path: root/gas/doc/as-all.texinfo

\input texinfo @c                               -*-Texinfo-*-
@c  Copyright (c) 1991 1992 Free Software Foundation, Inc.
@c %**start of header 
@setfilename as.info
@settitle Using as
@setchapternewpage odd
@c @smallbook
@c @cropmarks
@c %**end of header

@ifinfo
@format
START-INFO-DIR-ENTRY
* As: (as).			The GNU assembler.
END-INFO-DIR-ENTRY
@end format
@end ifinfo

@finalout
@syncodeindex ky cp

@c
@ifinfo
This file documents the GNU Assembler "as".

Copyright (C) 1991 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 as
@subtitle The GNU Assembler
@sp 1
@subtitle January 1992
@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
@c edited by: pesch@cygnus.com
@page
@tex
\def\$#1${{#1}}  % Kluge: collect RCS revision info without $...$
\xdef\manvers{\$Revision$}  % For use in headers, footers too
{\parskip=0pt
\hfill {\it Using {\tt as}} \manvers\par
\hfill \TeX{}info \texinfoversion\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 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
@page
@ifinfo
@node Top
@top Using as

This file is a user guide to the GNU assembler @code{as}.
@menu
* Overview::			Overview
* Invoking::			Command-Line Options
* Syntax::			Syntax
* Sections::			Sections and Relocation
* Symbols::			Symbols
* Expressions::			Expressions
* Pseudo Ops::			Assembler Directives
* Machine Dependent:: 	Machine Dependent Features
* Copying::			GNU GENERAL PUBLIC LICENSE
* Index::                       Index
@end menu
@end ifinfo

@node Overview
@chapter Overview
@iftex
This manual is a user guide to the GNU assembler @code{as}.
@end iftex

@cindex invocation summary
@cindex option summary
@cindex summary of options
Here is a brief summary of how to invoke @code{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
  as [ -a | -al | -as ] [ -D ] [ -f ] 
   [ -I @var{path} ] [ -K ] [ -L ]
   [ -o @var{objfile} ] [ -R ] [ -v ] [ -w ]
@c am29k has no machine-dependent assembler options
@c h8/300 has no machine-dependent assembler options
@c see md_parse_option in i960.c
   [ -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC ]
   [ -b ] [ -norelax ]
   [ -l ] [ -mc68000 | -mc68010 | -mc68020 ]
   [ -- | @var{files} @dots{} ]
@end smallexample

@table @code
@item -a | -al | -as
Turn on assembly listings; @samp{-al}, listing only, @samp{-as}, symbols
only, @samp{-a}, everything.

@item -D
This option is accepted only for script compatibility with calls to
other assemblers; it has no effect on @code{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
Issue warnings when difference tables altered for long displacements.

@item -L
Keep (in symbol table) local symbols, starting with @samp{L}

@item -o @var{objfile}
Name the object-file output from @code{as}

@item -R
Fold data section into text section

@item -v
Announce @code{as} version

@item -W
Suppress warning messages

@item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
(When configured for Intel 960). 
Specify which variant of the 960 architecture is the target.

@item -b
(When configured for Intel 960). 
Add code to collect statistics about branches taken.

@item -norelax
(When configured for Intel 960). 
Do not alter compare-and-branch instructions for long displacements;
error if necessary.

@item -l
(When configured for Motorola 68000).  
Shorten references to undefined symbols, to one word instead of two

@item -mc68000 | -mc68010 | -mc68020
(When configured for Motorola 68000).  
Specify what processor in the 68000 family is the target (default 68020)

@item -- | @var{files} @dots{}
Standard input, or source files to assemble
@end table

@menu
* Manual::			Structure of this Manual
* GNU Assembler::		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{as}.  We cover the syntax expected in source files, including
notation for symbols, constants, and expressions; the directives that
@code{as} understands; and of course how to invoke @code{as}.

This manual also describes some of the machine-dependent features of
various flavors of the assembler.
@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.  
You may want to consult the manufacturer's
machine architecture manual for this information.


@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{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{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 as, the GNU Assembler

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

@cindex purpose of @sc{gnu} @code{as}
@code{as} is primarily intended to assemble the output of the GNU C
compiler @code{gcc} for use by the linker @code{ld}.  Nevertheless,
we've tried to make @code{as} assemble correctly everything that the native
assembler would.
Any exceptions are documented explicitly (@pxref{Machine Dependent}).
This doesn't mean @code{as} always uses the same syntax as another
assembler for the same architecture; for example, we know of several
incompatible versions of 680x0 assembly language syntax.

Unlike older assemblers, @code{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}.

@node Command Line
@section Command Line

@cindex command line conventions
After the program name @code{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{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{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
as -o my-object-file.o mumble.s
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{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{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{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{as} no file names it attempts to read one input file
from the @code{as} standard input, which is normally your terminal.  You
may have to type @key{ctl-D} to tell @code{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{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{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{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{as} it produces an output file, which is
your assembly language program translated into numbers.  This file
is the object file, named @code{a.out} unless you tell @code{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.
@c This may still work, but hasn't been tested.

@cindex linker
@kindex ld
The object file is meant for input to the linker @code{ld}.  It contains
assembled program code, information to help @code{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{as}
@code{as} may write warnings and error messages to the standard error
file (usually your terminal).  This should not happen when  a compiler
runs @code{as} automatically.  Warnings report an assumption made so
that @code{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
(@pxref{Ln,,@code{.ln}})
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). @refill

@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{as}
This chapter describes command-line options available in @emph{all}
versions of the GNU assembler; @pxref{Machine Dependent}, for options specific
to particular machine architectures.

@section Enable Listings: @code{-a}, @code{-al}, @code{-as}

@kindex -a
@kindex -al
@kindex -as
@cindex listings, enabling
@cindex assembly listings, enabling
These options enable listing output from the assembler.  @samp{-a} by
itself requests all listing output; @samp{-al} requests only the
output-program listing, and @samp{-as} requests only a symbol table
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}.

If you do not request listing output with one of the @samp{-a} options, the
listing-control directives have no effect.

@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{as}.

@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{as} will not work correctly if
@samp{-f} is used.
@end quotation

@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{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{as}
searches any @samp{-I} directories in the same order as they were
specified (left to right) on the command line.

@section Difference Tables: @code{-K}

@kindex -K

@cindex difference tables, warning
@cindex warning for altered difference tables
@code{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.

@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{as} and @code{ld} discard such labels, so you don't
normally debug with them.

This option tells @code{as} to retain those @samp{L@dots{}} symbols
in the object file.  Usually if you do this you also tell the linker
@code{ld} to preserve symbols whose names begin with @samp{L}.

@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{as}.  By
default it has the name @file{a.out}.  You use this option (which
takes exactly one filename) to give the object file a different name.

Whatever the object file is called, @code{as} will overwrite any
existing file of the same name.

@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{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 it 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{as}.  In future, @code{-R} may work this way.

When @code{as} is configured for COFF output, 
this option is only useful if you use sections named @samp{.text} and
@samp{.data}.  

@section Announce Version: @code{-v}

@kindex -v
@kindex -version
@cindex @code{as} version
@cindex version of @code{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.

@section Suppress Warnings: @code{-W}

@kindex -W
@cindex suppressing warnings
@cindex warnings, suppressing
@code{as} should never give a warning or error message when
assembling compiler output.  But programs written by people often
cause @code{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{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{as} syntax is similar to what many other assemblers
use; it is inspired in BSD 4.2
assembler, except that @code{as} does not assemble Vax bit-fields.

@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{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
@samp{#} on the Vax;
@samp{#} on the i960;
@samp{|} on the 680x0;
@samp{;} for the AMD 29K family;
@samp{;} for the machine specific family;
@pxref{Machine Dependent}.  @refill
@c FIXME: fill in SPARC line comment char

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.

@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{as}.

@node Symbol Intro
@section Symbols

@cindex characters used in symbols
A @dfn{symbol} is one or more characters chosen from the set of all
letters (both upper and lower case), digits and 
the two characters @samp{_.}
On most machines, you can also use @code{$} in symbol names; exceptions
are noted in @ref{Machine Dependent}.  
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
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 Dependent}.)  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.

@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{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.  
Different versions of @code{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

@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
.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 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{as} to interpret the second character literally as a backslash
(which prevents @code{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{as} has no
other interpretation, so @code{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
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{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{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
@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{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{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{as} the rest of the number is a flonum.  
@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 AMD 29K and H8/300 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).
@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{as} does all processing using integers.  Flonums are computed
independently of any floating point hardware in the computer running
@code{as}.


@node Sections
@chapter Sections and Relocation
@cindex sections
@cindex relocation

@menu
* Secs Background::		Background
* ld Sections::		ld Sections
* as Sections::		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{ld} reads many object files (partial programs) and
combines their contents to form a runnable program.  When @code{as}
emits an object file, the partial program is assumed to start at address
0.  @code{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{as} uses sections.

@code{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.
For the H8/300, @code{as} pads sections if needed to ensure they end
on a word (sixteen bit) boundary.

@cindex standard @code{as} sections
An object file written by @code{as} has at least three sections, any
of which may be empty.  These are named @dfn{text}, @dfn{data} and
@dfn{bss} sections.  

When it generates COFF output, 
@code{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.

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{ld} know which data will change when the sections are
relocated, and how to change that data, @code{as} also writes to the
object file details of the relocation needed.  To perform relocation
@code{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{as} ever uses is expressed as
@display
(@var{section}) + (@var{offset into section})
@end display
@noindent
Further, every expression @code{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,,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{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{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{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{ld}; others are invented for
use of @code{as} and have no meaning except during assembly.

@node ld Sections
@section ld Sections
@code{ld} deals with just four kinds of sections, summarized below.

@table @strong

@cindex named sections
@cindex sections, named
@item named sections
@cindex text section
@cindex data section
@item text section
@itemx data section
These sections hold your program.  @code{as} and @code{ld} treat them as
separate but equal sections.  Anything you can say of one section is
true another.  
When the program is running, however, it is
customary for the text section to be unalterable.  The
text section is often shared among processes: it 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.

@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{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.  
The example uses the traditional section names @samp{.text} and @samp{.data}.
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 as Internal Sections

@cindex internal @code{as} sections
@cindex sections in messages, internal
These sections are meant only for the internal use of @code{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{as}
warning messages, so it might be helpful to have an idea of their
meanings to @code{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{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{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{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{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
Assembled bytes
conventionally
fall into two sections: text and data.  
You may have separate groups of
data in named sections
that you want to end up near to each other in the object
file, even though they are not contiguous in the assembler source.
@code{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.

Each subsection is zero-padded up to a multiple of four bytes.
(Subsections may be padded a different amount on different flavors
of @code{as}.)

Subsections appear in your object file in numeric order, lowest numbered
to highest.  (All this to be compatible with other people's assemblers.)
The object file contains no representation of subsections; @code{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.
When generating COFF output, you 
can also use an extra subsection
argument with arbitrary named sections: @samp{.section @var{name},
@var{expression}}.
@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{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{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
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 Dependent}.)
That character may be followed by any string of digits, letters,
dollar signs (unless otherwise noted in @ref{Machine Dependent}), 
and underscores.
Case of letters is significant:
@code{foo} is a different symbol name than @code{Foo}.

For the AMD 29K family, @samp{?} is also allowed in the
body of a symbol name, though not at its beginning.

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{as} and
@code{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{as} will retain these symbols in the
object file. If you also instruct @code{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{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
@samp{.block 4}.

@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. 

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

@menu
* Symbol Value::		Value
* Symbol Type::			Type
* a.out Symbols::		Symbol Attributes: @code{a.out}
* COFF Symbols::		Symbol Attributes for COFF
@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{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{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.

@node a.out Symbols
@subsection Symbol Attributes: @code{a.out}

@cindex @code{a.out} symbol attributes
@cindex symbol attributes, @code{a.out}

@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{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{as}.

@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{as} directives @code{.dim}, @code{.line}, @code{.scl},
@code{.size}, and @code{.tag} can generate auxiliary symbol table
information for COFF.

@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{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{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{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 present regardless of the target
machine configuration for the GNU assembler.  

@menu
* Abort::			@code{.abort}
* coff-ABORT::			@code{.ABORT}
* 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}}
* Def::				@code{.def @var{name}}
* Desc::			@code{.desc @var{symbol}, @var{abs-expression}}
* Dim::				@code{.dim}
* Double::			@code{.double @var{flonums}}
* Eject::			@code{.eject}
* Else::			@code{.else}
* Endef::			@code{.endef}
* Endif::			@code{.endif}
* Equ::				@code{.equ @var{symbol}, @var{expression}}
* Extern::			@code{.extern}
* File::			@code{.file @var{string}}
* 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}
* Line::			@code{.line @var{line-number}}
* Ln::				@code{.ln @var{line-number}}
* List::			@code{.list}
* Long::			@code{.long @var{expressions}}
* 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}"}
* Scl::				@code{.scl @var{class}}
* Section::                     @code{.section @var{name}, @var{subsection}}
* Set::				@code{.set @var{symbol}, @var{expression}}
* Short::			@code{.short @var{expressions}}
* Single::			@code{.single @var{flonums}}
* Size::			@code{.size}
* Space::			@code{.space @var{size} , @var{fill}}
* Stab::			@code{.stabd, .stabn, .stabs}
* Tag::				@code{.tag @var{structname}}
* Text::			@code{.text @var{subsection}}
* Title::			@code{.title "@var{heading}"}
* Type::			@code{.type @var{int}}
* Val::				@code{.val @var{addr}}
* 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{as} to
quit also.  One day @code{.abort} will not be supported.

@node coff-ABORT
@section @code{.ABORT}

@cindex @code{ABORT} directive
When producing COFF output, @code{as} accepts this directive as a
synonym for @samp{.abort}.


When producing @code{b.out} output, @code{as} accepts this directive,
but ignores it.

@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}
tells @code{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{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{ld} reserves memory addresses for it during linking, so no partial
program defines the location of the symbol.  Use @code{.comm} to tell
@code{ld} that it must be at least @var{length} bytes long.  @code{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{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.

@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.

This directive is only observed when @code{as} is configured for COFF
format output; when producing @code{b.out}, @samp{.def} is recognized,
but ignored.

@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.

The @samp{.desc} directive is not available when @code{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{as} will accept
it, but produce no output, when configured for 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.

@samp{.dim} is only meaningful when generating COFF format output; when
@code{as} is generating @code{b.out}, it accepts this directive but
ignores it.

@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.
The exact kind of floating point numbers emitted depends on how
@code{as} is configured.  @xref{Machine Dependent}.

@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{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.


@node Endef
@section @code{.endef}

@cindex @code{endef} directive
This directive flags the end of a symbol definition begun with
@code{.def}. 

@samp{.endef} is only meaningful when generating COFF format output; if
@code{as} is configured to generate @code{b.out}, it accepts this
directive but ignores it.

@node Endif
@section @code{.endif}

@cindex @code{endif} directive
@code{.endif} is part of the @code{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{as} treats
all undefined symbols as external.

@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{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{as} programs.
In some configurations of @code{as}, @code{.file} has already been
removed to avoid conflicts with other assemblers.  @xref{Machine Dependent}.

@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{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}.
The exact kind of floating point numbers emitted depends on how
@code{as} is configured.
@xref{Machine Dependent}.

@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{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.

This directive is a synonym for @samp{.short}; depending on the target
architecture, it may also be a synonym for @samp{.word}.

@node Ident
@section @code{.ident}

@cindex @code{ident} directive
This directive is used by some assemblers to place tags in object files.
@code{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.


@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.

@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
@cindex integers, 32-bit
Expect zero or more @var{expressions}, of any section, separated by
commas.  For each expression, emit a
32-bit 
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.

@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{ld}.

@node Lflags
@section @code{.lflags}

@cindex @code{lflags} directive (ignored)
@code{as} accepts this directive, for compatibility with other
assemblers, but ignores it.

@node Line
@section @code{.line @var{line-number}}

@cindex @code{line} directive
@cindex logical line number
Tell @code{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. @refill

@emph{Warning:} In the AMD29K configuration of as, this command is
only available with the name @code{.ln}, rather than as either
@code{.line} or @code{.ln}.  

@node Ln
@section @code{.ln @var{line-number}}

@cindex @code{ln} directive
@samp{.ln} is a synonym for @samp{.line}.

@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{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{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{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
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.@refill
@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.

@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.

@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.

The @samp{.scl} directive is primarily associated with COFF output; when
configured to generate @code{b.out} output format, @code{as} will
accept this directive but ignore it.

@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{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.

@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{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
@code{.short} is the same as @samp{.word}.  @xref{Word,,@code{.word}}.

@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}.
The exact kind of floating point numbers emitted depends on how
@code{as} is configured.  @xref{Machine Dependent}.

@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.

@samp{.size} is only meaningful when generating COFF format output; when
@code{as} is generating @code{b.out}, it accepts this directive but
ignores it.

@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.

On the 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, the directive
@code{.space} has the effect of @code{.block}  @xref{Machine Dependent}.
@end quotation

@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{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{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

@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.

@samp{.tag} is only used when generating COFF format output; when
@code{as} is generating @code{b.out}, it accepts this directive but
ignores it.

@node Text
@section @code{.text @var{subsection}}

@cindex @code{text} directive
Tells @code{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.

@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.

@samp{.type} is associated only with COFF format output; when
@code{as} is configured for @code{b.out} output, it accepts this
directive but ignores it.

@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.

@samp{.val} is used only for COFF output; when @code{as} is
configured for @code{b.out}, it accepts this directive but ignores it.

@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.

The size of the number emitted, and its byte order,
depends on what kind of computer will run the program.

@c on amd29k, i960, sparc the "special treatment to support compilers" doesn't
@c happen---32-bit addressability, period; no long/short jumps.
@cindex difference tables altered
@cindex altered difference tables
@quotation
@emph{Warning: Special Treatment to support Compilers}
@end quotation

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 Dependent}), you can ignore this issue.

In order to assemble compiler output into something that will work,
@code{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{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{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.


@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

@node Machine Dependent
@chapter Machine Dependent Features

@cindex machine dependencies
The machine instruction sets are (almost by definition) different on
each machine where @code{as} runs.  Floating point representations
vary as well, and @code{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{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
* Vax-Dependent::		VAX Dependent Features
* AMD29K-Dependent::		AMD 29K Dependent Features
* H8/300-Dependent::		Hitachi H8/300 Dependent Features
* i960-Dependent::		Intel 80960 Dependent Features
* M68K-Dependent::		M680x0 Dependent Features
* Sparc-Dependent::		SPARC Dependent Features
* i386-Dependent::		80386 Dependent Features
@end menu

@node Vax-Dependent
@section VAX Dependent Features

@cindex VAX support
@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
@subsection VAX Command-Line Options

@cindex command-line options ignored, VAX
@cindex VAX command-line options ignored
The Vax version of @code{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{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.  @code{as} does not use a temporary disk file, so 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{as} from modifying the
symbol-table entries for symbols that contain lowercase
characters (I think).  The @kbd{-+} option causes @code{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
@subsection 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
@subsection 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
@subsection 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
@subsection 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
@subsection 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
@subsection Not Supported on VAX

@cindex VAX bitfields not supported
@cindex bitfields, not supported on VAX
Vax bit fields can not be assembled with @code{as}.  Someone
can add the required code if they really need it.

@node AMD29K-Dependent
@section AMD 29K Dependent Features

@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
@subsection Options
@cindex AMD 29K options (none)
@cindex options for AMD29K (none)
@code{as} has no additional command-line options for the AMD
29K family.

@node AMD29K Syntax
@subsection Syntax
@menu
* AMD29K-Chars::		Special Characters
* AMD29K-Regs::			Register Names
@end menu

@node AMD29K-Chars
@subsubsection 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
@subsubsection 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{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
@subsection 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
@subsection 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
@subsection Opcodes

@cindex AMD 29K opcodes
@cindex opcodes for AMD 29K
@code{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.

@node H8/300-Dependent
@section 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
@subsection Options

@cindex H8/300 options (none)
@cindex options, H8/300 (none)
@code{as} has no additional command-line options for the Hitachi 
H8/300 family.

@node H8/300 Syntax
@subsection Syntax
@menu
* H8/300-Chars::		Special Characters
* H8/300-Regs::			Register Names
* H8/300-Addressing::           Addressing Modes
@end menu

@node H8/300-Chars
@subsubsection 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
@subsubsection Register Names

@cindex H8/300 registers
@cindex registers, 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). 

The two control registers are called @code{pc} (program counter; a
16-bit register) 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
@subsubsection Addressing Modes

@cindex addressing modes, H8/300
@cindex H8/300 addressing modes
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})
Register indirect: 16-bit displacement @var{d} from register @var{n}.
(You may specify the @samp{:16} for clarity if you wish, but it is not
required and has no effect.)

@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
Absolute address @code{aa}.  You may specify the @samp{:8} or @samp{:16}
for clarity, if you wish; but @code{as} neither requires this nor
uses it---the address size required is taken from context.

@item #@var{xx}
@itemx #@var{xx}:8
@itemx #@var{xx}:16
Immediate data @var{xx}.  You may specify the @samp{:8} or @samp{:16}
for clarity, if you wish; but @code{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{as} neither requires this nor uses it.
@end table

@node H8/300 Floating Point
@subsection Floating Point

@cindex floating point, H8/300 (@sc{ieee})
@cindex H8/300 floating point (@sc{ieee})
The H8/300 family uses @sc{ieee} floating-point numbers.

@node H8/300 Directives
@subsection 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{as} has no machine-dependent directives for the H8/300.
However, on this platform the @samp{.int} and @samp{.word} directives
generate 16-bit numbers.

@node H8/300 Opcodes
@subsection 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).

@code{as} implements all the standard H8/300 opcodes.  No additional
pseudo-instructions are needed on this family.  

The following table summarizes the opcodes and their arguments:
@c kluge due to lack of group outside example
@page
@smallexample
@group
            Rs   @r{source register}     
            Rd   @r{destination register}
            imm  @r{immediate data}      
            x:3  @r{a bit (as a number between 0 and 7)}
            d:8  @r{eight bit displacement from @code{pc}}
            d:16 @r{sixteen bit displacement from @code{Rs}}

add.b   Rs,Rd                  biand   #x:3,Rd        
add.b   #imm:8,Rd              biand   #x:3,@@Rd      
add.w   Rs,Rd                  biand   #x:3,@@aa:8    
adds    #1,Rd                  bild    #x:3,Rd        
adds    #2,Rd                  bild    #x:3,@@Rd      
addx    #imm:8,Rd              bild    #x:3,@@aa:8    
addx    Rs,Rd                  bior    #x:3,Rd        
and     #imm:8,Rd              bior    #x:3,@@Rd      
and     Rs,Rd                  bior    #x:3,@@aa:8    
andc    #imm:8,ccr             bist    #x:3,Rd        
band    #x:3,Rd                bist    #x:3,@@Rd      
band    #x:3,@@Rd               bist    #x:3,@@aa:8   
bra     d:8                    bixor   #x:3,Rd        
bt      d:8                    bixor   #x:3,@@Rd      
brn     d:8                    bixor   #x:3,@@aa:8    
bf      d:8                    bld     #x:3,Rd        
bhi     d:8                    bld     #x:3,@@Rd      
bls     d:8                    bld     #x:3,@@aa:8    
bcc     d:8                    bnot    #x:3,Rd        
bhs     d:8                    bnot    #x:3,@@Rd      
bcs     d:8                    bnot    #x:3,@@aa:8    
blo     d:8                    bnot    Rs,Rd          
bne     d:8                    bnot    Rs,@@Rd        
beq     d:8                    bnot    Rs,@@aa:8      
bvc     d:8                    bor     #x:3,Rd        
bvs     d:8                    bor     #x:3,@@Rd      
bpl     d:8                    bor     #x:3,@@aa:8    
bmi     d:8                    bset    #x:3,@@Rd      
bge     d:8                    bset    #x:3,@@aa:8    
blt     d:8                    bset    Rs,Rd          
bgt     d:8                    bset    Rs,@@Rd        
ble     d:8                    bset    Rs,@@aa:8      
bclr    #x:3,Rd                bsr     d:8            
bclr    #x:3,@@Rd               bst     #x:3,Rd       
bclr    #x:3,@@aa:8             bst     #x:3,@@Rd     
bclr    Rs,Rd                  bst     #x:3,@@aa:8    
bclr    Rs,@@Rd                 btst    #x:3,Rd       
@end group
@group
btst    #x:3,@@Rd               mov.w   @@(d:16, Rs),Rd       
btst    #x:3,@@aa:8             mov.w   @@Rs+,Rd              
btst    Rs,Rd                  mov.w   @@aa:16,Rd             
btst    Rs,@@Rd                 mov.w   Rs,@@Rd               
btst    Rs,@@aa:8               mov.w   Rs,@@(d:16, Rd)       
bxor    #x:3,Rd                mov.w   Rs,@@-Rd               
bxor    #x:3,@@Rd               mov.w   Rs,@@aa:16            
bxor    #x:3,@@aa:8             movfpe  @@aa:16,Rd            
cmp.b   #imm:8,Rd              movtpe  Rs,@@aa:16             
cmp.b   Rs,Rd                  mulxu   Rs,Rd                  
cmp.w   Rs,Rd                  neg     Rs                     
daa     Rs                     nop                            
das     Rs                     not     Rs                     
dec     Rs                     or      #imm:8,Rd              
divxu   Rs,Rd                  or      Rs,Rd                  
eepmov                         orc     #imm:8,ccr             
inc     Rs                     pop     Rs                     
jmp     @@Rs                    push    Rs                    
jmp     @@aa:16                 rotl    Rs                    
jmp     @@@@aa                   rotr    Rs                   
jsr     @@Rs                    rotxl   Rs                    
jsr     @@aa:16                 rotxr   Rs                    
jsr     @@@@aa:8                 rte                          
ldc     #imm:8,ccr             rts                            
ldc     Rs,ccr                 shal    Rs                     
mov.b   Rs,Rd                  shar    Rs                     
mov.b   #imm:8,Rd              shll    Rs                     
mov.b   @@Rs,Rd                 shlr    Rs                    
mov.b   @@(d:16, Rs),Rd         sleep                         
mov.b   @@Rs+,Rd                stc     ccr,Rd                
mov.b   @@aa:16,Rd              sub.b   Rs,Rd                 
mov.b   @@aa:8,Rd               sub.w   Rs,Rd                 
mov.b   Rs,@@Rd                 subs    #1,Rd                 
mov.b   Rs,@@(d:16, Rd)         subs    #2,Rd                 
mov.b   Rs,@@-Rd                subx    #imm:8,Rd             
mov.b   Rs,@@aa:16              subx    Rs,Rd                 
mov.b   Rs,@@aa:8               xor     #imm:8,Rd             
mov.w   Rs,Rd                  xor     Rs,Rd                  
mov.w   #imm:16,Rd             xorc    #imm:8,ccr             
mov.w   @@Rs,Rd
@end group
@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} and
@samp{.w} to specify the size of a memory operand.  @code{as}
supports these suffixes, but does not require them; since one of the
operands is always a register, @code{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{as} will issue a warning if
there's a mismatch between the suffix and the register size.

@node i960-Dependent
@section Intel 80960 Dependent Features

@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

@subsection 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{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{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{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{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
@subsection Floating Point

@cindex floating point, i960 (@sc{ieee})
@cindex i960 floating point (@sc{ieee})
@code{as} generates @sc{ieee} floating-point numbers for the directives
@samp{.float}, @samp{.double}, @samp{.extended}, and @samp{.single}.

@node Directives-i960
@subsection 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
@subsection 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
@subsubsection @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{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
@subsubsection 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{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{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

@node M68K-Dependent
@section M680x0 Dependent Features

@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
@subsection M680x0 Options

@cindex options, M680x0
@cindex M680x0 options
The Motorola 680x0 version of @code{as} has two machine dependent options.
One shortens undefined references from 32 to 16 bits, while the
other is used to tell @code{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{as}
cannot know where these symbols will end up, @code{as} can only allocate
space for the linker to fill in later.  Since @code{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{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{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
@subsection Syntax

@cindex M680x0 syntax
@cindex syntax, M680x0
@cindex M680x0 size modifiers
@cindex size modifiers, M680x0
The 680x0 version of @code{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}.


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

@node M68K-Float
@subsection 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
@subsection 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
@subsection 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
@subsubsection 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{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{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{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
@subsubsection 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.

@node Sparc-Dependent
@section SPARC Dependent Features

@cindex SPARC support
@menu
* Sparc-Opts::			Options
* Sparc-Float::			Floating Point
* Sparc-Directives::		Sparc Machine Directives
@end menu

@node Sparc-Opts
@subsection Options

@cindex options for SPARC (none)
@cindex SPARC options (none)
The Sparc has no machine dependent options.

@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
@subsection 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
@subsection Sparc Machine Directives

@cindex SPARC machine directives
@cindex machine directives, SPARC
The Sparc version of @code{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

@node i386-Dependent
@section 80386 Dependent Features

@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
@subsection Options

@cindex options for i386 (none)
@cindex i386 options (none)
The 80386 has no machine dependent options.

@node i386-Syntax
@subsection AT&T Syntax versus Intel Syntax

@cindex i386 syntax compatibility
@cindex syntax compatibility, i386
In order to maintain compatibility with the output of @code{gcc},
@code{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
@subsection 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{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{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
@subsection 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
@subsection 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
@subsection 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{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{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
@subsection 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{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
@subsection 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{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
@subsection 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{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}.


@node Copying
@unnumbered GNU GENERAL PUBLIC LICENSE

@cindex license
@cindex GPL
@cindex copying @code{as}
@center Version 2, June 1991

@display
Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
675 Mass Ave, Cambridge, MA 02139, USA

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

@unnumberedsec Preamble

  The licenses for most software are designed to take away your
freedom to share and change it.  By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software---to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  You can apply it to
your programs, too.

  When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it
in new free programs; and that you know you can do these things.

  To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

  For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

  We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

  Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

  Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

  The precise terms and conditions for copying, distribution and
modification follow.

@iftex
@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
@end iftex
@ifinfo
@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
@end ifinfo

@enumerate
@item
This License applies to any program or other work which contains
a notice placed by the copyright holder saying it may be distributed
under the terms of this General Public License.  The ``Program'', below,
refers to any such program or work, and a ``work based on the Program''
means either the Program or any derivative work under copyright law:
that is to say, a work containing the Program or a portion of it,
either verbatim or with modifications and/or translated into another
language.  (Hereinafter, translation is included without limitation in
the term ``modification''.)  Each licensee is addressed as ``you''.

Activities other than copying, distribution and modification are not
covered by this License; they are outside its scope.  The act of
running the Program is not restricted, and the output from the Program
is covered only if its contents constitute a work based on the
Program (independent of having been made by running the Program).
Whether that is true depends on what the Program does.

@item
You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an appropriate
copyright notice and disclaimer of warranty; keep intact all the
notices that refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of this License
along with the Program.

You may charge a fee for the physical act of transferring a copy, and
you may at your option offer warranty protection in exchange for a fee.

@item
You may modify your copy or copies of the Program or any portion
of it, thus forming a work based on the Program, and copy and
distribute such modifications or work under the terms of Section 1
above, provided that you also meet all of these conditions:

@enumerate a
@item
You must cause the modified files to carry prominent notices
stating that you changed the files and the date of any change.

@item
You must cause any work that you distribute or publish, that in
whole or in part contains or is derived from the Program or any
part thereof, to be licensed as a whole at no charge to all third
parties under the terms of this License.

@item
If the modified program normally reads commands interactively
when run, you must cause it, when started running for such
interactive use in the most ordinary way, to print or display an
announcement including an appropriate copyright notice and a
notice that there is no warranty (or else, saying that you provide
a warranty) and that users may redistribute the program under
these conditions, and telling the user how to view a copy of this
License.  (Exception: if the Program itself is interactive but
does not normally print such an announcement, your work based on
the Program is not required to print an announcement.)
@end enumerate

These requirements apply to the modified work as a whole.  If
identifiable sections of that work are not derived from the Program,
and can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works.  But when you
distribute the same sections as part of a whole which is a work based
on the Program, the distribution of the whole must be on the terms of
this License, whose permissions for other licensees extend to the
entire whole, and thus to each and every part regardless of who wrote it.

Thus, it is not the intent of this section to claim rights or contest
your rights to work written entirely by you; rather, the intent is to
exercise the right to control the distribution of derivative or
collective works based on the Program.

In addition, mere aggregation of another work not based on the Program
with the Program (or with a work based on the Program) on a volume of
a storage or distribution medium does not bring the other work under
the scope of this License.

@item
You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:

@enumerate a
@item
Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of Sections
1 and 2 above on a medium customarily used for software interchange; or,

@item
Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than your
cost of physically performing source distribution, a complete
machine-readable copy of the corresponding source code, to be
distributed under the terms of Sections 1 and 2 above on a medium
customarily used for software interchange; or,

@item
Accompany it with the information you received as to the offer
to distribute corresponding source code.  (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form with such
an offer, in accord with Subsection b above.)
@end enumerate

The source code for a work means the preferred form of the work for
making modifications to it.  For an executable work, complete source
code means all the source code for all modules it contains, plus any
associated interface definition files, plus the scripts used to
control compilation and installation of the executable.  However, as a
special exception, the source code distributed need not include
anything that is normally distributed (in either source or binary
form) with the major components (compiler, kernel, and so on) of the
operating system on which the executable runs, unless that component
itself accompanies the executable.

If distribution of executable or object code is made by offering
access to copy from a designated place, then offering equivalent
access to copy the source code from the same place counts as
distribution of the source code, even though third parties are not
compelled to copy the source along with the object code.

@item
You may not copy, modify, sublicense, or distribute the Program
except as expressly provided under this License.  Any attempt
otherwise to copy, modify, sublicense or distribute the Program is
void, and will automatically terminate your rights under this License.
However, parties who have received copies, or rights, from you under
this License will not have their licenses terminated so long as such
parties remain in full compliance.

@item
You are not required to accept this License, since you have not
signed it.  However, nothing else grants you permission to modify or
distribute the Program or its derivative works.  These actions are
prohibited by law if you do not accept this License.  Therefore, by
modifying or distributing the Program (or any work based on the
Program), you indicate your acceptance of this License to do so, and
all its terms and conditions for copying, distributing or modifying
the Program or works based on it.

@item
Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program subject to
these terms and conditions.  You may not impose any further
restrictions on the recipients' exercise of the rights granted herein.
You are not responsible for enforcing compliance by third parties to
this License.

@item
If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent issues),
conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot
distribute so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you
may not distribute the Program at all.  For example, if a patent
license would not permit royalty-free redistribution of the Program by
all those who receive copies directly or indirectly through you, then
the only way you could satisfy both it and this License would be to
refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under
any particular circumstance, the balance of the section is intended to
apply and the section as a whole is intended to apply in other
circumstances.

It is not the purpose of this section to induce you to infringe any
patents or other property right claims or to contest validity of any
such claims; this section has the sole purpose of protecting the
integrity of the free software distribution system, which is
implemented by public license practices.  Many people have made
generous contributions to the wide range of software distributed
through that system in reliance on consistent application of that
system; it is up to the author/donor to decide if he or she is willing
to distribute software through any other system and a licensee cannot
impose that choice.

This section is intended to make thoroughly clear what is believed to
be a consequence of the rest of this License.

@item
If the distribution and/or use of the Program is restricted in
certain countries either by patents or by copyrighted interfaces, the
original copyright holder who places the Program under this License
may add an explicit geographical distribution limitation excluding
those countries, so that distribution is permitted only in or among
countries not thus excluded.  In such case, this License incorporates
the limitation as if written in the body of this License.

@item
The Free Software Foundation may publish revised and/or new versions
of the General Public License from time to time.  Such new versions will
be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.

Each version is given a distinguishing version number.  If the Program
specifies a version number of this License which applies to it and ``any
later version'', you have the option of following the terms and conditions
either of that version or of any later version published by the Free
Software Foundation.  If the Program does not specify a version number of
this License, you may choose any version ever published by the Free Software
Foundation.

@item
If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the author
to ask for permission.  For software which is copyrighted by the Free
Software Foundation, write to the Free Software Foundation; we sometimes
make exceptions for this.  Our decision will be guided by the two goals
of preserving the free status of all derivatives of our free software and
of promoting the sharing and reuse of software generally.

@iftex
@heading NO WARRANTY
@end iftex
@ifinfo
@center NO WARRANTY
@end ifinfo

@item
BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
REPAIR OR CORRECTION.

@item
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.
@end enumerate

@iftex
@heading END OF TERMS AND CONDITIONS
@end iftex
@ifinfo
@center END OF TERMS AND CONDITIONS
@end ifinfo

@page
@unnumberedsec Applying These Terms to Your New Programs

  If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.

  To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the ``copyright'' line and a pointer to where the full notice is found.

@smallexample
@var{one line to give the program's name and an idea of what it does.}
Copyright (C) 19@var{yy}  @var{name of author}

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the 
Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.
@end smallexample

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:

@smallexample
Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author}
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'.  This is free software, and you are welcome
to redistribute it under certain conditions; type `show c' 
for details.
@end smallexample

The hypothetical commands @samp{show w} and @samp{show c} should show
the appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than @samp{show w} and
@samp{show c}; they could even be mouse-clicks or menu items---whatever
suits your program.

You should also get your employer (if you work as a programmer) or your
school, if any, to sign a ``copyright disclaimer'' for the program, if
necessary.  Here is a sample; alter the names:

@smallexample
Yoyodyne, Inc., hereby disclaims all copyright interest in
the program `Gnomovision' (which makes passes at compilers)
written by James Hacker.

@var{signature of Ty Coon}, 1 April 1989
Ty Coon, President of Vice
@end smallexample

This General Public License does not permit incorporating your program into
proprietary programs.  If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library.  If this is what you want to do, use the GNU Library General
Public License instead of this License.

@node Index
@unnumbered Index

@printindex cp

@summarycontents
@contents
@bye