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 This is as.info, produced by makeinfo version 4.8 from as.texinfo. INFO-DIR-SECTION Software development START-INFO-DIR-ENTRY * As: (as). The GNU assembler. * Gas: (as). The GNU assembler. END-INFO-DIR-ENTRY This file documents the GNU Assembler "as". Copyright (C) 1991-2013 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". File: as.info, Node: Top, Next: Overview, Up: (dir) Using as ******** This file is a user guide to the GNU assembler as' (GNU Binutils) version 2.23.91. This document is distributed under the terms of the GNU Free Documentation License. A copy of the license is included in the section entitled "GNU Free Documentation License". * Menu: * Overview:: Overview * Invoking:: Command-Line Options * Syntax:: Syntax * Sections:: Sections and Relocation * Symbols:: Symbols * Expressions:: Expressions * Pseudo Ops:: Assembler Directives * Object Attributes:: Object Attributes * Machine Dependencies:: Machine Dependent Features * Reporting Bugs:: Reporting Bugs * Acknowledgements:: Who Did What * GNU Free Documentation License:: GNU Free Documentation License * AS Index:: AS Index File: as.info, Node: Overview, Next: Invoking, Prev: Top, Up: Top 1 Overview ********** Here is a brief summary of how to invoke as'. For details, see *Note Command-Line Options: Invoking. as [-a[cdghlns][=FILE]] [-alternate] [-D] [-compress-debug-sections] [-nocompress-debug-sections] [-debug-prefix-map OLD=NEW] [-defsym SYM=VAL] [-f] [-g] [-gstabs] [-gstabs+] [-gdwarf-2] [-gdwarf-sections] [-help] [-I DIR] [-J] [-K] [-L] [-listing-lhs-width=NUM] [-listing-lhs-width2=NUM] [-listing-rhs-width=NUM] [-listing-cont-lines=NUM] [-keep-locals] [-o OBJFILE] [-R] [-reduce-memory-overheads] [-statistics] [-v] [-version] [-version] [-W] [-warn] [-fatal-warnings] [-w] [-x] [-Z] [@FILE] [-size-check=[error|warning]] [-target-help] [TARGET-OPTIONS] [-|FILES ...] _Target AArch64 options:_ [-EB|-EL] [-mabi=ABI] _Target Alpha options:_ [-mCPU] [-mdebug | -no-mdebug] [-replace | -noreplace] [-relax] [-g] [-GSIZE] [-F] [-32addr] _Target ARC options:_ [-marc[5|6|7|8]] [-EB|-EL] _Target ARM options:_ [-mcpu=PROCESSOR[+EXTENSION...]] [-march=ARCHITECTURE[+EXTENSION...]] [-mfpu=FLOATING-POINT-FORMAT] [-mfloat-abi=ABI] [-meabi=VER] [-mthumb] [-EB|-EL] [-mapcs-32|-mapcs-26|-mapcs-float| -mapcs-reentrant] [-mthumb-interwork] [-k] _Target Blackfin options:_ [-mcpu=PROCESSOR[-SIREVISION]] [-mfdpic] [-mno-fdpic] [-mnopic] _Target CRIS options:_ [-underscore | -no-underscore] [-pic] [-N] [-emulation=criself | -emulation=crisaout] [-march=v0_v10 | -march=v10 | -march=v32 | -march=common_v10_v32] _Target D10V options:_ [-O] _Target D30V options:_ [-O|-n|-N] _Target EPIPHANY options:_ [-mepiphany|-mepiphany16] _Target H8/300 options:_ [-h-tick-hex] _Target i386 options:_ [-32|-x32|-64] [-n] [-march=CPU[+EXTENSION...]] [-mtune=CPU] _Target i960 options:_ [-ACA|-ACA_A|-ACB|-ACC|-AKA|-AKB| -AKC|-AMC] [-b] [-no-relax] _Target IA-64 options:_ [-mconstant-gp|-mauto-pic] [-milp32|-milp64|-mlp64|-mp64] [-mle|mbe] [-mtune=itanium1|-mtune=itanium2] [-munwind-check=warning|-munwind-check=error] [-mhint.b=ok|-mhint.b=warning|-mhint.b=error] [-x|-xexplicit] [-xauto] [-xdebug] _Target IP2K options:_ [-mip2022|-mip2022ext] _Target M32C options:_ [-m32c|-m16c] [-relax] [-h-tick-hex] _Target M32R options:_ [-m32rx|-[no-]warn-explicit-parallel-conflicts| -W[n]p] _Target M680X0 options:_ [-l] [-m68000|-m68010|-m68020|...] _Target M68HC11 options:_ [-m68hc11|-m68hc12|-m68hcs12|-mm9s12x|-mm9s12xg] [-mshort|-mlong] [-mshort-double|-mlong-double] [-force-long-branches] [-short-branches] [-strict-direct-mode] [-print-insn-syntax] [-print-opcodes] [-generate-example] _Target MCORE options:_ [-jsri2bsr] [-sifilter] [-relax] [-mcpu=[210|340]] _Target Meta options:_ [-mcpu=CPU] [-mfpu=CPU] [-mdsp=CPU] _Target MICROBLAZE options:_ _Target MIPS options:_ [-nocpp] [-EL] [-EB] [-O[OPTIMIZATION LEVEL]] [-g[DEBUG LEVEL]] [-G NUM] [-KPIC] [-call_shared] [-non_shared] [-xgot [-mvxworks-pic] [-mabi=ABI] [-32] [-n32] [-64] [-mfp32] [-mgp32] [-march=CPU] [-mtune=CPU] [-mips1] [-mips2] [-mips3] [-mips4] [-mips5] [-mips32] [-mips32r2] [-mips64] [-mips64r2] [-construct-floats] [-no-construct-floats] [-mnan=ENCODING] [-trap] [-no-break] [-break] [-no-trap] [-mips16] [-no-mips16] [-mmicromips] [-mno-micromips] [-msmartmips] [-mno-smartmips] [-mips3d] [-no-mips3d] [-mdmx] [-no-mdmx] [-mdsp] [-mno-dsp] [-mdspr2] [-mno-dspr2] [-mmt] [-mno-mt] [-mmcu] [-mno-mcu] [-minsn32] [-mno-insn32] [-mfix7000] [-mno-fix7000] [-mfix-vr4120] [-mno-fix-vr4120] [-mfix-vr4130] [-mno-fix-vr4130] [-mdebug] [-no-mdebug] [-mpdr] [-mno-pdr] _Target MMIX options:_ [-fixed-special-register-names] [-globalize-symbols] [-gnu-syntax] [-relax] [-no-predefined-symbols] [-no-expand] [-no-merge-gregs] [-x] [-linker-allocated-gregs] _Target Nios II options:_ [-relax-all] [-relax-section] [-no-relax] [-EB] [-EL] _Target PDP11 options:_ [-mpic|-mno-pic] [-mall] [-mno-extensions] [-mEXTENSION|-mno-EXTENSION] [-mCPU] [-mMACHINE] _Target picoJava options:_ [-mb|-me] _Target PowerPC options:_ [-a32|-a64] [-mpwrx|-mpwr2|-mpwr|-m601|-mppc|-mppc32|-m603|-m604|-m403|-m405| -m440|-m464|-m476|-m7400|-m7410|-m7450|-m7455|-m750cl|-mppc64| -m620|-me500|-e500x2|-me500mc|-me500mc64|-me5500|-me6500|-mppc64bridge| -mbooke|-mpower4|-mpwr4|-mpower5|-mpwr5|-mpwr5x|-mpower6|-mpwr6| -mpower7|-mpwr7|-mpower8|-mpwr8|-ma2|-mcell|-mspe|-mtitan|-me300|-mcom] [-many] [-maltivec|-mvsx|-mhtm|-mvle] [-mregnames|-mno-regnames] [-mrelocatable|-mrelocatable-lib|-K PIC] [-memb] [-mlittle|-mlittle-endian|-le|-mbig|-mbig-endian|-be] [-msolaris|-mno-solaris] [-nops=COUNT] _Target RX options:_ [-mlittle-endian|-mbig-endian] [-m32bit-doubles|-m64bit-doubles] [-muse-conventional-section-names] [-msmall-data-limit] [-mpid] [-mrelax] [-mint-register=NUMBER] [-mgcc-abi|-mrx-abi] _Target s390 options:_ [-m31|-m64] [-mesa|-mzarch] [-march=CPU] [-mregnames|-mno-regnames] [-mwarn-areg-zero] _Target SCORE options:_ [-EB][-EL][-FIXDD][-NWARN] [-SCORE5][-SCORE5U][-SCORE7][-SCORE3] [-march=score7][-march=score3] [-USE_R1][-KPIC][-O0][-G NUM][-V] _Target SPARC options:_ [-Av6|-Av7|-Av8|-Asparclet|-Asparclite -Av8plus|-Av8plusa|-Av9|-Av9a] [-xarch=v8plus|-xarch=v8plusa] [-bump] [-32|-64] _Target TIC54X options:_ [-mcpu=54[123589]|-mcpu=54[56]lp] [-mfar-mode|-mf] [-merrors-to-file |-me ] _Target TIC6X options:_ [-march=ARCH] [-mbig-endian|-mlittle-endian] [-mdsbt|-mno-dsbt] [-mpid=no|-mpid=near|-mpid=far] [-mpic|-mno-pic] _Target TILE-Gx options:_ [-m32|-m64][-EB][-EL] _Target Xtensa options:_ [-[no-]text-section-literals] [-[no-]absolute-literals] [-[no-]target-align] [-[no-]longcalls] [-[no-]transform] [-rename-section OLDNAME=NEWNAME] _Target Z80 options:_ [-z80] [-r800] [ -ignore-undocumented-instructions] [-Wnud] [ -ignore-unportable-instructions] [-Wnup] [ -warn-undocumented-instructions] [-Wud] [ -warn-unportable-instructions] [-Wup] [ -forbid-undocumented-instructions] [-Fud] [ -forbid-unportable-instructions] [-Fup] @FILE' Read command-line options from FILE. The options read are inserted in place of the original @FILE option. If FILE does not exist, or cannot be read, then the option will be treated literally, and not removed. Options in FILE are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The FILE may itself contain additional @FILE options; any such options will be processed recursively. -a[cdghlmns]' Turn on listings, in any of a variety of ways: -ac' omit false conditionals -ad' omit debugging directives -ag' include general information, like as version and options passed -ah' include high-level source -al' include assembly -am' include macro expansions -an' omit forms processing -as' include symbols =file' set the name of the listing file You may combine these options; for example, use -aln' for assembly listing without forms processing. The =file' option, if used, must be the last one. By itself, -a' defaults to -ahls'. --alternate' Begin in alternate macro mode. *Note .altmacro': Altmacro. --compress-debug-sections' Compress DWARF debug sections using zlib. The debug sections are renamed to begin with .zdebug', and the resulting object file may not be compatible with older linkers and object file utilities. --nocompress-debug-sections' Do not compress DWARF debug sections. This is the default. -D' Ignored. This option is accepted for script compatibility with calls to other assemblers. --debug-prefix-map OLD=NEW' When assembling files in directory OLD', record debugging information describing them as in NEW' instead. --defsym SYM=VALUE' Define the symbol SYM to be VALUE before assembling the input file. VALUE must be an integer constant. As in C, a leading 0x' indicates a hexadecimal value, and a leading 0' indicates an octal value. The value of the symbol can be overridden inside a source file via the use of a .set' pseudo-op. -f' "fast"--skip whitespace and comment preprocessing (assume source is compiler output). -g' --gen-debug' Generate debugging information for each assembler source line using whichever debug format is preferred by the target. This currently means either STABS, ECOFF or DWARF2. --gstabs' Generate stabs debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it. --gstabs+' Generate stabs debugging information for each assembler line, with GNU extensions that probably only gdb can handle, and that could make other debuggers crash or refuse to read your program. This may help debugging assembler code. Currently the only GNU extension is the location of the current working directory at assembling time. --gdwarf-2' Generate DWARF2 debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it. Note--this option is only supported by some targets, not all of them. --gdwarf-sections' Instead of creating a .debug_line section, create a series of .debug_line.FOO sections where FOO is the name of the corresponding code section. For example a code section called .TEXT.FUNC will have its dwarf line number information placed into a section called .DEBUG_LINE.TEXT.FUNC. If the code section is just called .TEXT then debug line section will still be called just .DEBUG_LINE without any suffix. --size-check=error' --size-check=warning' Issue an error or warning for invalid ELF .size directive. --help' Print a summary of the command line options and exit. --target-help' Print a summary of all target specific options and exit. -I DIR' Add directory DIR to the search list for .include' directives. -J' Don't warn about signed overflow. -K' Issue warnings when difference tables altered for long displacements. -L' --keep-locals' Keep (in the symbol table) local symbols. These symbols start with system-specific local label prefixes, typically .L' for ELF systems or L' for traditional a.out systems. *Note Symbol Names::. --listing-lhs-width=NUMBER' Set the maximum width, in words, of the output data column for an assembler listing to NUMBER. --listing-lhs-width2=NUMBER' Set the maximum width, in words, of the output data column for continuation lines in an assembler listing to NUMBER. --listing-rhs-width=NUMBER' Set the maximum width of an input source line, as displayed in a listing, to NUMBER bytes. --listing-cont-lines=NUMBER' Set the maximum number of lines printed in a listing for a single line of input to NUMBER + 1. -o OBJFILE' Name the object-file output from as' OBJFILE. -R' Fold the data section into the text section. Set the default size of GAS's hash tables to a prime number close to NUMBER. Increasing this value can reduce the length of time it takes the assembler to perform its tasks, at the expense of increasing the assembler's memory requirements. Similarly reducing this value can reduce the memory requirements at the expense of speed. --reduce-memory-overheads' This option reduces GAS's memory requirements, at the expense of making the assembly processes slower. Currently this switch is a synonym for --hash-size=4051', but in the future it may have other effects as well. --statistics' Print the maximum space (in bytes) and total time (in seconds) used by assembly. --strip-local-absolute' Remove local absolute symbols from the outgoing symbol table. -v' -version' Print the as' version. --version' Print the as' version and exit. -W' --no-warn' Suppress warning messages. --fatal-warnings' Treat warnings as errors. --warn' Don't suppress warning messages or treat them as errors. -w' Ignored. -x' Ignored. -Z' Generate an object file even after errors. -- | FILES ...' Standard input, or source files to assemble. *Note AArch64 Options::, for the options available when as is configured for the 64-bit mode of the ARM Architecture (AArch64). *Note Alpha Options::, for the options available when as is configured for an Alpha processor. The following options are available when as is configured for an ARC processor. -marc[5|6|7|8]' This option selects the core processor variant. -EB | -EL' Select either big-endian (-EB) or little-endian (-EL) output. The following options are available when as is configured for the ARM processor family. -mcpu=PROCESSOR[+EXTENSION...]' Specify which ARM processor variant is the target. -march=ARCHITECTURE[+EXTENSION...]' Specify which ARM architecture variant is used by the target. -mfpu=FLOATING-POINT-FORMAT' Select which Floating Point architecture is the target. -mfloat-abi=ABI' Select which floating point ABI is in use. -mthumb' Enable Thumb only instruction decoding. -mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant' Select which procedure calling convention is in use. -EB | -EL' Select either big-endian (-EB) or little-endian (-EL) output. -mthumb-interwork' Specify that the code has been generated with interworking between Thumb and ARM code in mind. -k' Specify that PIC code has been generated. *Note Blackfin Options::, for the options available when as is configured for the Blackfin processor family. See the info pages for documentation of the CRIS-specific options. The following options are available when as is configured for a D10V processor. -O' Optimize output by parallelizing instructions. The following options are available when as is configured for a D30V processor. -O' Optimize output by parallelizing instructions. -n' Warn when nops are generated. -N' Warn when a nop after a 32-bit multiply instruction is generated. The following options are available when as is configured for the Adapteva EPIPHANY series. *Note Epiphany Options::, for the options available when as is configured for an Epiphany processor. *Note i386-Options::, for the options available when as is configured for an i386 processor. The following options are available when as is configured for the Intel 80960 processor. -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC' Specify which variant of the 960 architecture is the target. -b' Add code to collect statistics about branches taken. -no-relax' Do not alter compare-and-branch instructions for long displacements; error if necessary. The following options are available when as is configured for the Ubicom IP2K series. -mip2022ext' Specifies that the extended IP2022 instructions are allowed. -mip2022' Restores the default behaviour, which restricts the permitted instructions to just the basic IP2022 ones. The following options are available when as is configured for the Renesas M32C and M16C processors. -m32c' Assemble M32C instructions. -m16c' Assemble M16C instructions (the default). -relax' Enable support for link-time relaxations. -h-tick-hex' Support H'00 style hex constants in addition to 0x00 style. The following options are available when as is configured for the Renesas M32R (formerly Mitsubishi M32R) series. --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. --warn-explicit-parallel-conflicts or --Wp' Produce warning messages when questionable parallel constructs are encountered. --no-warn-explicit-parallel-conflicts or --Wnp' Do not produce warning messages when questionable parallel constructs are encountered. The following options are available when as is configured for the Motorola 68000 series. -l' Shorten references to undefined symbols, to one word instead of two. -m68000 | -m68008 | -m68010 | -m68020 | -m68030' | -m68040 | -m68060 | -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. -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. -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. *Note Nios II Options::, for the options available when as is configured for an Altera Nios II processor. For details about the PDP-11 machine dependent features options, see *Note PDP-11-Options::. -mpic | -mno-pic' Generate position-independent (or position-dependent) code. The default is -mpic'. -mall' -mall-extensions' Enable all instruction set extensions. This is the default. -mno-extensions' Disable all instruction set extensions. -mEXTENSION | -mno-EXTENSION' Enable (or disable) a particular instruction set extension. -mCPU' Enable the instruction set extensions supported by a particular CPU, and disable all other extensions. -mMACHINE' Enable the instruction set extensions supported by a particular machine model, and disable all other extensions. The following options are available when as is configured for a picoJava processor. -mb' Generate "big endian" format output. -ml' Generate "little endian" format output. The following options are available when as is configured for the Motorola 68HC11 or 68HC12 series. -m68hc11 | -m68hc12 | -m68hcs12 | -mm9s12x | -mm9s12xg' Specify what processor is the target. The default is defined by the configuration option when building the assembler. --xgate-ramoffset' Instruct the linker to offset RAM addresses from S12X address space into XGATE address space. -mshort' Specify to use the 16-bit integer ABI. -mlong' Specify to use the 32-bit integer ABI. -mshort-double' Specify to use the 32-bit double ABI. -mlong-double' Specify to use the 64-bit double ABI. --force-long-branches' Relative branches are turned into absolute ones. This concerns conditional branches, unconditional branches and branches to a sub routine. -S | --short-branches' Do not turn relative branches into absolute ones when the offset is out of range. --strict-direct-mode' Do not turn the direct addressing mode into extended addressing mode when the instruction does not support direct addressing mode. --print-insn-syntax' Print the syntax of instruction in case of error. --print-opcodes' Print the list of instructions with syntax and then exit. --generate-example' Print an example of instruction for each possible instruction and then exit. This option is only useful for testing as'. The following options are available when as' is configured for the SPARC architecture: -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite' -Av8plus | -Av8plusa | -Av9 | -Av9a' Explicitly select a variant of the SPARC architecture. -Av8plus' and -Av8plusa' select a 32 bit environment. -Av9' and -Av9a' select a 64 bit environment. -Av8plusa' and -Av9a' enable the SPARC V9 instruction set with UltraSPARC extensions. -xarch=v8plus | -xarch=v8plusa' For compatibility with the Solaris v9 assembler. These options are equivalent to -Av8plus and -Av8plusa, respectively. -bump' Warn when the assembler switches to another architecture. The following options are available when as is configured for the 'c54x architecture. -mfar-mode' Enable extended addressing mode. All addresses and relocations will assume extended addressing (usually 23 bits). -mcpu=CPU_VERSION' Sets the CPU version being compiled for. -merrors-to-file FILENAME' Redirect error output to a file, for broken systems which don't support such behaviour in the shell. The following options are available when as is configured for a MIPS processor. -G NUM' This option sets the largest size of an object that can be referenced implicitly with the gp' register. It is only accepted for targets that use ECOFF format, such as a DECstation running Ultrix. The default value is 8. -EB' Generate "big endian" format output. -EL' Generate "little endian" format output. -mips1' -mips2' -mips3' -mips4' -mips5' -mips32' -mips32r2' -mips64' -mips64r2' Generate code for a particular MIPS Instruction Set Architecture level. -mips1' is an alias for -march=r3000', -mips2' is an alias for -march=r6000', -mips3' is an alias for -march=r4000' and -mips4' is an alias for -march=r8000'. -mips5', -mips32', -mips32r2', -mips64', and -mips64r2' correspond to generic MIPS V, MIPS32, MIPS32 Release 2, MIPS64, and MIPS64 Release 2 ISA processors, respectively. -march=CPU' Generate code for a particular MIPS CPU. -mtune=CPU' Schedule and tune for a particular MIPS CPU. -mfix7000' -mno-fix7000' Cause nops to be inserted if the read of the destination register of an mfhi or mflo instruction occurs in the following two instructions. -mdebug' -no-mdebug' Cause stabs-style debugging output to go into an ECOFF-style .mdebug section instead of the standard ELF .stabs sections. -mpdr' -mno-pdr' Control generation of .pdr' sections. -mgp32' -mfp32' The register sizes are normally inferred from the ISA and ABI, but these flags force a certain group of registers to be treated as 32 bits wide at all times. -mgp32' controls the size of general-purpose registers and -mfp32' controls the size of floating-point registers. -mips16' -no-mips16' Generate code for the MIPS 16 processor. This is equivalent to putting .set mips16' at the start of the assembly file. -no-mips16' turns off this option. -mmicromips' -mno-micromips' Generate code for the microMIPS processor. This is equivalent to putting .set micromips' at the start of the assembly file. -mno-micromips' turns off this option. This is equivalent to putting .set nomicromips' at the start of the assembly file. -msmartmips' -mno-smartmips' Enables the SmartMIPS extension to the MIPS32 instruction set. This is equivalent to putting .set smartmips' at the start of the assembly file. -mno-smartmips' turns off this option. -mips3d' -no-mips3d' Generate code for the MIPS-3D Application Specific Extension. This tells the assembler to accept MIPS-3D instructions. -no-mips3d' turns off this option. -mdmx' -no-mdmx' Generate code for the MDMX Application Specific Extension. This tells the assembler to accept MDMX instructions. -no-mdmx' turns off this option. -mdsp' -mno-dsp' Generate code for the DSP Release 1 Application Specific Extension. This tells the assembler to accept DSP Release 1 instructions. -mno-dsp' turns off this option. -mdspr2' -mno-dspr2' Generate code for the DSP Release 2 Application Specific Extension. This option implies -mdsp. This tells the assembler to accept DSP Release 2 instructions. -mno-dspr2' turns off this option. -mmt' -mno-mt' Generate code for the MT Application Specific Extension. This tells the assembler to accept MT instructions. -mno-mt' turns off this option. -mmcu' -mno-mcu' Generate code for the MCU Application Specific Extension. This tells the assembler to accept MCU instructions. -mno-mcu' turns off this option. -minsn32' -mno-insn32' Only use 32-bit instruction encodings when generating code for the microMIPS processor. This option inhibits the use of any 16-bit instructions. This is equivalent to putting .set insn32' at the start of the assembly file. -mno-insn32' turns off this option. This is equivalent to putting .set noinsn32' at the start of the assembly file. By default -mno-insn32' is selected, allowing all instructions to be used. --construct-floats' --no-construct-floats' The --no-construct-floats' option disables the construction of double width floating point constants by loading the two halves of the value into the two single width floating point registers that make up the double width register. By default --construct-floats' is selected, allowing construction of these floating point constants. --relax-branch' --no-relax-branch' The --relax-branch' option enables the relaxation of out-of-range branches. By default --no-relax-branch' is selected, causing any out-of-range branches to produce an error. -mnan=ENCODING' Select between the IEEE 754-2008 (-mnan=2008') or the legacy (-mnan=legacy') NaN encoding format. The latter is the default. --emulation=NAME' This option was formerly used to switch between ELF and ECOFF output on targets like IRIX 5 that supported both. MIPS ECOFF support was removed in GAS 2.24, so the option now serves little purpose. It is retained for backwards compatibility. The available configuration names are: mipself', mipslelf' and mipsbelf'. Choosing mipself' now has no effect, since the output is always ELF. mipslelf' and mipsbelf' select little- and big-endian output respectively, but -EL' and -EB' are now the preferred options instead. -nocpp' as' ignores this option. It is accepted for compatibility with the native tools. --trap' --no-trap' --break' --no-break' Control how to deal with multiplication overflow and division by zero. --trap' or --no-break' (which are synonyms) take a trap exception (and only work for Instruction Set Architecture level 2 and higher); --break' or --no-trap' (also synonyms, and the default) take a break exception. -n' When this option is used, as' will issue a warning every time it generates a nop instruction from a macro. The following options are available when as is configured for an MCore processor. -jsri2bsr' -nojsri2bsr' Enable or disable the JSRI to BSR transformation. By default this is enabled. The command line option -nojsri2bsr' can be used to disable it. -sifilter' -nosifilter' Enable or disable the silicon filter behaviour. By default this is disabled. The default can be overridden by the -sifilter' command line option. -relax' Alter jump instructions for long displacements. -mcpu=[210|340]' Select the cpu type on the target hardware. This controls which instructions can be assembled. -EB' Assemble for a big endian target. -EL' Assemble for a little endian target. *Note Meta Options::, for the options available when as is configured for a Meta processor. See the info pages for documentation of the MMIX-specific options. *Note PowerPC-Opts::, for the options available when as is configured for a PowerPC processor. See the info pages for documentation of the RX-specific options. The following options are available when as is configured for the s390 processor family. -m31' -m64' Select the word size, either 31/32 bits or 64 bits. -mesa' -mzarch' Select the architecture mode, either the Enterprise System Architecture (esa) or the z/Architecture mode (zarch). -march=PROCESSOR' Specify which s390 processor variant is the target, g6', g6', z900', z990', z9-109', z9-ec', z10', z196', or zEC12'. -mregnames' -mno-regnames' Allow or disallow symbolic names for registers. -mwarn-areg-zero' Warn whenever the operand for a base or index register has been specified but evaluates to zero. *Note TIC6X Options::, for the options available when as is configured for a TMS320C6000 processor. *Note TILE-Gx Options::, for the options available when as is configured for a TILE-Gx processor. *Note Xtensa Options::, for the options available when as is configured for an Xtensa processor. The following options are available when as is configured for a Z80 family processor. -z80' Assemble for Z80 processor. -r800' Assemble for R800 processor. -ignore-undocumented-instructions' -Wnud' Assemble undocumented Z80 instructions that also work on R800 without warning. -ignore-unportable-instructions' -Wnup' Assemble all undocumented Z80 instructions without warning. -warn-undocumented-instructions' -Wud' Issue a warning for undocumented Z80 instructions that also work on R800. -warn-unportable-instructions' -Wup' Issue a warning for undocumented Z80 instructions that do not work on R800. -forbid-undocumented-instructions' -Fud' Treat all undocumented instructions as errors. -forbid-unportable-instructions' -Fup' Treat undocumented Z80 instructions that do not work on R800 as errors. * 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 File: as.info, Node: Manual, Next: GNU Assembler, Up: Overview 1.1 Structure of this Manual ============================ This manual is intended to describe what you need to know to use GNU as'. We cover the syntax expected in source files, including notation for symbols, constants, and expressions; the directives that as' understands; and of course how to invoke as'. This manual also describes some of the machine-dependent features of various flavors of the assembler. On the other hand, this manual is _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 _not_ describe the instruction set, standard mnemonics, registers or addressing modes that are standard to a particular architecture. You may want to consult the manufacturer's machine architecture manual for this information. File: as.info, Node: GNU Assembler, Next: Object Formats, Prev: Manual, Up: Overview 1.2 The GNU Assembler ===================== GNU as' is really a family of assemblers. If you use (or have used) the 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 "pseudo-ops") and assembler syntax. as' is primarily intended to assemble the output of the GNU C compiler gcc' for use by the linker ld'. Nevertheless, we've tried to make as' assemble correctly everything that other assemblers for the same machine would assemble. Any exceptions are documented explicitly (*note Machine Dependencies::). This doesn't mean 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. Unlike older assemblers, as' is designed to assemble a source program in one pass of the source file. This has a subtle impact on the .org' directive (*note .org': Org.). File: as.info, Node: Object Formats, Next: Command Line, Prev: GNU Assembler, Up: Overview 1.3 Object File Formats ======================= The 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. *Note Symbol Attributes: Symbol Attributes. File: as.info, Node: Command Line, Next: Input Files, Prev: Object Formats, Up: Overview 1.4 Command Line ================ After the program name 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. --' (two hyphens) by itself names the standard input file explicitly, as one of the files for as' to assemble. Except for --' any command line argument that begins with a hyphen (-') is an option. Each option changes the behavior of as'. No option changes the way another option works. An option is a -' 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 (GNU standard). These two command lines are equivalent: as -o my-object-file.o mumble.s as -omy-object-file.o mumble.s File: as.info, Node: Input Files, Next: Object, Prev: Command Line, Up: Overview 1.5 Input Files =============== We use the phrase "source program", abbreviated "source", to describe the program input to one run of 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. The source program is a concatenation of the text in all the files, in the order specified. Each time you run 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 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 as' no file names it attempts to read one input file from the as' standard input, which is normally your terminal. You may have to type to tell as' there is no more program to assemble. Use --' if you need to explicitly name the standard input file in your command line. If the source is empty, as' produces a small, empty object file. Filenames and Line-numbers -------------------------- 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. *Note Error and Warning Messages: Errors. "Physical files" are those files named in the command line given to as'. "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 as' source is itself synthesized from other files. as' understands the #' directives emitted by the gcc' preprocessor. See also *Note .file': File. File: as.info, Node: Object, Next: Errors, Prev: Input Files, Up: Overview 1.6 Output (Object) File ======================== Every time you run 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 a.out'. You can give it another name by using the -o' option. Conventionally, object file names end with .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 a.out' format.) The object file is meant for input to the linker ld'. It contains assembled program code, information to help ld' integrate the assembled program into a runnable file, and (optionally) symbolic information for the debugger. File: as.info, Node: Errors, Prev: Object, Up: Overview 1.7 Error and Warning Messages ============================== as' may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs as' automatically. Warnings report an assumption made so that as' could keep assembling a flawed program; errors report a grave problem that stops the assembly. Warning messages have the format file_name:NNN:Warning Message Text (where NNN is a line number). If a logical file name has been given (*note .file': File.) it is used for the filename, otherwise the name of the current input file is used. If a logical line number was given (*note .line': Line.) 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). Error messages have the format file_name:NNN:FATAL:Error Message Text 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. File: as.info, Node: Invoking, Next: Syntax, Prev: Overview, Up: Top 2 Command-Line Options ********************** This chapter describes command-line options available in _all_ versions of the GNU assembler; see *Note Machine Dependencies::, for options specific to particular machine architectures. If you are invoking as' via the GNU C compiler, you can use the -Wa' option to pass arguments through to the assembler. The assembler arguments must be separated from each other (and the -Wa') by commas. For example: gcc -c -g -O -Wa,-alh,-L file.c This passes two options to the assembler: -alh' (emit a listing to standard output with high-level and assembly source) and -L' (retain local symbols in the symbol table). Usually you do not need to use this -Wa' mechanism, since many compiler command-line options are automatically passed to the assembler by the compiler. (You can call the GNU compiler driver with the -v' option to see precisely what options it passes to each compilation pass, including the assembler.) * Menu: * a:: -a[cdghlns] enable listings * alternate:: --alternate enable alternate macro syntax * D:: -D for compatibility * f:: -f to work faster * I:: -I for .include search path * K:: -K for difference tables * L:: -L to retain local symbols * listing:: --listing-XXX to configure listing output * 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 File: as.info, Node: a, Next: alternate, Up: Invoking 2.1 Enable Listings: -a[cdghlns]' ================================== These options enable listing output from the assembler. By itself, -a' requests high-level, assembly, and symbols listing. You can use other letters to select specific options for the list: -ah' requests a high-level language listing, -al' requests an output-program assembly listing, and -as' requests a symbol table listing. High-level listings require that a compiler debugging option like -g' be used, and that assembly listings (-al') be requested also. Use the -ag' option to print a first section with general assembly information, like as version, switches passed, or time stamp. Use the -ac' option to omit false conditionals from a listing. Any lines which are not assembled because of a false .if' (or .ifdef', or any other conditional), or a true .if' followed by an .else', will be omitted from the listing. Use the -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 .list', .nolist', .psize', .eject', .title', and .sbttl'. The -an' option turns off all forms processing. If you do not request listing output with one of the -a' options, the listing-control directives have no effect. The letters after -a' may be combined into one option, _e.g._, -aln'. Note if the assembler source is coming from the standard input (e.g., because it is being created by gcc' and the -pipe' command line switch is being used) then the listing will not contain any comments or preprocessor directives. This is because the listing code buffers input source lines from stdin only after they have been preprocessed by the assembler. This reduces memory usage and makes the code more efficient. File: as.info, Node: alternate, Next: D, Prev: a, Up: Invoking 2.2 --alternate' ================= Begin in alternate macro mode, see *Note .altmacro': Altmacro. File: as.info, Node: D, Next: f, Prev: alternate, Up: Invoking 2.3 -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 as'. File: as.info, Node: f, Next: I, Prev: D, Up: Invoking 2.4 Work Faster: -f' ===================== -f' should only be used when assembling programs written by a (trusted) compiler. -f' stops the assembler from doing whitespace and comment preprocessing on the input file(s) before assembling them. *Note Preprocessing: Preprocessing. _Warning:_ if you use -f' when the files actually need to be preprocessed (if they contain comments, for example), as' does not work correctly. File: as.info, Node: I, Next: K, Prev: f, Up: Invoking 2.5 .include' Search Path: -I' PATH ===================================== Use this option to add a PATH to the list of directories as' searches for files specified in .include' directives (*note .include': Include.). You may use -I' as many times as necessary to include a variety of paths. The current working directory is always searched first; after that, as' searches any -I' directories in the same order as they were specified (left to right) on the command line. File: as.info, Node: K, Next: L, Prev: I, Up: Invoking 2.6 Difference Tables: -K' =========================== as' sometimes alters the code emitted for directives of the form .word SYM1-SYM2'. *Note .word': Word. You can use the -K' option if you want a warning issued when this is done. File: as.info, Node: L, Next: listing, Prev: K, Up: Invoking 2.7 Include Local Symbols: -L' =============================== Symbols beginning with system-specific local label prefixes, typically .L' for ELF systems or L' for traditional a.out systems, are called "local symbols". *Note Symbol Names::. Normally you do not see such symbols when debugging, because they are intended for the use of programs (like compilers) that compose assembler programs, not for your notice. Normally both as' and ld' discard such symbols, so you do not normally debug with them. This option tells as' to retain those local symbols in the object file. Usually if you do this you also tell the linker ld' to preserve those symbols. File: as.info, Node: listing, Next: M, Prev: L, Up: Invoking 2.8 Configuring listing output: --listing' =========================================== The listing feature of the assembler can be enabled via the command line switch -a' (*note a::). This feature combines the input source file(s) with a hex dump of the corresponding locations in the output object file, and displays them as a listing file. The format of this listing can be controlled by directives inside the assembler source (i.e., .list' (*note List::), .title' (*note Title::), .sbttl' (*note Sbttl::), .psize' (*note Psize::), and .eject' (*note Eject::) and also by the following switches: --listing-lhs-width=number'' Sets the maximum width, in words, of the first line of the hex byte dump. This dump appears on the left hand side of the listing output. --listing-lhs-width2=number'' Sets the maximum width, in words, of any further lines of the hex byte dump for a given input source line. If this value is not specified, it defaults to being the same as the value specified for --listing-lhs-width'. If neither switch is used the default is to one. --listing-rhs-width=number'' Sets the maximum width, in characters, of the source line that is displayed alongside the hex dump. The default value for this parameter is 100. The source line is displayed on the right hand side of the listing output. --listing-cont-lines=number'' Sets the maximum number of continuation lines of hex dump that will be displayed for a given single line of source input. The default value is 4. File: as.info, Node: M, Next: MD, Prev: listing, Up: Invoking 2.9 Assemble in MRI Compatibility Mode: -M' ============================================ The -M' or --mri' option selects MRI compatibility mode. This changes the syntax and pseudo-op handling of as' to make it compatible with the ASM68K' or the 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 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: * 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. 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. * 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. * END' pseudo-op specifying start address The MRI 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 -e' option to the linker, or in a linker script. * IDNT', .ident' and NAME' pseudo-ops The MRI IDNT', .ident' and NAME' pseudo-ops assign a module name to the output file. This is not supported by other object file formats. * ORG' pseudo-op The m68k MRI ORG' pseudo-op begins an absolute section at a given address. This differs from the usual as' .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. There are some other features of the MRI assembler which are not supported by as', typically either because they are difficult or because they seem of little consequence. Some of these may be supported in future releases. * EBCDIC strings EBCDIC strings are not supported. * packed binary coded decimal Packed binary coded decimal is not supported. This means that the DC.P' and DCB.P' pseudo-ops are not supported. * FEQU' pseudo-op The m68k FEQU' pseudo-op is not supported. * NOOBJ' pseudo-op The m68k NOOBJ' pseudo-op is not supported. * OPT' branch control options The m68k OPT' branch control options--B', BRS', BRB', BRL', and BRW'--are ignored. as' automatically relaxes all branches, whether forward or backward, to an appropriate size, so these options serve no purpose. * OPT' list control options The following m68k OPT' list control options are ignored: C', CEX', CL', CRE', E', G', I', M', MEX', MC', MD', X'. * other OPT' options The following m68k OPT' options are ignored: NEST', O', OLD', OP', P', PCO', PCR', PCS', R'. * OPT' D' option is default The m68k OPT' D' option is the default, unlike the MRI assembler. OPT NOD' may be used to turn it off. * XREF' pseudo-op. The m68k XREF' pseudo-op is ignored. * .debug' pseudo-op The i960 .debug' pseudo-op is not supported. * .extended' pseudo-op The i960 .extended' pseudo-op is not supported. * .list' pseudo-op. The various options of the i960 .list' pseudo-op are not supported. * .optimize' pseudo-op The i960 .optimize' pseudo-op is not supported. * .output' pseudo-op The i960 .output' pseudo-op is not supported. * .setreal' pseudo-op The i960 .setreal' pseudo-op is not supported. File: as.info, Node: MD, Next: o, Prev: M, Up: Invoking 2.10 Dependency Tracking: --MD' ================================ as' can generate a dependency file for the file it creates. This file consists of a single rule suitable for 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. File: as.info, Node: o, Next: R, Prev: MD, Up: Invoking 2.11 Name the Object File: -o' =============================== There is always one object file output when you run as'. By default it has the name a.out' (or b.out', for Intel 960 targets only). You use this option (which takes exactly one filename) to give the object file a different name. Whatever the object file is called, as' overwrites any existing file of the same name. File: as.info, Node: R, Next: statistics, Prev: o, Up: Invoking 2.12 Join Data and Text Sections: -R' ====================================== -R' tells 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. (*Note Sections and Relocation: Sections.) When you specify -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 as'. In future, -R' may work this way. When as' is configured for COFF or ELF output, this option is only useful if you use sections named .text' and .data'. -R' is not supported for any of the HPPA targets. Using -R' generates a warning from as'. File: as.info, Node: statistics, Next: traditional-format, Prev: R, Up: Invoking 2.13 Display Assembly Statistics: --statistics' ================================================ Use --statistics' to display two statistics about the resources used by as': the maximum amount of space allocated during the assembly (in bytes), and the total execution time taken for the assembly (in CPU seconds). File: as.info, Node: traditional-format, Next: v, Prev: statistics, Up: Invoking 2.14 Compatible Output: --traditional-format' ============================================== For some targets, the output of as' is different in some ways from the output of some existing assembler. This switch requests as' to use the traditional format instead. For example, it disables the exception frame optimizations which as' normally does by default on gcc' output. File: as.info, Node: v, Next: W, Prev: traditional-format, Up: Invoking 2.15 Announce Version: -v' =========================== You can find out what version of as is running by including the option -v' (which you can also spell as -version') on the command line. File: as.info, Node: W, Next: Z, Prev: v, Up: Invoking 2.16 Control Warnings: -W', --warn', --no-warn', --fatal-warnings' ====================================================================== as' should never give a warning or error message when assembling compiler output. But programs written by people often cause as' to give a warning that a particular assumption was made. All such warnings are directed to the standard error file. If you use the -W' and --no-warn' options, no warnings are issued. This only affects the warning messages: it does not change any particular of how as' assembles your file. Errors, which stop the assembly, are still reported. If you use the --fatal-warnings' option, as' considers files that generate warnings to be in error. You can switch these options off again by specifying --warn', which causes warnings to be output as usual. File: as.info, Node: Z, Prev: W, Up: Invoking 2.17 Generate Object File in Spite of Errors: -Z' ================================================== After an error message, as' normally produces no output. If for some reason you are interested in object file output even after as' gives an error message on your program, use the -Z' option. If there are any errors, as' continues anyways, and writes an object file after a final warning message of the form N errors, M warnings, generating bad object file.' File: as.info, Node: Syntax, Next: Sections, Prev: Invoking, Up: Top 3 Syntax ******** This chapter describes the machine-independent syntax allowed in a source file. as' syntax is similar to what many other assemblers use; it is inspired by the BSD 4.2 assembler, except that as' does not assemble Vax bit-fields. * Menu: * Preprocessing:: Preprocessing * Whitespace:: Whitespace * Comments:: Comments * Symbol Intro:: Symbols * Statements:: Statements * Constants:: Constants File: as.info, Node: Preprocessing, Next: Whitespace, Up: Syntax 3.1 Preprocessing ================= The as' internal preprocessor: * 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. * removes all comments, replacing them with a single space, or an appropriate number of newlines. * converts character constants into the appropriate numeric values. 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 .include' directive (*note .include': Include.). You can use the GNU C compiler driver to get other "CPP" style preprocessing by giving the input file a .S' suffix. *Note Options Controlling the Kind of Output: (gcc.info)Overall Options. Excess whitespace, comments, and character constants cannot be used in the portions of the input text that are not preprocessed. If the first line of an input file is #NO_APP' or if you use the -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 #APP' before the text that may contain whitespace or comments, and putting a line that says #NO_APP' after this text. This feature is mainly intend to support asm' statements in compilers whose output is otherwise free of comments and whitespace. File: as.info, Node: Whitespace, Next: Comments, Prev: Preprocessing, Up: Syntax 3.2 Whitespace ============== "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 (*note Character Constants: Characters.), any whitespace means the same as exactly one space. File: as.info, Node: Comments, Next: Symbol Intro, Prev: Whitespace, Up: Syntax 3.3 Comments ============ There are two ways of rendering comments to as'. In both cases the comment is equivalent to one space. Anything from /*' through the next */' is a comment. This means you may not nest these comments. /* 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. */ Anything from a "line comment" character up to the next newline is considered a comment and is ignored. The line comment character is target specific, and some targets multiple comment characters. Some targets also have line comment characters that only work if they are the first character on a line. Some targets use a sequence of two characters to introduce a line comment. Some targets can also change their line comment characters depending upon command line options that have been used. For more details see the _Syntax_ section in the documentation for individual targets. If the line comment character is the hash sign (#') then it still has the special ability to enable and disable preprocessing (*note Preprocessing::) and to specify logical line numbers: To be compatible with past assemblers, lines that begin with #' have a special interpretation. Following the #' should be an absolute expression (*note Expressions::): the logical line number of the _next_ line. Then a string (*note 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.) # This is an ordinary comment. # 42-6 "new_file_name" # New logical file name # This is logical line # 36. This feature is deprecated, and may disappear from future versions of as'. File: as.info, Node: Symbol Intro, Next: Statements, Prev: Comments, Up: Syntax 3.4 Symbols =========== A "symbol" is one or more characters chosen from the set of all letters (both upper and lower case), digits and the three characters _.$'. On most machines, you can also use $' in symbol names; exceptions are noted in *Note Machine Dependencies::. No symbol may begin with a digit. Case is significant. There is no length limit: all characters are significant. Multibyte characters are supported. 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). *Note Symbols::. File: as.info, Node: Statements, Next: Constants, Prev: Symbol Intro, Up: Syntax 3.5 Statements ============== A "statement" ends at a newline character (\n') or a "line separator character". The line separator character is target specific and described in the _Syntax_ section of each target's documentation. Not all targets support a line separator character. The newline or line separator character is considered to be part of the preceding statement. Newlines and separators within character constants are an exception: they do not end statements. It is an error to end any statement with end-of-file: the last character of any input file should be a newline. An empty statement is allowed, and may include whitespace. It is ignored. 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 .' 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 "instruction": it assembles into a machine language instruction. Different versions of as' for different computers recognize different instructions. In fact, the same symbol may represent a different instruction in a different computer's assembly language. A label is a symbol immediately followed by a colon (:'). Whitespace before a label or after a colon is permitted, but you may not have whitespace between a label's symbol and its colon. *Note Labels::. 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. label: .directive followed by something another_label: # This is an empty statement. instruction operand_1, operand_2, ... File: as.info, Node: Constants, Prev: Statements, Up: Syntax 3.6 Constants ============= A constant is a number, written so that its value is known by inspection, without knowing any context. Like this: .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. * Menu: * Characters:: Character Constants * Numbers:: Number Constants File: as.info, Node: Characters, Next: Numbers, Up: Constants 3.6.1 Character Constants ------------------------- There are two kinds of character constants. A "character" stands for one character in one byte and its value may be used in numeric expressions. String constants (properly called string _literals_) are potentially many bytes and their values may not be used in arithmetic expressions. * Menu: * Strings:: Strings * Chars:: Characters File: as.info, Node: Strings, Next: Chars, Up: Characters 3.6.1.1 Strings ............... A "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 "escape" these characters: precede them with a backslash \' character. For example \\' represents one backslash: the first \' is an escape which tells as' to interpret the second character literally as a backslash (which prevents as' from recognizing the second \' as an escape character). The complete list of escapes follows. \b' Mnemonic for backspace; for ASCII this is octal code 010. \f' Mnemonic for FormFeed; for ASCII this is octal code 014. \n' Mnemonic for newline; for ASCII this is octal code 012. \r' Mnemonic for carriage-Return; for ASCII this is octal code 015. \t' Mnemonic for horizontal Tab; for ASCII this is octal code 011. \ DIGIT DIGIT 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, \008' has the value 010, and \009' the value 011. \x' HEX-DIGITS...' A hex character code. All trailing hex digits are combined. Either upper or lower case x' works. \\' Represents one \' character. \"' Represents one "' character. Needed in strings to represent this character, because an unescaped "' would end the string. \ ANYTHING-ELSE' Any other character when escaped by \' gives a warning, but assembles as if the \' 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 as' has no other interpretation, so as' knows it is giving you the wrong code and warns you of the fact. 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. File: as.info, Node: Chars, Prev: Strings, Up: Characters 3.6.1.2 Characters .................. 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 '\\' where the first \' escapes the second \'. As you can see, the quote is an acute accent, not a grave accent. A newline 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. as' assumes your character code is ASCII: 'A' means 65, 'B' means 66, and so on. File: as.info, Node: Numbers, Prev: Characters, Up: Constants 3.6.2 Number Constants ---------------------- as' distinguishes three kinds of numbers according to how they are stored in the target machine. _Integers_ are numbers that would fit into an int' in the C language. _Bignums_ are integers, but they are stored in more than 32 bits. _Flonums_ are floating point numbers, described below. * Menu: * Integers:: Integers * Bignums:: Bignums * Flonums:: Flonums File: as.info, Node: Integers, Next: Bignums, Up: Numbers 3.6.2.1 Integers ................ A binary integer is 0b' or 0B' followed by zero or more of the binary digits 01'. An octal integer is 0' followed by zero or more of the octal digits (01234567'). A decimal integer starts with a non-zero digit followed by zero or more digits (0123456789'). A hexadecimal integer is 0x' or 0X' followed by one or more hexadecimal digits chosen from 0123456789abcdefABCDEF'. Integers have the usual values. To denote a negative integer, use the prefix operator -' discussed under expressions (*note Prefix Operators: Prefix Ops.). File: as.info, Node: Bignums, Next: Flonums, Prev: Integers, Up: Numbers 3.6.2.2 Bignums ............... A "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. File: as.info, Node: Flonums, Prev: Bignums, Up: Numbers 3.6.2.3 Flonums ............... A "flonum" represents a floating point number. The translation is indirect: a decimal floating point number from the text is converted by 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 as' specialized to that computer. A flonum is written by writing (in order) * The digit 0'. (0' is optional on the HPPA.) * A letter, to tell as' the rest of the number is a flonum. e' is recommended. Case is not important. On the H8/300, Renesas / SuperH SH, and AMD 29K architectures, the letter must be one of the letters DFPRSX' (in upper or lower case). On the ARC, the letter must be one of the letters DFRS' (in upper or lower case). On the Intel 960 architecture, the letter must be one of the letters DFT' (in upper or lower case). On the HPPA architecture, the letter must be E' (upper case only). * An optional sign: either +' or -'. * An optional "integer part": zero or more decimal digits. * An optional "fractional part": .' followed by zero or more decimal digits. * An optional exponent, consisting of: * An E' or e'. * Optional sign: either +' or -'. * One or more decimal digits. At least one of the integer part or the fractional part must be present. The floating point number has the usual base-10 value. as' does all processing using integers. Flonums are computed independently of any floating point hardware in the computer running as'. File: as.info, Node: Sections, Next: Symbols, Prev: Syntax, Up: Top 4 Sections and Relocation ************************* * Menu: * Secs Background:: Background * Ld Sections:: Linker Sections * As Sections:: Assembler Internal Sections * Sub-Sections:: Sub-Sections * bss:: bss Section File: as.info, Node: Secs Background, Next: Ld Sections, Up: Sections 4.1 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. The linker ld' reads many object files (partial programs) and combines their contents to form a runnable program. When as' emits an object file, the partial program is assumed to start at address 0. 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 as' uses sections. 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 _section_. Assigning run-time addresses to sections is called "relocation". It includes the task of adjusting mentions of object-file addresses so they refer to the proper run-time addresses. For the H8/300, and for the Renesas / SuperH SH, as' pads sections if needed to ensure they end on a word (sixteen bit) boundary. An object file written by as' has at least three sections, any of which may be empty. These are named "text", "data" and "bss" sections. When it generates COFF or ELF output, as' can also generate whatever other named sections you specify using the .section' directive (*note .section': Section.). If you do not use any directives that place output in the .text' or .data' sections, these sections still exist, but are empty. When as' generates SOM or ELF output for the HPPA, as' can also generate whatever other named sections you specify using the .space' and .subspace' directives. See HP9000 Series 800 Assembly Language Reference Manual' (HP 92432-90001) for details on the .space' and .subspace' assembler directives. Additionally, as' uses different names for the standard text, data, and bss sections when generating SOM output. Program text is placed into the $CODE$' section, data into $DATA$', and BSS into $BSS$'. Within the object file, the text section starts at address 0', the data section follows, and the bss section follows the data section. When generating either SOM or ELF output files on the HPPA, the text section starts at address 0', the data section at address 0x4000000', and the bss section follows the data section. To let ld' know which data changes when the sections are relocated, and how to change that data, as' also writes to the object file details of the relocation needed. To perform relocation ld' must know, each time an address in the object file is mentioned: * Where in the object file is the beginning of this reference to an address? * How long (in bytes) is this reference? * Which section does the address refer to? What is the numeric value of (ADDRESS) - (START-ADDRESS OF SECTION)? * Is the reference to an address "Program-Counter relative"? In fact, every address as' ever uses is expressed as (SECTION) + (OFFSET INTO SECTION) Further, most expressions as' computes have this section-relative nature. (For some object formats, such as SOM for the HPPA, some expressions are symbol-relative instead.) In this manual we use the notation {SECNAME N} to mean "offset N into section SECNAME." Apart from text, data and bss sections you need to know about the "absolute" section. When ld' mixes partial programs, addresses in the absolute section remain unchanged. For example, address {absolute 0}' is "relocated" to run-time address 0 by ld'. Although the linker never arranges two partial programs' data sections with overlapping addresses after linking, _by definition_ their absolute sections must overlap. Address {absolute 239}' in one part of a program is always the same address when the program is running as address {absolute 239}' in any other part of the program. The idea of sections is extended to the "undefined" section. Any address whose section is unknown at assembly time is by definition rendered {undefined U}--where 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 _undefined_. By analogy the word _section_ is used to describe groups of sections in the linked program. ld' puts all partial programs' text sections in contiguous addresses in the linked program. It is customary to refer to the _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 ld'; others are invented for use of as' and have no meaning except during assembly. File: as.info, Node: Ld Sections, Next: As Sections, Prev: Secs Background, Up: Sections 4.2 Linker Sections =================== ld' deals with just four kinds of sections, summarized below. *named sections* *text section* *data section* These sections hold your program. as' and ld' treat them as separate but equal sections. Anything you can say of one section is true of another. 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. *bss section* This section contains zeroed bytes when your program begins running. It is used to hold uninitialized 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. *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 ld' must not change when relocating. In this sense we speak of absolute addresses being "unrelocatable": they do not change during relocation. *undefined section* This "section" is a catch-all for address references to objects not in the preceding sections. An idealized example of three relocatable sections follows. The example uses the traditional section names .text' and .data'. Memory addresses are on the horizontal axis. +-----+----+--+ 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 ... File: as.info, Node: As Sections, Next: Sub-Sections, Prev: Ld Sections, Up: Sections 4.3 Assembler Internal Sections =============================== These sections are meant only for the internal use of 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 as' warning messages, so it might be helpful to have an idea of their meanings to as'. These sections are used to permit the value of every expression in your assembly language program to be a section-relative address. ASSEMBLER-INTERNAL-LOGIC-ERROR! An internal assembler logic error has been found. This means there is a bug in the assembler. 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. File: as.info, Node: Sub-Sections, Next: bss, Prev: As Sections, Up: Sections 4.4 Sub-Sections ================ Assembled bytes conventionally fall into two sections: text and data. You may have separate groups of data in named sections that you want to end up near to each other in the object file, even though they are not contiguous in the assembler source. as' allows you to use "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 .text 0' before each section of code being output, and a .text 1' before each group of constants being output. Subsections are optional. If you do not use subsections, everything goes in subsection number zero. Each subsection is zero-padded up to a multiple of four bytes. (Subsections may be padded a different amount on different flavors of as'.) 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; 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 .text EXPRESSION' or a .data EXPRESSION' statement. When generating COFF output, you can also use an extra subsection argument with arbitrary named sections: .section NAME, EXPRESSION'. When generating ELF output, you can also use the .subsection' directive (*note SubSection::) to specify a subsection: .subsection EXPRESSION'. EXPRESSION should be an absolute expression (*note Expressions::). If you just say .text' then .text 0' is assumed. Likewise .data' means .data 0'. Assembly begins in text 0'. For instance: .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 (*)." Each section has a "location counter" incremented by one for every byte assembled into that section. Because subsections are merely a convenience restricted to as' there is no concept of a subsection location counter. There is no way to directly manipulate a location counter--but the .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 "active" location counter. File: as.info, Node: bss, Prev: Sub-Sections, Up: Sections 4.5 bss Section =============== 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 .lcomm' pseudo-op defines a symbol in the bss section; see *Note .lcomm': Lcomm. The .comm' pseudo-op may be used to declare a common symbol, which is another form of uninitialized symbol; see *Note .comm': Comm. When assembling for a target which supports multiple sections, such as ELF or COFF, you may switch into the .bss' section and define symbols as usual; see *Note .section': Section. You may only assemble zero values into the section. Typically the section will only contain symbol definitions and .skip' directives (*note .skip': Skip.). File: as.info, Node: Symbols, Next: Expressions, Prev: Sections, Up: Top 5 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. _Warning:_ as' does not place symbols in the object file in the same order they were declared. This may break some debuggers. * Menu: * Labels:: Labels * Setting Symbols:: Giving Symbols Other Values * Symbol Names:: Symbol Names * Dot:: The Special Dot Symbol * Symbol Attributes:: Symbol Attributes File: as.info, Node: Labels, Next: Setting Symbols, Up: Symbols 5.1 Labels ========== A "label" is written as a symbol immediately followed by a colon :'. 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. 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 as' also provides a special directive .label' for defining labels more flexibly. File: as.info, Node: Setting Symbols, Next: Symbol Names, Prev: Labels, Up: Symbols 5.2 Giving Symbols Other Values =============================== A symbol can be given an arbitrary value by writing a symbol, followed by an equals sign =', followed by an expression (*note Expressions::). This is equivalent to using the .set' directive. *Note .set': Set. In the same way, using a double equals sign ='=' here represents an equivalent of the .eqv' directive. *Note .eqv': Eqv. Blackfin does not support symbol assignment with ='. File: as.info, Node: Symbol Names, Next: Dot, Prev: Setting Symbols, Up: Symbols 5.3 Symbol Names ================ Symbol names begin with a letter or with one of ._'. On most machines, you can also use $' in symbol names; exceptions are noted in *Note Machine Dependencies::. That character may be followed by any string of digits, letters, dollar signs (unless otherwise noted for a particular target machine), and underscores. Case of letters is significant: foo' is a different symbol name than Foo'. Multibyte characters are supported. To generate a symbol name containing multibyte characters enclose it within double quotes and use escape codes. cf *Note Strings::. Generating a multibyte symbol name from a label is not currently supported. Each symbol has exactly one name. Each name in an assembly language program refers to exactly one symbol. You may use that symbol name any number of times in a program. Local Symbol Names ------------------ A local symbol is any symbol beginning with certain local label prefixes. By default, the local label prefix is .L' for ELF systems or L' for traditional a.out systems, but each target may have its own set of local label prefixes. On the HPPA local symbols begin with L$'. Local symbols are defined and used within the assembler, but they are normally not saved in object files. Thus, they are not visible when debugging. You may use the -L' option (*note Include Local Symbols: -L': L.) to retain the local symbols in the object files. Local Labels ------------ Local labels help compilers and programmers use names temporarily. They create symbols which are guaranteed to be unique over the entire scope of the input source code and which can be referred to by a simple notation. To define a local label, write a label of the form N:' (where N represents any positive integer). To refer to the most recent previous definition of that label write Nb', using the same number as when you defined the label. To refer to the next definition of a local label, write Nf'--the b' stands for "backwards" and the f' stands for "forwards". There is no restriction on how you can use these labels, and you can reuse them too. So that it is possible to repeatedly define the same local label (using the same number N'), although you can only refer to the most recently defined local label of that number (for a backwards reference) or the next definition of a specific local label for a forward reference. It is also worth noting that the first 10 local labels (0:'...9:') are implemented in a slightly more efficient manner than the others. Here is an example: 1: branch 1f 2: branch 1b 1: branch 2f 2: branch 1b Which is the equivalent of: label_1: branch label_3 label_2: branch label_1 label_3: branch label_4 label_4: branch label_3 Local label names are only a notational device. They are immediately transformed into more conventional symbol names before the assembler uses them. The symbol names are stored in the symbol table, appear in error messages, and are optionally emitted to the object file. The names are constructed using these parts: _local label prefix_' All local symbols begin with the system-specific local label prefix. Normally both as' and ld' forget symbols that start with the local label prefix. These labels are used for symbols you are never intended to see. If you use the -L' option then as' retains these symbols in the object file. If you also instruct ld' to retain these symbols, you may use them in debugging. NUMBER' This is the number that was used in the local label definition. So if the label is written 55:' then the number is 55'. C-B' This unusual character is included so you do not accidentally invent a symbol of the same name. The character has ASCII value of \002' (control-B). _ordinal number_' This is a serial number to keep the labels distinct. The first definition of 0:' gets the number 1'. The 15th definition of 0:' gets the number 15', and so on. Likewise the first definition of 1:' gets the number 1' and its 15th definition gets 15' as well. So for example, the first 1:' may be named .L1C-B1', and the 44th 3:' may be named .L3C-B44'. Dollar Local Labels ------------------- as' also supports an even more local form of local labels called dollar labels. These labels go out of scope (i.e., they become undefined) as soon as a non-local label is defined. Thus they remain valid for only a small region of the input source code. Normal local labels, by contrast, remain in scope for the entire file, or until they are redefined by another occurrence of the same local label. Dollar labels are defined in exactly the same way as ordinary local labels, except that they have a dollar sign suffix to their numeric value, e.g., 55$:'. They can also be distinguished from ordinary local labels by their transformed names which use ASCII character \001' (control-A) as the magic character to distinguish them from ordinary labels. For example, the fifth definition of 6$' may be named .L6C-A5'. File: as.info, Node: Dot, Next: Symbol Attributes, Prev: Symbol Names, Up: Symbols 5.4 The Special Dot Symbol ========================== The special symbol .' refers to the current address that as' is assembling into. Thus, the expression melvin: .long .' defines melvin' to contain its own address. Assigning a value to .' is treated the same as a .org' directive. Thus, the expression .=.+4' is the same as saying .space 4'. File: as.info, Node: Symbol Attributes, Prev: Dot, Up: Symbols 5.5 Symbol Attributes ===================== Every symbol has, as well as its name, the attributes "Value" and "Type". Depending on output format, symbols can also have auxiliary attributes. If you use a symbol without defining it, 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 * a.out Symbols:: Symbol Attributes: a.out' * COFF Symbols:: Symbol Attributes for COFF * SOM Symbols:: Symbol Attributes for SOM File: as.info, Node: Symbol Value, Next: Symbol Type, Up: Symbol Attributes 5.5.1 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 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 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 .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. File: as.info, Node: Symbol Type, Next: a.out Symbols, Prev: Symbol Value, Up: Symbol Attributes 5.5.2 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. File: as.info, Node: a.out Symbols, Next: COFF Symbols, Prev: Symbol Type, Up: Symbol Attributes 5.5.3 Symbol Attributes: a.out' -------------------------------- * Menu: * Symbol Desc:: Descriptor * Symbol Other:: Other File: as.info, Node: Symbol Desc, Next: Symbol Other, Up: a.out Symbols 5.5.3.1 Descriptor .................. This is an arbitrary 16-bit value. You may establish a symbol's descriptor value by using a .desc' statement (*note .desc': Desc.). A descriptor value means nothing to as'. File: as.info, Node: Symbol Other, Prev: Symbol Desc, Up: a.out Symbols 5.5.3.2 Other ............. This is an arbitrary 8-bit value. It means nothing to as'. File: as.info, Node: COFF Symbols, Next: SOM Symbols, Prev: a.out Symbols, Up: Symbol Attributes 5.5.4 Symbol Attributes for COFF -------------------------------- The COFF format supports a multitude of auxiliary symbol attributes; like the primary symbol attributes, they are set between .def' and .endef' directives. 5.5.4.1 Primary Attributes .......................... The symbol name is set with .def'; the value and type, respectively, with .val' and .type'. 5.5.4.2 Auxiliary Attributes ............................ The as' directives .dim', .line', .scl', .size', .tag', and .weak' can generate auxiliary symbol table information for COFF. File: as.info, Node: SOM Symbols, Prev: COFF Symbols, Up: Symbol Attributes 5.5.5 Symbol Attributes for SOM ------------------------------- The SOM format for the HPPA supports a multitude of symbol attributes set with the .EXPORT' and .IMPORT' directives. The attributes are described in HP9000 Series 800 Assembly Language Reference Manual' (HP 92432-90001) under the IMPORT' and EXPORT' assembler directive documentation. File: as.info, Node: Expressions, Next: Pseudo Ops, Prev: Symbols, Up: Top 6 Expressions ************* An "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 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. as' aborts with an error message in this situation. * Menu: * Empty Exprs:: Empty Expressions * Integer Exprs:: Integer Expressions File: as.info, Node: Empty Exprs, Next: Integer Exprs, Up: Expressions 6.1 Empty Expressions ===================== An empty expression has no value: it is just whitespace or null. Wherever an absolute expression is required, you may omit the expression, and as' assumes a value of (absolute) 0. This is compatible with other assemblers. File: as.info, Node: Integer Exprs, Prev: Empty Exprs, Up: Expressions 6.2 Integer Expressions ======================= An "integer expression" is one or more _arguments_ delimited by _operators_. * Menu: * Arguments:: Arguments * Operators:: Operators * Prefix Ops:: Prefix Operators * Infix Ops:: Infix Operators File: as.info, Node: Arguments, Next: Operators, Up: Integer Exprs 6.2.1 Arguments --------------- "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 {SECTION NNN} where SECTION is one of text, data, bss, absolute, or undefined. 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 as' pretends these 32 bits are an integer. You may write integer-manipulating instructions that act on exotic constants, compatible with other assemblers. Subexpressions are a left parenthesis (' followed by an integer expression, followed by a right parenthesis )'; or a prefix operator followed by an argument. File: as.info, Node: Operators, Next: Prefix Ops, Prev: Arguments, Up: Integer Exprs 6.2.2 Operators --------------- "Operators" are arithmetic functions, like +' or %'. Prefix operators are followed by an argument. Infix operators appear between their arguments. Operators may be preceded and/or followed by whitespace. File: as.info, Node: Prefix Ops, Next: Infix Ops, Prev: Operators, Up: Integer Exprs 6.2.3 Prefix Operator --------------------- as' has the following "prefix operators". They each take one argument, which must be absolute. -' "Negation". Two's complement negation. ~' "Complementation". Bitwise not. File: as.info, Node: Infix Ops, Prev: Prefix Ops, Up: Integer Exprs 6.2.4 Infix Operators --------------------- "Infix operators" take two arguments, one on either side. Operators have precedence, but operations with equal precedence are performed left to right. Apart from +' or -', both arguments must be absolute, and the result is absolute. 1. Highest Precedence *' "Multiplication". /' "Division". Truncation is the same as the C operator /' %' "Remainder". <<' "Shift Left". Same as the C operator <<'. >>' "Shift Right". Same as the C operator >>'. 2. Intermediate precedence |' "Bitwise Inclusive Or". &' "Bitwise And". ^' "Bitwise Exclusive Or". !' "Bitwise Or Not". 3. Low Precedence +' "Addition". If either argument is absolute, the result has the section of the other argument. You may not add together arguments from different sections. -' "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. ==' "Is Equal To" <>' !=' "Is Not Equal To" <' "Is Less Than" >' "Is Greater Than" >=' "Is Greater Than Or Equal To" <=' "Is Less Than Or Equal To" The comparison operators can be used as infix operators. A true results has a value of -1 whereas a false result has a value of 0. Note, these operators perform signed comparisons. 4. Lowest Precedence &&' "Logical And". ||' "Logical Or". These two logical operations can be used to combine the results of sub expressions. Note, unlike the comparison operators a true result returns a value of 1 but a false results does still return 0. Also note that the logical or operator has a slightly lower precedence than logical and. In short, it's only meaningful to add or subtract the _offsets_ in an address; you can only have a defined section in one of the two arguments. File: as.info, Node: Pseudo Ops, Next: Object Attributes, Prev: Expressions, Up: Top 7 Assembler Directives ********************** All assembler directives have names that begin with a period (.'). 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 GNU assembler. Some machine configurations provide additional directives. *Note Machine Dependencies::. * Menu: * Abort:: .abort' * ABORT (COFF):: .ABORT' * Align:: .align ABS-EXPR , ABS-EXPR' * Altmacro:: .altmacro' * Ascii:: .ascii "STRING"'... * Asciz:: .asciz "STRING"'... * Balign:: .balign ABS-EXPR , ABS-EXPR' * Bundle directives:: .bundle_align_mode ABS-EXPR', .bundle_lock', .bundle_unlock' * Byte:: .byte EXPRESSIONS' * CFI directives:: .cfi_startproc [simple]', .cfi_endproc', etc. * Comm:: .comm SYMBOL , LENGTH ' * Data:: .data SUBSECTION' * Def:: .def NAME' * Desc:: .desc SYMBOL, ABS-EXPRESSION' * Dim:: .dim' * Double:: .double FLONUMS' * Eject:: .eject' * Else:: .else' * Elseif:: .elseif' * End:: .end' * Endef:: .endef' * Endfunc:: .endfunc' * Endif:: .endif' * Equ:: .equ SYMBOL, EXPRESSION' * Equiv:: .equiv SYMBOL, EXPRESSION' * Eqv:: .eqv SYMBOL, EXPRESSION' * Err:: .err' * Error:: .error STRING' * Exitm:: .exitm' * Extern:: .extern' * Fail:: .fail' * File:: .file' * Fill:: .fill REPEAT , SIZE , VALUE' * Float:: .float FLONUMS' * Func:: .func' * Global:: .global SYMBOL', .globl SYMBOL' * Gnu_attribute:: .gnu_attribute TAG,VALUE' * Hidden:: .hidden NAMES' * hword:: .hword EXPRESSIONS' * Ident:: .ident' * If:: .if ABSOLUTE EXPRESSION' * Incbin:: .incbin "FILE"[,SKIP[,COUNT]]' * Include:: .include "FILE"' * Int:: .int EXPRESSIONS' * Internal:: .internal NAMES' * Irp:: .irp SYMBOL,VALUES'... * Irpc:: .irpc SYMBOL,VALUES'... * Lcomm:: .lcomm SYMBOL , LENGTH' * Lflags:: .lflags' * Line:: .line LINE-NUMBER' * Linkonce:: .linkonce [TYPE]' * List:: .list' * Ln:: .ln LINE-NUMBER' * Loc:: .loc FILENO LINENO' * Loc_mark_labels:: .loc_mark_labels ENABLE' * Local:: .local NAMES' * Long:: .long EXPRESSIONS' * Macro:: .macro NAME ARGS'... * MRI:: .mri VAL' * Noaltmacro:: .noaltmacro' * Nolist:: .nolist' * Octa:: .octa BIGNUMS' * Offset:: .offset LOC' * Org:: .org NEW-LC, FILL' * P2align:: .p2align ABS-EXPR, ABS-EXPR, ABS-EXPR' * PopSection:: .popsection' * Previous:: .previous' * Print:: .print STRING' * Protected:: .protected NAMES' * Psize:: .psize LINES, COLUMNS' * Purgem:: .purgem NAME' * PushSection:: .pushsection NAME' * Quad:: .quad BIGNUMS' * Reloc:: .reloc OFFSET, RELOC_NAME[, EXPRESSION]' * Rept:: .rept COUNT' * Sbttl:: .sbttl "SUBHEADING"' * Scl:: .scl CLASS' * Section:: .section NAME[, FLAGS]' * Set:: .set SYMBOL, EXPRESSION' * Short:: .short EXPRESSIONS' * Single:: .single FLONUMS' * Size:: .size [NAME , EXPRESSION]' * Skip:: .skip SIZE , FILL' * Sleb128:: .sleb128 EXPRESSIONS' * Space:: .space SIZE , FILL' * Stab:: .stabd, .stabn, .stabs' * String:: .string "STR"', .string8 "STR"', .string16 "STR"', .string32 "STR"', .string64 "STR"' * Struct:: .struct EXPRESSION' * SubSection:: .subsection' * Symver:: .symver NAME,NAME2@NODENAME' * Tag:: .tag STRUCTNAME' * Text:: .text SUBSECTION' * Title:: .title "HEADING"' * Type:: .type ' * Uleb128:: .uleb128 EXPRESSIONS' * Val:: .val ADDR' * Version:: .version "STRING"' * VTableEntry:: .vtable_entry TABLE, OFFSET' * VTableInherit:: .vtable_inherit CHILD, PARENT' * Warning:: .warning STRING' * Weak:: .weak NAMES' * Weakref:: .weakref ALIAS, SYMBOL' * Word:: .word EXPRESSIONS' * Deprecated:: Deprecated Directives File: as.info, Node: Abort, Next: ABORT (COFF), Up: Pseudo Ops 7.1 .abort' ============ 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 as' to quit also. One day .abort' will not be supported. File: as.info, Node: ABORT (COFF), Next: Align, Prev: Abort, Up: Pseudo Ops 7.2 .ABORT' (COFF) =================== When producing COFF output, as' accepts this directive as a synonym for .abort'. File: as.info, Node: Align, Next: Altmacro, Prev: ABORT (COFF), Up: Pseudo Ops 7.3 .align ABS-EXPR, ABS-EXPR, ABS-EXPR' ========================================= 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 arc, hppa, i386 using ELF, i860, iq2000, m68k, or32, s390, sparc, tic4x, tic80 and xtensa, the first expression is the alignment request in bytes. For example .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 the tic54x, the first expression is the alignment request in words. For other systems, including ppc, i386 using a.out format, arm and strongarm, it is the number of low-order zero bits the location counter must have after advancement. For example .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 .balign' and .p2align' directives, described later, which have a consistent behavior across all architectures (but are specific to GAS). File: as.info, Node: Altmacro, Next: Ascii, Prev: Align, Up: Pseudo Ops 7.4 .altmacro' =============== Enable alternate macro mode, enabling: LOCAL NAME [ , ... ]' One additional directive, LOCAL', is available. It is used to generate a string replacement for each of the NAME arguments, and replace any instances of NAME in each macro expansion. The replacement string is unique in the assembly, and different for each separate macro expansion. LOCAL' allows you to write macros that define symbols, without fear of conflict between separate macro expansions. String delimiters' You can write strings delimited in these other ways besides "STRING"': 'STRING'' You can delimit strings with single-quote characters. ' You can delimit strings with matching angle brackets. single-character string escape' To include any single character literally in a string (even if the character would otherwise have some special meaning), you can prefix the character with !' (an exclamation mark). For example, you can write <4.3 !> 5.4!!>' to get the literal text 4.3 > 5.4!'. Expression results as strings' You can write %EXPR' to evaluate the expression EXPR and use the result as a string. File: as.info, Node: Ascii, Next: Asciz, Prev: Altmacro, Up: Pseudo Ops 7.5 .ascii "STRING"'... ======================== .ascii' expects zero or more string literals (*note Strings::) separated by commas. It assembles each string (with no automatic trailing zero byte) into consecutive addresses. File: as.info, Node: Asciz, Next: Balign, Prev: Ascii, Up: Pseudo Ops 7.6 .asciz "STRING"'... ======================== .asciz' is just like .ascii', but each string is followed by a zero byte. The "z" in .asciz' stands for "zero". File: as.info, Node: Balign, Next: Bundle directives, Prev: Asciz, Up: Pseudo Ops 7.7 .balign[wl] ABS-EXPR, ABS-EXPR, ABS-EXPR' ============================================== 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 .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. The .balignw' and .balignl' directives are variants of the .balign' directive. The .balignw' directive treats the fill pattern as a two byte word value. The .balignl' directives treats the fill pattern as a four byte longword value. For example, .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. File: as.info, Node: Bundle directives, Next: Byte, Prev: Balign, Up: Pseudo Ops 7.8 .bundle_align_mode ABS-EXPR' ================================= .bundle_align_mode' enables or disables "aligned instruction bundle" mode. In this mode, sequences of adjacent instructions are grouped into fixed-sized "bundles". If the argument is zero, this mode is disabled (which is the default state). If the argument it not zero, it gives the size of an instruction bundle as a power of two (as for the .p2align' directive, *note P2align::). For some targets, it's an ABI requirement that no instruction may span a certain aligned boundary. A "bundle" is simply a sequence of instructions that starts on an aligned boundary. For example, if ABS-EXPR is 5' then the bundle size is 32, so each aligned chunk of 32 bytes is a bundle. When aligned instruction bundle mode is in effect, no single instruction may span a boundary between bundles. If an instruction would start too close to the end of a bundle for the length of that particular instruction to fit within the bundle, then the space at the end of that bundle is filled with no-op instructions so the instruction starts in the next bundle. As a corollary, it's an error if any single instruction's encoding is longer than the bundle size. 7.9 .bundle_lock' and .bundle_unlock' ======================================= The .bundle_lock' and directive .bundle_unlock' directives allow explicit control over instruction bundle padding. These directives are only valid when .bundle_align_mode' has been used to enable aligned instruction bundle mode. It's an error if they appear when .bundle_align_mode' has not been used at all, or when the last directive was .bundle_align_mode 0'. For some targets, it's an ABI requirement that certain instructions may appear only as part of specified permissible sequences of multiple instructions, all within the same bundle. A pair of .bundle_lock' and .bundle_unlock' directives define a "bundle-locked" instruction sequence. For purposes of aligned instruction bundle mode, a sequence starting with .bundle_lock' and ending with .bundle_unlock' is treated as a single instruction. That is, the entire sequence must fit into a single bundle and may not span a bundle boundary. If necessary, no-op instructions will be inserted before the first instruction of the sequence so that the whole sequence starts on an aligned bundle boundary. It's an error if the sequence is longer than the bundle size. For convenience when using .bundle_lock' and .bundle_unlock' inside assembler macros (*note Macro::), bundle-locked sequences may be nested. That is, a second .bundle_lock' directive before the next .bundle_unlock' directive has no effect except that it must be matched by another closing .bundle_unlock' so that there is the same number of .bundle_lock' and .bundle_unlock' directives. File: as.info, Node: Byte, Next: CFI directives, Prev: Bundle directives, Up: Pseudo Ops 7.10 .byte EXPRESSIONS' ======================== .byte' expects zero or more expressions, separated by commas. Each expression is assembled into the next byte. File: as.info, Node: CFI directives, Next: Comm, Prev: Byte, Up: Pseudo Ops 7.11 .cfi_sections SECTION_LIST' ================================= .cfi_sections' may be used to specify whether CFI directives should emit .eh_frame' section and/or .debug_frame' section. If SECTION_LIST is .eh_frame', .eh_frame' is emitted, if SECTION_LIST is .debug_frame', .debug_frame' is emitted. To emit both use .eh_frame, .debug_frame'. The default if this directive is not used is .cfi_sections .eh_frame'. 7.12 .cfi_startproc [simple]' ============================== .cfi_startproc' is used at the beginning of each function that should have an entry in .eh_frame'. It initializes some internal data structures. Don't forget to close the function by .cfi_endproc'. Unless .cfi_startproc' is used along with parameter simple' it also emits some architecture dependent initial CFI instructions. 7.13 .cfi_endproc' =================== .cfi_endproc' is used at the end of a function where it closes its unwind entry previously opened by .cfi_startproc', and emits it to .eh_frame'. 7.14 .cfi_personality ENCODING [, EXP]' ======================================== .cfi_personality' defines personality routine and its encoding. ENCODING must be a constant determining how the personality should be encoded. If it is 255 (DW_EH_PE_omit'), second argument is not present, otherwise second argument should be a constant or a symbol name. When using indirect encodings, the symbol provided should be the location where personality can be loaded from, not the personality routine itself. The default after .cfi_startproc' is .cfi_personality 0xff', no personality routine. 7.15 .cfi_lsda ENCODING [, EXP]' ================================= .cfi_lsda' defines LSDA and its encoding. ENCODING must be a constant determining how the LSDA should be encoded. If it is 255 (DW_EH_PE_omit'), second argument is not present, otherwise second argument should be a constant or a symbol name. The default after .cfi_startproc' is .cfi_lsda 0xff', no LSDA. 7.16 .cfi_def_cfa REGISTER, OFFSET' ==================================== .cfi_def_cfa' defines a rule for computing CFA as: take address from REGISTER and add OFFSET to it. 7.17 .cfi_def_cfa_register REGISTER' ===================================== .cfi_def_cfa_register' modifies a rule for computing CFA. From now on REGISTER will be used instead of the old one. Offset remains the same. 7.18 .cfi_def_cfa_offset OFFSET' ================================= .cfi_def_cfa_offset' modifies a rule for computing CFA. Register remains the same, but OFFSET is new. Note that it is the absolute offset that will be added to a defined register to compute CFA address. 7.19 .cfi_adjust_cfa_offset OFFSET' ==================================== Same as .cfi_def_cfa_offset' but OFFSET is a relative value that is added/substracted from the previous offset. 7.20 .cfi_offset REGISTER, OFFSET' =================================== Previous value of REGISTER is saved at offset OFFSET from CFA. 7.21 .cfi_rel_offset REGISTER, OFFSET' ======================================= Previous value of REGISTER is saved at offset OFFSET from the current CFA register. This is transformed to .cfi_offset' using the known displacement of the CFA register from the CFA. This is often easier to use, because the number will match the code it's annotating. 7.22 .cfi_register REGISTER1, REGISTER2' ========================================= Previous value of REGISTER1 is saved in register REGISTER2. 7.23 .cfi_restore REGISTER' ============================ .cfi_restore' says that the rule for REGISTER is now the same as it was at the beginning of the function, after all initial instruction added by .cfi_startproc' were executed. 7.24 .cfi_undefined REGISTER' ============================== From now on the previous value of REGISTER can't be restored anymore. 7.25 .cfi_same_value REGISTER' =============================== Current value of REGISTER is the same like in the previous frame, i.e. no restoration needed. 7.26 .cfi_remember_state', =========================== First save all current rules for all registers by .cfi_remember_state', then totally screw them up by subsequent .cfi_*' directives and when everything is hopelessly bad, use .cfi_restore_state' to restore the previous saved state. 7.27 .cfi_return_column REGISTER' ================================== Change return column REGISTER, i.e. the return address is either directly in REGISTER or can be accessed by rules for REGISTER. 7.28 .cfi_signal_frame' ======================== Mark current function as signal trampoline. 7.29 .cfi_window_save' ======================= SPARC register window has been saved. 7.30 .cfi_escape' EXPRESSION[, ...] ==================================== Allows the user to add arbitrary bytes to the unwind info. One might use this to add OS-specific CFI opcodes, or generic CFI opcodes that GAS does not yet support. 7.31 .cfi_val_encoded_addr REGISTER, ENCODING, LABEL' ====================================================== The current value of REGISTER is LABEL. The value of LABEL will be encoded in the output file according to ENCODING; see the description of .cfi_personality' for details on this encoding. The usefulness of equating a register to a fixed label is probably limited to the return address register. Here, it can be useful to mark a code segment that has only one return address which is reached by a direct branch and no copy of the return address exists in memory or another register. File: as.info, Node: Comm, Next: Data, Prev: CFI directives, Up: Pseudo Ops 7.32 .comm SYMBOL , LENGTH ' ============================= .comm' declares a common symbol named 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 ld' does not see a definition for the symbol-just one or more common symbols-then it will allocate LENGTH bytes of uninitialized memory. LENGTH must be an absolute expression. If 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. When using ELF or (as a GNU extension) PE, the .comm' directive takes an optional third argument. This is the desired alignment of the symbol, specified for ELF as a byte boundary (for example, an alignment of 16 means that the least significant 4 bits of the address should be zero), and for PE as a power of two (for example, an alignment of 5 means aligned to a 32-byte boundary). The alignment must be an absolute expression, and it must be a power of two. If ld' allocates uninitialized memory for the common symbol, it will use the alignment when placing the symbol. If no alignment is specified, 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 on ELF, or the default section alignment of 4 on PE(1). The syntax for .comm' differs slightly on the HPPA. The syntax is SYMBOL .comm, LENGTH'; SYMBOL is optional. ---------- Footnotes ---------- (1) This is not the same as the executable image file alignment controlled by ld''s --section-alignment' option; image file sections in PE are aligned to multiples of 4096, which is far too large an alignment for ordinary variables. It is rather the default alignment for (non-debug) sections within object (*.o') files, which are less strictly aligned. File: as.info, Node: Data, Next: Def, Prev: Comm, Up: Pseudo Ops 7.33 .data SUBSECTION' ======================= .data' tells as' to assemble the following statements onto the end of the data subsection numbered SUBSECTION (which is an absolute expression). If SUBSECTION is omitted, it defaults to zero. File: as.info, Node: Def, Next: Desc, Prev: Data, Up: Pseudo Ops 7.34 .def NAME' ================ Begin defining debugging information for a symbol NAME; the definition extends until the .endef' directive is encountered. File: as.info, Node: Desc, Next: Dim, Prev: Def, Up: Pseudo Ops 7.35 .desc SYMBOL, ABS-EXPRESSION' =================================== This directive sets the descriptor of the symbol (*note Symbol Attributes::) to the low 16 bits of an absolute expression. The .desc' directive is not available when as' is configured for COFF output; it is only for a.out' or b.out' object format. For the sake of compatibility, as' accepts it, but produces no output, when configured for COFF. File: as.info, Node: Dim, Next: Double, Prev: Desc, Up: Pseudo Ops 7.36 .dim' =========== This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside .def'/.endef' pairs. File: as.info, Node: Double, Next: Eject, Prev: Dim, Up: Pseudo Ops 7.37 .double FLONUMS' ====================== .double' expects zero or more flonums, separated by commas. It assembles floating point numbers. The exact kind of floating point numbers emitted depends on how as' is configured. *Note Machine Dependencies::. File: as.info, Node: Eject, Next: Else, Prev: Double, Up: Pseudo Ops 7.38 .eject' ============= Force a page break at this point, when generating assembly listings. File: as.info, Node: Else, Next: Elseif, Prev: Eject, Up: Pseudo Ops 7.39 .else' ============ .else' is part of the as' support for conditional assembly; see *Note .if': If. It marks the beginning of a section of code to be assembled if the condition for the preceding .if' was false. File: as.info, Node: Elseif, Next: End, Prev: Else, Up: Pseudo Ops 7.40 .elseif' ============== .elseif' is part of the as' support for conditional assembly; see *Note .if': If. It is shorthand for beginning a new .if' block that would otherwise fill the entire .else' section. File: as.info, Node: End, Next: Endef, Prev: Elseif, Up: Pseudo Ops 7.41 .end' =========== .end' marks the end of the assembly file. as' does not process anything in the file past the .end' directive. File: as.info, Node: Endef, Next: Endfunc, Prev: End, Up: Pseudo Ops 7.42 .endef' ============= This directive flags the end of a symbol definition begun with .def'. File: as.info, Node: Endfunc, Next: Endif, Prev: Endef, Up: Pseudo Ops 7.43 .endfunc' =============== .endfunc' marks the end of a function specified with .func'. File: as.info, Node: Endif, Next: Equ, Prev: Endfunc, Up: Pseudo Ops 7.44 .endif' ============= .endif' is part of the as' support for conditional assembly; it marks the end of a block of code that is only assembled conditionally. *Note .if': If. File: as.info, Node: Equ, Next: Equiv, Prev: Endif, Up: Pseudo Ops 7.45 .equ SYMBOL, EXPRESSION' ============================== This directive sets the value of SYMBOL to EXPRESSION. It is synonymous with .set'; see *Note .set': Set. The syntax for equ' on the HPPA is SYMBOL .equ EXPRESSION'. The syntax for equ' on the Z80 is SYMBOL equ EXPRESSION'. On the Z80 it is an eror if SYMBOL is already defined, but the symbol is not protected from later redefinition. Compare *Note Equiv::. File: as.info, Node: Equiv, Next: Eqv, Prev: Equ, Up: Pseudo Ops 7.46 .equiv SYMBOL, EXPRESSION' ================================ The .equiv' directive is like .equ' and .set', except that the assembler will signal an error if SYMBOL is already defined. Note a symbol which has been referenced but not actually defined is considered to be undefined. Except for the contents of the error message, this is roughly equivalent to .ifdef SYM .err .endif .equ SYM,VAL plus it protects the symbol from later redefinition. File: as.info, Node: Eqv, Next: Err, Prev: Equiv, Up: Pseudo Ops 7.47 .eqv SYMBOL, EXPRESSION' ============================== The .eqv' directive is like .equiv', but no attempt is made to evaluate the expression or any part of it immediately. Instead each time the resulting symbol is used in an expression, a snapshot of its current value is taken. File: as.info, Node: Err, Next: Error, Prev: Eqv, Up: Pseudo Ops 7.48 .err' =========== If as' assembles a .err' directive, it will print an error message and, unless the -Z' option was used, it will not generate an object file. This can be used to signal an error in conditionally compiled code. File: as.info, Node: Error, Next: Exitm, Prev: Err, Up: Pseudo Ops 7.49 .error "STRING"' ====================== Similarly to .err', this directive emits an error, but you can specify a string that will be emitted as the error message. If you don't specify the message, it defaults to ".error directive invoked in source file"'. *Note Error and Warning Messages: Errors. .error "This code has not been assembled and tested." File: as.info, Node: Exitm, Next: Extern, Prev: Error, Up: Pseudo Ops 7.50 .exitm' ============= Exit early from the current macro definition. *Note Macro::. File: as.info, Node: Extern, Next: Fail, Prev: Exitm, Up: Pseudo Ops 7.51 .extern' ============== .extern' is accepted in the source program--for compatibility with other assemblers--but it is ignored. as' treats all undefined symbols as external. File: as.info, Node: Fail, Next: File, Prev: Extern, Up: Pseudo Ops 7.52 .fail EXPRESSION' ======================= Generates an error or a warning. If the value of the EXPRESSION is 500 or more, as' will print a warning message. If the value is less than 500, as' will print an error message. The message will include the value of EXPRESSION. This can occasionally be useful inside complex nested macros or conditional assembly. File: as.info, Node: File, Next: Fill, Prev: Fail, Up: Pseudo Ops 7.53 .file' ============ There are two different versions of the .file' directive. Targets that support DWARF2 line number information use the DWARF2 version of .file'. Other targets use the default version. Default Version --------------- This version of the .file' directive tells as' that we are about to start a new logical file. The syntax is: .file STRING STRING is the new file name. In general, the filename is recognized whether or not it is surrounded by quotes "'; but if you wish to specify an empty file name, you must give the quotes-""'. This statement may go away in future: it is only recognized to be compatible with old as' programs. DWARF2 Version -------------- When emitting DWARF2 line number information, .file' assigns filenames to the .debug_line' file name table. The syntax is: .file FILENO FILENAME The FILENO operand should be a unique positive integer to use as the index of the entry in the table. The FILENAME operand is a C string literal. The detail of filename indices is exposed to the user because the filename table is shared with the .debug_info' section of the DWARF2 debugging information, and thus the user must know the exact indices that table entries will have. File: as.info, Node: Fill, Next: Float, Prev: File, Up: Pseudo Ops 7.54 .fill REPEAT , SIZE , VALUE' ================================== REPEAT, SIZE and VALUE are absolute expressions. This emits REPEAT copies of SIZE bytes. REPEAT may be zero or more. 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 REPEAT bytes is taken from an 8-byte number. The highest order 4 bytes are zero. The lowest order 4 bytes are VALUE rendered in the byte-order of an integer on the computer as' is assembling for. Each SIZE bytes in a repetition is taken from the lowest order SIZE bytes of this number. Again, this bizarre behavior is compatible with other people's assemblers. SIZE and VALUE are optional. If the second comma and VALUE are absent, VALUE is assumed zero. If the first comma and following tokens are absent, SIZE is assumed to be 1. File: as.info, Node: Float, Next: Func, Prev: Fill, Up: Pseudo Ops 7.55 .float FLONUMS' ===================== This directive assembles zero or more flonums, separated by commas. It has the same effect as .single'. The exact kind of floating point numbers emitted depends on how as' is configured. *Note Machine Dependencies::. File: as.info, Node: Func, Next: Global, Prev: Float, Up: Pseudo Ops 7.56 .func NAME[,LABEL]' ========================= .func' emits debugging information to denote function NAME, and is ignored unless the file is assembled with debugging enabled. Only --gstabs[+]' is currently supported. LABEL is the entry point of the function and if omitted NAME prepended with the leading char' is used. leading char' is usually _' or nothing, depending on the target. All functions are currently defined to have void' return type. The function must be terminated with .endfunc'. File: as.info, Node: Global, Next: Gnu_attribute, Prev: Func, Up: Pseudo Ops 7.57 .global SYMBOL', .globl SYMBOL' ====================================== .global' makes the symbol visible to ld'. If you define SYMBOL in your partial program, its value is made available to other partial programs that are linked with it. Otherwise, SYMBOL takes its attributes from a symbol of the same name from another file linked into the same program. Both spellings (.globl' and .global') are accepted, for compatibility with other assemblers. On the HPPA, .global' is not always enough to make it accessible to other partial programs. You may need the HPPA-only .EXPORT' directive as well. *Note HPPA Assembler Directives: HPPA Directives. File: as.info, Node: Gnu_attribute, Next: Hidden, Prev: Global, Up: Pseudo Ops 7.58 .gnu_attribute TAG,VALUE' =============================== Record a GNU object attribute for this file. *Note Object Attributes::. File: as.info, Node: Hidden, Next: hword, Prev: Gnu_attribute, Up: Pseudo Ops 7.59 .hidden NAMES' ==================== This is one of the ELF visibility directives. The other two are .internal' (*note .internal': Internal.) and .protected' (*note .protected': 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 hidden' which means that the symbols are not visible to other components. Such symbols are always considered to be protected' as well. File: as.info, Node: hword, Next: Ident, Prev: Hidden, Up: Pseudo Ops 7.60 .hword EXPRESSIONS' ========================= This expects zero or more EXPRESSIONS, and emits a 16 bit number for each. This directive is a synonym for .short'; depending on the target architecture, it may also be a synonym for .word'. File: as.info, Node: Ident, Next: If, Prev: hword, Up: Pseudo Ops 7.61 .ident' ============= This directive is used by some assemblers to place tags in object files. The behavior of this directive varies depending on the target. When using the a.out object file format, as' simply accepts the directive for source-file compatibility with existing assemblers, but does not emit anything for it. When using COFF, comments are emitted to the .comment' or .rdata' section, depending on the target. When using ELF, comments are emitted to the .comment' section. File: as.info, Node: If, Next: Incbin, Prev: Ident, Up: Pseudo Ops 7.62 .if ABSOLUTE EXPRESSION' ============================== .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 ABSOLUTE EXPRESSION) is non-zero. The end of the conditional section of code must be marked by .endif' (*note .endif': Endif.); optionally, you may include code for the alternative condition, flagged by .else' (*note .else': Else.). If you have several conditions to check, .elseif' may be used to avoid nesting blocks if/else within each subsequent .else' block. The following variants of .if' are also supported: .ifdef SYMBOL' Assembles the following section of code if the specified SYMBOL has been defined. Note a symbol which has been referenced but not yet defined is considered to be undefined. .ifb TEXT' Assembles the following section of code if the operand is blank (empty). .ifc STRING1,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. .ifeq ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is zero. .ifeqs STRING1,STRING2' Another form of .ifc'. The strings must be quoted using double quotes. .ifge ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is greater than or equal to zero. .ifgt ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is greater than zero. .ifle ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is less than or equal to zero. .iflt ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is less than zero. .ifnb TEXT' Like .ifb', but the sense of the test is reversed: this assembles the following section of code if the operand is non-blank (non-empty). .ifnc STRING1,STRING2.' Like .ifc', but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same. .ifndef SYMBOL' .ifnotdef SYMBOL' Assembles the following section of code if the specified SYMBOL has not been defined. Both spelling variants are equivalent. Note a symbol which has been referenced but not yet defined is considered to be undefined. .ifne ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is not equal to zero (in other words, this is equivalent to .if'). .ifnes STRING1,STRING2' Like .ifeqs', but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same. File: as.info, Node: Incbin, Next: Include, Prev: If, Up: Pseudo Ops 7.63 .incbin "FILE"[,SKIP[,COUNT]]' ==================================== The incbin' directive includes FILE verbatim at the current location. You can control the search paths used with the -I' command-line option (*note Command-Line Options: Invoking.). Quotation marks are required around FILE. The SKIP argument skips a number of bytes from the start of the FILE. The COUNT argument indicates the maximum number of bytes to read. Note that the data is not aligned in any way, so it is the user's responsibility to make sure that proper alignment is provided both before and after the incbin' directive. File: as.info, Node: Include, Next: Int, Prev: Incbin, Up: Pseudo Ops 7.64 .include "FILE"' ====================== This directive provides a way to include supporting files at specified points in your source program. The code from FILE is assembled as if it followed the point of the .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 -I' command-line option (*note Command-Line Options: Invoking.). Quotation marks are required around FILE. File: as.info, Node: Int, Next: Internal, Prev: Include, Up: Pseudo Ops 7.65 .int EXPRESSIONS' ======================= Expect zero or more 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. File: as.info, Node: Internal, Next: Irp, Prev: Int, Up: Pseudo Ops 7.66 .internal NAMES' ====================== This is one of the ELF visibility directives. The other two are .hidden' (*note .hidden': Hidden.) and .protected' (*note .protected': 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 internal' which means that the symbols are considered to be hidden' (i.e., not visible to other components), and that some extra, processor specific processing must also be performed upon the symbols as well. File: as.info, Node: Irp, Next: Irpc, Prev: Internal, Up: Pseudo Ops 7.67 .irp SYMBOL,VALUES'... ============================ Evaluate a sequence of statements assigning different values to SYMBOL. The sequence of statements starts at the .irp' directive, and is terminated by an .endr' directive. For each VALUE, SYMBOL is set to VALUE, and the sequence of statements is assembled. If no VALUE is listed, the sequence of statements is assembled once, with SYMBOL set to the null string. To refer to SYMBOL within the sequence of statements, use \SYMBOL. For example, assembling .irp param,1,2,3 move d\param,sp@- .endr is equivalent to assembling move d1,sp@- move d2,sp@- move d3,sp@- For some caveats with the spelling of SYMBOL, see also *Note Macro::. File: as.info, Node: Irpc, Next: Lcomm, Prev: Irp, Up: Pseudo Ops 7.68 .irpc SYMBOL,VALUES'... ============================= Evaluate a sequence of statements assigning different values to SYMBOL. The sequence of statements starts at the .irpc' directive, and is terminated by an .endr' directive. For each character in VALUE, SYMBOL is set to the character, and the sequence of statements is assembled. If no VALUE is listed, the sequence of statements is assembled once, with SYMBOL set to the null string. To refer to SYMBOL within the sequence of statements, use \SYMBOL. For example, assembling .irpc param,123 move d\param,sp@- .endr is equivalent to assembling move d1,sp@- move d2,sp@- move d3,sp@- For some caveats with the spelling of SYMBOL, see also the discussion at *Note Macro::. File: as.info, Node: Lcomm, Next: Lflags, Prev: Irpc, Up: Pseudo Ops 7.69 .lcomm SYMBOL , LENGTH' ============================= Reserve LENGTH (an absolute expression) bytes for a local common denoted by SYMBOL. The section and value of 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. SYMBOL is not declared global (*note .global': Global.), so is normally not visible to ld'. Some targets permit a third argument to be used with .lcomm'. This argument specifies the desired alignment of the symbol in the bss section. The syntax for .lcomm' differs slightly on the HPPA. The syntax is SYMBOL .lcomm, LENGTH'; SYMBOL is optional. File: as.info, Node: Lflags, Next: Line, Prev: Lcomm, Up: Pseudo Ops 7.70 .lflags' ============== as' accepts this directive, for compatibility with other assemblers, but ignores it. File: as.info, Node: Line, Next: Linkonce, Prev: Lflags, Up: Pseudo Ops 7.71 .line LINE-NUMBER' ======================== Change the logical line number. 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 LINE-NUMBER - 1. One day as' will no longer support this directive: it is recognized only for compatibility with existing assembler programs. Even though this is a directive associated with the a.out' or b.out' object-code formats, as' still recognizes it when producing COFF output, and treats .line' as though it were the COFF .ln' _if_ it is found outside a .def'/.endef' pair. Inside a .def', .line' is, instead, one of the directives used by compilers to generate auxiliary symbol information for debugging. File: as.info, Node: Linkonce, Next: List, Prev: Line, Up: Pseudo Ops 7.72 .linkonce [TYPE]' ======================= 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 .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 TYPE argument is optional. If specified, it must be one of the following strings. For example: .linkonce same_size Not all types may be supported on all object file formats. discard' Silently discard duplicate sections. This is the default. one_only' Warn if there are duplicate sections, but still keep only one copy. same_size' Warn if any of the duplicates have different sizes. same_contents' Warn if any of the duplicates do not have exactly the same contents. File: as.info, Node: List, Next: Ln, Prev: Linkonce, Up: Pseudo Ops 7.73 .list' ============ Control (in conjunction with the .nolist' directive) whether or not assembly listings are generated. These two directives maintain an internal counter (which is zero initially). .list' increments the counter, and .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 -a' command line option; *note Command-Line Options: Invoking.), the initial value of the listing counter is one. File: as.info, Node: Ln, Next: Loc, Prev: List, Up: Pseudo Ops 7.74 .ln LINE-NUMBER' ====================== .ln' is a synonym for .line'. File: as.info, Node: Loc, Next: Loc_mark_labels, Prev: Ln, Up: Pseudo Ops 7.75 .loc FILENO LINENO [COLUMN] [OPTIONS]' ============================================ When emitting DWARF2 line number information, the .loc' directive will add a row to the .debug_line' line number matrix corresponding to the immediately following assembly instruction. The FILENO, LINENO, and optional COLUMN arguments will be applied to the .debug_line' state machine before the row is added. The OPTIONS are a sequence of the following tokens in any order: basic_block' This option will set the basic_block' register in the .debug_line' state machine to true'. prologue_end' This option will set the prologue_end' register in the .debug_line' state machine to true'. epilogue_begin' This option will set the epilogue_begin' register in the .debug_line' state machine to true'. is_stmt VALUE' This option will set the is_stmt' register in the .debug_line' state machine to value', which must be either 0 or 1. isa VALUE' This directive will set the isa' register in the .debug_line' state machine to VALUE, which must be an unsigned integer. discriminator VALUE' This directive will set the discriminator' register in the .debug_line' state machine to VALUE, which must be an unsigned integer. File: as.info, Node: Loc_mark_labels, Next: Local, Prev: Loc, Up: Pseudo Ops 7.76 .loc_mark_labels ENABLE' ============================== When emitting DWARF2 line number information, the .loc_mark_labels' directive makes the assembler emit an entry to the .debug_line' line number matrix with the basic_block' register in the state machine set whenever a code label is seen. The ENABLE argument should be either 1 or 0, to enable or disable this function respectively. File: as.info, Node: Local, Next: Long, Prev: Loc_mark_labels, Up: Pseudo Ops 7.77 .local NAMES' =================== This directive, which is available for ELF targets, marks each symbol in the comma-separated list of names' as a local symbol so that it will not be externally visible. If the symbols do not already exist, they will be created. For targets where the .lcomm' directive (*note Lcomm::) does not accept an alignment argument, which is the case for most ELF targets, the .local' directive can be used in combination with .comm' (*note Comm::) to define aligned local common data. File: as.info, Node: Long, Next: Macro, Prev: Local, Up: Pseudo Ops 7.78 .long EXPRESSIONS' ======================== .long' is the same as .int'. *Note .int': Int. File: as.info, Node: Macro, Next: MRI, Prev: Long, Up: Pseudo Ops 7.79 .macro' ============= The commands .macro' and .endm' allow you to define macros that generate assembly output. For example, this definition specifies a macro sum' that puts a sequence of numbers into memory: .macro sum from=0, to=5 .long \from .if \to-\from sum "(\from+1)",\to .endif .endm With that definition, SUM 0,5' is equivalent to this assembly input: .long 0 .long 1 .long 2 .long 3 .long 4 .long 5 .macro MACNAME' .macro MACNAME MACARGS ...' Begin the definition of a macro called MACNAME. If your macro definition requires arguments, specify their names after the macro name, separated by commas or spaces. You can qualify the macro argument to indicate whether all invocations must specify a non-blank value (through :req''), or whether it takes all of the remaining arguments (through :vararg''). You can supply a default value for any macro argument by following the name with =DEFLT'. You cannot define two macros with the same MACNAME unless it has been subject to the .purgem' directive (*note Purgem::) between the two definitions. For example, these are all valid .macro' statements: .macro comm' Begin the definition of a macro called comm', which takes no arguments. .macro plus1 p, p1' .macro plus1 p p1' Either statement begins the definition of a macro called plus1', which takes two arguments; within the macro definition, write \p' or \p1' to evaluate the arguments. .macro reserve_str p1=0 p2' Begin the definition of a macro called reserve_str', with two