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AS

Section: GNU Development Tools (1)
Updated: 2016-08-03
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NAME

AS - the portable GNU assembler.

SYNOPSIS

as [-a[cdghlns][=file]] [--alternate] [-D]
[--compress-debug-sections] [--nocompress-debug-sections]
[--debug-prefix-map old=new]
[--defsym sym=val] [-f] [-g] [--gstabs]
[--gstabs+] [--gdwarf-2] [--gdwarf-sections]
[--help] [-I dir] [-J]
[-K] [-L] [--listing-lhs-width=NUM]
[--listing-lhs-width2=NUM] [--listing-rhs-width=NUM]
[--listing-cont-lines=NUM] [--keep-locals]
[--no-pad-sections]
[-o objfile] [-R]
[--hash-size=NUM] [--reduce-memory-overheads]
[--statistics]
[-v] [-version] [--version]
[-W] [--warn] [--fatal-warnings] [-w] [-x]
[-Z] [@FILE]
[--sectname-subst] [--size-check=[error|warning]]
[--elf-stt-common=[no|yes]]
[--target-help] [target-options]
[--|files ...]

TARGET

Target AArch64 options:
[-EB|-EL]
[-mabi=ABI]

Target Alpha options:
   [-mcpu]
   [-mdebug | -no-mdebug]
   [-replace | -noreplace]
   [-relax] [-g] [-Gsize]
   [-F] [-32addr]

Target ARM options:
   [-mcpu=processor[+extension...]]
   [-march=architecture[+extension...]]
   [-mfpu=floating-point-format]
   [-mfloat-abi=abi]
   [-meabi=ver]
   [-mthumb]
   [-EB|-EL]
   [-mapcs-32|-mapcs-26|-mapcs-float|
    -mapcs-reentrant]
   [-mthumb-interwork] [-k]

Target Blackfin options:
   [-mcpu=processor[-sirevision]]
   [-mfdpic]
   [-mno-fdpic]
   [-mnopic]

Target D10V options:
[-O]

Target D30V options:
[-O|-n|-N]

Target EPIPHANY options:
[-mepiphany|-mepiphany16]

Target H8/300 options:
[-h-tick-hex]

Target i386 options:
[--32|--x32|--64] [-n]
[-march=CPU[+EXTENSION...]] [-mtune=CPU]

Target i960 options:
   [-ACA|-ACA_A|-ACB|-ACC|-AKA|-AKB|
    -AKC|-AMC]
   [-b] [-no-relax]

Target IP2K options:
[-mip2022|-mip2022ext]

Target M32C options:
[-m32c|-m16c] [-relax] [-h-tick-hex]

Target M32R options:
[--m32rx|--[no-]warn-explicit-parallel-conflicts|
--W[n]p]

Target M680X0 options:
[-l] [-m68000|-m68010|-m68020|...]

Target M68HC11 options:
   [-m68hc11|-m68hc12|-m68hcs12|-mm9s12x|-mm9s12xg]
   [-mshort|-mlong]
   [-mshort-double|-mlong-double]
   [--force-long-branches] [--short-branches]
   [--strict-direct-mode] [--print-insn-syntax]
   [--print-opcodes] [--generate-example]

Target MCORE options:
[-jsri2bsr] [-sifilter] [-relax]
[-mcpu=[210|340]]

Target Meta options:
[-mcpu=cpu] [-mfpu=cpu] [-mdsp=cpu] Target MICROBLAZE options:

Target MIPS options:
   [-nocpp] [-EL] [-EB] [-O[optimization level]]
   [-g[debug level]] [-G num] [-KPIC] [-call_shared]
   [-non_shared] [-xgot [-mvxworks-pic]
   [-mabi=ABI] [-32] [-n32] [-64] [-mfp32] [-mgp32]
   [-mfp64] [-mgp64] [-mfpxx]
   [-modd-spreg] [-mno-odd-spreg]
   [-march=CPU] [-mtune=CPU] [-mips1] [-mips2]
   [-mips3] [-mips4] [-mips5] [-mips32] [-mips32r2]
   [-mips32r3] [-mips32r5] [-mips32r6] [-mips64] [-mips64r2]
   [-mips64r3] [-mips64r5] [-mips64r6]
   [-construct-floats] [-no-construct-floats]
   [-mnan=encoding]
   [-trap] [-no-break] [-break] [-no-trap]
   [-mips16] [-no-mips16]
   [-mmicromips] [-mno-micromips]
   [-msmartmips] [-mno-smartmips]
   [-mips3d] [-no-mips3d]
   [-mdmx] [-no-mdmx]
   [-mdsp] [-mno-dsp]
   [-mdspr2] [-mno-dspr2]
   [-mdspr3] [-mno-dspr3]
   [-mmsa] [-mno-msa]
   [-mxpa] [-mno-xpa]
   [-mmt] [-mno-mt]
   [-mmcu] [-mno-mcu]
   [-minsn32] [-mno-insn32]
   [-mfix7000] [-mno-fix7000]
   [-mfix-rm7000] [-mno-fix-rm7000]
   [-mfix-vr4120] [-mno-fix-vr4120]
   [-mfix-vr4130] [-mno-fix-vr4130]
   [-mdebug] [-no-mdebug]
   [-mpdr] [-mno-pdr]

Target MMIX options:
   [--fixed-special-register-names] [--globalize-symbols]
   [--gnu-syntax] [--relax] [--no-predefined-symbols]
   [--no-expand] [--no-merge-gregs] [-x]
   [--linker-allocated-gregs]

Target Nios II options:
[-relax-all] [-relax-section] [-no-relax]
[-EB] [-EL]

Target NDS32 options:
    [-EL] [-EB] [-O] [-Os] [-mcpu=cpu]
    [-misa=isa] [-mabi=abi] [-mall-ext]
    [-m[no-]16-bit]  [-m[no-]perf-ext] [-m[no-]perf2-ext]
    [-m[no-]string-ext] [-m[no-]dsp-ext] [-m[no-]mac] [-m[no-]div]
    [-m[no-]audio-isa-ext] [-m[no-]fpu-sp-ext] [-m[no-]fpu-dp-ext]
    [-m[no-]fpu-fma] [-mfpu-freg=FREG] [-mreduced-regs]
    [-mfull-regs] [-m[no-]dx-regs] [-mpic] [-mno-relax]
    [-mb2bb]

Target PDP11 options:
   [-mpic|-mno-pic] [-mall] [-mno-extensions]
   [-mextension|-mno-extension]
   [-mcpu] [-mmachine]

Target picoJava options:
[-mb|-me]

Target RL78 options:
[-mg10]
[-m32bit-doubles|-m64bit-doubles]

Target RX options:
   [-mlittle-endian|-mbig-endian]
   [-m32bit-doubles|-m64bit-doubles]
   [-muse-conventional-section-names]
   [-msmall-data-limit]
   [-mpid]
   [-mrelax]
   [-mint-register=number]
   [-mgcc-abi|-mrx-abi]

Target s390 options:
   [-m31|-m64] [-mesa|-mzarch] [-march=CPU]
   [-mregnames|-mno-regnames]
   [-mwarn-areg-zero]

Target SCORE options:
   [-EB][-EL][-FIXDD][-NWARN]
   [-SCORE5][-SCORE5U][-SCORE7][-SCORE3]
   [-march=score7][-march=score3]
   [-USE_R1][-KPIC][-O0][-G num][-V]

Target TIC54X options:
[-mcpu=54[123589]|-mcpu=54[56]lp] [-mfar-mode|-mf]
[-merrors-to-file <filename>|-me <filename>]

Target TILE-Gx options:
[-m32|-m64][-EB][-EL]

Target Visium options:
[-mtune=arch]

Target Xtensa options:
[--[no-]text-section-literals] [--[no-]auto-litpools]
[--[no-]absolute-literals]
[--[no-]target-align] [--[no-]longcalls]
[--[no-]transform]
[--rename-section oldname=newname]
[--[no-]trampolines]

Target Z80 options:
  [-z80] [-r800]
  [ -ignore-undocumented-instructions] [-Wnud]
  [ -ignore-unportable-instructions] [-Wnup]
  [ -warn-undocumented-instructions] [-Wud]
  [ -warn-unportable-instructions] [-Wup]
  [ -forbid-undocumented-instructions] [-Fud]
  [ -forbid-unportable-instructions] [-Fup]

DESCRIPTION

GNU as is really a family of assemblers. If you use (or have used) the GNU assembler on one architecture, you should find a fairly similar environment when you use it on another architecture. Each version has much in common with the others, including object file formats, most assembler directives (often called pseudo-ops) and assembler syntax.

as is primarily intended to assemble the output of the GNU C compiler "gcc" for use by the linker "ld". Nevertheless, we've tried to make as assemble correctly everything that other assemblers for the same machine would assemble. Any exceptions are documented explicitly. This doesn't mean as always uses the same syntax as another assembler for the same architecture; for example, we know of several incompatible versions of 680x0 assembly language syntax.

Each time you run as it assembles exactly one source program. The source program is made up of one or more files. (The standard input is also a file.)

You give as a command line that has zero or more input file names. The input files are read (from left file name to right). A command line argument (in any position) that has no special meaning is taken to be an input file name.

If you give as no file names it attempts to read one input file from the as standard input, which is normally your terminal. You may have to type ctl-D to tell as there is no more program to assemble.

Use -- if you need to explicitly name the standard input file in your command line.

If the source is empty, as produces a small, empty object file.

as may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs as automatically. Warnings report an assumption made so that as could keep assembling a flawed program; errors report a grave problem that stops the assembly.

If you are invoking as via the GNU C compiler, you can use the -Wa option to pass arguments through to the assembler. The assembler arguments must be separated from each other (and the -Wa) by commas. For example:

        gcc -c -g -O -Wa,-alh,-L file.c

This passes two options to the assembler: -alh (emit a listing to standard output with high-level and assembly source) and -L (retain local symbols in the symbol table).

Usually you do not need to use this -Wa mechanism, since many compiler command-line options are automatically passed to the assembler by the compiler. (You can call the GNU compiler driver with the -v option to see precisely what options it passes to each compilation pass, including the assembler.)

OPTIONS

@file

Read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be treated literally, and not removed.

Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively.

-a[cdghlmns]

Turn on listings, in any of a variety of ways:

-ac: omit false conditionals
-ad: omit debugging directives
-ag: include general information, like as version and options passed
-ah: include high-level source
-al: include assembly
-am: include macro expansions
-an: omit forms processing
-as: include symbols
=file: set the name of the listing file

: You may combine these options; for example, use -aln for assembly listing without forms processing. The =file option, if used, must be the last one. By itself, -a defaults to -ahls.

--alternate

Begin in alternate macro mode.

--compress-debug-sections

Compress DWARF debug sections using zlib with SHF_COMPRESSED from the ELF ABI. The resulting object file may not be compatible with older linkers and object file utilities. Note if compression would make a given section larger then it is not compressed.

--compress-debug-sections=none

--compress-debug-sections=zlib

--compress-debug-sections=zlib-gnu

--compress-debug-sections=zlib-gabi

These options control how DWARF debug sections are compressed. --compress-debug-sections=none is equivalent to --nocompress-debug-sections. --compress-debug-sections=zlib and --compress-debug-sections=zlib-gabi are equivalent to --compress-debug-sections. --compress-debug-sections=zlib-gnu compresses DWARF debug sections using zlib. The debug sections are renamed to begin with .zdebug. Note if compression would make a given section larger then it is not compressed nor renamed.

--nocompress-debug-sections

Do not compress DWARF debug sections. This is usually the default for all targets except the x86/x86_64, but a configure time option can be used to override this.

-D

Ignored. This option is accepted for script compatibility with calls to other assemblers.

--debug-prefix-map old=new

When assembling files in directory old, record debugging information describing them as in new instead.

--defsym sym=value

Define the symbol sym to be value before assembling the input file. value must be an integer constant. As in C, a leading 0x indicates a hexadecimal value, and a leading 0 indicates an octal value. The value of the symbol can be overridden inside a source file via the use of a ".set" pseudo-op.

-f

``fast''---skip whitespace and comment preprocessing (assume source is compiler output).

-g

--gen-debug

Generate debugging information for each assembler source line using whichever debug format is preferred by the target. This currently means either STABS, ECOFF or DWARF2.

--gstabs

Generate stabs debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it.

--gstabs+

Generate stabs debugging information for each assembler line, with GNU extensions that probably only gdb can handle, and that could make other debuggers crash or refuse to read your program. This may help debugging assembler code. Currently the only GNU extension is the location of the current working directory at assembling time.

--gdwarf-2

Generate DWARF2 debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it. Note---this option is only supported by some targets, not all of them.

--gdwarf-sections

Instead of creating a .debug_line section, create a series of .debug_line.foo sections where foo is the name of the corresponding code section. For example a code section called .text.func will have its dwarf line number information placed into a section called .debug_line.text.func. If the code section is just called .text then debug line section will still be called just .debug_line without any suffix.

--size-check=error

--size-check=warning

Issue an error or warning for invalid ELF .size directive.

--elf-stt-common=no

--elf-stt-common=yes

These options control whether the ELF assembler should generate common symbols with the "STT_COMMON" type. The default can be controlled by a configure option --enable-elf-stt-common.

--help

Print a summary of the command line options and exit.

--target-help

Print a summary of all target specific options and exit.

-I dir

Add directory dir to the search list for ".include" directives.

-J

Don't warn about signed overflow.

-K

Issue warnings when difference tables altered for long displacements.

-L

--keep-locals

Keep (in the symbol table) local symbols. These symbols start with system-specific local label prefixes, typically .L for ELF systems or L for traditional a.out systems.

--listing-lhs-width=number

Set the maximum width, in words, of the output data column for an assembler listing to number.

--listing-lhs-width2=number

Set the maximum width, in words, of the output data column for continuation lines in an assembler listing to number.

--listing-rhs-width=number

Set the maximum width of an input source line, as displayed in a listing, to number bytes.

--listing-cont-lines=number

Set the maximum number of lines printed in a listing for a single line of input to number + 1.

--no-pad-sections

Stop the assembler for padding the ends of output sections to the alignment of that section. The default is to pad the sections, but this can waste space which might be needed on targets which have tight memory constraints.

-o objfile

Name the object-file output from as objfile.

-R

Fold the data section into the text section.

--hash-size=number

Set the default size of GAS's hash tables to a prime number close to number. Increasing this value can reduce the length of time it takes the assembler to perform its tasks, at the expense of increasing the assembler's memory requirements. Similarly reducing this value can reduce the memory requirements at the expense of speed.

--reduce-memory-overheads

This option reduces GAS's memory requirements, at the expense of making the assembly processes slower. Currently this switch is a synonym for --hash-size=4051, but in the future it may have other effects as well.

--sectname-subst

Honor substitution sequences in section names.

--statistics

Print the maximum space (in bytes) and total time (in seconds) used by assembly.

--strip-local-absolute

Remove local absolute symbols from the outgoing symbol table.

-v

-version

Print the as version.

--version

Print the as version and exit.

-W

--no-warn

Suppress warning messages.

--fatal-warnings

Treat warnings as errors.

--warn

Don't suppress warning messages or treat them as errors.

-w

Ignored.

-x

Ignored.

-Z

Generate an object file even after errors.

-- | files ...

Standard input, or source files to assemble.

The following options are available when as is configured for the 64-bit mode of the ARM Architecture (AArch64).

-EB

This option specifies that the output generated by the assembler should be marked as being encoded for a big-endian processor.

-EL

This option specifies that the output generated by the assembler should be marked as being encoded for a little-endian processor.

-mabi=abi

Specify which ABI the source code uses. The recognized arguments are: "ilp32" and "lp64", which decides the generated object file in ELF32 and ELF64 format respectively. The default is "lp64".

-mcpu=processor[+extension...]

This option specifies the target processor. The assembler will issue an error message if an attempt is made to assemble an instruction which will not execute on the target processor. The following processor names are recognized: "cortex-a35", "cortex-a53", "cortex-a57", "cortex-a72", "cortex-a73", "exynos-m1", "qdf24xx", "thunderx", "vulcan", "xgene1" and "xgene2". The special name "all" may be used to allow the assembler to accept instructions valid for any supported processor, including all optional extensions.

In addition to the basic instruction set, the assembler can be told to accept, or restrict, various extension mnemonics that extend the processor.

If some implementations of a particular processor can have an extension, then then those extensions are automatically enabled. Consequently, you will not normally have to specify any additional extensions.

-march=architecture[+extension...]

This option specifies the target architecture. The assembler will issue an error message if an attempt is made to assemble an instruction which will not execute on the target architecture. The following architecture names are recognized: "armv8-a", "armv8.1-a" and "armv8.2-a".

If both -mcpu and -march are specified, the assembler will use the setting for -mcpu. If neither are specified, the assembler will default to -mcpu=all.

The architecture option can be extended with the same instruction set extension options as the -mcpu option. Unlike -mcpu, extensions are not always enabled by default,

-mverbose-error

This option enables verbose error messages for AArch64 gas. This option is enabled by default.

-mno-verbose-error

This option disables verbose error messages in AArch64 gas.

The following options are available when as is configured for an Alpha processor.

-mcpu

This option specifies the target processor. If an attempt is made to assemble an instruction which will not execute on the target processor, the assembler may either expand the instruction as a macro or issue an error message. This option is equivalent to the ".arch" directive.

The following processor names are recognized: 21064, "21064a", 21066, 21068, 21164, "21164a", "21164pc", 21264, "21264a", "21264b", "ev4", "ev5", "lca45", "ev5", "ev56", "pca56", "ev6", "ev67", "ev68". The special name "all" may be used to allow the assembler to accept instructions valid for any Alpha processor.

In order to support existing practice in OSF/1 with respect to ".arch", and existing practice within MILO (the Linux ARC bootloader), the numbered processor names (e.g. 21064) enable the processor-specific PALcode instructions, while the ``electro-vlasic'' names (e.g. "ev4") do not.

-mdebug

-no-mdebug

Enables or disables the generation of ".mdebug" encapsulation for stabs directives and procedure descriptors. The default is to automatically enable ".mdebug" when the first stabs directive is seen.

-relax

This option forces all relocations to be put into the object file, instead of saving space and resolving some relocations at assembly time. Note that this option does not propagate all symbol arithmetic into the object file, because not all symbol arithmetic can be represented. However, the option can still be useful in specific applications.

-replace

-noreplace

Enables or disables the optimization of procedure calls, both at assemblage and at link time. These options are only available for VMS targets and "-replace" is the default. See section 1.4.1 of the OpenVMS Linker Utility Manual.

-g

This option is used when the compiler generates debug information. When gcc is using mips-tfile to generate debug information for ECOFF, local labels must be passed through to the object file. Otherwise this option has no effect.

-Gsize

A local common symbol larger than size is placed in ".bss", while smaller symbols are placed in ".sbss".

-F

-32addr

These options are ignored for backward compatibility.

The following options are available when as is configured for an ARC processor.

-mcpu=cpu: This option selects the core processor variant.
-EB | -EL: Select either big-endian (-EB) or little-endian (-EL) output.
-mcode-density: Enable Code Density extenssion instructions.

The following options are available when as is configured for the ARM processor family.

-mcpu=processor[+extension...]: Specify which ARM processor variant is the target.
-march=architecture[+extension...]: Specify which ARM architecture variant is used by the target.
-mfpu=floating-point-format: Select which Floating Point architecture is the target.
-mfloat-abi=abi: Select which floating point ABI is in use.
-mthumb: Enable Thumb only instruction decoding.
-mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant: Select which procedure calling convention is in use.
-EB | -EL: Select either big-endian (-EB) or little-endian (-EL) output.
-mthumb-interwork: Specify that the code has been generated with interworking between Thumb and ARM code in mind.
-mccs: Turns on CodeComposer Studio assembly syntax compatibility mode.
-k: Specify that PIC code has been generated.

The following options are available when as is configured for the Blackfin processor family.

-mcpu=processor[-sirevision]: This option specifies the target processor. The optional sirevision is not used in assembler. It's here such that GCC can easily pass down its "-mcpu=" option. 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: "bf504", "bf506", "bf512", "bf514", "bf516", "bf518", "bf522", "bf523", "bf524", "bf525", "bf526", "bf527", "bf531", "bf532", "bf533", "bf534", "bf535" (not implemented yet), "bf536", "bf537", "bf538", "bf539", "bf542", "bf542m", "bf544", "bf544m", "bf547", "bf547m", "bf548", "bf548m", "bf549", "bf549m", "bf561", and "bf592".
-mfdpic: Assemble for the FDPIC ABI.
-mno-fdpic
-mnopic: Disable -mfdpic.

See the info pages for documentation of the CRIS-specific options.

The following options are available when as is configured for a D10V processor.

-O: Optimize output by parallelizing instructions.

The following options are available when as is configured for a D30V processor.

-O: Optimize output by parallelizing instructions.
-n: Warn when nops are generated.
-N: Warn when a nop after a 32-bit multiply instruction is generated.

The following options are available when as is configured for an Epiphany processor.

-mepiphany: Specifies that the both 32 and 16 bit instructions are allowed. This is the default behavior.
-mepiphany16: Restricts the permitted instructions to just the 16 bit set.

The following options are available when as is configured for an H8/300 processor. @chapter H8/300 Dependent Features

Options

The Renesas H8/300 version of "as" has one machine-dependent option:

-h-tick-hex: Support H'00 style hex constants in addition to 0x00 style.
-mach=name: Sets the H8300 machine variant. The following machine names are recognised: "h8300h", "h8300hn", "h8300s", "h8300sn", "h8300sx" and "h8300sxn".

The following options are available when as is configured for an i386 processor.

--32 | --x32 | --64

Select the word size, either 32 bits or 64 bits. --32 implies Intel i386 architecture, while --x32 and --64 imply AMD x86-64 architecture with 32-bit or 64-bit word-size respectively.

These options are only available with the ELF object file format, and require that the necessary BFD support has been included (on a 32-bit platform you have to add --enable-64-bit-bfd to configure enable 64-bit usage and use x86-64 as target platform).

-n

By default, x86 GAS replaces multiple nop instructions used for alignment within code sections with multi-byte nop instructions such as leal 0(%esi,1),%esi. This switch disables the optimization.

--divide

On SVR4-derived platforms, the character / is treated as a comment character, which means that it cannot be used in expressions. The --divide option turns / into a normal character. This does not disable / at the beginning of a line starting a comment, or affect using # for starting a comment.

-march=CPU[+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: "i8086", "i186", "i286", "i386", "i486", "i586", "i686", "pentium", "pentiumpro", "pentiumii", "pentiumiii", "pentium4", "prescott", "nocona", "core", "core2", "corei7", "l1om", "k1om", "iamcu", "k6", "k6_2", "athlon", "opteron", "k8", "amdfam10", "bdver1", "bdver2", "bdver3", "bdver4", "znver1", "btver1", "btver2", "generic32" and "generic64".

In addition to the basic instruction set, the assembler can be told to accept various extension mnemonics. For example, "-march=i686+sse4+vmx" extends i686 with sse4 and vmx. The following extensions are currently supported: 8087, 287, 387, 687, "no87", "no287", "no387", "no687", "mmx", "nommx", "sse", "sse2", "sse3", "ssse3", "sse4.1", "sse4.2", "sse4", "nosse", "nosse2", "nosse3", "nossse3", "nosse4.1", "nosse4.2", "nosse4", "avx", "avx2", "noavx", "noavx2", "adx", "rdseed", "prfchw", "smap", "mpx", "sha", "rdpid", "prefetchwt1", "clflushopt", "se1", "clwb", "pcommit", "avx512f", "avx512cd", "avx512er", "avx512pf", "avx512vl", "avx512bw", "avx512dq", "avx512ifma", "avx512vbmi", "noavx512f", "noavx512cd", "noavx512er", "noavx512pf", "noavx512vl", "noavx512bw", "noavx512dq", "noavx512ifma", "noavx512vbmi", "vmx", "vmfunc", "smx", "xsave", "xsaveopt", "xsavec", "xsaves", "aes", "pclmul", "fsgsbase", "rdrnd", "f16c", "bmi2", "fma", "movbe", "ept", "lzcnt", "hle", "rtm", "invpcid", "clflush", "mwaitx", "clzero", "lwp", "fma4", "xop", "cx16", "syscall", "rdtscp", "3dnow", "3dnowa", "sse4a", "sse5", "svme", "abm" and "padlock". Note that rather than extending a basic instruction set, the extension mnemonics starting with "no" revoke the respective functionality.

When the ".arch" directive is used with -march, the ".arch" directive will take precedent.

-mtune=CPU

This option specifies a processor to optimize for. When used in conjunction with the -march option, only instructions of the processor specified by the -march option will be generated.

Valid CPU values are identical to the processor list of -march=CPU.

-msse2avx

This option specifies that the assembler should encode SSE instructions with VEX prefix.

-msse-check=none

-msse-check=warning

-msse-check=error

These options control if the assembler should check SSE instructions. -msse-check=none will make the assembler not to check SSE instructions, which is the default. -msse-check=warning will make the assembler issue a warning for any SSE instruction. -msse-check=error will make the assembler issue an error for any SSE instruction.

-mavxscalar=128

-mavxscalar=256

These options control how the assembler should encode scalar AVX instructions. -mavxscalar=128 will encode scalar AVX instructions with 128bit vector length, which is the default. -mavxscalar=256 will encode scalar AVX instructions with 256bit vector length.

-mevexlig=128

-mevexlig=256

-mevexlig=512

These options control how the assembler should encode length-ignored (LIG) EVEX instructions. -mevexlig=128 will encode LIG EVEX instructions with 128bit vector length, which is the default. -mevexlig=256 and -mevexlig=512 will encode LIG EVEX instructions with 256bit and 512bit vector length, respectively.

-mevexwig=0

-mevexwig=1

These options control how the assembler should encode w-ignored (WIG) EVEX instructions. -mevexwig=0 will encode WIG EVEX instructions with evex.w = 0, which is the default. -mevexwig=1 will encode WIG EVEX instructions with evex.w = 1.

-mmnemonic=att

-mmnemonic=intel

This option specifies instruction mnemonic for matching instructions. The ".att_mnemonic" and ".intel_mnemonic" directives will take precedent.

-msyntax=att

-msyntax=intel

This option specifies instruction syntax when processing instructions. The ".att_syntax" and ".intel_syntax" directives will take precedent.

-mnaked-reg

This opetion specifies that registers don't require a % prefix. The ".att_syntax" and ".intel_syntax" directives will take precedent.

-madd-bnd-prefix

This option forces the assembler to add BND prefix to all branches, even if such prefix was not explicitly specified in the source code.

-mno-shared

On ELF target, the assembler normally optimizes out non-PLT relocations against defined non-weak global branch targets with default visibility. The -mshared option tells the assembler to generate code which may go into a shared library where all non-weak global branch targets with default visibility can be preempted. The resulting code is slightly bigger. This option only affects the handling of branch instructions.

-mbig-obj

On x86-64 PE/COFF target this option forces the use of big object file format, which allows more than 32768 sections.

-momit-lock-prefix=no

-momit-lock-prefix=yes

These options control how the assembler should encode lock prefix. This option is intended as a workaround for processors, that fail on lock prefix. This option can only be safely used with single-core, single-thread computers -momit-lock-prefix=yes will omit all lock prefixes. -momit-lock-prefix=no will encode lock prefix as usual, which is the default.

-mfence-as-lock-add=no

-mfence-as-lock-add=yes

These options control how the assembler should encode lfence, mfence and sfence. -mfence-as-lock-add=yes will encode lfence, mfence and sfence as lock addl $0x0, (%rsp) in 64-bit mode and lock addl $0x0, (%esp) in 32-bit mode. -mfence-as-lock-add=no will encode lfence, mfence and sfence as usual, which is the default.

-mrelax-relocations=no

-mrelax-relocations=yes

These options control whether the assembler should generate relax relocations, R_386_GOT32X, in 32-bit mode, or R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX, in 64-bit mode. -mrelax-relocations=yes will generate relax relocations. -mrelax-relocations=no will not generate relax relocations. The default can be controlled by a configure option --enable-x86-relax-relocations.

-mevexrcig=rne

-mevexrcig=rd

-mevexrcig=ru

-mevexrcig=rz

These options control how the assembler should encode SAE-only EVEX instructions. -mevexrcig=rne will encode RC bits of EVEX instruction with 00, which is the default. -mevexrcig=rd, -mevexrcig=ru and -mevexrcig=rz will encode SAE-only EVEX instructions with 01, 10 and 11 RC bits, respectively.

-mamd64

-mintel64

This option specifies that the assembler should accept only AMD64 or Intel64 ISA in 64-bit mode. The default is to accept both.

The following options are available when as is configured for the Intel 80960 processor.

-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC: Specify which variant of the 960 architecture is the target.
-b: Add code to collect statistics about branches taken.
-no-relax: Do not alter compare-and-branch instructions for long displacements; error if necessary.

The following options are available when as is configured for the Ubicom IP2K series.

-mip2022ext: Specifies that the extended IP2022 instructions are allowed.
-mip2022: Restores the default behaviour, which restricts the permitted instructions to just the basic IP2022 ones.

The following options are available when as is configured for the Renesas M32C and M16C processors.

-m32c: Assemble M32C instructions.
-m16c: Assemble M16C instructions (the default).
-relax: Enable support for link-time relaxations.
-h-tick-hex: Support H'00 style hex constants in addition to 0x00 style.

The following options are available when as is configured for the Renesas M32R (formerly Mitsubishi M32R) series.

--m32rx: Specify which processor in the M32R family is the target. The default is normally the M32R, but this option changes it to the M32RX.
--warn-explicit-parallel-conflicts or --Wp: Produce warning messages when questionable parallel constructs are encountered.
--no-warn-explicit-parallel-conflicts or --Wnp: Do not produce warning messages when questionable parallel constructs are encountered.

The following options are available when as is configured for the Motorola 68000 series.

-l: Shorten references to undefined symbols, to one word instead of two.
-m68000 | -m68008 | -m68010 | -m68020 | -m68030
| -m68040 | -m68060 | -m68302 | -m68331 | -m68332
| -m68333 | -m68340 | -mcpu32 | -m5200: Specify what processor in the 68000 family is the target. The default is normally the 68020, but this can be changed at configuration time.
-m68881 | -m68882 | -mno-68881 | -mno-68882: The target machine does (or does not) have a floating-point coprocessor. The default is to assume a coprocessor for 68020, 68030, and cpu32. Although the basic 68000 is not compatible with the 68881, a combination of the two can be specified, since it's possible to do emulation of the coprocessor instructions with the main processor.
-m68851 | -mno-68851: The target machine does (or does not) have a memory-management unit coprocessor. The default is to assume an MMU for 68020 and up.

The following options are available when as is configured for an Altera Nios II processor.

-relax-section: Replace identified out-of-range branches with PC-relative "jmp" sequences when possible. The generated code sequences are suitable for use in position-independent code, but there is a practical limit on the extended branch range because of the length of the sequences. This option is the default.
-relax-all: Replace branch instructions not determinable to be in range and all call instructions with "jmp" and "callr" sequences (respectively). This option generates absolute relocations against the target symbols and is not appropriate for position-independent code.
-no-relax: Do not replace any branches or calls.
-EB: Generate big-endian output.
-EL: Generate little-endian output. This is the default.
-march=architecture: This option specifies the target architecture. The assembler issues 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: "r1", "r2". The default is "r1".

The following options are available when as is configured for a Meta processor.

-mcpu=metac11: Generate code for Meta 1.1.
-mcpu=metac12: Generate code for Meta 1.2.
-mcpu=metac21: Generate code for Meta 2.1.
-mfpu=metac21: Allow code to use FPU hardware of Meta 2.1.

See the info pages for documentation of the MMIX-specific options.

The following options are available when as is configured for a NDS32 processor.

-O1

Optimize for performance.

-Os

Optimize for space.

-EL

Produce little endian data output.

-EB

Produce little endian data output.

-mpic

Generate PIC.

-mno-fp-as-gp-relax

Suppress fp-as-gp relaxation for this file.

-mb2bb-relax

Back-to-back branch optimization.

-mno-all-relax

Suppress all relaxation for this file.

-march=<arch name>

Assemble for architecture <arch name> which could be v3, v3j, v3m, v3f, v3s, v2, v2j, v2f, v2s.

-mbaseline=<baseline>

Assemble for baseline <baseline> which could be v2, v3, v3m.

-mfpu-freg=FREG

Specify aFPUconfiguration. 0 8 SP / 4 DP registers 1 16 SP / 8 DP registers 2 32 SP / 16 DP registers 3 32 SP / 32 DP registers

-mabi=abi

Specify a abi version <abi> could be v1, v2, v2fp, v2fpp.

-m[no-]mac

Enable/Disable Multiply instructions support.

-m[no-]div

Enable/Disable Divide instructions support.

-m[no-]16bit-ext

Enable/Disable 16-bit extension

-m[no-]dx-regs

Enable/Disable d0/d1 registers

-m[no-]perf-ext

Enable/Disable Performance extension

-m[no-]perf2-ext

Enable/Disable Performance extension 2

-m[no-]string-ext

Enable/Disable String extension

-m[no-]reduced-regs

Enable/Disable Reduced Register configuration (GPR16) option

-m[no-]audio-isa-ext

Enable/DisableAUDIO ISAextension

-m[no-]fpu-sp-ext

Enable/DisableFPU SPextension

-m[no-]fpu-dp-ext

Enable/DisableFPU DPextension

-m[no-]fpu-fma

Enable/DisableFPUfused-multiply-add instructions

-mall-ext

Turn on all extensions and instructions support

The following options are available when as is configured for a PowerPC processor.

-a32: Generate ELF32 or XCOFF32.
-a64: Generate ELF64 or XCOFF64.
-K PIC: Set EF_PPC_RELOCATABLE_LIB in ELF flags.
-mpwrx | -mpwr2: Generate code for POWER/2 (RIOS2).
-mpwr: Generate code for POWER (RIOS1)
-m601: Generate code for PowerPC 601.
-mppc, -mppc32, -m603, -m604: Generate code for PowerPC 603/604.
-m403, -m405: Generate code for PowerPC 403/405.
-m440: Generate code for PowerPC 440. BookE and some 405 instructions.
-m464: Generate code for PowerPC 464.
-m476: Generate code for PowerPC 476.
-m7400, -m7410, -m7450, -m7455: Generate code for PowerPC 7400/7410/7450/7455.
-m750cl: Generate code for PowerPC 750CL.
-m821, -m850, -m860: Generate code for PowerPC 821/850/860.
-mppc64, -m620: Generate code for PowerPC 620/625/630.
-me500, -me500x2: Generate code for Motorola e500 core complex.
-me500mc: Generate code for Freescale e500mc core complex.
-me500mc64: Generate code for Freescale e500mc64 core complex.
-me5500: Generate code for Freescale e5500 core complex.
-me6500: Generate code for Freescale e6500 core complex.
-mspe: Generate code for Motorola SPE instructions.
-mtitan: Generate code for AppliedMicro Titan core complex.
-mppc64bridge: Generate code for PowerPC 64, including bridge insns.
-mbooke: Generate code for 32-bit BookE.
-ma2: Generate code for A2 architecture.
-me300: Generate code for PowerPC e300 family.
-maltivec: Generate code for processors with AltiVec instructions.
-mvle: Generate code for Freescale PowerPC VLE instructions.
-mvsx: Generate code for processors with Vector-Scalar (VSX) instructions.
-mhtm: Generate code for processors with Hardware Transactional Memory instructions.
-mpower4, -mpwr4: Generate code for Power4 architecture.
-mpower5, -mpwr5, -mpwr5x: Generate code for Power5 architecture.
-mpower6, -mpwr6: Generate code for Power6 architecture.
-mpower7, -mpwr7: Generate code for Power7 architecture.
-mpower8, -mpwr8: Generate code for Power8 architecture.
-mpower9, -mpwr9: Generate code for Power9 architecture.
-mcell
-mcell: Generate code for Cell Broadband Engine architecture.
-mcom: Generate code Power/PowerPC common instructions.
-many: Generate code for any architecture (PWR/PWRX/PPC).
-mregnames: Allow symbolic names for registers.
-mno-regnames: Do not allow symbolic names for registers.
-mrelocatable: Support for GCC's -mrelocatable option.
-mrelocatable-lib: Support for GCC's -mrelocatable-lib option.
-memb: Set PPC_EMB bit in ELF flags.
-mlittle, -mlittle-endian, -le: Generate code for a little endian machine.
-mbig, -mbig-endian, -be: Generate code for a big endian machine.
-msolaris: Generate code for Solaris.
-mno-solaris: Do not generate code for Solaris.
-nops=count: If an alignment directive inserts more than count nops, put a branch at the beginning to skip execution of the nops.

See the info pages for documentation of the RX-specific options.

The following options are available when as is configured for the s390 processor family.

-m31
-m64: Select the word size, either 31/32 bits or 64 bits.
-mesa
-mzarch: Select the architecture mode, either the Enterprise System Architecture (esa) or the z/Architecture mode (zarch).
-march=processor: Specify which s390 processor variant is the target, g6, g6, z900, z990, z9-109, z9-ec, z10, z196, zEC12, or z13.
-mregnames
-mno-regnames: Allow or disallow symbolic names for registers.
-mwarn-areg-zero: Warn whenever the operand for a base or index register has been specified but evaluates to zero.

The following options are available when as is configured for a TMS320C6000 processor.

-march=arch: Enable (only) instructions from architecture arch. By default, all instructions are permitted.
The following values of arch are accepted: "c62x", "c64x", "c64x+", "c67x", "c67x+", "c674x".
-mdsbt
-mno-dsbt: The -mdsbt option causes the assembler to generate the "Tag_ABI_DSBT" attribute with a value of 1, indicating that the code is using DSBT addressing. The -mno-dsbt option, the default, causes the tag to have a value of 0, indicating that the code does not use DSBT addressing. The linker will emit a warning if objects of different type (DSBT and non-DSBT) are linked together.
-mpid=no
-mpid=near
-mpid=far: The -mpid= option causes the assembler to generate the "Tag_ABI_PID" attribute with a value indicating the form of data addressing used by the code. -mpid=no, the default, indicates position-dependent data addressing, -mpid=near indicates position-independent addressing with GOT accesses using near DP addressing, and -mpid=far indicates position-independent addressing with GOT accesses using far DP addressing. The linker will emit a warning if objects built with different settings of this option are linked together.
-mpic
-mno-pic: The -mpic option causes the assembler to generate the "Tag_ABI_PIC" attribute with a value of 1, indicating that the code is using position-independent code addressing, The "-mno-pic" option, the default, causes the tag to have a value of 0, indicating position-dependent code addressing. The linker will emit a warning if objects of different type (position-dependent and position-independent) are linked together.
-mbig-endian
-mlittle-endian: Generate code for the specified endianness. The default is little-endian.

The following options are available when as is configured for a TILE-Gx processor.

-m32 | -m64: Select the word size, either 32 bits or 64 bits.
-EB | -EL: Select the endianness, either big-endian (-EB) or little-endian (-EL).

The following option is available when as is configured for a Visium processor.

-mtune=arch: This option specifies the target architecture. If an attempt is made to assemble an instruction that will not execute on the target architecture, the assembler will issue an error message.
The following names are recognized: "mcm24" "mcm" "gr5" "gr6"

The following options are available when as is configured for an Xtensa processor.

--text-section-literals | --no-text-section-literals: Control the treatment of literal pools. The default is --no-text-section-literals, which places literals in separate sections in the output file. This allows the literal pool to be placed in a data RAM/ROM. With --text-section-literals, the literals are interspersed in the text section in order to keep them as close as possible to their references. This may be necessary for large assembly files, where the literals would otherwise be out of range of the "L32R" instructions in the text section. Literals are grouped into pools following ".literal_position" directives or preceding "ENTRY" instructions. These options only affect literals referenced via PC-relative "L32R" instructions; literals for absolute mode "L32R" instructions are handled separately.
--auto-litpools | --no-auto-litpools: Control the treatment of literal pools. The default is --no-auto-litpools, which in the absence of --text-section-literals places literals in separate sections in the output file. This allows the literal pool to be placed in a data RAM/ROM. With --auto-litpools, the literals are interspersed in the text section in order to keep them as close as possible to their references, explicit ".literal_position" directives are not required. This may be necessary for very large functions, where single literal pool at the beginning of the function may not be reachable by "L32R" instructions at the end. These options only affect literals referenced via PC-relative "L32R" instructions; literals for absolute mode "L32R" instructions are handled separately. When used together with --text-section-literals, --auto-litpools takes precedence.
--absolute-literals | --no-absolute-literals: Indicate to the assembler whether "L32R" instructions use absolute or PC-relative addressing. If the processor includes the absolute addressing option, the default is to use absolute "L32R" relocations. Otherwise, only the PC-relative "L32R" relocations can be used.
--target-align | --no-target-align: Enable or disable automatic alignment to reduce branch penalties at some expense in code size. This optimization is enabled by default. Note that the assembler will always align instructions like "LOOP" that have fixed alignment requirements.
--longcalls | --no-longcalls: Enable or disable transformation of call instructions to allow calls across a greater range of addresses. This option should be used when call targets can potentially be out of range. It may degrade both code size and performance, but the linker can generally optimize away the unnecessary overhead when a call ends up within range. The default is --no-longcalls.
--transform | --no-transform: Enable or disable all assembler transformations of Xtensa instructions, including both relaxation and optimization. The default is --transform; --no-transform should only be used in the rare cases when the instructions must be exactly as specified in the assembly source. Using --no-transform causes out of range instruction operands to be errors.
--rename-section oldname=newname: Rename the oldname section to newname. This option can be used multiple times to rename multiple sections.
--trampolines | --no-trampolines: Enable or disable transformation of jump instructions to allow jumps across a greater range of addresses. This option should be used when jump targets can potentially be out of range. In the absence of such jumps this option does not affect code size or performance. The default is --trampolines.

The following options are available when as is configured for a Z80 family processor.

-z80: Assemble for Z80 processor.
-r800: Assemble for R800 processor.
-ignore-undocumented-instructions
-Wnud: Assemble undocumented Z80 instructions that also work on R800 without warning.
-ignore-unportable-instructions
-Wnup: Assemble all undocumented Z80 instructions without warning.
-warn-undocumented-instructions
-Wud: Issue a warning for undocumented Z80 instructions that also work on R800.
-warn-unportable-instructions
-Wup: Issue a warning for undocumented Z80 instructions that do not work on R800.
-forbid-undocumented-instructions
-Fud: Treat all undocumented instructions as errors.
-forbid-unportable-instructions
-Fup: Treat undocumented Z80 instructions that do not work on R800 as errors.

COPYRIGHT

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''.

Index

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SEE ALSO