1 \input texinfo @c -*-Texinfo-*-
2 @c Copyright (c) 1991, 92, 93, 94, 95, 96, 1997 Free Software Foundation, Inc.
3 @c UPDATE!! On future updates--
4 @c (1) check for new machine-dep cmdline options in
5 @c md_parse_option definitions in config/tc-*.c
6 @c (2) for platform-specific directives, examine md_pseudo_op
8 @c (3) for object-format specific directives, examine obj_pseudo_op
10 @c (4) portable directives in potable[] in read.c
14 @c defaults, config file may override:
17 @include asconfig.texi
19 @c common OR combinations of conditions
39 @set abnormal-separator
43 @settitle Using @value{AS}
46 @settitle Using @value{AS} (@value{TARGET})
48 @setchapternewpage odd
53 @c WARE! Some of the machine-dependent sections contain tables of machine
54 @c instructions. Except in multi-column format, these tables look silly.
55 @c Unfortunately, Texinfo doesn't have a general-purpose multi-col format, so
56 @c the multi-col format is faked within @example sections.
58 @c Again unfortunately, the natural size that fits on a page, for these tables,
59 @c is different depending on whether or not smallbook is turned on.
60 @c This matters, because of order: text flow switches columns at each page
63 @c The format faked in this source works reasonably well for smallbook,
64 @c not well for the default large-page format. This manual expects that if you
65 @c turn on @smallbook, you will also uncomment the "@set SMALL" to enable the
66 @c tables in question. You can turn on one without the other at your
67 @c discretion, of course.
70 @c the insn tables look just as silly in info files regardless of smallbook,
71 @c might as well show 'em anyways.
77 * As: (as). The GNU assembler.
86 This file documents the GNU Assembler "@value{AS}".
88 Copyright (C) 1991, 92, 93, 94, 95, 96, 1997 Free Software Foundation, Inc.
90 Permission is granted to make and distribute verbatim copies of
91 this manual provided the copyright notice and this permission notice
92 are preserved on all copies.
95 Permission is granted to process this file through Tex and print the
96 results, provided the printed document carries copying permission
97 notice identical to this one except for the removal of this paragraph
98 (this paragraph not being relevant to the printed manual).
101 Permission is granted to copy and distribute modified versions of this manual
102 under the conditions for verbatim copying, provided that the entire resulting
103 derived work is distributed under the terms of a permission notice identical to
106 Permission is granted to copy and distribute translations of this manual
107 into another language, under the above conditions for modified versions.
111 @title Using @value{AS}
112 @subtitle The @sc{gnu} Assembler
114 @subtitle for the @value{TARGET} family
117 @subtitle January 1994
120 The Free Software Foundation Inc. thanks The Nice Computer
121 Company of Australia for loaning Dean Elsner to write the
122 first (Vax) version of @code{as} for Project @sc{gnu}.
123 The proprietors, management and staff of TNCCA thank FSF for
124 distracting the boss while they got some work
127 @author Dean Elsner, Jay Fenlason & friends
131 \hfill {\it Using {\tt @value{AS}}}\par
132 \hfill Edited by Cygnus Support\par
134 %"boxit" macro for figures:
135 %Modified from Knuth's ``boxit'' macro from TeXbook (answer to exercise 21.3)
136 \gdef\boxit#1#2{\vbox{\hrule\hbox{\vrule\kern3pt
137 \vbox{\parindent=0pt\parskip=0pt\hsize=#1\kern3pt\strut\hfil
138 #2\hfil\strut\kern3pt}\kern3pt\vrule}\hrule}}%box with visible outline
139 \gdef\ibox#1#2{\hbox to #1{#2\hfil}\kern8pt}% invisible box
142 @vskip 0pt plus 1filll
143 Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 1997 Free Software Foundation, Inc.
145 Permission is granted to make and distribute verbatim copies of
146 this manual provided the copyright notice and this permission notice
147 are preserved on all copies.
149 Permission is granted to copy and distribute modified versions of this manual
150 under the conditions for verbatim copying, provided that the entire resulting
151 derived work is distributed under the terms of a permission notice identical to
154 Permission is granted to copy and distribute translations of this manual
155 into another language, under the above conditions for modified versions.
160 @top Using @value{AS}
162 This file is a user guide to the @sc{gnu} assembler @code{@value{AS}}.
164 This version of the file describes @code{@value{AS}} configured to generate
165 code for @value{TARGET} architectures.
168 * Overview:: Overview
169 * Invoking:: Command-Line Options
171 * Sections:: Sections and Relocation
173 * Expressions:: Expressions
174 * Pseudo Ops:: Assembler Directives
175 * Machine Dependencies:: Machine Dependent Features
176 * Reporting Bugs:: Reporting Bugs
177 * Acknowledgements:: Who Did What
185 This manual is a user guide to the @sc{gnu} assembler @code{@value{AS}}.
187 This version of the manual describes @code{@value{AS}} configured to generate
188 code for @value{TARGET} architectures.
192 @cindex invocation summary
193 @cindex option summary
194 @cindex summary of options
195 Here is a brief summary of how to invoke @code{@value{AS}}. For details,
196 @pxref{Invoking,,Comand-Line Options}.
198 @c We don't use deffn and friends for the following because they seem
199 @c to be limited to one line for the header.
201 @value{AS} [ -a[cdhlns][=file] ] [ -D ] [ --defsym @var{sym}=@var{val} ]
202 [ -f ] [ --gstabs ] [ --help ] [ -I @var{dir} ] [ -J ] [ -K ] [ -L ]
203 [ -o @var{objfile} ] [ -R ] [ --statistics ] [ -v ] [ -version ]
204 [ --version ] [ -W ] [ -w ] [ -x ] [ -Z ]
206 @c am29k has no machine-dependent assembler options
209 [ -mbig-endian | -mlittle-endian ]
212 [ -m[arm]1 | -m[arm]2 | -m[arm]250 | -m[arm]3 | -m[arm]6 | -m[arm]7[t][[d]m[i]] ]
213 [ -m[arm]v2 | -m[arm]v2a | -m[arm]v3 | -m[arm]v3m | -m[arm]v4 | -m[arm]v4t ]
215 [ -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu ]
217 [ -mapcs-32 | -mapcs-26 ]
224 @c Hitachi family chips have no machine-dependent assembler options
227 @c HPPA has no machine-dependent assembler options (yet).
230 @c The order here is important. See c-sparc.texi.
231 [ -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite | -Av9 | -Av9a ]
232 [ -xarch=v8plus | -xarch=v8plusa ] [ -bump ]
235 @c Z8000 has no machine-dependent assembler options
238 @c see md_parse_option in tc-i960.c
239 [ -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC ]
243 [ -l ] [ -m68000 | -m68010 | -m68020 | ... ]
246 [ -nocpp ] [ -EL ] [ -EB ] [ -G @var{num} ] [ -mcpu=@var{CPU} ]
247 [ -mips1 ] [ -mips2 ] [ -mips3 ] [ -m4650 ] [ -no-m4650 ]
248 [ --trap ] [ --break ]
249 [ --emulation=@var{name} ]
251 [ -- | @var{files} @dots{} ]
256 Turn on listings, in any of a variety of ways:
260 omit debugging directives
263 include high-level source
269 omit forms processing
275 set the name of the listing file
278 You may combine these options; for example, use @samp{-aln} for assembly
279 listing without forms processing. The @samp{=file} option, if used, must be
280 the last one. By itself, @samp{-a} defaults to @samp{-ahls}---that is, all
284 Ignored. This option is accepted for script compatibility with calls to
287 @item --defsym @var{sym}=@var{value}
288 Define the symbol @var{sym} to be @var{value} before assembling the input file.
289 @var{value} must be an integer constant. As in C, a leading @samp{0x}
290 indicates a hexadecimal value, and a leading @samp{0} indicates an octal value.
293 ``fast''---skip whitespace and comment preprocessing (assume source is
297 Generate stabs debugging information for each assembler line. This
298 may help debugging assembler code, if the debugger can handle it.
301 Print a summary of the command line options and exit.
304 Add directory @var{dir} to the search list for @code{.include} directives.
307 Don't warn about signed overflow.
310 @ifclear DIFF-TBL-KLUGE
311 This option is accepted but has no effect on the @value{TARGET} family.
313 @ifset DIFF-TBL-KLUGE
314 Issue warnings when difference tables altered for long displacements.
318 Keep (in the symbol table) local symbols, starting with @samp{L}.
320 @item -o @var{objfile}
321 Name the object-file output from @code{@value{AS}} @var{objfile}.
324 Fold the data section into the text section.
327 Print the maximum space (in bytes) and total time (in seconds) used by
332 Print the @code{as} version.
335 Print the @code{as} version and exit.
338 Suppress warning messages.
347 Generate an object file even after errors.
349 @item -- | @var{files} @dots{}
350 Standard input, or source files to assemble.
355 The following options are available when @value{AS} is configured for
360 @cindex ARC endianness
361 @cindex endianness, ARC
362 @cindex big endian output, ARC
364 Generate ``big endian'' format output.
366 @cindex little endian output, ARC
367 @item -mlittle-endian
368 Generate ``little endian'' format output.
374 The following options are available when @value{AS} is configured for the ARM
378 @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
379 Specify which variant of the ARM architecture is the target.
380 @item -mthumb | -mall
381 Enable or disable Thumb only instruction decoding.
382 @item -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu
383 Select which Floating Point architcture is the target.
384 @item -mapcs-32 | -mapcs-26
385 Select which procedure calling convention is in use.
387 Select either big-endian (-EB) or little-endian (-EL) output.
392 The following options are available when @value{AS} is configured for
395 @cindex D10V optimization
396 @cindex optimization, D10V
398 Optimize output by parallelizing instructions.
403 The following options are available when @value{AS} is configured for the
404 Intel 80960 processor.
407 @item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
408 Specify which variant of the 960 architecture is the target.
411 Add code to collect statistics about branches taken.
414 Do not alter compare-and-branch instructions for long displacements;
421 The following options are available when @value{AS} is configured for the
422 Motorola 68000 series.
427 Shorten references to undefined symbols, to one word instead of two.
429 @item -m68000 | -m68008 | -m68010 | -m68020 | -m68030 | -m68040 | -m68060
430 @itemx | -m68302 | -m68331 | -m68332 | -m68333 | -m68340 | -mcpu32 | -m5200
431 Specify what processor in the 68000 family is the target. The default
432 is normally the 68020, but this can be changed at configuration time.
434 @item -m68881 | -m68882 | -mno-68881 | -mno-68882
435 The target machine does (or does not) have a floating-point coprocessor.
436 The default is to assume a coprocessor for 68020, 68030, and cpu32. Although
437 the basic 68000 is not compatible with the 68881, a combination of the
438 two can be specified, since it's possible to do emulation of the
439 coprocessor instructions with the main processor.
441 @item -m68851 | -mno-68851
442 The target machine does (or does not) have a memory-management
443 unit coprocessor. The default is to assume an MMU for 68020 and up.
449 The following options are available when @code{@value{AS}} is configured
450 for the SPARC architecture:
453 @item -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite | -Av9 | -Av9a
454 Explicitly select a variant of the SPARC architecture.
456 @item -xarch=v8plus | -xarch=v8plusa
457 For compatibility with the Solaris v9 assembler. These options are
458 equivalent to -Av9 and -Av9a, respectively.
461 Warn when the assembler switches to another architecture.
466 The following options are available when @value{AS} is configured for
471 This option sets the largest size of an object that can be referenced
472 implicitly with the @code{gp} register. It is only accepted for targets that
473 use ECOFF format, such as a DECstation running Ultrix. The default value is 8.
475 @cindex MIPS endianness
476 @cindex endianness, MIPS
477 @cindex big endian output, MIPS
479 Generate ``big endian'' format output.
481 @cindex little endian output, MIPS
483 Generate ``little endian'' format output.
489 Generate code for a particular MIPS Instruction Set Architecture level.
490 @samp{-mips1} corresponds to the @sc{r2000} and @sc{r3000} processors,
491 @samp{-mips2} to the @sc{r6000} processor, and @samp{-mips3} to the @sc{r4000}
496 Generate code for the MIPS @sc{r4650} chip. This tells the assembler to accept
497 the @samp{mad} and @samp{madu} instruction, and to not schedule @samp{nop}
498 instructions around accesses to the @samp{HI} and @samp{LO} registers.
499 @samp{-no-m4650} turns off this option.
501 @item -mcpu=@var{CPU}
502 Generate code for a particular MIPS cpu. This has little effect on the
503 assembler, but it is passed by @code{@value{GCC}}.
506 @item --emulation=@var{name}
507 This option causes @code{@value{AS}} to emulate @code{@value{AS}} configured
508 for some other target, in all respects, including output format (choosing
509 between ELF and ECOFF only), handling of pseudo-opcodes which may generate
510 debugging information or store symbol table information, and default
511 endianness. The available configuration names are: @samp{mipsecoff},
512 @samp{mipself}, @samp{mipslecoff}, @samp{mipsbecoff}, @samp{mipslelf},
513 @samp{mipsbelf}. The first two do not alter the default endianness from that
514 of the primary target for which the assembler was configured; the others change
515 the default to little- or big-endian as indicated by the @samp{b} or @samp{l}
516 in the name. Using @samp{-EB} or @samp{-EL} will override the endianness
517 selection in any case.
519 This option is currently supported only when the primary target
520 @code{@value{AS}} is configured for is a MIPS ELF or ECOFF target.
521 Furthermore, the primary target or others specified with
522 @samp{--enable-targets=@dots{}} at configuration time must include support for
523 the other format, if both are to be available. For example, the Irix 5
524 configuration includes support for both.
526 Eventually, this option will support more configurations, with more
527 fine-grained control over the assembler's behavior, and will be supported for
531 @code{@value{AS}} ignores this option. It is accepted for compatibility with
539 Control how to deal with multiplication overflow and division by zero.
540 @samp{--trap} or @samp{--no-break} (which are synonyms) take a trap exception
541 (and only work for Instruction Set Architecture level 2 and higher);
542 @samp{--break} or @samp{--no-trap} (also synonyms, and the default) take a
548 * Manual:: Structure of this Manual
549 * GNU Assembler:: The GNU Assembler
550 * Object Formats:: Object File Formats
551 * Command Line:: Command Line
552 * Input Files:: Input Files
553 * Object:: Output (Object) File
554 * Errors:: Error and Warning Messages
558 @section Structure of this Manual
560 @cindex manual, structure and purpose
561 This manual is intended to describe what you need to know to use
562 @sc{gnu} @code{@value{AS}}. We cover the syntax expected in source files, including
563 notation for symbols, constants, and expressions; the directives that
564 @code{@value{AS}} understands; and of course how to invoke @code{@value{AS}}.
567 We also cover special features in the @value{TARGET}
568 configuration of @code{@value{AS}}, including assembler directives.
571 This manual also describes some of the machine-dependent features of
572 various flavors of the assembler.
575 @cindex machine instructions (not covered)
576 On the other hand, this manual is @emph{not} intended as an introduction
577 to programming in assembly language---let alone programming in general!
578 In a similar vein, we make no attempt to introduce the machine
579 architecture; we do @emph{not} describe the instruction set, standard
580 mnemonics, registers or addressing modes that are standard to a
581 particular architecture.
583 You may want to consult the manufacturer's
584 machine architecture manual for this information.
588 For information on the H8/300 machine instruction set, see @cite{H8/300
589 Series Programming Manual} (Hitachi ADE--602--025). For the H8/300H,
590 see @cite{H8/300H Series Programming Manual} (Hitachi).
593 For information on the H8/500 machine instruction set, see @cite{H8/500
594 Series Programming Manual} (Hitachi M21T001).
597 For information on the Hitachi SH machine instruction set, see
598 @cite{SH-Microcomputer User's Manual} (Hitachi Micro Systems, Inc.).
601 For information on the Z8000 machine instruction set, see @cite{Z8000 CPU Technical Manual}
605 @c I think this is premature---doc@cygnus.com, 17jan1991
607 Throughout this manual, we assume that you are running @dfn{GNU},
608 the portable operating system from the @dfn{Free Software
609 Foundation, Inc.}. This restricts our attention to certain kinds of
610 computer (in particular, the kinds of computers that @sc{gnu} can run on);
611 once this assumption is granted examples and definitions need less
614 @code{@value{AS}} is part of a team of programs that turn a high-level
615 human-readable series of instructions into a low-level
616 computer-readable series of instructions. Different versions of
617 @code{@value{AS}} are used for different kinds of computer.
620 @c There used to be a section "Terminology" here, which defined
621 @c "contents", "byte", "word", and "long". Defining "word" to any
622 @c particular size is confusing when the .word directive may generate 16
623 @c bits on one machine and 32 bits on another; in general, for the user
624 @c version of this manual, none of these terms seem essential to define.
625 @c They were used very little even in the former draft of the manual;
626 @c this draft makes an effort to avoid them (except in names of
630 @section The GNU Assembler
632 @sc{gnu} @code{as} is really a family of assemblers.
634 This manual describes @code{@value{AS}}, a member of that family which is
635 configured for the @value{TARGET} architectures.
637 If you use (or have used) the @sc{gnu} assembler on one architecture, you
638 should find a fairly similar environment when you use it on another
639 architecture. Each version has much in common with the others,
640 including object file formats, most assembler directives (often called
641 @dfn{pseudo-ops}) and assembler syntax.@refill
643 @cindex purpose of @sc{gnu} assembler
644 @code{@value{AS}} is primarily intended to assemble the output of the
645 @sc{gnu} C compiler @code{@value{GCC}} for use by the linker
646 @code{@value{LD}}. Nevertheless, we've tried to make @code{@value{AS}}
647 assemble correctly everything that other assemblers for the same
648 machine would assemble.
650 Any exceptions are documented explicitly (@pxref{Machine Dependencies}).
653 @c This remark should appear in generic version of manual; assumption
654 @c here is that generic version sets M680x0.
655 This doesn't mean @code{@value{AS}} always uses the same syntax as another
656 assembler for the same architecture; for example, we know of several
657 incompatible versions of 680x0 assembly language syntax.
660 Unlike older assemblers, @code{@value{AS}} is designed to assemble a source
661 program in one pass of the source file. This has a subtle impact on the
662 @kbd{.org} directive (@pxref{Org,,@code{.org}}).
665 @section Object File Formats
667 @cindex object file format
668 The @sc{gnu} assembler can be configured to produce several alternative
669 object file formats. For the most part, this does not affect how you
670 write assembly language programs; but directives for debugging symbols
671 are typically different in different file formats. @xref{Symbol
672 Attributes,,Symbol Attributes}.
675 On the @value{TARGET}, @code{@value{AS}} is configured to produce
676 @value{OBJ-NAME} format object files.
678 @c The following should exhaust all configs that set MULTI-OBJ, ideally
680 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
681 @code{a.out} or COFF format object files.
684 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
685 @code{b.out} or COFF format object files.
688 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
689 SOM or ELF format object files.
694 @section Command Line
696 @cindex command line conventions
697 After the program name @code{@value{AS}}, the command line may contain
698 options and file names. Options may appear in any order, and may be
699 before, after, or between file names. The order of file names is
702 @cindex standard input, as input file
704 @file{--} (two hyphens) by itself names the standard input file
705 explicitly, as one of the files for @code{@value{AS}} to assemble.
707 @cindex options, command line
708 Except for @samp{--} any command line argument that begins with a
709 hyphen (@samp{-}) is an option. Each option changes the behavior of
710 @code{@value{AS}}. No option changes the way another option works. An
711 option is a @samp{-} followed by one or more letters; the case of
712 the letter is important. All options are optional.
714 Some options expect exactly one file name to follow them. The file
715 name may either immediately follow the option's letter (compatible
716 with older assemblers) or it may be the next command argument (@sc{gnu}
717 standard). These two command lines are equivalent:
720 @value{AS} -o my-object-file.o mumble.s
721 @value{AS} -omy-object-file.o mumble.s
728 @cindex source program
730 We use the phrase @dfn{source program}, abbreviated @dfn{source}, to
731 describe the program input to one run of @code{@value{AS}}. The program may
732 be in one or more files; how the source is partitioned into files
733 doesn't change the meaning of the source.
735 @c I added "con" prefix to "catenation" just to prove I can overcome my
736 @c APL training... doc@cygnus.com
737 The source program is a concatenation of the text in all the files, in the
740 Each time you run @code{@value{AS}} it assembles exactly one source
741 program. The source program is made up of one or more files.
742 (The standard input is also a file.)
744 You give @code{@value{AS}} a command line that has zero or more input file
745 names. The input files are read (from left file name to right). A
746 command line argument (in any position) that has no special meaning
747 is taken to be an input file name.
749 If you give @code{@value{AS}} no file names it attempts to read one input file
750 from the @code{@value{AS}} standard input, which is normally your terminal. You
751 may have to type @key{ctl-D} to tell @code{@value{AS}} there is no more program
754 Use @samp{--} if you need to explicitly name the standard input file
755 in your command line.
757 If the source is empty, @code{@value{AS}} produces a small, empty object
760 @subheading Filenames and Line-numbers
762 @cindex input file linenumbers
763 @cindex line numbers, in input files
764 There are two ways of locating a line in the input file (or files) and
765 either may be used in reporting error messages. One way refers to a line
766 number in a physical file; the other refers to a line number in a
767 ``logical'' file. @xref{Errors, ,Error and Warning Messages}.
769 @dfn{Physical files} are those files named in the command line given
770 to @code{@value{AS}}.
772 @dfn{Logical files} are simply names declared explicitly by assembler
773 directives; they bear no relation to physical files. Logical file names
774 help error messages reflect the original source file, when @code{@value{AS}}
775 source is itself synthesized from other files.
776 @xref{App-File,,@code{.app-file}}.
779 @section Output (Object) File
785 Every time you run @code{@value{AS}} it produces an output file, which is
786 your assembly language program translated into numbers. This file
787 is the object file. Its default name is
795 @code{b.out} when @code{@value{AS}} is configured for the Intel 80960.
797 You can give it another name by using the @code{-o} option. Conventionally,
798 object file names end with @file{.o}. The default name is used for historical
799 reasons: older assemblers were capable of assembling self-contained programs
800 directly into a runnable program. (For some formats, this isn't currently
801 possible, but it can be done for the @code{a.out} format.)
805 The object file is meant for input to the linker @code{@value{LD}}. It contains
806 assembled program code, information to help @code{@value{LD}} integrate
807 the assembled program into a runnable file, and (optionally) symbolic
808 information for the debugger.
810 @c link above to some info file(s) like the description of a.out.
811 @c don't forget to describe @sc{gnu} info as well as Unix lossage.
814 @section Error and Warning Messages
816 @cindex error messsages
817 @cindex warning messages
818 @cindex messages from assembler
819 @code{@value{AS}} may write warnings and error messages to the standard error
820 file (usually your terminal). This should not happen when a compiler
821 runs @code{@value{AS}} automatically. Warnings report an assumption made so
822 that @code{@value{AS}} could keep assembling a flawed program; errors report a
823 grave problem that stops the assembly.
825 @cindex format of warning messages
826 Warning messages have the format
829 file_name:@b{NNN}:Warning Message Text
833 @cindex line numbers, in warnings/errors
834 (where @b{NNN} is a line number). If a logical file name has been given
835 (@pxref{App-File,,@code{.app-file}}) it is used for the filename,
836 otherwise the name of the current input file is used. If a logical line
839 (@pxref{Line,,@code{.line}})
843 (@pxref{Line,,@code{.line}})
846 (@pxref{Ln,,@code{.ln}})
849 then it is used to calculate the number printed,
850 otherwise the actual line in the current source file is printed. The
851 message text is intended to be self explanatory (in the grand Unix
854 @cindex format of error messages
855 Error messages have the format
857 file_name:@b{NNN}:FATAL:Error Message Text
859 The file name and line number are derived as for warning
860 messages. The actual message text may be rather less explanatory
861 because many of them aren't supposed to happen.
864 @chapter Command-Line Options
866 @cindex options, all versions of assembler
867 This chapter describes command-line options available in @emph{all}
868 versions of the @sc{gnu} assembler; @pxref{Machine Dependencies}, for options specific
870 to the @value{TARGET}.
873 to particular machine architectures.
876 If you are invoking @code{@value{AS}} via the @sc{gnu} C compiler (version 2), you
877 can use the @samp{-Wa} option to pass arguments through to the
878 assembler. The assembler arguments must be separated from each other
879 (and the @samp{-Wa}) by commas. For example:
882 gcc -c -g -O -Wa,-alh,-L file.c
886 emits a listing to standard output with high-level
889 Usually you do not need to use this @samp{-Wa} mechanism, since many compiler
890 command-line options are automatically passed to the assembler by the compiler.
891 (You can call the @sc{gnu} compiler driver with the @samp{-v} option to see
892 precisely what options it passes to each compilation pass, including the
896 * a:: -a[cdhlns] enable listings
897 * D:: -D for compatibility
898 * f:: -f to work faster
899 * I:: -I for .include search path
900 @ifclear DIFF-TBL-KLUGE
901 * K:: -K for compatibility
903 @ifset DIFF-TBL-KLUGE
904 * K:: -K for difference tables
907 * L:: -L to retain local labels
908 * M:: -M or --mri to assemble in MRI compatibility mode
909 * MD:: --MD for dependency tracking
910 * o:: -o to name the object file
911 * R:: -R to join data and text sections
912 * statistics:: --statistics to see statistics about assembly
913 * v:: -v to announce version
914 * W:: -W to suppress warnings
915 * Z:: -Z to make object file even after errors
919 @section Enable Listings: @code{-a[cdhlns]}
928 @cindex listings, enabling
929 @cindex assembly listings, enabling
931 These options enable listing output from the assembler. By itself,
932 @samp{-a} requests high-level, assembly, and symbols listing.
933 You can use other letters to select specific options for the list:
934 @samp{-ah} requests a high-level language listing,
935 @samp{-al} requests an output-program assembly listing, and
936 @samp{-as} requests a symbol table listing.
937 High-level listings require that a compiler debugging option like
938 @samp{-g} be used, and that assembly listings (@samp{-al}) be requested
941 Use the @samp{-ac} option to omit false conditionals from a listing. Any lines
942 which are not assembled because of a false @code{.if} (or @code{.ifdef}, or any
943 other conditional), or a true @code{.if} followed by an @code{.else}, will be
944 omitted from the listing.
946 Use the @samp{-ad} option to omit debugging directives from the
949 Once you have specified one of these options, you can further control
950 listing output and its appearance using the directives @code{.list},
951 @code{.nolist}, @code{.psize}, @code{.eject}, @code{.title}, and
953 The @samp{-an} option turns off all forms processing.
954 If you do not request listing output with one of the @samp{-a} options, the
955 listing-control directives have no effect.
957 The letters after @samp{-a} may be combined into one option,
958 @emph{e.g.}, @samp{-aln}.
964 This option has no effect whatsoever, but it is accepted to make it more
965 likely that scripts written for other assemblers also work with
969 @section Work Faster: @code{-f}
972 @cindex trusted compiler
973 @cindex faster processing (@code{-f})
974 @samp{-f} should only be used when assembling programs written by a
975 (trusted) compiler. @samp{-f} stops the assembler from doing whitespace
976 and comment preprocessing on
977 the input file(s) before assembling them. @xref{Preprocessing,
981 @emph{Warning:} if you use @samp{-f} when the files actually need to be
982 preprocessed (if they contain comments, for example), @code{@value{AS}} does
987 @section @code{.include} search path: @code{-I} @var{path}
989 @kindex -I @var{path}
990 @cindex paths for @code{.include}
991 @cindex search path for @code{.include}
992 @cindex @code{include} directive search path
993 Use this option to add a @var{path} to the list of directories
994 @code{@value{AS}} searches for files specified in @code{.include}
995 directives (@pxref{Include,,@code{.include}}). You may use @code{-I} as
996 many times as necessary to include a variety of paths. The current
997 working directory is always searched first; after that, @code{@value{AS}}
998 searches any @samp{-I} directories in the same order as they were
999 specified (left to right) on the command line.
1002 @section Difference Tables: @code{-K}
1005 @ifclear DIFF-TBL-KLUGE
1006 On the @value{TARGET} family, this option is allowed, but has no effect. It is
1007 permitted for compatibility with the @sc{gnu} assembler on other platforms,
1008 where it can be used to warn when the assembler alters the machine code
1009 generated for @samp{.word} directives in difference tables. The @value{TARGET}
1010 family does not have the addressing limitations that sometimes lead to this
1011 alteration on other platforms.
1014 @ifset DIFF-TBL-KLUGE
1015 @cindex difference tables, warning
1016 @cindex warning for altered difference tables
1017 @code{@value{AS}} sometimes alters the code emitted for directives of the form
1018 @samp{.word @var{sym1}-@var{sym2}}; @pxref{Word,,@code{.word}}.
1019 You can use the @samp{-K} option if you want a warning issued when this
1024 @section Include Local Labels: @code{-L}
1027 @cindex local labels, retaining in output
1028 Labels beginning with @samp{L} (upper case only) are called @dfn{local
1029 labels}. @xref{Symbol Names}. Normally you do not see such labels when
1030 debugging, because they are intended for the use of programs (like
1031 compilers) that compose assembler programs, not for your notice.
1032 Normally both @code{@value{AS}} and @code{@value{LD}} discard such labels, so you do not
1033 normally debug with them.
1035 This option tells @code{@value{AS}} to retain those @samp{L@dots{}} symbols
1036 in the object file. Usually if you do this you also tell the linker
1037 @code{@value{LD}} to preserve symbols whose names begin with @samp{L}.
1039 By default, a local label is any label beginning with @samp{L}, but each
1040 target is allowed to redefine the local label prefix.
1042 On the HPPA local labels begin with @samp{L$}.
1045 @samp{;} for the ARM family;
1049 @section Assemble in MRI Compatibility Mode: @code{-M}
1052 @cindex MRI compatibility mode
1053 The @code{-M} or @code{--mri} option selects MRI compatibility mode. This
1054 changes the syntax and pseudo-op handling of @code{@value{AS}} to make it
1055 compatible with the @code{ASM68K} or the @code{ASM960} (depending upon the
1056 configured target) assembler from Microtec Research. The exact nature of the
1057 MRI syntax will not be documented here; see the MRI manuals for more
1058 information. Note in particular that the handling of macros and macro
1059 arguments is somewhat different. The purpose of this option is to permit
1060 assembling existing MRI assembler code using @code{@value{AS}}.
1062 The MRI compatibility is not complete. Certain operations of the MRI assembler
1063 depend upon its object file format, and can not be supported using other object
1064 file formats. Supporting these would require enhancing each object file format
1065 individually. These are:
1068 @item global symbols in common section
1070 The m68k MRI assembler supports common sections which are merged by the linker.
1071 Other object file formats do not support this. @code{@value{AS}} handles
1072 common sections by treating them as a single common symbol. It permits local
1073 symbols to be defined within a common section, but it can not support global
1074 symbols, since it has no way to describe them.
1076 @item complex relocations
1078 The MRI assemblers support relocations against a negated section address, and
1079 relocations which combine the start addresses of two or more sections. These
1080 are not support by other object file formats.
1082 @item @code{END} pseudo-op specifying start address
1084 The MRI @code{END} pseudo-op permits the specification of a start address.
1085 This is not supported by other object file formats. The start address may
1086 instead be specified using the @code{-e} option to the linker, or in a linker
1089 @item @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops
1091 The MRI @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops assign a module
1092 name to the output file. This is not supported by other object file formats.
1094 @item @code{ORG} pseudo-op
1096 The m68k MRI @code{ORG} pseudo-op begins an absolute section at a given
1097 address. This differs from the usual @code{@value{AS}} @code{.org} pseudo-op,
1098 which changes the location within the current section. Absolute sections are
1099 not supported by other object file formats. The address of a section may be
1100 assigned within a linker script.
1103 There are some other features of the MRI assembler which are not supported by
1104 @code{@value{AS}}, typically either because they are difficult or because they
1105 seem of little consequence. Some of these may be supported in future releases.
1109 @item EBCDIC strings
1111 EBCDIC strings are not supported.
1113 @item packed binary coded decimal
1115 Packed binary coded decimal is not supported. This means that the @code{DC.P}
1116 and @code{DCB.P} pseudo-ops are not supported.
1118 @item @code{FEQU} pseudo-op
1120 The m68k @code{FEQU} pseudo-op is not supported.
1122 @item @code{NOOBJ} pseudo-op
1124 The m68k @code{NOOBJ} pseudo-op is not supported.
1126 @item @code{OPT} branch control options
1128 The m68k @code{OPT} branch control options---@code{B}, @code{BRS}, @code{BRB},
1129 @code{BRL}, and @code{BRW}---are ignored. @code{@value{AS}} automatically
1130 relaxes all branches, whether forward or backward, to an appropriate size, so
1131 these options serve no purpose.
1133 @item @code{OPT} list control options
1135 The following m68k @code{OPT} list control options are ignored: @code{C},
1136 @code{CEX}, @code{CL}, @code{CRE}, @code{E}, @code{G}, @code{I}, @code{M},
1137 @code{MEX}, @code{MC}, @code{MD}, @code{X}.
1139 @item other @code{OPT} options
1141 The following m68k @code{OPT} options are ignored: @code{NEST}, @code{O},
1142 @code{OLD}, @code{OP}, @code{P}, @code{PCO}, @code{PCR}, @code{PCS}, @code{R}.
1144 @item @code{OPT} @code{D} option is default
1146 The m68k @code{OPT} @code{D} option is the default, unlike the MRI assembler.
1147 @code{OPT NOD} may be used to turn it off.
1149 @item @code{XREF} pseudo-op.
1151 The m68k @code{XREF} pseudo-op is ignored.
1153 @item @code{.debug} pseudo-op
1155 The i960 @code{.debug} pseudo-op is not supported.
1157 @item @code{.extended} pseudo-op
1159 The i960 @code{.extended} pseudo-op is not supported.
1161 @item @code{.list} pseudo-op.
1163 The various options of the i960 @code{.list} pseudo-op are not supported.
1165 @item @code{.optimize} pseudo-op
1167 The i960 @code{.optimize} pseudo-op is not supported.
1169 @item @code{.output} pseudo-op
1171 The i960 @code{.output} pseudo-op is not supported.
1173 @item @code{.setreal} pseudo-op
1175 The i960 @code{.setreal} pseudo-op is not supported.
1180 @section Dependency tracking: @code{--MD}
1183 @cindex dependency tracking
1186 @code{@value{AS}} can generate a dependency file for the file it creates. This
1187 file consists of a single rule suitable for @code{make} describing the
1188 dependencies of the main source file.
1190 The rule is written to the file named in its argument.
1192 This feature is used in the automatic updating of makefiles.
1195 @section Name the Object File: @code{-o}
1198 @cindex naming object file
1199 @cindex object file name
1200 There is always one object file output when you run @code{@value{AS}}. By
1201 default it has the name
1204 @file{a.out} (or @file{b.out}, for Intel 960 targets only).
1218 You use this option (which takes exactly one filename) to give the
1219 object file a different name.
1221 Whatever the object file is called, @code{@value{AS}} overwrites any
1222 existing file of the same name.
1225 @section Join Data and Text Sections: @code{-R}
1228 @cindex data and text sections, joining
1229 @cindex text and data sections, joining
1230 @cindex joining text and data sections
1231 @cindex merging text and data sections
1232 @code{-R} tells @code{@value{AS}} to write the object file as if all
1233 data-section data lives in the text section. This is only done at
1234 the very last moment: your binary data are the same, but data
1235 section parts are relocated differently. The data section part of
1236 your object file is zero bytes long because all its bytes are
1237 appended to the text section. (@xref{Sections,,Sections and Relocation}.)
1239 When you specify @code{-R} it would be possible to generate shorter
1240 address displacements (because we do not have to cross between text and
1241 data section). We refrain from doing this simply for compatibility with
1242 older versions of @code{@value{AS}}. In future, @code{-R} may work this way.
1245 When @code{@value{AS}} is configured for COFF output,
1246 this option is only useful if you use sections named @samp{.text} and
1251 @code{-R} is not supported for any of the HPPA targets. Using
1252 @code{-R} generates a warning from @code{@value{AS}}.
1256 @section Display Assembly Statistics: @code{--statistics}
1258 @kindex --statistics
1259 @cindex statistics, about assembly
1260 @cindex time, total for assembly
1261 @cindex space used, maximum for assembly
1262 Use @samp{--statistics} to display two statistics about the resources used by
1263 @code{@value{AS}}: the maximum amount of space allocated during the assembly
1264 (in bytes), and the total execution time taken for the assembly (in @sc{cpu}
1268 @section Announce Version: @code{-v}
1272 @cindex assembler version
1273 @cindex version of assembler
1274 You can find out what version of as is running by including the
1275 option @samp{-v} (which you can also spell as @samp{-version}) on the
1279 @section Suppress Warnings: @code{-W}
1282 @cindex suppressing warnings
1283 @cindex warnings, suppressing
1284 @code{@value{AS}} should never give a warning or error message when
1285 assembling compiler output. But programs written by people often
1286 cause @code{@value{AS}} to give a warning that a particular assumption was
1287 made. All such warnings are directed to the standard error file.
1288 If you use this option, no warnings are issued. This option only
1289 affects the warning messages: it does not change any particular of how
1290 @code{@value{AS}} assembles your file. Errors, which stop the assembly, are
1294 @section Generate Object File in Spite of Errors: @code{-Z}
1295 @cindex object file, after errors
1296 @cindex errors, continuing after
1297 After an error message, @code{@value{AS}} normally produces no output. If for
1298 some reason you are interested in object file output even after
1299 @code{@value{AS}} gives an error message on your program, use the @samp{-Z}
1300 option. If there are any errors, @code{@value{AS}} continues anyways, and
1301 writes an object file after a final warning message of the form @samp{@var{n}
1302 errors, @var{m} warnings, generating bad object file.}
1307 @cindex machine-independent syntax
1308 @cindex syntax, machine-independent
1309 This chapter describes the machine-independent syntax allowed in a
1310 source file. @code{@value{AS}} syntax is similar to what many other
1311 assemblers use; it is inspired by the BSD 4.2
1316 assembler, except that @code{@value{AS}} does not assemble Vax bit-fields.
1320 * Preprocessing:: Preprocessing
1321 * Whitespace:: Whitespace
1322 * Comments:: Comments
1323 * Symbol Intro:: Symbols
1324 * Statements:: Statements
1325 * Constants:: Constants
1329 @section Preprocessing
1331 @cindex preprocessing
1332 The @code{@value{AS}} internal preprocessor:
1334 @cindex whitespace, removed by preprocessor
1336 adjusts and removes extra whitespace. It leaves one space or tab before
1337 the keywords on a line, and turns any other whitespace on the line into
1340 @cindex comments, removed by preprocessor
1342 removes all comments, replacing them with a single space, or an
1343 appropriate number of newlines.
1345 @cindex constants, converted by preprocessor
1347 converts character constants into the appropriate numeric values.
1350 It does not do macro processing, include file handling, or
1351 anything else you may get from your C compiler's preprocessor. You can
1352 do include file processing with the @code{.include} directive
1353 (@pxref{Include,,@code{.include}}). You can use the @sc{gnu} C compiler driver
1354 to get other ``CPP'' style preprocessing, by giving the input file a
1355 @samp{.S} suffix. @xref{Overall Options,, Options Controlling the Kind of
1356 Output, gcc.info, Using GNU CC}.
1358 Excess whitespace, comments, and character constants
1359 cannot be used in the portions of the input text that are not
1362 @cindex turning preprocessing on and off
1363 @cindex preprocessing, turning on and off
1366 If the first line of an input file is @code{#NO_APP} or if you use the
1367 @samp{-f} option, whitespace and comments are not removed from the input file.
1368 Within an input file, you can ask for whitespace and comment removal in
1369 specific portions of the by putting a line that says @code{#APP} before the
1370 text that may contain whitespace or comments, and putting a line that says
1371 @code{#NO_APP} after this text. This feature is mainly intend to support
1372 @code{asm} statements in compilers whose output is otherwise free of comments
1379 @dfn{Whitespace} is one or more blanks or tabs, in any order.
1380 Whitespace is used to separate symbols, and to make programs neater for
1381 people to read. Unless within character constants
1382 (@pxref{Characters,,Character Constants}), any whitespace means the same
1383 as exactly one space.
1389 There are two ways of rendering comments to @code{@value{AS}}. In both
1390 cases the comment is equivalent to one space.
1392 Anything from @samp{/*} through the next @samp{*/} is a comment.
1393 This means you may not nest these comments.
1397 The only way to include a newline ('\n') in a comment
1398 is to use this sort of comment.
1401 /* This sort of comment does not nest. */
1404 @cindex line comment character
1405 Anything from the @dfn{line comment} character to the next newline
1406 is considered a comment and is ignored. The line comment character is
1408 @samp{;} for the AMD 29K family;
1411 @samp{;} on the ARC;
1414 @samp{;} for the H8/300 family;
1417 @samp{!} for the H8/500 family;
1420 @samp{;} for the HPPA;
1423 @samp{#} on the i960;
1426 @samp{!} for the Hitachi SH;
1429 @samp{!} on the SPARC;
1432 @samp{|} on the 680x0;
1435 @samp{#} on the Vax;
1438 @samp{!} for the Z8000;
1440 see @ref{Machine Dependencies}. @refill
1441 @c FIXME What about i386, m88k, i860?
1444 On some machines there are two different line comment characters. One
1445 character only begins a comment if it is the first non-whitespace character on
1446 a line, while the other always begins a comment.
1450 @cindex lines starting with @code{#}
1451 @cindex logical line numbers
1452 To be compatible with past assemblers, lines that begin with @samp{#} have a
1453 special interpretation. Following the @samp{#} should be an absolute
1454 expression (@pxref{Expressions}): the logical line number of the @emph{next}
1455 line. Then a string (@pxref{Strings,, Strings}) is allowed: if present it is a
1456 new logical file name. The rest of the line, if any, should be whitespace.
1458 If the first non-whitespace characters on the line are not numeric,
1459 the line is ignored. (Just like a comment.)
1462 # This is an ordinary comment.
1463 # 42-6 "new_file_name" # New logical file name
1464 # This is logical line # 36.
1466 This feature is deprecated, and may disappear from future versions
1467 of @code{@value{AS}}.
1472 @cindex characters used in symbols
1473 @ifclear SPECIAL-SYMS
1474 A @dfn{symbol} is one or more characters chosen from the set of all
1475 letters (both upper and lower case), digits and the three characters
1481 A @dfn{symbol} is one or more characters chosen from the set of all
1482 letters (both upper and lower case), digits and the three characters
1483 @samp{._$}. (Save that, on the H8/300 only, you may not use @samp{$} in
1489 On most machines, you can also use @code{$} in symbol names; exceptions
1490 are noted in @ref{Machine Dependencies}.
1492 No symbol may begin with a digit. Case is significant.
1493 There is no length limit: all characters are significant. Symbols are
1494 delimited by characters not in that set, or by the beginning of a file
1495 (since the source program must end with a newline, the end of a file is
1496 not a possible symbol delimiter). @xref{Symbols}.
1497 @cindex length of symbols
1502 @cindex statements, structure of
1503 @cindex line separator character
1504 @cindex statement separator character
1506 @ifclear abnormal-separator
1507 A @dfn{statement} ends at a newline character (@samp{\n}) or at a
1508 semicolon (@samp{;}). The newline or semicolon is considered part of
1509 the preceding statement. Newlines and semicolons within character
1510 constants are an exception: they do not end statements.
1512 @ifset abnormal-separator
1514 A @dfn{statement} ends at a newline character (@samp{\n}) or an ``at''
1515 sign (@samp{@@}). The newline or at sign is considered part of the
1516 preceding statement. Newlines and at signs within character constants
1517 are an exception: they do not end statements.
1520 A @dfn{statement} ends at a newline character (@samp{\n}) or an exclamation
1521 point (@samp{!}). The newline or exclamation point is considered part of the
1522 preceding statement. Newlines and exclamation points within character
1523 constants are an exception: they do not end statements.
1526 A @dfn{statement} ends at a newline character (@samp{\n}); or (for the
1527 H8/300) a dollar sign (@samp{$}); or (for the
1530 (@samp{;}). The newline or separator character is considered part of
1531 the preceding statement. Newlines and separators within character
1532 constants are an exception: they do not end statements.
1537 A @dfn{statement} ends at a newline character (@samp{\n}) or line
1538 separator character. (The line separator is usually @samp{;}, unless
1539 this conflicts with the comment character; @pxref{Machine Dependencies}.) The
1540 newline or separator character is considered part of the preceding
1541 statement. Newlines and separators within character constants are an
1542 exception: they do not end statements.
1545 @cindex newline, required at file end
1546 @cindex EOF, newline must precede
1547 It is an error to end any statement with end-of-file: the last
1548 character of any input file should be a newline.@refill
1550 @cindex continuing statements
1551 @cindex multi-line statements
1552 @cindex statement on multiple lines
1553 You may write a statement on more than one line if you put a
1554 backslash (@kbd{\}) immediately in front of any newlines within the
1555 statement. When @code{@value{AS}} reads a backslashed newline both
1556 characters are ignored. You can even put backslashed newlines in
1557 the middle of symbol names without changing the meaning of your
1560 An empty statement is allowed, and may include whitespace. It is ignored.
1562 @cindex instructions and directives
1563 @cindex directives and instructions
1564 @c "key symbol" is not used elsewhere in the document; seems pedantic to
1565 @c @defn{} it in that case, as was done previously... doc@cygnus.com,
1567 A statement begins with zero or more labels, optionally followed by a
1568 key symbol which determines what kind of statement it is. The key
1569 symbol determines the syntax of the rest of the statement. If the
1570 symbol begins with a dot @samp{.} then the statement is an assembler
1571 directive: typically valid for any computer. If the symbol begins with
1572 a letter the statement is an assembly language @dfn{instruction}: it
1573 assembles into a machine language instruction.
1575 Different versions of @code{@value{AS}} for different computers
1576 recognize different instructions. In fact, the same symbol may
1577 represent a different instruction in a different computer's assembly
1581 @cindex @code{:} (label)
1582 @cindex label (@code{:})
1583 A label is a symbol immediately followed by a colon (@code{:}).
1584 Whitespace before a label or after a colon is permitted, but you may not
1585 have whitespace between a label's symbol and its colon. @xref{Labels}.
1588 For HPPA targets, labels need not be immediately followed by a colon, but
1589 the definition of a label must begin in column zero. This also implies that
1590 only one label may be defined on each line.
1594 label: .directive followed by something
1595 another_label: # This is an empty statement.
1596 instruction operand_1, operand_2, @dots{}
1603 A constant is a number, written so that its value is known by
1604 inspection, without knowing any context. Like this:
1607 .byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.
1608 .ascii "Ring the bell\7" # A string constant.
1609 .octa 0x123456789abcdef0123456789ABCDEF0 # A bignum.
1610 .float 0f-314159265358979323846264338327\
1611 95028841971.693993751E-40 # - pi, a flonum.
1616 * Characters:: Character Constants
1617 * Numbers:: Number Constants
1621 @subsection Character Constants
1623 @cindex character constants
1624 @cindex constants, character
1625 There are two kinds of character constants. A @dfn{character} stands
1626 for one character in one byte and its value may be used in
1627 numeric expressions. String constants (properly called string
1628 @emph{literals}) are potentially many bytes and their values may not be
1629 used in arithmetic expressions.
1633 * Chars:: Characters
1637 @subsubsection Strings
1639 @cindex string constants
1640 @cindex constants, string
1641 A @dfn{string} is written between double-quotes. It may contain
1642 double-quotes or null characters. The way to get special characters
1643 into a string is to @dfn{escape} these characters: precede them with
1644 a backslash @samp{\} character. For example @samp{\\} represents
1645 one backslash: the first @code{\} is an escape which tells
1646 @code{@value{AS}} to interpret the second character literally as a backslash
1647 (which prevents @code{@value{AS}} from recognizing the second @code{\} as an
1648 escape character). The complete list of escapes follows.
1650 @cindex escape codes, character
1651 @cindex character escape codes
1654 @c Mnemonic for ACKnowledge; for ASCII this is octal code 007.
1656 @cindex @code{\b} (backspace character)
1657 @cindex backspace (@code{\b})
1659 Mnemonic for backspace; for ASCII this is octal code 010.
1662 @c Mnemonic for EOText; for ASCII this is octal code 004.
1664 @cindex @code{\f} (formfeed character)
1665 @cindex formfeed (@code{\f})
1667 Mnemonic for FormFeed; for ASCII this is octal code 014.
1669 @cindex @code{\n} (newline character)
1670 @cindex newline (@code{\n})
1672 Mnemonic for newline; for ASCII this is octal code 012.
1675 @c Mnemonic for prefix; for ASCII this is octal code 033, usually known as @code{escape}.
1677 @cindex @code{\r} (carriage return character)
1678 @cindex carriage return (@code{\r})
1680 Mnemonic for carriage-Return; for ASCII this is octal code 015.
1683 @c Mnemonic for space; for ASCII this is octal code 040. Included for compliance with
1684 @c other assemblers.
1686 @cindex @code{\t} (tab)
1687 @cindex tab (@code{\t})
1689 Mnemonic for horizontal Tab; for ASCII this is octal code 011.
1692 @c Mnemonic for Vertical tab; for ASCII this is octal code 013.
1693 @c @item \x @var{digit} @var{digit} @var{digit}
1694 @c A hexadecimal character code. The numeric code is 3 hexadecimal digits.
1696 @cindex @code{\@var{ddd}} (octal character code)
1697 @cindex octal character code (@code{\@var{ddd}})
1698 @item \ @var{digit} @var{digit} @var{digit}
1699 An octal character code. The numeric code is 3 octal digits.
1700 For compatibility with other Unix systems, 8 and 9 are accepted as digits:
1701 for example, @code{\008} has the value 010, and @code{\009} the value 011.
1703 @cindex @code{\@var{xd...}} (hex character code)
1704 @cindex hex character code (@code{\@var{xd...}})
1705 @item \@code{x} @var{hex-digits...}
1706 A hex character code. All trailing hex digits are combined. Either upper or
1707 lower case @code{x} works.
1709 @cindex @code{\\} (@samp{\} character)
1710 @cindex backslash (@code{\\})
1712 Represents one @samp{\} character.
1715 @c Represents one @samp{'} (accent acute) character.
1716 @c This is needed in single character literals
1717 @c (@xref{Characters,,Character Constants}.) to represent
1720 @cindex @code{\"} (doublequote character)
1721 @cindex doublequote (@code{\"})
1723 Represents one @samp{"} character. Needed in strings to represent
1724 this character, because an unescaped @samp{"} would end the string.
1726 @item \ @var{anything-else}
1727 Any other character when escaped by @kbd{\} gives a warning, but
1728 assembles as if the @samp{\} was not present. The idea is that if
1729 you used an escape sequence you clearly didn't want the literal
1730 interpretation of the following character. However @code{@value{AS}} has no
1731 other interpretation, so @code{@value{AS}} knows it is giving you the wrong
1732 code and warns you of the fact.
1735 Which characters are escapable, and what those escapes represent,
1736 varies widely among assemblers. The current set is what we think
1737 the BSD 4.2 assembler recognizes, and is a subset of what most C
1738 compilers recognize. If you are in doubt, do not use an escape
1742 @subsubsection Characters
1744 @cindex single character constant
1745 @cindex character, single
1746 @cindex constant, single character
1747 A single character may be written as a single quote immediately
1748 followed by that character. The same escapes apply to characters as
1749 to strings. So if you want to write the character backslash, you
1750 must write @kbd{'\\} where the first @code{\} escapes the second
1751 @code{\}. As you can see, the quote is an acute accent, not a
1752 grave accent. A newline
1754 @ifclear abnormal-separator
1755 (or semicolon @samp{;})
1757 @ifset abnormal-separator
1759 (or at sign @samp{@@})
1762 (or dollar sign @samp{$}, for the H8/300; or semicolon @samp{;} for the
1768 immediately following an acute accent is taken as a literal character
1769 and does not count as the end of a statement. The value of a character
1770 constant in a numeric expression is the machine's byte-wide code for
1771 that character. @code{@value{AS}} assumes your character code is ASCII:
1772 @kbd{'A} means 65, @kbd{'B} means 66, and so on. @refill
1775 @subsection Number Constants
1777 @cindex constants, number
1778 @cindex number constants
1779 @code{@value{AS}} distinguishes three kinds of numbers according to how they
1780 are stored in the target machine. @emph{Integers} are numbers that
1781 would fit into an @code{int} in the C language. @emph{Bignums} are
1782 integers, but they are stored in more than 32 bits. @emph{Flonums}
1783 are floating point numbers, described below.
1786 * Integers:: Integers
1791 * Bit Fields:: Bit Fields
1797 @subsubsection Integers
1799 @cindex constants, integer
1801 @cindex binary integers
1802 @cindex integers, binary
1803 A binary integer is @samp{0b} or @samp{0B} followed by zero or more of
1804 the binary digits @samp{01}.
1806 @cindex octal integers
1807 @cindex integers, octal
1808 An octal integer is @samp{0} followed by zero or more of the octal
1809 digits (@samp{01234567}).
1811 @cindex decimal integers
1812 @cindex integers, decimal
1813 A decimal integer starts with a non-zero digit followed by zero or
1814 more digits (@samp{0123456789}).
1816 @cindex hexadecimal integers
1817 @cindex integers, hexadecimal
1818 A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or
1819 more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}.
1821 Integers have the usual values. To denote a negative integer, use
1822 the prefix operator @samp{-} discussed under expressions
1823 (@pxref{Prefix Ops,,Prefix Operators}).
1826 @subsubsection Bignums
1829 @cindex constants, bignum
1830 A @dfn{bignum} has the same syntax and semantics as an integer
1831 except that the number (or its negative) takes more than 32 bits to
1832 represent in binary. The distinction is made because in some places
1833 integers are permitted while bignums are not.
1836 @subsubsection Flonums
1838 @cindex floating point numbers
1839 @cindex constants, floating point
1841 @cindex precision, floating point
1842 A @dfn{flonum} represents a floating point number. The translation is
1843 indirect: a decimal floating point number from the text is converted by
1844 @code{@value{AS}} to a generic binary floating point number of more than
1845 sufficient precision. This generic floating point number is converted
1846 to a particular computer's floating point format (or formats) by a
1847 portion of @code{@value{AS}} specialized to that computer.
1849 A flonum is written by writing (in order)
1854 (@samp{0} is optional on the HPPA.)
1858 A letter, to tell @code{@value{AS}} the rest of the number is a flonum.
1860 @kbd{e} is recommended. Case is not important.
1862 @c FIXME: verify if flonum syntax really this vague for most cases
1863 (Any otherwise illegal letter works here, but that might be changed. Vax BSD
1864 4.2 assembler seems to allow any of @samp{defghDEFGH}.)
1867 On the H8/300, H8/500,
1869 and AMD 29K architectures, the letter must be
1870 one of the letters @samp{DFPRSX} (in upper or lower case).
1872 On the ARC, the letter must be one of the letters @samp{DFRS}
1873 (in upper or lower case).
1875 On the Intel 960 architecture, the letter must be
1876 one of the letters @samp{DFT} (in upper or lower case).
1878 On the HPPA architecture, the letter must be @samp{E} (upper case only).
1882 One of the letters @samp{DFPRSX} (in upper or lower case).
1885 One of the letters @samp{DFRS} (in upper or lower case).
1888 One of the letters @samp{DFPRSX} (in upper or lower case).
1891 The letter @samp{E} (upper case only).
1894 One of the letters @samp{DFT} (in upper or lower case).
1899 An optional sign: either @samp{+} or @samp{-}.
1902 An optional @dfn{integer part}: zero or more decimal digits.
1905 An optional @dfn{fractional part}: @samp{.} followed by zero
1906 or more decimal digits.
1909 An optional exponent, consisting of:
1913 An @samp{E} or @samp{e}.
1914 @c I can't find a config where "EXP_CHARS" is other than 'eE', but in
1915 @c principle this can perfectly well be different on different targets.
1917 Optional sign: either @samp{+} or @samp{-}.
1919 One or more decimal digits.
1924 At least one of the integer part or the fractional part must be
1925 present. The floating point number has the usual base-10 value.
1927 @code{@value{AS}} does all processing using integers. Flonums are computed
1928 independently of any floating point hardware in the computer running
1933 @c Bit fields are written as a general facility but are also controlled
1934 @c by a conditional-compilation flag---which is as of now (21mar91)
1935 @c turned on only by the i960 config of GAS.
1937 @subsubsection Bit Fields
1940 @cindex constants, bit field
1941 You can also define numeric constants as @dfn{bit fields}.
1942 specify two numbers separated by a colon---
1944 @var{mask}:@var{value}
1947 @code{@value{AS}} applies a bitwise @sc{and} between @var{mask} and
1950 The resulting number is then packed
1952 @c this conditional paren in case bit fields turned on elsewhere than 960
1953 (in host-dependent byte order)
1955 into a field whose width depends on which assembler directive has the
1956 bit-field as its argument. Overflow (a result from the bitwise and
1957 requiring more binary digits to represent) is not an error; instead,
1958 more constants are generated, of the specified width, beginning with the
1959 least significant digits.@refill
1961 The directives @code{.byte}, @code{.hword}, @code{.int}, @code{.long},
1962 @code{.short}, and @code{.word} accept bit-field arguments.
1967 @chapter Sections and Relocation
1972 * Secs Background:: Background
1973 * Ld Sections:: Linker Sections
1974 * As Sections:: Assembler Internal Sections
1975 * Sub-Sections:: Sub-Sections
1979 @node Secs Background
1982 Roughly, a section is a range of addresses, with no gaps; all data
1983 ``in'' those addresses is treated the same for some particular purpose.
1984 For example there may be a ``read only'' section.
1986 @cindex linker, and assembler
1987 @cindex assembler, and linker
1988 The linker @code{@value{LD}} reads many object files (partial programs) and
1989 combines their contents to form a runnable program. When @code{@value{AS}}
1990 emits an object file, the partial program is assumed to start at address 0.
1991 @code{@value{LD}} assigns the final addresses for the partial program, so that
1992 different partial programs do not overlap. This is actually an
1993 oversimplification, but it suffices to explain how @code{@value{AS}} uses
1996 @code{@value{LD}} moves blocks of bytes of your program to their run-time
1997 addresses. These blocks slide to their run-time addresses as rigid
1998 units; their length does not change and neither does the order of bytes
1999 within them. Such a rigid unit is called a @emph{section}. Assigning
2000 run-time addresses to sections is called @dfn{relocation}. It includes
2001 the task of adjusting mentions of object-file addresses so they refer to
2002 the proper run-time addresses.
2004 For the H8/300 and H8/500,
2005 and for the Hitachi SH,
2006 @code{@value{AS}} pads sections if needed to
2007 ensure they end on a word (sixteen bit) boundary.
2010 @cindex standard assembler sections
2011 An object file written by @code{@value{AS}} has at least three sections, any
2012 of which may be empty. These are named @dfn{text}, @dfn{data} and
2017 When it generates COFF output,
2019 @code{@value{AS}} can also generate whatever other named sections you specify
2020 using the @samp{.section} directive (@pxref{Section,,@code{.section}}).
2021 If you do not use any directives that place output in the @samp{.text}
2022 or @samp{.data} sections, these sections still exist, but are empty.
2027 When @code{@value{AS}} generates SOM or ELF output for the HPPA,
2029 @code{@value{AS}} can also generate whatever other named sections you
2030 specify using the @samp{.space} and @samp{.subspace} directives. See
2031 @cite{HP9000 Series 800 Assembly Language Reference Manual}
2032 (HP 92432-90001) for details on the @samp{.space} and @samp{.subspace}
2033 assembler directives.
2036 Additionally, @code{@value{AS}} uses different names for the standard
2037 text, data, and bss sections when generating SOM output. Program text
2038 is placed into the @samp{$CODE$} section, data into @samp{$DATA$}, and
2039 BSS into @samp{$BSS$}.
2043 Within the object file, the text section starts at address @code{0}, the
2044 data section follows, and the bss section follows the data section.
2047 When generating either SOM or ELF output files on the HPPA, the text
2048 section starts at address @code{0}, the data section at address
2049 @code{0x4000000}, and the bss section follows the data section.
2052 To let @code{@value{LD}} know which data changes when the sections are
2053 relocated, and how to change that data, @code{@value{AS}} also writes to the
2054 object file details of the relocation needed. To perform relocation
2055 @code{@value{LD}} must know, each time an address in the object
2059 Where in the object file is the beginning of this reference to
2062 How long (in bytes) is this reference?
2064 Which section does the address refer to? What is the numeric value of
2066 (@var{address}) @minus{} (@var{start-address of section})?
2069 Is the reference to an address ``Program-Counter relative''?
2072 @cindex addresses, format of
2073 @cindex section-relative addressing
2074 In fact, every address @code{@value{AS}} ever uses is expressed as
2076 (@var{section}) + (@var{offset into section})
2079 Further, most expressions @code{@value{AS}} computes have this section-relative
2082 (For some object formats, such as SOM for the HPPA, some expressions are
2083 symbol-relative instead.)
2086 In this manual we use the notation @{@var{secname} @var{N}@} to mean ``offset
2087 @var{N} into section @var{secname}.''
2089 Apart from text, data and bss sections you need to know about the
2090 @dfn{absolute} section. When @code{@value{LD}} mixes partial programs,
2091 addresses in the absolute section remain unchanged. For example, address
2092 @code{@{absolute 0@}} is ``relocated'' to run-time address 0 by
2093 @code{@value{LD}}. Although the linker never arranges two partial programs'
2094 data sections with overlapping addresses after linking, @emph{by definition}
2095 their absolute sections must overlap. Address @code{@{absolute@ 239@}} in one
2096 part of a program is always the same address when the program is running as
2097 address @code{@{absolute@ 239@}} in any other part of the program.
2099 The idea of sections is extended to the @dfn{undefined} section. Any
2100 address whose section is unknown at assembly time is by definition
2101 rendered @{undefined @var{U}@}---where @var{U} is filled in later.
2102 Since numbers are always defined, the only way to generate an undefined
2103 address is to mention an undefined symbol. A reference to a named
2104 common block would be such a symbol: its value is unknown at assembly
2105 time so it has section @emph{undefined}.
2107 By analogy the word @emph{section} is used to describe groups of sections in
2108 the linked program. @code{@value{LD}} puts all partial programs' text
2109 sections in contiguous addresses in the linked program. It is
2110 customary to refer to the @emph{text section} of a program, meaning all
2111 the addresses of all partial programs' text sections. Likewise for
2112 data and bss sections.
2114 Some sections are manipulated by @code{@value{LD}}; others are invented for
2115 use of @code{@value{AS}} and have no meaning except during assembly.
2118 @section Linker Sections
2119 @code{@value{LD}} deals with just four kinds of sections, summarized below.
2124 @cindex named sections
2125 @cindex sections, named
2126 @item named sections
2129 @cindex text section
2130 @cindex data section
2134 These sections hold your program. @code{@value{AS}} and @code{@value{LD}} treat them as
2135 separate but equal sections. Anything you can say of one section is
2138 When the program is running, however, it is
2139 customary for the text section to be unalterable. The
2140 text section is often shared among processes: it contains
2141 instructions, constants and the like. The data section of a running
2142 program is usually alterable: for example, C variables would be stored
2143 in the data section.
2148 This section contains zeroed bytes when your program begins running. It
2149 is used to hold unitialized variables or common storage. The length of
2150 each partial program's bss section is important, but because it starts
2151 out containing zeroed bytes there is no need to store explicit zero
2152 bytes in the object file. The bss section was invented to eliminate
2153 those explicit zeros from object files.
2155 @cindex absolute section
2156 @item absolute section
2157 Address 0 of this section is always ``relocated'' to runtime address 0.
2158 This is useful if you want to refer to an address that @code{@value{LD}} must
2159 not change when relocating. In this sense we speak of absolute
2160 addresses being ``unrelocatable'': they do not change during relocation.
2162 @cindex undefined section
2163 @item undefined section
2164 This ``section'' is a catch-all for address references to objects not in
2165 the preceding sections.
2166 @c FIXME: ref to some other doc on obj-file formats could go here.
2169 @cindex relocation example
2170 An idealized example of three relocatable sections follows.
2172 The example uses the traditional section names @samp{.text} and @samp{.data}.
2174 Memory addresses are on the horizontal axis.
2178 @c END TEXI2ROFF-KILL
2181 partial program # 1: |ttttt|dddd|00|
2188 partial program # 2: |TTT|DDD|000|
2191 +--+---+-----+--+----+---+-----+~~
2192 linked program: | |TTT|ttttt| |dddd|DDD|00000|
2193 +--+---+-----+--+----+---+-----+~~
2195 addresses: 0 @dots{}
2202 \line{\it Partial program \#1: \hfil}
2203 \line{\ibox{2.5cm}{\tt text}\ibox{2cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
2204 \line{\boxit{2.5cm}{\tt ttttt}\boxit{2cm}{\tt dddd}\boxit{1cm}{\tt 00}\hfil}
2206 \line{\it Partial program \#2: \hfil}
2207 \line{\ibox{1cm}{\tt text}\ibox{1.5cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
2208 \line{\boxit{1cm}{\tt TTT}\boxit{1.5cm}{\tt DDDD}\boxit{1cm}{\tt 000}\hfil}
2210 \line{\it linked program: \hfil}
2211 \line{\ibox{.5cm}{}\ibox{1cm}{\tt text}\ibox{2.5cm}{}\ibox{.75cm}{}\ibox{2cm}{\tt data}\ibox{1.5cm}{}\ibox{2cm}{\tt bss}\hfil}
2212 \line{\boxit{.5cm}{}\boxit{1cm}{\tt TTT}\boxit{2.5cm}{\tt
2213 ttttt}\boxit{.75cm}{}\boxit{2cm}{\tt dddd}\boxit{1.5cm}{\tt
2214 DDDD}\boxit{2cm}{\tt 00000}\ \dots\hfil}
2216 \line{\it addresses: \hfil}
2220 @c END TEXI2ROFF-KILL
2223 @section Assembler Internal Sections
2225 @cindex internal assembler sections
2226 @cindex sections in messages, internal
2227 These sections are meant only for the internal use of @code{@value{AS}}. They
2228 have no meaning at run-time. You do not really need to know about these
2229 sections for most purposes; but they can be mentioned in @code{@value{AS}}
2230 warning messages, so it might be helpful to have an idea of their
2231 meanings to @code{@value{AS}}. These sections are used to permit the
2232 value of every expression in your assembly language program to be a
2233 section-relative address.
2236 @cindex assembler internal logic error
2237 @item ASSEMBLER-INTERNAL-LOGIC-ERROR!
2238 An internal assembler logic error has been found. This means there is a
2239 bug in the assembler.
2241 @cindex expr (internal section)
2243 The assembler stores complex expression internally as combinations of
2244 symbols. When it needs to represent an expression as a symbol, it puts
2245 it in the expr section.
2247 @c FIXME item transfer[t] vector preload
2248 @c FIXME item transfer[t] vector postload
2249 @c FIXME item register
2253 @section Sub-Sections
2255 @cindex numbered subsections
2256 @cindex grouping data
2262 fall into two sections: text and data.
2264 You may have separate groups of
2266 data in named sections
2270 data in named sections
2276 that you want to end up near to each other in the object file, even though they
2277 are not contiguous in the assembler source. @code{@value{AS}} allows you to
2278 use @dfn{subsections} for this purpose. Within each section, there can be
2279 numbered subsections with values from 0 to 8192. Objects assembled into the
2280 same subsection go into the object file together with other objects in the same
2281 subsection. For example, a compiler might want to store constants in the text
2282 section, but might not want to have them interspersed with the program being
2283 assembled. In this case, the compiler could issue a @samp{.text 0} before each
2284 section of code being output, and a @samp{.text 1} before each group of
2285 constants being output.
2287 Subsections are optional. If you do not use subsections, everything
2288 goes in subsection number zero.
2291 Each subsection is zero-padded up to a multiple of four bytes.
2292 (Subsections may be padded a different amount on different flavors
2293 of @code{@value{AS}}.)
2297 On the H8/300 and H8/500 platforms, each subsection is zero-padded to a word
2298 boundary (two bytes).
2299 The same is true on the Hitachi SH.
2302 @c FIXME section padding (alignment)?
2303 @c Rich Pixley says padding here depends on target obj code format; that
2304 @c doesn't seem particularly useful to say without further elaboration,
2305 @c so for now I say nothing about it. If this is a generic BFD issue,
2306 @c these paragraphs might need to vanish from this manual, and be
2307 @c discussed in BFD chapter of binutils (or some such).
2310 On the AMD 29K family, no particular padding is added to section or
2311 subsection sizes; @value{AS} forces no alignment on this platform.
2315 Subsections appear in your object file in numeric order, lowest numbered
2316 to highest. (All this to be compatible with other people's assemblers.)
2317 The object file contains no representation of subsections; @code{@value{LD}} and
2318 other programs that manipulate object files see no trace of them.
2319 They just see all your text subsections as a text section, and all your
2320 data subsections as a data section.
2322 To specify which subsection you want subsequent statements assembled
2323 into, use a numeric argument to specify it, in a @samp{.text
2324 @var{expression}} or a @samp{.data @var{expression}} statement.
2327 When generating COFF output, you
2332 can also use an extra subsection
2333 argument with arbitrary named sections: @samp{.section @var{name},
2336 @var{Expression} should be an absolute expression.
2337 (@xref{Expressions}.) If you just say @samp{.text} then @samp{.text 0}
2338 is assumed. Likewise @samp{.data} means @samp{.data 0}. Assembly
2339 begins in @code{text 0}. For instance:
2341 .text 0 # The default subsection is text 0 anyway.
2342 .ascii "This lives in the first text subsection. *"
2344 .ascii "But this lives in the second text subsection."
2346 .ascii "This lives in the data section,"
2347 .ascii "in the first data subsection."
2349 .ascii "This lives in the first text section,"
2350 .ascii "immediately following the asterisk (*)."
2353 Each section has a @dfn{location counter} incremented by one for every byte
2354 assembled into that section. Because subsections are merely a convenience
2355 restricted to @code{@value{AS}} there is no concept of a subsection location
2356 counter. There is no way to directly manipulate a location counter---but the
2357 @code{.align} directive changes it, and any label definition captures its
2358 current value. The location counter of the section where statements are being
2359 assembled is said to be the @dfn{active} location counter.
2362 @section bss Section
2365 @cindex common variable storage
2366 The bss section is used for local common variable storage.
2367 You may allocate address space in the bss section, but you may
2368 not dictate data to load into it before your program executes. When
2369 your program starts running, all the contents of the bss
2370 section are zeroed bytes.
2372 The @code{.lcomm} pseudo-op defines a symbol in the bss section; see
2373 @ref{Lcomm,,@code{.lcomm}}.
2375 The @code{.comm} pseudo-op may be used to declare a common symbol, which is
2376 another form of uninitialized symbol; see @xref{Comm,,@code{.comm}}.
2379 When assembling for a target which supports multiple sections, such as ELF or
2380 COFF, you may switch into the @code{.bss} section and define symbols as usual;
2381 see @ref{Section,,@code{.section}}. You may only assemble zero values into the
2382 section. Typically the section will only contain symbol definitions and
2383 @code{.skip} directives (@pxref{Skip,,@code{.skip}}).
2390 Symbols are a central concept: the programmer uses symbols to name
2391 things, the linker uses symbols to link, and the debugger uses symbols
2395 @cindex debuggers, and symbol order
2396 @emph{Warning:} @code{@value{AS}} does not place symbols in the object file in
2397 the same order they were declared. This may break some debuggers.
2402 * Setting Symbols:: Giving Symbols Other Values
2403 * Symbol Names:: Symbol Names
2404 * Dot:: The Special Dot Symbol
2405 * Symbol Attributes:: Symbol Attributes
2412 A @dfn{label} is written as a symbol immediately followed by a colon
2413 @samp{:}. The symbol then represents the current value of the
2414 active location counter, and is, for example, a suitable instruction
2415 operand. You are warned if you use the same symbol to represent two
2416 different locations: the first definition overrides any other
2420 On the HPPA, the usual form for a label need not be immediately followed by a
2421 colon, but instead must start in column zero. Only one label may be defined on
2422 a single line. To work around this, the HPPA version of @code{@value{AS}} also
2423 provides a special directive @code{.label} for defining labels more flexibly.
2426 @node Setting Symbols
2427 @section Giving Symbols Other Values
2429 @cindex assigning values to symbols
2430 @cindex symbol values, assigning
2431 A symbol can be given an arbitrary value by writing a symbol, followed
2432 by an equals sign @samp{=}, followed by an expression
2433 (@pxref{Expressions}). This is equivalent to using the @code{.set}
2434 directive. @xref{Set,,@code{.set}}.
2437 @section Symbol Names
2439 @cindex symbol names
2440 @cindex names, symbol
2441 @ifclear SPECIAL-SYMS
2442 Symbol names begin with a letter or with one of @samp{._}. On most
2443 machines, you can also use @code{$} in symbol names; exceptions are
2444 noted in @ref{Machine Dependencies}. That character may be followed by any
2445 string of digits, letters, dollar signs (unless otherwise noted in
2446 @ref{Machine Dependencies}), and underscores.
2449 For the AMD 29K family, @samp{?} is also allowed in the
2450 body of a symbol name, though not at its beginning.
2455 Symbol names begin with a letter or with one of @samp{._}. On the
2457 H8/500, you can also use @code{$} in symbol names. That character may
2458 be followed by any string of digits, letters, dollar signs (save on the
2459 H8/300), and underscores.
2463 Case of letters is significant: @code{foo} is a different symbol name
2466 Each symbol has exactly one name. Each name in an assembly language program
2467 refers to exactly one symbol. You may use that symbol name any number of times
2470 @subheading Local Symbol Names
2472 @cindex local symbol names
2473 @cindex symbol names, local
2474 @cindex temporary symbol names
2475 @cindex symbol names, temporary
2476 Local symbols help compilers and programmers use names temporarily.
2477 There are ten local symbol names, which are re-used throughout the
2478 program. You may refer to them using the names @samp{0} @samp{1}
2479 @dots{} @samp{9}. To define a local symbol, write a label of the form
2480 @samp{@b{N}:} (where @b{N} represents any digit). To refer to the most
2481 recent previous definition of that symbol write @samp{@b{N}b}, using the
2482 same digit as when you defined the label. To refer to the next
2483 definition of a local label, write @samp{@b{N}f}---where @b{N} gives you
2484 a choice of 10 forward references. The @samp{b} stands for
2485 ``backwards'' and the @samp{f} stands for ``forwards''.
2487 Local symbols are not emitted by the current @sc{gnu} C compiler.
2489 There is no restriction on how you can use these labels, but
2490 remember that at any point in the assembly you can refer to at most
2491 10 prior local labels and to at most 10 forward local labels.
2493 Local symbol names are only a notation device. They are immediately
2494 transformed into more conventional symbol names before the assembler
2495 uses them. The symbol names stored in the symbol table, appearing in
2496 error messages and optionally emitted to the object file have these
2501 All local labels begin with @samp{L}. Normally both @code{@value{AS}} and
2502 @code{@value{LD}} forget symbols that start with @samp{L}. These labels are
2503 used for symbols you are never intended to see. If you use the
2504 @samp{-L} option then @code{@value{AS}} retains these symbols in the
2505 object file. If you also instruct @code{@value{LD}} to retain these symbols,
2506 you may use them in debugging.
2509 If the label is written @samp{0:} then the digit is @samp{0}.
2510 If the label is written @samp{1:} then the digit is @samp{1}.
2511 And so on up through @samp{9:}.
2514 This unusual character is included so you do not accidentally invent
2515 a symbol of the same name. The character has ASCII value
2518 @item @emph{ordinal number}
2519 This is a serial number to keep the labels distinct. The first
2520 @samp{0:} gets the number @samp{1}; The 15th @samp{0:} gets the
2521 number @samp{15}; @emph{etc.}. Likewise for the other labels @samp{1:}
2525 For instance, the first @code{1:} is named @code{L1@kbd{C-A}1}, the 44th
2526 @code{3:} is named @code{L3@kbd{C-A}44}.
2529 @section The Special Dot Symbol
2531 @cindex dot (symbol)
2532 @cindex @code{.} (symbol)
2533 @cindex current address
2534 @cindex location counter
2535 The special symbol @samp{.} refers to the current address that
2536 @code{@value{AS}} is assembling into. Thus, the expression @samp{melvin:
2537 .long .} defines @code{melvin} to contain its own address.
2538 Assigning a value to @code{.} is treated the same as a @code{.org}
2539 directive. Thus, the expression @samp{.=.+4} is the same as saying
2540 @ifclear no-space-dir
2549 @node Symbol Attributes
2550 @section Symbol Attributes
2552 @cindex symbol attributes
2553 @cindex attributes, symbol
2554 Every symbol has, as well as its name, the attributes ``Value'' and
2555 ``Type''. Depending on output format, symbols can also have auxiliary
2558 The detailed definitions are in @file{a.out.h}.
2561 If you use a symbol without defining it, @code{@value{AS}} assumes zero for
2562 all these attributes, and probably won't warn you. This makes the
2563 symbol an externally defined symbol, which is generally what you
2567 * Symbol Value:: Value
2568 * Symbol Type:: Type
2571 * a.out Symbols:: Symbol Attributes: @code{a.out}
2575 * a.out Symbols:: Symbol Attributes: @code{a.out}
2578 * a.out Symbols:: Symbol Attributes: @code{a.out}, @code{b.out}
2583 * COFF Symbols:: Symbol Attributes for COFF
2586 * SOM Symbols:: Symbol Attributes for SOM
2593 @cindex value of a symbol
2594 @cindex symbol value
2595 The value of a symbol is (usually) 32 bits. For a symbol which labels a
2596 location in the text, data, bss or absolute sections the value is the
2597 number of addresses from the start of that section to the label.
2598 Naturally for text, data and bss sections the value of a symbol changes
2599 as @code{@value{LD}} changes section base addresses during linking. Absolute
2600 symbols' values do not change during linking: that is why they are
2603 The value of an undefined symbol is treated in a special way. If it is
2604 0 then the symbol is not defined in this assembler source file, and
2605 @code{@value{LD}} tries to determine its value from other files linked into the
2606 same program. You make this kind of symbol simply by mentioning a symbol
2607 name without defining it. A non-zero value represents a @code{.comm}
2608 common declaration. The value is how much common storage to reserve, in
2609 bytes (addresses). The symbol refers to the first address of the
2615 @cindex type of a symbol
2617 The type attribute of a symbol contains relocation (section)
2618 information, any flag settings indicating that a symbol is external, and
2619 (optionally), other information for linkers and debuggers. The exact
2620 format depends on the object-code output format in use.
2625 @c The following avoids a "widow" subsection title. @group would be
2626 @c better if it were available outside examples.
2629 @subsection Symbol Attributes: @code{a.out}, @code{b.out}
2631 @cindex @code{b.out} symbol attributes
2632 @cindex symbol attributes, @code{b.out}
2633 These symbol attributes appear only when @code{@value{AS}} is configured for
2634 one of the Berkeley-descended object output formats---@code{a.out} or
2640 @subsection Symbol Attributes: @code{a.out}
2642 @cindex @code{a.out} symbol attributes
2643 @cindex symbol attributes, @code{a.out}
2649 @subsection Symbol Attributes: @code{a.out}
2651 @cindex @code{a.out} symbol attributes
2652 @cindex symbol attributes, @code{a.out}
2656 * Symbol Desc:: Descriptor
2657 * Symbol Other:: Other
2661 @subsubsection Descriptor
2663 @cindex descriptor, of @code{a.out} symbol
2664 This is an arbitrary 16-bit value. You may establish a symbol's
2665 descriptor value by using a @code{.desc} statement
2666 (@pxref{Desc,,@code{.desc}}). A descriptor value means nothing to
2670 @subsubsection Other
2672 @cindex other attribute, of @code{a.out} symbol
2673 This is an arbitrary 8-bit value. It means nothing to @code{@value{AS}}.
2678 @subsection Symbol Attributes for COFF
2680 @cindex COFF symbol attributes
2681 @cindex symbol attributes, COFF
2683 The COFF format supports a multitude of auxiliary symbol attributes;
2684 like the primary symbol attributes, they are set between @code{.def} and
2685 @code{.endef} directives.
2687 @subsubsection Primary Attributes
2689 @cindex primary attributes, COFF symbols
2690 The symbol name is set with @code{.def}; the value and type,
2691 respectively, with @code{.val} and @code{.type}.
2693 @subsubsection Auxiliary Attributes
2695 @cindex auxiliary attributes, COFF symbols
2696 The @code{@value{AS}} directives @code{.dim}, @code{.line}, @code{.scl},
2697 @code{.size}, and @code{.tag} can generate auxiliary symbol table
2698 information for COFF.
2703 @subsection Symbol Attributes for SOM
2705 @cindex SOM symbol attributes
2706 @cindex symbol attributes, SOM
2708 The SOM format for the HPPA supports a multitude of symbol attributes set with
2709 the @code{.EXPORT} and @code{.IMPORT} directives.
2711 The attributes are described in @cite{HP9000 Series 800 Assembly
2712 Language Reference Manual} (HP 92432-90001) under the @code{IMPORT} and
2713 @code{EXPORT} assembler directive documentation.
2717 @chapter Expressions
2721 @cindex numeric values
2722 An @dfn{expression} specifies an address or numeric value.
2723 Whitespace may precede and/or follow an expression.
2725 The result of an expression must be an absolute number, or else an offset into
2726 a particular section. If an expression is not absolute, and there is not
2727 enough information when @code{@value{AS}} sees the expression to know its
2728 section, a second pass over the source program might be necessary to interpret
2729 the expression---but the second pass is currently not implemented.
2730 @code{@value{AS}} aborts with an error message in this situation.
2733 * Empty Exprs:: Empty Expressions
2734 * Integer Exprs:: Integer Expressions
2738 @section Empty Expressions
2740 @cindex empty expressions
2741 @cindex expressions, empty
2742 An empty expression has no value: it is just whitespace or null.
2743 Wherever an absolute expression is required, you may omit the
2744 expression, and @code{@value{AS}} assumes a value of (absolute) 0. This
2745 is compatible with other assemblers.
2748 @section Integer Expressions
2750 @cindex integer expressions
2751 @cindex expressions, integer
2752 An @dfn{integer expression} is one or more @emph{arguments} delimited
2753 by @emph{operators}.
2756 * Arguments:: Arguments
2757 * Operators:: Operators
2758 * Prefix Ops:: Prefix Operators
2759 * Infix Ops:: Infix Operators
2763 @subsection Arguments
2765 @cindex expression arguments
2766 @cindex arguments in expressions
2767 @cindex operands in expressions
2768 @cindex arithmetic operands
2769 @dfn{Arguments} are symbols, numbers or subexpressions. In other
2770 contexts arguments are sometimes called ``arithmetic operands''. In
2771 this manual, to avoid confusing them with the ``instruction operands'' of
2772 the machine language, we use the term ``argument'' to refer to parts of
2773 expressions only, reserving the word ``operand'' to refer only to machine
2774 instruction operands.
2776 Symbols are evaluated to yield @{@var{section} @var{NNN}@} where
2777 @var{section} is one of text, data, bss, absolute,
2778 or undefined. @var{NNN} is a signed, 2's complement 32 bit
2781 Numbers are usually integers.
2783 A number can be a flonum or bignum. In this case, you are warned
2784 that only the low order 32 bits are used, and @code{@value{AS}} pretends
2785 these 32 bits are an integer. You may write integer-manipulating
2786 instructions that act on exotic constants, compatible with other
2789 @cindex subexpressions
2790 Subexpressions are a left parenthesis @samp{(} followed by an integer
2791 expression, followed by a right parenthesis @samp{)}; or a prefix
2792 operator followed by an argument.
2795 @subsection Operators
2797 @cindex operators, in expressions
2798 @cindex arithmetic functions
2799 @cindex functions, in expressions
2800 @dfn{Operators} are arithmetic functions, like @code{+} or @code{%}. Prefix
2801 operators are followed by an argument. Infix operators appear
2802 between their arguments. Operators may be preceded and/or followed by
2806 @subsection Prefix Operator
2808 @cindex prefix operators
2809 @code{@value{AS}} has the following @dfn{prefix operators}. They each take
2810 one argument, which must be absolute.
2812 @c the tex/end tex stuff surrounding this small table is meant to make
2813 @c it align, on the printed page, with the similar table in the next
2814 @c section (which is inside an enumerate).
2816 \global\advance\leftskip by \itemindent
2821 @dfn{Negation}. Two's complement negation.
2823 @dfn{Complementation}. Bitwise not.
2827 \global\advance\leftskip by -\itemindent
2831 @subsection Infix Operators
2833 @cindex infix operators
2834 @cindex operators, permitted arguments
2835 @dfn{Infix operators} take two arguments, one on either side. Operators
2836 have precedence, but operations with equal precedence are performed left
2837 to right. Apart from @code{+} or @code{-}, both arguments must be
2838 absolute, and the result is absolute.
2841 @cindex operator precedence
2842 @cindex precedence of operators
2849 @dfn{Multiplication}.
2852 @dfn{Division}. Truncation is the same as the C operator @samp{/}
2859 @dfn{Shift Left}. Same as the C operator @samp{<<}.
2863 @dfn{Shift Right}. Same as the C operator @samp{>>}.
2867 Intermediate precedence
2872 @dfn{Bitwise Inclusive Or}.
2878 @dfn{Bitwise Exclusive Or}.
2881 @dfn{Bitwise Or Not}.
2888 @cindex addition, permitted arguments
2889 @cindex plus, permitted arguments
2890 @cindex arguments for addition
2892 @dfn{Addition}. If either argument is absolute, the result has the section of
2893 the other argument. You may not add together arguments from different
2896 @cindex subtraction, permitted arguments
2897 @cindex minus, permitted arguments
2898 @cindex arguments for subtraction
2900 @dfn{Subtraction}. If the right argument is absolute, the
2901 result has the section of the left argument.
2902 If both arguments are in the same section, the result is absolute.
2903 You may not subtract arguments from different sections.
2904 @c FIXME is there still something useful to say about undefined - undefined ?
2908 In short, it's only meaningful to add or subtract the @emph{offsets} in an
2909 address; you can only have a defined section in one of the two arguments.
2912 @chapter Assembler Directives
2914 @cindex directives, machine independent
2915 @cindex pseudo-ops, machine independent
2916 @cindex machine independent directives
2917 All assembler directives have names that begin with a period (@samp{.}).
2918 The rest of the name is letters, usually in lower case.
2920 This chapter discusses directives that are available regardless of the
2921 target machine configuration for the @sc{gnu} assembler.
2923 Some machine configurations provide additional directives.
2924 @xref{Machine Dependencies}.
2927 @ifset machine-directives
2928 @xref{Machine Dependencies} for additional directives.
2933 * Abort:: @code{.abort}
2935 * ABORT:: @code{.ABORT}
2938 * Align:: @code{.align @var{abs-expr} , @var{abs-expr}}
2939 * App-File:: @code{.app-file @var{string}}
2940 * Ascii:: @code{.ascii "@var{string}"}@dots{}
2941 * Asciz:: @code{.asciz "@var{string}"}@dots{}
2942 * Balign:: @code{.balign @var{abs-expr} , @var{abs-expr}}
2943 * Byte:: @code{.byte @var{expressions}}
2944 * Comm:: @code{.comm @var{symbol} , @var{length} }
2945 * Data:: @code{.data @var{subsection}}
2947 * Def:: @code{.def @var{name}}
2950 * Desc:: @code{.desc @var{symbol}, @var{abs-expression}}
2956 * Double:: @code{.double @var{flonums}}
2957 * Eject:: @code{.eject}
2958 * Else:: @code{.else}
2960 * Endef:: @code{.endef}
2963 * Endif:: @code{.endif}
2964 * Equ:: @code{.equ @var{symbol}, @var{expression}}
2965 * Equiv:: @code{.equiv @var{symbol}, @var{expression}}
2967 * Extern:: @code{.extern}
2968 @ifclear no-file-dir
2969 * File:: @code{.file @var{string}}
2972 * Fill:: @code{.fill @var{repeat} , @var{size} , @var{value}}
2973 * Float:: @code{.float @var{flonums}}
2974 * Global:: @code{.global @var{symbol}}, @code{.globl @var{symbol}}
2975 * hword:: @code{.hword @var{expressions}}
2976 * Ident:: @code{.ident}
2977 * If:: @code{.if @var{absolute expression}}
2978 * Include:: @code{.include "@var{file}"}
2979 * Int:: @code{.int @var{expressions}}
2980 * Irp:: @code{.irp @var{symbol},@var{values}}@dots{}
2981 * Irpc:: @code{.irpc @var{symbol},@var{values}}@dots{}
2982 * Lcomm:: @code{.lcomm @var{symbol} , @var{length}}
2983 * Lflags:: @code{.lflags}
2984 @ifclear no-line-dir
2985 * Line:: @code{.line @var{line-number}}
2988 * Ln:: @code{.ln @var{line-number}}
2989 * Linkonce:: @code{.linkonce [@var{type}]}
2990 * List:: @code{.list}
2991 * Long:: @code{.long @var{expressions}}
2993 * Lsym:: @code{.lsym @var{symbol}, @var{expression}}
2996 * Macro:: @code{.macro @var{name} @var{args}}@dots{}
2997 * MRI:: @code{.mri @var{val}}
2999 * Nolist:: @code{.nolist}
3000 * Octa:: @code{.octa @var{bignums}}
3001 * Org:: @code{.org @var{new-lc} , @var{fill}}
3002 * P2align:: @code{.p2align @var{abs-expr} , @var{abs-expr}}
3003 * Psize:: @code{.psize @var{lines}, @var{columns}}
3004 * Quad:: @code{.quad @var{bignums}}
3005 * Rept:: @code{.rept @var{count}}
3006 * Sbttl:: @code{.sbttl "@var{subheading}"}
3008 * Scl:: @code{.scl @var{class}}
3009 * Section:: @code{.section @var{name}, @var{subsection}}
3012 * Set:: @code{.set @var{symbol}, @var{expression}}
3013 * Short:: @code{.short @var{expressions}}
3014 * Single:: @code{.single @var{flonums}}
3016 * Size:: @code{.size}
3019 * Skip:: @code{.skip @var{size} , @var{fill}}
3020 * Sleb128:: @code{.sleb128 @var{expressions}}
3021 * Space:: @code{.space @var{size} , @var{fill}}
3023 * Stab:: @code{.stabd, .stabn, .stabs}
3026 * String:: @code{.string "@var{str}"}
3028 * Symver:: @code{.symver @var{name},@var{name2@@nodename}}
3031 * Tag:: @code{.tag @var{structname}}
3034 * Text:: @code{.text @var{subsection}}
3035 * Title:: @code{.title "@var{heading}"}
3037 * Type:: @code{.type @var{int}}
3038 * Val:: @code{.val @var{addr}}
3041 * Uleb128:: @code{.uleb128 @var{expressions}}
3042 * Word:: @code{.word @var{expressions}}
3043 * Deprecated:: Deprecated Directives
3047 @section @code{.abort}
3049 @cindex @code{abort} directive
3050 @cindex stopping the assembly
3051 This directive stops the assembly immediately. It is for
3052 compatibility with other assemblers. The original idea was that the
3053 assembly language source would be piped into the assembler. If the sender
3054 of the source quit, it could use this directive tells @code{@value{AS}} to
3055 quit also. One day @code{.abort} will not be supported.
3059 @section @code{.ABORT}
3061 @cindex @code{ABORT} directive
3062 When producing COFF output, @code{@value{AS}} accepts this directive as a
3063 synonym for @samp{.abort}.
3066 When producing @code{b.out} output, @code{@value{AS}} accepts this directive,
3072 @section @code{.align @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
3074 @cindex padding the location counter
3075 @cindex @code{align} directive
3076 Pad the location counter (in the current subsection) to a particular storage
3077 boundary. The first expression (which must be absolute) is the alignment
3078 required, as described below.
3080 The second expression (also absolute) gives the fill value to be stored in the
3081 padding bytes. It (and the comma) may be omitted. If it is omitted, the
3082 padding bytes are normally zero. However, on some systems, if the section is
3083 marked as containing code and the fill value is omitted, the space is filled
3084 with no-op instructions.
3086 The third expression is also absolute, and is also optional. If it is present,
3087 it is the maximum number of bytes that should be skipped by this alignment
3088 directive. If doing the alignment would require skipping more bytes than the
3089 specified maximum, then the alignment is not done at all. You can omit the
3090 fill value (the second argument) entirely by simply using two commas after the
3091 required alignment; this can be useful if you want the alignment to be filled
3092 with no-op instructions when appropriate.
3094 The way the required alignment is specified varies from system to system.
3095 For the a29k, hppa, m68k, m88k, w65, sparc, and Hitachi SH, and i386 using ELF
3097 the first expression is the
3098 alignment request in bytes. For example @samp{.align 8} advances
3099 the location counter until it is a multiple of 8. If the location counter
3100 is already a multiple of 8, no change is needed.
3102 For other systems, including the i386 using a.out format, it is the
3103 number of low-order zero bits the location counter must have after
3104 advancement. For example @samp{.align 3} advances the location
3105 counter until it a multiple of 8. If the location counter is already a
3106 multiple of 8, no change is needed.
3108 This inconsistency is due to the different behaviors of the various
3109 native assemblers for these systems which GAS must emulate.
3110 GAS also provides @code{.balign} and @code{.p2align} directives,
3111 described later, which have a consistent behavior across all
3112 architectures (but are specific to GAS).
3115 @section @code{.app-file @var{string}}
3117 @cindex logical file name
3118 @cindex file name, logical
3119 @cindex @code{app-file} directive
3121 @ifclear no-file-dir
3122 (which may also be spelled @samp{.file})
3124 tells @code{@value{AS}} that we are about to start a new
3125 logical file. @var{string} is the new file name. In general, the
3126 filename is recognized whether or not it is surrounded by quotes @samp{"};
3127 but if you wish to specify an empty file name is permitted,
3128 you must give the quotes--@code{""}. This statement may go away in
3129 future: it is only recognized to be compatible with old @code{@value{AS}}
3133 @section @code{.ascii "@var{string}"}@dots{}
3135 @cindex @code{ascii} directive
3136 @cindex string literals
3137 @code{.ascii} expects zero or more string literals (@pxref{Strings})
3138 separated by commas. It assembles each string (with no automatic
3139 trailing zero byte) into consecutive addresses.
3142 @section @code{.asciz "@var{string}"}@dots{}
3144 @cindex @code{asciz} directive
3145 @cindex zero-terminated strings
3146 @cindex null-terminated strings
3147 @code{.asciz} is just like @code{.ascii}, but each string is followed by
3148 a zero byte. The ``z'' in @samp{.asciz} stands for ``zero''.
3151 @section @code{.balign[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
3153 @cindex padding the location counter given number of bytes
3154 @cindex @code{balign} directive
3155 Pad the location counter (in the current subsection) to a particular
3156 storage boundary. The first expression (which must be absolute) is the
3157 alignment request in bytes. For example @samp{.balign 8} advances
3158 the location counter until it is a multiple of 8. If the location counter
3159 is already a multiple of 8, no change is needed.
3161 The second expression (also absolute) gives the fill value to be stored in the
3162 padding bytes. It (and the comma) may be omitted. If it is omitted, the
3163 padding bytes are normally zero. However, on some systems, if the section is
3164 marked as containing code and the fill value is omitted, the space is filled
3165 with no-op instructions.
3167 The third expression is also absolute, and is also optional. If it is present,
3168 it is the maximum number of bytes that should be skipped by this alignment
3169 directive. If doing the alignment would require skipping more bytes than the
3170 specified maximum, then the alignment is not done at all. You can omit the
3171 fill value (the second argument) entirely by simply using two commas after the
3172 required alignment; this can be useful if you want the alignment to be filled
3173 with no-op instructions when appropriate.
3175 @cindex @code{balignw} directive
3176 @cindex @code{balignl} directive
3177 The @code{.balignw} and @code{.balignl} directives are variants of the
3178 @code{.balign} directive. The @code{.balignw} directive treats the fill
3179 pattern as a two byte word value. The @code{.balignl} directives treats the
3180 fill pattern as a four byte longword value. For example, @code{.balignw
3181 4,0x368d} will align to a multiple of 4. If it skips two bytes, they will be
3182 filled in with the value 0x368d (the exact placement of the bytes depends upon
3183 the endianness of the processor). If it skips 1 or 3 bytes, the fill value is
3187 @section @code{.byte @var{expressions}}
3189 @cindex @code{byte} directive
3190 @cindex integers, one byte
3191 @code{.byte} expects zero or more expressions, separated by commas.
3192 Each expression is assembled into the next byte.
3195 @section @code{.comm @var{symbol} , @var{length} }
3197 @cindex @code{comm} directive
3198 @cindex symbol, common
3199 @code{.comm} declares a common symbol named @var{symbol}. When linking, a
3200 common symbol in one object file may be merged with a defined or common symbol
3201 of the same name in another object file. If @code{@value{LD}} does not see a
3202 definition for the symbol--just one or more common symbols--then it will
3203 allocate @var{length} bytes of uninitialized memory. @var{length} must be an
3204 absolute expression. If @code{@value{LD}} sees multiple common symbols with
3205 the same name, and they do not all have the same size, it will allocate space
3206 using the largest size.
3209 When using ELF, the @code{.comm} directive takes an optional third argument.
3210 This is the desired alignment of the symbol, specified as a byte boundary (for
3211 example, an alignment of 16 means that the least significant 4 bits of the
3212 address should be zero). The alignment must be an absolute expression, and it
3213 must be a power of two. If @code{@value{LD}} allocates uninitialized memory
3214 for the common symbol, it will use the alignment when placing the symbol. If
3215 no alignment is specified, @code{@value{AS}} will set the alignment to the
3216 largest power of two less than or equal to the size of the symbol, up to a
3221 The syntax for @code{.comm} differs slightly on the HPPA. The syntax is
3222 @samp{@var{symbol} .comm, @var{length}}; @var{symbol} is optional.
3226 @section @code{.data @var{subsection}}
3228 @cindex @code{data} directive
3229 @code{.data} tells @code{@value{AS}} to assemble the following statements onto the
3230 end of the data subsection numbered @var{subsection} (which is an
3231 absolute expression). If @var{subsection} is omitted, it defaults
3236 @section @code{.def @var{name}}
3238 @cindex @code{def} directive
3239 @cindex COFF symbols, debugging
3240 @cindex debugging COFF symbols
3241 Begin defining debugging information for a symbol @var{name}; the
3242 definition extends until the @code{.endef} directive is encountered.
3245 This directive is only observed when @code{@value{AS}} is configured for COFF
3246 format output; when producing @code{b.out}, @samp{.def} is recognized,
3253 @section @code{.desc @var{symbol}, @var{abs-expression}}
3255 @cindex @code{desc} directive
3256 @cindex COFF symbol descriptor
3257 @cindex symbol descriptor, COFF
3258 This directive sets the descriptor of the symbol (@pxref{Symbol Attributes})
3259 to the low 16 bits of an absolute expression.
3262 The @samp{.desc} directive is not available when @code{@value{AS}} is
3263 configured for COFF output; it is only for @code{a.out} or @code{b.out}
3264 object format. For the sake of compatibility, @code{@value{AS}} accepts
3265 it, but produces no output, when configured for COFF.
3271 @section @code{.dim}
3273 @cindex @code{dim} directive
3274 @cindex COFF auxiliary symbol information
3275 @cindex auxiliary symbol information, COFF
3276 This directive is generated by compilers to include auxiliary debugging
3277 information in the symbol table. It is only permitted inside
3278 @code{.def}/@code{.endef} pairs.
3281 @samp{.dim} is only meaningful when generating COFF format output; when
3282 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
3288 @section @code{.double @var{flonums}}
3290 @cindex @code{double} directive
3291 @cindex floating point numbers (double)
3292 @code{.double} expects zero or more flonums, separated by commas. It
3293 assembles floating point numbers.
3295 The exact kind of floating point numbers emitted depends on how
3296 @code{@value{AS}} is configured. @xref{Machine Dependencies}.
3300 On the @value{TARGET} family @samp{.double} emits 64-bit floating-point numbers
3301 in @sc{ieee} format.
3306 @section @code{.eject}
3308 @cindex @code{eject} directive
3309 @cindex new page, in listings
3310 @cindex page, in listings
3311 @cindex listing control: new page
3312 Force a page break at this point, when generating assembly listings.
3315 @section @code{.else}
3317 @cindex @code{else} directive
3318 @code{.else} is part of the @code{@value{AS}} support for conditional
3319 assembly; @pxref{If,,@code{.if}}. It marks the beginning of a section
3320 of code to be assembled if the condition for the preceding @code{.if}
3324 @node End, Endef, Else, Pseudo Ops
3325 @section @code{.end}
3327 @cindex @code{end} directive
3328 This doesn't do anything---but isn't an s_ignore, so I suspect it's
3329 meant to do something eventually (which is why it isn't documented here
3330 as "for compatibility with blah").
3335 @section @code{.endef}
3337 @cindex @code{endef} directive
3338 This directive flags the end of a symbol definition begun with
3342 @samp{.endef} is only meaningful when generating COFF format output; if
3343 @code{@value{AS}} is configured to generate @code{b.out}, it accepts this
3344 directive but ignores it.
3349 @section @code{.endif}
3351 @cindex @code{endif} directive
3352 @code{.endif} is part of the @code{@value{AS}} support for conditional assembly;
3353 it marks the end of a block of code that is only assembled
3354 conditionally. @xref{If,,@code{.if}}.
3357 @section @code{.equ @var{symbol}, @var{expression}}
3359 @cindex @code{equ} directive
3360 @cindex assigning values to symbols
3361 @cindex symbols, assigning values to
3362 This directive sets the value of @var{symbol} to @var{expression}.
3363 It is synonymous with @samp{.set}; @pxref{Set,,@code{.set}}.
3366 The syntax for @code{equ} on the HPPA is
3367 @samp{@var{symbol} .equ @var{expression}}.
3371 @section @code{.equiv @var{symbol}, @var{expression}}
3372 @cindex @code{equiv} directive
3373 The @code{.equiv} directive is like @code{.equ} and @code{.set}, except that
3374 the assembler will signal an error if @var{symbol} is already defined.
3376 Except for the contents of the error message, this is roughly equivalent to
3385 @section @code{.err}
3386 @cindex @code{err} directive
3387 If @code{@value{AS}} assembles a @code{.err} directive, it will print an error
3388 message and, unless the @code{-Z} option was used, it will not generate an
3389 object file. This can be used to signal error an conditionally compiled code.
3392 @section @code{.extern}
3394 @cindex @code{extern} directive
3395 @code{.extern} is accepted in the source program---for compatibility
3396 with other assemblers---but it is ignored. @code{@value{AS}} treats
3397 all undefined symbols as external.
3399 @ifclear no-file-dir
3401 @section @code{.file @var{string}}
3403 @cindex @code{file} directive
3404 @cindex logical file name
3405 @cindex file name, logical
3406 @code{.file} (which may also be spelled @samp{.app-file}) tells
3407 @code{@value{AS}} that we are about to start a new logical file.
3408 @var{string} is the new file name. In general, the filename is
3409 recognized whether or not it is surrounded by quotes @samp{"}; but if
3410 you wish to specify an empty file name, you must give the
3411 quotes--@code{""}. This statement may go away in future: it is only
3412 recognized to be compatible with old @code{@value{AS}} programs.
3414 In some configurations of @code{@value{AS}}, @code{.file} has already been
3415 removed to avoid conflicts with other assemblers. @xref{Machine Dependencies}.
3420 @section @code{.fill @var{repeat} , @var{size} , @var{value}}
3422 @cindex @code{fill} directive
3423 @cindex writing patterns in memory
3424 @cindex patterns, writing in memory
3425 @var{result}, @var{size} and @var{value} are absolute expressions.
3426 This emits @var{repeat} copies of @var{size} bytes. @var{Repeat}
3427 may be zero or more. @var{Size} may be zero or more, but if it is
3428 more than 8, then it is deemed to have the value 8, compatible with
3429 other people's assemblers. The contents of each @var{repeat} bytes
3430 is taken from an 8-byte number. The highest order 4 bytes are
3431 zero. The lowest order 4 bytes are @var{value} rendered in the
3432 byte-order of an integer on the computer @code{@value{AS}} is assembling for.
3433 Each @var{size} bytes in a repetition is taken from the lowest order
3434 @var{size} bytes of this number. Again, this bizarre behavior is
3435 compatible with other people's assemblers.
3437 @var{size} and @var{value} are optional.
3438 If the second comma and @var{value} are absent, @var{value} is
3439 assumed zero. If the first comma and following tokens are absent,
3440 @var{size} is assumed to be 1.
3443 @section @code{.float @var{flonums}}
3445 @cindex floating point numbers (single)
3446 @cindex @code{float} directive
3447 This directive assembles zero or more flonums, separated by commas. It
3448 has the same effect as @code{.single}.
3450 The exact kind of floating point numbers emitted depends on how
3451 @code{@value{AS}} is configured.
3452 @xref{Machine Dependencies}.
3456 On the @value{TARGET} family, @code{.float} emits 32-bit floating point numbers
3457 in @sc{ieee} format.
3462 @section @code{.global @var{symbol}}, @code{.globl @var{symbol}}
3464 @cindex @code{global} directive
3465 @cindex symbol, making visible to linker
3466 @code{.global} makes the symbol visible to @code{@value{LD}}. If you define
3467 @var{symbol} in your partial program, its value is made available to
3468 other partial programs that are linked with it. Otherwise,
3469 @var{symbol} takes its attributes from a symbol of the same name
3470 from another file linked into the same program.
3472 Both spellings (@samp{.globl} and @samp{.global}) are accepted, for
3473 compatibility with other assemblers.
3476 On the HPPA, @code{.global} is not always enough to make it accessible to other
3477 partial programs. You may need the HPPA-only @code{.EXPORT} directive as well.
3478 @xref{HPPA Directives,, HPPA Assembler Directives}.
3482 @section @code{.hword @var{expressions}}
3484 @cindex @code{hword} directive
3485 @cindex integers, 16-bit
3486 @cindex numbers, 16-bit
3487 @cindex sixteen bit integers
3488 This expects zero or more @var{expressions}, and emits
3489 a 16 bit number for each.
3492 This directive is a synonym for @samp{.short}; depending on the target
3493 architecture, it may also be a synonym for @samp{.word}.
3497 This directive is a synonym for @samp{.short}.
3500 This directive is a synonym for both @samp{.short} and @samp{.word}.
3505 @section @code{.ident}
3507 @cindex @code{ident} directive
3508 This directive is used by some assemblers to place tags in object files.
3509 @code{@value{AS}} simply accepts the directive for source-file
3510 compatibility with such assemblers, but does not actually emit anything
3514 @section @code{.if @var{absolute expression}}
3516 @cindex conditional assembly
3517 @cindex @code{if} directive
3518 @code{.if} marks the beginning of a section of code which is only
3519 considered part of the source program being assembled if the argument
3520 (which must be an @var{absolute expression}) is non-zero. The end of
3521 the conditional section of code must be marked by @code{.endif}
3522 (@pxref{Endif,,@code{.endif}}); optionally, you may include code for the
3523 alternative condition, flagged by @code{.else} (@pxref{Else,,@code{.else}}).
3525 The following variants of @code{.if} are also supported:
3527 @cindex @code{ifdef} directive
3528 @item .ifdef @var{symbol}
3529 Assembles the following section of code if the specified @var{symbol}
3533 @cindex @code{ifeqs} directive
3535 Not yet implemented.
3538 @cindex @code{ifndef} directive
3539 @cindex @code{ifnotdef} directive
3540 @item .ifndef @var{symbol}
3541 @itemx .ifnotdef @var{symbol}
3542 Assembles the following section of code if the specified @var{symbol}
3543 has not been defined. Both spelling variants are equivalent.
3547 Not yet implemented.
3552 @section @code{.include "@var{file}"}
3554 @cindex @code{include} directive
3555 @cindex supporting files, including
3556 @cindex files, including
3557 This directive provides a way to include supporting files at specified
3558 points in your source program. The code from @var{file} is assembled as
3559 if it followed the point of the @code{.include}; when the end of the
3560 included file is reached, assembly of the original file continues. You
3561 can control the search paths used with the @samp{-I} command-line option
3562 (@pxref{Invoking,,Command-Line Options}). Quotation marks are required
3566 @section @code{.int @var{expressions}}
3568 @cindex @code{int} directive
3569 @cindex integers, 32-bit
3570 Expect zero or more @var{expressions}, of any section, separated by commas.
3571 For each expression, emit a number that, at run time, is the value of that
3572 expression. The byte order and bit size of the number depends on what kind
3573 of target the assembly is for.
3577 On the H8/500 and most forms of the H8/300, @code{.int} emits 16-bit
3578 integers. On the H8/300H and the Hitachi SH, however, @code{.int} emits
3584 @section @code{.irp @var{symbol},@var{values}}@dots{}
3586 @cindex @code{irp} directive
3587 Evaluate a sequence of statements assigning different values to @var{symbol}.
3588 The sequence of statements starts at the @code{.irp} directive, and is
3589 terminated by an @code{.endr} directive. For each @var{value}, @var{symbol} is
3590 set to @var{value}, and the sequence of statements is assembled. If no
3591 @var{value} is listed, the sequence of statements is assembled once, with
3592 @var{symbol} set to the null string. To refer to @var{symbol} within the
3593 sequence of statements, use @var{\symbol}.
3595 For example, assembling
3603 is equivalent to assembling
3612 @section @code{.irpc @var{symbol},@var{values}}@dots{}
3614 @cindex @code{irpc} directive
3615 Evaluate a sequence of statements assigning different values to @var{symbol}.
3616 The sequence of statements starts at the @code{.irpc} directive, and is
3617 terminated by an @code{.endr} directive. For each character in @var{value},
3618 @var{symbol} is set to the character, and the sequence of statements is
3619 assembled. If no @var{value} is listed, the sequence of statements is
3620 assembled once, with @var{symbol} set to the null string. To refer to
3621 @var{symbol} within the sequence of statements, use @var{\symbol}.
3623 For example, assembling
3631 is equivalent to assembling
3640 @section @code{.lcomm @var{symbol} , @var{length}}
3642 @cindex @code{lcomm} directive
3643 @cindex local common symbols
3644 @cindex symbols, local common
3645 Reserve @var{length} (an absolute expression) bytes for a local common
3646 denoted by @var{symbol}. The section and value of @var{symbol} are
3647 those of the new local common. The addresses are allocated in the bss
3648 section, so that at run-time the bytes start off zeroed. @var{Symbol}
3649 is not declared global (@pxref{Global,,@code{.global}}), so is normally
3650 not visible to @code{@value{LD}}.
3653 Some targets permit a third argument to be used with @code{.lcomm}. This
3654 argument specifies the desired alignment of the symbol in the bss section.
3658 The syntax for @code{.lcomm} differs slightly on the HPPA. The syntax is
3659 @samp{@var{symbol} .lcomm, @var{length}}; @var{symbol} is optional.
3663 @section @code{.lflags}
3665 @cindex @code{lflags} directive (ignored)
3666 @code{@value{AS}} accepts this directive, for compatibility with other
3667 assemblers, but ignores it.
3669 @ifclear no-line-dir
3671 @section @code{.line @var{line-number}}
3673 @cindex @code{line} directive
3677 @section @code{.ln @var{line-number}}
3679 @cindex @code{ln} directive
3681 @cindex logical line number
3683 Change the logical line number. @var{line-number} must be an absolute
3684 expression. The next line has that logical line number. Therefore any other
3685 statements on the current line (after a statement separator character) are
3686 reported as on logical line number @var{line-number} @minus{} 1. One day
3687 @code{@value{AS}} will no longer support this directive: it is recognized only
3688 for compatibility with existing assembler programs.
3692 @emph{Warning:} In the AMD29K configuration of @value{AS}, this command is
3693 not available; use the synonym @code{.ln} in that context.
3698 @ifclear no-line-dir
3699 Even though this is a directive associated with the @code{a.out} or
3700 @code{b.out} object-code formats, @code{@value{AS}} still recognizes it
3701 when producing COFF output, and treats @samp{.line} as though it
3702 were the COFF @samp{.ln} @emph{if} it is found outside a
3703 @code{.def}/@code{.endef} pair.
3705 Inside a @code{.def}, @samp{.line} is, instead, one of the directives
3706 used by compilers to generate auxiliary symbol information for
3711 @section @code{.linkonce [@var{type}]}
3713 @cindex @code{linkonce} directive
3714 @cindex common sections
3715 Mark the current section so that the linker only includes a single copy of it.
3716 This may be used to include the same section in several different object files,
3717 but ensure that the linker will only include it once in the final output file.
3718 The @code{.linkonce} pseudo-op must be used for each instance of the section.
3719 Duplicate sections are detected based on the section name, so it should be
3722 This directive is only supported by a few object file formats; as of this
3723 writing, the only object file format which supports it is the Portable
3724 Executable format used on Windows NT.
3726 The @var{type} argument is optional. If specified, it must be one of the
3727 following strings. For example:
3731 Not all types may be supported on all object file formats.
3735 Silently discard duplicate sections. This is the default.
3738 Warn if there are duplicate sections, but still keep only one copy.
3741 Warn if any of the duplicates have different sizes.
3744 Warn if any of the duplicates do not have exactly the same contents.
3748 @section @code{.ln @var{line-number}}
3750 @cindex @code{ln} directive
3751 @ifclear no-line-dir
3752 @samp{.ln} is a synonym for @samp{.line}.
3755 Tell @code{@value{AS}} to change the logical line number. @var{line-number}
3756 must be an absolute expression. The next line has that logical
3757 line number, so any other statements on the current line (after a
3758 statement separator character @code{;}) are reported as on logical
3759 line number @var{line-number} @minus{} 1.
3762 This directive is accepted, but ignored, when @code{@value{AS}} is
3763 configured for @code{b.out}; its effect is only associated with COFF
3769 @section @code{.mri @var{val}}
3771 @cindex @code{mri} directive
3772 @cindex MRI mode, temporarily
3773 If @var{val} is non-zero, this tells @code{@value{AS}} to enter MRI mode. If
3774 @var{val} is zero, this tells @code{@value{AS}} to exit MRI mode. This change
3775 affects code assembled until the next @code{.mri} directive, or until the end
3776 of the file. @xref{M, MRI mode, MRI mode}.
3779 @section @code{.list}
3781 @cindex @code{list} directive
3782 @cindex listing control, turning on
3783 Control (in conjunction with the @code{.nolist} directive) whether or
3784 not assembly listings are generated. These two directives maintain an
3785 internal counter (which is zero initially). @code{.list} increments the
3786 counter, and @code{.nolist} decrements it. Assembly listings are
3787 generated whenever the counter is greater than zero.
3789 By default, listings are disabled. When you enable them (with the
3790 @samp{-a} command line option; @pxref{Invoking,,Command-Line Options}),
3791 the initial value of the listing counter is one.
3794 @section @code{.long @var{expressions}}
3796 @cindex @code{long} directive
3797 @code{.long} is the same as @samp{.int}, @pxref{Int,,@code{.int}}.
3800 @c no one seems to know what this is for or whether this description is
3801 @c what it really ought to do
3803 @section @code{.lsym @var{symbol}, @var{expression}}
3805 @cindex @code{lsym} directive
3806 @cindex symbol, not referenced in assembly
3807 @code{.lsym} creates a new symbol named @var{symbol}, but does not put it in
3808 the hash table, ensuring it cannot be referenced by name during the
3809 rest of the assembly. This sets the attributes of the symbol to be
3810 the same as the expression value:
3812 @var{other} = @var{descriptor} = 0
3813 @var{type} = @r{(section of @var{expression})}
3814 @var{value} = @var{expression}
3817 The new symbol is not flagged as external.
3821 @section @code{.macro}
3824 The commands @code{.macro} and @code{.endm} allow you to define macros that
3825 generate assembly output. For example, this definition specifies a macro
3826 @code{sum} that puts a sequence of numbers into memory:
3829 .macro sum from=0, to=5
3838 With that definition, @samp{SUM 0,5} is equivalent to this assembly input:
3850 @item .macro @var{macname}
3851 @itemx .macro @var{macname} @var{macargs} @dots{}
3852 @cindex @code{macro} directive
3853 Begin the definition of a macro called @var{macname}. If your macro
3854 definition requires arguments, specify their names after the macro name,
3855 separated by commas or spaces. You can supply a default value for any
3856 macro argument by following the name with @samp{=@var{deflt}}. For
3857 example, these are all valid @code{.macro} statements:
3861 Begin the definition of a macro called @code{comm}, which takes no
3864 @item .macro plus1 p, p1
3865 @itemx .macro plus1 p p1
3866 Either statement begins the definition of a macro called @code{plus1},
3867 which takes two arguments; within the macro definition, write
3868 @samp{\p} or @samp{\p1} to evaluate the arguments.
3870 @item .macro reserve_str p1=0 p2
3871 Begin the definition of a macro called @code{reserve_str}, with two
3872 arguments. The first argument has a default value, but not the second.
3873 After the definition is complete, you can call the macro either as
3874 @samp{reserve_str @var{a},@var{b}} (with @samp{\p1} evaluating to
3875 @var{a} and @samp{\p2} evaluating to @var{b}), or as @samp{reserve_str
3876 ,@var{b}} (with @samp{\p1} evaluating as the default, in this case
3877 @samp{0}, and @samp{\p2} evaluating to @var{b}).
3880 When you call a macro, you can specify the argument values either by
3881 position, or by keyword. For example, @samp{sum 9,17} is equivalent to
3882 @samp{sum to=17, from=9}.
3885 @cindex @code{endm} directive
3886 Mark the end of a macro definition.
3889 @cindex @code{exitm} directive
3890 Exit early from the current macro definition.
3892 @cindex number of macros executed
3893 @cindex macros, count executed
3895 @code{@value{AS}} maintains a counter of how many macros it has
3896 executed in this pseudo-variable; you can copy that number to your
3897 output with @samp{\@@}, but @emph{only within a macro definition}.
3900 @item LOCAL @var{name} [ , @dots{} ]
3901 @emph{Warning: @code{LOCAL} is only available if you select ``alternate
3902 macro syntax'' with @samp{-a} or @samp{--alternate}.} @xref{Alternate,,
3903 Alternate macro syntax}.
3905 Generate a string replacement for each of the @var{name} arguments, and
3906 replace any instances of @var{name} in each macro expansion. The
3907 replacement string is unique in the assembly, and different for each
3908 separate macro expansion. @code{LOCAL} allows you to write macros that
3909 define symbols, without fear of conflict between separate macro expansions.
3914 @section @code{.nolist}
3916 @cindex @code{nolist} directive
3917 @cindex listing control, turning off
3918 Control (in conjunction with the @code{.list} directive) whether or
3919 not assembly listings are generated. These two directives maintain an
3920 internal counter (which is zero initially). @code{.list} increments the
3921 counter, and @code{.nolist} decrements it. Assembly listings are
3922 generated whenever the counter is greater than zero.
3925 @section @code{.octa @var{bignums}}
3927 @c FIXME: double size emitted for "octa" on i960, others? Or warn?
3928 @cindex @code{octa} directive
3929 @cindex integer, 16-byte
3930 @cindex sixteen byte integer
3931 This directive expects zero or more bignums, separated by commas. For each
3932 bignum, it emits a 16-byte integer.
3934 The term ``octa'' comes from contexts in which a ``word'' is two bytes;
3935 hence @emph{octa}-word for 16 bytes.
3938 @section @code{.org @var{new-lc} , @var{fill}}
3940 @cindex @code{org} directive
3941 @cindex location counter, advancing
3942 @cindex advancing location counter
3943 @cindex current address, advancing
3944 Advance the location counter of the current section to
3945 @var{new-lc}. @var{new-lc} is either an absolute expression or an
3946 expression with the same section as the current subsection. That is,
3947 you can't use @code{.org} to cross sections: if @var{new-lc} has the
3948 wrong section, the @code{.org} directive is ignored. To be compatible
3949 with former assemblers, if the section of @var{new-lc} is absolute,
3950 @code{@value{AS}} issues a warning, then pretends the section of @var{new-lc}
3951 is the same as the current subsection.
3953 @code{.org} may only increase the location counter, or leave it
3954 unchanged; you cannot use @code{.org} to move the location counter
3957 @c double negative used below "not undefined" because this is a specific
3958 @c reference to "undefined" (as SEG_UNKNOWN is called in this manual)
3959 @c section. doc@cygnus.com 18feb91
3960 Because @code{@value{AS}} tries to assemble programs in one pass, @var{new-lc}
3961 may not be undefined. If you really detest this restriction we eagerly await
3962 a chance to share your improved assembler.
3964 Beware that the origin is relative to the start of the section, not
3965 to the start of the subsection. This is compatible with other
3966 people's assemblers.
3968 When the location counter (of the current subsection) is advanced, the
3969 intervening bytes are filled with @var{fill} which should be an
3970 absolute expression. If the comma and @var{fill} are omitted,
3971 @var{fill} defaults to zero.
3974 @section @code{.p2align[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}}
3976 @cindex padding the location counter given a power of two
3977 @cindex @code{p2align} directive
3978 Pad the location counter (in the current subsection) to a particular
3979 storage boundary. The first expression (which must be absolute) is the
3980 number of low-order zero bits the location counter must have after
3981 advancement. For example @samp{.p2align 3} advances the location
3982 counter until it a multiple of 8. If the location counter is already a
3983 multiple of 8, no change is needed.
3985 The second expression (also absolute) gives the fill value to be stored in the
3986 padding bytes. It (and the comma) may be omitted. If it is omitted, the
3987 padding bytes are normally zero. However, on some systems, if the section is
3988 marked as containing code and the fill value is omitted, the space is filled
3989 with no-op instructions.
3991 The third expression is also absolute, and is also optional. If it is present,
3992 it is the maximum number of bytes that should be skipped by this alignment
3993 directive. If doing the alignment would require skipping more bytes than the
3994 specified maximum, then the alignment is not done at all. You can omit the
3995 fill value (the second argument) entirely by simply using two commas after the
3996 required alignment; this can be useful if you want the alignment to be filled
3997 with no-op instructions when appropriate.
3999 @cindex @code{p2alignw} directive
4000 @cindex @code{p2alignl} directive
4001 The @code{.p2alignw} and @code{.p2alignl} directives are variants of the
4002 @code{.p2align} directive. The @code{.p2alignw} directive treats the fill
4003 pattern as a two byte word value. The @code{.p2alignl} directives treats the
4004 fill pattern as a four byte longword value. For example, @code{.p2alignw
4005 2,0x368d} will align to a multiple of 4. If it skips two bytes, they will be
4006 filled in with the value 0x368d (the exact placement of the bytes depends upon
4007 the endianness of the processor). If it skips 1 or 3 bytes, the fill value is
4011 @section @code{.psize @var{lines} , @var{columns}}
4013 @cindex @code{psize} directive
4014 @cindex listing control: paper size
4015 @cindex paper size, for listings
4016 Use this directive to declare the number of lines---and, optionally, the
4017 number of columns---to use for each page, when generating listings.
4019 If you do not use @code{.psize}, listings use a default line-count
4020 of 60. You may omit the comma and @var{columns} specification; the
4021 default width is 200 columns.
4023 @code{@value{AS}} generates formfeeds whenever the specified number of
4024 lines is exceeded (or whenever you explicitly request one, using
4027 If you specify @var{lines} as @code{0}, no formfeeds are generated save
4028 those explicitly specified with @code{.eject}.
4031 @section @code{.quad @var{bignums}}
4033 @cindex @code{quad} directive
4034 @code{.quad} expects zero or more bignums, separated by commas. For
4035 each bignum, it emits
4037 an 8-byte integer. If the bignum won't fit in 8 bytes, it prints a
4038 warning message; and just takes the lowest order 8 bytes of the bignum.
4039 @cindex eight-byte integer
4040 @cindex integer, 8-byte
4042 The term ``quad'' comes from contexts in which a ``word'' is two bytes;
4043 hence @emph{quad}-word for 8 bytes.
4046 a 16-byte integer. If the bignum won't fit in 16 bytes, it prints a
4047 warning message; and just takes the lowest order 16 bytes of the bignum.
4048 @cindex sixteen-byte integer
4049 @cindex integer, 16-byte
4053 @section @code{.rept @var{count}}
4055 @cindex @code{rept} directive
4056 Repeat the sequence of lines between the @code{.rept} directive and the next
4057 @code{.endr} directive @var{count} times.
4059 For example, assembling
4067 is equivalent to assembling
4076 @section @code{.sbttl "@var{subheading}"}
4078 @cindex @code{sbttl} directive
4079 @cindex subtitles for listings
4080 @cindex listing control: subtitle
4081 Use @var{subheading} as the title (third line, immediately after the
4082 title line) when generating assembly listings.
4084 This directive affects subsequent pages, as well as the current page if
4085 it appears within ten lines of the top of a page.
4089 @section @code{.scl @var{class}}
4091 @cindex @code{scl} directive
4092 @cindex symbol storage class (COFF)
4093 @cindex COFF symbol storage class
4094 Set the storage-class value for a symbol. This directive may only be
4095 used inside a @code{.def}/@code{.endef} pair. Storage class may flag
4096 whether a symbol is static or external, or it may record further
4097 symbolic debugging information.
4100 The @samp{.scl} directive is primarily associated with COFF output; when
4101 configured to generate @code{b.out} output format, @code{@value{AS}}
4102 accepts this directive but ignores it.
4107 @section @code{.section @var{name}}
4109 @cindex @code{section} directive
4110 @cindex named section
4111 Use the @code{.section} directive to assemble the following code into a section
4114 This directive is only supported for targets that actually support arbitrarily
4115 named sections; on @code{a.out} targets, for example, it is not accepted, even
4116 with a standard @code{a.out} section name.
4119 For COFF targets, the @code{.section} directive is used in one of the following
4122 .section @var{name}[, "@var{flags}"]
4123 .section @var{name}[, @var{subsegment}]
4126 If the optional argument is quoted, it is taken as flags to use for the
4127 section. Each flag is a single character. The following flags are recognized:
4130 bss section (uninitialized data)
4132 section is not loaded
4143 If no flags are specified, the default flags depend upon the section name. If
4144 the section name is not recognized, the default will be for the section to be
4145 loaded and writable.
4147 If the optional argument to the @code{.section} directive is not quoted, it is
4148 taken as a subsegment number (@pxref{Sub-Sections}).
4152 For ELF targets, the @code{.section} directive is used like this:
4154 .section @var{name}[, "@var{flags}"[, @@@var{type}]]
4156 The optional @var{flags} argument is a quoted string which may contain any
4157 combintion of the following characters:
4160 section is allocatable
4164 section is executable
4167 The optional @var{type} argument may contain one of the following constants:
4170 section contains data
4172 section does not contain data (i.e., section only occupies space)
4175 If no flags are specified, the default flags depend upon the section name. If
4176 the section name is not recognized, the default will be for the section to have
4177 none of the above flags: it will not be allocated in memory, nor writable, nor
4178 executable. The section will contain data.
4180 For ELF targets, the assembler supports another type of @code{.section}
4181 directive for compatibility with the Solaris assembler:
4183 .section "@var{name}"[, @var{flags}...]
4185 Note that the section name is quoted. There may be a sequence of comma
4189 section is allocatable
4193 section is executable
4198 @section @code{.set @var{symbol}, @var{expression}}
4200 @cindex @code{set} directive
4201 @cindex symbol value, setting
4202 Set the value of @var{symbol} to @var{expression}. This
4203 changes @var{symbol}'s value and type to conform to
4204 @var{expression}. If @var{symbol} was flagged as external, it remains
4205 flagged (@pxref{Symbol Attributes}).
4207 You may @code{.set} a symbol many times in the same assembly.
4209 If you @code{.set} a global symbol, the value stored in the object
4210 file is the last value stored into it.
4213 The syntax for @code{set} on the HPPA is
4214 @samp{@var{symbol} .set @var{expression}}.
4218 @section @code{.short @var{expressions}}
4220 @cindex @code{short} directive
4222 @code{.short} is normally the same as @samp{.word}.
4223 @xref{Word,,@code{.word}}.
4225 In some configurations, however, @code{.short} and @code{.word} generate
4226 numbers of different lengths; @pxref{Machine Dependencies}.
4230 @code{.short} is the same as @samp{.word}. @xref{Word,,@code{.word}}.
4233 This expects zero or more @var{expressions}, and emits
4234 a 16 bit number for each.
4239 @section @code{.single @var{flonums}}
4241 @cindex @code{single} directive
4242 @cindex floating point numbers (single)
4243 This directive assembles zero or more flonums, separated by commas. It
4244 has the same effect as @code{.float}.
4246 The exact kind of floating point numbers emitted depends on how
4247 @code{@value{AS}} is configured. @xref{Machine Dependencies}.
4251 On the @value{TARGET} family, @code{.single} emits 32-bit floating point
4252 numbers in @sc{ieee} format.
4258 @section @code{.size}
4260 @cindex @code{size} directive
4261 This directive is generated by compilers to include auxiliary debugging
4262 information in the symbol table. It is only permitted inside
4263 @code{.def}/@code{.endef} pairs.
4266 @samp{.size} is only meaningful when generating COFF format output; when
4267 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
4273 @section @code{.sleb128 @var{expressions}}
4275 @cindex @code{sleb128} directive
4276 @var{sleb128} stands for ``signed little endian base 128.'' This is a
4277 compact, variable length representation of numbers used by the DWARF
4278 symbolic debugging format. @xref{Uleb128,@code{.uleb128}}.
4280 @ifclear no-space-dir
4282 @section @code{.skip @var{size} , @var{fill}}
4284 @cindex @code{skip} directive
4285 @cindex filling memory
4286 This directive emits @var{size} bytes, each of value @var{fill}. Both
4287 @var{size} and @var{fill} are absolute expressions. If the comma and
4288 @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same as
4292 @section @code{.space @var{size} , @var{fill}}
4294 @cindex @code{space} directive
4295 @cindex filling memory
4296 This directive emits @var{size} bytes, each of value @var{fill}. Both
4297 @var{size} and @var{fill} are absolute expressions. If the comma
4298 and @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same
4303 @emph{Warning:} @code{.space} has a completely different meaning for HPPA
4304 targets; use @code{.block} as a substitute. See @cite{HP9000 Series 800
4305 Assembly Language Reference Manual} (HP 92432-90001) for the meaning of the
4306 @code{.space} directive. @xref{HPPA Directives,,HPPA Assembler Directives},
4315 @section @code{.space}
4316 @cindex @code{space} directive
4318 On the AMD 29K, this directive is ignored; it is accepted for
4319 compatibility with other AMD 29K assemblers.
4322 @emph{Warning:} In most versions of the @sc{gnu} assembler, the directive
4323 @code{.space} has the effect of @code{.block} @xref{Machine Dependencies}.
4329 @section @code{.stabd, .stabn, .stabs}
4331 @cindex symbolic debuggers, information for
4332 @cindex @code{stab@var{x}} directives
4333 There are three directives that begin @samp{.stab}.
4334 All emit symbols (@pxref{Symbols}), for use by symbolic debuggers.
4335 The symbols are not entered in the @code{@value{AS}} hash table: they
4336 cannot be referenced elsewhere in the source file.
4337 Up to five fields are required:
4341 This is the symbol's name. It may contain any character except
4342 @samp{\000}, so is more general than ordinary symbol names. Some
4343 debuggers used to code arbitrarily complex structures into symbol names
4347 An absolute expression. The symbol's type is set to the low 8 bits of
4348 this expression. Any bit pattern is permitted, but @code{@value{LD}}
4349 and debuggers choke on silly bit patterns.
4352 An absolute expression. The symbol's ``other'' attribute is set to the
4353 low 8 bits of this expression.
4356 An absolute expression. The symbol's descriptor is set to the low 16
4357 bits of this expression.
4360 An absolute expression which becomes the symbol's value.
4363 If a warning is detected while reading a @code{.stabd}, @code{.stabn},
4364 or @code{.stabs} statement, the symbol has probably already been created;
4365 you get a half-formed symbol in your object file. This is
4366 compatible with earlier assemblers!
4369 @cindex @code{stabd} directive
4370 @item .stabd @var{type} , @var{other} , @var{desc}
4372 The ``name'' of the symbol generated is not even an empty string.
4373 It is a null pointer, for compatibility. Older assemblers used a
4374 null pointer so they didn't waste space in object files with empty
4377 The symbol's value is set to the location counter,
4378 relocatably. When your program is linked, the value of this symbol
4379 is the address of the location counter when the @code{.stabd} was
4382 @cindex @code{stabn} directive
4383 @item .stabn @var{type} , @var{other} , @var{desc} , @var{value}
4384 The name of the symbol is set to the empty string @code{""}.
4386 @cindex @code{stabs} directive
4387 @item .stabs @var{string} , @var{type} , @var{other} , @var{desc} , @var{value}
4388 All five fields are specified.
4394 @section @code{.string} "@var{str}"
4396 @cindex string, copying to object file
4397 @cindex @code{string} directive
4399 Copy the characters in @var{str} to the object file. You may specify more than
4400 one string to copy, separated by commas. Unless otherwise specified for a
4401 particular machine, the assembler marks the end of each string with a 0 byte.
4402 You can use any of the escape sequences described in @ref{Strings,,Strings}.
4406 @section @code{.symver}
4407 @cindex @code{symver} directive
4408 @cindex symbol versioning
4409 @cindex versions of symbols
4410 Use the @code{.symver} directive to bind symbols to specific version nodes
4411 within a source file. This is only supported on ELF platforms, and is
4412 typically used when assembling files to be linked into a shared library.
4413 There are cases where it may make sense to use this in objects to be bound
4414 into an application itself so as to override a versioned symbol from a
4417 For ELF targets, the @code{.symver} directive is used like this:
4419 .symver @var{name}, @var{name2@@nodename}
4421 In this case, the symbol @var{name} must exist and be defined within the file
4422 being assembled. The @code{.versym} directive effectively creates a symbol
4423 alias with the name @var{name2@@nodename}, and in fact the main reason that we
4424 just don't try and create a regular alias is that the @var{@@} character isn't
4425 permitted in symbol names. The @var{name2} part of the name is the actual name
4426 of the symbol by which it will be externally referenced. The name @var{name}
4427 itself is merely a name of convenience that is used so that it is possible to
4428 have definitions for multiple versions of a function within a single source
4429 file, and so that the compiler can unambiguously know which version of a
4430 function is being mentioned. The @var{nodename} portion of the alias should be
4431 the name of a node specified in the version script supplied to the linker when
4432 building a shared library. If you are attempting to override a versioned
4433 symbol from a shared library, then @var{nodename} should correspond to the
4434 nodename of the symbol you are trying to override.
4439 @section @code{.tag @var{structname}}
4441 @cindex COFF structure debugging
4442 @cindex structure debugging, COFF
4443 @cindex @code{tag} directive
4444 This directive is generated by compilers to include auxiliary debugging
4445 information in the symbol table. It is only permitted inside
4446 @code{.def}/@code{.endef} pairs. Tags are used to link structure
4447 definitions in the symbol table with instances of those structures.
4450 @samp{.tag} is only used when generating COFF format output; when
4451 @code{@value{AS}} is generating @code{b.out}, it accepts this directive but
4457 @section @code{.text @var{subsection}}
4459 @cindex @code{text} directive
4460 Tells @code{@value{AS}} to assemble the following statements onto the end of
4461 the text subsection numbered @var{subsection}, which is an absolute
4462 expression. If @var{subsection} is omitted, subsection number zero
4466 @section @code{.title "@var{heading}"}
4468 @cindex @code{title} directive
4469 @cindex listing control: title line
4470 Use @var{heading} as the title (second line, immediately after the
4471 source file name and pagenumber) when generating assembly listings.
4473 This directive affects subsequent pages, as well as the current page if
4474 it appears within ten lines of the top of a page.
4478 @section @code{.type @var{int}}
4480 @cindex COFF symbol type
4481 @cindex symbol type, COFF
4482 @cindex @code{type} directive
4483 This directive, permitted only within @code{.def}/@code{.endef} pairs,
4484 records the integer @var{int} as the type attribute of a symbol table entry.
4487 @samp{.type} is associated only with COFF format output; when
4488 @code{@value{AS}} is configured for @code{b.out} output, it accepts this
4489 directive but ignores it.
4495 @section @code{.val @var{addr}}
4497 @cindex @code{val} directive
4498 @cindex COFF value attribute
4499 @cindex value attribute, COFF
4500 This directive, permitted only within @code{.def}/@code{.endef} pairs,
4501 records the address @var{addr} as the value attribute of a symbol table
4505 @samp{.val} is used only for COFF output; when @code{@value{AS}} is
4506 configured for @code{b.out}, it accepts this directive but ignores it.
4511 @section @code{.uleb128 @var{expressions}}
4513 @cindex @code{uleb128} directive
4514 @var{uleb128} stands for ``unsigned little endian base 128.'' This is a
4515 compact, variable length representation of numbers used by the DWARF
4516 symbolic debugging format. @xref{Sleb128,@code{.sleb128}}.
4519 @section @code{.word @var{expressions}}
4521 @cindex @code{word} directive
4522 This directive expects zero or more @var{expressions}, of any section,
4523 separated by commas.
4526 For each expression, @code{@value{AS}} emits a 32-bit number.
4529 For each expression, @code{@value{AS}} emits a 16-bit number.
4534 The size of the number emitted, and its byte order,
4535 depend on what target computer the assembly is for.
4538 @c on amd29k, i960, sparc the "special treatment to support compilers" doesn't
4539 @c happen---32-bit addressability, period; no long/short jumps.
4540 @ifset DIFF-TBL-KLUGE
4541 @cindex difference tables altered
4542 @cindex altered difference tables
4544 @emph{Warning: Special Treatment to support Compilers}
4548 Machines with a 32-bit address space, but that do less than 32-bit
4549 addressing, require the following special treatment. If the machine of
4550 interest to you does 32-bit addressing (or doesn't require it;
4551 @pxref{Machine Dependencies}), you can ignore this issue.
4554 In order to assemble compiler output into something that works,
4555 @code{@value{AS}} occasionlly does strange things to @samp{.word} directives.
4556 Directives of the form @samp{.word sym1-sym2} are often emitted by
4557 compilers as part of jump tables. Therefore, when @code{@value{AS}} assembles a
4558 directive of the form @samp{.word sym1-sym2}, and the difference between
4559 @code{sym1} and @code{sym2} does not fit in 16 bits, @code{@value{AS}}
4560 creates a @dfn{secondary jump table}, immediately before the next label.
4561 This secondary jump table is preceded by a short-jump to the
4562 first byte after the secondary table. This short-jump prevents the flow
4563 of control from accidentally falling into the new table. Inside the
4564 table is a long-jump to @code{sym2}. The original @samp{.word}
4565 contains @code{sym1} minus the address of the long-jump to
4568 If there were several occurrences of @samp{.word sym1-sym2} before the
4569 secondary jump table, all of them are adjusted. If there was a
4570 @samp{.word sym3-sym4}, that also did not fit in sixteen bits, a
4571 long-jump to @code{sym4} is included in the secondary jump table,
4572 and the @code{.word} directives are adjusted to contain @code{sym3}
4573 minus the address of the long-jump to @code{sym4}; and so on, for as many
4574 entries in the original jump table as necessary.
4577 @emph{This feature may be disabled by compiling @code{@value{AS}} with the
4578 @samp{-DWORKING_DOT_WORD} option.} This feature is likely to confuse
4579 assembly language programmers.
4582 @c end DIFF-TBL-KLUGE
4585 @section Deprecated Directives
4587 @cindex deprecated directives
4588 @cindex obsolescent directives
4589 One day these directives won't work.
4590 They are included for compatibility with older assemblers.
4598 @node Machine Dependencies
4599 @chapter Machine Dependent Features
4601 @cindex machine dependencies
4602 The machine instruction sets are (almost by definition) different on
4603 each machine where @code{@value{AS}} runs. Floating point representations
4604 vary as well, and @code{@value{AS}} often supports a few additional
4605 directives or command-line options for compatibility with other
4606 assemblers on a particular platform. Finally, some versions of
4607 @code{@value{AS}} support special pseudo-instructions for branch
4610 This chapter discusses most of these differences, though it does not
4611 include details on any machine's instruction set. For details on that
4612 subject, see the hardware manufacturer's manual.
4616 * AMD29K-Dependent:: AMD 29K Dependent Features
4619 * ARC-Dependent:: ARC Dependent Features
4622 * ARM-Dependent:: ARM Dependent Features
4625 * D10V-Dependent:: D10V Dependent Features
4628 * H8/300-Dependent:: Hitachi H8/300 Dependent Features
4631 * H8/500-Dependent:: Hitachi H8/500 Dependent Features
4634 * HPPA-Dependent:: HPPA Dependent Features
4637 * i386-Dependent:: Intel 80386 Dependent Features
4640 * i960-Dependent:: Intel 80960 Dependent Features
4643 * M68K-Dependent:: M680x0 Dependent Features
4646 * MIPS-Dependent:: MIPS Dependent Features
4649 * SH-Dependent:: Hitachi SH Dependent Features
4652 * Sparc-Dependent:: SPARC Dependent Features
4655 * Z8000-Dependent:: Z8000 Dependent Features
4658 * Vax-Dependent:: VAX Dependent Features
4665 @c The following major nodes are *sections* in the GENERIC version, *chapters*
4666 @c in single-cpu versions. This is mainly achieved by @lowersections. There is a
4667 @c peculiarity: to preserve cross-references, there must be a node called
4668 @c "Machine Dependencies". Hence the conditional nodenames in each
4669 @c major node below. Node defaulting in makeinfo requires adjacency of
4670 @c node and sectioning commands; hence the repetition of @chapter BLAH
4671 @c in both conditional blocks.
4677 @chapter ARC Dependent Features
4680 @node Machine Dependencies
4681 @chapter ARC Dependent Features
4686 * ARC-Opts:: Options
4687 * ARC-Float:: Floating Point
4688 * ARC-Directives:: Sparc Machine Directives
4694 @cindex options for ARC
4696 @cindex architectures, ARC
4697 @cindex ARC architectures
4698 The ARC chip family includes several successive levels (or other
4699 variants) of chip, using the same core instruction set, but including
4700 a few additional instructions at each level.
4702 By default, @code{@value{AS}} assumes the core instruction set (ARC
4703 base). The @code{.cpu} pseudo-op is intended to be used to select
4707 @cindex @code{-mbig-endian} option (ARC)
4708 @cindex @code{-mlittle-endian} option (ARC)
4709 @cindex ARC big-endian output
4710 @cindex ARC little-endian output
4711 @cindex big-endian output, ARC
4712 @cindex little-endian output, ARC
4714 @itemx -mlittle-endian
4715 Any @sc{arc} configuration of @code{@value{AS}} can select big-endian or
4716 little-endian output at run time (unlike most other @sc{gnu} development
4717 tools, which must be configured for one or the other). Use
4718 @samp{-mbig-endian} to select big-endian output, and @samp{-mlittle-endian}
4723 @section Floating Point
4725 @cindex floating point, ARC (@sc{ieee})
4726 @cindex ARC floating point (@sc{ieee})
4727 The ARC cpu family currently does not have hardware floating point
4728 support. Software floating point support is provided by @code{GCC}
4729 and uses @sc{ieee} floating-point numbers.
4731 @node ARC-Directives
4732 @section ARC Machine Directives
4734 @cindex ARC machine directives
4735 @cindex machine directives, ARC
4736 The ARC version of @code{@value{AS}} supports the following additional
4741 @cindex @code{cpu} directive, SPARC
4742 This must be followed by the desired cpu.
4743 The ARC is intended to be customizable, @code{.cpu} is used to
4744 select the desired variant [though currently there are none].
4751 @include c-a29k.texi
4760 @node Machine Dependencies
4761 @chapter Machine Dependent Features
4763 The machine instruction sets are different on each Hitachi chip family,
4764 and there are also some syntax differences among the families. This
4765 chapter describes the specific @code{@value{AS}} features for each
4769 * H8/300-Dependent:: Hitachi H8/300 Dependent Features
4770 * H8/500-Dependent:: Hitachi H8/500 Dependent Features
4771 * SH-Dependent:: Hitachi SH Dependent Features
4778 @include c-d10v.texi
4782 @include c-h8300.texi
4786 @include c-h8500.texi
4790 @include c-hppa.texi
4794 @include c-i386.texi
4798 @include c-i960.texi
4802 @include c-m68k.texi
4806 @include c-mips.texi
4810 @include c-ns32k.texi
4818 @include c-sparc.texi
4830 @c reverse effect of @down at top of generic Machine-Dep chapter
4834 @node Reporting Bugs
4835 @chapter Reporting Bugs
4836 @cindex bugs in assembler
4837 @cindex reporting bugs in assembler
4839 Your bug reports play an essential role in making @code{@value{AS}} reliable.
4841 Reporting a bug may help you by bringing a solution to your problem, or it may
4842 not. But in any case the principal function of a bug report is to help the
4843 entire community by making the next version of @code{@value{AS}} work better.
4844 Bug reports are your contribution to the maintenance of @code{@value{AS}}.
4846 In order for a bug report to serve its purpose, you must include the
4847 information that enables us to fix the bug.
4850 * Bug Criteria:: Have you found a bug?
4851 * Bug Reporting:: How to report bugs
4855 @section Have you found a bug?
4856 @cindex bug criteria
4858 If you are not sure whether you have found a bug, here are some guidelines:
4861 @cindex fatal signal
4862 @cindex assembler crash
4863 @cindex crash of assembler
4865 If the assembler gets a fatal signal, for any input whatever, that is a
4866 @code{@value{AS}} bug. Reliable assemblers never crash.
4868 @cindex error on valid input
4870 If @code{@value{AS}} produces an error message for valid input, that is a bug.
4872 @cindex invalid input
4874 If @code{@value{AS}} does not produce an error message for invalid input, that
4875 is a bug. However, you should note that your idea of ``invalid input'' might
4876 be our idea of ``an extension'' or ``support for traditional practice''.
4879 If you are an experienced user of assemblers, your suggestions for improvement
4880 of @code{@value{AS}} are welcome in any case.
4884 @section How to report bugs
4886 @cindex assembler bugs, reporting
4888 A number of companies and individuals offer support for @sc{gnu} products. If
4889 you obtained @code{@value{AS}} from a support organization, we recommend you
4890 contact that organization first.
4892 You can find contact information for many support companies and
4893 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
4896 In any event, we also recommend that you send bug reports for @code{@value{AS}}
4897 to @samp{bug-gnu-utils@@prep.ai.mit.edu}.
4899 The fundamental principle of reporting bugs usefully is this:
4900 @strong{report all the facts}. If you are not sure whether to state a
4901 fact or leave it out, state it!
4903 Often people omit facts because they think they know what causes the problem
4904 and assume that some details do not matter. Thus, you might assume that the
4905 name of a symbol you use in an example does not matter. Well, probably it does
4906 not, but one cannot be sure. Perhaps the bug is a stray memory reference which
4907 happens to fetch from the location where that name is stored in memory;
4908 perhaps, if the name were different, the contents of that location would fool
4909 the assembler into doing the right thing despite the bug. Play it safe and
4910 give a specific, complete example. That is the easiest thing for you to do,
4911 and the most helpful.
4913 Keep in mind that the purpose of a bug report is to enable us to fix the bug if
4914 it is new to us. Therefore, always write your bug reports on the assumption
4915 that the bug has not been reported previously.
4917 Sometimes people give a few sketchy facts and ask, ``Does this ring a
4918 bell?'' Those bug reports are useless, and we urge everyone to
4919 @emph{refuse to respond to them} except to chide the sender to report
4922 To enable us to fix the bug, you should include all these things:
4926 The version of @code{@value{AS}}. @code{@value{AS}} announces it if you start
4927 it with the @samp{--version} argument.
4929 Without this, we will not know whether there is any point in looking for
4930 the bug in the current version of @code{@value{AS}}.
4933 Any patches you may have applied to the @code{@value{AS}} source.
4936 The type of machine you are using, and the operating system name and
4940 What compiler (and its version) was used to compile @code{@value{AS}}---e.g.
4944 The command arguments you gave the assembler to assemble your example and
4945 observe the bug. To guarantee you will not omit something important, list them
4946 all. A copy of the Makefile (or the output from make) is sufficient.
4948 If we were to try to guess the arguments, we would probably guess wrong
4949 and then we might not encounter the bug.
4952 A complete input file that will reproduce the bug. If the bug is observed when
4953 the assembler is invoked via a compiler, send the assembler source, not the
4954 high level language source. Most compilers will produce the assembler source
4955 when run with the @samp{-S} option. If you are using @code{@value{GCC}}, use
4956 the options @samp{-v --save-temps}; this will save the assembler source in a
4957 file with an extension of @file{.s}, and also show you exactly how
4958 @code{@value{AS}} is being run.
4961 A description of what behavior you observe that you believe is
4962 incorrect. For example, ``It gets a fatal signal.''
4964 Of course, if the bug is that @code{@value{AS}} gets a fatal signal, then we
4965 will certainly notice it. But if the bug is incorrect output, we might not
4966 notice unless it is glaringly wrong. You might as well not give us a chance to
4969 Even if the problem you experience is a fatal signal, you should still say so
4970 explicitly. Suppose something strange is going on, such as, your copy of
4971 @code{@value{AS}} is out of synch, or you have encountered a bug in the C
4972 library on your system. (This has happened!) Your copy might crash and ours
4973 would not. If you told us to expect a crash, then when ours fails to crash, we
4974 would know that the bug was not happening for us. If you had not told us to
4975 expect a crash, then we would not be able to draw any conclusion from our
4979 If you wish to suggest changes to the @code{@value{AS}} source, send us context
4980 diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or @samp{-p}
4981 option. Always send diffs from the old file to the new file. If you even
4982 discuss something in the @code{@value{AS}} source, refer to it by context, not
4985 The line numbers in our development sources will not match those in your
4986 sources. Your line numbers would convey no useful information to us.
4989 Here are some things that are not necessary:
4993 A description of the envelope of the bug.
4995 Often people who encounter a bug spend a lot of time investigating
4996 which changes to the input file will make the bug go away and which
4997 changes will not affect it.
4999 This is often time consuming and not very useful, because the way we
5000 will find the bug is by running a single example under the debugger
5001 with breakpoints, not by pure deduction from a series of examples.
5002 We recommend that you save your time for something else.
5004 Of course, if you can find a simpler example to report @emph{instead}
5005 of the original one, that is a convenience for us. Errors in the
5006 output will be easier to spot, running under the debugger will take
5007 less time, and so on.
5009 However, simplification is not vital; if you do not want to do this,
5010 report the bug anyway and send us the entire test case you used.
5013 A patch for the bug.
5015 A patch for the bug does help us if it is a good one. But do not omit
5016 the necessary information, such as the test case, on the assumption that
5017 a patch is all we need. We might see problems with your patch and decide
5018 to fix the problem another way, or we might not understand it at all.
5020 Sometimes with a program as complicated as @code{@value{AS}} it is very hard to
5021 construct an example that will make the program follow a certain path through
5022 the code. If you do not send us the example, we will not be able to construct
5023 one, so we will not be able to verify that the bug is fixed.
5025 And if we cannot understand what bug you are trying to fix, or why your
5026 patch should be an improvement, we will not install it. A test case will
5027 help us to understand.
5030 A guess about what the bug is or what it depends on.
5032 Such guesses are usually wrong. Even we cannot guess right about such
5033 things without first using the debugger to find the facts.
5036 @node Acknowledgements
5037 @chapter Acknowledgements
5039 If you have contributed to @code{@value{AS}} and your name isn't listed here,
5040 it is not meant as a slight. We just don't know about it. Send mail to the
5041 maintainer, and we'll correct the situation. Currently
5043 the maintainer is Ken Raeburn (email address @code{raeburn@@cygnus.com}).
5045 Dean Elsner wrote the original @sc{gnu} assembler for the VAX.@footnote{Any
5048 Jay Fenlason maintained GAS for a while, adding support for GDB-specific debug
5049 information and the 68k series machines, most of the preprocessing pass, and
5050 extensive changes in @file{messages.c}, @file{input-file.c}, @file{write.c}.
5052 K. Richard Pixley maintained GAS for a while, adding various enhancements and
5053 many bug fixes, including merging support for several processors, breaking GAS
5054 up to handle multiple object file format back ends (including heavy rewrite,
5055 testing, an integration of the coff and b.out back ends), adding configuration
5056 including heavy testing and verification of cross assemblers and file splits
5057 and renaming, converted GAS to strictly ANSI C including full prototypes, added
5058 support for m680[34]0 and cpu32, did considerable work on i960 including a COFF
5059 port (including considerable amounts of reverse engineering), a SPARC opcode
5060 file rewrite, DECstation, rs6000, and hp300hpux host ports, updated ``know''
5061 assertions and made them work, much other reorganization, cleanup, and lint.
5063 Ken Raeburn wrote the high-level BFD interface code to replace most of the code
5064 in format-specific I/O modules.
5066 The original VMS support was contributed by David L. Kashtan. Eric Youngdale
5067 has done much work with it since.
5069 The Intel 80386 machine description was written by Eliot Dresselhaus.
5071 Minh Tran-Le at IntelliCorp contributed some AIX 386 support.
5073 The Motorola 88k machine description was contributed by Devon Bowen of Buffalo
5074 University and Torbjorn Granlund of the Swedish Institute of Computer Science.
5076 Keith Knowles at the Open Software Foundation wrote the original MIPS back end
5077 (@file{tc-mips.c}, @file{tc-mips.h}), and contributed Rose format support
5078 (which hasn't been merged in yet). Ralph Campbell worked with the MIPS code to
5079 support a.out format.
5081 Support for the Zilog Z8k and Hitachi H8/300 and H8/500 processors (tc-z8k,
5082 tc-h8300, tc-h8500), and IEEE 695 object file format (obj-ieee), was written by
5083 Steve Chamberlain of Cygnus Support. Steve also modified the COFF back end to
5084 use BFD for some low-level operations, for use with the H8/300 and AMD 29k
5087 John Gilmore built the AMD 29000 support, added @code{.include} support, and
5088 simplified the configuration of which versions accept which directives. He
5089 updated the 68k machine description so that Motorola's opcodes always produced
5090 fixed-size instructions (e.g. @code{jsr}), while synthetic instructions
5091 remained shrinkable (@code{jbsr}). John fixed many bugs, including true tested
5092 cross-compilation support, and one bug in relaxation that took a week and
5093 required the proverbial one-bit fix.
5095 Ian Lance Taylor of Cygnus Support merged the Motorola and MIT syntax for the
5096 68k, completed support for some COFF targets (68k, i386 SVR3, and SCO Unix),
5097 added support for MIPS ECOFF and ELF targets, wrote the initial RS/6000 and
5098 PowerPC assembler, and made a few other minor patches.
5100 Steve Chamberlain made @code{@value{AS}} able to generate listings.
5102 Hewlett-Packard contributed support for the HP9000/300.
5104 Jeff Law wrote GAS and BFD support for the native HPPA object format (SOM)
5105 along with a fairly extensive HPPA testsuite (for both SOM and ELF object
5106 formats). This work was supported by both the Center for Software Science at
5107 the University of Utah and Cygnus Support.
5109 Support for ELF format files has been worked on by Mark Eichin of Cygnus
5110 Support (original, incomplete implementation for SPARC), Pete Hoogenboom and
5111 Jeff Law at the University of Utah (HPPA mainly), Michael Meissner of the Open
5112 Software Foundation (i386 mainly), and Ken Raeburn of Cygnus Support (sparc,
5113 and some initial 64-bit support).
5115 Richard Henderson rewrote the Alpha assembler. Klaus Kaempf wrote GAS and BFD
5116 support for openVMS/Alpha.
5118 Several engineers at Cygnus Support have also provided many small bug fixes and
5119 configuration enhancements.
5121 Many others have contributed large or small bugfixes and enhancements. If
5122 you have contributed significant work and are not mentioned on this list, and
5123 want to be, let us know. Some of the history has been lost; we are not
5124 intentionally leaving anyone out.