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 ] [ --warn ] [ --fatal-warnings ]
210 @c am29k has no machine-dependent assembler options
213 [ -mbig-endian | -mlittle-endian ]
216 [ -m[arm]1 | -m[arm]2 | -m[arm]250 | -m[arm]3 | -m[arm]6 | -m[arm]60 |
217 -m[arm]600 | -m[arm]610 | -m[arm]620 | -m[arm]7[t][[d]m[i]][fe] | -m[arm]70 |
218 -m[arm]700 | -m[arm]710[c] | -m[arm]7100 | -m[arm]7500 | -m[arm]8 |
219 -m[arm]810 | -m[arm]9 | -m[arm]920 | -m[arm]920t | -m[arm]9tdmi |
220 -mstrongarm | -mstrongarm110 | -mstrongarm1100 ]
221 [ -m[arm]v2 | -m[arm]v2a | -m[arm]v3 | -m[arm]v3m | -m[arm]v4 | -m[arm]v4t |
222 -m[arm]v5 | -[arm]v5t ]
224 [ -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu ]
226 [ -mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant ]
227 [ -mthumb-interwork ]
238 @c Hitachi family chips have no machine-dependent assembler options
241 @c HPPA has no machine-dependent assembler options (yet).
247 @c The order here is important. See c-sparc.texi.
248 [ -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
249 -Av8plus | -Av8plusa | -Av9 | -Av9a ]
250 [ -xarch=v8plus | -xarch=v8plusa ] [ -bump ] [ -32 | -64 ]
253 @c Z8000 has no machine-dependent assembler options
256 @c see md_parse_option in tc-i960.c
257 [ -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC ]
261 [ -l ] [ -m68000 | -m68010 | -m68020 | ... ]
264 [ -jsri2bsr ] [ -sifilter ] [ -relax ]
267 [ -nocpp ] [ -EL ] [ -EB ] [ -G @var{num} ] [ -mcpu=@var{CPU} ]
268 [ -mips1 ] [ -mips2 ] [ -mips3 ] [ -m4650 ] [ -no-m4650 ]
269 [ --trap ] [ --break ]
270 [ --emulation=@var{name} ]
272 [ -- | @var{files} @dots{} ]
277 Turn on listings, in any of a variety of ways:
281 omit false conditionals
284 omit debugging directives
287 include high-level source
293 include macro expansions
296 omit forms processing
302 set the name of the listing file
305 You may combine these options; for example, use @samp{-aln} for assembly
306 listing without forms processing. The @samp{=file} option, if used, must be
307 the last one. By itself, @samp{-a} defaults to @samp{-ahls}.
310 Ignored. This option is accepted for script compatibility with calls to
313 @item --defsym @var{sym}=@var{value}
314 Define the symbol @var{sym} to be @var{value} before assembling the input file.
315 @var{value} must be an integer constant. As in C, a leading @samp{0x}
316 indicates a hexadecimal value, and a leading @samp{0} indicates an octal value.
319 ``fast''---skip whitespace and comment preprocessing (assume source is
323 Generate stabs debugging information for each assembler line. This
324 may help debugging assembler code, if the debugger can handle it.
327 Generate DWARF2 debugging information for each assembler line. This
328 may help debugging assembler code, if the debugger can handle it.
331 Print a summary of the command line options and exit.
334 Add directory @var{dir} to the search list for @code{.include} directives.
337 Don't warn about signed overflow.
340 @ifclear DIFF-TBL-KLUGE
341 This option is accepted but has no effect on the @value{TARGET} family.
343 @ifset DIFF-TBL-KLUGE
344 Issue warnings when difference tables altered for long displacements.
349 Keep (in the symbol table) local symbols. On traditional a.out systems
350 these start with @samp{L}, but different systems have different local
353 @item -o @var{objfile}
354 Name the object-file output from @code{@value{AS}} @var{objfile}.
357 Fold the data section into the text section.
360 Print the maximum space (in bytes) and total time (in seconds) used by
363 @item --strip-local-absolute
364 Remove local absolute symbols from the outgoing symbol table.
368 Print the @code{as} version.
371 Print the @code{as} version and exit.
375 Suppress warning messages.
377 @item --fatal-warnings
378 Treat warnings as errors.
381 Don't suppress warning messages or treat them as errors.
390 Generate an object file even after errors.
392 @item -- | @var{files} @dots{}
393 Standard input, or source files to assemble.
398 The following options are available when @value{AS} is configured for
403 @cindex ARC endianness
404 @cindex endianness, ARC
405 @cindex big endian output, ARC
407 Generate ``big endian'' format output.
409 @cindex little endian output, ARC
410 @item -mlittle-endian
411 Generate ``little endian'' format output.
417 The following options are available when @value{AS} is configured for the ARM
421 @item -m[arm][1|2|3|6|7|8|9][...]
422 Specify which ARM processor variant is the target.
423 @item -m[arm]v[2|2a|3|3m|4|4t|5|5t]
424 Specify which ARM architecture variant is used by the target.
425 @item -mthumb | -mall
426 Enable or disable Thumb only instruction decoding.
427 @item -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu
428 Select which Floating Point architcture is the target.
429 @item -mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant | -moabi
430 Select which procedure calling convention is in use.
432 Select either big-endian (-EB) or little-endian (-EL) output.
433 @item -mthumb-interwork
434 Specify that the code has been generated with interworking between Thumb and
437 Specify that PIC code has been generated.
442 The following options are available when @value{AS} is configured for
445 @cindex D10V optimization
446 @cindex optimization, D10V
448 Optimize output by parallelizing instructions.
453 The following options are available when @value{AS} is configured for a D30V
456 @cindex D30V optimization
457 @cindex optimization, D30V
459 Optimize output by parallelizing instructions.
463 Warn when nops are generated.
465 @cindex D30V nops after 32-bit multiply
467 Warn when a nop after a 32-bit multiply instruction is generated.
472 The following options are available when @value{AS} is configured for the
473 Intel 80960 processor.
476 @item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
477 Specify which variant of the 960 architecture is the target.
480 Add code to collect statistics about branches taken.
483 Do not alter compare-and-branch instructions for long displacements;
491 The following options are available when @value{AS} is configured for the
492 Motorola 68000 series.
497 Shorten references to undefined symbols, to one word instead of two.
499 @item -m68000 | -m68008 | -m68010 | -m68020 | -m68030 | -m68040 | -m68060
500 @itemx | -m68302 | -m68331 | -m68332 | -m68333 | -m68340 | -mcpu32 | -m5200
501 Specify what processor in the 68000 family is the target. The default
502 is normally the 68020, but this can be changed at configuration time.
504 @item -m68881 | -m68882 | -mno-68881 | -mno-68882
505 The target machine does (or does not) have a floating-point coprocessor.
506 The default is to assume a coprocessor for 68020, 68030, and cpu32. Although
507 the basic 68000 is not compatible with the 68881, a combination of the
508 two can be specified, since it's possible to do emulation of the
509 coprocessor instructions with the main processor.
511 @item -m68851 | -mno-68851
512 The target machine does (or does not) have a memory-management
513 unit coprocessor. The default is to assume an MMU for 68020 and up.
519 The following options are available when @value{AS} is configured for
520 a picoJava processor.
524 @cindex PJ endianness
525 @cindex endianness, PJ
526 @cindex big endian output, PJ
528 Generate ``big endian'' format output.
530 @cindex little endian output, PJ
532 Generate ``little endian'' format output.
539 The following options are available when @code{@value{AS}} is configured
540 for the SPARC architecture:
543 @item -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
544 @itemx -Av8plus | -Av8plusa | -Av9 | -Av9a
545 Explicitly select a variant of the SPARC architecture.
547 @samp{-Av8plus} and @samp{-Av8plusa} select a 32 bit environment.
548 @samp{-Av9} and @samp{-Av9a} select a 64 bit environment.
550 @samp{-Av8plusa} and @samp{-Av9a} enable the SPARC V9 instruction set with
551 UltraSPARC extensions.
553 @item -xarch=v8plus | -xarch=v8plusa
554 For compatibility with the Solaris v9 assembler. These options are
555 equivalent to -Av8plus and -Av8plusa, respectively.
558 Warn when the assembler switches to another architecture.
563 The following options are available when @value{AS} is configured for
568 This option sets the largest size of an object that can be referenced
569 implicitly with the @code{gp} register. It is only accepted for targets that
570 use ECOFF format, such as a DECstation running Ultrix. The default value is 8.
572 @cindex MIPS endianness
573 @cindex endianness, MIPS
574 @cindex big endian output, MIPS
576 Generate ``big endian'' format output.
578 @cindex little endian output, MIPS
580 Generate ``little endian'' format output.
586 Generate code for a particular MIPS Instruction Set Architecture level.
587 @samp{-mips1} corresponds to the @sc{r2000} and @sc{r3000} processors,
588 @samp{-mips2} to the @sc{r6000} processor, and @samp{-mips3} to the @sc{r4000}
593 Generate code for the MIPS @sc{r4650} chip. This tells the assembler to accept
594 the @samp{mad} and @samp{madu} instruction, and to not schedule @samp{nop}
595 instructions around accesses to the @samp{HI} and @samp{LO} registers.
596 @samp{-no-m4650} turns off this option.
598 @item -mcpu=@var{CPU}
599 Generate code for a particular MIPS cpu. This has little effect on the
600 assembler, but it is passed by @code{@value{GCC}}.
603 @item --emulation=@var{name}
604 This option causes @code{@value{AS}} to emulate @code{@value{AS}} configured
605 for some other target, in all respects, including output format (choosing
606 between ELF and ECOFF only), handling of pseudo-opcodes which may generate
607 debugging information or store symbol table information, and default
608 endianness. The available configuration names are: @samp{mipsecoff},
609 @samp{mipself}, @samp{mipslecoff}, @samp{mipsbecoff}, @samp{mipslelf},
610 @samp{mipsbelf}. The first two do not alter the default endianness from that
611 of the primary target for which the assembler was configured; the others change
612 the default to little- or big-endian as indicated by the @samp{b} or @samp{l}
613 in the name. Using @samp{-EB} or @samp{-EL} will override the endianness
614 selection in any case.
616 This option is currently supported only when the primary target
617 @code{@value{AS}} is configured for is a MIPS ELF or ECOFF target.
618 Furthermore, the primary target or others specified with
619 @samp{--enable-targets=@dots{}} at configuration time must include support for
620 the other format, if both are to be available. For example, the Irix 5
621 configuration includes support for both.
623 Eventually, this option will support more configurations, with more
624 fine-grained control over the assembler's behavior, and will be supported for
628 @code{@value{AS}} ignores this option. It is accepted for compatibility with
636 Control how to deal with multiplication overflow and division by zero.
637 @samp{--trap} or @samp{--no-break} (which are synonyms) take a trap exception
638 (and only work for Instruction Set Architecture level 2 and higher);
639 @samp{--break} or @samp{--no-trap} (also synonyms, and the default) take a
645 The following options are available when @value{AS} is configured for
651 Enable or disable the JSRI to BSR transformation. By default this is enabled.
652 The command line option @samp{-nojsri2bsr} can be used to disable it.
656 Enable or disable the silicon filter behaviour. By default this is disabled.
657 The default can be overidden by the @samp{-sifilter} command line option.
660 Alter jump instructions for long displacements.
667 * Manual:: Structure of this Manual
668 * GNU Assembler:: The GNU Assembler
669 * Object Formats:: Object File Formats
670 * Command Line:: Command Line
671 * Input Files:: Input Files
672 * Object:: Output (Object) File
673 * Errors:: Error and Warning Messages
677 @section Structure of this Manual
679 @cindex manual, structure and purpose
680 This manual is intended to describe what you need to know to use
681 @sc{gnu} @code{@value{AS}}. We cover the syntax expected in source files, including
682 notation for symbols, constants, and expressions; the directives that
683 @code{@value{AS}} understands; and of course how to invoke @code{@value{AS}}.
686 We also cover special features in the @value{TARGET}
687 configuration of @code{@value{AS}}, including assembler directives.
690 This manual also describes some of the machine-dependent features of
691 various flavors of the assembler.
694 @cindex machine instructions (not covered)
695 On the other hand, this manual is @emph{not} intended as an introduction
696 to programming in assembly language---let alone programming in general!
697 In a similar vein, we make no attempt to introduce the machine
698 architecture; we do @emph{not} describe the instruction set, standard
699 mnemonics, registers or addressing modes that are standard to a
700 particular architecture.
702 You may want to consult the manufacturer's
703 machine architecture manual for this information.
707 For information on the H8/300 machine instruction set, see @cite{H8/300
708 Series Programming Manual} (Hitachi ADE--602--025). For the H8/300H,
709 see @cite{H8/300H Series Programming Manual} (Hitachi).
712 For information on the H8/500 machine instruction set, see @cite{H8/500
713 Series Programming Manual} (Hitachi M21T001).
716 For information on the Hitachi SH machine instruction set, see
717 @cite{SH-Microcomputer User's Manual} (Hitachi Micro Systems, Inc.).
720 For information on the Z8000 machine instruction set, see @cite{Z8000 CPU Technical Manual}
724 @c I think this is premature---doc@cygnus.com, 17jan1991
726 Throughout this manual, we assume that you are running @dfn{GNU},
727 the portable operating system from the @dfn{Free Software
728 Foundation, Inc.}. This restricts our attention to certain kinds of
729 computer (in particular, the kinds of computers that @sc{gnu} can run on);
730 once this assumption is granted examples and definitions need less
733 @code{@value{AS}} is part of a team of programs that turn a high-level
734 human-readable series of instructions into a low-level
735 computer-readable series of instructions. Different versions of
736 @code{@value{AS}} are used for different kinds of computer.
739 @c There used to be a section "Terminology" here, which defined
740 @c "contents", "byte", "word", and "long". Defining "word" to any
741 @c particular size is confusing when the .word directive may generate 16
742 @c bits on one machine and 32 bits on another; in general, for the user
743 @c version of this manual, none of these terms seem essential to define.
744 @c They were used very little even in the former draft of the manual;
745 @c this draft makes an effort to avoid them (except in names of
749 @section The GNU Assembler
751 @sc{gnu} @code{as} is really a family of assemblers.
753 This manual describes @code{@value{AS}}, a member of that family which is
754 configured for the @value{TARGET} architectures.
756 If you use (or have used) the @sc{gnu} assembler on one architecture, you
757 should find a fairly similar environment when you use it on another
758 architecture. Each version has much in common with the others,
759 including object file formats, most assembler directives (often called
760 @dfn{pseudo-ops}) and assembler syntax.@refill
762 @cindex purpose of @sc{gnu} assembler
763 @code{@value{AS}} is primarily intended to assemble the output of the
764 @sc{gnu} C compiler @code{@value{GCC}} for use by the linker
765 @code{@value{LD}}. Nevertheless, we've tried to make @code{@value{AS}}
766 assemble correctly everything that other assemblers for the same
767 machine would assemble.
769 Any exceptions are documented explicitly (@pxref{Machine Dependencies}).
772 @c This remark should appear in generic version of manual; assumption
773 @c here is that generic version sets M680x0.
774 This doesn't mean @code{@value{AS}} always uses the same syntax as another
775 assembler for the same architecture; for example, we know of several
776 incompatible versions of 680x0 assembly language syntax.
779 Unlike older assemblers, @code{@value{AS}} is designed to assemble a source
780 program in one pass of the source file. This has a subtle impact on the
781 @kbd{.org} directive (@pxref{Org,,@code{.org}}).
784 @section Object File Formats
786 @cindex object file format
787 The @sc{gnu} assembler can be configured to produce several alternative
788 object file formats. For the most part, this does not affect how you
789 write assembly language programs; but directives for debugging symbols
790 are typically different in different file formats. @xref{Symbol
791 Attributes,,Symbol Attributes}.
794 On the @value{TARGET}, @code{@value{AS}} is configured to produce
795 @value{OBJ-NAME} format object files.
797 @c The following should exhaust all configs that set MULTI-OBJ, ideally
799 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
800 @code{a.out} or COFF format object files.
803 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
804 @code{b.out} or COFF format object files.
807 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
808 SOM or ELF format object files.
813 @section Command Line
815 @cindex command line conventions
816 After the program name @code{@value{AS}}, the command line may contain
817 options and file names. Options may appear in any order, and may be
818 before, after, or between file names. The order of file names is
821 @cindex standard input, as input file
823 @file{--} (two hyphens) by itself names the standard input file
824 explicitly, as one of the files for @code{@value{AS}} to assemble.
826 @cindex options, command line
827 Except for @samp{--} any command line argument that begins with a
828 hyphen (@samp{-}) is an option. Each option changes the behavior of
829 @code{@value{AS}}. No option changes the way another option works. An
830 option is a @samp{-} followed by one or more letters; the case of
831 the letter is important. All options are optional.
833 Some options expect exactly one file name to follow them. The file
834 name may either immediately follow the option's letter (compatible
835 with older assemblers) or it may be the next command argument (@sc{gnu}
836 standard). These two command lines are equivalent:
839 @value{AS} -o my-object-file.o mumble.s
840 @value{AS} -omy-object-file.o mumble.s
847 @cindex source program
849 We use the phrase @dfn{source program}, abbreviated @dfn{source}, to
850 describe the program input to one run of @code{@value{AS}}. The program may
851 be in one or more files; how the source is partitioned into files
852 doesn't change the meaning of the source.
854 @c I added "con" prefix to "catenation" just to prove I can overcome my
855 @c APL training... doc@cygnus.com
856 The source program is a concatenation of the text in all the files, in the
859 Each time you run @code{@value{AS}} it assembles exactly one source
860 program. The source program is made up of one or more files.
861 (The standard input is also a file.)
863 You give @code{@value{AS}} a command line that has zero or more input file
864 names. The input files are read (from left file name to right). A
865 command line argument (in any position) that has no special meaning
866 is taken to be an input file name.
868 If you give @code{@value{AS}} no file names it attempts to read one input file
869 from the @code{@value{AS}} standard input, which is normally your terminal. You
870 may have to type @key{ctl-D} to tell @code{@value{AS}} there is no more program
873 Use @samp{--} if you need to explicitly name the standard input file
874 in your command line.
876 If the source is empty, @code{@value{AS}} produces a small, empty object
879 @subheading Filenames and Line-numbers
881 @cindex input file linenumbers
882 @cindex line numbers, in input files
883 There are two ways of locating a line in the input file (or files) and
884 either may be used in reporting error messages. One way refers to a line
885 number in a physical file; the other refers to a line number in a
886 ``logical'' file. @xref{Errors, ,Error and Warning Messages}.
888 @dfn{Physical files} are those files named in the command line given
889 to @code{@value{AS}}.
891 @dfn{Logical files} are simply names declared explicitly by assembler
892 directives; they bear no relation to physical files. Logical file names help
893 error messages reflect the original source file, when @code{@value{AS}} source
894 is itself synthesized from other files. @code{@value{AS}} understands the
895 @samp{#} directives emitted by the @code{@value{GCC}} preprocessor. See also
896 @ref{File,,@code{.file}}.
899 @section Output (Object) File
905 Every time you run @code{@value{AS}} it produces an output file, which is
906 your assembly language program translated into numbers. This file
907 is the object file. Its default name is
915 @code{b.out} when @code{@value{AS}} is configured for the Intel 80960.
917 You can give it another name by using the @code{-o} option. Conventionally,
918 object file names end with @file{.o}. The default name is used for historical
919 reasons: older assemblers were capable of assembling self-contained programs
920 directly into a runnable program. (For some formats, this isn't currently
921 possible, but it can be done for the @code{a.out} format.)
925 The object file is meant for input to the linker @code{@value{LD}}. It contains
926 assembled program code, information to help @code{@value{LD}} integrate
927 the assembled program into a runnable file, and (optionally) symbolic
928 information for the debugger.
930 @c link above to some info file(s) like the description of a.out.
931 @c don't forget to describe @sc{gnu} info as well as Unix lossage.
934 @section Error and Warning Messages
936 @cindex error messsages
937 @cindex warning messages
938 @cindex messages from assembler
939 @code{@value{AS}} may write warnings and error messages to the standard error
940 file (usually your terminal). This should not happen when a compiler
941 runs @code{@value{AS}} automatically. Warnings report an assumption made so
942 that @code{@value{AS}} could keep assembling a flawed program; errors report a
943 grave problem that stops the assembly.
945 @cindex format of warning messages
946 Warning messages have the format
949 file_name:@b{NNN}:Warning Message Text
953 @cindex line numbers, in warnings/errors
954 (where @b{NNN} is a line number). If a logical file name has been given
955 (@pxref{File,,@code{.file}}) it is used for the filename, otherwise the name of
956 the current input file is used. If a logical line number was given
958 (@pxref{Line,,@code{.line}})
962 (@pxref{Line,,@code{.line}})
965 (@pxref{Ln,,@code{.ln}})
968 then it is used to calculate the number printed,
969 otherwise the actual line in the current source file is printed. The
970 message text is intended to be self explanatory (in the grand Unix
973 @cindex format of error messages
974 Error messages have the format
976 file_name:@b{NNN}:FATAL:Error Message Text
978 The file name and line number are derived as for warning
979 messages. The actual message text may be rather less explanatory
980 because many of them aren't supposed to happen.
983 @chapter Command-Line Options
985 @cindex options, all versions of assembler
986 This chapter describes command-line options available in @emph{all}
987 versions of the @sc{gnu} assembler; @pxref{Machine Dependencies}, for options specific
989 to the @value{TARGET}.
992 to particular machine architectures.
995 If you are invoking @code{@value{AS}} via the @sc{gnu} C compiler (version 2),
996 you can use the @samp{-Wa} option to pass arguments through to the assembler.
997 The assembler arguments must be separated from each other (and the @samp{-Wa})
998 by commas. For example:
1001 gcc -c -g -O -Wa,-alh,-L file.c
1005 This passes two options to the assembler: @samp{-alh} (emit a listing to
1006 standard output with with high-level and assembly source) and @samp{-L} (retain
1007 local symbols in the symbol table).
1009 Usually you do not need to use this @samp{-Wa} mechanism, since many compiler
1010 command-line options are automatically passed to the assembler by the compiler.
1011 (You can call the @sc{gnu} compiler driver with the @samp{-v} option to see
1012 precisely what options it passes to each compilation pass, including the
1016 * a:: -a[cdhlns] enable listings
1017 * D:: -D for compatibility
1018 * f:: -f to work faster
1019 * I:: -I for .include search path
1020 @ifclear DIFF-TBL-KLUGE
1021 * K:: -K for compatibility
1023 @ifset DIFF-TBL-KLUGE
1024 * K:: -K for difference tables
1027 * L:: -L to retain local labels
1028 * M:: -M or --mri to assemble in MRI compatibility mode
1029 * MD:: --MD for dependency tracking
1030 * o:: -o to name the object file
1031 * R:: -R to join data and text sections
1032 * statistics:: --statistics to see statistics about assembly
1033 * traditional-format:: --traditional-format for compatible output
1034 * v:: -v to announce version
1035 * W:: -W, --no-warn, --warn, --fatal-warnings to control warnings
1036 * Z:: -Z to make object file even after errors
1040 @section Enable Listings: @code{-a[cdhlns]}
1049 @cindex listings, enabling
1050 @cindex assembly listings, enabling
1052 These options enable listing output from the assembler. By itself,
1053 @samp{-a} requests high-level, assembly, and symbols listing.
1054 You can use other letters to select specific options for the list:
1055 @samp{-ah} requests a high-level language listing,
1056 @samp{-al} requests an output-program assembly listing, and
1057 @samp{-as} requests a symbol table listing.
1058 High-level listings require that a compiler debugging option like
1059 @samp{-g} be used, and that assembly listings (@samp{-al}) be requested
1062 Use the @samp{-ac} option to omit false conditionals from a listing. Any lines
1063 which are not assembled because of a false @code{.if} (or @code{.ifdef}, or any
1064 other conditional), or a true @code{.if} followed by an @code{.else}, will be
1065 omitted from the listing.
1067 Use the @samp{-ad} option to omit debugging directives from the
1070 Once you have specified one of these options, you can further control
1071 listing output and its appearance using the directives @code{.list},
1072 @code{.nolist}, @code{.psize}, @code{.eject}, @code{.title}, and
1074 The @samp{-an} option turns off all forms processing.
1075 If you do not request listing output with one of the @samp{-a} options, the
1076 listing-control directives have no effect.
1078 The letters after @samp{-a} may be combined into one option,
1079 @emph{e.g.}, @samp{-aln}.
1085 This option has no effect whatsoever, but it is accepted to make it more
1086 likely that scripts written for other assemblers also work with
1090 @section Work Faster: @code{-f}
1093 @cindex trusted compiler
1094 @cindex faster processing (@code{-f})
1095 @samp{-f} should only be used when assembling programs written by a
1096 (trusted) compiler. @samp{-f} stops the assembler from doing whitespace
1097 and comment preprocessing on
1098 the input file(s) before assembling them. @xref{Preprocessing,
1102 @emph{Warning:} if you use @samp{-f} when the files actually need to be
1103 preprocessed (if they contain comments, for example), @code{@value{AS}} does
1108 @section @code{.include} search path: @code{-I} @var{path}
1110 @kindex -I @var{path}
1111 @cindex paths for @code{.include}
1112 @cindex search path for @code{.include}
1113 @cindex @code{include} directive search path
1114 Use this option to add a @var{path} to the list of directories
1115 @code{@value{AS}} searches for files specified in @code{.include}
1116 directives (@pxref{Include,,@code{.include}}). You may use @code{-I} as
1117 many times as necessary to include a variety of paths. The current
1118 working directory is always searched first; after that, @code{@value{AS}}
1119 searches any @samp{-I} directories in the same order as they were
1120 specified (left to right) on the command line.
1123 @section Difference Tables: @code{-K}
1126 @ifclear DIFF-TBL-KLUGE
1127 On the @value{TARGET} family, this option is allowed, but has no effect. It is
1128 permitted for compatibility with the @sc{gnu} assembler on other platforms,
1129 where it can be used to warn when the assembler alters the machine code
1130 generated for @samp{.word} directives in difference tables. The @value{TARGET}
1131 family does not have the addressing limitations that sometimes lead to this
1132 alteration on other platforms.
1135 @ifset DIFF-TBL-KLUGE
1136 @cindex difference tables, warning
1137 @cindex warning for altered difference tables
1138 @code{@value{AS}} sometimes alters the code emitted for directives of the form
1139 @samp{.word @var{sym1}-@var{sym2}}; @pxref{Word,,@code{.word}}.
1140 You can use the @samp{-K} option if you want a warning issued when this
1145 @section Include Local Labels: @code{-L}
1148 @cindex local labels, retaining in output
1149 Labels beginning with @samp{L} (upper case only) are called @dfn{local
1150 labels}. @xref{Symbol Names}. Normally you do not see such labels when
1151 debugging, because they are intended for the use of programs (like
1152 compilers) that compose assembler programs, not for your notice.
1153 Normally both @code{@value{AS}} and @code{@value{LD}} discard such labels, so you do not
1154 normally debug with them.
1156 This option tells @code{@value{AS}} to retain those @samp{L@dots{}} symbols
1157 in the object file. Usually if you do this you also tell the linker
1158 @code{@value{LD}} to preserve symbols whose names begin with @samp{L}.
1160 By default, a local label is any label beginning with @samp{L}, but each
1161 target is allowed to redefine the local label prefix.
1163 On the HPPA local labels begin with @samp{L$}.
1166 @samp{;} for the ARM family;
1170 @section Assemble in MRI Compatibility Mode: @code{-M}
1173 @cindex MRI compatibility mode
1174 The @code{-M} or @code{--mri} option selects MRI compatibility mode. This
1175 changes the syntax and pseudo-op handling of @code{@value{AS}} to make it
1176 compatible with the @code{ASM68K} or the @code{ASM960} (depending upon the
1177 configured target) assembler from Microtec Research. The exact nature of the
1178 MRI syntax will not be documented here; see the MRI manuals for more
1179 information. Note in particular that the handling of macros and macro
1180 arguments is somewhat different. The purpose of this option is to permit
1181 assembling existing MRI assembler code using @code{@value{AS}}.
1183 The MRI compatibility is not complete. Certain operations of the MRI assembler
1184 depend upon its object file format, and can not be supported using other object
1185 file formats. Supporting these would require enhancing each object file format
1186 individually. These are:
1189 @item global symbols in common section
1191 The m68k MRI assembler supports common sections which are merged by the linker.
1192 Other object file formats do not support this. @code{@value{AS}} handles
1193 common sections by treating them as a single common symbol. It permits local
1194 symbols to be defined within a common section, but it can not support global
1195 symbols, since it has no way to describe them.
1197 @item complex relocations
1199 The MRI assemblers support relocations against a negated section address, and
1200 relocations which combine the start addresses of two or more sections. These
1201 are not support by other object file formats.
1203 @item @code{END} pseudo-op specifying start address
1205 The MRI @code{END} pseudo-op permits the specification of a start address.
1206 This is not supported by other object file formats. The start address may
1207 instead be specified using the @code{-e} option to the linker, or in a linker
1210 @item @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops
1212 The MRI @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops assign a module
1213 name to the output file. This is not supported by other object file formats.
1215 @item @code{ORG} pseudo-op
1217 The m68k MRI @code{ORG} pseudo-op begins an absolute section at a given
1218 address. This differs from the usual @code{@value{AS}} @code{.org} pseudo-op,
1219 which changes the location within the current section. Absolute sections are
1220 not supported by other object file formats. The address of a section may be
1221 assigned within a linker script.
1224 There are some other features of the MRI assembler which are not supported by
1225 @code{@value{AS}}, typically either because they are difficult or because they
1226 seem of little consequence. Some of these may be supported in future releases.
1230 @item EBCDIC strings
1232 EBCDIC strings are not supported.
1234 @item packed binary coded decimal
1236 Packed binary coded decimal is not supported. This means that the @code{DC.P}
1237 and @code{DCB.P} pseudo-ops are not supported.
1239 @item @code{FEQU} pseudo-op
1241 The m68k @code{FEQU} pseudo-op is not supported.
1243 @item @code{NOOBJ} pseudo-op
1245 The m68k @code{NOOBJ} pseudo-op is not supported.
1247 @item @code{OPT} branch control options
1249 The m68k @code{OPT} branch control options---@code{B}, @code{BRS}, @code{BRB},
1250 @code{BRL}, and @code{BRW}---are ignored. @code{@value{AS}} automatically
1251 relaxes all branches, whether forward or backward, to an appropriate size, so
1252 these options serve no purpose.
1254 @item @code{OPT} list control options
1256 The following m68k @code{OPT} list control options are ignored: @code{C},
1257 @code{CEX}, @code{CL}, @code{CRE}, @code{E}, @code{G}, @code{I}, @code{M},
1258 @code{MEX}, @code{MC}, @code{MD}, @code{X}.
1260 @item other @code{OPT} options
1262 The following m68k @code{OPT} options are ignored: @code{NEST}, @code{O},
1263 @code{OLD}, @code{OP}, @code{P}, @code{PCO}, @code{PCR}, @code{PCS}, @code{R}.
1265 @item @code{OPT} @code{D} option is default
1267 The m68k @code{OPT} @code{D} option is the default, unlike the MRI assembler.
1268 @code{OPT NOD} may be used to turn it off.
1270 @item @code{XREF} pseudo-op.
1272 The m68k @code{XREF} pseudo-op is ignored.
1274 @item @code{.debug} pseudo-op
1276 The i960 @code{.debug} pseudo-op is not supported.
1278 @item @code{.extended} pseudo-op
1280 The i960 @code{.extended} pseudo-op is not supported.
1282 @item @code{.list} pseudo-op.
1284 The various options of the i960 @code{.list} pseudo-op are not supported.
1286 @item @code{.optimize} pseudo-op
1288 The i960 @code{.optimize} pseudo-op is not supported.
1290 @item @code{.output} pseudo-op
1292 The i960 @code{.output} pseudo-op is not supported.
1294 @item @code{.setreal} pseudo-op
1296 The i960 @code{.setreal} pseudo-op is not supported.
1301 @section Dependency tracking: @code{--MD}
1304 @cindex dependency tracking
1307 @code{@value{AS}} can generate a dependency file for the file it creates. This
1308 file consists of a single rule suitable for @code{make} describing the
1309 dependencies of the main source file.
1311 The rule is written to the file named in its argument.
1313 This feature is used in the automatic updating of makefiles.
1316 @section Name the Object File: @code{-o}
1319 @cindex naming object file
1320 @cindex object file name
1321 There is always one object file output when you run @code{@value{AS}}. By
1322 default it has the name
1325 @file{a.out} (or @file{b.out}, for Intel 960 targets only).
1339 You use this option (which takes exactly one filename) to give the
1340 object file a different name.
1342 Whatever the object file is called, @code{@value{AS}} overwrites any
1343 existing file of the same name.
1346 @section Join Data and Text Sections: @code{-R}
1349 @cindex data and text sections, joining
1350 @cindex text and data sections, joining
1351 @cindex joining text and data sections
1352 @cindex merging text and data sections
1353 @code{-R} tells @code{@value{AS}} to write the object file as if all
1354 data-section data lives in the text section. This is only done at
1355 the very last moment: your binary data are the same, but data
1356 section parts are relocated differently. The data section part of
1357 your object file is zero bytes long because all its bytes are
1358 appended to the text section. (@xref{Sections,,Sections and Relocation}.)
1360 When you specify @code{-R} it would be possible to generate shorter
1361 address displacements (because we do not have to cross between text and
1362 data section). We refrain from doing this simply for compatibility with
1363 older versions of @code{@value{AS}}. In future, @code{-R} may work this way.
1366 When @code{@value{AS}} is configured for COFF output,
1367 this option is only useful if you use sections named @samp{.text} and
1372 @code{-R} is not supported for any of the HPPA targets. Using
1373 @code{-R} generates a warning from @code{@value{AS}}.
1377 @section Display Assembly Statistics: @code{--statistics}
1379 @kindex --statistics
1380 @cindex statistics, about assembly
1381 @cindex time, total for assembly
1382 @cindex space used, maximum for assembly
1383 Use @samp{--statistics} to display two statistics about the resources used by
1384 @code{@value{AS}}: the maximum amount of space allocated during the assembly
1385 (in bytes), and the total execution time taken for the assembly (in @sc{cpu}
1388 @node traditional-format
1389 @section Compatible output: @code{--traditional-format}
1391 @kindex --traditional-format
1392 For some targets, the output of @code{@value{AS}} is different in some ways
1393 from the output of some existing assembler. This switch requests
1394 @code{@value{AS}} to use the traditional format instead.
1396 For example, it disables the exception frame optimizations which
1397 @code{@value{AS}} normally does by default on @code{@value{GCC}} output.
1400 @section Announce Version: @code{-v}
1404 @cindex assembler version
1405 @cindex version of assembler
1406 You can find out what version of as is running by including the
1407 option @samp{-v} (which you can also spell as @samp{-version}) on the
1411 @section Control Warnings: @code{-W}, @code{--warn}, @code{--no-warn}, @code{--fatal-warnings}
1413 @code{@value{AS}} should never give a warning or error message when
1414 assembling compiler output. But programs written by people often
1415 cause @code{@value{AS}} to give a warning that a particular assumption was
1416 made. All such warnings are directed to the standard error file.
1419 @kindex @samp{--no-warn}
1420 @cindex suppressing warnings
1421 @cindex warnings, suppressing
1422 If you use the @code{-W} and @code{--no-warn} options, no warnings are issued.
1423 This only affects the warning messages: it does not change any particular of
1424 how @code{@value{AS}} assembles your file. Errors, which stop the assembly,
1427 @kindex @samp{--fatal-warnings}
1428 @cindex errors, caused by warnings
1429 @cindex warnings, causing error
1430 If you use the @code{--fatal-warnings} option, @code{@value{AS}} considers
1431 files that generate warnings to be in error.
1433 @kindex @samp{--warn}
1434 @cindex warnings, switching on
1435 You can switch these options off again by specifying @code{--warn}, which
1436 causes warnings to be output as usual.
1439 @section Generate Object File in Spite of Errors: @code{-Z}
1440 @cindex object file, after errors
1441 @cindex errors, continuing after
1442 After an error message, @code{@value{AS}} normally produces no output. If for
1443 some reason you are interested in object file output even after
1444 @code{@value{AS}} gives an error message on your program, use the @samp{-Z}
1445 option. If there are any errors, @code{@value{AS}} continues anyways, and
1446 writes an object file after a final warning message of the form @samp{@var{n}
1447 errors, @var{m} warnings, generating bad object file.}
1452 @cindex machine-independent syntax
1453 @cindex syntax, machine-independent
1454 This chapter describes the machine-independent syntax allowed in a
1455 source file. @code{@value{AS}} syntax is similar to what many other
1456 assemblers use; it is inspired by the BSD 4.2
1461 assembler, except that @code{@value{AS}} does not assemble Vax bit-fields.
1465 * Preprocessing:: Preprocessing
1466 * Whitespace:: Whitespace
1467 * Comments:: Comments
1468 * Symbol Intro:: Symbols
1469 * Statements:: Statements
1470 * Constants:: Constants
1474 @section Preprocessing
1476 @cindex preprocessing
1477 The @code{@value{AS}} internal preprocessor:
1479 @cindex whitespace, removed by preprocessor
1481 adjusts and removes extra whitespace. It leaves one space or tab before
1482 the keywords on a line, and turns any other whitespace on the line into
1485 @cindex comments, removed by preprocessor
1487 removes all comments, replacing them with a single space, or an
1488 appropriate number of newlines.
1490 @cindex constants, converted by preprocessor
1492 converts character constants into the appropriate numeric values.
1495 It does not do macro processing, include file handling, or
1496 anything else you may get from your C compiler's preprocessor. You can
1497 do include file processing with the @code{.include} directive
1498 (@pxref{Include,,@code{.include}}). You can use the @sc{gnu} C compiler driver
1499 to get other ``CPP'' style preprocessing, by giving the input file a
1500 @samp{.S} suffix. @xref{Overall Options,, Options Controlling the Kind of
1501 Output, gcc.info, Using GNU CC}.
1503 Excess whitespace, comments, and character constants
1504 cannot be used in the portions of the input text that are not
1507 @cindex turning preprocessing on and off
1508 @cindex preprocessing, turning on and off
1511 If the first line of an input file is @code{#NO_APP} or if you use the
1512 @samp{-f} option, whitespace and comments are not removed from the input file.
1513 Within an input file, you can ask for whitespace and comment removal in
1514 specific portions of the by putting a line that says @code{#APP} before the
1515 text that may contain whitespace or comments, and putting a line that says
1516 @code{#NO_APP} after this text. This feature is mainly intend to support
1517 @code{asm} statements in compilers whose output is otherwise free of comments
1524 @dfn{Whitespace} is one or more blanks or tabs, in any order.
1525 Whitespace is used to separate symbols, and to make programs neater for
1526 people to read. Unless within character constants
1527 (@pxref{Characters,,Character Constants}), any whitespace means the same
1528 as exactly one space.
1534 There are two ways of rendering comments to @code{@value{AS}}. In both
1535 cases the comment is equivalent to one space.
1537 Anything from @samp{/*} through the next @samp{*/} is a comment.
1538 This means you may not nest these comments.
1542 The only way to include a newline ('\n') in a comment
1543 is to use this sort of comment.
1546 /* This sort of comment does not nest. */
1549 @cindex line comment character
1550 Anything from the @dfn{line comment} character to the next newline
1551 is considered a comment and is ignored. The line comment character is
1553 @samp{;} for the AMD 29K family;
1556 @samp{;} on the ARC;
1559 @samp{@@} on the ARM;
1562 @samp{;} for the H8/300 family;
1565 @samp{!} for the H8/500 family;
1568 @samp{;} for the HPPA;
1571 @samp{#} on the i960;
1574 @samp{;} for picoJava;
1577 @samp{!} for the Hitachi SH;
1580 @samp{!} on the SPARC;
1583 @samp{#} on the m32r;
1586 @samp{|} on the 680x0;
1589 @samp{#} on the Vax;
1592 @samp{!} for the Z8000;
1595 @samp{#} on the V850;
1597 see @ref{Machine Dependencies}. @refill
1598 @c FIXME What about i386, m88k, i860?
1601 On some machines there are two different line comment characters. One
1602 character only begins a comment if it is the first non-whitespace character on
1603 a line, while the other always begins a comment.
1607 The V850 assembler also supports a double dash as starting a comment that
1608 extends to the end of the line.
1614 @cindex lines starting with @code{#}
1615 @cindex logical line numbers
1616 To be compatible with past assemblers, lines that begin with @samp{#} have a
1617 special interpretation. Following the @samp{#} should be an absolute
1618 expression (@pxref{Expressions}): the logical line number of the @emph{next}
1619 line. Then a string (@pxref{Strings,, Strings}) is allowed: if present it is a
1620 new logical file name. The rest of the line, if any, should be whitespace.
1622 If the first non-whitespace characters on the line are not numeric,
1623 the line is ignored. (Just like a comment.)
1626 # This is an ordinary comment.
1627 # 42-6 "new_file_name" # New logical file name
1628 # This is logical line # 36.
1630 This feature is deprecated, and may disappear from future versions
1631 of @code{@value{AS}}.
1636 @cindex characters used in symbols
1637 @ifclear SPECIAL-SYMS
1638 A @dfn{symbol} is one or more characters chosen from the set of all
1639 letters (both upper and lower case), digits and the three characters
1645 A @dfn{symbol} is one or more characters chosen from the set of all
1646 letters (both upper and lower case), digits and the three characters
1647 @samp{._$}. (Save that, on the H8/300 only, you may not use @samp{$} in
1653 On most machines, you can also use @code{$} in symbol names; exceptions
1654 are noted in @ref{Machine Dependencies}.
1656 No symbol may begin with a digit. Case is significant.
1657 There is no length limit: all characters are significant. Symbols are
1658 delimited by characters not in that set, or by the beginning of a file
1659 (since the source program must end with a newline, the end of a file is
1660 not a possible symbol delimiter). @xref{Symbols}.
1661 @cindex length of symbols
1666 @cindex statements, structure of
1667 @cindex line separator character
1668 @cindex statement separator character
1670 @ifclear abnormal-separator
1671 A @dfn{statement} ends at a newline character (@samp{\n}) or at a
1672 semicolon (@samp{;}). The newline or semicolon is considered part of
1673 the preceding statement. Newlines and semicolons within character
1674 constants are an exception: they do not end statements.
1676 @ifset abnormal-separator
1678 A @dfn{statement} ends at a newline character (@samp{\n}) or an ``at''
1679 sign (@samp{@@}). The newline or at sign is considered part of the
1680 preceding statement. Newlines and at signs within character constants
1681 are an exception: they do not end statements.
1684 A @dfn{statement} ends at a newline character (@samp{\n}) or an exclamation
1685 point (@samp{!}). The newline or exclamation point is considered part of the
1686 preceding statement. Newlines and exclamation points within character
1687 constants are an exception: they do not end statements.
1690 A @dfn{statement} ends at a newline character (@samp{\n}); or (for the
1691 H8/300) a dollar sign (@samp{$}); or (for the
1694 (@samp{;}). The newline or separator character is considered part of
1695 the preceding statement. Newlines and separators within character
1696 constants are an exception: they do not end statements.
1701 A @dfn{statement} ends at a newline character (@samp{\n}) or line
1702 separator character. (The line separator is usually @samp{;}, unless
1703 this conflicts with the comment character; @pxref{Machine Dependencies}.) The
1704 newline or separator character is considered part of the preceding
1705 statement. Newlines and separators within character constants are an
1706 exception: they do not end statements.
1709 @cindex newline, required at file end
1710 @cindex EOF, newline must precede
1711 It is an error to end any statement with end-of-file: the last
1712 character of any input file should be a newline.@refill
1714 An empty statement is allowed, and may include whitespace. It is ignored.
1716 @cindex instructions and directives
1717 @cindex directives and instructions
1718 @c "key symbol" is not used elsewhere in the document; seems pedantic to
1719 @c @defn{} it in that case, as was done previously... doc@cygnus.com,
1721 A statement begins with zero or more labels, optionally followed by a
1722 key symbol which determines what kind of statement it is. The key
1723 symbol determines the syntax of the rest of the statement. If the
1724 symbol begins with a dot @samp{.} then the statement is an assembler
1725 directive: typically valid for any computer. If the symbol begins with
1726 a letter the statement is an assembly language @dfn{instruction}: it
1727 assembles into a machine language instruction.
1729 Different versions of @code{@value{AS}} for different computers
1730 recognize different instructions. In fact, the same symbol may
1731 represent a different instruction in a different computer's assembly
1735 @cindex @code{:} (label)
1736 @cindex label (@code{:})
1737 A label is a symbol immediately followed by a colon (@code{:}).
1738 Whitespace before a label or after a colon is permitted, but you may not
1739 have whitespace between a label's symbol and its colon. @xref{Labels}.
1742 For HPPA targets, labels need not be immediately followed by a colon, but
1743 the definition of a label must begin in column zero. This also implies that
1744 only one label may be defined on each line.
1748 label: .directive followed by something
1749 another_label: # This is an empty statement.
1750 instruction operand_1, operand_2, @dots{}
1757 A constant is a number, written so that its value is known by
1758 inspection, without knowing any context. Like this:
1761 .byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.
1762 .ascii "Ring the bell\7" # A string constant.
1763 .octa 0x123456789abcdef0123456789ABCDEF0 # A bignum.
1764 .float 0f-314159265358979323846264338327\
1765 95028841971.693993751E-40 # - pi, a flonum.
1770 * Characters:: Character Constants
1771 * Numbers:: Number Constants
1775 @subsection Character Constants
1777 @cindex character constants
1778 @cindex constants, character
1779 There are two kinds of character constants. A @dfn{character} stands
1780 for one character in one byte and its value may be used in
1781 numeric expressions. String constants (properly called string
1782 @emph{literals}) are potentially many bytes and their values may not be
1783 used in arithmetic expressions.
1787 * Chars:: Characters
1791 @subsubsection Strings
1793 @cindex string constants
1794 @cindex constants, string
1795 A @dfn{string} is written between double-quotes. It may contain
1796 double-quotes or null characters. The way to get special characters
1797 into a string is to @dfn{escape} these characters: precede them with
1798 a backslash @samp{\} character. For example @samp{\\} represents
1799 one backslash: the first @code{\} is an escape which tells
1800 @code{@value{AS}} to interpret the second character literally as a backslash
1801 (which prevents @code{@value{AS}} from recognizing the second @code{\} as an
1802 escape character). The complete list of escapes follows.
1804 @cindex escape codes, character
1805 @cindex character escape codes
1808 @c Mnemonic for ACKnowledge; for ASCII this is octal code 007.
1810 @cindex @code{\b} (backspace character)
1811 @cindex backspace (@code{\b})
1813 Mnemonic for backspace; for ASCII this is octal code 010.
1816 @c Mnemonic for EOText; for ASCII this is octal code 004.
1818 @cindex @code{\f} (formfeed character)
1819 @cindex formfeed (@code{\f})
1821 Mnemonic for FormFeed; for ASCII this is octal code 014.
1823 @cindex @code{\n} (newline character)
1824 @cindex newline (@code{\n})
1826 Mnemonic for newline; for ASCII this is octal code 012.
1829 @c Mnemonic for prefix; for ASCII this is octal code 033, usually known as @code{escape}.
1831 @cindex @code{\r} (carriage return character)
1832 @cindex carriage return (@code{\r})
1834 Mnemonic for carriage-Return; for ASCII this is octal code 015.
1837 @c Mnemonic for space; for ASCII this is octal code 040. Included for compliance with
1838 @c other assemblers.
1840 @cindex @code{\t} (tab)
1841 @cindex tab (@code{\t})
1843 Mnemonic for horizontal Tab; for ASCII this is octal code 011.
1846 @c Mnemonic for Vertical tab; for ASCII this is octal code 013.
1847 @c @item \x @var{digit} @var{digit} @var{digit}
1848 @c A hexadecimal character code. The numeric code is 3 hexadecimal digits.
1850 @cindex @code{\@var{ddd}} (octal character code)
1851 @cindex octal character code (@code{\@var{ddd}})
1852 @item \ @var{digit} @var{digit} @var{digit}
1853 An octal character code. The numeric code is 3 octal digits.
1854 For compatibility with other Unix systems, 8 and 9 are accepted as digits:
1855 for example, @code{\008} has the value 010, and @code{\009} the value 011.
1857 @cindex @code{\@var{xd...}} (hex character code)
1858 @cindex hex character code (@code{\@var{xd...}})
1859 @item \@code{x} @var{hex-digits...}
1860 A hex character code. All trailing hex digits are combined. Either upper or
1861 lower case @code{x} works.
1863 @cindex @code{\\} (@samp{\} character)
1864 @cindex backslash (@code{\\})
1866 Represents one @samp{\} character.
1869 @c Represents one @samp{'} (accent acute) character.
1870 @c This is needed in single character literals
1871 @c (@xref{Characters,,Character Constants}.) to represent
1874 @cindex @code{\"} (doublequote character)
1875 @cindex doublequote (@code{\"})
1877 Represents one @samp{"} character. Needed in strings to represent
1878 this character, because an unescaped @samp{"} would end the string.
1880 @item \ @var{anything-else}
1881 Any other character when escaped by @kbd{\} gives a warning, but
1882 assembles as if the @samp{\} was not present. The idea is that if
1883 you used an escape sequence you clearly didn't want the literal
1884 interpretation of the following character. However @code{@value{AS}} has no
1885 other interpretation, so @code{@value{AS}} knows it is giving you the wrong
1886 code and warns you of the fact.
1889 Which characters are escapable, and what those escapes represent,
1890 varies widely among assemblers. The current set is what we think
1891 the BSD 4.2 assembler recognizes, and is a subset of what most C
1892 compilers recognize. If you are in doubt, do not use an escape
1896 @subsubsection Characters
1898 @cindex single character constant
1899 @cindex character, single
1900 @cindex constant, single character
1901 A single character may be written as a single quote immediately
1902 followed by that character. The same escapes apply to characters as
1903 to strings. So if you want to write the character backslash, you
1904 must write @kbd{'\\} where the first @code{\} escapes the second
1905 @code{\}. As you can see, the quote is an acute accent, not a
1906 grave accent. A newline
1908 @ifclear abnormal-separator
1909 (or semicolon @samp{;})
1911 @ifset abnormal-separator
1913 (or at sign @samp{@@})
1916 (or dollar sign @samp{$}, for the H8/300; or semicolon @samp{;} for the
1922 immediately following an acute accent is taken as a literal character
1923 and does not count as the end of a statement. The value of a character
1924 constant in a numeric expression is the machine's byte-wide code for
1925 that character. @code{@value{AS}} assumes your character code is ASCII:
1926 @kbd{'A} means 65, @kbd{'B} means 66, and so on. @refill
1929 @subsection Number Constants
1931 @cindex constants, number
1932 @cindex number constants
1933 @code{@value{AS}} distinguishes three kinds of numbers according to how they
1934 are stored in the target machine. @emph{Integers} are numbers that
1935 would fit into an @code{int} in the C language. @emph{Bignums} are
1936 integers, but they are stored in more than 32 bits. @emph{Flonums}
1937 are floating point numbers, described below.
1940 * Integers:: Integers
1945 * Bit Fields:: Bit Fields
1951 @subsubsection Integers
1953 @cindex constants, integer
1955 @cindex binary integers
1956 @cindex integers, binary
1957 A binary integer is @samp{0b} or @samp{0B} followed by zero or more of
1958 the binary digits @samp{01}.
1960 @cindex octal integers
1961 @cindex integers, octal
1962 An octal integer is @samp{0} followed by zero or more of the octal
1963 digits (@samp{01234567}).
1965 @cindex decimal integers
1966 @cindex integers, decimal
1967 A decimal integer starts with a non-zero digit followed by zero or
1968 more digits (@samp{0123456789}).
1970 @cindex hexadecimal integers
1971 @cindex integers, hexadecimal
1972 A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or
1973 more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}.
1975 Integers have the usual values. To denote a negative integer, use
1976 the prefix operator @samp{-} discussed under expressions
1977 (@pxref{Prefix Ops,,Prefix Operators}).
1980 @subsubsection Bignums
1983 @cindex constants, bignum
1984 A @dfn{bignum} has the same syntax and semantics as an integer
1985 except that the number (or its negative) takes more than 32 bits to
1986 represent in binary. The distinction is made because in some places
1987 integers are permitted while bignums are not.
1990 @subsubsection Flonums
1992 @cindex floating point numbers
1993 @cindex constants, floating point
1995 @cindex precision, floating point
1996 A @dfn{flonum} represents a floating point number. The translation is
1997 indirect: a decimal floating point number from the text is converted by
1998 @code{@value{AS}} to a generic binary floating point number of more than
1999 sufficient precision. This generic floating point number is converted
2000 to a particular computer's floating point format (or formats) by a
2001 portion of @code{@value{AS}} specialized to that computer.
2003 A flonum is written by writing (in order)
2008 (@samp{0} is optional on the HPPA.)
2012 A letter, to tell @code{@value{AS}} the rest of the number is a flonum.
2014 @kbd{e} is recommended. Case is not important.
2016 @c FIXME: verify if flonum syntax really this vague for most cases
2017 (Any otherwise illegal letter works here, but that might be changed. Vax BSD
2018 4.2 assembler seems to allow any of @samp{defghDEFGH}.)
2021 On the H8/300, H8/500,
2023 and AMD 29K architectures, the letter must be
2024 one of the letters @samp{DFPRSX} (in upper or lower case).
2026 On the ARC, the letter must be one of the letters @samp{DFRS}
2027 (in upper or lower case).
2029 On the Intel 960 architecture, the letter must be
2030 one of the letters @samp{DFT} (in upper or lower case).
2032 On the HPPA architecture, the letter must be @samp{E} (upper case only).
2036 One of the letters @samp{DFPRSX} (in upper or lower case).
2039 One of the letters @samp{DFRS} (in upper or lower case).
2042 One of the letters @samp{DFPRSX} (in upper or lower case).
2045 The letter @samp{E} (upper case only).
2048 One of the letters @samp{DFT} (in upper or lower case).
2053 An optional sign: either @samp{+} or @samp{-}.
2056 An optional @dfn{integer part}: zero or more decimal digits.
2059 An optional @dfn{fractional part}: @samp{.} followed by zero
2060 or more decimal digits.
2063 An optional exponent, consisting of:
2067 An @samp{E} or @samp{e}.
2068 @c I can't find a config where "EXP_CHARS" is other than 'eE', but in
2069 @c principle this can perfectly well be different on different targets.
2071 Optional sign: either @samp{+} or @samp{-}.
2073 One or more decimal digits.
2078 At least one of the integer part or the fractional part must be
2079 present. The floating point number has the usual base-10 value.
2081 @code{@value{AS}} does all processing using integers. Flonums are computed
2082 independently of any floating point hardware in the computer running
2087 @c Bit fields are written as a general facility but are also controlled
2088 @c by a conditional-compilation flag---which is as of now (21mar91)
2089 @c turned on only by the i960 config of GAS.
2091 @subsubsection Bit Fields
2094 @cindex constants, bit field
2095 You can also define numeric constants as @dfn{bit fields}.
2096 specify two numbers separated by a colon---
2098 @var{mask}:@var{value}
2101 @code{@value{AS}} applies a bitwise @sc{and} between @var{mask} and
2104 The resulting number is then packed
2106 @c this conditional paren in case bit fields turned on elsewhere than 960
2107 (in host-dependent byte order)
2109 into a field whose width depends on which assembler directive has the
2110 bit-field as its argument. Overflow (a result from the bitwise and
2111 requiring more binary digits to represent) is not an error; instead,
2112 more constants are generated, of the specified width, beginning with the
2113 least significant digits.@refill
2115 The directives @code{.byte}, @code{.hword}, @code{.int}, @code{.long},
2116 @code{.short}, and @code{.word} accept bit-field arguments.
2121 @chapter Sections and Relocation
2126 * Secs Background:: Background
2127 * Ld Sections:: Linker Sections
2128 * As Sections:: Assembler Internal Sections
2129 * Sub-Sections:: Sub-Sections
2133 @node Secs Background
2136 Roughly, a section is a range of addresses, with no gaps; all data
2137 ``in'' those addresses is treated the same for some particular purpose.
2138 For example there may be a ``read only'' section.
2140 @cindex linker, and assembler
2141 @cindex assembler, and linker
2142 The linker @code{@value{LD}} reads many object files (partial programs) and
2143 combines their contents to form a runnable program. When @code{@value{AS}}
2144 emits an object file, the partial program is assumed to start at address 0.
2145 @code{@value{LD}} assigns the final addresses for the partial program, so that
2146 different partial programs do not overlap. This is actually an
2147 oversimplification, but it suffices to explain how @code{@value{AS}} uses
2150 @code{@value{LD}} moves blocks of bytes of your program to their run-time
2151 addresses. These blocks slide to their run-time addresses as rigid
2152 units; their length does not change and neither does the order of bytes
2153 within them. Such a rigid unit is called a @emph{section}. Assigning
2154 run-time addresses to sections is called @dfn{relocation}. It includes
2155 the task of adjusting mentions of object-file addresses so they refer to
2156 the proper run-time addresses.
2158 For the H8/300 and H8/500,
2159 and for the Hitachi SH,
2160 @code{@value{AS}} pads sections if needed to
2161 ensure they end on a word (sixteen bit) boundary.
2164 @cindex standard assembler sections
2165 An object file written by @code{@value{AS}} has at least three sections, any
2166 of which may be empty. These are named @dfn{text}, @dfn{data} and
2171 When it generates COFF output,
2173 @code{@value{AS}} can also generate whatever other named sections you specify
2174 using the @samp{.section} directive (@pxref{Section,,@code{.section}}).
2175 If you do not use any directives that place output in the @samp{.text}
2176 or @samp{.data} sections, these sections still exist, but are empty.
2181 When @code{@value{AS}} generates SOM or ELF output for the HPPA,
2183 @code{@value{AS}} can also generate whatever other named sections you
2184 specify using the @samp{.space} and @samp{.subspace} directives. See
2185 @cite{HP9000 Series 800 Assembly Language Reference Manual}
2186 (HP 92432-90001) for details on the @samp{.space} and @samp{.subspace}
2187 assembler directives.
2190 Additionally, @code{@value{AS}} uses different names for the standard
2191 text, data, and bss sections when generating SOM output. Program text
2192 is placed into the @samp{$CODE$} section, data into @samp{$DATA$}, and
2193 BSS into @samp{$BSS$}.
2197 Within the object file, the text section starts at address @code{0}, the
2198 data section follows, and the bss section follows the data section.
2201 When generating either SOM or ELF output files on the HPPA, the text
2202 section starts at address @code{0}, the data section at address
2203 @code{0x4000000}, and the bss section follows the data section.
2206 To let @code{@value{LD}} know which data changes when the sections are
2207 relocated, and how to change that data, @code{@value{AS}} also writes to the
2208 object file details of the relocation needed. To perform relocation
2209 @code{@value{LD}} must know, each time an address in the object
2213 Where in the object file is the beginning of this reference to
2216 How long (in bytes) is this reference?
2218 Which section does the address refer to? What is the numeric value of
2220 (@var{address}) @minus{} (@var{start-address of section})?
2223 Is the reference to an address ``Program-Counter relative''?
2226 @cindex addresses, format of
2227 @cindex section-relative addressing
2228 In fact, every address @code{@value{AS}} ever uses is expressed as
2230 (@var{section}) + (@var{offset into section})
2233 Further, most expressions @code{@value{AS}} computes have this section-relative
2236 (For some object formats, such as SOM for the HPPA, some expressions are
2237 symbol-relative instead.)
2240 In this manual we use the notation @{@var{secname} @var{N}@} to mean ``offset
2241 @var{N} into section @var{secname}.''
2243 Apart from text, data and bss sections you need to know about the
2244 @dfn{absolute} section. When @code{@value{LD}} mixes partial programs,
2245 addresses in the absolute section remain unchanged. For example, address
2246 @code{@{absolute 0@}} is ``relocated'' to run-time address 0 by
2247 @code{@value{LD}}. Although the linker never arranges two partial programs'
2248 data sections with overlapping addresses after linking, @emph{by definition}
2249 their absolute sections must overlap. Address @code{@{absolute@ 239@}} in one
2250 part of a program is always the same address when the program is running as
2251 address @code{@{absolute@ 239@}} in any other part of the program.
2253 The idea of sections is extended to the @dfn{undefined} section. Any
2254 address whose section is unknown at assembly time is by definition
2255 rendered @{undefined @var{U}@}---where @var{U} is filled in later.
2256 Since numbers are always defined, the only way to generate an undefined
2257 address is to mention an undefined symbol. A reference to a named
2258 common block would be such a symbol: its value is unknown at assembly
2259 time so it has section @emph{undefined}.
2261 By analogy the word @emph{section} is used to describe groups of sections in
2262 the linked program. @code{@value{LD}} puts all partial programs' text
2263 sections in contiguous addresses in the linked program. It is
2264 customary to refer to the @emph{text section} of a program, meaning all
2265 the addresses of all partial programs' text sections. Likewise for
2266 data and bss sections.
2268 Some sections are manipulated by @code{@value{LD}}; others are invented for
2269 use of @code{@value{AS}} and have no meaning except during assembly.
2272 @section Linker Sections
2273 @code{@value{LD}} deals with just four kinds of sections, summarized below.
2278 @cindex named sections
2279 @cindex sections, named
2280 @item named sections
2283 @cindex text section
2284 @cindex data section
2288 These sections hold your program. @code{@value{AS}} and @code{@value{LD}} treat them as
2289 separate but equal sections. Anything you can say of one section is
2292 When the program is running, however, it is
2293 customary for the text section to be unalterable. The
2294 text section is often shared among processes: it contains
2295 instructions, constants and the like. The data section of a running
2296 program is usually alterable: for example, C variables would be stored
2297 in the data section.
2302 This section contains zeroed bytes when your program begins running. It
2303 is used to hold unitialized variables or common storage. The length of
2304 each partial program's bss section is important, but because it starts
2305 out containing zeroed bytes there is no need to store explicit zero
2306 bytes in the object file. The bss section was invented to eliminate
2307 those explicit zeros from object files.
2309 @cindex absolute section
2310 @item absolute section
2311 Address 0 of this section is always ``relocated'' to runtime address 0.
2312 This is useful if you want to refer to an address that @code{@value{LD}} must
2313 not change when relocating. In this sense we speak of absolute
2314 addresses being ``unrelocatable'': they do not change during relocation.
2316 @cindex undefined section
2317 @item undefined section
2318 This ``section'' is a catch-all for address references to objects not in
2319 the preceding sections.
2320 @c FIXME: ref to some other doc on obj-file formats could go here.
2323 @cindex relocation example
2324 An idealized example of three relocatable sections follows.
2326 The example uses the traditional section names @samp{.text} and @samp{.data}.
2328 Memory addresses are on the horizontal axis.
2332 @c END TEXI2ROFF-KILL
2335 partial program # 1: |ttttt|dddd|00|
2342 partial program # 2: |TTT|DDD|000|
2345 +--+---+-----+--+----+---+-----+~~
2346 linked program: | |TTT|ttttt| |dddd|DDD|00000|
2347 +--+---+-----+--+----+---+-----+~~
2349 addresses: 0 @dots{}
2356 \line{\it Partial program \#1: \hfil}
2357 \line{\ibox{2.5cm}{\tt text}\ibox{2cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
2358 \line{\boxit{2.5cm}{\tt ttttt}\boxit{2cm}{\tt dddd}\boxit{1cm}{\tt 00}\hfil}
2360 \line{\it Partial program \#2: \hfil}
2361 \line{\ibox{1cm}{\tt text}\ibox{1.5cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
2362 \line{\boxit{1cm}{\tt TTT}\boxit{1.5cm}{\tt DDDD}\boxit{1cm}{\tt 000}\hfil}
2364 \line{\it linked program: \hfil}
2365 \line{\ibox{.5cm}{}\ibox{1cm}{\tt text}\ibox{2.5cm}{}\ibox{.75cm}{}\ibox{2cm}{\tt data}\ibox{1.5cm}{}\ibox{2cm}{\tt bss}\hfil}
2366 \line{\boxit{.5cm}{}\boxit{1cm}{\tt TTT}\boxit{2.5cm}{\tt
2367 ttttt}\boxit{.75cm}{}\boxit{2cm}{\tt dddd}\boxit{1.5cm}{\tt
2368 DDDD}\boxit{2cm}{\tt 00000}\ \dots\hfil}
2370 \line{\it addresses: \hfil}
2374 @c END TEXI2ROFF-KILL
2377 @section Assembler Internal Sections
2379 @cindex internal assembler sections
2380 @cindex sections in messages, internal
2381 These sections are meant only for the internal use of @code{@value{AS}}. They
2382 have no meaning at run-time. You do not really need to know about these
2383 sections for most purposes; but they can be mentioned in @code{@value{AS}}
2384 warning messages, so it might be helpful to have an idea of their
2385 meanings to @code{@value{AS}}. These sections are used to permit the
2386 value of every expression in your assembly language program to be a
2387 section-relative address.
2390 @cindex assembler internal logic error
2391 @item ASSEMBLER-INTERNAL-LOGIC-ERROR!
2392 An internal assembler logic error has been found. This means there is a
2393 bug in the assembler.
2395 @cindex expr (internal section)
2397 The assembler stores complex expression internally as combinations of
2398 symbols. When it needs to represent an expression as a symbol, it puts
2399 it in the expr section.
2401 @c FIXME item transfer[t] vector preload
2402 @c FIXME item transfer[t] vector postload
2403 @c FIXME item register
2407 @section Sub-Sections
2409 @cindex numbered subsections
2410 @cindex grouping data
2416 fall into two sections: text and data.
2418 You may have separate groups of
2420 data in named sections
2424 data in named sections
2430 that you want to end up near to each other in the object file, even though they
2431 are not contiguous in the assembler source. @code{@value{AS}} allows you to
2432 use @dfn{subsections} for this purpose. Within each section, there can be
2433 numbered subsections with values from 0 to 8192. Objects assembled into the
2434 same subsection go into the object file together with other objects in the same
2435 subsection. For example, a compiler might want to store constants in the text
2436 section, but might not want to have them interspersed with the program being
2437 assembled. In this case, the compiler could issue a @samp{.text 0} before each
2438 section of code being output, and a @samp{.text 1} before each group of
2439 constants being output.
2441 Subsections are optional. If you do not use subsections, everything
2442 goes in subsection number zero.
2445 Each subsection is zero-padded up to a multiple of four bytes.
2446 (Subsections may be padded a different amount on different flavors
2447 of @code{@value{AS}}.)
2451 On the H8/300 and H8/500 platforms, each subsection is zero-padded to a word
2452 boundary (two bytes).
2453 The same is true on the Hitachi SH.
2456 @c FIXME section padding (alignment)?
2457 @c Rich Pixley says padding here depends on target obj code format; that
2458 @c doesn't seem particularly useful to say without further elaboration,
2459 @c so for now I say nothing about it. If this is a generic BFD issue,
2460 @c these paragraphs might need to vanish from this manual, and be
2461 @c discussed in BFD chapter of binutils (or some such).
2464 On the AMD 29K family, no particular padding is added to section or
2465 subsection sizes; @value{AS} forces no alignment on this platform.
2469 Subsections appear in your object file in numeric order, lowest numbered
2470 to highest. (All this to be compatible with other people's assemblers.)
2471 The object file contains no representation of subsections; @code{@value{LD}} and
2472 other programs that manipulate object files see no trace of them.
2473 They just see all your text subsections as a text section, and all your
2474 data subsections as a data section.
2476 To specify which subsection you want subsequent statements assembled
2477 into, use a numeric argument to specify it, in a @samp{.text
2478 @var{expression}} or a @samp{.data @var{expression}} statement.
2481 When generating COFF output, you
2486 can also use an extra subsection
2487 argument with arbitrary named sections: @samp{.section @var{name},
2490 @var{Expression} should be an absolute expression.
2491 (@xref{Expressions}.) If you just say @samp{.text} then @samp{.text 0}
2492 is assumed. Likewise @samp{.data} means @samp{.data 0}. Assembly
2493 begins in @code{text 0}. For instance:
2495 .text 0 # The default subsection is text 0 anyway.
2496 .ascii "This lives in the first text subsection. *"
2498 .ascii "But this lives in the second text subsection."
2500 .ascii "This lives in the data section,"
2501 .ascii "in the first data subsection."
2503 .ascii "This lives in the first text section,"
2504 .ascii "immediately following the asterisk (*)."
2507 Each section has a @dfn{location counter} incremented by one for every byte
2508 assembled into that section. Because subsections are merely a convenience
2509 restricted to @code{@value{AS}} there is no concept of a subsection location
2510 counter. There is no way to directly manipulate a location counter---but the
2511 @code{.align} directive changes it, and any label definition captures its
2512 current value. The location counter of the section where statements are being
2513 assembled is said to be the @dfn{active} location counter.
2516 @section bss Section
2519 @cindex common variable storage
2520 The bss section is used for local common variable storage.
2521 You may allocate address space in the bss section, but you may
2522 not dictate data to load into it before your program executes. When
2523 your program starts running, all the contents of the bss
2524 section are zeroed bytes.
2526 The @code{.lcomm} pseudo-op defines a symbol in the bss section; see
2527 @ref{Lcomm,,@code{.lcomm}}.
2529 The @code{.comm} pseudo-op may be used to declare a common symbol, which is
2530 another form of uninitialized symbol; see @xref{Comm,,@code{.comm}}.
2533 When assembling for a target which supports multiple sections, such as ELF or
2534 COFF, you may switch into the @code{.bss} section and define symbols as usual;
2535 see @ref{Section,,@code{.section}}. You may only assemble zero values into the
2536 section. Typically the section will only contain symbol definitions and
2537 @code{.skip} directives (@pxref{Skip,,@code{.skip}}).
2544 Symbols are a central concept: the programmer uses symbols to name
2545 things, the linker uses symbols to link, and the debugger uses symbols
2549 @cindex debuggers, and symbol order
2550 @emph{Warning:} @code{@value{AS}} does not place symbols in the object file in
2551 the same order they were declared. This may break some debuggers.
2556 * Setting Symbols:: Giving Symbols Other Values
2557 * Symbol Names:: Symbol Names
2558 * Dot:: The Special Dot Symbol
2559 * Symbol Attributes:: Symbol Attributes
2566 A @dfn{label} is written as a symbol immediately followed by a colon
2567 @samp{:}. The symbol then represents the current value of the
2568 active location counter, and is, for example, a suitable instruction
2569 operand. You are warned if you use the same symbol to represent two
2570 different locations: the first definition overrides any other
2574 On the HPPA, the usual form for a label need not be immediately followed by a
2575 colon, but instead must start in column zero. Only one label may be defined on
2576 a single line. To work around this, the HPPA version of @code{@value{AS}} also
2577 provides a special directive @code{.label} for defining labels more flexibly.
2580 @node Setting Symbols
2581 @section Giving Symbols Other Values
2583 @cindex assigning values to symbols
2584 @cindex symbol values, assigning
2585 A symbol can be given an arbitrary value by writing a symbol, followed
2586 by an equals sign @samp{=}, followed by an expression
2587 (@pxref{Expressions}). This is equivalent to using the @code{.set}
2588 directive. @xref{Set,,@code{.set}}.
2591 @section Symbol Names
2593 @cindex symbol names
2594 @cindex names, symbol
2595 @ifclear SPECIAL-SYMS
2596 Symbol names begin with a letter or with one of @samp{._}. On most
2597 machines, you can also use @code{$} in symbol names; exceptions are
2598 noted in @ref{Machine Dependencies}. That character may be followed by any
2599 string of digits, letters, dollar signs (unless otherwise noted in
2600 @ref{Machine Dependencies}), and underscores.
2603 For the AMD 29K family, @samp{?} is also allowed in the
2604 body of a symbol name, though not at its beginning.
2609 Symbol names begin with a letter or with one of @samp{._}. On the
2611 H8/500, you can also use @code{$} in symbol names. That character may
2612 be followed by any string of digits, letters, dollar signs (save on the
2613 H8/300), and underscores.
2617 Case of letters is significant: @code{foo} is a different symbol name
2620 Each symbol has exactly one name. Each name in an assembly language program
2621 refers to exactly one symbol. You may use that symbol name any number of times
2624 @subheading Local Symbol Names
2626 @cindex local symbol names
2627 @cindex symbol names, local
2628 @cindex temporary symbol names
2629 @cindex symbol names, temporary
2630 Local symbols help compilers and programmers use names temporarily.
2631 There are ten local symbol names, which are re-used throughout the
2632 program. You may refer to them using the names @samp{0} @samp{1}
2633 @dots{} @samp{9}. To define a local symbol, write a label of the form
2634 @samp{@b{N}:} (where @b{N} represents any digit). To refer to the most
2635 recent previous definition of that symbol write @samp{@b{N}b}, using the
2636 same digit as when you defined the label. To refer to the next
2637 definition of a local label, write @samp{@b{N}f}---where @b{N} gives you
2638 a choice of 10 forward references. The @samp{b} stands for
2639 ``backwards'' and the @samp{f} stands for ``forwards''.
2641 Local symbols are not emitted by the current @sc{gnu} C compiler.
2643 There is no restriction on how you can use these labels, but
2644 remember that at any point in the assembly you can refer to at most
2645 10 prior local labels and to at most 10 forward local labels.
2647 Local symbol names are only a notation device. They are immediately
2648 transformed into more conventional symbol names before the assembler
2649 uses them. The symbol names stored in the symbol table, appearing in
2650 error messages and optionally emitted to the object file have these
2655 All local labels begin with @samp{L}. Normally both @code{@value{AS}} and
2656 @code{@value{LD}} forget symbols that start with @samp{L}. These labels are
2657 used for symbols you are never intended to see. If you use the
2658 @samp{-L} option then @code{@value{AS}} retains these symbols in the
2659 object file. If you also instruct @code{@value{LD}} to retain these symbols,
2660 you may use them in debugging.
2663 If the label is written @samp{0:} then the digit is @samp{0}.
2664 If the label is written @samp{1:} then the digit is @samp{1}.
2665 And so on up through @samp{9:}.
2668 This unusual character is included so you do not accidentally invent
2669 a symbol of the same name. The character has ASCII value
2672 @item @emph{ordinal number}
2673 This is a serial number to keep the labels distinct. The first
2674 @samp{0:} gets the number @samp{1}; The 15th @samp{0:} gets the
2675 number @samp{15}; @emph{etc.}. Likewise for the other labels @samp{1:}
2679 For instance, the first @code{1:} is named @code{L1@kbd{C-A}1}, the 44th
2680 @code{3:} is named @code{L3@kbd{C-A}44}.
2683 @section The Special Dot Symbol
2685 @cindex dot (symbol)
2686 @cindex @code{.} (symbol)
2687 @cindex current address
2688 @cindex location counter
2689 The special symbol @samp{.} refers to the current address that
2690 @code{@value{AS}} is assembling into. Thus, the expression @samp{melvin:
2691 .long .} defines @code{melvin} to contain its own address.
2692 Assigning a value to @code{.} is treated the same as a @code{.org}
2693 directive. Thus, the expression @samp{.=.+4} is the same as saying
2694 @ifclear no-space-dir
2703 @node Symbol Attributes
2704 @section Symbol Attributes
2706 @cindex symbol attributes
2707 @cindex attributes, symbol
2708 Every symbol has, as well as its name, the attributes ``Value'' and
2709 ``Type''. Depending on output format, symbols can also have auxiliary
2712 The detailed definitions are in @file{a.out.h}.
2715 If you use a symbol without defining it, @code{@value{AS}} assumes zero for
2716 all these attributes, and probably won't warn you. This makes the
2717 symbol an externally defined symbol, which is generally what you
2721 * Symbol Value:: Value
2722 * Symbol Type:: Type
2725 * a.out Symbols:: Symbol Attributes: @code{a.out}
2729 * a.out Symbols:: Symbol Attributes: @code{a.out}
2732 * a.out Symbols:: Symbol Attributes: @code{a.out}, @code{b.out}
2737 * COFF Symbols:: Symbol Attributes for COFF
2740 * SOM Symbols:: Symbol Attributes for SOM
2747 @cindex value of a symbol
2748 @cindex symbol value
2749 The value of a symbol is (usually) 32 bits. For a symbol which labels a
2750 location in the text, data, bss or absolute sections the value is the
2751 number of addresses from the start of that section to the label.
2752 Naturally for text, data and bss sections the value of a symbol changes
2753 as @code{@value{LD}} changes section base addresses during linking. Absolute
2754 symbols' values do not change during linking: that is why they are
2757 The value of an undefined symbol is treated in a special way. If it is
2758 0 then the symbol is not defined in this assembler source file, and
2759 @code{@value{LD}} tries to determine its value from other files linked into the
2760 same program. You make this kind of symbol simply by mentioning a symbol
2761 name without defining it. A non-zero value represents a @code{.comm}
2762 common declaration. The value is how much common storage to reserve, in
2763 bytes (addresses). The symbol refers to the first address of the
2769 @cindex type of a symbol
2771 The type attribute of a symbol contains relocation (section)
2772 information, any flag settings indicating that a symbol is external, and
2773 (optionally), other information for linkers and debuggers. The exact
2774 format depends on the object-code output format in use.
2779 @c The following avoids a "widow" subsection title. @group would be
2780 @c better if it were available outside examples.
2783 @subsection Symbol Attributes: @code{a.out}, @code{b.out}
2785 @cindex @code{b.out} symbol attributes
2786 @cindex symbol attributes, @code{b.out}
2787 These symbol attributes appear only when @code{@value{AS}} is configured for
2788 one of the Berkeley-descended object output formats---@code{a.out} or
2794 @subsection Symbol Attributes: @code{a.out}
2796 @cindex @code{a.out} symbol attributes
2797 @cindex symbol attributes, @code{a.out}
2803 @subsection Symbol Attributes: @code{a.out}
2805 @cindex @code{a.out} symbol attributes
2806 @cindex symbol attributes, @code{a.out}
2810 * Symbol Desc:: Descriptor
2811 * Symbol Other:: Other
2815 @subsubsection Descriptor
2817 @cindex descriptor, of @code{a.out} symbol
2818 This is an arbitrary 16-bit value. You may establish a symbol's
2819 descriptor value by using a @code{.desc} statement
2820 (@pxref{Desc,,@code{.desc}}). A descriptor value means nothing to
2824 @subsubsection Other
2826 @cindex other attribute, of @code{a.out} symbol
2827 This is an arbitrary 8-bit value. It means nothing to @code{@value{AS}}.
2832 @subsection Symbol Attributes for COFF
2834 @cindex COFF symbol attributes
2835 @cindex symbol attributes, COFF
2837 The COFF format supports a multitude of auxiliary symbol attributes;
2838 like the primary symbol attributes, they are set between @code{.def} and
2839 @code{.endef} directives.
2841 @subsubsection Primary Attributes
2843 @cindex primary attributes, COFF symbols
2844 The symbol name is set with @code{.def}; the value and type,
2845 respectively, with @code{.val} and @code{.type}.
2847 @subsubsection Auxiliary Attributes
2849 @cindex auxiliary attributes, COFF symbols
2850 The @code{@value{AS}} directives @code{.dim}, @code{.line}, @code{.scl},
2851 @code{.size}, and @code{.tag} can generate auxiliary symbol table
2852 information for COFF.
2857 @subsection Symbol Attributes for SOM
2859 @cindex SOM symbol attributes
2860 @cindex symbol attributes, SOM
2862 The SOM format for the HPPA supports a multitude of symbol attributes set with
2863 the @code{.EXPORT} and @code{.IMPORT} directives.
2865 The attributes are described in @cite{HP9000 Series 800 Assembly
2866 Language Reference Manual} (HP 92432-90001) under the @code{IMPORT} and
2867 @code{EXPORT} assembler directive documentation.
2871 @chapter Expressions
2875 @cindex numeric values
2876 An @dfn{expression} specifies an address or numeric value.
2877 Whitespace may precede and/or follow an expression.
2879 The result of an expression must be an absolute number, or else an offset into
2880 a particular section. If an expression is not absolute, and there is not
2881 enough information when @code{@value{AS}} sees the expression to know its
2882 section, a second pass over the source program might be necessary to interpret
2883 the expression---but the second pass is currently not implemented.
2884 @code{@value{AS}} aborts with an error message in this situation.
2887 * Empty Exprs:: Empty Expressions
2888 * Integer Exprs:: Integer Expressions
2892 @section Empty Expressions
2894 @cindex empty expressions
2895 @cindex expressions, empty
2896 An empty expression has no value: it is just whitespace or null.
2897 Wherever an absolute expression is required, you may omit the
2898 expression, and @code{@value{AS}} assumes a value of (absolute) 0. This
2899 is compatible with other assemblers.
2902 @section Integer Expressions
2904 @cindex integer expressions
2905 @cindex expressions, integer
2906 An @dfn{integer expression} is one or more @emph{arguments} delimited
2907 by @emph{operators}.
2910 * Arguments:: Arguments
2911 * Operators:: Operators
2912 * Prefix Ops:: Prefix Operators
2913 * Infix Ops:: Infix Operators
2917 @subsection Arguments
2919 @cindex expression arguments
2920 @cindex arguments in expressions
2921 @cindex operands in expressions
2922 @cindex arithmetic operands
2923 @dfn{Arguments} are symbols, numbers or subexpressions. In other
2924 contexts arguments are sometimes called ``arithmetic operands''. In
2925 this manual, to avoid confusing them with the ``instruction operands'' of
2926 the machine language, we use the term ``argument'' to refer to parts of
2927 expressions only, reserving the word ``operand'' to refer only to machine
2928 instruction operands.
2930 Symbols are evaluated to yield @{@var{section} @var{NNN}@} where
2931 @var{section} is one of text, data, bss, absolute,
2932 or undefined. @var{NNN} is a signed, 2's complement 32 bit
2935 Numbers are usually integers.
2937 A number can be a flonum or bignum. In this case, you are warned
2938 that only the low order 32 bits are used, and @code{@value{AS}} pretends
2939 these 32 bits are an integer. You may write integer-manipulating
2940 instructions that act on exotic constants, compatible with other
2943 @cindex subexpressions
2944 Subexpressions are a left parenthesis @samp{(} followed by an integer
2945 expression, followed by a right parenthesis @samp{)}; or a prefix
2946 operator followed by an argument.
2949 @subsection Operators
2951 @cindex operators, in expressions
2952 @cindex arithmetic functions
2953 @cindex functions, in expressions
2954 @dfn{Operators} are arithmetic functions, like @code{+} or @code{%}. Prefix
2955 operators are followed by an argument. Infix operators appear
2956 between their arguments. Operators may be preceded and/or followed by
2960 @subsection Prefix Operator
2962 @cindex prefix operators
2963 @code{@value{AS}} has the following @dfn{prefix operators}. They each take
2964 one argument, which must be absolute.
2966 @c the tex/end tex stuff surrounding this small table is meant to make
2967 @c it align, on the printed page, with the similar table in the next
2968 @c section (which is inside an enumerate).
2970 \global\advance\leftskip by \itemindent
2975 @dfn{Negation}. Two's complement negation.
2977 @dfn{Complementation}. Bitwise not.
2981 \global\advance\leftskip by -\itemindent
2985 @subsection Infix Operators
2987 @cindex infix operators
2988 @cindex operators, permitted arguments
2989 @dfn{Infix operators} take two arguments, one on either side. Operators
2990 have precedence, but operations with equal precedence are performed left
2991 to right. Apart from @code{+} or @code{-}, both arguments must be
2992 absolute, and the result is absolute.
2995 @cindex operator precedence
2996 @cindex precedence of operators
3003 @dfn{Multiplication}.
3006 @dfn{Division}. Truncation is the same as the C operator @samp{/}
3013 @dfn{Shift Left}. Same as the C operator @samp{<<}.
3017 @dfn{Shift Right}. Same as the C operator @samp{>>}.
3021 Intermediate precedence
3026 @dfn{Bitwise Inclusive Or}.
3032 @dfn{Bitwise Exclusive Or}.
3035 @dfn{Bitwise Or Not}.
3042 @cindex addition, permitted arguments
3043 @cindex plus, permitted arguments
3044 @cindex arguments for addition
3046 @dfn{Addition}. If either argument is absolute, the result has the section of
3047 the other argument. You may not add together arguments from different
3050 @cindex subtraction, permitted arguments
3051 @cindex minus, permitted arguments
3052 @cindex arguments for subtraction
3054 @dfn{Subtraction}. If the right argument is absolute, the
3055 result has the section of the left argument.
3056 If both arguments are in the same section, the result is absolute.
3057 You may not subtract arguments from different sections.
3058 @c FIXME is there still something useful to say about undefined - undefined ?
3062 In short, it's only meaningful to add or subtract the @emph{offsets} in an
3063 address; you can only have a defined section in one of the two arguments.
3066 @chapter Assembler Directives
3068 @cindex directives, machine independent
3069 @cindex pseudo-ops, machine independent
3070 @cindex machine independent directives
3071 All assembler directives have names that begin with a period (@samp{.}).
3072 The rest of the name is letters, usually in lower case.
3074 This chapter discusses directives that are available regardless of the
3075 target machine configuration for the @sc{gnu} assembler.
3077 Some machine configurations provide additional directives.
3078 @xref{Machine Dependencies}.
3081 @ifset machine-directives
3082 @xref{Machine Dependencies} for additional directives.
3087 * Abort:: @code{.abort}
3089 * ABORT:: @code{.ABORT}
3092 * Align:: @code{.align @var{abs-expr} , @var{abs-expr}}
3093 * Ascii:: @code{.ascii "@var{string}"}@dots{}
3094 * Asciz:: @code{.asciz "@var{string}"}@dots{}
3095 * Balign:: @code{.balign @var{abs-expr} , @var{abs-expr}}
3096 * Byte:: @code{.byte @var{expressions}}
3097 * Comm:: @code{.comm @var{symbol} , @var{length} }
3098 * Data:: @code{.data @var{subsection}}
3100 * Def:: @code{.def @var{name}}
3103 * Desc:: @code{.desc @var{symbol}, @var{abs-expression}}
3109 * Double:: @code{.double @var{flonums}}
3110 * Eject:: @code{.eject}
3111 * Else:: @code{.else}
3114 * Endef:: @code{.endef}
3117 * Endfunc:: @code{.endfunc}
3118 * Endif:: @code{.endif}
3119 * Equ:: @code{.equ @var{symbol}, @var{expression}}
3120 * Equiv:: @code{.equiv @var{symbol}, @var{expression}}
3122 * Exitm:: @code{.exitm}
3123 * Extern:: @code{.extern}
3124 * Fail:: @code{.fail}
3125 @ifclear no-file-dir
3126 * File:: @code{.file @var{string}}
3129 * Fill:: @code{.fill @var{repeat} , @var{size} , @var{value}}
3130 * Float:: @code{.float @var{flonums}}
3131 * Func:: @code{.func}
3132 * Global:: @code{.global @var{symbol}}, @code{.globl @var{symbol}}
3133 * hword:: @code{.hword @var{expressions}}
3134 * Ident:: @code{.ident}
3135 * If:: @code{.if @var{absolute expression}}
3136 * Include:: @code{.include "@var{file}"}
3137 * Int:: @code{.int @var{expressions}}
3138 * Irp:: @code{.irp @var{symbol},@var{values}}@dots{}
3139 * Irpc:: @code{.irpc @var{symbol},@var{values}}@dots{}
3140 * Lcomm:: @code{.lcomm @var{symbol} , @var{length}}
3141 * Lflags:: @code{.lflags}
3142 @ifclear no-line-dir
3143 * Line:: @code{.line @var{line-number}}
3146 * Ln:: @code{.ln @var{line-number}}
3147 * Linkonce:: @code{.linkonce [@var{type}]}
3148 * List:: @code{.list}
3149 * Long:: @code{.long @var{expressions}}
3151 * Lsym:: @code{.lsym @var{symbol}, @var{expression}}
3154 * Macro:: @code{.macro @var{name} @var{args}}@dots{}
3155 * MRI:: @code{.mri @var{val}}
3157 * Nolist:: @code{.nolist}
3158 * Octa:: @code{.octa @var{bignums}}
3159 * Org:: @code{.org @var{new-lc} , @var{fill}}
3160 * P2align:: @code{.p2align @var{abs-expr} , @var{abs-expr}}
3161 * Print:: @code{.print @var{string}}
3162 * Psize:: @code{.psize @var{lines}, @var{columns}}
3163 * Purgem:: @code{.purgem @var{name}}
3164 * Quad:: @code{.quad @var{bignums}}
3165 * Rept:: @code{.rept @var{count}}
3166 * Sbttl:: @code{.sbttl "@var{subheading}"}
3168 * Scl:: @code{.scl @var{class}}
3169 * Section:: @code{.section @var{name}, @var{subsection}}
3172 * Set:: @code{.set @var{symbol}, @var{expression}}
3173 * Short:: @code{.short @var{expressions}}
3174 * Single:: @code{.single @var{flonums}}
3176 * Size:: @code{.size}
3179 * Skip:: @code{.skip @var{size} , @var{fill}}
3180 * Sleb128:: @code{.sleb128 @var{expressions}}
3181 * Space:: @code{.space @var{size} , @var{fill}}
3183 * Stab:: @code{.stabd, .stabn, .stabs}
3186 * String:: @code{.string "@var{str}"}
3187 * Struct:: @code{.struct @var{expression}}
3189 * Symver:: @code{.symver @var{name},@var{name2@@nodename}}
3192 * Tag:: @code{.tag @var{structname}}
3195 * Text:: @code{.text @var{subsection}}
3196 * Title:: @code{.title "@var{heading}"}
3198 * Type:: @code{.type @var{int}}
3199 * Val:: @code{.val @var{addr}}
3202 * Visibility:: @code{.internal @var{name}, .hidden @var{name}, .protected @var{name}}
3205 * Uleb128:: @code{.uleb128 @var{expressions}}
3206 * Word:: @code{.word @var{expressions}}
3207 * Deprecated:: Deprecated Directives
3211 @section @code{.abort}
3213 @cindex @code{abort} directive
3214 @cindex stopping the assembly
3215 This directive stops the assembly immediately. It is for
3216 compatibility with other assemblers. The original idea was that the
3217 assembly language source would be piped into the assembler. If the sender
3218 of the source quit, it could use this directive tells @code{@value{AS}} to
3219 quit also. One day @code{.abort} will not be supported.
3223 @section @code{.ABORT}
3225 @cindex @code{ABORT} directive
3226 When producing COFF output, @code{@value{AS}} accepts this directive as a
3227 synonym for @samp{.abort}.
3230 When producing @code{b.out} output, @code{@value{AS}} accepts this directive,
3236 @section @code{.align @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
3238 @cindex padding the location counter
3239 @cindex @code{align} directive
3240 Pad the location counter (in the current subsection) to a particular storage
3241 boundary. The first expression (which must be absolute) is the alignment
3242 required, as described below.
3244 The second expression (also absolute) gives the fill value to be stored in the
3245 padding bytes. It (and the comma) may be omitted. If it is omitted, the
3246 padding bytes are normally zero. However, on some systems, if the section is
3247 marked as containing code and the fill value is omitted, the space is filled
3248 with no-op instructions.
3250 The third expression is also absolute, and is also optional. If it is present,
3251 it is the maximum number of bytes that should be skipped by this alignment
3252 directive. If doing the alignment would require skipping more bytes than the
3253 specified maximum, then the alignment is not done at all. You can omit the
3254 fill value (the second argument) entirely by simply using two commas after the
3255 required alignment; this can be useful if you want the alignment to be filled
3256 with no-op instructions when appropriate.
3258 The way the required alignment is specified varies from system to system.
3259 For the a29k, hppa, m68k, m88k, w65, sparc, and Hitachi SH, and i386 using ELF
3261 the first expression is the
3262 alignment request in bytes. For example @samp{.align 8} advances
3263 the location counter until it is a multiple of 8. If the location counter
3264 is already a multiple of 8, no change is needed.
3266 For other systems, including the i386 using a.out format, it is the
3267 number of low-order zero bits the location counter must have after
3268 advancement. For example @samp{.align 3} advances the location
3269 counter until it a multiple of 8. If the location counter is already a
3270 multiple of 8, no change is needed.
3272 This inconsistency is due to the different behaviors of the various
3273 native assemblers for these systems which GAS must emulate.
3274 GAS also provides @code{.balign} and @code{.p2align} directives,
3275 described later, which have a consistent behavior across all
3276 architectures (but are specific to GAS).
3279 @section @code{.ascii "@var{string}"}@dots{}
3281 @cindex @code{ascii} directive
3282 @cindex string literals
3283 @code{.ascii} expects zero or more string literals (@pxref{Strings})
3284 separated by commas. It assembles each string (with no automatic
3285 trailing zero byte) into consecutive addresses.
3288 @section @code{.asciz "@var{string}"}@dots{}
3290 @cindex @code{asciz} directive
3291 @cindex zero-terminated strings
3292 @cindex null-terminated strings
3293 @code{.asciz} is just like @code{.ascii}, but each string is followed by
3294 a zero byte. The ``z'' in @samp{.asciz} stands for ``zero''.
3297 @section @code{.balign[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
3299 @cindex padding the location counter given number of bytes
3300 @cindex @code{balign} directive
3301 Pad the location counter (in the current subsection) to a particular
3302 storage boundary. The first expression (which must be absolute) is the
3303 alignment request in bytes. For example @samp{.balign 8} advances
3304 the location counter until it is a multiple of 8. If the location counter
3305 is already a multiple of 8, no change is needed.
3307 The second expression (also absolute) gives the fill value to be stored in the
3308 padding bytes. It (and the comma) may be omitted. If it is omitted, the
3309 padding bytes are normally zero. However, on some systems, if the section is
3310 marked as containing code and the fill value is omitted, the space is filled
3311 with no-op instructions.
3313 The third expression is also absolute, and is also optional. If it is present,
3314 it is the maximum number of bytes that should be skipped by this alignment
3315 directive. If doing the alignment would require skipping more bytes than the
3316 specified maximum, then the alignment is not done at all. You can omit the
3317 fill value (the second argument) entirely by simply using two commas after the
3318 required alignment; this can be useful if you want the alignment to be filled
3319 with no-op instructions when appropriate.
3321 @cindex @code{balignw} directive
3322 @cindex @code{balignl} directive
3323 The @code{.balignw} and @code{.balignl} directives are variants of the
3324 @code{.balign} directive. The @code{.balignw} directive treats the fill
3325 pattern as a two byte word value. The @code{.balignl} directives treats the
3326 fill pattern as a four byte longword value. For example, @code{.balignw
3327 4,0x368d} will align to a multiple of 4. If it skips two bytes, they will be
3328 filled in with the value 0x368d (the exact placement of the bytes depends upon
3329 the endianness of the processor). If it skips 1 or 3 bytes, the fill value is
3333 @section @code{.byte @var{expressions}}
3335 @cindex @code{byte} directive
3336 @cindex integers, one byte
3337 @code{.byte} expects zero or more expressions, separated by commas.
3338 Each expression is assembled into the next byte.
3341 @section @code{.comm @var{symbol} , @var{length} }
3343 @cindex @code{comm} directive
3344 @cindex symbol, common
3345 @code{.comm} declares a common symbol named @var{symbol}. When linking, a
3346 common symbol in one object file may be merged with a defined or common symbol
3347 of the same name in another object file. If @code{@value{LD}} does not see a
3348 definition for the symbol--just one or more common symbols--then it will
3349 allocate @var{length} bytes of uninitialized memory. @var{length} must be an
3350 absolute expression. If @code{@value{LD}} sees multiple common symbols with
3351 the same name, and they do not all have the same size, it will allocate space
3352 using the largest size.
3355 When using ELF, the @code{.comm} directive takes an optional third argument.
3356 This is the desired alignment of the symbol, specified as a byte boundary (for
3357 example, an alignment of 16 means that the least significant 4 bits of the
3358 address should be zero). The alignment must be an absolute expression, and it
3359 must be a power of two. If @code{@value{LD}} allocates uninitialized memory
3360 for the common symbol, it will use the alignment when placing the symbol. If
3361 no alignment is specified, @code{@value{AS}} will set the alignment to the
3362 largest power of two less than or equal to the size of the symbol, up to a
3367 The syntax for @code{.comm} differs slightly on the HPPA. The syntax is
3368 @samp{@var{symbol} .comm, @var{length}}; @var{symbol} is optional.
3372 @section @code{.data @var{subsection}}
3374 @cindex @code{data} directive
3375 @code{.data} tells @code{@value{AS}} to assemble the following statements onto the
3376 end of the data subsection numbered @var{subsection} (which is an
3377 absolute expression). If @var{subsection} is omitted, it defaults
3382 @section @code{.def @var{name}}
3384 @cindex @code{def} directive
3385 @cindex COFF symbols, debugging
3386 @cindex debugging COFF symbols
3387 Begin defining debugging information for a symbol @var{name}; the
3388 definition extends until the @code{.endef} directive is encountered.
3391 This directive is only observed when @code{@value{AS}} is configured for COFF
3392 format output; when producing @code{b.out}, @samp{.def} is recognized,
3399 @section @code{.desc @var{symbol}, @var{abs-expression}}
3401 @cindex @code{desc} directive
3402 @cindex COFF symbol descriptor
3403 @cindex symbol descriptor, COFF
3404 This directive sets the descriptor of the symbol (@pxref{Symbol Attributes})
3405 to the low 16 bits of an absolute expression.
3408 The @samp{.desc} directive is not available when @code{@value{AS}} is
3409 configured for COFF output; it is only for @code{a.out} or @code{b.out}
3410 object format. For the sake of compatibility, @code{@value{AS}} accepts
3411 it, but produces no output, when configured for COFF.
3417 @section @code{.dim}
3419 @cindex @code{dim} directive
3420 @cindex COFF auxiliary symbol information
3421 @cindex auxiliary symbol information, COFF
3422 This directive is generated by compilers to include auxiliary debugging
3423 information in the symbol table. It is only permitted inside
3424 @code{.def}/@code{.endef} pairs.
3427 @samp{.dim} is only meaningful when generating COFF format output; when
3428 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
3434 @section @code{.double @var{flonums}}
3436 @cindex @code{double} directive
3437 @cindex floating point numbers (double)
3438 @code{.double} expects zero or more flonums, separated by commas. It
3439 assembles floating point numbers.
3441 The exact kind of floating point numbers emitted depends on how
3442 @code{@value{AS}} is configured. @xref{Machine Dependencies}.
3446 On the @value{TARGET} family @samp{.double} emits 64-bit floating-point numbers
3447 in @sc{ieee} format.
3452 @section @code{.eject}
3454 @cindex @code{eject} directive
3455 @cindex new page, in listings
3456 @cindex page, in listings
3457 @cindex listing control: new page
3458 Force a page break at this point, when generating assembly listings.
3461 @section @code{.else}
3463 @cindex @code{else} directive
3464 @code{.else} is part of the @code{@value{AS}} support for conditional
3465 assembly; @pxref{If,,@code{.if}}. It marks the beginning of a section
3466 of code to be assembled if the condition for the preceding @code{.if}
3470 @section @code{.end}
3472 @cindex @code{end} directive
3473 @code{.end} marks the end of the assembly file. @code{@value{AS}} does not
3474 process anything in the file past the @code{.end} directive.
3478 @section @code{.endef}
3480 @cindex @code{endef} directive
3481 This directive flags the end of a symbol definition begun with
3485 @samp{.endef} is only meaningful when generating COFF format output; if
3486 @code{@value{AS}} is configured to generate @code{b.out}, it accepts this
3487 directive but ignores it.
3492 @section @code{.endfunc}
3493 @cindex @code{endfunc} directive
3494 @code{.endfunc} marks the end of a function specified with @code{.func}.
3497 @section @code{.endif}
3499 @cindex @code{endif} directive
3500 @code{.endif} is part of the @code{@value{AS}} support for conditional assembly;
3501 it marks the end of a block of code that is only assembled
3502 conditionally. @xref{If,,@code{.if}}.
3505 @section @code{.equ @var{symbol}, @var{expression}}
3507 @cindex @code{equ} directive
3508 @cindex assigning values to symbols
3509 @cindex symbols, assigning values to
3510 This directive sets the value of @var{symbol} to @var{expression}.
3511 It is synonymous with @samp{.set}; @pxref{Set,,@code{.set}}.
3514 The syntax for @code{equ} on the HPPA is
3515 @samp{@var{symbol} .equ @var{expression}}.
3519 @section @code{.equiv @var{symbol}, @var{expression}}
3520 @cindex @code{equiv} directive
3521 The @code{.equiv} directive is like @code{.equ} and @code{.set}, except that
3522 the assembler will signal an error if @var{symbol} is already defined.
3524 Except for the contents of the error message, this is roughly equivalent to
3533 @section @code{.err}
3534 @cindex @code{err} directive
3535 If @code{@value{AS}} assembles a @code{.err} directive, it will print an error
3536 message and, unless the @code{-Z} option was used, it will not generate an
3537 object file. This can be used to signal error an conditionally compiled code.
3540 @section @code{.exitm}
3541 Exit early from the current macro definition. @xref{Macro}.
3544 @section @code{.extern}
3546 @cindex @code{extern} directive
3547 @code{.extern} is accepted in the source program---for compatibility
3548 with other assemblers---but it is ignored. @code{@value{AS}} treats
3549 all undefined symbols as external.
3552 @section @code{.fail @var{expression}}
3554 @cindex @code{fail} directive
3555 Generates an error or a warning. If the value of the @var{expression} is 500
3556 or more, @code{@value{AS}} will print a warning message. If the value is less
3557 than 500, @code{@value{AS}} will print an error message. The message will
3558 include the value of @var{expression}. This can occasionally be useful inside
3559 complex nested macros or conditional assembly.
3561 @ifclear no-file-dir
3563 @section @code{.file @var{string}}
3565 @cindex @code{file} directive
3566 @cindex logical file name
3567 @cindex file name, logical
3568 @code{.file} tells @code{@value{AS}} that we are about to start a new logical
3569 file. @var{string} is the new file name. In general, the filename is
3570 recognized whether or not it is surrounded by quotes @samp{"}; but if you wish
3571 to specify an empty file name, you must give the quotes--@code{""}. This
3572 statement may go away in future: it is only recognized to be compatible with
3573 old @code{@value{AS}} programs.
3575 In some configurations of @code{@value{AS}}, @code{.file} has already been
3576 removed to avoid conflicts with other assemblers. @xref{Machine Dependencies}.
3581 @section @code{.fill @var{repeat} , @var{size} , @var{value}}
3583 @cindex @code{fill} directive
3584 @cindex writing patterns in memory
3585 @cindex patterns, writing in memory
3586 @var{result}, @var{size} and @var{value} are absolute expressions.
3587 This emits @var{repeat} copies of @var{size} bytes. @var{Repeat}
3588 may be zero or more. @var{Size} may be zero or more, but if it is
3589 more than 8, then it is deemed to have the value 8, compatible with
3590 other people's assemblers. The contents of each @var{repeat} bytes
3591 is taken from an 8-byte number. The highest order 4 bytes are
3592 zero. The lowest order 4 bytes are @var{value} rendered in the
3593 byte-order of an integer on the computer @code{@value{AS}} is assembling for.
3594 Each @var{size} bytes in a repetition is taken from the lowest order
3595 @var{size} bytes of this number. Again, this bizarre behavior is
3596 compatible with other people's assemblers.
3598 @var{size} and @var{value} are optional.
3599 If the second comma and @var{value} are absent, @var{value} is
3600 assumed zero. If the first comma and following tokens are absent,
3601 @var{size} is assumed to be 1.
3604 @section @code{.float @var{flonums}}
3606 @cindex floating point numbers (single)
3607 @cindex @code{float} directive
3608 This directive assembles zero or more flonums, separated by commas. It
3609 has the same effect as @code{.single}.
3611 The exact kind of floating point numbers emitted depends on how
3612 @code{@value{AS}} is configured.
3613 @xref{Machine Dependencies}.
3617 On the @value{TARGET} family, @code{.float} emits 32-bit floating point numbers
3618 in @sc{ieee} format.
3623 @section @code{.func @var{name}[,@var{label}]}
3624 @cindex @code{func} directive
3625 @code{.func} emits debugging information to denote function @var{name}, and
3626 is ignored unless the file is assembled with debugging enabled.
3627 Only @samp{--gstabs} is currently supported.
3628 @var{label} is the entry point of the function and if omitted @var{name}
3629 prepended with the @samp{leading char} is used.
3630 @samp{leading char} is usually @code{_} or nothing, depending on the target.
3631 All functions are currently defined to have @code{void} return type.
3632 The function must be terminated with @code{.endfunc}.
3635 @section @code{.global @var{symbol}}, @code{.globl @var{symbol}}
3637 @cindex @code{global} directive
3638 @cindex symbol, making visible to linker
3639 @code{.global} makes the symbol visible to @code{@value{LD}}. If you define
3640 @var{symbol} in your partial program, its value is made available to
3641 other partial programs that are linked with it. Otherwise,
3642 @var{symbol} takes its attributes from a symbol of the same name
3643 from another file linked into the same program.
3645 Both spellings (@samp{.globl} and @samp{.global}) are accepted, for
3646 compatibility with other assemblers.
3649 On the HPPA, @code{.global} is not always enough to make it accessible to other
3650 partial programs. You may need the HPPA-only @code{.EXPORT} directive as well.
3651 @xref{HPPA Directives,, HPPA Assembler Directives}.
3655 @section @code{.hword @var{expressions}}
3657 @cindex @code{hword} directive
3658 @cindex integers, 16-bit
3659 @cindex numbers, 16-bit
3660 @cindex sixteen bit integers
3661 This expects zero or more @var{expressions}, and emits
3662 a 16 bit number for each.
3665 This directive is a synonym for @samp{.short}; depending on the target
3666 architecture, it may also be a synonym for @samp{.word}.
3670 This directive is a synonym for @samp{.short}.
3673 This directive is a synonym for both @samp{.short} and @samp{.word}.
3678 @section @code{.ident}
3680 @cindex @code{ident} directive
3681 This directive is used by some assemblers to place tags in object files.
3682 @code{@value{AS}} simply accepts the directive for source-file
3683 compatibility with such assemblers, but does not actually emit anything
3687 @section @code{.if @var{absolute expression}}
3689 @cindex conditional assembly
3690 @cindex @code{if} directive
3691 @code{.if} marks the beginning of a section of code which is only
3692 considered part of the source program being assembled if the argument
3693 (which must be an @var{absolute expression}) is non-zero. The end of
3694 the conditional section of code must be marked by @code{.endif}
3695 (@pxref{Endif,,@code{.endif}}); optionally, you may include code for the
3696 alternative condition, flagged by @code{.else} (@pxref{Else,,@code{.else}}).
3698 The following variants of @code{.if} are also supported:
3700 @cindex @code{ifdef} directive
3701 @item .ifdef @var{symbol}
3702 Assembles the following section of code if the specified @var{symbol}
3705 @cindex @code{ifc} directive
3706 @item .ifc @var{string1},@var{string2}
3707 Assembles the following section of code if the two strings are the same. The
3708 strings may be optionally quoted with single quotes. If they are not quoted,
3709 the first string stops at the first comma, and the second string stops at the
3710 end of the line. Strings which contain whitespace should be quoted. The
3711 string comparison is case sensitive.
3713 @cindex @code{ifeq} directive
3714 @item .ifeq @var{absolute expression}
3715 Assembles the following section of code if the argument is zero.
3717 @cindex @code{ifeqs} directive
3718 @item .ifeqs @var{string1},@var{string2}
3719 Another form of @code{.ifc}. The strings must be quoted using double quotes.
3721 @cindex @code{ifge} directive
3722 @item .ifge @var{absolute expression}
3723 Assembles the following section of code if the argument is greater than or
3726 @cindex @code{ifgt} directive
3727 @item .ifgt @var{absolute expression}
3728 Assembles the following section of code if the argument is greater than zero.
3730 @cindex @code{ifle} directive
3731 @item .ifle @var{absolute expression}
3732 Assembles the following section of code if the argument is less than or equal
3735 @cindex @code{iflt} directive
3736 @item .iflt @var{absolute expression}
3737 Assembles the following section of code if the argument is less than zero.
3739 @cindex @code{ifnc} directive
3740 @item .ifnc @var{string1},@var{string2}.
3741 Like @code{.ifc}, but the sense of the test is reversed: this assembles the
3742 following section of code if the two strings are not the same.
3744 @cindex @code{ifndef} directive
3745 @cindex @code{ifnotdef} directive
3746 @item .ifndef @var{symbol}
3747 @itemx .ifnotdef @var{symbol}
3748 Assembles the following section of code if the specified @var{symbol}
3749 has not been defined. Both spelling variants are equivalent.
3751 @cindex @code{ifne} directive
3752 @item .ifne @var{absolute expression}
3753 Assembles the following section of code if the argument is not equal to zero
3754 (in other words, this is equivalent to @code{.if}).
3756 @cindex @code{ifnes} directive
3757 @item .ifnes @var{string1},@var{string2}
3758 Like @code{.ifeqs}, but the sense of the test is reversed: this assembles the
3759 following section of code if the two strings are not the same.
3763 @section @code{.include "@var{file}"}
3765 @cindex @code{include} directive
3766 @cindex supporting files, including
3767 @cindex files, including
3768 This directive provides a way to include supporting files at specified
3769 points in your source program. The code from @var{file} is assembled as
3770 if it followed the point of the @code{.include}; when the end of the
3771 included file is reached, assembly of the original file continues. You
3772 can control the search paths used with the @samp{-I} command-line option
3773 (@pxref{Invoking,,Command-Line Options}). Quotation marks are required
3777 @section @code{.int @var{expressions}}
3779 @cindex @code{int} directive
3780 @cindex integers, 32-bit
3781 Expect zero or more @var{expressions}, of any section, separated by commas.
3782 For each expression, emit a number that, at run time, is the value of that
3783 expression. The byte order and bit size of the number depends on what kind
3784 of target the assembly is for.
3788 On the H8/500 and most forms of the H8/300, @code{.int} emits 16-bit
3789 integers. On the H8/300H and the Hitachi SH, however, @code{.int} emits
3795 @section @code{.irp @var{symbol},@var{values}}@dots{}
3797 @cindex @code{irp} directive
3798 Evaluate a sequence of statements assigning different values to @var{symbol}.
3799 The sequence of statements starts at the @code{.irp} directive, and is
3800 terminated by an @code{.endr} directive. For each @var{value}, @var{symbol} is
3801 set to @var{value}, and the sequence of statements is assembled. If no
3802 @var{value} is listed, the sequence of statements is assembled once, with
3803 @var{symbol} set to the null string. To refer to @var{symbol} within the
3804 sequence of statements, use @var{\symbol}.
3806 For example, assembling
3814 is equivalent to assembling
3823 @section @code{.irpc @var{symbol},@var{values}}@dots{}
3825 @cindex @code{irpc} directive
3826 Evaluate a sequence of statements assigning different values to @var{symbol}.
3827 The sequence of statements starts at the @code{.irpc} directive, and is
3828 terminated by an @code{.endr} directive. For each character in @var{value},
3829 @var{symbol} is set to the character, and the sequence of statements is
3830 assembled. If no @var{value} is listed, the sequence of statements is
3831 assembled once, with @var{symbol} set to the null string. To refer to
3832 @var{symbol} within the sequence of statements, use @var{\symbol}.
3834 For example, assembling
3842 is equivalent to assembling
3851 @section @code{.lcomm @var{symbol} , @var{length}}
3853 @cindex @code{lcomm} directive
3854 @cindex local common symbols
3855 @cindex symbols, local common
3856 Reserve @var{length} (an absolute expression) bytes for a local common
3857 denoted by @var{symbol}. The section and value of @var{symbol} are
3858 those of the new local common. The addresses are allocated in the bss
3859 section, so that at run-time the bytes start off zeroed. @var{Symbol}
3860 is not declared global (@pxref{Global,,@code{.global}}), so is normally
3861 not visible to @code{@value{LD}}.
3864 Some targets permit a third argument to be used with @code{.lcomm}. This
3865 argument specifies the desired alignment of the symbol in the bss section.
3869 The syntax for @code{.lcomm} differs slightly on the HPPA. The syntax is
3870 @samp{@var{symbol} .lcomm, @var{length}}; @var{symbol} is optional.
3874 @section @code{.lflags}
3876 @cindex @code{lflags} directive (ignored)
3877 @code{@value{AS}} accepts this directive, for compatibility with other
3878 assemblers, but ignores it.
3880 @ifclear no-line-dir
3882 @section @code{.line @var{line-number}}
3884 @cindex @code{line} directive
3888 @section @code{.ln @var{line-number}}
3890 @cindex @code{ln} directive
3892 @cindex logical line number
3894 Change the logical line number. @var{line-number} must be an absolute
3895 expression. The next line has that logical line number. Therefore any other
3896 statements on the current line (after a statement separator character) are
3897 reported as on logical line number @var{line-number} @minus{} 1. One day
3898 @code{@value{AS}} will no longer support this directive: it is recognized only
3899 for compatibility with existing assembler programs.
3903 @emph{Warning:} In the AMD29K configuration of @value{AS}, this command is
3904 not available; use the synonym @code{.ln} in that context.
3909 @ifclear no-line-dir
3910 Even though this is a directive associated with the @code{a.out} or
3911 @code{b.out} object-code formats, @code{@value{AS}} still recognizes it
3912 when producing COFF output, and treats @samp{.line} as though it
3913 were the COFF @samp{.ln} @emph{if} it is found outside a
3914 @code{.def}/@code{.endef} pair.
3916 Inside a @code{.def}, @samp{.line} is, instead, one of the directives
3917 used by compilers to generate auxiliary symbol information for
3922 @section @code{.linkonce [@var{type}]}
3924 @cindex @code{linkonce} directive
3925 @cindex common sections
3926 Mark the current section so that the linker only includes a single copy of it.
3927 This may be used to include the same section in several different object files,
3928 but ensure that the linker will only include it once in the final output file.
3929 The @code{.linkonce} pseudo-op must be used for each instance of the section.
3930 Duplicate sections are detected based on the section name, so it should be
3933 This directive is only supported by a few object file formats; as of this
3934 writing, the only object file format which supports it is the Portable
3935 Executable format used on Windows NT.
3937 The @var{type} argument is optional. If specified, it must be one of the
3938 following strings. For example:
3942 Not all types may be supported on all object file formats.
3946 Silently discard duplicate sections. This is the default.
3949 Warn if there are duplicate sections, but still keep only one copy.
3952 Warn if any of the duplicates have different sizes.
3955 Warn if any of the duplicates do not have exactly the same contents.
3959 @section @code{.ln @var{line-number}}
3961 @cindex @code{ln} directive
3962 @ifclear no-line-dir
3963 @samp{.ln} is a synonym for @samp{.line}.
3966 Tell @code{@value{AS}} to change the logical line number. @var{line-number}
3967 must be an absolute expression. The next line has that logical
3968 line number, so any other statements on the current line (after a
3969 statement separator character @code{;}) are reported as on logical
3970 line number @var{line-number} @minus{} 1.
3973 This directive is accepted, but ignored, when @code{@value{AS}} is
3974 configured for @code{b.out}; its effect is only associated with COFF
3980 @section @code{.mri @var{val}}
3982 @cindex @code{mri} directive
3983 @cindex MRI mode, temporarily
3984 If @var{val} is non-zero, this tells @code{@value{AS}} to enter MRI mode. If
3985 @var{val} is zero, this tells @code{@value{AS}} to exit MRI mode. This change
3986 affects code assembled until the next @code{.mri} directive, or until the end
3987 of the file. @xref{M, MRI mode, MRI mode}.
3990 @section @code{.list}
3992 @cindex @code{list} directive
3993 @cindex listing control, turning on
3994 Control (in conjunction with the @code{.nolist} directive) whether or
3995 not assembly listings are generated. These two directives maintain an
3996 internal counter (which is zero initially). @code{.list} increments the
3997 counter, and @code{.nolist} decrements it. Assembly listings are
3998 generated whenever the counter is greater than zero.
4000 By default, listings are disabled. When you enable them (with the
4001 @samp{-a} command line option; @pxref{Invoking,,Command-Line Options}),
4002 the initial value of the listing counter is one.
4005 @section @code{.long @var{expressions}}
4007 @cindex @code{long} directive
4008 @code{.long} is the same as @samp{.int}, @pxref{Int,,@code{.int}}.
4011 @c no one seems to know what this is for or whether this description is
4012 @c what it really ought to do
4014 @section @code{.lsym @var{symbol}, @var{expression}}
4016 @cindex @code{lsym} directive
4017 @cindex symbol, not referenced in assembly
4018 @code{.lsym} creates a new symbol named @var{symbol}, but does not put it in
4019 the hash table, ensuring it cannot be referenced by name during the
4020 rest of the assembly. This sets the attributes of the symbol to be
4021 the same as the expression value:
4023 @var{other} = @var{descriptor} = 0
4024 @var{type} = @r{(section of @var{expression})}
4025 @var{value} = @var{expression}
4028 The new symbol is not flagged as external.
4032 @section @code{.macro}
4035 The commands @code{.macro} and @code{.endm} allow you to define macros that
4036 generate assembly output. For example, this definition specifies a macro
4037 @code{sum} that puts a sequence of numbers into memory:
4040 .macro sum from=0, to=5
4049 With that definition, @samp{SUM 0,5} is equivalent to this assembly input:
4061 @item .macro @var{macname}
4062 @itemx .macro @var{macname} @var{macargs} @dots{}
4063 @cindex @code{macro} directive
4064 Begin the definition of a macro called @var{macname}. If your macro
4065 definition requires arguments, specify their names after the macro name,
4066 separated by commas or spaces. You can supply a default value for any
4067 macro argument by following the name with @samp{=@var{deflt}}. For
4068 example, these are all valid @code{.macro} statements:
4072 Begin the definition of a macro called @code{comm}, which takes no
4075 @item .macro plus1 p, p1
4076 @itemx .macro plus1 p p1
4077 Either statement begins the definition of a macro called @code{plus1},
4078 which takes two arguments; within the macro definition, write
4079 @samp{\p} or @samp{\p1} to evaluate the arguments.
4081 @item .macro reserve_str p1=0 p2
4082 Begin the definition of a macro called @code{reserve_str}, with two
4083 arguments. The first argument has a default value, but not the second.
4084 After the definition is complete, you can call the macro either as
4085 @samp{reserve_str @var{a},@var{b}} (with @samp{\p1} evaluating to
4086 @var{a} and @samp{\p2} evaluating to @var{b}), or as @samp{reserve_str
4087 ,@var{b}} (with @samp{\p1} evaluating as the default, in this case
4088 @samp{0}, and @samp{\p2} evaluating to @var{b}).
4091 When you call a macro, you can specify the argument values either by
4092 position, or by keyword. For example, @samp{sum 9,17} is equivalent to
4093 @samp{sum to=17, from=9}.
4096 @cindex @code{endm} directive
4097 Mark the end of a macro definition.
4100 @cindex @code{exitm} directive
4101 Exit early from the current macro definition.
4103 @cindex number of macros executed
4104 @cindex macros, count executed
4106 @code{@value{AS}} maintains a counter of how many macros it has
4107 executed in this pseudo-variable; you can copy that number to your
4108 output with @samp{\@@}, but @emph{only within a macro definition}.
4111 @item LOCAL @var{name} [ , @dots{} ]
4112 @emph{Warning: @code{LOCAL} is only available if you select ``alternate
4113 macro syntax'' with @samp{-a} or @samp{--alternate}.} @xref{Alternate,,
4114 Alternate macro syntax}.
4116 Generate a string replacement for each of the @var{name} arguments, and
4117 replace any instances of @var{name} in each macro expansion. The
4118 replacement string is unique in the assembly, and different for each
4119 separate macro expansion. @code{LOCAL} allows you to write macros that
4120 define symbols, without fear of conflict between separate macro expansions.
4125 @section @code{.nolist}
4127 @cindex @code{nolist} directive
4128 @cindex listing control, turning off
4129 Control (in conjunction with the @code{.list} directive) whether or
4130 not assembly listings are generated. These two directives maintain an
4131 internal counter (which is zero initially). @code{.list} increments the
4132 counter, and @code{.nolist} decrements it. Assembly listings are
4133 generated whenever the counter is greater than zero.
4136 @section @code{.octa @var{bignums}}
4138 @c FIXME: double size emitted for "octa" on i960, others? Or warn?
4139 @cindex @code{octa} directive
4140 @cindex integer, 16-byte
4141 @cindex sixteen byte integer
4142 This directive expects zero or more bignums, separated by commas. For each
4143 bignum, it emits a 16-byte integer.
4145 The term ``octa'' comes from contexts in which a ``word'' is two bytes;
4146 hence @emph{octa}-word for 16 bytes.
4149 @section @code{.org @var{new-lc} , @var{fill}}
4151 @cindex @code{org} directive
4152 @cindex location counter, advancing
4153 @cindex advancing location counter
4154 @cindex current address, advancing
4155 Advance the location counter of the current section to
4156 @var{new-lc}. @var{new-lc} is either an absolute expression or an
4157 expression with the same section as the current subsection. That is,
4158 you can't use @code{.org} to cross sections: if @var{new-lc} has the
4159 wrong section, the @code{.org} directive is ignored. To be compatible
4160 with former assemblers, if the section of @var{new-lc} is absolute,
4161 @code{@value{AS}} issues a warning, then pretends the section of @var{new-lc}
4162 is the same as the current subsection.
4164 @code{.org} may only increase the location counter, or leave it
4165 unchanged; you cannot use @code{.org} to move the location counter
4168 @c double negative used below "not undefined" because this is a specific
4169 @c reference to "undefined" (as SEG_UNKNOWN is called in this manual)
4170 @c section. doc@cygnus.com 18feb91
4171 Because @code{@value{AS}} tries to assemble programs in one pass, @var{new-lc}
4172 may not be undefined. If you really detest this restriction we eagerly await
4173 a chance to share your improved assembler.
4175 Beware that the origin is relative to the start of the section, not
4176 to the start of the subsection. This is compatible with other
4177 people's assemblers.
4179 When the location counter (of the current subsection) is advanced, the
4180 intervening bytes are filled with @var{fill} which should be an
4181 absolute expression. If the comma and @var{fill} are omitted,
4182 @var{fill} defaults to zero.
4185 @section @code{.p2align[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
4187 @cindex padding the location counter given a power of two
4188 @cindex @code{p2align} directive
4189 Pad the location counter (in the current subsection) to a particular
4190 storage boundary. The first expression (which must be absolute) is the
4191 number of low-order zero bits the location counter must have after
4192 advancement. For example @samp{.p2align 3} advances the location
4193 counter until it a multiple of 8. If the location counter is already a
4194 multiple of 8, no change is needed.
4196 The second expression (also absolute) gives the fill value to be stored in the
4197 padding bytes. It (and the comma) may be omitted. If it is omitted, the
4198 padding bytes are normally zero. However, on some systems, if the section is
4199 marked as containing code and the fill value is omitted, the space is filled
4200 with no-op instructions.
4202 The third expression is also absolute, and is also optional. If it is present,
4203 it is the maximum number of bytes that should be skipped by this alignment
4204 directive. If doing the alignment would require skipping more bytes than the
4205 specified maximum, then the alignment is not done at all. You can omit the
4206 fill value (the second argument) entirely by simply using two commas after the
4207 required alignment; this can be useful if you want the alignment to be filled
4208 with no-op instructions when appropriate.
4210 @cindex @code{p2alignw} directive
4211 @cindex @code{p2alignl} directive
4212 The @code{.p2alignw} and @code{.p2alignl} directives are variants of the
4213 @code{.p2align} directive. The @code{.p2alignw} directive treats the fill
4214 pattern as a two byte word value. The @code{.p2alignl} directives treats the
4215 fill pattern as a four byte longword value. For example, @code{.p2alignw
4216 2,0x368d} will align to a multiple of 4. If it skips two bytes, they will be
4217 filled in with the value 0x368d (the exact placement of the bytes depends upon
4218 the endianness of the processor). If it skips 1 or 3 bytes, the fill value is
4222 @section @code{.print @var{string}}
4224 @cindex @code{print} directive
4225 @code{@value{AS}} will print @var{string} on the standard output during
4226 assembly. You must put @var{string} in double quotes.
4229 @section @code{.psize @var{lines} , @var{columns}}
4231 @cindex @code{psize} directive
4232 @cindex listing control: paper size
4233 @cindex paper size, for listings
4234 Use this directive to declare the number of lines---and, optionally, the
4235 number of columns---to use for each page, when generating listings.
4237 If you do not use @code{.psize}, listings use a default line-count
4238 of 60. You may omit the comma and @var{columns} specification; the
4239 default width is 200 columns.
4241 @code{@value{AS}} generates formfeeds whenever the specified number of
4242 lines is exceeded (or whenever you explicitly request one, using
4245 If you specify @var{lines} as @code{0}, no formfeeds are generated save
4246 those explicitly specified with @code{.eject}.
4249 @section @code{.purgem @var{name}}
4251 @cindex @code{purgem} directive
4252 Undefine the macro @var{name}, so that later uses of the string will not be
4253 expanded. @xref{Macro}.
4256 @section @code{.quad @var{bignums}}
4258 @cindex @code{quad} directive
4259 @code{.quad} expects zero or more bignums, separated by commas. For
4260 each bignum, it emits
4262 an 8-byte integer. If the bignum won't fit in 8 bytes, it prints a
4263 warning message; and just takes the lowest order 8 bytes of the bignum.
4264 @cindex eight-byte integer
4265 @cindex integer, 8-byte
4267 The term ``quad'' comes from contexts in which a ``word'' is two bytes;
4268 hence @emph{quad}-word for 8 bytes.
4271 a 16-byte integer. If the bignum won't fit in 16 bytes, it prints a
4272 warning message; and just takes the lowest order 16 bytes of the bignum.
4273 @cindex sixteen-byte integer
4274 @cindex integer, 16-byte
4278 @section @code{.rept @var{count}}
4280 @cindex @code{rept} directive
4281 Repeat the sequence of lines between the @code{.rept} directive and the next
4282 @code{.endr} directive @var{count} times.
4284 For example, assembling
4292 is equivalent to assembling
4301 @section @code{.sbttl "@var{subheading}"}
4303 @cindex @code{sbttl} directive
4304 @cindex subtitles for listings
4305 @cindex listing control: subtitle
4306 Use @var{subheading} as the title (third line, immediately after the
4307 title line) when generating assembly listings.
4309 This directive affects subsequent pages, as well as the current page if
4310 it appears within ten lines of the top of a page.
4314 @section @code{.scl @var{class}}
4316 @cindex @code{scl} directive
4317 @cindex symbol storage class (COFF)
4318 @cindex COFF symbol storage class
4319 Set the storage-class value for a symbol. This directive may only be
4320 used inside a @code{.def}/@code{.endef} pair. Storage class may flag
4321 whether a symbol is static or external, or it may record further
4322 symbolic debugging information.
4325 The @samp{.scl} directive is primarily associated with COFF output; when
4326 configured to generate @code{b.out} output format, @code{@value{AS}}
4327 accepts this directive but ignores it.
4332 @section @code{.section @var{name}}
4334 @cindex @code{section} directive
4335 @cindex named section
4336 Use the @code{.section} directive to assemble the following code into a section
4339 This directive is only supported for targets that actually support arbitrarily
4340 named sections; on @code{a.out} targets, for example, it is not accepted, even
4341 with a standard @code{a.out} section name.
4344 For COFF targets, the @code{.section} directive is used in one of the following
4347 .section @var{name}[, "@var{flags}"]
4348 .section @var{name}[, @var{subsegment}]
4351 If the optional argument is quoted, it is taken as flags to use for the
4352 section. Each flag is a single character. The following flags are recognized:
4355 bss section (uninitialized data)
4357 section is not loaded
4367 shared section (meaningful for PE targets)
4370 If no flags are specified, the default flags depend upon the section name. If
4371 the section name is not recognized, the default will be for the section to be
4372 loaded and writable.
4374 If the optional argument to the @code{.section} directive is not quoted, it is
4375 taken as a subsegment number (@pxref{Sub-Sections}).
4379 For ELF targets, the @code{.section} directive is used like this:
4381 .section @var{name}[, "@var{flags}"[, @@@var{type}]]
4383 The optional @var{flags} argument is a quoted string which may contain any
4384 combintion of the following characters:
4387 section is allocatable
4391 section is executable
4394 The optional @var{type} argument may contain one of the following constants:
4397 section contains data
4399 section does not contain data (i.e., section only occupies space)
4402 If no flags are specified, the default flags depend upon the section name. If
4403 the section name is not recognized, the default will be for the section to have
4404 none of the above flags: it will not be allocated in memory, nor writable, nor
4405 executable. The section will contain data.
4407 For ELF targets, the assembler supports another type of @code{.section}
4408 directive for compatibility with the Solaris assembler:
4410 .section "@var{name}"[, @var{flags}...]
4412 Note that the section name is quoted. There may be a sequence of comma
4416 section is allocatable
4420 section is executable
4425 @section @code{.set @var{symbol}, @var{expression}}
4427 @cindex @code{set} directive
4428 @cindex symbol value, setting
4429 Set the value of @var{symbol} to @var{expression}. This
4430 changes @var{symbol}'s value and type to conform to
4431 @var{expression}. If @var{symbol} was flagged as external, it remains
4432 flagged (@pxref{Symbol Attributes}).
4434 You may @code{.set} a symbol many times in the same assembly.
4436 If you @code{.set} a global symbol, the value stored in the object
4437 file is the last value stored into it.
4440 The syntax for @code{set} on the HPPA is
4441 @samp{@var{symbol} .set @var{expression}}.
4445 @section @code{.short @var{expressions}}
4447 @cindex @code{short} directive
4449 @code{.short} is normally the same as @samp{.word}.
4450 @xref{Word,,@code{.word}}.
4452 In some configurations, however, @code{.short} and @code{.word} generate
4453 numbers of different lengths; @pxref{Machine Dependencies}.
4457 @code{.short} is the same as @samp{.word}. @xref{Word,,@code{.word}}.
4460 This expects zero or more @var{expressions}, and emits
4461 a 16 bit number for each.
4466 @section @code{.single @var{flonums}}
4468 @cindex @code{single} directive
4469 @cindex floating point numbers (single)
4470 This directive assembles zero or more flonums, separated by commas. It
4471 has the same effect as @code{.float}.
4473 The exact kind of floating point numbers emitted depends on how
4474 @code{@value{AS}} is configured. @xref{Machine Dependencies}.
4478 On the @value{TARGET} family, @code{.single} emits 32-bit floating point
4479 numbers in @sc{ieee} format.
4485 @section @code{.size}
4487 @cindex @code{size} directive
4488 This directive is generated by compilers to include auxiliary debugging
4489 information in the symbol table. It is only permitted inside
4490 @code{.def}/@code{.endef} pairs.
4493 @samp{.size} is only meaningful when generating COFF format output; when
4494 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
4500 @section @code{.sleb128 @var{expressions}}
4502 @cindex @code{sleb128} directive
4503 @var{sleb128} stands for ``signed little endian base 128.'' This is a
4504 compact, variable length representation of numbers used by the DWARF
4505 symbolic debugging format. @xref{Uleb128,@code{.uleb128}}.
4507 @ifclear no-space-dir
4509 @section @code{.skip @var{size} , @var{fill}}
4511 @cindex @code{skip} directive
4512 @cindex filling memory
4513 This directive emits @var{size} bytes, each of value @var{fill}. Both
4514 @var{size} and @var{fill} are absolute expressions. If the comma and
4515 @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same as
4519 @section @code{.space @var{size} , @var{fill}}
4521 @cindex @code{space} directive
4522 @cindex filling memory
4523 This directive emits @var{size} bytes, each of value @var{fill}. Both
4524 @var{size} and @var{fill} are absolute expressions. If the comma
4525 and @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same
4530 @emph{Warning:} @code{.space} has a completely different meaning for HPPA
4531 targets; use @code{.block} as a substitute. See @cite{HP9000 Series 800
4532 Assembly Language Reference Manual} (HP 92432-90001) for the meaning of the
4533 @code{.space} directive. @xref{HPPA Directives,,HPPA Assembler Directives},
4542 @section @code{.space}
4543 @cindex @code{space} directive
4545 On the AMD 29K, this directive is ignored; it is accepted for
4546 compatibility with other AMD 29K assemblers.
4549 @emph{Warning:} In most versions of the @sc{gnu} assembler, the directive
4550 @code{.space} has the effect of @code{.block} @xref{Machine Dependencies}.
4556 @section @code{.stabd, .stabn, .stabs}
4558 @cindex symbolic debuggers, information for
4559 @cindex @code{stab@var{x}} directives
4560 There are three directives that begin @samp{.stab}.
4561 All emit symbols (@pxref{Symbols}), for use by symbolic debuggers.
4562 The symbols are not entered in the @code{@value{AS}} hash table: they
4563 cannot be referenced elsewhere in the source file.
4564 Up to five fields are required:
4568 This is the symbol's name. It may contain any character except
4569 @samp{\000}, so is more general than ordinary symbol names. Some
4570 debuggers used to code arbitrarily complex structures into symbol names
4574 An absolute expression. The symbol's type is set to the low 8 bits of
4575 this expression. Any bit pattern is permitted, but @code{@value{LD}}
4576 and debuggers choke on silly bit patterns.
4579 An absolute expression. The symbol's ``other'' attribute is set to the
4580 low 8 bits of this expression.
4583 An absolute expression. The symbol's descriptor is set to the low 16
4584 bits of this expression.
4587 An absolute expression which becomes the symbol's value.
4590 If a warning is detected while reading a @code{.stabd}, @code{.stabn},
4591 or @code{.stabs} statement, the symbol has probably already been created;
4592 you get a half-formed symbol in your object file. This is
4593 compatible with earlier assemblers!
4596 @cindex @code{stabd} directive
4597 @item .stabd @var{type} , @var{other} , @var{desc}
4599 The ``name'' of the symbol generated is not even an empty string.
4600 It is a null pointer, for compatibility. Older assemblers used a
4601 null pointer so they didn't waste space in object files with empty
4604 The symbol's value is set to the location counter,
4605 relocatably. When your program is linked, the value of this symbol
4606 is the address of the location counter when the @code{.stabd} was
4609 @cindex @code{stabn} directive
4610 @item .stabn @var{type} , @var{other} , @var{desc} , @var{value}
4611 The name of the symbol is set to the empty string @code{""}.
4613 @cindex @code{stabs} directive
4614 @item .stabs @var{string} , @var{type} , @var{other} , @var{desc} , @var{value}
4615 All five fields are specified.
4621 @section @code{.string} "@var{str}"
4623 @cindex string, copying to object file
4624 @cindex @code{string} directive
4626 Copy the characters in @var{str} to the object file. You may specify more than
4627 one string to copy, separated by commas. Unless otherwise specified for a
4628 particular machine, the assembler marks the end of each string with a 0 byte.
4629 You can use any of the escape sequences described in @ref{Strings,,Strings}.
4632 @section @code{.struct @var{expression}}
4634 @cindex @code{struct} directive
4635 Switch to the absolute section, and set the section offset to @var{expression},
4636 which must be an absolute expression. You might use this as follows:
4645 This would define the symbol @code{field1} to have the value 0, the symbol
4646 @code{field2} to have the value 4, and the symbol @code{field3} to have the
4647 value 8. Assembly would be left in the absolute section, and you would need to
4648 use a @code{.section} directive of some sort to change to some other section
4649 before further assembly.
4653 @section @code{.symver}
4654 @cindex @code{symver} directive
4655 @cindex symbol versioning
4656 @cindex versions of symbols
4657 Use the @code{.symver} directive to bind symbols to specific version nodes
4658 within a source file. This is only supported on ELF platforms, and is
4659 typically used when assembling files to be linked into a shared library.
4660 There are cases where it may make sense to use this in objects to be bound
4661 into an application itself so as to override a versioned symbol from a
4664 For ELF targets, the @code{.symver} directive is used like this:
4666 .symver @var{name}, @var{name2@@nodename}
4668 In this case, the symbol @var{name} must exist and be defined within the file
4669 being assembled. The @code{.versym} directive effectively creates a symbol
4670 alias with the name @var{name2@@nodename}, and in fact the main reason that we
4671 just don't try and create a regular alias is that the @var{@@} character isn't
4672 permitted in symbol names. The @var{name2} part of the name is the actual name
4673 of the symbol by which it will be externally referenced. The name @var{name}
4674 itself is merely a name of convenience that is used so that it is possible to
4675 have definitions for multiple versions of a function within a single source
4676 file, and so that the compiler can unambiguously know which version of a
4677 function is being mentioned. The @var{nodename} portion of the alias should be
4678 the name of a node specified in the version script supplied to the linker when
4679 building a shared library. If you are attempting to override a versioned
4680 symbol from a shared library, then @var{nodename} should correspond to the
4681 nodename of the symbol you are trying to override.
4686 @section @code{.tag @var{structname}}
4688 @cindex COFF structure debugging
4689 @cindex structure debugging, COFF
4690 @cindex @code{tag} directive
4691 This directive is generated by compilers to include auxiliary debugging
4692 information in the symbol table. It is only permitted inside
4693 @code{.def}/@code{.endef} pairs. Tags are used to link structure
4694 definitions in the symbol table with instances of those structures.
4697 @samp{.tag} is only used when generating COFF format output; when
4698 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
4704 @section @code{.text @var{subsection}}
4706 @cindex @code{text} directive
4707 Tells @code{@value{AS}} to assemble the following statements onto the end of
4708 the text subsection numbered @var{subsection}, which is an absolute
4709 expression. If @var{subsection} is omitted, subsection number zero
4713 @section @code{.title "@var{heading}"}
4715 @cindex @code{title} directive
4716 @cindex listing control: title line
4717 Use @var{heading} as the title (second line, immediately after the
4718 source file name and pagenumber) when generating assembly listings.
4720 This directive affects subsequent pages, as well as the current page if
4721 it appears within ten lines of the top of a page.
4725 @section @code{.type @var{int}}
4727 @cindex COFF symbol type
4728 @cindex symbol type, COFF
4729 @cindex @code{type} directive
4730 This directive, permitted only within @code{.def}/@code{.endef} pairs,
4731 records the integer @var{int} as the type attribute of a symbol table entry.
4734 @samp{.type} is associated only with COFF format output; when
4735 @code{@value{AS}} is configured for @code{b.out} output, it accepts this
4736 directive but ignores it.
4742 @section @code{.val @var{addr}}
4744 @cindex @code{val} directive
4745 @cindex COFF value attribute
4746 @cindex value attribute, COFF
4747 This directive, permitted only within @code{.def}/@code{.endef} pairs,
4748 records the address @var{addr} as the value attribute of a symbol table
4752 @samp{.val} is used only for COFF output; when @code{@value{AS}} is
4753 configured for @code{b.out}, it accepts this directive but ignores it.
4758 @section @code{.uleb128 @var{expressions}}
4760 @cindex @code{uleb128} directive
4761 @var{uleb128} stands for ``unsigned little endian base 128.'' This is a
4762 compact, variable length representation of numbers used by the DWARF
4763 symbolic debugging format. @xref{Sleb128,@code{.sleb128}}.
4767 @section @code{.internal}, @code{.hidden}, @code{.protected}
4768 @cindex @code{internal} directive
4769 @cindex @code{hidden} directive
4770 @cindex @code{protected} directive
4771 @cindex symbol visibility
4773 These directives can be used to set the visibility of a specified symbol. By
4774 default a symbol's visibility is set by its binding (local, global or weak),
4775 but these directives can be used to override that.
4777 A visibility of @code{protected} means that any references to the symbol from
4778 within the component that defines the symbol must be resolved to the definition
4779 in that component, even if a definition in another component would normally
4782 A visibility of @code{hidden} means that the symbol is not visible to other
4783 components. Such a symbol is always considered to be protected as well.
4785 A visibility of @code{internal} is the same as a visibility of @code{hidden},
4786 except that some extra, processor specific processing must also be performed
4789 For ELF targets, the directives are used like this:
4792 .internal @var{name}
4794 .protected @var{name}
4800 @section @code{.word @var{expressions}}
4802 @cindex @code{word} directive
4803 This directive expects zero or more @var{expressions}, of any section,
4804 separated by commas.
4807 For each expression, @code{@value{AS}} emits a 32-bit number.
4810 For each expression, @code{@value{AS}} emits a 16-bit number.
4815 The size of the number emitted, and its byte order,
4816 depend on what target computer the assembly is for.
4819 @c on amd29k, i960, sparc the "special treatment to support compilers" doesn't
4820 @c happen---32-bit addressability, period; no long/short jumps.
4821 @ifset DIFF-TBL-KLUGE
4822 @cindex difference tables altered
4823 @cindex altered difference tables
4825 @emph{Warning: Special Treatment to support Compilers}
4829 Machines with a 32-bit address space, but that do less than 32-bit
4830 addressing, require the following special treatment. If the machine of
4831 interest to you does 32-bit addressing (or doesn't require it;
4832 @pxref{Machine Dependencies}), you can ignore this issue.
4835 In order to assemble compiler output into something that works,
4836 @code{@value{AS}} occasionlly does strange things to @samp{.word} directives.
4837 Directives of the form @samp{.word sym1-sym2} are often emitted by
4838 compilers as part of jump tables. Therefore, when @code{@value{AS}} assembles a
4839 directive of the form @samp{.word sym1-sym2}, and the difference between
4840 @code{sym1} and @code{sym2} does not fit in 16 bits, @code{@value{AS}}
4841 creates a @dfn{secondary jump table}, immediately before the next label.
4842 This secondary jump table is preceded by a short-jump to the
4843 first byte after the secondary table. This short-jump prevents the flow
4844 of control from accidentally falling into the new table. Inside the
4845 table is a long-jump to @code{sym2}. The original @samp{.word}
4846 contains @code{sym1} minus the address of the long-jump to
4849 If there were several occurrences of @samp{.word sym1-sym2} before the
4850 secondary jump table, all of them are adjusted. If there was a
4851 @samp{.word sym3-sym4}, that also did not fit in sixteen bits, a
4852 long-jump to @code{sym4} is included in the secondary jump table,
4853 and the @code{.word} directives are adjusted to contain @code{sym3}
4854 minus the address of the long-jump to @code{sym4}; and so on, for as many
4855 entries in the original jump table as necessary.
4858 @emph{This feature may be disabled by compiling @code{@value{AS}} with the
4859 @samp{-DWORKING_DOT_WORD} option.} This feature is likely to confuse
4860 assembly language programmers.
4863 @c end DIFF-TBL-KLUGE
4866 @section Deprecated Directives
4868 @cindex deprecated directives
4869 @cindex obsolescent directives
4870 One day these directives won't work.
4871 They are included for compatibility with older assemblers.
4878 @node Machine Dependencies
4879 @chapter Machine Dependent Features
4881 @cindex machine dependencies
4882 The machine instruction sets are (almost by definition) different on
4883 each machine where @code{@value{AS}} runs. Floating point representations
4884 vary as well, and @code{@value{AS}} often supports a few additional
4885 directives or command-line options for compatibility with other
4886 assemblers on a particular platform. Finally, some versions of
4887 @code{@value{AS}} support special pseudo-instructions for branch
4890 This chapter discusses most of these differences, though it does not
4891 include details on any machine's instruction set. For details on that
4892 subject, see the hardware manufacturer's manual.
4896 * AMD29K-Dependent:: AMD 29K Dependent Features
4899 * ARC-Dependent:: ARC Dependent Features
4902 * ARM-Dependent:: ARM Dependent Features
4905 * D10V-Dependent:: D10V Dependent Features
4908 * D30V-Dependent:: D30V Dependent Features
4911 * H8/300-Dependent:: Hitachi H8/300 Dependent Features
4914 * H8/500-Dependent:: Hitachi H8/500 Dependent Features
4917 * HPPA-Dependent:: HPPA Dependent Features
4920 * i386-Dependent:: Intel 80386 Dependent Features
4923 * i960-Dependent:: Intel 80960 Dependent Features
4926 * M68K-Dependent:: M680x0 Dependent Features
4929 * MIPS-Dependent:: MIPS Dependent Features
4932 * SH-Dependent:: Hitachi SH Dependent Features
4935 * PJ-Dependent:: picoJava Dependent Features
4938 * Sparc-Dependent:: SPARC Dependent Features
4941 * V850-Dependent:: V850 Dependent Features
4944 * Z8000-Dependent:: Z8000 Dependent Features
4947 * Vax-Dependent:: VAX Dependent Features
4954 @c The following major nodes are *sections* in the GENERIC version, *chapters*
4955 @c in single-cpu versions. This is mainly achieved by @lowersections. There is a
4956 @c peculiarity: to preserve cross-references, there must be a node called
4957 @c "Machine Dependencies". Hence the conditional nodenames in each
4958 @c major node below. Node defaulting in makeinfo requires adjacency of
4959 @c node and sectioning commands; hence the repetition of @chapter BLAH
4960 @c in both conditional blocks.
4966 @chapter ARC Dependent Features
4969 @node Machine Dependencies
4970 @chapter ARC Dependent Features
4975 * ARC-Opts:: Options
4976 * ARC-Float:: Floating Point
4977 * ARC-Directives:: Sparc Machine Directives
4983 @cindex options for ARC
4985 @cindex architectures, ARC
4986 @cindex ARC architectures
4987 The ARC chip family includes several successive levels (or other
4988 variants) of chip, using the same core instruction set, but including
4989 a few additional instructions at each level.
4991 By default, @code{@value{AS}} assumes the core instruction set (ARC
4992 base). The @code{.cpu} pseudo-op is intended to be used to select
4996 @cindex @code{-mbig-endian} option (ARC)
4997 @cindex @code{-mlittle-endian} option (ARC)
4998 @cindex ARC big-endian output
4999 @cindex ARC little-endian output
5000 @cindex big-endian output, ARC
5001 @cindex little-endian output, ARC
5003 @itemx -mlittle-endian
5004 Any @sc{arc} configuration of @code{@value{AS}} can select big-endian or
5005 little-endian output at run time (unlike most other @sc{gnu} development
5006 tools, which must be configured for one or the other). Use
5007 @samp{-mbig-endian} to select big-endian output, and @samp{-mlittle-endian}
5012 @section Floating Point
5014 @cindex floating point, ARC (@sc{ieee})
5015 @cindex ARC floating point (@sc{ieee})
5016 The ARC cpu family currently does not have hardware floating point
5017 support. Software floating point support is provided by @code{GCC}
5018 and uses @sc{ieee} floating-point numbers.
5020 @node ARC-Directives
5021 @section ARC Machine Directives
5023 @cindex ARC machine directives
5024 @cindex machine directives, ARC
5025 The ARC version of @code{@value{AS}} supports the following additional
5030 @cindex @code{cpu} directive, SPARC
5031 This must be followed by the desired cpu.
5032 The ARC is intended to be customizable, @code{.cpu} is used to
5033 select the desired variant [though currently there are none].
5040 @include c-a29k.texi
5049 @node Machine Dependencies
5050 @chapter Machine Dependent Features
5052 The machine instruction sets are different on each Hitachi chip family,
5053 and there are also some syntax differences among the families. This
5054 chapter describes the specific @code{@value{AS}} features for each
5058 * H8/300-Dependent:: Hitachi H8/300 Dependent Features
5059 * H8/500-Dependent:: Hitachi H8/500 Dependent Features
5060 * SH-Dependent:: Hitachi SH Dependent Features
5067 @include c-d10v.texi
5071 @include c-d30v.texi
5075 @include c-h8300.texi
5079 @include c-h8500.texi
5083 @include c-hppa.texi
5087 @include c-i386.texi
5091 @include c-i960.texi
5096 @include c-m68k.texi
5100 @include c-mips.texi
5104 @include c-ns32k.texi
5116 @include c-sparc.texi
5128 @include c-v850.texi
5132 @c reverse effect of @down at top of generic Machine-Dep chapter
5136 @node Reporting Bugs
5137 @chapter Reporting Bugs
5138 @cindex bugs in assembler
5139 @cindex reporting bugs in assembler
5141 Your bug reports play an essential role in making @code{@value{AS}} reliable.
5143 Reporting a bug may help you by bringing a solution to your problem, or it may
5144 not. But in any case the principal function of a bug report is to help the
5145 entire community by making the next version of @code{@value{AS}} work better.
5146 Bug reports are your contribution to the maintenance of @code{@value{AS}}.
5148 In order for a bug report to serve its purpose, you must include the
5149 information that enables us to fix the bug.
5152 * Bug Criteria:: Have you found a bug?
5153 * Bug Reporting:: How to report bugs
5157 @section Have you found a bug?
5158 @cindex bug criteria
5160 If you are not sure whether you have found a bug, here are some guidelines:
5163 @cindex fatal signal
5164 @cindex assembler crash
5165 @cindex crash of assembler
5167 If the assembler gets a fatal signal, for any input whatever, that is a
5168 @code{@value{AS}} bug. Reliable assemblers never crash.
5170 @cindex error on valid input
5172 If @code{@value{AS}} produces an error message for valid input, that is a bug.
5174 @cindex invalid input
5176 If @code{@value{AS}} does not produce an error message for invalid input, that
5177 is a bug. However, you should note that your idea of ``invalid input'' might
5178 be our idea of ``an extension'' or ``support for traditional practice''.
5181 If you are an experienced user of assemblers, your suggestions for improvement
5182 of @code{@value{AS}} are welcome in any case.
5186 @section How to report bugs
5188 @cindex assembler bugs, reporting
5190 A number of companies and individuals offer support for @sc{gnu} products. If
5191 you obtained @code{@value{AS}} from a support organization, we recommend you
5192 contact that organization first.
5194 You can find contact information for many support companies and
5195 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
5198 In any event, we also recommend that you send bug reports for @code{@value{AS}}
5199 to @samp{bug-gnu-utils@@gnu.org}.
5201 The fundamental principle of reporting bugs usefully is this:
5202 @strong{report all the facts}. If you are not sure whether to state a
5203 fact or leave it out, state it!
5205 Often people omit facts because they think they know what causes the problem
5206 and assume that some details do not matter. Thus, you might assume that the
5207 name of a symbol you use in an example does not matter. Well, probably it does
5208 not, but one cannot be sure. Perhaps the bug is a stray memory reference which
5209 happens to fetch from the location where that name is stored in memory;
5210 perhaps, if the name were different, the contents of that location would fool
5211 the assembler into doing the right thing despite the bug. Play it safe and
5212 give a specific, complete example. That is the easiest thing for you to do,
5213 and the most helpful.
5215 Keep in mind that the purpose of a bug report is to enable us to fix the bug if
5216 it is new to us. Therefore, always write your bug reports on the assumption
5217 that the bug has not been reported previously.
5219 Sometimes people give a few sketchy facts and ask, ``Does this ring a
5220 bell?'' Those bug reports are useless, and we urge everyone to
5221 @emph{refuse to respond to them} except to chide the sender to report
5224 To enable us to fix the bug, you should include all these things:
5228 The version of @code{@value{AS}}. @code{@value{AS}} announces it if you start
5229 it with the @samp{--version} argument.
5231 Without this, we will not know whether there is any point in looking for
5232 the bug in the current version of @code{@value{AS}}.
5235 Any patches you may have applied to the @code{@value{AS}} source.
5238 The type of machine you are using, and the operating system name and
5242 What compiler (and its version) was used to compile @code{@value{AS}}---e.g.
5246 The command arguments you gave the assembler to assemble your example and
5247 observe the bug. To guarantee you will not omit something important, list them
5248 all. A copy of the Makefile (or the output from make) is sufficient.
5250 If we were to try to guess the arguments, we would probably guess wrong
5251 and then we might not encounter the bug.
5254 A complete input file that will reproduce the bug. If the bug is observed when
5255 the assembler is invoked via a compiler, send the assembler source, not the
5256 high level language source. Most compilers will produce the assembler source
5257 when run with the @samp{-S} option. If you are using @code{@value{GCC}}, use
5258 the options @samp{-v --save-temps}; this will save the assembler source in a
5259 file with an extension of @file{.s}, and also show you exactly how
5260 @code{@value{AS}} is being run.
5263 A description of what behavior you observe that you believe is
5264 incorrect. For example, ``It gets a fatal signal.''
5266 Of course, if the bug is that @code{@value{AS}} gets a fatal signal, then we
5267 will certainly notice it. But if the bug is incorrect output, we might not
5268 notice unless it is glaringly wrong. You might as well not give us a chance to
5271 Even if the problem you experience is a fatal signal, you should still say so
5272 explicitly. Suppose something strange is going on, such as, your copy of
5273 @code{@value{AS}} is out of synch, or you have encountered a bug in the C
5274 library on your system. (This has happened!) Your copy might crash and ours
5275 would not. If you told us to expect a crash, then when ours fails to crash, we
5276 would know that the bug was not happening for us. If you had not told us to
5277 expect a crash, then we would not be able to draw any conclusion from our
5281 If you wish to suggest changes to the @code{@value{AS}} source, send us context
5282 diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or @samp{-p}
5283 option. Always send diffs from the old file to the new file. If you even
5284 discuss something in the @code{@value{AS}} source, refer to it by context, not
5287 The line numbers in our development sources will not match those in your
5288 sources. Your line numbers would convey no useful information to us.
5291 Here are some things that are not necessary:
5295 A description of the envelope of the bug.
5297 Often people who encounter a bug spend a lot of time investigating
5298 which changes to the input file will make the bug go away and which
5299 changes will not affect it.
5301 This is often time consuming and not very useful, because the way we
5302 will find the bug is by running a single example under the debugger
5303 with breakpoints, not by pure deduction from a series of examples.
5304 We recommend that you save your time for something else.
5306 Of course, if you can find a simpler example to report @emph{instead}
5307 of the original one, that is a convenience for us. Errors in the
5308 output will be easier to spot, running under the debugger will take
5309 less time, and so on.
5311 However, simplification is not vital; if you do not want to do this,
5312 report the bug anyway and send us the entire test case you used.
5315 A patch for the bug.
5317 A patch for the bug does help us if it is a good one. But do not omit
5318 the necessary information, such as the test case, on the assumption that
5319 a patch is all we need. We might see problems with your patch and decide
5320 to fix the problem another way, or we might not understand it at all.
5322 Sometimes with a program as complicated as @code{@value{AS}} it is very hard to
5323 construct an example that will make the program follow a certain path through
5324 the code. If you do not send us the example, we will not be able to construct
5325 one, so we will not be able to verify that the bug is fixed.
5327 And if we cannot understand what bug you are trying to fix, or why your
5328 patch should be an improvement, we will not install it. A test case will
5329 help us to understand.
5332 A guess about what the bug is or what it depends on.
5334 Such guesses are usually wrong. Even we cannot guess right about such
5335 things without first using the debugger to find the facts.
5338 @node Acknowledgements
5339 @chapter Acknowledgements
5341 If you have contributed to @code{@value{AS}} and your name isn't listed here,
5342 it is not meant as a slight. We just don't know about it. Send mail to the
5343 maintainer, and we'll correct the situation. Currently
5345 the maintainer is Ken Raeburn (email address @code{raeburn@@cygnus.com}).
5347 Dean Elsner wrote the original @sc{gnu} assembler for the VAX.@footnote{Any
5350 Jay Fenlason maintained GAS for a while, adding support for GDB-specific debug
5351 information and the 68k series machines, most of the preprocessing pass, and
5352 extensive changes in @file{messages.c}, @file{input-file.c}, @file{write.c}.
5354 K. Richard Pixley maintained GAS for a while, adding various enhancements and
5355 many bug fixes, including merging support for several processors, breaking GAS
5356 up to handle multiple object file format back ends (including heavy rewrite,
5357 testing, an integration of the coff and b.out back ends), adding configuration
5358 including heavy testing and verification of cross assemblers and file splits
5359 and renaming, converted GAS to strictly ANSI C including full prototypes, added
5360 support for m680[34]0 and cpu32, did considerable work on i960 including a COFF
5361 port (including considerable amounts of reverse engineering), a SPARC opcode
5362 file rewrite, DECstation, rs6000, and hp300hpux host ports, updated ``know''
5363 assertions and made them work, much other reorganization, cleanup, and lint.
5365 Ken Raeburn wrote the high-level BFD interface code to replace most of the code
5366 in format-specific I/O modules.
5368 The original VMS support was contributed by David L. Kashtan. Eric Youngdale
5369 has done much work with it since.
5371 The Intel 80386 machine description was written by Eliot Dresselhaus.
5373 Minh Tran-Le at IntelliCorp contributed some AIX 386 support.
5375 The Motorola 88k machine description was contributed by Devon Bowen of Buffalo
5376 University and Torbjorn Granlund of the Swedish Institute of Computer Science.
5378 Keith Knowles at the Open Software Foundation wrote the original MIPS back end
5379 (@file{tc-mips.c}, @file{tc-mips.h}), and contributed Rose format support
5380 (which hasn't been merged in yet). Ralph Campbell worked with the MIPS code to
5381 support a.out format.
5383 Support for the Zilog Z8k and Hitachi H8/300 and H8/500 processors (tc-z8k,
5384 tc-h8300, tc-h8500), and IEEE 695 object file format (obj-ieee), was written by
5385 Steve Chamberlain of Cygnus Support. Steve also modified the COFF back end to
5386 use BFD for some low-level operations, for use with the H8/300 and AMD 29k
5389 John Gilmore built the AMD 29000 support, added @code{.include} support, and
5390 simplified the configuration of which versions accept which directives. He
5391 updated the 68k machine description so that Motorola's opcodes always produced
5392 fixed-size instructions (e.g. @code{jsr}), while synthetic instructions
5393 remained shrinkable (@code{jbsr}). John fixed many bugs, including true tested
5394 cross-compilation support, and one bug in relaxation that took a week and
5395 required the proverbial one-bit fix.
5397 Ian Lance Taylor of Cygnus Support merged the Motorola and MIT syntax for the
5398 68k, completed support for some COFF targets (68k, i386 SVR3, and SCO Unix),
5399 added support for MIPS ECOFF and ELF targets, wrote the initial RS/6000 and
5400 PowerPC assembler, and made a few other minor patches.
5402 Steve Chamberlain made @code{@value{AS}} able to generate listings.
5404 Hewlett-Packard contributed support for the HP9000/300.
5406 Jeff Law wrote GAS and BFD support for the native HPPA object format (SOM)
5407 along with a fairly extensive HPPA testsuite (for both SOM and ELF object
5408 formats). This work was supported by both the Center for Software Science at
5409 the University of Utah and Cygnus Support.
5411 Support for ELF format files has been worked on by Mark Eichin of Cygnus
5412 Support (original, incomplete implementation for SPARC), Pete Hoogenboom and
5413 Jeff Law at the University of Utah (HPPA mainly), Michael Meissner of the Open
5414 Software Foundation (i386 mainly), and Ken Raeburn of Cygnus Support (sparc,
5415 and some initial 64-bit support).
5417 Richard Henderson rewrote the Alpha assembler. Klaus Kaempf wrote GAS and BFD
5418 support for openVMS/Alpha.
5420 Several engineers at Cygnus Support have also provided many small bug fixes and
5421 configuration enhancements.
5423 Many others have contributed large or small bugfixes and enhancements. If
5424 you have contributed significant work and are not mentioned on this list, and
5425 want to be, let us know. Some of the history has been lost; we are not
5426 intentionally leaving anyone out.
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