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 man : as Command: man perldoc info search(apropos)   File: as.info, Node: Top, Next: Overview, Up: (dir) Using as ******** This file is a user guide to the GNU assembler as' version 2.15. 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 * Machine Dependencies:: Machine Dependent Features * Reporting Bugs:: Reporting Bugs * Acknowledgements:: Who Did What * GNU Free Documentation License:: GNU Free Documentation License * Index:: 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, *note Command-Line Options: Invoking. as [-a[cdhlns][=FILE]] [-D] [-defsym SYM=VAL] [-f] [-gstabs] [-gstabs+] [-gdwarf2] [-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] [-statistics] [-v] [-version] [-version] [-W] [-warn] [-fatal-warnings] [-w] [-x] [-Z] [-target-help] [TARGET-OPTIONS] [-|FILES ...] _Target Alpha options:_ [-mCPU] [-mdebug | -no-mdebug] [-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] [-mthumb] [-EB|-EL] [-mapcs-32|-mapcs-26|-mapcs-float| -mapcs-reentrant] [-mthumb-interwork] [-moabi] [-k] _Target CRIS options:_ [-underscore | -no-underscore] [-pic] [-N] [-emulation=criself | -emulation=crisaout] _Target D10V options:_ [-O] _Target D30V options:_ [-O|-n|-N] _Target i386 options:_ [-32|-64] [-n] _Target i960 options:_ [-ACA|-ACA_A|-ACB|-ACC|-AKA|-AKB| -AKC|-AMC] [-b] [-no-relax] _Target IP2K options:_ [-mip2022|-mip2022ext] _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] [-mshort|-mlong] [-mshort-double|-mlong-double] [-force-long-branchs] [-short-branchs] [-strict-direct-mode] [-print-insn-syntax] [-print-opcodes] [-generate-example] _Target MCORE options:_ [-jsri2bsr] [-sifilter] [-relax] [-mcpu=[210|340]] _Target MIPS options:_ [-nocpp] [-EL] [-EB] [-O[OPTIMIZATION LEVEL]] [-g[DEBUG LEVEL]] [-G NUM] [-KPIC] [-call_shared] [-non_shared] [-xgot] [-membedded-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] [-trap] [-no-break] [-break] [-no-trap] [-mfix7000] [-mno-fix7000] [-mips16] [-no-mips16] [-mips3d] [-no-mips3d] [-mdmx] [-no-mdmx] [-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 PDP11 options:_ [-mpic|-mno-pic] [-mall] [-mno-extensions] [-mEXTENSION|-mno-EXTENSION] [-mCPU] [-mMACHINE] _Target picoJava options:_ [-mb|-me] _Target PowerPC options:_ [-mpwrx|-mpwr2|-mpwr|-m601|-mppc|-mppc32|-m603|-m604| -m403|-m405|-mppc64|-m620|-mppc64bridge|-mbooke| -mbooke32|-mbooke64] [-mcom|-many|-maltivec] [-memb] [-mregnames|-mno-regnames] [-mrelocatable|-mrelocatable-lib] [-mlittle|-mlittle-endian|-mbig|-mbig-endian] [-msolaris|-mno-solaris] _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 Xtensa options:_ [-[no-]density] [-[no-]relax] [-[no-]generics] [-[no-]text-section-literals] [-[no-]target-align] [-[no-]longcalls] -a[cdhlmns]' Turn on listings, in any of a variety of ways: -ac' omit false conditionals -ad' omit debugging directives -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'. -D' Ignored. This option is accepted for script compatibility with calls to other assemblers. --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. -f' "fast"--skip whitespace and comment preprocessing (assume source is compiler output). --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. --gdwarf2' 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. --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. On traditional a.out systems these start with L', but different systems have different local label prefixes. --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. --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. 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 | -moabi' 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. 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 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 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. 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' Specify what processor is the target. The default is defined by the configuration option when building the assembler. -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-branchs' Relative branches are turned into absolute ones. This concerns conditional branches, unconditional branches and branches to a sub routine. -S | --short-branchs' Do not turn relative branchs 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. -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. --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. --emulation=NAME' This option causes as' to emulate as' configured for some other target, in all respects, including output format (choosing between ELF and ECOFF only), handling of pseudo-opcodes which may generate debugging information or store symbol table information, and default endianness. The available configuration names are: mipsecoff', mipself', mipslecoff', mipsbecoff', mipslelf', mipsbelf'. The first two do not alter the default endianness from that of the primary target for which the assembler was configured; the others change the default to little- or big-endian as indicated by the b' or l' in the name. Using -EB' or -EL' will override the endianness selection in any case. This option is currently supported only when the primary target as' is configured for is a MIPS ELF or ECOFF target. Furthermore, the primary target or others specified with --enable-targets=...' at configuration time must include support for the other format, if both are to be available. For example, the Irix 5 configuration includes support for both. Eventually, this option will support more configurations, with more fine-grained control over the assembler's behavior, and will be supported for more processors. -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. See the info pages for documentation of the MMIX-specific options. The following options are available when as is configured for an Xtensa processor. --density | --no-density' Enable or disable use of instructions from the Xtensa code density option. This is enabled by default when the Xtensa processor supports the code density option. --relax | --no-relax' Enable or disable instruction relaxation. This is enabled by default. Note: In the current implementation, these options also control whether assembler optimizations are performed, making these options equivalent to --generics' and --no-generics'. --generics | --no-generics' Enable or disable all assembler transformations of Xtensa instructions. The default is --generics'; --no-generics' should be used only in the rare cases when the instructions must be exactly as specified in the assembly source. --text-section-literals | --no-text-section-literals' With --text-section-literals', literal pools are interspersed in the text section. The default is --no-text-section-literals', which places literals in a separate section in the output file. --target-align | --no-target-align' Enable or disable automatic alignment to reduce branch penalties at the expense of some code density. The default is --target-align'. --longcalls | --no-longcalls' Enable or disable transformation of call instructions to allow calls across a greater range of addresses. The default is --no-longcalls'. * 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', or b.out' when as' is configured for the Intel 80960. 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; *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[cdhlns] enable listings * 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 labels * 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: D, Up: Invoking 2.1 Enable Listings: -a[cdhlns]' ================================= 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 -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 (eg 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: D, Next: f, Prev: a, Up: Invoking 2.2 -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 2.3 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 2.4 .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 2.5 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 2.6 Include Local Labels: -L' ============================== Labels beginning with L' (upper case only) are called "local labels". *Note Symbol Names::. Normally you do not see such labels when debugging, because they are intended for the use of programs (like compilers) that compose assembler programs, not for your notice. Normally both as' and ld' discard such labels, so you do not normally debug with them. This option tells as' to retain those L...' symbols in the object file. Usually if you do this you also tell the linker ld' to preserve symbols whose names begin with L'. By default, a local label is any label beginning with L', but each target is allowed to redefine the local label prefix. On the HPPA local labels begin with L$'. File: as.info, Node: listing, Next: M, Prev: L, Up: Invoking 2.7 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 pseudo ops inside the assembler source (*note List:: *note Title:: *note Sbttl:: *note Psize:: *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 2.8 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 2.9 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 2.10 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 2.11 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 2.12 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 2.13 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 2.14 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 2.15 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 2.16 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 the "line comment" character to the next newline is considered a comment and is ignored. The line comment character is ;' for the AMD 29K family; ;' on the ARC; @' on the ARM; ;' for the H8/300 family; !' for the H8/500 family; ;' for the HPPA; #' on the i386 and x86-64; #' on the i960; ;' for the PDP-11; ;' for picoJava; #' for Motorola PowerPC; !' for the Renesas / SuperH SH; !' on the SPARC; #' on the ip2k; #' on the m32r; |' on the 680x0; #' on the 68HC11 and 68HC12; ;' on the M880x0; #' on the Vax; !' for the Z8000; #' on the V850; #' for Xtensa systems; see *Note Machine Dependencies::. On some machines there are two different line comment characters. One character only begins a comment if it is the first non-whitespace character on a line, while the other always begins a comment. The V850 assembler also supports a double dash as starting a comment that extends to the end of the line. --'; 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. 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 line separator character. (The line separator is usually ;', unless this conflicts with the comment character; *note Machine Dependencies::.) The newline or separator character is considered part of the preceding statement. Newlines and separators within character constants are an exception: they do not end statements. 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, H8/500, 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 H8/500, 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 or ELF output, you can also use an extra subsection argument with arbitrary named sections: .section NAME, 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. 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 in *Note Machine Dependencies::), and underscores. For the AMD 29K family, ?' is also allowed in the body of a symbol name, though not at its beginning. Case of letters is significant: foo' is a different symbol name than Foo'. Each symbol has exactly one name. Each name in an assembly language program refers to exactly one symbol. You may use that symbol name any number of times in a program. Local Symbol Names ------------------ Local symbols 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 symbol, write a label of the form N:' (where N represents any positive integer). To refer to the most recent previous definition of that symbol 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 symbol names are only a notational device. They are immediately transformed into more conventional symbol names before the assembler uses them. The symbol names stored in the symbol table, appearing in error messages and optionally emitted to the object file. The names are constructed using these parts: L' All local labels begin with L'. Normally both as' and ld' forget symbols that start with L'. 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 defintion gets 15' as well. So for example, the first 1:' is named L1C-B1', the 44th 3:' is 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 (ie 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 instead of being terminated by a colon, they are terminated by a dollar sign. eg 55$'. They can also be distinguished from ordinary local labels by their transformed name which uses ASCII character \001' (control-A) as the magic character to distinguish them from ordinary labels. Thus the 5th defintion of 6$' is 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', and .tag' 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: Machine Dependencies, 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:: .ABORT' * Align:: .align ABS-EXPR , ABS-EXPR' * Ascii:: .ascii "STRING"'... * Asciz:: .asciz "STRING"'... * Balign:: .balign ABS-EXPR , ABS-EXPR' * Byte:: .byte EXPRESSIONS' * Comm:: .comm SYMBOL , LENGTH ' * CFI directives:: .cfi_startproc', .cfi_endproc', etc. * 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' * Err:: .err' * Exitm:: .exitm' * Extern:: .extern' * Fail:: .fail' * File:: .file STRING' * Fill:: .fill REPEAT , SIZE , VALUE' * Float:: .float FLONUMS' * Func:: .func' * Global:: .global SYMBOL', .globl SYMBOL' * 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' * Ln:: .ln LINE-NUMBER' * Linkonce:: .linkonce [TYPE]' * List:: .list' * Long:: .long EXPRESSIONS' * Macro:: .macro NAME ARGS'... * MRI:: .mri VAL' * Nolist:: .nolist' * Octa:: .octa BIGNUMS' * Org:: .org NEW-LC , FILL' * P2align:: .p2align 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' * Rept:: .rept COUNT' * Sbttl:: .sbttl "SUBHEADING"' * Scl:: .scl CLASS' * Section:: .section NAME' * 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"' * 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' * Weak:: .weak NAMES' * Word:: .word EXPRESSIONS' * Deprecated:: Deprecated Directives File: as.info, Node: Abort, Next: ABORT, 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, Next: Align, Prev: Abort, Up: Pseudo Ops 7.2 .ABORT' ============ When producing COFF output, as' accepts this directive as a synonym for .abort'. When producing b.out' output, as' accepts this directive, but ignores it. File: as.info, Node: Align, Next: Ascii, Prev: ABORT, 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 a29k, arc, hppa, i386 using ELF, i860, iq2000, m68k, m88k, 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 the i386 using a.out format, and the arm and strongarm, it is the number of low-order zero bits the location counter must have after advancement. For example .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: Ascii, Next: Asciz, Prev: Align, Up: Pseudo Ops 7.4 .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 7.5 .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: Byte, Prev: Asciz, Up: Pseudo Ops 7.6 .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: Byte, Next: Comm, Prev: Balign, Up: Pseudo Ops 7.7 .byte EXPRESSIONS' ======================= .byte' expects zero or more expressions, separated by commas. Each expression is assembled into the next byte. File: as.info, Node: Comm, Next: CFI directives, Prev: Byte, Up: Pseudo Ops 7.8 .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, the .comm' directive takes an optional third argument. This is the desired alignment of the symbol, specified as a byte boundary (for example, an alignment of 16 means that the least significant 4 bits of the address should be zero). The alignment must be an absolute expression, and it must be a power of two. If 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. The syntax for .comm' differs slightly on the HPPA. The syntax is SYMBOL .comm, LENGTH'; SYMBOL is optional. File: as.info, Node: CFI directives, Next: Data, Prev: Comm, Up: Pseudo Ops 7.9 .cfi_startproc' ==================== .cfi_startproc' is used at the beginning of each function that should have an entry in .eh_frame'. It initializes some internal data structures and emits architecture dependent initial CFI instructions. Don't forget to close the function by .cfi_endproc'. 7.10 .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'. 7.11 .cfi_def_cfa REGISTER, OFFSET' ==================================== .cfi_def_cfa' defines a rule for computing CFA as: take address from REGISTER and add OFFSET to it. 7.12 .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. 7.13 .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. 7.14 .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. 7.15 .cfi_offset REGISTER, OFFSET' =================================== Previous value of REGISTER is saved at offset OFFSET from CFA. 7.16 .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. 7.17 .cfi_window_save' ======================= SPARC register window has been saved. 7.18 .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. File: as.info, Node: Data, Next: Def, Prev: CFI directives, Up: Pseudo Ops 7.19 .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 7.20 .def NAME' ================ Begin defining debugging information for a symbol NAME; the definition extends until the .endef' directive is encountered. This directive is only observed when as' is configured for COFF format output; when producing b.out', .def' is recognized, but ignored. File: as.info, Node: Desc, Next: Dim, Prev: Def, Up: Pseudo Ops 7.21 .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 7.22 .dim' =========== This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside .def'/.endef' pairs. .dim' is only meaningful when generating COFF format output; when as' is generating b.out', it accepts this directive but ignores it. File: as.info, Node: Double, Next: Eject, Prev: Dim, Up: Pseudo Ops 7.23 .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 7.24 .eject' ============= Force a page break at this point, when generating assembly listings. File: as.info, Node: Else, Next: Elseif, Prev: Eject, Up: Pseudo Ops 7.25 .else' ============ .else' is part of the as' support for conditional assembly; *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 7.26 .elseif' ============== .elseif' is part of the as' support for conditional assembly; *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 7.27 .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 7.28 .endef' ============= This directive flags the end of a symbol definition begun with .def'. .endef' is only meaningful when generating COFF format output; if as' is configured to generate b.out', it accepts this directive but ignores it. File: as.info, Node: Endfunc, Next: Endif, Prev: Endef, Up: Pseudo Ops 7.29 .endfunc' =============== .endfunc' marks the end of a function specified with .func'. File: as.info, Node: Endif, Next: Equ, Prev: Endfunc, Up: Pseudo Ops 7.30 .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 7.31 .equ SYMBOL, EXPRESSION' ============================== This directive sets the value of SYMBOL to EXPRESSION. It is synonymous with .set'; *note .set': Set. The syntax for equ' on the HPPA is SYMBOL .equ EXPRESSION'. File: as.info, Node: Equiv, Next: Err, Prev: Equ, Up: Pseudo Ops 7.32 .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 File: as.info, Node: Err, Next: Exitm, Prev: Equiv, Up: Pseudo Ops 7.33 .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 error an conditionally compiled code. File: as.info, Node: Exitm, Next: Extern, Prev: Err, Up: Pseudo Ops 7.34 .exitm' ============= Exit early from the current macro definition. *Note Macro::. File: as.info, Node: Extern, Next: Fail, Prev: Exitm, Up: Pseudo Ops 7.35 .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 7.36 .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 7.37 .file STRING' =================== .file' tells as' that we are about to start a new logical file. 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. In some configurations of as', .file' has already been removed to avoid conflicts with other assemblers. *Note Machine Dependencies::. File: as.info, Node: Fill, Next: Float, Prev: File, Up: Pseudo Ops 7.38 .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 7.39 .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 7.40 .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: Hidden, Prev: Func, Up: Pseudo Ops 7.41 .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: Hidden, Next: hword, Prev: Global, Up: Pseudo Ops 7.42 .hidden NAMES' ==================== This 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 7.43 .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 7.44 .ident' ============= This directive is used by some assemblers to place tags in object files. as' simply accepts the directive for source-file compatibility with such assemblers, but does not actually emit anything for it. File: as.info, Node: If, Next: Incbin, Prev: Ident, Up: Pseudo Ops 7.45 .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. .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. .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 7.46 .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 7.47 .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 7.48 .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 7.49 .internal NAMES' ====================== This 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 7.50 .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@- File: as.info, Node: Irpc, Next: Lcomm, Prev: Irp, Up: Pseudo Ops 7.51 .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@- File: as.info, Node: Lcomm, Next: Lflags, Prev: Irpc, Up: Pseudo Ops 7.52 .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 7.53 .lflags' ============== as' accepts this directive, for compatibility with other assemblers, but ignores it. File: as.info, Node: Line, Next: Ln, Prev: Lflags, Up: Pseudo Ops 7.54 .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. _Warning:_ In the AMD29K configuration of as, this command is not available; use the synonym .ln' in that context. 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: Ln, Next: Linkonce, Prev: Line, Up: Pseudo Ops 7.56 .ln LINE-NUMBER' ====================== .ln' is a synonym for .line'. File: as.info, Node: Linkonce, Next: List, Prev: Ln, Up: Pseudo Ops 7.55 .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: Long, Prev: Linkonce, Up: Pseudo Ops 7.58 .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: Long, Next: Macro, Prev: List, Up: Pseudo Ops 7.59 .long EXPRESSIONS' ======================== .long' is the same as .int', *note .int': Int. File: as.info, Node: Macro, Next: MRI, Prev: Long, Up: Pseudo Ops 7.60 .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 supply a default value for any macro argument by following the name with =DEFLT'. 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 arguments. The first argument has a default value, but not the second. After the definition is complete, you can call the macro either as reserve_str A,B' (with \p1' evaluating to A and \p2' evaluating to B), or as reserve_str ,B' (with \p1' evaluating as the default, in this case 0', and \p2' evaluating to B). When you call a macro, you can specify the argument values either by position, or by keyword. For example, sum 9,17' is equivalent to sum to=17, from=9'. .endm' Mark the end of a macro definition. .exitm' Exit early from the current macro definition. \@' as' maintains a counter of how many macros it has executed in this pseudo-variable; you can copy that number to your output with \@', but _only within a macro definition_. File: as.info, Node: MRI, Next: Nolist, Prev: Macro, Up: Pseudo Ops 7.57 .mri VAL' =============== If VAL is non-zero, this tells as' to enter MRI mode. If VAL is zero, this tells as' to exit MRI mode. This change affects code assembled until the next .mri' directive, or until the end of the file. *Note MRI mode: M. File: as.info, Node: Nolist, Next: Octa, Prev: MRI, Up: Pseudo Ops 7.61 .nolist' ============== Control (in conjunction with the .list' 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. File: as.info, Node: Octa, Next: Org, Prev: Nolist, Up: Pseudo Ops 7.62 .octa BIGNUMS' ==================== This directive expects zero or more bignums, separated by commas. For each bignum, it emits a 16-byte integer. The term "octa" comes from contexts in which a "word" is two bytes; hence _octa_-word for 16 bytes. File: as.info, Node: Org, Next: P2align, Prev: Octa, Up: Pseudo Ops 7.63 .org NEW-LC , FILL' ========================= Advance the location counter of the current section to NEW-LC. NEW-LC is either an absolute expression or an expression with the same section as the current subsection. That is, you can't use .org' to cross sections: if NEW-LC has the wrong section, the .org' directive is ignored. To be compatible with former assemblers, if the section of NEW-LC is absolute, as' issues a warning, then pretends the section of NEW-LC is the same as the current subsection. .org' may only increase the location counter, or leave it unchanged; you cannot use .org' to move the location counter backwards. Because as' tries to assemble programs in one pass, NEW-LC may not be undefined. If you really detest this restriction we eagerly await a chance to share your improved assembler. Beware that the origin is relative to the start of the section, not to the start of the subsection. This is compatible with other people's assemblers. When the location counter (of the current subsection) is advanced, the intervening bytes are filled with FILL which should be an absolute expression. If the comma and FILL are omitted, FILL defaults to zero. File: as.info, Node: P2align, Next: PopSection, Prev: Org, Up: Pseudo Ops 7.64 .p2align[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 number of low-order zero bits the location counter must have after advancement. For example .p2align 3' advances the location counter until it a multiple of 8. If the location counter is already a multiple of 8, no change is needed. The second expression (also absolute) gives the fill value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally zero. However, on some systems, if the section is marked as containing code and the fill value is omitted, the space is filled with no-op instructions. The third expression is also absolute, and is also optional. If it is present, it is the maximum number of bytes that should be skipped by this alignment directive. If doing the alignment would require skipping more bytes than the specified maximum, then the alignment is not done at all. You can omit the fill value (the second argument) entirely by simply using two commas after the required alignment; this can be useful if you want the alignment to be filled with no-op instructions when appropriate. The .p2alignw' and .p2alignl' directives are variants of the .p2align' directive. The .p2alignw' directive treats the fill pattern as a two byte word value. The .p2alignl' directives treats the fill pattern as a four byte longword value. For example, .p2alignw 2,0x368d' will align to a multiple of 4. If it skips two bytes, they will be filled in with the value 0x368d (the exact placement of the bytes depends upon the endianness of the processor). If it skips 1 or 3 bytes, the fill value is undefined. File: as.info, Node: PopSection, Next: Previous, Prev: P2align, Up: Pseudo Ops 7.66 .popsection' ================== This is one of the ELF section stack manipulation directives. The others are .section' (*note Section::), .subsection' (*note SubSection::), .pushsection' (*note PushSection::), and .previous' (*note Previous::). This directive replaces the current section (and subsection) with the top section (and subsection) on the section stack. This section is popped off the stack. File: as.info, Node: Previous, Next: Print, Prev: PopSection, Up: Pseudo Ops 7.65 .previous' ================ This is one of the ELF section stack manipulation directives. The others are .section' (*note Section::), .subsection' (*note SubSection::), .pushsection' (*note PushSection::), and .popsection' (*note PopSection::). This directive swaps the current section (and subsection) with most recently referenced section (and subsection) prior to this one. Multiple .previous' directives in a row will flip between two sections (and their subsections). In terms of the section stack, this directive swaps the current section with the top section on the section stack. File: as.info, Node: Print, Next: Protected, Prev: Previous, Up: Pseudo Ops 7.67 .print STRING' ==================== as' will print STRING on the standard output during assembly. You must put STRING in double quotes. File: as.info, Node: Protected, Next: Psize, Prev: Print, Up: Pseudo Ops 7.68 .protected NAMES' ======================= This one of the ELF visibility directives. The other two are .hidden' (*note Hidden::) and .internal' (*note Internal::). This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to protected' which means that any references to the symbols from within the components that defines them must be resolved to the definition in that component, even if a definition in another component would normally preempt this. File: as.info, Node: Psize, Next: Purgem, Prev: Protected, Up: Pseudo Ops 7.69 .psize LINES , COLUMNS' ============================= Use this directive to declare the number of lines--and, optionally, the number of columns--to use for each page, when generating listings. If you do not use .psize', listings use a default line-count of 60. You may omit the comma and COLUMNS specification; the default width is 200 columns. as' generates formfeeds whenever the specified number of lines is exceeded (or whenever you explicitly request one, using .eject'). If you specify LINES as 0', no formfeeds are generated save those explicitly specified with .eject'. File: as.info, Node: Purgem, Next: PushSection, Prev: Psize, Up: Pseudo Ops 7.70 .purgem NAME' =================== Undefine the macro NAME, so that later uses of the string will not be expanded. *Note Macro::. File: as.info, Node: PushSection, Next: Quad, Prev: Purgem, Up: Pseudo Ops 7.71 .pushsection NAME , SUBSECTION' ===================================== This is one of the ELF section stack manipulation directives. The others are .section' (*note Section::), .subsection' (*note SubSection::), .popsection' (*note PopSection::), and .previous' (*note Previous::). This directive is a synonym for .section'. It pushes the current section (and subsection) onto the top of the section stack, and then replaces the current section and subsection with name' and subsection'. File: as.info, Node: Quad, Next: Rept, Prev: PushSection, Up: Pseudo Ops 7.72 .quad BIGNUMS' ==================== .quad' expects zero or more bignums, separated by commas. For each bignum, it emits an 8-byte integer. If the bignum won't fit in 8 bytes, it prints a warning message; and just takes the lowest order 8 bytes of the bignum. The term "quad" comes from contexts in which a "word" is two bytes; hence _quad_-word for 8 bytes. File: as.info, Node: Rept, Next: Sbttl, Prev: Quad, Up: Pseudo Ops 7.73 .rept COUNT' ================== Repeat the sequence of lines between the .rept' directive and the next .endr' directive COUNT times. For example, assembling .rept 3 .long 0 .endr is equivalent to assembling .long 0 .long 0 .long 0 File: as.info, Node: Sbttl, Next: Scl, Prev: Rept, Up: Pseudo Ops 7.74 .sbttl "SUBHEADING"' ========================== Use SUBHEADING as the title (third line, immediately after the title line) when generating assembly listings. This directive affects subsequent pages, as well as the current page if it appears within ten lines of the top of a page. File: as.info, Node: Scl, Next: Section, Prev: Sbttl, Up: Pseudo Ops 7.75 .scl CLASS' ================= Set the storage-class value for a symbol. This directive may only be used inside a .def'/.endef' pair. Storage class may flag whether a symbol is static or external, or it may record further symbolic debugging information. The .scl' directive is primarily associated with COFF output; when configured to generate b.out' output format, as' accepts this directive but ignores it. File: as.info, Node: Section, Next: Set, Prev: Scl, Up: Pseudo Ops 7.76 .section NAME' ==================== Use the .section' directive to assemble the following code into a section named NAME. This directive is only supported for targets that actually support arbitrarily named sections; on a.out' targets, for example, it is not accepted, even with a standard a.out' section name. COFF Version ------------ For COFF targets, the .section' directive is used in one of the following ways: .section NAME[, "FLAGS"] .section NAME[, SUBSEGMENT] If the optional argument is quoted, it is taken as flags to use for the section. Each flag is a single character. The following flags are recognized: b' bss section (uninitialized data) n' section is not loaded w' writable section d' data section r' read-only section x' executable section s' shared section (meaningful for PE targets) a' ignored. (For compatibility with the ELF version) If no flags are specified, the default flags depend upon the section name. If the section name is not recognized, the default will be for the section to be loaded and writable. Note the n' and w' flags remove attributes from the section, rather than adding them, so if they are used on their own it will be as if no flags had been specified at all. If the optional argument to the .section' directive is not quoted, it is taken as a subsegment number (*note Sub-Sections::). ELF Version ----------- This is one of the ELF section stack manipulation directives. The others are .subsection' (*note SubSection::), .pushsection' (*note PushSection::), .popsection' (*note PopSection::), and .previous' (*note Previous::). For ELF targets, the .section' directive is used like this: .section NAME [, "FLAGS"[, @TYPE[, @ENTSIZE]]] The optional FLAGS argument is a quoted string which may contain any combination of the following characters: a' section is allocatable w' section is writable x' section is executable M' section is mergeable S' section contains zero terminated strings The optional TYPE argument may contain one of the following constants: @progbits' section contains data @nobits' section does not contain data (i.e., section only occupies space) Note on targets where the @' character is the start of a comment (eg ARM) then another character is used instead. For example the ARM port uses the %' character. If FLAGS contains M' flag, TYPE argument must be specified as well as ENTSIZE argument. Sections with M' flag but not S' flag must contain fixed size constants, each ENTSIZE octets long. Sections with both M' and S' must contain zero terminated strings where each character is ENTSIZE bytes long. The linker may remove duplicates within sections with the same name, same entity size and same flags. If no flags are specified, the default flags depend upon the section name. If the section name is not recognized, the default will be for the section to have none of the above flags: it will not be allocated in memory, nor writable, nor executable. The section will contain data. For ELF targets, the assembler supports another type of .section' directive for compatibility with the Solaris assembler: .section "NAME"[, FLAGS...] Note that the section name is quoted. There may be a sequence of comma separated flags: #alloc' section is allocatable #write' section is writable #execinstr' section is executable This directive replaces the current section and subsection. The replaced section and subsection are pushed onto the section stack. See the contents of the gas testsuite directory gas/testsuite/gas/elf' for some examples of how this directive and the other section stack directives work. File: as.info, Node: Set, Next: Short, Prev: Section, Up: Pseudo Ops 7.77 .set SYMBOL, EXPRESSION' ============================== Set the value of SYMBOL to EXPRESSION. This changes SYMBOL's value and type to conform to EXPRESSION. If SYMBOL was flagged as external, it remains flagged (*note Symbol Attributes::). You may .set' a symbol many times in the same assembly. If you .set' a global symbol, the value stored in the object file is the last value stored into it. The syntax for set' on the HPPA is SYMBOL .set EXPRESSION'. File: as.info, Node: Short, Next: Single, Prev: Set, Up: Pseudo Ops 7.78 .short EXPRESSIONS' ========================= .short' is normally the same as .word'. *Note .word': Word. In some configurations, however, .short' and .word' generate numbers of different lengths; *note Machine Dependencies::. File: as.info, Node: Single, Next: Size, Prev: Short, Up: Pseudo Ops 7.79 .single FLONUMS' ====================== This directive assembles zero or more flonums, separated by commas. It has the same effect as .float'. The exact kind of floating point numbers emitted depends on how as' is configured. *Note Machine Dependencies::. File: as.info, Node: Size, Next: Skip, Prev: Single, Up: Pseudo Ops 7.80 .size' ============ This directive is used to set the size associated with a symbol. COFF Version ------------ For COFF targets, the .size' directive is only permitted inside .def'/.endef' pairs. It is used like this: .size EXPRESSION .size' is only meaningful when generating COFF format output; when as' is generating b.out', it accepts this directive but ignores it. ELF Version ----------- For ELF targets, the .size' directive is used like this: .size NAME , EXPRESSION This directive sets the size associated with a symbol NAME. The size in bytes is computed from EXPRESSION which can make use of label arithmetic. This directive is typically used to set the size of function symbols. File: as.info, Node: Skip, Next: Sleb128, Prev: Size, Up: Pseudo Ops 7.82 .skip SIZE , FILL' ======================== This directive emits SIZE bytes, each of value FILL. Both SIZE and FILL are absolute expressions. If the comma and FILL are omitted, FILL is assumed to be zero. This is the same as .space'. File: as.info, Node: Sleb128, Next: Space, Prev: Skip, Up: Pseudo Ops 7.81 .sleb128 EXPRESSIONS' =========================== SLEB128 stands for "signed little endian base 128." This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format. *Note .uleb128': Uleb128. File: as.info, Node: Space, Next: Stab, Prev: Sleb128, Up: Pseudo Ops 7.83 .space SIZE , FILL' ========================= This directive emits SIZE bytes, each of value FILL. Both SIZE and FILL are absolute expressions. If the comma and FILL are omitted, FILL is assumed to be zero. This is the same as .skip'. _Warning:_ .space' has a completely different meaning for HPPA targets; use .block' as a substitute. See HP9000 Series 800 Assembly Language Reference Manual' (HP 92432-90001) for the meaning of the .space' directive. *Note HPPA Assembler Directives: HPPA Directives, for a summary. On the AMD 29K, this directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. _Warning:_ In most versions of the GNU assembler, the directive .space' has the effect of .block' *Note Machine Dependencies::. File: as.info, Node: Stab, Next: String, Prev: Space, Up: Pseudo Ops 7.84 .stabd, .stabn, .stabs' ============================= There are three directives that begin .stab'. All emit symbols (*note Symbols::), for use by symbolic debuggers. The symbols are not entered in the as' hash table: they cannot be referenced elsewhere in the source file. Up to five fields are required: STRING This is the symbol's name. It may contain any character except \000', so is more general than ordinary symbol names. Some debuggers used to code arbitrarily complex structures into symbol names using this field. TYPE An absolute expression. The symbol's type is set to the low 8 bits of this expression. Any bit pattern is permitted, but ld' and debuggers choke on silly bit patterns. OTHER An absolute expression. The symbol's "other" attribute is set to the low 8 bits of this expression. DESC An absolute expression. The symbol's descriptor is set to the low 16 bits of this expression. VALUE An absolute expression which becomes the symbol's value. If a warning is detected while reading a .stabd', .stabn', or .stabs' statement, the symbol has probably already been created; you get a half-formed symbol in your object file. This is compatible with earlier assemblers! .stabd TYPE , OTHER , DESC' The "name" of the symbol generated is not even an empty string. It is a null pointer, for compatibility. Older assemblers used a null pointer so they didn't waste space in object files with empty strings. The symbol's value is set to the location counter, relocatably. When your program is linked, the value of this symbol is the address of the location counter when the .stabd' was assembled. .stabn TYPE , OTHER , DESC , VALUE' The name of the symbol is set to the empty string ""'. .stabs STRING , TYPE , OTHER , DESC , VALUE' All five fields are specified. File: as.info, Node: String, Next: Struct, Prev: Stab, Up: Pseudo Ops 7.85 .string' "STR" ==================== Copy the characters in STR to the object file. You may specify more than one string to copy, separated by commas. Unless otherwise specified for a particular machine, the assembler marks the end of each string with a 0 byte. You can use any of the escape sequences described in *Note Strings: Strings. File: as.info, Node: Struct, Next: SubSection, Prev: String, Up: Pseudo Ops 7.86 .struct EXPRESSION' ========================= Switch to the absolute section, and set the section offset to EXPRESSION, which must be an absolute expression. You might use this as follows: .struct 0 field1: .struct field1 + 4 field2: .struct field2 + 4 field3: This would define the symbol field1' to have the value 0, the symbol field2' to have the value 4, and the symbol field3' to have the value 8. Assembly would be left in the absolute section, and you would need to use a .section' directive of some sort to change to some other section before further assembly. File: as.info, Node: SubSection, Next: Symver, Prev: Struct, Up: Pseudo Ops 7.87 .subsection NAME' ======================= This is one of the ELF section stack manipulation directives. The others are .section' (*note Section::), .pushsection' (*note PushSection::), .popsection' (*note PopSection::), and .previous' (*note Previous::). This directive replaces the current subsection with name'. The current section is not changed. The replaced subsection is put onto the section stack in place of the then current top of stack subsection. File: as.info, Node: Symver, Next: Tag, Prev: SubSection, Up: Pseudo Ops 7.88 .symver' ============== Use the .symver' directive to bind symbols to specific version nodes within a source file. This is only supported on ELF platforms, and is typically used when assembling files to be linked into a shared library. There are cases where it may make sense to use this in objects to be bound into an application itself so as to override a versioned symbol from a shared library. For ELF targets, the .symver' directive can be used like this: .symver NAME, NAME2@NODENAME If the symbol NAME is defined within the file being assembled, the .symver' directive effectively creates a symbol alias with the name NAME2@NODENAME, and in fact the main reason that we just don't try and create a regular alias is that the @ character isn't permitted in symbol names. The NAME2 part of the name is the actual name of the symbol by which it will be externally referenced. The name NAME itself is merely a name of convenience that is used so that it is possible to have definitions for multiple versions of a function within a single source file, and so that the compiler can unambiguously know which version of a function is being mentioned. The NODENAME portion of the alias should be the name of a node specified in the version script supplied to the linker when building a shared library. If you are attempting to override a versioned symbol from a shared library, then NODENAME should correspond to the nodename of the symbol you are trying to override. If the symbol NAME is not defined within the file being assembled, all references to NAME will be changed to NAME2@NODENAME. If no reference to NAME is made, NAME2@NODENAME will be removed from the symbol table. Another usage of the .symver' directive is: .symver NAME, NAME2@@NODENAME In this case, the symbol NAME must exist and be defined within the file being assembled. It is similar to NAME2@NODENAME. The difference is NAME2@@NODENAME will also be used to resolve references to NAME2 by the linker. The third usage of the .symver' directive is: .symver NAME, NAME2@@@NODENAME When NAME is not defined within the file being assembled, it is treated as NAME2@NODENAME. When NAME is defined within the file being assembled, the symbol name, NAME, will be changed to NAME2@@NODENAME. File: as.info, Node: Tag, Next: Text, Prev: Symver, Up: Pseudo Ops 7.89 .tag STRUCTNAME' ====================== This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside .def'/.endef' pairs. Tags are used to link structure definitions in the symbol table with instances of those structures. .tag' is only used when generating COFF format output; when as' is generating b.out', it accepts this directive but ignores it. File: as.info, Node: Text, Next: Title, Prev: Tag, Up: Pseudo Ops 7.90 .text SUBSECTION' ======================= Tells as' to assemble the following statements onto the end of the text subsection numbered SUBSECTION, which is an absolute expression. If SUBSECTION is omitted, subsection number zero is used. File: as.info, Node: Title, Next: Type, Prev: Text, Up: Pseudo Ops 7.91 .title "HEADING"' ======================= Use HEADING as the title (second line, immediately after the source file name and pagenumber) when generating assembly listings. This directive affects subsequent pages, as well as the current page if it appears within ten lines of the top of a page. File: as.info, Node: Type, Next: Uleb128, Prev: Title, Up: Pseudo Ops 7.92 .type' ============ This directive is used to set the type of a symbol. COFF Version ------------ For COFF targets, this directive is permitted only within .def'/.endef' pairs. It is used like this: .type INT This records the integer INT as the type attribute of a symbol table entry. .type' is associated only with COFF format output; when as' is configured for b.out' output, it accepts this directive but ignores it. ELF Version ----------- For ELF targets, the .type' directive is used like this: .type NAME , TYPE DESCRIPTION This sets the type of symbol NAME to be either a function symbol or an object symbol. There are five different syntaxes supported for the TYPE DESCRIPTION field, in order to provide compatibility with various other assemblers. The syntaxes supported are: .type ,#function .type ,#object .type ,@function .type ,@object .type ,%function .type ,%object .type ,"function" .type ,"object" .type STT_FUNCTION .type STT_OBJECT File: as.info, Node: Uleb128, Next: Val, Prev: Type, Up: Pseudo Ops 7.93 .uleb128 EXPRESSIONS' =========================== ULEB128 stands for "unsigned little endian base 128." This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format. *Note .sleb128': Sleb128. File: as.info, Node: Val, Next: Version, Prev: Uleb128, Up: Pseudo Ops 7.94 .val ADDR' ================ This directive, permitted only within .def'/.endef' pairs, records the address ADDR as the value attribute of a symbol table entry. .val' is used only for COFF output; when as' is configured for b.out', it accepts this directive but ignores it. File: as.info, Node: Version, Next: VTableEntry, Prev: Val, Up: Pseudo Ops 7.95 .version "STRING"' ======================== This directive creates a .note' section and places into it an ELF formatted note of type NT_VERSION. The note's name is set to string'. File: as.info, Node: VTableEntry, Next: VTableInherit, Prev: Version, Up: Pseudo Ops 7.96 .vtable_entry TABLE, OFFSET' ================================== This directive finds or creates a symbol table' and creates a VTABLE_ENTRY' relocation for it with an addend of offset'. File: as.info, Node: VTableInherit, Next: Weak, Prev: VTableEntry, Up: Pseudo Ops 7.97 .vtable_inherit CHILD, PARENT' ==================================== This directive finds the symbol child' and finds or creates the symbol parent' and then creates a VTABLE_INHERIT' relocation for the parent whose addend is the value of the child symbol. As a special case the parent name of 0' is treated as refering the *ABS*' section. File: as.info, Node: Weak, Next: Word, Prev: VTableInherit, Up: Pseudo Ops 7.98 .weak NAMES' ================== This directive sets the weak attribute on the comma separated list of symbol names'. If the symbols do not already exist, they will be created. File: as.info, Node: Word, Next: Deprecated, Prev: Weak, Up: Pseudo Ops 7.99 .word EXPRESSIONS' ======================== This directive expects zero or more EXPRESSIONS, of any section, separated by commas. The size of the number emitted, and its byte order, depend on what target computer the assembly is for. _Warning: Special Treatment to support Compilers_ Machines with a 32-bit address space, but that do less than 32-bit addressing, require the following special treatment. If the machine of interest to you does 32-bit addressing (or doesn't require it; *note Machine Dependencies::), you can ignore this issue. In order to assemble compiler output into something that works, as' occasionally does strange things to .word' directives. Directives of the form .word sym1-sym2' are often emitted by compilers as part of jump tables. Therefore, when as' assembles a directive of the form .word sym1-sym2', and the difference between sym1' and sym2' does not fit in 16 bits, as' creates a "secondary jump table", immediately before the next label. This secondary jump table is preceded by a short-jump to the first byte after the secondary table. This short-jump prevents the flow of control from accidentally falling into the new table. Inside the table is a long-jump to sym2'. The original .word' contains sym1' minus the address of the long-jump to sym2'. If there were several occurrences of .word sym1-sym2' before the secondary jump table, all of them are adjusted. If there was a .word sym3-sym4', that also did not fit in sixteen bits, a long-jump to sym4' is included in the secondary jump table, and the .word' directives are adjusted to contain sym3' minus the address of the long-jump to sym4'; and so on, for as many entries in the original jump table as necessary. File: as.info, Node: Deprecated, Prev: Word, Up: Pseudo Ops 7.100 Deprecated Directives =========================== One day these directives won't work. They are included for compatibility with older assemblers. .abort .line File: as.info, Node: Machine Dependencies, Next: Reporting Bugs, Prev: Pseudo Ops, Up: Top 8 Machine Dependent Features **************************** The machine instruction sets are (almost by definition) different on each machine where as' runs. Floating point representations vary as well, and as' often supports a few additional directives or command-line options for compatibility with other assemblers on a particular platform. Finally, some versions of as' support special pseudo-instructions for branch optimization. This chapter discusses most of these differences, though it does not include details on any machine's instruction set. For details on that subject, see the hardware manufacturer's manual. * Menu: * AMD29K-Dependent:: AMD 29K Dependent Features * Alpha-Dependent:: Alpha Dependent Features * ARC-Dependent:: ARC Dependent Features * ARM-Dependent:: ARM Dependent Features * CRIS-Dependent:: CRIS Dependent Features * D10V-Dependent:: D10V Dependent Features * D30V-Dependent:: D30V Dependent Features * H8/300-Dependent:: Renesas H8/300 Dependent Features * H8/500-Dependent:: Renesas H8/500 Dependent Features * HPPA-Dependent:: HPPA Dependent Features * ESA/390-Dependent:: IBM ESA/390 Dependent Features * i386-Dependent:: Intel 80386 and AMD x86-64 Dependent Features * i860-Dependent:: Intel 80860 Dependent Features * i960-Dependent:: Intel 80960 Dependent Features * IP2K-Dependent:: IP2K Dependent Features * M32R-Dependent:: M32R Dependent Features * M68K-Dependent:: M680x0 Dependent Features * M68HC11-Dependent:: M68HC11 and 68HC12 Dependent Features * M88K-Dependent:: M880x0 Dependent Features * MIPS-Dependent:: MIPS Dependent Features * MMIX-Dependent:: MMIX Dependent Features * MSP430-Dependent:: MSP430 Dependent Features * SH-Dependent:: Renesas / SuperH SH Dependent Features * SH64-Dependent:: SuperH SH64 Dependent Features * PDP-11-Dependent:: PDP-11 Dependent Features * PJ-Dependent:: picoJava Dependent Features * PPC-Dependent:: PowerPC Dependent Features * Sparc-Dependent:: SPARC Dependent Features * TIC54X-Dependent:: TI TMS320C54x Dependent Features * V850-Dependent:: V850 Dependent Features * Xtensa-Dependent:: Xtensa Dependent Features * Z8000-Dependent:: Z8000 Dependent Features * Vax-Dependent:: VAX Dependent Features File: as.info, Node: AMD29K-Dependent, Next: Alpha-Dependent, Up: Machine Dependencies 8.1 AMD 29K Dependent Features ============================== * Menu: * AMD29K Options:: Options * AMD29K Syntax:: Syntax * AMD29K Floating Point:: Floating Point * AMD29K Directives:: AMD 29K Machine Directives * AMD29K Opcodes:: Opcodes File: as.info, Node: AMD29K Options, Next: AMD29K Syntax, Up: AMD29K-Dependent 8.1.1 Options ------------- as' has no additional command-line options for the AMD 29K family. File: as.info, Node: AMD29K Syntax, Next: AMD29K Floating Point, Prev: AMD29K Options, Up: AMD29K-Dependent 8.1.2 Syntax ------------ * Menu: * AMD29K-Macros:: Macros * AMD29K-Chars:: Special Characters * AMD29K-Regs:: Register Names File: as.info, Node: AMD29K-Macros, Next: AMD29K-Chars, Up: AMD29K Syntax 8.1.2.1 Macros .............. The macro syntax used on the AMD 29K is like that described in the AMD 29K Family Macro Assembler Specification. Normal as' macros should still work. File: as.info, Node: AMD29K-Chars, Next: AMD29K-Regs, Prev: AMD29K-Macros, Up: AMD29K Syntax 8.1.2.2 Special Characters .......................... ;' is the line comment character. The character ?' is permitted in identifiers (but may not begin an identifier). File: as.info, Node: AMD29K-Regs, Prev: AMD29K-Chars, Up: AMD29K Syntax 8.1.2.3 Register Names ...................... General-purpose registers are represented by predefined symbols of the form GRNNN' (for global registers) or LRNNN' (for local registers), where NNN represents a number between 0' and 127', written with no leading zeros. The leading letters may be in either upper or lower case; for example, gr13' and LR7' are both valid register names. You may also refer to general-purpose registers by specifying the register number as the result of an expression (prefixed with %%' to flag the expression as a register number): %%EXPRESSION --where EXPRESSION must be an absolute expression evaluating to a number between 0' and 255'. The range [0, 127] refers to global registers, and the range [128, 255] to local registers. In addition, as' understands the following protected special-purpose register names for the AMD 29K family: vab chd pc0 ops chc pc1 cps rbp pc2 cfg tmc mmu cha tmr lru These unprotected special-purpose register names are also recognized: ipc alu fpe ipa bp inte ipb fc fps q cr exop File: as.info, Node: AMD29K Floating Point, Next: AMD29K Directives, Prev: AMD29K Syntax, Up: AMD29K-Dependent 8.1.3 Floating Point -------------------- The AMD 29K family uses IEEE floating-point numbers. File: as.info, Node: AMD29K Directives, Next: AMD29K Opcodes, Prev: AMD29K Floating Point, Up: AMD29K-Dependent 8.1.4 AMD 29K Machine Directives -------------------------------- .block SIZE , FILL' This directive emits SIZE bytes, each of value FILL. Both SIZE and FILL are absolute expressions. If the comma and FILL are omitted, FILL is assumed to be zero. In other versions of the GNU assembler, this directive is called .space'. .cputype' This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. .file' This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. _Warning:_ in other versions of the GNU assembler, .file' is used for the directive called .app-file' in the AMD 29K support. .line' This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. .sect' This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. .use SECTION NAME' Establishes the section and subsection for the following code; SECTION NAME may be one of .text', .data', .data1', or .lit'. With one of the first three SECTION NAME options, .use' is equivalent to the machine directive SECTION NAME; the remaining case, .use .lit', is the same as .data 200'. File: as.info, Node: AMD29K Opcodes, Prev: AMD29K Directives, Up: AMD29K-Dependent 8.1.5 Opcodes ------------- as' implements all the standard AMD 29K opcodes. No additional pseudo-instructions are needed on this family. For information on the 29K machine instruction set, see Am29000 User's Manual', Advanced Micro Devices, Inc. File: as.info, Node: Alpha-Dependent, Next: ARC-Dependent, Prev: AMD29K-Dependent, Up: Machine Dependencies 8.2 Alpha Dependent Features ============================ * Menu: * Alpha Notes:: Notes * Alpha Options:: Options * Alpha Syntax:: Syntax * Alpha Floating Point:: Floating Point * Alpha Directives:: Alpha Machine Directives * Alpha Opcodes:: Opcodes File: as.info, Node: Alpha Notes, Next: Alpha Options, Up: Alpha-Dependent 8.2.1 Notes ----------- The documentation here is primarily for the ELF object format. as' also supports the ECOFF and EVAX formats, but features specific to these formats are not yet documented. File: as.info, Node: Alpha Options, Next: Alpha Syntax, Prev: Alpha Notes, Up: Alpha-Dependent 8.2.2 Options ------------- -mCPU' This option specifies the target processor. If an attempt is made to assemble an instruction which will not execute on the target processor, the assembler may either expand the instruction as a macro or issue an error message. This option is equivalent to the .arch' directive. The following processor names are recognized: 21064', 21064a', 21066', 21068', 21164', 21164a', 21164pc', 21264', 21264a', 21264b', ev4', ev5', lca45', ev5', ev56', pca56', ev6', ev67', ev68'. The special name all' may be used to allow the assembler to accept instructions valid for any Alpha processor. In order to support existing practice in OSF/1 with respect to .arch', and existing practice within MILO' (the Linux ARC bootloader), the numbered processor names (e.g. 21064) enable the processor-specific PALcode instructions, while the "electro-vlasic" names (e.g. ev4') do not. -mdebug' -no-mdebug' Enables or disables the generation of .mdebug' encapsulation for stabs directives and procedure descriptors. The default is to automatically enable .mdebug' when the first stabs directive is seen. -relax' This option forces all relocations to be put into the object file, instead of saving space and resolving some relocations at assembly time. Note that this option does not propagate all symbol arithmetic into the object file, because not all symbol arithmetic can be represented. However, the option can still be useful in specific applications. -g' This option is used when the compiler generates debug information. When gcc' is using mips-tfile' to generate debug information for ECOFF, local labels must be passed through to the object file. Otherwise this option has no effect. -GSIZE' A local common symbol larger than SIZE is placed in .bss', while smaller symbols are placed in .sbss'. -F' -32addr' These options are ignored for backward compatibility. File: as.info, Node: Alpha Syntax, Next: Alpha Floating Point, Prev: Alpha Options, Up: Alpha-Dependent 8.2.3 Syntax ------------ The assembler syntax closely follow the Alpha Reference Manual; assembler directives and general syntax closely follow the OSF/1 and OpenVMS syntax, with a few differences for ELF. * Menu: * Alpha-Chars:: Special Characters * Alpha-Regs:: Register Names * Alpha-Relocs:: Relocations File: as.info, Node: Alpha-Chars, Next: Alpha-Regs, Up: Alpha Syntax 8.2.3.1 Special Characters .......................... #' is the line comment character. ;' can be used instead of a newline to separate statements. File: as.info, Node: Alpha-Regs, Next: Alpha-Relocs, Prev: Alpha-Chars, Up: Alpha Syntax 8.2.3.2 Register Names ...................... The 32 integer registers are referred to as $N' or $rN'. In addition, registers 15, 28, 29, and 30 may be referred to by the symbols $fp', $at', $gp', and $sp' respectively. The 32 floating-point registers are referred to as $fN'. File: as.info, Node: Alpha-Relocs, Prev: Alpha-Regs, Up: Alpha Syntax 8.2.3.3 Relocations ................... Some of these relocations are available for ECOFF, but mostly only for ELF. They are modeled after the relocation format introduced in Digital Unix 4.0, but there are additions. The format is !TAG' or !TAG!NUMBER' where TAG is the name of the relocation. In some cases NUMBER is used to relate specific instructions. The relocation is placed at the end of the instruction like so: ldah$0,a($29) !gprelhigh lda$0,a($0) !gprellow ldq$1,b($29) !literal!100 ldl$2,0($1) !lituse_base!100 !literal' !literal!N' Used with an ldq' instruction to load the address of a symbol from the GOT. A sequence number N is optional, and if present is used to pair lituse' relocations with this literal' relocation. The lituse' relocations are used by the linker to optimize the code based on the final location of the symbol. Note that these optimizations are dependent on the data flow of the program. Therefore, if _any_ lituse' is paired with a literal' relocation, then _all_ uses of the register set by the literal' instruction must also be marked with lituse' relocations. This is because the original literal' instruction may be deleted or transformed into another instruction. Also note that there may be a one-to-many relationship between literal' and lituse', but not a many-to-one. That is, if there are two code paths that load up the same address and feed the value to a single use, then the use may not use a lituse' relocation. !lituse_base!N' Used with any memory format instruction (e.g. ldl') to indicate that the literal is used for an address load. The offset field of the instruction must be zero. During relaxation, the code may be altered to use a gp-relative load. !lituse_jsr!N' Used with a register branch format instruction (e.g. jsr') to indicate that the literal is used for a call. During relaxation, the code may be altered to use a direct branch (e.g. bsr'). !lituse_bytoff!N' Used with a byte mask instruction (e.g. extbl') to indicate that only the low 3 bits of the address are relevant. During relaxation, the code may be altered to use an immediate instead of a register shift. !lituse_addr!N' Used with any other instruction to indicate that the original address is in fact used, and the original ldq' instruction may not be altered or deleted. This is useful in conjunction with lituse_jsr' to test whether a weak symbol is defined. ldq$27,foo($29) !literal!1 beq$27,is_undef !lituse_addr!1 jsr $26,($27),foo !lituse_jsr!1 !lituse_tlsgd!N' Used with a register branch format instruction to indicate that the literal is the call to __tls_get_addr' used to compute the address of the thread-local storage variable whose descriptor was loaded with !tlsgd!N'. !lituse_tlsldm!N' Used with a register branch format instruction to indicate that the literal is the call to __tls_get_addr' used to compute the address of the base of the thread-local storage block for the current module. The descriptor for the module must have been loaded with !tlsldm!N'. !gpdisp!N' Used with ldah' and lda' to load the GP from the current address, a-la the ldgp' macro. The source register for the ldah' instruction must contain the address of the ldah' instruction. There must be exactly one lda' instruction paired with the ldah' instruction, though it may appear anywhere in the instruction stream. The immediate operands must be zero. bsr $26,foo ldah$29,0($26) !gpdisp!1 lda$29,0($29) !gpdisp!1 !gprelhigh' Used with an ldah' instruction to add the high 16 bits of a 32-bit displacement from the GP. !gprellow' Used with any memory format instruction to add the low 16 bits of a 32-bit displacement from the GP. !gprel' Used with any memory format instruction to add a 16-bit displacement from the GP. !samegp' Used with any branch format instruction to skip the GP load at the target address. The referenced symbol must have the same GP as the source object file, and it must be declared to either not use $27' or perform a standard GP load in the first two instructions via the .prologue' directive. !tlsgd' !tlsgd!N' Used with an lda' instruction to load the address of a TLS descriptor for a symbol in the GOT. The sequence number N is optional, and if present it used to pair the descriptor load with both the literal' loading the address of the __tls_get_addr' function and the lituse_tlsgd' marking the call to that function. For proper relaxation, both the tlsgd', literal' and lituse' relocations must be in the same extended basic block. That is, the relocation with the lowest address must be executed first at runtime. !tlsldm' !tlsldm!N' Used with an lda' instruction to load the address of a TLS descriptor for the current module in the GOT. Similar in other respects to tlsgd'. !gotdtprel' Used with an ldq' instruction to load the offset of the TLS symbol within its module's thread-local storage block. Also known as the dynamic thread pointer offset or dtp-relative offset. !dtprelhi' !dtprello' !dtprel' Like gprel' relocations except they compute dtp-relative offsets. !gottprel' Used with an ldq' instruction to load the offset of the TLS symbol from the thread pointer. Also known as the tp-relative offset. !tprelhi' !tprello' !tprel' Like gprel' relocations except they compute tp-relative offsets. File: as.info, Node: Alpha Floating Point, Next: Alpha Directives, Prev: Alpha Syntax, Up: Alpha-Dependent 8.2.4 Floating Point -------------------- The Alpha family uses both IEEE and VAX floating-point numbers. File: as.info, Node: Alpha Directives, Next: Alpha Opcodes, Prev: Alpha Floating Point, Up: Alpha-Dependent 8.2.5 Alpha Assembler Directives -------------------------------- as' for the Alpha supports many additional directives for compatibility with the native assembler. This section describes them only briefly. These are the additional directives in as' for the Alpha: .arch CPU' Specifies the target processor. This is equivalent to the -mCPU' command-line option. *Note Options: Alpha Options, for a list of values for CPU. .ent FUNCTION[, N]' Mark the beginning of FUNCTION. An optional number may follow for compatibility with the OSF/1 assembler, but is ignored. When generating .mdebug' information, this will create a procedure descriptor for the function. In ELF, it will mark the symbol as a function a-la the generic .type' directive. .end FUNCTION' Mark the end of FUNCTION. In ELF, it will set the size of the symbol a-la the generic .size' directive. .mask MASK, OFFSET' Indicate which of the integer registers are saved in the current function's stack frame. MASK is interpreted a bit mask in which bit N set indicates that register N is saved. The registers are saved in a block located OFFSET bytes from the "canonical frame address" (CFA) which is the value of the stack pointer on entry to the function. The registers are saved sequentially, except that the return address register (normally $26') is saved first. This and the other directives that describe the stack frame are currently only used when generating .mdebug' information. They may in the future be used to generate DWARF2 .debug_frame' unwind information for hand written assembly. .fmask MASK, OFFSET' Indicate which of the floating-point registers are saved in the current stack frame. The MASK and OFFSET parameters are interpreted as with .mask'. .frame FRAMEREG, FRAMEOFFSET, RETREG[, ARGOFFSET]' Describes the shape of the stack frame. The frame pointer in use is FRAMEREG; normally this is either $fp' or $sp'. The frame pointer is FRAMEOFFSET bytes below the CFA. The return address is initially located in RETREG until it is saved as indicated in .mask'. For compatibility with OSF/1 an optional ARGOFFSET parameter is accepted and ignored. It is believed to indicate the offset from the CFA to the saved argument registers. .prologue N' Indicate that the stack frame is set up and all registers have been spilled. The argument N indicates whether and how the function uses the incoming "procedure vector" (the address of the called function) in $27'. 0 indicates that $27' is not used; 1 indicates that the first two instructions of the function use $27' to perform a load of the GP register; 2 indicates that $27' is used in some non-standard way and so the linker cannot elide the load of the procedure vector during relaxation. .usepv FUNCTION, WHICH' Used to indicate the use of the $27' register, similar to .prologue', but without the other semantics of needing to be inside an open .ent'/.end' block. The WHICH argument should be either no', indicating that $27' is not used, or std', indicating that the first two instructions of the function perform a GP load. One might use this directive instead of .prologue' if you are also using dwarf2 CFI directives. .gprel32 EXPRESSION' Computes the difference between the address in EXPRESSION and the GP for the current object file, and stores it in 4 bytes. In addition to being smaller than a full 8 byte address, this also does not require a dynamic relocation when used in a shared library. .t_floating EXPRESSION' Stores EXPRESSION as an IEEE double precision value. .s_floating EXPRESSION' Stores EXPRESSION as an IEEE single precision value. .f_floating EXPRESSION' Stores EXPRESSION as a VAX F format value. .g_floating EXPRESSION' Stores EXPRESSION as a VAX G format value. .d_floating EXPRESSION' Stores EXPRESSION as a VAX D format value. .set FEATURE' Enables or disables various assembler features. Using the positive name of the feature enables while using noFEATURE' disables. at' Indicates that macro expansions may clobber the "assembler temporary" ($at' or $28') register. Some macros may not be expanded without this and will generate an error message if noat' is in effect. When at' is in effect, a warning will be generated if $at' is used by the programmer. macro' Enables the expansion of macro instructions. Note that variants of real instructions, such as br label' vs br $31,label' are considered alternate forms and not macros. move' reorder' volatile' These control whether and how the assembler may re-order instructions. Accepted for compatibility with the OSF/1 assembler, but as' does not do instruction scheduling, so these features are ignored. The following directives are recognized for compatibility with the OSF/1 assembler but are ignored. .proc .aproc .reguse .livereg .option .aent .ugen .eflag .alias .noalias File: as.info, Node: Alpha Opcodes, Prev: Alpha Directives, Up: Alpha-Dependent 8.2.6 Opcodes ------------- For detailed information on the Alpha machine instruction set, see the Alpha Architecture Handbook (ftp://ftp.digital.com/pub/Digital/info/semiconductor/literature/alphaahb.pdf). File: as.info, Node: ARC-Dependent, Next: ARM-Dependent, Prev: Alpha-Dependent, Up: Machine Dependencies 8.3 ARC Dependent Features ========================== * Menu: * ARC Options:: Options * ARC Syntax:: Syntax * ARC Floating Point:: Floating Point * ARC Directives:: ARC Machine Directives * ARC Opcodes:: Opcodes File: as.info, Node: ARC Options, Next: ARC Syntax, Up: ARC-Dependent 8.3.1 Options ------------- -marc[5|6|7|8]' This option selects the core processor variant. Using -marc' is the same as -marc6', which is also the default. arc5' Base instruction set. arc6' Jump-and-link (jl) instruction. No requirement of an instruction between setting flags and conditional jump. For example: mov.f r0,r1 beq foo arc7' Break (brk) and sleep (sleep) instructions. arc8' Software interrupt (swi) instruction. Note: the .option' directive can to be used to select a core variant from within assembly code. -EB' This option specifies that the output generated by the assembler should be marked as being encoded for a big-endian processor. -EL' This option specifies that the output generated by the assembler should be marked as being encoded for a little-endian processor - this is the default. File: as.info, Node: ARC Syntax, Next: ARC Floating Point, Prev: ARC Options, Up: ARC-Dependent 8.3.2 Syntax ------------ * Menu: * ARC-Chars:: Special Characters * ARC-Regs:: Register Names File: as.info, Node: ARC-Chars, Next: ARC-Regs, Up: ARC Syntax 8.3.2.1 Special Characters .......................... *TODO* File: as.info, Node: ARC-Regs, Prev: ARC-Chars, Up: ARC Syntax 8.3.2.2 Register Names ...................... *TODO* File: as.info, Node: ARC Floating Point, Next: ARC Directives, Prev: ARC Syntax, Up: ARC-Dependent 8.3.3 Floating Point -------------------- The ARC core does not currently have hardware floating point support. Software floating point support is provided by GCC' and uses IEEE floating-point numbers. File: as.info, Node: ARC Directives, Next: ARC Opcodes, Prev: ARC Floating Point, Up: ARC-Dependent 8.3.4 ARC Machine Directives ---------------------------- The ARC version of as' supports the following additional machine directives: .2byte EXPRESSIONS' *TODO* .3byte EXPRESSIONS' *TODO* .4byte EXPRESSIONS' *TODO* .extAuxRegister NAME,ADDRESS,MODE' *TODO* .extAuxRegister mulhi,0x12,w .extCondCode SUFFIX,VALUE' *TODO* .extCondCode is_busy,0x14 .extCoreRegister NAME,REGNUM,MODE,SHORTCUT' *TODO* .extCoreRegister mlo,57,r,can_shortcut .extInstruction NAME,OPCODE,SUBOPCODE,SUFFIXCLASS,SYNTAXCLASS' *TODO* .extInstruction mul64,0x14,0x0,SUFFIX_COND,SYNTAX_3OP|OP1_MUST_BE_IMM .half EXPRESSIONS' *TODO* .long EXPRESSIONS' *TODO* .option ARC|ARC5|ARC6|ARC7|ARC8' The .option' directive must be followed by the desired core version. Again arc' is an alias for arc6'. Note: the .option' directive overrides the command line option -marc'; a warning is emitted when the version is not consistent between the two - even for the implicit default core version (arc6). .short EXPRESSIONS' *TODO* .word EXPRESSIONS' *TODO* File: as.info, Node: ARC Opcodes, Prev: ARC Directives, Up: ARC-Dependent 8.3.5 Opcodes ------------- For information on the ARC instruction set, see ARC Programmers Reference Manual', ARC Cores Ltd. File: as.info, Node: ARM-Dependent, Next: CRIS-Dependent, Prev: ARC-Dependent, Up: Machine Dependencies 8.4 ARM Dependent Features ========================== * Menu: * ARM Options:: Options * ARM Syntax:: Syntax * ARM Floating Point:: Floating Point * ARM Directives:: ARM Machine Directives * ARM Opcodes:: Opcodes * ARM Mapping Symbols:: Mapping Symbols File: as.info, Node: ARM Options, Next: ARM Syntax, Up: ARM-Dependent 8.4.1 Options ------------- -mcpu=PROCESSOR[+EXTENSION...]' This option specifies the target processor. The assembler will issue an error message if an attempt is made to assemble an instruction which will not execute on the target processor. The following processor names are recognized: arm1', arm2', arm250', arm3', arm6', arm60', arm600', arm610', arm620', arm7', arm7m', arm7d', arm7dm', arm7di', arm7dmi', arm70', arm700', arm700i', arm710', arm710t', arm720', arm720t', arm740t', arm710c', arm7100', arm7500', arm7500fe', arm7t', arm7tdmi', arm8', arm810', strongarm', strongarm1', strongarm110', strongarm1100', strongarm1110', arm9', arm920', arm920t', arm922t', arm940t', arm9tdmi', arm9e', arm926e', arm926ejs', arm946e-r0', arm946e', arm966e-r0', arm966e', arm10t', arm10e', arm1020', arm1020t', arm1020e', arm1026ejs', arm1136js', arm1136jfs', ep9312' (ARM920 with Cirrus Maverick coprocessor), i80200' (Intel XScale processor) iwmmxt' (Intel(r) XScale processor with Wireless MMX(tm) technology coprocessor) and xscale'. The special name all' may be used to allow the assembler to accept instructions valid for any ARM processor. In addition to the basic instruction set, the assembler can be told to accept various extension mnemonics that extend the processor using the co-processor instruction space. For example, -mcpu=arm920+maverick' is equivalent to specifying -mcpu=ep9312'. The following extensions are currently supported: +maverick' +iwmmxt' and +xscale'. -march=ARCHITECTURE[+EXTENSION...]' This option specifies the target architecture. The assembler will issue an error message if an attempt is made to assemble an instruction which will not execute on the target architecture. The following architecture names are recognized: armv1', armv2', armv2a', armv2s', armv3', armv3m', armv4', armv4xm', armv4t', armv4txm', armv5', armv5t', armv5txm', armv5te', armv5texp', armv6', armv6j', iwmmxt' and xscale'. If both -mcpu' and -march' are specified, the assembler will use the setting for -mcpu'. The architecture option can be extended with the same instruction set extension options as the -mcpu' option. -mfpu=FLOATING-POINT-FORMAT' This option specifies the floating point format to assemble for. The assembler will issue an error message if an attempt is made to assemble an instruction which will not execute on the target floating point unit. The following format options are recognized: softfpa', fpe', fpe2', fpe3', fpa', fpa10', fpa11', arm7500fe', softvfp', softvfp+vfp', vfp', vfp10', vfp10-r0', vfp9', vfpxd', arm1020t', arm1020e', arm1136jfs' and maverick'. In addition to determining which instructions are assembled, this option also affects the way in which the .double' assembler directive behaves when assembling little-endian code. The default is dependent on the processor selected. For Architecture 5 or later, the default is to assembler for VFP instructions; for earlier architectures the default is to assemble for FPA instructions. -mthumb' This option specifies that the assembler should start assembling Thumb instructions; that is, it should behave as though the file starts with a .code 16' directive. -mthumb-interwork' This option specifies that the output generated by the assembler should be marked as supporting interworking. -mapcs [26|32]'' This option specifies that the output generated by the assembler should be marked as supporting the indicated version of the Arm Procedure. Calling Standard. -matpcs' This option specifies that the output generated by the assembler should be marked as supporting the Arm/Thumb Procedure Calling Standard. If enabled this option will cause the assembler to create an empty debugging section in the object file called .arm.atpcs. Debuggers can use this to determine the ABI being used by. -mapcs-float' This indicates the floating point variant of the APCS should be used. In this variant floating point arguments are passed in FP registers rather than integer registers. -mapcs-reentrant' This indicates that the reentrant variant of the APCS should be used. This variant supports position independent code. -mfloat-abi=ABI' This option specifies that the output generated by the assembler should be marked as using specified floating point ABI. The following values are recognized: soft', softfp' and hard'. -EB' This option specifies that the output generated by the assembler should be marked as being encoded for a big-endian processor. -EL' This option specifies that the output generated by the assembler should be marked as being encoded for a little-endian processor. -k' This option specifies that the output of the assembler should be marked as position-independent code (PIC). -moabi' This indicates that the code should be assembled using the old ARM ELF conventions, based on a beta release release of the ARM-ELF specifications, rather than the default conventions which are based on the final release of the ARM-ELF specifications. File: as.info, Node: ARM Syntax, Next: ARM Floating Point, Prev: ARM Options, Up: ARM-Dependent 8.4.2 Syntax ------------ * Menu: * ARM-Chars:: Special Characters * ARM-Regs:: Register Names File: as.info, Node: ARM-Chars, Next: ARM-Regs, Up: ARM Syntax 8.4.2.1 Special Characters .......................... The presence of a @' on a line indicates the start of a comment that extends to the end of the current line. If a #' appears as the first character of a line, the whole line is treated as a comment. The ;' character can be used instead of a newline to separate statements. Either #' or $' can be used to indicate immediate operands. *TODO* Explain about /data modifier on symbols. File: as.info, Node: ARM-Regs, Prev: ARM-Chars, Up: ARM Syntax 8.4.2.2 Register Names ...................... *TODO* Explain about ARM register naming, and the predefined names. File: as.info, Node: ARM Floating Point, Next: ARM Directives, Prev: ARM Syntax, Up: ARM-Dependent 8.4.3 Floating Point -------------------- The ARM family uses IEEE floating-point numbers. File: as.info, Node: ARM Directives, Next: ARM Opcodes, Prev: ARM Floating Point, Up: ARM-Dependent 8.4.4 ARM Machine Directives ---------------------------- .align EXPRESSION [, EXPRESSION]' This is the generic .ALIGN directive. For the ARM however if the first argument is zero (ie no alignment is needed) the assembler will behave as if the argument had been 2 (ie pad to the next four byte boundary). This is for compatibility with ARM's own assembler. NAME .req REGISTER NAME' This creates an alias for REGISTER NAME called NAME. For example: foo .req r0 .unreq ALIAS-NAME' This undefines a register alias which was previously defined using the req' directive. For example: foo .req r0 .unreq foo An error occurs if the name is undefined. Note - this pseudo op can be used to delete builtin in register name aliases (eg 'r0'). This should only be done if it is really necessary. .code [16|32]'' This directive selects the instruction set being generated. The value 16 selects Thumb, with the value 32 selecting ARM. .thumb' This performs the same action as .CODE 16. .arm' This performs the same action as .CODE 32. .force_thumb' This directive forces the selection of Thumb instructions, even if the target processor does not support those instructions .thumb_func' This directive specifies that the following symbol is the name of a Thumb encoded function. This information is necessary in order to allow the assembler and linker to generate correct code for interworking between Arm and Thumb instructions and should be used even if interworking is not going to be performed. The presence of this directive also implies .thumb' .thumb_set' This performs the equivalent of a .set' directive in that it creates a symbol which is an alias for another symbol (possibly not yet defined). This directive also has the added property in that it marks the aliased symbol as being a thumb function entry point, in the same way that the .thumb_func' directive does. .ltorg' This directive causes the current contents of the literal pool to be dumped into the current section (which is assumed to be the .text section) at the current location (aligned to a word boundary). GAS' maintains a separate literal pool for each section and each sub-section. The .ltorg' directive will only affect the literal pool of the current section and sub-section. At the end of assembly all remaining, un-empty literal pools will automatically be dumped. Note - older versions of GAS' would dump the current literal pool any time a section change occurred. This is no longer done, since it prevents accurate control of the placement of literal pools. .pool' This is a synonym for .ltorg. File: as.info, Node: ARM Opcodes, Next: ARM Mapping Symbols, Prev: ARM Directives, Up: ARM-Dependent 8.4.5 Opcodes ------------- as' implements all the standard ARM opcodes. It also implements several pseudo opcodes, including several synthetic load instructions. NOP' nop This pseudo op will always evaluate to a legal ARM instruction that does nothing. Currently it will evaluate to MOV r0, r0. LDR' ldr , = If expression evaluates to a numeric constant then a MOV or MVN instruction will be used in place of the LDR instruction, if the constant can be generated by either of these instructions. Otherwise the constant will be placed into the nearest literal pool (if it not already there) and a PC relative LDR instruction will be generated. `ADR' adr
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