.Dd 2015-03-02
.Dt AS 7
.Os
.Sh NAME
.Nm as
.Nd Using as (machine specific)
.Sh Using as
This file is a user guide to the GNU assembler
.Xr as
version "2.17.50 [FreeBSD] 2007-07-03". This version of the file describes
.Xr as
configured to generate code for machine specific architectures.
.Pp
This document is distributed under the terms of the GNU Free Documentation
License. A copy of the license is included in the section entitled \(lqGNU Free
Documentation License\(rq.
.Pp
.Sh Overview
Here is a brief summary of how to invoke
.Xr as .
For details, see Invoking,,Command-Line Options.
.Pp
.Bd -literal -offset indent
as [-a[cdhlns][=file]] [--alternate] [-D]
[--defsym sym=val] [-f] [-g] [--gstabs]
[--gstabs+] [--gdwarf-2] [--help] [-I dir] [-J]
[-K] [-L] [--listing-lhs-width=NUM]
[--listing-lhs-width2=NUM] [--listing-rhs-width=NUM]
[--listing-cont-lines=NUM] [--keep-locals] [-o
objfile] [-R] [--reduce-memory-overheads] [--statistics]
[-v] [-version] [--version] [-W] [--warn]
[--fatal-warnings] [-w] [-x] [-Z] [@FILE]
[--target-help] [target-options]
[--|files ...]
Target ARM options:
[-mcpu=processor[+extension...]]
[-march=architecture[+extension...]]
[-mfpu=floating-point-format]
[-mfloat-abi=abi]
[-meabi=ver]
[-mthumb]
[-EB|-EL]
[-mapcs-32|-mapcs-26|-mapcs-float|
-mapcs-reentrant]
[-mthumb-interwork] [-k]
Target i386 options:
[--32|--64] [-n]
[-march=CPU] [-mtune=CPU]
Target IA-64 options:
[-mconstant-gp|-mauto-pic]
[-milp32|-milp64|-mlp64|-mp64]
[-mle|mbe]
[-mtune=itanium1|-mtune=itanium2]
[-munwind-check=warning|-munwind-check=error]
[-mhint.b=ok|-mhint.b=warning|-mhint.b=error]
[-x|-xexplicit] [-xauto] [-xdebug]
Target MIPS options:
[-nocpp] [-EL] [-EB] [-O[optimization level]]
[-g[debug level]] [-G num] [-KPIC] [-call_shared]
[-non_shared] [-xgot [-mvxworks-pic]
[-mabi=ABI] [-32] [-n32] [-64] [-mfp32] [-mgp32]
[-march=CPU] [-mtune=CPU] [-mips1] [-mips2]
[-mips3] [-mips4] [-mips5] [-mips32] [-mips32r2]
[-mips64] [-mips64r2]
[-construct-floats] [-no-construct-floats]
[-trap] [-no-break] [-break] [-no-trap]
[-mfix7000] [-mno-fix7000]
[-mips16] [-no-mips16]
[-msmartmips] [-mno-smartmips]
[-mips3d] [-no-mips3d]
[-mdmx] [-no-mdmx]
[-mdsp] [-mno-dsp]
[-mdspr2] [-mno-dspr2]
[-mmt] [-mno-mt]
[-mdebug] [-no-mdebug]
[-mpdr] [-mno-pdr]
Target PowerPC options:
[-mpwrx|-mpwr2|-mpwr|-m601|-mppc|-mppc32|-m603|-m604|
-m403|-m405|-mppc64|-m620|-mppc64bridge|-mbooke|
-mbooke32|-mbooke64]
[-mcom|-many|-maltivec] [-memb]
[-mregnames|-mno-regnames]
[-mrelocatable|-mrelocatable-lib]
[-mlittle|-mlittle-endian|-mbig|-mbig-endian]
[-msolaris|-mno-solaris]
Target SPARC options:
[-Av6|-Av7|-Av8|-Asparclet|-Asparclite
-Av8plus|-Av8plusa|-Av9|-Av9a]
[-xarch=v8plus|-xarch=v8plusa] [-bump]
[-32|-64]
.Ed
.Pp
.Bl -tag -width Ds
.It @ Va file
Read command-line options from
.Va file .
The options read are inserted in place of the original @
.Va file
option. If
.Va file
does not exist, or cannot be read, then the option will be treated literally,
and not removed.
.Pp
Options in
.Va file
are separated by whitespace. A whitespace character may be included in an
option by surrounding the entire option in either single or double quotes.
Any character (including a backslash) may be included by prefixing the character
to be included with a backslash. The
.Va file
may itself contain additional @
.Va file
options; any such options will be processed recursively.
.Pp
.It -a[cdhlmns]
Turn on listings, in any of a variety of ways:
.Pp
.Bl -tag -width Ds
.It -ac
omit false conditionals
.Pp
.It -ad
omit debugging directives
.Pp
.It -ah
include high-level source
.Pp
.It -al
include assembly
.Pp
.It -am
include macro expansions
.Pp
.It -an
omit forms processing
.Pp
.It -as
include symbols
.Pp
.It =file
set the name of the listing file
.El
.Pp
You may combine these options; for example, use
.Li -aln
for assembly listing without forms processing. The
.Li =file
option, if used, must be the last one. By itself,
.Li -a
defaults to
.Li -ahls .
.Pp
.It --alternate
Begin in alternate macro mode.See Section
.Dq Altmacro .
.Pp
.It -D
Ignored. This option is accepted for script compatibility with calls to other
assemblers.
.Pp
.It --defsym Va sym= Va value
Define the symbol
.Va sym
to be
.Va value
before assembling the input file.
.Va value
must be an integer constant. As in C, a leading
.Li 0x
indicates a hexadecimal value, and a leading
.Li 0
indicates an octal value. The value of the symbol can be overridden inside
a source file via the use of a
.Li .set
pseudo-op.
.Pp
.It -f
\(lqfast\(rq---skip whitespace and comment preprocessing (assume source is compiler
output).
.Pp
.It -g
.It --gen-debug
Generate debugging information for each assembler source line using whichever
debug format is preferred by the target. This currently means either STABS,
ECOFF or DWARF2.
.Pp
.It --gstabs
Generate stabs debugging information for each assembler line. This may help
debugging assembler code, if the debugger can handle it.
.Pp
.It --gstabs+
Generate stabs debugging information for each assembler line, with GNU extensions
that probably only gdb can handle, and that could make other debuggers crash
or refuse to read your program. This may help debugging assembler code. Currently
the only GNU extension is the location of the current working directory at
assembling time.
.Pp
.It --gdwarf-2
Generate DWARF2 debugging information for each assembler line. This may help
debugging assembler code, if the debugger can handle it. Note---this option
is only supported by some targets, not all of them.
.Pp
.It --help
Print a summary of the command line options and exit.
.Pp
.It --target-help
Print a summary of all target specific options and exit.
.Pp
.It -I Va dir
Add directory
.Va dir
to the search list for
.Li .include
directives.
.Pp
.It -J
Don't warn about signed overflow.
.Pp
.It -K
This option is accepted but has no effect on the machine specific family.
.Pp
.It -L
.It --keep-locals
Keep (in the symbol table) local symbols. These symbols start with system-specific
local label prefixes, typically
.Li .L
for ELF systems or
.Li L
for traditional a.out systems.See Section
.Dq Symbol Names .
.Pp
.It --listing-lhs-width= Va number
Set the maximum width, in words, of the output data column for an assembler
listing to
.Va number .
.Pp
.It --listing-lhs-width2= Va number
Set the maximum width, in words, of the output data column for continuation
lines in an assembler listing to
.Va number .
.Pp
.It --listing-rhs-width= Va number
Set the maximum width of an input source line, as displayed in a listing,
to
.Va number
bytes.
.Pp
.It --listing-cont-lines= Va number
Set the maximum number of lines printed in a listing for a single line of
input to
.Va number
+ 1.
.Pp
.It -o Va objfile
Name the object-file output from
.Xr as
.Va objfile .
.Pp
.It -R
Fold the data section into the text section.
.Pp
Set the default size of GAS's hash tables to a prime number close to
.Va number .
Increasing this value can reduce the length of time it takes the assembler
to perform its tasks, at the expense of increasing the assembler's memory
requirements. Similarly reducing this value can reduce the memory requirements
at the expense of speed.
.Pp
.It --reduce-memory-overheads
This option reduces GAS's memory requirements, at the expense of making the
assembly processes slower. Currently this switch is a synonym for
.Li --hash-size=4051 ,
but in the future it may have other effects as well.
.Pp
.It --statistics
Print the maximum space (in bytes) and total time (in seconds) used by assembly.
.Pp
.It --strip-local-absolute
Remove local absolute symbols from the outgoing symbol table.
.Pp
.It -v
.It -version
Print the
.Xr as
version.
.Pp
.It --version
Print the
.Xr as
version and exit.
.Pp
.It -W
.It --no-warn
Suppress warning messages.
.Pp
.It --fatal-warnings
Treat warnings as errors.
.Pp
.It --warn
Don't suppress warning messages or treat them as errors.
.Pp
.It -w
Ignored.
.Pp
.It -x
Ignored.
.Pp
.It -Z
Generate an object file even after errors.
.Pp
.It -- | Va files ...
Standard input, or source files to assemble.
.Pp
.El
The following options are available when as is configured for the ARM processor
family.
.Pp
.Bl -tag -width Ds
.It -mcpu= Va processor[+ Va extension...]
Specify which ARM processor variant is the target.
.It -march= Va architecture[+ Va extension...]
Specify which ARM architecture variant is used by the target.
.It -mfpu= Va floating-point-format
Select which Floating Point architecture is the target.
.It -mfloat-abi= Va abi
Select which floating point ABI is in use.
.It -mthumb
Enable Thumb only instruction decoding.
.It -mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant
Select which procedure calling convention is in use.
.It -EB | -EL
Select either big-endian (-EB) or little-endian (-EL) output.
.It -mthumb-interwork
Specify that the code has been generated with interworking between Thumb and
ARM code in mind.
.It -k
Specify that PIC code has been generated.
.El
.Pp
The following options are available when
.Xr as
is configured for the SPARC architecture:
.Pp
.Bl -tag -width Ds
.It -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
.It -Av8plus | -Av8plusa | -Av9 | -Av9a
Explicitly select a variant of the SPARC architecture.
.Pp
.Li -Av8plus
and
.Li -Av8plusa
select a 32 bit environment.
.Li -Av9
and
.Li -Av9a
select a 64 bit environment.
.Pp
.Li -Av8plusa
and
.Li -Av9a
enable the SPARC V9 instruction set with UltraSPARC extensions.
.Pp
.It -xarch=v8plus | -xarch=v8plusa
For compatibility with the Solaris v9 assembler. These options are equivalent
to -Av8plus and -Av8plusa, respectively.
.Pp
.It -bump
Warn when the assembler switches to another architecture.
.El
.Pp
The following options are available when as is configured for a mips processor.
.Pp
.Bl -tag -width Ds
.It -G Va num
This option sets the largest size of an object that can be referenced implicitly
with the
.Li gp
register. It is only accepted for targets that use ECOFF format, such as a
DECstation running Ultrix. The default value is 8.
.Pp
.It -EB
Generate \(lqbig endian\(rq format output.
.Pp
.It -EL
Generate \(lqlittle endian\(rq format output.
.Pp
.It -mips1
.It -mips2
.It -mips3
.It -mips4
.It -mips5
.It -mips32
.It -mips32r2
.It -mips64
.It -mips64r2
Generate code for a particular mips Instruction Set Architecture level.
.Li -mips1
is an alias for
.Li -march=r3000 ,
.Li -mips2
is an alias for
.Li -march=r6000 ,
.Li -mips3
is an alias for
.Li -march=r4000
and
.Li -mips4
is an alias for
.Li -march=r8000 .
.Li -mips5 ,
.Li -mips32 ,
.Li -mips32r2 ,
.Li -mips64 ,
and
.Li -mips64r2
correspond to generic
.Li MIPS V ,
.Li MIPS32 ,
.Li MIPS32 Release 2 ,
.Li MIPS64 ,
and
.Li MIPS64 Release 2
ISA processors, respectively.
.Pp
.It -march= Va CPU
Generate code for a particular mips cpu.
.Pp
.It -mtune= Va cpu
Schedule and tune for a particular mips cpu.
.Pp
.It -mfix7000
.It -mno-fix7000
Cause nops to be inserted if the read of the destination register of an mfhi
or mflo instruction occurs in the following two instructions.
.Pp
.It -mdebug
.It -no-mdebug
Cause stabs-style debugging output to go into an ECOFF-style .mdebug section
instead of the standard ELF .stabs sections.
.Pp
.It -mpdr
.It -mno-pdr
Control generation of
.Li .pdr
sections.
.Pp
.It -mgp32
.It -mfp32
The register sizes are normally inferred from the ISA and ABI, but these flags
force a certain group of registers to be treated as 32 bits wide at all times.
.Li -mgp32
controls the size of general-purpose registers and
.Li -mfp32
controls the size of floating-point registers.
.Pp
.It -mips16
.It -no-mips16
Generate code for the MIPS 16 processor. This is equivalent to putting
.Li .set mips16
at the start of the assembly file.
.Li -no-mips16
turns off this option.
.Pp
.It -msmartmips
.It -mno-smartmips
Enables the SmartMIPS extension to the MIPS32 instruction set. This is equivalent
to putting
.Li .set smartmips
at the start of the assembly file.
.Li -mno-smartmips
turns off this option.
.Pp
.It -mips3d
.It -no-mips3d
Generate code for the MIPS-3D Application Specific Extension. This tells the
assembler to accept MIPS-3D instructions.
.Li -no-mips3d
turns off this option.
.Pp
.It -mdmx
.It -no-mdmx
Generate code for the MDMX Application Specific Extension. This tells the
assembler to accept MDMX instructions.
.Li -no-mdmx
turns off this option.
.Pp
.It -mdsp
.It -mno-dsp
Generate code for the DSP Release 1 Application Specific Extension. This tells
the assembler to accept DSP Release 1 instructions.
.Li -mno-dsp
turns off this option.
.Pp
.It -mdspr2
.It -mno-dspr2
Generate code for the DSP Release 2 Application Specific Extension. This option
implies -mdsp. This tells the assembler to accept DSP Release 2 instructions.
.Li -mno-dspr2
turns off this option.
.Pp
.It -mmt
.It -mno-mt
Generate code for the MT Application Specific Extension. This tells the assembler
to accept MT instructions.
.Li -mno-mt
turns off this option.
.Pp
.It --construct-floats
.It --no-construct-floats
The
.Li --no-construct-floats
option disables the construction of double width floating point constants
by loading the two halves of the value into the two single width floating
point registers that make up the double width register. By default
.Li --construct-floats
is selected, allowing construction of these floating point constants.
.Pp
.It --emulation= Va name
This option causes
.Xr as
to emulate
.Xr as
configured for some other target, in all respects, including output format
(choosing between ELF and ECOFF only), handling of pseudo-opcodes which may
generate debugging information or store symbol table information, and default
endianness. The available configuration names are:
.Li mipsecoff ,
.Li mipself ,
.Li mipslecoff ,
.Li mipsbecoff ,
.Li mipslelf ,
.Li mipsbelf .
The first two do not alter the default endianness from that of the primary
target for which the assembler was configured; the others change the default
to little- or big-endian as indicated by the
.Li b
or
.Li l
in the name. Using
.Li -EB
or
.Li -EL
will override the endianness selection in any case.
.Pp
This option is currently supported only when the primary target
.Xr as
is configured for is a mips ELF or ECOFF target. Furthermore, the primary
target or others specified with
.Li --enable-targets=...
at configuration time must include support for the other format, if both are
to be available. For example, the Irix 5 configuration includes support for
both.
.Pp
Eventually, this option will support more configurations, with more fine-grained
control over the assembler's behavior, and will be supported for more processors.
.Pp
.It -nocpp
.Xr as
ignores this option. It is accepted for compatibility with the native tools.
.Pp
.It --trap
.It --no-trap
.It --break
.It --no-break
Control how to deal with multiplication overflow and division by zero.
.Li --trap
or
.Li --no-break
(which are synonyms) take a trap exception (and only work for Instruction
Set Architecture level 2 and higher);
.Li --break
or
.Li --no-trap
(also synonyms, and the default) take a break exception.
.Pp
.It -n
When this option is used,
.Xr as
will issue a warning every time it generates a nop instruction from a macro.
.El
.Pp
.Ss Structure of this Manual
This manual is intended to describe what you need to know to use GNU
.Xr as .
We cover the syntax expected in source files, including notation for symbols,
constants, and expressions; the directives that
.Xr as
understands; and of course how to invoke
.Xr as .
.Pp
We also cover special features in the machine specific configuration of
.Xr as ,
including assembler directives.
.Pp
On the other hand, this manual is
.Em not
intended as an introduction to programming in assembly language---let alone
programming in general! In a similar vein, we make no attempt to introduce
the machine architecture; we do
.Em not
describe the instruction set, standard mnemonics, registers or addressing
modes that are standard to a particular architecture.
.Pp
.Ss The GNU Assembler
GNU
.Xr as
is really a family of assemblers. This manual describes
.Xr as ,
a member of that family which is configured for the machine specific architectures.
If you use (or have used) the GNU assembler on one architecture, you should
find a fairly similar environment when you use it on another architecture.
Each version has much in common with the others, including object file formats,
most assembler directives (often called
.Em pseudo-ops )
and assembler syntax.
.Pp
.Xr as
is primarily intended to assemble the output of the GNU C compiler
.Li gcc
for use by the linker
.Li ld .
Nevertheless, we've tried to make
.Xr as
assemble correctly everything that other assemblers for the same machine would
assemble.
.Pp
Unlike older assemblers,
.Xr as
is designed to assemble a source program in one pass of the source file. This
has a subtle impact on the
.Li .org
directive (see Section
.Dq Org ) .
.Pp
.Ss Object File Formats
The GNU assembler can be configured to produce several alternative object
file formats. For the most part, this does not affect how you write assembly
language programs; but directives for debugging symbols are typically different
in different file formats.See Section
.Dq Symbol Attributes .
For the machine specific target,
.Xr as
is configured to produce ELF format object files.
.Pp
.Ss Command Line
After the program name
.Xr as ,
the command line may contain options and file names. Options may appear in
any order, and may be before, after, or between file names. The order of file
names is significant.
.Pp
.Pa --
(two hyphens) by itself names the standard input file explicitly, as one of
the files for
.Xr as
to assemble.
.Pp
Except for
.Li --
any command line argument that begins with a hyphen (
.Li - )
is an option. Each option changes the behavior of
.Xr as .
No option changes the way another option works. An option is a
.Li -
followed by one or more letters; the case of the letter is important. All
options are optional.
.Pp
Some options expect exactly one file name to follow them. The file name may
either immediately follow the option's letter (compatible with older assemblers)
or it may be the next command argument (GNU standard). These two command lines
are equivalent:
.Pp
.Bd -literal -offset indent
as -o my-object-file.o mumble.s
as -omy-object-file.o mumble.s
.Ed
.Pp
.Ss Input Files
We use the phrase
.Em source program ,
abbreviated
.Em source ,
to describe the program input to one run of
.Xr as .
The program may be in one or more files; how the source is partitioned into
files doesn't change the meaning of the source.
.Pp
The source program is a concatenation of the text in all the files, in the
order specified.
.Pp
Each time you run
.Xr as
it assembles exactly one source program. The source program is made up of
one or more files. (The standard input is also a file.)
.Pp
You give
.Xr as
a command line that has zero or more input file names. The input files are
read (from left file name to right). A command line argument (in any position)
that has no special meaning is taken to be an input file name.
.Pp
If you give
.Xr as
no file names it attempts to read one input file from the
.Xr as
standard input, which is normally your terminal. You may have to type ctl-D
to tell
.Xr as
there is no more program to assemble.
.Pp
Use
.Li --
if you need to explicitly name the standard input file in your command line.
.Pp
If the source is empty,
.Xr as
produces a small, empty object file.
.Pp
.Em Filenames and Line-numbers
.Pp
There are two ways of locating a line in the input file (or files) and either
may be used in reporting error messages. One way refers to a line number in
a physical file; the other refers to a line number in a \(lqlogical\(rq file.See Section
.Dq Errors .
.Pp
.Em Physical files
are those files named in the command line given to
.Xr as .
.Pp
.Em Logical files
are simply names declared explicitly by assembler directives; they bear no
relation to physical files. Logical file names help error messages reflect
the original source file, when
.Xr as
source is itself synthesized from other files.
.Xr as
understands the
.Li #
directives emitted by the
.Li gcc
preprocessor. See also File,,
.Li .file
\&.
.Pp
.Ss Output (Object) File
Every time you run
.Xr as
it produces an output file, which is your assembly language program translated
into numbers. This file is the object file. Its default name is
.Li a.out .
You can give it another name by using the
.Op -o
option. Conventionally, object file names end with
.Pa .o .
The default name is used for historical reasons: older assemblers were capable
of assembling self-contained programs directly into a runnable program. (For
some formats, this isn't currently possible, but it can be done for the
.Li a.out
format.)
.Pp
The object file is meant for input to the linker
.Li ld .
It contains assembled program code, information to help
.Li ld
integrate the assembled program into a runnable file, and (optionally) symbolic
information for the debugger.
.Pp
.Ss Error and Warning Messages
.Xr as
may write warnings and error messages to the standard error file (usually
your terminal). This should not happen when a compiler runs
.Xr as
automatically. Warnings report an assumption made so that
.Xr as
could keep assembling a flawed program; errors report a grave problem that
stops the assembly.
.Pp
Warning messages have the format
.Pp
.Bd -literal -offset indent
file_name:NNN:Warning Message Text
.Ed
.Pp
(where
.Sy NNN
is a line number). If a logical file name has been given (see Section
.Dq File )
it is used for the filename, otherwise the name of the current input file
is used. If a logical line number was given then it is used to calculate the
number printed, otherwise the actual line in the current source file is printed.
The message text is intended to be self explanatory (in the grand Unix tradition).
.Pp
Error messages have the format
.Bd -literal -offset indent
file_name:NNN:FATAL:Error Message Text
.Ed
The file name and line number are derived as for warning messages. The actual
message text may be rather less explanatory because many of them aren't supposed
to happen.
.Pp
.Sh Command-Line Options
This chapter describes command-line options available in
.Em all
versions of the GNU assembler; see Machine Dependencies, for options specific
to the machine specific target.
.Pp
If you are invoking
.Xr as
via the GNU C compiler, you can use the
.Li -Wa
option to pass arguments through to the assembler. The assembler arguments
must be separated from each other (and the
.Li -Wa )
by commas. For example:
.Pp
.Bd -literal -offset indent
gcc -c -g -O -Wa,-alh,-L file.c
.Ed
.Pp
This passes two options to the assembler:
.Li -alh
(emit a listing to standard output with high-level and assembly source) and
.Li -L
(retain local symbols in the symbol table).
.Pp
Usually you do not need to use this
.Li -Wa
mechanism, since many compiler command-line options are automatically passed
to the assembler by the compiler. (You can call the GNU compiler driver with
the
.Li -v
option to see precisely what options it passes to each compilation pass, including
the assembler.)
.Pp
.Ss Enable Listings: Op -a[cdhlns]
These options enable listing output from the assembler. By itself,
.Li -a
requests high-level, assembly, and symbols listing. You can use other letters
to select specific options for the list:
.Li -ah
requests a high-level language listing,
.Li -al
requests an output-program assembly listing, and
.Li -as
requests a symbol table listing. High-level listings require that a compiler
debugging option like
.Li -g
be used, and that assembly listings (
.Li -al )
be requested also.
.Pp
Use the
.Li -ac
option to omit false conditionals from a listing. Any lines which are not
assembled because of a false
.Li .if
(or
.Li .ifdef ,
or any other conditional), or a true
.Li .if
followed by an
.Li .else ,
will be omitted from the listing.
.Pp
Use the
.Li -ad
option to omit debugging directives from the listing.
.Pp
Once you have specified one of these options, you can further control listing
output and its appearance using the directives
.Li .list ,
.Li .nolist ,
.Li .psize ,
.Li .eject ,
.Li .title ,
and
.Li .sbttl .
The
.Li -an
option turns off all forms processing. If you do not request listing output
with one of the
.Li -a
options, the listing-control directives have no effect.
.Pp
The letters after
.Li -a
may be combined into one option,
.Em e.g. ,
.Li -aln .
.Pp
Note if the assembler source is coming from the standard input (e.g., because
it is being created by
.Li gcc
and the
.Li -pipe
command line switch is being used) then the listing will not contain any comments
or preprocessor directives. This is because the listing code buffers input
source lines from stdin only after they have been preprocessed by the assembler.
This reduces memory usage and makes the code more efficient.
.Pp
.Ss Op --alternate
Begin in alternate macro mode, see Altmacro,,
.Li .altmacro
\&.
.Pp
.Ss Op -D
This option has no effect whatsoever, but it is accepted to make it more likely
that scripts written for other assemblers also work with
.Xr as .
.Pp
.Ss Work Faster: Op -f
.Li -f
should only be used when assembling programs written by a (trusted) compiler.
.Li -f
stops the assembler from doing whitespace and comment preprocessing on the
input file(s) before assembling them.See Section
.Dq Preprocessing .
.Pp
.Qo
.Em Warning:
if you use
.Li -f
when the files actually need to be preprocessed (if they contain comments,
for example),
.Xr as
does not work correctly.
.Qc
.Pp
.Ss Li .include Search Path: Op -I Va path
Use this option to add a
.Va path
to the list of directories
.Xr as
searches for files specified in
.Li .include
directives (see Section
.Dq Include ) .
You may use
.Op -I
as many times as necessary to include a variety of paths. The current working
directory is always searched first; after that,
.Xr as
searches any
.Li -I
directories in the same order as they were specified (left to right) on the
command line.
.Pp
.Ss Difference Tables: Op -K
On the machine specific family, this option is allowed, but has no effect.
It is permitted for compatibility with the GNU assembler on other platforms,
where it can be used to warn when the assembler alters the machine code generated
for
.Li .word
directives in difference tables. The machine specific family does not have
the addressing limitations that sometimes lead to this alteration on other
platforms.
.Pp
.Ss Include Local Symbols: Op -L
Symbols beginning with system-specific local label prefixes, typically
.Li .L
for ELF systems or
.Li L
for traditional a.out systems, are called
.Em local symbols .
See Section.Dq Symbol Names .
Normally you do not see such symbols when debugging, because they are intended
for the use of programs (like compilers) that compose assembler programs,
not for your notice. Normally both
.Xr as
and
.Li ld
discard such symbols, so you do not normally debug with them.
.Pp
This option tells
.Xr as
to retain those local symbols in the object file. Usually if you do this you
also tell the linker
.Li ld
to preserve those symbols.
.Pp
.Ss Configuring listing output: Op --listing
The listing feature of the assembler can be enabled via the command line switch
.Li -a
(see Section
.Dq a ) .
This feature combines the input source file(s) with a hex dump of the corresponding
locations in the output object file, and displays them as a listing file.
The format of this listing can be controlled by directives inside the assembler
source (i.e.,
.Li .list
(see Section
.Dq List ) ,
.Li .title
(see Section
.Dq Title ) ,
.Li .sbttl
(see Section
.Dq Sbttl ) ,
.Li .psize
(see Section
.Dq Psize ) ,
and
.Li .eject
(see Section
.Dq Eject )
and also by the following switches:
.Pp
.Bl -tag -width Ds
.It --listing-lhs-width= Li number
Sets the maximum width, in words, of the first line of the hex byte dump.
This dump appears on the left hand side of the listing output.
.Pp
.It --listing-lhs-width2= Li number
Sets the maximum width, in words, of any further lines of the hex byte dump
for a given input source line. If this value is not specified, it defaults
to being the same as the value specified for
.Li --listing-lhs-width .
If neither switch is used the default is to one.
.Pp
.It --listing-rhs-width= Li number
Sets the maximum width, in characters, of the source line that is displayed
alongside the hex dump. The default value for this parameter is 100. The source
line is displayed on the right hand side of the listing output.
.Pp
.It --listing-cont-lines= Li number
Sets the maximum number of continuation lines of hex dump that will be displayed
for a given single line of source input. The default value is 4.
.El
.Pp
.Ss Assemble in MRI Compatibility Mode: Op -M
The
.Op -M
or
.Op --mri
option selects MRI compatibility mode. This changes the syntax and pseudo-op
handling of
.Xr as
to make it compatible with the
.Li ASM68K
or the
.Li ASM960
(depending upon the configured target) assembler from Microtec Research. The
exact nature of the MRI syntax will not be documented here; see the MRI manuals
for more information. Note in particular that the handling of macros and macro
arguments is somewhat different. The purpose of this option is to permit assembling
existing MRI assembler code using
.Xr as .
.Pp
The MRI compatibility is not complete. Certain operations of the MRI assembler
depend upon its object file format, and can not be supported using other object
file formats. Supporting these would require enhancing each object file format
individually. These are:
.Pp
.Bl -bullet
.It
global symbols in common section
.Pp
The m68k MRI assembler supports common sections which are merged by the linker.
Other object file formats do not support this.
.Xr as
handles common sections by treating them as a single common symbol. It permits
local symbols to be defined within a common section, but it can not support
global symbols, since it has no way to describe them.
.Pp
.It
complex relocations
.Pp
The MRI assemblers support relocations against a negated section address,
and relocations which combine the start addresses of two or more sections.
These are not support by other object file formats.
.Pp
.It
.Li END
pseudo-op specifying start address
.Pp
The MRI
.Li END
pseudo-op permits the specification of a start address. This is not supported
by other object file formats. The start address may instead be specified using
the
.Op -e
option to the linker, or in a linker script.
.Pp
.It
.Li IDNT ,
.Li .ident
and
.Li NAME
pseudo-ops
.Pp
The MRI
.Li IDNT ,
.Li .ident
and
.Li NAME
pseudo-ops assign a module name to the output file. This is not supported
by other object file formats.
.Pp
.It
.Li ORG
pseudo-op
.Pp
The m68k MRI
.Li ORG
pseudo-op begins an absolute section at a given address. This differs from
the usual
.Xr as
.Li .org
pseudo-op, which changes the location within the current section. Absolute
sections are not supported by other object file formats. The address of a
section may be assigned within a linker script.
.El
.Pp
There are some other features of the MRI assembler which are not supported
by
.Xr as ,
typically either because they are difficult or because they seem of little
consequence. Some of these may be supported in future releases.
.Pp
.Bl -bullet
.It
EBCDIC strings
.Pp
EBCDIC strings are not supported.
.Pp
.It
packed binary coded decimal
.Pp
Packed binary coded decimal is not supported. This means that the
.Li DC.P
and
.Li DCB.P
pseudo-ops are not supported.
.Pp
.It
.Li FEQU
pseudo-op
.Pp
The m68k
.Li FEQU
pseudo-op is not supported.
.Pp
.It
.Li NOOBJ
pseudo-op
.Pp
The m68k
.Li NOOBJ
pseudo-op is not supported.
.Pp
.It
.Li OPT
branch control options
.Pp
The m68k
.Li OPT
branch control options---
.Li B ,
.Li BRS ,
.Li BRB ,
.Li BRL ,
and
.Li BRW
---are ignored.
.Xr as
automatically relaxes all branches, whether forward or backward, to an appropriate
size, so these options serve no purpose.
.Pp
.It
.Li OPT
list control options
.Pp
The following m68k
.Li OPT
list control options are ignored:
.Li C ,
.Li CEX ,
.Li CL ,
.Li CRE ,
.Li E ,
.Li G ,
.Li I ,
.Li M ,
.Li MEX ,
.Li MC ,
.Li MD ,
.Li X .
.Pp
.It
other
.Li OPT
options
.Pp
The following m68k
.Li OPT
options are ignored:
.Li NEST ,
.Li O ,
.Li OLD ,
.Li OP ,
.Li P ,
.Li PCO ,
.Li PCR ,
.Li PCS ,
.Li R .
.Pp
.It
.Li OPT
.Li D
option is default
.Pp
The m68k
.Li OPT
.Li D
option is the default, unlike the MRI assembler.
.Li OPT NOD
may be used to turn it off.
.Pp
.It
.Li XREF
pseudo-op.
.Pp
The m68k
.Li XREF
pseudo-op is ignored.
.Pp
.It
.Li .debug
pseudo-op
.Pp
The i960
.Li .debug
pseudo-op is not supported.
.Pp
.It
.Li .extended
pseudo-op
.Pp
The i960
.Li .extended
pseudo-op is not supported.
.Pp
.It
.Li .list
pseudo-op.
.Pp
The various options of the i960
.Li .list
pseudo-op are not supported.
.Pp
.It
.Li .optimize
pseudo-op
.Pp
The i960
.Li .optimize
pseudo-op is not supported.
.Pp
.It
.Li .output
pseudo-op
.Pp
The i960
.Li .output
pseudo-op is not supported.
.Pp
.It
.Li .setreal
pseudo-op
.Pp
The i960
.Li .setreal
pseudo-op is not supported.
.Pp
.El
.Ss Dependency Tracking: Op --MD
.Xr as
can generate a dependency file for the file it creates. This file consists
of a single rule suitable for
.Li make
describing the dependencies of the main source file.
.Pp
The rule is written to the file named in its argument.
.Pp
This feature is used in the automatic updating of makefiles.
.Pp
.Ss Name the Object File: Op -o
There is always one object file output when you run
.Xr as .
By default it has the name
.Pa a.out .
You use this option (which takes exactly one filename) to give the object
file a different name.
.Pp
Whatever the object file is called,
.Xr as
overwrites any existing file of the same name.
.Pp
.Ss Join Data and Text Sections: Op -R
.Op -R
tells
.Xr as
to write the object file as if all data-section data lives in the text section.
This is only done at the very last moment: your binary data are the same,
but data section parts are relocated differently. The data section part of
your object file is zero bytes long because all its bytes are appended to
the text section. (See Section
.Dq Sections . )
.Pp
When you specify
.Op -R
it would be possible to generate shorter address displacements (because we
do not have to cross between text and data section). We refrain from doing
this simply for compatibility with older versions of
.Xr as .
In future,
.Op -R
may work this way.
.Pp
When
.Xr as
is configured for COFF or ELF output, this option is only useful if you use
sections named
.Li .text
and
.Li .data .
.Pp
.Ss Display Assembly Statistics: Op --statistics
Use
.Li --statistics
to display two statistics about the resources used by
.Xr as :
the maximum amount of space allocated during the assembly (in bytes), and
the total execution time taken for the assembly (in cpu seconds).
.Pp
.Ss Compatible Output: Op --traditional-format
For some targets, the output of
.Xr as
is different in some ways from the output of some existing assembler. This
switch requests
.Xr as
to use the traditional format instead.
.Pp
For example, it disables the exception frame optimizations which
.Xr as
normally does by default on
.Li gcc
output.
.Pp
.Ss Announce Version: Op -v
You can find out what version of as is running by including the option
.Li -v
(which you can also spell as
.Li -version )
on the command line.
.Pp
.Ss Control Warnings: Op -W, Op --warn, Op --no-warn, Op --fatal-warnings
.Xr as
should never give a warning or error message when assembling compiler output.
But programs written by people often cause
.Xr as
to give a warning that a particular assumption was made. All such warnings
are directed to the standard error file.
.Pp
If you use the
.Op -W
and
.Op --no-warn
options, no warnings are issued. This only affects the warning messages: it
does not change any particular of how
.Xr as
assembles your file. Errors, which stop the assembly, are still reported.
.Pp
If you use the
.Op --fatal-warnings
option,
.Xr as
considers files that generate warnings to be in error.
.Pp
You can switch these options off again by specifying
.Op --warn ,
which causes warnings to be output as usual.
.Pp
.Ss Generate Object File in Spite of Errors: Op -Z
After an error message,
.Xr as
normally produces no output. If for some reason you are interested in object
file output even after
.Xr as
gives an error message on your program, use the
.Li -Z
option. If there are any errors,
.Xr as
continues anyways, and writes an object file after a final warning message
of the form
.Li Va n errors, Va m warnings, generating bad object file.
.Pp
.Sh Syntax
This chapter describes the machine-independent syntax allowed in a source
file.
.Xr as
syntax is similar to what many other assemblers use; it is inspired by the
BSD 4.2 assembler.
.Pp
.Ss Preprocessing
The
.Xr as
internal preprocessor:
.Bl -bullet
.It
adjusts and removes extra whitespace. It leaves one space or tab before the
keywords on a line, and turns any other whitespace on the line into a single
space.
.Pp
.It
removes all comments, replacing them with a single space, or an appropriate
number of newlines.
.Pp
.It
converts character constants into the appropriate numeric values.
.El
.Pp
It does not do macro processing, include file handling, or anything else you
may get from your C compiler's preprocessor. You can do include file processing
with the
.Li .include
directive (see Section
.Dq Include ) .
You can use the GNU C compiler driver to get other \(lqCPP\(rq style preprocessing
by giving the input file a
.Li .S
suffix.See Section
.Dq Overall Options .
.Pp
Excess whitespace, comments, and character constants cannot be used in the
portions of the input text that are not preprocessed.
.Pp
If the first line of an input file is
.Li #NO_APP
or if you use the
.Li -f
option, whitespace and comments are not removed from the input file. Within
an input file, you can ask for whitespace and comment removal in specific
portions of the by putting a line that says
.Li #APP
before the text that may contain whitespace or comments, and putting a line
that says
.Li #NO_APP
after this text. This feature is mainly intend to support
.Li asm
statements in compilers whose output is otherwise free of comments and whitespace.
.Pp
.Ss Whitespace
.Em Whitespace
is one or more blanks or tabs, in any order. Whitespace is used to separate
symbols, and to make programs neater for people to read. Unless within character
constants (see Section
.Dq Characters ) ,
any whitespace means the same as exactly one space.
.Pp
.Ss Comments
There are two ways of rendering comments to
.Xr as .
In both cases the comment is equivalent to one space.
.Pp
Anything from
.Li /*
through the next
.Li */
is a comment. This means you may not nest these comments.
.Pp
.Bd -literal -offset indent
/*
The only way to include a newline ('\en') in a comment
is to use this sort of comment.
*/
/* This sort of comment does not nest. */
.Ed
.Pp
Anything from the
.Em line comment
character to the next newline is considered a comment and is ignored. The
line comment character is
.Li @
on the ARM;
.Li #
on the i386 and x86-64;
.Li #
for Motorola PowerPC;
.Li !
on the SPARC; see Machine Dependencies.
.Pp
To be compatible with past assemblers, lines that begin with
.Li #
have a special interpretation. Following the
.Li #
should be an absolute expression (see Section
.Dq Expressions ) :
the logical line number of the
.Em next
line. Then a string (see Section
.Dq Strings )
is allowed: if present it is a new logical file name. The rest of the line,
if any, should be whitespace.
.Pp
If the first non-whitespace characters on the line are not numeric, the line
is ignored. (Just like a comment.)
.Pp
.Bd -literal -offset indent
# This is an ordinary comment.
# 42-6 "new_file_name" # New logical file name
# This is logical line # 36.
.Ed
This feature is deprecated, and may disappear from future versions of
.Xr as .
.Pp
.Ss Symbols
A
.Em symbol
is one or more characters chosen from the set of all letters (both upper and
lower case), digits and the three characters
.Li _.$ .
No symbol may begin with a digit. Case is significant. There is no length
limit: all characters are significant. Symbols are delimited by characters
not in that set, or by the beginning of a file (since the source program must
end with a newline, the end of a file is not a possible symbol delimiter).See Section
.Dq Symbols .
.Pp
.Ss Statements
A
.Em statement
ends at a newline character (
.Li \en )
or at a semicolon (
.Li ; ) .
The newline or semicolon is considered part of the preceding statement. Newlines
and semicolons within character constants are an exception: they do not end
statements.
.Pp
It is an error to end any statement with end-of-file: the last character of
any input file should be a newline.
.Pp
An empty statement is allowed, and may include whitespace. It is ignored.
.Pp
A statement begins with zero or more labels, optionally followed by a key
symbol which determines what kind of statement it is. The key symbol determines
the syntax of the rest of the statement. If the symbol begins with a dot
.Li .
then the statement is an assembler directive: typically valid for any computer.
If the symbol begins with a letter the statement is an assembly language
.Em instruction :
it assembles into a machine language instruction.
.Pp
A label is a symbol immediately followed by a colon (
.Li : ) .
Whitespace before a label or after a colon is permitted, but you may not have
whitespace between a label's symbol and its colon.See Section
.Dq Labels .
.Pp
.Bd -literal -offset indent
label: .directive followed by something
another_label: # This is an empty statement.
instruction operand_1, operand_2, ...
.Ed
.Pp
.Ss Constants
A constant is a number, written so that its value is known by inspection,
without knowing any context. Like this:
.Bd -literal -offset indent
\&.byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\eJ # All the same value.
\&.ascii "Ring the bell\e7" # A string constant.
\&.octa 0x123456789abcdef0123456789ABCDEF0 # A biGNUm.
\&.float 0f-314159265358979323846264338327\e
95028841971.693993751E-40 # - pi, a flonum.
.Ed
.Pp
.Em Character Constants
.Pp
There are two kinds of character constants. A
.Em character
stands for one character in one byte and its value may be used in numeric
expressions. String constants (properly called string
.Em literals )
are potentially many bytes and their values may not be used in arithmetic
expressions.
.Pp
.No Strings
.Pp
A
.Em string
is written between double-quotes. It may contain double-quotes or null characters.
The way to get special characters into a string is to
.Em escape
these characters: precede them with a backslash
.Li \e
character. For example
.Li \e\e
represents one backslash: the first
.Li \e
is an escape which tells
.Xr as
to interpret the second character literally as a backslash (which prevents
.Xr as
from recognizing the second
.Li \e
as an escape character). The complete list of escapes follows.
.Pp
.Bl -tag -width Ds
.It \eb
Mnemonic for backspace; for ASCII this is octal code 010.
.Pp
.It \ef
Mnemonic for FormFeed; for ASCII this is octal code 014.
.Pp
.It \en
Mnemonic for newline; for ASCII this is octal code 012.
.Pp
.It \er
Mnemonic for carriage-Return; for ASCII this is octal code 015.
.Pp
.It \et
Mnemonic for horizontal Tab; for ASCII this is octal code 011.
.Pp
.It \e Va digit Va digit Va digit
An octal character code. The numeric code is 3 octal digits. For compatibility
with other Unix systems, 8 and 9 are accepted as digits: for example,
.Li \e008
has the value 010, and
.Li \e009
the value 011.
.Pp
.It \e Li x Va hex-digits...
A hex character code. All trailing hex digits are combined. Either upper or
lower case
.Li x
works.
.Pp
.It \e\e
Represents one
.Li \e
character.
.Pp
.It \e"
Represents one
.Li "
character. Needed in strings to represent this character, because an unescaped
.Li "
would end the string.
.Pp
.It \e Va anything-else
Any other character when escaped by
.Li \e
gives a warning, but assembles as if the
.Li \e
was not present. The idea is that if you used an escape sequence you clearly
didn't want the literal interpretation of the following character. However
.Xr as
has no other interpretation, so
.Xr as
knows it is giving you the wrong code and warns you of the fact.
.El
.Pp
Which characters are escapable, and what those escapes represent, varies widely
among assemblers. The current set is what we think the BSD 4.2 assembler recognizes,
and is a subset of what most C compilers recognize. If you are in doubt, do
not use an escape sequence.
.Pp
.No Characters
.Pp
A single character may be written as a single quote immediately followed by
that character. The same escapes apply to characters as to strings. So if
you want to write the character backslash, you must write
.Li '\e\e
where the first
.Li \e
escapes the second
.Li \e .
As you can see, the quote is an acute accent, not a grave accent. A newline
(or semicolon
.Li ; )
immediately following an acute accent is taken as a literal character and
does not count as the end of a statement. The value of a character constant
in a numeric expression is the machine's byte-wide code for that character.
.Xr as
assumes your character code is ASCII:
.Li 'A
means 65,
.Li 'B
means 66, and so on.
.Pp
.Em Number Constants
.Pp
.Xr as
distinguishes three kinds of numbers according to how they are stored in the
target machine.
.Em Integers
are numbers that would fit into an
.Li int
in the C language.
.Em BiGNUms
are integers, but they are stored in more than 32 bits.
.Em Flonums
are floating point numbers, described below.
.Pp
.No Integers
.Pp
A binary integer is
.Li 0b
or
.Li 0B
followed by zero or more of the binary digits
.Li 01 .
.Pp
An octal integer is
.Li 0
followed by zero or more of the octal digits (
.Li 01234567 ) .
.Pp
A decimal integer starts with a non-zero digit followed by zero or more digits
(
.Li 0123456789 ) .
.Pp
A hexadecimal integer is
.Li 0x
or
.Li 0X
followed by one or more hexadecimal digits chosen from
.Li 0123456789abcdefABCDEF .
.Pp
Integers have the usual values. To denote a negative integer, use the prefix
operator
.Li -
discussed under expressions (see Section
.Dq Prefix Ops ) .
.Pp
.No BiGNUms
.Pp
A
.Em biGNUm
has the same syntax and semantics as an integer except that the number (or
its negative) takes more than 32 bits to represent in binary. The distinction
is made because in some places integers are permitted while biGNUms are not.
.Pp
.No Flonums
.Pp
A
.Em flonum
represents a floating point number. The translation is indirect: a decimal
floating point number from the text is converted by
.Xr as
to a generic binary floating point number of more than sufficient precision.
This generic floating point number is converted to a particular computer's
floating point format (or formats) by a portion of
.Xr as
specialized to that computer.
.Pp
A flonum is written by writing (in order)
.Bl -bullet
.It
The digit
.Li 0 .
.Pp
.It
A letter, to tell
.Xr as
the rest of the number is a flonum.
.Pp
.It
An optional sign: either
.Li +
or
.Li - .
.Pp
.It
An optional
.Em integer part :
zero or more decimal digits.
.Pp
.It
An optional
.Em fractional part :
.Li .
followed by zero or more decimal digits.
.Pp
.It
An optional exponent, consisting of:
.Pp
.Bl -bullet
.It
An
.Li E
or
.Li e .
.It
Optional sign: either
.Li +
or
.Li - .
.It
One or more decimal digits.
.El
.Pp
.El
At least one of the integer part or the fractional part must be present. The
floating point number has the usual base-10 value.
.Pp
.Xr as
does all processing using integers. Flonums are computed independently of
any floating point hardware in the computer running
.Xr as .
.Pp
.Sh Sections and Relocation
.Ss Background
Roughly, a section is a range of addresses, with no gaps; all data \(lqin\(rq those
addresses is treated the same for some particular purpose. For example there
may be a \(lqread only\(rq section.
.Pp
The linker
.Li ld
reads many object files (partial programs) and combines their contents to
form a runnable program. When
.Xr as
emits an object file, the partial program is assumed to start at address 0.
.Li ld
assigns the final addresses for the partial program, so that different partial
programs do not overlap. This is actually an oversimplification, but it suffices
to explain how
.Xr as
uses sections.
.Pp
.Li ld
moves blocks of bytes of your program to their run-time addresses. These blocks
slide to their run-time addresses as rigid units; their length does not change
and neither does the order of bytes within them. Such a rigid unit is called
a
.Em section .
Assigning run-time addresses to sections is called
.Em relocation .
It includes the task of adjusting mentions of object-file addresses so they
refer to the proper run-time addresses.
.Pp
An object file written by
.Xr as
has at least three sections, any of which may be empty. These are named
.Em text ,
.Em data
and
.Em bss
sections.
.Pp
.Xr as
can also generate whatever other named sections you specify using the
.Li .section
directive (see Section
.Dq Section ) .
If you do not use any directives that place output in the
.Li .text
or
.Li .data
sections, these sections still exist, but are empty.
.Pp
Within the object file, the text section starts at address
.Li 0 ,
the data section follows, and the bss section follows the data section.
.Pp
To let
.Li ld
know which data changes when the sections are relocated, and how to change
that data,
.Xr as
also writes to the object file details of the relocation needed. To perform
relocation
.Li ld
must know, each time an address in the object file is mentioned:
.Bl -bullet
.It
Where in the object file is the beginning of this reference to an address?
.It
How long (in bytes) is this reference?
.It
Which section does the address refer to? What is the numeric value of
.Bd -filled -offset indent
(
.Va address )
\-(
.Va start-address of section ) ?
.Ed
.It
Is the reference to an address \(lqProgram-Counter relative\(rq?
.El
.Pp
In fact, every address
.Xr as
ever uses is expressed as
.Bd -filled -offset indent
(
.Va section )
+ (
.Va offset into section )
.Ed
Further, most expressions
.Xr as
computes have this section-relative nature.
.Pp
In this manual we use the notation {
.Va secname
.Va N
}to mean \(lqoffset
.Va N
into section
.Va secname
\&.\(rq
.Pp
Apart from text, data and bss sections you need to know about the
.Em absolute
section. When
.Li ld
mixes partial programs, addresses in the absolute section remain unchanged.
For example, address
.Li {absolute 0}
is \(lqrelocated\(rq to run-time address 0 by
.Li ld .
Although the linker never arranges two partial programs' data sections with
overlapping addresses after linking,
.Em by definition
their absolute sections must overlap. Address
.Li {absolute 239}
in one part of a program is always the same address when the program is running
as address
.Li {absolute 239}
in any other part of the program.
.Pp
The idea of sections is extended to the
.Em undefined
section. Any address whose section is unknown at assembly time is by definition
rendered {undefined
.Va U
}---where
.Va U
is filled in later. Since numbers are always defined, the only way to generate
an undefined address is to mention an undefined symbol. A reference to a named
common block would be such a symbol: its value is unknown at assembly time
so it has section
.Em undefined .
.Pp
By analogy the word
.Em section
is used to describe groups of sections in the linked program.
.Li ld
puts all partial programs' text sections in contiguous addresses in the linked
program. It is customary to refer to the
.Em text section
of a program, meaning all the addresses of all partial programs' text sections.
Likewise for data and bss sections.
.Pp
Some sections are manipulated by
.Li ld ;
others are invented for use of
.Xr as
and have no meaning except during assembly.
.Pp
.Ss Linker Sections
.Li ld
deals with just four kinds of sections, summarized below.
.Pp
.Bl -tag -width Ds
.It named sections
These sections hold your program.
.Xr as
and
.Li ld
treat them as separate but equal sections. Anything you can say of one section
is true of another. When the program is running, however, it is customary
for the text section to be unalterable. The text section is often shared among
processes: it contains instructions, constants and the like. The data section
of a running program is usually alterable: for example, C variables would
be stored in the data section.
.Pp
.It bss section
This section contains zeroed bytes when your program begins running. It is
used to hold uninitialized variables or common storage. The length of each
partial program's bss section is important, but because it starts out containing
zeroed bytes there is no need to store explicit zero bytes in the object file.
The bss section was invented to eliminate those explicit zeros from object
files.
.Pp
.It absolute section
Address 0 of this section is always \(lqrelocated\(rq to runtime address 0. This is
useful if you want to refer to an address that
.Li ld
must not change when relocating. In this sense we speak of absolute addresses
being \(lqunrelocatable\(rq: they do not change during relocation.
.Pp
.It undefined section
This \(lqsection\(rq is a catch-all for address references to objects not in the preceding
sections.
.El
.Pp
An idealized example of three relocatable sections follows. The example uses
the traditional section names
.Li .text
and
.Li .data .
Memory addresses are on the horizontal axis.
.Pp
.Bd -literal -offset indent
+-----+----+--+
partial program # 1: |ttttt|dddd|00|
+-----+----+--+
text data bss
seg. seg. seg.
+---+---+---+
partial program # 2: |TTT|DDD|000|
+---+---+---+
+--+---+-----+--+----+---+-----+~~
linked program: | |TTT|ttttt| |dddd|DDD|00000|
+--+---+-----+--+----+---+-----+~~
addresses: 0 ...
.Ed
.Pp
.Ss Assembler Internal Sections
These sections are meant only for the internal use of
.Xr as .
They have no meaning at run-time. You do not really need to know about these
sections for most purposes; but they can be mentioned in
.Xr as
warning messages, so it might be helpful to have an idea of their meanings
to
.Xr as .
These sections are used to permit the value of every expression in your assembly
language program to be a section-relative address.
.Pp
.Bl -tag -width Ds
.It ASSEMBLER-INTERNAL-LOGIC-ERROR!
An internal assembler logic error has been found. This means there is a bug
in the assembler.
.Pp
.It expr section
The assembler stores complex expression internally as combinations of symbols.
When it needs to represent an expression as a symbol, it puts it in the expr
section.
.El
.Pp
.Ss Sub-Sections
You may have separate groups of data in named sections that you want to end
up near to each other in the object file, even though they are not contiguous
in the assembler source.
.Xr as
allows you to use
.Em subsections
for this purpose. Within each section, there can be numbered subsections with
values from 0 to 8192. Objects assembled into the same subsection go into
the object file together with other objects in the same subsection. For example,
a compiler might want to store constants in the text section, but might not
want to have them interspersed with the program being assembled. In this case,
the compiler could issue a
.Li .text 0
before each section of code being output, and a
.Li .text 1
before each group of constants being output.
.Pp
Subsections are optional. If you do not use subsections, everything goes in
subsection number zero.
.Pp
Subsections appear in your object file in numeric order, lowest numbered to
highest. (All this to be compatible with other people's assemblers.) The object
file contains no representation of subsections;
.Li ld
and other programs that manipulate object files see no trace of them. They
just see all your text subsections as a text section, and all your data subsections
as a data section.
.Pp
To specify which subsection you want subsequent statements assembled into,
use a numeric argument to specify it, in a
.Li .text Va expression
or a
.Li .data Va expression
statement. You can also use the
.Li .subsection
directive (see Section
.Dq SubSection )
to specify a subsection:
.Li .subsection Va expression .
.Va Expression
should be an absolute expression (see Section
.Dq Expressions ) .
If you just say
.Li .text
then
.Li .text 0
is assumed. Likewise
.Li .data
means
.Li .data 0 .
Assembly begins in
.Li text 0 .
For instance:
.Bd -literal -offset indent
\&.text 0 # The default subsection is text 0 anyway.
\&.ascii "This lives in the first text subsection. *"
\&.text 1
\&.ascii "But this lives in the second text subsection."
\&.data 0
\&.ascii "This lives in the data section,"
\&.ascii "in the first data subsection."
\&.text 0
\&.ascii "This lives in the first text section,"
\&.ascii "immediately following the asterisk (*)."
.Ed
.Pp
Each section has a
.Em location counter
incremented by one for every byte assembled into that section. Because subsections
are merely a convenience restricted to
.Xr as
there is no concept of a subsection location counter. There is no way to directly
manipulate a location counter---but the
.Li .align
directive changes it, and any label definition captures its current value.
The location counter of the section where statements are being assembled is
said to be the
.Em active
location counter.
.Pp
.Ss bss Section
The bss section is used for local common variable storage. You may allocate
address space in the bss section, but you may not dictate data to load into
it before your program executes. When your program starts running, all the
contents of the bss section are zeroed bytes.
.Pp
The
.Li .lcomm
pseudo-op defines a symbol in the bss section; see Lcomm,,
.Li .lcomm
\&.
.Pp
The
.Li .comm
pseudo-op may be used to declare a common symbol, which is another form of
uninitialized symbol; see Comm,,
.Li .comm
\&.
.Pp
.Sh Symbols
Symbols are a central concept: the programmer uses symbols to name things,
the linker uses symbols to link, and the debugger uses symbols to debug.
.Pp
.Qo
.Em Warning:
.Xr as
does not place symbols in the object file in the same order they were declared.
This may break some debuggers.
.Qc
.Pp
.Ss Labels
A
.Em label
is written as a symbol immediately followed by a colon
.Li : .
The symbol then represents the current value of the active location counter,
and is, for example, a suitable instruction operand. You are warned if you
use the same symbol to represent two different locations: the first definition
overrides any other definitions.
.Pp
.Ss Giving Symbols Other Values
A symbol can be given an arbitrary value by writing a symbol, followed by
an equals sign
.Li = ,
followed by an expression (see Section
.Dq Expressions ) .
This is equivalent to using the
.Li .set
directive.See Section
.Dq Set .
In the same way, using a double equals sign
.Li =
.Li =
here represents an equivalent of the
.Li .eqv
directive.See Section
.Dq Eqv .
.Pp
.Ss Symbol Names
Symbol names begin with a letter or with one of
.Li ._ .
On most machines, you can also use
.Li $
in symbol names; exceptions are noted in Machine Dependencies. That character
may be followed by any string of digits, letters, dollar signs (unless otherwise
noted for a particular target machine), and underscores.
.Pp
Case of letters is significant:
.Li foo
is a different symbol name than
.Li Foo .
.Pp
Each symbol has exactly one name. Each name in an assembly language program
refers to exactly one symbol. You may use that symbol name any number of times
in a program.
.Pp
.Em Local Symbol Names
.Pp
A local symbol is any symbol beginning with certain local label prefixes.
By default, the local label prefix is
.Li .L
for ELF systems or
.Li L
for traditional a.out systems, but each target may have its own set of local
label prefixes.
.Pp
Local symbols are defined and used within the assembler, but they are normally
not saved in object files. Thus, they are not visible when debugging. You
may use the
.Li -L
option (see Section
.Dq L )
to retain the local symbols in the object files.
.Pp
.Em Local Labels
.Pp
Local labels help compilers and programmers use names temporarily. They create
symbols which are guaranteed to be unique over the entire scope of the input
source code and which can be referred to by a simple notation. To define a
local label, write a label of the form
.Li Sy N:
(where
.Sy N
represents any positive integer). To refer to the most recent previous definition
of that label write
.Li Sy Nb ,
using the same number as when you defined the label. To refer to the next
definition of a local label, write
.Li Sy Nf
---the
.Li b
stands for \(lqbackwards\(rq and the
.Li f
stands for \(lqforwards\(rq.
.Pp
There is no restriction on how you can use these labels, and you can reuse
them too. So that it is possible to repeatedly define the same local label
(using the same number
.Li Sy N ) ,
although you can only refer to the most recently defined local label of that
number (for a backwards reference) or the next definition of a specific local
label for a forward reference. It is also worth noting that the first 10 local
labels (
.Li Sy 0:
\&....Li Sy 9: )
are implemented in a slightly more efficient manner than the others.
.Pp
Here is an example:
.Pp
.Bd -literal -offset indent
1: branch 1f
2: branch 1b
1: branch 2f
2: branch 1b
.Ed
.Pp
Which is the equivalent of:
.Pp
.Bd -literal -offset indent
label_1: branch label_3
label_2: branch label_1
label_3: branch label_4
label_4: branch label_3
.Ed
.Pp
Local label names are only a notational device. They are immediately transformed
into more conventional symbol names before the assembler uses them. The symbol
names are stored in the symbol table, appear in error messages, and are optionally
emitted to the object file. The names are constructed using these parts:
.Pp
.Bl -tag -width Ds
.It Em local label prefix
All local symbols begin with the system-specific local label prefix. Normally
both
.Xr as
and
.Li ld
forget symbols that start with the local label prefix. These labels are used
for symbols you are never intended to see. If you use the
.Li -L
option then
.Xr as
retains these symbols in the object file. If you also instruct
.Li ld
to retain these symbols, you may use them in debugging.
.Pp
.It Va number
This is the number that was used in the local label definition. So if the
label is written
.Li 55:
then the number is
.Li 55 .
.Pp
.It Li C-B
This unusual character is included so you do not accidentally invent a symbol
of the same name. The character has ASCII value of
.Li \e002
(control-B).
.Pp
.It Em ordinal number
This is a serial number to keep the labels distinct. The first definition
of
.Li 0:
gets the number
.Li 1 .
The 15th definition of
.Li 0:
gets the number
.Li 15 ,
and so on. Likewise the first definition of
.Li 1:
gets the number
.Li 1
and its 15th definition gets
.Li 15
as well.
.El
.Pp
So for example, the first
.Li 1:
may be named
.Li .L1 Li C-B1 ,
and the 44th
.Li 3:
may be named
.Li .L3 Li C-B44 .
.Pp
.Em Dollar Local Labels
.Pp
.Li as
also supports an even more local form of local labels called dollar labels.
These labels go out of scope (i.e., they become undefined) as soon as a non-local
label is defined. Thus they remain valid for only a small region of the input
source code. Normal local labels, by contrast, remain in scope for the entire
file, or until they are redefined by another occurrence of the same local
label.
.Pp
Dollar labels are defined in exactly the same way as ordinary local labels,
except that instead of being terminated by a colon, they are terminated by
a dollar sign, e.g.,
.Li Sy 55$ .
.Pp
They can also be distinguished from ordinary local labels by their transformed
names which use ASCII character
.Li \e001
(control-A) as the magic character to distinguish them from ordinary labels.
For example, the fifth definition of
.Li 6$
may be named
.Li .L6 Li C-A5 .
.Pp
.Ss The Special Dot Symbol
The special symbol
.Li .
refers to the current address that
.Xr as
is assembling into. Thus, the expression
.Li melvin: .long .
defines
.Li melvin
to contain its own address. Assigning a value to
.Li .
is treated the same as a
.Li .org
directive. Thus, the expression
.Li .=.+4
is the same as saying
.Li .space 4 .
.Pp
.Ss Symbol Attributes
Every symbol has, as well as its name, the attributes \(lqValue\(rq and \(lqType\(rq. Depending
on output format, symbols can also have auxiliary attributes. The detailed
definitions are in
.Pa a.out.h .
.Pp
If you use a symbol without defining it,
.Xr as
assumes zero for all these attributes, and probably won't warn you. This makes
the symbol an externally defined symbol, which is generally what you would
want.
.Pp
.Em Value
.Pp
The value of a symbol is (usually) 32 bits. For a symbol which labels a location
in the text, data, bss or absolute sections the value is the number of addresses
from the start of that section to the label. Naturally for text, data and
bss sections the value of a symbol changes as
.Li ld
changes section base addresses during linking. Absolute symbols' values do
not change during linking: that is why they are called absolute.
.Pp
The value of an undefined symbol is treated in a special way. If it is 0 then
the symbol is not defined in this assembler source file, and
.Li ld
tries to determine its value from other files linked into the same program.
You make this kind of symbol simply by mentioning a symbol name without defining
it. A non-zero value represents a
.Li .comm
common declaration. The value is how much common storage to reserve, in bytes
(addresses). The symbol refers to the first address of the allocated storage.
.Pp
.Em Type
.Pp
The type attribute of a symbol contains relocation (section) information,
any flag settings indicating that a symbol is external, and (optionally),
other information for linkers and debuggers. The exact format depends on the
object-code output format in use.
.Pp
.Sh Expressions
An
.Em expression
specifies an address or numeric value. Whitespace may precede and/or follow
an expression.
.Pp
The result of an expression must be an absolute number, or else an offset
into a particular section. If an expression is not absolute, and there is
not enough information when
.Xr as
sees the expression to know its section, a second pass over the source program
might be necessary to interpret the expression---but the second pass is currently
not implemented.
.Xr as
aborts with an error message in this situation.
.Pp
.Ss Empty Expressions
An empty expression has no value: it is just whitespace or null. Wherever
an absolute expression is required, you may omit the expression, and
.Xr as
assumes a value of (absolute) 0. This is compatible with other assemblers.
.Pp
.Ss Integer Expressions
An
.Em integer expression
is one or more
.Em arguments
delimited by
.Em operators .
.Pp
.Em Arguments
.Pp
.Em Arguments
are symbols, numbers or subexpressions. In other contexts arguments are sometimes
called \(lqarithmetic operands\(rq. In this manual, to avoid confusing them with the
\(lqinstruction operands\(rq of the machine language, we use the term \(lqargument\(rq to
refer to parts of expressions only, reserving the word \(lqoperand\(rq to refer only
to machine instruction operands.
.Pp
Symbols are evaluated to yield {
.Va section
.Va NNN
}where
.Va section
is one of text, data, bss, absolute, or undefined.
.Va NNN
is a signed, 2's complement 32 bit integer.
.Pp
Numbers are usually integers.
.Pp
A number can be a flonum or biGNUm. In this case, you are warned that only
the low order 32 bits are used, and
.Xr as
pretends these 32 bits are an integer. You may write integer-manipulating
instructions that act on exotic constants, compatible with other assemblers.
.Pp
Subexpressions are a left parenthesis
.Li (
followed by an integer expression, followed by a right parenthesis
.Li ) ;
or a prefix operator followed by an argument.
.Pp
.Em Operators
.Pp
.Em Operators
are arithmetic functions, like
.Li +
or
.Li % .
Prefix operators are followed by an argument. Infix operators appear between
their arguments. Operators may be preceded and/or followed by whitespace.
.Pp
.Em Prefix Operator
.Pp
.Xr as
has the following
.Em prefix operators .
They each take one argument, which must be absolute.
.Pp
.Bl -tag -width Ds
.It -
.Em Negation .
Two's complement negation.
.It ~
.Em Complementation .
Bitwise not.
.El
.Pp
.Em Infix Operators
.Pp
.Em Infix operators
take two arguments, one on either side. Operators have precedence, but operations
with equal precedence are performed left to right. Apart from
.Li +
or
.Op - ,
both arguments must be absolute, and the result is absolute.
.Pp
.Bl -enum
.It
Highest Precedence
.Pp
.Bl -tag -width Ds
.It *
.Em Multiplication .
.Pp
.It /
.Em Division .
Truncation is the same as the C operator
.Li /
.Pp
.It %
.Em Remainder .
.Pp
.It <<
.Em Shift Left .
Same as the C operator
.Li << .
.Pp
.It >>
.Em Shift Right .
Same as the C operator
.Li >> .
.El
.Pp
.It
Intermediate precedence
.Pp
.Bl -tag -width Ds
.It |
.Pp
.Em Bitwise Inclusive Or .
.Pp
.It &
.Em Bitwise And .
.Pp
.It ^
.Em Bitwise Exclusive Or .
.Pp
.It !
.Em Bitwise Or Not .
.El
.Pp
.It
Low Precedence
.Pp
.Bl -tag -width Ds
.It +
.Em Addition .
If either argument is absolute, the result has the section of the other argument.
You may not add together arguments from different sections.
.Pp
.It -
.Em Subtraction .
If the right argument is absolute, the result has the section of the left
argument. If both arguments are in the same section, the result is absolute.
You may not subtract arguments from different sections.
.Pp
.It ==
.Em Is Equal To
.It <>
.It !=
.Em Is Not Equal To
.It <
.Em Is Less Than
.It >
.Em Is Greater Than
.It >=
.Em Is Greater Than Or Equal To
.It <=
.Em Is Less Than Or Equal To
.Pp
The comparison operators can be used as infix operators. A true results has
a value of -1 whereas a false result has a value of 0. Note, these operators
perform signed comparisons.
.El
.Pp
.It
Lowest Precedence
.Pp
.Bl -tag -width Ds
.It &&
.Em Logical And .
.Pp
.It ||
.Em Logical Or .
.Pp
These two logical operations can be used to combine the results of sub expressions.
Note, unlike the comparison operators a true result returns a value of 1 but
a false results does still return 0. Also note that the logical or operator
has a slightly lower precedence than logical and.
.Pp
.El
.El
In short, it's only meaningful to add or subtract the
.Em offsets
in an address; you can only have a defined section in one of the two arguments.
.Pp
.Sh Assembler Directives
All assembler directives have names that begin with a period (
.Li . ) .
The rest of the name is letters, usually in lower case.
.Pp
This chapter discusses directives that are available regardless of the target
machine configuration for the GNU assembler.
.Pp
.Ss Li .abort
This directive stops the assembly immediately. It is for compatibility with
other assemblers. The original idea was that the assembly language source
would be piped into the assembler. If the sender of the source quit, it could
use this directive tells
.Xr as
to quit also. One day
.Li .abort
will not be supported.
.Pp
.Ss Li .align Va abs-expr, Va abs-expr, Va abs-expr
Pad the location counter (in the current subsection) to a particular storage
boundary. The first expression (which must be absolute) is the alignment required,
as described below.
.Pp
The second expression (also absolute) gives the fill value to be stored in
the padding bytes. It (and the comma) may be omitted. If it is omitted, the
padding bytes are normally zero. However, on some systems, if the section
is marked as containing code and the fill value is omitted, the space is filled
with no-op instructions.
.Pp
The third expression is also absolute, and is also optional. If it is present,
it is the maximum number of bytes that should be skipped by this alignment
directive. If doing the alignment would require skipping more bytes than the
specified maximum, then the alignment is not done at all. You can omit the
fill value (the second argument) entirely by simply using two commas after
the required alignment; this can be useful if you want the alignment to be
filled with no-op instructions when appropriate.
.Pp
The way the required alignment is specified varies from system to system.
For the arc, hppa, i386 using ELF, i860, iq2000, m68k, or32, s390, sparc,
tic4x, tic80 and xtensa, the first expression is the alignment request in
bytes. For example
.Li .align 8
advances the location counter until it is a multiple of 8. If the location
counter is already a multiple of 8, no change is needed. For the tic54x, the
first expression is the alignment request in words.
.Pp
For other systems, including the i386 using a.out format, and the arm and
strongarm, it is the number of low-order zero bits the location counter must
have after advancement. For example
.Li .align 3
advances the location counter until it a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
.Pp
This inconsistency is due to the different behaviors of the various native
assemblers for these systems which GAS must emulate. GAS also provides
.Li .balign
and
.Li .p2align
directives, described later, which have a consistent behavior across all architectures
(but are specific to GAS).
.Pp
.Ss Li .ascii " Va string"...
.Li .ascii
expects zero or more string literals (see Section
.Dq Strings )
separated by commas. It assembles each string (with no automatic trailing
zero byte) into consecutive addresses.
.Pp
.Ss Li .asciz " Va string"...
.Li .asciz
is just like
.Li .ascii ,
but each string is followed by a zero byte. The \(lqz\(rq in
.Li .asciz
stands for \(lqzero\(rq.
.Pp
.Ss Li .balign[wl] Va abs-expr, Va abs-expr, Va abs-expr
Pad the location counter (in the current subsection) to a particular storage
boundary. The first expression (which must be absolute) is the alignment request
in bytes. For example
.Li .balign 8
advances the location counter until it is a multiple of 8. If the location
counter is already a multiple of 8, no change is needed.
.Pp
The second expression (also absolute) gives the fill value to be stored in
the padding bytes. It (and the comma) may be omitted. If it is omitted, the
padding bytes are normally zero. However, on some systems, if the section
is marked as containing code and the fill value is omitted, the space is filled
with no-op instructions.
.Pp
The third expression is also absolute, and is also optional. If it is present,
it is the maximum number of bytes that should be skipped by this alignment
directive. If doing the alignment would require skipping more bytes than the
specified maximum, then the alignment is not done at all. You can omit the
fill value (the second argument) entirely by simply using two commas after
the required alignment; this can be useful if you want the alignment to be
filled with no-op instructions when appropriate.
.Pp
The
.Li .balignw
and
.Li .balignl
directives are variants of the
.Li .balign
directive. The
.Li .balignw
directive treats the fill pattern as a two byte word value. The
.Li .balignl
directives treats the fill pattern as a four byte longword value. For example,
.Li .balignw 4,0x368d
will align to a multiple of 4. If it skips two bytes, they will be filled
in with the value 0x368d (the exact placement of the bytes depends upon the
endianness of the processor). If it skips 1 or 3 bytes, the fill value is
undefined.
.Pp
.Ss Li .byte Va expressions
.Li .byte
expects zero or more expressions, separated by commas. Each expression is
assembled into the next byte.
.Pp
.Ss Li .comm Va symbol , Va length
.Li .comm
declares a common symbol named
.Va symbol .
When linking, a common symbol in one object file may be merged with a defined
or common symbol of the same name in another object file. If
.Li ld
does not see a definition for the symbol--just one or more common symbols--then
it will allocate
.Va length
bytes of uninitialized memory.
.Va length
must be an absolute expression. If
.Li ld
sees multiple common symbols with the same name, and they do not all have
the same size, it will allocate space using the largest size.
.Pp
When using ELF, the
.Li .comm
directive takes an optional third argument. This is the desired alignment
of the symbol, specified as a byte boundary (for example, an alignment of
16 means that the least significant 4 bits of the address should be zero).
The alignment must be an absolute expression, and it must be a power of two.
If
.Li ld
allocates uninitialized memory for the common symbol, it will use the alignment
when placing the symbol. If no alignment is specified,
.Xr as
will set the alignment to the largest power of two less than or equal to the
size of the symbol, up to a maximum of 16.
.Pp
.Ss Li .cfi_startproc [simple]
.Li .cfi_startproc
is used at the beginning of each function that should have an entry in
.Li .eh_frame .
It initializes some internal data structures. Don't forget to close the function
by
.Li .cfi_endproc .
.Pp
Unless
.Li .cfi_startproc
is used along with parameter
.Li simple
it also emits some architecture dependent initial CFI instructions.
.Ss Li .cfi_endproc
.Li .cfi_endproc
is used at the end of a function where it closes its unwind entry previously
opened by
.Li .cfi_startproc ,
and emits it to
.Li .eh_frame .
.Pp
.Ss Li .cfi_personality Va encoding [, Va exp]
.Li .cfi_personality
defines personality routine and its encoding.
.Va encoding
must be a constant determining how the personality should be encoded. If it
is 255 (
.Li DW_EH_PE_omit ) ,
second argument is not present, otherwise second argument should be a constant
or a symbol name. When using indirect encodings, the symbol provided should
be the location where personality can be loaded from, not the personality
routine itself. The default after
.Li .cfi_startproc
is
.Li .cfi_personality 0xff ,
no personality routine.
.Pp
.Ss Li .cfi_lsda Va encoding [, Va exp]
.Li .cfi_lsda
defines LSDA and its encoding.
.Va encoding
must be a constant determining how the LSDA should be encoded. If it is 255
(
.Li DW_EH_PE_omit ) ,
second argument is not present, otherwise second argument should be a constant
or a symbol name. The default after
.Li .cfi_startproc
is
.Li .cfi_lsda 0xff ,
no LSDA.
.Pp
.Ss Li .cfi_def_cfa Va register, Va offset
.Li .cfi_def_cfa
defines a rule for computing CFA as:
.Em take address from Va register and add Va offset to it .
.Pp
.Ss Li .cfi_def_cfa_register Va register
.Li .cfi_def_cfa_register
modifies a rule for computing CFA. From now on
.Va register
will be used instead of the old one. Offset remains the same.
.Pp
.Ss Li .cfi_def_cfa_offset Va offset
.Li .cfi_def_cfa_offset
modifies a rule for computing CFA. Register remains the same, but
.Va offset
is new. Note that it is the absolute offset that will be added to a defined
register to compute CFA address.
.Pp
.Ss Li .cfi_adjust_cfa_offset Va offset
Same as
.Li .cfi_def_cfa_offset
but
.Va offset
is a relative value that is added/substracted from the previous offset.
.Pp
.Ss Li .cfi_offset Va register, Va offset
Previous value of
.Va register
is saved at offset
.Va offset
from CFA.
.Pp
.Ss Li .cfi_rel_offset Va register, Va offset
Previous value of
.Va register
is saved at offset
.Va offset
from the current CFA register. This is transformed to
.Li .cfi_offset
using the known displacement of the CFA register from the CFA. This is often
easier to use, because the number will match the code it's annotating.
.Pp
.Ss Li .cfi_register Va register1, Va register2
Previous value of
.Va register1
is saved in register
.Va register2 .
.Pp
.Ss Li .cfi_restore Va register
.Li .cfi_restore
says that the rule for
.Va register
is now the same as it was at the beginning of the function, after all initial
instruction added by
.Li .cfi_startproc
were executed.
.Pp
.Ss Li .cfi_undefined Va register
From now on the previous value of
.Va register
can't be restored anymore.
.Pp
.Ss Li .cfi_same_value Va register
Current value of
.Va register
is the same like in the previous frame, i.e. no restoration needed.
.Pp
.Ss Li .cfi_remember_state,
First save all current rules for all registers by
.Li .cfi_remember_state ,
then totally screw them up by subsequent
.Li .cfi_*
directives and when everything is hopelessly bad, use
.Li .cfi_restore_state
to restore the previous saved state.
.Pp
.Ss Li .cfi_return_column Va register
Change return column
.Va register ,
i.e. the return address is either directly in
.Va register
or can be accessed by rules for
.Va register .
.Pp
.Ss Li .cfi_signal_frame
Mark current function as signal trampoline.
.Pp
.Ss Li .cfi_window_save
SPARC register window has been saved.
.Pp
.Ss Li .cfi_escape Va expression[, ...]
Allows the user to add arbitrary bytes to the unwind info. One might use this
to add OS-specific CFI opcodes, or generic CFI opcodes that GAS does not yet
support.
.Pp
.Ss Li .file Va fileno Va filename
When emitting dwarf2 line number information
.Li .file
assigns filenames to the
.Li .debug_line
file name table. The
.Va fileno
operand should be a unique positive integer to use as the index of the entry
in the table. The
.Va filename
operand is a C string literal.
.Pp
The detail of filename indices is exposed to the user because the filename
table is shared with the
.Li .debug_info
section of the dwarf2 debugging information, and thus the user must know the
exact indices that table entries will have.
.Pp
.Ss Li .loc Va fileno Va lineno [ Va column] [ Va options]
The
.Li .loc
directive will add row to the
.Li .debug_line
line number matrix corresponding to the immediately following assembly instruction.
The
.Va fileno ,
.Va lineno ,
and optional
.Va column
arguments will be applied to the
.Li .debug_line
state machine before the row is added.
.Pp
The
.Va options
are a sequence of the following tokens in any order:
.Pp
.Bl -tag -width Ds
.It basic_block
This option will set the
.Li basic_block
register in the
.Li .debug_line
state machine to
.Li true .
.Pp
.It prologue_end
This option will set the
.Li prologue_end
register in the
.Li .debug_line
state machine to
.Li true .
.Pp
.It epilogue_begin
This option will set the
.Li epilogue_begin
register in the
.Li .debug_line
state machine to
.Li true .
.Pp
.It is_stmt Va value
This option will set the
.Li is_stmt
register in the
.Li .debug_line
state machine to
.Li value ,
which must be either 0 or 1.
.Pp
.It isa Va value
This directive will set the
.Li isa
register in the
.Li .debug_line
state machine to
.Va value ,
which must be an unsigned integer.
.Pp
.El
.Ss Li .loc_mark_blocks Va enable
The
.Li .loc_mark_blocks
directive makes the assembler emit an entry to the
.Li .debug_line
line number matrix with the
.Li basic_block
register in the state machine set whenever a code label is seen. The
.Va enable
argument should be either 1 or 0, to enable or disable this function respectively.
.Pp
.Ss Li .data Va subsection
.Li .data
tells
.Xr as
to assemble the following statements onto the end of the data subsection numbered
.Va subsection
(which is an absolute expression). If
.Va subsection
is omitted, it defaults to zero.
.Pp
.Ss Li .double Va flonums
.Li .double
expects zero or more flonums, separated by commas. It assembles floating point
numbers.
.Pp
.Ss Li .eject
Force a page break at this point, when generating assembly listings.
.Pp
.Ss Li .else
.Li .else
is part of the
.Xr as
support for conditional assembly; see If,,
.Li .if
\&. It marks the beginning of a section of code to be assembled if the condition
for the preceding
.Li .if
was false.
.Pp
.Ss Li .elseif
.Li .elseif
is part of the
.Xr as
support for conditional assembly; see If,,
.Li .if
\&. It is shorthand for beginning a new
.Li .if
block that would otherwise fill the entire
.Li .else
section.
.Pp
.Ss Li .end
.Li .end
marks the end of the assembly file.
.Xr as
does not process anything in the file past the
.Li .end
directive.
.Pp
.Ss Li .endfunc
.Li .endfunc
marks the end of a function specified with
.Li .func .
.Pp
.Ss Li .endif
.Li .endif
is part of the
.Xr as
support for conditional assembly; it marks the end of a block of code that
is only assembled conditionally.See Section
.Dq If .
.Pp
.Ss Li .equ Va symbol, Va expression
This directive sets the value of
.Va symbol
to
.Va expression .
It is synonymous with
.Li .set ;
see Set,,
.Li .set
\&.
.Pp
.Ss Li .equiv Va symbol, Va expression
The
.Li .equiv
directive is like
.Li .equ
and
.Li .set ,
except that the assembler will signal an error if
.Va symbol
is already defined. Note a symbol which has been referenced but not actually
defined is considered to be undefined.
.Pp
Except for the contents of the error message, this is roughly equivalent to
.Bd -literal -offset indent
\&.ifdef SYM
\&.err
\&.endif
\&.equ SYM,VAL
.Ed
plus it protects the symbol from later redefinition.
.Pp
.Ss Li .eqv Va symbol, Va expression
The
.Li .eqv
directive is like
.Li .equiv ,
but no attempt is made to evaluate the expression or any part of it immediately.
Instead each time the resulting symbol is used in an expression, a snapshot
of its current value is taken.
.Pp
.Ss Li .err
If
.Xr as
assembles a
.Li .err
directive, it will print an error message and, unless the
.Op -Z
option was used, it will not generate an object file. This can be used to
signal an error in conditionally compiled code.
.Pp
.Ss Li .error " Va string"
Similarly to
.Li .err ,
this directive emits an error, but you can specify a string that will be emitted
as the error message. If you don't specify the message, it defaults to
.Li ".error directive invoked in source file" .
See Section.Dq Errors .
.Pp
.Bd -literal -offset indent
.error "This code has not been assembled and tested."
.Ed
.Pp
.Ss Li .exitm
Exit early from the current macro definition.See Section
.Dq Macro .
.Pp
.Ss Li .extern
.Li .extern
is accepted in the source program---for compatibility with other assemblers---but
it is ignored.
.Xr as
treats all undefined symbols as external.
.Pp
.Ss Li .fail Va expression
Generates an error or a warning. If the value of the
.Va expression
is 500 or more,
.Xr as
will print a warning message. If the value is less than 500,
.Xr as
will print an error message. The message will include the value of
.Va expression .
This can occasionally be useful inside complex nested macros or conditional
assembly.
.Pp
.Ss Li .file Va string
.Li .file
tells
.Xr as
that we are about to start a new logical file.
.Va string
is the new file name. In general, the filename is recognized whether or not
it is surrounded by quotes
.Li " ;
but if you wish to specify an empty file name, you must give the quotes--
.Li "" .
This statement may go away in future: it is only recognized to be compatible
with old
.Xr as
programs.
.Pp
.Ss Li .fill Va repeat , Va size , Va value
.Va repeat ,
.Va size
and
.Va value
are absolute expressions. This emits
.Va repeat
copies of
.Va size
bytes.
.Va Repeat
may be zero or more.
.Va Size
may be zero or more, but if it is more than 8, then it is deemed to have the
value 8, compatible with other people's assemblers. The contents of each
.Va repeat
bytes is taken from an 8-byte number. The highest order 4 bytes are zero.
The lowest order 4 bytes are
.Va value
rendered in the byte-order of an integer on the computer
.Xr as
is assembling for. Each
.Va size
bytes in a repetition is taken from the lowest order
.Va size
bytes of this number. Again, this bizarre behavior is compatible with other
people's assemblers.
.Pp
.Va size
and
.Va value
are optional. If the second comma and
.Va value
are absent,
.Va value
is assumed zero. If the first comma and following tokens are absent,
.Va size
is assumed to be 1.
.Pp
.Ss Li .float Va flonums
This directive assembles zero or more flonums, separated by commas. It has
the same effect as
.Li .single .
.Pp
.Ss Li .func Va name[, Va label]
.Li .func
emits debugging information to denote function
.Va name ,
and is ignored unless the file is assembled with debugging enabled. Only
.Li --gstabs[+]
is currently supported.
.Va label
is the entry point of the function and if omitted
.Va name
prepended with the
.Li leading char
is used.
.Li leading char
is usually
.Li _
or nothing, depending on the target. All functions are currently defined to
have
.Li void
return type. The function must be terminated with
.Li .endfunc .
.Pp
.Ss Li .global Va symbol, Li .globl Va symbol
.Li .global
makes the symbol visible to
.Li ld .
If you define
.Va symbol
in your partial program, its value is made available to other partial programs
that are linked with it. Otherwise,
.Va symbol
takes its attributes from a symbol of the same name from another file linked
into the same program.
.Pp
Both spellings (
.Li .globl
and
.Li .global )
are accepted, for compatibility with other assemblers.
.Pp
.Ss Li .hidden Va names
This is one of the ELF visibility directives. The other two are
.Li .internal
(see Section
.Dq Internal )
and
.Li .protected
(see Section
.Dq Protected ) .
.Pp
This directive overrides the named symbols default visibility (which is set
by their binding: local, global or weak). The directive sets the visibility
to
.Li hidden
which means that the symbols are not visible to other components. Such symbols
are always considered to be
.Li protected
as well.
.Pp
.Ss Li .hword Va expressions
This expects zero or more
.Va expressions ,
and emits a 16 bit number for each.
.Pp
This directive is a synonym for
.Li .short .
.Pp
.Ss Li .ident
This directive is used by some assemblers to place tags in object files. The
behavior of this directive varies depending on the target. When using the
a.out object file format,
.Xr as
simply accepts the directive for source-file compatibility with existing assemblers,
but does not emit anything for it. When using COFF, comments are emitted to
the
.Li .comment
or
.Li .rdata
section, depending on the target. When using ELF, comments are emitted to
the
.Li .comment
section.
.Pp
.Ss Li .if Va absolute expression
.Li .if
marks the beginning of a section of code which is only considered part of
the source program being assembled if the argument (which must be an
.Va absolute expression )
is non-zero. The end of the conditional section of code must be marked by
.Li .endif
(see Section
.Dq Endif ) ;
optionally, you may include code for the alternative condition, flagged by
.Li .else
(see Section
.Dq Else ) .
If you have several conditions to check,
.Li .elseif
may be used to avoid nesting blocks if/else within each subsequent
.Li .else
block.
.Pp
The following variants of
.Li .if
are also supported:
.Bl -tag -width Ds
.It .ifdef Va symbol
Assembles the following section of code if the specified
.Va symbol
has been defined. Note a symbol which has been referenced but not yet defined
is considered to be undefined.
.Pp
.It .ifb Va text
Assembles the following section of code if the operand is blank (empty).
.Pp
.It .ifc Va string1, Va string2
Assembles the following section of code if the two strings are the same. The
strings may be optionally quoted with single quotes. If they are not quoted,
the first string stops at the first comma, and the second string stops at
the end of the line. Strings which contain whitespace should be quoted. The
string comparison is case sensitive.
.Pp
.It .ifeq Va absolute expression
Assembles the following section of code if the argument is zero.
.Pp
.It .ifeqs Va string1, Va string2
Another form of
.Li .ifc .
The strings must be quoted using double quotes.
.Pp
.It .ifge Va absolute expression
Assembles the following section of code if the argument is greater than or
equal to zero.
.Pp
.It .ifgt Va absolute expression
Assembles the following section of code if the argument is greater than zero.
.Pp
.It .ifle Va absolute expression
Assembles the following section of code if the argument is less than or equal
to zero.
.Pp
.It .iflt Va absolute expression
Assembles the following section of code if the argument is less than zero.
.Pp
.It .ifnb Va text
Like
.Li .ifb ,
but the sense of the test is reversed: this assembles the following section
of code if the operand is non-blank (non-empty).
.Pp
.It .ifnc Va string1, Va string2.
Like
.Li .ifc ,
but the sense of the test is reversed: this assembles the following section
of code if the two strings are not the same.
.Pp
.It .ifndef Va symbol
.It .ifnotdef Va symbol
Assembles the following section of code if the specified
.Va symbol
has not been defined. Both spelling variants are equivalent. Note a symbol
which has been referenced but not yet defined is considered to be undefined.
.Pp
.It .ifne Va absolute expression
Assembles the following section of code if the argument is not equal to zero
(in other words, this is equivalent to
.Li .if ) .
.Pp
.It .ifnes Va string1, Va string2
Like
.Li .ifeqs ,
but the sense of the test is reversed: this assembles the following section
of code if the two strings are not the same.
.El
.Pp
.Ss Li .incbin " Va file"[, Va skip[, Va count]]
The
.Li incbin
directive includes
.Va file
verbatim at the current location. You can control the search paths used with
the
.Li -I
command-line option (see Section
.Dq Invoking ) .
Quotation marks are required around
.Va file .
.Pp
The
.Va skip
argument skips a number of bytes from the start of the
.Va file .
The
.Va count
argument indicates the maximum number of bytes to read. Note that the data
is not aligned in any way, so it is the user's responsibility to make sure
that proper alignment is provided both before and after the
.Li incbin
directive.
.Pp
.Ss Li .include " Va file"
This directive provides a way to include supporting files at specified points
in your source program. The code from
.Va file
is assembled as if it followed the point of the
.Li .include ;
when the end of the included file is reached, assembly of the original file
continues. You can control the search paths used with the
.Li -I
command-line option (see Section
.Dq Invoking ) .
Quotation marks are required around
.Va file .
.Pp
.Ss Li .int Va expressions
Expect zero or more
.Va expressions ,
of any section, separated by commas. For each expression, emit a number that,
at run time, is the value of that expression. The byte order and bit size
of the number depends on what kind of target the assembly is for.
.Pp
.Ss Li .internal Va names
This is one of the ELF visibility directives. The other two are
.Li .hidden
(see Section
.Dq Hidden )
and
.Li .protected
(see Section
.Dq Protected ) .
.Pp
This directive overrides the named symbols default visibility (which is set
by their binding: local, global or weak). The directive sets the visibility
to
.Li internal
which means that the symbols are considered to be
.Li hidden
(i.e., not visible to other components), and that some extra, processor specific
processing must also be performed upon the symbols as well.
.Pp
.Ss Li .irp Va symbol, Va values...
Evaluate a sequence of statements assigning different values to
.Va symbol .
The sequence of statements starts at the
.Li .irp
directive, and is terminated by an
.Li .endr
directive. For each
.Va value ,
.Va symbol
is set to
.Va value ,
and the sequence of statements is assembled. If no
.Va value
is listed, the sequence of statements is assembled once, with
.Va symbol
set to the null string. To refer to
.Va symbol
within the sequence of statements, use
.Va \esymbol .
.Pp
For example, assembling
.Pp
.Bd -literal -offset indent
.irp param,1,2,3
move d\eparam,sp@-
.endr
.Ed
.Pp
is equivalent to assembling
.Pp
.Bd -literal -offset indent
move d1,sp@-
move d2,sp@-
move d3,sp@-
.Ed
.Pp
For some caveats with the spelling of
.Va symbol ,
see also Macro.
.Pp
.Ss Li .irpc Va symbol, Va values...
Evaluate a sequence of statements assigning different values to
.Va symbol .
The sequence of statements starts at the
.Li .irpc
directive, and is terminated by an
.Li .endr
directive. For each character in
.Va value ,
.Va symbol
is set to the character, and the sequence of statements is assembled. If no
.Va value
is listed, the sequence of statements is assembled once, with
.Va symbol
set to the null string. To refer to
.Va symbol
within the sequence of statements, use
.Va \esymbol .
.Pp
For example, assembling
.Pp
.Bd -literal -offset indent
.irpc param,123
move d\eparam,sp@-
.endr
.Ed
.Pp
is equivalent to assembling
.Pp
.Bd -literal -offset indent
move d1,sp@-
move d2,sp@-
move d3,sp@-
.Ed
.Pp
For some caveats with the spelling of
.Va symbol ,
see also the discussion atSee Section
.Dq Macro .
.Pp
.Ss Li .lcomm Va symbol , Va length
Reserve
.Va length
(an absolute expression) bytes for a local common denoted by
.Va symbol .
The section and value of
.Va symbol
are those of the new local common. The addresses are allocated in the bss
section, so that at run-time the bytes start off zeroed.
.Va Symbol
is not declared global (see Section
.Dq Global ) ,
so is normally not visible to
.Li ld .
.Pp
.Ss Li .lflags
.Xr as
accepts this directive, for compatibility with other assemblers, but ignores
it.
.Pp
.Ss Li .line Va line-number
Even though this is a directive associated with the
.Li a.out
or
.Li b.out
object-code formats,
.Xr as
still recognizes it when producing COFF output, and treats
.Li .line
as though it were the COFF
.Li .ln
.Em if
it is found outside a
.Li .def
/
.Li .endef
pair.
.Pp
Inside a
.Li .def ,
.Li .line
is, instead, one of the directives used by compilers to generate auxiliary
symbol information for debugging.
.Pp
.Ss Li .linkonce [ Va type]
Mark the current section so that the linker only includes a single copy of
it. This may be used to include the same section in several different object
files, but ensure that the linker will only include it once in the final output
file. The
.Li .linkonce
pseudo-op must be used for each instance of the section. Duplicate sections
are detected based on the section name, so it should be unique.
.Pp
This directive is only supported by a few object file formats; as of this
writing, the only object file format which supports it is the Portable Executable
format used on Windows NT.
.Pp
The
.Va type
argument is optional. If specified, it must be one of the following strings.
For example:
.Bd -literal -offset indent
\&.linkonce same_size
.Ed
Not all types may be supported on all object file formats.
.Pp
.Bl -tag -width Ds
.It discard
Silently discard duplicate sections. This is the default.
.Pp
.It one_only
Warn if there are duplicate sections, but still keep only one copy.
.Pp
.It same_size
Warn if any of the duplicates have different sizes.
.Pp
.It same_contents
Warn if any of the duplicates do not have exactly the same contents.
.El
.Pp
.Ss Li .ln Va line-number
.Li .ln
is a synonym for
.Li .line .
.Pp
.Ss Li .mri Va val
If
.Va val
is non-zero, this tells
.Xr as
to enter MRI mode. If
.Va val
is zero, this tells
.Xr as
to exit MRI mode. This change affects code assembled until the next
.Li .mri
directive, or until the end of the file.See Section
.Dq M .
.Pp
.Ss Li .list
Control (in conjunction with the
.Li .nolist
directive) whether or not assembly listings are generated. These two directives
maintain an internal counter (which is zero initially).
.Li .list
increments the counter, and
.Li .nolist
decrements it. Assembly listings are generated whenever the counter is greater
than zero.
.Pp
By default, listings are disabled. When you enable them (with the
.Li -a
command line option;see Section
.Dq Invoking ) ,
the initial value of the listing counter is one.
.Pp
.Ss Li .long Va expressions
.Li .long
is the same as
.Li .int .
See Section.Dq Int .
.Pp
.Ss Li .macro
The commands
.Li .macro
and
.Li .endm
allow you to define macros that generate assembly output. For example, this
definition specifies a macro
.Li sum
that puts a sequence of numbers into memory:
.Pp
.Bd -literal -offset indent
.macro sum from=0, to=5
.long \efrom
.if \eto-\efrom
sum "(\efrom+1)",\eto
.endif
.endm
.Ed
.Pp
With that definition,
.Li SUM 0,5
is equivalent to this assembly input:
.Pp
.Bd -literal -offset indent
.long 0
.long 1
.long 2
.long 3
.long 4
.long 5
.Ed
.Pp
.Bl -tag -width Ds
.It .macro Va macname
.It .macro Va macname Va macargs ...
Begin the definition of a macro called
.Va macname .
If your macro definition requires arguments, specify their names after the
macro name, separated by commas or spaces. You can qualify the macro argument
to indicate whether all invocations must specify a non-blank value (through
.Li : Li req ) ,
or whether it takes all of the remaining arguments (through
.Li : Li vararg ) .
You can supply a default value for any macro argument by following the name
with
.Li = Va deflt .
You cannot define two macros with the same
.Va macname
unless it has been subject to the
.Li .purgem
directive (see Section
.Dq Purgem )
between the two definitions. For example, these are all valid
.Li .macro
statements:
.Pp
.Bl -tag -width Ds
.It .macro comm
Begin the definition of a macro called
.Li comm ,
which takes no arguments.
.Pp
.It .macro plus1 p, p1
.It .macro plus1 p p1
Either statement begins the definition of a macro called
.Li plus1 ,
which takes two arguments; within the macro definition, write
.Li \ep
or
.Li \ep1
to evaluate the arguments.
.Pp
.It .macro reserve_str p1=0 p2
Begin the definition of a macro called
.Li reserve_str ,
with two arguments. The first argument has a default value, but not the second.
After the definition is complete, you can call the macro either as
.Li reserve_str Va a, Va b
(with
.Li \ep1
evaluating to
.Va a
and
.Li \ep2
evaluating to
.Va b ) ,
or as
.Li reserve_str , Va b
(with
.Li \ep1
evaluating as the default, in this case
.Li 0 ,
and
.Li \ep2
evaluating to
.Va b ) .
.Pp
.It .macro m p1:req, p2=0, p3:vararg
Begin the definition of a macro called
.Li m ,
with at least three arguments. The first argument must always have a value
specified, but not the second, which instead has a default value. The third
formal will get assigned all remaining arguments specified at invocation time.
.Pp
When you call a macro, you can specify the argument values either by position,
or by keyword. For example,
.Li sum 9,17
is equivalent to
.Li sum to=17, from=9 .
.Pp
.El
Note that since each of the
.Va macargs
can be an identifier exactly as any other one permitted by the target architecture,
there may be occasional problems if the target hand-crafts special meanings
to certain characters when they occur in a special position. For example,
if the colon (
.Li : )
is generally permitted to be part of a symbol name, but the architecture specific
code special-cases it when occurring as the final character of a symbol (to
denote a label), then the macro parameter replacement code will have no way
of knowing that and consider the whole construct (including the colon) an
identifier, and check only this identifier for being the subject to parameter
substitution. So for example this macro definition:
.Pp
.Bd -literal -offset indent
.macro label l
\el:
.endm
.Ed
.Pp
might not work as expected. Invoking
.Li label foo
might not create a label called
.Li foo
but instead just insert the text
.Li \el:
into the assembler source, probably generating an error about an unrecognised
identifier.
.Pp
Similarly problems might occur with the period character (
.Li . )
which is often allowed inside opcode names (and hence identifier names). So
for example constructing a macro to build an opcode from a base name and a
length specifier like this:
.Pp
.Bd -literal -offset indent
.macro opcode base length
\ebase.\elength
.endm
.Ed
.Pp
and invoking it as
.Li opcode store l
will not create a
.Li store.l
instruction but instead generate some kind of error as the assembler tries
to interpret the text
.Li \ebase.\elength .
.Pp
There are several possible ways around this problem:
.Pp
.Bl -tag -width Ds
.It Insert white space
If it is possible to use white space characters then this is the simplest
solution. eg:
.Pp
.Bd -literal -offset indent
.macro label l
\el :
.endm
.Ed
.Pp
.It Use Li \e()
The string
.Li \e()
can be used to separate the end of a macro argument from the following text.
eg:
.Pp
.Bd -literal -offset indent
.macro opcode base length
\ebase\e().\elength
.endm
.Ed
.Pp
.It Use the alternate macro syntax mode
In the alternative macro syntax mode the ampersand character (
.Li & )
can be used as a separator. eg:
.Pp
.Bd -literal -offset indent
.altmacro
.macro label l
l&:
.endm
.Ed
.El
.Pp
Note: this problem of correctly identifying string parameters to pseudo ops
also applies to the identifiers used in
.Li .irp
(see Section
.Dq Irp )
and
.Li .irpc
(see Section
.Dq Irpc )
as well.
.Pp
.It .endm
Mark the end of a macro definition.
.Pp
.It .exitm
Exit early from the current macro definition.
.Pp
.It \e@
.Xr as
maintains a counter of how many macros it has executed in this pseudo-variable;
you can copy that number to your output with
.Li \e@ ,
but
.Em only within a macro definition .
.Pp
.It LOCAL Va name [ , ... ]
.Em Warning: Li LOCAL is only available if you select \(lqalternate macro syntax\(rq with Li --alternate or Li .altmacro.
See Section.Dq Altmacro .
.El
.Pp
.Ss Li .altmacro
Enable alternate macro mode, enabling:
.Pp
.Bl -tag -width Ds
.It LOCAL Va name [ , ... ]
One additional directive,
.Li LOCAL ,
is available. It is used to generate a string replacement for each of the
.Va name
arguments, and replace any instances of
.Va name
in each macro expansion. The replacement string is unique in the assembly,
and different for each separate macro expansion.
.Li LOCAL
allows you to write macros that define symbols, without fear of conflict between
separate macro expansions.
.Pp
.It String delimiters
You can write strings delimited in these other ways besides
.Li " Va string" :
.Pp
.Bl -tag -width Ds
.It ' Va string'
You can delimit strings with single-quote characters.
.Pp
.It < Va string>
You can delimit strings with matching angle brackets.
.El
.Pp
.It single-character string escape
To include any single character literally in a string (even if the character
would otherwise have some special meaning), you can prefix the character with
.Li !
(an exclamation mark). For example, you can write
.Li <4.3 !> 5.4!!>
to get the literal text
.Li 4.3 > 5.4! .
.Pp
.It Expression results as strings
You can write
.Li % Va expr
to evaluate the expression
.Va expr
and use the result as a string.
.El
.Pp
.Ss Li .noaltmacro
Disable alternate macro mode.See Section
.Dq Altmacro .
.Pp
.Ss Li .nolist
Control (in conjunction with the
.Li .list
directive) whether or not assembly listings are generated. These two directives
maintain an internal counter (which is zero initially).
.Li .list
increments the counter, and
.Li .nolist
decrements it. Assembly listings are generated whenever the counter is greater
than zero.
.Pp
.Ss Li .octa Va biGNUms
This directive expects zero or more biGNUms, separated by commas. For each
biGNUm, it emits a 16-byte integer.
.Pp
The term \(lqocta\(rq comes from contexts in which a \(lqword\(rq is two bytes; hence
.Em octa
-word for 16 bytes.
.Pp
.Ss Li .org Va new-lc , Va fill
Advance the location counter of the current section to
.Va new-lc .
.Va new-lc
is either an absolute expression or an expression with the same section as
the current subsection. That is, you can't use
.Li .org
to cross sections: if
.Va new-lc
has the wrong section, the
.Li .org
directive is ignored. To be compatible with former assemblers, if the section
of
.Va new-lc
is absolute,
.Xr as
issues a warning, then pretends the section of
.Va new-lc
is the same as the current subsection.
.Pp
.Li .org
may only increase the location counter, or leave it unchanged; you cannot
use
.Li .org
to move the location counter backwards.
.Pp
Because
.Xr as
tries to assemble programs in one pass,
.Va new-lc
may not be undefined. If you really detest this restriction we eagerly await
a chance to share your improved assembler.
.Pp
Beware that the origin is relative to the start of the section, not to the
start of the subsection. This is compatible with other people's assemblers.
.Pp
When the location counter (of the current subsection) is advanced, the intervening
bytes are filled with
.Va fill
which should be an absolute expression. If the comma and
.Va fill
are omitted,
.Va fill
defaults to zero.
.Pp
.Ss Li .p2align[wl] Va abs-expr, Va abs-expr, Va abs-expr
Pad the location counter (in the current subsection) to a particular storage
boundary. The first expression (which must be absolute) is the number of low-order
zero bits the location counter must have after advancement. For example
.Li .p2align 3
advances the location counter until it a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
.Pp
The second expression (also absolute) gives the fill value to be stored in
the padding bytes. It (and the comma) may be omitted. If it is omitted, the
padding bytes are normally zero. However, on some systems, if the section
is marked as containing code and the fill value is omitted, the space is filled
with no-op instructions.
.Pp
The third expression is also absolute, and is also optional. If it is present,
it is the maximum number of bytes that should be skipped by this alignment
directive. If doing the alignment would require skipping more bytes than the
specified maximum, then the alignment is not done at all. You can omit the
fill value (the second argument) entirely by simply using two commas after
the required alignment; this can be useful if you want the alignment to be
filled with no-op instructions when appropriate.
.Pp
The
.Li .p2alignw
and
.Li .p2alignl
directives are variants of the
.Li .p2align
directive. The
.Li .p2alignw
directive treats the fill pattern as a two byte word value. The
.Li .p2alignl
directives treats the fill pattern as a four byte longword value. For example,
.Li .p2alignw 2,0x368d
will align to a multiple of 4. If it skips two bytes, they will be filled
in with the value 0x368d (the exact placement of the bytes depends upon the
endianness of the processor). If it skips 1 or 3 bytes, the fill value is
undefined.
.Pp
.Ss Li .previous
This is one of the ELF section stack manipulation directives. The others are
.Li .section
(see Section
.Dq Section ) ,
.Li .subsection
(see Section
.Dq SubSection ) ,
.Li .pushsection
(see Section
.Dq PushSection ) ,
and
.Li .popsection
(see Section
.Dq PopSection ) .
.Pp
This directive swaps the current section (and subsection) with most recently
referenced section (and subsection) prior to this one. Multiple
.Li .previous
directives in a row will flip between two sections (and their subsections).
.Pp
In terms of the section stack, this directive swaps the current section with
the top section on the section stack.
.Pp
.Ss Li .popsection
This is one of the ELF section stack manipulation directives. The others are
.Li .section
(see Section
.Dq Section ) ,
.Li .subsection
(see Section
.Dq SubSection ) ,
.Li .pushsection
(see Section
.Dq PushSection ) ,
and
.Li .previous
(see Section
.Dq Previous ) .
.Pp
This directive replaces the current section (and subsection) with the top
section (and subsection) on the section stack. This section is popped off
the stack.
.Pp
.Ss Li .print Va string
.Xr as
will print
.Va string
on the standard output during assembly. You must put
.Va string
in double quotes.
.Pp
.Ss Li .protected Va names
This is one of the ELF visibility directives. The other two are
.Li .hidden
(see Section
.Dq Hidden )
and
.Li .internal
(see Section
.Dq Internal ) .
.Pp
This directive overrides the named symbols default visibility (which is set
by their binding: local, global or weak). The directive sets the visibility
to
.Li protected
which means that any references to the symbols from within the components
that defines them must be resolved to the definition in that component, even
if a definition in another component would normally preempt this.
.Pp
.Ss Li .psize Va lines , Va columns
Use this directive to declare the number of lines---and, optionally, the number
of columns---to use for each page, when generating listings.
.Pp
If you do not use
.Li .psize ,
listings use a default line-count of 60. You may omit the comma and
.Va columns
specification; the default width is 200 columns.
.Pp
.Xr as
generates formfeeds whenever the specified number of lines is exceeded (or
whenever you explicitly request one, using
.Li .eject ) .
.Pp
If you specify
.Va lines
as
.Li 0 ,
no formfeeds are generated save those explicitly specified with
.Li .eject .
.Pp
.Ss Li .purgem Va name
Undefine the macro
.Va name ,
so that later uses of the string will not be expanded.See Section
.Dq Macro .
.Pp
.Ss Li .pushsection Va name , Va subsection
This is one of the ELF section stack manipulation directives. The others are
.Li .section
(see Section
.Dq Section ) ,
.Li .subsection
(see Section
.Dq SubSection ) ,
.Li .popsection
(see Section
.Dq PopSection ) ,
and
.Li .previous
(see Section
.Dq Previous ) .
.Pp
This directive pushes the current section (and subsection) onto the top of
the section stack, and then replaces the current section and subsection with
.Li name
and
.Li subsection .
.Pp
.Ss Li .quad Va biGNUms
.Li .quad
expects zero or more biGNUms, separated by commas. For each bignum, it emits
an 8-byte integer. If the biGNUm won't fit in 8 bytes, it prints a warning
message; and just takes the lowest order 8 bytes of the biGNUm.
.Pp
The term \(lqquad\(rq comes from contexts in which a \(lqword\(rq is two bytes; hence
.Em quad
-word for 8 bytes.
.Pp
.Ss Li .reloc Va offset, Va reloc_name[, Va expression]
Generate a relocation at
.Va offset
of type
.Va reloc_name
with value
.Va expression .
If
.Va offset
is a number, the relocation is generated in the current section. If
.Va offset
is an expression that resolves to a symbol plus offset, the relocation is
generated in the given symbol's section.
.Va expression ,
if present, must resolve to a symbol plus addend or to an absolute value,
but note that not all targets support an addend. e.g. ELF REL targets such
as i386 store an addend in the section contents rather than in the relocation.
This low level interface does not support addends stored in the section.
.Pp
.Ss Li .rept Va count
Repeat the sequence of lines between the
.Li .rept
directive and the next
.Li .endr
directive
.Va count
times.
.Pp
For example, assembling
.Pp
.Bd -literal -offset indent
.rept 3
.long 0
.endr
.Ed
.Pp
is equivalent to assembling
.Pp
.Bd -literal -offset indent
.long 0
.long 0
.long 0
.Ed
.Pp
.Ss Li .sbttl " Va subheading"
Use
.Va subheading
as the title (third line, immediately after the title line) when generating
assembly listings.
.Pp
This directive affects subsequent pages, as well as the current page if it
appears within ten lines of the top of a page.
.Pp
.Ss Li .section Va name
Use the
.Li .section
directive to assemble the following code into a section named
.Va name .
.Pp
This directive is only supported for targets that actually support arbitrarily
named sections; on
.Li a.out
targets, for example, it is not accepted, even with a standard
.Li a.out
section name.
.Pp
This is one of the ELF section stack manipulation directives. The others are
.Li .subsection
(see Section
.Dq SubSection ) ,
.Li .pushsection
(see Section
.Dq PushSection ) ,
.Li .popsection
(see Section
.Dq PopSection ) ,
and
.Li .previous
(see Section
.Dq Previous ) .
.Pp
For ELF targets, the
.Li .section
directive is used like this:
.Pp
.Bd -literal -offset indent
\&.section name [, "flags"[, @type[,flag_specific_arguments]]]
.Ed
.Pp
The optional
.Va flags
argument is a quoted string which may contain any combination of the following
characters:
.Bl -tag -width Ds
.It a
section is allocatable
.It w
section is writable
.It x
section is executable
.It M
section is mergeable
.It S
section contains zero terminated strings
.It G
section is a member of a section group
.It T
section is used for thread-local-storage
.El
.Pp
The optional
.Va type
argument may contain one of the following constants:
.Bl -tag -width Ds
.It @progbits
section contains data
.It @nobits
section does not contain data (i.e., section only occupies space)
.It @note
section contains data which is used by things other than the program
.It @init_array
section contains an array of pointers to init functions
.It @fini_array
section contains an array of pointers to finish functions
.It @preinit_array
section contains an array of pointers to pre-init functions
.El
.Pp
Many targets only support the first three section types.
.Pp
Note on targets where the
.Li @
character is the start of a comment (eg ARM) then another character is used
instead. For example the ARM port uses the
.Li %
character.
.Pp
If
.Va flags
contains the
.Li M
symbol then the
.Va type
argument must be specified as well as an extra argument---
.Va entsize
---like this:
.Pp
.Bd -literal -offset indent
\&.section name , "flags"M, @type, entsize
.Ed
.Pp
Sections with the
.Li M
flag but not
.Li S
flag must contain fixed size constants, each
.Va entsize
octets long. Sections with both
.Li M
and
.Li S
must contain zero terminated strings where each character is
.Va entsize
bytes long. The linker may remove duplicates within sections with the same
name, same entity size and same flags.
.Va entsize
must be an absolute expression.
.Pp
If
.Va flags
contains the
.Li G
symbol then the
.Va type
argument must be present along with an additional field like this:
.Pp
.Bd -literal -offset indent
\&.section name , "flags"G, @type, GroupName[, linkage]
.Ed
.Pp
The
.Va GroupName
field specifies the name of the section group to which this particular section
belongs. The optional linkage field can contain:
.Bl -tag -width Ds
.It comdat
indicates that only one copy of this section should be retained
.It .GNU.linkonce
an alias for comdat
.El
.Pp
Note: if both the
.Va M
and
.Va G
flags are present then the fields for the Merge flag should come first, like
this:
.Pp
.Bd -literal -offset indent
\&.section name , "flags"MG, @type, entsize, GroupName[, linkage]
.Ed
.Pp
If no flags are specified, the default flags depend upon the section name.
If the section name is not recognized, the default will be for the section
to have none of the above flags: it will not be allocated in memory, nor writable,
nor executable. The section will contain data.
.Pp
For ELF targets, the assembler supports another type of
.Li .section
directive for compatibility with the Solaris assembler:
.Pp
.Bd -literal -offset indent
\&.section "name"[, flags...]
.Ed
.Pp
Note that the section name is quoted. There may be a sequence of comma separated
flags:
.Bl -tag -width Ds
.It #alloc
section is allocatable
.It #write
section is writable
.It #execinstr
section is executable
.It #tls
section is used for thread local storage
.El
.Pp
This directive replaces the current section and subsection. See the contents
of the gas testsuite directory
.Li gas/testsuite/gas/elf
for some examples of how this directive and the other section stack directives
work.
.Pp
.Ss Li .set Va symbol, Va expression
Set the value of
.Va symbol
to
.Va expression .
This changes
.Va symbol
\&'s value and type to conform to
.Va expression .
If
.Va symbol
was flagged as external, it remains flagged (see Section
.Dq Symbol Attributes ) .
.Pp
You may
.Li .set
a symbol many times in the same assembly.
.Pp
If you
.Li .set
a global symbol, the value stored in the object file is the last value stored
into it.
.Pp
.Ss Li .short Va expressions
This expects zero or more
.Va expressions ,
and emits a 16 bit number for each.
.Pp
.Ss Li .single Va flonums
This directive assembles zero or more flonums, separated by commas. It has
the same effect as
.Li .float .
.Pp
.Ss Li .size
This directive is used to set the size associated with a symbol.
.Pp
For ELF targets, the
.Li .size
directive is used like this:
.Pp
.Bd -literal -offset indent
\&.size name , expression
.Ed
.Pp
This directive sets the size associated with a symbol
.Va name .
The size in bytes is computed from
.Va expression
which can make use of label arithmetic. This directive is typically used to
set the size of function symbols.
.Pp
.Ss Li .sleb128 Va expressions
.Va sleb128
stands for \(lqsigned little endian base 128.\(rq This is a compact, variable length
representation of numbers used by the DWARF symbolic debugging format.See Section
.Dq Uleb128 .
.Pp
.Ss Li .skip Va size , Va fill
This directive emits
.Va size
bytes, each of value
.Va fill .
Both
.Va size
and
.Va fill
are absolute expressions. If the comma and
.Va fill
are omitted,
.Va fill
is assumed to be zero. This is the same as
.Li .space .
.Pp
.Ss Li .space Va size , Va fill
This directive emits
.Va size
bytes, each of value
.Va fill .
Both
.Va size
and
.Va fill
are absolute expressions. If the comma and
.Va fill
are omitted,
.Va fill
is assumed to be zero. This is the same as
.Li .skip .
.Pp
.Ss Li .stabd, .stabn, .stabs
There are three directives that begin
.Li .stab .
All emit symbols (see Section
.Dq Symbols ) ,
for use by symbolic debuggers. The symbols are not entered in the
.Xr as
hash table: they cannot be referenced elsewhere in the source file. Up to
five fields are required:
.Pp
.Bl -tag -width Ds
.It string
This is the symbol's name. It may contain any character except
.Li \e000 ,
so is more general than ordinary symbol names. Some debuggers used to code
arbitrarily complex structures into symbol names using this field.
.Pp
.It type
An absolute expression. The symbol's type is set to the low 8 bits of this
expression. Any bit pattern is permitted, but
.Li ld
and debuggers choke on silly bit patterns.
.Pp
.It other
An absolute expression. The symbol's \(lqother\(rq attribute is set to the low 8 bits
of this expression.
.Pp
.It desc
An absolute expression. The symbol's descriptor is set to the low 16 bits
of this expression.
.Pp
.It value
An absolute expression which becomes the symbol's value.
.El
.Pp
If a warning is detected while reading a
.Li .stabd ,
.Li .stabn ,
or
.Li .stabs
statement, the symbol has probably already been created; you get a half-formed
symbol in your object file. This is compatible with earlier assemblers!
.Pp
.Bl -tag -width Ds
.It .stabd Va type , Va other , Va desc
.Pp
The \(lqname\(rq of the symbol generated is not even an empty string. It is a null
pointer, for compatibility. Older assemblers used a null pointer so they didn't
waste space in object files with empty strings.
.Pp
The symbol's value is set to the location counter, relocatably. When your
program is linked, the value of this symbol is the address of the location
counter when the
.Li .stabd
was assembled.
.Pp
.It .stabn Va type , Va other , Va desc , Va value
The name of the symbol is set to the empty string
.Li "" .
.Pp
.It .stabs Va string , Va type , Va other , Va desc , Va value
All five fields are specified.
.El
.Pp
.Ss Li .string " Va str"
Copy the characters in
.Va str
to the object file. You may specify more than one string to copy, separated
by commas. Unless otherwise specified for a particular machine, the assembler
marks the end of each string with a 0 byte. You can use any of the escape
sequences described in Strings,,Strings.
.Pp
.Ss Li .struct Va expression
Switch to the absolute section, and set the section offset to
.Va expression ,
which must be an absolute expression. You might use this as follows:
.Bd -literal -offset indent
.struct 0
field1:
.struct field1 + 4
field2:
.struct field2 + 4
field3:
.Ed
This would define the symbol
.Li field1
to have the value 0, the symbol
.Li field2
to have the value 4, and the symbol
.Li field3
to have the value 8. Assembly would be left in the absolute section, and you
would need to use a
.Li .section
directive of some sort to change to some other section before further assembly.
.Pp
.Ss Li .subsection Va name
This is one of the ELF section stack manipulation directives. The others are
.Li .section
(see Section
.Dq Section ) ,
.Li .pushsection
(see Section
.Dq PushSection ) ,
.Li .popsection
(see Section
.Dq PopSection ) ,
and
.Li .previous
(see Section
.Dq Previous ) .
.Pp
This directive replaces the current subsection with
.Li name .
The current section is not changed. The replaced subsection is put onto the
section stack in place of the then current top of stack subsection.
.Pp
.Ss Li .symver
Use the
.Li .symver
directive to bind symbols to specific version nodes within a source file.
This is only supported on ELF platforms, and is typically used when assembling
files to be linked into a shared library. There are cases where it may make
sense to use this in objects to be bound into an application itself so as
to override a versioned symbol from a shared library.
.Pp
For ELF targets, the
.Li .symver
directive can be used like this:
.Bd -literal -offset indent
\&.symver name, name2@nodename
.Ed
If the symbol
.Va name
is defined within the file being assembled, the
.Li .symver
directive effectively creates a symbol alias with the name
.Va name2@nodename ,
and in fact the main reason that we just don't try and create a regular alias
is that the
.Va @
character isn't permitted in symbol names. The
.Va name2
part of the name is the actual name of the symbol by which it will be externally
referenced. The name
.Va name
itself is merely a name of convenience that is used so that it is possible
to have definitions for multiple versions of a function within a single source
file, and so that the compiler can unambiguously know which version of a function
is being mentioned. The
.Va nodename
portion of the alias should be the name of a node specified in the version
script supplied to the linker when building a shared library. If you are attempting
to override a versioned symbol from a shared library, then
.Va nodename
should correspond to the nodename of the symbol you are trying to override.
.Pp
If the symbol
.Va name
is not defined within the file being assembled, all references to
.Va name
will be changed to
.Va name2@nodename .
If no reference to
.Va name
is made,
.Va name2@nodename
will be removed from the symbol table.
.Pp
Another usage of the
.Li .symver
directive is:
.Bd -literal -offset indent
\&.symver name, name2@@nodename
.Ed
In this case, the symbol
.Va name
must exist and be defined within the file being assembled. It is similar to
.Va name2@nodename .
The difference is
.Va name2@@nodename
will also be used to resolve references to
.Va name2
by the linker.
.Pp
The third usage of the
.Li .symver
directive is:
.Bd -literal -offset indent
\&.symver name, name2@@@nodename
.Ed
When
.Va name
is not defined within the file being assembled, it is treated as
.Va name2@nodename .
When
.Va name
is defined within the file being assembled, the symbol name,
.Va name ,
will be changed to
.Va name2@@nodename .
.Pp
.Ss Li .text Va subsection
Tells
.Xr as
to assemble the following statements onto the end of the text subsection numbered
.Va subsection ,
which is an absolute expression. If
.Va subsection
is omitted, subsection number zero is used.
.Pp
.Ss Li .title " Va heading"
Use
.Va heading
as the title (second line, immediately after the source file name and pagenumber)
when generating assembly listings.
.Pp
This directive affects subsequent pages, as well as the current page if it
appears within ten lines of the top of a page.
.Pp
.Ss Li .type
This directive is used to set the type of a symbol.
.Pp
For ELF targets, the
.Li .type
directive is used like this:
.Pp
.Bd -literal -offset indent
\&.type name , type description
.Ed
.Pp
This sets the type of symbol
.Va name
to be either a function symbol or an object symbol. There are five different
syntaxes supported for the
.Va type description
field, in order to provide compatibility with various other assemblers.
.Pp
Because some of the characters used in these syntaxes (such as
.Li @
and
.Li # )
are comment characters for some architectures, some of the syntaxes below
do not work on all architectures. The first variant will be accepted by the
GNU assembler on all architectures so that variant should be used for maximum
portability, if you do not need to assemble your code with other assemblers.
.Pp
The syntaxes supported are:
.Pp
.Bd -literal -offset indent
.type <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"
.Ed
.Pp
.Ss Li .uleb128 Va expressions
.Va uleb128
stands for \(lqunsigned little endian base 128.\(rq This is a compact, variable length
representation of numbers used by the DWARF symbolic debugging format.See Section
.Dq Sleb128 .
.Pp
.Ss Li .version " Va string"
This directive creates a
.Li .note
section and places into it an ELF formatted note of type NT_VERSION. The note's
name is set to
.Li string .
.Pp
.Ss Li .vtable_entry Va table, Va offset
This directive finds or creates a symbol
.Li table
and creates a
.Li VTABLE_ENTRY
relocation for it with an addend of
.Li offset .
.Pp
.Ss Li .vtable_inherit Va child, Va parent
This directive finds the symbol
.Li child
and finds or creates the symbol
.Li parent
and then creates a
.Li VTABLE_INHERIT
relocation for the parent whose addend is the value of the child symbol. As
a special case the parent name of
.Li 0
is treated as referring to the
.Li *ABS*
section.
.Pp
.Ss Li .warning " Va string"
Similar to the directive
.Li .error
(see Section
.Dq Error ) ,
but just emits a warning.
.Pp
.Ss Li .weak Va names
This directive sets the weak attribute on the comma separated list of symbol
.Li names .
If the symbols do not already exist, they will be created.
.Pp
On COFF targets other than PE, weak symbols are a GNU extension. This directive
sets the weak attribute on the comma separated list of symbol
.Li names .
If the symbols do not already exist, they will be created.
.Pp
On the PE target, weak symbols are supported natively as weak aliases. When
a weak symbol is created that is not an alias, GAS creates an alternate symbol
to hold the default value.
.Pp
.Ss Li .weakref Va alias, Va target
This directive creates an alias to the target symbol that enables the symbol
to be referenced with weak-symbol semantics, but without actually making it
weak. If direct references or definitions of the symbol are present, then
the symbol will not be weak, but if all references to it are through weak
references, the symbol will be marked as weak in the symbol table.
.Pp
The effect is equivalent to moving all references to the alias to a separate
assembly source file, renaming the alias to the symbol in it, declaring the
symbol as weak there, and running a reloadable link to merge the object files
resulting from the assembly of the new source file and the old source file
that had the references to the alias removed.
.Pp
The alias itself never makes to the symbol table, and is entirely handled
within the assembler.
.Pp
.Ss Li .word Va expressions
This directive expects zero or more
.Va expressions ,
of any section, separated by commas. For each expression,
.Xr as
emits a 32-bit number.
.Pp
.Ss Deprecated Directives
One day these directives won't work. They are included for compatibility with
older assemblers.
.Bl -tag -width Ds
.It .abort
.It .line
.El
.Pp
.Sh ARM Dependent Features
.Ss Options
.Bl -tag -width Ds
.It -mcpu= Va processor[+ Va extension...]
This option specifies the target processor. The assembler will issue an error
message if an attempt is made to assemble an instruction which will not execute
on the target processor. The following processor names are recognized:
.Li arm1 ,
.Li arm2 ,
.Li arm250 ,
.Li arm3 ,
.Li arm6 ,
.Li arm60 ,
.Li arm600 ,
.Li arm610 ,
.Li arm620 ,
.Li arm7 ,
.Li arm7m ,
.Li arm7d ,
.Li arm7dm ,
.Li arm7di ,
.Li arm7dmi ,
.Li arm70 ,
.Li arm700 ,
.Li arm700i ,
.Li arm710 ,
.Li arm710t ,
.Li arm720 ,
.Li arm720t ,
.Li arm740t ,
.Li arm710c ,
.Li arm7100 ,
.Li arm7500 ,
.Li arm7500fe ,
.Li arm7t ,
.Li arm7tdmi ,
.Li arm7tdmi-s ,
.Li arm8 ,
.Li arm810 ,
.Li strongarm ,
.Li strongarm1 ,
.Li strongarm110 ,
.Li strongarm1100 ,
.Li strongarm1110 ,
.Li arm9 ,
.Li arm920 ,
.Li arm920t ,
.Li arm922t ,
.Li arm940t ,
.Li arm9tdmi ,
.Li arm9e ,
.Li arm926e ,
.Li arm926ej-s ,
.Li arm946e-r0 ,
.Li arm946e ,
.Li arm946e-s ,
.Li arm966e-r0 ,
.Li arm966e ,
.Li arm966e-s ,
.Li arm968e-s ,
.Li arm10t ,
.Li arm10tdmi ,
.Li arm10e ,
.Li arm1020 ,
.Li arm1020t ,
.Li arm1020e ,
.Li arm1022e ,
.Li arm1026ej-s ,
.Li arm1136j-s ,
.Li arm1136jf-s ,
.Li arm1156t2-s ,
.Li arm1156t2f-s ,
.Li arm1176jz-s ,
.Li arm1176jzf-s ,
.Li mpcore ,
.Li mpcorenovfp ,
.Li cortex-a8 ,
.Li cortex-r4 ,
.Li cortex-m3 ,
.Li ep9312
(ARM920 with Cirrus Maverick coprocessor),
.Li i80200
(Intel XScale processor)
.Li iwmmxt
(Intel(r) XScale processor with Wireless MMX(tm) technology coprocessor) and
.Li xscale .
The special name
.Li all
may be used to allow the assembler to accept instructions valid for any ARM
processor.
.Pp
In addition to the basic instruction set, the assembler can be told to accept
various extension mnemonics that extend the processor using the co-processor
instruction space. For example,
.Li -mcpu=arm920+maverick
is equivalent to specifying
.Li -mcpu=ep9312 .
The following extensions are currently supported:
.Li +maverick
.Li +iwmmxt
and
.Li +xscale .
.Pp
.It -march= Va architecture[+ Va extension...]
This option specifies the target architecture. The assembler will issue an
error message if an attempt is made to assemble an instruction which will
not execute on the target architecture. The following architecture names are
recognized:
.Li armv1 ,
.Li armv2 ,
.Li armv2a ,
.Li armv2s ,
.Li armv3 ,
.Li armv3m ,
.Li armv4 ,
.Li armv4xm ,
.Li armv4t ,
.Li armv4txm ,
.Li armv5 ,
.Li armv5t ,
.Li armv5txm ,
.Li armv5te ,
.Li armv5texp ,
.Li armv6 ,
.Li armv6j ,
.Li armv6k ,
.Li armv6z ,
.Li armv6zk ,
.Li armv7 ,
.Li armv7-a ,
.Li armv7-r ,
.Li armv7-m ,
.Li iwmmxt
and
.Li xscale .
If both
.Li -mcpu
and
.Li -march
are specified, the assembler will use the setting for
.Li -mcpu .
.Pp
The architecture option can be extended with the same instruction set extension
options as the
.Li -mcpu
option.
.Pp
.It -mfpu= Va floating-point-format
.Pp
This option specifies the floating point format to assemble for. The assembler
will issue an error message if an attempt is made to assemble an instruction
which will not execute on the target floating point unit. The following format
options are recognized:
.Li softfpa ,
.Li fpe ,
.Li fpe2 ,
.Li fpe3 ,
.Li fpa ,
.Li fpa10 ,
.Li fpa11 ,
.Li arm7500fe ,
.Li softvfp ,
.Li softvfp+vfp ,
.Li vfp ,
.Li vfp10 ,
.Li vfp10-r0 ,
.Li vfp9 ,
.Li vfpxd ,
.Li arm1020t ,
.Li arm1020e ,
.Li arm1136jf-s
and
.Li maverick .
.Pp
In addition to determining which instructions are assembled, this option also
affects the way in which the
.Li .double
assembler directive behaves when assembling little-endian code.
.Pp
The default is dependent on the processor selected. For Architecture 5 or
later, the default is to assembler for VFP instructions; for earlier architectures
the default is to assemble for FPA instructions.
.Pp
.It -mthumb
This option specifies that the assembler should start assembling Thumb instructions;
that is, it should behave as though the file starts with a
.Li .code 16
directive.
.Pp
.It -mthumb-interwork
This option specifies that the output generated by the assembler should be
marked as supporting interworking.
.Pp
.It -mapcs Li [26|32]
This option specifies that the output generated by the assembler should be
marked as supporting the indicated version of the Arm Procedure. Calling Standard.
.Pp
.It -matpcs
This option specifies that the output generated by the assembler should be
marked as supporting the Arm/Thumb Procedure Calling Standard. If enabled
this option will cause the assembler to create an empty debugging section
in the object file called .arm.atpcs. Debuggers can use this to determine
the ABI being used by.
.Pp
.It -mapcs-float
This indicates the floating point variant of the APCS should be used. In this
variant floating point arguments are passed in FP registers rather than integer
registers.
.Pp
.It -mapcs-reentrant
This indicates that the reentrant variant of the APCS should be used. This
variant supports position independent code.
.Pp
.It -mfloat-abi= Va abi
This option specifies that the output generated by the assembler should be
marked as using specified floating point ABI. The following values are recognized:
.Li soft ,
.Li softfp
and
.Li hard .
.Pp
.It -meabi= Va ver
This option specifies which EABI version the produced object files should
conform to. The following values are recognized:
.Li GNU ,
.Li 4
and
.Li 5 .
.Pp
.It -EB
This option specifies that the output generated by the assembler should be
marked as being encoded for a big-endian processor.
.Pp
.It -EL
This option specifies that the output generated by the assembler should be
marked as being encoded for a little-endian processor.
.Pp
.It -k
This option specifies that the output of the assembler should be marked as
position-independent code (PIC).
.Pp
.El
.Ss Syntax
.Em Special Characters
.Pp
The presence of a
.Li @
on a line indicates the start of a comment that extends to the end of the
current line. If a
.Li #
appears as the first character of a line, the whole line is treated as a comment.
.Pp
The
.Li ;
character can be used instead of a newline to separate statements.
.Pp
Either
.Li #
or
.Li $
can be used to indicate immediate operands.
.Pp
*TODO* Explain about /data modifier on symbols.
.Pp
.Em Register Names
.Pp
*TODO* Explain about ARM register naming, and the predefined names.
.Pp
.Em ARM relocation generation
.Pp
Specific data relocations can be generated by putting the relocation name
in parentheses after the symbol name. For example:
.Pp
.Bd -literal -offset indent
.word foo(TARGET1)
.Ed
.Pp
This will generate an
.Li R_ARM_TARGET1
relocation against the symbol
.Va foo .
The following relocations are supported:
.Li GOT ,
.Li GOTOFF ,
.Li TARGET1 ,
.Li TARGET2 ,
.Li SBREL ,
.Li TLSGD ,
.Li TLSLDM ,
.Li TLSLDO ,
.Li GOTTPOFF
and
.Li TPOFF .
.Pp
For compatibility with older toolchains the assembler also accepts
.Li (PLT)
after branch targets. This will generate the deprecated
.Li R_ARM_PLT32
relocation.
.Pp
Relocations for
.Li MOVW
and
.Li MOVT
instructions can be generated by prefixing the value with
.Li #:lower16:
and
.Li #:upper16
respectively. For example to load the 32-bit address of foo into r0:
.Pp
.Bd -literal -offset indent
MOVW r0, #:lower16:foo
MOVT r0, #:upper16:foo
.Ed
.Pp
.Ss Floating Point
The ARM family uses ieee floating-point numbers.
.Pp
.Ss ARM Machine Directives
.Bl -tag -width Ds
.It .align Va expression [, Va expression]
This is the generic
.Va .align
directive. For the ARM however if the first argument is zero (ie no alignment
is needed) the assembler will behave as if the argument had been 2 (ie pad
to the next four byte boundary). This is for compatibility with ARM's own
assembler.
.Pp
.It Va name .req Va register name
This creates an alias for
.Va register name
called
.Va name .
For example:
.Pp
.Bd -literal -offset indent
foo .req r0
.Ed
.Pp
.It .unreq Va alias-name
This undefines a register alias which was previously defined using the
.Li req ,
.Li dn
or
.Li qn
directives. For example:
.Pp
.Bd -literal -offset indent
foo .req r0
.unreq foo
.Ed
.Pp
An error occurs if the name is undefined. Note - this pseudo op can be used
to delete builtin in register name aliases (eg 'r0'). This should only be
done if it is really necessary.
.Pp
.It Va name .dn Va register name [ Va .type] [ Va [index]]
.It Va name .qn Va register name [ Va .type] [ Va [index]]
.Pp
The
.Li dn
and
.Li qn
directives are used to create typed and/or indexed register aliases for use
in Advanced SIMD Extension (Neon) instructions. The former should be used
to create aliases of double-precision registers, and the latter to create
aliases of quad-precision registers.
.Pp
If these directives are used to create typed aliases, those aliases can be
used in Neon instructions instead of writing types after the mnemonic or after
each operand. For example:
.Pp
.Bd -literal -offset indent
x .dn d2.f32
y .dn d3.f32
z .dn d4.f32[1]
vmul x,y,z
.Ed
.Pp
This is equivalent to writing the following:
.Pp
.Bd -literal -offset indent
vmul.f32 d2,d3,d4[1]
.Ed
.Pp
Aliases created using
.Li dn
or
.Li qn
can be destroyed using
.Li unreq .
.Pp
.It .code Li [16|32]
This directive selects the instruction set being generated. The value 16 selects
Thumb, with the value 32 selecting ARM.
.Pp
.It .thumb
This performs the same action as
.Va .code 16 .
.Pp
.It .arm
This performs the same action as
.Va .code 32 .
.Pp
.It .force_thumb
This directive forces the selection of Thumb instructions, even if the target
processor does not support those instructions
.Pp
.It .thumb_func
This directive specifies that the following symbol is the name of a Thumb
encoded function. This information is necessary in order to allow the assembler
and linker to generate correct code for interworking between Arm and Thumb
instructions and should be used even if interworking is not going to be performed.
The presence of this directive also implies
.Li .thumb
.Pp
This directive is not neccessary when generating EABI objects. On these targets
the encoding is implicit when generating Thumb code.
.Pp
.It .thumb_set
This performs the equivalent of a
.Li .set
directive in that it creates a symbol which is an alias for another symbol
(possibly not yet defined). This directive also has the added property in
that it marks the aliased symbol as being a thumb function entry point, in
the same way that the
.Li .thumb_func
directive does.
.Pp
.It .ltorg
This directive causes the current contents of the literal pool to be dumped
into the current section (which is assumed to be the .text section) at the
current location (aligned to a word boundary).
.Li GAS
maintains a separate literal pool for each section and each sub-section. The
.Li .ltorg
directive will only affect the literal pool of the current section and sub-section.
At the end of assembly all remaining, un-empty literal pools will automatically
be dumped.
.Pp
Note - older versions of
.Li GAS
would dump the current literal pool any time a section change occurred. This
is no longer done, since it prevents accurate control of the placement of
literal pools.
.Pp
.It .pool
This is a synonym for .ltorg.
.Pp
.It .unwind_fnstart
Marks the start of a function with an unwind table entry.
.Pp
.It .unwind_fnend
Marks the end of a function with an unwind table entry. The unwind index table
entry is created when this directive is processed.
.Pp
If no personality routine has been specified then standard personality routine
0 or 1 will be used, depending on the number of unwind opcodes required.
.Pp
.It .cantunwind
Prevents unwinding through the current function. No personality routine or
exception table data is required or permitted.
.Pp
.It .personality Va name
Sets the personality routine for the current function to
.Va name .
.Pp
.It .personalityindex Va index
Sets the personality routine for the current function to the EABI standard
routine number
.Va index
.Pp
.It .handlerdata
Marks the end of the current function, and the start of the exception table
entry for that function. Anything between this directive and the
.Li .fnend
directive will be added to the exception table entry.
.Pp
Must be preceded by a
.Li .personality
or
.Li .personalityindex
directive.
.Pp
.It .save Va reglist
Generate unwinder annotations to restore the registers in
.Va reglist .
The format of
.Va reglist
is the same as the corresponding store-multiple instruction.
.Pp
.Bd -literal -offset indent
.save {r4, r5, r6, lr}
stmfd sp!, {r4, r5, r6, lr}
.save f4, 2
sfmfd f4, 2, [sp]!
.save {d8, d9, d10}
fstmdx sp!, {d8, d9, d10}
.save {wr10, wr11}
wstrd wr11, [sp, #-8]!
wstrd wr10, [sp, #-8]!
or
.save wr11
wstrd wr11, [sp, #-8]!
.save wr10
wstrd wr10, [sp, #-8]!
.Ed
.Pp
.It .vsave Va vfp-reglist
Generate unwinder annotations to restore the VFP registers in
.Va vfp-reglist
using FLDMD. Also works for VFPv3 registers that are to be restored using
VLDM. The format of
.Va vfp-reglist
is the same as the corresponding store-multiple instruction.
.Pp
.Bd -literal -offset indent
.vsave {d8, d9, d10}
fstmdd sp!, {d8, d9, d10}
.vsave {d15, d16, d17}
vstm sp!, {d15, d16, d17}
.Ed
.Pp
Since FLDMX and FSTMX are now deprecated, this directive should be used in
favour of
.Li .save
for saving VFP registers for ARMv6 and above.
.Pp
.It .pad # Va count
Generate unwinder annotations for a stack adjustment of
.Va count
bytes. A positive value indicates the function prologue allocated stack space
by decrementing the stack pointer.
.Pp
.It .movsp Va reg [, # Va offset]
Tell the unwinder that
.Va reg
contains an offset from the current stack pointer. If
.Va offset
is not specified then it is assumed to be zero.
.Pp
.It .setfp Va fpreg, Va spreg [, # Va offset]
Make all unwinder annotations relaive to a frame pointer. Without this the
unwinder will use offsets from the stack pointer.
.Pp
The syntax of this directive is the same as the
.Li sub
or
.Li mov
instruction used to set the frame pointer.
.Va spreg
must be either
.Li sp
or mentioned in a previous
.Li .movsp
directive.
.Pp
.Bd -literal -offset indent
\&.movsp ip
mov ip, sp
\&...
\&.setfp fp, ip, #4
sub fp, ip, #4
.Ed
.Pp
.It .raw Va offset, Va byte1, ...
Insert one of more arbitary unwind opcode bytes, which are known to adjust
the stack pointer by
.Va offset
bytes.
.Pp
For example
.Li .unwind_raw 4, 0xb1, 0x01
is equivalent to
.Li .save {r0}
.Pp
.It .cpu Va name
Select the target processor. Valid values for
.Va name
are the same as for the
.Op -mcpu
commandline option.
.Pp
.It .arch Va name
Select the target architecture. Valid values for
.Va name
are the same as for the
.Op -march
commandline option.
.Pp
.It .object_arch Va name
Override the architecture recorded in the EABI object attribute section. Valid
values for
.Va name
are the same as for the
.Li .arch
directive. Typically this is useful when code uses runtime detection of CPU
features.
.Pp
.It .fpu Va name
Select the floating point unit to assemble for. Valid values for
.Va name
are the same as for the
.Op -mfpu
commandline option.
.Pp
.It .eabi_attribute Va tag, Va value
Set the EABI object attribute number
.Va tag
to
.Va value .
The value is either a
.Li number ,
.Li "string" ,
or
.Li number, "string"
depending on the tag.
.Pp
.El
.Ss Opcodes
.Li as
implements all the standard ARM opcodes. It also implements several pseudo
opcodes, including several synthetic load instructions.
.Pp
.Bl -tag -width Ds
.It NOP
.Bd -literal -offset indent
nop
.Ed
.Pp
This pseudo op will always evaluate to a legal ARM instruction that does nothing.
Currently it will evaluate to MOV r0, r0.
.Pp
.It LDR
.Bd -literal -offset indent
ldr <register> , = <expression>
.Ed
.Pp
If expression evaluates to a numeric constant then a MOV or MVN instruction
will be used in place of the LDR instruction, if the constant can be generated
by either of these instructions. Otherwise the constant will be placed into
the nearest literal pool (if it not already there) and a PC relative LDR instruction
will be generated.
.Pp
.It ADR
.Bd -literal -offset indent
adr <register> <label>
.Ed
.Pp
This instruction will load the address of
.Va 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.
.Pp
.It ADRL
.Bd -literal -offset indent
adrl <register> <label>
.Ed
.Pp
This instruction will load the address of
.Va 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.
.Pp
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.
.Pp
.El
For information on the ARM or Thumb instruction sets, see
.Em ARM Software Development Toolkit Reference Manual ,
Advanced RISC Machines Ltd.
.Pp
.Ss Mapping Symbols
The ARM ELF specification requires that special symbols be inserted into object
files to mark certain features:
.Pp
.Bl -tag -width Ds
.It $a
At the start of a region of code containing ARM instructions.
.Pp
.It $t
At the start of a region of code containing THUMB instructions.
.Pp
.It $d
At the start of a region of data.
.Pp
.El
The assembler will automatically insert these symbols for you - there is no
need to code them yourself. Support for tagging symbols ($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.
.Pp
.Sh 80386 Dependent Features
The i386 version
.Li 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.
.Pp
.Ss Options
The i386 version of
.Li as
has a few machine dependent options:
.Pp
.Bl -tag -width Ds
.It --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.
.Pp
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).
.Pp
.It -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.
.Pp
.It --divide
On SVR4-derived platforms, the character
.Li /
is treated as a comment character, which means that it cannot be used in expressions.
The
.Li --divide
option turns
.Li /
into a normal character. This does not disable
.Li /
at the beginning of a line starting a comment, or affect using
.Li #
for starting a comment.
.Pp
.It -march= Va CPU
This option specifies an instruction set architecture for generating instructions.
The following architectures are recognized:
.Li i8086 ,
.Li i186 ,
.Li i286 ,
.Li i386 ,
.Li i486 ,
.Li i586 ,
.Li i686 ,
.Li pentium ,
.Li pentiumpro ,
.Li pentiumii ,
.Li pentiumiii ,
.Li pentium4 ,
.Li prescott ,
.Li nocona ,
.Li core ,
.Li core2 ,
.Li k6 ,
.Li k6_2 ,
.Li athlon ,
.Li sledgehammer ,
.Li opteron ,
.Li k8 ,
.Li generic32
and
.Li generic64 .
.Pp
This option only affects instructions generated by the assembler. The
.Li .arch
directive will take precedent.
.Pp
.It -mtune= Va CPU
This option specifies a processor to optimize for. When used in conjunction
with the
.Op -march
option, only instructions of the processor specified by the
.Op -march
option will be generated.
.Pp
Valid
.Va CPU
values are identical to
.Op -march= Va CPU .
.Pp
.El
.Ss AT&T Syntax versus Intel Syntax
.Li as
now supports assembly using Intel assembler syntax.
.Li .intel_syntax
selects Intel mode, and
.Li .att_syntax
switches back to the usual AT&T mode for compatibility with the output of
.Li gcc .
Either of these directives may have an optional argument,
.Li prefix ,
or
.Li noprefix
specifying whether registers require a
.Li %
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:
.Pp
.Bl -bullet
.It
AT&T immediate operands are preceded by
.Li $ ;
Intel immediate operands are undelimited (Intel
.Li push 4
is AT&T
.Li pushl $4 ) .
AT&T register operands are preceded by
.Li % ;
Intel register operands are undelimited. AT&T absolute (as opposed to PC relative)
jump/call operands are prefixed by
.Li * ;
they are undelimited in Intel syntax.
.Pp
.It
AT&T and Intel syntax use the opposite order for source and destination operands.
Intel
.Li add eax, 4
is
.Li addl $4, %eax .
The
.Li source, dest
convention is maintained for compatibility with previous Unix assemblers.
Note that instructions with more than one source operand, such as the
.Li enter
instruction, do
.Em not
have reversed order. i386-Bugs.
.Pp
.It
In AT&T syntax the size of memory operands is determined from the last character
of the instruction mnemonic. Mnemonic suffixes of
.Li b ,
.Li w ,
.Li l
and
.Li 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
(
.Em not
the instruction mnemonics) with
.Li byte ptr ,
.Li word ptr ,
.Li dword ptr
and
.Li qword ptr .
Thus, Intel
.Li mov al, byte ptr Va foo
is
.Li movb Va foo, %al
in AT&T syntax.
.Pp
.It
Immediate form long jumps and calls are
.Li lcall/ljmp $ Va section, $ Va offset
in AT&T syntax; the Intel syntax is
.Li call/jmp far Va section: Va offset .
Also, the far return instruction is
.Li lret $ Va stack-adjust
in AT&T syntax; Intel syntax is
.Li ret far Va stack-adjust .
.Pp
.It
The AT&T assembler does not provide support for multiple section programs.
Unix style systems expect all programs to be single sections.
.El
.Pp
.Ss Instruction Naming
Instruction mnemonics are suffixed with one character modifiers which specify
the size of operands. The letters
.Li b ,
.Li w ,
.Li l
and
.Li q
specify byte, word, long and quadruple word operands. If no suffix is specified
by an instruction then
.Li as
tries to fill in the missing suffix based on the destination register operand
(the last one by convention). Thus,
.Li mov %ax, %bx
is equivalent to
.Li movw %ax, %bx ;
also,
.Li mov $1, %bx
is equivalent to
.Li 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.)
.Pp
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
.Em from
and a size to zero extend
.Em to .
This is accomplished by using two instruction mnemonic suffixes in AT&T syntax.
Base names for sign extend and zero extend are
.Li movs...
and
.Li movz...
in AT&T syntax (
.Li movsx
and
.Li movzx
in Intel syntax). The instruction mnemonic suffixes are tacked on to this
base name, the
.Em from
suffix before the
.Em to
suffix. Thus,
.Li movsbl %al, %edx
is AT&T syntax for \(lqmove sign extend
.Em from
%al
.Em to
%edx.\(rq Possible suffixes, thus, are
.Li bl
(from byte to long),
.Li bw
(from byte to word),
.Li wl
(from word to long),
.Li bq
(from byte to quadruple word),
.Li wq
(from word to quadruple word), and
.Li lq
(from long to quadruple word).
.Pp
The Intel-syntax conversion instructions
.Pp
.Bl -bullet
.It
.Li cbw
--- sign-extend byte in
.Li %al
to word in
.Li %ax ,
.Pp
.It
.Li cwde
--- sign-extend word in
.Li %ax
to long in
.Li %eax ,
.Pp
.It
.Li cwd
--- sign-extend word in
.Li %ax
to long in
.Li %dx:%ax ,
.Pp
.It
.Li cdq
--- sign-extend dword in
.Li %eax
to quad in
.Li %edx:%eax ,
.Pp
.It
.Li cdqe
--- sign-extend dword in
.Li %eax
to quad in
.Li %rax
(x86-64 only),
.Pp
.It
.Li cqo
--- sign-extend quad in
.Li %rax
to octuple in
.Li %rdx:%rax
(x86-64 only),
.El
.Pp
are called
.Li cbtw ,
.Li cwtl ,
.Li cwtd ,
.Li cltd ,
.Li cltq ,
and
.Li cqto
in AT&T naming.
.Li as
accepts either naming for these instructions.
.Pp
Far call/jump instructions are
.Li lcall
and
.Li ljmp
in AT&T syntax, but are
.Li call far
and
.Li jump far
in Intel convention.
.Pp
.Ss Register Naming
Register operands are always prefixed with
.Li % .
The 80386 registers consist of
.Pp
.Bl -bullet
.It
the 8 32-bit registers
.Li %eax
(the accumulator),
.Li %ebx ,
.Li %ecx ,
.Li %edx ,
.Li %edi ,
.Li %esi ,
.Li %ebp
(the frame pointer), and
.Li %esp
(the stack pointer).
.Pp
.It
the 8 16-bit low-ends of these:
.Li %ax ,
.Li %bx ,
.Li %cx ,
.Li %dx ,
.Li %di ,
.Li %si ,
.Li %bp ,
and
.Li %sp .
.Pp
.It
the 8 8-bit registers:
.Li %ah ,
.Li %al ,
.Li %bh ,
.Li %bl ,
.Li %ch ,
.Li %cl ,
.Li %dh ,
and
.Li %dl
(These are the high-bytes and low-bytes of
.Li %ax ,
.Li %bx ,
.Li %cx ,
and
.Li %dx )
.Pp
.It
the 6 section registers
.Li %cs
(code section),
.Li %ds
(data section),
.Li %ss
(stack section),
.Li %es ,
.Li %fs ,
and
.Li %gs .
.Pp
.It
the 3 processor control registers
.Li %cr0 ,
.Li %cr2 ,
and
.Li %cr3 .
.Pp
.It
the 6 debug registers
.Li %db0 ,
.Li %db1 ,
.Li %db2 ,
.Li %db3 ,
.Li %db6 ,
and
.Li %db7 .
.Pp
.It
the 2 test registers
.Li %tr6
and
.Li %tr7 .
.Pp
.It
the 8 floating point register stack
.Li %st
or equivalently
.Li %st(0) ,
.Li %st(1) ,
.Li %st(2) ,
.Li %st(3) ,
.Li %st(4) ,
.Li %st(5) ,
.Li %st(6) ,
and
.Li %st(7) .
These registers are overloaded by 8 MMX registers
.Li %mm0 ,
.Li %mm1 ,
.Li %mm2 ,
.Li %mm3 ,
.Li %mm4 ,
.Li %mm5 ,
.Li %mm6
and
.Li %mm7 .
.Pp
.It
the 8 SSE registers registers
.Li %xmm0 ,
.Li %xmm1 ,
.Li %xmm2 ,
.Li %xmm3 ,
.Li %xmm4 ,
.Li %xmm5 ,
.Li %xmm6
and
.Li %xmm7 .
.El
.Pp
The AMD x86-64 architecture extends the register set by:
.Pp
.Bl -bullet
.It
enhancing the 8 32-bit registers to 64-bit:
.Li %rax
(the accumulator),
.Li %rbx ,
.Li %rcx ,
.Li %rdx ,
.Li %rdi ,
.Li %rsi ,
.Li %rbp
(the frame pointer),
.Li %rsp
(the stack pointer)
.Pp
.It
the 8 extended registers
.Li %r8
--
.Li %r15 .
.Pp
.It
the 8 32-bit low ends of the extended registers:
.Li %r8d
--
.Li %r15d
.Pp
.It
the 8 16-bit low ends of the extended registers:
.Li %r8w
--
.Li %r15w
.Pp
.It
the 8 8-bit low ends of the extended registers:
.Li %r8b
--
.Li %r15b
.Pp
.It
the 4 8-bit registers:
.Li %sil ,
.Li %dil ,
.Li %bpl ,
.Li %spl .
.Pp
.It
the 8 debug registers:
.Li %db8
--
.Li %db15 .
.Pp
.It
the 8 SSE registers:
.Li %xmm8
--
.Li %xmm15 .
.El
.Pp
.Ss 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 \(lqoperand size\(rq prefix.) Instruction prefixes are best written on the
same line as the instruction they act upon. For example, the
.Li scas
(scan string) instruction is repeated with:
.Pp
.Bd -literal -offset indent
repne scas %es:(%edi),%al
.Ed
.Pp
You may also place prefixes on the lines immediately preceding the instruction,
but this circumvents checks that
.Li as
does with prefixes, and will not work with all prefixes.
.Pp
Here is a list of instruction prefixes:
.Pp
.Bl -bullet
.It
Section override prefixes
.Li cs ,
.Li ds ,
.Li ss ,
.Li es ,
.Li fs ,
.Li gs .
These are automatically added by specifying using the
.Va section
:
.Va memory-operand
form for memory references.
.Pp
.It
Operand/Address size prefixes
.Li data16
and
.Li addr16
change 32-bit operands/addresses into 16-bit operands/addresses, while
.Li data32
and
.Li addr32
change 16-bit ones (in a
.Li .code16
section) into 32-bit operands/addresses. These prefixes
.Em must
appear on the same line of code as the instruction they modify. For example,
in a 16-bit
.Li .code16
section, you might write:
.Pp
.Bd -literal -offset indent
addr32 jmpl *(%ebx)
.Ed
.Pp
.It
The bus lock prefix
.Li lock
inhibits interrupts during execution of the instruction it precedes. (This
is only valid with certain instructions; see a 80386 manual for details).
.Pp
.It
The wait for coprocessor prefix
.Li wait
waits for the coprocessor to complete the current instruction. This should
never be needed for the 80386/80387 combination.
.Pp
.It
The
.Li rep ,
.Li repe ,
and
.Li repne
prefixes are added to string instructions to make them repeat
.Li %ecx
times (
.Li %cx
times if the current address size is 16-bits).
.It
The
.Li rex
family of prefixes is used by x86-64 to encode extensions to i386 instruction
set. The
.Li rex
prefix has four bits --- an operand size overwrite (
.Li 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.
.Pp
You may write the
.Li rex
prefixes directly. The
.Li rex64xyz
instruction emits
.Li rex
prefix with all the bits set. By omitting the
.Li 64 ,
.Li x ,
.Li y
or
.Li 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.
.El
.Pp
.Ss Memory References
An Intel syntax indirect memory reference of the form
.Pp
.Bd -literal -offset indent
section:[base + index*scale + disp]
.Ed
.Pp
is translated into the AT&T syntax
.Pp
.Bd -literal -offset indent
section:disp(base, index, scale)
.Ed
.Pp
where
.Va base
and
.Va index
are the optional 32-bit base and index registers,
.Va disp
is the optional displacement, and
.Va scale ,
taking the values 1, 2, 4, and 8, multiplies
.Va index
to calculate the address of the operand. If no
.Va scale
is specified,
.Va scale
is taken to be 1.
.Va 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
.Em must
be preceded by a
.Li % .
If you specify a section override which coincides with the default section
register,
.Li as
does
.Em 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.
.Pp
Here are some examples of Intel and AT&T style memory references:
.Pp
.Bl -tag -width Ds
.It AT&T: Li -4(%ebp), Intel: Li [ebp - 4]
.Va base
is
.Li %ebp ;
.Va disp
is
.Li -4 .
.Va section
is missing, and the default section is used (
.Li %ss
for addressing with
.Li %ebp
as the base register).
.Va index ,
.Va scale
are both missing.
.Pp
.It AT&T: Li foo(,%eax,4), Intel: Li [foo + eax*4]
.Va index
is
.Li %eax
(scaled by a
.Va scale
4);
.Va disp
is
.Li foo .
All other fields are missing. The section register here defaults to
.Li %ds .
.Pp
.It AT&T: Li foo(,1); Intel Li [foo]
This uses the value pointed to by
.Li foo
as a memory operand. Note that
.Va base
and
.Va index
are both missing, but there is only
.Em one
.Li , .
This is a syntactic exception.
.Pp
.It AT&T: Li %gs:foo; Intel Li gs:foo
This selects the contents of the variable
.Li foo
with section register
.Va section
being
.Li %gs .
.El
.Pp
Absolute (as opposed to PC relative) call and jump operands must be prefixed
with
.Li * .
If no
.Li *
is specified,
.Li as
always chooses PC relative addressing for jump/call labels.
.Pp
Any instruction that has a memory operand, but no register operand,
.Em must
specify its size (byte, word, long, or quadruple) with an instruction mnemonic
suffix (
.Li b ,
.Li w ,
.Li l
or
.Li q ,
respectively).
.Pp
The x86-64 architecture adds an RIP (instruction pointer relative) addressing.
This addressing mode is specified by using
.Li rip
as a base register. Only constant offsets are valid. For example:
.Pp
.Bl -tag -width Ds
.It AT&T: Li 1234(%rip), Intel: Li [rip + 1234]
Points to the address 1234 bytes past the end of the current instruction.
.Pp
.It AT&T: Li symbol(%rip), Intel: Li [rip + symbol]
Points to the
.Li symbol
in RIP relative way, this is shorter than the default absolute addressing.
.El
.Pp
Other addressing modes remain unchanged in x86-64 architecture, except registers
used are 64-bit instead of 32-bit.
.Pp
.Ss 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
.Li data16
instruction prefix), since the 80386 insists upon masking
.Li %eip
to 16 bits after the word displacement is added. (See alsosee Section
.Dq i386-Arch )
.Pp
Note that the
.Li jcxz ,
.Li jecxz ,
.Li loop ,
.Li loopz ,
.Li loope ,
.Li loopnz
and
.Li loopne
instructions only come in byte displacements, so that if you use these instructions
(
.Li 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
.Li jcxz foo
to
.Pp
.Bd -literal -offset indent
jcxz cx_zero
jmp cx_nonzero
cx_zero: jmp foo
cx_nonzero:
.Ed
.Pp
.Ss 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.
.Pp
.Bl -bullet
.It
Floating point constructors are
.Li .float
or
.Li .single ,
.Li .double ,
and
.Li .tfloat
for 32-, 64-, and 80-bit formats. These correspond to instruction mnemonic
suffixes
.Li s ,
.Li l ,
and
.Li t .
.Li t
stands for 80-bit (ten byte) real. The 80387 only supports this format via
the
.Li fldt
(load 80-bit real to stack top) and
.Li fstpt
(store 80-bit real and pop stack) instructions.
.Pp
.It
Integer constructors are
.Li .word ,
.Li .long
or
.Li .int ,
and
.Li .quad
for the 16-, 32-, and 64-bit integer formats. The corresponding instruction
mnemonic suffixes are
.Li s
(single),
.Li l
(long), and
.Li q
(quad). As with the 80-bit real format, the 64-bit
.Li q
format is only present in the
.Li fildq
(load quad integer to stack top) and
.Li fistpq
(store quad integer and pop stack) instructions.
.El
.Pp
Register to register operations should not use instruction mnemonic suffixes.
.Li fstl %st, %st(1)
will give a warning, and be assembled as if you wrote
.Li fst %st, %st(1) ,
since all register to register operations use 80-bit floating point operands.
(Contrast this with
.Li fstl %st, mem ,
which converts
.Li %st
from 80-bit to 64-bit floating point format, then stores the result in the
4 byte location
.Li mem )
.Pp
.Ss Intel's MMX and AMD's 3DNow! SIMD Operations
.Li 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.
.Pp
Currently,
.Li as
does not support Intel's floating point SIMD, Katmai (KNI).
.Pp
The eight 64-bit MMX operands, also used by 3DNow!, are called
.Li %mm0 ,
.Li %mm1 ,
\&...
.Li %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.
.Pp
See Intel and AMD documentation, keeping in mind that the operand order in
instructions is reversed from the Intel syntax.
.Pp
.Ss Writing 16-bit Code
While
.Li as
normally writes only \(lqpure\(rq 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
.Li .code16
or
.Li .code16gcc
directive before the assembly language instructions to be run in 16-bit mode.
You can switch
.Li as
back to writing normal 32-bit code with the
.Li .code32
directive.
.Pp
.Li .code16gcc
provides experimental support for generating 16-bit code from gcc, and differs
from
.Li .code16
in that
.Li call ,
.Li ret ,
.Li enter ,
.Li leave ,
.Li push ,
.Li pop ,
.Li pusha ,
.Li popa ,
.Li pushf ,
and
.Li popf
instructions default to 32-bit size. This is so that the stack pointer is
manipulated in the same way over function calls, allowing access to function
parameters at the same stack offsets as in 32-bit mode.
.Li .code16gcc
also automatically adds address size prefixes where necessary to use the 32-bit
addressing modes that gcc generates.
.Pp
The code which
.Li 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
.Em any
32-bit constructs which require
.Li as
to output address or operand size prefixes.
.Pp
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
.Li 66 6a 04 ,
which pushes the value
.Li 4
onto the stack, decrementing
.Li %esp
by 2.
.Pp
.Bd -literal -offset indent
pushw $4
.Ed
.Pp
The same code in a 16-bit code section would generate the machine opcode bytes
.Li 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.
.Pp
.Ss 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.
.Pp
For example
.Pp
.Bd -literal -offset indent
fsub %st,%st(3)
.Ed
results in
.Li %st(3)
being updated to
.Li %st - %st(3)
rather than the expected
.Li %st(3) - %st .
This happens with all the non-commutative arithmetic floating point operations
with two register operands where the source register is
.Li %st
and the destination register is
.Li %st(i) .
.Pp
.Ss Specifying CPU Architecture
.Li as
may be told to assemble for a particular CPU (sub-)architecture with the
.Li .arch Va cpu_type
directive. This directive enables a warning when gas detects an instruction
that is not supported on the CPU specified. The choices for
.Va cpu_type
are:
.Pp
.TS
l l l l.
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
.TE
.Pp
Apart from the warning, there are only two other effects on
.Li as
operation; Firstly, if you specify a CPU other than
.Li i486 ,
then shift by one instructions such as
.Li 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
.Li sarl %eax .
Secondly, if you specify
.Li i8086 ,
.Li i186 ,
or
.Li i286 ,
.Em and
.Li .code16
or
.Li .code16gcc
then byte offset conditional jumps will be promoted when necessary to a two
instruction sequence consisting of a conditional jump of the opposite sense
around an unconditional jump to the target.
.Pp
Following the CPU architecture (but not a sub-architecture, which are those
starting with a dot), you may specify
.Li jumps
or
.Li nojumps
to control automatic promotion of conditional jumps.
.Li 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
.Dq i386-Jumps )
.Li nojumps
leaves external conditional jumps as byte offset jumps, and warns about file-local
conditional jumps that
.Li as
promotes. Unconditional jumps are treated as for
.Li jumps .
.Pp
For example
.Pp
.Bd -literal -offset indent
.arch i8086,nojumps
.Ed
.Pp
.Ss Notes
There is some trickery concerning the
.Li mul
and
.Li imul
instructions that deserves mention. The 16-, 32-, 64- and 128-bit expanding
multiplies (base opcode
.Li 0xf6 ;
extension 4 for
.Li mul
and 5 for
.Li imul )
can be output only in the one operand form. Thus,
.Li imul %ebx, %eax
does
.Em not
select the expanding multiply; the expanding multiply would clobber the
.Li %edx
register, and this would confuse
.Li gcc
output. Use
.Li imul %ebx
to get the 64-bit product in
.Li %edx:%eax .
.Pp
We have added a two operand form of
.Li 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
.Li %eax
by 69, for example, can be done with
.Li imul $69, %eax
rather than
.Li imul $69, %eax, %eax .
.Pp
.Sh IA-64 Dependent Features
.Ss Options
.Bl -tag -width Ds
.It -mconstant-gp
This option instructs the assembler to mark the resulting object file as using
the \(lqconstant GP\(rq 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.
.Pp
.It -mauto-pic
This option instructs the assembler to mark the resulting object file as using
the \(lqconstant GP without function descriptor\(rq data model. This model is like
the \(lqconstant GP\(rq 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.
.Pp
.It -milp32
.It -milp64
.It -mlp64
.It -mp64
These options select the data model. The assembler defaults to
.Li -mlp64
(LP64 data model).
.Pp
.It -mle
.It -mbe
These options select the byte order. The
.Li -mle
option selects little-endian byte order (default) and
.Li -mbe
selects big-endian byte order. Note that IA-64 machine code always uses little-endian
byte order.
.Pp
.It -mtune=itanium1
.It -mtune=itanium2
Tune for a particular IA-64 CPU,
.Va itanium1
or
.Va itanium2 .
The default is
.Va itanium2 .
.Pp
.It -munwind-check=warning
.It -munwind-check=error
These options control what the assembler will do when performing consistency
checks on unwind directives.
.Li -munwind-check=warning
will make the assembler issue a warning when an unwind directive check fails.
This is the default.
.Li -munwind-check=error
will make the assembler issue an error when an unwind directive check fails.
.Pp
.It -mhint.b=ok
.It -mhint.b=warning
.It -mhint.b=error
These options control what the assembler will do when the
.Li hint.b
instruction is used.
.Li -mhint.b=ok
will make the assembler accept
.Li hint.b .
.Li -mint.b=warning
will make the assembler issue a warning when
.Li hint.b
is used.
.Li -mhint.b=error
will make the assembler treat
.Li hint.b
as an error, which is the default.
.Pp
.It -x
.It -xexplicit
These options turn on dependency violation checking.
.Pp
.It -xauto
This option instructs the assembler to automatically insert stop bits where
necessary to remove dependency violations. This is the default mode.
.Pp
.It -xnone
This option turns off dependency violation checking.
.Pp
.It -xdebug
This turns on debug output intended to help tracking down bugs in the dependency
violation checker.
.Pp
.It -xdebugn
This is a shortcut for -xnone -xdebug.
.Pp
.It -xdebugx
This is a shortcut for -xexplicit -xdebug.
.Pp
.El
.Ss Syntax
The assembler syntax closely follows the IA-64 Assembly Language Reference
Guide.
.Pp
.Em Special Characters
.Pp
.Li //
is the line comment token.
.Pp
.Li ;
can be used instead of a newline to separate statements.
.Pp
.Em Register Names
.Pp
The 128 integer registers are referred to as
.Li r Va n .
The 128 floating-point registers are referred to as
.Li f Va n .
The 128 application registers are referred to as
.Li ar Va n .
The 128 control registers are referred to as
.Li cr Va n .
The 64 one-bit predicate registers are referred to as
.Li p Va n .
The 8 branch registers are referred to as
.Li b Va n .
In addition, the assembler defines a number of aliases:
.Li gp
(
.Li r1 ) ,
.Li sp
(
.Li r12 ) ,
.Li rp
(
.Li b0 ) ,
.Li ret0
(
.Li r8 ) ,
.Li ret1
(
.Li r9 ) ,
.Li ret2
(
.Li r10 ) ,
.Li ret3
(
.Li r9 ) ,
.Li farg Va n
(
.Li f8+ Va n ) ,
and
.Li fret Va n
(
.Li f8+ Va n ) .
.Pp
For convenience, the assembler also defines aliases for all named application
and control registers. For example,
.Li ar.bsp
refers to the register backing store pointer (
.Li ar17 ) .
Similarly,
.Li cr.eoi
refers to the end-of-interrupt register (
.Li cr67 ) .
.Pp
.Em IA-64 Processor-Status-Register (PSR) Bit Names
.Pp
The assembler defines bit masks for each of the bits in the IA-64 processor
status register. For example,
.Li psr.ic
corresponds to a value of 0x2000. These masks are primarily intended for use
with the
.Li ssm
/
.Li sum
and
.Li rsm
/
.Li rum
instructions, but they can be used anywhere else where an integer constant
is expected.
.Pp
.Ss Opcodes
For detailed information on the IA-64 machine instruction set, see the
.Lk http://developer.intel.com/design/itanium/arch_spec.htm .
.Pp
.Sh MIPS Dependent Features
GNU
.Li 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
.Em MIPS RISC Architecture ,
by Kane and Heindrich (Prentice-Hall). For an overview of mips assembly conventions,
see \(lqAppendix D: Assembly Language Programming\(rq in the same work.
.Pp
.Ss Assembler options
The mips configurations of GNU
.Li as
support these special options:
.Pp
.Bl -tag -width Ds
.It -G Va num
This option sets the largest size of an object that can be referenced implicitly
with the
.Li gp
register. It is only accepted for targets that use ecoff format. The default
value is 8.
.Pp
.It -EB
.It -EL
Any mips configuration of
.Li 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
.Li -EB
to select big-endian output, and
.Li -EL
for little-endian.
.Pp
.It -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.
.Pp
.It -mvxworks-pic
Generate VxWorks PIC. This option tells the assembler to generate VxWorks-style
position-independent macro expansions.
.Pp
.It -mips1
.It -mips2
.It -mips3
.It -mips4
.It -mips5
.It -mips32
.It -mips32r2
.It -mips64
.It -mips64r2
Generate code for a particular MIPS Instruction Set Architecture level.
.Li -mips1
corresponds to the r2000 and r3000 processors,
.Li -mips2
to the r6000 processor,
.Li -mips3
to the r4000 processor, and
.Li -mips4
to the r8000 and r10000 processors.
.Li -mips5 ,
.Li -mips32 ,
.Li -mips32r2 ,
.Li -mips64 ,
and
.Li -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.
.Pp
.It -mgp32
.It -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.
.Li -mgp32
controls the size of general-purpose registers and
.Li -mfp32
controls the size of floating-point registers.
.Pp
The
.Li .set gp=32
and
.Li .set fp=32
directives allow the size of registers to be changed for parts of an object.
The default value is restored by
.Li .set gp=default
and
.Li .set fp=default .
.Pp
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.
.Pp
.It -mgp64
.It -mfp64
Assume that 64-bit registers are available. This is provided in the interests
of symmetry with
.Li -mgp32
and
.Li -mfp32 .
.Pp
The
.Li .set gp=64
and
.Li .set fp=64
directives allow the size of registers to be changed for parts of an object.
The default value is restored by
.Li .set gp=default
and
.Li .set fp=default .
.Pp
.It -mips16
.It -no-mips16
Generate code for the MIPS 16 processor. This is equivalent to putting
.Li .set mips16
at the start of the assembly file.
.Li -no-mips16
turns off this option.
.Pp
.It -msmartmips
.It -mno-smartmips
Enables the SmartMIPS extensions to the MIPS32 instruction set, which provides
a number of new instructions which target smartcard and cryptographic applications.
This is equivalent to putting
.Li .set smartmips
at the start of the assembly file.
.Li -mno-smartmips
turns off this option.
.Pp
.It -mips3d
.It -no-mips3d
Generate code for the MIPS-3D Application Specific Extension. This tells the
assembler to accept MIPS-3D instructions.
.Li -no-mips3d
turns off this option.
.Pp
.It -mdmx
.It -no-mdmx
Generate code for the MDMX Application Specific Extension. This tells the
assembler to accept MDMX instructions.
.Li -no-mdmx
turns off this option.
.Pp
.It -mdsp
.It -mno-dsp
Generate code for the DSP Release 1 Application Specific Extension. This tells
the assembler to accept DSP Release 1 instructions.
.Li -mno-dsp
turns off this option.
.Pp
.It -mdspr2
.It -mno-dspr2
Generate code for the DSP Release 2 Application Specific Extension. This option
implies -mdsp. This tells the assembler to accept DSP Release 2 instructions.
.Li -mno-dspr2
turns off this option.
.Pp
.It -mmt
.It -mno-mt
Generate code for the MT Application Specific Extension. This tells the assembler
to accept MT instructions.
.Li -mno-mt
turns off this option.
.Pp
.It -mfix7000
.It -mno-fix7000
Cause nops to be inserted if the read of the destination register of an mfhi
or mflo instruction occurs in the following two instructions.
.Pp
.It -mfix-vr4120
.It -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.
.Pp
.It -mfix-vr4130
.It -no-mfix-vr4130
Insert nops to work around the VR4130
.Li mflo
/
.Li mfhi
errata.
.Pp
.It -m4010
.It -no-m4010
Generate code for the LSI r4010 chip. This tells the assembler to accept the
r4010 specific instructions (
.Li addciu ,
.Li ffc ,
etc.), and to not schedule
.Li nop
instructions around accesses to the
.Li HI
and
.Li LO
registers.
.Li -no-m4010
turns off this option.
.Pp
.It -m4650
.It -no-m4650
Generate code for the MIPS r4650 chip. This tells the assembler to accept
the
.Li mad
and
.Li madu
instruction, and to not schedule
.Li nop
instructions around accesses to the
.Li HI
and
.Li LO
registers.
.Li -no-m4650
turns off this option.
.Pp
.It -m3900
.It -no-m3900
.It -m4100
.It -no-m4100
For each option
.Li -m Va nnnn ,
generate code for the MIPS r
.Va nnnn
chip. This tells the assembler to accept instructions specific to that chip,
and to schedule for that chip's hazards.
.Pp
.It -march= Va cpu
Generate code for a particular MIPS cpu. It is exactly equivalent to
.Li -m Va cpu ,
except that there are more value of
.Va cpu
understood. Valid
.Va cpu
value are:
.Pp
.Qo
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
.Qc
.Pp
.It -mtune= Va cpu
Schedule and tune for a particular MIPS cpu. Valid
.Va cpu
values are identical to
.Li -march= Va cpu .
.Pp
.It -mabi= Va abi
Record which ABI the source code uses. The recognized arguments are:
.Li 32 ,
.Li n32 ,
.Li o64 ,
.Li 64
and
.Li eabi .
.Pp
.It -msym32
.It -mno-sym32
Equivalent to adding
.Li .set sym32
or
.Li .set nosym32
to the beginning of the assembler input.See Section
.Dq MIPS symbol sizes .
.Pp
.It -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
.Li as ,
there is no need for
.Li -nocpp ,
because the GNU assembler itself never runs the C preprocessor.
.Pp
.It --construct-floats
.It --no-construct-floats
The
.Li --no-construct-floats
option disables the construction of double width floating point constants
by loading the two halves of the value into the two single width floating
point registers that make up the double width register. 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.
.Pp
By default
.Li --construct-floats
is selected, allowing construction of these floating point constants.
.Pp
.It --trap
.It --no-break
.Li as
automatically macro expands certain division and multiplication instructions
to check for overflow and division by zero. This option causes
.Li 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.
.Pp
.It --break
.It --no-trap
Generate code to take a break exception rather than a trap exception when
an error is detected. This is the default.
.Pp
.It -mpdr
.It -mno-pdr
Control generation of
.Li .pdr
sections. Off by default on IRIX, on elsewhere.
.Pp
.It -mshared
.It -mno-shared
When generating code using the Unix calling conventions (selected by
.Li -KPIC
or
.Li -mcall_shared ) ,
gas will normally generate code which can go into a shared library. The
.Li -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
.Li .cpload
and
.Li .cpsetup
pseudo-ops.
.El
.Pp
.Ss MIPS ECOFF object code
Assembling for a mips ecoff target supports some additional sections besides
the usual
.Li .text ,
.Li .data
and
.Li .bss .
The additional sections are
.Li .rdata ,
used for read-only data,
.Li .sdata ,
used for small data, and
.Li .sbss ,
used for small common objects.
.Pp
When assembling for ecoff, the assembler uses the
.Li $gp
(
.Li $28 )
register to form the address of a \(lqsmall object\(rq. Any object in the
.Li .sdata
or
.Li .sbss
sections is considered \(lqsmall\(rq in this sense. For external objects, or for objects
in the
.Li .bss
section, you can use the
.Li gcc
.Li -G
option to control the size of objects addressed via
.Li $gp ;
the default value is 8, meaning that a reference to any object eight bytes
or smaller uses
.Li $gp .
Passing
.Li -G 0
to
.Li as
prevents it from using the
.Li $gp
register on the basis of object size (but the assembler uses
.Li $gp
for objects in
.Li .sdata
or
.Li sbss
in any case). The size of an object in the
.Li .bss
section is set by the
.Li .comm
or
.Li .lcomm
directive that defines it. The size of an external object may be set with
the
.Li .extern
directive. For example,
.Li .extern sym,4
declares that the object at
.Li sym
is 4 bytes in length, whie leaving
.Li sym
otherwise undefined.
.Pp
Using small ecoff objects requires linker support, and assumes that the
.Li $gp
register is correctly initialized (normally done automatically by the startup
code). mips ecoff assembly code must not modify the
.Li $gp
register.
.Pp
.Ss Directives for debugging information
mips ecoff
.Li as
supports several directives used for generating debugging information which
are not support by traditional mips assemblers. These are
.Li .def ,
.Li .endef ,
.Li .dim ,
.Li .file ,
.Li .scl ,
.Li .size ,
.Li .tag ,
.Li .type ,
.Li .val ,
.Li .stabd ,
.Li .stabn ,
and
.Li .stabs .
The debugging information generated by the three
.Li .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!
.Pp
.Ss 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
.Li dla $4,sym
is usually:
.Pp
.Bd -literal -offset indent
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
.Ed
.Pp
whereas the 32-bit expansion is simply:
.Pp
.Bd -literal -offset indent
lui $4,%hi(sym)
daddiu $4,$4,%lo(sym)
.Ed
.Pp
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.
.Pp
You can use the
.Li .set sym32
directive to tell the assembler that, from this point on, all expressions
of the form
.Li Va symbol
or
.Li Va symbol + Va offset
have 32-bit values. For example:
.Pp
.Bd -literal -offset indent
\&.set sym32
dla $4,sym
lw $4,sym+16
sw $4,sym+0x8000($4)
.Ed
.Pp
will cause the assembler to treat
.Li sym ,
.Li sym+16
and
.Li sym+0x8000
as 32-bit values. The handling of non-symbolic addresses is not affected.
.Pp
The directive
.Li .set nosym32
ends a
.Li .set sym32
block and reverts to the normal behavior. It is also possible to change the
symbol size using the command-line options
.Op -msym32
and
.Op -mno-sym32 .
.Pp
These options and directives are always accepted, but at present, they have
no effect for anything other than n64.
.Pp
.Ss Directives to override the ISA level
GNU
.Li as
supports an additional directive to change the mips Instruction Set Architecture
level on the fly:
.Li .set mips Va n .
.Va 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.
.Li .set mips Va n
affects not only which instructions are permitted, but also how certain macros
are expanded.
.Li .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!
.Pp
The
.Li .set arch= Va 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
.Li -march
command line option are also selectable by this directive. The original value
is restored by
.Li .set arch=default .
.Pp
The directive
.Li .set mips16
puts the assembler into MIPS 16 mode, in which it will assemble instructions
for the MIPS 16 processor. Use
.Li .set nomips16
to return to normal 32 bit mode.
.Pp
Traditional mips assemblers do not support this directive.
.Pp
.Ss Directives for extending MIPS 16 bit instructions
By default, MIPS 16 instructions are automatically extended to 32 bits when
necessary. The directive
.Li .set noautoextend
will turn this off. When
.Li .set noautoextend
is in effect, any 32 bit instruction must be explicitly extended with the
.Li .e
modifier (e.g.,
.Li li.e $4,1000 ) .
The directive
.Li .set autoextend
may be used to once again automatically extend instructions when necessary.
.Pp
This directive is only meaningful when in MIPS 16 mode. Traditional mips assemblers
do not support this directive.
.Pp
.Ss Directive to mark data as an instruction
The
.Li .insn
directive tells
.Li as
that the following data is actually instructions. This makes a difference
in MIPS 16 mode: when loading the address of a label which precedes instructions,
.Li as
automatically adds 1 to the value, so that jumping to the loaded address will
do the right thing.
.Pp
.Ss Directives to save and restore options
The directives
.Li .set push
and
.Li .set pop
may be used to save and restore the current settings for all the options which
are controlled by
.Li .set .
The
.Li .set push
directive saves the current settings on a stack. The
.Li .set pop
directive pops the stack and restores the settings.
.Pp
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.
.Pp
Traditional mips assemblers do not support these directives.
.Pp
.Ss Directives to control generation of MIPS ASE instructions
The directive
.Li .set mips3d
makes the assembler accept instructions from the MIPS-3D Application Specific
Extension from that point on in the assembly. The
.Li .set nomips3d
directive prevents MIPS-3D instructions from being accepted.
.Pp
The directive
.Li .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
.Li .set nosmartmips
directive prevents SmartMIPS instructions from being accepted.
.Pp
The directive
.Li .set mdmx
makes the assembler accept instructions from the MDMX Application Specific
Extension from that point on in the assembly. The
.Li .set nomdmx
directive prevents MDMX instructions from being accepted.
.Pp
The directive
.Li .set dsp
makes the assembler accept instructions from the DSP Release 1 Application
Specific Extension from that point on in the assembly. The
.Li .set nodsp
directive prevents DSP Release 1 instructions from being accepted.
.Pp
The directive
.Li .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
.Li .set dsp .
The
.Li .set nodspr2
directive prevents DSP Release 2 instructions from being accepted.
.Pp
The directive
.Li .set mt
makes the assembler accept instructions from the MT Application Specific Extension
from that point on in the assembly. The
.Li .set nomt
directive prevents MT instructions from being accepted.
.Pp
Traditional mips assemblers do not support these directives.
.Pp
.Sh PowerPC Dependent Features
.Ss 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.
.Pp
The following table lists all available PowerPC options.
.Pp
.Bl -tag -width Ds
.It -mpwrx | -mpwr2
Generate code for POWER/2 (RIOS2).
.Pp
.It -mpwr
Generate code for POWER (RIOS1)
.Pp
.It -m601
Generate code for PowerPC 601.
.Pp
.It -mppc, -mppc32, -m603, -m604
Generate code for PowerPC 603/604.
.Pp
.It -m403, -m405
Generate code for PowerPC 403/405.
.Pp
.It -m440
Generate code for PowerPC 440. BookE and some 405 instructions.
.Pp
.It -m7400, -m7410, -m7450, -m7455
Generate code for PowerPC 7400/7410/7450/7455.
.Pp
.It -mppc64, -m620
Generate code for PowerPC 620/625/630.
.Pp
.It -me500, -me500x2
Generate code for Motorola e500 core complex.
.Pp
.It -mspe
Generate code for Motorola SPE instructions.
.Pp
.It -mppc64bridge
Generate code for PowerPC 64, including bridge insns.
.Pp
.It -mbooke64
Generate code for 64-bit BookE.
.Pp
.It -mbooke, mbooke32
Generate code for 32-bit BookE.
.Pp
.It -me300
Generate code for PowerPC e300 family.
.Pp
.It -maltivec
Generate code for processors with AltiVec instructions.
.Pp
.It -mpower4
Generate code for Power4 architecture.
.Pp
.It -mpower5
Generate code for Power5 architecture.
.Pp
.It -mpower6
Generate code for Power6 architecture.
.Pp
.It -mcell
Generate code for Cell Broadband Engine architecture.
.Pp
.It -mcom
Generate code Power/PowerPC common instructions.
.Pp
.It -many
Generate code for any architecture (PWR/PWRX/PPC).
.Pp
.It -mregnames
Allow symbolic names for registers.
.Pp
.It -mno-regnames
Do not allow symbolic names for registers.
.Pp
.It -mrelocatable
Support for GCC's -mrelocatable option.
.Pp
.It -mrelocatable-lib
Support for GCC's -mrelocatable-lib option.
.Pp
.It -memb
Set PPC_EMB bit in ELF flags.
.Pp
.It -mlittle, -mlittle-endian
Generate code for a little endian machine.
.Pp
.It -mbig, -mbig-endian
Generate code for a big endian machine.
.Pp
.It -msolaris
Generate code for Solaris.
.Pp
.It -mno-solaris
Do not generate code for Solaris.
.El
.Pp
.Ss PowerPC Assembler Directives
A number of assembler directives are available for PowerPC. The following
table is far from complete.
.Pp
.Bl -tag -width Ds
.It .machine "string"
This directive allows you to change the machine for which code is generated.
.Li "string"
may be any of the -m cpu selection options (without the -m) enclosed in double
quotes,
.Li "push" ,
or
.Li "pop" .
.Li .machine "push"
saves the currently selected cpu, which may be restored with
.Li .machine "pop" .
.El
.Pp
.Sh SPARC Dependent Features
.Ss 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.
.Pp
By default,
.Li as
assumes the core instruction set (SPARC v6), but \(lqbumps\(rq the architecture level
as needed: it switches to successively higher architectures as it encounters
instructions that only exist in the higher levels.
.Pp
If not configured for SPARC v9 (
.Li sparc64-*-* )
GAS will not bump passed sparclite by default, an option must be passed to
enable the v9 instructions.
.Pp
GAS treats sparclite as being compatible with v8, unless an architecture is
explicitly requested. SPARC v9 is always incompatible with sparclite.
.Pp
.Bl -tag -width Ds
.It -Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
.It -Av8plus | -Av8plusa | -Av9 | -Av9a
Use one of the
.Li -A
options to select one of the SPARC architectures explicitly. If you select
an architecture explicitly,
.Li as
reports a fatal error if it encounters an instruction or feature requiring
an incompatible or higher level.
.Pp
.Li -Av8plus
and
.Li -Av8plusa
select a 32 bit environment.
.Pp
.Li -Av9
and
.Li -Av9a
select a 64 bit environment and are not available unless GAS is explicitly
configured with 64 bit environment support.
.Pp
.Li -Av8plusa
and
.Li -Av9a
enable the SPARC V9 instruction set with UltraSPARC extensions.
.Pp
.It -xarch=v8plus | -xarch=v8plusa
For compatibility with the Solaris v9 assembler. These options are equivalent
to -Av8plus and -Av8plusa, respectively.
.Pp
.It -bump
Warn 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).
.Pp
.It -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.
.El
.Pp
.Ss Enforcing aligned data
SPARC GAS normally permits data to be misaligned. For example, it permits
the
.Li .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.
.Pp
You can use the
.Li --enforce-aligned-data
option to make SPARC GAS also issue an error about misaligned data, just as
the SunOS and Solaris assemblers do.
.Pp
The
.Li --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
.Li packed
attribute). You may have to assemble with GAS in order to initialize packed
data structures in your own code.
.Pp
.Ss Floating Point
The Sparc uses ieee floating-point numbers.
.Pp
.Ss Sparc Machine Directives
The Sparc version of
.Li as
supports the following additional machine directives:
.Pp
.Bl -tag -width Ds
.It .align
This must be followed by the desired alignment in bytes.
.Pp
.It .common
This must be followed by a symbol name, a positive number, and
.Li "bss" .
This behaves somewhat like
.Li .comm ,
but the syntax is different.
.Pp
.It .half
This is functionally identical to
.Li .short .
.Pp
.It .nword
On the Sparc, the
.Li .nword
directive produces native word sized value, ie. if assembling with -32 it
is equivalent to
.Li .word ,
if assembling with -64 it is equivalent to
.Li .xword .
.Pp
.It .proc
This directive is ignored. Any text following it on the same line is also
ignored.
.Pp
.It .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
.Li #scratch ,
it is a scratch register, if it is
.Li #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.
.Pp
.It .reserve
This must be followed by a symbol name, a positive number, and
.Li "bss" .
This behaves somewhat like
.Li .lcomm ,
but the syntax is different.
.Pp
.It .seg
This must be followed by
.Li "text" ,
.Li "data" ,
or
.Li "data1" .
It behaves like
.Li .text ,
.Li .data ,
or
.Li .data 1 .
.Pp
.It .skip
This is functionally identical to the
.Li .space
directive.
.Pp
.It .word
On the Sparc, the
.Li .word
directive produces 32 bit values, instead of the 16 bit values it produces
on many other machines.
.Pp
.It .xword
On the Sparc V9 processor, the
.Li .xword
directive produces 64 bit values.
.El
.Pp
.Sh Reporting Bugs
Your bug reports play an essential role in making
.Xr as
reliable.
.Pp
Reporting a bug may help you by bringing a solution to your problem, or 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
.Xr as
work better. Bug reports are your contribution to the maintenance of
.Xr as .
.Pp
In order for a bug report to serve its purpose, you must include the information
that enables us to fix the bug.
.Pp
.Ss Have You Found a Bug?
If you are not sure whether you have found a bug, here are some guidelines:
.Pp
.Bl -bullet
.It
If the assembler gets a fatal signal, for any input whatever, that is a
.Xr as
bug. Reliable assemblers never crash.
.Pp
.It
If
.Xr as
produces an error message for valid input, that is a bug.
.Pp
.It
If
.Xr as
does not produce an error message for invalid input, that is a bug. However,
you should note that your idea of \(lqinvalid input\(rq might be our idea of \(lqan extension\(rq
or \(lqsupport for traditional practice\(rq.
.Pp
.It
If you are an experienced user of assemblers, your suggestions for improvement
of
.Xr as
are welcome in any case.
.El
.Pp
.Ss How to Report Bugs
A number of companies and individuals offer support for GNU products. If you
obtained
.Xr as
from a support organization, we recommend you contact that organization first.
.Pp
You can find contact information for many support companies and individuals
in the file
.Pa etc/SERVICE
in the GNU Emacs distribution.
.Pp
The fundamental principle of reporting bugs usefully is this:
.Sy report all the facts .
If you are not sure whether to state a fact or leave it out, state it!
.Pp
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.
.Pp
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.
.Pp
Sometimes people give a few sketchy facts and ask, \(lqDoes this ring a bell?\(rq
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.
.Pp
To enable us to fix the bug, you should include all these things:
.Pp
.Bl -bullet
.It
The version of
.Xr as .
.Xr as
announces it if you start it with the
.Li --version
argument.
.Pp
Without this, we will not know whether there is any point in looking for the
bug in the current version of
.Xr as .
.Pp
.It
Any patches you may have applied to the
.Xr as
source.
.Pp
.It
The type of machine you are using, and the operating system name and version
number.
.Pp
.It
What compiler (and its version) was used to compile
.Xr as
---e.g. \(lq
.Li gcc-2.7
\(rq\&.
.Pp
.It
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.
.Pp
If we were to try to guess the arguments, we would probably guess wrong and
then we might not encounter the bug.
.Pp
.It
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
.Li -S
option. If you are using
.Li gcc ,
use the options
.Li -v --save-temps ;
this will save the assembler source in a file with an extension of
.Pa .s ,
and also show you exactly how
.Xr as
is being run.
.Pp
.It
A description of what behavior you observe that you believe is incorrect.
For example, \(lqIt gets a fatal signal.\(rq
.Pp
Of course, if the bug is that
.Xr 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.
.Pp
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
.Xr 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.
.Pp
.It
If you wish to suggest changes to the
.Xr as
source, send us context diffs, as generated by
.Li diff
with the
.Li -u ,
.Li -c ,
or
.Li -p
option. Always send diffs from the old file to the new file. If you even discuss
something in the
.Xr as
source, refer to it by context, not by line number.
.Pp
The line numbers in our development sources will not match those in your sources.
Your line numbers would convey no useful information to us.
.El
.Pp
Here are some things that are not necessary:
.Pp
.Bl -bullet
.It
A description of the envelope of the bug.
.Pp
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.
.Pp
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.
.Pp
Of course, if you can find a simpler example to report
.Em 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.
.Pp
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.
.Pp
.It
A patch for the bug.
.Pp
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.
.Pp
Sometimes with a program as complicated as
.Xr 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.
.Pp
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.
.Pp
.It
A guess about what the bug is or what it depends on.
.Pp
Such guesses are usually wrong. Even we cannot guess right about such things
without first using the debugger to find the facts.
.El
.Pp
.Sh 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
.Li raeburn@cyGNUs.com ) .
.Pp
Dean Elsner wrote the original GNU assembler for the VAX.
.Pp
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
.Pa messages.c ,
.Pa input-file.c ,
.Pa write.c .
.Pp
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
\(lqknow\(rq assertions and made them work, much other reorganization, cleanup, and
lint.
.Pp
Ken Raeburn wrote the high-level BFD interface code to replace most of the
code in format-specific I/O modules.
.Pp
The original VMS support was contributed by David L. Kashtan. Eric Youngdale
has done much work with it since.
.Pp
The Intel 80386 machine description was written by Eliot Dresselhaus.
.Pp
Minh Tran-Le at IntelliCorp contributed some AIX 386 support.
.Pp
The Motorola 88k machine description was contributed by Devon Bowen of Buffalo
University and Torbjorn Granlund of the Swedish Institute of Computer Science.
.Pp
Keith Knowles at the Open Software Foundation wrote the original MIPS back
end (
.Pa tc-mips.c ,
.Pa 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.
.Pp
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.
.Pp
John Gilmore built the AMD 29000 support, added
.Li .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.,
.Li jsr ) ,
while synthetic instructions remained shrinkable (
.Li 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.
.Pp
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.
.Pp
Steve Chamberlain made GAS able to generate listings.
.Pp
Hewlett-Packard contributed support for the HP9000/300.
.Pp
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.
.Pp
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).
.Pp
Linas Vepstas added GAS support for the ESA/390 \(lqIBM 370\(rq architecture.
.Pp
Richard Henderson rewrote the Alpha assembler. Klaus Kaempf wrote GAS and
BFD support for openVMS/Alpha.
.Pp
Timothy Wall, Michael Hayes, and Greg Smart contributed to the various tic*
flavors.
.Pp
David Heine, Sterling Augustine, Bob Wilson and John Ruttenberg from Tensilica,
Inc. added support for Xtensa processors.
.Pp
Several engineers at CyGNUs Support have also provided many small bug fixes
and configuration enhancements.
.Pp
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.
.Pp
.Sh GNU Free Documentation License
.Bd -filled -offset indent
Copyright (C) 2000, 2003 Free Software Foundation, Inc. 51 Franklin Street,
Fifth Floor, Boston, MA 02110-1301 USA
.Pp
Everyone is permitted to copy and distribute verbatim copies of this license
document, but changing it is not allowed.
.Ed
.Pp
.Bl -enum
.It
PREAMBLE
.Pp
The purpose of this License is to make a manual, textbook, or other written
document \(lqfree\(rq in the sense of freedom: to assure everyone the effective freedom
to copy and redistribute it, with or without modifying it, either commercially
or noncommercially. Secondarily, this License preserves for the author and
publisher a way to get credit for their work, while not being considered responsible
for modifications made by others.
.Pp
This License is a kind of \(lqcopyleft\(rq, which means that derivative works of the
document must themselves be free in the same sense. It complements the GNU
General Public License, which is a copyleft license designed for free software.
.Pp
We have designed this License in order to use it for manuals for free software,
because free software needs free documentation: a free program should come
with manuals providing the same freedoms that the software does. But this
License is not limited to software manuals; it can be used for any textual
work, regardless of subject matter or whether it is published as a printed
book. We recommend this License principally for works whose purpose is instruction
or reference.
.Pp
.It
APPLICABILITY AND DEFINITIONS
.Pp
This License applies to any manual or other work that contains a notice placed
by the copyright holder saying it can be distributed under the terms of this
License. The \(lqDocument\(rq, below, refers to any such manual or work. Any member
of the public is a licensee, and is addressed as \(lqyou.\(rq
.Pp
A \(lqModified Version\(rq of the Document means any work containing the Document
or a portion of it, either copied verbatim, or with modifications and/or translated
into another language.
.Pp
A \(lqSecondary Section\(rq is a named appendix or a front-matter section of the Document
that deals exclusively with the relationship of the publishers or authors
of the Document to the Document's overall subject (or to related matters)
and contains nothing that could fall directly within that overall subject.
(For example, if the Document is in part a textbook of mathematics, a Secondary
Section may not explain any mathematics.) The relationship could be a matter
of historical connection with the subject or with related matters, or of legal,
commercial, philosophical, ethical or political position regarding them.
.Pp
The \(lqInvariant Sections\(rq are certain Secondary Sections whose titles are designated,
as being those of Invariant Sections, in the notice that says that the Document
is released under this License.
.Pp
The \(lqCover Texts\(rq are certain short passages of text that are listed, as Front-Cover
Texts or Back-Cover Texts, in the notice that says that the Document is released
under this License.
.Pp
A \(lqTransparent\(rq copy of the Document means a machine-readable copy, represented
in a format whose specification is available to the general public, whose
contents can be viewed and edited directly and straightforwardly with generic
text editors or (for images composed of pixels) generic paint programs or
(for drawings) some widely available drawing editor, and that is suitable
for input to text formatters or for automatic translation to a variety of
formats suitable for input to text formatters. A copy made in an otherwise
Transparent file format whose markup has been designed to thwart or discourage
subsequent modification by readers is not Transparent. A copy that is not
\(lqTransparent\(rq is called \(lqOpaque.\(rq
.Pp
Examples of suitable formats for Transparent copies include plain ASCII without
markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly
available DTD, and standard-conforming simple HTML designed for human modification.
Opaque formats include PostScript, PDF, proprietary formats that can be read
and edited only by proprietary word processors, SGML or XML for which the
DTD and/or processing tools are not generally available, and the machine-generated
HTML produced by some word processors for output purposes only.
.Pp
The \(lqTitle Page\(rq means, for a printed book, the title page itself, plus such
following pages as are needed to hold, legibly, the material this License
requires to appear in the title page. For works in formats which do not have
any title page as such, \(lqTitle Page\(rq means the text near the most prominent
appearance of the work's title, preceding the beginning of the body of the
text.
.Pp
.It
VERBATIM COPYING
.Pp
You may copy and distribute the Document in any medium, either commercially
or noncommercially, provided that this License, the copyright notices, and
the license notice saying this License applies to the Document are reproduced
in all copies, and that you add no other conditions whatsoever to those of
this License. You may not use technical measures to obstruct or control the
reading or further copying of the copies you make or distribute. However,
you may accept compensation in exchange for copies. If you distribute a large
enough number of copies you must also follow the conditions in section 3.
.Pp
You may also lend copies, under the same conditions stated above, and you
may publicly display copies.
.Pp
.It
COPYING IN QUANTITY
.Pp
If you publish printed copies of the Document numbering more than 100, and
the Document's license notice requires Cover Texts, you must enclose the copies
in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover
Texts on the front cover, and Back-Cover Texts on the back cover. Both covers
must also clearly and legibly identify you as the publisher of these copies.
The front cover must present the full title with all words of the title equally
prominent and visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve the title
of the Document and satisfy these conditions, can be treated as verbatim copying
in other respects.
.Pp
If the required texts for either cover are too voluminous to fit legibly,
you should put the first ones listed (as many as fit reasonably) on the actual
cover, and continue the rest onto adjacent pages.
.Pp
If you publish or distribute Opaque copies of the Document numbering more
than 100, you must either include a machine-readable Transparent copy along
with each Opaque copy, or state in or with each Opaque copy a publicly-accessible
computer-network location containing a complete Transparent copy of the Document,
free of added material, which the general network-using public has access
to download anonymously at no charge using public-standard network protocols.
If you use the latter option, you must take reasonably prudent steps, when
you begin distribution of Opaque copies in quantity, to ensure that this Transparent
copy will remain thus accessible at the stated location until at least one
year after the last time you distribute an Opaque copy (directly or through
your agents or retailers) of that edition to the public.
.Pp
It is requested, but not required, that you contact the authors of the Document
well before redistributing any large number of copies, to give them a chance
to provide you with an updated version of the Document.
.Pp
.It
MODIFICATIONS
.Pp
You may copy and distribute a Modified Version of the Document under the conditions
of sections 2 and 3 above, provided that you release the Modified Version
under precisely this License, with the Modified Version filling the role of
the Document, thus licensing distribution and modification of the Modified
Version to whoever possesses a copy of it. In addition, you must do these
things in the Modified Version:
.Pp
A. Use in the Title Page (and on the covers, if any) a title distinct from
that of the Document, and from those of previous versions (which should, if
there were any, be listed in the History section of the Document). You may
use the same title as a previous version if the original publisher of that
version gives permission. B. List on the Title Page, as authors, one or more
persons or entities responsible for authorship of the modifications in the
Modified Version, together with at least five of the principal authors of
the Document (all of its principal authors, if it has less than five). C.
State on the Title page the name of the publisher of the Modified Version,
as the publisher. D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications adjacent to
the other copyright notices. F. Include, immediately after the copyright
notices, a license notice giving the public permission to use the Modified
Version under the terms of this License, in the form shown in the Addendum
below. G. Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice. H. Include
an unaltered copy of this License. I. Preserve the section entitled \(lqHistory\(rq,
and its title, and add to it an item stating at least the title, year, new
authors, and publisher of the Modified Version as given on the Title Page.
If there is no section entitled \(lqHistory\(rq in the Document, create one stating
the title, year, authors, and publisher of the Document as given on its Title
Page, then add an item describing the Modified Version as stated in the previous
sentence. J. Preserve the network location, if any, given in the Document
for public access to a Transparent copy of the Document, and likewise the
network locations given in the Document for previous versions it was based
on. These may be placed in the \(lqHistory\(rq section. You may omit a network location
for a work that was published at least four years before the Document itself,
or if the original publisher of the version it refers to gives permission.
K. In any section entitled \(lqAcknowledgements\(rq or \(lqDedications\(rq, preserve the section's
title, and preserve in the section all the substance and tone of each of the
contributor acknowledgements and/or dedications given therein. L. Preserve
all the Invariant Sections of the Document, unaltered in their text and in
their titles. Section numbers or the equivalent are not considered part of
the section titles. M. Delete any section entitled \(lqEndorsements.\(rq Such a section
may not be included in the Modified Version. N. Do not retitle any existing
section as \(lqEndorsements\(rq or to conflict in title with any Invariant Section.
.Pp
If the Modified Version includes new front-matter sections or appendices that
qualify as Secondary Sections and contain no material copied from the Document,
you may at your option designate some or all of these sections as invariant.
To do this, add their titles to the list of Invariant Sections in the Modified
Version's license notice. These titles must be distinct from any other section
titles.
.Pp
You may add a section entitled \(lqEndorsements\(rq, provided it contains nothing
but endorsements of your Modified Version by various parties--for example,
statements of peer review or that the text has been approved by an organization
as the authoritative definition of a standard.
.Pp
You may add a passage of up to five words as a Front-Cover Text, and a passage
of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts
in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover
Text may be added by (or through arrangements made by) any one entity. If
the Document already includes a cover text for the same cover, previously
added by you or by arrangement made by the same entity you are acting on behalf
of, you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.
.Pp
The author(s) and publisher(s) of the Document do not by this License give
permission to use their names for publicity for or to assert or imply endorsement
of any Modified Version.
.Pp
.It
COMBINING DOCUMENTS
.Pp
You may combine the Document with other documents released under this License,
under the terms defined in section 4 above for modified versions, provided
that you include in the combination all of the Invariant Sections of all of
the original documents, unmodified, and list them all as Invariant Sections
of your combined work in its license notice.
.Pp
The combined work need only contain one copy of this License, and multiple
identical Invariant Sections may be replaced with a single copy. If there
are multiple Invariant Sections with the same name but different contents,
make the title of each such section unique by adding at the end of it, in
parentheses, the name of the original author or publisher of that section
if known, or else a unique number. Make the same adjustment to the section
titles in the list of Invariant Sections in the license notice of the combined
work.
.Pp
In the combination, you must combine any sections entitled \(lqHistory\(rq in the
various original documents, forming one section entitled \(lqHistory\(rq; likewise
combine any sections entitled \(lqAcknowledgements\(rq, and any sections entitled
\(lqDedications.\(rq You must delete all sections entitled \(lqEndorsements.\(rq
.Pp
.It
COLLECTIONS OF DOCUMENTS
.Pp
You may make a collection consisting of the Document and other documents released
under this License, and replace the individual copies of this License in the
various documents with a single copy that is included in the collection, provided
that you follow the rules of this License for verbatim copying of each of
the documents in all other respects.
.Pp
You may extract a single document from such a collection, and distribute it
individually under this License, provided you insert a copy of this License
into the extracted document, and follow this License in all other respects
regarding verbatim copying of that document.
.Pp
.It
AGGREGATION WITH INDEPENDENT WORKS
.Pp
A compilation of the Document or its derivatives with other separate and independent
documents or works, in or on a volume of a storage or distribution medium,
does not as a whole count as a Modified Version of the Document, provided
no compilation copyright is claimed for the compilation. Such a compilation
is called an \(lqaggregate\(rq, and this License does not apply to the other self-contained
works thus compiled with the Document, on account of their being thus compiled,
if they are not themselves derivative works of the Document.
.Pp
If the Cover Text requirement of section 3 is applicable to these copies of
the Document, then if the Document is less than one quarter of the entire
aggregate, the Document's Cover Texts may be placed on covers that surround
only the Document within the aggregate. Otherwise they must appear on covers
around the whole aggregate.
.Pp
.It
TRANSLATION
.Pp
Translation is considered a kind of modification, so you may distribute translations
of the Document under the terms of section 4. Replacing Invariant Sections
with translations requires special permission from their copyright holders,
but you may include translations of some or all Invariant Sections in addition
to the original versions of these Invariant Sections. You may include a translation
of this License provided that you also include the original English version
of this License. In case of a disagreement between the translation and the
original English version of this License, the original English version will
prevail.
.Pp
.It
TERMINATION
.Pp
You may not copy, modify, sublicense, or distribute the Document except as
expressly provided for under this License. Any other attempt to copy, modify,
sublicense or distribute the Document is void, and will automatically terminate
your rights under this License. However, parties who have received copies,
or rights, from you under this License will not have their licenses terminated
so long as such parties remain in full compliance.
.Pp
.It
FUTURE REVISIONS OF THIS LICENSE
.Pp
The Free Software Foundation may publish new, revised versions of the GNU
Free Documentation License from time to time. Such new versions will be similar
in spirit to the present version, but may differ in detail to address new
problems or concerns. See http://www.gnu.org/copyleft/.
.Pp
Each version of the License is given a distinguishing version number. If the
Document specifies that a particular numbered version of this License \(lqor any
later version\(rq applies to it, you have the option of following the terms and
conditions either of that specified version or of any later version that has
been published (not as a draft) by the Free Software Foundation. If the Document
does not specify a version number of this License, you may choose any version
ever published (not as a draft) by the Free Software Foundation.
.Pp
.El
.Ss ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the
License in the document and put the following copyright and license notices
just after the title page:
.Pp
.Bd -literal -offset indent
Copyright (C) year your name.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with the Invariant Sections being list their titles, with the
Front-Cover Texts being list, and with the Back-Cover Texts being list.
A copy of the license is included in the section entitled "GNU
Free Documentation License."
.Ed
.Pp
If you have no Invariant Sections, write \(lqwith no Invariant Sections\(rq instead
of saying which ones are invariant. If you have no Front-Cover Texts, write
\(lqno Front-Cover Texts\(rq instead of \(lqFront-Cover Texts being
.Va list
\(rq; likewise for Back-Cover Texts.
.Pp
If your document contains nontrivial examples of program code, we recommend
releasing these examples in parallel under your choice of free software license,
such as the GNU General Public License, to permit their use in free software.
.Pp
.Sh AS Index