.Dd 2015-03-02 .Dt AS 7 .Os .Sh NAME .Nm as .Nd Using as (machine specific) .Sh Using as This file is a user guide to the GNU assembler .Xr as version "2.17.50 [FreeBSD] 2007-07-03". This version of the file describes .Xr as configured to generate code for machine specific architectures. .Pp This document is distributed under the terms of the GNU Free Documentation License. A copy of the license is included in the section entitled \(lqGNU Free Documentation License\(rq. .Pp .Sh Overview Here is a brief summary of how to invoke .Xr as . For details, see Invoking,,Command-Line Options. .Pp .Bd -literal -offset indent 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] .Ed .Pp .Bl -tag -width Ds .It @ Va file Read command-line options from .Va file . The options read are inserted in place of the original @ .Va file option. If .Va file does not exist, or cannot be read, then the option will be treated literally, and not removed. .Pp Options in .Va 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 .Va file may itself contain additional @ .Va file options; any such options will be processed recursively. .Pp .It -a[cdhlmns] Turn on listings, in any of a variety of ways: .Pp .Bl -tag -width Ds .It -ac omit false conditionals .Pp .It -ad omit debugging directives .Pp .It -ah include high-level source .Pp .It -al include assembly .Pp .It -am include macro expansions .Pp .It -an omit forms processing .Pp .It -as include symbols .Pp .It =file set the name of the listing file .El .Pp You may combine these options; for example, use .Li -aln for assembly listing without forms processing. The .Li =file option, if used, must be the last one. By itself, .Li -a defaults to .Li -ahls . .Pp .It --alternate Begin in alternate macro mode.See Section .Dq Altmacro . .Pp .It -D Ignored. This option is accepted for script compatibility with calls to other assemblers. .Pp .It --defsym Va sym= Va value Define the symbol .Va sym to be .Va value before assembling the input file. .Va value must be an integer constant. As in C, a leading .Li 0x indicates a hexadecimal value, and a leading .Li 0 indicates an octal value. The value of the symbol can be overridden inside a source file via the use of a .Li .set pseudo-op. .Pp .It -f \(lqfast\(rq---skip whitespace and comment preprocessing (assume source is compiler output). .Pp .It -g .It --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. .Pp .It --gstabs Generate stabs debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it. .Pp .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. .Pp .It --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. .Pp .It --help Print a summary of the command line options and exit. .Pp .It --target-help Print a summary of all target specific options and exit. .Pp .It -I Va dir Add directory .Va dir to the search list for .Li .include directives. .Pp .It -J Don't warn about signed overflow. .Pp .It -K This option is accepted but has no effect on the machine specific family. .Pp .It -L .It --keep-locals Keep (in the symbol table) local symbols. These symbols start with system-specific local label prefixes, typically .Li .L for ELF systems or .Li L for traditional a.out systems.See Section .Dq Symbol Names . .Pp .It --listing-lhs-width= Va number Set the maximum width, in words, of the output data column for an assembler listing to .Va number . .Pp .It --listing-lhs-width2= Va number Set the maximum width, in words, of the output data column for continuation lines in an assembler listing to .Va number . .Pp .It --listing-rhs-width= Va number Set the maximum width of an input source line, as displayed in a listing, to .Va number bytes. .Pp .It --listing-cont-lines= Va number Set the maximum number of lines printed in a listing for a single line of input to .Va number + 1. .Pp .It -o Va objfile Name the object-file output from .Xr as .Va objfile . .Pp .It -R Fold the data section into the text section. .Pp Set the default size of GAS's hash tables to a prime number close to .Va 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. .Pp .It --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 .Li --hash-size=4051 , but in the future it may have other effects as well. .Pp .It --statistics Print the maximum space (in bytes) and total time (in seconds) used by assembly. .Pp .It --strip-local-absolute Remove local absolute symbols from the outgoing symbol table. .Pp .It -v .It -version Print the .Xr as version. .Pp .It --version Print the .Xr as version and exit. .Pp .It -W .It --no-warn Suppress warning messages. .Pp .It --fatal-warnings Treat warnings as errors. .Pp .It --warn Don't suppress warning messages or treat them as errors. .Pp .It -w Ignored. .Pp .It -x Ignored. .Pp .It -Z Generate an object file even after errors. .Pp .It -- | Va files ... Standard input, or source files to assemble. .Pp .El The following options are available when as is configured for the ARM processor family. .Pp .Bl -tag -width Ds .It -mcpu= Va processor[+ Va extension...] Specify which ARM processor variant is the target. .It -march= Va architecture[+ Va extension...] Specify which ARM architecture variant is used by the target. .It -mfpu= Va floating-point-format Select which Floating Point architecture is the target. .It -mfloat-abi= Va abi Select which floating point ABI is in use. .It -mthumb Enable Thumb only instruction decoding. .It -mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant Select which procedure calling convention is in use. .It -EB | -EL Select either big-endian (-EB) or little-endian (-EL) output. .It -mthumb-interwork Specify that the code has been generated with interworking between Thumb and ARM code in mind. .It -k Specify that PIC code has been generated. .El .Pp The following options are available when .Xr as is configured for the SPARC architecture: .Pp .Bl -tag -width Ds .It -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite .It -Av8plus | -Av8plusa | -Av9 | -Av9a Explicitly select a variant of the SPARC architecture. .Pp .Li -Av8plus and .Li -Av8plusa select a 32 bit environment. .Li -Av9 and .Li -Av9a select a 64 bit environment. .Pp .Li -Av8plusa and .Li -Av9a enable the SPARC V9 instruction set with UltraSPARC extensions. .Pp .It -xarch=v8plus | -xarch=v8plusa For compatibility with the Solaris v9 assembler. These options are equivalent to -Av8plus and -Av8plusa, respectively. .Pp .It -bump Warn when the assembler switches to another architecture. .El .Pp The following options are available when as is configured for a mips processor. .Pp .Bl -tag -width Ds .It -G Va num This option sets the largest size of an object that can be referenced implicitly with the .Li gp register. It is only accepted for targets that use ECOFF format, such as a DECstation running Ultrix. The default value is 8. .Pp .It -EB Generate \(lqbig endian\(rq format output. .Pp .It -EL Generate \(lqlittle endian\(rq format output. .Pp .It -mips1 .It -mips2 .It -mips3 .It -mips4 .It -mips5 .It -mips32 .It -mips32r2 .It -mips64 .It -mips64r2 Generate code for a particular mips Instruction Set Architecture level. .Li -mips1 is an alias for .Li -march=r3000 , .Li -mips2 is an alias for .Li -march=r6000 , .Li -mips3 is an alias for .Li -march=r4000 and .Li -mips4 is an alias for .Li -march=r8000 . .Li -mips5 , .Li -mips32 , .Li -mips32r2 , .Li -mips64 , and .Li -mips64r2 correspond to generic .Li MIPS V , .Li MIPS32 , .Li MIPS32 Release 2 , .Li MIPS64 , and .Li MIPS64 Release 2 ISA processors, respectively. .Pp .It -march= Va CPU Generate code for a particular mips cpu. .Pp .It -mtune= Va cpu Schedule and tune for a particular mips cpu. .Pp .It -mfix7000 .It -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. .Pp .It -mdebug .It -no-mdebug Cause stabs-style debugging output to go into an ECOFF-style .mdebug section instead of the standard ELF .stabs sections. .Pp .It -mpdr .It -mno-pdr Control generation of .Li .pdr sections. .Pp .It -mgp32 .It -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. .Li -mgp32 controls the size of general-purpose registers and .Li -mfp32 controls the size of floating-point registers. .Pp .It -mips16 .It -no-mips16 Generate code for the MIPS 16 processor. This is equivalent to putting .Li .set mips16 at the start of the assembly file. .Li -no-mips16 turns off this option. .Pp .It -msmartmips .It -mno-smartmips Enables the SmartMIPS extension to the MIPS32 instruction set. This is equivalent to putting .Li .set smartmips at the start of the assembly file. .Li -mno-smartmips turns off this option. .Pp .It -mips3d .It -no-mips3d Generate code for the MIPS-3D Application Specific Extension. This tells the assembler to accept MIPS-3D instructions. .Li -no-mips3d turns off this option. .Pp .It -mdmx .It -no-mdmx Generate code for the MDMX Application Specific Extension. This tells the assembler to accept MDMX instructions. .Li -no-mdmx turns off this option. .Pp .It -mdsp .It -mno-dsp Generate code for the DSP Release 1 Application Specific Extension. This tells the assembler to accept DSP Release 1 instructions. .Li -mno-dsp turns off this option. .Pp .It -mdspr2 .It -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. .Li -mno-dspr2 turns off this option. .Pp .It -mmt .It -mno-mt Generate code for the MT Application Specific Extension. This tells the assembler to accept MT instructions. .Li -mno-mt turns off this option. .Pp .It --construct-floats .It --no-construct-floats The .Li --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 .Li --construct-floats is selected, allowing construction of these floating point constants. .Pp .It --emulation= Va name This option causes .Xr as to emulate .Xr 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: .Li mipsecoff , .Li mipself , .Li mipslecoff , .Li mipsbecoff , .Li mipslelf , .Li 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 .Li b or .Li l in the name. Using .Li -EB or .Li -EL will override the endianness selection in any case. .Pp This option is currently supported only when the primary target .Xr as is configured for is a mips ELF or ECOFF target. Furthermore, the primary target or others specified with .Li --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. .Pp Eventually, this option will support more configurations, with more fine-grained control over the assembler's behavior, and will be supported for more processors. .Pp .It -nocpp .Xr as ignores this option. It is accepted for compatibility with the native tools. .Pp .It --trap .It --no-trap .It --break .It --no-break Control how to deal with multiplication overflow and division by zero. .Li --trap or .Li --no-break (which are synonyms) take a trap exception (and only work for Instruction Set Architecture level 2 and higher); .Li --break or .Li --no-trap (also synonyms, and the default) take a break exception. .Pp .It -n When this option is used, .Xr as will issue a warning every time it generates a nop instruction from a macro. .El .Pp .Ss Structure of this Manual This manual is intended to describe what you need to know to use GNU .Xr as . We cover the syntax expected in source files, including notation for symbols, constants, and expressions; the directives that .Xr as understands; and of course how to invoke .Xr as . .Pp We also cover special features in the machine specific configuration of .Xr as , including assembler directives. .Pp On the other hand, this manual is .Em 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 .Em not describe the instruction set, standard mnemonics, registers or addressing modes that are standard to a particular architecture. .Pp .Ss The GNU Assembler GNU .Xr as is really a family of assemblers. This manual describes .Xr 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 .Em pseudo-ops ) and assembler syntax. .Pp .Xr as is primarily intended to assemble the output of the GNU C compiler .Li gcc for use by the linker .Li ld . Nevertheless, we've tried to make .Xr as assemble correctly everything that other assemblers for the same machine would assemble. .Pp Unlike older assemblers, .Xr as is designed to assemble a source program in one pass of the source file. This has a subtle impact on the .Li .org directive (see Section .Dq Org ) . .Pp .Ss 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.See Section .Dq Symbol Attributes . For the machine specific target, .Xr as is configured to produce ELF format object files. .Pp .Ss Command Line After the program name .Xr 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. .Pp .Pa -- (two hyphens) by itself names the standard input file explicitly, as one of the files for .Xr as to assemble. .Pp Except for .Li -- any command line argument that begins with a hyphen ( .Li - ) is an option. Each option changes the behavior of .Xr as . No option changes the way another option works. An option is a .Li - followed by one or more letters; the case of the letter is important. All options are optional. .Pp 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: .Pp .Bd -literal -offset indent as -o my-object-file.o mumble.s as -omy-object-file.o mumble.s .Ed .Pp .Ss Input Files We use the phrase .Em source program , abbreviated .Em source , to describe the program input to one run of .Xr 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. .Pp The source program is a concatenation of the text in all the files, in the order specified. .Pp Each time you run .Xr 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.) .Pp You give .Xr 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. .Pp If you give .Xr as no file names it attempts to read one input file from the .Xr as standard input, which is normally your terminal. You may have to type ctl-D to tell .Xr as there is no more program to assemble. .Pp Use .Li -- if you need to explicitly name the standard input file in your command line. .Pp If the source is empty, .Xr as produces a small, empty object file. .Pp .Em Filenames and Line-numbers .Pp 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 \(lqlogical\(rq file.See Section .Dq Errors . .Pp .Em Physical files are those files named in the command line given to .Xr as . .Pp .Em 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 .Xr as source is itself synthesized from other files. .Xr as understands the .Li # directives emitted by the .Li gcc preprocessor. See also File,, .Li .file \&. .Pp .Ss Output (Object) File Every time you run .Xr 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 .Li a.out . You can give it another name by using the .Op -o option. Conventionally, object file names end with .Pa .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 .Li a.out format.) .Pp The object file is meant for input to the linker .Li ld . It contains assembled program code, information to help .Li ld integrate the assembled program into a runnable file, and (optionally) symbolic information for the debugger. .Pp .Ss Error and Warning Messages .Xr as may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs .Xr as automatically. Warnings report an assumption made so that .Xr as could keep assembling a flawed program; errors report a grave problem that stops the assembly. .Pp Warning messages have the format .Pp .Bd -literal -offset indent file_name:NNN:Warning Message Text .Ed .Pp (where .Sy NNN is a line number). If a logical file name has been given (see Section .Dq 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). .Pp Error messages have the format .Bd -literal -offset indent file_name:NNN:FATAL:Error Message Text .Ed 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. .Pp .Sh Command-Line Options This chapter describes command-line options available in .Em all versions of the GNU assembler; see Machine Dependencies, for options specific to the machine specific target. .Pp If you are invoking .Xr as via the GNU C compiler, you can use the .Li -Wa option to pass arguments through to the assembler. The assembler arguments must be separated from each other (and the .Li -Wa ) by commas. For example: .Pp .Bd -literal -offset indent gcc -c -g -O -Wa,-alh,-L file.c .Ed .Pp This passes two options to the assembler: .Li -alh (emit a listing to standard output with high-level and assembly source) and .Li -L (retain local symbols in the symbol table). .Pp Usually you do not need to use this .Li -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 .Li -v option to see precisely what options it passes to each compilation pass, including the assembler.) .Pp .Ss Enable Listings: Op -a[cdhlns] These options enable listing output from the assembler. By itself, .Li -a requests high-level, assembly, and symbols listing. You can use other letters to select specific options for the list: .Li -ah requests a high-level language listing, .Li -al requests an output-program assembly listing, and .Li -as requests a symbol table listing. High-level listings require that a compiler debugging option like .Li -g be used, and that assembly listings ( .Li -al ) be requested also. .Pp Use the .Li -ac option to omit false conditionals from a listing. Any lines which are not assembled because of a false .Li .if (or .Li .ifdef , or any other conditional), or a true .Li .if followed by an .Li .else , will be omitted from the listing. .Pp Use the .Li -ad option to omit debugging directives from the listing. .Pp Once you have specified one of these options, you can further control listing output and its appearance using the directives .Li .list , .Li .nolist , .Li .psize , .Li .eject , .Li .title , and .Li .sbttl . The .Li -an option turns off all forms processing. If you do not request listing output with one of the .Li -a options, the listing-control directives have no effect. .Pp The letters after .Li -a may be combined into one option, .Em e.g. , .Li -aln . .Pp Note if the assembler source is coming from the standard input (e.g., because it is being created by .Li gcc and the .Li -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. .Pp .Ss Op --alternate Begin in alternate macro mode, see Altmacro,, .Li .altmacro \&. .Pp .Ss Op -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 .Xr as . .Pp .Ss Work Faster: Op -f .Li -f should only be used when assembling programs written by a (trusted) compiler. .Li -f stops the assembler from doing whitespace and comment preprocessing on the input file(s) before assembling them.See Section .Dq Preprocessing . .Pp .Qo .Em Warning: if you use .Li -f when the files actually need to be preprocessed (if they contain comments, for example), .Xr as does not work correctly. .Qc .Pp .Ss Li .include Search Path: Op -I Va path Use this option to add a .Va path to the list of directories .Xr as searches for files specified in .Li .include directives (see Section .Dq Include ) . You may use .Op -I as many times as necessary to include a variety of paths. The current working directory is always searched first; after that, .Xr as searches any .Li -I directories in the same order as they were specified (left to right) on the command line. .Pp .Ss Difference Tables: Op -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 .Li .word directives in difference tables. The machine specific family does not have the addressing limitations that sometimes lead to this alteration on other platforms. .Pp .Ss Include Local Symbols: Op -L Symbols beginning with system-specific local label prefixes, typically .Li .L for ELF systems or .Li L for traditional a.out systems, are called .Em local symbols . See Section.Dq 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 .Xr as and .Li ld discard such symbols, so you do not normally debug with them. .Pp This option tells .Xr as to retain those local symbols in the object file. Usually if you do this you also tell the linker .Li ld to preserve those symbols. .Pp .Ss Configuring listing output: Op --listing The listing feature of the assembler can be enabled via the command line switch .Li -a (see Section .Dq 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., .Li .list (see Section .Dq List ) , .Li .title (see Section .Dq Title ) , .Li .sbttl (see Section .Dq Sbttl ) , .Li .psize (see Section .Dq Psize ) , and .Li .eject (see Section .Dq Eject ) and also by the following switches: .Pp .Bl -tag -width Ds .It --listing-lhs-width= Li 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. .Pp .It --listing-lhs-width2= Li 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 .Li --listing-lhs-width . If neither switch is used the default is to one. .Pp .It --listing-rhs-width= Li 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. .Pp .It --listing-cont-lines= Li 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. .El .Pp .Ss Assemble in MRI Compatibility Mode: Op -M The .Op -M or .Op --mri option selects MRI compatibility mode. This changes the syntax and pseudo-op handling of .Xr as to make it compatible with the .Li ASM68K or the .Li 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 .Xr as . .Pp 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: .Pp .Bl -bullet .It global symbols in common section .Pp The m68k MRI assembler supports common sections which are merged by the linker. Other object file formats do not support this. .Xr 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. .Pp .It complex relocations .Pp 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. .Pp .It .Li END pseudo-op specifying start address .Pp The MRI .Li 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 .Op -e option to the linker, or in a linker script. .Pp .It .Li IDNT , .Li .ident and .Li NAME pseudo-ops .Pp The MRI .Li IDNT , .Li .ident and .Li NAME pseudo-ops assign a module name to the output file. This is not supported by other object file formats. .Pp .It .Li ORG pseudo-op .Pp The m68k MRI .Li ORG pseudo-op begins an absolute section at a given address. This differs from the usual .Xr as .Li .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. .El .Pp There are some other features of the MRI assembler which are not supported by .Xr as , typically either because they are difficult or because they seem of little consequence. Some of these may be supported in future releases. .Pp .Bl -bullet .It EBCDIC strings .Pp EBCDIC strings are not supported. .Pp .It packed binary coded decimal .Pp Packed binary coded decimal is not supported. This means that the .Li DC.P and .Li DCB.P pseudo-ops are not supported. .Pp .It .Li FEQU pseudo-op .Pp The m68k .Li FEQU pseudo-op is not supported. .Pp .It .Li NOOBJ pseudo-op .Pp The m68k .Li NOOBJ pseudo-op is not supported. .Pp .It .Li OPT branch control options .Pp The m68k .Li OPT branch control options--- .Li B , .Li BRS , .Li BRB , .Li BRL , and .Li BRW ---are ignored. .Xr as automatically relaxes all branches, whether forward or backward, to an appropriate size, so these options serve no purpose. .Pp .It .Li OPT list control options .Pp The following m68k .Li OPT list control options are ignored: .Li C , .Li CEX , .Li CL , .Li CRE , .Li E , .Li G , .Li I , .Li M , .Li MEX , .Li MC , .Li MD , .Li X . .Pp .It other .Li OPT options .Pp The following m68k .Li OPT options are ignored: .Li NEST , .Li O , .Li OLD , .Li OP , .Li P , .Li PCO , .Li PCR , .Li PCS , .Li R . .Pp .It .Li OPT .Li D option is default .Pp The m68k .Li OPT .Li D option is the default, unlike the MRI assembler. .Li OPT NOD may be used to turn it off. .Pp .It .Li XREF pseudo-op. .Pp The m68k .Li XREF pseudo-op is ignored. .Pp .It .Li .debug pseudo-op .Pp The i960 .Li .debug pseudo-op is not supported. .Pp .It .Li .extended pseudo-op .Pp The i960 .Li .extended pseudo-op is not supported. .Pp .It .Li .list pseudo-op. .Pp The various options of the i960 .Li .list pseudo-op are not supported. .Pp .It .Li .optimize pseudo-op .Pp The i960 .Li .optimize pseudo-op is not supported. .Pp .It .Li .output pseudo-op .Pp The i960 .Li .output pseudo-op is not supported. .Pp .It .Li .setreal pseudo-op .Pp The i960 .Li .setreal pseudo-op is not supported. .Pp .El .Ss Dependency Tracking: Op --MD .Xr as can generate a dependency file for the file it creates. This file consists of a single rule suitable for .Li make describing the dependencies of the main source file. .Pp The rule is written to the file named in its argument. .Pp This feature is used in the automatic updating of makefiles. .Pp .Ss Name the Object File: Op -o There is always one object file output when you run .Xr as . By default it has the name .Pa a.out . You use this option (which takes exactly one filename) to give the object file a different name. .Pp Whatever the object file is called, .Xr as overwrites any existing file of the same name. .Pp .Ss Join Data and Text Sections: Op -R .Op -R tells .Xr 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. (See Section .Dq Sections . ) .Pp When you specify .Op -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 .Xr as . In future, .Op -R may work this way. .Pp When .Xr as is configured for COFF or ELF output, this option is only useful if you use sections named .Li .text and .Li .data . .Pp .Ss Display Assembly Statistics: Op --statistics Use .Li --statistics to display two statistics about the resources used by .Xr as : the maximum amount of space allocated during the assembly (in bytes), and the total execution time taken for the assembly (in cpu seconds). .Pp .Ss Compatible Output: Op --traditional-format For some targets, the output of .Xr as is different in some ways from the output of some existing assembler. This switch requests .Xr as to use the traditional format instead. .Pp For example, it disables the exception frame optimizations which .Xr as normally does by default on .Li gcc output. .Pp .Ss Announce Version: Op -v You can find out what version of as is running by including the option .Li -v (which you can also spell as .Li -version ) on the command line. .Pp .Ss Control Warnings: Op -W, Op --warn, Op --no-warn, Op --fatal-warnings .Xr as should never give a warning or error message when assembling compiler output. But programs written by people often cause .Xr as to give a warning that a particular assumption was made. All such warnings are directed to the standard error file. .Pp If you use the .Op -W and .Op --no-warn options, no warnings are issued. This only affects the warning messages: it does not change any particular of how .Xr as assembles your file. Errors, which stop the assembly, are still reported. .Pp If you use the .Op --fatal-warnings option, .Xr as considers files that generate warnings to be in error. .Pp You can switch these options off again by specifying .Op --warn , which causes warnings to be output as usual. .Pp .Ss Generate Object File in Spite of Errors: Op -Z After an error message, .Xr as normally produces no output. If for some reason you are interested in object file output even after .Xr as gives an error message on your program, use the .Li -Z option. If there are any errors, .Xr as continues anyways, and writes an object file after a final warning message of the form .Li Va n errors, Va m warnings, generating bad object file. .Pp .Sh Syntax This chapter describes the machine-independent syntax allowed in a source file. .Xr as syntax is similar to what many other assemblers use; it is inspired by the BSD 4.2 assembler. .Pp .Ss Preprocessing The .Xr as internal preprocessor: .Bl -bullet .It 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. .Pp .It removes all comments, replacing them with a single space, or an appropriate number of newlines. .Pp .It converts character constants into the appropriate numeric values. .El .Pp 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 .Li .include directive (see Section .Dq Include ) . You can use the GNU C compiler driver to get other \(lqCPP\(rq style preprocessing by giving the input file a .Li .S suffix.See Section .Dq Overall Options . .Pp Excess whitespace, comments, and character constants cannot be used in the portions of the input text that are not preprocessed. .Pp If the first line of an input file is .Li #NO_APP or if you use the .Li -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 .Li #APP before the text that may contain whitespace or comments, and putting a line that says .Li #NO_APP after this text. This feature is mainly intend to support .Li asm statements in compilers whose output is otherwise free of comments and whitespace. .Pp .Ss Whitespace .Em 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 (see Section .Dq Characters ) , any whitespace means the same as exactly one space. .Pp .Ss Comments There are two ways of rendering comments to .Xr as . In both cases the comment is equivalent to one space. .Pp Anything from .Li /* through the next .Li */ is a comment. This means you may not nest these comments. .Pp .Bd -literal -offset indent /* The only way to include a newline ('\en') in a comment is to use this sort of comment. */ /* This sort of comment does not nest. */ .Ed .Pp Anything from the .Em line comment character to the next newline is considered a comment and is ignored. The line comment character is .Li @ on the ARM; .Li # on the i386 and x86-64; .Li # for Motorola PowerPC; .Li ! on the SPARC; see Machine Dependencies. .Pp To be compatible with past assemblers, lines that begin with .Li # have a special interpretation. Following the .Li # should be an absolute expression (see Section .Dq Expressions ) : the logical line number of the .Em next line. Then a string (see Section .Dq Strings ) is allowed: if present it is a new logical file name. The rest of the line, if any, should be whitespace. .Pp If the first non-whitespace characters on the line are not numeric, the line is ignored. (Just like a comment.) .Pp .Bd -literal -offset indent # This is an ordinary comment. # 42-6 "new_file_name" # New logical file name # This is logical line # 36. .Ed This feature is deprecated, and may disappear from future versions of .Xr as . .Pp .Ss Symbols A .Em symbol is one or more characters chosen from the set of all letters (both upper and lower case), digits and the three characters .Li _.$ . 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).See Section .Dq Symbols . .Pp .Ss Statements A .Em statement ends at a newline character ( .Li \en ) or at a semicolon ( .Li ; ) . 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. .Pp It is an error to end any statement with end-of-file: the last character of any input file should be a newline. .Pp An empty statement is allowed, and may include whitespace. It is ignored. .Pp 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 .Li . 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 .Em instruction : it assembles into a machine language instruction. .Pp A label is a symbol immediately followed by a colon ( .Li : ) . Whitespace before a label or after a colon is permitted, but you may not have whitespace between a label's symbol and its colon.See Section .Dq Labels . .Pp .Bd -literal -offset indent label: .directive followed by something another_label: # This is an empty statement. instruction operand_1, operand_2, ... .Ed .Pp .Ss Constants A constant is a number, written so that its value is known by inspection, without knowing any context. Like this: .Bd -literal -offset indent \&.byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\eJ # All the same value. \&.ascii "Ring the bell\e7" # A string constant. \&.octa 0x123456789abcdef0123456789ABCDEF0 # A biGNUm. \&.float 0f-314159265358979323846264338327\e 95028841971.693993751E-40 # - pi, a flonum. .Ed .Pp .Em Character Constants .Pp There are two kinds of character constants. A .Em character stands for one character in one byte and its value may be used in numeric expressions. String constants (properly called string .Em literals ) are potentially many bytes and their values may not be used in arithmetic expressions. .Pp .No Strings .Pp A .Em 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 .Em escape these characters: precede them with a backslash .Li \e character. For example .Li \e\e represents one backslash: the first .Li \e is an escape which tells .Xr as to interpret the second character literally as a backslash (which prevents .Xr as from recognizing the second .Li \e as an escape character). The complete list of escapes follows. .Pp .Bl -tag -width Ds .It \eb Mnemonic for backspace; for ASCII this is octal code 010. .Pp .It \ef Mnemonic for FormFeed; for ASCII this is octal code 014. .Pp .It \en Mnemonic for newline; for ASCII this is octal code 012. .Pp .It \er Mnemonic for carriage-Return; for ASCII this is octal code 015. .Pp .It \et Mnemonic for horizontal Tab; for ASCII this is octal code 011. .Pp .It \e Va digit Va digit Va 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, .Li \e008 has the value 010, and .Li \e009 the value 011. .Pp .It \e Li x Va hex-digits... A hex character code. All trailing hex digits are combined. Either upper or lower case .Li x works. .Pp .It \e\e Represents one .Li \e character. .Pp .It \e" Represents one .Li " character. Needed in strings to represent this character, because an unescaped .Li " would end the string. .Pp .It \e Va anything-else Any other character when escaped by .Li \e gives a warning, but assembles as if the .Li \e 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 .Xr as has no other interpretation, so .Xr as knows it is giving you the wrong code and warns you of the fact. .El .Pp 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. .Pp .No Characters .Pp 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 .Li '\e\e where the first .Li \e escapes the second .Li \e . As you can see, the quote is an acute accent, not a grave accent. A newline (or semicolon .Li ; ) 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. .Xr as assumes your character code is ASCII: .Li 'A means 65, .Li 'B means 66, and so on. .Pp .Em Number Constants .Pp .Xr as distinguishes three kinds of numbers according to how they are stored in the target machine. .Em Integers are numbers that would fit into an .Li int in the C language. .Em BiGNUms are integers, but they are stored in more than 32 bits. .Em Flonums are floating point numbers, described below. .Pp .No Integers .Pp A binary integer is .Li 0b or .Li 0B followed by zero or more of the binary digits .Li 01 . .Pp An octal integer is .Li 0 followed by zero or more of the octal digits ( .Li 01234567 ) . .Pp A decimal integer starts with a non-zero digit followed by zero or more digits ( .Li 0123456789 ) . .Pp A hexadecimal integer is .Li 0x or .Li 0X followed by one or more hexadecimal digits chosen from .Li 0123456789abcdefABCDEF . .Pp Integers have the usual values. To denote a negative integer, use the prefix operator .Li - discussed under expressions (see Section .Dq Prefix Ops ) . .Pp .No BiGNUms .Pp A .Em 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. .Pp .No Flonums .Pp A .Em flonum represents a floating point number. The translation is indirect: a decimal floating point number from the text is converted by .Xr 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 .Xr as specialized to that computer. .Pp A flonum is written by writing (in order) .Bl -bullet .It The digit .Li 0 . .Pp .It A letter, to tell .Xr as the rest of the number is a flonum. .Pp .It An optional sign: either .Li + or .Li - . .Pp .It An optional .Em integer part : zero or more decimal digits. .Pp .It An optional .Em fractional part : .Li . followed by zero or more decimal digits. .Pp .It An optional exponent, consisting of: .Pp .Bl -bullet .It An .Li E or .Li e . .It Optional sign: either .Li + or .Li - . .It One or more decimal digits. .El .Pp .El At least one of the integer part or the fractional part must be present. The floating point number has the usual base-10 value. .Pp .Xr as does all processing using integers. Flonums are computed independently of any floating point hardware in the computer running .Xr as . .Pp .Sh Sections and Relocation .Ss Background Roughly, a section is a range of addresses, with no gaps; all data \(lqin\(rq those addresses is treated the same for some particular purpose. For example there may be a \(lqread only\(rq section. .Pp The linker .Li ld reads many object files (partial programs) and combines their contents to form a runnable program. When .Xr as emits an object file, the partial program is assumed to start at address 0. .Li 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 .Xr as uses sections. .Pp .Li 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 .Em section . Assigning run-time addresses to sections is called .Em relocation . It includes the task of adjusting mentions of object-file addresses so they refer to the proper run-time addresses. .Pp An object file written by .Xr as has at least three sections, any of which may be empty. These are named .Em text , .Em data and .Em bss sections. .Pp .Xr as can also generate whatever other named sections you specify using the .Li .section directive (see Section .Dq Section ) . If you do not use any directives that place output in the .Li .text or .Li .data sections, these sections still exist, but are empty. .Pp Within the object file, the text section starts at address .Li 0 , the data section follows, and the bss section follows the data section. .Pp To let .Li ld know which data changes when the sections are relocated, and how to change that data, .Xr as also writes to the object file details of the relocation needed. To perform relocation .Li ld must know, each time an address in the object file is mentioned: .Bl -bullet .It Where in the object file is the beginning of this reference to an address? .It How long (in bytes) is this reference? .It Which section does the address refer to? What is the numeric value of .Bd -filled -offset indent ( .Va address ) \-( .Va start-address of section ) ? .Ed .It Is the reference to an address \(lqProgram-Counter relative\(rq? .El .Pp In fact, every address .Xr as ever uses is expressed as .Bd -filled -offset indent ( .Va section ) + ( .Va offset into section ) .Ed Further, most expressions .Xr as computes have this section-relative nature. .Pp In this manual we use the notation { .Va secname .Va N }to mean \(lqoffset .Va N into section .Va secname \&.\(rq .Pp Apart from text, data and bss sections you need to know about the .Em absolute section. When .Li ld mixes partial programs, addresses in the absolute section remain unchanged. For example, address .Li {absolute 0} is \(lqrelocated\(rq to run-time address 0 by .Li ld . Although the linker never arranges two partial programs' data sections with overlapping addresses after linking, .Em by definition their absolute sections must overlap. Address .Li {absolute 239} in one part of a program is always the same address when the program is running as address .Li {absolute 239} in any other part of the program. .Pp The idea of sections is extended to the .Em undefined section. Any address whose section is unknown at assembly time is by definition rendered {undefined .Va U }---where .Va 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 .Em undefined . .Pp By analogy the word .Em section is used to describe groups of sections in the linked program. .Li ld puts all partial programs' text sections in contiguous addresses in the linked program. It is customary to refer to the .Em text section of a program, meaning all the addresses of all partial programs' text sections. Likewise for data and bss sections. .Pp Some sections are manipulated by .Li ld ; others are invented for use of .Xr as and have no meaning except during assembly. .Pp .Ss Linker Sections .Li ld deals with just four kinds of sections, summarized below. .Pp .Bl -tag -width Ds .It named sections These sections hold your program. .Xr as and .Li 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. .Pp .It 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. .Pp .It absolute section Address 0 of this section is always \(lqrelocated\(rq to runtime address 0. This is useful if you want to refer to an address that .Li ld must not change when relocating. In this sense we speak of absolute addresses being \(lqunrelocatable\(rq: they do not change during relocation. .Pp .It undefined section This \(lqsection\(rq is a catch-all for address references to objects not in the preceding sections. .El .Pp An idealized example of three relocatable sections follows. The example uses the traditional section names .Li .text and .Li .data . Memory addresses are on the horizontal axis. .Pp .Bd -literal -offset indent +-----+----+--+ 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 ... .Ed .Pp .Ss Assembler Internal Sections These sections are meant only for the internal use of .Xr 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 .Xr as warning messages, so it might be helpful to have an idea of their meanings to .Xr as . These sections are used to permit the value of every expression in your assembly language program to be a section-relative address. .Pp .Bl -tag -width Ds .It ASSEMBLER-INTERNAL-LOGIC-ERROR! An internal assembler logic error has been found. This means there is a bug in the assembler. .Pp .It 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. .El .Pp .Ss 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. .Xr as allows you to use .Em 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 .Li .text 0 before each section of code being output, and a .Li .text 1 before each group of constants being output. .Pp Subsections are optional. If you do not use subsections, everything goes in subsection number zero. .Pp 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; .Li 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. .Pp To specify which subsection you want subsequent statements assembled into, use a numeric argument to specify it, in a .Li .text Va expression or a .Li .data Va expression statement. You can also use the .Li .subsection directive (see Section .Dq SubSection ) to specify a subsection: .Li .subsection Va expression . .Va Expression should be an absolute expression (see Section .Dq Expressions ) . If you just say .Li .text then .Li .text 0 is assumed. Likewise .Li .data means .Li .data 0 . Assembly begins in .Li text 0 . For instance: .Bd -literal -offset indent \&.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 (*)." .Ed .Pp Each section has a .Em location counter incremented by one for every byte assembled into that section. Because subsections are merely a convenience restricted to .Xr as there is no concept of a subsection location counter. There is no way to directly manipulate a location counter---but the .Li .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 .Em active location counter. .Pp .Ss 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. .Pp The .Li .lcomm pseudo-op defines a symbol in the bss section; see Lcomm,, .Li .lcomm \&. .Pp The .Li .comm pseudo-op may be used to declare a common symbol, which is another form of uninitialized symbol; see Comm,, .Li .comm \&. .Pp .Sh 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. .Pp .Qo .Em Warning: .Xr as does not place symbols in the object file in the same order they were declared. This may break some debuggers. .Qc .Pp .Ss Labels A .Em label is written as a symbol immediately followed by a colon .Li : . 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. .Pp .Ss Giving Symbols Other Values A symbol can be given an arbitrary value by writing a symbol, followed by an equals sign .Li = , followed by an expression (see Section .Dq Expressions ) . This is equivalent to using the .Li .set directive.See Section .Dq Set . In the same way, using a double equals sign .Li = .Li = here represents an equivalent of the .Li .eqv directive.See Section .Dq Eqv . .Pp .Ss Symbol Names Symbol names begin with a letter or with one of .Li ._ . On most machines, you can also use .Li $ in symbol names; exceptions are noted in 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. .Pp Case of letters is significant: .Li foo is a different symbol name than .Li Foo . .Pp 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. .Pp .Em Local Symbol Names .Pp A local symbol is any symbol beginning with certain local label prefixes. By default, the local label prefix is .Li .L for ELF systems or .Li L for traditional a.out systems, but each target may have its own set of local label prefixes. .Pp 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 .Li -L option (see Section .Dq L ) to retain the local symbols in the object files. .Pp .Em Local Labels .Pp 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 .Li Sy N: (where .Sy N represents any positive integer). To refer to the most recent previous definition of that label write .Li Sy Nb , using the same number as when you defined the label. To refer to the next definition of a local label, write .Li Sy Nf ---the .Li b stands for \(lqbackwards\(rq and the .Li f stands for \(lqforwards\(rq. .Pp 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 .Li Sy 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 ( .Li Sy 0: \&....Li Sy 9: ) are implemented in a slightly more efficient manner than the others. .Pp Here is an example: .Pp .Bd -literal -offset indent 1: branch 1f 2: branch 1b 1: branch 2f 2: branch 1b .Ed .Pp Which is the equivalent of: .Pp .Bd -literal -offset indent label_1: branch label_3 label_2: branch label_1 label_3: branch label_4 label_4: branch label_3 .Ed .Pp 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: .Pp .Bl -tag -width Ds .It Em local label prefix All local symbols begin with the system-specific local label prefix. Normally both .Xr as and .Li 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 .Li -L option then .Xr as retains these symbols in the object file. If you also instruct .Li ld to retain these symbols, you may use them in debugging. .Pp .It Va number This is the number that was used in the local label definition. So if the label is written .Li 55: then the number is .Li 55 . .Pp .It Li 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 .Li \e002 (control-B). .Pp .It Em ordinal number This is a serial number to keep the labels distinct. The first definition of .Li 0: gets the number .Li 1 . The 15th definition of .Li 0: gets the number .Li 15 , and so on. Likewise the first definition of .Li 1: gets the number .Li 1 and its 15th definition gets .Li 15 as well. .El .Pp So for example, the first .Li 1: may be named .Li .L1 Li C-B1 , and the 44th .Li 3: may be named .Li .L3 Li C-B44 . .Pp .Em Dollar Local Labels .Pp .Li 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. .Pp 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., .Li Sy 55$ . .Pp They can also be distinguished from ordinary local labels by their transformed names which use ASCII character .Li \e001 (control-A) as the magic character to distinguish them from ordinary labels. For example, the fifth definition of .Li 6$ may be named .Li .L6 Li C-A5 . .Pp .Ss The Special Dot Symbol The special symbol .Li . refers to the current address that .Xr as is assembling into. Thus, the expression .Li melvin: .long . defines .Li melvin to contain its own address. Assigning a value to .Li . is treated the same as a .Li .org directive. Thus, the expression .Li .=.+4 is the same as saying .Li .space 4 . .Pp .Ss Symbol Attributes Every symbol has, as well as its name, the attributes \(lqValue\(rq and \(lqType\(rq. Depending on output format, symbols can also have auxiliary attributes. The detailed definitions are in .Pa a.out.h . .Pp If you use a symbol without defining it, .Xr 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. .Pp .Em Value .Pp 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 .Li ld changes section base addresses during linking. Absolute symbols' values do not change during linking: that is why they are called absolute. .Pp 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 .Li 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 .Li .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. .Pp .Em Type .Pp 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. .Pp .Sh Expressions An .Em expression specifies an address or numeric value. Whitespace may precede and/or follow an expression. .Pp 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 .Xr 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. .Xr as aborts with an error message in this situation. .Pp .Ss 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 .Xr as assumes a value of (absolute) 0. This is compatible with other assemblers. .Pp .Ss Integer Expressions An .Em integer expression is one or more .Em arguments delimited by .Em operators . .Pp .Em Arguments .Pp .Em Arguments are symbols, numbers or subexpressions. In other contexts arguments are sometimes called \(lqarithmetic operands\(rq. In this manual, to avoid confusing them with the \(lqinstruction operands\(rq of the machine language, we use the term \(lqargument\(rq to refer to parts of expressions only, reserving the word \(lqoperand\(rq to refer only to machine instruction operands. .Pp Symbols are evaluated to yield { .Va section .Va NNN }where .Va section is one of text, data, bss, absolute, or undefined. .Va NNN is a signed, 2's complement 32 bit integer. .Pp Numbers are usually integers. .Pp A number can be a flonum or biGNUm. In this case, you are warned that only the low order 32 bits are used, and .Xr as pretends these 32 bits are an integer. You may write integer-manipulating instructions that act on exotic constants, compatible with other assemblers. .Pp Subexpressions are a left parenthesis .Li ( followed by an integer expression, followed by a right parenthesis .Li ) ; or a prefix operator followed by an argument. .Pp .Em Operators .Pp .Em Operators are arithmetic functions, like .Li + or .Li % . Prefix operators are followed by an argument. Infix operators appear between their arguments. Operators may be preceded and/or followed by whitespace. .Pp .Em Prefix Operator .Pp .Xr as has the following .Em prefix operators . They each take one argument, which must be absolute. .Pp .Bl -tag -width Ds .It - .Em Negation . Two's complement negation. .It ~ .Em Complementation . Bitwise not. .El .Pp .Em Infix Operators .Pp .Em Infix operators take two arguments, one on either side. Operators have precedence, but operations with equal precedence are performed left to right. Apart from .Li + or .Op - , both arguments must be absolute, and the result is absolute. .Pp .Bl -enum .It Highest Precedence .Pp .Bl -tag -width Ds .It * .Em Multiplication . .Pp .It / .Em Division . Truncation is the same as the C operator .Li / .Pp .It % .Em Remainder . .Pp .It << .Em Shift Left . Same as the C operator .Li << . .Pp .It >> .Em Shift Right . Same as the C operator .Li >> . .El .Pp .It Intermediate precedence .Pp .Bl -tag -width Ds .It | .Pp .Em Bitwise Inclusive Or . .Pp .It & .Em Bitwise And . .Pp .It ^ .Em Bitwise Exclusive Or . .Pp .It ! .Em Bitwise Or Not . .El .Pp .It Low Precedence .Pp .Bl -tag -width Ds .It + .Em Addition . If either argument is absolute, the result has the section of the other argument. You may not add together arguments from different sections. .Pp .It - .Em 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. .Pp .It == .Em Is Equal To .It <> .It != .Em Is Not Equal To .It < .Em Is Less Than .It > .Em Is Greater Than .It >= .Em Is Greater Than Or Equal To .It <= .Em Is Less Than Or Equal To .Pp 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. .El .Pp .It Lowest Precedence .Pp .Bl -tag -width Ds .It && .Em Logical And . .Pp .It || .Em Logical Or . .Pp 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. .Pp .El .El In short, it's only meaningful to add or subtract the .Em offsets in an address; you can only have a defined section in one of the two arguments. .Pp .Sh Assembler Directives All assembler directives have names that begin with a period ( .Li . ) . The rest of the name is letters, usually in lower case. .Pp This chapter discusses directives that are available regardless of the target machine configuration for the GNU assembler. .Pp .Ss Li .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 .Xr as to quit also. One day .Li .abort will not be supported. .Pp .Ss Li .align Va abs-expr, Va abs-expr, Va 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. .Pp 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. .Pp 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. .Pp 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 .Li .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. .Pp 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 .Li .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. .Pp This inconsistency is due to the different behaviors of the various native assemblers for these systems which GAS must emulate. GAS also provides .Li .balign and .Li .p2align directives, described later, which have a consistent behavior across all architectures (but are specific to GAS). .Pp .Ss Li .ascii " Va string"... .Li .ascii expects zero or more string literals (see Section .Dq Strings ) separated by commas. It assembles each string (with no automatic trailing zero byte) into consecutive addresses. .Pp .Ss Li .asciz " Va string"... .Li .asciz is just like .Li .ascii , but each string is followed by a zero byte. The \(lqz\(rq in .Li .asciz stands for \(lqzero\(rq. .Pp .Ss Li .balign[wl] Va abs-expr, Va abs-expr, Va 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 .Li .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. .Pp 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. .Pp 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. .Pp The .Li .balignw and .Li .balignl directives are variants of the .Li .balign directive. The .Li .balignw directive treats the fill pattern as a two byte word value. The .Li .balignl directives treats the fill pattern as a four byte longword value. For example, .Li .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. .Pp .Ss Li .byte Va expressions .Li .byte expects zero or more expressions, separated by commas. Each expression is assembled into the next byte. .Pp .Ss Li .comm Va symbol , Va length .Li .comm declares a common symbol named .Va 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 .Li ld does not see a definition for the symbol--just one or more common symbols--then it will allocate .Va length bytes of uninitialized memory. .Va length must be an absolute expression. If .Li 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. .Pp When using ELF, the .Li .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 .Li ld allocates uninitialized memory for the common symbol, it will use the alignment when placing the symbol. If no alignment is specified, .Xr 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. .Pp .Ss Li .cfi_startproc [simple] .Li .cfi_startproc is used at the beginning of each function that should have an entry in .Li .eh_frame . It initializes some internal data structures. Don't forget to close the function by .Li .cfi_endproc . .Pp Unless .Li .cfi_startproc is used along with parameter .Li simple it also emits some architecture dependent initial CFI instructions. .Ss Li .cfi_endproc .Li .cfi_endproc is used at the end of a function where it closes its unwind entry previously opened by .Li .cfi_startproc , and emits it to .Li .eh_frame . .Pp .Ss Li .cfi_personality Va encoding [, Va exp] .Li .cfi_personality defines personality routine and its encoding. .Va encoding must be a constant determining how the personality should be encoded. If it is 255 ( .Li 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 .Li .cfi_startproc is .Li .cfi_personality 0xff , no personality routine. .Pp .Ss Li .cfi_lsda Va encoding [, Va exp] .Li .cfi_lsda defines LSDA and its encoding. .Va encoding must be a constant determining how the LSDA should be encoded. If it is 255 ( .Li DW_EH_PE_omit ) , second argument is not present, otherwise second argument should be a constant or a symbol name. The default after .Li .cfi_startproc is .Li .cfi_lsda 0xff , no LSDA. .Pp .Ss Li .cfi_def_cfa Va register, Va offset .Li .cfi_def_cfa defines a rule for computing CFA as: .Em take address from Va register and add Va offset to it . .Pp .Ss Li .cfi_def_cfa_register Va register .Li .cfi_def_cfa_register modifies a rule for computing CFA. From now on .Va register will be used instead of the old one. Offset remains the same. .Pp .Ss Li .cfi_def_cfa_offset Va offset .Li .cfi_def_cfa_offset modifies a rule for computing CFA. Register remains the same, but .Va offset is new. Note that it is the absolute offset that will be added to a defined register to compute CFA address. .Pp .Ss Li .cfi_adjust_cfa_offset Va offset Same as .Li .cfi_def_cfa_offset but .Va offset is a relative value that is added/substracted from the previous offset. .Pp .Ss Li .cfi_offset Va register, Va offset Previous value of .Va register is saved at offset .Va offset from CFA. .Pp .Ss Li .cfi_rel_offset Va register, Va offset Previous value of .Va register is saved at offset .Va offset from the current CFA register. This is transformed to .Li .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. .Pp .Ss Li .cfi_register Va register1, Va register2 Previous value of .Va register1 is saved in register .Va register2 . .Pp .Ss Li .cfi_restore Va register .Li .cfi_restore says that the rule for .Va register is now the same as it was at the beginning of the function, after all initial instruction added by .Li .cfi_startproc were executed. .Pp .Ss Li .cfi_undefined Va register From now on the previous value of .Va register can't be restored anymore. .Pp .Ss Li .cfi_same_value Va register Current value of .Va register is the same like in the previous frame, i.e. no restoration needed. .Pp .Ss Li .cfi_remember_state, First save all current rules for all registers by .Li .cfi_remember_state , then totally screw them up by subsequent .Li .cfi_* directives and when everything is hopelessly bad, use .Li .cfi_restore_state to restore the previous saved state. .Pp .Ss Li .cfi_return_column Va register Change return column .Va register , i.e. the return address is either directly in .Va register or can be accessed by rules for .Va register . .Pp .Ss Li .cfi_signal_frame Mark current function as signal trampoline. .Pp .Ss Li .cfi_window_save SPARC register window has been saved. .Pp .Ss Li .cfi_escape Va 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. .Pp .Ss Li .file Va fileno Va filename When emitting dwarf2 line number information .Li .file assigns filenames to the .Li .debug_line file name table. The .Va fileno operand should be a unique positive integer to use as the index of the entry in the table. The .Va filename operand is a C string literal. .Pp The detail of filename indices is exposed to the user because the filename table is shared with the .Li .debug_info section of the dwarf2 debugging information, and thus the user must know the exact indices that table entries will have. .Pp .Ss Li .loc Va fileno Va lineno [ Va column] [ Va options] The .Li .loc directive will add row to the .Li .debug_line line number matrix corresponding to the immediately following assembly instruction. The .Va fileno , .Va lineno , and optional .Va column arguments will be applied to the .Li .debug_line state machine before the row is added. .Pp The .Va options are a sequence of the following tokens in any order: .Pp .Bl -tag -width Ds .It basic_block This option will set the .Li basic_block register in the .Li .debug_line state machine to .Li true . .Pp .It prologue_end This option will set the .Li prologue_end register in the .Li .debug_line state machine to .Li true . .Pp .It epilogue_begin This option will set the .Li epilogue_begin register in the .Li .debug_line state machine to .Li true . .Pp .It is_stmt Va value This option will set the .Li is_stmt register in the .Li .debug_line state machine to .Li value , which must be either 0 or 1. .Pp .It isa Va value This directive will set the .Li isa register in the .Li .debug_line state machine to .Va value , which must be an unsigned integer. .Pp .El .Ss Li .loc_mark_blocks Va enable The .Li .loc_mark_blocks directive makes the assembler emit an entry to the .Li .debug_line line number matrix with the .Li basic_block register in the state machine set whenever a code label is seen. The .Va enable argument should be either 1 or 0, to enable or disable this function respectively. .Pp .Ss Li .data Va subsection .Li .data tells .Xr as to assemble the following statements onto the end of the data subsection numbered .Va subsection (which is an absolute expression). If .Va subsection is omitted, it defaults to zero. .Pp .Ss Li .double Va flonums .Li .double expects zero or more flonums, separated by commas. It assembles floating point numbers. .Pp .Ss Li .eject Force a page break at this point, when generating assembly listings. .Pp .Ss Li .else .Li .else is part of the .Xr as support for conditional assembly; see If,, .Li .if \&. It marks the beginning of a section of code to be assembled if the condition for the preceding .Li .if was false. .Pp .Ss Li .elseif .Li .elseif is part of the .Xr as support for conditional assembly; see If,, .Li .if \&. It is shorthand for beginning a new .Li .if block that would otherwise fill the entire .Li .else section. .Pp .Ss Li .end .Li .end marks the end of the assembly file. .Xr as does not process anything in the file past the .Li .end directive. .Pp .Ss Li .endfunc .Li .endfunc marks the end of a function specified with .Li .func . .Pp .Ss Li .endif .Li .endif is part of the .Xr as support for conditional assembly; it marks the end of a block of code that is only assembled conditionally.See Section .Dq If . .Pp .Ss Li .equ Va symbol, Va expression This directive sets the value of .Va symbol to .Va expression . It is synonymous with .Li .set ; see Set,, .Li .set \&. .Pp .Ss Li .equiv Va symbol, Va expression The .Li .equiv directive is like .Li .equ and .Li .set , except that the assembler will signal an error if .Va symbol is already defined. Note a symbol which has been referenced but not actually defined is considered to be undefined. .Pp Except for the contents of the error message, this is roughly equivalent to .Bd -literal -offset indent \&.ifdef SYM \&.err \&.endif \&.equ SYM,VAL .Ed plus it protects the symbol from later redefinition. .Pp .Ss Li .eqv Va symbol, Va expression The .Li .eqv directive is like .Li .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. .Pp .Ss Li .err If .Xr as assembles a .Li .err directive, it will print an error message and, unless the .Op -Z option was used, it will not generate an object file. This can be used to signal an error in conditionally compiled code. .Pp .Ss Li .error " Va string" Similarly to .Li .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 .Li ".error directive invoked in source file" . See Section.Dq Errors . .Pp .Bd -literal -offset indent .error "This code has not been assembled and tested." .Ed .Pp .Ss Li .exitm Exit early from the current macro definition.See Section .Dq Macro . .Pp .Ss Li .extern .Li .extern is accepted in the source program---for compatibility with other assemblers---but it is ignored. .Xr as treats all undefined symbols as external. .Pp .Ss Li .fail Va expression Generates an error or a warning. If the value of the .Va expression is 500 or more, .Xr as will print a warning message. If the value is less than 500, .Xr as will print an error message. The message will include the value of .Va expression . This can occasionally be useful inside complex nested macros or conditional assembly. .Pp .Ss Li .file Va string .Li .file tells .Xr as that we are about to start a new logical file. .Va string is the new file name. In general, the filename is recognized whether or not it is surrounded by quotes .Li " ; but if you wish to specify an empty file name, you must give the quotes-- .Li "" . This statement may go away in future: it is only recognized to be compatible with old .Xr as programs. .Pp .Ss Li .fill Va repeat , Va size , Va value .Va repeat , .Va size and .Va value are absolute expressions. This emits .Va repeat copies of .Va size bytes. .Va Repeat may be zero or more. .Va 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 .Va repeat bytes is taken from an 8-byte number. The highest order 4 bytes are zero. The lowest order 4 bytes are .Va value rendered in the byte-order of an integer on the computer .Xr as is assembling for. Each .Va size bytes in a repetition is taken from the lowest order .Va size bytes of this number. Again, this bizarre behavior is compatible with other people's assemblers. .Pp .Va size and .Va value are optional. If the second comma and .Va value are absent, .Va value is assumed zero. If the first comma and following tokens are absent, .Va size is assumed to be 1. .Pp .Ss Li .float Va flonums This directive assembles zero or more flonums, separated by commas. It has the same effect as .Li .single . .Pp .Ss Li .func Va name[, Va label] .Li .func emits debugging information to denote function .Va name , and is ignored unless the file is assembled with debugging enabled. Only .Li --gstabs[+] is currently supported. .Va label is the entry point of the function and if omitted .Va name prepended with the .Li leading char is used. .Li leading char is usually .Li _ or nothing, depending on the target. All functions are currently defined to have .Li void return type. The function must be terminated with .Li .endfunc . .Pp .Ss Li .global Va symbol, Li .globl Va symbol .Li .global makes the symbol visible to .Li ld . If you define .Va symbol in your partial program, its value is made available to other partial programs that are linked with it. Otherwise, .Va symbol takes its attributes from a symbol of the same name from another file linked into the same program. .Pp Both spellings ( .Li .globl and .Li .global ) are accepted, for compatibility with other assemblers. .Pp .Ss Li .hidden Va names This is one of the ELF visibility directives. The other two are .Li .internal (see Section .Dq Internal ) and .Li .protected (see Section .Dq Protected ) . .Pp This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to .Li hidden which means that the symbols are not visible to other components. Such symbols are always considered to be .Li protected as well. .Pp .Ss Li .hword Va expressions This expects zero or more .Va expressions , and emits a 16 bit number for each. .Pp This directive is a synonym for .Li .short . .Pp .Ss Li .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, .Xr 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 .Li .comment or .Li .rdata section, depending on the target. When using ELF, comments are emitted to the .Li .comment section. .Pp .Ss Li .if Va absolute expression .Li .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 .Va absolute expression ) is non-zero. The end of the conditional section of code must be marked by .Li .endif (see Section .Dq Endif ) ; optionally, you may include code for the alternative condition, flagged by .Li .else (see Section .Dq Else ) . If you have several conditions to check, .Li .elseif may be used to avoid nesting blocks if/else within each subsequent .Li .else block. .Pp The following variants of .Li .if are also supported: .Bl -tag -width Ds .It .ifdef Va symbol Assembles the following section of code if the specified .Va symbol has been defined. Note a symbol which has been referenced but not yet defined is considered to be undefined. .Pp .It .ifb Va text Assembles the following section of code if the operand is blank (empty). .Pp .It .ifc Va string1, Va 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. .Pp .It .ifeq Va absolute expression Assembles the following section of code if the argument is zero. .Pp .It .ifeqs Va string1, Va string2 Another form of .Li .ifc . The strings must be quoted using double quotes. .Pp .It .ifge Va absolute expression Assembles the following section of code if the argument is greater than or equal to zero. .Pp .It .ifgt Va absolute expression Assembles the following section of code if the argument is greater than zero. .Pp .It .ifle Va absolute expression Assembles the following section of code if the argument is less than or equal to zero. .Pp .It .iflt Va absolute expression Assembles the following section of code if the argument is less than zero. .Pp .It .ifnb Va text Like .Li .ifb , but the sense of the test is reversed: this assembles the following section of code if the operand is non-blank (non-empty). .Pp .It .ifnc Va string1, Va string2. Like .Li .ifc , but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same. .Pp .It .ifndef Va symbol .It .ifnotdef Va symbol Assembles the following section of code if the specified .Va 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. .Pp .It .ifne Va absolute expression Assembles the following section of code if the argument is not equal to zero (in other words, this is equivalent to .Li .if ) . .Pp .It .ifnes Va string1, Va string2 Like .Li .ifeqs , but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same. .El .Pp .Ss Li .incbin " Va file"[, Va skip[, Va count]] The .Li incbin directive includes .Va file verbatim at the current location. You can control the search paths used with the .Li -I command-line option (see Section .Dq Invoking ) . Quotation marks are required around .Va file . .Pp The .Va skip argument skips a number of bytes from the start of the .Va file . The .Va 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 .Li incbin directive. .Pp .Ss Li .include " Va file" This directive provides a way to include supporting files at specified points in your source program. The code from .Va file is assembled as if it followed the point of the .Li .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 .Li -I command-line option (see Section .Dq Invoking ) . Quotation marks are required around .Va file . .Pp .Ss Li .int Va expressions Expect zero or more .Va 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. .Pp .Ss Li .internal Va names This is one of the ELF visibility directives. The other two are .Li .hidden (see Section .Dq Hidden ) and .Li .protected (see Section .Dq Protected ) . .Pp This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to .Li internal which means that the symbols are considered to be .Li hidden (i.e., not visible to other components), and that some extra, processor specific processing must also be performed upon the symbols as well. .Pp .Ss Li .irp Va symbol, Va values... Evaluate a sequence of statements assigning different values to .Va symbol . The sequence of statements starts at the .Li .irp directive, and is terminated by an .Li .endr directive. For each .Va value , .Va symbol is set to .Va value , and the sequence of statements is assembled. If no .Va value is listed, the sequence of statements is assembled once, with .Va symbol set to the null string. To refer to .Va symbol within the sequence of statements, use .Va \esymbol . .Pp For example, assembling .Pp .Bd -literal -offset indent .irp param,1,2,3 move d\eparam,sp@- .endr .Ed .Pp is equivalent to assembling .Pp .Bd -literal -offset indent move d1,sp@- move d2,sp@- move d3,sp@- .Ed .Pp For some caveats with the spelling of .Va symbol , see also Macro. .Pp .Ss Li .irpc Va symbol, Va values... Evaluate a sequence of statements assigning different values to .Va symbol . The sequence of statements starts at the .Li .irpc directive, and is terminated by an .Li .endr directive. For each character in .Va value , .Va symbol is set to the character, and the sequence of statements is assembled. If no .Va value is listed, the sequence of statements is assembled once, with .Va symbol set to the null string. To refer to .Va symbol within the sequence of statements, use .Va \esymbol . .Pp For example, assembling .Pp .Bd -literal -offset indent .irpc param,123 move d\eparam,sp@- .endr .Ed .Pp is equivalent to assembling .Pp .Bd -literal -offset indent move d1,sp@- move d2,sp@- move d3,sp@- .Ed .Pp For some caveats with the spelling of .Va symbol , see also the discussion atSee Section .Dq Macro . .Pp .Ss Li .lcomm Va symbol , Va length Reserve .Va length (an absolute expression) bytes for a local common denoted by .Va symbol . The section and value of .Va 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. .Va Symbol is not declared global (see Section .Dq Global ) , so is normally not visible to .Li ld . .Pp .Ss Li .lflags .Xr as accepts this directive, for compatibility with other assemblers, but ignores it. .Pp .Ss Li .line Va line-number Even though this is a directive associated with the .Li a.out or .Li b.out object-code formats, .Xr as still recognizes it when producing COFF output, and treats .Li .line as though it were the COFF .Li .ln .Em if it is found outside a .Li .def / .Li .endef pair. .Pp Inside a .Li .def , .Li .line is, instead, one of the directives used by compilers to generate auxiliary symbol information for debugging. .Pp .Ss Li .linkonce [ Va 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 .Li .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. .Pp 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. .Pp The .Va type argument is optional. If specified, it must be one of the following strings. For example: .Bd -literal -offset indent \&.linkonce same_size .Ed Not all types may be supported on all object file formats. .Pp .Bl -tag -width Ds .It discard Silently discard duplicate sections. This is the default. .Pp .It one_only Warn if there are duplicate sections, but still keep only one copy. .Pp .It same_size Warn if any of the duplicates have different sizes. .Pp .It same_contents Warn if any of the duplicates do not have exactly the same contents. .El .Pp .Ss Li .ln Va line-number .Li .ln is a synonym for .Li .line . .Pp .Ss Li .mri Va val If .Va val is non-zero, this tells .Xr as to enter MRI mode. If .Va val is zero, this tells .Xr as to exit MRI mode. This change affects code assembled until the next .Li .mri directive, or until the end of the file.See Section .Dq M . .Pp .Ss Li .list Control (in conjunction with the .Li .nolist directive) whether or not assembly listings are generated. These two directives maintain an internal counter (which is zero initially). .Li .list increments the counter, and .Li .nolist decrements it. Assembly listings are generated whenever the counter is greater than zero. .Pp By default, listings are disabled. When you enable them (with the .Li -a command line option;see Section .Dq Invoking ) , the initial value of the listing counter is one. .Pp .Ss Li .long Va expressions .Li .long is the same as .Li .int . See Section.Dq Int . .Pp .Ss Li .macro The commands .Li .macro and .Li .endm allow you to define macros that generate assembly output. For example, this definition specifies a macro .Li sum that puts a sequence of numbers into memory: .Pp .Bd -literal -offset indent .macro sum from=0, to=5 .long \efrom .if \eto-\efrom sum "(\efrom+1)",\eto .endif .endm .Ed .Pp With that definition, .Li SUM 0,5 is equivalent to this assembly input: .Pp .Bd -literal -offset indent .long 0 .long 1 .long 2 .long 3 .long 4 .long 5 .Ed .Pp .Bl -tag -width Ds .It .macro Va macname .It .macro Va macname Va macargs ... Begin the definition of a macro called .Va 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 .Li : Li req ) , or whether it takes all of the remaining arguments (through .Li : Li vararg ) . You can supply a default value for any macro argument by following the name with .Li = Va deflt . You cannot define two macros with the same .Va macname unless it has been subject to the .Li .purgem directive (see Section .Dq Purgem ) between the two definitions. For example, these are all valid .Li .macro statements: .Pp .Bl -tag -width Ds .It .macro comm Begin the definition of a macro called .Li comm , which takes no arguments. .Pp .It .macro plus1 p, p1 .It .macro plus1 p p1 Either statement begins the definition of a macro called .Li plus1 , which takes two arguments; within the macro definition, write .Li \ep or .Li \ep1 to evaluate the arguments. .Pp .It .macro reserve_str p1=0 p2 Begin the definition of a macro called .Li 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 .Li reserve_str Va a, Va b (with .Li \ep1 evaluating to .Va a and .Li \ep2 evaluating to .Va b ) , or as .Li reserve_str , Va b (with .Li \ep1 evaluating as the default, in this case .Li 0 , and .Li \ep2 evaluating to .Va b ) . .Pp .It .macro m p1:req, p2=0, p3:vararg Begin the definition of a macro called .Li 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. .Pp When you call a macro, you can specify the argument values either by position, or by keyword. For example, .Li sum 9,17 is equivalent to .Li sum to=17, from=9 . .Pp .El Note that since each of the .Va 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 ( .Li : ) 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: .Pp .Bd -literal -offset indent .macro label l \el: .endm .Ed .Pp might not work as expected. Invoking .Li label foo might not create a label called .Li foo but instead just insert the text .Li \el: into the assembler source, probably generating an error about an unrecognised identifier. .Pp Similarly problems might occur with the period character ( .Li . ) 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: .Pp .Bd -literal -offset indent .macro opcode base length \ebase.\elength .endm .Ed .Pp and invoking it as .Li opcode store l will not create a .Li store.l instruction but instead generate some kind of error as the assembler tries to interpret the text .Li \ebase.\elength . .Pp There are several possible ways around this problem: .Pp .Bl -tag -width Ds .It Insert white space If it is possible to use white space characters then this is the simplest solution. eg: .Pp .Bd -literal -offset indent .macro label l \el : .endm .Ed .Pp .It Use Li \e() The string .Li \e() can be used to separate the end of a macro argument from the following text. eg: .Pp .Bd -literal -offset indent .macro opcode base length \ebase\e().\elength .endm .Ed .Pp .It Use the alternate macro syntax mode In the alternative macro syntax mode the ampersand character ( .Li & ) can be used as a separator. eg: .Pp .Bd -literal -offset indent .altmacro .macro label l l&: .endm .Ed .El .Pp Note: this problem of correctly identifying string parameters to pseudo ops also applies to the identifiers used in .Li .irp (see Section .Dq Irp ) and .Li .irpc (see Section .Dq Irpc ) as well. .Pp .It .endm Mark the end of a macro definition. .Pp .It .exitm Exit early from the current macro definition. .Pp .It \e@ .Xr as maintains a counter of how many macros it has executed in this pseudo-variable; you can copy that number to your output with .Li \e@ , but .Em only within a macro definition . .Pp .It LOCAL Va name [ , ... ] .Em Warning: Li LOCAL is only available if you select \(lqalternate macro syntax\(rq with Li --alternate or Li .altmacro. See Section.Dq Altmacro . .El .Pp .Ss Li .altmacro Enable alternate macro mode, enabling: .Pp .Bl -tag -width Ds .It LOCAL Va name [ , ... ] One additional directive, .Li LOCAL , is available. It is used to generate a string replacement for each of the .Va name arguments, and replace any instances of .Va name in each macro expansion. The replacement string is unique in the assembly, and different for each separate macro expansion. .Li LOCAL allows you to write macros that define symbols, without fear of conflict between separate macro expansions. .Pp .It String delimiters You can write strings delimited in these other ways besides .Li " Va string" : .Pp .Bl -tag -width Ds .It ' Va string' You can delimit strings with single-quote characters. .Pp .It < Va string> You can delimit strings with matching angle brackets. .El .Pp .It 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 .Li ! (an exclamation mark). For example, you can write .Li <4.3 !> 5.4!!> to get the literal text .Li 4.3 > 5.4! . .Pp .It Expression results as strings You can write .Li % Va expr to evaluate the expression .Va expr and use the result as a string. .El .Pp .Ss Li .noaltmacro Disable alternate macro mode.See Section .Dq Altmacro . .Pp .Ss Li .nolist Control (in conjunction with the .Li .list directive) whether or not assembly listings are generated. These two directives maintain an internal counter (which is zero initially). .Li .list increments the counter, and .Li .nolist decrements it. Assembly listings are generated whenever the counter is greater than zero. .Pp .Ss Li .octa Va biGNUms This directive expects zero or more biGNUms, separated by commas. For each biGNUm, it emits a 16-byte integer. .Pp The term \(lqocta\(rq comes from contexts in which a \(lqword\(rq is two bytes; hence .Em octa -word for 16 bytes. .Pp .Ss Li .org Va new-lc , Va fill Advance the location counter of the current section to .Va new-lc . .Va new-lc is either an absolute expression or an expression with the same section as the current subsection. That is, you can't use .Li .org to cross sections: if .Va new-lc has the wrong section, the .Li .org directive is ignored. To be compatible with former assemblers, if the section of .Va new-lc is absolute, .Xr as issues a warning, then pretends the section of .Va new-lc is the same as the current subsection. .Pp .Li .org may only increase the location counter, or leave it unchanged; you cannot use .Li .org to move the location counter backwards. .Pp Because .Xr as tries to assemble programs in one pass, .Va new-lc may not be undefined. If you really detest this restriction we eagerly await a chance to share your improved assembler. .Pp 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. .Pp When the location counter (of the current subsection) is advanced, the intervening bytes are filled with .Va fill which should be an absolute expression. If the comma and .Va fill are omitted, .Va fill defaults to zero. .Pp .Ss Li .p2align[wl] Va abs-expr, Va abs-expr, Va 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 .Li .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. .Pp 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. .Pp 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. .Pp The .Li .p2alignw and .Li .p2alignl directives are variants of the .Li .p2align directive. The .Li .p2alignw directive treats the fill pattern as a two byte word value. The .Li .p2alignl directives treats the fill pattern as a four byte longword value. For example, .Li .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. .Pp .Ss Li .previous This is one of the ELF section stack manipulation directives. The others are .Li .section (see Section .Dq Section ) , .Li .subsection (see Section .Dq SubSection ) , .Li .pushsection (see Section .Dq PushSection ) , and .Li .popsection (see Section .Dq PopSection ) . .Pp This directive swaps the current section (and subsection) with most recently referenced section (and subsection) prior to this one. Multiple .Li .previous directives in a row will flip between two sections (and their subsections). .Pp In terms of the section stack, this directive swaps the current section with the top section on the section stack. .Pp .Ss Li .popsection This is one of the ELF section stack manipulation directives. The others are .Li .section (see Section .Dq Section ) , .Li .subsection (see Section .Dq SubSection ) , .Li .pushsection (see Section .Dq PushSection ) , and .Li .previous (see Section .Dq Previous ) . .Pp 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. .Pp .Ss Li .print Va string .Xr as will print .Va string on the standard output during assembly. You must put .Va string in double quotes. .Pp .Ss Li .protected Va names This is one of the ELF visibility directives. The other two are .Li .hidden (see Section .Dq Hidden ) and .Li .internal (see Section .Dq Internal ) . .Pp This directive overrides the named symbols default visibility (which is set by their binding: local, global or weak). The directive sets the visibility to .Li 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. .Pp .Ss Li .psize Va lines , Va columns Use this directive to declare the number of lines---and, optionally, the number of columns---to use for each page, when generating listings. .Pp If you do not use .Li .psize , listings use a default line-count of 60. You may omit the comma and .Va columns specification; the default width is 200 columns. .Pp .Xr as generates formfeeds whenever the specified number of lines is exceeded (or whenever you explicitly request one, using .Li .eject ) . .Pp If you specify .Va lines as .Li 0 , no formfeeds are generated save those explicitly specified with .Li .eject . .Pp .Ss Li .purgem Va name Undefine the macro .Va name , so that later uses of the string will not be expanded.See Section .Dq Macro . .Pp .Ss Li .pushsection Va name , Va subsection This is one of the ELF section stack manipulation directives. The others are .Li .section (see Section .Dq Section ) , .Li .subsection (see Section .Dq SubSection ) , .Li .popsection (see Section .Dq PopSection ) , and .Li .previous (see Section .Dq Previous ) . .Pp This directive pushes the current section (and subsection) onto the top of the section stack, and then replaces the current section and subsection with .Li name and .Li subsection . .Pp .Ss Li .quad Va biGNUms .Li .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. .Pp The term \(lqquad\(rq comes from contexts in which a \(lqword\(rq is two bytes; hence .Em quad -word for 8 bytes. .Pp .Ss Li .reloc Va offset, Va reloc_name[, Va expression] Generate a relocation at .Va offset of type .Va reloc_name with value .Va expression . If .Va offset is a number, the relocation is generated in the current section. If .Va offset is an expression that resolves to a symbol plus offset, the relocation is generated in the given symbol's section. .Va 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. .Pp .Ss Li .rept Va count Repeat the sequence of lines between the .Li .rept directive and the next .Li .endr directive .Va count times. .Pp For example, assembling .Pp .Bd -literal -offset indent .rept 3 .long 0 .endr .Ed .Pp is equivalent to assembling .Pp .Bd -literal -offset indent .long 0 .long 0 .long 0 .Ed .Pp .Ss Li .sbttl " Va subheading" Use .Va subheading as the title (third line, immediately after the title line) when generating assembly listings. .Pp This directive affects subsequent pages, as well as the current page if it appears within ten lines of the top of a page. .Pp .Ss Li .section Va name Use the .Li .section directive to assemble the following code into a section named .Va name . .Pp This directive is only supported for targets that actually support arbitrarily named sections; on .Li a.out targets, for example, it is not accepted, even with a standard .Li a.out section name. .Pp This is one of the ELF section stack manipulation directives. The others are .Li .subsection (see Section .Dq SubSection ) , .Li .pushsection (see Section .Dq PushSection ) , .Li .popsection (see Section .Dq PopSection ) , and .Li .previous (see Section .Dq Previous ) . .Pp For ELF targets, the .Li .section directive is used like this: .Pp .Bd -literal -offset indent \&.section name [, "flags"[, @type[,flag_specific_arguments]]] .Ed .Pp The optional .Va flags argument is a quoted string which may contain any combination of the following characters: .Bl -tag -width Ds .It a section is allocatable .It w section is writable .It x section is executable .It M section is mergeable .It S section contains zero terminated strings .It G section is a member of a section group .It T section is used for thread-local-storage .El .Pp The optional .Va type argument may contain one of the following constants: .Bl -tag -width Ds .It @progbits section contains data .It @nobits section does not contain data (i.e., section only occupies space) .It @note section contains data which is used by things other than the program .It @init_array section contains an array of pointers to init functions .It @fini_array section contains an array of pointers to finish functions .It @preinit_array section contains an array of pointers to pre-init functions .El .Pp Many targets only support the first three section types. .Pp Note on targets where the .Li @ character is the start of a comment (eg ARM) then another character is used instead. For example the ARM port uses the .Li % character. .Pp If .Va flags contains the .Li M symbol then the .Va type argument must be specified as well as an extra argument--- .Va entsize ---like this: .Pp .Bd -literal -offset indent \&.section name , "flags"M, @type, entsize .Ed .Pp Sections with the .Li M flag but not .Li S flag must contain fixed size constants, each .Va entsize octets long. Sections with both .Li M and .Li S must contain zero terminated strings where each character is .Va entsize bytes long. The linker may remove duplicates within sections with the same name, same entity size and same flags. .Va entsize must be an absolute expression. .Pp If .Va flags contains the .Li G symbol then the .Va type argument must be present along with an additional field like this: .Pp .Bd -literal -offset indent \&.section name , "flags"G, @type, GroupName[, linkage] .Ed .Pp The .Va GroupName field specifies the name of the section group to which this particular section belongs. The optional linkage field can contain: .Bl -tag -width Ds .It comdat indicates that only one copy of this section should be retained .It .GNU.linkonce an alias for comdat .El .Pp Note: if both the .Va M and .Va G flags are present then the fields for the Merge flag should come first, like this: .Pp .Bd -literal -offset indent \&.section name , "flags"MG, @type, entsize, GroupName[, linkage] .Ed .Pp 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. .Pp For ELF targets, the assembler supports another type of .Li .section directive for compatibility with the Solaris assembler: .Pp .Bd -literal -offset indent \&.section "name"[, flags...] .Ed .Pp Note that the section name is quoted. There may be a sequence of comma separated flags: .Bl -tag -width Ds .It #alloc section is allocatable .It #write section is writable .It #execinstr section is executable .It #tls section is used for thread local storage .El .Pp This directive replaces the current section and subsection. See the contents of the gas testsuite directory .Li gas/testsuite/gas/elf for some examples of how this directive and the other section stack directives work. .Pp .Ss Li .set Va symbol, Va expression Set the value of .Va symbol to .Va expression . This changes .Va symbol \&'s value and type to conform to .Va expression . If .Va symbol was flagged as external, it remains flagged (see Section .Dq Symbol Attributes ) . .Pp You may .Li .set a symbol many times in the same assembly. .Pp If you .Li .set a global symbol, the value stored in the object file is the last value stored into it. .Pp .Ss Li .short Va expressions This expects zero or more .Va expressions , and emits a 16 bit number for each. .Pp .Ss Li .single Va flonums This directive assembles zero or more flonums, separated by commas. It has the same effect as .Li .float . .Pp .Ss Li .size This directive is used to set the size associated with a symbol. .Pp For ELF targets, the .Li .size directive is used like this: .Pp .Bd -literal -offset indent \&.size name , expression .Ed .Pp This directive sets the size associated with a symbol .Va name . The size in bytes is computed from .Va expression which can make use of label arithmetic. This directive is typically used to set the size of function symbols. .Pp .Ss Li .sleb128 Va expressions .Va sleb128 stands for \(lqsigned little endian base 128.\(rq This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format.See Section .Dq Uleb128 . .Pp .Ss Li .skip Va size , Va fill This directive emits .Va size bytes, each of value .Va fill . Both .Va size and .Va fill are absolute expressions. If the comma and .Va fill are omitted, .Va fill is assumed to be zero. This is the same as .Li .space . .Pp .Ss Li .space Va size , Va fill This directive emits .Va size bytes, each of value .Va fill . Both .Va size and .Va fill are absolute expressions. If the comma and .Va fill are omitted, .Va fill is assumed to be zero. This is the same as .Li .skip . .Pp .Ss Li .stabd, .stabn, .stabs There are three directives that begin .Li .stab . All emit symbols (see Section .Dq Symbols ) , for use by symbolic debuggers. The symbols are not entered in the .Xr as hash table: they cannot be referenced elsewhere in the source file. Up to five fields are required: .Pp .Bl -tag -width Ds .It string This is the symbol's name. It may contain any character except .Li \e000 , so is more general than ordinary symbol names. Some debuggers used to code arbitrarily complex structures into symbol names using this field. .Pp .It type An absolute expression. The symbol's type is set to the low 8 bits of this expression. Any bit pattern is permitted, but .Li ld and debuggers choke on silly bit patterns. .Pp .It other An absolute expression. The symbol's \(lqother\(rq attribute is set to the low 8 bits of this expression. .Pp .It desc An absolute expression. The symbol's descriptor is set to the low 16 bits of this expression. .Pp .It value An absolute expression which becomes the symbol's value. .El .Pp If a warning is detected while reading a .Li .stabd , .Li .stabn , or .Li .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! .Pp .Bl -tag -width Ds .It .stabd Va type , Va other , Va desc .Pp The \(lqname\(rq 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. .Pp 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 .Li .stabd was assembled. .Pp .It .stabn Va type , Va other , Va desc , Va value The name of the symbol is set to the empty string .Li "" . .Pp .It .stabs Va string , Va type , Va other , Va desc , Va value All five fields are specified. .El .Pp .Ss Li .string " Va str" Copy the characters in .Va 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 Strings,,Strings. .Pp .Ss Li .struct Va expression Switch to the absolute section, and set the section offset to .Va expression , which must be an absolute expression. You might use this as follows: .Bd -literal -offset indent .struct 0 field1: .struct field1 + 4 field2: .struct field2 + 4 field3: .Ed This would define the symbol .Li field1 to have the value 0, the symbol .Li field2 to have the value 4, and the symbol .Li field3 to have the value 8. Assembly would be left in the absolute section, and you would need to use a .Li .section directive of some sort to change to some other section before further assembly. .Pp .Ss Li .subsection Va name This is one of the ELF section stack manipulation directives. The others are .Li .section (see Section .Dq Section ) , .Li .pushsection (see Section .Dq PushSection ) , .Li .popsection (see Section .Dq PopSection ) , and .Li .previous (see Section .Dq Previous ) . .Pp This directive replaces the current subsection with .Li 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. .Pp .Ss Li .symver Use the .Li .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. .Pp For ELF targets, the .Li .symver directive can be used like this: .Bd -literal -offset indent \&.symver name, name2@nodename .Ed If the symbol .Va name is defined within the file being assembled, the .Li .symver directive effectively creates a symbol alias with the name .Va name2@nodename , and in fact the main reason that we just don't try and create a regular alias is that the .Va @ character isn't permitted in symbol names. The .Va name2 part of the name is the actual name of the symbol by which it will be externally referenced. The name .Va 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 .Va 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 .Va nodename should correspond to the nodename of the symbol you are trying to override. .Pp If the symbol .Va name is not defined within the file being assembled, all references to .Va name will be changed to .Va name2@nodename . If no reference to .Va name is made, .Va name2@nodename will be removed from the symbol table. .Pp Another usage of the .Li .symver directive is: .Bd -literal -offset indent \&.symver name, name2@@nodename .Ed In this case, the symbol .Va name must exist and be defined within the file being assembled. It is similar to .Va name2@nodename . The difference is .Va name2@@nodename will also be used to resolve references to .Va name2 by the linker. .Pp The third usage of the .Li .symver directive is: .Bd -literal -offset indent \&.symver name, name2@@@nodename .Ed When .Va name is not defined within the file being assembled, it is treated as .Va name2@nodename . When .Va name is defined within the file being assembled, the symbol name, .Va name , will be changed to .Va name2@@nodename . .Pp .Ss Li .text Va subsection Tells .Xr as to assemble the following statements onto the end of the text subsection numbered .Va subsection , which is an absolute expression. If .Va subsection is omitted, subsection number zero is used. .Pp .Ss Li .title " Va heading" Use .Va heading as the title (second line, immediately after the source file name and pagenumber) when generating assembly listings. .Pp This directive affects subsequent pages, as well as the current page if it appears within ten lines of the top of a page. .Pp .Ss Li .type This directive is used to set the type of a symbol. .Pp For ELF targets, the .Li .type directive is used like this: .Pp .Bd -literal -offset indent \&.type name , type description .Ed .Pp This sets the type of symbol .Va name to be either a function symbol or an object symbol. There are five different syntaxes supported for the .Va type description field, in order to provide compatibility with various other assemblers. .Pp Because some of the characters used in these syntaxes (such as .Li @ and .Li # ) 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. .Pp The syntaxes supported are: .Pp .Bd -literal -offset indent .type STT_FUNCTION .type STT_OBJECT .type ,#function .type ,#object .type ,@function .type ,@object .type ,%function .type ,%object .type ,"function" .type ,"object" .Ed .Pp .Ss Li .uleb128 Va expressions .Va uleb128 stands for \(lqunsigned little endian base 128.\(rq This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format.See Section .Dq Sleb128 . .Pp .Ss Li .version " Va string" This directive creates a .Li .note section and places into it an ELF formatted note of type NT_VERSION. The note's name is set to .Li string . .Pp .Ss Li .vtable_entry Va table, Va offset This directive finds or creates a symbol .Li table and creates a .Li VTABLE_ENTRY relocation for it with an addend of .Li offset . .Pp .Ss Li .vtable_inherit Va child, Va parent This directive finds the symbol .Li child and finds or creates the symbol .Li parent and then creates a .Li VTABLE_INHERIT relocation for the parent whose addend is the value of the child symbol. As a special case the parent name of .Li 0 is treated as referring to the .Li *ABS* section. .Pp .Ss Li .warning " Va string" Similar to the directive .Li .error (see Section .Dq Error ) , but just emits a warning. .Pp .Ss Li .weak Va names This directive sets the weak attribute on the comma separated list of symbol .Li names . If the symbols do not already exist, they will be created. .Pp 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 .Li names . If the symbols do not already exist, they will be created. .Pp 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. .Pp .Ss Li .weakref Va alias, Va 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. .Pp 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. .Pp The alias itself never makes to the symbol table, and is entirely handled within the assembler. .Pp .Ss Li .word Va expressions This directive expects zero or more .Va expressions , of any section, separated by commas. For each expression, .Xr as emits a 32-bit number. .Pp .Ss Deprecated Directives One day these directives won't work. They are included for compatibility with older assemblers. .Bl -tag -width Ds .It .abort .It .line .El .Pp .Sh ARM Dependent Features .Ss Options .Bl -tag -width Ds .It -mcpu= Va processor[+ Va 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: .Li arm1 , .Li arm2 , .Li arm250 , .Li arm3 , .Li arm6 , .Li arm60 , .Li arm600 , .Li arm610 , .Li arm620 , .Li arm7 , .Li arm7m , .Li arm7d , .Li arm7dm , .Li arm7di , .Li arm7dmi , .Li arm70 , .Li arm700 , .Li arm700i , .Li arm710 , .Li arm710t , .Li arm720 , .Li arm720t , .Li arm740t , .Li arm710c , .Li arm7100 , .Li arm7500 , .Li arm7500fe , .Li arm7t , .Li arm7tdmi , .Li arm7tdmi-s , .Li arm8 , .Li arm810 , .Li strongarm , .Li strongarm1 , .Li strongarm110 , .Li strongarm1100 , .Li strongarm1110 , .Li arm9 , .Li arm920 , .Li arm920t , .Li arm922t , .Li arm940t , .Li arm9tdmi , .Li arm9e , .Li arm926e , .Li arm926ej-s , .Li arm946e-r0 , .Li arm946e , .Li arm946e-s , .Li arm966e-r0 , .Li arm966e , .Li arm966e-s , .Li arm968e-s , .Li arm10t , .Li arm10tdmi , .Li arm10e , .Li arm1020 , .Li arm1020t , .Li arm1020e , .Li arm1022e , .Li arm1026ej-s , .Li arm1136j-s , .Li arm1136jf-s , .Li arm1156t2-s , .Li arm1156t2f-s , .Li arm1176jz-s , .Li arm1176jzf-s , .Li mpcore , .Li mpcorenovfp , .Li cortex-a8 , .Li cortex-r4 , .Li cortex-m3 , .Li ep9312 (ARM920 with Cirrus Maverick coprocessor), .Li i80200 (Intel XScale processor) .Li iwmmxt (Intel(r) XScale processor with Wireless MMX(tm) technology coprocessor) and .Li xscale . The special name .Li all may be used to allow the assembler to accept instructions valid for any ARM processor. .Pp 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, .Li -mcpu=arm920+maverick is equivalent to specifying .Li -mcpu=ep9312 . The following extensions are currently supported: .Li +maverick .Li +iwmmxt and .Li +xscale . .Pp .It -march= Va architecture[+ Va 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: .Li armv1 , .Li armv2 , .Li armv2a , .Li armv2s , .Li armv3 , .Li armv3m , .Li armv4 , .Li armv4xm , .Li armv4t , .Li armv4txm , .Li armv5 , .Li armv5t , .Li armv5txm , .Li armv5te , .Li armv5texp , .Li armv6 , .Li armv6j , .Li armv6k , .Li armv6z , .Li armv6zk , .Li armv7 , .Li armv7-a , .Li armv7-r , .Li armv7-m , .Li iwmmxt and .Li xscale . If both .Li -mcpu and .Li -march are specified, the assembler will use the setting for .Li -mcpu . .Pp The architecture option can be extended with the same instruction set extension options as the .Li -mcpu option. .Pp .It -mfpu= Va floating-point-format .Pp 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: .Li softfpa , .Li fpe , .Li fpe2 , .Li fpe3 , .Li fpa , .Li fpa10 , .Li fpa11 , .Li arm7500fe , .Li softvfp , .Li softvfp+vfp , .Li vfp , .Li vfp10 , .Li vfp10-r0 , .Li vfp9 , .Li vfpxd , .Li arm1020t , .Li arm1020e , .Li arm1136jf-s and .Li maverick . .Pp In addition to determining which instructions are assembled, this option also affects the way in which the .Li .double assembler directive behaves when assembling little-endian code. .Pp 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. .Pp .It -mthumb This option specifies that the assembler should start assembling Thumb instructions; that is, it should behave as though the file starts with a .Li .code 16 directive. .Pp .It -mthumb-interwork This option specifies that the output generated by the assembler should be marked as supporting interworking. .Pp .It -mapcs Li [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. .Pp .It -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. .Pp .It -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. .Pp .It -mapcs-reentrant This indicates that the reentrant variant of the APCS should be used. This variant supports position independent code. .Pp .It -mfloat-abi= Va 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: .Li soft , .Li softfp and .Li hard . .Pp .It -meabi= Va ver This option specifies which EABI version the produced object files should conform to. The following values are recognized: .Li GNU , .Li 4 and .Li 5 . .Pp .It -EB This option specifies that the output generated by the assembler should be marked as being encoded for a big-endian processor. .Pp .It -EL This option specifies that the output generated by the assembler should be marked as being encoded for a little-endian processor. .Pp .It -k This option specifies that the output of the assembler should be marked as position-independent code (PIC). .Pp .El .Ss Syntax .Em Special Characters .Pp The presence of a .Li @ on a line indicates the start of a comment that extends to the end of the current line. If a .Li # appears as the first character of a line, the whole line is treated as a comment. .Pp The .Li ; character can be used instead of a newline to separate statements. .Pp Either .Li # or .Li $ can be used to indicate immediate operands. .Pp *TODO* Explain about /data modifier on symbols. .Pp .Em Register Names .Pp *TODO* Explain about ARM register naming, and the predefined names. .Pp .Em ARM relocation generation .Pp Specific data relocations can be generated by putting the relocation name in parentheses after the symbol name. For example: .Pp .Bd -literal -offset indent .word foo(TARGET1) .Ed .Pp This will generate an .Li R_ARM_TARGET1 relocation against the symbol .Va foo . The following relocations are supported: .Li GOT , .Li GOTOFF , .Li TARGET1 , .Li TARGET2 , .Li SBREL , .Li TLSGD , .Li TLSLDM , .Li TLSLDO , .Li GOTTPOFF and .Li TPOFF . .Pp For compatibility with older toolchains the assembler also accepts .Li (PLT) after branch targets. This will generate the deprecated .Li R_ARM_PLT32 relocation. .Pp Relocations for .Li MOVW and .Li MOVT instructions can be generated by prefixing the value with .Li #:lower16: and .Li #:upper16 respectively. For example to load the 32-bit address of foo into r0: .Pp .Bd -literal -offset indent MOVW r0, #:lower16:foo MOVT r0, #:upper16:foo .Ed .Pp .Ss Floating Point The ARM family uses ieee floating-point numbers. .Pp .Ss ARM Machine Directives .Bl -tag -width Ds .It .align Va expression [, Va expression] This is the generic .Va .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. .Pp .It Va name .req Va register name This creates an alias for .Va register name called .Va name . For example: .Pp .Bd -literal -offset indent foo .req r0 .Ed .Pp .It .unreq Va alias-name This undefines a register alias which was previously defined using the .Li req , .Li dn or .Li qn directives. For example: .Pp .Bd -literal -offset indent foo .req r0 .unreq foo .Ed .Pp 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. .Pp .It Va name .dn Va register name [ Va .type] [ Va [index]] .It Va name .qn Va register name [ Va .type] [ Va [index]] .Pp The .Li dn and .Li 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. .Pp 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: .Pp .Bd -literal -offset indent x .dn d2.f32 y .dn d3.f32 z .dn d4.f32[1] vmul x,y,z .Ed .Pp This is equivalent to writing the following: .Pp .Bd -literal -offset indent vmul.f32 d2,d3,d4[1] .Ed .Pp Aliases created using .Li dn or .Li qn can be destroyed using .Li unreq . .Pp .It .code Li [16|32] This directive selects the instruction set being generated. The value 16 selects Thumb, with the value 32 selecting ARM. .Pp .It .thumb This performs the same action as .Va .code 16 . .Pp .It .arm This performs the same action as .Va .code 32 . .Pp .It .force_thumb This directive forces the selection of Thumb instructions, even if the target processor does not support those instructions .Pp .It .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 .Li .thumb .Pp This directive is not neccessary when generating EABI objects. On these targets the encoding is implicit when generating Thumb code. .Pp .It .thumb_set This performs the equivalent of a .Li .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 .Li .thumb_func directive does. .Pp .It .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). .Li GAS maintains a separate literal pool for each section and each sub-section. The .Li .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. .Pp Note - older versions of .Li 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. .Pp .It .pool This is a synonym for .ltorg. .Pp .It .unwind_fnstart Marks the start of a function with an unwind table entry. .Pp .It .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. .Pp 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. .Pp .It .cantunwind Prevents unwinding through the current function. No personality routine or exception table data is required or permitted. .Pp .It .personality Va name Sets the personality routine for the current function to .Va name . .Pp .It .personalityindex Va index Sets the personality routine for the current function to the EABI standard routine number .Va index .Pp .It .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 .Li .fnend directive will be added to the exception table entry. .Pp Must be preceded by a .Li .personality or .Li .personalityindex directive. .Pp .It .save Va reglist Generate unwinder annotations to restore the registers in .Va reglist . The format of .Va reglist is the same as the corresponding store-multiple instruction. .Pp .Bd -literal -offset indent .save {r4, r5, r6, lr} stmfd sp!, {r4, r5, r6, lr} .save f4, 2 sfmfd f4, 2, [sp]! .save {d8, d9, d10} fstmdx sp!, {d8, d9, d10} .save {wr10, wr11} wstrd wr11, [sp, #-8]! wstrd wr10, [sp, #-8]! or .save wr11 wstrd wr11, [sp, #-8]! .save wr10 wstrd wr10, [sp, #-8]! .Ed .Pp .It .vsave Va vfp-reglist Generate unwinder annotations to restore the VFP registers in .Va vfp-reglist using FLDMD. Also works for VFPv3 registers that are to be restored using VLDM. The format of .Va vfp-reglist is the same as the corresponding store-multiple instruction. .Pp .Bd -literal -offset indent .vsave {d8, d9, d10} fstmdd sp!, {d8, d9, d10} .vsave {d15, d16, d17} vstm sp!, {d15, d16, d17} .Ed .Pp Since FLDMX and FSTMX are now deprecated, this directive should be used in favour of .Li .save for saving VFP registers for ARMv6 and above. .Pp .It .pad # Va count Generate unwinder annotations for a stack adjustment of .Va count bytes. A positive value indicates the function prologue allocated stack space by decrementing the stack pointer. .Pp .It .movsp Va reg [, # Va offset] Tell the unwinder that .Va reg contains an offset from the current stack pointer. If .Va offset is not specified then it is assumed to be zero. .Pp .It .setfp Va fpreg, Va spreg [, # Va offset] Make all unwinder annotations relaive to a frame pointer. Without this the unwinder will use offsets from the stack pointer. .Pp The syntax of this directive is the same as the .Li sub or .Li mov instruction used to set the frame pointer. .Va spreg must be either .Li sp or mentioned in a previous .Li .movsp directive. .Pp .Bd -literal -offset indent \&.movsp ip mov ip, sp \&... \&.setfp fp, ip, #4 sub fp, ip, #4 .Ed .Pp .It .raw Va offset, Va byte1, ... Insert one of more arbitary unwind opcode bytes, which are known to adjust the stack pointer by .Va offset bytes. .Pp For example .Li .unwind_raw 4, 0xb1, 0x01 is equivalent to .Li .save {r0} .Pp .It .cpu Va name Select the target processor. Valid values for .Va name are the same as for the .Op -mcpu commandline option. .Pp .It .arch Va name Select the target architecture. Valid values for .Va name are the same as for the .Op -march commandline option. .Pp .It .object_arch Va name Override the architecture recorded in the EABI object attribute section. Valid values for .Va name are the same as for the .Li .arch directive. Typically this is useful when code uses runtime detection of CPU features. .Pp .It .fpu Va name Select the floating point unit to assemble for. Valid values for .Va name are the same as for the .Op -mfpu commandline option. .Pp .It .eabi_attribute Va tag, Va value Set the EABI object attribute number .Va tag to .Va value . The value is either a .Li number , .Li "string" , or .Li number, "string" depending on the tag. .Pp .El .Ss Opcodes .Li as implements all the standard ARM opcodes. It also implements several pseudo opcodes, including several synthetic load instructions. .Pp .Bl -tag -width Ds .It NOP .Bd -literal -offset indent nop .Ed .Pp This pseudo op will always evaluate to a legal ARM instruction that does nothing. Currently it will evaluate to MOV r0, r0. .Pp .It LDR .Bd -literal -offset indent ldr , = .Ed .Pp 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. .Pp .It ADR .Bd -literal -offset indent adr