# Man

Command Section
AS(7)              FreeBSD Miscellaneous Information Manual              AS(7)

NAME
as - Using as (machine specific)

Using as
This file is a user guide to the GNU assembler as version "2.17.50
[FreeBSD] 2007-07-03". This version of the file describes as configured
to generate code for machine specific architectures.

Documentation License. A copy of the license is included in the section

Overview
Here is a brief summary of how to invoke as.  For details, see
Invoking,,Command-Line Options.

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
[-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]

inserted in place of the original @ file option. If file does not
exist, or cannot be read, then the option will be treated
literally, and not removed.

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

-a[cdhlmns]
Turn on listings, in any of a variety of ways:

-ac     omit false conditionals

-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.See Section Altmacro''.

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

--defsym sym= value
Define the symbol sym to be value before assembling the input
file.  value must be an integer constant. As in C, a leading 0x
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
This may help debugging assembler code. Currently the only GNU
extension is the location of the current working directory at
assembling time.

--gdwarf-2
Generate DWARF2 debugging information for each assembler line.
This may help debugging assembler code, if the debugger can
handle it. Note---this option is only supported by some targets,
not all of them.

--help  Print a summary of the command line options and exit.

--target-help
Print a summary of all target specific options and exit.

-I dir  Add directory dir to the search list for .include directives.

-J      Don't warn about signed overflow.

-K      This option is accepted but has no effect on the machine specific
family.

-L

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

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

--listing-lhs-width2= number
Set the maximum width, in words, of the output data column for
continuation lines in an assembler listing to number.

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

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

-o objfile
Name the object-file output from as objfile.

-R      Fold the data section into the text section.

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

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

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

--strip-local-absolute
Remove local absolute symbols from the outgoing symbol table.

-v

-version
Print the as version.

--version
Print the as version and exit.

-W

--no-warn
Suppress warning messages.

--fatal-warnings
Treat warnings as errors.

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

-w      Ignored.

-x      Ignored.

-Z      Generate an object file even after errors.

-- | files ...
Standard input, or source files to assemble.

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

-mcpu= processor[+ extension...]
Specify which ARM processor variant is the target.

-march= architecture[+ extension...]
Specify which ARM architecture variant is used by the target.

-mfpu= floating-point-format
Select which Floating Point architecture is the target.

-mfloat-abi= abi
Select which floating point ABI is in use.

-mthumb
Enable Thumb only instruction decoding.

-mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant
Select which procedure calling convention is in use.

-EB | -EL
Select either big-endian (-EB) or little-endian (-EL) output.

-mthumb-interwork
Specify that the code has been generated with interworking
between Thumb and ARM code in mind.

-k      Specify that PIC code has been generated.

The following options are available when as is configured for the SPARC
architecture:

-Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite

-Av8plus | -Av8plusa | -Av9 | -Av9a
Explicitly select a variant of the SPARC architecture.

-Av8plus and -Av8plusa select a 32 bit environment.  -Av9 and
-Av9a select a 64 bit environment.

-Av8plusa and -Av9a enable the SPARC V9 instruction set with
UltraSPARC extensions.

-xarch=v8plus | -xarch=v8plusa
For compatibility with the Solaris v9 assembler. These options
are equivalent to -Av8plus and -Av8plusa, respectively.

-bump   Warn when the assembler switches to another architecture.

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

-G num  This option sets the largest size of an object that can be
referenced implicitly with the gp register. It is only accepted
for targets that use ECOFF format, such as a DECstation running
Ultrix. The default value is 8.

-EB     Generate "big endian" format output.

-EL     Generate "little endian" format output.

-mips1

-mips2

-mips3

-mips4

-mips5

-mips32

-mips32r2

-mips64

-mips64r2
Generate code for a particular mips Instruction Set Architecture
level.  -mips1 is an alias for -march=r3000, -mips2 is an alias
for -march=r6000, -mips3 is an alias for -march=r4000 and -mips4
is an alias for -march=r8000.  -mips5, -mips32, -mips32r2,
-mips64, and -mips64r2 correspond to generic MIPS V, MIPS32,
MIPS32 Release 2, MIPS64, and MIPS64 Release 2 ISA processors,
respectively.

-march= CPU
Generate code for a particular mips cpu.

-mtune= cpu
Schedule and tune for a particular mips cpu.

-mfix7000

-mno-fix7000
Cause nops to be inserted if the read of the destination register
of an mfhi or mflo instruction occurs in the following two
instructions.

-mdebug

-no-mdebug
Cause stabs-style debugging output to go into an ECOFF-style
.mdebug section instead of the standard ELF .stabs sections.

-mpdr

-mno-pdr
Control generation of .pdr sections.

-mgp32

-mfp32  The register sizes are normally inferred from the ISA and ABI,
but these flags force a certain group of registers to be treated
as 32 bits wide at all times.  -mgp32 controls the size of
general-purpose registers and -mfp32 controls the size of
floating-point registers.

-mips16

-no-mips16
Generate code for the MIPS 16 processor. This is equivalent to
putting .set mips16 at the start of the assembly file.
-no-mips16 turns off this option.

-msmartmips

-mno-smartmips
Enables the SmartMIPS extension to the MIPS32 instruction set.
This is equivalent to putting .set smartmips at the start of the
assembly file.  -mno-smartmips turns off this option.

-mips3d

-no-mips3d
Generate code for the MIPS-3D Application Specific Extension.
This tells the assembler to accept MIPS-3D instructions.
-no-mips3d turns off this option.

-mdmx

-no-mdmx
Generate code for the MDMX Application Specific Extension. This
tells the assembler to accept MDMX instructions.  -no-mdmx turns
off this option.

-mdsp

-mno-dsp
Generate code for the DSP Release 1 Application Specific
Extension. This tells the assembler to accept DSP Release 1
instructions.  -mno-dsp turns off this option.

-mdspr2

-mno-dspr2
Generate code for the DSP Release 2 Application Specific
Extension. This option implies -mdsp. This tells the assembler to
accept DSP Release 2 instructions.  -mno-dspr2 turns off this
option.

-mmt

-mno-mt
Generate code for the MT Application Specific Extension. This
tells the assembler to accept MT instructions.  -mno-mt turns off
this option.

--construct-floats

--no-construct-floats
The --no-construct-floats option disables the construction of
of the value into the two single width floating point registers
that make up the double width register. By default
--construct-floats is selected, allowing construction of these
floating point constants.

--emulation= name
This option causes as to emulate as configured for some other
target, in all respects, including output format (choosing
between ELF and ECOFF only), handling of pseudo-opcodes which may
generate debugging information or store symbol table information,
and default endianness. The available configuration names are:
mipsecoff, mipself, mipslecoff, mipsbecoff, mipslelf, mipsbelf.
The first two do not alter the default endianness from that of
the primary target for which the assembler was configured; the
others change the default to little- or big-endian as indicated
by the b or l in the name. Using -EB or -EL will override the
endianness selection in any case.

This option is currently supported only when the primary target
as is configured for is a mips ELF or ECOFF target. Furthermore,
the primary target or others specified with --enable-targets=...
at configuration time must include support for the other format,
if both are to be available. For example, the Irix 5
configuration includes support for both.

Eventually, this option will support more configurations, with
more fine-grained control over the assembler's behavior, and will
be supported for more processors.

-nocpp  as ignores this option. It is accepted for compatibility with the
native tools.

--trap

--no-trap

--break

--no-break
Control how to deal with multiplication overflow and division by
zero.  --trap or --no-break (which are synonyms) take a trap
exception (and only work for Instruction Set Architecture level 2
and higher); --break or --no-trap (also synonyms, and the
default) take a break exception.

-n      When this option is used, as will issue a warning every time it
generates a nop instruction from a macro.

Structure of this Manual
This manual is intended to describe what you need to know to use GNU as.
We cover the syntax expected in source files, including notation for
symbols, constants, and expressions; the directives that as understands;
and of course how to invoke as.

We also cover special features in the machine specific configuration of
as, including assembler directives.

On the other hand, this manual is not intended as an introduction to
programming in assembly language---let alone programming in general! In a
similar vein, we make no attempt to introduce the machine architecture;
we do not describe the instruction set, standard mnemonics, registers or
addressing modes that are standard to a particular architecture.

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

as is primarily intended to assemble the output of the GNU C compiler gcc
for use by the linker ld.  Nevertheless, we've tried to make as assemble
correctly everything that other assemblers for the same machine would
assemble.

Unlike older assemblers, as is designed to assemble a source program in
one pass of the source file. This has a subtle impact on the .org
directive (see Section Org'').

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 Symbol
Attributes''.  For the machine specific target, as is configured to
produce ELF format object files.

Command Line
After the program name as, the command line may contain options and file
names. Options may appear in any order, and may be before, after, or
between file names. The order of file names is significant.

-- (two hyphens) by itself names the standard input file explicitly, as
one of the files for as to assemble.

Except for -- any command line argument that begins with a hyphen ( -) is
an option. Each option changes the behavior of as.  No option changes the
way another option works. An option is a - followed by one or more
letters; the case of the letter is important. All options are optional.

Some options expect exactly one file name to follow them. The file name
may either immediately follow the option's letter (compatible with older
assemblers) or it may be the next command argument (GNU standard). These
two command lines are equivalent:

as -o my-object-file.o mumble.s
as -omy-object-file.o mumble.s

Input Files
We use the phrase source program, abbreviated source, to describe the
program input to one run of as.  The program may be in one or more files;
how the source is partitioned into files doesn't change the meaning of
the source.

The source program is a concatenation of the text in all the files, in
the order specified.

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

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

If you give as no file names it attempts to read one input file from the
as standard input, which is normally your terminal. You may have to type
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.

Filenames and Line-numbers

There are two ways of locating a line in the input file (or files) and
either may be used in reporting error messages. One way refers to a line
number in a physical file; the other refers to a line number in a
"logical" file.See Section Errors''.

Physical files are those files named in the command line given to as.

Logical files are simply names declared explicitly by assembler
directives; they bear no relation to physical files. Logical file names
help error messages reflect the original source file, when as source is
itself synthesized from other files.  as understands the # directives

Output (Object) File
Every time you run as it produces an output file, which is your assembly
language program translated into numbers. This file is the object file.
Its default name is a.out.  You can give it another name by using the
[-o] option. Conventionally, object file names end with .o.  The default
name is used for historical reasons: older assemblers were capable of
assembling self-contained programs directly into a runnable program. (For
some formats, this isn't currently possible, but it can be done for the
a.out format.)

The object file is meant for input to the linker ld.  It contains
assembled program code, information to help ld integrate the assembled
program into a runnable file, and (optionally) symbolic information for
the debugger.

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

Warning messages have the format

file_name:NNN:Warning Message Text

(where NNN is a line number). If a logical file name has been given (see
Section File'') it is used for the filename, otherwise the name of the
current input file is used. If a logical line number was given then it is
used to calculate the number printed, otherwise the actual line in the
current source file is printed.  The message text is intended to be self
explanatory (in the grand Unix tradition).

Error messages have the format

file_name:NNN:FATAL:Error Message Text
The file name and line number are derived as for warning messages. The
actual message text may be rather less explanatory because many of them
aren't supposed to happen.

Command-Line Options
This chapter describes command-line options available in all versions of
the GNU assembler; see Machine Dependencies, for options specific to the
machine specific target.

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

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

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

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

Enable Listings: [-a[cdhlns]]
These options enable listing output from the assembler. By itself, -a
requests high-level, assembly, and symbols listing. You can use other
letters to select specific options for the list: -ah requests a high-
level language listing, -al requests an output-program assembly listing,
and -as requests a symbol table listing. High-level listings require that
a compiler debugging option like -g be used, and that assembly listings (
-al) be requested also.

Use the -ac option to omit false conditionals from a listing. Any lines
which are not assembled because of a false .if (or .ifdef, or any other
conditional), or a true .if followed by an .else, will be omitted from
the listing.

Use the -ad option to omit debugging directives from the listing.

Once you have specified one of these options, you can further control
listing output and its appearance using the directives .list, .nolist,
.psize, .eject, .title, and .sbttl.  The -an option turns off all forms
processing. If you do not request listing output with one of the -a
options, the listing-control directives have no effect.

The letters after -a may be combined into one option, e.g., -aln.

Note if the assembler source is coming from the standard input (e.g.,
because it is being created by gcc and the -pipe command line switch is
being used) then the listing will not contain any comments or
preprocessor directives. This is because the listing code buffers input
source lines from stdin only after they have been preprocessed by the
assembler.  This reduces memory usage and makes the code more efficient.

[--alternate]
Begin in alternate macro mode, see Altmacro,, .altmacro .

[-D]
This option has no effect whatsoever, but it is accepted to make it more
likely that scripts written for other assemblers also work with as.

Work Faster: [-f]
-f should only be used when assembling programs written by a (trusted)
compiler.  -f stops the assembler from doing whitespace and comment
preprocessing on the input file(s) before assembling them.See Section
Preprocessing''.

"Warning: if you use -f when the files actually need to be preprocessed
(if they contain comments, for example), as does not work correctly."

.include Search Path: [-I path]
Use this option to add a path to the list of directories as searches for
files specified in .include directives (see Section Include'').  You
may use [-I] as many times as necessary to include a variety of paths.
The current working directory is always searched first; after that, as
searches any -I directories in the same order as they were specified
(left to right) on the command line.

Difference Tables: [-K]
On the machine specific family, this option is allowed, but has no
effect.  It is permitted for compatibility with the GNU assembler on
other platforms, where it can be used to warn when the assembler alters
the machine code generated for .word directives in difference tables. The
machine specific family does not have the addressing limitations that
sometimes lead to this alteration on other platforms.

Include Local Symbols: [-L]
Symbols beginning with system-specific local label prefixes, typically .L
for ELF systems or L for traditional a.out systems, are called local
symbols.  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 as and ld discard such symbols, so you do not normally
debug with them.

This option tells as to retain those local symbols in the object file.
Usually if you do this you also tell the linker ld to preserve those
symbols.

Configuring listing output: [--listing]
The listing feature of the assembler can be enabled via the command line
switch -a (see Section a'').  This feature combines the input source
file(s) with a hex dump of the corresponding locations in the output
object file, and displays them as a listing file.  The format of this
listing can be controlled by directives inside the assembler source
(i.e., .list (see Section List''), .title (see Section Title''),
.sbttl (see Section Sbttl''), .psize (see Section Psize''), and
.eject (see Section Eject'') and also by the following switches:

--listing-lhs-width= number
Sets the maximum width, in words, of the first line of the hex
byte dump.  This dump appears on the left hand side of the
listing output.

--listing-lhs-width2= number
Sets the maximum width, in words, of any further lines of the hex
byte dump for a given input source line. If this value is not
specified, it defaults to being the same as the value specified
for --listing-lhs-width.  If neither switch is used the default
is to one.

--listing-rhs-width= number
Sets the maximum width, in characters, of the source line that is
displayed alongside the hex dump. The default value for this
parameter is 100. The source line is displayed on the right hand
side of the listing output.

--listing-cont-lines= number
Sets the maximum number of continuation lines of hex dump that
will be displayed for a given single line of source input. The
default value is 4.

Assemble in MRI Compatibility Mode: [-M]
The [-M] or [--mri] option selects MRI compatibility mode. This changes
the syntax and pseudo-op handling of as to make it compatible with the
ASM68K or the ASM960 (depending upon the configured target) assembler
from Microtec Research. The exact nature of the MRI syntax will not be
particular that the handling of macros and macro arguments is somewhat
different. The purpose of this option is to permit assembling existing
MRI assembler code using as.

The MRI compatibility is not complete. Certain operations of the MRI
assembler depend upon its object file format, and can not be supported
using other object file formats. Supporting these would require enhancing
each object file format individually. These are:

•   global symbols in common section

The m68k MRI assembler supports common sections which are merged by
the linker.  Other object file formats do not support this.  as
handles common sections by treating them as a single common symbol.
It permits local symbols to be defined within a common section, but
it can not support global symbols, since it has no way to describe
them.

•   complex relocations

The MRI assemblers support relocations against a negated section
more sections.  These are not support by other object file formats.

•   END pseudo-op specifying start address

The MRI END pseudo-op permits the specification of a start address.
This is not supported by other object file formats. The start address
may instead be specified using the [-e] option to the linker, or in a

•   IDNT, .ident and NAME pseudo-ops

The MRI IDNT, .ident and NAME pseudo-ops assign a module name to the
output file. This is not supported by other object file formats.

•   ORG pseudo-op

The m68k MRI ORG pseudo-op begins an absolute section at a given
address. This differs from the usual as .org pseudo-op, which changes
the location within the current section. Absolute sections are not
supported by other object file formats. The address of a section may
be assigned within a linker script.

There are some other features of the MRI assembler which are not
supported by as, typically either because they are difficult or because
they seem of little consequence. Some of these may be supported in future
releases.

•   EBCDIC strings

EBCDIC strings are not supported.

•   packed binary coded decimal

Packed binary coded decimal is not supported. This means that the
DC.P and DCB.P pseudo-ops are not supported.

•   FEQU pseudo-op

The m68k FEQU pseudo-op is not supported.

•   NOOBJ pseudo-op

The m68k NOOBJ pseudo-op is not supported.

•   OPT branch control options

The m68k OPT branch control options--- B, BRS, BRB, BRL, and BRW
---are ignored.  as automatically relaxes all branches, whether
forward or backward, to an appropriate size, so these options serve
no purpose.

•   OPT list control options

The following m68k OPT list control options are ignored: C, CEX, CL,
CRE, E, G, I, M, MEX, MC, MD, X.

•   other OPT options

The following m68k OPT options are ignored: NEST, O, OLD, OP, P, PCO,
PCR, PCS, R.

•   OPT D option is default

The m68k OPT D option is the default, unlike the MRI assembler.  OPT
NOD may be used to turn it off.

•   XREF pseudo-op.

The m68k XREF pseudo-op is ignored.

•   .debug pseudo-op

The i960 .debug pseudo-op is not supported.

•   .extended pseudo-op

The i960 .extended pseudo-op is not supported.

•   .list pseudo-op.

The various options of the i960 .list pseudo-op are not supported.

•   .optimize pseudo-op

The i960 .optimize pseudo-op is not supported.

•   .output pseudo-op

The i960 .output pseudo-op is not supported.

•   .setreal pseudo-op

The i960 .setreal pseudo-op is not supported.

Dependency Tracking: [--MD]
as can generate a dependency file for the file it creates. This file
consists of a single rule suitable for make describing the dependencies
of the main source file.

The rule is written to the file named in its argument.

This feature is used in the automatic updating of makefiles.

Name the Object File: [-o]
There is always one object file output when you run as.  By default it
has the name a.out.  You use this option (which takes exactly one
filename) to give the object file a different name.

Whatever the object file is called, as overwrites any existing file of
the same name.

Join Data and Text Sections: [-R]
[-R] tells as to write the object file as if all data-section data lives
in the text section.  This is only done at the very last moment: your
binary data are the same, but data section parts are relocated
differently. The data section part of your object file is zero bytes long
because all its bytes are appended to the text section. (See Section
Sections''.)

When you specify [-R] it would be possible to generate shorter address
displacements (because we do not have to cross between text and data
section). We refrain from doing this simply for compatibility with older
versions of as.  In future, [-R] may work this way.

When as is configured for COFF or ELF output, this option is only useful
if you use sections named .text and .data.

Display Assembly Statistics: [--statistics]
Use --statistics to display two statistics about the resources used by
as: the maximum amount of space allocated during the assembly (in bytes),
and the total execution time taken for the assembly (in cpu seconds).

For some targets, the output of as is different in some ways from the
output of some existing assembler. This switch requests as to use the

For example, it disables the exception frame optimizations which as
normally does by default on gcc output.

Announce Version: [-v]
You can find out what version of as is running by including the option -v
(which you can also spell as -version) on the command line.

Control Warnings: [-W, [--warn, [--no-warn, [--fatal-warnings]]]]
as should never give a warning or error message when assembling compiler
output.  But programs written by people often cause as to give a warning
that a particular assumption was made. All such warnings are directed to
the standard error file.

If you use the [-W] and [--no-warn] options, no warnings are issued. This
only affects the warning messages: it does not change any particular of
how as assembles your file. Errors, which stop the assembly, are still
reported.

If you use the [--fatal-warnings] option, as considers files that
generate warnings to be in error.

You can switch these options off again by specifying [--warn], which
causes warnings to be output as usual.

Generate Object File in Spite of Errors: [-Z]
After an error message, as normally produces no output. If for some
reason you are interested in object file output even after as gives an
error message on your program, use the -Z option. If there are any
errors, as continues anyways, and writes an object file after a final
warning message of the form n errors, m warnings, generating bad object
file.

Syntax
This chapter describes the machine-independent syntax allowed in a source
file.  as syntax is similar to what many other assemblers use; it is
inspired by the BSD 4.2 assembler.

Preprocessing
The as internal preprocessor:

•   adjusts and removes extra whitespace. It leaves one space or tab
before the keywords on a line, and turns any other whitespace on the
line into a single space.

•   removes all comments, replacing them with a single space, or an
appropriate number of newlines.

•   converts character constants into the appropriate numeric values.

It does not do macro processing, include file handling, or anything else
you may get from your C compiler's preprocessor. You can do include file
processing with the .include directive (see Section Include'').  You
can use the GNU C compiler driver to get other "CPP" style preprocessing
by giving the input file a .S suffix.See Section Overall Options''.

Excess whitespace, comments, and character constants cannot be used in
the portions of the input text that are not preprocessed.

If the first line of an input file is #NO_APP or if you use the -f
option, whitespace and comments are not removed from the input file.
Within an input file, you can ask for whitespace and comment removal in
specific portions of the by putting a line that says #APP before the text
that may contain whitespace or comments, and putting a line that says
#NO_APP after this text. This feature is mainly intend to support asm
statements in compilers whose output is otherwise free of comments and
whitespace.

Whitespace
Whitespace is one or more blanks or tabs, in any order. Whitespace is
used to separate symbols, and to make programs neater for people to read.
Unless within character constants (see Section Characters''), any
whitespace means the same as exactly one space.

There are two ways of rendering comments to as.  In both cases the
comment is equivalent to one space.

Anything from /* through the next */ is a comment. This means you may not

/*
The only way to include a newline ('\n') in a comment
is to use this sort of comment.
*/

/* This sort of comment does not nest. */

Anything from the line comment character to the next newline is
considered a comment and is ignored. The line comment character is @ on
the ARM; # on the i386 and x86-64; # for Motorola PowerPC; !  on the
SPARC; see Machine Dependencies.

To be compatible with past assemblers, lines that begin with # have a
special interpretation. Following the # should be an absolute expression
(see Section Expressions''): the logical line number of the next line.
Then a string (see Section Strings'') is allowed: if present it is a
new logical file name. The rest of the line, if any, should be
whitespace.

If the first non-whitespace characters on the line are not numeric, the
line is ignored. (Just like a comment.)

# This is an ordinary comment.
# 42-6 "new_file_name"    # New logical file name
# This is logical line # 36.
This feature is deprecated, and may disappear from future versions of as.

Symbols
A symbol is one or more characters chosen from the set of all letters
(both upper and lower case), digits and the three characters _.. No symbol may begin with a digit. Case is significant. There is no length limit: all characters are significant. Symbols are delimited by characters not in that set, or by the beginning of a file (since the source program must end with a newline, the end of a file is not a possible symbol delimiter).See Section Symbols''. Statements A statement ends at a newline character ( \n) or at a semicolon ( ;). The newline or semicolon is considered part of the preceding statement. Newlines and semicolons within character constants are an exception: they do not end statements. It is an error to end any statement with end-of-file: the last character of any input file should be a newline. An empty statement is allowed, and may include whitespace. It is ignored. A statement begins with zero or more labels, optionally followed by a key symbol which determines what kind of statement it is. The key symbol determines the syntax of the rest of the statement. If the symbol begins with a dot . then the statement is an assembler directive: typically valid for any computer. If the symbol begins with a letter the statement is an assembly language instruction: it assembles into a machine language instruction. A label is a symbol immediately followed by a colon ( :). Whitespace before a label or after a colon is permitted, but you may not have whitespace between a label's symbol and its colon.See Section Labels''. label: .directive followed by something another_label: # This is an empty statement. instruction operand_1, operand_2, ... Constants A constant is a number, written so that its value is known by inspection, without knowing any context. Like this: .byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value. .ascii "Ring the bell\7" # A string constant. .octa 0x123456789abcdef0123456789ABCDEF0 # A biGNUm. .float 0f-314159265358979323846264338327\ 95028841971.693993751E-40 # - pi, a flonum. Character Constants There are two kinds of character constants. A character stands for one character in one byte and its value may be used in numeric expressions. String constants (properly called string literals) are potentially many bytes and their values may not be used in arithmetic expressions. Strings A string is written between double-quotes. It may contain double-quotes or null characters. The way to get special characters into a string is to escape these characters: precede them with a backslash \ character. For example \\ represents one backslash: the first \ is an escape which tells as to interpret the second character literally as a backslash (which prevents as from recognizing the second \ as an escape character). The complete list of escapes follows. \b Mnemonic for backspace; for ASCII this is octal code 010. \f Mnemonic for FormFeed; for ASCII this is octal code 014. \n Mnemonic for newline; for ASCII this is octal code 012. \r Mnemonic for carriage-Return; for ASCII this is octal code 015. \t Mnemonic for horizontal Tab; for ASCII this is octal code 011. \ digit digit digit An octal character code. The numeric code is 3 octal digits. For compatibility with other Unix systems, 8 and 9 are accepted as digits: for example, \008 has the value 010, and \009 the value 011. \ x hex-digits... A hex character code. All trailing hex digits are combined. Either upper or lower case x works. \\ Represents one \ character. \" Represents one character. Needed in strings to represent this character, because an unescaped would end the string. \ anything-else Any other character when escaped by \ gives a warning, but assembles as if the \ was not present. The idea is that if you used an escape sequence you clearly didn't want the literal interpretation of the following character. However as has no other interpretation, so as knows it is giving you the wrong code and warns you of the fact. Which characters are escapable, and what those escapes represent, varies widely among assemblers. The current set is what we think the BSD 4.2 assembler recognizes, and is a subset of what most C compilers recognize. If you are in doubt, do not use an escape sequence. Characters A single character may be written as a single quote immediately followed by that character. The same escapes apply to characters as to strings. So if you want to write the character backslash, you must write '\\ where the first \ escapes the second \. As you can see, the quote is an acute accent, not a grave accent. A newline (or semicolon ;) immediately following an acute accent is taken as a literal character and does not count as the end of a statement. The value of a character constant in a numeric expression is the machine's byte-wide code for that character. as assumes your character code is ASCII: 'A means 65, 'B means 66, and so on. Number Constants as distinguishes three kinds of numbers according to how they are stored in the target machine. Integers are numbers that would fit into an int in the C language. BiGNUms are integers, but they are stored in more than 32 bits. Flonums are floating point numbers, described below. Integers A binary integer is 0b or 0B followed by zero or more of the binary digits 01. An octal integer is 0 followed by zero or more of the octal digits ( 01234567). A decimal integer starts with a non-zero digit followed by zero or more digits ( 0123456789). A hexadecimal integer is 0x or 0X followed by one or more hexadecimal digits chosen from 0123456789abcdefABCDEF. Integers have the usual values. To denote a negative integer, use the prefix operator - discussed under expressions (see Section Prefix Ops''). BiGNUms A biGNUm has the same syntax and semantics as an integer except that the number (or its negative) takes more than 32 bits to represent in binary. The distinction is made because in some places integers are permitted while biGNUms are not. Flonums A flonum represents a floating point number. The translation is indirect: a decimal floating point number from the text is converted by as to a generic binary floating point number of more than sufficient precision. This generic floating point number is converted to a particular computer's floating point format (or formats) by a portion of as specialized to that computer. A flonum is written by writing (in order) • The digit 0. • A letter, to tell as the rest of the number is a flonum. • An optional sign: either + or -. • An optional integer part: zero or more decimal digits. • An optional fractional part: . followed by zero or more decimal digits. • An optional exponent, consisting of: • An E or e. • Optional sign: either + or -. • One or more decimal digits. At least one of the integer part or the fractional part must be present. The floating point number has the usual base-10 value. as does all processing using integers. Flonums are computed independently of any floating point hardware in the computer running as. Sections and Relocation Background Roughly, a section is a range of addresses, with no gaps; all data "in" those addresses is treated the same for some particular purpose. For example there may be a "read only" section. The linker ld reads many object files (partial programs) and combines their contents to form a runnable program. When as emits an object file, the partial program is assumed to start at address 0. ld assigns the final addresses for the partial program, so that different partial programs do not overlap. This is actually an oversimplification, but it suffices to explain how as uses sections. ld moves blocks of bytes of your program to their run-time addresses. These blocks slide to their run-time addresses as rigid units; their length does not change and neither does the order of bytes within them. Such a rigid unit is called a section. Assigning run-time addresses to sections is called relocation. It includes the task of adjusting mentions of object-file addresses so they refer to the proper run-time addresses. An object file written by as has at least three sections, any of which may be empty. These are named text, data and bss sections. as can also generate whatever other named sections you specify using the .section directive (see Section Section''). If you do not use any directives that place output in the .text or .data sections, these sections still exist, but are empty. Within the object file, the text section starts at address 0, the data section follows, and the bss section follows the data section. To let ld know which data changes when the sections are relocated, and how to change that data, as also writes to the object file details of the relocation needed. To perform relocation ld must know, each time an address in the object file is mentioned: • Where in the object file is the beginning of this reference to an address? • How long (in bytes) is this reference? • Which section does the address refer to? What is the numeric value of ( address) -( start-address of section)? • Is the reference to an address "Program-Counter relative"? In fact, every address as ever uses is expressed as ( section) + ( offset into section) Further, most expressions as computes have this section-relative nature. In this manual we use the notation { secname N }to mean "offset N into section secname ." Apart from text, data and bss sections you need to know about the absolute section. When ld mixes partial programs, addresses in the absolute section remain unchanged. For example, address {absolute 0} is "relocated" to run-time address 0 by ld. Although the linker never arranges two partial programs' data sections with overlapping addresses after linking, by definition their absolute sections must overlap. Address {absolute 239} in one part of a program is always the same address when the program is running as address {absolute 239} in any other part of the program. The idea of sections is extended to the undefined section. Any address whose section is unknown at assembly time is by definition rendered {undefined U }---where U is filled in later. Since numbers are always defined, the only way to generate an undefined address is to mention an undefined symbol. A reference to a named common block would be such a symbol: its value is unknown at assembly time so it has section undefined. By analogy the word section is used to describe groups of sections in the linked program. ld puts all partial programs' text sections in contiguous addresses in the linked program. It is customary to refer to the text section of a program, meaning all the addresses of all partial programs' text sections. Likewise for data and bss sections. Some sections are manipulated by ld; others are invented for use of as and have no meaning except during assembly. Linker Sections ld deals with just four kinds of sections, summarized below. named sections These sections hold your program. as and ld treat them as separate but equal sections. Anything you can say of one section is true of another. When the program is running, however, it is customary for the text section to be unalterable. The text section is often shared among processes: it contains instructions, constants and the like. The data section of a running program is usually alterable: for example, C variables would be stored in the data section. bss section This section contains zeroed bytes when your program begins running. It is used to hold uninitialized variables or common storage. The length of each partial program's bss section is important, but because it starts out containing zeroed bytes there is no need to store explicit zero bytes in the object file. The bss section was invented to eliminate those explicit zeros from object files. absolute section Address 0 of this section is always "relocated" to runtime address 0. This is useful if you want to refer to an address that ld must not change when relocating. In this sense we speak of absolute addresses being "unrelocatable": they do not change during relocation. undefined section This "section" is a catch-all for address references to objects not in the preceding sections. An idealized example of three relocatable sections follows. The example uses the traditional section names .text and .data. Memory addresses are on the horizontal axis. +-----+----+--+ partial program # 1: |ttttt|dddd|00| +-----+----+--+ text data bss seg. seg. seg. +---+---+---+ partial program # 2: |TTT|DDD|000| +---+---+---+ +--+---+-----+--+----+---+-----+~~ linked program: | |TTT|ttttt| |dddd|DDD|00000| +--+---+-----+--+----+---+-----+~~ addresses: 0 ... Assembler Internal Sections These sections are meant only for the internal use of as. They have no meaning at run-time. You do not really need to know about these sections for most purposes; but they can be mentioned in as warning messages, so it might be helpful to have an idea of their meanings to as. These sections are used to permit the value of every expression in your assembly language program to be a section-relative address. ASSEMBLER-INTERNAL-LOGIC-ERROR! An internal assembler logic error has been found. This means there is a bug in the assembler. expr section The assembler stores complex expression internally as combinations of symbols. When it needs to represent an expression as a symbol, it puts it in the expr section. Sub-Sections You may have separate groups of data in named sections that you want to end up near to each other in the object file, even though they are not contiguous in the assembler source. as allows you to use subsections for this purpose. Within each section, there can be numbered subsections with values from 0 to 8192. Objects assembled into the same subsection go into the object file together with other objects in the same subsection. For example, a compiler might want to store constants in the text section, but might not want to have them interspersed with the program being assembled. In this case, the compiler could issue a .text 0 before each section of code being output, and a .text 1 before each group of constants being output. Subsections are optional. If you do not use subsections, everything goes in subsection number zero. Subsections appear in your object file in numeric order, lowest numbered to highest. (All this to be compatible with other people's assemblers.) The object file contains no representation of subsections; ld and other programs that manipulate object files see no trace of them. They just see all your text subsections as a text section, and all your data subsections as a data section. To specify which subsection you want subsequent statements assembled into, use a numeric argument to specify it, in a .text expression or a .data expression statement. You can also use the .subsection directive (see Section SubSection'') to specify a subsection: .subsection expression. Expression should be an absolute expression (see Section Expressions''). If you just say .text then .text 0 is assumed. Likewise .data means .data 0. Assembly begins in text 0. For instance: .text 0 # The default subsection is text 0 anyway. .ascii "This lives in the first text subsection. *" .text 1 .ascii "But this lives in the second text subsection." .data 0 .ascii "This lives in the data section," .ascii "in the first data subsection." .text 0 .ascii "This lives in the first text section," .ascii "immediately following the asterisk (*)." Each section has a location counter incremented by one for every byte assembled into that section. Because subsections are merely a convenience restricted to as there is no concept of a subsection location counter. There is no way to directly manipulate a location counter---but the .align directive changes it, and any label definition captures its current value. The location counter of the section where statements are being assembled is said to be the active location counter. bss Section The bss section is used for local common variable storage. You may allocate address space in the bss section, but you may not dictate data to load into it before your program executes. When your program starts running, all the contents of the bss section are zeroed bytes. The .lcomm pseudo-op defines a symbol in the bss section; see Lcomm,, .lcomm . The .comm pseudo-op may be used to declare a common symbol, which is another form of uninitialized symbol; see Comm,, .comm . Symbols Symbols are a central concept: the programmer uses symbols to name things, the linker uses symbols to link, and the debugger uses symbols to debug. "Warning: as does not place symbols in the object file in the same order they were declared. This may break some debuggers." Labels A label is written as a symbol immediately followed by a colon :. The symbol then represents the current value of the active location counter, and is, for example, a suitable instruction operand. You are warned if you use the same symbol to represent two different locations: the first definition overrides any other definitions. Giving Symbols Other Values A symbol can be given an arbitrary value by writing a symbol, followed by an equals sign =, followed by an expression (see Section Expressions''). This is equivalent to using the .set directive.See Section Set''. In the same way, using a double equals sign = = here represents an equivalent of the .eqv directive.See Section Eqv''. Symbol Names Symbol names begin with a letter or with one of ._. On most machines, you can also use in symbol names; exceptions are noted in Machine
Dependencies. That character may be followed by any string of digits,
letters, dollar signs (unless otherwise noted for a particular target
machine), and underscores.

Case of letters is significant: foo is a different symbol name than Foo.

Each symbol has exactly one name. Each name in an assembly language
program refers to exactly one symbol. You may use that symbol name any
number of times in a program.

Local Symbol Names

A local symbol is any symbol beginning with certain local label prefixes.
By default, the local label prefix is .L for ELF systems or L for
traditional a.out systems, but each target may have its own set of local
label prefixes.

Local symbols are defined and used within the assembler, but they are
normally not saved in object files. Thus, they are not visible when
debugging. You may use the -L option (see Section L'') to retain the
local symbols in the object files.

Local Labels

Local labels help compilers and programmers use names temporarily. They
create symbols which are guaranteed to be unique over the entire scope of
the input source code and which can be referred to by a simple notation.
To define a local label, write a label of the form N: (where N represents
any positive integer). To refer to the most recent previous definition of
that label write Nb, using the same number as when you defined the label.
To refer to the next definition of a local label, write Nf ---the b
stands for "backwards" and the f stands for "forwards".

There is no restriction on how you can use these labels, and you can
reuse them too. So that it is possible to repeatedly define the same
local label (using the same number N), although you can only refer to the
most recently defined local label of that number (for a backwards
reference) or the next definition of a specific local label for a forward
reference. It is also worth noting that the first 10 local labels ( 0:
....Li  Sy 9: ) are implemented in a slightly more efficient manner than
the others.

Here is an example:

1:        branch 1f
2:        branch 1b
1:        branch 2f
2:        branch 1b

Which is the equivalent of:

label_1:  branch label_3
label_2:  branch label_1
label_3:  branch label_4
label_4:  branch label_3

Local label names are only a notational device. They are immediately
transformed into more conventional symbol names before the assembler uses
them. The symbol names are stored in the symbol table, appear in error
messages, and are optionally emitted to the object file. The names are
constructed using these parts:

local label prefix
All local symbols begin with the system-specific local label
the local label prefix. These labels are used for symbols you are
never intended to see. If you use the -L option then as retains
these symbols in the object file. If you also instruct ld to
retain these symbols, you may use them in debugging.

number  This is the number that was used in the local label definition.
So if the label is written 55: then the number is 55.

C-B     This unusual character is included so you do not accidentally
invent a symbol of the same name. The character has ASCII value
of \002 (control-B).

ordinal number
This is a serial number to keep the labels distinct. The first
definition of 0: gets the number 1.  The 15th definition of 0:
gets the number 15, and so on. Likewise the first definition of
1: gets the number 1 and its 15th definition gets 15 as well.

So for example, the first 1: may be named .L1 C-B1, and the 44th 3: may
be named .L3 C-B44.

Dollar Local Labels

as also supports an even more local form of local labels called dollar
labels.  These labels go out of scope (i.e., they become undefined) as
soon as a non-local label is defined. Thus they remain valid for only a
small region of the input source code. Normal local labels, by contrast,
remain in scope for the entire file, or until they are redefined by
another occurrence of the same local label.

Dollar labels are defined in exactly the same way as ordinary local
labels, except that instead of being terminated by a colon, they are
terminated by a dollar sign, e.g., 55$. They can also be distinguished from ordinary local labels by their transformed names which use ASCII character \001 (control-A) as the magic character to distinguish them from ordinary labels. For example, the fifth definition of 6$ may be named .L6 C-A5.

The Special Dot Symbol
The special symbol .  refers to the current address that as is assembling
into. Thus, the expression melvin: .long.  defines melvin to contain its
own address. Assigning a value to .  is treated the same as a .org
directive. Thus, the expression .=.+4 is the same as saying .space 4.

Symbol Attributes
Every symbol has, as well as its name, the attributes "Value" and "Type".
Depending on output format, symbols can also have auxiliary attributes.
The detailed definitions are in a.out.h.

If you use a symbol without defining it, as assumes zero for all these
attributes, and probably won't warn you. This makes the symbol an
externally defined symbol, which is generally what you would want.

Value

The value of a symbol is (usually) 32 bits. For a symbol which labels a
location in the text, data, bss or absolute sections the value is the
number of addresses from the start of that section to the label.
Naturally for text, data and bss sections the value of a symbol changes
values do not change during linking: that is why they are called
absolute.

The value of an undefined symbol is treated in a special way. If it is 0
then the symbol is not defined in this assembler source file, and ld
tries to determine its value from other files linked into the same
program.  You make this kind of symbol simply by mentioning a symbol name
without defining it. A non-zero value represents a .comm common
declaration. The value is how much common storage to reserve, in bytes
storage.

Type

The type attribute of a symbol contains relocation (section) information,
any flag settings indicating that a symbol is external, and (optionally),
other information for linkers and debuggers. The exact format depends on
the object-code output format in use.

Expressions
An expression specifies an address or numeric value. Whitespace may

The result of an expression must be an absolute number, or else an offset
into a particular section. If an expression is not absolute, and there is
not enough information when as sees the expression to know its section, a
second pass over the source program might be necessary to interpret the
expression---but the second pass is currently not implemented.  as aborts
with an error message in this situation.

Empty Expressions
An empty expression has no value: it is just whitespace or null. Wherever
an absolute expression is required, you may omit the expression, and as
assumes a value of (absolute) 0. This is compatible with other
assemblers.

Integer Expressions
An integer expression is one or more arguments delimited by operators.

Arguments

Arguments are symbols, numbers or subexpressions. In other contexts
arguments are sometimes called "arithmetic operands". In this manual, to
avoid confusing them with the "instruction operands" of the machine
language, we use the term "argument" to refer to parts of expressions
only, reserving the word "operand" to refer only to machine instruction
operands.

Symbols are evaluated to yield { section NNN }where section is one of
text, data, bss, absolute, or undefined.  NNN is a signed, 2's complement
32 bit integer.

Numbers are usually integers.

A number can be a flonum or biGNUm. In this case, you are warned that
only the low order 32 bits are used, and as pretends these 32 bits are an
integer. You may write integer-manipulating instructions that act on
exotic constants, compatible with other assemblers.

Subexpressions are a left parenthesis ( followed by an integer
expression, followed by a right parenthesis ); or a prefix operator
followed by an argument.

Operators

Operators are arithmetic functions, like + or %.  Prefix operators are
followed by an argument. Infix operators appear between their arguments.
Operators may be preceded and/or followed by whitespace.

Prefix Operator

as has the following prefix operators.  They each take one argument,
which must be absolute.

-       Negation.  Two's complement negation.

~       Complementation.  Bitwise not.

Infix Operators

Infix operators take two arguments, one on either side. Operators have
precedence, but operations with equal precedence are performed left to
right. Apart from + or [-], both arguments must be absolute, and the
result is absolute.

1.   Highest Precedence

*       Multiplication.

/       Division.  Truncation is the same as the C operator /

%       Remainder.

<<      Shift Left.  Same as the C operator <<.

>>      Shift Right.  Same as the C operator >>.

2.   Intermediate precedence

|

Bitwise Inclusive Or.

&       Bitwise And.

^       Bitwise Exclusive Or.

!       Bitwise Or Not.

3.   Low Precedence

+       Addition.  If either argument is absolute, the result has
the section of the other argument.  You may not add together
arguments from different sections.

-       Subtraction.  If the right argument is absolute, the result
has the section of the left argument. If both arguments are
in the same section, the result is absolute.  You may not
subtract arguments from different sections.

==      Is Equal To

<>

!=      Is Not Equal To

<       Is Less Than

>       Is Greater Than

>=      Is Greater Than Or Equal To

<=      Is Less Than Or Equal To

The comparison operators can be used as infix operators. A
true results has a value of -1 whereas a false result has a
value of 0. Note, these operators perform signed
comparisons.

4.   Lowest Precedence

&&      Logical And.

||      Logical Or.

These two logical operations can be used to combine the
results of sub expressions.  Note, unlike the comparison
operators a true result returns a value of 1 but a false
results does still return 0. Also note that the logical or
operator has a slightly lower precedence than logical and.

In short, it's only meaningful to add or subtract the offsets in an
address; you can only have a defined section in one of the two arguments.

Assembler Directives
All assembler directives have names that begin with a period ( .).  The
rest of the name is letters, usually in lower case.

This chapter discusses directives that are available regardless of the
target machine configuration for the GNU assembler.

.abort
This directive stops the assembly immediately. It is for compatibility
with other assemblers. The original idea was that the assembly language
source would be piped into the assembler. If the sender of the source
quit, it could use this directive tells as to quit also. One day .abort
will not be supported.

.align abs-expr, abs-expr, abs-expr
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
alignment required, as described below.

The second expression (also absolute) gives the fill value to be stored
in the padding bytes. It (and the comma) may be omitted. If it is
omitted, the padding bytes are normally zero. However, on some systems,
if the section is marked as containing code and the fill value is
omitted, the space is filled with no-op instructions.

The third expression is also absolute, and is also optional. If it is
present, it is the maximum number of bytes that should be skipped by this
alignment directive. If doing the alignment would require skipping more
bytes than the specified maximum, then the alignment is not done at all.
You can omit the fill value (the second argument) entirely by simply
using two commas after the required alignment; this can be useful if you
want the alignment to be filled with no-op instructions when appropriate.

The way the required alignment is specified varies from system to system.
For the arc, hppa, i386 using ELF, i860, iq2000, m68k, or32, s390, sparc,
tic4x, tic80 and xtensa, the first expression is the alignment request in
bytes. For example .align 8 advances the location counter until it is a
multiple of 8. If the location counter is already a multiple of 8, no
change is needed. For the tic54x, the first expression is the alignment
request in words.

For other systems, including the i386 using a.out format, and the arm and
strongarm, it is the number of low-order zero bits the location counter
counter until it a multiple of 8. If the location counter is already a
multiple of 8, no change is needed.

This inconsistency is due to the different behaviors of the various
native assemblers for these systems which GAS must emulate. GAS also
provides .balign and .p2align directives, described later, which have a
consistent behavior across all architectures (but are specific to GAS).

.ascii  Va string ...
.ascii expects zero or more string literals (see Section Strings'')
separated by commas. It assembles each string (with no automatic trailing

.asciz  Va string ...
.asciz is just like .ascii, but each string is followed by a zero byte.
The "z" in .asciz stands for "zero".

.balign[wl] abs-expr, abs-expr, abs-expr
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
alignment request in bytes. For example .balign 8 advances the location
counter until it is a multiple of 8. If the location counter is already a
multiple of 8, no change is needed.

The second expression (also absolute) gives the fill value to be stored
in the padding bytes. It (and the comma) may be omitted. If it is
omitted, the padding bytes are normally zero. However, on some systems,
if the section is marked as containing code and the fill value is
omitted, the space is filled with no-op instructions.

The third expression is also absolute, and is also optional. If it is
present, it is the maximum number of bytes that should be skipped by this
alignment directive. If doing the alignment would require skipping more
bytes than the specified maximum, then the alignment is not done at all.
You can omit the fill value (the second argument) entirely by simply
using two commas after the required alignment; this can be useful if you
want the alignment to be filled with no-op instructions when appropriate.

The .balignw and .balignl directives are variants of the .balign
directive. The .balignw directive treats the fill pattern as a two byte
word value. The .balignl directives treats the fill pattern as a four
byte longword value. For example, .balignw 4,0x368d will align to a
multiple of 4. If it skips two bytes, they will be filled in with the
value 0x368d (the exact placement of the bytes depends upon the
endianness of the processor). If it skips 1 or 3 bytes, the fill value is
undefined.

.byte expressions
.byte expects zero or more expressions, separated by commas. Each
expression is assembled into the next byte.

.comm symbol, length
.comm declares a common symbol named symbol.  When linking, a common
symbol in one object file may be merged with a defined or common symbol
of the same name in another object file. If ld does not see a definition
for the symbol--just one or more common symbols--then it will allocate
length bytes of uninitialized memory.  length must be an absolute
expression. If ld sees multiple common symbols with the same name, and
they do not all have the same size, it will allocate space using the
largest size.

When using ELF, the .comm directive takes an optional third argument.
This is the desired alignment of the symbol, specified as a byte boundary
(for example, an alignment of 16 means that the least significant 4 bits
of the address should be zero).  The alignment must be an absolute
expression, and it must be a power of two.  If ld allocates uninitialized
memory for the common symbol, it will use the alignment when placing the
symbol. If no alignment is specified, as will set the alignment to the
largest power of two less than or equal to the size of the symbol, up to
a maximum of 16.

.cfi_startproc [simple]
.cfi_startproc is used at the beginning of each function that should have
an entry in .eh_frame.  It initializes some internal data structures.
Don't forget to close the function by .cfi_endproc.

Unless .cfi_startproc is used along with parameter simple it also emits
some architecture dependent initial CFI instructions.

.cfi_endproc
.cfi_endproc is used at the end of a function where it closes its unwind
entry previously opened by .cfi_startproc, and emits it to .eh_frame.

.cfi_personality encoding [, exp]
.cfi_personality defines personality routine and its encoding.  encoding
must be a constant determining how the personality should be encoded. If
it is 255 ( DW_EH_PE_omit), second argument is not present, otherwise
second argument should be a constant or a symbol name. When using
indirect encodings, the symbol provided should be the location where
personality can be loaded from, not the personality routine itself. The
default after .cfi_startproc is .cfi_personality 0xff, no personality
routine.

.cfi_lsda encoding [, exp]
.cfi_lsda defines LSDA and its encoding.  encoding must be a constant
determining how the LSDA should be encoded. If it is 255 (
DW_EH_PE_omit), second argument is not present, otherwise second argument
should be a constant or a symbol name. The default after .cfi_startproc
is .cfi_lsda 0xff, no LSDA.

.cfi_def_cfa register, offset
.cfi_def_cfa defines a rule for computing CFA as: take address from
register and add offset to it.

.cfi_def_cfa_register register
.cfi_def_cfa_register modifies a rule for computing CFA. From now on
register will be used instead of the old one. Offset remains the same.

.cfi_def_cfa_offset offset
.cfi_def_cfa_offset modifies a rule for computing CFA. Register remains
the same, but offset is new. Note that it is the absolute offset that

Same as .cfi_def_cfa_offset but offset is a relative value that is

.cfi_offset register, offset
Previous value of register is saved at offset offset from CFA.

.cfi_rel_offset register, offset
Previous value of register is saved at offset offset from the current CFA
register. This is transformed to .cfi_offset using the known displacement
of the CFA register from the CFA. This is often easier to use, because
the number will match the code it's annotating.

.cfi_register register1, register2
Previous value of register1 is saved in register register2.

.cfi_restore register
.cfi_restore says that the rule for register is now the same as it was at
the beginning of the function, after all initial instruction added by
.cfi_startproc were executed.

.cfi_undefined register
From now on the previous value of register can't be restored anymore.

.cfi_same_value register
Current value of register is the same like in the previous frame, i.e. no
restoration needed.

.cfi_remember_state,
First save all current rules for all registers by .cfi_remember_state,
then totally screw them up by subsequent .cfi_* directives and when
everything is hopelessly bad, use .cfi_restore_state to restore the
previous saved state.

.cfi_return_column register
Change return column register, i.e. the return address is either directly
in register or can be accessed by rules for register.

.cfi_signal_frame
Mark current function as signal trampoline.

.cfi_window_save
SPARC register window has been saved.

.cfi_escape expression[, ...]
Allows the user to add arbitrary bytes to the unwind info. One might use
this to add OS-specific CFI opcodes, or generic CFI opcodes that GAS does
not yet support.

.file fileno filename
When emitting dwarf2 line number information .file assigns filenames to
the .debug_line file name table. The fileno operand should be a unique
positive integer to use as the index of the entry in the table. The
filename operand is a C string literal.

The detail of filename indices is exposed to the user because the
filename table is shared with the .debug_info section of the dwarf2
debugging information, and thus the user must know the exact indices that
table entries will have.

.loc fileno lineno [column] [options]
The .loc directive will add row to the .debug_line line number matrix
corresponding to the immediately following assembly instruction.  The
fileno, lineno, and optional column arguments will be applied to the
.debug_line state machine before the row is added.

The options are a sequence of the following tokens in any order:

basic_block
This option will set the basic_block register in the .debug_line
state machine to true.

prologue_end
This option will set the prologue_end register in the .debug_line
state machine to true.

epilogue_begin
This option will set the epilogue_begin register in the
.debug_line state machine to true.

is_stmt value
This option will set the is_stmt register in the .debug_line
state machine to value, which must be either 0 or 1.

isa value
This directive will set the isa register in the .debug_line state
machine to value, which must be an unsigned integer.

.loc_mark_blocks enable
The .loc_mark_blocks directive makes the assembler emit an entry to the
.debug_line line number matrix with the basic_block register in the state
machine set whenever a code label is seen. The enable argument should be
either 1 or 0, to enable or disable this function respectively.

.data subsection
.data tells as to assemble the following statements onto the end of the
data subsection numbered subsection (which is an absolute expression). If
subsection is omitted, it defaults to zero.

.double flonums
.double expects zero or more flonums, separated by commas. It assembles
floating point numbers.

.eject
Force a page break at this point, when generating assembly listings.

.else
.else is part of the as support for conditional assembly; see If,, .if .
It marks the beginning of a section of code to be assembled if the
condition for the preceding .if was false.

.elseif
.elseif is part of the as support for conditional assembly; see If,, .if
. It is shorthand for beginning a new .if block that would otherwise fill
the entire .else section.

.end
.end marks the end of the assembly file.  as does not process anything in
the file past the .end directive.

.endfunc
.endfunc marks the end of a function specified with .func.

.endif
.endif is part of the as support for conditional assembly; it marks the
end of a block of code that is only assembled conditionally.See Section
If''.

.equ symbol, expression
This directive sets the value of symbol to expression.  It is synonymous
with .set; see Set,, .set .

.equiv symbol, expression
The .equiv directive is like .equ and .set, except that the assembler
will signal an error if symbol is already defined. Note a symbol which
has been referenced but not actually defined is considered to be
undefined.

Except for the contents of the error message, this is roughly equivalent
to

.ifdef SYM
.err
.endif
.equ SYM,VAL
plus it protects the symbol from later redefinition.

.eqv symbol, expression
The .eqv directive is like .equiv, but no attempt is made to evaluate the
expression or any part of it immediately.  Instead each time the
resulting symbol is used in an expression, a snapshot of its current
value is taken.

.err
If as assembles a .err directive, it will print an error message and,
unless the [-Z] option was used, it will not generate an object file.
This can be used to signal an error in conditionally compiled code.

.error  Va string
Similarly to .err, this directive emits an error, but you can specify a
string that will be emitted as the error message. If you don't specify
the message, it defaults to .error directive invoked in source file.  See
Section.Dq Errors .

.error "This code has not been assembled and tested."

.exitm
Exit early from the current macro definition.See Section Macro''.

.extern
.extern is accepted in the source program---for compatibility with other
assemblers---but it is ignored.  as treats all undefined symbols as
external.

.fail expression
Generates an error or a warning. If the value of the expression is 500 or
more, as will print a warning message. If the value is less than 500, as
will print an error message. The message will include the value of
expression.  This can occasionally be useful inside complex nested macros
or conditional assembly.

.file string
.file tells as that we are about to start a new logical file.  string is
the new file name. In general, the filename is recognized whether or not
it is surrounded by quotes  ; but if you wish to specify an empty file
name, you must give the quotes-- .  This statement may go away in future:
it is only recognized to be compatible with old as programs.

.fill repeat, size, value
repeat, size and value are absolute expressions. This emits repeat copies
of size bytes.  Repeat may be zero or more.  Size may be zero or more,
but if it is more than 8, then it is deemed to have the value 8,
compatible with other people's assemblers. The contents of each repeat
bytes is taken from an 8-byte number. The highest order 4 bytes are zero.
The lowest order 4 bytes are value rendered in the byte-order of an
integer on the computer as is assembling for. Each size bytes in a
repetition is taken from the lowest order size bytes of this number.
Again, this bizarre behavior is compatible with other people's
assemblers.

size and value are optional. If the second comma and value are absent,
value is assumed zero. If the first comma and following tokens are
absent, size is assumed to be 1.

.float flonums
This directive assembles zero or more flonums, separated by commas. It
has the same effect as .single.

.func name[, label]
.func emits debugging information to denote function name, and is ignored
unless the file is assembled with debugging enabled. Only --gstabs[+] is
currently supported.  label is the entry point of the function and if
omitted name prepended with the leading char is used.  leading char is
usually _ or nothing, depending on the target. All functions are
currently defined to have void return type. The function must be
terminated with .endfunc.

.global symbol, .globl symbol
.global makes the symbol visible to ld.  If you define symbol in your
partial program, its value is made available to other partial programs
that are linked with it. Otherwise, symbol takes its attributes from a
symbol of the same name from another file linked into the same program.

Both spellings ( .globl and .global) are accepted, for compatibility with
other assemblers.

.hidden names
This is one of the ELF visibility directives. The other two are .internal
(see Section Internal'') and .protected (see Section Protected'').

This directive overrides the named symbols default visibility (which is
set by their binding: local, global or weak). The directive sets the
visibility to hidden which means that the symbols are not visible to
other components. Such symbols are always considered to be protected as
well.

.hword expressions
This expects zero or more expressions, and emits a 16 bit number for
each.

This directive is a synonym for .short.

.ident
This directive is used by some assemblers to place tags in object files.
The behavior of this directive varies depending on the target. When using
the a.out object file format, as simply accepts the directive for source-
file compatibility with existing assemblers, but does not emit anything
for it. When using COFF, comments are emitted to the .comment or .rdata
section, depending on the target. When using ELF, comments are emitted to
the .comment section.

.if absolute expression
.if marks the beginning of a section of code which is only considered
part of the source program being assembled if the argument (which must be
an absolute expression) is non-zero. The end of the conditional section
of code must be marked by .endif (see Section Endif''); optionally, you
may include code for the alternative condition, flagged by .else (see
Section Else'').  If you have several conditions to check, .elseif may
be used to avoid nesting blocks if/else within each subsequent .else
block.

The following variants of .if are also supported:

.ifdef symbol
Assembles the following section of code if the specified symbol
has been defined. Note a symbol which has been referenced but not
yet defined is considered to be undefined.

.ifb text
Assembles the following section of code if the operand is blank
(empty).

.ifc string1, string2
Assembles the following section of code if the two strings are
the same. The strings may be optionally quoted with single
quotes. If they are not quoted, the first string stops at the
first comma, and the second string stops at the end of the line.
Strings which contain whitespace should be quoted. The string
comparison is case sensitive.

.ifeq absolute expression
Assembles the following section of code if the argument is zero.

.ifeqs string1, string2
Another form of .ifc.  The strings must be quoted using double
quotes.

.ifge absolute expression
Assembles the following section of code if the argument is
greater than or equal to zero.

.ifgt absolute expression
Assembles the following section of code if the argument is
greater than zero.

.ifle absolute expression
Assembles the following section of code if the argument is less
than or equal to zero.

.iflt absolute expression
Assembles the following section of code if the argument is less
than zero.

.ifnb text
Like .ifb, but the sense of the test is reversed: this assembles
the following section of code if the operand is non-blank (non-
empty).

.ifnc string1, string2.
Like .ifc, but the sense of the test is reversed: this assembles
the following section of code if the two strings are not the
same.

.ifndef symbol

.ifnotdef symbol
Assembles the following section of code if the specified symbol
has not been defined. Both spelling variants are equivalent. Note
a symbol which has been referenced but not yet defined is
considered to be undefined.

.ifne absolute expression
Assembles the following section of code if the argument is not
equal to zero (in other words, this is equivalent to .if).

.ifnes string1, string2
Like .ifeqs, but the sense of the test is reversed: this
assembles the following section of code if the two strings are
not the same.

.incbin  Va file [, skip[, count]]
The incbin directive includes file verbatim at the current location. You
can control the search paths used with the -I command-line option (see
Section Invoking'').  Quotation marks are required around file.

The skip argument skips a number of bytes from the start of the file.
The count argument indicates the maximum number of bytes to read. Note
that the data is not aligned in any way, so it is the user's
responsibility to make sure that proper alignment is provided both before
and after the incbin directive.

.include  Va file
This directive provides a way to include supporting files at specified
points in your source program. The code from file is assembled as if it
followed the point of the .include; when the end of the included file is
reached, assembly of the original file continues. You can control the
search paths used with the -I command-line option (see Section
Invoking'').  Quotation marks are required around file.

.int expressions
Expect zero or more expressions, of any section, separated by commas. For
each expression, emit a number that, at run time, is the value of that
expression. The byte order and bit size of the number depends on what
kind of target the assembly is for.

.internal names
This is one of the ELF visibility directives. The other two are .hidden
(see Section Hidden'') and .protected (see Section Protected'').

This directive overrides the named symbols default visibility (which is
set by their binding: local, global or weak). The directive sets the
visibility to internal which means that the symbols are considered to be
hidden (i.e., not visible to other components), and that some extra,
processor specific processing must also be performed upon the symbols as
well.

.irp symbol, values...
Evaluate a sequence of statements assigning different values to symbol.
The sequence of statements starts at the .irp directive, and is
terminated by an .endr directive. For each value, symbol is set to value,
and the sequence of statements is assembled. If no value is listed, the
sequence of statements is assembled once, with symbol set to the null
string. To refer to symbol within the sequence of statements, use
\symbol.

For example, assembling

.irp    param,1,2,3
move    d\param,[email protected]
.endr

is equivalent to assembling

move    d1,[email protected]
move    d2,[email protected]
move    d3,[email protected]

.irpc symbol, values...
Evaluate a sequence of statements assigning different values to symbol.
The sequence of statements starts at the .irpc directive, and is
terminated by an .endr directive. For each character in value, symbol is
set to the character, and the sequence of statements is assembled. If no
value is listed, the sequence of statements is assembled once, with
symbol set to the null string. To refer to symbol within the sequence of
statements, use \symbol.

For example, assembling

.irpc    param,123
move    d\param,[email protected]
.endr

is equivalent to assembling

move    d1,[email protected]
move    d2,[email protected]
move    d3,[email protected]

For some caveats with the spelling of symbol, see also the discussion
atSee Section Macro''.

.lcomm symbol, length
Reserve length (an absolute expression) bytes for a local common denoted
by symbol.  The section and value of symbol are those of the new local
common. The addresses are allocated in the bss section, so that at run-
time the bytes start off zeroed.  Symbol is not declared global (see
Section Global''), so is normally not visible to ld.

.lflags
as accepts this directive, for compatibility with other assemblers, but
ignores it.

.line line-number
Even though this is a directive associated with the a.out or b.out
object-code formats, as still recognizes it when producing COFF output,
and treats .line as though it were the COFF .ln if it is found outside a
.def / .endef pair.

Inside a .def, .line is, instead, one of the directives used by compilers
to generate auxiliary symbol information for debugging.

Mark the current section so that the linker only includes a single copy
of it. This may be used to include the same section in several different
object files, but ensure that the linker will only include it once in the
final output file. The .linkonce pseudo-op must be used for each instance
of the section. Duplicate sections are detected based on the section
name, so it should be unique.

This directive is only supported by a few object file formats; as of this
writing, the only object file format which supports it is the Portable
Executable format used on Windows NT.

The type argument is optional. If specified, it must be one of the
following strings.  For example:

Not all types may be supported on all object file formats.

Silently discard duplicate sections. This is the default.

one_only
Warn if there are duplicate sections, but still keep only one
copy.

same_size
Warn if any of the duplicates have different sizes.

same_contents
Warn if any of the duplicates do not have exactly the same
contents.

.ln line-number
.ln is a synonym for .line.

.mri val
If val is non-zero, this tells as to enter MRI mode. If val is zero, this
tells as to exit MRI mode. This change affects code assembled until the
next .mri directive, or until the end of the file.See Section M''.

.list
Control (in conjunction with the .nolist directive) whether or not
assembly listings are generated. These two directives maintain an
internal counter (which is zero initially).  .list increments the
counter, and .nolist decrements it. Assembly listings are generated
whenever the counter is greater than zero.

By default, listings are disabled. When you enable them (with the -a
command line option;see Section Invoking''), the initial value of the
listing counter is one.

.long expressions
.long is the same as .int.  See Section.Dq Int .

.macro
The commands .macro and .endm allow you to define macros that generate
assembly output. For example, this definition specifies a macro sum that
puts a sequence of numbers into memory:

.macro  sum from=0, to=5
.long   \from
.if     \to-\from
sum     "(\from+1)",\to
.endif
.endm

With that definition, SUM 0,5 is equivalent to this assembly input:

.long   0
.long   1
.long   2
.long   3
.long   4
.long   5

.macro macname

.macro macname macargs ...
Begin the definition of a macro called macname.  If your macro
definition requires arguments, specify their names after the
macro name, separated by commas or spaces. You can qualify the
macro argument to indicate whether all invocations must specify a
non-blank value (through : req), or whether it takes all of the
remaining arguments (through : vararg).  You can supply a default
value for any macro argument by following the name with = deflt.
You cannot define two macros with the same macname unless it has
been subject to the .purgem directive (see Section Purgem'')
between the two definitions. For example, these are all valid
.macro statements:

.macro comm
Begin the definition of a macro called comm, which takes
no arguments.

.macro plus1 p, p1

.macro plus1 p p1
Either statement begins the definition of a macro called
plus1, which takes two arguments; within the macro
definition, write \p or \p1 to evaluate the arguments.

.macro reserve_str p1=0 p2
Begin the definition of a macro called reserve_str, with
two arguments. The first argument has a default value,
but not the second.  After the definition is complete,
you can call the macro either as reserve_str a, b (with
\p1 evaluating to a and \p2 evaluating to b), or as
reserve_str, b (with \p1 evaluating as the default, in
this case 0, and \p2 evaluating to b).

.macro m p1:req, p2=0, p3:vararg
Begin the definition of a macro called m, with at least
three arguments. The first argument must always have a
value specified, but not the second, which instead has a
default value. The third formal will get assigned all
remaining arguments specified at invocation time.

When you call a macro, you can specify the argument
values either by position, or by keyword. For example,
sum 9,17 is equivalent to sum to=17, from=9.

Note that since each of the macargs can be an identifier exactly
as any other one permitted by the target architecture, there may
be occasional problems if the target hand-crafts special meanings
to certain characters when they occur in a special position. For
example, if the colon ( :) is generally permitted to be part of a
symbol name, but the architecture specific code special-cases it
when occurring as the final character of a symbol (to denote a
label), then the macro parameter replacement code will have no
way of knowing that and consider the whole construct (including
the colon) an identifier, and check only this identifier for
being the subject to parameter substitution. So for example this
macro definition:

.macro label l
\l:
.endm

might not work as expected. Invoking label foo might not create a
label called foo but instead just insert the text \l: into the
assembler source, probably generating an error about an
unrecognised identifier.

Similarly problems might occur with the period character ( .)
which is often allowed inside opcode names (and hence identifier
names). So for example constructing a macro to build an opcode
from a base name and a length specifier like this:

.macro opcode base length
\base.\length
.endm

and invoking it as opcode store l will not create a store.l
instruction but instead generate some kind of error as the
assembler tries to interpret the text \base.\length.

There are several possible ways around this problem:

Insert white space
If it is possible to use white space characters then this
is the simplest solution. eg:

.macro label l
\l :
.endm

Use \()
The string \() can be used to separate the end of a macro
argument from the following text.  eg:

.macro opcode base length
\base\().\length
.endm

Use the alternate macro syntax mode
In the alternative macro syntax mode the ampersand
character ( &) can be used as a separator. eg:

.altmacro
.macro label l
l&:
.endm

Note: this problem of correctly identifying string parameters to
pseudo ops also applies to the identifiers used in .irp (see
Section Irp'') and .irpc (see Section Irpc'') as well.

.endm   Mark the end of a macro definition.

.exitm  Exit early from the current macro definition.

\@      as maintains a counter of how many macros it has executed in this
pseudo-variable; you can copy that number to your output with \@,
but only within a macro definition.

LOCAL name [, ...]
Warning: LOCAL is only available if you select "alternate macro
syntax" with --alternate or .altmacro. See Section.Dq Altmacro .

.altmacro
Enable alternate macro mode, enabling:

LOCAL name [, ...]
One additional directive, LOCAL, is available. It is used to
generate a string replacement for each of the name arguments, and
replace any instances of name in each macro expansion. The
replacement string is unique in the assembly, and different for
each separate macro expansion.  LOCAL allows you to write macros
that define symbols, without fear of conflict between separate
macro expansions.

String delimiters
You can write strings delimited in these other ways besides  Va
string:

' string'
You can delimit strings with single-quote characters.

< string>
You can delimit strings with matching angle brackets.

single-character string escape
To include any single character literally in a string (even if
the character would otherwise have some special meaning), you can
prefix the character with !  (an exclamation mark). For example,
you can write <4.3 !> 5.4!!> to get the literal text 4.3 > 5.4!.

Expression results as strings
You can write % expr to evaluate the expression expr and use the
result as a string.

.noaltmacro
Disable alternate macro mode.See Section Altmacro''.

.nolist
Control (in conjunction with the .list directive) whether or not assembly
listings are generated. These two directives maintain an internal counter
(which is zero initially).  .list increments the counter, and .nolist
decrements it. Assembly listings are generated whenever the counter is
greater than zero.

.octa biGNUms
This directive expects zero or more biGNUms, separated by commas. For
each biGNUm, it emits a 16-byte integer.

The term "octa" comes from contexts in which a "word" is two bytes; hence
octa -word for 16 bytes.

.org new-lc, fill
Advance the location counter of the current section to new-lc.  new-lc is
either an absolute expression or an expression with the same section as
the current subsection. That is, you can't use .org to cross sections: if
new-lc has the wrong section, the .org directive is ignored. To be
compatible with former assemblers, if the section of new-lc is absolute,
as issues a warning, then pretends the section of new-lc is the same as
the current subsection.

.org may only increase the location counter, or leave it unchanged; you
cannot use .org to move the location counter backwards.

Because as tries to assemble programs in one pass, new-lc may not be
undefined. If you really detest this restriction we eagerly await a
chance to share your improved assembler.

Beware that the origin is relative to the start of the section, not to
the start of the subsection. This is compatible with other people's
assemblers.

When the location counter (of the current subsection) is advanced, the
intervening bytes are filled with fill which should be an absolute
expression. If the comma and fill are omitted, fill defaults to zero.

.p2align[wl] abs-expr, abs-expr, abs-expr
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
number of low-order zero bits the location counter must have after
it a multiple of 8. If the location counter is already a multiple of 8,
no change is needed.

The second expression (also absolute) gives the fill value to be stored
in the padding bytes. It (and the comma) may be omitted. If it is
omitted, the padding bytes are normally zero. However, on some systems,
if the section is marked as containing code and the fill value is
omitted, the space is filled with no-op instructions.

The third expression is also absolute, and is also optional. If it is
present, it is the maximum number of bytes that should be skipped by this
alignment directive. If doing the alignment would require skipping more
bytes than the specified maximum, then the alignment is not done at all.
You can omit the fill value (the second argument) entirely by simply
using two commas after the required alignment; this can be useful if you
want the alignment to be filled with no-op instructions when appropriate.

The .p2alignw and .p2alignl directives are variants of the .p2align
directive. The .p2alignw directive treats the fill pattern as a two byte
word value. The .p2alignl directives treats the fill pattern as a four
byte longword value. For example, .p2alignw 2,0x368d will align to a
multiple of 4. If it skips two bytes, they will be filled in with the
value 0x368d (the exact placement of the bytes depends upon the
endianness of the processor). If it skips 1 or 3 bytes, the fill value is
undefined.

.previous
This is one of the ELF section stack manipulation directives. The others
are .section (see Section Section''), .subsection (see Section
SubSection''), .pushsection (see Section PushSection''), and
.popsection (see Section PopSection'').

This directive swaps the current section (and subsection) with most
recently referenced section (and subsection) prior to this one. Multiple
.previous directives in a row will flip between two sections (and their
subsections).

In terms of the section stack, this directive swaps the current section
with the top section on the section stack.

.popsection
This is one of the ELF section stack manipulation directives. The others
are .section (see Section Section''), .subsection (see Section
SubSection''), .pushsection (see Section PushSection''), and
.previous (see Section Previous'').

This directive replaces the current section (and subsection) with the top
section (and subsection) on the section stack. This section is popped off
the stack.

.print string
as will print string on the standard output during assembly. You must put
string in double quotes.

.protected names
This is one of the ELF visibility directives. The other two are .hidden
(see Section Hidden'') and .internal (see Section Internal'').

This directive overrides the named symbols default visibility (which is
set by their binding: local, global or weak). The directive sets the
visibility to protected which means that any references to the symbols
from within the components that defines them must be resolved to the
definition in that component, even if a definition in another component
would normally preempt this.

.psize lines, columns
Use this directive to declare the number of lines---and, optionally, the
number of columns---to use for each page, when generating listings.

If you do not use .psize, listings use a default line-count of 60. You
may omit the comma and columns specification; the default width is 200
columns.

as generates formfeeds whenever the specified number of lines is exceeded
(or whenever you explicitly request one, using .eject).

If you specify lines as 0, no formfeeds are generated save those
explicitly specified with .eject.

.purgem name
Undefine the macro name, so that later uses of the string will not be
expanded.See Section Macro''.

.pushsection name, subsection
This is one of the ELF section stack manipulation directives. The others
are .section (see Section Section''), .subsection (see Section
SubSection''), .popsection (see Section PopSection''), and .previous
(see Section Previous'').

This directive pushes the current section (and subsection) onto the top
of the section stack, and then replaces the current section and
subsection with name and subsection.

.quad expects zero or more biGNUms, separated by commas. For each bignum,
it emits an 8-byte integer. If the biGNUm won't fit in 8 bytes, it prints
a warning message; and just takes the lowest order 8 bytes of the biGNUm.

The term "quad" comes from contexts in which a "word" is two bytes; hence

.reloc offset, reloc_name[, expression]
Generate a relocation at offset of type reloc_name with value expression.
If offset is a number, the relocation is generated in the current
section. If offset is an expression that resolves to a symbol plus
offset, the relocation is generated in the given symbol's section.
expression, if present, must resolve to a symbol plus addend or to an
absolute value, but note that not all targets support an addend. e.g. ELF
REL targets such as i386 store an addend in the section contents rather
than in the relocation.  This low level interface does not support

.rept count
Repeat the sequence of lines between the .rept directive and the next
.endr directive count times.

For example, assembling

.rept   3
.long   0
.endr

is equivalent to assembling

.long   0
.long   0
.long   0

Use subheading as the title (third line, immediately after the title
line) when generating assembly listings.

This directive affects subsequent pages, as well as the current page if
it appears within ten lines of the top of a page.

.section name
Use the .section directive to assemble the following code into a section
named name.

This directive is only supported for targets that actually support
arbitrarily named sections; on a.out targets, for example, it is not
accepted, even with a standard a.out section name.

This is one of the ELF section stack manipulation directives. The others
are .subsection (see Section SubSection''), .pushsection (see Section
PushSection''), .popsection (see Section PopSection''), and .previous
(see Section Previous'').

For ELF targets, the .section directive is used like this:

.section name [, "flags"[, @type[,flag_specific_arguments]]]

The optional flags argument is a quoted string which may contain any
combination of the following characters:

a       section is allocatable

w       section is writable

x       section is executable

M       section is mergeable

S       section contains zero terminated strings

G       section is a member of a section group

T       section is used for thread-local-storage

The optional type argument may contain one of the following constants:

@progbits
section contains data

@nobits
section does not contain data (i.e., section only occupies space)

@note   section contains data which is used by things other than the
program

@init_array
section contains an array of pointers to init functions

@fini_array
section contains an array of pointers to finish functions

@preinit_array
section contains an array of pointers to pre-init functions

Many targets only support the first three section types.

Note on targets where the @ character is the start of a comment (eg ARM)
then another character is used instead. For example the ARM port uses the
% character.

If flags contains the M symbol then the type argument must be specified
as well as an extra argument--- entsize ---like this:

.section name , "flags"M, @type, entsize

Sections with the M flag but not S flag must contain fixed size
constants, each entsize octets long. Sections with both M and S must
contain zero terminated strings where each character is entsize bytes
long. The linker may remove duplicates within sections with the same
name, same entity size and same flags.  entsize must be an absolute
expression.

If flags contains the G symbol then the type argument must be present
along with an additional field like this:

.section name , "flags"G, @type, GroupName[, linkage]

The GroupName field specifies the name of the section group to which this
particular section belongs. The optional linkage field can contain:

comdat  indicates that only one copy of this section should be retained

an alias for comdat

Note: if both the M and G flags are present then the fields for the Merge
flag should come first, like this:

.section name , "flags"MG, @type, entsize, GroupName[, linkage]

If no flags are specified, the default flags depend upon the section
name.  If the section name is not recognized, the default will be for the
section to have none of the above flags: it will not be allocated in
memory, nor writable, nor executable. The section will contain data.

For ELF targets, the assembler supports another type of .section
directive for compatibility with the Solaris assembler:

.section "name"[, flags...]

Note that the section name is quoted. There may be a sequence of comma
separated flags:

#alloc  section is allocatable

#write  section is writable

#execinstr
section is executable

#tls    section is used for thread local storage

This directive replaces the current section and subsection. See the
contents of the gas testsuite directory gas/testsuite/gas/elf for some
examples of how this directive and the other section stack directives
work.

.set symbol, expression
Set the value of symbol to expression.  This changes symbol 's value and
type to conform to expression.  If symbol was flagged as external, it
remains flagged (see Section Symbol Attributes'').

You may .set a symbol many times in the same assembly.

If you .set a global symbol, the value stored in the object file is the
last value stored into it.

.short expressions
This expects zero or more expressions, and emits a 16 bit number for
each.

.single flonums
This directive assembles zero or more flonums, separated by commas. It
has the same effect as .float.

.size
This directive is used to set the size associated with a symbol.

For ELF targets, the .size directive is used like this:

.size name , expression

This directive sets the size associated with a symbol name.  The size in
bytes is computed from expression which can make use of label arithmetic.
This directive is typically used to set the size of function symbols.

.sleb128 expressions
sleb128 stands for "signed little endian base 128." This is a compact,
variable length representation of numbers used by the DWARF symbolic
debugging format.See Section Uleb128''.

.skip size, fill
This directive emits size bytes, each of value fill.  Both size and fill
are absolute expressions. If the comma and fill are omitted, fill is
assumed to be zero. This is the same as .space.

.space size, fill
This directive emits size bytes, each of value fill.  Both size and fill
are absolute expressions. If the comma and fill are omitted, fill is
assumed to be zero. This is the same as .skip.

.stabd, .stabn, .stabs
There are three directives that begin .stab.  All emit symbols (see
Section Symbols''), for use by symbolic debuggers. The symbols are not
entered in the as hash table: they cannot be referenced elsewhere in the
source file. Up to five fields are required:

string  This is the symbol's name. It may contain any character except
\000, so is more general than ordinary symbol names. Some
debuggers used to code arbitrarily complex structures into symbol
names using this field.

type    An absolute expression. The symbol's type is set to the low 8
bits of this expression. Any bit pattern is permitted, but ld and
debuggers choke on silly bit patterns.

other   An absolute expression. The symbol's "other" attribute is set to
the low 8 bits of this expression.

desc    An absolute expression. The symbol's descriptor is set to the low
16 bits of this expression.

value   An absolute expression which becomes the symbol's value.

If a warning is detected while reading a .stabd, .stabn, or .stabs
statement, the symbol has probably already been created; you get a half-
formed symbol in your object file. This is compatible with earlier
assemblers!

.stabd type, other, desc

The "name" of the symbol generated is not even an empty string.
It is a null pointer, for compatibility. Older assemblers used a
null pointer so they didn't waste space in object files with
empty strings.

The symbol's value is set to the location counter, relocatably.
When your program is linked, the value of this symbol is the
address of the location counter when the .stabd was assembled.

.stabn type, other, desc, value
The name of the symbol is set to the empty string .

.stabs string, type, other, desc, value
All five fields are specified.

.string  Va str
Copy the characters in str to the object file. You may specify more than
one string to copy, separated by commas. Unless otherwise specified for a
particular machine, the assembler marks the end of each string with a 0
byte. You can use any of the escape sequences described in
Strings,,Strings.

.struct expression
Switch to the absolute section, and set the section offset to expression,
which must be an absolute expression. You might use this as follows:

.struct 0
field1:
.struct field1 + 4
field2:
.struct field2 + 4
field3:
This would define the symbol field1 to have the value 0, the symbol
field2 to have the value 4, and the symbol field3 to have the value 8.
Assembly would be left in the absolute section, and you would need to use
a .section directive of some sort to change to some other section before
further assembly.

.subsection name
This is one of the ELF section stack manipulation directives. The others
are .section (see Section Section''), .pushsection (see Section
PushSection''), .popsection (see Section PopSection''), and .previous
(see Section Previous'').

This directive replaces the current subsection with name.  The current
section is not changed. The replaced subsection is put onto the section
stack in place of the then current top of stack subsection.

.symver
Use the .symver directive to bind symbols to specific version nodes
within a source file.  This is only supported on ELF platforms, and is
typically used when assembling files to be linked into a shared library.
There are cases where it may make sense to use this in objects to be
bound into an application itself so as to override a versioned symbol
from a shared library.

For ELF targets, the .symver directive can be used like this:

.symver name, [email protected]
If the symbol name is defined within the file being assembled, the
.symver directive effectively creates a symbol alias with the name
[email protected], and in fact the main reason that we just don't try and
create a regular alias is that the @ character isn't permitted in symbol
names. The name2 part of the name is the actual name of the symbol by
which it will be externally referenced. The name name itself is merely a
name of convenience that is used so that it is possible to have
definitions for multiple versions of a function within a single source
file, and so that the compiler can unambiguously know which version of a
function is being mentioned. The nodename portion of the alias should be
the name of a node specified in the version script supplied to the linker
when building a shared library. If you are attempting to override a
versioned symbol from a shared library, then nodename should correspond
to the nodename of the symbol you are trying to override.

If the symbol name is not defined within the file being assembled, all
references to name will be changed to [email protected].  If no reference to
name is made, [email protected] will be removed from the symbol table.

Another usage of the .symver directive is:

.symver name, [email protected]@nodename
In this case, the symbol name must exist and be defined within the file
being assembled. It is similar to [email protected].  The difference is
[email protected]@nodename will also be used to resolve references to name2 by the

The third usage of the .symver directive is:

.symver name, [email protected]@@nodename
When name is not defined within the file being assembled, it is treated
as [email protected].  When name is defined within the file being assembled,
the symbol name, name, will be changed to [email protected]@nodename.

.text subsection
Tells as to assemble the following statements onto the end of the text
subsection numbered subsection, which is an absolute expression. If
subsection is omitted, subsection number zero is used.

Use heading as the title (second line, immediately after the source file
name and pagenumber) when generating assembly listings.

This directive affects subsequent pages, as well as the current page if
it appears within ten lines of the top of a page.

.type
This directive is used to set the type of a symbol.

For ELF targets, the .type directive is used like this:

.type name , type description

This sets the type of symbol name to be either a function symbol or an
object symbol. There are five different syntaxes supported for the type
description field, in order to provide compatibility with various other
assemblers.

Because some of the characters used in these syntaxes (such as @ and #)
are comment characters for some architectures, some of the syntaxes below
do not work on all architectures. The first variant will be accepted by
the GNU assembler on all architectures so that variant should be used for
maximum portability, if you do not need to assemble your code with other
assemblers.

The syntaxes supported are:

.type <name> STT_FUNCTION
.type <name> STT_OBJECT

.type <name>,#function
.type <name>,#object

.type <name>,@function
.type <name>,@object

.type <name>,%function
.type <name>,%object

.type <name>,"function"
.type <name>,"object"

.uleb128 expressions
uleb128 stands for "unsigned little endian base 128." This is a compact,
variable length representation of numbers used by the DWARF symbolic
debugging format.See Section Sleb128''.

.version  Va string
This directive creates a .note section and places into it an ELF
formatted note of type NT_VERSION. The note's name is set to string.

.vtable_entry table, offset
This directive finds or creates a symbol table and creates a VTABLE_ENTRY
relocation for it with an addend of offset.

.vtable_inherit child, parent
This directive finds the symbol child and finds or creates the symbol
parent and then creates a VTABLE_INHERIT relocation for the parent whose
addend is the value of the child symbol. As a special case the parent
name of 0 is treated as referring to the *ABS* section.

.warning  Va string
Similar to the directive .error (see Section Error''), but just emits a
warning.

.weak names
This directive sets the weak attribute on the comma separated list of
symbol names.  If the symbols do not already exist, they will be created.

On COFF targets other than PE, weak symbols are a GNU extension. This
directive sets the weak attribute on the comma separated list of symbol
names.  If the symbols do not already exist, they will be created.

On the PE target, weak symbols are supported natively as weak aliases.
When a weak symbol is created that is not an alias, GAS creates an
alternate symbol to hold the default value.

.weakref alias, target
This directive creates an alias to the target symbol that enables the
symbol to be referenced with weak-symbol semantics, but without actually
making it weak. If direct references or definitions of the symbol are
present, then the symbol will not be weak, but if all references to it
are through weak references, the symbol will be marked as weak in the
symbol table.

The effect is equivalent to moving all references to the alias to a
separate assembly source file, renaming the alias to the symbol in it,
declaring the symbol as weak there, and running a reloadable link to
merge the object files resulting from the assembly of the new source file
and the old source file that had the references to the alias removed.

The alias itself never makes to the symbol table, and is entirely handled
within the assembler.

.word expressions
This directive expects zero or more expressions, of any section,
separated by commas. For each expression, as emits a 32-bit number.

Deprecated Directives
One day these directives won't work. They are included for compatibility
with older assemblers.

.abort

.line

ARM Dependent Features
Options
-mcpu= processor[+ extension...]
This option specifies the target processor. The assembler will
issue an error message if an attempt is made to assemble an
instruction which will not execute on the target processor. The
following processor names are recognized: arm1, arm2, arm250,
arm3, arm6, arm60, arm600, arm610, arm620, arm7, arm7m, arm7d,
arm7dm, arm7di, arm7dmi, arm70, arm700, arm700i, arm710, arm710t,
arm720, arm720t, arm740t, arm710c, arm7100, arm7500, arm7500fe,
arm7t, arm7tdmi, arm7tdmi-s, arm8, arm810, strongarm, strongarm1,
strongarm110, strongarm1100, strongarm1110, arm9, arm920,
arm920t, arm922t, arm940t, arm9tdmi, arm9e, arm926e, arm926ej-s,
arm946e-r0, arm946e, arm946e-s, arm966e-r0, arm966e, arm966e-s,
arm968e-s, arm10t, arm10tdmi, arm10e, arm1020, arm1020t,
arm1020e, arm1022e, arm1026ej-s, arm1136j-s, arm1136jf-s,
arm1156t2-s, arm1156t2f-s, arm1176jz-s, arm1176jzf-s, mpcore,
mpcorenovfp, cortex-a8, cortex-r4, cortex-m3, ep9312 (ARM920 with
Cirrus Maverick coprocessor), i80200 (Intel XScale processor)
iwmmxt (Intel(r) XScale processor with Wireless MMX(tm)
technology coprocessor) and xscale.  The special name all may be
used to allow the assembler to accept instructions valid for any
ARM processor.

In addition to the basic instruction set, the assembler can be
told to accept various extension mnemonics that extend the
processor using the co-processor instruction space. For example,
-mcpu=arm920+maverick is equivalent to specifying -mcpu=ep9312.
The following extensions are currently supported: +maverick
+iwmmxt and +xscale.

-march= architecture[+ extension...]
This option specifies the target architecture. The assembler will
issue an error message if an attempt is made to assemble an
instruction which will not execute on the target architecture.
The following architecture names are recognized: armv1, armv2,
armv2a, armv2s, armv3, armv3m, armv4, armv4xm, armv4t, armv4txm,
armv5, armv5t, armv5txm, armv5te, armv5texp, armv6, armv6j,
armv6k, armv6z, armv6zk, armv7, armv7-a, armv7-r, armv7-m, iwmmxt
and xscale.  If both -mcpu and -march are specified, the
assembler will use the setting for -mcpu.

The architecture option can be extended with the same instruction
set extension options as the -mcpu option.

-mfpu= floating-point-format

This option specifies the floating point format to assemble for.
The assembler will issue an error message if an attempt is made
to assemble an instruction which will not execute on the target
floating point unit. The following format options are recognized:
softfpa, fpe, fpe2, fpe3, fpa, fpa10, fpa11, arm7500fe, softvfp,
softvfp+vfp, vfp, vfp10, vfp10-r0, vfp9, vfpxd, arm1020t,
arm1020e, arm1136jf-s and maverick.

In addition to determining which instructions are assembled, this
option also affects the way in which the .double assembler
directive behaves when assembling little-endian code.

The default is dependent on the processor selected. For
Architecture 5 or later, the default is to assembler for VFP
instructions; for earlier architectures the default is to
assemble for FPA instructions.

-mthumb
This option specifies that the assembler should start assembling
Thumb instructions; that is, it should behave as though the file
starts with a .code 16 directive.

-mthumb-interwork
This option specifies that the output generated by the assembler
should be marked as supporting interworking.

-mapcs [26|32]
This option specifies that the output generated by the assembler
should be marked as supporting the indicated version of the Arm
Procedure. Calling Standard.

-matpcs
This option specifies that the output generated by the assembler
should be marked as supporting the Arm/Thumb Procedure Calling
Standard. If enabled this option will cause the assembler to
create an empty debugging section in the object file called
.arm.atpcs. Debuggers can use this to determine the ABI being
used by.

-mapcs-float
This indicates the floating point variant of the APCS should be
used. In this variant floating point arguments are passed in FP
registers rather than integer registers.

-mapcs-reentrant
This indicates that the reentrant variant of the APCS should be
used. This variant supports position independent code.

-mfloat-abi= abi
This option specifies that the output generated by the assembler
should be marked as using specified floating point ABI. The
following values are recognized: soft, softfp and hard.

-meabi= ver
This option specifies which EABI version the produced object
files should conform to. The following values are recognized:
GNU, 4 and 5.

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

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

-k      This option specifies that the output of the assembler should be
marked as position-independent code (PIC).

Syntax
Special Characters

The presence of a @ on a line indicates the start of a comment that
extends to the end of the current line. If a # appears as the first
character of a line, the whole line is treated as a comment.

The ; character can be used instead of a newline to separate statements.

Either # or can be used to indicate immediate operands. *TODO* Explain about /data modifier on symbols. Register Names *TODO* Explain about ARM register naming, and the predefined names. ARM relocation generation Specific data relocations can be generated by putting the relocation name in parentheses after the symbol name. For example: .word foo(TARGET1) This will generate an R_ARM_TARGET1 relocation against the symbol foo. The following relocations are supported: GOT, GOTOFF, TARGET1, TARGET2, SBREL, TLSGD, TLSLDM, TLSLDO, GOTTPOFF and TPOFF. For compatibility with older toolchains the assembler also accepts (PLT) after branch targets. This will generate the deprecated R_ARM_PLT32 relocation. Relocations for MOVW and MOVT instructions can be generated by prefixing the value with #:lower16: and #:upper16 respectively. For example to load the 32-bit address of foo into r0: MOVW r0, #:lower16:foo MOVT r0, #:upper16:foo Floating Point The ARM family uses ieee floating-point numbers. ARM Machine Directives .align expression [, expression] This is the generic .align directive. For the ARM however if the first argument is zero (ie no alignment is needed) the assembler will behave as if the argument had been 2 (ie pad to the next four byte boundary). This is for compatibility with ARM's own assembler. name .req register name This creates an alias for register name called name. For example: foo .req r0 .unreq alias-name This undefines a register alias which was previously defined using the req, dn or qn directives. For example: foo .req r0 .unreq foo An error occurs if the name is undefined. Note - this pseudo op can be used to delete builtin in register name aliases (eg 'r0'). This should only be done if it is really necessary. name .dn register name [.type] [[index]] name .qn register name [.type] [[index]] The dn and qn directives are used to create typed and/or indexed register aliases for use in Advanced SIMD Extension (Neon) instructions. The former should be used to create aliases of double-precision registers, and the latter to create aliases of quad-precision registers. If these directives are used to create typed aliases, those aliases can be used in Neon instructions instead of writing types after the mnemonic or after each operand. For example: x .dn d2.f32 y .dn d3.f32 z .dn d4.f32[1] vmul x,y,z This is equivalent to writing the following: vmul.f32 d2,d3,d4[1] Aliases created using dn or qn can be destroyed using unreq. .code [16|32] This directive selects the instruction set being generated. The value 16 selects Thumb, with the value 32 selecting ARM. .thumb This performs the same action as .code 16. .arm This performs the same action as .code 32. .force_thumb This directive forces the selection of Thumb instructions, even if the target processor does not support those instructions .thumb_func This directive specifies that the following symbol is the name of a Thumb encoded function. This information is necessary in order to allow the assembler and linker to generate correct code for interworking between Arm and Thumb instructions and should be used even if interworking is not going to be performed. The presence of this directive also implies .thumb This directive is not neccessary when generating EABI objects. On these targets the encoding is implicit when generating Thumb code. .thumb_set This performs the equivalent of a .set directive in that it creates a symbol which is an alias for another symbol (possibly not yet defined). This directive also has the added property in that it marks the aliased symbol as being a thumb function entry point, in the same way that the .thumb_func directive does. .ltorg This directive causes the current contents of the literal pool to be dumped into the current section (which is assumed to be the .text section) at the current location (aligned to a word boundary). GAS maintains a separate literal pool for each section and each sub-section. The .ltorg directive will only affect the literal pool of the current section and sub-section. At the end of assembly all remaining, un-empty literal pools will automatically be dumped. Note - older versions of GAS would dump the current literal pool any time a section change occurred. This is no longer done, since it prevents accurate control of the placement of literal pools. .pool This is a synonym for .ltorg. .unwind_fnstart Marks the start of a function with an unwind table entry. .unwind_fnend Marks the end of a function with an unwind table entry. The unwind index table entry is created when this directive is processed. If no personality routine has been specified then standard personality routine 0 or 1 will be used, depending on the number of unwind opcodes required. .cantunwind Prevents unwinding through the current function. No personality routine or exception table data is required or permitted. .personality name Sets the personality routine for the current function to name. .personalityindex index Sets the personality routine for the current function to the EABI standard routine number index .handlerdata Marks the end of the current function, and the start of the exception table entry for that function. Anything between this directive and the .fnend directive will be added to the exception table entry. Must be preceded by a .personality or .personalityindex directive. .save reglist Generate unwinder annotations to restore the registers in reglist. The format of reglist is the same as the corresponding store-multiple instruction. .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]! .vsave vfp-reglist Generate unwinder annotations to restore the VFP registers in vfp-reglist using FLDMD. Also works for VFPv3 registers that are to be restored using VLDM. The format of vfp-reglist is the same as the corresponding store-multiple instruction. .vsave {d8, d9, d10} fstmdd sp!, {d8, d9, d10} .vsave {d15, d16, d17} vstm sp!, {d15, d16, d17} Since FLDMX and FSTMX are now deprecated, this directive should be used in favour of .save for saving VFP registers for ARMv6 and above. .pad # count Generate unwinder annotations for a stack adjustment of count bytes. A positive value indicates the function prologue allocated stack space by decrementing the stack pointer. .movsp reg [, # offset] Tell the unwinder that reg contains an offset from the current stack pointer. If offset is not specified then it is assumed to be zero. .setfp fpreg, spreg [, # offset] Make all unwinder annotations relaive to a frame pointer. Without this the unwinder will use offsets from the stack pointer. The syntax of this directive is the same as the sub or mov instruction used to set the frame pointer. spreg must be either sp or mentioned in a previous .movsp directive. .movsp ip mov ip, sp ... .setfp fp, ip, #4 sub fp, ip, #4 .raw offset, byte1, ... Insert one of more arbitary unwind opcode bytes, which are known to adjust the stack pointer by offset bytes. For example .unwind_raw 4, 0xb1, 0x01 is equivalent to .save {r0} .cpu name Select the target processor. Valid values for name are the same as for the [-mcpu] commandline option. .arch name Select the target architecture. Valid values for name are the same as for the [-march] commandline option. .object_arch name Override the architecture recorded in the EABI object attribute section. Valid values for name are the same as for the .arch directive. Typically this is useful when code uses runtime detection of CPU features. .fpu name Select the floating point unit to assemble for. Valid values for name are the same as for the [-mfpu] commandline option. .eabi_attribute tag, value Set the EABI object attribute number tag to value. The value is either a number, string, or number, string depending on the tag. Opcodes as implements all the standard ARM opcodes. It also implements several pseudo opcodes, including several synthetic load instructions. NOP nop This pseudo op will always evaluate to a legal ARM instruction that does nothing. Currently it will evaluate to MOV r0, r0. LDR ldr <register> , = <expression> If expression evaluates to a numeric constant then a MOV or MVN instruction will be used in place of the LDR instruction, if the constant can be generated by either of these instructions. Otherwise the constant will be placed into the nearest literal pool (if it not already there) and a PC relative LDR instruction will be generated. ADR adr <register> <label> This instruction will load the address of label into the indicated register. The instruction will evaluate to a PC relative ADD or SUB instruction depending upon where the label is located. If the label is out of range, or if it is not defined in the same file (and section) as the ADR instruction, then an error will be generated. This instruction will not make use of the literal pool. ADRL adrl <register> <label> This instruction will load the address of label into the indicated register. The instruction will evaluate to one or two PC relative ADD or SUB instructions depending upon where the label is located. If a second instruction is not needed a NOP instruction will be generated in its place, so that this instruction is always 8 bytes long. If the label is out of range, or if it is not defined in the same file (and section) as the ADRL instruction, then an error will be generated. This instruction will not make use of the literal pool. For information on the ARM or Thumb instruction sets, see ARM Software Development Toolkit Reference Manual, Advanced RISC Machines Ltd. Mapping Symbols The ARM ELF specification requires that special symbols be inserted into object files to mark certain features:a      At the start of a region of code containing ARM instructions.

$t At the start of a region of code containing THUMB instructions.$d      At the start of a region of data.

The assembler will automatically insert these symbols for you - there is
no need to code them yourself. Support for tagging symbols ($b,$f, $p and$m) which is also mentioned in the current ARM ELF specification is
not implemented.  This is because they have been dropped from the new
EABI and so tools cannot rely upon their presence.

80386 Dependent Features
The i386 version as supports both the original Intel 386 architecture in
both 16 and 32-bit mode as well as AMD x86-64 architecture extending the
Intel architecture to 64-bits.

Options
The i386 version of as has a few machine dependent options:

--32 | --64
Select the word size, either 32 bits or 64 bits. Selecting 32-bit
implies Intel i386 architecture, while 64-bit implies AMD x86-64
architecture.

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
This option specifies an instruction set architecture for
generating instructions.  The following architectures are
recognized: i8086, i186, i286, i386, i486, i586, i686, pentium,
pentiumpro, pentiumii, pentiumiii, pentium4, prescott, nocona,
core, core2, k6, k6_2, athlon, sledgehammer, opteron, k8,
generic32 and generic64.

This option only affects instructions generated by the assembler.
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 [-march= CPU].

AT&T Syntax versus Intel Syntax
as now supports assembly using Intel assembler syntax.  .intel_syntax
selects Intel mode, and .att_syntax switches back to the usual AT&T mode
for compatibility with the output of gcc.  Either of these directives may
have an optional argument, prefix, or noprefix specifying whether
registers require a % prefix. AT&T System V/386 assembler syntax is quite
different from Intel syntax.  We mention these differences because almost
all 80386 documents use Intel syntax. Notable differences between the two
syntaxes are:

•   AT&T immediate operands are preceded by $; Intel immediate operands are undelimited (Intel push 4 is AT&T pushl$4).  AT&T register
operands are preceded by %; Intel register operands are undelimited.
AT&T absolute (as opposed to PC relative) jump/call operands are
prefixed by *; they are undelimited in Intel syntax.

•   AT&T and Intel syntax use the opposite order for source and
destination operands.  Intel add eax, 4 is addl $4, %eax. The source, dest convention is maintained for compatibility with previous Unix assemblers. Note that instructions with more than one source operand, such as the enter instruction, do not have reversed order. i386-Bugs. • In AT&T syntax the size of memory operands is determined from the last character of the instruction mnemonic. Mnemonic suffixes of b, w, l and q specify byte (8-bit), word (16-bit), long (32-bit) and quadruple word (64-bit) memory references. Intel syntax accomplishes this by prefixing memory operands ( not the instruction mnemonics) with byte ptr, word ptr, dword ptr and qword ptr. Thus, Intel mov al, byte ptr foo is movb foo, %al in AT&T syntax. • Immediate form long jumps and calls are lcall/ljmp$ section, $offset in AT&T syntax; the Intel syntax is call/jmp far section: offset. Also, the far return instruction is lret$ stack-adjust in
AT&T syntax; Intel syntax is ret far stack-adjust.

•   The AT&T assembler does not provide support for multiple section
programs.  Unix style systems expect all programs to be single
sections.

Instruction Naming
Instruction mnemonics are suffixed with one character modifiers which
specify the size of operands. The letters b, w, l and q specify byte,
word, long and quadruple word operands. If no suffix is specified by an
instruction then as tries to fill in the missing suffix based on the
destination register operand (the last one by convention). Thus, mov %ax,
%bx is equivalent to movw %ax, %bx; also, mov $1, %bx is equivalent to movw$1, bx.  Note that this is incompatible with the AT&T Unix assembler
which assumes that a missing mnemonic suffix implies long operand size.
(This incompatibility does not affect compiler output since compilers
always explicitly specify the mnemonic suffix.)

Almost all instructions have the same names in AT&T and Intel format.
There are a few exceptions. The sign extend and zero extend instructions
need two sizes to specify them. They need a size to sign/zero extend from
and a size to zero extend to.  This is accomplished by using two
instruction mnemonic suffixes in AT&T syntax.  Base names for sign extend
and zero extend are movs... and movz... in AT&T syntax ( movsx and movzx
in Intel syntax). The instruction mnemonic suffixes are tacked on to this
base name, the from suffix before the to suffix. Thus, movsbl %al, %edx
is AT&T syntax for "move sign extend from %al to %edx." Possible
suffixes, thus, are bl (from byte to long), bw (from byte to word), wl
(from word to long), bq (from byte to quadruple word), wq (from word to

The Intel-syntax conversion instructions

•   cbw --- sign-extend byte in %al to word in %ax,

•   cwde --- sign-extend word in %ax to long in %eax,

•   cwd --- sign-extend word in %ax to long in %dx:%ax,

•   cdq --- sign-extend dword in %eax to quad in %edx:%eax,

•   cdqe --- sign-extend dword in %eax to quad in %rax (x86-64 only),

•   cqo --- sign-extend quad in %rax to octuple in %rdx:%rax (x86-64
only),

are called cbtw, cwtl, cwtd, cltd, cltq, and cqto in AT&T naming.  as
accepts either naming for these instructions.

Far call/jump instructions are lcall and ljmp in AT&T syntax, but are
call far and jump far in Intel convention.

Register Naming
Register operands are always prefixed with %.  The 80386 registers
consist of

•   the 8 32-bit registers %eax (the accumulator), %ebx, %ecx, %edx,
%edi, %esi, %ebp (the frame pointer), and %esp (the stack pointer).

•   the 8 16-bit low-ends of these: %ax, %bx, %cx, %dx, %di, %si, %bp,
and %sp.

•   the 8 8-bit registers: %ah, %al, %bh, %bl, %ch, %cl, %dh, and %dl
(These are the high-bytes and low-bytes of %ax, %bx, %cx, and %dx)

•   the 6 section registers %cs (code section), %ds (data section), %ss
(stack section), %es, %fs, and %gs.

•   the 3 processor control registers %cr0, %cr2, and %cr3.

•   the 6 debug registers %db0, %db1, %db2, %db3, %db6, and %db7.

•   the 2 test registers %tr6 and %tr7.

•   the 8 floating point register stack %st or equivalently %st(0),
%st(1), %st(2), %st(3), %st(4), %st(5), %st(6), and %st(7).  These
registers are overloaded by 8 MMX registers %mm0, %mm1, %mm2, %mm3,
%mm4, %mm5, %mm6 and %mm7.

•   the 8 SSE registers registers %xmm0, %xmm1, %xmm2, %xmm3, %xmm4,
%xmm5, %xmm6 and %xmm7.

The AMD x86-64 architecture extends the register set by:

•   enhancing the 8 32-bit registers to 64-bit: %rax (the accumulator),
%rbx, %rcx, %rdx, %rdi, %rsi, %rbp (the frame pointer), %rsp (the
stack pointer)

•   the 8 extended registers %r8 -- %r15.

•   the 8 32-bit low ends of the extended registers: %r8d -- %r15d

•   the 8 16-bit low ends of the extended registers: %r8w -- %r15w

•   the 8 8-bit low ends of the extended registers: %r8b -- %r15b

•   the 4 8-bit registers: %sil, %dil, %bpl, %spl.

•   the 8 debug registers: %db8 -- %db15.

•   the 8 SSE registers: %xmm8 -- %xmm15.

Instruction Prefixes
Instruction prefixes are used to modify the following instruction. They
are used to repeat string instructions, to provide section overrides, to
perform bus lock operations, and to change operand and address sizes.
(Most instructions that normally operate on 32-bit operands will use
16-bit operands if the instruction has an "operand size" prefix.)
Instruction prefixes are best written on the same line as the instruction
they act upon. For example, the scas (scan string) instruction is
repeated with:

repne scas %es:(%edi),%al

You may also place prefixes on the lines immediately preceding the
instruction, but this circumvents checks that as does with prefixes, and
will not work with all prefixes.

Here is a list of instruction prefixes:

•   Section override prefixes cs, ds, ss, es, fs, gs.  These are
automatically added by specifying using the section : memory-operand
form for memory references.

addr32 change 16-bit ones (in a .code16 section) into 32-bit
operands/addresses. These prefixes must appear on the same line of
code as the instruction they modify. For example, in a 16-bit .code16
section, you might write:

•   The bus lock prefix lock inhibits interrupts during execution of the
instruction it precedes. (This is only valid with certain
instructions; see a 80386 manual for details).

•   The wait for coprocessor prefix wait waits for the coprocessor to
complete the current instruction. This should never be needed for the
80386/80387 combination.

•   The rep, repe, and repne prefixes are added to string instructions to
make them repeat %ecx times ( %cx times if the current address size
is 16-bits).

•   The rex family of prefixes is used by x86-64 to encode extensions to
i386 instruction set. The rex prefix has four bits --- an operand
size overwrite ( 64) used to change operand size from 32-bit to
64-bit and X, Y and Z extensions bits used to extend the register
set.

You may write the rex prefixes directly. The rex64xyz instruction
emits rex prefix with all the bits set. By omitting the 64, x, y or z
you may write other prefixes as well. Normally, there is no need to
write the prefixes explicitly, since gas will automatically generate
them based on the instruction operands.

Memory References
An Intel syntax indirect memory reference of the form

section:[base + index*scale + disp]

is translated into the AT&T syntax

section:disp(base, index, scale)

where base and index are the optional 32-bit base and index registers,
disp is the optional displacement, and scale, taking the values 1, 2, 4,
and 8, multiplies index to calculate the address of the operand. If no
scale is specified, scale is taken to be 1.  section specifies the
optional section register for the memory operand, and may override the
default section register (see a 80386 manual for section register
defaults).  Note that section overrides in AT&T syntax must be preceded
by a %.  If you specify a section override which coincides with the
default section register, as does not output any section register
override prefixes to assemble the given instruction.  Thus, section
overrides can be specified to emphasize which section register is used
for a given memory operand.

Here are some examples of Intel and AT&T style memory references:

AT&T: -4(%ebp), Intel: [ebp - 4]
base is %ebp; disp is -4.  section is missing, and the default
section is used ( %ss for addressing with %ebp as the base
register).  index, scale are both missing.

AT&T: foo(,%eax,4), Intel: [foo + eax*4]
index is %eax (scaled by a scale 4); disp is foo.  All other
fields are missing. The section register here defaults to %ds.

AT&T: foo(,1); Intel [foo]
This uses the value pointed to by foo as a memory operand. Note
that base and index are both missing, but there is only one ,.
This is a syntactic exception.

AT&T: %gs:foo; Intel gs:foo
This selects the contents of the variable foo with section
register section being %gs.

Absolute (as opposed to PC relative) call and jump operands must be
prefixed with *.  If no * is specified, as always chooses PC relative

Any instruction that has a memory operand, but no register operand, must
specify its size (byte, word, long, or quadruple) with an instruction
mnemonic suffix ( b, w, l or q, respectively).

The x86-64 architecture adds an RIP (instruction pointer relative)
addressing.  This addressing mode is specified by using rip as a base
register. Only constant offsets are valid. For example:

AT&T: 1234(%rip), Intel: [rip + 1234]
Points to the address 1234 bytes past the end of the current
instruction.

AT&T: symbol(%rip), Intel: [rip + symbol]
Points to the symbol in RIP relative way, this is shorter than

Other addressing modes remain unchanged in x86-64 architecture, except
registers used are 64-bit instead of 32-bit.

Handling of Jump Instructions
Jump instructions are always optimized to use the smallest possible
displacements.  This is accomplished by using byte (8-bit) displacement
jumps whenever the target is sufficiently close. If a byte displacement
is insufficient a long displacement is used. We do not support word
(16-bit) displacement jumps in 32-bit mode (i.e. prefixing the jump
instruction with the data16 instruction prefix), since the 80386 insists
upon masking %eip to 16 bits after the word displacement is added. (See
alsosee Section i386-Arch'')

Note that the jcxz, jecxz, loop, loopz, loope, loopnz and loopne
instructions only come in byte displacements, so that if you use these
instructions ( gcc does not use them) you may get an error message (and
incorrect code). The AT&T 80386 assembler tries to get around this
problem by expanding jcxz foo to

jcxz cx_zero
jmp cx_nonzero
cx_zero: jmp foo
cx_nonzero:

Floating Point
All 80387 floating point types except packed BCD are supported. (BCD
support may be added without much difficulty). These data types are 16-,
32-, and 64- bit integers, and single (32-bit), double (64-bit), and
extended (80-bit) precision floating point. Each supported type has an
instruction mnemonic suffix and a constructor associated with it.
Instruction mnemonic suffixes specify the operand's data type.
Constructors build these data types into memory.

•   Floating point constructors are .float or .single, .double, and
.tfloat for 32-, 64-, and 80-bit formats. These correspond to
instruction mnemonic suffixes s, l, and t.  t stands for 80-bit (ten
byte) real. The 80387 only supports this format via the fldt (load
80-bit real to stack top) and fstpt (store 80-bit real and pop stack)
instructions.

•   Integer constructors are .word, .long or .int, and .quad for the 16-,
32-, and 64-bit integer formats. The corresponding instruction
mnemonic suffixes are s (single), l (long), and q (quad). As with the
80-bit real format, the 64-bit q format is only present in the fildq
pop stack) instructions.

Register to register operations should not use instruction mnemonic
suffixes.  fstl %st, %st(1) will give a warning, and be assembled as if
you wrote fst %st, %st(1), since all register to register operations use
80-bit floating point operands.  (Contrast this with fstl %st, mem, which
converts %st from 80-bit to 64-bit floating point format, then stores the
result in the 4 byte location mem)

Intel's MMX and AMD's 3DNow! SIMD Operations
as supports Intel's MMX instruction set (SIMD instructions for integer
data), available on Intel's Pentium MMX processors and Pentium II
processors, AMD's K6 and K6-2 processors, Cyrix' M2 processor, and
probably others. It also supports AMD's 3DNow! instruction set (SIMD
instructions for 32-bit floating point data) available on AMD's K6-2
processor and possibly others in the future.

Currently, as does not support Intel's floating point SIMD, Katmai (KNI).

The eight 64-bit MMX operands, also used by 3DNow!, are called %mm0,
%mm1, ...  %mm7.  They contain eight 8-bit integers, four 16-bit
integers, two 32-bit integers, one 64-bit integer, or two 32-bit floating
point values. The MMX registers cannot be used at the same time as the
floating point stack.

See Intel and AMD documentation, keeping in mind that the operand order
in instructions is reversed from the Intel syntax.

Writing 16-bit Code
While as normally writes only "pure" 32-bit i386 code or 64-bit x86-64
code depending on the default configuration, it also supports writing
code to run in real mode or in 16-bit protected mode code segments. To do
this, put a .code16 or .code16gcc directive before the assembly language
instructions to be run in 16-bit mode.  You can switch as back to writing
normal 32-bit code with the .code32 directive.

.code16gcc provides experimental support for generating 16-bit code from
gcc, and differs from .code16 in that call, ret, enter, leave, push, pop,
pusha, popa, pushf, and popf instructions default to 32-bit size. This is
so that the stack pointer is manipulated in the same way over function
prefixes where necessary to use the 32-bit addressing modes that gcc
generates.

The code which as generates in 16-bit mode will not necessarily run on a
16-bit pre-80386 processor.  To write code that runs on such a processor,
you must refrain from using any 32-bit constructs which require as to
output address or operand size prefixes.

Note that writing 16-bit code instructions by explicitly specifying a
prefix or an instruction mnemonic suffix within a 32-bit code section
generates different machine instructions than those generated for a
16-bit code segment. In a 32-bit code section, the following code
generates the machine opcode bytes 66 6a 04, which pushes the value 4
onto the stack, decrementing %esp by 2.

pushw $4 The same code in a 16-bit code section would generate the machine opcode bytes 6a 04 (i.e., without the operand size prefix), which is correct since the processor default operand size is assumed to be 16 bits in a 16-bit code section. AT&T Syntax bugs The UnixWare assembler, and probably other AT&T derived ix86 Unix assemblers, generate floating point instructions with reversed source and destination registers in certain cases. Unfortunately, gcc and possibly many other programs use this reversed syntax, so we're stuck with it. For example fsub %st,%st(3) results in %st(3) being updated to %st - %st(3) rather than the expected %st(3) - %st. This happens with all the non-commutative arithmetic floating point operations with two register operands where the source register is %st and the destination register is %st(i). Specifying CPU Architecture as may be told to assemble for a particular CPU (sub-)architecture with the .arch cpu_type directive. This directive enables a warning when gas detects an instruction that is not supported on the CPU specified. The choices for cpu_type are: i8086 i186 i286 i386 i486 i586 i686 pentium pentiumpro pentiumii pentiumiii pentium4 prescott nocona core core2 amdfam10 k6 athlon sledgehammer k8 .mmx .sse .sse2 .sse3 .ssse3 .sse4.1 .sse4.2 .sse4 .sse4a .3dnow .3dnowa .padlock .pacifica .svme .abm Apart from the warning, there are only two other effects on as operation; Firstly, if you specify a CPU other than i486, then shift by one instructions such as sarl$1, %eax will automatically use a two byte
opcode sequence. The larger three byte opcode sequence is used on the 486
(and when no architecture is specified) because it executes faster on the
486. Note that you can explicitly request the two byte opcode by writing
sarl %eax.  Secondly, if you specify i8086, i186, or i286, and .code16 or
.code16gcc then byte offset conditional jumps will be promoted when
necessary to a two instruction sequence consisting of a conditional jump

Following the CPU architecture (but not a sub-architecture, which are
those starting with a dot), you may specify jumps or nojumps to control
automatic promotion of conditional jumps.  jumps is the default, and
enables jump promotion; All external jumps will be of the long variety,
and file-local jumps will be promoted as necessary. (see Section
i386-Jumps'') nojumps leaves external conditional jumps as byte offset
jumps, and warns about file-local conditional jumps that as promotes.
Unconditional jumps are treated as for jumps.

For example

.arch i8086,nojumps

Notes
There is some trickery concerning the mul and imul instructions that
deserves mention. The 16-, 32-, 64- and 128-bit expanding multiplies
(base opcode 0xf6; extension 4 for mul and 5 for imul) can be output only
in the one operand form. Thus, imul %ebx, %eax does not select the
expanding multiply; the expanding multiply would clobber the %edx
register, and this would confuse gcc output. Use imul %ebx to get the
64-bit product in %edx:%eax.

We have added a two operand form of imul when the first operand is an
immediate mode expression and the second operand is a register. This is
just a shorthand, so that, multiplying %eax by 69, for example, can be
done with imul $69, %eax rather than imul$69, %eax, %eax.

IA-64 Dependent Features
Options
-mconstant-gp
This option instructs the assembler to mark the resulting object
file as using the "constant GP" model. With this model, it is
assumed that the entire program uses a single global pointer (GP)
value. Note that this option does not in any fashion affect the
machine code emitted by the assembler. All it does is turn on the
EF_IA_64_CONS_GP flag in the ELF file header.

-mauto-pic
This option instructs the assembler to mark the resulting object
file as using the "constant GP without function descriptor" data
model. This model is like the "constant GP" model, except that it
additionally does away with function descriptors. What this means
is that the address of a function refers directly to the
function's code entry-point. Normally, such an address would
refer to a function descriptor, which contains both the code
entry-point and the GP-value needed by the function. Note that
this option does not in any fashion affect the machine code
emitted by the assembler. All it does is turn on the
EF_IA_64_NOFUNCDESC_CONS_GP flag in the ELF file header.

-milp32

-milp64

-mlp64

-mp64   These options select the data model. The assembler defaults to
-mlp64 (LP64 data model).

-mle

-mbe    These options select the byte order. The -mle option selects
little-endian byte order (default) and -mbe selects big-endian
byte order. Note that IA-64 machine code always uses little-
endian byte order.

-mtune=itanium1

-mtune=itanium2
Tune for a particular IA-64 CPU, itanium1 or itanium2.  The
default is itanium2.

-munwind-check=warning

-munwind-check=error
These options control what the assembler will do when performing
consistency checks on unwind directives.  -munwind-check=warning
will make the assembler issue a warning when an unwind directive
check fails.  This is the default.  -munwind-check=error will
make the assembler issue an error when an unwind directive check
fails.

-mhint.b=ok

-mhint.b=warning

-mhint.b=error
These options control what the assembler will do when the hint.b
instruction is used.  -mhint.b=ok will make the assembler accept
hint.b.  -mint.b=warning will make the assembler issue a warning
when hint.b is used.  -mhint.b=error will make the assembler
treat hint.b as an error, which is the default.

-x

-xexplicit
These options turn on dependency violation checking.

-xauto  This option instructs the assembler to automatically insert stop
bits where necessary to remove dependency violations. This is the
default mode.

-xnone  This option turns off dependency violation checking.

-xdebug
This turns on debug output intended to help tracking down bugs in
the dependency violation checker.

-xdebugn
This is a shortcut for -xnone -xdebug.

-xdebugx
This is a shortcut for -xexplicit -xdebug.

Syntax
The assembler syntax closely follows the IA-64 Assembly Language
Reference Guide.

Special Characters

// is the line comment token.

; can be used instead of a newline to separate statements.

Register Names

The 128 integer registers are referred to as r n.  The 128 floating-point
registers are referred to as f n.  The 128 application registers are
referred to as ar n.  The 128 control registers are referred to as cr n.
The 64 one-bit predicate registers are referred to as p n.  The 8 branch
registers are referred to as b n.  In addition, the assembler defines a
number of aliases: gp ( r1), sp ( r12), rp ( b0), ret0 ( r8), ret1 ( r9),
ret2 ( r10), ret3 ( r9), farg n ( f8+ n), and fret n ( f8+ n).

For convenience, the assembler also defines aliases for all named
application and control registers. For example, ar.bsp refers to the
register backing store pointer ( ar17).  Similarly, cr.eoi refers to the
end-of-interrupt register ( cr67).

IA-64 Processor-Status-Register (PSR) Bit Names

The assembler defines bit masks for each of the bits in the IA-64
processor status register. For example, psr.ic corresponds to a value of
0x2000. These masks are primarily intended for use with the ssm / sum and
rsm / rum instructions, but they can be used anywhere else where an
integer constant is expected.

Opcodes
For detailed information on the IA-64 machine instruction set, see the
http://developer.intel.com/design/itanium/arch_spec.htm.

MIPS Dependent Features
GNU as for mips architectures supports several different mips processors,
and MIPS ISA levels I through V, MIPS32, and MIPS64. For information
about the mips instruction set, see MIPS RISC Architecture, by Kane and
Heindrich (Prentice-Hall). For an overview of mips assembly conventions,
see "Appendix D: Assembly Language Programming" in the same work.

Assembler options
The mips configurations of GNU as support these special options:

-G num  This option sets the largest size of an object that can be
referenced implicitly with the gp register. It is only accepted
for targets that use ecoff format. The default value is 8.

-EB

-EL     Any mips configuration of as can select big-endian or little-
endian output at run time (unlike the other GNU development
tools, which must be configured for one or the other). Use -EB to
select big-endian output, and -EL for little-endian.

-KPIC   Generate SVR4-style PIC. This option tells the assembler to
generate SVR4-style position-independent macro expansions. It
also tells the assembler to mark the output file as PIC.

-mvxworks-pic
Generate VxWorks PIC. This option tells the assembler to generate
VxWorks-style position-independent macro expansions.

-mips1

-mips2

-mips3

-mips4

-mips5

-mips32

-mips32r2

-mips64

-mips64r2
Generate code for a particular MIPS Instruction Set Architecture
level.  -mips1 corresponds to the r2000 and r3000 processors,
-mips2 to the r6000 processor, -mips3 to the r4000 processor, and
-mips4 to the r8000 and r10000 processors.  -mips5, -mips32,
-mips32r2, -mips64, and -mips64r2 correspond to generic MIPS V,
MIPS32, MIPS32 Release 2, MIPS64, and MIPS64 Release 2 ISA
processors, respectively. You can also switch instruction sets
during the assembly; see MIPS ISA, Directives to override the ISA
level.

-mgp32

-mfp32  Some macros have different expansions for 32-bit and 64-bit
registers. The register sizes are normally inferred from the ISA
and ABI, but these flags force a certain group of registers to be
treated as 32 bits wide at all times.  -mgp32 controls the size
of general-purpose registers and -mfp32 controls the size of
floating-point registers.

The .set gp=32 and .set fp=32 directives allow the size of
registers to be changed for parts of an object.  The default
value is restored by .set gp=default and .set fp=default.

On some MIPS variants there is a 32-bit mode flag; when this flag
is set, 64-bit instructions generate a trap. Also, some 32-bit
OSes only save the 32-bit registers on a context switch, so it is
essential never to use the 64-bit registers.

-mgp64

-mfp64  Assume that 64-bit registers are available. This is provided in
the interests of symmetry with -mgp32 and -mfp32.

The .set gp=64 and .set fp=64 directives allow the size of
registers to be changed for parts of an object.  The default
value is restored by .set gp=default and .set fp=default.

-mips16

-no-mips16
Generate code for the MIPS 16 processor. This is equivalent to
putting .set mips16 at the start of the assembly file.
-no-mips16 turns off this option.

-msmartmips

-mno-smartmips
Enables the SmartMIPS extensions to the MIPS32 instruction set,
which provides a number of new instructions which target
smartcard and cryptographic applications.  This is equivalent to
putting .set smartmips at the start of the assembly file.
-mno-smartmips turns off this option.

-mips3d

-no-mips3d
Generate code for the MIPS-3D Application Specific Extension.
This tells the assembler to accept MIPS-3D instructions.
-no-mips3d turns off this option.

-mdmx

-no-mdmx
Generate code for the MDMX Application Specific Extension. This
tells the assembler to accept MDMX instructions.  -no-mdmx turns
off this option.

-mdsp

-mno-dsp
Generate code for the DSP Release 1 Application Specific
Extension. This tells the assembler to accept DSP Release 1
instructions.  -mno-dsp turns off this option.

-mdspr2

-mno-dspr2
Generate code for the DSP Release 2 Application Specific
Extension. This option implies -mdsp. This tells the assembler to
accept DSP Release 2 instructions.  -mno-dspr2 turns off this
option.

-mmt

-mno-mt
Generate code for the MT Application Specific Extension. This
tells the assembler to accept MT instructions.  -mno-mt turns off
this option.

-mfix7000

-mno-fix7000
Cause nops to be inserted if the read of the destination register
of an mfhi or mflo instruction occurs in the following two
instructions.

-mfix-vr4120

-no-mfix-vr4120
Insert nops to work around certain VR4120 errata. This option is
intended to be used on GCC-generated code: it is not designed to
catch all problems in hand-written assembler code.

-mfix-vr4130

-no-mfix-vr4130
Insert nops to work around the VR4130 mflo / mfhi errata.

-m4010

-no-m4010
Generate code for the LSI r4010 chip. This tells the assembler to
accept the r4010 specific instructions ( addciu, ffc, etc.), and
to not schedule nop instructions around accesses to the HI and LO
registers.  -no-m4010 turns off this option.

-m4650

-no-m4650
Generate code for the MIPS r4650 chip. This tells the assembler
to accept the mad and madu instruction, and to not schedule nop
instructions around accesses to the HI and LO registers.
-no-m4650 turns off this option.

-m3900

-no-m3900

-m4100

-no-m4100
For each option -m nnnn, generate code for the MIPS r nnnn chip.
This tells the assembler to accept instructions specific to that
chip, and to schedule for that chip's hazards.

-march= cpu
Generate code for a particular MIPS cpu. It is exactly equivalent
to -m cpu, except that there are more value of cpu understood.
Valid cpu value are:

"2000, 3000, 3900, 4000, 4010, 4100, 4111, vr4120, vr4130,
vr4181, 4300, 4400, 4600, 4650, 5000, rm5200, rm5230, rm5231,
rm5261, rm5721, vr5400, vr5500, 6000, rm7000, 8000, rm9000,
10000, 12000, 4kc, 4km, 4kp, 4ksc, 4kec, 4kem, 4kep, 4ksd, m4k,
m4kp, 24kc, 24kf, 24kx, 24kec, 24kef, 24kex, 34kc, 34kf, 34kx,
74kc, 74kf, 74kx, 5kc, 5kf, 20kc, 25kf, sb1, sb1a"

-mtune= cpu
Schedule and tune for a particular MIPS cpu. Valid cpu values are
identical to -march= cpu.

-mabi= abi
Record which ABI the source code uses. The recognized arguments
are: 32, n32, o64, 64 and eabi.

-msym32

-mno-sym32
Equivalent to adding .set sym32 or .set nosym32 to the beginning
of the assembler input.See Section MIPS symbol sizes''.

-nocpp  This option is ignored. It is accepted for command-line
compatibility with other assemblers, which use it to turn off C
style preprocessing. With GNU as, there is no need for -nocpp,
because the GNU assembler itself never runs the C preprocessor.

--construct-floats

--no-construct-floats
The --no-construct-floats option disables the construction of
of the value into the two single width floating point registers
that make up the double width register. This feature is useful if
the processor support the FR bit in its status register, and this
bit is known (by the programmer) to be set. This bit prevents the
aliasing of the double width register by the single width
registers.

By default --construct-floats is selected, allowing construction
of these floating point constants.

--trap

--no-break
as automatically macro expands certain division and
multiplication instructions to check for overflow and division by
zero. This option causes as to generate code to take a trap
exception rather than a break exception when an error is
detected. The trap instructions are only supported at Instruction
Set Architecture level 2 and higher.

--break

--no-trap
Generate code to take a break exception rather than a trap
exception when an error is detected. This is the default.

-mpdr

-mno-pdr
Control generation of .pdr sections. Off by default on IRIX, on
elsewhere.

-mshared

-mno-shared
When generating code using the Unix calling conventions (selected
by -KPIC or -mcall_shared), gas will normally generate code which
can go into a shared library. The -mno-shared option tells gas to
generate code which uses the calling convention, but can not go
into a shared library. The resulting code is slightly more
efficient.  This option only affects the handling of the .cpload
and .cpsetup pseudo-ops.

MIPS ECOFF object code
Assembling for a mips ecoff target supports some additional sections
besides the usual .text, .data and .bss.  The additional sections are
.rdata, used for read-only data, .sdata, used for small data, and .sbss,
used for small common objects.

When assembling for ecoff, the assembler uses the $gp ($28) register to
form the address of a "small object". Any object in the .sdata or .sbss
sections is considered "small" in this sense. For external objects, or
for objects in the .bss section, you can use the gcc -G option to control
the size of objects addressed via $gp; the default value is 8, meaning that a reference to any object eight bytes or smaller uses$gp.  Passing
-G 0 to as prevents it from using the $gp register on the basis of object size (but the assembler uses$gp for objects in .sdata or sbss in any
case). The size of an object in the .bss section is set by the .comm or
.lcomm directive that defines it. The size of an external object may be
set with the .extern directive. For example, .extern sym,4 declares that
the object at sym is 4 bytes in length, whie leaving sym otherwise
undefined.

Using small ecoff objects requires linker support, and assumes that the
$gp register is correctly initialized (normally done automatically by the startup code). mips ecoff assembly code must not modify the$gp register.

Directives for debugging information
mips ecoff as supports several directives used for generating debugging
information which are not support by traditional mips assemblers. These
are .def, .endef, .dim, .file, .scl, .size, .tag, .type, .val, .stabd,
.stabn, and .stabs.  The debugging information generated by the three
.stab directives can only be read by gdb, not by traditional mips
debuggers (this enhancement is required to fully support C++ debugging).
These directives are primarily used by compilers, not assembly language
programmers!

Directives to override the size of symbols
The n64 ABI allows symbols to have any 64-bit value. Although this
provides a great deal of flexibility, it means that some macros have much
longer expansions than their 32-bit counterparts. For example, the non-
PIC expansion of dla $4,sym is usually: lui$4,%highest(sym)
lui     $1,%hi(sym) daddiu$4,$4,%higher(sym) daddiu$1,$1,%lo(sym) dsll32$4,$4,0 daddu$4,$4,$1

whereas the 32-bit expansion is simply:

lui     $4,%hi(sym) daddiu$4,$4,%lo(sym) n64 code is sometimes constructed in such a way that all symbolic constants are known to have 32-bit values, and in such cases, it's preferable to use the 32-bit expansion instead of the 64-bit expansion. You can use the .set sym32 directive to tell the assembler that, from this point on, all expressions of the form symbol or symbol + offset have 32-bit values. For example: .set sym32 dla$4,sym
lw      $4,sym+16 sw$4,sym+0x8000($4) will cause the assembler to treat sym, sym+16 and sym+0x8000 as 32-bit values. The handling of non-symbolic addresses is not affected. The directive .set nosym32 ends a .set sym32 block and reverts to the normal behavior. It is also possible to change the symbol size using the command-line options [-msym32] and [-mno-sym32]. These options and directives are always accepted, but at present, they have no effect for anything other than n64. Directives to override the ISA level GNU as supports an additional directive to change the mips Instruction Set Architecture level on the fly: .set mips n. n should be a number from 0 to 5, or 32, 32r2, 64 or 64r2. The values other than 0 make the assembler accept instructions for the corresponding isa level, from that point on in the assembly. .set mips n affects not only which instructions are permitted, but also how certain macros are expanded. .set mips0 restores the isa level to its original level: either the level you selected with command line options, or the default for your configuration. You can use this feature to permit specific mips3 instructions while assembling in 32 bit mode. Use this directive with care! The .set arch= cpu directive provides even finer control. It changes the effective CPU target and allows the assembler to use instructions specific to a particular CPU. All CPUs supported by the -march command line option are also selectable by this directive. The original value is restored by .set arch=default. The directive .set mips16 puts the assembler into MIPS 16 mode, in which it will assemble instructions for the MIPS 16 processor. Use .set nomips16 to return to normal 32 bit mode. Traditional mips assemblers do not support this directive. Directives for extending MIPS 16 bit instructions By default, MIPS 16 instructions are automatically extended to 32 bits when necessary. The directive .set noautoextend will turn this off. When .set noautoextend is in effect, any 32 bit instruction must be explicitly extended with the .e modifier (e.g., li.e$4,1000).  The directive .set
autoextend may be used to once again automatically extend instructions
when necessary.

This directive is only meaningful when in MIPS 16 mode. Traditional mips
assemblers do not support this directive.

Directive to mark data as an instruction
The .insn directive tells as that the following data is actually
instructions. This makes a difference in MIPS 16 mode: when loading the
to the value, so that jumping to the loaded address will do the right
thing.

Directives to save and restore options
The directives .set push and .set pop may be used to save and restore the
current settings for all the options which are controlled by .set.  The
.set push directive saves the current settings on a stack. The .set pop
directive pops the stack and restores the settings.

These directives can be useful inside an macro which must change an
option such as the ISA level or instruction reordering but does not want
to change the state of the code which invoked the macro.

Traditional mips assemblers do not support these directives.

Directives to control generation of MIPS ASE instructions
The directive .set mips3d makes the assembler accept instructions from
the MIPS-3D Application Specific Extension from that point on in the
assembly. The .set nomips3d directive prevents MIPS-3D instructions from
being accepted.

The directive .set smartmips makes the assembler accept instructions from
the SmartMIPS Application Specific Extension to the MIPS32 isa from that
point on in the assembly. The .set nosmartmips directive prevents
SmartMIPS instructions from being accepted.

The directive .set mdmx makes the assembler accept instructions from the
MDMX Application Specific Extension from that point on in the assembly.
The .set nomdmx directive prevents MDMX instructions from being accepted.

The directive .set dsp makes the assembler accept instructions from the
DSP Release 1 Application Specific Extension from that point on in the
assembly. The .set nodsp directive prevents DSP Release 1 instructions
from being accepted.

The directive .set dspr2 makes the assembler accept instructions from the
DSP Release 2 Application Specific Extension from that point on in the
assembly. This dirctive implies .set dsp.  The .set nodspr2 directive
prevents DSP Release 2 instructions from being accepted.

The directive .set mt makes the assembler accept instructions from the MT
Application Specific Extension from that point on in the assembly. The
.set nomt directive prevents MT instructions from being accepted.

Traditional mips assemblers do not support these directives.

PowerPC Dependent Features
Options
The PowerPC chip family includes several successive levels, using the
same core instruction set, but including a few additional instructions at
each level. There are exceptions to this however. For details on what
instructions each variant supports, please see the chip's architecture
reference manual.

The following table lists all available PowerPC options.

-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.

-m7400, -m7410, -m7450, -m7455
Generate code for PowerPC 7400/7410/7450/7455.

-mppc64, -m620
Generate code for PowerPC 620/625/630.

-me500, -me500x2
Generate code for Motorola e500 core complex.

-mspe   Generate code for Motorola SPE instructions.

-mppc64bridge
Generate code for PowerPC 64, including bridge insns.

-mbooke64
Generate code for 64-bit BookE.

-mbooke, mbooke32
Generate code for 32-bit BookE.

-me300  Generate code for PowerPC e300 family.

-maltivec
Generate code for processors with AltiVec instructions.

-mpower4
Generate code for Power4 architecture.

-mpower5
Generate code for Power5 architecture.

-mpower6
Generate code for Power6 architecture.

-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
Generate code for a little endian machine.

-mbig, -mbig-endian
Generate code for a big endian machine.

-msolaris
Generate code for Solaris.

-mno-solaris
Do not generate code for Solaris.

PowerPC Assembler Directives
A number of assembler directives are available for PowerPC. The following
table is far from complete.

.machine string
This directive allows you to change the machine for which code is
generated.  string may be any of the -m cpu selection options
(without the -m) enclosed in double quotes, push, or pop.
.machine push saves the currently selected cpu, which may be
restored with .machine pop.

SPARC Dependent Features
Options
The SPARC chip family includes several successive levels, using the same
core instruction set, but including a few additional instructions at each
level.  There are exceptions to this however. For details on what
instructions each variant supports, please see the chip's architecture
reference manual.

By default, as assumes the core instruction set (SPARC v6), but "bumps"
the architecture level as needed: it switches to successively higher
architectures as it encounters instructions that only exist in the higher
levels.

If not configured for SPARC v9 ( sparc64-*-*) GAS will not bump passed
sparclite by default, an option must be passed to enable the v9
instructions.

GAS treats sparclite as being compatible with v8, unless an architecture
is explicitly requested. SPARC v9 is always incompatible with sparclite.

-Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite

-Av8plus | -Av8plusa | -Av9 | -Av9a
Use one of the -A options to select one of the SPARC
architectures explicitly. If you select an architecture
explicitly, as reports a fatal error if it encounters an
instruction or feature requiring an incompatible or higher level.

-Av8plus and -Av8plusa select a 32 bit environment.

-Av9 and -Av9a select a 64 bit environment and are not available
unless GAS is explicitly configured with 64 bit environment
support.

-Av8plusa and -Av9a enable the SPARC V9 instruction set with
UltraSPARC extensions.

-xarch=v8plus | -xarch=v8plusa
For compatibility with the Solaris v9 assembler. These options
are equivalent to -Av8plus and -Av8plusa, respectively.

-bump   Warn whenever it is necessary to switch to another level. If an
architecture level is explicitly requested, GAS will not issue
warnings until that level is reached, and will then bump the
level as required (except between incompatible levels).

-32 | -64
Select the word size, either 32 bits or 64 bits. These options
are only available with the ELF object file format, and require
that the necessary BFD support has been included.

Enforcing aligned data
SPARC GAS normally permits data to be misaligned. For example, it permits
the .long pseudo-op to be used on a byte boundary. However, the native
SunOS and Solaris assemblers issue an error when they see misaligned
data.

You can use the --enforce-aligned-data option to make SPARC GAS also
issue an error about misaligned data, just as the SunOS and Solaris
assemblers do.

The --enforce-aligned-data option is not the default because gcc issues
misaligned data pseudo-ops when it initializes certain packed data
structures (structures defined using the packed attribute). You may have
to assemble with GAS in order to initialize packed data structures in

Floating Point
The Sparc uses ieee floating-point numbers.

Sparc Machine Directives
The Sparc version of as supports the following additional machine
directives:

.align  This must be followed by the desired alignment in bytes.

.common
This must be followed by a symbol name, a positive number, and
bss.  This behaves somewhat like .comm, but the syntax is
different.

.half   This is functionally identical to .short.

.nword  On the Sparc, the .nword directive produces native word sized
value, ie. if assembling with -32 it is equivalent to .word, if
assembling with -64 it is equivalent to .xword.

.proc   This directive is ignored. Any text following it on the same line
is also ignored.

.register
This directive declares use of a global application or system
register. It must be followed by a register name %g2, %g3, %g6 or
%g7, comma and the symbol name for that register. If symbol name
is #scratch, it is a scratch register, if it is #ignore, it just
suppresses any errors about using undeclared global register, but
does not emit any information about it into the object file. This
can be useful e.g. if you save the register before use and
restore it after.

.reserve
This must be followed by a symbol name, a positive number, and
bss.  This behaves somewhat like .lcomm, but the syntax is
different.

.seg    This must be followed by text, data, or data1.  It behaves like
.text, .data, or .data 1.

.skip   This is functionally identical to the .space directive.

.word   On the Sparc, the .word directive produces 32 bit values, instead
of the 16 bit values it produces on many other machines.

.xword  On the Sparc V9 processor, the .xword directive produces 64 bit
values.

Reporting Bugs
Your bug reports play an essential role in making as reliable.

it may not. But in any case the principal function of a bug report is to
help the entire community by making the next version of as work better.
Bug reports are your contribution to the maintenance of as.

In order for a bug report to serve its purpose, you must include the
information that enables us to fix the bug.

Have You Found a Bug?
If you are not sure whether you have found a bug, here are some
guidelines:

•   If the assembler gets a fatal signal, for any input whatever, that is
a as bug. Reliable assemblers never crash.

•   If as produces an error message for valid input, that is a bug.

•   If as does not produce an error message for invalid input, that is a
bug. However, you should note that your idea of "invalid input" might
be our idea of "an extension" or "support for traditional practice".

•   If you are an experienced user of assemblers, your suggestions for
improvement of as are welcome in any case.

How to Report Bugs
A number of companies and individuals offer support for GNU products. If
you obtained as from a support organization, we recommend you contact
that organization first.

You can find contact information for many support companies and
individuals in the file etc/SERVICE in the GNU Emacs distribution.

The fundamental principle of reporting bugs usefully is this: report all
the facts.  If you are not sure whether to state a fact or leave it out,
state it!

Often people omit facts because they think they know what causes the
problem and assume that some details do not matter. Thus, you might
assume that the name of a symbol you use in an example does not matter.
Well, probably it does not, but one cannot be sure. Perhaps the bug is a
stray memory reference which happens to fetch from the location where
that name is stored in memory; perhaps, if the name were different, the
contents of that location would fool the assembler into doing the right
thing despite the bug. Play it safe and give a specific, complete
example. That is the easiest thing for you to do, and the most helpful.

Keep in mind that the purpose of a bug report is to enable us to fix the
bug if it is new to us. Therefore, always write your bug reports on the
assumption that the bug has not been reported previously.

Sometimes people give a few sketchy facts and ask, "Does this ring a
bell?" This cannot help us fix a bug, so it is basically useless. We
respond by asking for enough details to enable us to investigate. You
might as well expedite matters by sending them to begin with.

To enable us to fix the bug, you should include all these things:

•   The version of as.  as announces it if you start it with the
--version argument.

Without this, we will not know whether there is any point in looking
for the bug in the current version of as.

•   Any patches you may have applied to the as source.

•   The type of machine you are using, and the operating system name and
version number.

•   What compiler (and its version) was used to compile as ---e.g. "
gcc-2.7 ".

•   The command arguments you gave the assembler to assemble your example
and observe the bug. To guarantee you will not omit something
important, list them all. A copy of the Makefile (or the output from
make) is sufficient.

If we were to try to guess the arguments, we would probably guess
wrong and then we might not encounter the bug.

•   A complete input file that will reproduce the bug. If the bug is
observed when the assembler is invoked via a compiler, send the
assembler source, not the high level language source. Most compilers
will produce the assembler source when run with the -S option. If you
are using gcc, use the options -v --save-temps; this will save the
assembler source in a file with an extension of .s, and also show you
exactly how as is being run.

•   A description of what behavior you observe that you believe is
incorrect.  For example, "It gets a fatal signal."

Of course, if the bug is that as gets a fatal signal, then we will
certainly notice it. But if the bug is incorrect output, we might not
notice unless it is glaringly wrong. You might as well not give us a
chance to make a mistake.

Even if the problem you experience is a fatal signal, you should
still say so explicitly. Suppose something strange is going on, such
as, your copy of as is out of sync, or you have encountered a bug in
the C library on your system.  (This has happened!) Your copy might
crash and ours would not. If you told us to expect a crash, then when
ours fails to crash, we would know that the bug was not happening for
us. If you had not told us to expect a crash, then we would not be
able to draw any conclusion from our observations.

•   If you wish to suggest changes to the as source, send us context
diffs, as generated by diff with the -u, -c, or -p option. Always
send diffs from the old file to the new file. If you even discuss
something in the as source, refer to it by context, not by line
number.

The line numbers in our development sources will not match those in
to us.

Here are some things that are not necessary:

•   A description of the envelope of the bug.

Often people who encounter a bug spend a lot of time investigating
which changes to the input file will make the bug go away and which
changes will not affect it.

This is often time consuming and not very useful, because the way we
will find the bug is by running a single example under the debugger
with breakpoints, not by pure deduction from a series of examples. We
recommend that you save your time for something else.

Of course, if you can find a simpler example to report instead of the
original one, that is a convenience for us. Errors in the output will
be easier to spot, running under the debugger will take less time,
and so on.

However, simplification is not vital; if you do not want to do this,
report the bug anyway and send us the entire test case you used.

•   A patch for the bug.

A patch for the bug does help us if it is a good one. But do not omit
the necessary information, such as the test case, on the assumption
that a patch is all we need. We might see problems with your patch
and decide to fix the problem another way, or we might not understand
it at all.

Sometimes with a program as complicated as as it is very hard to
construct an example that will make the program follow a certain path
through the code. If you do not send us the example, we will not be
able to construct one, so we will not be able to verify that the bug
is fixed.

And if we cannot understand what bug you are trying to fix, or why
your patch should be an improvement, we will not install it. A test
case will help us to understand.

•   A guess about what the bug is or what it depends on.

Such guesses are usually wrong. Even we cannot guess right about such
things without first using the debugger to find the facts.

Acknowledgements
If you have contributed to GAS and your name isn't listed here, it is not
meant as a slight. We just don't know about it. Send mail to the
maintainer, and we'll correct the situation. Currently the maintainer is
Ken Raeburn (email address [email protected]).

Dean Elsner wrote the original GNU assembler for the VAX.

Jay Fenlason maintained GAS for a while, adding support for GDB-specific
debug information and the 68k series machines, most of the preprocessing
pass, and extensive changes in messages.c, input-file.c, write.c.

K. Richard Pixley maintained GAS for a while, adding various enhancements
and many bug fixes, including merging support for several processors,
breaking GAS up to handle multiple object file format back ends
(including heavy rewrite, testing, an integration of the coff and b.out
back ends), adding configuration including heavy testing and verification
of cross assemblers and file splits and renaming, converted GAS to
strictly ANSI C including full prototypes, added support for m680[34]0
and cpu32, did considerable work on i960 including a COFF port (including
considerable amounts of reverse engineering), a SPARC opcode file
rewrite, DECstation, rs6000, and hp300hpux host ports, updated "know"
assertions and made them work, much other reorganization, cleanup, and
lint.

Ken Raeburn wrote the high-level BFD interface code to replace most of
the code in format-specific I/O modules.

The original VMS support was contributed by David L. Kashtan. Eric
Youngdale has done much work with it since.

The Intel 80386 machine description was written by Eliot Dresselhaus.

Minh Tran-Le at IntelliCorp contributed some AIX 386 support.

The Motorola 88k machine description was contributed by Devon Bowen of
Buffalo University and Torbjorn Granlund of the Swedish Institute of
Computer Science.

Keith Knowles at the Open Software Foundation wrote the original MIPS
back end ( tc-mips.c, tc-mips.h), and contributed Rose format support
(which hasn't been merged in yet). Ralph Campbell worked with the MIPS
code to support a.out format.

Support for the Zilog Z8k and Renesas H8/300 processors (tc-z8k, tc-
h8300), and IEEE 695 object file format (obj-ieee), was written by Steve
Chamberlain of CyGNUs Support. Steve also modified the COFF back end to
use BFD for some low-level operations, for use with the H8/300 and AMD
29k targets.

John Gilmore built the AMD 29000 support, added .include support, and
simplified the configuration of which versions accept which directives.
He updated the 68k machine description so that Motorola's opcodes always
produced fixed-size instructions (e.g., jsr), while synthetic
instructions remained shrinkable ( jbsr).  John fixed many bugs,
including true tested cross-compilation support, and one bug in
relaxation that took a week and required the proverbial one-bit fix.

Ian Lance Taylor of CyGNUs Support merged the Motorola and MIT syntax for
the 68k, completed support for some COFF targets (68k, i386 SVR3, and SCO
Unix), added support for MIPS ECOFF and ELF targets, wrote the initial
RS/6000 and PowerPC assembler, and made a few other minor patches.

Steve Chamberlain made GAS able to generate listings.

Hewlett-Packard contributed support for the HP9000/300.

Jeff Law wrote GAS and BFD support for the native HPPA object format
(SOM) along with a fairly extensive HPPA testsuite (for both SOM and ELF
object formats). This work was supported by both the Center for Software
Science at the University of Utah and CyGNUs Support.

Support for ELF format files has been worked on by Mark Eichin of CyGNUs
Support (original, incomplete implementation for SPARC), Pete Hoogenboom
and Jeff Law at the University of Utah (HPPA mainly), Michael Meissner of
the Open Software Foundation (i386 mainly), and Ken Raeburn of CyGNUs
Support (sparc, and some initial 64-bit support).

Linas Vepstas added GAS support for the ESA/390 "IBM 370" architecture.

Richard Henderson rewrote the Alpha assembler. Klaus Kaempf wrote GAS and
BFD support for openVMS/Alpha.

Timothy Wall, Michael Hayes, and Greg Smart contributed to the various
tic* flavors.

David Heine, Sterling Augustine, Bob Wilson and John Ruttenberg from
Tensilica, Inc. added support for Xtensa processors.

Several engineers at CyGNUs Support have also provided many small bug
fixes and configuration enhancements.

Many others have contributed large or small bugfixes and enhancements. If
you have contributed significant work and are not mentioned on this list,
and want to be, let us know. Some of the history has been lost; we are
not intentionally leaving anyone out.

Copyright (C) 2000, 2003 Free Software Foundation, Inc. 51 Franklin
Street, Fifth Floor, Boston, MA 02110-1301 USA

Everyone is permitted to copy and distribute verbatim copies of
this license document, but changing it is not allowed.

1.   PREAMBLE

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AS Index

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