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 ] [ --help ] [ -I @var{dir} ] [ -J ] [ -K ] [ -L ]
206 [ --keep-locals ] [ -o @var{objfile} ] [ -R ] [ --statistics ] [ -v ]
207 [ -version ] [ --version ] [ -W ] [ -w ] [ -x ] [ -Z ]
209 @c am29k has no machine-dependent assembler options
212 [ -mbig-endian | -mlittle-endian ]
215 [ -m[arm]1 | -m[arm]2 | -m[arm]250 | -m[arm]3 | -m[arm]6 | -m[arm]7[t][[d]m[i]] ]
216 [ -m[arm]v2 | -m[arm]v2a | -m[arm]v3 | -m[arm]v3m | -m[arm]v4 | -m[arm]v4t ]
218 [ -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu ]
220 [ -mapcs-32 | -mapcs-26 ]
225 @c start-sanitize-d30v
231 @c Hitachi family chips have no machine-dependent assembler options
234 @c HPPA has no machine-dependent assembler options (yet).
237 @c The order here is important. See c-sparc.texi.
238 [ -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
239 -Av8plus | -Av8plusa | -Av9 | -Av9a ]
240 [ -xarch=v8plus | -xarch=v8plusa ] [ -bump ] [ -32 | -64 ]
243 @c Z8000 has no machine-dependent assembler options
246 @c see md_parse_option in tc-i960.c
247 [ -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC ]
250 @c start-sanitize-m32rx
252 [ --m32rx | --[no-]warn-explicit-parallel-conflicts | --W[n]p ]
254 @c end-sanitize-m32rx
256 [ -l ] [ -m68000 | -m68010 | -m68020 | ... ]
259 [ -nocpp ] [ -EL ] [ -EB ] [ -G @var{num} ] [ -mcpu=@var{CPU} ]
260 [ -mips1 ] [ -mips2 ] [ -mips3 ] [ -m4650 ] [ -no-m4650 ]
261 [ --trap ] [ --break ]
262 [ --emulation=@var{name} ]
264 [ -- | @var{files} @dots{} ]
269 Turn on listings, in any of a variety of ways:
273 omit false conditionals
276 omit debugging directives
279 include high-level source
285 include macro expansions
288 omit forms processing
294 set the name of the listing file
297 You may combine these options; for example, use @samp{-aln} for assembly
298 listing without forms processing. The @samp{=file} option, if used, must be
299 the last one. By itself, @samp{-a} defaults to @samp{-ahls}.
302 Ignored. This option is accepted for script compatibility with calls to
305 @item --defsym @var{sym}=@var{value}
306 Define the symbol @var{sym} to be @var{value} before assembling the input file.
307 @var{value} must be an integer constant. As in C, a leading @samp{0x}
308 indicates a hexadecimal value, and a leading @samp{0} indicates an octal value.
311 ``fast''---skip whitespace and comment preprocessing (assume source is
315 Generate stabs debugging information for each assembler line. This
316 may help debugging assembler code, if the debugger can handle it.
319 Print a summary of the command line options and exit.
322 Add directory @var{dir} to the search list for @code{.include} directives.
325 Don't warn about signed overflow.
328 @ifclear DIFF-TBL-KLUGE
329 This option is accepted but has no effect on the @value{TARGET} family.
331 @ifset DIFF-TBL-KLUGE
332 Issue warnings when difference tables altered for long displacements.
337 Keep (in the symbol table) local symbols. On traditional a.out systems
338 these start with @samp{L}, but different systems have different local
341 @item -o @var{objfile}
342 Name the object-file output from @code{@value{AS}} @var{objfile}.
345 Fold the data section into the text section.
348 Print the maximum space (in bytes) and total time (in seconds) used by
351 @item --strip-local-absolute
352 Remove local absolute symbols from the outgoing symbol table.
356 Print the @code{as} version.
359 Print the @code{as} version and exit.
362 Suppress warning messages.
371 Generate an object file even after errors.
373 @item -- | @var{files} @dots{}
374 Standard input, or source files to assemble.
379 The following options are available when @value{AS} is configured for
384 @cindex ARC endianness
385 @cindex endianness, ARC
386 @cindex big endian output, ARC
388 Generate ``big endian'' format output.
390 @cindex little endian output, ARC
391 @item -mlittle-endian
392 Generate ``little endian'' format output.
398 The following options are available when @value{AS} is configured for the ARM
402 @item -m[arm]1 | -m[arm]2 | -m[arm]250 | -m[arm]3 | -m[arm]6 | -m[arm]7[t][[d]m] | -m[arm]v2 | -m[arm]v2a | -m[arm]v3 | -m[arm]v3m | -m[arm]v4 | -m[arm]v4t
403 Specify which variant of the ARM architecture is the target.
404 @item -mthumb | -mall
405 Enable or disable Thumb only instruction decoding.
406 @item -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu
407 Select which Floating Point architcture is the target.
408 @item -mapcs-32 | -mapcs-26
409 Select which procedure calling convention is in use.
411 Select either big-endian (-EB) or little-endian (-EL) output.
416 The following options are available when @value{AS} is configured for
419 @cindex D10V optimization
420 @cindex optimization, D10V
422 Optimize output by parallelizing instructions.
426 @c start-sanitize-d30v
428 The following options are available when @value{AS} is configured for a D30V
431 @cindex D30V optimization
432 @cindex optimization, D30V
434 Optimize output by parallelizing instructions.
438 Warn when nops are generated.
440 @cindex D30V nops after 32-bit multiply
442 Warn when a nop after a 32-bit multiply instruction is generated.
448 The following options are available when @value{AS} is configured for the
449 Intel 80960 processor.
452 @item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
453 Specify which variant of the 960 architecture is the target.
456 Add code to collect statistics about branches taken.
459 Do not alter compare-and-branch instructions for long displacements;
465 @c start-sanitize-m32rx
467 The following options are available when @value{AS} is configured for the
468 Mitsubishi M32R series.
473 Specify which processor in the M32R family is the target. The default
474 is normally the M32R, but this option changes it to the M32RX.
476 @item --warn-explicit-parallel-conflicts or --Wp
477 Produce warning messages when questionable parallel constructs are
480 @item --no-warn-explicit-parallel-conflicts or --Wnp
481 Do not produce warning messages when questionable parallel constructs are
486 @c end-sanitize-m32rx
489 The following options are available when @value{AS} is configured for the
490 Motorola 68000 series.
495 Shorten references to undefined symbols, to one word instead of two.
497 @item -m68000 | -m68008 | -m68010 | -m68020 | -m68030 | -m68040 | -m68060
498 @itemx | -m68302 | -m68331 | -m68332 | -m68333 | -m68340 | -mcpu32 | -m5200
499 Specify what processor in the 68000 family is the target. The default
500 is normally the 68020, but this can be changed at configuration time.
502 @item -m68881 | -m68882 | -mno-68881 | -mno-68882
503 The target machine does (or does not) have a floating-point coprocessor.
504 The default is to assume a coprocessor for 68020, 68030, and cpu32. Although
505 the basic 68000 is not compatible with the 68881, a combination of the
506 two can be specified, since it's possible to do emulation of the
507 coprocessor instructions with the main processor.
509 @item -m68851 | -mno-68851
510 The target machine does (or does not) have a memory-management
511 unit coprocessor. The default is to assume an MMU for 68020 and up.
517 The following options are available when @code{@value{AS}} is configured
518 for the SPARC architecture:
521 @item -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
522 @itemx -Av8plus | -Av8plusa | -Av9 | -Av9a
523 Explicitly select a variant of the SPARC architecture.
525 @samp{-Av8plus} and @samp{-Av8plusa} select a 32 bit environment.
526 @samp{-Av9} and @samp{-Av9a} select a 64 bit environment.
528 @samp{-Av8plusa} and @samp{-Av9a} enable the SPARC V9 instruction set with
529 UltraSPARC extensions.
531 @item -xarch=v8plus | -xarch=v8plusa
532 For compatibility with the Solaris v9 assembler. These options are
533 equivalent to -Av8plus and -Av8plusa, respectively.
536 Warn when the assembler switches to another architecture.
541 The following options are available when @value{AS} is configured for
546 This option sets the largest size of an object that can be referenced
547 implicitly with the @code{gp} register. It is only accepted for targets that
548 use ECOFF format, such as a DECstation running Ultrix. The default value is 8.
550 @cindex MIPS endianness
551 @cindex endianness, MIPS
552 @cindex big endian output, MIPS
554 Generate ``big endian'' format output.
556 @cindex little endian output, MIPS
558 Generate ``little endian'' format output.
564 Generate code for a particular MIPS Instruction Set Architecture level.
565 @samp{-mips1} corresponds to the @sc{r2000} and @sc{r3000} processors,
566 @samp{-mips2} to the @sc{r6000} processor, and @samp{-mips3} to the @sc{r4000}
571 Generate code for the MIPS @sc{r4650} chip. This tells the assembler to accept
572 the @samp{mad} and @samp{madu} instruction, and to not schedule @samp{nop}
573 instructions around accesses to the @samp{HI} and @samp{LO} registers.
574 @samp{-no-m4650} turns off this option.
576 @item -mcpu=@var{CPU}
577 Generate code for a particular MIPS cpu. This has little effect on the
578 assembler, but it is passed by @code{@value{GCC}}.
581 @item --emulation=@var{name}
582 This option causes @code{@value{AS}} to emulate @code{@value{AS}} configured
583 for some other target, in all respects, including output format (choosing
584 between ELF and ECOFF only), handling of pseudo-opcodes which may generate
585 debugging information or store symbol table information, and default
586 endianness. The available configuration names are: @samp{mipsecoff},
587 @samp{mipself}, @samp{mipslecoff}, @samp{mipsbecoff}, @samp{mipslelf},
588 @samp{mipsbelf}. The first two do not alter the default endianness from that
589 of the primary target for which the assembler was configured; the others change
590 the default to little- or big-endian as indicated by the @samp{b} or @samp{l}
591 in the name. Using @samp{-EB} or @samp{-EL} will override the endianness
592 selection in any case.
594 This option is currently supported only when the primary target
595 @code{@value{AS}} is configured for is a MIPS ELF or ECOFF target.
596 Furthermore, the primary target or others specified with
597 @samp{--enable-targets=@dots{}} at configuration time must include support for
598 the other format, if both are to be available. For example, the Irix 5
599 configuration includes support for both.
601 Eventually, this option will support more configurations, with more
602 fine-grained control over the assembler's behavior, and will be supported for
606 @code{@value{AS}} ignores this option. It is accepted for compatibility with
614 Control how to deal with multiplication overflow and division by zero.
615 @samp{--trap} or @samp{--no-break} (which are synonyms) take a trap exception
616 (and only work for Instruction Set Architecture level 2 and higher);
617 @samp{--break} or @samp{--no-trap} (also synonyms, and the default) take a
623 * Manual:: Structure of this Manual
624 * GNU Assembler:: The GNU Assembler
625 * Object Formats:: Object File Formats
626 * Command Line:: Command Line
627 * Input Files:: Input Files
628 * Object:: Output (Object) File
629 * Errors:: Error and Warning Messages
633 @section Structure of this Manual
635 @cindex manual, structure and purpose
636 This manual is intended to describe what you need to know to use
637 @sc{gnu} @code{@value{AS}}. We cover the syntax expected in source files, including
638 notation for symbols, constants, and expressions; the directives that
639 @code{@value{AS}} understands; and of course how to invoke @code{@value{AS}}.
642 We also cover special features in the @value{TARGET}
643 configuration of @code{@value{AS}}, including assembler directives.
646 This manual also describes some of the machine-dependent features of
647 various flavors of the assembler.
650 @cindex machine instructions (not covered)
651 On the other hand, this manual is @emph{not} intended as an introduction
652 to programming in assembly language---let alone programming in general!
653 In a similar vein, we make no attempt to introduce the machine
654 architecture; we do @emph{not} describe the instruction set, standard
655 mnemonics, registers or addressing modes that are standard to a
656 particular architecture.
658 You may want to consult the manufacturer's
659 machine architecture manual for this information.
663 For information on the H8/300 machine instruction set, see @cite{H8/300
664 Series Programming Manual} (Hitachi ADE--602--025). For the H8/300H,
665 see @cite{H8/300H Series Programming Manual} (Hitachi).
668 For information on the H8/500 machine instruction set, see @cite{H8/500
669 Series Programming Manual} (Hitachi M21T001).
672 For information on the Hitachi SH machine instruction set, see
673 @cite{SH-Microcomputer User's Manual} (Hitachi Micro Systems, Inc.).
676 For information on the Z8000 machine instruction set, see @cite{Z8000 CPU Technical Manual}
680 @c I think this is premature---doc@cygnus.com, 17jan1991
682 Throughout this manual, we assume that you are running @dfn{GNU},
683 the portable operating system from the @dfn{Free Software
684 Foundation, Inc.}. This restricts our attention to certain kinds of
685 computer (in particular, the kinds of computers that @sc{gnu} can run on);
686 once this assumption is granted examples and definitions need less
689 @code{@value{AS}} is part of a team of programs that turn a high-level
690 human-readable series of instructions into a low-level
691 computer-readable series of instructions. Different versions of
692 @code{@value{AS}} are used for different kinds of computer.
695 @c There used to be a section "Terminology" here, which defined
696 @c "contents", "byte", "word", and "long". Defining "word" to any
697 @c particular size is confusing when the .word directive may generate 16
698 @c bits on one machine and 32 bits on another; in general, for the user
699 @c version of this manual, none of these terms seem essential to define.
700 @c They were used very little even in the former draft of the manual;
701 @c this draft makes an effort to avoid them (except in names of
705 @section The GNU Assembler
707 @sc{gnu} @code{as} is really a family of assemblers.
709 This manual describes @code{@value{AS}}, a member of that family which is
710 configured for the @value{TARGET} architectures.
712 If you use (or have used) the @sc{gnu} assembler on one architecture, you
713 should find a fairly similar environment when you use it on another
714 architecture. Each version has much in common with the others,
715 including object file formats, most assembler directives (often called
716 @dfn{pseudo-ops}) and assembler syntax.@refill
718 @cindex purpose of @sc{gnu} assembler
719 @code{@value{AS}} is primarily intended to assemble the output of the
720 @sc{gnu} C compiler @code{@value{GCC}} for use by the linker
721 @code{@value{LD}}. Nevertheless, we've tried to make @code{@value{AS}}
722 assemble correctly everything that other assemblers for the same
723 machine would assemble.
725 Any exceptions are documented explicitly (@pxref{Machine Dependencies}).
728 @c This remark should appear in generic version of manual; assumption
729 @c here is that generic version sets M680x0.
730 This doesn't mean @code{@value{AS}} always uses the same syntax as another
731 assembler for the same architecture; for example, we know of several
732 incompatible versions of 680x0 assembly language syntax.
735 Unlike older assemblers, @code{@value{AS}} is designed to assemble a source
736 program in one pass of the source file. This has a subtle impact on the
737 @kbd{.org} directive (@pxref{Org,,@code{.org}}).
740 @section Object File Formats
742 @cindex object file format
743 The @sc{gnu} assembler can be configured to produce several alternative
744 object file formats. For the most part, this does not affect how you
745 write assembly language programs; but directives for debugging symbols
746 are typically different in different file formats. @xref{Symbol
747 Attributes,,Symbol Attributes}.
750 On the @value{TARGET}, @code{@value{AS}} is configured to produce
751 @value{OBJ-NAME} format object files.
753 @c The following should exhaust all configs that set MULTI-OBJ, ideally
755 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
756 @code{a.out} or COFF format object files.
759 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
760 @code{b.out} or COFF format object files.
763 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
764 SOM or ELF format object files.
769 @section Command Line
771 @cindex command line conventions
772 After the program name @code{@value{AS}}, the command line may contain
773 options and file names. Options may appear in any order, and may be
774 before, after, or between file names. The order of file names is
777 @cindex standard input, as input file
779 @file{--} (two hyphens) by itself names the standard input file
780 explicitly, as one of the files for @code{@value{AS}} to assemble.
782 @cindex options, command line
783 Except for @samp{--} any command line argument that begins with a
784 hyphen (@samp{-}) is an option. Each option changes the behavior of
785 @code{@value{AS}}. No option changes the way another option works. An
786 option is a @samp{-} followed by one or more letters; the case of
787 the letter is important. All options are optional.
789 Some options expect exactly one file name to follow them. The file
790 name may either immediately follow the option's letter (compatible
791 with older assemblers) or it may be the next command argument (@sc{gnu}
792 standard). These two command lines are equivalent:
795 @value{AS} -o my-object-file.o mumble.s
796 @value{AS} -omy-object-file.o mumble.s
803 @cindex source program
805 We use the phrase @dfn{source program}, abbreviated @dfn{source}, to
806 describe the program input to one run of @code{@value{AS}}. The program may
807 be in one or more files; how the source is partitioned into files
808 doesn't change the meaning of the source.
810 @c I added "con" prefix to "catenation" just to prove I can overcome my
811 @c APL training... doc@cygnus.com
812 The source program is a concatenation of the text in all the files, in the
815 Each time you run @code{@value{AS}} it assembles exactly one source
816 program. The source program is made up of one or more files.
817 (The standard input is also a file.)
819 You give @code{@value{AS}} a command line that has zero or more input file
820 names. The input files are read (from left file name to right). A
821 command line argument (in any position) that has no special meaning
822 is taken to be an input file name.
824 If you give @code{@value{AS}} no file names it attempts to read one input file
825 from the @code{@value{AS}} standard input, which is normally your terminal. You
826 may have to type @key{ctl-D} to tell @code{@value{AS}} there is no more program
829 Use @samp{--} if you need to explicitly name the standard input file
830 in your command line.
832 If the source is empty, @code{@value{AS}} produces a small, empty object
835 @subheading Filenames and Line-numbers
837 @cindex input file linenumbers
838 @cindex line numbers, in input files
839 There are two ways of locating a line in the input file (or files) and
840 either may be used in reporting error messages. One way refers to a line
841 number in a physical file; the other refers to a line number in a
842 ``logical'' file. @xref{Errors, ,Error and Warning Messages}.
844 @dfn{Physical files} are those files named in the command line given
845 to @code{@value{AS}}.
847 @dfn{Logical files} are simply names declared explicitly by assembler
848 directives; they bear no relation to physical files. Logical file names help
849 error messages reflect the original source file, when @code{@value{AS}} source
850 is itself synthesized from other files. @code{@value{AS}} understands the
851 @samp{#} directives emitted by the @code{@value{GCC}} preprocessor. See also
852 @ref{File,,@code{.file}}.
855 @section Output (Object) File
861 Every time you run @code{@value{AS}} it produces an output file, which is
862 your assembly language program translated into numbers. This file
863 is the object file. Its default name is
871 @code{b.out} when @code{@value{AS}} is configured for the Intel 80960.
873 You can give it another name by using the @code{-o} option. Conventionally,
874 object file names end with @file{.o}. The default name is used for historical
875 reasons: older assemblers were capable of assembling self-contained programs
876 directly into a runnable program. (For some formats, this isn't currently
877 possible, but it can be done for the @code{a.out} format.)
881 The object file is meant for input to the linker @code{@value{LD}}. It contains
882 assembled program code, information to help @code{@value{LD}} integrate
883 the assembled program into a runnable file, and (optionally) symbolic
884 information for the debugger.
886 @c link above to some info file(s) like the description of a.out.
887 @c don't forget to describe @sc{gnu} info as well as Unix lossage.
890 @section Error and Warning Messages
892 @cindex error messsages
893 @cindex warning messages
894 @cindex messages from assembler
895 @code{@value{AS}} may write warnings and error messages to the standard error
896 file (usually your terminal). This should not happen when a compiler
897 runs @code{@value{AS}} automatically. Warnings report an assumption made so
898 that @code{@value{AS}} could keep assembling a flawed program; errors report a
899 grave problem that stops the assembly.
901 @cindex format of warning messages
902 Warning messages have the format
905 file_name:@b{NNN}:Warning Message Text
909 @cindex line numbers, in warnings/errors
910 (where @b{NNN} is a line number). If a logical file name has been given
911 (@pxref{File,,@code{.file}}) it is used for the filename, otherwise the name of
912 the current input file is used. If a logical line number was given
914 (@pxref{Line,,@code{.line}})
918 (@pxref{Line,,@code{.line}})
921 (@pxref{Ln,,@code{.ln}})
924 then it is used to calculate the number printed,
925 otherwise the actual line in the current source file is printed. The
926 message text is intended to be self explanatory (in the grand Unix
929 @cindex format of error messages
930 Error messages have the format
932 file_name:@b{NNN}:FATAL:Error Message Text
934 The file name and line number are derived as for warning
935 messages. The actual message text may be rather less explanatory
936 because many of them aren't supposed to happen.
939 @chapter Command-Line Options
941 @cindex options, all versions of assembler
942 This chapter describes command-line options available in @emph{all}
943 versions of the @sc{gnu} assembler; @pxref{Machine Dependencies}, for options specific
945 to the @value{TARGET}.
948 to particular machine architectures.
951 If you are invoking @code{@value{AS}} via the @sc{gnu} C compiler (version 2),
952 you can use the @samp{-Wa} option to pass arguments through to the assembler.
953 The assembler arguments must be separated from each other (and the @samp{-Wa})
954 by commas. For example:
957 gcc -c -g -O -Wa,-alh,-L file.c
961 This passes two options to the assembler: @samp{-alh} (emit a listing to
962 standard output with with high-level and assembly source) and @samp{-L} (retain
963 local symbols in the symbol table).
965 Usually you do not need to use this @samp{-Wa} mechanism, since many compiler
966 command-line options are automatically passed to the assembler by the compiler.
967 (You can call the @sc{gnu} compiler driver with the @samp{-v} option to see
968 precisely what options it passes to each compilation pass, including the
972 * a:: -a[cdhlns] enable listings
973 * D:: -D for compatibility
974 * f:: -f to work faster
975 * I:: -I for .include search path
976 @ifclear DIFF-TBL-KLUGE
977 * K:: -K for compatibility
979 @ifset DIFF-TBL-KLUGE
980 * K:: -K for difference tables
983 * L:: -L to retain local labels
984 * M:: -M or --mri to assemble in MRI compatibility mode
985 * MD:: --MD for dependency tracking
986 * o:: -o to name the object file
987 * R:: -R to join data and text sections
988 * statistics:: --statistics to see statistics about assembly
989 * traditional-format:: --traditional-format for compatible output
990 * v:: -v to announce version
991 * W:: -W to suppress warnings
992 * Z:: -Z to make object file even after errors
996 @section Enable Listings: @code{-a[cdhlns]}
1005 @cindex listings, enabling
1006 @cindex assembly listings, enabling
1008 These options enable listing output from the assembler. By itself,
1009 @samp{-a} requests high-level, assembly, and symbols listing.
1010 You can use other letters to select specific options for the list:
1011 @samp{-ah} requests a high-level language listing,
1012 @samp{-al} requests an output-program assembly listing, and
1013 @samp{-as} requests a symbol table listing.
1014 High-level listings require that a compiler debugging option like
1015 @samp{-g} be used, and that assembly listings (@samp{-al}) be requested
1018 Use the @samp{-ac} option to omit false conditionals from a listing. Any lines
1019 which are not assembled because of a false @code{.if} (or @code{.ifdef}, or any
1020 other conditional), or a true @code{.if} followed by an @code{.else}, will be
1021 omitted from the listing.
1023 Use the @samp{-ad} option to omit debugging directives from the
1026 Once you have specified one of these options, you can further control
1027 listing output and its appearance using the directives @code{.list},
1028 @code{.nolist}, @code{.psize}, @code{.eject}, @code{.title}, and
1030 The @samp{-an} option turns off all forms processing.
1031 If you do not request listing output with one of the @samp{-a} options, the
1032 listing-control directives have no effect.
1034 The letters after @samp{-a} may be combined into one option,
1035 @emph{e.g.}, @samp{-aln}.
1041 This option has no effect whatsoever, but it is accepted to make it more
1042 likely that scripts written for other assemblers also work with
1046 @section Work Faster: @code{-f}
1049 @cindex trusted compiler
1050 @cindex faster processing (@code{-f})
1051 @samp{-f} should only be used when assembling programs written by a
1052 (trusted) compiler. @samp{-f} stops the assembler from doing whitespace
1053 and comment preprocessing on
1054 the input file(s) before assembling them. @xref{Preprocessing,
1058 @emph{Warning:} if you use @samp{-f} when the files actually need to be
1059 preprocessed (if they contain comments, for example), @code{@value{AS}} does
1064 @section @code{.include} search path: @code{-I} @var{path}
1066 @kindex -I @var{path}
1067 @cindex paths for @code{.include}
1068 @cindex search path for @code{.include}
1069 @cindex @code{include} directive search path
1070 Use this option to add a @var{path} to the list of directories
1071 @code{@value{AS}} searches for files specified in @code{.include}
1072 directives (@pxref{Include,,@code{.include}}). You may use @code{-I} as
1073 many times as necessary to include a variety of paths. The current
1074 working directory is always searched first; after that, @code{@value{AS}}
1075 searches any @samp{-I} directories in the same order as they were
1076 specified (left to right) on the command line.
1079 @section Difference Tables: @code{-K}
1082 @ifclear DIFF-TBL-KLUGE
1083 On the @value{TARGET} family, this option is allowed, but has no effect. It is
1084 permitted for compatibility with the @sc{gnu} assembler on other platforms,
1085 where it can be used to warn when the assembler alters the machine code
1086 generated for @samp{.word} directives in difference tables. The @value{TARGET}
1087 family does not have the addressing limitations that sometimes lead to this
1088 alteration on other platforms.
1091 @ifset DIFF-TBL-KLUGE
1092 @cindex difference tables, warning
1093 @cindex warning for altered difference tables
1094 @code{@value{AS}} sometimes alters the code emitted for directives of the form
1095 @samp{.word @var{sym1}-@var{sym2}}; @pxref{Word,,@code{.word}}.
1096 You can use the @samp{-K} option if you want a warning issued when this
1101 @section Include Local Labels: @code{-L}
1104 @cindex local labels, retaining in output
1105 Labels beginning with @samp{L} (upper case only) are called @dfn{local
1106 labels}. @xref{Symbol Names}. Normally you do not see such labels when
1107 debugging, because they are intended for the use of programs (like
1108 compilers) that compose assembler programs, not for your notice.
1109 Normally both @code{@value{AS}} and @code{@value{LD}} discard such labels, so you do not
1110 normally debug with them.
1112 This option tells @code{@value{AS}} to retain those @samp{L@dots{}} symbols
1113 in the object file. Usually if you do this you also tell the linker
1114 @code{@value{LD}} to preserve symbols whose names begin with @samp{L}.
1116 By default, a local label is any label beginning with @samp{L}, but each
1117 target is allowed to redefine the local label prefix.
1119 On the HPPA local labels begin with @samp{L$}.
1122 @samp{;} for the ARM family;
1126 @section Assemble in MRI Compatibility Mode: @code{-M}
1129 @cindex MRI compatibility mode
1130 The @code{-M} or @code{--mri} option selects MRI compatibility mode. This
1131 changes the syntax and pseudo-op handling of @code{@value{AS}} to make it
1132 compatible with the @code{ASM68K} or the @code{ASM960} (depending upon the
1133 configured target) assembler from Microtec Research. The exact nature of the
1134 MRI syntax will not be documented here; see the MRI manuals for more
1135 information. Note in particular that the handling of macros and macro
1136 arguments is somewhat different. The purpose of this option is to permit
1137 assembling existing MRI assembler code using @code{@value{AS}}.
1139 The MRI compatibility is not complete. Certain operations of the MRI assembler
1140 depend upon its object file format, and can not be supported using other object
1141 file formats. Supporting these would require enhancing each object file format
1142 individually. These are:
1145 @item global symbols in common section
1147 The m68k MRI assembler supports common sections which are merged by the linker.
1148 Other object file formats do not support this. @code{@value{AS}} handles
1149 common sections by treating them as a single common symbol. It permits local
1150 symbols to be defined within a common section, but it can not support global
1151 symbols, since it has no way to describe them.
1153 @item complex relocations
1155 The MRI assemblers support relocations against a negated section address, and
1156 relocations which combine the start addresses of two or more sections. These
1157 are not support by other object file formats.
1159 @item @code{END} pseudo-op specifying start address
1161 The MRI @code{END} pseudo-op permits the specification of a start address.
1162 This is not supported by other object file formats. The start address may
1163 instead be specified using the @code{-e} option to the linker, or in a linker
1166 @item @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops
1168 The MRI @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops assign a module
1169 name to the output file. This is not supported by other object file formats.
1171 @item @code{ORG} pseudo-op
1173 The m68k MRI @code{ORG} pseudo-op begins an absolute section at a given
1174 address. This differs from the usual @code{@value{AS}} @code{.org} pseudo-op,
1175 which changes the location within the current section. Absolute sections are
1176 not supported by other object file formats. The address of a section may be
1177 assigned within a linker script.
1180 There are some other features of the MRI assembler which are not supported by
1181 @code{@value{AS}}, typically either because they are difficult or because they
1182 seem of little consequence. Some of these may be supported in future releases.
1186 @item EBCDIC strings
1188 EBCDIC strings are not supported.
1190 @item packed binary coded decimal
1192 Packed binary coded decimal is not supported. This means that the @code{DC.P}
1193 and @code{DCB.P} pseudo-ops are not supported.
1195 @item @code{FEQU} pseudo-op
1197 The m68k @code{FEQU} pseudo-op is not supported.
1199 @item @code{NOOBJ} pseudo-op
1201 The m68k @code{NOOBJ} pseudo-op is not supported.
1203 @item @code{OPT} branch control options
1205 The m68k @code{OPT} branch control options---@code{B}, @code{BRS}, @code{BRB},
1206 @code{BRL}, and @code{BRW}---are ignored. @code{@value{AS}} automatically
1207 relaxes all branches, whether forward or backward, to an appropriate size, so
1208 these options serve no purpose.
1210 @item @code{OPT} list control options
1212 The following m68k @code{OPT} list control options are ignored: @code{C},
1213 @code{CEX}, @code{CL}, @code{CRE}, @code{E}, @code{G}, @code{I}, @code{M},
1214 @code{MEX}, @code{MC}, @code{MD}, @code{X}.
1216 @item other @code{OPT} options
1218 The following m68k @code{OPT} options are ignored: @code{NEST}, @code{O},
1219 @code{OLD}, @code{OP}, @code{P}, @code{PCO}, @code{PCR}, @code{PCS}, @code{R}.
1221 @item @code{OPT} @code{D} option is default
1223 The m68k @code{OPT} @code{D} option is the default, unlike the MRI assembler.
1224 @code{OPT NOD} may be used to turn it off.
1226 @item @code{XREF} pseudo-op.
1228 The m68k @code{XREF} pseudo-op is ignored.
1230 @item @code{.debug} pseudo-op
1232 The i960 @code{.debug} pseudo-op is not supported.
1234 @item @code{.extended} pseudo-op
1236 The i960 @code{.extended} pseudo-op is not supported.
1238 @item @code{.list} pseudo-op.
1240 The various options of the i960 @code{.list} pseudo-op are not supported.
1242 @item @code{.optimize} pseudo-op
1244 The i960 @code{.optimize} pseudo-op is not supported.
1246 @item @code{.output} pseudo-op
1248 The i960 @code{.output} pseudo-op is not supported.
1250 @item @code{.setreal} pseudo-op
1252 The i960 @code{.setreal} pseudo-op is not supported.
1257 @section Dependency tracking: @code{--MD}
1260 @cindex dependency tracking
1263 @code{@value{AS}} can generate a dependency file for the file it creates. This
1264 file consists of a single rule suitable for @code{make} describing the
1265 dependencies of the main source file.
1267 The rule is written to the file named in its argument.
1269 This feature is used in the automatic updating of makefiles.
1272 @section Name the Object File: @code{-o}
1275 @cindex naming object file
1276 @cindex object file name
1277 There is always one object file output when you run @code{@value{AS}}. By
1278 default it has the name
1281 @file{a.out} (or @file{b.out}, for Intel 960 targets only).
1295 You use this option (which takes exactly one filename) to give the
1296 object file a different name.
1298 Whatever the object file is called, @code{@value{AS}} overwrites any
1299 existing file of the same name.
1302 @section Join Data and Text Sections: @code{-R}
1305 @cindex data and text sections, joining
1306 @cindex text and data sections, joining
1307 @cindex joining text and data sections
1308 @cindex merging text and data sections
1309 @code{-R} tells @code{@value{AS}} to write the object file as if all
1310 data-section data lives in the text section. This is only done at
1311 the very last moment: your binary data are the same, but data
1312 section parts are relocated differently. The data section part of
1313 your object file is zero bytes long because all its bytes are
1314 appended to the text section. (@xref{Sections,,Sections and Relocation}.)
1316 When you specify @code{-R} it would be possible to generate shorter
1317 address displacements (because we do not have to cross between text and
1318 data section). We refrain from doing this simply for compatibility with
1319 older versions of @code{@value{AS}}. In future, @code{-R} may work this way.
1322 When @code{@value{AS}} is configured for COFF output,
1323 this option is only useful if you use sections named @samp{.text} and
1328 @code{-R} is not supported for any of the HPPA targets. Using
1329 @code{-R} generates a warning from @code{@value{AS}}.
1333 @section Display Assembly Statistics: @code{--statistics}
1335 @kindex --statistics
1336 @cindex statistics, about assembly
1337 @cindex time, total for assembly
1338 @cindex space used, maximum for assembly
1339 Use @samp{--statistics} to display two statistics about the resources used by
1340 @code{@value{AS}}: the maximum amount of space allocated during the assembly
1341 (in bytes), and the total execution time taken for the assembly (in @sc{cpu}
1344 @node traditional-format
1345 @section Compatible output: @code{--traditional-format}
1347 @kindex --traditional-format
1348 For some targets, the output of @code{@value{AS}} is different in some ways
1349 from the output of some existing assembler. This switch requests
1350 @code{@value{AS}} to use the traditional format instead.
1352 For example, it disables the exception frame optimizations which
1353 @code{@value{AS}} normally does by default on @code{@value{GCC}} output.
1356 @section Announce Version: @code{-v}
1360 @cindex assembler version
1361 @cindex version of assembler
1362 You can find out what version of as is running by including the
1363 option @samp{-v} (which you can also spell as @samp{-version}) on the
1367 @section Suppress Warnings: @code{-W}
1370 @cindex suppressing warnings
1371 @cindex warnings, suppressing
1372 @code{@value{AS}} should never give a warning or error message when
1373 assembling compiler output. But programs written by people often
1374 cause @code{@value{AS}} to give a warning that a particular assumption was
1375 made. All such warnings are directed to the standard error file.
1376 If you use this option, no warnings are issued. This option only
1377 affects the warning messages: it does not change any particular of how
1378 @code{@value{AS}} assembles your file. Errors, which stop the assembly, are
1382 @section Generate Object File in Spite of Errors: @code{-Z}
1383 @cindex object file, after errors
1384 @cindex errors, continuing after
1385 After an error message, @code{@value{AS}} normally produces no output. If for
1386 some reason you are interested in object file output even after
1387 @code{@value{AS}} gives an error message on your program, use the @samp{-Z}
1388 option. If there are any errors, @code{@value{AS}} continues anyways, and
1389 writes an object file after a final warning message of the form @samp{@var{n}
1390 errors, @var{m} warnings, generating bad object file.}
1395 @cindex machine-independent syntax
1396 @cindex syntax, machine-independent
1397 This chapter describes the machine-independent syntax allowed in a
1398 source file. @code{@value{AS}} syntax is similar to what many other
1399 assemblers use; it is inspired by the BSD 4.2
1404 assembler, except that @code{@value{AS}} does not assemble Vax bit-fields.
1408 * Preprocessing:: Preprocessing
1409 * Whitespace:: Whitespace
1410 * Comments:: Comments
1411 * Symbol Intro:: Symbols
1412 * Statements:: Statements
1413 * Constants:: Constants
1417 @section Preprocessing
1419 @cindex preprocessing
1420 The @code{@value{AS}} internal preprocessor:
1422 @cindex whitespace, removed by preprocessor
1424 adjusts and removes extra whitespace. It leaves one space or tab before
1425 the keywords on a line, and turns any other whitespace on the line into
1428 @cindex comments, removed by preprocessor
1430 removes all comments, replacing them with a single space, or an
1431 appropriate number of newlines.
1433 @cindex constants, converted by preprocessor
1435 converts character constants into the appropriate numeric values.
1438 It does not do macro processing, include file handling, or
1439 anything else you may get from your C compiler's preprocessor. You can
1440 do include file processing with the @code{.include} directive
1441 (@pxref{Include,,@code{.include}}). You can use the @sc{gnu} C compiler driver
1442 to get other ``CPP'' style preprocessing, by giving the input file a
1443 @samp{.S} suffix. @xref{Overall Options,, Options Controlling the Kind of
1444 Output, gcc.info, Using GNU CC}.
1446 Excess whitespace, comments, and character constants
1447 cannot be used in the portions of the input text that are not
1450 @cindex turning preprocessing on and off
1451 @cindex preprocessing, turning on and off
1454 If the first line of an input file is @code{#NO_APP} or if you use the
1455 @samp{-f} option, whitespace and comments are not removed from the input file.
1456 Within an input file, you can ask for whitespace and comment removal in
1457 specific portions of the by putting a line that says @code{#APP} before the
1458 text that may contain whitespace or comments, and putting a line that says
1459 @code{#NO_APP} after this text. This feature is mainly intend to support
1460 @code{asm} statements in compilers whose output is otherwise free of comments
1467 @dfn{Whitespace} is one or more blanks or tabs, in any order.
1468 Whitespace is used to separate symbols, and to make programs neater for
1469 people to read. Unless within character constants
1470 (@pxref{Characters,,Character Constants}), any whitespace means the same
1471 as exactly one space.
1477 There are two ways of rendering comments to @code{@value{AS}}. In both
1478 cases the comment is equivalent to one space.
1480 Anything from @samp{/*} through the next @samp{*/} is a comment.
1481 This means you may not nest these comments.
1485 The only way to include a newline ('\n') in a comment
1486 is to use this sort of comment.
1489 /* This sort of comment does not nest. */
1492 @cindex line comment character
1493 Anything from the @dfn{line comment} character to the next newline
1494 is considered a comment and is ignored. The line comment character is
1496 @samp{;} for the AMD 29K family;
1499 @samp{;} on the ARC;
1502 @samp{;} for the H8/300 family;
1505 @samp{!} for the H8/500 family;
1508 @samp{;} for the HPPA;
1511 @samp{#} on the i960;
1514 @samp{!} for the Hitachi SH;
1517 @samp{!} on the SPARC;
1520 @samp{#} on the m32r;
1523 @samp{|} on the 680x0;
1526 @samp{#} on the Vax;
1529 @samp{!} for the Z8000;
1532 @samp{#} on the V850;
1534 see @ref{Machine Dependencies}. @refill
1535 @c FIXME What about i386, m88k, i860?
1538 On some machines there are two different line comment characters. One
1539 character only begins a comment if it is the first non-whitespace character on
1540 a line, while the other always begins a comment.
1544 The V850 assembler also supports a double dash as starting a comment that
1545 extends to the end of the line.
1551 @cindex lines starting with @code{#}
1552 @cindex logical line numbers
1553 To be compatible with past assemblers, lines that begin with @samp{#} have a
1554 special interpretation. Following the @samp{#} should be an absolute
1555 expression (@pxref{Expressions}): the logical line number of the @emph{next}
1556 line. Then a string (@pxref{Strings,, Strings}) is allowed: if present it is a
1557 new logical file name. The rest of the line, if any, should be whitespace.
1559 If the first non-whitespace characters on the line are not numeric,
1560 the line is ignored. (Just like a comment.)
1563 # This is an ordinary comment.
1564 # 42-6 "new_file_name" # New logical file name
1565 # This is logical line # 36.
1567 This feature is deprecated, and may disappear from future versions
1568 of @code{@value{AS}}.
1573 @cindex characters used in symbols
1574 @ifclear SPECIAL-SYMS
1575 A @dfn{symbol} is one or more characters chosen from the set of all
1576 letters (both upper and lower case), digits and the three characters
1582 A @dfn{symbol} is one or more characters chosen from the set of all
1583 letters (both upper and lower case), digits and the three characters
1584 @samp{._$}. (Save that, on the H8/300 only, you may not use @samp{$} in
1590 On most machines, you can also use @code{$} in symbol names; exceptions
1591 are noted in @ref{Machine Dependencies}.
1593 No symbol may begin with a digit. Case is significant.
1594 There is no length limit: all characters are significant. Symbols are
1595 delimited by characters not in that set, or by the beginning of a file
1596 (since the source program must end with a newline, the end of a file is
1597 not a possible symbol delimiter). @xref{Symbols}.
1598 @cindex length of symbols
1603 @cindex statements, structure of
1604 @cindex line separator character
1605 @cindex statement separator character
1607 @ifclear abnormal-separator
1608 A @dfn{statement} ends at a newline character (@samp{\n}) or at a
1609 semicolon (@samp{;}). The newline or semicolon is considered part of
1610 the preceding statement. Newlines and semicolons within character
1611 constants are an exception: they do not end statements.
1613 @ifset abnormal-separator
1615 A @dfn{statement} ends at a newline character (@samp{\n}) or an ``at''
1616 sign (@samp{@@}). The newline or at sign is considered part of the
1617 preceding statement. Newlines and at signs within character constants
1618 are an exception: they do not end statements.
1621 A @dfn{statement} ends at a newline character (@samp{\n}) or an exclamation
1622 point (@samp{!}). The newline or exclamation point is considered part of the
1623 preceding statement. Newlines and exclamation points within character
1624 constants are an exception: they do not end statements.
1627 A @dfn{statement} ends at a newline character (@samp{\n}); or (for the
1628 H8/300) a dollar sign (@samp{$}); or (for the
1631 (@samp{;}). The newline or separator character is considered part of
1632 the preceding statement. Newlines and separators within character
1633 constants are an exception: they do not end statements.
1638 A @dfn{statement} ends at a newline character (@samp{\n}) or line
1639 separator character. (The line separator is usually @samp{;}, unless
1640 this conflicts with the comment character; @pxref{Machine Dependencies}.) The
1641 newline or separator character is considered part of the preceding
1642 statement. Newlines and separators within character constants are an
1643 exception: they do not end statements.
1646 @cindex newline, required at file end
1647 @cindex EOF, newline must precede
1648 It is an error to end any statement with end-of-file: the last
1649 character of any input file should be a newline.@refill
1651 An empty statement is allowed, and may include whitespace. It is ignored.
1653 @cindex instructions and directives
1654 @cindex directives and instructions
1655 @c "key symbol" is not used elsewhere in the document; seems pedantic to
1656 @c @defn{} it in that case, as was done previously... doc@cygnus.com,
1658 A statement begins with zero or more labels, optionally followed by a
1659 key symbol which determines what kind of statement it is. The key
1660 symbol determines the syntax of the rest of the statement. If the
1661 symbol begins with a dot @samp{.} then the statement is an assembler
1662 directive: typically valid for any computer. If the symbol begins with
1663 a letter the statement is an assembly language @dfn{instruction}: it
1664 assembles into a machine language instruction.
1666 Different versions of @code{@value{AS}} for different computers
1667 recognize different instructions. In fact, the same symbol may
1668 represent a different instruction in a different computer's assembly
1672 @cindex @code{:} (label)
1673 @cindex label (@code{:})
1674 A label is a symbol immediately followed by a colon (@code{:}).
1675 Whitespace before a label or after a colon is permitted, but you may not
1676 have whitespace between a label's symbol and its colon. @xref{Labels}.
1679 For HPPA targets, labels need not be immediately followed by a colon, but
1680 the definition of a label must begin in column zero. This also implies that
1681 only one label may be defined on each line.
1685 label: .directive followed by something
1686 another_label: # This is an empty statement.
1687 instruction operand_1, operand_2, @dots{}
1694 A constant is a number, written so that its value is known by
1695 inspection, without knowing any context. Like this:
1698 .byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.
1699 .ascii "Ring the bell\7" # A string constant.
1700 .octa 0x123456789abcdef0123456789ABCDEF0 # A bignum.
1701 .float 0f-314159265358979323846264338327\
1702 95028841971.693993751E-40 # - pi, a flonum.
1707 * Characters:: Character Constants
1708 * Numbers:: Number Constants
1712 @subsection Character Constants
1714 @cindex character constants
1715 @cindex constants, character
1716 There are two kinds of character constants. A @dfn{character} stands
1717 for one character in one byte and its value may be used in
1718 numeric expressions. String constants (properly called string
1719 @emph{literals}) are potentially many bytes and their values may not be
1720 used in arithmetic expressions.
1724 * Chars:: Characters
1728 @subsubsection Strings
1730 @cindex string constants
1731 @cindex constants, string
1732 A @dfn{string} is written between double-quotes. It may contain
1733 double-quotes or null characters. The way to get special characters
1734 into a string is to @dfn{escape} these characters: precede them with
1735 a backslash @samp{\} character. For example @samp{\\} represents
1736 one backslash: the first @code{\} is an escape which tells
1737 @code{@value{AS}} to interpret the second character literally as a backslash
1738 (which prevents @code{@value{AS}} from recognizing the second @code{\} as an
1739 escape character). The complete list of escapes follows.
1741 @cindex escape codes, character
1742 @cindex character escape codes
1745 @c Mnemonic for ACKnowledge; for ASCII this is octal code 007.
1747 @cindex @code{\b} (backspace character)
1748 @cindex backspace (@code{\b})
1750 Mnemonic for backspace; for ASCII this is octal code 010.
1753 @c Mnemonic for EOText; for ASCII this is octal code 004.
1755 @cindex @code{\f} (formfeed character)
1756 @cindex formfeed (@code{\f})
1758 Mnemonic for FormFeed; for ASCII this is octal code 014.
1760 @cindex @code{\n} (newline character)
1761 @cindex newline (@code{\n})
1763 Mnemonic for newline; for ASCII this is octal code 012.
1766 @c Mnemonic for prefix; for ASCII this is octal code 033, usually known as @code{escape}.
1768 @cindex @code{\r} (carriage return character)
1769 @cindex carriage return (@code{\r})
1771 Mnemonic for carriage-Return; for ASCII this is octal code 015.
1774 @c Mnemonic for space; for ASCII this is octal code 040. Included for compliance with
1775 @c other assemblers.
1777 @cindex @code{\t} (tab)
1778 @cindex tab (@code{\t})
1780 Mnemonic for horizontal Tab; for ASCII this is octal code 011.
1783 @c Mnemonic for Vertical tab; for ASCII this is octal code 013.
1784 @c @item \x @var{digit} @var{digit} @var{digit}
1785 @c A hexadecimal character code. The numeric code is 3 hexadecimal digits.
1787 @cindex @code{\@var{ddd}} (octal character code)
1788 @cindex octal character code (@code{\@var{ddd}})
1789 @item \ @var{digit} @var{digit} @var{digit}
1790 An octal character code. The numeric code is 3 octal digits.
1791 For compatibility with other Unix systems, 8 and 9 are accepted as digits:
1792 for example, @code{\008} has the value 010, and @code{\009} the value 011.
1794 @cindex @code{\@var{xd...}} (hex character code)
1795 @cindex hex character code (@code{\@var{xd...}})
1796 @item \@code{x} @var{hex-digits...}
1797 A hex character code. All trailing hex digits are combined. Either upper or
1798 lower case @code{x} works.
1800 @cindex @code{\\} (@samp{\} character)
1801 @cindex backslash (@code{\\})
1803 Represents one @samp{\} character.
1806 @c Represents one @samp{'} (accent acute) character.
1807 @c This is needed in single character literals
1808 @c (@xref{Characters,,Character Constants}.) to represent
1811 @cindex @code{\"} (doublequote character)
1812 @cindex doublequote (@code{\"})
1814 Represents one @samp{"} character. Needed in strings to represent
1815 this character, because an unescaped @samp{"} would end the string.
1817 @item \ @var{anything-else}
1818 Any other character when escaped by @kbd{\} gives a warning, but
1819 assembles as if the @samp{\} was not present. The idea is that if
1820 you used an escape sequence you clearly didn't want the literal
1821 interpretation of the following character. However @code{@value{AS}} has no
1822 other interpretation, so @code{@value{AS}} knows it is giving you the wrong
1823 code and warns you of the fact.
1826 Which characters are escapable, and what those escapes represent,
1827 varies widely among assemblers. The current set is what we think
1828 the BSD 4.2 assembler recognizes, and is a subset of what most C
1829 compilers recognize. If you are in doubt, do not use an escape
1833 @subsubsection Characters
1835 @cindex single character constant
1836 @cindex character, single
1837 @cindex constant, single character
1838 A single character may be written as a single quote immediately
1839 followed by that character. The same escapes apply to characters as
1840 to strings. So if you want to write the character backslash, you
1841 must write @kbd{'\\} where the first @code{\} escapes the second
1842 @code{\}. As you can see, the quote is an acute accent, not a
1843 grave accent. A newline
1845 @ifclear abnormal-separator
1846 (or semicolon @samp{;})
1848 @ifset abnormal-separator
1850 (or at sign @samp{@@})
1853 (or dollar sign @samp{$}, for the H8/300; or semicolon @samp{;} for the
1859 immediately following an acute accent is taken as a literal character
1860 and does not count as the end of a statement. The value of a character
1861 constant in a numeric expression is the machine's byte-wide code for
1862 that character. @code{@value{AS}} assumes your character code is ASCII:
1863 @kbd{'A} means 65, @kbd{'B} means 66, and so on. @refill
1866 @subsection Number Constants
1868 @cindex constants, number
1869 @cindex number constants
1870 @code{@value{AS}} distinguishes three kinds of numbers according to how they
1871 are stored in the target machine. @emph{Integers} are numbers that
1872 would fit into an @code{int} in the C language. @emph{Bignums} are
1873 integers, but they are stored in more than 32 bits. @emph{Flonums}
1874 are floating point numbers, described below.
1877 * Integers:: Integers
1882 * Bit Fields:: Bit Fields
1888 @subsubsection Integers
1890 @cindex constants, integer
1892 @cindex binary integers
1893 @cindex integers, binary
1894 A binary integer is @samp{0b} or @samp{0B} followed by zero or more of
1895 the binary digits @samp{01}.
1897 @cindex octal integers
1898 @cindex integers, octal
1899 An octal integer is @samp{0} followed by zero or more of the octal
1900 digits (@samp{01234567}).
1902 @cindex decimal integers
1903 @cindex integers, decimal
1904 A decimal integer starts with a non-zero digit followed by zero or
1905 more digits (@samp{0123456789}).
1907 @cindex hexadecimal integers
1908 @cindex integers, hexadecimal
1909 A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or
1910 more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}.
1912 Integers have the usual values. To denote a negative integer, use
1913 the prefix operator @samp{-} discussed under expressions
1914 (@pxref{Prefix Ops,,Prefix Operators}).
1917 @subsubsection Bignums
1920 @cindex constants, bignum
1921 A @dfn{bignum} has the same syntax and semantics as an integer
1922 except that the number (or its negative) takes more than 32 bits to
1923 represent in binary. The distinction is made because in some places
1924 integers are permitted while bignums are not.
1927 @subsubsection Flonums
1929 @cindex floating point numbers
1930 @cindex constants, floating point
1932 @cindex precision, floating point
1933 A @dfn{flonum} represents a floating point number. The translation is
1934 indirect: a decimal floating point number from the text is converted by
1935 @code{@value{AS}} to a generic binary floating point number of more than
1936 sufficient precision. This generic floating point number is converted
1937 to a particular computer's floating point format (or formats) by a
1938 portion of @code{@value{AS}} specialized to that computer.
1940 A flonum is written by writing (in order)
1945 (@samp{0} is optional on the HPPA.)
1949 A letter, to tell @code{@value{AS}} the rest of the number is a flonum.
1951 @kbd{e} is recommended. Case is not important.
1953 @c FIXME: verify if flonum syntax really this vague for most cases
1954 (Any otherwise illegal letter works here, but that might be changed. Vax BSD
1955 4.2 assembler seems to allow any of @samp{defghDEFGH}.)
1958 On the H8/300, H8/500,
1960 and AMD 29K architectures, the letter must be
1961 one of the letters @samp{DFPRSX} (in upper or lower case).
1963 On the ARC, the letter must be one of the letters @samp{DFRS}
1964 (in upper or lower case).
1966 On the Intel 960 architecture, the letter must be
1967 one of the letters @samp{DFT} (in upper or lower case).
1969 On the HPPA architecture, the letter must be @samp{E} (upper case only).
1973 One of the letters @samp{DFPRSX} (in upper or lower case).
1976 One of the letters @samp{DFRS} (in upper or lower case).
1979 One of the letters @samp{DFPRSX} (in upper or lower case).
1982 The letter @samp{E} (upper case only).
1985 One of the letters @samp{DFT} (in upper or lower case).
1990 An optional sign: either @samp{+} or @samp{-}.
1993 An optional @dfn{integer part}: zero or more decimal digits.
1996 An optional @dfn{fractional part}: @samp{.} followed by zero
1997 or more decimal digits.
2000 An optional exponent, consisting of:
2004 An @samp{E} or @samp{e}.
2005 @c I can't find a config where "EXP_CHARS" is other than 'eE', but in
2006 @c principle this can perfectly well be different on different targets.
2008 Optional sign: either @samp{+} or @samp{-}.
2010 One or more decimal digits.
2015 At least one of the integer part or the fractional part must be
2016 present. The floating point number has the usual base-10 value.
2018 @code{@value{AS}} does all processing using integers. Flonums are computed
2019 independently of any floating point hardware in the computer running
2024 @c Bit fields are written as a general facility but are also controlled
2025 @c by a conditional-compilation flag---which is as of now (21mar91)
2026 @c turned on only by the i960 config of GAS.
2028 @subsubsection Bit Fields
2031 @cindex constants, bit field
2032 You can also define numeric constants as @dfn{bit fields}.
2033 specify two numbers separated by a colon---
2035 @var{mask}:@var{value}
2038 @code{@value{AS}} applies a bitwise @sc{and} between @var{mask} and
2041 The resulting number is then packed
2043 @c this conditional paren in case bit fields turned on elsewhere than 960
2044 (in host-dependent byte order)
2046 into a field whose width depends on which assembler directive has the
2047 bit-field as its argument. Overflow (a result from the bitwise and
2048 requiring more binary digits to represent) is not an error; instead,
2049 more constants are generated, of the specified width, beginning with the
2050 least significant digits.@refill
2052 The directives @code{.byte}, @code{.hword}, @code{.int}, @code{.long},
2053 @code{.short}, and @code{.word} accept bit-field arguments.
2058 @chapter Sections and Relocation
2063 * Secs Background:: Background
2064 * Ld Sections:: Linker Sections
2065 * As Sections:: Assembler Internal Sections
2066 * Sub-Sections:: Sub-Sections
2070 @node Secs Background
2073 Roughly, a section is a range of addresses, with no gaps; all data
2074 ``in'' those addresses is treated the same for some particular purpose.
2075 For example there may be a ``read only'' section.
2077 @cindex linker, and assembler
2078 @cindex assembler, and linker
2079 The linker @code{@value{LD}} reads many object files (partial programs) and
2080 combines their contents to form a runnable program. When @code{@value{AS}}
2081 emits an object file, the partial program is assumed to start at address 0.
2082 @code{@value{LD}} assigns the final addresses for the partial program, so that
2083 different partial programs do not overlap. This is actually an
2084 oversimplification, but it suffices to explain how @code{@value{AS}} uses
2087 @code{@value{LD}} moves blocks of bytes of your program to their run-time
2088 addresses. These blocks slide to their run-time addresses as rigid
2089 units; their length does not change and neither does the order of bytes
2090 within them. Such a rigid unit is called a @emph{section}. Assigning
2091 run-time addresses to sections is called @dfn{relocation}. It includes
2092 the task of adjusting mentions of object-file addresses so they refer to
2093 the proper run-time addresses.
2095 For the H8/300 and H8/500,
2096 and for the Hitachi SH,
2097 @code{@value{AS}} pads sections if needed to
2098 ensure they end on a word (sixteen bit) boundary.
2101 @cindex standard assembler sections
2102 An object file written by @code{@value{AS}} has at least three sections, any
2103 of which may be empty. These are named @dfn{text}, @dfn{data} and
2108 When it generates COFF output,
2110 @code{@value{AS}} can also generate whatever other named sections you specify
2111 using the @samp{.section} directive (@pxref{Section,,@code{.section}}).
2112 If you do not use any directives that place output in the @samp{.text}
2113 or @samp{.data} sections, these sections still exist, but are empty.
2118 When @code{@value{AS}} generates SOM or ELF output for the HPPA,
2120 @code{@value{AS}} can also generate whatever other named sections you
2121 specify using the @samp{.space} and @samp{.subspace} directives. See
2122 @cite{HP9000 Series 800 Assembly Language Reference Manual}
2123 (HP 92432-90001) for details on the @samp{.space} and @samp{.subspace}
2124 assembler directives.
2127 Additionally, @code{@value{AS}} uses different names for the standard
2128 text, data, and bss sections when generating SOM output. Program text
2129 is placed into the @samp{$CODE$} section, data into @samp{$DATA$}, and
2130 BSS into @samp{$BSS$}.
2134 Within the object file, the text section starts at address @code{0}, the
2135 data section follows, and the bss section follows the data section.
2138 When generating either SOM or ELF output files on the HPPA, the text
2139 section starts at address @code{0}, the data section at address
2140 @code{0x4000000}, and the bss section follows the data section.
2143 To let @code{@value{LD}} know which data changes when the sections are
2144 relocated, and how to change that data, @code{@value{AS}} also writes to the
2145 object file details of the relocation needed. To perform relocation
2146 @code{@value{LD}} must know, each time an address in the object
2150 Where in the object file is the beginning of this reference to
2153 How long (in bytes) is this reference?
2155 Which section does the address refer to? What is the numeric value of
2157 (@var{address}) @minus{} (@var{start-address of section})?
2160 Is the reference to an address ``Program-Counter relative''?
2163 @cindex addresses, format of
2164 @cindex section-relative addressing
2165 In fact, every address @code{@value{AS}} ever uses is expressed as
2167 (@var{section}) + (@var{offset into section})
2170 Further, most expressions @code{@value{AS}} computes have this section-relative
2173 (For some object formats, such as SOM for the HPPA, some expressions are
2174 symbol-relative instead.)
2177 In this manual we use the notation @{@var{secname} @var{N}@} to mean ``offset
2178 @var{N} into section @var{secname}.''
2180 Apart from text, data and bss sections you need to know about the
2181 @dfn{absolute} section. When @code{@value{LD}} mixes partial programs,
2182 addresses in the absolute section remain unchanged. For example, address
2183 @code{@{absolute 0@}} is ``relocated'' to run-time address 0 by
2184 @code{@value{LD}}. Although the linker never arranges two partial programs'
2185 data sections with overlapping addresses after linking, @emph{by definition}
2186 their absolute sections must overlap. Address @code{@{absolute@ 239@}} in one
2187 part of a program is always the same address when the program is running as
2188 address @code{@{absolute@ 239@}} in any other part of the program.
2190 The idea of sections is extended to the @dfn{undefined} section. Any
2191 address whose section is unknown at assembly time is by definition
2192 rendered @{undefined @var{U}@}---where @var{U} is filled in later.
2193 Since numbers are always defined, the only way to generate an undefined
2194 address is to mention an undefined symbol. A reference to a named
2195 common block would be such a symbol: its value is unknown at assembly
2196 time so it has section @emph{undefined}.
2198 By analogy the word @emph{section} is used to describe groups of sections in
2199 the linked program. @code{@value{LD}} puts all partial programs' text
2200 sections in contiguous addresses in the linked program. It is
2201 customary to refer to the @emph{text section} of a program, meaning all
2202 the addresses of all partial programs' text sections. Likewise for
2203 data and bss sections.
2205 Some sections are manipulated by @code{@value{LD}}; others are invented for
2206 use of @code{@value{AS}} and have no meaning except during assembly.
2209 @section Linker Sections
2210 @code{@value{LD}} deals with just four kinds of sections, summarized below.
2215 @cindex named sections
2216 @cindex sections, named
2217 @item named sections
2220 @cindex text section
2221 @cindex data section
2225 These sections hold your program. @code{@value{AS}} and @code{@value{LD}} treat them as
2226 separate but equal sections. Anything you can say of one section is
2229 When the program is running, however, it is
2230 customary for the text section to be unalterable. The
2231 text section is often shared among processes: it contains
2232 instructions, constants and the like. The data section of a running
2233 program is usually alterable: for example, C variables would be stored
2234 in the data section.
2239 This section contains zeroed bytes when your program begins running. It
2240 is used to hold unitialized variables or common storage. The length of
2241 each partial program's bss section is important, but because it starts
2242 out containing zeroed bytes there is no need to store explicit zero
2243 bytes in the object file. The bss section was invented to eliminate
2244 those explicit zeros from object files.
2246 @cindex absolute section
2247 @item absolute section
2248 Address 0 of this section is always ``relocated'' to runtime address 0.
2249 This is useful if you want to refer to an address that @code{@value{LD}} must
2250 not change when relocating. In this sense we speak of absolute
2251 addresses being ``unrelocatable'': they do not change during relocation.
2253 @cindex undefined section
2254 @item undefined section
2255 This ``section'' is a catch-all for address references to objects not in
2256 the preceding sections.
2257 @c FIXME: ref to some other doc on obj-file formats could go here.
2260 @cindex relocation example
2261 An idealized example of three relocatable sections follows.
2263 The example uses the traditional section names @samp{.text} and @samp{.data}.
2265 Memory addresses are on the horizontal axis.
2269 @c END TEXI2ROFF-KILL
2272 partial program # 1: |ttttt|dddd|00|
2279 partial program # 2: |TTT|DDD|000|
2282 +--+---+-----+--+----+---+-----+~~
2283 linked program: | |TTT|ttttt| |dddd|DDD|00000|
2284 +--+---+-----+--+----+---+-----+~~
2286 addresses: 0 @dots{}
2293 \line{\it Partial program \#1: \hfil}
2294 \line{\ibox{2.5cm}{\tt text}\ibox{2cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
2295 \line{\boxit{2.5cm}{\tt ttttt}\boxit{2cm}{\tt dddd}\boxit{1cm}{\tt 00}\hfil}
2297 \line{\it Partial program \#2: \hfil}
2298 \line{\ibox{1cm}{\tt text}\ibox{1.5cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
2299 \line{\boxit{1cm}{\tt TTT}\boxit{1.5cm}{\tt DDDD}\boxit{1cm}{\tt 000}\hfil}
2301 \line{\it linked program: \hfil}
2302 \line{\ibox{.5cm}{}\ibox{1cm}{\tt text}\ibox{2.5cm}{}\ibox{.75cm}{}\ibox{2cm}{\tt data}\ibox{1.5cm}{}\ibox{2cm}{\tt bss}\hfil}
2303 \line{\boxit{.5cm}{}\boxit{1cm}{\tt TTT}\boxit{2.5cm}{\tt
2304 ttttt}\boxit{.75cm}{}\boxit{2cm}{\tt dddd}\boxit{1.5cm}{\tt
2305 DDDD}\boxit{2cm}{\tt 00000}\ \dots\hfil}
2307 \line{\it addresses: \hfil}
2311 @c END TEXI2ROFF-KILL
2314 @section Assembler Internal Sections
2316 @cindex internal assembler sections
2317 @cindex sections in messages, internal
2318 These sections are meant only for the internal use of @code{@value{AS}}. They
2319 have no meaning at run-time. You do not really need to know about these
2320 sections for most purposes; but they can be mentioned in @code{@value{AS}}
2321 warning messages, so it might be helpful to have an idea of their
2322 meanings to @code{@value{AS}}. These sections are used to permit the
2323 value of every expression in your assembly language program to be a
2324 section-relative address.
2327 @cindex assembler internal logic error
2328 @item ASSEMBLER-INTERNAL-LOGIC-ERROR!
2329 An internal assembler logic error has been found. This means there is a
2330 bug in the assembler.
2332 @cindex expr (internal section)
2334 The assembler stores complex expression internally as combinations of
2335 symbols. When it needs to represent an expression as a symbol, it puts
2336 it in the expr section.
2338 @c FIXME item transfer[t] vector preload
2339 @c FIXME item transfer[t] vector postload
2340 @c FIXME item register
2344 @section Sub-Sections
2346 @cindex numbered subsections
2347 @cindex grouping data
2353 fall into two sections: text and data.
2355 You may have separate groups of
2357 data in named sections
2361 data in named sections
2367 that you want to end up near to each other in the object file, even though they
2368 are not contiguous in the assembler source. @code{@value{AS}} allows you to
2369 use @dfn{subsections} for this purpose. Within each section, there can be
2370 numbered subsections with values from 0 to 8192. Objects assembled into the
2371 same subsection go into the object file together with other objects in the same
2372 subsection. For example, a compiler might want to store constants in the text
2373 section, but might not want to have them interspersed with the program being
2374 assembled. In this case, the compiler could issue a @samp{.text 0} before each
2375 section of code being output, and a @samp{.text 1} before each group of
2376 constants being output.
2378 Subsections are optional. If you do not use subsections, everything
2379 goes in subsection number zero.
2382 Each subsection is zero-padded up to a multiple of four bytes.
2383 (Subsections may be padded a different amount on different flavors
2384 of @code{@value{AS}}.)
2388 On the H8/300 and H8/500 platforms, each subsection is zero-padded to a word
2389 boundary (two bytes).
2390 The same is true on the Hitachi SH.
2393 @c FIXME section padding (alignment)?
2394 @c Rich Pixley says padding here depends on target obj code format; that
2395 @c doesn't seem particularly useful to say without further elaboration,
2396 @c so for now I say nothing about it. If this is a generic BFD issue,
2397 @c these paragraphs might need to vanish from this manual, and be
2398 @c discussed in BFD chapter of binutils (or some such).
2401 On the AMD 29K family, no particular padding is added to section or
2402 subsection sizes; @value{AS} forces no alignment on this platform.
2406 Subsections appear in your object file in numeric order, lowest numbered
2407 to highest. (All this to be compatible with other people's assemblers.)
2408 The object file contains no representation of subsections; @code{@value{LD}} and
2409 other programs that manipulate object files see no trace of them.
2410 They just see all your text subsections as a text section, and all your
2411 data subsections as a data section.
2413 To specify which subsection you want subsequent statements assembled
2414 into, use a numeric argument to specify it, in a @samp{.text
2415 @var{expression}} or a @samp{.data @var{expression}} statement.
2418 When generating COFF output, you
2423 can also use an extra subsection
2424 argument with arbitrary named sections: @samp{.section @var{name},
2427 @var{Expression} should be an absolute expression.
2428 (@xref{Expressions}.) If you just say @samp{.text} then @samp{.text 0}
2429 is assumed. Likewise @samp{.data} means @samp{.data 0}. Assembly
2430 begins in @code{text 0}. For instance:
2432 .text 0 # The default subsection is text 0 anyway.
2433 .ascii "This lives in the first text subsection. *"
2435 .ascii "But this lives in the second text subsection."
2437 .ascii "This lives in the data section,"
2438 .ascii "in the first data subsection."
2440 .ascii "This lives in the first text section,"
2441 .ascii "immediately following the asterisk (*)."
2444 Each section has a @dfn{location counter} incremented by one for every byte
2445 assembled into that section. Because subsections are merely a convenience
2446 restricted to @code{@value{AS}} there is no concept of a subsection location
2447 counter. There is no way to directly manipulate a location counter---but the
2448 @code{.align} directive changes it, and any label definition captures its
2449 current value. The location counter of the section where statements are being
2450 assembled is said to be the @dfn{active} location counter.
2453 @section bss Section
2456 @cindex common variable storage
2457 The bss section is used for local common variable storage.
2458 You may allocate address space in the bss section, but you may
2459 not dictate data to load into it before your program executes. When
2460 your program starts running, all the contents of the bss
2461 section are zeroed bytes.
2463 The @code{.lcomm} pseudo-op defines a symbol in the bss section; see
2464 @ref{Lcomm,,@code{.lcomm}}.
2466 The @code{.comm} pseudo-op may be used to declare a common symbol, which is
2467 another form of uninitialized symbol; see @xref{Comm,,@code{.comm}}.
2470 When assembling for a target which supports multiple sections, such as ELF or
2471 COFF, you may switch into the @code{.bss} section and define symbols as usual;
2472 see @ref{Section,,@code{.section}}. You may only assemble zero values into the
2473 section. Typically the section will only contain symbol definitions and
2474 @code{.skip} directives (@pxref{Skip,,@code{.skip}}).
2481 Symbols are a central concept: the programmer uses symbols to name
2482 things, the linker uses symbols to link, and the debugger uses symbols
2486 @cindex debuggers, and symbol order
2487 @emph{Warning:} @code{@value{AS}} does not place symbols in the object file in
2488 the same order they were declared. This may break some debuggers.
2493 * Setting Symbols:: Giving Symbols Other Values
2494 * Symbol Names:: Symbol Names
2495 * Dot:: The Special Dot Symbol
2496 * Symbol Attributes:: Symbol Attributes
2503 A @dfn{label} is written as a symbol immediately followed by a colon
2504 @samp{:}. The symbol then represents the current value of the
2505 active location counter, and is, for example, a suitable instruction
2506 operand. You are warned if you use the same symbol to represent two
2507 different locations: the first definition overrides any other
2511 On the HPPA, the usual form for a label need not be immediately followed by a
2512 colon, but instead must start in column zero. Only one label may be defined on
2513 a single line. To work around this, the HPPA version of @code{@value{AS}} also
2514 provides a special directive @code{.label} for defining labels more flexibly.
2517 @node Setting Symbols
2518 @section Giving Symbols Other Values
2520 @cindex assigning values to symbols
2521 @cindex symbol values, assigning
2522 A symbol can be given an arbitrary value by writing a symbol, followed
2523 by an equals sign @samp{=}, followed by an expression
2524 (@pxref{Expressions}). This is equivalent to using the @code{.set}
2525 directive. @xref{Set,,@code{.set}}.
2528 @section Symbol Names
2530 @cindex symbol names
2531 @cindex names, symbol
2532 @ifclear SPECIAL-SYMS
2533 Symbol names begin with a letter or with one of @samp{._}. On most
2534 machines, you can also use @code{$} in symbol names; exceptions are
2535 noted in @ref{Machine Dependencies}. That character may be followed by any
2536 string of digits, letters, dollar signs (unless otherwise noted in
2537 @ref{Machine Dependencies}), and underscores.
2540 For the AMD 29K family, @samp{?} is also allowed in the
2541 body of a symbol name, though not at its beginning.
2546 Symbol names begin with a letter or with one of @samp{._}. On the
2548 H8/500, you can also use @code{$} in symbol names. That character may
2549 be followed by any string of digits, letters, dollar signs (save on the
2550 H8/300), and underscores.
2554 Case of letters is significant: @code{foo} is a different symbol name
2557 Each symbol has exactly one name. Each name in an assembly language program
2558 refers to exactly one symbol. You may use that symbol name any number of times
2561 @subheading Local Symbol Names
2563 @cindex local symbol names
2564 @cindex symbol names, local
2565 @cindex temporary symbol names
2566 @cindex symbol names, temporary
2567 Local symbols help compilers and programmers use names temporarily.
2568 There are ten local symbol names, which are re-used throughout the
2569 program. You may refer to them using the names @samp{0} @samp{1}
2570 @dots{} @samp{9}. To define a local symbol, write a label of the form
2571 @samp{@b{N}:} (where @b{N} represents any digit). To refer to the most
2572 recent previous definition of that symbol write @samp{@b{N}b}, using the
2573 same digit as when you defined the label. To refer to the next
2574 definition of a local label, write @samp{@b{N}f}---where @b{N} gives you
2575 a choice of 10 forward references. The @samp{b} stands for
2576 ``backwards'' and the @samp{f} stands for ``forwards''.
2578 Local symbols are not emitted by the current @sc{gnu} C compiler.
2580 There is no restriction on how you can use these labels, but
2581 remember that at any point in the assembly you can refer to at most
2582 10 prior local labels and to at most 10 forward local labels.
2584 Local symbol names are only a notation device. They are immediately
2585 transformed into more conventional symbol names before the assembler
2586 uses them. The symbol names stored in the symbol table, appearing in
2587 error messages and optionally emitted to the object file have these
2592 All local labels begin with @samp{L}. Normally both @code{@value{AS}} and
2593 @code{@value{LD}} forget symbols that start with @samp{L}. These labels are
2594 used for symbols you are never intended to see. If you use the
2595 @samp{-L} option then @code{@value{AS}} retains these symbols in the
2596 object file. If you also instruct @code{@value{LD}} to retain these symbols,
2597 you may use them in debugging.
2600 If the label is written @samp{0:} then the digit is @samp{0}.
2601 If the label is written @samp{1:} then the digit is @samp{1}.
2602 And so on up through @samp{9:}.
2605 This unusual character is included so you do not accidentally invent
2606 a symbol of the same name. The character has ASCII value
2609 @item @emph{ordinal number}
2610 This is a serial number to keep the labels distinct. The first
2611 @samp{0:} gets the number @samp{1}; The 15th @samp{0:} gets the
2612 number @samp{15}; @emph{etc.}. Likewise for the other labels @samp{1:}
2616 For instance, the first @code{1:} is named @code{L1@kbd{C-A}1}, the 44th
2617 @code{3:} is named @code{L3@kbd{C-A}44}.
2620 @section The Special Dot Symbol
2622 @cindex dot (symbol)
2623 @cindex @code{.} (symbol)
2624 @cindex current address
2625 @cindex location counter
2626 The special symbol @samp{.} refers to the current address that
2627 @code{@value{AS}} is assembling into. Thus, the expression @samp{melvin:
2628 .long .} defines @code{melvin} to contain its own address.
2629 Assigning a value to @code{.} is treated the same as a @code{.org}
2630 directive. Thus, the expression @samp{.=.+4} is the same as saying
2631 @ifclear no-space-dir
2640 @node Symbol Attributes
2641 @section Symbol Attributes
2643 @cindex symbol attributes
2644 @cindex attributes, symbol
2645 Every symbol has, as well as its name, the attributes ``Value'' and
2646 ``Type''. Depending on output format, symbols can also have auxiliary
2649 The detailed definitions are in @file{a.out.h}.
2652 If you use a symbol without defining it, @code{@value{AS}} assumes zero for
2653 all these attributes, and probably won't warn you. This makes the
2654 symbol an externally defined symbol, which is generally what you
2658 * Symbol Value:: Value
2659 * Symbol Type:: Type
2662 * a.out Symbols:: Symbol Attributes: @code{a.out}
2666 * a.out Symbols:: Symbol Attributes: @code{a.out}
2669 * a.out Symbols:: Symbol Attributes: @code{a.out}, @code{b.out}
2674 * COFF Symbols:: Symbol Attributes for COFF
2677 * SOM Symbols:: Symbol Attributes for SOM
2684 @cindex value of a symbol
2685 @cindex symbol value
2686 The value of a symbol is (usually) 32 bits. For a symbol which labels a
2687 location in the text, data, bss or absolute sections the value is the
2688 number of addresses from the start of that section to the label.
2689 Naturally for text, data and bss sections the value of a symbol changes
2690 as @code{@value{LD}} changes section base addresses during linking. Absolute
2691 symbols' values do not change during linking: that is why they are
2694 The value of an undefined symbol is treated in a special way. If it is
2695 0 then the symbol is not defined in this assembler source file, and
2696 @code{@value{LD}} tries to determine its value from other files linked into the
2697 same program. You make this kind of symbol simply by mentioning a symbol
2698 name without defining it. A non-zero value represents a @code{.comm}
2699 common declaration. The value is how much common storage to reserve, in
2700 bytes (addresses). The symbol refers to the first address of the
2706 @cindex type of a symbol
2708 The type attribute of a symbol contains relocation (section)
2709 information, any flag settings indicating that a symbol is external, and
2710 (optionally), other information for linkers and debuggers. The exact
2711 format depends on the object-code output format in use.
2716 @c The following avoids a "widow" subsection title. @group would be
2717 @c better if it were available outside examples.
2720 @subsection Symbol Attributes: @code{a.out}, @code{b.out}
2722 @cindex @code{b.out} symbol attributes
2723 @cindex symbol attributes, @code{b.out}
2724 These symbol attributes appear only when @code{@value{AS}} is configured for
2725 one of the Berkeley-descended object output formats---@code{a.out} or
2731 @subsection Symbol Attributes: @code{a.out}
2733 @cindex @code{a.out} symbol attributes
2734 @cindex symbol attributes, @code{a.out}
2740 @subsection Symbol Attributes: @code{a.out}
2742 @cindex @code{a.out} symbol attributes
2743 @cindex symbol attributes, @code{a.out}
2747 * Symbol Desc:: Descriptor
2748 * Symbol Other:: Other
2752 @subsubsection Descriptor
2754 @cindex descriptor, of @code{a.out} symbol
2755 This is an arbitrary 16-bit value. You may establish a symbol's
2756 descriptor value by using a @code{.desc} statement
2757 (@pxref{Desc,,@code{.desc}}). A descriptor value means nothing to
2761 @subsubsection Other
2763 @cindex other attribute, of @code{a.out} symbol
2764 This is an arbitrary 8-bit value. It means nothing to @code{@value{AS}}.
2769 @subsection Symbol Attributes for COFF
2771 @cindex COFF symbol attributes
2772 @cindex symbol attributes, COFF
2774 The COFF format supports a multitude of auxiliary symbol attributes;
2775 like the primary symbol attributes, they are set between @code{.def} and
2776 @code{.endef} directives.
2778 @subsubsection Primary Attributes
2780 @cindex primary attributes, COFF symbols
2781 The symbol name is set with @code{.def}; the value and type,
2782 respectively, with @code{.val} and @code{.type}.
2784 @subsubsection Auxiliary Attributes
2786 @cindex auxiliary attributes, COFF symbols
2787 The @code{@value{AS}} directives @code{.dim}, @code{.line}, @code{.scl},
2788 @code{.size}, and @code{.tag} can generate auxiliary symbol table
2789 information for COFF.
2794 @subsection Symbol Attributes for SOM
2796 @cindex SOM symbol attributes
2797 @cindex symbol attributes, SOM
2799 The SOM format for the HPPA supports a multitude of symbol attributes set with
2800 the @code{.EXPORT} and @code{.IMPORT} directives.
2802 The attributes are described in @cite{HP9000 Series 800 Assembly
2803 Language Reference Manual} (HP 92432-90001) under the @code{IMPORT} and
2804 @code{EXPORT} assembler directive documentation.
2808 @chapter Expressions
2812 @cindex numeric values
2813 An @dfn{expression} specifies an address or numeric value.
2814 Whitespace may precede and/or follow an expression.
2816 The result of an expression must be an absolute number, or else an offset into
2817 a particular section. If an expression is not absolute, and there is not
2818 enough information when @code{@value{AS}} sees the expression to know its
2819 section, a second pass over the source program might be necessary to interpret
2820 the expression---but the second pass is currently not implemented.
2821 @code{@value{AS}} aborts with an error message in this situation.
2824 * Empty Exprs:: Empty Expressions
2825 * Integer Exprs:: Integer Expressions
2829 @section Empty Expressions
2831 @cindex empty expressions
2832 @cindex expressions, empty
2833 An empty expression has no value: it is just whitespace or null.
2834 Wherever an absolute expression is required, you may omit the
2835 expression, and @code{@value{AS}} assumes a value of (absolute) 0. This
2836 is compatible with other assemblers.
2839 @section Integer Expressions
2841 @cindex integer expressions
2842 @cindex expressions, integer
2843 An @dfn{integer expression} is one or more @emph{arguments} delimited
2844 by @emph{operators}.
2847 * Arguments:: Arguments
2848 * Operators:: Operators
2849 * Prefix Ops:: Prefix Operators
2850 * Infix Ops:: Infix Operators
2854 @subsection Arguments
2856 @cindex expression arguments
2857 @cindex arguments in expressions
2858 @cindex operands in expressions
2859 @cindex arithmetic operands
2860 @dfn{Arguments} are symbols, numbers or subexpressions. In other
2861 contexts arguments are sometimes called ``arithmetic operands''. In
2862 this manual, to avoid confusing them with the ``instruction operands'' of
2863 the machine language, we use the term ``argument'' to refer to parts of
2864 expressions only, reserving the word ``operand'' to refer only to machine
2865 instruction operands.
2867 Symbols are evaluated to yield @{@var{section} @var{NNN}@} where
2868 @var{section} is one of text, data, bss, absolute,
2869 or undefined. @var{NNN} is a signed, 2's complement 32 bit
2872 Numbers are usually integers.
2874 A number can be a flonum or bignum. In this case, you are warned
2875 that only the low order 32 bits are used, and @code{@value{AS}} pretends
2876 these 32 bits are an integer. You may write integer-manipulating
2877 instructions that act on exotic constants, compatible with other
2880 @cindex subexpressions
2881 Subexpressions are a left parenthesis @samp{(} followed by an integer
2882 expression, followed by a right parenthesis @samp{)}; or a prefix
2883 operator followed by an argument.
2886 @subsection Operators
2888 @cindex operators, in expressions
2889 @cindex arithmetic functions
2890 @cindex functions, in expressions
2891 @dfn{Operators} are arithmetic functions, like @code{+} or @code{%}. Prefix
2892 operators are followed by an argument. Infix operators appear
2893 between their arguments. Operators may be preceded and/or followed by
2897 @subsection Prefix Operator
2899 @cindex prefix operators
2900 @code{@value{AS}} has the following @dfn{prefix operators}. They each take
2901 one argument, which must be absolute.
2903 @c the tex/end tex stuff surrounding this small table is meant to make
2904 @c it align, on the printed page, with the similar table in the next
2905 @c section (which is inside an enumerate).
2907 \global\advance\leftskip by \itemindent
2912 @dfn{Negation}. Two's complement negation.
2914 @dfn{Complementation}. Bitwise not.
2918 \global\advance\leftskip by -\itemindent
2922 @subsection Infix Operators
2924 @cindex infix operators
2925 @cindex operators, permitted arguments
2926 @dfn{Infix operators} take two arguments, one on either side. Operators
2927 have precedence, but operations with equal precedence are performed left
2928 to right. Apart from @code{+} or @code{-}, both arguments must be
2929 absolute, and the result is absolute.
2932 @cindex operator precedence
2933 @cindex precedence of operators
2940 @dfn{Multiplication}.
2943 @dfn{Division}. Truncation is the same as the C operator @samp{/}
2950 @dfn{Shift Left}. Same as the C operator @samp{<<}.
2954 @dfn{Shift Right}. Same as the C operator @samp{>>}.
2958 Intermediate precedence
2963 @dfn{Bitwise Inclusive Or}.
2969 @dfn{Bitwise Exclusive Or}.
2972 @dfn{Bitwise Or Not}.
2979 @cindex addition, permitted arguments
2980 @cindex plus, permitted arguments
2981 @cindex arguments for addition
2983 @dfn{Addition}. If either argument is absolute, the result has the section of
2984 the other argument. You may not add together arguments from different
2987 @cindex subtraction, permitted arguments
2988 @cindex minus, permitted arguments
2989 @cindex arguments for subtraction
2991 @dfn{Subtraction}. If the right argument is absolute, the
2992 result has the section of the left argument.
2993 If both arguments are in the same section, the result is absolute.
2994 You may not subtract arguments from different sections.
2995 @c FIXME is there still something useful to say about undefined - undefined ?
2999 In short, it's only meaningful to add or subtract the @emph{offsets} in an
3000 address; you can only have a defined section in one of the two arguments.
3003 @chapter Assembler Directives
3005 @cindex directives, machine independent
3006 @cindex pseudo-ops, machine independent
3007 @cindex machine independent directives
3008 All assembler directives have names that begin with a period (@samp{.}).
3009 The rest of the name is letters, usually in lower case.
3011 This chapter discusses directives that are available regardless of the
3012 target machine configuration for the @sc{gnu} assembler.
3014 Some machine configurations provide additional directives.
3015 @xref{Machine Dependencies}.
3018 @ifset machine-directives
3019 @xref{Machine Dependencies} for additional directives.
3024 * Abort:: @code{.abort}
3026 * ABORT:: @code{.ABORT}
3029 * Align:: @code{.align @var{abs-expr} , @var{abs-expr}}
3030 * Ascii:: @code{.ascii "@var{string}"}@dots{}
3031 * Asciz:: @code{.asciz "@var{string}"}@dots{}
3032 * Balign:: @code{.balign @var{abs-expr} , @var{abs-expr}}
3033 * Byte:: @code{.byte @var{expressions}}
3034 * Comm:: @code{.comm @var{symbol} , @var{length} }
3035 * Data:: @code{.data @var{subsection}}
3037 * Def:: @code{.def @var{name}}
3040 * Desc:: @code{.desc @var{symbol}, @var{abs-expression}}
3046 * Double:: @code{.double @var{flonums}}
3047 * Eject:: @code{.eject}
3048 * Else:: @code{.else}
3051 * Endef:: @code{.endef}
3054 * Endfunc:: @code{.endfunc}
3055 * Endif:: @code{.endif}
3056 * Equ:: @code{.equ @var{symbol}, @var{expression}}
3057 * Equiv:: @code{.equiv @var{symbol}, @var{expression}}
3059 * Exitm:: @code{.exitm}
3060 * Extern:: @code{.extern}
3061 * Fail:: @code{.fail}
3062 @ifclear no-file-dir
3063 * File:: @code{.file @var{string}}
3066 * Fill:: @code{.fill @var{repeat} , @var{size} , @var{value}}
3067 * Float:: @code{.float @var{flonums}}
3068 * Func:: @code{.func}
3069 * Global:: @code{.global @var{symbol}}, @code{.globl @var{symbol}}
3070 * hword:: @code{.hword @var{expressions}}
3071 * Ident:: @code{.ident}
3072 * If:: @code{.if @var{absolute expression}}
3073 * Include:: @code{.include "@var{file}"}
3074 * Int:: @code{.int @var{expressions}}
3075 * Irp:: @code{.irp @var{symbol},@var{values}}@dots{}
3076 * Irpc:: @code{.irpc @var{symbol},@var{values}}@dots{}
3077 * Lcomm:: @code{.lcomm @var{symbol} , @var{length}}
3078 * Lflags:: @code{.lflags}
3079 @ifclear no-line-dir
3080 * Line:: @code{.line @var{line-number}}
3083 * Ln:: @code{.ln @var{line-number}}
3084 * Linkonce:: @code{.linkonce [@var{type}]}
3085 * List:: @code{.list}
3086 * Long:: @code{.long @var{expressions}}
3088 * Lsym:: @code{.lsym @var{symbol}, @var{expression}}
3091 * Macro:: @code{.macro @var{name} @var{args}}@dots{}
3092 * MRI:: @code{.mri @var{val}}
3094 * Nolist:: @code{.nolist}
3095 * Octa:: @code{.octa @var{bignums}}
3096 * Org:: @code{.org @var{new-lc} , @var{fill}}
3097 * P2align:: @code{.p2align @var{abs-expr} , @var{abs-expr}}
3098 * Print:: @code{.print @var{string}}
3099 * Psize:: @code{.psize @var{lines}, @var{columns}}
3100 * Purgem:: @code{.purgem @var{name}}
3101 * Quad:: @code{.quad @var{bignums}}
3102 * Rept:: @code{.rept @var{count}}
3103 * Sbttl:: @code{.sbttl "@var{subheading}"}
3105 * Scl:: @code{.scl @var{class}}
3106 * Section:: @code{.section @var{name}, @var{subsection}}
3109 * Set:: @code{.set @var{symbol}, @var{expression}}
3110 * Short:: @code{.short @var{expressions}}
3111 * Single:: @code{.single @var{flonums}}
3113 * Size:: @code{.size}
3116 * Skip:: @code{.skip @var{size} , @var{fill}}
3117 * Sleb128:: @code{.sleb128 @var{expressions}}
3118 * Space:: @code{.space @var{size} , @var{fill}}
3120 * Stab:: @code{.stabd, .stabn, .stabs}
3123 * String:: @code{.string "@var{str}"}
3124 * Struct:: @code{.struct @var{expression}}
3126 * Symver:: @code{.symver @var{name},@var{name2@@nodename}}
3129 * Tag:: @code{.tag @var{structname}}
3132 * Text:: @code{.text @var{subsection}}
3133 * Title:: @code{.title "@var{heading}"}
3135 * Type:: @code{.type @var{int}}
3136 * Val:: @code{.val @var{addr}}
3139 * Uleb128:: @code{.uleb128 @var{expressions}}
3140 * Word:: @code{.word @var{expressions}}
3141 * Deprecated:: Deprecated Directives
3145 @section @code{.abort}
3147 @cindex @code{abort} directive
3148 @cindex stopping the assembly
3149 This directive stops the assembly immediately. It is for
3150 compatibility with other assemblers. The original idea was that the
3151 assembly language source would be piped into the assembler. If the sender
3152 of the source quit, it could use this directive tells @code{@value{AS}} to
3153 quit also. One day @code{.abort} will not be supported.
3157 @section @code{.ABORT}
3159 @cindex @code{ABORT} directive
3160 When producing COFF output, @code{@value{AS}} accepts this directive as a
3161 synonym for @samp{.abort}.
3164 When producing @code{b.out} output, @code{@value{AS}} accepts this directive,
3170 @section @code{.align @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
3172 @cindex padding the location counter
3173 @cindex @code{align} directive
3174 Pad the location counter (in the current subsection) to a particular storage
3175 boundary. The first expression (which must be absolute) is the alignment
3176 required, as described below.
3178 The second expression (also absolute) gives the fill value to be stored in the
3179 padding bytes. It (and the comma) may be omitted. If it is omitted, the
3180 padding bytes are normally zero. However, on some systems, if the section is
3181 marked as containing code and the fill value is omitted, the space is filled
3182 with no-op instructions.
3184 The third expression is also absolute, and is also optional. If it is present,
3185 it is the maximum number of bytes that should be skipped by this alignment
3186 directive. If doing the alignment would require skipping more bytes than the
3187 specified maximum, then the alignment is not done at all. You can omit the
3188 fill value (the second argument) entirely by simply using two commas after the
3189 required alignment; this can be useful if you want the alignment to be filled
3190 with no-op instructions when appropriate.
3192 The way the required alignment is specified varies from system to system.
3193 For the a29k, hppa, m68k, m88k, w65, sparc, and Hitachi SH, and i386 using ELF
3195 the first expression is the
3196 alignment request in bytes. For example @samp{.align 8} advances
3197 the location counter until it is a multiple of 8. If the location counter
3198 is already a multiple of 8, no change is needed.
3200 For other systems, including the i386 using a.out format, it is the
3201 number of low-order zero bits the location counter must have after
3202 advancement. For example @samp{.align 3} advances the location
3203 counter until it a multiple of 8. If the location counter is already a
3204 multiple of 8, no change is needed.
3206 This inconsistency is due to the different behaviors of the various
3207 native assemblers for these systems which GAS must emulate.
3208 GAS also provides @code{.balign} and @code{.p2align} directives,
3209 described later, which have a consistent behavior across all
3210 architectures (but are specific to GAS).
3213 @section @code{.ascii "@var{string}"}@dots{}
3215 @cindex @code{ascii} directive
3216 @cindex string literals
3217 @code{.ascii} expects zero or more string literals (@pxref{Strings})
3218 separated by commas. It assembles each string (with no automatic
3219 trailing zero byte) into consecutive addresses.
3222 @section @code{.asciz "@var{string}"}@dots{}
3224 @cindex @code{asciz} directive
3225 @cindex zero-terminated strings
3226 @cindex null-terminated strings
3227 @code{.asciz} is just like @code{.ascii}, but each string is followed by
3228 a zero byte. The ``z'' in @samp{.asciz} stands for ``zero''.
3231 @section @code{.balign[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
3233 @cindex padding the location counter given number of bytes
3234 @cindex @code{balign} directive
3235 Pad the location counter (in the current subsection) to a particular
3236 storage boundary. The first expression (which must be absolute) is the
3237 alignment request in bytes. For example @samp{.balign 8} advances
3238 the location counter until it is a multiple of 8. If the location counter
3239 is already a multiple of 8, no change is needed.
3241 The second expression (also absolute) gives the fill value to be stored in the
3242 padding bytes. It (and the comma) may be omitted. If it is omitted, the
3243 padding bytes are normally zero. However, on some systems, if the section is
3244 marked as containing code and the fill value is omitted, the space is filled
3245 with no-op instructions.
3247 The third expression is also absolute, and is also optional. If it is present,
3248 it is the maximum number of bytes that should be skipped by this alignment
3249 directive. If doing the alignment would require skipping more bytes than the
3250 specified maximum, then the alignment is not done at all. You can omit the
3251 fill value (the second argument) entirely by simply using two commas after the
3252 required alignment; this can be useful if you want the alignment to be filled
3253 with no-op instructions when appropriate.
3255 @cindex @code{balignw} directive
3256 @cindex @code{balignl} directive
3257 The @code{.balignw} and @code{.balignl} directives are variants of the
3258 @code{.balign} directive. The @code{.balignw} directive treats the fill
3259 pattern as a two byte word value. The @code{.balignl} directives treats the
3260 fill pattern as a four byte longword value. For example, @code{.balignw
3261 4,0x368d} will align to a multiple of 4. If it skips two bytes, they will be
3262 filled in with the value 0x368d (the exact placement of the bytes depends upon
3263 the endianness of the processor). If it skips 1 or 3 bytes, the fill value is
3267 @section @code{.byte @var{expressions}}
3269 @cindex @code{byte} directive
3270 @cindex integers, one byte
3271 @code{.byte} expects zero or more expressions, separated by commas.
3272 Each expression is assembled into the next byte.
3275 @section @code{.comm @var{symbol} , @var{length} }
3277 @cindex @code{comm} directive
3278 @cindex symbol, common
3279 @code{.comm} declares a common symbol named @var{symbol}. When linking, a
3280 common symbol in one object file may be merged with a defined or common symbol
3281 of the same name in another object file. If @code{@value{LD}} does not see a
3282 definition for the symbol--just one or more common symbols--then it will
3283 allocate @var{length} bytes of uninitialized memory. @var{length} must be an
3284 absolute expression. If @code{@value{LD}} sees multiple common symbols with
3285 the same name, and they do not all have the same size, it will allocate space
3286 using the largest size.
3289 When using ELF, the @code{.comm} directive takes an optional third argument.
3290 This is the desired alignment of the symbol, specified as a byte boundary (for
3291 example, an alignment of 16 means that the least significant 4 bits of the
3292 address should be zero). The alignment must be an absolute expression, and it
3293 must be a power of two. If @code{@value{LD}} allocates uninitialized memory
3294 for the common symbol, it will use the alignment when placing the symbol. If
3295 no alignment is specified, @code{@value{AS}} will set the alignment to the
3296 largest power of two less than or equal to the size of the symbol, up to a
3301 The syntax for @code{.comm} differs slightly on the HPPA. The syntax is
3302 @samp{@var{symbol} .comm, @var{length}}; @var{symbol} is optional.
3306 @section @code{.data @var{subsection}}
3308 @cindex @code{data} directive
3309 @code{.data} tells @code{@value{AS}} to assemble the following statements onto the
3310 end of the data subsection numbered @var{subsection} (which is an
3311 absolute expression). If @var{subsection} is omitted, it defaults
3316 @section @code{.def @var{name}}
3318 @cindex @code{def} directive
3319 @cindex COFF symbols, debugging
3320 @cindex debugging COFF symbols
3321 Begin defining debugging information for a symbol @var{name}; the
3322 definition extends until the @code{.endef} directive is encountered.
3325 This directive is only observed when @code{@value{AS}} is configured for COFF
3326 format output; when producing @code{b.out}, @samp{.def} is recognized,
3333 @section @code{.desc @var{symbol}, @var{abs-expression}}
3335 @cindex @code{desc} directive
3336 @cindex COFF symbol descriptor
3337 @cindex symbol descriptor, COFF
3338 This directive sets the descriptor of the symbol (@pxref{Symbol Attributes})
3339 to the low 16 bits of an absolute expression.
3342 The @samp{.desc} directive is not available when @code{@value{AS}} is
3343 configured for COFF output; it is only for @code{a.out} or @code{b.out}
3344 object format. For the sake of compatibility, @code{@value{AS}} accepts
3345 it, but produces no output, when configured for COFF.
3351 @section @code{.dim}
3353 @cindex @code{dim} directive
3354 @cindex COFF auxiliary symbol information
3355 @cindex auxiliary symbol information, COFF
3356 This directive is generated by compilers to include auxiliary debugging
3357 information in the symbol table. It is only permitted inside
3358 @code{.def}/@code{.endef} pairs.
3361 @samp{.dim} is only meaningful when generating COFF format output; when
3362 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
3368 @section @code{.double @var{flonums}}
3370 @cindex @code{double} directive
3371 @cindex floating point numbers (double)
3372 @code{.double} expects zero or more flonums, separated by commas. It
3373 assembles floating point numbers.
3375 The exact kind of floating point numbers emitted depends on how
3376 @code{@value{AS}} is configured. @xref{Machine Dependencies}.
3380 On the @value{TARGET} family @samp{.double} emits 64-bit floating-point numbers
3381 in @sc{ieee} format.
3386 @section @code{.eject}
3388 @cindex @code{eject} directive
3389 @cindex new page, in listings
3390 @cindex page, in listings
3391 @cindex listing control: new page
3392 Force a page break at this point, when generating assembly listings.
3395 @section @code{.else}
3397 @cindex @code{else} directive
3398 @code{.else} is part of the @code{@value{AS}} support for conditional
3399 assembly; @pxref{If,,@code{.if}}. It marks the beginning of a section
3400 of code to be assembled if the condition for the preceding @code{.if}
3404 @section @code{.end}
3406 @cindex @code{end} directive
3407 @code{.end} marks the end of the assembly file. @code{@value{AS}} does not
3408 process anything in the file past the @code{.end} directive.
3412 @section @code{.endef}
3414 @cindex @code{endef} directive
3415 This directive flags the end of a symbol definition begun with
3419 @samp{.endef} is only meaningful when generating COFF format output; if
3420 @code{@value{AS}} is configured to generate @code{b.out}, it accepts this
3421 directive but ignores it.
3426 @section @code{.endfunc}
3427 @cindex @code{endfunc} directive
3428 @code{.endfunc} marks the end of a function specified with @code{.func}.
3431 @section @code{.endif}
3433 @cindex @code{endif} directive
3434 @code{.endif} is part of the @code{@value{AS}} support for conditional assembly;
3435 it marks the end of a block of code that is only assembled
3436 conditionally. @xref{If,,@code{.if}}.
3439 @section @code{.equ @var{symbol}, @var{expression}}
3441 @cindex @code{equ} directive
3442 @cindex assigning values to symbols
3443 @cindex symbols, assigning values to
3444 This directive sets the value of @var{symbol} to @var{expression}.
3445 It is synonymous with @samp{.set}; @pxref{Set,,@code{.set}}.
3448 The syntax for @code{equ} on the HPPA is
3449 @samp{@var{symbol} .equ @var{expression}}.
3453 @section @code{.equiv @var{symbol}, @var{expression}}
3454 @cindex @code{equiv} directive
3455 The @code{.equiv} directive is like @code{.equ} and @code{.set}, except that
3456 the assembler will signal an error if @var{symbol} is already defined.
3458 Except for the contents of the error message, this is roughly equivalent to
3467 @section @code{.err}
3468 @cindex @code{err} directive
3469 If @code{@value{AS}} assembles a @code{.err} directive, it will print an error
3470 message and, unless the @code{-Z} option was used, it will not generate an
3471 object file. This can be used to signal error an conditionally compiled code.
3474 @section @code{.exitm}
3475 Exit early from the current macro definition. @xref{Macro}.
3478 @section @code{.extern}
3480 @cindex @code{extern} directive
3481 @code{.extern} is accepted in the source program---for compatibility
3482 with other assemblers---but it is ignored. @code{@value{AS}} treats
3483 all undefined symbols as external.
3486 @section @code{.fail @var{expression}}
3488 @cindex @code{fail} directive
3489 Generates an error or a warning. If the value of the @var{expression} is 500
3490 or more, @code{@value{AS}} will print a warning message. If the value is less
3491 than 500, @code{@value{AS}} will print an error message. The message will
3492 include the value of @var{expression}. This can occasionally be useful inside
3493 complex nested macros or conditional assembly.
3495 @ifclear no-file-dir
3497 @section @code{.file @var{string}}
3499 @cindex @code{file} directive
3500 @cindex logical file name
3501 @cindex file name, logical
3502 @code{.file} tells @code{@value{AS}} that we are about to start a new logical
3503 file. @var{string} is the new file name. In general, the filename is
3504 recognized whether or not it is surrounded by quotes @samp{"}; but if you wish
3505 to specify an empty file name, you must give the quotes--@code{""}. This
3506 statement may go away in future: it is only recognized to be compatible with
3507 old @code{@value{AS}} programs.
3509 In some configurations of @code{@value{AS}}, @code{.file} has already been
3510 removed to avoid conflicts with other assemblers. @xref{Machine Dependencies}.
3515 @section @code{.fill @var{repeat} , @var{size} , @var{value}}
3517 @cindex @code{fill} directive
3518 @cindex writing patterns in memory
3519 @cindex patterns, writing in memory
3520 @var{result}, @var{size} and @var{value} are absolute expressions.
3521 This emits @var{repeat} copies of @var{size} bytes. @var{Repeat}
3522 may be zero or more. @var{Size} may be zero or more, but if it is
3523 more than 8, then it is deemed to have the value 8, compatible with
3524 other people's assemblers. The contents of each @var{repeat} bytes
3525 is taken from an 8-byte number. The highest order 4 bytes are
3526 zero. The lowest order 4 bytes are @var{value} rendered in the
3527 byte-order of an integer on the computer @code{@value{AS}} is assembling for.
3528 Each @var{size} bytes in a repetition is taken from the lowest order
3529 @var{size} bytes of this number. Again, this bizarre behavior is
3530 compatible with other people's assemblers.
3532 @var{size} and @var{value} are optional.
3533 If the second comma and @var{value} are absent, @var{value} is
3534 assumed zero. If the first comma and following tokens are absent,
3535 @var{size} is assumed to be 1.
3538 @section @code{.float @var{flonums}}
3540 @cindex floating point numbers (single)
3541 @cindex @code{float} directive
3542 This directive assembles zero or more flonums, separated by commas. It
3543 has the same effect as @code{.single}.
3545 The exact kind of floating point numbers emitted depends on how
3546 @code{@value{AS}} is configured.
3547 @xref{Machine Dependencies}.
3551 On the @value{TARGET} family, @code{.float} emits 32-bit floating point numbers
3552 in @sc{ieee} format.
3557 @section @code{.func @var{name}[,@var{label}]}
3558 @cindex @code{func} directive
3559 @code{.func} emits debugging information to denote function @var{name}, and
3560 is ignored unless the file is assembled with debugging enabled.
3561 Only @samp{--gstabs} is currently supported.
3562 @var{label} is the entry point of the function and if omitted @var{name}
3563 prepended with the @samp{leading char} is used.
3564 @samp{leading char} is usually @code{_} or nothing, depending on the target.
3565 All functions are currently defined to have @code{void} return type.
3566 The function must be terminated with @code{.endfunc}.
3569 @section @code{.global @var{symbol}}, @code{.globl @var{symbol}}
3571 @cindex @code{global} directive
3572 @cindex symbol, making visible to linker
3573 @code{.global} makes the symbol visible to @code{@value{LD}}. If you define
3574 @var{symbol} in your partial program, its value is made available to
3575 other partial programs that are linked with it. Otherwise,
3576 @var{symbol} takes its attributes from a symbol of the same name
3577 from another file linked into the same program.
3579 Both spellings (@samp{.globl} and @samp{.global}) are accepted, for
3580 compatibility with other assemblers.
3583 On the HPPA, @code{.global} is not always enough to make it accessible to other
3584 partial programs. You may need the HPPA-only @code{.EXPORT} directive as well.
3585 @xref{HPPA Directives,, HPPA Assembler Directives}.
3589 @section @code{.hword @var{expressions}}
3591 @cindex @code{hword} directive
3592 @cindex integers, 16-bit
3593 @cindex numbers, 16-bit
3594 @cindex sixteen bit integers
3595 This expects zero or more @var{expressions}, and emits
3596 a 16 bit number for each.
3599 This directive is a synonym for @samp{.short}; depending on the target
3600 architecture, it may also be a synonym for @samp{.word}.
3604 This directive is a synonym for @samp{.short}.
3607 This directive is a synonym for both @samp{.short} and @samp{.word}.
3612 @section @code{.ident}
3614 @cindex @code{ident} directive
3615 This directive is used by some assemblers to place tags in object files.
3616 @code{@value{AS}} simply accepts the directive for source-file
3617 compatibility with such assemblers, but does not actually emit anything
3621 @section @code{.if @var{absolute expression}}
3623 @cindex conditional assembly
3624 @cindex @code{if} directive
3625 @code{.if} marks the beginning of a section of code which is only
3626 considered part of the source program being assembled if the argument
3627 (which must be an @var{absolute expression}) is non-zero. The end of
3628 the conditional section of code must be marked by @code{.endif}
3629 (@pxref{Endif,,@code{.endif}}); optionally, you may include code for the
3630 alternative condition, flagged by @code{.else} (@pxref{Else,,@code{.else}}).
3632 The following variants of @code{.if} are also supported:
3634 @cindex @code{ifdef} directive
3635 @item .ifdef @var{symbol}
3636 Assembles the following section of code if the specified @var{symbol}
3639 @cindex @code{ifc} directive
3640 @item .ifc @var{string1},@var{string2}
3641 Assembles the following section of code if the two strings are the same. The
3642 strings may be optionally quoted with single quotes. If they are not quoted,
3643 the first string stops at the first comma, and the second string stops at the
3644 end of the line. Strings which contain whitespace should be quoted. The
3645 string comparison is case sensitive.
3647 @cindex @code{ifeq} directive
3648 @item .ifeq @var{absolute expression}
3649 Assembles the following section of code if the argument is zero.
3651 @cindex @code{ifeqs} directive
3652 @item .ifeqs @var{string1},@var{string2}
3653 Another form of @code{.ifc}. The strings must be quoted using double quotes.
3655 @cindex @code{ifge} directive
3656 @item .ifge @var{absolute expression}
3657 Assembles the following section of code if the argument is greater than or
3660 @cindex @code{ifgt} directive
3661 @item .ifgt @var{absolute expression}
3662 Assembles the following section of code if the argument is greater than zero.
3664 @cindex @code{ifle} directive
3665 @item .ifle @var{absolute expression}
3666 Assembles the following section of code if the argument is less than or equal
3669 @cindex @code{iflt} directive
3670 @item .iflt @var{absolute expression}
3671 Assembles the following section of code if the argument is less than zero.
3673 @cindex @code{ifnc} directive
3674 @item .ifnc @var{string1},@var{string2}.
3675 Like @code{.ifc}, but the sense of the test is reversed: this assembles the
3676 following section of code if the two strings are not the same.
3678 @cindex @code{ifndef} directive
3679 @cindex @code{ifnotdef} directive
3680 @item .ifndef @var{symbol}
3681 @itemx .ifnotdef @var{symbol}
3682 Assembles the following section of code if the specified @var{symbol}
3683 has not been defined. Both spelling variants are equivalent.
3685 @cindex @code{ifne} directive
3686 @item .ifne @var{absolute expression}
3687 Assembles the following section of code if the argument is not equal to zero
3688 (in other words, this is equivalent to @code{.if}).
3690 @cindex @code{ifnes} directive
3691 @item .ifnes @var{string1},@var{string2}
3692 Like @code{.ifeqs}, but the sense of the test is reversed: this assembles the
3693 following section of code if the two strings are not the same.
3697 @section @code{.include "@var{file}"}
3699 @cindex @code{include} directive
3700 @cindex supporting files, including
3701 @cindex files, including
3702 This directive provides a way to include supporting files at specified
3703 points in your source program. The code from @var{file} is assembled as
3704 if it followed the point of the @code{.include}; when the end of the
3705 included file is reached, assembly of the original file continues. You
3706 can control the search paths used with the @samp{-I} command-line option
3707 (@pxref{Invoking,,Command-Line Options}). Quotation marks are required
3711 @section @code{.int @var{expressions}}
3713 @cindex @code{int} directive
3714 @cindex integers, 32-bit
3715 Expect zero or more @var{expressions}, of any section, separated by commas.
3716 For each expression, emit a number that, at run time, is the value of that
3717 expression. The byte order and bit size of the number depends on what kind
3718 of target the assembly is for.
3722 On the H8/500 and most forms of the H8/300, @code{.int} emits 16-bit
3723 integers. On the H8/300H and the Hitachi SH, however, @code{.int} emits
3729 @section @code{.irp @var{symbol},@var{values}}@dots{}
3731 @cindex @code{irp} directive
3732 Evaluate a sequence of statements assigning different values to @var{symbol}.
3733 The sequence of statements starts at the @code{.irp} directive, and is
3734 terminated by an @code{.endr} directive. For each @var{value}, @var{symbol} is
3735 set to @var{value}, and the sequence of statements is assembled. If no
3736 @var{value} is listed, the sequence of statements is assembled once, with
3737 @var{symbol} set to the null string. To refer to @var{symbol} within the
3738 sequence of statements, use @var{\symbol}.
3740 For example, assembling
3748 is equivalent to assembling
3757 @section @code{.irpc @var{symbol},@var{values}}@dots{}
3759 @cindex @code{irpc} directive
3760 Evaluate a sequence of statements assigning different values to @var{symbol}.
3761 The sequence of statements starts at the @code{.irpc} directive, and is
3762 terminated by an @code{.endr} directive. For each character in @var{value},
3763 @var{symbol} is set to the character, and the sequence of statements is
3764 assembled. If no @var{value} is listed, the sequence of statements is
3765 assembled once, with @var{symbol} set to the null string. To refer to
3766 @var{symbol} within the sequence of statements, use @var{\symbol}.
3768 For example, assembling
3776 is equivalent to assembling
3785 @section @code{.lcomm @var{symbol} , @var{length}}
3787 @cindex @code{lcomm} directive
3788 @cindex local common symbols
3789 @cindex symbols, local common
3790 Reserve @var{length} (an absolute expression) bytes for a local common
3791 denoted by @var{symbol}. The section and value of @var{symbol} are
3792 those of the new local common. The addresses are allocated in the bss
3793 section, so that at run-time the bytes start off zeroed. @var{Symbol}
3794 is not declared global (@pxref{Global,,@code{.global}}), so is normally
3795 not visible to @code{@value{LD}}.
3798 Some targets permit a third argument to be used with @code{.lcomm}. This
3799 argument specifies the desired alignment of the symbol in the bss section.
3803 The syntax for @code{.lcomm} differs slightly on the HPPA. The syntax is
3804 @samp{@var{symbol} .lcomm, @var{length}}; @var{symbol} is optional.
3808 @section @code{.lflags}
3810 @cindex @code{lflags} directive (ignored)
3811 @code{@value{AS}} accepts this directive, for compatibility with other
3812 assemblers, but ignores it.
3814 @ifclear no-line-dir
3816 @section @code{.line @var{line-number}}
3818 @cindex @code{line} directive
3822 @section @code{.ln @var{line-number}}
3824 @cindex @code{ln} directive
3826 @cindex logical line number
3828 Change the logical line number. @var{line-number} must be an absolute
3829 expression. The next line has that logical line number. Therefore any other
3830 statements on the current line (after a statement separator character) are
3831 reported as on logical line number @var{line-number} @minus{} 1. One day
3832 @code{@value{AS}} will no longer support this directive: it is recognized only
3833 for compatibility with existing assembler programs.
3837 @emph{Warning:} In the AMD29K configuration of @value{AS}, this command is
3838 not available; use the synonym @code{.ln} in that context.
3843 @ifclear no-line-dir
3844 Even though this is a directive associated with the @code{a.out} or
3845 @code{b.out} object-code formats, @code{@value{AS}} still recognizes it
3846 when producing COFF output, and treats @samp{.line} as though it
3847 were the COFF @samp{.ln} @emph{if} it is found outside a
3848 @code{.def}/@code{.endef} pair.
3850 Inside a @code{.def}, @samp{.line} is, instead, one of the directives
3851 used by compilers to generate auxiliary symbol information for
3856 @section @code{.linkonce [@var{type}]}
3858 @cindex @code{linkonce} directive
3859 @cindex common sections
3860 Mark the current section so that the linker only includes a single copy of it.
3861 This may be used to include the same section in several different object files,
3862 but ensure that the linker will only include it once in the final output file.
3863 The @code{.linkonce} pseudo-op must be used for each instance of the section.
3864 Duplicate sections are detected based on the section name, so it should be
3867 This directive is only supported by a few object file formats; as of this
3868 writing, the only object file format which supports it is the Portable
3869 Executable format used on Windows NT.
3871 The @var{type} argument is optional. If specified, it must be one of the
3872 following strings. For example:
3876 Not all types may be supported on all object file formats.
3880 Silently discard duplicate sections. This is the default.
3883 Warn if there are duplicate sections, but still keep only one copy.
3886 Warn if any of the duplicates have different sizes.
3889 Warn if any of the duplicates do not have exactly the same contents.
3893 @section @code{.ln @var{line-number}}
3895 @cindex @code{ln} directive
3896 @ifclear no-line-dir
3897 @samp{.ln} is a synonym for @samp{.line}.
3900 Tell @code{@value{AS}} to change the logical line number. @var{line-number}
3901 must be an absolute expression. The next line has that logical
3902 line number, so any other statements on the current line (after a
3903 statement separator character @code{;}) are reported as on logical
3904 line number @var{line-number} @minus{} 1.
3907 This directive is accepted, but ignored, when @code{@value{AS}} is
3908 configured for @code{b.out}; its effect is only associated with COFF
3914 @section @code{.mri @var{val}}
3916 @cindex @code{mri} directive
3917 @cindex MRI mode, temporarily
3918 If @var{val} is non-zero, this tells @code{@value{AS}} to enter MRI mode. If
3919 @var{val} is zero, this tells @code{@value{AS}} to exit MRI mode. This change
3920 affects code assembled until the next @code{.mri} directive, or until the end
3921 of the file. @xref{M, MRI mode, MRI mode}.
3924 @section @code{.list}
3926 @cindex @code{list} directive
3927 @cindex listing control, turning on
3928 Control (in conjunction with the @code{.nolist} directive) whether or
3929 not assembly listings are generated. These two directives maintain an
3930 internal counter (which is zero initially). @code{.list} increments the
3931 counter, and @code{.nolist} decrements it. Assembly listings are
3932 generated whenever the counter is greater than zero.
3934 By default, listings are disabled. When you enable them (with the
3935 @samp{-a} command line option; @pxref{Invoking,,Command-Line Options}),
3936 the initial value of the listing counter is one.
3939 @section @code{.long @var{expressions}}
3941 @cindex @code{long} directive
3942 @code{.long} is the same as @samp{.int}, @pxref{Int,,@code{.int}}.
3945 @c no one seems to know what this is for or whether this description is
3946 @c what it really ought to do
3948 @section @code{.lsym @var{symbol}, @var{expression}}
3950 @cindex @code{lsym} directive
3951 @cindex symbol, not referenced in assembly
3952 @code{.lsym} creates a new symbol named @var{symbol}, but does not put it in
3953 the hash table, ensuring it cannot be referenced by name during the
3954 rest of the assembly. This sets the attributes of the symbol to be
3955 the same as the expression value:
3957 @var{other} = @var{descriptor} = 0
3958 @var{type} = @r{(section of @var{expression})}
3959 @var{value} = @var{expression}
3962 The new symbol is not flagged as external.
3966 @section @code{.macro}
3969 The commands @code{.macro} and @code{.endm} allow you to define macros that
3970 generate assembly output. For example, this definition specifies a macro
3971 @code{sum} that puts a sequence of numbers into memory:
3974 .macro sum from=0, to=5
3983 With that definition, @samp{SUM 0,5} is equivalent to this assembly input:
3995 @item .macro @var{macname}
3996 @itemx .macro @var{macname} @var{macargs} @dots{}
3997 @cindex @code{macro} directive
3998 Begin the definition of a macro called @var{macname}. If your macro
3999 definition requires arguments, specify their names after the macro name,
4000 separated by commas or spaces. You can supply a default value for any
4001 macro argument by following the name with @samp{=@var{deflt}}. For
4002 example, these are all valid @code{.macro} statements:
4006 Begin the definition of a macro called @code{comm}, which takes no
4009 @item .macro plus1 p, p1
4010 @itemx .macro plus1 p p1
4011 Either statement begins the definition of a macro called @code{plus1},
4012 which takes two arguments; within the macro definition, write
4013 @samp{\p} or @samp{\p1} to evaluate the arguments.
4015 @item .macro reserve_str p1=0 p2
4016 Begin the definition of a macro called @code{reserve_str}, with two
4017 arguments. The first argument has a default value, but not the second.
4018 After the definition is complete, you can call the macro either as
4019 @samp{reserve_str @var{a},@var{b}} (with @samp{\p1} evaluating to
4020 @var{a} and @samp{\p2} evaluating to @var{b}), or as @samp{reserve_str
4021 ,@var{b}} (with @samp{\p1} evaluating as the default, in this case
4022 @samp{0}, and @samp{\p2} evaluating to @var{b}).
4025 When you call a macro, you can specify the argument values either by
4026 position, or by keyword. For example, @samp{sum 9,17} is equivalent to
4027 @samp{sum to=17, from=9}.
4030 @cindex @code{endm} directive
4031 Mark the end of a macro definition.
4034 @cindex @code{exitm} directive
4035 Exit early from the current macro definition.
4037 @cindex number of macros executed
4038 @cindex macros, count executed
4040 @code{@value{AS}} maintains a counter of how many macros it has
4041 executed in this pseudo-variable; you can copy that number to your
4042 output with @samp{\@@}, but @emph{only within a macro definition}.
4045 @item LOCAL @var{name} [ , @dots{} ]
4046 @emph{Warning: @code{LOCAL} is only available if you select ``alternate
4047 macro syntax'' with @samp{-a} or @samp{--alternate}.} @xref{Alternate,,
4048 Alternate macro syntax}.
4050 Generate a string replacement for each of the @var{name} arguments, and
4051 replace any instances of @var{name} in each macro expansion. The
4052 replacement string is unique in the assembly, and different for each
4053 separate macro expansion. @code{LOCAL} allows you to write macros that
4054 define symbols, without fear of conflict between separate macro expansions.
4059 @section @code{.nolist}
4061 @cindex @code{nolist} directive
4062 @cindex listing control, turning off
4063 Control (in conjunction with the @code{.list} directive) whether or
4064 not assembly listings are generated. These two directives maintain an
4065 internal counter (which is zero initially). @code{.list} increments the
4066 counter, and @code{.nolist} decrements it. Assembly listings are
4067 generated whenever the counter is greater than zero.
4070 @section @code{.octa @var{bignums}}
4072 @c FIXME: double size emitted for "octa" on i960, others? Or warn?
4073 @cindex @code{octa} directive
4074 @cindex integer, 16-byte
4075 @cindex sixteen byte integer
4076 This directive expects zero or more bignums, separated by commas. For each
4077 bignum, it emits a 16-byte integer.
4079 The term ``octa'' comes from contexts in which a ``word'' is two bytes;
4080 hence @emph{octa}-word for 16 bytes.
4083 @section @code{.org @var{new-lc} , @var{fill}}
4085 @cindex @code{org} directive
4086 @cindex location counter, advancing
4087 @cindex advancing location counter
4088 @cindex current address, advancing
4089 Advance the location counter of the current section to
4090 @var{new-lc}. @var{new-lc} is either an absolute expression or an
4091 expression with the same section as the current subsection. That is,
4092 you can't use @code{.org} to cross sections: if @var{new-lc} has the
4093 wrong section, the @code{.org} directive is ignored. To be compatible
4094 with former assemblers, if the section of @var{new-lc} is absolute,
4095 @code{@value{AS}} issues a warning, then pretends the section of @var{new-lc}
4096 is the same as the current subsection.
4098 @code{.org} may only increase the location counter, or leave it
4099 unchanged; you cannot use @code{.org} to move the location counter
4102 @c double negative used below "not undefined" because this is a specific
4103 @c reference to "undefined" (as SEG_UNKNOWN is called in this manual)
4104 @c section. doc@cygnus.com 18feb91
4105 Because @code{@value{AS}} tries to assemble programs in one pass, @var{new-lc}
4106 may not be undefined. If you really detest this restriction we eagerly await
4107 a chance to share your improved assembler.
4109 Beware that the origin is relative to the start of the section, not
4110 to the start of the subsection. This is compatible with other
4111 people's assemblers.
4113 When the location counter (of the current subsection) is advanced, the
4114 intervening bytes are filled with @var{fill} which should be an
4115 absolute expression. If the comma and @var{fill} are omitted,
4116 @var{fill} defaults to zero.
4119 @section @code{.p2align[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
4121 @cindex padding the location counter given a power of two
4122 @cindex @code{p2align} directive
4123 Pad the location counter (in the current subsection) to a particular
4124 storage boundary. The first expression (which must be absolute) is the
4125 number of low-order zero bits the location counter must have after
4126 advancement. For example @samp{.p2align 3} advances the location
4127 counter until it a multiple of 8. If the location counter is already a
4128 multiple of 8, no change is needed.
4130 The second expression (also absolute) gives the fill value to be stored in the
4131 padding bytes. It (and the comma) may be omitted. If it is omitted, the
4132 padding bytes are normally zero. However, on some systems, if the section is
4133 marked as containing code and the fill value is omitted, the space is filled
4134 with no-op instructions.
4136 The third expression is also absolute, and is also optional. If it is present,
4137 it is the maximum number of bytes that should be skipped by this alignment
4138 directive. If doing the alignment would require skipping more bytes than the
4139 specified maximum, then the alignment is not done at all. You can omit the
4140 fill value (the second argument) entirely by simply using two commas after the
4141 required alignment; this can be useful if you want the alignment to be filled
4142 with no-op instructions when appropriate.
4144 @cindex @code{p2alignw} directive
4145 @cindex @code{p2alignl} directive
4146 The @code{.p2alignw} and @code{.p2alignl} directives are variants of the
4147 @code{.p2align} directive. The @code{.p2alignw} directive treats the fill
4148 pattern as a two byte word value. The @code{.p2alignl} directives treats the
4149 fill pattern as a four byte longword value. For example, @code{.p2alignw
4150 2,0x368d} will align to a multiple of 4. If it skips two bytes, they will be
4151 filled in with the value 0x368d (the exact placement of the bytes depends upon
4152 the endianness of the processor). If it skips 1 or 3 bytes, the fill value is
4156 @section @code{.print @var{string}}
4158 @cindex @code{print} directive
4159 @code{@value{AS}} will print @var{string} on the standard output during
4160 assembly. You must put @var{string} in double quotes.
4163 @section @code{.psize @var{lines} , @var{columns}}
4165 @cindex @code{psize} directive
4166 @cindex listing control: paper size
4167 @cindex paper size, for listings
4168 Use this directive to declare the number of lines---and, optionally, the
4169 number of columns---to use for each page, when generating listings.
4171 If you do not use @code{.psize}, listings use a default line-count
4172 of 60. You may omit the comma and @var{columns} specification; the
4173 default width is 200 columns.
4175 @code{@value{AS}} generates formfeeds whenever the specified number of
4176 lines is exceeded (or whenever you explicitly request one, using
4179 If you specify @var{lines} as @code{0}, no formfeeds are generated save
4180 those explicitly specified with @code{.eject}.
4183 @section @code{.purgem @var{name}}
4185 @cindex @code{purgem} directive
4186 Undefine the macro @var{name}, so that later uses of the string will not be
4187 expanded. @xref{Macro}.
4190 @section @code{.quad @var{bignums}}
4192 @cindex @code{quad} directive
4193 @code{.quad} expects zero or more bignums, separated by commas. For
4194 each bignum, it emits
4196 an 8-byte integer. If the bignum won't fit in 8 bytes, it prints a
4197 warning message; and just takes the lowest order 8 bytes of the bignum.
4198 @cindex eight-byte integer
4199 @cindex integer, 8-byte
4201 The term ``quad'' comes from contexts in which a ``word'' is two bytes;
4202 hence @emph{quad}-word for 8 bytes.
4205 a 16-byte integer. If the bignum won't fit in 16 bytes, it prints a
4206 warning message; and just takes the lowest order 16 bytes of the bignum.
4207 @cindex sixteen-byte integer
4208 @cindex integer, 16-byte
4212 @section @code{.rept @var{count}}
4214 @cindex @code{rept} directive
4215 Repeat the sequence of lines between the @code{.rept} directive and the next
4216 @code{.endr} directive @var{count} times.
4218 For example, assembling
4226 is equivalent to assembling
4235 @section @code{.sbttl "@var{subheading}"}
4237 @cindex @code{sbttl} directive
4238 @cindex subtitles for listings
4239 @cindex listing control: subtitle
4240 Use @var{subheading} as the title (third line, immediately after the
4241 title line) when generating assembly listings.
4243 This directive affects subsequent pages, as well as the current page if
4244 it appears within ten lines of the top of a page.
4248 @section @code{.scl @var{class}}
4250 @cindex @code{scl} directive
4251 @cindex symbol storage class (COFF)
4252 @cindex COFF symbol storage class
4253 Set the storage-class value for a symbol. This directive may only be
4254 used inside a @code{.def}/@code{.endef} pair. Storage class may flag
4255 whether a symbol is static or external, or it may record further
4256 symbolic debugging information.
4259 The @samp{.scl} directive is primarily associated with COFF output; when
4260 configured to generate @code{b.out} output format, @code{@value{AS}}
4261 accepts this directive but ignores it.
4266 @section @code{.section @var{name}}
4268 @cindex @code{section} directive
4269 @cindex named section
4270 Use the @code{.section} directive to assemble the following code into a section
4273 This directive is only supported for targets that actually support arbitrarily
4274 named sections; on @code{a.out} targets, for example, it is not accepted, even
4275 with a standard @code{a.out} section name.
4278 For COFF targets, the @code{.section} directive is used in one of the following
4281 .section @var{name}[, "@var{flags}"]
4282 .section @var{name}[, @var{subsegment}]
4285 If the optional argument is quoted, it is taken as flags to use for the
4286 section. Each flag is a single character. The following flags are recognized:
4289 bss section (uninitialized data)
4291 section is not loaded
4302 If no flags are specified, the default flags depend upon the section name. If
4303 the section name is not recognized, the default will be for the section to be
4304 loaded and writable.
4306 If the optional argument to the @code{.section} directive is not quoted, it is
4307 taken as a subsegment number (@pxref{Sub-Sections}).
4311 For ELF targets, the @code{.section} directive is used like this:
4313 .section @var{name}[, "@var{flags}"[, @@@var{type}]]
4315 The optional @var{flags} argument is a quoted string which may contain any
4316 combintion of the following characters:
4319 section is allocatable
4323 section is executable
4326 The optional @var{type} argument may contain one of the following constants:
4329 section contains data
4331 section does not contain data (i.e., section only occupies space)
4334 If no flags are specified, the default flags depend upon the section name. If
4335 the section name is not recognized, the default will be for the section to have
4336 none of the above flags: it will not be allocated in memory, nor writable, nor
4337 executable. The section will contain data.
4339 For ELF targets, the assembler supports another type of @code{.section}
4340 directive for compatibility with the Solaris assembler:
4342 .section "@var{name}"[, @var{flags}...]
4344 Note that the section name is quoted. There may be a sequence of comma
4348 section is allocatable
4352 section is executable
4357 @section @code{.set @var{symbol}, @var{expression}}
4359 @cindex @code{set} directive
4360 @cindex symbol value, setting
4361 Set the value of @var{symbol} to @var{expression}. This
4362 changes @var{symbol}'s value and type to conform to
4363 @var{expression}. If @var{symbol} was flagged as external, it remains
4364 flagged (@pxref{Symbol Attributes}).
4366 You may @code{.set} a symbol many times in the same assembly.
4368 If you @code{.set} a global symbol, the value stored in the object
4369 file is the last value stored into it.
4372 The syntax for @code{set} on the HPPA is
4373 @samp{@var{symbol} .set @var{expression}}.
4377 @section @code{.short @var{expressions}}
4379 @cindex @code{short} directive
4381 @code{.short} is normally the same as @samp{.word}.
4382 @xref{Word,,@code{.word}}.
4384 In some configurations, however, @code{.short} and @code{.word} generate
4385 numbers of different lengths; @pxref{Machine Dependencies}.
4389 @code{.short} is the same as @samp{.word}. @xref{Word,,@code{.word}}.
4392 This expects zero or more @var{expressions}, and emits
4393 a 16 bit number for each.
4398 @section @code{.single @var{flonums}}
4400 @cindex @code{single} directive
4401 @cindex floating point numbers (single)
4402 This directive assembles zero or more flonums, separated by commas. It
4403 has the same effect as @code{.float}.
4405 The exact kind of floating point numbers emitted depends on how
4406 @code{@value{AS}} is configured. @xref{Machine Dependencies}.
4410 On the @value{TARGET} family, @code{.single} emits 32-bit floating point
4411 numbers in @sc{ieee} format.
4417 @section @code{.size}
4419 @cindex @code{size} directive
4420 This directive is generated by compilers to include auxiliary debugging
4421 information in the symbol table. It is only permitted inside
4422 @code{.def}/@code{.endef} pairs.
4425 @samp{.size} is only meaningful when generating COFF format output; when
4426 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
4432 @section @code{.sleb128 @var{expressions}}
4434 @cindex @code{sleb128} directive
4435 @var{sleb128} stands for ``signed little endian base 128.'' This is a
4436 compact, variable length representation of numbers used by the DWARF
4437 symbolic debugging format. @xref{Uleb128,@code{.uleb128}}.
4439 @ifclear no-space-dir
4441 @section @code{.skip @var{size} , @var{fill}}
4443 @cindex @code{skip} directive
4444 @cindex filling memory
4445 This directive emits @var{size} bytes, each of value @var{fill}. Both
4446 @var{size} and @var{fill} are absolute expressions. If the comma and
4447 @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same as
4451 @section @code{.space @var{size} , @var{fill}}
4453 @cindex @code{space} directive
4454 @cindex filling memory
4455 This directive emits @var{size} bytes, each of value @var{fill}. Both
4456 @var{size} and @var{fill} are absolute expressions. If the comma
4457 and @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same
4462 @emph{Warning:} @code{.space} has a completely different meaning for HPPA
4463 targets; use @code{.block} as a substitute. See @cite{HP9000 Series 800
4464 Assembly Language Reference Manual} (HP 92432-90001) for the meaning of the
4465 @code{.space} directive. @xref{HPPA Directives,,HPPA Assembler Directives},
4474 @section @code{.space}
4475 @cindex @code{space} directive
4477 On the AMD 29K, this directive is ignored; it is accepted for
4478 compatibility with other AMD 29K assemblers.
4481 @emph{Warning:} In most versions of the @sc{gnu} assembler, the directive
4482 @code{.space} has the effect of @code{.block} @xref{Machine Dependencies}.
4488 @section @code{.stabd, .stabn, .stabs}
4490 @cindex symbolic debuggers, information for
4491 @cindex @code{stab@var{x}} directives
4492 There are three directives that begin @samp{.stab}.
4493 All emit symbols (@pxref{Symbols}), for use by symbolic debuggers.
4494 The symbols are not entered in the @code{@value{AS}} hash table: they
4495 cannot be referenced elsewhere in the source file.
4496 Up to five fields are required:
4500 This is the symbol's name. It may contain any character except
4501 @samp{\000}, so is more general than ordinary symbol names. Some
4502 debuggers used to code arbitrarily complex structures into symbol names
4506 An absolute expression. The symbol's type is set to the low 8 bits of
4507 this expression. Any bit pattern is permitted, but @code{@value{LD}}
4508 and debuggers choke on silly bit patterns.
4511 An absolute expression. The symbol's ``other'' attribute is set to the
4512 low 8 bits of this expression.
4515 An absolute expression. The symbol's descriptor is set to the low 16
4516 bits of this expression.
4519 An absolute expression which becomes the symbol's value.
4522 If a warning is detected while reading a @code{.stabd}, @code{.stabn},
4523 or @code{.stabs} statement, the symbol has probably already been created;
4524 you get a half-formed symbol in your object file. This is
4525 compatible with earlier assemblers!
4528 @cindex @code{stabd} directive
4529 @item .stabd @var{type} , @var{other} , @var{desc}
4531 The ``name'' of the symbol generated is not even an empty string.
4532 It is a null pointer, for compatibility. Older assemblers used a
4533 null pointer so they didn't waste space in object files with empty
4536 The symbol's value is set to the location counter,
4537 relocatably. When your program is linked, the value of this symbol
4538 is the address of the location counter when the @code{.stabd} was
4541 @cindex @code{stabn} directive
4542 @item .stabn @var{type} , @var{other} , @var{desc} , @var{value}
4543 The name of the symbol is set to the empty string @code{""}.
4545 @cindex @code{stabs} directive
4546 @item .stabs @var{string} , @var{type} , @var{other} , @var{desc} , @var{value}
4547 All five fields are specified.
4553 @section @code{.string} "@var{str}"
4555 @cindex string, copying to object file
4556 @cindex @code{string} directive
4558 Copy the characters in @var{str} to the object file. You may specify more than
4559 one string to copy, separated by commas. Unless otherwise specified for a
4560 particular machine, the assembler marks the end of each string with a 0 byte.
4561 You can use any of the escape sequences described in @ref{Strings,,Strings}.
4564 @section @code{.struct @var{expression}}
4566 @cindex @code{struct} directive
4567 Switch to the absolute section, and set the section offset to @var{expression},
4568 which must be an absolute expression. You might use this as follows:
4577 This would define the symbol @code{field1} to have the value 0, the symbol
4578 @code{field2} to have the value 4, and the symbol @code{field3} to have the
4579 value 8. Assembly would be left in the absolute section, and you would need to
4580 use a @code{.section} directive of some sort to change to some other section
4581 before further assembly.
4585 @section @code{.symver}
4586 @cindex @code{symver} directive
4587 @cindex symbol versioning
4588 @cindex versions of symbols
4589 Use the @code{.symver} directive to bind symbols to specific version nodes
4590 within a source file. This is only supported on ELF platforms, and is
4591 typically used when assembling files to be linked into a shared library.
4592 There are cases where it may make sense to use this in objects to be bound
4593 into an application itself so as to override a versioned symbol from a
4596 For ELF targets, the @code{.symver} directive is used like this:
4598 .symver @var{name}, @var{name2@@nodename}
4600 In this case, the symbol @var{name} must exist and be defined within the file
4601 being assembled. The @code{.versym} directive effectively creates a symbol
4602 alias with the name @var{name2@@nodename}, and in fact the main reason that we
4603 just don't try and create a regular alias is that the @var{@@} character isn't
4604 permitted in symbol names. The @var{name2} part of the name is the actual name
4605 of the symbol by which it will be externally referenced. The name @var{name}
4606 itself is merely a name of convenience that is used so that it is possible to
4607 have definitions for multiple versions of a function within a single source
4608 file, and so that the compiler can unambiguously know which version of a
4609 function is being mentioned. The @var{nodename} portion of the alias should be
4610 the name of a node specified in the version script supplied to the linker when
4611 building a shared library. If you are attempting to override a versioned
4612 symbol from a shared library, then @var{nodename} should correspond to the
4613 nodename of the symbol you are trying to override.
4618 @section @code{.tag @var{structname}}
4620 @cindex COFF structure debugging
4621 @cindex structure debugging, COFF
4622 @cindex @code{tag} directive
4623 This directive is generated by compilers to include auxiliary debugging
4624 information in the symbol table. It is only permitted inside
4625 @code{.def}/@code{.endef} pairs. Tags are used to link structure
4626 definitions in the symbol table with instances of those structures.
4629 @samp{.tag} is only used when generating COFF format output; when
4630 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
4636 @section @code{.text @var{subsection}}
4638 @cindex @code{text} directive
4639 Tells @code{@value{AS}} to assemble the following statements onto the end of
4640 the text subsection numbered @var{subsection}, which is an absolute
4641 expression. If @var{subsection} is omitted, subsection number zero
4645 @section @code{.title "@var{heading}"}
4647 @cindex @code{title} directive
4648 @cindex listing control: title line
4649 Use @var{heading} as the title (second line, immediately after the
4650 source file name and pagenumber) when generating assembly listings.
4652 This directive affects subsequent pages, as well as the current page if
4653 it appears within ten lines of the top of a page.
4657 @section @code{.type @var{int}}
4659 @cindex COFF symbol type
4660 @cindex symbol type, COFF
4661 @cindex @code{type} directive
4662 This directive, permitted only within @code{.def}/@code{.endef} pairs,
4663 records the integer @var{int} as the type attribute of a symbol table entry.
4666 @samp{.type} is associated only with COFF format output; when
4667 @code{@value{AS}} is configured for @code{b.out} output, it accepts this
4668 directive but ignores it.
4674 @section @code{.val @var{addr}}
4676 @cindex @code{val} directive
4677 @cindex COFF value attribute
4678 @cindex value attribute, COFF
4679 This directive, permitted only within @code{.def}/@code{.endef} pairs,
4680 records the address @var{addr} as the value attribute of a symbol table
4684 @samp{.val} is used only for COFF output; when @code{@value{AS}} is
4685 configured for @code{b.out}, it accepts this directive but ignores it.
4690 @section @code{.uleb128 @var{expressions}}
4692 @cindex @code{uleb128} directive
4693 @var{uleb128} stands for ``unsigned little endian base 128.'' This is a
4694 compact, variable length representation of numbers used by the DWARF
4695 symbolic debugging format. @xref{Sleb128,@code{.sleb128}}.
4698 @section @code{.word @var{expressions}}
4700 @cindex @code{word} directive
4701 This directive expects zero or more @var{expressions}, of any section,
4702 separated by commas.
4705 For each expression, @code{@value{AS}} emits a 32-bit number.
4708 For each expression, @code{@value{AS}} emits a 16-bit number.
4713 The size of the number emitted, and its byte order,
4714 depend on what target computer the assembly is for.
4717 @c on amd29k, i960, sparc the "special treatment to support compilers" doesn't
4718 @c happen---32-bit addressability, period; no long/short jumps.
4719 @ifset DIFF-TBL-KLUGE
4720 @cindex difference tables altered
4721 @cindex altered difference tables
4723 @emph{Warning: Special Treatment to support Compilers}
4727 Machines with a 32-bit address space, but that do less than 32-bit
4728 addressing, require the following special treatment. If the machine of
4729 interest to you does 32-bit addressing (or doesn't require it;
4730 @pxref{Machine Dependencies}), you can ignore this issue.
4733 In order to assemble compiler output into something that works,
4734 @code{@value{AS}} occasionlly does strange things to @samp{.word} directives.
4735 Directives of the form @samp{.word sym1-sym2} are often emitted by
4736 compilers as part of jump tables. Therefore, when @code{@value{AS}} assembles a
4737 directive of the form @samp{.word sym1-sym2}, and the difference between
4738 @code{sym1} and @code{sym2} does not fit in 16 bits, @code{@value{AS}}
4739 creates a @dfn{secondary jump table}, immediately before the next label.
4740 This secondary jump table is preceded by a short-jump to the
4741 first byte after the secondary table. This short-jump prevents the flow
4742 of control from accidentally falling into the new table. Inside the
4743 table is a long-jump to @code{sym2}. The original @samp{.word}
4744 contains @code{sym1} minus the address of the long-jump to
4747 If there were several occurrences of @samp{.word sym1-sym2} before the
4748 secondary jump table, all of them are adjusted. If there was a
4749 @samp{.word sym3-sym4}, that also did not fit in sixteen bits, a
4750 long-jump to @code{sym4} is included in the secondary jump table,
4751 and the @code{.word} directives are adjusted to contain @code{sym3}
4752 minus the address of the long-jump to @code{sym4}; and so on, for as many
4753 entries in the original jump table as necessary.
4756 @emph{This feature may be disabled by compiling @code{@value{AS}} with the
4757 @samp{-DWORKING_DOT_WORD} option.} This feature is likely to confuse
4758 assembly language programmers.
4761 @c end DIFF-TBL-KLUGE
4764 @section Deprecated Directives
4766 @cindex deprecated directives
4767 @cindex obsolescent directives
4768 One day these directives won't work.
4769 They are included for compatibility with older assemblers.
4776 @node Machine Dependencies
4777 @chapter Machine Dependent Features
4779 @cindex machine dependencies
4780 The machine instruction sets are (almost by definition) different on
4781 each machine where @code{@value{AS}} runs. Floating point representations
4782 vary as well, and @code{@value{AS}} often supports a few additional
4783 directives or command-line options for compatibility with other
4784 assemblers on a particular platform. Finally, some versions of
4785 @code{@value{AS}} support special pseudo-instructions for branch
4788 This chapter discusses most of these differences, though it does not
4789 include details on any machine's instruction set. For details on that
4790 subject, see the hardware manufacturer's manual.
4794 * AMD29K-Dependent:: AMD 29K Dependent Features
4797 * ARC-Dependent:: ARC Dependent Features
4800 * ARM-Dependent:: ARM Dependent Features
4803 * D10V-Dependent:: D10V Dependent Features
4805 @c start-sanitize-d30v
4807 * D30V-Dependent:: D30V Dependent Features
4809 @c end-sanitize-d30v
4811 * H8/300-Dependent:: Hitachi H8/300 Dependent Features
4814 * H8/500-Dependent:: Hitachi H8/500 Dependent Features
4817 * HPPA-Dependent:: HPPA Dependent Features
4820 * i386-Dependent:: Intel 80386 Dependent Features
4823 * i960-Dependent:: Intel 80960 Dependent Features
4825 @c start-sanitize-m32rx
4827 * M32R-Dependent:: M32R Dependent Features
4829 @c end-sanitize-m32rx
4831 * M68K-Dependent:: M680x0 Dependent Features
4834 * MIPS-Dependent:: MIPS Dependent Features
4837 * SH-Dependent:: Hitachi SH Dependent Features
4840 * Sparc-Dependent:: SPARC Dependent Features
4843 * V850-Dependent:: V850 Dependent Features
4846 * Z8000-Dependent:: Z8000 Dependent Features
4849 * Vax-Dependent:: VAX Dependent Features
4856 @c The following major nodes are *sections* in the GENERIC version, *chapters*
4857 @c in single-cpu versions. This is mainly achieved by @lowersections. There is a
4858 @c peculiarity: to preserve cross-references, there must be a node called
4859 @c "Machine Dependencies". Hence the conditional nodenames in each
4860 @c major node below. Node defaulting in makeinfo requires adjacency of
4861 @c node and sectioning commands; hence the repetition of @chapter BLAH
4862 @c in both conditional blocks.
4868 @chapter ARC Dependent Features
4871 @node Machine Dependencies
4872 @chapter ARC Dependent Features
4877 * ARC-Opts:: Options
4878 * ARC-Float:: Floating Point
4879 * ARC-Directives:: Sparc Machine Directives
4885 @cindex options for ARC
4887 @cindex architectures, ARC
4888 @cindex ARC architectures
4889 The ARC chip family includes several successive levels (or other
4890 variants) of chip, using the same core instruction set, but including
4891 a few additional instructions at each level.
4893 By default, @code{@value{AS}} assumes the core instruction set (ARC
4894 base). The @code{.cpu} pseudo-op is intended to be used to select
4898 @cindex @code{-mbig-endian} option (ARC)
4899 @cindex @code{-mlittle-endian} option (ARC)
4900 @cindex ARC big-endian output
4901 @cindex ARC little-endian output
4902 @cindex big-endian output, ARC
4903 @cindex little-endian output, ARC
4905 @itemx -mlittle-endian
4906 Any @sc{arc} configuration of @code{@value{AS}} can select big-endian or
4907 little-endian output at run time (unlike most other @sc{gnu} development
4908 tools, which must be configured for one or the other). Use
4909 @samp{-mbig-endian} to select big-endian output, and @samp{-mlittle-endian}
4914 @section Floating Point
4916 @cindex floating point, ARC (@sc{ieee})
4917 @cindex ARC floating point (@sc{ieee})
4918 The ARC cpu family currently does not have hardware floating point
4919 support. Software floating point support is provided by @code{GCC}
4920 and uses @sc{ieee} floating-point numbers.
4922 @node ARC-Directives
4923 @section ARC Machine Directives
4925 @cindex ARC machine directives
4926 @cindex machine directives, ARC
4927 The ARC version of @code{@value{AS}} supports the following additional
4932 @cindex @code{cpu} directive, SPARC
4933 This must be followed by the desired cpu.
4934 The ARC is intended to be customizable, @code{.cpu} is used to
4935 select the desired variant [though currently there are none].
4942 @include c-a29k.texi
4951 @node Machine Dependencies
4952 @chapter Machine Dependent Features
4954 The machine instruction sets are different on each Hitachi chip family,
4955 and there are also some syntax differences among the families. This
4956 chapter describes the specific @code{@value{AS}} features for each
4960 * H8/300-Dependent:: Hitachi H8/300 Dependent Features
4961 * H8/500-Dependent:: Hitachi H8/500 Dependent Features
4962 * SH-Dependent:: Hitachi SH Dependent Features
4969 @include c-d10v.texi
4972 @c start-sanitize-d30v
4974 @include c-d30v.texi
4976 @c end-sanitize-d30v
4979 @include c-h8300.texi
4983 @include c-h8500.texi
4987 @include c-hppa.texi
4991 @include c-i386.texi
4995 @include c-i960.texi
4998 @c start-sanitize-m32rx
5000 @include c-m32r.texi
5002 @c end-sanitize-m32rx
5005 @include c-m68k.texi
5009 @include c-mips.texi
5013 @include c-ns32k.texi
5021 @include c-sparc.texi
5033 @include c-v850.texi
5037 @c reverse effect of @down at top of generic Machine-Dep chapter
5041 @node Reporting Bugs
5042 @chapter Reporting Bugs
5043 @cindex bugs in assembler
5044 @cindex reporting bugs in assembler
5046 Your bug reports play an essential role in making @code{@value{AS}} reliable.
5048 Reporting a bug may help you by bringing a solution to your problem, or it may
5049 not. But in any case the principal function of a bug report is to help the
5050 entire community by making the next version of @code{@value{AS}} work better.
5051 Bug reports are your contribution to the maintenance of @code{@value{AS}}.
5053 In order for a bug report to serve its purpose, you must include the
5054 information that enables us to fix the bug.
5057 * Bug Criteria:: Have you found a bug?
5058 * Bug Reporting:: How to report bugs
5062 @section Have you found a bug?
5063 @cindex bug criteria
5065 If you are not sure whether you have found a bug, here are some guidelines:
5068 @cindex fatal signal
5069 @cindex assembler crash
5070 @cindex crash of assembler
5072 If the assembler gets a fatal signal, for any input whatever, that is a
5073 @code{@value{AS}} bug. Reliable assemblers never crash.
5075 @cindex error on valid input
5077 If @code{@value{AS}} produces an error message for valid input, that is a bug.
5079 @cindex invalid input
5081 If @code{@value{AS}} does not produce an error message for invalid input, that
5082 is a bug. However, you should note that your idea of ``invalid input'' might
5083 be our idea of ``an extension'' or ``support for traditional practice''.
5086 If you are an experienced user of assemblers, your suggestions for improvement
5087 of @code{@value{AS}} are welcome in any case.
5091 @section How to report bugs
5093 @cindex assembler bugs, reporting
5095 A number of companies and individuals offer support for @sc{gnu} products. If
5096 you obtained @code{@value{AS}} from a support organization, we recommend you
5097 contact that organization first.
5099 You can find contact information for many support companies and
5100 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
5103 In any event, we also recommend that you send bug reports for @code{@value{AS}}
5104 to @samp{bug-gnu-utils@@gnu.org}.
5106 The fundamental principle of reporting bugs usefully is this:
5107 @strong{report all the facts}. If you are not sure whether to state a
5108 fact or leave it out, state it!
5110 Often people omit facts because they think they know what causes the problem
5111 and assume that some details do not matter. Thus, you might assume that the
5112 name of a symbol you use in an example does not matter. Well, probably it does
5113 not, but one cannot be sure. Perhaps the bug is a stray memory reference which
5114 happens to fetch from the location where that name is stored in memory;
5115 perhaps, if the name were different, the contents of that location would fool
5116 the assembler into doing the right thing despite the bug. Play it safe and
5117 give a specific, complete example. That is the easiest thing for you to do,
5118 and the most helpful.
5120 Keep in mind that the purpose of a bug report is to enable us to fix the bug if
5121 it is new to us. Therefore, always write your bug reports on the assumption
5122 that the bug has not been reported previously.
5124 Sometimes people give a few sketchy facts and ask, ``Does this ring a
5125 bell?'' Those bug reports are useless, and we urge everyone to
5126 @emph{refuse to respond to them} except to chide the sender to report
5129 To enable us to fix the bug, you should include all these things:
5133 The version of @code{@value{AS}}. @code{@value{AS}} announces it if you start
5134 it with the @samp{--version} argument.
5136 Without this, we will not know whether there is any point in looking for
5137 the bug in the current version of @code{@value{AS}}.
5140 Any patches you may have applied to the @code{@value{AS}} source.
5143 The type of machine you are using, and the operating system name and
5147 What compiler (and its version) was used to compile @code{@value{AS}}---e.g.
5151 The command arguments you gave the assembler to assemble your example and
5152 observe the bug. To guarantee you will not omit something important, list them
5153 all. A copy of the Makefile (or the output from make) is sufficient.
5155 If we were to try to guess the arguments, we would probably guess wrong
5156 and then we might not encounter the bug.
5159 A complete input file that will reproduce the bug. If the bug is observed when
5160 the assembler is invoked via a compiler, send the assembler source, not the
5161 high level language source. Most compilers will produce the assembler source
5162 when run with the @samp{-S} option. If you are using @code{@value{GCC}}, use
5163 the options @samp{-v --save-temps}; this will save the assembler source in a
5164 file with an extension of @file{.s}, and also show you exactly how
5165 @code{@value{AS}} is being run.
5168 A description of what behavior you observe that you believe is
5169 incorrect. For example, ``It gets a fatal signal.''
5171 Of course, if the bug is that @code{@value{AS}} gets a fatal signal, then we
5172 will certainly notice it. But if the bug is incorrect output, we might not
5173 notice unless it is glaringly wrong. You might as well not give us a chance to
5176 Even if the problem you experience is a fatal signal, you should still say so
5177 explicitly. Suppose something strange is going on, such as, your copy of
5178 @code{@value{AS}} is out of synch, or you have encountered a bug in the C
5179 library on your system. (This has happened!) Your copy might crash and ours
5180 would not. If you told us to expect a crash, then when ours fails to crash, we
5181 would know that the bug was not happening for us. If you had not told us to
5182 expect a crash, then we would not be able to draw any conclusion from our
5186 If you wish to suggest changes to the @code{@value{AS}} source, send us context
5187 diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or @samp{-p}
5188 option. Always send diffs from the old file to the new file. If you even
5189 discuss something in the @code{@value{AS}} source, refer to it by context, not
5192 The line numbers in our development sources will not match those in your
5193 sources. Your line numbers would convey no useful information to us.
5196 Here are some things that are not necessary:
5200 A description of the envelope of the bug.
5202 Often people who encounter a bug spend a lot of time investigating
5203 which changes to the input file will make the bug go away and which
5204 changes will not affect it.
5206 This is often time consuming and not very useful, because the way we
5207 will find the bug is by running a single example under the debugger
5208 with breakpoints, not by pure deduction from a series of examples.
5209 We recommend that you save your time for something else.
5211 Of course, if you can find a simpler example to report @emph{instead}
5212 of the original one, that is a convenience for us. Errors in the
5213 output will be easier to spot, running under the debugger will take
5214 less time, and so on.
5216 However, simplification is not vital; if you do not want to do this,
5217 report the bug anyway and send us the entire test case you used.
5220 A patch for the bug.
5222 A patch for the bug does help us if it is a good one. But do not omit
5223 the necessary information, such as the test case, on the assumption that
5224 a patch is all we need. We might see problems with your patch and decide
5225 to fix the problem another way, or we might not understand it at all.
5227 Sometimes with a program as complicated as @code{@value{AS}} it is very hard to
5228 construct an example that will make the program follow a certain path through
5229 the code. If you do not send us the example, we will not be able to construct
5230 one, so we will not be able to verify that the bug is fixed.
5232 And if we cannot understand what bug you are trying to fix, or why your
5233 patch should be an improvement, we will not install it. A test case will
5234 help us to understand.
5237 A guess about what the bug is or what it depends on.
5239 Such guesses are usually wrong. Even we cannot guess right about such
5240 things without first using the debugger to find the facts.
5243 @node Acknowledgements
5244 @chapter Acknowledgements
5246 If you have contributed to @code{@value{AS}} and your name isn't listed here,
5247 it is not meant as a slight. We just don't know about it. Send mail to the
5248 maintainer, and we'll correct the situation. Currently
5250 the maintainer is Ken Raeburn (email address @code{raeburn@@cygnus.com}).
5252 Dean Elsner wrote the original @sc{gnu} assembler for the VAX.@footnote{Any
5255 Jay Fenlason maintained GAS for a while, adding support for GDB-specific debug
5256 information and the 68k series machines, most of the preprocessing pass, and
5257 extensive changes in @file{messages.c}, @file{input-file.c}, @file{write.c}.
5259 K. Richard Pixley maintained GAS for a while, adding various enhancements and
5260 many bug fixes, including merging support for several processors, breaking GAS
5261 up to handle multiple object file format back ends (including heavy rewrite,
5262 testing, an integration of the coff and b.out back ends), adding configuration
5263 including heavy testing and verification of cross assemblers and file splits
5264 and renaming, converted GAS to strictly ANSI C including full prototypes, added
5265 support for m680[34]0 and cpu32, did considerable work on i960 including a COFF
5266 port (including considerable amounts of reverse engineering), a SPARC opcode
5267 file rewrite, DECstation, rs6000, and hp300hpux host ports, updated ``know''
5268 assertions and made them work, much other reorganization, cleanup, and lint.
5270 Ken Raeburn wrote the high-level BFD interface code to replace most of the code
5271 in format-specific I/O modules.
5273 The original VMS support was contributed by David L. Kashtan. Eric Youngdale
5274 has done much work with it since.
5276 The Intel 80386 machine description was written by Eliot Dresselhaus.
5278 Minh Tran-Le at IntelliCorp contributed some AIX 386 support.
5280 The Motorola 88k machine description was contributed by Devon Bowen of Buffalo
5281 University and Torbjorn Granlund of the Swedish Institute of Computer Science.
5283 Keith Knowles at the Open Software Foundation wrote the original MIPS back end
5284 (@file{tc-mips.c}, @file{tc-mips.h}), and contributed Rose format support
5285 (which hasn't been merged in yet). Ralph Campbell worked with the MIPS code to
5286 support a.out format.
5288 Support for the Zilog Z8k and Hitachi H8/300 and H8/500 processors (tc-z8k,
5289 tc-h8300, tc-h8500), and IEEE 695 object file format (obj-ieee), was written by
5290 Steve Chamberlain of Cygnus Support. Steve also modified the COFF back end to
5291 use BFD for some low-level operations, for use with the H8/300 and AMD 29k
5294 John Gilmore built the AMD 29000 support, added @code{.include} support, and
5295 simplified the configuration of which versions accept which directives. He
5296 updated the 68k machine description so that Motorola's opcodes always produced
5297 fixed-size instructions (e.g. @code{jsr}), while synthetic instructions
5298 remained shrinkable (@code{jbsr}). John fixed many bugs, including true tested
5299 cross-compilation support, and one bug in relaxation that took a week and
5300 required the proverbial one-bit fix.
5302 Ian Lance Taylor of Cygnus Support merged the Motorola and MIT syntax for the
5303 68k, completed support for some COFF targets (68k, i386 SVR3, and SCO Unix),
5304 added support for MIPS ECOFF and ELF targets, wrote the initial RS/6000 and
5305 PowerPC assembler, and made a few other minor patches.
5307 Steve Chamberlain made @code{@value{AS}} able to generate listings.
5309 Hewlett-Packard contributed support for the HP9000/300.
5311 Jeff Law wrote GAS and BFD support for the native HPPA object format (SOM)
5312 along with a fairly extensive HPPA testsuite (for both SOM and ELF object
5313 formats). This work was supported by both the Center for Software Science at
5314 the University of Utah and Cygnus Support.
5316 Support for ELF format files has been worked on by Mark Eichin of Cygnus
5317 Support (original, incomplete implementation for SPARC), Pete Hoogenboom and
5318 Jeff Law at the University of Utah (HPPA mainly), Michael Meissner of the Open
5319 Software Foundation (i386 mainly), and Ken Raeburn of Cygnus Support (sparc,
5320 and some initial 64-bit support).
5322 Richard Henderson rewrote the Alpha assembler. Klaus Kaempf wrote GAS and BFD
5323 support for openVMS/Alpha.
5325 Several engineers at Cygnus Support have also provided many small bug fixes and
5326 configuration enhancements.
5328 Many others have contributed large or small bugfixes and enhancements. If
5329 you have contributed significant work and are not mentioned on this list, and
5330 want to be, let us know. Some of the history has been lost; we are not
5331 intentionally leaving anyone out.