
(v4i32,
(v2i64,
(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);
v16i8);
v8i16);
v4i32);
v2i64);

(v16i8,
(v8i16,
(v4i32,
(v2i64,
(v16i8,
(v8i16,
(v4i32,
(v2i64,

(void
(void
(void
(void

*,
*,
*,
*,

imm0_15, i32);
imm0_7, i32);
imm0_3, i32);
imm0_1, i64);
imm0_15, v16i8);
imm0_7, v8i16);
imm0_3, v4i32);
imm0_1, v2i64);

imm_n512_511);
imm_n1024_1022);
imm_n2048_2044);
imm_n4096_4088);

(imm_n512_511);
(imm_n512_511);
(imm_n512_511);
(imm_n512_511);

v8i16 __builtin_msa_madd_q_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_madd_q_w (v4i32, v4i32, v4i32);
v8i16 __builtin_msa_maddr_q_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_maddr_q_w (v4i32, v4i32, v4i32);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_maddv_b
__builtin_msa_maddv_h
__builtin_msa_maddv_w
__builtin_msa_maddv_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8,
v8i16,
v4i32,
v2i64,

v16i8
v8i16
v4i32
v2i64

__builtin_msa_max_a_b
__builtin_msa_max_a_h
__builtin_msa_max_a_w
__builtin_msa_max_a_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_max_s_b
__builtin_msa_max_s_h
__builtin_msa_max_s_w
__builtin_msa_max_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8);
v8i16);
v4i32);
v2i64);

Chapter 6: Extensions to the C Language Family

v16u8
v8u16
v4u32
v2u64

__builtin_msa_max_u_b
__builtin_msa_max_u_h
__builtin_msa_max_u_w
__builtin_msa_max_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_maxi_s_b
__builtin_msa_maxi_s_h
__builtin_msa_maxi_s_w
__builtin_msa_maxi_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm_n16_15);
imm_n16_15);
imm_n16_15);
imm_n16_15);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_maxi_u_b
__builtin_msa_maxi_u_h
__builtin_msa_maxi_u_w
__builtin_msa_maxi_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

imm0_31);
imm0_31);
imm0_31);
imm0_31);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_min_a_b
__builtin_msa_min_a_h
__builtin_msa_min_a_w
__builtin_msa_min_a_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_min_s_b
__builtin_msa_min_s_h
__builtin_msa_min_s_w
__builtin_msa_min_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_min_u_b
__builtin_msa_min_u_h
__builtin_msa_min_u_w
__builtin_msa_min_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_mini_s_b
__builtin_msa_mini_s_h
__builtin_msa_mini_s_w
__builtin_msa_mini_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm_n16_15);
imm_n16_15);
imm_n16_15);
imm_n16_15);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_mini_u_b
__builtin_msa_mini_u_h
__builtin_msa_mini_u_w
__builtin_msa_mini_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

imm0_31);
imm0_31);
imm0_31);
imm0_31);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_mod_s_b
__builtin_msa_mod_s_h
__builtin_msa_mod_s_w
__builtin_msa_mod_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_mod_u_b
__builtin_msa_mod_u_h
__builtin_msa_mod_u_w
__builtin_msa_mod_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16i8 __builtin_msa_move_v (v16i8);
v8i16 __builtin_msa_msub_q_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_msub_q_w (v4i32, v4i32, v4i32);
v8i16 __builtin_msa_msubr_q_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_msubr_q_w (v4i32, v4i32, v4i32);

665

666

Using the GNU Compiler Collection (GCC)

v16i8
v8i16
v4i32
v2i64

__builtin_msa_msubv_b
__builtin_msa_msubv_h
__builtin_msa_msubv_w
__builtin_msa_msubv_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8,
v8i16,
v4i32,
v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v8i16 __builtin_msa_mul_q_h (v8i16, v8i16);
v4i32 __builtin_msa_mul_q_w (v4i32, v4i32);
v8i16 __builtin_msa_mulr_q_h (v8i16, v8i16);
v4i32 __builtin_msa_mulr_q_w (v4i32, v4i32);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_mulv_b
__builtin_msa_mulv_h
__builtin_msa_mulv_w
__builtin_msa_mulv_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8
v8i16
v4i32
v2i64

__builtin_msa_nloc_b
__builtin_msa_nloc_h
__builtin_msa_nloc_w
__builtin_msa_nloc_d

(v16i8);
(v8i16);
(v4i32);
(v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_nlzc_b
__builtin_msa_nlzc_h
__builtin_msa_nlzc_w
__builtin_msa_nlzc_d

(v16i8);
(v8i16);
(v4i32);
(v2i64);

v16i8);
v8i16);
v4i32);
v2i64);

v16u8 __builtin_msa_nor_v (v16u8, v16u8);
v16u8 __builtin_msa_nori_b (v16u8, imm0_255);
v16u8 __builtin_msa_or_v (v16u8, v16u8);
v16u8 __builtin_msa_ori_b (v16u8, imm0_255);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_pckev_b
__builtin_msa_pckev_h
__builtin_msa_pckev_w
__builtin_msa_pckev_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_pckod_b
__builtin_msa_pckod_h
__builtin_msa_pckod_w
__builtin_msa_pckod_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_pcnt_b
__builtin_msa_pcnt_h
__builtin_msa_pcnt_w
__builtin_msa_pcnt_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_sat_s_b
__builtin_msa_sat_s_h
__builtin_msa_sat_s_w
__builtin_msa_sat_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_sat_u_b
__builtin_msa_sat_u_h
__builtin_msa_sat_u_w
__builtin_msa_sat_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

(v16i8);
(v8i16);
(v4i32);
(v2i64);

Chapter 6: Extensions to the C Language Family

v16i8 __builtin_msa_shf_b (v16i8, imm0_255);
v8i16 __builtin_msa_shf_h (v8i16, imm0_255);
v4i32 __builtin_msa_shf_w (v4i32, imm0_255);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_sld_b
__builtin_msa_sld_h
__builtin_msa_sld_w
__builtin_msa_sld_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8,
v8i16,
v4i32,
v2i64,

v16i8
v8i16
v4i32
v2i64

__builtin_msa_sldi_b
__builtin_msa_sldi_h
__builtin_msa_sldi_w
__builtin_msa_sldi_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_sll_b
__builtin_msa_sll_h
__builtin_msa_sll_w
__builtin_msa_sll_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_slli_b
__builtin_msa_slli_h
__builtin_msa_slli_w
__builtin_msa_slli_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_splat_b
__builtin_msa_splat_h
__builtin_msa_splat_w
__builtin_msa_splat_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_splati_b
__builtin_msa_splati_h
__builtin_msa_splati_w
__builtin_msa_splati_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_sra_b
__builtin_msa_sra_h
__builtin_msa_sra_w
__builtin_msa_sra_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_srai_b
__builtin_msa_srai_h
__builtin_msa_srai_w
__builtin_msa_srai_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_srar_b
__builtin_msa_srar_h
__builtin_msa_srar_w
__builtin_msa_srar_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_srari_b
__builtin_msa_srari_h
__builtin_msa_srari_w
__builtin_msa_srari_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

i32);
i32);
i32);
i32);

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8,
v8i16,
v4i32,
v2i64,

imm0_15);
imm0_7);
imm0_3);
imm0_1);

v16i8);
v8i16);
v4i32);
v2i64);

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

(v16i8,
(v8i16,
(v4i32,
(v2i64,

i32);
i32);
i32);
i32);

(v16i8,
(v8i16,
(v4i32,
(v2i64,

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_15);
imm0_7);
imm0_3);
imm0_1);

v16i8);
v8i16);
v4i32);
v2i64);

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

v16i8 __builtin_msa_srl_b (v16i8, v16i8);
v8i16 __builtin_msa_srl_h (v8i16, v8i16);
v4i32 __builtin_msa_srl_w (v4i32, v4i32);

667

668

Using the GNU Compiler Collection (GCC)

v2i64 __builtin_msa_srl_d (v2i64, v2i64);
v16i8
v8i16
v4i32
v2i64

__builtin_msa_srli_b
__builtin_msa_srli_h
__builtin_msa_srli_w
__builtin_msa_srli_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_srlr_b
__builtin_msa_srlr_h
__builtin_msa_srlr_w
__builtin_msa_srlr_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_srlri_b
__builtin_msa_srlri_h
__builtin_msa_srlri_w
__builtin_msa_srlri_d

void
void
void
void

__builtin_msa_st_b
__builtin_msa_st_h
__builtin_msa_st_w
__builtin_msa_st_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_7);
imm0_15);
imm0_31);
imm0_63);

void
void
void
void

*,
*,
*,
*,

imm_n512_511);
imm_n1024_1022);
imm_n2048_2044);
imm_n4096_4088);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_subs_s_b
__builtin_msa_subs_s_h
__builtin_msa_subs_s_w
__builtin_msa_subs_s_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_subs_u_b
__builtin_msa_subs_u_h
__builtin_msa_subs_u_w
__builtin_msa_subs_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16u8
v8u16
v4u32
v2u64

__builtin_msa_subsus_u_b
__builtin_msa_subsus_u_h
__builtin_msa_subsus_u_w
__builtin_msa_subsus_u_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16i8);
v8i16);
v4i32);
v2i64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_subsuu_s_b
__builtin_msa_subsuu_s_h
__builtin_msa_subsuu_s_w
__builtin_msa_subsuu_s_d

(v16u8,
(v8u16,
(v4u32,
(v2u64,

v16u8);
v8u16);
v4u32);
v2u64);

v16i8
v8i16
v4i32
v2i64

__builtin_msa_subv_b
__builtin_msa_subv_h
__builtin_msa_subv_w
__builtin_msa_subv_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_subvi_b
__builtin_msa_subvi_h
__builtin_msa_subvi_w
__builtin_msa_subvi_d

v16i8
v8i16
v4i32
v2i64

__builtin_msa_vshf_b
__builtin_msa_vshf_h
__builtin_msa_vshf_w
__builtin_msa_vshf_d

(v16i8,
(v8i16,
(v4i32,
(v2i64,
(v16i8,
(v8i16,
(v4i32,
(v2i64,

v16i8);
v8i16);
v4i32);
v2i64);

(v16i8,
(v8i16,
(v4i32,
(v2i64,

imm0_31);
imm0_31);
imm0_31);
imm0_31);
v16i8,
v8i16,
v4i32,
v2i64,

v16u8 __builtin_msa_xor_v (v16u8, v16u8);

v16i8);
v8i16);
v4i32);
v2i64);

Chapter 6: Extensions to the C Language Family

669

v16u8 __builtin_msa_xori_b (v16u8, imm0_255);

6.59.17 Other MIPS Built-in Functions
GCC provides other MIPS-specific built-in functions:
void __builtin_mips_cache (int op, const volatile void *addr)
Insert a ‘cache’ instruction with operands op and addr. GCC defines the
preprocessor macro ___GCC_HAVE_BUILTIN_MIPS_CACHE when this function is
available.
unsigned int __builtin_mips_get_fcsr (void)
void __builtin_mips_set_fcsr (unsigned int value)
Get and set the contents of the floating-point control and status register (FPU
control register 31). These functions are only available in hard-float code but
can be called in both MIPS16 and non-MIPS16 contexts.
__builtin_mips_set_fcsr can be used to change any bit of the register except
the condition codes, which GCC assumes are preserved.

6.59.18 MSP430 Built-in Functions
GCC provides a couple of special builtin functions to aid in the writing of interrupt handlers
in C.
__bic_SR_register_on_exit (int mask)
This clears the indicated bits in the saved copy of the status register currently
residing on the stack. This only works inside interrupt handlers and the changes
to the status register will only take affect once the handler returns.
__bis_SR_register_on_exit (int mask)
This sets the indicated bits in the saved copy of the status register currently
residing on the stack. This only works inside interrupt handlers and the changes
to the status register will only take affect once the handler returns.
__delay_cycles (long long cycles)
This inserts an instruction sequence that takes exactly cycles cycles (between
0 and about 17E9) to complete. The inserted sequence may use jumps, loops,
or no-ops, and does not interfere with any other instructions. Note that cycles
must be a compile-time constant integer - that is, you must pass a number, not
a variable that may be optimized to a constant later. The number of cycles
delayed by this builtin is exact.

6.59.19 NDS32 Built-in Functions
These built-in functions are available for the NDS32 target:

void __builtin_nds32_isync (int *addr)

[Built-in Function]
Insert an ISYNC instruction into the instruction stream where addr is an instruction
address for serialization.

void __builtin_nds32_isb (void)
Insert an ISB instruction into the instruction stream.

[Built-in Function]

670

Using the GNU Compiler Collection (GCC)

int __builtin_nds32_mfsr (int sr)

[Built-in Function]

Return the content of a system register which is mapped by sr.

int __builtin_nds32_mfusr (int usr)

[Built-in Function]
Return the content of a user space register which is mapped by usr.

void __builtin_nds32_mtsr (int value, int sr)

[Built-in Function]

Move the value to a system register which is mapped by sr.

void __builtin_nds32_mtusr (int value, int usr)

[Built-in Function]

Move the value to a user space register which is mapped by usr.

void __builtin_nds32_setgie_en (void)

[Built-in Function]

Enable global interrupt.

void __builtin_nds32_setgie_dis (void)

[Built-in Function]

Disable global interrupt.

6.59.20 picoChip Built-in Functions
GCC provides an interface to selected machine instructions from the picoChip instruction
set.
int __builtin_sbc (int value)
Sign bit count. Return the number of consecutive bits in value that have the
same value as the sign bit. The result is the number of leading sign bits minus
one, giving the number of redundant sign bits in value.
int __builtin_byteswap (int value)
Byte swap. Return the result of swapping the upper and lower bytes of value.
int __builtin_brev (int value)
Bit reversal. Return the result of reversing the bits in value. Bit 15 is swapped
with bit 0, bit 14 is swapped with bit 1, and so on.
int __builtin_adds (int x, int y)
Saturating addition. Return the result of adding x and y, storing the value
32767 if the result overflows.
int __builtin_subs (int x, int y)
Saturating subtraction. Return the result of subtracting y from x, storing the
value −32768 if the result overflows.
void __builtin_halt (void)
Halt. The processor stops execution. This built-in is useful for implementing
assertions.

6.59.21 PowerPC Built-in Functions
The following built-in functions are always available and can be used to check the PowerPC
target platform type:

void __builtin_cpu_init (void)

[Built-in Function]
This function is a nop on the PowerPC platform and is included solely to maintain
API compatibility with the x86 builtins.

Chapter 6: Extensions to the C Language Family

671

int __builtin_cpu_is (const char *cpuname)

[Built-in Function]
This function returns a value of 1 if the run-time CPU is of type cpuname and returns
0 otherwise

The __builtin_cpu_is function requires GLIBC 2.23 or newer which exports the
hardware capability bits. GCC defines the macro __BUILTIN_CPU_SUPPORTS__ if the
__builtin_cpu_supports built-in function is fully supported.
If GCC was configured to use a GLIBC before 2.23, the built-in function __builtin_
cpu_is always returns a 0 and the compiler issues a warning.
The following CPU names can be detected:
‘power9’

IBM POWER9 Server CPU.

‘power8’

IBM POWER8 Server CPU.

‘power7’

IBM POWER7 Server CPU.

‘power6x’

IBM POWER6 Server CPU (RAW mode).

‘power6’

IBM POWER6 Server CPU (Architected mode).

‘power5+’

IBM POWER5+ Server CPU.

‘power5’

IBM POWER5 Server CPU.

‘ppc970’

IBM 970 Server CPU (ie, Apple G5).

‘power4’

IBM POWER4 Server CPU.

‘ppca2’

IBM A2 64-bit Embedded CPU

‘ppc476’

IBM PowerPC 476FP 32-bit Embedded CPU.

‘ppc464’

IBM PowerPC 464 32-bit Embedded CPU.

‘ppc440’

PowerPC 440 32-bit Embedded CPU.

‘ppc405’

PowerPC 405 32-bit Embedded CPU.

‘ppc-cell-be’
IBM PowerPC Cell Broadband Engine Architecture CPU.
Here is an example:
#ifdef __BUILTIN_CPU_SUPPORTS__
if (__builtin_cpu_is ("power8"))
{
do_power8 (); // POWER8 specific implementation.
}
else
#endif
{
do_generic (); // Generic implementation.
}

int __builtin_cpu_supports (const char *feature)

[Built-in Function]
This function returns a value of 1 if the run-time CPU supports the HWCAP feature
feature and returns 0 otherwise.

672

Using the GNU Compiler Collection (GCC)

The __builtin_cpu_supports function requires GLIBC 2.23 or newer which exports
the hardware capability bits. GCC defines the macro __BUILTIN_CPU_SUPPORTS__ if
the __builtin_cpu_supports built-in function is fully supported.
If GCC was configured to use a GLIBC before 2.23, the built-in function __builtin_
cpu_suports always returns a 0 and the compiler issues a warning.
The following features can be detected:
‘4xxmac’

4xx CPU has a Multiply Accumulator.

‘altivec’

CPU has a SIMD/Vector Unit.

‘arch_2_05’
CPU supports ISA 2.05 (eg, POWER6)
‘arch_2_06’
CPU supports ISA 2.06 (eg, POWER7)
‘arch_2_07’
CPU supports ISA 2.07 (eg, POWER8)
‘arch_3_00’
CPU supports ISA 3.0 (eg, POWER9)
‘archpmu’

CPU supports the set of compatible performance monitoring events.

‘booke’

CPU supports the Embedded ISA category.

‘cellbe’

CPU has a CELL broadband engine.

‘dfp’

CPU has a decimal floating point unit.

‘dscr’

CPU supports the data stream control register.

‘ebb’

CPU supports event base branching.

‘efpdouble’
CPU has a SPE double precision floating point unit.
‘efpsingle’
CPU has a SPE single precision floating point unit.
‘fpu’

CPU has a floating point unit.

‘htm’

CPU has hardware transaction memory instructions.

‘htm-nosc’
Kernel aborts hardware transactions when a syscall is made.
‘ic_snoop’
CPU supports icache snooping capabilities.
‘ieee128’

CPU supports 128-bit IEEE binary floating point instructions.

‘isel’

CPU supports the integer select instruction.

‘mmu’

CPU has a memory management unit.

‘notb’

CPU does not have a timebase (eg, 601 and 403gx).

Chapter 6: Extensions to the C Language Family

673

‘pa6t’

CPU supports the PA Semi 6T CORE ISA.

‘power4’

CPU supports ISA 2.00 (eg, POWER4)

‘power5’

CPU supports ISA 2.02 (eg, POWER5)

‘power5+’

CPU supports ISA 2.03 (eg, POWER5+)

‘power6x’

CPU supports ISA 2.05 (eg, POWER6) extended opcodes mffgpr and
mftgpr.

‘ppc32’

CPU supports 32-bit mode execution.

‘ppc601’

CPU supports the old POWER ISA (eg, 601)

‘ppc64’

CPU supports 64-bit mode execution.

‘ppcle’

CPU supports a little-endian mode that uses address swizzling.

‘smt’

CPU support simultaneous multi-threading.

‘spe’

CPU has a signal processing extension unit.

‘tar’

CPU supports the target address register.

‘true_le’

CPU supports true little-endian mode.

‘ucache’

CPU has unified I/D cache.

‘vcrypto’

CPU supports the vector cryptography instructions.

‘vsx’

CPU supports the vector-scalar extension.

Here is an example:
#ifdef __BUILTIN_CPU_SUPPORTS__
if (__builtin_cpu_supports ("fpu"))
{
asm("fadd %0,%1,%2" : "=d"(dst) : "d"(src1), "d"(src2));
}
else
#endif
{
dst = __fadd (src1, src2); // Software FP addition function.
}

These built-in functions are available for the PowerPC family of processors:
float __builtin_recipdivf (float, float);
float __builtin_rsqrtf (float);
double __builtin_recipdiv (double, double);
double __builtin_rsqrt (double);
uint64_t __builtin_ppc_get_timebase ();
unsigned long __builtin_ppc_mftb ();
double __builtin_unpack_longdouble (long double, int);
long double __builtin_pack_longdouble (double, double);
__ibm128 __builtin_unpack_ibm128 (__ibm128, int);
__ibm128 __builtin_pack_ibm128 (double, double);

The vec_rsqrt, __builtin_rsqrt, and __builtin_rsqrtf functions generate multiple
instructions to implement the reciprocal sqrt functionality using reciprocal sqrt estimate
instructions.

674

Using the GNU Compiler Collection (GCC)

The __builtin_recipdiv, and __builtin_recipdivf functions generate multiple instructions to implement division using the reciprocal estimate instructions.
The __builtin_ppc_get_timebase and __builtin_ppc_mftb functions generate
instructions to read the Time Base Register. The __builtin_ppc_get_timebase function
may generate multiple instructions and always returns the 64 bits of the Time Base
Register. The __builtin_ppc_mftb function always generates one instruction and returns
the Time Base Register value as an unsigned long, throwing away the most significant
word on 32-bit environments.
The __builtin_unpack_longdouble function takes a long double argument and a compile time constant of 0 or 1. If the constant is 0, the first double within the long double
is returned, otherwise the second double is returned. The __builtin_unpack_longdouble
function is only availble if long double uses the IBM extended double representation.
The __builtin_pack_longdouble function takes two double arguments and returns a
long double value that combines the two arguments. The __builtin_pack_longdouble
function is only availble if long double uses the IBM extended double representation.
The __builtin_unpack_ibm128 function takes a __ibm128 argument and a compile time
constant of 0 or 1. If the constant is 0, the first double within the __ibm128 is returned,
otherwise the second double is returned.
The __builtin_pack_ibm128 function takes two double arguments and returns a __
ibm128 value that combines the two arguments.
Additional built-in functions are available for the 64-bit PowerPC family of processors,
for efficient use of 128-bit floating point (__float128) values.
Previous versions of GCC supported some ’q’ builtins for IEEE 128-bit floating point.
These functions are now mapped into the equivalent ’f128’ builtin functions.
__builtin_fabsq is mapped into __builtin_fabsf128
__builtin_copysignq is mapped into __builtin_copysignf128
__builtin_infq is mapped into __builtin_inff128
__builtin_huge_valq is mapped into __builtin_huge_valf128
__builtin_nanq is mapped into __builtin_nanf128
__builtin_nansq is mapped into __builtin_nansf128

The following built-in functions are available on Linux 64-bit systems that use the ISA
3.0 instruction set.
__float128 __builtin_sqrtf128 (__float128)
Perform a 128-bit IEEE floating point square root operation.
__float128 __builtin_fmaf128 (__float128, __float128, __float128)
Perform a 128-bit IEEE floating point fused multiply and add operation.
__float128 __builtin_addf128_round_to_odd (__float128, __float128)
Perform a 128-bit IEEE floating point add using round to odd as the rounding
mode.
__float128 __builtin_subf128_round_to_odd (__float128, __float128)
Perform a 128-bit IEEE floating point subtract using round to odd as the rounding mode.
__float128 __builtin_mulf128_round_to_odd (__float128, __float128)
Perform a 128-bit IEEE floating point multiply using round to odd as the
rounding mode.

Chapter 6: Extensions to the C Language Family

675

__float128 __builtin_divf128_round_to_odd (__float128, __float128)
Perform a 128-bit IEEE floating point divide using round to odd as the rounding
mode.
__float128 __builtin_sqrtf128_round_to_odd (__float128)
Perform a 128-bit IEEE floating point square root using round to odd as the
rounding mode.
__float128 __builtin_fmaf128 (__float128, __float128, __float128)
Perform a 128-bit IEEE floating point fused multiply and add operation using
round to odd as the rounding mode.
double __builtin_truncf128_round_to_odd (__float128)
Convert a 128-bit IEEE floating point value to double using round to odd as
the rounding mode.
The following built-in functions are available for the PowerPC family of processors, starting with ISA 2.05 or later (‘-mcpu=power6’ or ‘-mcmpb’):
unsigned long long __builtin_cmpb (unsigned long long int, unsigned long long int);
unsigned int __builtin_cmpb (unsigned int, unsigned int);

The __builtin_cmpb function performs a byte-wise compare on the contents of its two
arguments, returning the result of the byte-wise comparison as the returned value. For
each byte comparison, the corresponding byte of the return value holds 0xff if the input
bytes are equal and 0 if the input bytes are not equal. If either of the arguments to this
built-in function is wider than 32 bits, the function call expands into the form that expects
unsigned long long int arguments which is only available on 64-bit targets.
The following built-in functions are available for the PowerPC family of processors, starting with ISA 2.06 or later (‘-mcpu=power7’ or ‘-mpopcntd’):
long __builtin_bpermd (long, long);
int __builtin_divwe (int, int);
unsigned int __builtin_divweu (unsigned int, unsigned int);
long __builtin_divde (long, long);
unsigned long __builtin_divdeu (unsigned long, unsigned long);
unsigned int cdtbcd (unsigned int);
unsigned int cbcdtd (unsigned int);
unsigned int addg6s (unsigned int, unsigned int);
void __builtin_rs6000_speculation_barrier (void);

The __builtin_divde and __builtin_divdeu functions require a 64-bit environment
supporting ISA 2.06 or later.
The following built-in functions are available for the PowerPC family of processors, starting with ISA 3.0 or later (‘-mcpu=power9’):
long long __builtin_darn (void);
long long __builtin_darn_raw (void);
int __builtin_darn_32 (void);
unsigned int scalar_extract_exp (double source);
unsigned long long int scalar_extract_exp (__ieee128 source);
unsigned long long int scalar_extract_sig (double source);
unsigned __int128 scalar_extract_sig (__ieee128 source);
double

676

Using the GNU Compiler Collection (GCC)

scalar_insert_exp (unsigned long long int significand, unsigned long long int exponent);
double
scalar_insert_exp (double significand, unsigned long long int exponent);
ieee_128
scalar_insert_exp (unsigned __int128 significand, unsigned long long int exponent);
ieee_128
scalar_insert_exp (ieee_128 significand, unsigned long long int exponent);
int
int
int
int

scalar_cmp_exp_gt (double arg1, double
scalar_cmp_exp_lt (double arg1, double
scalar_cmp_exp_eq (double arg1, double
scalar_cmp_exp_unordered (double arg1,

arg2);
arg2);
arg2);
double arg2);

bool scalar_test_data_class (float source, const int condition);
bool scalar_test_data_class (double source, const int condition);
bool scalar_test_data_class (__ieee128 source, const int condition);
bool scalar_test_neg (float source);
bool scalar_test_neg (double source);
bool scalar_test_neg (__ieee128 source);
int __builtin_byte_in_set (unsigned char u, unsigned long long set);
int __builtin_byte_in_range (unsigned char u, unsigned int range);
int __builtin_byte_in_either_range (unsigned char u, unsigned int ranges);
int
int
int
int

__builtin_dfp_dtstsfi_lt (unsigned int comparison, _Decimal64 value);
__builtin_dfp_dtstsfi_lt (unsigned int comparison, _Decimal128 value);
__builtin_dfp_dtstsfi_lt_dd (unsigned int comparison, _Decimal64 value);
__builtin_dfp_dtstsfi_lt_td (unsigned int comparison, _Decimal128 value);

int
int
int
int

__builtin_dfp_dtstsfi_gt (unsigned int comparison, _Decimal64 value);
__builtin_dfp_dtstsfi_gt (unsigned int comparison, _Decimal128 value);
__builtin_dfp_dtstsfi_gt_dd (unsigned int comparison, _Decimal64 value);
__builtin_dfp_dtstsfi_gt_td (unsigned int comparison, _Decimal128 value);

int
int
int
int

__builtin_dfp_dtstsfi_eq (unsigned int comparison, _Decimal64 value);
__builtin_dfp_dtstsfi_eq (unsigned int comparison, _Decimal128 value);
__builtin_dfp_dtstsfi_eq_dd (unsigned int comparison, _Decimal64 value);
__builtin_dfp_dtstsfi_eq_td (unsigned int comparison, _Decimal128 value);

int
int
int
int

__builtin_dfp_dtstsfi_ov (unsigned int comparison, _Decimal64 value);
__builtin_dfp_dtstsfi_ov (unsigned int comparison, _Decimal128 value);
__builtin_dfp_dtstsfi_ov_dd (unsigned int comparison, _Decimal64 value);
__builtin_dfp_dtstsfi_ov_td (unsigned int comparison, _Decimal128 value);

The __builtin_darn and __builtin_darn_raw functions require a 64-bit environment
supporting ISA 3.0 or later. The __builtin_darn function provides a 64-bit conditioned
random number. The __builtin_darn_raw function provides a 64-bit raw random number.
The __builtin_darn_32 function provides a 32-bit random number.
The scalar_extract_exp and scalar_extract_sig functions require a 64-bit environment supporting ISA 3.0 or later. The scalar_extract_exp and scalar_extract_sig
built-in functions return the significand and the biased exponent value respectively of their
source arguments. When supplied with a 64-bit source argument, the result returned by
scalar_extract_sig has the 0x0010000000000000 bit set if the function’s source argument is in normalized form. Otherwise, this bit is set to 0. When supplied with a 128-bit

Chapter 6: Extensions to the C Language Family

677

source argument, the 0x00010000000000000000000000000000 bit of the result is treated
similarly. Note that the sign of the significand is not represented in the result returned from
the scalar_extract_sig function. Use the scalar_test_neg function to test the sign of
its double argument.
The scalar_insert_exp functions require a 64-bit environment supporting ISA 3.0 or
later. When supplied with a 64-bit first argument, the scalar_insert_exp built-in function
returns a double-precision floating point value that is constructed by assembling the values
of its significand and exponent arguments. The sign of the result is copied from the most
significant bit of the significand argument. The significand and exponent components of
the result are composed of the least significant 11 bits of the exponent argument and the
least significant 52 bits of the significand argument respectively.
When supplied with a 128-bit first argument, the scalar_insert_exp built-in function
returns a quad-precision ieee floating point value. The sign bit of the result is copied
from the most significant bit of the significand argument. The significand and exponent
components of the result are composed of the least significant 15 bits of the exponent
argument and the least significant 112 bits of the significand argument respectively.
The scalar_cmp_exp_gt, scalar_cmp_exp_lt, scalar_cmp_exp_eq, and scalar_cmp_
exp_unordered built-in functions return a non-zero value if arg1 is greater than, less than,
equal to, or not comparable to arg2 respectively. The arguments are not comparable if one
or the other equals NaN (not a number).
The scalar_test_data_class built-in function returns 1 if any of the condition tests
enabled by the value of the condition variable are true, and 0 otherwise. The condition
argument must be a compile-time constant integer with value not exceeding 127. The
condition argument is encoded as a bitmask with each bit enabling the testing of a different
condition, as characterized by the following:
0x40
0x20
0x10
0x08
0x04
0x02
0x01

Test
Test
Test
Test
Test
Test
Test

for
for
for
for
for
for
for

NaN
+Infinity
-Infinity
+Zero
-Zero
+Denormal
-Denormal

The scalar_test_neg built-in function returns 1 if its source argument holds a negative
value, 0 otherwise.
The __builtin_byte_in_set function requires a 64-bit environment supporting ISA 3.0
or later. This function returns a non-zero value if and only if its u argument exactly equals
one of the eight bytes contained within its 64-bit set argument.
The __builtin_byte_in_range and __builtin_byte_in_either_range require an environment supporting ISA 3.0 or later. For these two functions, the range argument is
encoded as 4 bytes, organized as hi_1:lo_1:hi_2:lo_2. The __builtin_byte_in_range
function returns a non-zero value if and only if its u argument is within the range bounded
between lo_2 and hi_2 inclusive. The __builtin_byte_in_either_range function returns
non-zero if and only if its u argument is within either the range bounded between lo_1 and
hi_1 inclusive or the range bounded between lo_2 and hi_2 inclusive.
The __builtin_dfp_dtstsfi_lt function returns a non-zero value if and only if the number of signficant digits of its value argument is less than its comparison argument. The __

678

Using the GNU Compiler Collection (GCC)

builtin_dfp_dtstsfi_lt_dd and __builtin_dfp_dtstsfi_lt_td functions behave similarly, but require that the type of the value argument be __Decimal64 and __Decimal128
respectively.
The __builtin_dfp_dtstsfi_gt function returns a non-zero value if and only if the
number of signficant digits of its value argument is greater than its comparison argument. The __builtin_dfp_dtstsfi_gt_dd and __builtin_dfp_dtstsfi_gt_td functions
behave similarly, but require that the type of the value argument be __Decimal64 and __
Decimal128 respectively.
The __builtin_dfp_dtstsfi_eq function returns a non-zero value if and only if the
number of signficant digits of its value argument equals its comparison argument. The __
builtin_dfp_dtstsfi_eq_dd and __builtin_dfp_dtstsfi_eq_td functions behave similarly, but require that the type of the value argument be __Decimal64 and __Decimal128
respectively.
The __builtin_dfp_dtstsfi_ov function returns a non-zero value if and only if its value
argument has an undefined number of significant digits, such as when value is an encoding of
NaN. The __builtin_dfp_dtstsfi_ov_dd and __builtin_dfp_dtstsfi_ov_td functions
behave similarly, but require that the type of the value argument be __Decimal64 and
__Decimal128 respectively.
The following built-in functions are also available for the PowerPC family of processors,
starting with ISA 3.0 or later (‘-mcpu=power9’). These string functions are described separately in order to group the descriptions closer to the function prototypes:
int
int
int
int
int
int

vec_all_nez
vec_all_nez
vec_all_nez
vec_all_nez
vec_all_nez
vec_all_nez

(vector
(vector
(vector
(vector
(vector
(vector

signed char, vector signed char);
unsigned char, vector unsigned char);
signed short, vector signed short);
unsigned short, vector unsigned short);
signed int, vector signed int);
unsigned int, vector unsigned int);

int
int
int
int
int
int

vec_any_eqz
vec_any_eqz
vec_any_eqz
vec_any_eqz
vec_any_eqz
vec_any_eqz

(vector
(vector
(vector
(vector
(vector
(vector

signed char, vector signed char);
unsigned char, vector unsigned char);
signed short, vector signed short);
unsigned short, vector unsigned short);
signed int, vector signed int);
unsigned int, vector unsigned int);

vector
vector
vector
vector
vector
vector

bool
bool
bool
bool
bool
bool

char vec_cmpnez (vector signed char arg1, vector signed char arg2);
char vec_cmpnez (vector unsigned char arg1, vector unsigned char arg2);
short vec_cmpnez (vector signed short arg1, vector signed short arg2);
short vec_cmpnez (vector unsigned short arg1, vector unsigned short arg2);
int vec_cmpnez (vector signed int arg1, vector signed int arg2);
int vec_cmpnez (vector unsigned int, vector unsigned int);

vector
vector
vector
vector
vector
vector
vector
vector

signed char vec_cnttz (vector signed char);
unsigned char vec_cnttz (vector unsigned char);
signed short vec_cnttz (vector signed short);
unsigned short vec_cnttz (vector unsigned short);
signed int vec_cnttz (vector signed int);
unsigned int vec_cnttz (vector unsigned int);
signed long long vec_cnttz (vector signed long long);
unsigned long long vec_cnttz (vector unsigned long long);

signed int vec_cntlz_lsbb (vector signed char);

Chapter 6: Extensions to the C Language Family

signed int vec_cntlz_lsbb (vector unsigned char);
signed int vec_cnttz_lsbb (vector signed char);
signed int vec_cnttz_lsbb (vector unsigned char);
unsigned int vec_first_match_index (vector signed char, vector signed char);
unsigned int vec_first_match_index (vector unsigned char,
vector unsigned char);
unsigned int vec_first_match_index (vector signed int, vector signed int);
unsigned int vec_first_match_index (vector unsigned int, vector unsigned int);
unsigned int vec_first_match_index (vector signed short, vector signed short);
unsigned int vec_first_match_index (vector unsigned short,
vector unsigned short);
unsigned int vec_first_match_or_eos_index (vector signed char,
vector signed char);
unsigned int vec_first_match_or_eos_index (vector unsigned char,
vector unsigned char);
unsigned int vec_first_match_or_eos_index (vector signed int,
vector signed int);
unsigned int vec_first_match_or_eos_index (vector unsigned int,
vector unsigned int);
unsigned int vec_first_match_or_eos_index (vector signed short,
vector signed short);
unsigned int vec_first_match_or_eos_index (vector unsigned short,
vector unsigned short);
unsigned int vec_first_mismatch_index (vector signed char,
vector signed char);
unsigned int vec_first_mismatch_index (vector unsigned char,
vector unsigned char);
unsigned int vec_first_mismatch_index (vector signed int,
vector signed int);
unsigned int vec_first_mismatch_index (vector unsigned int,
vector unsigned int);
unsigned int vec_first_mismatch_index (vector signed short,
vector signed short);
unsigned int vec_first_mismatch_index (vector unsigned short,
vector unsigned short);
unsigned int vec_first_mismatch_or_eos_index (vector signed char,
vector signed char);
unsigned int vec_first_mismatch_or_eos_index (vector unsigned char,
vector unsigned char);
unsigned int vec_first_mismatch_or_eos_index (vector signed int,
vector signed int);
unsigned int vec_first_mismatch_or_eos_index (vector unsigned int,
vector unsigned int);
unsigned int vec_first_mismatch_or_eos_index (vector signed short,
vector signed short);
unsigned int vec_first_mismatch_or_eos_index (vector unsigned short,
vector unsigned short);
vector unsigned short vec_pack_to_short_fp32 (vector float, vector float);
vector
vector
vector
vector
vector
vector

signed char vec_xl_be (signed long long, signed char *);
unsigned char vec_xl_be (signed long long, unsigned char *);
signed int vec_xl_be (signed long long, signed int *);
unsigned int vec_xl_be (signed long long, unsigned int *);
signed __int128 vec_xl_be (signed long long, signed __int128 *);
unsigned __int128 vec_xl_be (signed long long, unsigned __int128 *);

679

680

Using the GNU Compiler Collection (GCC)

vector
vector
vector
vector
vector
vector

signed long long vec_xl_be (signed long long, signed long long *);
unsigned long long vec_xl_be (signed long long, unsigned long long *);
signed short vec_xl_be (signed long long, signed short *);
unsigned short vec_xl_be (signed long long, unsigned short *);
double vec_xl_be (signed long long, double *);
float vec_xl_be (signed long long, float *);

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

signed char vec_xl_len (signed char *addr, size_t len);
unsigned char vec_xl_len (unsigned char *addr, size_t len);
signed int vec_xl_len (signed int *addr, size_t len);
unsigned int vec_xl_len (unsigned int *addr, size_t len);
signed __int128 vec_xl_len (signed __int128 *addr, size_t len);
unsigned __int128 vec_xl_len (unsigned __int128 *addr, size_t len);
signed long long vec_xl_len (signed long long *addr, size_t len);
unsigned long long vec_xl_len (unsigned long long *addr, size_t len);
signed short vec_xl_len (signed short *addr, size_t len);
unsigned short vec_xl_len (unsigned short *addr, size_t len);
double vec_xl_len (double *addr, size_t len);
float vec_xl_len (float *addr, size_t len);

vector unsigned char vec_xl_len_r (unsigned char *addr, size_t len);
void
void
void
void
void
void
void
void
void
void
void
void

vec_xst_len
vec_xst_len
vec_xst_len
vec_xst_len
vec_xst_len
vec_xst_len
vec_xst_len
vec_xst_len
vec_xst_len
vec_xst_len
vec_xst_len
vec_xst_len

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

signed char data, signed char *addr, size_t len);
unsigned char data, unsigned char *addr, size_t len);
signed int data, signed int *addr, size_t len);
unsigned int data, unsigned int *addr, size_t len);
unsigned __int128 data, unsigned __int128 *addr, size_t len);
signed long long data, signed long long *addr, size_t len);
unsigned long long data, unsigned long long *addr, size_t len);
signed short data, signed short *addr, size_t len);
unsigned short data, unsigned short *addr, size_t len);
signed __int128 data, signed __int128 *addr, size_t len);
double data, double *addr, size_t len);
float data, float *addr, size_t len);

void vec_xst_len_r (vector unsigned char data, unsigned char *addr, size_t len);
signed char vec_xlx (unsigned int index, vector signed char data);
unsigned char vec_xlx (unsigned int index, vector unsigned char data);
signed short vec_xlx (unsigned int index, vector signed short data);
unsigned short vec_xlx (unsigned int index, vector unsigned short data);
signed int vec_xlx (unsigned int index, vector signed int data);
unsigned int vec_xlx (unsigned int index, vector unsigned int data);
float vec_xlx (unsigned int index, vector float data);
signed char vec_xrx (unsigned int index, vector signed char data);
unsigned char vec_xrx (unsigned int index, vector unsigned char data);
signed short vec_xrx (unsigned int index, vector signed short data);
unsigned short vec_xrx (unsigned int index, vector unsigned short data);
signed int vec_xrx (unsigned int index, vector signed int data);
unsigned int vec_xrx (unsigned int index, vector unsigned int data);
float vec_xrx (unsigned int index, vector float data);

The vec_all_nez, vec_any_eqz, and vec_cmpnez perform pairwise comparisons between
the elements at the same positions within their two vector arguments. The vec_all_nez
function returns a non-zero value if and only if all pairwise comparisons are not equal and
no element of either vector argument contains a zero. The vec_any_eqz function returns
a non-zero value if and only if at least one pairwise comparison is equal or if at least one

Chapter 6: Extensions to the C Language Family

681

element of either vector argument contains a zero. The vec_cmpnez function returns a
vector of the same type as its two arguments, within which each element consists of all ones
to denote that either the corresponding elements of the incoming arguments are not equal
or that at least one of the corresponding elements contains zero. Otherwise, the element of
the returned vector contains all zeros.
The vec_cntlz_lsbb function returns the count of the number of consecutive leading
byte elements (starting from position 0 within the supplied vector argument) for which
the least-significant bit equals zero. The vec_cnttz_lsbb function returns the count of
the number of consecutive trailing byte elements (starting from position 15 and counting
backwards within the supplied vector argument) for which the least-significant bit equals
zero.
The vec_xl_len and vec_xst_len functions require a 64-bit environment supporting
ISA 3.0 or later. The vec_xl_len function loads a variable length vector from memory.
The vec_xst_len function stores a variable length vector to memory. With both the vec_
xl_len and vec_xst_len functions, the addr argument represents the memory address to
or from which data will be transferred, and the len argument represents the number of
bytes to be transferred, as computed by the C expression min((len & 0xff), 16). If this
expression’s value is not a multiple of the vector element’s size, the behavior of this function
is undefined. In the case that the underlying computer is configured to run in big-endian
mode, the data transfer moves bytes 0 to (len - 1) of the corresponding vector. In littleendian mode, the data transfer moves bytes (16 - len) to 15 of the corresponding vector.
For the load function, any bytes of the result vector that are not loaded from memory are
set to zero. The value of the addr argument need not be aligned on a multiple of the vector’s
element size.
The vec_xlx and vec_xrx functions extract the single element selected by the index
argument from the vector represented by the data argument. The index argument always
specifies a byte offset, regardless of the size of the vector element. With vec_xlx, index is
the offset of the first byte of the element to be extracted. With vec_xrx, index represents
the last byte of the element to be extracted, measured from the right end of the vector. In
other words, the last byte of the element to be extracted is found at position (15 - index).
There is no requirement that index be a multiple of the vector element size. However, if
the size of the vector element added to index is greater than 15, the content of the returned
value is undefined.
The following built-in functions are available for the PowerPC family of processors when
hardware decimal floating point (‘-mhard-dfp’) is available:
long long __builtin_dxex (_Decimal64);
long long __builtin_dxexq (_Decimal128);
_Decimal64 __builtin_ddedpd (int, _Decimal64);
_Decimal128 __builtin_ddedpdq (int, _Decimal128);
_Decimal64 __builtin_denbcd (int, _Decimal64);
_Decimal128 __builtin_denbcdq (int, _Decimal128);
_Decimal64 __builtin_diex (long long, _Decimal64);
_Decimal128 _builtin_diexq (long long, _Decimal128);
_Decimal64 __builtin_dscli (_Decimal64, int);
_Decimal128 __builtin_dscliq (_Decimal128, int);
_Decimal64 __builtin_dscri (_Decimal64, int);
_Decimal128 __builtin_dscriq (_Decimal128, int);
unsigned long long __builtin_unpack_dec128 (_Decimal128, int);

682

Using the GNU Compiler Collection (GCC)

_Decimal128 __builtin_pack_dec128 (unsigned long long, unsigned long long);

The following built-in functions are available for the PowerPC family of processors when
the Vector Scalar (vsx) instruction set is available:
unsigned long long __builtin_unpack_vector_int128 (vector __int128_t, int);
vector __int128_t __builtin_pack_vector_int128 (unsigned long long,
unsigned long long);

6.59.22 PowerPC AltiVec Built-in Functions
GCC provides an interface for the PowerPC family of processors to access the AltiVec
operations described in Motorola’s AltiVec Programming Interface Manual. The interface
is made available by including  and using ‘-maltivec’ and ‘-mabi=altivec’.
The interface supports the following vector types.
vector unsigned char
vector signed char
vector bool char
vector
vector
vector
vector

unsigned short
signed short
bool short
pixel

vector
vector
vector
vector

unsigned int
signed int
bool int
float

If ‘-mvsx’ is used the following additional vector types are implemented.
vector unsigned long
vector signed long
vector double

The long types are only implemented for 64-bit code generation, and the long type is only
used in the floating point/integer conversion instructions.
GCC’s implementation of the high-level language interface available from C and C++ code
differs from Motorola’s documentation in several ways.
• A vector constant is a list of constant expressions within curly braces.
• A vector initializer requires no cast if the vector constant is of the same type as the
variable it is initializing.
• If signed or unsigned is omitted, the signedness of the vector type is the default
signedness of the base type. The default varies depending on the operating system, so
a portable program should always specify the signedness.
• Compiling with ‘-maltivec’ adds keywords __vector, vector, __pixel, pixel, __
bool and bool. When compiling ISO C, the context-sensitive substitution of the keywords vector, pixel and bool is disabled. To use them, you must include 
instead.
• GCC allows using a typedef name as the type specifier for a vector type.
• For C, overloaded functions are implemented with macros so the following does not
work:
vec_add ((vector signed int){1, 2, 3, 4}, foo);

Chapter 6: Extensions to the C Language Family

683

Since vec_add is a macro, the vector constant in the example is treated as four separate
arguments. Wrap the entire argument in parentheses for this to work.
Note: Only the  interface is supported. Internally, GCC uses built-in functions to achieve the functionality in the aforementioned header file, but they are not supported and are subject to change without notice.
GCC complies with the OpenPOWER 64-Bit ELF V2 ABI Specification, which may
be found at http: / / openpowerfoundation . org / wp-content / uploads / resources /
leabi-prd / content / index . html. Appendix A of this document lists the vector
API interfaces that must be provided by compliant compilers. Programmers should
preferentially use the interfaces described therein. However, historically GCC has provided
additional interfaces for access to vector instructions. These are briefly described below.
The following interfaces are supported for the generic and specific AltiVec operations
and the AltiVec predicates. In cases where there is a direct mapping between generic and
specific operations, only the generic names are shown here, although the specific operations
can also be used.
Arguments that are documented as const int require literal integral values within the
range required for that operation.
vector
vector
vector
vector

signed char vec_abs (vector signed char);
signed short vec_abs (vector signed short);
signed int vec_abs (vector signed int);
float vec_abs (vector float);

vector signed char vec_abss (vector signed char);
vector signed short vec_abss (vector signed short);
vector signed int vec_abss (vector signed int);
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

signed char vec_add (vector bool char, vector signed char);
signed char vec_add (vector signed char, vector bool char);
signed char vec_add (vector signed char, vector signed char);
unsigned char vec_add (vector bool char, vector unsigned char);
unsigned char vec_add (vector unsigned char, vector bool char);
unsigned char vec_add (vector unsigned char,
vector unsigned char);
signed short vec_add (vector bool short, vector signed short);
signed short vec_add (vector signed short, vector bool short);
signed short vec_add (vector signed short, vector signed short);
unsigned short vec_add (vector bool short,
vector unsigned short);
unsigned short vec_add (vector unsigned short,
vector bool short);
unsigned short vec_add (vector unsigned short,
vector unsigned short);
signed int vec_add (vector bool int, vector signed int);
signed int vec_add (vector signed int, vector bool int);
signed int vec_add (vector signed int, vector signed int);
unsigned int vec_add (vector bool int, vector unsigned int);
unsigned int vec_add (vector unsigned int, vector bool int);
unsigned int vec_add (vector unsigned int, vector unsigned int);
float vec_add (vector float, vector float);

vector float vec_vaddfp (vector float, vector float);
vector signed int vec_vadduwm (vector bool int, vector signed int);

684

Using the GNU Compiler Collection (GCC)

vector
vector
vector
vector
vector

signed int vec_vadduwm (vector signed int, vector bool int);
signed int vec_vadduwm (vector signed int, vector signed int);
unsigned int vec_vadduwm (vector bool int, vector unsigned int);
unsigned int vec_vadduwm (vector unsigned int, vector bool int);
unsigned int vec_vadduwm (vector unsigned int,
vector unsigned int);

vector signed short vec_vadduhm (vector bool short,
vector signed short);
vector signed short vec_vadduhm (vector signed short,
vector bool short);
vector signed short vec_vadduhm (vector signed short,
vector signed short);
vector unsigned short vec_vadduhm (vector bool short,
vector unsigned short);
vector unsigned short vec_vadduhm (vector unsigned short,
vector bool short);
vector unsigned short vec_vadduhm (vector unsigned short,
vector unsigned short);
vector
vector
vector
vector

signed char vec_vaddubm (vector bool char, vector signed char);
signed char vec_vaddubm (vector signed char, vector bool char);
signed char vec_vaddubm (vector signed char, vector signed char);
unsigned char vec_vaddubm (vector bool char,
vector unsigned char);
vector unsigned char vec_vaddubm (vector unsigned char,
vector bool char);
vector unsigned char vec_vaddubm (vector unsigned char,
vector unsigned char);
vector unsigned int vec_addc (vector unsigned int, vector unsigned int);
vector unsigned char vec_adds (vector bool char, vector unsigned char);
vector unsigned char vec_adds (vector unsigned char, vector bool char);
vector unsigned char vec_adds (vector unsigned char,
vector unsigned char);
vector signed char vec_adds (vector bool char, vector signed char);
vector signed char vec_adds (vector signed char, vector bool char);
vector signed char vec_adds (vector signed char, vector signed char);
vector unsigned short vec_adds (vector bool short,
vector unsigned short);
vector unsigned short vec_adds (vector unsigned short,
vector bool short);
vector unsigned short vec_adds (vector unsigned short,
vector unsigned short);
vector signed short vec_adds (vector bool short, vector signed short);
vector signed short vec_adds (vector signed short, vector bool short);
vector signed short vec_adds (vector signed short, vector signed short);
vector unsigned int vec_adds (vector bool int, vector unsigned int);
vector unsigned int vec_adds (vector unsigned int, vector bool int);
vector unsigned int vec_adds (vector unsigned int, vector unsigned int);
vector signed int vec_adds (vector bool int, vector signed int);
vector signed int vec_adds (vector signed int, vector bool int);
vector signed int vec_adds (vector signed int, vector signed int);
vector signed int vec_vaddsws (vector bool int, vector signed int);
vector signed int vec_vaddsws (vector signed int, vector bool int);
vector signed int vec_vaddsws (vector signed int, vector signed int);

Chapter 6: Extensions to the C Language Family

vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
vector unsigned int vec_vadduws (vector unsigned int,
vector unsigned int);
vector signed short vec_vaddshs (vector
vector
vector signed short vec_vaddshs (vector
vector
vector signed short vec_vaddshs (vector
vector

bool short,
signed short);
signed short,
bool short);
signed short,
signed short);

vector unsigned short vec_vadduhs (vector
vector
vector unsigned short vec_vadduhs (vector
vector
vector unsigned short vec_vadduhs (vector
vector

bool short,
unsigned short);
unsigned short,
bool short);
unsigned short,
unsigned short);

vector signed char vec_vaddsbs (vector bool char, vector signed char);
vector signed char vec_vaddsbs (vector signed char, vector bool char);
vector signed char vec_vaddsbs (vector signed char, vector signed char);
vector unsigned char vec_vaddubs (vector
vector
vector unsigned char vec_vaddubs (vector
vector
vector unsigned char vec_vaddubs (vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

bool char,
unsigned char);
unsigned char,
bool char);
unsigned char,
unsigned char);

float vec_and (vector float, vector float);
float vec_and (vector float, vector bool int);
float vec_and (vector bool int, vector float);
bool long long vec_and (vector bool long long int,
vector bool long long);
bool int vec_and (vector bool int, vector bool int);
signed int vec_and (vector bool int, vector signed int);
signed int vec_and (vector signed int, vector bool int);
signed int vec_and (vector signed int, vector signed int);
unsigned int vec_and (vector bool int, vector unsigned int);
unsigned int vec_and (vector unsigned int, vector bool int);
unsigned int vec_and (vector unsigned int, vector unsigned int);
bool short vec_and (vector bool short, vector bool short);
signed short vec_and (vector bool short, vector signed short);
signed short vec_and (vector signed short, vector bool short);
signed short vec_and (vector signed short, vector signed short);
unsigned short vec_and (vector bool short,
vector unsigned short);
unsigned short vec_and (vector unsigned short,
vector bool short);
unsigned short vec_and (vector unsigned short,
vector unsigned short);
signed char vec_and (vector bool char, vector signed char);
bool char vec_and (vector bool char, vector bool char);
signed char vec_and (vector signed char, vector bool char);
signed char vec_and (vector signed char, vector signed char);
unsigned char vec_and (vector bool char, vector unsigned char);

685

686

Using the GNU Compiler Collection (GCC)

vector unsigned char vec_and (vector unsigned char, vector bool char);
vector unsigned char vec_and (vector unsigned char,
vector unsigned char);
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

float vec_andc (vector float, vector float);
float vec_andc (vector float, vector bool int);
float vec_andc (vector bool int, vector float);
bool int vec_andc (vector bool int, vector bool int);
signed int vec_andc (vector bool int, vector signed int);
signed int vec_andc (vector signed int, vector bool int);
signed int vec_andc (vector signed int, vector signed int);
unsigned int vec_andc (vector bool int, vector unsigned int);
unsigned int vec_andc (vector unsigned int, vector bool int);
unsigned int vec_andc (vector unsigned int, vector unsigned int);
bool short vec_andc (vector bool short, vector bool short);
signed short vec_andc (vector bool short, vector signed short);
signed short vec_andc (vector signed short, vector bool short);
signed short vec_andc (vector signed short, vector signed short);
unsigned short vec_andc (vector bool short,
vector unsigned short);
unsigned short vec_andc (vector unsigned short,
vector bool short);
unsigned short vec_andc (vector unsigned short,
vector unsigned short);
signed char vec_andc (vector bool char, vector signed char);
bool char vec_andc (vector bool char, vector bool char);
signed char vec_andc (vector signed char, vector bool char);
signed char vec_andc (vector signed char, vector signed char);
unsigned char vec_andc (vector bool char, vector unsigned char);
unsigned char vec_andc (vector unsigned char, vector bool char);
unsigned char vec_andc (vector unsigned char,
vector unsigned char);

vector unsigned char vec_avg (vector unsigned char,
vector unsigned char);
vector signed char vec_avg (vector signed char, vector signed char);
vector unsigned short vec_avg (vector unsigned short,
vector unsigned short);
vector signed short vec_avg (vector signed short, vector signed short);
vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
vector signed int vec_avg (vector signed int, vector signed int);
vector signed int vec_vavgsw (vector signed int, vector signed int);
vector unsigned int vec_vavguw (vector unsigned int,
vector unsigned int);
vector signed short vec_vavgsh (vector signed short,
vector signed short);
vector unsigned short vec_vavguh (vector unsigned short,
vector unsigned short);
vector signed char vec_vavgsb (vector signed char, vector signed char);
vector unsigned char vec_vavgub (vector unsigned char,
vector unsigned char);

Chapter 6: Extensions to the C Language Family

vector float vec_copysign (vector float);
vector float vec_ceil (vector float);
vector signed int vec_cmpb (vector float, vector float);
vector
vector
vector
vector
vector
vector
vector

bool
bool
bool
bool
bool
bool
bool

char vec_cmpeq (vector bool char, vector bool char);
short vec_cmpeq (vector bool short, vector bool short);
int vec_cmpeq (vector bool int, vector bool int);
char vec_cmpeq (vector signed char, vector signed char);
char vec_cmpeq (vector unsigned char, vector unsigned char);
short vec_cmpeq (vector signed short, vector signed short);
short vec_cmpeq (vector unsigned short,
vector unsigned short);
vector bool int vec_cmpeq (vector signed int, vector signed int);
vector bool int vec_cmpeq (vector unsigned int, vector unsigned int);
vector bool int vec_cmpeq (vector float, vector float);
vector bool int vec_vcmpeqfp (vector float, vector float);
vector bool int vec_vcmpequw (vector signed int, vector signed int);
vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);
vector bool short vec_vcmpequh (vector
vector
vector bool short vec_vcmpequh (vector
vector

signed short,
signed short);
unsigned short,
unsigned short);

vector bool char vec_vcmpequb (vector signed char, vector signed char);
vector bool char vec_vcmpequb (vector unsigned char,
vector unsigned char);
vector bool int vec_cmpge (vector float, vector float);
vector bool char vec_cmpgt (vector unsigned char, vector unsigned char);
vector bool char vec_cmpgt (vector signed char, vector signed char);
vector bool short vec_cmpgt (vector unsigned short,
vector unsigned short);
vector bool short vec_cmpgt (vector signed short, vector signed short);
vector bool int vec_cmpgt (vector unsigned int, vector unsigned int);
vector bool int vec_cmpgt (vector signed int, vector signed int);
vector bool int vec_cmpgt (vector float, vector float);
vector bool int vec_vcmpgtfp (vector float, vector float);
vector bool int vec_vcmpgtsw (vector signed int, vector signed int);
vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);
vector bool short vec_vcmpgtsh (vector signed short,
vector signed short);
vector bool short vec_vcmpgtuh (vector unsigned short,
vector unsigned short);
vector bool char vec_vcmpgtsb (vector signed char, vector signed char);
vector bool char vec_vcmpgtub (vector unsigned char,

687

688

Using the GNU Compiler Collection (GCC)

vector unsigned char);
vector bool int vec_cmple (vector float, vector float);
vector bool char vec_cmplt (vector unsigned char, vector unsigned char);
vector bool char vec_cmplt (vector signed char, vector signed char);
vector bool short vec_cmplt (vector unsigned short,
vector unsigned short);
vector bool short vec_cmplt (vector signed short, vector signed short);
vector bool int vec_cmplt (vector unsigned int, vector unsigned int);
vector bool int vec_cmplt (vector signed int, vector signed int);
vector bool int vec_cmplt (vector float, vector float);
vector float vec_cpsgn (vector float, vector float);
vector
vector
vector
vector

float vec_ctf (vector unsigned int, const int);
float vec_ctf (vector signed int, const int);
double vec_ctf (vector unsigned long, const int);
double vec_ctf (vector signed long, const int);

vector float vec_vcfsx (vector signed int, const int);
vector float vec_vcfux (vector unsigned int, const int);
vector signed int vec_cts (vector float, const int);
vector signed long vec_cts (vector double, const int);
vector unsigned int vec_ctu (vector float, const int);
vector unsigned long vec_ctu (vector double, const int);
vector double vec_doublee (vector float);
vector double vec_doublee (vector signed int);
vector double vec_doublee (vector unsigned int);
vector double vec_doubleo (vector float);
vector double vec_doubleo (vector signed int);
vector double vec_doubleo (vector unsigned int);
vector double vec_doubleh (vector float);
vector double vec_doubleh (vector signed int);
vector double vec_doubleh (vector unsigned int);
vector double vec_doublel (vector float);
vector double vec_doublel (vector signed int);
vector double vec_doublel (vector unsigned int);
void vec_dss (const int);
void vec_dssall (void);
void
void
void
void
void
void
void
void

vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst

(const
(const
(const
(const
(const
(const
(const
(const

vector
vector
vector
vector
vector
vector
vector
vector

unsigned char *, int, const int);
signed char *, int, const int);
bool char *, int, const int);
unsigned short *, int, const int);
signed short *, int, const int);
bool short *, int, const int);
pixel *, int, const int);
unsigned int *, int, const int);

Chapter 6: Extensions to the C Language Family

void
void
void
void
void
void
void
void
void
void
void
void

vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst
vec_dst

(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const

void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void

vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst
vec_dstst

void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void

vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt
vec_dststt

vector signed int *, int, const int);
vector bool int *, int, const int);
vector float *, int, const int);
unsigned char *, int, const int);
signed char *, int, const int);
unsigned short *, int, const int);
short *, int, const int);
unsigned int *, int, const int);
int *, int, const int);
unsigned long *, int, const int);
long *, int, const int);
float *, int, const int);

(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const

vector unsigned char *, int, const int);
vector signed char *, int, const int);
vector bool char *, int, const int);
vector unsigned short *, int, const int);
vector signed short *, int, const int);
vector bool short *, int, const int);
vector pixel *, int, const int);
vector unsigned int *, int, const int);
vector signed int *, int, const int);
vector bool int *, int, const int);
vector float *, int, const int);
unsigned char *, int, const int);
signed char *, int, const int);
unsigned short *, int, const int);
short *, int, const int);
unsigned int *, int, const int);
int *, int, const int);
unsigned long *, int, const int);
long *, int, const int);
float *, int, const int);
vector unsigned char *, int, const int);
vector signed char *, int, const int);
vector bool char *, int, const int);
vector unsigned short *, int, const int);
vector signed short *, int, const int);
vector bool short *, int, const int);
vector pixel *, int, const int);
vector unsigned int *, int, const int);
vector signed int *, int, const int);
vector bool int *, int, const int);
vector float *, int, const int);
unsigned char *, int, const int);
signed char *, int, const int);
unsigned short *, int, const int);
short *, int, const int);
unsigned int *, int, const int);
int *, int, const int);
unsigned long *, int, const int);
long *, int, const int);
float *, int, const int);

void vec_dstt (const vector unsigned char *, int, const int);
void vec_dstt (const vector signed char *, int, const int);
void vec_dstt (const vector bool char *, int, const int);

689

690

Using the GNU Compiler Collection (GCC)

void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void

vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt
vec_dstt

(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const
(const

vector unsigned short *, int, const int);
vector signed short *, int, const int);
vector bool short *, int, const int);
vector pixel *, int, const int);
vector unsigned int *, int, const int);
vector signed int *, int, const int);
vector bool int *, int, const int);
vector float *, int, const int);
unsigned char *, int, const int);
signed char *, int, const int);
unsigned short *, int, const int);
short *, int, const int);
unsigned int *, int, const int);
int *, int, const int);
unsigned long *, int, const int);
long *, int, const int);
float *, int, const int);

vector float vec_expte (vector float);
vector float vec_floor (vector float);
vector float vec_float (vector signed int);
vector float vec_float (vector unsigned int);
vector float vec_float2 (vector signed long long, vector signed long long);
vector float vec_float2 (vector unsigned long long, vector signed long long);
vector float vec_floate (vector double);
vector float vec_floate (vector signed long long);
vector float vec_floate (vector unsigned long long);
vector float vec_floato (vector double);
vector float vec_floato (vector signed long long);
vector float vec_floato (vector unsigned long long);
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

float vec_ld (int, const vector float *);
float vec_ld (int, const float *);
bool int vec_ld (int, const vector bool int *);
signed int vec_ld (int, const vector signed int *);
signed int vec_ld (int, const int *);
signed int vec_ld (int, const long *);
unsigned int vec_ld (int, const vector unsigned int *);
unsigned int vec_ld (int, const unsigned int *);
unsigned int vec_ld (int, const unsigned long *);
bool short vec_ld (int, const vector bool short *);
pixel vec_ld (int, const vector pixel *);
signed short vec_ld (int, const vector signed short *);
signed short vec_ld (int, const short *);
unsigned short vec_ld (int, const vector unsigned short *);
unsigned short vec_ld (int, const unsigned short *);
bool char vec_ld (int, const vector bool char *);
signed char vec_ld (int, const vector signed char *);
signed char vec_ld (int, const signed char *);
unsigned char vec_ld (int, const vector unsigned char *);
unsigned char vec_ld (int, const unsigned char *);

vector signed char vec_lde (int, const signed char *);

Chapter 6: Extensions to the C Language Family

691

vector
vector
vector
vector
vector
vector
vector
vector

unsigned char vec_lde (int, const unsigned char *);
signed short vec_lde (int, const short *);
unsigned short vec_lde (int, const unsigned short *);
float vec_lde (int, const float *);
signed int vec_lde (int, const int *);
unsigned int vec_lde (int, const unsigned int *);
signed int vec_lde (int, const long *);
unsigned int vec_lde (int, const unsigned long *);

vector
vector
vector
vector
vector

float vec_lvewx (int, float *);
signed int vec_lvewx (int, int *);
unsigned int vec_lvewx (int, unsigned int *);
signed int vec_lvewx (int, long *);
unsigned int vec_lvewx (int, unsigned long *);

vector signed short vec_lvehx (int, short *);
vector unsigned short vec_lvehx (int, unsigned short *);
vector signed char vec_lvebx (int, char *);
vector unsigned char vec_lvebx (int, unsigned char *);
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

float vec_ldl (int, const vector float *);
float vec_ldl (int, const float *);
bool int vec_ldl (int, const vector bool int *);
signed int vec_ldl (int, const vector signed int *);
signed int vec_ldl (int, const int *);
signed int vec_ldl (int, const long *);
unsigned int vec_ldl (int, const vector unsigned int *);
unsigned int vec_ldl (int, const unsigned int *);
unsigned int vec_ldl (int, const unsigned long *);
bool short vec_ldl (int, const vector bool short *);
pixel vec_ldl (int, const vector pixel *);
signed short vec_ldl (int, const vector signed short *);
signed short vec_ldl (int, const short *);
unsigned short vec_ldl (int, const vector unsigned short *);
unsigned short vec_ldl (int, const unsigned short *);
bool char vec_ldl (int, const vector bool char *);
signed char vec_ldl (int, const vector signed char *);
signed char vec_ldl (int, const signed char *);
unsigned char vec_ldl (int, const vector unsigned char *);
unsigned char vec_ldl (int, const unsigned char *);

vector float vec_loge (vector float);
vector
vector
vector
vector
vector
vector
vector
vector
vector

unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned

char
char
char
char
char
char
char
char
char

vec_lvsl
vec_lvsl
vec_lvsl
vec_lvsl
vec_lvsl
vec_lvsl
vec_lvsl
vec_lvsl
vec_lvsl

(int,
(int,
(int,
(int,
(int,
(int,
(int,
(int,
(int,

const
const
const
const
const
const
const
const
const

volatile
volatile
volatile
volatile
volatile
volatile
volatile
volatile
volatile

unsigned char *);
signed char *);
unsigned short *);
short *);
unsigned int *);
int *);
unsigned long *);
long *);
float *);

vector
vector
vector
vector

unsigned
unsigned
unsigned
unsigned

char
char
char
char

vec_lvsr
vec_lvsr
vec_lvsr
vec_lvsr

(int,
(int,
(int,
(int,

const
const
const
const

volatile
volatile
volatile
volatile

unsigned char *);
signed char *);
unsigned short *);
short *);

692

Using the GNU Compiler Collection (GCC)

vector
vector
vector
vector
vector

unsigned
unsigned
unsigned
unsigned
unsigned

char
char
char
char
char

vec_lvsr
vec_lvsr
vec_lvsr
vec_lvsr
vec_lvsr

(int,
(int,
(int,
(int,
(int,

const
const
const
const
const

volatile
volatile
volatile
volatile
volatile

unsigned int *);
int *);
unsigned long *);
long *);
float *);

vector float vec_madd (vector float, vector float, vector float);
vector signed short vec_madds (vector signed short,
vector signed short,
vector signed short);
vector unsigned char vec_max (vector bool char, vector unsigned char);
vector unsigned char vec_max (vector unsigned char, vector bool char);
vector unsigned char vec_max (vector unsigned char,
vector unsigned char);
vector signed char vec_max (vector bool char, vector signed char);
vector signed char vec_max (vector signed char, vector bool char);
vector signed char vec_max (vector signed char, vector signed char);
vector unsigned short vec_max (vector bool short,
vector unsigned short);
vector unsigned short vec_max (vector unsigned short,
vector bool short);
vector unsigned short vec_max (vector unsigned short,
vector unsigned short);
vector signed short vec_max (vector bool short, vector signed short);
vector signed short vec_max (vector signed short, vector bool short);
vector signed short vec_max (vector signed short, vector signed short);
vector unsigned int vec_max (vector bool int, vector unsigned int);
vector unsigned int vec_max (vector unsigned int, vector bool int);
vector unsigned int vec_max (vector unsigned int, vector unsigned int);
vector signed int vec_max (vector bool int, vector signed int);
vector signed int vec_max (vector signed int, vector bool int);
vector signed int vec_max (vector signed int, vector signed int);
vector float vec_max (vector float, vector float);
vector float vec_vmaxfp (vector float, vector float);
vector signed int vec_vmaxsw (vector bool int, vector signed int);
vector signed int vec_vmaxsw (vector signed int, vector bool int);
vector signed int vec_vmaxsw (vector signed int, vector signed int);
vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
vector unsigned int vec_vmaxuw (vector unsigned int,
vector unsigned int);
vector signed short vec_vmaxsh (vector bool short, vector signed short);
vector signed short vec_vmaxsh (vector signed short, vector bool short);
vector signed short vec_vmaxsh (vector signed short,
vector signed short);
vector unsigned short vec_vmaxuh (vector
vector
vector unsigned short vec_vmaxuh (vector
vector
vector unsigned short vec_vmaxuh (vector
vector

bool short,
unsigned short);
unsigned short,
bool short);
unsigned short,
unsigned short);

Chapter 6: Extensions to the C Language Family

vector signed char vec_vmaxsb (vector bool char, vector signed char);
vector signed char vec_vmaxsb (vector signed char, vector bool char);
vector signed char vec_vmaxsb (vector signed char, vector signed char);
vector unsigned char vec_vmaxub (vector
vector
vector unsigned char vec_vmaxub (vector
vector
vector unsigned char vec_vmaxub (vector
vector

bool char,
unsigned char);
unsigned char,
bool char);
unsigned char,
unsigned char);

vector bool char vec_mergeh (vector bool char, vector bool char);
vector signed char vec_mergeh (vector signed char, vector signed char);
vector unsigned char vec_mergeh (vector unsigned char,
vector unsigned char);
vector bool short vec_mergeh (vector bool short, vector bool short);
vector pixel vec_mergeh (vector pixel, vector pixel);
vector signed short vec_mergeh (vector signed short,
vector signed short);
vector unsigned short vec_mergeh (vector unsigned short,
vector unsigned short);
vector float vec_mergeh (vector float, vector float);
vector bool int vec_mergeh (vector bool int, vector bool int);
vector signed int vec_mergeh (vector signed int, vector signed int);
vector unsigned int vec_mergeh (vector unsigned int,
vector unsigned int);
vector
vector
vector
vector

float vec_vmrghw (vector float, vector float);
bool int vec_vmrghw (vector bool int, vector bool int);
signed int vec_vmrghw (vector signed int, vector signed int);
unsigned int vec_vmrghw (vector unsigned int,
vector unsigned int);

vector bool short vec_vmrghh (vector bool short, vector bool short);
vector signed short vec_vmrghh (vector signed short,
vector signed short);
vector unsigned short vec_vmrghh (vector unsigned short,
vector unsigned short);
vector pixel vec_vmrghh (vector pixel, vector pixel);
vector bool char vec_vmrghb (vector bool char, vector bool char);
vector signed char vec_vmrghb (vector signed char, vector signed char);
vector unsigned char vec_vmrghb (vector unsigned char,
vector unsigned char);
vector bool char vec_mergel (vector bool char, vector bool char);
vector signed char vec_mergel (vector signed char, vector signed char);
vector unsigned char vec_mergel (vector unsigned char,
vector unsigned char);
vector bool short vec_mergel (vector bool short, vector bool short);
vector pixel vec_mergel (vector pixel, vector pixel);
vector signed short vec_mergel (vector signed short,
vector signed short);
vector unsigned short vec_mergel (vector unsigned short,
vector unsigned short);
vector float vec_mergel (vector float, vector float);
vector bool int vec_mergel (vector bool int, vector bool int);

693

694

Using the GNU Compiler Collection (GCC)

vector signed int vec_mergel (vector signed int, vector signed int);
vector unsigned int vec_mergel (vector unsigned int,
vector unsigned int);
vector float vec_vmrglw (vector float, vector float);
vector signed int vec_vmrglw (vector signed int, vector signed int);
vector unsigned int vec_vmrglw (vector unsigned int,
vector unsigned int);
vector bool int vec_vmrglw (vector bool int, vector bool int);
vector bool short vec_vmrglh (vector bool short, vector bool short);
vector signed short vec_vmrglh (vector signed short,
vector signed short);
vector unsigned short vec_vmrglh (vector unsigned short,
vector unsigned short);
vector pixel vec_vmrglh (vector pixel, vector pixel);
vector bool char vec_vmrglb (vector bool char, vector bool char);
vector signed char vec_vmrglb (vector signed char, vector signed char);
vector unsigned char vec_vmrglb (vector unsigned char,
vector unsigned char);
vector unsigned short vec_mfvscr (void);
vector unsigned char vec_min (vector bool char, vector unsigned char);
vector unsigned char vec_min (vector unsigned char, vector bool char);
vector unsigned char vec_min (vector unsigned char,
vector unsigned char);
vector signed char vec_min (vector bool char, vector signed char);
vector signed char vec_min (vector signed char, vector bool char);
vector signed char vec_min (vector signed char, vector signed char);
vector unsigned short vec_min (vector bool short,
vector unsigned short);
vector unsigned short vec_min (vector unsigned short,
vector bool short);
vector unsigned short vec_min (vector unsigned short,
vector unsigned short);
vector signed short vec_min (vector bool short, vector signed short);
vector signed short vec_min (vector signed short, vector bool short);
vector signed short vec_min (vector signed short, vector signed short);
vector unsigned int vec_min (vector bool int, vector unsigned int);
vector unsigned int vec_min (vector unsigned int, vector bool int);
vector unsigned int vec_min (vector unsigned int, vector unsigned int);
vector signed int vec_min (vector bool int, vector signed int);
vector signed int vec_min (vector signed int, vector bool int);
vector signed int vec_min (vector signed int, vector signed int);
vector float vec_min (vector float, vector float);
vector float vec_vminfp (vector float, vector float);
vector signed int vec_vminsw (vector bool int, vector signed int);
vector signed int vec_vminsw (vector signed int, vector bool int);
vector signed int vec_vminsw (vector signed int, vector signed int);
vector unsigned int vec_vminuw (vector bool int, vector unsigned int);
vector unsigned int vec_vminuw (vector unsigned int, vector bool int);
vector unsigned int vec_vminuw (vector unsigned int,
vector unsigned int);

Chapter 6: Extensions to the C Language Family

vector signed short vec_vminsh (vector bool short, vector signed short);
vector signed short vec_vminsh (vector signed short, vector bool short);
vector signed short vec_vminsh (vector signed short,
vector signed short);
vector unsigned short vec_vminuh (vector
vector
vector unsigned short vec_vminuh (vector
vector
vector unsigned short vec_vminuh (vector
vector

bool short,
unsigned short);
unsigned short,
bool short);
unsigned short,
unsigned short);

vector signed char vec_vminsb (vector bool char, vector signed char);
vector signed char vec_vminsb (vector signed char, vector bool char);
vector signed char vec_vminsb (vector signed char, vector signed char);
vector unsigned char vec_vminub (vector
vector
vector unsigned char vec_vminub (vector
vector
vector unsigned char vec_vminub (vector
vector

bool char,
unsigned char);
unsigned char,
bool char);
unsigned char,
unsigned char);

vector signed short vec_mladd (vector signed short,
vector signed short,
vector signed short);
vector signed short vec_mladd (vector signed short,
vector unsigned short,
vector unsigned short);
vector signed short vec_mladd (vector unsigned short,
vector signed short,
vector signed short);
vector unsigned short vec_mladd (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector signed short vec_mradds (vector signed short,
vector signed short,
vector signed short);
vector unsigned int vec_msum (vector unsigned char,
vector unsigned char,
vector unsigned int);
vector signed int vec_msum (vector signed char,
vector unsigned char,
vector signed int);
vector unsigned int vec_msum (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_msum (vector signed short,
vector signed short,
vector signed int);
vector signed int vec_vmsumshm (vector signed short,
vector signed short,
vector signed int);

695

696

Using the GNU Compiler Collection (GCC)

vector unsigned int vec_vmsumuhm (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_vmsummbm (vector signed char,
vector unsigned char,
vector signed int);
vector unsigned int vec_vmsumubm (vector unsigned char,
vector unsigned char,
vector unsigned int);
vector unsigned int vec_msums (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_msums (vector signed short,
vector signed short,
vector signed int);
vector signed int vec_vmsumshs (vector signed short,
vector signed short,
vector signed int);
vector unsigned int vec_vmsumuhs (vector unsigned short,
vector unsigned short,
vector unsigned int);
void
void
void
void
void
void
void
void
void
void

vec_mtvscr
vec_mtvscr
vec_mtvscr
vec_mtvscr
vec_mtvscr
vec_mtvscr
vec_mtvscr
vec_mtvscr
vec_mtvscr
vec_mtvscr

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

signed int);
unsigned int);
bool int);
signed short);
unsigned short);
bool short);
pixel);
signed char);
unsigned char);
bool char);

vector unsigned short vec_mule (vector unsigned char,
vector unsigned char);
vector signed short vec_mule (vector signed char,
vector signed char);
vector unsigned int vec_mule (vector unsigned short,
vector unsigned short);
vector signed int vec_mule (vector signed short, vector signed short);
vector unsigned long long vec_mule (vector unsigned int,
vector unsigned int);
vector signed long long vec_mule (vector signed int,
vector signed int);
vector signed int vec_vmulesh (vector signed short,
vector signed short);
vector unsigned int vec_vmuleuh (vector unsigned short,
vector unsigned short);
vector signed short vec_vmulesb (vector signed char,
vector signed char);

Chapter 6: Extensions to the C Language Family

vector unsigned short vec_vmuleub (vector unsigned char,
vector unsigned char);
vector unsigned short vec_mulo (vector unsigned char,
vector unsigned char);
vector signed short vec_mulo (vector signed char, vector signed char);
vector unsigned int vec_mulo (vector unsigned short,
vector unsigned short);
vector signed int vec_mulo (vector signed short, vector signed short);
vector unsigned long long vec_mulo (vector unsigned int,
vector unsigned int);
vector signed long long vec_mulo (vector signed int,
vector signed int);
vector signed int vec_vmulosh (vector signed short,
vector signed short);
vector unsigned int vec_vmulouh (vector unsigned short,
vector unsigned short);
vector signed short vec_vmulosb (vector signed char,
vector signed char);
vector unsigned short vec_vmuloub (vector unsigned char,
vector unsigned char);
vector float vec_nmsub (vector float, vector float, vector float);
vector
vector
vector
vector
vector

signed char vec_nabs (vector signed char);
signed short vec_nabs (vector signed short);
signed int vec_nabs (vector signed int);
float vec_nabs (vector float);
double vec_nabs (vector double);

vector
vector
vector
vector
vector
vector

signed
signed
signed
signed
float
double

vector
vector
vector
vector
vector
vector

float vec_nor (vector float, vector float);
signed int vec_nor (vector signed int, vector signed int);
unsigned int vec_nor (vector unsigned int, vector unsigned int);
bool int vec_nor (vector bool int, vector bool int);
signed short vec_nor (vector signed short, vector signed short);
unsigned short vec_nor (vector unsigned short,
vector unsigned short);
bool short vec_nor (vector bool short, vector bool short);
signed char vec_nor (vector signed char, vector signed char);
unsigned char vec_nor (vector unsigned char,
vector unsigned char);
bool char vec_nor (vector bool char, vector bool char);

vector
vector
vector
vector

char vec_neg (vector signed char);
short vec_neg (vector signed short);
int vec_neg (vector signed int);
long long vec_neg (vector signed long long);
char vec_neg (vector float);
vec_neg (vector double);

vector float vec_or (vector float, vector float);
vector float vec_or (vector float, vector bool int);
vector float vec_or (vector bool int, vector float);

697

698

Using the GNU Compiler Collection (GCC)

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

bool int vec_or (vector bool int, vector bool int);
signed int vec_or (vector bool int, vector signed int);
signed int vec_or (vector signed int, vector bool int);
signed int vec_or (vector signed int, vector signed int);
unsigned int vec_or (vector bool int, vector unsigned int);
unsigned int vec_or (vector unsigned int, vector bool int);
unsigned int vec_or (vector unsigned int, vector unsigned int);
bool short vec_or (vector bool short, vector bool short);
signed short vec_or (vector bool short, vector signed short);
signed short vec_or (vector signed short, vector bool short);
signed short vec_or (vector signed short, vector signed short);
unsigned short vec_or (vector bool short, vector unsigned short);
unsigned short vec_or (vector unsigned short, vector bool short);
unsigned short vec_or (vector unsigned short,
vector unsigned short);
signed char vec_or (vector bool char, vector signed char);
bool char vec_or (vector bool char, vector bool char);
signed char vec_or (vector signed char, vector bool char);
signed char vec_or (vector signed char, vector signed char);
unsigned char vec_or (vector bool char, vector unsigned char);
unsigned char vec_or (vector unsigned char, vector bool char);
unsigned char vec_or (vector unsigned char,
vector unsigned char);

vector signed char vec_pack (vector signed short, vector signed short);
vector unsigned char vec_pack (vector unsigned short,
vector unsigned short);
vector bool char vec_pack (vector bool short, vector bool short);
vector signed short vec_pack (vector signed int, vector signed int);
vector unsigned short vec_pack (vector unsigned int,
vector unsigned int);
vector bool short vec_pack (vector bool int, vector bool int);
vector bool short vec_vpkuwum (vector bool int, vector bool int);
vector signed short vec_vpkuwum (vector signed int, vector signed int);
vector unsigned short vec_vpkuwum (vector unsigned int,
vector unsigned int);
vector bool char vec_vpkuhum (vector bool short, vector bool short);
vector signed char vec_vpkuhum (vector signed short,
vector signed short);
vector unsigned char vec_vpkuhum (vector unsigned short,
vector unsigned short);
vector pixel vec_packpx (vector unsigned int, vector unsigned int);
vector unsigned char vec_packs (vector unsigned short,
vector unsigned short);
vector signed char vec_packs (vector signed short, vector signed short);
vector unsigned short vec_packs (vector unsigned int,
vector unsigned int);
vector signed short vec_packs (vector signed int, vector signed int);
vector signed short vec_vpkswss (vector signed int, vector signed int);
vector unsigned short vec_vpkuwus (vector unsigned int,
vector unsigned int);

Chapter 6: Extensions to the C Language Family

vector signed char vec_vpkshss (vector signed short,
vector signed short);
vector unsigned char vec_vpkuhus (vector unsigned short,
vector unsigned short);
vector unsigned char vec_packsu (vector unsigned short,
vector unsigned short);
vector unsigned char vec_packsu (vector signed short,
vector signed short);
vector unsigned short vec_packsu (vector unsigned int,
vector unsigned int);
vector unsigned short vec_packsu (vector signed int, vector signed int);
vector unsigned short vec_vpkswus (vector signed int,
vector signed int);
vector unsigned char vec_vpkshus (vector signed short,
vector signed short);
vector float vec_perm (vector float,
vector float,
vector unsigned char);
vector signed int vec_perm (vector signed int,
vector signed int,
vector unsigned char);
vector unsigned int vec_perm (vector unsigned int,
vector unsigned int,
vector unsigned char);
vector bool int vec_perm (vector bool int,
vector bool int,
vector unsigned char);
vector signed short vec_perm (vector signed short,
vector signed short,
vector unsigned char);
vector unsigned short vec_perm (vector unsigned short,
vector unsigned short,
vector unsigned char);
vector bool short vec_perm (vector bool short,
vector bool short,
vector unsigned char);
vector pixel vec_perm (vector pixel,
vector pixel,
vector unsigned char);
vector signed char vec_perm (vector signed char,
vector signed char,
vector unsigned char);
vector unsigned char vec_perm (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector bool char vec_perm (vector bool char,
vector bool char,
vector unsigned char);
vector float vec_re (vector float);
vector bool char vec_reve (vector bool char);
vector signed char vec_reve (vector signed char);

699

700

Using the GNU Compiler Collection (GCC)

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

unsigned char vec_reve (vector unsigned char);
bool int vec_reve (vector bool int);
signed int vec_reve (vector signed int);
unsigned int vec_reve (vector unsigned int);
bool long long vec_reve (vector bool long long);
signed long long vec_reve (vector signed long long);
unsigned long long vec_reve (vector unsigned long long);
bool short vec_reve (vector bool short);
signed short vec_reve (vector signed short);
unsigned short vec_reve (vector unsigned short);

vector signed char vec_rl (vector signed char,
vector unsigned char);
vector unsigned char vec_rl (vector unsigned char,
vector unsigned char);
vector signed short vec_rl (vector signed short, vector unsigned short);
vector unsigned short vec_rl (vector unsigned short,
vector unsigned short);
vector signed int vec_rl (vector signed int, vector unsigned int);
vector unsigned int vec_rl (vector unsigned int, vector unsigned int);
vector signed int vec_vrlw (vector signed int, vector unsigned int);
vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int);
vector signed short vec_vrlh (vector signed short,
vector unsigned short);
vector unsigned short vec_vrlh (vector unsigned short,
vector unsigned short);
vector signed char vec_vrlb (vector signed char, vector unsigned char);
vector unsigned char vec_vrlb (vector unsigned char,
vector unsigned char);
vector float vec_round (vector float);
vector float vec_recip (vector float, vector float);
vector float vec_rsqrt (vector float);
vector float vec_rsqrte (vector float);
vector float vec_sel (vector float, vector float, vector bool int);
vector float vec_sel (vector float, vector float, vector unsigned int);
vector signed int vec_sel (vector signed int,
vector signed int,
vector bool int);
vector signed int vec_sel (vector signed int,
vector signed int,
vector unsigned int);
vector unsigned int vec_sel (vector unsigned int,
vector unsigned int,
vector bool int);
vector unsigned int vec_sel (vector unsigned int,
vector unsigned int,
vector unsigned int);
vector bool int vec_sel (vector bool int,
vector bool int,
vector bool int);

Chapter 6: Extensions to the C Language Family

vector bool int vec_sel (vector bool int,
vector bool int,
vector unsigned int);
vector signed short vec_sel (vector signed short,
vector signed short,
vector bool short);
vector signed short vec_sel (vector signed short,
vector signed short,
vector unsigned short);
vector unsigned short vec_sel (vector unsigned short,
vector unsigned short,
vector bool short);
vector unsigned short vec_sel (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector bool short vec_sel (vector bool short,
vector bool short,
vector bool short);
vector bool short vec_sel (vector bool short,
vector bool short,
vector unsigned short);
vector signed char vec_sel (vector signed char,
vector signed char,
vector bool char);
vector signed char vec_sel (vector signed char,
vector signed char,
vector unsigned char);
vector unsigned char vec_sel (vector unsigned char,
vector unsigned char,
vector bool char);
vector unsigned char vec_sel (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector bool char vec_sel (vector bool char,
vector bool char,
vector bool char);
vector bool char vec_sel (vector bool char,
vector bool char,
vector unsigned char);
vector signed long long vec_signed (vector double);
vector signed int vec_signed (vector float);
vector signed int vec_signede (vector double);
vector signed int vec_signedo (vector double);
vector signed int vec_signed2 (vector double, vector double);
vector signed char vec_sl (vector signed char,
vector unsigned char);
vector unsigned char vec_sl (vector unsigned char,
vector unsigned char);
vector signed short vec_sl (vector signed short, vector unsigned short);
vector unsigned short vec_sl (vector unsigned short,
vector unsigned short);
vector signed int vec_sl (vector signed int, vector unsigned int);
vector unsigned int vec_sl (vector unsigned int, vector unsigned int);
vector signed int vec_vslw (vector signed int, vector unsigned int);

701

702

Using the GNU Compiler Collection (GCC)

vector unsigned int vec_vslw (vector unsigned int, vector unsigned int);
vector signed short vec_vslh (vector signed short,
vector unsigned short);
vector unsigned short vec_vslh (vector unsigned short,
vector unsigned short);
vector signed char vec_vslb (vector signed char, vector unsigned char);
vector unsigned char vec_vslb (vector unsigned char,
vector unsigned char);
vector float vec_sld (vector float, vector float, const int);
vector double vec_sld (vector double, vector double, const int);
vector signed int vec_sld (vector signed int,
vector signed int,
const int);
vector unsigned int vec_sld (vector unsigned int,
vector unsigned int,
const int);
vector bool int vec_sld (vector bool int,
vector bool int,
const int);
vector signed short vec_sld (vector signed short,
vector signed short,
const int);
vector unsigned short vec_sld (vector unsigned short,
vector unsigned short,
const int);
vector bool short vec_sld (vector bool short,
vector bool short,
const int);
vector pixel vec_sld (vector pixel,
vector pixel,
const int);
vector signed char vec_sld (vector signed char,
vector signed char,
const int);
vector unsigned char vec_sld (vector unsigned char,
vector unsigned char,
const int);
vector bool char vec_sld (vector bool char,
vector bool char,
const int);
vector bool long long int vec_sld (vector bool long long int,
vector bool long long int, const int);
vector long long int vec_sld (vector long long int,
vector long long int, const int);
vector unsigned long long int vec_sld (vector unsigned long long int,
vector unsigned long long int,
const int);
vector signed char vec_sldw (vector signed char,
vector signed char,
const int);
vector unsigned char vec_sldw (vector unsigned char,
vector unsigned char,
const int);

Chapter 6: Extensions to the C Language Family

vector signed short vec_sldw (vector signed short,
vector signed short,
const int);
vector unsigned short vec_sldw (vector unsigned short,
vector unsigned short,
const int);
vector signed int vec_sldw (vector signed int,
vector signed int,
const int);
vector unsigned int vec_sldw (vector unsigned int,
vector unsigned int,
const int);
vector signed long long vec_sldw (vector signed long long,
vector signed long long,
const int);
vector unsigned long long vec_sldw (vector unsigned long long,
vector unsigned long long,
const int);
vector signed int vec_sll (vector signed int,
vector unsigned int);
vector signed int vec_sll (vector signed int,
vector unsigned short);
vector signed int vec_sll (vector signed int,
vector unsigned char);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned int);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned short);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned char);
vector bool int vec_sll (vector bool int,
vector unsigned int);
vector bool int vec_sll (vector bool int,
vector unsigned short);
vector bool int vec_sll (vector bool int,
vector unsigned char);
vector signed short vec_sll (vector signed short,
vector unsigned int);
vector signed short vec_sll (vector signed short,
vector unsigned short);
vector signed short vec_sll (vector signed short,
vector unsigned char);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned int);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned short);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned char);
vector long long int vec_sll (vector long long int,
vector unsigned char);
vector unsigned long long int vec_sll (vector unsigned long long int,
vector unsigned char);
vector bool short vec_sll (vector bool short, vector unsigned int);
vector bool short vec_sll (vector bool short, vector unsigned short);
vector bool short vec_sll (vector bool short, vector unsigned char);
vector pixel vec_sll (vector pixel, vector unsigned int);
vector pixel vec_sll (vector pixel, vector unsigned short);

703

704

Using the GNU Compiler Collection (GCC)

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

pixel vec_sll (vector pixel, vector unsigned char);
signed char vec_sll (vector signed char, vector unsigned int);
signed char vec_sll (vector signed char, vector unsigned short);
signed char vec_sll (vector signed char, vector unsigned char);
unsigned char vec_sll (vector unsigned char,
vector unsigned int);
unsigned char vec_sll (vector unsigned char,
vector unsigned short);
unsigned char vec_sll (vector unsigned char,
vector unsigned char);
bool char vec_sll (vector bool char, vector unsigned int);
bool char vec_sll (vector bool char, vector unsigned short);
bool char vec_sll (vector bool char, vector unsigned char);

vector
vector
vector
vector

float vec_slo (vector float, vector signed char);
float vec_slo (vector float, vector unsigned char);
signed int vec_slo (vector signed int, vector signed char);
signed int vec_slo (vector signed int, vector unsigned char);
unsigned int vec_slo (vector unsigned int, vector signed char);
unsigned int vec_slo (vector unsigned int, vector unsigned char);
signed short vec_slo (vector signed short, vector signed char);
signed short vec_slo (vector signed short, vector unsigned char);
unsigned short vec_slo (vector unsigned short,
vector signed char);
unsigned short vec_slo (vector unsigned short,
vector unsigned char);
pixel vec_slo (vector pixel, vector signed char);
pixel vec_slo (vector pixel, vector unsigned char);
signed char vec_slo (vector signed char, vector signed char);
signed char vec_slo (vector signed char, vector unsigned char);
unsigned char vec_slo (vector unsigned char, vector signed char);
unsigned char vec_slo (vector unsigned char,
vector unsigned char);
signed long long vec_slo (vector signed long long, vector signed char);
signed long long vec_slo (vector signed long long, vector unsigned char);
unsigned long long vec_slo (vector unsigned long long, vector signed char);
unsigned long long vec_slo (vector unsigned long long, vector unsigned char);

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

signed char vec_splat (vector signed char, const int);
unsigned char vec_splat (vector unsigned char, const int);
bool char vec_splat (vector bool char, const int);
signed short vec_splat (vector signed short, const int);
unsigned short vec_splat (vector unsigned short, const int);
bool short vec_splat (vector bool short, const int);
pixel vec_splat (vector pixel, const int);
float vec_splat (vector float, const int);
signed int vec_splat (vector signed int, const int);
unsigned int vec_splat (vector unsigned int, const int);
bool int vec_splat (vector bool int, const int);
signed long vec_splat (vector signed long, const int);
unsigned long vec_splat (vector unsigned long, const int);

vector
vector
vector
vector
vector
vector

signed char vec_splats (signed char);
unsigned char vec_splats (unsigned char);
signed short vec_splats (signed short);
unsigned short vec_splats (unsigned short);
signed int vec_splats (signed int);
unsigned int vec_splats (unsigned int);

vector
vector
vector
vector
vector
vector
vector

Chapter 6: Extensions to the C Language Family

vector float vec_splats (float);
vector
vector
vector
vector

float vec_vspltw (vector float, const int);
signed int vec_vspltw (vector signed int, const int);
unsigned int vec_vspltw (vector unsigned int, const int);
bool int vec_vspltw (vector bool int, const int);

vector
vector
vector
vector

bool short vec_vsplth (vector bool short, const int);
signed short vec_vsplth (vector signed short, const int);
unsigned short vec_vsplth (vector unsigned short, const int);
pixel vec_vsplth (vector pixel, const int);

vector signed char vec_vspltb (vector signed char, const int);
vector unsigned char vec_vspltb (vector unsigned char, const int);
vector bool char vec_vspltb (vector bool char, const int);
vector signed char vec_splat_s8 (const int);
vector signed short vec_splat_s16 (const int);
vector signed int vec_splat_s32 (const int);
vector unsigned char vec_splat_u8 (const int);
vector unsigned short vec_splat_u16 (const int);
vector unsigned int vec_splat_u32 (const int);
vector signed char vec_sr (vector signed char, vector unsigned char);
vector unsigned char vec_sr (vector unsigned char,
vector unsigned char);
vector signed short vec_sr (vector signed short,
vector unsigned short);
vector unsigned short vec_sr (vector unsigned short,
vector unsigned short);
vector signed int vec_sr (vector signed int, vector unsigned int);
vector unsigned int vec_sr (vector unsigned int, vector unsigned int);
vector signed int vec_vsrw (vector signed int, vector unsigned int);
vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int);
vector signed short vec_vsrh (vector signed short,
vector unsigned short);
vector unsigned short vec_vsrh (vector unsigned short,
vector unsigned short);
vector signed char vec_vsrb (vector signed char, vector unsigned char);
vector unsigned char vec_vsrb (vector unsigned char,
vector unsigned char);
vector signed char vec_sra (vector signed char, vector unsigned char);
vector unsigned char vec_sra (vector unsigned char,
vector unsigned char);
vector signed short vec_sra (vector signed short,
vector unsigned short);
vector unsigned short vec_sra (vector unsigned short,
vector unsigned short);
vector signed int vec_sra (vector signed int, vector unsigned int);

705

706

Using the GNU Compiler Collection (GCC)

vector unsigned int vec_sra (vector unsigned int, vector unsigned int);
vector signed int vec_vsraw (vector signed int, vector unsigned int);
vector unsigned int vec_vsraw (vector unsigned int,
vector unsigned int);
vector signed short vec_vsrah (vector signed short,
vector unsigned short);
vector unsigned short vec_vsrah (vector unsigned short,
vector unsigned short);
vector signed char vec_vsrab (vector signed char, vector unsigned char);
vector unsigned char vec_vsrab (vector unsigned char,
vector unsigned char);
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

signed int vec_srl (vector signed int, vector unsigned int);
signed int vec_srl (vector signed int, vector unsigned short);
signed int vec_srl (vector signed int, vector unsigned char);
unsigned int vec_srl (vector unsigned int, vector unsigned int);
unsigned int vec_srl (vector unsigned int,
vector unsigned short);
unsigned int vec_srl (vector unsigned int, vector unsigned char);
bool int vec_srl (vector bool int, vector unsigned int);
bool int vec_srl (vector bool int, vector unsigned short);
bool int vec_srl (vector bool int, vector unsigned char);
signed short vec_srl (vector signed short, vector unsigned int);
signed short vec_srl (vector signed short,
vector unsigned short);
signed short vec_srl (vector signed short, vector unsigned char);
unsigned short vec_srl (vector unsigned short,
vector unsigned int);
unsigned short vec_srl (vector unsigned short,
vector unsigned short);
unsigned short vec_srl (vector unsigned short,
vector unsigned char);
long long int vec_srl (vector long long int,
vector unsigned char);
unsigned long long int vec_srl (vector unsigned long long int,
vector unsigned char);
bool short vec_srl (vector bool short, vector unsigned int);
bool short vec_srl (vector bool short, vector unsigned short);
bool short vec_srl (vector bool short, vector unsigned char);
pixel vec_srl (vector pixel, vector unsigned int);
pixel vec_srl (vector pixel, vector unsigned short);
pixel vec_srl (vector pixel, vector unsigned char);
signed char vec_srl (vector signed char, vector unsigned int);
signed char vec_srl (vector signed char, vector unsigned short);
signed char vec_srl (vector signed char, vector unsigned char);
unsigned char vec_srl (vector unsigned char,
vector unsigned int);
unsigned char vec_srl (vector unsigned char,
vector unsigned short);
unsigned char vec_srl (vector unsigned char,
vector unsigned char);
bool char vec_srl (vector bool char, vector unsigned int);
bool char vec_srl (vector bool char, vector unsigned short);
bool char vec_srl (vector bool char, vector unsigned char);

Chapter 6: Extensions to the C Language Family

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void

float vec_sro (vector float, vector signed char);
float vec_sro (vector float, vector unsigned char);
signed int vec_sro (vector signed int, vector signed char);
signed int vec_sro (vector signed int, vector unsigned char);
unsigned int vec_sro (vector unsigned int, vector signed char);
unsigned int vec_sro (vector unsigned int, vector unsigned char);
signed short vec_sro (vector signed short, vector signed char);
signed short vec_sro (vector signed short, vector unsigned char);
unsigned short vec_sro (vector unsigned short,
vector signed char);
unsigned short vec_sro (vector unsigned short,
vector unsigned char);
long long int vec_sro (vector long long int,
vector char);
long long int vec_sro (vector long long int,
vector unsigned char);
unsigned long long int vec_sro (vector unsigned long long int,
vector char);
unsigned long long int vec_sro (vector unsigned long long int,
vector unsigned char);
pixel vec_sro (vector pixel, vector signed char);
pixel vec_sro (vector pixel, vector unsigned char);
signed char vec_sro (vector signed char, vector signed char);
signed char vec_sro (vector signed char, vector unsigned char);
unsigned char vec_sro (vector unsigned char, vector signed char);
unsigned char vec_sro (vector unsigned char,
vector unsigned char);

vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st
vec_st

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

float, int, vector float *);
float, int, float *);
signed int, int, vector signed int *);
signed int, int, int *);
unsigned int, int, vector unsigned int *);
unsigned int, int, unsigned int *);
bool int, int, vector bool int *);
bool int, int, unsigned int *);
bool int, int, int *);
signed short, int, vector signed short *);
signed short, int, short *);
unsigned short, int, vector unsigned short *);
unsigned short, int, unsigned short *);
bool short, int, vector bool short *);
bool short, int, unsigned short *);
pixel, int, vector pixel *);
pixel, int, unsigned short *);
pixel, int, short *);
bool short, int, short *);
signed char, int, vector signed char *);
signed char, int, signed char *);
unsigned char, int, vector unsigned char *);
unsigned char, int, unsigned char *);
bool char, int, vector bool char *);
bool char, int, unsigned char *);
bool char, int, signed char *);

void vec_ste (vector signed char, int, signed char *);
void vec_ste (vector unsigned char, int, unsigned char *);
void vec_ste (vector bool char, int, signed char *);

707

708

Using the GNU Compiler Collection (GCC)

void
void
void
void
void
void
void
void
void
void
void
void

vec_ste
vec_ste
vec_ste
vec_ste
vec_ste
vec_ste
vec_ste
vec_ste
vec_ste
vec_ste
vec_ste
vec_ste

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

void
void
void
void
void

vec_stvewx
vec_stvewx
vec_stvewx
vec_stvewx
vec_stvewx

(vector
(vector
(vector
(vector
(vector

float, int, float *);
signed int, int, int *);
unsigned int, int, unsigned int *);
bool int, int, int *);
bool int, int, unsigned int *);

void
void
void
void
void
void

vec_stvehx
vec_stvehx
vec_stvehx
vec_stvehx
vec_stvehx
vec_stvehx

(vector
(vector
(vector
(vector
(vector
(vector

signed short, int, short *);
unsigned short, int, unsigned short *);
bool short, int, short *);
bool short, int, unsigned short *);
pixel, int, short *);
pixel, int, unsigned short *);

void
void
void
void

vec_stvebx
vec_stvebx
vec_stvebx
vec_stvebx

(vector
(vector
(vector
(vector

signed char, int, signed char *);
unsigned char, int, unsigned char *);
bool char, int, signed char *);
bool char, int, unsigned char *);

void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void

vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl
vec_stl

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool char, int, unsigned char *);
signed short, int, short *);
unsigned short, int, unsigned short *);
bool short, int, short *);
bool short, int, unsigned short *);
pixel, int, short *);
pixel, int, unsigned short *);
float, int, float *);
signed int, int, int *);
unsigned int, int, unsigned int *);
bool int, int, int *);
bool int, int, unsigned int *);

float, int, vector float *);
float, int, float *);
signed int, int, vector signed int *);
signed int, int, int *);
unsigned int, int, vector unsigned int *);
unsigned int, int, unsigned int *);
bool int, int, vector bool int *);
bool int, int, unsigned int *);
bool int, int, int *);
signed short, int, vector signed short *);
signed short, int, short *);
unsigned short, int, vector unsigned short *);
unsigned short, int, unsigned short *);
bool short, int, vector bool short *);
bool short, int, unsigned short *);
bool short, int, short *);
pixel, int, vector pixel *);
pixel, int, unsigned short *);
pixel, int, short *);
signed char, int, vector signed char *);
signed char, int, signed char *);
unsigned char, int, vector unsigned char *);
unsigned char, int, unsigned char *);
bool char, int, vector bool char *);
bool char, int, unsigned char *);
bool char, int, signed char *);

Chapter 6: Extensions to the C Language Family

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

signed char vec_sub (vector bool char, vector signed char);
signed char vec_sub (vector signed char, vector bool char);
signed char vec_sub (vector signed char, vector signed char);
unsigned char vec_sub (vector bool char, vector unsigned char);
unsigned char vec_sub (vector unsigned char, vector bool char);
unsigned char vec_sub (vector unsigned char,
vector unsigned char);
signed short vec_sub (vector bool short, vector signed short);
signed short vec_sub (vector signed short, vector bool short);
signed short vec_sub (vector signed short, vector signed short);
unsigned short vec_sub (vector bool short,
vector unsigned short);
unsigned short vec_sub (vector unsigned short,
vector bool short);
unsigned short vec_sub (vector unsigned short,
vector unsigned short);
signed int vec_sub (vector bool int, vector signed int);
signed int vec_sub (vector signed int, vector bool int);
signed int vec_sub (vector signed int, vector signed int);
unsigned int vec_sub (vector bool int, vector unsigned int);
unsigned int vec_sub (vector unsigned int, vector bool int);
unsigned int vec_sub (vector unsigned int, vector unsigned int);
float vec_sub (vector float, vector float);

vector float vec_vsubfp (vector float, vector float);
vector
vector
vector
vector
vector
vector

signed int vec_vsubuwm (vector bool int, vector signed int);
signed int vec_vsubuwm (vector signed int, vector bool int);
signed int vec_vsubuwm (vector signed int, vector signed int);
unsigned int vec_vsubuwm (vector bool int, vector unsigned int);
unsigned int vec_vsubuwm (vector unsigned int, vector bool int);
unsigned int vec_vsubuwm (vector unsigned int,
vector unsigned int);

vector signed short vec_vsubuhm (vector bool short,
vector signed short);
vector signed short vec_vsubuhm (vector signed short,
vector bool short);
vector signed short vec_vsubuhm (vector signed short,
vector signed short);
vector unsigned short vec_vsubuhm (vector bool short,
vector unsigned short);
vector unsigned short vec_vsubuhm (vector unsigned short,
vector bool short);
vector unsigned short vec_vsubuhm (vector unsigned short,
vector unsigned short);
vector
vector
vector
vector

signed char vec_vsububm (vector bool char, vector signed char);
signed char vec_vsububm (vector signed char, vector bool char);
signed char vec_vsububm (vector signed char, vector signed char);
unsigned char vec_vsububm (vector bool char,
vector unsigned char);
vector unsigned char vec_vsububm (vector unsigned char,
vector bool char);
vector unsigned char vec_vsububm (vector unsigned char,
vector unsigned char);
vector signed int vec_subc (vector signed int, vector signed int);

709

710

Using the GNU Compiler Collection (GCC)

vector unsigned int vec_subc (vector unsigned int, vector unsigned int);
vector signed __int128 vec_subc (vector signed __int128,
vector signed __int128);
vector unsigned __int128 vec_subc (vector unsigned __int128,
vector unsigned __int128);
vector signed int vec_sube (vector signed int, vector signed int,
vector signed int);
vector unsigned int vec_sube (vector unsigned int, vector unsigned int,
vector unsigned int);
vector signed __int128 vec_sube (vector signed __int128,
vector signed __int128,
vector signed __int128);
vector unsigned __int128 vec_sube (vector unsigned __int128,
vector unsigned __int128,
vector unsigned __int128);
vector signed int vec_subec (vector signed int, vector signed int,
vector signed int);
vector unsigned int vec_subec (vector unsigned int, vector unsigned int,
vector unsigned int);
vector signed __int128 vec_subec (vector signed __int128,
vector signed __int128,
vector signed __int128);
vector unsigned __int128 vec_subec (vector unsigned __int128,
vector unsigned __int128,
vector unsigned __int128);
vector unsigned char vec_subs (vector bool char, vector unsigned char);
vector unsigned char vec_subs (vector unsigned char, vector bool char);
vector unsigned char vec_subs (vector unsigned char,
vector unsigned char);
vector signed char vec_subs (vector bool char, vector signed char);
vector signed char vec_subs (vector signed char, vector bool char);
vector signed char vec_subs (vector signed char, vector signed char);
vector unsigned short vec_subs (vector bool short,
vector unsigned short);
vector unsigned short vec_subs (vector unsigned short,
vector bool short);
vector unsigned short vec_subs (vector unsigned short,
vector unsigned short);
vector signed short vec_subs (vector bool short, vector signed short);
vector signed short vec_subs (vector signed short, vector bool short);
vector signed short vec_subs (vector signed short, vector signed short);
vector unsigned int vec_subs (vector bool int, vector unsigned int);
vector unsigned int vec_subs (vector unsigned int, vector bool int);
vector unsigned int vec_subs (vector unsigned int, vector unsigned int);
vector signed int vec_subs (vector bool int, vector signed int);
vector signed int vec_subs (vector signed int, vector bool int);
vector signed int vec_subs (vector signed int, vector signed int);
vector signed int vec_vsubsws (vector bool int, vector signed int);
vector signed int vec_vsubsws (vector signed int, vector bool int);
vector signed int vec_vsubsws (vector signed int, vector signed int);
vector unsigned int vec_vsubuws (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuws (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuws (vector unsigned int,

Chapter 6: Extensions to the C Language Family

vector unsigned int);
vector signed short vec_vsubshs (vector
vector
vector signed short vec_vsubshs (vector
vector
vector signed short vec_vsubshs (vector
vector

bool short,
signed short);
signed short,
bool short);
signed short,
signed short);

vector unsigned short vec_vsubuhs (vector
vector
vector unsigned short vec_vsubuhs (vector
vector
vector unsigned short vec_vsubuhs (vector
vector

bool short,
unsigned short);
unsigned short,
bool short);
unsigned short,
unsigned short);

vector signed char vec_vsubsbs (vector bool char, vector signed char);
vector signed char vec_vsubsbs (vector signed char, vector bool char);
vector signed char vec_vsubsbs (vector signed char, vector signed char);
vector unsigned char vec_vsububs (vector
vector
vector unsigned char vec_vsububs (vector
vector
vector unsigned char vec_vsububs (vector
vector

bool char,
unsigned char);
unsigned char,
bool char);
unsigned char,
unsigned char);

vector unsigned int vec_sum4s (vector unsigned char,
vector unsigned int);
vector signed int vec_sum4s (vector signed char, vector signed int);
vector signed int vec_sum4s (vector signed short, vector signed int);
vector signed int vec_vsum4shs (vector signed short, vector signed int);
vector signed int vec_vsum4sbs (vector signed char, vector signed int);
vector unsigned int vec_vsum4ubs (vector unsigned char,
vector unsigned int);
vector signed int vec_sum2s (vector signed int, vector signed int);
vector signed int vec_sums (vector signed int, vector signed int);
vector float vec_trunc (vector float);
vector signed long long vec_unsigned (vector double);
vector signed int vec_unsigned (vector float);
vector signed int vec_unsignede (vector double);
vector signed int vec_unsignedo (vector double);
vector signed int vec_unsigned2 (vector double, vector double);
vector
vector
vector
vector
vector
vector

signed short vec_unpackh (vector signed char);
bool short vec_unpackh (vector bool char);
signed int vec_unpackh (vector signed short);
bool int vec_unpackh (vector bool short);
unsigned int vec_unpackh (vector pixel);
double vec_unpackh (vector float);

711

712

Using the GNU Compiler Collection (GCC)

vector bool int vec_vupkhsh (vector bool short);
vector signed int vec_vupkhsh (vector signed short);
vector unsigned int vec_vupkhpx (vector pixel);
vector bool short vec_vupkhsb (vector bool char);
vector signed short vec_vupkhsb (vector signed char);
vector
vector
vector
vector
vector
vector

signed short vec_unpackl (vector signed char);
bool short vec_unpackl (vector bool char);
unsigned int vec_unpackl (vector pixel);
signed int vec_unpackl (vector signed short);
bool int vec_unpackl (vector bool short);
double vec_unpackl (vector float);

vector unsigned int vec_vupklpx (vector pixel);
vector bool int vec_vupklsh (vector bool short);
vector signed int vec_vupklsh (vector signed short);
vector bool short vec_vupklsb (vector bool char);
vector signed short vec_vupklsb (vector signed char);
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

int
int
int
int
int

float vec_xor (vector float, vector float);
float vec_xor (vector float, vector bool int);
float vec_xor (vector bool int, vector float);
bool int vec_xor (vector bool int, vector bool int);
signed int vec_xor (vector bool int, vector signed int);
signed int vec_xor (vector signed int, vector bool int);
signed int vec_xor (vector signed int, vector signed int);
unsigned int vec_xor (vector bool int, vector unsigned int);
unsigned int vec_xor (vector unsigned int, vector bool int);
unsigned int vec_xor (vector unsigned int, vector unsigned int);
bool short vec_xor (vector bool short, vector bool short);
signed short vec_xor (vector bool short, vector signed short);
signed short vec_xor (vector signed short, vector bool short);
signed short vec_xor (vector signed short, vector signed short);
unsigned short vec_xor (vector bool short,
vector unsigned short);
unsigned short vec_xor (vector unsigned short,
vector bool short);
unsigned short vec_xor (vector unsigned short,
vector unsigned short);
signed char vec_xor (vector bool char, vector signed char);
bool char vec_xor (vector bool char, vector bool char);
signed char vec_xor (vector signed char, vector bool char);
signed char vec_xor (vector signed char, vector signed char);
unsigned char vec_xor (vector bool char, vector unsigned char);
unsigned char vec_xor (vector unsigned char, vector bool char);
unsigned char vec_xor (vector unsigned char,
vector unsigned char);

vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq

(vector
(vector
(vector
(vector
(vector

signed char, vector bool char);
signed char, vector signed char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector bool char);

Chapter 6: Extensions to the C Language Family

int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq
vec_all_eq

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool char, vector unsigned char);
bool char, vector signed char);
signed short, vector bool short);
signed short, vector signed short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector bool short);
bool short, vector unsigned short);
bool short, vector signed short);
pixel, vector pixel);
signed int, vector bool int);
signed int, vector signed int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector bool int);
bool int, vector unsigned int);
bool int, vector signed int);
float, vector float);

int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge
vec_all_ge

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool char, vector unsigned char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector signed char);
signed char, vector bool char);
signed char, vector signed char);
bool short, vector unsigned short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
signed short, vector signed short);
bool short, vector signed short);
signed short, vector bool short);
bool int, vector unsigned int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector signed int);
signed int, vector bool int);
signed int, vector signed int);
float, vector float);

int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt
vec_all_gt

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool char, vector unsigned char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector signed char);
signed char, vector bool char);
signed char, vector signed char);
bool short, vector unsigned short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector signed short);
signed short, vector bool short);
signed short, vector signed short);
bool int, vector unsigned int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector signed int);
signed int, vector bool int);
signed int, vector signed int);
float, vector float);

713

714

Using the GNU Compiler Collection (GCC)

int vec_all_in (vector float, vector float);
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le
vec_all_le

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool char, vector unsigned char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector signed char);
signed char, vector bool char);
signed char, vector signed char);
bool short, vector unsigned short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector signed short);
signed short, vector bool short);
signed short, vector signed short);
bool int, vector unsigned int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector signed int);
signed int, vector bool int);
signed int, vector signed int);
float, vector float);

int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt
vec_all_lt

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool char, vector unsigned char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector signed char);
signed char, vector bool char);
signed char, vector signed char);
bool short, vector unsigned short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector signed short);
signed short, vector bool short);
signed short, vector signed short);
bool int, vector unsigned int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector signed int);
signed int, vector bool int);
signed int, vector signed int);
float, vector float);

int vec_all_nan (vector float);
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

signed char, vector bool char);
signed char, vector signed char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector bool char);
bool char, vector unsigned char);
bool char, vector signed char);
signed short, vector bool short);
signed short, vector signed short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector bool short);
bool short, vector unsigned short);

Chapter 6: Extensions to the C Language Family

int
int
int
int
int
int
int
int
int
int

vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne
vec_all_ne

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool short, vector signed short);
pixel, vector pixel);
signed int, vector bool int);
signed int, vector signed int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector bool int);
bool int, vector unsigned int);
bool int, vector signed int);
float, vector float);

int vec_all_nge (vector float, vector float);
int vec_all_ngt (vector float, vector float);
int vec_all_nle (vector float, vector float);
int vec_all_nlt (vector float, vector float);
int vec_all_numeric (vector float);
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq
vec_any_eq

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

signed char, vector bool char);
signed char, vector signed char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector bool char);
bool char, vector unsigned char);
bool char, vector signed char);
signed short, vector bool short);
signed short, vector signed short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector bool short);
bool short, vector unsigned short);
bool short, vector signed short);
pixel, vector pixel);
signed int, vector bool int);
signed int, vector signed int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector bool int);
bool int, vector unsigned int);
bool int, vector signed int);
float, vector float);

int
int
int
int
int
int
int
int
int
int
int
int
int

vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

signed char, vector bool char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
signed char, vector signed char);
bool char, vector unsigned char);
bool char, vector signed char);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
signed short, vector signed short);
signed short, vector bool short);
bool short, vector unsigned short);
bool short, vector signed short);
signed int, vector bool int);

715

716

Using the GNU Compiler Collection (GCC)

int
int
int
int
int
int

vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge
vec_any_ge

(vector
(vector
(vector
(vector
(vector
(vector

unsigned int, vector bool int);
unsigned int, vector unsigned int);
signed int, vector signed int);
bool int, vector unsigned int);
bool int, vector signed int);
float, vector float);

int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt
vec_any_gt

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool char, vector unsigned char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector signed char);
signed char, vector bool char);
signed char, vector signed char);
bool short, vector unsigned short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector signed short);
signed short, vector bool short);
signed short, vector signed short);
bool int, vector unsigned int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector signed int);
signed int, vector bool int);
signed int, vector signed int);
float, vector float);

int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le
vec_any_le

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool char, vector unsigned char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector signed char);
signed char, vector bool char);
signed char, vector signed char);
bool short, vector unsigned short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector signed short);
signed short, vector bool short);
signed short, vector signed short);
bool int, vector unsigned int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector signed int);
signed int, vector bool int);
signed int, vector signed int);
float, vector float);

int
int
int
int
int
int
int
int
int
int
int

vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

bool char, vector unsigned char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector signed char);
signed char, vector bool char);
signed char, vector signed char);
bool short, vector unsigned short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector signed short);
signed short, vector bool short);

Chapter 6: Extensions to the C Language Family

int
int
int
int
int
int
int
int

vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt
vec_any_lt

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

717

signed short, vector signed short);
bool int, vector unsigned int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector signed int);
signed int, vector bool int);
signed int, vector signed int);
float, vector float);

int vec_any_nan (vector float);
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int
int

vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne
vec_any_ne

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

signed char, vector bool char);
signed char, vector signed char);
unsigned char, vector bool char);
unsigned char, vector unsigned char);
bool char, vector bool char);
bool char, vector unsigned char);
bool char, vector signed char);
signed short, vector bool short);
signed short, vector signed short);
unsigned short, vector bool short);
unsigned short, vector unsigned short);
bool short, vector bool short);
bool short, vector unsigned short);
bool short, vector signed short);
pixel, vector pixel);
signed int, vector bool int);
signed int, vector signed int);
unsigned int, vector bool int);
unsigned int, vector unsigned int);
bool int, vector bool int);
bool int, vector unsigned int);
bool int, vector signed int);
float, vector float);

int vec_any_nge (vector float, vector float);
int vec_any_ngt (vector float, vector float);
int vec_any_nle (vector float, vector float);
int vec_any_nlt (vector float, vector float);
int vec_any_numeric (vector float);
int vec_any_out (vector float, vector float);

If the vector/scalar (VSX) instruction set is available, the following additional functions
are available:
vector
vector
vector
vector
vector
vector
vector
vector
vector

double vec_abs (vector double);
double vec_add (vector double, vector double);
double vec_and (vector double, vector double);
double vec_and (vector double, vector bool long);
double vec_and (vector bool long, vector double);
long vec_and (vector long, vector long);
long vec_and (vector long, vector bool long);
long vec_and (vector bool long, vector long);
unsigned long vec_and (vector unsigned long, vector unsigned long);

718

Using the GNU Compiler Collection (GCC)

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

unsigned long vec_and (vector unsigned long, vector bool long);
unsigned long vec_and (vector bool long, vector unsigned long);
double vec_andc (vector double, vector double);
double vec_andc (vector double, vector bool long);
double vec_andc (vector bool long, vector double);
long vec_andc (vector long, vector long);
long vec_andc (vector long, vector bool long);
long vec_andc (vector bool long, vector long);
unsigned long vec_andc (vector unsigned long, vector unsigned long);
unsigned long vec_andc (vector unsigned long, vector bool long);
unsigned long vec_andc (vector bool long, vector unsigned long);
double vec_ceil (vector double);
bool long vec_cmpeq (vector double, vector double);
bool long vec_cmpge (vector double, vector double);
bool long vec_cmpgt (vector double, vector double);
bool long vec_cmple (vector double, vector double);
bool long vec_cmplt (vector double, vector double);
double vec_cpsgn (vector double, vector double);
float vec_div (vector float, vector float);
double vec_div (vector double, vector double);
long vec_div (vector long, vector long);
unsigned long vec_div (vector unsigned long, vector unsigned long);
double vec_floor (vector double);
__int128 vec_ld (int, const vector __int128 *);
unsigned __int128 vec_ld (int, const vector unsigned __int128 *);
__int128 vec_ld (int, const __int128 *);
unsigned __int128 vec_ld (int, const unsigned __int128 *);
double vec_ld (int, const vector double *);
double vec_ld (int, const double *);
double vec_ldl (int, const vector double *);
double vec_ldl (int, const double *);
unsigned char vec_lvsl (int, const volatile double *);
unsigned char vec_lvsr (int, const volatile double *);
double vec_madd (vector double, vector double, vector double);
double vec_max (vector double, vector double);
signed long vec_mergeh (vector signed long, vector signed long);
signed long vec_mergeh (vector signed long, vector bool long);
signed long vec_mergeh (vector bool long, vector signed long);
unsigned long vec_mergeh (vector unsigned long, vector unsigned long);
unsigned long vec_mergeh (vector unsigned long, vector bool long);
unsigned long vec_mergeh (vector bool long, vector unsigned long);
signed long vec_mergel (vector signed long, vector signed long);
signed long vec_mergel (vector signed long, vector bool long);
signed long vec_mergel (vector bool long, vector signed long);
unsigned long vec_mergel (vector unsigned long, vector unsigned long);
unsigned long vec_mergel (vector unsigned long, vector bool long);
unsigned long vec_mergel (vector bool long, vector unsigned long);
double vec_min (vector double, vector double);
float vec_msub (vector float, vector float, vector float);
double vec_msub (vector double, vector double, vector double);
float vec_mul (vector float, vector float);
double vec_mul (vector double, vector double);
long vec_mul (vector long, vector long);
unsigned long vec_mul (vector unsigned long, vector unsigned long);
float vec_nearbyint (vector float);
double vec_nearbyint (vector double);
float vec_nmadd (vector float, vector float, vector float);
double vec_nmadd (vector double, vector double, vector double);

Chapter 6: Extensions to the C Language Family

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

double vec_nmsub (vector double, vector double, vector double);
double vec_nor (vector double, vector double);
long vec_nor (vector long, vector long);
long vec_nor (vector long, vector bool long);
long vec_nor (vector bool long, vector long);
unsigned long vec_nor (vector unsigned long, vector unsigned long);
unsigned long vec_nor (vector unsigned long, vector bool long);
unsigned long vec_nor (vector bool long, vector unsigned long);
double vec_or (vector double, vector double);
double vec_or (vector double, vector bool long);
double vec_or (vector bool long, vector double);
long vec_or (vector long, vector long);
long vec_or (vector long, vector bool long);
long vec_or (vector bool long, vector long);
unsigned long vec_or (vector unsigned long, vector unsigned long);
unsigned long vec_or (vector unsigned long, vector bool long);
unsigned long vec_or (vector bool long, vector unsigned long);
double vec_perm (vector double, vector double, vector unsigned char);
long vec_perm (vector long, vector long, vector unsigned char);
unsigned long vec_perm (vector unsigned long, vector unsigned long,
vector unsigned char);
vector bool char vec_permxor (vector bool char, vector bool char,
vector bool char);
vector unsigned char vec_permxor (vector signed char, vector signed char,
vector signed char);
vector unsigned char vec_permxor (vector unsigned char, vector unsigned char,
vector unsigned char);
vector double vec_rint (vector double);
vector double vec_recip (vector double, vector double);
vector double vec_rsqrt (vector double);
vector double vec_rsqrte (vector double);
vector double vec_sel (vector double, vector double, vector bool long);
vector double vec_sel (vector double, vector double, vector unsigned long);
vector long vec_sel (vector long, vector long, vector long);
vector long vec_sel (vector long, vector long, vector unsigned long);
vector long vec_sel (vector long, vector long, vector bool long);
vector unsigned long vec_sel (vector unsigned long, vector unsigned long,
vector long);
vector unsigned long vec_sel (vector unsigned long, vector unsigned long,
vector unsigned long);
vector unsigned long vec_sel (vector unsigned long, vector unsigned long,
vector bool long);
vector double vec_splats (double);
vector signed long vec_splats (signed long);
vector unsigned long vec_splats (unsigned long);
vector float vec_sqrt (vector float);
vector double vec_sqrt (vector double);
void vec_st (vector double, int, vector double *);
void vec_st (vector double, int, double *);
vector double vec_sub (vector double, vector double);
vector double vec_trunc (vector double);
vector double vec_xl (int, vector double *);
vector double vec_xl (int, double *);
vector long long vec_xl (int, vector long long *);
vector long long vec_xl (int, long long *);
vector unsigned long long vec_xl (int, vector unsigned long long *);
vector unsigned long long vec_xl (int, unsigned long long *);
vector float vec_xl (int, vector float *);

719

720

Using the GNU Compiler Collection (GCC)

vector float vec_xl (int, float *);
vector int vec_xl (int, vector int *);
vector int vec_xl (int, int *);
vector unsigned int vec_xl (int, vector unsigned int *);
vector unsigned int vec_xl (int, unsigned int *);
vector double vec_xor (vector double, vector double);
vector double vec_xor (vector double, vector bool long);
vector double vec_xor (vector bool long, vector double);
vector long vec_xor (vector long, vector long);
vector long vec_xor (vector long, vector bool long);
vector long vec_xor (vector bool long, vector long);
vector unsigned long vec_xor (vector unsigned long, vector unsigned long);
vector unsigned long vec_xor (vector unsigned long, vector bool long);
vector unsigned long vec_xor (vector bool long, vector unsigned long);
void vec_xst (vector double, int, vector double *);
void vec_xst (vector double, int, double *);
void vec_xst (vector long long, int, vector long long *);
void vec_xst (vector long long, int, long long *);
void vec_xst (vector unsigned long long, int, vector unsigned long long *);
void vec_xst (vector unsigned long long, int, unsigned long long *);
void vec_xst (vector float, int, vector float *);
void vec_xst (vector float, int, float *);
void vec_xst (vector int, int, vector int *);
void vec_xst (vector int, int, int *);
void vec_xst (vector unsigned int, int, vector unsigned int *);
void vec_xst (vector unsigned int, int, unsigned int *);
int vec_all_eq (vector double, vector double);
int vec_all_ge (vector double, vector double);
int vec_all_gt (vector double, vector double);
int vec_all_le (vector double, vector double);
int vec_all_lt (vector double, vector double);
int vec_all_nan (vector double);
int vec_all_ne (vector double, vector double);
int vec_all_nge (vector double, vector double);
int vec_all_ngt (vector double, vector double);
int vec_all_nle (vector double, vector double);
int vec_all_nlt (vector double, vector double);
int vec_all_numeric (vector double);
int vec_any_eq (vector double, vector double);
int vec_any_ge (vector double, vector double);
int vec_any_gt (vector double, vector double);
int vec_any_le (vector double, vector double);
int vec_any_lt (vector double, vector double);
int vec_any_nan (vector double);
int vec_any_ne (vector double, vector double);
int vec_any_nge (vector double, vector double);
int vec_any_ngt (vector double, vector double);
int vec_any_nle (vector double, vector double);
int vec_any_nlt (vector double, vector double);
int vec_any_numeric (vector double);
vector
vector
vector
vector
vector
vector
vector

double vec_vsx_ld (int, const vector double *);
double vec_vsx_ld (int, const double *);
float vec_vsx_ld (int, const vector float *);
float vec_vsx_ld (int, const float *);
bool int vec_vsx_ld (int, const vector bool int *);
signed int vec_vsx_ld (int, const vector signed int *);
signed int vec_vsx_ld (int, const int *);

Chapter 6: Extensions to the C Language Family

vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void
void

signed int vec_vsx_ld (int, const long *);
unsigned int vec_vsx_ld (int, const vector unsigned int *);
unsigned int vec_vsx_ld (int, const unsigned int *);
unsigned int vec_vsx_ld (int, const unsigned long *);
bool short vec_vsx_ld (int, const vector bool short *);
pixel vec_vsx_ld (int, const vector pixel *);
signed short vec_vsx_ld (int, const vector signed short *);
signed short vec_vsx_ld (int, const short *);
unsigned short vec_vsx_ld (int, const vector unsigned short *);
unsigned short vec_vsx_ld (int, const unsigned short *);
bool char vec_vsx_ld (int, const vector bool char *);
signed char vec_vsx_ld (int, const vector signed char *);
signed char vec_vsx_ld (int, const signed char *);
unsigned char vec_vsx_ld (int, const vector unsigned char *);
unsigned char vec_vsx_ld (int, const unsigned char *);

vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st
vec_vsx_st

vector
vector
vector
vector
vector
vector
vector
vector
vector

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

double, int, vector double *);
double, int, double *);
float, int, vector float *);
float, int, float *);
signed int, int, vector signed int *);
signed int, int, int *);
unsigned int, int, vector unsigned int *);
unsigned int, int, unsigned int *);
bool int, int, vector bool int *);
bool int, int, unsigned int *);
bool int, int, int *);
signed short, int, vector signed short *);
signed short, int, short *);
unsigned short, int, vector unsigned short *);
unsigned short, int, unsigned short *);
bool short, int, vector bool short *);
bool short, int, unsigned short *);
pixel, int, vector pixel *);
pixel, int, unsigned short *);
pixel, int, short *);
bool short, int, short *);
signed char, int, vector signed char *);
signed char, int, signed char *);
unsigned char, int, vector unsigned char *);
unsigned char, int, unsigned char *);
bool char, int, vector bool char *);
bool char, int, unsigned char *);
bool char, int, signed char *);

double vec_xxpermdi (vector double, vector double, const int);
float vec_xxpermdi (vector float, vector float, const int);
long long vec_xxpermdi (vector long long, vector long long, const int);
unsigned long long vec_xxpermdi (vector unsigned long long,
vector unsigned long long, const int);
int vec_xxpermdi (vector int, vector int, const int);
unsigned int vec_xxpermdi (vector unsigned int,
vector unsigned int, const int);
short vec_xxpermdi (vector short, vector short, const int);
unsigned short vec_xxpermdi (vector unsigned short,
vector unsigned short, const int);
signed char vec_xxpermdi (vector signed char, vector signed char,
const int);

721

722

Using the GNU Compiler Collection (GCC)

vector unsigned char vec_xxpermdi (vector unsigned char,
vector unsigned char, const int);
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

double vec_xxsldi (vector double, vector double, int);
float vec_xxsldi (vector float, vector float, int);
long long vec_xxsldi (vector long long, vector long long, int);
unsigned long long vec_xxsldi (vector unsigned long long,
vector unsigned long long, int);
int vec_xxsldi (vector int, vector int, int);
unsigned int vec_xxsldi (vector unsigned int, vector unsigned int, int);
short vec_xxsldi (vector short, vector short, int);
unsigned short vec_xxsldi (vector unsigned short,
vector unsigned short, int);
signed char vec_xxsldi (vector signed char, vector signed char, int);
unsigned char vec_xxsldi (vector unsigned char,
vector unsigned char, int);

Note that the ‘vec_ld’ and ‘vec_st’ built-in functions always generate the AltiVec ‘LVX’
and ‘STVX’ instructions even if the VSX instruction set is available. The ‘vec_vsx_ld’ and
‘vec_vsx_st’ built-in functions always generate the VSX ‘LXVD2X’, ‘LXVW4X’, ‘STXVD2X’,
and ‘STXVW4X’ instructions.
If the ISA 2.07 additions to the vector/scalar (power8-vector) instruction set are available,
the following additional functions are available for both 32-bit and 64-bit targets. For 64bit targets, you can use vector long instead of vector long long, vector bool long instead of
vector bool long long, and vector unsigned long instead of vector unsigned long long.
vector long long vec_abs (vector long long);
vector long long vec_add (vector long long, vector long long);
vector unsigned long long vec_add (vector unsigned long long,
vector unsigned long long);
int
int
int
int
int
int
int
int
int
int
int
int

vec_all_eq
vec_all_eq
vec_all_ge
vec_all_ge
vec_all_gt
vec_all_gt
vec_all_le
vec_all_le
vec_all_lt
vec_all_lt
vec_all_ne
vec_all_ne

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned

int
int
int
int
int
int
int
int
int
int
int
int

vec_any_eq
vec_any_eq
vec_any_ge
vec_any_ge
vec_any_gt
vec_any_gt
vec_any_le
vec_any_le
vec_any_lt
vec_any_lt
vec_any_ne
vec_any_ne

(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector
(vector

long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned
long long, vector long long);
unsigned long long, vector unsigned

long long);
long long);
long long);
long long);
long long);
long long);

long long);
long long);
long long);
long long);
long long);
long long);

Chapter 6: Extensions to the C Language Family

vector bool long long vec_cmpeq (vector bool long long, vector bool long long);
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

long long vec_eqv (vector long long, vector long long);
long long vec_eqv (vector bool long long, vector long long);
long long vec_eqv (vector long long, vector bool long long);
unsigned long long vec_eqv (vector unsigned long long,
vector unsigned long long);
unsigned long long vec_eqv (vector bool long long,
vector unsigned long long);
unsigned long long vec_eqv (vector unsigned long long,
vector bool long long);
int vec_eqv (vector int, vector int);
int vec_eqv (vector bool int, vector int);
int vec_eqv (vector int, vector bool int);
unsigned int vec_eqv (vector unsigned int, vector unsigned int);
unsigned int vec_eqv (vector bool unsigned int,
vector unsigned int);
unsigned int vec_eqv (vector unsigned int,
vector bool unsigned int);
short vec_eqv (vector short, vector short);
short vec_eqv (vector bool short, vector short);
short vec_eqv (vector short, vector bool short);
unsigned short vec_eqv (vector unsigned short, vector unsigned short);
unsigned short vec_eqv (vector bool unsigned short,
vector unsigned short);
unsigned short vec_eqv (vector unsigned short,
vector bool unsigned short);
signed char vec_eqv (vector signed char, vector signed char);
signed char vec_eqv (vector bool signed char, vector signed char);
signed char vec_eqv (vector signed char, vector bool signed char);
unsigned char vec_eqv (vector unsigned char, vector unsigned char);
unsigned char vec_eqv (vector bool unsigned char, vector unsigned char);
unsigned char vec_eqv (vector unsigned char, vector bool unsigned char);

vector long long vec_max (vector long long, vector long long);
vector unsigned long long vec_max (vector unsigned long long,
vector unsigned long long);
vector signed int vec_mergee (vector signed int, vector signed int);
vector unsigned int vec_mergee (vector unsigned int, vector unsigned int);
vector bool int vec_mergee (vector bool int, vector bool int);
vector signed int vec_mergeo (vector signed int, vector signed int);
vector unsigned int vec_mergeo (vector unsigned int, vector unsigned int);
vector bool int vec_mergeo (vector bool int, vector bool int);
vector long long vec_min (vector long long, vector long long);
vector unsigned long long vec_min (vector unsigned long long,
vector unsigned long long);
vector signed long long vec_nabs (vector signed long long);
vector
vector
vector
vector

long long vec_nand
long long vec_nand
long long vec_nand
unsigned long long

(vector long long, vector long long);
(vector bool long long, vector long long);
(vector long long, vector bool long long);
vec_nand (vector unsigned long long,
vector unsigned long long);
vector unsigned long long vec_nand (vector bool long long,

723

724

Using the GNU Compiler Collection (GCC)

vector unsigned long long);
vector unsigned long long vec_nand (vector unsigned long long,
vector bool long long);
vector int vec_nand (vector int, vector int);
vector int vec_nand (vector bool int, vector int);
vector int vec_nand (vector int, vector bool int);
vector unsigned int vec_nand (vector unsigned int, vector unsigned int);
vector unsigned int vec_nand (vector bool unsigned int,
vector unsigned int);
vector unsigned int vec_nand (vector unsigned int,
vector bool unsigned int);
vector short vec_nand (vector short, vector short);
vector short vec_nand (vector bool short, vector short);
vector short vec_nand (vector short, vector bool short);
vector unsigned short vec_nand (vector unsigned short, vector unsigned short);
vector unsigned short vec_nand (vector bool unsigned short,
vector unsigned short);
vector unsigned short vec_nand (vector unsigned short,
vector bool unsigned short);
vector signed char vec_nand (vector signed char, vector signed char);
vector signed char vec_nand (vector bool signed char, vector signed char);
vector signed char vec_nand (vector signed char, vector bool signed char);
vector unsigned char vec_nand (vector unsigned char, vector unsigned char);
vector unsigned char vec_nand (vector bool unsigned char, vector unsigned char);
vector unsigned char vec_nand (vector unsigned char, vector bool unsigned char);
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

long long vec_orc (vector long long, vector long long);
long long vec_orc (vector bool long long, vector long long);
long long vec_orc (vector long long, vector bool long long);
unsigned long long vec_orc (vector unsigned long long,
vector unsigned long long);
unsigned long long vec_orc (vector bool long long,
vector unsigned long long);
unsigned long long vec_orc (vector unsigned long long,
vector bool long long);
int vec_orc (vector int, vector int);
int vec_orc (vector bool int, vector int);
int vec_orc (vector int, vector bool int);
unsigned int vec_orc (vector unsigned int, vector unsigned int);
unsigned int vec_orc (vector bool unsigned int,
vector unsigned int);
unsigned int vec_orc (vector unsigned int,
vector bool unsigned int);
short vec_orc (vector short, vector short);
short vec_orc (vector bool short, vector short);
short vec_orc (vector short, vector bool short);
unsigned short vec_orc (vector unsigned short, vector unsigned short);
unsigned short vec_orc (vector bool unsigned short,
vector unsigned short);
unsigned short vec_orc (vector unsigned short,
vector bool unsigned short);
signed char vec_orc (vector signed char, vector signed char);
signed char vec_orc (vector bool signed char, vector signed char);
signed char vec_orc (vector signed char, vector bool signed char);
unsigned char vec_orc (vector unsigned char, vector unsigned char);
unsigned char vec_orc (vector bool unsigned char, vector unsigned char);
unsigned char vec_orc (vector unsigned char, vector bool unsigned char);

Chapter 6: Extensions to the C Language Family

vector int vec_pack (vector long long, vector long long);
vector unsigned int vec_pack (vector unsigned long long,
vector unsigned long long);
vector bool int vec_pack (vector bool long long, vector bool long long);
vector float vec_pack (vector double, vector double);
vector int vec_packs (vector long long, vector long long);
vector unsigned int vec_packs (vector unsigned long long,
vector unsigned long long);
test_vsi_packsu_vssi_vssi (vector signed short x,
vector
vector
vector
vector

unsigned
unsigned
unsigned
unsigned

char vec_packsu (vector signed short, vector signed short )
char vec_packsu (vector unsigned short, vector unsigned short )
short int vec_packsu (vector signed int, vector signed int);
short int vec_packsu (vector unsigned int,
vector unsigned int);
vector unsigned int vec_packsu (vector long long, vector long long);
vector unsigned int vec_packsu (vector unsigned long long,
vector unsigned long long);
vector unsigned int vec_packsu (vector signed long long,
vector signed long long);
vector
vector
vector
vector
vector
vector
vector
vector

unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned

char vec_popcnt (vector signed char);
char vec_popcnt (vector unsigned char);
short vec_popcnt (vector signed short);
short vec_popcnt (vector unsigned short);
int vec_popcnt (vector signed int);
int vec_popcnt (vector unsigned int);
long long vec_popcnt (vector signed long long);
long long vec_popcnt (vector unsigned long long);

vector long long vec_rl (vector
vector
vector long long vec_rl (vector
vector

long long,
unsigned long long);
unsigned long long,
unsigned long long);

vector long long vec_sl (vector long long, vector unsigned long long);
vector long long vec_sl (vector unsigned long long,
vector unsigned long long);
vector long long vec_sr (vector long long, vector unsigned long long);
vector unsigned long long char vec_sr (vector unsigned long long,
vector unsigned long long);
vector long long vec_sra (vector long long, vector unsigned long long);
vector unsigned long long vec_sra (vector unsigned long long,
vector unsigned long long);
vector long long vec_sub (vector long long, vector long long);
vector unsigned long long vec_sub (vector unsigned long long,
vector unsigned long long);
vector long long vec_unpackh (vector int);
vector unsigned long long vec_unpackh (vector unsigned int);
vector long long vec_unpackl (vector int);
vector unsigned long long vec_unpackl (vector unsigned int);

725

726

Using the GNU Compiler Collection (GCC)

vector
vector
vector
vector

long long vec_vaddudm (vector long long, vector long
long long vec_vaddudm (vector bool long long, vector
long long vec_vaddudm (vector long long, vector bool
unsigned long long vec_vaddudm (vector unsigned long
vector unsigned long
vector unsigned long long vec_vaddudm (vector bool unsigned
vector unsigned long
vector unsigned long long vec_vaddudm (vector unsigned long
vector bool unsigned

long);
long long);
long long);
long,
long);
long long,
long);
long,
long long);

vector long long vec_vbpermq (vector signed char, vector signed char);
vector long long vec_vbpermq (vector unsigned char, vector unsigned char);
vector unsigned char vec_bperm (vector unsigned char, vector unsigned char);
vector unsigned char vec_bperm (vector unsigned long long,
vector unsigned char);
vector unsigned long long vec_bperm (vector unsigned __int128,
vector unsigned char);
vector
vector
vector
vector
vector
vector
vector
vector

long long vec_cntlz (vector long long);
unsigned long long vec_cntlz (vector unsigned long long);
int vec_cntlz (vector int);
unsigned int vec_cntlz (vector int);
short vec_cntlz (vector short);
unsigned short vec_cntlz (vector unsigned short);
signed char vec_cntlz (vector signed char);
unsigned char vec_cntlz (vector unsigned char);

vector
vector
vector
vector
vector
vector
vector
vector

long long vec_vclz (vector long long);
unsigned long long vec_vclz (vector unsigned long long);
int vec_vclz (vector int);
unsigned int vec_vclz (vector int);
short vec_vclz (vector short);
unsigned short vec_vclz (vector unsigned short);
signed char vec_vclz (vector signed char);
unsigned char vec_vclz (vector unsigned char);

vector signed char vec_vclzb (vector signed char);
vector unsigned char vec_vclzb (vector unsigned char);
vector long long vec_vclzd (vector long long);
vector unsigned long long vec_vclzd (vector unsigned long long);
vector short vec_vclzh (vector short);
vector unsigned short vec_vclzh (vector unsigned short);
vector int vec_vclzw (vector int);
vector unsigned int vec_vclzw (vector int);
vector signed char vec_vgbbd (vector signed char);
vector unsigned char vec_vgbbd (vector unsigned char);
vector long long vec_vmaxsd (vector long long, vector long long);
vector unsigned long long vec_vmaxud (vector unsigned long long,
unsigned vector long long);

Chapter 6: Extensions to the C Language Family

727

vector long long vec_vminsd (vector long long, vector long long);
vector unsigned long long vec_vminud (vector long long,
vector long long);
vector int vec_vpksdss (vector long long, vector long long);
vector unsigned int vec_vpksdss (vector long long, vector long long);
vector unsigned int vec_vpkudus (vector unsigned long long,
vector unsigned long long);
vector int vec_vpkudum (vector long long, vector long long);
vector unsigned int vec_vpkudum (vector unsigned long long,
vector unsigned long long);
vector bool int vec_vpkudum (vector bool long long, vector bool long long);
vector
vector
vector
vector
vector
vector
vector
vector

long long vec_vpopcnt (vector long long);
unsigned long long vec_vpopcnt (vector unsigned long long);
int vec_vpopcnt (vector int);
unsigned int vec_vpopcnt (vector int);
short vec_vpopcnt (vector short);
unsigned short vec_vpopcnt (vector unsigned short);
signed char vec_vpopcnt (vector signed char);
unsigned char vec_vpopcnt (vector unsigned char);

vector signed char vec_vpopcntb (vector signed char);
vector unsigned char vec_vpopcntb (vector unsigned char);
vector long long vec_vpopcntd (vector long long);
vector unsigned long long vec_vpopcntd (vector unsigned long long);
vector short vec_vpopcnth (vector short);
vector unsigned short vec_vpopcnth (vector unsigned short);
vector int vec_vpopcntw (vector int);
vector unsigned int vec_vpopcntw (vector int);
vector long long vec_vrld (vector long long, vector unsigned long long);
vector unsigned long long vec_vrld (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsld (vector long long, vector unsigned long long);
vector long long vec_vsld (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsrad (vector long long, vector unsigned long long);
vector unsigned long long vec_vsrad (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsrd (vector long long, vector unsigned long long);
vector unsigned long long char vec_vsrd (vector unsigned long long,
vector unsigned long long);
vector
vector
vector
vector

long long vec_vsubudm (vector long long, vector long
long long vec_vsubudm (vector bool long long, vector
long long vec_vsubudm (vector long long, vector bool
unsigned long long vec_vsubudm (vector unsigned long
vector unsigned long

long);
long long);
long long);
long,
long);

728

Using the GNU Compiler Collection (GCC)

vector unsigned long long vec_vsubudm (vector
vector
vector unsigned long long vec_vsubudm (vector
vector

bool long long,
unsigned long long);
unsigned long long,
bool long long);

vector long long vec_vupkhsw (vector int);
vector unsigned long long vec_vupkhsw (vector unsigned int);
vector long long vec_vupklsw (vector int);
vector unsigned long long vec_vupklsw (vector int);

If the ISA 2.07 additions to the vector/scalar (power8-vector) instruction set are available,
the following additional functions are available for 64-bit targets. New vector types (vector
int128 t and vector uint128 t) are available to hold the int128 t and uint128 t types
to use these builtins.
The normal vector extract, and set operations work on vector
uint128 t types, but the index value must be 0.

int128 t and vector

vector __int128_t vec_vaddcuq (vector __int128_t, vector __int128_t);
vector __uint128_t vec_vaddcuq (vector __uint128_t, vector __uint128_t);
vector __int128_t vec_vadduqm (vector __int128_t, vector __int128_t);
vector __uint128_t vec_vadduqm (vector __uint128_t, vector __uint128_t);
vector __int128_t vec_vaddecuq (vector __int128_t, vector __int128_t,
vector __int128_t);
vector __uint128_t vec_vaddecuq (vector __uint128_t, vector __uint128_t,
vector __uint128_t);
vector __int128_t vec_vaddeuqm (vector __int128_t, vector __int128_t,
vector __int128_t);
vector __uint128_t vec_vaddeuqm (vector __uint128_t, vector __uint128_t,
vector __uint128_t);
vector __int128_t vec_vsubecuq (vector __int128_t, vector __int128_t,
vector __int128_t);
vector __uint128_t vec_vsubecuq (vector __uint128_t, vector __uint128_t,
vector __uint128_t);
vector __int128_t vec_vsubeuqm (vector __int128_t, vector __int128_t,
vector __int128_t);
vector __uint128_t vec_vsubeuqm (vector __uint128_t, vector __uint128_t,
vector __uint128_t);
vector __int128_t vec_vsubcuq (vector __int128_t, vector __int128_t);
vector __uint128_t vec_vsubcuq (vector __uint128_t, vector __uint128_t);
__int128_t vec_vsubuqm (__int128_t, __int128_t);
__uint128_t vec_vsubuqm (__uint128_t, __uint128_t);
vector __int128_t __builtin_bcdadd (vector __int128_t, vector __int128_t);
int __builtin_bcdadd_lt (vector __int128_t, vector __int128_t);
int __builtin_bcdadd_eq (vector __int128_t, vector __int128_t);
int __builtin_bcdadd_gt (vector __int128_t, vector __int128_t);
int __builtin_bcdadd_ov (vector __int128_t, vector __int128_t);
vector __int128_t bcdsub (vector __int128_t, vector __int128_t);
int __builtin_bcdsub_lt (vector __int128_t, vector __int128_t);
int __builtin_bcdsub_eq (vector __int128_t, vector __int128_t);

Chapter 6: Extensions to the C Language Family

int __builtin_bcdsub_gt (vector __int128_t, vector __int128_t);
int __builtin_bcdsub_ov (vector __int128_t, vector __int128_t);

If the ISA 3.0 instruction set additions (‘-mcpu=power9’) are available:
vector unsigned long long vec_bperm (vector unsigned long long,
vector unsigned char);
vector
vector
vector
vector
vector
vector
vector
vector

bool
bool
bool
bool
bool
bool
bool
bool

vector bool
vector
vector
vector
vector
vector

bool
bool
bool
bool
bool

char vec_cmpne (vector bool char, vector bool char);
char vec_cmpne (vector signed char, vector signed char);
char vec_cmpne (vector unsigned char, vector unsigned char);
int vec_cmpne (vector bool int, vector bool int);
int vec_cmpne (vector signed int, vector signed int);
int vec_cmpne (vector unsigned int, vector unsigned int);
long long vec_cmpne (vector bool long long, vector bool long long);
long long vec_cmpne (vector signed long long,
vector signed long long);
long long vec_cmpne (vector unsigned long long,
vector unsigned long long);
short vec_cmpne (vector bool short, vector bool short);
short vec_cmpne (vector signed short, vector signed short);
short vec_cmpne (vector unsigned short, vector unsigned short);
long long vec_cmpne (vector double, vector double);
int vec_cmpne (vector float, vector float);

vector float vec_extract_fp32_from_shorth (vector unsigned short);
vector float vec_extract_fp32_from_shortl (vector unsigned short);
vector
vector
vector
vector
vector
vector
vector
vector

long long vec_vctz (vector long long);
unsigned long long vec_vctz (vector unsigned long long);
int vec_vctz (vector int);
unsigned int vec_vctz (vector int);
short vec_vctz (vector short);
unsigned short vec_vctz (vector unsigned short);
signed char vec_vctz (vector signed char);
unsigned char vec_vctz (vector unsigned char);

vector signed char vec_vctzb (vector signed char);
vector unsigned char vec_vctzb (vector unsigned char);
vector long long vec_vctzd (vector long long);
vector unsigned long long vec_vctzd (vector unsigned long long);
vector short vec_vctzh (vector short);
vector unsigned short vec_vctzh (vector unsigned short);
vector int vec_vctzw (vector int);
vector unsigned int vec_vctzw (vector int);
vector unsigned long long vec_extract4b (vector unsigned char, const int);
vector unsigned char vec_insert4b (vector signed int, vector unsigned char,
const int);
vector unsigned char vec_insert4b (vector unsigned int, vector unsigned char,
const int);
vector
vector
vector
vector

unsigned
unsigned
unsigned
unsigned

int vec_parity_lsbb (vector signed int);
int vec_parity_lsbb (vector unsigned int);
__int128 vec_parity_lsbb (vector signed __int128);
__int128 vec_parity_lsbb (vector unsigned __int128);

729

730

Using the GNU Compiler Collection (GCC)

vector unsigned long long vec_parity_lsbb (vector signed long long);
vector unsigned long long vec_parity_lsbb (vector unsigned long long);
vector
vector
vector
vector

int vec_vprtyb (vector int);
unsigned int vec_vprtyb (vector unsigned int);
long long vec_vprtyb (vector long long);
unsigned long long vec_vprtyb (vector unsigned long long);

vector int vec_vprtybw (vector int);
vector unsigned int vec_vprtybw (vector unsigned int);
vector long long vec_vprtybd (vector long long);
vector unsigned long long vec_vprtybd (vector unsigned long long);

On 64-bit targets, if the ISA 3.0 additions (‘-mcpu=power9’) are available:
vector
vector
vector
vector

long vec_vprtyb (vector long);
unsigned long vec_vprtyb (vector unsigned long);
__int128_t vec_vprtyb (vector __int128_t);
__uint128_t vec_vprtyb (vector __uint128_t);

vector long vec_vprtybd (vector long);
vector unsigned long vec_vprtybd (vector unsigned long);
vector __int128_t vec_vprtybq (vector __int128_t);
vector __uint128_t vec_vprtybd (vector __uint128_t);

The following built-in vector functions are available for the PowerPC family of processors,
starting with ISA 3.0 or later (‘-mcpu=power9’):
__vector unsigned
vec_slv (__vector
__vector unsigned
vec_srv (__vector

char
unsigned char src, __vector unsigned char shift_distance);
char
unsigned char src, __vector unsigned char shift_distance);

The vec_slv and vec_srv functions operate on all of the bytes of their src and shift_
distance arguments in parallel. The behavior of the vec_slv is as if there existed a temporary array of 17 unsigned characters slv_array within which elements 0 through 15 are the
same as the entries in the src array and element 16 equals 0. The result returned from the
vec_slv function is a __vector of 16 unsigned characters within which element i is computed using the C expression 0xff & (*((unsigned short *)(slv_array + i)) << (0x07
& shift_distance[i])), with this resulting value coerced to the unsigned char type. The
behavior of the vec_srv is as if there existed a temporary array of 17 unsigned characters
srv_array within which element 0 equals zero and elements 1 through 16 equal the elements
0 through 15 of the src array. The result returned from the vec_srv function is a __vector
of 16 unsigned characters within which element i is computed using the C expression 0xff
& (*((unsigned short *)(srv_array + i)) >> (0x07 & shift_distance[i])), with this
resulting value coerced to the unsigned char type.
The following built-in functions are available for the PowerPC family of processors, starting with ISA 3.0 or later (‘-mcpu=power9’):
__vector
vec_absd
__vector
vec_absd
__vector
vec_absd

unsigned char
(__vector unsigned char arg1, __vector unsigned char arg2);
unsigned short
(__vector unsigned short arg1, __vector unsigned short arg2);
unsigned int
(__vector unsigned int arg1, __vector unsigned int arg2);

Chapter 6: Extensions to the C Language Family

731

__vector unsigned char
vec_absdb (__vector unsigned char arg1, __vector unsigned char arg2);
__vector unsigned short
vec_absdh (__vector unsigned short arg1, __vector unsigned short arg2);
__vector unsigned int
vec_absdw (__vector unsigned int arg1, __vector unsigned int arg2);

The vec_absd, vec_absdb, vec_absdh, and vec_absdw built-in functions each computes
the absolute differences of the pairs of vector elements supplied in its two vector arguments,
placing the absolute differences into the corresponding elements of the vector result.
The following built-in functions are available for the PowerPC family of processors, starting with ISA 3.0 or later (‘-mcpu=power9’):
__vector unsigned int
vec_extract_exp (__vector float source);
__vector unsigned long long int
vec_extract_exp (__vector double source);
__vector unsigned int
vec_extract_sig (__vector float source);
__vector unsigned long long int
vec_extract_sig (__vector double source);
__vector float
vec_insert_exp (__vector
__vector
__vector float
vec_insert_exp (__vector
__vector
__vector double
vec_insert_exp (__vector
__vector
__vector double
vec_insert_exp (__vector
__vector

unsigned int significands,
unsigned int exponents);
unsigned float significands,
unsigned int exponents);
unsigned long long int significands,
unsigned long long int exponents);
unsigned double significands,
unsigned long long int exponents);

__vector bool int vec_test_data_class (__vector float source,
const int condition);
__vector bool long long int vec_test_data_class (__vector double source,
const int condition);

The vec_extract_sig and vec_extract_exp built-in functions return vectors representing the significands and biased exponent values of their source arguments respectively.
Within the result vector returned by vec_extract_sig, the 0x800000 bit of each vector
element returned when the function’s source argument is of type float is set to 1 if the
corresponding floating point value is in normalized form. Otherwise, this bit is set to 0.
When the source argument is of type double, the 0x10000000000000 bit within each of
the result vector’s elements is set according to the same rules. Note that the sign of the
significand is not represented in the result returned from the vec_extract_sig function.
To extract the sign bits, use the vec_cpsgn function, which returns a new vector within
which all of the sign bits of its second argument vector are overwritten with the sign bits
copied from the coresponding elements of its first argument vector, and all other (non-sign)
bits of the second argument vector are copied unchanged into the result vector.
The vec_insert_exp built-in functions return a vector of single- or double-precision floating point values constructed by assembling the values of their significands and exponents

732

Using the GNU Compiler Collection (GCC)

arguments into the corresponding elements of the returned vector. The sign of each element
of the result is copied from the most significant bit of the corresponding entry within the
significands argument. Note that the relevant bits of the significands argument are the
same, for both integer and floating point types. The significand and exponent components
of each element of the result are composed of the least significant bits of the corresponding significands element and the least significant bits of the corresponding exponents
element.
The vec_test_data_class built-in function returns a vector representing the results
of testing the source vector for the condition selected by the condition argument. The
condition argument must be a compile-time constant integer with value not exceeding 127.
The condition argument is encoded as a bitmask with each bit enabling the testing of a
different condition, as characterized by the following:
0x40
0x20
0x10
0x08
0x04
0x02
0x01

Test
Test
Test
Test
Test
Test
Test

for
for
for
for
for
for
for

NaN
+Infinity
-Infinity
+Zero
-Zero
+Denormal
-Denormal

If any of the enabled test conditions is true, the corresponding entry in the result vector
is -1. Otherwise (all of the enabled test conditions are false), the corresponding entry of the
result vector is 0.
The following built-in functions are available for the PowerPC family of processors, starting with ISA 3.0 or later (‘-mcpu=power9’):
vector unsigned int vec_rlmi (vector unsigned int, vector unsigned int,
vector unsigned int);
vector unsigned long long vec_rlmi (vector unsigned long long,
vector unsigned long long,
vector unsigned long long);
vector unsigned int vec_rlnm (vector unsigned int, vector unsigned int,
vector unsigned int);
vector unsigned long long vec_rlnm (vector unsigned long long,
vector unsigned long long,
vector unsigned long long);
vector unsigned int vec_vrlnm (vector unsigned int, vector unsigned int);
vector unsigned long long vec_vrlnm (vector unsigned long long,
vector unsigned long long);

The result of vec_rlmi is obtained by rotating each element of the first argument vector
left and inserting it under mask into the second argument vector. The third argument
vector contains the mask beginning in bits 11:15, the mask end in bits 19:23, and the shift
count in bits 27:31, of each element.
The result of vec_rlnm is obtained by rotating each element of the first argument vector
left and ANDing it with a mask specified by the second and third argument vectors. The
second argument vector contains the shift count for each element in the low-order byte. The
third argument vector contains the mask end for each element in the low-order byte, with
the mask begin in the next higher byte.
The result of vec_vrlnm is obtained by rotating each element of the first argument vector
left and ANDing it with a mask. The second argument vector contains the mask beginning
in bits 11:15, the mask end in bits 19:23, and the shift count in bits 27:31, of each element.

Chapter 6: Extensions to the C Language Family

733

If the ISA 3.0 instruction set additions (‘-mcpu=power9’) are available:
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector
vector

signed bool char vec_revb (vector signed char);
signed char vec_revb (vector signed char);
unsigned char vec_revb (vector unsigned char);
bool short vec_revb (vector bool short);
short vec_revb (vector short);
unsigned short vec_revb (vector unsigned short);
bool int vec_revb (vector bool int);
int vec_revb (vector int);
unsigned int vec_revb (vector unsigned int);
float vec_revb (vector float);
bool long long vec_revb (vector bool long long);
long long vec_revb (vector long long);
unsigned long long vec_revb (vector unsigned long long);
double vec_revb (vector double);

On 64-bit targets, if the ISA 3.0 additions (‘-mcpu=power9’) are available:
vector
vector
vector
vector

long vec_revb (vector long);
unsigned long vec_revb (vector unsigned long);
__int128_t vec_revb (vector __int128_t);
__uint128_t vec_revb (vector __uint128_t);

The vec_revb built-in function reverses the bytes on an element by element basis. A
vector of vector unsigned char or vector signed char reverses the bytes in the whole
word.
If the cryptographic instructions are enabled (‘-mcrypto’ or ‘-mcpu=power8’), the following builtins are enabled.
vector unsigned long long __builtin_crypto_vsbox (vector unsigned long long);
vector unsigned long long __builtin_crypto_vcipher (vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vcipherlast
(vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vncipher (vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vncipherlast
(vector unsigned long long,
vector unsigned long long);
vector unsigned char __builtin_crypto_vpermxor (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector unsigned short __builtin_crypto_vpermxor (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector unsigned int __builtin_crypto_vpermxor (vector unsigned int,
vector unsigned int,
vector unsigned int);
vector unsigned long long __builtin_crypto_vpermxor (vector unsigned long long,
vector unsigned long long,

734

Using the GNU Compiler Collection (GCC)

vector unsigned long long);
vector unsigned char __builtin_crypto_vpmsumb (vector unsigned char,
vector unsigned char);
vector unsigned short __builtin_crypto_vpmsumb (vector unsigned short,
vector unsigned short);
vector unsigned int __builtin_crypto_vpmsumb (vector unsigned int,
vector unsigned int);
vector unsigned long long __builtin_crypto_vpmsumb (vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vshasigmad
(vector unsigned long long, int, int);
vector unsigned int __builtin_crypto_vshasigmaw (vector unsigned int,
int, int);

The second argument to builtin crypto vshasigmad and builtin crypto vshasigmaw
must be a constant integer that is 0 or 1. The third argument to these built-in functions
must be a constant integer in the range of 0 to 15.
If the ISA 3.0 instruction set additions are enabled (‘-mcpu=power9’), the following additional functions are available for both 32-bit and 64-bit targets.
vector short vec xl (int, vector short *); vector short vec xl (int, short *); vector unsigned
short vec xl (int, vector unsigned short *); vector unsigned short vec xl (int, unsigned short
*); vector char vec xl (int, vector char *); vector char vec xl (int, char *); vector unsigned
char vec xl (int, vector unsigned char *); vector unsigned char vec xl (int, unsigned char
*);
void vec xst (vector short, int, vector short *); void vec xst (vector short, int, short
*); void vec xst (vector unsigned short, int, vector unsigned short *); void vec xst (vector
unsigned short, int, unsigned short *); void vec xst (vector char, int, vector char *); void
vec xst (vector char, int, char *); void vec xst (vector unsigned char, int, vector unsigned
char *); void vec xst (vector unsigned char, int, unsigned char *);

6.59.23 PowerPC Hardware Transactional Memory Built-in
Functions
GCC provides two interfaces for accessing the Hardware Transactional Memory (HTM)
instructions available on some of the PowerPC family of processors (eg, POWER8). The two
interfaces come in a low level interface, consisting of built-in functions specific to PowerPC
and a higher level interface consisting of inline functions that are common between PowerPC
and S/390.

6.59.23.1 PowerPC HTM Low Level Built-in Functions
The following low level built-in functions are available with ‘-mhtm’ or ‘-mcpu=CPU’ where
CPU is ‘power8’ or later. They all generate the machine instruction that is part of the
name.
The HTM builtins (with the exception of __builtin_tbegin) return the full 4-bit condition register value set by their associated hardware instruction. The header file htmintrin.h

Chapter 6: Extensions to the C Language Family

735

defines some macros that can be used to decipher the return value. The __builtin_tbegin
builtin returns a simple true or false value depending on whether a transaction was successfully started or not. The arguments of the builtins match exactly the type and order of
the associated hardware instruction’s operands, except for the __builtin_tcheck builtin,
which does not take any input arguments. Refer to the ISA manual for a description of
each instruction’s operands.
unsigned int __builtin_tbegin (unsigned int)
unsigned int __builtin_tend (unsigned int)
unsigned
unsigned
unsigned
unsigned
unsigned

int
int
int
int
int

__builtin_tabort (unsigned int)
__builtin_tabortdc (unsigned int, unsigned int, unsigned int)
__builtin_tabortdci (unsigned int, unsigned int, int)
__builtin_tabortwc (unsigned int, unsigned int, unsigned int)
__builtin_tabortwci (unsigned int, unsigned int, int)

unsigned
unsigned
unsigned
unsigned

int
int
int
int

__builtin_tcheck (void)
__builtin_treclaim (unsigned int)
__builtin_trechkpt (void)
__builtin_tsr (unsigned int)

In addition to the above HTM built-ins, we have added built-ins for some common extended mnemonics of the HTM instructions:
unsigned int __builtin_tendall (void)
unsigned int __builtin_tresume (void)
unsigned int __builtin_tsuspend (void)

Note that the semantics of the above HTM builtins are required to mimic
the locking semantics used for critical sections.
Builtins that are used to create
a new transaction or restart a suspended transaction must have lock acquisition like semantics while those builtins that end or suspend a transaction must
have lock release like semantics.
Specifically, this must mimic lock semantics
as specified by C++11, for example: Lock acquisition is as-if an execution of
atomic exchange n(&globallock,1, ATOMIC ACQUIRE) that returns 0, and lock
atomic store(&globallock,0, ATOMIC RELEASE),
release is as-if an execution of
with globallock being an implicit implementation-defined lock used for all transactions.
The HTM instructions associated with with the builtins inherently provide the correct
acquisition and release hardware barriers required. However, the compiler must also be
prohibited from moving loads and stores across the builtins in a way that would violate
their semantics. This has been accomplished by adding memory barriers to the associated
HTM instructions (which is a conservative approach to provide acquire and release
semantics). Earlier versions of the compiler did not treat the HTM instructions as memory
barriers. A __TM_FENCE__ macro has been added, which can be used to determine whether
the current compiler treats HTM instructions as memory barriers or not. This allows the
user to explicitly add memory barriers to their code when using an older version of the
compiler.
The following set of built-in functions are available to gain access to the HTM specific
special purpose registers.
unsigned
unsigned
unsigned
unsigned

long
long
long
long

__builtin_get_texasr (void)
__builtin_get_texasru (void)
__builtin_get_tfhar (void)
__builtin_get_tfiar (void)

736

Using the GNU Compiler Collection (GCC)

void
void
void
void

__builtin_set_texasr (unsigned long);
__builtin_set_texasru (unsigned long);
__builtin_set_tfhar (unsigned long);
__builtin_set_tfiar (unsigned long);

Example usage of these low level built-in functions may look like:
#include 
int num_retries = 10;
while (1)
{
if (__builtin_tbegin (0))
{
/* Transaction State Initiated. */
if (is_locked (lock))
__builtin_tabort (0);
... transaction code...
__builtin_tend (0);
break;
}
else
{
/* Transaction State Failed. Use locks if the transaction
failure is "persistent" or we’ve tried too many times. */
if (num_retries-- <= 0
|| _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
{
acquire_lock (lock);
... non transactional fallback path...
release_lock (lock);
break;
}
}
}

One final built-in function has been added that returns the value of the 2-bit Transaction
State field of the Machine Status Register (MSR) as stored in CR0.
unsigned long __builtin_ttest (void)

This built-in can be used to determine the current transaction state using the following
code example:
#include 
unsigned char tx_state = _HTM_STATE (__builtin_ttest ());
if (tx_state == _HTM_TRANSACTIONAL)
{
/* Code to use in transactional state. */
}
else if (tx_state == _HTM_NONTRANSACTIONAL)
{
/* Code to use in non-transactional state. */
}
else if (tx_state == _HTM_SUSPENDED)
{
/* Code to use in transaction suspended state.
}

*/

Chapter 6: Extensions to the C Language Family

737

6.59.23.2 PowerPC HTM High Level Inline Functions
The following high level HTM interface is made available by including 
and using ‘-mhtm’ or ‘-mcpu=CPU’ where CPU is ‘power8’ or later. This interface is common
between PowerPC and S/390, allowing users to write one HTM source implementation that
can be compiled and executed on either system.
long
long
long
void
void
void
void

__TM_simple_begin (void)
__TM_begin (void* const TM_buff)
__TM_end (void)
__TM_abort (void)
__TM_named_abort (unsigned char const code)
__TM_resume (void)
__TM_suspend (void)

long
long
long
long
long
long
long
long
long
long

__TM_is_user_abort (void* const TM_buff)
__TM_is_named_user_abort (void* const TM_buff, unsigned char *code)
__TM_is_illegal (void* const TM_buff)
__TM_is_footprint_exceeded (void* const TM_buff)
__TM_nesting_depth (void* const TM_buff)
__TM_is_nested_too_deep(void* const TM_buff)
__TM_is_conflict(void* const TM_buff)
__TM_is_failure_persistent(void* const TM_buff)
__TM_failure_address(void* const TM_buff)
long __TM_failure_code(void* const TM_buff)

Using these common set of HTM inline functions, we can create a more portable version
of the HTM example in the previous section that will work on either PowerPC or S/390:
#include 
int num_retries = 10;
TM_buff_type TM_buff;
while (1)
{
if (__TM_begin (TM_buff) == _HTM_TBEGIN_STARTED)
{
/* Transaction State Initiated. */
if (is_locked (lock))
__TM_abort ();
... transaction code...
__TM_end ();
break;
}
else
{
/* Transaction State Failed. Use locks if the transaction
failure is "persistent" or we’ve tried too many times. */
if (num_retries-- <= 0
|| __TM_is_failure_persistent (TM_buff))
{
acquire_lock (lock);
... non transactional fallback path...
release_lock (lock);
break;
}
}
}

738

Using the GNU Compiler Collection (GCC)

6.59.24 PowerPC Atomic Memory Operation Functions
ISA 3.0 of the PowerPC added new atomic memory operation (amo) instructions. GCC
provides support for these instructions in 64-bit environments. All of the functions are
declared in the include file amo.h.
The functions supported are:
#include 
uint32_t
uint32_t
uint32_t
uint32_t
uint32_t
uint32_t
uint32_t
int32_t
int32_t
int32_t
int32_t

amo_lwat_add (uint32_t *, uint32_t);
amo_lwat_xor (uint32_t *, uint32_t);
amo_lwat_ior (uint32_t *, uint32_t);
amo_lwat_and (uint32_t *, uint32_t);
amo_lwat_umax (uint32_t *, uint32_t);
amo_lwat_umin (uint32_t *, uint32_t);
amo_lwat_swap (uint32_t *, uint32_t);

uint64_t
uint64_t
uint64_t
uint64_t
uint64_t
uint64_t
uint64_t

amo_lwat_sadd (int32_t *, int32_t);
amo_lwat_smax (int32_t *, int32_t);
amo_lwat_smin (int32_t *, int32_t);
amo_lwat_sswap (int32_t *, int32_t);

int64_t
int64_t
int64_t
int64_t
void
void
void
void
void
void

amo_ldat_add (uint64_t *, uint64_t);
amo_ldat_xor (uint64_t *, uint64_t);
amo_ldat_ior (uint64_t *, uint64_t);
amo_ldat_and (uint64_t *, uint64_t);
amo_ldat_umax (uint64_t *, uint64_t);
amo_ldat_umin (uint64_t *, uint64_t);
amo_ldat_swap (uint64_t *, uint64_t);
amo_ldat_sadd (int64_t *, int64_t);
amo_ldat_smax (int64_t *, int64_t);
amo_ldat_smin (int64_t *, int64_t);
amo_ldat_sswap (int64_t *, int64_t);

amo_stwat_add (uint32_t *, uint32_t);
amo_stwat_xor (uint32_t *, uint32_t);
amo_stwat_ior (uint32_t *, uint32_t);
amo_stwat_and (uint32_t *, uint32_t);
amo_stwat_umax (uint32_t *, uint32_t);
amo_stwat_umin (uint32_t *, uint32_t);

void amo_stwat_sadd (int32_t *, int32_t);
void amo_stwat_smax (int32_t *, int32_t);
void amo_stwat_smin (int32_t *, int32_t);
void
void
void
void
void
void

amo_stdat_add (uint64_t *, uint64_t);
amo_stdat_xor (uint64_t *, uint64_t);
amo_stdat_ior (uint64_t *, uint64_t);
amo_stdat_and (uint64_t *, uint64_t);
amo_stdat_umax (uint64_t *, uint64_t);
amo_stdat_umin (uint64_t *, uint64_t);

void amo_stdat_sadd (int64_t *, int64_t);
void amo_stdat_smax (int64_t *, int64_t);
void amo_stdat_smin (int64_t *, int64_t);

Chapter 6: Extensions to the C Language Family

739

6.59.25 RX Built-in Functions
GCC supports some of the RX instructions which cannot be expressed in the C programming
language via the use of built-in functions. The following functions are supported:

void __builtin_rx_brk (void)

[Built-in Function]

Generates the brk machine instruction.

void __builtin_rx_clrpsw (int)

[Built-in Function]
Generates the clrpsw machine instruction to clear the specified bit in the processor
status word.

void __builtin_rx_int (int)

[Built-in Function]
Generates the int machine instruction to generate an interrupt with the specified
value.

void __builtin_rx_machi (int, int)

[Built-in Function]
Generates the machi machine instruction to add the result of multiplying the top 16
bits of the two arguments into the accumulator.

void __builtin_rx_maclo (int, int)

[Built-in Function]
Generates the maclo machine instruction to add the result of multiplying the bottom
16 bits of the two arguments into the accumulator.

void __builtin_rx_mulhi (int, int)

[Built-in Function]
Generates the mulhi machine instruction to place the result of multiplying the top
16 bits of the two arguments into the accumulator.

void __builtin_rx_mullo (int, int)

[Built-in Function]
Generates the mullo machine instruction to place the result of multiplying the bottom
16 bits of the two arguments into the accumulator.

int __builtin_rx_mvfachi (void)

[Built-in Function]
Generates the mvfachi machine instruction to read the top 32 bits of the accumulator.

int __builtin_rx_mvfacmi (void)

[Built-in Function]
Generates the mvfacmi machine instruction to read the middle 32 bits of the accumulator.

int __builtin_rx_mvfc (int)

[Built-in Function]
Generates the mvfc machine instruction which reads the control register specified in
its argument and returns its value.

void __builtin_rx_mvtachi (int)

[Built-in Function]
Generates the mvtachi machine instruction to set the top 32 bits of the accumulator.

void __builtin_rx_mvtaclo (int)

[Built-in Function]
Generates the mvtaclo machine instruction to set the bottom 32 bits of the accumulator.

void __builtin_rx_mvtc (int reg, int val)

[Built-in Function]
Generates the mvtc machine instruction which sets control register number reg to
val.

740

Using the GNU Compiler Collection (GCC)

void __builtin_rx_mvtipl (int)

[Built-in Function]
Generates the mvtipl machine instruction set the interrupt priority level.

void __builtin_rx_racw (int)

[Built-in Function]
Generates the racw machine instruction to round the accumulator according to the
specified mode.

int __builtin_rx_revw (int)

[Built-in Function]
Generates the revw machine instruction which swaps the bytes in the argument so
that bits 0–7 now occupy bits 8–15 and vice versa, and also bits 16–23 occupy bits
24–31 and vice versa.

void __builtin_rx_rmpa (void)

[Built-in Function]
Generates the rmpa machine instruction which initiates a repeated multiply and accumulate sequence.

void __builtin_rx_round (float)

[Built-in Function]
Generates the round machine instruction which returns the floating-point argument
rounded according to the current rounding mode set in the floating-point status word
register.

int __builtin_rx_sat (int)

[Built-in Function]
Generates the sat machine instruction which returns the saturated value of the argument.

void __builtin_rx_setpsw (int)

[Built-in Function]
Generates the setpsw machine instruction to set the specified bit in the processor
status word.

void __builtin_rx_wait (void)

[Built-in Function]

Generates the wait machine instruction.

6.59.26 S/390 System z Built-in Functions
int __builtin_tbegin (void*)

[Built-in Function]
Generates the tbegin machine instruction starting a non-constrained hardware transaction. If the parameter is non-NULL the memory area is used to store the transaction
diagnostic buffer and will be passed as first operand to tbegin. This buffer can be
defined using the struct __htm_tdb C struct defined in htmintrin.h and must reside on a double-word boundary. The second tbegin operand is set to 0xff0c. This
enables save/restore of all GPRs and disables aborts for FPR and AR manipulations
inside the transaction body. The condition code set by the tbegin instruction is returned as integer value. The tbegin instruction by definition overwrites the content
of all FPRs. The compiler will generate code which saves and restores the FPRs. For
soft-float code it is recommended to used the *_nofloat variant. In order to prevent
a TDB from being written it is required to pass a constant zero value as parameter.
Passing a zero value through a variable is not sufficient. Although modifications of
access registers inside the transaction will not trigger an transaction abort it is not
supported to actually modify them. Access registers do not get saved when entering
a transaction. They will have undefined state when reaching the abort code.

Chapter 6: Extensions to the C Language Family

741

Macros for the possible return codes of tbegin are defined in the htmintrin.h header file:
_HTM_TBEGIN_STARTED
tbegin has been executed as part of normal processing. The transaction body
is supposed to be executed.
_HTM_TBEGIN_INDETERMINATE
The transaction was aborted due to an indeterminate condition which might
be persistent.
_HTM_TBEGIN_TRANSIENT
The transaction aborted due to a transient failure. The transaction should be
re-executed in that case.
_HTM_TBEGIN_PERSISTENT
The transaction aborted due to a persistent failure. Re-execution under same
circumstances will not be productive.
[Macro]
The _HTM_FIRST_USER_ABORT_CODE defined in htmintrin.h specifies the first abort
code which can be used for __builtin_tabort. Values below this threshold are
reserved for machine use.

_HTM_FIRST_USER_ABORT_CODE

[Data type]
The struct __htm_tdb defined in htmintrin.h describes the structure of the transaction diagnostic block as specified in the Principles of Operation manual chapter
5-91.

struct __htm_tdb

int __builtin_tbegin_nofloat (void*)

[Built-in Function]
Same as __builtin_tbegin but without FPR saves and restores. Using this variant
in code making use of FPRs will leave the FPRs in undefined state when entering the
transaction abort handler code.

int __builtin_tbegin_retry (void*, int)

[Built-in Function]
In addition to __builtin_tbegin a loop for transient failures is generated. If tbegin
returns a condition code of 2 the transaction will be retried as often as specified in the
second argument. The perform processor assist instruction is used to tell the CPU
about the number of fails so far.

int __builtin_tbegin_retry_nofloat (void*, int)

[Built-in Function]
Same as __builtin_tbegin_retry but without FPR saves and restores. Using this
variant in code making use of FPRs will leave the FPRs in undefined state when
entering the transaction abort handler code.

void __builtin_tbeginc (void)

[Built-in Function]
Generates the tbeginc machine instruction starting a constrained hardware transaction. The second operand is set to 0xff08.

int __builtin_tend (void)

[Built-in Function]
Generates the tend machine instruction finishing a transaction and making the
changes visible to other threads. The condition code generated by tend is returned
as integer value.

742

Using the GNU Compiler Collection (GCC)

void __builtin_tabort (int)

[Built-in Function]
Generates the tabort machine instruction with the specified abort code. Abort codes
from 0 through 255 are reserved and will result in an error message.

void __builtin_tx_assist (int)

[Built-in Function]
Generates the ppa rX,rY,1 machine instruction. Where the integer parameter is
loaded into rX and a value of zero is loaded into rY. The integer parameter specifies
the number of times the transaction repeatedly aborted.

int __builtin_tx_nesting_depth (void)

[Built-in Function]
Generates the etnd machine instruction. The current nesting depth is returned as
integer value. For a nesting depth of 0 the code is not executed as part of an transaction.

void __builtin_non_tx_store (uint64 t *, uint64 t)

[Built-in Function]
Generates the ntstg machine instruction. The second argument is written to the
first arguments location. The store operation will not be rolled-back in case of an
transaction abort.

6.59.27 SH Built-in Functions
The following built-in functions are supported on the SH1, SH2, SH3 and SH4 families of
processors:

void __builtin_set_thread_pointer (void *ptr)

[Built-in Function]
Sets the ‘GBR’ register to the specified value ptr. This is usually used by system
code that manages threads and execution contexts. The compiler normally does not
generate code that modifies the contents of ‘GBR’ and thus the value is preserved across
function calls. Changing the ‘GBR’ value in user code must be done with caution, since
the compiler might use ‘GBR’ in order to access thread local variables.

void * __builtin_thread_pointer (void)

[Built-in Function]
Returns the value that is currently set in the ‘GBR’ register. Memory loads and stores
that use the thread pointer as a base address are turned into ‘GBR’ based displacement
loads and stores, if possible. For example:
struct my_tcb
{
int a, b, c, d, e;
};
int get_tcb_value (void)
{
// Generate ‘mov.l @(8,gbr),r0’ instruction
return ((my_tcb*)__builtin_thread_pointer ())->c;
}

unsigned int __builtin_sh_get_fpscr (void)

[Built-in Function]

Returns the value that is currently set in the ‘FPSCR’ register.

void __builtin_sh_set_fpscr (unsigned int val)

[Built-in Function]
Sets the ‘FPSCR’ register to the specified value val, while preserving the current values
of the FR, SZ and PR bits.

Chapter 6: Extensions to the C Language Family

743

6.59.28 SPARC VIS Built-in Functions
GCC supports SIMD operations on the SPARC using both the generic vector extensions
(see Section 6.50 [Vector Extensions], page 598) as well as built-in functions for the SPARC
Visual Instruction Set (VIS). When you use the ‘-mvis’ switch, the VIS extension is exposed
as the following built-in functions:
typedef
typedef
typedef
typedef
typedef
typedef

int v1si __attribute__ ((vector_size (4)));
int v2si __attribute__ ((vector_size (8)));
short v4hi __attribute__ ((vector_size (8)));
short v2hi __attribute__ ((vector_size (4)));
unsigned char v8qi __attribute__ ((vector_size (8)));
unsigned char v4qi __attribute__ ((vector_size (4)));

void __builtin_vis_write_gsr (int64_t);
int64_t __builtin_vis_read_gsr (void);
void * __builtin_vis_alignaddr (void *, long);
void * __builtin_vis_alignaddrl (void *, long);
int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
v2si __builtin_vis_faligndatav2si (v2si, v2si);
v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);
v4hi __builtin_vis_fexpand (v4qi);
v4hi
v4hi
v4hi
v4hi
v4hi
v2si
v2si

__builtin_vis_fmul8x16 (v4qi, v4hi);
__builtin_vis_fmul8x16au (v4qi, v2hi);
__builtin_vis_fmul8x16al (v4qi, v2hi);
__builtin_vis_fmul8sux16 (v8qi, v4hi);
__builtin_vis_fmul8ulx16 (v8qi, v4hi);
__builtin_vis_fmuld8sux16 (v4qi, v2hi);
__builtin_vis_fmuld8ulx16 (v4qi, v2hi);

v4qi
v8qi
v2hi
v8qi

__builtin_vis_fpack16 (v4hi);
__builtin_vis_fpack32 (v2si, v8qi);
__builtin_vis_fpackfix (v2si);
__builtin_vis_fpmerge (v4qi, v4qi);

int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);
long
long
long
long
long
long

__builtin_vis_edge8 (void *, void *);
__builtin_vis_edge8l (void *, void *);
__builtin_vis_edge16 (void *, void *);
__builtin_vis_edge16l (void *, void *);
__builtin_vis_edge32 (void *, void *);
__builtin_vis_edge32l (void *, void *);

long
long
long
long
long
long
long
long

__builtin_vis_fcmple16
__builtin_vis_fcmple32
__builtin_vis_fcmpne16
__builtin_vis_fcmpne32
__builtin_vis_fcmpgt16
__builtin_vis_fcmpgt32
__builtin_vis_fcmpeq16
__builtin_vis_fcmpeq32

(v4hi,
(v2si,
(v4hi,
(v2si,
(v4hi,
(v2si,
(v4hi,
(v2si,

v4hi);
v2si);
v4hi);
v2si);
v4hi);
v2si);
v4hi);
v2si);

v4hi __builtin_vis_fpadd16 (v4hi, v4hi);
v2hi __builtin_vis_fpadd16s (v2hi, v2hi);

744

Using the GNU Compiler Collection (GCC)

v2si
v1si
v4hi
v2hi
v2si
v1si

__builtin_vis_fpadd32 (v2si, v2si);
__builtin_vis_fpadd32s (v1si, v1si);
__builtin_vis_fpsub16 (v4hi, v4hi);
__builtin_vis_fpsub16s (v2hi, v2hi);
__builtin_vis_fpsub32 (v2si, v2si);
__builtin_vis_fpsub32s (v1si, v1si);

long __builtin_vis_array8 (long, long);
long __builtin_vis_array16 (long, long);
long __builtin_vis_array32 (long, long);

When you use the ‘-mvis2’ switch, the VIS version 2.0 built-in functions also become
available:
long __builtin_vis_bmask (long, long);
int64_t __builtin_vis_bshuffledi (int64_t, int64_t);
v2si __builtin_vis_bshufflev2si (v2si, v2si);
v4hi __builtin_vis_bshufflev2si (v4hi, v4hi);
v8qi __builtin_vis_bshufflev2si (v8qi, v8qi);
long
long
long
long
long
long

__builtin_vis_edge8n (void *, void *);
__builtin_vis_edge8ln (void *, void *);
__builtin_vis_edge16n (void *, void *);
__builtin_vis_edge16ln (void *, void *);
__builtin_vis_edge32n (void *, void *);
__builtin_vis_edge32ln (void *, void *);

When you use the ‘-mvis3’ switch, the VIS version 3.0 built-in functions also become
available:
void __builtin_vis_cmask8 (long);
void __builtin_vis_cmask16 (long);
void __builtin_vis_cmask32 (long);
v4hi __builtin_vis_fchksm16 (v4hi, v4hi);
v4hi
v4hi
v4hi
v4hi
v2si
v2si
v2si
v2si

__builtin_vis_fsll16 (v4hi, v4hi);
__builtin_vis_fslas16 (v4hi, v4hi);
__builtin_vis_fsrl16 (v4hi, v4hi);
__builtin_vis_fsra16 (v4hi, v4hi);
__builtin_vis_fsll16 (v2si, v2si);
__builtin_vis_fslas16 (v2si, v2si);
__builtin_vis_fsrl16 (v2si, v2si);
__builtin_vis_fsra16 (v2si, v2si);

long __builtin_vis_pdistn (v8qi, v8qi);
v4hi __builtin_vis_fmean16 (v4hi, v4hi);
int64_t __builtin_vis_fpadd64 (int64_t, int64_t);
int64_t __builtin_vis_fpsub64 (int64_t, int64_t);
v4hi
v2hi
v4hi
v2hi
v2si
v1si
v2si
v1si

__builtin_vis_fpadds16 (v4hi, v4hi);
__builtin_vis_fpadds16s (v2hi, v2hi);
__builtin_vis_fpsubs16 (v4hi, v4hi);
__builtin_vis_fpsubs16s (v2hi, v2hi);
__builtin_vis_fpadds32 (v2si, v2si);
__builtin_vis_fpadds32s (v1si, v1si);
__builtin_vis_fpsubs32 (v2si, v2si);
__builtin_vis_fpsubs32s (v1si, v1si);

Chapter 6: Extensions to the C Language Family

long
long
long
long

__builtin_vis_fucmple8
__builtin_vis_fucmpne8
__builtin_vis_fucmpgt8
__builtin_vis_fucmpeq8

(v8qi,
(v8qi,
(v8qi,
(v8qi,

745

v8qi);
v8qi);
v8qi);
v8qi);

float __builtin_vis_fhadds (float, float);
double __builtin_vis_fhaddd (double, double);
float __builtin_vis_fhsubs (float, float);
double __builtin_vis_fhsubd (double, double);
float __builtin_vis_fnhadds (float, float);
double __builtin_vis_fnhaddd (double, double);
int64_t __builtin_vis_umulxhi (int64_t, int64_t);
int64_t __builtin_vis_xmulx (int64_t, int64_t);
int64_t __builtin_vis_xmulxhi (int64_t, int64_t);

When you use the ‘-mvis4’ switch, the VIS version 4.0 built-in functions also become
available:
v8qi
v8qi
v8qi
v4hi

__builtin_vis_fpadd8 (v8qi, v8qi);
__builtin_vis_fpadds8 (v8qi, v8qi);
__builtin_vis_fpaddus8 (v8qi, v8qi);
__builtin_vis_fpaddus16 (v4hi, v4hi);

v8qi
v8qi
v8qi
v4hi

__builtin_vis_fpsub8 (v8qi, v8qi);
__builtin_vis_fpsubs8 (v8qi, v8qi);
__builtin_vis_fpsubus8 (v8qi, v8qi);
__builtin_vis_fpsubus16 (v4hi, v4hi);

long
long
long
long
long
long

__builtin_vis_fpcmple8 (v8qi, v8qi);
__builtin_vis_fpcmpgt8 (v8qi, v8qi);
__builtin_vis_fpcmpule16 (v4hi, v4hi);
__builtin_vis_fpcmpugt16 (v4hi, v4hi);
__builtin_vis_fpcmpule32 (v2si, v2si);
__builtin_vis_fpcmpugt32 (v2si, v2si);

v8qi __builtin_vis_fpmax8 (v8qi, v8qi);
v4hi __builtin_vis_fpmax16 (v4hi, v4hi);
v2si __builtin_vis_fpmax32 (v2si, v2si);
v8qi __builtin_vis_fpmaxu8 (v8qi, v8qi);
v4hi __builtin_vis_fpmaxu16 (v4hi, v4hi);
v2si __builtin_vis_fpmaxu32 (v2si, v2si);

v8qi __builtin_vis_fpmin8 (v8qi, v8qi);
v4hi __builtin_vis_fpmin16 (v4hi, v4hi);
v2si __builtin_vis_fpmin32 (v2si, v2si);
v8qi __builtin_vis_fpminu8 (v8qi, v8qi);
v4hi __builtin_vis_fpminu16 (v4hi, v4hi);
v2si __builtin_vis_fpminu32 (v2si, v2si);

When you use the ‘-mvis4b’ switch, the VIS version 4.0B built-in functions also become
available:
v8qi __builtin_vis_dictunpack8 (double, int);
v4hi __builtin_vis_dictunpack16 (double, int);
v2si __builtin_vis_dictunpack32 (double, int);

746

Using the GNU Compiler Collection (GCC)

long
long
long
long

__builtin_vis_fpcmple8shl
__builtin_vis_fpcmpgt8shl
__builtin_vis_fpcmpeq8shl
__builtin_vis_fpcmpne8shl

(v8qi,
(v8qi,
(v8qi,
(v8qi,

v8qi,
v8qi,
v8qi,
v8qi,

int);
int);
int);
int);

long
long
long
long

__builtin_vis_fpcmple16shl
__builtin_vis_fpcmpgt16shl
__builtin_vis_fpcmpeq16shl
__builtin_vis_fpcmpne16shl

(v4hi,
(v4hi,
(v4hi,
(v4hi,

v4hi,
v4hi,
v4hi,
v4hi,

int);
int);
int);
int);

long
long
long
long

__builtin_vis_fpcmple32shl
__builtin_vis_fpcmpgt32shl
__builtin_vis_fpcmpeq32shl
__builtin_vis_fpcmpne32shl

(v2si,
(v2si,
(v2si,
(v2si,

v2si,
v2si,
v2si,
v2si,

int);
int);
int);
int);

long
long
long
long
long
long

__builtin_vis_fpcmpule8shl (v8qi, v8qi, int);
__builtin_vis_fpcmpugt8shl (v8qi, v8qi, int);
__builtin_vis_fpcmpule16shl (v4hi, v4hi, int);
__builtin_vis_fpcmpugt16shl (v4hi, v4hi, int);
__builtin_vis_fpcmpule32shl (v2si, v2si, int);
__builtin_vis_fpcmpugt32shl (v2si, v2si, int);

long __builtin_vis_fpcmpde8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmpde16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmpde32shl (v2si, v2si, int);
long __builtin_vis_fpcmpur8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmpur16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmpur32shl (v2si, v2si, int);

6.59.29 SPU Built-in Functions
GCC provides extensions for the SPU processor as described in the Sony/Toshiba/IBM
SPU Language Extensions Specification. GCC’s implementation differs in several ways.
• The optional extension of specifying vector constants in parentheses is not supported.
• A vector initializer requires no cast if the vector constant is of the same type as the
variable it is initializing.
• If signed or unsigned is omitted, the signedness of the vector type is the default
signedness of the base type. The default varies depending on the operating system, so
a portable program should always specify the signedness.
• By default, the keyword __vector is added. The macro vector is defined in  and can be undefined.
• GCC allows using a typedef name as the type specifier for a vector type.
• For C, overloaded functions are implemented with macros so the following does not
work:
spu_add ((vector signed int){1, 2, 3, 4}, foo);

Since spu_add is a macro, the vector constant in the example is treated as four separate
arguments. Wrap the entire argument in parentheses for this to work.
• The extended version of __builtin_expect is not supported.

Chapter 6: Extensions to the C Language Family

747

Note: Only the interface described in the aforementioned specification is supported.
Internally, GCC uses built-in functions to implement the required functionality, but these
are not supported and are subject to change without notice.

6.59.30 TI C6X Built-in Functions
GCC provides intrinsics to access certain instructions of the TI C6X processors. These
intrinsics, listed below, are available after inclusion of the c6x_intrinsics.h header file.
They map directly to C6X instructions.
int _sadd (int, int)
int _ssub (int, int)
int _sadd2 (int, int)
int _ssub2 (int, int)
long long _mpy2 (int, int)
long long _smpy2 (int, int)
int _add4 (int, int)
int _sub4 (int, int)
int _saddu4 (int, int)
int
int
int
int

_smpy (int, int)
_smpyh (int, int)
_smpyhl (int, int)
_smpylh (int, int)

int _sshl (int, int)
int _subc (int, int)
int _avg2 (int, int)
int _avgu4 (int, int)
int
int
int
int
int

_clrr (int, int)
_extr (int, int)
_extru (int, int)
_abs (int)
_abs2 (int)

6.59.31 TILE-Gx Built-in Functions
GCC provides intrinsics to access every instruction of the TILE-Gx processor. The intrinsics
are of the form:
unsigned long long __insn_op (...)

Where op is the name of the instruction. Refer to the ISA manual for the complete list
of instructions.
GCC also provides intrinsics to directly access the network registers. The intrinsics are:
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned

long
long
long
long
long
long

long
long
long
long
long
long

__tile_idn0_receive
__tile_idn1_receive
__tile_udn0_receive
__tile_udn1_receive
__tile_udn2_receive
__tile_udn3_receive

(void)
(void)
(void)
(void)
(void)
(void)

748

Using the GNU Compiler Collection (GCC)

void __tile_idn_send (unsigned long long)
void __tile_udn_send (unsigned long long)

The intrinsic void __tile_network_barrier (void) is used to guarantee that no network operations before it are reordered with those after it.

6.59.32 TILEPro Built-in Functions
GCC provides intrinsics to access every instruction of the TILEPro processor. The intrinsics
are of the form:
unsigned __insn_op (...)

where op is the name of the instruction. Refer to the ISA manual for the complete list of
instructions.
GCC also provides intrinsics to directly access the network registers. The intrinsics are:
unsigned __tile_idn0_receive (void)
unsigned __tile_idn1_receive (void)
unsigned __tile_sn_receive (void)
unsigned __tile_udn0_receive (void)
unsigned __tile_udn1_receive (void)
unsigned __tile_udn2_receive (void)
unsigned __tile_udn3_receive (void)
void __tile_idn_send (unsigned)
void __tile_sn_send (unsigned)
void __tile_udn_send (unsigned)

The intrinsic void __tile_network_barrier (void) is used to guarantee that no network operations before it are reordered with those after it.

6.59.33 x86 Built-in Functions
These built-in functions are available for the x86-32 and x86-64 family of computers, depending on the command-line switches used.
If you specify command-line switches such as ‘-msse’, the compiler could use the extended
instruction sets even if the built-ins are not used explicitly in the program. For this reason,
applications that perform run-time CPU detection must compile separate files for each
supported architecture, using the appropriate flags. In particular, the file containing the
CPU detection code should be compiled without these options.
The following machine modes are available for use with MMX built-in functions (see
Section 6.50 [Vector Extensions], page 598): V2SI for a vector of two 32-bit integers, V4HI
for a vector of four 16-bit integers, and V8QI for a vector of eight 8-bit integers. Some of
the built-in functions operate on MMX registers as a whole 64-bit entity, these use V1DI as
their mode.
If 3DNow! extensions are enabled, V2SF is used as a mode for a vector of two 32-bit
floating-point values.
If SSE extensions are enabled, V4SF is used for a vector of four 32-bit floating-point
values. Some instructions use a vector of four 32-bit integers, these use V4SI. Finally, some

Chapter 6: Extensions to the C Language Family

749

instructions operate on an entire vector register, interpreting it as a 128-bit integer, these
use mode TI.
The x86-32 and x86-64 family of processors use additional built-in functions for efficient
use of TF (__float128) 128-bit floating point and TC 128-bit complex floating-point values.
The following floating-point built-in functions are always available. All of them implement
the function that is part of the name.
__float128 __builtin_fabsq (__float128)
__float128 __builtin_copysignq (__float128, __float128)

The following built-in functions are always available.
__float128 __builtin_infq (void)
Similar to __builtin_inf, except the return type is __float128.
__float128 __builtin_huge_valq (void)
Similar to __builtin_huge_val, except the return type is __float128.
__float128 __builtin_nanq (void)
Similar to __builtin_nan, except the return type is __float128.
__float128 __builtin_nansq (void)
Similar to __builtin_nans, except the return type is __float128.
The following built-in function is always available.
void __builtin_ia32_pause (void)
Generates the pause machine instruction with a compiler memory barrier.
The following built-in functions are always available and can be used to check the target
platform type.

void __builtin_cpu_init (void)

[Built-in Function]
This function runs the CPU detection code to check the type of CPU and the features
supported. This built-in function needs to be invoked along with the built-in functions
to check CPU type and features, __builtin_cpu_is and __builtin_cpu_supports,
only when used in a function that is executed before any constructors are called. The
CPU detection code is automatically executed in a very high priority constructor.
For example, this function has to be used in ifunc resolvers that check for CPU type
using the built-in functions __builtin_cpu_is and __builtin_cpu_supports, or in
constructors on targets that don’t support constructor priority.
static void (*resolve_memcpy (void)) (void)
{
// ifunc resolvers fire before constructors, explicitly call the init
// function.
__builtin_cpu_init ();
if (__builtin_cpu_supports ("ssse3"))
return ssse3_memcpy; // super fast memcpy with ssse3 instructions.
else
return default_memcpy;
}
void *memcpy (void *, const void *, size_t)
__attribute__ ((ifunc ("resolve_memcpy")));

750

Using the GNU Compiler Collection (GCC)

int __builtin_cpu_is (const char *cpuname)

[Built-in Function]
This function returns a positive integer if the run-time CPU is of type cpuname and
returns 0 otherwise. The following CPU names can be detected:
‘intel’

Intel CPU.

‘atom’

Intel Atom CPU.

‘core2’

Intel Core 2 CPU.

‘corei7’

Intel Core i7 CPU.

‘nehalem’

Intel Core i7 Nehalem CPU.

‘westmere’
Intel Core i7 Westmere CPU.
‘sandybridge’
Intel Core i7 Sandy Bridge CPU.
‘amd’

AMD CPU.

‘amdfam10h’
AMD Family 10h CPU.
‘barcelona’
AMD Family 10h Barcelona CPU.
‘shanghai’
AMD Family 10h Shanghai CPU.
‘istanbul’
AMD Family 10h Istanbul CPU.
‘btver1’

AMD Family 14h CPU.

‘amdfam15h’
AMD Family 15h CPU.
‘bdver1’

AMD Family 15h Bulldozer version 1.

‘bdver2’

AMD Family 15h Bulldozer version 2.

‘bdver3’

AMD Family 15h Bulldozer version 3.

‘bdver4’

AMD Family 15h Bulldozer version 4.

‘btver2’

AMD Family 16h CPU.

‘amdfam17h’
AMD Family 17h CPU.
‘znver1’

AMD Family 17h Zen version 1.

Here is an example:
if (__builtin_cpu_is ("corei7"))
{
do_corei7 (); // Core i7 specific implementation.
}
else
{
do_generic (); // Generic implementation.
}

Chapter 6: Extensions to the C Language Family

751

int __builtin_cpu_supports (const char *feature)

[Built-in Function]
This function returns a positive integer if the run-time CPU supports feature and
returns 0 otherwise. The following features can be detected:
‘cmov’

CMOV instruction.

‘mmx’

MMX instructions.

‘popcnt’

POPCNT instruction.

‘sse’

SSE instructions.

‘sse2’

SSE2 instructions.

‘sse3’

SSE3 instructions.

‘ssse3’

SSSE3 instructions.

‘sse4.1’

SSE4.1 instructions.

‘sse4.2’

SSE4.2 instructions.

‘avx’

AVX instructions.

‘avx2’

AVX2 instructions.

‘avx512f’

AVX512F instructions.

Here is an example:
if (__builtin_cpu_supports ("popcnt"))
{
asm("popcnt %1,%0" : "=r"(count) : "rm"(n) : "cc");
}
else
{
count = generic_countbits (n); //generic implementation.
}

The following built-in functions are made available by ‘-mmmx’. All of them generate the
machine instruction that is part of the name.
v8qi __builtin_ia32_paddb (v8qi, v8qi)
v4hi __builtin_ia32_paddw (v4hi, v4hi)
v2si __builtin_ia32_paddd (v2si, v2si)
v8qi __builtin_ia32_psubb (v8qi, v8qi)
v4hi __builtin_ia32_psubw (v4hi, v4hi)
v2si __builtin_ia32_psubd (v2si, v2si)
v8qi __builtin_ia32_paddsb (v8qi, v8qi)
v4hi __builtin_ia32_paddsw (v4hi, v4hi)
v8qi __builtin_ia32_psubsb (v8qi, v8qi)
v4hi __builtin_ia32_psubsw (v4hi, v4hi)
v8qi __builtin_ia32_paddusb (v8qi, v8qi)
v4hi __builtin_ia32_paddusw (v4hi, v4hi)
v8qi __builtin_ia32_psubusb (v8qi, v8qi)
v4hi __builtin_ia32_psubusw (v4hi, v4hi)
v4hi __builtin_ia32_pmullw (v4hi, v4hi)
v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
di __builtin_ia32_pand (di, di)
di __builtin_ia32_pandn (di,di)
di __builtin_ia32_por (di, di)
di __builtin_ia32_pxor (di, di)

752

Using the GNU Compiler Collection (GCC)

v8qi
v4hi
v2si
v8qi
v4hi
v2si
v8qi
v4hi
v2si
v8qi
v4hi
v2si
v8qi
v4hi
v8qi

__builtin_ia32_pcmpeqb (v8qi, v8qi)
__builtin_ia32_pcmpeqw (v4hi, v4hi)
__builtin_ia32_pcmpeqd (v2si, v2si)
__builtin_ia32_pcmpgtb (v8qi, v8qi)
__builtin_ia32_pcmpgtw (v4hi, v4hi)
__builtin_ia32_pcmpgtd (v2si, v2si)
__builtin_ia32_punpckhbw (v8qi, v8qi)
__builtin_ia32_punpckhwd (v4hi, v4hi)
__builtin_ia32_punpckhdq (v2si, v2si)
__builtin_ia32_punpcklbw (v8qi, v8qi)
__builtin_ia32_punpcklwd (v4hi, v4hi)
__builtin_ia32_punpckldq (v2si, v2si)
__builtin_ia32_packsswb (v4hi, v4hi)
__builtin_ia32_packssdw (v2si, v2si)
__builtin_ia32_packuswb (v4hi, v4hi)

v4hi
v2si
v1di
v4hi
v2si
v1di
v4hi
v2si
v4hi
v2si
v1di
v4hi
v2si
v1di
v4hi
v2si

__builtin_ia32_psllw (v4hi, v4hi)
__builtin_ia32_pslld (v2si, v2si)
__builtin_ia32_psllq (v1di, v1di)
__builtin_ia32_psrlw (v4hi, v4hi)
__builtin_ia32_psrld (v2si, v2si)
__builtin_ia32_psrlq (v1di, v1di)
__builtin_ia32_psraw (v4hi, v4hi)
__builtin_ia32_psrad (v2si, v2si)
__builtin_ia32_psllwi (v4hi, int)
__builtin_ia32_pslldi (v2si, int)
__builtin_ia32_psllqi (v1di, int)
__builtin_ia32_psrlwi (v4hi, int)
__builtin_ia32_psrldi (v2si, int)
__builtin_ia32_psrlqi (v1di, int)
__builtin_ia32_psrawi (v4hi, int)
__builtin_ia32_psradi (v2si, int)

The following built-in functions are made available either with ‘-msse’, or with
‘-m3dnowa’. All of them generate the machine instruction that is part of the name.
v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
v8qi __builtin_ia32_pavgb (v8qi, v8qi)
v4hi __builtin_ia32_pavgw (v4hi, v4hi)
v1di __builtin_ia32_psadbw (v8qi, v8qi)
v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
v8qi __builtin_ia32_pminub (v8qi, v8qi)
v4hi __builtin_ia32_pminsw (v4hi, v4hi)
int __builtin_ia32_pmovmskb (v8qi)
void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
void __builtin_ia32_movntq (di *, di)
void __builtin_ia32_sfence (void)

The following built-in functions are available when ‘-msse’ is used. All of them generate
the machine instruction that is part of the name.
int
int
int
int
int
int
int

__builtin_ia32_comieq (v4sf, v4sf)
__builtin_ia32_comineq (v4sf, v4sf)
__builtin_ia32_comilt (v4sf, v4sf)
__builtin_ia32_comile (v4sf, v4sf)
__builtin_ia32_comigt (v4sf, v4sf)
__builtin_ia32_comige (v4sf, v4sf)
__builtin_ia32_ucomieq (v4sf, v4sf)

Chapter 6: Extensions to the C Language Family

int __builtin_ia32_ucomineq (v4sf, v4sf)
int __builtin_ia32_ucomilt (v4sf, v4sf)
int __builtin_ia32_ucomile (v4sf, v4sf)
int __builtin_ia32_ucomigt (v4sf, v4sf)
int __builtin_ia32_ucomige (v4sf, v4sf)
v4sf __builtin_ia32_addps (v4sf, v4sf)
v4sf __builtin_ia32_subps (v4sf, v4sf)
v4sf __builtin_ia32_mulps (v4sf, v4sf)
v4sf __builtin_ia32_divps (v4sf, v4sf)
v4sf __builtin_ia32_addss (v4sf, v4sf)
v4sf __builtin_ia32_subss (v4sf, v4sf)
v4sf __builtin_ia32_mulss (v4sf, v4sf)
v4sf __builtin_ia32_divss (v4sf, v4sf)
v4sf __builtin_ia32_cmpeqps (v4sf, v4sf)
v4sf __builtin_ia32_cmpltps (v4sf, v4sf)
v4sf __builtin_ia32_cmpleps (v4sf, v4sf)
v4sf __builtin_ia32_cmpgtps (v4sf, v4sf)
v4sf __builtin_ia32_cmpgeps (v4sf, v4sf)
v4sf __builtin_ia32_cmpunordps (v4sf, v4sf)
v4sf __builtin_ia32_cmpneqps (v4sf, v4sf)
v4sf __builtin_ia32_cmpnltps (v4sf, v4sf)
v4sf __builtin_ia32_cmpnleps (v4sf, v4sf)
v4sf __builtin_ia32_cmpngtps (v4sf, v4sf)
v4sf __builtin_ia32_cmpngeps (v4sf, v4sf)
v4sf __builtin_ia32_cmpordps (v4sf, v4sf)
v4sf __builtin_ia32_cmpeqss (v4sf, v4sf)
v4sf __builtin_ia32_cmpltss (v4sf, v4sf)
v4sf __builtin_ia32_cmpless (v4sf, v4sf)
v4sf __builtin_ia32_cmpunordss (v4sf, v4sf)
v4sf __builtin_ia32_cmpneqss (v4sf, v4sf)
v4sf __builtin_ia32_cmpnltss (v4sf, v4sf)
v4sf __builtin_ia32_cmpnless (v4sf, v4sf)
v4sf __builtin_ia32_cmpordss (v4sf, v4sf)
v4sf __builtin_ia32_maxps (v4sf, v4sf)
v4sf __builtin_ia32_maxss (v4sf, v4sf)
v4sf __builtin_ia32_minps (v4sf, v4sf)
v4sf __builtin_ia32_minss (v4sf, v4sf)
v4sf __builtin_ia32_andps (v4sf, v4sf)
v4sf __builtin_ia32_andnps (v4sf, v4sf)
v4sf __builtin_ia32_orps (v4sf, v4sf)
v4sf __builtin_ia32_xorps (v4sf, v4sf)
v4sf __builtin_ia32_movss (v4sf, v4sf)
v4sf __builtin_ia32_movhlps (v4sf, v4sf)
v4sf __builtin_ia32_movlhps (v4sf, v4sf)
v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
v2si __builtin_ia32_cvtps2pi (v4sf)
int __builtin_ia32_cvtss2si (v4sf)
v2si __builtin_ia32_cvttps2pi (v4sf)
int __builtin_ia32_cvttss2si (v4sf)
v4sf __builtin_ia32_rcpps (v4sf)
v4sf __builtin_ia32_rsqrtps (v4sf)
v4sf __builtin_ia32_sqrtps (v4sf)
v4sf __builtin_ia32_rcpss (v4sf)
v4sf __builtin_ia32_rsqrtss (v4sf)
v4sf __builtin_ia32_sqrtss (v4sf)

753

754

Using the GNU Compiler Collection (GCC)

v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
void __builtin_ia32_movntps (float *, v4sf)
int __builtin_ia32_movmskps (v4sf)

The following built-in functions are available when ‘-msse’ is used.
v4sf __builtin_ia32_loadups (float *)
Generates the movups machine instruction as a load from memory.
void __builtin_ia32_storeups (float *, v4sf)
Generates the movups machine instruction as a store to memory.
v4sf __builtin_ia32_loadss (float *)
Generates the movss machine instruction as a load from memory.
v4sf __builtin_ia32_loadhps (v4sf, const v2sf *)
Generates the movhps machine instruction as a load from memory.
v4sf __builtin_ia32_loadlps (v4sf, const v2sf *)
Generates the movlps machine instruction as a load from memory
void __builtin_ia32_storehps (v2sf *, v4sf)
Generates the movhps machine instruction as a store to memory.
void __builtin_ia32_storelps (v2sf *, v4sf)
Generates the movlps machine instruction as a store to memory.
The following built-in functions are available when ‘-msse2’ is used. All of them generate
the machine instruction that is part of the name.
int __builtin_ia32_comisdeq (v2df, v2df)
int __builtin_ia32_comisdlt (v2df, v2df)
int __builtin_ia32_comisdle (v2df, v2df)
int __builtin_ia32_comisdgt (v2df, v2df)
int __builtin_ia32_comisdge (v2df, v2df)
int __builtin_ia32_comisdneq (v2df, v2df)
int __builtin_ia32_ucomisdeq (v2df, v2df)
int __builtin_ia32_ucomisdlt (v2df, v2df)
int __builtin_ia32_ucomisdle (v2df, v2df)
int __builtin_ia32_ucomisdgt (v2df, v2df)
int __builtin_ia32_ucomisdge (v2df, v2df)
int __builtin_ia32_ucomisdneq (v2df, v2df)
v2df __builtin_ia32_cmpeqpd (v2df, v2df)
v2df __builtin_ia32_cmpltpd (v2df, v2df)
v2df __builtin_ia32_cmplepd (v2df, v2df)
v2df __builtin_ia32_cmpgtpd (v2df, v2df)
v2df __builtin_ia32_cmpgepd (v2df, v2df)
v2df __builtin_ia32_cmpunordpd (v2df, v2df)
v2df __builtin_ia32_cmpneqpd (v2df, v2df)
v2df __builtin_ia32_cmpnltpd (v2df, v2df)
v2df __builtin_ia32_cmpnlepd (v2df, v2df)
v2df __builtin_ia32_cmpngtpd (v2df, v2df)
v2df __builtin_ia32_cmpngepd (v2df, v2df)
v2df __builtin_ia32_cmpordpd (v2df, v2df)
v2df __builtin_ia32_cmpeqsd (v2df, v2df)
v2df __builtin_ia32_cmpltsd (v2df, v2df)
v2df __builtin_ia32_cmplesd (v2df, v2df)
v2df __builtin_ia32_cmpunordsd (v2df, v2df)
v2df __builtin_ia32_cmpneqsd (v2df, v2df)

Chapter 6: Extensions to the C Language Family

v2df __builtin_ia32_cmpnltsd (v2df, v2df)
v2df __builtin_ia32_cmpnlesd (v2df, v2df)
v2df __builtin_ia32_cmpordsd (v2df, v2df)
v2di __builtin_ia32_paddq (v2di, v2di)
v2di __builtin_ia32_psubq (v2di, v2di)
v2df __builtin_ia32_addpd (v2df, v2df)
v2df __builtin_ia32_subpd (v2df, v2df)
v2df __builtin_ia32_mulpd (v2df, v2df)
v2df __builtin_ia32_divpd (v2df, v2df)
v2df __builtin_ia32_addsd (v2df, v2df)
v2df __builtin_ia32_subsd (v2df, v2df)
v2df __builtin_ia32_mulsd (v2df, v2df)
v2df __builtin_ia32_divsd (v2df, v2df)
v2df __builtin_ia32_minpd (v2df, v2df)
v2df __builtin_ia32_maxpd (v2df, v2df)
v2df __builtin_ia32_minsd (v2df, v2df)
v2df __builtin_ia32_maxsd (v2df, v2df)
v2df __builtin_ia32_andpd (v2df, v2df)
v2df __builtin_ia32_andnpd (v2df, v2df)
v2df __builtin_ia32_orpd (v2df, v2df)
v2df __builtin_ia32_xorpd (v2df, v2df)
v2df __builtin_ia32_movsd (v2df, v2df)
v2df __builtin_ia32_unpckhpd (v2df, v2df)
v2df __builtin_ia32_unpcklpd (v2df, v2df)
v16qi __builtin_ia32_paddb128 (v16qi, v16qi)
v8hi __builtin_ia32_paddw128 (v8hi, v8hi)
v4si __builtin_ia32_paddd128 (v4si, v4si)
v2di __builtin_ia32_paddq128 (v2di, v2di)
v16qi __builtin_ia32_psubb128 (v16qi, v16qi)
v8hi __builtin_ia32_psubw128 (v8hi, v8hi)
v4si __builtin_ia32_psubd128 (v4si, v4si)
v2di __builtin_ia32_psubq128 (v2di, v2di)
v8hi __builtin_ia32_pmullw128 (v8hi, v8hi)
v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi)
v2di __builtin_ia32_pand128 (v2di, v2di)
v2di __builtin_ia32_pandn128 (v2di, v2di)
v2di __builtin_ia32_por128 (v2di, v2di)
v2di __builtin_ia32_pxor128 (v2di, v2di)
v16qi __builtin_ia32_pavgb128 (v16qi, v16qi)
v8hi __builtin_ia32_pavgw128 (v8hi, v8hi)
v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpeqd128 (v4si, v4si)
v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpgtd128 (v4si, v4si)
v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi)
v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi)
v16qi __builtin_ia32_pminub128 (v16qi, v16qi)
v8hi __builtin_ia32_pminsw128 (v8hi, v8hi)
v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckhdq128 (v4si, v4si)
v2di __builtin_ia32_punpckhqdq128 (v2di, v2di)
v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckldq128 (v4si, v4si)
v2di __builtin_ia32_punpcklqdq128 (v2di, v2di)

755

756

Using the GNU Compiler Collection (GCC)

v16qi __builtin_ia32_packsswb128 (v8hi, v8hi)
v8hi __builtin_ia32_packssdw128 (v4si, v4si)
v16qi __builtin_ia32_packuswb128 (v8hi, v8hi)
v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi)
void __builtin_ia32_maskmovdqu (v16qi, v16qi)
v2df __builtin_ia32_loadupd (double *)
void __builtin_ia32_storeupd (double *, v2df)
v2df __builtin_ia32_loadhpd (v2df, double const *)
v2df __builtin_ia32_loadlpd (v2df, double const *)
int __builtin_ia32_movmskpd (v2df)
int __builtin_ia32_pmovmskb128 (v16qi)
void __builtin_ia32_movnti (int *, int)
void __builtin_ia32_movnti64 (long long int *, long long int)
void __builtin_ia32_movntpd (double *, v2df)
void __builtin_ia32_movntdq (v2df *, v2df)
v4si __builtin_ia32_pshufd (v4si, int)
v8hi __builtin_ia32_pshuflw (v8hi, int)
v8hi __builtin_ia32_pshufhw (v8hi, int)
v2di __builtin_ia32_psadbw128 (v16qi, v16qi)
v2df __builtin_ia32_sqrtpd (v2df)
v2df __builtin_ia32_sqrtsd (v2df)
v2df __builtin_ia32_shufpd (v2df, v2df, int)
v2df __builtin_ia32_cvtdq2pd (v4si)
v4sf __builtin_ia32_cvtdq2ps (v4si)
v4si __builtin_ia32_cvtpd2dq (v2df)
v2si __builtin_ia32_cvtpd2pi (v2df)
v4sf __builtin_ia32_cvtpd2ps (v2df)
v4si __builtin_ia32_cvttpd2dq (v2df)
v2si __builtin_ia32_cvttpd2pi (v2df)
v2df __builtin_ia32_cvtpi2pd (v2si)
int __builtin_ia32_cvtsd2si (v2df)
int __builtin_ia32_cvttsd2si (v2df)
long long __builtin_ia32_cvtsd2si64 (v2df)
long long __builtin_ia32_cvttsd2si64 (v2df)
v4si __builtin_ia32_cvtps2dq (v4sf)
v2df __builtin_ia32_cvtps2pd (v4sf)
v4si __builtin_ia32_cvttps2dq (v4sf)
v2df __builtin_ia32_cvtsi2sd (v2df, int)
v2df __builtin_ia32_cvtsi642sd (v2df, long long)
v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df)
v2df __builtin_ia32_cvtss2sd (v2df, v4sf)
void __builtin_ia32_clflush (const void *)
void __builtin_ia32_lfence (void)
void __builtin_ia32_mfence (void)
v16qi __builtin_ia32_loaddqu (const char *)
void __builtin_ia32_storedqu (char *, v16qi)
v1di __builtin_ia32_pmuludq (v2si, v2si)
v2di __builtin_ia32_pmuludq128 (v4si, v4si)
v8hi __builtin_ia32_psllw128 (v8hi, v8hi)
v4si __builtin_ia32_pslld128 (v4si, v4si)
v2di __builtin_ia32_psllq128 (v2di, v2di)
v8hi __builtin_ia32_psrlw128 (v8hi, v8hi)
v4si __builtin_ia32_psrld128 (v4si, v4si)
v2di __builtin_ia32_psrlq128 (v2di, v2di)
v8hi __builtin_ia32_psraw128 (v8hi, v8hi)
v4si __builtin_ia32_psrad128 (v4si, v4si)
v2di __builtin_ia32_pslldqi128 (v2di, int)
v8hi __builtin_ia32_psllwi128 (v8hi, int)

Chapter 6: Extensions to the C Language Family

v4si
v2di
v2di
v8hi
v4si
v2di
v8hi
v4si
v4si
v2di

757

__builtin_ia32_pslldi128 (v4si, int)
__builtin_ia32_psllqi128 (v2di, int)
__builtin_ia32_psrldqi128 (v2di, int)
__builtin_ia32_psrlwi128 (v8hi, int)
__builtin_ia32_psrldi128 (v4si, int)
__builtin_ia32_psrlqi128 (v2di, int)
__builtin_ia32_psrawi128 (v8hi, int)
__builtin_ia32_psradi128 (v4si, int)
__builtin_ia32_pmaddwd128 (v8hi, v8hi)
__builtin_ia32_movq128 (v2di)

The following built-in functions are available when ‘-msse3’ is used. All of them generate
the machine instruction that is part of the name.
v2df __builtin_ia32_addsubpd (v2df, v2df)
v4sf __builtin_ia32_addsubps (v4sf, v4sf)
v2df __builtin_ia32_haddpd (v2df, v2df)
v4sf __builtin_ia32_haddps (v4sf, v4sf)
v2df __builtin_ia32_hsubpd (v2df, v2df)
v4sf __builtin_ia32_hsubps (v4sf, v4sf)
v16qi __builtin_ia32_lddqu (char const *)
void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
v4sf __builtin_ia32_movshdup (v4sf)
v4sf __builtin_ia32_movsldup (v4sf)
void __builtin_ia32_mwait (unsigned int, unsigned int)

The following built-in functions are available when ‘-mssse3’ is used. All of them generate
the machine instruction that is part of the name.
v2si
v4hi
v4hi
v2si
v4hi
v4hi
v4hi
v4hi
v8qi
v8qi
v2si
v4hi
v1di
v8qi
v2si
v4hi

__builtin_ia32_phaddd (v2si, v2si)
__builtin_ia32_phaddw (v4hi, v4hi)
__builtin_ia32_phaddsw (v4hi, v4hi)
__builtin_ia32_phsubd (v2si, v2si)
__builtin_ia32_phsubw (v4hi, v4hi)
__builtin_ia32_phsubsw (v4hi, v4hi)
__builtin_ia32_pmaddubsw (v8qi, v8qi)
__builtin_ia32_pmulhrsw (v4hi, v4hi)
__builtin_ia32_pshufb (v8qi, v8qi)
__builtin_ia32_psignb (v8qi, v8qi)
__builtin_ia32_psignd (v2si, v2si)
__builtin_ia32_psignw (v4hi, v4hi)
__builtin_ia32_palignr (v1di, v1di, int)
__builtin_ia32_pabsb (v8qi)
__builtin_ia32_pabsd (v2si)
__builtin_ia32_pabsw (v4hi)

The following built-in functions are available when ‘-mssse3’ is used. All of them generate
the machine instruction that is part of the name.
v4si __builtin_ia32_phaddd128 (v4si, v4si)
v8hi __builtin_ia32_phaddw128 (v8hi, v8hi)
v8hi __builtin_ia32_phaddsw128 (v8hi, v8hi)
v4si __builtin_ia32_phsubd128 (v4si, v4si)
v8hi __builtin_ia32_phsubw128 (v8hi, v8hi)
v8hi __builtin_ia32_phsubsw128 (v8hi, v8hi)
v8hi __builtin_ia32_pmaddubsw128 (v16qi, v16qi)
v8hi __builtin_ia32_pmulhrsw128 (v8hi, v8hi)
v16qi __builtin_ia32_pshufb128 (v16qi, v16qi)
v16qi __builtin_ia32_psignb128 (v16qi, v16qi)
v4si __builtin_ia32_psignd128 (v4si, v4si)
v8hi __builtin_ia32_psignw128 (v8hi, v8hi)

758

Using the GNU Compiler Collection (GCC)

v2di __builtin_ia32_palignr128 (v2di, v2di, int)
v16qi __builtin_ia32_pabsb128 (v16qi)
v4si __builtin_ia32_pabsd128 (v4si)
v8hi __builtin_ia32_pabsw128 (v8hi)

The following built-in functions are available when ‘-msse4.1’ is used. All of them
generate the machine instruction that is part of the name.
v2df __builtin_ia32_blendpd (v2df, v2df, const int)
v4sf __builtin_ia32_blendps (v4sf, v4sf, const int)
v2df __builtin_ia32_blendvpd (v2df, v2df, v2df)
v4sf __builtin_ia32_blendvps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_dppd (v2df, v2df, const int)
v4sf __builtin_ia32_dpps (v4sf, v4sf, const int)
v4sf __builtin_ia32_insertps128 (v4sf, v4sf, const int)
v2di __builtin_ia32_movntdqa (v2di *);
v16qi __builtin_ia32_mpsadbw128 (v16qi, v16qi, const int)
v8hi __builtin_ia32_packusdw128 (v4si, v4si)
v16qi __builtin_ia32_pblendvb128 (v16qi, v16qi, v16qi)
v8hi __builtin_ia32_pblendw128 (v8hi, v8hi, const int)
v2di __builtin_ia32_pcmpeqq (v2di, v2di)
v8hi __builtin_ia32_phminposuw128 (v8hi)
v16qi __builtin_ia32_pmaxsb128 (v16qi, v16qi)
v4si __builtin_ia32_pmaxsd128 (v4si, v4si)
v4si __builtin_ia32_pmaxud128 (v4si, v4si)
v8hi __builtin_ia32_pmaxuw128 (v8hi, v8hi)
v16qi __builtin_ia32_pminsb128 (v16qi, v16qi)
v4si __builtin_ia32_pminsd128 (v4si, v4si)
v4si __builtin_ia32_pminud128 (v4si, v4si)
v8hi __builtin_ia32_pminuw128 (v8hi, v8hi)
v4si __builtin_ia32_pmovsxbd128 (v16qi)
v2di __builtin_ia32_pmovsxbq128 (v16qi)
v8hi __builtin_ia32_pmovsxbw128 (v16qi)
v2di __builtin_ia32_pmovsxdq128 (v4si)
v4si __builtin_ia32_pmovsxwd128 (v8hi)
v2di __builtin_ia32_pmovsxwq128 (v8hi)
v4si __builtin_ia32_pmovzxbd128 (v16qi)
v2di __builtin_ia32_pmovzxbq128 (v16qi)
v8hi __builtin_ia32_pmovzxbw128 (v16qi)
v2di __builtin_ia32_pmovzxdq128 (v4si)
v4si __builtin_ia32_pmovzxwd128 (v8hi)
v2di __builtin_ia32_pmovzxwq128 (v8hi)
v2di __builtin_ia32_pmuldq128 (v4si, v4si)
v4si __builtin_ia32_pmulld128 (v4si, v4si)
int __builtin_ia32_ptestc128 (v2di, v2di)
int __builtin_ia32_ptestnzc128 (v2di, v2di)
int __builtin_ia32_ptestz128 (v2di, v2di)
v2df __builtin_ia32_roundpd (v2df, const int)
v4sf __builtin_ia32_roundps (v4sf, const int)
v2df __builtin_ia32_roundsd (v2df, v2df, const int)
v4sf __builtin_ia32_roundss (v4sf, v4sf, const int)

The following built-in functions are available when ‘-msse4.1’ is used.
v4sf __builtin_ia32_vec_set_v4sf (v4sf, float, const int)
Generates the insertps machine instruction.
int __builtin_ia32_vec_ext_v16qi (v16qi, const int)
Generates the pextrb machine instruction.

Chapter 6: Extensions to the C Language Family

759

v16qi __builtin_ia32_vec_set_v16qi (v16qi, int, const int)
Generates the pinsrb machine instruction.
v4si __builtin_ia32_vec_set_v4si (v4si, int, const int)
Generates the pinsrd machine instruction.
v2di __builtin_ia32_vec_set_v2di (v2di, long long, const int)
Generates the pinsrq machine instruction in 64bit mode.
The following built-in functions are changed to generate new SSE4.1 instructions when
‘-msse4.1’ is used.
float __builtin_ia32_vec_ext_v4sf (v4sf, const int)
Generates the extractps machine instruction.
int __builtin_ia32_vec_ext_v4si (v4si, const int)
Generates the pextrd machine instruction.
long long __builtin_ia32_vec_ext_v2di (v2di, const int)
Generates the pextrq machine instruction in 64bit mode.
The following built-in functions are available when ‘-msse4.2’ is used. All of them
generate the machine instruction that is part of the name.
v16qi __builtin_ia32_pcmpestrm128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestri128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestria128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestric128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestrio128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestris128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestriz128 (v16qi, int, v16qi, int, const int)
v16qi __builtin_ia32_pcmpistrm128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistri128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistria128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistric128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistrio128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistris128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistriz128 (v16qi, v16qi, const int)
v2di __builtin_ia32_pcmpgtq (v2di, v2di)

The following built-in functions are available when ‘-msse4.2’ is used.
unsigned int __builtin_ia32_crc32qi (unsigned int, unsigned char)
Generates the crc32b machine instruction.
unsigned int __builtin_ia32_crc32hi (unsigned int, unsigned short)
Generates the crc32w machine instruction.
unsigned int __builtin_ia32_crc32si (unsigned int, unsigned int)
Generates the crc32l machine instruction.
unsigned long long __builtin_ia32_crc32di (unsigned long long, unsigned long
long)
Generates the crc32q machine instruction.
The following built-in functions are changed to generate new SSE4.2 instructions when
‘-msse4.2’ is used.

760

Using the GNU Compiler Collection (GCC)

int __builtin_popcount (unsigned int)
Generates the popcntl machine instruction.
int __builtin_popcountl (unsigned long)
Generates the popcntl or popcntq machine instruction, depending on the size
of unsigned long.
int __builtin_popcountll (unsigned long long)
Generates the popcntq machine instruction.
The following built-in functions are available when ‘-mavx’ is used. All of them generate
the machine instruction that is part of the name.
v4df __builtin_ia32_addpd256 (v4df,v4df)
v8sf __builtin_ia32_addps256 (v8sf,v8sf)
v4df __builtin_ia32_addsubpd256 (v4df,v4df)
v8sf __builtin_ia32_addsubps256 (v8sf,v8sf)
v4df __builtin_ia32_andnpd256 (v4df,v4df)
v8sf __builtin_ia32_andnps256 (v8sf,v8sf)
v4df __builtin_ia32_andpd256 (v4df,v4df)
v8sf __builtin_ia32_andps256 (v8sf,v8sf)
v4df __builtin_ia32_blendpd256 (v4df,v4df,int)
v8sf __builtin_ia32_blendps256 (v8sf,v8sf,int)
v4df __builtin_ia32_blendvpd256 (v4df,v4df,v4df)
v8sf __builtin_ia32_blendvps256 (v8sf,v8sf,v8sf)
v2df __builtin_ia32_cmppd (v2df,v2df,int)
v4df __builtin_ia32_cmppd256 (v4df,v4df,int)
v4sf __builtin_ia32_cmpps (v4sf,v4sf,int)
v8sf __builtin_ia32_cmpps256 (v8sf,v8sf,int)
v2df __builtin_ia32_cmpsd (v2df,v2df,int)
v4sf __builtin_ia32_cmpss (v4sf,v4sf,int)
v4df __builtin_ia32_cvtdq2pd256 (v4si)
v8sf __builtin_ia32_cvtdq2ps256 (v8si)
v4si __builtin_ia32_cvtpd2dq256 (v4df)
v4sf __builtin_ia32_cvtpd2ps256 (v4df)
v8si __builtin_ia32_cvtps2dq256 (v8sf)
v4df __builtin_ia32_cvtps2pd256 (v4sf)
v4si __builtin_ia32_cvttpd2dq256 (v4df)
v8si __builtin_ia32_cvttps2dq256 (v8sf)
v4df __builtin_ia32_divpd256 (v4df,v4df)
v8sf __builtin_ia32_divps256 (v8sf,v8sf)
v8sf __builtin_ia32_dpps256 (v8sf,v8sf,int)
v4df __builtin_ia32_haddpd256 (v4df,v4df)
v8sf __builtin_ia32_haddps256 (v8sf,v8sf)
v4df __builtin_ia32_hsubpd256 (v4df,v4df)
v8sf __builtin_ia32_hsubps256 (v8sf,v8sf)
v32qi __builtin_ia32_lddqu256 (pcchar)
v32qi __builtin_ia32_loaddqu256 (pcchar)
v4df __builtin_ia32_loadupd256 (pcdouble)
v8sf __builtin_ia32_loadups256 (pcfloat)
v2df __builtin_ia32_maskloadpd (pcv2df,v2df)
v4df __builtin_ia32_maskloadpd256 (pcv4df,v4df)
v4sf __builtin_ia32_maskloadps (pcv4sf,v4sf)
v8sf __builtin_ia32_maskloadps256 (pcv8sf,v8sf)
void __builtin_ia32_maskstorepd (pv2df,v2df,v2df)
void __builtin_ia32_maskstorepd256 (pv4df,v4df,v4df)
void __builtin_ia32_maskstoreps (pv4sf,v4sf,v4sf)
void __builtin_ia32_maskstoreps256 (pv8sf,v8sf,v8sf)
v4df __builtin_ia32_maxpd256 (v4df,v4df)

Chapter 6: Extensions to the C Language Family

v8sf __builtin_ia32_maxps256 (v8sf,v8sf)
v4df __builtin_ia32_minpd256 (v4df,v4df)
v8sf __builtin_ia32_minps256 (v8sf,v8sf)
v4df __builtin_ia32_movddup256 (v4df)
int __builtin_ia32_movmskpd256 (v4df)
int __builtin_ia32_movmskps256 (v8sf)
v8sf __builtin_ia32_movshdup256 (v8sf)
v8sf __builtin_ia32_movsldup256 (v8sf)
v4df __builtin_ia32_mulpd256 (v4df,v4df)
v8sf __builtin_ia32_mulps256 (v8sf,v8sf)
v4df __builtin_ia32_orpd256 (v4df,v4df)
v8sf __builtin_ia32_orps256 (v8sf,v8sf)
v2df __builtin_ia32_pd_pd256 (v4df)
v4df __builtin_ia32_pd256_pd (v2df)
v4sf __builtin_ia32_ps_ps256 (v8sf)
v8sf __builtin_ia32_ps256_ps (v4sf)
int __builtin_ia32_ptestc256 (v4di,v4di,ptest)
int __builtin_ia32_ptestnzc256 (v4di,v4di,ptest)
int __builtin_ia32_ptestz256 (v4di,v4di,ptest)
v8sf __builtin_ia32_rcpps256 (v8sf)
v4df __builtin_ia32_roundpd256 (v4df,int)
v8sf __builtin_ia32_roundps256 (v8sf,int)
v8sf __builtin_ia32_rsqrtps_nr256 (v8sf)
v8sf __builtin_ia32_rsqrtps256 (v8sf)
v4df __builtin_ia32_shufpd256 (v4df,v4df,int)
v8sf __builtin_ia32_shufps256 (v8sf,v8sf,int)
v4si __builtin_ia32_si_si256 (v8si)
v8si __builtin_ia32_si256_si (v4si)
v4df __builtin_ia32_sqrtpd256 (v4df)
v8sf __builtin_ia32_sqrtps_nr256 (v8sf)
v8sf __builtin_ia32_sqrtps256 (v8sf)
void __builtin_ia32_storedqu256 (pchar,v32qi)
void __builtin_ia32_storeupd256 (pdouble,v4df)
void __builtin_ia32_storeups256 (pfloat,v8sf)
v4df __builtin_ia32_subpd256 (v4df,v4df)
v8sf __builtin_ia32_subps256 (v8sf,v8sf)
v4df __builtin_ia32_unpckhpd256 (v4df,v4df)
v8sf __builtin_ia32_unpckhps256 (v8sf,v8sf)
v4df __builtin_ia32_unpcklpd256 (v4df,v4df)
v8sf __builtin_ia32_unpcklps256 (v8sf,v8sf)
v4df __builtin_ia32_vbroadcastf128_pd256 (pcv2df)
v8sf __builtin_ia32_vbroadcastf128_ps256 (pcv4sf)
v4df __builtin_ia32_vbroadcastsd256 (pcdouble)
v4sf __builtin_ia32_vbroadcastss (pcfloat)
v8sf __builtin_ia32_vbroadcastss256 (pcfloat)
v2df __builtin_ia32_vextractf128_pd256 (v4df,int)
v4sf __builtin_ia32_vextractf128_ps256 (v8sf,int)
v4si __builtin_ia32_vextractf128_si256 (v8si,int)
v4df __builtin_ia32_vinsertf128_pd256 (v4df,v2df,int)
v8sf __builtin_ia32_vinsertf128_ps256 (v8sf,v4sf,int)
v8si __builtin_ia32_vinsertf128_si256 (v8si,v4si,int)
v4df __builtin_ia32_vperm2f128_pd256 (v4df,v4df,int)
v8sf __builtin_ia32_vperm2f128_ps256 (v8sf,v8sf,int)
v8si __builtin_ia32_vperm2f128_si256 (v8si,v8si,int)
v2df __builtin_ia32_vpermil2pd (v2df,v2df,v2di,int)
v4df __builtin_ia32_vpermil2pd256 (v4df,v4df,v4di,int)
v4sf __builtin_ia32_vpermil2ps (v4sf,v4sf,v4si,int)
v8sf __builtin_ia32_vpermil2ps256 (v8sf,v8sf,v8si,int)

761

762

Using the GNU Compiler Collection (GCC)

v2df __builtin_ia32_vpermilpd (v2df,int)
v4df __builtin_ia32_vpermilpd256 (v4df,int)
v4sf __builtin_ia32_vpermilps (v4sf,int)
v8sf __builtin_ia32_vpermilps256 (v8sf,int)
v2df __builtin_ia32_vpermilvarpd (v2df,v2di)
v4df __builtin_ia32_vpermilvarpd256 (v4df,v4di)
v4sf __builtin_ia32_vpermilvarps (v4sf,v4si)
v8sf __builtin_ia32_vpermilvarps256 (v8sf,v8si)
int __builtin_ia32_vtestcpd (v2df,v2df,ptest)
int __builtin_ia32_vtestcpd256 (v4df,v4df,ptest)
int __builtin_ia32_vtestcps (v4sf,v4sf,ptest)
int __builtin_ia32_vtestcps256 (v8sf,v8sf,ptest)
int __builtin_ia32_vtestnzcpd (v2df,v2df,ptest)
int __builtin_ia32_vtestnzcpd256 (v4df,v4df,ptest)
int __builtin_ia32_vtestnzcps (v4sf,v4sf,ptest)
int __builtin_ia32_vtestnzcps256 (v8sf,v8sf,ptest)
int __builtin_ia32_vtestzpd (v2df,v2df,ptest)
int __builtin_ia32_vtestzpd256 (v4df,v4df,ptest)
int __builtin_ia32_vtestzps (v4sf,v4sf,ptest)
int __builtin_ia32_vtestzps256 (v8sf,v8sf,ptest)
void __builtin_ia32_vzeroall (void)
void __builtin_ia32_vzeroupper (void)
v4df __builtin_ia32_xorpd256 (v4df,v4df)
v8sf __builtin_ia32_xorps256 (v8sf,v8sf)

The following built-in functions are available when ‘-mavx2’ is used. All of them generate
the machine instruction that is part of the name.
v32qi __builtin_ia32_mpsadbw256 (v32qi,v32qi,int)
v32qi __builtin_ia32_pabsb256 (v32qi)
v16hi __builtin_ia32_pabsw256 (v16hi)
v8si __builtin_ia32_pabsd256 (v8si)
v16hi __builtin_ia32_packssdw256 (v8si,v8si)
v32qi __builtin_ia32_packsswb256 (v16hi,v16hi)
v16hi __builtin_ia32_packusdw256 (v8si,v8si)
v32qi __builtin_ia32_packuswb256 (v16hi,v16hi)
v32qi __builtin_ia32_paddb256 (v32qi,v32qi)
v16hi __builtin_ia32_paddw256 (v16hi,v16hi)
v8si __builtin_ia32_paddd256 (v8si,v8si)
v4di __builtin_ia32_paddq256 (v4di,v4di)
v32qi __builtin_ia32_paddsb256 (v32qi,v32qi)
v16hi __builtin_ia32_paddsw256 (v16hi,v16hi)
v32qi __builtin_ia32_paddusb256 (v32qi,v32qi)
v16hi __builtin_ia32_paddusw256 (v16hi,v16hi)
v4di __builtin_ia32_palignr256 (v4di,v4di,int)
v4di __builtin_ia32_andsi256 (v4di,v4di)
v4di __builtin_ia32_andnotsi256 (v4di,v4di)
v32qi __builtin_ia32_pavgb256 (v32qi,v32qi)
v16hi __builtin_ia32_pavgw256 (v16hi,v16hi)
v32qi __builtin_ia32_pblendvb256 (v32qi,v32qi,v32qi)
v16hi __builtin_ia32_pblendw256 (v16hi,v16hi,int)
v32qi __builtin_ia32_pcmpeqb256 (v32qi,v32qi)
v16hi __builtin_ia32_pcmpeqw256 (v16hi,v16hi)
v8si __builtin_ia32_pcmpeqd256 (c8si,v8si)
v4di __builtin_ia32_pcmpeqq256 (v4di,v4di)
v32qi __builtin_ia32_pcmpgtb256 (v32qi,v32qi)
v16hi __builtin_ia32_pcmpgtw256 (16hi,v16hi)
v8si __builtin_ia32_pcmpgtd256 (v8si,v8si)
v4di __builtin_ia32_pcmpgtq256 (v4di,v4di)

Chapter 6: Extensions to the C Language Family

v16hi __builtin_ia32_phaddw256 (v16hi,v16hi)
v8si __builtin_ia32_phaddd256 (v8si,v8si)
v16hi __builtin_ia32_phaddsw256 (v16hi,v16hi)
v16hi __builtin_ia32_phsubw256 (v16hi,v16hi)
v8si __builtin_ia32_phsubd256 (v8si,v8si)
v16hi __builtin_ia32_phsubsw256 (v16hi,v16hi)
v32qi __builtin_ia32_pmaddubsw256 (v32qi,v32qi)
v16hi __builtin_ia32_pmaddwd256 (v16hi,v16hi)
v32qi __builtin_ia32_pmaxsb256 (v32qi,v32qi)
v16hi __builtin_ia32_pmaxsw256 (v16hi,v16hi)
v8si __builtin_ia32_pmaxsd256 (v8si,v8si)
v32qi __builtin_ia32_pmaxub256 (v32qi,v32qi)
v16hi __builtin_ia32_pmaxuw256 (v16hi,v16hi)
v8si __builtin_ia32_pmaxud256 (v8si,v8si)
v32qi __builtin_ia32_pminsb256 (v32qi,v32qi)
v16hi __builtin_ia32_pminsw256 (v16hi,v16hi)
v8si __builtin_ia32_pminsd256 (v8si,v8si)
v32qi __builtin_ia32_pminub256 (v32qi,v32qi)
v16hi __builtin_ia32_pminuw256 (v16hi,v16hi)
v8si __builtin_ia32_pminud256 (v8si,v8si)
int __builtin_ia32_pmovmskb256 (v32qi)
v16hi __builtin_ia32_pmovsxbw256 (v16qi)
v8si __builtin_ia32_pmovsxbd256 (v16qi)
v4di __builtin_ia32_pmovsxbq256 (v16qi)
v8si __builtin_ia32_pmovsxwd256 (v8hi)
v4di __builtin_ia32_pmovsxwq256 (v8hi)
v4di __builtin_ia32_pmovsxdq256 (v4si)
v16hi __builtin_ia32_pmovzxbw256 (v16qi)
v8si __builtin_ia32_pmovzxbd256 (v16qi)
v4di __builtin_ia32_pmovzxbq256 (v16qi)
v8si __builtin_ia32_pmovzxwd256 (v8hi)
v4di __builtin_ia32_pmovzxwq256 (v8hi)
v4di __builtin_ia32_pmovzxdq256 (v4si)
v4di __builtin_ia32_pmuldq256 (v8si,v8si)
v16hi __builtin_ia32_pmulhrsw256 (v16hi, v16hi)
v16hi __builtin_ia32_pmulhuw256 (v16hi,v16hi)
v16hi __builtin_ia32_pmulhw256 (v16hi,v16hi)
v16hi __builtin_ia32_pmullw256 (v16hi,v16hi)
v8si __builtin_ia32_pmulld256 (v8si,v8si)
v4di __builtin_ia32_pmuludq256 (v8si,v8si)
v4di __builtin_ia32_por256 (v4di,v4di)
v16hi __builtin_ia32_psadbw256 (v32qi,v32qi)
v32qi __builtin_ia32_pshufb256 (v32qi,v32qi)
v8si __builtin_ia32_pshufd256 (v8si,int)
v16hi __builtin_ia32_pshufhw256 (v16hi,int)
v16hi __builtin_ia32_pshuflw256 (v16hi,int)
v32qi __builtin_ia32_psignb256 (v32qi,v32qi)
v16hi __builtin_ia32_psignw256 (v16hi,v16hi)
v8si __builtin_ia32_psignd256 (v8si,v8si)
v4di __builtin_ia32_pslldqi256 (v4di,int)
v16hi __builtin_ia32_psllwi256 (16hi,int)
v16hi __builtin_ia32_psllw256(v16hi,v8hi)
v8si __builtin_ia32_pslldi256 (v8si,int)
v8si __builtin_ia32_pslld256(v8si,v4si)
v4di __builtin_ia32_psllqi256 (v4di,int)
v4di __builtin_ia32_psllq256(v4di,v2di)
v16hi __builtin_ia32_psrawi256 (v16hi,int)
v16hi __builtin_ia32_psraw256 (v16hi,v8hi)

763

764

Using the GNU Compiler Collection (GCC)

v8si __builtin_ia32_psradi256 (v8si,int)
v8si __builtin_ia32_psrad256 (v8si,v4si)
v4di __builtin_ia32_psrldqi256 (v4di, int)
v16hi __builtin_ia32_psrlwi256 (v16hi,int)
v16hi __builtin_ia32_psrlw256 (v16hi,v8hi)
v8si __builtin_ia32_psrldi256 (v8si,int)
v8si __builtin_ia32_psrld256 (v8si,v4si)
v4di __builtin_ia32_psrlqi256 (v4di,int)
v4di __builtin_ia32_psrlq256(v4di,v2di)
v32qi __builtin_ia32_psubb256 (v32qi,v32qi)
v32hi __builtin_ia32_psubw256 (v16hi,v16hi)
v8si __builtin_ia32_psubd256 (v8si,v8si)
v4di __builtin_ia32_psubq256 (v4di,v4di)
v32qi __builtin_ia32_psubsb256 (v32qi,v32qi)
v16hi __builtin_ia32_psubsw256 (v16hi,v16hi)
v32qi __builtin_ia32_psubusb256 (v32qi,v32qi)
v16hi __builtin_ia32_psubusw256 (v16hi,v16hi)
v32qi __builtin_ia32_punpckhbw256 (v32qi,v32qi)
v16hi __builtin_ia32_punpckhwd256 (v16hi,v16hi)
v8si __builtin_ia32_punpckhdq256 (v8si,v8si)
v4di __builtin_ia32_punpckhqdq256 (v4di,v4di)
v32qi __builtin_ia32_punpcklbw256 (v32qi,v32qi)
v16hi __builtin_ia32_punpcklwd256 (v16hi,v16hi)
v8si __builtin_ia32_punpckldq256 (v8si,v8si)
v4di __builtin_ia32_punpcklqdq256 (v4di,v4di)
v4di __builtin_ia32_pxor256 (v4di,v4di)
v4di __builtin_ia32_movntdqa256 (pv4di)
v4sf __builtin_ia32_vbroadcastss_ps (v4sf)
v8sf __builtin_ia32_vbroadcastss_ps256 (v4sf)
v4df __builtin_ia32_vbroadcastsd_pd256 (v2df)
v4di __builtin_ia32_vbroadcastsi256 (v2di)
v4si __builtin_ia32_pblendd128 (v4si,v4si)
v8si __builtin_ia32_pblendd256 (v8si,v8si)
v32qi __builtin_ia32_pbroadcastb256 (v16qi)
v16hi __builtin_ia32_pbroadcastw256 (v8hi)
v8si __builtin_ia32_pbroadcastd256 (v4si)
v4di __builtin_ia32_pbroadcastq256 (v2di)
v16qi __builtin_ia32_pbroadcastb128 (v16qi)
v8hi __builtin_ia32_pbroadcastw128 (v8hi)
v4si __builtin_ia32_pbroadcastd128 (v4si)
v2di __builtin_ia32_pbroadcastq128 (v2di)
v8si __builtin_ia32_permvarsi256 (v8si,v8si)
v4df __builtin_ia32_permdf256 (v4df,int)
v8sf __builtin_ia32_permvarsf256 (v8sf,v8sf)
v4di __builtin_ia32_permdi256 (v4di,int)
v4di __builtin_ia32_permti256 (v4di,v4di,int)
v4di __builtin_ia32_extract128i256 (v4di,int)
v4di __builtin_ia32_insert128i256 (v4di,v2di,int)
v8si __builtin_ia32_maskloadd256 (pcv8si,v8si)
v4di __builtin_ia32_maskloadq256 (pcv4di,v4di)
v4si __builtin_ia32_maskloadd (pcv4si,v4si)
v2di __builtin_ia32_maskloadq (pcv2di,v2di)
void __builtin_ia32_maskstored256 (pv8si,v8si,v8si)
void __builtin_ia32_maskstoreq256 (pv4di,v4di,v4di)
void __builtin_ia32_maskstored (pv4si,v4si,v4si)
void __builtin_ia32_maskstoreq (pv2di,v2di,v2di)
v8si __builtin_ia32_psllv8si (v8si,v8si)
v4si __builtin_ia32_psllv4si (v4si,v4si)

Chapter 6: Extensions to the C Language Family

v4di
v2di
v8si
v4si
v8si
v4si
v4di
v2di
v2df
v4df
v2df
v4df
v4sf
v8sf
v4sf
v4sf
v2di
v4di
v2di
v4di
v4si
v8si
v4si
v4si

765

__builtin_ia32_psllv4di (v4di,v4di)
__builtin_ia32_psllv2di (v2di,v2di)
__builtin_ia32_psrav8si (v8si,v8si)
__builtin_ia32_psrav4si (v4si,v4si)
__builtin_ia32_psrlv8si (v8si,v8si)
__builtin_ia32_psrlv4si (v4si,v4si)
__builtin_ia32_psrlv4di (v4di,v4di)
__builtin_ia32_psrlv2di (v2di,v2di)
__builtin_ia32_gathersiv2df (v2df, pcdouble,v4si,v2df,int)
__builtin_ia32_gathersiv4df (v4df, pcdouble,v4si,v4df,int)
__builtin_ia32_gatherdiv2df (v2df, pcdouble,v2di,v2df,int)
__builtin_ia32_gatherdiv4df (v4df, pcdouble,v4di,v4df,int)
__builtin_ia32_gathersiv4sf (v4sf, pcfloat,v4si,v4sf,int)
__builtin_ia32_gathersiv8sf (v8sf, pcfloat,v8si,v8sf,int)
__builtin_ia32_gatherdiv4sf (v4sf, pcfloat,v2di,v4sf,int)
__builtin_ia32_gatherdiv4sf256 (v4sf, pcfloat,v4di,v4sf,int)
__builtin_ia32_gathersiv2di (v2di, pcint64,v4si,v2di,int)
__builtin_ia32_gathersiv4di (v4di, pcint64,v4si,v4di,int)
__builtin_ia32_gatherdiv2di (v2di, pcint64,v2di,v2di,int)
__builtin_ia32_gatherdiv4di (v4di, pcint64,v4di,v4di,int)
__builtin_ia32_gathersiv4si (v4si, pcint,v4si,v4si,int)
__builtin_ia32_gathersiv8si (v8si, pcint,v8si,v8si,int)
__builtin_ia32_gatherdiv4si (v4si, pcint,v2di,v4si,int)
__builtin_ia32_gatherdiv4si256 (v4si, pcint,v4di,v4si,int)

The following built-in functions are available when ‘-maes’ is used. All of them generate
the machine instruction that is part of the name.
v2di
v2di
v2di
v2di
v2di
v2di

__builtin_ia32_aesenc128 (v2di, v2di)
__builtin_ia32_aesenclast128 (v2di, v2di)
__builtin_ia32_aesdec128 (v2di, v2di)
__builtin_ia32_aesdeclast128 (v2di, v2di)
__builtin_ia32_aeskeygenassist128 (v2di, const int)
__builtin_ia32_aesimc128 (v2di)

The following built-in function is available when ‘-mpclmul’ is used.
v2di __builtin_ia32_pclmulqdq128 (v2di, v2di, const int)
Generates the pclmulqdq machine instruction.
The following built-in function is available when ‘-mfsgsbase’ is used. All of them
generate the machine instruction that is part of the name.
unsigned int __builtin_ia32_rdfsbase32 (void)
unsigned long long __builtin_ia32_rdfsbase64 (void)
unsigned int __builtin_ia32_rdgsbase32 (void)
unsigned long long __builtin_ia32_rdgsbase64 (void)
void _writefsbase_u32 (unsigned int)
void _writefsbase_u64 (unsigned long long)
void _writegsbase_u32 (unsigned int)
void _writegsbase_u64 (unsigned long long)

The following built-in function is available when ‘-mrdrnd’ is used. All of them generate
the machine instruction that is part of the name.
unsigned int __builtin_ia32_rdrand16_step (unsigned short *)
unsigned int __builtin_ia32_rdrand32_step (unsigned int *)
unsigned int __builtin_ia32_rdrand64_step (unsigned long long *)

The following built-in functions are available when ‘-msse4a’ is used. All of them generate
the machine instruction that is part of the name.

766

Using the GNU Compiler Collection (GCC)

void
void
v2di
v2di
v2di
v2di

__builtin_ia32_movntsd (double *, v2df)
__builtin_ia32_movntss (float *, v4sf)
__builtin_ia32_extrq (v2di, v16qi)
__builtin_ia32_extrqi (v2di, const unsigned int, const unsigned int)
__builtin_ia32_insertq (v2di, v2di)
__builtin_ia32_insertqi (v2di, v2di, const unsigned int, const unsigned int)

The following built-in functions are available when ‘-mxop’ is used.
v2df __builtin_ia32_vfrczpd (v2df)
v4sf __builtin_ia32_vfrczps (v4sf)
v2df __builtin_ia32_vfrczsd (v2df)
v4sf __builtin_ia32_vfrczss (v4sf)
v4df __builtin_ia32_vfrczpd256 (v4df)
v8sf __builtin_ia32_vfrczps256 (v8sf)
v2di __builtin_ia32_vpcmov (v2di, v2di, v2di)
v2di __builtin_ia32_vpcmov_v2di (v2di, v2di, v2di)
v4si __builtin_ia32_vpcmov_v4si (v4si, v4si, v4si)
v8hi __builtin_ia32_vpcmov_v8hi (v8hi, v8hi, v8hi)
v16qi __builtin_ia32_vpcmov_v16qi (v16qi, v16qi, v16qi)
v2df __builtin_ia32_vpcmov_v2df (v2df, v2df, v2df)
v4sf __builtin_ia32_vpcmov_v4sf (v4sf, v4sf, v4sf)
v4di __builtin_ia32_vpcmov_v4di256 (v4di, v4di, v4di)
v8si __builtin_ia32_vpcmov_v8si256 (v8si, v8si, v8si)
v16hi __builtin_ia32_vpcmov_v16hi256 (v16hi, v16hi, v16hi)
v32qi __builtin_ia32_vpcmov_v32qi256 (v32qi, v32qi, v32qi)
v4df __builtin_ia32_vpcmov_v4df256 (v4df, v4df, v4df)
v8sf __builtin_ia32_vpcmov_v8sf256 (v8sf, v8sf, v8sf)
v16qi __builtin_ia32_vpcomeqb (v16qi, v16qi)
v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
v4si __builtin_ia32_vpcomeqd (v4si, v4si)
v2di __builtin_ia32_vpcomeqq (v2di, v2di)
v16qi __builtin_ia32_vpcomequb (v16qi, v16qi)
v4si __builtin_ia32_vpcomequd (v4si, v4si)
v2di __builtin_ia32_vpcomequq (v2di, v2di)
v8hi __builtin_ia32_vpcomequw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
v16qi __builtin_ia32_vpcomfalseb (v16qi, v16qi)
v4si __builtin_ia32_vpcomfalsed (v4si, v4si)
v2di __builtin_ia32_vpcomfalseq (v2di, v2di)
v16qi __builtin_ia32_vpcomfalseub (v16qi, v16qi)
v4si __builtin_ia32_vpcomfalseud (v4si, v4si)
v2di __builtin_ia32_vpcomfalseuq (v2di, v2di)
v8hi __builtin_ia32_vpcomfalseuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomfalsew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomgeb (v16qi, v16qi)
v4si __builtin_ia32_vpcomged (v4si, v4si)
v2di __builtin_ia32_vpcomgeq (v2di, v2di)
v16qi __builtin_ia32_vpcomgeub (v16qi, v16qi)
v4si __builtin_ia32_vpcomgeud (v4si, v4si)
v2di __builtin_ia32_vpcomgeuq (v2di, v2di)
v8hi __builtin_ia32_vpcomgeuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomgew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomgtb (v16qi, v16qi)
v4si __builtin_ia32_vpcomgtd (v4si, v4si)
v2di __builtin_ia32_vpcomgtq (v2di, v2di)
v16qi __builtin_ia32_vpcomgtub (v16qi, v16qi)
v4si __builtin_ia32_vpcomgtud (v4si, v4si)
v2di __builtin_ia32_vpcomgtuq (v2di, v2di)
v8hi __builtin_ia32_vpcomgtuw (v8hi, v8hi)

Chapter 6: Extensions to the C Language Family

v8hi __builtin_ia32_vpcomgtw (v8hi, v8hi)
v16qi __builtin_ia32_vpcomleb (v16qi, v16qi)
v4si __builtin_ia32_vpcomled (v4si, v4si)
v2di __builtin_ia32_vpcomleq (v2di, v2di)
v16qi __builtin_ia32_vpcomleub (v16qi, v16qi)
v4si __builtin_ia32_vpcomleud (v4si, v4si)
v2di __builtin_ia32_vpcomleuq (v2di, v2di)
v8hi __builtin_ia32_vpcomleuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomlew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomltb (v16qi, v16qi)
v4si __builtin_ia32_vpcomltd (v4si, v4si)
v2di __builtin_ia32_vpcomltq (v2di, v2di)
v16qi __builtin_ia32_vpcomltub (v16qi, v16qi)
v4si __builtin_ia32_vpcomltud (v4si, v4si)
v2di __builtin_ia32_vpcomltuq (v2di, v2di)
v8hi __builtin_ia32_vpcomltuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomltw (v8hi, v8hi)
v16qi __builtin_ia32_vpcomneb (v16qi, v16qi)
v4si __builtin_ia32_vpcomned (v4si, v4si)
v2di __builtin_ia32_vpcomneq (v2di, v2di)
v16qi __builtin_ia32_vpcomneub (v16qi, v16qi)
v4si __builtin_ia32_vpcomneud (v4si, v4si)
v2di __builtin_ia32_vpcomneuq (v2di, v2di)
v8hi __builtin_ia32_vpcomneuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomnew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomtrueb (v16qi, v16qi)
v4si __builtin_ia32_vpcomtrued (v4si, v4si)
v2di __builtin_ia32_vpcomtrueq (v2di, v2di)
v16qi __builtin_ia32_vpcomtrueub (v16qi, v16qi)
v4si __builtin_ia32_vpcomtrueud (v4si, v4si)
v2di __builtin_ia32_vpcomtrueuq (v2di, v2di)
v8hi __builtin_ia32_vpcomtrueuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomtruew (v8hi, v8hi)
v4si __builtin_ia32_vphaddbd (v16qi)
v2di __builtin_ia32_vphaddbq (v16qi)
v8hi __builtin_ia32_vphaddbw (v16qi)
v2di __builtin_ia32_vphadddq (v4si)
v4si __builtin_ia32_vphaddubd (v16qi)
v2di __builtin_ia32_vphaddubq (v16qi)
v8hi __builtin_ia32_vphaddubw (v16qi)
v2di __builtin_ia32_vphaddudq (v4si)
v4si __builtin_ia32_vphadduwd (v8hi)
v2di __builtin_ia32_vphadduwq (v8hi)
v4si __builtin_ia32_vphaddwd (v8hi)
v2di __builtin_ia32_vphaddwq (v8hi)
v8hi __builtin_ia32_vphsubbw (v16qi)
v2di __builtin_ia32_vphsubdq (v4si)
v4si __builtin_ia32_vphsubwd (v8hi)
v4si __builtin_ia32_vpmacsdd (v4si, v4si, v4si)
v2di __builtin_ia32_vpmacsdqh (v4si, v4si, v2di)
v2di __builtin_ia32_vpmacsdql (v4si, v4si, v2di)
v4si __builtin_ia32_vpmacssdd (v4si, v4si, v4si)
v2di __builtin_ia32_vpmacssdqh (v4si, v4si, v2di)
v2di __builtin_ia32_vpmacssdql (v4si, v4si, v2di)
v4si __builtin_ia32_vpmacsswd (v8hi, v8hi, v4si)
v8hi __builtin_ia32_vpmacssww (v8hi, v8hi, v8hi)
v4si __builtin_ia32_vpmacswd (v8hi, v8hi, v4si)
v8hi __builtin_ia32_vpmacsww (v8hi, v8hi, v8hi)

767

768

Using the GNU Compiler Collection (GCC)

v4si __builtin_ia32_vpmadcsswd (v8hi, v8hi, v4si)
v4si __builtin_ia32_vpmadcswd (v8hi, v8hi, v4si)
v16qi __builtin_ia32_vpperm (v16qi, v16qi, v16qi)
v16qi __builtin_ia32_vprotb (v16qi, v16qi)
v4si __builtin_ia32_vprotd (v4si, v4si)
v2di __builtin_ia32_vprotq (v2di, v2di)
v8hi __builtin_ia32_vprotw (v8hi, v8hi)
v16qi __builtin_ia32_vpshab (v16qi, v16qi)
v4si __builtin_ia32_vpshad (v4si, v4si)
v2di __builtin_ia32_vpshaq (v2di, v2di)
v8hi __builtin_ia32_vpshaw (v8hi, v8hi)
v16qi __builtin_ia32_vpshlb (v16qi, v16qi)
v4si __builtin_ia32_vpshld (v4si, v4si)
v2di __builtin_ia32_vpshlq (v2di, v2di)
v8hi __builtin_ia32_vpshlw (v8hi, v8hi)

The following built-in functions are available when ‘-mfma4’ is used. All of them generate
the machine instruction that is part of the name.
v2df
v4sf
v2df
v4sf
v2df
v4sf
v2df
v4sf
v2df
v4sf
v2df
v4sf
v2df
v4sf
v2df
v4sf
v2df
v4sf
v2df
v4sf
v4df
v8sf
v4df
v8sf
v4df
v8sf
v4df
v8sf
v4df
v8sf
v4df
v8sf

__builtin_ia32_vfmaddpd (v2df, v2df, v2df)
__builtin_ia32_vfmaddps (v4sf, v4sf, v4sf)
__builtin_ia32_vfmaddsd (v2df, v2df, v2df)
__builtin_ia32_vfmaddss (v4sf, v4sf, v4sf)
__builtin_ia32_vfmsubpd (v2df, v2df, v2df)
__builtin_ia32_vfmsubps (v4sf, v4sf, v4sf)
__builtin_ia32_vfmsubsd (v2df, v2df, v2df)
__builtin_ia32_vfmsubss (v4sf, v4sf, v4sf)
__builtin_ia32_vfnmaddpd (v2df, v2df, v2df)
__builtin_ia32_vfnmaddps (v4sf, v4sf, v4sf)
__builtin_ia32_vfnmaddsd (v2df, v2df, v2df)
__builtin_ia32_vfnmaddss (v4sf, v4sf, v4sf)
__builtin_ia32_vfnmsubpd (v2df, v2df, v2df)
__builtin_ia32_vfnmsubps (v4sf, v4sf, v4sf)
__builtin_ia32_vfnmsubsd (v2df, v2df, v2df)
__builtin_ia32_vfnmsubss (v4sf, v4sf, v4sf)
__builtin_ia32_vfmaddsubpd (v2df, v2df, v2df)
__builtin_ia32_vfmaddsubps (v4sf, v4sf, v4sf)
__builtin_ia32_vfmsubaddpd (v2df, v2df, v2df)
__builtin_ia32_vfmsubaddps (v4sf, v4sf, v4sf)
__builtin_ia32_vfmaddpd256 (v4df, v4df, v4df)
__builtin_ia32_vfmaddps256 (v8sf, v8sf, v8sf)
__builtin_ia32_vfmsubpd256 (v4df, v4df, v4df)
__builtin_ia32_vfmsubps256 (v8sf, v8sf, v8sf)
__builtin_ia32_vfnmaddpd256 (v4df, v4df, v4df)
__builtin_ia32_vfnmaddps256 (v8sf, v8sf, v8sf)
__builtin_ia32_vfnmsubpd256 (v4df, v4df, v4df)
__builtin_ia32_vfnmsubps256 (v8sf, v8sf, v8sf)
__builtin_ia32_vfmaddsubpd256 (v4df, v4df, v4df)
__builtin_ia32_vfmaddsubps256 (v8sf, v8sf, v8sf)
__builtin_ia32_vfmsubaddpd256 (v4df, v4df, v4df)
__builtin_ia32_vfmsubaddps256 (v8sf, v8sf, v8sf)

The following built-in functions are available when ‘-mlwp’ is used.
void
void
void
void
void
void

__builtin_ia32_llwpcb16 (void *);
__builtin_ia32_llwpcb32 (void *);
__builtin_ia32_llwpcb64 (void *);
* __builtin_ia32_llwpcb16 (void);
* __builtin_ia32_llwpcb32 (void);
* __builtin_ia32_llwpcb64 (void);

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void __builtin_ia32_lwpval16 (unsigned short, unsigned int, unsigned short)
void __builtin_ia32_lwpval32 (unsigned int, unsigned int, unsigned int)
void __builtin_ia32_lwpval64 (unsigned __int64, unsigned int, unsigned int)
unsigned char __builtin_ia32_lwpins16 (unsigned short, unsigned int, unsigned short)
unsigned char __builtin_ia32_lwpins32 (unsigned int, unsigned int, unsigned int)
unsigned char __builtin_ia32_lwpins64 (unsigned __int64, unsigned int, unsigned int)

The following built-in functions are available when ‘-mbmi’ is used. All of them generate
the machine instruction that is part of the name.
unsigned int __builtin_ia32_bextr_u32(unsigned int, unsigned int);
unsigned long long __builtin_ia32_bextr_u64 (unsigned long long, unsigned long long);

The following built-in functions are available when ‘-mbmi2’ is used. All of them generate
the machine instruction that is part of the name.
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned

int _bzhi_u32 (unsigned int, unsigned int)
int _pdep_u32 (unsigned int, unsigned int)
int _pext_u32 (unsigned int, unsigned int)
long long _bzhi_u64 (unsigned long long, unsigned long long)
long long _pdep_u64 (unsigned long long, unsigned long long)
long long _pext_u64 (unsigned long long, unsigned long long)

The following built-in functions are available when ‘-mlzcnt’ is used. All of them generate
the machine instruction that is part of the name.
unsigned short __builtin_ia32_lzcnt_u16(unsigned short);
unsigned int __builtin_ia32_lzcnt_u32(unsigned int);
unsigned long long __builtin_ia32_lzcnt_u64 (unsigned long long);

The following built-in functions are available when ‘-mfxsr’ is used. All of them generate
the machine instruction that is part of the name.
void
void
void
void

__builtin_ia32_fxsave (void *)
__builtin_ia32_fxrstor (void *)
__builtin_ia32_fxsave64 (void *)
__builtin_ia32_fxrstor64 (void *)

The following built-in functions are available when ‘-mxsave’ is used. All of them generate
the machine instruction that is part of the name.
void
void
void
void

__builtin_ia32_xsave (void *, long long)
__builtin_ia32_xrstor (void *, long long)
__builtin_ia32_xsave64 (void *, long long)
__builtin_ia32_xrstor64 (void *, long long)

The following built-in functions are available when ‘-mxsaveopt’ is used. All of them
generate the machine instruction that is part of the name.
void __builtin_ia32_xsaveopt (void *, long long)
void __builtin_ia32_xsaveopt64 (void *, long long)

The following built-in functions are available when ‘-mtbm’ is used. Both of them generate
the immediate form of the bextr machine instruction.
unsigned int __builtin_ia32_bextri_u32 (unsigned int,
const unsigned int);
unsigned long long __builtin_ia32_bextri_u64 (unsigned long long,
const unsigned long long);

The following built-in functions are available when ‘-m3dnow’ is used. All of them generate
the machine instruction that is part of the name.
void __builtin_ia32_femms (void)
v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
v2si __builtin_ia32_pf2id (v2sf)

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Using the GNU Compiler Collection (GCC)

v2sf
v2sf
v2si
v2si
v2si
v2sf
v2sf
v2sf
v2sf
v2sf
v2sf
v2sf
v2sf
v2sf
v2sf
v4hi

__builtin_ia32_pfacc (v2sf, v2sf)
__builtin_ia32_pfadd (v2sf, v2sf)
__builtin_ia32_pfcmpeq (v2sf, v2sf)
__builtin_ia32_pfcmpge (v2sf, v2sf)
__builtin_ia32_pfcmpgt (v2sf, v2sf)
__builtin_ia32_pfmax (v2sf, v2sf)
__builtin_ia32_pfmin (v2sf, v2sf)
__builtin_ia32_pfmul (v2sf, v2sf)
__builtin_ia32_pfrcp (v2sf)
__builtin_ia32_pfrcpit1 (v2sf, v2sf)
__builtin_ia32_pfrcpit2 (v2sf, v2sf)
__builtin_ia32_pfrsqrt (v2sf)
__builtin_ia32_pfsub (v2sf, v2sf)
__builtin_ia32_pfsubr (v2sf, v2sf)
__builtin_ia32_pi2fd (v2si)
__builtin_ia32_pmulhrw (v4hi, v4hi)

The following built-in functions are available when ‘-m3dnowa’ is used. All of them
generate the machine instruction that is part of the name.
v2si
v2sf
v2sf
v2sf
v2sf
v2si

__builtin_ia32_pf2iw (v2sf)
__builtin_ia32_pfnacc (v2sf, v2sf)
__builtin_ia32_pfpnacc (v2sf, v2sf)
__builtin_ia32_pi2fw (v2si)
__builtin_ia32_pswapdsf (v2sf)
__builtin_ia32_pswapdsi (v2si)

The following built-in functions are available when ‘-mrtm’ is used They are used for
restricted transactional memory. These are the internal low level functions. Normally the
functions in Section 6.59.34 [x86 transactional memory intrinsics], page 771 should be used
instead.
int __builtin_ia32_xbegin ()
void __builtin_ia32_xend ()
void __builtin_ia32_xabort (status)
int __builtin_ia32_xtest ()

The following built-in functions are available when ‘-mmwaitx’ is used. All of them
generate the machine instruction that is part of the name.
void __builtin_ia32_monitorx (void *, unsigned int, unsigned int)
void __builtin_ia32_mwaitx (unsigned int, unsigned int, unsigned int)

The following built-in functions are available when ‘-mclzero’ is used. All of them
generate the machine instruction that is part of the name.
void __builtin_i32_clzero (void *)

The following built-in functions are available when ‘-mpku’ is used. They generate reads
and writes to PKRU.
void __builtin_ia32_wrpkru (unsigned int)
unsigned int __builtin_ia32_rdpkru ()

The following built-in functions are available when ‘-mcet’ or ‘-mshstk’ option is used.
They support shadow stack machine instructions from Intel Control-flow Enforcement Technology (CET). Each built-in function generates the machine instruction that is part of the
function’s name. These are the internal low-level functions. Normally the functions in
Section 6.59.35 [x86 control-flow protection intrinsics], page 772 should be used instead.
unsigned int __builtin_ia32_rdsspd (void)
unsigned long long __builtin_ia32_rdsspq (void)
void __builtin_ia32_incsspd (unsigned int)

Chapter 6: Extensions to the C Language Family

void
void
void
void
void
void
void
void
void

771

__builtin_ia32_incsspq (unsigned long long)
__builtin_ia32_saveprevssp(void);
__builtin_ia32_rstorssp(void *);
__builtin_ia32_wrssd(unsigned int, void *);
__builtin_ia32_wrssq(unsigned long long, void *);
__builtin_ia32_wrussd(unsigned int, void *);
__builtin_ia32_wrussq(unsigned long long, void *);
__builtin_ia32_setssbsy(void);
__builtin_ia32_clrssbsy(void *);

6.59.34 x86 Transactional Memory Intrinsics
These hardware transactional memory intrinsics for x86 allow you to use memory transactions with RTM (Restricted Transactional Memory). This support is enabled with the
‘-mrtm’ option. For using HLE (Hardware Lock Elision) see Section 6.55 [x86 specific memory model extensions for transactional memory], page 609 instead.
A memory transaction commits all changes to memory in an atomic way, as visible to
other threads. If the transaction fails it is rolled back and all side effects discarded.
Generally there is no guarantee that a memory transaction ever succeeds and suitable
fallback code always needs to be supplied.

unsigned _xbegin ()

[RTM Function]
Start a RTM (Restricted Transactional Memory) transaction. Returns _XBEGIN_
STARTED when the transaction started successfully (note this is not 0, so the constant
has to be explicitly tested).
If the transaction aborts, all side effects are undone and an abort code encoded as a
bit mask is returned. The following macros are defined:
_XABORT_EXPLICIT
Transaction was explicitly aborted with _xabort. The parameter passed
to _xabort is available with _XABORT_CODE(status).
_XABORT_RETRY
Transaction retry is possible.
_XABORT_CONFLICT
Transaction abort due to a memory conflict with another thread.
_XABORT_CAPACITY
Transaction abort due to the transaction using too much memory.
_XABORT_DEBUG
Transaction abort due to a debug trap.
_XABORT_NESTED
Transaction abort in an inner nested transaction.
There is no guarantee any transaction ever succeeds, so there always needs to be a
valid fallback path.

void _xend ()

[RTM Function]
Commit the current transaction. When no transaction is active this faults. All
memory side effects of the transaction become visible to other threads in an atomic
manner.

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int _xtest ()

[RTM Function]
Return a nonzero value if a transaction is currently active, otherwise 0.

void _xabort (status)

[RTM Function]
Abort the current transaction. When no transaction is active this is a no-op. The
status is an 8-bit constant; its value is encoded in the return value from _xbegin.

Here is an example showing handling for _XABORT_RETRY and a fallback path for other
failures:
#include 
int n_tries, max_tries;
unsigned status = _XABORT_EXPLICIT;
...
for (n_tries = 0; n_tries < max_tries; n_tries++)
{
status = _xbegin ();
if (status == _XBEGIN_STARTED || !(status & _XABORT_RETRY))
break;
}
if (status == _XBEGIN_STARTED)
{
... transaction code...
_xend ();
}
else
{
... non-transactional fallback path...
}

Note that, in most cases, the transactional and non-transactional code must synchronize
together to ensure consistency.

6.59.35 x86 Control-Flow Protection Intrinsics
ret_type _get_ssp (void)

[CET Function]
Get the current value of shadow stack pointer if shadow stack support from Intel CET
is enabled in the hardware or 0 otherwise. The ret_type is unsigned long long for
64-bit targets and unsigned int for 32-bit targets.

void _inc_ssp (unsigned int)

[CET Function]
Increment the current shadow stack pointer by the size specified by the function argument. The argument is masked to a byte value for security reasons, so to increment
by more than 255 bytes you must call the function multiple times.

The shadow stack unwind code looks like:
#include 
/* Unwind the shadow stack for EH. */
#define _Unwind_Frames_Extra(x)
\
do
\
{
\
_Unwind_Word ssp = _get_ssp (); \
if (ssp != 0)
\

Chapter 6: Extensions to the C Language Family

{
_Unwind_Word tmp = (x);
while (tmp > 255)
{
_inc_ssp (tmp);
tmp -= 255;
}
_inc_ssp (tmp);
}
}
while (0)

773

\
\
\
\
\
\
\
\
\
\

This code runs unconditionally on all 64-bit processors. For 32-bit processors the code runs
on those that support multi-byte NOP instructions.

6.60 Format Checks Specific to Particular Target Machines
For some target machines, GCC supports additional options to the format attribute (see
Section 6.31 [Declaring Attributes of Functions], page 464).

6.60.1 Solaris Format Checks
Solaris targets support the cmn_err (or __cmn_err__) format check. cmn_err accepts a subset of the standard printf conversions, and the two-argument %b conversion for displaying
bit-fields. See the Solaris man page for cmn_err for more information.

6.60.2 Darwin Format Checks
Darwin targets support the CFString (or __CFString__) in the format attribute context.
Declarations made with such attribution are parsed for correct syntax and format argument
types. However, parsing of the format string itself is currently undefined and is not carried
out by this version of the compiler.
Additionally, CFStringRefs (defined by the CoreFoundation headers) may also be used
as format arguments. Note that the relevant headers are only likely to be available on
Darwin (OSX) installations. On such installations, the XCode and system documentation
provide descriptions of CFString, CFStringRefs and associated functions.

6.61 Pragmas Accepted by GCC
GCC supports several types of pragmas, primarily in order to compile code originally written
for other compilers. Note that in general we do not recommend the use of pragmas; See
Section 6.31 [Function Attributes], page 464, for further explanation.

6.61.1 AArch64 Pragmas
The pragmas defined by the AArch64 target correspond to the AArch64 target function
attributes. They can be specified as below:
#pragma GCC target("string")

where string can be any string accepted as an AArch64 target attribute. See
Section 6.31.2 [AArch64 Function Attributes], page 481, for more details on the permissible
values of string.

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6.61.2 ARM Pragmas
The ARM target defines pragmas for controlling the default addition of long_call and
short_call attributes to functions. See Section 6.31 [Function Attributes], page 464, for
information about the effects of these attributes.
long_calls
Set all subsequent functions to have the long_call attribute.
no_long_calls
Set all subsequent functions to have the short_call attribute.
long_calls_off
Do not affect the long_call or short_call attributes of subsequent functions.

6.61.3 M32C Pragmas
GCC memregs number
Overrides the command-line option -memregs= for the current file. Use with
care! This pragma must be before any function in the file, and mixing different
memregs values in different objects may make them incompatible. This pragma
is useful when a performance-critical function uses a memreg for temporary
values, as it may allow you to reduce the number of memregs used.
ADDRESS name address
For any declared symbols matching name, this does three things to that symbol:
it forces the symbol to be located at the given address (a number), it forces
the symbol to be volatile, and it changes the symbol’s scope to be static. This
pragma exists for compatibility with other compilers, but note that the common
1234H numeric syntax is not supported (use 0x1234 instead). Example:
#pragma ADDRESS port3 0x103
char port3;

6.61.4 MeP Pragmas
custom io_volatile (on|off)
Overrides the command-line option -mio-volatile for the current file. Note
that for compatibility with future GCC releases, this option should only be
used once before any io variables in each file.
GCC coprocessor available registers
Specifies which coprocessor registers are available to the register allocator. registers may be a single register, register range separated by ellipses, or commaseparated list of those. Example:
#pragma GCC coprocessor available $c0...$c10, $c28

GCC coprocessor call_saved registers
Specifies which coprocessor registers are to be saved and restored by any function using them. registers may be a single register, register range separated by
ellipses, or comma-separated list of those. Example:
#pragma GCC coprocessor call_saved $c4...$c6, $c31

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GCC coprocessor subclass ’(A|B|C|D)’ = registers
Creates and defines a register class. These register classes can be used by inline
asm constructs. registers may be a single register, register range separated by
ellipses, or comma-separated list of those. Example:
#pragma GCC coprocessor subclass ’B’ = $c2, $c4, $c6
asm ("cpfoo %0" : "=B" (x));

GCC disinterrupt name , name ...
For the named functions, the compiler adds code to disable interrupts for the
duration of those functions. If any functions so named are not encountered in
the source, a warning is emitted that the pragma is not used. Examples:
#pragma disinterrupt foo
#pragma disinterrupt bar, grill
int foo () { ... }

GCC call name , name ...
For the named functions, the compiler always uses a register-indirect call model
when calling the named functions. Examples:
extern int foo ();
#pragma call foo

6.61.5 RS/6000 and PowerPC Pragmas
The RS/6000 and PowerPC targets define one pragma for controlling whether or not the
longcall attribute is added to function declarations by default. This pragma overrides the
‘-mlongcall’ option, but not the longcall and shortcall attributes. See Section 3.18.40
[RS/6000 and PowerPC Options], page 345, for more information about when long calls are
and are not necessary.
longcall (1)
Apply the longcall attribute to all subsequent function declarations.
longcall (0)
Do not apply the longcall attribute to subsequent function declarations.

6.61.6 S/390 Pragmas
The pragmas defined by the S/390 target correspond to the S/390 target function attributes
and some the additional options:
‘zvector’
‘no-zvector’
Note that options of the pragma, unlike options of the target attribute, do change the
value of preprocessor macros like __VEC__. They can be specified as below:
#pragma GCC target("string[,string]...")
#pragma GCC target("string"[,"string"]...)

6.61.7 Darwin Pragmas
The following pragmas are available for all architectures running the Darwin operating
system. These are useful for compatibility with other Mac OS compilers.

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Using the GNU Compiler Collection (GCC)

mark tokens...
This pragma is accepted, but has no effect.
options align=alignment
This pragma sets the alignment of fields in structures. The values of alignment
may be mac68k, to emulate m68k alignment, or power, to emulate PowerPC
alignment. Uses of this pragma nest properly; to restore the previous setting,
use reset for the alignment.
segment tokens...
This pragma is accepted, but has no effect.
unused (var [, var]...)
This pragma declares variables to be possibly unused. GCC does not produce
warnings for the listed variables. The effect is similar to that of the unused
attribute, except that this pragma may appear anywhere within the variables’
scopes.

6.61.8 Solaris Pragmas
The Solaris target supports #pragma redefine_extname (see Section 6.61.9 [SymbolRenaming Pragmas], page 776). It also supports additional #pragma directives for
compatibility with the system compiler.
align alignment (variable [, variable]...)
Increase the minimum alignment of each variable to alignment. This is the same
as GCC’s aligned attribute see Section 6.32 [Variable Attributes], page 513).
Macro expansion occurs on the arguments to this pragma when compiling C
and Objective-C. It does not currently occur when compiling C++, but this is
a bug which may be fixed in a future release.
fini (function [, function]...)
This pragma causes each listed function to be called after main, or during shared
module unloading, by adding a call to the .fini section.
init (function [, function]...)
This pragma causes each listed function to be called during initialization (before
main) or during shared module loading, by adding a call to the .init section.

6.61.9 Symbol-Renaming Pragmas
GCC supports a #pragma directive that changes the name used in assembly for a given
declaration. While this pragma is supported on all platforms, it is intended primarily to
provide compatibility with the Solaris system headers. This effect can also be achieved
using the asm labels extension (see Section 6.45.4 [Asm Labels], page 592).
redefine_extname oldname newname
This pragma gives the C function oldname the assembly symbol newname. The
preprocessor macro __PRAGMA_REDEFINE_EXTNAME is defined if this pragma is
available (currently on all platforms).
This pragma and the asm labels extension interact in a complicated manner. Here are
some corner cases you may want to be aware of:

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1. This pragma silently applies only to declarations with external linkage. Asm labels do
not have this restriction.
2. In C++, this pragma silently applies only to declarations with “C” linkage. Again, asm
labels do not have this restriction.
3. If either of the ways of changing the assembly name of a declaration are applied to a
declaration whose assembly name has already been determined (either by a previous
use of one of these features, or because the compiler needed the assembly name in order
to generate code), and the new name is different, a warning issues and the name does
not change.
4. The oldname used by #pragma redefine_extname is always the C-language name.

6.61.10 Structure-Layout Pragmas
For compatibility with Microsoft Windows compilers, GCC supports a set of #pragma directives that change the maximum alignment of members of structures (other than zero-width
bit-fields), unions, and classes subsequently defined. The n value below always is required
to be a small power of two and specifies the new alignment in bytes.
1. #pragma pack(n) simply sets the new alignment.
2. #pragma pack() sets the alignment to the one that was in effect when compilation
started (see also command-line option ‘-fpack-struct[=n]’ see Section 3.16 [Code
Gen Options], page 202).
3. #pragma pack(push[,n]) pushes the current alignment setting on an internal stack
and then optionally sets the new alignment.
4. #pragma pack(pop) restores the alignment setting to the one saved at the top of the
internal stack (and removes that stack entry). Note that #pragma pack([n]) does not
influence this internal stack; thus it is possible to have #pragma pack(push) followed
by multiple #pragma pack(n) instances and finalized by a single #pragma pack(pop).
Some targets, e.g. x86 and PowerPC, support the #pragma ms_struct directive which
lays out structures and unions subsequently defined as the documented __attribute__
((ms_struct)).
1. #pragma ms_struct on turns on the Microsoft layout.
2. #pragma ms_struct off turns off the Microsoft layout.
3. #pragma ms_struct reset goes back to the default layout.
Most targets also support the #pragma scalar_storage_order directive which lays out
structures and unions subsequently defined as the documented __attribute__ ((scalar_
storage_order)).
1. #pragma scalar_storage_order big-endian sets the storage order of the scalar fields
to big-endian.
2. #pragma scalar_storage_order little-endian sets the storage order of the scalar
fields to little-endian.
3. #pragma scalar_storage_order default goes back to the endianness that
was in effect when compilation started (see also command-line option
‘-fsso-struct=endianness’ see Section 3.4 [C Dialect Options], page 35).

778

Using the GNU Compiler Collection (GCC)

6.61.11 Weak Pragmas
For compatibility with SVR4, GCC supports a set of #pragma directives for declaring symbols to be weak, and defining weak aliases.
#pragma weak symbol
This pragma declares symbol to be weak, as if the declaration had the attribute
of the same name. The pragma may appear before or after the declaration of
symbol. It is not an error for symbol to never be defined at all.
#pragma weak symbol1 = symbol2
This pragma declares symbol1 to be a weak alias of symbol2. It is an error if
symbol2 is not defined in the current translation unit.

6.61.12 Diagnostic Pragmas
GCC allows the user to selectively enable or disable certain types of diagnostics, and change
the kind of the diagnostic. For example, a project’s policy might require that all sources
compile with ‘-Werror’ but certain files might have exceptions allowing specific types of
warnings. Or, a project might selectively enable diagnostics and treat them as errors depending on which preprocessor macros are defined.
#pragma GCC diagnostic kind option
Modifies the disposition of a diagnostic. Note that not all diagnostics are modifiable; at the moment only warnings (normally controlled by ‘-W...’) can be
controlled, and not all of them. Use ‘-fdiagnostics-show-option’ to determine which diagnostics are controllable and which option controls them.
kind is ‘error’ to treat this diagnostic as an error, ‘warning’ to treat it like
a warning (even if ‘-Werror’ is in effect), or ‘ignored’ if the diagnostic is to
be ignored. option is a double quoted string that matches the command-line
option.
#pragma GCC diagnostic warning "-Wformat"
#pragma GCC diagnostic error "-Wformat"
#pragma GCC diagnostic ignored "-Wformat"

Note that these pragmas override any command-line options. GCC keeps track
of the location of each pragma, and issues diagnostics according to the state
as of that point in the source file. Thus, pragmas occurring after a line do not
affect diagnostics caused by that line.
#pragma GCC diagnostic push
#pragma GCC diagnostic pop
Causes GCC to remember the state of the diagnostics as of each push, and
restore to that point at each pop. If a pop has no matching push, the commandline options are restored.
#pragma GCC
foo(a);
#pragma GCC
#pragma GCC
foo(b);
#pragma GCC
foo(c);
#pragma GCC
foo(d);

diagnostic error "-Wuninitialized"
/* error is given for this one */
diagnostic push
diagnostic ignored "-Wuninitialized"
/* no diagnostic for this one */
diagnostic pop
/* error is given for this one */
diagnostic pop
/* depends on command-line options */

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GCC also offers a simple mechanism for printing messages during compilation.
#pragma message string
Prints string as a compiler message on compilation. The message is informational only, and is neither a compilation warning nor an error.
#pragma message "Compiling " __FILE__ "..."

string may be parenthesized, and is printed with location information. For
example,
#define DO_PRAGMA(x) _Pragma (#x)
#define TODO(x) DO_PRAGMA(message ("TODO - " #x))
TODO(Remember to fix this)

prints
this’.

‘/tmp/file.c:4: note: #pragma message: TODO - Remember to fix

6.61.13 Visibility Pragmas
#pragma GCC visibility push(visibility)
#pragma GCC visibility pop
This pragma allows the user to set the visibility for multiple declarations without having to give each a visibility attribute (see Section 6.31 [Function Attributes], page 464).
In C++, ‘#pragma GCC visibility’ affects only namespace-scope declarations.
Class members and template specializations are not affected; if you want to
override the visibility for a particular member or instantiation, you must use
an attribute.

6.61.14 Push/Pop Macro Pragmas
For compatibility with Microsoft Windows compilers, GCC supports ‘#pragma
push_macro("macro_name")’ and ‘#pragma pop_macro("macro_name")’.
#pragma push_macro("macro_name")
This pragma saves the value of the macro named as macro name to the top of
the stack for this macro.
#pragma pop_macro("macro_name")
This pragma sets the value of the macro named as macro name to the value
on top of the stack for this macro. If the stack for macro name is empty, the
value of the macro remains unchanged.
For example:
#define X 1
#pragma push_macro("X")
#undef X
#define X -1
#pragma pop_macro("X")
int x [X];

In this example, the definition of X as 1 is saved by #pragma push_macro and restored by
#pragma pop_macro.

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6.61.15 Function Specific Option Pragmas
#pragma GCC target ("string"...)
This pragma allows you to set target specific options for functions defined later
in the source file. One or more strings can be specified. Each function that
is defined after this point is as if attribute((target("STRING"))) was specified for that function. The parenthesis around the options is optional. See
Section 6.31 [Function Attributes], page 464, for more information about the
target attribute and the attribute syntax.
The #pragma GCC target pragma is presently implemented for x86, ARM,
AArch64, PowerPC, S/390, and Nios II targets only.
#pragma GCC optimize ("string"...)
This pragma allows you to set global optimization options for functions defined
later in the source file. One or more strings can be specified. Each function
that is defined after this point is as if attribute((optimize("STRING"))) was
specified for that function. The parenthesis around the options is optional. See
Section 6.31 [Function Attributes], page 464, for more information about the
optimize attribute and the attribute syntax.
#pragma GCC push_options
#pragma GCC pop_options
These pragmas maintain a stack of the current target and optimization options.
It is intended for include files where you temporarily want to switch to using
a different ‘#pragma GCC target’ or ‘#pragma GCC optimize’ and then to pop
back to the previous options.
#pragma GCC reset_options
This pragma clears the current #pragma GCC target and #pragma GCC
optimize to use the default switches as specified on the command line.

6.61.16 Loop-Specific Pragmas
#pragma GCC ivdep
With this pragma, the programmer asserts that there are no loop-carried dependencies which would prevent consecutive iterations of the following loop from
executing concurrently with SIMD (single instruction multiple data) instructions.
For example, the compiler can only unconditionally vectorize the following loop
with the pragma:
void foo (int n, int *a, int *b, int *c)
{
int i, j;
#pragma GCC ivdep
for (i = 0; i < n; ++i)
a[i] = b[i] + c[i];
}

In this example, using the restrict qualifier had the same effect. In the
following example, that would not be possible. Assume k < −m or k >= m.
Only with the pragma, the compiler knows that it can unconditionally vectorize
the following loop:

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void ignore_vec_dep (int *a, int k, int c, int m)
{
#pragma GCC ivdep
for (int i = 0; i < m; i++)
a[i] = a[i + k] * c;
}

#pragma GCC unroll n
You can use this pragma to control how many times a loop should be unrolled.
It must be placed immediately before a for, while or do loop or a #pragma
GCC ivdep, and applies only to the loop that follows. n is an integer constant
expression specifying the unrolling factor. The values of 0 and 1 block any
unrolling of the loop.

6.62 Unnamed Structure and Union Fields
As permitted by ISO C11 and for compatibility with other compilers, GCC allows you to
define a structure or union that contains, as fields, structures and unions without names.
For example:
struct {
int a;
union {
int b;
float c;
};
int d;
} foo;

In this example, you are able to access members of the unnamed union with code like
‘foo.b’. Note that only unnamed structs and unions are allowed, you may not have, for
example, an unnamed int.
You must never create such structures that cause ambiguous field definitions. For example, in this structure:
struct {
int a;
struct {
int a;
};
} foo;

it is ambiguous which a is being referred to with ‘foo.a’. The compiler gives errors for such
constructs.
Unless ‘-fms-extensions’ is used, the unnamed field must be a structure or union definition without a tag (for example, ‘struct { int a; };’). If ‘-fms-extensions’ is used, the
field may also be a definition with a tag such as ‘struct foo { int a; };’, a reference to
a previously defined structure or union such as ‘struct foo;’, or a reference to a typedef
name for a previously defined structure or union type.
The option ‘-fplan9-extensions’ enables ‘-fms-extensions’ as well as two other extensions. First, a pointer to a structure is automatically converted to a pointer to an
anonymous field for assignments and function calls. For example:
struct s1 { int a; };
struct s2 { struct s1; };

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Using the GNU Compiler Collection (GCC)

extern void f1 (struct s1 *);
void f2 (struct s2 *p) { f1 (p); }

In the call to f1 inside f2, the pointer p is converted into a pointer to the anonymous field.
Second, when the type of an anonymous field is a typedef for a struct or union, code
may refer to the field using the name of the typedef.
typedef struct { int a; } s1;
struct s2 { s1; };
s1 f1 (struct s2 *p) { return p->s1; }

These usages are only permitted when they are not ambiguous.

6.63 Thread-Local Storage
Thread-local storage (TLS) is a mechanism by which variables are allocated such that there
is one instance of the variable per extant thread. The runtime model GCC uses to implement this originates in the IA-64 processor-specific ABI, but has since been migrated
to other processors as well. It requires significant support from the linker (ld), dynamic
linker (ld.so), and system libraries (‘libc.so’ and ‘libpthread.so’), so it is not available
everywhere.
At the user level, the extension is visible with a new storage class keyword: __thread.
For example:
__thread int i;
extern __thread struct state s;
static __thread char *p;

The __thread specifier may be used alone, with the extern or static specifiers, but
with no other storage class specifier. When used with extern or static, __thread must
appear immediately after the other storage class specifier.
The __thread specifier may be applied to any global, file-scoped static, function-scoped
static, or static data member of a class. It may not be applied to block-scoped automatic
or non-static data member.
When the address-of operator is applied to a thread-local variable, it is evaluated at
run time and returns the address of the current thread’s instance of that variable. An
address so obtained may be used by any thread. When a thread terminates, any pointers
to thread-local variables in that thread become invalid.
No static initialization may refer to the address of a thread-local variable.
In C++, if an initializer is present for a thread-local variable, it must be a constantexpression, as defined in 5.19.2 of the ANSI/ISO C++ standard.
See ELF Handling For Thread-Local Storage for a detailed explanation of the four threadlocal storage addressing models, and how the runtime is expected to function.

6.63.1 ISO/IEC 9899:1999 Edits for Thread-Local Storage
The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that document the
exact semantics of the language extension.
• 5.1.2 Execution environments
Add new text after paragraph 1
Within either execution environment, a thread is a flow of control within
a program. It is implementation defined whether or not there may be

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more than one thread associated with a program. It is implementation
defined how threads beyond the first are created, the name and type of
the function called at thread startup, and how threads may be terminated.
However, objects with thread storage duration shall be initialized before
thread startup.
• 6.2.4 Storage durations of objects
Add new text before paragraph 3
An object whose identifier is declared with the storage-class specifier
__thread has thread storage duration. Its lifetime is the entire execution
of the thread, and its stored value is initialized only once, prior to thread
startup.
• 6.4.1 Keywords
Add __thread.
• 6.7.1 Storage-class specifiers
Add __thread to the list of storage class specifiers in paragraph 1.
Change paragraph 2 to
With the exception of __thread, at most one storage-class specifier may
be given [. . . ]. The __thread specifier may be used alone, or immediately
following extern or static.
Add new text after paragraph 6
The declaration of an identifier for a variable that has block scope that
specifies __thread shall also specify either extern or static.
The __thread specifier shall be used only with variables.

6.63.2 ISO/IEC 14882:1998 Edits for Thread-Local Storage
The following are a set of changes to ISO/IEC 14882:1998 (aka C++98) that document the
exact semantics of the language extension.
• [intro.execution]
New text after paragraph 4
A thread is a flow of control within the abstract machine. It is implementation defined whether or not there may be more than one thread.
New text after paragraph 7
It is unspecified whether additional action must be taken to ensure when
and whether side effects are visible to other threads.
• [lex.key]
Add __thread.
• [basic.start.main]
Add after paragraph 5
The thread that begins execution at the main function is called the main
thread. It is implementation defined how functions beginning threads other
than the main thread are designated or typed. A function so designated,

784

•

•

•

•

•

•

•

Using the GNU Compiler Collection (GCC)

as well as the main function, is called a thread startup function. It is implementation defined what happens if a thread startup function returns. It
is implementation defined what happens to other threads when any thread
calls exit.
[basic.start.init]
Add after paragraph 4
The storage for an object of thread storage duration shall be statically
initialized before the first statement of the thread startup function. An
object of thread storage duration shall not require dynamic initialization.
[basic.start.term]
Add after paragraph 3
The type of an object with thread storage duration shall not have a nontrivial destructor, nor shall it be an array type whose elements (directly or
indirectly) have non-trivial destructors.
[basic.stc]
Add “thread storage duration” to the list in paragraph 1.
Change paragraph 2
Thread, static, and automatic storage durations are associated with objects
introduced by declarations [. . . ].
Add __thread to the list of specifiers in paragraph 3.
[basic.stc.thread]
New section before [basic.stc.static]
The keyword __thread applied to a non-local object gives the object thread
storage duration.
A local variable or class data member declared both static and __thread
gives the variable or member thread storage duration.
[basic.stc.static]
Change paragraph 1
All objects that have neither thread storage duration, dynamic storage
duration nor are local [. . . ].
[dcl.stc]
Add __thread to the list in paragraph 1.
Change paragraph 1
With the exception of __thread, at most one storage-class-specifier shall
appear in a given decl-specifier-seq. The __thread specifier may be used
alone, or immediately following the extern or static specifiers. [. . . ]
Add after paragraph 5
The __thread specifier can be applied only to the names of objects and to
anonymous unions.
[class.mem]
Add after paragraph 6
Non-static members shall not be __thread.

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6.64 Binary Constants using the ‘0b’ Prefix
Integer constants can be written as binary constants, consisting of a sequence of ‘0’ and ‘1’
digits, prefixed by ‘0b’ or ‘0B’. This is particularly useful in environments that operate a
lot on the bit level (like microcontrollers).
The following statements are identical:
i
i
i
i

=
42;
=
0x2a;
=
052;
= 0b101010;

The type of these constants follows the same rules as for octal or hexadecimal integer
constants, so suffixes like ‘L’ or ‘UL’ can be applied.

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7 Extensions to the C++ Language
The GNU compiler provides these extensions to the C++ language (and you can also use
most of the C language extensions in your C++ programs). If you want to write code
that checks whether these features are available, you can test for the GNU compiler the
same way as for C programs: check for a predefined macro __GNUC__. You can also use
__GNUG__ to test specifically for GNU C++ (see Section “Predefined Macros” in The GNU
C Preprocessor).

7.1 When is a Volatile C++ Object Accessed?
The C++ standard differs from the C standard in its treatment of volatile objects. It fails to
specify what constitutes a volatile access, except to say that C++ should behave in a similar
manner to C with respect to volatiles, where possible. However, the different lvalueness of
expressions between C and C++ complicate the behavior. G++ behaves the same as GCC
for volatile access, See Chapter 6 [Volatiles], page 439, for a description of GCC’s behavior.
The C and C++ language specifications differ when an object is accessed in a void context:
volatile int *src = somevalue;
*src;

The C++ standard specifies that such expressions do not undergo lvalue to rvalue conversion, and that the type of the dereferenced object may be incomplete. The C++ standard
does not specify explicitly that it is lvalue to rvalue conversion that is responsible for causing
an access. There is reason to believe that it is, because otherwise certain simple expressions become undefined. However, because it would surprise most programmers, G++ treats
dereferencing a pointer to volatile object of complete type as GCC would do for an equivalent type in C. When the object has incomplete type, G++ issues a warning; if you wish to
force an error, you must force a conversion to rvalue with, for instance, a static cast.
When using a reference to volatile, G++ does not treat equivalent expressions as accesses
to volatiles, but instead issues a warning that no volatile is accessed. The rationale for
this is that otherwise it becomes difficult to determine where volatile access occur, and not
possible to ignore the return value from functions returning volatile references. Again, if
you wish to force a read, cast the reference to an rvalue.
G++ implements the same behavior as GCC does when assigning to a volatile object—
there is no reread of the assigned-to object, the assigned rvalue is reused. Note that in C++
assignment expressions are lvalues, and if used as an lvalue, the volatile object is referred
to. For instance, vref refers to vobj, as expected, in the following example:
volatile int vobj;
volatile int &vref = vobj = something;

7.2 Restricting Pointer Aliasing
As with the C front end, G++ understands the C99 feature of restricted pointers, specified
with the __restrict__, or __restrict type qualifier. Because you cannot compile C++ by
specifying the ‘-std=c99’ language flag, restrict is not a keyword in C++.
In addition to allowing restricted pointers, you can specify restricted references, which
indicate that the reference is not aliased in the local context.

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void fn (int *__restrict__ rptr, int &__restrict__ rref)
{
/* . . . */
}

In the body of fn, rptr points to an unaliased integer and rref refers to a (different) unaliased
integer.
You may also specify whether a member function’s this pointer is unaliased by using
__restrict__ as a member function qualifier.
void T::fn () __restrict__
{
/* . . . */
}

Within the body of T::fn, this has the effective definition T *__restrict__ const this.
Notice that the interpretation of a __restrict__ member function qualifier is different to
that of const or volatile qualifier, in that it is applied to the pointer rather than the
object. This is consistent with other compilers that implement restricted pointers.
As with all outermost parameter qualifiers, __restrict__ is ignored in function definition
matching. This means you only need to specify __restrict__ in a function definition,
rather than in a function prototype as well.

7.3 Vague Linkage
There are several constructs in C++ that require space in the object file but are not clearly
tied to a single translation unit. We say that these constructs have “vague linkage”. Typically such constructs are emitted wherever they are needed, though sometimes we can be
more clever.
Inline Functions
Inline functions are typically defined in a header file which can be included
in many different compilations. Hopefully they can usually be inlined, but
sometimes an out-of-line copy is necessary, if the address of the function is taken
or if inlining fails. In general, we emit an out-of-line copy in all translation units
where one is needed. As an exception, we only emit inline virtual functions with
the vtable, since it always requires a copy.
Local static variables and string constants used in an inline function are also
considered to have vague linkage, since they must be shared between all inlined
and out-of-line instances of the function.
VTables

C++ virtual functions are implemented in most compilers using a lookup table,
known as a vtable. The vtable contains pointers to the virtual functions provided by a class, and each object of the class contains a pointer to its vtable (or
vtables, in some multiple-inheritance situations). If the class declares any noninline, non-pure virtual functions, the first one is chosen as the “key method”
for the class, and the vtable is only emitted in the translation unit where the
key method is defined.
Note: If the chosen key method is later defined as inline, the vtable is still
emitted in every translation unit that defines it. Make sure that any inline
virtuals are declared inline in the class body, even if they are not defined there.

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type_info objects
C++ requires information about types to be written out in order to implement
‘dynamic_cast’, ‘typeid’ and exception handling. For polymorphic classes
(classes with virtual functions), the ‘type_info’ object is written out along
with the vtable so that ‘dynamic_cast’ can determine the dynamic type of a
class object at run time. For all other types, we write out the ‘type_info’
object when it is used: when applying ‘typeid’ to an expression, throwing an
object, or referring to a type in a catch clause or exception specification.
Template Instantiations
Most everything in this section also applies to template instantiations, but there
are other options as well. See Section 7.5 [Where’s the Template?], page 790.
When used with GNU ld version 2.8 or later on an ELF system such as GNU/Linux or
Solaris 2, or on Microsoft Windows, duplicate copies of these constructs will be discarded
at link time. This is known as COMDAT support.
On targets that don’t support COMDAT, but do support weak symbols, GCC uses them.
This way one copy overrides all the others, but the unused copies still take up space in the
executable.
For targets that do not support either COMDAT or weak symbols, most entities with
vague linkage are emitted as local symbols to avoid duplicate definition errors from the
linker. This does not happen for local statics in inlines, however, as having multiple copies
almost certainly breaks things.
See Section 7.4 [Declarations and Definitions in One Header], page 789, for another way
to control placement of these constructs.

7.4 C++ Interface and Implementation Pragmas
#pragma interface and #pragma implementation provide the user with a way of explicitly
directing the compiler to emit entities with vague linkage (and debugging information) in a
particular translation unit.
Note: These #pragmas have been superceded as of GCC 2.7.2 by COMDAT support and
the “key method” heuristic mentioned in Section 7.3 [Vague Linkage], page 788. Using
them can actually cause your program to grow due to unnecessary out-of-line copies of
inline functions.
#pragma interface
#pragma interface "subdir/objects.h"
Use this directive in header files that define object classes, to save space in
most of the object files that use those classes. Normally, local copies of certain
information (backup copies of inline member functions, debugging information,
and the internal tables that implement virtual functions) must be kept in each
object file that includes class definitions. You can use this pragma to avoid such
duplication. When a header file containing ‘#pragma interface’ is included in
a compilation, this auxiliary information is not generated (unless the main
input source file itself uses ‘#pragma implementation’). Instead, the object
files contain references to be resolved at link time.

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The second form of this directive is useful for the case where you have multiple
headers with the same name in different directories. If you use this form, you
must specify the same string to ‘#pragma implementation’.
#pragma implementation
#pragma implementation "objects.h"
Use this pragma in a main input file, when you want full output from included
header files to be generated (and made globally visible). The included header
file, in turn, should use ‘#pragma interface’. Backup copies of inline member
functions, debugging information, and the internal tables used to implement
virtual functions are all generated in implementation files.
If you use ‘#pragma implementation’ with no argument, it applies to an
include file with the same basename1 as your source file. For example, in
‘allclass.cc’, giving just ‘#pragma implementation’ by itself is equivalent
to ‘#pragma implementation "allclass.h"’.
Use the string argument if you want a single implementation file to include code
from multiple header files. (You must also use ‘#include’ to include the header
file; ‘#pragma implementation’ only specifies how to use the file—it doesn’t
actually include it.)
There is no way to split up the contents of a single header file into multiple
implementation files.
‘#pragma implementation’ and ‘#pragma interface’ also have an effect on function inlining.
If you define a class in a header file marked with ‘#pragma interface’, the effect on
an inline function defined in that class is similar to an explicit extern declaration—the
compiler emits no code at all to define an independent version of the function. Its definition
is used only for inlining with its callers.
Conversely, when you include the same header file in a main source file that declares it
as ‘#pragma implementation’, the compiler emits code for the function itself; this defines
a version of the function that can be found via pointers (or by callers compiled without
inlining). If all calls to the function can be inlined, you can avoid emitting the function by
compiling with ‘-fno-implement-inlines’. If any calls are not inlined, you will get linker
errors.

7.5 Where’s the Template?
C++ templates were the first language feature to require more intelligence from the environment than was traditionally found on a UNIX system. Somehow the compiler and linker
have to make sure that each template instance occurs exactly once in the executable if it
is needed, and not at all otherwise. There are two basic approaches to this problem, which
are referred to as the Borland model and the Cfront model.
Borland model
Borland C++ solved the template instantiation problem by adding the code
equivalent of common blocks to their linker; the compiler emits template in1

A file’s basename is the name stripped of all leading path information and of trailing suffixes, such as ‘.h’
or ‘.C’ or ‘.cc’.

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stances in each translation unit that uses them, and the linker collapses them
together. The advantage of this model is that the linker only has to consider
the object files themselves; there is no external complexity to worry about. The
disadvantage is that compilation time is increased because the template code
is being compiled repeatedly. Code written for this model tends to include
definitions of all templates in the header file, since they must be seen to be
instantiated.
Cfront model
The AT&T C++ translator, Cfront, solved the template instantiation problem
by creating the notion of a template repository, an automatically maintained
place where template instances are stored. A more modern version of the repository works as follows: As individual object files are built, the compiler places
any template definitions and instantiations encountered in the repository. At
link time, the link wrapper adds in the objects in the repository and compiles
any needed instances that were not previously emitted. The advantages of this
model are more optimal compilation speed and the ability to use the system
linker; to implement the Borland model a compiler vendor also needs to replace
the linker. The disadvantages are vastly increased complexity, and thus potential for error; for some code this can be just as transparent, but in practice
it can been very difficult to build multiple programs in one directory and one
program in multiple directories. Code written for this model tends to separate
definitions of non-inline member templates into a separate file, which should be
compiled separately.
G++ implements the Borland model on targets where the linker supports it, including
ELF targets (such as GNU/Linux), Mac OS X and Microsoft Windows. Otherwise G++
implements neither automatic model.
You have the following options for dealing with template instantiations:
1. Do nothing. Code written for the Borland model works fine, but each translation
unit contains instances of each of the templates it uses. The duplicate instances will
be discarded by the linker, but in a large program, this can lead to an unacceptable
amount of code duplication in object files or shared libraries.
Duplicate instances of a template can be avoided by defining an explicit instantiation
in one object file, and preventing the compiler from doing implicit instantiations in
any other object files by using an explicit instantiation declaration, using the extern
template syntax:
extern template int max (int, int);

This syntax is defined in the C++ 2011 standard, but has been supported by G++ and
other compilers since well before 2011.
Explicit instantiations can be used for the largest or most frequently duplicated instances, without having to know exactly which other instances are used in the rest
of the program. You can scatter the explicit instantiations throughout your program,
perhaps putting them in the translation units where the instances are used or the
translation units that define the templates themselves; you can put all of the explicit
instantiations you need into one big file; or you can create small files like
#include "Foo.h"

792

Using the GNU Compiler Collection (GCC)

#include "Foo.cc"
template class Foo;
template ostream& operator <<
(ostream&, const Foo&);

for each of the instances you need, and create a template instantiation library from
those.
This is the simplest option, but also offers flexibility and fine-grained control when
necessary. It is also the most portable alternative and programs using this approach
will work with most modern compilers.
2. Compile your template-using code with ‘-frepo’. The compiler generates files with
the extension ‘.rpo’ listing all of the template instantiations used in the corresponding
object files that could be instantiated there; the link wrapper, ‘collect2’, then updates
the ‘.rpo’ files to tell the compiler where to place those instantiations and rebuild any
affected object files. The link-time overhead is negligible after the first pass, as the
compiler continues to place the instantiations in the same files.
This can be a suitable option for application code written for the Borland model, as it
usually just works. Code written for the Cfront model needs to be modified so that the
template definitions are available at one or more points of instantiation; usually this is
as simple as adding #include  to the end of each template header.
For library code, if you want the library to provide all of the template instantiations
it needs, just try to link all of its object files together; the link will fail, but cause
the instantiations to be generated as a side effect. Be warned, however, that this may
cause conflicts if multiple libraries try to provide the same instantiations. For greater
control, use explicit instantiation as described in the next option.
3. Compile your code with ‘-fno-implicit-templates’ to disable the implicit generation
of template instances, and explicitly instantiate all the ones you use. This approach
requires more knowledge of exactly which instances you need than do the others, but it’s
less mysterious and allows greater control if you want to ensure that only the intended
instances are used.
If you are using Cfront-model code, you can probably get away with not using
‘-fno-implicit-templates’ when compiling files that don’t ‘#include’ the member
template definitions.
If you use one big file to do the instantiations, you may want to compile it without
‘-fno-implicit-templates’ so you get all of the instances required by your explicit
instantiations (but not by any other files) without having to specify them as well.
In addition to forward declaration of explicit instantiations (with extern), G++ has
extended the template instantiation syntax to support instantiation of the compiler
support data for a template class (i.e. the vtable) without instantiating any of its
members (with inline), and instantiation of only the static data members of a template
class, without the support data or member functions (with static):
inline template class Foo;
static template class Foo;

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7.6 Extracting the Function Pointer from a Bound Pointer
to Member Function
In C++, pointer to member functions (PMFs) are implemented using a wide pointer of sorts
to handle all the possible call mechanisms; the PMF needs to store information about how
to adjust the ‘this’ pointer, and if the function pointed to is virtual, where to find the
vtable, and where in the vtable to look for the member function. If you are using PMFs in
an inner loop, you should really reconsider that decision. If that is not an option, you can
extract the pointer to the function that would be called for a given object/PMF pair and
call it directly inside the inner loop, to save a bit of time.
Note that you still pay the penalty for the call through a function pointer; on most
modern architectures, such a call defeats the branch prediction features of the CPU. This
is also true of normal virtual function calls.
The syntax for this extension is
extern A a;
extern int (A::*fp)();
typedef int (*fptr)(A *);
fptr p = (fptr)(a.*fp);

For PMF constants (i.e. expressions of the form ‘&Klasse::Member’), no object is needed
to obtain the address of the function. They can be converted to function pointers directly:
fptr p1 = (fptr)(&A::foo);

You must specify ‘-Wno-pmf-conversions’ to use this extension.

7.7 C++-Specific Variable, Function, and Type Attributes
Some attributes only make sense for C++ programs.
abi_tag ("tag", ...)
The abi_tag attribute can be applied to a function, variable, or class declaration. It modifies the mangled name of the entity to incorporate the tag name, in
order to distinguish the function or class from an earlier version with a different
ABI; perhaps the class has changed size, or the function has a different return
type that is not encoded in the mangled name.
The attribute can also be applied to an inline namespace, but does not affect
the mangled name of the namespace; in this case it is only used for ‘-Wabi-tag’
warnings and automatic tagging of functions and variables. Tagging inline
namespaces is generally preferable to tagging individual declarations, but the
latter is sometimes necessary, such as when only certain members of a class
need to be tagged.
The argument can be a list of strings of arbitrary length. The strings are sorted
on output, so the order of the list is unimportant.
A redeclaration of an entity must not add new ABI tags, since doing so would
change the mangled name.
The ABI tags apply to a name, so all instantiations and specializations of a
template have the same tags. The attribute will be ignored if applied to an
explicit specialization or instantiation.
The ‘-Wabi-tag’ flag enables a warning about a class which does not have all
the ABI tags used by its subobjects and virtual functions; for users with code

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that needs to coexist with an earlier ABI, using this option can help to find all
affected types that need to be tagged.
When a type involving an ABI tag is used as the type of a variable or return type of a function where that tag is not already present in the signature
of the function, the tag is automatically applied to the variable or function.
‘-Wabi-tag’ also warns about this situation; this warning can be avoided by
explicitly tagging the variable or function or moving it into a tagged inline
namespace.
init_priority (priority)
In Standard C++, objects defined at namespace scope are guaranteed to be
initialized in an order in strict accordance with that of their definitions in a given
translation unit. No guarantee is made for initializations across translation
units. However, GNU C++ allows users to control the order of initialization
of objects defined at namespace scope with the init_priority attribute by
specifying a relative priority, a constant integral expression currently bounded
between 101 and 65535 inclusive. Lower numbers indicate a higher priority.
In the following example, A would normally be created before B, but the init_
priority attribute reverses that order:
Some_Class
Some_Class

A
B

__attribute__ ((init_priority (2000)));
__attribute__ ((init_priority (543)));

Note that the particular values of priority do not matter; only their relative
ordering.
warn_unused
For C++ types with non-trivial constructors and/or destructors it is impossible
for the compiler to determine whether a variable of this type is truly unused if
it is not referenced. This type attribute informs the compiler that variables of
this type should be warned about if they appear to be unused, just like variables
of fundamental types.
This attribute is appropriate for types which just represent a value, such as
std::string; it is not appropriate for types which control a resource, such as
std::lock_guard.
This attribute is also accepted in C, but it is unnecessary because C does not
have constructors or destructors.

7.8 Function Multiversioning
With the GNU C++ front end, for x86 targets, you may specify multiple versions of a
function, where each function is specialized for a specific target feature. At runtime, the
appropriate version of the function is automatically executed depending on the characteristics of the execution platform. Here is an example.
__attribute__ ((target ("default")))
int foo ()
{
// The default version of foo.
return 0;
}

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__attribute__ ((target ("sse4.2")))
int foo ()
{
// foo version for SSE4.2
return 1;
}
__attribute__ ((target ("arch=atom")))
int foo ()
{
// foo version for the Intel ATOM processor
return 2;
}
__attribute__ ((target ("arch=amdfam10")))
int foo ()
{
// foo version for the AMD Family 0x10 processors.
return 3;
}
int main ()
{
int (*p)() = &foo;
assert ((*p) () == foo ());
return 0;
}

In the above example, four versions of function foo are created. The first version of foo
with the target attribute "default" is the default version. This version gets executed when
no other target specific version qualifies for execution on a particular platform. A new
version of foo is created by using the same function signature but with a different target
string. Function foo is called or a pointer to it is taken just like a regular function. GCC
takes care of doing the dispatching to call the right version at runtime. Refer to the GCC
wiki on Function Multiversioning for more details.

7.9 Type Traits
The C++ front end implements syntactic extensions that allow compile-time determination
of various characteristics of a type (or of a pair of types).
__has_nothrow_assign (type)
If type is const qualified or is a reference type then the trait is false. Otherwise
if __has_trivial_assign (type) is true then the trait is true, else if type is
a cv class or union type with copy assignment operators that are known not
to throw an exception then the trait is true, else it is false. Requires: type
shall be a complete type, (possibly cv-qualified) void, or an array of unknown
bound.
__has_nothrow_copy (type)
If __has_trivial_copy (type) is true then the trait is true, else if type is
a cv class or union type with copy constructors that are known not to throw
an exception then the trait is true, else it is false. Requires: type shall be a
complete type, (possibly cv-qualified) void, or an array of unknown bound.

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__has_nothrow_constructor (type)
If __has_trivial_constructor (type) is true then the trait is true, else if
type is a cv class or union type (or array thereof) with a default constructor
that is known not to throw an exception then the trait is true, else it is false.
Requires: type shall be a complete type, (possibly cv-qualified) void, or an
array of unknown bound.
__has_trivial_assign (type)
If type is const qualified or is a reference type then the trait is false. Otherwise
if __is_pod (type) is true then the trait is true, else if type is a cv class or
union type with a trivial copy assignment ([class.copy]) then the trait is true,
else it is false. Requires: type shall be a complete type, (possibly cv-qualified)
void, or an array of unknown bound.
__has_trivial_copy (type)
If __is_pod (type) is true or type is a reference type then the trait is true, else
if type is a cv class or union type with a trivial copy constructor ([class.copy])
then the trait is true, else it is false. Requires: type shall be a complete type,
(possibly cv-qualified) void, or an array of unknown bound.
__has_trivial_constructor (type)
If __is_pod (type) is true then the trait is true, else if type is a cv class or
union type (or array thereof) with a trivial default constructor ([class.ctor])
then the trait is true, else it is false. Requires: type shall be a complete type,
(possibly cv-qualified) void, or an array of unknown bound.
__has_trivial_destructor (type)
If __is_pod (type) is true or type is a reference type then the trait is true, else
if type is a cv class or union type (or array thereof) with a trivial destructor
([class.dtor]) then the trait is true, else it is false. Requires: type shall be a
complete type, (possibly cv-qualified) void, or an array of unknown bound.
__has_virtual_destructor (type)
If type is a class type with a virtual destructor ([class.dtor]) then the trait
is true, else it is false. Requires: type shall be a complete type, (possibly
cv-qualified) void, or an array of unknown bound.
__is_abstract (type)
If type is an abstract class ([class.abstract]) then the trait is true, else it is
false. Requires: type shall be a complete type, (possibly cv-qualified) void, or
an array of unknown bound.
__is_base_of (base_type, derived_type)
If base_type is a base class of derived_type ([class.derived]) then the trait
is true, otherwise it is false. Top-level cv qualifications of base_type and
derived_type are ignored. For the purposes of this trait, a class type is considered is own base. Requires: if __is_class (base_type) and __is_class
(derived_type) are true and base_type and derived_type are not the same
type (disregarding cv-qualifiers), derived_type shall be a complete type. A
diagnostic is produced if this requirement is not met.

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__is_class (type)
If type is a cv class type, and not a union type ([basic.compound]) the trait is
true, else it is false.
__is_empty (type)
If __is_class (type) is false then the trait is false. Otherwise type is considered empty if and only if: type has no non-static data members, or all
non-static data members, if any, are bit-fields of length 0, and type has no
virtual members, and type has no virtual base classes, and type has no base
classes base_type for which __is_empty (base_type) is false. Requires: type
shall be a complete type, (possibly cv-qualified) void, or an array of unknown
bound.
__is_enum (type)
If type is a cv enumeration type ([basic.compound]) the trait is true, else it is
false.
__is_literal_type (type)
If type is a literal type ([basic.types]) the trait is true, else it is false. Requires:
type shall be a complete type, (possibly cv-qualified) void, or an array of
unknown bound.
__is_pod (type)
If type is a cv POD type ([basic.types]) then the trait is true, else it is false.
Requires: type shall be a complete type, (possibly cv-qualified) void, or an
array of unknown bound.
__is_polymorphic (type)
If type is a polymorphic class ([class.virtual]) then the trait is true, else it is
false. Requires: type shall be a complete type, (possibly cv-qualified) void, or
an array of unknown bound.
__is_standard_layout (type)
If type is a standard-layout type ([basic.types]) the trait is true, else it is false.
Requires: type shall be a complete type, (possibly cv-qualified) void, or an
array of unknown bound.
__is_trivial (type)
If type is a trivial type ([basic.types]) the trait is true, else it is false. Requires:
type shall be a complete type, (possibly cv-qualified) void, or an array of
unknown bound.
__is_union (type)
If type is a cv union type ([basic.compound]) the trait is true, else it is false.
__underlying_type (type)
The underlying type of type. Requires: type shall be an enumeration type
([dcl.enum]).
__integer_pack (length)
When used as the pattern of a pack expansion within a template definition,
expands to a template argument pack containing integers from 0 to length-1.
This is provided for efficient implementation of std::make_integer_sequence.

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7.10 C++ Concepts
C++ concepts provide much-improved support for generic programming. In particular, they
allow the specification of constraints on template arguments. The constraints are used to
extend the usual overloading and partial specialization capabilities of the language, allowing
generic data structures and algorithms to be “refined” based on their properties rather than
their type names.
The following keywords are reserved for concepts.
assumes

States an expression as an assumption, and if possible, verifies that the assumption is valid. For example, assume(n > 0).

axiom

Introduces an axiom definition. Axioms introduce requirements on values.

forall

Introduces a universally quantified object in an axiom. For example, forall
(int n) n + 0 == n).

concept

Introduces a concept definition. Concepts are sets of syntactic and semantic
requirements on types and their values.

requires

Introduces constraints on template arguments or requirements for a member
function of a class template.

The front end also exposes a number of internal mechanism that can be used to simplify
the writing of type traits. Note that some of these traits are likely to be removed in the
future.
__is_same (type1, type2)
A binary type trait: true whenever the type arguments are the same.

7.11 Deprecated Features
In the past, the GNU C++ compiler was extended to experiment with new features, at a
time when the C++ language was still evolving. Now that the C++ standard is complete,
some of those features are superseded by superior alternatives. Using the old features might
cause a warning in some cases that the feature will be dropped in the future. In other cases,
the feature might be gone already.
While the list below is not exhaustive, it documents some of the options that are now
deprecated or have been removed:
-fno-for-scope
-ffriend-injection
These two options provide compatibility with pre-standard C++.
Section 7.12 [Backwards Compatibility], page 799.

See

G++ allows a virtual function returning ‘void *’ to be overridden by one returning a
different pointer type. This extension to the covariant return type rules is now deprecated
and will be removed from a future version.
The use of default arguments in function pointers, function typedefs and other places
where they are not permitted by the standard is deprecated and will be removed from a
future version of G++.

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799

G++ allows floating-point literals to appear in integral constant expressions, e.g. ‘ enum E
{ e = int(2.2 * 3.7) } ’ This extension is deprecated and will be removed from a future
version.
G++ allows static data members of const floating-point type to be declared with an
initializer in a class definition. The standard only allows initializers for static members of
const integral types and const enumeration types so this extension has been deprecated and
will be removed from a future version.
G++ allows attributes to follow a parenthesized direct initializer, e.g. ‘ int f (0)
__attribute__ ((something)); ’ This extension has been ignored since G++ 3.3 and is
deprecated.
G++ allows anonymous structs and unions to have members that are not public non-static
data members (i.e. fields). These extensions are deprecated.

7.12 Backwards Compatibility
Now that there is a definitive ISO standard C++, G++ has a specification to adhere to. The
C++ language evolved over time, and features that used to be acceptable in previous drafts of
the standard, such as the ARM [Annotated C++ Reference Manual], are no longer accepted.
In order to allow compilation of C++ written to such drafts, G++ contains some backwards
compatibilities. All such backwards compatibility features are liable to disappear in future
versions of G++. They should be considered deprecated. See Section 7.11 [Deprecated
Features], page 798.
For scope If a variable is declared at for scope, it used to remain in scope until the end
of the scope that contained the for statement (rather than just within the for
scope). The deprecated ‘-fno-for-scope’ option enables this non-standard
behavior. Without the option, G++ retains this, but issues a warning, if such a
variable is accessed outside the for scope.
The behavior is deprecated, only available with ‘-std=c++98’ ‘-std=gnu++98’
languages and you must use the ‘-fpermissive’ option to enable it. The behavior will be removed.
Friend Injection
The ‘-ffriend-injection’ option makes injected friends visible to regular
name lookup, unlike standard C++. This option is deprecated and will be
removed.
Implicit C language
Old C system header files did not contain an extern "C" {...} scope to set
the language. On such systems, all header files are implicitly scoped inside a
C language scope. Also, an empty prototype () is treated as an unspecified
number of arguments, rather than no arguments, as C++ demands.

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801

8 GNU Objective-C Features
This document is meant to describe some of the GNU Objective-C features. It is not
intended to teach you Objective-C. There are several resources on the Internet that present
the language.

8.1 GNU Objective-C Runtime API
This section is specific for the GNU Objective-C runtime. If you are using a different
runtime, you can skip it.
The GNU Objective-C runtime provides an API that allows you to interact with the
Objective-C runtime system, querying the live runtime structures and even manipulating
them. This allows you for example to inspect and navigate classes, methods and protocols;
to define new classes or new methods, and even to modify existing classes or protocols.
If you are using a “Foundation” library such as GNUstep-Base, this library will provide
you with a rich set of functionality to do most of the inspection tasks, and you probably
will only need direct access to the GNU Objective-C runtime API to define new classes or
methods.

8.1.1 Modern GNU Objective-C Runtime API
The GNU Objective-C runtime provides an API which is similar to the one provided by
the “Objective-C 2.0” Apple/NeXT Objective-C runtime. The API is documented in the
public header files of the GNU Objective-C runtime:
• ‘objc/objc.h’: this is the basic Objective-C header file, defining the basic ObjectiveC types such as id, Class and BOOL. You have to include this header to do almost
anything with Objective-C.
• ‘objc/runtime.h’: this header declares most of the public runtime API functions allowing you to inspect and manipulate the Objective-C runtime data structures. These
functions are fairly standardized across Objective-C runtimes and are almost identical to the Apple/NeXT Objective-C runtime ones. It does not declare functions
in some specialized areas (constructing and forwarding message invocations, threading) which are in the other headers below. You have to include ‘objc/objc.h’ and
‘objc/runtime.h’ to use any of the functions, such as class_getName(), declared in
‘objc/runtime.h’.
• ‘objc/message.h’: this header declares public functions used to construct, deconstruct
and forward message invocations. Because messaging is done in quite a different way
on different runtimes, functions in this header are specific to the GNU Objective-C
runtime implementation.
• ‘objc/objc-exception.h’: this header declares some public functions related to
Objective-C exceptions. For example functions in this header allow you to throw an
Objective-C exception from plain C/C++ code.
• ‘objc/objc-sync.h’: this header declares some public functions related to the
Objective-C @synchronized() syntax, allowing you to emulate an Objective-C
@synchronized() block in plain C/C++ code.

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• ‘objc/thr.h’: this header declares a public runtime API threading layer that is only
provided by the GNU Objective-C runtime. It declares functions such as objc_mutex_
lock(), which provide a platform-independent set of threading functions.
The header files contain detailed documentation for each function in the GNU ObjectiveC runtime API.

8.1.2 Traditional GNU Objective-C Runtime API
The GNU Objective-C runtime used to provide a different API, which we call the “traditional” GNU Objective-C runtime API. Functions belonging to this API are easy to recognize because they use a different naming convention, such as class_get_super_class()
(traditional API) instead of class_getSuperclass() (modern API). Software using this
API includes the file ‘objc/objc-api.h’ where it is declared.
Starting with GCC 4.7.0, the traditional GNU runtime API is no longer available.

8.2 +load: Executing Code before main
This section is specific for the GNU Objective-C runtime. If you are using a different
runtime, you can skip it.
The GNU Objective-C runtime provides a way that allows you to execute code before
the execution of the program enters the main function. The code is executed on a per-class
and a per-category basis, through a special class method +load.
This facility is very useful if you want to initialize global variables which can be accessed
by the program directly, without sending a message to the class first. The usual way
to initialize global variables, in the +initialize method, might not be useful because
+initialize is only called when the first message is sent to a class object, which in some
cases could be too late.
Suppose for example you have a FileStream class that declares Stdin, Stdout and
Stderr as global variables, like below:
FileStream *Stdin = nil;
FileStream *Stdout = nil;
FileStream *Stderr = nil;
@implementation FileStream
+ (void)initialize
{
Stdin = [[FileStream new] initWithFd:0];
Stdout = [[FileStream new] initWithFd:1];
Stderr = [[FileStream new] initWithFd:2];
}
/* Other methods here */
@end

In this example, the initialization of Stdin, Stdout and Stderr in +initialize occurs
too late. The programmer can send a message to one of these objects before the variables
are actually initialized, thus sending messages to the nil object. The +initialize method
which actually initializes the global variables is not invoked until the first message is sent

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to the class object. The solution would require these variables to be initialized just before
entering main.
The correct solution of the above problem is to use the +load method instead of
+initialize:
@implementation FileStream
+ (void)load
{
Stdin = [[FileStream new] initWithFd:0];
Stdout = [[FileStream new] initWithFd:1];
Stderr = [[FileStream new] initWithFd:2];
}
/* Other methods here */
@end

The +load is a method that is not overridden by categories. If a class and a category of
it both implement +load, both methods are invoked. This allows some additional initializations to be performed in a category.
This mechanism is not intended to be a replacement for +initialize. You should be
aware of its limitations when you decide to use it instead of +initialize.

8.2.1 What You Can and Cannot Do in +load
+load is to be used only as a last resort. Because it is executed very early, most of the
Objective-C runtime machinery will not be ready when +load is executed; hence +load
works best for executing C code that is independent on the Objective-C runtime.
The +load implementation in the GNU runtime guarantees you the following things:
• you can write whatever C code you like;
• you can allocate and send messages to objects whose class is implemented in the same
file;
• the +load implementation of all super classes of a class are executed before the +load
of that class is executed;
• the +load implementation of a class is executed before the +load implementation of
any category.
In particular, the following things, even if they can work in a particular case, are not
guaranteed:
• allocation of or sending messages to arbitrary objects;
• allocation of or sending messages to objects whose classes have a category implemented
in the same file;
• sending messages to Objective-C constant strings (@"this is a constant string");
You should make no assumptions about receiving +load in sibling classes when you write
+load of a class. The order in which sibling classes receive +load is not guaranteed.
The order in which +load and +initialize are called could be problematic if this matters. If you don’t allocate objects inside +load, it is guaranteed that +load is called before
+initialize. If you create an object inside +load the +initialize method of object’s

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class is invoked even if +load was not invoked. Note if you explicitly call +load on a class,
+initialize will be called first. To avoid possible problems try to implement only one of
these methods.
The +load method is also invoked when a bundle is dynamically loaded into your running
program. This happens automatically without any intervening operation from you. When
you write bundles and you need to write +load you can safely create and send messages to
objects whose classes already exist in the running program. The same restrictions as above
apply to classes defined in bundle.

8.3 Type Encoding
This is an advanced section. Type encodings are used extensively by the compiler and by
the runtime, but you generally do not need to know about them to use Objective-C.
The Objective-C compiler generates type encodings for all the types. These type encodings are used at runtime to find out information about selectors and methods and about
objects and classes.
The types are encoded in the following way:
_Bool
char
unsigned char
short
unsigned short
int
unsigned int
long
unsigned long
long long
unsigned long long
float
double
long double
void
id
Class
SEL
char*
enum

unknown type
Complex types
bit-fields

B
c
C
s
S
i
I
l
L
q
Q
f
d
D
v
@
#
:
*
an enum is encoded exactly as the integer type that the compiler
uses for it, which depends on the enumeration values. Often the
compiler users unsigned int, which is then encoded as I.
?
j followed by the inner type. For example _Complex double is
encoded as "jd".
b followed by the starting position of the bit-field, the type of the
bit-field and the size of the bit-field (the bit-fields encoding was
changed from the NeXT’s compiler encoding, see below)

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The encoding of bit-fields has changed to allow bit-fields to be properly handled by the
runtime functions that compute sizes and alignments of types that contain bit-fields. The
previous encoding contained only the size of the bit-field. Using only this information it is
not possible to reliably compute the size occupied by the bit-field. This is very important
in the presence of the Boehm’s garbage collector because the objects are allocated using
the typed memory facility available in this collector. The typed memory allocation requires
information about where the pointers are located inside the object.
The position in the bit-field is the position, counting in bits, of the bit closest to the
beginning of the structure.
The non-atomic types are encoded as follows:
pointers
arrays
structures
unions
vectors

‘^’ followed by the pointed type.
‘[’ followed by the number of elements in the array followed by the
type of the elements followed by ‘]’
‘{’ followed by the name of the structure (or ‘?’ if the structure is
unnamed), the ‘=’ sign, the type of the members and by ‘}’
‘(’ followed by the name of the structure (or ‘?’ if the union is unnamed), the ‘=’ sign, the type of the members followed by ‘)’
‘![’ followed by the vector size (the number of bytes composing the
vector) followed by a comma, followed by the alignment (in bytes) of
the vector, followed by the type of the elements followed by ‘]’

Here are some types and their encodings, as they are generated by the compiler on an
i386 machine:
Objective-C type

Compiler encoding
[10i]

int a[10];
struct {
int i;
float f[3];
int a:3;
int b:2;
char c;
}

{?=i[3f]b128i3b131i2c}

int a __attribute__ ((vector_size (16)));

![16,16i] (alignment depends on
the machine)

In addition to the types the compiler also encodes the type specifiers. The table below
describes the encoding of the current Objective-C type specifiers:
Specifier
const
in
inout
out
bycopy

Encoding
r
n
N
o
O

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byref
oneway

R
V

The type specifiers are encoded just before the type. Unlike types however, the type
specifiers are only encoded when they appear in method argument types.
Note how const interacts with pointers:
Objective-C type
const int

Compiler encoding
ri

const int*

^ri

int *const

r^i

const int* is a pointer to a const int, and so is encoded as ^ri. int* const, instead,
is a const pointer to an int, and so is encoded as r^i.
Finally, there is a complication when encoding const char * versus char * const. Because char * is encoded as * and not as ^c, there is no way to express the fact that r applies
to the pointer or to the pointee.
Hence, it is assumed as a convention that r* means const char * (since it is what is
most often meant), and there is no way to encode char *const. char *const would simply
be encoded as *, and the const is lost.

8.3.1 Legacy Type Encoding
Unfortunately, historically GCC used to have a number of bugs in its encoding code. The
NeXT runtime expects GCC to emit type encodings in this historical format (compatible
with GCC-3.3), so when using the NeXT runtime, GCC will introduce on purpose a number
of incorrect encodings:
• the read-only qualifier of the pointee gets emitted before the ’^’. The read-only qualifier
of the pointer itself gets ignored, unless it is a typedef. Also, the ’r’ is only emitted for
the outermost type.
• 32-bit longs are encoded as ’l’ or ’L’, but not always. For typedefs, the compiler uses
’i’ or ’I’ instead if encoding a struct field or a pointer.
• enums are always encoded as ’i’ (int) even if they are actually unsigned or long.
In addition to that, the NeXT runtime uses a different encoding for bitfields. It encodes
them as b followed by the size, without a bit offset or the underlying field type.

8.3.2 @encode
GNU Objective-C supports the @encode syntax that allows you to create a type encoding
from a C/Objective-C type. For example, @encode(int) is compiled by the compiler into
"i".
@encode does not support type qualifiers other than const. For example, @encode(const
char*) is valid and is compiled into "r*", while @encode(bycopy char *) is invalid and
will cause a compilation error.

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8.3.3 Method Signatures
This section documents the encoding of method types, which is rarely needed to use
Objective-C. You should skip it at a first reading; the runtime provides functions that
will work on methods and can walk through the list of parameters and interpret them for
you. These functions are part of the public “API” and are the preferred way to interact
with method signatures from user code.
But if you need to debug a problem with method signatures and need to know how they
are implemented (i.e., the “ABI”), read on.
Methods have their “signature” encoded and made available to the runtime. The “signature” encodes all the information required to dynamically build invocations of the method
at runtime: return type and arguments.
The “signature” is a null-terminated string, composed of the following:
• The return type, including type qualifiers. For example, a method returning int would
have i here.
• The total size (in bytes) required to pass all the parameters. This includes the two
hidden parameters (the object self and the method selector _cmd).
• Each argument, with the type encoding, followed by the offset (in bytes) of the argument in the list of parameters.
For example, a method with no arguments and returning int would have the signature
i8@0:4 if the size of a pointer is 4. The signature is interpreted as follows: the i is the
return type (an int), the 8 is the total size of the parameters in bytes (two pointers each
of size 4), the @0 is the first parameter (an object at byte offset 0) and :4 is the second
parameter (a SEL at byte offset 4).
You can easily find more examples by running the “strings” program on an Objective-C
object file compiled by GCC. You’ll see a lot of strings that look very much like i8@0:4.
They are signatures of Objective-C methods.

8.4 Garbage Collection
This section is specific for the GNU Objective-C runtime. If you are using a different
runtime, you can skip it.
Support for garbage collection with the GNU runtime has been added by using a powerful
conservative garbage collector, known as the Boehm-Demers-Weiser conservative garbage
collector.
To enable the support for it you have to configure the compiler using an additional argument, ‘--enable-objc-gc’. This will build the boehm-gc library, and build an additional
runtime library which has several enhancements to support the garbage collector. The
new library has a new name, ‘libobjc_gc.a’ to not conflict with the non-garbage-collected
library.
When the garbage collector is used, the objects are allocated using the so-called typed
memory allocation mechanism available in the Boehm-Demers-Weiser collector. This mode
requires precise information on where pointers are located inside objects. This information
is computed once per class, immediately after the class has been initialized.

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There is a new runtime function class_ivar_set_gcinvisible() which can be used to
declare a so-called weak pointer reference. Such a pointer is basically hidden for the garbage
collector; this can be useful in certain situations, especially when you want to keep track
of the allocated objects, yet allow them to be collected. This kind of pointers can only be
members of objects, you cannot declare a global pointer as a weak reference. Every type
which is a pointer type can be declared a weak pointer, including id, Class and SEL.
Here is an example of how to use this feature. Suppose you want to implement a class
whose instances hold a weak pointer reference; the following class does this:
@interface WeakPointer : Object
{
const void* weakPointer;
}
- initWithPointer:(const void*)p;
- (const void*)weakPointer;
@end

@implementation WeakPointer
+ (void)initialize
{
if (self == objc_lookUpClass ("WeakPointer"))
class_ivar_set_gcinvisible (self, "weakPointer", YES);
}
- initWithPointer:(const void*)p
{
weakPointer = p;
return self;
}
- (const void*)weakPointer
{
return weakPointer;
}
@end

Weak pointers are supported through a new type character specifier represented by the
‘!’ character. The class_ivar_set_gcinvisible() function adds or removes this specifier
to the string type description of the instance variable named as argument.

8.5 Constant String Objects
GNU Objective-C provides constant string objects that are generated directly by the compiler. You declare a constant string object by prefixing a C constant string with the character
‘@’:
id myString = @"this is a constant string object";

The constant string objects are by default instances of the NXConstantString class which
is provided by the GNU Objective-C runtime. To get the definition of this class you must
include the ‘objc/NXConstStr.h’ header file.

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User defined libraries may want to implement their own constant string class. To be able
to support them, the GNU Objective-C compiler provides a new command line options
‘-fconstant-string-class=class-name’. The provided class should adhere to a strict
structure, the same as NXConstantString’s structure:
@interface MyConstantStringClass
{
Class isa;
char *c_string;
unsigned int len;
}
@end

NXConstantString inherits from Object; user class libraries may choose to inherit the
customized constant string class from a different class than Object. There is no requirement
in the methods the constant string class has to implement, but the final ivar layout of the
class must be the compatible with the given structure.
When the compiler creates the statically allocated constant string object, the c_string
field will be filled by the compiler with the string; the length field will be filled by the
compiler with the string length; the isa pointer will be filled with NULL by the compiler,
and it will later be fixed up automatically at runtime by the GNU Objective-C runtime
library to point to the class which was set by the ‘-fconstant-string-class’ option when
the object file is loaded (if you wonder how it works behind the scenes, the name of the
class to use, and the list of static objects to fixup, are stored by the compiler in the object
file in a place where the GNU runtime library will find them at runtime).
As a result, when a file is compiled with the ‘-fconstant-string-class’ option, all the
constant string objects will be instances of the class specified as argument to this option. It
is possible to have multiple compilation units referring to different constant string classes,
neither the compiler nor the linker impose any restrictions in doing this.

8.6 compatibility_alias
The keyword @compatibility_alias allows you to define a class name as equivalent to
another class name. For example:
@compatibility_alias WOApplication GSWApplication;

tells the compiler that each time it encounters WOApplication as a class name, it
should replace it with GSWApplication (that is, WOApplication is just an alias for
GSWApplication).
There are some constraints on how this can be used—
• WOApplication (the alias) must not be an existing class;
• GSWApplication (the real class) must be an existing class.

8.7 Exceptions
GNU Objective-C provides exception support built into the language, as in the following
example:
@try {
...

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@throw expr;
...
}
@catch (AnObjCClass *exc) {
...
@throw expr;
...
@throw;
...
}
@catch (AnotherClass *exc) {
...
}
@catch (id allOthers) {
...
}
@finally {
...
@throw expr;
...
}

The @throw statement may appear anywhere in an Objective-C or Objective-C++ program; when used inside of a @catch block, the @throw may appear without an argument
(as shown above), in which case the object caught by the @catch will be rethrown.
Note that only (pointers to) Objective-C objects may be thrown and caught using this
scheme. When an object is thrown, it will be caught by the nearest @catch clause capable
of handling objects of that type, analogously to how catch blocks work in C++ and Java.
A @catch(id ...) clause (as shown above) may also be provided to catch any and all
Objective-C exceptions not caught by previous @catch clauses (if any).
The @finally clause, if present, will be executed upon exit from the immediately preceding @try ... @catch section. This will happen regardless of whether any exceptions
are thrown, caught or rethrown inside the @try ... @catch section, analogously to the
behavior of the finally clause in Java.
There are several caveats to using the new exception mechanism:
• The ‘-fobjc-exceptions’ command line option must be used when compiling
Objective-C files that use exceptions.
• With the GNU runtime, exceptions are always implemented as “native” exceptions
and it is recommended that the ‘-fexceptions’ and ‘-shared-libgcc’ options are
used when linking.
• With the NeXT runtime, although currently designed to be binary compatible with NS_
HANDLER-style idioms provided by the NSException class, the new exceptions can only
be used on Mac OS X 10.3 (Panther) and later systems, due to additional functionality
needed in the NeXT Objective-C runtime.
• As mentioned above, the new exceptions do not support handling types other than
Objective-C objects. Furthermore, when used from Objective-C++, the Objective-C
exception model does not interoperate with C++ exceptions at this time. This means
you cannot @throw an exception from Objective-C and catch it in C++, or vice versa
(i.e., throw ... @catch).

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8.8 Synchronization
GNU Objective-C provides support for synchronized blocks:
@synchronized (ObjCClass *guard) {
...
}

Upon entering the @synchronized block, a thread of execution shall first check whether
a lock has been placed on the corresponding guard object by another thread. If it has, the
current thread shall wait until the other thread relinquishes its lock. Once guard becomes
available, the current thread will place its own lock on it, execute the code contained in the
@synchronized block, and finally relinquish the lock (thereby making guard available to
other threads).
Unlike Java, Objective-C does not allow for entire methods to be marked @synchronized.
Note that throwing exceptions out of @synchronized blocks is allowed, and will cause the
guarding object to be unlocked properly.
Because of the interactions between synchronization and exception handling, you can only
use @synchronized when compiling with exceptions enabled, that is with the command line
option ‘-fobjc-exceptions’.

8.9 Fast Enumeration
8.9.1 Using Fast Enumeration
GNU Objective-C provides support for the fast enumeration syntax:
id array = ...;
id object;
for (object in array)
{
/* Do something with ’object’ */
}

array needs to be an Objective-C object (usually a collection object, for example an array,
a dictionary or a set) which implements the “Fast Enumeration Protocol” (see below). If
you are using a Foundation library such as GNUstep Base or Apple Cocoa Foundation, all
collection objects in the library implement this protocol and can be used in this way.
The code above would iterate over all objects in array. For each of them, it assigns it to
object, then executes the Do something with ’object’ statements.
Here is a fully worked-out example using a Foundation library (which provides the implementation of NSArray, NSString and NSLog):
NSArray *array = [NSArray arrayWithObjects: @"1", @"2", @"3", nil];
NSString *object;
for (object in array)
NSLog (@"Iterating over %@", object);

8.9.2 C99-Like Fast Enumeration Syntax
A c99-like declaration syntax is also allowed:
id array = ...;

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for (id object in array)
{
/* Do something with ’object’
}

*/

this is completely equivalent to:
id array = ...;
{
id object;
for (object in array)
{
/* Do something with ’object’
}

*/

}

but can save some typing.
Note that the option ‘-std=c99’ is not required to allow this syntax in Objective-C.

8.9.3 Fast Enumeration Details
Here is a more technical description with the gory details. Consider the code
for (object expression in collection expression)
{
statements
}

here is what happens when you run it:
• collection expression is evaluated exactly once and the result is used as the collection object to iterate over. This means it is safe to write code such as for (object in
[NSDictionary keyEnumerator]) ....
• the iteration is implemented by the compiler by repeatedly getting batches of objects
from the collection object using the fast enumeration protocol (see below), then iterating over all objects in the batch. This is faster than a normal enumeration where
objects are retrieved one by one (hence the name “fast enumeration”).
• if there are no objects in the collection, then object expression is set to nil and the
loop immediately terminates.
• if there are objects in the collection, then for each object in the collection (in the
order they are returned) object expression is set to the object, then statements are
executed.
• statements can contain break and continue commands, which will abort the iteration
or skip to the next loop iteration as expected.
• when the iteration ends because there are no more objects to iterate over, object
expression is set to nil. This allows you to determine whether the iteration finished
because a break command was used (in which case object expression will remain
set to the last object that was iterated over) or because it iterated over all the objects
(in which case object expression will be set to nil).
• statements must not make any changes to the collection object; if they do, it is a hard
error and the fast enumeration terminates by invoking objc_enumerationMutation, a
runtime function that normally aborts the program but which can be customized by
Foundation libraries via objc_set_mutation_handler to do something different, such
as raising an exception.

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8.9.4 Fast Enumeration Protocol
If you want your own collection object to be usable with fast enumeration, you need to have
it implement the method
- (unsigned long) countByEnumeratingWithState: (NSFastEnumerationState *)state
objects: (id *)objects
count: (unsigned long)len;

where NSFastEnumerationState must be defined in your code as follows:
typedef struct
{
unsigned long state;
id
*itemsPtr;
unsigned long *mutationsPtr;
unsigned long extra[5];
} NSFastEnumerationState;

If no NSFastEnumerationState is defined in your code, the compiler will automatically
replace NSFastEnumerationState * with struct __objcFastEnumerationState *, where
that type is silently defined by the compiler in an identical way. This can be confusing and
we recommend that you define NSFastEnumerationState (as shown above) instead.
The method is called repeatedly during a fast enumeration to retrieve batches of objects.
Each invocation of the method should retrieve the next batch of objects.
The return value of the method is the number of objects in the current batch; this should
not exceed len, which is the maximum size of a batch as requested by the caller. The batch
itself is returned in the itemsPtr field of the NSFastEnumerationState struct.
To help with returning the objects, the objects array is a C array preallocated by the
caller (on the stack) of size len. In many cases you can put the objects you want to return in
that objects array, then do itemsPtr = objects. But you don’t have to; if your collection
already has the objects to return in some form of C array, it could return them from there
instead.
The state and extra fields of the NSFastEnumerationState structure allows your collection object to keep track of the state of the enumeration. In a simple array implementation,
state may keep track of the index of the last object that was returned, and extra may be
unused.
The mutationsPtr field of the NSFastEnumerationState is used to keep track of mutations. It should point to a number; before working on each object, the fast enumeration
loop will check that this number has not changed. If it has, a mutation has happened and
the fast enumeration will abort. So, mutationsPtr could be set to point to some sort of
version number of your collection, which is increased by one every time there is a change
(for example when an object is added or removed). Or, if you are content with less strict
mutation checks, it could point to the number of objects in your collection or some other
value that can be checked to perform an approximate check that the collection has not been
mutated.
Finally, note how we declared the len argument and the return value to be of type
unsigned long. They could also be declared to be of type unsigned int and everything
would still work.

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8.10 Messaging with the GNU Objective-C Runtime
This section is specific for the GNU Objective-C runtime. If you are using a different
runtime, you can skip it.
The implementation of messaging in the GNU Objective-C runtime is designed to be
portable, and so is based on standard C.
Sending a message in the GNU Objective-C runtime is composed of two separate steps.
First, there is a call to the lookup function, objc_msg_lookup () (or, in the case of messages to super, objc_msg_lookup_super ()). This runtime function takes as argument the
receiver and the selector of the method to be called; it returns the IMP, that is a pointer
to the function implementing the method. The second step of method invocation consists
of casting this pointer function to the appropriate function pointer type, and calling the
function pointed to it with the right arguments.
For example, when the compiler encounters a method invocation such as [object init],
it compiles it into a call to objc_msg_lookup (object, @selector(init)) followed by a
cast of the returned value to the appropriate function pointer type, and then it calls it.

8.10.1 Dynamically Registering Methods
If objc_msg_lookup() does not find a suitable method implementation, because the receiver
does not implement the required method, it tries to see if the class can dynamically register
the method.
To do so, the runtime checks if the class of the receiver implements the method
+ (BOOL) resolveInstanceMethod: (SEL)selector;

in the case of an instance method, or
+ (BOOL) resolveClassMethod: (SEL)selector;

in the case of a class method. If the class implements it, the runtime invokes it, passing
as argument the selector of the original method, and if it returns YES, the runtime tries the
lookup again, which could now succeed if a matching method was added dynamically by
+resolveInstanceMethod: or +resolveClassMethod:.
This allows classes to dynamically register methods (by adding them to the class using class_addMethod) when they are first called. To do so, a class should implement
+resolveInstanceMethod: (or, depending on the case, +resolveClassMethod:) and have
it recognize the selectors of methods that can be registered dynamically at runtime, register them, and return YES. It should return NO for methods that it does not dynamically
registered at runtime.
If +resolveInstanceMethod: (or +resolveClassMethod:) is not implemented or returns
NO, the runtime then tries the forwarding hook.
Support for +resolveInstanceMethod: and resolveClassMethod: was added to the
GNU Objective-C runtime in GCC version 4.6.

8.10.2 Forwarding Hook
The GNU Objective-C runtime provides a hook, called __objc_msg_forward2, which is
called by objc_msg_lookup() when it cannot find a method implementation in the runtime
tables and after calling +resolveInstanceMethod: and +resolveClassMethod: has been
attempted and did not succeed in dynamically registering the method.

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To configure the hook, you set the global variable __objc_msg_forward2 to a function with the same argument and return types of objc_msg_lookup(). When objc_msg_
lookup() can not find a method implementation, it invokes the hook function you provided
to get a method implementation to return. So, in practice __objc_msg_forward2 allows you
to extend objc_msg_lookup() by adding some custom code that is called to do a further
lookup when no standard method implementation can be found using the normal lookup.
This hook is generally reserved for “Foundation” libraries such as GNUstep Base, which
use it to implement their high-level method forwarding API, typically based around the
forwardInvocation: method. So, unless you are implementing your own “Foundation”
library, you should not set this hook.
In a typical forwarding implementation, the __objc_msg_forward2 hook function determines the argument and return type of the method that is being looked up, and then creates
a function that takes these arguments and has that return type, and returns it to the caller.
Creating this function is non-trivial and is typically performed using a dedicated library
such as libffi.
The forwarding method implementation thus created is returned by objc_msg_lookup()
and is executed as if it was a normal method implementation. When the forwarding method
implementation is called, it is usually expected to pack all arguments into some sort of
object (typically, an NSInvocation in a “Foundation” library), and hand it over to the
programmer (forwardInvocation:) who is then allowed to manipulate the method invocation using a high-level API provided by the “Foundation” library. For example, the
programmer may want to examine the method invocation arguments and name and potentially change them before forwarding the method invocation to one or more local objects
(performInvocation:) or even to remote objects (by using Distributed Objects or some
other mechanism). When all this completes, the return value is passed back and must be
returned correctly to the original caller.
Note that the GNU Objective-C runtime currently provides no support for method forwarding or method invocations other than the __objc_msg_forward2 hook.
If the forwarding hook does not exist or returns NULL, the runtime currently attempts
forwarding using an older, deprecated API, and if that fails, it aborts the program. In
future versions of the GNU Objective-C runtime, the runtime will immediately abort.

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9 Binary Compatibility
Binary compatibility encompasses several related concepts:
application binary interface (ABI)
The set of runtime conventions followed by all of the tools that deal with binary representations of a program, including compilers, assemblers, linkers, and
language runtime support. Some ABIs are formal with a written specification,
possibly designed by multiple interested parties. Others are simply the way
things are actually done by a particular set of tools.
ABI conformance
A compiler conforms to an ABI if it generates code that follows all of the
specifications enumerated by that ABI. A library conforms to an ABI if it is
implemented according to that ABI. An application conforms to an ABI if it
is built using tools that conform to that ABI and does not contain source code
that specifically changes behavior specified by the ABI.
calling conventions
Calling conventions are a subset of an ABI that specify of how arguments are
passed and function results are returned.
interoperability
Different sets of tools are interoperable if they generate files that can be used
in the same program. The set of tools includes compilers, assemblers, linkers,
libraries, header files, startup files, and debuggers. Binaries produced by different sets of tools are not interoperable unless they implement the same ABI.
This applies to different versions of the same tools as well as tools from different
vendors.
intercallability
Whether a function in a binary built by one set of tools can call a function in
a binary built by a different set of tools is a subset of interoperability.
implementation-defined features
Language standards include lists of implementation-defined features whose behavior can vary from one implementation to another. Some of these features
are normally covered by a platform’s ABI and others are not. The features
that are not covered by an ABI generally affect how a program behaves, but
not intercallability.
compatibility
Conformance to the same ABI and the same behavior of implementation-defined
features are both relevant for compatibility.
The application binary interface implemented by a C or C++ compiler affects code generation and runtime support for:
• size and alignment of data types
• layout of structured types
• calling conventions

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• register usage conventions
• interfaces for runtime arithmetic support
• object file formats
In addition, the application binary interface implemented by a C++ compiler affects code
generation and runtime support for:
• name mangling
• exception handling
• invoking constructors and destructors
• layout, alignment, and padding of classes
• layout and alignment of virtual tables
Some GCC compilation options cause the compiler to generate code that does not conform to the platform’s default ABI. Other options cause different program behavior for
implementation-defined features that are not covered by an ABI. These options are provided for consistency with other compilers that do not follow the platform’s default ABI
or the usual behavior of implementation-defined features for the platform. Be very careful
about using such options.
Most platforms have a well-defined ABI that covers C code, but ABIs that cover C++
functionality are not yet common.
Starting with GCC 3.2, GCC binary conventions for C++ are based on a written, vendorneutral C++ ABI that was designed to be specific to 64-bit Itanium but also includes generic
specifications that apply to any platform. This C++ ABI is also implemented by other
compiler vendors on some platforms, notably GNU/Linux and BSD systems. We have tried
hard to provide a stable ABI that will be compatible with future GCC releases, but it is
possible that we will encounter problems that make this difficult. Such problems could
include different interpretations of the C++ ABI by different vendors, bugs in the ABI, or
bugs in the implementation of the ABI in different compilers. GCC’s ‘-Wabi’ switch warns
when G++ generates code that is probably not compatible with the C++ ABI.
The C++ library used with a C++ compiler includes the Standard C++ Library, with
functionality defined in the C++ Standard, plus language runtime support. The runtime
support is included in a C++ ABI, but there is no formal ABI for the Standard C++ Library.
Two implementations of that library are interoperable if one follows the de-facto ABI of the
other and if they are both built with the same compiler, or with compilers that conform to
the same ABI for C++ compiler and runtime support.
When G++ and another C++ compiler conform to the same C++ ABI, but the implementations of the Standard C++ Library that they normally use do not follow the same ABI for
the Standard C++ Library, object files built with those compilers can be used in the same
program only if they use the same C++ library. This requires specifying the location of the
C++ library header files when invoking the compiler whose usual library is not being used.
The location of GCC’s C++ header files depends on how the GCC build was configured, but
can be seen by using the G++ ‘-v’ option. With default configuration options for G++ 3.3
the compile line for a different C++ compiler needs to include
-Igcc_install_directory/include/c++/3.3

Similarly, compiling code with G++ that must use a C++ library other than the GNU C++
library requires specifying the location of the header files for that other library.

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The most straightforward way to link a program to use a particular C++ library is to
use a C++ driver that specifies that C++ library by default. The g++ driver, for example,
tells the linker where to find GCC’s C++ library (‘libstdc++’) plus the other libraries and
startup files it needs, in the proper order.
If a program must use a different C++ library and it’s not possible to do the final link
using a C++ driver that uses that library by default, it is necessary to tell g++ the location
and name of that library. It might also be necessary to specify different startup files and
other runtime support libraries, and to suppress the use of GCC’s support libraries with
one or more of the options ‘-nostdlib’, ‘-nostartfiles’, and ‘-nodefaultlibs’.

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10 gcov—a Test Coverage Program
gcov is a tool you can use in conjunction with GCC to test code coverage in your programs.

10.1 Introduction to gcov
gcov is a test coverage program. Use it in concert with GCC to analyze your programs
to help create more efficient, faster running code and to discover untested parts of your
program. You can use gcov as a profiling tool to help discover where your optimization
efforts will best affect your code. You can also use gcov along with the other profiling tool,
gprof, to assess which parts of your code use the greatest amount of computing time.
Profiling tools help you analyze your code’s performance. Using a profiler such as gcov
or gprof, you can find out some basic performance statistics, such as:
• how often each line of code executes
• what lines of code are actually executed
• how much computing time each section of code uses
Once you know these things about how your code works when compiled, you can look at
each module to see which modules should be optimized. gcov helps you determine where
to work on optimization.
Software developers also use coverage testing in concert with testsuites, to make sure
software is actually good enough for a release. Testsuites can verify that a program works
as expected; a coverage program tests to see how much of the program is exercised by the
testsuite. Developers can then determine what kinds of test cases need to be added to the
testsuites to create both better testing and a better final product.
You should compile your code without optimization if you plan to use gcov because
the optimization, by combining some lines of code into one function, may not give you
as much information as you need to look for ‘hot spots’ where the code is using a great
deal of computer time. Likewise, because gcov accumulates statistics by line (at the lowest
resolution), it works best with a programming style that places only one statement on each
line. If you use complicated macros that expand to loops or to other control structures,
the statistics are less helpful—they only report on the line where the macro call appears.
If your complex macros behave like functions, you can replace them with inline functions
to solve this problem.
gcov creates a logfile called ‘sourcefile.gcov’ which indicates how many times each line
of a source file ‘sourcefile.c’ has executed. You can use these logfiles along with gprof
to aid in fine-tuning the performance of your programs. gprof gives timing information
you can use along with the information you get from gcov.
gcov works only on code compiled with GCC. It is not compatible with any other profiling
or test coverage mechanism.

10.2 Invoking gcov
gcov [options] files

gcov accepts the following options:

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-a
--all-blocks
Write individual execution counts for every basic block. Normally gcov outputs
execution counts only for the main blocks of a line. With this option you can
determine if blocks within a single line are not being executed.
-b
--branch-probabilities
Write branch frequencies to the output file, and write branch summary info to
the standard output. This option allows you to see how often each branch in
your program was taken. Unconditional branches will not be shown, unless the
‘-u’ option is given.
-c
--branch-counts
Write branch frequencies as the number of branches taken, rather than the
percentage of branches taken.
-d
--display-progress
Display the progress on the standard output.
-f
--function-summaries
Output summaries for each function in addition to the file level summary.
-h
--help

Display help about using gcov (on the standard output), and exit without doing
any further processing.

-i
--intermediate-format
Output gcov file in an easy-to-parse intermediate text format that can be used
by lcov or other tools. The output is a single ‘.gcov’ file per ‘.gcda’ file. No
source code is required.
The format of the intermediate ‘.gcov’ file is plain text with one entry per line
version:gcc_version
file:source_file_name
function:start_line_number,end_line_number,execution_count,function_name
lcount:line number,execution_count,has_unexecuted_block
branch:line_number,branch_coverage_type
Where the branch_coverage_type is
notexec (Branch not executed)
taken (Branch executed and taken)
nottaken (Branch executed, but not taken)

There can be multiple file entries in an intermediate gcov file. All entries
following a file pertain to that source file until the next file entry. If there
are multiple functions that start on a single line, then corresponding lcount is
repeated multiple times.
Here is a sample when ‘-i’ is used in conjunction with ‘-b’ option:

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version: 8.1.0 20180103
file:tmp.cpp
function:7,7,0,_ZN3FooIcEC2Ev
function:7,7,1,_ZN3FooIiEC2Ev
function:8,8,0,_ZN3FooIcE3incEv
function:8,8,2,_ZN3FooIiE3incEv
function:18,37,1,main
lcount:7,0,1
lcount:7,1,0
lcount:8,0,1
lcount:8,2,0
lcount:18,1,0
lcount:21,1,0
branch:21,taken
branch:21,nottaken
lcount:23,1,0
branch:23,taken
branch:23,nottaken
lcount:24,1,0
branch:24,taken
branch:24,nottaken
lcount:25,1,0
lcount:27,11,0
branch:27,taken
branch:27,taken
lcount:28,10,0
lcount:30,1,1
branch:30,nottaken
branch:30,taken
lcount:32,1,0
branch:32,nottaken
branch:32,taken
lcount:33,0,1
branch:33,notexec
branch:33,notexec
lcount:35,1,0
branch:35,taken
branch:35,nottaken
lcount:36,1,0

-j
--human-readable
Write counts in human readable format (like 24k).
-k
--use-colors
Use colors for lines of code that have zero coverage. We use red color for nonexceptional lines and cyan for exceptional. Same colors are used for basic blocks
with ‘-a’ option.
-l
--long-file-names
Create long file names for included source files. For example, if the header
file ‘x.h’ contains code, and was included in the file ‘a.c’, then running gcov
on the file ‘a.c’ will produce an output file called ‘a.c##x.h.gcov’ instead of
‘x.h.gcov’. This can be useful if ‘x.h’ is included in multiple source files and

824

Using the GNU Compiler Collection (GCC)

you want to see the individual contributions. If you use the ‘-p’ option, both
the including and included file names will be complete path names.
-m
--demangled-names
Display demangled function names in output. The default is to show mangled
function names.
-n
--no-output
Do not create the gcov output file.
-o directory|file
--object-directory directory
--object-file file
Specify either the directory containing the gcov data files, or the object path
name. The ‘.gcno’, and ‘.gcda’ data files are searched for using this option. If
a directory is specified, the data files are in that directory and named after the
input file name, without its extension. If a file is specified here, the data files
are named after that file, without its extension.
-p
--preserve-paths
Preserve complete path information in the names of generated ‘.gcov’ files.
Without this option, just the filename component is used. With this option, all
directories are used, with ‘/’ characters translated to ‘#’ characters, ‘.’ directory
components removed and unremoveable ‘..’ components renamed to ‘^’. This
is useful if sourcefiles are in several different directories.
-r
--relative-only
Only output information about source files with a relative pathname (after
source prefix elision). Absolute paths are usually system header files and coverage of any inline functions therein is normally uninteresting.
-s directory
--source-prefix directory
A prefix for source file names to remove when generating the output coverage
files. This option is useful when building in a separate directory, and the pathname to the source directory is not wanted when determining the output file
names. Note that this prefix detection is applied before determining whether
the source file is absolute.
-u
--unconditional-branches
When branch probabilities are given, include those of unconditional branches.
Unconditional branches are normally not interesting.
-v
--version
Display the gcov version number (on the standard output), and exit without
doing any further processing.

Chapter 10: gcov—a Test Coverage Program

825

-w
--verbose
Print verbose informations related to basic blocks and arcs.
-x
--hash-filenames
By default, gcov uses the full pathname of the source files to to create an output
filename. This can lead to long filenames that can overflow filesystem limits.
This option creates names of the form ‘source-file##md5.gcov’, where the
source-file component is the final filename part and the md5 component is
calculated from the full mangled name that would have been used otherwise.
gcov should be run with the current directory the same as that when you invoked the
compiler. Otherwise it will not be able to locate the source files. gcov produces files called
‘mangledname.gcov’ in the current directory. These contain the coverage information of
the source file they correspond to. One ‘.gcov’ file is produced for each source (or header)
file containing code, which was compiled to produce the data files. The mangledname part
of the output file name is usually simply the source file name, but can be something more
complicated if the ‘-l’ or ‘-p’ options are given. Refer to those options for details.
If you invoke gcov with multiple input files, the contributions from each input file are
summed. Typically you would invoke it with the same list of files as the final link of your
executable.
The ‘.gcov’ files contain the ‘:’ separated fields along with program source code. The
format is
execution_count:line_number:source line text

Additional block information may succeed each line, when requested by command line
option. The execution count is ‘-’ for lines containing no code. Unexecuted lines are
marked ‘#####’ or ‘=====’, depending on whether they are reachable by non-exceptional
paths or only exceptional paths such as C++ exception handlers, respectively. Given ‘-a’
option, unexecuted blocks are marked ‘$$$$$’ or ‘%%%%%’, depending on whether a basic
block is reachable via non-exceptional or exceptional paths. Executed basic blocks having a
statement with zero execution count end with ‘*’ character and are colored with magenta
color with ‘-k’ option. The functionality is not supported in Ada.
Note that GCC can completely remove the bodies of functions that are not needed – for
instance if they are inlined everywhere. Such functions are marked with ‘-’, which can be
confusing. Use the ‘-fkeep-inline-functions’ and ‘-fkeep-static-functions’ options
to retain these functions and allow gcov to properly show their execution count.
Some lines of information at the start have line number of zero. These preamble lines
are of the form
-:0:tag:value

The ordering and number of these preamble lines will be augmented as gcov development
progresses — do not rely on them remaining unchanged. Use tag to locate a particular
preamble line.
The additional block information is of the form
tag information

The information is human readable, but designed to be simple enough for machine parsing
too.

826

Using the GNU Compiler Collection (GCC)

When printing percentages, 0% and 100% are only printed when the values are exactly
0% and 100% respectively. Other values which would conventionally be rounded to 0% or
100% are instead printed as the nearest non-boundary value.
When using gcov, you must first compile your program with two special GCC options:
‘-fprofile-arcs -ftest-coverage’. This tells the compiler to generate additional information needed by gcov (basically a flow graph of the program) and also includes additional
code in the object files for generating the extra profiling information needed by gcov. These
additional files are placed in the directory where the object file is located.
Running the program will cause profile output to be generated. For each source file
compiled with ‘-fprofile-arcs’, an accompanying ‘.gcda’ file will be placed in the object
file directory.
Running gcov with your program’s source file names as arguments will now produce a
listing of the code along with frequency of execution for each line. For example, if your
program is called ‘tmp.cpp’, this is what you see when you use the basic gcov facility:
$ g++ -fprofile-arcs -ftest-coverage tmp.cpp
$ a.out
$ gcov tmp.cpp -m
File ’tmp.cpp’
Lines executed:92.86% of 14
Creating ’tmp.cpp.gcov’

The file ‘tmp.cpp.gcov’ contains output from gcov. Here is a sample:
-:
0:Source:tmp.cpp
-:
0:Graph:tmp.gcno
-:
0:Data:tmp.gcda
-:
0:Runs:1
-:
0:Programs:1
-:
1:#include 
-:
2:
-:
3:template
-:
4:class Foo
-:
5:{
-:
6: public:
1*:
7: Foo(): b (1000) {}
-----------------Foo::Foo():
#####:
7: Foo(): b (1000) {}
-----------------Foo::Foo():
1:
7: Foo(): b (1000) {}
-----------------2*:
8: void inc () { b++; }
-----------------Foo::inc():
#####:
8: void inc () { b++; }
-----------------Foo::inc():
2:
8: void inc () { b++; }
------------------:
9:
-:
10: private:
-:
11: int b;
-:
12:};
-:
13:

Chapter 10: gcov—a Test Coverage Program

-:
-:
-:
-:
1:
-:
-:
1:
-:
1:
1:
1:
-:
11:
10:
-:
1*:
-:
1:
#####:
-:
1:
1:
-:

827

14:template class Foo;
15:template class Foo;
16:
17:int
18:main (void)
19:{
20: int i, total;
21: Foo counter;
22:
23: counter.inc();
24: counter.inc();
25: total = 0;
26:
27: for (i = 0; i < 10; i++)
28:
total += i;
29:
30: int v = total > 100 ? 1 : 2;
31:
32: if (total != 45)
33:
printf ("Failure\n");
34: else
35:
printf ("Success\n");
36: return 0;
37:}

Note that line 7 is shown in the report multiple times. First occurrence presents total
number of execution of the line and the next two belong to instances of class Foo constructors. As you can also see, line 30 contains some unexecuted basic blocks and thus execution
count has asterisk symbol.
When you use the ‘-a’ option, you will get individual block counts, and the output looks
like this:
-:
0:Source:tmp.cpp
-:
0:Graph:tmp.gcno
-:
0:Data:tmp.gcda
-:
0:Runs:1
-:
0:Programs:1
-:
1:#include 
-:
2:
-:
3:template
-:
4:class Foo
-:
5:{
-:
6: public:
1*:
7: Foo(): b (1000) {}
-----------------Foo::Foo():
#####:
7: Foo(): b (1000) {}
-----------------Foo::Foo():
1:
7: Foo(): b (1000) {}
-----------------2*:
8: void inc () { b++; }
-----------------Foo::inc():
#####:
8: void inc () { b++; }
-----------------Foo::inc():
2:
8: void inc () { b++; }

828

Using the GNU Compiler Collection (GCC)

------------------:
9:
-:
10: private:
-:
11: int b;
-:
12:};
-:
13:
-:
14:template class Foo;
-:
15:template class Foo;
-:
16:
-:
17:int
1:
18:main (void)
-:
19:{
-:
20: int i, total;
1:
21: Foo counter;
1:
21-block 0
-:
22:
1:
23: counter.inc();
1:
23-block 0
1:
24: counter.inc();
1:
24-block 0
1:
25: total = 0;
-:
26:
11:
27: for (i = 0; i < 10; i++)
1:
27-block 0
11:
27-block 1
10:
28:
total += i;
10:
28-block 0
-:
29:
1*:
30: int v = total > 100 ? 1 : 2;
1:
30-block 0
%%%%%:
30-block 1
1:
30-block 2
-:
31:
1:
32: if (total != 45)
1:
32-block 0
#####:
33:
printf ("Failure\n");
%%%%%:
33-block 0
-:
34: else
1:
35:
printf ("Success\n");
1:
35-block 0
1:
36: return 0;
1:
36-block 0
-:
37:}

In this mode, each basic block is only shown on one line – the last line of the block.
A multi-line block will only contribute to the execution count of that last line, and other
lines will not be shown to contain code, unless previous blocks end on those lines. The
total execution count of a line is shown and subsequent lines show the execution counts for
individual blocks that end on that line. After each block, the branch and call counts of the
block will be shown, if the ‘-b’ option is given.
Because of the way GCC instruments calls, a call count can be shown after a line with
no individual blocks. As you can see, line 33 contains a basic block that was not executed.
When you use the ‘-b’ option, your output looks like this:
-:
-:
-:

0:Source:tmp.cpp
0:Graph:tmp.gcno
0:Data:tmp.gcda

Chapter 10: gcov—a Test Coverage Program

-:
0:Runs:1
-:
0:Programs:1
-:
1:#include 
-:
2:
-:
3:template
-:
4:class Foo
-:
5:{
-:
6: public:
1*:
7: Foo(): b (1000) {}
-----------------Foo::Foo():
function Foo::Foo() called 0 returned 0% blocks executed 0%
#####:
7: Foo(): b (1000) {}
-----------------Foo::Foo():
function Foo::Foo() called 1 returned 100% blocks executed 100%
1:
7: Foo(): b (1000) {}
-----------------2*:
8: void inc () { b++; }
-----------------Foo::inc():
function Foo::inc() called 0 returned 0% blocks executed 0%
#####:
8: void inc () { b++; }
-----------------Foo::inc():
function Foo::inc() called 2 returned 100% blocks executed 100%
2:
8: void inc () { b++; }
------------------:
9:
-:
10: private:
-:
11: int b;
-:
12:};
-:
13:
-:
14:template class Foo;
-:
15:template class Foo;
-:
16:
-:
17:int
function main called 1 returned 100% blocks executed 81%
1:
18:main (void)
-:
19:{
-:
20: int i, total;
1:
21: Foo counter;
call
0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
-:
22:
1:
23: counter.inc();
call
0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
1:
24: counter.inc();
call
0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
1:
25: total = 0;
-:
26:
11:
27: for (i = 0; i < 10; i++)
branch 0 taken 91% (fallthrough)

829

830

Using the GNU Compiler Collection (GCC)

branch

1 taken 9%
10:
28:
total += i;
-:
29:
1*:
30: int v = total > 100 ? 1 : 2;
branch 0 taken 0% (fallthrough)
branch 1 taken 100%
-:
31:
1:
32: if (total != 45)
branch 0 taken 0% (fallthrough)
branch 1 taken 100%
#####:
33:
printf ("Failure\n");
call
0 never executed
branch 1 never executed
branch 2 never executed
-:
34: else
1:
35:
printf ("Success\n");
call
0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
1:
36: return 0;
-:
37:}

For each function, a line is printed showing how many times the function is called, how
many times it returns and what percentage of the function’s blocks were executed.
For each basic block, a line is printed after the last line of the basic block describing the
branch or call that ends the basic block. There can be multiple branches and calls listed for
a single source line if there are multiple basic blocks that end on that line. In this case, the
branches and calls are each given a number. There is no simple way to map these branches
and calls back to source constructs. In general, though, the lowest numbered branch or call
will correspond to the leftmost construct on the source line.
For a branch, if it was executed at least once, then a percentage indicating the number
of times the branch was taken divided by the number of times the branch was executed will
be printed. Otherwise, the message “never executed” is printed.
For a call, if it was executed at least once, then a percentage indicating the number of
times the call returned divided by the number of times the call was executed will be printed.
This will usually be 100%, but may be less for functions that call exit or longjmp, and
thus may not return every time they are called.
The execution counts are cumulative. If the example program were executed again without removing the ‘.gcda’ file, the count for the number of times each line in the source was
executed would be added to the results of the previous run(s). This is potentially useful in
several ways. For example, it could be used to accumulate data over a number of program
runs as part of a test verification suite, or to provide more accurate long-term information
over a large number of program runs.
The data in the ‘.gcda’ files is saved immediately before the program exits. For each
source file compiled with ‘-fprofile-arcs’, the profiling code first attempts to read in an
existing ‘.gcda’ file; if the file doesn’t match the executable (differing number of basic block
counts) it will ignore the contents of the file. It then adds in the new execution counts and
finally writes the data to the file.

Chapter 10: gcov—a Test Coverage Program

831

10.3 Using gcov with GCC Optimization
If you plan to use gcov to help optimize your code, you must first compile your program
with two special GCC options: ‘-fprofile-arcs -ftest-coverage’. Aside from that, you
can use any other GCC options; but if you want to prove that every single line in your
program was executed, you should not compile with optimization at the same time. On
some machines the optimizer can eliminate some simple code lines by combining them with
other lines. For example, code like this:
if (a != b)
c = 1;
else
c = 0;

can be compiled into one instruction on some machines. In this case, there is no way for
gcov to calculate separate execution counts for each line because there isn’t separate code
for each line. Hence the gcov output looks like this if you compiled the program with
optimization:
100:
100:
100:
100:

12:if (a != b)
13: c = 1;
14:else
15: c = 0;

The output shows that this block of code, combined by optimization, executed 100 times.
In one sense this result is correct, because there was only one instruction representing all
four of these lines. However, the output does not indicate how many times the result was
0 and how many times the result was 1.
Inlineable functions can create unexpected line counts. Line counts are shown for the
source code of the inlineable function, but what is shown depends on where the function is
inlined, or if it is not inlined at all.
If the function is not inlined, the compiler must emit an out of line copy of the function, in
any object file that needs it. If ‘fileA.o’ and ‘fileB.o’ both contain out of line bodies of a
particular inlineable function, they will also both contain coverage counts for that function.
When ‘fileA.o’ and ‘fileB.o’ are linked together, the linker will, on many systems, select
one of those out of line bodies for all calls to that function, and remove or ignore the other.
Unfortunately, it will not remove the coverage counters for the unused function body. Hence
when instrumented, all but one use of that function will show zero counts.
If the function is inlined in several places, the block structure in each location might not
be the same. For instance, a condition might now be calculable at compile time in some
instances. Because the coverage of all the uses of the inline function will be shown for the
same source lines, the line counts themselves might seem inconsistent.
Long-running applications can use the __gcov_reset and __gcov_dump facilities to restrict profile collection to the program region of interest. Calling __gcov_reset(void)
will clear all profile counters to zero, and calling __gcov_dump(void) will cause the profile
information collected at that point to be dumped to ‘.gcda’ output files. Instrumented applications use a static destructor with priority 99 to invoke the __gcov_dump function. Thus
__gcov_dump is executed after all user defined static destructors, as well as handlers registered with atexit. If an executable loads a dynamic shared object via dlopen functionality,
‘-Wl,--dynamic-list-data’ is needed to dump all profile data.

832

Using the GNU Compiler Collection (GCC)

10.4 Brief Description of gcov Data Files
gcov uses two files for profiling. The names of these files are derived from the original object
file by substituting the file suffix with either ‘.gcno’, or ‘.gcda’. The files contain coverage
and profile data stored in a platform-independent format. The ‘.gcno’ files are placed in
the same directory as the object file. By default, the ‘.gcda’ files are also stored in the same
directory as the object file, but the GCC ‘-fprofile-dir’ option may be used to store the
‘.gcda’ files in a separate directory.
The ‘.gcno’ notes file is generated when the source file is compiled with the GCC
‘-ftest-coverage’ option. It contains information to reconstruct the basic block graphs
and assign source line numbers to blocks.
The ‘.gcda’ count data file is generated when a program containing object files built with
the GCC ‘-fprofile-arcs’ option is executed. A separate ‘.gcda’ file is created for each
object file compiled with this option. It contains arc transition counts, value profile counts,
and some summary information.
It is not recommended to access the coverage files directly. Consumers should use the
intermediate format that is provided by gcov tool via ‘--intermediate-format’ option.

10.5 Data File Relocation to Support Cross-Profiling
Running the program will cause profile output to be generated. For each source file compiled with ‘-fprofile-arcs’, an accompanying ‘.gcda’ file will be placed in the object file
directory. That implicitly requires running the program on the same system as it was built
or having the same absolute directory structure on the target system. The program will try
to create the needed directory structure, if it is not already present.
To support cross-profiling, a program compiled with ‘-fprofile-arcs’ can relocate the
data files based on two environment variables:
• GCOV PREFIX contains the prefix to add to the absolute paths in the object file.
Prefix can be absolute, or relative. The default is no prefix.
• GCOV PREFIX STRIP indicates the how many initial directory names to strip off
the hardwired absolute paths. Default value is 0.
Note: If GCOV PREFIX STRIP is set without GCOV PREFIX is undefined, then a
relative path is made out of the hardwired absolute paths.
For example, if the object file ‘/user/build/foo.o’ was built with ‘-fprofile-arcs’,
the final executable will try to create the data file ‘/user/build/foo.gcda’ when running
on the target system. This will fail if the corresponding directory does not exist and it
is unable to create it. This can be overcome by, for example, setting the environment as
‘GCOV_PREFIX=/target/run’ and ‘GCOV_PREFIX_STRIP=1’. Such a setting will name the
data file ‘/target/run/build/foo.gcda’.
You must move the data files to the expected directory tree in order to use them for
profile directed optimizations (‘-fprofile-use’), or to use the gcov tool.

Chapter 11: gcov-tool—an Offline Gcda Profile Processing Tool

833

11 gcov-tool—an Offline Gcda Profile Processing
Tool
gcov-tool is a tool you can use in conjunction with GCC to manipulate or process gcda
profile files offline.

11.1 Introduction to gcov-tool
gcov-tool is an offline tool to process gcc’s gcda profile files.
Current gcov-tool supports the following functionalities:
• merge two sets of profiles with weights.
• read one set of profile and rewrite profile contents. One can scale or normalize the
count values.
Examples of the use cases for this tool are:
• Collect the profiles for different set of inputs, and use this tool to merge them. One
can specify the weight to factor in the relative importance of each input.
• Rewrite the profile after removing a subset of the gcda files, while maintaining the
consistency of the summary and the histogram.
• It can also be used to debug or libgcov code as the tools shares the majority code as
the runtime library.
Note that for the merging operation, this profile generated offline may contain slight
different values from the online merged profile. Here are a list of typical differences:
• histogram difference: This offline tool recomputes the histogram after merging the
counters. The resulting histogram, therefore, is precise. The online merging does not
have this capability – the histogram is merged from two histograms and the result is
an approximation.
• summary checksum difference: Summary checksum uses a CRC32 operation. The value
depends on the link list order of gcov-info objects. This order is different in gcov-tool
from that in the online merge. It’s expected to have different summary checksums. It
does not really matter as the compiler does not use this checksum anywhere.
• value profile counter values difference: Some counter values for value profile are runtime
dependent, like heap addresses. It’s normal to see some difference in these kind of
counters.

11.2 Invoking gcov-tool
gcov-tool [global-options] SUB_COMMAND [sub_command-options] profile_dir

gcov-tool accepts the following options:
-h
--help

Display help about using gcov-tool (on the standard output), and exit without
doing any further processing.

-v
--version
Display the gcov-tool version number (on the standard output), and exit
without doing any further processing.

834

merge

Using the GNU Compiler Collection (GCC)

Merge two profile directories.
-o directory
--output directory
Set the output profile directory. Default output directory name is
merged profile.
-v
--verbose
Set the verbose mode.
-w w1,w2
--weight w1,w2
Set the merge weights of the directory1 and directory2, respectively.
The default weights are 1 for both.

rewrite

Read the specified profile directory and rewrite to a new directory.
-n long_long_value
--normalize 
Normalize the profile. The specified value is the max counter value
in the new profile.
-o directory
--output directory
Set the output profile directory.
rewrite profile.

Default output name is

-s float_or_simple-frac_value
--scale float_or_simple-frac_value
Scale the profile counters. The specified value can be in floating
point value, or simple fraction value form, such 1, 2, 2/3, and 5/3.
-v
--verbose
Set the verbose mode.
overlap

Compute the overlap score between the two specified profile directories. The
overlap score is computed based on the arc profiles. It is defined as the sum
of min (p1 counter[i] / p1 sum all, p2 counter[i] / p2 sum all), for all arc
counter i, where p1 counter[i] and p2 counter[i] are two matched counters and
p1 sum all and p2 sum all are the sum of counter values in profile 1 and profile
2, respectively.
-f
--function
Print function level overlap score.
-F
--fullname
Print full gcda filename.
-h
--hotonly
Only print info for hot objects/functions.

Chapter 11: gcov-tool—an Offline Gcda Profile Processing Tool

-o
--object

Print object level overlap score.

-t float
--hot_threshold 
Set the threshold for hot counter value.
-v
--verbose
Set the verbose mode.

835

Chapter 12: gcov-dump—an Offline Gcda and Gcno Profile Dump Tool

837

12 gcov-dump—an Offline Gcda and Gcno Profile
Dump Tool
12.1 Introduction to gcov-dump
gcov-dump is a tool you can use in conjunction with GCC to dump content of gcda and
gcno profile files offline.

12.2 Invoking gcov-dump
Usage: gcov-dump [OPTION] ... gcovfiles

gcov-dump accepts the following options:
-h
--help
-l
--long

Display help about using gcov-dump (on the standard output), and exit without
doing any further processing.
Dump content of records.

-p
--positions
Dump positions of records.
-v
--version
Display the gcov-dump version number (on the standard output), and exit
without doing any further processing.
-w
--working-sets
Dump working set computed from summary.

Chapter 13: Known Causes of Trouble with GCC

839

13 Known Causes of Trouble with GCC
This section describes known problems that affect users of GCC. Most of these are not
GCC bugs per se—if they were, we would fix them. But the result for a user may be like
the result of a bug.
Some of these problems are due to bugs in other software, some are missing features that
are too much work to add, and some are places where people’s opinions differ as to what is
best.

13.1 Actual Bugs We Haven’t Fixed Yet
• The fixincludes script interacts badly with automounters; if the directory of system
header files is automounted, it tends to be unmounted while fixincludes is running.
This would seem to be a bug in the automounter. We don’t know any good way to
work around it.

13.2 Interoperation
This section lists various difficulties encountered in using GCC together with other compilers
or with the assemblers, linkers, libraries and debuggers on certain systems.
• On many platforms, GCC supports a different ABI for C++ than do other compilers, so
the object files compiled by GCC cannot be used with object files generated by another
C++ compiler.
An area where the difference is most apparent is name mangling. The use of different
name mangling is intentional, to protect you from more subtle problems. Compilers
differ as to many internal details of C++ implementation, including: how class instances
are laid out, how multiple inheritance is implemented, and how virtual function calls
are handled. If the name encoding were made the same, your programs would link
against libraries provided from other compilers—but the programs would then crash
when run. Incompatible libraries are then detected at link time, rather than at run
time.
• On some BSD systems, including some versions of Ultrix, use of profiling causes static
variable destructors (currently used only in C++) not to be run.
• On a SPARC, GCC aligns all values of type double on an 8-byte boundary, and it
expects every double to be so aligned. The Sun compiler usually gives double values
8-byte alignment, with one exception: function arguments of type double may not be
aligned.
As a result, if a function compiled with Sun CC takes the address of an argument
of type double and passes this pointer of type double * to a function compiled with
GCC, dereferencing the pointer may cause a fatal signal.
One way to solve this problem is to compile your entire program with GCC. Another
solution is to modify the function that is compiled with Sun CC to copy the argument
into a local variable; local variables are always properly aligned. A third solution is to
modify the function that uses the pointer to dereference it via the following function
access_double instead of directly with ‘*’:

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inline double
access_double (double *unaligned_ptr)
{
union d2i { double d; int i[2]; };
union d2i *p = (union d2i *) unaligned_ptr;
union d2i u;
u.i[0] = p->i[0];
u.i[1] = p->i[1];
return u.d;
}

•

•

•
•
•

•

•

Storing into the pointer can be done likewise with the same union.
On Solaris, the malloc function in the ‘libmalloc.a’ library may allocate memory
that is only 4 byte aligned. Since GCC on the SPARC assumes that doubles are 8 byte
aligned, this may result in a fatal signal if doubles are stored in memory allocated by
the ‘libmalloc.a’ library.
The solution is to not use the ‘libmalloc.a’ library. Use instead malloc and related
functions from ‘libc.a’; they do not have this problem.
On the HP PA machine, ADB sometimes fails to work on functions compiled with
GCC. Specifically, it fails to work on functions that use alloca or variable-size arrays.
This is because GCC doesn’t generate HP-UX unwind descriptors for such functions.
It may even be impossible to generate them.
Debugging (‘-g’) is not supported on the HP PA machine, unless you use the preliminary GNU tools.
Taking the address of a label may generate errors from the HP-UX PA assembler. GAS
for the PA does not have this problem.
Using floating point parameters for indirect calls to static functions will not work when
using the HP assembler. There simply is no way for GCC to specify what registers hold
arguments for static functions when using the HP assembler. GAS for the PA does not
have this problem.
In extremely rare cases involving some very large functions you may receive errors from
the HP linker complaining about an out of bounds unconditional branch offset. This
used to occur more often in previous versions of GCC, but is now exceptionally rare.
If you should run into it, you can work around by making your function smaller.
GCC compiled code sometimes emits warnings from the HP-UX assembler of the form:
(warning) Use of GR3 when
frame >= 8192 may cause conflict.

These warnings are harmless and can be safely ignored.
• In extremely rare cases involving some very large functions you may receive errors from
the AIX Assembler complaining about a displacement that is too large. If you should
run into it, you can work around by making your function smaller.
• The ‘libstdc++.a’ library in GCC relies on the SVR4 dynamic linker semantics which
merges global symbols between libraries and applications, especially necessary for C++
streams functionality. This is not the default behavior of AIX shared libraries and
dynamic linking. ‘libstdc++.a’ is built on AIX with “runtime-linking” enabled so

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that symbol merging can occur. To utilize this feature, the application linked with
‘libstdc++.a’ must include the ‘-Wl,-brtl’ flag on the link line. G++ cannot impose
this because this option may interfere with the semantics of the user program and users
may not always use ‘g++’ to link his or her application. Applications are not required to
use the ‘-Wl,-brtl’ flag on the link line—the rest of the ‘libstdc++.a’ library which
is not dependent on the symbol merging semantics will continue to function correctly.
• An application can interpose its own definition of functions for functions invoked by
‘libstdc++.a’ with “runtime-linking” enabled on AIX. To accomplish this the application must be linked with “runtime-linking” option and the functions explicitly must
be exported by the application (‘-Wl,-brtl,-bE:exportfile’).
• AIX on the RS/6000 provides support (NLS) for environments outside of the United
States. Compilers and assemblers use NLS to support locale-specific representations
of various objects including floating-point numbers (‘.’ vs ‘,’ for separating decimal
fractions). There have been problems reported where the library linked with GCC does
not produce the same floating-point formats that the assembler accepts. If you have
this problem, set the LANG environment variable to ‘C’ or ‘En_US’.
• Even if you specify ‘-fdollars-in-identifiers’, you cannot successfully use ‘$’ in
identifiers on the RS/6000 due to a restriction in the IBM assembler. GAS supports
these identifiers.

13.3 Incompatibilities of GCC
There are several noteworthy incompatibilities between GNU C and K&R (non-ISO) versions of C.
• GCC normally makes string constants read-only. If several identical-looking string
constants are used, GCC stores only one copy of the string.
One consequence is that you cannot call mktemp with a string constant argument. The
function mktemp always alters the string its argument points to.
Another consequence is that sscanf does not work on some very old systems when
passed a string constant as its format control string or input. This is because sscanf
incorrectly tries to write into the string constant. Likewise fscanf and scanf.
The solution to these problems is to change the program to use char-array variables
with initialization strings for these purposes instead of string constants.
• -2147483648 is positive.
This is because 2147483648 cannot fit in the type int, so (following the ISO C rules)
its data type is unsigned long int. Negating this value yields 2147483648 again.
• GCC does not substitute macro arguments when they appear inside of string constants.
For example, the following macro in GCC
#define foo(a) "a"

will produce output "a" regardless of what the argument a is.
• When you use setjmp and longjmp, the only automatic variables guaranteed to remain valid are those declared volatile. This is a consequence of automatic register
allocation. Consider this function:
jmp_buf j;

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foo ()
{
int a, b;
a = fun1 ();
if (setjmp (j))
return a;
a = fun2 ();
/* longjmp (j) may occur in fun3. */
return a + fun3 ();
}

Here a may or may not be restored to its first value when the longjmp occurs. If a is
allocated in a register, then its first value is restored; otherwise, it keeps the last value
stored in it.
If you use the ‘-W’ option with the ‘-O’ option, you will get a warning when GCC thinks
such a problem might be possible.
• Programs that use preprocessing directives in the middle of macro arguments do not
work with GCC. For example, a program like this will not work:
foobar (
#define luser
hack)

ISO C does not permit such a construct.
• K&R compilers allow comments to cross over an inclusion boundary (i.e. started in an
include file and ended in the including file).
• Declarations of external variables and functions within a block apply only to the block
containing the declaration. In other words, they have the same scope as any other
declaration in the same place.
In some other C compilers, an extern declaration affects all the rest of the file even if
it happens within a block.
• In traditional C, you can combine long, etc., with a typedef name, as shown here:
typedef int foo;
typedef long foo bar;

In ISO C, this is not allowed: long and other type modifiers require an explicit int.
• PCC allows typedef names to be used as function parameters.
• Traditional C allows the following erroneous pair of declarations to appear together in
a given scope:
typedef int foo;
typedef foo foo;

• GCC treats all characters of identifiers as significant. According to K&R-1 (2.2), “No
more than the first eight characters are significant, although more may be used.”. Also
according to K&R-1 (2.2), “An identifier is a sequence of letters and digits; the first
character must be a letter. The underscore counts as a letter.”, but GCC also allows
dollar signs in identifiers.
• PCC allows whitespace in the middle of compound assignment operators such as ‘+=’.
GCC, following the ISO standard, does not allow this.

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• GCC complains about unterminated character constants inside of preprocessing conditionals that fail. Some programs have English comments enclosed in conditionals
that are guaranteed to fail; if these comments contain apostrophes, GCC will probably
report an error. For example, this code would produce an error:
#if 0
You can’t expect this to work.
#endif

The best solution to such a problem is to put the text into an actual C comment
delimited by ‘/*...*/’.
• Many user programs contain the declaration ‘long time ();’. In the past, the system
header files on many systems did not actually declare time, so it did not matter what
type your program declared it to return. But in systems with ISO C headers, time is
declared to return time_t, and if that is not the same as long, then ‘long time ();’
is erroneous.
The solution is to change your program to use appropriate system headers (
on systems with ISO C headers) and not to declare time if the system header files
declare it, or failing that to use time_t as the return type of time.
• When compiling functions that return float, PCC converts it to a double. GCC
actually returns a float. If you are concerned with PCC compatibility, you should
declare your functions to return double; you might as well say what you mean.
• When compiling functions that return structures or unions, GCC output code normally
uses a method different from that used on most versions of Unix. As a result, code
compiled with GCC cannot call a structure-returning function compiled with PCC,
and vice versa.
The method used by GCC is as follows: a structure or union which is 1, 2, 4 or 8
bytes long is returned like a scalar. A structure or union with any other size is stored
into an address supplied by the caller (usually in a special, fixed register, but on some
machines it is passed on the stack). The target hook TARGET_STRUCT_VALUE_RTX tells
GCC where to pass this address.
By contrast, PCC on most target machines returns structures and unions of any size
by copying the data into an area of static storage, and then returning the address of
that storage as if it were a pointer value. The caller must copy the data from that
memory area to the place where the value is wanted. GCC does not use this method
because it is slower and nonreentrant.
On some newer machines, PCC uses a reentrant convention for all structure and union
returning. GCC on most of these machines uses a compatible convention when returning structures and unions in memory, but still returns small structures and unions in
registers.
You can tell GCC to use a compatible convention for all structure and union returning
with the option ‘-fpcc-struct-return’.
• GCC complains about program fragments such as ‘0x74ae-0x4000’ which appear to be
two hexadecimal constants separated by the minus operator. Actually, this string is a
single preprocessing token. Each such token must correspond to one token in C. Since
this does not, GCC prints an error message. Although it may appear obvious that

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what is meant is an operator and two values, the ISO C standard specifically requires
that this be treated as erroneous.
A preprocessing token is a preprocessing number if it begins with a digit and is followed
by letters, underscores, digits, periods and ‘e+’, ‘e-’, ‘E+’, ‘E-’, ‘p+’, ‘p-’, ‘P+’, or ‘P-’
character sequences. (In strict C90 mode, the sequences ‘p+’, ‘p-’, ‘P+’ and ‘P-’ cannot
appear in preprocessing numbers.)
To make the above program fragment valid, place whitespace in front of the minus
sign. This whitespace will end the preprocessing number.

13.4 Fixed Header Files
GCC needs to install corrected versions of some system header files. This is because most
target systems have some header files that won’t work with GCC unless they are changed.
Some have bugs, some are incompatible with ISO C, and some depend on special features
of other compilers.
Installing GCC automatically creates and installs the fixed header files, by running a
program called fixincludes. Normally, you don’t need to pay attention to this. But there
are cases where it doesn’t do the right thing automatically.
• If you update the system’s header files, such as by installing a new system version, the fixed header files of GCC are not automatically updated.
They can be updated using the mkheaders script installed in
‘libexecdir/gcc/target/version/install-tools/’.
• On some systems, header file directories contain machine-specific symbolic links in
certain places. This makes it possible to share most of the header files among hosts
running the same version of the system on different machine models.
The programs that fix the header files do not understand this special way of using
symbolic links; therefore, the directory of fixed header files is good only for the machine
model used to build it.
It is possible to make separate sets of fixed header files for the different machine models,
and arrange a structure of symbolic links so as to use the proper set, but you’ll have
to do this by hand.

13.5 Standard Libraries
GCC by itself attempts to be a conforming freestanding implementation. See Chapter 2
[Language Standards Supported by GCC], page 5, for details of what this means. Beyond
the library facilities required of such an implementation, the rest of the C library is supplied
by the vendor of the operating system. If that C library doesn’t conform to the C standards,
then your programs might get warnings (especially when using ‘-Wall’) that you don’t
expect.
For example, the sprintf function on SunOS 4.1.3 returns char * while the C standard
says that sprintf returns an int. The fixincludes program could make the prototype
for this function match the Standard, but that would be wrong, since the function will still
return char *.
If you need a Standard compliant library, then you need to find one, as GCC does not
provide one. The GNU C library (called glibc) provides ISO C, POSIX, BSD, SystemV and

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X/Open compatibility for GNU/Linux and HURD-based GNU systems; no recent version
of it supports other systems, though some very old versions did. Version 2.2 of the GNU
C library includes nearly complete C99 support. You could also ask your operating system
vendor if newer libraries are available.

13.6 Disappointments and Misunderstandings
These problems are perhaps regrettable, but we don’t know any practical way around them.
• Certain local variables aren’t recognized by debuggers when you compile with optimization.
This occurs because sometimes GCC optimizes the variable out of existence. There
is no way to tell the debugger how to compute the value such a variable “would have
had”, and it is not clear that would be desirable anyway. So GCC simply does not
mention the eliminated variable when it writes debugging information.
You have to expect a certain amount of disagreement between the executable and your
source code, when you use optimization.
• Users often think it is a bug when GCC reports an error for code like this:
int foo (struct mumble *);
struct mumble { ... };
int foo (struct mumble *x)
{ ... }

This code really is erroneous, because the scope of struct mumble in the prototype
is limited to the argument list containing it. It does not refer to the struct mumble
defined with file scope immediately below—they are two unrelated types with similar
names in different scopes.
But in the definition of foo, the file-scope type is used because that is available to be
inherited. Thus, the definition and the prototype do not match, and you get an error.
This behavior may seem silly, but it’s what the ISO standard specifies. It is easy enough
for you to make your code work by moving the definition of struct mumble above the
prototype. It’s not worth being incompatible with ISO C just to avoid an error for the
example shown above.
• Accesses to bit-fields even in volatile objects works by accessing larger objects, such as
a byte or a word. You cannot rely on what size of object is accessed in order to read or
write the bit-field; it may even vary for a given bit-field according to the precise usage.
If you care about controlling the amount of memory that is accessed, use volatile but
do not use bit-fields.
• GCC comes with shell scripts to fix certain known problems in system header files.
They install corrected copies of various header files in a special directory where only
GCC will normally look for them. The scripts adapt to various systems by searching
all the system header files for the problem cases that we know about.
If new system header files are installed, nothing automatically arranges to update the
corrected header files. They can be updated using the mkheaders script installed in
‘libexecdir/gcc/target/version/install-tools/’.

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• On 68000 and x86 systems, for instance, you can get paradoxical results if you test
the precise values of floating point numbers. For example, you can find that a floating
point value which is not a NaN is not equal to itself. This results from the fact that
the floating point registers hold a few more bits of precision than fit in a double in
memory. Compiled code moves values between memory and floating point registers at
its convenience, and moving them into memory truncates them.
You can partially avoid this problem by using the ‘-ffloat-store’ option (see
Section 3.10 [Optimize Options], page 114).
• On AIX and other platforms without weak symbol support, templates need to be instantiated explicitly and symbols for static members of templates will not be generated.
• On AIX, GCC scans object files and library archives for static constructors and destructors when linking an application before the linker prunes unreferenced symbols.
This is necessary to prevent the AIX linker from mistakenly assuming that static constructor or destructor are unused and removing them before the scanning can occur.
All static constructors and destructors found will be referenced even though the modules in which they occur may not be used by the program. This may lead to both
increased executable size and unexpected symbol references.

13.7 Common Misunderstandings with GNU C++
C++ is a complex language and an evolving one, and its standard definition (the ISO C++
standard) was only recently completed. As a result, your C++ compiler may occasionally
surprise you, even when its behavior is correct. This section discusses some areas that
frequently give rise to questions of this sort.

13.7.1 Declare and Define Static Members
When a class has static data members, it is not enough to declare the static member; you
must also define it. For example:
class Foo
{
...
void method();
static int bar;
};

This declaration only establishes that the class Foo has an int named Foo::bar, and a
member function named Foo::method. But you still need to define both method and bar
elsewhere. According to the ISO standard, you must supply an initializer in one (and only
one) source file, such as:
int Foo::bar = 0;

Other C++ compilers may not correctly implement the standard behavior. As a result,
when you switch to g++ from one of these compilers, you may discover that a program
that appeared to work correctly in fact does not conform to the standard: g++ reports as
undefined symbols any static data members that lack definitions.

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13.7.2 Name Lookup, Templates, and Accessing Members of Base
Classes
The C++ standard prescribes that all names that are not dependent on template parameters
are bound to their present definitions when parsing a template function or class.1 Only
names that are dependent are looked up at the point of instantiation. For example, consider
void foo(double);
struct A {
template 
void f () {
foo (1);
// 1
int i = N;
// 2
T t;
t.bar();
// 3
foo (t);
// 4
}
static const int N;
};

Here, the names foo and N appear in a context that does not depend on the type of T.
The compiler will thus require that they are defined in the context of use in the template,
not only before the point of instantiation, and will here use ::foo(double) and A::N,
respectively. In particular, it will convert the integer value to a double when passing it to
::foo(double).
Conversely, bar and the call to foo in the fourth marked line are used in contexts that do
depend on the type of T, so they are only looked up at the point of instantiation, and you
can provide declarations for them after declaring the template, but before instantiating it.
In particular, if you instantiate A::f, the last line will call an overloaded ::foo(int)
if one was provided, even if after the declaration of struct A.
This distinction between lookup of dependent and non-dependent names is called twostage (or dependent) name lookup. G++ implements it since version 3.4.
Two-stage name lookup sometimes leads to situations with behavior different from nontemplate codes. The most common is probably this:
template  struct Base {
int i;
};
template  struct Derived : public Base {
int get_i() { return i; }
};

In get_i(), i is not used in a dependent context, so the compiler will look for a name
declared at the enclosing namespace scope (which is the global scope here). It will not look
into the base class, since that is dependent and you may declare specializations of Base
even after declaring Derived, so the compiler cannot really know what i would refer to. If
there is no global variable i, then you will get an error message.
In order to make it clear that you want the member of the base class, you need to defer
lookup until instantiation time, at which the base class is known. For this, you need to
1

The C++ standard just uses the term “dependent” for names that depend on the type or value of template
parameters. This shorter term will also be used in the rest of this section.

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access i in a dependent context, by either using this->i (remember that this is of type
Derived*, so is obviously dependent), or using Base::i. Alternatively, Base::i
might be brought into scope by a using-declaration.
Another, similar example involves calling member functions of a base class:
template  struct Base {
int f();
};
template  struct Derived : Base {
int g() { return f(); };
};

Again, the call to f() is not dependent on template arguments (there are no arguments
that depend on the type T, and it is also not otherwise specified that the call should be
in a dependent context). Thus a global declaration of such a function must be available,
since the one in the base class is not visible until instantiation time. The compiler will
consequently produce the following error message:
x.cc: In member function ‘int Derived::g()’:
x.cc:6: error: there are no arguments to ‘f’ that depend on a template
parameter, so a declaration of ‘f’ must be available
x.cc:6: error: (if you use ‘-fpermissive’, G++ will accept your code, but
allowing the use of an undeclared name is deprecated)

To make the code valid either use this->f(), or Base::f().
Using the
‘-fpermissive’ flag will also let the compiler accept the code, by marking all function
calls for which no declaration is visible at the time of definition of the template for later
lookup at instantiation time, as if it were a dependent call. We do not recommend using
‘-fpermissive’ to work around invalid code, and it will also only catch cases where
functions in base classes are called, not where variables in base classes are used (as in the
example above).
Note that some compilers (including G++ versions prior to 3.4) get these examples wrong
and accept above code without an error. Those compilers do not implement two-stage name
lookup correctly.

13.7.3 Temporaries May Vanish Before You Expect
It is dangerous to use pointers or references to portions of a temporary object. The compiler
may very well delete the object before you expect it to, leaving a pointer to garbage. The
most common place where this problem crops up is in classes like string classes, especially
ones that define a conversion function to type char * or const char *—which is one reason
why the standard string class requires you to call the c_str member function. However,
any class that returns a pointer to some internal structure is potentially subject to this
problem.
For example, a program may use a function strfunc that returns string objects, and
another function charfunc that operates on pointers to char:
string strfunc ();
void charfunc (const char *);
void
f ()
{
const char *p = strfunc().c_str();

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...
charfunc (p);
...
charfunc (p);
}

In this situation, it may seem reasonable to save a pointer to the C string returned by
the c_str member function and use that rather than call c_str repeatedly. However, the
temporary string created by the call to strfunc is destroyed after p is initialized, at which
point p is left pointing to freed memory.
Code like this may run successfully under some other compilers, particularly obsolete
cfront-based compilers that delete temporaries along with normal local variables. However, the GNU C++ behavior is standard-conforming, so if your program depends on late
destruction of temporaries it is not portable.
The safe way to write such code is to give the temporary a name, which forces it to
remain until the end of the scope of the name. For example:
const string& tmp = strfunc ();
charfunc (tmp.c_str ());

13.7.4 Implicit Copy-Assignment for Virtual Bases
When a base class is virtual, only one subobject of the base class belongs to each full
object. Also, the constructors and destructors are invoked only once, and called from the
most-derived class. However, such objects behave unspecified when being assigned. For
example:
struct Base{
char *name;
Base(char *n) : name(strdup(n)){}
Base& operator= (const Base& other){
free (name);
name = strdup (other.name);
}
};
struct A:virtual Base{
int val;
A():Base("A"){}
};
struct B:virtual Base{
int bval;
B():Base("B"){}
};
struct Derived:public A, public B{
Derived():Base("Derived"){}
};
void func(Derived &d1, Derived &d2)
{
d1 = d2;
}

The C++ standard specifies that ‘Base::Base’ is only called once when constructing or
copy-constructing a Derived object. It is unspecified whether ‘Base::operator=’ is called

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more than once when the implicit copy-assignment for Derived objects is invoked (as it is
inside ‘func’ in the example).
G++ implements the “intuitive” algorithm for copy-assignment: assign all direct bases,
then assign all members. In that algorithm, the virtual base subobject can be encountered
more than once. In the example, copying proceeds in the following order: ‘val’, ‘name’ (via
strdup), ‘bval’, and ‘name’ again.
If application code relies on copy-assignment, a user-defined copy-assignment operator
removes any uncertainties. With such an operator, the application can define whether and
how the virtual base subobject is assigned.

13.8 Certain Changes We Don’t Want to Make
This section lists changes that people frequently request, but which we do not make because
we think GCC is better without them.
• Checking the number and type of arguments to a function which has an old-fashioned
definition and no prototype.
Such a feature would work only occasionally—only for calls that appear in the same
file as the called function, following the definition. The only way to check all calls
reliably is to add a prototype for the function. But adding a prototype eliminates the
motivation for this feature. So the feature is not worthwhile.
• Warning about using an expression whose type is signed as a shift count.
Shift count operands are probably signed more often than unsigned. Warning about
this would cause far more annoyance than good.
• Warning about assigning a signed value to an unsigned variable.
Such assignments must be very common; warning about them would cause more annoyance than good.
• Warning when a non-void function value is ignored.
C contains many standard functions that return a value that most programs choose to
ignore. One obvious example is printf. Warning about this practice only leads the
defensive programmer to clutter programs with dozens of casts to void. Such casts
are required so frequently that they become visual noise. Writing those casts becomes
so automatic that they no longer convey useful information about the intentions of
the programmer. For functions where the return value should never be ignored, use
the warn_unused_result function attribute (see Section 6.31 [Function Attributes],
page 464).
• Making ‘-fshort-enums’ the default.
This would cause storage layout to be incompatible with most other C compilers. And
it doesn’t seem very important, given that you can get the same result in other ways.
The case where it matters most is when the enumeration-valued object is inside a
structure, and in that case you can specify a field width explicitly.
• Making bit-fields unsigned by default on particular machines where “the ABI standard”
says to do so.
The ISO C standard leaves it up to the implementation whether a bit-field declared
plain int is signed or not. This in effect creates two alternative dialects of C.

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The GNU C compiler supports both dialects; you can specify the signed dialect with
‘-fsigned-bitfields’ and the unsigned dialect with ‘-funsigned-bitfields’. However, this leaves open the question of which dialect to use by default.
Currently, the preferred dialect makes plain bit-fields signed, because this is simplest.
Since int is the same as signed int in every other context, it is cleanest for them to
be the same in bit-fields as well.
Some computer manufacturers have published Application Binary Interface standards
which specify that plain bit-fields should be unsigned. It is a mistake, however, to say
anything about this issue in an ABI. This is because the handling of plain bit-fields
distinguishes two dialects of C. Both dialects are meaningful on every type of machine.
Whether a particular object file was compiled using signed bit-fields or unsigned is of
no concern to other object files, even if they access the same bit-fields in the same data
structures.
A given program is written in one or the other of these two dialects. The program
stands a chance to work on most any machine if it is compiled with the proper dialect.
It is unlikely to work at all if compiled with the wrong dialect.
Many users appreciate the GNU C compiler because it provides an environment that is
uniform across machines. These users would be inconvenienced if the compiler treated
plain bit-fields differently on certain machines.
Occasionally users write programs intended only for a particular machine type. On
these occasions, the users would benefit if the GNU C compiler were to support by
default the same dialect as the other compilers on that machine. But such applications
are rare. And users writing a program to run on more than one type of machine cannot
possibly benefit from this kind of compatibility.
This is why GCC does and will treat plain bit-fields in the same fashion on all types
of machines (by default).
There are some arguments for making bit-fields unsigned by default on all machines.
If, for example, this becomes a universal de facto standard, it would make sense for
GCC to go along with it. This is something to be considered in the future.
(Of course, users strongly concerned about portability should indicate explicitly in each
bit-field whether it is signed or not. In this way, they write programs which have the
same meaning in both C dialects.)
• Undefining __STDC__ when ‘-ansi’ is not used.
Currently, GCC defines __STDC__ unconditionally. This provides good results in practice.
Programmers normally use conditionals on __STDC__ to ask whether it is safe to use
certain features of ISO C, such as function prototypes or ISO token concatenation.
Since plain gcc supports all the features of ISO C, the correct answer to these questions
is “yes”.
Some users try to use __STDC__ to check for the availability of certain library facilities.
This is actually incorrect usage in an ISO C program, because the ISO C standard says
that a conforming freestanding implementation should define __STDC__ even though it
does not have the library facilities. ‘gcc -ansi -pedantic’ is a conforming freestanding
implementation, and it is therefore required to define __STDC__, even though it does
not come with an ISO C library.

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Using the GNU Compiler Collection (GCC)

Sometimes people say that defining __STDC__ in a compiler that does not completely
conform to the ISO C standard somehow violates the standard. This is illogical. The
standard is a standard for compilers that claim to support ISO C, such as ‘gcc -ansi’—
not for other compilers such as plain gcc. Whatever the ISO C standard says is
relevant to the design of plain gcc without ‘-ansi’ only for pragmatic reasons, not as
a requirement.
GCC normally defines __STDC__ to be 1, and in addition defines __STRICT_ANSI__ if
you specify the ‘-ansi’ option, or a ‘-std’ option for strict conformance to some version
of ISO C. On some hosts, system include files use a different convention, where __STDC_
_ is normally 0, but is 1 if the user specifies strict conformance to the C Standard. GCC
follows the host convention when processing system include files, but when processing
user files it follows the usual GNU C convention.
• Undefining __STDC__ in C++.
Programs written to compile with C++-to-C translators get the value of __STDC__ that
goes with the C compiler that is subsequently used. These programs must test __STDC_
_ to determine what kind of C preprocessor that compiler uses: whether they should
concatenate tokens in the ISO C fashion or in the traditional fashion.
These programs work properly with GNU C++ if __STDC__ is defined. They would not
work otherwise.
In addition, many header files are written to provide prototypes in ISO C but not in
traditional C. Many of these header files can work without change in C++ provided
__STDC__ is defined. If __STDC__ is not defined, they will all fail, and will all need to
be changed to test explicitly for C++ as well.
• Deleting “empty” loops.
Historically, GCC has not deleted “empty” loops under the assumption that the most
likely reason you would put one in a program is to have a delay, so deleting them will
not make real programs run any faster.
However, the rationale here is that optimization of a nonempty loop cannot produce an
empty one. This held for carefully written C compiled with less powerful optimizers but
is not always the case for carefully written C++ or with more powerful optimizers. Thus
GCC will remove operations from loops whenever it can determine those operations
are not externally visible (apart from the time taken to execute them, of course). In
case the loop can be proved to be finite, GCC will also remove the loop itself.
Be aware of this when performing timing tests, for instance the following loop can be
completely removed, provided some_expression can provably not change any global
state.
{
int sum = 0;
int ix;
for (ix = 0; ix != 10000; ix++)
sum += some_expression;
}

Even though sum is accumulated in the loop, no use is made of that summation, so the
accumulation can be removed.
• Making side effects happen in the same order as in some other compiler.

Chapter 13: Known Causes of Trouble with GCC

853

It is never safe to depend on the order of evaluation of side effects. For example, a
function call like this may very well behave differently from one compiler to another:
void func (int, int);
int i = 2;
func (i++, i++);

There is no guarantee (in either the C or the C++ standard language definitions) that the
increments will be evaluated in any particular order. Either increment might happen
first. func might get the arguments ‘2, 3’, or it might get ‘3, 2’, or even ‘2, 2’.
• Making certain warnings into errors by default.
Some ISO C testsuites report failure when the compiler does not produce an error
message for a certain program.
ISO C requires a “diagnostic” message for certain kinds of invalid programs, but a
warning is defined by GCC to count as a diagnostic. If GCC produces a warning but
not an error, that is correct ISO C support. If testsuites call this “failure”, they should
be run with the GCC option ‘-pedantic-errors’, which will turn these warnings into
errors.

13.9 Warning Messages and Error Messages
The GNU compiler can produce two kinds of diagnostics: errors and warnings. Each kind
has a different purpose:
Errors report problems that make it impossible to compile your program. GCC reports
errors with the source file name and line number where the problem is apparent.
Warnings report other unusual conditions in your code that may indicate a problem,
although compilation can (and does) proceed. Warning messages also report the source
file name and line number, but include the text ‘warning:’ to distinguish them from
error messages.
Warnings may indicate danger points where you should check to make sure that your
program really does what you intend; or the use of obsolete features; or the use of nonstandard features of GNU C or C++. Many warnings are issued only if you ask for them, with
one of the ‘-W’ options (for instance, ‘-Wall’ requests a variety of useful warnings).
GCC always tries to compile your program if possible; it never gratuitously rejects a
program whose meaning is clear merely because (for instance) it fails to conform to a
standard. In some cases, however, the C and C++ standards specify that certain extensions
are forbidden, and a diagnostic must be issued by a conforming compiler. The ‘-pedantic’
option tells GCC to issue warnings in such cases; ‘-pedantic-errors’ says to make them
errors instead. This does not mean that all non-ISO constructs get warnings or errors.
See Section 3.8 [Options to Request or Suppress Warnings], page 62, for more detail on
these and related command-line options.

Chapter 14: Reporting Bugs

855

14 Reporting Bugs
Your bug reports play an essential role in making GCC reliable.
When you encounter a problem, the first thing to do is to see if it is already known. See
Chapter 13 [Trouble], page 839. If it isn’t known, then you should report the problem.

14.1 Have You Found a Bug?
If you are not sure whether you have found a bug, here are some guidelines:
• If the compiler gets a fatal signal, for any input whatever, that is a compiler bug.
Reliable compilers never crash.
• If the compiler produces invalid assembly code, for any input whatever (except an
asm statement), that is a compiler bug, unless the compiler reports errors (not just
warnings) which would ordinarily prevent the assembler from being run.
• If the compiler produces valid assembly code that does not correctly execute the input
source code, that is a compiler bug.
However, you must double-check to make sure, because you may have a program whose
behavior is undefined, which happened by chance to give the desired results with another C or C++ compiler.
For example, in many nonoptimizing compilers, you can write ‘x;’ at the end of a
function instead of ‘return x;’, with the same results. But the value of the function
is undefined if return is omitted; it is not a bug when GCC produces different results.
Problems often result from expressions with two increment operators, as in f (*p++,
*p++). Your previous compiler might have interpreted that expression the way you
intended; GCC might interpret it another way. Neither compiler is wrong. The bug is
in your code.
After you have localized the error to a single source line, it should be easy to check for
these things. If your program is correct and well defined, you have found a compiler
bug.
• If the compiler produces an error message for valid input, that is a compiler bug.
• If the compiler does not produce an error message for invalid input, that is a compiler
bug. However, you should note that your idea of “invalid input” might be someone
else’s idea of “an extension” or “support for traditional practice”.
• If you are an experienced user of one of the languages GCC supports, your suggestions
for improvement of GCC are welcome in any case.

14.2 How and Where to Report Bugs
Bugs should be reported to the bug database at http://gcc.gnu.org/bugs/.

Chapter 15: How To Get Help with GCC

857

15 How To Get Help with GCC
If you need help installing, using or changing GCC, there are two ways to find it:
• Send a message to a suitable network mailing list. First try gcc-help@gcc.gnu.org (for
help installing or using GCC), and if that brings no response, try gcc@gcc.gnu.org.
For help changing GCC, ask gcc@gcc.gnu.org. If you think you have found a bug in
GCC, please report it following the instructions at see Section 14.2 [Bug Reporting],
page 855.
• Look in the service directory for someone who might help you for a fee. The service
directory is found at http://www.fsf.org/resources/service.
For further information, see http://gcc.gnu.org/faq.html#support.

Chapter 16: Contributing to GCC Development

859

16 Contributing to GCC Development
If you would like to help pretest GCC releases to assure they work well, current development
sources are available by SVN (see http://gcc.gnu.org/svn.html). Source and binary
snapshots are also available for FTP; see http://gcc.gnu.org/snapshots.html.
If you would like to work on improvements to GCC, please read the advice at these URLs:
http://gcc.gnu.org/contribute.html
http://gcc.gnu.org/contributewhy.html

for information on how to make useful contributions and avoid duplication of effort. Suggested projects are listed at http://gcc.gnu.org/projects/.

Funding Free Software

861

Funding Free Software
If you want to have more free software a few years from now, it makes sense for you to
help encourage people to contribute funds for its development. The most effective approach
known is to encourage commercial redistributors to donate.
Users of free software systems can boost the pace of development by encouraging for-afee distributors to donate part of their selling price to free software developers—the Free
Software Foundation, and others.
The way to convince distributors to do this is to demand it and expect it from them. So
when you compare distributors, judge them partly by how much they give to free software
development. Show distributors they must compete to be the one who gives the most.
To make this approach work, you must insist on numbers that you can compare, such as,
“We will donate ten dollars to the Frobnitz project for each disk sold.” Don’t be satisfied
with a vague promise, such as “A portion of the profits are donated,” since it doesn’t give
a basis for comparison.
Even a precise fraction “of the profits from this disk” is not very meaningful, since creative
accounting and unrelated business decisions can greatly alter what fraction of the sales price
counts as profit. If the price you pay is $50, ten percent of the profit is probably less than
a dollar; it might be a few cents, or nothing at all.
Some redistributors do development work themselves. This is useful too; but to keep
everyone honest, you need to inquire how much they do, and what kind. Some kinds of
development make much more long-term difference than others. For example, maintaining
a separate version of a program contributes very little; maintaining the standard version
of a program for the whole community contributes much. Easy new ports contribute little,
since someone else would surely do them; difficult ports such as adding a new CPU to the
GNU Compiler Collection contribute more; major new features or packages contribute the
most.
By establishing the idea that supporting further development is “the proper thing to
do” when distributing free software for a fee, we can assure a steady flow of resources into
making more free software.
Copyright c 1994 Free Software Foundation, Inc.
Verbatim copying and redistribution of this section is permitted
without royalty; alteration is not permitted.

The GNU Project and GNU/Linux

863

The GNU Project and GNU/Linux
The GNU Project was launched in 1984 to develop a complete Unix-like operating system
which is free software: the GNU system. (GNU is a recursive acronym for “GNU’s Not
Unix”; it is pronounced “guh-NEW”.) Variants of the GNU operating system, which use the
kernel Linux, are now widely used; though these systems are often referred to as “Linux”,
they are more accurately called GNU/Linux systems.
For more information, see:
http://www.gnu.org/
http://www.gnu.org/gnu/linux-and-gnu.html

GNU General Public License

865

GNU General Public License
Version 3, 29 June 2007
Copyright c 2007 Free Software Foundation, Inc. http://fsf.org/
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.

Preamble
The GNU General Public License is a free, copyleft license for software and other kinds of
works.
The licenses for most software and other practical works are designed to take away your
freedom to share and change the works. By contrast, the GNU General Public License is
intended to guarantee your freedom to share and change all versions of a program–to make
sure it remains free software for all its users. We, the Free Software Foundation, use the
GNU General Public License for most of our software; it applies also to any other work
released this way by its authors. You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General
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it if you want it, that you can change the software or use pieces of it in new free programs,
and that you know you can do these things.
To protect your rights, we need to prevent others from denying you these rights or asking
you to surrender the rights. Therefore, you have certain responsibilities if you distribute
copies of the software, or if you modify it: responsibilities to respect the freedom of others.
For example, if you distribute copies of such a program, whether gratis or for a fee, you
must pass on to the recipients the same freedoms that you received. You must make sure
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they know their rights.
Developers that use the GNU GPL protect your rights with two steps: (1) assert copyright
on the software, and (2) offer you this License giving you legal permission to copy, distribute
and/or modify it.
For the developers’ and authors’ protection, the GPL clearly explains that there is no
warranty for this free software. For both users’ and authors’ sake, the GPL requires that
modified versions be marked as changed, so that their problems will not be attributed
erroneously to authors of previous versions.
Some devices are designed to deny users access to install or run modified versions of the
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pattern of such abuse occurs in the area of products for individuals to use, which is precisely where it is most unacceptable. Therefore, we have designed this version of the GPL
to prohibit the practice for those products. If such problems arise substantially in other
domains, we stand ready to extend this provision to those domains in future versions of the
GPL, as needed to protect the freedom of users.

866

Using the GNU Compiler Collection (GCC)

Finally, every program is threatened constantly by software patents. States should not
allow patents to restrict development and use of software on general-purpose computers, but
in those that do, we wish to avoid the special danger that patents applied to a free program
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The precise terms and conditions for copying, distribution and modification follow.

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868

Using the GNU Compiler Collection (GCC)

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All other non-permissive additional terms are considered “further restrictions” within
the meaning of section 10. If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a
further restriction, you may remove that term. If a license document contains a further
restriction but permits relicensing or conveying under this License, you may add to a
covered work material governed by the terms of that license document, provided that
the further restriction does not survive such relicensing or conveying.
If you add terms to a covered work in accord with this section, you must place, in the
relevant source files, a statement of the additional terms that apply to those files, or a
notice indicating where to find the applicable terms.
Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as exceptions; the above requirements apply either
way.
8. Termination.
You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will
automatically terminate your rights under this License (including any patent licenses
granted under the third paragraph of section 11).
However, if you cease all violation of this License, then your license from a particular
copyright holder is reinstated (a) provisionally, unless and until the copyright holder
explicitly and finally terminates your license, and (b) permanently, if the copyright
holder fails to notify you of the violation by some reasonable means prior to 60 days
after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if
the copyright holder notifies you of the violation by some reasonable means, this is the
first time you have received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after your receipt of the
notice.
Termination of your rights under this section does not terminate the licenses of parties
who have received copies or rights from you under this License. If your rights have
been terminated and not permanently reinstated, you do not qualify to receive new
licenses for the same material under section 10.
9. Acceptance Not Required for Having Copies.
You are not required to accept this License in order to receive or run a copy of the
Program. Ancillary propagation of a covered work occurring solely as a consequence of
using peer-to-peer transmission to receive a copy likewise does not require acceptance.

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However, nothing other than this License grants you permission to propagate or modify
any covered work. These actions infringe copyright if you do not accept this License.
Therefore, by modifying or propagating a covered work, you indicate your acceptance
of this License to do so.
10. Automatic Licensing of Downstream Recipients.
Each time you convey a covered work, the recipient automatically receives a license
from the original licensors, to run, modify and propagate that work, subject to this
License. You are not responsible for enforcing compliance by third parties with this
License.
An “entity transaction” is a transaction transferring control of an organization, or
substantially all assets of one, or subdividing an organization, or merging organizations.
If propagation of a covered work results from an entity transaction, each party to that
transaction who receives a copy of the work also receives whatever licenses to the work
the party’s predecessor in interest had or could give under the previous paragraph, plus
a right to possession of the Corresponding Source of the work from the predecessor in
interest, if the predecessor has it or can get it with reasonable efforts.
You may not impose any further restrictions on the exercise of the rights granted or
affirmed under this License. For example, you may not impose a license fee, royalty, or
other charge for exercise of rights granted under this License, and you may not initiate
litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent
claim is infringed by making, using, selling, offering for sale, or importing the Program
or any portion of it.
11. Patents.
A “contributor” is a copyright holder who authorizes use under this License of the
Program or a work on which the Program is based. The work thus licensed is called
the contributor’s “contributor version”.
A contributor’s “essential patent claims” are all patent claims owned or controlled by
the contributor, whether already acquired or hereafter acquired, that would be infringed
by some manner, permitted by this License, of making, using, or selling its contributor
version, but do not include claims that would be infringed only as a consequence of
further modification of the contributor version. For purposes of this definition, “control” includes the right to grant patent sublicenses in a manner consistent with the
requirements of this License.
Each contributor grants you a non-exclusive, worldwide, royalty-free patent license
under the contributor’s essential patent claims, to make, use, sell, offer for sale, import
and otherwise run, modify and propagate the contents of its contributor version.
In the following three paragraphs, a “patent license” is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission
to practice a patent or covenant not to sue for patent infringement). To “grant” such
a patent license to a party means to make such an agreement or commitment not to
enforce a patent against the party.
If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under
the terms of this License, through a publicly available network server or other readily
accessible means, then you must either (1) cause the Corresponding Source to be so

GNU General Public License

873

available, or (2) arrange to deprive yourself of the benefit of the patent license for this
particular work, or (3) arrange, in a manner consistent with the requirements of this
License, to extend the patent license to downstream recipients. “Knowingly relying”
means you have actual knowledge that, but for the patent license, your conveying the
covered work in a country, or your recipient’s use of the covered work in a country,
would infringe one or more identifiable patents in that country that you have reason
to believe are valid.
If, pursuant to or in connection with a single transaction or arrangement, you convey,
or propagate by procuring conveyance of, a covered work, and grant a patent license
to some of the parties receiving the covered work authorizing them to use, propagate,
modify or convey a specific copy of the covered work, then the patent license you grant
is automatically extended to all recipients of the covered work and works based on it.
A patent license is “discriminatory” if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the
rights that are specifically granted under this License. You may not convey a covered
work if you are a party to an arrangement with a third party that is in the business of
distributing software, under which you make payment to the third party based on the
extent of your activity of conveying the work, and under which the third party grants,
to any of the parties who would receive the covered work from you, a discriminatory
patent license (a) in connection with copies of the covered work conveyed by you (or
copies made from those copies), or (b) primarily for and in connection with specific
products or compilations that contain the covered work, unless you entered into that
arrangement, or that patent license was granted, prior to 28 March 2007.
Nothing in this License shall be construed as excluding or limiting any implied license or
other defenses to infringement that may otherwise be available to you under applicable
patent law.
12. No Surrender of Others’ Freedom.
If conditions are imposed on you (whether by court order, agreement or otherwise) that
contradict the conditions of this License, they do not excuse you from the conditions
of this License. If you cannot convey a covered work so as to satisfy simultaneously
your obligations under this License and any other pertinent obligations, then as a
consequence you may not convey it at all. For example, if you agree to terms that
obligate you to collect a royalty for further conveying from those to whom you convey
the Program, the only way you could satisfy both those terms and this License would
be to refrain entirely from conveying the Program.
13. Use with the GNU Affero General Public License.
Notwithstanding any other provision of this License, you have permission to link or
combine any covered work with a work licensed under version 3 of the GNU Affero
General Public License into a single combined work, and to convey the resulting work.
The terms of this License will continue to apply to the part which is the covered work,
but the special requirements of the GNU Affero General Public License, section 13,
concerning interaction through a network will apply to the combination as such.
14. Revised Versions of this License.

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The Free Software Foundation may publish revised and/or new versions of the GNU
General Public License from time to time. Such new versions will be similar in spirit
to the present version, but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies that
a certain numbered version of the GNU General Public License “or any later version”
applies to it, you have the option of following the terms and conditions either of that
numbered version or of any later version published by the Free Software Foundation.
If the Program does not specify a version number of the GNU General Public License,
you may choose any version ever published by the Free Software Foundation.
If the Program specifies that a proxy can decide which future versions of the GNU
General Public License can be used, that proxy’s public statement of acceptance of a
version permanently authorizes you to choose that version for the Program.
Later license versions may give you additional or different permissions. However, no
additional obligations are imposed on any author or copyright holder as a result of your
choosing to follow a later version.
15. Disclaimer of Warranty.
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN
WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE
THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE
OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR
CORRECTION.
16. Limitation of Liability.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO
MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE
LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO
LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM
TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR
OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
17. Interpretation of Sections 15 and 16.
If the disclaimer of warranty and limitation of liability provided above cannot be given
local legal effect according to their terms, reviewing courts shall apply local law that
most closely approximates an absolute waiver of all civil liability in connection with
the Program, unless a warranty or assumption of liability accompanies a copy of the
Program in return for a fee.

GNU General Public License

875

END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
If you develop a new program, and you want it to be of the greatest possible use to the public,
the best way to achieve this is to make it free software which everyone can redistribute and
change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the
start of each source file to most effectively state the exclusion of warranty; and each file
should have at least the “copyright” line and a pointer to where the full notice is found.
one line to give the program’s name and a brief idea of what it does.
Copyright (C) year name of author
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.

Also add information on how to contact you by electronic and paper mail.
If the program does terminal interaction, make it output a short notice like this when it
starts in an interactive mode:
program Copyright (C) year name of author
This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’.
This is free software, and you are welcome to redistribute it
under certain conditions; type ‘show c’ for details.

The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of
the General Public License. Of course, your program’s commands might be different; for a
GUI interface, you would use an “about box”.
You should also get your employer (if you work as a programmer) or school, if any, to
sign a “copyright disclaimer” for the program, if necessary. For more information on this,
and how to apply and follow the GNU GPL, see http://www.gnu.org/licenses/.
The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful
to permit linking proprietary applications with the library. If this is what you want to do,
use the GNU Lesser General Public License instead of this License. But first, please read
http://www.gnu.org/philosophy/why-not-lgpl.html.

GNU Free Documentation License

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GNU Free Documentation License
Version 1.3, 3 November 2008
c
Copyright
2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other functional and
useful document free in the sense of freedom: to assure everyone the effective freedom
to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible for modifications
made by others.
This License is a kind of “copyleft”, which means that derivative works of the document
must themselves be free in the same sense. It complements the GNU General Public
License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because
free software needs free documentation: a free program should come with manuals
providing the same freedoms that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book. We recommend this License principally for
works whose purpose is instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium, that contains a
notice placed by the copyright holder saying it can be distributed under the terms
of this License. Such a notice grants a world-wide, royalty-free license, unlimited in
duration, to use that work under the conditions stated herein. The “Document”,
below, refers to any such manual or work. Any member of the public is a licensee, and
is addressed as “you”. You accept the license if you copy, modify or distribute the work
in a way requiring permission under copyright law.
A “Modified Version” of the Document means any work containing the Document or
a portion of it, either copied verbatim, or with modifications and/or translated into
another language.
A “Secondary Section” is a named appendix or a front-matter section of the Document
that deals exclusively with the relationship of the publishers or authors of the Document
to the Document’s overall subject (or to related matters) and contains nothing that
could fall directly within that overall subject. (Thus, if the Document is in part a
textbook of mathematics, a Secondary Section may not explain any mathematics.) The
relationship could be a matter of historical connection with the subject or with related
matters, or of legal, commercial, philosophical, ethical or political position regarding
them.
The “Invariant Sections” are certain Secondary Sections whose titles are designated, as
being those of Invariant Sections, in the notice that says that the Document is released

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under this License. If a section does not fit the above definition of Secondary then it is
not allowed to be designated as Invariant. The Document may contain zero Invariant
Sections. If the Document does not identify any Invariant Sections then there are none.
The “Cover Texts” are certain short passages of text that are listed, as Front-Cover
Texts or Back-Cover Texts, in the notice that says that the Document is released under
this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may
be at most 25 words.
A “Transparent” copy of the Document means a machine-readable copy, represented
in a format whose specification is available to the general public, that is suitable for
revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing
editor, and that is suitable for input to text formatters or for automatic translation to
a variety of formats suitable for input to text formatters. A copy made in an otherwise
Transparent file format whose markup, or absence of markup, has been arranged to
thwart or discourage subsequent modification by readers is not Transparent. An image
format is not Transparent if used for any substantial amount of text. A copy that is
not “Transparent” is called “Opaque”.
Examples of suitable formats for Transparent copies include plain ascii without
markup, Texinfo input format, LaTEX input format, SGML or XML using a publicly
available DTD, and standard-conforming simple HTML, PostScript or PDF designed
for human modification. Examples of transparent image formats include PNG, XCF
and JPG. Opaque formats include proprietary formats that can be read and edited
only by proprietary word processors, SGML or XML for which the DTD and/or
processing tools are not generally available, and the machine-generated HTML,
PostScript or PDF produced by some word processors for output purposes only.
The “Title Page” means, for a printed book, the title page itself, plus such following
pages as are needed to hold, legibly, the material this License requires to appear in the
title page. For works in formats which do not have any title page as such, “Title Page”
means the text near the most prominent appearance of the work’s title, preceding the
beginning of the body of the text.
The “publisher” means any person or entity that distributes copies of the Document
to the public.
A section “Entitled XYZ” means a named subunit of the Document whose title either
is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in
another language. (Here XYZ stands for a specific section name mentioned below, such
as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve
the Title” of such a section when you modify the Document means that it remains a
section “Entitled XYZ” according to this definition.
The Document may include Warranty Disclaimers next to the notice which states that
this License applies to the Document. These Warranty Disclaimers are considered to
be included by reference in this License, but only as regards disclaiming warranties:
any other implication that these Warranty Disclaimers may have is void and has no
effect on the meaning of this License.
2. VERBATIM COPYING

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You may copy and distribute the Document in any medium, either commercially or
noncommercially, provided that this License, the copyright notices, and the license
notice saying this License applies to the Document are reproduced in all copies, and
that you add no other conditions whatsoever to those of this License. You may not use
technical measures to obstruct or control the reading or further copying of the copies
you make or distribute. However, you may accept compensation in exchange for copies.
If you distribute a large enough number of copies you must also follow the conditions
in section 3.
You may also lend copies, under the same conditions stated above, and you may publicly
display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have printed covers) of
the Document, numbering more than 100, and the Document’s license notice requires
Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all
these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover. Both covers must also clearly and legibly identify you as the publisher
of these copies. The front cover must present the full title with all words of the title
equally prominent and visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve the title of the
Document and satisfy these conditions, can be treated as verbatim copying in other
respects.
If the required texts for either cover are too voluminous to fit legibly, you should put
the first ones listed (as many as fit reasonably) on the actual cover, and continue the
rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100,
you must either include a machine-readable Transparent copy along with each Opaque
copy, or state in or with each Opaque copy a computer-network location from which
the general network-using public has access to download using public-standard network
protocols a complete Transparent copy of the Document, free of added material. If
you use the latter option, you must take reasonably prudent steps, when you begin
distribution of Opaque copies in quantity, to ensure that this Transparent copy will
remain thus accessible at the stated location until at least one year after the last time
you distribute an Opaque copy (directly or through your agents or retailers) of that
edition to the public.
It is requested, but not required, that you contact the authors of the Document well
before redistributing any large number of copies, to give them a chance to provide you
with an updated version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the conditions
of sections 2 and 3 above, provided that you release the Modified Version under precisely
this License, with the Modified Version filling the role of the Document, thus licensing
distribution and modification of the Modified Version to whoever possesses a copy of
it. In addition, you must do these things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title distinct from that of the
Document, and from those of previous versions (which should, if there were any,

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be listed in the History section of the Document). You may use the same title as
a previous version if the original publisher of that version gives permission.
B. List on the Title Page, as authors, one or more persons or entities responsible for
authorship of the modifications in the Modified Version, together with at least five
of the principal authors of the Document (all of its principal authors, if it has fewer
than five), unless they release you from this requirement.
C. State on the Title page the name of the publisher of the Modified Version, as the
publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications adjacent to the other
copyright notices.
F. Include, immediately after the copyright notices, a license notice giving the public
permission to use the Modified Version under the terms of this License, in the form
shown in the Addendum below.
G. Preserve in that license notice the full lists of Invariant Sections and required Cover
Texts given in the Document’s license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled “History”, Preserve its Title, and add to it an item
stating at least the title, year, new authors, and publisher of the Modified Version
as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document
as given on its Title Page, then add an item describing the Modified Version as
stated in the previous sentence.
J. Preserve the network location, if any, given in the Document for public access to
a Transparent copy of the Document, and likewise the network locations given in
the Document for previous versions it was based on. These may be placed in the
“History” section. You may omit a network location for a work that was published
at least four years before the Document itself, or if the original publisher of the
version it refers to gives permission.
K. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title
of the section, and preserve in the section all the substance and tone of each of the
contributor acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document, unaltered in their text and
in their titles. Section numbers or the equivalent are not considered part of the
section titles.
M. Delete any section Entitled “Endorsements”. Such a section may not be included
in the Modified Version.
N. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in
title with any Invariant Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify
as Secondary Sections and contain no material copied from the Document, you may at
your option designate some or all of these sections as invariant. To do this, add their

GNU Free Documentation License

881

titles to the list of Invariant Sections in the Modified Version’s license notice. These
titles must be distinct from any other section titles.
You may add a section Entitled “Endorsements”, provided it contains nothing but
endorsements of your Modified Version by various parties—for example, statements of
peer review or that the text has been approved by an organization as the authoritative
definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up
to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified
Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be
added by (or through arrangements made by) any one entity. If the Document already
includes a cover text for the same cover, previously added by you or by arrangement
made by the same entity you are acting on behalf of, you may not add another; but
you may replace the old one, on explicit permission from the previous publisher that
added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission
to use their names for publicity for or to assert or imply endorsement of any Modified
Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this License,
under the terms defined in section 4 above for modified versions, provided that you
include in the combination all of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your combined work in its license
notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical
Invariant Sections may be replaced with a single copy. If there are multiple Invariant
Sections with the same name but different contents, make the title of each such section
unique by adding at the end of it, in parentheses, the name of the original author or
publisher of that section if known, or else a unique number. Make the same adjustment
to the section titles in the list of Invariant Sections in the license notice of the combined
work.
In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any
sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You
must delete all sections Entitled “Endorsements.”
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents released
under this License, and replace the individual copies of this License in the various
documents with a single copy that is included in the collection, provided that you
follow the rules of this License for verbatim copying of each of the documents in all
other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted
document, and follow this License in all other respects regarding verbatim copying of
that document.

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7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent
documents or works, in or on a volume of a storage or distribution medium, is called
an “aggregate” if the copyright resulting from the compilation is not used to limit the
legal rights of the compilation’s users beyond what the individual works permit. When
the Document is included in an aggregate, this License does not apply to the other
works in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document,
then if the Document is less than one half of the entire aggregate, the Document’s Cover
Texts may be placed on covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form. Otherwise they
must appear on printed covers that bracket the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may distribute translations
of the Document under the terms of section 4. Replacing Invariant Sections with
translations requires special permission from their copyright holders, but you may
include translations of some or all Invariant Sections in addition to the original versions
of these Invariant Sections. You may include a translation of this License, and all the
license notices in the Document, and any Warranty Disclaimers, provided that you
also include the original English version of this License and the original versions of
those notices and disclaimers. In case of a disagreement between the translation and
the original version of this License or a notice or disclaimer, the original version will
prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require
changing the actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as expressly
provided under this License. Any attempt otherwise to copy, modify, sublicense, or
distribute it is void, and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your license from a particular
copyright holder is reinstated (a) provisionally, unless and until the copyright holder
explicitly and finally terminates your license, and (b) permanently, if the copyright
holder fails to notify you of the violation by some reasonable means prior to 60 days
after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if
the copyright holder notifies you of the violation by some reasonable means, this is the
first time you have received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after your receipt of the
notice.
Termination of your rights under this section does not terminate the licenses of parties
who have received copies or rights from you under this License. If your rights have
been terminated and not permanently reinstated, receipt of a copy of some or all of the
same material does not give you any rights to use it.

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10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free
Documentation License from time to time. Such new versions will be similar in spirit
to the present version, but may differ in detail to address new problems or concerns.
See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document
specifies that a particular numbered version of this License “or any later version”
applies to it, you have the option of following the terms and conditions either of that
specified version or of any later version that has been published (not as a draft) by
the Free Software Foundation. If the Document does not specify a version number of
this License, you may choose any version ever published (not as a draft) by the Free
Software Foundation. If the Document specifies that a proxy can decide which future
versions of this License can be used, that proxy’s public statement of acceptance of a
version permanently authorizes you to choose that version for the Document.
11. RELICENSING
“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide
Web server that publishes copyrightable works and also provides prominent facilities
for anybody to edit those works. A public wiki that anybody can edit is an example of
such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the
site means any set of copyrightable works thus published on the MMC site.
“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal
place of business in San Francisco, California, as well as future copyleft versions of that
license published by that same organization.
“Incorporate” means to publish or republish a Document, in whole or in part, as part
of another Document.
An MMC is “eligible for relicensing” if it is licensed under this License, and if all works
that were first published under this License somewhere other than this MMC, and
subsequently incorporated in whole or in part into the MMC, (1) had no cover texts
or invariant sections, and (2) were thus incorporated prior to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site under
CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is
eligible for relicensing.

884

Using the GNU Compiler Collection (GCC)

ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the
document and put the following copyright and license notices just after the title page:
Copyright (C) year your name.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ‘‘GNU
Free Documentation License’’.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the
“with...Texts.” line with this:
with the Invariant Sections being list their titles, with
the Front-Cover Texts being list, and with the Back-Cover Texts
being list.

If you have Invariant Sections without Cover Texts, or some other combination of the
three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing
these examples in parallel under your choice of free software license, such as the GNU
General Public License, to permit their use in free software.

Contributors to GCC

885

Contributors to GCC
The GCC project would like to thank its many contributors. Without them the project
would not have been nearly as successful as it has been. Any omissions in this list are
accidental. Feel free to contact law@redhat.com or gerald@pfeifer.com if you have been
left out or some of your contributions are not listed. Please keep this list in alphabetical
order.
• Analog Devices helped implement the support for complex data types and iterators.
• John David Anglin for threading-related fixes and improvements to libstdc++-v3, and
the HP-UX port.
• James van Artsdalen wrote the code that makes efficient use of the Intel 80387 register
stack.
• Abramo and Roberto Bagnara for the SysV68 Motorola 3300 Delta Series port.
• Alasdair Baird for various bug fixes.
• Giovanni Bajo for analyzing lots of complicated C++ problem reports.
• Peter Barada for his work to improve code generation for new ColdFire cores.
• Gerald Baumgartner added the signature extension to the C++ front end.
• Godmar Back for his Java improvements and encouragement.
• Scott Bambrough for help porting the Java compiler.
• Wolfgang Bangerth for processing tons of bug reports.
• Jon Beniston for his Microsoft Windows port of Java and port to Lattice Mico32.
• Daniel Berlin for better DWARF 2 support, faster/better optimizations, improved alias
analysis, plus migrating GCC to Bugzilla.
• Geoff Berry for his Java object serialization work and various patches.
• David Binderman tests weekly snapshots of GCC trunk against Fedora Rawhide for
several architectures.
• Laurynas Biveinis for memory management work and DJGPP port fixes.
• Uros Bizjak for the implementation of x87 math built-in functions and for various
middle end and i386 back end improvements and bug fixes.
• Eric Blake for helping to make GCJ and libgcj conform to the specifications.
• Janne Blomqvist for contributions to GNU Fortran.
• Hans-J. Boehm for his garbage collector, IA-64 libffi port, and other Java work.
• Segher Boessenkool for helping maintain the PowerPC port and the instruction combiner plus various contributions to the middle end.
• Neil Booth for work on cpplib, lang hooks, debug hooks and other miscellaneous cleanups.
• Steven Bosscher for integrating the GNU Fortran front end into GCC and for contributing to the tree-ssa branch.
• Eric Botcazou for fixing middle- and backend bugs left and right.
• Per Bothner for his direction via the steering committee and various improvements
to the infrastructure for supporting new languages. Chill front end implementation.

886

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Initial implementations of cpplib, fix-header, config.guess, libio, and past C++ library
(libg++) maintainer. Dreaming up, designing and implementing much of GCJ.
Devon Bowen helped port GCC to the Tahoe.
Don Bowman for mips-vxworks contributions.
James Bowman for the FT32 port.
Dave Brolley for work on cpplib and Chill.
Paul Brook for work on the ARM architecture and maintaining GNU Fortran.
Robert Brown implemented the support for Encore 32000 systems.
Christian Bruel for improvements to local store elimination.
Herman A.J. ten Brugge for various fixes.
Joerg Brunsmann for Java compiler hacking and help with the GCJ FAQ.
Joe Buck for his direction via the steering committee from its creation to 2013.
Craig Burley for leadership of the G77 Fortran effort.
Tobias Burnus for contributions to GNU Fortran.
Stephan Buys for contributing Doxygen notes for libstdc++.
Paolo Carlini for libstdc++ work: lots of efficiency improvements to the C++ strings,
streambufs and formatted I/O, hard detective work on the frustrating localization
issues, and keeping up with the problem reports.
John Carr for his alias work, SPARC hacking, infrastructure improvements, previous
contributions to the steering committee, loop optimizations, etc.
Stephane Carrez for 68HC11 and 68HC12 ports.
Steve Chamberlain for support for the Renesas SH and H8 processors and the PicoJava
processor, and for GCJ config fixes.
Glenn Chambers for help with the GCJ FAQ.
John-Marc Chandonia for various libgcj patches.
Denis Chertykov for contributing and maintaining the AVR port, the first GCC port
for an 8-bit architecture.
Kito Cheng for his work on the RISC-V port, including bringing up the test suite and
maintenance.
Scott Christley for his Objective-C contributions.
Eric Christopher for his Java porting help and clean-ups.
Branko Cibej for more warning contributions.
The GNU Classpath project for all of their merged runtime code.
Nick Clifton for arm, mcore, fr30, v850, m32r, msp430 rx work, ‘--help’, and other
random hacking.
Michael Cook for libstdc++ cleanup patches to reduce warnings.
R. Kelley Cook for making GCC buildable from a read-only directory as well as other
miscellaneous build process and documentation clean-ups.
Ralf Corsepius for SH testing and minor bug fixing.
François-Xavier Coudert for contributions to GNU Fortran.

Contributors to GCC

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887

Stan Cox for care and feeding of the x86 port and lots of behind the scenes hacking.
Alex Crain provided changes for the 3b1.
Ian Dall for major improvements to the NS32k port.
Paul Dale for his work to add uClinux platform support to the m68k backend.
Palmer Dabbelt for his work maintaining the RISC-V port.
Dario Dariol contributed the four varieties of sample programs that print a copy of
their source.
Russell Davidson for fstream and stringstream fixes in libstdc++.
Bud Davis for work on the G77 and GNU Fortran compilers.
Mo DeJong for GCJ and libgcj bug fixes.
Jerry DeLisle for contributions to GNU Fortran.
DJ Delorie for the DJGPP port, build and libiberty maintenance, various bug fixes,
and the M32C, MeP, MSP430, and RL78 ports.
Arnaud Desitter for helping to debug GNU Fortran.
Gabriel Dos Reis for contributions to G++, contributions and maintenance of GCC
diagnostics infrastructure, libstdc++-v3, including valarray<>, complex<>, maintaining the numerics library (including that pesky  :-) and keeping up-to-date
anything to do with numbers.
Ulrich Drepper for his work on glibc, testing of GCC using glibc, ISO C99 support,
CFG dumping support, etc., plus support of the C++ runtime libraries including for all
kinds of C interface issues, contributing and maintaining complex<>, sanity checking
and disbursement, configuration architecture, libio maintenance, and early math work.
François Dumont for his work on libstdc++-v3, especially maintaining and improving
debug-mode and associative and unordered containers.
Zdenek Dvorak for a new loop unroller and various fixes.
Michael Eager for his work on the Xilinx MicroBlaze port.
Richard Earnshaw for his ongoing work with the ARM.
David Edelsohn for his direction via the steering committee, ongoing work with the
RS6000/PowerPC port, help cleaning up Haifa loop changes, doing the entire AIX
port of libstdc++ with his bare hands, and for ensuring GCC properly keeps working
on AIX.
Kevin Ediger for the floating point formatting of num put::do put in libstdc++.
Phil Edwards for libstdc++ work including configuration hackery, documentation maintainer, chief breaker of the web pages, the occasional iostream bug fix, and work on
shared library symbol versioning.
Paul Eggert for random hacking all over GCC.
Mark Elbrecht for various DJGPP improvements, and for libstdc++ configuration support for locales and fstream-related fixes.
Vadim Egorov for libstdc++ fixes in strings, streambufs, and iostreams.
Christian Ehrhardt for dealing with bug reports.
Ben Elliston for his work to move the Objective-C runtime into its own subdirectory
and for his work on autoconf.

888

Using the GNU Compiler Collection (GCC)

• Revital Eres for work on the PowerPC 750CL port.
• Marc Espie for OpenBSD support.
• Doug Evans for much of the global optimization framework, arc, m32r, and SPARC
work.
• Christopher Faylor for his work on the Cygwin port and for caring and feeding the
gcc.gnu.org box and saving its users tons of spam.
• Fred Fish for BeOS support and Ada fixes.
• Ivan Fontes Garcia for the Portuguese translation of the GCJ FAQ.
• Peter Gerwinski for various bug fixes and the Pascal front end.
• Kaveh R. Ghazi for his direction via the steering committee, amazing work to make
‘-W -Wall -W* -Werror’ useful, and testing GCC on a plethora of platforms. Kaveh
extends his gratitude to the CAIP Center at Rutgers University for providing him with
computing resources to work on Free Software from the late 1980s to 2010.
• John Gilmore for a donation to the FSF earmarked improving GNU Java.
• Judy Goldberg for c++ contributions.
• Torbjorn Granlund for various fixes and the c-torture testsuite, multiply- and divideby-constant optimization, improved long long support, improved leaf function register
allocation, and his direction via the steering committee.
• Jonny Grant for improvements to collect2’s ‘--help’ documentation.
• Anthony Green for his ‘-Os’ contributions, the moxie port, and Java front end work.
• Stu Grossman for gdb hacking, allowing GCJ developers to debug Java code.
• Michael K. Gschwind contributed the port to the PDP-11.
• Richard Biener for his ongoing middle-end contributions and bug fixes and for release
management.
• Ron Guilmette implemented the protoize and unprotoize tools, the support for
DWARF 1 symbolic debugging information, and much of the support for System V
Release 4. He has also worked heavily on the Intel 386 and 860 support.
• Sumanth Gundapaneni for contributing the CR16 port.
• Mostafa Hagog for Swing Modulo Scheduling (SMS) and post reload GCSE.
• Bruno Haible for improvements in the runtime overhead for EH, new warnings and
assorted bug fixes.
• Andrew Haley for his amazing Java compiler and library efforts.
• Chris Hanson assisted in making GCC work on HP-UX for the 9000 series 300.
• Michael Hayes for various thankless work he’s done trying to get the c30/c40 ports
functional. Lots of loop and unroll improvements and fixes.
• Dara Hazeghi for wading through myriads of target-specific bug reports.
• Kate Hedstrom for staking the G77 folks with an initial testsuite.
• Richard Henderson for his ongoing SPARC, alpha, ia32, and ia64 work, loop opts, and
generally fixing lots of old problems we’ve ignored for years, flow rewrite and lots of
further stuff, including reviewing tons of patches.
• Aldy Hernandez for working on the PowerPC port, SIMD support, and various fixes.

Contributors to GCC

889

• Nobuyuki Hikichi of Software Research Associates, Tokyo, contributed the support for
the Sony NEWS machine.
• Kazu Hirata for caring and feeding the Renesas H8/300 port and various fixes.
• Katherine Holcomb for work on GNU Fortran.
• Manfred Hollstein for his ongoing work to keep the m88k alive, lots of testing and bug
fixing, particularly of GCC configury code.
• Steve Holmgren for MachTen patches.
• Mat Hostetter for work on the TILE-Gx and TILEPro ports.
• Jan Hubicka for his x86 port improvements.
• Falk Hueffner for working on C and optimization bug reports.
• Bernardo Innocenti for his m68k work, including merging of ColdFire improvements
and uClinux support.
• Christian Iseli for various bug fixes.
• Kamil Iskra for general m68k hacking.
• Lee Iverson for random fixes and MIPS testing.
• Balaji V. Iyer for Cilk+ development and merging.
• Andreas Jaeger for testing and benchmarking of GCC and various bug fixes.
• Martin Jambor for his work on inter-procedural optimizations, the switch conversion
pass, and scalar replacement of aggregates.
• Jakub Jelinek for his SPARC work and sibling call optimizations as well as lots of bug
fixes and test cases, and for improving the Java build system.
• Janis Johnson for ia64 testing and fixes, her quality improvement sidetracks, and web
page maintenance.
• Kean Johnston for SCO OpenServer support and various fixes.
• Tim Josling for the sample language treelang based originally on Richard Kenner’s
“toy” language.
• Nicolai Josuttis for additional libstdc++ documentation.
• Klaus Kaempf for his ongoing work to make alpha-vms a viable target.
• Steven G. Kargl for work on GNU Fortran.
• David Kashtan of SRI adapted GCC to VMS.
• Ryszard Kabatek for many, many libstdc++ bug fixes and optimizations of strings,
especially member functions, and for auto ptr fixes.
• Geoffrey Keating for his ongoing work to make the PPC work for GNU/Linux and his
automatic regression tester.
• Brendan Kehoe for his ongoing work with G++ and for a lot of early work in just about
every part of libstdc++.
• Oliver M. Kellogg of Deutsche Aerospace contributed the port to the MIL-STD-1750A.
• Richard Kenner of the New York University Ultracomputer Research Laboratory wrote
the machine descriptions for the AMD 29000, the DEC Alpha, the IBM RT PC, and
the IBM RS/6000 as well as the support for instruction attributes. He also made
changes to better support RISC processors including changes to common subexpression

890

Using the GNU Compiler Collection (GCC)

elimination, strength reduction, function calling sequence handling, and condition code
support, in addition to generalizing the code for frame pointer elimination and delay
slot scheduling. Richard Kenner was also the head maintainer of GCC for several years.
• Mumit Khan for various contributions to the Cygwin and Mingw32 ports and maintaining binary releases for Microsoft Windows hosts, and for massive libstdc++ porting
work to Cygwin/Mingw32.
• Robin Kirkham for cpu32 support.
• Mark Klein for PA improvements.
• Thomas Koenig for various bug fixes.
• Bruce Korb for the new and improved fixincludes code.
• Benjamin Kosnik for his G++ work and for leading the libstdc++-v3 effort.
• Maxim Kuvyrkov for contributions to the instruction scheduler, the Android and
m68k/Coldfire ports, and optimizations.
• Charles LaBrec contributed the support for the Integrated Solutions 68020 system.
• Asher Langton and Mike Kumbera for contributing Cray pointer support to GNU
Fortran, and for other GNU Fortran improvements.
• Jeff Law for his direction via the steering committee, coordinating the entire egcs
project and GCC 2.95, rolling out snapshots and releases, handling merges from GCC2,
reviewing tons of patches that might have fallen through the cracks else, and random
but extensive hacking.
• Walter Lee for work on the TILE-Gx and TILEPro ports.
• Marc Lehmann for his direction via the steering committee and helping with analysis
and improvements of x86 performance.
• Victor Leikehman for work on GNU Fortran.
• Ted Lemon wrote parts of the RTL reader and printer.
• Kriang Lerdsuwanakij for C++ improvements including template as template parameter
support, and many C++ fixes.
• Warren Levy for tremendous work on libgcj (Java Runtime Library) and random work
on the Java front end.
• Alain Lichnewsky ported GCC to the MIPS CPU.
• Oskar Liljeblad for hacking on AWT and his many Java bug reports and patches.
• Robert Lipe for OpenServer support, new testsuites, testing, etc.
• Chen Liqin for various S+core related fixes/improvement, and for maintaining the
S+core port.
• Martin Liska for his work on identical code folding, the sanitizers, HSA, general bug
fixing and for running automated regression testing of GCC and reporting numerous
bugs.
• Weiwen Liu for testing and various bug fixes.
• Manuel López-Ibá~
nez for improving ‘-Wconversion’ and many other diagnostics fixes
and improvements.
• Dave Love for his ongoing work with the Fortran front end and runtime libraries.

Contributors to GCC

891

• Martin von Löwis for internal consistency checking infrastructure, various C++ improvements including namespace support, and tons of assistance with libstdc++/compiler
merges.
• H.J. Lu for his previous contributions to the steering committee, many x86 bug reports,
prototype patches, and keeping the GNU/Linux ports working.
• Greg McGary for random fixes and (someday) bounded pointers.
• Andrew MacLeod for his ongoing work in building a real EH system, various code
generation improvements, work on the global optimizer, etc.
• Vladimir Makarov for hacking some ugly i960 problems, PowerPC hacking improvements to compile-time performance, overall knowledge and direction in the area of
instruction scheduling, design and implementation of the automaton based instruction
scheduler and design and implementation of the integrated and local register allocators.
• David Malcolm for his work on improving GCC diagnostics, JIT, self-tests and unit
testing.
• Bob Manson for his behind the scenes work on dejagnu.
• John Marino for contributing the DragonFly BSD port.
• Philip Martin for lots of libstdc++ string and vector iterator fixes and improvements,
and string clean up and testsuites.
• Michael Matz for his work on dominance tree discovery, the x86-64 port, link-time
optimization framework and general optimization improvements.
• All of the Mauve project contributors for Java test code.
• Bryce McKinlay for numerous GCJ and libgcj fixes and improvements.
• Adam Megacz for his work on the Microsoft Windows port of GCJ.
• Michael Meissner for LRS framework, ia32, m32r, v850, m88k, MIPS, powerpc, haifa,
ECOFF debug support, and other assorted hacking.
• Jason Merrill for his direction via the steering committee and leading the G++ effort.
• Martin Michlmayr for testing GCC on several architectures using the entire Debian
archive.
• David Miller for his direction via the steering committee, lots of SPARC work, improvements in jump.c and interfacing with the Linux kernel developers.
• Gary Miller ported GCC to Charles River Data Systems machines.
• Alfred Minarik for libstdc++ string and ios bug fixes, and turning the entire libstdc++
testsuite namespace-compatible.
• Mark Mitchell for his direction via the steering committee, mountains of C++ work,
load/store hoisting out of loops, alias analysis improvements, ISO C restrict support,
and serving as release manager from 2000 to 2011.
• Alan Modra for various GNU/Linux bits and testing.
• Toon Moene for his direction via the steering committee, Fortran maintenance, and his
ongoing work to make us make Fortran run fast.
• Jason Molenda for major help in the care and feeding of all the services on the
gcc.gnu.org (formerly egcs.cygnus.com) machine—mail, web services, ftp services, etc
etc. Doing all this work on scrap paper and the backs of envelopes would have been. . .
difficult.

892

Using the GNU Compiler Collection (GCC)

• Catherine Moore for fixing various ugly problems we have sent her way, including the
haifa bug which was killing the Alpha & PowerPC Linux kernels.
• Mike Moreton for his various Java patches.
• David Mosberger-Tang for various Alpha improvements, and for the initial IA-64 port.
• Stephen Moshier contributed the floating point emulator that assists in crosscompilation and permits support for floating point numbers wider than 64 bits and
for ISO C99 support.
• Bill Moyer for his behind the scenes work on various issues.
• Philippe De Muyter for his work on the m68k port.
• Joseph S. Myers for his work on the PDP-11 port, format checking and ISO C99
support, and continuous emphasis on (and contributions to) documentation.
• Nathan Myers for his work on libstdc++-v3: architecture and authorship through the
first three snapshots, including implementation of locale infrastructure, string, shadow
C headers, and the initial project documentation (DESIGN, CHECKLIST, and so
forth). Later, more work on MT-safe string and shadow headers.
• Felix Natter for documentation on porting libstdc++.
• Nathanael Nerode for cleaning up the configuration/build process.
• NeXT, Inc. donated the front end that supports the Objective-C language.
• Hans-Peter Nilsson for the CRIS and MMIX ports, improvements to the search engine
setup, various documentation fixes and other small fixes.
• Geoff Noer for his work on getting cygwin native builds working.
• Vegard Nossum for running automated regression testing of GCC and reporting numerous bugs.
• Diego Novillo for his work on Tree SSA, OpenMP, SPEC performance tracking web
pages, GIMPLE tuples, and assorted fixes.
• David O’Brien for the FreeBSD/alpha, FreeBSD/AMD x86-64, FreeBSD/ARM,
FreeBSD/PowerPC, and FreeBSD/SPARC64 ports and related infrastructure
improvements.
• Alexandre Oliva for various build infrastructure improvements, scripts and amazing
testing work, including keeping libtool issues sane and happy.
• Stefan Olsson for work on mt alloc.
• Melissa O’Neill for various NeXT fixes.
• Rainer Orth for random MIPS work, including improvements to GCC’s o32 ABI support, improvements to dejagnu’s MIPS support, Java configuration clean-ups and porting work, and maintaining the IRIX, Solaris 2, and Tru64 UNIX ports.
• Steven Pemberton for his contribution of ‘enquire’ which allowed GCC to determine
various properties of the floating point unit and generate ‘float.h’ in older versions
of GCC.
• Hartmut Penner for work on the s390 port.
• Paul Petersen wrote the machine description for the Alliant FX/8.
• Alexandre Petit-Bianco for implementing much of the Java compiler and continued
Java maintainership.

Contributors to GCC

893

• Matthias Pfaller for major improvements to the NS32k port.
• Gerald Pfeifer for his direction via the steering committee, pointing out lots of problems
we need to solve, maintenance of the web pages, and taking care of documentation
maintenance in general.
• Marek Polacek for his work on the C front end, the sanitizers and general bug fixing.
• Andrew Pinski for processing bug reports by the dozen.
• Ovidiu Predescu for his work on the Objective-C front end and runtime libraries.
• Jerry Quinn for major performance improvements in C++ formatted I/O.
• Ken Raeburn for various improvements to checker, MIPS ports and various cleanups
in the compiler.
• Rolf W. Rasmussen for hacking on AWT.
• David Reese of Sun Microsystems contributed to the Solaris on PowerPC port.
• John Regehr for running automated regression testing of GCC and reporting numerous
bugs.
• Volker Reichelt for running automated regression testing of GCC and reporting numerous bugs and for keeping up with the problem reports.
• Joern Rennecke for maintaining the sh port, loop, regmove & reload hacking and developing and maintaining the Epiphany port.
• Loren J. Rittle for improvements to libstdc++-v3 including the FreeBSD port, threading
fixes, thread-related configury changes, critical threading documentation, and solutions
to really tricky I/O problems, as well as keeping GCC properly working on FreeBSD
and continuous testing.
• Craig Rodrigues for processing tons of bug reports.
• Ola Rönnerup for work on mt alloc.
• Gavin Romig-Koch for lots of behind the scenes MIPS work.
• David Ronis inspired and encouraged Craig to rewrite the G77 documentation in texinfo
format by contributing a first pass at a translation of the old ‘g77-0.5.16/f/DOC’ file.
• Ken Rose for fixes to GCC’s delay slot filling code.
• Ira Rosen for her contributions to the auto-vectorizer.
• Paul Rubin wrote most of the preprocessor.
• Pétur Runólfsson for major performance improvements in C++ formatted I/O and large
file support in C++ filebuf.
• Chip Salzenberg for libstdc++ patches and improvements to locales, traits, Makefiles,
libio, libtool hackery, and “long long” support.
• Juha Sarlin for improvements to the H8 code generator.
• Greg Satz assisted in making GCC work on HP-UX for the 9000 series 300.
• Roger Sayle for improvements to constant folding and GCC’s RTL optimizers as well
as for fixing numerous bugs.
• Bradley Schatz for his work on the GCJ FAQ.
• Peter Schauer wrote the code to allow debugging to work on the Alpha.
• William Schelter did most of the work on the Intel 80386 support.

894

Using the GNU Compiler Collection (GCC)

• Tobias Schlüter for work on GNU Fortran.
• Bernd Schmidt for various code generation improvements and major work in the reload
pass, serving as release manager for GCC 2.95.3, and work on the Blackfin and C6X
ports.
• Peter Schmid for constant testing of libstdc++—especially application testing, going
above and beyond what was requested for the release criteria—and libstdc++ header
file tweaks.
• Jason Schroeder for jcf-dump patches.
• Andreas Schwab for his work on the m68k port.
• Lars Segerlund for work on GNU Fortran.
• Dodji Seketeli for numerous C++ bug fixes and debug info improvements.
• Tim Shen for major work on .
• Joel Sherrill for his direction via the steering committee, RTEMS contributions and
RTEMS testing.
• Nathan Sidwell for many C++ fixes/improvements.
• Jeffrey Siegal for helping RMS with the original design of GCC, some code which
handles the parse tree and RTL data structures, constant folding and help with the
original VAX & m68k ports.
• Kenny Simpson for prompting libstdc++ fixes due to defect reports from the LWG
(thereby keeping GCC in line with updates from the ISO).
• Franz Sirl for his ongoing work with making the PPC port stable for GNU/Linux.
• Andrey Slepuhin for assorted AIX hacking.
• Trevor Smigiel for contributing the SPU port.
• Christopher Smith did the port for Convex machines.
• Danny Smith for his major efforts on the Mingw (and Cygwin) ports. Retired from
GCC maintainership August 2010, having mentored two new maintainers into the role.
• Randy Smith finished the Sun FPA support.
• Ed Smith-Rowland for his continuous work on libstdc++-v3, special functions,
, and various improvements to C++11 features.
• Scott Snyder for queue, iterator, istream, and string fixes and libstdc++ testsuite entries. Also for providing the patch to G77 to add rudimentary support for INTEGER*1,
INTEGER*2, and LOGICAL*1.
• Zdenek Sojka for running automated regression testing of GCC and reporting numerous
bugs.
• Arseny Solokha for running automated regression testing of GCC and reporting numerous bugs.
• Jayant Sonar for contributing the CR16 port.
• Brad Spencer for contributions to the GLIBCPP FORCE NEW technique.
• Richard Stallman, for writing the original GCC and launching the GNU project.
• Jan Stein of the Chalmers Computer Society provided support for Genix, as well as
part of the 32000 machine description.

Contributors to GCC

895

• Gerhard Steinmetz for running automated regression testing of GCC and reporting
numerous bugs.
• Nigel Stephens for various mips16 related fixes/improvements.
• Jonathan Stone wrote the machine description for the Pyramid computer.
• Graham Stott for various infrastructure improvements.
• John Stracke for his Java HTTP protocol fixes.
• Mike Stump for his Elxsi port, G++ contributions over the years and more recently his
vxworks contributions
• Jeff Sturm for Java porting help, bug fixes, and encouragement.
• Zhendong Su for running automated regression testing of GCC and reporting numerous
bugs.
• Chengnian Sun for running automated regression testing of GCC and reporting numerous bugs.
• Shigeya Suzuki for this fixes for the bsdi platforms.
• Ian Lance Taylor for the Go frontend, the initial mips16 and mips64 support, general
configury hacking, fixincludes, etc.
• Holger Teutsch provided the support for the Clipper CPU.
• Gary Thomas for his ongoing work to make the PPC work for GNU/Linux.
• Paul Thomas for contributions to GNU Fortran.
• Philipp Thomas for random bug fixes throughout the compiler
• Jason Thorpe for thread support in libstdc++ on NetBSD.
• Kresten Krab Thorup wrote the run time support for the Objective-C language and
the fantastic Java bytecode interpreter.
• Michael Tiemann for random bug fixes, the first instruction scheduler, initial C++
support, function integration, NS32k, SPARC and M88k machine description work,
delay slot scheduling.
• Andreas Tobler for his work porting libgcj to Darwin.
• Teemu Torma for thread safe exception handling support.
• Leonard Tower wrote parts of the parser, RTL generator, and RTL definitions, and of
the VAX machine description.
• Daniel Towner and Hariharan Sandanagobalane contributed and maintain the picoChip
port.
• Tom Tromey for internationalization support and for his many Java contributions and
libgcj maintainership.
• Lassi Tuura for improvements to config.guess to determine HP processor types.
• Petter Urkedal for libstdc++ CXXFLAGS, math, and algorithms fixes.
• Andy Vaught for the design and initial implementation of the GNU Fortran front end.
• Brent Verner for work with the libstdc++ cshadow files and their associated configure
steps.
• Todd Vierling for contributions for NetBSD ports.
• Andrew Waterman for contributing the RISC-V port, as well as maintaining it.

896

Using the GNU Compiler Collection (GCC)

• Jonathan Wakely for contributing libstdc++ Doxygen notes and XHTML guidance and
maintaining libstdc++.
• Dean Wakerley for converting the install documentation from HTML to texinfo in time
for GCC 3.0.
• Krister Walfridsson for random bug fixes.
• Feng Wang for contributions to GNU Fortran.
• Stephen M. Webb for time and effort on making libstdc++ shadow files work with the
tricky Solaris 8+ headers, and for pushing the build-time header tree. Also, for starting
and driving the  effort.
• John Wehle for various improvements for the x86 code generator, related infrastructure
improvements to help x86 code generation, value range propagation and other work,
WE32k port.
• Ulrich Weigand for work on the s390 port.
• Janus Weil for contributions to GNU Fortran.
• Zack Weinberg for major work on cpplib and various other bug fixes.
• Matt Welsh for help with Linux Threads support in GCJ.
• Urban Widmark for help fixing java.io.
• Mark Wielaard for new Java library code and his work integrating with Classpath.
• Dale Wiles helped port GCC to the Tahoe.
• Bob Wilson from Tensilica, Inc. for the Xtensa port.
• Jim Wilson for his direction via the steering committee, tackling hard problems in
various places that nobody else wanted to work on, strength reduction and other loop
optimizations.
• Paul Woegerer and Tal Agmon for the CRX port.
• Carlo Wood for various fixes.
• Tom Wood for work on the m88k port.
• Chung-Ju Wu for his work on the Andes NDS32 port.
• Canqun Yang for work on GNU Fortran.
• Masanobu Yuhara of Fujitsu Laboratories implemented the machine description for the
Tron architecture (specifically, the Gmicro).
• Kevin Zachmann helped port GCC to the Tahoe.
• Ayal Zaks for Swing Modulo Scheduling (SMS).
• Qirun Zhang for running automated regression testing of GCC and reporting numerous
bugs.
• Xiaoqiang Zhang for work on GNU Fortran.
• Gilles Zunino for help porting Java to Irix.
The following people are recognized for their contributions to GNAT, the Ada front end
of GCC:
• Bernard Banner
• Romain Berrendonner

Contributors to GCC

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Geert Bosch
Emmanuel Briot
Joel Brobecker
Ben Brosgol
Vincent Celier
Arnaud Charlet
Chien Chieng
Cyrille Comar
Cyrille Crozes
Robert Dewar
Gary Dismukes
Robert Duff
Ed Falis
Ramon Fernandez
Sam Figueroa
Vasiliy Fofanov
Michael Friess
Franco Gasperoni
Ted Giering
Matthew Gingell
Laurent Guerby
Jerome Guitton
Olivier Hainque
Jerome Hugues
Hristian Kirtchev
Jerome Lambourg
Bruno Leclerc
Albert Lee
Sean McNeil
Javier Miranda
Laurent Nana
Pascal Obry
Dong-Ik Oh
Laurent Pautet
Brett Porter
Thomas Quinot
Nicolas Roche
Pat Rogers
Jose Ruiz

897

898

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Douglas Rupp
Sergey Rybin
Gail Schenker
Ed Schonberg
Nicolas Setton
Samuel Tardieu

The following people are recognized for their contributions of new features, bug reports,
testing and integration of classpath/libgcj for GCC version 4.1:
• Lillian Angel for JTree implementation and lots Free Swing additions and bug fixes.
• Wolfgang Baer for GapContent bug fixes.
• Anthony Balkissoon for JList, Free Swing 1.5 updates and mouse event fixes, lots of
Free Swing work including JTable editing.
• Stuart Ballard for RMI constant fixes.
• Goffredo Baroncelli for HTTPURLConnection fixes.
• Gary Benson for MessageFormat fixes.
• Daniel Bonniot for Serialization fixes.
• Chris Burdess for lots of gnu.xml and http protocol fixes, StAX and DOM xml:id support.
• Ka-Hing Cheung for TreePath and TreeSelection fixes.
• Archie Cobbs for build fixes, VM interface updates, URLClassLoader updates.
• Kelley Cook for build fixes.
• Martin Cordova for Suggestions for better SocketTimeoutException.
• David Daney for BitSet bug fixes, HttpURLConnection rewrite and improvements.
• Thomas Fitzsimmons for lots of upgrades to the gtk+ AWT and Cairo 2D support.
Lots of imageio framework additions, lots of AWT and Free Swing bug fixes.
• Jeroen Frijters for ClassLoader and nio cleanups, serialization fixes, better Proxy
support, bug fixes and IKVM integration.
• Santiago Gala for AccessControlContext fixes.
• Nicolas Geoffray for VMClassLoader and AccessController improvements.
• David Gilbert for basic and metal icon and plaf support and lots of documenting,
Lots of Free Swing and metal theme additions. MetalIconFactory implementation.
• Anthony Green for MIDI framework, ALSA and DSSI providers.
• Andrew Haley for Serialization and URLClassLoader fixes, gcj build speedups.
• Kim Ho for JFileChooser implementation.
• Andrew John Hughes for Locale and net fixes, URI RFC2986 updates, Serialization
fixes, Properties XML support and generic branch work, VMIntegration guide update.
• Bastiaan Huisman for TimeZone bug fixing.
• Andreas Jaeger for mprec updates.
• Paul Jenner for better ‘-Werror’ support.
• Ito Kazumitsu for NetworkInterface implementation and updates.

Contributors to GCC

899

• Roman Kennke for BoxLayout, GrayFilter and SplitPane, plus bug fixes all over.
Lots of Free Swing work including styled text.
• Simon Kitching for String cleanups and optimization suggestions.
• Michael Koch for configuration fixes, Locale updates, bug and build fixes.
• Guilhem Lavaux for configuration, thread and channel fixes and Kaffe integration. JCL
native Pointer updates. Logger bug fixes.
• David Lichteblau for JCL support library global/local reference cleanups.
• Aaron Luchko for JDWP updates and documentation fixes.
• Ziga Mahkovec for Graphics2D upgraded to Cairo 0.5 and new regex features.
• Sven de Marothy for BMP imageio support, CSS and TextLayout fixes. GtkImage
rewrite, 2D, awt, free swing and date/time fixes and implementing the Qt4 peers.
• Casey Marshall for crypto algorithm fixes, FileChannel lock, SystemLogger and
FileHandler rotate implementations, NIO FileChannel.map support, security and
policy updates.
• Bryce McKinlay for RMI work.
• Audrius Meskauskas for lots of Free Corba, RMI and HTML work plus testing and
documenting.
• Kalle Olavi Niemitalo for build fixes.
• Rainer Orth for build fixes.
• Andrew Overholt for File locking fixes.
• Ingo Proetel for Image, Logger and URLClassLoader updates.
• Olga Rodimina for MenuSelectionManager implementation.
• Jan Roehrich for BasicTreeUI and JTree fixes.
• Julian Scheid for documentation updates and gjdoc support.
• Christian Schlichtherle for zip fixes and cleanups.
• Robert Schuster for documentation updates and beans fixes, TreeNode enumerations
and ActionCommand and various fixes, XML and URL, AWT and Free Swing bug fixes.
• Keith Seitz for lots of JDWP work.
• Christian Thalinger for 64-bit cleanups, Configuration and VM interface fixes and
CACAO integration, fdlibm updates.
• Gael Thomas for VMClassLoader boot packages support suggestions.
• Andreas Tobler for Darwin and Solaris testing and fixing, Qt4 support for Darwin/OS
X, Graphics2D support, gtk+ updates.
• Dalibor Topic for better DEBUG support, build cleanups and Kaffe integration. Qt4
build infrastructure, SHA1PRNG and GdkPixbugDecoder updates.
• Tom Tromey for Eclipse integration, generics work, lots of bug fixes and gcj integration
including coordinating The Big Merge.
• Mark Wielaard for bug fixes, packaging and release management, Clipboard implementation, system call interrupts and network timeouts and GdkPixpufDecoder fixes.
In addition to the above, all of which also contributed time and energy in testing GCC,
we would like to thank the following for their contributions to testing:

900

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Using the GNU Compiler Collection (GCC)

Michael Abd-El-Malek
Thomas Arend
Bonzo Armstrong
Steven Ashe
Chris Baldwin
David Billinghurst
Jim Blandy
Stephane Bortzmeyer
Horst von Brand
Frank Braun
Rodney Brown
Sidney Cadot
Bradford Castalia
Robert Clark
Jonathan Corbet
Ralph Doncaster
Richard Emberson
Levente Farkas
Graham Fawcett
Mark Fernyhough
Robert A. French
Jörgen Freyh
Mark K. Gardner
Charles-Antoine Gauthier
Yung Shing Gene
David Gilbert
Simon Gornall
Fred Gray
John Griffin
Patrik Hagglund
Phil Hargett
Amancio Hasty
Takafumi Hayashi
Bryan W. Headley
Kevin B. Hendricks
Joep Jansen
Christian Joensson
Michel Kern
David Kidd

Contributors to GCC

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Tobias Kuipers
Anand Krishnaswamy
A. O. V. Le Blanc
llewelly
Damon Love
Brad Lucier
Matthias Klose
Martin Knoblauch
Rick Lutowski
Jesse Macnish
Stefan Morrell
Anon A. Mous
Matthias Mueller
Pekka Nikander
Rick Niles
Jon Olson
Magnus Persson
Chris Pollard
Richard Polton
Derk Reefman
David Rees
Paul Reilly
Tom Reilly
Torsten Rueger
Danny Sadinoff
Marc Schifer
Erik Schnetter
Wayne K. Schroll
David Schuler
Vin Shelton
Tim Souder
Adam Sulmicki
Bill Thorson
George Talbot
Pedro A. M. Vazquez
Gregory Warnes
Ian Watson
David E. Young
And many others

901

902

Using the GNU Compiler Collection (GCC)

And finally we’d like to thank everyone who uses the compiler, provides feedback and
generally reminds us why we’re doing this work in the first place.

Option Index

903

Option Index
GCC’s command line options are indexed here without any initial ‘-’ or ‘--’. Where an
option has both positive and negative forms (such as ‘-foption’ and ‘-fno-option’), relevant entries in the manual are indexed under the most appropriate form; it may sometimes
be useful to look up both forms.

#

D

### . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193,
da . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193,
dead_strip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dependency-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dumpfullversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dumpmachine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dumpspecs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dumpversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dylib_file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dylinker_install_name . . . . . . . . . . . . . . . . . . . . . .
dynamic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
dynamiclib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D.............................................

-fipa-bit-cp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
-fipa-vrp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
-mfunction-return . . . . . . . . . . . . . . . . . . . . . . . . . . 411
-mindirect-branch . . . . . . . . . . . . . . . . . . . . . . . . . . 410
-mindirect-branch-register . . . . . . . . . . . . . . . . 411
-mlow-precision-div . . . . . . . . . . . . . . . . . . . . . . . . 230
-mlow-precision-sqrt . . . . . . . . . . . . . . . . . . . . . . . 230
-mno-low-precision-div . . . . . . . . . . . . . . . . . . . . . 230
-mno-low-precision-sqrt . . . . . . . . . . . . . . . . . . . 230
-Wabi-tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
-Wno-scalar-storage-order . . . . . . . . . . . . . . . . . . 99
-Wscalar-storage-order . . . . . . . . . . . . . . . . . . . . . . 99

8
80387 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397

A
all_load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
allowable_client. . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
ansi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 35, 614, 851
arch_errors_fatal . . . . . . . . . . . . . . . . . . . . . . . . . . 274
aux-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

B
Bdynamic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
bind_at_load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.............................................
Bstatic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
bundle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
bundle_loader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

389
274
201
389
274
274

C
c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31,
CC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
client_name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
compatibility_version . . . . . . . . . . . . . . . . . . . . . .
coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
current_version . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C.............................................

195
192
276
276
173
276
192

213
216
216
216
276
276
216
193
193
193
216
217
228
228
228
228
194
217
276
276
276
274
187

E
EB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244,
EL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244,
exported_symbols_list . . . . . . . . . . . . . . . . . . . . . .
E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31,

304
304
276
195

F
fabi-compat-version . . . . . . . . . . . . . . . . . . . . . . . . . 43
fabi-version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
fada-spec-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
faggressive-loop-optimizations . . . . . . . . . . . 122
falign-functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
falign-jumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
falign-labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
falign-loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
faligned-new . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
fallow-parameterless-variadic-functions . . 38
fasan-shadow-offset . . . . . . . . . . . . . . . . . . . . . . . . 179
fassociative-math . . . . . . . . . . . . . . . . . . . . . . . . . . 148
fasynchronous-unwind-tables . . . . . . . . . . . . . . . 205
fauto-inc-dec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
fauto-profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

904

Using the GNU Compiler Collection (GCC)

fbounds-check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
fbranch-probabilities . . . . . . . . . . . . . . . . . . . . . . 150
fbranch-target-load-optimize . . . . . . . . . . . . . . 152
fbranch-target-load-optimize2 . . . . . . . . . . . . . 153
fbtr-bb-exclusive . . . . . . . . . . . . . . . . . . . . . . . . . . 153
fcall-saved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
fcall-used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
fcaller-saves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
fcf-protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
fcheck-new. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
fcheck-pointer-bounds . . . . . . . . . . . . . . . . . . . . . . 180
fchecking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
fchkp-check-incomplete-type . . . . . . . . . . . . . . . 181
fchkp-check-read. . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
fchkp-check-write . . . . . . . . . . . . . . . . . . . . . . . . . . 182
fchkp-first-field-has-own-bounds . . . . . . . . . 181
fchkp-flexible-struct-trailing-arrays . . . 181
fchkp-instrument-calls . . . . . . . . . . . . . . . . . . . . . 182
fchkp-instrument-marked-only . . . . . . . . . . . . . . 182
fchkp-narrow-bounds . . . . . . . . . . . . . . . . . . . . . . . . 181
fchkp-narrow-to-innermost-array . . . . . . . . . . 181
fchkp-optimize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
fchkp-store-bounds . . . . . . . . . . . . . . . . . . . . . . . . . 182
fchkp-treat-zero-dynamic-size-as-infinite
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
fchkp-use-fast-string-functions . . . . . . . . . . 181
fchkp-use-nochk-string-functions . . . . . . . . . 181
fchkp-use-static-bounds . . . . . . . . . . . . . . . . . . . 181
fchkp-use-static-const-bounds . . . . . . . . . . . . . 181
fchkp-use-wrappers . . . . . . . . . . . . . . . . . . . . . . . . . 182
fcode-hoisting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
fcombine-stack-adjustments . . . . . . . . . . . . . . . . 129
fcommon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
fcompare-debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
fcompare-debug-second . . . . . . . . . . . . . . . . . . . . . . 225
fcompare-elim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
fconcepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
fcond-mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
fconserve-stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
fconstant-string-class . . . . . . . . . . . . . . . . . . . . . . 55
fconstexpr-depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
fconstexpr-loop-limit . . . . . . . . . . . . . . . . . . . . . . . 44
fcprop-registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
fcrossjumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
fcse-follow-jumps . . . . . . . . . . . . . . . . . . . . . . . . . . 121
fcse-skip-blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
fcx-fortran-rules . . . . . . . . . . . . . . . . . . . . . . . . . . 150
fcx-limited-range . . . . . . . . . . . . . . . . . . . . . . . . . . 150
fdata-sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
fdbg-cnt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
fdbg-cnt-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
fdce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
fdebug-cpp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
fdebug-prefix-map . . . . . . . . . . . . . . . . . . . . . . . . . . 110
fdebug-types-section . . . . . . . . . . . . . . . . . . . . . . . 110
fdeclone-ctor-dtor . . . . . . . . . . . . . . . . . . . . . . . . . 123
fdeduce-init-list. . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
fdelayed-branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

fdelete-dead-exceptions . . . . . . . . . . . . . . . . . . . 205
fdelete-null-pointer-checks . . . . . . . . . . . . . . . 123
fdevirtualize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
fdevirtualize-at-ltrans . . . . . . . . . . . . . . . . . . . 124
fdevirtualize-speculatively . . . . . . . . . . . . . . . 124
fdiagnostics-color . . . . . . . . . . . . . . . . . . . . . . . . . . 59
fdiagnostics-generate-patch . . . . . . . . . . . . . . . . 61
fdiagnostics-parseable-fixits . . . . . . . . . . . . . . 61
fdiagnostics-show-caret . . . . . . . . . . . . . . . . . . . . . 61
fdiagnostics-show-location . . . . . . . . . . . . . . . . . 59
fdiagnostics-show-option . . . . . . . . . . . . . . . . . . . 61
fdiagnostics-show-template-tree . . . . . . . . . . . 61
fdirectives-only. . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
fdisable- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
fdollars-in-identifiers . . . . . . . . . . . . . . . 190, 841
fdpic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
fdse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
fdump-ada-spec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
fdump-final-insns . . . . . . . . . . . . . . . . . . . . . . . . . . 224
fdump-go-spec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
fdump-ipa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
fdump-lang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
fdump-lang-all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
fdump-noaddr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
fdump-passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
fdump-rtl-alignments . . . . . . . . . . . . . . . . . . . . . . . 213
fdump-rtl-all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-asmcons . . . . . . . . . . . . . . . . . . . . . . . . . . 213
fdump-rtl-auto_inc_dec . . . . . . . . . . . . . . . . . . . . . 213
fdump-rtl-barriers . . . . . . . . . . . . . . . . . . . . . . . . . 213
fdump-rtl-bbpart. . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
fdump-rtl-bbro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
fdump-rtl-btl2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
fdump-rtl-bypass. . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-ce1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-ce2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-ce3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-combine . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-compgotos . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-cprop_hardreg . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-csa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-cse1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-cse2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-dbr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-dce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-dce1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-dce2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-dfinish . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-dfinit. . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-eh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-eh_ranges . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-expand. . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-fwprop1 . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-fwprop2 . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-gcse1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-gcse2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
fdump-rtl-init-regs . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-initvals . . . . . . . . . . . . . . . . . . . . . . . . . 215

Option Index

fdump-rtl-into_cfglayout . . . . . . . . . . . . . . . . . . 215
fdump-rtl-ira . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-jump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-loop2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-mach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-mode_sw . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-outof_cfglayout . . . . . . . . . . . . . . . . . 215
fdump-rtl-pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
fdump-rtl-peephole2 . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-postreload . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-pro_and_epilogue . . . . . . . . . . . . . . . . 215
fdump-rtl-ree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-regclass . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-rnreg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-sched1. . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-sched2. . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-seqabstr . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-shorten . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-sibling . . . . . . . . . . . . . . . . . . . . . . . . . . 215
fdump-rtl-sms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-split1. . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-split2. . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-split3. . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-split4. . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-split5. . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-subreg1 . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-subreg2 . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-subregs_of_mode_finish . . . . . . . . . 216
fdump-rtl-subregs_of_mode_init . . . . . . . . . . . 216
fdump-rtl-unshare . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-vartrack . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-vregs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-rtl-web . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
fdump-statistics. . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
fdump-tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
fdump-tree-all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
fdump-unnumbered. . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
fdump-unnumbered-links . . . . . . . . . . . . . . . . . . . . . 217
fdwarf2-cfi-asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
fearly-inlining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
felide-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
feliminate-unused-debug-symbols . . . . . . . . . . 109
feliminate-unused-debug-types . . . . . . . . . . . . . 114
femit-class-debug-always . . . . . . . . . . . . . . . . . . 109
femit-struct-debug-baseonly . . . . . . . . . . . . . . . 113
femit-struct-debug-detailed . . . . . . . . . . . . . . . 113
femit-struct-debug-reduced . . . . . . . . . . . . . . . . 113
fenable- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
fexceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
fexcess-precision . . . . . . . . . . . . . . . . . . . . . . . . . . 147
fexec-charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
fexpensive-optimizations . . . . . . . . . . . . . . . . . . 124
fext-numeric-literals . . . . . . . . . . . . . . . . . . . . . . . 53
fextended-identifiers . . . . . . . . . . . . . . . . . . . . . . 190
fextern-tls-init . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
ffast-math . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
ffat-lto-objects. . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

905

ffile-prefix-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
ffinite-math-only . . . . . . . . . . . . . . . . . . . . . . . . . . 148
ffix-and-continue . . . . . . . . . . . . . . . . . . . . . . . . . . 274
ffixed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
ffloat-store . . . . . . . . . . . . . . . . . . . . . . . . . . . 147, 846
ffor-scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
fforward-propagate . . . . . . . . . . . . . . . . . . . . . . . . . 118
ffp-contract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
ffreestanding . . . . . . . . . . . . . . . . . . . . . 6, 40, 67, 469
ffriend-injection. . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
ffunction-sections . . . . . . . . . . . . . . . . . . . . . . . . . 152
fgcse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
fgcse-after-reload . . . . . . . . . . . . . . . . . . . . . . . . . 122
fgcse-las . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
fgcse-lm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
fgcse-sm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
fgimple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
fgnu-runtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
fgnu-tm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
fgnu89-inline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
fgraphite-identity . . . . . . . . . . . . . . . . . . . . . . . . . 133
fhoist-adjacent-loads . . . . . . . . . . . . . . . . . . . . . . 130
fhosted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
fif-conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
fif-conversion2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
filelist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
findirect-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
findirect-inlining . . . . . . . . . . . . . . . . . . . . . . . . . 119
finhibit-size-directive . . . . . . . . . . . . . . . . . . . 206
finline-functions . . . . . . . . . . . . . . . . . . . . . . . . . . 119
finline-functions-called-once . . . . . . . . . . . . . 119
finline-limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
finline-small-functions . . . . . . . . . . . . . . . . . . . 118
finput-charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
finstrument-functions . . . . . . . . . . . . . . . . . 185, 473
finstrument-functions-exclude-file-list
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
finstrument-functions-exclude-function-list
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
fipa-cp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
fipa-cp-clone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
fipa-icf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
fipa-profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
fipa-pta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
fipa-pure-const . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
fipa-ra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
fipa-reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
fipa-sra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
fira-algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
fira-hoist-pressure . . . . . . . . . . . . . . . . . . . . . . . . 125
fira-loop-pressure . . . . . . . . . . . . . . . . . . . . . . . . . 125
fira-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
fira-verbose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
fisolate-erroneous-paths-attribute . . . . . . . 131
fisolate-erroneous-paths-dereference. . . . . 131
fivar-visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
fivopts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
fkeep-inline-functions . . . . . . . . . . . . . . . . 120, 539

906

Using the GNU Compiler Collection (GCC)

fkeep-static-consts . . . . . . . . . . . . . . . . . . . . . . . . 120
fkeep-static-functions . . . . . . . . . . . . . . . . . . . . . 120
flat_namespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
flax-vector-conversions . . . . . . . . . . . . . . . . . . . . . 41
fleading-underscore . . . . . . . . . . . . . . . . . . . . . . . . 210
flive-range-shrinkage . . . . . . . . . . . . . . . . . . . . . . 125
flocal-ivars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
floop-block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
floop-interchange . . . . . . . . . . . . . . . . . . . . . . . . . . 134
floop-nest-optimize . . . . . . . . . . . . . . . . . . . . . . . . 133
floop-parallelize-all . . . . . . . . . . . . . . . . . . . . . . 133
floop-strip-mine. . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
floop-unroll-and-jam . . . . . . . . . . . . . . . . . . . . . . . 134
flra-remat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
flto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
flto-compression-level . . . . . . . . . . . . . . . . . . . . . 144
flto-odr-type-merging . . . . . . . . . . . . . . . . . . . . . . 144
flto-partition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
flto-report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
flto-report-wpa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
fmacro-prefix-map . . . . . . . . . . . . . . . . . . . . . . . . . . 191
fmax-errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
fmem-report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
fmem-report-wpa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
fmerge-all-constants . . . . . . . . . . . . . . . . . . . . . . . 120
fmerge-constants. . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
fmerge-debug-strings . . . . . . . . . . . . . . . . . . . . . . . 110
fmessage-length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
fmodulo-sched . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
fmodulo-sched-allow-regmoves . . . . . . . . . . . . . . 120
fmove-loop-invariants . . . . . . . . . . . . . . . . . . . . . . 152
fms-extensions . . . . . . . . . . . . . . . . . . . . . . . 40, 46, 781
fnew-inheriting-ctors . . . . . . . . . . . . . . . . . . . . . . . 46
fnew-ttp-matching. . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
fnext-runtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
fno-access-control . . . . . . . . . . . . . . . . . . . . . . . . . . 43
fno-asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
fno-branch-count-reg . . . . . . . . . . . . . . . . . . . . . . . 121
fno-builtin . . . . . . . . . . . . . . . . . . . . . 39, 67, 469, 613
fno-canonical-system-headers . . . . . . . . . . . . . . 190
fno-check-pointer-bounds . . . . . . . . . . . . . . . . . . 180
fno-checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
fno-chkp-check-incomplete-type . . . . . . . . . . . 181
fno-chkp-check-read . . . . . . . . . . . . . . . . . . . . . . . . 182
fno-chkp-check-write . . . . . . . . . . . . . . . . . . . . . . . 182
fno-chkp-first-field-has-own-bounds . . . . . . 181
fno-chkp-flexible-struct-trailing-arrays
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
fno-chkp-instrument-calls . . . . . . . . . . . . . . . . . 182
fno-chkp-instrument-marked-only . . . . . . . . . . 182
fno-chkp-narrow-bounds . . . . . . . . . . . . . . . . . . . . . 181
fno-chkp-narrow-to-innermost-array . . . . . . . 181
fno-chkp-optimize . . . . . . . . . . . . . . . . . . . . . . . . . . 181
fno-chkp-store-bounds . . . . . . . . . . . . . . . . . . . . . . 182
fno-chkp-treat-zero-dynamic-size-asinfinite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
fno-chkp-use-fast-string-functions . . . . . . . 181
fno-chkp-use-nochk-string-functions . . . . . . 181

fno-chkp-use-static-bounds . . . . . . . . . . . . . . . . 181
fno-chkp-use-static-const-bounds . . . . . . . . . 181
fno-chkp-use-wrappers . . . . . . . . . . . . . . . . . . . . . . 182
fno-common . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206, 515
fno-compare-debug . . . . . . . . . . . . . . . . . . . . . . . . . . 224
fno-debug-types-section . . . . . . . . . . . . . . . . . . . 110
fno-default-inline . . . . . . . . . . . . . . . . . . . . . . . . . 540
fno-defer-pop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
fno-diagnostics-show-caret . . . . . . . . . . . . . . . . . 61
fno-diagnostics-show-option . . . . . . . . . . . . . . . . 61
fno-dwarf2-cfi-asm . . . . . . . . . . . . . . . . . . . . . . . . . 114
fno-elide-constructors . . . . . . . . . . . . . . . . . . . . . . 45
fno-elide-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
fno-eliminate-unused-debug-types . . . . . . . . . 114
fno-enforce-eh-specs . . . . . . . . . . . . . . . . . . . . . . . . 45
fno-ext-numeric-literals . . . . . . . . . . . . . . . . . . . 53
fno-extern-tls-init . . . . . . . . . . . . . . . . . . . . . . . . . 45
fno-for-scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
fno-fp-int-builtin-inexact . . . . . . . . . . . . . . . . 150
fno-function-cse. . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
fno-gnu-keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
fno-gnu-unique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
fno-guess-branch-probability . . . . . . . . . . . . . . 138
fno-ident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
fno-implement-inlines . . . . . . . . . . . . . . . . . . 46, 790
fno-implicit-inline-templates . . . . . . . . . . . . . . 46
fno-implicit-templates . . . . . . . . . . . . . . . . . 46, 792
fno-inline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
fno-ira-share-save-slots . . . . . . . . . . . . . . . . . . 125
fno-ira-share-spill-slots . . . . . . . . . . . . . . . . . 125
fno-jump-tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
fno-keep-inline-dllexport . . . . . . . . . . . . . . . . . 120
fno-lifetime-dse. . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
fno-local-ivars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
fno-math-errno . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
fno-merge-debug-strings . . . . . . . . . . . . . . . . . . . 110
fno-nil-receivers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
fno-nonansi-builtins . . . . . . . . . . . . . . . . . . . . . . . . 46
fno-operator-names . . . . . . . . . . . . . . . . . . . . . . . . . . 46
fno-optional-diags . . . . . . . . . . . . . . . . . . . . . . . . . . 46
fno-peephole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
fno-peephole2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
fno-plt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
fno-pretty-templates . . . . . . . . . . . . . . . . . . . . . . . . 47
fno-printf-return-value . . . . . . . . . . . . . . . . . . . 137
fno-rtti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
fno-sanitize-recover . . . . . . . . . . . . . . . . . . . . . . . 179
fno-sanitize=all. . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
fno-sched-interblock . . . . . . . . . . . . . . . . . . . . . . . 126
fno-sched-spec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
fno-set-stack-executable . . . . . . . . . . . . . . . . . . 413
fno-show-column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
fno-signed-bitfields . . . . . . . . . . . . . . . . . . . . . . . . 42
fno-signed-zeros. . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
fno-stack-limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
fno-threadsafe-statics . . . . . . . . . . . . . . . . . . . . . . 48
fno-toplevel-reorder . . . . . . . . . . . . . . . . . . . . . . . 141
fno-trapping-math . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Option Index

fno-unsigned-bitfields . . . . . . . . . . . . . . . . . . . . . . 42
fno-use-cxa-get-exception-ptr . . . . . . . . . . . . . . 48
fno-var-tracking-assignments . . . . . . . . . . . . . . 110
fno-var-tracking-assignments-toggle . . . . . . 225
fno-weak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
fno-working-directory . . . . . . . . . . . . . . . . . . . . . . 192
fno-writable-relocated-rdata . . . . . . . . . . . . . . 413
fno-zero-initialized-in-bss . . . . . . . . . . . . . . . 121
fnon-call-exceptions . . . . . . . . . . . . . . . . . . . . . . . 204
fnothrow-opt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
fobjc-abi-version. . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
fobjc-call-cxx-cdtors . . . . . . . . . . . . . . . . . . . . . . . 56
fobjc-direct-dispatch . . . . . . . . . . . . . . . . . . . . . . . 56
fobjc-exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
fobjc-gc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
fobjc-nilcheck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
fobjc-std . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
fomit-frame-pointer . . . . . . . . . . . . . . . . . . . . . . . . 118
fopenacc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
fopenacc-dim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
fopenmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
fopenmp-simd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
fopt-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
foptimize-sibling-calls . . . . . . . . . . . . . . . . . . . 118
foptimize-strlen. . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
force_cpusubtype_ALL . . . . . . . . . . . . . . . . . . . . . . . 274
force_flat_namespace . . . . . . . . . . . . . . . . . . . . . . . 276
fpack-struct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
fpartial-inlining . . . . . . . . . . . . . . . . . . . . . . . . . . 137
fpatchable-function-entry . . . . . . . . . . . . . . . . . 186
fpcc-struct-return . . . . . . . . . . . . . . . . . . . . 205, 843
fpch-deps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
fpch-preprocess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
fpeel-loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
fpermissive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
fpermitted-flt-eval-methods . . . . . . . . . . . . . . . . 38
fpermitted-flt-eval-methods=c11 . . . . . . . . . . . 38
fpermitted-flt-eval-methods=ts-18661-3 . . . 38
fpic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
fPIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
fpie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
fPIE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
fplan9-extensions . . . . . . . . . . . . . . . . . . . . . . . 41, 781
fplugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
fplugin-arg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
fpost-ipa-mem-report . . . . . . . . . . . . . . . . . . . . . . . 226
fpre-ipa-mem-report . . . . . . . . . . . . . . . . . . . . . . . . 226
fpredictive-commoning . . . . . . . . . . . . . . . . . . . . . . 137
fprefetch-loop-arrays . . . . . . . . . . . . . . . . . . . . . . 137
fpreprocessed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
fprofile-abs-path . . . . . . . . . . . . . . . . . . . . . . . . . . 174
fprofile-arcs . . . . . . . . . . . . . . . . . . . . . . . . . . 173, 620
fprofile-correction . . . . . . . . . . . . . . . . . . . . . . . . 146
fprofile-dir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
fprofile-generate . . . . . . . . . . . . . . . . . . . . . . . . . . 174
fprofile-reorder-functions . . . . . . . . . . . . . . . . 151
fprofile-report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
fprofile-update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

907

fprofile-use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
fprofile-values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
fpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
frandom-seed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
freciprocal-math. . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
frecord-gcc-switches . . . . . . . . . . . . . . . . . . . . . . . 208
free . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
freg-struct-return . . . . . . . . . . . . . . . . . . . . . . . . . 205
frename-registers . . . . . . . . . . . . . . . . . . . . . . . . . . 151
freorder-blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
freorder-blocks-algorithm . . . . . . . . . . . . . . . . . 138
freorder-blocks-and-partition . . . . . . . . . . . . . 138
freorder-functions . . . . . . . . . . . . . . . . . . . . . . . . . 138
freplace-objc-classes . . . . . . . . . . . . . . . . . . . . . . . 57
frepo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47, 792
freport-bug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
frerun-cse-after-loop . . . . . . . . . . . . . . . . . . . . . . 122
freschedule-modulo-scheduled-loops . . . . . . . 128
frounding-math . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
fsanitize-address-use-after-scope . . . . . . . . 179
fsanitize-coverage=trace-cmp . . . . . . . . . . . . . . 180
fsanitize-coverage=trace-pc . . . . . . . . . . . . . . . 180
fsanitize-recover . . . . . . . . . . . . . . . . . . . . . . . . . . 179
fsanitize-sections . . . . . . . . . . . . . . . . . . . . . . . . . 179
fsanitize-undefined-trap-on-error . . . . . . . . 180
fsanitize=address . . . . . . . . . . . . . . . . . . . . . . . . . . 175
fsanitize=alignment . . . . . . . . . . . . . . . . . . . . . . . . 177
fsanitize=bool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
fsanitize=bounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
fsanitize=bounds-strict . . . . . . . . . . . . . . . . . . . 177
fsanitize=builtin . . . . . . . . . . . . . . . . . . . . . . . . . . 178
fsanitize=enum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
fsanitize=float-cast-overflow . . . . . . . . . . . . . 178
fsanitize=float-divide-by-zero . . . . . . . . . . . 178
fsanitize=integer-divide-by-zero . . . . . . . . . 176
fsanitize=kernel-address . . . . . . . . . . . . . . . . . . 175
fsanitize=leak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
fsanitize=nonnull-attribute . . . . . . . . . . . . . . . 178
fsanitize=null . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
fsanitize=object-size . . . . . . . . . . . . . . . . . . . . . . 178
fsanitize=pointer-compare . . . . . . . . . . . . . . . . . 175
fsanitize=pointer-overflow . . . . . . . . . . . . . . . . 178
fsanitize=pointer-subtract . . . . . . . . . . . . . . . . 175
fsanitize=return. . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
fsanitize=returns-nonnull-attribute . . . . . . 178
fsanitize=shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
fsanitize=shift-base . . . . . . . . . . . . . . . . . . . . . . . 176
fsanitize=shift-exponent . . . . . . . . . . . . . . . . . . 176
fsanitize=signed-integer-overflow . . . . . . . . 177
fsanitize=thread. . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
fsanitize=undefined . . . . . . . . . . . . . . . . . . . . . . . . 176
fsanitize=unreachable . . . . . . . . . . . . . . . . . . . . . . 177
fsanitize=vla-bound . . . . . . . . . . . . . . . . . . . . . . . . 177
fsanitize=vptr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
fsched-critical-path-heuristic . . . . . . . . . . . 127
fsched-dep-count-heuristic . . . . . . . . . . . . . . . . 128
fsched-group-heuristic . . . . . . . . . . . . . . . . . . . . . 127
fsched-last-insn-heuristic . . . . . . . . . . . . . . . . 128

908

Using the GNU Compiler Collection (GCC)

fsched-pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
fsched-rank-heuristic . . . . . . . . . . . . . . . . . . . . . . 128
fsched-spec-insn-heuristic . . . . . . . . . . . . . . . . 127
fsched-spec-load. . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
fsched-spec-load-dangerous . . . . . . . . . . . . . . . . 127
fsched-stalled-insns . . . . . . . . . . . . . . . . . . . . . . . 127
fsched-stalled-insns-dep . . . . . . . . . . . . . . . . . . 127
fsched-verbose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
fsched2-use-superblocks . . . . . . . . . . . . . . . . . . . 127
fschedule-fusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
fschedule-insns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
fschedule-insns2. . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
fsection-anchors. . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
fsel-sched-pipelining . . . . . . . . . . . . . . . . . . . . . . 128
fsel-sched-pipelining-outer-loops . . . . . . . . 128
fselective-scheduling . . . . . . . . . . . . . . . . . . . . . . 128
fselective-scheduling2 . . . . . . . . . . . . . . . . . . . . . 128
fsemantic-interposition . . . . . . . . . . . . . . . . . . . 128
fshort-enums . . . . . . . . . . . . . . . . . . 206, 434, 528, 850
fshort-wchar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
fshrink-wrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
fshrink-wrap-separate . . . . . . . . . . . . . . . . . . . . . . 129
fsignaling-nans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
fsigned-bitfields . . . . . . . . . . . . . . . . . . . . . . . 42, 850
fsigned-char. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41, 430
fsimd-cost-model. . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
fsingle-precision-constant . . . . . . . . . . . . . . . . 150
fsized-deallocation . . . . . . . . . . . . . . . . . . . . . . . . . 47
fsplit-ivs-in-unroller . . . . . . . . . . . . . . . . . . . . . 136
fsplit-loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
fsplit-paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
fsplit-stack . . . . . . . . . . . . . . . . . . . . . . . . . . . 184, 474
fsplit-wide-types . . . . . . . . . . . . . . . . . . . . . . . . . . 121
fssa-backprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
fssa-phiopt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
fsso-struct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
fstack-check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
fstack-clash-protection . . . . . . . . . . . . . . . . . . . 184
fstack-limit-register . . . . . . . . . . . . . . . . . . . . . . 184
fstack-limit-symbol . . . . . . . . . . . . . . . . . . . . . . . . 184
fstack-protector. . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
fstack-protector-all . . . . . . . . . . . . . . . . . . . . . . . 183
fstack-protector-explicit . . . . . . . . . . . . . . . . . 183
fstack-protector-strong . . . . . . . . . . . . . . . . . . . 183
fstack-usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
fstack_reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
fstats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
fstdarg-opt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
fstore-merging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
fstrict-aliasing. . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
fstrict-enums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
fstrict-overflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
fstrict-volatile-bitfields . . . . . . . . . . . . . . . . 212
fstrong-eval-order . . . . . . . . . . . . . . . . . . . . . . . . . . 47
fsync-libcalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
fsyntax-only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
ftabstop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
ftemplate-backtrace-limit . . . . . . . . . . . . . . . . . . 48

ftemplate-depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
ftest-coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
fthread-jumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
ftime-report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
ftime-report-details . . . . . . . . . . . . . . . . . . . . . . . 225
ftls-model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
ftracer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
ftrack-macro-expansion . . . . . . . . . . . . . . . . . . . . . 190
ftrampolines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
ftrapv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
ftree-bit-ccp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
ftree-builtin-call-dce . . . . . . . . . . . . . . . . . . . . . 132
ftree-ccp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
ftree-ch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
ftree-coalesce-vars . . . . . . . . . . . . . . . . . . . . . . . . 133
ftree-copy-prop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
ftree-dce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
ftree-dominator-opts . . . . . . . . . . . . . . . . . . . . . . . 132
ftree-dse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
ftree-forwprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
ftree-fre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
ftree-loop-distribute-patterns . . . . . . . . . . . 134
ftree-loop-distribution . . . . . . . . . . . . . . . . . . . 134
ftree-loop-if-convert . . . . . . . . . . . . . . . . . . . . . . 133
ftree-loop-im . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
ftree-loop-ivcanon . . . . . . . . . . . . . . . . . . . . . . . . . 135
ftree-loop-linear . . . . . . . . . . . . . . . . . . . . . . . . . . 133
ftree-loop-optimize . . . . . . . . . . . . . . . . . . . . . . . . 133
ftree-loop-vectorize . . . . . . . . . . . . . . . . . . . . . . . 136
ftree-parallelize-loops . . . . . . . . . . . . . . . . . . . 135
ftree-partial-pre . . . . . . . . . . . . . . . . . . . . . . . . . . 130
ftree-phiprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
ftree-pre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
ftree-pta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
ftree-reassoc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
ftree-sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
ftree-slp-vectorize . . . . . . . . . . . . . . . . . . . . . . . . 136
ftree-slsr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
ftree-sra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
ftree-switch-conversion . . . . . . . . . . . . . . . . . . . 132
ftree-tail-merge. . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
ftree-ter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
ftree-vectorize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
ftree-vrp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
funconstrained-commons . . . . . . . . . . . . . . . . . . . . . 123
funit-at-a-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
funroll-all-loops . . . . . . . . . . . . . . . . . . . . . . . . . . 152
funroll-loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
funsafe-math-optimizations . . . . . . . . . . . . . . . . 148
funsigned-bitfields . . . . . . . . . . . . . . . . 42, 433, 850
funsigned-char . . . . . . . . . . . . . . . . . . . . . . . . . . 41, 430
funswitch-loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
funwind-tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
fuse-cxa-atexit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
fuse-ld=bfd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
fuse-ld=gold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
fuse-linker-plugin . . . . . . . . . . . . . . . . . . . . . . . . . 145
fvar-tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Option Index

fvar-tracking-assignments . . . . . . . . . . . . . . . . . 110
fvar-tracking-assignments-toggle . . . . . . . . . 225
fvariable-expansion-in-unroller . . . . . . . . . . 137
fvect-cost-model. . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
fverbose-asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
fvisibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
fvisibility-inlines-hidden . . . . . . . . . . . . . . . . . 48
fvisibility-ms-compat . . . . . . . . . . . . . . . . . . . . . . . 49
fvpt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
fvtable-verify . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
fvtv-counts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
fvtv-debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
fweb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
fwhole-program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
fwide-exec-charset . . . . . . . . . . . . . . . . . . . . . . . . . 191
fworking-directory . . . . . . . . . . . . . . . . . . . . . . . . . 192
fwrapv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
fwrapv-pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
fzero-link. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

G
g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
gas-loc-support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
gas-locview-support . . . . . . . . . . . . . . . . . . . . . . . . 111
gcolumn-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
gdwarf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
gen-decls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
gfull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
ggdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
ggnu-pubnames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
ginline-points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
ginternal-reset-location-views . . . . . . . . . . . 112
gno-as-loc-support . . . . . . . . . . . . . . . . . . . . . . . . . 111
gno-column-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
gno-inline-points . . . . . . . . . . . . . . . . . . . . . . . . . . 113
gno-internal-reset-location-views . . . . . . . . 112
gno-record-gcc-switches . . . . . . . . . . . . . . . . . . . 111
gno-statement-frontiers . . . . . . . . . . . . . . . . . . . 112
gno-strict-dwarf. . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
gno-variable-location-views . . . . . . . . . . . . . . . 112
gpubnames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
grecord-gcc-switches . . . . . . . . . . . . . . . . . . . . . . . 111
gsplit-dwarf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
gstabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
gstabs+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
gstatement-frontiers . . . . . . . . . . . . . . . . . . . . . . . 112
gstrict-dwarf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
gtoggle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
gused . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
gvariable-location-views . . . . . . . . . . . . . . . . . . 112
gvariable-location-views=incompat5 . . . . . . . 112
gvms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
gxcoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
gxcoff+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
gz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
G . . . . . . . . . . . . . . . . 241, 294, 311, 323, 339, 358, 383

909

H
headerpad_max_install_names . . . . . . . . . . . . . . . 276
help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

I
I- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
idirafter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iframework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
imacros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
image_base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
imultilib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
include . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
init . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
install_name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iplugindir= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iprefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iquote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
isysroot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
isystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iwithprefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iwithprefixbefore . . . . . . . . . . . . . . . . . . . . . . . . . .
I.............................................

200
200
273
188
276
201
188
276
276
201
201
200
201
200
201
201
200

K
keep_private_externs . . . . . . . . . . . . . . . . . . . . . . . 276

L
l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
lobjc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

M
m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337,
m1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m128bit-long-double . . . . . . . . . . . . . . . . . . . . . . . .
m16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m16-bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271,
m1reg- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m210 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m2a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m2a-nofpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m2a-single . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m2a-single-only . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m31 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m32 . . . . . . . . . . . . . . . . . . . . . . . 328, 350, 380, 384,
m32-bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m32bit-doubles . . . . . . . . . . . . . . . . . . . . . . . . . 345,
m32r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m32r2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m32rx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

355
369
329
398
411
323
235
369
301
369
369
369
369
369
366
411
271
361
293
293
293

910

m340 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m3dnow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m3dnowa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m3e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-100-nofpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-100-single . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-100-single-only . . . . . . . . . . . . . . . . . . . . . . . . .
m4-200 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-200-nofpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-200-single . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-200-single-only . . . . . . . . . . . . . . . . . . . . . . . . .
m4-300 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-300-nofpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-300-single . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-300-single-only . . . . . . . . . . . . . . . . . . . . . . . . .
m4-340 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-500 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-nofpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-single . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4-single-only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m40 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m45 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4a-nofpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4a-single . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4a-single-only . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m4byte-functions. . . . . . . . . . . . . . . . . . . . . . . . . . . .
m5200 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m5206e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m528x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m5307 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m5407 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m64 . . . . . . . . . . . . . . . . . . . 328, 350, 366, 380, 384,
m64bit-doubles . . . . . . . . . . . . . . . . . . . . . . . . . 345,
m68000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m68010 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m68020 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m68020-40 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m68020-60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m68030 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m68040 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m68060 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m68881 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m8-bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m8bit-idiv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m8byte-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
m96bit-long-double . . . . . . . . . . . . . . . . . . . . . . . . .
mA6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mA7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mabi . . . . . . . . . . . . . . . . . . 228, 245, 337, 342, 356,
mabi=32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mabi=64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mabi=eabi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mabi=elfv1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338,
mabi=elfv2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338,

Using the GNU Compiler Collection (GCC)

301
401
401
369
369
369
369
369
369
369
370
370
370
370
370
370
370
370
370
369
369
369
329
329
370
370
370
370
370
300
297
297
297
297
297
411
361
296
296
296
297
297
296
296
297
298
271
410
387
398
235
235
405
306
306
306
356
356

mabi=gnu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
mabi=ibmlongdouble . . . . . . . . . . . . . . . . . . . . 337, 356
mabi=ieeelongdouble . . . . . . . . . . . . . . . . . . . 337, 356
mabi=mmixware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
mabi=n32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
mabi=no-spe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
mabi=o64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
mabi=spe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
mabicalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
mabm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
mabort-on-noreturn . . . . . . . . . . . . . . . . . . . . . . . . . 254
mabs=2008 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
mabs=legacy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
mabsdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
mabsdiff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
mabshi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
mac0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
macc-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
macc-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
maccumulate-args. . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
maccumulate-outgoing-args . . . . . . . . . . . . 374, 406
maddress-mode=long . . . . . . . . . . . . . . . . . . . . . . . . . 412
maddress-mode=short . . . . . . . . . . . . . . . . . . . . . . . . 412
maddress-space-conversion . . . . . . . . . . . . . . . . . 382
mads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338, 356
maes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
maix-struct-return . . . . . . . . . . . . . . . . . . . . 337, 355
maix32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333, 351
maix64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
malign-300 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
malign-call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
malign-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
malign-double . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
malign-int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
malign-labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
malign-loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
malign-natural . . . . . . . . . . . . . . . . . . . . . . . . . 334, 351
malign-power . . . . . . . . . . . . . . . . . . . . . . . . . . . 334, 351
mall-opts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
malloc-cc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
mallow-string-insns . . . . . . . . . . . . . . . . . . . . . . . . 364
mallregs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
maltivec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
maltivec=be . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
maltivec=le . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
mam33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
mam33-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
mam34 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
mandroid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
mannotate-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
mapcs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
mapcs-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
mapp-regs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375, 387
mARC600 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
mARC601 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
mARC700 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
march . . 230, 246, 270, 286, 288, 295, 304, 323, 325,
343, 367, 389

Option Index

marclinux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
marclinux_prof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
margonaut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
marm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
mas100-syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
masm-hex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
masm-syntax-unified . . . . . . . . . . . . . . . . . . . . . . . . 257
masm=dialect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
matomic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
matomic-model=model . . . . . . . . . . . . . . . . . . . . . . . . 371
matomic-updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383
mauto-litpools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
mauto-modify-reg. . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
mauto-pic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
maverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
mavoid-indexed-addresses . . . . . . . . . . . . . . 334, 352
mavx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx256-split-unaligned-load . . . . . . . . . . . . . . 410
mavx256-split-unaligned-store . . . . . . . . . . . . . 410
mavx512bitalg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
mavx512bw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx512cd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx512dq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx512er . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx512f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx512ifma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx512pf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx512vbmi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx512vbmi2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
mavx512vl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mavx512vpopcntdq. . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
max-vect-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
mb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
mbackchain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365
mbarrel-shift-enabled . . . . . . . . . . . . . . . . . . . . . . 292
mbarrel-shifter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
mbarrel_shifter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
mbase-addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
mbased= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
mbbit-peephole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
mbcopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
mbcopy-builtin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
mbe8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
mbig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335, 354
mbig-endian . . . . 228, 244, 246, 270, 289, 300, 303,
322, 335, 354, 384
mbig-endian-data. . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
mbig-switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
mbigtable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
mbionic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
mbit-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
mbit-ops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
mbitfield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
mbitops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301, 371
mblock-compare-inline-limit . . . . . . . . . . . . . . . 358
mblock-compare-inline-loop-limit . . . . . . . . . 358
mblock-move-inline-limit . . . . . . . . . . . . . . 339, 358

911

mbmi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mbranch-cheap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mbranch-cost . . . . . . . . . . . . . . . . . . 233, 261, 316,
mbranch-cost=num. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mbranch-cost=number . . . . . . . . . . . . . . . . . . . . . . . .
mbranch-expensive . . . . . . . . . . . . . . . . . . . . . . . . . .
mbranch-hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mbranch-likely . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mbranch-predict . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mbss-plt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332,
mbuild-constants. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mbwx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mbypass-cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mc= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mc68000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mc68020 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcache-block-size . . . . . . . . . . . . . . . . . . . . . . . . . .
mcache-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcache-volatile . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcall-eabi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336,
mcall-freebsd . . . . . . . . . . . . . . . . . . . . . . . . . . 337,
mcall-linux. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337,
mcall-ms2sysv-xlogues . . . . . . . . . . . . . . . . . . . . . .
mcall-netbsd . . . . . . . . . . . . . . . . . . . . . . . . . . . 337,
mcall-prologues . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcall-sysv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336,
mcall-sysv-eabi . . . . . . . . . . . . . . . . . . . . . . . . 336,
mcall-sysv-noeabi . . . . . . . . . . . . . . . . . . . . . . 337,
mcallee-super-interworking . . . . . . . . . . . . . . . .
mcaller-copies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcaller-super-interworking . . . . . . . . . . . . . . . .
mcallgraph-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcase-vector-pcrel . . . . . . . . . . . . . . . . . . . . . . . . .
mcbcond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcbranch-force-delay-slot . . . . . . . . . . . . . . . . .
mcc-init . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcfv4e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcheck-zero-division . . . . . . . . . . . . . . . . . . . . . . .
mcix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mclear-hwcap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mclflushopt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mclip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mclzero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323,
mcmodel=kernel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcmodel=large . . . . . . . . . . . . . . . . . 229, 348, 384,
mcmodel=medany . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcmodel=medium . . . . . . . . . . . . . . . . . . . . . . . . . 348,
mcmodel=medlow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcmodel=small . . . . . . . . . . . . . . . . . 229, 347, 384,
mcmodel=tiny . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcmov . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcmove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcmpb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcmse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcode-density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mcode-readable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

402
330
342
374
294
330
382
316
319
349
278
278
325
301
296
296
323
382
325
355
355
355
405
355
261
355
355
355
256
286
256
300
242
379
374
271
297
313
278
403
375
401
301
402
380
412
412
343
412
343
411
229
322
233
346
258
237
312

912

Using the GNU Compiler Collection (GCC)

mcode-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
mcompact-branches=always . . . . . . . . . . . . . . . . . . 316
mcompact-branches=never . . . . . . . . . . . . . . . . . . . 316
mcompact-branches=optimal . . . . . . . . . . . . . . . . . 316
mcompact-casesi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
mcompat-align-parm . . . . . . . . . . . . . . . . . . . . 341, 361
mcompress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
mcond-exec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
mcond-move . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
mconfig= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
mconsole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
mconst-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
mconst16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
mconstant-gp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
mcop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
mcop32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
mcop64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
mcorea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
mcoreb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
mcpu . . . 231, 235, 252, 270, 279, 285, 295, 330, 331,
344, 347, 362, 377, 384, 388, 396
mcpu= . . . . . . . . . . . . . . . . . . . . . . . . . . 267, 293, 303, 321
mcpu32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
mcr16c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
mcr16cplus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
mcrc32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
mcrypto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
mcsync-anomaly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
mctor-dtor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
mcustom-fpu-cfg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
mcustom-insn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
mcx16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
mdalign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
mdata-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
mdata-model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
mdata-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
mdc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
mdebug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294, 367, 387
mdebug-main=prefix . . . . . . . . . . . . . . . . . . . . . . . . . 388
mdec-asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
mdisable-callt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
mdisable-fpregs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
mdisable-indexing . . . . . . . . . . . . . . . . . . . . . . . . . . 286
mdiv . . . . . . . . . . . . . . . . . . . . . . . . . . . 298, 300, 302, 343
mdiv-rem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
mdiv=strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
mdivide-breaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
mdivide-enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
mdivide-traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
mdivsi3_libfunc=name . . . . . . . . . . . . . . . . . . . . . . . 374
mdll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
mdlmzb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
mdmx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
mdouble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
mdouble-float . . . . . . . . . . . . . . . . . . . . . 308, 334, 352
mdpfp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
mdpfp-compact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
mdpfp-fast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

mdpfp_compact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdpfp_fast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdsp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdsp-packa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdsp_packa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdspr2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdual-nops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdump-tune-features . . . . . . . . . . . . . . . . . . . . . . . .
mdvbf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdwarf2-asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mdynamic-no-pic . . . . . . . . . . . . . . . . . . . . . . . . 335,
MD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mea32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mea64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
meabi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338,
mearly-cbranchsi. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mearly-stop-bits. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mEA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
meb . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302, 320, 325,
mel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302, 320, 325,
melf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272,
memb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338,
membedded-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
memregs= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mepsilon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
merror-reloc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mesa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
metrax100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
metrax4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
meva . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mexpand-adddi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mexplicit-relocs . . . . . . . . . . . . . . . . . . . . . . . 279,
mexr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mextern-sdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mf16c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfast-fp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfast-indirect-calls . . . . . . . . . . . . . . . . . . . . . . .
mfast-sw-div . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfaster-structs . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfdiv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfdpic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfentry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-24k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-and-continue . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-at697f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-cortex-a53-835769 . . . . . . . . . . . . . . . . . . . . .
mfix-cortex-a53-843419 . . . . . . . . . . . . . . . . . . . . .
mfix-cortex-m3-ldrd . . . . . . . . . . . . . . . . . . . . . . . .
mfix-gr712rc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-r10000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-r4000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-r4400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-rm7000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-sb1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

244
244
309
240
244
309
383
403
240
290
281
354
189
237
382
382
357
242
290
244
368
368
319
357
312
293
384
318
381
366
271
271
310
242
312
285
311
401
269
286
325
377
343
282
409
278
314
274
380
229
229
257
380
314
314
314
314
315

Option Index

mfix-ut699 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-ut700 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-vr4120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfix-vr4130 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfixed-cc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfixed-range . . . . . . . . . . . . . . . . . . 287, 290, 374,
mflat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mflip-mips16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mflip-thumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfloat-abi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfloat-gprs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfloat-ieee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfloat-vax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfloat128 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332,
mfloat128-hardware . . . . . . . . . . . . . . . . . . . . . . . . .
mfloat32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfloat64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mflush-func . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mflush-func=name. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mflush-trap=number . . . . . . . . . . . . . . . . . . . . . . . . .
mfma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfma4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfmaf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfmovd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mforce-indirect-call . . . . . . . . . . . . . . . . . . . . . . .
mforce-no-pic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfp-exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfp-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfp-reg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfp-rounding-mode . . . . . . . . . . . . . . . . . . . . . . . . . .
mfp-trap-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfp16-format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfp32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfp64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfpmath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147,
mfpr-32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfpr-64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfprnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfpu . . . . . . . . . . . . . . . . . . 238, 253, 329, 352, 376,
mfpxx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfract-convert-truncate . . . . . . . . . . . . . . . . . . .
mframe-header-opt . . . . . . . . . . . . . . . . . . . . . . . . . .
mfriz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfsca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfsgsbase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfsmuld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfsrra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mft32b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfull-regs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mfull-toc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333,
mfused-madd . . . . . 290, 313, 335, 353, 367, 374,
mfxsr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mg10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mg13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mg14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mgas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

913

380
380
314
315
281
382
376
306
256
245
332
279
279
350
350
330
330
316
295
294
401
401
380
371
405
414
317
234
276
277
277
254
308
308
396
281
281
346
387
308
262
318
360
374
401
380
375
281
322
350
413
402
189
387
345
345
345
287

mgas-isr-prologues . . . . . . . . . . . . . . . . . . . . . . . . . 261
mgcc-abi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
mgeneral-regs-only . . . . . . . . . . . . . . . . . . . . 228, 410
mgfni . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
mghs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
mglibc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
mgnu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
mgnu-as . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
mgnu-attribute . . . . . . . . . . . . . . . . . . . . . . . . . 338, 356
mgnu-ld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287, 289
mgomp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
mgotplt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
mgp32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
mgp64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
mgpopt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311, 323
mgpr-32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
mgpr-64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
mgprel-ro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
mgprel-sec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
MG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
mh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
mhal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
mhalf-reg-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
mhard-dfp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346, 365
mhard-float . . . . 281, 298, 302, 308, 334, 352, 364,
376, 386, 387, 397
mhard-quad-float. . . . . . . . . . . . . . . . . . . . . . . . . . . . 376
mhardlit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
mhint-max-distance . . . . . . . . . . . . . . . . . . . . . . . . . 383
mhint-max-nops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383
mhotpatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
mhp-ld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
mhtm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349, 366
mhw-div . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
mhw-mul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
mhw-mulx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
mhwmult= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
miamcu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
micplb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
mid-shared-library . . . . . . . . . . . . . . . . . . . . . . . . . 268
mieee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277, 371
mieee-conformant. . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
mieee-fp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
mieee-with-inexact . . . . . . . . . . . . . . . . . . . . . . . . . 277
milp32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
mimadd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
mimpure-text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
mincoming-stack-boundary . . . . . . . . . . . . . . . . . . 400
mindexed-loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
minline-all-stringops . . . . . . . . . . . . . . . . . . . . . . 408
minline-float-divide-max-throughput . . . . . . 290
minline-float-divide-min-latency . . . . . . . . . 290
minline-ic_invalidate . . . . . . . . . . . . . . . . . . . . . . 371
minline-int-divide-max-throughput . . . . . . . . 290
minline-int-divide-min-latency . . . . . . . . . . . 290
minline-plt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269, 282
minline-sqrt-max-throughput . . . . . . . . . . . . . . . 290
minline-sqrt-min-latency . . . . . . . . . . . . . . . . . . 290

914

Using the GNU Compiler Collection (GCC)

minline-stringops-dynamically . . . . . . . . . . . . . 408
minrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
minsert-sched-nops . . . . . . . . . . . . . . . . . . . . 336, 354
mint-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
mint16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
mint32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272, 286, 330
mint8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
minterlink-compressed . . . . . . . . . . . . . . . . . . . . . . 306
minterlink-mips16 . . . . . . . . . . . . . . . . . . . . . . . . . . 306
mio-volatile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
mips1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
mips2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips32r3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips32r5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips32r6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips3d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
mips4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips64r2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips64r3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips64r5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
mips64r6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
mirq-ctrl-saved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
misel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332, 349
misize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241, 371
misr-vector-size. . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
missue-rate=number . . . . . . . . . . . . . . . . . . . . . . . . . 294
mivc2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
mjli-alawys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
mjsr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
mjump-in-delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
mkernel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
mknuthdiv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302, 370
mlarge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
mlarge-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
mlarge-data-threshold . . . . . . . . . . . . . . . . . . . . . . 399
mlarge-mem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
mlarge-text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
mleadz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
mleaf-id-shared-library . . . . . . . . . . . . . . . . . . . 268
mlibfuncs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
mlibrary-pic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
mlinked-fp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
mlinker-opt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
mlinux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
mlittle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335, 354
mlittle-endian . . . . . 229, 244, 246, 270, 289, 300,
303, 322, 335, 354, 384
mlittle-endian-data . . . . . . . . . . . . . . . . . . . . . . . . 362
mliw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
mll64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
mllsc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
mload-store-pairs . . . . . . . . . . . . . . . . . . . . . . . . . . 313
mlocal-sdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

mlock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlong-calls . . . . . 234, 241, 254, 269, 283, 313,
mlong-double-128 . . . . . . . . . . . . . . . . . . . . . . . 365,
mlong-double-64 . . . . . . . . . . . . . . . . . . . . . . . . 365,
mlong-double-80 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlong-jump-table-offsets . . . . . . . . . . . . . . . . . .
mlong-jumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlong-load-store. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlong32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlong64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlongcall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340,
mlongcalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mloop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlow-64k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlow-precision-recip-sqrt . . . . . . . . . . . . . . . . .
mlp64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlpc-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242, 281,
mlra-priority-compact . . . . . . . . . . . . . . . . . . . . . .
mlra-priority-noncompact . . . . . . . . . . . . . . . . . .
mlra-priority-none . . . . . . . . . . . . . . . . . . . . . . . . .
mlwp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlxc1-sxc1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mlzcnt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272,
mmac-24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmac-d16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmac_24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmac_d16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmadd4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmain-is-OS_task. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmainkernel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmalloc64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmax-constant-size . . . . . . . . . . . . . . . . . . . . . . . . .
mmax-stack-frame. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmcount-ra-address . . . . . . . . . . . . . . . . . . . . . . . . .
mmcu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258,
mmcu= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MMD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmedia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmedium-calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmemcpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303,
mmemcpy-strategy=strategy . . . . . . . . . . . . . . . . .
mmemory-latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmemory-model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmemset-strategy=strategy . . . . . . . . . . . . . . . . .
mmfcrf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331,
mmfpgpr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmicromips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mminimal-toc . . . . . . . . . . . . . . . . . . . . . . . . . . . 333,
mminmax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmitigate-rop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmixed-code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmmx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmodel=large . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

240
384
398
398
398
300
386
287
310
310
358
415
386
268
230
291
240
377
243
243
242
401
318
402
302
368
240
240
244
244
313
318
261
328
388
278
363
271
317
310
321
190
282
241
313
408
280
381
409
346
346
310
350
302
410
243
401
294

Option Index

mmodel=medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmodel=small . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmovbe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmovdir64b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmovdiri . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmpx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmpy-option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mms-bitfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmul-bug-workaround . . . . . . . . . . . . . . . . . . . . . . . .
mmul.x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmul32x16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmul64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmuladd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmulhw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmult . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmult-bug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmultcost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmulti-cond-exec. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmulticore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmultiple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334,
mmusl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmvcle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mmvme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338,
mmwaitx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mn-flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnan=2008 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnan=legacy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mneon-for-64bits. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnested-cond-exec . . . . . . . . . . . . . . . . . . . . . . . . . .
mnhwloop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-16-bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-4byte-functions . . . . . . . . . . . . . . . . . . . . . . . .
mno-8byte-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-abicalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-abshi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-ac0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-address-space-conversion . . . . . . . . . . . . . .
mno-align-double. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-align-int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-align-loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-align-stringops . . . . . . . . . . . . . . . . . . . . . . . .
mno-allow-string-insns . . . . . . . . . . . . . . . . . . . . .
mno-altivec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-am33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-app-regs . . . . . . . . . . . . . . . . . . . . . . . . . . . 375,
mno-as100-syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-atomic-updates . . . . . . . . . . . . . . . . . . . . . . . . .
mno-auto-litpools . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-avoid-indexed-addresses . . . . . . . . . . 334,
mno-backchain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-base-addresses . . . . . . . . . . . . . . . . . . . . . . . . .
mno-bit-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-bitfield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-branch-likely . . . . . . . . . . . . . . . . . . . . . . . . . .

915

293
293
404
402
402
402
238
406
310
344
271
320
237
237
282
353
302
319
244
284
269
352
285
367
356
402
188
285
261
309
309
257
284
368
323
300
387
307
330
329
382
397
299
294
408
364
348
319
387
363
383
414
352
365
319
353
298
316

mno-branch-predict . . . . . . . . . . . . . . . . . . . . . . . . .
mno-brcc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-bwx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-bypass-cache. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-cache-volatile . . . . . . . . . . . . . . . . . . . . . . . . .
mno-call-ms2sysv-xlogues . . . . . . . . . . . . . . . . . .
mno-callgraph-data . . . . . . . . . . . . . . . . . . . . . . . . .
mno-cbcond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-check-zero-division . . . . . . . . . . . . . . . . . . .
mno-cix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-clearbss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-cmov . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-cmpb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-cond-exec . . . . . . . . . . . . . . . . . . . . . . . . . . 242,
mno-cond-move . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-const-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-const16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-crt0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-crypto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-csync-anomaly . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-custom-insn . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-data-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-default . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-disable-callt . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-div . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298,
mno-dlmzb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-double . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-dpfp-lrsr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-dsp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-dspr2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-dwarf2-asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-dword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-eabi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338,
mno-early-stop-bits . . . . . . . . . . . . . . . . . . . . . . . .
mno-eflags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-embedded-data . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-ep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-epsilon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-eva . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-explicit-relocs . . . . . . . . . . . . . . . . . . . 279,
mno-exr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-extern-sdata. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fancy-math-387 . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fast-sw-div . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-faster-structs . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fix-24k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fix-cortex-a53-835769 . . . . . . . . . . . . . . . . .
mno-fix-cortex-a53-843419 . . . . . . . . . . . . . . . . .
mno-fix-r10000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fix-r4000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fix-r4400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-flat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-float128 . . . . . . . . . . . . . . . . . . . . . . . . . . . 332,
mno-float128-hardware . . . . . . . . . . . . . . . . . . . . . .
mno-float32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

319
242
278
325
325
405
300
379
313
278
303
322
346
284
283
271
413
320
349
268
325
271
367
403
385
300
353
282
237
309
309
290
282
357
290
283
312
384
318
310
312
285
311
397
325
377
278
314
229
229
314
314
314
376
308
350
350
330

916

mno-float64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-flush-func . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-flush-trap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fmaf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fp-in-toc . . . . . . . . . . . . . . . . . . . . . . . . . . 333,
mno-fp-regs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fp-ret-in-387 . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fprnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376,
mno-fsca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fsmuld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fsrra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-fused-madd . . 290, 313, 335, 353, 367, 374,
mno-gnu-as . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-gnu-attribute . . . . . . . . . . . . . . . . . . . . . . 338,
mno-gnu-ld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-gotplt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-gpopt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311,
mno-hard-dfp . . . . . . . . . . . . . . . . . . . . . . . . . . . 346,
mno-hardlit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-htm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349,
mno-hw-div . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-hw-mul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-hw-mulx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-id-shared-library . . . . . . . . . . . . . . . . . . . . . .
mno-ieee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-ieee-fp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-imadd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-inline-float-divide . . . . . . . . . . . . . . . . . . .
mno-inline-int-divide . . . . . . . . . . . . . . . . . . . . . .
mno-inline-sqrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-int16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-int32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-interlink-compressed . . . . . . . . . . . . . . . . . .
mno-interlink-mips16 . . . . . . . . . . . . . . . . . . . . . . .
mno-interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-isel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332,
mno-jsr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-knuthdiv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-leaf-id-shared-library . . . . . . . . . . . . . . . .
mno-libfuncs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-llsc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-load-store-pairs . . . . . . . . . . . . . . . . . . . . . . .
mno-local-sdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-long-calls . . . . . . . . . . . 254, 269, 288, 313,
mno-long-jumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-longcall . . . . . . . . . . . . . . . . . . . . . . . . . . . 340,
mno-longcalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-low-64k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-low-precision-recip-sqrt . . . . . . . . . . . . . .
mno-lra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-lsim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281,
mno-mad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mcount-ra-address . . . . . . . . . . . . . . . . . . . . . .
mno-mcu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mdmx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Using the GNU Compiler Collection (GCC)

330
295
294
380
350
276
397
346
387
374
380
375
413
289
356
289
272
323
365
300
366
325
325
325
268
371
397
313
290
290
290
330
330
306
306
261
349
364
319
268
318
309
313
311
384
386
358
415
268
230
377
301
313
278
317
310
310
282

mno-memcpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mfcrf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331,
mno-mfpgpr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-millicode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mips16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mips3d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mmicromips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-ms-bitfields. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mul-bug-workaround . . . . . . . . . . . . . . . . . . . . .
mno-muladd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mulhw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-mult-bug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-multi-cond-exec . . . . . . . . . . . . . . . . . . . . . . . .
mno-multiple . . . . . . . . . . . . . . . . . . . . . . . . . . . 334,
mno-mvcle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-nested-cond-exec . . . . . . . . . . . . . . . . . . . . . . .
mno-odd-spreg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-omit-leaf-frame-pointer . . . . . . . . . . . . . . .
mno-optimize-membar . . . . . . . . . . . . . . . . . . . . . . . .
mno-opts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-pack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-packed-stack. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-paired . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-paired-single . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-pc-relative-literal-loads . . . . . . . . . . . . .
mno-perf-ext . . . . . . . . . . . . . . . . . . . . . . . . . . . 322,
mno-pic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-pid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-plt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-popc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-popcntb. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331,
mno-popcntd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-postinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-postmodify . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-power8-fusion . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-power8-vector . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-powerpc-gfxopt . . . . . . . . . . . . . . . . . . . . . . . . .
mno-powerpc-gpopt . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-powerpc64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-prolog-function . . . . . . . . . . . . . . . . . . . . . . . .
mno-prologue-epilogue . . . . . . . . . . . . . . . . . . . . . .
mno-prototype . . . . . . . . . . . . . . . . . . . . . . . . . . 338,
mno-push-args . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-quad-memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-quad-memory-atomic . . . . . . . . . . . . . . . . . . . . .
mno-readonly-in-sdata . . . . . . . . . . . . . . . . . . . . . .
mno-red-zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-register-names . . . . . . . . . . . . . . . . . . . . . . . . .
mno-regnames . . . . . . . . . . . . . . . . . . . . . . . . . . . 340,
mno-relax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-relax-immediate . . . . . . . . . . . . . . . . . . . . . . . .
mno-relocatable . . . . . . . . . . . . . . . . . . . . . . . . 335,
mno-relocatable-lib . . . . . . . . . . . . . . . . . . . 335,
mno-renesas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-round-nearest . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-rtd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

313
346
346
243
306
310
310
237
406
310
271
282
353
319
284
352
367
284
308
229
284
302
283
365
349
310
231
323
289
363
307
380
346
346
235
235
349
349
346
346
346
384
271
356
406
349
349
358
411
289
358
386
300
353
353
371
234
298

Option Index

mno-save-mduc-in-interrupts . . . . . . . . . . . . . . .
mno-scc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-sched-ar-data-spec . . . . . . . . . . . . . . . . . . . . .
mno-sched-ar-in-data-spec . . . . . . . . . . . . . . . . .
mno-sched-br-data-spec . . . . . . . . . . . . . . . . . . . . .
mno-sched-br-in-data-spec . . . . . . . . . . . . . . . . .
mno-sched-control-spec . . . . . . . . . . . . . . . . . . . . .
mno-sched-count-spec-in-critical-path . . .
mno-sched-in-control-spec . . . . . . . . . . . . . . . . .
mno-sched-prefer-non-control-spec-insns
.........................................
mno-sched-prefer-non-data-spec-insns. . . . .
mno-sched-prolog. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-sdata . . . . . . . . . . . . . . . . . . . . . 241, 289, 339,
mno-sep-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-serialize-volatile . . . . . . . . . . . . . . . . . . . . .
mno-short . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-side-effects. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-sim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-single-exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-slow-bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-small-exec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-smartmips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-soft-cmpsf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-soft-float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-space-regs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-spe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-specld-anomaly . . . . . . . . . . . . . . . . . . . . . . . . .
mno-split-addresses . . . . . . . . . . . . . . . . . . . . . . . .
mno-stack-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-stack-bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-std-struct-return . . . . . . . . . . . . . . . . . . . . . .
mno-strict-align . . . . . . . . . . . . . . . . . . 299, 335,
mno-subxc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-sum-in-toc . . . . . . . . . . . . . . . . . . . . . . . . . 333,
mno-sym32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-target-align. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-text-section-literals . . . . . . . . . . . . . . . . .
mno-tls-markers . . . . . . . . . . . . . . . . . . . . . . . . 340,
mno-toc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335,
mno-toplevel-symbols . . . . . . . . . . . . . . . . . . . . . . .
mno-tpf-trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-unaligned-access . . . . . . . . . . . . . . . . . . . . . . .
mno-unaligned-doubles . . . . . . . . . . . . . . . . . . . . . .
mno-uninit-const-in-rodata . . . . . . . . . . . . . . . .
mno-update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334,
mno-user-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-usermode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-v3push . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-v8plus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vect-double . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-virt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vis2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vis3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vis4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vis4b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vliw-branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

917

345
283
291
291
291
291
291
292
291
292
292
245
358
269
414
298
271
362
319
300
366
310
233
276
286
332
268
312
271
381
377
353
380
350
311
414
414
359
354
319
367
257
376
312
352
377
373
323
379
235
310
379
379
379
379
379
284

mno-volatile-asm-stop . . . . . . . . . . . . . . . . . . . . . .
mno-volatile-cache . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vrsave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vsx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-vx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-warn-mcu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-warn-multiple-fast-interrupts . . . . . . . .
mno-wide-bitfields . . . . . . . . . . . . . . . . . . . . . . . . .
mno-xgot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299,
mno-xl-compat . . . . . . . . . . . . . . . . . . . . . . . . . . 333,
mno-xpa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-zdcbranch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-zero-extend . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mno-zvector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnobitfield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnodiv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnoliw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnomacsave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnop-fun-dllimport . . . . . . . . . . . . . . . . . . . . . . . . .
mnop-mcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnopm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnorm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnosetlb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mnosplit-lohi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
modd-spreg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
momit-leaf-frame-pointer . . . . . . . . . 229, 267,
mone-byte-bool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
moptimize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
moptimize-membar. . . . . . . . . . . . . . . . . . . . . . . . . . . .
moverride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpa-risc-1-0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpa-risc-1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpa-risc-2-0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpacked-stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpadstruct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpaired . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpaired-single . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpc-relative-literal-loads . . . . . . . . . . . . . . . .
mpc32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpc64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpc80 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpclmul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpconfig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpcrel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpdebug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpe-aligned-commons . . . . . . . . . . . . . . . . . . . . . . . .
mperf-ext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322,
mpic-data-is-text-relative . . . . . . . . . . . . . . . .
mpic-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpku . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mplt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpointer-size=size . . . . . . . . . . . . . . . . . . . . . . . . .
mpointers-to-nested-functions . . . . . . . . 341,
mpoke-function-name . . . . . . . . . . . . . . . . . . . . . . . .

289
241
348
349
366
321
364
300
307
351
310
374
318
366
298
281
320
371
412
409
281
233
237
320
235
308
409
274
329
284
231
286
286
286
283
365
371
349
310
231
400
400
400
401
401
299
271
351
413
323
255
255
363
402
307
388
360
255

918

mpopc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpopcnt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpopcntb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331,
mpopcntd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mportable-runtime . . . . . . . . . . . . . . . . . . . . . . . . . .
mpower8-fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpower8-vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpowerpc-gfxopt . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpowerpc-gpopt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpowerpc64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mprefer-avx128 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mprefer-short-insn-regs . . . . . . . . . . . . . . . . . . .
mprefer-vector-width . . . . . . . . . . . . . . . . . . . . . . .
mprefergot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpreferred-stack-boundary . . . . . . . . . . . . 343,
mprefetchwt1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpretend-cmove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mprint-tune-info. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mprioritize-restricted-insns . . . . . . . . . 336,
mprolog-function. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mprologue-epilogue . . . . . . . . . . . . . . . . . . . . . . . . .
mprototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338,
mpure-code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mpush-args . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mq-class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mquad-memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mquad-memory-atomic . . . . . . . . . . . . . . . . . . . . . . . .
MQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mr0rel-sec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mr10k-cache-barrier . . . . . . . . . . . . . . . . . . . . . . . .
mRcq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mRcw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrdrnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mreadonly-in-sdata . . . . . . . . . . . . . . . . . . . . . . . . .
mrecip. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340, 359,
mrecip-precision . . . . . . . . . . . . . . . . . . . . . . . 341,
mrecip=opt . . . . . . . . . . . . . . . . . . . . . . . . . 340, 359,
mrecord-mcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mreduced-regs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mregister-names . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mregnames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340,
mregparm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrelax . . . . . . 261, 285, 320, 321, 323, 363, 371,
mrelax-immediate. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrelax-pic-calls. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrelocatable . . . . . . . . . . . . . . . . . . . . . . . . . . . 335,
mrelocatable-lib . . . . . . . . . . . . . . . . . . . . . . . 335,
mrenesas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrepeat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrestrict-it . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mreturn-pointer-on-d0 . . . . . . . . . . . . . . . . . . . . . .
mrf16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrgf-banked-regs. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrh850-abi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrl78 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrmw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrtd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298, 399,

Using the GNU Compiler Collection (GCC)

380
401
346
346
287
349
349
346
346
346
403
233
403
373
400
401
375
257
354
384
271
356
257
406
189
243
349
349
189
324
315
243
243
401
358
404
360
404
409
322
289
358
399
386
300
317
353
353
371
302
257
320
240
240
386
345
261
506

mrtm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrtp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mrtsc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285,
ms2600 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msafe-dma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msafe-hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msahf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msatur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msave-acc-in-interrupts . . . . . . . . . . . . . . . . . . .
msave-mduc-in-interrupts . . . . . . . . . . . . . . . . . .
msave-restore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msave-toc-indirect . . . . . . . . . . . . . . . . . . . . 341,
mscc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msched-ar-data-spec . . . . . . . . . . . . . . . . . . . . . . . .
msched-ar-in-data-spec . . . . . . . . . . . . . . . . . . . . .
msched-br-data-spec . . . . . . . . . . . . . . . . . . . . . . . .
msched-br-in-data-spec . . . . . . . . . . . . . . . . . . . . .
msched-control-spec . . . . . . . . . . . . . . . . . . . . . . . .
msched-costly-dep . . . . . . . . . . . . . . . . . . . . . . 336,
msched-count-spec-in-critical-path . . . . . . .
msched-fp-mem-deps-zero-cost . . . . . . . . . . . . . .
msched-in-control-spec . . . . . . . . . . . . . . . . . . . . .
msched-max-memory-insns . . . . . . . . . . . . . . . . . . .
msched-max-memory-insns-hard-limit . . . . . . .
msched-prefer-non-control-spec-insns. . . . .
msched-prefer-non-data-spec-insns . . . . . . . .
msched-spec-ldc . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msched-stop-bits-after-every-cycle . . . . . . .
mschedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mscore5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mscore5u . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mscore7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mscore7d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msdata. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289, 339,
msdata=all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msdata=data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339,
msdata=default . . . . . . . . . . . . . . . . . . . . 270, 339,
msdata=eabi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339,
msdata=none . . . . . . . . . . . . . . . . . . . 270, 294, 339,
msdata=sdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msdata=sysv. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339,
msdata=use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msdram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270,
msecure-plt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332,
msel-sched-dont-check-control-spec . . . . . . .
msep-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mserialize-volatile . . . . . . . . . . . . . . . . . . . . . . . .
msetlb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mshared-library-id . . . . . . . . . . . . . . . . . . . . . . . . .
mshort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mshort-calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mshstk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
msign-extend-enabled . . . . . . . . . . . . . . . . . . . . . . .
msign-return-address . . . . . . . . . . . . . . . . . . . . . . .
msilicon-errata . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

402
388
240
302
285
382
383
404
302
363
345
343
361
283
291
291
291
291
291
354
292
292
291
292
292
292
292
292
292
287
368
368
368
368
385
357
270
357
357
357
358
294
357
294
302
348
292
269
414
320
401
268
298
261
404
293
232
322

Option Index

msilicon-errata-warn . . . . . . . . . . . . . . . . . . . . . . . 322
msim . . . 267, 270, 272, 281, 293, 302, 321, 338, 344,
356, 362, 387, 413
msimd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
msimnovec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
msimple-fpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
msingle-exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
msingle-float . . . . . . . . . . . . . . . . . . . . . 308, 334, 352
msingle-pic-base . . . . . . . . . . . . . . . . . . 255, 336, 354
msio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
msize-level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
mskip-rax-setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
mslow-bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
mslow-flash-data. . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
msmall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
msmall-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
msmall-data-limit . . . . . . . . . . . . . . . . . . . . . . 343, 362
msmall-divides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
msmall-exec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
msmall-mem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
msmall-model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
msmall-text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
msmall16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
msmallc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
msmartmips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
msoft-float . . . . 237, 276, 281, 287, 298, 302, 308,
329, 334, 352, 364, 376, 386, 387, 397
msoft-quad-float. . . . . . . . . . . . . . . . . . . . . . . . . . . . 376
msoft-stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
msp8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
mspace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
mspe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332
mspecld-anomaly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
mspfp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
mspfp-compact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
mspfp-fast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
mspfp_compact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
mspfp_fast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
msplit-addresses. . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
msplit-vecmove-early . . . . . . . . . . . . . . . . . . . . . . . 235
msse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
msse2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
msse2avx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
msse3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
msse4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
msse4.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
msse4.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
msse4a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
msseregparm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
mssse3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
mstack-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
mstack-bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
mstack-check-l1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
mstack-guard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
mstack-increment. . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
mstack-offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
mstack-protector-guard . . . . . . . . . . . 342, 361, 410
mstack-protector-guard-offset . . . 342, 361, 410

919

mstack-protector-guard-reg. . . . . . . 342, 361, 410
mstack-protector-guard-symbol . . . . . . . . 342, 361
mstack-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
mstackrealign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400
mstd-struct-return . . . . . . . . . . . . . . . . . . . . . . . . . 377
mstdmain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
mstrict-align . . . . . . . . . . . . 229, 299, 335, 343, 353
mstrict-X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
mstring-compare-inline-limit . . . . . . . . . . . . . . 358
mstringop-strategy=alg . . . . . . . . . . . . . . . . . . . . . 408
mstructure-size-boundary . . . . . . . . . . . . . . . . . . 254
msubxc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
msv-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
msve-vector-bits. . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
msvr4-struct-return . . . . . . . . . . . . . . . . . . . 337, 355
mswap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
mswape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
msym32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
msynci . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
msys-crt0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
msys-lib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
mtarget-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
mtas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
mtbm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
mtda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
mtelephony . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
mtext-section-literals . . . . . . . . . . . . . . . . . . . . . 414
mtf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
mthread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
mthreads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
mthumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
mthumb-interwork. . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
mtiny-stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
mtiny= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
mtls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
mtls-dialect . . . . . . . . . . . . . . . . . . . . . . . . . . . 256, 406
mtls-dialect=desc . . . . . . . . . . . . . . . . . . . . . . . . . . 229
mtls-dialect=traditional . . . . . . . . . . . . . . . . . . 229
mtls-direct-seg-refs . . . . . . . . . . . . . . . . . . . . . . . 409
mtls-markers . . . . . . . . . . . . . . . . . . . . . . . . . . . 340, 359
mtls-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229, 291
mTLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
mtoc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335, 354
mtomcat-stats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
mtoplevel-symbols . . . . . . . . . . . . . . . . . . . . . . . . . . 319
mtp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
mtp-regno . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
mtpcs-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
mtpcs-leaf-frame. . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
mtpf-trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
mtraceback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
mtrap-precision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
mtune . . 231, 243, 245, 251, 270, 280, 291, 296, 305,
320, 332, 343, 347, 367, 378, 388, 395
mtune-ctrl=feature-list . . . . . . . . . . . . . . . . . . . 403
MT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
muclibc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
muls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368

920

multcost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
multcost=number . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
multi_module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
multilib-library-pic . . . . . . . . . . . . . . . . . . . . . . .
multiply-enabled. . . . . . . . . . . . . . . . . . . . . . . . . . . .
multiply_defined. . . . . . . . . . . . . . . . . . . . . . . . . . . .
multiply_defined_unused . . . . . . . . . . . . . . . . . . .
munalign-prob-threshold . . . . . . . . . . . . . . . . . . .
munaligned-access . . . . . . . . . . . . . . . . . . . . . . . . . .
munaligned-doubles . . . . . . . . . . . . . . . . . . . . . . . . .
municode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
muniform-simt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
muninit-const-in-rodata . . . . . . . . . . . . . . . . . . .
munix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
munix-asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
munsafe-dma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mupdate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334,
muser-enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
muser-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377,
musermode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv3push . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv850 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv850e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv850e1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv850e2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv850e2v3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv850e2v4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv850e3v5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv850es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mv8plus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvaes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mveclibabi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360,
mvect8-ret-in-mem . . . . . . . . . . . . . . . . . . . . . . . . . .
mverbose-cost-dump . . . . . . . . . . . . . . . . . . . . 231,
mvirt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvis2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvis3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvis4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvis4b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvliw-branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvms-return-codes . . . . . . . . . . . . . . . . . . . . . . . . . .
mvolatile-asm-stop . . . . . . . . . . . . . . . . . . . . . . . . .
mvolatile-cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvpclmulqdq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvr4130-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvrsave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvsx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mvxworks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338,
mvzeroupper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mwarn-dynamicstack . . . . . . . . . . . . . . . . . . . . . . . . .
mwarn-framesize . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mwarn-mcu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mwarn-multiple-fast-interrupts . . . . . . . . . . .
mwarn-reloc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mwbnoinvd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mwide-bitfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Using the GNU Compiler Collection (GCC)

245
373
276
282
293
276
276
244
257
376
412
329
312
387
330
382
352
293
388
373
323
385
385
385
385
385
385
385
385
379
402
405
399
257
310
379
379
379
379
379
284
388
289
241
402
317
348
349
366
357
403
368
367
321
364
381
401
300

mwin32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mwindows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mword-relocations . . . . . . . . . . . . . . . . . . . . . . . . . .
mx32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxgot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299,
mxilinx-fpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxl-barrel-shift. . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxl-compat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333,
mxl-float-convert . . . . . . . . . . . . . . . . . . . . . . . . . .
mxl-float-sqrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxl-gp-opt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxl-multiply-high . . . . . . . . . . . . . . . . . . . . . . . . . .
mxl-pattern-compare . . . . . . . . . . . . . . . . . . . . . . . .
mxl-reorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxl-soft-div . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxl-soft-mul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxl-stack-check . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxpa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxsave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxsavec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxsaveopt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxsaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
myellowknife . . . . . . . . . . . . . . . . . . . . . . . . . . . 338,
mzarch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mzda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mzdcbranch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mzero-extend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
mzvector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M.............................................

412
413
256
411
307
352
303
351
303
303
303
303
303
303
303
303
303
401
310
402
402
402
402
241
357
366
385
374
318
366
188

N
no-80387 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
no-canonical-prefixes . . . . . . . . . . . . . . . . . . . . . .
no-integrated-cpp . . . . . . . . . . . . . . . . . . . . . . . . . .
no-pie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
no-sysroot-suffix . . . . . . . . . . . . . . . . . . . . . . . . . .
no_dead_strip_inits_and_terms . . . . . . . . . . . . .
noall_load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nocpp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nodefaultlibs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nodevicelib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nofixprebinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nofpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nolibdld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nomultidefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
non-static . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
noprebind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
noseglinkedit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nostartfiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nostdinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
nostdinc++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49,
nostdlib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

397
202
194
196
202
276
276
314
196
262
276
362
289
276
389
276
276
195
201
201
196

Option Index

O
o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
O0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
O1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
O2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
O3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Ofast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Og . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Os . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

P
p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
pagezero_size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
param . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
pass-exit-codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
pedantic . . . . . . . . . . . . . . . . . . . . . 5, 63, 439, 595, 853
pedantic-errors. . . . . . . . . . . . . . . . . . . . . . . 5, 64, 853
pg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
pie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
plt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
prebind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
prebind_all_twolevel_modules . . . . . . . . . . . . . . 276
print-file-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
print-libgcc-file-name . . . . . . . . . . . . . . . . . . . . . 227
print-multi-directory . . . . . . . . . . . . . . . . . . . . . . 227
print-multi-lib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
print-multi-os-directory . . . . . . . . . . . . . . . . . . 227
print-multiarch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
print-objc-runtime-info . . . . . . . . . . . . . . . . . . . . . 59
print-prog-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
print-search-dirs . . . . . . . . . . . . . . . . . . . . . . . . . . 227
print-sysroot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
print-sysroot-headers-suffix . . . . . . . . . . . . . . 228
private_bundle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
pthread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188, 196
pthreads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

Q
Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
Qn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383
Qy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383

R
rdynamic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
read_only_relocs. . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
remap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

S
s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
save-temps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
save-temps=obj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

921

sectalign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
sectcreate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
sectobjectsymbols . . . . . . . . . . . . . . . . . . . . . . . . . . 276
sectorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
seg_addr_table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
seg_addr_table_filename . . . . . . . . . . . . . . . . . . . 276
seg1addr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
segaddr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
seglinkedit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
segprot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
segs_read_only_addr . . . . . . . . . . . . . . . . . . . . . . . . 276
segs_read_write_addr . . . . . . . . . . . . . . . . . . . . . . . 276
shared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
shared-libgcc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
short-calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
sim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
sim2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
single_module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
specs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
static. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197, 276, 289
static-libasan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
static-libgcc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
static-liblsan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
static-libmpx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
static-libmpxwrappers . . . . . . . . . . . . . . . . . . . . . . 198
static-libstdc++. . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
static-libtsan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
static-libubsan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
static-pie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
std . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 36, 614, 851
sub_library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
sub_umbrella . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
symbolic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
sysroot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31, 195

T
target-help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
tno-android-cc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
tno-android-ld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
traditional. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192, 841
traditional-cpp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
trigraphs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
twolevel_namespace . . . . . . . . . . . . . . . . . . . . . . . . . 276
T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

U
u.............................................
umbrella . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
undef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
undefined . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
unexported_symbols_list . . . . . . . . . . . . . . . . . . .
U.............................................

199
276
188
276
276
187

922

Using the GNU Compiler Collection (GCC)

V

Wdiv-by-zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Wdouble-promotion. . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Wduplicate-decl-specifier . . . . . . . . . . . . . . . . . . 67
Wduplicated-branches . . . . . . . . . . . . . . . . . . . . . . . . 88
Wduplicated-cond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
weak_reference_mismatches . . . . . . . . . . . . . . . . . 276
Weffc++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Wempty-body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wendif-labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wenum-compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Werror . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Werror= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Wexpansion-to-defined . . . . . . . . . . . . . . . . . . . . . . . 94
Wextra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65, 102, 103
Wextra-semi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wfatal-errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Wfloat-conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Wfloat-equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Wformat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67, 85, 468
Wformat-contains-nul . . . . . . . . . . . . . . . . . . . . . . . . 67
Wformat-extra-args . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Wformat-nonliteral . . . . . . . . . . . . . . . . . . . . . . 69, 469
Wformat-overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Wformat-security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Wformat-signedness . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Wformat-truncation . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Wformat-y2k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Wformat-zero-length . . . . . . . . . . . . . . . . . . . . . . . . . 69
Wformat= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Wformat=1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Wformat=2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Wframe-address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Wframe-larger-than . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Wfree-nonheap-object . . . . . . . . . . . . . . . . . . . . . . . . 92
whatsloaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
whyload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
Wif-not-aligned . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Wignored-attributes . . . . . . . . . . . . . . . . . . . . . . . . . 73
Wignored-qualifiers . . . . . . . . . . . . . . . . . . . . . . . . . 73
Wimplicit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Wimplicit-fallthrough . . . . . . . . . . . . . . . . . . . . . . . 71
Wimplicit-fallthrough= . . . . . . . . . . . . . . . . . . . . . . 71
Wimplicit-function-declaration . . . . . . . . . . . . . 71
Wimplicit-int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Wincompatible-pointer-types . . . . . . . . . . . . . . . . 89
Winherited-variadic-ctor . . . . . . . . . . . . . . . . . . 105
Winit-self. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Winline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105, 540
Wint-conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Wint-in-bool-context . . . . . . . . . . . . . . . . . . . . . . . 105
Wint-to-pointer-cast . . . . . . . . . . . . . . . . . . . . . . . 106
Winvalid-memory-model . . . . . . . . . . . . . . . . . . . . . . . 80
Winvalid-offsetof . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Winvalid-pch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Wjump-misses-init. . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Wlarger-than-len . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Wlarger-than=len . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

W
w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65, 102, 103, 842
Wa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
Wabi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Wabi-tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Waddr-space-convert . . . . . . . . . . . . . . . . . . . . . . . . 262
Waddress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Waggregate-return . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Waggressive-loop-optimizations . . . . . . . . . . . 101
Waligned-new . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64, 844
Walloc-zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Walloca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Warray-bounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Wassign-intercept. . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Wattributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Wbad-function-cast . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wbool-compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Wbool-operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Wbuiltin-declaration-mismatch . . . . . . . . . . . . . 101
Wbuiltin-macro-redefined . . . . . . . . . . . . . . . . . . 101
Wc++-compat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wc++11-compat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wc++14-compat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wc++17-compat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wc90-c99-compat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wc99-c11-compat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wcast-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wcast-align=strict . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wcast-function-type . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wcast-qual. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wcatch-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wchar-subscripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Wchkp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Wclass-memaccess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Wclobbered. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wcomment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wcomments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wconditionally-supported . . . . . . . . . . . . . . . . . . . 97
Wconversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wconversion-null . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wctor-dtor-privacy . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Wdangling-else . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wdate-time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wdeclaration-after-statement . . . . . . . . . . . . . . . 91
Wdelete-incomplete . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wdelete-non-virtual-dtor . . . . . . . . . . . . . . . . . . . 51
Wdeprecated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Wdeprecated-declarations . . . . . . . . . . . . . . . . . . 103
Wdisabled-optimization . . . . . . . . . . . . . . . . . . . . . 107
Wdiscarded-array-qualifiers . . . . . . . . . . . . . . . . 89
Wdiscarded-qualifiers . . . . . . . . . . . . . . . . . . . . . . . 89

Option Index

Wliteral-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Wlogical-not-parentheses . . . . . . . . . . . . . . . . . . 100
Wlogical-op . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Wlong-long . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Wlto-type-mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Wmain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Wmaybe-uninitialized . . . . . . . . . . . . . . . . . . . . . . . . 80
Wmemset-elt-size. . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Wmemset-transposed-args . . . . . . . . . . . . . . . . . . . 100
Wmisleading-indentation . . . . . . . . . . . . . . . . . . . . . 73
Wmissing-attributes . . . . . . . . . . . . . . . . . . . . . . . . . 74
Wmissing-braces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Wmissing-declarations . . . . . . . . . . . . . . . . . . . . . . 102
Wmissing-field-initializers . . . . . . . . . . . . . . . 102
Wmissing-format-attribute . . . . . . . . . . . . . . . . . . 85
Wmissing-include-dirs . . . . . . . . . . . . . . . . . . . . . . . 75
Wmissing-parameter-type . . . . . . . . . . . . . . . . . . . 101
Wmissing-prototypes . . . . . . . . . . . . . . . . . . . . . . . . 101
Wmisspelled-isr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
Wmultichar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Wmultiple-inheritance . . . . . . . . . . . . . . . . . . . . . . . 55
Wmultistatement-macros . . . . . . . . . . . . . . . . . . . . . . 75
Wnamespaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Wnarrowing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Wnested-externs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Wno-abi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Wno-address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Wno-aggregate-return . . . . . . . . . . . . . . . . . . . . . . . 101
Wno-aggressive-loop-optimizations . . . . . . . . 101
Wno-aligned-new . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Wno-all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Wno-alloc-zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Wno-alloca. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Wno-array-bounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Wno-assign-intercept . . . . . . . . . . . . . . . . . . . . . . . . 58
Wno-attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Wno-bad-function-cast . . . . . . . . . . . . . . . . . . . . . . . 95
Wno-bool-compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Wno-bool-operation . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Wno-builtin-declaration-mismatch . . . . . . . . . 101
Wno-builtin-macro-redefined . . . . . . . . . . . . . . . 101
Wno-c90-c99-compat . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wno-c99-c11-compat . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wno-cast-align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wno-cast-function-type . . . . . . . . . . . . . . . . . . . . . . 96
Wno-cast-qual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wno-catch-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wno-char-subscripts . . . . . . . . . . . . . . . . . . . . . . . . . 66
Wno-clobbered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wno-conditionally-supported . . . . . . . . . . . . . . . . 97
Wno-conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wno-conversion-null . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wno-coverage-mismatch . . . . . . . . . . . . . . . . . . . . . . . 66
Wno-ctor-dtor-privacy . . . . . . . . . . . . . . . . . . . . . . . 51
Wno-dangling-else. . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wno-date-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wno-declaration-after-statement . . . . . . . . . . . 91
Wno-delete-incomplete . . . . . . . . . . . . . . . . . . . . . . . 98

923

Wno-delete-non-virtual-dtor . . . . . . . . . . . . . . . . 51
Wno-deprecated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Wno-deprecated-declarations . . . . . . . . . . . . . . . 103
Wno-disabled-optimization . . . . . . . . . . . . . . . . . 107
Wno-discarded-array-qualifiers . . . . . . . . . . . . . 89
Wno-discarded-qualifiers . . . . . . . . . . . . . . . . . . . 89
Wno-div-by-zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Wno-double-promotion . . . . . . . . . . . . . . . . . . . . . . . . 66
Wno-duplicate-decl-specifier . . . . . . . . . . . . . . . 67
Wno-duplicated-branches . . . . . . . . . . . . . . . . . . . . . 88
Wno-duplicated-cond . . . . . . . . . . . . . . . . . . . . . . . . . 88
Wno-effc++. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Wno-empty-body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wno-endif-labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wno-enum-compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wno-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Wno-error=. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Wno-extra . . . . . . . . . . . . . . . . . . . . . . . . . . . 65, 102, 103
Wno-extra-semi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wno-fatal-errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Wno-float-conversion . . . . . . . . . . . . . . . . . . . . . . . . 99
Wno-float-equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Wno-format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67, 85
Wno-format-contains-nul . . . . . . . . . . . . . . . . . . . . . 67
Wno-format-extra-args . . . . . . . . . . . . . . . . . . . . . . . 67
Wno-format-nonliteral . . . . . . . . . . . . . . . . . . . . . . . 69
Wno-format-overflow . . . . . . . . . . . . . . . . . . . . . . 68, 70
Wno-format-security . . . . . . . . . . . . . . . . . . . . . . . . . 69
Wno-format-signedness . . . . . . . . . . . . . . . . . . . . . . . 70
Wno-format-truncation . . . . . . . . . . . . . . . . . . . . . . . 70
Wno-format-y2k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Wno-format-zero-length . . . . . . . . . . . . . . . . . . . . . . 69
Wno-frame-address. . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Wno-free-nonheap-object . . . . . . . . . . . . . . . . . . . . . 92
Wno-if-not-aligned . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Wno-ignored-attributes . . . . . . . . . . . . . . . . . . . . . . 73
Wno-ignored-qualifiers . . . . . . . . . . . . . . . . . . . . . . 73
Wno-implicit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Wno-implicit-fallthrough . . . . . . . . . . . . . . . . . . . 71
Wno-implicit-function-declaration . . . . . . . . . 71
Wno-implicit-int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Wno-incompatible-pointer-types . . . . . . . . . . . . . 89
Wno-inherited-variadic-ctor . . . . . . . . . . . . . . . 105
Wno-init-self . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Wno-inline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Wno-int-conversion . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Wno-int-in-bool-context . . . . . . . . . . . . . . . . . . . 105
Wno-int-to-pointer-cast . . . . . . . . . . . . . . . . . . . 106
Wno-invalid-memory-model . . . . . . . . . . . . . . . . . . . 80
Wno-invalid-offsetof . . . . . . . . . . . . . . . . . . . . . . . 105
Wno-invalid-pch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Wno-jump-misses-init . . . . . . . . . . . . . . . . . . . . . . . . 98
Wno-literal-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Wno-logical-not-parentheses . . . . . . . . . . . . . . . 100
Wno-logical-op . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Wno-long-long . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Wno-lto-type-mismatch . . . . . . . . . . . . . . . . . . . . . . . 52
Wno-main . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

924

Using the GNU Compiler Collection (GCC)

Wno-maybe-uninitialized . . . . . . . . . . . . . . . . . . . . . 80
Wno-memset-elt-size . . . . . . . . . . . . . . . . . . . . . . . . 100
Wno-memset-transposed-args . . . . . . . . . . . . . . . . 100
Wno-misleading-indentation . . . . . . . . . . . . . . . . . 73
Wno-missing-attributes . . . . . . . . . . . . . . . . . . . . . . 74
Wno-missing-braces . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Wno-missing-declarations . . . . . . . . . . . . . . . . . . 102
Wno-missing-field-initializers . . . . . . . . . . . 102
Wno-missing-format-attribute . . . . . . . . . . . . . . . 85
Wno-missing-include-dirs . . . . . . . . . . . . . . . . . . . 75
Wno-missing-parameter-type . . . . . . . . . . . . . . . . 101
Wno-missing-prototypes . . . . . . . . . . . . . . . . . . . . . 101
Wno-multichar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Wno-multistatement-macros . . . . . . . . . . . . . . . . . . 75
Wno-narrowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Wno-nested-externs . . . . . . . . . . . . . . . . . . . . . . . . . 105
Wno-noexcept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Wno-noexcept-type. . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Wno-non-template-friend . . . . . . . . . . . . . . . . . . . . . 54
Wno-non-virtual-dtor . . . . . . . . . . . . . . . . . . . . . . . . 53
Wno-nonnull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Wno-nonnull-compare . . . . . . . . . . . . . . . . . . . . . . . . . 70
Wno-normalized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Wno-null-dereference . . . . . . . . . . . . . . . . . . . . . . . . 71
Wno-odr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Wno-old-style-cast . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Wno-old-style-declaration . . . . . . . . . . . . . . . . . 101
Wno-old-style-definition . . . . . . . . . . . . . . . . . . 101
Wno-overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Wno-overlength-strings . . . . . . . . . . . . . . . . . . . . . 107
Wno-overloaded-virtual . . . . . . . . . . . . . . . . . . . . . . 54
Wno-override-init . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Wno-override-init-side-effects . . . . . . . . . . . 104
Wno-packed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Wno-packed-bitfield-compat . . . . . . . . . . . . . . . . 104
Wno-packed-not-aligned . . . . . . . . . . . . . . . . . . . . . 104
Wno-padded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Wno-parentheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Wno-pedantic-ms-format . . . . . . . . . . . . . . . . . . . . . . 93
Wno-placement-new. . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Wno-pmf-conversions . . . . . . . . . . . . . . . . . . . . 54, 793
Wno-pointer-arith. . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wno-pointer-compare . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wno-pointer-sign. . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Wno-pointer-to-int-cast . . . . . . . . . . . . . . . . . . . 106
Wno-pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Wno-protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Wno-redundant-decls . . . . . . . . . . . . . . . . . . . . . . . . 104
Wno-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Wno-reorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Wno-restrict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Wno-return-local-addr . . . . . . . . . . . . . . . . . . . . . . . 76
Wno-return-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Wno-selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Wno-sequence-point . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Wno-shadow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Wno-shadow-ivar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Wno-shift-count-negative . . . . . . . . . . . . . . . . . . . 77

Wno-shift-count-overflow . . . . . . . . . . . . . . . . . . . 77
Wno-shift-negative-value . . . . . . . . . . . . . . . . . . . 77
Wno-shift-overflow . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Wno-sign-compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Wno-sign-conversion . . . . . . . . . . . . . . . . . . . . . . . . . 99
Wno-sign-promo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Wno-sized-deallocation . . . . . . . . . . . . . . . . . . . . . . 99
Wno-sizeof-array-argument . . . . . . . . . . . . . . . . . 100
Wno-sizeof-pointer-div . . . . . . . . . . . . . . . . . . . . . . 99
Wno-sizeof-pointer-memaccess . . . . . . . . . . . . . . . 99
Wno-stack-protector . . . . . . . . . . . . . . . . . . . . . . . . 107
Wno-strict-aliasing . . . . . . . . . . . . . . . . . . . . . . . . . 81
Wno-strict-null-sentinel . . . . . . . . . . . . . . . . . . . 54
Wno-strict-overflow . . . . . . . . . . . . . . . . . . . . . . . . . 82
Wno-strict-prototypes . . . . . . . . . . . . . . . . . . . . . . 101
Wno-strict-selector-match . . . . . . . . . . . . . . . . . . 58
Wno-stringop-overflow . . . . . . . . . . . . . . . . . . . . . . . 83
Wno-stringop-truncation . . . . . . . . . . . . . . . . . . . . . 84
Wno-subobject-linkage . . . . . . . . . . . . . . . . . . . . . . . 97
Wno-suggest-attribute= . . . . . . . . . . . . . . . . . . . . . . 85
Wno-suggest-attribute=cold . . . . . . . . . . . . . . . . . 86
Wno-suggest-attribute=const . . . . . . . . . . . . . . . . 85
Wno-suggest-attribute=format . . . . . . . . . . . . . . . 85
Wno-suggest-attribute=malloc . . . . . . . . . . . . . . . 85
Wno-suggest-attribute=noreturn . . . . . . . . . . . . . 85
Wno-suggest-attribute=pure . . . . . . . . . . . . . . . . . 85
Wno-suggest-final-methods . . . . . . . . . . . . . . . . . . 86
Wno-suggest-final-types . . . . . . . . . . . . . . . . . . . . . 86
Wno-switch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Wno-switch-bool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Wno-switch-default . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Wno-switch-enum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Wno-switch-unreachable . . . . . . . . . . . . . . . . . . . . . . 78
Wno-sync-nand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Wno-system-headers . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Wno-tautological-compare . . . . . . . . . . . . . . . . . . . 89
Wno-terminate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Wno-traditional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Wno-traditional-conversion . . . . . . . . . . . . . . . . . 91
Wno-trampolines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Wno-type-limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wno-undeclared-selector . . . . . . . . . . . . . . . . . . . . . 58
Wno-undef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wno-uninitialized. . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
Wno-unknown-pragmas . . . . . . . . . . . . . . . . . . . . . . . . . 81
Wno-unused. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
Wno-unused-but-set-parameter . . . . . . . . . . . . . . . 78
Wno-unused-but-set-variable . . . . . . . . . . . . . . . . 78
Wno-unused-const-variable . . . . . . . . . . . . . . . . . . 79
Wno-unused-function . . . . . . . . . . . . . . . . . . . . . . . . . 78
Wno-unused-label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Wno-unused-parameter . . . . . . . . . . . . . . . . . . . . . . . . 79
Wno-unused-result. . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Wno-unused-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Wno-unused-variable . . . . . . . . . . . . . . . . . . . . . . . . . 79
Wno-useless-cast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wno-varargs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Wno-variadic-macros . . . . . . . . . . . . . . . . . . . . . . . . 106

Option Index

Wno-vector-operation-performance . . . . . . . . . 106
Wno-virtual-move-assign . . . . . . . . . . . . . . . . . . . 106
Wno-vla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Wno-volatile-register-var . . . . . . . . . . . . . . . . . 107
Wno-write-strings. . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wno-zero-as-null-pointer-constant . . . . . . . . . 97
Wnoexcept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Wnoexcept-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Wnon-template-friend . . . . . . . . . . . . . . . . . . . . . . . . 54
Wnon-virtual-dtor. . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Wnonnull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Wnonnull-compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Wnormalized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Wnormalized= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Wnull-dereference. . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Wodr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Wold-style-cast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Wold-style-declaration . . . . . . . . . . . . . . . . . . . . . 101
Wold-style-definition . . . . . . . . . . . . . . . . . . . . . . 101
Wopenm-simd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Woverflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Woverlength-strings . . . . . . . . . . . . . . . . . . . . . . . . 107
Woverloaded-virtual . . . . . . . . . . . . . . . . . . . . . . . . . 54
Woverride-init . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Woverride-init-side-effects . . . . . . . . . . . . . . . 104
Wp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
Wpacked . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Wpacked-bitfield-compat . . . . . . . . . . . . . . . . . . . 104
Wpacked-not-aligned . . . . . . . . . . . . . . . . . . . . . . . . 104
Wpadded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Wparentheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Wpedantic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Wpedantic-ms-format . . . . . . . . . . . . . . . . . . . . . . . . . 93
Wplacement-new . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Wpmf-conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Wpointer-arith . . . . . . . . . . . . . . . . . . . . . . . . . . 94, 459
Wpointer-compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wpointer-sign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Wpointer-to-int-cast . . . . . . . . . . . . . . . . . . . . . . . 106
Wpragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Wprotocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
wrapper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Wredundant-decls. . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Wregister . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Wreorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Wrestrict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Wreturn-local-addr . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Wreturn-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Wselector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Wsequence-point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Wshadow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Wshadow-ivar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Wshadow=compatible-local . . . . . . . . . . . . . . . . . . . 92
Wshadow=local . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Wshift-count-negative . . . . . . . . . . . . . . . . . . . . . . . 77
Wshift-count-overflow . . . . . . . . . . . . . . . . . . . . . . . 77
Wshift-negative-value . . . . . . . . . . . . . . . . . . . . . . . 77
Wshift-overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

925

Wsign-compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Wsign-conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Wsign-promo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Wsized-deallocation . . . . . . . . . . . . . . . . . . . . . . . . . 99
Wsizeof-array-argument . . . . . . . . . . . . . . . . . . . . . 100
Wsizeof-pointer-div . . . . . . . . . . . . . . . . . . . . . . . . . 99
Wsizeof-pointer-memaccess . . . . . . . . . . . . . . . . . . 99
Wstack-protector. . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Wstack-usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Wstrict-aliasing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Wstrict-aliasing=n . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Wstrict-null-sentinel . . . . . . . . . . . . . . . . . . . . . . . 54
Wstrict-overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Wstrict-prototypes . . . . . . . . . . . . . . . . . . . . . . . . . 101
Wstrict-selector-match . . . . . . . . . . . . . . . . . . . . . . 58
Wstringop-overflow . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Wstringop-truncation . . . . . . . . . . . . . . . . . . . . . . . . 84
Wsubobject-linkage . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Wsuggest-attribute= . . . . . . . . . . . . . . . . . . . . . . . . . 85
Wsuggest-attribute=cold . . . . . . . . . . . . . . . . . . . . . 86
Wsuggest-attribute=const . . . . . . . . . . . . . . . . . . . 85
Wsuggest-attribute=format . . . . . . . . . . . . . . . . . . 85
Wsuggest-attribute=malloc . . . . . . . . . . . . . . . . . . 85
Wsuggest-attribute=noreturn . . . . . . . . . . . . . . . . 85
Wsuggest-attribute=pure . . . . . . . . . . . . . . . . . . . . . 85
Wsuggest-final-methods . . . . . . . . . . . . . . . . . . . . . . 86
Wsuggest-final-types . . . . . . . . . . . . . . . . . . . . . . . . 86
Wswitch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Wswitch-bool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Wswitch-default . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Wswitch-enum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Wswitch-unreachable . . . . . . . . . . . . . . . . . . . . . . . . . 78
Wsync-nand. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Wsystem-headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Wtautological-compare . . . . . . . . . . . . . . . . . . . . . . . 89
Wtemplates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Wterminate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Wtraditional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Wtraditional-conversion . . . . . . . . . . . . . . . . . . . . . 91
Wtrampolines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Wtrigraphs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wtype-limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wundeclared-selector . . . . . . . . . . . . . . . . . . . . . . . . 58
Wundef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Wuninitialized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
Wunknown-pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Wunsuffixed-float-constants . . . . . . . . . . . . . . . 107
Wunused . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
Wunused-but-set-parameter . . . . . . . . . . . . . . . . . . 78
Wunused-but-set-variable . . . . . . . . . . . . . . . . . . . 78
Wunused-const-variable . . . . . . . . . . . . . . . . . . . . . . 79
Wunused-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Wunused-label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Wunused-local-typedefs . . . . . . . . . . . . . . . . . . . . . . 79
Wunused-macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Wunused-parameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Wunused-result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Wunused-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

926

Using the GNU Compiler Collection (GCC)

Wunused-variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Wuseless-cast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Wvarargs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Wvariadic-macros. . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Wvector-operation-performance . . . . . . . . . . . . . 106
Wvirtual-inheritance . . . . . . . . . . . . . . . . . . . . . . . . 55
Wvirtual-move-assign . . . . . . . . . . . . . . . . . . . . . . . 106
Wvla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Wvolatile-register-var . . . . . . . . . . . . . . . . . . . . . 107
Wwrite-strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wzero-as-null-pointer-constant . . . . . . . . . . . . . 97

Xassembler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Xbind-lazy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Xbind-now . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Xlinker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Xpreprocessor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

X

Z

x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

194
389
389
199
194

Y
Ym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383
YP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383

Keyword Index

927

Keyword Index
#
#pragma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
#pragma implementation . . . . . . . . . . . . . . . . . . . . .
#pragma implementation, implied . . . . . . . . . . . .
#pragma interface . . . . . . . . . . . . . . . . . . . . . . . . . . .

<
773
790
790
789

‘<’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560

=
‘=’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562

$
$ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538

%
‘%’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
%include . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
%include_noerr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
%rename . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

‘>’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560

?
563
415
415
415

&
‘&’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563

’
’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 842

*
*__builtin_alloca . . . . . . . . . . . . . . . . . . . . . . . . . . 615
*__builtin_alloca_with_align . . . . . . . . . . . . . . 616
*__builtin_alloca_with_align_and_max. . . . . 616

+
‘+’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562

‘-lgcc’, use with ‘-nodefaultlibs’ . . . . . . . . . . .
‘-lgcc’, use with ‘-nostdlib’ . . . . . . . . . . . . . . . . .
‘-march’ feature modifiers. . . . . . . . . . . . . . . . . . . . .
‘-mcpu’ feature modifiers . . . . . . . . . . . . . . . . . . . . . .
‘-nodefaultlibs’ and unresolved references . . .
‘-nostdlib’ and unresolved references . . . . . . . .

>

196
196
232
232
196
196

.
.sdata/.sdata2 references (PowerPC) . . . . . 339, 358

/
// . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538

?: extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
?: side effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448

‘_’ in variables in macros . . . . . . . . . . . . . . . . . . . . .
__atomic_add_fetch . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_always_lock_free . . . . . . . . . . . . . . . . .
__atomic_and_fetch . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_clear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_compare_exchange . . . . . . . . . . . . . . . . .
__atomic_compare_exchange_n . . . . . . . . . . . . . . .
__atomic_exchange . . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_exchange_n . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_fetch_add . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_fetch_and . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_fetch_nand . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_fetch_or . . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_fetch_sub . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_fetch_xor . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_is_lock_free . . . . . . . . . . . . . . . . . . . . . .
__atomic_load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_load_n . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_nand_fetch . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_or_fetch . . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_signal_fence . . . . . . . . . . . . . . . . . . . . . .
__atomic_store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_store_n. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_sub_fetch . . . . . . . . . . . . . . . . . . . . . . . . .
__atomic_test_and_set . . . . . . . . . . . . . . . . . . . . . .
__atomic_thread_fence . . . . . . . . . . . . . . . . . . . . . .
__atomic_xor_fetch . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin___bnd_chk_ptr_bounds . . . . . . . 611,
__builtin___bnd_chk_ptr_lbounds. . . . . . 611,
__builtin___bnd_chk_ptr_ubounds. . . . . . 611,
__builtin___bnd_copy_ptr_bounds. . . . . . 611,
__builtin___bnd_get_ptr_lbound . . . . . . . 611,
__builtin___bnd_get_ptr_ubound . . . . . . . 611,
__builtin___bnd_init_ptr_bounds. . . . . . 611,
__builtin___bnd_narrow_ptr_bounds . . . 611,
__builtin___bnd_null_ptr_bounds. . . . . . 611,

446
605
606
605
606
605
605
605
605
606
606
606
606
606
606
607
604
604
605
605
606
604
604
605
606
606
605
613
612
613
612
613
613
612
612
612

928

__builtin___bnd_set_ptr_bounds . . . . . . . . . . .
__builtin___bnd_store_ptr_bounds . . . . 611,
__builtin___clear_cache . . . . . . . . . . . . . . . . . . .
__builtin___fprintf_chk . . . . . . . . . . . . . . . . . . .
__builtin___memcpy_chk . . . . . . . . . . . . . . . . . . . . .
__builtin___memmove_chk . . . . . . . . . . . . . . . . . . .
__builtin___mempcpy_chk . . . . . . . . . . . . . . . . . . .
__builtin___memset_chk . . . . . . . . . . . . . . . . . . . . .
__builtin___printf_chk . . . . . . . . . . . . . . . . . . . . .
__builtin___snprintf_chk . . . . . . . . . . . . . . . . . .
__builtin___sprintf_chk . . . . . . . . . . . . . . . . . . .
__builtin___stpcpy_chk . . . . . . . . . . . . . . . . . . . . .
__builtin___strcat_chk . . . . . . . . . . . . . . . . . . . . .
__builtin___strcpy_chk . . . . . . . . . . . . . . . . . . . . .
__builtin___strncat_chk . . . . . . . . . . . . . . . . . . .
__builtin___strncpy_chk . . . . . . . . . . . . . . . . . . .
__builtin___vfprintf_chk . . . . . . . . . . . . . . . . . .
__builtin___vprintf_chk . . . . . . . . . . . . . . . . . . .
__builtin___vsnprintf_chk . . . . . . . . . . . . . . . . .
__builtin___vsprintf_chk . . . . . . . . . . . . . . . . . .
__builtin_add_overflow . . . . . . . . . . . . . . . . . . . . .
__builtin_add_overflow_p . . . . . . . . . . . . . . . . . .
__builtin_addf128_round_to_odd . . . . . . . . . . .
__builtin_alloca. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_alloca_with_align . . . . . . . . . . . . . . .
__builtin_alloca_with_align_and_max . . . . . .
__builtin_apply . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_apply_args . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_aligned . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_brk . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_core_read . . . . . . . . . . . . . . . . . . .
__builtin_arc_core_write . . . . . . . . . . . . . . . . . .
__builtin_arc_divaw . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_flag . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_lr. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_mul64 . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_mulu64 . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_nop . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_norm . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_normw . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_rtie . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_sleep . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_sr. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_swap . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_swi . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_sync . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_trap_s . . . . . . . . . . . . . . . . . . . . . . .
__builtin_arc_unimp_s . . . . . . . . . . . . . . . . . . . . . .
__builtin_assume_aligned . . . . . . . . . . . . . . . . . .
__builtin_bswap16 . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_bswap32 . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_bswap64 . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_call_with_static_chain . . . . 613,
__builtin_choose_expr . . . . . . . . . . . . . . . . . . . . . .
__builtin_clrsb . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_clrsbl. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_clrsbll . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_clz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Using the GNU Compiler Collection (GCC)

611
612
622
609
609
609
609
609
609
609
609
609
609
609
609
609
609
609
609
609
607
608
674
613
613
613
445
444
630
630
630
630
630
630
631
631
631
631
631
631
631
631
631
631
632
632
632
632
621
626
626
626
617
617
625
625
626
625

__builtin_clzl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_clzll . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_complex . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_constant_p . . . . . . . . . . . . . . . . . . . . . . .
__builtin_cpu_init . . . . . . . . . . . . . . . . . . . . 670,
__builtin_cpu_is . . . . . . . . . . . . . . . . . . . . . . . 671,
__builtin_cpu_supports . . . . . . . . . . . . . . . . 671,
__builtin_ctz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_ctzl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_ctzll . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_divf128_round_to_odd . . . . . . . . . . .
__builtin_expect. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_extend_pointer . . . . . . . . . . . . . . 613,
__builtin_extract_return_addr . . . . . . . . . . . . .
__builtin_ffs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_ffsl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_ffsll . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_FILE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_fmaf128 . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_fmaf128_round_to_odd . . . . . . . . . . .
__builtin_fpclassify . . . . . . . . . . . . . . . . . . 613,
__builtin_frame_address . . . . . . . . . . . . . . . . . . .
__builtin_frob_return_address . . . . . . . . . . . . .
__builtin_FUNCTION . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_huge_val . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_huge_valf . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_huge_valfn . . . . . . . . . . . . . . . . . . . . . . .
__builtin_huge_valfnx . . . . . . . . . . . . . . . . . . . . . .
__builtin_huge_vall . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_huge_valq . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_inf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_infd128 . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_infd32. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_infd64. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_inff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_inffn . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_inffnx. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_infl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_infq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_isfinite . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_isgreater . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_isgreaterequal . . . . . . . . . . . . . . . . . .
__builtin_isinf_sign . . . . . . . . . . . . . . . . . . 613,
__builtin_isless. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_islessequal . . . . . . . . . . . . . . . . . . . . . .
__builtin_islessgreater . . . . . . . . . . . . . . . . . . .
__builtin_isnormal . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_isunordered . . . . . . . . . . . . . . . . . . . . . .
__builtin_LINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_mul_overflow . . . . . . . . . . . . . . . . . . . . .
__builtin_mul_overflow_p . . . . . . . . . . . . . . . . . .
__builtin_mulf128_round_to_odd . . . . . . . . . . .
__builtin_nan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nand128 . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nand32. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nand64. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nanfn . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

625
625
619
619
749
750
751
625
625
626
675
620
626
597
625
625
625
621
674
675
623
597
597
621
623
623
623
623
623
749
623
623
623
623
623
623
624
623
749
613
613
613
624
613
613
613
613
613
621
608
608
674
624
624
624
624
624
624

Keyword Index

__builtin_nanfnx. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nanl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nanq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nansf . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nansfn. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nansfnx . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nansl . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nansq . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nds32_isb . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nds32_isync . . . . . . . . . . . . . . . . . . . . . .
__builtin_nds32_mfsr . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nds32_mfusr . . . . . . . . . . . . . . . . . . . . . .
__builtin_nds32_mtsr . . . . . . . . . . . . . . . . . . . . . . .
__builtin_nds32_mtusr . . . . . . . . . . . . . . . . . . . . . .
__builtin_nds32_setgie_dis . . . . . . . . . . . . . . . .
__builtin_nds32_setgie_en . . . . . . . . . . . . . . . . .
__builtin_non_tx_store . . . . . . . . . . . . . . . . . . . . .
__builtin_object_size . . . . . . . . . . . . . . . . . 609,
__builtin_offsetof . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_parity. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_parityl . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_parityll . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_popcount . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_popcountl . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_popcountll . . . . . . . . . . . . . . . . . . . . . . .
__builtin_powi . . . . . . . . . . . . . . . . . . . . . . . . . 613,
__builtin_powif . . . . . . . . . . . . . . . . . . . . . . . . 613,
__builtin_powil . . . . . . . . . . . . . . . . . . . . . . . . 613,
__builtin_prefetch . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_return. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_return_address . . . . . . . . . . . . . . . . . .
__builtin_rx_brk. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_clrpsw . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_int. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_machi . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_maclo . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_mulhi . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_mullo . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_mvfachi . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_mvfacmi . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_mvfc . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_mvtachi . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_mvtaclo . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_mvtc . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_mvtipl . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_racw . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_revw . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_rmpa . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_round . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_sat. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_setpsw . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_rx_wait . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_sadd_overflow . . . . . . . . . . . . . . . . . . .
__builtin_saddl_overflow . . . . . . . . . . . . . . . . . .
__builtin_saddll_overflow . . . . . . . . . . . . . . . . .
__builtin_set_thread_pointer . . . . . . . . . . . . . .
__builtin_sh_get_fpscr . . . . . . . . . . . . . . . . . . . . .

929

624
624
749
624
624
625
625
624
749
669
669
670
670
670
670
670
670
742
610
600
625
625
626
625
625
626
626
626
626
622
445
597
739
739
739
739
739
739
739
739
739
739
739
739
739
740
740
740
740
740
740
740
740
607
607
607
742
742

__builtin_sh_set_fpscr . . . . . . . . . . . . . . . . . . . . .
__builtin_shuffle . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_smul_overflow . . . . . . . . . . . . . . . . . . .
__builtin_smull_overflow . . . . . . . . . . . . . . . . . .
__builtin_smulll_overflow . . . . . . . . . . . . . . . . .
__builtin_sqrtf128 . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_sqrtf128_round_to_odd . . . . . . . . . .
__builtin_ssub_overflow . . . . . . . . . . . . . . . . . . .
__builtin_ssubl_overflow . . . . . . . . . . . . . . . . . .
__builtin_ssubll_overflow . . . . . . . . . . . . . . . . .
__builtin_sub_overflow . . . . . . . . . . . . . . . . . . . . .
__builtin_sub_overflow_p . . . . . . . . . . . . . . . . . .
__builtin_subf128_round_to_odd . . . . . . . . . . .
__builtin_tabort. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_tbegin. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_tbegin_nofloat . . . . . . . . . . . . . . . . . .
__builtin_tbegin_retry . . . . . . . . . . . . . . . . . . . . .
__builtin_tbegin_retry_nofloat . . . . . . . . . . .
__builtin_tbeginc . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_tend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_tgmath. . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_thread_pointer . . . . . . . . . . . . . . . . . .
__builtin_trap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_truncf128_round_to_odd . . . . . . . . .
__builtin_tx_assist . . . . . . . . . . . . . . . . . . . . . . . .
__builtin_tx_nesting_depth . . . . . . . . . . . . . . . .
__builtin_types_compatible_p . . . . . . . . . . . . . .
__builtin_uadd_overflow . . . . . . . . . . . . . . . . . . .
__builtin_uaddl_overflow . . . . . . . . . . . . . . . . . .
__builtin_uaddll_overflow . . . . . . . . . . . . . . . . .
__builtin_umul_overflow . . . . . . . . . . . . . . . . . . .
__builtin_umull_overflow . . . . . . . . . . . . . . . . . .
__builtin_umulll_overflow . . . . . . . . . . . . . . . . .
__builtin_unreachable . . . . . . . . . . . . . . . . . . . . . .
__builtin_usub_overflow . . . . . . . . . . . . . . . . . . .
__builtin_usubl_overflow . . . . . . . . . . . . . . . . . .
__builtin_usubll_overflow . . . . . . . . . . . . . . . . .
__builtin_va_arg_pack . . . . . . . . . . . . . . . . . . . . . .
__builtin_va_arg_pack_len . . . . . . . . . . . . . . . . .
__complex__ keyword . . . . . . . . . . . . . . . . . . . . . . . .
__declspec(dllexport) . . . . . . . . . . . . . . . . . . . . . .
__declspec(dllimport) . . . . . . . . . . . . . . . . . . . . . .
__ea SPU Named Address Spaces . . . . . . . . . . . . .
__extension__ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__far M32C Named Address Spaces . . . . . . . . . .
__far RL78 Named Address Spaces . . . . . . . . . . .
__flash AVR Named Address Spaces . . . . . . . . .
__flash1 AVR Named Address Spaces . . . . . . . .
__flash2 AVR Named Address Spaces . . . . . . . .
__flash3 AVR Named Address Spaces . . . . . . . .
__flash4 AVR Named Address Spaces . . . . . . . .
__flash5 AVR Named Address Spaces . . . . . . . .
__float128 data type . . . . . . . . . . . . . . . . . . . . . . . .
__float80 data type . . . . . . . . . . . . . . . . . . . . . . . . .
__fp16 data type . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
__func__ identifier . . . . . . . . . . . . . . . . . . . . . . . . . . .
__FUNCTION__ identifier . . . . . . . . . . . . . . . . . . . . . . .
__ibm128 data type. . . . . . . . . . . . . . . . . . . . . . . . . . .

742
599
608
608
608
674
675
607
607
608
607
608
674
742
740
741
741
741
741
741
618
742
620
675
742
742
617
607
607
607
608
608
608
620
608
608
608
445
445
448
493
494
455
595
455
455
453
454
454
454
454
454
449
449
450
596
596
449

930

Using the GNU Compiler Collection (GCC)

__imag__ keyword . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
__int128 data types . . . . . . . . . . . . . . . . . . . . . . . . . . 448
__memx AVR Named Address Spaces . . . . . . . . . . 454
__PRETTY_FUNCTION__ identifier . . . . . . . . . . . . . . . 596
__real__ keyword . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
__seg_fs x86 named address space . . . . . . . . . . . 456
__seg_gs x86 named address space . . . . . . . . . . . 456
__STDC_HOSTED__ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
__sync_add_and_fetch . . . . . . . . . . . . . . . . . . . . . . . 602
__sync_and_and_fetch . . . . . . . . . . . . . . . . . . . . . . . 602
__sync_bool_compare_and_swap . . . . . . . . . . . . . . 602
__sync_fetch_and_add . . . . . . . . . . . . . . . . . . . . . . . 601
__sync_fetch_and_and . . . . . . . . . . . . . . . . . . . . . . . 601
__sync_fetch_and_nand . . . . . . . . . . . . . . . . . . . . . . 601
__sync_fetch_and_or . . . . . . . . . . . . . . . . . . . . . . . . 601
__sync_fetch_and_sub . . . . . . . . . . . . . . . . . . . . . . . 601
__sync_fetch_and_xor . . . . . . . . . . . . . . . . . . . . . . . 601
__sync_lock_release . . . . . . . . . . . . . . . . . . . . . . . . 602
__sync_lock_test_and_set . . . . . . . . . . . . . . . . . . 602
__sync_nand_and_fetch . . . . . . . . . . . . . . . . . . . . . . 602
__sync_or_and_fetch . . . . . . . . . . . . . . . . . . . . . . . . 602
__sync_sub_and_fetch . . . . . . . . . . . . . . . . . . . . . . . 602
__sync_synchronize . . . . . . . . . . . . . . . . . . . . . . . . . 602
__sync_val_compare_and_swap . . . . . . . . . . . . . . . 602
__sync_xor_and_fetch . . . . . . . . . . . . . . . . . . . . . . . 602
__thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782
_Accum data type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
_Complex keyword . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
_Decimal128 data type . . . . . . . . . . . . . . . . . . . . . . . 451
_Decimal32 data type . . . . . . . . . . . . . . . . . . . . . . . . 451
_Decimal64 data type . . . . . . . . . . . . . . . . . . . . . . . . 451
_Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
_exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
_Floatn data types . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
_Floatnx data types . . . . . . . . . . . . . . . . . . . . . . . . . . 449
_Fract data type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
_get_ssp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772
_HTM_FIRST_USER_ABORT_CODE . . . . . . . . . . . . . . . . 741
_inc_ssp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772
_Sat data type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
_xabort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772
_xbegin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 771
_xend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 771
_xtest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772

absdata variable attribute, AVR . . . . . . . . . . . . . . 519
accessing volatiles. . . . . . . . . . . . . . . . . . . . . . . . 540, 787
acos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
acosf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
acosh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
acoshf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
acoshl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
acosl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
Ada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
additional floating types . . . . . . . . . . . . . . . . . . . . . . 449
address constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . 562
address of a label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
address variable attribute, AVR . . . . . . . . . . . . . . 519
address_operand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562
alias function attribute . . . . . . . . . . . . . . . . . . . . . . 464
aligned function attribute. . . . . . . . . . . . . . . . . . . . 464
aligned type attribute . . . . . . . . . . . . . . . . . . . . . . . 525
aligned variable attribute . . . . . . . . . . . . . . . . . . . . 513
alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538
alloc_align function attribute . . . . . . . . . . . . . . . 465
alloc_size function attribute . . . . . . . . . . . . . . . . 465
alloca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
alloca vs variable-length arrays . . . . . . . . . . . . . . 458
Allow nesting in an interrupt handler on the
Blackfin processor . . . . . . . . . . . . . . . . . . . . . . . . 488
Altera Nios II options . . . . . . . . . . . . . . . . . . . . . . . . 323
alternate keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . 595
altivec type attribute, PowerPC . . . . . . . . . . . . . 531
altivec variable attribute, PowerPC . . . . . . . . . 523
always_inline function attribute . . . . . . . . . . . . . 465
AMD1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ANSI C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ANSI C standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ANSI C89 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ANSI support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
ANSI X3.159-1989 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
apostrophes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
application binary interface . . . . . . . . . . . . . . . . . . . 817
ARC options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
arch= function attribute, AArch64 . . . . . . . . . . . . 482
arch= function attribute, ARM . . . . . . . . . . . . . . . 485
ARM [Annotated C++ Reference Manual] . . . . . 799
ARM options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
arrays of length zero . . . . . . . . . . . . . . . . . . . . . . . . . . 456
arrays of variable length . . . . . . . . . . . . . . . . . . . . . . 457
arrays, non-lvalue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
artificial function attribute . . . . . . . . . . . . . . . . 466
asin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
asinf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
asinh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
asinhf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
asinhl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
asinl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
asm assembler template . . . . . . . . . . . . . . . . . . . . . . . 547
asm clobbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
asm constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
asm expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
asm flag output operands . . . . . . . . . . . . . . . . . . . . . 551

0
‘0’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561

A
AArch64 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
abi_tag function attribute. . . . . . . . . . . . . . . . . . . .
abi_tag type attribute . . . . . . . . . . . . . . . . . . . . . . .
abi_tag variable attribute . . . . . . . . . . . . . . . . . . . .
ABI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
abort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
abs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

228
793
793
793
817
613
613

Keyword Index

asm goto labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
asm input operands . . . . . . . . . . . . . . . . . . . . . . . . . . .
asm keyword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
asm output operands. . . . . . . . . . . . . . . . . . . . . . . . . .
asm scratch registers . . . . . . . . . . . . . . . . . . . . . . . . . .
asm volatile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
assembler names for identifiers . . . . . . . . . . . . . . . .
assembly code, invalid . . . . . . . . . . . . . . . . . . . . . . . .
assembly language in C . . . . . . . . . . . . . . . . . . . . . . .
assembly language in C, basic. . . . . . . . . . . . . . . . .
assembly language in C, extended . . . . . . . . . . . . .
assume_aligned function attribute. . . . . . . . . . . .
atan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
atan2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
atan2f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
atan2l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
atanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
atanh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
atanhf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
atanhl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
atanl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
attribute of types . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
attribute of variables . . . . . . . . . . . . . . . . . . . . . . . . .
attribute syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
autoincrement/decrement addressing . . . . . . . . . .
automatic inline for C++ member fns . . . . . . . .
aux variable attribute, ARC . . . . . . . . . . . . . . . . . .
AVR Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

931

556
552
541
548
553
545
592
855
541
542
543
466
613
613
613
613
613
613
613
613
613
524
513
534
560
540
518
258

B
Backwards Compatibility . . . . . . . . . . . . . . . . . . . . .
bank_switch function attribute, M32C . . . . . . . .
base class members . . . . . . . . . . . . . . . . . . . . . . . . . . .
based type attribute, MeP . . . . . . . . . . . . . . . . . . . .
based variable attribute, MeP . . . . . . . . . . . . . . . .
basic asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
bcmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
below100 variable attribute, Xstormy16 . . . . . . .
binary compatibility . . . . . . . . . . . . . . . . . . . . . . . . . .
Binary constants using the ‘0b’ prefix . . . . . . . . .
Blackfin Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
bnd_instrument function attribute. . . . . . . . . . . .
bnd_legacy function attribute . . . . . . . . . . . . . . . .
bnd_variable_size type attribute . . . . . . . . . . . .
bound pointer to member function . . . . . . . . . . . .
break handler functions . . . . . . . . . . . . . . . . . . . . . . .
break_handler function attribute, MicroBlaze
.........................................
brk_interrupt function attribute, RL78 . . . . . .
bug criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
bugs, known . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
built-in functions . . . . . . . . . . . . . . . . . . . . . . . . . 39,
bzero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

799
490
847
531
521
542
613
524
817
785
267
466
466
526
793
493
493
502
855
855
839
613
613

C
c++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
C compilation options . . . . . . . . . . . . . . . . . . . . . . . . . . 9
C intermediate output, nonexistent . . . . . . . . . . . . . 3
C language extensions . . . . . . . . . . . . . . . . . . . . . . . . 439
C language, traditional . . . . . . . . . . . . . . . . . . . . . . . 192
C standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
C++ comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538
C++ interface and implementation headers . . . . 789
C++ language extensions . . . . . . . . . . . . . . . . . . . . . . 787
C++ member fns, automatically inline . . . . . . . 540
C++ misunderstandings . . . . . . . . . . . . . . . . . . . . . . . 846
C++ options, command-line . . . . . . . . . . . . . . . . . . . . 42
C++ pragmas, effect on inlining . . . . . . . . . . . . . . . 790
C++ source file suffixes . . . . . . . . . . . . . . . . . . . . . . . . . 34
C++ static data, declaring and defining . . . . . . . . 846
C_INCLUDE_PATH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
C11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C17 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C1X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C6X Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
C89 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C90 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C94 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C95 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C99 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C9X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
cabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cabsf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cabsl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cacos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cacosf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cacosh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cacoshf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cacoshl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cacosl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
callee_pop_aggregate_return function attribute,
x86 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
calling functions through the function vector on
SH2A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505
calloc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
carg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cargf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cargl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
case labels in initializers . . . . . . . . . . . . . . . . . . . . . . 461
case ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
casin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
casinf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
casinh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
casinhf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
casinhl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
casinl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cast to a union . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
catan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
catanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
catanh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613

932

Using the GNU Compiler Collection (GCC)

catanhf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
catanhl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
catanl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cb variable attribute, MeP . . . . . . . . . . . . . . . . . . . . 521
cbrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cbrtf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cbrtl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ccos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ccosf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ccosh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ccoshf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ccoshl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ccosl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cdecl function attribute, x86-32 . . . . . . . . . . . . . . 506
ceil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ceilf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ceill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cexpf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cexpl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
character set, execution . . . . . . . . . . . . . . . . . . . . . . . 191
character set, input . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
character set, input normalization . . . . . . . . . . . . 102
character set, wide execution . . . . . . . . . . . . . . . . . 191
cimag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cimagf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cimagl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cleanup variable attribute . . . . . . . . . . . . . . . . . . . . 514
clog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
clog10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
clog10f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
clog10l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
clogf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
clogl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cmodel= function attribute, AArch64 . . . . . . . . . 482
COBOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
code generation conventions . . . . . . . . . . . . . . . . . . 202
code, mixed with declarations. . . . . . . . . . . . . . . . . 463
cold function attribute . . . . . . . . . . . . . . . . . . . . . . . 466
cold label attribute . . . . . . . . . . . . . . . . . . . . . . . . . . 532
command options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
comments, C++ style. . . . . . . . . . . . . . . . . . . . . . . . . . 538
common variable attribute . . . . . . . . . . . . . . . . . . . . . 515
comparison of signed and unsigned values, warning
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
compilation statistics . . . . . . . . . . . . . . . . . . . . . . . . . 212
compiler bugs, reporting . . . . . . . . . . . . . . . . . . . . . . 855
compiler compared to C++ preprocessor . . . . . . . . . 3
compiler options, C++ . . . . . . . . . . . . . . . . . . . . . . . . . 42
compiler options, Objective-C and Objective-C++
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
compiler version, specifying . . . . . . . . . . . . . . . . . . . . . 9
COMPILER_PATH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
complex conjugation . . . . . . . . . . . . . . . . . . . . . . . . . . 449
complex numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
compound literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
computed gotos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
conditional expressions, extensions . . . . . . . . . . . . 447

conflicting types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845
conj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
conjf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
conjl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
const applied to function . . . . . . . . . . . . . . . . . . . . . 464
const function attribute . . . . . . . . . . . . . . . . . . . . . . 466
const qualifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
constants in constraints . . . . . . . . . . . . . . . . . . . . . . . 560
constraint modifier characters . . . . . . . . . . . . . . . . . 562
constraint, matching . . . . . . . . . . . . . . . . . . . . . . . . . . 561
constraints, asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
constraints, machine specific . . . . . . . . . . . . . . . . . . 563
constructing calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
constructor expressions . . . . . . . . . . . . . . . . . . . . . . . 460
constructor function attribute . . . . . . . . . . . . . . . 467
contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885
copysign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
copysignf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
copysignl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
core dump. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
cos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cosf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cosh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
coshf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
coshl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cosl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
CPATH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
CPLUS_INCLUDE_PATH . . . . . . . . . . . . . . . . . . . . . . . . . 424
cpow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cpowf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cpowl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cproj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cprojf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cprojl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
cpu= function attribute, AArch64 . . . . . . . . . . . . . 482
CR16 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
creal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
crealf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
creall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
CRIS Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
critical function attribute, MSP430 . . . . . . . . . 496
cross compiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
csin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
csinf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
csinh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
csinhf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
csinhl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
csinl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
csqrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
csqrtf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
csqrtl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ctan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ctanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ctanh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ctanhf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ctanhl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ctanl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613

Keyword Index

933

D

E

Darwin options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
dcgettext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
dd integer suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
DD integer suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
deallocating variable length arrays . . . . . . . . . . . . 457
debug dump options . . . . . . . . . . . . . . . . . . . . . . . . . . 212
debugging GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
debugging information options . . . . . . . . . . . . . . . . 108
decimal floating types . . . . . . . . . . . . . . . . . . . . . . . . 451
declaration scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
declarations inside expressions . . . . . . . . . . . . . . . . 439
declarations, mixed with code. . . . . . . . . . . . . . . . . 463
declaring attributes of functions . . . . . . . . . . . . . . 464
declaring static data in C++ . . . . . . . . . . . . . . . . . . 846
defining static data in C++ . . . . . . . . . . . . . . . . . . . . 846
dependencies for make as output . . . . . . . . . . . . . . 425
dependencies, make . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
DEPENDENCIES_OUTPUT . . . . . . . . . . . . . . . . . . . . . . . . 425
dependent name lookup . . . . . . . . . . . . . . . . . . . . . . 847
deprecated enumerator attribute . . . . . . . . . . . . . 533
deprecated function attribute . . . . . . . . . . . . . . . . 467
deprecated type attribute . . . . . . . . . . . . . . . . . . . . 527
deprecated variable attribute . . . . . . . . . . . . . . . . 515
designated initializers . . . . . . . . . . . . . . . . . . . . . . . . . 461
designated_init type attribute . . . . . . . . . . . . . . 527
designator lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
designators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
destructor function attribute . . . . . . . . . . . . . . . . 467
developer options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
df integer suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
DF integer suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
dgettext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
diagnostic messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
dialect options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
diff-delete GCC_COLORS capability . . . . . . . . . . . . 60
diff-filename GCC_COLORS capability . . . . . . . . . 60
diff-hunk GCC_COLORS capability . . . . . . . . . . . . . . 60
diff-insert GCC_COLORS capability . . . . . . . . . . . . 60
digits in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
directory options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
disinterrupt function attribute, Epiphany . . . 488
disinterrupt function attribute, MeP . . . . . . . . 492
dl integer suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
DL integer suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
dllexport function attribute . . . . . . . . . . . . . . . . . 493
dllexport variable attribute . . . . . . . . . . . . . . . . . . 522
dllimport function attribute . . . . . . . . . . . . . . . . . 494
dllimport variable attribute . . . . . . . . . . . . . . . . . . 522
dollar signs in identifier names . . . . . . . . . . . . . . . . 538
double-word arithmetic . . . . . . . . . . . . . . . . . . . . . . . 448
downward funargs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
drem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
dremf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
dreml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
dump options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

‘E’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
earlyclobber operand . . . . . . . . . . . . . . . . . . . . . . . . . 563
eight-bit data on the H8/300, H8/300H, and H8S
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
eightbit_data variable attribute, H8/300 . . . . 520
EIND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
either function attribute, MSP430 . . . . . . . . . . . 497
either variable attribute, MSP430 . . . . . . . . . . . 523
empty structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
Enumerator Attributes . . . . . . . . . . . . . . . . . . . . . . . 533
environment variables . . . . . . . . . . . . . . . . . . . . . . . . 422
erf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
erfc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
erfcf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
erfcl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
erff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
erfl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
error function attribute . . . . . . . . . . . . . . . . . . . . . . 467
error GCC_COLORS capability . . . . . . . . . . . . . . . . . . . 60
error messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
escaped newlines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
exception function attribute . . . . . . . . . . . . . . . . . 497
exception handler functions, Blackfin . . . . . . . . . 487
exception handler functions, NDS32 . . . . . . . . . . 497
exception_handler function attribute . . . . . . . . 487
exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
exp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
exp10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
exp10f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
exp10l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
exp2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
exp2f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
exp2l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
expf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
expl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
explicit register variables . . . . . . . . . . . . . . . . . . . . . 592
expm1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
expm1f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
expm1l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
expressions containing statements . . . . . . . . . . . . . 439
expressions, constructor . . . . . . . . . . . . . . . . . . . . . . 460
extended asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543
extensible constraints . . . . . . . . . . . . . . . . . . . . . . . . . 562
extensions, ?: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
extensions, C language . . . . . . . . . . . . . . . . . . . . . . . 439
extensions, C++ language . . . . . . . . . . . . . . . . . . . . . 787
external declaration scope . . . . . . . . . . . . . . . . . . . . 842
externally_visible function attribute . . . . . . . 468
extra NOP instructions at the function entry point
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

F
‘F’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
fabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
fabsf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
fabsl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

561
613
613
613

934

Using the GNU Compiler Collection (GCC)

fallthrough statement attribute . . . . . . . . . . . . . 534
far function attribute, MeP . . . . . . . . . . . . . . . . . . 492
far function attribute, MIPS . . . . . . . . . . . . . . . . . 495
far type attribute, MeP . . . . . . . . . . . . . . . . . . . . . . 531
far variable attribute, MeP. . . . . . . . . . . . . . . . . . . 521
fast_interrupt function attribute, M32C . . . . 490
fast_interrupt function attribute, MicroBlaze
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
fast_interrupt function attribute, RX . . . . . . . 503
fastcall function attribute, x86-32 . . . . . . . . . . . 506
fatal signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
fdim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fdimf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fdiml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
FDL, GNU Free Documentation License . . . . . . 877
ffs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
file name suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
file names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
fix-cortex-a53-835769 function attribute,
AArch64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
fixed-point types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
fixit-delete GCC_COLORS capability . . . . . . . . . . . 60
fixit-insert GCC_COLORS capability . . . . . . . . . . . 60
flatten function attribute. . . . . . . . . . . . . . . . . . . . 468
flexible array members . . . . . . . . . . . . . . . . . . . . . . . . 456
float as function value type . . . . . . . . . . . . . . . . . . 843
floating point precision . . . . . . . . . . . . . . . . . . . . . . . 846
floating-point precision . . . . . . . . . . . . . . . . . . . . . . . 147
floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
floorf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
floorl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fmaf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fmal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fmax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fmaxf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fmaxl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fmin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fminf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fminl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fmod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fmodf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fmodl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
force_align_arg_pointer function attribute, x86
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508
format function attribute . . . . . . . . . . . . . . . . . . . . . 468
format_arg function attribute . . . . . . . . . . . . . . . . 469
Fortran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
forwarder_section function attribute, Epiphany
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
forwarding calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
fprintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fprintf_unlocked. . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fputs_unlocked . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
FR30 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
freestanding environment . . . . . . . . . . . . . . . . . . . . . . . 5
freestanding implementation . . . . . . . . . . . . . . . . . . . . 5

frexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
frexpf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
frexpl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
FRV Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
fscanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
fscanf, and constant strings . . . . . . . . . . . . . . . . . . 841
FT32 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
function addressability on the M32R/D . . . . . . . 491
function attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
function pointers, arithmetic . . . . . . . . . . . . . . . . . . 459
function prototype declarations . . . . . . . . . . . . . . . 537
function versions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
function, size of pointer to . . . . . . . . . . . . . . . . . . . . 459
function_return function attribute, x86. . . . . . 511
function_vector function attribute, H8/300 . . 489
function_vector function attribute, M16C/M32C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
function_vector function attribute, SH . . . . . . 505
functions in arbitrary sections . . . . . . . . . . . . . . . . 477
functions that are dynamically resolved . . . . . . . 470
functions that are passed arguments in registers on
x86-32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
functions that behave like malloc . . . . . . . . . . . . . 472
functions that have no side effects . . . . . . . . 466, 476
functions that never return . . . . . . . . . . . . . . . . . . . 475
functions that pop the argument stack on x86-32
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506, 507, 508
functions that return more than once . . . . . . . . . 477
functions with non-null pointer arguments . . . . 474
functions with printf, scanf, strftime or
strfmon style arguments . . . . . . . . . . . . . . . . . 468

G
‘g’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
g++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
‘G’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
G++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
gamma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
gamma_r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
gammaf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
gammaf_r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
gammal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
gammal_r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
gcc_struct type attribute, PowerPC . . . . . . . . . 531
gcc_struct type attribute, x86 . . . . . . . . . . . . . . . 532
gcc_struct variable attribute, PowerPC . . . . . . 523
gcc_struct variable attribute, x86 . . . . . . . . . . . . 524
GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
GCC command options . . . . . . . . . . . . . . . . . . . . . . . . . 9
GCC_COLORS environment variable . . . . . . . . . . . . . . 59
GCC_COMPARE_DEBUG . . . . . . . . . . . . . . . . . . . . . . . . . . 423
GCC_EXEC_PREFIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
gcov . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
general-regs-only function attribute, AArch64
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
gettext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
global offset table . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

Keyword Index

global register after longjmp . . . . . . . . . . . . . . . . . . 593
global register variables . . . . . . . . . . . . . . . . . . . . . . . 593
GNAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
gnu_inline function attribute . . . . . . . . . . . . . . . . 470
GNU C Compiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
GNU Compiler Collection . . . . . . . . . . . . . . . . . . . . . . . 3
Go . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
goto with computed label . . . . . . . . . . . . . . . . . . . . . 441
gprof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
grouping options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

H
‘H’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
half-precision floating point . . . . . . . . . . . . . . . . . . . 450
hardware models and configurations, specifying
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
hex floats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
highlight, color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
hk fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
HK fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
hosted environment . . . . . . . . . . . . . . . . . . . . . . 5, 39, 40
hosted implementation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
hot function attribute . . . . . . . . . . . . . . . . . . . . . . . . 470
hot label attribute. . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
hotpatch function attribute, S/390 . . . . . . . . . . . 504
HPPA Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
hr fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
HR fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
hypot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
hypotf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
hypotl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613

I
‘i’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
‘I’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
IA-64 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
IBM RS/6000 and PowerPC Options . . . . . . . . . 345
identifier names, dollar signs in . . . . . . . . . . . . . . . 538
identifiers, names in assembler code . . . . . . . . . . . 592
ifunc function attribute . . . . . . . . . . . . . . . . . . . . . . 470
ilogb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ilogbf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ilogbl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
imaxabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
implementation-defined behavior, C language
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
implementation-defined behavior, C++ language
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
implied #pragma implementation . . . . . . . . . . . . . 790
incompatibilities of GCC . . . . . . . . . . . . . . . . . . . . . 841
increment operators . . . . . . . . . . . . . . . . . . . . . . . . . . 855
index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
indirect calls, ARC . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
indirect calls, ARM . . . . . . . . . . . . . . . . . . . . . . . . . . . 485
indirect calls, Blackfin . . . . . . . . . . . . . . . . . . . . . . . . 488
indirect calls, Epiphany . . . . . . . . . . . . . . . . . . . . . . . 489

935

indirect calls, MIPS . . . . . . . . . . . . . . . . . . . . . . . . . . 495
indirect calls, PowerPC . . . . . . . . . . . . . . . . . . . . . . . 499
indirect functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
indirect_branch function attribute, x86. . . . . . 511
init_priority variable attribute . . . . . . . . . . . . . 794
initializations in expressions . . . . . . . . . . . . . . . . . . 460
initializers with labeled elements . . . . . . . . . . . . . . 461
initializers, non-constant . . . . . . . . . . . . . . . . . . . . . . 460
inline assembly language . . . . . . . . . . . . . . . . . . . . . . 541
inline automatic for C++ member fns . . . . . . . . 540
inline functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539
inline functions, omission of. . . . . . . . . . . . . . . . . . . 539
inlining and C++ pragmas . . . . . . . . . . . . . . . . . . . . 790
installation trouble . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
instrumentation options . . . . . . . . . . . . . . . . . . . . . . 172
integrating function code . . . . . . . . . . . . . . . . . . . . . 539
interface and implementation headers, C++ . . . . 789
intermediate C version, nonexistent . . . . . . . . . . . . . 3
interrupt function attribute, ARC . . . . . . . . . . . 483
interrupt function attribute, ARM . . . . . . . . . . 484
interrupt function attribute, AVR . . . . . . . . . . . 486
interrupt function attribute, CR16 . . . . . . . . . . 488
interrupt function attribute, Epiphany . . . . . . 489
interrupt function attribute, m68k . . . . . . . . . . . 492
interrupt function attribute, M32C . . . . . . . . . . 491
interrupt function attribute, M32R/D . . . . . . . 491
interrupt function attribute, MeP . . . . . . . . . . . 492
interrupt function attribute, MIPS . . . . . . . . . . 494
interrupt function attribute, MSP430 . . . . . . . . 496
interrupt function attribute, NDS32 . . . . . . . . . 498
interrupt function attribute, RL78 . . . . . . . . . . . 502
interrupt function attribute, RX. . . . . . . . . . . . . 503
interrupt function attribute, V850 . . . . . . . . . . . 506
interrupt function attribute, Visium . . . . . . . . . 506
interrupt function attribute, x86 . . . . . . . . . . . . 508
interrupt function attribute, Xstormy16 . . . . . 513
interrupt_handler function attribute, Blackfin
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
interrupt_handler function attribute, H8/300
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
interrupt_handler function attribute, m68k
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
interrupt_handler function attribute, MicroBlaze
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
interrupt_handler function attribute, SH . . . . 505
interrupt_handler function attribute, V850 . . 506
interrupt_thread function attribute, fido . . . . 492
introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
invalid assembly code . . . . . . . . . . . . . . . . . . . . . . . . . 855
invalid input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
invoking g++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
io variable attribute, AVR. . . . . . . . . . . . . . . . . . . . 519
io variable attribute, MeP . . . . . . . . . . . . . . . . . . . . 521
io_low variable attribute, AVR . . . . . . . . . . . . . . . 519
isalnum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
isalpha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
isascii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
isblank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613

936

Using the GNU Compiler Collection (GCC)

iscntrl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
isdigit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
isgraph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
islower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ISO 9899 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C17 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C1X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C90 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C94 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C95 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C99 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO C9X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
ISO/IEC 9899 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
isprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ispunct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
isr function attribute, ARM . . . . . . . . . . . . . . . . . 484
isspace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
isupper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswalnum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswalpha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswblank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswcntrl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswdigit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswgraph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswlower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswpunct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswspace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswupper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
iswxdigit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
isxdigit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613

known causes of trouble . . . . . . . . . . . . . . . . . . . . . . 839
kspisusp function attribute, Blackfin . . . . . . . . . 488

J
j0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
j0f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
j0l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
j1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
j1f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
j1l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
jli_always function attribute, ARC . . . . . . . . . .
jli_fixed function attribute, ARC . . . . . . . . . . .
jn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
jnf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
jnl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

613
613
613
613
613
613
484
484
613
613
613

K
k fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
K fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
keep_interrupts_masked function attribute, MIPS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
kernel attribute, Nvidia PTX . . . . . . . . . . . . . . . . 499
keywords, alternate . . . . . . . . . . . . . . . . . . . . . . . . . . . 595

L
l1_data variable attribute, Blackfin . . . . . . . . . . . 520
l1_data_A variable attribute, Blackfin . . . . . . . . 520
l1_data_B variable attribute, Blackfin . . . . . . . . 520
l1_text function attribute, Blackfin . . . . . . . . . . 488
l2 function attribute, Blackfin . . . . . . . . . . . . . . . . 488
l2 variable attribute, Blackfin . . . . . . . . . . . . . . . . 520
Label Attributes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
labeled elements in initializers . . . . . . . . . . . . . . . . 461
labels as values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
labs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
language dialect options . . . . . . . . . . . . . . . . . . . . . . . 35
LANG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423, 424
LC_ALL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
LC_CTYPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
LC_MESSAGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
ldexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ldexpf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
ldexpl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
leaf function attribute . . . . . . . . . . . . . . . . . . . . . . . 472
length-zero arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
lgamma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lgamma_r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lgammaf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lgammaf_r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lgammal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lgammal_r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
Libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
LIBRARY_PATH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
link options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
linker script . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
lk fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
LK fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
LL integer suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
llabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
llk fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
LLK fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
llr fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
LLR fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
llrint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
llrintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
llrintl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
llround . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
llroundf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
llroundl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
LM32 options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
load address instruction . . . . . . . . . . . . . . . . . . . . . . 562
local labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
local variables in macros . . . . . . . . . . . . . . . . . . . . . . 446
local variables, specifying registers . . . . . . . . . . . . 594
locale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
locale definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
locus GCC_COLORS capability . . . . . . . . . . . . . . . . . . . 60
log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613

Keyword Index

937

log10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
log10f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
log10l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
log1p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
log1pf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
log1pl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
log2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
log2f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
log2l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
logb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
logbf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
logbl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
logf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
logl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
long long data types . . . . . . . . . . . . . . . . . . . . . . . . . 448
long_call function attribute, ARC . . . . . . . . . . . 484
long_call function attribute, ARM . . . . . . . . . . 485
long_call function attribute, Epiphany . . . . . . 489
long_call function attribute, MIPS . . . . . . . . . . 495
longcall function attribute, Blackfin . . . . . . . . . 488
longcall function attribute, PowerPC . . . . . . . . 499
longjmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
longjmp incompatibilities . . . . . . . . . . . . . . . . . . . . . 841
longjmp warnings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
lower function attribute, MSP430 . . . . . . . . . . . . 497
lower variable attribute, MSP430 . . . . . . . . . . . . . 523
lr fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
LR fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
lrint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lrintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lrintl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lround . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lroundf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
lroundl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613

M
‘m’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M32C options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M32R/D options . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M680x0 options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
machine specific constraints . . . . . . . . . . . . . . . . . . .
machine-dependent options . . . . . . . . . . . . . . . . . . .
macro with variable arguments . . . . . . . . . . . . . . .
macros, inline alternative . . . . . . . . . . . . . . . . . . . . .
macros, local labels . . . . . . . . . . . . . . . . . . . . . . . . . . .
macros, local variables in . . . . . . . . . . . . . . . . . . . . .
macros, statements in expressions . . . . . . . . . . . . .
macros, types of arguments . . . . . . . . . . . . . . . . . . .
make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
malloc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
malloc function attribute . . . . . . . . . . . . . . . . . . . . .
matching constraint . . . . . . . . . . . . . . . . . . . . . . . . . .
may_alias type attribute . . . . . . . . . . . . . . . . . . . . .
MCore options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
medium_call function attribute, ARC . . . . . . . . .
member fns, automatically inline . . . . . . . . . . . .
memchr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

560
293
293
295
563
228
458
539
440
446
439
446
188
613
472
561
527
300
484
540
613

memcmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
memcpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
memory references in constraints. . . . . . . . . . . . . . 560
mempcpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
memset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
MeP options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
message formatting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
messages, warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
messages, warning and error . . . . . . . . . . . . . . . . . . 853
MicroBlaze Options . . . . . . . . . . . . . . . . . . . . . . . . . . 302
micromips function attribute . . . . . . . . . . . . . . . . . 496
middle-operands, omitted . . . . . . . . . . . . . . . . . . . . . 447
mips16 function attribute, MIPS . . . . . . . . . . . . . . 496
MIPS options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
misunderstandings in C++ . . . . . . . . . . . . . . . . . . . . 846
mixed declarations and code . . . . . . . . . . . . . . . . . . 463
mixing assembly language and C . . . . . . . . . . . . . . 541
mktemp, and constant strings . . . . . . . . . . . . . . . . . . 841
MMIX Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
MN10300 options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
mode variable attribute . . . . . . . . . . . . . . . . . . . . . . . 516
model function attribute, M32R/D . . . . . . . . . . . . 491
model variable attribute, IA-64 . . . . . . . . . . . . . . . 520
model-name variable attribute, M32R/D . . . . . . 521
modf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
modff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
modfl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
modifiers in constraints . . . . . . . . . . . . . . . . . . . . . . . 562
Moxie Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
ms_abi function attribute, x86 . . . . . . . . . . . . . . . . 507
ms_hook_prologue function attribute, x86 . . . . 507
ms_struct type attribute, PowerPC. . . . . . . . . . . 531
ms_struct type attribute, x86 . . . . . . . . . . . . . . . . 532
ms_struct variable attribute, PowerPC . . . . . . . 523
ms_struct variable attribute, x86 . . . . . . . . . . . . . 524
MSP430 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
multiple alternative constraints . . . . . . . . . . . . . . . 562
multiprecision arithmetic . . . . . . . . . . . . . . . . . . . . . 448

N
‘n’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
naked function attribute, ARM . . . . . . . . . . . . . . .
naked function attribute, AVR . . . . . . . . . . . . . . . .
naked function attribute, MCORE . . . . . . . . . . . .
naked function attribute, MSP430 . . . . . . . . . . . .
naked function attribute, NDS32 . . . . . . . . . . . . . .
naked function attribute, RISC-V . . . . . . . . . . . . .
naked function attribute, RL78 . . . . . . . . . . . . . . .
naked function attribute, RX . . . . . . . . . . . . . . . . .
naked function attribute, SPU . . . . . . . . . . . . . . . .
naked function attribute, x86 . . . . . . . . . . . . . . . . .
Named Address Spaces . . . . . . . . . . . . . . . . . . . . . . .
names used in assembler code . . . . . . . . . . . . . . . . .
naming convention, implementation headers . . .
NDS32 Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
near function attribute, MeP . . . . . . . . . . . . . . . . .

560
485
486
492
497
498
502
503
503
506
507
453
592
790
322
492

938

Using the GNU Compiler Collection (GCC)

near function attribute, MIPS . . . . . . . . . . . . . . . . 495
near type attribute, MeP . . . . . . . . . . . . . . . . . . . . . 531
near variable attribute, MeP . . . . . . . . . . . . . . . . . 521
nearbyint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
nearbyintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
nearbyintl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
nested function attribute, NDS32 . . . . . . . . . . . . 498
nested functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
nested_ready function attribute, NDS32. . . . . . 498
nesting function attribute, Blackfin . . . . . . . . . . 488
newlines (escaped) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
nextafter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
nextafterf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
nextafterl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
nexttoward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
nexttowardf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
nexttowardl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
NFC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
NFKC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Nios II options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
nmi function attribute, NDS32 . . . . . . . . . . . . . . . . 498
nmi_handler function attribute, Blackfin . . . . . . 488
NMI handler functions on the Blackfin processor
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
no_caller_saved_registers function attribute,
x86 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508
no_gccisr function attribute, AVR . . . . . . . . . . . 486
no_icf function attribute . . . . . . . . . . . . . . . . . . . . . 473
no_instrument_function function attribute . . 473
no_profile_instrument_function function
attribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
no_reorder function attribute . . . . . . . . . . . . . . . . 473
no_sanitize function attribute . . . . . . . . . . . . . . . 473
no_sanitize_address function attribute . . . . . . 473
no_sanitize_thread function attribute . . . . . . . 473
no_sanitize_undefined function attribute . . . 473
no_split_stack function attribute. . . . . . . . . . . . 474
no_stack_limit function attribute. . . . . . . . . . . . 474
nocf_check function attribute . . . . . . . . . . . . . . . . 511
noclone function attribute. . . . . . . . . . . . . . . . . . . . 474
nocommon variable attribute . . . . . . . . . . . . . . . . . . . 515
nocompression function attribute, MIPS . . . . . . 496
noinit variable attribute, MSP430 . . . . . . . . . . . 522
noinline function attribute . . . . . . . . . . . . . . . . . . 474
noipa function attribute . . . . . . . . . . . . . . . . . . . . . . 474
nomicromips function attribute . . . . . . . . . . . . . . . 496
nomips16 function attribute, MIPS . . . . . . . . . . . 496
non-constant initializers . . . . . . . . . . . . . . . . . . . . . . 460
non-static inline function . . . . . . . . . . . . . . . . . . . . . 540
nonnull function attribute. . . . . . . . . . . . . . . . . . . . 474
nonstring variable attribute . . . . . . . . . . . . . . . . . . 515
noplt function attribute . . . . . . . . . . . . . . . . . . . . . . 475
noreturn function attribute . . . . . . . . . . . . . . . . . . 475
nosave_low_regs function attribute, SH . . . . . . 505
not_nested function attribute, NDS32 . . . . . . . . 498
note GCC_COLORS capability . . . . . . . . . . . . . . . . . . . . 60
nothrow function attribute. . . . . . . . . . . . . . . . . . . . 475
notshared type attribute, ARM . . . . . . . . . . . . . . 531

Nvidia PTX options . . . . . . . . . . . . . . . . . . . . . . . . . . 328
nvptx options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328

O
‘o’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
OBJC_INCLUDE_PATH . . . . . . . . . . . . . . . . . . . . . . . . . . 424
Objective-C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 7
Objective-C and Objective-C++ options,
command-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Objective-C++. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 7
offsettable address . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
old-style function definitions . . . . . . . . . . . . . . . . . . 537
omit-leaf-frame-pointer function attribute,
AArch64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
omitted middle-operands . . . . . . . . . . . . . . . . . . . . . 447
open coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539
OpenACC accelerator programming . . . . . . . . . . . . 40
OpenMP parallel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
OpenMP SIMD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
operand constraints, asm . . . . . . . . . . . . . . . . . . . . . . 559
optimize function attribute . . . . . . . . . . . . . . . . . . 475
optimize options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
options to control diagnostics formatting . . . . . . . 59
options to control warnings . . . . . . . . . . . . . . . . . . . . 62
options, C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
options, code generation . . . . . . . . . . . . . . . . . . . . . . 202
options, debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
options, dialect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
options, directory search . . . . . . . . . . . . . . . . . . . . . . 199
options, GCC command . . . . . . . . . . . . . . . . . . . . . . . . 9
options, grouping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
options, linking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
options, Objective-C and Objective-C++ . . . . . . . 55
options, optimization . . . . . . . . . . . . . . . . . . . . . . . . . 114
options, order. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
options, preprocessor . . . . . . . . . . . . . . . . . . . . . . . . . 187
options, profiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
options, program instrumentation . . . . . . . . . . . . . 172
options, run-time error checking . . . . . . . . . . . . . . 172
order of evaluation, side effects . . . . . . . . . . . . . . . 852
order of options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
OS_main function attribute, AVR . . . . . . . . . . . . . 487
OS_task function attribute, AVR . . . . . . . . . . . . . 487
other register constraints . . . . . . . . . . . . . . . . . . . . . 562
output file option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
overloaded virtual function, warning . . . . . . . . . . . 54

P
‘p’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562
packed type attribute . . . . . . . . . . . . . . . . . . . . . . . . 528
packed variable attribute . . . . . . . . . . . . . . . . . . . . . 516
parameter forward declaration . . . . . . . . . . . . . . . . 458
partial_save function attribute, NDS32. . . . . . 498
Pascal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
patchable_function_entry function attribute
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

Keyword Index

pcs function attribute, ARM . . . . . . . . . . . . . . . . . 485
PDP-11 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
persistent variable attribute, MSP430 . . . . . . . 523
picoChip options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
PIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
pmf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
pointer arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466
Pointer Bounds Checker attributes . . . . . . . 466, 526
Pointer Bounds Checker builtins . . . . . . . . . . . . . . 611
Pointer Bounds Checker options . . . . . . . . . . . . . . 180
pointer to member function . . . . . . . . . . . . . . . . . . . 793
pointers to arrays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
portions of temporary objects, pointers to. . . . . 848
pow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
pow10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
pow10f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
pow10l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
PowerPC options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
PowerPC SPE options . . . . . . . . . . . . . . . . . . . . . . . . 331
powf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
powl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
pragma GCC ivdep . . . . . . . . . . . . . . . . . . . . . . . . . . . 780
pragma GCC optimize . . . . . . . . . . . . . . . . . . . . . . . . 780
pragma GCC pop options . . . . . . . . . . . . . . . . . . . . 780
pragma GCC push options . . . . . . . . . . . . . . . . . . . 780
pragma GCC reset options . . . . . . . . . . . . . . . . . . . 780
pragma GCC target . . . . . . . . . . . . . . . . . . . . . . . . . . 780
pragma GCC unroll n . . . . . . . . . . . . . . . . . . . . . . . . 781
pragma, address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774
pragma, align . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
pragma, call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775
pragma, coprocessor available . . . . . . . . . . . . . . . . . 774
pragma, coprocessor call saved. . . . . . . . . . . . . . . . 774
pragma, coprocessor subclass . . . . . . . . . . . . . . . . . 775
pragma, custom io volatile. . . . . . . . . . . . . . . . . . . . 774
pragma, diagnostic. . . . . . . . . . . . . . . . . . . . . . . 778, 779
pragma, disinterrupt . . . . . . . . . . . . . . . . . . . . . . . . . . 775
pragma, fini . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
pragma, init . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
pragma, long calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774
pragma, long calls off . . . . . . . . . . . . . . . . . . . . . . . . 774
pragma, longcall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775
pragma, mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
pragma, memregs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774
pragma, no long calls . . . . . . . . . . . . . . . . . . . . . . . . 774
pragma, options align. . . . . . . . . . . . . . . . . . . . . . . . . 776
pragma, pop macro . . . . . . . . . . . . . . . . . . . . . . . . . . 779
pragma, push macro. . . . . . . . . . . . . . . . . . . . . . . . . . 779
pragma, redefine extname . . . . . . . . . . . . . . . . . . . . 776
pragma, segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
pragma, unused . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
pragma, visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779
pragma, weak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
pragmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773
pragmas in C++, effect on inlining. . . . . . . . . . . . . 790
pragmas, interface and implementation . . . . . . . 789
pragmas, warning of unknown . . . . . . . . . . . . . . . . . 81
precompiled headers . . . . . . . . . . . . . . . . . . . . . . . . . . 425

939

preprocessing numbers . . . . . . . . . . . . . . . . . . . . . . . .
preprocessing tokens . . . . . . . . . . . . . . . . . . . . . . . . . .
preprocessor options . . . . . . . . . . . . . . . . . . . . . . . . . .
printf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
printf_unlocked . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
prof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
profiling options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
progmem variable attribute, AVR . . . . . . . . . . . . . .
program instrumentation options . . . . . . . . . . . . .
promotion of formal parameters. . . . . . . . . . . . . . .
pure function attribute . . . . . . . . . . . . . . . . . . . . . . .
push address instruction . . . . . . . . . . . . . . . . . . . . . .
putchar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
puts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

843
843
187
613
613
173
172
518
172
537
476
562
613
613

Q
q floating point suffix . . . . . . . . . . . . . . . . . . . . . . . . . 449
Q floating point suffix . . . . . . . . . . . . . . . . . . . . . . . . . 449
qsort, and global register variables . . . . . . . . . . . 593
quote GCC_COLORS capability . . . . . . . . . . . . . . . . . . . 60

R
r fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
‘r’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
R fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
RAMPD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
RAMPX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
RAMPY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
RAMPZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
range1 GCC_COLORS capability. . . . . . . . . . . . . . . . . . 60
range2 GCC_COLORS capability. . . . . . . . . . . . . . . . . . 60
ranges in case statements . . . . . . . . . . . . . . . . . . . . . 463
read-only strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
reentrant function attribute, MSP430 . . . . . . . . 497
register variable after longjmp . . . . . . . . . . . . . . . . 593
registers for local variables . . . . . . . . . . . . . . . . . . . . 594
registers in constraints . . . . . . . . . . . . . . . . . . . . . . . . 560
registers, global allocation . . . . . . . . . . . . . . . . . . . . 593
registers, global variables in. . . . . . . . . . . . . . . . . . . 593
regparm function attribute, x86 . . . . . . . . . . . . . . . 507
relocation truncated to fit (ColdFire) . . . . . . . . . 300
relocation truncated to fit (MIPS) . . . . . . . . . . . . 307
remainder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
remainderf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
remainderl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
remquo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
remquof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
remquol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
renesas function attribute, SH . . . . . . . . . . . . . . . 505
reordering, warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
reporting bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
resbank function attribute, SH . . . . . . . . . . . . . . . 505
reset function attribute, NDS32 . . . . . . . . . . . . . . 498
reset handler functions . . . . . . . . . . . . . . . . . . . . . . . 498
rest argument (in macro) . . . . . . . . . . . . . . . . . . . . . 458
restricted pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787

940

restricted references . . . . . . . . . . . . . . . . . . . . . . . . . .
restricted this pointer. . . . . . . . . . . . . . . . . . . . . . . . .
returns_nonnull function attribute . . . . . . . . . .
returns_twice function attribute . . . . . . . . . . . . .
rindex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
rint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
rintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
rintl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RISC-V Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RL78 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
round . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
roundf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
roundl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RS/6000 and PowerPC Options . . . . . . . . . . . . . . .
RTTI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
run-time error checking options . . . . . . . . . . . . . . .
run-time options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RX Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Using the GNU Compiler Collection (GCC)

787
787
476
477
613
613
613
613
342
344
613
613
613
345
789
172
202
361

S
‘s’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
S/390 and zSeries Options . . . . . . . . . . . . . . . . . . . . 364
saddr variable attribute, RL78. . . . . . . . . . . . . . . . 523
save all registers on the Blackfin . . . . . . . . . . . . . . 488
save all registers on the H8/300, H8/300H, and
H8S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
save_all function attribute, NDS32 . . . . . . . . . . 498
save_volatiles function attribute, MicroBlaze
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
saveall function attribute, Blackfin . . . . . . . . . . 488
saveall function attribute, H8/300 . . . . . . . . . . . 490
scalar_storage_order type attribute . . . . . . . . 529
scalb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
scalbf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
scalbl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
scalbln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
scalblnf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
scalbn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
scalbnf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
scanf, and constant strings . . . . . . . . . . . . . . . . . . . 841
scanfnl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
scope of a variable length array . . . . . . . . . . . . . . . 457
scope of declaration . . . . . . . . . . . . . . . . . . . . . . . . . . 845
scope of external declarations . . . . . . . . . . . . . . . . . 842
Score Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
sda variable attribute, V850 . . . . . . . . . . . . . . . . . . 523
search path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
section function attribute. . . . . . . . . . . . . . . . . . . . 477
section variable attribute . . . . . . . . . . . . . . . . . . . . 516
secure_call function attribute, ARC . . . . . . . . . 484
selectany variable attribute . . . . . . . . . . . . . . . . . . 522
sentinel function attribute . . . . . . . . . . . . . . . . . . 477
setjmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
setjmp incompatibilities . . . . . . . . . . . . . . . . . . . . . . 841
shared attribute, Nvidia PTX . . . . . . . . . . . . . . . . 523
shared strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
shared variable attribute . . . . . . . . . . . . . . . . . . . . . 522

short_call function attribute, ARC . . . . . . . . . . 484
short_call function attribute, ARM . . . . . . . . . 485
short_call function attribute, Epiphany . . . . . 489
short_call function attribute, MIPS . . . . . . . . . 495
shortcall function attribute, Blackfin . . . . . . . . 488
shortcall function attribute, PowerPC . . . . . . . 499
side effect in ?:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
side effects, macro argument . . . . . . . . . . . . . . . . . . 439
side effects, order of evaluation . . . . . . . . . . . . . . . 852
sign-return-address function attribute, AArch64
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
signal function attribute, AVR. . . . . . . . . . . . . . . 487
signbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
signbitd128 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
signbitd32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
signbitd64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
signbitf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
signbitl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
signed and unsigned values, comparison warning
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
significand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
significandf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
significandl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
simd function attribute . . . . . . . . . . . . . . . . . . . . . . . 477
SIMD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
simple constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
sin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sincos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sincosf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sincosl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sinf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sinh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sinhf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sinhl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sinl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sizeof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
smaller data references . . . . . . . . . . . . . . . . . . . 294, 323
smaller data references (PowerPC) . . . . . . . 339, 358
snprintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
Solaris 2 options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
SOURCE_DATE_EPOCH . . . . . . . . . . . . . . . . . . . . . . . . . . 425
sp_switch function attribute, SH . . . . . . . . . . . . . 505
SPARC options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
Spec Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
specified registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
specifying compiler version and target machine . . 9
specifying hardware config . . . . . . . . . . . . . . . . . . . . 228
specifying machine version . . . . . . . . . . . . . . . . . . . . . . 9
specifying registers for local variables . . . . . . . . . 594
speed of compilation . . . . . . . . . . . . . . . . . . . . . . . . . . 425
sprintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
spu_vector type attribute, SPU . . . . . . . . . . . . . . 531
spu_vector variable attribute, SPU . . . . . . . . . . . 523
SPU options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
sqrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sqrtf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sqrtl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
sscanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613

Keyword Index

sscanf, and constant strings . . . . . . . . . . . . . . . . . . 841
sseregparm function attribute, x86 . . . . . . . . . . . 508
stack_protect function attribute . . . . . . . . . . . . . 478
Statement Attributes . . . . . . . . . . . . . . . . . . . . . . . . . 533
statements inside expressions . . . . . . . . . . . . . . . . . 439
static data in C++, declaring and defining . . . . . 846
stdcall function attribute, x86-32 . . . . . . . . . . . . 508
stpcpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
stpncpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strcasecmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strcat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strchr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strcmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strcpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strcspn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strdup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strfmon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strftime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strict-align function attribute, AArch64 . . . . 482
string constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
strlen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strncasecmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strncat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strncmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strncpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strndup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strpbrk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strrchr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strspn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
strstr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
struct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 781
struct __htm_tdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . 741
structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
structures, constructor expression . . . . . . . . . . . . . 460
submodel options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
subscripting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
subscripting and function values . . . . . . . . . . . . . . 459
suffixes for C++ source . . . . . . . . . . . . . . . . . . . . . . . . . 34
SUNPRO_DEPENDENCIES . . . . . . . . . . . . . . . . . . . . . . . . 425
suppressing warnings . . . . . . . . . . . . . . . . . . . . . . . . . . 62
surprises in C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
syntax checking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
syscall_linkage function attribute, IA-64 . . . 490
system headers, warnings from . . . . . . . . . . . . . . . . . 89
sysv_abi function attribute, x86 . . . . . . . . . . . . . . 507

T
tan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
tanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
tanh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
tanhf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
tanhl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
tanl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
target function attribute . . . . . . 478, 485, 498, 499,
504, 509
target machine, specifying . . . . . . . . . . . . . . . . . . . . . . 9
target("abm") function attribute, x86 . . . . . . . . 509

941

target("aes") function attribute, x86 . . . . . . . . 509
target("align-stringops") function attribute,
x86 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
target("altivec") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499
target("arch=ARCH") function attribute, x86
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
target("arm") function attribute, ARM . . . . . . 485
target("avoid-indexed-addresses") function
attribute, PowerPC . . . . . . . . . . . . . . . . . . . . . . 502
target("cld") function attribute, x86 . . . . . . . . 510
target("cmpb") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499
target("cpu=CPU") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
target("custom-fpu-cfg=name") function
attribute, Nios II. . . . . . . . . . . . . . . . . . . . . . . . . 499
target("custom-insn=N") function attribute, Nios
II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
target("default") function attribute, x86 . . . 509
target("dlmzb") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
target("fancy-math-387") function attribute,
x86 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
target("fma4") function attribute, x86 . . . . . . . 510
target("fpmath=FPMATH") function attribute, x86
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
target("fprnd") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
target("fpu=") function attribute, ARM . . . . . 485
target("friz") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
target("hard-dfp") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
target("ieee-fp") function attribute, x86 . . . 510
target("inline-all-stringops") function
attribute, x86 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
target("inline-stringops-dynamically")
function attribute, x86 . . . . . . . . . . . . . . . . . . . 511
target("isel") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
target("longcall") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
target("lwp") function attribute, x86 . . . . . . . . 510
target("mfcrf") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
target("mfpgpr") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
target("mmx") function attribute, x86 . . . . . . . . 509
target("mulhw") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
target("multiple") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
target("no-custom-insn") function attribute,
Nios II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
target("paired") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
target("pclmul") function attribute, x86 . . . . 509

942

target("popcnt") function attribute, x86 . . . . 509
target("popcntb") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
target("popcntd") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
target("powerpc-gfxopt") function attribute,
PowerPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
target("powerpc-gpopt") function attribute,
PowerPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
target("recip") function attribute, x86. . . . . . 511
target("recip-precision") function attribute,
PowerPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
target("sse") function attribute, x86 . . . . . . . . 510
target("sse2") function attribute, x86 . . . . . . . 510
target("sse3") function attribute, x86 . . . . . . . 510
target("sse4") function attribute, x86 . . . . . . . 510
target("sse4.1") function attribute, x86 . . . . 510
target("sse4.2") function attribute, x86 . . . . 510
target("sse4a") function attribute, x86. . . . . . 510
target("ssse3") function attribute, x86. . . . . . 510
target("string") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
target("thumb") function attribute, ARM . . . . 485
target("tune=TUNE") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
target("tune=TUNE") function attribute, x86
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
target("update") function attribute, PowerPC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
target("vsx") function attribute, PowerPC . . 501
target("xop") function attribute, x86 . . . . . . . . 510
target-dependent options . . . . . . . . . . . . . . . . . . . . . 228
target_clones function attribute . . . . . . . . . . . . . 478
TC1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
TC2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
TC3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
tda variable attribute, V850 . . . . . . . . . . . . . . . . . . 523
Technical Corrigenda . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Technical Corrigendum 1 . . . . . . . . . . . . . . . . . . . . . . . 5
Technical Corrigendum 2 . . . . . . . . . . . . . . . . . . . . . . . 5
Technical Corrigendum 3 . . . . . . . . . . . . . . . . . . . . . . . 5
template instantiation . . . . . . . . . . . . . . . . . . . . . . . . 790
temporaries, lifetime of . . . . . . . . . . . . . . . . . . . . . . . 848
tentative definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 206
tgamma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
tgammaf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
tgammal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
thiscall function attribute, x86-32 . . . . . . . . . . . 507
Thread-Local Storage . . . . . . . . . . . . . . . . . . . . . . . . . 782
thunks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
TILE-Gx options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
TILEPro options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
tiny data section on the H8/300H and H8S . . . 520
tiny type attribute, MeP . . . . . . . . . . . . . . . . . . . . . 531
tiny variable attribute, MeP . . . . . . . . . . . . . . . . . 521
tiny_data variable attribute, H8/300 . . . . . . . . . 520
tls-dialect= function attribute, AArch64 . . . . 482
tls_model variable attribute . . . . . . . . . . . . . . . . . . 517

Using the GNU Compiler Collection (GCC)

TLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782

TMPDIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
toascii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
tolower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
toupper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
towlower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
towupper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
traditional C language . . . . . . . . . . . . . . . . . . . . . . . . 192
transparent_union type attribute . . . . . . . . . . . . 529
trap_exit function attribute, SH . . . . . . . . . . . . . 506
trapa_handler function attribute, SH . . . . . . . . 506
trunc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
truncf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
truncl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613
tune= function attribute, AArch64 . . . . . . . . . . . . 482
two-stage name lookup . . . . . . . . . . . . . . . . . . . . . . . 847
type alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538
type attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
type-diff GCC_COLORS capability . . . . . . . . . . . . . . 60
type_info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
typedef names as function parameters. . . . . . . . . 842
typeof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446

U
uhk fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
UHK fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
uhr fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
UHR fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
uk fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
UK fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
ulk fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
ULK fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
ULL integer suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
ullk fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
ULLK fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
ullr fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
ULLR fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
ulr fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
ULR fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
uncached type attribute, ARC . . . . . . . . . . . . . . . . 531
undefined behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
undefined function value . . . . . . . . . . . . . . . . . . . . . . 855
underscores in variables in macros . . . . . . . . . . . . 446
union . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 781
union, casting to a. . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
unions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
unknown pragmas, warning . . . . . . . . . . . . . . . . . . . . 81
unresolved references and ‘-nodefaultlibs’ . . . 196
unresolved references and ‘-nostdlib’ . . . . . . . . 196
unused function attribute . . . . . . . . . . . . . . . . . . . . . 479
unused label attribute . . . . . . . . . . . . . . . . . . . . . . . . 532
unused type attribute . . . . . . . . . . . . . . . . . . . . . . . . 530
unused variable attribute . . . . . . . . . . . . . . . . . . . . . 517
upper function attribute, MSP430 . . . . . . . . . . . . 497
upper variable attribute, MSP430 . . . . . . . . . . . . . 523
ur fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
UR fixed-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452

Keyword Index

943

use_debug_exception_return function attribute,
MIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
use_shadow_register_set function attribute,
MIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
used function attribute . . . . . . . . . . . . . . . . . . . . . . . 479
used variable attribute . . . . . . . . . . . . . . . . . . . . . . . 517
User stack pointer in interrupts on the Blackfin
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488

V
‘V’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V850 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vague linkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
value after longjmp . . . . . . . . . . . . . . . . . . . . . . . . . . .
variable addressability on the M32R/D . . . . . . .
variable alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . .
variable attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . .
variable number of arguments. . . . . . . . . . . . . . . . .
variable-length array in a structure . . . . . . . . . . .
variable-length array scope . . . . . . . . . . . . . . . . . . .
variable-length arrays . . . . . . . . . . . . . . . . . . . . . . . . .
variables in specified registers . . . . . . . . . . . . . . . . .
variables, local, in macros. . . . . . . . . . . . . . . . . . . . .
variadic macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VAX options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vector function attribute, RX . . . . . . . . . . . . . . . .
vector_size variable attribute . . . . . . . . . . . . . . .
version_id function attribute, IA-64 . . . . . . . . .
vfprintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vfscanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
visibility function attribute . . . . . . . . . . . . . . . .
visibility type attribute . . . . . . . . . . . . . . . . . . . .
visibility variable attribute . . . . . . . . . . . . . . . .
Visium options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VLAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vliw function attribute, MeP . . . . . . . . . . . . . . . . .
void pointers, arithmetic . . . . . . . . . . . . . . . . . . . . . .
void, size of pointer to . . . . . . . . . . . . . . . . . . . . . . . .
volatile access . . . . . . . . . . . . . . . . . . . . . . . . . . . 540,
volatile applied to function . . . . . . . . . . . . . . . . .
volatile asm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
volatile read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540,
volatile write . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540,
vprintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vscanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vsnprintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vsprintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vsscanf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vtable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VxWorks Options . . . . . . . . . . . . . . . . . . . . . . . . . . . .

560
384
788
593
521
538
513
458
457
457
457
592
446
458
387
503
517
490
613
613
479
530
518
387
457
492
459
459
787
464
545
787
787
613
613
613
613
613
788
388

W
w floating point suffix . . . . . . . . . . . . . . . . . . . . . . . . . 449
W floating point suffix . . . . . . . . . . . . . . . . . . . . . . . . . 449
wakeup function attribute, MSP430 . . . . . . . . . . . 497
warm function attribute, NDS32 . . . . . . . . . . . . . . . 498
warn_if_not_aligned type attribute. . . . . . . . . . 526
warn_if_not_aligned variable attribute . . . . . . 514
warn_unused type attribute . . . . . . . . . . . . . . . . . . . 794
warn_unused_result function attribute . . . . . . . 480
warning for comparison of signed and unsigned
values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
warning for overloaded virtual function . . . . . . . . 54
warning for reordering of member initializers . . . 53
warning for unknown pragmas . . . . . . . . . . . . . . . . . 81
warning function attribute. . . . . . . . . . . . . . . . . . . . 467
warning GCC_COLORS capability . . . . . . . . . . . . . . . . 60
warning messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
warnings from system headers . . . . . . . . . . . . . . . . . 89
warnings vs errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
weak function attribute . . . . . . . . . . . . . . . . . . . . . . . 481
weak variable attribute . . . . . . . . . . . . . . . . . . . . . . . 518
weakref function attribute. . . . . . . . . . . . . . . . . . . . 481
whitespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
Windows Options for x86 . . . . . . . . . . . . . . . . . . . . . 412

X
x86 named address spaces . . . . . . . . . . . . . . . . . . . . 455
x86 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389
x86 Windows Options . . . . . . . . . . . . . . . . . . . . . . . . 412
‘X’ in constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
X3.159-1989 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Xstormy16 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
Xtensa Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413

Y
y0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
y0f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
y0l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
y1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
y1f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
y1l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
yn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ynf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ynl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

613
613
613
613
613
613
613
613
613

Z
zda variable attribute, V850 . . . . . . . . . . . . . . . . . .
zero-length arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . .
zero-size structures . . . . . . . . . . . . . . . . . . . . . . . . . . .
zSeries options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

524
456
457
415



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