\input texinfo @c -*-Texinfo-*- @c Copyright (c) 1991, 92, 93, 94, 95, 96, 97, 98, 2000 @c Free Software Foundation, Inc. @c UPDATE!! On future updates-- @c (1) check for new machine-dep cmdline options in @c md_parse_option definitions in config/tc-*.c @c (2) for platform-specific directives, examine md_pseudo_op @c in config/tc-*.c @c (3) for object-format specific directives, examine obj_pseudo_op @c in config/obj-*.c @c (4) portable directives in potable[] in read.c @c %**start of header @setfilename as.info @c ---config--- @c defaults, config file may override: @set have-stabs @c --- @include asconfig.texi @include gasver.texi @c --- @c common OR combinations of conditions @ifset AOUT @set aout-bout @end ifset @ifset ARM/Thumb @set ARM @end ifset @ifset BOUT @set aout-bout @end ifset @ifset H8/300 @set H8 @end ifset @ifset H8/500 @set H8 @end ifset @ifset SH @set H8 @end ifset @ifset HPPA @set abnormal-separator @end ifset @c ------------ @ifset GENERIC @settitle Using @value{AS} @end ifset @ifclear GENERIC @settitle Using @value{AS} (@value{TARGET}) @end ifclear @setchapternewpage odd @c %**end of header @c @smallbook @c @set SMALL @c WARE! Some of the machine-dependent sections contain tables of machine @c instructions. Except in multi-column format, these tables look silly. @c Unfortunately, Texinfo doesn't have a general-purpose multi-col format, so @c the multi-col format is faked within @example sections. @c @c Again unfortunately, the natural size that fits on a page, for these tables, @c is different depending on whether or not smallbook is turned on. @c This matters, because of order: text flow switches columns at each page @c break. @c @c The format faked in this source works reasonably well for smallbook, @c not well for the default large-page format. This manual expects that if you @c turn on @smallbook, you will also uncomment the "@set SMALL" to enable the @c tables in question. You can turn on one without the other at your @c discretion, of course. @ifinfo @set SMALL @c the insn tables look just as silly in info files regardless of smallbook, @c might as well show 'em anyways. @end ifinfo @ifinfo @format START-INFO-DIR-ENTRY * As: (as). The GNU assembler. END-INFO-DIR-ENTRY @end format @end ifinfo @finalout @syncodeindex ky cp @ifinfo This file documents the GNU Assembler "@value{AS}". Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. @ignore Permission is granted to process this file through Tex and print the results, provided the printed document carries copying permission notice identical to this one except for the removal of this paragraph (this paragraph not being relevant to the printed manual). @end ignore Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions. @end ifinfo @titlepage @title Using @value{AS} @subtitle The @sc{gnu} Assembler @ifclear GENERIC @subtitle for the @value{TARGET} family @end ifclear @sp 1 @subtitle Version @value{VERSION} @sp 1 @sp 13 The Free Software Foundation Inc. thanks The Nice Computer Company of Australia for loaning Dean Elsner to write the first (Vax) version of @code{as} for Project @sc{gnu}. The proprietors, management and staff of TNCCA thank FSF for distracting the boss while they got some work done. @sp 3 @author Dean Elsner, Jay Fenlason & friends @page @tex {\parskip=0pt \hfill {\it Using {\tt @value{AS}}}\par \hfill Edited by Cygnus Support\par } %"boxit" macro for figures: %Modified from Knuth's ``boxit'' macro from TeXbook (answer to exercise 21.3) \gdef\boxit#1#2{\vbox{\hrule\hbox{\vrule\kern3pt \vbox{\parindent=0pt\parskip=0pt\hsize=#1\kern3pt\strut\hfil #2\hfil\strut\kern3pt}\kern3pt\vrule}\hrule}}%box with visible outline \gdef\ibox#1#2{\hbox to #1{#2\hfil}\kern8pt}% invisible box @end tex @vskip 0pt plus 1filll Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions. @end titlepage @ifinfo @node Top @top Using @value{AS} This file is a user guide to the @sc{gnu} assembler @code{@value{AS}} version @value{VERSION}. @ifclear GENERIC This version of the file describes @code{@value{AS}} configured to generate code for @value{TARGET} architectures. @end ifclear @menu * Overview:: Overview * Invoking:: Command-Line Options * Syntax:: Syntax * Sections:: Sections and Relocation * Symbols:: Symbols * Expressions:: Expressions * Pseudo Ops:: Assembler Directives * Machine Dependencies:: Machine Dependent Features * Reporting Bugs:: Reporting Bugs * Acknowledgements:: Who Did What * Index:: Index @end menu @end ifinfo @node Overview @chapter Overview @iftex This manual is a user guide to the @sc{gnu} assembler @code{@value{AS}}. @ifclear GENERIC This version of the manual describes @code{@value{AS}} configured to generate code for @value{TARGET} architectures. @end ifclear @end iftex @cindex invocation summary @cindex option summary @cindex summary of options Here is a brief summary of how to invoke @code{@value{AS}}. For details, @pxref{Invoking,,Comand-Line Options}. @c We don't use deffn and friends for the following because they seem @c to be limited to one line for the header. @smallexample @value{AS} [ -a[cdhlns][=file] ] [ -D ] [ --defsym @var{sym}=@var{val} ] [ -f ] [ --gstabs ] [ --gdwarf2 ] [ --help ] [ -I @var{dir} ] [ -J ] [ -K ] [ -L ] [ --keep-locals ] [ -o @var{objfile} ] [ -R ] [ --statistics ] [ -v ] [ -version ] [ --version ] [ -W ] [ --warn ] [ --fatal-warnings ] [ -w ] [ -x ] [ -Z ] @ifset A29K @c am29k has no machine-dependent assembler options @end ifset @ifset ARC [ -mbig-endian | -mlittle-endian ] @end ifset @ifset ARM [ -m[arm]1 | -m[arm]2 | -m[arm]250 | -m[arm]3 | -m[arm]6 | -m[arm]60 | -m[arm]600 | -m[arm]610 | -m[arm]620 | -m[arm]7[t][[d]m[i]][fe] | -m[arm]70 | -m[arm]700 | -m[arm]710[c] | -m[arm]7100 | -m[arm]7500 | -m[arm]8 | -m[arm]810 | -m[arm]9 | -m[arm]920 | -m[arm]920t | -m[arm]9tdmi | -mstrongarm | -mstrongarm110 | -mstrongarm1100 ] [ -m[arm]v2 | -m[arm]v2a | -m[arm]v3 | -m[arm]v3m | -m[arm]v4 | -m[arm]v4t | -m[arm]v5 | -[arm]v5t ] [ -mthumb | -mall ] [ -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu ] [ -EB | -EL ] [ -mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant ] [ -mthumb-interwork ] [ -moabi ] [ -k ] @end ifset @ifset D10V [ -O ] @end ifset @ifset D30V [ -O | -n | -N ] @end ifset @ifset H8 @c Hitachi family chips have no machine-dependent assembler options @end ifset @ifset HPPA @c HPPA has no machine-dependent assembler options (yet). @end ifset @ifset PJ [ -mb | -me ] @end ifset @ifset SPARC @c The order here is important. See c-sparc.texi. [ -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite -Av8plus | -Av8plusa | -Av9 | -Av9a ] [ -xarch=v8plus | -xarch=v8plusa ] [ -bump ] [ -32 | -64 ] @end ifset @ifset TIC54X [ -mcpu=54[123589] | -mcpu=54[56]lp ] [ -mfar-mode | -mf ] [ -merrors-to-file | -me ] @end ifset @ifset Z8000 @c Z8000 has no machine-dependent assembler options @end ifset @ifset I960 @c see md_parse_option in tc-i960.c [ -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC ] [ -b ] [ -no-relax ] @end ifset @ifset M32R [ --m32rx | --[no-]warn-explicit-parallel-conflicts | --W[n]p ] @end ifset @ifset M680X0 [ -l ] [ -m68000 | -m68010 | -m68020 | ... ] @end ifset @ifset MCORE [ -jsri2bsr ] [ -sifilter ] [ -relax ] [ -mcpu=[210|340] ] @end ifset @ifset M68HC11 [ -m68hc11 | -m68hc12 ] [ --force-long-branchs ] [ --short-branchs ] [ --strict-direct-mode ] [ --print-insn-syntax ] [ --print-opcodes ] [ --generate-example ] @end ifset @ifset MIPS [ -nocpp ] [ -EL ] [ -EB ] [ -G @var{num} ] [ -mcpu=@var{CPU} ] [ -mips1 ] [ -mips2 ] [ -mips3 ] [ -m4650 ] [ -no-m4650 ] [ --trap ] [ --break ] [ --emulation=@var{name} ] @end ifset [ -- | @var{files} @dots{} ] @end smallexample @table @code @item -a[cdhlmns] Turn on listings, in any of a variety of ways: @table @code @item -ac omit false conditionals @item -ad omit debugging directives @item -ah include high-level source @item -al include assembly @item -am include macro expansions @item -an omit forms processing @item -as include symbols @item =file set the name of the listing file @end table You may combine these options; for example, use @samp{-aln} for assembly listing without forms processing. The @samp{=file} option, if used, must be the last one. By itself, @samp{-a} defaults to @samp{-ahls}. @item -D Ignored. This option is accepted for script compatibility with calls to other assemblers. @item --defsym @var{sym}=@var{value} Define the symbol @var{sym} to be @var{value} before assembling the input file. @var{value} must be an integer constant. As in C, a leading @samp{0x} indicates a hexadecimal value, and a leading @samp{0} indicates an octal value. @item -f ``fast''---skip whitespace and comment preprocessing (assume source is compiler output). @item --gstabs Generate stabs debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it. @item --gdwarf2 Generate DWARF2 debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it. @item --help Print a summary of the command line options and exit. @item -I @var{dir} Add directory @var{dir} to the search list for @code{.include} directives. @item -J Don't warn about signed overflow. @item -K @ifclear DIFF-TBL-KLUGE This option is accepted but has no effect on the @value{TARGET} family. @end ifclear @ifset DIFF-TBL-KLUGE Issue warnings when difference tables altered for long displacements. @end ifset @item -L @itemx --keep-locals Keep (in the symbol table) local symbols. On traditional a.out systems these start with @samp{L}, but different systems have different local label prefixes. @item -o @var{objfile} Name the object-file output from @code{@value{AS}} @var{objfile}. @item -R Fold the data section into the text section. @item --statistics Print the maximum space (in bytes) and total time (in seconds) used by assembly. @item --strip-local-absolute Remove local absolute symbols from the outgoing symbol table. @item -v @itemx -version Print the @code{as} version. @item --version Print the @code{as} version and exit. @item -W @itemx --no-warn Suppress warning messages. @item --fatal-warnings Treat warnings as errors. @item --warn Don't suppress warning messages or treat them as errors. @item -w Ignored. @item -x Ignored. @item -Z Generate an object file even after errors. @item -- | @var{files} @dots{} Standard input, or source files to assemble. @end table @ifset ARC The following options are available when @value{AS} is configured for an ARC processor. @table @code @cindex ARC endianness @cindex endianness, ARC @cindex big endian output, ARC @item -mbig-endian Generate ``big endian'' format output. @cindex little endian output, ARC @item -mlittle-endian Generate ``little endian'' format output. @end table @end ifset @ifset ARM The following options are available when @value{AS} is configured for the ARM processor family. @table @code @item -m[arm][1|2|3|6|7|8|9][...] Specify which ARM processor variant is the target. @item -m[arm]v[2|2a|3|3m|4|4t|5|5t] Specify which ARM architecture variant is used by the target. @item -mthumb | -mall Enable or disable Thumb only instruction decoding. @item -mfpa10 | -mfpa11 | -mfpe-old | -mno-fpu Select which Floating Point architcture is the target. @item -mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant | -moabi Select which procedure calling convention is in use. @item -EB | -EL Select either big-endian (-EB) or little-endian (-EL) output. @item -mthumb-interwork Specify that the code has been generated with interworking between Thumb and ARM code in mind. @item -k Specify that PIC code has been generated. @end table @end ifset @ifset D10V The following options are available when @value{AS} is configured for a D10V processor. @table @code @cindex D10V optimization @cindex optimization, D10V @item -O Optimize output by parallelizing instructions. @end table @end ifset @ifset D30V The following options are available when @value{AS} is configured for a D30V processor. @table @code @cindex D30V optimization @cindex optimization, D30V @item -O Optimize output by parallelizing instructions. @cindex D30V nops @item -n Warn when nops are generated. @cindex D30V nops after 32-bit multiply @item -N Warn when a nop after a 32-bit multiply instruction is generated. @end table @end ifset @ifset I960 The following options are available when @value{AS} is configured for the Intel 80960 processor. @table @code @item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC Specify which variant of the 960 architecture is the target. @item -b Add code to collect statistics about branches taken. @item -no-relax Do not alter compare-and-branch instructions for long displacements; error if necessary. @end table @end ifset @ifset M32R The following options are available when @value{AS} is configured for the Mitsubishi M32R series. @table @code @item --m32rx Specify which processor in the M32R family is the target. The default is normally the M32R, but this option changes it to the M32RX. @item --warn-explicit-parallel-conflicts or --Wp Produce warning messages when questionable parallel constructs are encountered. @item --no-warn-explicit-parallel-conflicts or --Wnp Do not produce warning messages when questionable parallel constructs are encountered. @end table @end ifset @ifset M680X0 The following options are available when @value{AS} is configured for the Motorola 68000 series. @table @code @item -l Shorten references to undefined symbols, to one word instead of two. @item -m68000 | -m68008 | -m68010 | -m68020 | -m68030 | -m68040 | -m68060 @itemx | -m68302 | -m68331 | -m68332 | -m68333 | -m68340 | -mcpu32 | -m5200 Specify what processor in the 68000 family is the target. The default is normally the 68020, but this can be changed at configuration time. @item -m68881 | -m68882 | -mno-68881 | -mno-68882 The target machine does (or does not) have a floating-point coprocessor. The default is to assume a coprocessor for 68020, 68030, and cpu32. Although the basic 68000 is not compatible with the 68881, a combination of the two can be specified, since it's possible to do emulation of the coprocessor instructions with the main processor. @item -m68851 | -mno-68851 The target machine does (or does not) have a memory-management unit coprocessor. The default is to assume an MMU for 68020 and up. @end table @end ifset @ifset PJ The following options are available when @value{AS} is configured for a picoJava processor. @table @code @cindex PJ endianness @cindex endianness, PJ @cindex big endian output, PJ @item -mb Generate ``big endian'' format output. @cindex little endian output, PJ @item -ml Generate ``little endian'' format output. @end table @end ifset @ifset M68HC11 The following options are available when @value{AS} is configured for the Motorola 68HC11 or 68HC12 series. @table @code @item -m68hc11 | -m68hc12 Specify what processor is the target. The default is defined by the configuration option when building the assembler. @item --force-long-branchs Relative branches are turned into absolute ones. This concerns conditional branches, unconditional branches and branches to a sub routine. @item -S | --short-branchs Do not turn relative branchs into absolute ones when the offset is out of range. @item --strict-direct-mode Do not turn the direct addressing mode into extended addressing mode when the instruction does not support direct addressing mode. @item --print-insn-syntax Print the syntax of instruction in case of error. @item --print-opcodes print the list of instructions with syntax and then exit. @item --generate-example print an example of instruction for each possible instruction and then exit. This option is only useful for testing @code{@value{AS}}. @end table @end ifset @ifset SPARC The following options are available when @code{@value{AS}} is configured for the SPARC architecture: @table @code @item -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite @itemx -Av8plus | -Av8plusa | -Av9 | -Av9a Explicitly select a variant of the SPARC architecture. @samp{-Av8plus} and @samp{-Av8plusa} select a 32 bit environment. @samp{-Av9} and @samp{-Av9a} select a 64 bit environment. @samp{-Av8plusa} and @samp{-Av9a} enable the SPARC V9 instruction set with UltraSPARC extensions. @item -xarch=v8plus | -xarch=v8plusa For compatibility with the Solaris v9 assembler. These options are equivalent to -Av8plus and -Av8plusa, respectively. @item -bump Warn when the assembler switches to another architecture. @end table @end ifset @ifset TIC54X The following options are available when @value{AS} is configured for the 'c54x architecture. @table @code @item -mfar-mode Enable extended addressing mode. All addresses and relocations will assume extended addressing (usually 23 bits). @item -mcpu=@var{CPU_VERSION} Sets the CPU version being compiled for. @item -merrors-to-file @var{FILENAME} Redirect error output to a file, for broken systems which don't support such behaviour in the shell. @end table @end ifset @ifset MIPS The following options are available when @value{AS} is configured for a MIPS processor. @table @code @item -G @var{num} This option sets the largest size of an object that can be referenced implicitly with the @code{gp} register. It is only accepted for targets that use ECOFF format, such as a DECstation running Ultrix. The default value is 8. @cindex MIPS endianness @cindex endianness, MIPS @cindex big endian output, MIPS @item -EB Generate ``big endian'' format output. @cindex little endian output, MIPS @item -EL Generate ``little endian'' format output. @cindex MIPS ISA @item -mips1 @itemx -mips2 @itemx -mips3 Generate code for a particular MIPS Instruction Set Architecture level. @samp{-mips1} corresponds to the @sc{r2000} and @sc{r3000} processors, @samp{-mips2} to the @sc{r6000} processor, and @samp{-mips3} to the @sc{r4000} processor. @item -m4650 @itemx -no-m4650 Generate code for the MIPS @sc{r4650} chip. This tells the assembler to accept the @samp{mad} and @samp{madu} instruction, and to not schedule @samp{nop} instructions around accesses to the @samp{HI} and @samp{LO} registers. @samp{-no-m4650} turns off this option. @item -mcpu=@var{CPU} Generate code for a particular MIPS cpu. This has little effect on the assembler, but it is passed by @code{@value{GCC}}. @cindex emulation @item --emulation=@var{name} This option causes @code{@value{AS}} to emulate @code{@value{AS}} configured for some other target, in all respects, including output format (choosing between ELF and ECOFF only), handling of pseudo-opcodes which may generate debugging information or store symbol table information, and default endianness. The available configuration names are: @samp{mipsecoff}, @samp{mipself}, @samp{mipslecoff}, @samp{mipsbecoff}, @samp{mipslelf}, @samp{mipsbelf}. The first two do not alter the default endianness from that of the primary target for which the assembler was configured; the others change the default to little- or big-endian as indicated by the @samp{b} or @samp{l} in the name. Using @samp{-EB} or @samp{-EL} will override the endianness selection in any case. This option is currently supported only when the primary target @code{@value{AS}} is configured for is a MIPS ELF or ECOFF target. Furthermore, the primary target or others specified with @samp{--enable-targets=@dots{}} at configuration time must include support for the other format, if both are to be available. For example, the Irix 5 configuration includes support for both. Eventually, this option will support more configurations, with more fine-grained control over the assembler's behavior, and will be supported for more processors. @item -nocpp @code{@value{AS}} ignores this option. It is accepted for compatibility with the native tools. @need 900 @item --trap @itemx --no-trap @itemx --break @itemx --no-break Control how to deal with multiplication overflow and division by zero. @samp{--trap} or @samp{--no-break} (which are synonyms) take a trap exception (and only work for Instruction Set Architecture level 2 and higher); @samp{--break} or @samp{--no-trap} (also synonyms, and the default) take a break exception. @end table @end ifset @ifset MCORE The following options are available when @value{AS} is configured for an MCore processor. @table @code @item -jsri2bsr @itemx -nojsri2bsr Enable or disable the JSRI to BSR transformation. By default this is enabled. The command line option @samp{-nojsri2bsr} can be used to disable it. @item -sifilter @itemx -nosifilter Enable or disable the silicon filter behaviour. By default this is disabled. The default can be overidden by the @samp{-sifilter} command line option. @item -relax Alter jump instructions for long displacements. @item -mcpu=[210|340] Select the cpu type on the target hardware. This controls which instructions can be assembled. @item -EB Assemble for a big endian target. @item -EL Assemble for a little endian target. @end table @end ifset @menu * Manual:: Structure of this Manual * GNU Assembler:: The GNU Assembler * Object Formats:: Object File Formats * Command Line:: Command Line * Input Files:: Input Files * Object:: Output (Object) File * Errors:: Error and Warning Messages @end menu @node Manual @section Structure of this Manual @cindex manual, structure and purpose This manual is intended to describe what you need to know to use @sc{gnu} @code{@value{AS}}. We cover the syntax expected in source files, including notation for symbols, constants, and expressions; the directives that @code{@value{AS}} understands; and of course how to invoke @code{@value{AS}}. @ifclear GENERIC We also cover special features in the @value{TARGET} configuration of @code{@value{AS}}, including assembler directives. @end ifclear @ifset GENERIC This manual also describes some of the machine-dependent features of various flavors of the assembler. @end ifset @cindex machine instructions (not covered) On the other hand, this manual is @emph{not} intended as an introduction to programming in assembly language---let alone programming in general! In a similar vein, we make no attempt to introduce the machine architecture; we do @emph{not} describe the instruction set, standard mnemonics, registers or addressing modes that are standard to a particular architecture. @ifset GENERIC You may want to consult the manufacturer's machine architecture manual for this information. @end ifset @ifclear GENERIC @ifset H8/300 For information on the H8/300 machine instruction set, see @cite{H8/300 Series Programming Manual} (Hitachi ADE--602--025). For the H8/300H, see @cite{H8/300H Series Programming Manual} (Hitachi). @end ifset @ifset H8/500 For information on the H8/500 machine instruction set, see @cite{H8/500 Series Programming Manual} (Hitachi M21T001). @end ifset @ifset SH For information on the Hitachi SH machine instruction set, see @cite{SH-Microcomputer User's Manual} (Hitachi Micro Systems, Inc.). @end ifset @ifset Z8000 For information on the Z8000 machine instruction set, see @cite{Z8000 CPU Technical Manual} @end ifset @end ifclear @c I think this is premature---doc@cygnus.com, 17jan1991 @ignore Throughout this manual, we assume that you are running @dfn{GNU}, the portable operating system from the @dfn{Free Software Foundation, Inc.}. This restricts our attention to certain kinds of computer (in particular, the kinds of computers that @sc{gnu} can run on); once this assumption is granted examples and definitions need less qualification. @code{@value{AS}} is part of a team of programs that turn a high-level human-readable series of instructions into a low-level computer-readable series of instructions. Different versions of @code{@value{AS}} are used for different kinds of computer. @end ignore @c There used to be a section "Terminology" here, which defined @c "contents", "byte", "word", and "long". Defining "word" to any @c particular size is confusing when the .word directive may generate 16 @c bits on one machine and 32 bits on another; in general, for the user @c version of this manual, none of these terms seem essential to define. @c They were used very little even in the former draft of the manual; @c this draft makes an effort to avoid them (except in names of @c directives). @node GNU Assembler @section The GNU Assembler @sc{gnu} @code{as} is really a family of assemblers. @ifclear GENERIC This manual describes @code{@value{AS}}, a member of that family which is configured for the @value{TARGET} architectures. @end ifclear If you use (or have used) the @sc{gnu} assembler on one architecture, you should find a fairly similar environment when you use it on another architecture. Each version has much in common with the others, including object file formats, most assembler directives (often called @dfn{pseudo-ops}) and assembler syntax.@refill @cindex purpose of @sc{gnu} assembler @code{@value{AS}} is primarily intended to assemble the output of the @sc{gnu} C compiler @code{@value{GCC}} for use by the linker @code{@value{LD}}. Nevertheless, we've tried to make @code{@value{AS}} assemble correctly everything that other assemblers for the same machine would assemble. @ifset VAX Any exceptions are documented explicitly (@pxref{Machine Dependencies}). @end ifset @ifset M680X0 @c This remark should appear in generic version of manual; assumption @c here is that generic version sets M680x0. This doesn't mean @code{@value{AS}} always uses the same syntax as another assembler for the same architecture; for example, we know of several incompatible versions of 680x0 assembly language syntax. @end ifset Unlike older assemblers, @code{@value{AS}} is designed to assemble a source program in one pass of the source file. This has a subtle impact on the @kbd{.org} directive (@pxref{Org,,@code{.org}}). @node Object Formats @section Object File Formats @cindex object file format The @sc{gnu} assembler can be configured to produce several alternative object file formats. For the most part, this does not affect how you write assembly language programs; but directives for debugging symbols are typically different in different file formats. @xref{Symbol Attributes,,Symbol Attributes}. @ifclear GENERIC @ifclear MULTI-OBJ On the @value{TARGET}, @code{@value{AS}} is configured to produce @value{OBJ-NAME} format object files. @end ifclear @c The following should exhaust all configs that set MULTI-OBJ, ideally @ifset A29K On the @value{TARGET}, @code{@value{AS}} can be configured to produce either @code{a.out} or COFF format object files. @end ifset @ifset I960 On the @value{TARGET}, @code{@value{AS}} can be configured to produce either @code{b.out} or COFF format object files. @end ifset @ifset HPPA On the @value{TARGET}, @code{@value{AS}} can be configured to produce either SOM or ELF format object files. @end ifset @end ifclear @node Command Line @section Command Line @cindex command line conventions After the program name @code{@value{AS}}, the command line may contain options and file names. Options may appear in any order, and may be before, after, or between file names. The order of file names is significant. @cindex standard input, as input file @kindex -- @file{--} (two hyphens) by itself names the standard input file explicitly, as one of the files for @code{@value{AS}} to assemble. @cindex options, command line Except for @samp{--} any command line argument that begins with a hyphen (@samp{-}) is an option. Each option changes the behavior of @code{@value{AS}}. No option changes the way another option works. An option is a @samp{-} followed by one or more letters; the case of the letter is important. All options are optional. Some options expect exactly one file name to follow them. The file name may either immediately follow the option's letter (compatible with older assemblers) or it may be the next command argument (@sc{gnu} standard). These two command lines are equivalent: @smallexample @value{AS} -o my-object-file.o mumble.s @value{AS} -omy-object-file.o mumble.s @end smallexample @node Input Files @section Input Files @cindex input @cindex source program @cindex files, input We use the phrase @dfn{source program}, abbreviated @dfn{source}, to describe the program input to one run of @code{@value{AS}}. The program may be in one or more files; how the source is partitioned into files doesn't change the meaning of the source. @c I added "con" prefix to "catenation" just to prove I can overcome my @c APL training... doc@cygnus.com The source program is a concatenation of the text in all the files, in the order specified. Each time you run @code{@value{AS}} it assembles exactly one source program. The source program is made up of one or more files. (The standard input is also a file.) You give @code{@value{AS}} a command line that has zero or more input file names. The input files are read (from left file name to right). A command line argument (in any position) that has no special meaning is taken to be an input file name. If you give @code{@value{AS}} no file names it attempts to read one input file from the @code{@value{AS}} standard input, which is normally your terminal. You may have to type @key{ctl-D} to tell @code{@value{AS}} there is no more program to assemble. Use @samp{--} if you need to explicitly name the standard input file in your command line. If the source is empty, @code{@value{AS}} produces a small, empty object file. @subheading Filenames and Line-numbers @cindex input file linenumbers @cindex line numbers, in input files There are two ways of locating a line in the input file (or files) and either may be used in reporting error messages. One way refers to a line number in a physical file; the other refers to a line number in a ``logical'' file. @xref{Errors, ,Error and Warning Messages}. @dfn{Physical files} are those files named in the command line given to @code{@value{AS}}. @dfn{Logical files} are simply names declared explicitly by assembler directives; they bear no relation to physical files. Logical file names help error messages reflect the original source file, when @code{@value{AS}} source is itself synthesized from other files. @code{@value{AS}} understands the @samp{#} directives emitted by the @code{@value{GCC}} preprocessor. See also @ref{File,,@code{.file}}. @node Object @section Output (Object) File @cindex object file @cindex output file @kindex a.out @kindex .o Every time you run @code{@value{AS}} it produces an output file, which is your assembly language program translated into numbers. This file is the object file. Its default name is @ifclear BOUT @code{a.out}. @end ifclear @ifset BOUT @ifset GENERIC @code{a.out}, or @end ifset @code{b.out} when @code{@value{AS}} is configured for the Intel 80960. @end ifset You can give it another name by using the @code{-o} option. Conventionally, object file names end with @file{.o}. The default name is used for historical reasons: older assemblers were capable of assembling self-contained programs directly into a runnable program. (For some formats, this isn't currently possible, but it can be done for the @code{a.out} format.) @cindex linker @kindex ld The object file is meant for input to the linker @code{@value{LD}}. It contains assembled program code, information to help @code{@value{LD}} integrate the assembled program into a runnable file, and (optionally) symbolic information for the debugger. @c link above to some info file(s) like the description of a.out. @c don't forget to describe @sc{gnu} info as well as Unix lossage. @node Errors @section Error and Warning Messages @cindex error messsages @cindex warning messages @cindex messages from assembler @code{@value{AS}} may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs @code{@value{AS}} automatically. Warnings report an assumption made so that @code{@value{AS}} could keep assembling a flawed program; errors report a grave problem that stops the assembly. @cindex format of warning messages Warning messages have the format @smallexample file_name:@b{NNN}:Warning Message Text @end smallexample @noindent @cindex line numbers, in warnings/errors (where @b{NNN} is a line number). If a logical file name has been given (@pxref{File,,@code{.file}}) it is used for the filename, otherwise the name of the current input file is used. If a logical line number was given @ifset GENERIC (@pxref{Line,,@code{.line}}) @end ifset @ifclear GENERIC @ifclear A29K (@pxref{Line,,@code{.line}}) @end ifclear @ifset A29K (@pxref{Ln,,@code{.ln}}) @end ifset @end ifclear then it is used to calculate the number printed, otherwise the actual line in the current source file is printed. The message text is intended to be self explanatory (in the grand Unix tradition). @cindex format of error messages Error messages have the format @smallexample file_name:@b{NNN}:FATAL:Error Message Text @end smallexample The file name and line number are derived as for warning messages. The actual message text may be rather less explanatory because many of them aren't supposed to happen. @node Invoking @chapter Command-Line Options @cindex options, all versions of assembler This chapter describes command-line options available in @emph{all} versions of the @sc{gnu} assembler; @pxref{Machine Dependencies}, for options specific @ifclear GENERIC to the @value{TARGET}. @end ifclear @ifset GENERIC to particular machine architectures. @end ifset If you are invoking @code{@value{AS}} via the @sc{gnu} C compiler (version 2), you can use the @samp{-Wa} option to pass arguments through to the assembler. The assembler arguments must be separated from each other (and the @samp{-Wa}) by commas. For example: @smallexample gcc -c -g -O -Wa,-alh,-L file.c @end smallexample @noindent This passes two options to the assembler: @samp{-alh} (emit a listing to standard output with with high-level and assembly source) and @samp{-L} (retain local symbols in the symbol table). Usually you do not need to use this @samp{-Wa} mechanism, since many compiler command-line options are automatically passed to the assembler by the compiler. (You can call the @sc{gnu} compiler driver with the @samp{-v} option to see precisely what options it passes to each compilation pass, including the assembler.) @menu * a:: -a[cdhlns] enable listings * D:: -D for compatibility * f:: -f to work faster * I:: -I for .include search path @ifclear DIFF-TBL-KLUGE * K:: -K for compatibility @end ifclear @ifset DIFF-TBL-KLUGE * K:: -K for difference tables @end ifset * L:: -L to retain local labels * M:: -M or --mri to assemble in MRI compatibility mode * MD:: --MD for dependency tracking * o:: -o to name the object file * R:: -R to join data and text sections * statistics:: --statistics to see statistics about assembly * traditional-format:: --traditional-format for compatible output * v:: -v to announce version * W:: -W, --no-warn, --warn, --fatal-warnings to control warnings * Z:: -Z to make object file even after errors @end menu @node a @section Enable Listings: @code{-a[cdhlns]} @kindex -a @kindex -ac @kindex -ad @kindex -ah @kindex -al @kindex -an @kindex -as @cindex listings, enabling @cindex assembly listings, enabling These options enable listing output from the assembler. By itself, @samp{-a} requests high-level, assembly, and symbols listing. You can use other letters to select specific options for the list: @samp{-ah} requests a high-level language listing, @samp{-al} requests an output-program assembly listing, and @samp{-as} requests a symbol table listing. High-level listings require that a compiler debugging option like @samp{-g} be used, and that assembly listings (@samp{-al}) be requested also. Use the @samp{-ac} option to omit false conditionals from a listing. Any lines which are not assembled because of a false @code{.if} (or @code{.ifdef}, or any other conditional), or a true @code{.if} followed by an @code{.else}, will be omitted from the listing. Use the @samp{-ad} option to omit debugging directives from the listing. Once you have specified one of these options, you can further control listing output and its appearance using the directives @code{.list}, @code{.nolist}, @code{.psize}, @code{.eject}, @code{.title}, and @code{.sbttl}. The @samp{-an} option turns off all forms processing. If you do not request listing output with one of the @samp{-a} options, the listing-control directives have no effect. The letters after @samp{-a} may be combined into one option, @emph{e.g.}, @samp{-aln}. @node D @section @code{-D} @kindex -D This option has no effect whatsoever, but it is accepted to make it more likely that scripts written for other assemblers also work with @code{@value{AS}}. @node f @section Work Faster: @code{-f} @kindex -f @cindex trusted compiler @cindex faster processing (@code{-f}) @samp{-f} should only be used when assembling programs written by a (trusted) compiler. @samp{-f} stops the assembler from doing whitespace and comment preprocessing on the input file(s) before assembling them. @xref{Preprocessing, ,Preprocessing}. @quotation @emph{Warning:} if you use @samp{-f} when the files actually need to be preprocessed (if they contain comments, for example), @code{@value{AS}} does not work correctly. @end quotation @node I @section @code{.include} search path: @code{-I} @var{path} @kindex -I @var{path} @cindex paths for @code{.include} @cindex search path for @code{.include} @cindex @code{include} directive search path Use this option to add a @var{path} to the list of directories @code{@value{AS}} searches for files specified in @code{.include} directives (@pxref{Include,,@code{.include}}). You may use @code{-I} as many times as necessary to include a variety of paths. The current working directory is always searched first; after that, @code{@value{AS}} searches any @samp{-I} directories in the same order as they were specified (left to right) on the command line. @node K @section Difference Tables: @code{-K} @kindex -K @ifclear DIFF-TBL-KLUGE On the @value{TARGET} family, this option is allowed, but has no effect. It is permitted for compatibility with the @sc{gnu} assembler on other platforms, where it can be used to warn when the assembler alters the machine code generated for @samp{.word} directives in difference tables. The @value{TARGET} family does not have the addressing limitations that sometimes lead to this alteration on other platforms. @end ifclear @ifset DIFF-TBL-KLUGE @cindex difference tables, warning @cindex warning for altered difference tables @code{@value{AS}} sometimes alters the code emitted for directives of the form @samp{.word @var{sym1}-@var{sym2}}; @pxref{Word,,@code{.word}}. You can use the @samp{-K} option if you want a warning issued when this is done. @end ifset @node L @section Include Local Labels: @code{-L} @kindex -L @cindex local labels, retaining in output Labels beginning with @samp{L} (upper case only) are called @dfn{local labels}. @xref{Symbol Names}. Normally you do not see such labels when debugging, because they are intended for the use of programs (like compilers) that compose assembler programs, not for your notice. Normally both @code{@value{AS}} and @code{@value{LD}} discard such labels, so you do not normally debug with them. This option tells @code{@value{AS}} to retain those @samp{L@dots{}} symbols in the object file. Usually if you do this you also tell the linker @code{@value{LD}} to preserve symbols whose names begin with @samp{L}. By default, a local label is any label beginning with @samp{L}, but each target is allowed to redefine the local label prefix. @ifset HPPA On the HPPA local labels begin with @samp{L$}. @end ifset @node M @section Assemble in MRI Compatibility Mode: @code{-M} @kindex -M @cindex MRI compatibility mode The @code{-M} or @code{--mri} option selects MRI compatibility mode. This changes the syntax and pseudo-op handling of @code{@value{AS}} to make it compatible with the @code{ASM68K} or the @code{ASM960} (depending upon the configured target) assembler from Microtec Research. The exact nature of the MRI syntax will not be documented here; see the MRI manuals for more information. Note in particular that the handling of macros and macro arguments is somewhat different. The purpose of this option is to permit assembling existing MRI assembler code using @code{@value{AS}}. The MRI compatibility is not complete. Certain operations of the MRI assembler depend upon its object file format, and can not be supported using other object file formats. Supporting these would require enhancing each object file format individually. These are: @itemize @bullet @item global symbols in common section The m68k MRI assembler supports common sections which are merged by the linker. Other object file formats do not support this. @code{@value{AS}} handles common sections by treating them as a single common symbol. It permits local symbols to be defined within a common section, but it can not support global symbols, since it has no way to describe them. @item complex relocations The MRI assemblers support relocations against a negated section address, and relocations which combine the start addresses of two or more sections. These are not support by other object file formats. @item @code{END} pseudo-op specifying start address The MRI @code{END} pseudo-op permits the specification of a start address. This is not supported by other object file formats. The start address may instead be specified using the @code{-e} option to the linker, or in a linker script. @item @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops The MRI @code{IDNT}, @code{.ident} and @code{NAME} pseudo-ops assign a module name to the output file. This is not supported by other object file formats. @item @code{ORG} pseudo-op The m68k MRI @code{ORG} pseudo-op begins an absolute section at a given address. This differs from the usual @code{@value{AS}} @code{.org} pseudo-op, which changes the location within the current section. Absolute sections are not supported by other object file formats. The address of a section may be assigned within a linker script. @end itemize There are some other features of the MRI assembler which are not supported by @code{@value{AS}}, typically either because they are difficult or because they seem of little consequence. Some of these may be supported in future releases. @itemize @bullet @item EBCDIC strings EBCDIC strings are not supported. @item packed binary coded decimal Packed binary coded decimal is not supported. This means that the @code{DC.P} and @code{DCB.P} pseudo-ops are not supported. @item @code{FEQU} pseudo-op The m68k @code{FEQU} pseudo-op is not supported. @item @code{NOOBJ} pseudo-op The m68k @code{NOOBJ} pseudo-op is not supported. @item @code{OPT} branch control options The m68k @code{OPT} branch control options---@code{B}, @code{BRS}, @code{BRB}, @code{BRL}, and @code{BRW}---are ignored. @code{@value{AS}} automatically relaxes all branches, whether forward or backward, to an appropriate size, so these options serve no purpose. @item @code{OPT} list control options The following m68k @code{OPT} list control options are ignored: @code{C}, @code{CEX}, @code{CL}, @code{CRE}, @code{E}, @code{G}, @code{I}, @code{M}, @code{MEX}, @code{MC}, @code{MD}, @code{X}. @item other @code{OPT} options The following m68k @code{OPT} options are ignored: @code{NEST}, @code{O}, @code{OLD}, @code{OP}, @code{P}, @code{PCO}, @code{PCR}, @code{PCS}, @code{R}. @item @code{OPT} @code{D} option is default The m68k @code{OPT} @code{D} option is the default, unlike the MRI assembler. @code{OPT NOD} may be used to turn it off. @item @code{XREF} pseudo-op. The m68k @code{XREF} pseudo-op is ignored. @item @code{.debug} pseudo-op The i960 @code{.debug} pseudo-op is not supported. @item @code{.extended} pseudo-op The i960 @code{.extended} pseudo-op is not supported. @item @code{.list} pseudo-op. The various options of the i960 @code{.list} pseudo-op are not supported. @item @code{.optimize} pseudo-op The i960 @code{.optimize} pseudo-op is not supported. @item @code{.output} pseudo-op The i960 @code{.output} pseudo-op is not supported. @item @code{.setreal} pseudo-op The i960 @code{.setreal} pseudo-op is not supported. @end itemize @node MD @section Dependency tracking: @code{--MD} @kindex --MD @cindex dependency tracking @cindex make rules @code{@value{AS}} can generate a dependency file for the file it creates. This file consists of a single rule suitable for @code{make} describing the dependencies of the main source file. The rule is written to the file named in its argument. This feature is used in the automatic updating of makefiles. @node o @section Name the Object File: @code{-o} @kindex -o @cindex naming object file @cindex object file name There is always one object file output when you run @code{@value{AS}}. By default it has the name @ifset GENERIC @ifset I960 @file{a.out} (or @file{b.out}, for Intel 960 targets only). @end ifset @ifclear I960 @file{a.out}. @end ifclear @end ifset @ifclear GENERIC @ifset I960 @file{b.out}. @end ifset @ifclear I960 @file{a.out}. @end ifclear @end ifclear You use this option (which takes exactly one filename) to give the object file a different name. Whatever the object file is called, @code{@value{AS}} overwrites any existing file of the same name. @node R @section Join Data and Text Sections: @code{-R} @kindex -R @cindex data and text sections, joining @cindex text and data sections, joining @cindex joining text and data sections @cindex merging text and data sections @code{-R} tells @code{@value{AS}} to write the object file as if all data-section data lives in the text section. This is only done at the very last moment: your binary data are the same, but data section parts are relocated differently. The data section part of your object file is zero bytes long because all its bytes are appended to the text section. (@xref{Sections,,Sections and Relocation}.) When you specify @code{-R} it would be possible to generate shorter address displacements (because we do not have to cross between text and data section). We refrain from doing this simply for compatibility with older versions of @code{@value{AS}}. In future, @code{-R} may work this way. @ifset COFF When @code{@value{AS}} is configured for COFF output, this option is only useful if you use sections named @samp{.text} and @samp{.data}. @end ifset @ifset HPPA @code{-R} is not supported for any of the HPPA targets. Using @code{-R} generates a warning from @code{@value{AS}}. @end ifset @node statistics @section Display Assembly Statistics: @code{--statistics} @kindex --statistics @cindex statistics, about assembly @cindex time, total for assembly @cindex space used, maximum for assembly Use @samp{--statistics} to display two statistics about the resources used by @code{@value{AS}}: the maximum amount of space allocated during the assembly (in bytes), and the total execution time taken for the assembly (in @sc{cpu} seconds). @node traditional-format @section Compatible output: @code{--traditional-format} @kindex --traditional-format For some targets, the output of @code{@value{AS}} is different in some ways from the output of some existing assembler. This switch requests @code{@value{AS}} to use the traditional format instead. For example, it disables the exception frame optimizations which @code{@value{AS}} normally does by default on @code{@value{GCC}} output. @node v @section Announce Version: @code{-v} @kindex -v @kindex -version @cindex assembler version @cindex version of assembler You can find out what version of as is running by including the option @samp{-v} (which you can also spell as @samp{-version}) on the command line. @node W @section Control Warnings: @code{-W}, @code{--warn}, @code{--no-warn}, @code{--fatal-warnings} @code{@value{AS}} should never give a warning or error message when assembling compiler output. But programs written by people often cause @code{@value{AS}} to give a warning that a particular assumption was made. All such warnings are directed to the standard error file. @kindex @samp{-W} @kindex @samp{--no-warn} @cindex suppressing warnings @cindex warnings, suppressing If you use the @code{-W} and @code{--no-warn} options, no warnings are issued. This only affects the warning messages: it does not change any particular of how @code{@value{AS}} assembles your file. Errors, which stop the assembly, are still reported. @kindex @samp{--fatal-warnings} @cindex errors, caused by warnings @cindex warnings, causing error If you use the @code{--fatal-warnings} option, @code{@value{AS}} considers files that generate warnings to be in error. @kindex @samp{--warn} @cindex warnings, switching on You can switch these options off again by specifying @code{--warn}, which causes warnings to be output as usual. @node Z @section Generate Object File in Spite of Errors: @code{-Z} @cindex object file, after errors @cindex errors, continuing after After an error message, @code{@value{AS}} normally produces no output. If for some reason you are interested in object file output even after @code{@value{AS}} gives an error message on your program, use the @samp{-Z} option. If there are any errors, @code{@value{AS}} continues anyways, and writes an object file after a final warning message of the form @samp{@var{n} errors, @var{m} warnings, generating bad object file.} @node Syntax @chapter Syntax @cindex machine-independent syntax @cindex syntax, machine-independent This chapter describes the machine-independent syntax allowed in a source file. @code{@value{AS}} syntax is similar to what many other assemblers use; it is inspired by the BSD 4.2 @ifclear VAX assembler. @end ifclear @ifset VAX assembler, except that @code{@value{AS}} does not assemble Vax bit-fields. @end ifset @menu * Preprocessing:: Preprocessing * Whitespace:: Whitespace * Comments:: Comments * Symbol Intro:: Symbols * Statements:: Statements * Constants:: Constants @end menu @node Preprocessing @section Preprocessing @cindex preprocessing The @code{@value{AS}} internal preprocessor: @itemize @bullet @cindex whitespace, removed by preprocessor @item adjusts and removes extra whitespace. It leaves one space or tab before the keywords on a line, and turns any other whitespace on the line into a single space. @cindex comments, removed by preprocessor @item removes all comments, replacing them with a single space, or an appropriate number of newlines. @cindex constants, converted by preprocessor @item converts character constants into the appropriate numeric values. @end itemize It does not do macro processing, include file handling, or anything else you may get from your C compiler's preprocessor. You can do include file processing with the @code{.include} directive (@pxref{Include,,@code{.include}}). You can use the @sc{gnu} C compiler driver to get other ``CPP'' style preprocessing, by giving the input file a @samp{.S} suffix. @xref{Overall Options,, Options Controlling the Kind of Output, gcc.info, Using GNU CC}. Excess whitespace, comments, and character constants cannot be used in the portions of the input text that are not preprocessed. @cindex turning preprocessing on and off @cindex preprocessing, turning on and off @kindex #NO_APP @kindex #APP If the first line of an input file is @code{#NO_APP} or if you use the @samp{-f} option, whitespace and comments are not removed from the input file. Within an input file, you can ask for whitespace and comment removal in specific portions of the by putting a line that says @code{#APP} before the text that may contain whitespace or comments, and putting a line that says @code{#NO_APP} after this text. This feature is mainly intend to support @code{asm} statements in compilers whose output is otherwise free of comments and whitespace. @node Whitespace @section Whitespace @cindex whitespace @dfn{Whitespace} is one or more blanks or tabs, in any order. Whitespace is used to separate symbols, and to make programs neater for people to read. Unless within character constants (@pxref{Characters,,Character Constants}), any whitespace means the same as exactly one space. @node Comments @section Comments @cindex comments There are two ways of rendering comments to @code{@value{AS}}. In both cases the comment is equivalent to one space. Anything from @samp{/*} through the next @samp{*/} is a comment. This means you may not nest these comments. @smallexample /* The only way to include a newline ('\n') in a comment is to use this sort of comment. */ /* This sort of comment does not nest. */ @end smallexample @cindex line comment character Anything from the @dfn{line comment} character to the next newline is considered a comment and is ignored. The line comment character is @ifset A29K @samp{;} for the AMD 29K family; @end ifset @ifset ARC @samp{;} on the ARC; @end ifset @ifset ARM @samp{@@} on the ARM; @end ifset @ifset H8/300 @samp{;} for the H8/300 family; @end ifset @ifset H8/500 @samp{!} for the H8/500 family; @end ifset @ifset HPPA @samp{;} for the HPPA; @end ifset @ifset I960 @samp{#} on the i960; @end ifset @ifset PJ @samp{;} for picoJava; @end ifset @ifset SH @samp{!} for the Hitachi SH; @end ifset @ifset SPARC @samp{!} on the SPARC; @end ifset @ifset M32R @samp{#} on the m32r; @end ifset @ifset M680X0 @samp{|} on the 680x0; @end ifset @ifset M68HC11 @samp{#} on the 68HC11 and 68HC12; @end ifset @ifset VAX @samp{#} on the Vax; @end ifset @ifset Z8000 @samp{!} for the Z8000; @end ifset @ifset V850 @samp{#} on the V850; @end ifset see @ref{Machine Dependencies}. @refill @c FIXME What about i386, m88k, i860? @ifset GENERIC On some machines there are two different line comment characters. One character only begins a comment if it is the first non-whitespace character on a line, while the other always begins a comment. @end ifset @ifset V850 The V850 assembler also supports a double dash as starting a comment that extends to the end of the line. @samp{--}; @end ifset @kindex # @cindex lines starting with @code{#} @cindex logical line numbers To be compatible with past assemblers, lines that begin with @samp{#} have a special interpretation. Following the @samp{#} should be an absolute expression (@pxref{Expressions}): the logical line number of the @emph{next} line. Then a string (@pxref{Strings,, Strings}) is allowed: if present it is a new logical file name. The rest of the line, if any, should be whitespace. If the first non-whitespace characters on the line are not numeric, the line is ignored. (Just like a comment.) @smallexample # This is an ordinary comment. # 42-6 "new_file_name" # New logical file name # This is logical line # 36. @end smallexample This feature is deprecated, and may disappear from future versions of @code{@value{AS}}. @node Symbol Intro @section Symbols @cindex characters used in symbols @ifclear SPECIAL-SYMS A @dfn{symbol} is one or more characters chosen from the set of all letters (both upper and lower case), digits and the three characters @samp{_.$}. @end ifclear @ifset SPECIAL-SYMS @ifclear GENERIC @ifset H8 A @dfn{symbol} is one or more characters chosen from the set of all letters (both upper and lower case), digits and the three characters @samp{._$}. (Save that, on the H8/300 only, you may not use @samp{$} in symbol names.) @end ifset @end ifclear @end ifset @ifset GENERIC On most machines, you can also use @code{$} in symbol names; exceptions are noted in @ref{Machine Dependencies}. @end ifset No symbol may begin with a digit. Case is significant. There is no length limit: all characters are significant. Symbols are delimited by characters not in that set, or by the beginning of a file (since the source program must end with a newline, the end of a file is not a possible symbol delimiter). @xref{Symbols}. @cindex length of symbols @node Statements @section Statements @cindex statements, structure of @cindex line separator character @cindex statement separator character @ifclear GENERIC @ifclear abnormal-separator A @dfn{statement} ends at a newline character (@samp{\n}) or at a semicolon (@samp{;}). The newline or semicolon is considered part of the preceding statement. Newlines and semicolons within character constants are an exception: they do not end statements. @end ifclear @ifset abnormal-separator @ifset A29K A @dfn{statement} ends at a newline character (@samp{\n}) or an ``at'' sign (@samp{@@}). The newline or at sign is considered part of the preceding statement. Newlines and at signs within character constants are an exception: they do not end statements. @end ifset @ifset HPPA A @dfn{statement} ends at a newline character (@samp{\n}) or an exclamation point (@samp{!}). The newline or exclamation point is considered part of the preceding statement. Newlines and exclamation points within character constants are an exception: they do not end statements. @end ifset @ifset H8 A @dfn{statement} ends at a newline character (@samp{\n}); or (for the H8/300) a dollar sign (@samp{$}); or (for the Hitachi-SH or the H8/500) a semicolon (@samp{;}). The newline or separator character is considered part of the preceding statement. Newlines and separators within character constants are an exception: they do not end statements. @end ifset @end ifset @end ifclear @ifset GENERIC A @dfn{statement} ends at a newline character (@samp{\n}) or line separator character. (The line separator is usually @samp{;}, unless this conflicts with the comment character; @pxref{Machine Dependencies}.) The newline or separator character is considered part of the preceding statement. Newlines and separators within character constants are an exception: they do not end statements. @end ifset @cindex newline, required at file end @cindex EOF, newline must precede It is an error to end any statement with end-of-file: the last character of any input file should be a newline.@refill An empty statement is allowed, and may include whitespace. It is ignored. @cindex instructions and directives @cindex directives and instructions @c "key symbol" is not used elsewhere in the document; seems pedantic to @c @defn{} it in that case, as was done previously... doc@cygnus.com, @c 13feb91. A statement begins with zero or more labels, optionally followed by a key symbol which determines what kind of statement it is. The key symbol determines the syntax of the rest of the statement. If the symbol begins with a dot @samp{.} then the statement is an assembler directive: typically valid for any computer. If the symbol begins with a letter the statement is an assembly language @dfn{instruction}: it assembles into a machine language instruction. @ifset GENERIC Different versions of @code{@value{AS}} for different computers recognize different instructions. In fact, the same symbol may represent a different instruction in a different computer's assembly language.@refill @end ifset @cindex @code{:} (label) @cindex label (@code{:}) A label is a symbol immediately followed by a colon (@code{:}). Whitespace before a label or after a colon is permitted, but you may not have whitespace between a label's symbol and its colon. @xref{Labels}. @ifset HPPA For HPPA targets, labels need not be immediately followed by a colon, but the definition of a label must begin in column zero. This also implies that only one label may be defined on each line. @end ifset @smallexample label: .directive followed by something another_label: # This is an empty statement. instruction operand_1, operand_2, @dots{} @end smallexample @node Constants @section Constants @cindex constants A constant is a number, written so that its value is known by inspection, without knowing any context. Like this: @smallexample @group .byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value. .ascii "Ring the bell\7" # A string constant. .octa 0x123456789abcdef0123456789ABCDEF0 # A bignum. .float 0f-314159265358979323846264338327\ 95028841971.693993751E-40 # - pi, a flonum. @end group @end smallexample @menu * Characters:: Character Constants * Numbers:: Number Constants @end menu @node Characters @subsection Character Constants @cindex character constants @cindex constants, character There are two kinds of character constants. A @dfn{character} stands for one character in one byte and its value may be used in numeric expressions. String constants (properly called string @emph{literals}) are potentially many bytes and their values may not be used in arithmetic expressions. @menu * Strings:: Strings * Chars:: Characters @end menu @node Strings @subsubsection Strings @cindex string constants @cindex constants, string A @dfn{string} is written between double-quotes. It may contain double-quotes or null characters. The way to get special characters into a string is to @dfn{escape} these characters: precede them with a backslash @samp{\} character. For example @samp{\\} represents one backslash: the first @code{\} is an escape which tells @code{@value{AS}} to interpret the second character literally as a backslash (which prevents @code{@value{AS}} from recognizing the second @code{\} as an escape character). The complete list of escapes follows. @cindex escape codes, character @cindex character escape codes @table @kbd @c @item \a @c Mnemonic for ACKnowledge; for ASCII this is octal code 007. @c @cindex @code{\b} (backspace character) @cindex backspace (@code{\b}) @item \b Mnemonic for backspace; for ASCII this is octal code 010. @c @item \e @c Mnemonic for EOText; for ASCII this is octal code 004. @c @cindex @code{\f} (formfeed character) @cindex formfeed (@code{\f}) @item \f Mnemonic for FormFeed; for ASCII this is octal code 014. @cindex @code{\n} (newline character) @cindex newline (@code{\n}) @item \n Mnemonic for newline; for ASCII this is octal code 012. @c @item \p @c Mnemonic for prefix; for ASCII this is octal code 033, usually known as @code{escape}. @c @cindex @code{\r} (carriage return character) @cindex carriage return (@code{\r}) @item \r Mnemonic for carriage-Return; for ASCII this is octal code 015. @c @item \s @c Mnemonic for space; for ASCII this is octal code 040. Included for compliance with @c other assemblers. @c @cindex @code{\t} (tab) @cindex tab (@code{\t}) @item \t Mnemonic for horizontal Tab; for ASCII this is octal code 011. @c @item \v @c Mnemonic for Vertical tab; for ASCII this is octal code 013. @c @item \x @var{digit} @var{digit} @var{digit} @c A hexadecimal character code. The numeric code is 3 hexadecimal digits. @c @cindex @code{\@var{ddd}} (octal character code) @cindex octal character code (@code{\@var{ddd}}) @item \ @var{digit} @var{digit} @var{digit} An octal character code. The numeric code is 3 octal digits. For compatibility with other Unix systems, 8 and 9 are accepted as digits: for example, @code{\008} has the value 010, and @code{\009} the value 011. @cindex @code{\@var{xd...}} (hex character code) @cindex hex character code (@code{\@var{xd...}}) @item \@code{x} @var{hex-digits...} A hex character code. All trailing hex digits are combined. Either upper or lower case @code{x} works. @cindex @code{\\} (@samp{\} character) @cindex backslash (@code{\\}) @item \\ Represents one @samp{\} character. @c @item \' @c Represents one @samp{'} (accent acute) character. @c This is needed in single character literals @c (@xref{Characters,,Character Constants}.) to represent @c a @samp{'}. @c @cindex @code{\"} (doublequote character) @cindex doublequote (@code{\"}) @item \" Represents one @samp{"} character. Needed in strings to represent this character, because an unescaped @samp{"} would end the string. @item \ @var{anything-else} Any other character when escaped by @kbd{\} gives a warning, but assembles as if the @samp{\} was not present. The idea is that if you used an escape sequence you clearly didn't want the literal interpretation of the following character. However @code{@value{AS}} has no other interpretation, so @code{@value{AS}} knows it is giving you the wrong code and warns you of the fact. @end table Which characters are escapable, and what those escapes represent, varies widely among assemblers. The current set is what we think the BSD 4.2 assembler recognizes, and is a subset of what most C compilers recognize. If you are in doubt, do not use an escape sequence. @node Chars @subsubsection Characters @cindex single character constant @cindex character, single @cindex constant, single character A single character may be written as a single quote immediately followed by that character. The same escapes apply to characters as to strings. So if you want to write the character backslash, you must write @kbd{'\\} where the first @code{\} escapes the second @code{\}. As you can see, the quote is an acute accent, not a grave accent. A newline @ifclear GENERIC @ifclear abnormal-separator (or semicolon @samp{;}) @end ifclear @ifset abnormal-separator @ifset A29K (or at sign @samp{@@}) @end ifset @ifset H8 (or dollar sign @samp{$}, for the H8/300; or semicolon @samp{;} for the Hitachi SH or H8/500) @end ifset @end ifset @end ifclear immediately following an acute accent is taken as a literal character and does not count as the end of a statement. The value of a character constant in a numeric expression is the machine's byte-wide code for that character. @code{@value{AS}} assumes your character code is ASCII: @kbd{'A} means 65, @kbd{'B} means 66, and so on. @refill @node Numbers @subsection Number Constants @cindex constants, number @cindex number constants @code{@value{AS}} distinguishes three kinds of numbers according to how they are stored in the target machine. @emph{Integers} are numbers that would fit into an @code{int} in the C language. @emph{Bignums} are integers, but they are stored in more than 32 bits. @emph{Flonums} are floating point numbers, described below. @menu * Integers:: Integers * Bignums:: Bignums * Flonums:: Flonums @ifclear GENERIC @ifset I960 * Bit Fields:: Bit Fields @end ifset @end ifclear @end menu @node Integers @subsubsection Integers @cindex integers @cindex constants, integer @cindex binary integers @cindex integers, binary A binary integer is @samp{0b} or @samp{0B} followed by zero or more of the binary digits @samp{01}. @cindex octal integers @cindex integers, octal An octal integer is @samp{0} followed by zero or more of the octal digits (@samp{01234567}). @cindex decimal integers @cindex integers, decimal A decimal integer starts with a non-zero digit followed by zero or more digits (@samp{0123456789}). @cindex hexadecimal integers @cindex integers, hexadecimal A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}. Integers have the usual values. To denote a negative integer, use the prefix operator @samp{-} discussed under expressions (@pxref{Prefix Ops,,Prefix Operators}). @node Bignums @subsubsection Bignums @cindex bignums @cindex constants, bignum A @dfn{bignum} has the same syntax and semantics as an integer except that the number (or its negative) takes more than 32 bits to represent in binary. The distinction is made because in some places integers are permitted while bignums are not. @node Flonums @subsubsection Flonums @cindex flonums @cindex floating point numbers @cindex constants, floating point @cindex precision, floating point A @dfn{flonum} represents a floating point number. The translation is indirect: a decimal floating point number from the text is converted by @code{@value{AS}} to a generic binary floating point number of more than sufficient precision. This generic floating point number is converted to a particular computer's floating point format (or formats) by a portion of @code{@value{AS}} specialized to that computer. A flonum is written by writing (in order) @itemize @bullet @item The digit @samp{0}. @ifset HPPA (@samp{0} is optional on the HPPA.) @end ifset @item A letter, to tell @code{@value{AS}} the rest of the number is a flonum. @ifset GENERIC @kbd{e} is recommended. Case is not important. @ignore @c FIXME: verify if flonum syntax really this vague for most cases (Any otherwise illegal letter works here, but that might be changed. Vax BSD 4.2 assembler seems to allow any of @samp{defghDEFGH}.) @end ignore On the H8/300, H8/500, Hitachi SH, and AMD 29K architectures, the letter must be one of the letters @samp{DFPRSX} (in upper or lower case). On the ARC, the letter must be one of the letters @samp{DFRS} (in upper or lower case). On the Intel 960 architecture, the letter must be one of the letters @samp{DFT} (in upper or lower case). On the HPPA architecture, the letter must be @samp{E} (upper case only). @end ifset @ifclear GENERIC @ifset A29K One of the letters @samp{DFPRSX} (in upper or lower case). @end ifset @ifset ARC One of the letters @samp{DFRS} (in upper or lower case). @end ifset @ifset H8 One of the letters @samp{DFPRSX} (in upper or lower case). @end ifset @ifset HPPA The letter @samp{E} (upper case only). @end ifset @ifset I960 One of the letters @samp{DFT} (in upper or lower case). @end ifset @end ifclear @item An optional sign: either @samp{+} or @samp{-}. @item An optional @dfn{integer part}: zero or more decimal digits. @item An optional @dfn{fractional part}: @samp{.} followed by zero or more decimal digits. @item An optional exponent, consisting of: @itemize @bullet @item An @samp{E} or @samp{e}. @c I can't find a config where "EXP_CHARS" is other than 'eE', but in @c principle this can perfectly well be different on different targets. @item Optional sign: either @samp{+} or @samp{-}. @item One or more decimal digits. @end itemize @end itemize At least one of the integer part or the fractional part must be present. The floating point number has the usual base-10 value. @code{@value{AS}} does all processing using integers. Flonums are computed independently of any floating point hardware in the computer running @code{@value{AS}}. @ifclear GENERIC @ifset I960 @c Bit fields are written as a general facility but are also controlled @c by a conditional-compilation flag---which is as of now (21mar91) @c turned on only by the i960 config of GAS. @node Bit Fields @subsubsection Bit Fields @cindex bit fields @cindex constants, bit field You can also define numeric constants as @dfn{bit fields}. specify two numbers separated by a colon--- @example @var{mask}:@var{value} @end example @noindent @code{@value{AS}} applies a bitwise @sc{and} between @var{mask} and @var{value}. The resulting number is then packed @ifset GENERIC @c this conditional paren in case bit fields turned on elsewhere than 960 (in host-dependent byte order) @end ifset into a field whose width depends on which assembler directive has the bit-field as its argument. Overflow (a result from the bitwise and requiring more binary digits to represent) is not an error; instead, more constants are generated, of the specified width, beginning with the least significant digits.@refill The directives @code{.byte}, @code{.hword}, @code{.int}, @code{.long}, @code{.short}, and @code{.word} accept bit-field arguments. @end ifset @end ifclear @node Sections @chapter Sections and Relocation @cindex sections @cindex relocation @menu * Secs Background:: Background * Ld Sections:: Linker Sections * As Sections:: Assembler Internal Sections * Sub-Sections:: Sub-Sections * bss:: bss Section @end menu @node Secs Background @section Background Roughly, a section is a range of addresses, with no gaps; all data ``in'' those addresses is treated the same for some particular purpose. For example there may be a ``read only'' section. @cindex linker, and assembler @cindex assembler, and linker The linker @code{@value{LD}} reads many object files (partial programs) and combines their contents to form a runnable program. When @code{@value{AS}} emits an object file, the partial program is assumed to start at address 0. @code{@value{LD}} assigns the final addresses for the partial program, so that different partial programs do not overlap. This is actually an oversimplification, but it suffices to explain how @code{@value{AS}} uses sections. @code{@value{LD}} moves blocks of bytes of your program to their run-time addresses. These blocks slide to their run-time addresses as rigid units; their length does not change and neither does the order of bytes within them. Such a rigid unit is called a @emph{section}. Assigning run-time addresses to sections is called @dfn{relocation}. It includes the task of adjusting mentions of object-file addresses so they refer to the proper run-time addresses. @ifset H8 For the H8/300 and H8/500, and for the Hitachi SH, @code{@value{AS}} pads sections if needed to ensure they end on a word (sixteen bit) boundary. @end ifset @cindex standard assembler sections An object file written by @code{@value{AS}} has at least three sections, any of which may be empty. These are named @dfn{text}, @dfn{data} and @dfn{bss} sections. @ifset COFF @ifset GENERIC When it generates COFF output, @end ifset @code{@value{AS}} can also generate whatever other named sections you specify using the @samp{.section} directive (@pxref{Section,,@code{.section}}). If you do not use any directives that place output in the @samp{.text} or @samp{.data} sections, these sections still exist, but are empty. @end ifset @ifset HPPA @ifset GENERIC When @code{@value{AS}} generates SOM or ELF output for the HPPA, @end ifset @code{@value{AS}} can also generate whatever other named sections you specify using the @samp{.space} and @samp{.subspace} directives. See @cite{HP9000 Series 800 Assembly Language Reference Manual} (HP 92432-90001) for details on the @samp{.space} and @samp{.subspace} assembler directives. @ifset SOM Additionally, @code{@value{AS}} uses different names for the standard text, data, and bss sections when generating SOM output. Program text is placed into the @samp{$CODE$} section, data into @samp{$DATA$}, and BSS into @samp{$BSS$}. @end ifset @end ifset Within the object file, the text section starts at address @code{0}, the data section follows, and the bss section follows the data section. @ifset HPPA When generating either SOM or ELF output files on the HPPA, the text section starts at address @code{0}, the data section at address @code{0x4000000}, and the bss section follows the data section. @end ifset To let @code{@value{LD}} know which data changes when the sections are relocated, and how to change that data, @code{@value{AS}} also writes to the object file details of the relocation needed. To perform relocation @code{@value{LD}} must know, each time an address in the object file is mentioned: @itemize @bullet @item Where in the object file is the beginning of this reference to an address? @item How long (in bytes) is this reference? @item Which section does the address refer to? What is the numeric value of @display (@var{address}) @minus{} (@var{start-address of section})? @end display @item Is the reference to an address ``Program-Counter relative''? @end itemize @cindex addresses, format of @cindex section-relative addressing In fact, every address @code{@value{AS}} ever uses is expressed as @display (@var{section}) + (@var{offset into section}) @end display @noindent Further, most expressions @code{@value{AS}} computes have this section-relative nature. @ifset SOM (For some object formats, such as SOM for the HPPA, some expressions are symbol-relative instead.) @end ifset In this manual we use the notation @{@var{secname} @var{N}@} to mean ``offset @var{N} into section @var{secname}.'' Apart from text, data and bss sections you need to know about the @dfn{absolute} section. When @code{@value{LD}} mixes partial programs, addresses in the absolute section remain unchanged. For example, address @code{@{absolute 0@}} is ``relocated'' to run-time address 0 by @code{@value{LD}}. Although the linker never arranges two partial programs' data sections with overlapping addresses after linking, @emph{by definition} their absolute sections must overlap. Address @code{@{absolute@ 239@}} in one part of a program is always the same address when the program is running as address @code{@{absolute@ 239@}} in any other part of the program. The idea of sections is extended to the @dfn{undefined} section. Any address whose section is unknown at assembly time is by definition rendered @{undefined @var{U}@}---where @var{U} is filled in later. Since numbers are always defined, the only way to generate an undefined address is to mention an undefined symbol. A reference to a named common block would be such a symbol: its value is unknown at assembly time so it has section @emph{undefined}. By analogy the word @emph{section} is used to describe groups of sections in the linked program. @code{@value{LD}} puts all partial programs' text sections in contiguous addresses in the linked program. It is customary to refer to the @emph{text section} of a program, meaning all the addresses of all partial programs' text sections. Likewise for data and bss sections. Some sections are manipulated by @code{@value{LD}}; others are invented for use of @code{@value{AS}} and have no meaning except during assembly. @node Ld Sections @section Linker Sections @code{@value{LD}} deals with just four kinds of sections, summarized below. @table @strong @ifset COFF @cindex named sections @cindex sections, named @item named sections @end ifset @ifset aout-bout @cindex text section @cindex data section @itemx text section @itemx data section @end ifset These sections hold your program. @code{@value{AS}} and @code{@value{LD}} treat them as separate but equal sections. Anything you can say of one section is true another. @ifset aout-bout When the program is running, however, it is customary for the text section to be unalterable. The text section is often shared among processes: it contains instructions, constants and the like. The data section of a running program is usually alterable: for example, C variables would be stored in the data section. @end ifset @cindex bss section @item bss section This section contains zeroed bytes when your program begins running. It is used to hold unitialized variables or common storage. The length of each partial program's bss section is important, but because it starts out containing zeroed bytes there is no need to store explicit zero bytes in the object file. The bss section was invented to eliminate those explicit zeros from object files. @cindex absolute section @item absolute section Address 0 of this section is always ``relocated'' to runtime address 0. This is useful if you want to refer to an address that @code{@value{LD}} must not change when relocating. In this sense we speak of absolute addresses being ``unrelocatable'': they do not change during relocation. @cindex undefined section @item undefined section This ``section'' is a catch-all for address references to objects not in the preceding sections. @c FIXME: ref to some other doc on obj-file formats could go here. @end table @cindex relocation example An idealized example of three relocatable sections follows. @ifset COFF The example uses the traditional section names @samp{.text} and @samp{.data}. @end ifset Memory addresses are on the horizontal axis. @c TEXI2ROFF-KILL @ifinfo @c END TEXI2ROFF-KILL @smallexample +-----+----+--+ partial program # 1: |ttttt|dddd|00| +-----+----+--+ text data bss seg. seg. seg. +---+---+---+ partial program # 2: |TTT|DDD|000| +---+---+---+ +--+---+-----+--+----+---+-----+~~ linked program: | |TTT|ttttt| |dddd|DDD|00000| +--+---+-----+--+----+---+-----+~~ addresses: 0 @dots{} @end smallexample @c TEXI2ROFF-KILL @end ifinfo @need 5000 @tex \line{\it Partial program \#1: \hfil} \line{\ibox{2.5cm}{\tt text}\ibox{2cm}{\tt data}\ibox{1cm}{\tt bss}\hfil} \line{\boxit{2.5cm}{\tt ttttt}\boxit{2cm}{\tt dddd}\boxit{1cm}{\tt 00}\hfil} \line{\it Partial program \#2: \hfil} \line{\ibox{1cm}{\tt text}\ibox{1.5cm}{\tt data}\ibox{1cm}{\tt bss}\hfil} \line{\boxit{1cm}{\tt TTT}\boxit{1.5cm}{\tt DDDD}\boxit{1cm}{\tt 000}\hfil} \line{\it linked program: \hfil} \line{\ibox{.5cm}{}\ibox{1cm}{\tt text}\ibox{2.5cm}{}\ibox{.75cm}{}\ibox{2cm}{\tt data}\ibox{1.5cm}{}\ibox{2cm}{\tt bss}\hfil} \line{\boxit{.5cm}{}\boxit{1cm}{\tt TTT}\boxit{2.5cm}{\tt ttttt}\boxit{.75cm}{}\boxit{2cm}{\tt dddd}\boxit{1.5cm}{\tt DDDD}\boxit{2cm}{\tt 00000}\ \dots\hfil} \line{\it addresses: \hfil} \line{0\dots\hfil} @end tex @c END TEXI2ROFF-KILL @node As Sections @section Assembler Internal Sections @cindex internal assembler sections @cindex sections in messages, internal These sections are meant only for the internal use of @code{@value{AS}}. They have no meaning at run-time. You do not really need to know about these sections for most purposes; but they can be mentioned in @code{@value{AS}} warning messages, so it might be helpful to have an idea of their meanings to @code{@value{AS}}. These sections are used to permit the value of every expression in your assembly language program to be a section-relative address. @table @b @cindex assembler internal logic error @item ASSEMBLER-INTERNAL-LOGIC-ERROR! An internal assembler logic error has been found. This means there is a bug in the assembler. @cindex expr (internal section) @item expr section The assembler stores complex expression internally as combinations of symbols. When it needs to represent an expression as a symbol, it puts it in the expr section. @c FIXME item debug @c FIXME item transfer[t] vector preload @c FIXME item transfer[t] vector postload @c FIXME item register @end table @node Sub-Sections @section Sub-Sections @cindex numbered subsections @cindex grouping data @ifset aout-bout Assembled bytes @ifset COFF conventionally @end ifset fall into two sections: text and data. @end ifset You may have separate groups of @ifset GENERIC data in named sections @end ifset @ifclear GENERIC @ifclear aout-bout data in named sections @end ifclear @ifset aout-bout text or data @end ifset @end ifclear that you want to end up near to each other in the object file, even though they are not contiguous in the assembler source. @code{@value{AS}} allows you to use @dfn{subsections} for this purpose. Within each section, there can be numbered subsections with values from 0 to 8192. Objects assembled into the same subsection go into the object file together with other objects in the same subsection. For example, a compiler might want to store constants in the text section, but might not want to have them interspersed with the program being assembled. In this case, the compiler could issue a @samp{.text 0} before each section of code being output, and a @samp{.text 1} before each group of constants being output. Subsections are optional. If you do not use subsections, everything goes in subsection number zero. @ifset GENERIC Each subsection is zero-padded up to a multiple of four bytes. (Subsections may be padded a different amount on different flavors of @code{@value{AS}}.) @end ifset @ifclear GENERIC @ifset H8 On the H8/300 and H8/500 platforms, each subsection is zero-padded to a word boundary (two bytes). The same is true on the Hitachi SH. @end ifset @ifset I960 @c FIXME section padding (alignment)? @c Rich Pixley says padding here depends on target obj code format; that @c doesn't seem particularly useful to say without further elaboration, @c so for now I say nothing about it. If this is a generic BFD issue, @c these paragraphs might need to vanish from this manual, and be @c discussed in BFD chapter of binutils (or some such). @end ifset @ifset A29K On the AMD 29K family, no particular padding is added to section or subsection sizes; @value{AS} forces no alignment on this platform. @end ifset @end ifclear Subsections appear in your object file in numeric order, lowest numbered to highest. (All this to be compatible with other people's assemblers.) The object file contains no representation of subsections; @code{@value{LD}} and other programs that manipulate object files see no trace of them. They just see all your text subsections as a text section, and all your data subsections as a data section. To specify which subsection you want subsequent statements assembled into, use a numeric argument to specify it, in a @samp{.text @var{expression}} or a @samp{.data @var{expression}} statement. @ifset COFF @ifset GENERIC When generating COFF output, you @end ifset @ifclear GENERIC You @end ifclear can also use an extra subsection argument with arbitrary named sections: @samp{.section @var{name}, @var{expression}}. @end ifset @var{Expression} should be an absolute expression. (@xref{Expressions}.) If you just say @samp{.text} then @samp{.text 0} is assumed. Likewise @samp{.data} means @samp{.data 0}. Assembly begins in @code{text 0}. For instance: @smallexample .text 0 # The default subsection is text 0 anyway. .ascii "This lives in the first text subsection. *" .text 1 .ascii "But this lives in the second text subsection." .data 0 .ascii "This lives in the data section," .ascii "in the first data subsection." .text 0 .ascii "This lives in the first text section," .ascii "immediately following the asterisk (*)." @end smallexample Each section has a @dfn{location counter} incremented by one for every byte assembled into that section. Because subsections are merely a convenience restricted to @code{@value{AS}} there is no concept of a subsection location counter. There is no way to directly manipulate a location counter---but the @code{.align} directive changes it, and any label definition captures its current value. The location counter of the section where statements are being assembled is said to be the @dfn{active} location counter. @node bss @section bss Section @cindex bss section @cindex common variable storage The bss section is used for local common variable storage. You may allocate address space in the bss section, but you may not dictate data to load into it before your program executes. When your program starts running, all the contents of the bss section are zeroed bytes. The @code{.lcomm} pseudo-op defines a symbol in the bss section; see @ref{Lcomm,,@code{.lcomm}}. The @code{.comm} pseudo-op may be used to declare a common symbol, which is another form of uninitialized symbol; see @xref{Comm,,@code{.comm}}. @ifset GENERIC When assembling for a target which supports multiple sections, such as ELF or COFF, you may switch into the @code{.bss} section and define symbols as usual; see @ref{Section,,@code{.section}}. You may only assemble zero values into the section. Typically the section will only contain symbol definitions and @code{.skip} directives (@pxref{Skip,,@code{.skip}}). @end ifset @node Symbols @chapter Symbols @cindex symbols Symbols are a central concept: the programmer uses symbols to name things, the linker uses symbols to link, and the debugger uses symbols to debug. @quotation @cindex debuggers, and symbol order @emph{Warning:} @code{@value{AS}} does not place symbols in the object file in the same order they were declared. This may break some debuggers. @end quotation @menu * Labels:: Labels * Setting Symbols:: Giving Symbols Other Values * Symbol Names:: Symbol Names * Dot:: The Special Dot Symbol * Symbol Attributes:: Symbol Attributes @end menu @node Labels @section Labels @cindex labels A @dfn{label} is written as a symbol immediately followed by a colon @samp{:}. The symbol then represents the current value of the active location counter, and is, for example, a suitable instruction operand. You are warned if you use the same symbol to represent two different locations: the first definition overrides any other definitions. @ifset HPPA On the HPPA, the usual form for a label need not be immediately followed by a colon, but instead must start in column zero. Only one label may be defined on a single line. To work around this, the HPPA version of @code{@value{AS}} also provides a special directive @code{.label} for defining labels more flexibly. @end ifset @node Setting Symbols @section Giving Symbols Other Values @cindex assigning values to symbols @cindex symbol values, assigning A symbol can be given an arbitrary value by writing a symbol, followed by an equals sign @samp{=}, followed by an expression (@pxref{Expressions}). This is equivalent to using the @code{.set} directive. @xref{Set,,@code{.set}}. @node Symbol Names @section Symbol Names @cindex symbol names @cindex names, symbol @ifclear SPECIAL-SYMS Symbol names begin with a letter or with one of @samp{._}. On most machines, you can also use @code{$} in symbol names; exceptions are noted in @ref{Machine Dependencies}. That character may be followed by any string of digits, letters, dollar signs (unless otherwise noted in @ref{Machine Dependencies}), and underscores. @end ifclear @ifset A29K For the AMD 29K family, @samp{?} is also allowed in the body of a symbol name, though not at its beginning. @end ifset @ifset SPECIAL-SYMS @ifset H8 Symbol names begin with a letter or with one of @samp{._}. On the Hitachi SH or the H8/500, you can also use @code{$} in symbol names. That character may be followed by any string of digits, letters, dollar signs (save on the H8/300), and underscores. @end ifset @end ifset Case of letters is significant: @code{foo} is a different symbol name than @code{Foo}. Each symbol has exactly one name. Each name in an assembly language program refers to exactly one symbol. You may use that symbol name any number of times in a program. @subheading Local Symbol Names @cindex local symbol names @cindex symbol names, local @cindex temporary symbol names @cindex symbol names, temporary Local symbols help compilers and programmers use names temporarily. There are ten local symbol names, which are re-used throughout the program. You may refer to them using the names @samp{0} @samp{1} @dots{} @samp{9}. To define a local symbol, write a label of the form @samp{@b{N}:} (where @b{N} represents any digit). To refer to the most recent previous definition of that symbol write @samp{@b{N}b}, using the same digit as when you defined the label. To refer to the next definition of a local label, write @samp{@b{N}f}---where @b{N} gives you a choice of 10 forward references. The @samp{b} stands for ``backwards'' and the @samp{f} stands for ``forwards''. Local symbols are not emitted by the current @sc{gnu} C compiler. There is no restriction on how you can use these labels, but remember that at any point in the assembly you can refer to at most 10 prior local labels and to at most 10 forward local labels. Local symbol names are only a notation device. They are immediately transformed into more conventional symbol names before the assembler uses them. The symbol names stored in the symbol table, appearing in error messages and optionally emitted to the object file have these parts: @table @code @item L All local labels begin with @samp{L}. Normally both @code{@value{AS}} and @code{@value{LD}} forget symbols that start with @samp{L}. These labels are used for symbols you are never intended to see. If you use the @samp{-L} option then @code{@value{AS}} retains these symbols in the object file. If you also instruct @code{@value{LD}} to retain these symbols, you may use them in debugging. @item @var{digit} If the label is written @samp{0:} then the digit is @samp{0}. If the label is written @samp{1:} then the digit is @samp{1}. And so on up through @samp{9:}. @item @kbd{C-A} This unusual character is included so you do not accidentally invent a symbol of the same name. The character has ASCII value @samp{\001}. @item @emph{ordinal number} This is a serial number to keep the labels distinct. The first @samp{0:} gets the number @samp{1}; The 15th @samp{0:} gets the number @samp{15}; @emph{etc.}. Likewise for the other labels @samp{1:} through @samp{9:}. @end table For instance, the first @code{1:} is named @code{L1@kbd{C-A}1}, the 44th @code{3:} is named @code{L3@kbd{C-A}44}. @node Dot @section The Special Dot Symbol @cindex dot (symbol) @cindex @code{.} (symbol) @cindex current address @cindex location counter The special symbol @samp{.} refers to the current address that @code{@value{AS}} is assembling into. Thus, the expression @samp{melvin: .long .} defines @code{melvin} to contain its own address. Assigning a value to @code{.} is treated the same as a @code{.org} directive. Thus, the expression @samp{.=.+4} is the same as saying @ifclear no-space-dir @samp{.space 4}. @end ifclear @ifset no-space-dir @ifset A29K @samp{.block 4}. @end ifset @end ifset @node Symbol Attributes @section Symbol Attributes @cindex symbol attributes @cindex attributes, symbol Every symbol has, as well as its name, the attributes ``Value'' and ``Type''. Depending on output format, symbols can also have auxiliary attributes. @ifset INTERNALS The detailed definitions are in @file{a.out.h}. @end ifset If you use a symbol without defining it, @code{@value{AS}} assumes zero for all these attributes, and probably won't warn you. This makes the symbol an externally defined symbol, which is generally what you would want. @menu * Symbol Value:: Value * Symbol Type:: Type @ifset aout-bout @ifset GENERIC * a.out Symbols:: Symbol Attributes: @code{a.out} @end ifset @ifclear GENERIC @ifclear BOUT * a.out Symbols:: Symbol Attributes: @code{a.out} @end ifclear @ifset BOUT * a.out Symbols:: Symbol Attributes: @code{a.out}, @code{b.out} @end ifset @end ifclear @end ifset @ifset COFF * COFF Symbols:: Symbol Attributes for COFF @end ifset @ifset SOM * SOM Symbols:: Symbol Attributes for SOM @end ifset @end menu @node Symbol Value @subsection Value @cindex value of a symbol @cindex symbol value The value of a symbol is (usually) 32 bits. For a symbol which labels a location in the text, data, bss or absolute sections the value is the number of addresses from the start of that section to the label. Naturally for text, data and bss sections the value of a symbol changes as @code{@value{LD}} changes section base addresses during linking. Absolute symbols' values do not change during linking: that is why they are called absolute. The value of an undefined symbol is treated in a special way. If it is 0 then the symbol is not defined in this assembler source file, and @code{@value{LD}} tries to determine its value from other files linked into the same program. You make this kind of symbol simply by mentioning a symbol name without defining it. A non-zero value represents a @code{.comm} common declaration. The value is how much common storage to reserve, in bytes (addresses). The symbol refers to the first address of the allocated storage. @node Symbol Type @subsection Type @cindex type of a symbol @cindex symbol type The type attribute of a symbol contains relocation (section) information, any flag settings indicating that a symbol is external, and (optionally), other information for linkers and debuggers. The exact format depends on the object-code output format in use. @ifset aout-bout @ifclear GENERIC @ifset BOUT @c The following avoids a "widow" subsection title. @group would be @c better if it were available outside examples. @need 1000 @node a.out Symbols @subsection Symbol Attributes: @code{a.out}, @code{b.out} @cindex @code{b.out} symbol attributes @cindex symbol attributes, @code{b.out} These symbol attributes appear only when @code{@value{AS}} is configured for one of the Berkeley-descended object output formats---@code{a.out} or @code{b.out}. @end ifset @ifclear BOUT @node a.out Symbols @subsection Symbol Attributes: @code{a.out} @cindex @code{a.out} symbol attributes @cindex symbol attributes, @code{a.out} @end ifclear @end ifclear @ifset GENERIC @node a.out Symbols @subsection Symbol Attributes: @code{a.out} @cindex @code{a.out} symbol attributes @cindex symbol attributes, @code{a.out} @end ifset @menu * Symbol Desc:: Descriptor * Symbol Other:: Other @end menu @node Symbol Desc @subsubsection Descriptor @cindex descriptor, of @code{a.out} symbol This is an arbitrary 16-bit value. You may establish a symbol's descriptor value by using a @code{.desc} statement (@pxref{Desc,,@code{.desc}}). A descriptor value means nothing to @code{@value{AS}}. @node Symbol Other @subsubsection Other @cindex other attribute, of @code{a.out} symbol This is an arbitrary 8-bit value. It means nothing to @code{@value{AS}}. @end ifset @ifset COFF @node COFF Symbols @subsection Symbol Attributes for COFF @cindex COFF symbol attributes @cindex symbol attributes, COFF The COFF format supports a multitude of auxiliary symbol attributes; like the primary symbol attributes, they are set between @code{.def} and @code{.endef} directives. @subsubsection Primary Attributes @cindex primary attributes, COFF symbols The symbol name is set with @code{.def}; the value and type, respectively, with @code{.val} and @code{.type}. @subsubsection Auxiliary Attributes @cindex auxiliary attributes, COFF symbols The @code{@value{AS}} directives @code{.dim}, @code{.line}, @code{.scl}, @code{.size}, and @code{.tag} can generate auxiliary symbol table information for COFF. @end ifset @ifset SOM @node SOM Symbols @subsection Symbol Attributes for SOM @cindex SOM symbol attributes @cindex symbol attributes, SOM The SOM format for the HPPA supports a multitude of symbol attributes set with the @code{.EXPORT} and @code{.IMPORT} directives. The attributes are described in @cite{HP9000 Series 800 Assembly Language Reference Manual} (HP 92432-90001) under the @code{IMPORT} and @code{EXPORT} assembler directive documentation. @end ifset @node Expressions @chapter Expressions @cindex expressions @cindex addresses @cindex numeric values An @dfn{expression} specifies an address or numeric value. Whitespace may precede and/or follow an expression. The result of an expression must be an absolute number, or else an offset into a particular section. If an expression is not absolute, and there is not enough information when @code{@value{AS}} sees the expression to know its section, a second pass over the source program might be necessary to interpret the expression---but the second pass is currently not implemented. @code{@value{AS}} aborts with an error message in this situation. @menu * Empty Exprs:: Empty Expressions * Integer Exprs:: Integer Expressions @end menu @node Empty Exprs @section Empty Expressions @cindex empty expressions @cindex expressions, empty An empty expression has no value: it is just whitespace or null. Wherever an absolute expression is required, you may omit the expression, and @code{@value{AS}} assumes a value of (absolute) 0. This is compatible with other assemblers. @node Integer Exprs @section Integer Expressions @cindex integer expressions @cindex expressions, integer An @dfn{integer expression} is one or more @emph{arguments} delimited by @emph{operators}. @menu * Arguments:: Arguments * Operators:: Operators * Prefix Ops:: Prefix Operators * Infix Ops:: Infix Operators @end menu @node Arguments @subsection Arguments @cindex expression arguments @cindex arguments in expressions @cindex operands in expressions @cindex arithmetic operands @dfn{Arguments} are symbols, numbers or subexpressions. In other contexts arguments are sometimes called ``arithmetic operands''. In this manual, to avoid confusing them with the ``instruction operands'' of the machine language, we use the term ``argument'' to refer to parts of expressions only, reserving the word ``operand'' to refer only to machine instruction operands. Symbols are evaluated to yield @{@var{section} @var{NNN}@} where @var{section} is one of text, data, bss, absolute, or undefined. @var{NNN} is a signed, 2's complement 32 bit integer. Numbers are usually integers. A number can be a flonum or bignum. In this case, you are warned that only the low order 32 bits are used, and @code{@value{AS}} pretends these 32 bits are an integer. You may write integer-manipulating instructions that act on exotic constants, compatible with other assemblers. @cindex subexpressions Subexpressions are a left parenthesis @samp{(} followed by an integer expression, followed by a right parenthesis @samp{)}; or a prefix operator followed by an argument. @node Operators @subsection Operators @cindex operators, in expressions @cindex arithmetic functions @cindex functions, in expressions @dfn{Operators} are arithmetic functions, like @code{+} or @code{%}. Prefix operators are followed by an argument. Infix operators appear between their arguments. Operators may be preceded and/or followed by whitespace. @node Prefix Ops @subsection Prefix Operator @cindex prefix operators @code{@value{AS}} has the following @dfn{prefix operators}. They each take one argument, which must be absolute. @c the tex/end tex stuff surrounding this small table is meant to make @c it align, on the printed page, with the similar table in the next @c section (which is inside an enumerate). @tex \global\advance\leftskip by \itemindent @end tex @table @code @item - @dfn{Negation}. Two's complement negation. @item ~ @dfn{Complementation}. Bitwise not. @end table @tex \global\advance\leftskip by -\itemindent @end tex @node Infix Ops @subsection Infix Operators @cindex infix operators @cindex operators, permitted arguments @dfn{Infix operators} take two arguments, one on either side. Operators have precedence, but operations with equal precedence are performed left to right. Apart from @code{+} or @code{-}, both arguments must be absolute, and the result is absolute. @enumerate @cindex operator precedence @cindex precedence of operators @item Highest Precedence @table @code @item * @dfn{Multiplication}. @item / @dfn{Division}. Truncation is the same as the C operator @samp{/} @item % @dfn{Remainder}. @item < @itemx << @dfn{Shift Left}. Same as the C operator @samp{<<}. @item > @itemx >> @dfn{Shift Right}. Same as the C operator @samp{>>}. @end table @item Intermediate precedence @table @code @item | @dfn{Bitwise Inclusive Or}. @item & @dfn{Bitwise And}. @item ^ @dfn{Bitwise Exclusive Or}. @item ! @dfn{Bitwise Or Not}. @end table @item Lowest Precedence @table @code @cindex addition, permitted arguments @cindex plus, permitted arguments @cindex arguments for addition @item + @dfn{Addition}. If either argument is absolute, the result has the section of the other argument. You may not add together arguments from different sections. @cindex subtraction, permitted arguments @cindex minus, permitted arguments @cindex arguments for subtraction @item - @dfn{Subtraction}. If the right argument is absolute, the result has the section of the left argument. If both arguments are in the same section, the result is absolute. You may not subtract arguments from different sections. @c FIXME is there still something useful to say about undefined - undefined ? @end table @end enumerate In short, it's only meaningful to add or subtract the @emph{offsets} in an address; you can only have a defined section in one of the two arguments. @node Pseudo Ops @chapter Assembler Directives @cindex directives, machine independent @cindex pseudo-ops, machine independent @cindex machine independent directives All assembler directives have names that begin with a period (@samp{.}). The rest of the name is letters, usually in lower case. This chapter discusses directives that are available regardless of the target machine configuration for the @sc{gnu} assembler. @ifset GENERIC Some machine configurations provide additional directives. @xref{Machine Dependencies}. @end ifset @ifclear GENERIC @ifset machine-directives @xref{Machine Dependencies} for additional directives. @end ifset @end ifclear @menu * Abort:: @code{.abort} @ifset COFF * ABORT:: @code{.ABORT} @end ifset * Align:: @code{.align @var{abs-expr} , @var{abs-expr}} * Ascii:: @code{.ascii "@var{string}"}@dots{} * Asciz:: @code{.asciz "@var{string}"}@dots{} * Balign:: @code{.balign @var{abs-expr} , @var{abs-expr}} * Byte:: @code{.byte @var{expressions}} * Comm:: @code{.comm @var{symbol} , @var{length} } * Data:: @code{.data @var{subsection}} @ifset COFF * Def:: @code{.def @var{name}} @end ifset @ifset aout-bout * Desc:: @code{.desc @var{symbol}, @var{abs-expression}} @end ifset @ifset COFF * Dim:: @code{.dim} @end ifset * Double:: @code{.double @var{flonums}} * Eject:: @code{.eject} * Else:: @code{.else} * Elseif:: @code{.elseif} * End:: @code{.end} @ifset COFF * Endef:: @code{.endef} @end ifset * Endfunc:: @code{.endfunc} * Endif:: @code{.endif} * Equ:: @code{.equ @var{symbol}, @var{expression}} * Equiv:: @code{.equiv @var{symbol}, @var{expression}} * Err:: @code{.err} * Exitm:: @code{.exitm} * Extern:: @code{.extern} * Fail:: @code{.fail} @ifclear no-file-dir * File:: @code{.file @var{string}} @end ifclear * Fill:: @code{.fill @var{repeat} , @var{size} , @var{value}} * Float:: @code{.float @var{flonums}} * Func:: @code{.func} * Global:: @code{.global @var{symbol}}, @code{.globl @var{symbol}} @ifset ELF * Hidden:: @code{.hidden @var{names}} @end ifset * hword:: @code{.hword @var{expressions}} * Ident:: @code{.ident} * If:: @code{.if @var{absolute expression}} * Include:: @code{.include "@var{file}"} * Int:: @code{.int @var{expressions}} @ifset ELF * Internal:: @code{.internal @var{names}} @end ifset * Irp:: @code{.irp @var{symbol},@var{values}}@dots{} * Irpc:: @code{.irpc @var{symbol},@var{values}}@dots{} * Lcomm:: @code{.lcomm @var{symbol} , @var{length}} * Lflags:: @code{.lflags} @ifclear no-line-dir * Line:: @code{.line @var{line-number}} @end ifclear * Ln:: @code{.ln @var{line-number}} * Linkonce:: @code{.linkonce [@var{type}]} * List:: @code{.list} * Long:: @code{.long @var{expressions}} @ignore * Lsym:: @code{.lsym @var{symbol}, @var{expression}} @end ignore * Macro:: @code{.macro @var{name} @var{args}}@dots{} * MRI:: @code{.mri @var{val}} * Nolist:: @code{.nolist} * Octa:: @code{.octa @var{bignums}} * Org:: @code{.org @var{new-lc} , @var{fill}} * P2align:: @code{.p2align @var{abs-expr} , @var{abs-expr}} @ifset ELF * PopSection:: @code{.popsection} * Previous:: @code{.previous} @end ifset * Print:: @code{.print @var{string}} @ifset ELF * Protected:: @code{.protected @var{names}} @end ifset * Psize:: @code{.psize @var{lines}, @var{columns}} * Purgem:: @code{.purgem @var{name}} @ifset ELF * PushSection:: @code{.pushsection @var{name}} @end ifset * Quad:: @code{.quad @var{bignums}} * Rept:: @code{.rept @var{count}} * Sbttl:: @code{.sbttl "@var{subheading}"} @ifset COFF * Scl:: @code{.scl @var{class}} * Section:: @code{.section @var{name}, @var{subsection}} @end ifset * Set:: @code{.set @var{symbol}, @var{expression}} * Short:: @code{.short @var{expressions}} * Single:: @code{.single @var{flonums}} * Size:: @code{.size [@var{name} , @var{expression}]} * Skip:: @code{.skip @var{size} , @var{fill}} * Sleb128:: @code{.sleb128 @var{expressions}} * Space:: @code{.space @var{size} , @var{fill}} @ifset have-stabs * Stab:: @code{.stabd, .stabn, .stabs} @end ifset * String:: @code{.string "@var{str}"} * Struct:: @code{.struct @var{expression}} @ifset ELF * SubSection:: @code{.subsection} * Symver:: @code{.symver @var{name},@var{name2@@nodename}} @end ifset @ifset COFF * Tag:: @code{.tag @var{structname}} @end ifset * Text:: @code{.text @var{subsection}} * Title:: @code{.title "@var{heading}"} * Type:: @code{.type <@var{int} | @var{name} , @var{type description}>} * Uleb128:: @code{.uleb128 @var{expressions}} @ifset COFF * Val:: @code{.val @var{addr}} @end ifset @ifset ELF * Version:: @code{.version "@var{string}"} * VTableEntry:: @code{.vtable_entry @var{table}, @var{offset}} * VTableInherit:: @code{.vtable_inherit @var{child}, @var{parent}} * Weak:: @code{.weak @var{names}} @end ifset * Word:: @code{.word @var{expressions}} * Deprecated:: Deprecated Directives @end menu @node Abort @section @code{.abort} @cindex @code{abort} directive @cindex stopping the assembly This directive stops the assembly immediately. It is for compatibility with other assemblers. The original idea was that the assembly language source would be piped into the assembler. If the sender of the source quit, it could use this directive tells @code{@value{AS}} to quit also. One day @code{.abort} will not be supported. @ifset COFF @node ABORT @section @code{.ABORT} @cindex @code{ABORT} directive When producing COFF output, @code{@value{AS}} accepts this directive as a synonym for @samp{.abort}. @ifset BOUT When producing @code{b.out} output, @code{@value{AS}} accepts this directive, but ignores it. @end ifset @end ifset @node Align @section @code{.align @var{abs-expr}, @var{abs-expr}, @var{abs-expr}} @cindex padding the location counter @cindex @code{align} directive Pad the location counter (in the current subsection) to a particular storage boundary. The first expression (which must be absolute) is the alignment required, as described below. The second expression (also absolute) gives the fill value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally zero. However, on some systems, if the section is marked as containing code and the fill value is omitted, the space is filled with no-op instructions. The third expression is also absolute, and is also optional. If it is present, it is the maximum number of bytes that should be skipped by this alignment directive. If doing the alignment would require skipping more bytes than the specified maximum, then the alignment is not done at all. You can omit the fill value (the second argument) entirely by simply using two commas after the required alignment; this can be useful if you want the alignment to be filled with no-op instructions when appropriate. The way the required alignment is specified varies from system to system. For the a29k, hppa, m68k, m88k, w65, sparc, and Hitachi SH, and i386 using ELF format, the first expression is the alignment request in bytes. For example @samp{.align 8} advances the location counter until it is a multiple of 8. If the location counter is already a multiple of 8, no change is needed. For other systems, including the i386 using a.out format, and the arm and strongarm, it is the number of low-order zero bits the location counter must have after advancement. For example @samp{.align 3} advances the location counter until it a multiple of 8. If the location counter is already a multiple of 8, no change is needed. This inconsistency is due to the different behaviors of the various native assemblers for these systems which GAS must emulate. GAS also provides @code{.balign} and @code{.p2align} directives, described later, which have a consistent behavior across all architectures (but are specific to GAS). @node Ascii @section @code{.ascii "@var{string}"}@dots{} @cindex @code{ascii} directive @cindex string literals @code{.ascii} expects zero or more string literals (@pxref{Strings}) separated by commas. It assembles each string (with no automatic trailing zero byte) into consecutive addresses. @node Asciz @section @code{.asciz "@var{string}"}@dots{} @cindex @code{asciz} directive @cindex zero-terminated strings @cindex null-terminated strings @code{.asciz} is just like @code{.ascii}, but each string is followed by a zero byte. The ``z'' in @samp{.asciz} stands for ``zero''. @node Balign @section @code{.balign[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}} @cindex padding the location counter given number of bytes @cindex @code{balign} directive Pad the location counter (in the current subsection) to a particular storage boundary. The first expression (which must be absolute) is the alignment request in bytes. For example @samp{.balign 8} advances the location counter until it is a multiple of 8. If the location counter is already a multiple of 8, no change is needed. The second expression (also absolute) gives the fill value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally zero. However, on some systems, if the section is marked as containing code and the fill value is omitted, the space is filled with no-op instructions. The third expression is also absolute, and is also optional. If it is present, it is the maximum number of bytes that should be skipped by this alignment directive. If doing the alignment would require skipping more bytes than the specified maximum, then the alignment is not done at all. You can omit the fill value (the second argument) entirely by simply using two commas after the required alignment; this can be useful if you want the alignment to be filled with no-op instructions when appropriate. @cindex @code{balignw} directive @cindex @code{balignl} directive The @code{.balignw} and @code{.balignl} directives are variants of the @code{.balign} directive. The @code{.balignw} directive treats the fill pattern as a two byte word value. The @code{.balignl} directives treats the fill pattern as a four byte longword value. For example, @code{.balignw 4,0x368d} will align to a multiple of 4. If it skips two bytes, they will be filled in with the value 0x368d (the exact placement of the bytes depends upon the endianness of the processor). If it skips 1 or 3 bytes, the fill value is undefined. @node Byte @section @code{.byte @var{expressions}} @cindex @code{byte} directive @cindex integers, one byte @code{.byte} expects zero or more expressions, separated by commas. Each expression is assembled into the next byte. @node Comm @section @code{.comm @var{symbol} , @var{length} } @cindex @code{comm} directive @cindex symbol, common @code{.comm} declares a common symbol named @var{symbol}. When linking, a common symbol in one object file may be merged with a defined or common symbol of the same name in another object file. If @code{@value{LD}} does not see a definition for the symbol--just one or more common symbols--then it will allocate @var{length} bytes of uninitialized memory. @var{length} must be an absolute expression. If @code{@value{LD}} sees multiple common symbols with the same name, and they do not all have the same size, it will allocate space using the largest size. @ifset ELF When using ELF, the @code{.comm} directive takes an optional third argument. This is the desired alignment of the symbol, specified as a byte boundary (for example, an alignment of 16 means that the least significant 4 bits of the address should be zero). The alignment must be an absolute expression, and it must be a power of two. If @code{@value{LD}} allocates uninitialized memory for the common symbol, it will use the alignment when placing the symbol. If no alignment is specified, @code{@value{AS}} will set the alignment to the largest power of two less than or equal to the size of the symbol, up to a maximum of 16. @end ifset @ifset HPPA The syntax for @code{.comm} differs slightly on the HPPA. The syntax is @samp{@var{symbol} .comm, @var{length}}; @var{symbol} is optional. @end ifset @node Data @section @code{.data @var{subsection}} @cindex @code{data} directive @code{.data} tells @code{@value{AS}} to assemble the following statements onto the end of the data subsection numbered @var{subsection} (which is an absolute expression). If @var{subsection} is omitted, it defaults to zero. @ifset COFF @node Def @section @code{.def @var{name}} @cindex @code{def} directive @cindex COFF symbols, debugging @cindex debugging COFF symbols Begin defining debugging information for a symbol @var{name}; the definition extends until the @code{.endef} directive is encountered. @ifset BOUT This directive is only observed when @code{@value{AS}} is configured for COFF format output; when producing @code{b.out}, @samp{.def} is recognized, but ignored. @end ifset @end ifset @ifset aout-bout @node Desc @section @code{.desc @var{symbol}, @var{abs-expression}} @cindex @code{desc} directive @cindex COFF symbol descriptor @cindex symbol descriptor, COFF This directive sets the descriptor of the symbol (@pxref{Symbol Attributes}) to the low 16 bits of an absolute expression. @ifset COFF The @samp{.desc} directive is not available when @code{@value{AS}} is configured for COFF output; it is only for @code{a.out} or @code{b.out} object format. For the sake of compatibility, @code{@value{AS}} accepts it, but produces no output, when configured for COFF. @end ifset @end ifset @ifset COFF @node Dim @section @code{.dim} @cindex @code{dim} directive @cindex COFF auxiliary symbol information @cindex auxiliary symbol information, COFF This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside @code{.def}/@code{.endef} pairs. @ifset BOUT @samp{.dim} is only meaningful when generating COFF format output; when @code{@value{AS}} is generating @code{b.out}, it accepts this directive but ignores it. @end ifset @end ifset @node Double @section @code{.double @var{flonums}} @cindex @code{double} directive @cindex floating point numbers (double) @code{.double} expects zero or more flonums, separated by commas. It assembles floating point numbers. @ifset GENERIC The exact kind of floating point numbers emitted depends on how @code{@value{AS}} is configured. @xref{Machine Dependencies}. @end ifset @ifclear GENERIC @ifset IEEEFLOAT On the @value{TARGET} family @samp{.double} emits 64-bit floating-point numbers in @sc{ieee} format. @end ifset @end ifclear @node Eject @section @code{.eject} @cindex @code{eject} directive @cindex new page, in listings @cindex page, in listings @cindex listing control: new page Force a page break at this point, when generating assembly listings. @node Else @section @code{.else} @cindex @code{else} directive @code{.else} is part of the @code{@value{AS}} support for conditional assembly; @pxref{If,,@code{.if}}. It marks the beginning of a section of code to be assembled if the condition for the preceding @code{.if} was false. @node Elseif @section @code{.elseif} @cindex @code{elseif} directive @code{.elseif} is part of the @code{@value{AS}} support for conditional assembly; @pxref{If,,@code{.if}}. It is shorthand for beginning a new @code{.if} block that would otherwise fill the entire @code{.else} section. @node End @section @code{.end} @cindex @code{end} directive @code{.end} marks the end of the assembly file. @code{@value{AS}} does not process anything in the file past the @code{.end} directive. @ifset COFF @node Endef @section @code{.endef} @cindex @code{endef} directive This directive flags the end of a symbol definition begun with @code{.def}. @ifset BOUT @samp{.endef} is only meaningful when generating COFF format output; if @code{@value{AS}} is configured to generate @code{b.out}, it accepts this directive but ignores it. @end ifset @end ifset @node Endfunc @section @code{.endfunc} @cindex @code{endfunc} directive @code{.endfunc} marks the end of a function specified with @code{.func}. @node Endif @section @code{.endif} @cindex @code{endif} directive @code{.endif} is part of the @code{@value{AS}} support for conditional assembly; it marks the end of a block of code that is only assembled conditionally. @xref{If,,@code{.if}}. @node Equ @section @code{.equ @var{symbol}, @var{expression}} @cindex @code{equ} directive @cindex assigning values to symbols @cindex symbols, assigning values to This directive sets the value of @var{symbol} to @var{expression}. It is synonymous with @samp{.set}; @pxref{Set,,@code{.set}}. @ifset HPPA The syntax for @code{equ} on the HPPA is @samp{@var{symbol} .equ @var{expression}}. @end ifset @node Equiv @section @code{.equiv @var{symbol}, @var{expression}} @cindex @code{equiv} directive The @code{.equiv} directive is like @code{.equ} and @code{.set}, except that the assembler will signal an error if @var{symbol} is already defined. Except for the contents of the error message, this is roughly equivalent to @smallexample .ifdef SYM .err .endif .equ SYM,VAL @end smallexample @node Err @section @code{.err} @cindex @code{err} directive If @code{@value{AS}} assembles a @code{.err} directive, it will print an error message and, unless the @code{-Z} option was used, it will not generate an object file. This can be used to signal error an conditionally compiled code. @node Exitm @section @code{.exitm} Exit early from the current macro definition. @xref{Macro}. @node Extern @section @code{.extern} @cindex @code{extern} directive @code{.extern} is accepted in the source program---for compatibility with other assemblers---but it is ignored. @code{@value{AS}} treats all undefined symbols as external. @node Fail @section @code{.fail @var{expression}} @cindex @code{fail} directive Generates an error or a warning. If the value of the @var{expression} is 500 or more, @code{@value{AS}} will print a warning message. If the value is less than 500, @code{@value{AS}} will print an error message. The message will include the value of @var{expression}. This can occasionally be useful inside complex nested macros or conditional assembly. @ifclear no-file-dir @node File @section @code{.file @var{string}} @cindex @code{file} directive @cindex logical file name @cindex file name, logical @code{.file} tells @code{@value{AS}} that we are about to start a new logical file. @var{string} is the new file name. In general, the filename is recognized whether or not it is surrounded by quotes @samp{"}; but if you wish to specify an empty file name, you must give the quotes--@code{""}. This statement may go away in future: it is only recognized to be compatible with old @code{@value{AS}} programs. @ifset A29K In some configurations of @code{@value{AS}}, @code{.file} has already been removed to avoid conflicts with other assemblers. @xref{Machine Dependencies}. @end ifset @end ifclear @node Fill @section @code{.fill @var{repeat} , @var{size} , @var{value}} @cindex @code{fill} directive @cindex writing patterns in memory @cindex patterns, writing in memory @var{result}, @var{size} and @var{value} are absolute expressions. This emits @var{repeat} copies of @var{size} bytes. @var{Repeat} may be zero or more. @var{Size} may be zero or more, but if it is more than 8, then it is deemed to have the value 8, compatible with other people's assemblers. The contents of each @var{repeat} bytes is taken from an 8-byte number. The highest order 4 bytes are zero. The lowest order 4 bytes are @var{value} rendered in the byte-order of an integer on the computer @code{@value{AS}} is assembling for. Each @var{size} bytes in a repetition is taken from the lowest order @var{size} bytes of this number. Again, this bizarre behavior is compatible with other people's assemblers. @var{size} and @var{value} are optional. If the second comma and @var{value} are absent, @var{value} is assumed zero. If the first comma and following tokens are absent, @var{size} is assumed to be 1. @node Float @section @code{.float @var{flonums}} @cindex floating point numbers (single) @cindex @code{float} directive This directive assembles zero or more flonums, separated by commas. It has the same effect as @code{.single}. @ifset GENERIC The exact kind of floating point numbers emitted depends on how @code{@value{AS}} is configured. @xref{Machine Dependencies}. @end ifset @ifclear GENERIC @ifset IEEEFLOAT On the @value{TARGET} family, @code{.float} emits 32-bit floating point numbers in @sc{ieee} format. @end ifset @end ifclear @node Func @section @code{.func @var{name}[,@var{label}]} @cindex @code{func} directive @code{.func} emits debugging information to denote function @var{name}, and is ignored unless the file is assembled with debugging enabled. Only @samp{--gstabs} is currently supported. @var{label} is the entry point of the function and if omitted @var{name} prepended with the @samp{leading char} is used. @samp{leading char} is usually @code{_} or nothing, depending on the target. All functions are currently defined to have @code{void} return type. The function must be terminated with @code{.endfunc}. @node Global @section @code{.global @var{symbol}}, @code{.globl @var{symbol}} @cindex @code{global} directive @cindex symbol, making visible to linker @code{.global} makes the symbol visible to @code{@value{LD}}. If you define @var{symbol} in your partial program, its value is made available to other partial programs that are linked with it. Otherwise, @var{symbol} takes its attributes from a symbol of the same name from another file linked into the same program. Both spellings (@samp{.globl} and @samp{.global}) are accepted, for compatibility with other assemblers. @ifset HPPA On the HPPA, @code{.global} is not always enough to make it accessible to other partial programs. You may need the HPPA-only @code{.EXPORT} directive as well. @xref{HPPA Directives,, HPPA Assembler Directives}. @end ifset @ifset ELF @node Hidden @section @code{.hidden @var{names}} @cindex @code{.hidden} directive @cindex Visibility This one of the ELF visibility directives. The other two are @pxref{Internal,,@code{.internal}} and @pxref{Protected,,@code{.protected}} This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to @code{hidden} which means that the symbols are not visible to other components. Such symbols are always considered to be @code{protected} as well. @end ifset @node hword @section @code{.hword @var{expressions}} @cindex @code{hword} directive @cindex integers, 16-bit @cindex numbers, 16-bit @cindex sixteen bit integers This expects zero or more @var{expressions}, and emits a 16 bit number for each. @ifset GENERIC This directive is a synonym for @samp{.short}; depending on the target architecture, it may also be a synonym for @samp{.word}. @end ifset @ifclear GENERIC @ifset W32 This directive is a synonym for @samp{.short}. @end ifset @ifset W16 This directive is a synonym for both @samp{.short} and @samp{.word}. @end ifset @end ifclear @node Ident @section @code{.ident} @cindex @code{ident} directive This directive is used by some assemblers to place tags in object files. @code{@value{AS}} simply accepts the directive for source-file compatibility with such assemblers, but does not actually emit anything for it. @node If @section @code{.if @var{absolute expression}} @cindex conditional assembly @cindex @code{if} directive @code{.if} marks the beginning of a section of code which is only considered part of the source program being assembled if the argument (which must be an @var{absolute expression}) is non-zero. The end of the conditional section of code must be marked by @code{.endif} (@pxref{Endif,,@code{.endif}}); optionally, you may include code for the alternative condition, flagged by @code{.else} (@pxref{Else,,@code{.else}}). If you have several conditions to check, @code{.elseif} may be used to avoid nesting blocks if/else within each subsequent @code{.else} block. The following variants of @code{.if} are also supported: @table @code @cindex @code{ifdef} directive @item .ifdef @var{symbol} Assembles the following section of code if the specified @var{symbol} has been defined. @cindex @code{ifc} directive @item .ifc @var{string1},@var{string2} Assembles the following section of code if the two strings are the same. The strings may be optionally quoted with single quotes. If they are not quoted, the first string stops at the first comma, and the second string stops at the end of the line. Strings which contain whitespace should be quoted. The string comparison is case sensitive. @cindex @code{ifeq} directive @item .ifeq @var{absolute expression} Assembles the following section of code if the argument is zero. @cindex @code{ifeqs} directive @item .ifeqs @var{string1},@var{string2} Another form of @code{.ifc}. The strings must be quoted using double quotes. @cindex @code{ifge} directive @item .ifge @var{absolute expression} Assembles the following section of code if the argument is greater than or equal to zero. @cindex @code{ifgt} directive @item .ifgt @var{absolute expression} Assembles the following section of code if the argument is greater than zero. @cindex @code{ifle} directive @item .ifle @var{absolute expression} Assembles the following section of code if the argument is less than or equal to zero. @cindex @code{iflt} directive @item .iflt @var{absolute expression} Assembles the following section of code if the argument is less than zero. @cindex @code{ifnc} directive @item .ifnc @var{string1},@var{string2}. Like @code{.ifc}, but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same. @cindex @code{ifndef} directive @cindex @code{ifnotdef} directive @item .ifndef @var{symbol} @itemx .ifnotdef @var{symbol} Assembles the following section of code if the specified @var{symbol} has not been defined. Both spelling variants are equivalent. @cindex @code{ifne} directive @item .ifne @var{absolute expression} Assembles the following section of code if the argument is not equal to zero (in other words, this is equivalent to @code{.if}). @cindex @code{ifnes} directive @item .ifnes @var{string1},@var{string2} Like @code{.ifeqs}, but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same. @end table @node Include @section @code{.include "@var{file}"} @cindex @code{include} directive @cindex supporting files, including @cindex files, including This directive provides a way to include supporting files at specified points in your source program. The code from @var{file} is assembled as if it followed the point of the @code{.include}; when the end of the included file is reached, assembly of the original file continues. You can control the search paths used with the @samp{-I} command-line option (@pxref{Invoking,,Command-Line Options}). Quotation marks are required around @var{file}. @node Int @section @code{.int @var{expressions}} @cindex @code{int} directive @cindex integers, 32-bit Expect zero or more @var{expressions}, of any section, separated by commas. For each expression, emit a number that, at run time, is the value of that expression. The byte order and bit size of the number depends on what kind of target the assembly is for. @ifclear GENERIC @ifset H8 On the H8/500 and most forms of the H8/300, @code{.int} emits 16-bit integers. On the H8/300H and the Hitachi SH, however, @code{.int} emits 32-bit integers. @end ifset @end ifclear @ifset ELF @node Internal @section @code{.internal @var{names}} @cindex @code{.internal} directive @cindex Visibility This one of the ELF visibility directives. The other two are @pxref{Hidden,,@code{.hidden}} and @pxref{Protected,,@code{.protected}} This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to @code{internal} which means that the symbols are considered to be @code{hidden} (ie not visible to other components), and that some extra, processor specific processing must also be performed upon the symbols as well. @end ifset @node Irp @section @code{.irp @var{symbol},@var{values}}@dots{} @cindex @code{irp} directive Evaluate a sequence of statements assigning different values to @var{symbol}. The sequence of statements starts at the @code{.irp} directive, and is terminated by an @code{.endr} directive. For each @var{value}, @var{symbol} is set to @var{value}, and the sequence of statements is assembled. If no @var{value} is listed, the sequence of statements is assembled once, with @var{symbol} set to the null string. To refer to @var{symbol} within the sequence of statements, use @var{\symbol}. For example, assembling @example .irp param,1,2,3 move d\param,sp@@- .endr @end example is equivalent to assembling @example move d1,sp@@- move d2,sp@@- move d3,sp@@- @end example @node Irpc @section @code{.irpc @var{symbol},@var{values}}@dots{} @cindex @code{irpc} directive Evaluate a sequence of statements assigning different values to @var{symbol}. The sequence of statements starts at the @code{.irpc} directive, and is terminated by an @code{.endr} directive. For each character in @var{value}, @var{symbol} is set to the character, and the sequence of statements is assembled. If no @var{value} is listed, the sequence of statements is assembled once, with @var{symbol} set to the null string. To refer to @var{symbol} within the sequence of statements, use @var{\symbol}. For example, assembling @example .irpc param,123 move d\param,sp@@- .endr @end example is equivalent to assembling @example move d1,sp@@- move d2,sp@@- move d3,sp@@- @end example @node Lcomm @section @code{.lcomm @var{symbol} , @var{length}} @cindex @code{lcomm} directive @cindex local common symbols @cindex symbols, local common Reserve @var{length} (an absolute expression) bytes for a local common denoted by @var{symbol}. The section and value of @var{symbol} are those of the new local common. The addresses are allocated in the bss section, so that at run-time the bytes start off zeroed. @var{Symbol} is not declared global (@pxref{Global,,@code{.global}}), so is normally not visible to @code{@value{LD}}. @ifset GENERIC Some targets permit a third argument to be used with @code{.lcomm}. This argument specifies the desired alignment of the symbol in the bss section. @end ifset @ifset HPPA The syntax for @code{.lcomm} differs slightly on the HPPA. The syntax is @samp{@var{symbol} .lcomm, @var{length}}; @var{symbol} is optional. @end ifset @node Lflags @section @code{.lflags} @cindex @code{lflags} directive (ignored) @code{@value{AS}} accepts this directive, for compatibility with other assemblers, but ignores it. @ifclear no-line-dir @node Line @section @code{.line @var{line-number}} @cindex @code{line} directive @end ifclear @ifset no-line-dir @node Ln @section @code{.ln @var{line-number}} @cindex @code{ln} directive @end ifset @cindex logical line number @ifset aout-bout Change the logical line number. @var{line-number} must be an absolute expression. The next line has that logical line number. Therefore any other statements on the current line (after a statement separator character) are reported as on logical line number @var{line-number} @minus{} 1. One day @code{@value{AS}} will no longer support this directive: it is recognized only for compatibility with existing assembler programs. @ifset GENERIC @ifset A29K @emph{Warning:} In the AMD29K configuration of @value{AS}, this command is not available; use the synonym @code{.ln} in that context. @end ifset @end ifset @end ifset @ifclear no-line-dir Even though this is a directive associated with the @code{a.out} or @code{b.out} object-code formats, @code{@value{AS}} still recognizes it when producing COFF output, and treats @samp{.line} as though it were the COFF @samp{.ln} @emph{if} it is found outside a @code{.def}/@code{.endef} pair. Inside a @code{.def}, @samp{.line} is, instead, one of the directives used by compilers to generate auxiliary symbol information for debugging. @end ifclear @node Linkonce @section @code{.linkonce [@var{type}]} @cindex COMDAT @cindex @code{linkonce} directive @cindex common sections Mark the current section so that the linker only includes a single copy of it. This may be used to include the same section in several different object files, but ensure that the linker will only include it once in the final output file. The @code{.linkonce} pseudo-op must be used for each instance of the section. Duplicate sections are detected based on the section name, so it should be unique. This directive is only supported by a few object file formats; as of this writing, the only object file format which supports it is the Portable Executable format used on Windows NT. The @var{type} argument is optional. If specified, it must be one of the following strings. For example: @smallexample .linkonce same_size @end smallexample Not all types may be supported on all object file formats. @table @code @item discard Silently discard duplicate sections. This is the default. @item one_only Warn if there are duplicate sections, but still keep only one copy. @item same_size Warn if any of the duplicates have different sizes. @item same_contents Warn if any of the duplicates do not have exactly the same contents. @end table @node Ln @section @code{.ln @var{line-number}} @cindex @code{ln} directive @ifclear no-line-dir @samp{.ln} is a synonym for @samp{.line}. @end ifclear @ifset no-line-dir Tell @code{@value{AS}} to change the logical line number. @var{line-number} must be an absolute expression. The next line has that logical line number, so any other statements on the current line (after a statement separator character @code{;}) are reported as on logical line number @var{line-number} @minus{} 1. @ifset BOUT This directive is accepted, but ignored, when @code{@value{AS}} is configured for @code{b.out}; its effect is only associated with COFF output format. @end ifset @end ifset @node MRI @section @code{.mri @var{val}} @cindex @code{mri} directive @cindex MRI mode, temporarily If @var{val} is non-zero, this tells @code{@value{AS}} to enter MRI mode. If @var{val} is zero, this tells @code{@value{AS}} to exit MRI mode. This change affects code assembled until the next @code{.mri} directive, or until the end of the file. @xref{M, MRI mode, MRI mode}. @node List @section @code{.list} @cindex @code{list} directive @cindex listing control, turning on Control (in conjunction with the @code{.nolist} directive) whether or not assembly listings are generated. These two directives maintain an internal counter (which is zero initially). @code{.list} increments the counter, and @code{.nolist} decrements it. Assembly listings are generated whenever the counter is greater than zero. By default, listings are disabled. When you enable them (with the @samp{-a} command line option; @pxref{Invoking,,Command-Line Options}), the initial value of the listing counter is one. @node Long @section @code{.long @var{expressions}} @cindex @code{long} directive @code{.long} is the same as @samp{.int}, @pxref{Int,,@code{.int}}. @ignore @c no one seems to know what this is for or whether this description is @c what it really ought to do @node Lsym @section @code{.lsym @var{symbol}, @var{expression}} @cindex @code{lsym} directive @cindex symbol, not referenced in assembly @code{.lsym} creates a new symbol named @var{symbol}, but does not put it in the hash table, ensuring it cannot be referenced by name during the rest of the assembly. This sets the attributes of the symbol to be the same as the expression value: @smallexample @var{other} = @var{descriptor} = 0 @var{type} = @r{(section of @var{expression})} @var{value} = @var{expression} @end smallexample @noindent The new symbol is not flagged as external. @end ignore @node Macro @section @code{.macro} @cindex macros The commands @code{.macro} and @code{.endm} allow you to define macros that generate assembly output. For example, this definition specifies a macro @code{sum} that puts a sequence of numbers into memory: @example .macro sum from=0, to=5 .long \from .if \to-\from sum "(\from+1)",\to .endif .endm @end example @noindent With that definition, @samp{SUM 0,5} is equivalent to this assembly input: @example .long 0 .long 1 .long 2 .long 3 .long 4 .long 5 @end example @ftable @code @item .macro @var{macname} @itemx .macro @var{macname} @var{macargs} @dots{} @cindex @code{macro} directive Begin the definition of a macro called @var{macname}. If your macro definition requires arguments, specify their names after the macro name, separated by commas or spaces. You can supply a default value for any macro argument by following the name with @samp{=@var{deflt}}. For example, these are all valid @code{.macro} statements: @table @code @item .macro comm Begin the definition of a macro called @code{comm}, which takes no arguments. @item .macro plus1 p, p1 @itemx .macro plus1 p p1 Either statement begins the definition of a macro called @code{plus1}, which takes two arguments; within the macro definition, write @samp{\p} or @samp{\p1} to evaluate the arguments. @item .macro reserve_str p1=0 p2 Begin the definition of a macro called @code{reserve_str}, with two arguments. The first argument has a default value, but not the second. After the definition is complete, you can call the macro either as @samp{reserve_str @var{a},@var{b}} (with @samp{\p1} evaluating to @var{a} and @samp{\p2} evaluating to @var{b}), or as @samp{reserve_str ,@var{b}} (with @samp{\p1} evaluating as the default, in this case @samp{0}, and @samp{\p2} evaluating to @var{b}). @end table When you call a macro, you can specify the argument values either by position, or by keyword. For example, @samp{sum 9,17} is equivalent to @samp{sum to=17, from=9}. @item .endm @cindex @code{endm} directive Mark the end of a macro definition. @item .exitm @cindex @code{exitm} directive Exit early from the current macro definition. @cindex number of macros executed @cindex macros, count executed @item \@@ @code{@value{AS}} maintains a counter of how many macros it has executed in this pseudo-variable; you can copy that number to your output with @samp{\@@}, but @emph{only within a macro definition}. @ignore @item LOCAL @var{name} [ , @dots{} ] @emph{Warning: @code{LOCAL} is only available if you select ``alternate macro syntax'' with @samp{-a} or @samp{--alternate}.} @xref{Alternate,, Alternate macro syntax}. Generate a string replacement for each of the @var{name} arguments, and replace any instances of @var{name} in each macro expansion. The replacement string is unique in the assembly, and different for each separate macro expansion. @code{LOCAL} allows you to write macros that define symbols, without fear of conflict between separate macro expansions. @end ignore @end ftable @node Nolist @section @code{.nolist} @cindex @code{nolist} directive @cindex listing control, turning off Control (in conjunction with the @code{.list} directive) whether or not assembly listings are generated. These two directives maintain an internal counter (which is zero initially). @code{.list} increments the counter, and @code{.nolist} decrements it. Assembly listings are generated whenever the counter is greater than zero. @node Octa @section @code{.octa @var{bignums}} @c FIXME: double size emitted for "octa" on i960, others? Or warn? @cindex @code{octa} directive @cindex integer, 16-byte @cindex sixteen byte integer This directive expects zero or more bignums, separated by commas. For each bignum, it emits a 16-byte integer. The term ``octa'' comes from contexts in which a ``word'' is two bytes; hence @emph{octa}-word for 16 bytes. @node Org @section @code{.org @var{new-lc} , @var{fill}} @cindex @code{org} directive @cindex location counter, advancing @cindex advancing location counter @cindex current address, advancing Advance the location counter of the current section to @var{new-lc}. @var{new-lc} is either an absolute expression or an expression with the same section as the current subsection. That is, you can't use @code{.org} to cross sections: if @var{new-lc} has the wrong section, the @code{.org} directive is ignored. To be compatible with former assemblers, if the section of @var{new-lc} is absolute, @code{@value{AS}} issues a warning, then pretends the section of @var{new-lc} is the same as the current subsection. @code{.org} may only increase the location counter, or leave it unchanged; you cannot use @code{.org} to move the location counter backwards. @c double negative used below "not undefined" because this is a specific @c reference to "undefined" (as SEG_UNKNOWN is called in this manual) @c section. doc@cygnus.com 18feb91 Because @code{@value{AS}} tries to assemble programs in one pass, @var{new-lc} may not be undefined. If you really detest this restriction we eagerly await a chance to share your improved assembler. Beware that the origin is relative to the start of the section, not to the start of the subsection. This is compatible with other people's assemblers. When the location counter (of the current subsection) is advanced, the intervening bytes are filled with @var{fill} which should be an absolute expression. If the comma and @var{fill} are omitted, @var{fill} defaults to zero. @node P2align @section @code{.p2align[wl] @var{abs-expr}, @var{abs-expr}, @var{abs-expr}} @cindex padding the location counter given a power of two @cindex @code{p2align} directive Pad the location counter (in the current subsection) to a particular storage boundary. The first expression (which must be absolute) is the number of low-order zero bits the location counter must have after advancement. For example @samp{.p2align 3} advances the location counter until it a multiple of 8. If the location counter is already a multiple of 8, no change is needed. The second expression (also absolute) gives the fill value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally zero. However, on some systems, if the section is marked as containing code and the fill value is omitted, the space is filled with no-op instructions. The third expression is also absolute, and is also optional. If it is present, it is the maximum number of bytes that should be skipped by this alignment directive. If doing the alignment would require skipping more bytes than the specified maximum, then the alignment is not done at all. You can omit the fill value (the second argument) entirely by simply using two commas after the required alignment; this can be useful if you want the alignment to be filled with no-op instructions when appropriate. @cindex @code{p2alignw} directive @cindex @code{p2alignl} directive The @code{.p2alignw} and @code{.p2alignl} directives are variants of the @code{.p2align} directive. The @code{.p2alignw} directive treats the fill pattern as a two byte word value. The @code{.p2alignl} directives treats the fill pattern as a four byte longword value. For example, @code{.p2alignw 2,0x368d} will align to a multiple of 4. If it skips two bytes, they will be filled in with the value 0x368d (the exact placement of the bytes depends upon the endianness of the processor). If it skips 1 or 3 bytes, the fill value is undefined. @ifset ELF @node Previous @section @code{.previous} @cindex @code{.previous} directive @cindex Section Stack This is one of the ELF section stack manipulation directives. The others are @pxref{Section}, @xref{SubSection}, @pxref{PushSection}, and @pxref{PopSection}. This directive swaps the current section (and subsection) with most recently referenced section (and subsection) prior to this one. Multiple @code{.previous} directives in a row will flip between two sections (and their subsections). In terms of the section stack, this directive swaps the current section with the top section on the section stack. @end ifset @ifset ELF @node PopSection @section @code{.popsection} @cindex @code{.popsection} directive @cindex Section Stack This is one of the ELF section stack manipulation directives. The others are @pxref{Section}, @xref{SubSection}, @pxref{PushSection}, and @pxref{Previous}. This directive replaces the current section (and subsection) with the top section (and subsection) on the section stack. This section is popped off the stack. @end ifset @node Print @section @code{.print @var{string}} @cindex @code{print} directive @code{@value{AS}} will print @var{string} on the standard output during assembly. You must put @var{string} in double quotes. @ifset ELF @node Protected @section @code{.protected @var{names}} @cindex @code{.protected} directive @cindex Visibility This one of the ELF visibility directives. The other two are @pxref{Hidden} and @pxref{Internal} This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to @code{protected} which means that any references to the symbols from within the components that defines them must be resolved to the definition in that component, even if a definition in another component would normally preempt this. @end ifset @node Psize @section @code{.psize @var{lines} , @var{columns}} @cindex @code{psize} directive @cindex listing control: paper size @cindex paper size, for listings Use this directive to declare the number of lines---and, optionally, the number of columns---to use for each page, when generating listings. If you do not use @code{.psize}, listings use a default line-count of 60. You may omit the comma and @var{columns} specification; the default width is 200 columns. @code{@value{AS}} generates formfeeds whenever the specified number of lines is exceeded (or whenever you explicitly request one, using @code{.eject}). If you specify @var{lines} as @code{0}, no formfeeds are generated save those explicitly specified with @code{.eject}. @node Purgem @section @code{.purgem @var{name}} @cindex @code{purgem} directive Undefine the macro @var{name}, so that later uses of the string will not be expanded. @xref{Macro}. @ifset ELF @node PushSection @section @code{.pushsection @var{name} , @var{subsection}} @cindex @code{.pushsection} directive @cindex Section Stack This is one of the ELF section stack manipulation directives. The others are @pxref{Section}, @xref{SubSection}, @pxref{PopSection}, and @pxref{Previous}. This directive is a synonym for @code{.section}. It psuhes the current section (and subsection) onto the top of the section stack, and then replaces the current section and subsection with @code{name} and @code{subsection}. @end ifset @node Quad @section @code{.quad @var{bignums}} @cindex @code{quad} directive @code{.quad} expects zero or more bignums, separated by commas. For each bignum, it emits @ifclear bignum-16 an 8-byte integer. If the bignum won't fit in 8 bytes, it prints a warning message; and just takes the lowest order 8 bytes of the bignum. @cindex eight-byte integer @cindex integer, 8-byte The term ``quad'' comes from contexts in which a ``word'' is two bytes; hence @emph{quad}-word for 8 bytes. @end ifclear @ifset bignum-16 a 16-byte integer. If the bignum won't fit in 16 bytes, it prints a warning message; and just takes the lowest order 16 bytes of the bignum. @cindex sixteen-byte integer @cindex integer, 16-byte @end ifset @node Rept @section @code{.rept @var{count}} @cindex @code{rept} directive Repeat the sequence of lines between the @code{.rept} directive and the next @code{.endr} directive @var{count} times. For example, assembling @example .rept 3 .long 0 .endr @end example is equivalent to assembling @example .long 0 .long 0 .long 0 @end example @node Sbttl @section @code{.sbttl "@var{subheading}"} @cindex @code{sbttl} directive @cindex subtitles for listings @cindex listing control: subtitle Use @var{subheading} as the title (third line, immediately after the title line) when generating assembly listings. This directive affects subsequent pages, as well as the current page if it appears within ten lines of the top of a page. @ifset COFF @node Scl @section @code{.scl @var{class}} @cindex @code{scl} directive @cindex symbol storage class (COFF) @cindex COFF symbol storage class Set the storage-class value for a symbol. This directive may only be used inside a @code{.def}/@code{.endef} pair. Storage class may flag whether a symbol is static or external, or it may record further symbolic debugging information. @ifset BOUT The @samp{.scl} directive is primarily associated with COFF output; when configured to generate @code{b.out} output format, @code{@value{AS}} accepts this directive but ignores it. @end ifset @end ifset @node Section @section @code{.section @var{name}} (COFF version) @cindex @code{section} directive @cindex named section Use the @code{.section} directive to assemble the following code into a section named @var{name}. This directive is only supported for targets that actually support arbitrarily named sections; on @code{a.out} targets, for example, it is not accepted, even with a standard @code{a.out} section name. For COFF targets, the @code{.section} directive is used in one of the following ways: @smallexample .section @var{name}[, "@var{flags}"] .section @var{name}[, @var{subsegment}] @end smallexample If the optional argument is quoted, it is taken as flags to use for the section. Each flag is a single character. The following flags are recognized: @table @code @item b bss section (uninitialized data) @item n section is not loaded @item w writable section @item d data section @item r read-only section @item x executable section @item s shared section (meaningful for PE targets) @end table If no flags are specified, the default flags depend upon the section name. If the section name is not recognized, the default will be for the section to be loaded and writable. If the optional argument to the @code{.section} directive is not quoted, it is taken as a subsegment number (@pxref{Sub-Sections}). @section @code{.section @var{name}} (ELF version) @cindex @code{section} directive @cindex named section @ifset ELF @cindex Section Stack This is one of the ELF section stack manipulation directives. The others are @xref{SubSection}, @pxref{PushSection}@pxref{PopSection}, and @pxref{Previous}. @end ifset For ELF targets, the @code{.section} directive is used like this: @smallexample .section @var{name} [, "@var{flags}"[, @@@var{type}]] @end smallexample The optional @var{flags} argument is a quoted string which may contain any combintion of the following characters: @table @code @item a section is allocatable @item w section is writable @item x section is executable @end table The optional @var{type} argument may contain one of the following constants: @table @code @item @@progbits section contains data @item @@nobits section does not contain data (i.e., section only occupies space) @end table If no flags are specified, the default flags depend upon the section name. If the section name is not recognized, the default will be for the section to have none of the above flags: it will not be allocated in memory, nor writable, nor executable. The section will contain data. For ELF targets, the assembler supports another type of @code{.section} directive for compatibility with the Solaris assembler: @smallexample .section "@var{name}"[, @var{flags}...] @end smallexample Note that the section name is quoted. There may be a sequence of comma separated flags: @table @code @item #alloc section is allocatable @item #write section is writable @item #execinstr section is executable @end table This directive replaces the current section and subsection. The replaced section and subsection are pushed onto the section stack. See the contents of the gas testsuite directory @code{gas/testsuite/gas/elf} for some examples of how this directive and the other section stack directives work. @node Set @section @code{.set @var{symbol}, @var{expression}} @cindex @code{set} directive @cindex symbol value, setting Set the value of @var{symbol} to @var{expression}. This changes @var{symbol}'s value and type to conform to @var{expression}. If @var{symbol} was flagged as external, it remains flagged (@pxref{Symbol Attributes}). You may @code{.set} a symbol many times in the same assembly. If you @code{.set} a global symbol, the value stored in the object file is the last value stored into it. @ifset HPPA The syntax for @code{set} on the HPPA is @samp{@var{symbol} .set @var{expression}}. @end ifset @node Short @section @code{.short @var{expressions}} @cindex @code{short} directive @ifset GENERIC @code{.short} is normally the same as @samp{.word}. @xref{Word,,@code{.word}}. In some configurations, however, @code{.short} and @code{.word} generate numbers of different lengths; @pxref{Machine Dependencies}. @end ifset @ifclear GENERIC @ifset W16 @code{.short} is the same as @samp{.word}. @xref{Word,,@code{.word}}. @end ifset @ifset W32 This expects zero or more @var{expressions}, and emits a 16 bit number for each. @end ifset @end ifclear @node Single @section @code{.single @var{flonums}} @cindex @code{single} directive @cindex floating point numbers (single) This directive assembles zero or more flonums, separated by commas. It has the same effect as @code{.float}. @ifset GENERIC The exact kind of floating point numbers emitted depends on how @code{@value{AS}} is configured. @xref{Machine Dependencies}. @end ifset @ifclear GENERIC @ifset IEEEFLOAT On the @value{TARGET} family, @code{.single} emits 32-bit floating point numbers in @sc{ieee} format. @end ifset @end ifclear @node Size @section @code{.size} (COFF version) @cindex @code{size} directive This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside @code{.def}/@code{.endef} pairs. @ifset BOUT @samp{.size} is only meaningful when generating COFF format output; when @code{@value{AS}} is generating @code{b.out}, it accepts this directive but ignores it. @end ifset @section @code{.size @var{name} , @var{expression}} (ELF version) @cindex @code{size} directive This directive is used to set the size associated with a symbol @var{name}. The size in bytes is computed from @var{expression} which can make use of label arithmetic. This directive is typically used to set the size of function symbols. @node Sleb128 @section @code{.sleb128 @var{expressions}} @cindex @code{sleb128} directive @var{sleb128} stands for ``signed little endian base 128.'' This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format. @xref{Uleb128,@code{.uleb128}}. @ifclear no-space-dir @node Skip @section @code{.skip @var{size} , @var{fill}} @cindex @code{skip} directive @cindex filling memory This directive emits @var{size} bytes, each of value @var{fill}. Both @var{size} and @var{fill} are absolute expressions. If the comma and @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same as @samp{.space}. @node Space @section @code{.space @var{size} , @var{fill}} @cindex @code{space} directive @cindex filling memory This directive emits @var{size} bytes, each of value @var{fill}. Both @var{size} and @var{fill} are absolute expressions. If the comma and @var{fill} are omitted, @var{fill} is assumed to be zero. This is the same as @samp{.skip}. @ifset HPPA @quotation @emph{Warning:} @code{.space} has a completely different meaning for HPPA targets; use @code{.block} as a substitute. See @cite{HP9000 Series 800 Assembly Language Reference Manual} (HP 92432-90001) for the meaning of the @code{.space} directive. @xref{HPPA Directives,,HPPA Assembler Directives}, for a summary. @end quotation @end ifset @end ifclear @ifset A29K @ifclear GENERIC @node Space @section @code{.space} @cindex @code{space} directive @end ifclear On the AMD 29K, this directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. @quotation @emph{Warning:} In most versions of the @sc{gnu} assembler, the directive @code{.space} has the effect of @code{.block} @xref{Machine Dependencies}. @end quotation @end ifset @ifset have-stabs @node Stab @section @code{.stabd, .stabn, .stabs} @cindex symbolic debuggers, information for @cindex @code{stab@var{x}} directives There are three directives that begin @samp{.stab}. All emit symbols (@pxref{Symbols}), for use by symbolic debuggers. The symbols are not entered in the @code{@value{AS}} hash table: they cannot be referenced elsewhere in the source file. Up to five fields are required: @table @var @item string This is the symbol's name. It may contain any character except @samp{\000}, so is more general than ordinary symbol names. Some debuggers used to code arbitrarily complex structures into symbol names using this field. @item type An absolute expression. The symbol's type is set to the low 8 bits of this expression. Any bit pattern is permitted, but @code{@value{LD}} and debuggers choke on silly bit patterns. @item other An absolute expression. The symbol's ``other'' attribute is set to the low 8 bits of this expression. @item desc An absolute expression. The symbol's descriptor is set to the low 16 bits of this expression. @item value An absolute expression which becomes the symbol's value. @end table If a warning is detected while reading a @code{.stabd}, @code{.stabn}, or @code{.stabs} statement, the symbol has probably already been created; you get a half-formed symbol in your object file. This is compatible with earlier assemblers! @table @code @cindex @code{stabd} directive @item .stabd @var{type} , @var{other} , @var{desc} The ``name'' of the symbol generated is not even an empty string. It is a null pointer, for compatibility. Older assemblers used a null pointer so they didn't waste space in object files with empty strings. The symbol's value is set to the location counter, relocatably. When your program is linked, the value of this symbol is the address of the location counter when the @code{.stabd} was assembled. @cindex @code{stabn} directive @item .stabn @var{type} , @var{other} , @var{desc} , @var{value} The name of the symbol is set to the empty string @code{""}. @cindex @code{stabs} directive @item .stabs @var{string} , @var{type} , @var{other} , @var{desc} , @var{value} All five fields are specified. @end table @end ifset @c end have-stabs @node String @section @code{.string} "@var{str}" @cindex string, copying to object file @cindex @code{string} directive Copy the characters in @var{str} to the object file. You may specify more than one string to copy, separated by commas. Unless otherwise specified for a particular machine, the assembler marks the end of each string with a 0 byte. You can use any of the escape sequences described in @ref{Strings,,Strings}. @node Struct @section @code{.struct @var{expression}} @cindex @code{struct} directive Switch to the absolute section, and set the section offset to @var{expression}, which must be an absolute expression. You might use this as follows: @smallexample .struct 0 field1: .struct field1 + 4 field2: .struct field2 + 4 field3: @end smallexample This would define the symbol @code{field1} to have the value 0, the symbol @code{field2} to have the value 4, and the symbol @code{field3} to have the value 8. Assembly would be left in the absolute section, and you would need to use a @code{.section} directive of some sort to change to some other section before further assembly. @ifset ELF @node SubSection @section @code{.subsection @var{name}} @cindex @code{.subsection} directive @cindex Section Stack This is one of the ELF section stack manipulation directives. The others are @pxref{Section}, @xref{PushSection}, @pxref{PopSection}, and @pxref{Previous}. This directive replaces the current subsection with @code{name}. The current section is not changed. The replaced subsection is put onto the section stack in place of the then current top of stack subsection. @end ifset @ifset ELF @node Symver @section @code{.symver} @cindex @code{symver} directive @cindex symbol versioning @cindex versions of symbols Use the @code{.symver} directive to bind symbols to specific version nodes within a source file. This is only supported on ELF platforms, and is typically used when assembling files to be linked into a shared library. There are cases where it may make sense to use this in objects to be bound into an application itself so as to override a versioned symbol from a shared library. For ELF targets, the @code{.symver} directive is used like this: @smallexample .symver @var{name}, @var{name2@@nodename} @end smallexample In this case, the symbol @var{name} must exist and be defined within the file being assembled. The @code{.versym} directive effectively creates a symbol alias with the name @var{name2@@nodename}, and in fact the main reason that we just don't try and create a regular alias is that the @var{@@} character isn't permitted in symbol names. The @var{name2} part of the name is the actual name of the symbol by which it will be externally referenced. The name @var{name} itself is merely a name of convenience that is used so that it is possible to have definitions for multiple versions of a function within a single source file, and so that the compiler can unambiguously know which version of a function is being mentioned. The @var{nodename} portion of the alias should be the name of a node specified in the version script supplied to the linker when building a shared library. If you are attempting to override a versioned symbol from a shared library, then @var{nodename} should correspond to the nodename of the symbol you are trying to override. @end ifset @ifset COFF @node Tag @section @code{.tag @var{structname}} @cindex COFF structure debugging @cindex structure debugging, COFF @cindex @code{tag} directive This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside @code{.def}/@code{.endef} pairs. Tags are used to link structure definitions in the symbol table with instances of those structures. @ifset BOUT @samp{.tag} is only used when generating COFF format output; when @code{@value{AS}} is generating @code{b.out}, it accepts this directive but ignores it. @end ifset @end ifset @node Text @section @code{.text @var{subsection}} @cindex @code{text} directive Tells @code{@value{AS}} to assemble the following statements onto the end of the text subsection numbered @var{subsection}, which is an absolute expression. If @var{subsection} is omitted, subsection number zero is used. @node Title @section @code{.title "@var{heading}"} @cindex @code{title} directive @cindex listing control: title line Use @var{heading} as the title (second line, immediately after the source file name and pagenumber) when generating assembly listings. This directive affects subsequent pages, as well as the current page if it appears within ten lines of the top of a page. @node Type @section @code{.type @var{int}} (COFF version) @cindex COFF symbol type @cindex symbol type, COFF @cindex @code{type} directive This directive, permitted only within @code{.def}/@code{.endef} pairs, records the integer @var{int} as the type attribute of a symbol table entry. @ifset BOUT @samp{.type} is associated only with COFF format output; when @code{@value{AS}} is configured for @code{b.out} output, it accepts this directive but ignores it. @end ifset @section @code{.type @var{name} , @var{type description}} (ELF version) @cindex ELF symbol type @cindex symbol type, ELF @cindex @code{type} directive This directive is used to set the type of symbol @var{name} to be either a function symbol or an ojbect symbol. There are five different syntaxes supported for the @var{type description} field, in order to provide comptability with various other assemblers. The syntaxes supported are: @smallexample .type ,#function .type ,#object .type ,@@function .type ,@@object .type ,%function .type ,%object .type ,"function" .type ,"object" .type STT_FUNCTION .type STT_OBJECT @end smallexample @node Uleb128 @section @code{.uleb128 @var{expressions}} @cindex @code{uleb128} directive @var{uleb128} stands for ``unsigned little endian base 128.'' This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format. @xref{Sleb128,@code{.sleb128}}. @ifset COFF @node Val @section @code{.val @var{addr}} @cindex @code{val} directive @cindex COFF value attribute @cindex value attribute, COFF This directive, permitted only within @code{.def}/@code{.endef} pairs, records the address @var{addr} as the value attribute of a symbol table entry. @ifset BOUT @samp{.val} is used only for COFF output; when @code{@value{AS}} is configured for @code{b.out}, it accepts this directive but ignores it. @end ifset @end ifset @ifset ELF @node Version @section @code{.version "@var{string}"} @cindex @code{.version} This directive creates a @code{.note} section and places into it an ELF formatted note of type NT_VERSION. The note's name is set to @code{string}. @end ifset @ifset ELF @node VTableEntry @section @code{.vtable_entry @var{table}, @var{offset}} @cindex @code{.vtable_entry} This directive finds or creates a symbol @code{table} and creates a @code{VTABLE_ENTRY} relocation for it with an addend of @code{offset}. @node VTableInherit @section @code{.vtable_inherit @var{child}, @var{parent}} @cindex @code{.vtable_inherit} This directive finds the symbol @code{child} and finds or creates the symbol @code{parent} and then creates a @code{VTABLE_INHERIT} relocation for the parent whoes addend is the value of the child symbol. As a special case the parent name of @code{0} is treated as refering the @code{*ABS*} section. @end ifset @ifset ELF @node Weak @section @code{.weak @var{names}} @cindex @code{.weak} This directive sets the weak attribute on the comma seperated list of symbol @code{names}. If the symbols do not already exist, they will be created. @end ifset @node Word @section @code{.word @var{expressions}} @cindex @code{word} directive This directive expects zero or more @var{expressions}, of any section, separated by commas. @ifclear GENERIC @ifset W32 For each expression, @code{@value{AS}} emits a 32-bit number. @end ifset @ifset W16 For each expression, @code{@value{AS}} emits a 16-bit number. @end ifset @end ifclear @ifset GENERIC The size of the number emitted, and its byte order, depend on what target computer the assembly is for. @end ifset @c on amd29k, i960, sparc the "special treatment to support compilers" doesn't @c happen---32-bit addressability, period; no long/short jumps. @ifset DIFF-TBL-KLUGE @cindex difference tables altered @cindex altered difference tables @quotation @emph{Warning: Special Treatment to support Compilers} @end quotation @ifset GENERIC Machines with a 32-bit address space, but that do less than 32-bit addressing, require the following special treatment. If the machine of interest to you does 32-bit addressing (or doesn't require it; @pxref{Machine Dependencies}), you can ignore this issue. @end ifset In order to assemble compiler output into something that works, @code{@value{AS}} occasionlly does strange things to @samp{.word} directives. Directives of the form @samp{.word sym1-sym2} are often emitted by compilers as part of jump tables. Therefore, when @code{@value{AS}} assembles a directive of the form @samp{.word sym1-sym2}, and the difference between @code{sym1} and @code{sym2} does not fit in 16 bits, @code{@value{AS}} creates a @dfn{secondary jump table}, immediately before the next label. This secondary jump table is preceded by a short-jump to the first byte after the secondary table. This short-jump prevents the flow of control from accidentally falling into the new table. Inside the table is a long-jump to @code{sym2}. The original @samp{.word} contains @code{sym1} minus the address of the long-jump to @code{sym2}. If there were several occurrences of @samp{.word sym1-sym2} before the secondary jump table, all of them are adjusted. If there was a @samp{.word sym3-sym4}, that also did not fit in sixteen bits, a long-jump to @code{sym4} is included in the secondary jump table, and the @code{.word} directives are adjusted to contain @code{sym3} minus the address of the long-jump to @code{sym4}; and so on, for as many entries in the original jump table as necessary. @ifset INTERNALS @emph{This feature may be disabled by compiling @code{@value{AS}} with the @samp{-DWORKING_DOT_WORD} option.} This feature is likely to confuse assembly language programmers. @end ifset @end ifset @c end DIFF-TBL-KLUGE @node Deprecated @section Deprecated Directives @cindex deprecated directives @cindex obsolescent directives One day these directives won't work. They are included for compatibility with older assemblers. @table @t @item .abort @item .line @end table @ifset GENERIC @node Machine Dependencies @chapter Machine Dependent Features @cindex machine dependencies The machine instruction sets are (almost by definition) different on each machine where @code{@value{AS}} runs. Floating point representations vary as well, and @code{@value{AS}} often supports a few additional directives or command-line options for compatibility with other assemblers on a particular platform. Finally, some versions of @code{@value{AS}} support special pseudo-instructions for branch optimization. This chapter discusses most of these differences, though it does not include details on any machine's instruction set. For details on that subject, see the hardware manufacturer's manual. @menu @ifset A29K * AMD29K-Dependent:: AMD 29K Dependent Features @end ifset @ifset ARC * ARC-Dependent:: ARC Dependent Features @end ifset @ifset ARM * ARM-Dependent:: ARM Dependent Features @end ifset @ifset D10V * D10V-Dependent:: D10V Dependent Features @end ifset @ifset D30V * D30V-Dependent:: D30V Dependent Features @end ifset @ifset H8/300 * H8/300-Dependent:: Hitachi H8/300 Dependent Features @end ifset @ifset H8/500 * H8/500-Dependent:: Hitachi H8/500 Dependent Features @end ifset @ifset HPPA * HPPA-Dependent:: HPPA Dependent Features @end ifset @ifset I370 * ESA/390-Dependent:: IBM ESA/390 Dependent Features @end ifset @ifset I80386 * i386-Dependent:: Intel 80386 Dependent Features @end ifset @ifset I860 * i860-Dependent:: Intel 80860 Dependent Features @end ifset @ifset I960 * i960-Dependent:: Intel 80960 Dependent Features @end ifset @ifset M32R * M32R-Dependent:: M32R Dependent Features @end ifset @ifset M680X0 * M68K-Dependent:: M680x0 Dependent Features @end ifset @ifset M68HC11 * M68HC11-Dependent:: M68HC11 and 68HC12 Dependent Features @end ifset @ifset MIPS * MIPS-Dependent:: MIPS Dependent Features @end ifset @ifset SH * SH-Dependent:: Hitachi SH Dependent Features @end ifset @ifset PJ * PJ-Dependent:: picoJava Dependent Features @end ifset @ifset SPARC * Sparc-Dependent:: SPARC Dependent Features @end ifset @ifset TIC54X * TIC54X-Dependent:: TI TMS320C54x Dependent Features @end ifset @ifset V850 * V850-Dependent:: V850 Dependent Features @end ifset @ifset Z8000 * Z8000-Dependent:: Z8000 Dependent Features @end ifset @ifset VAX * Vax-Dependent:: VAX Dependent Features @end ifset @end menu @lowersections @end ifset @c The following major nodes are *sections* in the GENERIC version, *chapters* @c in single-cpu versions. This is mainly achieved by @lowersections. There is a @c peculiarity: to preserve cross-references, there must be a node called @c "Machine Dependencies". Hence the conditional nodenames in each @c major node below. Node defaulting in makeinfo requires adjacency of @c node and sectioning commands; hence the repetition of @chapter BLAH @c in both conditional blocks. @ifset ARC @ifset GENERIC @page @node ARC-Dependent @chapter ARC Dependent Features @end ifset @ifclear GENERIC @node Machine Dependencies @chapter ARC Dependent Features @end ifclear @cindex ARC support @menu * ARC-Opts:: Options * ARC-Float:: Floating Point * ARC-Directives:: Sparc Machine Directives @end menu @node ARC-Opts @section Options @cindex options for ARC @cindex ARC options @cindex architectures, ARC @cindex ARC architectures The ARC chip family includes several successive levels (or other variants) of chip, using the same core instruction set, but including a few additional instructions at each level. By default, @code{@value{AS}} assumes the core instruction set (ARC base). The @code{.cpu} pseudo-op is intended to be used to select the variant. @table @code @cindex @code{-mbig-endian} option (ARC) @cindex @code{-mlittle-endian} option (ARC) @cindex ARC big-endian output @cindex ARC little-endian output @cindex big-endian output, ARC @cindex little-endian output, ARC @item -mbig-endian @itemx -mlittle-endian Any @sc{arc} configuration of @code{@value{AS}} can select big-endian or little-endian output at run time (unlike most other @sc{gnu} development tools, which must be configured for one or the other). Use @samp{-mbig-endian} to select big-endian output, and @samp{-mlittle-endian} for little-endian. @end table @node ARC-Float @section Floating Point @cindex floating point, ARC (@sc{ieee}) @cindex ARC floating point (@sc{ieee}) The ARC cpu family currently does not have hardware floating point support. Software floating point support is provided by @code{GCC} and uses @sc{ieee} floating-point numbers. @node ARC-Directives @section ARC Machine Directives @cindex ARC machine directives @cindex machine directives, ARC The ARC version of @code{@value{AS}} supports the following additional machine directives: @table @code @item .cpu @cindex @code{cpu} directive, SPARC This must be followed by the desired cpu. The ARC is intended to be customizable, @code{.cpu} is used to select the desired variant [though currently there are none]. @end table @end ifset @ifset A29K @include c-a29k.texi @end ifset @ifset ARM @include c-arm.texi @end ifset @ifset Hitachi-all @ifclear GENERIC @node Machine Dependencies @chapter Machine Dependent Features The machine instruction sets are different on each Hitachi chip family, and there are also some syntax differences among the families. This chapter describes the specific @code{@value{AS}} features for each family. @menu * H8/300-Dependent:: Hitachi H8/300 Dependent Features * H8/500-Dependent:: Hitachi H8/500 Dependent Features * SH-Dependent:: Hitachi SH Dependent Features @end menu @lowersections @end ifclear @end ifset @ifset D10V @include c-d10v.texi @end ifset @ifset D30V @include c-d30v.texi @end ifset @ifset H8/300 @include c-h8300.texi @end ifset @ifset H8/500 @include c-h8500.texi @end ifset @ifset HPPA @include c-hppa.texi @end ifset @ifset I370 @include c-i370.texi @end ifset @ifset I80386 @include c-i386.texi @end ifset @ifset I860 @include c-i860.texi @end ifset @ifset I960 @include c-i960.texi @end ifset @ifset M32R @include c-m32r.texi @end ifset @ifset M680X0 @include c-m68k.texi @end ifset @ifset M68HC11 @include c-m68hc11.texi @end ifset @ifset MIPS @include c-mips.texi @end ifset @ifset NS32K @include c-ns32k.texi @end ifset @ifset PJ @include c-pj.texi @end ifset @ifset SH @include c-sh.texi @end ifset @ifset SPARC @include c-sparc.texi @end ifset @ifset TIC54X @include c-tic54x.texi @end ifset @ifset Z8000 @include c-z8k.texi @end ifset @ifset VAX @include c-vax.texi @end ifset @ifset V850 @include c-v850.texi @end ifset @ifset GENERIC @c reverse effect of @down at top of generic Machine-Dep chapter @raisesections @end ifset @node Reporting Bugs @chapter Reporting Bugs @cindex bugs in assembler @cindex reporting bugs in assembler Your bug reports play an essential role in making @code{@value{AS}} reliable. Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of @code{@value{AS}} work better. Bug reports are your contribution to the maintenance of @code{@value{AS}}. In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug. @menu * Bug Criteria:: Have you found a bug? * Bug Reporting:: How to report bugs @end menu @node Bug Criteria @section Have you found a bug? @cindex bug criteria If you are not sure whether you have found a bug, here are some guidelines: @itemize @bullet @cindex fatal signal @cindex assembler crash @cindex crash of assembler @item If the assembler gets a fatal signal, for any input whatever, that is a @code{@value{AS}} bug. Reliable assemblers never crash. @cindex error on valid input @item If @code{@value{AS}} produces an error message for valid input, that is a bug. @cindex invalid input @item If @code{@value{AS}} does not produce an error message for invalid input, that is a bug. However, you should note that your idea of ``invalid input'' might be our idea of ``an extension'' or ``support for traditional practice''. @item If you are an experienced user of assemblers, your suggestions for improvement of @code{@value{AS}} are welcome in any case. @end itemize @node Bug Reporting @section How to report bugs @cindex bug reports @cindex assembler bugs, reporting A number of companies and individuals offer support for @sc{gnu} products. If you obtained @code{@value{AS}} from a support organization, we recommend you contact that organization first. You can find contact information for many support companies and individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs distribution. In any event, we also recommend that you send bug reports for @code{@value{AS}} to @samp{bug-gnu-utils@@gnu.org}. The fundamental principle of reporting bugs usefully is this: @strong{report all the facts}. If you are not sure whether to state a fact or leave it out, state it! Often people omit facts because they think they know what causes the problem and assume that some details do not matter. Thus, you might assume that the name of a symbol you use in an example does not matter. Well, probably it does not, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the assembler into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful. Keep in mind that the purpose of a bug report is to enable us to fix the bug if it is new to us. Therefore, always write your bug reports on the assumption that the bug has not been reported previously. Sometimes people give a few sketchy facts and ask, ``Does this ring a bell?'' Those bug reports are useless, and we urge everyone to @emph{refuse to respond to them} except to chide the sender to report bugs properly. To enable us to fix the bug, you should include all these things: @itemize @bullet @item The version of @code{@value{AS}}. @code{@value{AS}} announces it if you start it with the @samp{--version} argument. Without this, we will not know whether there is any point in looking for the bug in the current version of @code{@value{AS}}. @item Any patches you may have applied to the @code{@value{AS}} source. @item The type of machine you are using, and the operating system name and version number. @item What compiler (and its version) was used to compile @code{@value{AS}}---e.g. ``@code{gcc-2.7}''. @item The command arguments you gave the assembler to assemble your example and observe the bug. To guarantee you will not omit something important, list them all. A copy of the Makefile (or the output from make) is sufficient. If we were to try to guess the arguments, we would probably guess wrong and then we might not encounter the bug. @item A complete input file that will reproduce the bug. If the bug is observed when the assembler is invoked via a compiler, send the assembler source, not the high level language source. Most compilers will produce the assembler source when run with the @samp{-S} option. If you are using @code{@value{GCC}}, use the options @samp{-v --save-temps}; this will save the assembler source in a file with an extension of @file{.s}, and also show you exactly how @code{@value{AS}} is being run. @item A description of what behavior you observe that you believe is incorrect. For example, ``It gets a fatal signal.'' Of course, if the bug is that @code{@value{AS}} gets a fatal signal, then we will certainly notice it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. You might as well not give us a chance to make a mistake. Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of @code{@value{AS}} is out of synch, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and ours would not. If you told us to expect a crash, then when ours fails to crash, we would know that the bug was not happening for us. If you had not told us to expect a crash, then we would not be able to draw any conclusion from our observations. @item If you wish to suggest changes to the @code{@value{AS}} source, send us context diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or @samp{-p} option. Always send diffs from the old file to the new file. If you even discuss something in the @code{@value{AS}} source, refer to it by context, not by line number. The line numbers in our development sources will not match those in your sources. Your line numbers would convey no useful information to us. @end itemize Here are some things that are not necessary: @itemize @bullet @item A description of the envelope of the bug. Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it. This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. We recommend that you save your time for something else. Of course, if you can find a simpler example to report @emph{instead} of the original one, that is a convenience for us. Errors in the output will be easier to spot, running under the debugger will take less time, and so on. However, simplification is not vital; if you do not want to do this, report the bug anyway and send us the entire test case you used. @item A patch for the bug. A patch for the bug does help us if it is a good one. But do not omit the necessary information, such as the test case, on the assumption that a patch is all we need. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all. Sometimes with a program as complicated as @code{@value{AS}} it is very hard to construct an example that will make the program follow a certain path through the code. If you do not send us the example, we will not be able to construct one, so we will not be able to verify that the bug is fixed. And if we cannot understand what bug you are trying to fix, or why your patch should be an improvement, we will not install it. A test case will help us to understand. @item A guess about what the bug is or what it depends on. Such guesses are usually wrong. Even we cannot guess right about such things without first using the debugger to find the facts. @end itemize @node Acknowledgements @chapter Acknowledgements If you have contributed to @code{@value{AS}} and your name isn't listed here, it is not meant as a slight. We just don't know about it. Send mail to the maintainer, and we'll correct the situation. Currently @c (January 1994), the maintainer is Ken Raeburn (email address @code{raeburn@@cygnus.com}). Dean Elsner wrote the original @sc{gnu} assembler for the VAX.@footnote{Any more details?} Jay Fenlason maintained GAS for a while, adding support for GDB-specific debug information and the 68k series machines, most of the preprocessing pass, and extensive changes in @file{messages.c}, @file{input-file.c}, @file{write.c}. K. Richard Pixley maintained GAS for a while, adding various enhancements and many bug fixes, including merging support for several processors, breaking GAS up to handle multiple object file format back ends (including heavy rewrite, testing, an integration of the coff and b.out back ends), adding configuration including heavy testing and verification of cross assemblers and file splits and renaming, converted GAS to strictly ANSI C including full prototypes, added support for m680[34]0 and cpu32, did considerable work on i960 including a COFF port (including considerable amounts of reverse engineering), a SPARC opcode file rewrite, DECstation, rs6000, and hp300hpux host ports, updated ``know'' assertions and made them work, much other reorganization, cleanup, and lint. Ken Raeburn wrote the high-level BFD interface code to replace most of the code in format-specific I/O modules. The original VMS support was contributed by David L. Kashtan. Eric Youngdale has done much work with it since. The Intel 80386 machine description was written by Eliot Dresselhaus. Minh Tran-Le at IntelliCorp contributed some AIX 386 support. The Motorola 88k machine description was contributed by Devon Bowen of Buffalo University and Torbjorn Granlund of the Swedish Institute of Computer Science. Keith Knowles at the Open Software Foundation wrote the original MIPS back end (@file{tc-mips.c}, @file{tc-mips.h}), and contributed Rose format support (which hasn't been merged in yet). Ralph Campbell worked with the MIPS code to support a.out format. Support for the Zilog Z8k and Hitachi H8/300 and H8/500 processors (tc-z8k, tc-h8300, tc-h8500), and IEEE 695 object file format (obj-ieee), was written by Steve Chamberlain of Cygnus Support. Steve also modified the COFF back end to use BFD for some low-level operations, for use with the H8/300 and AMD 29k targets. John Gilmore built the AMD 29000 support, added @code{.include} support, and simplified the configuration of which versions accept which directives. He updated the 68k machine description so that Motorola's opcodes always produced fixed-size instructions (e.g. @code{jsr}), while synthetic instructions remained shrinkable (@code{jbsr}). John fixed many bugs, including true tested cross-compilation support, and one bug in relaxation that took a week and required the proverbial one-bit fix. Ian Lance Taylor of Cygnus Support merged the Motorola and MIT syntax for the 68k, completed support for some COFF targets (68k, i386 SVR3, and SCO Unix), added support for MIPS ECOFF and ELF targets, wrote the initial RS/6000 and PowerPC assembler, and made a few other minor patches. Steve Chamberlain made @code{@value{AS}} able to generate listings. Hewlett-Packard contributed support for the HP9000/300. Jeff Law wrote GAS and BFD support for the native HPPA object format (SOM) along with a fairly extensive HPPA testsuite (for both SOM and ELF object formats). This work was supported by both the Center for Software Science at the University of Utah and Cygnus Support. Support for ELF format files has been worked on by Mark Eichin of Cygnus Support (original, incomplete implementation for SPARC), Pete Hoogenboom and Jeff Law at the University of Utah (HPPA mainly), Michael Meissner of the Open Software Foundation (i386 mainly), and Ken Raeburn of Cygnus Support (sparc, and some initial 64-bit support). Linas Vepstas added GAS support for the ESA/390 "IBM 370" architecture. Richard Henderson rewrote the Alpha assembler. Klaus Kaempf wrote GAS and BFD support for openVMS/Alpha. Timothy Wall, Michael Hayes, and Greg Smart contributed to the various tic* flavors. Several engineers at Cygnus Support have also provided many small bug fixes and configuration enhancements. Many others have contributed large or small bugfixes and enhancements. If you have contributed significant work and are not mentioned on this list, and want to be, let us know. Some of the history has been lost; we are not intentionally leaving anyone out. @node Index @unnumbered Index @printindex cp @contents @bye @c Local Variables: @c fill-column: 79 @c End: