START-INFO-DIR-ENTRY * As: (as). The GNU assembler. * Gas: (as). The GNU assembler. END-INFO-DIR-ENTRY Using as 1 Overview 1.1 Structure of this Manual 1.2 The GNU Assembler 1.3 Object File Formats 1.4 Command Line 1.5 Input Files 1.6 Output (Object) File 1.7 Error and Warning Messages 2 Command-Line Options 2.1 Enable Listings: '-a[cdhlns]' 2.2 '--alternate' 2.3 '-D' 2.4 Work Faster: '-f' 2.5 '.include' Search Path: '-I' PATH 2.6 Difference Tables: '-K' 2.7 Include Local Symbols: '-L' 2.8 Configuring listing output: '--listing' 2.9 Assemble in MRI Compatibility Mode: '-M' 2.10 Dependency Tracking: '--MD' 2.11 Name the Object File: '-o' 2.12 Join Data and Text Sections: '-R' 2.13 Display Assembly Statistics: '--statistics' 2.14 Compatible Output: '--traditional-format' 2.15 Announce Version: '-v' 2.16 Control Warnings: '-W', '--warn', '--no-warn', '--fatal-warnings' 2.17 Generate Object File in Spite of Errors: '-Z' 3 Syntax 3.1 Preprocessing 3.2 Whitespace 3.3 Comments 3.4 Symbols 3.5 Statements 3.6 Constants 3.6.1 Character Constants 3.6.1.1 Strings 3.6.1.2 Characters 3.6.2 Number Constants 3.6.2.1 Integers 3.6.2.2 Bignums 3.6.2.3 Flonums 4 Sections and Relocation 4.1 Background 4.2 Linker Sections 4.3 Assembler Internal Sections 4.4 Sub-Sections 4.5 bss Section 5 Symbols 5.1 Labels 5.2 Giving Symbols Other Values 5.3 Symbol Names 5.4 The Special Dot Symbol 5.5 Symbol Attributes 5.5.1 Value 5.5.2 Type 6 Expressions 6.1 Empty Expressions 6.2 Integer Expressions 6.2.1 Arguments 6.2.2 Operators 6.2.3 Prefix Operator 6.2.4 Infix Operators 7 Assembler Directives 7.1 '.abort' 7.2 '.align ABS-EXPR, ABS-EXPR, ABS-EXPR' 7.3 '.ascii "STRING"'... 7.4 '.asciz "STRING"'... 7.5 '.balign[wl] ABS-EXPR, ABS-EXPR, ABS-EXPR' 7.6 '.byte EXPRESSIONS' 7.7 '.comm SYMBOL , LENGTH ' 7.8 '.cfi_startproc [simple]' 7.9 '.cfi_endproc' 7.10 '.cfi_personality ENCODING [, EXP]' 7.11 '.cfi_lsda ENCODING [, EXP]' 7.12 '.cfi_def_cfa REGISTER, OFFSET' 7.13 '.cfi_def_cfa_register REGISTER' 7.14 '.cfi_def_cfa_offset OFFSET' 7.15 '.cfi_adjust_cfa_offset OFFSET' 7.16 '.cfi_offset REGISTER, OFFSET' 7.17 '.cfi_rel_offset REGISTER, OFFSET' 7.18 '.cfi_register REGISTER1, REGISTER2' 7.19 '.cfi_restore REGISTER' 7.20 '.cfi_undefined REGISTER' 7.21 '.cfi_same_value REGISTER' 7.22 '.cfi_remember_state', 7.23 '.cfi_return_column REGISTER' 7.24 '.cfi_signal_frame' 7.25 '.cfi_window_save' 7.26 '.cfi_escape' EXPRESSION[, ...] 7.27 '.file FILENO FILENAME' 7.28 '.loc FILENO LINENO [COLUMN] [OPTIONS]' 7.29 '.loc_mark_blocks ENABLE' 7.30 '.data SUBSECTION' 7.31 '.double FLONUMS' 7.32 '.eject' 7.33 '.else' 7.34 '.elseif' 7.35 '.end' 7.36 '.endfunc' 7.37 '.endif' 7.38 '.equ SYMBOL, EXPRESSION' 7.39 '.equiv SYMBOL, EXPRESSION' 7.40 '.eqv SYMBOL, EXPRESSION' 7.41 '.err' 7.42 '.error "STRING"' 7.43 '.exitm' 7.44 '.extern' 7.45 '.fail EXPRESSION' 7.46 '.file STRING' 7.47 '.fill REPEAT , SIZE , VALUE' 7.48 '.float FLONUMS' 7.49 '.func NAME[,LABEL]' 7.50 '.global SYMBOL', '.globl SYMBOL' 7.51 '.hidden NAMES' 7.52 '.hword EXPRESSIONS' 7.53 '.ident' 7.54 '.if ABSOLUTE EXPRESSION' 7.55 '.incbin "FILE"[,SKIP[,COUNT]]' 7.56 '.include "FILE"' 7.57 '.int EXPRESSIONS' 7.58 '.internal NAMES' 7.59 '.irp SYMBOL,VALUES'... 7.60 '.irpc SYMBOL,VALUES'... 7.61 '.lcomm SYMBOL , LENGTH' 7.62 '.lflags' 7.63 '.line LINE-NUMBER' 7.64 '.linkonce [TYPE]' 7.65 '.ln LINE-NUMBER' 7.66 '.mri VAL' 7.67 '.list' 7.68 '.long EXPRESSIONS' 7.69 '.macro' 7.70 '.altmacro' 7.71 '.noaltmacro' 7.72 '.nolist' 7.73 '.octa BIGNUMS' 7.74 '.org NEW-LC , FILL' 7.75 '.p2align[wl] ABS-EXPR, ABS-EXPR, ABS-EXPR' 7.76 '.previous' 7.77 '.popsection' 7.78 '.print STRING' 7.79 '.protected NAMES' 7.80 '.psize LINES , COLUMNS' 7.81 '.purgem NAME' 7.82 '.pushsection NAME , SUBSECTION' 7.83 '.quad BIGNUMS' 7.84 '.reloc OFFSET, RELOC_NAME[, EXPRESSION]' 7.85 '.rept COUNT' 7.86 '.sbttl "SUBHEADING"' 7.87 '.section NAME' 7.88 '.set SYMBOL, EXPRESSION' 7.89 '.short EXPRESSIONS' 7.90 '.single FLONUMS' 7.91 '.size' 7.92 '.sleb128 EXPRESSIONS' 7.93 '.skip SIZE , FILL' 7.94 '.space SIZE , FILL' 7.95 '.stabd, .stabn, .stabs' 7.96 '.string' "STR" 7.97 '.struct EXPRESSION' 7.98 '.subsection NAME' 7.99 '.symver' 7.100 '.text SUBSECTION' 7.101 '.title "HEADING"' 7.102 '.type' 7.103 '.uleb128 EXPRESSIONS' 7.104 '.version "STRING"' 7.105 '.vtable_entry TABLE, OFFSET' 7.106 '.vtable_inherit CHILD, PARENT' 7.107 '.warning "STRING"' 7.108 '.weak NAMES' 7.109 '.weakref ALIAS, TARGET' 7.110 '.word EXPRESSIONS' 7.111 Deprecated Directives 8 ARM Dependent Features 8.1 Options 8.2 Syntax 8.2.1 Special Characters 8.2.2 Register Names 8.2.3 ARM relocation generation 8.3 Floating Point 8.4 ARM Machine Directives 8.5 Opcodes 8.6 Mapping Symbols 9 80386 Dependent Features 9.1 Options 9.2 AT&T Syntax versus Intel Syntax 9.3 Instruction Naming 9.4 Register Naming 9.5 Instruction Prefixes 9.6 Memory References 9.7 Handling of Jump Instructions 9.8 Floating Point 9.9 Intel's MMX and AMD's 3DNow! SIMD Operations 9.10 Writing 16-bit Code 9.11 AT&T Syntax bugs 9.12 Specifying CPU Architecture 9.13 Notes 10 IA-64 Dependent Features 10.1 Options 10.2 Syntax 10.2.1 Special Characters 10.2.2 Register Names 10.2.3 IA-64 Processor-Status-Register (PSR) Bit Names 10.3 Opcodes 11 MIPS Dependent Features 11.1 Assembler options 11.2 MIPS ECOFF object code 11.3 Directives for debugging information 11.4 Directives to override the size of symbols 11.5 Directives to override the ISA level 11.6 Directives for extending MIPS 16 bit instructions 11.7 Directive to mark data as an instruction 11.8 Directives to save and restore options 11.9 Directives to control generation of MIPS ASE instructions 12 PowerPC Dependent Features 12.1 Options 12.2 PowerPC Assembler Directives 13 SPARC Dependent Features 13.1 Options 13.2 Enforcing aligned data 13.3 Floating Point 13.4 Sparc Machine Directives 14 Reporting Bugs 14.1 Have You Found a Bug? 14.2 How to Report Bugs 15 Acknowledgements Appendix A GNU Free Documentation License ADDENDUM: How to use this License for your documents AS Index Using as ******** This file is a user guide to the GNU assembler 'as' version "2.17.50 [FreeBSD] 2007-07-03". This version of the file describes 'as' configured to generate code for machine specific architectures. 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". 1 Overview ********** Here is a brief summary of how to invoke 'as'. For details, see *note Command-Line Options: Invoking. as [-a[cdhlns][=FILE]] [-alternate] [-D] [-defsym SYM=VAL] [-f] [-g] [-gstabs] [-gstabs+] [-gdwarf-2] [-help] [-I DIR] [-J] [-K] [-L] [-listing-lhs-width=NUM] [-listing-lhs-width2=NUM] [-listing-rhs-width=NUM] [-listing-cont-lines=NUM] [-keep-locals] [-o OBJFILE] [-R] [-reduce-memory-overheads] [-statistics] [-v] [-version] [-version] [-W] [-warn] [-fatal-warnings] [-w] [-x] [-Z] [@FILE] [-target-help] [TARGET-OPTIONS] [-|FILES ...] _Target ARM options:_ [-mcpu=PROCESSOR[+EXTENSION...]] [-march=ARCHITECTURE[+EXTENSION...]] [-mfpu=FLOATING-POINT-FORMAT] [-mfloat-abi=ABI] [-meabi=VER] [-mthumb] [-EB|-EL] [-mapcs-32|-mapcs-26|-mapcs-float| -mapcs-reentrant] [-mthumb-interwork] [-k] _Target i386 options:_ [-32|-64] [-n] [-march=CPU] [-mtune=CPU] _Target IA-64 options:_ [-mconstant-gp|-mauto-pic] [-milp32|-milp64|-mlp64|-mp64] [-mle|mbe] [-mtune=itanium1|-mtune=itanium2] [-munwind-check=warning|-munwind-check=error] [-mhint.b=ok|-mhint.b=warning|-mhint.b=error] [-x|-xexplicit] [-xauto] [-xdebug] _Target MIPS options:_ [-nocpp] [-EL] [-EB] [-O[OPTIMIZATION LEVEL]] [-g[DEBUG LEVEL]] [-G NUM] [-KPIC] [-call_shared] [-non_shared] [-xgot [-mvxworks-pic] [-mabi=ABI] [-32] [-n32] [-64] [-mfp32] [-mgp32] [-march=CPU] [-mtune=CPU] [-mips1] [-mips2] [-mips3] [-mips4] [-mips5] [-mips32] [-mips32r2] [-mips64] [-mips64r2] [-construct-floats] [-no-construct-floats] [-trap] [-no-break] [-break] [-no-trap] [-mfix7000] [-mno-fix7000] [-mips16] [-no-mips16] [-msmartmips] [-mno-smartmips] [-mips3d] [-no-mips3d] [-mdmx] [-no-mdmx] [-mdsp] [-mno-dsp] [-mdspr2] [-mno-dspr2] [-mmt] [-mno-mt] [-mdebug] [-no-mdebug] [-mpdr] [-mno-pdr] _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] '@FILE' Read command-line options from FILE. The options read are inserted in place of the original @FILE option. If FILE does not exist, or cannot be read, then the option will be treated literally, and not removed. Options in FILE are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The FILE may itself contain additional @FILE options; any such options will be processed recursively. '-a[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'. '--alternate' Begin in alternate macro mode. *Note '.altmacro': Altmacro. '-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. The value of the symbol can be overridden inside a source file via the use of a '.set' pseudo-op. '-f' "fast"--skip whitespace and comment preprocessing (assume source is compiler output). '-g' '--gen-debug' Generate debugging information for each assembler source line using whichever debug format is preferred by the target. This currently means either STABS, ECOFF or DWARF2. '--gstabs' Generate stabs debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it. '--gstabs+' Generate stabs debugging information for each assembler line, with GNU extensions that probably only gdb can handle, and that could make other debuggers crash or refuse to read your program. This may help debugging assembler code. Currently the only GNU extension is the location of the current working directory at assembling time. '--gdwarf-2' Generate DWARF2 debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it. Note--this option is only supported by some targets, not all of them. '--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' This option is accepted but has no effect on the machine specific family. '-L' '--keep-locals' Keep (in the symbol table) local symbols. These symbols start with system-specific local label prefixes, typically '.L' for ELF systems or 'L' for traditional a.out systems. *Note Symbol Names::. '--listing-lhs-width=NUMBER' Set the maximum width, in words, of the output data column for an assembler listing to NUMBER. '--listing-lhs-width2=NUMBER' Set the maximum width, in words, of the output data column for continuation lines in an assembler listing to NUMBER. '--listing-rhs-width=NUMBER' Set the maximum width of an input source line, as displayed in a listing, to NUMBER bytes. '--listing-cont-lines=NUMBER' Set the maximum number of lines printed in a listing for a single line of input to NUMBER + 1. '-o OBJFILE' Name the object-file output from 'as' OBJFILE. '-R' Fold the data section into the text section. Set the default size of GAS's hash tables to a prime number close to NUMBER. Increasing this value can reduce the length of time it takes the assembler to perform its tasks, at the expense of increasing the assembler's memory requirements. Similarly reducing this value can reduce the memory requirements at the expense of speed. '--reduce-memory-overheads' This option reduces GAS's memory requirements, at the expense of making the assembly processes slower. Currently this switch is a synonym for '--hash-size=4051', but in the future it may have other effects as well. '--statistics' Print the maximum space (in bytes) and total time (in seconds) used by assembly. '--strip-local-absolute' Remove local absolute symbols from the outgoing symbol table. '-v' '-version' Print the 'as' version. '--version' Print the 'as' version and exit. '-W' '--no-warn' Suppress warning messages. '--fatal-warnings' Treat warnings as errors. '--warn' Don't suppress warning messages or treat them as errors. '-w' Ignored. '-x' Ignored. '-Z' Generate an object file even after errors. '-- | FILES ...' Standard input, or source files to assemble. The following options are available when as is configured for the ARM processor family. '-mcpu=PROCESSOR[+EXTENSION...]' Specify which ARM processor variant is the target. '-march=ARCHITECTURE[+EXTENSION...]' Specify which ARM architecture variant is used by the target. '-mfpu=FLOATING-POINT-FORMAT' Select which Floating Point architecture is the target. '-mfloat-abi=ABI' Select which floating point ABI is in use. '-mthumb' Enable Thumb only instruction decoding. '-mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant' Select which procedure calling convention is in use. '-EB | -EL' Select either big-endian (-EB) or little-endian (-EL) output. '-mthumb-interwork' Specify that the code has been generated with interworking between Thumb and ARM code in mind. '-k' Specify that PIC code has been generated. 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 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. '-msmartmips' '-mno-smartmips' Enables the SmartMIPS extension to the MIPS32 instruction set. This is equivalent to putting '.set smartmips' at the start of the assembly file. '-mno-smartmips' turns off this option. '-mips3d' '-no-mips3d' Generate code for the MIPS-3D Application Specific Extension. This tells the assembler to accept MIPS-3D instructions. '-no-mips3d' turns off this option. '-mdmx' '-no-mdmx' Generate code for the MDMX Application Specific Extension. This tells the assembler to accept MDMX instructions. '-no-mdmx' turns off this option. '-mdsp' '-mno-dsp' Generate code for the DSP Release 1 Application Specific Extension. This tells the assembler to accept DSP Release 1 instructions. '-mno-dsp' turns off this option. '-mdspr2' '-mno-dspr2' Generate code for the DSP Release 2 Application Specific Extension. This option implies -mdsp. This tells the assembler to accept DSP Release 2 instructions. '-mno-dspr2' turns off this option. '-mmt' '-mno-mt' Generate code for the MT Application Specific Extension. This tells the assembler to accept MT instructions. '-mno-mt' turns off this option. '--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. 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'. We also cover special features in the machine specific configuration of 'as', including assembler directives. 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. 1.2 The GNU Assembler ===================== GNU 'as' is really a family of assemblers. This manual describes 'as', a member of that family which is configured for the machine specific architectures. 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. 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.). 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. For the machine specific target, 'as' is configured to produce ELF format object files. 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 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. 1.6 Output (Object) File ======================== Every time you run 'as' it produces an output file, which is your assembly language program translated into numbers. This file is the object file. Its default name is 'a.out'. You can give it another name by using the '-o' option. Conventionally, object file names end with '.o'. The default name is used for historical reasons: older assemblers were capable of assembling self-contained programs directly into a runnable program. (For some formats, this isn't currently possible, but it can be done for the 'a.out' format.) The object file is meant for input to the linker 'ld'. It contains assembled program code, information to help 'ld' integrate the assembled program into a runnable file, and (optionally) symbolic information for the debugger. 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 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. 2 Command-Line Options ********************** This chapter describes command-line options available in _all_ versions of the GNU assembler; see *note Machine Dependencies::, for options specific to the machine specific target. 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.) 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 (e.g., because it is being created by 'gcc' and the '-pipe' command line switch is being used) then the listing will not contain any comments or preprocessor directives. This is because the listing code buffers input source lines from stdin only after they have been preprocessed by the assembler. This reduces memory usage and makes the code more efficient. 2.2 '--alternate' ================= Begin in alternate macro mode, see *note '.altmacro': Altmacro. 2.3 '-D' ======== This option has no effect whatsoever, but it is accepted to make it more likely that scripts written for other assemblers also work with 'as'. 2.4 Work Faster: '-f' ===================== '-f' should only be used when assembling programs written by a (trusted) compiler. '-f' stops the assembler from doing whitespace and comment preprocessing on the input file(s) before assembling them. *Note Preprocessing: Preprocessing. _Warning:_ if you use '-f' when the files actually need to be preprocessed (if they contain comments, for example), 'as' does not work correctly. 2.5 '.include' Search Path: '-I' PATH ===================================== Use this option to add a PATH to the list of directories 'as' searches for files specified in '.include' directives (*note '.include': Include.). You may use '-I' as many times as necessary to include a variety of paths. The current working directory is always searched first; after that, 'as' searches any '-I' directories in the same order as they were specified (left to right) on the command line. 2.6 Difference Tables: '-K' =========================== On the machine specific family, this option is allowed, but has no effect. It is permitted for compatibility with the GNU assembler on other platforms, where it can be used to warn when the assembler alters the machine code generated for '.word' directives in difference tables. The machine specific family does not have the addressing limitations that sometimes lead to this alteration on other platforms. 2.7 Include Local Symbols: '-L' =============================== Symbols beginning with system-specific local label prefixes, typically '.L' for ELF systems or 'L' for traditional a.out systems, are called "local symbols". *Note Symbol Names::. Normally you do not see such symbols when debugging, because they are intended for the use of programs (like compilers) that compose assembler programs, not for your notice. Normally both 'as' and 'ld' discard such symbols, so you do not normally debug with them. This option tells 'as' to retain those local symbols in the object file. Usually if you do this you also tell the linker 'ld' to preserve those symbols. 2.8 Configuring listing output: '--listing' =========================================== The listing feature of the assembler can be enabled via the command line switch '-a' (*note a::). This feature combines the input source file(s) with a hex dump of the corresponding locations in the output object file, and displays them as a listing file. The format of this listing can be controlled by directives inside the assembler source (i.e., '.list' (*note List::), '.title' (*note Title::), '.sbttl' (*note Sbttl::), '.psize' (*note Psize::), and '.eject' (*note Eject::) and also by the following switches: '--listing-lhs-width='number'' Sets the maximum width, in words, of the first line of the hex byte dump. This dump appears on the left hand side of the listing output. '--listing-lhs-width2='number'' Sets the maximum width, in words, of any further lines of the hex byte dump for a given input source line. If this value is not specified, it defaults to being the same as the value specified for '--listing-lhs-width'. If neither switch is used the default is to one. '--listing-rhs-width='number'' Sets the maximum width, in characters, of the source line that is displayed alongside the hex dump. The default value for this parameter is 100. The source line is displayed on the right hand side of the listing output. '--listing-cont-lines='number'' Sets the maximum number of continuation lines of hex dump that will be displayed for a given single line of source input. The default value is 4. 2.9 Assemble in MRI Compatibility Mode: '-M' ============================================ The '-M' or '--mri' option selects MRI compatibility mode. This changes the syntax and pseudo-op handling of 'as' to make it compatible with the 'ASM68K' or the 'ASM960' (depending upon the configured target) assembler from Microtec Research. The exact nature of the MRI syntax will not be documented here; see the MRI manuals for more information. Note in particular that the handling of macros and macro arguments is somewhat different. The purpose of this option is to permit assembling existing MRI assembler code using 'as'. The MRI compatibility is not complete. Certain operations of the MRI assembler depend upon its object file format, and can not be supported using other object file formats. Supporting these would require enhancing each object file format individually. These are: * global symbols in common section The m68k MRI assembler supports common sections which are merged by the linker. Other object file formats do not support this. 'as' handles common sections by treating them as a single common symbol. It permits local symbols to be defined within a common section, but it can not support global symbols, since it has no way to describe them. * complex relocations The MRI assemblers support relocations against a negated section address, and relocations which combine the start addresses of two or more sections. These are not support by other object file formats. * 'END' pseudo-op specifying start address The MRI 'END' pseudo-op permits the specification of a start address. This is not supported by other object file formats. The start address may instead be specified using the '-e' option to the linker, or in a linker script. * 'IDNT', '.ident' and 'NAME' pseudo-ops The MRI 'IDNT', '.ident' and 'NAME' pseudo-ops assign a module name to the output file. This is not supported by other object file formats. * 'ORG' pseudo-op The m68k MRI 'ORG' pseudo-op begins an absolute section at a given address. This differs from the usual 'as' '.org' pseudo-op, which changes the location within the current section. Absolute sections are not supported by other object file formats. The address of a section may be assigned within a linker script. There are some other features of the MRI assembler which are not supported by 'as', typically either because they are difficult or because they seem of little consequence. Some of these may be supported in future releases. * EBCDIC strings EBCDIC strings are not supported. * packed binary coded decimal Packed binary coded decimal is not supported. This means that the 'DC.P' and 'DCB.P' pseudo-ops are not supported. * 'FEQU' pseudo-op The m68k 'FEQU' pseudo-op is not supported. * 'NOOBJ' pseudo-op The m68k 'NOOBJ' pseudo-op is not supported. * 'OPT' branch control options The m68k 'OPT' branch control options--'B', 'BRS', 'BRB', 'BRL', and 'BRW'--are ignored. 'as' automatically relaxes all branches, whether forward or backward, to an appropriate size, so these options serve no purpose. * 'OPT' list control options The following m68k 'OPT' list control options are ignored: 'C', 'CEX', 'CL', 'CRE', 'E', 'G', 'I', 'M', 'MEX', 'MC', 'MD', 'X'. * other 'OPT' options The following m68k 'OPT' options are ignored: 'NEST', 'O', 'OLD', 'OP', 'P', 'PCO', 'PCR', 'PCS', 'R'. * 'OPT' 'D' option is default The m68k 'OPT' 'D' option is the default, unlike the MRI assembler. 'OPT NOD' may be used to turn it off. * 'XREF' pseudo-op. The m68k 'XREF' pseudo-op is ignored. * '.debug' pseudo-op The i960 '.debug' pseudo-op is not supported. * '.extended' pseudo-op The i960 '.extended' pseudo-op is not supported. * '.list' pseudo-op. The various options of the i960 '.list' pseudo-op are not supported. * '.optimize' pseudo-op The i960 '.optimize' pseudo-op is not supported. * '.output' pseudo-op The i960 '.output' pseudo-op is not supported. * '.setreal' pseudo-op The i960 '.setreal' pseudo-op is not supported. 2.10 Dependency Tracking: '--MD' ================================ 'as' can generate a dependency file for the file it creates. This file consists of a single rule suitable for 'make' describing the dependencies of the main source file. The rule is written to the file named in its argument. This feature is used in the automatic updating of makefiles. 2.11 Name the Object File: '-o' =============================== There is always one object file output when you run 'as'. By default it has the name 'a.out'. 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. 2.12 Join Data and Text Sections: '-R' ====================================== '-R' tells 'as' to write the object file as if all data-section data lives in the text section. This is only done at the very last moment: your binary data are the same, but data section parts are relocated differently. The data section part of your object file is zero bytes long because all its bytes are appended to the text section. (*Note Sections and Relocation: Sections.) When you specify '-R' it would be possible to generate shorter address displacements (because we do not have to cross between text and data section). We refrain from doing this simply for compatibility with older versions of 'as'. In future, '-R' may work this way. When 'as' is configured for COFF or ELF output, this option is only useful if you use sections named '.text' and '.data'. 2.13 Display Assembly Statistics: '--statistics' ================================================ Use '--statistics' to display two statistics about the resources used by 'as': the maximum amount of space allocated during the assembly (in bytes), and the total execution time taken for the assembly (in CPU seconds). 2.14 Compatible Output: '--traditional-format' ============================================== For some targets, the output of 'as' is different in some ways from the output of some existing assembler. This switch requests 'as' to use the traditional format instead. For example, it disables the exception frame optimizations which 'as' normally does by default on 'gcc' output. 2.15 Announce Version: '-v' =========================== You can find out what version of as is running by including the option '-v' (which you can also spell as '-version') on the command line. 2.16 Control Warnings: '-W', '--warn', '--no-warn', '--fatal-warnings' ====================================================================== 'as' should never give a warning or error message when assembling compiler output. But programs written by people often cause 'as' to give a warning that a particular assumption was made. All such warnings are directed to the standard error file. If you use the '-W' and '--no-warn' options, no warnings are issued. This only affects the warning messages: it does not change any particular of how 'as' assembles your file. Errors, which stop the assembly, are still reported. If you use the '--fatal-warnings' option, 'as' considers files that generate warnings to be in error. You can switch these options off again by specifying '--warn', which causes warnings to be output as usual. 2.17 Generate Object File in Spite of Errors: '-Z' ================================================== After an error message, 'as' normally produces no output. If for some reason you are interested in object file output even after 'as' gives an error message on your program, use the '-Z' option. If there are any errors, 'as' continues anyways, and writes an object file after a final warning message of the form 'N errors, M warnings, generating bad object file.' 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. 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. 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. 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 '@' on the ARM; '#' on the i386 and x86-64; '#' for Motorola PowerPC; '!' on the SPARC; see *note Machine Dependencies::. 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'. 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 '_.$'. 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::. 3.5 Statements ============== A "statement" ends at a newline character ('\n') or at a semicolon (';'). The newline or semicolon is considered part of the preceding statement. Newlines and semicolons within character constants are an exception: they do not end statements. 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. 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::. label: .directive followed by something another_label: # This is an empty statement. instruction operand_1, operand_2, ... 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. 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. 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. 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 (or semicolon ';') 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. 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. 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.). 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. 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'. * A letter, to tell 'as' the rest of the number is a flonum. * 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'. 4 Sections and Relocation ************************* 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. 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. '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. Within the object file, the text section starts at address '0', the data section follows, 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. 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. 4.2 Linker Sections =================== 'ld' deals with just four kinds of sections, summarized below. *named sections* 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 ... 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. 4.4 Sub-Sections ================ 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. 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. You can also use the '.subsection' directive (*note SubSection::) to specify a subsection: '.subsection EXPRESSION'. EXPRESSION should be an absolute expression (*note Expressions::). If you just say '.text' then '.text 0' is assumed. Likewise '.data' means '.data 0'. Assembly begins in 'text 0'. For instance: .text 0 # The default subsection is text 0 anyway. .ascii "This lives in the first text subsection. *" .text 1 .ascii "But this lives in the second text subsection." .data 0 .ascii "This lives in the data section," .ascii "in the first data subsection." .text 0 .ascii "This lives in the first text section," .ascii "immediately following the asterisk (*)." Each section has a "location counter" incremented by one for every byte assembled into that section. Because subsections are merely a convenience restricted to 'as' there is no concept of a subsection location counter. There is no way to directly manipulate a location counter--but the '.align' directive changes it, and any label definition captures its current value. The location counter of the section where statements are being assembled is said to be the "active" location counter. 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. 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. 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. 5.2 Giving Symbols Other Values =============================== A symbol can be given an arbitrary value by writing a symbol, followed by an equals sign '=', followed by an expression (*note Expressions::). This is equivalent to using the '.set' directive. *Note '.set': Set. In the same way, using a double equals sign '=''=' here represents an equivalent of the '.eqv' directive. *Note '.eqv': Eqv. 5.3 Symbol Names ================ Symbol names begin with a letter or with one of '._'. On most machines, you can also use '$' in symbol names; exceptions are noted in *note Machine Dependencies::. That character may be followed by any string of digits, letters, dollar signs (unless otherwise noted for a particular target machine), and underscores. Case of letters is significant: 'foo' is a different symbol name than 'Foo'. Each symbol has exactly one name. Each name in an assembly language program refers to exactly one symbol. You may use that symbol name any number of times in a program. Local Symbol Names ------------------ A local symbol is any symbol beginning with certain local label prefixes. By default, the local label prefix is '.L' for ELF systems or 'L' for traditional a.out systems, but each target may have its own set of local label prefixes. Local symbols are defined and used within the assembler, but they are normally not saved in object files. Thus, they are not visible when debugging. You may use the '-L' option (*note Include Local Symbols: '-L': L.) to retain the local symbols in the object files. Local Labels ------------ Local labels help compilers and programmers use names temporarily. They create symbols which are guaranteed to be unique over the entire scope of the input source code and which can be referred to by a simple notation. To define a local label, write a label of the form 'N:' (where N represents any positive integer). To refer to the most recent previous definition of that label write 'Nb', using the same number as when you defined the label. To refer to the next definition of a local label, write 'Nf'--the 'b' stands for "backwards" and the 'f' stands for "forwards". There is no restriction on how you can use these labels, and you can reuse them too. So that it is possible to repeatedly define the same local label (using the same number 'N'), although you can only refer to the most recently defined local label of that number (for a backwards reference) or the next definition of a specific local label for a forward reference. It is also worth noting that the first 10 local labels ('0:'...'9:') are implemented in a slightly more efficient manner than the others. Here is an example: 1: branch 1f 2: branch 1b 1: branch 2f 2: branch 1b Which is the equivalent of: label_1: branch label_3 label_2: branch label_1 label_3: branch label_4 label_4: branch label_3 Local label names are only a notational device. They are immediately transformed into more conventional symbol names before the assembler uses them. The symbol names are stored in the symbol table, appear in error messages, and are optionally emitted to the object file. The names are constructed using these parts: '_local label prefix_' All local symbols begin with the system-specific local label prefix. Normally both 'as' and 'ld' forget symbols that start with the local label prefix. These labels are used for symbols you are never intended to see. If you use the '-L' option then 'as' retains these symbols in the object file. If you also instruct 'ld' to retain these symbols, you may use them in debugging. 'NUMBER' This is the number that was used in the local label definition. So if the label is written '55:' then the number is '55'. 'C-B' This unusual character is included so you do not accidentally invent a symbol of the same name. The character has ASCII value of '\002' (control-B). '_ordinal number_' This is a serial number to keep the labels distinct. The first definition of '0:' gets the number '1'. The 15th definition of '0:' gets the number '15', and so on. Likewise the first definition of '1:' gets the number '1' and its 15th definition gets '15' as well. So for example, the first '1:' may be named '.L1C-B1', and the 44th '3:' may be named '.L3C-B44'. Dollar Local Labels ------------------- 'as' also supports an even more local form of local labels called dollar labels. These labels go out of scope (i.e., they become undefined) as soon as a non-local label is defined. Thus they remain valid for only a small region of the input source code. Normal local labels, by contrast, remain in scope for the entire file, or until they are redefined by another occurrence of the same local label. Dollar labels are defined in exactly the same way as ordinary local labels, except that instead of being terminated by a colon, they are terminated by a dollar sign, e.g., '55$'. They can also be distinguished from ordinary local labels by their transformed names which use ASCII character '\001' (control-A) as the magic character to distinguish them from ordinary labels. For example, the fifth definition of '6$' may be named '.L6'C-A'5'. 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'. 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. The detailed definitions are in 'a.out.h'. 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. 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. 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. 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. 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. 6.2 Integer Expressions ======================= An "integer expression" is one or more _arguments_ delimited by _operators_. 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. 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. 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. 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. 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. 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. 7.2 '.align ABS-EXPR, ABS-EXPR, ABS-EXPR' ========================================= Pad the location counter (in the current subsection) to a particular storage boundary. The first expression (which must be absolute) is the alignment required, as described below. The second expression (also absolute) gives the fill value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally zero. However, on some systems, if the section is marked as containing code and the fill value is omitted, the space is filled with no-op instructions. The third expression is also absolute, and is also optional. If it is present, it is the maximum number of bytes that should be skipped by this alignment directive. If doing the alignment would require skipping more bytes than the specified maximum, then the alignment is not done at all. You can omit the fill value (the second argument) entirely by simply using two commas after the required alignment; this can be useful if you want the alignment to be filled with no-op instructions when appropriate. The way the required alignment is specified varies from system to system. For the arc, hppa, i386 using ELF, i860, iq2000, m68k, or32, s390, sparc, tic4x, tic80 and xtensa, the first expression is the alignment request in bytes. For example '.align 8' advances the location counter until it is a multiple of 8. If the location counter is already a multiple of 8, no change is needed. For the tic54x, the first expression is the alignment request in words. For other systems, including 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). 7.3 '.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. 7.4 '.asciz "STRING"'... ======================== '.asciz' is just like '.ascii', but each string is followed by a zero byte. The "z" in '.asciz' stands for "zero". 7.5 '.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. 7.6 '.byte EXPRESSIONS' ======================= '.byte' expects zero or more expressions, separated by commas. Each expression is assembled into the next byte. 7.7 '.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. 7.8 '.cfi_startproc [simple]' ============================= '.cfi_startproc' is used at the beginning of each function that should have an entry in '.eh_frame'. It initializes some internal data structures. Don't forget to close the function by '.cfi_endproc'. Unless '.cfi_startproc' is used along with parameter 'simple' it also emits some architecture dependent initial CFI instructions. 7.9 '.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'. 7.10 '.cfi_personality ENCODING [, EXP]' ======================================== '.cfi_personality' defines personality routine and its encoding. ENCODING must be a constant determining how the personality should be encoded. If it is 255 ('DW_EH_PE_omit'), second argument is not present, otherwise second argument should be a constant or a symbol name. When using indirect encodings, the symbol provided should be the location where personality can be loaded from, not the personality routine itself. The default after '.cfi_startproc' is '.cfi_personality 0xff', no personality routine. 7.11 '.cfi_lsda ENCODING [, EXP]' ================================= '.cfi_lsda' defines LSDA and its encoding. ENCODING must be a constant determining how the LSDA should be encoded. If it is 255 ('DW_EH_PE_omit'), second argument is not present, otherwise second argument should be a constant or a symbol name. The default after '.cfi_startproc' is '.cfi_lsda 0xff', no LSDA. 7.12 '.cfi_def_cfa REGISTER, OFFSET' ==================================== '.cfi_def_cfa' defines a rule for computing CFA as: take address from REGISTER and add OFFSET to it. 7.13 '.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. 7.14 '.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. 7.15 '.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. 7.16 '.cfi_offset REGISTER, OFFSET' =================================== Previous value of REGISTER is saved at offset OFFSET from CFA. 7.17 '.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. 7.18 '.cfi_register REGISTER1, REGISTER2' ========================================= Previous value of REGISTER1 is saved in register REGISTER2. 7.19 '.cfi_restore REGISTER' ============================ '.cfi_restore' says that the rule for REGISTER is now the same as it was at the beginning of the function, after all initial instruction added by '.cfi_startproc' were executed. 7.20 '.cfi_undefined REGISTER' ============================== From now on the previous value of REGISTER can't be restored anymore. 7.21 '.cfi_same_value REGISTER' =============================== Current value of REGISTER is the same like in the previous frame, i.e. no restoration needed. 7.22 '.cfi_remember_state', =========================== First save all current rules for all registers by '.cfi_remember_state', then totally screw them up by subsequent '.cfi_*' directives and when everything is hopelessly bad, use '.cfi_restore_state' to restore the previous saved state. 7.23 '.cfi_return_column REGISTER' ================================== Change return column REGISTER, i.e. the return address is either directly in REGISTER or can be accessed by rules for REGISTER. 7.24 '.cfi_signal_frame' ======================== Mark current function as signal trampoline. 7.25 '.cfi_window_save' ======================= SPARC register window has been saved. 7.26 '.cfi_escape' EXPRESSION[, ...] ==================================== Allows the user to add arbitrary bytes to the unwind info. One might use this to add OS-specific CFI opcodes, or generic CFI opcodes that GAS does not yet support. 7.27 '.file FILENO FILENAME' ============================ When emitting dwarf2 line number information '.file' assigns filenames to the '.debug_line' file name table. The FILENO operand should be a unique positive integer to use as the index of the entry in the table. The FILENAME operand is a C string literal. The detail of filename indices is exposed to the user because the filename table is shared with the '.debug_info' section of the dwarf2 debugging information, and thus the user must know the exact indices that table entries will have. 7.28 '.loc FILENO LINENO [COLUMN] [OPTIONS]' ============================================ The '.loc' directive will add row to the '.debug_line' line number matrix corresponding to the immediately following assembly instruction. The FILENO, LINENO, and optional COLUMN arguments will be applied to the '.debug_line' state machine before the row is added. The OPTIONS are a sequence of the following tokens in any order: 'basic_block' This option will set the 'basic_block' register in the '.debug_line' state machine to 'true'. 'prologue_end' This option will set the 'prologue_end' register in the '.debug_line' state machine to 'true'. 'epilogue_begin' This option will set the 'epilogue_begin' register in the '.debug_line' state machine to 'true'. 'is_stmt VALUE' This option will set the 'is_stmt' register in the '.debug_line' state machine to 'value', which must be either 0 or 1. 'isa VALUE' This directive will set the 'isa' register in the '.debug_line' state machine to VALUE, which must be an unsigned integer. 7.29 '.loc_mark_blocks ENABLE' ============================== The '.loc_mark_blocks' directive makes the assembler emit an entry to the '.debug_line' line number matrix with the 'basic_block' register in the state machine set whenever a code label is seen. The ENABLE argument should be either 1 or 0, to enable or disable this function respectively. 7.30 '.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. 7.31 '.double FLONUMS' ====================== '.double' expects zero or more flonums, separated by commas. It assembles floating point numbers. 7.32 '.eject' ============= Force a page break at this point, when generating assembly listings. 7.33 '.else' ============ '.else' is part of the 'as' support for conditional assembly; see *note '.if': If. It marks the beginning of a section of code to be assembled if the condition for the preceding '.if' was false. 7.34 '.elseif' ============== '.elseif' is part of the 'as' support for conditional assembly; see *note '.if': If. It is shorthand for beginning a new '.if' block that would otherwise fill the entire '.else' section. 7.35 '.end' =========== '.end' marks the end of the assembly file. 'as' does not process anything in the file past the '.end' directive. 7.36 '.endfunc' =============== '.endfunc' marks the end of a function specified with '.func'. 7.37 '.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. 7.38 '.equ SYMBOL, EXPRESSION' ============================== This directive sets the value of SYMBOL to EXPRESSION. It is synonymous with '.set'; see *note '.set': Set. 7.39 '.equiv SYMBOL, EXPRESSION' ================================ The '.equiv' directive is like '.equ' and '.set', except that the assembler will signal an error if SYMBOL is already defined. Note a symbol which has been referenced but not actually defined is considered to be undefined. Except for the contents of the error message, this is roughly equivalent to .ifdef SYM .err .endif .equ SYM,VAL plus it protects the symbol from later redefinition. 7.40 '.eqv SYMBOL, EXPRESSION' ============================== The '.eqv' directive is like '.equiv', but no attempt is made to evaluate the expression or any part of it immediately. Instead each time the resulting symbol is used in an expression, a snapshot of its current value is taken. 7.41 '.err' =========== If 'as' assembles a '.err' directive, it will print an error message and, unless the '-Z' option was used, it will not generate an object file. This can be used to signal an error in conditionally compiled code. 7.42 '.error "STRING"' ====================== Similarly to '.err', this directive emits an error, but you can specify a string that will be emitted as the error message. If you don't specify the message, it defaults to '".error directive invoked in source file"'. *Note Error and Warning Messages: Errors. .error "This code has not been assembled and tested." 7.43 '.exitm' ============= Exit early from the current macro definition. *Note Macro::. 7.44 '.extern' ============== '.extern' is accepted in the source program--for compatibility with other assemblers--but it is ignored. 'as' treats all undefined symbols as external. 7.45 '.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. 7.46 '.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. 7.47 '.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. 7.48 '.float FLONUMS' ===================== This directive assembles zero or more flonums, separated by commas. It has the same effect as '.single'. 7.49 '.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'. 7.50 '.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. 7.51 '.hidden NAMES' ==================== This is one of the ELF visibility directives. The other two are '.internal' (*note '.internal': Internal.) and '.protected' (*note '.protected': Protected.). This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to 'hidden' which means that the symbols are not visible to other components. Such symbols are always considered to be 'protected' as well. 7.52 '.hword EXPRESSIONS' ========================= This expects zero or more EXPRESSIONS, and emits a 16 bit number for each. This directive is a synonym for '.short'. 7.53 '.ident' ============= This directive is used by some assemblers to place tags in object files. The behavior of this directive varies depending on the target. When using the a.out object file format, 'as' simply accepts the directive for source-file compatibility with existing assemblers, but does not emit anything for it. When using COFF, comments are emitted to the '.comment' or '.rdata' section, depending on the target. When using ELF, comments are emitted to the '.comment' section. 7.54 '.if ABSOLUTE EXPRESSION' ============================== '.if' marks the beginning of a section of code which is only considered part of the source program being assembled if the argument (which must be an ABSOLUTE EXPRESSION) is non-zero. The end of the conditional section of code must be marked by '.endif' (*note '.endif': Endif.); optionally, you may include code for the alternative condition, flagged by '.else' (*note '.else': Else.). If you have several conditions to check, '.elseif' may be used to avoid nesting blocks if/else within each subsequent '.else' block. The following variants of '.if' are also supported: '.ifdef SYMBOL' Assembles the following section of code if the specified SYMBOL has been defined. Note a symbol which has been referenced but not yet defined is considered to be undefined. '.ifb TEXT' Assembles the following section of code if the operand is blank (empty). '.ifc STRING1,STRING2' Assembles the following section of code if the two strings are the same. The strings may be optionally quoted with single quotes. If they are not quoted, the first string stops at the first comma, and the second string stops at the end of the line. Strings which contain whitespace should be quoted. The string comparison is case sensitive. '.ifeq ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is zero. '.ifeqs STRING1,STRING2' Another form of '.ifc'. The strings must be quoted using double quotes. '.ifge ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is greater than or equal to zero. '.ifgt ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is greater than zero. '.ifle ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is less than or equal to zero. '.iflt ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is less than zero. '.ifnb TEXT' Like '.ifb', but the sense of the test is reversed: this assembles the following section of code if the operand is non-blank (non-empty). '.ifnc STRING1,STRING2.' Like '.ifc', but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same. '.ifndef SYMBOL' '.ifnotdef SYMBOL' Assembles the following section of code if the specified SYMBOL has not been defined. Both spelling variants are equivalent. Note a symbol which has been referenced but not yet defined is considered to be undefined. '.ifne ABSOLUTE EXPRESSION' Assembles the following section of code if the argument is not equal to zero (in other words, this is equivalent to '.if'). '.ifnes STRING1,STRING2' Like '.ifeqs', but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same. 7.55 '.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. 7.56 '.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. 7.57 '.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. 7.58 '.internal NAMES' ====================== This is one of the ELF visibility directives. The other two are '.hidden' (*note '.hidden': Hidden.) and '.protected' (*note '.protected': Protected.). This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to 'internal' which means that the symbols are considered to be 'hidden' (i.e., not visible to other components), and that some extra, processor specific processing must also be performed upon the symbols as well. 7.59 '.irp SYMBOL,VALUES'... ============================ Evaluate a sequence of statements assigning different values to SYMBOL. The sequence of statements starts at the '.irp' directive, and is terminated by an '.endr' directive. For each VALUE, SYMBOL is set to VALUE, and the sequence of statements is assembled. If no VALUE is listed, the sequence of statements is assembled once, with SYMBOL set to the null string. To refer to SYMBOL within the sequence of statements, use \SYMBOL. For example, assembling .irp param,1,2,3 move d\param,sp@- .endr is equivalent to assembling move d1,sp@- move d2,sp@- move d3,sp@- For some caveats with the spelling of SYMBOL, see also *note Macro::. 7.60 '.irpc SYMBOL,VALUES'... ============================= Evaluate a sequence of statements assigning different values to SYMBOL. The sequence of statements starts at the '.irpc' directive, and is terminated by an '.endr' directive. For each character in VALUE, SYMBOL is set to the character, and the sequence of statements is assembled. If no VALUE is listed, the sequence of statements is assembled once, with SYMBOL set to the null string. To refer to SYMBOL within the sequence of statements, use \SYMBOL. For example, assembling .irpc param,123 move d\param,sp@- .endr is equivalent to assembling move d1,sp@- move d2,sp@- move d3,sp@- For some caveats with the spelling of SYMBOL, see also the discussion at *Note Macro::. 7.61 '.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'. 7.62 '.lflags' ============== 'as' accepts this directive, for compatibility with other assemblers, but ignores it. 7.63 '.line LINE-NUMBER' ======================== 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. 7.64 '.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. 7.65 '.ln LINE-NUMBER' ====================== '.ln' is a synonym for '.line'. 7.66 '.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. 7.67 '.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. 7.68 '.long EXPRESSIONS' ======================== '.long' is the same as '.int'. *Note '.int': Int. 7.69 '.macro' ============= The commands '.macro' and '.endm' allow you to define macros that generate assembly output. For example, this definition specifies a macro 'sum' that puts a sequence of numbers into memory: .macro sum from=0, to=5 .long \from .if \to-\from sum "(\from+1)",\to .endif .endm With that definition, 'SUM 0,5' is equivalent to this assembly input: .long 0 .long 1 .long 2 .long 3 .long 4 .long 5 '.macro MACNAME' '.macro MACNAME MACARGS ...' Begin the definition of a macro called MACNAME. If your macro definition requires arguments, specify their names after the macro name, separated by commas or spaces. You can qualify the macro argument to indicate whether all invocations must specify a non-blank value (through ':'req''), or whether it takes all of the remaining arguments (through ':'vararg''). You can supply a default value for any macro argument by following the name with '=DEFLT'. You cannot define two macros with the same MACNAME unless it has been subject to the '.purgem' directive (*note Purgem::) between the two definitions. For example, these are all valid '.macro' statements: '.macro comm' Begin the definition of a macro called 'comm', which takes no arguments. '.macro plus1 p, p1' '.macro plus1 p p1' Either statement begins the definition of a macro called 'plus1', which takes two arguments; within the macro definition, write '\p' or '\p1' to evaluate the arguments. '.macro reserve_str p1=0 p2' Begin the definition of a macro called 'reserve_str', with two 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). '.macro m p1:req, p2=0, p3:vararg' Begin the definition of a macro called 'm', with at least three arguments. The first argument must always have a value specified, but not the second, which instead has a default value. The third formal will get assigned all remaining arguments specified at invocation time. 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'. Note that since each of the MACARGS can be an identifier exactly as any other one permitted by the target architecture, there may be occasional problems if the target hand-crafts special meanings to certain characters when they occur in a special position. For example, if the colon (':') is generally permitted to be part of a symbol name, but the architecture specific code special-cases it when occurring as the final character of a symbol (to denote a label), then the macro parameter replacement code will have no way of knowing that and consider the whole construct (including the colon) an identifier, and check only this identifier for being the subject to parameter substitution. So for example this macro definition: .macro label l \l: .endm might not work as expected. Invoking 'label foo' might not create a label called 'foo' but instead just insert the text '\l:' into the assembler source, probably generating an error about an unrecognised identifier. Similarly problems might occur with the period character ('.') which is often allowed inside opcode names (and hence identifier names). So for example constructing a macro to build an opcode from a base name and a length specifier like this: .macro opcode base length \base.\length .endm and invoking it as 'opcode store l' will not create a 'store.l' instruction but instead generate some kind of error as the assembler tries to interpret the text '\base.\length'. There are several possible ways around this problem: 'Insert white space' If it is possible to use white space characters then this is the simplest solution. eg: .macro label l \l : .endm 'Use '\()'' The string '\()' can be used to separate the end of a macro argument from the following text. eg: .macro opcode base length \base\().\length .endm 'Use the alternate macro syntax mode' In the alternative macro syntax mode the ampersand character ('&') can be used as a separator. eg: .altmacro .macro label l l&: .endm Note: this problem of correctly identifying string parameters to pseudo ops also applies to the identifiers used in '.irp' (*note Irp::) and '.irpc' (*note Irpc::) as well. '.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_. 'LOCAL NAME [ , ... ]' _Warning: 'LOCAL' is only available if you select "alternate macro syntax" with '--alternate' or '.altmacro'._ *Note '.altmacro': Altmacro. 7.70 '.altmacro' ================ Enable alternate macro mode, enabling: 'LOCAL NAME [ , ... ]' One additional directive, 'LOCAL', is available. It is used to generate a string replacement for each of the NAME arguments, and replace any instances of NAME in each macro expansion. The replacement string is unique in the assembly, and different for each separate macro expansion. 'LOCAL' allows you to write macros that define symbols, without fear of conflict between separate macro expansions. 'String delimiters' You can write strings delimited in these other ways besides '"STRING"': ''STRING'' You can delimit strings with single-quote characters. '' You can delimit strings with matching angle brackets. 'single-character string escape' To include any single character literally in a string (even if the character would otherwise have some special meaning), you can prefix the character with '!' (an exclamation mark). For example, you can write '<4.3 !> 5.4!!>' to get the literal text '4.3 > 5.4!'. 'Expression results as strings' You can write '%EXPR' to evaluate the expression EXPR and use the result as a string. 7.71 '.noaltmacro' ================== Disable alternate macro mode. *Note Altmacro::. 7.72 '.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. 7.73 '.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. 7.74 '.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. 7.75 '.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. 7.76 '.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. 7.77 '.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. 7.78 '.print STRING' ==================== 'as' will print STRING on the standard output during assembly. You must put STRING in double quotes. 7.79 '.protected NAMES' ======================= This is 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. 7.80 '.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'. 7.81 '.purgem NAME' =================== Undefine the macro NAME, so that later uses of the string will not be expanded. *Note Macro::. 7.82 '.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 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'. 7.83 '.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. 7.84 '.reloc OFFSET, RELOC_NAME[, EXPRESSION]' ============================================== Generate a relocation at OFFSET of type RELOC_NAME with value EXPRESSION. If OFFSET is a number, the relocation is generated in the current section. If OFFSET is an expression that resolves to a symbol plus offset, the relocation is generated in the given symbol's section. EXPRESSION, if present, must resolve to a symbol plus addend or to an absolute value, but note that not all targets support an addend. e.g. ELF REL targets such as i386 store an addend in the section contents rather than in the relocation. This low level interface does not support addends stored in the section. 7.85 '.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 7.86 '.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. 7.87 '.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. 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[,FLAG_SPECIFIC_ARGUMENTS]]] 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 'G' section is a member of a section group 'T' section is used for thread-local-storage 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' section contains data which is used by things other than the program '@init_array' section contains an array of pointers to init functions '@fini_array' section contains an array of pointers to finish functions '@preinit_array' section contains an array of pointers to pre-init functions Many targets only support the first three section types. 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 the 'M' symbol then the TYPE argument must be specified as well as an extra argument--ENTSIZE--like this: .section NAME , "FLAGS"M, @TYPE, ENTSIZE Sections with the '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. ENTSIZE must be an absolute expression. If FLAGS contains the 'G' symbol then the TYPE argument must be present along with an additional field like this: .section NAME , "FLAGS"G, @TYPE, GROUPNAME[, LINKAGE] The GROUPNAME field specifies the name of the section group to which this particular section belongs. The optional linkage field can contain: 'comdat' indicates that only one copy of this section should be retained '.gnu.linkonce' an alias for comdat Note: if both the M and G flags are present then the fields for the Merge flag should come first, like this: .section NAME , "FLAGS"MG, @TYPE, ENTSIZE, GROUPNAME[, LINKAGE] 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 '#tls' section is used for thread local storage This directive replaces the current section and subsection. 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. 7.88 '.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. 7.89 '.short EXPRESSIONS' ========================= This expects zero or more EXPRESSIONS, and emits a 16 bit number for each. 7.90 '.single FLONUMS' ====================== This directive assembles zero or more flonums, separated by commas. It has the same effect as '.float'. 7.91 '.size' ============ This directive is used to set the size associated with a symbol. 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. 7.92 '.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. 7.93 '.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'. 7.94 '.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'. 7.95 '.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. 7.96 '.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. 7.97 '.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. 7.98 '.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. 7.99 '.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. 7.100 '.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. 7.101 '.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. 7.102 '.type' ============= This directive is used to set the type of a symbol. 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. Because some of the characters used in these syntaxes (such as '@' and '#') are comment characters for some architectures, some of the syntaxes below do not work on all architectures. The first variant will be accepted by the GNU assembler on all architectures so that variant should be used for maximum portability, if you do not need to assemble your code with other assemblers. The syntaxes supported are: .type STT_FUNCTION .type STT_OBJECT .type ,#function .type ,#object .type ,@function .type ,@object .type ,%function .type ,%object .type ,"function" .type ,"object" 7.103 '.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. 7.104 '.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'. 7.105 '.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'. 7.106 '.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 referring to the '*ABS*' section. 7.107 '.warning "STRING"' ========================= Similar to the directive '.error' (*note '.error "STRING"': Error.), but just emits a warning. 7.108 '.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. On COFF targets other than PE, weak symbols are a GNU extension. 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. On the PE target, weak symbols are supported natively as weak aliases. When a weak symbol is created that is not an alias, GAS creates an alternate symbol to hold the default value. 7.109 '.weakref ALIAS, TARGET' ============================== This directive creates an alias to the target symbol that enables the symbol to be referenced with weak-symbol semantics, but without actually making it weak. If direct references or definitions of the symbol are present, then the symbol will not be weak, but if all references to it are through weak references, the symbol will be marked as weak in the symbol table. The effect is equivalent to moving all references to the alias to a separate assembly source file, renaming the alias to the symbol in it, declaring the symbol as weak there, and running a reloadable link to merge the object files resulting from the assembly of the new source file and the old source file that had the references to the alias removed. The alias itself never makes to the symbol table, and is entirely handled within the assembler. 7.110 '.word EXPRESSIONS' ========================= This directive expects zero or more EXPRESSIONS, of any section, separated by commas. For each expression, 'as' emits a 32-bit number. 7.111 Deprecated Directives =========================== One day these directives won't work. They are included for compatibility with older assemblers. .abort .line 8 ARM Dependent Features ************************ 8.1 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', 'arm7tdmi-s', 'arm8', 'arm810', 'strongarm', 'strongarm1', 'strongarm110', 'strongarm1100', 'strongarm1110', 'arm9', 'arm920', 'arm920t', 'arm922t', 'arm940t', 'arm9tdmi', 'arm9e', 'arm926e', 'arm926ej-s', 'arm946e-r0', 'arm946e', 'arm946e-s', 'arm966e-r0', 'arm966e', 'arm966e-s', 'arm968e-s', 'arm10t', 'arm10tdmi', 'arm10e', 'arm1020', 'arm1020t', 'arm1020e', 'arm1022e', 'arm1026ej-s', 'arm1136j-s', 'arm1136jf-s', 'arm1156t2-s', 'arm1156t2f-s', 'arm1176jz-s', 'arm1176jzf-s', 'mpcore', 'mpcorenovfp', 'cortex-a8', 'cortex-r4', 'cortex-m3', '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', 'armv6k', 'armv6z', 'armv6zk', 'armv7', 'armv7-a', 'armv7-r', 'armv7-m', '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', 'arm1136jf-s' 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'. '-meabi=VER' This option specifies which EABI version the produced object files should conform to. The following values are recognized: 'gnu', '4' and '5'. '-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). 8.2 Syntax ========== 8.2.1 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. 8.2.2 Register Names -------------------- *TODO* Explain about ARM register naming, and the predefined names. 8.2.3 ARM relocation generation ------------------------------- Specific data relocations can be generated by putting the relocation name in parentheses after the symbol name. For example: .word foo(TARGET1) This will generate an 'R_ARM_TARGET1' relocation against the symbol FOO. The following relocations are supported: 'GOT', 'GOTOFF', 'TARGET1', 'TARGET2', 'SBREL', 'TLSGD', 'TLSLDM', 'TLSLDO', 'GOTTPOFF' and 'TPOFF'. For compatibility with older toolchains the assembler also accepts '(PLT)' after branch targets. This will generate the deprecated 'R_ARM_PLT32' relocation. Relocations for 'MOVW' and 'MOVT' instructions can be generated by prefixing the value with '#:lower16:' and '#:upper16' respectively. For example to load the 32-bit address of foo into r0: MOVW r0, #:lower16:foo MOVT r0, #:upper16:foo 8.3 Floating Point ================== The ARM family uses IEEE floating-point numbers. 8.4 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', 'dn' or 'qn' directives. 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. 'NAME .dn REGISTER NAME [.TYPE] [[INDEX]]' 'NAME .qn REGISTER NAME [.TYPE] [[INDEX]]' The 'dn' and 'qn' directives are used to create typed and/or indexed register aliases for use in Advanced SIMD Extension (Neon) instructions. The former should be used to create aliases of double-precision registers, and the latter to create aliases of quad-precision registers. If these directives are used to create typed aliases, those aliases can be used in Neon instructions instead of writing types after the mnemonic or after each operand. For example: x .dn d2.f32 y .dn d3.f32 z .dn d4.f32[1] vmul x,y,z This is equivalent to writing the following: vmul.f32 d2,d3,d4[1] Aliases created using 'dn' or 'qn' can be destroyed using 'unreq'. '.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' This directive is not neccessary when generating EABI objects. On these targets the encoding is implicit when generating Thumb code. '.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. '.unwind_fnstart' Marks the start of a function with an unwind table entry. '.unwind_fnend' Marks the end of a function with an unwind table entry. The unwind index table entry is created when this directive is processed. If no personality routine has been specified then standard personality routine 0 or 1 will be used, depending on the number of unwind opcodes required. '.cantunwind' Prevents unwinding through the current function. No personality routine or exception table data is required or permitted. '.personality NAME' Sets the personality routine for the current function to NAME. '.personalityindex INDEX' Sets the personality routine for the current function to the EABI standard routine number INDEX '.handlerdata' Marks the end of the current function, and the start of the exception table entry for that function. Anything between this directive and the '.fnend' directive will be added to the exception table entry. Must be preceded by a '.personality' or '.personalityindex' directive. '.save REGLIST' Generate unwinder annotations to restore the registers in REGLIST. The format of REGLIST is the same as the corresponding store-multiple instruction. _core registers_ .save {r4, r5, r6, lr} stmfd sp!, {r4, r5, r6, lr} _FPA registers_ .save f4, 2 sfmfd f4, 2, [sp]! _VFP registers_ .save {d8, d9, d10} fstmdx sp!, {d8, d9, d10} _iWMMXt registers_ .save {wr10, wr11} wstrd wr11, [sp, #-8]! wstrd wr10, [sp, #-8]! or .save wr11 wstrd wr11, [sp, #-8]! .save wr10 wstrd wr10, [sp, #-8]! '.vsave VFP-REGLIST' Generate unwinder annotations to restore the VFP registers in VFP-REGLIST using FLDMD. Also works for VFPv3 registers that are to be restored using VLDM. The format of VFP-REGLIST is the same as the corresponding store-multiple instruction. _VFP registers_ .vsave {d8, d9, d10} fstmdd sp!, {d8, d9, d10} _VFPv3 registers_ .vsave {d15, d16, d17} vstm sp!, {d15, d16, d17} Since FLDMX and FSTMX are now deprecated, this directive should be used in favour of '.save' for saving VFP registers for ARMv6 and above. '.pad #COUNT' Generate unwinder annotations for a stack adjustment of COUNT bytes. A positive value indicates the function prologue allocated stack space by decrementing the stack pointer. '.movsp REG [, #OFFSET]' Tell the unwinder that REG contains an offset from the current stack pointer. If OFFSET is not specified then it is assumed to be zero. '.setfp FPREG, SPREG [, #OFFSET]' Make all unwinder annotations relaive to a frame pointer. Without this the unwinder will use offsets from the stack pointer. The syntax of this directive is the same as the 'sub' or 'mov' instruction used to set the frame pointer. SPREG must be either 'sp' or mentioned in a previous '.movsp' directive. .movsp ip mov ip, sp ... .setfp fp, ip, #4 sub fp, ip, #4 '.raw OFFSET, BYTE1, ...' Insert one of more arbitary unwind opcode bytes, which are known to adjust the stack pointer by OFFSET bytes. For example '.unwind_raw 4, 0xb1, 0x01' is equivalent to '.save {r0}' '.cpu NAME' Select the target processor. Valid values for NAME are the same as for the '-mcpu' commandline option. '.arch NAME' Select the target architecture. Valid values for NAME are the same as for the '-march' commandline option. '.object_arch NAME' Override the architecture recorded in the EABI object attribute section. Valid values for NAME are the same as for the '.arch' directive. Typically this is useful when code uses runtime detection of CPU features. '.fpu NAME' Select the floating point unit to assemble for. Valid values for NAME are the same as for the '-mfpu' commandline option. '.eabi_attribute TAG, VALUE' Set the EABI object attribute number TAG to VALUE. The value is either a 'number', '"string"', or 'number, "string"' depending on the tag. 8.5 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