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darling-gdb/gas/doc/as.texinfo
Roland Pesch 8d8ddccbe0 Updates for Hitachi H8/300H
1993-07-10 00:31:03 +00:00

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\input texinfo @c -*-Texinfo-*-
@c Copyright (c) 1991 1992 1993 Free Software Foundation, Inc.
@c %**start of header
@setfilename as.info
@c ---config---
@c defaults, config file may override:
@set have-stabs
@c ---
@include asdoc-config.texi
@c ---
@c common OR combinations of conditions
@ifset AOUT
@set aout-bout
@end ifset
@ifset BOUT
@set aout-bout
@end ifset
@ifset H8/300
@set H8
@end ifset
@ifset H8/500
@set H8
@end ifset
@ifset SH
@set H8
@end ifset
@c ------------
@ifset GENERIC
@settitle Using @value{AS}
@end ifset
@ifclear GENERIC
@settitle Using @value{AS} (@value{TARGET})
@end ifclear
@setchapternewpage odd
@c %**end of header
@ifinfo
@format
START-INFO-DIR-ENTRY
* As:: The GNU assembler.
END-INFO-DIR-ENTRY
@end format
@end ifinfo
@finalout
@syncodeindex ky cp
@ifinfo
This file documents the GNU Assembler "@value{AS}".
Copyright (C) 1991, 1992, 1993 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
@ignore
Permission is granted to process this file through Tex and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).
@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
section entitled ``GNU General Public License'' is included exactly as
in the original, and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to this
one.
Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that the section entitled ``GNU General Public License'' may be
included in a translation approved by the Free Software Foundation
instead of in the original English.
@end ifinfo
@titlepage
@title Using @value{AS}
@subtitle The GNU Assembler
@ifclear GENERIC
@subtitle for the @value{TARGET} family
@end ifclear
@sp 1
@subtitle March 1993
@sp 1
@sp 13
The Free Software Foundation Inc. thanks The Nice Computer
Company of Australia for loaning Dean Elsner to write the
first (Vax) version of @code{as} for Project GNU.
The proprietors, management and staff of TNCCA thank FSF for
distracting the boss while they got some work
done.
@sp 3
@author Dean Elsner, Jay Fenlason & friends
@page
@tex
{\parskip=0pt
\hfill {\it Using {\tt @value{AS}}}\par
\hfill Edited by Roland Pesch for Cygnus Support\par
}
%"boxit" macro for figures:
%Modified from Knuth's ``boxit'' macro from TeXbook (answer to exercise 21.3)
\gdef\boxit#1#2{\vbox{\hrule\hbox{\vrule\kern3pt
\vbox{\parindent=0pt\parskip=0pt\hsize=#1\kern3pt\strut\hfil
#2\hfil\strut\kern3pt}\kern3pt\vrule}\hrule}}%box with visible outline
\gdef\ibox#1#2{\hbox to #1{#2\hfil}\kern8pt}% invisible box
@end tex
@vskip 0pt plus 1filll
Copyright @copyright{} 1991, 1992, 1993 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
section entitled ``GNU General Public License'' is included exactly as
in the original, and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to this
one.
Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that the section entitled ``GNU General Public License'' may be
included in a translation approved by the Free Software Foundation
instead of in the original English.
@end titlepage
@ifinfo
@node Top
@top Using @value{AS}
This file is a user guide to the GNU assembler @code{@value{AS}}.
@ifclear GENERIC
This version of the file describes @code{@value{AS}} configured to generate
code for @value{TARGET} architectures.
@end ifclear
@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
@ifset GENERIC
* Copying:: GNU GENERAL PUBLIC LICENSE
@end ifset
* Index:: Index
@end menu
@end ifinfo
@node Overview
@chapter Overview
@iftex
This manual is a user guide to the GNU assembler @code{@value{AS}}.
@ifclear GENERIC
This version of the manual describes @code{@value{AS}} configured to generate
code for @value{TARGET} architectures.
@end ifclear
@end iftex
@cindex invocation summary
@cindex option summary
@cindex summary of options
Here is a brief summary of how to invoke @code{@value{AS}}. For details,
@pxref{Invoking,,Comand-Line Options}.
@c We don't use deffn and friends for the following because they seem
@c to be limited to one line for the header.
@smallexample
@value{AS} [ -a[dhlns] ] [ -D ] [ -f ]
[ -I @var{path} ] [ -K ] [ -L ]
[ -o @var{objfile} ] [ -R ] [ -v ] [ -w ]
@ifset A29K
@c am29k has no machine-dependent assembler options
@end ifset
@ifset H8
@c Hitachi family chips have no machine-dependent assembler options
@end ifset
@ifset SPARC
[ -Av6 | -Av7 | -Av8 | -Asparclite | -bump ]
@end ifset
@ifset Z8000
@c Z8000 has no machine-dependent assembler options
@end ifset
@ifset I960
@c see md_parse_option in tc-i960.c
[ -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC ]
[ -b ] [ -norelax ]
@end ifset
@ifset M680X0
[ -l ] [ -m68000 | -m68010 | -m68020 | ... ]
@end ifset
@ifset MIPS
[ -nocpp ] [ -EL ] [ -EB ] [ -G @var{num} ]
@end ifset
[ -- | @var{files} @dots{} ]
@end smallexample
@table @code
@item -a[dhlns]
Turn on listings;
@samp{-ad}, omit debugging pseudo-ops from listing,
@samp{-ah}, include high-level source,
@samp{-al}, assembly listing,
@samp{-an}, no forms processing,
@samp{-as}, symbols.
These options may be combined; @emph{e.g.}, @samp{-aln} for assembly
listing without forms processing. By itself, @samp{-a} defaults to
@samp{-ahls} --- that is, all listings turned on.
@item -D
This option is accepted only for script compatibility with calls to
other assemblers; it has no effect on @code{@value{AS}}.
@item -f
``fast''---skip preprocessing (assume source is compiler output)
@item -I @var{path}
Add @var{path} to the search list for @code{.include} directives
@item -K
@ifclear DIFF-TBL-KLUGE
This option is accepted but has no effect on the @value{TARGET} family.
@end ifclear
@ifset DIFF-TBL-KLUGE
Issue warnings when difference tables altered for long displacements.
@end ifset
@item -L
Keep (in symbol table) local symbols, starting with @samp{L}
@item -o @var{objfile}
Name the object-file output from @code{@value{AS}}
@item -R
Fold data section into text section
@item -v
Announce @code{as} version
@item -W
Suppress warning messages
@item -- | @var{files} @dots{}
Standard input, or source files to assemble.
@end table
@ifset I960
The following options are available when @value{AS} is configured for the
Intel 80960 processor.
@table @code
@item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
Specify which variant of the 960 architecture is the target.
@item -b
Add code to collect statistics about branches taken.
@item -norelax
Do not alter compare-and-branch instructions for long displacements;
error if necessary.
@end table
@end ifset
@ifset M680X0
The following options are available when @value{AS} is configured for the
Motorola 68000 series.
@table @code
@item -l
Shorten references to undefined symbols, to one word instead of two.
@item -m68000 | -m68008 | -m68010 | -m68020 | -m68030 | -m68040
@itemx | -m68302 | -m68331 | -m68332 | -m68333 | -m68340 | -mcpu32
Specify what processor in the 68000 family is the target. The default
is normally the 68020, but this can be changed at configuration time.
@item -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.
@item -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.
@end table
@end ifset
@ifset SPARC
The following options are available when @code{@value{AS}} is configured
for the SPARC architecture:
@table @code
@item -Av6 | -Av7 | -Av8 | -Asparclite
Explicitly select a variant of the SPARC architecture.
@item -bump
Warn when the assembler switches to another architecture.
@end table
@end ifset
@ifset MIPS
The following options are available when @value{AS} is configured for
the MIPS R2000/R3000 processors.
@table @code
@item -G @var{num}
This option sets the largest size of an object that will be referenced
implicitly with the @code{gp} register. It is only accepted for targets
that use ECOFF format, such as a DECstation running Ultrix. The default
value is 8.
@item -nocpp
@itemx -EB, -EL
These options are ignored. They are accepted for compatibility with the
native tools.
@end table
@end ifset
@menu
* Manual:: Structure of this Manual
* GNU Assembler:: @value{AS}, 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
@end menu
@node Manual
@section Structure of this Manual
@cindex manual, structure and purpose
This manual is intended to describe what you need to know to use
@sc{gnu} @code{@value{AS}}. We cover the syntax expected in source files, including
notation for symbols, constants, and expressions; the directives that
@code{@value{AS}} understands; and of course how to invoke @code{@value{AS}}.
@ifclear GENERIC
We also cover special features in the @value{TARGET}
configuration of @code{@value{AS}}, including assembler directives.
@end ifclear
@ifset GENERIC
This manual also describes some of the machine-dependent features of
various flavors of the assembler.
@end ifset
@ifset INTERNALS
This manual also describes how the assembler works internally, and
provides some information that may be useful to people attempting to
port the assembler to another machine.
@end ifset
@refill
@cindex machine instructions (not covered)
On the other hand, this manual is @emph{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 @emph{not} describe the instruction set, standard
mnemonics, registers or addressing modes that are standard to a
particular architecture.
@ifset GENERIC
You may want to consult the manufacturer's
machine architecture manual for this information.
@end ifset
@ifclear GENERIC
@ifset H8/300
For information on the H8/300 machine instruction set, see @cite{H8/300
Series Programming Manual} (Hitachi ADE--602--025). For the H8/300H,
see @cite{H8/300H Series Programming Manual} (Hitachi).
@end ifset
@ifset H8/500
For information on the H8/500 machine instruction set, see @cite{H8/500
Series Programming Manual} (Hitachi M21T001).
@end ifset
@ifset SH
For information on the Hitachi SH machine instruction set, see
@cite{SH-Microcomputer User's Manual} (Hitachi Micro Systems, Inc.).
@end ifset
@ifset Z8000
For information on the Z8000 machine instruction set, see @cite{Z8000 CPU Technical Manual}
@end ifset
@end ifclear
@c I think this is premature---pesch@cygnus.com, 17jan1991
@ignore
Throughout this manual, we assume that you are running @dfn{GNU},
the portable operating system from the @dfn{Free Software
Foundation, Inc.}. This restricts our attention to certain kinds of
computer (in particular, the kinds of computers that GNU can run on);
once this assumption is granted examples and definitions need less
qualification.
@code{@value{AS}} is part of a team of programs that turn a high-level
human-readable series of instructions into a low-level
computer-readable series of instructions. Different versions of
@code{@value{AS}} are used for different kinds of computer.
@end ignore
@c There used to be a section "Terminology" here, which defined
@c "contents", "byte", "word", and "long". Defining "word" to any
@c particular size is confusing when the .word directive may generate 16
@c bits on one machine and 32 bits on another; in general, for the user
@c version of this manual, none of these terms seem essential to define.
@c They were used very little even in the former draft of the manual;
@c this draft makes an effort to avoid them (except in names of
@c directives).
@node GNU Assembler
@section @value{AS}, the GNU Assembler
GNU @code{as} is really a family of assemblers.
@ifclear GENERIC
This manual describes @code{@value{AS}}, a member of that family which is
configured for the @value{TARGET} architectures.
@end ifclear
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
@dfn{pseudo-ops}) and assembler syntax.@refill
@cindex purpose of @sc{gnu} @code{@value{AS}}
@code{@value{AS}} is primarily intended to assemble the output of the
GNU C compiler @code{@value{GCC}} for use by the linker
@code{@value{LD}}. Nevertheless, we've tried to make @code{@value{AS}}
assemble correctly everything that other assemblers for the same
machine would assemble.
@ifset VAX
Any exceptions are documented explicitly (@pxref{Machine Dependencies}).
@end ifset
@ifset M680X0
@c This remark should appear in generic version of manual; assumption
@c here is that generic version sets M680x0.
This doesn't mean @code{@value{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.
@end ifset
Unlike older assemblers, @code{@value{AS}} is designed to assemble a source
program in one pass of the source file. This has a subtle impact on the
@kbd{.org} directive (@pxref{Org,,@code{.org}}).
@node Object Formats
@section Object File Formats
@cindex object file format
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. @xref{Symbol
Attributes,,Symbol Attributes}.
@ifclear GENERIC
@ifclear MULTI-OBJ
On the @value{TARGET}, @code{@value{AS}} is configured to produce
@value{OBJ-NAME} format object files.
@end ifclear
@c The following should exhaust all configs that set MULTI-OBJ, ideally
@ifset A29K
On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
@code{a.out} or COFF format object files.
@end ifset
@ifset I960
On the @value{TARGET}, @code{@value{AS}} can be configured to produce either
@code{b.out} or COFF format object files.
@end ifset
@end ifclear
@node Command Line
@section Command Line
@cindex command line conventions
After the program name @code{@value{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.
@cindex standard input, as input file
@kindex --
@file{--} (two hyphens) by itself names the standard input file
explicitly, as one of the files for @code{@value{AS}} to assemble.
@cindex options, command line
Except for @samp{--} any command line argument that begins with a
hyphen (@samp{-}) is an option. Each option changes the behavior of
@code{@value{AS}}. No option changes the way another option works. An
option is a @samp{-} 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:
@smallexample
@value{AS} -o my-object-file.o mumble.s
@value{AS} -omy-object-file.o mumble.s
@end smallexample
@node Input Files
@section Input Files
@cindex input
@cindex source program
@cindex files, input
We use the phrase @dfn{source program}, abbreviated @dfn{source}, to
describe the program input to one run of @code{@value{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.
@c I added "con" prefix to "catenation" just to prove I can overcome my
@c APL training... pesch@cygnus.com
The source program is a concatenation of the text in all the files, in the
order specified.
Each time you run @code{@value{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 @code{@value{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 @code{@value{AS}} no file names it attempts to read one input file
from the @code{@value{AS}} standard input, which is normally your terminal. You
may have to type @key{ctl-D} to tell @code{@value{AS}} there is no more program
to assemble.
Use @samp{--} if you need to explicitly name the standard input file
in your command line.
If the source is empty, @code{@value{AS}} will produce a small, empty object
file.
@subheading Filenames and Line-numbers
@cindex input file linenumbers
@cindex line numbers, in input files
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. @xref{Errors, ,Error and Warning Messages}.
@dfn{Physical files} are those files named in the command line given
to @code{@value{AS}}.
@dfn{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 @code{@value{AS}}
source is itself synthesized from other files.
@xref{App-File,,@code{.app-file}}.
@node Object
@section Output (Object) File
@cindex object file
@cindex output file
@kindex a.out
@kindex .o
Every time you run @code{@value{AS}} it produces an output file, which is
your assembly language program translated into numbers. This file
is the object file, named
@ifset BOUT
@code{b.out},
@ifset GENERIC
if @code{@value{AS}} is configured for the Intel 80960, or
@end ifset
@end ifset
@ifclear BOUT
@code{a.out},
@end ifclear
unless you tell @code{@value{AS}} to
give it another name by using the @code{-o} option. Conventionally,
object file names end with @file{.o}. The default name of
@file{a.out} 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
@code{a.out} format.)
@cindex linker
@kindex ld
The object file is meant for input to the linker @code{@value{LD}}. It contains
assembled program code, information to help @code{@value{LD}} integrate
the assembled program into a runnable file, and (optionally) symbolic
information for the debugger.
@c link above to some info file(s) like the description of a.out.
@c don't forget to describe GNU info as well as Unix lossage.
@node Errors
@section Error and Warning Messages
@cindex error messsages
@cindex warning messages
@cindex messages from @code{@value{AS}}
@code{@value{AS}} may write warnings and error messages to the standard error
file (usually your terminal). This should not happen when a compiler
runs @code{@value{AS}} automatically. Warnings report an assumption made so
that @code{@value{AS}} could keep assembling a flawed program; errors report a
grave problem that stops the assembly.
@cindex format of warning messages
Warning messages have the format
@smallexample
file_name:@b{NNN}:Warning Message Text
@end smallexample
@noindent
@cindex line numbers, in warnings/errors
(where @b{NNN} is a line number). If a logical file name has been given
(@pxref{App-File,,@code{.app-file}}) it is used for the filename,
otherwise the name of the current input file is used. If a logical line
number was given
@ifset GENERIC
(@pxref{Line,,@code{.line}})
@end ifset
@ifclear GENERIC
@ifclear A29K
(@pxref{Line,,@code{.line}})
@end ifclear
@ifset A29K
(@pxref{Ln,,@code{.ln}})
@end ifset
@end ifclear
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).
@cindex format of error messages
Error messages have the format
@smallexample
file_name:@b{NNN}:FATAL:Error Message Text
@end smallexample
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.
@node Invoking
@chapter Command-Line Options
@cindex options, all versions of @code{@value{AS}}
This chapter describes command-line options available in @emph{all}
versions of the GNU assembler; @pxref{Machine Dependencies}, for options specific
@ifclear GENERIC
to the @value{TARGET}.
@end ifclear
@ifset GENERIC
to particular machine architectures.
@end ifset
If you are invoking @code{@value{AS}} via the GNU C compiler (version 2), you
can use the @samp{-Wa} option to pass arguments through to the
assembler. The assembler arguments must be separated from each other
(and the @samp{-Wa}) by commas. For example:
@smallexample
gcc -c -g -O -Wa,-alh,-L file.c
@end smallexample
will cause a listing to be emitted to standard output with high-level
and assembly source.
Many compiler command-line options, such as @samp{-R} and many
machine-specific options, will be automatically be passed to the
assembler by the compiler, so usually you do not need to use this
@samp{-Wa} mechanism.
@menu
* a:: -a[dhlns] enable listings
* D:: -D for compatibility
* f:: -f to work faster
* I:: -I for .include search path
@ifclear DIFF-TBL-KLUGE
* K:: -K for compatibility
@end ifclear
@ifset DIFF-TBL-KLUGE
* K:: -K for difference tables
@end ifset
* L:: -L to retain local labels
* o:: -o to name the object file
* R:: -R to join data and text sections
* v:: -v to announce version
* W:: -W to suppress warnings
@end menu
@node a
@section Enable Listings: @code{-a[dhlns]}
@kindex -a
@kindex -ad
@kindex -ah
@kindex -al
@kindex -an
@kindex -as
@cindex listings, enabling
@cindex assembly listings, enabling
These options enable listing output from the assembler. By itself,
@samp{-a} requests high-level, assembly, and symbols listing.
Other letters may be used to select specific options for the list:
@samp{-ah} requests a high-level language listing,
@samp{-al} requests an output-program assembly listing, and
@samp{-as} requests a symbol table listing.
High-level listings require that a compiler debugging option like
@samp{-g} be used, and that assembly listings (@samp{-al}) be requested
also.
The @samp{-ad} option may be used to omit debugging pseudo-ops from the
listing.
Once you have specified one of these options, you can further control
listing output and its appearance using the directives @code{.list},
@code{.nolist}, @code{.psize}, @code{.eject}, @code{.title}, and
@code{.sbttl}.
The @samp{-an} option turns off all forms processing.
If you do not request listing output with one of the @samp{-a} options, the
listing-control directives have no effect.
The letters after @samp{-a} may be combined into one option,
@emph{e.g.}, @samp{-aln}.
@node D
@section @code{-D}
@kindex -D
This option has no effect whatsoever, but it is accepted to make it more
likely that scripts written for other assemblers will also work with
@code{@value{AS}}.
@node f
@section Work Faster: @code{-f}
@kindex -f
@cindex trusted compiler
@cindex faster processing (@code{-f})
@samp{-f} should only be used when assembling programs written by a
(trusted) compiler. @samp{-f} stops the assembler from pre-processing
the input file(s) before assembling them. @xref{Pre-processing,
,Pre-processing}.
@quotation
@emph{Warning:} if the files actually need to be pre-processed (if they
contain comments, for example), @code{@value{AS}} will not work correctly if
@samp{-f} is used.
@end quotation
@node I
@section @code{.include} search path: @code{-I} @var{path}
@kindex -I @var{path}
@cindex paths for @code{.include}
@cindex search path for @code{.include}
@cindex @code{include} directive search path
Use this option to add a @var{path} to the list of directories
@code{@value{AS}} will search for files specified in @code{.include}
directives (@pxref{Include,,@code{.include}}). You may use @code{-I} as
many times as necessary to include a variety of paths. The current
working directory is always searched first; after that, @code{@value{AS}}
searches any @samp{-I} directories in the same order as they were
specified (left to right) on the command line.
@node K
@section Difference Tables: @code{-K}
@kindex -K
@ifclear DIFF-TBL-KLUGE
On the @value{TARGET} family, this option is allowed, but has no effect. It is
permitted for compatibility with the GNU assembler on other platforms,
where it can be used to warn when the assembler alters the machine code
generated for @samp{.word} directives in difference tables. The @value{TARGET}
family does not have the addressing limitations that sometimes lead to this
alteration on other platforms.
@end ifclear
@ifset DIFF-TBL-KLUGE
@cindex difference tables, warning
@cindex warning for altered difference tables
@code{@value{AS}} sometimes alters the code emitted for directives of the form
@samp{.word @var{sym1}-@var{sym2}}; @pxref{Word,,@code{.word}}.
You can use the @samp{-K} option if you want a warning issued when this
is done.
@end ifset
@node L
@section Include Local Labels: @code{-L}
@kindex -L
@cindex local labels, retaining in output
Labels beginning with @samp{L} (upper case only) are called @dfn{local
labels}. @xref{Symbol Names}. Normally you don't 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 @code{@value{AS}} and @code{@value{LD}} discard such labels, so you don't
normally debug with them.
This option tells @code{@value{AS}} to retain those @samp{L@dots{}} symbols
in the object file. Usually if you do this you also tell the linker
@code{@value{LD}} to preserve symbols whose names begin with @samp{L}.
@node o
@section Name the Object File: @code{-o}
@kindex -o
@cindex naming object file
@cindex object file name
There is always one object file output when you run @code{@value{AS}}. By
default it has the name
@ifset GENERIC
@ifset I960
@file{a.out} (or @file{b.out}, for Intel 960 targets only).
@end ifset
@ifclear I960
@file{a.out}.
@end ifclear
@end ifset
@ifclear GENERIC
@ifset I960
@file{b.out}.
@end ifset
@ifclear I960
@file{a.out}.
@end ifclear
@end ifclear
You use this option (which takes exactly one filename) to give the
object file a different name.
Whatever the object file is called, @code{@value{AS}} will overwrite any
existing file of the same name.
@node R
@section Join Data and Text Sections: @code{-R}
@kindex -R
@cindex data and text sections, joining
@cindex text and data sections, joining
@cindex joining text and data sections
@cindex merging text and data sections
@code{-R} tells @code{@value{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. (@xref{Sections,,Sections and Relocation}.)
When you specify @code{-R} it would be possible to generate shorter
address displacements (because we don't have to cross between text and
data section). We refrain from doing this simply for compatibility with
older versions of @code{@value{AS}}. In future, @code{-R} may work this way.
@ifset COFF
When @code{@value{AS}} is configured for COFF output,
this option is only useful if you use sections named @samp{.text} and
@samp{.data}.
@end ifset
@node v
@section Announce Version: @code{-v}
@kindex -v
@kindex -version
@cindex @code{@value{AS}} version
@cindex version of @code{@value{AS}}
You can find out what version of as is running by including the
option @samp{-v} (which you can also spell as @samp{-version}) on the
command line.
@node W
@section Suppress Warnings: @code{-W}
@kindex -W
@cindex suppressing warnings
@cindex warnings, suppressing
@code{@value{AS}} should never give a warning or error message when
assembling compiler output. But programs written by people often
cause @code{@value{AS}} to give a warning that a particular assumption was
made. All such warnings are directed to the standard error file.
If you use this option, no warnings are issued. This option only
affects the warning messages: it does not change any particular of how
@code{@value{AS}} assembles your file. Errors, which stop the assembly, are
still reported.
@node Syntax
@chapter Syntax
@cindex machine-independent syntax
@cindex syntax, machine-independent
This chapter describes the machine-independent syntax allowed in a
source file. @code{@value{AS}} syntax is similar to what many other
assemblers use; it is inspired by the BSD 4.2
@ifclear VAX
assembler.
@end ifclear
@ifset VAX
assembler, except that @code{@value{AS}} does not assemble Vax bit-fields.
@end ifset
@menu
* Pre-processing:: Pre-processing
* Whitespace:: Whitespace
* Comments:: Comments
* Symbol Intro:: Symbols
* Statements:: Statements
* Constants:: Constants
@end menu
@node Pre-processing
@section Pre-Processing
@cindex preprocessing
The pre-processor:
@itemize @bullet
@cindex whitespace, removed by preprocessor
@item
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.
@cindex comments, removed by preprocessor
@item
removes all comments, replacing them with a single space, or an
appropriate number of newlines.
@cindex constants, converted by preprocessor
@item
converts character constants into the appropriate numeric values.
@end itemize
Excess whitespace, comments, and character constants
cannot be used in the portions of the input text that are not
pre-processed.
@cindex turning preprocessing on and off
@cindex preprocessing, turning on and off
@kindex #NO_APP
@kindex #APP
If the first line of an input file is @code{#NO_APP} or the @samp{-f}
option is given, the input file will not be pre-processed. Within such
an input file, parts of the file can be pre-processed by putting a line
that says @code{#APP} before the text that should be pre-processed, and
putting a line that says @code{#NO_APP} after them. This feature is
mainly intend to support @code{asm} statements in compilers whose output
normally does not need to be pre-processed.
@node Whitespace
@section Whitespace
@cindex whitespace
@dfn{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
(@pxref{Characters,,Character Constants}), any whitespace means the same
as exactly one space.
@node Comments
@section Comments
@cindex comments
There are two ways of rendering comments to @code{@value{AS}}. In both
cases the comment is equivalent to one space.
Anything from @samp{/*} through the next @samp{*/} is a comment.
This means you may not nest these comments.
@smallexample
/*
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. */
@end smallexample
@cindex line comment character
Anything from the @dfn{line comment} character to the next newline
is considered a comment and is ignored. The line comment character is
@ifset VAX
@samp{#} on the Vax;
@end ifset
@ifset I960
@samp{#} on the i960;
@end ifset
@ifset SPARC
@samp{!} on the SPARC;
@end ifset
@ifset M680X0
@samp{|} on the 680x0;
@end ifset
@ifset A29K
@samp{;} for the AMD 29K family;
@end ifset
@ifset H8/300
@samp{;} for the H8/300 family;
@end ifset
@ifset H8/500
@samp{!} for the H8/500 family;
@end ifset
@ifset SH
@samp{!} for the Hitachi SH;
@end ifset
@ifset Z8000
@samp{!} for the Z8000;
@end ifset
see @ref{Machine Dependencies}. @refill
@c FIXME What about i386, m88k, i860?
@ifset GENERIC
On some machines there are two different line comment characters. One
will only begin a comment if it is the first non-whitespace character on
a line, while the other will always begin a comment.
@end ifset
@kindex #
@cindex lines starting with @code{#}
@cindex logical line numbers
To be compatible with past assemblers, a special interpretation is
given to lines that begin with @samp{#}. Following the @samp{#} an
absolute expression (@pxref{Expressions}) is expected: this will be
the logical line number of the @b{next} line. Then a string
(@xref{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.)
@smallexample
# This is an ordinary comment.
# 42-6 "new_file_name" # New logical file name
# This is logical line # 36.
@end smallexample
This feature is deprecated, and may disappear from future versions
of @code{@value{AS}}.
@node Symbol Intro
@section Symbols
@cindex characters used in symbols
@ifclear SPECIAL-SYMS
A @dfn{symbol} is one or more characters chosen from the set of all
letters (both upper and lower case), digits and the three characters
@samp{_.$}.
@end ifclear
@ifset SPECIAL-SYMS
@ifclear GENERIC
@ifset H8
A @dfn{symbol} is one or more characters chosen from the set of all
letters (both upper and lower case), digits and the three characters
@samp{._$}. (Save that, on the H8/300 only, you may not use @samp{$} in
symbol names.)
@end ifset
@end ifclear
@end ifset
@ifset GENERIC
On most machines, you can also use @code{$} in symbol names; exceptions
are noted in @ref{Machine Dependencies}.
@end ifset
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). @xref{Symbols}.
@cindex length of symbols
@node Statements
@section Statements
@cindex statements, structure of
@cindex line separator character
@cindex statement separator character
@ifclear GENERIC
@ifclear abnormal-separator
A @dfn{statement} ends at a newline character (@samp{\n}) or at a
semicolon (@samp{;}). The newline or semicolon is considered part of
the preceding statement. Newlines and semicolons within character
constants are an exception: they don't end statements.
@end ifclear
@ifset abnormal-separator
@ifset A29K
A @dfn{statement} ends at a newline character (@samp{\n}) or an ``at''
sign (@samp{@@}). The newline or at sign is considered part of the
preceding statement. Newlines and at signs within character constants
are an exception: they don't end statements.
@end ifset
@ifset H8
A @dfn{statement} ends at a newline character (@samp{\n}); or (for the
H8/300) a dollar sign (@samp{$}); or (for the
Hitachi-SH or the
H8/500) a semicolon
(@samp{;}). The newline or separator character is considered part of
the preceding statement. Newlines and separators within character
constants are an exception: they don't end statements.
@end ifset
@end ifset
@end ifclear
@ifset GENERIC
A @dfn{statement} ends at a newline character (@samp{\n}) or line
separator character. (The line separator is usually @samp{;}, unless
this conflicts with the comment character; @pxref{Machine Dependencies}.) The
newline or separator character is considered part of the preceding
statement. Newlines and separators within character constants are an
exception: they don't end statements.
@end ifset
@cindex newline, required at file end
@cindex EOF, newline must precede
It is an error to end any statement with end-of-file: the last
character of any input file should be a newline.@refill
@cindex continuing statements
@cindex multi-line statements
@cindex statement on multiple lines
You may write a statement on more than one line if you put a
backslash (@kbd{\}) immediately in front of any newlines within the
statement. When @code{@value{AS}} reads a backslashed newline both
characters are ignored. You can even put backslashed newlines in
the middle of symbol names without changing the meaning of your
source program.
An empty statement is allowed, and may include whitespace. It is ignored.
@cindex instructions and directives
@cindex directives and instructions
@c "key symbol" is not used elsewhere in the document; seems pedantic to
@c @defn{} it in that case, as was done previously... pesch@cygnus.com,
@c 13feb91.
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 @samp{.} 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 @dfn{instruction}: it
will assemble into a machine language instruction.
@ifset GENERIC
Different versions of @code{@value{AS}} for different computers will
recognize different instructions. In fact, the same symbol may
represent a different instruction in a different computer's assembly
language.@refill
@end ifset
@cindex @code{:} (label)
@cindex label (@code{:})
A label is a symbol immediately followed by a colon (@code{:}).
Whitespace before a label or after a colon is permitted, but you may not
have whitespace between a label's symbol and its colon. @xref{Labels}.
@smallexample
label: .directive followed by something
another_label: # This is an empty statement.
instruction operand_1, operand_2, @dots{}
@end smallexample
@node Constants
@section Constants
@cindex constants
A constant is a number, written so that its value is known by
inspection, without knowing any context. Like this:
@smallexample
@group
.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.
@end group
@end smallexample
@menu
* Characters:: Character Constants
* Numbers:: Number Constants
@end menu
@node Characters
@subsection Character Constants
@cindex character constants
@cindex constants, character
There are two kinds of character constants. A @dfn{character} stands
for one character in one byte and its value may be used in
numeric expressions. String constants (properly called string
@emph{literals}) are potentially many bytes and their values may not be
used in arithmetic expressions.
@menu
* Strings:: Strings
* Chars:: Characters
@end menu
@node Strings
@subsubsection Strings
@cindex string constants
@cindex constants, string
A @dfn{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 @dfn{escape} these characters: precede them with
a backslash @samp{\} character. For example @samp{\\} represents
one backslash: the first @code{\} is an escape which tells
@code{@value{AS}} to interpret the second character literally as a backslash
(which prevents @code{@value{AS}} from recognizing the second @code{\} as an
escape character). The complete list of escapes follows.
@cindex escape codes, character
@cindex character escape codes
@table @kbd
@c @item \a
@c Mnemonic for ACKnowledge; for ASCII this is octal code 007.
@c
@item \b
@cindex @code{\b} (backspace character)
@cindex backspace (@code{\b})
Mnemonic for backspace; for ASCII this is octal code 010.
@c @item \e
@c Mnemonic for EOText; for ASCII this is octal code 004.
@c
@item \f
@cindex @code{\f} (formfeed character)
@cindex formfeed (@code{\f})
Mnemonic for FormFeed; for ASCII this is octal code 014.
@item \n
@cindex @code{\n} (newline character)
@cindex newline (@code{\n})
Mnemonic for newline; for ASCII this is octal code 012.
@c @item \p
@c Mnemonic for prefix; for ASCII this is octal code 033, usually known as @code{escape}.
@c
@item \r
@cindex @code{\r} (carriage return character)
@cindex carriage return (@code{\r})
Mnemonic for carriage-Return; for ASCII this is octal code 015.
@c @item \s
@c Mnemonic for space; for ASCII this is octal code 040. Included for compliance with
@c other assemblers.
@c
@item \t
@cindex @code{\t} (tab)
@cindex tab (@code{\t})
Mnemonic for horizontal Tab; for ASCII this is octal code 011.
@c @item \v
@c Mnemonic for Vertical tab; for ASCII this is octal code 013.
@c @item \x @var{digit} @var{digit} @var{digit}
@c A hexadecimal character code. The numeric code is 3 hexadecimal digits.
@c
@item \ @var{digit} @var{digit} @var{digit}
@cindex @code{\@var{ddd}} (octal character code)
@cindex octal character code (@code{\@var{ddd}})
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, @code{\008} has the value 010, and @code{\009} the value 011.
@item \\
@cindex @code{\\} (@samp{\} character)
@cindex backslash (@code{\\})
Represents one @samp{\} character.
@c @item \'
@c Represents one @samp{'} (accent acute) character.
@c This is needed in single character literals
@c (@xref{Characters,,Character Constants}.) to represent
@c a @samp{'}.
@c
@item \"
@cindex @code{\"} (doublequote character)
@cindex doublequote (@code{\"})
Represents one @samp{"} character. Needed in strings to represent
this character, because an unescaped @samp{"} would end the string.
@item \ @var{anything-else}
Any other character when escaped by @kbd{\} will give a warning, but
assemble as if the @samp{\} 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 @code{@value{AS}} has no
other interpretation, so @code{@value{AS}} knows it is giving you the wrong
code and warns you of the fact.
@end table
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, don't use an escape
sequence.
@node Chars
@subsubsection Characters
@cindex single character constant
@cindex character, single
@cindex constant, single character
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 @kbd{'\\} where the first @code{\} escapes the second
@code{\}. As you can see, the quote is an acute accent, not a
grave accent. A newline
@ifclear GENERIC
@ifclear abnormal-separator
(or semicolon @samp{;})
@end ifclear
@ifset abnormal-separator
@ifset A29K
(or at sign @samp{@@})
@end ifset
@ifset H8
(or dollar sign @samp{$}, for the H8/300; or semicolon @samp{;} for the
Hitachi SH or
H8/500)
@end ifset
@end ifset
@end ifclear
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. @code{@value{AS}} assumes your character code is ASCII:
@kbd{'A} means 65, @kbd{'B} means 66, and so on. @refill
@node Numbers
@subsection Number Constants
@cindex constants, number
@cindex number constants
@code{@value{AS}} distinguishes three kinds of numbers according to how they
are stored in the target machine. @emph{Integers} are numbers that
would fit into an @code{int} in the C language. @emph{Bignums} are
integers, but they are stored in more than 32 bits. @emph{Flonums}
are floating point numbers, described below.
@menu
* Integers:: Integers
* Bignums:: Bignums
* Flonums:: Flonums
@ifclear GENERIC
@ifset I960
* Bit Fields:: Bit Fields
@end ifset
@end ifclear
@end menu
@node Integers
@subsubsection Integers
@cindex integers
@cindex constants, integer
@cindex binary integers
@cindex integers, binary
A binary integer is @samp{0b} or @samp{0B} followed by zero or more of
the binary digits @samp{01}.
@cindex octal integers
@cindex integers, octal
An octal integer is @samp{0} followed by zero or more of the octal
digits (@samp{01234567}).
@cindex decimal integers
@cindex integers, decimal
A decimal integer starts with a non-zero digit followed by zero or
more digits (@samp{0123456789}).
@cindex hexadecimal integers
@cindex integers, hexadecimal
A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or
more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}.
Integers have the usual values. To denote a negative integer, use
the prefix operator @samp{-} discussed under expressions
(@pxref{Prefix Ops,,Prefix Operators}).
@node Bignums
@subsubsection Bignums
@cindex bignums
@cindex constants, bignum
A @dfn{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.
@node Flonums
@subsubsection Flonums
@cindex flonums
@cindex floating point numbers
@cindex constants, floating point
@cindex precision, floating point
A @dfn{flonum} represents a floating point number. The translation is
indirect: a decimal floating point number from the text is converted by
@code{@value{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 @code{@value{AS}} specialized to that computer.
A flonum is written by writing (in order)
@itemize @bullet
@item
The digit @samp{0}.
@item
A letter, to tell @code{@value{AS}} the rest of the number is a flonum.
@ifset GENERIC
@kbd{e} is recommended. Case is not important.
@ignore
@c FIXME: verify if flonum syntax really this vague for most cases
(Any otherwise illegal letter
will work here, but that might be changed. Vax BSD 4.2 assembler seems
to allow any of @samp{defghDEFGH}.)
@end ignore
On the H8/300, H8/500,
Hitachi SH,
and AMD 29K architectures, the letter must be
one of the letters @samp{DFPRSX} (in upper or lower case).
On the Intel 960 architecture, the letter must be
one of the letters @samp{DFT} (in upper or lower case).
@end ifset
@ifclear GENERIC
@ifset A29K
One of the letters @samp{DFPRSX} (in upper or lower case).
@end ifset
@ifset H8
One of the letters @samp{DFPRSX} (in upper or lower case).
@end ifset
@ifset I960
One of the letters @samp{DFT} (in upper or lower case).
@end ifset
@end ifclear
@item
An optional sign: either @samp{+} or @samp{-}.
@item
An optional @dfn{integer part}: zero or more decimal digits.
@item
An optional @dfn{fractional part}: @samp{.} followed by zero
or more decimal digits.
@item
An optional exponent, consisting of:
@itemize @bullet
@item
An @samp{E} or @samp{e}.
@c I can't find a config where "EXP_CHARS" is other than 'eE', but in
@c principle this can perfectly well be different on different targets.
@item
Optional sign: either @samp{+} or @samp{-}.
@item
One or more decimal digits.
@end itemize
@end itemize
At least one of the integer part or the fractional part must be
present. The floating point number has the usual base-10 value.
@code{@value{AS}} does all processing using integers. Flonums are computed
independently of any floating point hardware in the computer running
@code{@value{AS}}.
@ifclear GENERIC
@ifset I960
@c Bit fields are written as a general facility but are also controlled
@c by a conditional-compilation flag---which is as of now (21mar91)
@c turned on only by the i960 config of GAS.
@node Bit Fields
@subsubsection Bit Fields
@cindex bit fields
@cindex constants, bit field
You can also define numeric constants as @dfn{bit fields}.
specify two numbers separated by a colon---
@example
@var{mask}:@var{value}
@end example
@noindent
the first will act as a mask; @code{@value{AS}} will bitwise-and it with the
second value.
The resulting number is then packed
@ifset GENERIC
@c this conditional paren in case bit fields turned on elsewhere than 960
(in host-dependent byte order)
@end ifset
into a field whose width depends on which assembler directive has the
bit-field as its argument. Overflow (a result from the bitwise and
requiring more binary digits to represent) is not an error; instead,
more constants are generated, of the specified width, beginning with the
least significant digits.@refill
The directives @code{.byte}, @code{.hword}, @code{.int}, @code{.long},
@code{.short}, and @code{.word} accept bit-field arguments.
@end ifset
@end ifclear
@node Sections
@chapter Sections and Relocation
@cindex sections
@cindex relocation
@menu
* Secs Background:: Background
* Ld Sections:: @value{LD} Sections
* As Sections:: @value{AS} Internal Sections
* Sub-Sections:: Sub-Sections
* bss:: bss Section
@end menu
@node Secs Background
@section 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.
@cindex linker, and assembler
@cindex assembler, and linker
The linker @code{@value{LD}} reads many object files (partial programs) and
combines their contents to form a runnable program. When @code{@value{AS}}
emits an object file, the partial program is assumed to start at address
0. @code{@value{LD}} will assign the final addresses the partial program
occupies, so that different partial programs don't overlap. This is
actually an over-simplification, but it will suffice to explain how
@code{@value{AS}} uses sections.
@code{@value{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 @emph{section}. Assigning
run-time addresses to sections is called @dfn{relocation}. It includes
the task of adjusting mentions of object-file addresses so they refer to
the proper run-time addresses.
@ifset H8
For the H8/300 and H8/500,
and for the Hitachi SH,
@code{@value{AS}} pads sections if needed to
ensure they end on a word (sixteen bit) boundary.
@end ifset
@cindex standard @code{@value{AS}} sections
An object file written by @code{@value{AS}} has at least three sections, any
of which may be empty. These are named @dfn{text}, @dfn{data} and
@dfn{bss} sections.
@ifset COFF
@ifset GENERIC
When it generates COFF output,
@end ifset
@code{@value{AS}} can also generate whatever other named sections you specify
using the @samp{.section} directive (@pxref{Section,,@code{.section}}).
If you don't use any directives that place output in the @samp{.text}
or @samp{.data} sections, these sections will still exist, but will be empty.
@end ifset
Within the object file, the text section starts at address @code{0}, the
data section follows, and the bss section follows the data section.
To let @code{@value{LD}} know which data will change when the sections are
relocated, and how to change that data, @code{@value{AS}} also writes to the
object file details of the relocation needed. To perform relocation
@code{@value{LD}} must know, each time an address in the object
file is mentioned:
@itemize @bullet
@item
Where in the object file is the beginning of this reference to
an address?
@item
How long (in bytes) is this reference?
@item
Which section does the address refer to? What is the numeric value of
@display
(@var{address}) @minus{} (@var{start-address of section})?
@end display
@item
Is the reference to an address ``Program-Counter relative''?
@end itemize
@cindex addresses, format of
@cindex section-relative addressing
In fact, every address @code{@value{AS}} ever uses is expressed as
@display
(@var{section}) + (@var{offset into section})
@end display
@noindent
Further, every expression @code{@value{AS}} computes is of this section-relative
nature. @dfn{Absolute expression} means an expression with section
``absolute'' (@pxref{Ld Sections}). A @dfn{pass1 expression} means
an expression with section ``pass1'' (@pxref{As Sections,,@value{AS}
Internal Sections}). In this manual we use the notation @{@var{secname}
@var{N}@} to mean ``offset @var{N} into section @var{secname}''.
Apart from text, data and bss sections you need to know about the
@dfn{absolute} section. When @code{@value{LD}} mixes partial programs,
addresses in the absolute section remain unchanged. For example, address
@code{@{absolute 0@}} is ``relocated'' to run-time address 0 by @code{@value{LD}}.
Although two partial programs' data sections will not overlap addresses
after linking, @emph{by definition} their absolute sections will overlap.
Address @code{@{absolute@ 239@}} in one partial program will always be the same
address when the program is running as address @code{@{absolute@ 239@}} in any
other partial program.
The idea of sections is extended to the @dfn{undefined} section. Any
address whose section is unknown at assembly time is by definition
rendered @{undefined @var{U}@}---where @var{U} will be 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 @emph{undefined}.
By analogy the word @emph{section} is used to describe groups of sections in
the linked program. @code{@value{LD}} puts all partial programs' text
sections in contiguous addresses in the linked program. It is
customary to refer to the @emph{text section} of a program, meaning all
the addresses of all partial program's text sections. Likewise for
data and bss sections.
Some sections are manipulated by @code{@value{LD}}; others are invented for
use of @code{@value{AS}} and have no meaning except during assembly.
@node Ld Sections
@section @value{LD} Sections
@code{@value{LD}} deals with just four kinds of sections, summarized below.
@table @strong
@ifset COFF
@cindex named sections
@cindex sections, named
@item named sections
@end ifset
@ifset aout-bout
@cindex text section
@cindex data section
@item text section
@itemx data section
@end ifset
These sections hold your program. @code{@value{AS}} and @code{@value{LD}} treat them as
separate but equal sections. Anything you can say of one section is
true another.
@ifset aout-bout
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 will contain
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.
@end ifset
@cindex bss section
@item bss section
This section contains zeroed bytes when your program begins running. It
is used to hold unitialized 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.
@cindex absolute section
@item 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 @code{@value{LD}} must
not change when relocating. In this sense we speak of absolute
addresses being ``unrelocatable'': they don't change during relocation.
@cindex undefined section
@item undefined section
This ``section'' is a catch-all for address references to objects not in
the preceding sections.
@c FIXME: ref to some other doc on obj-file formats could go here.
@end table
@cindex relocation example
An idealized example of three relocatable sections follows.
@ifset COFF
The example uses the traditional section names @samp{.text} and @samp{.data}.
@end ifset
Memory addresses are on the horizontal axis.
@c TEXI2ROFF-KILL
@ifinfo
@c END TEXI2ROFF-KILL
@smallexample
+-----+----+--+
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 @dots{}
@end smallexample
@c TEXI2ROFF-KILL
@end ifinfo
@c FIXME make sure no page breaks inside figure!!
@tex
\line{\it Partial program \#1: \hfil}
\line{\ibox{2.5cm}{\tt text}\ibox{2cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
\line{\boxit{2.5cm}{\tt ttttt}\boxit{2cm}{\tt dddd}\boxit{1cm}{\tt 00}\hfil}
\line{\it Partial program \#2: \hfil}
\line{\ibox{1cm}{\tt text}\ibox{1.5cm}{\tt data}\ibox{1cm}{\tt bss}\hfil}
\line{\boxit{1cm}{\tt TTT}\boxit{1.5cm}{\tt DDDD}\boxit{1cm}{\tt 000}\hfil}
\line{\it linked program: \hfil}
\line{\ibox{.5cm}{}\ibox{1cm}{\tt text}\ibox{2.5cm}{}\ibox{.75cm}{}\ibox{2cm}{\tt data}\ibox{1.5cm}{}\ibox{2cm}{\tt bss}\hfil}
\line{\boxit{.5cm}{}\boxit{1cm}{\tt TTT}\boxit{2.5cm}{\tt
ttttt}\boxit{.75cm}{}\boxit{2cm}{\tt dddd}\boxit{1.5cm}{\tt
DDDD}\boxit{2cm}{\tt 00000}\ \dots\hfil}
\line{\it addresses: \hfil}
\line{0\dots\hfil}
@end tex
@c END TEXI2ROFF-KILL
@node As Sections
@section @value{AS} Internal Sections
@cindex internal @code{@value{AS}} sections
@cindex sections in messages, internal
These sections are meant only for the internal use of @code{@value{AS}}. They
have no meaning at run-time. You don't really need to know about these
sections for most purposes; but they can be mentioned in @code{@value{AS}}
warning messages, so it might be helpful to have an idea of their
meanings to @code{@value{AS}}. These sections are used to permit the
value of every expression in your assembly language program to be a
section-relative address.
@table @b
@item absent
@cindex absent (internal section)
An expression was expected and none was found.
@item ASSEMBLER-INTERNAL-LOGIC-ERROR!
@cindex assembler internal logic error
An internal assembler logic error has been found. This means there is a
bug in the assembler.
@item bignum/flonum
@cindex bignum/flonum (internal section)
If a number can't be written as a C @code{int} constant (a bignum or a
flonum, but not an integer), it is recorded as belonging to this
``section''. @code{@value{AS}} has to remember that a flonum or a bignum
does not fit into 32 bits, and cannot be an argument (@pxref{Arguments})
in an expression: this is done by making a flonum or bignum be in a
separate internal section. This is purely for internal @code{@value{AS}}
convenience; bignum/flonum section behaves similarly to absolute
section.
@item pass1 section
@cindex pass1 (internal section)
The expression was impossible to evaluate in the first pass. The
assembler will attempt a second pass (second reading of the source) to
evaluate the expression. Your expression mentioned an undefined symbol
in a way that defies the one-pass (section + offset in section) assembly
process. No compiler need emit such an expression.
@quotation
@emph{Warning:} the second pass is currently not implemented. @code{@value{AS}}
will abort with an error message if one is required.
@end quotation
@item difference section
@cindex difference (internal section)
As an assist to the C compiler, expressions of the forms
@display
(@var{undefined symbol}) @minus{} (@var{expression})
@var{something} @minus{} (@var{undefined symbol})
(@var{undefined symbol}) @minus{} (@var{undefined symbol})
@end display
are permitted, and belong to the difference section. @code{@value{AS}}
re-evaluates such expressions after the source file has been read and
the symbol table built. If by that time there are no undefined symbols
in the expression then the expression assumes a new section. The
intention is to permit statements like
@samp{.word label - base_of_table}
to be assembled in one pass where both @code{label} and
@code{base_of_table} are undefined. This is useful for compiling C and
Algol switch statements, Pascal case statements, FORTRAN computed goto
statements and the like.
@c FIXME item debug
@c FIXME item transfer[t] vector preload
@c FIXME item transfer[t] vector postload
@c FIXME item register
@end table
@node Sub-Sections
@section Sub-Sections
@cindex numbered subsections
@cindex grouping data
@ifset aout-bout
Assembled bytes
@ifset COFF
conventionally
@end ifset
fall into two sections: text and data.
@end ifset
You may have separate groups of
@ifset GENERIC
data in named sections
@end ifset
@ifclear GENERIC
@ifclear aout-bout
data in named sections
@end ifclear
@ifset aout-bout
text or data
@end ifset
@end ifclear
that you want to end up near to each other in the object file, even
though they are not contiguous in the assembler source.
@code{@value{AS}} allows you to use @dfn{subsections} for this purpose.
Within each section, there can be numbered subsections with values from
0 to 8192. Objects assembled into the same subsection will be grouped
with other objects in the same subsection when they are all put into the
object file. 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
@samp{.text 0} before each section of code being output, and a
@samp{.text 1} before each group of constants being output.
Subsections are optional. If you don't use subsections, everything
will be stored in subsection number zero.
@ifset GENERIC
Each subsection is zero-padded up to a multiple of four bytes.
(Subsections may be padded a different amount on different flavors
of @code{@value{AS}}.)
@end ifset
@ifclear GENERIC
@ifset H8
On the H8/300 and H8/500 platforms, each subsection is zero-padded to a word
boundary (two bytes).
The same is true on the Hitachi SH.
@end ifset
@ifset I960
@c FIXME section padding (alignment)?
@c Rich Pixley says padding here depends on target obj code format; that
@c doesn't seem particularly useful to say without further elaboration,
@c so for now I say nothing about it. If this is a generic BFD issue,
@c these paragraphs might need to vanish from this manual, and be
@c discussed in BFD chapter of binutils (or some such).
@end ifset
@ifset A29K
On the AMD 29K family, no particular padding is added to section or
subsection sizes; @value{AS} forces no alignment on this platform.
@end ifset
@end ifclear
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; @code{@value{LD}} and
other programs that manipulate object files will 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 @samp{.text
@var{expression}} or a @samp{.data @var{expression}} statement.
@ifset COFF
@ifset GENERIC
When generating COFF output, you
@end ifset
@ifclear GENERIC
You
@end ifclear
can also use an extra subsection
argument with arbitrary named sections: @samp{.section @var{name},
@var{expression}}.
@end ifset
@var{Expression} should be an absolute expression.
(@xref{Expressions}.) If you just say @samp{.text} then @samp{.text 0}
is assumed. Likewise @samp{.data} means @samp{.data 0}. Assembly
begins in @code{text 0}. For instance:
@smallexample
.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 (*)."
@end smallexample
Each section has a @dfn{location counter} incremented by one for every
byte assembled into that section. Because subsections are merely a
convenience restricted to @code{@value{AS}} there is no concept of a subsection
location counter. There is no way to directly manipulate a location
counter---but the @code{.align} directive will change it, and any label
definition will capture its current value. The location counter of the
section that statements are being assembled into is said to be the
@dfn{active} location counter.
@node bss
@section bss Section
@cindex bss section
@cindex common variable storage
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.
Addresses in the bss section are allocated with special directives; you
may not assemble anything directly into the bss section. Hence there
are no bss subsections. @xref{Comm,,@code{.comm}},
@pxref{Lcomm,,@code{.lcomm}}.
@node Symbols
@chapter Symbols
@cindex 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.
@quotation
@cindex debuggers, and symbol order
@emph{Warning:} @code{@value{AS}} does not place symbols in the object file in
the same order they were declared. This may break some debuggers.
@end quotation
@menu
* Labels:: Labels
* Setting Symbols:: Giving Symbols Other Values
* Symbol Names:: Symbol Names
* Dot:: The Special Dot Symbol
* Symbol Attributes:: Symbol Attributes
@end menu
@node Labels
@section Labels
@cindex labels
A @dfn{label} is written as a symbol immediately followed by a colon
@samp{:}. 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.
@node Setting Symbols
@section Giving Symbols Other Values
@cindex assigning values to symbols
@cindex symbol values, assigning
A symbol can be given an arbitrary value by writing a symbol, followed
by an equals sign @samp{=}, followed by an expression
(@pxref{Expressions}). This is equivalent to using the @code{.set}
directive. @xref{Set,,@code{.set}}.
@node Symbol Names
@section Symbol Names
@cindex symbol names
@cindex names, symbol
@ifclear SPECIAL-SYMS
Symbol names begin with a letter or with one of @samp{._}. On most
machines, you can also use @code{$} in symbol names; exceptions are
noted in @ref{Machine Dependencies}. That character may be followed by any
string of digits, letters, dollar signs (unless otherwise noted in
@ref{Machine Dependencies}), and underscores.
@end ifclear
@ifset A29K
For the AMD 29K family, @samp{?} is also allowed in the
body of a symbol name, though not at its beginning.
@end ifset
@ifset SPECIAL-SYMS
@ifset H8
Symbol names begin with a letter or with one of @samp{._}. On the
Hitachi SH or the
H8/500, you can also use @code{$} in symbol names. That character may
be followed by any string of digits, letters, dollar signs (save on the
H8/300), and underscores.
@end ifset
@end ifset
Case of letters is significant: @code{foo} is a different symbol name
than @code{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.
@subheading Local Symbol Names
@cindex local symbol names
@cindex symbol names, local
@cindex temporary symbol names
@cindex symbol names, temporary
Local symbols help compilers and programmers use names temporarily.
There are ten local symbol names, which are re-used throughout the
program. You may refer to them using the names @samp{0} @samp{1}
@dots{} @samp{9}. To define a local symbol, write a label of the form
@samp{@b{N}:} (where @b{N} represents any digit). To refer to the most
recent previous definition of that symbol write @samp{@b{N}b}, using the
same digit as when you defined the label. To refer to the next
definition of a local label, write @samp{@b{N}f}---where @b{N} gives you
a choice of 10 forward references. The @samp{b} stands for
``backwards'' and the @samp{f} stands for ``forwards''.
Local symbols are not emitted by the current GNU C compiler.
There is no restriction on how you can use these labels, but
remember that at any point in the assembly you can refer to at most
10 prior local labels and to at most 10 forward local labels.
Local symbol names are only a notation 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 have these
parts:
@table @code
@item L
All local labels begin with @samp{L}. Normally both @code{@value{AS}} and
@code{@value{LD}} forget symbols that start with @samp{L}. These labels are
used for symbols you are never intended to see. If you give the
@samp{-L} option then @code{@value{AS}} will retain these symbols in the
object file. If you also instruct @code{@value{LD}} to retain these symbols,
you may use them in debugging.
@item @var{digit}
If the label is written @samp{0:} then the digit is @samp{0}.
If the label is written @samp{1:} then the digit is @samp{1}.
And so on up through @samp{9:}.
@item @ctrl{A}
This unusual character is included so you don't accidentally invent
a symbol of the same name. The character has ASCII value
@samp{\001}.
@item @emph{ordinal number}
This is a serial number to keep the labels distinct. The first
@samp{0:} gets the number @samp{1}; The 15th @samp{0:} gets the
number @samp{15}; @emph{etc.}. Likewise for the other labels @samp{1:}
through @samp{9:}.
@end table
For instance, the first @code{1:} is named @code{L1@ctrl{A}1}, the 44th
@code{3:} is named @code{L3@ctrl{A}44}.
@node Dot
@section The Special Dot Symbol
@cindex dot (symbol)
@cindex @code{.} (symbol)
@cindex current address
@cindex location counter
The special symbol @samp{.} refers to the current address that
@code{@value{AS}} is assembling into. Thus, the expression @samp{melvin:
.long .} will cause @code{melvin} to contain its own address.
Assigning a value to @code{.} is treated the same as a @code{.org}
directive. Thus, the expression @samp{.=.+4} is the same as saying
@ifclear no-space-dir
@samp{.space 4}.
@end ifclear
@ifset no-space-dir
@ifset A29K
@samp{.block 4}.
@end ifset
@end ifset
@node Symbol Attributes
@section Symbol Attributes
@cindex symbol attributes
@cindex attributes, symbol
Every symbol has, as well as its name, the attributes ``Value'' and
``Type''. Depending on output format, symbols can also have auxiliary
attributes.
@ifset INTERNALS
The detailed definitions are in @file{a.out.h}.
@end ifset
If you use a symbol without defining it, @code{@value{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
@ifset aout-bout
@ifset GENERIC
* a.out Symbols:: Symbol Attributes: @code{a.out}
@end ifset
@ifclear GENERIC
@ifclear BOUT
* a.out Symbols:: Symbol Attributes: @code{a.out}
@end ifclear
@ifset BOUT
* a.out Symbols:: Symbol Attributes: @code{a.out}, @code{b.out}
@end ifset
@end ifclear
@end ifset
@ifset COFF
* COFF Symbols:: Symbol Attributes for COFF
@end ifset
@end menu
@node Symbol Value
@subsection Value
@cindex value of a symbol
@cindex symbol 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 @code{@value{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 program, and
@code{@value{LD}} will try to determine its value from other programs it is
linked with. You make this kind of symbol simply by mentioning a symbol
name without defining it. A non-zero value represents a @code{.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.
@node Symbol Type
@subsection Type
@cindex type of a symbol
@cindex symbol 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.
@ifset aout-bout
@ifclear GENERIC
@ifset BOUT
@c The following avoids a "widow" subsection title. @group would be
@c better if it were available outside examples.
@need 1000
@node a.out Symbols
@subsection Symbol Attributes: @code{a.out}, @code{b.out}
@cindex @code{b.out} symbol attributes
@cindex symbol attributes, @code{b.out}
These symbol attributes appear only when @code{@value{AS}} is configured for
one of the Berkeley-descended object output formats---@code{a.out} or
@code{b.out}.
@end ifset
@ifclear BOUT
@node a.out Symbols
@subsection Symbol Attributes: @code{a.out}
@cindex @code{a.out} symbol attributes
@cindex symbol attributes, @code{a.out}
@end ifclear
@end ifclear
@ifset GENERIC
@node a.out Symbols
@subsection Symbol Attributes: @code{a.out}
@cindex @code{a.out} symbol attributes
@cindex symbol attributes, @code{a.out}
@end ifset
@menu
* Symbol Desc:: Descriptor
* Symbol Other:: Other
@end menu
@node Symbol Desc
@subsubsection Descriptor
@cindex descriptor, of @code{a.out} symbol
This is an arbitrary 16-bit value. You may establish a symbol's
descriptor value by using a @code{.desc} statement
(@pxref{Desc,,@code{.desc}}). A descriptor value means nothing to
@code{@value{AS}}.
@node Symbol Other
@subsubsection Other
@cindex other attribute, of @code{a.out} symbol
This is an arbitrary 8-bit value. It means nothing to @code{@value{AS}}.
@end ifset
@ifset COFF
@node COFF Symbols
@subsection Symbol Attributes for COFF
@cindex COFF symbol attributes
@cindex symbol attributes, COFF
The COFF format supports a multitude of auxiliary symbol attributes;
like the primary symbol attributes, they are set between @code{.def} and
@code{.endef} directives.
@subsubsection Primary Attributes
@cindex primary attributes, COFF symbols
The symbol name is set with @code{.def}; the value and type,
respectively, with @code{.val} and @code{.type}.
@subsubsection Auxiliary Attributes
@cindex auxiliary attributes, COFF symbols
The @code{@value{AS}} directives @code{.dim}, @code{.line}, @code{.scl},
@code{.size}, and @code{.tag} can generate auxiliary symbol table
information for COFF.
@end ifset
@node Expressions
@chapter Expressions
@cindex expressions
@cindex addresses
@cindex numeric values
An @dfn{expression} specifies an address or numeric value.
Whitespace may precede and/or follow an expression.
@menu
* Empty Exprs:: Empty Expressions
* Integer Exprs:: Integer Expressions
@end menu
@node Empty Exprs
@section Empty Expressions
@cindex empty expressions
@cindex expressions, empty
An empty expression has no value: it is just whitespace or null.
Wherever an absolute expression is required, you may omit the
expression and @code{@value{AS}} will assume a value of (absolute) 0. This
is compatible with other assemblers.
@node Integer Exprs
@section Integer Expressions
@cindex integer expressions
@cindex expressions, integer
An @dfn{integer expression} is one or more @emph{arguments} delimited
by @emph{operators}.
@menu
* Arguments:: Arguments
* Operators:: Operators
* Prefix Ops:: Prefix Operators
* Infix Ops:: Infix Operators
@end menu
@node Arguments
@subsection Arguments
@cindex expression arguments
@cindex arguments in expressions
@cindex operands in expressions
@cindex arithmetic operands
@dfn{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 @{@var{section} @var{NNN}@} where
@var{section} is one of text, data, bss, absolute,
or undefined. @var{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 @code{@value{AS}} pretends
these 32 bits are an integer. You may write integer-manipulating
instructions that act on exotic constants, compatible with other
assemblers.
@cindex subexpressions
Subexpressions are a left parenthesis @samp{(} followed by an integer
expression, followed by a right parenthesis @samp{)}; or a prefix
operator followed by an argument.
@node Operators
@subsection Operators
@cindex operators, in expressions
@cindex arithmetic functions
@cindex functions, in expressions
@dfn{Operators} are arithmetic functions, like @code{+} or @code{%}. Prefix
operators are followed by an argument. Infix operators appear
between their arguments. Operators may be preceded and/or followed by
whitespace.
@node Prefix Ops
@subsection Prefix Operator
@cindex prefix operators
@code{@value{AS}} has the following @dfn{prefix operators}. They each take
one argument, which must be absolute.
@c the tex/end tex stuff surrounding this small table is meant to make
@c it align, on the printed page, with the similar table in the next
@c section (which is inside an enumerate).
@tex
\global\advance\leftskip by \itemindent
@end tex
@table @code
@item -
@dfn{Negation}. Two's complement negation.
@item ~
@dfn{Complementation}. Bitwise not.
@end table
@tex
\global\advance\leftskip by -\itemindent
@end tex
@node Infix Ops
@subsection Infix Operators
@cindex infix operators
@cindex operators, permitted arguments
@dfn{Infix operators} take two arguments, one on either side. Operators
have precedence, but operations with equal precedence are performed left
to right. Apart from @code{+} or @code{-}, both arguments must be
absolute, and the result is absolute.
@enumerate
@cindex operator precedence
@cindex precedence of operators
@item
Highest Precedence
@table @code
@item *
@dfn{Multiplication}.
@item /
@dfn{Division}. Truncation is the same as the C operator @samp{/}
@item %
@dfn{Remainder}.
@item <
@itemx <<
@dfn{Shift Left}. Same as the C operator @samp{<<}.
@item >
@itemx >>
@dfn{Shift Right}. Same as the C operator @samp{>>}.
@end table
@item
Intermediate precedence
@table @code
@item |
@dfn{Bitwise Inclusive Or}.
@item &
@dfn{Bitwise And}.
@item ^
@dfn{Bitwise Exclusive Or}.
@item !
@dfn{Bitwise Or Not}.
@end table
@item
Lowest Precedence
@table @code
@item +
@cindex addition, permitted arguments
@cindex plus, permitted arguments
@cindex arguments for addition
@dfn{Addition}. If either argument is absolute, the result
has the section of the other argument.
If either argument is pass1 or undefined, the result is pass1.
Otherwise @code{+} is illegal.
@item -
@cindex subtraction, permitted arguments
@cindex minus, permitted arguments
@cindex arguments for subtraction
@dfn{Subtraction}. If the right argument is absolute, the
result has the section of the left argument.
If either argument is pass1 the result is pass1.
If either argument is undefined the result is difference section.
If both arguments are in the same section, the result is absolute---provided
that section is one of text, data or bss.
Otherwise subtraction is illegal.
@end table
@end enumerate
The sense of the rule for addition is that it's only meaningful to add
the @emph{offsets} in an address; you can only have a defined section in
one of the two arguments.
Similarly, you can't subtract quantities from two different sections.
@node Pseudo Ops
@chapter Assembler Directives
@cindex directives, machine independent
@cindex pseudo-ops, machine independent
@cindex machine independent directives
All assembler directives have names that begin with a period (@samp{.}).
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.
@ifset GENERIC
Some machine configurations provide additional directives.
@xref{Machine Dependencies}.
@end ifset
@ifclear GENERIC
@ifset machine-directives
@xref{Machine Dependencies} for additional directives.
@end ifset
@end ifclear
@menu
* Abort:: @code{.abort}
@ifset COFF
* ABORT:: @code{.ABORT}
@end ifset
* Align:: @code{.align @var{abs-expr} , @var{abs-expr}}
* App-File:: @code{.app-file @var{string}}
* Ascii:: @code{.ascii "@var{string}"}@dots{}
* Asciz:: @code{.asciz "@var{string}"}@dots{}
* Byte:: @code{.byte @var{expressions}}
* Comm:: @code{.comm @var{symbol} , @var{length} }
* Data:: @code{.data @var{subsection}}
@ifset COFF
* Def:: @code{.def @var{name}}
@end ifset
@ifset aout-bout
* Desc:: @code{.desc @var{symbol}, @var{abs-expression}}
@end ifset
@ifset COFF
* Dim:: @code{.dim}
@end ifset
* Double:: @code{.double @var{flonums}}
* Eject:: @code{.eject}
* Else:: @code{.else}
@ifset COFF
* Endef:: @code{.endef}
@end ifset
* Endif:: @code{.endif}
* Equ:: @code{.equ @var{symbol}, @var{expression}}
* Extern:: @code{.extern}
@ifclear no-file-dir
* File:: @code{.file @var{string}}
@end ifclear
* Fill:: @code{.fill @var{repeat} , @var{size} , @var{value}}
* Float:: @code{.float @var{flonums}}
* Global:: @code{.global @var{symbol}}, @code{.globl @var{symbol}}
* hword:: @code{.hword @var{expressions}}
* Ident:: @code{.ident}
* If:: @code{.if @var{absolute expression}}
* Include:: @code{.include "@var{file}"}
* Int:: @code{.int @var{expressions}}
* Lcomm:: @code{.lcomm @var{symbol} , @var{length}}
* Lflags:: @code{.lflags}
@ifclear no-line-dir
* Line:: @code{.line @var{line-number}}
@end ifclear
* Ln:: @code{.ln @var{line-number}}
* List:: @code{.list}
* Long:: @code{.long @var{expressions}}
@ignore
* Lsym:: @code{.lsym @var{symbol}, @var{expression}}
@end ignore
* Nolist:: @code{.nolist}
* Octa:: @code{.octa @var{bignums}}
* Org:: @code{.org @var{new-lc} , @var{fill}}
* Psize:: @code{.psize @var{lines}, @var{columns}}
* Quad:: @code{.quad @var{bignums}}
* Sbttl:: @code{.sbttl "@var{subheading}"}
@ifset COFF
* Scl:: @code{.scl @var{class}}
@end ifset
@ifset COFF
* Section:: @code{.section @var{name}, @var{subsection}}
@end ifset
* Set:: @code{.set @var{symbol}, @var{expression}}
* Short:: @code{.short @var{expressions}}
* Single:: @code{.single @var{flonums}}
@ifset COFF
* Size:: @code{.size}
@end ifset
* Space:: @code{.space @var{size} , @var{fill}}
@ifset have-stabs
* Stab:: @code{.stabd, .stabn, .stabs}
@end ifset
@ifset COFF
* Tag:: @code{.tag @var{structname}}
@end ifset
* Text:: @code{.text @var{subsection}}
* Title:: @code{.title "@var{heading}"}
@ifset COFF
* Type:: @code{.type @var{int}}
* Val:: @code{.val @var{addr}}
@end ifset
* Word:: @code{.word @var{expressions}}
* Deprecated:: Deprecated Directives
@end menu
@node Abort
@section @code{.abort}
@cindex @code{abort} directive
@cindex stopping the assembly
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 @code{@value{AS}} to
quit also. One day @code{.abort} will not be supported.
@ifset COFF
@node ABORT
@section @code{.ABORT}
@cindex @code{ABORT} directive
When producing COFF output, @code{@value{AS}} accepts this directive as a
synonym for @samp{.abort}.
@ifset BOUT
When producing @code{b.out} output, @code{@value{AS}} accepts this directive,
but ignores it.
@end ifset
@end ifset
@node Align
@section @code{.align @var{abs-expr} , @var{abs-expr}}
@cindex padding the location counter
@cindex @code{align} directive
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
number of low-order zero bits the location counter will have after
advancement. For example @samp{.align 3} will advance the location
counter until it a multiple of 8. If the location counter is already a
multiple of 8, no change is needed.
The second expression (also absolute) gives the value to be stored in
the padding bytes. It (and the comma) may be omitted. If it is
omitted, the padding bytes are zero.
@node App-File
@section @code{.app-file @var{string}}
@cindex logical file name
@cindex file name, logical
@cindex @code{app-file} directive
@code{.app-file}
@ifclear no-file-dir
(which may also be spelled @samp{.file})
@end ifclear
tells @code{@value{AS}} that we are about to start a new
logical file. @var{string} is the new file name. In general, the
filename is recognized whether or not it is surrounded by quotes @samp{"};
but if you wish to specify an empty file name is permitted,
you must give the quotes--@code{""}. This statement may go away in
future: it is only recognized to be compatible with old @code{@value{AS}}
programs.@refill
@node Ascii
@section @code{.ascii "@var{string}"}@dots{}
@cindex @code{ascii} directive
@cindex string literals
@code{.ascii} expects zero or more string literals (@pxref{Strings})
separated by commas. It assembles each string (with no automatic
trailing zero byte) into consecutive addresses.
@node Asciz
@section @code{.asciz "@var{string}"}@dots{}
@cindex @code{asciz} directive
@cindex zero-terminated strings
@cindex null-terminated strings
@code{.asciz} is just like @code{.ascii}, but each string is followed by
a zero byte. The ``z'' in @samp{.asciz} stands for ``zero''.
@node Byte
@section @code{.byte @var{expressions}}
@cindex @code{byte} directive
@cindex integers, one byte
@code{.byte} expects zero or more expressions, separated by commas.
Each expression is assembled into the next byte.
@node Comm
@section @code{.comm @var{symbol} , @var{length} }
@cindex @code{comm} directive
@cindex symbol, common
@code{.comm} declares a named common area in the bss section. Normally
@code{@value{LD}} reserves memory addresses for it during linking, so no partial
program defines the location of the symbol. Use @code{.comm} to tell
@code{@value{LD}} that it must be at least @var{length} bytes long. @code{@value{LD}}
will allocate space for each @code{.comm} symbol that is at least as
long as the longest @code{.comm} request in any of the partial programs
linked. @var{length} is an absolute expression.
@node Data
@section @code{.data @var{subsection}}
@cindex @code{data} directive
@code{.data} tells @code{@value{AS}} to assemble the following statements onto the
end of the data subsection numbered @var{subsection} (which is an
absolute expression). If @var{subsection} is omitted, it defaults
to zero.
@ifset COFF
@node Def
@section @code{.def @var{name}}
@cindex @code{def} directive
@cindex COFF symbols, debugging
@cindex debugging COFF symbols
Begin defining debugging information for a symbol @var{name}; the
definition extends until the @code{.endef} directive is encountered.
@ifset BOUT
This directive is only observed when @code{@value{AS}} is configured for COFF
format output; when producing @code{b.out}, @samp{.def} is recognized,
but ignored.
@end ifset
@end ifset
@ifset aout-bout
@node Desc
@section @code{.desc @var{symbol}, @var{abs-expression}}
@cindex @code{desc} directive
@cindex COFF symbol descriptor
@cindex symbol descriptor, COFF
This directive sets the descriptor of the symbol (@pxref{Symbol Attributes})
to the low 16 bits of an absolute expression.
@ifset COFF
The @samp{.desc} directive is not available when @code{@value{AS}} is
configured for COFF output; it is only for @code{a.out} or @code{b.out}
object format. For the sake of compatibility, @code{@value{AS}} will accept
it, but produce no output, when configured for COFF.
@end ifset
@end ifset
@ifset COFF
@node Dim
@section @code{.dim}
@cindex @code{dim} directive
@cindex COFF auxiliary symbol information
@cindex auxiliary symbol information, COFF
This directive is generated by compilers to include auxiliary debugging
information in the symbol table. It is only permitted inside
@code{.def}/@code{.endef} pairs.
@ifset BOUT
@samp{.dim} is only meaningful when generating COFF format output; when
@code{@value{AS}} is generating @code{b.out}, it accepts this directive but
ignores it.
@end ifset
@end ifset
@node Double
@section @code{.double @var{flonums}}
@cindex @code{double} directive
@cindex floating point numbers (double)
@code{.double} expects zero or more flonums, separated by commas. It
assembles floating point numbers.
@ifset GENERIC
The exact kind of floating point numbers emitted depends on how
@code{@value{AS}} is configured. @xref{Machine Dependencies}.
@end ifset
@ifclear GENERIC
@ifset IEEEFLOAT
On the @value{TARGET} family @samp{.double} emits 64-bit floating-point numbers
in @sc{ieee} format.
@end ifset
@end ifclear
@node Eject
@section @code{.eject}
@cindex @code{eject} directive
@cindex new page, in listings
@cindex page, in listings
@cindex listing control: new page
Force a page break at this point, when generating assembly listings.
@node Else
@section @code{.else}
@cindex @code{else} directive
@code{.else} is part of the @code{@value{AS}} support for conditional
assembly; @pxref{If,,@code{.if}}. It marks the beginning of a section
of code to be assembled if the condition for the preceding @code{.if}
was false.
@ignore
@node End, Endef, Else, Pseudo Ops
@section @code{.end}
@cindex @code{end} directive
This doesn't do anything---but isn't an s_ignore, so I suspect it's
meant to do something eventually (which is why it isn't documented here
as "for compatibility with blah").
@end ignore
@ifset COFF
@node Endef
@section @code{.endef}
@cindex @code{endef} directive
This directive flags the end of a symbol definition begun with
@code{.def}.
@ifset BOUT
@samp{.endef} is only meaningful when generating COFF format output; if
@code{@value{AS}} is configured to generate @code{b.out}, it accepts this
directive but ignores it.
@end ifset
@end ifset
@node Endif
@section @code{.endif}
@cindex @code{endif} directive
@code{.endif} is part of the @code{@value{AS}} support for conditional assembly;
it marks the end of a block of code that is only assembled
conditionally. @xref{If,,@code{.if}}.
@node Equ
@section @code{.equ @var{symbol}, @var{expression}}
@cindex @code{equ} directive
@cindex assigning values to symbols
@cindex symbols, assigning values to
This directive sets the value of @var{symbol} to @var{expression}.
It is synonymous with @samp{.set}; @pxref{Set,,@code{.set}}.
@node Extern
@section @code{.extern}
@cindex @code{extern} directive
@code{.extern} is accepted in the source program---for compatibility
with other assemblers---but it is ignored. @code{@value{AS}} treats
all undefined symbols as external.
@ifclear no-file-dir
@node File
@section @code{.file @var{string}}
@cindex @code{file} directive
@cindex logical file name
@cindex file name, logical
@code{.file} (which may also be spelled @samp{.app-file}) tells
@code{@value{AS}} that we are about to start a new logical file.
@var{string} is the new file name. In general, the filename is
recognized whether or not it is surrounded by quotes @samp{"}; but if
you wish to specify an empty file name, you must give the
quotes--@code{""}. This statement may go away in future: it is only
recognized to be compatible with old @code{@value{AS}} programs.
@ifset A29K
In some configurations of @code{@value{AS}}, @code{.file} has already been
removed to avoid conflicts with other assemblers. @xref{Machine Dependencies}.
@end ifset
@end ifclear
@node Fill
@section @code{.fill @var{repeat} , @var{size} , @var{value}}
@cindex @code{fill} directive
@cindex writing patterns in memory
@cindex patterns, writing in memory
@var{result}, @var{size} and @var{value} are absolute expressions.
This emits @var{repeat} copies of @var{size} bytes. @var{Repeat}
may be zero or more. @var{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 @var{repeat} bytes
is taken from an 8-byte number. The highest order 4 bytes are
zero. The lowest order 4 bytes are @var{value} rendered in the
byte-order of an integer on the computer @code{@value{AS}} is assembling for.
Each @var{size} bytes in a repetition is taken from the lowest order
@var{size} bytes of this number. Again, this bizarre behavior is
compatible with other people's assemblers.
@var{size} and @var{value} are optional.
If the second comma and @var{value} are absent, @var{value} is
assumed zero. If the first comma and following tokens are absent,
@var{size} is assumed to be 1.
@node Float
@section @code{.float @var{flonums}}
@cindex floating point numbers (single)
@cindex @code{float} directive
This directive assembles zero or more flonums, separated by commas. It
has the same effect as @code{.single}.
@ifset GENERIC
The exact kind of floating point numbers emitted depends on how
@code{@value{AS}} is configured.
@xref{Machine Dependencies}.
@end ifset
@ifclear GENERIC
@ifset IEEEFLOAT
On the @value{TARGET} family, @code{.float} emits 32-bit floating point numbers
in @sc{ieee} format.
@end ifset
@end ifclear
@node Global
@section @code{.global @var{symbol}}, @code{.globl @var{symbol}}
@cindex @code{global} directive
@cindex symbol, making visible to linker
@code{.global} makes the symbol visible to @code{@value{LD}}. If you define
@var{symbol} in your partial program, its value is made available to
other partial programs that are linked with it. Otherwise,
@var{symbol} will take its attributes from a symbol of the same name
from another partial program it is linked with.
Both spellings (@samp{.globl} and @samp{.global}) are accepted, for
compatibility with other assemblers.
@node hword
@section @code{.hword @var{expressions}}
@cindex @code{hword} directive
@cindex integers, 16-bit
@cindex numbers, 16-bit
@cindex sixteen bit integers
This expects zero or more @var{expressions}, and emits
a 16 bit number for each.
@ifset GENERIC
This directive is a synonym for @samp{.short}; depending on the target
architecture, it may also be a synonym for @samp{.word}.
@end ifset
@ifclear GENERIC
@ifset W32
This directive is a synonym for @samp{.short}.
@end ifset
@ifset W16
This directive is a synonym for both @samp{.short} and @samp{.word}.
@end ifset
@end ifclear
@node Ident
@section @code{.ident}
@cindex @code{ident} directive
This directive is used by some assemblers to place tags in object files.
@code{@value{AS}} simply accepts the directive for source-file
compatibility with such assemblers, but does not actually emit anything
for it.
@node If
@section @code{.if @var{absolute expression}}
@cindex conditional assembly
@cindex @code{if} directive
@code{.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 @var{absolute expression}) is non-zero. The end of
the conditional section of code must be marked by @code{.endif}
(@pxref{Endif,,@code{.endif}}); optionally, you may include code for the
alternative condition, flagged by @code{.else} (@pxref{Else,,@code{.else}}.
The following variants of @code{.if} are also supported:
@table @code
@item .ifdef @var{symbol}
@cindex @code{ifdef} directive
Assembles the following section of code if the specified @var{symbol}
has been defined.
@ignore
@item .ifeqs
@cindex @code{ifeqs} directive
Not yet implemented.
@end ignore
@item .ifndef @var{symbol}
@itemx ifnotdef @var{symbol}
@cindex @code{ifndef} directive
@cindex @code{ifnotdef} directive
Assembles the following section of code if the specified @var{symbol}
has not been defined. Both spelling variants are equivalent.
@ignore
@item ifnes
Not yet implemented.
@end ignore
@end table
@node Include
@section @code{.include "@var{file}"}
@cindex @code{include} directive
@cindex supporting files, including
@cindex files, including
This directive provides a way to include supporting files at specified
points in your source program. The code from @var{file} is assembled as
if it followed the point of the @code{.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 @samp{-I} command-line option
(@pxref{Invoking,,Command-Line Options}). Quotation marks are required
around @var{file}.
@node Int
@section @code{.int @var{expressions}}
@cindex @code{int} directive
@ifset GENERIC
@cindex integers, 32-bit
Expect zero or more @var{expressions}, of any section, separated by
commas. For each expression, emit a 32-bit
@end ifset
@ifclear GENERIC
@ifclear H8
@cindex integers, 32-bit
Expect zero or more @var{expressions}, of any section, separated by
commas. For each expression, emit a 32-bit
@end ifclear
@ifset H8
@cindex integers
Expect zero or more @var{expressions}, of any section, separated by
commas. For each expression, emit a
@end ifset
@end ifclear
number that will, at run time, be the value of that expression. The
byte order of the expression depends on what kind of computer will run
the program.
@ifclear GENERIC
@ifset H8
On the H8/500 and most forms of the H8/300, @code{.int} emits 16-bit
integers. On the H8/300H and the Hitachi SH, however, @code{.int} emits
32-bit integers.
@end ifset
@end ifclear
@node Lcomm
@section @code{.lcomm @var{symbol} , @var{length}}
@cindex @code{lcomm} directive
@cindex local common symbols
@cindex symbols, local common
Reserve @var{length} (an absolute expression) bytes for a local common
denoted by @var{symbol}. The section and value of @var{symbol} are
those of the new local common. The addresses are allocated in the bss
section, so at run-time the bytes will start off zeroed. @var{Symbol}
is not declared global (@pxref{Global,,@code{.global}}), so is normally
not visible to @code{@value{LD}}.
@node Lflags
@section @code{.lflags}
@cindex @code{lflags} directive (ignored)
@code{@value{AS}} accepts this directive, for compatibility with other
assemblers, but ignores it.
@ifclear no-line-dir
@node Line
@section @code{.line @var{line-number}}
@cindex @code{line} directive
@end ifclear
@ifset no-line-dir
@node Ln
@section @code{.ln @var{line-number}}
@cindex @code{ln} directive
@end ifset
@cindex logical line number
@ifset aout-bout
Tell @code{@value{AS}} to change the logical line number. @var{line-number} must be
an absolute expression. The next line will have that logical line
number. So any other statements on the current line (after a statement
separator character)
will be reported as on logical line number
@var{line-number} @minus{} 1.
One day this directive will be unsupported: it is used only
for compatibility with existing assembler programs.
@ifset GENERIC
@ifset A29K
@emph{Warning:} In the AMD29K configuration of @value{AS}, this command is
only available with the name @code{.ln}, rather than as either
@code{.line} or @code{.ln}.
@end ifset
@end ifset
@end ifset
@ifclear no-line-dir
Even though this is a directive associated with the @code{a.out} or
@code{b.out} object-code formats, @code{@value{AS}} will still recognize it
when producing COFF output, and will treat @samp{.line} as though it
were the COFF @samp{.ln} @emph{if} it is found outside a
@code{.def}/@code{.endef} pair.
Inside a @code{.def}, @samp{.line} is, instead, one of the directives
used by compilers to generate auxiliary symbol information for
debugging.
@end ifclear
@node Ln
@section @code{.ln @var{line-number}}
@cindex @code{ln} directive
@ifclear no-line-dir
@samp{.ln} is a synonym for @samp{.line}.
@end ifclear
@ifset no-line-dir
Tell @code{@value{AS}} to change the logical line number. @var{line-number}
must be an absolute expression. The next line will have that logical
line number, so any other statements on the current line (after a
statement separator character @code{;}) will be reported as on logical
line number @var{line-number} @minus{} 1.
@ifset BOUT
This directive is accepted, but ignored, when @code{@value{AS}} is
configured for @code{b.out}; its effect is only associated with COFF
output format.
@end ifset
@end ifset
@node List
@section @code{.list}
@cindex @code{list} directive
@cindex listing control, turning on
Control (in conjunction with the @code{.nolist} directive) whether or
not assembly listings are generated. These two directives maintain an
internal counter (which is zero initially). @code{.list} increments the
counter, and @code{.nolist} decrements it. Assembly listings are
generated whenever the counter is greater than zero.
By default, listings are disabled. When you enable them (with the
@samp{-a} command line option; @pxref{Invoking,,Command-Line Options}),
the initial value of the listing counter is one.
@node Long
@section @code{.long @var{expressions}}
@cindex @code{long} directive
@code{.long} is the same as @samp{.int}, @pxref{Int,,@code{.int}}.
@ignore
@c no one seems to know what this is for or whether this description is
@c what it really ought to do
@node Lsym
@section @code{.lsym @var{symbol}, @var{expression}}
@cindex @code{lsym} directive
@cindex symbol, not referenced in assembly
@code{.lsym} creates a new symbol named @var{symbol}, but does not put it in
the hash table, ensuring it cannot be referenced by name during the
rest of the assembly. This sets the attributes of the symbol to be
the same as the expression value:
@smallexample
@var{other} = @var{descriptor} = 0
@var{type} = @r{(section of @var{expression})}
@var{value} = @var{expression}
@end smallexample
@noindent
The new symbol is not flagged as external.
@end ignore
@node Nolist
@section @code{.nolist}
@cindex @code{nolist} directive
@cindex listing control, turning off
Control (in conjunction with the @code{.list} directive) whether or
not assembly listings are generated. These two directives maintain an
internal counter (which is zero initially). @code{.list} increments the
counter, and @code{.nolist} decrements it. Assembly listings are
generated whenever the counter is greater than zero.
@node Octa
@section @code{.octa @var{bignums}}
@c FIXME: double size emitted for "octa" on i960, others? Or warn?
@cindex @code{octa} directive
@cindex integer, 16-byte
@cindex sixteen byte integer
This directive expects zero or more bignums, separated by commas. For each
bignum, it emits a 16-byte integer.
The term ``octa'' comes from contexts in which a ``word'' is two bytes;
hence @emph{octa}-word for 16 bytes.
@node Org
@section @code{.org @var{new-lc} , @var{fill}}
@cindex @code{org} directive
@cindex location counter, advancing
@cindex advancing location counter
@cindex current address, advancing
@code{.org} will advance the location counter of the current section to
@var{new-lc}. @var{new-lc} is either an absolute expression or an
expression with the same section as the current subsection. That is,
you can't use @code{.org} to cross sections: if @var{new-lc} has the
wrong section, the @code{.org} directive is ignored. To be compatible
with former assemblers, if the section of @var{new-lc} is absolute,
@code{@value{AS}} will issue a warning, then pretend the section of @var{new-lc}
is the same as the current subsection.
@code{.org} may only increase the location counter, or leave it
unchanged; you cannot use @code{.org} to move the location counter
backwards.
@c double negative used below "not undefined" because this is a specific
@c reference to "undefined" (as SEG_UNKNOWN is called in this manual)
@c section. pesch@cygnus.com 18feb91
Because @code{@value{AS}} tries to assemble programs in one pass @var{new-lc}
may not be undefined. If you really detest this restriction we eagerly await
a chance to share your improved assembler.
Beware that the origin is relative to the start of the section, not
to the start of the subsection. This is compatible with other
people's assemblers.
When the location counter (of the current subsection) is advanced, the
intervening bytes are filled with @var{fill} which should be an
absolute expression. If the comma and @var{fill} are omitted,
@var{fill} defaults to zero.
@node Psize
@section @code{.psize @var{lines} , @var{columns}}
@cindex @code{psize} directive
@cindex listing control: paper size
@cindex paper size, for listings
Use this directive to declare the number of lines---and, optionally, the
number of columns---to use for each page, when generating listings.
If you don't use @code{.psize}, listings will use a default line-count
of 60. You may omit the comma and @var{columns} specification; the
default width is 200 columns.
@code{@value{AS}} will generate formfeeds whenever the specified number of
lines is exceeded (or whenever you explicitly request one, using
@code{.eject}).
If you specify @var{lines} as @code{0}, no formfeeds are generated save
those explicitly specified with @code{.eject}.
@node Quad
@section @code{.quad @var{bignums}}
@cindex @code{quad} directive
@code{.quad} expects zero or more bignums, separated by commas. For
each bignum, it emits
@ifclear bignum-16
an 8-byte integer. If the bignum won't fit in 8 bytes, it prints a
warning message; and just takes the lowest order 8 bytes of the bignum.
@cindex eight-byte integer
@cindex integer, 8-byte
The term ``quad'' comes from contexts in which a ``word'' is two bytes;
hence @emph{quad}-word for 8 bytes.
@end ifclear
@ifset bignum-16
a 16-byte integer. If the bignum won't fit in 16 bytes, it prints a
warning message; and just takes the lowest order 16 bytes of the bignum.
@cindex sixteen-byte integer
@cindex integer, 16-byte
@end ifset
@node Sbttl
@section @code{.sbttl "@var{subheading}"}
@cindex @code{sbttl} directive
@cindex subtitles for listings
@cindex listing control: subtitle
Use @var{subheading} as the title (third line, immediately after the
title line) when generating assembly listings.
This directive affects subsequent pages, as well as the current page if
it appears within ten lines of the top of a page.
@ifset COFF
@node Scl
@section @code{.scl @var{class}}
@cindex @code{scl} directive
@cindex symbol storage class (COFF)
@cindex COFF symbol storage class
Set the storage-class value for a symbol. This directive may only be
used inside a @code{.def}/@code{.endef} pair. Storage class may flag
whether a symbol is static or external, or it may record further
symbolic debugging information.
@ifset BOUT
The @samp{.scl} directive is primarily associated with COFF output; when
configured to generate @code{b.out} output format, @code{@value{AS}} will
accept this directive but ignore it.
@end ifset
@end ifset
@ifset COFF
@node Section
@section @code{.section @var{name}, @var{subsection}}
@cindex @code{section} directive
@cindex named section (COFF)
@cindex COFF named section
Assemble the following code into end of subsection numbered
@var{subsection} in the COFF named section @var{name}. If you omit
@var{subsection}, @code{@value{AS}} uses subsection number zero.
@samp{.section .text} is equivalent to the @code{.text} directive;
@samp{.section .data} is equivalent to the @code{.data} directive.
@end ifset
@node Set
@section @code{.set @var{symbol}, @var{expression}}
@cindex @code{set} directive
@cindex symbol value, setting
This directive sets the value of @var{symbol} to @var{expression}. This
will change @var{symbol}'s value and type to conform to
@var{expression}. If @var{symbol} was flagged as external, it remains
flagged. (@xref{Symbol Attributes}.)
You may @code{.set} a symbol many times in the same assembly.
If the expression's section is unknowable during pass 1, a second
pass over the source program will be forced. The second pass is
currently not implemented. @code{@value{AS}} will abort with an error
message if one is required.
If you @code{.set} a global symbol, the value stored in the object
file is the last value stored into it.
@node Short
@section @code{.short @var{expressions}}
@cindex @code{short} directive
@ifset GENERIC
@code{.short} is normally the same as @samp{.word}.
@xref{Word,,@code{.word}}.
In some configurations, however, @code{.short} and @code{.word} generate
numbers of different lengths; @pxref{Machine Dependencies}.
@end ifset
@ifclear GENERIC
@ifset W16
@code{.short} is the same as @samp{.word}. @xref{Word,,@code{.word}}.
@end ifset
@ifset W32
This expects zero or more @var{expressions}, and emits
a 16 bit number for each.
@end ifset
@end ifclear
@node Single
@section @code{.single @var{flonums}}
@cindex @code{single} directive
@cindex floating point numbers (single)
This directive assembles zero or more flonums, separated by commas. It
has the same effect as @code{.float}.
@ifset GENERIC
The exact kind of floating point numbers emitted depends on how
@code{@value{AS}} is configured. @xref{Machine Dependencies}.
@end ifset
@ifclear GENERIC
@ifset IEEEFLOAT
On the @value{TARGET} family, @code{.single} emits 32-bit floating point
numbers in @sc{ieee} format.
@end ifset
@end ifclear
@ifset COFF
@node Size
@section @code{.size}
@cindex @code{size} directive
This directive is generated by compilers to include auxiliary debugging
information in the symbol table. It is only permitted inside
@code{.def}/@code{.endef} pairs.
@ifset BOUT
@samp{.size} is only meaningful when generating COFF format output; when
@code{@value{AS}} is generating @code{b.out}, it accepts this directive but
ignores it.
@end ifset
@end ifset
@ifclear no-space-dir
@node Space
@section @code{.space @var{size} , @var{fill}}
@cindex @code{space} directive
@cindex filling memory
This directive emits @var{size} bytes, each of value @var{fill}. Both
@var{size} and @var{fill} are absolute expressions. If the comma
and @var{fill} are omitted, @var{fill} is assumed to be zero.
@end ifclear
@ifset A29K
@ifclear GENERIC
@node Space
@section @code{.space}
@cindex @code{space} directive
@end ifclear
On the AMD 29K, this directive is ignored; it is accepted for
compatibility with other AMD 29K assemblers.
@quotation
@emph{Warning:} In most versions of the GNU assembler, the directive
@code{.space} has the effect of @code{.block} @xref{Machine Dependencies}.
@end quotation
@end ifset
@ifset have-stabs
@node Stab
@section @code{.stabd, .stabn, .stabs}
@cindex symbolic debuggers, information for
@cindex @code{stab@var{x}} directives
There are three directives that begin @samp{.stab}.
All emit symbols (@pxref{Symbols}), for use by symbolic debuggers.
The symbols are not entered in the @code{@value{AS}} hash table: they
cannot be referenced elsewhere in the source file.
Up to five fields are required:
@table @var
@item string
This is the symbol's name. It may contain any character except
@samp{\000}, so is more general than ordinary symbol names. Some
debuggers used to code arbitrarily complex structures into symbol names
using this field.
@item type
An absolute expression. The symbol's type is set to the low 8 bits of
this expression. Any bit pattern is permitted, but @code{@value{LD}}
and debuggers will choke on silly bit patterns.
@item other
An absolute expression. The symbol's ``other'' attribute is set to the
low 8 bits of this expression.
@item desc
An absolute expression. The symbol's descriptor is set to the low 16
bits of this expression.
@item value
An absolute expression which becomes the symbol's value.
@end table
If a warning is detected while reading a @code{.stabd}, @code{.stabn},
or @code{.stabs} statement, the symbol has probably already been created
and you will get a half-formed symbol in your object file. This is
compatible with earlier assemblers!
@table @code
@cindex @code{stabd} directive
@item .stabd @var{type} , @var{other} , @var{desc}
The ``name'' of the symbol generated is not even an empty string.
It is a null pointer, for compatibility. Older assemblers used a
null pointer so they didn't waste space in object files with empty
strings.
The symbol's value is set to the location counter,
relocatably. When your program is linked, the value of this symbol
will be where the location counter was when the @code{.stabd} was
assembled.
@item .stabn @var{type} , @var{other} , @var{desc} , @var{value}
@cindex @code{stabn} directive
The name of the symbol is set to the empty string @code{""}.
@item .stabs @var{string} , @var{type} , @var{other} , @var{desc} , @var{value}
@cindex @code{stabs} directive
All five fields are specified.
@end table
@end ifset
@c end have-stabs
@ifset COFF
@node Tag
@section @code{.tag @var{structname}}
@cindex COFF structure debugging
@cindex structure debugging, COFF
@cindex @code{tag} directive
This directive is generated by compilers to include auxiliary debugging
information in the symbol table. It is only permitted inside
@code{.def}/@code{.endef} pairs. Tags are used to link structure
definitions in the symbol table with instances of those structures.
@ifset BOUT
@samp{.tag} is only used when generating COFF format output; when
@code{@value{AS}} is generating @code{b.out}, it accepts this directive but
ignores it.
@end ifset
@end ifset
@node Text
@section @code{.text @var{subsection}}
@cindex @code{text} directive
Tells @code{@value{AS}} to assemble the following statements onto the end of
the text subsection numbered @var{subsection}, which is an absolute
expression. If @var{subsection} is omitted, subsection number zero
is used.
@node Title
@section @code{.title "@var{heading}"}
@cindex @code{title} directive
@cindex listing control: title line
Use @var{heading} as the title (second line, immediately after the
source file name and pagenumber) when generating assembly listings.
This directive affects subsequent pages, as well as the current page if
it appears within ten lines of the top of a page.
@ifset COFF
@node Type
@section @code{.type @var{int}}
@cindex COFF symbol type
@cindex symbol type, COFF
@cindex @code{type} directive
This directive, permitted only within @code{.def}/@code{.endef} pairs,
records the integer @var{int} as the type attribute of a symbol table entry.
@ifset BOUT
@samp{.type} is associated only with COFF format output; when
@code{@value{AS}} is configured for @code{b.out} output, it accepts this
directive but ignores it.
@end ifset
@end ifset
@ifset COFF
@node Val
@section @code{.val @var{addr}}
@cindex @code{val} directive
@cindex COFF value attribute
@cindex value attribute, COFF
This directive, permitted only within @code{.def}/@code{.endef} pairs,
records the address @var{addr} as the value attribute of a symbol table
entry.
@ifset BOUT
@samp{.val} is used only for COFF output; when @code{@value{AS}} is
configured for @code{b.out}, it accepts this directive but ignores it.
@end ifset
@end ifset
@node Word
@section @code{.word @var{expressions}}
@cindex @code{word} directive
This directive expects zero or more @var{expressions}, of any section,
separated by commas.
@ifclear GENERIC
@ifset W32
For each expression, @code{@value{AS}} emits a 32-bit number.
@end ifset
@ifset W16
For each expression, @code{@value{AS}} emits a 16-bit number.
@end ifset
@end ifclear
@ifset GENERIC
The size of the number emitted, and its byte order,
depends on what kind of computer will run the program.
@end ifset
@c on amd29k, i960, sparc the "special treatment to support compilers" doesn't
@c happen---32-bit addressability, period; no long/short jumps.
@ifset DIFF-TBL-KLUGE
@cindex difference tables altered
@cindex altered difference tables
@quotation
@emph{Warning: Special Treatment to support Compilers}
@end quotation
@ifset GENERIC
Machines with a 32-bit address space, but that do less than 32-bit
addressing, require the following special treatment. If the machine of
interest to you does 32-bit addressing (or doesn't require it;
@pxref{Machine Dependencies}), you can ignore this issue.
@end ifset
In order to assemble compiler output into something that will work,
@code{@value{AS}} will occasionlly do strange things to @samp{.word} directives.
Directives of the form @samp{.word sym1-sym2} are often emitted by
compilers as part of jump tables. Therefore, when @code{@value{AS}} assembles a
directive of the form @samp{.word sym1-sym2}, and the difference between
@code{sym1} and @code{sym2} does not fit in 16 bits, @code{@value{AS}} will
create a @dfn{secondary jump table}, immediately before the next label.
This secondary jump table will be preceded by a short-jump to the
first byte after the secondary table. This short-jump prevents the flow
of control from accidentally falling into the new table. Inside the
table will be a long-jump to @code{sym2}. The original @samp{.word}
will contain @code{sym1} minus the address of the long-jump to
@code{sym2}.
If there were several occurrences of @samp{.word sym1-sym2} before the
secondary jump table, all of them will be adjusted. If there was a
@samp{.word sym3-sym4}, that also did not fit in sixteen bits, a
long-jump to @code{sym4} will be included in the secondary jump table,
and the @code{.word} directives will be adjusted to contain @code{sym3}
minus the address of the long-jump to @code{sym4}; and so on, for as many
entries in the original jump table as necessary.
@ifset INTERNALS
@emph{This feature may be disabled by compiling @code{@value{AS}} with the
@samp{-DWORKING_DOT_WORD} option.} This feature is likely to confuse
assembly language programmers.
@end ifset
@end ifset
@c end DIFF-TBL-KLUGE
@node Deprecated
@section Deprecated Directives
@cindex deprecated directives
@cindex obsolescent directives
One day these directives won't work.
They are included for compatibility with older assemblers.
@table @t
@item .abort
@item .app-file
@item .line
@end table
@ifset GENERIC
@node Machine Dependencies
@chapter Machine Dependent Features
@cindex machine dependencies
The machine instruction sets are (almost by definition) different on
each machine where @code{@value{AS}} runs. Floating point representations
vary as well, and @code{@value{AS}} often supports a few additional
directives or command-line options for compatibility with other
assemblers on a particular platform. Finally, some versions of
@code{@value{AS}} support special pseudo-instructions for branch
optimization.
This chapter discusses most of these differences, though it does not
include details on any machine's instruction set. For details on that
subject, see the hardware manufacturer's manual.
@menu
@ifset VAX
* Vax-Dependent:: VAX Dependent Features
@end ifset
@ifset A29K
* AMD29K-Dependent:: AMD 29K Dependent Features
@end ifset
@ifset H8/300
* H8/300-Dependent:: Hitachi H8/300 Dependent Features
@end ifset
@ifset H8/500
* H8/500-Dependent:: Hitachi H8/500 Dependent Features
@end ifset
@ifset SH
* SH-Dependent:: Hitachi SH Dependent Features
@end ifset
@ifset I960
* i960-Dependent:: Intel 80960 Dependent Features
@end ifset
@ifset M680X0
* M68K-Dependent:: M680x0 Dependent Features
@end ifset
@ifset SPARC
* Sparc-Dependent:: SPARC Dependent Features
@end ifset
@ifset Z8000
* Z8000-Dependent:: Z8000 Dependent Features
@end ifset
@ifset I80386
* i386-Dependent:: 80386 Dependent Features
@end ifset
@end menu
@down
@end ifset
@c The following major nodes are *sections* in the GENERIC version, *chapters*
@c in single-cpu versions. This is mainly achieved by @down. There is a
@c peculiarity: to preserve cross-references, there must be a node called
@c "Machine Dependencies". Hence the conditional nodenames in each
@c major node below. Node defaulting in makeinfo requires adjacency of
@c node and sectioning commands; hence the repetition of @chapter BLAH
@c in both conditional blocks.
@c
@ifset VAX
@ifset GENERIC
@node Vax-Dependent
@chapter VAX Dependent Features
@cindex VAX support
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter VAX Dependent Features
@cindex VAX support
@end ifclear
@menu
* Vax-Opts:: VAX Command-Line Options
* VAX-float:: VAX Floating Point
* VAX-directives:: Vax Machine Directives
* VAX-opcodes:: VAX Opcodes
* VAX-branch:: VAX Branch Improvement
* VAX-operands:: VAX Operands
* VAX-no:: Not Supported on VAX
@end menu
@node Vax-Opts
@section VAX Command-Line Options
@cindex command-line options ignored, VAX
@cindex VAX command-line options ignored
The Vax version of @code{@value{AS}} accepts any of the following options,
gives a warning message that the option was ignored and proceeds.
These options are for compatibility with scripts designed for other
people's assemblers.
@table @asis
@item @kbd{-D} (Debug)
@itemx @kbd{-S} (Symbol Table)
@itemx @kbd{-T} (Token Trace)
@cindex @code{-D}, ignored on VAX
@cindex @code{-S}, ignored on VAX
@cindex @code{-T}, ignored on VAX
These are obsolete options used to debug old assemblers.
@item @kbd{-d} (Displacement size for JUMPs)
@cindex @code{-d}, VAX option
This option expects a number following the @kbd{-d}. Like options
that expect filenames, the number may immediately follow the
@kbd{-d} (old standard) or constitute the whole of the command line
argument that follows @kbd{-d} (GNU standard).
@item @kbd{-V} (Virtualize Interpass Temporary File)
@cindex @code{-V}, redundant on VAX
Some other assemblers use a temporary file. This option
commanded them to keep the information in active memory rather
than in a disk file. @code{@value{AS}} always does this, so this
option is redundant.
@item @kbd{-J} (JUMPify Longer Branches)
@cindex @code{-J}, ignored on VAX
Many 32-bit computers permit a variety of branch instructions
to do the same job. Some of these instructions are short (and
fast) but have a limited range; others are long (and slow) but
can branch anywhere in virtual memory. Often there are 3
flavors of branch: short, medium and long. Some other
assemblers would emit short and medium branches, unless told by
this option to emit short and long branches.
@item @kbd{-t} (Temporary File Directory)
@cindex @code{-t}, ignored on VAX
Some other assemblers may use a temporary file, and this option
takes a filename being the directory to site the temporary
file. Since @code{@value{AS}} does not use a temporary disk file, this
option makes no difference. @kbd{-t} needs exactly one
filename.
@end table
@cindex VMS (VAX) options
@cindex options for VAX/VMS
@cindex VAX/VMS options
@cindex @code{-h} option, VAX/VMS
@cindex @code{-+} option, VAX/VMS
@cindex Vax-11 C compatibility
@cindex symbols with lowercase, VAX/VMS
@c FIXME! look into "I think" below, correct if needed, delete.
The Vax version of the assembler accepts two options when
compiled for VMS. They are @kbd{-h}, and @kbd{-+}. The
@kbd{-h} option prevents @code{@value{AS}} from modifying the
symbol-table entries for symbols that contain lowercase
characters (I think). The @kbd{-+} option causes @code{@value{AS}} to
print warning messages if the FILENAME part of the object file,
or any symbol name is larger than 31 characters. The @kbd{-+}
option also insertes some code following the @samp{_main}
symbol so that the object file will be compatible with Vax-11
"C".
@node VAX-float
@section VAX Floating Point
@cindex VAX floating point
@cindex floating point, VAX
Conversion of flonums to floating point is correct, and
compatible with previous assemblers. Rounding is
towards zero if the remainder is exactly half the least significant bit.
@code{D}, @code{F}, @code{G} and @code{H} floating point formats
are understood.
Immediate floating literals (@emph{e.g.} @samp{S`$6.9})
are rendered correctly. Again, rounding is towards zero in the
boundary case.
@cindex @code{float} directive, VAX
@cindex @code{double} directive, VAX
The @code{.float} directive produces @code{f} format numbers.
The @code{.double} directive produces @code{d} format numbers.
@node VAX-directives
@section Vax Machine Directives
@cindex machine directives, VAX
@cindex VAX machine directives
The Vax version of the assembler supports four directives for
generating Vax floating point constants. They are described in the
table below.
@cindex wide floating point directives, VAX
@table @code
@item .dfloat
@cindex @code{dfloat} directive, VAX
This expects zero or more flonums, separated by commas, and
assembles Vax @code{d} format 64-bit floating point constants.
@item .ffloat
@cindex @code{ffloat} directive, VAX
This expects zero or more flonums, separated by commas, and
assembles Vax @code{f} format 32-bit floating point constants.
@item .gfloat
@cindex @code{gfloat} directive, VAX
This expects zero or more flonums, separated by commas, and
assembles Vax @code{g} format 64-bit floating point constants.
@item .hfloat
@cindex @code{hfloat} directive, VAX
This expects zero or more flonums, separated by commas, and
assembles Vax @code{h} format 128-bit floating point constants.
@end table
@node VAX-opcodes
@section VAX Opcodes
@cindex VAX opcode mnemonics
@cindex opcode mnemonics, VAX
@cindex mnemonics for opcodes, VAX
All DEC mnemonics are supported. Beware that @code{case@dots{}}
instructions have exactly 3 operands. The dispatch table that
follows the @code{case@dots{}} instruction should be made with
@code{.word} statements. This is compatible with all unix
assemblers we know of.
@node VAX-branch
@section VAX Branch Improvement
@cindex VAX branch improvement
@cindex branch improvement, VAX
@cindex pseudo-ops for branch, VAX
Certain pseudo opcodes are permitted. They are for branch
instructions. They expand to the shortest branch instruction that
will reach the target. Generally these mnemonics are made by
substituting @samp{j} for @samp{b} at the start of a DEC mnemonic.
This feature is included both for compatibility and to help
compilers. If you don't need this feature, don't use these
opcodes. Here are the mnemonics, and the code they can expand into.
@table @code
@item jbsb
@samp{Jsb} is already an instruction mnemonic, so we chose @samp{jbsb}.
@table @asis
@item (byte displacement)
@kbd{bsbb @dots{}}
@item (word displacement)
@kbd{bsbw @dots{}}
@item (long displacement)
@kbd{jsb @dots{}}
@end table
@item jbr
@itemx jr
Unconditional branch.
@table @asis
@item (byte displacement)
@kbd{brb @dots{}}
@item (word displacement)
@kbd{brw @dots{}}
@item (long displacement)
@kbd{jmp @dots{}}
@end table
@item j@var{COND}
@var{COND} may be any one of the conditional branches
@code{neq}, @code{nequ}, @code{eql}, @code{eqlu}, @code{gtr},
@code{geq}, @code{lss}, @code{gtru}, @code{lequ}, @code{vc}, @code{vs},
@code{gequ}, @code{cc}, @code{lssu}, @code{cs}.
@var{COND} may also be one of the bit tests
@code{bs}, @code{bc}, @code{bss}, @code{bcs}, @code{bsc}, @code{bcc},
@code{bssi}, @code{bcci}, @code{lbs}, @code{lbc}.
@var{NOTCOND} is the opposite condition to @var{COND}.
@table @asis
@item (byte displacement)
@kbd{b@var{COND} @dots{}}
@item (word displacement)
@kbd{b@var{NOTCOND} foo ; brw @dots{} ; foo:}
@item (long displacement)
@kbd{b@var{NOTCOND} foo ; jmp @dots{} ; foo:}
@end table
@item jacb@var{X}
@var{X} may be one of @code{b d f g h l w}.
@table @asis
@item (word displacement)
@kbd{@var{OPCODE} @dots{}}
@item (long displacement)
@example
@var{OPCODE} @dots{}, foo ;
brb bar ;
foo: jmp @dots{} ;
bar:
@end example
@end table
@item jaob@var{YYY}
@var{YYY} may be one of @code{lss leq}.
@item jsob@var{ZZZ}
@var{ZZZ} may be one of @code{geq gtr}.
@table @asis
@item (byte displacement)
@kbd{@var{OPCODE} @dots{}}
@item (word displacement)
@example
@var{OPCODE} @dots{}, foo ;
brb bar ;
foo: brw @var{destination} ;
bar:
@end example
@item (long displacement)
@example
@var{OPCODE} @dots{}, foo ;
brb bar ;
foo: jmp @var{destination} ;
bar:
@end example
@end table
@item aobleq
@itemx aoblss
@itemx sobgeq
@itemx sobgtr
@table @asis
@item (byte displacement)
@kbd{@var{OPCODE} @dots{}}
@item (word displacement)
@example
@var{OPCODE} @dots{}, foo ;
brb bar ;
foo: brw @var{destination} ;
bar:
@end example
@item (long displacement)
@example
@var{OPCODE} @dots{}, foo ;
brb bar ;
foo: jmp @var{destination} ;
bar:
@end example
@end table
@end table
@node VAX-operands
@section VAX Operands
@cindex VAX operand notation
@cindex operand notation, VAX
@cindex immediate character, VAX
@cindex VAX immediate character
The immediate character is @samp{$} for Unix compatibility, not
@samp{#} as DEC writes it.
@cindex indirect character, VAX
@cindex VAX indirect character
The indirect character is @samp{*} for Unix compatibility, not
@samp{@@} as DEC writes it.
@cindex displacement sizing character, VAX
@cindex VAX displacement sizing character
The displacement sizing character is @samp{`} (an accent grave) for
Unix compatibility, not @samp{^} as DEC writes it. The letter
preceding @samp{`} may have either case. @samp{G} is not
understood, but all other letters (@code{b i l s w}) are understood.
@cindex register names, VAX
@cindex VAX register names
Register names understood are @code{r0 r1 r2 @dots{} r15 ap fp sp
pc}. Any case of letters will do.
For instance
@smallexample
tstb *w`$4(r5)
@end smallexample
Any expression is permitted in an operand. Operands are comma
separated.
@c There is some bug to do with recognizing expressions
@c in operands, but I forget what it is. It is
@c a syntax clash because () is used as an address mode
@c and to encapsulate sub-expressions.
@node VAX-no
@section Not Supported on VAX
@cindex VAX bitfields not supported
@cindex bitfields, not supported on VAX
Vax bit fields can not be assembled with @code{@value{AS}}. Someone
can add the required code if they really need it.
@end ifset
@ifset A29K
@ifset GENERIC
@page
@node AMD29K-Dependent
@chapter AMD 29K Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter AMD 29K Dependent Features
@end ifclear
@cindex AMD 29K support
@cindex 29K support
@menu
* AMD29K Options:: Options
* AMD29K Syntax:: Syntax
* AMD29K Floating Point:: Floating Point
* AMD29K Directives:: AMD 29K Machine Directives
* AMD29K Opcodes:: Opcodes
@end menu
@node AMD29K Options
@section Options
@cindex AMD 29K options (none)
@cindex options for AMD29K (none)
@code{@value{AS}} has no additional command-line options for the AMD
29K family.
@node AMD29K Syntax
@section Syntax
@menu
* AMD29K-Chars:: Special Characters
* AMD29K-Regs:: Register Names
@end menu
@node AMD29K-Chars
@subsection Special Characters
@cindex line comment character, AMD 29K
@cindex AMD 29K line comment character
@samp{;} is the line comment character.
@cindex line separator, AMD 29K
@cindex AMD 29K line separator
@cindex statement separator, AMD 29K
@cindex AMD 29K statement separator
@samp{@@} can be used instead of a newline to separate statements.
@cindex identifiers, AMD 29K
@cindex AMD 29K identifiers
The character @samp{?} is permitted in identifiers (but may not begin
an identifier).
@node AMD29K-Regs
@subsection Register Names
@cindex AMD 29K register names
@cindex register names, AMD 29K
General-purpose registers are represented by predefined symbols of the
form @samp{GR@var{nnn}} (for global registers) or @samp{LR@var{nnn}}
(for local registers), where @var{nnn} represents a number between
@code{0} and @code{127}, written with no leading zeros. The leading
letters may be in either upper or lower case; for example, @samp{gr13}
and @samp{LR7} are both valid register names.
You may also refer to general-purpose registers by specifying the
register number as the result of an expression (prefixed with @samp{%%}
to flag the expression as a register number):
@smallexample
%%@var{expression}
@end smallexample
@noindent
---where @var{expression} must be an absolute expression evaluating to a
number between @code{0} and @code{255}. The range [0, 127] refers to
global registers, and the range [128, 255] to local registers.
@cindex special purpose registers, AMD 29K
@cindex AMD 29K special purpose registers
@cindex protected registers, AMD 29K
@cindex AMD 29K protected registers
In addition, @code{@value{AS}} understands the following protected
special-purpose register names for the AMD 29K family:
@smallexample
vab chd pc0
ops chc pc1
cps rbp pc2
cfg tmc mmu
cha tmr lru
@end smallexample
These unprotected special-purpose register names are also recognized:
@smallexample
ipc alu fpe
ipa bp inte
ipb fc fps
q cr exop
@end smallexample
@node AMD29K Floating Point
@section Floating Point
@cindex floating point, AMD 29K (@sc{ieee})
@cindex AMD 29K floating point (@sc{ieee})
The AMD 29K family uses @sc{ieee} floating-point numbers.
@node AMD29K Directives
@section AMD 29K Machine Directives
@cindex machine directives, AMD 29K
@cindex AMD 29K machine directives
@table @code
@item .block @var{size} , @var{fill}
@cindex @code{block} directive, AMD 29K
This directive emits @var{size} bytes, each of value @var{fill}. Both
@var{size} and @var{fill} are absolute expressions. If the comma
and @var{fill} are omitted, @var{fill} is assumed to be zero.
In other versions of the GNU assembler, this directive is called
@samp{.space}.
@end table
@table @code
@item .cputype
@cindex @code{cputype} directive, AMD 29K
This directive is ignored; it is accepted for compatibility with other
AMD 29K assemblers.
@item .file
@cindex @code{file} directive, AMD 29K
This directive is ignored; it is accepted for compatibility with other
AMD 29K assemblers.
@quotation
@emph{Warning:} in other versions of the GNU assembler, @code{.file} is
used for the directive called @code{.app-file} in the AMD 29K support.
@end quotation
@item .line
@cindex @code{line} directive, AMD 29K
This directive is ignored; it is accepted for compatibility with other
AMD 29K assemblers.
@ignore
@c since we're ignoring .lsym...
@item .reg @var{symbol}, @var{expression}
@cindex @code{reg} directive, AMD 29K
@code{.reg} has the same effect as @code{.lsym}; @pxref{Lsym,,@code{.lsym}}.
@end ignore
@item .sect
@cindex @code{sect} directive, AMD 29K
This directive is ignored; it is accepted for compatibility with other
AMD 29K assemblers.
@item .use @var{section name}
@cindex @code{use} directive, AMD 29K
Establishes the section and subsection for the following code;
@var{section name} may be one of @code{.text}, @code{.data},
@code{.data1}, or @code{.lit}. With one of the first three @var{section
name} options, @samp{.use} is equivalent to the machine directive
@var{section name}; the remaining case, @samp{.use .lit}, is the same as
@samp{.data 200}.
@end table
@node AMD29K Opcodes
@section Opcodes
@cindex AMD 29K opcodes
@cindex opcodes for AMD 29K
@code{@value{AS}} implements all the standard AMD 29K opcodes. No
additional pseudo-instructions are needed on this family.
For information on the 29K machine instruction set, see @cite{Am29000
User's Manual}, Advanced Micro Devices, Inc.
@end ifset
@ifset Hitachi-all
@ifclear GENERIC
@node Machine Dependencies
@chapter Machine Dependent Features
The machine instruction sets are different on each Hitachi chip family,
and there are also some syntax differences among the families. This
chapter describes the specific @code{@value{AS}} features for each
family.
@menu
* H8/300-Dependent:: Hitachi H8/300 Dependent Features
* H8/500-Dependent:: Hitachi H8/500 Dependent Features
* SH-Dependent:: Hitachi SH Dependent Features
@end menu
@down
@end ifclear
@end ifset
@ifset H8/300
@ifset GENERIC
@page
@end ifset
@node H8/300-Dependent
@chapter H8/300 Dependent Features
@cindex H8/300 support
@menu
* H8/300 Options:: Options
* H8/300 Syntax:: Syntax
* H8/300 Floating Point:: Floating Point
* H8/300 Directives:: H8/300 Machine Directives
* H8/300 Opcodes:: Opcodes
@end menu
@node H8/300 Options
@section Options
@cindex H8/300 options (none)
@cindex options, H8/300 (none)
@code{@value{AS}} has no additional command-line options for the Hitachi
H8/300 family.
@node H8/300 Syntax
@section Syntax
@menu
* H8/300-Chars:: Special Characters
* H8/300-Regs:: Register Names
* H8/300-Addressing:: Addressing Modes
@end menu
@node H8/300-Chars
@subsection Special Characters
@cindex line comment character, H8/300
@cindex H8/300 line comment character
@samp{;} is the line comment character.
@cindex line separator, H8/300
@cindex statement separator, H8/300
@cindex H8/300 line separator
@samp{$} can be used instead of a newline to separate statements.
Therefore @emph{you may not use @samp{$} in symbol names} on the H8/300.
@node H8/300-Regs
@subsection Register Names
@cindex H8/300 registers
@cindex register names, H8/300
You can use predefined symbols of the form @samp{r@var{n}h} and
@samp{r@var{n}l} to refer to the H8/300 registers as sixteen 8-bit
general-purpose registers. @var{n} is a digit from @samp{0} to
@samp{7}); for instance, both @samp{r0h} and @samp{r7l} are valid
register names.
You can also use the eight predefined symbols @samp{r@var{n}} to refer
to the H8/300 registers as 16-bit registers (you must use this form for
addressing).
On the H8/300H, you can also use the eight predefined symbols
@samp{er@var{n}} (@samp{er0} @dots{} @samp{er7}) to refer to the 32-bit
general purpose registers.
The two control registers are called @code{pc} (program counter; a
16-bit register, except on the H8/300H where it is 24 bits) and
@code{ccr} (condition code register; an 8-bit register). @code{r7} is
used as the stack pointer, and can also be called @code{sp}.
@node H8/300-Addressing
@subsection Addressing Modes
@cindex addressing modes, H8/300
@cindex H8/300 addressing modes
@value{AS} understands the following addressing modes for the H8/300:
@table @code
@item r@var{n}
Register direct
@item @@r@var{n}
Register indirect
@item @@(@var{d}, r@var{n})
@itemx @@(@var{d}:16, r@var{n})
@itemx @@(@var{d}:24, r@var{n})
Register indirect: 16-bit or 24-bit displacement @var{d} from register
@var{n}. (24-bit displacements are only meaningful on the H8/300H.)
@item @@r@var{n}+
Register indirect with post-increment
@item @@-r@var{n}
Register indirect with pre-decrement
@item @code{@@}@var{aa}
@itemx @code{@@}@var{aa}:8
@itemx @code{@@}@var{aa}:16
@itemx @code{@@}@var{aa}:24
Absolute address @code{aa}. (The address size @samp{:24} only makes
sense on the H8/300H.)
@item #@var{xx}
@itemx #@var{xx}:8
@itemx #@var{xx}:16
@itemx #@var{xx}:32
Immediate data @var{xx}. You may specify the @samp{:8}, @samp{:16}, or
@samp{:32} for clarity, if you wish; but @code{@value{AS}} neither
requires this nor uses it---the data size required is taken from
context.
@item @code{@@}@code{@@}@var{aa}
@itemx @code{@@}@code{@@}@var{aa}:8
Memory indirect. You may specify the @samp{:8} for clarity, if you
wish; but @code{@value{AS}} neither requires this nor uses it.
@end table
@node H8/300 Floating Point
@section Floating Point
@cindex floating point, H8/300 (@sc{ieee})
@cindex H8/300 floating point (@sc{ieee})
The H8/300 family has no hardware floating point, but the @code{.float}
directive generates @sc{ieee} floating-point numbers for compatibility
with other development tools.
@page
@node H8/300 Directives
@section H8/300 Machine Directives
@cindex H8/300 machine directives (none)
@cindex machine directives, H8/300 (none)
@cindex @code{word} directive, H8/300
@cindex @code{int} directive, H8/300
@code{@value{AS}} has only one machine-dependent directive for the
H8/300:
@table @code
@item .h300h
@cindex H8/300H, assembling for
Recognize and emit additional instructions for the H8/300H variant, and
also make @code{.int} emit 32-bit numbers rather than the usual (16-bit)
for the H8/300 family.
@end table
On the H8/300 family (including the H8/300H) @samp{.word} directives
generate 16-bit numbers.
@node H8/300 Opcodes
@section Opcodes
@cindex H8/300 opcode summary
@cindex opcode summary, H8/300
@cindex mnemonics, H8/300
@cindex instruction summary, H8/300
For detailed information on the H8/300 machine instruction set, see
@cite{H8/300 Series Programming Manual} (Hitachi ADE--602--025). For
information specific to the H8/300H, see @cite{H8/300H Series
Programming Manual} (Hitachi).
@code{@value{AS}} implements all the standard H8/300 opcodes. No additional
pseudo-instructions are needed on this family.
The following table summarizes the H8/300 opcodes, and their arguments.
Entries marked @samp{*} are opcodes used only on the H8/300H.
@smallexample
@c Using @group seems to use the normal baselineskip, not the smallexample
@c baselineskip; looks approx doublespaced.
@i{Legend:}
Rs @r{source register}
Rd @r{destination register}
abs @r{absolute address}
imm @r{immediate data}
disp:N @r{N-bit displacement from a register}
pcrel:N @r{N-bit displacement relative to program counter}
add.b #imm,rd * andc #imm,ccr
add.b rs,rd band #imm,rd
add.w rs,rd band #imm,@@rd
* add.w #imm,rd band #imm,@@abs:8
* add.l rs,rd bra pcrel:8
* add.l #imm,rd * bra pcrel:16
adds #imm,rd bt pcrel:8
addx #imm,rd * bt pcrel:16
addx rs,rd brn pcrel:8
and.b #imm,rd * brn pcrel:16
and.b rs,rd bf pcrel:8
* and.w rs,rd * bf pcrel:16
* and.w #imm,rd bhi pcrel:8
* and.l #imm,rd * bhi pcrel:16
* and.l rs,rd bls pcrel:8
@page
* bls pcrel:16 bld #imm,rd
bcc pcrel:8 bld #imm,@@rd
* bcc pcrel:16 bld #imm,@@abs:8
bhs pcrel:8 bnot #imm,rd
* bhs pcrel:16 bnot #imm,@@rd
bcs pcrel:8 bnot #imm,@@abs:8
* bcs pcrel:16 bnot rs,rd
blo pcrel:8 bnot rs,@@rd
* blo pcrel:16 bnot rs,@@abs:8
bne pcrel:8 bor #imm,rd
* bne pcrel:16 bor #imm,@@rd
beq pcrel:8 bor #imm,@@abs:8
* beq pcrel:16 bset #imm,rd
bvc pcrel:8 bset #imm,@@rd
* bvc pcrel:16 bset #imm,@@abs:8
bvs pcrel:8 bset rs,rd
* bvs pcrel:16 bset rs,@@rd
bpl pcrel:8 bset rs,@@abs:8
* bpl pcrel:16 bsr pcrel:8
bmi pcrel:8 bsr pcrel:16
* bmi pcrel:16 bst #imm,rd
bge pcrel:8 bst #imm,@@rd
* bge pcrel:16 bst #imm,@@abs:8
blt pcrel:8 btst #imm,rd
* blt pcrel:16 btst #imm,@@rd
bgt pcrel:8 btst #imm,@@abs:8
* bgt pcrel:16 btst rs,rd
ble pcrel:8 btst rs,@@rd
* ble pcrel:16 btst rs,@@abs:8
bclr #imm,rd bxor #imm,rd
bclr #imm,@@rd bxor #imm,@@rd
bclr #imm,@@abs:8 bxor #imm,@@abs:8
bclr rs,rd cmp.b #imm,rd
bclr rs,@@rd cmp.b rs,rd
bclr rs,@@abs:8 cmp.w rs,rd
biand #imm,rd cmp.w rs,rd
biand #imm,@@rd * cmp.w #imm,rd
biand #imm,@@abs:8 * cmp.l #imm,rd
bild #imm,rd * cmp.l rs,rd
bild #imm,@@rd daa rs
bild #imm,@@abs:8 das rs
bior #imm,rd dec.b rs
bior #imm,@@rd * dec.w #imm,rd
bior #imm,@@abs:8 * dec.l #imm,rd
bist #imm,rd divxu.b rs,rd
bist #imm,@@rd * divxu.w rs,rd
bist #imm,@@abs:8 * divxs.b rs,rd
bixor #imm,rd * divxs.w rs,rd
bixor #imm,@@rd eepmov
bixor #imm,@@abs:8 * eepmovw
@page
* exts.w rd mov.w rs,@@abs:16
* exts.l rd * mov.l #imm,rd
* extu.w rd * mov.l rs,rd
* extu.l rd * mov.l @@rs,rd
inc rs * mov.l @@(disp:16,rs),rd
* inc.w #imm,rd * mov.l @@(disp:24,rs),rd
* inc.l #imm,rd * mov.l @@rs+,rd
jmp @@rs * mov.l @@abs:16,rd
jmp abs * mov.l @@abs:24,rd
jmp @@@@abs:8 * mov.l rs,@@rd
jsr @@rs * mov.l rs,@@(disp:16,rd)
jsr abs * mov.l rs,@@(disp:24,rd)
jsr @@@@abs:8 * mov.l rs,@@-rd
ldc #imm,ccr * mov.l rs,@@abs:16
ldc rs,ccr * mov.l rs,@@abs:24
* ldc @@abs:16,ccr movfpe @@abs:16,rd
* ldc @@abs:24,ccr movtpe rs,@@abs:16
* ldc @@(disp:16,rs),ccr mulxu.b rs,rd
* ldc @@(disp:24,rs),ccr * mulxu.w rs,rd
* ldc @@rs+,ccr * mulxs.b rs,rd
* ldc @@rs,ccr * mulxs.w rs,rd
* mov.b @@(disp:24,rs),rd neg.b rs
* mov.b rs,@@(disp:24,rd) * neg.w rs
mov.b @@abs:16,rd * neg.l rs
mov.b rs,rd nop
mov.b @@abs:8,rd not.b rs
mov.b rs,@@abs:8 * not.w rs
mov.b rs,rd * not.l rs
mov.b #imm,rd or.b #imm,rd
mov.b @@rs,rd or.b rs,rd
mov.b @@(disp:16,rs),rd * or.w #imm,rd
mov.b @@rs+,rd * or.w rs,rd
mov.b @@abs:8,rd * or.l #imm,rd
mov.b rs,@@rd * or.l rs,rd
mov.b rs,@@(disp:16,rd) orc #imm,ccr
mov.b rs,@@-rd pop.w rs
mov.b rs,@@abs:8 * pop.l rs
mov.w rs,@@rd push.w rs
* mov.w @@(disp:24,rs),rd * push.l rs
* mov.w rs,@@(disp:24,rd) rotl.b rs
* mov.w @@abs:24,rd * rotl.w rs
* mov.w rs,@@abs:24 * rotl.l rs
mov.w rs,rd rotr.b rs
mov.w #imm,rd * rotr.w rs
mov.w @@rs,rd * rotr.l rs
mov.w @@(disp:16,rs),rd rotxl.b rs
mov.w @@rs+,rd * rotxl.w rs
mov.w @@abs:16,rd * rotxl.l rs
mov.w rs,@@(disp:16,rd) rotxr.b rs
mov.w rs,@@-rd * rotxr.w rs
@page
* rotxr.l rs * stc ccr,@@(disp:24,rd)
bpt * stc ccr,@@-rd
rte * stc ccr,@@abs:16
rts * stc ccr,@@abs:24
shal.b rs sub.b rs,rd
* shal.w rs sub.w rs,rd
* shal.l rs * sub.w #imm,rd
shar.b rs * sub.l rs,rd
* shar.w rs * sub.l #imm,rd
* shar.l rs subs #imm,rd
shll.b rs subx #imm,rd
* shll.w rs subx rs,rd
* shll.l rs * trapa #imm
shlr.b rs xor #imm,rd
* shlr.w rs xor rs,rd
* shlr.l rs * xor.w #imm,rd
sleep * xor.w rs,rd
stc ccr,rd * xor.l #imm,rd
* stc ccr,@@rs * xor.l rs,rd
* stc ccr,@@(disp:16,rd) xorc #imm,ccr
@end smallexample
@cindex size suffixes, H8/300
@cindex H8/300 size suffixes
Four H8/300 instructions (@code{add}, @code{cmp}, @code{mov},
@code{sub}) are defined with variants using the suffixes @samp{.b},
@samp{.w}, and @samp{.l} to specify the size of a memory operand.
@code{@value{AS}} supports these suffixes, but does not require them;
since one of the operands is always a register, @code{@value{AS}} can
deduce the correct size.
For example, since @code{r0} refers to a 16-bit register,
@example
mov r0,@@foo
@exdent is equivalent to
mov.w r0,@@foo
@end example
If you use the size suffixes, @code{@value{AS}} issues a warning when
the suffix and the register size do not match.
@end ifset
@ifset H8/500
@page
@node H8/500-Dependent
@chapter H8/500 Dependent Features
@cindex H8/500 support
@menu
* H8/500 Options:: Options
* H8/500 Syntax:: Syntax
* H8/500 Floating Point:: Floating Point
* H8/500 Directives:: H8/500 Machine Directives
* H8/500 Opcodes:: Opcodes
@end menu
@node H8/500 Options
@section Options
@cindex H8/500 options (none)
@cindex options, H8/500 (none)
@code{@value{AS}} has no additional command-line options for the Hitachi
H8/500 family.
@node H8/500 Syntax
@section Syntax
@menu
* H8/500-Chars:: Special Characters
* H8/500-Regs:: Register Names
* H8/500-Addressing:: Addressing Modes
@end menu
@node H8/500-Chars
@subsection Special Characters
@cindex line comment character, H8/500
@cindex H8/500 line comment character
@samp{!} is the line comment character.
@cindex line separator, H8/500
@cindex statement separator, H8/500
@cindex H8/500 line separator
@samp{;} can be used instead of a newline to separate statements.
@cindex symbol names, @samp{$} in
@cindex @code{$} in symbol names
Since @samp{$} has no special meaning, you may use it in symbol names.
@node H8/500-Regs
@subsection Register Names
@cindex H8/500 registers
@cindex registers, H8/500
You can use the predefined symbols @samp{r0}, @samp{r1}, @samp{r2},
@samp{r3}, @samp{r4}, @samp{r5}, @samp{r6}, and @samp{r7} to refer to
the H8/500 registers.
The H8/500 also has these control registers:
@table @code
@item cp
code pointer
@item dp
data pointer
@item bp
base pointer
@item tp
stack top pointer
@item ep
extra pointer
@item sr
status register
@item ccr
condition code register
@end table
All registers are 16 bits long. To represent 32 bit numbers, use two
adjacent registers; for distant memory addresses, use one of the segment
pointers (@code{cp} for the program counter; @code{dp} for
@code{r0}--@code{r3}; @code{ep} for @code{r4} and @code{r5}; and
@code{tp} for @code{r6} and @code{r7}.
@node H8/500-Addressing
@subsection Addressing Modes
@cindex addressing modes, H8/500
@cindex H8/500 addressing modes
@value{AS} understands the following addressing modes for the H8/500:
@table @code
@item R@var{n}
Register direct
@item @@R@var{n}
Register indirect
@item @@(d:8, R@var{n})
Register indirect with 8 bit signed displacement
@item @@(d:16, R@var{n})
Register indirect with 16 bit signed displacement
@item @@-R@var{n}
Register indirect with pre-decrement
@item @@R@var{n}+
Register indirect with post-increment
@item @@@var{aa}:8
8 bit absolute address
@item @@@var{aa}:16
16 bit absolute address
@item #@var{xx}:8
8 bit immediate
@item #@var{xx}:16
16 bit immediate
@end table
@node H8/500 Floating Point
@section Floating Point
@cindex floating point, H8/500 (@sc{ieee})
@cindex H8/500 floating point (@sc{ieee})
The H8/500 family uses @sc{ieee} floating-point numbers.
@node H8/500 Directives
@section H8/500 Machine Directives
@cindex H8/500 machine directives (none)
@cindex machine directives, H8/500 (none)
@cindex @code{word} directive, H8/500
@cindex @code{int} directive, H8/500
@code{@value{AS}} has no machine-dependent directives for the H8/500.
However, on this platform the @samp{.int} and @samp{.word} directives
generate 16-bit numbers.
@node H8/500 Opcodes
@section Opcodes
@cindex H8/500 opcode summary
@cindex opcode summary, H8/500
@cindex mnemonics, H8/500
@cindex instruction summary, H8/500
For detailed information on the H8/500 machine instruction set, see
@cite{H8/500 Series Programming Manual} (Hitachi M21T001).
@code{@value{AS}} implements all the standard H8/500 opcodes. No additional
pseudo-instructions are needed on this family.
The following table summarizes H8/500 opcodes and their operands:
@c Use @group if it ever works, instead of @page
@page
@smallexample
@i{Legend:}
abs8 @r{8-bit absolute address}
abs16 @r{16-bit absolute address}
abs24 @r{24-bit absolute address}
crb @r{@code{ccr}, @code{br}, @code{ep}, @code{dp}, @code{tp}, @code{dp}}
disp8 @r{8-bit displacement}
ea @r{@code{rn}, @code{@@rn}, @code{@@(d:8, rn)}, @code{@@(d:16, rn)},}
@r{@code{@@-rn}, @code{@@rn+}, @code{@@aa:8}, @code{@@aa:16},}
@r{@code{#xx:8}, @code{#xx:16}}
ea_mem @r{@code{@@rn}, @code{@@(d:8, rn)}, @code{@@(d:16, rn)},}
@r{@code{@@-rn}, @code{@@rn+}, @code{@@aa:8}, @code{@@aa:16}}
ea_noimm @r{@code{rn}, @code{@@rn}, @code{@@(d:8, rn)}, @code{@@(d:16, rn)},}
@r{@code{@@-rn}, @code{@@rn+}, @code{@@aa:8}, @code{@@aa:16}}
fp r6
imm4 @r{4-bit immediate data}
imm8 @r{8-bit immediate data}
imm16 @r{16-bit immediate data}
pcrel8 @r{8-bit offset from program counter}
pcrel16 @r{16-bit offset from program counter}
qim @r{@code{-2}, @code{-1}, @code{1}, @code{2}}
rd @r{any register}
rs @r{a register distinct from rd}
rlist @r{comma-separated list of registers in parentheses;}
@r{register ranges @code{rd-rs} are allowed}
sp @r{stack pointer (@code{r7})}
sr @r{status register}
sz @r{size; @samp{.b} or @samp{.w}. If omitted, default @samp{.w}}
ldc[.b] ea,crb bcc[.w] pcrel16
ldc[.w] ea,sr bcc[.b] pcrel8
add[:q] sz qim,ea_noimm bhs[.w] pcrel16
add[:g] sz ea,rd bhs[.b] pcrel8
adds sz ea,rd bcs[.w] pcrel16
addx sz ea,rd bcs[.b] pcrel8
and sz ea,rd blo[.w] pcrel16
andc[.b] imm8,crb blo[.b] pcrel8
andc[.w] imm16,sr bne[.w] pcrel16
bpt bne[.b] pcrel8
bra[.w] pcrel16 beq[.w] pcrel16
bra[.b] pcrel8 beq[.b] pcrel8
bt[.w] pcrel16 bvc[.w] pcrel16
bt[.b] pcrel8 bvc[.b] pcrel8
brn[.w] pcrel16 bvs[.w] pcrel16
brn[.b] pcrel8 bvs[.b] pcrel8
bf[.w] pcrel16 bpl[.w] pcrel16
bf[.b] pcrel8 bpl[.b] pcrel8
bhi[.w] pcrel16 bmi[.w] pcrel16
bhi[.b] pcrel8 bmi[.b] pcrel8
bls[.w] pcrel16 bge[.w] pcrel16
bls[.b] pcrel8 bge[.b] pcrel8
@page
blt[.w] pcrel16 mov[:g][.b] imm8,ea_mem
blt[.b] pcrel8 mov[:g][.w] imm16,ea_mem
bgt[.w] pcrel16 movfpe[.b] ea,rd
bgt[.b] pcrel8 movtpe[.b] rs,ea_noimm
ble[.w] pcrel16 mulxu sz ea,rd
ble[.b] pcrel8 neg sz ea
bclr sz imm4,ea_noimm nop
bclr sz rs,ea_noimm not sz ea
bnot sz imm4,ea_noimm or sz ea,rd
bnot sz rs,ea_noimm orc[.b] imm8,crb
bset sz imm4,ea_noimm orc[.w] imm16,sr
bset sz rs,ea_noimm pjmp abs24
bsr[.b] pcrel8 pjmp @@rd
bsr[.w] pcrel16 pjsr abs24
btst sz imm4,ea_noimm pjsr @@rd
btst sz rs,ea_noimm prtd imm8
clr sz ea prtd imm16
cmp[:e][.b] imm8,rd prts
cmp[:i][.w] imm16,rd rotl sz ea
cmp[:g].b imm8,ea_noimm rotr sz ea
cmp[:g][.w] imm16,ea_noimm rotxl sz ea
Cmp[:g] sz ea,rd rotxr sz ea
dadd rs,rd rtd imm8
divxu sz ea,rd rtd imm16
dsub rs,rd rts
exts[.b] rd scb/f rs,pcrel8
extu[.b] rd scb/ne rs,pcrel8
jmp @@rd scb/eq rs,pcrel8
jmp @@(imm8,rd) shal sz ea
jmp @@(imm16,rd) shar sz ea
jmp abs16 shll sz ea
jsr @@rd shlr sz ea
jsr @@(imm8,rd) sleep
jsr @@(imm16,rd) stc[.b] crb,ea_noimm
jsr abs16 stc[.w] sr,ea_noimm
ldm @@sp+,(rlist) stm (rlist),@@-sp
link fp,imm8 sub sz ea,rd
link fp,imm16 subs sz ea,rd
mov[:e][.b] imm8,rd subx sz ea,rd
mov[:i][.w] imm16,rd swap[.b] rd
mov[:l][.w] abs8,rd tas[.b] ea
mov[:l].b abs8,rd trapa imm4
mov[:s][.w] rs,abs8 trap/vs
mov[:s].b rs,abs8 tst sz ea
mov[:f][.w] @@(disp8,fp),rd unlk fp
mov[:f][.w] rs,@@(disp8,fp) xch[.w] rs,rd
mov[:f].b @@(disp8,fp),rd xor sz ea,rd
mov[:f].b rs,@@(disp8,fp) xorc.b imm8,crb
mov[:g] sz rs,ea_mem xorc.w imm16,sr
mov[:g] sz ea,rd
@end smallexample
@end ifset
@ifset SH
@page
@node SH-Dependent
@chapter Hitachi SH Dependent Features
@cindex SH support
@menu
* SH Options:: Options
* SH Syntax:: Syntax
* SH Floating Point:: Floating Point
* SH Directives:: SH Machine Directives
* SH Opcodes:: Opcodes
@end menu
@node SH Options
@section Options
@cindex SH options (none)
@cindex options, SH (none)
@code{@value{AS}} has no additional command-line options for the Hitachi
SH family.
@node SH Syntax
@section Syntax
@menu
* SH-Chars:: Special Characters
* SH-Regs:: Register Names
* SH-Addressing:: Addressing Modes
@end menu
@node SH-Chars
@subsection Special Characters
@cindex line comment character, SH
@cindex SH line comment character
@samp{!} is the line comment character.
@cindex line separator, SH
@cindex statement separator, SH
@cindex SH line separator
You can use @samp{;} instead of a newline to separate statements.
@cindex symbol names, @samp{$} in
@cindex @code{$} in symbol names
Since @samp{$} has no special meaning, you may use it in symbol names.
@node SH-Regs
@subsection Register Names
@cindex SH registers
@cindex registers, SH
You can use the predefined symbols @samp{r0}, @samp{r1}, @samp{r2},
@samp{r3}, @samp{r4}, @samp{r5}, @samp{r6}, @samp{r7}, @samp{r8},
@samp{r9}, @samp{r10}, @samp{r11}, @samp{r12}, @samp{r13}, @samp{r14},
and @samp{r15} to refer to the SH registers.
The SH also has these control registers:
@table @code
@item pr
procedure register (holds return address)
@item pc
program counter
@item mach
@itemx macl
high and low multiply accumulator registers
@item sr
status register
@item gbr
global base register
@item vbr
vector base register (for interrupt vectors)
@end table
@node SH-Addressing
@subsection Addressing Modes
@cindex addressing modes, SH
@cindex SH addressing modes
@code{@value{AS}} understands the following addressing modes for the SH.
@code{R@var{n}} in the following refers to any of the numbered
registers, but @emph{not} the control registers.
@table @code
@item R@var{n}
Register direct
@item @@R@var{n}
Register indirect
@item @@-R@var{n}
Register indirect with pre-decrement
@item @@R@var{n}+
Register indirect with post-increment
@item @@(@var{disp}, R@var{n})
Register indirect with displacement
@item @@(R0, R@var{n})
Register indexed
@item @@(@var{disp}, GBR)
@code{GBR} offset
@item @@(R0, GBR)
GBR indexed
@item @var{addr}
@itemx @@(@var{disp}, PC)
PC relative address (for branch or for addressing memory). The
@code{@value{AS}} implementation allows you to use the simpler form
@var{addr} anywhere a PC relative address is called for; the alternate
form is supported for compatibility with other assemblers.
@item #@var{imm}
Immediate data
@end table
@node SH Floating Point
@section Floating Point
@cindex floating point, SH (@sc{ieee})
@cindex SH floating point (@sc{ieee})
The SH family uses @sc{ieee} floating-point numbers.
@node SH Directives
@section SH Machine Directives
@cindex SH machine directives (none)
@cindex machine directives, SH (none)
@cindex @code{word} directive, SH
@cindex @code{int} directive, SH
@code{@value{AS}} has no machine-dependent directives for the SH.
@node SH Opcodes
@section Opcodes
@cindex SH opcode summary
@cindex opcode summary, SH
@cindex mnemonics, SH
@cindex instruction summary, SH
For detailed information on the SH machine instruction set, see
@cite{SH-Microcomputer User's Manual} (Hitachi Micro Systems, Inc.).
@code{@value{AS}} implements all the standard SH opcodes. No additional
pseudo-instructions are needed on this family. Note, however, that
because @code{@value{AS}} supports a simpler form of PC-relative
addressing, you may simply write (for example)
@example
mov.l bar,r0
@end example
@noindent
where other assemblers might require an explicit displacement to
@code{bar} from the program counter:
@example
mov.l @@(@var{disp}, PC)
@end example
Here is a summary of SH opcodes:
@page
@smallexample
@i{Legend:}
Rn @r{a numbered register}
Rm @r{another numbered register}
#imm @r{immediate data}
disp @r{displacement}
disp8 @r{8-bit displacement}
disp12 @r{12-bit displacement}
add #imm,Rn lds.l @@Rn+,PR
add Rm,Rn mac.w @@Rm+,@@Rn+
addc Rm,Rn mov #imm,Rn
addv Rm,Rn mov Rm,Rn
and #imm,R0 mov.b Rm,@@(R0,Rn)
and Rm,Rn mov.b Rm,@@-Rn
and.b #imm,@@(R0,GBR) mov.b Rm,@@Rn
bf disp8 mov.b @@(disp,Rm),R0
bra disp12 mov.b @@(disp,GBR),R0
bsr disp12 mov.b @@(R0,Rm),Rn
bt disp8 mov.b @@Rm+,Rn
clrm mov.b @@Rm,Rn
clrt mov.b R0,@@(disp,Rm)
cmp/eq #imm,R0 mov.b R0,@@(disp,GBR)
cmp/eq Rm,Rn mov.l Rm,@@(disp,Rn)
cmp/ge Rm,Rn mov.l Rm,@@(R0,Rn)
cmp/gt Rm,Rn mov.l Rm,@@-Rn
cmp/hi Rm,Rn mov.l Rm,@@Rn
cmp/hs Rm,Rn mov.l @@(disp,Rn),Rm
cmp/pl Rn mov.l @@(disp,GBR),R0
cmp/pz Rn mov.l @@(disp,PC),Rn
cmp/str Rm,Rn mov.l @@(R0,Rm),Rn
div0s Rm,Rn mov.l @@Rm+,Rn
div0u mov.l @@Rm,Rn
div1 Rm,Rn mov.l R0,@@(disp,GBR)
exts.b Rm,Rn mov.w Rm,@@(R0,Rn)
exts.w Rm,Rn mov.w Rm,@@-Rn
extu.b Rm,Rn mov.w Rm,@@Rn
extu.w Rm,Rn mov.w @@(disp,Rm),R0
jmp @@Rn mov.w @@(disp,GBR),R0
jsr @@Rn mov.w @@(disp,PC),Rn
ldc Rn,GBR mov.w @@(R0,Rm),Rn
ldc Rn,SR mov.w @@Rm+,Rn
ldc Rn,VBR mov.w @@Rm,Rn
ldc.l @@Rn+,GBR mov.w R0,@@(disp,Rm)
ldc.l @@Rn+,SR mov.w R0,@@(disp,GBR)
ldc.l @@Rn+,VBR mova @@(disp,PC),R0
lds Rn,MACH movt Rn
lds Rn,MACL muls Rm,Rn
lds Rn,PR mulu Rm,Rn
lds.l @@Rn+,MACH neg Rm,Rn
lds.l @@Rn+,MACL negc Rm,Rn
@page
nop stc VBR,Rn
not Rm,Rn stc.l GBR,@@-Rn
or #imm,R0 stc.l SR,@@-Rn
or Rm,Rn stc.l VBR,@@-Rn
or.b #imm,@@(R0,GBR) sts MACH,Rn
rotcl Rn sts MACL,Rn
rotcr Rn sts PR,Rn
rotl Rn sts.l MACH,@@-Rn
rotr Rn sts.l MACL,@@-Rn
rte sts.l PR,@@-Rn
rts sub Rm,Rn
sett subc Rm,Rn
shal Rn subv Rm,Rn
shar Rn swap.b Rm,Rn
shll Rn swap.w Rm,Rn
shll16 Rn tas.b @@Rn
shll2 Rn trapa #imm
shll8 Rn tst #imm,R0
shlr Rn tst Rm,Rn
shlr16 Rn tst.b #imm,@@(R0,GBR)
shlr2 Rn xor #imm,R0
shlr8 Rn xor Rm,Rn
sleep xor.b #imm,@@(R0,GBR)
stc GBR,Rn xtrct Rm,Rn
stc SR,Rn
@end smallexample
@ifset Hitachi-all
@ifclear GENERIC
@up
@end ifclear
@end ifset
@end ifset
@ifset I960
@ifset GENERIC
@page
@node i960-Dependent
@chapter Intel 80960 Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter Intel 80960 Dependent Features
@end ifclear
@cindex i960 support
@menu
* Options-i960:: i960 Command-line Options
* Floating Point-i960:: Floating Point
* Directives-i960:: i960 Machine Directives
* Opcodes for i960:: i960 Opcodes
@end menu
@c FIXME! Add Syntax sec with discussion of bitfields here, at least so
@c long as they're not turned on for other machines than 960.
@node Options-i960
@section i960 Command-line Options
@cindex i960 options
@cindex options, i960
@table @code
@item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
@cindex i960 architecture options
@cindex architecture options, i960
@cindex @code{-A} options, i960
Select the 80960 architecture. Instructions or features not supported
by the selected architecture cause fatal errors.
@samp{-ACA} is equivalent to @samp{-ACA_A}; @samp{-AKC} is equivalent to
@samp{-AMC}. Synonyms are provided for compatibility with other tools.
If none of these options is specified, @code{@value{AS}} will generate code for any
instruction or feature that is supported by @emph{some} version of the
960 (even if this means mixing architectures!). In principle,
@code{@value{AS}} will attempt to deduce the minimal sufficient processor
type if none is specified; depending on the object code format, the
processor type may be recorded in the object file. If it is critical
that the @code{@value{AS}} output match a specific architecture, specify that
architecture explicitly.
@item -b
@cindex @code{-b} option, i960
@cindex branch recording, i960
@cindex i960 branch recording
Add code to collect information about conditional branches taken, for
later optimization using branch prediction bits. (The conditional branch
instructions have branch prediction bits in the CA, CB, and CC
architectures.) If @var{BR} represents a conditional branch instruction,
the following represents the code generated by the assembler when
@samp{-b} is specified:
@smallexample
call @var{increment routine}
.word 0 # pre-counter
Label: @var{BR}
call @var{increment routine}
.word 0 # post-counter
@end smallexample
The counter following a branch records the number of times that branch
was @emph{not} taken; the differenc between the two counters is the
number of times the branch @emph{was} taken.
@cindex @code{gbr960}, i960 postprocessor
@cindex branch statistics table, i960
A table of every such @code{Label} is also generated, so that the
external postprocessor @code{gbr960} (supplied by Intel) can locate all
the counters. This table is always labelled @samp{__BRANCH_TABLE__};
this is a local symbol to permit collecting statistics for many separate
object files. The table is word aligned, and begins with a two-word
header. The first word, initialized to 0, is used in maintaining linked
lists of branch tables. The second word is a count of the number of
entries in the table, which follow immediately: each is a word, pointing
to one of the labels illustrated above.
@c TEXI2ROFF-KILL
@ifinfo
@c END TEXI2ROFF-KILL
@example
+------------+------------+------------+ ... +------------+
| | | | | |
| *NEXT | COUNT: N | *BRLAB 1 | | *BRLAB N |
| | | | | |
+------------+------------+------------+ ... +------------+
__BRANCH_TABLE__ layout
@end example
@c TEXI2ROFF-KILL
@end ifinfo
@tex
\vskip 1pc
\line{\leftskip=0pt\hskip\tableindent
\boxit{2cm}{\tt *NEXT}\boxit{2cm}{\tt COUNT: \it N}\boxit{2cm}{\tt
*BRLAB 1}\ibox{1cm}{\quad\dots}\boxit{2cm}{\tt *BRLAB \it N}\hfil}
\centerline{\it {\tt \_\_BRANCH\_TABLE\_\_} layout}
@end tex
@c END TEXI2ROFF-KILL
The first word of the header is used to locate multiple branch tables,
since each object file may contain one. Normally the links are
maintained with a call to an initialization routine, placed at the
beginning of each function in the file. The GNU C compiler will
generate these calls automatically when you give it a @samp{-b} option.
For further details, see the documentation of @samp{gbr960}.
@item -norelax
@cindex @code{-norelax} option, i960
Normally, Compare-and-Branch instructions with targets that require
displacements greater than 13 bits (or that have external targets) are
replaced with the corresponding compare (or @samp{chkbit}) and branch
instructions. You can use the @samp{-norelax} option to specify that
@code{@value{AS}} should generate errors instead, if the target displacement
is larger than 13 bits.
This option does not affect the Compare-and-Jump instructions; the code
emitted for them is @emph{always} adjusted when necessary (depending on
displacement size), regardless of whether you use @samp{-norelax}.
@end table
@node Floating Point-i960
@section Floating Point
@cindex floating point, i960 (@sc{ieee})
@cindex i960 floating point (@sc{ieee})
@code{@value{AS}} generates @sc{ieee} floating-point numbers for the directives
@samp{.float}, @samp{.double}, @samp{.extended}, and @samp{.single}.
@node Directives-i960
@section i960 Machine Directives
@cindex machine directives, i960
@cindex i960 machine directives
@table @code
@cindex @code{bss} directive, i960
@item .bss @var{symbol}, @var{length}, @var{align}
Reserve @var{length} bytes in the bss section for a local @var{symbol},
aligned to the power of two specified by @var{align}. @var{length} and
@var{align} must be positive absolute expressions. This directive
differs from @samp{.lcomm} only in that it permits you to specify
an alignment. @xref{Lcomm,,@code{.lcomm}}.
@end table
@table @code
@item .extended @var{flonums}
@cindex @code{extended} directive, i960
@code{.extended} expects zero or more flonums, separated by commas; for
each flonum, @samp{.extended} emits an @sc{ieee} extended-format (80-bit)
floating-point number.
@item .leafproc @var{call-lab}, @var{bal-lab}
@cindex @code{leafproc} directive, i960
You can use the @samp{.leafproc} directive in conjunction with the
optimized @code{callj} instruction to enable faster calls of leaf
procedures. If a procedure is known to call no other procedures, you
may define an entry point that skips procedure prolog code (and that does
not depend on system-supplied saved context), and declare it as the
@var{bal-lab} using @samp{.leafproc}. If the procedure also has an
entry point that goes through the normal prolog, you can specify that
entry point as @var{call-lab}.
A @samp{.leafproc} declaration is meant for use in conjunction with the
optimized call instruction @samp{callj}; the directive records the data
needed later to choose between converting the @samp{callj} into a
@code{bal} or a @code{call}.
@var{call-lab} is optional; if only one argument is present, or if the
two arguments are identical, the single argument is assumed to be the
@code{bal} entry point.
@item .sysproc @var{name}, @var{index}
@cindex @code{sysproc} directive, i960
The @samp{.sysproc} directive defines a name for a system procedure.
After you define it using @samp{.sysproc}, you can use @var{name} to
refer to the system procedure identified by @var{index} when calling
procedures with the optimized call instruction @samp{callj}.
Both arguments are required; @var{index} must be between 0 and 31
(inclusive).
@end table
@node Opcodes for i960
@section i960 Opcodes
@cindex opcodes, i960
@cindex i960 opcodes
All Intel 960 machine instructions are supported;
@pxref{Options-i960,,i960 Command-line Options} for a discussion of
selecting the instruction subset for a particular 960
architecture.@refill
Some opcodes are processed beyond simply emitting a single corresponding
instruction: @samp{callj}, and Compare-and-Branch or Compare-and-Jump
instructions with target displacements larger than 13 bits.
@menu
* callj-i960:: @code{callj}
* Compare-and-branch-i960:: Compare-and-Branch
@end menu
@node callj-i960
@subsection @code{callj}
@cindex @code{callj}, i960 pseudo-opcode
@cindex i960 @code{callj} pseudo-opcode
You can write @code{callj} to have the assembler or the linker determine
the most appropriate form of subroutine call: @samp{call},
@samp{bal}, or @samp{calls}. If the assembly source contains
enough information---a @samp{.leafproc} or @samp{.sysproc} directive
defining the operand---then @code{@value{AS}} will translate the
@code{callj}; if not, it will simply emit the @code{callj}, leaving it
for the linker to resolve.
@node Compare-and-branch-i960
@subsection Compare-and-Branch
@cindex i960 compare/branch instructions
@cindex compare/branch instructions, i960
The 960 architectures provide combined Compare-and-Branch instructions
that permit you to store the branch target in the lower 13 bits of the
instruction word itself. However, if you specify a branch target far
enough away that its address won't fit in 13 bits, the assembler can
either issue an error, or convert your Compare-and-Branch instruction
into separate instructions to do the compare and the branch.
@cindex compare and jump expansions, i960
@cindex i960 compare and jump expansions
Whether @code{@value{AS}} gives an error or expands the instruction depends
on two choices you can make: whether you use the @samp{-norelax} option,
and whether you use a ``Compare and Branch'' instruction or a ``Compare
and Jump'' instruction. The ``Jump'' instructions are @emph{always}
expanded if necessary; the ``Branch'' instructions are expanded when
necessary @emph{unless} you specify @code{-norelax}---in which case
@code{@value{AS}} gives an error instead.
These are the Compare-and-Branch instructions, their ``Jump'' variants,
and the instruction pairs they may expand into:
@c TEXI2ROFF-KILL
@ifinfo
@c END TEXI2ROFF-KILL
@example
Compare and
Branch Jump Expanded to
------ ------ ------------
bbc chkbit; bno
bbs chkbit; bo
cmpibe cmpije cmpi; be
cmpibg cmpijg cmpi; bg
cmpibge cmpijge cmpi; bge
cmpibl cmpijl cmpi; bl
cmpible cmpijle cmpi; ble
cmpibno cmpijno cmpi; bno
cmpibne cmpijne cmpi; bne
cmpibo cmpijo cmpi; bo
cmpobe cmpoje cmpo; be
cmpobg cmpojg cmpo; bg
cmpobge cmpojge cmpo; bge
cmpobl cmpojl cmpo; bl
cmpoble cmpojle cmpo; ble
cmpobne cmpojne cmpo; bne
@end example
@c TEXI2ROFF-KILL
@end ifinfo
@tex
\hskip\tableindent
\halign{\hfil {\tt #}\quad&\hfil {\tt #}\qquad&{\tt #}\hfil\cr
\omit{\hfil\it Compare and\hfil}\span\omit&\cr
{\it Branch}&{\it Jump}&{\it Expanded to}\cr
bbc& & chkbit; bno\cr
bbs& & chkbit; bo\cr
cmpibe& cmpije& cmpi; be\cr
cmpibg& cmpijg& cmpi; bg\cr
cmpibge& cmpijge& cmpi; bge\cr
cmpibl& cmpijl& cmpi; bl\cr
cmpible& cmpijle& cmpi; ble\cr
cmpibno& cmpijno& cmpi; bno\cr
cmpibne& cmpijne& cmpi; bne\cr
cmpibo& cmpijo& cmpi; bo\cr
cmpobe& cmpoje& cmpo; be\cr
cmpobg& cmpojg& cmpo; bg\cr
cmpobge& cmpojge& cmpo; bge\cr
cmpobl& cmpojl& cmpo; bl\cr
cmpoble& cmpojle& cmpo; ble\cr
cmpobne& cmpojne& cmpo; bne\cr}
@end tex
@c END TEXI2ROFF-KILL
@end ifset
@ifset M680X0
@ifset GENERIC
@page
@node M68K-Dependent
@chapter M680x0 Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter M680x0 Dependent Features
@end ifclear
@cindex M680x0 support
@menu
* M68K-Opts:: M680x0 Options
* M68K-Syntax:: Syntax
* M68K-Float:: Floating Point
* M68K-Directives:: 680x0 Machine Directives
* M68K-opcodes:: Opcodes
@end menu
@node M68K-Opts
@section M680x0 Options
@cindex options, M680x0
@cindex M680x0 options
The Motorola 680x0 version of @code{@value{AS}} has two machine dependent options.
One shortens undefined references from 32 to 16 bits, while the
other is used to tell @code{@value{AS}} what kind of machine it is
assembling for.
@cindex @code{-l} option, M680x0
You can use the @kbd{-l} option to shorten the size of references to
undefined symbols. If the @kbd{-l} option is not given, references to
undefined symbols will be a full long (32 bits) wide. (Since @code{@value{AS}}
cannot know where these symbols will end up, @code{@value{AS}} can only allocate
space for the linker to fill in later. Since @code{@value{AS}} doesn't know how
far away these symbols will be, it allocates as much space as it can.)
If this option is given, the references will only be one word wide (16
bits). This may be useful if you want the object file to be as small as
possible, and you know that the relevant symbols will be less than 17
bits away.
@cindex @code{-m68000} and related options
@cindex architecture options, M680x0
@cindex M680x0 architecture options
The 680x0 version of @code{@value{AS}} is most frequently used to assemble
programs for the Motorola MC68020 microprocessor. Occasionally it is
used to assemble programs for the mostly similar, but slightly different
MC68000 or MC68010 microprocessors. You can give @code{@value{AS}} the options
@samp{-m68000}, @samp{-mc68000}, @samp{-m68010}, @samp{-mc68010},
@samp{-m68020}, and @samp{-mc68020} to tell it what processor is the
target.
@node M68K-Syntax
@section Syntax
@cindex M680x0 syntax
@cindex syntax, M680x0
@cindex M680x0 size modifiers
@cindex size modifiers, M680x0
The 680x0 version of @code{@value{AS}} uses syntax similar to the Sun assembler.
Size modifiers are appended directly to the end of the opcode without an
intervening period. For example, write @samp{movl} rather than
@samp{move.l}.
@ifset INTERNALS
If @code{@value{AS}} is compiled with SUN_ASM_SYNTAX defined, it will also allow
Sun-style local labels of the form @samp{1$} through @samp{$9}.
@end ifset
In the following table @dfn{apc} stands for any of the address
registers (@samp{a0} through @samp{a7}), nothing, (@samp{}), the
Program Counter (@samp{pc}), or the zero-address relative to the
program counter (@samp{zpc}).
@cindex M680x0 addressing modes
@cindex addressing modes, M680x0
The following addressing modes are understood:
@table @dfn
@item Immediate
@samp{#@var{digits}}
@item Data Register
@samp{d0} through @samp{d7}
@item Address Register
@samp{a0} through @samp{a7}
@item Address Register Indirect
@samp{a0@@} through @samp{a7@@}
@item Address Register Postincrement
@samp{a0@@+} through @samp{a7@@+}
@item Address Register Predecrement
@samp{a0@@-} through @samp{a7@@-}
@item Indirect Plus Offset
@samp{@var{apc}@@(@var{digits})}
@item Index
@samp{@var{apc}@@(@var{digits},@var{register}:@var{size}:@var{scale})}
or @samp{@var{apc}@@(@var{register}:@var{size}:@var{scale})}
@item Postindex
@samp{@var{apc}@@(@var{digits})@@(@var{digits},@var{register}:@var{size}:@var{scale})}
or @samp{@var{apc}@@(@var{digits})@@(@var{register}:@var{size}:@var{scale})}
@item Preindex
@samp{@var{apc}@@(@var{digits},@var{register}:@var{size}:@var{scale})@@(@var{digits})}
or @samp{@var{apc}@@(@var{register}:@var{size}:@var{scale})@@(@var{digits})}
@item Memory Indirect
@samp{@var{apc}@@(@var{digits})@@(@var{digits})}
@item Absolute
@samp{@var{symbol}}, or @samp{@var{digits}}
@ignore
@c pesch@cygnus.com: gnu, rich concur the following needs careful
@c research before documenting.
, or either of the above followed
by @samp{:b}, @samp{:w}, or @samp{:l}.
@end ignore
@end table
For some configurations, especially those where the compiler normally
does not prepend an underscore to the names of user variables, the
assembler requires a @samp{%} before any use of a register name. This
is intended to let the assembler distinguish between user variables and
registers named @samp{a0} through @samp{a7}, et cetera. The @samp{%} is
always accepted, but is only required for some configurations, notably
@samp{m68k-coff}.
@node M68K-Float
@section Floating Point
@cindex floating point, M680x0
@cindex M680x0 floating point
@c FIXME is this "not too well tested" crud STILL true?
The floating point code is not too well tested, and may have
subtle bugs in it.
Packed decimal (P) format floating literals are not supported.
Feel free to add the code!
The floating point formats generated by directives are these.
@table @code
@item .float
@cindex @code{float} directive, M680x0
@code{Single} precision floating point constants.
@item .double
@cindex @code{double} directive, M680x0
@code{Double} precision floating point constants.
@end table
There is no directive to produce regions of memory holding
extended precision numbers, however they can be used as
immediate operands to floating-point instructions. Adding a
directive to create extended precision numbers would not be
hard, but it has not yet seemed necessary.
@node M68K-Directives
@section 680x0 Machine Directives
@cindex M680x0 directives
@cindex directives, M680x0
In order to be compatible with the Sun assembler the 680x0 assembler
understands the following directives.
@table @code
@item .data1
@cindex @code{data1} directive, M680x0
This directive is identical to a @code{.data 1} directive.
@item .data2
@cindex @code{data2} directive, M680x0
This directive is identical to a @code{.data 2} directive.
@item .even
@cindex @code{even} directive, M680x0
This directive is identical to a @code{.align 1} directive.
@c Is this true? does it work???
@item .skip
@cindex @code{skip} directive, M680x0
This directive is identical to a @code{.space} directive.
@end table
@node M68K-opcodes
@section Opcodes
@cindex M680x0 opcodes
@cindex opcodes, M680x0
@cindex instruction set, M680x0
@c pesch@cygnus.com: I don't see any point in the following
@c paragraph. Bugs are bugs; how does saying this
@c help anyone?
@ignore
Danger: Several bugs have been found in the opcode table (and
fixed). More bugs may exist. Be careful when using obscure
instructions.
@end ignore
@menu
* M68K-Branch:: Branch Improvement
* M68K-Chars:: Special Characters
@end menu
@node M68K-Branch
@subsection Branch Improvement
@cindex pseudo-opcodes, M680x0
@cindex M680x0 pseudo-opcodes
@cindex branch improvement, M680x0
@cindex M680x0 branch improvement
Certain pseudo opcodes are permitted for branch instructions.
They expand to the shortest branch instruction that will reach the
target. Generally these mnemonics are made by substituting @samp{j} for
@samp{b} at the start of a Motorola mnemonic.
The following table summarizes the pseudo-operations. A @code{*} flags
cases that are more fully described after the table:
@smallexample
Displacement
+-------------------------------------------------
| 68020 68000/10
Pseudo-Op |BYTE WORD LONG LONG non-PC relative
+-------------------------------------------------
jbsr |bsrs bsr bsrl jsr jsr
jra |bras bra bral jmp jmp
* jXX |bXXs bXX bXXl bNXs;jmpl bNXs;jmp
* dbXX |dbXX dbXX dbXX; bra; jmpl
* fjXX |fbXXw fbXXw fbXXl fbNXw;jmp
XX: condition
NX: negative of condition XX
@end smallexample
@center @code{*}---see full description below
@table @code
@item jbsr
@itemx jra
These are the simplest jump pseudo-operations; they always map to one
particular machine instruction, depending on the displacement to the
branch target.
@item j@var{XX}
Here, @samp{j@var{XX}} stands for an entire family of pseudo-operations,
where @var{XX} is a conditional branch or condition-code test. The full
list of pseudo-ops in this family is:
@smallexample
jhi jls jcc jcs jne jeq jvc
jvs jpl jmi jge jlt jgt jle
@end smallexample
For the cases of non-PC relative displacements and long displacements on
the 68000 or 68010, @code{@value{AS}} will issue a longer code fragment in terms of
@var{NX}, the opposite condition to @var{XX}. For example, for the
non-PC relative case:
@smallexample
j@var{XX} foo
@end smallexample
gives
@smallexample
b@var{NX}s oof
jmp foo
oof:
@end smallexample
@item db@var{XX}
The full family of pseudo-operations covered here is
@smallexample
dbhi dbls dbcc dbcs dbne dbeq dbvc
dbvs dbpl dbmi dbge dblt dbgt dble
dbf dbra dbt
@end smallexample
Other than for word and byte displacements, when the source reads
@samp{db@var{XX} foo}, @code{@value{AS}} will emit
@smallexample
db@var{XX} oo1
bra oo2
oo1:jmpl foo
oo2:
@end smallexample
@item fj@var{XX}
This family includes
@smallexample
fjne fjeq fjge fjlt fjgt fjle fjf
fjt fjgl fjgle fjnge fjngl fjngle fjngt
fjnle fjnlt fjoge fjogl fjogt fjole fjolt
fjor fjseq fjsf fjsne fjst fjueq fjuge
fjugt fjule fjult fjun
@end smallexample
For branch targets that are not PC relative, @code{@value{AS}} emits
@smallexample
fb@var{NX} oof
jmp foo
oof:
@end smallexample
when it encounters @samp{fj@var{XX} foo}.
@end table
@node M68K-Chars
@subsection Special Characters
@cindex special characters, M680x0
@cindex M680x0 immediate character
@cindex immediate character, M680x0
@cindex M680x0 line comment character
@cindex line comment character, M680x0
@cindex comments, M680x0
The immediate character is @samp{#} for Sun compatibility. The
line-comment character is @samp{|}. If a @samp{#} appears at the
beginning of a line, it is treated as a comment unless it looks like
@samp{# line file}, in which case it is treated normally.
@end ifset
@ignore
@c FIXME! Stop ignoring when filled in.
@node 32x32
@chapter 32x32
@section Options
The 32x32 version of @code{@value{AS}} accepts a @kbd{-m32032} option to
specify thiat it is compiling for a 32032 processor, or a
@kbd{-m32532} to specify that it is compiling for a 32532 option.
The default (if neither is specified) is chosen when the assembler
is compiled.
@section Syntax
I don't know anything about the 32x32 syntax assembled by
@code{@value{AS}}. Someone who undersands the processor (I've never seen
one) and the possible syntaxes should write this section.
@section Floating Point
The 32x32 uses @sc{ieee} floating point numbers, but @code{@value{AS}}
will only create single or double precision values. I don't know if the
32x32 understands extended precision numbers.
@section 32x32 Machine Directives
The 32x32 has no machine dependent directives.
@end ignore
@ifset SPARC
@ifset GENERIC
@page
@node Sparc-Dependent
@chapter SPARC Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter SPARC Dependent Features
@end ifclear
@cindex SPARC support
@menu
* Sparc-Opts:: Options
* Sparc-Float:: Floating Point
* Sparc-Directives:: Sparc Machine Directives
@end menu
@node Sparc-Opts
@section Options
@cindex options for SPARC
@cindex SPARC options
@cindex architectures, SPARC
@cindex SPARC architectures
The SPARC chip family includes several successive levels (or other
variants) of chip, using the same core instruction set, but including
a few additional instructions at each level.
By default, @code{@value{AS}} assumes the core instruction set (SPARC
v6), but ``bumps'' the architecture level as needed: it switches to
successively higher architectures as it encounters instructions that
only exist in the higher levels.
@table @code
@item -Av6 | -Av7 | -Av8 | -Asparclite
@kindex -Av6
@kindex Av7
@kindex -Av8
@kindex -Asparclite
Use one of the @samp{-A} options to select one of the SPARC
architectures explicitly. If you select an architecture explicitly,
@code{@value{AS}} reports a fatal error if it encounters an instruction
or feature requiring a higher level.
@item -bump
Permit the assembler to ``bump'' the architecture level as required, but
warn whenever it is necessary to switch to another level.
@end table
@ignore
@c FIXME: (sparc) Fill in "syntax" section!
@c subsection syntax
I don't know anything about Sparc syntax. Someone who does
will have to write this section.
@end ignore
@node Sparc-Float
@section Floating Point
@cindex floating point, SPARC (@sc{ieee})
@cindex SPARC floating point (@sc{ieee})
The Sparc uses @sc{ieee} floating-point numbers.
@node Sparc-Directives
@section Sparc Machine Directives
@cindex SPARC machine directives
@cindex machine directives, SPARC
The Sparc version of @code{@value{AS}} supports the following additional
machine directives:
@table @code
@item .common
@cindex @code{common} directive, SPARC
This must be followed by a symbol name, a positive number, and
@code{"bss"}. This behaves somewhat like @code{.comm}, but the
syntax is different.
@item .half
@cindex @code{half} directive, SPARC
This is functionally identical to @code{.short}.
@item .proc
@cindex @code{proc} directive, SPARC
This directive is ignored. Any text following it on the same
line is also ignored.
@item .reserve
@cindex @code{reserve} directive, SPARC
This must be followed by a symbol name, a positive number, and
@code{"bss"}. This behaves somewhat like @code{.lcomm}, but the
syntax is different.
@item .seg
@cindex @code{seg} directive, SPARC
This must be followed by @code{"text"}, @code{"data"}, or
@code{"data1"}. It behaves like @code{.text}, @code{.data}, or
@code{.data 1}.
@item .skip
@cindex @code{skip} directive, SPARC
This is functionally identical to the @code{.space} directive.
@item .word
@cindex @code{word} directive, SPARC
On the Sparc, the .word directive produces 32 bit values,
instead of the 16 bit values it produces on many other machines.
@end table
@end ifset
@ifset I80386
@ifset GENERIC
@page
@node i386-Dependent
@chapter 80386 Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter 80386 Dependent Features
@end ifclear
@cindex i386 support
@cindex i80306 support
@menu
* i386-Options:: Options
* i386-Syntax:: AT&T Syntax versus Intel Syntax
* i386-Opcodes:: Opcode Naming
* i386-Regs:: Register Naming
* i386-prefixes:: Opcode Prefixes
* i386-Memory:: Memory References
* i386-jumps:: Handling of Jump Instructions
* i386-Float:: Floating Point
* i386-Notes:: Notes
@end menu
@node i386-Options
@section Options
@cindex options for i386 (none)
@cindex i386 options (none)
The 80386 has no machine dependent options.
@node i386-Syntax
@section AT&T Syntax versus Intel Syntax
@cindex i386 syntax compatibility
@cindex syntax compatibility, i386
In order to maintain compatibility with the output of @code{@value{GCC}},
@code{@value{AS}} supports AT&T System V/386 assembler syntax. This is quite
different from Intel syntax. We mention these differences because
almost all 80386 documents used only Intel syntax. Notable differences
between the two syntaxes are:
@itemize @bullet
@item
@cindex immediate operands, i386
@cindex i386 immediate operands
@cindex register operands, i386
@cindex i386 register operands
@cindex jump/call operands, i386
@cindex i386 jump/call operands
@cindex operand delimiters, i386
AT&T immediate operands are preceded by @samp{$}; Intel immediate
operands are undelimited (Intel @samp{push 4} is AT&T @samp{pushl $4}).
AT&T register operands are preceded by @samp{%}; Intel register operands
are undelimited. AT&T absolute (as opposed to PC relative) jump/call
operands are prefixed by @samp{*}; they are undelimited in Intel syntax.
@item
@cindex i386 source, destination operands
@cindex source, destination operands; i386
AT&T and Intel syntax use the opposite order for source and destination
operands. Intel @samp{add eax, 4} is @samp{addl $4, %eax}. The
@samp{source, dest} convention is maintained for compatibility with
previous Unix assemblers.
@item
@cindex opcode suffixes, i386
@cindex sizes operands, i386
@cindex i386 size suffixes
In AT&T syntax the size of memory operands is determined from the last
character of the opcode name. Opcode suffixes of @samp{b}, @samp{w},
and @samp{l} specify byte (8-bit), word (16-bit), and long (32-bit)
memory references. Intel syntax accomplishes this by prefixes memory
operands (@emph{not} the opcodes themselves) with @samp{byte ptr},
@samp{word ptr}, and @samp{dword ptr}. Thus, Intel @samp{mov al, byte
ptr @var{foo}} is @samp{movb @var{foo}, %al} in AT&T syntax.
@item
@cindex return instructions, i386
@cindex i386 jump, call, return
Immediate form long jumps and calls are
@samp{lcall/ljmp $@var{section}, $@var{offset}} in AT&T syntax; the
Intel syntax is
@samp{call/jmp far @var{section}:@var{offset}}. Also, the far return
instruction
is @samp{lret $@var{stack-adjust}} in AT&T syntax; Intel syntax is
@samp{ret far @var{stack-adjust}}.
@item
@cindex sections, i386
@cindex i386 sections
The AT&T assembler does not provide support for multiple section
programs. Unix style systems expect all programs to be single sections.
@end itemize
@node i386-Opcodes
@section Opcode Naming
@cindex i386 opcode naming
@cindex opcode naming, i386
Opcode names are suffixed with one character modifiers which specify the
size of operands. The letters @samp{b}, @samp{w}, and @samp{l} specify
byte, word, and long operands. If no suffix is specified by an
instruction and it contains no memory operands then @code{@value{AS}} tries to
fill in the missing suffix based on the destination register operand
(the last one by convention). Thus, @samp{mov %ax, %bx} is equivalent
to @samp{movw %ax, %bx}; also, @samp{mov $1, %bx} is equivalent to
@samp{movw $1, %bx}. Note that this is incompatible with the AT&T Unix
assembler which assumes that a missing opcode suffix implies long
operand size. (This incompatibility does not affect compiler output
since compilers always explicitly specify the opcode suffix.)
Almost all opcodes have the same names in AT&T and Intel format. There
are a few exceptions. The sign extend and zero extend instructions need
two sizes to specify them. They need a size to sign/zero extend
@emph{from} and a size to zero extend @emph{to}. This is accomplished
by using two opcode suffixes in AT&T syntax. Base names for sign extend
and zero extend are @samp{movs@dots{}} and @samp{movz@dots{}} in AT&T
syntax (@samp{movsx} and @samp{movzx} in Intel syntax). The opcode
suffixes are tacked on to this base name, the @emph{from} suffix before
the @emph{to} suffix. Thus, @samp{movsbl %al, %edx} is AT&T syntax for
``move sign extend @emph{from} %al @emph{to} %edx.'' Possible suffixes,
thus, are @samp{bl} (from byte to long), @samp{bw} (from byte to word),
and @samp{wl} (from word to long).
@cindex conversion instructions, i386
@cindex i386 conversion instructions
The Intel-syntax conversion instructions
@itemize @bullet
@item
@samp{cbw} --- sign-extend byte in @samp{%al} to word in @samp{%ax},
@item
@samp{cwde} --- sign-extend word in @samp{%ax} to long in @samp{%eax},
@item
@samp{cwd} --- sign-extend word in @samp{%ax} to long in @samp{%dx:%ax},
@item
@samp{cdq} --- sign-extend dword in @samp{%eax} to quad in @samp{%edx:%eax},
@end itemize
@noindent
are called @samp{cbtw}, @samp{cwtl}, @samp{cwtd}, and @samp{cltd} in
AT&T naming. @code{@value{AS}} accepts either naming for these instructions.
@cindex jump instructions, i386
@cindex call instructions, i386
Far call/jump instructions are @samp{lcall} and @samp{ljmp} in
AT&T syntax, but are @samp{call far} and @samp{jump far} in Intel
convention.
@node i386-Regs
@section Register Naming
@cindex i386 registers
@cindex registers, i386
Register operands are always prefixes with @samp{%}. The 80386 registers
consist of
@itemize @bullet
@item
the 8 32-bit registers @samp{%eax} (the accumulator), @samp{%ebx},
@samp{%ecx}, @samp{%edx}, @samp{%edi}, @samp{%esi}, @samp{%ebp} (the
frame pointer), and @samp{%esp} (the stack pointer).
@item
the 8 16-bit low-ends of these: @samp{%ax}, @samp{%bx}, @samp{%cx},
@samp{%dx}, @samp{%di}, @samp{%si}, @samp{%bp}, and @samp{%sp}.
@item
the 8 8-bit registers: @samp{%ah}, @samp{%al}, @samp{%bh},
@samp{%bl}, @samp{%ch}, @samp{%cl}, @samp{%dh}, and @samp{%dl} (These
are the high-bytes and low-bytes of @samp{%ax}, @samp{%bx},
@samp{%cx}, and @samp{%dx})
@item
the 6 section registers @samp{%cs} (code section), @samp{%ds}
(data section), @samp{%ss} (stack section), @samp{%es}, @samp{%fs},
and @samp{%gs}.
@item
the 3 processor control registers @samp{%cr0}, @samp{%cr2}, and
@samp{%cr3}.
@item
the 6 debug registers @samp{%db0}, @samp{%db1}, @samp{%db2},
@samp{%db3}, @samp{%db6}, and @samp{%db7}.
@item
the 2 test registers @samp{%tr6} and @samp{%tr7}.
@item
the 8 floating point register stack @samp{%st} or equivalently
@samp{%st(0)}, @samp{%st(1)}, @samp{%st(2)}, @samp{%st(3)},
@samp{%st(4)}, @samp{%st(5)}, @samp{%st(6)}, and @samp{%st(7)}.
@end itemize
@node i386-prefixes
@section Opcode Prefixes
@cindex i386 opcode prefixes
@cindex opcode prefixes, i386
@cindex prefixes, i386
Opcode prefixes are used to modify the following opcode. They are used
to repeat string instructions, to provide section overrides, to perform
bus lock operations, and to give operand and address size (16-bit
operands are specified in an instruction by prefixing what would
normally be 32-bit operands with a ``operand size'' opcode prefix).
Opcode prefixes are usually given as single-line instructions with no
operands, and must directly precede the instruction they act upon. For
example, the @samp{scas} (scan string) instruction is repeated with:
@smallexample
repne
scas
@end smallexample
Here is a list of opcode prefixes:
@itemize @bullet
@item
@cindex section override prefixes, i386
Section override prefixes @samp{cs}, @samp{ds}, @samp{ss}, @samp{es},
@samp{fs}, @samp{gs}. These are automatically added by specifying
using the @var{section}:@var{memory-operand} form for memory references.
@item
@cindex size prefixes, i386
Operand/Address size prefixes @samp{data16} and @samp{addr16}
change 32-bit operands/addresses into 16-bit operands/addresses. Note
that 16-bit addressing modes (i.e. 8086 and 80286 addressing modes)
are not supported (yet).
@item
@cindex bus lock prefixes, i386
@cindex inhibiting interrupts, i386
The bus lock prefix @samp{lock} inhibits interrupts during
execution of the instruction it precedes. (This is only valid with
certain instructions; see a 80386 manual for details).
@item
@cindex coprocessor wait, i386
The wait for coprocessor prefix @samp{wait} waits for the
coprocessor to complete the current instruction. This should never be
needed for the 80386/80387 combination.
@item
@cindex repeat prefixes, i386
The @samp{rep}, @samp{repe}, and @samp{repne} prefixes are added
to string instructions to make them repeat @samp{%ecx} times.
@end itemize
@node i386-Memory
@section Memory References
@cindex i386 memory references
@cindex memory references, i386
An Intel syntax indirect memory reference of the form
@smallexample
@var{section}:[@var{base} + @var{index}*@var{scale} + @var{disp}]
@end smallexample
@noindent
is translated into the AT&T syntax
@smallexample
@var{section}:@var{disp}(@var{base}, @var{index}, @var{scale})
@end smallexample
@noindent
where @var{base} and @var{index} are the optional 32-bit base and
index registers, @var{disp} is the optional displacement, and
@var{scale}, taking the values 1, 2, 4, and 8, multiplies @var{index}
to calculate the address of the operand. If no @var{scale} is
specified, @var{scale} is taken to be 1. @var{section} specifies the
optional section register for the memory operand, and may override the
default section register (see a 80386 manual for section register
defaults). Note that section overrides in AT&T syntax @emph{must} have
be preceded by a @samp{%}. If you specify a section override which
coincides with the default section register, @code{@value{AS}} will @emph{not}
output any section register override prefixes to assemble the given
instruction. Thus, section overrides can be specified to emphasize which
section register is used for a given memory operand.
Here are some examples of Intel and AT&T style memory references:
@table @asis
@item AT&T: @samp{-4(%ebp)}, Intel: @samp{[ebp - 4]}
@var{base} is @samp{%ebp}; @var{disp} is @samp{-4}. @var{section} is
missing, and the default section is used (@samp{%ss} for addressing with
@samp{%ebp} as the base register). @var{index}, @var{scale} are both missing.
@item AT&T: @samp{foo(,%eax,4)}, Intel: @samp{[foo + eax*4]}
@var{index} is @samp{%eax} (scaled by a @var{scale} 4); @var{disp} is
@samp{foo}. All other fields are missing. The section register here
defaults to @samp{%ds}.
@item AT&T: @samp{foo(,1)}; Intel @samp{[foo]}
This uses the value pointed to by @samp{foo} as a memory operand.
Note that @var{base} and @var{index} are both missing, but there is only
@emph{one} @samp{,}. This is a syntactic exception.
@item AT&T: @samp{%gs:foo}; Intel @samp{gs:foo}
This selects the contents of the variable @samp{foo} with section
register @var{section} being @samp{%gs}.
@end table
Absolute (as opposed to PC relative) call and jump operands must be
prefixed with @samp{*}. If no @samp{*} is specified, @code{@value{AS}} will
always choose PC relative addressing for jump/call labels.
Any instruction that has a memory operand @emph{must} specify its size (byte,
word, or long) with an opcode suffix (@samp{b}, @samp{w}, or @samp{l},
respectively).
@node i386-jumps
@section Handling of Jump Instructions
@cindex jump optimization, i386
@cindex i386 jump optimization
Jump instructions are always optimized to use the smallest possible
displacements. This is accomplished by using byte (8-bit) displacement
jumps whenever the target is sufficiently close. If a byte displacement
is insufficient a long (32-bit) displacement is used. We do not support
word (16-bit) displacement jumps (i.e. prefixing the jump instruction
with the @samp{addr16} opcode prefix), since the 80386 insists upon masking
@samp{%eip} to 16 bits after the word displacement is added.
Note that the @samp{jcxz}, @samp{jecxz}, @samp{loop}, @samp{loopz},
@samp{loope}, @samp{loopnz} and @samp{loopne} instructions only come in
byte displacements, so that it is possible that use of these
instructions (@code{@value{GCC}} does not use them) will cause the assembler to
print an error message (and generate incorrect code). The AT&T 80386
assembler tries to get around this problem by expanding @samp{jcxz foo} to
@smallexample
jcxz cx_zero
jmp cx_nonzero
cx_zero: jmp foo
cx_nonzero:
@end smallexample
@node i386-Float
@section Floating Point
@cindex i386 floating point
@cindex floating point, i386
All 80387 floating point types except packed BCD are supported.
(BCD support may be added without much difficulty). These data
types are 16-, 32-, and 64- bit integers, and single (32-bit),
double (64-bit), and extended (80-bit) precision floating point.
Each supported type has an opcode suffix and a constructor
associated with it. Opcode suffixes specify operand's data
types. Constructors build these data types into memory.
@itemize @bullet
@item
@cindex @code{float} directive, i386
@cindex @code{single} directive, i386
@cindex @code{double} directive, i386
@cindex @code{tfloat} directive, i386
Floating point constructors are @samp{.float} or @samp{.single},
@samp{.double}, and @samp{.tfloat} for 32-, 64-, and 80-bit formats.
These correspond to opcode suffixes @samp{s}, @samp{l}, and @samp{t}.
@samp{t} stands for temporary real, and that the 80387 only supports
this format via the @samp{fldt} (load temporary real to stack top) and
@samp{fstpt} (store temporary real and pop stack) instructions.
@item
@cindex @code{word} directive, i386
@cindex @code{long} directive, i386
@cindex @code{int} directive, i386
@cindex @code{quad} directive, i386
Integer constructors are @samp{.word}, @samp{.long} or @samp{.int}, and
@samp{.quad} for the 16-, 32-, and 64-bit integer formats. The corresponding
opcode suffixes are @samp{s} (single), @samp{l} (long), and @samp{q}
(quad). As with the temporary real format the 64-bit @samp{q} format is
only present in the @samp{fildq} (load quad integer to stack top) and
@samp{fistpq} (store quad integer and pop stack) instructions.
@end itemize
Register to register operations do not require opcode suffixes,
so that @samp{fst %st, %st(1)} is equivalent to @samp{fstl %st, %st(1)}.
@cindex i386 @code{fwait} instruction
@cindex @code{fwait instruction}, i386
Since the 80387 automatically synchronizes with the 80386 @samp{fwait}
instructions are almost never needed (this is not the case for the
80286/80287 and 8086/8087 combinations). Therefore, @code{@value{AS}} suppresses
the @samp{fwait} instruction whenever it is implicitly selected by one
of the @samp{fn@dots{}} instructions. For example, @samp{fsave} and
@samp{fnsave} are treated identically. In general, all the @samp{fn@dots{}}
instructions are made equivalent to @samp{f@dots{}} instructions. If
@samp{fwait} is desired it must be explicitly coded.
@node i386-Notes
@section Notes
@cindex i386 @code{mul}, @code{imul} instructions
@cindex @code{mul} instruction, i386
@cindex @code{imul} instruction, i386
There is some trickery concerning the @samp{mul} and @samp{imul}
instructions that deserves mention. The 16-, 32-, and 64-bit expanding
multiplies (base opcode @samp{0xf6}; extension 4 for @samp{mul} and 5
for @samp{imul}) can be output only in the one operand form. Thus,
@samp{imul %ebx, %eax} does @emph{not} select the expanding multiply;
the expanding multiply would clobber the @samp{%edx} register, and this
would confuse @code{@value{GCC}} output. Use @samp{imul %ebx} to get the
64-bit product in @samp{%edx:%eax}.
We have added a two operand form of @samp{imul} when the first operand
is an immediate mode expression and the second operand is a register.
This is just a shorthand, so that, multiplying @samp{%eax} by 69, for
example, can be done with @samp{imul $69, %eax} rather than @samp{imul
$69, %eax, %eax}.
@end ifset
@ifset Z8000
@ifset GENERIC
@page
@node Z8000-Dependent
@chapter Z8000 Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter Z8000 Dependent Features
@end ifclear
@cindex Z8000 support
The Z8000 @value{AS} supports both members of the Z8000 family: the
unsegmented Z8002, with 16 bit addresses, and the segmented Z8001 with
24 bit addresses.
When the assembler is in unsegmented mode (specified with the
@code{unsegm} directive), an address will take up one word (16 bit)
sized register. When the assembler is in segmented mode (specified with
the @code{segm} directive), a 24-bit address takes up a long (32 bit)
register. @xref{Z8000 Directives,,Assembler Directives for the Z8000},
for a list of other Z8000 specific assembler directives.
@menu
* Z8000 Options:: No special command-line options for Z8000
* Z8000 Syntax:: Assembler syntax for the Z8000
* Z8000 Directives:: Special directives for the Z8000
* Z8000 Opcodes:: Opcodes
@end menu
@node Z8000 Options
@section Options
@cindex Z8000 options
@cindex options, Z8000
@code{@value{AS}} has no additional command-line options for the Zilog
Z8000 family.
@node Z8000 Syntax
@section Syntax
@menu
* Z8000-Chars:: Special Characters
* Z8000-Regs:: Register Names
* Z8000-Addressing:: Addressing Modes
@end menu
@node Z8000-Chars
@subsection Special Characters
@cindex line comment character, Z8000
@cindex Z8000 line comment character
@samp{!} is the line comment character.
@cindex line separator, Z8000
@cindex statement separator, Z8000
@cindex Z8000 line separator
You can use @samp{;} instead of a newline to separate statements.
@node Z8000-Regs
@subsection Register Names
@cindex Z8000 registers
@cindex registers, Z8000
The Z8000 has sixteen 16 bit registers, numbered 0 to 15. You can refer
to different sized groups of registers by register number, with the
prefix @samp{r} for 16 bit registers, @samp{rr} for 32 bit registers and
@samp{rq} for 64 bit registers. You can also refer to the contents of
the first eight (of the sixteen 16 bit registers) by bytes. They are
named @samp{r@var{n}h} and @samp{r@var{n}l}.
@smallexample
@exdent @emph{byte registers}
r0l r0h r1h r1l r2h r2l r3h r3l
r4h r4l r5h r5l r6h r6l r7h r7l
@exdent @emph{word registers}
r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r13 r14 r15
@exdent @emph{long word registers}
rr0 rr2 rr4 rr6 rr8 rr10 rr12 rr14
@exdent @emph{quad word registers}
rq0 rq4 rq8 rq12
@end smallexample
@node Z8000-Addressing
@subsection Addressing Modes
@cindex addressing modes, Z8000
@cindex Z800 addressing modes
@value{AS} understands the following addressing modes for the Z8000:
@table @code
@item r@var{n}
Register direct
@item @@r@var{n}
Indirect register
@item @var{addr}
Direct: the 16 bit or 24 bit address (depending on whether the assembler
is in segmented or unsegmented mode) of the operand is in the instruction.
@item address(r@var{n})
Indexed: the 16 or 24 bit address is added to the 16 bit register to produce
the final address in memory of the operand.
@item r@var{n}(#@var{imm})
Base Address: the 16 or 24 bit register is added to the 16 bit sign
extended immediate displacement to produce the final address in memory
of the operand.
@item r@var{n}(r@var{m})
Base Index: the 16 or 24 bit register r@var{n} is added to the sign
extended 16 bit index register r@var{m} to produce the final address in
memory of the operand.
@item #@var{xx}
Immediate data @var{xx}.
@end table
@node Z8000 Directives
@section Assembler Directives for the Z8000
@cindex Z8000 directives
@cindex directives, Z8000
The Z8000 port of @value{AS} includes these additional assembler directives,
for compatibility with other Z8000 assemblers. As shown, these do not
begin with @samp{.} (unlike the ordinary @value{AS} directives).
@table @code
@item segm
@kindex segm
Generates code for the segmented Z8001.
@item unsegm
@kindex unsegm
Generates code for the unsegmented Z8002.
@item name
@kindex name
Synonym for @code{.file}
@item global
@kindex global
Synonum for @code{.global}
@item wval
@kindex wval
Synonym for @code{.word}
@item lval
@kindex lval
Synonym for @code{.long}
@item bval
@kindex bval
Synonym for @code{.byte}
@item sval
@kindex sval
Assemble a string. @code{sval} expects one string literal, delimited by
single quotes. It assembles each byte of the string into consecutive
addresses. You can use the escape sequence @samp{%@var{xx}} (where
@var{xx} represents a two-digit hexadecimal number) to represent the
character whose @sc{ascii} value is @var{xx}. Use this feature to
describe single quote and other characters that may not appear in string
literals as themselves. For example, the C statement @w{@samp{char *a =
"he said \"it's 50% off\"";}} is represented in Z8000 assembly language
(shown with the assembler output in hex at the left) as
@iftex
@begingroup
@let@nonarrowing=@comment
@end iftex
@smallexample
68652073 sval 'he said %22it%27s 50%25 off%22%00'
61696420
22697427
73203530
25206F66
662200
@end smallexample
@iftex
@endgroup
@end iftex
@item rsect
@kindex rsect
synonym for @code{.section}
@item block
@kindex block
synonym for @code{.space}
@item even
@kindex even
synonym for @code{.align 1}
@end table
@node Z8000 Opcodes
@section Opcodes
@cindex Z8000 opcode summary
@cindex opcode summary, Z8000
@cindex mnemonics, Z8000
@cindex instruction summary, Z8000
For detailed information on the Z8000 machine instruction set, see
@cite{Z8000 Technical Manual}.
The following table summarizes the opcodes and their arguments:
@iftex
@begingroup
@let@nonarrowing=@comment
@end iftex
@smallexample
rs @r{16 bit source register}
rd @r{16 bit destination register}
rbs @r{8 bit source register}
rbd @r{8 bit destination register}
rrs @r{32 bit source register}
rrd @r{32 bit destination register}
rqs @r{64 bit source register}
rqd @r{64 bit destination register}
addr @r{16/24 bit address}
imm @r{immediate data}
adc rd,rs clrb addr cpsir @@rd,@@rs,rr,cc
adcb rbd,rbs clrb addr(rd) cpsirb @@rd,@@rs,rr,cc
add rd,@@rs clrb rbd dab rbd
add rd,addr com @@rd dbjnz rbd,disp7
add rd,addr(rs) com addr dec @@rd,imm4m1
add rd,imm16 com addr(rd) dec addr(rd),imm4m1
add rd,rs com rd dec addr,imm4m1
addb rbd,@@rs comb @@rd dec rd,imm4m1
addb rbd,addr comb addr decb @@rd,imm4m1
addb rbd,addr(rs) comb addr(rd) decb addr(rd),imm4m1
addb rbd,imm8 comb rbd decb addr,imm4m1
addb rbd,rbs comflg flags decb rbd,imm4m1
addl rrd,@@rs cp @@rd,imm16 di i2
addl rrd,addr cp addr(rd),imm16 div rrd,@@rs
addl rrd,addr(rs) cp addr,imm16 div rrd,addr
addl rrd,imm32 cp rd,@@rs div rrd,addr(rs)
addl rrd,rrs cp rd,addr div rrd,imm16
and rd,@@rs cp rd,addr(rs) div rrd,rs
and rd,addr cp rd,imm16 divl rqd,@@rs
and rd,addr(rs) cp rd,rs divl rqd,addr
and rd,imm16 cpb @@rd,imm8 divl rqd,addr(rs)
and rd,rs cpb addr(rd),imm8 divl rqd,imm32
andb rbd,@@rs cpb addr,imm8 divl rqd,rrs
andb rbd,addr cpb rbd,@@rs djnz rd,disp7
andb rbd,addr(rs) cpb rbd,addr ei i2
andb rbd,imm8 cpb rbd,addr(rs) ex rd,@@rs
andb rbd,rbs cpb rbd,imm8 ex rd,addr
bit @@rd,imm4 cpb rbd,rbs ex rd,addr(rs)
bit addr(rd),imm4 cpd rd,@@rs,rr,cc ex rd,rs
bit addr,imm4 cpdb rbd,@@rs,rr,cc exb rbd,@@rs
bit rd,imm4 cpdr rd,@@rs,rr,cc exb rbd,addr
bit rd,rs cpdrb rbd,@@rs,rr,cc exb rbd,addr(rs)
bitb @@rd,imm4 cpi rd,@@rs,rr,cc exb rbd,rbs
bitb addr(rd),imm4 cpib rbd,@@rs,rr,cc ext0e imm8
bitb addr,imm4 cpir rd,@@rs,rr,cc ext0f imm8
bitb rbd,imm4 cpirb rbd,@@rs,rr,cc ext8e imm8
bitb rbd,rs cpl rrd,@@rs ext8f imm8
bpt cpl rrd,addr exts rrd
call @@rd cpl rrd,addr(rs) extsb rd
call addr cpl rrd,imm32 extsl rqd
call addr(rd) cpl rrd,rrs halt
calr disp12 cpsd @@rd,@@rs,rr,cc in rd,@@rs
clr @@rd cpsdb @@rd,@@rs,rr,cc in rd,imm16
clr addr cpsdr @@rd,@@rs,rr,cc inb rbd,@@rs
clr addr(rd) cpsdrb @@rd,@@rs,rr,cc inb rbd,imm16
clr rd cpsi @@rd,@@rs,rr,cc inc @@rd,imm4m1
clrb @@rd cpsib @@rd,@@rs,rr,cc inc addr(rd),imm4m1
inc addr,imm4m1 ldb rbd,rs(rx) mult rrd,addr(rs)
inc rd,imm4m1 ldb rd(imm16),rbs mult rrd,imm16
incb @@rd,imm4m1 ldb rd(rx),rbs mult rrd,rs
incb addr(rd),imm4m1 ldctl ctrl,rs multl rqd,@@rs
incb addr,imm4m1 ldctl rd,ctrl multl rqd,addr
incb rbd,imm4m1 ldd @@rs,@@rd,rr multl rqd,addr(rs)
ind @@rd,@@rs,ra lddb @@rs,@@rd,rr multl rqd,imm32
indb @@rd,@@rs,rba lddr @@rs,@@rd,rr multl rqd,rrs
inib @@rd,@@rs,ra lddrb @@rs,@@rd,rr neg @@rd
inibr @@rd,@@rs,ra ldi @@rd,@@rs,rr neg addr
iret ldib @@rd,@@rs,rr neg addr(rd)
jp cc,@@rd ldir @@rd,@@rs,rr neg rd
jp cc,addr ldirb @@rd,@@rs,rr negb @@rd
jp cc,addr(rd) ldk rd,imm4 negb addr
jr cc,disp8 ldl @@rd,rrs negb addr(rd)
ld @@rd,imm16 ldl addr(rd),rrs negb rbd
ld @@rd,rs ldl addr,rrs nop
ld addr(rd),imm16 ldl rd(imm16),rrs or rd,@@rs
ld addr(rd),rs ldl rd(rx),rrs or rd,addr
ld addr,imm16 ldl rrd,@@rs or rd,addr(rs)
ld addr,rs ldl rrd,addr or rd,imm16
ld rd(imm16),rs ldl rrd,addr(rs) or rd,rs
ld rd(rx),rs ldl rrd,imm32 orb rbd,@@rs
ld rd,@@rs ldl rrd,rrs orb rbd,addr
ld rd,addr ldl rrd,rs(imm16) orb rbd,addr(rs)
ld rd,addr(rs) ldl rrd,rs(rx) orb rbd,imm8
ld rd,imm16 ldm @@rd,rs,n orb rbd,rbs
ld rd,rs ldm addr(rd),rs,n out @@rd,rs
ld rd,rs(imm16) ldm addr,rs,n out imm16,rs
ld rd,rs(rx) ldm rd,@@rs,n outb @@rd,rbs
lda rd,addr ldm rd,addr(rs),n outb imm16,rbs
lda rd,addr(rs) ldm rd,addr,n outd @@rd,@@rs,ra
lda rd,rs(imm16) ldps @@rs outdb @@rd,@@rs,rba
lda rd,rs(rx) ldps addr outib @@rd,@@rs,ra
ldar rd,disp16 ldps addr(rs) outibr @@rd,@@rs,ra
ldb @@rd,imm8 ldr disp16,rs pop @@rd,@@rs
ldb @@rd,rbs ldr rd,disp16 pop addr(rd),@@rs
ldb addr(rd),imm8 ldrb disp16,rbs pop addr,@@rs
ldb addr(rd),rbs ldrb rbd,disp16 pop rd,@@rs
ldb addr,imm8 ldrl disp16,rrs popl @@rd,@@rs
ldb addr,rbs ldrl rrd,disp16 popl addr(rd),@@rs
ldb rbd,@@rs mbit popl addr,@@rs
ldb rbd,addr mreq rd popl rrd,@@rs
ldb rbd,addr(rs) mres push @@rd,@@rs
ldb rbd,imm8 mset push @@rd,addr
ldb rbd,rbs mult rrd,@@rs push @@rd,addr(rs)
ldb rbd,rs(imm16) mult rrd,addr push @@rd,imm16
push @@rd,rs set addr,imm4 subl rrd,imm32
pushl @@rd,@@rs set rd,imm4 subl rrd,rrs
pushl @@rd,addr set rd,rs tcc cc,rd
pushl @@rd,addr(rs) setb @@rd,imm4 tccb cc,rbd
pushl @@rd,rrs setb addr(rd),imm4 test @@rd
res @@rd,imm4 setb addr,imm4 test addr
res addr(rd),imm4 setb rbd,imm4 test addr(rd)
res addr,imm4 setb rbd,rs test rd
res rd,imm4 setflg imm4 testb @@rd
res rd,rs sinb rbd,imm16 testb addr
resb @@rd,imm4 sinb rd,imm16 testb addr(rd)
resb addr(rd),imm4 sind @@rd,@@rs,ra testb rbd
resb addr,imm4 sindb @@rd,@@rs,rba testl @@rd
resb rbd,imm4 sinib @@rd,@@rs,ra testl addr
resb rbd,rs sinibr @@rd,@@rs,ra testl addr(rd)
resflg imm4 sla rd,imm8 testl rrd
ret cc slab rbd,imm8 trdb @@rd,@@rs,rba
rl rd,imm1or2 slal rrd,imm8 trdrb @@rd,@@rs,rba
rlb rbd,imm1or2 sll rd,imm8 trib @@rd,@@rs,rbr
rlc rd,imm1or2 sllb rbd,imm8 trirb @@rd,@@rs,rbr
rlcb rbd,imm1or2 slll rrd,imm8 trtdrb @@ra,@@rb,rbr
rldb rbb,rba sout imm16,rs trtib @@ra,@@rb,rr
rr rd,imm1or2 soutb imm16,rbs trtirb @@ra,@@rb,rbr
rrb rbd,imm1or2 soutd @@rd,@@rs,ra trtrb @@ra,@@rb,rbr
rrc rd,imm1or2 soutdb @@rd,@@rs,rba tset @@rd
rrcb rbd,imm1or2 soutib @@rd,@@rs,ra tset addr
rrdb rbb,rba soutibr @@rd,@@rs,ra tset addr(rd)
rsvd36 sra rd,imm8 tset rd
rsvd38 srab rbd,imm8 tsetb @@rd
rsvd78 sral rrd,imm8 tsetb addr
rsvd7e srl rd,imm8 tsetb addr(rd)
rsvd9d srlb rbd,imm8 tsetb rbd
rsvd9f srll rrd,imm8 xor rd,@@rs
rsvdb9 sub rd,@@rs xor rd,addr
rsvdbf sub rd,addr xor rd,addr(rs)
sbc rd,rs sub rd,addr(rs) xor rd,imm16
sbcb rbd,rbs sub rd,imm16 xor rd,rs
sc imm8 sub rd,rs xorb rbd,@@rs
sda rd,rs subb rbd,@@rs xorb rbd,addr
sdab rbd,rs subb rbd,addr xorb rbd,addr(rs)
sdal rrd,rs subb rbd,addr(rs) xorb rbd,imm8
sdl rd,rs subb rbd,imm8 xorb rbd,rbs
sdlb rbd,rs subb rbd,rbs xorb rbd,rbs
sdll rrd,rs subl rrd,@@rs
set @@rd,imm4 subl rrd,addr
set addr(rd),imm4 subl rrd,addr(rs)
@end smallexample
@iftex
@endgroup
@end iftex
@end ifset
@ifset MIPS
@ifset GENERIC
@page
@node MIPS-Dependent
@chapter MIPS Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter MIPS Dependent Features
@end ifclear
The MIPS @value{AS} supports the MIPS R2000 and R3000 processors.
It ignores the @kbd{-nocpp}, @kbd{-EL}, and @kbd{-EB} options.
Not all traditional MIPS macro instructions are currently supported.
Specifically, @code{li.d} and @code{li.s} are not currently supported.
When using @code{@value{GCC}} with MIPS @value{AS}, @code{@value{GCC}}
must be configured using the -with-gnu-as switch (this is the case for
Cygnus distributions) or @code{@value{GCC}} must be invoked with the
-mgas option.
Assembling for a MIPS ECOFF target supports some additional sections
besides the usual @code{.text}, @code{.data} and @code{.bss}. The
additional sections are @code{.rdata}, used for readonly data,
@code{.sdata}, used for small data, and @code{.sbss}, used for small
common objects.
When assembling for ECOFF, the assembler will automatically use the $gp
($28) register when forming the address of a small object. Any object
in the .sdata or .sbss sections is considered to be small. For external
objects or objects in the @code{.bss} section, the -G switch may be used
to control the size of objects for which the $gp register will be used;
the default value is 8, meaning that a reference to any object eight
bytes or smaller will use $gp. Passing -G 0 to @value{AS} will prevent
it from using the $gp register. The size of an object in the
@code{.bss} section is set by the @code{.comm} or @code{.lcomm}
pseudo-op that defines it. The size of an external object may be set
using the @code{.extern} pseudo-op. For example, @samp{.extern sym,4}
declares that the object at @code{sym} is 4 bytes in length, whie
leaving @code{sym} otherwise undefined.
Using small ECOFF objects requires linker support, and assumes that the
$gp register has been correctly initialized (normally done automatically
by the startup code). MIPS ECOFF assembly code must avoid modifying the
$gp register.
MIPS ECOFF @value{AS} supports several pseudo-ops used for generating
debugging information which are not support by traditional MIPS
assemblers. These are @code{.def}, @code{.endef}, @code{.dim},
@code{.file}, @code{.scl}, @code{.size}, @code{.tag}, @code{.type},
@code{.val}, @code{.stabd}, @code{.stabn}, and @code{.stabs}. The
debugging information generated by the three @code{.stab} pseudo-ops can
only be read by GDB, not by traditional MIPS debuggers (this enhancement
is required to fully support C++ debugging). These psuedo-ops are
primarily used by compilers, not assembly language programmers, and are
described elsewhere in the manual.
@end ifset
@ifset GENERIC
@c reverse effect of @down at top of generic Machine-Dep chapter
@up
@end ifset
@ifset INTERNALS
@c pesch@cygnus.com: we ignore the following chapters, since internals are
@c changing rapidly. These may need to be moved to another
@c book anyhow, if we adopt the model of user/modifier
@c books.
@node Maintenance
@chapter Maintaining the Assembler
[[this chapter is still being built]]
@section Design
We had these goals, in descending priority:
@table @b
@item Accuracy.
For every program composed by a compiler, @code{@value{AS}} should emit
``correct'' code. This leaves some latitude in choosing addressing
modes, order of @code{relocation_info} structures in the object
file, @emph{etc}.
@item Speed, for usual case.
By far the most common use of @code{@value{AS}} will be assembling compiler
emissions.
@item Upward compatibility for existing assembler code.
Well @dots{} we don't support Vax bit fields but everything else
seems to be upward compatible.
@item Readability.
The code should be maintainable with few surprises. (JF: ha!)
@end table
We assumed that disk I/O was slow and expensive while memory was
fast and access to memory was cheap. We expect the in-memory data
structures to be less than 10 times the size of the emitted object
file. (Contrast this with the C compiler where in-memory structures
might be 100 times object file size!)
This suggests:
@itemize @bullet
@item
Try to read the source file from disk only one time. For other
reasons, we keep large chunks of the source file in memory during
assembly so this is not a problem. Also the assembly algorithm
should only scan the source text once if the compiler composed the
text according to a few simple rules.
@item
Emit the object code bytes only once. Don't store values and then
backpatch later.
@item
Build the object file in memory and do direct writes to disk of
large buffers.
@end itemize
RMS suggested a one-pass algorithm which seems to work well. By not
parsing text during a second pass considerable time is saved on
large programs (@emph{e.g.} the sort of C program @code{yacc} would
emit).
It happened that the data structures needed to emit relocation
information to the object file were neatly subsumed into the data
structures that do backpatching of addresses after pass 1.
Many of the functions began life as re-usable modules, loosely
connected. RMS changed this to gain speed. For example, input
parsing routines which used to work on pre-sanitized strings now
must parse raw data. Hence they have to import knowledge of the
assemblers' comment conventions @emph{etc}.
@section Deprecated Feature(?)s
We have stopped supporting some features:
@itemize @bullet
@item
@code{.org} statements must have @b{defined} expressions.
@item
Vax Bit fields (@kbd{:} operator) are entirely unsupported.
@end itemize
It might be a good idea to not support these features in a future release:
@itemize @bullet
@item
@kbd{#} should begin a comment, even in column 1.
@item
Why support the logical line & file concept any more?
@item
Subsections are a good candidate for flushing.
Depends on which compilers need them I guess.
@end itemize
@section Bugs, Ideas, Further Work
Clearly the major improvement is DON'T USE A TEXT-READING
ASSEMBLER for the back end of a compiler. It is much faster to
interpret binary gobbledygook from a compiler's tables than to
ask the compiler to write out human-readable code just so the
assembler can parse it back to binary.
Assuming you use @code{@value{AS}} for human written programs: here are
some ideas:
@itemize @bullet
@item
Document (here) @code{APP}.
@item
Take advantage of knowing no spaces except after opcode
to speed up @code{@value{AS}}. (Modify @code{app.c} to flush useless spaces:
only keep space/tabs at begin of line or between 2
symbols.)
@item
Put pointers in this documentation to @file{a.out} documentation.
@item
Split the assembler into parts so it can gobble direct binary
from @emph{e.g.} @code{cc}. It is silly for@code{cc} to compose text
just so @code{@value{AS}} can parse it back to binary.
@item
Rewrite hash functions: I want a more modular, faster library.
@item
Clean up LOTS of code.
@item
Include all the non-@file{.c} files in the maintenance chapter.
@item
Document flonums.
@item
Implement flonum short literals.
@item
Change all talk of expression operands to expression quantities,
or perhaps to expression arguments.
@item
Implement pass 2.
@item
Whenever a @code{.text} or @code{.data} statement is seen, we close
of the current frag with an imaginary @code{.fill 0}. This is
because we only have one obstack for frags, and we can't grow new
frags for a new subsection, then go back to the old subsection and
append bytes to the old frag. All this nonsense goes away if we
give each subsection its own obstack. It makes code simpler in
about 10 places, but nobody has bothered to do it because C compiler
output rarely changes subsections (compared to ending frags with
relaxable addresses, which is common).
@end itemize
@section Sources
@c The following files in the @file{@value{AS}} directory
@c are symbolic links to other files, of
@c the same name, in a different directory.
@c @itemize @bullet
@c @item
@c @file{atof_generic.c}
@c @item
@c @file{atof_vax.c}
@c @item
@c @file{flonum_const.c}
@c @item
@c @file{flonum_copy.c}
@c @item
@c @file{flonum_get.c}
@c @item
@c @file{flonum_multip.c}
@c @item
@c @file{flonum_normal.c}
@c @item
@c @file{flonum_print.c}
@c @end itemize
Here is a list of the source files in the @file{@value{AS}} directory.
@table @file
@item app.c
This contains the pre-processing phase, which deletes comments,
handles whitespace, etc. This was recently re-written, since app
used to be a separate program, but RMS wanted it to be inline.
@item append.c
This is a subroutine to append a string to another string returning a
pointer just after the last @code{char} appended. (JF: All these
little routines should probably all be put in one file.)
@item as.c
Here you will find the main program of the assembler @code{@value{AS}}.
@item expr.c
This is a branch office of @file{read.c}. This understands
expressions, arguments. Inside @code{@value{AS}}, arguments are called
(expression) @emph{operands}. This is confusing, because we also talk
(elsewhere) about instruction @emph{operands}. Also, expression
operands are called @emph{quantities} explicitly to avoid confusion
with instruction operands. What a mess.
@item frags.c
This implements the @b{frag} concept. Without frags, finding the
right size for branch instructions would be a lot harder.
@item hash.c
This contains the symbol table, opcode table @emph{etc.} hashing
functions.
@item hex_value.c
This is a table of values of digits, for use in atoi() type
functions. Could probably be flushed by using calls to strtol(), or
something similar.
@item input-file.c
This contains Operating system dependent source file reading
routines. Since error messages often say where we are in reading
the source file, they live here too. Since @code{@value{AS}} is intended to
run under GNU and Unix only, this might be worth flushing. Anyway,
almost all C compilers support stdio.
@item input-scrub.c
This deals with calling the pre-processor (if needed) and feeding the
chunks back to the rest of the assembler the right way.
@item messages.c
This contains operating system independent parts of fatal and
warning message reporting. See @file{append.c} above.
@item output-file.c
This contains operating system dependent functions that write an
object file for @code{@value{AS}}. See @file{input-file.c} above.
@item read.c
This implements all the directives of @code{@value{AS}}. This also deals
with passing input lines to the machine dependent part of the
assembler.
@item strstr.c
This is a C library function that isn't in most C libraries yet.
See @file{append.c} above.
@item subsegs.c
This implements subsections.
@item symbols.c
This implements symbols.
@item write.c
This contains the code to perform relaxation, and to write out
the object file. It is mostly operating system independent, but
different OSes have different object file formats in any case.
@item xmalloc.c
This implements @code{malloc()} or bust. See @file{append.c} above.
@item xrealloc.c
This implements @code{realloc()} or bust. See @file{append.c} above.
@item atof-generic.c
The following files were taken from a machine-independent subroutine
library for manipulating floating point numbers and very large
integers.
@file{atof-generic.c} turns a string into a flonum internal format
floating-point number.
@item flonum-const.c
This contains some potentially useful floating point numbers in
flonum format.
@item flonum-copy.c
This copies a flonum.
@item flonum-multip.c
This multiplies two flonums together.
@item bignum-copy.c
This copies a bignum.
@end table
Here is a table of all the machine-specific files (this includes
both source and header files). Typically, there is a
@var{machine}.c file, a @var{machine}-opcode.h file, and an
atof-@var{machine}.c file. The @var{machine}-opcode.h file should
be identical to the one used by GDB (which uses it for disassembly.)
@table @file
@item atof-ieee.c
This contains code to turn a flonum into a ieee literal constant.
This is used by tye 680x0, 32x32, sparc, and i386 versions of @code{@value{AS}}.
@item i386-opcode.h
This is the opcode-table for the i386 version of the assembler.
@item i386.c
This contains all the code for the i386 version of the assembler.
@item i386.h
This defines constants and macros used by the i386 version of the assembler.
@item m-generic.h
generic 68020 header file. To be linked to m68k.h on a
non-sun3, non-hpux system.
@item m-sun2.h
68010 header file for Sun2 workstations. Not well tested. To be linked
to m68k.h on a sun2. (See also @samp{-DSUN_ASM_SYNTAX} in the
@file{Makefile}.)
@item m-sun3.h
68020 header file for Sun3 workstations. To be linked to m68k.h before
compiling on a Sun3 system. (See also @samp{-DSUN_ASM_SYNTAX} in the
@file{Makefile}.)
@item m-hpux.h
68020 header file for a HPUX (system 5?) box. Which box, which
version of HPUX, etc? I don't know.
@item m68k.h
A hard- or symbolic- link to one of @file{m-generic.h},
@file{m-hpux.h} or @file{m-sun3.h} depending on which kind of
680x0 you are assembling for. (See also @samp{-DSUN_ASM_SYNTAX} in the
@file{Makefile}.)
@item m68k-opcode.h
Opcode table for 68020. This is now a link to the opcode table
in the @code{GDB} source directory.
@item m68k.c
All the mc680x0 code, in one huge, slow-to-compile file.
@item ns32k.c
This contains the code for the ns32032/ns32532 version of the
assembler.
@item ns32k-opcode.h
This contains the opcode table for the ns32032/ns32532 version
of the assembler.
@item vax-inst.h
Vax specific file for describing Vax operands and other Vax-ish things.
@item vax-opcode.h
Vax opcode table.
@item vax.c
Vax specific parts of @code{@value{AS}}. Also includes the former files
@file{vax-ins-parse.c}, @file{vax-reg-parse.c} and @file{vip-op.c}.
@item atof-vax.c
Turns a flonum into a Vax constant.
@item vms.c
This file contains the special code needed to put out a VMS
style object file for the Vax.
@end table
Here is a list of the header files in the source directory.
(Warning: This section may not be very accurate. I didn't
write the header files; I just report them.) Also note that I
think many of these header files could be cleaned up or
eliminated.
@table @file
@item a.out.h
This describes the structures used to create the binary header data
inside the object file. Perhaps we should use the one in
@file{/usr/include}?
@item as.h
This defines all the globally useful things, and pulls in @file{stdio.h}
and @file{assert.h}.
@item bignum.h
This defines macros useful for dealing with bignums.
@item expr.h
Structure and macros for dealing with expression()
@item flonum.h
This defines the structure for dealing with floating point
numbers. It #includes @file{bignum.h}.
@item frags.h
This contains macro for appending a byte to the current frag.
@item hash.h
Structures and function definitions for the hashing functions.
@item input-file.h
Function headers for the input-file.c functions.
@item md.h
structures and function headers for things defined in the
machine dependent part of the assembler.
@item obstack.h
This is the GNU systemwide include file for manipulating obstacks.
Since nobody is running under real GNU yet, we include this file.
@item read.h
Macros and function headers for reading in source files.
@item struct-symbol.h
Structure definition and macros for dealing with the @value{AS}
internal form of a symbol.
@item subsegs.h
structure definition for dealing with the numbered subsections
of the text and data sections.
@item symbols.h
Macros and function headers for dealing with symbols.
@item write.h
Structure for doing section fixups.
@end table
@c ~subsection Test Directory
@c (Note: The test directory seems to have disappeared somewhere
@c along the line. If you want it, you'll probably have to find a
@c REALLY OLD dump tape~dots{})
@c
@c The ~file{test/} directory is used for regression testing.
@c After you modify ~@code{@value{AS}}, you can get a quick go/nogo
@c confidence test by running the new ~@code{@value{AS}} over the source
@c files in this directory. You use a shell script ~file{test/do}.
@c
@c The tests in this suite are evolving. They are not comprehensive.
@c They have, however, caught hundreds of bugs early in the debugging
@c cycle of ~@code{@value{AS}}. Most test statements in this suite were naturally
@c selected: they were used to demonstrate actual ~@code{@value{AS}} bugs rather
@c than being written ~i{a prioi}.
@c
@c Another testing suggestion: over 30 bugs have been found simply by
@c running examples from this manual through ~@code{@value{AS}}.
@c Some examples in this manual are selected
@c to distinguish boundary conditions; they are good for testing ~@code{@value{AS}}.
@c
@c ~subsubsection Regression Testing
@c Each regression test involves assembling a file and comparing the
@c actual output of ~@code{@value{AS}} to ``known good'' output files. Both
@c the object file and the error/warning message file (stderr) are
@c inspected. Optionally the ~@code{@value{AS}} exit status may be checked.
@c Discrepencies are reported. Each discrepency means either that
@c you broke some part of ~@code{@value{AS}} or that the ``known good'' files
@c are now out of date and should be changed to reflect the new
@c definition of ``good''.
@c
@c Each regression test lives in its own directory, in a tree
@c rooted in the directory ~file{test/}. Each such directory
@c has a name ending in ~file{.ret}, where `ret' stands for
@c REgression Test. The ~file{.ret} ending allows ~code{find
@c (1)} to find all regression tests in the tree, without
@c needing to list them explicitly.
@c
@c Any ~file{.ret} directory must contain a file called
@c ~file{input} which is the source file to assemble. During
@c testing an object file ~file{output} is created, as well as
@c a file ~file{stdouterr} which contains the output to both
@c stderr and stderr. If there is a file ~file{output.good} in
@c the directory, and if ~file{output} contains exactly the
@c same data as ~file{output.good}, the file ~file{output} is
@c deleted. Likewise ~file{stdouterr} is removed if it exactly
@c matches a file ~file{stdouterr.good}. If file
@c ~file{status.good} is present, containing a decimal number
@c before a newline, the exit status of ~@code{@value{AS}} is compared
@c to this number. If the status numbers are not equal, a file
@c ~file{status} is written to the directory, containing the
@c actual status as a decimal number followed by newline.
@c
@c Should any of the ~file{*.good} files fail to match their corresponding
@c actual files, this is noted by a 1-line message on the screen during
@c the regression test, and you can use ~@code{find (1)} to find any
@c files named ~file{status}, ~file {output} or ~file{stdouterr}.
@c
@node Retargeting
@chapter Teaching the Assembler about a New Machine
This chapter describes the steps required in order to make the
assembler work with another machine's assembly language. This
chapter is not complete, and only describes the steps in the
broadest terms. You should look at the source for the
currently supported machine in order to discover some of the
details that aren't mentioned here.
You should create a new file called @file{@var{machine}.c}, and
add the appropriate lines to the file @file{Makefile} so that
you can compile your new version of the assembler. This should
be straighforward; simply add lines similar to the ones there
for the four current versions of the assembler.
If you want to be compatible with GDB, (and the current
machine-dependent versions of the assembler), you should create
a file called @file{@var{machine}-opcode.h} which should
contain all the information about the names of the machine
instructions, their opcodes, and what addressing modes they
support. If you do this right, the assembler and GDB can share
this file, and you'll only have to write it once. Note that
while you're writing @code{@value{AS}}, you may want to use an
independent program (if you have access to one), to make sure
that @code{@value{AS}} is emitting the correct bytes. Since @code{@value{AS}}
and @code{GDB} share the opcode table, an incorrect opcode
table entry may make invalid bytes look OK when you disassemble
them with @code{GDB}.
@section Functions You will Have to Write
Your file @file{@var{machine}.c} should contain definitions for
the following functions and variables. It will need to include
some header files in order to use some of the structures
defined in the machine-independent part of the assembler. The
needed header files are mentioned in the descriptions of the
functions that will need them.
@table @code
@item long omagic;
This long integer holds the value to place at the beginning of
the @file{a.out} file. It is usually @samp{OMAGIC}, except on
machines that store additional information in the magic-number.
@item char comment_chars[];
This character array holds the values of the characters that
start a comment anywhere in a line. Comments are stripped off
automatically by the machine independent part of the
assembler. Note that the @samp{/*} will always start a
comment, and that only @samp{*/} will end a comment started by
@samp{*/}.
@item char line_comment_chars[];
This character array holds the values of the chars that start a
comment only if they are the first (non-whitespace) character
on a line. If the character @samp{#} does not appear in this
list, you may get unexpected results. (Various
machine-independent parts of the assembler treat the comments
@samp{#APP} and @samp{#NO_APP} specially, and assume that lines
that start with @samp{#} are comments.)
@item char EXP_CHARS[];
This character array holds the letters that can separate the
mantissa and the exponent of a floating point number. Typical
values are @samp{e} and @samp{E}.
@item char FLT_CHARS[];
This character array holds the letters that--when they appear
immediately after a leading zero--indicate that a number is a
floating-point number. (Sort of how 0x indicates that a
hexadecimal number follows.)
@item pseudo_typeS md_pseudo_table[];
(@var{pseudo_typeS} is defined in @file{md.h})
This array contains a list of the machine_dependent directives
the assembler must support. It contains the name of each
pseudo op (Without the leading @samp{.}), a pointer to a
function to be called when that directive is encountered, and
an integer argument to be passed to that function.
@item void md_begin(void)
This function is called as part of the assembler's
initialization. It should do any initialization required by
any of your other routines.
@item int md_parse_option(char **optionPTR, int *argcPTR, char ***argvPTR)
This routine is called once for each option on the command line
that the machine-independent part of @code{@value{AS}} does not
understand. This function should return non-zero if the option
pointed to by @var{optionPTR} is a valid option. If it is not
a valid option, this routine should return zero. The variables
@var{argcPTR} and @var{argvPTR} are provided in case the option
requires a filename or something similar as an argument. If
the option is multi-character, @var{optionPTR} should be
advanced past the end of the option, otherwise every letter in
the option will be treated as a separate single-character
option.
@item void md_assemble(char *string)
This routine is called for every machine-dependent
non-directive line in the source file. It does all the real
work involved in reading the opcode, parsing the operands,
etc. @var{string} is a pointer to a null-terminated string,
that comprises the input line, with all excess whitespace and
comments removed.
@item void md_number_to_chars(char *outputPTR,long value,int nbytes)
This routine is called to turn a C long int, short int, or char
into the series of bytes that represents that number on the
target machine. @var{outputPTR} points to an array where the
result should be stored; @var{value} is the value to store; and
@var{nbytes} is the number of bytes in 'value' that should be
stored.
@item void md_number_to_imm(char *outputPTR,long value,int nbytes)
This routine is called to turn a C long int, short int, or char
into the series of bytes that represent an immediate value on
the target machine. It is identical to the function @code{md_number_to_chars},
except on NS32K machines.@refill
@item void md_number_to_disp(char *outputPTR,long value,int nbytes)
This routine is called to turn a C long int, short int, or char
into the series of bytes that represent an displacement value on
the target machine. It is identical to the function @code{md_number_to_chars},
except on NS32K machines.@refill
@item void md_number_to_field(char *outputPTR,long value,int nbytes)
This routine is identical to @code{md_number_to_chars},
except on NS32K machines.
@item void md_ri_to_chars(struct relocation_info *riPTR,ri)
(@code{struct relocation_info} is defined in @file{a.out.h})
This routine emits the relocation info in @var{ri}
in the appropriate bit-pattern for the target machine.
The result should be stored in the location pointed
to by @var{riPTR}. This routine may be a no-op unless you are
attempting to do cross-assembly.
@item char *md_atof(char type,char *outputPTR,int *sizePTR)
This routine turns a series of digits into the appropriate
internal representation for a floating-point number.
@var{type} is a character from @var{FLT_CHARS[]} that describes
what kind of floating point number is wanted; @var{outputPTR}
is a pointer to an array that the result should be stored in;
and @var{sizePTR} is a pointer to an integer where the size (in
bytes) of the result should be stored. This routine should
return an error message, or an empty string (not (char *)0) for
success.
@item int md_short_jump_size;
This variable holds the (maximum) size in bytes of a short (16
bit or so) jump created by @code{md_create_short_jump()}. This
variable is used as part of the broken-word feature, and isn't
needed if the assembler is compiled with
@samp{-DWORKING_DOT_WORD}.
@item int md_long_jump_size;
This variable holds the (maximum) size in bytes of a long (32
bit or so) jump created by @code{md_create_long_jump()}. This
variable is used as part of the broken-word feature, and isn't
needed if the assembler is compiled with
@samp{-DWORKING_DOT_WORD}.
@item void md_create_short_jump(char *resultPTR,long from_addr,
@code{long to_addr,fragS *frag,symbolS *to_symbol)}
This function emits a jump from @var{from_addr} to @var{to_addr} in
the array of bytes pointed to by @var{resultPTR}. If this creates a
type of jump that must be relocated, this function should call
@code{fix_new()} with @var{frag} and @var{to_symbol}. The jump
emitted by this function may be smaller than @var{md_short_jump_size},
but it must never create a larger one.
(If it creates a smaller jump, the extra bytes of memory will not be
used.) This function is used as part of the broken-word feature,
and isn't needed if the assembler is compiled with
@samp{-DWORKING_DOT_WORD}.@refill
@item void md_create_long_jump(char *ptr,long from_addr,
@code{long to_addr,fragS *frag,symbolS *to_symbol)}
This function is similar to the previous function,
@code{md_create_short_jump()}, except that it creates a long
jump instead of a short one. This function is used as part of
the broken-word feature, and isn't needed if the assembler is
compiled with @samp{-DWORKING_DOT_WORD}.
@item int md_estimate_size_before_relax(fragS *fragPTR,int segment_type)
This function does the initial setting up for relaxation. This
includes forcing references to still-undefined symbols to the
appropriate addressing modes.
@item relax_typeS md_relax_table[];
(relax_typeS is defined in md.h)
This array describes the various machine dependent states a
frag may be in before relaxation. You will need one group of
entries for each type of addressing mode you intend to relax.
@item void md_convert_frag(fragS *fragPTR)
(@var{fragS} is defined in @file{as.h})
This routine does the required cleanup after relaxation.
Relaxation has changed the type of the frag to a type that can
reach its destination. This function should adjust the opcode
of the frag to use the appropriate addressing mode.
@var{fragPTR} points to the frag to clean up.
@item void md_end(void)
This function is called just before the assembler exits. It
need not free up memory unless the operating system doesn't do
it automatically on exit. (In which case you'll also have to
track down all the other places where the assembler allocates
space but never frees it.)
@end table
@section External Variables You will Need to Use
You will need to refer to or change the following external variables
from within the machine-dependent part of the assembler.
@table @code
@item extern char flagseen[];
This array holds non-zero values in locations corresponding to
the options that were on the command line. Thus, if the
assembler was called with @samp{-W}, @var{flagseen['W']} would
be non-zero.
@item extern fragS *frag_now;
This pointer points to the current frag--the frag that bytes
are currently being added to. If nothing else, you will need
to pass it as an argument to various machine-independent
functions. It is maintained automatically by the
frag-manipulating functions; you should never have to change it
yourself.
@item extern LITTLENUM_TYPE generic_bignum[];
(@var{LITTLENUM_TYPE} is defined in @file{bignum.h}.
This is where @dfn{bignums}--numbers larger than 32 bits--are
returned when they are encountered in an expression. You will
need to use this if you need to implement directives (or
anything else) that must deal with these large numbers.
@code{Bignums} are of @code{segT} @code{SEG_BIG} (defined in
@file{as.h}, and have a positive @code{X_add_number}. The
@code{X_add_number} of a @code{bignum} is the number of
@code{LITTLENUMS} in @var{generic_bignum} that the number takes
up.
@item extern FLONUM_TYPE generic_floating_point_number;
(@var{FLONUM_TYPE} is defined in @file{flonum.h}.
The is where @dfn{flonums}--floating-point numbers within
expressions--are returned. @code{Flonums} are of @code{segT}
@code{SEG_BIG}, and have a negative @code{X_add_number}.
@code{Flonums} are returned in a generic format. You will have
to write a routine to turn this generic format into the
appropriate floating-point format for your machine.
@item extern int need_pass_2;
If this variable is non-zero, the assembler has encountered an
expression that cannot be assembled in a single pass. Since
the second pass isn't implemented, this flag means that the
assembler is punting, and is only looking for additional syntax
errors. (Or something like that.)
@item extern segT now_seg;
This variable holds the value of the section the assembler is
currently assembling into.
@end table
@section External functions will you need
You will find the following external functions useful (or
indispensable) when you're writing the machine-dependent part
of the assembler.
@table @code
@item char *frag_more(int bytes)
This function allocates @var{bytes} more bytes in the current
frag (or starts a new frag, if it can't expand the current frag
any more.) for you to store some object-file bytes in. It
returns a pointer to the bytes, ready for you to store data in.
@item void fix_new(fragS *frag, int where, short size, symbolS *add_symbol, symbolS *sub_symbol, long offset, int pcrel)
This function stores a relocation fixup to be acted on later.
@var{frag} points to the frag the relocation belongs in;
@var{where} is the location within the frag where the relocation begins;
@var{size} is the size of the relocation, and is usually 1 (a single byte),
2 (sixteen bits), or 4 (a longword). The value @var{add_symbol}
@minus{} @var{sub_symbol} + @var{offset}, is added to the byte(s) at
@var{frag->literal[where]}. If @var{pcrel} is non-zero, the address of
the location is subtracted from the result. A relocation entry is also
added to the @file{a.out} file. @var{add_symbol}, @var{sub_symbol},
and/or @var{offset} may be NULL.@refill
@item char *frag_var(relax_stateT type, int max_chars, int var,
@code{relax_substateT subtype, symbolS *symbol, char *opcode)}
This function creates a machine-dependent frag of type @var{type}
(usually @code{rs_machine_dependent}).
@var{max_chars} is the maximum size in bytes that the frag may grow by;
@var{var} is the current size of the variable end of the frag;
@var{subtype} is the sub-type of the frag. The sub-type is used to index into
@var{md_relax_table[]} during @code{relaxation}.
@var{symbol} is the symbol whose value should be used to when relax-ing this frag.
@var{opcode} points into a byte whose value may have to be modified if the
addressing mode used by this frag changes. It typically points into the
@var{fr_literal[]} of the previous frag, and is used to point to a location
that @code{md_convert_frag()}, may have to change.@refill
@item void frag_wane(fragS *fragPTR)
This function is useful from within @code{md_convert_frag}. It
changes a frag to type rs_fill, and sets the variable-sized
piece of the frag to zero. The frag will never change in size
again.
@item segT expression(expressionS *retval)
(@var{segT} is defined in @file{as.h}; @var{expressionS} is defined in @file{expr.h})
This function parses the string pointed to by the external char
pointer @var{input_line_pointer}, and returns the section-type
of the expression. It also stores the results in the
@var{expressionS} pointed to by @var{retval}.
@var{input_line_pointer} is advanced to point past the end of
the expression. (@var{input_line_pointer} is used by other
parts of the assembler. If you modify it, be sure to restore
it to its original value.)
@item as_warn(char *message,@dots{})
If warning messages are disabled, this function does nothing.
Otherwise, it prints out the current file name, and the current
line number, then uses @code{fprintf} to print the
@var{message} and any arguments it was passed.
@item as_bad(char *message,@dots{})
This function should be called when @code{@value{AS}} encounters
conditions that are bad enough that @code{@value{AS}} should not
produce an object file, but should continue reading input and
printing warning and bad error messages.
@item as_fatal(char *message,@dots{})
This function prints out the current file name and line number,
prints the word @samp{FATAL:}, then uses @code{fprintf} to
print the @var{message} and any arguments it was passed. Then
the assembler exits. This function should only be used for
serious, unrecoverable errors.
@item void float_const(int float_type)
This function reads floating-point constants from the current
input line, and calls @code{md_atof} to assemble them. It is
useful as the function to call for the directives
@samp{.single}, @samp{.double}, @samp{.float}, etc.
@var{float_type} must be a character from @var{FLT_CHARS}.
@item void demand_empty_rest_of_line(void);
This function can be used by machine-dependent directives to
make sure the rest of the input line is empty. It prints a
warning message if there are additional characters on the line.
@item long int get_absolute_expression(void)
This function can be used by machine-dependent directives to
read an absolute number from the current input line. It
returns the result. If it isn't given an absolute expression,
it prints a warning message and returns zero.
@end table
@section The concept of Frags
This assembler works to optimize the size of certain addressing
modes. (e.g. branch instructions) This means the size of many
pieces of object code cannot be determined until after assembly
is finished. (This means that the addresses of symbols cannot be
determined until assembly is finished.) In order to do this,
@code{@value{AS}} stores the output bytes as @dfn{frags}.
Here is the definition of a frag (from @file{as.h})
@smallexample
struct frag
@{
long int fr_fix;
long int fr_var;
relax_stateT fr_type;
relax_substateT fr_substate;
unsigned long fr_address;
long int fr_offset;
struct symbol *fr_symbol;
char *fr_opcode;
struct frag *fr_next;
char fr_literal[];
@}
@end smallexample
@table @var
@item fr_fix
is the size of the fixed-size piece of the frag.
@item fr_var
is the maximum (?) size of the variable-sized piece of the frag.
@item fr_type
is the type of the frag.
Current types are:
rs_fill
rs_align
rs_org
rs_machine_dependent
@item fr_substate
This stores the type of machine-dependent frag this is. (what
kind of addressing mode is being used, and what size is being
tried/will fit/etc.
@item fr_address
@var{fr_address} is only valid after relaxation is finished.
Before relaxation, the only way to store an address is (pointer
to frag containing the address) plus (offset into the frag).
@item fr_offset
This contains a number, whose meaning depends on the type of
the frag.
for machine_dependent frags, this contains the offset from
fr_symbol that the frag wants to go to. Thus, for branch
instructions it is usually zero. (unless the instruction was
@samp{jba foo+12} or something like that.)
@item fr_symbol
for machine_dependent frags, this points to the symbol the frag
needs to reach.
@item fr_opcode
This points to the location in the frag (or in a previous frag)
of the opcode for the instruction that caused this to be a frag.
@var{fr_opcode} is needed if the actual opcode must be changed
in order to use a different form of the addressing mode.
(For example, if a conditional branch only comes in size tiny,
a large-size branch could be implemented by reversing the sense
of the test, and turning it into a tiny branch over a large jump.
This would require changing the opcode.)
@var{fr_literal} is a variable-size array that contains the
actual object bytes. A frag consists of a fixed size piece of
object data, (which may be zero bytes long), followed by a
piece of object data whose size may not have been determined
yet. Other information includes the type of the frag (which
controls how it is relaxed),
@item fr_next
This is the next frag in the singly-linked list. This is
usually only needed by the machine-independent part of
@code{@value{AS}}.
@end table
@end ifset
@ifset GENERIC
@include gpl.texinfo
@end ifset
@node Index
@unnumbered Index
@printindex cp
@contents
@bye
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