File: as.info, Node: Top, Next: Overview, Up: (dir)
Using as
********
This file is a user guide to the GNU assembler `as' version 2.15.92.0.2.
This document is distributed under the terms of the GNU Free
Documentation License. A copy of the license is included in the
section entitled "GNU Free Documentation License".
* Menu:
* Overview:: Overview
* Invoking:: Command-Line Options
* Syntax:: Syntax
* Sections:: Sections and Relocation
* Symbols:: Symbols
* Expressions:: Expressions
* Pseudo Ops:: Assembler Directives
* Machine Dependencies:: Machine Dependent Features
* Reporting Bugs:: Reporting Bugs
* Acknowledgements:: Who Did What
* GNU Free Documentation License:: GNU Free Documentation License
* Index:: Index
File: as.info, Node: Overview, Next: Invoking, Prev: Top, Up: Top
1 Overview
**********
Here is a brief summary of how to invoke `as'. For details, *note
Command-Line Options: Invoking.
as [-a[cdhlns][=FILE]] [-alternate] [-D]
[-defsym SYM=VAL] [-f] [-g] [-gstabs] [-gstabs+]
[-gdwarf-2] [-help] [-I DIR] [-J] [-K] [-L]
[-listing-lhs-width=NUM] [-listing-lhs-width2=NUM]
[-listing-rhs-width=NUM] [-listing-cont-lines=NUM]
[-keep-locals] [-o OBJFILE] [-R] [-statistics] [-v]
[-version] [-version] [-W] [-warn] [-fatal-warnings]
[-w] [-x] [-Z] [-target-help] [TARGET-OPTIONS]
[-|FILES ...]
_Target Alpha options:_
[-mCPU]
[-mdebug | -no-mdebug]
[-relax] [-g] [-GSIZE]
[-F] [-32addr]
_Target ARC options:_
[-marc[5|6|7|8]]
[-EB|-EL]
_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] [-moabi] [-k]
_Target CRIS options:_
[-underscore | -no-underscore]
[-pic] [-N]
[-emulation=criself | -emulation=crisaout]
_Target D10V options:_
[-O]
_Target D30V options:_
[-O|-n|-N]
_Target i386 options:_
[-32|-64] [-n]
_Target i960 options:_
[-ACA|-ACA_A|-ACB|-ACC|-AKA|-AKB|
-AKC|-AMC]
[-b] [-no-relax]
_Target IA-64 options:_
[-mconstant-gp|-mauto-pic]
[-milp32|-milp64|-mlp64|-mp64]
[-mle|mbe]
[-mhint.b=ok|-mhint.b=warning|-mhint.b=error]
[-x|-xexplicit] [-xauto] [-xdebug]
_Target IP2K options:_
[-mip2022|-mip2022ext]
_Target M32R options:_
[-m32rx|-[no-]warn-explicit-parallel-conflicts|
-W[n]p]
_Target M680X0 options:_
[-l] [-m68000|-m68010|-m68020|...]
_Target M68HC11 options:_
[-m68hc11|-m68hc12|-m68hcs12]
[-mshort|-mlong]
[-mshort-double|-mlong-double]
[-force-long-branchs] [-short-branchs]
[-strict-direct-mode] [-print-insn-syntax]
[-print-opcodes] [-generate-example]
_Target MCORE options:_
[-jsri2bsr] [-sifilter] [-relax]
[-mcpu=[210|340]]
_Target MIPS options:_
[-nocpp] [-EL] [-EB] [-O[OPTIMIZATION LEVEL]]
[-g[DEBUG LEVEL]] [-G NUM] [-KPIC] [-call_shared]
[-non_shared] [-xgot]
[-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]
[-mips3d] [-no-mips3d]
[-mdmx] [-no-mdmx]
[-mdebug] [-no-mdebug]
[-mpdr] [-mno-pdr]
_Target MMIX options:_
[-fixed-special-register-names] [-globalize-symbols]
[-gnu-syntax] [-relax] [-no-predefined-symbols]
[-no-expand] [-no-merge-gregs] [-x]
[-linker-allocated-gregs]
_Target PDP11 options:_
[-mpic|-mno-pic] [-mall] [-mno-extensions]
[-mEXTENSION|-mno-EXTENSION]
[-mCPU] [-mMACHINE]
_Target picoJava options:_
[-mb|-me]
_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]
_Target TIC54X options:_
[-mcpu=54[123589]|-mcpu=54[56]lp] [-mfar-mode|-mf]
[-merrors-to-file <FILENAME>|-me <FILENAME>]
_Target Xtensa options:_
[-[no-]density] [-[no-]relax] [-[no-]generics]
[-[no-]text-section-literals]
[-[no-]target-align] [-[no-]longcalls]
`-a[cdhlmns]'
Turn on listings, in any of a variety of ways:
`-ac'
omit false conditionals
`-ad'
omit debugging directives
`-ah'
include high-level source
`-al'
include assembly
`-am'
include macro expansions
`-an'
omit forms processing
`-as'
include symbols
`=file'
set the name of the listing file
You may combine these options; for example, use `-aln' for assembly
listing without forms processing. The `=file' option, if used,
must be the last one. By itself, `-a' defaults to `-ahls'.
`--alternate'
Begin in alternate macro mode, see *Note `.altmacro': Altmacro.
`-D'
Ignored. This option is accepted for script compatibility with
calls to other assemblers.
`--defsym SYM=VALUE'
Define the symbol SYM to be VALUE before assembling the input file.
VALUE must be an integer constant. As in C, a leading `0x'
indicates a hexadecimal value, and a leading `0' indicates an
octal value.
`-f'
"fast"--skip whitespace and comment preprocessing (assume source is
compiler output).
`-g'
`--gen-debug'
Generate debugging information for each assembler source line
using whichever debug format is preferred by the target. This
currently means either STABS, ECOFF or DWARF2.
`--gstabs'
Generate stabs debugging information for each assembler line. This
may help debugging assembler code, if the debugger can handle it.
`--gstabs+'
Generate stabs debugging information for each assembler line, with
GNU extensions that probably only gdb can handle, and that could
make other debuggers crash or refuse to read your program. This
may help debugging assembler code. Currently the only GNU
extension is the location of the current working directory at
assembling time.
`--gdwarf-2'
Generate DWARF2 debugging information for each assembler line.
This may help debugging assembler code, if the debugger can handle
it. Note--this option is only supported by some targets, not all
of them.
`--help'
Print a summary of the command line options and exit.
`--target-help'
Print a summary of all target specific options and exit.
`-I DIR'
Add directory DIR to the search list for `.include' directives.
`-J'
Don't warn about signed overflow.
`-K'
Issue warnings when difference tables altered for long
displacements.
`-L'
`--keep-locals'
Keep (in the symbol table) local symbols. On traditional a.out
systems these start with `L', but different systems have different
local label prefixes.
`--listing-lhs-width=NUMBER'
Set the maximum width, in words, of the output data column for an
assembler listing to NUMBER.
`--listing-lhs-width2=NUMBER'
Set the maximum width, in words, of the output data column for
continuation lines in an assembler listing to NUMBER.
`--listing-rhs-width=NUMBER'
Set the maximum width of an input source line, as displayed in a
listing, to NUMBER bytes.
`--listing-cont-lines=NUMBER'
Set the maximum number of lines printed in a listing for a single
line of input to NUMBER + 1.
`-o OBJFILE'
Name the object-file output from `as' OBJFILE.
`-R'
Fold the data section into the text section.
`--statistics'
Print the maximum space (in bytes) and total time (in seconds)
used by assembly.
`--strip-local-absolute'
Remove local absolute symbols from the outgoing symbol table.
`-v'
`-version'
Print the `as' version.
`--version'
Print the `as' version and exit.
`-W'
`--no-warn'
Suppress warning messages.
`--fatal-warnings'
Treat warnings as errors.
`--warn'
Don't suppress warning messages or treat them as errors.
`-w'
Ignored.
`-x'
Ignored.
`-Z'
Generate an object file even after errors.
`-- | FILES ...'
Standard input, or source files to assemble.
The following options are available when as is configured for an ARC
processor.
`-marc[5|6|7|8]'
This option selects the core processor variant.
`-EB | -EL'
Select either big-endian (-EB) or little-endian (-EL) output.
The following options are available when as is configured for the ARM
processor family.
`-mcpu=PROCESSOR[+EXTENSION...]'
Specify which ARM processor variant is the target.
`-march=ARCHITECTURE[+EXTENSION...]'
Specify which ARM architecture variant is used by the target.
`-mfpu=FLOATING-POINT-FORMAT'
Select which Floating Point architecture is the target.
`-mfloat-abi=ABI'
Select which floating point ABI is in use.
`-mthumb'
Enable Thumb only instruction decoding.
`-mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant | -moabi'
Select which procedure calling convention is in use.
`-EB | -EL'
Select either big-endian (-EB) or little-endian (-EL) output.
`-mthumb-interwork'
Specify that the code has been generated with interworking between
Thumb and ARM code in mind.
`-k'
Specify that PIC code has been generated.
See the info pages for documentation of the CRIS-specific options.
The following options are available when as is configured for a D10V
processor.
`-O'
Optimize output by parallelizing instructions.
The following options are available when as is configured for a D30V
processor.
`-O'
Optimize output by parallelizing instructions.
`-n'
Warn when nops are generated.
`-N'
Warn when a nop after a 32-bit multiply instruction is generated.
The following options are available when as is configured for the
Intel 80960 processor.
`-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC'
Specify which variant of the 960 architecture is the target.
`-b'
Add code to collect statistics about branches taken.
`-no-relax'
Do not alter compare-and-branch instructions for long
displacements; error if necessary.
The following options are available when as is configured for the
Ubicom IP2K series.
`-mip2022ext'
Specifies that the extended IP2022 instructions are allowed.
`-mip2022'
Restores the default behaviour, which restricts the permitted
instructions to just the basic IP2022 ones.
The following options are available when as is configured for the
Renesas M32R (formerly Mitsubishi M32R) series.
`--m32rx'
Specify which processor in the M32R family is the target. The
default is normally the M32R, but this option changes it to the
M32RX.
`--warn-explicit-parallel-conflicts or --Wp'
Produce warning messages when questionable parallel constructs are
encountered.
`--no-warn-explicit-parallel-conflicts or --Wnp'
Do not produce warning messages when questionable parallel
constructs are encountered.
The following options are available when as is configured for the
Motorola 68000 series.
`-l'
Shorten references to undefined symbols, to one word instead of
two.
`-m68000 | -m68008 | -m68010 | -m68020 | -m68030'
`| -m68040 | -m68060 | -m68302 | -m68331 | -m68332'
`| -m68333 | -m68340 | -mcpu32 | -m5200'
Specify what processor in the 68000 family is the target. The
default is normally the 68020, but this can be changed at
configuration time.
`-m68881 | -m68882 | -mno-68881 | -mno-68882'
The target machine does (or does not) have a floating-point
coprocessor. The default is to assume a coprocessor for 68020,
68030, and cpu32. Although the basic 68000 is not compatible with
the 68881, a combination of the two can be specified, since it's
possible to do emulation of the coprocessor instructions with the
main processor.
`-m68851 | -mno-68851'
The target machine does (or does not) have a memory-management
unit coprocessor. The default is to assume an MMU for 68020 and
up.
For details about the PDP-11 machine dependent features options, see
*Note PDP-11-Options::.
`-mpic | -mno-pic'
Generate position-independent (or position-dependent) code. The
default is `-mpic'.
`-mall'
`-mall-extensions'
Enable all instruction set extensions. This is the default.
`-mno-extensions'
Disable all instruction set extensions.
`-mEXTENSION | -mno-EXTENSION'
Enable (or disable) a particular instruction set extension.
`-mCPU'
Enable the instruction set extensions supported by a particular
CPU, and disable all other extensions.
`-mMACHINE'
Enable the instruction set extensions supported by a particular
machine model, and disable all other extensions.
The following options are available when as is configured for a
picoJava processor.
`-mb'
Generate "big endian" format output.
`-ml'
Generate "little endian" format output.
The following options are available when as is configured for the
Motorola 68HC11 or 68HC12 series.
`-m68hc11 | -m68hc12 | -m68hcs12'
Specify what processor is the target. The default is defined by
the configuration option when building the assembler.
`-mshort'
Specify to use the 16-bit integer ABI.
`-mlong'
Specify to use the 32-bit integer ABI.
`-mshort-double'
Specify to use the 32-bit double ABI.
`-mlong-double'
Specify to use the 64-bit double ABI.
`--force-long-branchs'
Relative branches are turned into absolute ones. This concerns
conditional branches, unconditional branches and branches to a sub
routine.
`-S | --short-branchs'
Do not turn relative branchs into absolute ones when the offset is
out of range.
`--strict-direct-mode'
Do not turn the direct addressing mode into extended addressing
mode when the instruction does not support direct addressing mode.
`--print-insn-syntax'
Print the syntax of instruction in case of error.
`--print-opcodes'
print the list of instructions with syntax and then exit.
`--generate-example'
print an example of instruction for each possible instruction and
then exit. This option is only useful for testing `as'.
The following options are available when `as' is configured for the
SPARC architecture:
`-Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite'
`-Av8plus | -Av8plusa | -Av9 | -Av9a'
Explicitly select a variant of the SPARC architecture.
`-Av8plus' and `-Av8plusa' select a 32 bit environment. `-Av9'
and `-Av9a' select a 64 bit environment.
`-Av8plusa' and `-Av9a' enable the SPARC V9 instruction set with
UltraSPARC extensions.
`-xarch=v8plus | -xarch=v8plusa'
For compatibility with the Solaris v9 assembler. These options are
equivalent to -Av8plus and -Av8plusa, respectively.
`-bump'
Warn when the assembler switches to another architecture.
The following options are available when as is configured for the
'c54x architecture.
`-mfar-mode'
Enable extended addressing mode. All addresses and relocations
will assume extended addressing (usually 23 bits).
`-mcpu=CPU_VERSION'
Sets the CPU version being compiled for.
`-merrors-to-file FILENAME'
Redirect error output to a file, for broken systems which don't
support such behaviour in the shell.
The following options are available when as is configured for a MIPS
processor.
`-G NUM'
This option sets the largest size of an object that can be
referenced implicitly with the `gp' register. It is only accepted
for targets that use ECOFF format, such as a DECstation running
Ultrix. The default value is 8.
`-EB'
Generate "big endian" format output.
`-EL'
Generate "little endian" format output.
`-mips1'
`-mips2'
`-mips3'
`-mips4'
`-mips5'
`-mips32'
`-mips32r2'
`-mips64'
`-mips64r2'
Generate code for a particular MIPS Instruction Set Architecture
level. `-mips1' is an alias for `-march=r3000', `-mips2' is an
alias for `-march=r6000', `-mips3' is an alias for `-march=r4000'
and `-mips4' is an alias for `-march=r8000'. `-mips5', `-mips32',
`-mips32r2', `-mips64', and `-mips64r2' correspond to generic
`MIPS V', `MIPS32', `MIPS32 Release 2', `MIPS64', and `MIPS64
Release 2' ISA processors, respectively.
`-march=CPU'
Generate code for a particular MIPS cpu.
`-mtune=CPU'
Schedule and tune for a particular MIPS cpu.
`-mfix7000'
`-mno-fix7000'
Cause nops to be inserted if the read of the destination register
of an mfhi or mflo instruction occurs in the following two
instructions.
`-mdebug'
`-no-mdebug'
Cause stabs-style debugging output to go into an ECOFF-style
.mdebug section instead of the standard ELF .stabs sections.
`-mpdr'
`-mno-pdr'
Control generation of `.pdr' sections.
`-mgp32'
`-mfp32'
The register sizes are normally inferred from the ISA and ABI, but
these flags force a certain group of registers to be treated as 32
bits wide at all times. `-mgp32' controls the size of
general-purpose registers and `-mfp32' controls the size of
floating-point registers.
`-mips16'
`-no-mips16'
Generate code for the MIPS 16 processor. This is equivalent to
putting `.set mips16' at the start of the assembly file.
`-no-mips16' turns off this option.
`-mips3d'
`-no-mips3d'
Generate code for the MIPS-3D Application Specific Extension.
This tells the assembler to accept MIPS-3D instructions.
`-no-mips3d' turns off this option.
`-mdmx'
`-no-mdmx'
Generate code for the MDMX Application Specific Extension. This
tells the assembler to accept MDMX instructions. `-no-mdmx' turns
off this option.
`--construct-floats'
`--no-construct-floats'
The `--no-construct-floats' option disables the construction of
double width floating point constants by loading the two halves of
the value into the two single width floating point registers that
make up the double width register. By default
`--construct-floats' is selected, allowing construction of these
floating point constants.
`--emulation=NAME'
This option causes `as' to emulate `as' configured for some other
target, in all respects, including output format (choosing between
ELF and ECOFF only), handling of pseudo-opcodes which may generate
debugging information or store symbol table information, and
default endianness. The available configuration names are:
`mipsecoff', `mipself', `mipslecoff', `mipsbecoff', `mipslelf',
`mipsbelf'. The first two do not alter the default endianness
from that of the primary target for which the assembler was
configured; the others change the default to little- or big-endian
as indicated by the `b' or `l' in the name. Using `-EB' or `-EL'
will override the endianness selection in any case.
This option is currently supported only when the primary target
`as' is configured for is a MIPS ELF or ECOFF target.
Furthermore, the primary target or others specified with
`--enable-targets=...' at configuration time must include support
for the other format, if both are to be available. For example,
the Irix 5 configuration includes support for both.
Eventually, this option will support more configurations, with more
fine-grained control over the assembler's behavior, and will be
supported for more processors.
`-nocpp'
`as' ignores this option. It is accepted for compatibility with
the native tools.
`--trap'
`--no-trap'
`--break'
`--no-break'
Control how to deal with multiplication overflow and division by
zero. `--trap' or `--no-break' (which are synonyms) take a trap
exception (and only work for Instruction Set Architecture level 2
and higher); `--break' or `--no-trap' (also synonyms, and the
default) take a break exception.
`-n'
When this option is used, `as' will issue a warning every time it
generates a nop instruction from a macro.
The following options are available when as is configured for an
MCore processor.
`-jsri2bsr'
`-nojsri2bsr'
Enable or disable the JSRI to BSR transformation. By default this
is enabled. The command line option `-nojsri2bsr' can be used to
disable it.
`-sifilter'
`-nosifilter'
Enable or disable the silicon filter behaviour. By default this
is disabled. The default can be overridden by the `-sifilter'
command line option.
`-relax'
Alter jump instructions for long displacements.
`-mcpu=[210|340]'
Select the cpu type on the target hardware. This controls which
instructions can be assembled.
`-EB'
Assemble for a big endian target.
`-EL'
Assemble for a little endian target.
See the info pages for documentation of the MMIX-specific options.
The following options are available when as is configured for an
Xtensa processor.
`--density | --no-density'
Enable or disable use of instructions from the Xtensa code density
option. This is enabled by default when the Xtensa processor
supports the code density option.
`--relax | --no-relax'
Enable or disable instruction relaxation. This is enabled by
default. Note: In the current implementation, these options also
control whether assembler optimizations are performed, making
these options equivalent to `--generics' and `--no-generics'.
`--generics | --no-generics'
Enable or disable all assembler transformations of Xtensa
instructions. The default is `--generics'; `--no-generics' should
be used only in the rare cases when the instructions must be
exactly as specified in the assembly source.
`--text-section-literals | --no-text-section-literals'
With `--text-section-literals', literal pools are interspersed in
the text section. The default is `--no-text-section-literals',
which places literals in a separate section in the output file.
`--target-align | --no-target-align'
Enable or disable automatic alignment to reduce branch penalties
at the expense of some code density. The default is
`--target-align'.
`--longcalls | --no-longcalls'
Enable or disable transformation of call instructions to allow
calls across a greater range of addresses. The default is
`--no-longcalls'.
* Menu:
* Manual:: Structure of this Manual
* GNU Assembler:: The GNU Assembler
* Object Formats:: Object File Formats
* Command Line:: Command Line
* Input Files:: Input Files
* Object:: Output (Object) File
* Errors:: Error and Warning Messages
File: as.info, Node: Manual, Next: GNU Assembler, Up: Overview
1.1 Structure of this Manual
============================
This manual is intended to describe what you need to know to use GNU
`as'. We cover the syntax expected in source files, including notation
for symbols, constants, and expressions; the directives that `as'
understands; and of course how to invoke `as'.
This manual also describes some of the machine-dependent features of
various flavors of the assembler.
On the other hand, this manual is _not_ intended as an introduction
to programming in assembly language--let alone programming in general!
In a similar vein, we make no attempt to introduce the machine
architecture; we do _not_ describe the instruction set, standard
mnemonics, registers or addressing modes that are standard to a
particular architecture. You may want to consult the manufacturer's
machine architecture manual for this information.
File: as.info, Node: GNU Assembler, Next: Object Formats, Prev: Manual, Up: Overview
1.2 The GNU Assembler
=====================
GNU `as' is really a family of assemblers. If you use (or have used)
the GNU assembler on one architecture, you should find a fairly similar
environment when you use it on another architecture. Each version has
much in common with the others, including object file formats, most
assembler directives (often called "pseudo-ops") and assembler syntax.
`as' is primarily intended to assemble the output of the GNU C
compiler `gcc' for use by the linker `ld'. Nevertheless, we've tried
to make `as' assemble correctly everything that other assemblers for
the same machine would assemble. Any exceptions are documented
explicitly (*note Machine Dependencies::). This doesn't mean `as'
always uses the same syntax as another assembler for the same
architecture; for example, we know of several incompatible versions of
680x0 assembly language syntax.
Unlike older assemblers, `as' is designed to assemble a source
program in one pass of the source file. This has a subtle impact on the
`.org' directive (*note `.org': Org.).
File: as.info, Node: Object Formats, Next: Command Line, Prev: GNU Assembler, Up: Overview
1.3 Object File Formats
=======================
The GNU assembler can be configured to produce several alternative
object file formats. For the most part, this does not affect how you
write assembly language programs; but directives for debugging symbols
are typically different in different file formats. *Note Symbol
Attributes: Symbol Attributes.
File: as.info, Node: Command Line, Next: Input Files, Prev: Object Formats, Up: Overview
1.4 Command Line
================
After the program name `as', the command line may contain options and
file names. Options may appear in any order, and may be before, after,
or between file names. The order of file names is significant.
`--' (two hyphens) by itself names the standard input file
explicitly, as one of the files for `as' to assemble.
Except for `--' any command line argument that begins with a hyphen
(`-') is an option. Each option changes the behavior of `as'. No
option changes the way another option works. An option is a `-'
followed by one or more letters; the case of the letter is important.
All options are optional.
Some options expect exactly one file name to follow them. The file
name may either immediately follow the option's letter (compatible with
older assemblers) or it may be the next command argument (GNU
standard). These two command lines are equivalent:
as -o my-object-file.o mumble.s
as -omy-object-file.o mumble.s
File: as.info, Node: Input Files, Next: Object, Prev: Command Line, Up: Overview
1.5 Input Files
===============
We use the phrase "source program", abbreviated "source", to describe
the program input to one run of `as'. The program may be in one or
more files; how the source is partitioned into files doesn't change the
meaning of the source.
The source program is a concatenation of the text in all the files,
in the order specified.
Each time you run `as' it assembles exactly one source program. The
source program is made up of one or more files. (The standard input is
also a file.)
You give `as' a command line that has zero or more input file names.
The input files are read (from left file name to right). A command
line argument (in any position) that has no special meaning is taken to
be an input file name.
If you give `as' no file names it attempts to read one input file
from the `as' standard input, which is normally your terminal. You may
have to type <ctl-D> to tell `as' there is no more program to assemble.
Use `--' if you need to explicitly name the standard input file in
your command line.
If the source is empty, `as' produces a small, empty object file.
Filenames and Line-numbers
--------------------------
There are two ways of locating a line in the input file (or files) and
either may be used in reporting error messages. One way refers to a
line number in a physical file; the other refers to a line number in a
"logical" file. *Note Error and Warning Messages: Errors.
"Physical files" are those files named in the command line given to
`as'.
"Logical files" are simply names declared explicitly by assembler
directives; they bear no relation to physical files. Logical file
names help error messages reflect the original source file, when `as'
source is itself synthesized from other files. `as' understands the
`#' directives emitted by the `gcc' preprocessor. See also *Note
`.file': File.
File: as.info, Node: Object, Next: Errors, Prev: Input Files, Up: Overview
1.6 Output (Object) File
========================
Every time you run `as' it produces an output file, which is your
assembly language program translated into numbers. This file is the
object file. Its default name is `a.out', or `b.out' when `as' is
configured for the Intel 80960. You can give it another name by using
the `-o' option. Conventionally, object file names end with `.o'. The
default name is used for historical reasons: older assemblers were
capable of assembling self-contained programs directly into a runnable
program. (For some formats, this isn't currently possible, but it can
be done for the `a.out' format.)
The object file is meant for input to the linker `ld'. It contains
assembled program code, information to help `ld' integrate the
assembled program into a runnable file, and (optionally) symbolic
information for the debugger.
File: as.info, Node: Errors, Prev: Object, Up: Overview
1.7 Error and Warning Messages
==============================
`as' may write warnings and error messages to the standard error file
(usually your terminal). This should not happen when a compiler runs
`as' automatically. Warnings report an assumption made so that `as'
could keep assembling a flawed program; errors report a grave problem
that stops the assembly.
Warning messages have the format
file_name:NNN:Warning Message Text
(where NNN is a line number). If a logical file name has been given
(*note `.file': File.) it is used for the filename, otherwise the name
of the current input file is used. If a logical line number was given
(*note `.line': Line.) then it is used to calculate the number printed,
otherwise the actual line in the current source file is printed. The
message text is intended to be self explanatory (in the grand Unix
tradition).
Error messages have the format
file_name:NNN:FATAL:Error Message Text
The file name and line number are derived as for warning messages.
The actual message text may be rather less explanatory because many of
them aren't supposed to happen.
File: as.info, Node: Invoking, Next: Syntax, Prev: Overview, Up: Top
2 Command-Line Options
**********************
This chapter describes command-line options available in _all_ versions
of the GNU assembler; *note Machine Dependencies::, for options specific
to particular machine architectures.
If you are invoking `as' via the GNU C compiler, you can use the
`-Wa' option to pass arguments through to the assembler. The assembler
arguments must be separated from each other (and the `-Wa') by commas.
For example:
gcc -c -g -O -Wa,-alh,-L file.c
This passes two options to the assembler: `-alh' (emit a listing to
standard output with high-level and assembly source) and `-L' (retain
local symbols in the symbol table).
Usually you do not need to use this `-Wa' mechanism, since many
compiler command-line options are automatically passed to the assembler
by the compiler. (You can call the GNU compiler driver with the `-v'
option to see precisely what options it passes to each compilation
pass, including the assembler.)
* Menu:
* a:: -a[cdhlns] enable listings
* alternate:: --alternate enable alternate macro syntax
* D:: -D for compatibility
* f:: -f to work faster
* I:: -I for .include search path
* K:: -K for difference tables
* L:: -L to retain local labels
* listing:: --listing-XXX to configure listing output
* M:: -M or --mri to assemble in MRI compatibility mode
* MD:: --MD for dependency tracking
* o:: -o to name the object file
* R:: -R to join data and text sections
* statistics:: --statistics to see statistics about assembly
* traditional-format:: --traditional-format for compatible output
* v:: -v to announce version
* W:: -W, --no-warn, --warn, --fatal-warnings to control warnings
* Z:: -Z to make object file even after errors
File: as.info, Node: a, Next: alternate, Up: Invoking
2.1 Enable Listings: `-a[cdhlns]'
=================================
These options enable listing output from the assembler. By itself,
`-a' requests high-level, assembly, and symbols listing. You can use
other letters to select specific options for the list: `-ah' requests a
high-level language listing, `-al' requests an output-program assembly
listing, and `-as' requests a symbol table listing. High-level
listings require that a compiler debugging option like `-g' be used,
and that assembly listings (`-al') be requested also.
Use the `-ac' option to omit false conditionals from a listing. Any
lines which are not assembled because of a false `.if' (or `.ifdef', or
any other conditional), or a true `.if' followed by an `.else', will be
omitted from the listing.
Use the `-ad' option to omit debugging directives from the listing.
Once you have specified one of these options, you can further control
listing output and its appearance using the directives `.list',
`.nolist', `.psize', `.eject', `.title', and `.sbttl'. The `-an'
option turns off all forms processing. If you do not request listing
output with one of the `-a' options, the listing-control directives
have no effect.
The letters after `-a' may be combined into one option, _e.g._,
`-aln'.
Note if the assembler source is coming from the standard input (eg
because it is being created by `gcc' and the `-pipe' command line switch
is being used) then the listing will not contain any comments or
preprocessor directives. This is because the listing code buffers
input source lines from stdin only after they have been preprocessed by
the assembler. This reduces memory usage and makes the code more
efficient.
File: as.info, Node: alternate, Next: D, Prev: a, Up: Invoking
2.2 `--alternate'
=================
Begin in alternate macro mode, see *Note `.altmacro': Altmacro.
File: as.info, Node: D, Next: f, Prev: alternate, Up: Invoking
2.3 `-D'
========
This option has no effect whatsoever, but it is accepted to make it more
likely that scripts written for other assemblers also work with `as'.
File: as.info, Node: f, Next: I, Prev: D, Up: Invoking
2.4 Work Faster: `-f'
=====================
`-f' should only be used when assembling programs written by a
(trusted) compiler. `-f' stops the assembler from doing whitespace and
comment preprocessing on the input file(s) before assembling them.
*Note Preprocessing: Preprocessing.
_Warning:_ if you use `-f' when the files actually need to be
preprocessed (if they contain comments, for example), `as' does
not work correctly.
File: as.info, Node: I, Next: K, Prev: f, Up: Invoking
2.5 `.include' Search Path: `-I' PATH
=====================================
Use this option to add a PATH to the list of directories `as' searches
for files specified in `.include' directives (*note `.include':
Include.). You may use `-I' as many times as necessary to include a
variety of paths. The current working directory is always searched
first; after that, `as' searches any `-I' directories in the same order
as they were specified (left to right) on the command line.
File: as.info, Node: K, Next: L, Prev: I, Up: Invoking
2.6 Difference Tables: `-K'
===========================
`as' sometimes alters the code emitted for directives of the form
`.word SYM1-SYM2'; *note `.word': Word. You can use the `-K' option if
you want a warning issued when this is done.
File: as.info, Node: L, Next: listing, Prev: K, Up: Invoking
2.7 Include Local Labels: `-L'
==============================
Labels beginning with `L' (upper case only) are called "local labels".
*Note Symbol Names::. Normally you do not see such labels when
debugging, because they are intended for the use of programs (like
compilers) that compose assembler programs, not for your notice.
Normally both `as' and `ld' discard such labels, so you do not normally
debug with them.
This option tells `as' to retain those `L...' symbols in the object
file. Usually if you do this you also tell the linker `ld' to preserve
symbols whose names begin with `L'.
By default, a local label is any label beginning with `L', but each
target is allowed to redefine the local label prefix. On the HPPA
local labels begin with `L$'.
File: as.info, Node: listing, Next: M, Prev: L, Up: Invoking
2.8 Configuring listing output: `--listing'
===========================================
The listing feature of the assembler can be enabled via the command
line switch `-a' (*note a::). This feature combines the input source
file(s) with a hex dump of the corresponding locations in the output
object file, and displays them as a listing file. The format of this
listing can be controlled by pseudo ops inside the assembler source
(*note List:: *note Title:: *note Sbttl:: *note Psize:: *note Eject::)
and also by the following switches:
`--listing-lhs-width=`number''
Sets the maximum width, in words, of the first line of the hex
byte dump. This dump appears on the left hand side of the listing
output.
`--listing-lhs-width2=`number''
Sets the maximum width, in words, of any further lines of the hex
byte dump for a given input source line. If this value is not
specified, it defaults to being the same as the value specified
for `--listing-lhs-width'. If neither switch is used the default
is to one.
`--listing-rhs-width=`number''
Sets the maximum width, in characters, of the source line that is
displayed alongside the hex dump. The default value for this
parameter is 100. The source line is displayed on the right hand
side of the listing output.
`--listing-cont-lines=`number''
Sets the maximum number of continuation lines of hex dump that
will be displayed for a given single line of source input. The
default value is 4.
File: as.info, Node: M, Next: MD, Prev: listing, Up: Invoking
2.9 Assemble in MRI Compatibility Mode: `-M'
============================================
The `-M' or `--mri' option selects MRI compatibility mode. This
changes the syntax and pseudo-op handling of `as' to make it compatible
with the `ASM68K' or the `ASM960' (depending upon the configured
target) assembler from Microtec Research. The exact nature of the MRI
syntax will not be documented here; see the MRI manuals for more
information. Note in particular that the handling of macros and macro
arguments is somewhat different. The purpose of this option is to
permit assembling existing MRI assembler code using `as'.
The MRI compatibility is not complete. Certain operations of the
MRI assembler depend upon its object file format, and can not be
supported using other object file formats. Supporting these would
require enhancing each object file format individually. These are:
* global symbols in common section
The m68k MRI assembler supports common sections which are merged
by the linker. Other object file formats do not support this.
`as' handles common sections by treating them as a single common
symbol. It permits local symbols to be defined within a common
section, but it can not support global symbols, since it has no
way to describe them.
* complex relocations
The MRI assemblers support relocations against a negated section
address, and relocations which combine the start addresses of two
or more sections. These are not support by other object file
formats.
* `END' pseudo-op specifying start address
The MRI `END' pseudo-op permits the specification of a start
address. This is not supported by other object file formats. The
start address may instead be specified using the `-e' option to
the linker, or in a linker script.
* `IDNT', `.ident' and `NAME' pseudo-ops
The MRI `IDNT', `.ident' and `NAME' pseudo-ops assign a module
name to the output file. This is not supported by other object
file formats.
* `ORG' pseudo-op
The m68k MRI `ORG' pseudo-op begins an absolute section at a given
address. This differs from the usual `as' `.org' pseudo-op, which
changes the location within the current section. Absolute
sections are not supported by other object file formats. The
address of a section may be assigned within a linker script.
There are some other features of the MRI assembler which are not
supported by `as', typically either because they are difficult or
because they seem of little consequence. Some of these may be
supported in future releases.
* EBCDIC strings
EBCDIC strings are not supported.
* packed binary coded decimal
Packed binary coded decimal is not supported. This means that the
`DC.P' and `DCB.P' pseudo-ops are not supported.
* `FEQU' pseudo-op
The m68k `FEQU' pseudo-op is not supported.
* `NOOBJ' pseudo-op
The m68k `NOOBJ' pseudo-op is not supported.
* `OPT' branch control options
The m68k `OPT' branch control options--`B', `BRS', `BRB', `BRL',
and `BRW'--are ignored. `as' automatically relaxes all branches,
whether forward or backward, to an appropriate size, so these
options serve no purpose.
* `OPT' list control options
The following m68k `OPT' list control options are ignored: `C',
`CEX', `CL', `CRE', `E', `G', `I', `M', `MEX', `MC', `MD', `X'.
* other `OPT' options
The following m68k `OPT' options are ignored: `NEST', `O', `OLD',
`OP', `P', `PCO', `PCR', `PCS', `R'.
* `OPT' `D' option is default
The m68k `OPT' `D' option is the default, unlike the MRI assembler.
`OPT NOD' may be used to turn it off.
* `XREF' pseudo-op.
The m68k `XREF' pseudo-op is ignored.
* `.debug' pseudo-op
The i960 `.debug' pseudo-op is not supported.
* `.extended' pseudo-op
The i960 `.extended' pseudo-op is not supported.
* `.list' pseudo-op.
The various options of the i960 `.list' pseudo-op are not
supported.
* `.optimize' pseudo-op
The i960 `.optimize' pseudo-op is not supported.
* `.output' pseudo-op
The i960 `.output' pseudo-op is not supported.
* `.setreal' pseudo-op
The i960 `.setreal' pseudo-op is not supported.
File: as.info, Node: MD, Next: o, Prev: M, Up: Invoking
2.10 Dependency Tracking: `--MD'
================================
`as' can generate a dependency file for the file it creates. This file
consists of a single rule suitable for `make' describing the
dependencies of the main source file.
The rule is written to the file named in its argument.
This feature is used in the automatic updating of makefiles.
File: as.info, Node: o, Next: R, Prev: MD, Up: Invoking
2.11 Name the Object File: `-o'
===============================
There is always one object file output when you run `as'. By default
it has the name `a.out' (or `b.out', for Intel 960 targets only). You
use this option (which takes exactly one filename) to give the object
file a different name.
Whatever the object file is called, `as' overwrites any existing
file of the same name.
File: as.info, Node: R, Next: statistics, Prev: o, Up: Invoking
2.12 Join Data and Text Sections: `-R'
======================================
`-R' tells `as' to write the object file as if all data-section data
lives in the text section. This is only done at the very last moment:
your binary data are the same, but data section parts are relocated
differently. The data section part of your object file is zero bytes
long because all its bytes are appended to the text section. (*Note
Sections and Relocation: Sections.)
When you specify `-R' it would be possible to generate shorter
address displacements (because we do not have to cross between text and
data section). We refrain from doing this simply for compatibility with
older versions of `as'. In future, `-R' may work this way.
When `as' is configured for COFF or ELF output, this option is only
useful if you use sections named `.text' and `.data'.
`-R' is not supported for any of the HPPA targets. Using `-R'
generates a warning from `as'.
File: as.info, Node: statistics, Next: traditional-format, Prev: R, Up: Invoking
2.13 Display Assembly Statistics: `--statistics'
================================================
Use `--statistics' to display two statistics about the resources used by
`as': the maximum amount of space allocated during the assembly (in
bytes), and the total execution time taken for the assembly (in CPU
seconds).
File: as.info, Node: traditional-format, Next: v, Prev: statistics, Up: Invoking
2.14 Compatible Output: `--traditional-format'
==============================================
For some targets, the output of `as' is different in some ways from the
output of some existing assembler. This switch requests `as' to use
the traditional format instead.
For example, it disables the exception frame optimizations which
`as' normally does by default on `gcc' output.
File: as.info, Node: v, Next: W, Prev: traditional-format, Up: Invoking
2.15 Announce Version: `-v'
===========================
You can find out what version of as is running by including the option
`-v' (which you can also spell as `-version') on the command line.
File: as.info, Node: W, Next: Z, Prev: v, Up: Invoking
2.16 Control Warnings: `-W', `--warn', `--no-warn', `--fatal-warnings'
======================================================================
`as' should never give a warning or error message when assembling
compiler output. But programs written by people often cause `as' to
give a warning that a particular assumption was made. All such
warnings are directed to the standard error file.
If you use the `-W' and `--no-warn' options, no warnings are issued.
This only affects the warning messages: it does not change any
particular of how `as' assembles your file. Errors, which stop the
assembly, are still reported.
If you use the `--fatal-warnings' option, `as' considers files that
generate warnings to be in error.
You can switch these options off again by specifying `--warn', which
causes warnings to be output as usual.
File: as.info, Node: Z, Prev: W, Up: Invoking
2.17 Generate Object File in Spite of Errors: `-Z'
==================================================
After an error message, `as' normally produces no output. If for some
reason you are interested in object file output even after `as' gives
an error message on your program, use the `-Z' option. If there are
any errors, `as' continues anyways, and writes an object file after a
final warning message of the form `N errors, M warnings, generating bad
object file.'
File: as.info, Node: Syntax, Next: Sections, Prev: Invoking, Up: Top
3 Syntax
********
This chapter describes the machine-independent syntax allowed in a
source file. `as' syntax is similar to what many other assemblers use;
it is inspired by the BSD 4.2 assembler, except that `as' does not
assemble Vax bit-fields.
* Menu:
* Preprocessing:: Preprocessing
* Whitespace:: Whitespace
* Comments:: Comments
* Symbol Intro:: Symbols
* Statements:: Statements
* Constants:: Constants
File: as.info, Node: Preprocessing, Next: Whitespace, Up: Syntax
3.1 Preprocessing
=================
The `as' internal preprocessor:
* adjusts and removes extra whitespace. It leaves one space or tab
before the keywords on a line, and turns any other whitespace on
the line into a single space.
* removes all comments, replacing them with a single space, or an
appropriate number of newlines.
* converts character constants into the appropriate numeric values.
It does not do macro processing, include file handling, or anything
else you may get from your C compiler's preprocessor. You can do
include file processing with the `.include' directive (*note
`.include': Include.). You can use the GNU C compiler driver to get
other "CPP" style preprocessing by giving the input file a `.S' suffix.
*Note Options Controlling the Kind of Output: (gcc.info)Overall
Options.
Excess whitespace, comments, and character constants cannot be used
in the portions of the input text that are not preprocessed.
If the first line of an input file is `#NO_APP' or if you use the
`-f' option, whitespace and comments are not removed from the input
file. Within an input file, you can ask for whitespace and comment
removal in specific portions of the by putting a line that says `#APP'
before the text that may contain whitespace or comments, and putting a
line that says `#NO_APP' after this text. This feature is mainly
intend to support `asm' statements in compilers whose output is
otherwise free of comments and whitespace.
File: as.info, Node: Whitespace, Next: Comments, Prev: Preprocessing, Up: Syntax
3.2 Whitespace
==============
"Whitespace" is one or more blanks or tabs, in any order. Whitespace
is used to separate symbols, and to make programs neater for people to
read. Unless within character constants (*note Character Constants:
Characters.), any whitespace means the same as exactly one space.
File: as.info, Node: Comments, Next: Symbol Intro, Prev: Whitespace, Up: Syntax
3.3 Comments
============
There are two ways of rendering comments to `as'. In both cases the
comment is equivalent to one space.
Anything from `/*' through the next `*/' is a comment. This means
you may not nest these comments.
/*
The only way to include a newline ('\n') in a comment
is to use this sort of comment.
*/
/* This sort of comment does not nest. */
Anything from the "line comment" character to the next newline is
considered a comment and is ignored. The line comment character is `;'
for the AMD 29K family; `;' on the ARC; `@' on the ARM; `;' for the
H8/300 family; `!' for the H8/500 family; `;' for the HPPA; `#' on the
i386 and x86-64; `#' on the i960; `;' for the PDP-11; `;' for picoJava;
`#' for Motorola PowerPC; `!' for the Renesas / SuperH SH; `!' on the
SPARC; `#' on the ip2k; `#' on the m32r; `|' on the 680x0; `#' on the
68HC11 and 68HC12; `;' on the M880x0; `#' on the Vax; `!' for the Z8000;
`#' on the V850; `#' for Xtensa systems; see *Note Machine
Dependencies::.
On some machines there are two different line comment characters.
One character only begins a comment if it is the first non-whitespace
character on a line, while the other always begins a comment.
The V850 assembler also supports a double dash as starting a comment
that extends to the end of the line.
`--';
To be compatible with past assemblers, lines that begin with `#'
have a special interpretation. Following the `#' should be an absolute
expression (*note Expressions::): the logical line number of the _next_
line. Then a string (*note Strings: Strings.) is allowed: if present
it is a new logical file name. The rest of the line, if any, should be
whitespace.
If the first non-whitespace characters on the line are not numeric,
the line is ignored. (Just like a comment.)
# This is an ordinary comment.
# 42-6 "new_file_name" # New logical file name
# This is logical line # 36.
This feature is deprecated, and may disappear from future versions
of `as'.
File: as.info, Node: Symbol Intro, Next: Statements, Prev: Comments, Up: Syntax
3.4 Symbols
===========
A "symbol" is one or more characters chosen from the set of all letters
(both upper and lower case), digits and the three characters `_.$'. On
most machines, you can also use `$' in symbol names; exceptions are
noted in *Note Machine Dependencies::. No symbol may begin with a
digit. Case is significant. There is no length limit: all characters
are significant. Symbols are delimited by characters not in that set,
or by the beginning of a file (since the source program must end with a
newline, the end of a file is not a possible symbol delimiter). *Note
Symbols::.
File: as.info, Node: Statements, Next: Constants, Prev: Symbol Intro, Up: Syntax
3.5 Statements
==============
A "statement" ends at a newline character (`\n') or line separator
character. (The line separator is usually `;', unless this conflicts
with the comment character; *note Machine Dependencies::.) The newline
or separator character is considered part of the preceding statement.
Newlines and separators within character constants are an exception:
they do not end statements.
It is an error to end any statement with end-of-file: the last
character of any input file should be a newline.
An empty statement is allowed, and may include whitespace. It is
ignored.
A statement begins with zero or more labels, optionally followed by a
key symbol which determines what kind of statement it is. The key
symbol determines the syntax of the rest of the statement. If the
symbol begins with a dot `.' then the statement is an assembler
directive: typically valid for any computer. If the symbol begins with
a letter the statement is an assembly language "instruction": it
assembles into a machine language instruction. Different versions of
`as' for different computers recognize different instructions. In
fact, the same symbol may represent a different instruction in a
different computer's assembly language.
A label is a symbol immediately followed by a colon (`:').
Whitespace before a label or after a colon is permitted, but you may not
have whitespace between a label's symbol and its colon. *Note Labels::.
For HPPA targets, labels need not be immediately followed by a
colon, but the definition of a label must begin in column zero. This
also implies that only one label may be defined on each line.
label: .directive followed by something
another_label: # This is an empty statement.
instruction operand_1, operand_2, ...
File: as.info, Node: Constants, Prev: Statements, Up: Syntax
3.6 Constants
=============
A constant is a number, written so that its value is known by
inspection, without knowing any context. Like this:
.byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.
.ascii "Ring the bell\7" # A string constant.
.octa 0x123456789abcdef0123456789ABCDEF0 # A bignum.
.float 0f-314159265358979323846264338327\
95028841971.693993751E-40 # - pi, a flonum.
* Menu:
* Characters:: Character Constants
* Numbers:: Number Constants
File: as.info, Node: Characters, Next: Numbers, Up: Constants
3.6.1 Character Constants
-------------------------
There are two kinds of character constants. A "character" stands for
one character in one byte and its value may be used in numeric
expressions. String constants (properly called string _literals_) are
potentially many bytes and their values may not be used in arithmetic
expressions.
* Menu:
* Strings:: Strings
* Chars:: Characters
File: as.info, Node: Strings, Next: Chars, Up: Characters
3.6.1.1 Strings
...............
A "string" is written between double-quotes. It may contain
double-quotes or null characters. The way to get special characters
into a string is to "escape" these characters: precede them with a
backslash `\' character. For example `\\' represents one backslash:
the first `\' is an escape which tells `as' to interpret the second
character literally as a backslash (which prevents `as' from
recognizing the second `\' as an escape character). The complete list
of escapes follows.
`\b'
Mnemonic for backspace; for ASCII this is octal code 010.
`\f'
Mnemonic for FormFeed; for ASCII this is octal code 014.
`\n'
Mnemonic for newline; for ASCII this is octal code 012.
`\r'
Mnemonic for carriage-Return; for ASCII this is octal code 015.
`\t'
Mnemonic for horizontal Tab; for ASCII this is octal code 011.
`\ DIGIT DIGIT DIGIT'
An octal character code. The numeric code is 3 octal digits. For
compatibility with other Unix systems, 8 and 9 are accepted as
digits: for example, `\008' has the value 010, and `\009' the
value 011.
`\`x' HEX-DIGITS...'
A hex character code. All trailing hex digits are combined.
Either upper or lower case `x' works.
`\\'
Represents one `\' character.
`\"'
Represents one `"' character. Needed in strings to represent this
character, because an unescaped `"' would end the string.
`\ ANYTHING-ELSE'
Any other character when escaped by `\' gives a warning, but
assembles as if the `\' was not present. The idea is that if you
used an escape sequence you clearly didn't want the literal
interpretation of the following character. However `as' has no
other interpretation, so `as' knows it is giving you the wrong
code and warns you of the fact.
Which characters are escapable, and what those escapes represent,
varies widely among assemblers. The current set is what we think the
BSD 4.2 assembler recognizes, and is a subset of what most C compilers
recognize. If you are in doubt, do not use an escape sequence.
File: as.info, Node: Chars, Prev: Strings, Up: Characters
3.6.1.2 Characters
..................
A single character may be written as a single quote immediately
followed by that character. The same escapes apply to characters as to
strings. So if you want to write the character backslash, you must
write `'\\' where the first `\' escapes the second `\'. As you can
see, the quote is an acute accent, not a grave accent. A newline
immediately following an acute accent is taken as a literal character
and does not count as the end of a statement. The value of a character
constant in a numeric expression is the machine's byte-wide code for
that character. `as' assumes your character code is ASCII: `'A' means
65, `'B' means 66, and so on.
File: as.info, Node: Numbers, Prev: Characters, Up: Constants
3.6.2 Number Constants
----------------------
`as' distinguishes three kinds of numbers according to how they are
stored in the target machine. _Integers_ are numbers that would fit
into an `int' in the C language. _Bignums_ are integers, but they are
stored in more than 32 bits. _Flonums_ are floating point numbers,
described below.
* Menu:
* Integers:: Integers
* Bignums:: Bignums
* Flonums:: Flonums
File: as.info, Node: Integers, Next: Bignums, Up: Numbers
3.6.2.1 Integers
................
A binary integer is `0b' or `0B' followed by zero or more of the binary
digits `01'.
An octal integer is `0' followed by zero or more of the octal digits
(`01234567').
A decimal integer starts with a non-zero digit followed by zero or
more digits (`0123456789').
A hexadecimal integer is `0x' or `0X' followed by one or more
hexadecimal digits chosen from `0123456789abcdefABCDEF'.
Integers have the usual values. To denote a negative integer, use
the prefix operator `-' discussed under expressions (*note Prefix
Operators: Prefix Ops.).
File: as.info, Node: Bignums, Next: Flonums, Prev: Integers, Up: Numbers
3.6.2.2 Bignums
...............
A "bignum" has the same syntax and semantics as an integer except that
the number (or its negative) takes more than 32 bits to represent in
binary. The distinction is made because in some places integers are
permitted while bignums are not.
File: as.info, Node: Flonums, Prev: Bignums, Up: Numbers
3.6.2.3 Flonums
...............
A "flonum" represents a floating point number. The translation is
indirect: a decimal floating point number from the text is converted by
`as' to a generic binary floating point number of more than sufficient
precision. This generic floating point number is converted to a
particular computer's floating point format (or formats) by a portion
of `as' specialized to that computer.
A flonum is written by writing (in order)
* The digit `0'. (`0' is optional on the HPPA.)
* A letter, to tell `as' the rest of the number is a flonum. `e' is
recommended. Case is not important.
On the H8/300, H8/500, Renesas / SuperH SH, and AMD 29K
architectures, the letter must be one of the letters `DFPRSX' (in
upper or lower case).
On the ARC, the letter must be one of the letters `DFRS' (in upper
or lower case).
On the Intel 960 architecture, the letter must be one of the
letters `DFT' (in upper or lower case).
On the HPPA architecture, the letter must be `E' (upper case only).
* An optional sign: either `+' or `-'.
* An optional "integer part": zero or more decimal digits.
* An optional "fractional part": `.' followed by zero or more
decimal digits.
* An optional exponent, consisting of:
* An `E' or `e'.
* Optional sign: either `+' or `-'.
* One or more decimal digits.
At least one of the integer part or the fractional part must be
present. The floating point number has the usual base-10 value.
`as' does all processing using integers. Flonums are computed
independently of any floating point hardware in the computer running
`as'.
File: as.info, Node: Sections, Next: Symbols, Prev: Syntax, Up: Top
4 Sections and Relocation
*************************
* Menu:
* Secs Background:: Background
* Ld Sections:: Linker Sections
* As Sections:: Assembler Internal Sections
* Sub-Sections:: Sub-Sections
* bss:: bss Section
File: as.info, Node: Secs Background, Next: Ld Sections, Up: Sections
4.1 Background
==============
Roughly, a section is a range of addresses, with no gaps; all data "in"
those addresses is treated the same for some particular purpose. For
example there may be a "read only" section.
The linker `ld' reads many object files (partial programs) and
combines their contents to form a runnable program. When `as' emits an
object file, the partial program is assumed to start at address 0.
`ld' assigns the final addresses for the partial program, so that
different partial programs do not overlap. This is actually an
oversimplification, but it suffices to explain how `as' uses sections.
`ld' moves blocks of bytes of your program to their run-time
addresses. These blocks slide to their run-time addresses as rigid
units; their length does not change and neither does the order of bytes
within them. Such a rigid unit is called a _section_. Assigning
run-time addresses to sections is called "relocation". It includes the
task of adjusting mentions of object-file addresses so they refer to
the proper run-time addresses. For the H8/300 and H8/500, and for the
Renesas / SuperH SH, `as' pads sections if needed to ensure they end on
a word (sixteen bit) boundary.
An object file written by `as' has at least three sections, any of
which may be empty. These are named "text", "data" and "bss" sections.
When it generates COFF or ELF output, `as' can also generate
whatever other named sections you specify using the `.section'
directive (*note `.section': Section.). If you do not use any
directives that place output in the `.text' or `.data' sections, these
sections still exist, but are empty.
When `as' generates SOM or ELF output for the HPPA, `as' can also
generate whatever other named sections you specify using the `.space'
and `.subspace' directives. See `HP9000 Series 800 Assembly Language
Reference Manual' (HP 92432-90001) for details on the `.space' and
`.subspace' assembler directives.
Additionally, `as' uses different names for the standard text, data,
and bss sections when generating SOM output. Program text is placed
into the `$CODE$' section, data into `$DATA$', and BSS into `$BSS$'.
Within the object file, the text section starts at address `0', the
data section follows, and the bss section follows the data section.
When generating either SOM or ELF output files on the HPPA, the text
section starts at address `0', the data section at address `0x4000000',
and the bss section follows the data section.
To let `ld' know which data changes when the sections are relocated,
and how to change that data, `as' also writes to the object file
details of the relocation needed. To perform relocation `ld' must
know, each time an address in the object file is mentioned:
* Where in the object file is the beginning of this reference to an
address?
* How long (in bytes) is this reference?
* Which section does the address refer to? What is the numeric
value of
(ADDRESS) - (START-ADDRESS OF SECTION)?
* Is the reference to an address "Program-Counter relative"?
In fact, every address `as' ever uses is expressed as
(SECTION) + (OFFSET INTO SECTION)
Further, most expressions `as' computes have this section-relative
nature. (For some object formats, such as SOM for the HPPA, some
expressions are symbol-relative instead.)
In this manual we use the notation {SECNAME N} to mean "offset N
into section SECNAME."
Apart from text, data and bss sections you need to know about the
"absolute" section. When `ld' mixes partial programs, addresses in the
absolute section remain unchanged. For example, address `{absolute 0}'
is "relocated" to run-time address 0 by `ld'. Although the linker
never arranges two partial programs' data sections with overlapping
addresses after linking, _by definition_ their absolute sections must
overlap. Address `{absolute 239}' in one part of a program is always
the same address when the program is running as address `{absolute
239}' in any other part of the program.
The idea of sections is extended to the "undefined" section. Any
address whose section is unknown at assembly time is by definition
rendered {undefined U}--where U is filled in later. Since numbers are
always defined, the only way to generate an undefined address is to
mention an undefined symbol. A reference to a named common block would
be such a symbol: its value is unknown at assembly time so it has
section _undefined_.
By analogy the word _section_ is used to describe groups of sections
in the linked program. `ld' puts all partial programs' text sections
in contiguous addresses in the linked program. It is customary to
refer to the _text section_ of a program, meaning all the addresses of
all partial programs' text sections. Likewise for data and bss
sections.
Some sections are manipulated by `ld'; others are invented for use
of `as' and have no meaning except during assembly.
File: as.info, Node: Ld Sections, Next: As Sections, Prev: Secs Background, Up: Sections
4.2 Linker Sections
===================
`ld' deals with just four kinds of sections, summarized below.
*named sections*
*text section*
*data section*
These sections hold your program. `as' and `ld' treat them as
separate but equal sections. Anything you can say of one section
is true of another. When the program is running, however, it is
customary for the text section to be unalterable. The text
section is often shared among processes: it contains instructions,
constants and the like. The data section of a running program is
usually alterable: for example, C variables would be stored in the
data section.
*bss section*
This section contains zeroed bytes when your program begins
running. It is used to hold uninitialized variables or common
storage. The length of each partial program's bss section is
important, but because it starts out containing zeroed bytes there
is no need to store explicit zero bytes in the object file. The
bss section was invented to eliminate those explicit zeros from
object files.
*absolute section*
Address 0 of this section is always "relocated" to runtime address
0. This is useful if you want to refer to an address that `ld'
must not change when relocating. In this sense we speak of
absolute addresses being "unrelocatable": they do not change
during relocation.
*undefined section*
This "section" is a catch-all for address references to objects
not in the preceding sections.
An idealized example of three relocatable sections follows. The
example uses the traditional section names `.text' and `.data'. Memory
addresses are on the horizontal axis.
+-----+----+--+
partial program # 1: |ttttt|dddd|00|
+-----+----+--+
text data bss
seg. seg. seg.
+---+---+---+
partial program # 2: |TTT|DDD|000|
+---+---+---+
+--+---+-----+--+----+---+-----+~~
linked program: | |TTT|ttttt| |dddd|DDD|00000|
+--+---+-----+--+----+---+-----+~~
addresses: 0 ...
File: as.info, Node: As Sections, Next: Sub-Sections, Prev: Ld Sections, Up: Sections
4.3 Assembler Internal Sections
===============================
These sections are meant only for the internal use of `as'. They have
no meaning at run-time. You do not really need to know about these
sections for most purposes; but they can be mentioned in `as' warning
messages, so it might be helpful to have an idea of their meanings to
`as'. These sections are used to permit the value of every expression
in your assembly language program to be a section-relative address.
ASSEMBLER-INTERNAL-LOGIC-ERROR!
An internal assembler logic error has been found. This means
there is a bug in the assembler.
expr section
The assembler stores complex expression internally as combinations
of symbols. When it needs to represent an expression as a symbol,
it puts it in the expr section.
File: as.info, Node: Sub-Sections, Next: bss, Prev: As Sections, Up: Sections
4.4 Sub-Sections
================
Assembled bytes conventionally fall into two sections: text and data.
You may have separate groups of data in named sections that you want to
end up near to each other in the object file, even though they are not
contiguous in the assembler source. `as' allows you to use
"subsections" for this purpose. Within each section, there can be
numbered subsections with values from 0 to 8192. Objects assembled
into the same subsection go into the object file together with other
objects in the same subsection. For example, a compiler might want to
store constants in the text section, but might not want to have them
interspersed with the program being assembled. In this case, the
compiler could issue a `.text 0' before each section of code being
output, and a `.text 1' before each group of constants being output.
Subsections are optional. If you do not use subsections, everything
goes in subsection number zero.
Each subsection is zero-padded up to a multiple of four bytes.
(Subsections may be padded a different amount on different flavors of
`as'.)
Subsections appear in your object file in numeric order, lowest
numbered to highest. (All this to be compatible with other people's
assemblers.) The object file contains no representation of
subsections; `ld' and other programs that manipulate object files see
no trace of them. They just see all your text subsections as a text
section, and all your data subsections as a data section.
To specify which subsection you want subsequent statements assembled
into, use a numeric argument to specify it, in a `.text EXPRESSION' or
a `.data EXPRESSION' statement. When generating COFF output, you can
also use an extra subsection argument with arbitrary named sections:
`.section NAME, EXPRESSION'. When generating ELF output, you can also
use the `.subsection' directive (*note SubSection::) to specify a
subsection: `.subsection EXPRESSION'. EXPRESSION should be an absolute
expression. (*Note Expressions::.) If you just say `.text' then
`.text 0' is assumed. Likewise `.data' means `.data 0'. Assembly
begins in `text 0'. For instance:
.text 0 # The default subsection is text 0 anyway.
.ascii "This lives in the first text subsection. *"
.text 1
.ascii "But this lives in the second text subsection."
.data 0
.ascii "This lives in the data section,"
.ascii "in the first data subsection."
.text 0
.ascii "This lives in the first text section,"
.ascii "immediately following the asterisk (*)."
Each section has a "location counter" incremented by one for every
byte assembled into that section. Because subsections are merely a
convenience restricted to `as' there is no concept of a subsection
location counter. There is no way to directly manipulate a location
counter--but the `.align' directive changes it, and any label
definition captures its current value. The location counter of the
section where statements are being assembled is said to be the "active"
location counter.
File: as.info, Node: bss, Prev: Sub-Sections, Up: Sections
4.5 bss Section
===============
The bss section is used for local common variable storage. You may
allocate address space in the bss section, but you may not dictate data
to load into it before your program executes. When your program starts
running, all the contents of the bss section are zeroed bytes.
The `.lcomm' pseudo-op defines a symbol in the bss section; see
*Note `.lcomm': Lcomm.
The `.comm' pseudo-op may be used to declare a common symbol, which
is another form of uninitialized symbol; see *Note `.comm': Comm.
When assembling for a target which supports multiple sections, such
as ELF or COFF, you may switch into the `.bss' section and define
symbols as usual; see *Note `.section': Section. You may only assemble
zero values into the section. Typically the section will only contain
symbol definitions and `.skip' directives (*note `.skip': Skip.).
File: as.info, Node: Symbols, Next: Expressions, Prev: Sections, Up: Top
5 Symbols
*********
Symbols are a central concept: the programmer uses symbols to name
things, the linker uses symbols to link, and the debugger uses symbols
to debug.
_Warning:_ `as' does not place symbols in the object file in the
same order they were declared. This may break some debuggers.
* Menu:
* Labels:: Labels
* Setting Symbols:: Giving Symbols Other Values
* Symbol Names:: Symbol Names
* Dot:: The Special Dot Symbol
* Symbol Attributes:: Symbol Attributes
File: as.info, Node: Labels, Next: Setting Symbols, Up: Symbols
5.1 Labels
==========
A "label" is written as a symbol immediately followed by a colon `:'.
The symbol then represents the current value of the active location
counter, and is, for example, a suitable instruction operand. You are
warned if you use the same symbol to represent two different locations:
the first definition overrides any other definitions.
On the HPPA, the usual form for a label need not be immediately
followed by a colon, but instead must start in column zero. Only one
label may be defined on a single line. To work around this, the HPPA
version of `as' also provides a special directive `.label' for defining
labels more flexibly.
File: as.info, Node: Setting Symbols, Next: Symbol Names, Prev: Labels, Up: Symbols
5.2 Giving Symbols Other Values
===============================
A symbol can be given an arbitrary value by writing a symbol, followed
by an equals sign `=', followed by an expression (*note Expressions::).
This is equivalent to using the `.set' directive. *Note `.set': Set.
File: as.info, Node: Symbol Names, Next: Dot, Prev: Setting Symbols, Up: Symbols
5.3 Symbol Names
================
Symbol names begin with a letter or with one of `._'. On most
machines, you can also use `$' in symbol names; exceptions are noted in
*Note Machine Dependencies::. That character may be followed by any
string of digits, letters, dollar signs (unless otherwise noted in
*Note Machine Dependencies::), and underscores. For the AMD 29K
family, `?' is also allowed in the body of a symbol name, though not at
its beginning.
Case of letters is significant: `foo' is a different symbol name than
`Foo'.
Each symbol has exactly one name. Each name in an assembly language
program refers to exactly one symbol. You may use that symbol name any
number of times in a program.
Local Symbol Names
------------------
Local symbols 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 symbol, write a label of the form `N:'
(where N represents any positive integer). To refer to the most recent
previous definition of that symbol write `Nb', using the same number as
when you defined the label. To refer to the next definition of a local
label, write `Nf'-- The `b' stands for"backwards" and the `f' stands
for "forwards".
There is no restriction on how you can use these labels, and you can
reuse them too. So that it is possible to repeatedly define the same
local label (using the same number `N'), although you can only refer to
the most recently defined local label of that number (for a backwards
reference) or the next definition of a specific local label for a
forward reference. It is also worth noting that the first 10 local
labels (`0:'...`9:') are implemented in a slightly more efficient
manner than the others.
Here is an example:
1: branch 1f
2: branch 1b
1: branch 2f
2: branch 1b
Which is the equivalent of:
label_1: branch label_3
label_2: branch label_1
label_3: branch label_4
label_4: branch label_3
Local symbol names are only a notational device. They are
immediately transformed into more conventional symbol names before the
assembler uses them. The symbol names stored in the symbol table,
appearing in error messages and optionally emitted to the object file.
The names are constructed using these parts:
`L'
All local labels begin with `L'. Normally both `as' and `ld'
forget symbols that start with `L'. These labels are used for
symbols you are never intended to see. If you use the `-L' option
then `as' retains these symbols in the object file. If you also
instruct `ld' to retain these symbols, you may use them in
debugging.
`NUMBER'
This is the number that was used in the local label definition.
So if the label is written `55:' then the number is `55'.
`C-B'
This unusual character is included so you do not accidentally
invent a symbol of the same name. The character has ASCII value
of `\002' (control-B).
`_ordinal number_'
This is a serial number to keep the labels distinct. The first
definition of `0:' gets the number `1'. The 15th definition of
`0:' gets the number `15', and so on. Likewise the first
definition of `1:' gets the number `1' and its 15th defintion gets
`15' as well.
So for example, the first `1:' is named `L1C-B1', the 44th `3:' is
named `L3C-B44'.
Dollar Local Labels
-------------------
`as' also supports an even more local form of local labels called
dollar labels. These labels go out of scope (ie they become undefined)
as soon as a non-local label is defined. Thus they remain valid for
only a small region of the input source code. Normal local labels, by
contrast, remain in scope for the entire file, or until they are
redefined by another occurrence of the same local label.
Dollar labels are defined in exactly the same way as ordinary local
labels, except that instead of being terminated by a colon, they are
terminated by a dollar sign. eg `55$'.
They can also be distinguished from ordinary local labels by their
transformed name which uses ASCII character `\001' (control-A) as the
magic character to distinguish them from ordinary labels. Thus the 5th
defintion of `6$' is named `L6C-A5'.
File: as.info, Node: Dot, Next: Symbol Attributes, Prev: Symbol Names, Up: Symbols
5.4 The Special Dot Symbol
==========================
The special symbol `.' refers to the current address that `as' is
assembling into. Thus, the expression `melvin: .long .' defines
`melvin' to contain its own address. Assigning a value to `.' is
treated the same as a `.org' directive. Thus, the expression `.=.+4'
is the same as saying `.space 4'.
File: as.info, Node: Symbol Attributes, Prev: Dot, Up: Symbols
5.5 Symbol Attributes
=====================
Every symbol has, as well as its name, the attributes "Value" and
"Type". Depending on output format, symbols can also have auxiliary
attributes.
If you use a symbol without defining it, `as' assumes zero for all
these attributes, and probably won't warn you. This makes the symbol
an externally defined symbol, which is generally what you would want.
* Menu:
* Symbol Value:: Value
* Symbol Type:: Type
* a.out Symbols:: Symbol Attributes: `a.out'
* COFF Symbols:: Symbol Attributes for COFF
* SOM Symbols:: Symbol Attributes for SOM
File: as.info, Node: Symbol Value, Next: Symbol Type, Up: Symbol Attributes
5.5.1 Value
-----------
The value of a symbol is (usually) 32 bits. For a symbol which labels a
location in the text, data, bss or absolute sections the value is the
number of addresses from the start of that section to the label.
Naturally for text, data and bss sections the value of a symbol changes
as `ld' changes section base addresses during linking. Absolute
symbols' values do not change during linking: that is why they are
called absolute.
The value of an undefined symbol is treated in a special way. If it
is 0 then the symbol is not defined in this assembler source file, and
`ld' tries to determine its value from other files linked into the same
program. You make this kind of symbol simply by mentioning a symbol
name without defining it. A non-zero value represents a `.comm' common
declaration. The value is how much common storage to reserve, in bytes
(addresses). The symbol refers to the first address of the allocated
storage.
File: as.info, Node: Symbol Type, Next: a.out Symbols, Prev: Symbol Value, Up: Symbol Attributes
5.5.2 Type
----------
The type attribute of a symbol contains relocation (section)
information, any flag settings indicating that a symbol is external, and
(optionally), other information for linkers and debuggers. The exact
format depends on the object-code output format in use.
File: as.info, Node: a.out Symbols, Next: COFF Symbols, Prev: Symbol Type, Up: Symbol Attributes
5.5.3 Symbol Attributes: `a.out'
--------------------------------
* Menu:
* Symbol Desc:: Descriptor
* Symbol Other:: Other
File: as.info, Node: Symbol Desc, Next: Symbol Other, Up: a.out Symbols
5.5.3.1 Descriptor
..................
This is an arbitrary 16-bit value. You may establish a symbol's
descriptor value by using a `.desc' statement (*note `.desc': Desc.).
A descriptor value means nothing to `as'.
File: as.info, Node: Symbol Other, Prev: Symbol Desc, Up: a.out Symbols
5.5.3.2 Other
.............
This is an arbitrary 8-bit value. It means nothing to `as'.
File: as.info, Node: COFF Symbols, Next: SOM Symbols, Prev: a.out Symbols, Up: Symbol Attributes
5.5.4 Symbol Attributes for COFF
--------------------------------
The COFF format supports a multitude of auxiliary symbol attributes;
like the primary symbol attributes, they are set between `.def' and
`.endef' directives.
5.5.4.1 Primary Attributes
..........................
The symbol name is set with `.def'; the value and type, respectively,
with `.val' and `.type'.
5.5.4.2 Auxiliary Attributes
............................
The `as' directives `.dim', `.line', `.scl', `.size', `.tag', and
`.weak' can generate auxiliary symbol table information for COFF.
File: as.info, Node: SOM Symbols, Prev: COFF Symbols, Up: Symbol Attributes
5.5.5 Symbol Attributes for SOM
-------------------------------
The SOM format for the HPPA supports a multitude of symbol attributes
set with the `.EXPORT' and `.IMPORT' directives.
The attributes are described in `HP9000 Series 800 Assembly Language
Reference Manual' (HP 92432-90001) under the `IMPORT' and `EXPORT'
assembler directive documentation.
File: as.info, Node: Expressions, Next: Pseudo Ops, Prev: Symbols, Up: Top
6 Expressions
*************
An "expression" specifies an address or numeric value. Whitespace may
precede and/or follow an expression.
The result of an expression must be an absolute number, or else an
offset into a particular section. If an expression is not absolute,
and there is not enough information when `as' sees the expression to
know its section, a second pass over the source program might be
necessary to interpret the expression--but the second pass is currently
not implemented. `as' aborts with an error message in this situation.
* Menu:
* Empty Exprs:: Empty Expressions
* Integer Exprs:: Integer Expressions
File: as.info, Node: Empty Exprs, Next: Integer Exprs, Up: Expressions
6.1 Empty Expressions
=====================
An empty expression has no value: it is just whitespace or null.
Wherever an absolute expression is required, you may omit the
expression, and `as' assumes a value of (absolute) 0. This is
compatible with other assemblers.
File: as.info, Node: Integer Exprs, Prev: Empty Exprs, Up: Expressions
6.2 Integer Expressions
=======================
An "integer expression" is one or more _arguments_ delimited by
_operators_.
* Menu:
* Arguments:: Arguments
* Operators:: Operators
* Prefix Ops:: Prefix Operators
* Infix Ops:: Infix Operators
File: as.info, Node: Arguments, Next: Operators, Up: Integer Exprs
6.2.1 Arguments
---------------
"Arguments" are symbols, numbers or subexpressions. In other contexts
arguments are sometimes called "arithmetic operands". In this manual,
to avoid confusing them with the "instruction operands" of the machine
language, we use the term "argument" to refer to parts of expressions
only, reserving the word "operand" to refer only to machine instruction
operands.
Symbols are evaluated to yield {SECTION NNN} where SECTION is one of
text, data, bss, absolute, or undefined. NNN is a signed, 2's
complement 32 bit integer.
Numbers are usually integers.
A number can be a flonum or bignum. In this case, you are warned
that only the low order 32 bits are used, and `as' pretends these 32
bits are an integer. You may write integer-manipulating instructions
that act on exotic constants, compatible with other assemblers.
Subexpressions are a left parenthesis `(' followed by an integer
expression, followed by a right parenthesis `)'; or a prefix operator
followed by an argument.
File: as.info, Node: Operators, Next: Prefix Ops, Prev: Arguments, Up: Integer Exprs
6.2.2 Operators
---------------
"Operators" are arithmetic functions, like `+' or `%'. Prefix
operators are followed by an argument. Infix operators appear between
their arguments. Operators may be preceded and/or followed by
whitespace.
File: as.info, Node: Prefix Ops, Next: Infix Ops, Prev: Operators, Up: Integer Exprs
6.2.3 Prefix Operator
---------------------
`as' has the following "prefix operators". They each take one
argument, which must be absolute.
`-'
"Negation". Two's complement negation.
`~'
"Complementation". Bitwise not.
File: as.info, Node: Infix Ops, Prev: Prefix Ops, Up: Integer Exprs
6.2.4 Infix Operators
---------------------
"Infix operators" take two arguments, one on either side. Operators
have precedence, but operations with equal precedence are performed left
to right. Apart from `+' or `-', both arguments must be absolute, and
the result is absolute.
1. Highest Precedence
`*'
"Multiplication".
`/'
"Division". Truncation is the same as the C operator `/'
`%'
"Remainder".
`<'
`<<'
"Shift Left". Same as the C operator `<<'.
`>'
`>>'
"Shift Right". Same as the C operator `>>'.
2. Intermediate precedence
`|'
"Bitwise Inclusive Or".
`&'
"Bitwise And".
`^'
"Bitwise Exclusive Or".
`!'
"Bitwise Or Not".
3. Low Precedence
`+'
"Addition". If either argument is absolute, the result has
the section of the other argument. You may not add together
arguments from different sections.
`-'
"Subtraction". If the right argument is absolute, the result
has the section of the left argument. If both arguments are
in the same section, the result is absolute. You may not
subtract arguments from different sections.
`=='
"Is Equal To"
`<>'
"Is Not Equal To"
`<'
"Is Less Than"
`>'
"Is Greater Than"
`>='
"Is Greater Than Or Equal To"
`<='
"Is Less Than Or Equal To"
The comparison operators can be used as infix operators. A
true results has a value of -1 whereas a false result has a
value of 0. Note, these operators perform signed
comparisons.
4. Lowest Precedence
`&&'
"Logical And".
`||'
"Logical Or".
These two logical operations can be used to combine the
results of sub expressions. Note, unlike the comparison
operators a true result returns a value of 1 but a false
results does still return 0. Also note that the logical or
operator has a slightly lower precedence than logical and.
In short, it's only meaningful to add or subtract the _offsets_ in an
address; you can only have a defined section in one of the two
arguments.
File: as.info, Node: Pseudo Ops, Next: Machine Dependencies, Prev: Expressions, Up: Top
7 Assembler Directives
**********************
All assembler directives have names that begin with a period (`.').
The rest of the name is letters, usually in lower case.
This chapter discusses directives that are available regardless of
the target machine configuration for the GNU assembler. Some machine
configurations provide additional directives. *Note Machine
Dependencies::.
* Menu:
* Abort:: `.abort'
* ABORT:: `.ABORT'
* Align:: `.align ABS-EXPR , ABS-EXPR'
* Altmacro:: `.altmacro'
* Ascii:: `.ascii "STRING"'...
* Asciz:: `.asciz "STRING"'...
* Balign:: `.balign ABS-EXPR , ABS-EXPR'
* Byte:: `.byte EXPRESSIONS'
* Comm:: `.comm SYMBOL , LENGTH '
* CFI directives:: `.cfi_startproc', `.cfi_endproc', etc.
* Data:: `.data SUBSECTION'
* Def:: `.def NAME'
* Desc:: `.desc SYMBOL, ABS-EXPRESSION'
* Dim:: `.dim'
* Double:: `.double FLONUMS'
* Eject:: `.eject'
* Else:: `.else'
* Elseif:: `.elseif'
* End:: `.end'
* Endef:: `.endef'
* Endfunc:: `.endfunc'
* Endif:: `.endif'
* Equ:: `.equ SYMBOL, EXPRESSION'
* Equiv:: `.equiv SYMBOL, EXPRESSION'
* Err:: `.err'
* Exitm:: `.exitm'
* Extern:: `.extern'
* Fail:: `.fail'
* File:: `.file STRING'
* Fill:: `.fill REPEAT , SIZE , VALUE'
* Float:: `.float FLONUMS'
* Func:: `.func'
* Global:: `.global SYMBOL', `.globl SYMBOL'
* Hidden:: `.hidden NAMES'
* hword:: `.hword EXPRESSIONS'
* Ident:: `.ident'
* If:: `.if ABSOLUTE EXPRESSION'
* Incbin:: `.incbin "FILE"[,SKIP[,COUNT]]'
* Include:: `.include "FILE"'
* Int:: `.int EXPRESSIONS'
* Internal:: `.internal NAMES'
* Irp:: `.irp SYMBOL,VALUES'...
* Irpc:: `.irpc SYMBOL,VALUES'...
* Lcomm:: `.lcomm SYMBOL , LENGTH'
* Lflags:: `.lflags'
* Line:: `.line LINE-NUMBER'
* Ln:: `.ln LINE-NUMBER'
* Linkonce:: `.linkonce [TYPE]'
* List:: `.list'
* Long:: `.long EXPRESSIONS'
* Macro:: `.macro NAME ARGS'...
* MRI:: `.mri VAL'
* Noaltmacro:: `.noaltmacro'
* Nolist:: `.nolist'
* Octa:: `.octa BIGNUMS'
* Org:: `.org NEW-LC , FILL'
* P2align:: `.p2align ABS-EXPR , ABS-EXPR'
* PopSection:: `.popsection'
* Previous:: `.previous'
* Print:: `.print STRING'
* Protected:: `.protected NAMES'
* Psize:: `.psize LINES, COLUMNS'
* Purgem:: `.purgem NAME'
* PushSection:: `.pushsection NAME'
* Quad:: `.quad BIGNUMS'
* Rept:: `.rept COUNT'
* Sbttl:: `.sbttl "SUBHEADING"'
* Scl:: `.scl CLASS'
* Section:: `.section NAME'
* Set:: `.set SYMBOL, EXPRESSION'
* Short:: `.short EXPRESSIONS'
* Single:: `.single FLONUMS'
* Size:: `.size [NAME , EXPRESSION]'
* Skip:: `.skip SIZE , FILL'
* Sleb128:: `.sleb128 EXPRESSIONS'
* Space:: `.space SIZE , FILL'
* Stab:: `.stabd, .stabn, .stabs'
* String:: `.string "STR"'
* Struct:: `.struct EXPRESSION'
* SubSection:: `.subsection'
* Symver:: `.symver NAME,NAME2@NODENAME'
* Tag:: `.tag STRUCTNAME'
* Text:: `.text SUBSECTION'
* Title:: `.title "HEADING"'
* Type:: `.type <INT | NAME , TYPE DESCRIPTION>'
* Uleb128:: `.uleb128 EXPRESSIONS'
* Val:: `.val ADDR'
* Version:: `.version "STRING"'
* VTableEntry:: `.vtable_entry TABLE, OFFSET'
* VTableInherit:: `.vtable_inherit CHILD, PARENT'
* Weak:: `.weak NAMES'
* Weakref:: `.weakref ALIAS, SYMBOL'
* Word:: `.word EXPRESSIONS'
* Deprecated:: Deprecated Directives
File: as.info, Node: Abort, Next: ABORT, Up: Pseudo Ops
7.1 `.abort'
============
This directive stops the assembly immediately. It is for compatibility
with other assemblers. The original idea was that the assembly
language source would be piped into the assembler. If the sender of
the source quit, it could use this directive tells `as' to quit also.
One day `.abort' will not be supported.
File: as.info, Node: ABORT, Next: Align, Prev: Abort, Up: Pseudo Ops
7.2 `.ABORT'
============
When producing COFF output, `as' accepts this directive as a synonym
for `.abort'.
When producing `b.out' output, `as' accepts this directive, but
ignores it.
File: as.info, Node: Align, Next: Altmacro, Prev: ABORT, Up: Pseudo Ops
7.3 `.align ABS-EXPR, ABS-EXPR, ABS-EXPR'
=========================================
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
alignment required, as described below.
The second expression (also absolute) gives the fill value to be
stored in the padding bytes. It (and the comma) may be omitted. If it
is omitted, the padding bytes are normally zero. However, on some
systems, if the section is marked as containing code and the fill value
is omitted, the space is filled with no-op instructions.
The third expression is also absolute, and is also optional. If it
is present, it is the maximum number of bytes that should be skipped by
this alignment directive. If doing the alignment would require
skipping more bytes than the specified maximum, then the alignment is
not done at all. You can omit the fill value (the second argument)
entirely by simply using two commas after the required alignment; this
can be useful if you want the alignment to be filled with no-op
instructions when appropriate.
The way the required alignment is specified varies from system to
system. For the a29k, arc, hppa, i386 using ELF, i860, iq2000, m68k,
m88k, or32, s390, sparc, tic4x, tic80 and xtensa, the first expression
is the alignment request in bytes. For example `.align 8' advances the
location counter until it is a multiple of 8. If the location counter
is already a multiple of 8, no change is needed. For the tic54x, the
first expression is the alignment request in words.
For other systems, including the i386 using a.out format, and the
arm and strongarm, it is the number of low-order zero bits the location
counter must have after advancement. For example `.align 3' advances
the location counter until it a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
This inconsistency is due to the different behaviors of the various
native assemblers for these systems which GAS must emulate. GAS also
provides `.balign' and `.p2align' directives, described later, which
have a consistent behavior across all architectures (but are specific
to GAS).
File: as.info, Node: Altmacro, Next: Ascii, Prev: Align, Up: Pseudo Ops
7.62 `.altmacro'
================
Enable alternate macro mode, enabling:
`LOCAL NAME [ , ... ]'
One additional directive, `LOCAL', is available. It is used to
generate a string replacement for each of the NAME arguments, and
replace any instances of NAME in each macro expansion. The
replacement string is unique in the assembly, and different for
each separate macro expansion. `LOCAL' allows you to write macros
that define symbols, without fear of conflict between separate
macro expansions.
`String delimiters'
You can write strings delimited in these other ways besides
`"STRING"':
`'STRING''
You can delimit strings with single-quote charaters.
`<STRING>'
You can delimit strings with matching angle brackets.
`single-character string escape'
To include any single character literally in a string (even if the
character would otherwise have some special meaning), you can
prefix the character with `!' (an exclamation mark). For example,
you can write `<4.3 !> 5.4!!>' to get the literal text `4.3 >
5.4!'.
`Expression results as strings'
You can write `%EXPR' to evaluate the expression EXPR and use the
result as a string.
File: as.info, Node: Ascii, Next: Asciz, Prev: Altmacro, Up: Pseudo Ops
7.4 `.ascii "STRING"'...
========================
`.ascii' expects zero or more string literals (*note Strings::)
separated by commas. It assembles each string (with no automatic
trailing zero byte) into consecutive addresses.
File: as.info, Node: Asciz, Next: Balign, Prev: Ascii, Up: Pseudo Ops
7.5 `.asciz "STRING"'...
========================
`.asciz' is just like `.ascii', but each string is followed by a zero
byte. The "z" in `.asciz' stands for "zero".
File: as.info, Node: Balign, Next: Byte, Prev: Asciz, Up: Pseudo Ops
7.6 `.balign[wl] ABS-EXPR, ABS-EXPR, ABS-EXPR'
==============================================
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
alignment request in bytes. For example `.balign 8' advances the
location counter until it is a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
The second expression (also absolute) gives the fill value to be
stored in the padding bytes. It (and the comma) may be omitted. If it
is omitted, the padding bytes are normally zero. However, on some
systems, if the section is marked as containing code and the fill value
is omitted, the space is filled with no-op instructions.
The third expression is also absolute, and is also optional. If it
is present, it is the maximum number of bytes that should be skipped by
this alignment directive. If doing the alignment would require
skipping more bytes than the specified maximum, then the alignment is
not done at all. You can omit the fill value (the second argument)
entirely by simply using two commas after the required alignment; this
can be useful if you want the alignment to be filled with no-op
instructions when appropriate.
The `.balignw' and `.balignl' directives are variants of the
`.balign' directive. The `.balignw' directive treats the fill pattern
as a two byte word value. The `.balignl' directives treats the fill
pattern as a four byte longword value. For example, `.balignw
4,0x368d' will align to a multiple of 4. If it skips two bytes, they
will be filled in with the value 0x368d (the exact placement of the
bytes depends upon the endianness of the processor). If it skips 1 or
3 bytes, the fill value is undefined.
File: as.info, Node: Byte, Next: Comm, Prev: Balign, Up: Pseudo Ops
7.7 `.byte EXPRESSIONS'
=======================
`.byte' expects zero or more expressions, separated by commas. Each
expression is assembled into the next byte.
File: as.info, Node: Comm, Next: CFI directives, Prev: Byte, Up: Pseudo Ops
7.8 `.comm SYMBOL , LENGTH '
============================
`.comm' declares a common symbol named SYMBOL. When linking, a common
symbol in one object file may be merged with a defined or common symbol
of the same name in another object file. If `ld' does not see a
definition for the symbol-just one or more common symbols-then it will
allocate LENGTH bytes of uninitialized memory. LENGTH must be an
absolute expression. If `ld' sees multiple common symbols with the
same name, and they do not all have the same size, it will allocate
space using the largest size.
When using ELF, the `.comm' directive takes an optional third
argument. This is the desired alignment of the symbol, specified as a
byte boundary (for example, an alignment of 16 means that the least
significant 4 bits of the address should be zero). The alignment must
be an absolute expression, and it must be a power of two. If `ld'
allocates uninitialized memory for the common symbol, it will use the
alignment when placing the symbol. If no alignment is specified, `as'
will set the alignment to the largest power of two less than or equal
to the size of the symbol, up to a maximum of 16.
The syntax for `.comm' differs slightly on the HPPA. The syntax is
`SYMBOL .comm, LENGTH'; SYMBOL is optional.
File: as.info, Node: CFI directives, Next: Data, Prev: Comm, Up: Pseudo Ops
7.9 `.cfi_startproc'
====================
`.cfi_startproc' is used at the beginning of each function that should
have an entry in `.eh_frame'. It initializes some internal data
structures and emits architecture dependent initial CFI instructions.
Don't forget to close the function by `.cfi_endproc'.
7.10 `.cfi_endproc'
===================
`.cfi_endproc' is used at the end of a function where it closes its
unwind entry previously opened by `.cfi_startproc'. and emits it to
`.eh_frame'.
7.11 `.cfi_def_cfa REGISTER, OFFSET'
====================================
`.cfi_def_cfa' defines a rule for computing CFA as: take address from
REGISTER and add OFFSET to it.
7.12 `.cfi_def_cfa_register REGISTER'
=====================================
`.cfi_def_cfa_register' modifies a rule for computing CFA. From now on
REGISTER will be used instead of the old one. Offset remains the same.
7.13 `.cfi_def_cfa_offset OFFSET'
=================================
`.cfi_def_cfa_offset' modifies a rule for computing CFA. Register
remains the same, but OFFSET is new. Note that it is the absolute
offset that will be added to a defined register to compute CFA address.
7.14 `.cfi_adjust_cfa_offset OFFSET'
====================================
Same as `.cfi_def_cfa_offset' but OFFSET is a relative value that is
added/substracted from the previous offset.
7.15 `.cfi_offset REGISTER, OFFSET'
===================================
Previous value of REGISTER is saved at offset OFFSET from CFA.
7.16 `.cfi_rel_offset REGISTER, OFFSET'
=======================================
Previous value of REGISTER is saved at offset OFFSET from the current
CFA register. This is transformed to `.cfi_offset' using the known
displacement of the CFA register from the CFA. This is often easier to
use, because the number will match the code it's annotating.
7.17 `.cfi_signal_frame'
========================
Mark current function as signal trampoline.
7.18 `.cfi_window_save'
=======================
SPARC register window has been saved.
7.19 `.cfi_escape' EXPRESSION[, ...]
====================================
Allows the user to add arbitrary bytes to the unwind info. One might
use this to add OS-specific CFI opcodes, or generic CFI opcodes that
GAS does not yet support.
File: as.info, Node: Data, Next: Def, Prev: CFI directives, Up: Pseudo Ops
7.20 `.data SUBSECTION'
=======================
`.data' tells `as' to assemble the following statements onto the end of
the data subsection numbered SUBSECTION (which is an absolute
expression). If SUBSECTION is omitted, it defaults to zero.
File: as.info, Node: Def, Next: Desc, Prev: Data, Up: Pseudo Ops
7.21 `.def NAME'
================
Begin defining debugging information for a symbol NAME; the definition
extends until the `.endef' directive is encountered.
This directive is only observed when `as' is configured for COFF
format output; when producing `b.out', `.def' is recognized, but
ignored.
File: as.info, Node: Desc, Next: Dim, Prev: Def, Up: Pseudo Ops
7.22 `.desc SYMBOL, ABS-EXPRESSION'
===================================
This directive sets the descriptor of the symbol (*note Symbol
Attributes::) to the low 16 bits of an absolute expression.
The `.desc' directive is not available when `as' is configured for
COFF output; it is only for `a.out' or `b.out' object format. For the
sake of compatibility, `as' accepts it, but produces no output, when
configured for COFF.
File: as.info, Node: Dim, Next: Double, Prev: Desc, Up: Pseudo Ops
7.23 `.dim'
===========
This directive is generated by compilers to include auxiliary debugging
information in the symbol table. It is only permitted inside
`.def'/`.endef' pairs.
`.dim' is only meaningful when generating COFF format output; when
`as' is generating `b.out', it accepts this directive but ignores it.
File: as.info, Node: Double, Next: Eject, Prev: Dim, Up: Pseudo Ops
7.24 `.double FLONUMS'
======================
`.double' expects zero or more flonums, separated by commas. It
assembles floating point numbers. The exact kind of floating point
numbers emitted depends on how `as' is configured. *Note Machine
Dependencies::.
File: as.info, Node: Eject, Next: Else, Prev: Double, Up: Pseudo Ops
7.25 `.eject'
=============
Force a page break at this point, when generating assembly listings.
File: as.info, Node: Else, Next: Elseif, Prev: Eject, Up: Pseudo Ops
7.26 `.else'
============
`.else' is part of the `as' support for conditional assembly; *note
`.if': If. It marks the beginning of a section of code to be assembled
if the condition for the preceding `.if' was false.
File: as.info, Node: Elseif, Next: End, Prev: Else, Up: Pseudo Ops
7.27 `.elseif'
==============
`.elseif' is part of the `as' support for conditional assembly; *note
`.if': If. It is shorthand for beginning a new `.if' block that would
otherwise fill the entire `.else' section.
File: as.info, Node: End, Next: Endef, Prev: Elseif, Up: Pseudo Ops
7.28 `.end'
===========
`.end' marks the end of the assembly file. `as' does not process
anything in the file past the `.end' directive.
File: as.info, Node: Endef, Next: Endfunc, Prev: End, Up: Pseudo Ops
7.29 `.endef'
=============
This directive flags the end of a symbol definition begun with `.def'.
`.endef' is only meaningful when generating COFF format output; if
`as' is configured to generate `b.out', it accepts this directive but
ignores it.
File: as.info, Node: Endfunc, Next: Endif, Prev: Endef, Up: Pseudo Ops
7.30 `.endfunc'
===============
`.endfunc' marks the end of a function specified with `.func'.
File: as.info, Node: Endif, Next: Equ, Prev: Endfunc, Up: Pseudo Ops
7.31 `.endif'
=============
`.endif' is part of the `as' support for conditional assembly; it marks
the end of a block of code that is only assembled conditionally. *Note
`.if': If.
File: as.info, Node: Equ, Next: Equiv, Prev: Endif, Up: Pseudo Ops
7.32 `.equ SYMBOL, EXPRESSION'
==============================
This directive sets the value of SYMBOL to EXPRESSION. It is
synonymous with `.set'; *note `.set': Set.
The syntax for `equ' on the HPPA is `SYMBOL .equ EXPRESSION'.
File: as.info, Node: Equiv, Next: Err, Prev: Equ, Up: Pseudo Ops
7.33 `.equiv SYMBOL, EXPRESSION'
================================
The `.equiv' directive is like `.equ' and `.set', except that the
assembler will signal an error if SYMBOL is already defined. Note a
symbol which has been referenced but not actually defined is considered
to be undefined.
Except for the contents of the error message, this is roughly
equivalent to
.ifdef SYM
.err
.endif
.equ SYM,VAL
File: as.info, Node: Err, Next: Exitm, Prev: Equiv, Up: Pseudo Ops
7.34 `.err'
===========
If `as' assembles a `.err' directive, it will print an error message
and, unless the `-Z' option was used, it will not generate an object
file. This can be used to signal error an conditionally compiled code.
File: as.info, Node: Exitm, Next: Extern, Prev: Err, Up: Pseudo Ops
7.35 `.exitm'
=============
Exit early from the current macro definition. *Note Macro::.
File: as.info, Node: Extern, Next: Fail, Prev: Exitm, Up: Pseudo Ops
7.36 `.extern'
==============
`.extern' is accepted in the source program--for compatibility with
other assemblers--but it is ignored. `as' treats all undefined symbols
as external.
File: as.info, Node: Fail, Next: File, Prev: Extern, Up: Pseudo Ops
7.37 `.fail EXPRESSION'
=======================
Generates an error or a warning. If the value of the EXPRESSION is 500
or more, `as' will print a warning message. If the value is less than
500, `as' will print an error message. The message will include the
value of EXPRESSION. This can occasionally be useful inside complex
nested macros or conditional assembly.
File: as.info, Node: File, Next: Fill, Prev: Fail, Up: Pseudo Ops
7.38 `.file STRING'
===================
`.file' tells `as' that we are about to start a new logical file.
STRING is the new file name. In general, the filename is recognized
whether or not it is surrounded by quotes `"'; but if you wish to
specify an empty file name, you must give the quotes-`""'. This
statement may go away in future: it is only recognized to be compatible
with old `as' programs. In some configurations of `as', `.file' has
already been removed to avoid conflicts with other assemblers. *Note
Machine Dependencies::.
File: as.info, Node: Fill, Next: Float, Prev: File, Up: Pseudo Ops
7.39 `.fill REPEAT , SIZE , VALUE'
==================================
REPEAT, SIZE and VALUE are absolute expressions. This emits REPEAT
copies of SIZE bytes. REPEAT may be zero or more. SIZE may be zero or
more, but if it is more than 8, then it is deemed to have the value 8,
compatible with other people's assemblers. The contents of each REPEAT
bytes is taken from an 8-byte number. The highest order 4 bytes are
zero. The lowest order 4 bytes are VALUE rendered in the byte-order of
an integer on the computer `as' is assembling for. Each SIZE bytes in
a repetition is taken from the lowest order SIZE bytes of this number.
Again, this bizarre behavior is compatible with other people's
assemblers.
SIZE and VALUE are optional. If the second comma and VALUE are
absent, VALUE is assumed zero. If the first comma and following tokens
are absent, SIZE is assumed to be 1.
File: as.info, Node: Float, Next: Func, Prev: Fill, Up: Pseudo Ops
7.40 `.float FLONUMS'
=====================
This directive assembles zero or more flonums, separated by commas. It
has the same effect as `.single'. The exact kind of floating point
numbers emitted depends on how `as' is configured. *Note Machine
Dependencies::.
File: as.info, Node: Func, Next: Global, Prev: Float, Up: Pseudo Ops
7.41 `.func NAME[,LABEL]'
=========================
`.func' emits debugging information to denote function NAME, and is
ignored unless the file is assembled with debugging enabled. Only
`--gstabs[+]' is currently supported. LABEL is the entry point of the
function and if omitted NAME prepended with the `leading char' is used.
`leading char' is usually `_' or nothing, depending on the target. All
functions are currently defined to have `void' return type. The
function must be terminated with `.endfunc'.
File: as.info, Node: Global, Next: Hidden, Prev: Func, Up: Pseudo Ops
7.42 `.global SYMBOL', `.globl SYMBOL'
======================================
`.global' makes the symbol visible to `ld'. If you define SYMBOL in
your partial program, its value is made available to other partial
programs that are linked with it. Otherwise, SYMBOL takes its
attributes from a symbol of the same name from another file linked into
the same program.
Both spellings (`.globl' and `.global') are accepted, for
compatibility with other assemblers.
On the HPPA, `.global' is not always enough to make it accessible to
other partial programs. You may need the HPPA-only `.EXPORT' directive
as well. *Note HPPA Assembler Directives: HPPA Directives.
File: as.info, Node: Hidden, Next: hword, Prev: Global, Up: Pseudo Ops
7.43 `.hidden NAMES'
====================
This is one of the ELF visibility directives. The other two are
`.internal' (*note `.internal': Internal.) and `.protected' (*note
`.protected': Protected.).
This directive overrides the named symbols default visibility (which
is set by their binding: local, global or weak). The directive sets
the visibility to `hidden' which means that the symbols are not visible
to other components. Such symbols are always considered to be
`protected' as well.
File: as.info, Node: hword, Next: Ident, Prev: Hidden, Up: Pseudo Ops
7.44 `.hword EXPRESSIONS'
=========================
This expects zero or more EXPRESSIONS, and emits a 16 bit number for
each.
This directive is a synonym for `.short'; depending on the target
architecture, it may also be a synonym for `.word'.
File: as.info, Node: Ident, Next: If, Prev: hword, Up: Pseudo Ops
7.45 `.ident'
=============
This directive is used by some assemblers to place tags in object files.
`as' simply accepts the directive for source-file compatibility with
such assemblers, but does not actually emit anything for it.
File: as.info, Node: If, Next: Incbin, Prev: Ident, Up: Pseudo Ops
7.46 `.if ABSOLUTE EXPRESSION'
==============================
`.if' marks the beginning of a section of code which is only considered
part of the source program being assembled if the argument (which must
be an ABSOLUTE EXPRESSION) is non-zero. The end of the conditional
section of code must be marked by `.endif' (*note `.endif': Endif.);
optionally, you may include code for the alternative condition, flagged
by `.else' (*note `.else': Else.). If you have several conditions to
check, `.elseif' may be used to avoid nesting blocks if/else within
each subsequent `.else' block.
The following variants of `.if' are also supported:
`.ifdef SYMBOL'
Assembles the following section of code if the specified SYMBOL
has been defined. Note a symbol which has been referenced but not
yet defined is considered to be undefined.
`.ifc STRING1,STRING2'
Assembles the following section of code if the two strings are the
same. The strings may be optionally quoted with single quotes.
If they are not quoted, the first string stops at the first comma,
and the second string stops at the end of the line. Strings which
contain whitespace should be quoted. The string comparison is
case sensitive.
`.ifeq ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is zero.
`.ifeqs STRING1,STRING2'
Another form of `.ifc'. The strings must be quoted using double
quotes.
`.ifge ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is greater
than or equal to zero.
`.ifgt ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is greater
than zero.
`.ifle ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is less
than or equal to zero.
`.iflt ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is less
than zero.
`.ifnc STRING1,STRING2.'
Like `.ifc', but the sense of the test is reversed: this assembles
the following section of code if the two strings are not the same.
`.ifndef SYMBOL'
`.ifnotdef SYMBOL'
Assembles the following section of code if the specified SYMBOL
has not been defined. Both spelling variants are equivalent.
Note a symbol which has been referenced but not yet defined is
considered to be undefined.
`.ifne ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is not
equal to zero (in other words, this is equivalent to `.if').
`.ifnes STRING1,STRING2'
Like `.ifeqs', but the sense of the test is reversed: this
assembles the following section of code if the two strings are not
the same.
File: as.info, Node: Incbin, Next: Include, Prev: If, Up: Pseudo Ops
7.47 `.incbin "FILE"[,SKIP[,COUNT]]'
====================================
The `incbin' directive includes FILE verbatim at the current location.
You can control the search paths used with the `-I' command-line option
(*note Command-Line Options: Invoking.). Quotation marks are required
around FILE.
The SKIP argument skips a number of bytes from the start of the
FILE. The COUNT argument indicates the maximum number of bytes to
read. Note that the data is not aligned in any way, so it is the user's
responsibility to make sure that proper alignment is provided both
before and after the `incbin' directive.
File: as.info, Node: Include, Next: Int, Prev: Incbin, Up: Pseudo Ops
7.48 `.include "FILE"'
======================
This directive provides a way to include supporting files at specified
points in your source program. The code from FILE is assembled as if
it followed the point of the `.include'; when the end of the included
file is reached, assembly of the original file continues. You can
control the search paths used with the `-I' command-line option (*note
Command-Line Options: Invoking.). Quotation marks are required around
FILE.
File: as.info, Node: Int, Next: Internal, Prev: Include, Up: Pseudo Ops
7.49 `.int EXPRESSIONS'
=======================
Expect zero or more EXPRESSIONS, of any section, separated by commas.
For each expression, emit a number that, at run time, is the value of
that expression. The byte order and bit size of the number depends on
what kind of target the assembly is for.
File: as.info, Node: Internal, Next: Irp, Prev: Int, Up: Pseudo Ops
7.50 `.internal NAMES'
======================
This is one of the ELF visibility directives. The other two are
`.hidden' (*note `.hidden': Hidden.) and `.protected' (*note
`.protected': Protected.).
This directive overrides the named symbols default visibility (which
is set by their binding: local, global or weak). The directive sets
the visibility to `internal' which means that the symbols are
considered to be `hidden' (i.e., not visible to other components), and
that some extra, processor specific processing must also be performed
upon the symbols as well.
File: as.info, Node: Irp, Next: Irpc, Prev: Internal, Up: Pseudo Ops
7.51 `.irp SYMBOL,VALUES'...
============================
Evaluate a sequence of statements assigning different values to SYMBOL.
The sequence of statements starts at the `.irp' directive, and is
terminated by an `.endr' directive. For each VALUE, SYMBOL is set to
VALUE, and the sequence of statements is assembled. If no VALUE is
listed, the sequence of statements is assembled once, with SYMBOL set
to the null string. To refer to SYMBOL within the sequence of
statements, use \SYMBOL.
For example, assembling
.irp param,1,2,3
move d\param,sp@-
.endr
is equivalent to assembling
move d1,sp@-
move d2,sp@-
move d3,sp@-
File: as.info, Node: Irpc, Next: Lcomm, Prev: Irp, Up: Pseudo Ops
7.52 `.irpc SYMBOL,VALUES'...
=============================
Evaluate a sequence of statements assigning different values to SYMBOL.
The sequence of statements starts at the `.irpc' directive, and is
terminated by an `.endr' directive. For each character in VALUE,
SYMBOL is set to the character, and the sequence of statements is
assembled. If no VALUE is listed, the sequence of statements is
assembled once, with SYMBOL set to the null string. To refer to SYMBOL
within the sequence of statements, use \SYMBOL.
For example, assembling
.irpc param,123
move d\param,sp@-
.endr
is equivalent to assembling
move d1,sp@-
move d2,sp@-
move d3,sp@-
File: as.info, Node: Lcomm, Next: Lflags, Prev: Irpc, Up: Pseudo Ops
7.53 `.lcomm SYMBOL , LENGTH'
=============================
Reserve LENGTH (an absolute expression) bytes for a local common
denoted by SYMBOL. The section and value of SYMBOL are those of the
new local common. The addresses are allocated in the bss section, so
that at run-time the bytes start off zeroed. SYMBOL is not declared
global (*note `.global': Global.), so is normally not visible to `ld'.
Some targets permit a third argument to be used with `.lcomm'. This
argument specifies the desired alignment of the symbol in the bss
section.
The syntax for `.lcomm' differs slightly on the HPPA. The syntax is
`SYMBOL .lcomm, LENGTH'; SYMBOL is optional.
File: as.info, Node: Lflags, Next: Line, Prev: Lcomm, Up: Pseudo Ops
7.54 `.lflags'
==============
`as' accepts this directive, for compatibility with other assemblers,
but ignores it.
File: as.info, Node: Line, Next: Ln, Prev: Lflags, Up: Pseudo Ops
7.55 `.line LINE-NUMBER'
========================
Change the logical line number. LINE-NUMBER must be an absolute
expression. The next line has that logical line number. Therefore any
other statements on the current line (after a statement separator
character) are reported as on logical line number LINE-NUMBER - 1. One
day `as' will no longer support this directive: it is recognized only
for compatibility with existing assembler programs.
_Warning:_ In the AMD29K configuration of as, this command is not
available; use the synonym `.ln' in that context.
Even though this is a directive associated with the `a.out' or
`b.out' object-code formats, `as' still recognizes it when producing
COFF output, and treats `.line' as though it were the COFF `.ln' _if_
it is found outside a `.def'/`.endef' pair.
Inside a `.def', `.line' is, instead, one
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