1 \input texinfo @c -*-Texinfo-*-
2 @c Copyright (c) 1991, 92, 93, 94, 95, 96, 97, 1998
3 @c Free Software Foundation, Inc.
4 @c UPDATE!! On future updates--
5 @c (1) check for new machine-dep cmdline options in
6 @c md_parse_option definitions in config/tc-*.c
7 @c (2) for platform-specific directives, examine md_pseudo_op
9 @c (3) for object-format specific directives, examine obj_pseudo_op
11 @c (4) portable directives in potable[] in read.c
15 @c defaults, config file may override:
18 @include asconfig.texi
21 @c common OR combinations of conditions
41 @set abnormal-separator
45 @settitle Using @value{AS}
48 @settitle Using @value{AS} (@value{TARGET})
50 @setchapternewpage odd
55 @c WARE! Some of the machine-dependent sections contain tables of machine
56 @c instructions. Except in multi-column format, these tables look silly.
57 @c Unfortunately, Texinfo doesn't have a general-purpose multi-col format, so
58 @c the multi-col format is faked within @example sections.
60 @c Again unfortunately, the natural size that fits on a page, for these tables,
61 @c is different depending on whether or not smallbook is turned on.
62 @c This matters, because of order: text flow switches columns at each page
65 @c The format faked in this source works reasonably well for smallbook,
66 @c not well for the default large-page format. This manual expects that if you
67 @c turn on @smallbook, you will also uncomment the "@set SMALL" to enable the
68 @c tables in question. You can turn on one without the other at your
69 @c discretion, of course.
72 @c the insn tables look just as silly in info files regardless of smallbook,
73 @c might as well show 'em anyways.
79 * As: (as). The GNU assembler.
88 This file documents the GNU Assembler "@value{AS}".
90 Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 1998 Free Software Foundation, Inc.
92 Permission is granted to make and distribute verbatim copies of
93 this manual provided the copyright notice and this permission notice
94 are preserved on all copies.
97 Permission is granted to process this file through Tex and print the
98 results, provided the printed document carries copying permission
99 notice identical to this one except for the removal of this paragraph
100 (this paragraph not being relevant to the printed manual).
103 Permission is granted to copy and distribute modified versions of this manual
104 under the conditions for verbatim copying, provided that the entire resulting
105 derived work is distributed under the terms of a permission notice identical to
108 Permission is granted to copy and distribute translations of this manual
109 into another language, under the above conditions for modified versions.
113 @title Using @value{AS}
114 @subtitle The @sc{gnu} Assembler
116 @subtitle for the @value{TARGET} family
119 @subtitle Version @value{VERSION}
122 The Free Software Foundation Inc. thanks The Nice Computer
123 Company of Australia for loaning Dean Elsner to write the
124 first (Vax) version of @code{as} for Project @sc{gnu}.
125 The proprietors, management and staff of TNCCA thank FSF for
126 distracting the boss while they got some work
129 @author Dean Elsner, Jay Fenlason & friends
133 \hfill {\it Using {\tt @value{AS}}}\par
134 \hfill Edited by Cygnus Support\par
136 %"boxit" macro for figures:
137 %Modified from Knuth's ``boxit'' macro from TeXbook (answer to exercise 21.3)
138 \gdef\boxit#1#2{\vbox{\hrule\hbox{\vrule\kern3pt
139 \vbox{\parindent=0pt\parskip=0pt\hsize=#1\kern3pt\strut\hfil
140 #2\hfil\strut\kern3pt}\kern3pt\vrule}\hrule}}%box with visible outline
141 \gdef\ibox#1#2{\hbox to #1{#2\hfil}\kern8pt}% invisible box
144 @vskip 0pt plus 1filll
145 Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 1998 Free Software Foundation, Inc.
147 Permission is granted to make and distribute verbatim copies of
148 this manual provided the copyright notice and this permission notice
149 are preserved on all copies.
151 Permission is granted to copy and distribute modified versions of this manual
152 under the conditions for verbatim copying, provided that the entire resulting
153 derived work is distributed under the terms of a permission notice identical to
156 Permission is granted to copy and distribute translations of this manual
157 into another language, under the above conditions for modified versions.
162 @top Using @value{AS}
164 This file is a user guide to the @sc{gnu} assembler @code{@value{AS}} version
167 This version of the file describes @code{@value{AS}} configured to generate
168 code for @value{TARGET} architectures.
171 * Overview:: Overview
172 * Invoking:: Command-Line Options
174 * Sections:: Sections and Relocation
176 * Expressions:: Expressions
177 * Pseudo Ops:: Assembler Directives
178 * Machine Dependencies:: Machine Dependent Features
179 * Reporting Bugs:: Reporting Bugs
180 * Acknowledgements:: Who Did What
188 This manual is a user guide to the @sc{gnu} assembler @code{@value{AS}}.
190 This version of the manual describes @code{@value{AS}} configured to generate
191 code for @value{TARGET} architectures.
195 @cindex invocation summary
196 @cindex option summary
197 @cindex summary of options
198 Here is a brief summary of how to invoke @code{@value{AS}}. For details,
199 @pxref{Invoking,,Comand-Line Options}.
201 @c We don't use deffn and friends for the following because they seem
202 @c to be limited to one line for the header.
204 @value{AS} [ -a[cdhlns][=file] ] [ -D ] [ --defsym @var{sym}=@var{val} ]
205 [ -f ] [ --gstabs ] [ --gdwarf2 ] [ --help ] [ -I @var{dir} ] [ -J ] [ -K ] [ -L ]
206 [ --keep-locals ] [ -o @var{objfile} ] [ -R ] [ --statistics ] [ -v ]
207 [ -version ] [ --version ] [ -W ] [ -w ] [ -x ] [ -Z ]
209 @c am29k has no machine-dependent assembler options
212 [ -mbig-endian | -mlittle-endian ]
215 [ -m[arm]1 | -m[arm]2 | -m[arm]250 | -m[arm]3 | -m[arm]6 | -m[arm]60 |
216 -m[arm]600 | -m[arm]610 | -m[arm]620 | -m[arm]7[t][[d]m[i]][fe] | -m[arm]70 |
217 -m[arm]700 | -m[arm]710[c] | -m[arm]7100 | -m[arm]7500 | -m[arm]8 |
218 -m[arm]810 | -m[arm]9 | -m[arm]920 | -m[arm]920t | -m[arm]9tdmi |
219 -mstrongarm | -mstrongarm110 | -mstrongarm1100 ]
220 [ -m[arm]v2 | -m[arm]v2a | -m[arm]v3 | -m[arm]v3m | -m[arm]v4 | -m[arm]v4t |
221 -m[arm]v5 | -[arm]v5t ]
223 [ -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu ]
225 [ -mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant ]
226 [ -mthumb-interwork ]
237 @c Hitachi family chips have no machine-dependent assembler options
240 @c HPPA has no machine-dependent assembler options (yet).
246 @c The order here is important. See c-sparc.texi.
247 [ -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
248 -Av8plus | -Av8plusa | -Av9 | -Av9a ]
249 [ -xarch=v8plus | -xarch=v8plusa ] [ -bump ] [ -32 | -64 ]
252 @c Z8000 has no machine-dependent assembler options
255 @c see md_parse_option in tc-i960.c
256 [ -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC ]
260 [ -l ] [ -m68000 | -m68010 | -m68020 | ... ]
263 [ -jsri2bsr ] [ -sifilter ] [ -relax ]
266 [ -nocpp ] [ -EL ] [ -EB ] [ -G @var{num} ] [ -mcpu=@var{CPU} ]
267 [ -mips1 ] [ -mips2 ] [ -mips3 ] [ -m4650 ] [ -no-m4650 ]
268 [ --trap ] [ --break ]
269 [ --emulation=@var{name} ]
271 [ -- | @var{files} @dots{} ]
276 Turn on listings, in any of a variety of ways:
280 omit false conditionals
283 omit debugging directives
286 include high-level source
292 include macro expansions
295 omit forms processing
301 set the name of the listing file
304 You may combine these options; for example, use @samp{-aln} for assembly
305 listing without forms processing. The @samp{=file} option, if used, must be
306 the last one. By itself, @samp{-a} defaults to @samp{-ahls}.
309 Ignored. This option is accepted for script compatibility with calls to
312 @item --defsym @var{sym}=@var{value}
313 Define the symbol @var{sym} to be @var{value} before assembling the input file.
314 @var{value} must be an integer constant. As in C, a leading @samp{0x}
315 indicates a hexadecimal value, and a leading @samp{0} indicates an octal value.
318 ``fast''---skip whitespace and comment preprocessing (assume source is
322 Generate stabs debugging information for each assembler line. This
323 may help debugging assembler code, if the debugger can handle it.
326 Generate DWARF2 debugging information for each assembler line. This
327 may help debugging assembler code, if the debugger can handle it.
330 Print a summary of the command line options and exit.
333 Add directory @var{dir} to the search list for @code{.include} directives.
336 Don't warn about signed overflow.
339 @ifclear DIFF-TBL-KLUGE
340 This option is accepted but has no effect on the @value{TARGET} family.
342 @ifset DIFF-TBL-KLUGE
343 Issue warnings when difference tables altered for long displacements.
348 Keep (in the symbol table) local symbols. On traditional a.out systems
349 these start with @samp{L}, but different systems have different local
352 @item -o @var{objfile}
353 Name the object-file output from @code{@value{AS}} @var{objfile}.
356 Fold the data section into the text section.
359 Print the maximum space (in bytes) and total time (in seconds) used by
362 @item --strip-local-absolute
363 Remove local absolute symbols from the outgoing symbol table.
367 Print the @code{as} version.
370 Print the @code{as} version and exit.
373 Suppress warning messages.
382 Generate an object file even after errors.
384 @item -- | @var{files} @dots{}
385 Standard input, or source files to assemble.
390 The following options are available when @value{AS} is configured for
395 @cindex ARC endianness
396 @cindex endianness, ARC
397 @cindex big endian output, ARC
399 Generate ``big endian'' format output.
401 @cindex little endian output, ARC
402 @item -mlittle-endian
403 Generate ``little endian'' format output.
409 The following options are available when @value{AS} is configured for the ARM
413 @item -m[arm][1|2|3|6|7|8|9][...]
414 Specify which ARM processor variant is the target.
415 @item -m[arm]v[2|2a|3|3m|4|4t|5|5t]
416 Specify which ARM architecture variant is used by the target.
417 @item -mthumb | -mall
418 Enable or disable Thumb only instruction decoding.
419 @item -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu
420 Select which Floating Point architcture is the target.
421 @item -mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant | -moabi
422 Select which procedure calling convention is in use.
424 Select either big-endian (-EB) or little-endian (-EL) output.
425 @item -mthumb-interwork
426 Specify that the code has been generated with interworking between Thumb and
429 Specify that PIC code has been generated.
434 The following options are available when @value{AS} is configured for
437 @cindex D10V optimization
438 @cindex optimization, D10V
440 Optimize output by parallelizing instructions.
445 The following options are available when @value{AS} is configured for a D30V
448 @cindex D30V optimization
449 @cindex optimization, D30V
451 Optimize output by parallelizing instructions.
455 Warn when nops are generated.
457 @cindex D30V nops after 32-bit multiply
459 Warn when a nop after a 32-bit multiply instruction is generated.
464 The following options are available when @value{AS} is configured for the
465 Intel 80960 processor.
468 @item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
469 Specify which variant of the 960 architecture is the target.
472 Add code to collect statistics about branches taken.
475 Do not alter compare-and-branch instructions for long displacements;
483 The following options are available when @value{AS} is configured for the
484 Motorola 68000 series.
489 Shorten references to undefined symbols, to one word instead of two.
491 @item -m68000 | -m68008 | -m68010 | -m68020 | -m68030 | -m68040 | -m68060
492 @itemx | -m68302 | -m68331 | -m68332 | -m68333 | -m68340 | -mcpu32 | -m5200
493 Specify what processor in the 68000 family is the target. The default
494 is normally the 68020, but this can be changed at configuration time.
496 @item -m68881 | -m68882 | -mno-68881 | -mno-68882
497 The target machine does (or does not) have a floating-point coprocessor.
498 The default is to assume a coprocessor for 68020, 68030, and cpu32. Although
499 the basic 68000 is not compatible with the 68881, a combination of the
500 two can be specified, since it's possible to do emulation of the
501 coprocessor instructions with the main processor.
503 @item -m68851 | -mno-68851
504 The target machine does (or does not) have a memory-management
505 unit coprocessor. The default is to assume an MMU for 68020 and up.
511 The following options are available when @value{AS} is configured for
512 a picoJava processor.
516 @cindex PJ endianness
517 @cindex endianness, PJ
518 @cindex big endian output, PJ
520 Generate ``big endian'' format output.
522 @cindex little endian output, PJ
524 Generate ``little endian'' format output.
531 The following options are available when @code{@value{AS}} is configured
532 for the SPARC architecture:
535 @item -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
536 @itemx -Av8plus | -Av8plusa | -Av9 | -Av9a
537 Explicitly select a variant of the SPARC architecture.
539 @samp{-Av8plus} and @samp{-Av8plusa} select a 32 bit environment.
540 @samp{-Av9} and @samp{-Av9a} select a 64 bit environment.
542 @samp{-Av8plusa} and @samp{-Av9a} enable the SPARC V9 instruction set with
543 UltraSPARC extensions.
545 @item -xarch=v8plus | -xarch=v8plusa
546 For compatibility with the Solaris v9 assembler. These options are
547 equivalent to -Av8plus and -Av8plusa, respectively.
550 Warn when the assembler switches to another architecture.
555 The following options are available when @value{AS} is configured for
560 This option sets the largest size of an object that can be referenced
561 implicitly with the @code{gp} register. It is only accepted for targets that
562 use ECOFF format, such as a DECstation running Ultrix. The default value is 8.
564 @cindex MIPS endianness
565 @cindex endianness, MIPS
566 @cindex big endian output, MIPS
568 Generate ``big endian'' format output.
570 @cindex little endian output, MIPS
572 Generate ``little endian'' format output.
578 Generate code for a particular MIPS Instruction Set Architecture level.
579 @samp{-mips1} corresponds to the @sc{r2000} and @sc{r3000} processors,
580 @samp{-mips2} to the @sc{r6000} processor, and @samp{-mips3} to the @sc{r4000}
585 Generate code for the MIPS @sc{r4650} chip. This tells the assembler to accept
586 the @samp{mad} and @samp{madu} instruction, and to not schedule @samp{nop}
587 instructions around accesses to the @samp{HI} and @samp{LO} registers.
588 @samp{-no-m4650} turns off this option.
590 @item -mcpu=@var{CPU}
591 Generate code for a particular MIPS cpu. This has little effect on the
592 assembler, but it is passed by @code{@value{GCC}}.
595 @item --emulation=@var{name}
596 This option causes @code{@value{AS}} to emulate @code{@value{AS}} configured
597 for some other target, in all respects, including output format (choosing
598 between ELF and ECOFF only), handling of pseudo-opcodes which may generate
599 debugging information or store symbol table information, and default
600 endianness. The available configuration names are: @samp{mipsecoff},
601 @samp{mipself}, @samp{mipslecoff}, @samp{mipsbecoff}, @samp{mipslelf},
602 @samp{mipsbelf}. The first two do not alter the default endianness from that
603 of the primary target for which the assembler was configured; the others change
604 the default to little- or big-endian as indicated by the @samp{b} or @samp{l}
605 in the name. Using @samp{-EB} or @samp{-EL} will override the endianness
606 selection in any case.
608 This option is currently supported only when the primary target
609 @code{@value{AS}} is configured for is a MIPS ELF or ECOFF target.
610 Furthermore, the primary target or others specified with
611 @samp{--enable-targets=@dots{}} at configuration time must include support for
612 the other format, if both are to be available. For example, the Irix 5
613 configuration includes support for both.
615 Eventually, this option will support more configurations, with more
616 fine-grained control over the assembler's behavior, and will be supported for
620 @code{@value{AS}} ignores this option. It is accepted for compatibility with
628 Control how to deal with multiplication overflow and division by zero.
629 @samp{--trap} or @samp{--no-break} (which are synonyms) take a trap exception
630 (and only work for Instruction Set Architecture level 2 and higher);
631 @samp{--break} or @samp{--no-trap} (also synonyms, and the default) take a
637 The following options are available when @value{AS} is configured for
643 Enable or disable the JSRI to BSR transformation. By default this is enabled.
644 The command line option @samp{-nojsri2bsr} can be used to disable it.
648 Enable or disable the silicon filter behaviour. By default this is disabled.
649 The default can be overidden by the @samp{-sifilter} command line option.
652 Alter jump instructions for long displacements.
659 * Manual:: Structure of this Manual
660 * GNU Assembler:: The GNU Assembler
661 * Object Formats:: Object File Formats
662 * Command Line:: Command Line
663 * Input Files:: Input Files
664 * Object:: Output (Object) File
665 * Errors:: Error and Warning Messages
669 @section Structure of this Manual
671 @cindex manual, structure and purpose
672 This manual is intended to describe what you need to know to use
673 @sc{gnu} @code{@value{AS}}. We cover the syntax expected in source files, including
674 notation for symbols, constants, and expressions; the directives that
675 @code{@value{AS}} understands; and of course how to invoke @code{@value{AS}}.
678 We also cover special features in the @value{TARGET}
679 configuration of @code{@value{AS}}, including assembler directives.
682 This manual also describes some of the machine-dependent features of
683 various flavors of the assembler.
686 @cindex machine instructions (not covered)
687 On the other hand, this manual is @emph{not} intended as an introduction
688 to programming in assembly language---let alone programming in general!
689 In a similar vein, we make no attempt to introduce the machine
690 architecture; we do @emph{not} describe the instruction set, standard
691 mnemonics, registers or addressing modes that are standard to a
692 particular architecture.
694 You may want to consult the manufacturer's
695 machine architecture manual for this information.
699 For information on the H8/300 machine instruction set, see @cite{H8/300
700 Series Programming Manual} (Hitachi ADE--602--025). For the H8/300H,
701 see @cite{H8/300H Series Programming Manual} (Hitachi).
704 For information on the H8/500 machine instruction set, see @cite{H8/500
705 Series Programming Manual} (Hitachi M21T001).
708 For information on the Hitachi SH machine instruction set, see
709 @cite{SH-Microcomputer User's Manual} (Hitachi Micro Systems, Inc.).
712 For information on the Z8000 machine instruction set, see @cite{Z8000 CPU Technical Manual}
716 @c I think this is premature---doc@cygnus.com, 17jan1991
718 Throughout this manual, we assume that you are running @dfn{GNU},
719 the portable operating system from the @dfn{Free Software
720 Foundation, Inc.}. This restricts our attention to certain kinds of
721 computer (in particular, the kinds of computers that @sc{gnu} can run on);
722 once this assumption is granted examples and definitions need less
725 @code{@value{AS}} is part of a team of programs that turn a high-level
726 human-readable series of instructions into a low-level
727 computer-readable series of instructions. Different versions of
728 @code{@value{AS}} are used for different kinds of computer.
731 @c There used to be a section "Terminology" here, which defined
732 @c "contents", "byte", "word", and "long". Defining "word" to any
733 @c particular size is confusing when the .word directive may generate 16
734 @c bits on one machine and 32 bits on another; in general, for the user
735 @c version of this manual, none of these terms seem essential to define.
736 @c They were used very little even in the former draft of the manual;
737 @c this draft makes an effort to avoid them (except in names of
741 @section The GNU Assembler
743 @sc{gnu} @code{as} is really a family of assemblers.
745 This manual describes @code{@value{AS}}, a member of that family which is
746 configured for the @value{TARGET} architectures.
748 If you use (or have used) the @sc{gnu} assembler on one architecture, you
749 should find a fairly similar environment when you use it on another
750 architecture. Each version has much in common with the others,
751 including object file formats, most assembler directives (often called
752 @dfn{pseudo-ops}) and assembler syntax.@refill
754 @cindex purpose of @sc{gnu} assembler
755 @code{@value{AS}} is primarily intended to assemble the output of the
756 @sc{gnu} C compiler @code{@value{GCC}} for use by the linker
757 @code{@value{LD}}. Nevertheless, we've tried to make @code{@value{AS}}
758 assemble correctly everything that other assemblers for the same
759 machine would assemble.
761 Any exceptions are documented explicitly (@pxref{Machine Dependencies}).
764 @c This remark should appear in generic version of manual; assumption
765 @c here is that generic version sets M680x0.
766 This doesn't mean @code{@value{AS}} always uses the same syntax as another
767 assembler for the same architecture; for example, we know of several
768 incompatible versions of 680x0 assembly language syntax.
771 Unlike older assemblers, @code{@value{AS}} is designed to assemble a source
772 program in one pass of the source file. This has a subtle impact on the
773 @kbd{.org} directive (@pxref{Org,,@code{.org}}).
776 @section Object File Formats
778 @cindex object file format
779 The @sc{gnu} assembler can be configured to produce several alternative
780 object file formats. For the most part, this does not affect how you
781 write assembly language programs; but directives for debugging symbols
782 are typically different in different file formats. @xref{Symbol
783 Attributes,,Symbol Attributes}.
786 On the @value{TARGET}, @code{@value{AS}} is configured to produce
787 @value{OBJ-NAME} format object files.
789 @c The following should exhaust all configs that set MULTI-OBJ, ideally
791 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
792 @code{a.out} or COFF format object files.
795 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
796 @code{b.out} or COFF format object files.
799 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
800 SOM or ELF format object files.
805 @section Command Line
807 @cindex command line conventions
808 After the program name @code{@value{AS}}, the command line may contain
809 options and file names. Options may appear in any order, and may be
810 before, after, or between file names. The order of file names is
813 @cindex standard input, as input file
815 @file{--} (two hyphens) by itself names the standard input file
816 explicitly, as one of the files for @code{@value{AS}} to assemble.
818 @cindex options, command line
819 Except for @samp{--} any command line argument that begins with a
820 hyphen (@samp{-}) is an option. Each option changes the behavior of
821 @code{@value{AS}}. No option changes the way another option works. An
822 option is a @samp{-} followed by one or more letters; the case of
823 the letter is important. All options are optional.
825 Some options expect exactly one file name to follow them. The file
826 name may either immediately follow the option's letter (compatible
827 with older assemblers) or it may be the next command argument (@sc{gnu}
828 standard). These two command lines are equivalent:
831 @value{AS} -o my-object-file.o mumble.s
832 @value{AS} -omy-object-file.o mumble.s
839 @cindex source program
841 We use the phrase @dfn{source program}, abbreviated @dfn{source}, to
842 describe the program input to one run of @code{@value{AS}}. The program may
843 be in one or more files; how the source is partitioned into files
844 doesn't change the meaning of the source.
846 @c I added "con" prefix to "catenation" just to prove I can overcome my
847 @c APL training... doc@cygnus.com
848 The source program is a concatenation of the text in all the files, in the
851 Each time you run @code{@value{AS}} it assembles exactly one source
852 program. The source program is made up of one or more files.
853 (The standard input is also a file.)
855 You give @code{@value{AS}} a command line that has zero or more input file
856 names. The input files are read (from left file name to right). A
857 command line argument (in any position) that has no special meaning
858 is taken to be an input file name.
860 If you give @code{@value{AS}} no file names it attempts to read one input file
861 from the @code{@value{AS}} standard input, which is normally your terminal. You
862 may have to type @key{ctl-D} to tell @code{@value{AS}} there is no more program
865 Use @samp{--} if you need to explicitly name the standard input file
866 in your command line.
868 If the source is empty, @code{@value{AS}} produces a small, empty object
871 @subheading Filenames and Line-numbers
873 @cindex input file linenumbers
874 @cindex line numbers, in input files
875 There are two ways of locating a line in the input file (or files) and
876 either may be used in reporting error messages. One way refers to a line
877 number in a physical file; the other refers to a line number in a
878 ``logical'' file. @xref{Errors, ,Error and Warning Messages}.
880 @dfn{Physical files} are those files named in the command line given
881 to @code{@value{AS}}.
883 @dfn{Logical files} are simply names declared explicitly by assembler
884 directives; they bear no relation to physical files. Logical file names help
885 error messages reflect the original source file, when @code{@value{AS}} source
886 is itself synthesized from other files. @code{@value{AS}} understands the
887 @samp{#} directives emitted by the @code{@value{GCC}} preprocessor. See also
888 @ref{File,,@code{.file}}.
891 @section Output (Object) File
897 Every time you run @code{@value{AS}} it produces an output file, which is
898 your assembly language program translated into numbers. This file
899 is the object file. Its default name is
907 @code{b.out} when @code{@value{AS}} is configured for the Intel 80960.
909 You can give it another name by using the @code{-o} option. Conventionally,
910 object file names end with @file{.o}. The default name is used for historical
911 reasons: older assemblers were capable of assembling self-contained programs
912 directly into a runnable program. (For some formats, this isn't currently
913 possible, but it can be done for the @code{a.out} format.)
917 The object file is meant for input to the linker @code{@value{LD}}. It contains
918 assembled program code, information to help @code{@value{LD}} integrate
919 the assembled program into a runnable file, and (optionally) symbolic
920 information for the debugger.
922 @c link above to some info file(s) like the description of a.out.
923 @c don't forget to describe @sc{gnu} info as well as Unix lossage.
926 @section Error and Warning Messages
928 @cindex error messsages
929 @cindex warning messages
930 @cindex messages from assembler
931 @code{@value{AS}} may write warnings and error messages to the standard error
932 file (usually your terminal). This should not happen when a compiler
933 runs @code{@value{AS}} automatically. Warnings report an assumption made so
934 that @code{@value{AS}} could keep assembling a flawed program; errors report a
935 grave problem that stops the assembly.
937 @cindex format of warning messages
938 Warning messages have the format
941 file_name:@b{NNN}:Warning Message Text
945 @cindex line numbers, in warnings/errors
946 (where @b{NNN} is a line number). If a logical file name has been given
947 (@pxref{File,,@code{.file}}) it is used for the filename, otherwise the name of
948 the current input file is used. If a logical line number was given
950 (@pxref{Line,,@code{.line}})
954 (@pxref{Line,,@code{.line}})
957 (@pxref{Ln,,@code{.ln}})
960 then it is used to calculate the number printed,
961 otherwise the actual line in the current source file is printed. The
962 message text is intended to be self explanatory (in the grand Unix
965 @cindex format of error messages
966 Error messages have the format
968 file_name:@b{NNN}:FATAL:Error Message Text
970 The file name and line number are derived as for warning
971 messages. The actual message text may be rather less explanatory
972 because many of them aren't supposed to happen.
975 @chapter Command-Line Options
977 @cindex options, all versions of assembler
978 This chapter describes command-line options available in @emph{all}
979 versions of the @sc{gnu} assembler; @pxref{Machine Dependencies}, for options specific
981 to the @value{TARGET}.
984 to particular machine architectures.
987 If you are invoking @code{@value{AS}} via the @sc{gnu} C compiler (version 2),
988 you can use the @samp{-Wa} option to pass arguments through to the assembler.
989 The assembler arguments must be separated from each other (and the @samp{-Wa})
990 by commas. For example:
993 gcc -c -g -O -Wa,-alh,-L file.c
997 This passes two options to the assembler: @samp{-alh} (emit a listing to
998 standard output with with high-level and assembly source) and @samp{-L} (retain
999 local symbols in the symbol table).
1001 Usually you do not need to use this @samp{-Wa} mechanism, since many compiler
1002 command-line options are automatically passed to the assembler by the compiler.
1003 (You can call the @sc{gnu} compiler driver with the @samp{-v} option to see
1004 precisely what options it passes to each compilation pass, including the
1008 * a:: -a[cdhlns] enable listings
1009 * D:: -D for compatibility
1010 * f:: -f to work faster
1011 * I:: -I for .include search path
1012 @ifclear DIFF-TBL-KLUGE
1013 * K:: -K for compatibility
1015 @ifset DIFF-TBL-KLUGE
1016 * K:: -K for difference tables
1019 * L:: -L to retain local labels
1020 * M:: -M or --mri to assemble in MRI compatibility mode
1021 * MD:: --MD for dependency tracking
1022 * o:: -o to name the object file
1023 * R:: -R to join data and text sections
1024 * statistics:: --statistics to see statistics about assembly
1025 * traditional-format:: --traditional-format for compatible output
1026 * v:: -v to announce version
1027 * W:: -W to suppress warnings
1028 * Z:: -Z to make object file even after errors
1032 @section Enable Listings: @code{-a[cdhlns]}
1041 @cindex listings, enabling
1042 @cindex assembly listings, enabling
1044 These options enable listing output from the assembler. By itself,
1045 @samp{-a} requests high-level, assembly, and symbols listing.
1046 You can use other letters to select specific options for the list:
1047 @samp{-ah} requests a high-level language listing,
1048 @samp{-al} requests an output-program assembly listing, and
1049 @samp{-as} requests a symbol table listing.
1050 High-level listings require that a compiler debugging option like
1051 @samp{-g} be used, and that assembly listings (@samp{-al}) be requested
1054 Use the @samp{-ac} option to omit false conditionals from a listing. Any lines
1055 which are not assembled because of a false @code{.if} (or @code{.ifdef}, or any
1056 other conditional), or a true @code{.if} followed by an @code{.else}, will be
1057 omitted from the listing.
1059 Use the @samp{-ad} option to omit debugging directives from the
1062 Once you have specified one of these options, you can further control
1063 listing output and its appearance using the directives @code{.list},
1064 @code{.nolist}, @code{.psize}, @code{.eject}, @code{.title}, and
1066 The @samp{-an} option turns off all forms processing.
1067 If you do not request listing output with one of the @samp{-a} options, the
1068 listing-control directives have no effect.
1070 The letters after @samp{-a} may be combined into one option,
1071 @emph{e.g.}, @samp{-aln}.
1077 This option has no effect whatsoever, but it is accepted to make it more
1078 likely that scripts written for other assemblers also work with
1082 @section Work Faster: @code{-f}
1085 @cindex trusted compiler
1086 @cindex faster processing (@code{-f})
1087 @samp{-f} should only be used when assembling programs written by a
1088 (trusted) compiler. @samp{-f} stops the assembler from doing whitespace
1089 and comment preprocessing on
1090 the input file(s) before assembling them. @xref{Preprocessing,
1094 @emph{Warning:} if you use @samp{-f} when the files actually need to be
1095 preprocessed (if they contain comments, for example), @code{@value{AS}} does
1100 @section @code{.include} search path: @code{-I} @var{path}
1102 @kindex -I @var{path}
1103 @cindex paths for @code{.include}
1104 @cindex search path for @code{.include}
1105 @cindex @code{include} directive search path
1106 Use this option to add a @var{path} to the list of directories
1107 @code{@value{AS}} searches for files specified in @code{.include}
1108 directives (@pxref{Include,,@code{.include}}). You may use @code{-I} as
1109 many times as necessary to include a variety of paths. The current
1110 working directory is always searched first; after that, @code{@value{AS}}
1111 searches any @samp{-I} directories in the same order as they were
1112 specified (left to right) on the command line.
1115 @section Difference Tables: @code{-K}
1118 @ifclear DIFF-TBL-KLUGE
1119 On the @value{TARGET} family, this option is allowed, but has no effect. It is
1120 permitted for compatibility with the @sc{gnu} assembler on other platforms,
1121 where it can be used to warn when the assembler alters the machine code
1122 generated for @samp{.word} directives in difference tables. The @value{TARGET}
1123 family does not have the addressing limitations that sometimes lead to this
1124 alteration on other platforms.
1127 @ifset DIFF-TBL-KLUGE
1128 @cindex difference tables, warning
1129 @cindex warning for altered difference tables
1130 @code{@value{AS}} sometimes alters the code emitted for directives of the form
1131 @samp{.word @var{sym1}-@var{sym2}}; @pxref{Word,,@code{.word}}.
1132 You can use the @samp{-K} option if you want a warning issued when this
1137 @section Include Local Labels: @code{-L}
1140 @cindex local labels, retaining in output
1141 Labels beginning with @samp{L} (upper case only) are called @dfn{local
1142 labels}. @xref{Symbol Names}. Normally you do not see such labels when
1143 debugging, because they are intended for the use of programs (like
1144 compilers) that compose assembler programs, not for your notice.
1145 Normally both @code{@value{AS}} and @code{@value{LD}} discard such labels, so you do not
1146 normally debug with them.
1148 This option tells @code{@value{AS}} to retain those @samp{L@dots{}} symbols
1149 in the object file. Usually if you do this you also tell the linker
1150 @code{@value{LD}} to preserve symbols whose names begin with @samp{L}.
1152 By default, a local label is any label beginning with @samp{L}, but each
1153 target is allowed to redefine the local label prefix.
1155 On the HPPA local labels begin with @samp{L$}.
1158 @samp{;} for the ARM family;
1162 @section Assemble in MRI Compatibility Mode: @code{-M}
1165 @cindex MRI compatibility mode
1166 The @code{-M} or @code{--mri} option selects MRI compatibility mode. This
1167 changes the syntax and pseudo-op handling of @code{@value{AS}} to make it
1168 compatible with the @code{ASM68K} or the @code{ASM960} (depending upon the
1169 configured target) assembler from Microtec Research. The exact nature of the
1170 MRI syntax will not be documented here; see the MRI manuals for more
1171 information. Note in particular that the handling of macros and macro
1172 arguments is somewhat different. The purpose of this option is to permit
1173 assembling existing MRI assembler code using @code{@value{AS}}.
1175 The MRI compatibility is not complete. Certain operations of the MRI assembler
1176 depend upon its object file format, and can not be supported using other object
1177 file formats. Supporting these would require enhancing each object file format
1178 individually. These are:
1181 @item global symbols in common section
1183 The m68k MRI assembler supports common sections which are merged by the linker.
1184 Other object file formats do not support this. @code{@value{AS}} handles
1185 common sections by treating them as a single common symbol. It permits local
1186 symbols to be defined within a common section, but it can not support global
1187 symbols, since it has no way to describe them.
1189 @item complex relocations
1191 The MRI assemblers support relocations against a negated section address, and
1192 relocations which combine the start addresses of two or more sections. These
1193 are not support by other object file formats.
1195 @item @code{END} pseudo-op specifying start address
1197 The MRI @code{END} pseudo-op permits the specification of a start address.
1198 This is not supported by other object file formats. The start address may
1199 instead be specified using the @code{-e} option to the linker, or in a linker
1202 @item @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops
1204 The MRI @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops assign a module
1205 name to the output file. This is not supported by other object file formats.
1207 @item @code{ORG} pseudo-op
1209 The m68k MRI @code{ORG} pseudo-op begins an absolute section at a given
1210 address. This differs from the usual @code{@value{AS}} @code{.org} pseudo-op,
1211 which changes the location within the current section. Absolute sections are
1212 not supported by other object file formats. The address of a section may be
1213 assigned within a linker script.
1216 There are some other features of the MRI assembler which are not supported by
1217 @code{@value{AS}}, typically either because they are difficult or because they
1218 seem of little consequence. Some of these may be supported in future releases.
1222 @item EBCDIC strings
1224 EBCDIC strings are not supported.
1226 @item packed binary coded decimal
1228 Packed binary coded decimal is not supported. This means that the @code{DC.P}
1229 and @code{DCB.P} pseudo-ops are not supported.
1231 @item @code{FEQU} pseudo-op
1233 The m68k @code{FEQU} pseudo-op is not supported.
1235 @item @code{NOOBJ} pseudo-op
1237 The m68k @code{NOOBJ} pseudo-op is not supported.
1239 @item @code{OPT} branch control options
1241 The m68k @code{OPT} branch control options---@code{B}, @code{BRS}, @code{BRB},
1242 @code{BRL}, and @code{BRW}---are ignored. @code{@value{AS}} automatically
1243 relaxes all branches, whether forward or backward, to an appropriate size, so
1244 these options serve no purpose.
1246 @item @code{OPT} list control options
1248 The following m68k @code{OPT} list control options are ignored: @code{C},
1249 @code{CEX}, @code{CL}, @code{CRE}, @code{E}, @code{G}, @code{I}, @code{M},
1250 @code{MEX}, @code{MC}, @code{MD}, @code{X}.
1252 @item other @code{OPT} options
1254 The following m68k @code{OPT} options are ignored: @code{NEST}, @code{O},
1255 @code{OLD}, @code{OP}, @code{P}, @code{PCO}, @code{PCR}, @code{PCS}, @code{R}.
1257 @item @code{OPT} @code{D} option is default
1259 The m68k @code{OPT} @code{D} option is the default, unlike the MRI assembler.
1260 @code{OPT NOD} may be used to turn it off.
1262 @item @code{XREF} pseudo-op.
1264 The m68k @code{XREF} pseudo-op is ignored.
1266 @item @code{.debug} pseudo-op
1268 The i960 @code{.debug} pseudo-op is not supported.
1270 @item @code{.extended} pseudo-op
1272 The i960 @code{.extended} pseudo-op is not supported.
1274 @item @code{.list} pseudo-op.
1276 The various options of the i960 @code{.list} pseudo-op are not supported.
1278 @item @code{.optimize} pseudo-op
1280 The i960 @code{.optimize} pseudo-op is not supported.
1282 @item @code{.output} pseudo-op
1284 The i960 @code{.output} pseudo-op is not supported.
1286 @item @code{.setreal} pseudo-op
1288 The i960 @code{.setreal} pseudo-op is not supported.
1293 @section Dependency tracking: @code{--MD}
1296 @cindex dependency tracking
1299 @code{@value{AS}} can generate a dependency file for the file it creates. This
1300 file consists of a single rule suitable for @code{make} describing the
1301 dependencies of the main source file.
1303 The rule is written to the file named in its argument.
1305 This feature is used in the automatic updating of makefiles.
1308 @section Name the Object File: @code{-o}
1311 @cindex naming object file
1312 @cindex object file name
1313 There is always one object file output when you run @code{@value{AS}}. By
1314 default it has the name
1317 @file{a.out} (or @file{b.out}, for Intel 960 targets only).
1331 You use this option (which takes exactly one filename) to give the
1332 object file a different name.
1334 Whatever the object file is called, @code{@value{AS}} overwrites any
1335 existing file of the same name.
1338 @section Join Data and Text Sections: @code{-R}
1341 @cindex data and text sections, joining
1342 @cindex text and data sections, joining
1343 @cindex joining text and data sections
1344 @cindex merging text and data sections
1345 @code{-R} tells @code{@value{AS}} to write the object file as if all
1346 data-section data lives in the text section. This is only done at
1347 the very last moment: your binary data are the same, but data
1348 section parts are relocated differently. The data section part of
1349 your object file is zero bytes long because all its bytes are
1350 appended to the text section. (@xref{Sections,,Sections and Relocation}.)
1352 When you specify @code{-R} it would be possible to generate shorter
1353 address displacements (because we do not have to cross between text and
1354 data section). We refrain from doing this simply for compatibility with
1355 older versions of @code{@value{AS}}. In future, @code{-R} may work this way.
1358 When @code{@value{AS}} is configured for COFF output,
1359 this option is only useful if you use sections named @samp{.text} and
1364 @code{-R} is not supported for any of the HPPA targets. Using
1365 @code{-R} generates a warning from @code{@value{AS}}.
1369 @section Display Assembly Statistics: @code{--statistics}
1371 @kindex --statistics
1372 @cindex statistics, about assembly
1373 @cindex time, total for assembly
1374 @cindex space used, maximum for assembly
1375 Use @samp{--statistics} to display two statistics about the resources used by
1376 @code{@value{AS}}: the maximum amount of space allocated during the assembly
1377 (in bytes), and the total execution time taken for the assembly (in @sc{cpu}
1380 @node traditional-format
1381 @section Compatible output: @code{--traditional-format}
1383 @kindex --traditional-format
1384 For some targets, the output of @code{@value{AS}} is different in some ways
1385 from the output of some existing assembler. This switch requests
1386 @code{@value{AS}} to use the traditional format instead.
1388 For example, it disables the exception frame optimizations which
1389 @code{@value{AS}} normally does by default on @code{@value{GCC}} output.
1392 @section Announce Version: @code{-v}
1396 @cindex assembler version
1397 @cindex version of assembler
1398 You can find out what version of as is running by including the
1399 option @samp{-v} (which you can also spell as @samp{-version}) on the
1403 @section Suppress Warnings: @code{-W}
1406 @cindex suppressing warnings
1407 @cindex warnings, suppressing
1408 @code{@value{AS}} should never give a warning or error message when
1409 assembling compiler output. But programs written by people often
1410 cause @code{@value{AS}} to give a warning that a particular assumption was
1411 made. All such warnings are directed to the standard error file.
1412 If you use this option, no warnings are issued. This option only
1413 affects the warning messages: it does not change any particular of how
1414 @code{@value{AS}} assembles your file. Errors, which stop the assembly, are
1418 @section Generate Object File in Spite of Errors: @code{-Z}
1419 @cindex object file, after errors
1420 @cindex errors, continuing after
1421 After an error message, @code{@value{AS}} normally produces no output. If for
1422 some reason you are interested in object file output even after
1423 @code{@value{AS}} gives an error message on your program, use the @samp{-Z}
1424 option. If there are any errors, @code{@value{AS}} continues anyways, and
1425 writes an object file after a final warning message of the form @samp{@var{n}
1426 errors, @var{m} warnings, generating bad object file.}
1431 @cindex machine-independent syntax
1432 @cindex syntax, machine-independent
1433 This chapter describes the machine-independent syntax allowed in a
1434 source file. @code{@value{AS}} syntax is similar to what many other
1435 assemblers use; it is inspired by the BSD 4.2
1440 assembler, except that @code{@value{AS}} does not assemble Vax bit-fields.
1444 * Preprocessing:: Preprocessing
1445 * Whitespace:: Whitespace
1446 * Comments:: Comments
1447 * Symbol Intro:: Symbols
1448 * Statements:: Statements
1449 * Constants:: Constants
1453 @section Preprocessing
1455 @cindex preprocessing
1456 The @code{@value{AS}} internal preprocessor:
1458 @cindex whitespace, removed by preprocessor
1460 adjusts and removes extra whitespace. It leaves one space or tab before
1461 the keywords on a line, and turns any other whitespace on the line into
1464 @cindex comments, removed by preprocessor
1466 removes all comments, replacing them with a single space, or an
1467 appropriate number of newlines.
1469 @cindex constants, converted by preprocessor
1471 converts character constants into the appropriate numeric values.
1474 It does not do macro processing, include file handling, or
1475 anything else you may get from your C compiler's preprocessor. You can
1476 do include file processing with the @code{.include} directive
1477 (@pxref{Include,,@code{.include}}). You can use the @sc{gnu} C compiler driver
1478 to get other ``CPP'' style preprocessing, by giving the input file a
1479 @samp{.S} suffix. @xref{Overall Options,, Options Controlling the Kind of
1480 Output, gcc.info, Using GNU CC}.
1482 Excess whitespace, comments, and character constants
1483 cannot be used in the portions of the input text that are not
1486 @cindex turning preprocessing on and off
1487 @cindex preprocessing, turning on and off
1490 If the first line of an input file is @code{#NO_APP} or if you use the
1491 @samp{-f} option, whitespace and comments are not removed from the input file.
1492 Within an input file, you can ask for whitespace and comment removal in
1493 specific portions of the by putting a line that says @code{#APP} before the
1494 text that may contain whitespace or comments, and putting a line that says
1495 @code{#NO_APP} after this text. This feature is mainly intend to support
1496 @code{asm} statements in compilers whose output is otherwise free of comments
1503 @dfn{Whitespace} is one or more blanks or tabs, in any order.
1504 Whitespace is used to separate symbols, and to make programs neater for
1505 people to read. Unless within character constants
1506 (@pxref{Characters,,Character Constants}), any whitespace means the same
1507 as exactly one space.
1513 There are two ways of rendering comments to @code{@value{AS}}. In both
1514 cases the comment is equivalent to one space.
1516 Anything from @samp{/*} through the next @samp{*/} is a comment.
1517 This means you may not nest these comments.
1521 The only way to include a newline ('\n') in a comment
1522 is to use this sort of comment.
1525 /* This sort of comment does not nest. */
1528 @cindex line comment character
1529 Anything from the @dfn{line comment} character to the next newline
1530 is considered a comment and is ignored. The line comment character is
1532 @samp{;} for the AMD 29K family;
1535 @samp{;} on the ARC;
1538 @samp{;} for the H8/300 family;
1541 @samp{!} for the H8/500 family;
1544 @samp{;} for the HPPA;
1547 @samp{#} on the i960;
1550 @samp{;} for picoJava;
1553 @samp{!} for the Hitachi SH;
1556 @samp{!} on the SPARC;
1559 @samp{#} on the m32r;
1562 @samp{|} on the 680x0;
1565 @samp{#} on the Vax;
1568 @samp{!} for the Z8000;
1571 @samp{#} on the V850;
1573 see @ref{Machine Dependencies}. @refill
1574 @c FIXME What about i386, m88k, i860?
1577 On some machines there are two different line comment characters. One
1578 character only begins a comment if it is the first non-whitespace character on
1579 a line, while the other always begins a comment.
1583 The V850 assembler also supports a double dash as starting a comment that
1584 extends to the end of the line.
1590 @cindex lines starting with @code{#}
1591 @cindex logical line numbers
1592 To be compatible with past assemblers, lines that begin with @samp{#} have a
1593 special interpretation. Following the @samp{#} should be an absolute
1594 expression (@pxref{Expressions}): the logical line number of the @emph{next}
1595 line. Then a string (@pxref{Strings,, Strings}) is allowed: if present it is a
1596 new logical file name. The rest of the line, if any, should be whitespace.
1598 If the first non-whitespace characters on the line are not numeric,
1599 the line is ignored. (Just like a comment.)
1602 # This is an ordinary comment.
1603 # 42-6 "new_file_name" # New logical file name
1604 # This is logical line # 36.
1606 This feature is deprecated, and may disappear from future versions
1607 of @code{@value{AS}}.
1612 @cindex characters used in symbols
1613 @ifclear SPECIAL-SYMS
1614 A @dfn{symbol} is one or more characters chosen from the set of all
1615 letters (both upper and lower case), digits and the three characters
1621 A @dfn{symbol} is one or more characters chosen from the set of all
1622 letters (both upper and lower case), digits and the three characters
1623 @samp{._$}. (Save that, on the H8/300 only, you may not use @samp{$} in
1629 On most machines, you can also use @code{$} in symbol names; exceptions
1630 are noted in @ref{Machine Dependencies}.
1632 No symbol may begin with a digit. Case is significant.
1633 There is no length limit: all characters are significant. Symbols are
1634 delimited by characters not in that set, or by the beginning of a file
1635 (since the source program must end with a newline, the end of a file is
1636 not a possible symbol delimiter). @xref{Symbols}.
1637 @cindex length of symbols
1642 @cindex statements, structure of
1643 @cindex line separator character
1644 @cindex statement separator character
1646 @ifclear abnormal-separator
1647 A @dfn{statement} ends at a newline character (@samp{\n}) or at a
1648 semicolon (@samp{;}). The newline or semicolon is considered part of
1649 the preceding statement. Newlines and semicolons within character
1650 constants are an exception: they do not end statements.
1652 @ifset abnormal-separator
1654 A @dfn{statement} ends at a newline character (@samp{\n}) or an ``at''
1655 sign (@samp{@@}). The newline or at sign is considered part of the
1656 preceding statement. Newlines and at signs within character constants
1657 are an exception: they do not end statements.
1660 A @dfn{statement} ends at a newline character (@samp{\n}) or an exclamation
1661 point (@samp{!}). The newline or exclamation point is considered part of the
1662 preceding statement. Newlines and exclamation points within character
1663 constants are an exception: they do not end statements.
1666 A @dfn{statement} ends at a newline character (@samp{\n}); or (for the
1667 H8/300) a dollar sign (@samp{$}); or (for the
1670 (@samp{;}). The newline or separator character is considered part of
1671 the preceding statement. Newlines and separators within character
1672 constants are an exception: they do not end statements.
1677 A @dfn{statement} ends at a newline character (@samp{\n}) or line
1678 separator character. (The line separator is usually @samp{;}, unless
1679 this conflicts with the comment character; @pxref{Machine Dependencies}.) The
1680 newline or separator character is considered part of the preceding
1681 statement. Newlines and separators within character constants are an
1682 exception: they do not end statements.
1685 @cindex newline, required at file end
1686 @cindex EOF, newline must precede
1687 It is an error to end any statement with end-of-file: the last
1688 character of any input file should be a newline.@refill
1690 An empty statement is allowed, and may include whitespace. It is ignored.
1692 @cindex instructions and directives
1693 @cindex directives and instructions
1694 @c "key symbol" is not used elsewhere in the document; seems pedantic to
1695 @c @defn{} it in that case, as was done previously... doc@cygnus.com,
1697 A statement begins with zero or more labels, optionally followed by a
1698 key symbol which determines what kind of statement it is. The key
1699 symbol determines the syntax of the rest of the statement. If the
1700 symbol begins with a dot @samp{.} then the statement is an assembler
1701 directive: typically valid for any computer. If the symbol begins with
1702 a letter the statement is an assembly language @dfn{instruction}: it
1703 assembles into a machine language instruction.
1705 Different versions of @code{@value{AS}} for different computers
1706 recognize different instructions. In fact, the same symbol may
1707 represent a different instruction in a different computer's assembly
1711 @cindex @code{:} (label)
1712 @cindex label (@code{:})
1713 A label is a symbol immediately followed by a colon (@code{:}).
1714 Whitespace before a label or after a colon is permitted, but you may not
1715 have whitespace between a label's symbol and its colon. @xref{Labels}.
1718 For HPPA targets, labels need not be immediately followed by a colon, but
1719 the definition of a label must begin in column zero. This also implies that
1720 only one label may be defined on each line.
1724 label: .directive followed by something
1725 another_label: # This is an empty statement.
1726 instruction operand_1, operand_2, @dots{}
1733 A constant is a number, written so that its value is known by
1734 inspection, without knowing any context. Like this:
1737 .byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.
1738 .ascii "Ring the bell\7" # A string constant.
1739 .octa 0x123456789abcdef0123456789ABCDEF0 # A bignum.
1740 .float 0f-314159265358979323846264338327\
1741 95028841971.693993751E-40 # - pi, a flonum.
1746 * Characters:: Character Constants
1747 * Numbers:: Number Constants
1751 @subsection Character Constants
1753 @cindex character constants
1754 @cindex constants, character
1755 There are two kinds of character constants. A @dfn{character} stands
1756 for one character in one byte and its value may be used in
1757 numeric expressions. String constants (properly called string
1758 @emph{literals}) are potentially many bytes and their values may not be
1759 used in arithmetic expressions.
1763 * Chars:: Characters
1767 @subsubsection Strings
1769 @cindex string constants
1770 @cindex constants, string
1771 A @dfn{string} is written between double-quotes. It may contain
1772 double-quotes or null characters. The way to get special characters
1773 into a string is to @dfn{escape} these characters: precede them with
1774 a backslash @samp{\} character. For example @samp{\\} represents
1775 one backslash: the first @code{\} is an escape which tells
1776 @code{@value{AS}} to interpret the second character literally as a backslash
1777 (which prevents @code{@value{AS}} from recognizing the second @code{\} as an
1778 escape character). The complete list of escapes follows.
1780 @cindex escape codes, character
1781 @cindex character escape codes
1784 @c Mnemonic for ACKnowledge; for ASCII this is octal code 007.
1786 @cindex @code{\b} (backspace character)
1787 @cindex backspace (@code{\b})
1789 Mnemonic for backspace; for ASCII this is octal code 010.
1792 @c Mnemonic for EOText; for ASCII this is octal code 004.
1794 @cindex @code{\f} (formfeed character)
1795 @cindex formfeed (@code{\f})
1797 Mnemonic for FormFeed; for ASCII this is octal code 014.
1799 @cindex @code{\n} (newline character)
1800 @cindex newline (@code{\n})
1802 Mnemonic for newline; for ASCII this is octal code 012.
1805 @c Mnemonic for prefix; for ASCII this is octal code 033, usually known as @code{escape}.
1807 @cindex @code{\r} (carriage return character)
1808 @cindex carriage return (@code{\r})
1810 Mnemonic for carriage-Return; for ASCII this is octal code 015.
1813 @c Mnemonic for space; for ASCII this is octal code 040. Included for compliance with
1814 @c other assemblers.
1816 @cindex @code{\t} (tab)
1817 @cindex tab (@code{\t})
1819 Mnemonic for horizontal Tab; for ASCII this is octal code 011.
1822 @c Mnemonic for Vertical tab; for ASCII this is octal code 013.
1823 @c @item \x @var{digit} @var{digit} @var{digit}
1824 @c A hexadecimal character code. The numeric code is 3 hexadecimal digits.
1826 @cindex @code{\@var{ddd}} (octal character code)
1827 @cindex octal character code (@code{\@var{ddd}})
1828 @item \ @var{digit} @var{digit} @var{digit}
1829 An octal character code. The numeric code is 3 octal digits.
1830 For compatibility with other Unix systems, 8 and 9 are accepted as digits:
1831 for example, @code{\008} has the value 010, and @code{\009} the value 011.
1833 @cindex @code{\@var{xd...}} (hex character code)
1834 @cindex hex character code (@code{\@var{xd...}})
1835 @item \@code{x} @var{hex-digits...}
1836 A hex character code. All trailing hex digits are combined. Either upper or
1837 lower case @code{x} works.
1839 @cindex @code{\\} (@samp{\} character)
1840 @cindex backslash (@code{\\})
1842 Represents one @samp{\} character.
1845 @c Represents one @samp{'} (accent acute) character.
1846 @c This is needed in single character literals
1847 @c (@xref{Characters,,Character Constants}.) to represent
1850 @cindex @code{\"} (doublequote character)
1851 @cindex doublequote (@code{\"})
1853 Represents one @samp{"} character. Needed in strings to represent
1854 this character, because an unescaped @samp{"} would end the string.
1856 @item \ @var{anything-else}
1857 Any other character when escaped by @kbd{\} gives a warning, but
1858 assembles as if the @samp{\} was not present. The idea is that if
1859 you used an escape sequence you clearly didn't want the literal
1860 interpretation of the following character. However @code{@value{AS}} has no
1861 other interpretation, so @code{@value{AS}} knows it is giving you the wrong
1862 code and warns you of the fact.
1865 Which characters are escapable, and what those escapes represent,
1866 varies widely among assemblers. The current set is what we think
1867 the BSD 4.2 assembler recognizes, and is a subset of what most C
1868 compilers recognize. If you are in doubt, do not use an escape
1872 @subsubsection Characters
1874 @cindex single character constant
1875 @cindex character, single
1876 @cindex constant, single character
1877 A single character may be written as a single quote immediately
1878 followed by that character. The same escapes apply to characters as
1879 to strings. So if you want to write the character backslash, you
1880 must write @kbd{'\\} where the first @code{\} escapes the second
1881 @code{\}. As you can see, the quote is an acute accent, not a
1882 grave accent. A newline
1884 @ifclear abnormal-separator
1885 (or semicolon @samp{;})
1887 @ifset abnormal-separator
1889 (or at sign @samp{@@})
1892 (or dollar sign @samp{$}, for the H8/300; or semicolon @samp{;} for the
1898 immediately following an acute accent is taken as a literal character
1899 and does not count as the end of a statement. The value of a character
1900 constant in a numeric expression is the machine's byte-wide code for
1901 that character. @code{@value{AS}} assumes your character code is ASCII:
1902 @kbd{'A} means 65, @kbd{'B} means 66, and so on. @refill
1905 @subsection Number Constants
1907 @cindex constants, number
1908 @cindex number constants
1909 @code{@value{AS}} distinguishes three kinds of numbers according to how they
1910 are stored in the target machine. @emph{Integers} are numbers that
1911 would fit into an @code{int} in the C language. @emph{Bignums} are
1912 integers, but they are stored in more than 32 bits. @emph{Flonums}
1913 are floating point numbers, described below.
1916 * Integers:: Integers
1921 * Bit Fields:: Bit Fields
1927 @subsubsection Integers
1929 @cindex constants, integer
1931 @cindex binary integers
1932 @cindex integers, binary
1933 A binary integer is @samp{0b} or @samp{0B} followed by zero or more of
1934 the binary digits @samp{01}.
1936 @cindex octal integers
1937 @cindex integers, octal
1938 An octal integer is @samp{0} followed by zero or more of the octal
1939 digits (@samp{01234567}).
1941 @cindex decimal integers
1942 @cindex integers, decimal
1943 A decimal integer starts with a non-zero digit followed by zero or
1944 more digits (@samp{0123456789}).
1946 @cindex hexadecimal integers
1947 @cindex integers, hexadecimal
1948 A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or
1949 more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}.
1951 Integers have the usual values. To denote a negative integer, use
1952 the prefix operator @samp{-} discussed under expressions
1953 (@pxref{Prefix Ops,,Prefix Operators}).
1956 @subsubsection Bignums
1959 @cindex constants, bignum
1960 A @dfn{bignum} has the same syntax and semantics as an integer
1961 except that the number (or its negative) takes more than 32 bits to
1962 represent in binary. The distinction is made because in some places
1963 integers are permitted while bignums are not.
1966 @subsubsection Flonums
1968 @cindex floating point numbers
1969 @cindex constants, floating point
1971 @cindex precision, floating point
1972 A @dfn{flonum} represents a floating point number. The translation is
1973 indirect: a decimal floating point number from the text is converted by
1974 @code{@value{AS}} to a generic binary floating point number of more than
1975 sufficient precision. This generic floating point number is converted
1976 to a particular computer's floating point format (or formats) by a
1977 portion of @code{@value{AS}} specialized to that computer.
1979 A flonum is written by writing (in order)
1984 (@samp{0} is optional on the HPPA.)
1988 A letter, to tell @code{@value{AS}} the rest of the number is a flonum.
1990 @kbd{e} is recommended. Case is not important.
1992 @c FIXME: verify if flonum syntax really this vague for most cases
1993 (Any otherwise illegal letter works here, but that might be changed. Vax BSD
1994 4.2 assembler seems to allow any of @samp{defghDEFGH}.)
1997 On the H8/300, H8/500,
1999 and AMD 29K architectures, the letter must be
2000 one of the letters @samp{DFPRSX} (in upper or lower case).
2002 On the ARC, the letter must be one of the letters @samp{DFRS}
2003 (in upper or lower case).
2005 On the Intel 960 architecture, the letter must be
2006 one of the letters @samp{DFT} (in upper or lower case).
2008 On the HPPA architecture, the letter must be @samp{E} (upper case only).
2012 One of the letters @samp{DFPRSX} (in upper or lower case).
2015 One of the letters @samp{DFRS} (in upper or lower case).
2018 One of the letters @samp{DFPRSX} (in upper or lower case).
2021 The letter @samp{E} (upper case only).
2024 One of the letters @samp{DFT} (in upper or lower case).
2029 An optional sign: either @samp{+} or @samp{-}.
2032 An optional @dfn{integer part}: zero or more decimal digits.
2035 An optional @dfn{fractional part}: @samp{.} followed by zero
2036 or more decimal digits.
2039 An optional exponent, consisting of:
2043 An @samp{E} or @samp{e}.
2044 @c I can't find a config where "EXP_CHARS" is other than 'eE', but in
2045 @c principle this can perfectly well be different on different targets.
2047 Optional sign: either @samp{+} or @samp{-}.
2049 One or more decimal digits.
2054 At least one of the integer part or the fractional part must be
2055 present. The floating point number has the usual base-10 value.
2057 @code{@value{AS}} does all processing using integers. Flonums are computed
2058 independently of any floating point hardware in the computer running
2063 @c Bit fields are written as a general facility but are also controlled
2064 @c by a conditional-compilation flag---which is as of now (21mar91)
2065 @c turned on only by the i960 config of GAS.
2067 @subsubsection Bit Fields
2070 @cindex constants, bit field
2071 You can also define numeric constants as @dfn{bit fields}.
2072 specify two numbers separated by a colon---
2074 @var{mask}:@var{value}
2077 @code{@value{AS}} applies a bitwise @sc{and} between @var{mask} and
2080 The resulting number is then packed
2082 @c this conditional paren in case bit fields turned on elsewhere than 960
2083 (in host-dependent byte order)
2085 into a field whose width depends on which assembler directive has the
2086 bit-field as its argument. Overflow (a result from the bitwise and
2087 requiring more binary digits to represent) is not an error; instead,
2088 more constants are generated, of the specified width, beginning with the
2089 least significant digits.@refill
2091 The directives @code{.byte}, @code{.hword}, @code{.int}, @code{.long},
2092 @code{.short}, and @code{.word} accept bit-field arguments.
2097 @chapter Sections and Relocation
2102 * Secs Background:: Background
2103 * Ld Sections:: Linker Sections
2104 * As Sections:: Assembler Internal Sections
2105 * Sub-Sections:: Sub-Sections
2109 @node Secs Background
2112 Roughly, a section is a range of addresses, with no gaps; all data
2113 ``in'' those addresses is treated the same for some particular purpose.
2114 For example there may be a ``read only'' section.
2116 @cindex linker, and assembler
2117 @cindex assembler, and linker
2118 The linker @code{@value{LD}} reads many object files (partial programs) and
2119 combines their contents to form a runnable program. When @code{@value{AS}}
2120 emits an object file, the partial program is assumed to start at address 0.
2121 @code{@value{LD}} assigns the final addresses for the partial program, so that
2122 different partial programs do not overlap. This is actually an
2123 oversimplification, but it suffices to explain how @code{@value{AS}} uses
2126 @code{@value{LD}} moves blocks of bytes of your program to their run-time
2127 addresses. These blocks slide to their run-time addresses as rigid
2128 units; their length does not change and neither does the order of bytes
2129 within them. Such a rigid unit is called a @emph{section}. Assigning
2130 run-time addresses to sections is called @dfn{relocation}. It includes
2131 the task of adjusting mentions of object-file addresses so they refer to
2132 the proper run-time addresses.
2134 For the H8/300 and H8/500,
2135 and for the Hitachi SH,
2136 @code{@value{AS}} pads sections if needed to
2137 ensure they end on a word (sixteen bit) boundary.
2140 @cindex standard assembler sections
2141 An object file written by @code{@value{AS}} has at least three sections, any
2142 of which may be empty. These are named @dfn{text}, @dfn{data} and
2147 When it generates COFF output,
2149 @code{@value{AS}} can also generate whatever other named sections you specify
2150 using the @samp{.section} directive (@pxref{Section,,@code{.section}}).
2151 If you do not use any directives that place output in the @samp{.text}
2152 or @samp{.data} sections, these sections still exist, but are empty.
2157 When @code{@value{AS}} generates SOM or ELF output for the HPPA,
2159 @code{@value{AS}} can also generate whatever other named sections you
2160 specify using the @samp{.space} and @samp{.subspace} directives. See
2161 @cite{HP9000 Series 800 Assembly Language Reference Manual}
2162 (HP 92432-90001) for details on the @samp{.space} and @samp{.subspace}
2163 assembler directives.
2166 Additionally, @code{@value{AS}} uses different names for the standard
2167 text, data, and bss sections when generating SOM output. Program text
2168 is placed into the @samp{$CODE$} section, data into @samp{$DATA$}, and
2169 BSS into @samp{$BSS$}.
2173 Within the object file, the text section starts at address @code{0}, the
2174 data section follows, and the bss section follows the data section.
2177 When generating either SOM or ELF output files on the HPPA, the text
2178 section starts at address @code{0}, the data section at address
2179 @code{0x4000000}, and the bss section follows the data section.
2182 To let @code{@value{LD}} know which data changes when the sections are
2183 relocated, and how to change that data, @code{@value{AS}} also writes to the
2184 object file details of the relocation needed. To perform relocation
2185 @code{@value{LD}} must know, each time an address in the object
2189 Where in the object file is the beginning of this reference to
2192 How long (in bytes) is this reference?
2194 Which section does the address refer to? What is the numeric value of
2196 (@var{address}) @minus{} (@var{start-address of section})?
2199 Is the reference to an address ``Program-Counter relative''?
2202 @cindex addresses, format of
2203 @cindex section-relative addressing
2204 In fact, every address @code{@value{AS}} ever uses is expressed as
2206 (@var{section}) + (@var{offset into section})
2209 Further, most expressions @code{@value{AS}} computes have this section-relative
2212 (For some object formats, such as SOM for the HPPA, some expressions are
2213 symbol-relative instead.)
2216 In this manual we use the notation @{@var{secname} @var{N}@} to mean ``offset
2217 @var{N} into section @var{secname}.''
2219 Apart from text, data and bss sections you need to know about the
2220 @dfn{absolute} section. When @code{@value{LD}} mixes partial programs,
2221 addresses in the absolute section remain unchanged. For example, address
2222 @code{@{absolute 0@}} is ``relocated'' to run-time address 0 by
2223 @code{@value{LD}}. Although the linker never arranges two partial programs'
2224 data sections with overlapping addresses after linking, @emph{by definition}
2225 their absolute sections must overlap. Address @code{@{absolute@ 239@}} in one
2226 part of a program is always the same address when the program is running as
2227 address @code{@{absolute@ 239@}} in any other part of the program.
2229 The idea of sections is extended to the @dfn{undefined} section. Any
2230 address whose section is unknown at assembly time is by definition
2231 rendered @{undefined @var{U}@}---where @var{U} is filled in later.
2232 Since numbers are always defined, the only way to generate an undefined
2233 address is to mention an undefined symbol. A reference to a named
2234 common block would be such a symbol: its value is unknown at assembly
2235 time so it has section @emph{undefined}.
2237 By analogy the word @emph{section} is used to describe groups of sections in
2238 the linked program. @code{@value{LD}} puts all partial programs' text
2239 sections in contiguous addresses in the linked program. It is
2240 customary to refer to the @emph{text section} of a program, meaning all
2241 the addresses of all partial programs' text sections. Likewise for
2242 data and bss sections.
2244 Some sections are manipulated by @code{@value{LD}}; others are invented for
2245 use of @code{@value{AS}} and have no meaning except during assembly.
2248 @section Linker Sections
2249 @code{@value{LD}} deals with just four kinds of sections, summarized below.
2254 @cindex named sections
2255 @cindex sections, named
2256 @item named sections
2259 @cindex text section
2260 @cindex data section
2264 These sections hold your program. @code{@value{AS}} and @code{@value{LD}} treat them as
2265 separate but equal sections. Anything you can say of one section is
2268 When the program is running, however, it is
2269 customary for the text section to be unalterable. The
2270 text section is often shared among processes: it contains
2271 instructions, constants and the like. The data section of a running
2272 program is usually alterable: for example, C variables would be stored
2273 in the data section.
2278 This section contains zeroed bytes when your program begins running. It
2279 is used to hold unitialized variables or common storage. The length of
2280 each partial program's bss section is important, but because it starts
2281 out containing zeroed bytes there is no need to store explicit zero
2282 bytes in the object file. The bss section was invented to eliminate
2283 those explicit zeros from object files.
2285 @cindex absolute section
2286 @item absolute section
2287 Address 0 of this section is always ``relocated'' to runtime address 0.
2288 This is useful if you want to refer to an address that @code{@value{LD}} must
2289 not change when relocating. In this sense we speak of absolute
2290 addresses being ``unrelocatable'': they do not change during relocation.
2292 @cindex undefined section
2293 @item undefined section
2294 This ``section'' is a catch-all for address references to objects not in
2295 the preceding sections.
2296 @c FIXME: ref to some other doc on obj-file formats could go here.
2299 @cindex relocation example
2300 An idealized example of three relocatable sections follows.
2302 The example uses the traditional section names @samp{.text} and @samp{.data}.
2304 Memory addresses are on the horizontal axis.
2308 @c END TEXI2ROFF-KILL
2311 partial program # 1: |ttttt|dddd|00|
2318 partial program # 2: |TTT|DDD|000|
2321 +--+---+-----+--+----+---+-----+~~
2322 linked program: | |TTT|ttttt| |dddd|DDD|00000|
2323 +--+---+-----+--+----+---+-----+~~
2325 addresses: 0 @dots{}
2332 \line{\it Partial program \#1: \hfil}
2333 \line{\ibox{2.5cm}{\tt text}\ibox{2cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
2334 \line{\boxit{2.5cm}{\tt ttttt}\boxit{2cm}{\tt dddd}\boxit{1cm}{\tt 00}\hfil}
2336 \line{\it Partial program \#2: \hfil}
2337 \line{\ibox{1cm}{\tt text}\ibox{1.5cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
2338 \line{\boxit{1cm}{\tt TTT}\boxit{1.5cm}{\tt DDDD}\boxit{1cm}{\tt 000}\hfil}
2340 \line{\it linked program: \hfil}
2341 \line{\ibox{.5cm}{}\ibox{1cm}{\tt text}\ibox{2.5cm}{}\ibox{.75cm}{}\ibox{2cm}{\tt data}\ibox{1.5cm}{}\ibox{2cm}{\tt bss}\hfil}
2342 \line{\boxit{.5cm}{}\boxit{1cm}{\tt TTT}\boxit{2.5cm}{\tt
2343 ttttt}\boxit{.75cm}{}\boxit{2cm}{\tt dddd}\boxit{1.5cm}{\tt
2344 DDDD}\boxit{2cm}{\tt 00000}\ \dots\hfil}
2346 \line{\it addresses: \hfil}
2350 @c END TEXI2ROFF-KILL
2353 @section Assembler Internal Sections
2355 @cindex internal assembler sections
2356 @cindex sections in messages, internal
2357 These sections are meant only for the internal use of @code{@value{AS}}. They
2358 have no meaning at run-time. You do not really need to know about these
2359 sections for most purposes; but they can be mentioned in @code{@value{AS}}
2360 warning messages, so it might be helpful to have an idea of their
2361 meanings to @code{@value{AS}}. These sections are used to permit the
2362 value of every expression in your assembly language program to be a
2363 section-relative address.
2366 @cindex assembler internal logic error
2367 @item ASSEMBLER-INTERNAL-LOGIC-ERROR!
2368 An internal assembler logic error has been found. This means there is a
2369 bug in the assembler.
2371 @cindex expr (internal section)
2373 The assembler stores complex expression internally as combinations of
2374 symbols. When it needs to represent an expression as a symbol, it puts
2375 it in the expr section.
2377 @c FIXME item transfer[t] vector preload
2378 @c FIXME item transfer[t] vector postload
2379 @c FIXME item register
2383 @section Sub-Sections
2385 @cindex numbered subsections
2386 @cindex grouping data
2392 fall into two sections: text and data.
2394 You may have separate groups of
2396 data in named sections
2400 data in named sections
2406 that you want to end up near to each other in the object file, even though they
2407 are not contiguous in the assembler source. @code{@value{AS}} allows you to
2408 use @dfn{subsections} for this purpose. Within each section, there can be
2409 numbered subsections with values from 0 to 8192. Objects assembled into the
2410 same subsection go into the object file together with other objects in the same
2411 subsection. For example, a compiler might want to store constants in the text
2412 section, but might not want to have them interspersed with the program being
2413 assembled. In this case, the compiler could issue a @samp{.text 0} before each
2414 section of code being output, and a @samp{.text 1} before each group of
2415 constants being output.
2417 Subsections are optional. If you do not use subsections, everything
2418 goes in subsection number zero.
2421 Each subsection is zero-padded up to a multiple of four bytes.
2422 (Subsections may be padded a different amount on different flavors
2423 of @code{@value{AS}}.)
2427 On the H8/300 and H8/500 platforms, each subsection is zero-padded to a word
2428 boundary (two bytes).
2429 The same is true on the Hitachi SH.
2432 @c FIXME section padding (alignment)?
2433 @c Rich Pixley says padding here depends on target obj code format; that
2434 @c doesn't seem particularly useful to say without further elaboration,
2435 @c so for now I say nothing about it. If this is a generic BFD issue,
2436 @c these paragraphs might need to vanish from this manual, and be
2437 @c discussed in BFD chapter of binutils (or some such).
2440 On the AMD 29K family, no particular padding is added to section or
2441 subsection sizes; @value{AS} forces no alignment on this platform.
2445 Subsections appear in your object file in numeric order, lowest numbered
2446 to highest. (All this to be compatible with other people's assemblers.)
2447 The object file contains no representation of subsections; @code{@value{LD}} and
2448 other programs that manipulate object files see no trace of them.
2449 They just see all your text subsections as a text section, and all your
2450 data subsections as a data section.
2452 To specify which subsection you want subsequent statements assembled
2453 into, use a numeric argument to specify it, in a @samp{.text
2454 @var{expression}} or a @samp{.data @var{expression}} statement.
2457 When generating COFF output, you
2462 can also use an extra subsection
2463 argument with arbitrary named sections: @samp{.section @var{name},
2466 @var{Expression} should be an absolute expression.
2467 (@xref{Expressions}.) If you just say @samp{.text} then @samp{.text 0}
2468 is assumed. Likewise @samp{.data} means @samp{.data 0}. Assembly
2469 begins in @code{text 0}. For instance:
2471 .text 0 # The default subsection is text 0 anyway.
2472 .ascii "This lives in the first text subsection. *"
2474 .ascii "But this lives in the second text subsection."
2476 .ascii "This lives in the data section,"
2477 .ascii "in the first data subsection."
2479 .ascii "This lives in the first text section,"
2480 .ascii "immediately following the asterisk (*)."
2483 Each section has a @dfn{location counter} incremented by one for every byte
2484 assembled into that section. Because subsections are merely a convenience
2485 restricted to @code{@value{AS}} there is no concept of a subsection location
2486 counter. There is no way to directly manipulate a location counter---but the
2487 @code{.align} directive changes it, and any label definition captures its
2488 current value. The location counter of the section where statements are being
2489 assembled is said to be the @dfn{active} location counter.
2492 @section bss Section
2495 @cindex common variable storage
2496 The bss section is used for local common variable storage.
2497 You may allocate address space in the bss section, but you may
2498 not dictate data to load into it before your program executes. When
2499 your program starts running, all the contents of the bss
2500 section are zeroed bytes.
2502 The @code{.lcomm} pseudo-op defines a symbol in the bss section; see
2503 @ref{Lcomm,,@code{.lcomm}}.
2505 The @code{.comm} pseudo-op may be used to declare a common symbol, which is
2506 another form of uninitialized symbol; see @xref{Comm,,@code{.comm}}.
2509 When assembling for a target which supports multiple sections, such as ELF or
2510 COFF, you may switch into the @code{.bss} section and define symbols as usual;
2511 see @ref{Section,,@code{.section}}. You may only assemble zero values into the
2512 section. Typically the section will only contain symbol definitions and
2513 @code{.skip} directives (@pxref{Skip,,@code{.skip}}).
2520 Symbols are a central concept: the programmer uses symbols to name
2521 things, the linker uses symbols to link, and the debugger uses symbols
2525 @cindex debuggers, and symbol order
2526 @emph{Warning:} @code{@value{AS}} does not place symbols in the object file in
2527 the same order they were declared. This may break some debuggers.
2532 * Setting Symbols:: Giving Symbols Other Values
2533 * Symbol Names:: Symbol Names
2534 * Dot:: The Special Dot Symbol
2535 * Symbol Attributes:: Symbol Attributes
2542 A @dfn{label} is written as a symbol immediately followed by a colon
2543 @samp{:}. The symbol then represents the current value of the
2544 active location counter, and is, for example, a suitable instruction
2545 operand. You are warned if you use the same symbol to represent two
2546 different locations: the first definition overrides any other
2550 On the HPPA, the usual form for a label need not be immediately followed by a
2551 colon, but instead must start in column zero. Only one label may be defined on
2552 a single line. To work around this, the HPPA version of @code{@value{AS}} also
2553 provides a special directive @code{.label} for defining labels more flexibly.
2556 @node Setting Symbols
2557 @section Giving Symbols Other Values
2559 @cindex assigning values to symbols
2560 @cindex symbol values, assigning
2561 A symbol can be given an arbitrary value by writing a symbol, followed
2562 by an equals sign @samp{=}, followed by an expression
2563 (@pxref{Expressions}). This is equivalent to using the @code{.set}
2564 directive. @xref{Set,,@code{.set}}.
2567 @section Symbol Names
2569 @cindex symbol names
2570 @cindex names, symbol
2571 @ifclear SPECIAL-SYMS
2572 Symbol names begin with a letter or with one of @samp{._}. On most
2573 machines, you can also use @code{$} in symbol names; exceptions are
2574 noted in @ref{Machine Dependencies}. That character may be followed by any
2575 string of digits, letters, dollar signs (unless otherwise noted in
2576 @ref{Machine Dependencies}), and underscores.
2579 For the AMD 29K family, @samp{?} is also allowed in the
2580 body of a symbol name, though not at its beginning.
2585 Symbol names begin with a letter or with one of @samp{._}. On the
2587 H8/500, you can also use @code{$} in symbol names. That character may
2588 be followed by any string of digits, letters, dollar signs (save on the
2589 H8/300), and underscores.
2593 Case of letters is significant: @code{foo} is a different symbol name
2596 Each symbol has exactly one name. Each name in an assembly language program
2597 refers to exactly one symbol. You may use that symbol name any number of times
2600 @subheading Local Symbol Names
2602 @cindex local symbol names
2603 @cindex symbol names, local
2604 @cindex temporary symbol names
2605 @cindex symbol names, temporary
2606 Local symbols help compilers and programmers use names temporarily.
2607 There are ten local symbol names, which are re-used throughout the
2608 program. You may refer to them using the names @samp{0} @samp{1}
2609 @dots{} @samp{9}. To define a local symbol, write a label of the form
2610 @samp{@b{N}:} (where @b{N} represents any digit). To refer to the most
2611 recent previous definition of that symbol write @samp{@b{N}b}, using the
2612 same digit as when you defined the label. To refer to the next
2613 definition of a local label, write @samp{@b{N}f}---where @b{N} gives you
2614 a choice of 10 forward references. The @samp{b} stands for
2615 ``backwards'' and the @samp{f} stands for ``forwards''.
2617 Local symbols are not emitted by the current @sc{gnu} C compiler.
2619 There is no restriction on how you can use these labels, but
2620 remember that at any point in the assembly you can refer to at most
2621 10 prior local labels and to at most 10 forward local labels.
2623 Local symbol names are only a notation device. They are immediately
2624 transformed into more conventional symbol names before the assembler
2625 uses them. The symbol names stored in the symbol table, appearing in
2626 error messages and optionally emitted to the object file have these
2631 All local labels begin with @samp{L}. Normally both @code{@value{AS}} and
2632 @code{@value{LD}} forget symbols that start with @samp{L}. These labels are
2633 used for symbols you are never intended to see. If you use the
2634 @samp{-L} option then @code{@value{AS}} retains these symbols in the
2635 object file. If you also instruct @code{@value{LD}} to retain these symbols,
2636 you may use them in debugging.
2639 If the label is written @samp{0:} then the digit is @samp{0}.
2640 If the label is written @samp{1:} then the digit is @samp{1}.
2641 And so on up through @samp{9:}.
2644 This unusual character is included so you do not accidentally invent
2645 a symbol of the same name. The character has ASCII value
2648 @item @emph{ordinal number}
2649 This is a serial number to keep the labels distinct. The first
2650 @samp{0:} gets the number @samp{1}; The 15th @samp{0:} gets the
2651 number @samp{15}; @emph{etc.}. Likewise for the other labels @samp{1:}
2655 For instance, the first @code{1:} is named @code{L1@kbd{C-A}1}, the 44th
2656 @code{3:} is named @code{L3@kbd{C-A}44}.
2659 @section The Special Dot Symbol
2661 @cindex dot (symbol)
2662 @cindex @code{.} (symbol)
2663 @cindex current address
2664 @cindex location counter
2665 The special symbol @samp{.} refers to the current address that
2666 @code{@value{AS}} is assembling into. Thus, the expression @samp{melvin:
2667 .long .} defines @code{melvin} to contain its own address.
2668 Assigning a value to @code{.} is treated the same as a @code{.org}
2669 directive. Thus, the expression @samp{.=.+4} is the same as saying
2670 @ifclear no-space-dir
2679 @node Symbol Attributes
2680 @section Symbol Attributes
2682 @cindex symbol attributes
2683 @cindex attributes, symbol
2684 Every symbol has, as well as its name, the attributes ``Value'' and
2685 ``Type''. Depending on output format, symbols can also have auxiliary
2688 The detailed definitions are in @file{a.out.h}.
2691 If you use a symbol without defining it, @code{@value{AS}} assumes zero for
2692 all these attributes, and probably won't warn you. This makes the
2693 symbol an externally defined symbol, which is generally what you
2697 * Symbol Value:: Value
2698 * Symbol Type:: Type
2701 * a.out Symbols:: Symbol Attributes: @code{a.out}
2705 * a.out Symbols:: Symbol Attributes: @code{a.out}
2708 * a.out Symbols:: Symbol Attributes: @code{a.out}, @code{b.out}
2713 * COFF Symbols:: Symbol Attributes for COFF
2716 * SOM Symbols:: Symbol Attributes for SOM
2723 @cindex value of a symbol
2724 @cindex symbol value
2725 The value of a symbol is (usually) 32 bits. For a symbol which labels a
2726 location in the text, data, bss or absolute sections the value is the
2727 number of addresses from the start of that section to the label.
2728 Naturally for text, data and bss sections the value of a symbol changes
2729 as @code{@value{LD}} changes section base addresses during linking. Absolute
2730 symbols' values do not change during linking: that is why they are
2733 The value of an undefined symbol is treated in a special way. If it is
2734 0 then the symbol is not defined in this assembler source file, and
2735 @code{@value{LD}} tries to determine its value from other files linked into the
2736 same program. You make this kind of symbol simply by mentioning a symbol
2737 name without defining it. A non-zero value represents a @code{.comm}
2738 common declaration. The value is how much common storage to reserve, in
2739 bytes (addresses). The symbol refers to the first address of the
2745 @cindex type of a symbol
2747 The type attribute of a symbol contains relocation (section)
2748 information, any flag settings indicating that a symbol is external, and
2749 (optionally), other information for linkers and debuggers. The exact
2750 format depends on the object-code output format in use.
2755 @c The following avoids a "widow" subsection title. @group would be
2756 @c better if it were available outside examples.
2759 @subsection Symbol Attributes: @code{a.out}, @code{b.out}
2761 @cindex @code{b.out} symbol attributes
2762 @cindex symbol attributes, @code{b.out}
2763 These symbol attributes appear only when @code{@value{AS}} is configured for
2764 one of the Berkeley-descended object output formats---@code{a.out} or
2770 @subsection Symbol Attributes: @code{a.out}
2772 @cindex @code{a.out} symbol attributes
2773 @cindex symbol attributes, @code{a.out}
2779 @subsection Symbol Attributes: @code{a.out}
2781 @cindex @code{a.out} symbol attributes
2782 @cindex symbol attributes, @code{a.out}
2786 * Symbol Desc:: Descriptor
2787 * Symbol Other:: Other
2791 @subsubsection Descriptor
2793 @cindex descriptor, of @code{a.out} symbol
2794 This is an arbitrary 16-bit value. You may establish a symbol's
2795 descriptor value by using a @code{.desc} statement
2796 (@pxref{Desc,,@code{.desc}}). A descriptor value means nothing to
2800 @subsubsection Other
2802 @cindex other attribute, of @code{a.out} symbol
2803 This is an arbitrary 8-bit value. It means nothing to @code{@value{AS}}.
2808 @subsection Symbol Attributes for COFF
2810 @cindex COFF symbol attributes
2811 @cindex symbol attributes, COFF
2813 The COFF format supports a multitude of auxiliary symbol attributes;
2814 like the primary symbol attributes, they are set between @code{.def} and
2815 @code{.endef} directives.
2817 @subsubsection Primary Attributes
2819 @cindex primary attributes, COFF symbols
2820 The symbol name is set with @code{.def}; the value and type,
2821 respectively, with @code{.val} and @code{.type}.
2823 @subsubsection Auxiliary Attributes
2825 @cindex auxiliary attributes, COFF symbols
2826 The @code{@value{AS}} directives @code{.dim}, @code{.line}, @code{.scl},
2827 @code{.size}, and @code{.tag} can generate auxiliary symbol table
2828 information for COFF.
2833 @subsection Symbol Attributes for SOM
2835 @cindex SOM symbol attributes
2836 @cindex symbol attributes, SOM
2838 The SOM format for the HPPA supports a multitude of symbol attributes set with
2839 the @code{.EXPORT} and @code{.IMPORT} directives.
2841 The attributes are described in @cite{HP9000 Series 800 Assembly
2842 Language Reference Manual} (HP 92432-90001) under the @code{IMPORT} and
2843 @code{EXPORT} assembler directive documentation.
2847 @chapter Expressions
2851 @cindex numeric values
2852 An @dfn{expression} specifies an address or numeric value.
2853 Whitespace may precede and/or follow an expression.
2855 The result of an expression must be an absolute number, or else an offset into
2856 a particular section. If an expression is not absolute, and there is not
2857 enough information when @code{@value{AS}} sees the expression to know its
2858 section, a second pass over the source program might be necessary to interpret
2859 the expression---but the second pass is currently not implemented.
2860 @code{@value{AS}} aborts with an error message in this situation.
2863 * Empty Exprs:: Empty Expressions
2864 * Integer Exprs:: Integer Expressions
2868 @section Empty Expressions
2870 @cindex empty expressions
2871 @cindex expressions, empty
2872 An empty expression has no value: it is just whitespace or null.
2873 Wherever an absolute expression is required, you may omit the
2874 expression, and @code{@value{AS}} assumes a value of (absolute) 0. This
2875 is compatible with other assemblers.
2878 @section Integer Expressions
2880 @cindex integer expressions
2881 @cindex expressions, integer
2882 An @dfn{integer expression} is one or more @emph{arguments} delimited
2883 by @emph{operators}.
2886 * Arguments:: Arguments
2887 * Operators:: Operators
2888 * Prefix Ops:: Prefix Operators
2889 * Infix Ops:: Infix Operators
2893 @subsection Arguments
2895 @cindex expression arguments
2896 @cindex arguments in expressions
2897 @cindex operands in expressions
2898 @cindex arithmetic operands
2899 @dfn{Arguments} are symbols, numbers or subexpressions. In other
2900 contexts arguments are sometimes called ``arithmetic operands''. In
2901 this manual, to avoid confusing them with the ``instruction operands'' of
2902 the machine language, we use the term ``argument'' to refer to parts of
2903 expressions only, reserving the word ``operand'' to refer only to machine
2904 instruction operands.
2906 Symbols are evaluated to yield @{@var{section} @var{NNN}@} where
2907 @var{section} is one of text, data, bss, absolute,
2908 or undefined. @var{NNN} is a signed, 2's complement 32 bit
2911 Numbers are usually integers.
2913 A number can be a flonum or bignum. In this case, you are warned
2914 that only the low order 32 bits are used, and @code{@value{AS}} pretends
2915 these 32 bits are an integer. You may write integer-manipulating
2916 instructions that act on exotic constants, compatible with other
2919 @cindex subexpressions
2920 Subexpressions are a left parenthesis @samp{(} followed by an integer
2921 expression, followed by a right parenthesis @samp{)}; or a prefix
2922 operator followed by an argument.
2925 @subsection Operators
2927 @cindex operators, in expressions
2928 @cindex arithmetic functions
2929 @cindex functions, in expressions
2930 @dfn{Operators} are arithmetic functions, like @code{+} or @code{%}. Prefix
2931 operators are followed by an argument. Infix operators appear
2932 between their arguments. Operators may be preceded and/or followed by
2936 @subsection Prefix Operator
2938 @cindex prefix operators
2939 @code{@value{AS}} has the following @dfn{prefix operators}. They each take
2940 one argument, which must be absolute.
2942 @c the tex/end tex stuff surrounding this small table is meant to make
2943 @c it align, on the printed page, with the similar table in the next
2944 @c section (which is inside an enumerate).
2946 \global\advance\leftskip by \itemindent
2951 @dfn{Negation}. Two's complement negation.
2953 @dfn{Complementation}. Bitwise not.
2957 \global\advance\leftskip by -\itemindent
2961 @subsection Infix Operators
2963 @cindex infix operators
2964 @cindex operators, permitted arguments
2965 @dfn{Infix operators} take two arguments, one on either side. Operators
2966 have precedence, but operations with equal precedence are performed left
2967 to right. Apart from @code{+} or @code{-}, both arguments must be
2968 absolute, and the result is absolute.
2971 @cindex operator precedence
2972 @cindex precedence of operators
2979 @dfn{Multiplication}.
2982 @dfn{Division}. Truncation is the same as the C operator @samp{/}
2989 @dfn{Shift Left}. Same as the C operator @samp{<<}.
2993 @dfn{Shift Right}. Same as the C operator @samp{>>}.
2997 Intermediate precedence
3002 @dfn{Bitwise Inclusive Or}.
3008 @dfn{Bitwise Exclusive Or}.
3011 @dfn{Bitwise Or Not}.
3018 @cindex addition, permitted arguments
3019 @cindex plus, permitted arguments
3020 @cindex arguments for addition
3022 @dfn{Addition}. If either argument is absolute, the result has the section of
3023 the other argument. You may not add together arguments from different
3026 @cindex subtraction, permitted arguments
3027 @cindex minus, permitted arguments
3028 @cindex arguments for subtraction
3030 @dfn{Subtraction}. If the right argument is absolute, the
3031 result has the section of the left argument.
3032 If both arguments are in the same section, the result is absolute.
3033 You may not subtract arguments from different sections.
3034 @c FIXME is there still something useful to say about undefined - undefined ?
3038 In short, it's only meaningful to add or subtract the @emph{offsets} in an
3039 address; you can only have a defined section in one of the two arguments.
3042 @chapter Assembler Directives
3044 @cindex directives, machine independent
3045 @cindex pseudo-ops, machine independent
3046 @cindex machine independent directives
3047 All assembler directives have names that begin with a period (@samp{.}).
3048 The rest of the name is letters, usually in lower case.
3050 This chapter discusses directives that are available regardless of the
3051 target machine configuration for the @sc{gnu} assembler.
3053 Some machine configurations provide additional directives.
3054 @xref{Machine Dependencies}.
3057 @ifset machine-directives
3058 @xref{Machine Dependencies} for additional directives.
3063 * Abort:: @code{.abort}
3065 * ABORT:: @code{.ABORT}
3068 * Align:: @code{.align @var{abs-expr} , @var{abs-expr}}
3069 * Ascii:: @code{.ascii "@var{string}"}@dots{}
3070 * Asciz:: @code{.asciz "@var{string}"}@dots{}
3071 * Balign:: @code{.balign @var{abs-expr} , @var{abs-expr}}
3072 * Byte:: @code{.byte @var{expressions}}
3073 * Comm:: @code{.comm @var{symbol} , @var{length} }
3074 * Data:: @code{.data @var{subsection}}
3076 * Def:: @code{.def @var{name}}
3079 * Desc:: @code{.desc @var{symbol}, @var{abs-expression}}
3085 * Double:: @code{.double @var{flonums}}
3086 * Eject:: @code{.eject}
3087 * Else:: @code{.else}
3090 * Endef:: @code{.endef}
3093 * Endfunc:: @code{.endfunc}
3094 * Endif:: @code{.endif}
3095 * Equ:: @code{.equ @var{symbol}, @var{expression}}
3096 * Equiv:: @code{.equiv @var{symbol}, @var{expression}}
3098 * Exitm:: @code{.exitm}
3099 * Extern:: @code{.extern}
3100 * Fail:: @code{.fail}
3101 @ifclear no-file-dir
3102 * File:: @code{.file @var{string}}
3105 * Fill:: @code{.fill @var{repeat} , @var{size} , @var{value}}
3106 * Float:: @code{.float @var{flonums}}
3107 * Func:: @code{.func}
3108 * Global:: @code{.global @var{symbol}}, @code{.globl @var{symbol}}
3109 * hword:: @code{.hword @var{expressions}}
3110 * Ident:: @code{.ident}
3111 * If:: @code{.if @var{absolute expression}}
3112 * Include:: @code{.include "@var{file}"}
3113 * Int:: @code{.int @var{expressions}}
3114 * Irp:: @code{.irp @var{symbol},@var{values}}@dots{}
3115 * Irpc:: @code{.irpc @var{symbol},@var{values}}@dots{}
3116 * Lcomm:: @code{.lcomm @var{symbol} , @var{length}}
3117 * Lflags:: @code{.lflags}
3118 @ifclear no-line-dir
3119 * Line:: @code{.line @var{line-number}}
3122 * Ln:: @code{.ln @var{line-number}}
3123 * Linkonce:: @code{.linkonce [@var{type}]}
3124 * List:: @code{.list}
3125 * Long:: @code{.long @var{expressions}}
3127 * Lsym:: @code{.lsym @var{symbol}, @var{expression}}
3130 * Macro:: @code{.macro @var{name} @var{args}}@dots{}
3131 * MRI:: @code{.mri @var{val}}
3133 * Nolist:: @code{.nolist}
3134 * Octa:: @code{.octa @var{bignums}}
3135 * Org:: @code{.org @var{new-lc} , @var{fill}}
3136 * P2align:: @code{.p2align @var{abs-expr} , @var{abs-expr}}
3137 * Print:: @code{.print @var{string}}
3138 * Psize:: @code{.psize @var{lines}, @var{columns}}
3139 * Purgem:: @code{.purgem @var{name}}
3140 * Quad:: @code{.quad @var{bignums}}
3141 * Rept:: @code{.rept @var{count}}
3142 * Sbttl:: @code{.sbttl "@var{subheading}"}
3144 * Scl:: @code{.scl @var{class}}
3145 * Section:: @code{.section @var{name}, @var{subsection}}
3148 * Set:: @code{.set @var{symbol}, @var{expression}}
3149 * Short:: @code{.short @var{expressions}}
3150 * Single:: @code{.single @var{flonums}}
3152 * Size:: @code{.size}
3155 * Skip:: @code{.skip @var{size} , @var{fill}}
3156 * Sleb128:: @code{.sleb128 @var{expressions}}
3157 * Space:: @code{.space @var{size} , @var{fill}}
3159 * Stab:: @code{.stabd, .stabn, .stabs}
3162 * String:: @code{.string "@var{str}"}
3163 * Struct:: @code{.struct @var{expression}}
3165 * Symver:: @code{.symver @var{name},@var{name2@@nodename}}
3168 * Tag:: @code{.tag @var{structname}}
3171 * Text:: @code{.text @var{subsection}}
3172 * Title:: @code{.title "@var{heading}"}
3174 * Type:: @code{.type @var{int}}
3175 * Val:: @code{.val @var{addr}}
3178 * Uleb128:: @code{.uleb128 @var{expressions}}
3179 * Word:: @code{.word @var{expressions}}
3180 * Deprecated:: Deprecated Directives
3184 @section @code{.abort}
3186 @cindex @code{abort} directive
3187 @cindex stopping the assembly
3188 This directive stops the assembly immediately. It is for
3189 compatibility with other assemblers. The original idea was that the
3190 assembly language source would be piped into the assembler. If the sender
3191 of the source quit, it could use this directive tells @code{@value{AS}} to
3192 quit also. One day @code{.abort} will not be supported.
3196 @section @code{.ABORT}
3198 @cindex @code{ABORT} directive
3199 When producing COFF output, @code{@value{AS}} accepts this directive as a
3200 synonym for @samp{.abort}.
3203 When producing @code{b.out} output, @code{@value{AS}} accepts this directive,
3209 @section @code{.align @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
3211 @cindex padding the location counter
3212 @cindex @code{align} directive
3213 Pad the location counter (in the current subsection) to a particular storage
3214 boundary. The first expression (which must be absolute) is the alignment
3215 required, as described below.
3217 The second expression (also absolute) gives the fill value to be stored in the
3218 padding bytes. It (and the comma) may be omitted. If it is omitted, the
3219 padding bytes are normally zero. However, on some systems, if the section is
3220 marked as containing code and the fill value is omitted, the space is filled
3221 with no-op instructions.
3223 The third expression is also absolute, and is also optional. If it is present,
3224 it is the maximum number of bytes that should be skipped by this alignment
3225 directive. If doing the alignment would require skipping more bytes than the
3226 specified maximum, then the alignment is not done at all. You can omit the
3227 fill value (the second argument) entirely by simply using two commas after the
3228 required alignment; this can be useful if you want the alignment to be filled
3229 with no-op instructions when appropriate.
3231 The way the required alignment is specified varies from system to system.
3232 For the a29k, hppa, m68k, m88k, w65, sparc, and Hitachi SH, and i386 using ELF
3234 the first expression is the
3235 alignment request in bytes. For example @samp{.align 8} advances
3236 the location counter until it is a multiple of 8. If the location counter
3237 is already a multiple of 8, no change is needed.
3239 For other systems, including the i386 using a.out format, it is the
3240 number of low-order zero bits the location counter must have after
3241 advancement. For example @samp{.align 3} advances the location
3242 counter until it a multiple of 8. If the location counter is already a
3243 multiple of 8, no change is needed.
3245 This inconsistency is due to the different behaviors of the various
3246 native assemblers for these systems which GAS must emulate.
3247 GAS also provides @code{.balign} and @code{.p2align} directives,
3248 described later, which have a consistent behavior across all
3249 architectures (but are specific to GAS).
3252 @section @code{.ascii "@var{string}"}@dots{}
3254 @cindex @code{ascii} directive
3255 @cindex string literals
3256 @code{.ascii} expects zero or more string literals (@pxref{Strings})
3257 separated by commas. It assembles each string (with no automatic
3258 trailing zero byte) into consecutive addresses.
3261 @section @code{.asciz "@var{string}"}@dots{}
3263 @cindex @code{asciz} directive
3264 @cindex zero-terminated strings
3265 @cindex null-terminated strings
3266 @code{.asciz} is just like @code{.ascii}, but each string is followed by
3267 a zero byte. The ``z'' in @samp{.asciz} stands for ``zero''.
3270 @section @code{.balign[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
3272 @cindex padding the location counter given number of bytes
3273 @cindex @code{balign} directive
3274 Pad the location counter (in the current subsection) to a particular
3275 storage boundary. The first expression (which must be absolute) is the
3276 alignment request in bytes. For example @samp{.balign 8} advances
3277 the location counter until it is a multiple of 8. If the location counter
3278 is already a multiple of 8, no change is needed.
3280 The second expression (also absolute) gives the fill value to be stored in the
3281 padding bytes. It (and the comma) may be omitted. If it is omitted, the
3282 padding bytes are normally zero. However, on some systems, if the section is
3283 marked as containing code and the fill value is omitted, the space is filled
3284 with no-op instructions.
3286 The third expression is also absolute, and is also optional. If it is present,
3287 it is the maximum number of bytes that should be skipped by this alignment
3288 directive. If doing the alignment would require skipping more bytes than the
3289 specified maximum, then the alignment is not done at all. You can omit the
3290 fill value (the second argument) entirely by simply using two commas after the
3291 required alignment; this can be useful if you want the alignment to be filled
3292 with no-op instructions when appropriate.
3294 @cindex @code{balignw} directive
3295 @cindex @code{balignl} directive
3296 The @code{.balignw} and @code{.balignl} directives are variants of the
3297 @code{.balign} directive. The @code{.balignw} directive treats the fill
3298 pattern as a two byte word value. The @code{.balignl} directives treats the
3299 fill pattern as a four byte longword value. For example, @code{.balignw
3300 4,0x368d} will align to a multiple of 4. If it skips two bytes, they will be
3301 filled in with the value 0x368d (the exact placement of the bytes depends upon
3302 the endianness of the processor). If it skips 1 or 3 bytes, the fill value is
3306 @section @code{.byte @var{expressions}}
3308 @cindex @code{byte} directive
3309 @cindex integers, one byte
3310 @code{.byte} expects zero or more expressions, separated by commas.
3311 Each expression is assembled into the next byte.
3314 @section @code{.comm @var{symbol} , @var{length} }
3316 @cindex @code{comm} directive
3317 @cindex symbol, common
3318 @code{.comm} declares a common symbol named @var{symbol}. When linking, a
3319 common symbol in one object file may be merged with a defined or common symbol
3320 of the same name in another object file. If @code{@value{LD}} does not see a
3321 definition for the symbol--just one or more common symbols--then it will
3322 allocate @var{length} bytes of uninitialized memory. @var{length} must be an
3323 absolute expression. If @code{@value{LD}} sees multiple common symbols with
3324 the same name, and they do not all have the same size, it will allocate space
3325 using the largest size.
3328 When using ELF, the @code{.comm} directive takes an optional third argument.
3329 This is the desired alignment of the symbol, specified as a byte boundary (for
3330 example, an alignment of 16 means that the least significant 4 bits of the
3331 address should be zero). The alignment must be an absolute expression, and it
3332 must be a power of two. If @code{@value{LD}} allocates uninitialized memory
3333 for the common symbol, it will use the alignment when placing the symbol. If
3334 no alignment is specified, @code{@value{AS}} will set the alignment to the
3335 largest power of two less than or equal to the size of the symbol, up to a
3340 The syntax for @code{.comm} differs slightly on the HPPA. The syntax is
3341 @samp{@var{symbol} .comm, @var{length}}; @var{symbol} is optional.
3345 @section @code{.data @var{subsection}}
3347 @cindex @code{data} directive
3348 @code{.data} tells @code{@value{AS}} to assemble the following statements onto the
3349 end of the data subsection numbered @var{subsection} (which is an
3350 absolute expression). If @var{subsection} is omitted, it defaults
3355 @section @code{.def @var{name}}
3357 @cindex @code{def} directive
3358 @cindex COFF symbols, debugging
3359 @cindex debugging COFF symbols
3360 Begin defining debugging information for a symbol @var{name}; the
3361 definition extends until the @code{.endef} directive is encountered.
3364 This directive is only observed when @code{@value{AS}} is configured for COFF
3365 format output; when producing @code{b.out}, @samp{.def} is recognized,
3372 @section @code{.desc @var{symbol}, @var{abs-expression}}
3374 @cindex @code{desc} directive
3375 @cindex COFF symbol descriptor
3376 @cindex symbol descriptor, COFF
3377 This directive sets the descriptor of the symbol (@pxref{Symbol Attributes})
3378 to the low 16 bits of an absolute expression.
3381 The @samp{.desc} directive is not available when @code{@value{AS}} is
3382 configured for COFF output; it is only for @code{a.out} or @code{b.out}
3383 object format. For the sake of compatibility, @code{@value{AS}} accepts
3384 it, but produces no output, when configured for COFF.
3390 @section @code{.dim}
3392 @cindex @code{dim} directive
3393 @cindex COFF auxiliary symbol information
3394 @cindex auxiliary symbol information, COFF
3395 This directive is generated by compilers to include auxiliary debugging
3396 information in the symbol table. It is only permitted inside
3397 @code{.def}/@code{.endef} pairs.
3400 @samp{.dim} is only meaningful when generating COFF format output; when
3401 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
3407 @section @code{.double @var{flonums}}
3409 @cindex @code{double} directive
3410 @cindex floating point numbers (double)
3411 @code{.double} expects zero or more flonums, separated by commas. It
3412 assembles floating point numbers.
3414 The exact kind of floating point numbers emitted depends on how
3415 @code{@value{AS}} is configured. @xref{Machine Dependencies}.
3419 On the @value{TARGET} family @samp{.double} emits 64-bit floating-point numbers
3420 in @sc{ieee} format.
3425 @section @code{.eject}
3427 @cindex @code{eject} directive
3428 @cindex new page, in listings
3429 @cindex page, in listings
3430 @cindex listing control: new page
3431 Force a page break at this point, when generating assembly listings.
3434 @section @code{.else}
3436 @cindex @code{else} directive
3437 @code{.else} is part of the @code{@value{AS}} support for conditional
3438 assembly; @pxref{If,,@code{.if}}. It marks the beginning of a section
3439 of code to be assembled if the condition for the preceding @code{.if}
3443 @section @code{.end}
3445 @cindex @code{end} directive
3446 @code{.end} marks the end of the assembly file. @code{@value{AS}} does not
3447 process anything in the file past the @code{.end} directive.
3451 @section @code{.endef}
3453 @cindex @code{endef} directive
3454 This directive flags the end of a symbol definition begun with
3458 @samp{.endef} is only meaningful when generating COFF format output; if
3459 @code{@value{AS}} is configured to generate @code{b.out}, it accepts this
3460 directive but ignores it.
3465 @section @code{.endfunc}
3466 @cindex @code{endfunc} directive
3467 @code{.endfunc} marks the end of a function specified with @code{.func}.
3470 @section @code{.endif}
3472 @cindex @code{endif} directive
3473 @code{.endif} is part of the @code{@value{AS}} support for conditional assembly;
3474 it marks the end of a block of code that is only assembled
3475 conditionally. @xref{If,,@code{.if}}.
3478 @section @code{.equ @var{symbol}, @var{expression}}
3480 @cindex @code{equ} directive
3481 @cindex assigning values to symbols
3482 @cindex symbols, assigning values to
3483 This directive sets the value of @var{symbol} to @var{expression}.
3484 It is synonymous with @samp{.set}; @pxref{Set,,@code{.set}}.
3487 The syntax for @code{equ} on the HPPA is
3488 @samp{@var{symbol} .equ @var{expression}}.
3492 @section @code{.equiv @var{symbol}, @var{expression}}
3493 @cindex @code{equiv} directive
3494 The @code{.equiv} directive is like @code{.equ} and @code{.set}, except that
3495 the assembler will signal an error if @var{symbol} is already defined.
3497 Except for the contents of the error message, this is roughly equivalent to
3506 @section @code{.err}
3507 @cindex @code{err} directive
3508 If @code{@value{AS}} assembles a @code{.err} directive, it will print an error
3509 message and, unless the @code{-Z} option was used, it will not generate an
3510 object file. This can be used to signal error an conditionally compiled code.
3513 @section @code{.exitm}
3514 Exit early from the current macro definition. @xref{Macro}.
3517 @section @code{.extern}
3519 @cindex @code{extern} directive
3520 @code{.extern} is accepted in the source program---for compatibility
3521 with other assemblers---but it is ignored. @code{@value{AS}} treats
3522 all undefined symbols as external.
3525 @section @code{.fail @var{expression}}
3527 @cindex @code{fail} directive
3528 Generates an error or a warning. If the value of the @var{expression} is 500
3529 or more, @code{@value{AS}} will print a warning message. If the value is less
3530 than 500, @code{@value{AS}} will print an error message. The message will
3531 include the value of @var{expression}. This can occasionally be useful inside
3532 complex nested macros or conditional assembly.
3534 @ifclear no-file-dir
3536 @section @code{.file @var{string}}
3538 @cindex @code{file} directive
3539 @cindex logical file name
3540 @cindex file name, logical
3541 @code{.file} tells @code{@value{AS}} that we are about to start a new logical
3542 file. @var{string} is the new file name. In general, the filename is
3543 recognized whether or not it is surrounded by quotes @samp{"}; but if you wish
3544 to specify an empty file name, you must give the quotes--@code{""}. This
3545 statement may go away in future: it is only recognized to be compatible with
3546 old @code{@value{AS}} programs.
3548 In some configurations of @code{@value{AS}}, @code{.file} has already been
3549 removed to avoid conflicts with other assemblers. @xref{Machine Dependencies}.
3554 @section @code{.fill @var{repeat} , @var{size} , @var{value}}
3556 @cindex @code{fill} directive
3557 @cindex writing patterns in memory
3558 @cindex patterns, writing in memory
3559 @var{result}, @var{size} and @var{value} are absolute expressions.
3560 This emits @var{repeat} copies of @var{size} bytes. @var{Repeat}
3561 may be zero or more. @var{Size} may be zero or more, but if it is
3562 more than 8, then it is deemed to have the value 8, compatible with
3563 other people's assemblers. The contents of each @var{repeat} bytes
3564 is taken from an 8-byte number. The highest order 4 bytes are
3565 zero. The lowest order 4 bytes are @var{value} rendered in the
3566 byte-order of an integer on the computer @code{@value{AS}} is assembling for.
3567 Each @var{size} bytes in a repetition is taken from the lowest order
3568 @var{size} bytes of this number. Again, this bizarre behavior is
3569 compatible with other people's assemblers.
3571 @var{size} and @var{value} are optional.
3572 If the second comma and @var{value} are absent, @var{value} is
3573 assumed zero. If the first comma and following tokens are absent,
3574 @var{size} is assumed to be 1.
3577 @section @code{.float @var{flonums}}
3579 @cindex floating point numbers (single)
3580 @cindex @code{float} directive
3581 This directive assembles zero or more flonums, separated by commas. It
3582 has the same effect as @code{.single}.
3584 The exact kind of floating point numbers emitted depends on how
3585 @code{@value{AS}} is configured.
3586 @xref{Machine Dependencies}.
3590 On the @value{TARGET} family, @code{.float} emits 32-bit floating point numbers
3591 in @sc{ieee} format.
3596 @section @code{.func @var{name}[,@var{label}]}
3597 @cindex @code{func} directive
3598 @code{.func} emits debugging information to denote function @var{name}, and
3599 is ignored unless the file is assembled with debugging enabled.
3600 Only @samp{--gstabs} is currently supported.
3601 @var{label} is the entry point of the function and if omitted @var{name}
3602 prepended with the @samp{leading char} is used.
3603 @samp{leading char} is usually @code{_} or nothing, depending on the target.
3604 All functions are currently defined to have @code{void} return type.
3605 The function must be terminated with @code{.endfunc}.
3608 @section @code{.global @var{symbol}}, @code{.globl @var{symbol}}
3610 @cindex @code{global} directive
3611 @cindex symbol, making visible to linker
3612 @code{.global} makes the symbol visible to @code{@value{LD}}. If you define
3613 @var{symbol} in your partial program, its value is made available to
3614 other partial programs that are linked with it. Otherwise,
3615 @var{symbol} takes its attributes from a symbol of the same name
3616 from another file linked into the same program.
3618 Both spellings (@samp{.globl} and @samp{.global}) are accepted, for
3619 compatibility with other assemblers.
3622 On the HPPA, @code{.global} is not always enough to make it accessible to other
3623 partial programs. You may need the HPPA-only @code{.EXPORT} directive as well.
3624 @xref{HPPA Directives,, HPPA Assembler Directives}.
3628 @section @code{.hword @var{expressions}}
3630 @cindex @code{hword} directive
3631 @cindex integers, 16-bit
3632 @cindex numbers, 16-bit
3633 @cindex sixteen bit integers
3634 This expects zero or more @var{expressions}, and emits
3635 a 16 bit number for each.
3638 This directive is a synonym for @samp{.short}; depending on the target
3639 architecture, it may also be a synonym for @samp{.word}.
3643 This directive is a synonym for @samp{.short}.
3646 This directive is a synonym for both @samp{.short} and @samp{.word}.
3651 @section @code{.ident}
3653 @cindex @code{ident} directive
3654 This directive is used by some assemblers to place tags in object files.
3655 @code{@value{AS}} simply accepts the directive for source-file
3656 compatibility with such assemblers, but does not actually emit anything
3660 @section @code{.if @var{absolute expression}}
3662 @cindex conditional assembly
3663 @cindex @code{if} directive
3664 @code{.if} marks the beginning of a section of code which is only
3665 considered part of the source program being assembled if the argument
3666 (which must be an @var{absolute expression}) is non-zero. The end of
3667 the conditional section of code must be marked by @code{.endif}
3668 (@pxref{Endif,,@code{.endif}}); optionally, you may include code for the
3669 alternative condition, flagged by @code{.else} (@pxref{Else,,@code{.else}}).
3671 The following variants of @code{.if} are also supported:
3673 @cindex @code{ifdef} directive
3674 @item .ifdef @var{symbol}
3675 Assembles the following section of code if the specified @var{symbol}
3678 @cindex @code{ifc} directive
3679 @item .ifc @var{string1},@var{string2}
3680 Assembles the following section of code if the two strings are the same. The
3681 strings may be optionally quoted with single quotes. If they are not quoted,
3682 the first string stops at the first comma, and the second string stops at the
3683 end of the line. Strings which contain whitespace should be quoted. The
3684 string comparison is case sensitive.
3686 @cindex @code{ifeq} directive
3687 @item .ifeq @var{absolute expression}
3688 Assembles the following section of code if the argument is zero.
3690 @cindex @code{ifeqs} directive
3691 @item .ifeqs @var{string1},@var{string2}
3692 Another form of @code{.ifc}. The strings must be quoted using double quotes.
3694 @cindex @code{ifge} directive
3695 @item .ifge @var{absolute expression}
3696 Assembles the following section of code if the argument is greater than or
3699 @cindex @code{ifgt} directive
3700 @item .ifgt @var{absolute expression}
3701 Assembles the following section of code if the argument is greater than zero.
3703 @cindex @code{ifle} directive
3704 @item .ifle @var{absolute expression}
3705 Assembles the following section of code if the argument is less than or equal
3708 @cindex @code{iflt} directive
3709 @item .iflt @var{absolute expression}
3710 Assembles the following section of code if the argument is less than zero.
3712 @cindex @code{ifnc} directive
3713 @item .ifnc @var{string1},@var{string2}.
3714 Like @code{.ifc}, but the sense of the test is reversed: this assembles the
3715 following section of code if the two strings are not the same.
3717 @cindex @code{ifndef} directive
3718 @cindex @code{ifnotdef} directive
3719 @item .ifndef @var{symbol}
3720 @itemx .ifnotdef @var{symbol}
3721 Assembles the following section of code if the specified @var{symbol}
3722 has not been defined. Both spelling variants are equivalent.
3724 @cindex @code{ifne} directive
3725 @item .ifne @var{absolute expression}
3726 Assembles the following section of code if the argument is not equal to zero
3727 (in other words, this is equivalent to @code{.if}).
3729 @cindex @code{ifnes} directive
3730 @item .ifnes @var{string1},@var{string2}
3731 Like @code{.ifeqs}, but the sense of the test is reversed: this assembles the
3732 following section of code if the two strings are not the same.
3736 @section @code{.include "@var{file}"}
3738 @cindex @code{include} directive
3739 @cindex supporting files, including
3740 @cindex files, including
3741 This directive provides a way to include supporting files at specified
3742 points in your source program. The code from @var{file} is assembled as
3743 if it followed the point of the @code{.include}; when the end of the
3744 included file is reached, assembly of the original file continues. You
3745 can control the search paths used with the @samp{-I} command-line option
3746 (@pxref{Invoking,,Command-Line Options}). Quotation marks are required
3750 @section @code{.int @var{expressions}}
3752 @cindex @code{int} directive
3753 @cindex integers, 32-bit
3754 Expect zero or more @var{expressions}, of any section, separated by commas.
3755 For each expression, emit a number that, at run time, is the value of that
3756 expression. The byte order and bit size of the number depends on what kind
3757 of target the assembly is for.
3761 On the H8/500 and most forms of the H8/300, @code{.int} emits 16-bit
3762 integers. On the H8/300H and the Hitachi SH, however, @code{.int} emits
3768 @section @code{.irp @var{symbol},@var{values}}@dots{}
3770 @cindex @code{irp} directive
3771 Evaluate a sequence of statements assigning different values to @var{symbol}.
3772 The sequence of statements starts at the @code{.irp} directive, and is
3773 terminated by an @code{.endr} directive. For each @var{value}, @var{symbol} is
3774 set to @var{value}, and the sequence of statements is assembled. If no
3775 @var{value} is listed, the sequence of statements is assembled once, with
3776 @var{symbol} set to the null string. To refer to @var{symbol} within the
3777 sequence of statements, use @var{\symbol}.
3779 For example, assembling
3787 is equivalent to assembling
3796 @section @code{.irpc @var{symbol},@var{values}}@dots{}
3798 @cindex @code{irpc} directive
3799 Evaluate a sequence of statements assigning different values to @var{symbol}.
3800 The sequence of statements starts at the @code{.irpc} directive, and is
3801 terminated by an @code{.endr} directive. For each character in @var{value},
3802 @var{symbol} is set to the character, and the sequence of statements is
3803 assembled. If no @var{value} is listed, the sequence of statements is
3804 assembled once, with @var{symbol} set to the null string. To refer to
3805 @var{symbol} within the sequence of statements, use @var{\symbol}.
3807 For example, assembling
3815 is equivalent to assembling
3824 @section @code{.lcomm @var{symbol} , @var{length}}
3826 @cindex @code{lcomm} directive
3827 @cindex local common symbols
3828 @cindex symbols, local common
3829 Reserve @var{length} (an absolute expression) bytes for a local common
3830 denoted by @var{symbol}. The section and value of @var{symbol} are
3831 those of the new local common. The addresses are allocated in the bss
3832 section, so that at run-time the bytes start off zeroed. @var{Symbol}
3833 is not declared global (@pxref{Global,,@code{.global}}), so is normally
3834 not visible to @code{@value{LD}}.
3837 Some targets permit a third argument to be used with @code{.lcomm}. This
3838 argument specifies the desired alignment of the symbol in the bss section.
3842 The syntax for @code{.lcomm} differs slightly on the HPPA. The syntax is
3843 @samp{@var{symbol} .lcomm, @var{length}}; @var{symbol} is optional.
3847 @section @code{.lflags}
3849 @cindex @code{lflags} directive (ignored)
3850 @code{@value{AS}} accepts this directive, for compatibility with other
3851 assemblers, but ignores it.
3853 @ifclear no-line-dir
3855 @section @code{.line @var{line-number}}
3857 @cindex @code{line} directive
3861 @section @code{.ln @var{line-number}}
3863 @cindex @code{ln} directive
3865 @cindex logical line number
3867 Change the logical line number. @var{line-number} must be an absolute
3868 expression. The next line has that logical line number. Therefore any other
3869 statements on the current line (after a statement separator character) are
3870 reported as on logical line number @var{line-number} @minus{} 1. One day
3871 @code{@value{AS}} will no longer support this directive: it is recognized only
3872 for compatibility with existing assembler programs.
3876 @emph{Warning:} In the AMD29K configuration of @value{AS}, this command is
3877 not available; use the synonym @code{.ln} in that context.
3882 @ifclear no-line-dir
3883 Even though this is a directive associated with the @code{a.out} or
3884 @code{b.out} object-code formats, @code{@value{AS}} still recognizes it
3885 when producing COFF output, and treats @samp{.line} as though it
3886 were the COFF @samp{.ln} @emph{if} it is found outside a
3887 @code{.def}/@code{.endef} pair.
3889 Inside a @code{.def}, @samp{.line} is, instead, one of the directives
3890 used by compilers to generate auxiliary symbol information for
3895 @section @code{.linkonce [@var{type}]}
3897 @cindex @code{linkonce} directive
3898 @cindex common sections
3899 Mark the current section so that the linker only includes a single copy of it.
3900 This may be used to include the same section in several different object files,
3901 but ensure that the linker will only include it once in the final output file.
3902 The @code{.linkonce} pseudo-op must be used for each instance of the section.
3903 Duplicate sections are detected based on the section name, so it should be
3906 This directive is only supported by a few object file formats; as of this
3907 writing, the only object file format which supports it is the Portable
3908 Executable format used on Windows NT.
3910 The @var{type} argument is optional. If specified, it must be one of the
3911 following strings. For example:
3915 Not all types may be supported on all object file formats.
3919 Silently discard duplicate sections. This is the default.
3922 Warn if there are duplicate sections, but still keep only one copy.
3925 Warn if any of the duplicates have different sizes.
3928 Warn if any of the duplicates do not have exactly the same contents.
3932 @section @code{.ln @var{line-number}}
3934 @cindex @code{ln} directive
3935 @ifclear no-line-dir
3936 @samp{.ln} is a synonym for @samp{.line}.
3939 Tell @code{@value{AS}} to change the logical line number. @var{line-number}
3940 must be an absolute expression. The next line has that logical
3941 line number, so any other statements on the current line (after a
3942 statement separator character @code{;}) are reported as on logical
3943 line number @var{line-number} @minus{} 1.
3946 This directive is accepted, but ignored, when @code{@value{AS}} is
3947 configured for @code{b.out}; its effect is only associated with COFF
3953 @section @code{.mri @var{val}}
3955 @cindex @code{mri} directive
3956 @cindex MRI mode, temporarily
3957 If @var{val} is non-zero, this tells @code{@value{AS}} to enter MRI mode. If
3958 @var{val} is zero, this tells @code{@value{AS}} to exit MRI mode. This change
3959 affects code assembled until the next @code{.mri} directive, or until the end
3960 of the file. @xref{M, MRI mode, MRI mode}.
3963 @section @code{.list}
3965 @cindex @code{list} directive
3966 @cindex listing control, turning on
3967 Control (in conjunction with the @code{.nolist} directive) whether or
3968 not assembly listings are generated. These two directives maintain an
3969 internal counter (which is zero initially). @code{.list} increments the
3970 counter, and @code{.nolist} decrements it. Assembly listings are
3971 generated whenever the counter is greater than zero.
3973 By default, listings are disabled. When you enable them (with the
3974 @samp{-a} command line option; @pxref{Invoking,,Command-Line Options}),
3975 the initial value of the listing counter is one.
3978 @section @code{.long @var{expressions}}
3980 @cindex @code{long} directive
3981 @code{.long} is the same as @samp{.int}, @pxref{Int,,@code{.int}}.
3984 @c no one seems to know what this is for or whether this description is
3985 @c what it really ought to do
3987 @section @code{.lsym @var{symbol}, @var{expression}}
3989 @cindex @code{lsym} directive
3990 @cindex symbol, not referenced in assembly
3991 @code{.lsym} creates a new symbol named @var{symbol}, but does not put it in
3992 the hash table, ensuring it cannot be referenced by name during the
3993 rest of the assembly. This sets the attributes of the symbol to be
3994 the same as the expression value:
3996 @var{other} = @var{descriptor} = 0
3997 @var{type} = @r{(section of @var{expression})}
3998 @var{value} = @var{expression}
4001 The new symbol is not flagged as external.
4005 @section @code{.macro}
4008 The commands @code{.macro} and @code{.endm} allow you to define macros that
4009 generate assembly output. For example, this definition specifies a macro
4010 @code{sum} that puts a sequence of numbers into memory:
4013 .macro sum from=0, to=5
4022 With that definition, @samp{SUM 0,5} is equivalent to this assembly input:
4034 @item .macro @var{macname}
4035 @itemx .macro @var{macname} @var{macargs} @dots{}
4036 @cindex @code{macro} directive
4037 Begin the definition of a macro called @var{macname}. If your macro
4038 definition requires arguments, specify their names after the macro name,
4039 separated by commas or spaces. You can supply a default value for any
4040 macro argument by following the name with @samp{=@var{deflt}}. For
4041 example, these are all valid @code{.macro} statements:
4045 Begin the definition of a macro called @code{comm}, which takes no
4048 @item .macro plus1 p, p1
4049 @itemx .macro plus1 p p1
4050 Either statement begins the definition of a macro called @code{plus1},
4051 which takes two arguments; within the macro definition, write
4052 @samp{\p} or @samp{\p1} to evaluate the arguments.
4054 @item .macro reserve_str p1=0 p2
4055 Begin the definition of a macro called @code{reserve_str}, with two
4056 arguments. The first argument has a default value, but not the second.
4057 After the definition is complete, you can call the macro either as
4058 @samp{reserve_str @var{a},@var{b}} (with @samp{\p1} evaluating to
4059 @var{a} and @samp{\p2} evaluating to @var{b}), or as @samp{reserve_str
4060 ,@var{b}} (with @samp{\p1} evaluating as the default, in this case
4061 @samp{0}, and @samp{\p2} evaluating to @var{b}).
4064 When you call a macro, you can specify the argument values either by
4065 position, or by keyword. For example, @samp{sum 9,17} is equivalent to
4066 @samp{sum to=17, from=9}.
4069 @cindex @code{endm} directive
4070 Mark the end of a macro definition.
4073 @cindex @code{exitm} directive
4074 Exit early from the current macro definition.
4076 @cindex number of macros executed
4077 @cindex macros, count executed
4079 @code{@value{AS}} maintains a counter of how many macros it has
4080 executed in this pseudo-variable; you can copy that number to your
4081 output with @samp{\@@}, but @emph{only within a macro definition}.
4084 @item LOCAL @var{name} [ , @dots{} ]
4085 @emph{Warning: @code{LOCAL} is only available if you select ``alternate
4086 macro syntax'' with @samp{-a} or @samp{--alternate}.} @xref{Alternate,,
4087 Alternate macro syntax}.
4089 Generate a string replacement for each of the @var{name} arguments, and
4090 replace any instances of @var{name} in each macro expansion. The
4091 replacement string is unique in the assembly, and different for each
4092 separate macro expansion. @code{LOCAL} allows you to write macros that
4093 define symbols, without fear of conflict between separate macro expansions.
4098 @section @code{.nolist}
4100 @cindex @code{nolist} directive
4101 @cindex listing control, turning off
4102 Control (in conjunction with the @code{.list} directive) whether or
4103 not assembly listings are generated. These two directives maintain an
4104 internal counter (which is zero initially). @code{.list} increments the
4105 counter, and @code{.nolist} decrements it. Assembly listings are
4106 generated whenever the counter is greater than zero.
4109 @section @code{.octa @var{bignums}}
4111 @c FIXME: double size emitted for "octa" on i960, others? Or warn?
4112 @cindex @code{octa} directive
4113 @cindex integer, 16-byte
4114 @cindex sixteen byte integer
4115 This directive expects zero or more bignums, separated by commas. For each
4116 bignum, it emits a 16-byte integer.
4118 The term ``octa'' comes from contexts in which a ``word'' is two bytes;
4119 hence @emph{octa}-word for 16 bytes.
4122 @section @code{.org @var{new-lc} , @var{fill}}
4124 @cindex @code{org} directive
4125 @cindex location counter, advancing
4126 @cindex advancing location counter
4127 @cindex current address, advancing
4128 Advance the location counter of the current section to
4129 @var{new-lc}. @var{new-lc} is either an absolute expression or an
4130 expression with the same section as the current subsection. That is,
4131 you can't use @code{.org} to cross sections: if @var{new-lc} has the
4132 wrong section, the @code{.org} directive is ignored. To be compatible
4133 with former assemblers, if the section of @var{new-lc} is absolute,
4134 @code{@value{AS}} issues a warning, then pretends the section of @var{new-lc}
4135 is the same as the current subsection.
4137 @code{.org} may only increase the location counter, or leave it
4138 unchanged; you cannot use @code{.org} to move the location counter
4141 @c double negative used below "not undefined" because this is a specific
4142 @c reference to "undefined" (as SEG_UNKNOWN is called in this manual)
4143 @c section. doc@cygnus.com 18feb91
4144 Because @code{@value{AS}} tries to assemble programs in one pass, @var{new-lc}
4145 may not be undefined. If you really detest this restriction we eagerly await
4146 a chance to share your improved assembler.
4148 Beware that the origin is relative to the start of the section, not
4149 to the start of the subsection. This is compatible with other
4150 people's assemblers.
4152 When the location counter (of the current subsection) is advanced, the
4153 intervening bytes are filled with @var{fill} which should be an
4154 absolute expression. If the comma and @var{fill} are omitted,
4155 @var{fill} defaults to zero.
4158 @section @code{.p2align[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
4160 @cindex padding the location counter given a power of two
4161 @cindex @code{p2align} directive
4162 Pad the location counter (in the current subsection) to a particular
4163 storage boundary. The first expression (which must be absolute) is the
4164 number of low-order zero bits the location counter must have after
4165 advancement. For example @samp{.p2align 3} advances the location
4166 counter until it a multiple of 8. If the location counter is already a
4167 multiple of 8, no change is needed.
4169 The second expression (also absolute) gives the fill value to be stored in the
4170 padding bytes. It (and the comma) may be omitted. If it is omitted, the
4171 padding bytes are normally zero. However, on some systems, if the section is
4172 marked as containing code and the fill value is omitted, the space is filled
4173 with no-op instructions.
4175 The third expression is also absolute, and is also optional. If it is present,
4176 it is the maximum number of bytes that should be skipped by this alignment
4177 directive. If doing the alignment would require skipping more bytes than the
4178 specified maximum, then the alignment is not done at all. You can omit the
4179 fill value (the second argument) entirely by simply using two commas after the
4180 required alignment; this can be useful if you want the alignment to be filled
4181 with no-op instructions when appropriate.
4183 @cindex @code{p2alignw} directive
4184 @cindex @code{p2alignl} directive
4185 The @code{.p2alignw} and @code{.p2alignl} directives are variants of the
4186 @code{.p2align} directive. The @code{.p2alignw} directive treats the fill
4187 pattern as a two byte word value. The @code{.p2alignl} directives treats the
4188 fill pattern as a four byte longword value. For example, @code{.p2alignw
4189 2,0x368d} will align to a multiple of 4. If it skips two bytes, they will be
4190 filled in with the value 0x368d (the exact placement of the bytes depends upon
4191 the endianness of the processor). If it skips 1 or 3 bytes, the fill value is
4195 @section @code{.print @var{string}}
4197 @cindex @code{print} directive
4198 @code{@value{AS}} will print @var{string} on the standard output during
4199 assembly. You must put @var{string} in double quotes.
4202 @section @code{.psize @var{lines} , @var{columns}}
4204 @cindex @code{psize} directive
4205 @cindex listing control: paper size
4206 @cindex paper size, for listings
4207 Use this directive to declare the number of lines---and, optionally, the
4208 number of columns---to use for each page, when generating listings.
4210 If you do not use @code{.psize}, listings use a default line-count
4211 of 60. You may omit the comma and @var{columns} specification; the
4212 default width is 200 columns.
4214 @code{@value{AS}} generates formfeeds whenever the specified number of
4215 lines is exceeded (or whenever you explicitly request one, using
4218 If you specify @var{lines} as @code{0}, no formfeeds are generated save
4219 those explicitly specified with @code{.eject}.
4222 @section @code{.purgem @var{name}}
4224 @cindex @code{purgem} directive
4225 Undefine the macro @var{name}, so that later uses of the string will not be
4226 expanded. @xref{Macro}.
4229 @section @code{.quad @var{bignums}}
4231 @cindex @code{quad} directive
4232 @code{.quad} expects zero or more bignums, separated by commas. For
4233 each bignum, it emits
4235 an 8-byte integer. If the bignum won't fit in 8 bytes, it prints a
4236 warning message; and just takes the lowest order 8 bytes of the bignum.
4237 @cindex eight-byte integer
4238 @cindex integer, 8-byte
4240 The term ``quad'' comes from contexts in which a ``word'' is two bytes;
4241 hence @emph{quad}-word for 8 bytes.
4244 a 16-byte integer. If the bignum won't fit in 16 bytes, it prints a
4245 warning message; and just takes the lowest order 16 bytes of the bignum.
4246 @cindex sixteen-byte integer
4247 @cindex integer, 16-byte
4251 @section @code{.rept @var{count}}
4253 @cindex @code{rept} directive
4254 Repeat the sequence of lines between the @code{.rept} directive and the next
4255 @code{.endr} directive @var{count} times.
4257 For example, assembling
4265 is equivalent to assembling
4274 @section @code{.sbttl "@var{subheading}"}
4276 @cindex @code{sbttl} directive
4277 @cindex subtitles for listings
4278 @cindex listing control: subtitle
4279 Use @var{subheading} as the title (third line, immediately after the
4280 title line) when generating assembly listings.
4282 This directive affects subsequent pages, as well as the current page if
4283 it appears within ten lines of the top of a page.
4287 @section @code{.scl @var{class}}
4289 @cindex @code{scl} directive
4290 @cindex symbol storage class (COFF)
4291 @cindex COFF symbol storage class
4292 Set the storage-class value for a symbol. This directive may only be
4293 used inside a @code{.def}/@code{.endef} pair. Storage class may flag
4294 whether a symbol is static or external, or it may record further
4295 symbolic debugging information.
4298 The @samp{.scl} directive is primarily associated with COFF output; when
4299 configured to generate @code{b.out} output format, @code{@value{AS}}
4300 accepts this directive but ignores it.
4305 @section @code{.section @var{name}}
4307 @cindex @code{section} directive
4308 @cindex named section
4309 Use the @code{.section} directive to assemble the following code into a section
4312 This directive is only supported for targets that actually support arbitrarily
4313 named sections; on @code{a.out} targets, for example, it is not accepted, even
4314 with a standard @code{a.out} section name.
4317 For COFF targets, the @code{.section} directive is used in one of the following
4320 .section @var{name}[, "@var{flags}"]
4321 .section @var{name}[, @var{subsegment}]
4324 If the optional argument is quoted, it is taken as flags to use for the
4325 section. Each flag is a single character. The following flags are recognized:
4328 bss section (uninitialized data)
4330 section is not loaded
4340 shared section (meaningful for PE targets)
4343 If no flags are specified, the default flags depend upon the section name. If
4344 the section name is not recognized, the default will be for the section to be
4345 loaded and writable.
4347 If the optional argument to the @code{.section} directive is not quoted, it is
4348 taken as a subsegment number (@pxref{Sub-Sections}).
4352 For ELF targets, the @code{.section} directive is used like this:
4354 .section @var{name}[, "@var{flags}"[, @@@var{type}]]
4356 The optional @var{flags} argument is a quoted string which may contain any
4357 combintion of the following characters:
4360 section is allocatable
4364 section is executable
4367 The optional @var{type} argument may contain one of the following constants:
4370 section contains data
4372 section does not contain data (i.e., section only occupies space)
4375 If no flags are specified, the default flags depend upon the section name. If
4376 the section name is not recognized, the default will be for the section to have
4377 none of the above flags: it will not be allocated in memory, nor writable, nor
4378 executable. The section will contain data.
4380 For ELF targets, the assembler supports another type of @code{.section}
4381 directive for compatibility with the Solaris assembler:
4383 .section "@var{name}"[, @var{flags}...]
4385 Note that the section name is quoted. There may be a sequence of comma
4389 section is allocatable
4393 section is executable
4398 @section @code{.set @var{symbol}, @var{expression}}
4400 @cindex @code{set} directive
4401 @cindex symbol value, setting
4402 Set the value of @var{symbol} to @var{expression}. This
4403 changes @var{symbol}'s value and type to conform to
4404 @var{expression}. If @var{symbol} was flagged as external, it remains
4405 flagged (@pxref{Symbol Attributes}).
4407 You may @code{.set} a symbol many times in the same assembly.
4409 If you @code{.set} a global symbol, the value stored in the object
4410 file is the last value stored into it.
4413 The syntax for @code{set} on the HPPA is
4414 @samp{@var{symbol} .set @var{expression}}.
4418 @section @code{.short @var{expressions}}
4420 @cindex @code{short} directive
4422 @code{.short} is normally the same as @samp{.word}.
4423 @xref{Word,,@code{.word}}.
4425 In some configurations, however, @code{.short} and @code{.word} generate
4426 numbers of different lengths; @pxref{Machine Dependencies}.
4430 @code{.short} is the same as @samp{.word}. @xref{Word,,@code{.word}}.
4433 This expects zero or more @var{expressions}, and emits
4434 a 16 bit number for each.
4439 @section @code{.single @var{flonums}}
4441 @cindex @code{single} directive
4442 @cindex floating point numbers (single)
4443 This directive assembles zero or more flonums, separated by commas. It
4444 has the same effect as @code{.float}.
4446 The exact kind of floating point numbers emitted depends on how
4447 @code{@value{AS}} is configured. @xref{Machine Dependencies}.
4451 On the @value{TARGET} family, @code{.single} emits 32-bit floating point
4452 numbers in @sc{ieee} format.
4458 @section @code{.size}
4460 @cindex @code{size} directive
4461 This directive is generated by compilers to include auxiliary debugging
4462 information in the symbol table. It is only permitted inside
4463 @code{.def}/@code{.endef} pairs.
4466 @samp{.size} is only meaningful when generating COFF format output; when
4467 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
4473 @section @code{.sleb128 @var{expressions}}
4475 @cindex @code{sleb128} directive
4476 @var{sleb128} stands for ``signed little endian base 128.'' This is a
4477 compact, variable length representation of numbers used by the DWARF
4478 symbolic debugging format. @xref{Uleb128,@code{.uleb128}}.
4480 @ifclear no-space-dir
4482 @section @code{.skip @var{size} , @var{fill}}
4484 @cindex @code{skip} directive
4485 @cindex filling memory
4486 This directive emits @var{size} bytes, each of value @var{fill}. Both
4487 @var{size} and @var{fill} are absolute expressions. If the comma and
4488 @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same as
4492 @section @code{.space @var{size} , @var{fill}}
4494 @cindex @code{space} directive
4495 @cindex filling memory
4496 This directive emits @var{size} bytes, each of value @var{fill}. Both
4497 @var{size} and @var{fill} are absolute expressions. If the comma
4498 and @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same
4503 @emph{Warning:} @code{.space} has a completely different meaning for HPPA
4504 targets; use @code{.block} as a substitute. See @cite{HP9000 Series 800
4505 Assembly Language Reference Manual} (HP 92432-90001) for the meaning of the
4506 @code{.space} directive. @xref{HPPA Directives,,HPPA Assembler Directives},
4515 @section @code{.space}
4516 @cindex @code{space} directive
4518 On the AMD 29K, this directive is ignored; it is accepted for
4519 compatibility with other AMD 29K assemblers.
4522 @emph{Warning:} In most versions of the @sc{gnu} assembler, the directive
4523 @code{.space} has the effect of @code{.block} @xref{Machine Dependencies}.
4529 @section @code{.stabd, .stabn, .stabs}
4531 @cindex symbolic debuggers, information for
4532 @cindex @code{stab@var{x}} directives
4533 There are three directives that begin @samp{.stab}.
4534 All emit symbols (@pxref{Symbols}), for use by symbolic debuggers.
4535 The symbols are not entered in the @code{@value{AS}} hash table: they
4536 cannot be referenced elsewhere in the source file.
4537 Up to five fields are required:
4541 This is the symbol's name. It may contain any character except
4542 @samp{\000}, so is more general than ordinary symbol names. Some
4543 debuggers used to code arbitrarily complex structures into symbol names
4547 An absolute expression. The symbol's type is set to the low 8 bits of
4548 this expression. Any bit pattern is permitted, but @code{@value{LD}}
4549 and debuggers choke on silly bit patterns.
4552 An absolute expression. The symbol's ``other'' attribute is set to the
4553 low 8 bits of this expression.
4556 An absolute expression. The symbol's descriptor is set to the low 16
4557 bits of this expression.
4560 An absolute expression which becomes the symbol's value.
4563 If a warning is detected while reading a @code{.stabd}, @code{.stabn},
4564 or @code{.stabs} statement, the symbol has probably already been created;
4565 you get a half-formed symbol in your object file. This is
4566 compatible with earlier assemblers!
4569 @cindex @code{stabd} directive
4570 @item .stabd @var{type} , @var{other} , @var{desc}
4572 The ``name'' of the symbol generated is not even an empty string.
4573 It is a null pointer, for compatibility. Older assemblers used a
4574 null pointer so they didn't waste space in object files with empty
4577 The symbol's value is set to the location counter,
4578 relocatably. When your program is linked, the value of this symbol
4579 is the address of the location counter when the @code{.stabd} was
4582 @cindex @code{stabn} directive
4583 @item .stabn @var{type} , @var{other} , @var{desc} , @var{value}
4584 The name of the symbol is set to the empty string @code{""}.
4586 @cindex @code{stabs} directive
4587 @item .stabs @var{string} , @var{type} , @var{other} , @var{desc} , @var{value}
4588 All five fields are specified.
4594 @section @code{.string} "@var{str}"
4596 @cindex string, copying to object file
4597 @cindex @code{string} directive
4599 Copy the characters in @var{str} to the object file. You may specify more than
4600 one string to copy, separated by commas. Unless otherwise specified for a
4601 particular machine, the assembler marks the end of each string with a 0 byte.
4602 You can use any of the escape sequences described in @ref{Strings,,Strings}.
4605 @section @code{.struct @var{expression}}
4607 @cindex @code{struct} directive
4608 Switch to the absolute section, and set the section offset to @var{expression},
4609 which must be an absolute expression. You might use this as follows:
4618 This would define the symbol @code{field1} to have the value 0, the symbol
4619 @code{field2} to have the value 4, and the symbol @code{field3} to have the
4620 value 8. Assembly would be left in the absolute section, and you would need to
4621 use a @code{.section} directive of some sort to change to some other section
4622 before further assembly.
4626 @section @code{.symver}
4627 @cindex @code{symver} directive
4628 @cindex symbol versioning
4629 @cindex versions of symbols
4630 Use the @code{.symver} directive to bind symbols to specific version nodes
4631 within a source file. This is only supported on ELF platforms, and is
4632 typically used when assembling files to be linked into a shared library.
4633 There are cases where it may make sense to use this in objects to be bound
4634 into an application itself so as to override a versioned symbol from a
4637 For ELF targets, the @code{.symver} directive is used like this:
4639 .symver @var{name}, @var{name2@@nodename}
4641 In this case, the symbol @var{name} must exist and be defined within the file
4642 being assembled. The @code{.versym} directive effectively creates a symbol
4643 alias with the name @var{name2@@nodename}, and in fact the main reason that we
4644 just don't try and create a regular alias is that the @var{@@} character isn't
4645 permitted in symbol names. The @var{name2} part of the name is the actual name
4646 of the symbol by which it will be externally referenced. The name @var{name}
4647 itself is merely a name of convenience that is used so that it is possible to
4648 have definitions for multiple versions of a function within a single source
4649 file, and so that the compiler can unambiguously know which version of a
4650 function is being mentioned. The @var{nodename} portion of the alias should be
4651 the name of a node specified in the version script supplied to the linker when
4652 building a shared library. If you are attempting to override a versioned
4653 symbol from a shared library, then @var{nodename} should correspond to the
4654 nodename of the symbol you are trying to override.
4659 @section @code{.tag @var{structname}}
4661 @cindex COFF structure debugging
4662 @cindex structure debugging, COFF
4663 @cindex @code{tag} directive
4664 This directive is generated by compilers to include auxiliary debugging
4665 information in the symbol table. It is only permitted inside
4666 @code{.def}/@code{.endef} pairs. Tags are used to link structure
4667 definitions in the symbol table with instances of those structures.
4670 @samp{.tag} is only used when generating COFF format output; when
4671 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
4677 @section @code{.text @var{subsection}}
4679 @cindex @code{text} directive
4680 Tells @code{@value{AS}} to assemble the following statements onto the end of
4681 the text subsection numbered @var{subsection}, which is an absolute
4682 expression. If @var{subsection} is omitted, subsection number zero
4686 @section @code{.title "@var{heading}"}
4688 @cindex @code{title} directive
4689 @cindex listing control: title line
4690 Use @var{heading} as the title (second line, immediately after the
4691 source file name and pagenumber) when generating assembly listings.
4693 This directive affects subsequent pages, as well as the current page if
4694 it appears within ten lines of the top of a page.
4698 @section @code{.type @var{int}}
4700 @cindex COFF symbol type
4701 @cindex symbol type, COFF
4702 @cindex @code{type} directive
4703 This directive, permitted only within @code{.def}/@code{.endef} pairs,
4704 records the integer @var{int} as the type attribute of a symbol table entry.
4707 @samp{.type} is associated only with COFF format output; when
4708 @code{@value{AS}} is configured for @code{b.out} output, it accepts this
4709 directive but ignores it.
4715 @section @code{.val @var{addr}}
4717 @cindex @code{val} directive
4718 @cindex COFF value attribute
4719 @cindex value attribute, COFF
4720 This directive, permitted only within @code{.def}/@code{.endef} pairs,
4721 records the address @var{addr} as the value attribute of a symbol table
4725 @samp{.val} is used only for COFF output; when @code{@value{AS}} is
4726 configured for @code{b.out}, it accepts this directive but ignores it.
4731 @section @code{.uleb128 @var{expressions}}
4733 @cindex @code{uleb128} directive
4734 @var{uleb128} stands for ``unsigned little endian base 128.'' This is a
4735 compact, variable length representation of numbers used by the DWARF
4736 symbolic debugging format. @xref{Sleb128,@code{.sleb128}}.
4739 @section @code{.word @var{expressions}}
4741 @cindex @code{word} directive
4742 This directive expects zero or more @var{expressions}, of any section,
4743 separated by commas.
4746 For each expression, @code{@value{AS}} emits a 32-bit number.
4749 For each expression, @code{@value{AS}} emits a 16-bit number.
4754 The size of the number emitted, and its byte order,
4755 depend on what target computer the assembly is for.
4758 @c on amd29k, i960, sparc the "special treatment to support compilers" doesn't
4759 @c happen---32-bit addressability, period; no long/short jumps.
4760 @ifset DIFF-TBL-KLUGE
4761 @cindex difference tables altered
4762 @cindex altered difference tables
4764 @emph{Warning: Special Treatment to support Compilers}
4768 Machines with a 32-bit address space, but that do less than 32-bit
4769 addressing, require the following special treatment. If the machine of
4770 interest to you does 32-bit addressing (or doesn't require it;
4771 @pxref{Machine Dependencies}), you can ignore this issue.
4774 In order to assemble compiler output into something that works,
4775 @code{@value{AS}} occasionlly does strange things to @samp{.word} directives.
4776 Directives of the form @samp{.word sym1-sym2} are often emitted by
4777 compilers as part of jump tables. Therefore, when @code{@value{AS}} assembles a
4778 directive of the form @samp{.word sym1-sym2}, and the difference between
4779 @code{sym1} and @code{sym2} does not fit in 16 bits, @code{@value{AS}}
4780 creates a @dfn{secondary jump table}, immediately before the next label.
4781 This secondary jump table is preceded by a short-jump to the
4782 first byte after the secondary table. This short-jump prevents the flow
4783 of control from accidentally falling into the new table. Inside the
4784 table is a long-jump to @code{sym2}. The original @samp{.word}
4785 contains @code{sym1} minus the address of the long-jump to
4788 If there were several occurrences of @samp{.word sym1-sym2} before the
4789 secondary jump table, all of them are adjusted. If there was a
4790 @samp{.word sym3-sym4}, that also did not fit in sixteen bits, a
4791 long-jump to @code{sym4} is included in the secondary jump table,
4792 and the @code{.word} directives are adjusted to contain @code{sym3}
4793 minus the address of the long-jump to @code{sym4}; and so on, for as many
4794 entries in the original jump table as necessary.
4797 @emph{This feature may be disabled by compiling @code{@value{AS}} with the
4798 @samp{-DWORKING_DOT_WORD} option.} This feature is likely to confuse
4799 assembly language programmers.
4802 @c end DIFF-TBL-KLUGE
4805 @section Deprecated Directives
4807 @cindex deprecated directives
4808 @cindex obsolescent directives
4809 One day these directives won't work.
4810 They are included for compatibility with older assemblers.
4817 @node Machine Dependencies
4818 @chapter Machine Dependent Features
4820 @cindex machine dependencies
4821 The machine instruction sets are (almost by definition) different on
4822 each machine where @code{@value{AS}} runs. Floating point representations
4823 vary as well, and @code{@value{AS}} often supports a few additional
4824 directives or command-line options for compatibility with other
4825 assemblers on a particular platform. Finally, some versions of
4826 @code{@value{AS}} support special pseudo-instructions for branch
4829 This chapter discusses most of these differences, though it does not
4830 include details on any machine's instruction set. For details on that
4831 subject, see the hardware manufacturer's manual.
4835 * AMD29K-Dependent:: AMD 29K Dependent Features
4838 * ARC-Dependent:: ARC Dependent Features
4841 * ARM-Dependent:: ARM Dependent Features
4844 * D10V-Dependent:: D10V Dependent Features
4847 * D30V-Dependent:: D30V Dependent Features
4850 * H8/300-Dependent:: Hitachi H8/300 Dependent Features
4853 * H8/500-Dependent:: Hitachi H8/500 Dependent Features
4856 * HPPA-Dependent:: HPPA Dependent Features
4859 * i386-Dependent:: Intel 80386 Dependent Features
4862 * i960-Dependent:: Intel 80960 Dependent Features
4865 * M68K-Dependent:: M680x0 Dependent Features
4868 * MIPS-Dependent:: MIPS Dependent Features
4871 * SH-Dependent:: Hitachi SH Dependent Features
4874 * PJ-Dependent:: picoJava Dependent Features
4877 * Sparc-Dependent:: SPARC Dependent Features
4880 * V850-Dependent:: V850 Dependent Features
4883 * Z8000-Dependent:: Z8000 Dependent Features
4886 * Vax-Dependent:: VAX Dependent Features
4893 @c The following major nodes are *sections* in the GENERIC version, *chapters*
4894 @c in single-cpu versions. This is mainly achieved by @lowersections. There is a
4895 @c peculiarity: to preserve cross-references, there must be a node called
4896 @c "Machine Dependencies". Hence the conditional nodenames in each
4897 @c major node below. Node defaulting in makeinfo requires adjacency of
4898 @c node and sectioning commands; hence the repetition of @chapter BLAH
4899 @c in both conditional blocks.
4905 @chapter ARC Dependent Features
4908 @node Machine Dependencies
4909 @chapter ARC Dependent Features
4914 * ARC-Opts:: Options
4915 * ARC-Float:: Floating Point
4916 * ARC-Directives:: Sparc Machine Directives
4922 @cindex options for ARC
4924 @cindex architectures, ARC
4925 @cindex ARC architectures
4926 The ARC chip family includes several successive levels (or other
4927 variants) of chip, using the same core instruction set, but including
4928 a few additional instructions at each level.
4930 By default, @code{@value{AS}} assumes the core instruction set (ARC
4931 base). The @code{.cpu} pseudo-op is intended to be used to select
4935 @cindex @code{-mbig-endian} option (ARC)
4936 @cindex @code{-mlittle-endian} option (ARC)
4937 @cindex ARC big-endian output
4938 @cindex ARC little-endian output
4939 @cindex big-endian output, ARC
4940 @cindex little-endian output, ARC
4942 @itemx -mlittle-endian
4943 Any @sc{arc} configuration of @code{@value{AS}} can select big-endian or
4944 little-endian output at run time (unlike most other @sc{gnu} development
4945 tools, which must be configured for one or the other). Use
4946 @samp{-mbig-endian} to select big-endian output, and @samp{-mlittle-endian}
4951 @section Floating Point
4953 @cindex floating point, ARC (@sc{ieee})
4954 @cindex ARC floating point (@sc{ieee})
4955 The ARC cpu family currently does not have hardware floating point
4956 support. Software floating point support is provided by @code{GCC}
4957 and uses @sc{ieee} floating-point numbers.
4959 @node ARC-Directives
4960 @section ARC Machine Directives
4962 @cindex ARC machine directives
4963 @cindex machine directives, ARC
4964 The ARC version of @code{@value{AS}} supports the following additional
4969 @cindex @code{cpu} directive, SPARC
4970 This must be followed by the desired cpu.
4971 The ARC is intended to be customizable, @code{.cpu} is used to
4972 select the desired variant [though currently there are none].
4979 @include c-a29k.texi
4988 @node Machine Dependencies
4989 @chapter Machine Dependent Features
4991 The machine instruction sets are different on each Hitachi chip family,
4992 and there are also some syntax differences among the families. This
4993 chapter describes the specific @code{@value{AS}} features for each
4997 * H8/300-Dependent:: Hitachi H8/300 Dependent Features
4998 * H8/500-Dependent:: Hitachi H8/500 Dependent Features
4999 * SH-Dependent:: Hitachi SH Dependent Features
5006 @include c-d10v.texi
5010 @include c-d30v.texi
5014 @include c-h8300.texi
5018 @include c-h8500.texi
5022 @include c-hppa.texi
5026 @include c-i386.texi
5030 @include c-i960.texi
5035 @include c-m68k.texi
5039 @include c-mips.texi
5043 @include c-ns32k.texi
5055 @include c-sparc.texi
5067 @include c-v850.texi
5071 @c reverse effect of @down at top of generic Machine-Dep chapter
5075 @node Reporting Bugs
5076 @chapter Reporting Bugs
5077 @cindex bugs in assembler
5078 @cindex reporting bugs in assembler
5080 Your bug reports play an essential role in making @code{@value{AS}} reliable.
5082 Reporting a bug may help you by bringing a solution to your problem, or it may
5083 not. But in any case the principal function of a bug report is to help the
5084 entire community by making the next version of @code{@value{AS}} work better.
5085 Bug reports are your contribution to the maintenance of @code{@value{AS}}.
5087 In order for a bug report to serve its purpose, you must include the
5088 information that enables us to fix the bug.
5091 * Bug Criteria:: Have you found a bug?
5092 * Bug Reporting:: How to report bugs
5096 @section Have you found a bug?
5097 @cindex bug criteria
5099 If you are not sure whether you have found a bug, here are some guidelines:
5102 @cindex fatal signal
5103 @cindex assembler crash
5104 @cindex crash of assembler
5106 If the assembler gets a fatal signal, for any input whatever, that is a
5107 @code{@value{AS}} bug. Reliable assemblers never crash.
5109 @cindex error on valid input
5111 If @code{@value{AS}} produces an error message for valid input, that is a bug.
5113 @cindex invalid input
5115 If @code{@value{AS}} does not produce an error message for invalid input, that
5116 is a bug. However, you should note that your idea of ``invalid input'' might
5117 be our idea of ``an extension'' or ``support for traditional practice''.
5120 If you are an experienced user of assemblers, your suggestions for improvement
5121 of @code{@value{AS}} are welcome in any case.
5125 @section How to report bugs
5127 @cindex assembler bugs, reporting
5129 A number of companies and individuals offer support for @sc{gnu} products. If
5130 you obtained @code{@value{AS}} from a support organization, we recommend you
5131 contact that organization first.
5133 You can find contact information for many support companies and
5134 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
5137 In any event, we also recommend that you send bug reports for @code{@value{AS}}
5138 to @samp{bug-gnu-utils@@gnu.org}.
5140 The fundamental principle of reporting bugs usefully is this:
5141 @strong{report all the facts}. If you are not sure whether to state a
5142 fact or leave it out, state it!
5144 Often people omit facts because they think they know what causes the problem
5145 and assume that some details do not matter. Thus, you might assume that the
5146 name of a symbol you use in an example does not matter. Well, probably it does
5147 not, but one cannot be sure. Perhaps the bug is a stray memory reference which
5148 happens to fetch from the location where that name is stored in memory;
5149 perhaps, if the name were different, the contents of that location would fool
5150 the assembler into doing the right thing despite the bug. Play it safe and
5151 give a specific, complete example. That is the easiest thing for you to do,
5152 and the most helpful.
5154 Keep in mind that the purpose of a bug report is to enable us to fix the bug if
5155 it is new to us. Therefore, always write your bug reports on the assumption
5156 that the bug has not been reported previously.
5158 Sometimes people give a few sketchy facts and ask, ``Does this ring a
5159 bell?'' Those bug reports are useless, and we urge everyone to
5160 @emph{refuse to respond to them} except to chide the sender to report
5163 To enable us to fix the bug, you should include all these things:
5167 The version of @code{@value{AS}}. @code{@value{AS}} announces it if you start
5168 it with the @samp{--version} argument.
5170 Without this, we will not know whether there is any point in looking for
5171 the bug in the current version of @code{@value{AS}}.
5174 Any patches you may have applied to the @code{@value{AS}} source.
5177 The type of machine you are using, and the operating system name and
5181 What compiler (and its version) was used to compile @code{@value{AS}}---e.g.
5185 The command arguments you gave the assembler to assemble your example and
5186 observe the bug. To guarantee you will not omit something important, list them
5187 all. A copy of the Makefile (or the output from make) is sufficient.
5189 If we were to try to guess the arguments, we would probably guess wrong
5190 and then we might not encounter the bug.
5193 A complete input file that will reproduce the bug. If the bug is observed when
5194 the assembler is invoked via a compiler, send the assembler source, not the
5195 high level language source. Most compilers will produce the assembler source
5196 when run with the @samp{-S} option. If you are using @code{@value{GCC}}, use
5197 the options @samp{-v --save-temps}; this will save the assembler source in a
5198 file with an extension of @file{.s}, and also show you exactly how
5199 @code{@value{AS}} is being run.
5202 A description of what behavior you observe that you believe is
5203 incorrect. For example, ``It gets a fatal signal.''
5205 Of course, if the bug is that @code{@value{AS}} gets a fatal signal, then we
5206 will certainly notice it. But if the bug is incorrect output, we might not
5207 notice unless it is glaringly wrong. You might as well not give us a chance to
5210 Even if the problem you experience is a fatal signal, you should still say so
5211 explicitly. Suppose something strange is going on, such as, your copy of
5212 @code{@value{AS}} is out of synch, or you have encountered a bug in the C
5213 library on your system. (This has happened!) Your copy might crash and ours
5214 would not. If you told us to expect a crash, then when ours fails to crash, we
5215 would know that the bug was not happening for us. If you had not told us to
5216 expect a crash, then we would not be able to draw any conclusion from our
5220 If you wish to suggest changes to the @code{@value{AS}} source, send us context
5221 diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or @samp{-p}
5222 option. Always send diffs from the old file to the new file. If you even
5223 discuss something in the @code{@value{AS}} source, refer to it by context, not
5226 The line numbers in our development sources will not match those in your
5227 sources. Your line numbers would convey no useful information to us.
5230 Here are some things that are not necessary:
5234 A description of the envelope of the bug.
5236 Often people who encounter a bug spend a lot of time investigating
5237 which changes to the input file will make the bug go away and which
5238 changes will not affect it.
5240 This is often time consuming and not very useful, because the way we
5241 will find the bug is by running a single example under the debugger
5242 with breakpoints, not by pure deduction from a series of examples.
5243 We recommend that you save your time for something else.
5245 Of course, if you can find a simpler example to report @emph{instead}
5246 of the original one, that is a convenience for us. Errors in the
5247 output will be easier to spot, running under the debugger will take
5248 less time, and so on.
5250 However, simplification is not vital; if you do not want to do this,
5251 report the bug anyway and send us the entire test case you used.
5254 A patch for the bug.
5256 A patch for the bug does help us if it is a good one. But do not omit
5257 the necessary information, such as the test case, on the assumption that
5258 a patch is all we need. We might see problems with your patch and decide
5259 to fix the problem another way, or we might not understand it at all.
5261 Sometimes with a program as complicated as @code{@value{AS}} it is very hard to
5262 construct an example that will make the program follow a certain path through
5263 the code. If you do not send us the example, we will not be able to construct
5264 one, so we will not be able to verify that the bug is fixed.
5266 And if we cannot understand what bug you are trying to fix, or why your
5267 patch should be an improvement, we will not install it. A test case will
5268 help us to understand.
5271 A guess about what the bug is or what it depends on.
5273 Such guesses are usually wrong. Even we cannot guess right about such
5274 things without first using the debugger to find the facts.
5277 @node Acknowledgements
5278 @chapter Acknowledgements
5280 If you have contributed to @code{@value{AS}} and your name isn't listed here,
5281 it is not meant as a slight. We just don't know about it. Send mail to the
5282 maintainer, and we'll correct the situation. Currently
5284 the maintainer is Ken Raeburn (email address @code{raeburn@@cygnus.com}).
5286 Dean Elsner wrote the original @sc{gnu} assembler for the VAX.@footnote{Any
5289 Jay Fenlason maintained GAS for a while, adding support for GDB-specific debug
5290 information and the 68k series machines, most of the preprocessing pass, and
5291 extensive changes in @file{messages.c}, @file{input-file.c}, @file{write.c}.
5293 K. Richard Pixley maintained GAS for a while, adding various enhancements and
5294 many bug fixes, including merging support for several processors, breaking GAS
5295 up to handle multiple object file format back ends (including heavy rewrite,
5296 testing, an integration of the coff and b.out back ends), adding configuration
5297 including heavy testing and verification of cross assemblers and file splits
5298 and renaming, converted GAS to strictly ANSI C including full prototypes, added
5299 support for m680[34]0 and cpu32, did considerable work on i960 including a COFF
5300 port (including considerable amounts of reverse engineering), a SPARC opcode
5301 file rewrite, DECstation, rs6000, and hp300hpux host ports, updated ``know''
5302 assertions and made them work, much other reorganization, cleanup, and lint.
5304 Ken Raeburn wrote the high-level BFD interface code to replace most of the code
5305 in format-specific I/O modules.
5307 The original VMS support was contributed by David L. Kashtan. Eric Youngdale
5308 has done much work with it since.
5310 The Intel 80386 machine description was written by Eliot Dresselhaus.
5312 Minh Tran-Le at IntelliCorp contributed some AIX 386 support.
5314 The Motorola 88k machine description was contributed by Devon Bowen of Buffalo
5315 University and Torbjorn Granlund of the Swedish Institute of Computer Science.
5317 Keith Knowles at the Open Software Foundation wrote the original MIPS back end
5318 (@file{tc-mips.c}, @file{tc-mips.h}), and contributed Rose format support
5319 (which hasn't been merged in yet). Ralph Campbell worked with the MIPS code to
5320 support a.out format.
5322 Support for the Zilog Z8k and Hitachi H8/300 and H8/500 processors (tc-z8k,
5323 tc-h8300, tc-h8500), and IEEE 695 object file format (obj-ieee), was written by
5324 Steve Chamberlain of Cygnus Support. Steve also modified the COFF back end to
5325 use BFD for some low-level operations, for use with the H8/300 and AMD 29k
5328 John Gilmore built the AMD 29000 support, added @code{.include} support, and
5329 simplified the configuration of which versions accept which directives. He
5330 updated the 68k machine description so that Motorola's opcodes always produced
5331 fixed-size instructions (e.g. @code{jsr}), while synthetic instructions
5332 remained shrinkable (@code{jbsr}). John fixed many bugs, including true tested
5333 cross-compilation support, and one bug in relaxation that took a week and
5334 required the proverbial one-bit fix.
5336 Ian Lance Taylor of Cygnus Support merged the Motorola and MIT syntax for the
5337 68k, completed support for some COFF targets (68k, i386 SVR3, and SCO Unix),
5338 added support for MIPS ECOFF and ELF targets, wrote the initial RS/6000 and
5339 PowerPC assembler, and made a few other minor patches.
5341 Steve Chamberlain made @code{@value{AS}} able to generate listings.
5343 Hewlett-Packard contributed support for the HP9000/300.
5345 Jeff Law wrote GAS and BFD support for the native HPPA object format (SOM)
5346 along with a fairly extensive HPPA testsuite (for both SOM and ELF object
5347 formats). This work was supported by both the Center for Software Science at
5348 the University of Utah and Cygnus Support.
5350 Support for ELF format files has been worked on by Mark Eichin of Cygnus
5351 Support (original, incomplete implementation for SPARC), Pete Hoogenboom and
5352 Jeff Law at the University of Utah (HPPA mainly), Michael Meissner of the Open
5353 Software Foundation (i386 mainly), and Ken Raeburn of Cygnus Support (sparc,
5354 and some initial 64-bit support).
5356 Richard Henderson rewrote the Alpha assembler. Klaus Kaempf wrote GAS and BFD
5357 support for openVMS/Alpha.
5359 Several engineers at Cygnus Support have also provided many small bug fixes and
5360 configuration enhancements.
5362 Many others have contributed large or small bugfixes and enhancements. If
5363 you have contributed significant work and are not mentioned on this list, and
5364 want to be, let us know. Some of the history has been lost; we are not
5365 intentionally leaving anyone out.