Using as
The gnu Assembler
(GNU Tools for ARM Embedded Processors)
Version 2.22.0
The Free Software Foundation Inc. thanks The Nice Computer Company of Australia for
loaning Dean Elsner to write the first (Vax) version of as for Project gnu. The proprietors,
management and staff of TNCCA thank FSF for distracting the boss while they got some
work done.
Dean Elsner, Jay Fenlason & friends
Using as
Edited by Cygnus Support
Copyright c 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2006,
2007, 2008, 2009, 2010, 2011 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 no Invariant Sections, with no Front-Cover Texts, and with
no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free
Documentation License”.
i
Table of Contents
1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
2
Structure of this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The GNU Assembler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Object File Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Command Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output (Object) File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Error and Warning Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Command-Line Options . . . . . . . . . . . . . . . . . . . . . . . 19
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
2.14
2.15
2.16
Enable Listings: ‘-a[cdghlns]’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
‘--alternate’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
‘-D’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Work Faster: ‘-f’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.include Search Path: ‘-I’ path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Difference Tables: ‘-K’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Include Local Symbols: ‘-L’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Configuring listing output: ‘--listing’ . . . . . . . . . . . . . . . . . . . . . . .
Assemble in MRI Compatibility Mode: ‘-M’ . . . . . . . . . . . . . . . . . . . .
Dependency Tracking: ‘--MD’. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Name the Object File: ‘-o’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Join Data and Text Sections: ‘-R’ . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Display Assembly Statistics: ‘--statistics’ . . . . . . . . . . . . . . . . .
Compatible Output: ‘--traditional-format’. . . . . . . . . . . . . . . .
Announce Version: ‘-v’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Control Warnings: ‘-W’, ‘--warn’, ‘--no-warn’,
‘--fatal-warnings’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.17 Generate Object File in Spite of Errors: ‘-Z’. . . . . . . . . . . . . . . . . .
3
15
15
16
16
16
17
17
19
19
20
20
20
20
20
20
21
23
23
23
23
23
23
24
24
Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.1
3.2
3.3
3.4
3.5
3.6
Preprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Whitespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.1 Character Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.1.1 Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.1.2 Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.2 Number Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.2.1 Integers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.2.2 Bignums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.2.3 Flonums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
25
25
26
26
27
27
27
28
28
28
29
29
ii
4
Using as
Sections and Relocation. . . . . . . . . . . . . . . . . . . . . . . 31
4.1
4.2
4.3
4.4
4.5
5
Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Giving Symbols Other Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Symbol Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Special Dot Symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Symbol Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.1 Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.2 Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.3 Symbol Attributes: a.out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.3.1 Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.3.2 Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.4 Symbol Attributes for COFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.4.1 Primary Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.4.2 Auxiliary Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.5 Symbol Attributes for SOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
37
37
39
39
39
39
39
40
40
40
40
40
40
Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.1
6.2
7
31
32
33
33
34
Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.1
5.2
5.3
5.4
5.5
6
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Linker Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Assembler Internal Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sub-Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
bss Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Empty Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Integer Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.1 Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.2 Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.3 Prefix Operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.4 Infix Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41
41
41
41
41
42
Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10
7.11
7.12
7.13
7.14
7.15
.abort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.ABORT (COFF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.align abs-expr , abs-expr , abs-expr . . . . . . . . . . . . . . . . . . . . . .
.altmacro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.ascii "string ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.asciz "string ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.balign[wl] abs-expr , abs-expr , abs-expr . . . . . . . . . . . . . . . .
.byte expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_sections section_list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_startproc [simple] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_endproc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_personality encoding [, exp ] . . . . . . . . . . . . . . . . . . . . . . .
.cfi_lsda encoding [, exp ] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_def_cfa register , offset . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_def_cfa_register register . . . . . . . . . . . . . . . . . . . . . . . . . .
45
45
45
46
46
46
46
47
47
47
47
47
47
48
48
iii
7.16
7.17
7.18
7.19
7.20
7.21
7.22
7.23
7.24
7.25
7.26
7.27
7.28
7.29
7.30
7.31
7.32
7.33
7.34
7.35
7.36
7.37
7.38
7.39
7.40
7.41
7.42
7.43
7.44
7.45
7.46
7.47
7.48
7.49
7.50
7.51
7.52
7.53
7.54
7.55
7.56
7.57
7.58
7.59
7.60
7.61
7.62
7.63
.cfi_def_cfa_offset offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_adjust_cfa_offset offset . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_offset register , offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_rel_offset register , offset . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_register register1 , register2 . . . . . . . . . . . . . . . . . . . . . .
.cfi_restore register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_undefined register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_same_value register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_remember_state, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_return_column register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_signal_frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_window_save. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_escape expression[, . . . ] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.cfi_val_encoded_addr register , encoding , label . . . . . .
.comm symbol , length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.data subsection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.def name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.desc symbol , abs-expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.dim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.double flonums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.eject . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.else. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.elseif . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.endef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.endfunc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.endif . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.equ symbol , expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.equiv symbol , expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.eqv symbol , expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.err . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.error "string " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.exitm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.extern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.fail expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.file. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.fill repeat , size , value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.float flonums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.func name [,label ] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.global symbol , .globl symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.gnu_attribute tag ,value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.hidden names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.hword expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.ident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.if absolute expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.incbin "file "[,skip [,count ]] . . . . . . . . . . . . . . . . . . . . . . . . . . .
.include "file " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.int expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
48
48
48
48
48
48
48
48
48
49
49
49
49
49
49
50
50
50
50
50
50
50
50
51
51
51
51
51
51
51
51
52
52
52
52
52
53
53
53
53
53
53
54
54
54
55
55
56
iv
Using as
7.64
7.65
7.66
7.67
7.68
7.69
7.70
7.71
7.72
7.73
7.74
7.75
7.76
7.77
7.78
7.79
7.80
7.81
7.82
7.83
7.84
7.85
7.86
7.87
7.88
7.89
7.90
7.91
.internal names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.irp symbol ,values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.irpc symbol ,values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.lcomm symbol , length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.lflags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.line line-number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.linkonce [type ] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.ln line-number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.loc fileno lineno [column ] [options ] . . . . . . . . . . . . . . . . . .
.loc_mark_labels enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.local names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.long expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.mri val . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.noaltmacro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.nolist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.octa bignums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.offset loc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.org new-lc , fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.p2align[wl] abs-expr , abs-expr , abs-expr . . . . . . . . . . . . .
.popsection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.previous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.print string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.protected names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.psize lines , columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.purgem name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.pushsection name [, subsection ] [, "flags "[,
@type [,arguments ]]] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.92 .quad bignums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.93 .reloc offset , reloc_name [, expression ] . . . . . . . . . . . . . . . .
7.94 .rept count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.95 .sbttl "subheading " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.96 .scl class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.97 .section name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.98 .set symbol , expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.99 .short expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.100 .single flonums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.101 .size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.102 .skip size , fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.103 .sleb128 expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.104 .space size , fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.105 .stabd, .stabn, .stabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.106 .string "str", .string8 "str", .string16 . . . . . . . . . . . . . . . . .
7.107 .struct expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.108 .subsection name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.109 .symver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.110 .tag structname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
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v
7.111
7.112
7.113
7.114
7.115
7.116
7.117
7.118
7.119
7.120
7.121
7.122
7.123
8
.text subsection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.title "heading ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.uleb128 expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.val addr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.version "string " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.vtable_entry table , offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.vtable_inherit child , parent . . . . . . . . . . . . . . . . . . . . . . . . . .
.warning "string " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.weak names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.weakref alias , target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.word expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Deprecated Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Object Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
8.1 gnu Object Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.1 Common gnu attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.2 MIPS Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.3 PowerPC Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.2 Defining New Object Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
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78
Machine Dependent Features . . . . . . . . . . . . . . . . . 79
9.1
Alpha Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1.1 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1.2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1.3 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1.3.1 Special Characters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1.3.2 Register Names. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1.3.3 Relocations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1.4 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1.5 Alpha Assembler Directives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1.6 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2 ARC Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2.2.1 Special Characters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2.2.2 Register Names. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2.3 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2.4 ARC Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2.5 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3 ARM Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3.2.1 Instruction Set Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3.2.2 Special Characters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3.2.3 Register Names. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3.2.4 NEON Alignment Specifiers . . . . . . . . . . . . . . . . . . . . . . . . .
9.3.3 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Using as
9.3.3.1 ARM relocation generation . . . . . . . . . . . . . . . . . . . . . . . . . . 95
9.3.4 ARM Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
9.3.5 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
9.3.6 Mapping Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
9.3.7 Unwinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
9.4 AVR Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
9.4.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
9.4.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
9.4.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
9.4.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
9.4.2.3 Relocatable Expression Modifiers . . . . . . . . . . . . . . . . . . . 106
9.4.3 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
9.5 Blackfin Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
9.5.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
9.5.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
9.5.3 Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
9.6 CR16 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
9.6.1 CR16 Operand Qualifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
9.6.2 CR16 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
9.6.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
9.7 CRIS Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
9.7.1 Command-line Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
9.7.2 Instruction expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
9.7.3 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
9.7.4 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
9.7.4.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
9.7.4.2 Symbols in position-independent code . . . . . . . . . . . . . . 118
9.7.4.3 Register names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
9.7.4.4 Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
9.8 D10V Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
9.8.1 D10V Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
9.8.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
9.8.2.1 Size Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
9.8.2.2 Sub-Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
9.8.2.3 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
9.8.2.4 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
9.8.2.5 Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
9.8.2.6 @WORD Modifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
9.8.3 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
9.8.4 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
9.9 D30V Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
9.9.1 D30V Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
9.9.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
9.9.2.1 Size Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
9.9.2.2 Sub-Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
9.9.2.3 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
9.9.2.4 Guarded Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
9.9.2.5 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
vii
9.9.2.6 Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.9.3 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.9.4 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10 H8/300 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10.2.3 Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10.3 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10.4 H8/300 Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10.5 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.11 HPPA Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.11.1 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.11.2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.11.3 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.11.4 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.11.5 HPPA Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.11.6 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.12 ESA/390 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.12.1 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.12.2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.12.3 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.12.4 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.12.5 ESA/390 Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . .
9.12.6 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13 80386 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.2 x86 specific Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.3 i386 Syntactical Considerations. . . . . . . . . . . . . . . . . . . . . . . . .
9.13.3.1 AT&T Syntax versus Intel Syntax . . . . . . . . . . . . . . . . .
9.13.3.2 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.4 Instruction Naming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.5 AT&T Mnemonic versus Intel Mnemonic . . . . . . . . . . . . . . .
9.13.6 Register Naming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.7 Instruction Prefixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.8 Memory References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.9 Handling of Jump Instructions . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.10 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.11 Intel’s MMX and AMD’s 3DNow! SIMD Operations . . .
9.13.12 AMD’s Lightweight Profiling Instructions . . . . . . . . . . . . .
9.13.13 Bit Manipulation Instructions . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.14 AMD’s Trailing Bit Manipulation Instructions . . . . . . . . .
9.13.15 Writing 16-bit Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.16 AT&T Syntax bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.17 Specifying CPU Architecture . . . . . . . . . . . . . . . . . . . . . . . . . .
9.13.18 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.14 Intel i860 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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9.14.1 i860 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.14.2 i860 Command-line Options . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.14.2.1 SVR4 compatibility options . . . . . . . . . . . . . . . . . . . . . . .
9.14.2.2 Other options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.14.3 i860 Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.14.4 i860 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.14.4.1 Other instruction support (pseudo-instructions) . . . .
9.14.5 i860 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.14.5.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.15 Intel 80960 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.15.1 i960 Command-line Options . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.15.2 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.15.3 i960 Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.15.4 i960 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.15.4.1 callj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.15.4.2 Compare-and-Branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.15.5 Syntax for the i960 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.15.5.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.16 IA-64 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.16.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.16.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.16.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.16.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.16.2.3 IA-64 Processor-Status-Register (PSR) Bit Names
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9.16.2.4 Relocations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.16.3 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.17 IP2K Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.17.1 IP2K Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.17.2 IP2K Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.17.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.18 LM32 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.18.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.18.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.18.2.1 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.18.2.2 Relocatable Expression Modifiers . . . . . . . . . . . . . . . . . .
9.18.2.3 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.18.3 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.19 M32C Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.19.1 M32C Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.19.2 M32C Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.19.2.1 Symbolic Operand Modifiers . . . . . . . . . . . . . . . . . . . . . .
9.19.2.2 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.20 M32R Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.20.1 M32R Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.20.2 M32R Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.20.3 M32R Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.21 M680x0 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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9.21.1 M680x0 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
9.21.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
9.21.3 Motorola Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
9.21.4 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
9.21.5 680x0 Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
9.21.6 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
9.21.6.1 Branch Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
9.21.6.2 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
9.22 M68HC11 and M68HC12 Dependent Features . . . . . . . . . . . . . . . 178
9.22.1 M68HC11 and M68HC12 Options . . . . . . . . . . . . . . . . . . . . . . 178
9.22.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
9.22.3 Symbolic Operand Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
9.22.4 Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
9.22.5 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
9.22.6 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
9.22.6.1 Branch Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
9.23 MicroBlaze Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
9.23.1 Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
9.23.2 Syntax for the MicroBlaze. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
9.23.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
9.24 MIPS Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
9.24.1 Assembler options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
9.24.2 MIPS ECOFF object code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
9.24.3 Directives for debugging information . . . . . . . . . . . . . . . . . . . 189
9.24.4 Directives to override the size of symbols . . . . . . . . . . . . . . . 189
9.24.5 Directives to override the ISA level . . . . . . . . . . . . . . . . . . . . . 190
9.24.6 Directives for extending MIPS 16 bit instructions . . . . . . . 190
9.24.7 Directive to mark data as an instruction . . . . . . . . . . . . . . . . 190
9.24.8 Directives to save and restore options . . . . . . . . . . . . . . . . . . 191
9.24.9 Directives to control generation of MIPS ASE instructions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
9.24.10 Directives to override floating-point options . . . . . . . . . . . 192
9.24.11 Syntactical considerations for the MIPS assembler . . . . . 192
9.24.11.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
9.25 MMIX Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
9.25.1 Command-line Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
9.25.2 Instruction expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
9.25.3 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
9.25.3.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
9.25.3.2 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
9.25.3.3 Register names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
9.25.3.4 Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
9.25.4 Differences to mmixal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
9.26 MSP 430 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
9.26.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
9.26.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
9.26.2.1 Macros. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
9.26.2.2 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
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9.26.2.3 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.26.2.4 Assembler Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.26.3 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.26.4 MSP 430 Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.26.5 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.26.6 Profiling Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.27 NS32K Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.27.1 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.27.1.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.28 PDP-11 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.28.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.28.1.1 Code Generation Options . . . . . . . . . . . . . . . . . . . . . . . . .
9.28.1.2 Instruction Set Extension Options . . . . . . . . . . . . . . . . .
9.28.1.3 CPU Model Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.28.1.4 Machine Model Options . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.28.2 Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.28.3 PDP-11 Assembly Language Syntax . . . . . . . . . . . . . . . . . . . .
9.28.4 Instruction Naming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.28.5 Synthetic Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.29 picoJava Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.29.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.29.2 PJ Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.29.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.30 PowerPC Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.30.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.30.2 PowerPC Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . .
9.30.3 PowerPC Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.30.3.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.31 RX Dependent Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.31.1 RX Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.31.2 Symbolic Operand Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.31.3 Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.31.4 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.31.5 Syntax for the RX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.31.5.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32 IBM S/390 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.2 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.3 Instruction syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.3.1 Register naming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.3.2 Instruction Mnemonics . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.3.3 Instruction Operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.3.4 Instruction Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.3.5 Instruction Aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.3.6 Instruction Operand Modifier . . . . . . . . . . . . . . . . . . . . .
9.32.3.7 Instruction Marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.3.8 Literal Pool Entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.32.4 Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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9.32.5 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.33 SCORE Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.33.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.33.2 SCORE Assembler Directives . . . . . . . . . . . . . . . . . . . . . . . . . .
9.33.3 SCORE Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.33.3.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.34 Renesas / SuperH SH Dependent Features . . . . . . . . . . . . . . . . . .
9.34.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.34.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.34.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.34.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.34.2.3 Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.34.3 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.34.4 SH Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.34.5 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.35 SuperH SH64 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.35.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.35.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.35.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.35.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.35.2.3 Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.35.3 SH64 Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.35.4 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36 SPARC Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.2 Enforcing aligned data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.3 Sparc Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.3.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.3.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.3.3 Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.3.4 Relocations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.3.5 Size Translations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.4 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.36.5 Sparc Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37 TIC54X Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.2 Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.3 Environment Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.4 Constants Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.5 String Substitution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.6 Local Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.7 Math Builtins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.8 Extended Addressing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.9 Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.10 Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.11 Memory-mapped Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.12 TIC54X Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.37.12.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
229
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xii
Using as
9.38 TIC6X Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.38.1 TIC6X Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.38.2 TIC6X Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.38.3 TIC6X Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.39 TILE-Gx Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.39.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.39.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.39.2.1 Opcode Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.39.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.39.2.3 Symbolic Operand Modifiers . . . . . . . . . . . . . . . . . . . . . .
9.39.3 TILE-Gx Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.40 TILEPro Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.40.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.40.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.40.2.1 Opcode Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.40.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.40.2.3 Symbolic Operand Modifiers . . . . . . . . . . . . . . . . . . . . . .
9.40.3 TILEPro Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.41 Z80 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.41.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.41.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.41.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.41.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.41.2.3 Case Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.41.3 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.41.4 Z80 Assembler Directives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.41.5 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.42 Z8000 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.42.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.42.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.42.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.42.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.42.2.3 Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.42.3 Assembler Directives for the Z8000 . . . . . . . . . . . . . . . . . . . . .
9.42.4 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43 VAX Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43.1 VAX Command-Line Options . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43.2 VAX Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43.3 Vax Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43.4 VAX Opcodes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43.5 VAX Branch Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43.6 VAX Operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43.7 Not Supported on VAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43.8 VAX Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.43.8.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.44 v850 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.44.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.44.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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xiii
9.44.2.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.44.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.44.3 Floating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.44.4 V850 Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.44.5 Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.45 XStormy16 Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.45.1 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.45.1.1 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.45.2 XStormy16 Machine Directives . . . . . . . . . . . . . . . . . . . . . . . . .
9.45.3 XStormy16 Pseudo-Opcodes . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46 Xtensa Dependent Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.1 Command Line Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.2 Assembler Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.2.1 Opcode Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.2.2 Register Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.3 Xtensa Optimizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.3.1 Using Density Instructions . . . . . . . . . . . . . . . . . . . . . . . .
9.46.3.2 Automatic Instruction Alignment . . . . . . . . . . . . . . . . . .
9.46.4 Xtensa Relaxation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.4.1 Conditional Branch Relaxation . . . . . . . . . . . . . . . . . . . .
9.46.4.2 Function Call Relaxation . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.4.3 Other Immediate Field Relaxation . . . . . . . . . . . . . . . . .
9.46.5 Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.5.1 schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.5.2 longcalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.5.3 transform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.5.4 literal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.5.5 literal position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.5.6 literal prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.46.5.7 absolute-literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
Reporting Bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
10.1
10.2
11
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283
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285
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286
287
287
288
288
289
289
289
289
290
290
291
291
292
293
293
293
293
294
295
295
Have You Found a Bug? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
How to Report Bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . 301
Appendix A GNU Free Documentation License
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
AS Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
Chapter 1: Overview
1
1 Overview
This manual is a user guide to the gnu assembler as.
Here is a brief summary of how to invoke as. For details, see Chapter 2 [Command-Line
Options], page 19.
as [-a[cdghlns][=file ]] [–alternate] [-D]
[–compress-debug-sections] [–nocompress-debug-sections]
[–debug-prefix-map old =new ]
[–defsym sym =val ] [-f] [-g] [–gstabs]
[–gstabs+] [–gdwarf-2] [–help] [-I dir ] [-J]
[-K] [-L] [–listing-lhs-width=NUM ]
[–listing-lhs-width2=NUM ] [–listing-rhs-width=NUM ]
[–listing-cont-lines=NUM ] [–keep-locals] [-o
objfile ] [-R] [–reduce-memory-overheads] [–statistics]
[-v] [-version] [–version] [-W] [–warn]
[–fatal-warnings] [-w] [-x] [-Z] [@FILE]
[–size-check=[error|warning]]
[–target-help] [target-options ]
[–|files ...]
Target Alpha options:
[-mcpu]
[-mdebug | -no-mdebug]
[-replace | -noreplace]
[-relax] [-g] [-Gsize]
[-F] [-32addr]
Target ARC options:
[-marc[5|6|7|8]]
[-EB|-EL]
Target ARM options:
[-mcpu=processor [+extension ...]]
[-march=architecture [+extension ...]]
[-mfpu=floating-point-format ]
[-mfloat-abi=abi ]
[-meabi=ver ]
[-mthumb]
[-EB|-EL]
[-mapcs-32|-mapcs-26|-mapcs-float|
-mapcs-reentrant]
[-mthumb-interwork] [-k]
Target Blackfin options:
[-mcpu=processor [-sirevision ]]
[-mfdpic]
[-mno-fdpic]
[-mnopic]
Target CRIS options:
[–underscore | –no-underscore]
[–pic] [-N]
[–emulation=criself | –emulation=crisaout]
[–march=v0 v10 | –march=v10 | –march=v32 | –march=common v10 v32]
Target D10V options:
[-O]
2
Using as
Target D30V options:
[-O|-n|-N]
Target H8/300 options:
[-h-tick-hex]
Target i386 options:
[–32|–n32|–64] [-n]
[-march=CPU [+EXTENSION ...]] [-mtune=CPU ]
Target i960 options:
[-ACA|-ACA A|-ACB|-ACC|-AKA|-AKB|
-AKC|-AMC]
[-b] [-no-relax]
Target IA-64 options:
[-mconstant-gp|-mauto-pic]
[-milp32|-milp64|-mlp64|-mp64]
[-mle|mbe]
[-mtune=itanium1|-mtune=itanium2]
[-munwind-check=warning|-munwind-check=error]
[-mhint.b=ok|-mhint.b=warning|-mhint.b=error]
[-x|-xexplicit] [-xauto] [-xdebug]
Target IP2K options:
[-mip2022|-mip2022ext]
Target M32C options:
[-m32c|-m16c] [-relax] [-h-tick-hex]
Target M32R options:
[–m32rx|–[no-]warn-explicit-parallel-conflicts|
–W[n]p]
Target M680X0 options:
[-l] [-m68000|-m68010|-m68020|...]
Target M68HC11 options:
[-m68hc11|-m68hc12|-m68hcs12]
[-mshort|-mlong]
[-mshort-double|-mlong-double]
[–force-long-branches] [–short-branches]
[–strict-direct-mode] [–print-insn-syntax]
[–print-opcodes] [–generate-example]
Target MCORE options:
[-jsri2bsr] [-sifilter] [-relax]
[-mcpu=[210|340]]
Target MICROBLAZE options:
Target MIPS options:
[-nocpp] [-EL] [-EB] [-O[optimization level ]]
[-g[debug level ]] [-G num ] [-KPIC] [-call shared]
[-non shared] [-xgot [-mvxworks-pic]
[-mabi=ABI ] [-32] [-n32] [-64] [-mfp32] [-mgp32]
[-march=CPU ] [-mtune=CPU ] [-mips1] [-mips2]
[-mips3] [-mips4] [-mips5] [-mips32] [-mips32r2]
Chapter 1: Overview
[-mips64] [-mips64r2]
[-construct-floats] [-no-construct-floats]
[-trap] [-no-break] [-break] [-no-trap]
[-mips16] [-no-mips16]
[-mmicromips] [-mno-micromips]
[-msmartmips] [-mno-smartmips]
[-mips3d] [-no-mips3d]
[-mdmx] [-no-mdmx]
[-mdsp] [-mno-dsp]
[-mdspr2] [-mno-dspr2]
[-mmt] [-mno-mt]
[-mmcu] [-mno-mcu]
[-mfix7000] [-mno-fix7000]
[-mfix-vr4120] [-mno-fix-vr4120]
[-mfix-vr4130] [-mno-fix-vr4130]
[-mdebug] [-no-mdebug]
[-mpdr] [-mno-pdr]
Target MMIX options:
[–fixed-special-register-names] [–globalize-symbols]
[–gnu-syntax] [–relax] [–no-predefined-symbols]
[–no-expand] [–no-merge-gregs] [-x]
[–linker-allocated-gregs]
Target PDP11 options:
[-mpic|-mno-pic] [-mall] [-mno-extensions]
[-mextension |-mno-extension ]
[-mcpu ] [-mmachine ]
Target picoJava options:
[-mb|-me]
Target PowerPC options:
[-a32|-a64]
[-mpwrx|-mpwr2|-mpwr|-m601|-mppc|-mppc32|-m603|-m604|-m403|-m405|
-m440|-m464|-m476|-m7400|-m7410|-m7450|-m7455|-m750cl|-mppc64|
-m620|-me500|-e500x2|-me500mc|-me500mc64|-mppc64bridge|-mbooke|
-mpower4|-mpr4|-mpower5|-mpwr5|-mpwr5x|-mpower6|-mpwr6|
-mpower7|-mpw7|-ma2|-mcell|-mspe|-mtitan|-me300|-mcom]
[-many] [-maltivec|-mvsx]
[-mregnames|-mno-regnames]
[-mrelocatable|-mrelocatable-lib|-K PIC] [-memb]
[-mlittle|-mlittle-endian|-le|-mbig|-mbig-endian|-be]
[-msolaris|-mno-solaris]
[-nops=count]
Target RX options:
[-mlittle-endian|-mbig-endian]
[-m32bit-ints|-m16bit-ints]
[-m32bit-doubles|-m64bit-doubles]
Target s390 options:
[-m31|-m64] [-mesa|-mzarch] [-march=CPU ]
[-mregnames|-mno-regnames]
[-mwarn-areg-zero]
Target SCORE options:
[-EB][-EL][-FIXDD][-NWARN]
3
4
Using as
[-SCORE5][-SCORE5U][-SCORE7][-SCORE3]
[-march=score7][-march=score3]
[-USE R1][-KPIC][-O0][-G num ][-V]
Target SPARC options:
[-Av6|-Av7|-Av8|-Asparclet|-Asparclite
-Av8plus|-Av8plusa|-Av9|-Av9a]
[-xarch=v8plus|-xarch=v8plusa] [-bump]
[-32|-64]
Target TIC54X options:
[-mcpu=54[123589]|-mcpu=54[56]lp] [-mfar-mode|-mf]
[-merrors-to-file |-me ]
Target TIC6X options:
[-march=arch] [-mbig-endian|-mlittle-endian]
[-mdsbt|-mno-dsbt] [-mpid=no|-mpid=near|-mpid=far]
[-mpic|-mno-pic]
Target TILE-Gx options:
[-m32|-m64]
Target Xtensa options:
[–[no-]text-section-literals] [–[no-]absolute-literals]
[–[no-]target-align] [–[no-]longcalls]
[–[no-]transform]
[–rename-section oldname =newname ]
Target Z80 options:
[-z80] [-r800]
[ -ignore-undocumented-instructions] [-Wnud]
[ -ignore-unportable-instructions] [-Wnup]
[ -warn-undocumented-instructions] [-Wud]
[ -warn-unportable-instructions] [-Wup]
[ -forbid-undocumented-instructions] [-Fud]
[ -forbid-unportable-instructions] [-Fup]
@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.
-a[cdghlmns]
Turn on listings, in any of a variety of ways:
-ac
omit false conditionals
-ad
omit debugging directives
Chapter 1: Overview
5
-ag
include general information, like as version and options passed
-ah
include high-level source
-al
include assembly
-am
include macro expansions
-an
omit forms processing
-as
include symbols
=file
set the name of the listing file
You may combine these options; for example, use ‘-aln’ for assembly listing
without forms processing. The ‘=file’ option, if used, must be the last one.
By itself, ‘-a’ defaults to ‘-ahls’.
--alternate
Begin in alternate macro mode. See Section 7.4 [.altmacro], page 46.
--compress-debug-sections
Compress DWARF debug sections using zlib. The debug sections are renamed
to begin with ‘.zdebug’, and the resulting object file may not be compatible
with older linkers and object file utilities.
--nocompress-debug-sections
Do not compress DWARF debug sections. This is the default.
-D
Ignored. This option is accepted for script compatibility with calls to other
assemblers.
--debug-prefix-map old =new
When assembling files in directory ‘old ’, record debugging information describing them as in ‘new ’ instead.
--defsym sym =value
Define the symbol sym to be value before assembling the input file. value must
be an integer constant. As in C, a leading ‘0x’ indicates a hexadecimal value,
and a leading ‘0’ indicates an octal value. The value of the symbol can be
overridden inside a source file via the use of a .set pseudo-op.
-f
“fast”—skip whitespace and comment preprocessing (assume source is compiler
output).
-g
--gen-debug
Generate debugging information for each assembler source line using whichever
debug format is preferred by the target. This currently means either STABS,
ECOFF or DWARF2.
--gstabs
Generate stabs debugging information for each assembler line. This may help
debugging assembler code, if the debugger can handle it.
--gstabs+
Generate stabs debugging information for each assembler line, with GNU extensions that probably only gdb can handle, and that could make other debuggers
6
Using as
crash or refuse to read your program. This may help debugging assembler
code. Currently the only GNU extension is the location of the current working
directory at assembling time.
--gdwarf-2
Generate DWARF2 debugging information for each assembler line. This may
help debugging assembler code, if the debugger can handle it. Note—this option
is only supported by some targets, not all of them.
--size-check=error
--size-check=warning
Issue an error or warning for invalid ELF .size directive.
--help
Print a summary of the command line options and exit.
--target-help
Print a summary of all target specific options and exit.
-I dir
Add directory dir to the search list for .include directives.
-J
Don’t warn about signed overflow.
-K
Issue warnings when difference tables altered for long displacements.
-L
--keep-locals
Keep (in the symbol table) local symbols. These symbols start with systemspecific local label prefixes, typically ‘.L’ for ELF systems or ‘L’ for traditional
a.out systems. See Section 5.3 [Symbol Names], page 37.
--listing-lhs-width=number
Set the maximum width, in words, of the output data column for an assembler
listing to number.
--listing-lhs-width2=number
Set the maximum width, in words, of the output data column for continuation
lines in an assembler listing to number.
--listing-rhs-width=number
Set the maximum width of an input source line, as displayed in a listing, to
number bytes.
--listing-cont-lines=number
Set the maximum number of lines printed in a listing for a single line of input
to number + 1.
-o objfile
Name the object-file output from as objfile.
-R
Fold the data section into the text section.
Set the default size of GAS’s hash tables to a prime number close to number.
Increasing this value can reduce the length of time it takes the assembler to
perform its tasks, at the expense of increasing the assembler’s memory requirements. Similarly reducing this value can reduce the memory requirements at
the expense of speed.
Chapter 1: Overview
7
--reduce-memory-overheads
This option reduces GAS’s memory requirements, at the expense of making
the assembly processes slower. Currently this switch is a synonym for
‘--hash-size=4051’, but in the future it may have other effects as well.
--statistics
Print the maximum space (in bytes) and total time (in seconds) used by assembly.
--strip-local-absolute
Remove local absolute symbols from the outgoing symbol table.
-v
-version
Print the as version.
--version
Print the as version and exit.
-W
--no-warn
Suppress warning messages.
--fatal-warnings
Treat warnings as errors.
--warn
Don’t suppress warning messages or treat them as errors.
-w
Ignored.
-x
Ignored.
-Z
Generate an object file even after errors.
-- | files ...
Standard input, or source files to assemble.
See Section 9.1.2 [Alpha Options], page 80, for the options available when as is configured
for an Alpha processor.
The following options are available when as is configured for an ARC processor.
-marc[5|6|7|8]
This option selects the core processor variant.
-EB | -EL Select either big-endian (-EB) or little-endian (-EL) output.
The following options are available when as is configured for the ARM processor family.
-mcpu=processor [+extension ...]
Specify which ARM processor variant is the target.
-march=architecture [+extension ...]
Specify which ARM architecture variant is used by the target.
-mfpu=floating-point-format
Select which Floating Point architecture is the target.
-mfloat-abi=abi
Select which floating point ABI is in use.
8
Using as
-mthumb
Enable Thumb only instruction decoding.
-mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant
Select which procedure calling convention is in use.
-EB | -EL Select either big-endian (-EB) or little-endian (-EL) output.
-mthumb-interwork
Specify that the code has been generated with interworking between Thumb
and ARM code in mind.
Specify that PIC code has been generated.
-k
See Section 9.5.1 [Blackfin Options], page 110, for the options available when as is
configured for the Blackfin processor family.
See the info pages for documentation of the CRIS-specific options.
The following options are available when as is configured for a D10V processor.
Optimize output by parallelizing instructions.
-O
The following options are available when as is configured for a D30V processor.
-O
Optimize output by parallelizing instructions.
-n
Warn when nops are generated.
-N
Warn when a nop after a 32-bit multiply instruction is generated.
See Section 9.13.1 [i386-Options], page 140, for the options available when as is configured
for an i386 processor.
The following options are available when as is configured for the Intel 80960 processor.
-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
Specify which variant of the 960 architecture is the target.
Add code to collect statistics about branches taken.
-b
-no-relax
Do not alter compare-and-branch instructions for long displacements; error if
necessary.
The following options are available when as is configured for the Ubicom IP2K series.
-mip2022ext
Specifies that the extended IP2022 instructions are allowed.
-mip2022
Restores the default behaviour, which restricts the permitted instructions to
just the basic IP2022 ones.
The following options are available when as is configured for the Renesas M32C and
M16C processors.
-m32c
Assemble M32C instructions.
-m16c
Assemble M16C instructions (the default).
-relax
Enable support for link-time relaxations.
Chapter 1: Overview
9
-h-tick-hex
Support H’00 style hex constants in addition to 0x00 style.
The following options are available when as is configured for the Renesas M32R (formerly
Mitsubishi M32R) series.
--m32rx
Specify which processor in the M32R family is the target. The default is normally the M32R, but this option changes it to the M32RX.
--warn-explicit-parallel-conflicts or --Wp
Produce warning messages when questionable parallel constructs are encountered.
--no-warn-explicit-parallel-conflicts or --Wnp
Do not produce warning messages when questionable parallel constructs are
encountered.
The following options are available when as is configured for the Motorola 68000 series.
-l
Shorten references to undefined symbols, to one word instead of two.
-m68000 | -m68008 | -m68010 | -m68020 | -m68030
| -m68040 | -m68060 | -m68302 | -m68331 | -m68332
| -m68333 | -m68340 | -mcpu32 | -m5200
Specify what processor in the 68000 family is the target. The default is normally
the 68020, but this can be changed at configuration time.
-m68881 | -m68882 | -mno-68881 | -mno-68882
The target machine does (or does not) have a floating-point coprocessor. The
default is to assume a coprocessor for 68020, 68030, and cpu32. Although the
basic 68000 is not compatible with the 68881, a combination of the two can
be specified, since it’s possible to do emulation of the coprocessor instructions
with the main processor.
-m68851 | -mno-68851
The target machine does (or does not) have a memory-management unit coprocessor. The default is to assume an MMU for 68020 and up.
For details about the PDP-11 machine dependent features options, see Section 9.28.1
[PDP-11-Options], page 205.
-mpic | -mno-pic
Generate position-independent (or position-dependent) code. The default is
‘-mpic’.
-mall
-mall-extensions
Enable all instruction set extensions. This is the default.
-mno-extensions
Disable all instruction set extensions.
-mextension | -mno-extension
Enable (or disable) a particular instruction set extension.
10
Using as
-mcpu
Enable the instruction set extensions supported by a particular CPU, and disable all other extensions.
-mmachine
Enable the instruction set extensions supported by a particular machine model,
and disable all other extensions.
The following options are available when as is configured for a picoJava processor.
-mb
Generate “big endian” format output.
-ml
Generate “little endian” format output.
The following options are available when as is configured for the Motorola 68HC11 or
68HC12 series.
-m68hc11 | -m68hc12 | -m68hcs12
Specify what processor is the target. The default is defined by the configuration
option when building the assembler.
-mshort
Specify to use the 16-bit integer ABI.
-mlong
Specify to use the 32-bit integer ABI.
-mshort-double
Specify to use the 32-bit double ABI.
-mlong-double
Specify to use the 64-bit double ABI.
--force-long-branches
Relative branches are turned into absolute ones. This concerns conditional
branches, unconditional branches and branches to a sub routine.
-S | --short-branches
Do not turn relative branches into absolute ones when the offset is out of range.
--strict-direct-mode
Do not turn the direct addressing mode into extended addressing mode when
the instruction does not support direct addressing mode.
--print-insn-syntax
Print the syntax of instruction in case of error.
--print-opcodes
print the list of instructions with syntax and then exit.
--generate-example
print an example of instruction for each possible instruction and then exit. This
option is only useful for testing as.
The following options are available when as is configured for the SPARC architecture:
-Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
-Av8plus | -Av8plusa | -Av9 | -Av9a
Explicitly select a variant of the SPARC architecture.
Chapter 1: Overview
11
‘-Av8plus’ and ‘-Av8plusa’ select a 32 bit environment. ‘-Av9’ and ‘-Av9a’
select a 64 bit environment.
‘-Av8plusa’ and ‘-Av9a’ enable the SPARC V9 instruction set with UltraSPARC extensions.
-xarch=v8plus | -xarch=v8plusa
For compatibility with the Solaris v9 assembler. These options are equivalent
to -Av8plus and -Av8plusa, respectively.
-bump
Warn when the assembler switches to another architecture.
The following options are available when as is configured for the ’c54x architecture.
-mfar-mode
Enable extended addressing mode. All addresses and relocations will assume
extended addressing (usually 23 bits).
-mcpu=CPU_VERSION
Sets the CPU version being compiled for.
-merrors-to-file FILENAME
Redirect error output to a file, for broken systems which don’t support such
behaviour in the shell.
The following options are available when as is configured for a mips processor.
-G num
This option sets the largest size of an object that can be referenced implicitly
with the gp register. It is only accepted for targets that use ECOFF format,
such as a DECstation running Ultrix. The default value is 8.
-EB
Generate “big endian” format output.
-EL
Generate “little endian” format output.
-mips1
-mips2
-mips3
-mips4
-mips5
-mips32
-mips32r2
-mips64
-mips64r2
Generate code for a particular mips Instruction Set Architecture level. ‘-mips1’
is an alias for ‘-march=r3000’, ‘-mips2’ is an alias for ‘-march=r6000’, ‘-mips3’
is an alias for ‘-march=r4000’ and ‘-mips4’ is an alias for ‘-march=r8000’.
‘-mips5’, ‘-mips32’, ‘-mips32r2’, ‘-mips64’, and ‘-mips64r2’ correspond to
generic ‘MIPS V’, ‘MIPS32’, ‘MIPS32 Release 2’, ‘MIPS64’, and ‘MIPS64 Release
2’ ISA processors, respectively.
-march=CPU
Generate code for a particular mips cpu.
-mtune=cpu
Schedule and tune for a particular mips cpu.
12
Using as
-mfix7000
-mno-fix7000
Cause nops to be inserted if the read of the destination register of an mfhi or
mflo instruction occurs in the following two instructions.
-mdebug
-no-mdebug
Cause stabs-style debugging output to go into an ECOFF-style .mdebug section
instead of the standard ELF .stabs sections.
-mpdr
-mno-pdr
-mgp32
-mfp32
Control generation of .pdr sections.
The register sizes are normally inferred from the ISA and ABI, but these flags
force a certain group of registers to be treated as 32 bits wide at all times.
‘-mgp32’ controls the size of general-purpose registers and ‘-mfp32’ controls the
size of floating-point registers.
-mips16
-no-mips16
Generate code for the MIPS 16 processor. This is equivalent to putting .set
mips16 at the start of the assembly file. ‘-no-mips16’ turns off this option.
-mmicromips
-mno-micromips
Generate code for the microMIPS processor. This is equivalent to putting .set
micromips at the start of the assembly file. ‘-mno-micromips’ turns off this
option. This is equivalent to putting .set nomicromips at the start of the
assembly file.
-msmartmips
-mno-smartmips
Enables the SmartMIPS extension to the MIPS32 instruction set. This
is equivalent to putting .set smartmips at the start of the assembly file.
‘-mno-smartmips’ turns off this option.
-mips3d
-no-mips3d
Generate code for the MIPS-3D Application Specific Extension. This tells the
assembler to accept MIPS-3D instructions. ‘-no-mips3d’ turns off this option.
-mdmx
-no-mdmx
-mdsp
-mno-dsp
Generate code for the MDMX Application Specific Extension. This tells the
assembler to accept MDMX instructions. ‘-no-mdmx’ turns off this option.
Generate code for the DSP Release 1 Application Specific Extension. This tells
the assembler to accept DSP Release 1 instructions. ‘-mno-dsp’ turns off this
option.
Chapter 1: Overview
13
-mdspr2
-mno-dspr2
Generate code for the DSP Release 2 Application Specific Extension. This
option implies -mdsp. This tells the assembler to accept DSP Release 2 instructions. ‘-mno-dspr2’ turns off this option.
-mmt
-mno-mt
-mmcu
-mno-mcu
Generate code for the MT Application Specific Extension. This tells the assembler to accept MT instructions. ‘-mno-mt’ turns off this option.
Generate code for the MCU Application Specific Extension. This tells the
assembler to accept MCU instructions. ‘-mno-mcu’ turns off this option.
--construct-floats
--no-construct-floats
The ‘--no-construct-floats’ option disables the construction of double width
floating point constants by loading the two halves of the value into the two
single width floating point registers that make up the double width register.
By default ‘--construct-floats’ is selected, allowing construction of these
floating point constants.
--emulation=name
This option causes as to emulate as configured for some other target, in all
respects, including output format (choosing between ELF and ECOFF only),
handling of pseudo-opcodes which may generate debugging information or store
symbol table information, and default endianness. The available configuration
names are: ‘mipsecoff’, ‘mipself’, ‘mipslecoff’, ‘mipsbecoff’, ‘mipslelf’,
‘mipsbelf’. The first two do not alter the default endianness from that of the
primary target for which the assembler was configured; the others change the
default to little- or big-endian as indicated by the ‘b’ or ‘l’ in the name. Using
‘-EB’ or ‘-EL’ will override the endianness selection in any case.
This option is currently supported only when the primary target as is configured for is a mips ELF or ECOFF target. Furthermore, the primary target
or others specified with ‘--enable-targets=...’ at configuration time must
include support for the other format, if both are to be available. For example,
the Irix 5 configuration includes support for both.
Eventually, this option will support more configurations, with more fine-grained
control over the assembler’s behavior, and will be supported for more processors.
-nocpp
as ignores this option. It is accepted for compatibility with the native tools.
--trap
--no-trap
--break
--no-break
Control how to deal with multiplication overflow and division by zero. ‘--trap’
or ‘--no-break’ (which are synonyms) take a trap exception (and only work
for Instruction Set Architecture level 2 and higher); ‘--break’ or ‘--no-trap’
(also synonyms, and the default) take a break exception.
14
Using as
-n
When this option is used, as will issue a warning every time it generates a nop
instruction from a macro.
The following options are available when as is configured for an MCore processor.
-jsri2bsr
-nojsri2bsr
Enable or disable the JSRI to BSR transformation. By default this is enabled.
The command line option ‘-nojsri2bsr’ can be used to disable it.
-sifilter
-nosifilter
Enable or disable the silicon filter behaviour. By default this is disabled. The
default can be overridden by the ‘-sifilter’ command line option.
-relax
Alter jump instructions for long displacements.
-mcpu=[210|340]
Select the cpu type on the target hardware. This controls which instructions
can be assembled.
-EB
Assemble for a big endian target.
-EL
Assemble for a little endian target.
See the info pages for documentation of the MMIX-specific options.
See Section 9.30.1 [PowerPC-Opts], page 210, for the options available when as is configured for a PowerPC processor.
See the info pages for documentation of the RX-specific options.
The following options are available when as is configured for the s390 processor family.
-m31
-m64
Select the word size, either 31/32 bits or 64 bits.
-mesa
-mzarch
Select the architecture mode, either the Enterprise System Architecture (esa)
or the z/Architecture mode (zarch).
-march=processor
Specify which s390 processor variant is the target, ‘g6’, ‘g6’, ‘z900’, ‘z990’,
‘z9-109’, ‘z9-ec’, or ‘z10’.
-mregnames
-mno-regnames
Allow or disallow symbolic names for registers.
-mwarn-areg-zero
Warn whenever the operand for a base or index register has been specified but
evaluates to zero.
See Section 9.38.1 [TIC6X Options], page 258, for the options available when as is
configured for a TMS320C6000 processor.
See Section 9.39.1 [TILE-Gx Options], page 261, for the options available when as is
configured for a TILE-Gx processor.
Chapter 1: Overview
15
See Section 9.46.1 [Xtensa Options], page 287, for the options available when as is
configured for an Xtensa processor.
The following options are available when as is configured for a Z80 family processor.
-z80
Assemble for Z80 processor.
-r800
Assemble for R800 processor.
-ignore-undocumented-instructions
-Wnud
Assemble undocumented Z80 instructions that also work on R800 without warning.
-ignore-unportable-instructions
-Wnup
Assemble all undocumented Z80 instructions without warning.
-warn-undocumented-instructions
-Wud
Issue a warning for undocumented Z80 instructions that also work on R800.
-warn-unportable-instructions
-Wup
Issue a warning for undocumented Z80 instructions that do not work on R800.
-forbid-undocumented-instructions
-Fud
Treat all undocumented instructions as errors.
-forbid-unportable-instructions
-Fup
Treat undocumented Z80 instructions that do not work on R800 as errors.
1.1 Structure of this Manual
This manual is intended to describe what you need to know to use gnu as. We cover the
syntax expected in source files, including notation for symbols, constants, and expressions;
the directives that as understands; and of course how to invoke as.
This manual also describes some of the machine-dependent features of various flavors of
the assembler.
On the other hand, this manual is not intended as an introduction to programming
in assembly language—let alone programming in general! In a similar vein, we make no
attempt to introduce the machine architecture; we do not describe the instruction set,
standard mnemonics, registers or addressing modes that are standard to a particular architecture. You may want to consult the manufacturer’s machine architecture manual for this
information.
1.2 The GNU Assembler
gnu as is really a family of assemblers. If you use (or have used) the gnu assembler on
one architecture, you should find a fairly similar environment when you use it on another
architecture. Each version has much in common with the others, including object file
formats, most assembler directives (often called pseudo-ops) and assembler syntax.
as is primarily intended to assemble the output of the gnu C compiler gcc for use by
the linker ld. Nevertheless, we’ve tried to make as assemble correctly everything that other
assemblers for the same machine would assemble. Any exceptions are documented explicitly
(see Chapter 9 [Machine Dependencies], page 79). This doesn’t mean as always uses the
16
Using as
same syntax as another assembler for the same architecture; for example, we know of several
incompatible versions of 680x0 assembly language syntax.
Unlike older assemblers, as is designed to assemble a source program in one pass of the
source file. This has a subtle impact on the .org directive (see Section 7.83 [.org], page 62).
1.3 Object File Formats
The gnu assembler can be configured to produce several alternative object file formats. For
the most part, this does not affect how you write assembly language programs; but directives for debugging symbols are typically different in different file formats. See Section 5.5
[Symbol Attributes], page 39.
1.4 Command Line
After the program name as, the command line may contain options and file names. Options
may appear in any order, and may be before, after, or between file names. The order of file
names is significant.
‘--’ (two hyphens) by itself names the standard input file explicitly, as one of the files
for as to assemble.
Except for ‘--’ any command line argument that begins with a hyphen (‘-’) is an option.
Each option changes the behavior of as. No option changes the way another option works.
An option is a ‘-’ followed by one or more letters; the case of the letter is important. All
options are optional.
Some options expect exactly one file name to follow them. The file name may either
immediately follow the option’s letter (compatible with older assemblers) or it may be the
next command argument (gnu standard). These two command lines are equivalent:
as -o my-object-file.o mumble.s
as -omy-object-file.o mumble.s
1.5 Input Files
We use the phrase source program, abbreviated source, to describe the program input to
one run of as. The program may be in one or more files; how the source is partitioned into
files doesn’t change the meaning of the source.
The source program is a concatenation of the text in all the files, in the order specified.
Each time you run as it assembles exactly one source program. The source program is
made up of one or more files. (The standard input is also a file.)
You give as a command line that has zero or more input file names. The input files are
read (from left file name to right). A command line argument (in any position) that has no
special meaning is taken to be an input file name.
If you give as no file names it attempts to read one input file from the as standard input,
which is normally your terminal. You may have to type ctl-D to tell as there is no more
program to assemble.
Use ‘--’ if you need to explicitly name the standard input file in your command line.
If the source is empty, as produces a small, empty object file.
Chapter 1: Overview
17
Filenames and Line-numbers
There are two ways of locating a line in the input file (or files) and either may be used in
reporting error messages. One way refers to a line number in a physical file; the other refers
to a line number in a “logical” file. See Section 1.7 [Error and Warning Messages], page 17.
Physical files are those files named in the command line given to as.
Logical files are simply names declared explicitly by assembler directives; they bear no
relation to physical files. Logical file names help error messages reflect the original source
file, when as source is itself synthesized from other files. as understands the ‘#’ directives
emitted by the gcc preprocessor. See also Section 7.51 [.file], page 52.
1.6 Output (Object) File
Every time you run as it produces an output file, which is your assembly language program
translated into numbers. This file is the object file. Its default name is a.out. You can
give it another name by using the ‘-o’ option. Conventionally, object file names end with
‘.o’. The default name is used for historical reasons: older assemblers were capable of
assembling self-contained programs directly into a runnable program. (For some formats,
this isn’t currently possible, but it can be done for the a.out format.)
The object file is meant for input to the linker ld. It contains assembled program code,
information to help ld integrate the assembled program into a runnable file, and (optionally)
symbolic information for the debugger.
1.7 Error and Warning Messages
as may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs as automatically. Warnings report an
assumption made so that as could keep assembling a flawed program; errors report a grave
problem that stops the assembly.
Warning messages have the format
file_name:NNN:Warning Message Text
(where NNN is a line number). If a logical file name has been given (see Section 7.51
[.file], page 52) it is used for the filename, otherwise the name of the current input file
is used. If a logical line number was given (see Section 7.69 [.line], page 57) then it is
used to calculate the number printed, otherwise the actual line in the current source file is
printed. The message text is intended to be self explanatory (in the grand Unix tradition).
Error messages have the format
file_name:NNN:FATAL:Error Message Text
The file name and line number are derived as for warning messages. The actual message
text may be rather less explanatory because many of them aren’t supposed to happen.
Chapter 2: Command-Line Options
19
2 Command-Line Options
This chapter describes command-line options available in all versions of the gnu assembler;
see Chapter 9 [Machine Dependencies], page 79, for options specific to particular machine
architectures.
If you are invoking as via the gnu C compiler, you can use the ‘-Wa’ option to pass
arguments through to the assembler. The assembler arguments must be separated from
each other (and the ‘-Wa’) by commas. For example:
gcc -c -g -O -Wa,-alh,-L file.c
This passes two options to the assembler: ‘-alh’ (emit a listing to standard output with
high-level and assembly source) and ‘-L’ (retain local symbols in the symbol table).
Usually you do not need to use this ‘-Wa’ mechanism, since many compiler commandline options are automatically passed to the assembler by the compiler. (You can call the
gnu compiler driver with the ‘-v’ option to see precisely what options it passes to each
compilation pass, including the assembler.)
2.1 Enable Listings: ‘-a[cdghlns]’
These options enable listing output from the assembler. By itself, ‘-a’ requests high-level,
assembly, and symbols listing. You can use other letters to select specific options for the
list: ‘-ah’ requests a high-level language listing, ‘-al’ requests an output-program assembly
listing, and ‘-as’ requests a symbol table listing. High-level listings require that a compiler
debugging option like ‘-g’ be used, and that assembly listings (‘-al’) be requested also.
Use the ‘-ag’ option to print a first section with general assembly information, like as
version, switches passed, or time stamp.
Use the ‘-ac’ option to omit false conditionals from a listing. Any lines which are not
assembled because of a false .if (or .ifdef, or any other conditional), or a true .if followed
by an .else, will be omitted from the listing.
Use the ‘-ad’ option to omit debugging directives from the listing.
Once you have specified one of these options, you can further control listing output and
its appearance using the directives .list, .nolist, .psize, .eject, .title, and .sbttl.
The ‘-an’ option turns off all forms processing. If you do not request listing output with
one of the ‘-a’ options, the listing-control directives have no effect.
The letters after ‘-a’ may be combined into one option, e.g., ‘-aln’.
Note if the assembler source is coming from the standard input (e.g., because it is being
created by gcc and the ‘-pipe’ command line switch is being used) then the listing will not
contain any comments or preprocessor directives. This is because the listing code buffers
input source lines from stdin only after they have been preprocessed by the assembler. This
reduces memory usage and makes the code more efficient.
2.2 ‘--alternate’
Begin in alternate macro mode, see Section 7.4 [.altmacro], page 46.
20
Using as
2.3 ‘-D’
This option has no effect whatsoever, but it is accepted to make it more likely that scripts
written for other assemblers also work with as.
2.4 Work Faster: ‘-f’
‘-f’ should only be used when assembling programs written by a (trusted) compiler. ‘-f’
stops the assembler from doing whitespace and comment preprocessing on the input file(s)
before assembling them. See Section 3.1 [Preprocessing], page 25.
Warning: if you use ‘-f’ when the files actually need to be preprocessed (if
they contain comments, for example), as does not work correctly.
2.5 .include Search Path: ‘-I’ path
Use this option to add a path to the list of directories as searches for files specified in
.include directives (see Section 7.62 [.include], page 55). You may use ‘-I’ as many
times as necessary to include a variety of paths. The current working directory is always
searched first; after that, as searches any ‘-I’ directories in the same order as they were
specified (left to right) on the command line.
2.6 Difference Tables: ‘-K’
as sometimes alters the code emitted for directives of the form ‘.word sym1 -sym2 ’. See
Section 7.122 [.word], page 75. You can use the ‘-K’ option if you want a warning issued
when this is done.
2.7 Include Local Symbols: ‘-L’
Symbols beginning with system-specific local label prefixes, typically ‘.L’ for ELF systems or
‘L’ for traditional a.out systems, are called local symbols. See Section 5.3 [Symbol Names],
page 37. Normally you do not see such symbols when debugging, because they are intended
for the use of programs (like compilers) that compose assembler programs, not for your
notice. Normally both as and ld discard such symbols, so you do not normally debug with
them.
This option tells as to retain those local symbols in the object file. Usually if you do
this you also tell the linker ld to preserve those symbols.
2.8 Configuring listing output: ‘--listing’
The listing feature of the assembler can be enabled via the command line switch ‘-a’ (see
Section 2.1 [a], page 19). This feature combines the input source file(s) with a hex dump
of the corresponding locations in the output object file, and displays them as a listing file.
The format of this listing can be controlled by directives inside the assembler source (i.e.,
.list (see Section 7.71 [List], page 58), .title (see Section 7.112 [Title], page 72), .sbttl
(see Section 7.95 [Sbttl], page 66), .psize (see Section 7.89 [Psize], page 64), and .eject
(see Section 7.36 [Eject], page 50) and also by the following switches:
Chapter 2: Command-Line Options
21
--listing-lhs-width=‘number’
Sets the maximum width, in words, of the first line of the hex byte dump. This
dump appears on the left hand side of the listing output.
--listing-lhs-width2=‘number’
Sets the maximum width, in words, of any further lines of the hex byte dump
for a given input source line. If this value is not specified, it defaults to being
the same as the value specified for ‘--listing-lhs-width’. If neither switch
is used the default is to one.
--listing-rhs-width=‘number’
Sets the maximum width, in characters, of the source line that is displayed
alongside the hex dump. The default value for this parameter is 100. The
source line is displayed on the right hand side of the listing output.
--listing-cont-lines=‘number’
Sets the maximum number of continuation lines of hex dump that will be displayed for a given single line of source input. The default value is 4.
2.9 Assemble in MRI Compatibility Mode: ‘-M’
The ‘-M’ or ‘--mri’ option selects MRI compatibility mode. This changes the syntax and
pseudo-op handling of as to make it compatible with the ASM68K or the ASM960 (depending
upon the configured target) assembler from Microtec Research. The exact nature of the
MRI syntax will not be documented here; see the MRI manuals for more information. Note
in particular that the handling of macros and macro arguments is somewhat different. The
purpose of this option is to permit assembling existing MRI assembler code using as.
The MRI compatibility is not complete. Certain operations of the MRI assembler depend upon its object file format, and can not be supported using other object file formats.
Supporting these would require enhancing each object file format individually. These are:
• global symbols in common section
The m68k MRI assembler supports common sections which are merged by the linker.
Other object file formats do not support this. as handles common sections by treating
them as a single common symbol. It permits local symbols to be defined within a
common section, but it can not support global symbols, since it has no way to describe
them.
• complex relocations
The MRI assemblers support relocations against a negated section address, and relocations which combine the start addresses of two or more sections. These are not support
by other object file formats.
• END pseudo-op specifying start address
The MRI END pseudo-op permits the specification of a start address. This is not
supported by other object file formats. The start address may instead be specified
using the ‘-e’ option to the linker, or in a linker script.
• IDNT, .ident and NAME pseudo-ops
The MRI IDNT, .ident and NAME pseudo-ops assign a module name to the output file.
This is not supported by other object file formats.
22
Using as
• ORG pseudo-op
The m68k MRI ORG pseudo-op begins an absolute section at a given address. This
differs from the usual as .org pseudo-op, which changes the location within the current
section. Absolute sections are not supported by other object file formats. The address
of a section may be assigned within a linker script.
There are some other features of the MRI assembler which are not supported by as,
typically either because they are difficult or because they seem of little consequence. Some
of these may be supported in future releases.
• EBCDIC strings
EBCDIC strings are not supported.
• packed binary coded decimal
Packed binary coded decimal is not supported. This means that the DC.P and DCB.P
pseudo-ops are not supported.
• FEQU pseudo-op
The m68k FEQU pseudo-op is not supported.
• NOOBJ pseudo-op
The m68k NOOBJ pseudo-op is not supported.
• OPT branch control options
The m68k OPT branch control options—B, BRS, BRB, BRL, and BRW—are ignored. as
automatically relaxes all branches, whether forward or backward, to an appropriate
size, so these options serve no purpose.
• OPT list control options
The following m68k OPT list control options are ignored: C, CEX, CL, CRE, E, G, I, M,
MEX, MC, MD, X.
• other OPT options
The following m68k OPT options are ignored: NEST, O, OLD, OP, P, PCO, PCR, PCS, R.
• OPT D option is default
The m68k OPT D option is the default, unlike the MRI assembler. OPT NOD may be used
to turn it off.
• XREF pseudo-op.
The m68k XREF pseudo-op is ignored.
• .debug pseudo-op
The i960 .debug pseudo-op is not supported.
• .extended pseudo-op
The i960 .extended pseudo-op is not supported.
• .list pseudo-op.
The various options of the i960 .list pseudo-op are not supported.
• .optimize pseudo-op
The i960 .optimize pseudo-op is not supported.
• .output pseudo-op
The i960 .output pseudo-op is not supported.
Chapter 2: Command-Line Options
23
• .setreal pseudo-op
The i960 .setreal pseudo-op is not supported.
2.10 Dependency Tracking: ‘--MD’
as can generate a dependency file for the file it creates. This file consists of a single rule
suitable for make describing the dependencies of the main source file.
The rule is written to the file named in its argument.
This feature is used in the automatic updating of makefiles.
2.11 Name the Object File: ‘-o’
There is always one object file output when you run as. By default it has the name ‘a.out’
(or ‘b.out’, for Intel 960 targets only). You use this option (which takes exactly one
filename) to give the object file a different name.
Whatever the object file is called, as overwrites any existing file of the same name.
2.12 Join Data and Text Sections: ‘-R’
‘-R’ tells as to write the object file as if all data-section data lives in the text section. This
is only done at the very last moment: your binary data are the same, but data section parts
are relocated differently. The data section part of your object file is zero bytes long because
all its bytes are appended to the text section. (See Chapter 4 [Sections and Relocation],
page 31.)
When you specify ‘-R’ it would be possible to generate shorter address displacements
(because we do not have to cross between text and data section). We refrain from doing
this simply for compatibility with older versions of as. In future, ‘-R’ may work this way.
When as is configured for COFF or ELF output, this option is only useful if you use
sections named ‘.text’ and ‘.data’.
‘-R’ is not supported for any of the HPPA targets. Using ‘-R’ generates a warning from
as.
2.13 Display Assembly Statistics: ‘--statistics’
Use ‘--statistics’ to display two statistics about the resources used by as: the maximum
amount of space allocated during the assembly (in bytes), and the total execution time
taken for the assembly (in cpu seconds).
2.14 Compatible Output: ‘--traditional-format’
For some targets, the output of as is different in some ways from the output of some existing
assembler. This switch requests as to use the traditional format instead.
For example, it disables the exception frame optimizations which as normally does by
default on gcc output.
2.15 Announce Version: ‘-v’
You can find out what version of as is running by including the option ‘-v’ (which you can
also spell as ‘-version’) on the command line.
24
Using as
2.16 Control Warnings: ‘-W’, ‘--warn’, ‘--no-warn’,
‘--fatal-warnings’
as should never give a warning or error message when assembling compiler output. But
programs written by people often cause as to give a warning that a particular assumption
was made. All such warnings are directed to the standard error file.
If you use the ‘-W’ and ‘--no-warn’ options, no warnings are issued. This only affects the
warning messages: it does not change any particular of how as assembles your file. Errors,
which stop the assembly, are still reported.
If you use the ‘--fatal-warnings’ option, as considers files that generate warnings to
be in error.
You can switch these options off again by specifying ‘--warn’, which causes warnings to
be output as usual.
2.17 Generate Object File in Spite of Errors: ‘-Z’
After an error message, as normally produces no output. If for some reason you are interested in object file output even after as gives an error message on your program, use the ‘-Z’
option. If there are any errors, as continues anyways, and writes an object file after a final
warning message of the form ‘n errors, m warnings, generating bad object file.’
Chapter 3: Syntax
25
3 Syntax
This chapter describes the machine-independent syntax allowed in a source file. as syntax is
similar to what many other assemblers use; it is inspired by the BSD 4.2 assembler, except
that as does not assemble Vax bit-fields.
3.1 Preprocessing
The as internal preprocessor:
• adjusts and removes extra whitespace. It leaves one space or tab before the keywords
on a line, and turns any other whitespace on the line into a single space.
• removes all comments, replacing them with a single space, or an appropriate number
of newlines.
• converts character constants into the appropriate numeric values.
It does not do macro processing, include file handling, or anything else you may get
from your C compiler’s preprocessor. You can do include file processing with the .include
directive (see Section 7.62 [.include], page 55). You can use the gnu C compiler driver
to get other “CPP” style preprocessing by giving the input file a ‘.S’ suffix. See Section
“Options Controlling the Kind of Output” in Using GNU CC.
Excess whitespace, comments, and character constants cannot be used in the portions
of the input text that are not preprocessed.
If the first line of an input file is #NO_APP or if you use the ‘-f’ option, whitespace
and comments are not removed from the input file. Within an input file, you can ask for
whitespace and comment removal in specific portions of the by putting a line that says
#APP before the text that may contain whitespace or comments, and putting a line that
says #NO_APP after this text. This feature is mainly intend to support asm statements in
compilers whose output is otherwise free of comments and whitespace.
3.2 Whitespace
Whitespace is one or more blanks or tabs, in any order. Whitespace is used to separate
symbols, and to make programs neater for people to read. Unless within character constants
(see Section 3.6.1 [Character Constants], page 27), any whitespace means the same as
exactly one space.
3.3 Comments
There are two ways of rendering comments to as. In both cases the comment is equivalent
to one space.
Anything from ‘/*’ through the next ‘*/’ is a comment. This means you may not nest
these comments.
/*
The only way to include a newline (’\n’) in a comment
is to use this sort of comment.
*/
/* This sort of comment does not nest. */
26
Using as
Anything from a line comment character up to the next newline is considered a comment
and is ignored. The line comment character is target specific, and some targets multiple
comment characters. Some targets also have line comment characters that only work if they
are the first character on a line. Some targets use a sequence of two characters to introduce
a line comment. Some targets can also change their line comment characters depending
upon command line options that have been used. For more details see the Syntax section
in the documentation for individual targets.
If the line comment character is the hash sign (‘#’) then it still has the special ability to
enable and disable preprocessing (see Section 3.1 [Preprocessing], page 25) and to specify
logical line numbers:
To be compatible with past assemblers, lines that begin with ‘#’ have a special interpretation. Following the ‘#’ should be an absolute expression (see Chapter 6 [Expressions],
page 41): the logical line number of the next line. Then a string (see Section 3.6.1.1 [Strings],
page 27) is allowed: if present it is a new logical file name. The rest of the line, if any,
should be whitespace.
If the first non-whitespace characters on the line are not numeric, the line is ignored.
(Just like a comment.)
# 42-6 "new_file_name"
# This is an ordinary comment.
# New logical file name
# This is logical line # 36.
This feature is deprecated, and may disappear from future versions of as.
3.4 Symbols
A symbol is one or more characters chosen from the set of all letters (both upper and
lower case), digits and the three characters ‘_.$’. On most machines, you can also use $
in symbol names; exceptions are noted in Chapter 9 [Machine Dependencies], page 79. No
symbol may begin with a digit. Case is significant. There is no length limit: all characters
are significant. Symbols are delimited by characters not in that set, or by the beginning of
a file (since the source program must end with a newline, the end of a file is not a possible
symbol delimiter). See Chapter 5 [Symbols], page 37.
3.5 Statements
A statement ends at a newline character (‘\n’) or a line separator character. The line
separator character is target specific and described in the Syntax section of each target’s
documentation. Not all targets support a line separator character. The newline or line
separator character is considered to be part of the preceding statement. Newlines and
separators within character constants are an exception: they do not end statements.
It is an error to end any statement with end-of-file: the last character of any input file
should be a newline.
An empty statement is allowed, and may include whitespace. It is ignored.
A statement begins with zero or more labels, optionally followed by a key symbol which
determines what kind of statement it is. The key symbol determines the syntax of the rest
of the statement. If the symbol begins with a dot ‘.’ then the statement is an assembler
directive: typically valid for any computer. If the symbol begins with a letter the statement
is an assembly language instruction: it assembles into a machine language instruction.
Chapter 3: Syntax
27
Different versions of as for different computers recognize different instructions. In fact,
the same symbol may represent a different instruction in a different computer’s assembly
language.
A label is a symbol immediately followed by a colon (:). Whitespace before a label or
after a colon is permitted, but you may not have whitespace between a label’s symbol and
its colon. See Section 5.1 [Labels], page 37.
For HPPA targets, labels need not be immediately followed by a colon, but the definition
of a label must begin in column zero. This also implies that only one label may be defined
on each line.
label:
.directive
another_label:
instruction
followed by something
# This is an empty statement.
operand_1, operand_2, ...
3.6 Constants
A constant is a number, written so that its value is known by inspection, without knowing
any context. Like this:
.byte 74, 0112, 092, 0x4A, 0X4a, ’J, ’\J
.ascii "Ring the bell\7"
.octa 0x123456789abcdef0123456789ABCDEF0
.float 0f-314159265358979323846264338327\
95028841971.693993751E-40
# All the same value.
# A string constant.
# A bignum.
# - pi, a flonum.
3.6.1 Character Constants
There are two kinds of character constants. A character stands for one character in one
byte and its value may be used in numeric expressions. String constants (properly called
string literals) are potentially many bytes and their values may not be used in arithmetic
expressions.
3.6.1.1 Strings
A string is written between double-quotes. It may contain double-quotes or null characters.
The way to get special characters into a string is to escape these characters: precede them
with a backslash ‘\’ character. For example ‘\\’ represents one backslash: the first \ is
an escape which tells as to interpret the second character literally as a backslash (which
prevents as from recognizing the second \ as an escape character). The complete list of
escapes follows.
\b
Mnemonic for backspace; for ASCII this is octal code 010.
\f
Mnemonic for FormFeed; for ASCII this is octal code 014.
\n
Mnemonic for newline; for ASCII this is octal code 012.
\r
Mnemonic for carriage-Return; for ASCII this is octal code 015.
\t
Mnemonic for horizontal Tab; for ASCII this is octal code 011.
\ digit digit digit
An octal character code. The numeric code is 3 octal digits. For compatibility
with other Unix systems, 8 and 9 are accepted as digits: for example, \008 has
the value 010, and \009 the value 011.
28
Using as
\x hex-digits...
A hex character code. All trailing hex digits are combined. Either upper or
lower case x works.
\\
Represents one ‘\’ character.
\"
Represents one ‘"’ character. Needed in strings to represent this character,
because an unescaped ‘"’ would end the string.
\ anything-else
Any other character when escaped by \ gives a warning, but assembles as if the
‘\’ was not present. The idea is that if you used an escape sequence you clearly
didn’t want the literal interpretation of the following character. However as
has no other interpretation, so as knows it is giving you the wrong code and
warns you of the fact.
Which characters are escapable, and what those escapes represent, varies widely among
assemblers. The current set is what we think the BSD 4.2 assembler recognizes, and is
a subset of what most C compilers recognize. If you are in doubt, do not use an escape
sequence.
3.6.1.2 Characters
A single character may be written as a single quote immediately followed by that character.
The same escapes apply to characters as to strings. So if you want to write the character
backslash, you must write ’\\ where the first \ escapes the second \. As you can see, the
quote is an acute accent, not a grave accent. A newline immediately following an acute
accent is taken as a literal character and does not count as the end of a statement. The
value of a character constant in a numeric expression is the machine’s byte-wide code for
that character. as assumes your character code is ASCII: ’A means 65, ’B means 66, and
so on.
3.6.2 Number Constants
as distinguishes three kinds of numbers according to how they are stored in the target
machine. Integers are numbers that would fit into an int in the C language. Bignums are
integers, but they are stored in more than 32 bits. Flonums are floating point numbers,
described below.
3.6.2.1 Integers
A binary integer is ‘0b’ or ‘0B’ followed by zero or more of the binary digits ‘01’.
An octal integer is ‘0’ followed by zero or more of the octal digits (‘01234567’).
A decimal integer starts with a non-zero digit followed by zero or more digits
(‘0123456789’).
A hexadecimal integer is ‘0x’ or ‘0X’ followed by one or more hexadecimal digits chosen
from ‘0123456789abcdefABCDEF’.
Integers have the usual values. To denote a negative integer, use the prefix operator ‘-’
discussed under expressions (see Section 6.2.3 [Prefix Operators], page 41).
Chapter 3: Syntax
29
3.6.2.2 Bignums
A bignum has the same syntax and semantics as an integer except that the number (or its
negative) takes more than 32 bits to represent in binary. The distinction is made because
in some places integers are permitted while bignums are not.
3.6.2.3 Flonums
A flonum represents a floating point number. The translation is indirect: a decimal floating
point number from the text is converted by as to a generic binary floating point number
of more than sufficient precision. This generic floating point number is converted to a
particular computer’s floating point format (or formats) by a portion of as specialized to
that computer.
A flonum is written by writing (in order)
• The digit ‘0’. (‘0’ is optional on the HPPA.)
• A letter, to tell as the rest of the number is a flonum. e is recommended. Case is not
important.
On the H8/300, Renesas / SuperH SH, and AMD 29K architectures, the letter must
be one of the letters ‘DFPRSX’ (in upper or lower case).
On the ARC, the letter must be one of the letters ‘DFRS’ (in upper or lower case).
On the Intel 960 architecture, the letter must be one of the letters ‘DFT’ (in upper or
lower case).
On the HPPA architecture, the letter must be ‘E’ (upper case only).
• An optional sign: either ‘+’ or ‘-’.
• An optional integer part: zero or more decimal digits.
• An optional fractional part: ‘.’ followed by zero or more decimal digits.
• An optional exponent, consisting of:
• An ‘E’ or ‘e’.
• Optional sign: either ‘+’ or ‘-’.
• One or more decimal digits.
At least one of the integer part or the fractional part must be present. The floating point
number has the usual base-10 value.
as does all processing using integers. Flonums are computed independently of any
floating point hardware in the computer running as.
Chapter 4: Sections and Relocation
31
4 Sections and Relocation
4.1 Background
Roughly, a section is a range of addresses, with no gaps; all data “in” those addresses is
treated the same for some particular purpose. For example there may be a “read only”
section.
The linker ld reads many object files (partial programs) and combines their contents to
form a runnable program. When as emits an object file, the partial program is assumed to
start at address 0. ld assigns the final addresses for the partial program, so that different
partial programs do not overlap. This is actually an oversimplification, but it suffices to
explain how as uses sections.
ld moves blocks of bytes of your program to their run-time addresses. These blocks
slide to their run-time addresses as rigid units; their length does not change and neither
does the order of bytes within them. Such a rigid unit is called a section. Assigning runtime addresses to sections is called relocation. It includes the task of adjusting mentions of
object-file addresses so they refer to the proper run-time addresses. For the H8/300, and for
the Renesas / SuperH SH, as pads sections if needed to ensure they end on a word (sixteen
bit) boundary.
An object file written by as has at least three sections, any of which may be empty.
These are named text, data and bss sections.
When it generates COFF or ELF output, as can also generate whatever other named
sections you specify using the ‘.section’ directive (see Section 7.97 [.section], page 66).
If you do not use any directives that place output in the ‘.text’ or ‘.data’ sections, these
sections still exist, but are empty.
When as generates SOM or ELF output for the HPPA, as can also generate whatever other named sections you specify using the ‘.space’ and ‘.subspace’ directives. See
HP9000 Series 800 Assembly Language Reference Manual (HP 92432-90001) for details on
the ‘.space’ and ‘.subspace’ assembler directives.
Additionally, as uses different names for the standard text, data, and bss sections
when generating SOM output. Program text is placed into the ‘$CODE$’ section, data
into ‘$DATA$’, and BSS into ‘$BSS$’.
Within the object file, the text section starts at address 0, the data section follows, and
the bss section follows the data section.
When generating either SOM or ELF output files on the HPPA, the text section starts
at address 0, the data section at address 0x4000000, and the bss section follows the data
section.
To let ld know which data changes when the sections are relocated, and how to change
that data, as also writes to the object file details of the relocation needed. To perform
relocation ld must know, each time an address in the object file is mentioned:
• Where in the object file is the beginning of this reference to an address?
• How long (in bytes) is this reference?
• Which section does the address refer to? What is the numeric value of
(address) − (start-address of section)?
32
Using as
• Is the reference to an address “Program-Counter relative”?
In fact, every address as ever uses is expressed as
(section) + (offset into section)
Further, most expressions as computes have this section-relative nature. (For some object
formats, such as SOM for the HPPA, some expressions are symbol-relative instead.)
In this manual we use the notation {secname N } to mean “offset N into section secname.”
Apart from text, data and bss sections you need to know about the absolute section.
When ld mixes partial programs, addresses in the absolute section remain unchanged. For
example, address {absolute 0} is “relocated” to run-time address 0 by ld. Although the
linker never arranges two partial programs’ data sections with overlapping addresses after
linking, by definition their absolute sections must overlap. Address {absolute 239} in
one part of a program is always the same address when the program is running as address
{absolute 239} in any other part of the program.
The idea of sections is extended to the undefined section. Any address whose section is
unknown at assembly time is by definition rendered {undefined U }—where U is filled in
later. Since numbers are always defined, the only way to generate an undefined address is
to mention an undefined symbol. A reference to a named common block would be such a
symbol: its value is unknown at assembly time so it has section undefined.
By analogy the word section is used to describe groups of sections in the linked program.
ld puts all partial programs’ text sections in contiguous addresses in the linked program.
It is customary to refer to the text section of a program, meaning all the addresses of all
partial programs’ text sections. Likewise for data and bss sections.
Some sections are manipulated by ld; others are invented for use of as and have no
meaning except during assembly.
4.2 Linker Sections
ld deals with just four kinds of sections, summarized below.
named sections
text section
data section
These sections hold your program. as and ld treat them as separate but equal
sections. Anything you can say of one section is true of another. When the program is running, however, it is customary for the text section to be unalterable.
The text section is often shared among processes: it contains instructions, constants and the like. The data section of a running program is usually alterable:
for example, C variables would be stored in the data section.
bss section
This section contains zeroed bytes when your program begins running. It is
used to hold uninitialized variables or common storage. The length of each
partial program’s bss section is important, but because it starts out containing
zeroed bytes there is no need to store explicit zero bytes in the object file. The
bss section was invented to eliminate those explicit zeros from object files.
Chapter 4: Sections and Relocation
33
absolute section
Address 0 of this section is always “relocated” to runtime address 0. This
is useful if you want to refer to an address that ld must not change when
relocating. In this sense we speak of absolute addresses being “unrelocatable”:
they do not change during relocation.
undefined section
This “section” is a catch-all for address references to objects not in the preceding
sections.
An idealized example of three relocatable sections follows. The example uses the traditional section names ‘.text’ and ‘.data’. Memory addresses are on the horizontal axis.
Partial program #1:
text
data
ttttt
dddd
bss
00
Partial program #2:
text data
bss
TTT
DDDD
000
linked program:
text
TTT
ttttt
data
dddd
DDDD
bss
00000
...
addresses:
0. . .
4.3 Assembler Internal Sections
These sections are meant only for the internal use of as. They have no meaning at run-time.
You do not really need to know about these sections for most purposes; but they can be
mentioned in as warning messages, so it might be helpful to have an idea of their meanings
to as. These sections are used to permit the value of every expression in your assembly
language program to be a section-relative address.
ASSEMBLER-INTERNAL-LOGIC-ERROR!
An internal assembler logic error has been found. This means there is a bug in
the assembler.
expr section
The assembler stores complex expression internally as combinations of symbols.
When it needs to represent an expression as a symbol, it puts it in the expr
section.
4.4 Sub-Sections
Assembled bytes conventionally fall into two sections: text and data. You may have separate
groups of data in named sections that you want to end up near to each other in the object
file, even though they are not contiguous in the assembler source. as allows you to use
subsections for this purpose. Within each section, there can be numbered subsections with
values from 0 to 8192. Objects assembled into the same subsection go into the object file
34
Using as
together with other objects in the same subsection. For example, a compiler might want
to store constants in the text section, but might not want to have them interspersed with
the program being assembled. In this case, the compiler could issue a ‘.text 0’ before each
section of code being output, and a ‘.text 1’ before each group of constants being output.
Subsections are optional. If you do not use subsections, everything goes in subsection
number zero.
Each subsection is zero-padded up to a multiple of four bytes. (Subsections may be
padded a different amount on different flavors of as.)
Subsections appear in your object file in numeric order, lowest numbered to highest.
(All this to be compatible with other people’s assemblers.) The object file contains no
representation of subsections; ld and other programs that manipulate object files see no
trace of them. They just see all your text subsections as a text section, and all your data
subsections as a data section.
To specify which subsection you want subsequent statements assembled into, use a numeric argument to specify it, in a ‘.text expression ’ or a ‘.data expression ’ statement.
When generating COFF output, you can also use an extra subsection argument with arbitrary named sections: ‘.section name , expression ’. When generating ELF output, you
can also use the .subsection directive (see Section 7.108 [SubSection], page 71) to specify
a subsection: ‘.subsection expression ’. Expression should be an absolute expression
(see Chapter 6 [Expressions], page 41). If you just say ‘.text’ then ‘.text 0’ is assumed.
Likewise ‘.data’ means ‘.data 0’. Assembly begins in text 0. For instance:
.text 0
# The default subsection is text 0 anyway.
.ascii "This lives in the first text subsection. *"
.text 1
.ascii "But this lives in the second text subsection."
.data 0
.ascii "This lives in the data section,"
.ascii "in the first data subsection."
.text 0
.ascii "This lives in the first text section,"
.ascii "immediately following the asterisk (*)."
Each section has a location counter incremented by one for every byte assembled into
that section. Because subsections are merely a convenience restricted to as there is no
concept of a subsection location counter. There is no way to directly manipulate a location
counter—but the .align directive changes it, and any label definition captures its current
value. The location counter of the section where statements are being assembled is said to
be the active location counter.
4.5 bss Section
The bss section is used for local common variable storage. You may allocate address space in
the bss section, but you may not dictate data to load into it before your program executes.
When your program starts running, all the contents of the bss section are zeroed bytes.
The .lcomm pseudo-op defines a symbol in the bss section; see Section 7.67 [.lcomm],
page 57.
The .comm pseudo-op may be used to declare a common symbol, which is another form
of uninitialized symbol; see Section 7.30 [.comm], page 49.
Chapter 4: Sections and Relocation
35
When assembling for a target which supports multiple sections, such as ELF or COFF,
you may switch into the .bss section and define symbols as usual; see Section 7.97
[.section], page 66. You may only assemble zero values into the section. Typically
the section will only contain symbol definitions and .skip directives (see Section 7.102
[.skip], page 69).
Chapter 5: Symbols
37
5 Symbols
Symbols are a central concept: the programmer uses symbols to name things, the linker
uses symbols to link, and the debugger uses symbols to debug.
Warning: as does not place symbols in the object file in the same order they
were declared. This may break some debuggers.
5.1 Labels
A label is written as a symbol immediately followed by a colon ‘:’. The symbol then
represents the current value of the active location counter, and is, for example, a suitable
instruction operand. You are warned if you use the same symbol to represent two different
locations: the first definition overrides any other definitions.
On the HPPA, the usual form for a label need not be immediately followed by a colon,
but instead must start in column zero. Only one label may be defined on a single line.
To work around this, the HPPA version of as also provides a special directive .label for
defining labels more flexibly.
5.2 Giving Symbols Other Values
A symbol can be given an arbitrary value by writing a symbol, followed by an equals sign
‘=’, followed by an expression (see Chapter 6 [Expressions], page 41). This is equivalent to
using the .set directive. See Section 7.98 [.set], page 69. In the same way, using a double
equals sign ‘=’‘=’ here represents an equivalent of the .eqv directive. See Section 7.45 [.eqv],
page 51.
Blackfin does not support symbol assignment with ‘=’.
5.3 Symbol Names
Symbol names begin with a letter or with one of ‘._’. On most machines, you can also use
$ in symbol names; exceptions are noted in Chapter 9 [Machine Dependencies], page 79.
That character may be followed by any string of digits, letters, dollar signs (unless otherwise
noted for a particular target machine), and underscores.
Case of letters is significant: foo is a different symbol name than Foo.
Each symbol has exactly one name. Each name in an assembly language program refers
to exactly one symbol. You may use that symbol name any number of times in a program.
Local Symbol Names
A local symbol is any symbol beginning with certain local label prefixes. By default, the
local label prefix is ‘.L’ for ELF systems or ‘L’ for traditional a.out systems, but each target
may have its own set of local label prefixes. On the HPPA local symbols begin with ‘L$’.
Local symbols are defined and used within the assembler, but they are normally not
saved in object files. Thus, they are not visible when debugging. You may use the ‘-L’
option (see Section 2.7 [Include Local Symbols: ‘-L’], page 20) to retain the local symbols
in the object files.
38
Using as
Local Labels
Local labels help compilers and programmers use names temporarily. They create symbols
which are guaranteed to be unique over the entire scope of the input source code and which
can be referred to by a simple notation. To define a local label, write a label of the form ‘N:’
(where N represents any positive integer). To refer to the most recent previous definition
of that label write ‘Nb’, using the same number as when you defined the label. To refer to
the next definition of a local label, write ‘Nf’—the ‘b’ stands for “backwards” and the ‘f’
stands for “forwards”.
There is no restriction on how you can use these labels, and you can reuse them too. So
that it is possible to repeatedly define the same local label (using the same number ‘N’),
although you can only refer to the most recently defined local label of that number (for a
backwards reference) or the next definition of a specific local label for a forward reference.
It is also worth noting that the first 10 local labels (‘0:’. . . ‘9:’) are implemented in a slightly
more efficient manner than the others.
Here is an example:
1:
2:
1:
2:
branch
branch
branch
branch
1f
1b
2f
1b
Which is the equivalent of:
label_1:
label_2:
label_3:
label_4:
branch
branch
branch
branch
label_3
label_1
label_4
label_3
Local label names are only a notational device. They are immediately transformed into
more conventional symbol names before the assembler uses them. The symbol names are
stored in the symbol table, appear in error messages, and are optionally emitted to the
object file. The names are constructed using these parts:
local label prefix
All local symbols begin with the system-specific local label prefix. Normally
both as and ld forget symbols that start with the local label prefix. These
labels are used for symbols you are never intended to see. If you use the ‘-L’
option then as retains these symbols in the object file. If you also instruct ld
to retain these symbols, you may use them in debugging.
number
This is the number that was used in the local label definition. So if the label is
written ‘55:’ then the number is ‘55’.
C-B
This unusual character is included so you do not accidentally invent a symbol
of the same name. The character has ASCII value of ‘\002’ (control-B).
ordinal number
This is a serial number to keep the labels distinct. The first definition of ‘0:’
gets the number ‘1’. The 15th definition of ‘0:’ gets the number ‘15’, and so on.
Likewise the first definition of ‘1:’ gets the number ‘1’ and its 15th definition
gets ‘15’ as well.
So for example, the first 1: may be named .L1C-B1, and the 44th 3: may be named
.L3C-B44.
Chapter 5: Symbols
39
Dollar Local Labels
as also supports an even more local form of local labels called dollar labels. These labels
go out of scope (i.e., they become undefined) as soon as a non-local label is defined. Thus
they remain valid for only a small region of the input source code. Normal local labels, by
contrast, remain in scope for the entire file, or until they are redefined by another occurrence
of the same local label.
Dollar labels are defined in exactly the same way as ordinary local labels, except that
they have a dollar sign suffix to their numeric value, e.g., ‘55$:’.
They can also be distinguished from ordinary local labels by their transformed names
which use ASCII character ‘\001’ (control-A) as the magic character to distinguish them
from ordinary labels. For example, the fifth definition of ‘6$’ may be named ‘.L6C-A5’.
5.4 The Special Dot Symbol
The special symbol ‘.’ refers to the current address that as is assembling into. Thus, the
expression ‘melvin: .long .’ defines melvin to contain its own address. Assigning a value
to . is treated the same as a .org directive. Thus, the expression ‘.=.+4’ is the same as
saying ‘.space 4’.
5.5 Symbol Attributes
Every symbol has, as well as its name, the attributes “Value” and “Type”. Depending on
output format, symbols can also have auxiliary attributes.
If you use a symbol without defining it, as assumes zero for all these attributes, and
probably won’t warn you. This makes the symbol an externally defined symbol, which is
generally what you would want.
5.5.1 Value
The value of a symbol is (usually) 32 bits. For a symbol which labels a location in the
text, data, bss or absolute sections the value is the number of addresses from the start of
that section to the label. Naturally for text, data and bss sections the value of a symbol
changes as ld changes section base addresses during linking. Absolute symbols’ values do
not change during linking: that is why they are called absolute.
The value of an undefined symbol is treated in a special way. If it is 0 then the symbol
is not defined in this assembler source file, and ld tries to determine its value from other
files linked into the same program. You make this kind of symbol simply by mentioning a
symbol name without defining it. A non-zero value represents a .comm common declaration.
The value is how much common storage to reserve, in bytes (addresses). The symbol refers
to the first address of the allocated storage.
5.5.2 Type
The type attribute of a symbol contains relocation (section) information, any flag settings
indicating that a symbol is external, and (optionally), other information for linkers and
debuggers. The exact format depends on the object-code output format in use.
5.5.3 Symbol Attributes: a.out
40
Using as
5.5.3.1 Descriptor
This is an arbitrary 16-bit value. You may establish a symbol’s descriptor value by using a
.desc statement (see Section 7.33 [.desc], page 50). A descriptor value means nothing to
as.
5.5.3.2 Other
This is an arbitrary 8-bit value. It means nothing to as.
5.5.4 Symbol Attributes for COFF
The COFF format supports a multitude of auxiliary symbol attributes; like the primary
symbol attributes, they are set between .def and .endef directives.
5.5.4.1 Primary Attributes
The symbol name is set with .def; the value and type, respectively, with .val and .type.
5.5.4.2 Auxiliary Attributes
The as directives .dim, .line, .scl, .size, .tag, and .weak can generate auxiliary symbol
table information for COFF.
5.5.5 Symbol Attributes for SOM
The SOM format for the HPPA supports a multitude of symbol attributes set with the
.EXPORT and .IMPORT directives.
The attributes are described in HP9000 Series 800 Assembly Language Reference Manual
(HP 92432-90001) under the IMPORT and EXPORT assembler directive documentation.
Chapter 6: Expressions
41
6 Expressions
An expression specifies an address or numeric value. Whitespace may precede and/or follow
an expression.
The result of an expression must be an absolute number, or else an offset into a particular
section. If an expression is not absolute, and there is not enough information when as sees
the expression to know its section, a second pass over the source program might be necessary
to interpret the expression—but the second pass is currently not implemented. as aborts
with an error message in this situation.
6.1 Empty Expressions
An empty expression has no value: it is just whitespace or null. Wherever an absolute
expression is required, you may omit the expression, and as assumes a value of (absolute)
0. This is compatible with other assemblers.
6.2 Integer Expressions
An integer expression is one or more arguments delimited by operators.
6.2.1 Arguments
Arguments are symbols, numbers or subexpressions. In other contexts arguments are sometimes called “arithmetic operands”. In this manual, to avoid confusing them with the
“instruction operands” of the machine language, we use the term “argument” to refer to
parts of expressions only, reserving the word “operand” to refer only to machine instruction
operands.
Symbols are evaluated to yield {section NNN } where section is one of text, data, bss,
absolute, or undefined. NNN is a signed, 2’s complement 32 bit integer.
Numbers are usually integers.
A number can be a flonum or bignum. In this case, you are warned that only the low
order 32 bits are used, and as pretends these 32 bits are an integer. You may write integermanipulating instructions that act on exotic constants, compatible with other assemblers.
Subexpressions are a left parenthesis ‘(’ followed by an integer expression, followed by a
right parenthesis ‘)’; or a prefix operator followed by an argument.
6.2.2 Operators
Operators are arithmetic functions, like + or %. Prefix operators are followed by an argument. Infix operators appear between their arguments. Operators may be preceded and/or
followed by whitespace.
6.2.3 Prefix Operator
as has the following prefix operators. They each take one argument, which must be absolute.
-
Negation. Two’s complement negation.
~
Complementation. Bitwise not.
42
Using as
6.2.4 Infix Operators
Infix operators take two arguments, one on either side. Operators have precedence, but
operations with equal precedence are performed left to right. Apart from + or ‘-’, both
arguments must be absolute, and the result is absolute.
1. Highest Precedence
*
Multiplication.
/
Division. Truncation is the same as the C operator ‘/’
%
Remainder.
<<
Shift Left. Same as the C operator ‘<<’.
>>
Shift Right. Same as the C operator ‘>>’.
2. Intermediate precedence
|
Bitwise Inclusive Or.
&
Bitwise And.
^
Bitwise Exclusive Or.
!
Bitwise Or Not.
3. Low Precedence
+
Addition. If either argument is absolute, the result has the section of
the other argument. You may not add together arguments from different
sections.
-
Subtraction. If the right argument is absolute, the result has the section
of the left argument. If both arguments are in the same section, the result
is absolute. You may not subtract arguments from different sections.
==
Is Equal To
<>
!=
Is Not Equal To
<
Is Less Than
>
Is Greater Than
>=
Is Greater Than Or Equal To
<=
Is Less Than Or Equal To
The comparison operators can be used as infix operators. A true results has
a value of -1 whereas a false result has a value of 0. Note, these operators
perform signed comparisons.
4. Lowest Precedence
&&
Logical And.
Chapter 6: Expressions
||
43
Logical Or.
These two logical operations can be used to combine the results of sub
expressions. Note, unlike the comparison operators a true result returns a
value of 1 but a false results does still return 0. Also note that the logical
or operator has a slightly lower precedence than logical and.
In short, it’s only meaningful to add or subtract the offsets in an address; you can only
have a defined section in one of the two arguments.
Chapter 7: Assembler Directives
45
7 Assembler Directives
All assembler directives have names that begin with a period (‘.’). The rest of the name is
letters, usually in lower case.
This chapter discusses directives that are available regardless of the target machine
configuration for the gnu assembler. Some machine configurations provide additional directives. See Chapter 9 [Machine Dependencies], page 79.
7.1 .abort
This directive stops the assembly immediately. It is for compatibility with other assemblers.
The original idea was that the assembly language source would be piped into the assembler.
If the sender of the source quit, it could use this directive tells as to quit also. One day
.abort will not be supported.
7.2 .ABORT (COFF)
When producing COFF output, as accepts this directive as a synonym for ‘.abort’.
7.3 .align abs-expr , abs-expr , abs-expr
Pad the location counter (in the current subsection) to a particular storage boundary. The
first expression (which must be absolute) is the alignment required, as described below.
The second expression (also absolute) gives the fill value to be stored in the padding
bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally
zero. However, on some systems, if the section is marked as containing code and the fill
value is omitted, the space is filled with no-op instructions.
The third expression is also absolute, and is also optional. If it is present, it is the
maximum number of bytes that should be skipped by this alignment directive. If doing
the alignment would require skipping more bytes than the specified maximum, then the
alignment is not done at all. You can omit the fill value (the second argument) entirely by
simply using two commas after the required alignment; this can be useful if you want the
alignment to be filled with no-op instructions when appropriate.
The way the required alignment is specified varies from system to system. For the arc,
hppa, i386 using ELF, i860, iq2000, m68k, or32, s390, sparc, tic4x, tic80 and xtensa, the
first expression is the alignment request in bytes. For example ‘.align 8’ advances the
location counter until it is a multiple of 8. If the location counter is already a multiple of 8,
no change is needed. For the tic54x, the first expression is the alignment request in words.
For other systems, including ppc, i386 using a.out format, arm and strongarm, it is
the number of low-order zero bits the location counter must have after advancement. For
example ‘.align 3’ advances the location counter until it a multiple of 8. If the location
counter is already a multiple of 8, no change is needed.
This inconsistency is due to the different behaviors of the various native assemblers
for these systems which GAS must emulate. GAS also provides .balign and .p2align
directives, described later, which have a consistent behavior across all architectures (but
are specific to GAS).
46
Using as
7.4 .altmacro
Enable alternate macro mode, enabling:
LOCAL name [ , ... ]
One additional directive, LOCAL, is available. It is used to generate a string
replacement for each of the name arguments, and replace any instances of name
in each macro expansion. The replacement string is unique in the assembly, and
different for each separate macro expansion. LOCAL allows you to write macros
that define symbols, without fear of conflict between separate macro expansions.
String delimiters
You can write strings delimited in these other ways besides "string ":
’string ’ You can delimit strings with single-quote characters.
You can delimit strings with matching angle brackets.
single-character string escape
To include any single character literally in a string (even if the character would
otherwise have some special meaning), you can prefix the character with ‘!’ (an
exclamation mark). For example, you can write ‘<4.3 !> 5.4!!>’ to get the
literal text ‘4.3 > 5.4!’.
Expression results as strings
You can write ‘%expr ’ to evaluate the expression expr and use the result as a
string.
7.5 .ascii "string ". . .
.ascii expects zero or more string literals (see Section 3.6.1.1 [Strings], page 27) separated
by commas. It assembles each string (with no automatic trailing zero byte) into consecutive
addresses.
7.6 .asciz "string ". . .
.asciz is just like .ascii, but each string is followed by a zero byte. The “z” in ‘.asciz’
stands for “zero”.
7.7 .balign[wl] abs-expr , abs-expr , abs-expr
Pad the location counter (in the current subsection) to a particular storage boundary. The
first expression (which must be absolute) is the alignment request in bytes. For example
‘.balign 8’ advances the location counter until it is a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
The second expression (also absolute) gives the fill value to be stored in the padding
bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally
zero. However, on some systems, if the section is marked as containing code and the fill
value is omitted, the space is filled with no-op instructions.
The third expression is also absolute, and is also optional. If it is present, it is the
maximum number of bytes that should be skipped by this alignment directive. If doing
the alignment would require skipping more bytes than the specified maximum, then the
Chapter 7: Assembler Directives
47
alignment is not done at all. You can omit the fill value (the second argument) entirely by
simply using two commas after the required alignment; this can be useful if you want the
alignment to be filled with no-op instructions when appropriate.
The .balignw and .balignl directives are variants of the .balign directive. The
.balignw directive treats the fill pattern as a two byte word value. The .balignl directives
treats the fill pattern as a four byte longword value. For example, .balignw 4,0x368d will
align to a multiple of 4. If it skips two bytes, they will be filled in with the value 0x368d
(the exact placement of the bytes depends upon the endianness of the processor). If it skips
1 or 3 bytes, the fill value is undefined.
7.8 .byte expressions
.byte expects zero or more expressions, separated by commas. Each expression is assembled
into the next byte.
7.9 .cfi_sections section_list
.cfi_sections may be used to specify whether CFI directives should emit .eh_frame
section and/or .debug_frame section. If section list is .eh_frame, .eh_frame is emitted,
if section list is .debug_frame, .debug_frame is emitted. To emit both use .eh_frame,
.debug_frame. The default if this directive is not used is .cfi_sections .eh_frame.
7.10 .cfi_startproc [simple]
.cfi_startproc is used at the beginning of each function that should have an entry in
.eh_frame. It initializes some internal data structures. Don’t forget to close the function
by .cfi_endproc.
Unless .cfi_startproc is used along with parameter simple it also emits some architecture dependent initial CFI instructions.
7.11 .cfi_endproc
.cfi_endproc is used at the end of a function where it closes its unwind entry previously
opened by .cfi_startproc, and emits it to .eh_frame.
7.12 .cfi_personality encoding [, exp ]
.cfi_personality defines personality routine and its encoding. encoding must be a constant determining how the personality should be encoded. If it is 255 (DW_EH_PE_omit),
second argument is not present, otherwise second argument should be a constant or a symbol name. When using indirect encodings, the symbol provided should be the location
where personality can be loaded from, not the personality routine itself. The default after
.cfi_startproc is .cfi_personality 0xff, no personality routine.
7.13 .cfi_lsda encoding [, exp ]
.cfi_lsda defines LSDA and its encoding. encoding must be a constant determining how
the LSDA should be encoded. If it is 255 (DW_EH_PE_omit), second argument is not present,
otherwise second argument should be a constant or a symbol name. The default after .cfi_
startproc is .cfi_lsda 0xff, no LSDA.
48
Using as
7.14 .cfi_def_cfa register , offset
.cfi_def_cfa defines a rule for computing CFA as: take address from register and add
offset to it.
7.15 .cfi_def_cfa_register register
.cfi_def_cfa_register modifies a rule for computing CFA. From now on register will be
used instead of the old one. Offset remains the same.
7.16 .cfi_def_cfa_offset offset
.cfi_def_cfa_offset modifies a rule for computing CFA. Register remains the same, but
offset is new. Note that it is the absolute offset that will be added to a defined register to
compute CFA address.
7.17 .cfi_adjust_cfa_offset offset
Same as .cfi_def_cfa_offset but offset is a relative value that is added/substracted from
the previous offset.
7.18 .cfi_offset register , offset
Previous value of register is saved at offset offset from CFA.
7.19 .cfi_rel_offset register , offset
Previous value of register is saved at offset offset from the current CFA register. This is
transformed to .cfi_offset using the known displacement of the CFA register from the
CFA. This is often easier to use, because the number will match the code it’s annotating.
7.20 .cfi_register register1 , register2
Previous value of register1 is saved in register register2.
7.21 .cfi_restore register
.cfi_restore says that the rule for register is now the same as it was at the beginning of
the function, after all initial instruction added by .cfi_startproc were executed.
7.22 .cfi_undefined register
From now on the previous value of register can’t be restored anymore.
7.23 .cfi_same_value register
Current value of register is the same like in the previous frame, i.e. no restoration needed.
7.24 .cfi_remember_state,
First save all current rules for all registers by .cfi_remember_state, then totally screw
them up by subsequent .cfi_* directives and when everything is hopelessly bad, use .cfi_
restore_state to restore the previous saved state.
Chapter 7: Assembler Directives
49
7.25 .cfi_return_column register
Change return column register, i.e. the return address is either directly in register or can
be accessed by rules for register.
7.26 .cfi_signal_frame
Mark current function as signal trampoline.
7.27 .cfi_window_save
SPARC register window has been saved.
7.28 .cfi_escape expression[, . . . ]
Allows the user to add arbitrary bytes to the unwind info. One might use this to add
OS-specific CFI opcodes, or generic CFI opcodes that GAS does not yet support.
7.29 .cfi_val_encoded_addr register , encoding , label
The current value of register is label. The value of label will be encoded in the output
file according to encoding; see the description of .cfi_personality for details on this
encoding.
The usefulness of equating a register to a fixed label is probably limited to the return
address register. Here, it can be useful to mark a code segment that has only one return
address which is reached by a direct branch and no copy of the return address exists in
memory or another register.
7.30 .comm symbol , length
.comm declares a common symbol named symbol. When linking, a common symbol in
one object file may be merged with a defined or common symbol of the same name in
another object file. If ld does not see a definition for the symbol–just one or more common
symbols–then it will allocate length bytes of uninitialized memory. length must be an
absolute expression. If ld sees multiple common symbols with the same name, and they do
not all have the same size, it will allocate space using the largest size.
When using ELF or (as a GNU extension) PE, the .comm directive takes an optional
third argument. This is the desired alignment of the symbol, specified for ELF as a byte
boundary (for example, an alignment of 16 means that the least significant 4 bits of the
address should be zero), and for PE as a power of two (for example, an alignment of 5
means aligned to a 32-byte boundary). The alignment must be an absolute expression, and
it must be a power of two. If ld allocates uninitialized memory for the common symbol, it
will use the alignment when placing the symbol. If no alignment is specified, as will set the
alignment to the largest power of two less than or equal to the size of the symbol, up to a
maximum of 16 on ELF, or the default section alignment of 4 on PE1 .
1
This is not the same as the executable image file alignment controlled by ld’s ‘--section-alignment’
option; image file sections in PE are aligned to multiples of 4096, which is far too large an alignment for
ordinary variables. It is rather the default alignment for (non-debug) sections within object (‘*.o’) files,
which are less strictly aligned.
50
Using as
The syntax for .comm differs slightly on the HPPA. The syntax is ‘symbol .comm,
length ’; symbol is optional.
7.31 .data subsection
.data tells as to assemble the following statements onto the end of the data subsection
numbered subsection (which is an absolute expression). If subsection is omitted, it defaults
to zero.
7.32 .def name
Begin defining debugging information for a symbol name; the definition extends until the
.endef directive is encountered.
7.33 .desc symbol , abs-expression
This directive sets the descriptor of the symbol (see Section 5.5 [Symbol Attributes], page 39)
to the low 16 bits of an absolute expression.
The ‘.desc’ directive is not available when as is configured for COFF output; it is only
for a.out or b.out object format. For the sake of compatibility, as accepts it, but produces
no output, when configured for COFF.
7.34 .dim
This directive is generated by compilers to include auxiliary debugging information in the
symbol table. It is only permitted inside .def/.endef pairs.
7.35 .double flonums
.double expects zero or more flonums, separated by commas. It assembles floating point
numbers. The exact kind of floating point numbers emitted depends on how as is configured.
See Chapter 9 [Machine Dependencies], page 79.
7.36 .eject
Force a page break at this point, when generating assembly listings.
7.37 .else
.else is part of the as support for conditional assembly; see Section 7.60 [.if], page 54. It
marks the beginning of a section of code to be assembled if the condition for the preceding
.if was false.
7.38 .elseif
.elseif is part of the as support for conditional assembly; see Section 7.60 [.if], page 54.
It is shorthand for beginning a new .if block that would otherwise fill the entire .else
section.
Chapter 7: Assembler Directives
51
7.39 .end
.end marks the end of the assembly file. as does not process anything in the file past the
.end directive.
7.40 .endef
This directive flags the end of a symbol definition begun with .def.
7.41 .endfunc
.endfunc marks the end of a function specified with .func.
7.42 .endif
.endif is part of the as support for conditional assembly; it marks the end of a block of
code that is only assembled conditionally. See Section 7.60 [.if], page 54.
7.43 .equ symbol , expression
This directive sets the value of symbol to expression. It is synonymous with ‘.set’; see
Section 7.98 [.set], page 69.
The syntax for equ on the HPPA is ‘symbol .equ expression ’.
The syntax for equ on the Z80 is ‘symbol equ expression ’. On the Z80 it is an eror if
symbol is already defined, but the symbol is not protected from later redefinition. Compare
Section 7.44 [Equiv], page 51.
7.44 .equiv symbol , expression
The .equiv directive is like .equ and .set, except that the assembler will signal an error
if symbol is already defined. Note a symbol which has been referenced but not actually
defined is considered to be undefined.
Except for the contents of the error message, this is roughly equivalent to
.ifdef SYM
.err
.endif
.equ SYM,VAL
plus it protects the symbol from later redefinition.
7.45 .eqv symbol , expression
The .eqv directive is like .equiv, but no attempt is made to evaluate the expression or any
part of it immediately. Instead each time the resulting symbol is used in an expression, a
snapshot of its current value is taken.
7.46 .err
If as assembles a .err directive, it will print an error message and, unless the ‘-Z’ option was
used, it will not generate an object file. This can be used to signal an error in conditionally
compiled code.
52
Using as
7.47 .error "string "
Similarly to .err, this directive emits an error, but you can specify a string that will be emitted as the error message. If you don’t specify the message, it defaults to ".error directive
invoked in source file". See Section 1.7 [Error and Warning Messages], page 17.
.error "This code has not been assembled and tested."
7.48 .exitm
Exit early from the current macro definition. See Section 7.77 [Macro], page 59.
7.49 .extern
.extern is accepted in the source program—for compatibility with other assemblers—but
it is ignored. as treats all undefined symbols as external.
7.50 .fail expression
Generates an error or a warning. If the value of the expression is 500 or more, as will print a
warning message. If the value is less than 500, as will print an error message. The message
will include the value of expression. This can occasionally be useful inside complex nested
macros or conditional assembly.
7.51 .file
There are two different versions of the .file directive. Targets that support DWARF2
line number information use the DWARF2 version of .file. Other targets use the default
version.
Default Version
This version of the .file directive tells as that we are about to start a new logical file.
The syntax is:
.file string
string is the new file name. In general, the filename is recognized whether or not it is
surrounded by quotes ‘"’; but if you wish to specify an empty file name, you must give the
quotes–"". This statement may go away in future: it is only recognized to be compatible
with old as programs.
DWARF2 Version
When emitting DWARF2 line number information, .file assigns filenames to the .debug_
line file name table. The syntax is:
.file fileno filename
The fileno operand should be a unique positive integer to use as the index of the entry
in the table. The filename operand is a C string literal.
The detail of filename indices is exposed to the user because the filename table is shared
with the .debug_info section of the DWARF2 debugging information, and thus the user
must know the exact indices that table entries will have.
Chapter 7: Assembler Directives
53
7.52 .fill repeat , size , value
repeat, size and value are absolute expressions. This emits repeat copies of size bytes.
Repeat may be zero or more. Size may be zero or more, but if it is more than 8, then it
is deemed to have the value 8, compatible with other people’s assemblers. The contents of
each repeat bytes is taken from an 8-byte number. The highest order 4 bytes are zero. The
lowest order 4 bytes are value rendered in the byte-order of an integer on the computer as
is assembling for. Each size bytes in a repetition is taken from the lowest order size bytes
of this number. Again, this bizarre behavior is compatible with other people’s assemblers.
size and value are optional. If the second comma and value are absent, value is assumed
zero. If the first comma and following tokens are absent, size is assumed to be 1.
7.53 .float flonums
This directive assembles zero or more flonums, separated by commas. It has the same
effect as .single. The exact kind of floating point numbers emitted depends on how as is
configured. See Chapter 9 [Machine Dependencies], page 79.
7.54 .func name [,label ]
.func emits debugging information to denote function name, and is ignored unless the file
is assembled with debugging enabled. Only ‘--gstabs[+]’ is currently supported. label is
the entry point of the function and if omitted name prepended with the ‘leading char’
is used. ‘leading char’ is usually _ or nothing, depending on the target. All functions
are currently defined to have void return type. The function must be terminated with
.endfunc.
7.55 .global symbol , .globl symbol
.global makes the symbol visible to ld. If you define symbol in your partial program, its
value is made available to other partial programs that are linked with it. Otherwise, symbol
takes its attributes from a symbol of the same name from another file linked into the same
program.
Both spellings (‘.globl’ and ‘.global’) are accepted, for compatibility with other assemblers.
On the HPPA, .global is not always enough to make it accessible to other partial
programs. You may need the HPPA-only .EXPORT directive as well. See Section 9.11.5
[HPPA Assembler Directives], page 132.
7.56 .gnu_attribute tag ,value
Record a gnu object attribute for this file. See Chapter 8 [Object Attributes], page 77.
7.57 .hidden names
This is one of the ELF visibility directives. The other two are .internal (see Section 7.64
[.internal], page 56) and .protected (see Section 7.88 [.protected], page 64).
This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to hidden which means that
54
Using as
the symbols are not visible to other components. Such symbols are always considered to be
protected as well.
7.58 .hword expressions
This expects zero or more expressions, and emits a 16 bit number for each.
This directive is a synonym for ‘.short’; depending on the target architecture, it may
also be a synonym for ‘.word’.
7.59 .ident
This directive is used by some assemblers to place tags in object files. The behavior of
this directive varies depending on the target. When using the a.out object file format, as
simply accepts the directive for source-file compatibility with existing assemblers, but does
not emit anything for it. When using COFF, comments are emitted to the .comment or
.rdata section, depending on the target. When using ELF, comments are emitted to the
.comment section.
7.60 .if absolute expression
.if marks the beginning of a section of code which is only considered part of the source
program being assembled if the argument (which must be an absolute expression) is nonzero. The end of the conditional section of code must be marked by .endif (see Section 7.42
[.endif], page 51); optionally, you may include code for the alternative condition, flagged by
.else (see Section 7.37 [.else], page 50). If you have several conditions to check, .elseif
may be used to avoid nesting blocks if/else within each subsequent .else block.
The following variants of .if are also supported:
.ifdef symbol
Assembles the following section of code if the specified symbol has been defined.
Note a symbol which has been referenced but not yet defined is considered to
be undefined.
.ifb text
Assembles the following section of code if the operand is blank (empty).
.ifc string1 ,string2
Assembles the following section of code if the two strings are the same. The
strings may be optionally quoted with single quotes. If they are not quoted,
the first string stops at the first comma, and the second string stops at the end
of the line. Strings which contain whitespace should be quoted. The string
comparison is case sensitive.
.ifeq absolute expression
Assembles the following section of code if the argument is zero.
.ifeqs string1 ,string2
Another form of .ifc. The strings must be quoted using double quotes.
.ifge absolute expression
Assembles the following section of code if the argument is greater than or equal
to zero.
Chapter 7: Assembler Directives
55
.ifgt absolute expression
Assembles the following section of code if the argument is greater than zero.
.ifle absolute expression
Assembles the following section of code if the argument is less than or equal to
zero.
.iflt absolute expression
Assembles the following section of code if the argument is less than zero.
.ifnb text
Like .ifb, but the sense of the test is reversed: this assembles the following
section of code if the operand is non-blank (non-empty).
.ifnc string1 ,string2 .
Like .ifc, but the sense of the test is reversed: this assembles the following
section of code if the two strings are not the same.
.ifndef symbol
.ifnotdef symbol
Assembles the following section of code if the specified symbol has not been
defined. Both spelling variants are equivalent. Note a symbol which has been
referenced but not yet defined is considered to be undefined.
.ifne absolute expression
Assembles the following section of code if the argument is not equal to zero (in
other words, this is equivalent to .if).
.ifnes string1 ,string2
Like .ifeqs, but the sense of the test is reversed: this assembles the following
section of code if the two strings are not the same.
7.61 .incbin "file "[,skip [,count ]]
The incbin directive includes file verbatim at the current location. You can control the
search paths used with the ‘-I’ command-line option (see Chapter 2 [Command-Line Options], page 19). Quotation marks are required around file.
The skip argument skips a number of bytes from the start of the file. The count argument
indicates the maximum number of bytes to read. Note that the data is not aligned in any
way, so it is the user’s responsibility to make sure that proper alignment is provided both
before and after the incbin directive.
7.62 .include "file "
This directive provides a way to include supporting files at specified points in your source
program. The code from file is assembled as if it followed the point of the .include; when
the end of the included file is reached, assembly of the original file continues. You can control
the search paths used with the ‘-I’ command-line option (see Chapter 2 [Command-Line
Options], page 19). Quotation marks are required around file.
56
Using as
7.63 .int expressions
Expect zero or more expressions, of any section, separated by commas. For each expression,
emit a number that, at run time, is the value of that expression. The byte order and bit
size of the number depends on what kind of target the assembly is for.
7.64 .internal names
This is one of the ELF visibility directives. The other two are .hidden (see Section 7.57
[.hidden], page 53) and .protected (see Section 7.88 [.protected], page 64).
This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to internal which means that
the symbols are considered to be hidden (i.e., not visible to other components), and that
some extra, processor specific processing must also be performed upon the symbols as well.
7.65 .irp symbol ,values . . .
Evaluate a sequence of statements assigning different values to symbol. The sequence of
statements starts at the .irp directive, and is terminated by an .endr directive. For each
value, symbol is set to value, and the sequence of statements is assembled. If no value is
listed, the sequence of statements is assembled once, with symbol set to the null string. To
refer to symbol within the sequence of statements, use \symbol.
For example, assembling
.irp
move
.endr
param,1,2,3
d\param,sp@-
is equivalent to assembling
move
move
move
d1,sp@d2,sp@d3,sp@-
For some caveats with the spelling of symbol, see also Section 7.77 [Macro], page 59.
7.66 .irpc symbol ,values . . .
Evaluate a sequence of statements assigning different values to symbol. The sequence of
statements starts at the .irpc directive, and is terminated by an .endr directive. For
each character in value, symbol is set to the character, and the sequence of statements is
assembled. If no value is listed, the sequence of statements is assembled once, with symbol
set to the null string. To refer to symbol within the sequence of statements, use \symbol.
For example, assembling
.irpc
move
.endr
param,123
d\param,sp@-
is equivalent to assembling
move
move
d1,sp@d2,sp@-
Chapter 7: Assembler Directives
move
57
d3,sp@-
For some caveats with the spelling of symbol, see also the discussion at See Section 7.77
[Macro], page 59.
7.67 .lcomm symbol , length
Reserve length (an absolute expression) bytes for a local common denoted by symbol. The
section and value of symbol are those of the new local common. The addresses are allocated
in the bss section, so that at run-time the bytes start off zeroed. Symbol is not declared
global (see Section 7.55 [.global], page 53), so is normally not visible to ld.
Some targets permit a third argument to be used with .lcomm. This argument specifies
the desired alignment of the symbol in the bss section.
The syntax for .lcomm differs slightly on the HPPA. The syntax is ‘symbol .lcomm,
length ’; symbol is optional.
7.68 .lflags
as accepts this directive, for compatibility with other assemblers, but ignores it.
7.69 .line line-number
Change the logical line number. line-number must be an absolute expression. The next
line has that logical line number. Therefore any other statements on the current line (after
a statement separator character) are reported as on logical line number line-number − 1.
One day as will no longer support this directive: it is recognized only for compatibility with
existing assembler programs.
Even though this is a directive associated with the a.out or b.out object-code formats,
as still recognizes it when producing COFF output, and treats ‘.line’ as though it were
the COFF ‘.ln’ if it is found outside a .def/.endef pair.
Inside a .def, ‘.line’ is, instead, one of the directives used by compilers to generate
auxiliary symbol information for debugging.
7.70 .linkonce [type ]
Mark the current section so that the linker only includes a single copy of it. This may be
used to include the same section in several different object files, but ensure that the linker
will only include it once in the final output file. The .linkonce pseudo-op must be used
for each instance of the section. Duplicate sections are detected based on the section name,
so it should be unique.
This directive is only supported by a few object file formats; as of this writing, the only
object file format which supports it is the Portable Executable format used on Windows
NT.
The type argument is optional. If specified, it must be one of the following strings. For
example:
.linkonce same_size
Not all types may be supported on all object file formats.
58
Using as
discard
Silently discard duplicate sections. This is the default.
one_only
Warn if there are duplicate sections, but still keep only one copy.
same_size
Warn if any of the duplicates have different sizes.
same_contents
Warn if any of the duplicates do not have exactly the same contents.
7.71 .list
Control (in conjunction with the .nolist directive) whether or not assembly listings are
generated. These two directives maintain an internal counter (which is zero initially).
.list increments the counter, and .nolist decrements it. Assembly listings are generated
whenever the counter is greater than zero.
By default, listings are disabled. When you enable them (with the ‘-a’ command line
option; see Chapter 2 [Command-Line Options], page 19), the initial value of the listing
counter is one.
7.72 .ln line-number
‘.ln’ is a synonym for ‘.line’.
7.73 .loc fileno lineno [column ] [options ]
When emitting DWARF2 line number information, the .loc directive will add a row to
the .debug_line line number matrix corresponding to the immediately following assembly
instruction. The fileno, lineno, and optional column arguments will be applied to the
.debug_line state machine before the row is added.
The options are a sequence of the following tokens in any order:
basic_block
This option will set the basic_block register in the .debug_line state machine
to true.
prologue_end
This option will set the prologue_end register in the .debug_line state machine to true.
epilogue_begin
This option will set the epilogue_begin register in the .debug_line state
machine to true.
is_stmt value
This option will set the is_stmt register in the .debug_line state machine to
value, which must be either 0 or 1.
isa value
This directive will set the isa register in the .debug_line state machine to
value, which must be an unsigned integer.
Chapter 7: Assembler Directives
59
discriminator value
This directive will set the discriminator register in the .debug_line state
machine to value, which must be an unsigned integer.
7.74 .loc_mark_labels enable
When emitting DWARF2 line number information, the .loc_mark_labels directive makes
the assembler emit an entry to the .debug_line line number matrix with the basic_block
register in the state machine set whenever a code label is seen. The enable argument should
be either 1 or 0, to enable or disable this function respectively.
7.75 .local names
This directive, which is available for ELF targets, marks each symbol in the commaseparated list of names as a local symbol so that it will not be externally visible. If the
symbols do not already exist, they will be created.
For targets where the .lcomm directive (see Section 7.67 [Lcomm], page 57) does not
accept an alignment argument, which is the case for most ELF targets, the .local directive
can be used in combination with .comm (see Section 7.30 [Comm], page 49) to define aligned
local common data.
7.76 .long expressions
.long is the same as ‘.int’. See Section 7.63 [.int], page 56.
7.77 .macro
The commands .macro and .endm allow you to define macros that generate assembly output.
For example, this definition specifies a macro sum that puts a sequence of numbers into
memory:
.macro
.long
.if
sum
.endif
.endm
sum from=0, to=5
\from
\to-\from
"(\from+1)",\to
With that definition, ‘SUM 0,5’ is equivalent to this assembly input:
.long
.long
.long
.long
.long
.long
0
1
2
3
4
5
.macro macname
.macro macname macargs ...
Begin the definition of a macro called macname. If your macro definition
requires arguments, specify their names after the macro name, separated by
60
Using as
commas or spaces. You can qualify the macro argument to indicate whether
all invocations must specify a non-blank value (through ‘:req’), or whether it
takes all of the remaining arguments (through ‘:vararg’). You can supply a
default value for any macro argument by following the name with ‘=deflt ’.
You cannot define two macros with the same macname unless it has been subject to the .purgem directive (see Section 7.90 [Purgem], page 65) between the
two definitions. For example, these are all valid .macro statements:
.macro comm
Begin the definition of a macro called comm, which takes no arguments.
.macro plus1 p, p1
.macro plus1 p p1
Either statement begins the definition of a macro called plus1,
which takes two arguments; within the macro definition, write ‘\p’
or ‘\p1’ to evaluate the arguments.
.macro reserve_str p1=0 p2
Begin the definition of a macro called reserve_str, with two arguments. The first argument has a default value, but not the second.
After the definition is complete, you can call the macro either as
‘reserve_str a ,b ’ (with ‘\p1’ evaluating to a and ‘\p2’ evaluating
to b), or as ‘reserve_str ,b ’ (with ‘\p1’ evaluating as the default,
in this case ‘0’, and ‘\p2’ evaluating to b).
.macro m p1:req, p2=0, p3:vararg
Begin the definition of a macro called m, with at least three arguments. The first argument must always have a value specified,
but not the second, which instead has a default value. The third
formal will get assigned all remaining arguments specified at invocation time.
When you call a macro, you can specify the argument values either
by position, or by keyword. For example, ‘sum 9,17’ is equivalent
to ‘sum to=17, from=9’.
Note that since each of the macargs can be an identifier exactly as any other
one permitted by the target architecture, there may be occasional problems if
the target hand-crafts special meanings to certain characters when they occur
in a special position. For example, if the colon (:) is generally permitted to
be part of a symbol name, but the architecture specific code special-cases it
when occurring as the final character of a symbol (to denote a label), then
the macro parameter replacement code will have no way of knowing that and
consider the whole construct (including the colon) an identifier, and check only
this identifier for being the subject to parameter substitution. So for example
this macro definition:
.macro label l
\l:
.endm
Chapter 7: Assembler Directives
61
might not work as expected. Invoking ‘label foo’ might not create a label
called ‘foo’ but instead just insert the text ‘\l:’ into the assembler source,
probably generating an error about an unrecognised identifier.
Similarly problems might occur with the period character (‘.’) which is often
allowed inside opcode names (and hence identifier names). So for example
constructing a macro to build an opcode from a base name and a length specifier
like this:
.macro opcode base length
\base.\length
.endm
and invoking it as ‘opcode store l’ will not create a ‘store.l’ instruction but
instead generate some kind of error as the assembler tries to interpret the text
‘\base.\length’.
There are several possible ways around this problem:
Insert white space
If it is possible to use white space characters then this is the simplest
solution. eg:
.macro label l
\l :
.endm
Use ‘\()’ The string ‘\()’ can be used to separate the end of a macro argument from the following text. eg:
.macro opcode base length
\base\().\length
.endm
Use the alternate macro syntax mode
In the alternative macro syntax mode the ampersand character (‘&’)
can be used as a separator. eg:
.altmacro
.macro label l
l&:
.endm
Note: this problem of correctly identifying string parameters to pseudo ops
also applies to the identifiers used in .irp (see Section 7.65 [Irp], page 56) and
.irpc (see Section 7.66 [Irpc], page 56) as well.
.endm
Mark the end of a macro definition.
.exitm
Exit early from the current macro definition.
\@
as maintains a counter of how many macros it has executed in this pseudovariable; you can copy that number to your output with ‘\@’, but only within
a macro definition.
LOCAL name [ , ... ]
Warning: LOCAL is only available if you select “alternate macro syntax” with
‘--alternate’ or .altmacro. See Section 7.4 [.altmacro], page 46.
62
Using as
7.78 .mri val
If val is non-zero, this tells as to enter MRI mode. If val is zero, this tells as to exit MRI
mode. This change affects code assembled until the next .mri directive, or until the end of
the file. See Section 2.9 [MRI mode], page 21.
7.79 .noaltmacro
Disable alternate macro mode. See Section 7.4 [Altmacro], page 46.
7.80 .nolist
Control (in conjunction with the .list directive) whether or not assembly listings are
generated. These two directives maintain an internal counter (which is zero initially).
.list increments the counter, and .nolist decrements it. Assembly listings are generated
whenever the counter is greater than zero.
7.81 .octa bignums
This directive expects zero or more bignums, separated by commas. For each bignum, it
emits a 16-byte integer.
The term “octa” comes from contexts in which a “word” is two bytes; hence octa-word
for 16 bytes.
7.82 .offset loc
Set the location counter to loc in the absolute section. loc must be an absolute expression.
This directive may be useful for defining symbols with absolute values. Do not confuse it
with the .org directive.
7.83 .org new-lc , fill
Advance the location counter of the current section to new-lc. new-lc is either an absolute
expression or an expression with the same section as the current subsection. That is, you
can’t use .org to cross sections: if new-lc has the wrong section, the .org directive is
ignored. To be compatible with former assemblers, if the section of new-lc is absolute, as
issues a warning, then pretends the section of new-lc is the same as the current subsection.
.org may only increase the location counter, or leave it unchanged; you cannot use .org
to move the location counter backwards.
Because as tries to assemble programs in one pass, new-lc may not be undefined. If you
really detest this restriction we eagerly await a chance to share your improved assembler.
Beware that the origin is relative to the start of the section, not to the start of the
subsection. This is compatible with other people’s assemblers.
When the location counter (of the current subsection) is advanced, the intervening bytes
are filled with fill which should be an absolute expression. If the comma and fill are omitted,
fill defaults to zero.
Chapter 7: Assembler Directives
63
7.84 .p2align[wl] abs-expr , abs-expr , abs-expr
Pad the location counter (in the current subsection) to a particular storage boundary. The
first expression (which must be absolute) is the number of low-order zero bits the location
counter must have after advancement. For example ‘.p2align 3’ advances the location
counter until it a multiple of 8. If the location counter is already a multiple of 8, no change
is needed.
The second expression (also absolute) gives the fill value to be stored in the padding
bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally
zero. However, on some systems, if the section is marked as containing code and the fill
value is omitted, the space is filled with no-op instructions.
The third expression is also absolute, and is also optional. If it is present, it is the
maximum number of bytes that should be skipped by this alignment directive. If doing
the alignment would require skipping more bytes than the specified maximum, then the
alignment is not done at all. You can omit the fill value (the second argument) entirely by
simply using two commas after the required alignment; this can be useful if you want the
alignment to be filled with no-op instructions when appropriate.
The .p2alignw and .p2alignl directives are variants of the .p2align directive. The
.p2alignw directive treats the fill pattern as a two byte word value. The .p2alignl directives treats the fill pattern as a four byte longword value. For example, .p2alignw
2,0x368d will align to a multiple of 4. If it skips two bytes, they will be filled in with
the value 0x368d (the exact placement of the bytes depends upon the endianness of the
processor). If it skips 1 or 3 bytes, the fill value is undefined.
7.85 .popsection
This is one of the ELF section stack manipulation directives. The others are .section (see
Section 7.97 [Section], page 66), .subsection (see Section 7.108 [SubSection], page 71),
.pushsection (see Section 7.91 [PushSection], page 65), and .previous (see Section 7.86
[Previous], page 63).
This directive replaces the current section (and subsection) with the top section (and
subsection) on the section stack. This section is popped off the stack.
7.86 .previous
This is one of the ELF section stack manipulation directives. The others are .section (see
Section 7.97 [Section], page 66), .subsection (see Section 7.108 [SubSection], page 71),
.pushsection (see Section 7.91 [PushSection], page 65), and .popsection (see Section 7.85
[PopSection], page 63).
This directive swaps the current section (and subsection) with most recently referenced
section/subsection pair prior to this one. Multiple .previous directives in a row will flip
between two sections (and their subsections). For example:
.section A
.subsection 1
.word 0x1234
.subsection 2
.word 0x5678
.previous
64
Using as
.word 0x9abc
Will place 0x1234 and 0x9abc into subsection 1 and 0x5678 into subsection 2 of section
A. Whilst:
.section A
.subsection 1
# Now in section
.word 0x1234
.section B
.subsection 0
# Now in section
.word 0x5678
.subsection 1
# Now in section
.word 0x9abc
.previous
# Now in section
.word 0xdef0
A subsection 1
B subsection 0
B subsection 1
B subsection 0
Will place 0x1234 into section A, 0x5678 and 0xdef0 into subsection 0 of section B and
0x9abc into subsection 1 of section B.
In terms of the section stack, this directive swaps the current section with the top section
on the section stack.
7.87 .print string
as will print string on the standard output during assembly. You must put string in double
quotes.
7.88 .protected names
This is one of the ELF visibility directives. The other two are .hidden (see Section 7.57
[Hidden], page 53) and .internal (see Section 7.64 [Internal], page 56).
This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to protected which means
that any references to the symbols from within the components that defines them must
be resolved to the definition in that component, even if a definition in another component
would normally preempt this.
7.89 .psize lines , columns
Use this directive to declare the number of lines—and, optionally, the number of columns—
to use for each page, when generating listings.
If you do not use .psize, listings use a default line-count of 60. You may omit the
comma and columns specification; the default width is 200 columns.
as generates formfeeds whenever the specified number of lines is exceeded (or whenever
you explicitly request one, using .eject).
If you specify lines as 0, no formfeeds are generated save those explicitly specified with
.eject.
Chapter 7: Assembler Directives
65
7.90 .purgem name
Undefine the macro name, so that later uses of the string will not be expanded. See
Section 7.77 [Macro], page 59.
7.91 .pushsection name [, subsection ] [, "flags "[,
@type [,arguments ]]]
This is one of the ELF section stack manipulation directives. The others are .section (see
Section 7.97 [Section], page 66), .subsection (see Section 7.108 [SubSection], page 71),
.popsection (see Section 7.85 [PopSection], page 63), and .previous (see Section 7.86
[Previous], page 63).
This directive pushes the current section (and subsection) onto the top of the section
stack, and then replaces the current section and subsection with name and subsection.
The optional flags, type and arguments are treated the same as in the .section (see
Section 7.97 [Section], page 66) directive.
7.92 .quad bignums
.quad expects zero or more bignums, separated by commas. For each bignum, it emits an
8-byte integer. If the bignum won’t fit in 8 bytes, it prints a warning message; and just
takes the lowest order 8 bytes of the bignum.
The term “quad” comes from contexts in which a “word” is two bytes; hence quad-word
for 8 bytes.
7.93 .reloc offset , reloc_name [, expression ]
Generate a relocation at offset of type reloc name with value expression. If offset is a
number, the relocation is generated in the current section. If offset is an expression that
resolves to a symbol plus offset, the relocation is generated in the given symbol’s section.
expression, if present, must resolve to a symbol plus addend or to an absolute value, but
note that not all targets support an addend. e.g. ELF REL targets such as i386 store an
addend in the section contents rather than in the relocation. This low level interface does
not support addends stored in the section.
7.94 .rept count
Repeat the sequence of lines between the .rept directive and the next .endr directive count
times.
For example, assembling
.rept
.long
.endr
3
0
is equivalent to assembling
.long
.long
.long
0
0
0
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Using as
7.95 .sbttl "subheading "
Use subheading as the title (third line, immediately after the title line) when generating
assembly listings.
This directive affects subsequent pages, as well as the current page if it appears within
ten lines of the top of a page.
7.96 .scl class
Set the storage-class value for a symbol. This directive may only be used inside a
.def/.endef pair. Storage class may flag whether a symbol is static or external, or it may
record further symbolic debugging information.
7.97 .section name
Use the .section directive to assemble the following code into a section named name.
This directive is only supported for targets that actually support arbitrarily named
sections; on a.out targets, for example, it is not accepted, even with a standard a.out
section name.
COFF Version
For COFF targets, the .section directive is used in one of the following ways:
.section name [, "flags "]
.section name [, subsection ]
If the optional argument is quoted, it is taken as flags to use for the section. Each flag
is a single character. The following flags are recognized:
b
bss section (uninitialized data)
n
section is not loaded
w
writable section
d
data section
r
read-only section
x
executable section
s
shared section (meaningful for PE targets)
a
ignored. (For compatibility with the ELF version)
y
section is not readable (meaningful for PE targets)
0-9
single-digit power-of-two section alignment (GNU extension)
If no flags are specified, the default flags depend upon the section name. If the section
name is not recognized, the default will be for the section to be loaded and writable. Note
the n and w flags remove attributes from the section, rather than adding them, so if they
are used on their own it will be as if no flags had been specified at all.
If the optional argument to the .section directive is not quoted, it is taken as a subsection number (see Section 4.4 [Sub-Sections], page 33).
Chapter 7: Assembler Directives
67
ELF Version
This is one of the ELF section stack manipulation directives. The others are .subsection
(see Section 7.108 [SubSection], page 71), .pushsection (see Section 7.91 [PushSection],
page 65), .popsection (see Section 7.85 [PopSection], page 63), and .previous (see
Section 7.86 [Previous], page 63).
For ELF targets, the .section directive is used like this:
.section name [, "flags "[, @type [,flag_specific_arguments ]]]
The optional flags argument is a quoted string which may contain any combination of
the following characters:
a
section is allocatable
e
section is excluded from executable and shared library.
w
section is writable
x
section is executable
M
section is mergeable
S
section contains zero terminated strings
G
section is a member of a section group
T
section is used for thread-local-storage
?
section is a member of the previously-current section’s group, if any
The optional type argument may contain one of the following constants:
@progbits
section contains data
@nobits
section does not contain data (i.e., section only occupies space)
@note
section contains data which is used by things other than the program
@init_array
section contains an array of pointers to init functions
@fini_array
section contains an array of pointers to finish functions
@preinit_array
section contains an array of pointers to pre-init functions
Many targets only support the first three section types.
Note on targets where the @ character is the start of a comment (eg ARM) then another
character is used instead. For example the ARM port uses the % character.
If flags contains the M symbol then the type argument must be specified as well as an
extra argument—entsize—like this:
.section name , "flags "M, @type , entsize
Sections with the M flag but not S flag must contain fixed size constants, each entsize
octets long. Sections with both M and S must contain zero terminated strings where each
character is entsize bytes long. The linker may remove duplicates within sections with the
68
Using as
same name, same entity size and same flags. entsize must be an absolute expression. For
sections with both M and S, a string which is a suffix of a larger string is considered a
duplicate. Thus "def" will be merged with "abcdef"; A reference to the first "def" will
be changed to a reference to "abcdef"+3.
If flags contains the G symbol then the type argument must be present along with an
additional field like this:
.section name , "flags "G, @type , GroupName [, linkage ]
The GroupName field specifies the name of the section group to which this particular
section belongs. The optional linkage field can contain:
comdat
indicates that only one copy of this section should be retained
.gnu.linkonce
an alias for comdat
Note: if both the M and G flags are present then the fields for the Merge flag should
come first, like this:
.section name , "flags "MG, @type , entsize , GroupName [, linkage ]
If flags contains the ? symbol then it may not also contain the G symbol and the GroupName or linkage fields should not be present. Instead, ? says to consider the section that’s
current before this directive. If that section used G, then the new section will use G with
those same GroupName and linkage fields implicitly. If not, then the ? symbol has no effect.
If no flags are specified, the default flags depend upon the section name. If the section
name is not recognized, the default will be for the section to have none of the above flags:
it will not be allocated in memory, nor writable, nor executable. The section will contain
data.
For ELF targets, the assembler supports another type of .section directive for compatibility with the Solaris assembler:
.section "name "[, flags ...]
Note that the section name is quoted. There may be a sequence of comma separated
flags:
#alloc
section is allocatable
#write
section is writable
#execinstr
section is executable
#exclude
section is excluded from executable and shared library.
#tls
section is used for thread local storage
This directive replaces the current section and subsection. See the contents of the gas
testsuite directory gas/testsuite/gas/elf for some examples of how this directive and
the other section stack directives work.
Chapter 7: Assembler Directives
69
7.98 .set symbol , expression
Set the value of symbol to expression. This changes symbol’s value and type to conform to
expression. If symbol was flagged as external, it remains flagged (see Section 5.5 [Symbol
Attributes], page 39).
You may .set a symbol many times in the same assembly.
If you .set a global symbol, the value stored in the object file is the last value stored
into it.
On Z80 set is a real instruction, use ‘symbol defl expression ’ instead.
7.99 .short expressions
.short is normally the same as ‘.word’. See Section 7.122 [.word], page 75.
In some configurations, however, .short and .word generate numbers of different
lengths. See Chapter 9 [Machine Dependencies], page 79.
7.100 .single flonums
This directive assembles zero or more flonums, separated by commas. It has the same
effect as .float. The exact kind of floating point numbers emitted depends on how as is
configured. See Chapter 9 [Machine Dependencies], page 79.
7.101 .size
This directive is used to set the size associated with a symbol.
COFF Version
For COFF targets, the .size directive is only permitted inside .def/.endef pairs. It is
used like this:
.size expression
ELF Version
For ELF targets, the .size directive is used like this:
.size name , expression
This directive sets the size associated with a symbol name. The size in bytes is computed
from expression which can make use of label arithmetic. This directive is typically used to
set the size of function symbols.
7.102 .skip size , fill
This directive emits size bytes, each of value fill. Both size and fill are absolute expressions.
If the comma and fill are omitted, fill is assumed to be zero. This is the same as ‘.space’.
7.103 .sleb128 expressions
sleb128 stands for “signed little endian base 128.” This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format. See Section 7.114
[.uleb128], page 74.
70
Using as
7.104 .space size , fill
This directive emits size bytes, each of value fill. Both size and fill are absolute expressions.
If the comma and fill are omitted, fill is assumed to be zero. This is the same as ‘.skip’.
Warning: .space has a completely different meaning for HPPA targets; use
.block as a substitute. See HP9000 Series 800 Assembly Language Reference Manual (HP 92432-90001) for the meaning of the .space directive. See
Section 9.11.5 [HPPA Assembler Directives], page 132, for a summary.
7.105 .stabd, .stabn, .stabs
There are three directives that begin ‘.stab’. All emit symbols (see Chapter 5 [Symbols],
page 37), for use by symbolic debuggers. The symbols are not entered in the as hash table:
they cannot be referenced elsewhere in the source file. Up to five fields are required:
string
This is the symbol’s name. It may contain any character except ‘\000’, so
is more general than ordinary symbol names. Some debuggers used to code
arbitrarily complex structures into symbol names using this field.
type
An absolute expression. The symbol’s type is set to the low 8 bits of this
expression. Any bit pattern is permitted, but ld and debuggers choke on silly
bit patterns.
other
An absolute expression. The symbol’s “other” attribute is set to the low 8 bits
of this expression.
desc
An absolute expression. The symbol’s descriptor is set to the low 16 bits of this
expression.
value
An absolute expression which becomes the symbol’s value.
If a warning is detected while reading a .stabd, .stabn, or .stabs statement, the
symbol has probably already been created; you get a half-formed symbol in your object file.
This is compatible with earlier assemblers!
.stabd type , other , desc
The “name” of the symbol generated is not even an empty string. It is a null
pointer, for compatibility. Older assemblers used a null pointer so they didn’t
waste space in object files with empty strings.
The symbol’s value is set to the location counter, relocatably. When your
program is linked, the value of this symbol is the address of the location counter
when the .stabd was assembled.
.stabn type , other , desc , value
The name of the symbol is set to the empty string "".
.stabs string , type , other , desc , value
All five fields are specified.
Chapter 7: Assembler Directives
71
7.106 .string "str", .string8 "str", .string16
"str", .string32 "str", .string64 "str"
Copy the characters in str to the object file. You may specify more than one string
to copy, separated by commas. Unless otherwise specified for a particular machine, the
assembler marks the end of each string with a 0 byte. You can use any of the escape
sequences described in Section 3.6.1.1 [Strings], page 27.
The variants string16, string32 and string64 differ from the string pseudo opcode
in that each 8-bit character from str is copied and expanded to 16, 32 or 64 bits respectively.
The expanded characters are stored in target endianness byte order.
Example:
.string32 "BYE"
expands to:
.string
"B\0\0\0Y\0\0\0E\0\0\0"
.string
"\0\0\0B\0\0\0Y\0\0\0E"
/* On little endian targets. */
/* On big endian targets. */
7.107 .struct expression
Switch to the absolute section, and set the section offset to expression, which must be an
absolute expression. You might use this as follows:
.struct 0
field1:
.struct field1 + 4
field2:
.struct field2 + 4
field3:
This would define the symbol field1 to have the value 0, the symbol field2 to have
the value 4, and the symbol field3 to have the value 8. Assembly would be left in the
absolute section, and you would need to use a .section directive of some sort to change to
some other section before further assembly.
7.108 .subsection name
This is one of the ELF section stack manipulation directives. The others are .section (see
Section 7.97 [Section], page 66), .pushsection (see Section 7.91 [PushSection], page 65),
.popsection (see Section 7.85 [PopSection], page 63), and .previous (see Section 7.86
[Previous], page 63).
This directive replaces the current subsection with name. The current section is not
changed. The replaced subsection is put onto the section stack in place of the then current
top of stack subsection.
7.109 .symver
Use the .symver directive to bind symbols to specific version nodes within a source file.
This is only supported on ELF platforms, and is typically used when assembling files to be
linked into a shared library. There are cases where it may make sense to use this in objects
to be bound into an application itself so as to override a versioned symbol from a shared
library.
For ELF targets, the .symver directive can be used like this:
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Using as
.symver name , name2@nodename
If the symbol name is defined within the file being assembled, the .symver directive
effectively creates a symbol alias with the name name2@nodename, and in fact the main
reason that we just don’t try and create a regular alias is that the @ character isn’t permitted
in symbol names. The name2 part of the name is the actual name of the symbol by which
it will be externally referenced. The name name itself is merely a name of convenience that
is used so that it is possible to have definitions for multiple versions of a function within
a single source file, and so that the compiler can unambiguously know which version of a
function is being mentioned. The nodename portion of the alias should be the name of a
node specified in the version script supplied to the linker when building a shared library. If
you are attempting to override a versioned symbol from a shared library, then nodename
should correspond to the nodename of the symbol you are trying to override.
If the symbol name is not defined within the file being assembled, all references to name
will be changed to name2@nodename. If no reference to name is made, name2@nodename
will be removed from the symbol table.
Another usage of the .symver directive is:
.symver name , name2@@nodename
In this case, the symbol name must exist and be defined within the file being assembled.
It is similar to name2@nodename. The difference is name2@@nodename will also be used to
resolve references to name2 by the linker.
The third usage of the .symver directive is:
.symver name , name2@@@nodename
When name is not defined within the file being assembled, it is treated as
name2@nodename. When name is defined within the file being assembled, the symbol
name, name, will be changed to name2@@nodename.
7.110 .tag structname
This directive is generated by compilers to include auxiliary debugging information in the
symbol table. It is only permitted inside .def/.endef pairs. Tags are used to link structure
definitions in the symbol table with instances of those structures.
7.111 .text subsection
Tells as to assemble the following statements onto the end of the text subsection numbered
subsection, which is an absolute expression. If subsection is omitted, subsection number
zero is used.
7.112 .title "heading "
Use heading as the title (second line, immediately after the source file name and pagenumber) when generating assembly listings.
This directive affects subsequent pages, as well as the current page if it appears within
ten lines of the top of a page.
Chapter 7: Assembler Directives
73
7.113 .type
This directive is used to set the type of a symbol.
COFF Version
For COFF targets, this directive is permitted only within .def/.endef pairs. It is used
like this:
.type int
This records the integer int as the type attribute of a symbol table entry.
ELF Version
For ELF targets, the .type directive is used like this:
.type name , type description
This sets the type of symbol name to be either a function symbol or an object symbol.
There are five different syntaxes supported for the type description field, in order to provide
compatibility with various other assemblers.
Because some of the characters used in these syntaxes (such as ‘@’ and ‘#’) are comment
characters for some architectures, some of the syntaxes below do not work on all architectures. The first variant will be accepted by the GNU assembler on all architectures so that
variant should be used for maximum portability, if you do not need to assemble your code
with other assemblers.
The syntaxes supported are:
.type
.type
.type
.type
.type
STT_,#,@,%,""
The types supported are:
STT_FUNC
function
Mark the symbol as being a function name.
STT_GNU_IFUNC
gnu_indirect_function
Mark the symbol as an indirect function when evaluated during reloc processing.
(This is only supported on assemblers targeting GNU systems).
STT_OBJECT
object
Mark the symbol as being a data object.
STT_TLS
tls_object
Mark the symbol as being a thead-local data object.
STT_COMMON
common
Mark the symbol as being a common data object.
STT_NOTYPE
notype
Does not mark the symbol in any way. It is supported just for completeness.
74
Using as
gnu_unique_object
Marks the symbol as being a globally unique data object. The dynamic linker
will make sure that in the entire process there is just one symbol with this
name and type in use. (This is only supported on assemblers targeting GNU
systems).
Note: Some targets support extra types in addition to those listed above.
7.114 .uleb128 expressions
uleb128 stands for “unsigned little endian base 128.” This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format. See Section 7.103
[.sleb128], page 69.
7.115 .val addr
This directive, permitted only within .def/.endef pairs, records the address addr as the
value attribute of a symbol table entry.
7.116 .version "string "
This directive creates a .note section and places into it an ELF formatted note of type
NT VERSION. The note’s name is set to string.
7.117 .vtable_entry table , offset
This directive finds or creates a symbol table and creates a VTABLE_ENTRY relocation for
it with an addend of offset.
7.118 .vtable_inherit child , parent
This directive finds the symbol child and finds or creates the symbol parent and then
creates a VTABLE_INHERIT relocation for the parent whose addend is the value of the child
symbol. As a special case the parent name of 0 is treated as referring to the *ABS* section.
7.119 .warning "string "
Similar to the directive .error (see Section 7.47 [.error "string "], page 52), but just
emits a warning.
7.120 .weak names
This directive sets the weak attribute on the comma separated list of symbol names. If the
symbols do not already exist, they will be created.
On COFF targets other than PE, weak symbols are a GNU extension. This directive
sets the weak attribute on the comma separated list of symbol names. If the symbols do
not already exist, they will be created.
On the PE target, weak symbols are supported natively as weak aliases. When a weak
symbol is created that is not an alias, GAS creates an alternate symbol to hold the default
value.
Chapter 7: Assembler Directives
75
7.121 .weakref alias , target
This directive creates an alias to the target symbol that enables the symbol to be referenced
with weak-symbol semantics, but without actually making it weak. If direct references or
definitions of the symbol are present, then the symbol will not be weak, but if all references
to it are through weak references, the symbol will be marked as weak in the symbol table.
The effect is equivalent to moving all references to the alias to a separate assembly source
file, renaming the alias to the symbol in it, declaring the symbol as weak there, and running
a reloadable link to merge the object files resulting from the assembly of the new source file
and the old source file that had the references to the alias removed.
The alias itself never makes to the symbol table, and is entirely handled within the
assembler.
7.122 .word expressions
This directive expects zero or more expressions, of any section, separated by commas.
The size of the number emitted, and its byte order, depend on what target computer
the assembly is for.
Warning: Special Treatment to support Compilers
Machines with a 32-bit address space, but that do less than 32-bit addressing, require
the following special treatment. If the machine of interest to you does 32-bit addressing
(or doesn’t require it; see Chapter 9 [Machine Dependencies], page 79), you can ignore this
issue.
In order to assemble compiler output into something that works, as occasionally does
strange things to ‘.word’ directives. Directives of the form ‘.word sym1-sym2’ are often
emitted by compilers as part of jump tables. Therefore, when as assembles a directive of
the form ‘.word sym1-sym2’, and the difference between sym1 and sym2 does not fit in 16
bits, as creates a secondary jump table, immediately before the next label. This secondary
jump table is preceded by a short-jump to the first byte after the secondary table. This
short-jump prevents the flow of control from accidentally falling into the new table. Inside
the table is a long-jump to sym2. The original ‘.word’ contains sym1 minus the address of
the long-jump to sym2.
If there were several occurrences of ‘.word sym1-sym2’ before the secondary jump table,
all of them are adjusted. If there was a ‘.word sym3-sym4’, that also did not fit in sixteen
bits, a long-jump to sym4 is included in the secondary jump table, and the .word directives
are adjusted to contain sym3 minus the address of the long-jump to sym4; and so on, for as
many entries in the original jump table as necessary.
7.123 Deprecated Directives
One day these directives won’t work. They are included for compatibility with older assemblers.
.abort
.line
Chapter 8: Object Attributes
77
8 Object Attributes
as assembles source files written for a specific architecture into object files for that architecture. But not all object files are alike. Many architectures support incompatible variations.
For instance, floating point arguments might be passed in floating point registers if the
object file requires hardware floating point support—or floating point arguments might be
passed in integer registers if the object file supports processors with no hardware floating
point unit. Or, if two objects are built for different generations of the same architecture,
the combination may require the newer generation at run-time.
This information is useful during and after linking. At link time, ld can warn about
incompatible object files. After link time, tools like gdb can use it to process the linked file
correctly.
Compatibility information is recorded as a series of object attributes. Each attribute has
a vendor, tag, and value. The vendor is a string, and indicates who sets the meaning of the
tag. The tag is an integer, and indicates what property the attribute describes. The value
may be a string or an integer, and indicates how the property affects this object. Missing
attributes are the same as attributes with a zero value or empty string value.
Object attributes were developed as part of the ABI for the ARM Architecture. The file
format is documented in ELF for the ARM Architecture.
8.1 gnu Object Attributes
The .gnu_attribute directive records an object attribute with vendor ‘gnu’.
Except for ‘Tag_compatibility’, which has both an integer and a string for its value,
gnu attributes have a string value if the tag number is odd and an integer value if the tag
number is even. The second bit (tag & 2 is set for architecture-independent attributes and
clear for architecture-dependent ones.
8.1.1 Common gnu attributes
These attributes are valid on all architectures.
Tag compatibility (32)
The compatibility attribute takes an integer flag value and a vendor name. If
the flag value is 0, the file is compatible with other toolchains. If it is 1, then
the file is only compatible with the named toolchain. If it is greater than 1, the
file can only be processed by other toolchains under some private arrangement
indicated by the flag value and the vendor name.
8.1.2 MIPS Attributes
Tag GNU MIPS ABI FP (4)
The floating-point ABI used by this object file. The value will be:
• 0 for files not affected by the floating-point ABI.
• 1 for files using the hardware floating-point with a standard
double-precision FPU.
• 2 for files using the hardware floating-point ABI with a single-precision
FPU.
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• 3 for files using the software floating-point ABI.
• 4 for files using the hardware floating-point ABI with 64-bit wide doubleprecision floating-point registers and 32-bit wide general purpose registers.
8.1.3 PowerPC Attributes
Tag GNU Power ABI FP (4)
The floating-point ABI used by this object file. The value will be:
• 0 for files not affected by the floating-point ABI.
• 1 for files using double-precision hardware floating-point ABI.
• 2 for files using the software floating-point ABI.
• 3 for files using single-precision hardware floating-point ABI.
Tag GNU Power ABI Vector (8)
The vector ABI used by this object file. The value will be:
• 0 for files not affected by the vector ABI.
• 1 for files using general purpose registers to pass vectors.
• 2 for files using AltiVec registers to pass vectors.
• 3 for files using SPE registers to pass vectors.
8.2 Defining New Object Attributes
If you want to define a new gnu object attribute, here are the places you will need to
modify. New attributes should be discussed on the ‘binutils’ mailing list.
• This manual, which is the official register of attributes.
• The header for your architecture ‘include/elf’, to define the tag.
• The ‘bfd’ support file for your architecture, to merge the attribute and issue any
appropriate link warnings.
• Test cases in ‘ld/testsuite’ for merging and link warnings.
• ‘binutils/readelf.c’ to display your attribute.
• GCC, if you want the compiler to mark the attribute automatically.
Chapter 9: Machine Dependent Features
79
9 Machine Dependent Features
The machine instruction sets are (almost by definition) different on each machine where as
runs. Floating point representations vary as well, and as often supports a few additional
directives or command-line options for compatibility with other assemblers on a particular platform. Finally, some versions of as support special pseudo-instructions for branch
optimization.
This chapter discusses most of these differences, though it does not include details on
any machine’s instruction set. For details on that subject, see the hardware manufacturer’s
manual.
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9.1 Alpha Dependent Features
9.1.1 Notes
The documentation here is primarily for the ELF object format. as also supports the
ECOFF and EVAX formats, but features specific to these formats are not yet documented.
9.1.2 Options
-mcpu
This option specifies the target processor. If an attempt is made to assemble an
instruction which will not execute on the target processor, the assembler may
either expand the instruction as a macro or issue an error message. This option
is equivalent to the .arch directive.
The following processor names are recognized: 21064, 21064a, 21066, 21068,
21164, 21164a, 21164pc, 21264, 21264a, 21264b, ev4, ev5, lca45, ev5, ev56,
pca56, ev6, ev67, ev68. The special name all may be used to allow the
assembler to accept instructions valid for any Alpha processor.
In order to support existing practice in OSF/1 with respect to .arch, and existing practice within MILO (the Linux ARC bootloader), the numbered processor
names (e.g. 21064) enable the processor-specific PALcode instructions, while
the “electro-vlasic” names (e.g. ev4) do not.
-mdebug
-no-mdebug
Enables or disables the generation of .mdebug encapsulation for stabs directives
and procedure descriptors. The default is to automatically enable .mdebug
when the first stabs directive is seen.
-relax
This option forces all relocations to be put into the object file, instead of saving
space and resolving some relocations at assembly time. Note that this option
does not propagate all symbol arithmetic into the object file, because not all
symbol arithmetic can be represented. However, the option can still be useful
in specific applications.
-replace
-noreplace
Enables or disables the optimization of procedure calls, both at assemblage and
at link time. These options are only available for VMS targets and -replace
is the default. See section 1.4.1 of the OpenVMS Linker Utility Manual.
-g
This option is used when the compiler generates debug information. When gcc
is using mips-tfile to generate debug information for ECOFF, local labels
must be passed through to the object file. Otherwise this option has no effect.
-Gsize
A local common symbol larger than size is placed in .bss, while smaller symbols
are placed in .sbss.
-F
-32addr
These options are ignored for backward compatibility.
Chapter 9: Machine Dependent Features
81
9.1.3 Syntax
The assembler syntax closely follow the Alpha Reference Manual; assembler directives and
general syntax closely follow the OSF/1 and OpenVMS syntax, with a few differences for
ELF.
9.1.3.1 Special Characters
‘#’ is the line comment character. Note that if ‘#’ is the first character on a line then
it can also be a logical line number directive (see Section 3.3 [Comments], page 25) or a
preprocessor control command (see Section 3.1 [Preprocessing], page 25).
‘;’ can be used instead of a newline to separate statements.
9.1.3.2 Register Names
The 32 integer registers are referred to as ‘$n ’ or ‘$rn ’. In addition, registers 15, 28, 29,
and 30 may be referred to by the symbols ‘$fp’, ‘$at’, ‘$gp’, and ‘$sp’ respectively.
The 32 floating-point registers are referred to as ‘$fn ’.
9.1.3.3 Relocations
Some of these relocations are available for ECOFF, but mostly only for ELF. They are
modeled after the relocation format introduced in Digital Unix 4.0, but there are additions.
The format is ‘!tag ’ or ‘!tag !number ’ where tag is the name of the relocation. In some
cases number is used to relate specific instructions.
The relocation is placed at the end of the instruction like so:
ldah
lda
ldq
ldl
$0,a($29)
$0,a($0)
$1,b($29)
$2,0($1)
!gprelhigh
!gprellow
!literal!100
!lituse_base!100
!literal
!literal!N
Used with an ldq instruction to load the address of a symbol from the GOT.
A sequence number N is optional, and if present is used to pair lituse relocations with this literal relocation. The lituse relocations are used by the
linker to optimize the code based on the final location of the symbol.
Note that these optimizations are dependent on the data flow of the program.
Therefore, if any lituse is paired with a literal relocation, then all uses of
the register set by the literal instruction must also be marked with lituse
relocations. This is because the original literal instruction may be deleted or
transformed into another instruction.
Also note that there may be a one-to-many relationship between literal and
lituse, but not a many-to-one. That is, if there are two code paths that load
up the same address and feed the value to a single use, then the use may not
use a lituse relocation.
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!lituse_base!N
Used with any memory format instruction (e.g. ldl) to indicate that the literal
is used for an address load. The offset field of the instruction must be zero.
During relaxation, the code may be altered to use a gp-relative load.
!lituse_jsr!N
Used with a register branch format instruction (e.g. jsr) to indicate that the
literal is used for a call. During relaxation, the code may be altered to use a
direct branch (e.g. bsr).
!lituse_jsrdirect!N
Similar to lituse_jsr, but also that this call cannot be vectored through a
PLT entry. This is useful for functions with special calling conventions which
do not allow the normal call-clobbered registers to be clobbered.
!lituse_bytoff!N
Used with a byte mask instruction (e.g. extbl) to indicate that only the low 3
bits of the address are relevant. During relaxation, the code may be altered to
use an immediate instead of a register shift.
!lituse_addr!N
Used with any other instruction to indicate that the original address is in fact
used, and the original ldq instruction may not be altered or deleted. This is
useful in conjunction with lituse_jsr to test whether a weak symbol is defined.
ldq $27,foo($29)
!literal!1
beq $27,is_undef
!lituse_addr!1
jsr $26,($27),foo !lituse_jsr!1
!lituse_tlsgd!N
Used with a register branch format instruction to indicate that the literal is
the call to __tls_get_addr used to compute the address of the thread-local
storage variable whose descriptor was loaded with !tlsgd!N .
!lituse_tlsldm!N
Used with a register branch format instruction to indicate that the literal is the
call to __tls_get_addr used to compute the address of the base of the threadlocal storage block for the current module. The descriptor for the module must
have been loaded with !tlsldm!N .
!gpdisp!N
Used with ldah and lda to load the GP from the current address, a-la the ldgp
macro. The source register for the ldah instruction must contain the address
of the ldah instruction. There must be exactly one lda instruction paired with
the ldah instruction, though it may appear anywhere in the instruction stream.
The immediate operands must be zero.
bsr $26,foo
ldah $29,0($26)
!gpdisp!1
lda $29,0($29)
!gpdisp!1
!gprelhigh
Used with an ldah instruction to add the high 16 bits of a 32-bit displacement
from the GP.
Chapter 9: Machine Dependent Features
83
!gprellow
Used with any memory format instruction to add the low 16 bits of a 32-bit
displacement from the GP.
!gprel
Used with any memory format instruction to add a 16-bit displacement from
the GP.
!samegp
Used with any branch format instruction to skip the GP load at the target
address. The referenced symbol must have the same GP as the source object
file, and it must be declared to either not use $27 or perform a standard GP
load in the first two instructions via the .prologue directive.
!tlsgd
!tlsgd!N
Used with an lda instruction to load the address of a TLS descriptor for a
symbol in the GOT.
The sequence number N is optional, and if present it used to pair the descriptor
load with both the literal loading the address of the __tls_get_addr function
and the lituse_tlsgd marking the call to that function.
For proper relaxation, both the tlsgd, literal and lituse relocations must
be in the same extended basic block. That is, the relocation with the lowest
address must be executed first at runtime.
!tlsldm
!tlsldm!N
Used with an lda instruction to load the address of a TLS descriptor for the
current module in the GOT.
Similar in other respects to tlsgd.
!gotdtprel
Used with an ldq instruction to load the offset of the TLS symbol within its
module’s thread-local storage block. Also known as the dynamic thread pointer
offset or dtp-relative offset.
!dtprelhi
!dtprello
!dtprel
Like gprel relocations except they compute dtp-relative offsets.
!gottprel
Used with an ldq instruction to load the offset of the TLS symbol from the
thread pointer. Also known as the tp-relative offset.
!tprelhi
!tprello
!tprel
Like gprel relocations except they compute tp-relative offsets.
9.1.4 Floating Point
The Alpha family uses both ieee and VAX floating-point numbers.
9.1.5 Alpha Assembler Directives
as for the Alpha supports many additional directives for compatibility with the native
assembler. This section describes them only briefly.
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Using as
These are the additional directives in as for the Alpha:
.arch cpu
Specifies the target processor. This is equivalent to the ‘-mcpu ’ command-line
option. See Section 9.1.2 [Alpha Options], page 80, for a list of values for cpu.
.ent function [, n ]
Mark the beginning of function. An optional number may follow for compatibility with the OSF/1 assembler, but is ignored. When generating .mdebug
information, this will create a procedure descriptor for the function. In ELF,
it will mark the symbol as a function a-la the generic .type directive.
.end function
Mark the end of function. In ELF, it will set the size of the symbol a-la the
generic .size directive.
.mask mask , offset
Indicate which of the integer registers are saved in the current function’s stack
frame. mask is interpreted a bit mask in which bit n set indicates that register
n is saved. The registers are saved in a block located offset bytes from the
canonical frame address (CFA) which is the value of the stack pointer on entry
to the function. The registers are saved sequentially, except that the return
address register (normally $26) is saved first.
This and the other directives that describe the stack frame are currently only
used when generating .mdebug information. They may in the future be used
to generate DWARF2 .debug_frame unwind information for hand written assembly.
.fmask mask , offset
Indicate which of the floating-point registers are saved in the current stack
frame. The mask and offset parameters are interpreted as with .mask.
.frame framereg , frameoffset , retreg [, argoffset ]
Describes the shape of the stack frame. The frame pointer in use is framereg;
normally this is either $fp or $sp. The frame pointer is frameoffset bytes
below the CFA. The return address is initially located in retreg until it is saved
as indicated in .mask. For compatibility with OSF/1 an optional argoffset
parameter is accepted and ignored. It is believed to indicate the offset from the
CFA to the saved argument registers.
.prologue n
Indicate that the stack frame is set up and all registers have been spilled. The
argument n indicates whether and how the function uses the incoming procedure
vector (the address of the called function) in $27. 0 indicates that $27 is not
used; 1 indicates that the first two instructions of the function use $27 to
perform a load of the GP register; 2 indicates that $27 is used in some nonstandard way and so the linker cannot elide the load of the procedure vector
during relaxation.
.usepv function , which
Used to indicate the use of the $27 register, similar to .prologue, but without
the other semantics of needing to be inside an open .ent/.end block.
Chapter 9: Machine Dependent Features
85
The which argument should be either no, indicating that $27 is not used, or
std, indicating that the first two instructions of the function perform a GP
load.
One might use this directive instead of .prologue if you are also using dwarf2
CFI directives.
.gprel32 expression
Computes the difference between the address in expression and the GP for the
current object file, and stores it in 4 bytes. In addition to being smaller than a
full 8 byte address, this also does not require a dynamic relocation when used
in a shared library.
.t_floating expression
Stores expression as an ieee double precision value.
.s_floating expression
Stores expression as an ieee single precision value.
.f_floating expression
Stores expression as a VAX F format value.
.g_floating expression
Stores expression as a VAX G format value.
.d_floating expression
Stores expression as a VAX D format value.
.set feature
Enables or disables various assembler features. Using the positive name of the
feature enables while using ‘nofeature ’ disables.
at
Indicates that macro expansions may clobber the assembler temporary ($at or $28) register. Some macros may not be expanded
without this and will generate an error message if noat is in effect.
When at is in effect, a warning will be generated if $at is used by
the programmer.
macro
Enables the expansion of macro instructions. Note that variants of
real instructions, such as br label vs br $31,label are considered
alternate forms and not macros.
move
reorder
volatile
These control whether and how the assembler may re-order instructions. Accepted for compatibility with the OSF/1 assembler, but
as does not do instruction scheduling, so these features are ignored.
The following directives are recognized for compatibility with the OSF/1 assembler but
are ignored.
.proc
.aproc
.reguse
.livereg
.option
.aent
.ugen
.eflag
.alias
.noalias
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9.1.6 Opcodes
For detailed information on the Alpha machine instruction set, see the Alpha Architecture
Handbook located at
ftp://ftp.digital.com/pub/Digital/info/semiconductor/literature/alphaahb.pdf
Chapter 9: Machine Dependent Features
87
9.2 ARC Dependent Features
9.2.1 Options
-marc[5|6|7|8]
This option selects the core processor variant. Using -marc is the same as
-marc6, which is also the default.
arc5
Base instruction set.
arc6
Jump-and-link (jl) instruction. No requirement of an instruction
between setting flags and conditional jump. For example:
mov.f r0,r1
beq
foo
arc7
Break (brk) and sleep (sleep) instructions.
arc8
Software interrupt (swi) instruction.
Note: the .option directive can to be used to select a core variant from within
assembly code.
-EB
This option specifies that the output generated by the assembler should be
marked as being encoded for a big-endian processor.
-EL
This option specifies that the output generated by the assembler should be
marked as being encoded for a little-endian processor - this is the default.
9.2.2 Syntax
9.2.2.1 Special Characters
The presence of a ‘#’ on a line indicates the start of a comment that extends to the end of the
current line. Note that if a line starts with a ‘#’ character then it can also be a logical line
number directive (see Section 3.3 [Comments], page 25) or a preprocessor control command
(see Section 3.1 [Preprocessing], page 25).
The ARC assembler does not support a line separator character.
9.2.2.2 Register Names
*TODO*
9.2.3 Floating Point
The ARC core does not currently have hardware floating point support. Software floating
point support is provided by GCC and uses ieee floating-point numbers.
9.2.4 ARC Machine Directives
The ARC version of as supports the following additional machine directives:
.2byte expressions
*TODO*
.3byte expressions
*TODO*
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Using as
.4byte expressions
*TODO*
.extAuxRegister name ,address ,mode
The ARCtangent A4 has extensible auxiliary register space. The auxiliary
registers can be defined in the assembler source code by using this directive.
The first parameter is the name of the new auxiallry register. The second
parameter is the address of the register in the auxiliary register memory map
for the variant of the ARC. The third parameter specifies the mode in which
the register can be operated is and it can be one of:
r (readonly)
w (write only)
r|w (read or write)
For example:
.extAuxRegister mulhi,0x12,w
This specifies an extension auxiliary register called mulhi which is at address
0x12 in the memory space and which is only writable.
.extCondCode suffix ,value
The condition codes on the ARCtangent A4 are extensible and can be specified
by means of this assembler directive. They are specified by the suffix and the
value for the condition code. They can be used to specify extra condition codes
with any values. For example:
.extCondCode is_busy,0x14
add.is_busy
bis_busy
r1,r2,r3
_main
.extCoreRegister name ,regnum ,mode ,shortcut
Specifies an extension core register name for the application. This allows a
register name with a valid regnum between 0 and 60, with the following as
valid values for mode
‘r (readonly)’
‘w (write only)’
‘r|w (read or write)’
The other parameter gives a description of the register having a shortcut in the
pipeline. The valid values are:
can_shortcut
cannot_shortcut
For example:
.extCoreRegister mlo,57,r,can_shortcut
This defines an extension core register mlo with the value 57 which can shortcut
the pipeline.
.extInstruction name ,opcode ,subopcode ,suffixclass ,syntaxclass
The ARCtangent A4 allows the user to specify extension instructions. The
extension instructions are not macros. The assembler creates encodings for use
Chapter 9: Machine Dependent Features
89
of these instructions according to the specification by the user. The parameters
are:
•name
Name of the extension instruction
•opcode
Opcode to be used. (Bits 27:31 in the encoding). Valid values
0x10-0x1f or 0x03
•subopcode
Subopcode to be used. Valid values are from 0x09-0x3f. However
the correct value also depends on syntaxclass
•suffixclass
Determines the kinds of suffixes to be allowed. Valid values are
SUFFIX_NONE, SUFFIX_COND, SUFFIX_FLAG which indicates the absence or presence of conditional suffixes and flag setting by the extension instruction. It is also possible to specify that an instruction
sets the flags and is conditional by using SUFFIX_CODE | SUFFIX_
FLAG.
•syntaxclass
Determines the syntax class for the instruction. It can have the
following values:
SYNTAX_2OP:
2 Operand Instruction
SYNTAX_3OP:
3 Operand Instruction
In addition there could be modifiers for the syntax class as described
below:
Syntax Class Modifiers are:
− OP1_MUST_BE_IMM: Modifies syntax class SYNTAX 3OP,
specifying that the first operand of a three-operand
instruction must be an immediate (i.e., the result is
discarded). OP1 MUST BE IMM is used by bitwise ORing
it with SYNTAX 3OP as given in the example below.
This could usually be used to set the flags using specific
instructions and not retain results.
− OP1_IMM_IMPLIED: Modifies syntax class SYNTAX 20P,
it specifies that there is an implied immediate destination
operand which does not appear in the syntax. For example, if
the source code contains an instruction like:
inst r1,r2
it really means that the first argument is an implied immediate
(that is, the result is discarded). This is the same as though the
source code were: inst 0,r1,r2. You use OP1 IMM IMPLIED
by bitwise ORing it with SYNTAX 20P.
For example, defining 64-bit multiplier with immediate operands:
90
Using as
.extInstruction mp64,0x14,0x0,SUFFIX_COND | SUFFIX_FLAG ,
SYNTAX_3OP|OP1_MUST_BE_IMM
The above specifies an extension instruction called mp64 which has 3 operands,
sets the flags, can be used with a condition code, for which the first operand is
an immediate. (Equivalent to discarding the result of the operation).
.extInstruction mul64,0x14,0x00,SUFFIX_COND, SYNTAX_2OP|OP1_IMM_IMPLIED
This describes a 2 operand instruction with an implicit first immediate operand.
The result of this operation would be discarded.
.half expressions
*TODO*
.long expressions
*TODO*
.option arc|arc5|arc6|arc7|arc8
The .option directive must be followed by the desired core version. Again arc
is an alias for arc6.
Note: the .option directive overrides the command line option -marc; a warning is emitted when the version is not consistent between the two - even for the
implicit default core version (arc6).
.short expressions
*TODO*
.word expressions
*TODO*
9.2.5 Opcodes
For information on the ARC instruction set, see ARC Programmers Reference Manual,
ARC International (www.arc.com)
Chapter 9: Machine Dependent Features
91
9.3 ARM Dependent Features
9.3.1 Options
-mcpu=processor [+extension ...]
This option specifies the target processor. The assembler will issue an
error message if an attempt is made to assemble an instruction which will
not execute on the target processor. The following processor names are
recognized: arm1, arm2, arm250, arm3, arm6, arm60, arm600, arm610, arm620,
arm7, arm7m, arm7d, arm7dm, arm7di, arm7dmi, arm70, arm700, arm700i,
arm710, arm710t, arm720, arm720t, arm740t, arm710c, arm7100, arm7500,
arm7500fe, arm7t, arm7tdmi, arm7tdmi-s, arm8, arm810, strongarm,
strongarm1, strongarm110, strongarm1100, strongarm1110, arm9,
arm920, arm920t, arm922t, arm940t, arm9tdmi, fa526 (Faraday FA526
processor), fa626 (Faraday FA626 processor), arm9e, arm926e, arm926ej-s,
arm946e-r0, arm946e, arm946e-s, arm966e-r0, arm966e, arm966e-s,
arm968e-s, arm10t, arm10tdmi, arm10e, arm1020, arm1020t, arm1020e,
arm1022e, arm1026ej-s, fa606te (Faraday FA606TE processor), fa616te
(Faraday FA616TE processor), fa626te (Faraday FA626TE processor),
fmp626 (Faraday FMP626 processor), fa726te (Faraday FA726TE processor),
arm1136j-s, arm1136jf-s, arm1156t2-s, arm1156t2f-s, arm1176jz-s,
arm1176jzf-s, mpcore, mpcorenovfp, cortex-a5, cortex-a7, cortex-a8,
cortex-a9, cortex-a15, cortex-r4, cortex-r4f, cortex-m4, cortex-m3,
cortex-m1, cortex-m0, cortex-m0plus, ep9312 (ARM920 with Cirrus
Maverick coprocessor), i80200 (Intel XScale processor) iwmmxt (Intel(r)
XScale processor with Wireless MMX(tm) technology coprocessor) and
xscale. The special name all may be used to allow the assembler to accept
instructions valid for any ARM processor.
In addition to the basic instruction set, the assembler can be told to accept
various extension mnemonics that extend the processor using the co-processor
instruction space. For example, -mcpu=arm920+maverick is equivalent to specifying -mcpu=ep9312.
Multiple extensions may be specified, separated by a +. The extensions should
be specified in ascending alphabetical order.
Some extensions may be restricted to particular architectures; this is documented in the list of extensions below.
Extension mnemonics may also be removed from those the assembler accepts.
This is done be prepending no to the option that adds the extension.
Extensions that are removed should be listed after all extensions which
have been added, again in ascending alphabetical order. For example,
-mcpu=ep9312+nomaverick is equivalent to specifying -mcpu=arm920.
The following extensions are currently supported: idiv, (Integer Divide Extensions for v7-A and v7-R architectures), iwmmxt, iwmmxt2, maverick, mp
(Multiprocessing Extensions for v7-A and v7-R architectures), os (Operating
System for v6M architecture), sec (Security Extensions for v6K and v7-A archi-
92
Using as
tectures), virt (Virtualization Extensions for v7-A architecture, implies idiv),
and xscale.
-march=architecture [+extension ...]
This option specifies the target architecture. The assembler will issue an
error message if an attempt is made to assemble an instruction which will
not execute on the target architecture. The following architecture names are
recognized: armv1, armv2, armv2a, armv2s, armv3, armv3m, armv4, armv4xm,
armv4t, armv4txm, armv5, armv5t, armv5txm, armv5te, armv5texp, armv6,
armv6j, armv6k, armv6z, armv6zk, armv6-m, armv6s-m, armv7, armv7-a,
armv7-r, armv7-m, armv7e-m, iwmmxt and xscale. If both -mcpu and -march
are specified, the assembler will use the setting for -mcpu.
The architecture option can be extended with the same instruction set extension
options as the -mcpu option.
-mfpu=floating-point-format
This option specifies the floating point format to assemble for. The assembler
will issue an error message if an attempt is made to assemble an instruction
which will not execute on the target floating point unit. The following
format options are recognized: softfpa, fpe, fpe2, fpe3, fpa, fpa10,
fpa11, arm7500fe, softvfp, softvfp+vfp, vfp, vfp10, vfp10-r0, vfp9,
vfpxd, vfpv2, vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd,
vfpv3xd-d16, vfpv4, vfpv4-d16, fpv4-sp-d16, arm1020t, arm1020e,
arm1136jf-s, maverick, neon, and neon-vfpv4.
In addition to determining which instructions are assembled, this option also
affects the way in which the .double assembler directive behaves when assembling little-endian code.
The default is dependent on the processor selected. For Architecture 5 or later,
the default is to assembler for VFP instructions; for earlier architectures the
default is to assemble for FPA instructions.
-mthumb
This option specifies that the assembler should start assembling Thumb instructions; that is, it should behave as though the file starts with a .code 16
directive.
-mthumb-interwork
This option specifies that the output generated by the assembler should be
marked as supporting interworking.
-mimplicit-it=never
-mimplicit-it=always
-mimplicit-it=arm
-mimplicit-it=thumb
The -mimplicit-it option controls the behavior of the assembler when conditional instructions are not enclosed in IT blocks. There are four possible
behaviors. If never is specified, such constructs cause a warning in ARM code
and an error in Thumb-2 code. If always is specified, such constructs are accepted in both ARM and Thumb-2 code, where the IT instruction is added
implicitly. If arm is specified, such constructs are accepted in ARM code and
Chapter 9: Machine Dependent Features
93
cause an error in Thumb-2 code. If thumb is specified, such constructs cause
a warning in ARM code and are accepted in Thumb-2 code. If you omit this
option, the behavior is equivalent to -mimplicit-it=arm.
-mapcs-26
-mapcs-32
These options specify that the output generated by the assembler should be
marked as supporting the indicated version of the Arm Procedure. Calling
Standard.
-matpcs
This option specifies that the output generated by the assembler should be
marked as supporting the Arm/Thumb Procedure Calling Standard. If enabled
this option will cause the assembler to create an empty debugging section in
the object file called .arm.atpcs. Debuggers can use this to determine the ABI
being used by.
-mapcs-float
This indicates the floating point variant of the APCS should be used. In this
variant floating point arguments are passed in FP registers rather than integer
registers.
-mapcs-reentrant
This indicates that the reentrant variant of the APCS should be used. This
variant supports position independent code.
-mfloat-abi=abi
This option specifies that the output generated by the assembler should be
marked as using specified floating point ABI. The following values are recognized: soft, softfp and hard.
-meabi=ver
This option specifies which EABI version the produced object files should conform to. The following values are recognized: gnu, 4 and 5.
-EB
This option specifies that the output generated by the assembler should be
marked as being encoded for a big-endian processor.
-EL
This option specifies that the output generated by the assembler should be
marked as being encoded for a little-endian processor.
-k
This option specifies that the output of the assembler should be marked as
position-independent code (PIC).
--fix-v4bx
Allow BX instructions in ARMv4 code. This is intended for use with the linker
option of the same name.
-mwarn-deprecated
-mno-warn-deprecated
Enable or disable warnings about using deprecated options or features. The
default is to warn.
9.3.2 Syntax
94
Using as
9.3.2.1 Instruction Set Syntax
Two slightly different syntaxes are support for ARM and THUMB instructions. The default,
divided, uses the old style where ARM and THUMB instructions had their own, separate
syntaxes. The new, unified syntax, which can be selected via the .syntax directive, and
has the following main features:
•
Immediate operands do not require a # prefix.
•
The IT instruction may appear, and if it does it is validated against subsequent conditional affixes. In ARM mode it does not generate machine code, in
THUMB mode it does.
•
For ARM instructions the conditional affixes always appear at the end of the
instruction. For THUMB instructions conditional affixes can be used, but only
inside the scope of an IT instruction.
•
All of the instructions new to the V6T2 architecture (and later) are available.
(Only a few such instructions can be written in the divided syntax).
•
The .N and .W suffixes are recognized and honored.
•
All instructions set the flags if and only if they have an s affix.
9.3.2.2 Special Characters
The presence of a ‘@’ anywhere on a line indicates the start of a comment that extends to
the end of that line.
If a ‘#’ appears as the first character of a line then the whole line is treated as a comment,
but in this case the line could also be a logical line number directive (see Section 3.3
[Comments], page 25) or a preprocessor control command (see Section 3.1 [Preprocessing],
page 25).
The ‘;’ character can be used instead of a newline to separate statements.
Either ‘#’ or ‘$’ can be used to indicate immediate operands.
*TODO* Explain about /data modifier on symbols.
9.3.2.3 Register Names
*TODO* Explain about ARM register naming, and the predefined names.
9.3.2.4 NEON Alignment Specifiers
Some NEON load/store instructions allow an optional address alignment qualifier. The
ARM documentation specifies that this is indicated by ‘@ align ’. However GAS already
interprets the ‘@’ character as a "line comment" start, so ‘: align ’ is used instead. For
example:
vld1.8 {q0}, [r0, :128]
9.3.3 Floating Point
The ARM family uses ieee floating-point numbers.
Chapter 9: Machine Dependent Features
95
9.3.3.1 ARM relocation generation
Specific data relocations can be generated by putting the relocation name in parentheses
after the symbol name. For example:
.word foo(TARGET1)
This will generate an ‘R_ARM_TARGET1’ relocation against the symbol foo. The following
relocations are supported: GOT, GOTOFF, TARGET1, TARGET2, SBREL, TLSGD, TLSLDM, TLSLDO,
TLSDESC, TLSCALL, GOTTPOFF, GOT_PREL and TPOFF.
For compatibility with older toolchains the assembler also accepts (PLT) after branch
targets. This will generate the deprecated ‘R_ARM_PLT32’ relocation.
Relocations for ‘MOVW’ and ‘MOVT’ instructions can be generated by prefixing the value
with ‘#:lower16:’ and ‘#:upper16’ respectively. For example to load the 32-bit address of
foo into r0:
MOVW r0, #:lower16:foo
MOVT r0, #:upper16:foo
9.3.4 ARM Machine Directives
.2byte expression [, expression ]*
.4byte expression [, expression ]*
.8byte expression [, expression ]*
These directives write 2, 4 or 8 byte values to the output section.
.align expression [, expression ]
This is the generic .align directive. For the ARM however if the first argument
is zero (ie no alignment is needed) the assembler will behave as if the argument
had been 2 (ie pad to the next four byte boundary). This is for compatibility
with ARM’s own assembler.
.arch name
Select the target architecture. Valid values for name are the same as for the
‘-march’ commandline option.
Specifying .arch clears any previously selected architecture extensions.
.arch_extension name
Add or remove an architecture extension to the target architecture. Valid values
for name are the same as those accepted as architectural extensions by the
‘-mcpu’ commandline option.
.arch_extension may be used multiple times to add or remove extensions
incrementally to the architecture being compiled for.
.arm
This performs the same action as .code 32.
.pad #count
Generate unwinder annotations for a stack adjustment of count bytes. A positive value indicates the function prologue allocated stack space by decrementing
the stack pointer.
.bss
This directive switches to the .bss section.
96
Using as
.cantunwind
Prevents unwinding through the current function. No personality routine or
exception table data is required or permitted.
.code [16|32]
This directive selects the instruction set being generated. The value 16 selects
Thumb, with the value 32 selecting ARM.
.cpu name
Select the target processor. Valid values for name are the same as for the
‘-mcpu’ commandline option.
Specifying .cpu clears any previously selected architecture extensions.
name .dn register name [.type ] [[index ]]
name .qn register name [.type ] [[index ]]
The dn and qn directives are used to create typed and/or indexed register aliases
for use in Advanced SIMD Extension (Neon) instructions. The former should
be used to create aliases of double-precision registers, and the latter to create
aliases of quad-precision registers.
If these directives are used to create typed aliases, those aliases can be used
in Neon instructions instead of writing types after the mnemonic or after each
operand. For example:
x .dn d2.f32
y .dn d3.f32
z .dn d4.f32[1]
vmul x,y,z
This is equivalent to writing the following:
vmul.f32 d2,d3,d4[1]
Aliases created using dn or qn can be destroyed using unreq.
.eabi_attribute tag , value
Set the EABI object attribute tag to value.
The tag is either an attribute number, or one of the following: Tag_
CPU_raw_name, Tag_CPU_name, Tag_CPU_arch, Tag_CPU_arch_profile,
Tag_ARM_ISA_use, Tag_THUMB_ISA_use, Tag_FP_arch, Tag_WMMX_arch,
Tag_Advanced_SIMD_arch,
Tag_PCS_config,
Tag_ABI_PCS_R9_use,
Tag_ABI_PCS_RW_data,
Tag_ABI_PCS_RO_data,
Tag_ABI_PCS_GOT_use,
Tag_ABI_PCS_wchar_t,
Tag_ABI_FP_rounding,
Tag_ABI_FP_denormal,
Tag_ABI_FP_exceptions,
Tag_ABI_FP_user_exceptions,
Tag_ABI_FP_
number_model,
Tag_ABI_align_needed,
Tag_ABI_align_preserved,
Tag_ABI_enum_size,
Tag_ABI_HardFP_use,
Tag_ABI_VFP_args,
Tag_ABI_WMMX_args,
Tag_ABI_optimization_goals,
Tag_ABI_FP_
optimization_goals, Tag_compatibility, Tag_CPU_unaligned_access,
Tag_FP_HP_extension,
Tag_ABI_FP_16bit_format,
Tag_MPextension_
use,
Tag_DIV_use,
Tag_nodefaults,
Tag_also_compatible_with,
Tag_conformance, Tag_T2EE_use, Tag_Virtualization_use
The value is either a number, "string", or number, "string" depending on
the tag.
Chapter 9: Machine Dependent Features
97
Note - the following legacy values are also accepted by tag: Tag_VFP_arch, Tag_
ABI_align8_needed, Tag_ABI_align8_preserved, Tag_VFP_HP_extension,
.even
This directive aligns to an even-numbered address.
.extend expression [, expression ]*
.ldouble expression [, expression ]*
These directives write 12byte long double floating-point values to the output
section. These are not compatible with current ARM processors or ABIs.
.fnend
Marks the end of a function with an unwind table entry. The unwind index
table entry is created when this directive is processed.
If no personality routine has been specified then standard personality routine
0 or 1 will be used, depending on the number of unwind opcodes required.
.fnstart
Marks the start of a function with an unwind table entry.
.force_thumb
This directive forces the selection of Thumb instructions, even if the target
processor does not support those instructions
.fpu name
Select the floating-point unit to assemble for. Valid values for name are the
same as for the ‘-mfpu’ commandline option.
.handlerdata
Marks the end of the current function, and the start of the exception table entry
for that function. Anything between this directive and the .fnend directive will
be added to the exception table entry.
Must be preceded by a .personality or .personalityindex directive.
.inst opcode [ , ... ]
.inst.n opcode [ , ... ]
.inst.w opcode [ , ... ]
Generates the instruction corresponding to the numerical value opcode.
.inst.n and .inst.w allow the Thumb instruction size to be specified
explicitly, overriding the normal encoding rules.
.ldouble expression [, expression ]*
See .extend.
.ltorg
This directive causes the current contents of the literal pool to be dumped into
the current section (which is assumed to be the .text section) at the current
location (aligned to a word boundary). GAS maintains a separate literal pool
for each section and each sub-section. The .ltorg directive will only affect the
literal pool of the current section and sub-section. At the end of assembly all
remaining, un-empty literal pools will automatically be dumped.
Note - older versions of GAS would dump the current literal pool any time a
section change occurred. This is no longer done, since it prevents accurate
control of the placement of literal pools.
.movsp reg [, #offset ]
Tell the unwinder that reg contains an offset from the current stack pointer. If
offset is not specified then it is assumed to be zero.
98
Using as
.object_arch name
Override the architecture recorded in the EABI object attribute section. Valid
values for name are the same as for the .arch directive. Typically this is useful
when code uses runtime detection of CPU features.
.packed expression [, expression ]*
This directive writes 12-byte packed floating-point values to the output section.
These are not compatible with current ARM processors or ABIs.
.pad #count
Generate unwinder annotations for a stack adjustment of count bytes. A positive value indicates the function prologue allocated stack space by decrementing
the stack pointer.
.personality name
Sets the personality routine for the current function to name.
.personalityindex index
Sets the personality routine for the current function to the EABI standard
routine number index
.pool
This is a synonym for .ltorg.
name .req register name
This creates an alias for register name called name. For example:
foo .req r0
.save reglist
Generate unwinder annotations to restore the registers in reglist. The format
of reglist is the same as the corresponding store-multiple instruction.
core registers
.save {r4, r5, r6, lr}
stmfd sp!, {r4, r5, r6, lr}
FPA registers
.save f4, 2
sfmfd f4, 2, [sp]!
VFP registers
.save {d8, d9, d10}
fstmdx sp!, {d8, d9, d10}
iWMMXt registers
.save {wr10, wr11}
wstrd wr11, [sp, #-8]!
wstrd wr10, [sp, #-8]!
or
.save wr11
wstrd wr11, [sp, #-8]!
.save wr10
wstrd wr10, [sp, #-8]!
.setfp fpreg , spreg [, #offset ]
Make all unwinder annotations relative to a frame pointer. Without this the
unwinder will use offsets from the stack pointer.
The syntax of this directive is the same as the add or mov instruction used to set
the frame pointer. spreg must be either sp or mentioned in a previous .movsp
directive.
Chapter 9: Machine Dependent Features
99
.movsp ip
mov ip, sp
...
.setfp fp, ip, #4
add fp, ip, #4
.secrel32 expression [, expression ]*
This directive emits relocations that evaluate to the section-relative offset of
each expression’s symbol. This directive is only supported for PE targets.
.syntax [unified | divided]
This directive sets the Instruction Set Syntax as described in the Section 9.3.2.1
[ARM-Instruction-Set], page 94 section.
.thumb
This performs the same action as .code 16.
.thumb_func
This directive specifies that the following symbol is the name of a Thumb encoded function. This information is necessary in order to allow the assembler
and linker to generate correct code for interworking between Arm and Thumb
instructions and should be used even if interworking is not going to be performed. The presence of this directive also implies .thumb
This directive is not neccessary when generating EABI objects. On these targets
the encoding is implicit when generating Thumb code.
.thumb_set
This performs the equivalent of a .set directive in that it creates a symbol
which is an alias for another symbol (possibly not yet defined). This directive
also has the added property in that it marks the aliased symbol as being a
thumb function entry point, in the same way that the .thumb_func directive
does.
.tlsdescseq tls-variable
This directive is used to annotate parts of an inlined TLS descriptor trampoline.
Normally the trampoline is provided by the linker, and this directive is not
needed.
.unreq alias-name
This undefines a register alias which was previously defined using the req, dn
or qn directives. For example:
foo .req r0
.unreq foo
An error occurs if the name is undefined. Note - this pseudo op can be used to
delete builtin in register name aliases (eg ’r0’). This should only be done if it
is really necessary.
.unwind_raw offset , byte1 , ...
Insert one of more arbitary unwind opcode bytes, which are known to adjust
the stack pointer by offset bytes.
For example .unwind_raw 4, 0xb1, 0x01 is equivalent to .save {r0}
100
Using as
.vsave vfp-reglist
Generate unwinder annotations to restore the VFP registers in vfp-reglist using
FLDMD. Also works for VFPv3 registers that are to be restored using VLDM.
The format of vfp-reglist is the same as the corresponding store-multiple instruction.
VFP registers
.vsave {d8, d9, d10}
fstmdd sp!, {d8, d9, d10}
VFPv3 registers
.vsave {d15, d16, d17}
vstm sp!, {d15, d16, d17}
Since FLDMX and FSTMX are now deprecated, this directive should be used
in favour of .save for saving VFP registers for ARMv6 and above.
9.3.5 Opcodes
as implements all the standard ARM opcodes. It also implements several pseudo opcodes,
including several synthetic load instructions.
NOP
nop
This pseudo op will always evaluate to a legal ARM instruction that does nothing. Currently it will evaluate to MOV r0, r0.
LDR
ldr , =
If expression evaluates to a numeric constant then a MOV or MVN instruction
will be used in place of the LDR instruction, if the constant can be generated
by either of these instructions. Otherwise the constant will be placed into the
nearest literal pool (if it not already there) and a PC relative LDR instruction
will be generated.
ADR
adr
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