4742 lines
182 KiB
Plaintext
4742 lines
182 KiB
Plaintext
\input texinfo
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@c @tex
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@c \special{twoside}
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@c @end tex
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_if__(_ALL_ARCH__)
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@setfilename as.info
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_fi__(_ALL_ARCH__)
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_if__(_AMD29K__ && !_ALL_ARCH__)
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@setfilename as-29k.info
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_fi__(_AMD29K__ && !_ALL_ARCH__)
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_if__(_I960__ && !_ALL_ARCH__)
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@setfilename as-960.info
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_fi__(_I960__ && !_ALL_ARCH__)
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_if__(_M680X0__ && !_ALL_ARCH__)
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@setfilename as-m680x0.info
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_fi__(_M680X0__ && !_ALL_ARCH__)
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@c
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@c NOTE: this manual is marked up for preprocessing with a collection
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@c of m4 macros called "pretex.m4". If you see <_if__> and <_fi__>
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@c scattered around the source, you have the full source before
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@c preprocessing; if you don't, you have the source configured for
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@c _HOST__ architectures (and you can of course get the full source,
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@c with all configurations, from wherever you got this).
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_if__(0)
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THIS IS THE FULL SOURCE. The full source needs to be run through m4
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before either tex- or info- formatting: for example,
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m4 pretex.m4 none.m4 m680x0.m4 as.texinfo >as-680x0.texinfo
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will produce (assuming your path finds either GNU or SysV m4; Berkeley
|
|
won't do) a file suitable for formatting. See the text in "pretex.m4"
|
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for a fuller explanation (and the macro definitions).
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_fi__(0)
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@c
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@synindex ky cp
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@ifinfo
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This file documents the GNU Assembler "_AS__".
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Copyright (C) 1991 Free Software Foundation, Inc.
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Permission is granted to make and distribute verbatim copies of
|
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this manual provided the copyright notice and this permission notice
|
|
are preserved on all copies.
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|
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@ignore
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|
Permission is granted to process this file through Tex and print the
|
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results, provided the printed document carries copying permission
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notice identical to this one except for the removal of this paragraph
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(this paragraph not being relevant to the printed manual).
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|
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@end ignore
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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.
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|
|
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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 author instead of in the
|
|
original English.
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@end ifinfo
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@iftex
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@finalout
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@end iftex
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@smallbook
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@setchapternewpage odd
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_if__(_ALL_ARCH__)
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@settitle Using _AS__
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_fi__(_ALL_ARCH__)
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_if__(!_ALL_ARCH__)
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@settitle Using _AS__ (_HOST__)
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_fi__(!_ALL_ARCH__)
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@titlepage
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@title{Using _AS__}
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@subtitle{The GNU Assembler}
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_if__(!_ALL_ARCH__)
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@subtitle{for the _HOST__ family}
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_fi__(!_ALL_ARCH__)
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@sp 1
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@subtitle March 1991
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@sp 13
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The Free Software Foundation Inc. thanks The Nice Computer
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Company of Australia for loaning Dean Elsner to write the
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first (Vax) version of @code{as} for Project GNU.
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The proprietors, management and staff of TNCCA thank FSF for
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distracting the boss while they got some work
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done.
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@sp 3
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@author{Dean Elsner, Jay Fenlason & friends}
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@author{revised by Roland Pesch for Cygnus Support}
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@c pesch@cygnus.com
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@page
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@tex
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\def\$#1${{#1}} % Kluge: collect RCS revision info without $...$
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\xdef\manvers{\$Revision$} % For use in headers, footers too
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{\parskip=0pt
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\hfill Cygnus Support\par
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\hfill \manvers\par
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\hfill \TeX{}info \texinfoversion\par
|
|
}
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%"boxit" macro for figures:
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|
%Modified from Knuth's ``boxit'' macro from TeXbook (answer to exercise 21.3)
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\gdef\boxit#1#2{\vbox{\hrule\hbox{\vrule\kern3pt
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\vbox{\parindent=0pt\parskip=0pt\hsize=#1\kern3pt\strut\hfil
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#2\hfil\strut\kern3pt}\kern3pt\vrule}\hrule}}%box with visible outline
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\gdef\ibox#1#2{\hbox to #1{#2\hfil}\kern8pt}% invisible box
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@end tex
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@vskip 0pt plus 1filll
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Copyright @copyright{} 1991 Free Software Foundation, Inc.
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|
|
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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 author instead of in the
|
|
original English.
|
|
@end titlepage
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|
@page
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@node Top,,,
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@ifinfo
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This file is a user guide to the GNU assembler @code{_AS__}.
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_if__(!_ALL_ARCH__)
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|
This version of the file describes @code{_AS__} configured to generate
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|
code for _HOST__ architectures.
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_fi__(!_ALL_ARCH__)
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@end ifinfo
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|
@node Overview,,,
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|
@chapter Overview
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@iftex
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|
This manual is a user guide to the GNU assembler @code{_AS__}.
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_if__(!_ALL_ARCH__)
|
|
This version of the manual describes @code{_AS__} configured to generate
|
|
code for _HOST__ architectures.
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|
_fi__(!_ALL_ARCH__)
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@end iftex
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|
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@node Invoking,,,
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@section Invoking @code{_AS__}
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Here is a brief summary of how to invoke @code{_AS__}. For details,
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@pxref{Options}.
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@c We don't use @deffn and friends for the following because they seem
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@c to be limited to one line for the header.
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@smallexample
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_AS__ [ -D ] [ -f ] [ -I @var{path} ] [ -k ] [ -L ]
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[ -o @var{objfile} ] [ -R ] [ -v ] [ -w ]
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_if__(_AMD29K__)
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@c am29k has no machine-dependent assembler options
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|
_fi__(_AMD29K__)
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|
_if__(_I960__)
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|
@c see md_parse_option in i960.c
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|
[ -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC ]
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[ -b ] [ -norelax ]
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_fi__(_I960__)
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|
_if__(_M680X0__)
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[ -l ] [ -mc68000 | -mc68010 | -mc68020 ]
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|
_fi__(_M680X0__)
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|
[ -- | @var{files} @dots{} ]
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@end smallexample
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|
|
|
@table @code
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@item -D
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This option is accepted only for script compatibility with calls to
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other assemblers; it has no effect on @code{_AS__}.
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@item -f
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``fast''---skip preprocessing (assume source is compiler output)
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@item -I @var{path}
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Add @var{path} to the search list for @code{.include} directives
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@item -k
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_if__(_AMD29K__ || _I960__)
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|
This option is accepted but has no effect on the _HOST__ family.
|
|
_fi__(_AMD29K__ || _I960__)
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|
_if__(!(_AMD29K__||_I960__))
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|
Issue warnings when difference tables altered for long displacements
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|
_fi__(!(_AMD29K__||_I960__))
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|
@item -L
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|
Keep (in symbol table) local symbols, starting with @samp{L}
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@item -o @var{objfile}
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Name the object-file output from @code{_AS__}
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@item -R
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|
Fold data segment into text segment
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|
@item -W
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Suppress warning messages
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|
_if__(_I960__)
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|
@item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
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|
Specify which variant of the 960 architecture is the target.
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|
|
@item -b
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|
Add code to collect statistics about branches taken.
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|
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@item -norelax
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|
Do not alter compare-and-branch instructions for long displaements;
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error if necessary.
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_fi__(_I960__)
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|
_if__(_M680X0__)
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@item -l
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|
Shorten references to undefined symbols, to one word instead of two
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|
@item -mc68000 | -mc68010 | -mc68020
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|
Specify what processor in the 68000 family is the target (default 68020)
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|
_fi__(_M680X0__)
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|
@item -- | @var{files} @dots{}
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Source files to assemble, or standard input
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|
@end table
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|
@node Manual, GNU Assembler, Invoking, Overview
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|
@section Structure of this Manual
|
|
This document is intended to describe what you need to know to use
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|
@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__}.
|
|
|
|
_if__(!_ALL_ARCH__)
|
|
We also cover special features in the _HOST__
|
|
configuration of @code{_AS__}, including assembler directives.
|
|
_fi__(!_ALL_ARCH__)
|
|
_if__(_ALL_ARCH__)
|
|
This document also describes some of the machine-dependent features of
|
|
various flavors of the assembler.
|
|
_fi__(_ALL_ARCH__)
|
|
_if__(_INTERNALS__)
|
|
This document also describes how the assembler works internally, and
|
|
provides some information that may be useful to people attempting to
|
|
port the assembler to another machine.
|
|
_fi__(_INTERNALS__)
|
|
@refill
|
|
|
|
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.
|
|
|
|
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|
@c I think this is premature---pesch@cygnus.com, 17jan1991
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|
@ignore
|
|
Throughout this document, 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__(!_ALL_ARCH__)
|
|
This manual describes @samp{_AS__}, a member of that family which is
|
|
configured for the _HOST__ architectures.
|
|
_fi__(!_ALL_ARCH__)
|
|
If you use (or have used) the GNU assembler on another architecture, you
|
|
should find a fairly similar environment. 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
|
|
|
|
@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.
|
|
_if__(_VAX__)
|
|
Any exceptions are documented explicitly (@pxref{_MACH_DEP__}).
|
|
_fi__(_VAX__)
|
|
_if__(_ALL_ARCH__||_M680X0__)
|
|
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.
|
|
_fi__(_ALL_ARCH__||_M680X0__)
|
|
|
|
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}).
|
|
|
|
@node Object Formats,,,
|
|
@section Object File Formats
|
|
The GNU assembler can be configured to produce several alternative
|
|
object file formats.
|
|
_if__(!_ALL_ARCH__)
|
|
_if__(!_I960__)
|
|
@code{_AS__} is configured to produce @code{a.out} format object
|
|
files.@refill
|
|
_fi__(!_I960__)
|
|
_if__(_I960__)
|
|
@code{_AS__} can be configured to produce either @code{b.out} or COFF
|
|
format object files.
|
|
_fi__(_I960__)
|
|
_fi__(!_ALL_ARCH__)
|
|
|
|
@node Command Line,,,
|
|
@section Command Line
|
|
|
|
After the program name @code{_AS__}, the command line may contain
|
|
options and file names. Options may be in any order, and may be
|
|
before, after, or between file names. The order of file names is
|
|
significant.
|
|
|
|
@file{--} (two hyphens) by itself names the standard input file
|
|
explicitly, as one of the files for @code{_AS__} to assemble.
|
|
|
|
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
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|
_AS__ -omy-object-file.o mumble.s
|
|
@end smallexample
|
|
|
|
@node Input Files, Object, Command Line, Overview
|
|
@section Input Files
|
|
|
|
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 @code{_AS__} is given 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.
|
|
|
|
@node Filenames, , Input Files, Input Files
|
|
@subsection Filenames and Line-numbers
|
|
There are two ways of locating a line in the input file (or files) and both
|
|
are 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.
|
|
|
|
@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}.
|
|
|
|
@node Object, Errors, Input Files, Overview
|
|
@section Output (Object) File
|
|
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.
|
|
|
|
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.
|
|
|
|
@comment link above to some info file(s) like the description of a.out.
|
|
@comment don't forget to describe GNU info as well as Unix lossage.
|
|
|
|
@node Errors, Options, Object, Overview
|
|
@section Error and Warning Messages
|
|
|
|
@code{_AS__} may write warnings and error messages to the standard error
|
|
file (usually your terminal). This should not happen when @code{_AS__} is
|
|
run automatically by a compiler. Warnings report an assumption made so
|
|
that @code{_AS__} could keep assembling a flawed program; errors report a
|
|
grave problem that stops the assembly.
|
|
|
|
Warning messages have the format
|
|
@smallexample
|
|
file_name:@b{NNN}:Warning Message Text
|
|
@end smallexample
|
|
@noindent(where @b{NNN} is a line number). If a logical file name has
|
|
been given (@pxref{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
|
|
_if__(!_AMD29K__)
|
|
(@pxref{Line})
|
|
_fi__(!_AMD29K__)
|
|
_if__(_AMD29K__)
|
|
(@pxref{Ln})
|
|
_fi__(_AMD29K__)
|
|
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
|
|
|
|
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 Options, , Errors, Overview
|
|
@section Options
|
|
This section describes command-line options available in @emph{all}
|
|
versions of the GNU assembler; @pxref{_MACH_DEP__}, for options specific
|
|
to the _HOST__.
|
|
|
|
@subsection @code{-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__}.
|
|
|
|
@subsection Work Faster: @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.
|
|
@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
|
|
|
|
@subsection @code{.include} search path: @code{-I} @var{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}). 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.
|
|
|
|
@subsection Difference Tables: @code{-k}
|
|
_if__(_AMD29K__ || _I960__)
|
|
On the _HOST__ family, this option is allowed, but has no effect. It is
|
|
permitted for compatibility with the GNU assembler on other platforms,
|
|
where it can be used to warn when the assembler alters the machine code
|
|
generated for @samp{.word} directives in difference tables. The _HOST__
|
|
family does not have the addressing limitations that sometimes lead to this
|
|
alteration on other platforms.
|
|
_fi__(_AMD29K__ || _I960__)
|
|
|
|
_if__(! (_AMD29K__ || _I960__) )
|
|
@code{_AS__} sometimes alters the code emitted for directives of the form
|
|
@samp{.word @var{sym1}-@var{sym2}}; @pxref{Word}.
|
|
You can use the @samp{-k} option if you want a warning issued when this
|
|
is done.
|
|
_fi__(! (_AMD29K__ || _I960__) )
|
|
|
|
@subsection Include Local Labels: @code{-L}
|
|
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}.
|
|
|
|
@subsection Name the Object File: @code{-o}
|
|
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.
|
|
|
|
@subsection Join Data and Text Segments: @code{-R}
|
|
@code{-R} tells @code{_AS__} to write the object file as if all
|
|
data-segment data lives in the text segment. This is only done at
|
|
the very last moment: your binary data are the same, but data
|
|
segment parts are relocated differently. The data segment part of
|
|
your object file is zero bytes long because all it bytes are
|
|
appended to the text segment. (@xref{Segments}.)
|
|
|
|
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 segment). We refrain from doing this simply for compatibility with
|
|
older versions of @code{_AS__}. In future, @code{-R} may work this way.
|
|
|
|
@subsection Suppress Warnings: @code{-W}
|
|
@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, Segments, Overview, Top
|
|
@chapter Syntax
|
|
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
|
|
_if__(!_VAX__)
|
|
assembler. @refill
|
|
_fi__(!_VAX__)
|
|
_if__(_VAX__)
|
|
assembler, except that @code{_AS__} does not assemble Vax bit-fields.
|
|
_fi__(_VAX__)
|
|
|
|
@node Pre-processing, Whitespace, Syntax, Syntax
|
|
@section Pre-processing
|
|
|
|
The pre-processor:
|
|
@itemize @bullet
|
|
@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.
|
|
|
|
@item
|
|
removes all comments, replacing them with a single space, or an
|
|
appropriate number of newlines.
|
|
|
|
@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.
|
|
|
|
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, Comments, Pre-processing, Syntax
|
|
@section 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}), any whitespace means the same as exactly one
|
|
space.
|
|
|
|
@node Comments, Symbol Intro, Whitespace, Syntax
|
|
@section 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
|
|
|
|
Anything from the @dfn{line comment} character to the next newline
|
|
is considered a comment and is ignored. The line comment character is
|
|
_if__(_VAX__ || _I960__)
|
|
@samp{#} on the _HOST__;
|
|
_fi__(_VAX__ || _I960__)
|
|
_if__(_M680X0__)
|
|
@samp{|} on the 680x0;
|
|
_fi__(_M680X0__)
|
|
_if__(_AMD29K__)
|
|
@samp{;} for the AMD 29K family;
|
|
_fi__(_AMD29K__)
|
|
@pxref{_MACH_DEP__}. @refill
|
|
|
|
_if__(_ALL_ARCH__)
|
|
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.
|
|
_fi__(_ALL_ARCH__)
|
|
|
|
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, Statements, Comments, Syntax
|
|
@section Symbols
|
|
A @dfn{symbol} is one or more characters chosen from the set of all
|
|
letters (both upper and lower case), digits and the three characters
|
|
@samp{_.$}. 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}.
|
|
|
|
@node Statements, Constants, Symbol Intro, Syntax
|
|
@section Statements
|
|
_if__(!_AMD29K__)
|
|
A @dfn{statement} ends at a newline character (@samp{\n}) or at a
|
|
semicolon (@samp{;}). The newline or semicolon is considered part of
|
|
the preceding statement. Newlines and semicolons within character
|
|
constants are an exception: they don't end statements.
|
|
_fi__(!_AMD29K__)
|
|
_if__(_AMD29K__)
|
|
A @dfn{statement} ends at a newline character (@samp{\n}) or an ``at''
|
|
sign (@samp{@@}). The newline or at sign is considered part of the
|
|
preceding statement. Newlines and at signs within character constants
|
|
are an exception: they don't end statements.
|
|
_fi__(_AMD29K__)
|
|
|
|
It is an error to end any statement with end-of-file: the last
|
|
character of any input file should be a newline.@refill
|
|
|
|
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.
|
|
|
|
@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.
|
|
_if__(_ALL_ARCH__)
|
|
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
|
|
_fi__(_ALL_ARCH__)
|
|
|
|
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, , Statements, Syntax
|
|
@section 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
|
|
|
|
@node Characters, Numbers, Constants, Constants
|
|
@subsection Character Constants
|
|
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.
|
|
|
|
@node Strings, Chars, Characters, Characters
|
|
@subsubsection Strings
|
|
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.
|
|
|
|
@table @kbd
|
|
@c @item \a
|
|
@c Mnemonic for ACKnowledge; for ASCII this is octal code 007.
|
|
@item \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.
|
|
@item \f
|
|
Mnemonic for FormFeed; for ASCII this is octal code 014.
|
|
@item \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}.
|
|
@item \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.
|
|
@item \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.
|
|
@item \ @var{digit} @var{digit} @var{digit}
|
|
An octal character code. The numeric code is 3 octal digits.
|
|
For compatibility with other Unix systems, 8 and 9 are accepted as digits:
|
|
for example, @code{\008} has the value 010, and @code{\009} the value 011.
|
|
@item \\
|
|
Represents one @samp{\} character.
|
|
@c @item \'
|
|
@c Represents one @samp{'} (accent acute) character.
|
|
@c This is needed in single character literals
|
|
@c (@xref{Characters}.) to represent
|
|
@c a @samp{'}.
|
|
@item \"
|
|
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, , Strings, Characters
|
|
@subsubsection Characters
|
|
A single character may be written as a single quote immediately
|
|
followed by that character. The same escapes apply to characters as
|
|
to strings. So if you want to write the character backslash, you
|
|
must write @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
|
|
_if__(!_AMD29K__)
|
|
(or semicolon @samp{;})
|
|
_fi__(!_AMD29K__)
|
|
_if__(_AMD29K__)
|
|
(or at sign @samp{@@})
|
|
_fi__(_AMD29K__)
|
|
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
|
|
@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.
|
|
|
|
@node Integers,,,
|
|
@subsubsection Integers
|
|
A binary integer is @samp{0b} or @samp{0B} followed by zero or more of
|
|
the binary digits @samp{01}.
|
|
|
|
An octal integer is @samp{0} followed by zero or more of the octal
|
|
digits (@samp{01234567}).
|
|
|
|
A decimal integer starts with a non-zero digit followed by zero or
|
|
more digits (@samp{0123456789}).
|
|
|
|
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}).
|
|
|
|
@node Bignums,,,
|
|
@subsubsection Bignums
|
|
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
|
|
A @dfn{flonum} represents a floating point number. The translation is
|
|
complex: 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
|
|
_if__(_AMD29K__)
|
|
One of the letters @samp{DFPRSX} (in upper or lower case), to tell
|
|
@code{_AS__} the rest of the number is a flonum.
|
|
_fi__(_AMD29K__)
|
|
_if__(_I960__)
|
|
One of the letters @samp{DFT} (in upper or lower case), to tell
|
|
@code{_AS__} the rest of the number is a flonum.
|
|
_fi__(_I960__)
|
|
_if__(!(_AMD29K__||_I960__))
|
|
A letter, to tell @code{_AS__} the rest of the number is a flonum. @kbd{e}
|
|
is recommended. Case is not important. (Any otherwise illegal letter
|
|
will work here, but that might be changed. Vax BSD 4.2 assembler seems
|
|
to allow any of @samp{defghDEFGH}.)
|
|
_fi__(!(_AMD29K__||_I960__))
|
|
@item
|
|
An optional sign: either @samp{+} or @samp{-}.
|
|
@item
|
|
An optional @dfn{integer part}: zero or more decimal digits.
|
|
@item
|
|
An optional @dfn{fraction 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 @var{integer part} or @var{fraction 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__}.
|
|
|
|
_if__(_I960__)
|
|
@c Bit fields are written as a general facility but are also controlled
|
|
@c by a conditional-compilation flag---which is as of now (21mar91)
|
|
@c turned on only by the i960 config of GAS.
|
|
@node Bit Fields,,,
|
|
@subsubsection Bit Fields
|
|
You can also define numeric constants as @dfn{bit fields}.
|
|
specify two numbers separated by a colon---
|
|
@example
|
|
@var{mask}:@var{value}
|
|
@end example
|
|
@noindent
|
|
the first will act as a mask; @code{_AS__} will bitwise-and it with the
|
|
second value.
|
|
|
|
The resulting number is then packed
|
|
_if__(_ALL_ARCH__)
|
|
(in host-dependent byte order)
|
|
_fi__(_ALL_ARCH__)
|
|
into a field whose width depends on which assembler directive has the
|
|
bit-field as its argument. Overflow (a result from the bitwise and
|
|
requiring more binary digits to represent) is not an error; instead,
|
|
more constants are generated, of the specified width, beginning with the
|
|
least significant digits.@refill
|
|
|
|
The directives @code{.byte}, @code{.hword}, @code{.int}, @code{.long},
|
|
@code{.short}, and @code{.word} accept bit-field arguments.
|
|
_fi__(_I960__)
|
|
|
|
@node Segments, Symbols, Syntax, Top
|
|
@chapter Segments and Relocation
|
|
|
|
@node Segs Background, _LD__ Segments, Segments, Segments
|
|
@section Background
|
|
Roughly, a segment 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'' segment.
|
|
|
|
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 segments.
|
|
|
|
@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{segment}. Assigning
|
|
run-time addresses to segments is called @dfn{relocation}. It includes
|
|
the task of adjusting mentions of object-file addresses so they refer to
|
|
the proper run-time addresses.
|
|
|
|
An object file written by @code{_AS__} has three segments, any of which may
|
|
be empty. These are named @dfn{text}, @dfn{data} and @dfn{bss}
|
|
segments.
|
|
_if__(_COFF__)
|
|
|
|
@c Thanks, Rich!
|
|
@quotation
|
|
@emph{Warning:} @code{_AS__} can only assign output to one of these
|
|
three segments, even when configured for COFF output; the
|
|
@code{.section} directive is not supported.
|
|
@end quotation
|
|
_fi__(_COFF__)
|
|
|
|
Within the object file, the text segment starts at address @code{0}, the
|
|
data segment follows, and the bss segment follows the data segment.
|
|
|
|
To let @code{_LD__} know which data will change when the segments 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 segment does the address refer to? What is the numeric value of
|
|
@display
|
|
(@var{address}) @minus{} (@var{start-address of segment})?
|
|
@end display
|
|
@item
|
|
Is the reference to an address ``Program-Counter relative''?
|
|
@end itemize
|
|
|
|
In fact, every address @code{_AS__} ever uses is expressed as
|
|
@display
|
|
(@var{segment}) + (@var{offset into segment})
|
|
@end display
|
|
@noindent
|
|
Further, every expression @code{_AS__} computes is of this segmented
|
|
nature. @dfn{Absolute expression} means an expression with segment
|
|
``absolute'' (@pxref{_LD__ Segments}). A @dfn{pass1 expression} means
|
|
an expression with segment ``pass1'' (@pxref{_AS__ Segments}). In this
|
|
manual we use the notation @{@var{segname} @var{N}@} to mean ``offset
|
|
@var{N} into segment @var{segname}''.
|
|
|
|
Apart from text, data and bss segments you need to know about the
|
|
@dfn{absolute} segment. When @code{_LD__} mixes partial programs,
|
|
addresses in the absolute segment remain unchanged. That is, address
|
|
@code{@{absolute 0@}} is ``relocated'' to run-time address 0 by @code{_LD__}.
|
|
Although two partial programs' data segments will not overlap addresses
|
|
after linking, @emph{by definition} their absolute segments 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 segments is extended to the @dfn{undefined} segment. Any
|
|
address whose segment 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 segment @emph{undefined}.
|
|
|
|
By analogy the word @emph{segment} is used to describe groups of segments in
|
|
the linked program. @code{_LD__} puts all partial programs' text
|
|
segments in contiguous addresses in the linked program. It is
|
|
customary to refer to the @emph{text segment} of a program, meaning all
|
|
the addresses of all partial program's text segments. Likewise for
|
|
data and bss segments.
|
|
|
|
Some segments are manipulated by @code{_LD__}; others are invented for
|
|
use of @code{_AS__} and have no meaning except during assembly.
|
|
|
|
@node _LD__ Segments, _AS__ Segments, Segs Background, Segments
|
|
@section _LD__ Segments
|
|
@code{_LD__} deals with just five kinds of segments, summarized below.
|
|
|
|
@table @strong
|
|
|
|
@item text segment
|
|
@itemx data segment
|
|
These segments hold your program. @code{_AS__} and @code{_LD__} treat them as
|
|
separate but equal segments. Anything you can say of one segment is
|
|
true of the other. When the program is running, however, it is
|
|
customary for the text segment to be unalterable. The
|
|
text segment is often shared among processes: it will contain
|
|
instructions, constants and the like. The data segment of a running
|
|
program is usually alterable: for example, C variables would be stored
|
|
in the data segment.
|
|
|
|
@item bss segment
|
|
This segment 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 segment 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 segment was invented to eliminate
|
|
those explicit zeros from object files.
|
|
|
|
@item absolute segment
|
|
Address 0 of this segment 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.
|
|
|
|
@item undefined segment
|
|
This ``segment'' is a catch-all for address references to objects not in
|
|
the preceding segments.
|
|
@c FIXME: ref to some other doc on obj-file formats could go here.
|
|
|
|
@end table
|
|
|
|
An idealized example of the three relocatable segments follows. Memory
|
|
addresses are on the horizontal axis.
|
|
|
|
@ifinfo
|
|
@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
|
|
@end ifinfo
|
|
@tex
|
|
|
|
{\it Partial program \#1: }
|
|
|
|
\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}
|
|
|
|
{\it Partial program \#2:}
|
|
|
|
\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}
|
|
|
|
{\it linked program: }
|
|
|
|
\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}
|
|
|
|
{\it addresses:}
|
|
|
|
\line{0\dots\hfil}
|
|
|
|
@end tex
|
|
|
|
@node _AS__ Segments, Sub-Segments, _LD__ Segments, Segments
|
|
@section _AS__ Internal Segments
|
|
These segments are invented for the internal use of @code{_AS__}. They
|
|
have no meaning at run-time. You don't need to know about these
|
|
segments except that they might be mentioned in the @code{_AS__} warning
|
|
messages. These segments are invented to permit the value of every
|
|
expression in your assembly language program to be a segmented
|
|
address.
|
|
|
|
@table @b
|
|
@item absent segment
|
|
An expression was expected and none was
|
|
found.
|
|
|
|
@item goof segment
|
|
An internal assembler logic error has been
|
|
found. This means there is a bug in the assembler.
|
|
|
|
@item grand segment
|
|
A @dfn{grand number} is a bignum or a flonum, but not an integer. If a
|
|
number can't be written as a C @code{int} constant, it is a grand
|
|
number. @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 segment
|
|
grand. This is purely for internal @code{_AS__} convenience; grand
|
|
segment behaves similarly to absolute segment.
|
|
|
|
@item pass1 segment
|
|
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 (segment + offset in segment) 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 segment
|
|
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 segment. @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 segment. 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.
|
|
@end table
|
|
|
|
@node Sub-Segments, bss, _AS__ Segments, Segments
|
|
@section Sub-Segments
|
|
Assembled bytes fall into two segments: text and data.
|
|
Because you may have groups of text or data that you want to end up near
|
|
to each other in the object file, @code{_AS__} allows you to use
|
|
@dfn{subsegments}. Within each segment, there can be numbered
|
|
subsegments with values from 0 to 8192. Objects assembled into the same
|
|
subsegment will be grouped with other objects in the same subsegment
|
|
when they are all put into the object file. For example, a compiler
|
|
might want to store constants in the text segment, but might not want to
|
|
have them interspersed with the program being assembled. In this case,
|
|
the compiler could issue a @code{text 0} before each section of code
|
|
being output, and a @code{text 1} before each group of constants being
|
|
output.
|
|
|
|
Subsegments are optional. If you don't use subsegments, everything
|
|
will be stored in subsegment number zero.
|
|
|
|
_if__(!(_AMD29K__||_I960__))
|
|
Each subsegment is zero-padded up to a multiple of four bytes.
|
|
(Subsegments may be padded a different amount on different flavors
|
|
of @code{_AS__}.)
|
|
_fi__(!(_AMD29K__||_I960__))
|
|
_if__(_I960__)
|
|
@c Rich Pixley says padding here depends on target obj code format; that
|
|
@c doesn't seem particularly useful to say without further elaboration,
|
|
@c so for now I say nothing about it. If this is a generic BFD issue,
|
|
@c these paragraphs might need to vanish from this manual, and be
|
|
@c discussed in BFD chapter of binutils (or some such).
|
|
_fi__(_I960__)
|
|
_if__(_AMD29K__)
|
|
On the AMD 29K family, no particular padding is added to segment sizes;
|
|
_AS__ forces no alignment on this platform.
|
|
_fi__(_AMD29K__)
|
|
Subsegments 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 subsegments; @code{_LD__} and
|
|
other programs that manipulate object files will see no trace of them.
|
|
They just see all your text subsegments as a text segment, and all your
|
|
data subsegments as a data segment.
|
|
|
|
To specify which subsegment you want subsequent statements assembled
|
|
into, use a @samp{.text @var{expression}} or a @samp{.data
|
|
@var{expression}} statement. @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 subsegment is text 0 anyway.
|
|
.ascii "This lives in the first text subsegment. *"
|
|
.text 1
|
|
.ascii "But this lives in the second text subsegment."
|
|
.data 0
|
|
.ascii "This lives in the data segment,"
|
|
.ascii "in the first data subsegment."
|
|
.text 0
|
|
.ascii "This lives in the first text segment,"
|
|
.ascii "immediately following the asterisk (*)."
|
|
@end smallexample
|
|
|
|
Each segment has a @dfn{location counter} incremented by one for every
|
|
byte assembled into that segment. Because subsegments are merely a
|
|
convenience restricted to @code{_AS__} there is no concept of a subsegment
|
|
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
|
|
segment that statements are being assembled into is said to be the
|
|
@dfn{active} location counter.
|
|
|
|
@node bss, , Sub-Segments, Segments
|
|
@section bss Segment
|
|
The bss segment is used for local common variable storage.
|
|
You may allocate address space in the bss segment, 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
|
|
segment are zeroed bytes.
|
|
|
|
Addresses in the bss segment are allocated with special directives;
|
|
you may not assemble anything directly into the bss segment. Hence
|
|
there are no bss subsegments. @xref{Comm}; @pxref{Lcomm}.
|
|
|
|
@node Symbols, Expressions, Segments, Top
|
|
@chapter 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
|
|
@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
|
|
|
|
@node Labels, Setting Symbols, Symbols, Symbols
|
|
@section 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, Symbol Names, Labels, Symbols
|
|
@section Giving Symbols Other Values
|
|
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}.
|
|
|
|
@node Symbol Names, Dot, Setting Symbols, Symbols
|
|
@section Symbol Names
|
|
Symbol names begin with a letter or with one of @samp{$._}. That
|
|
character may be followed by any string of digits, letters,
|
|
underscores and dollar signs. Case of letters is significant:
|
|
@code{foo} is a different symbol name than @code{Foo}.
|
|
|
|
_if__(_AMD29K__)
|
|
For the AMD 29K family, @samp{?} is also allowed in the
|
|
body of a symbol name, though not at its beginning.
|
|
_fi__(_AMD29K__)
|
|
|
|
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.
|
|
|
|
@node Local Symbols, , Symbol Names, Symbol Names
|
|
@subsection Local Symbol Names
|
|
|
|
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, Symbol Attributes, Symbol Names, Symbols
|
|
@section The Special Dot Symbol
|
|
|
|
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
|
|
_if__(!_AMD29K__)
|
|
@samp{.space 4}.
|
|
_fi__(!_AMD29K__)
|
|
_if__(_AMD29K__)
|
|
@samp{.block 4}.
|
|
_fi__(_AMD29K__)
|
|
|
|
@node Symbol Attributes, , Dot, Symbols
|
|
@section Symbol Attributes
|
|
Every symbol has, as well as its name, the attributes ``Value'' and
|
|
``Type''. Depending on output format, symbols also have auxiliary attributes.
|
|
_if__(_INTERNALS__)
|
|
The detailed definitions are in _0__<a.out.h>_1__.
|
|
_fi__(_INTERNALS__)
|
|
|
|
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.
|
|
|
|
@node Symbol Value, Symbol Type, Symbol Attributes, Symbol Attributes
|
|
@subsection Value
|
|
The value of a symbol is (usually) 32 bits, the size of one GNU C
|
|
@code{int}. For a symbol which labels a location in the text, data, bss
|
|
or absolute segments the value is the number of addresses from the start
|
|
of that segment to the label. Naturally for text, data and bss segments
|
|
the value of a symbol changes as @code{_LD__} changes segment 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, Symbol Desc, Symbol Value, Symbol Attributes
|
|
@subsection Type
|
|
The type attribute of a symbol contains relocation (segment)
|
|
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.
|
|
|
|
_if__(_AOUT__||_BOUT__)
|
|
@node a.out Symbols,,,
|
|
@subsection Symbol Attributes: @code{a.out}, @code{b.out}
|
|
These symbol attributes appear only when @code{_AS__} is configured for
|
|
one of the Berkeley-descended object output formats.
|
|
|
|
@node Symbol Desc, Symbol Other, Symbol Type, Symbol Attributes
|
|
@subsubsection Descriptor
|
|
This is an arbitrary 16-bit value. You may establish a symbol's
|
|
descriptor value by using a @code{.desc} statement (@pxref{Desc}).
|
|
A descriptor value means nothing to @code{_AS__}.
|
|
|
|
@node Symbol Other, , Symbol Desc, Symbol Attributes
|
|
@subsubsection Other
|
|
This is an arbitrary 8-bit value. It means nothing to @code{_AS__}.
|
|
_fi__(_AOUT__||_BOUT__)
|
|
|
|
_if__(_COFF__)
|
|
@node COFF Symbols,,,
|
|
@subsection Symbol Attributes for 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
|
|
The symbol name is set with @code{.def}; the value and type,
|
|
respectively, with @code{.val} and @code{.type}.
|
|
|
|
@subsubsection Auxiliary Attributes
|
|
The @code{_AS__} directives @code{.dim}, @code{.line}, @code{.scl},
|
|
@code{.size}, and @code{.tag} can generate auxiliary symbol table
|
|
information for COFF.
|
|
_fi__(_COFF__)
|
|
|
|
@node Expressions, Pseudo Ops, Symbols, Top
|
|
@chapter Expressions
|
|
An @dfn{expression} specifies an address or numeric value.
|
|
Whitespace may precede and/or follow an expression.
|
|
|
|
@node Empty Exprs, Integer Exprs, Expressions, Expressions
|
|
@section Empty Expressions
|
|
An empty expression has no value: it is just whitespace or null.
|
|
Wherever an absolute expression is required, you may omit the
|
|
expression and @code{_AS__} will assume a value of (absolute) 0. This
|
|
is compatible with other assemblers.
|
|
|
|
@node Integer Exprs, , Empty Exprs, Expressions
|
|
@section Integer Expressions
|
|
An @dfn{integer expression} is one or more @emph{arguments} delimited
|
|
by @emph{operators}.
|
|
|
|
@node Arguments, Operators, Integer Exprs, Integer Exprs
|
|
@subsection Arguments
|
|
|
|
@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{segment} @var{NNN}@} where
|
|
@var{segment} 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.
|
|
|
|
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, Prefix Ops, Arguments, Integer Exprs
|
|
@subsection Operators
|
|
@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, Infix Ops, Operators, Integer Exprs
|
|
@subsection 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, , Prefix Ops, Integer Exprs
|
|
@subsection Infix Operators
|
|
|
|
@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
|
|
|
|
@item
|
|
Highest Precedence
|
|
@table @code
|
|
@item *
|
|
@dfn{Multiplication}.
|
|
@item /
|
|
@dfn{Division}. Truncation is the same as the C operator @samp{/}
|
|
@item %
|
|
@dfn{Remainder}.
|
|
@item _0__<_1__
|
|
@itemx _0__<<_1__
|
|
@dfn{Shift Left}. Same as the C operator @samp{_0__<<_1__}
|
|
@item _0__>_1__
|
|
@itemx _0__>>_1__
|
|
@dfn{Shift Right}. Same as the C operator @samp{_0__>>_1__}
|
|
@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 +
|
|
@dfn{Addition}. If either argument is absolute, the result
|
|
has the segment of the other argument.
|
|
If either argument is pass1 or undefined, the result is pass1.
|
|
Otherwise @code{+} is illegal.
|
|
@item -
|
|
@dfn{Subtraction}. If the right argument is absolute, the
|
|
result has the segment of the left argument.
|
|
If either argument is pass1 the result is pass1.
|
|
If either argument is undefined the result is difference segment.
|
|
If both arguments are in the same segment, the result is absolute---provided
|
|
that segment 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 segment in
|
|
one of the two arguments.
|
|
|
|
Similarly, you can't subtract quantities from two different segments.
|
|
|
|
@node Pseudo Ops, _MACH_DEP__, Expressions, Top
|
|
@chapter Assembler Directives
|
|
|
|
All assembler directives have names that begin with a period (@samp{.}).
|
|
The rest of the name is letters: their case does not matter.
|
|
|
|
This chapter discusses directives present regardless of the target
|
|
machine configuration for the GNU assembler; @pxref{_MACH_DEP__} for
|
|
additional directives.
|
|
|
|
@node Abort,,,
|
|
@section @code{.abort}
|
|
This directive stops the assembly immediately. It is for
|
|
compatibility with other assemblers. The original idea was that the
|
|
assembly language source would be piped into the assembler. If the sender
|
|
of the source quit, it could use this directive tells @code{_AS__} to
|
|
quit also. One day @code{.abort} will not be supported.
|
|
|
|
_if__(_COFF__)
|
|
@node coff-ABORT,,,
|
|
@section @code{.ABORT}
|
|
When producing COFF output, @code{_AS__} accepts this directive as a
|
|
synonym for @samp{.abort}.
|
|
_fi__(_COFF__)
|
|
_if__(_BOUT__)
|
|
_if__(!_COFF__)
|
|
@node bout-ABORT,,,
|
|
@section @code{.ABORT}
|
|
_fi__(!_COFF__)
|
|
|
|
When producing @code{b.out} output, @code{_AS__} accepts this directive,
|
|
but ignores it.
|
|
_fi__(_BOUT__)
|
|
|
|
@node Align,,,
|
|
@section @code{.align @var{abs-expr} , @var{abs-expr}}
|
|
Pad the location counter (in the current subsegment) 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}}
|
|
@code{.app-file}
|
|
_if__(!_AMD29K__)
|
|
(which may also be spelled @samp{.file})
|
|
_fi__(!_AMD29K__)
|
|
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{}
|
|
@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, Byte, Ascii, Pseudo Ops
|
|
@section @code{.asciz "@var{string}"}@dots{}
|
|
@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, Comm, Asciz, Pseudo Ops
|
|
@section @code{.byte @var{expressions}}
|
|
|
|
@code{.byte} expects zero or more expressions, separated by commas.
|
|
Each expression is assembled into the next byte.
|
|
|
|
@node Comm, Data, Byte, Pseudo Ops
|
|
@section @code{.comm @var{symbol} , @var{length} }
|
|
@code{.comm} declares a named common area in the bss segment. 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, Desc, Comm, Pseudo Ops
|
|
@section @code{.data @var{subsegment}}
|
|
@code{.data} tells @code{_AS__} to assemble the following statements onto the
|
|
end of the data subsegment numbered @var{subsegment} (which is an
|
|
absolute expression). If @var{subsegment} is omitted, it defaults
|
|
to zero.
|
|
|
|
_if__(_COFF__)
|
|
@node Def,,,
|
|
@section @code{.def @var{name}}
|
|
Begin defining debugging information for a symbol @var{name}; the
|
|
definition extends until the @code{.endef} directive is encountered.
|
|
_if__(_BOUT__)
|
|
|
|
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.
|
|
_fi__(_BOUT__)
|
|
_fi__(_COFF__)
|
|
|
|
_if__(_AOUT__||_BOUT__)
|
|
@node Desc, Double, Data, Pseudo Ops
|
|
@section @code{.desc @var{symbol}, @var{abs-expression}}
|
|
This directive sets the descriptor of the symbol (@pxref{Symbol Attributes})
|
|
to the low 16 bits of an absolute expression.
|
|
|
|
_if__(_COFF__)
|
|
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.
|
|
_fi__(_COFF__)
|
|
_fi__(_AOUT__||_BOUT__)
|
|
|
|
_if__(_COFF__)
|
|
@node Dim,,,
|
|
@section @code{.dim}
|
|
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.
|
|
_if__(_BOUT__)
|
|
|
|
@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.
|
|
_fi__(_BOUT__)
|
|
_fi__(_COFF__)
|
|
|
|
@node Double, Else, Desc, Pseudo Ops
|
|
@section @code{.double @var{flonums}}
|
|
@code{.double} expects zero or more flonums, separated by commas. It
|
|
assembles floating point numbers.
|
|
_if__(_ALL_ARCH__)
|
|
The exact kind of floating point numbers emitted depends on how
|
|
@code{_AS__} is configured. @xref{_MACH_DEP__}.
|
|
_fi__(_ALL_ARCH__)
|
|
_if__(_AMD29K__ || _I960__)
|
|
On the _HOST__ family @samp{.double} emits 64-bit floating-point numbers
|
|
in IEEE format.
|
|
_fi__(_AMD29K__ || _I960__)
|
|
|
|
@node Else,,,
|
|
@section @code{.else}
|
|
@code{.else} is part of the @code{_AS__} support for conditional assembly;
|
|
@pxref{If}. It marks the beginning of a section of code to be assembled
|
|
if the condition for the preceding @code{.if} was false.
|
|
|
|
_if__(0)
|
|
@node End,,,
|
|
@section @code{.end}
|
|
This doesn't do anything---but isn't an s_ignore, so I suspect it's
|
|
meant to do something eventually (which is why it isn't documented here
|
|
as "for compatibility with blah").
|
|
_fi__(0)
|
|
|
|
_if__(_COFF__)
|
|
@node Endef,,,
|
|
@section @code{.endef}
|
|
This directive flags the end of a symbol definition begun with
|
|
@code{.def}.
|
|
_if__(_BOUT__)
|
|
|
|
@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.
|
|
_fi__(_BOUT__)
|
|
_fi__(_COFF__)
|
|
|
|
@node Endif, Equ, End, Pseudo Ops
|
|
@section @code{.endif}
|
|
@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}.
|
|
|
|
@node Equ, Extern, Endif, Pseudo Ops
|
|
@section @code{.equ @var{symbol}, @var{expression}}
|
|
|
|
This directive sets the value of @var{symbol} to @var{expression}.
|
|
It is synonymous with @samp{.set}; @pxref{Set}.
|
|
|
|
@node Extern,,,
|
|
@section @code{.extern}
|
|
@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.
|
|
|
|
_if__(!_AMD29K__)
|
|
@node File,,,
|
|
@section @code{.app-file @var{string}}
|
|
@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.
|
|
_fi__(!_AMD29K__)
|
|
|
|
|
|
@node Fill,,,
|
|
@section @code{.fill @var{repeat} , @var{size} , @var{value}}
|
|
@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, Global, Fill, Pseudo Ops
|
|
@section @code{.float @var{flonums}}
|
|
This directive assembles zero or more flonums, separated by commas. It
|
|
has the same effect as @code{.single}.
|
|
_if__(_ALL_ARCH__)
|
|
The exact kind of floating point numbers emitted depends on how
|
|
@code{_AS__} is configured.
|
|
@xref{_MACH_DEP__}.
|
|
_fi__(_ALL_ARCH__)
|
|
_if__(_AMD29K__ || _I960__)
|
|
On the _HOST__ family, @code{.float} emits 32-bit floating point numbers
|
|
in IEEE format.
|
|
_fi__(_AMD29K__ || _I960__)
|
|
|
|
@node Global, Ident, Float, Pseudo Ops
|
|
@section @code{.global @var{symbol}}, @code{.globl @var{symbol}}
|
|
@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.
|
|
|
|
_if__(!_I960__)
|
|
@c FIXME BFD implications; this is different in COFF.
|
|
This is done by setting the @code{N_EXT} bit of that symbol's type byte
|
|
to 1. @xref{Symbol Attributes}.
|
|
_fi__(!_I960__)
|
|
|
|
Both spellings (@samp{.globl} and @samp{.global}) are accepted, for
|
|
compatibility with other assemblers.
|
|
|
|
@node hword, line, file, Machine Directives
|
|
@section @code{.hword @var{expressions}}
|
|
This expects zero or more @var{expressions}, and emits
|
|
a 16 bit number for each.
|
|
|
|
_if__(_ALL_ARCH__)
|
|
This directive is a synonym for @samp{.short}; depending on the target
|
|
architecture, it may also be a synonym for @samp{.word}.
|
|
_fi__(_ALL_ARCH__)
|
|
_if__( (_AMD29K__ || _I960__) && !_ALL_ARCH__ )
|
|
This directive is a synonym for @samp{.short}.
|
|
_fi__( (_AMD29K__ || _I960__) && !_ALL_ARCH__ )
|
|
|
|
_if__(_AOUT__||_BOUT__||_COFF__)
|
|
@node Ident, If, Global, Pseudo Ops
|
|
@section @code{.ident}
|
|
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.
|
|
_fi__(_AOUT__||_BOUT__||_COFF__)
|
|
|
|
@node If, Include, Ident, Pseudo Ops
|
|
@section @code{.if @var{absolute expression}}
|
|
@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}); optionally, you may include code for the
|
|
alternative condition, flagged by @code{.else} (@pxref{Else}.
|
|
|
|
The following variants of @code{.if} are also supported:
|
|
@table @code
|
|
@item ifdef @var{symbol}
|
|
Assembles the following section of code if the specified @var{symbol}
|
|
has been defined.
|
|
|
|
_if__(0)
|
|
@item ifeqs
|
|
Not yet implemented.
|
|
_fi__(0)
|
|
|
|
@item ifndef @var{symbol}
|
|
@itemx ifnotdef @var{symbol}
|
|
Assembles the following section of code if the specified @var{symbol}
|
|
has not been defined. Both spelling variants are equivalent.
|
|
|
|
_if__(0)
|
|
@item ifnes
|
|
Not yet implemented.
|
|
_fi__(0)
|
|
@end table
|
|
|
|
@node Include, Int, If, Pseudo Ops
|
|
@section @code{.include "@var{file}"}
|
|
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{Options}). Quotation marks are required around @var{file}.
|
|
|
|
@node Int, Lcomm, Include, Pseudo Ops
|
|
@section @code{.int @var{expressions}}
|
|
Expect zero or more @var{expressions}, of any segment, 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, Line, Int, Pseudo Ops
|
|
@section @code{.lcomm @var{symbol} , @var{length}}
|
|
Reserve @var{length} (an absolute expression) bytes for a local
|
|
common denoted by @var{symbol}. The segment and value of @var{symbol} are
|
|
those of the new local common. The addresses are allocated in the
|
|
bss segment, so at run-time the bytes will start off zeroed.
|
|
@var{Symbol} is not declared global (@pxref{Global}), so is normally
|
|
not visible to @code{_LD__}.
|
|
|
|
_if__(_AOUT__||_BOUT__||_COFF__)
|
|
_if__(!_AMD29K__)
|
|
@node Line,,,
|
|
@section @code{.line @var{line-number}}
|
|
_fi__(!_AMD29K__)
|
|
_if__(_AMD29K__)
|
|
@node Ln,,,
|
|
@section @code{.ln @var{line-number}}
|
|
_fi__(_AMD29K__)
|
|
_fi__(_AOUT__||_BOUT__||_COFF__)
|
|
_if__(_AOUT__||_BOUT__)
|
|
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
|
|
_if__(_AMD29K__)
|
|
@samp{@@})
|
|
_fi__(_AMD29K__)
|
|
_if__(!_AMD29K__)
|
|
@code{;})
|
|
_fi__(!_AMD29K__)
|
|
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
|
|
_fi__(_AOUT__||_BOUT__)
|
|
_if__(_COFF__)
|
|
|
|
Even though this is a directive associated with the @code{a.out} or
|
|
@code{b.out} object-code formats, @code{_AS__} will still recognize it
|
|
when producing COFF output, and will treat @samp{.line} as though it
|
|
were the COFF @samp{.ln} @emph{if} it is found outside a
|
|
@code{.def}/@code{.endef} pair.
|
|
|
|
Inside a @code{.def}, @samp{.line} is, instead, one of the directives
|
|
used by compilers to generate auxiliary symbol information for
|
|
debugging.
|
|
_fi__(_COFF__)
|
|
|
|
_if__(_AOUT__&&!_AMD29K__)
|
|
@node Ln,,,
|
|
@section @code{.ln @var{line-number}}
|
|
@samp{.ln} is a synonym for @samp{.line}.
|
|
_fi__(_AOUT__&&!_AMD29K__)
|
|
|
|
_if__(_COFF__&&!_AOUT__)
|
|
@node Ln,,,
|
|
@section @code{.ln @var{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 @code{;}) will be reported as on logical
|
|
line number @var{line-number} @minus{} 1.
|
|
_if__(_BOUT__)
|
|
|
|
This directive is accepted, but ignored, when @code{_AS__} is configured for
|
|
@code{b.out}; its effect is only associated with COFF output format.
|
|
_fi__(_BOUT__)
|
|
_fi__(_COFF__&&!_AOUT__)
|
|
|
|
@node List,,,
|
|
@section @code{.list} and related directives
|
|
@code{_AS__} ignores the directives @code{.list}, @code{.nolist},
|
|
@code{.eject}, @code{.lflags}, @code{.title}, @code{.sbttl}; however,
|
|
they're accepted for compatibility with assemblers that use them.
|
|
|
|
@node Long, Lsym, List, Pseudo Ops
|
|
@section @code{.long @var{expressions}}
|
|
@code{.long} is the same as @samp{.int}, @pxref{Int}.
|
|
|
|
@node Lsym, Octa, Long, Pseudo Ops
|
|
@section @code{.lsym @var{symbol}, @var{expression}}
|
|
@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{(segment of @var{expression})}
|
|
@var{value} = @var{expression}
|
|
@end smallexample
|
|
@noindent
|
|
The new symbol is not flagged as external.
|
|
|
|
@c FIXME: double size emitted for "octa" on i960, others? Or warn?
|
|
@node Octa, Org, Lsym, Pseudo Ops
|
|
@section @code{.octa @var{bignums}}
|
|
This directive expects zero or more bignums, separated by commas. For each
|
|
bignum, it emits a 16-byte integer.
|
|
|
|
The term ``octa'' comes from contexts in which a ``word'' is two bytes;
|
|
hence @emph{octa}-word for 16 bytes.
|
|
|
|
@node Org, Quad, Octa, Pseudo Ops
|
|
@section @code{.org @var{new-lc} , @var{fill}}
|
|
|
|
@code{.org} will advance the location counter of the current segment to
|
|
@var{new-lc}. @var{new-lc} is either an absolute expression or an
|
|
expression with the same segment as the current subsegment. That is,
|
|
you can't use @code{.org} to cross segments: if @var{new-lc} has the
|
|
wrong segment, the @code{.org} directive is ignored. To be compatible
|
|
with former assemblers, if the segment of @var{new-lc} is absolute,
|
|
@code{_AS__} will issue a warning, then pretend the segment of @var{new-lc}
|
|
is the same as the current subsegment.
|
|
|
|
@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 segment. 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 segment, not
|
|
to the start of the subsegment. This is compatible with other
|
|
people's assemblers.
|
|
|
|
When the location counter (of the current subsegment) 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 Quad, Set, Org, Pseudo Ops
|
|
@section @code{.quad @var{bignums}}
|
|
@code{.quad} expects zero or more bignums, separated by commas. For
|
|
each bignum, it emits
|
|
_if__(!_I960__)
|
|
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
|
|
|
|
The term ``quad'' comes from contexts in which a ``word'' is two bytes;
|
|
hence @emph{quad}-word for 8 bytes.
|
|
_fi__(!_I960__)
|
|
_if__(_I960__)
|
|
a 16-byte integer. If the bignum won't fit in 16 bytes, it prints a
|
|
warning message; and just takes the lowest order 16 bytes of the
|
|
bignum.@refill
|
|
_fi__(_I960__)
|
|
|
|
_if__(_COFF__)
|
|
@node Scl,,,
|
|
@section @code{.scl @var{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.
|
|
_if__(_BOUT__)
|
|
|
|
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.
|
|
_fi__(_BOUT__)
|
|
_fi__(_COFF__)
|
|
|
|
|
|
@node Set,,,
|
|
@section @code{.set @var{symbol}, @var{expression}}
|
|
|
|
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 segment 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, Single, Set, Pseudo Ops
|
|
@section @code{.short @var{expressions}}
|
|
_if__(! (_SPARC__ || _AMD29K__ || _I960__) )
|
|
@code{.short} is the same as @samp{.word}. @xref{Word}.
|
|
_fi__(! (_SPARC__ || _AMD29K__ || _I960__) )
|
|
_if__(_SPARC__ || _AMD29K__ || _I960__)
|
|
This expects zero or more @var{expressions}, and emits
|
|
a 16 bit number for each.
|
|
_fi__(_SPARC__ || _AMD29K__ || _I960__)
|
|
|
|
@node Single,,,
|
|
@section @code{.single @var{flonums}}
|
|
This directive assembles zero or more flonums, separated by commas. It
|
|
has the same effect as @code{.float}.
|
|
_if__(_ALL_ARCH__)
|
|
The exact kind of floating point numbers emitted depends on how
|
|
@code{_AS__} is configured. @xref{_MACH_DEP__}.
|
|
_fi__(_ALL_ARCH__)
|
|
_if__(_AMD29K__ || _I960__)
|
|
On the _HOST__ family, @code{.single} emits 32-bit floating point
|
|
numbers in IEEE format.
|
|
_fi__(_AMD29K__ || _I960__)
|
|
|
|
_if__(_COFF__)
|
|
@node Size,,,
|
|
@section @code{.size}
|
|
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.
|
|
_if__(_BOUT__)
|
|
|
|
@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.
|
|
_fi__(_BOUT__)
|
|
_fi__(_COFF__)
|
|
|
|
@node Space,,,
|
|
_if__(!_AMD29K__)
|
|
@section @code{.space @var{size} , @var{fill}}
|
|
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.
|
|
_fi__(!_AMD29K__)
|
|
|
|
_if__(_AMD29K__)
|
|
@section @code{.space}
|
|
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 Directives}.
|
|
@end quotation
|
|
_fi__(_AMD29K__)
|
|
|
|
_if__(_AOUT__||_BOUT__||_COFF__)
|
|
@node Stab, Text, Space, Pseudo Ops
|
|
@section @code{.stabd, .stabn, .stabs}
|
|
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
|
|
@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}
|
|
|
|
The name of the symbol is set to the empty string @code{""}.
|
|
|
|
@item .stabs @var{string} , @var{type} , @var{other} , @var{desc} , @var{value}
|
|
|
|
All five fields are specified.
|
|
@end table
|
|
_fi__(_AOUT__||_BOUT__||_COFF__)
|
|
|
|
_if__(_COFF__)
|
|
@node Tag,,,
|
|
@section @code{.tag @var{structname}}
|
|
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.
|
|
_if__(_BOUT__)
|
|
|
|
@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.
|
|
_fi__(_BOUT__)
|
|
_fi__(_COFF__)
|
|
|
|
@node Text,,,
|
|
@section @code{.text @var{subsegment}}
|
|
Tells @code{_AS__} to assemble the following statements onto the end of
|
|
the text subsegment numbered @var{subsegment}, which is an absolute
|
|
expression. If @var{subsegment} is omitted, subsegment number zero
|
|
is used.
|
|
|
|
_if__(_COFF__)
|
|
@node Type,,,
|
|
@section @code{.type @var{int}}
|
|
This directive, permitted only within @code{.def}/@code{.endef} pairs,
|
|
records the integer @var{int} as the type attribute of a symbol table entry.
|
|
_if__(_BOUT__)
|
|
|
|
@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.
|
|
_fi__(_BOUT__)
|
|
_fi__(_COFF__)
|
|
|
|
_if__(_COFF__)
|
|
@node Val,,,
|
|
@section @code{.val @var{addr}}
|
|
This directive, permitted only within @code{.def}/@code{.endef} pairs,
|
|
records the address @var{addr} as the value attribute of a symbol table
|
|
entry.
|
|
_if__(_BOUT__)
|
|
|
|
@samp{.val} is used only for COFF output; when @code{_AS__} is
|
|
configured for @code{b.out}, it accepts this directive but ignores it.
|
|
_fi__(_BOUT__)
|
|
_fi__(_COFF__)
|
|
|
|
@node Word,,,
|
|
@section @code{.word @var{expressions}}
|
|
This directive expects zero or more @var{expressions}, of any segment,
|
|
separated by commas.
|
|
_if__(_SPARC__ || _AMD29K__ || _I960__)
|
|
For each expression, @code{_AS__} emits a 32-bit number.
|
|
_fi__(_SPARC__ || _AMD29K__ || _I960__)
|
|
_if__(! (_SPARC__ || _AMD29K__ || _I960__) )
|
|
For each expression, @code{_AS__} emits a 16-bit number.
|
|
_fi__(! (_SPARC__ || _AMD29K__ || _I960__) )
|
|
|
|
_if__(_ALL_ARCH__)
|
|
The byte order of the expression depends on what kind of computer will
|
|
run the program.
|
|
_fi__(_ALL_ARCH__)
|
|
|
|
@c on these boxes the "special treatment to support compilers" doesn't
|
|
@c happen---32-bit addressability, period; no long/short jumps.
|
|
_if__(! (_AMD29K__ || _I960__) )
|
|
@subsection Special Treatment to support Compilers
|
|
|
|
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 @var{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.
|
|
|
|
_if__(_INTERNALS__)
|
|
@emph{This feature may be disabled by compiling @code{_AS__} with the
|
|
@samp{-DWORKING_DOT_WORD} option.} This feature is likely to confuse
|
|
assembly language programmers.
|
|
_fi__(_INTERNALS__)
|
|
_fi__(! (_AMD29K__ || _I960__) )
|
|
|
|
@node Deprecated, _MACH_DEP__, Word, Pseudo Ops
|
|
@section Deprecated 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 _MACH_DEP__,,,
|
|
_if__(_ALL_ARCH__)
|
|
@chapter Machine Dependent Features
|
|
_fi__(_ALL_ARCH__)
|
|
_if__(_VAX__)
|
|
@group
|
|
_CHAPSEC__(0+_ALL_ARCH__) VAX Dependent Features
|
|
_CHAPSEC__(1+_ALL_ARCH__) Options
|
|
|
|
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.
|
|
@end group
|
|
|
|
@table @asis
|
|
@item @kbd{-D} (Debug)
|
|
@itemx @kbd{-S} (Symbol Table)
|
|
@itemx @kbd{-T} (Token Trace)
|
|
These are obsolete options used to debug old assemblers.
|
|
|
|
@item @kbd{-d} (Displacement size for JUMPs)
|
|
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)
|
|
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)
|
|
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)
|
|
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
|
|
|
|
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".
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Floating Point
|
|
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.
|
|
|
|
The @code{.float} directive produces @code{f} format numbers.
|
|
The @code{.double} directive produces @code{d} format numbers.
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Machine Directives
|
|
The Vax version of the assembler supports four directives for
|
|
generating Vax floating point constants. They are described in the
|
|
table below.
|
|
|
|
@table @code
|
|
@item .dfloat
|
|
This expects zero or more flonums, separated by commas, and
|
|
assembles Vax @code{d} format 64-bit floating point constants.
|
|
|
|
@item .ffloat
|
|
This expects zero or more flonums, separated by commas, and
|
|
assembles Vax @code{f} format 32-bit floating point constants.
|
|
|
|
@item .gfloat
|
|
This expects zero or more flonums, separated by commas, and
|
|
assembles Vax @code{g} format 64-bit floating point constants.
|
|
|
|
@item .hfloat
|
|
This expects zero or more flonums, separated by commas, and
|
|
assembles Vax @code{h} format 128-bit floating point constants.
|
|
|
|
@end table
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Opcodes
|
|
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.
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Branch Improvement
|
|
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 nequ eql eqlu gtr geq lss gtru lequ vc vs gequ cc lssu cs}.
|
|
@var{COND} may also be one of the bit tests
|
|
@code{bs bc bss bcs bsc bcc bssi bcci lbs 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{UNCOND} foo ; brw @dots{} ; foo:}
|
|
@item (long displacement)
|
|
@kbd{b@var{UNCOND} 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)
|
|
@kbd{@var{OPCODE} @dots{}, foo ; brb bar ; foo: jmp @dots{} ; bar:}
|
|
@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)
|
|
@kbd{@var{OPCODE} @dots{}, foo ; brb bar ; foo: brw @var{destination} ; bar:}
|
|
@item (long displacement)
|
|
@kbd{@var{OPCODE} @dots{}, foo ; brb bar ; foo: jmp @var{destination} ; bar: }
|
|
@end table
|
|
@item aobleq
|
|
@itemx aoblss
|
|
@itemx sobgeq
|
|
@itemx sobgtr
|
|
@table @asis
|
|
@item (byte displacement)
|
|
@kbd{@var{OPCODE} @dots{}}
|
|
@item (word displacement)
|
|
@kbd{@var{OPCODE} @dots{}, foo ; brb bar ; foo: brw @var{destination} ; bar:}
|
|
@item (long displacement)
|
|
@kbd{@var{OPCODE} @dots{}, foo ; brb bar ; foo: jmp @var{destination} ; bar:}
|
|
@end table
|
|
@end table
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) operands
|
|
The immediate character is @samp{$} for Unix compatibility, not
|
|
@samp{#} as DEC writes it.
|
|
|
|
The indirect character is @samp{*} for Unix compatibility, not
|
|
@samp{@@} as DEC writes it.
|
|
|
|
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.
|
|
|
|
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.
|
|
_CHAPSEC__(1+_ALL_ARCH__) Not Supported
|
|
Vax bit fields can not be assembled with @code{_AS__}. Someone
|
|
can add the required code if they really need it.
|
|
_fi__(_VAX__)
|
|
_if__(_AMD29K__)
|
|
@group
|
|
_CHAPSEC__(0+_ALL_ARCH__) AMD 29K Dependent Features
|
|
@node AMD29K Options, AMD29K Syntax, _MACH_DEP__, _MACH_DEP__
|
|
_CHAPSEC__(1+_ALL_ARCH__) Options
|
|
@code{_AS__} has no additional command-line options for the AMD
|
|
29K family.
|
|
@end group
|
|
|
|
@node AMD29K Syntax, AMD29K Floating Point, AMD29K Options, _MACH_DEP__
|
|
@group
|
|
_CHAPSEC__(1+_ALL_ARCH__) Syntax
|
|
_CHAPSEC__(2+_ALL_ARCH__) Special Characters
|
|
@samp{;} is the line comment character.
|
|
|
|
@samp{@@} can be used instead of a newline to separate statements.
|
|
|
|
The character @samp{?} is permitted in identifiers (but may not begin
|
|
an identifier).
|
|
@end group
|
|
|
|
_CHAPSEC__(2+_ALL_ARCH__) Register Names
|
|
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.
|
|
|
|
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, AMD29K Directives, AMD29K Syntax, _MACH_DEP__
|
|
_CHAPSEC__(1+_ALL_ARCH__) Floating Point
|
|
The AMD 29K family uses IEEE floating-point numbers.
|
|
|
|
@group
|
|
@node AMD29K Directives, AMD29K Opcodes, AMD29K Floating Point, _MACH_DEP__
|
|
_CHAPSEC__(1+_ALL_ARCH__) Machine Directives
|
|
|
|
@node block, cputype, AMD29K Directives, AMD29K Directives
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.block @var{size} , @var{fill}}
|
|
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 group
|
|
|
|
@node cputype, file, block, Machine Directives
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.cputype}
|
|
This directive is ignored; it is accepted for compatibility with other
|
|
AMD 29K assemblers.
|
|
|
|
@node file, hword, cputype, Machine Directives
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.file}
|
|
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
|
|
|
|
@node line, reg, hword, Machine Directives
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.line}
|
|
This directive is ignored; it is accepted for compatibility with other
|
|
AMD 29K assemblers.
|
|
|
|
@node reg, sect, line, Machine Directives
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.reg @var{symbol}, @var{expression}}
|
|
@code{.reg} has the same effect as @code{.lsym}; @pxref{Lsym}.
|
|
|
|
@node sect, use, reg, Machine Directives
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.sect}
|
|
This directive is ignored; it is accepted for compatibility with other
|
|
AMD 29K assemblers.
|
|
|
|
@node use, , sect, Machine Directives
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.use @var{segment name}}
|
|
Establishes the segment and subsegment for the following code;
|
|
@var{segment name} may be one of @code{.text}, @code{.data},
|
|
@code{.data1}, or @code{.lit}. With one of the first three @var{segment
|
|
name} options, @samp{.use} is equivalent to the machine directive
|
|
@var{segment name}; the remaining case, @samp{.use .lit}, is the same as
|
|
@samp{.data 200}.
|
|
|
|
|
|
@node AMD29K Opcodes, , AMD29K Directives, _MACH_DEP__
|
|
@section Opcodes
|
|
@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.
|
|
|
|
_fi__(_AMD29K__)
|
|
_if__(_I960__)
|
|
_CHAPSEC__(0+_ALL_ARCH__) Intel 80960 Dependent Features
|
|
@node Options-i960,,,
|
|
_CHAPSEC__(1+_ALL_ARCH__) Command-line Options
|
|
@table @code
|
|
|
|
@item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
|
|
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
|
|
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.
|
|
|
|
A table of all such @code{Label}s is also generated, so that the
|
|
external postprocessor @samp{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.
|
|
|
|
@ifinfo
|
|
@example
|
|
+------------+------------+------------+ ... +------------+
|
|
| | | | | |
|
|
| *NEXT | COUNT: N | *BRLAB 1 | | *BRLAB N |
|
|
| | | | | |
|
|
+------------+------------+------------+ ... +------------+
|
|
|
|
__BRANCH_TABLE__ layout
|
|
@end example
|
|
@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
|
|
|
|
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
|
|
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,,,
|
|
_CHAPSEC__(1+_ALL_ARCH__) Floating Point
|
|
@code{_AS__} generates IEEE floating-point numbers for the directives
|
|
@samp{.float}, @samp{.double}, @samp{extended}, and @samp{.single}.
|
|
|
|
@group
|
|
@node Directives-i960,,,
|
|
_CHAPSEC__(1+_ALL_ARCH__) Machine Directives
|
|
|
|
@node bss-i960,,,
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.bss @var{symbol}, @var{length}, @var{align}}
|
|
Reserve @var{length} bytes in the bss segment 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}.
|
|
@end group
|
|
|
|
@node extended-i960,,,
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.extended @var{flonums}}
|
|
@code{.extended} expects zero or more flonums, separated by commas; for
|
|
each flonum, @samp{.extended} emits an IEEE extended-format (80-bit)
|
|
floating-point number.
|
|
|
|
@node leafproc-i960,,,
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.leafproc @var{call-lab}, @var{bal-lab}}
|
|
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.
|
|
|
|
@node sysproc-i960,,,
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{.sysproc @var{name}, @var{index}}
|
|
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).
|
|
|
|
@node Opcodes for i960,,,
|
|
_CHAPSEC__(1+_ALL_ARCH__) i960 Opcodes
|
|
All Intel 960 machine instructions are supported; @pxref{Options-i960}
|
|
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.
|
|
|
|
@node callj-i960
|
|
_CHAPSEC__(2+_ALL_ARCH__) @code{callj}
|
|
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
|
|
_CHAPSEC__(2+_ALL_ARCH__) Compare-and-Branch
|
|
|
|
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.
|
|
|
|
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:
|
|
|
|
@ifinfo
|
|
@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
|
|
@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
|
|
|
|
_fi__(_I960__)
|
|
_if__(_M680X0__)
|
|
@group
|
|
_CHAPSEC__(0+_ALL_ARCH__) M680x0 Dependent Features
|
|
_CHAPSEC__(1+_ALL_ARCH__) 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.
|
|
@end group
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Syntax
|
|
|
|
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}.
|
|
|
|
_if__(_INTERNALS__)
|
|
If @code{_AS__} is compiled with SUN_ASM_SYNTAX defined, it will also allow
|
|
Sun-style local labels of the form @samp{1$} through @samp{$9}.
|
|
_fi__(_INTERNALS__)
|
|
|
|
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}).
|
|
|
|
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
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Floating Point
|
|
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
|
|
@code{Single} precision floating point constants.
|
|
@item .double
|
|
@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.
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Machine Directives
|
|
In order to be compatible with the Sun assembler the 680x0 assembler
|
|
understands the following directives.
|
|
@table @code
|
|
@item .data1
|
|
This directive is identical to a @code{.data 1} directive.
|
|
@item .data2
|
|
This directive is identical to a @code{.data 2} directive.
|
|
@item .even
|
|
This directive is identical to a @code{.align 1} directive.
|
|
@c Is this true? does it work???
|
|
@item .skip
|
|
This directive is identical to a @code{.space} directive.
|
|
@end table
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Opcodes
|
|
@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
|
|
|
|
_CHAPSEC__(2+_ALL_ARCH__) 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}:
|
|
@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
|
|
|
|
_CHAPSEC__(2+_ALL_ARCH__) Special Characters
|
|
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.
|
|
_fi__(_M680X0__)
|
|
@c pesch@cygnus.com: conditionalize on something other than 0 when filled in.
|
|
_if__(0)
|
|
@section 32x32
|
|
@section Options
|
|
The 32x32 version of @code{_AS__} accepts a @kbd{-m32032} option to
|
|
specify thiat it is compiling for a 32032 processor, or a
|
|
@kbd{-m32532} to specify that it is compiling for a 32532 option.
|
|
The default (if neither is specified) is chosen when the assembler
|
|
is compiled.
|
|
|
|
@subsection Syntax
|
|
I don't know anything about the 32x32 syntax assembled by
|
|
@code{_AS__}. Someone who undersands the processor (I've never seen
|
|
one) and the possible syntaxes should write this section.
|
|
|
|
@subsection Floating Point
|
|
The 32x32 uses IEEE floating point numbers, but @code{_AS__} will only
|
|
create single or double precision values. I don't know if the 32x32
|
|
understands extended precision numbers.
|
|
|
|
@subsection Machine Directives
|
|
The 32x32 has no machine dependent directives.
|
|
_fi__(0)
|
|
_if__(_SPARC__)
|
|
@c fixme (sparc): Fill in "syntax" section!
|
|
_CHAPSEC__(0+_ALL_ARCH__) SPARC Dependent Features
|
|
@section Sparc
|
|
@subsection Options
|
|
The sparc has no machine dependent options.
|
|
|
|
@subsection syntax
|
|
I don't know anything about Sparc syntax. Someone who does
|
|
will have to write this section.
|
|
|
|
@subsection Floating Point
|
|
The Sparc uses ieee floating-point numbers.
|
|
|
|
@subsection Machine Directives
|
|
The Sparc version of @code{_AS__} supports the following additional
|
|
machine directives:
|
|
|
|
@table @code
|
|
@item .common
|
|
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 .global
|
|
This is functionally identical to @code{.globl}.
|
|
|
|
@item .half
|
|
This is functionally identical to @code{.short}.
|
|
|
|
@item .proc
|
|
This directive is ignored. Any text following it on the same
|
|
line is also ignored.
|
|
|
|
@item .reserve
|
|
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
|
|
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
|
|
This is functionally identical to the .space directive.
|
|
|
|
@item .word
|
|
On the Sparc, the .word directive produces 32 bit values,
|
|
instead of the 16 bit values it produces on every other machine.
|
|
|
|
@end table
|
|
_fi__(_SPARC__)
|
|
_if__(_I80386__)
|
|
_CHAPSEC__(0+_ALL_ARCH__) 80386 Dependent Features
|
|
_CHAPSEC__(1+_ALL_ARCH__) Options
|
|
The 80386 has no machine dependent options.
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) AT&T Syntax versus Intel Syntax
|
|
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
|
|
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
|
|
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
|
|
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
|
|
Immediate form long jumps and calls are
|
|
@samp{lcall/ljmp $@var{segment}, $@var{offset}} in AT&T syntax; the
|
|
Intel syntax is
|
|
@samp{call/jmp far @var{segment}:@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
|
|
The AT&T assembler does not provide support for multiple segment
|
|
programs. Unix style systems expect all programs to be single segments.
|
|
@end itemize
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Opcode Naming
|
|
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).
|
|
|
|
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
|
|
are called @samp{cbtw}, @samp{cwtl}, @samp{cwtd}, and @samp{cltd} in
|
|
AT&T naming. @code{_AS__} accepts either naming for these instructions.
|
|
|
|
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.
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Register Naming
|
|
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 segment registers @samp{%cs} (code segment), @samp{%ds}
|
|
(data segment), @samp{%ss} (stack segment), @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
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Opcode Prefixes
|
|
Opcode prefixes are used to modify the following opcode. They are used
|
|
to repeat string instructions, to provide segment 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
|
|
Segment override prefixes @samp{cs}, @samp{ds}, @samp{ss}, @samp{es},
|
|
@samp{fs}, @samp{gs}. These are automatically added by specifying
|
|
using the @var{segment}:@var{memory-operand} form for memory references.
|
|
|
|
@item
|
|
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
|
|
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
|
|
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
|
|
The @samp{rep}, @samp{repe}, and @samp{repne} prefixes are added
|
|
to string instructions to make them repeat @samp{%ecx} times.
|
|
@end itemize
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Memory References
|
|
An Intel syntax indirect memory reference of the form
|
|
@smallexample
|
|
@var{segment}:[@var{base} + @var{index}*@var{scale} + @var{disp}]
|
|
@end smallexample
|
|
is translated into the AT&T syntax
|
|
@smallexample
|
|
@var{segment}:@var{disp}(@var{base}, @var{index}, @var{scale})
|
|
@end smallexample
|
|
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{segment} specifies the
|
|
optional segment register for the memory operand, and may override the
|
|
default segment register (see a 80386 manual for segment register
|
|
defaults). Note that segment overrides in AT&T syntax @emph{must} have
|
|
be preceded by a @samp{%}. If you specify a segment override which
|
|
coincides with the default segment register, @code{_AS__} will @emph{not}
|
|
output any segment register override prefixes to assemble the given
|
|
instruction. Thus, segment overrides can be specified to emphasize which
|
|
segment 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{segment} is
|
|
missing, and the default segment 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 segment 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 segment
|
|
register @var{segment} 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).
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Handling of Jump Instructions
|
|
Jump instructions are always optimized to use the smallest possible
|
|
displacements. This is accomplished by using byte (8-bit) displacement
|
|
jumps whenever the target is sufficiently close. If a byte displacement
|
|
is insufficient a long (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
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Floating Point
|
|
All 80387 floating point types except packed BCD are supported.
|
|
(BCD support may be added without much difficulty). These data
|
|
types are 16-, 32-, and 64- bit integers, and single (32-bit),
|
|
double (64-bit), and extended (80-bit) precision floating point.
|
|
Each supported type has an 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
|
|
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
|
|
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)}.
|
|
|
|
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.
|
|
|
|
_CHAPSEC__(1+_ALL_ARCH__) Notes
|
|
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}.
|
|
_fi__(_I80386__)
|
|
_if__(0)
|
|
@c pesch@cygnus.com: we ignore the following chapters, since internals are
|
|
@c changing rapidly. These may need to be moved to another
|
|
@c book anyhow, if we adopt the model of user/modifier
|
|
@c books.
|
|
@node Maintenance, Retargeting, _MACH_DEP__, Top
|
|
@chapter Maintaining the Assembler
|
|
[[this chapter is still being built]]
|
|
|
|
@section Design
|
|
We had these goals, in descending priority:
|
|
@table @b
|
|
@item Accuracy.
|
|
For every program composed by a compiler, @code{_AS__} should emit
|
|
``correct'' code. This leaves some latitude in choosing addressing
|
|
modes, order of @code{relocation_info} structures in the object
|
|
file, @emph{etc}.
|
|
|
|
@item Speed, for usual case.
|
|
By far the most common use of @code{_AS__} will be assembling compiler
|
|
emissions.
|
|
|
|
@item Upward compatibility for existing assembler code.
|
|
Well @dots{} we don't support Vax bit fields but everything else
|
|
seems to be upward compatible.
|
|
|
|
@item Readability.
|
|
The code should be maintainable with few surprises. (JF: ha!)
|
|
|
|
@end table
|
|
|
|
We assumed that disk I/O was slow and expensive while memory was
|
|
fast and access to memory was cheap. We expect the in-memory data
|
|
structures to be less than 10 times the size of the emitted object
|
|
file. (Contrast this with the C compiler where in-memory structures
|
|
might be 100 times object file size!)
|
|
This suggests:
|
|
@itemize @bullet
|
|
@item
|
|
Try to read the source file from disk only one time. For other
|
|
reasons, we keep large chunks of the source file in memory during
|
|
assembly so this is not a problem. Also the assembly algorithm
|
|
should only scan the source text once if the compiler composed the
|
|
text according to a few simple rules.
|
|
@item
|
|
Emit the object code bytes only once. Don't store values and then
|
|
backpatch later.
|
|
@item
|
|
Build the object file in memory and do direct writes to disk of
|
|
large buffers.
|
|
@end itemize
|
|
|
|
RMS suggested a one-pass algorithm which seems to work well. By not
|
|
parsing text during a second pass considerable time is saved on
|
|
large programs (@emph{e.g.} the sort of C program @code{yacc} would
|
|
emit).
|
|
|
|
It happened that the data structures needed to emit relocation
|
|
information to the object file were neatly subsumed into the data
|
|
structures that do backpatching of addresses after pass 1.
|
|
|
|
Many of the functions began life as re-usable modules, loosely
|
|
connected. RMS changed this to gain speed. For example, input
|
|
parsing routines which used to work on pre-sanitized strings now
|
|
must parse raw data. Hence they have to import knowledge of the
|
|
assemblers' comment conventions @emph{etc}.
|
|
|
|
@section Deprecated Feature(?)s
|
|
We have stopped supporting some features:
|
|
@itemize @bullet
|
|
@item
|
|
@code{.org} statements must have @b{defined} expressions.
|
|
@item
|
|
Vax Bit fields (@kbd{:} operator) are entirely unsupported.
|
|
@end itemize
|
|
|
|
It might be a good idea to not support these features in a future release:
|
|
@itemize @bullet
|
|
@item
|
|
@kbd{#} should begin a comment, even in column 1.
|
|
@item
|
|
Why support the logical line & file concept any more?
|
|
@item
|
|
Subsegments are a good candidate for flushing.
|
|
Depends on which compilers need them I guess.
|
|
@end itemize
|
|
|
|
@section Bugs, Ideas, Further Work
|
|
Clearly the major improvement is DON'T USE A TEXT-READING
|
|
ASSEMBLER for the back end of a compiler. It is much faster to
|
|
interpret binary gobbledygook from a compiler's tables than to
|
|
ask the compiler to write out human-readable code just so the
|
|
assembler can parse it back to binary.
|
|
|
|
Assuming you use @code{_AS__} for human written programs: here are
|
|
some ideas:
|
|
@itemize @bullet
|
|
@item
|
|
Document (here) @code{APP}.
|
|
@item
|
|
Take advantage of knowing no spaces except after opcode
|
|
to speed up @code{_AS__}. (Modify @code{app.c} to flush useless spaces:
|
|
only keep space/tabs at begin of line or between 2
|
|
symbols.)
|
|
@item
|
|
Put pointers in this documentation to @file{a.out} documentation.
|
|
@item
|
|
Split the assembler into parts so it can gobble direct binary
|
|
from @emph{e.g.} @code{cc}. It is silly for@code{cc} to compose text
|
|
just so @code{_AS__} can parse it back to binary.
|
|
@item
|
|
Rewrite hash functions: I want a more modular, faster library.
|
|
@item
|
|
Clean up LOTS of code.
|
|
@item
|
|
Include all the non-@file{.c} files in the maintenance chapter.
|
|
@item
|
|
Document flonums.
|
|
@item
|
|
Implement flonum short literals.
|
|
@item
|
|
Change all talk of expression operands to expression quantities,
|
|
or perhaps to expression arguments.
|
|
@item
|
|
Implement pass 2.
|
|
@item
|
|
Whenever a @code{.text} or @code{.data} statement is seen, we close
|
|
of the current frag with an imaginary @code{.fill 0}. This is
|
|
because we only have one obstack for frags, and we can't grow new
|
|
frags for a new subsegment, then go back to the old subsegment and
|
|
append bytes to the old frag. All this nonsense goes away if we
|
|
give each subsegment its own obstack. It makes code simpler in
|
|
about 10 places, but nobody has bothered to do it because C compiler
|
|
output rarely changes subsegments (compared to ending frags with
|
|
relaxable addresses, which is common).
|
|
@end itemize
|
|
|
|
@section Sources
|
|
@c The following files in the @file{_AS__} directory
|
|
@c are symbolic links to other files, of
|
|
@c the same name, in a different directory.
|
|
@c @itemize @bullet
|
|
@c @item
|
|
@c @file{atof_generic.c}
|
|
@c @item
|
|
@c @file{atof_vax.c}
|
|
@c @item
|
|
@c @file{flonum_const.c}
|
|
@c @item
|
|
@c @file{flonum_copy.c}
|
|
@c @item
|
|
@c @file{flonum_get.c}
|
|
@c @item
|
|
@c @file{flonum_multip.c}
|
|
@c @item
|
|
@c @file{flonum_normal.c}
|
|
@c @item
|
|
@c @file{flonum_print.c}
|
|
@c @end itemize
|
|
|
|
Here is a list of the source files in the @file{_AS__} directory.
|
|
|
|
@table @file
|
|
@item app.c
|
|
This contains the pre-processing phase, which deletes comments,
|
|
handles whitespace, etc. This was recently re-written, since app
|
|
used to be a separate program, but RMS wanted it to be inline.
|
|
|
|
@item append.c
|
|
This is a subroutine to append a string to another string returning a
|
|
pointer just after the last @code{char} appended. (JF: All these
|
|
little routines should probably all be put in one file.)
|
|
|
|
@item as.c
|
|
Here you will find the main program of the assembler @code{_AS__}.
|
|
|
|
@item expr.c
|
|
This is a branch office of @file{read.c}. This understands
|
|
expressions, arguments. Inside @code{_AS__}, arguments are called
|
|
(expression) @emph{operands}. This is confusing, because we also talk
|
|
(elsewhere) about instruction @emph{operands}. Also, expression
|
|
operands are called @emph{quantities} explicitly to avoid confusion
|
|
with instruction operands. What a mess.
|
|
|
|
@item frags.c
|
|
This implements the @b{frag} concept. Without frags, finding the
|
|
right size for branch instructions would be a lot harder.
|
|
|
|
@item hash.c
|
|
This contains the symbol table, opcode table @emph{etc.} hashing
|
|
functions.
|
|
|
|
@item hex_value.c
|
|
This is a table of values of digits, for use in atoi() type
|
|
functions. Could probably be flushed by using calls to strtol(), or
|
|
something similar.
|
|
|
|
@item input-file.c
|
|
This contains Operating system dependent source file reading
|
|
routines. Since error messages often say where we are in reading
|
|
the source file, they live here too. Since @code{_AS__} is intended to
|
|
run under GNU and Unix only, this might be worth flushing. Anyway,
|
|
almost all C compilers support stdio.
|
|
|
|
@item input-scrub.c
|
|
This deals with calling the pre-processor (if needed) and feeding the
|
|
chunks back to the rest of the assembler the right way.
|
|
|
|
@item messages.c
|
|
This contains operating system independent parts of fatal and
|
|
warning message reporting. See @file{append.c} above.
|
|
|
|
@item output-file.c
|
|
This contains operating system dependent functions that write an
|
|
object file for @code{_AS__}. See @file{input-file.c} above.
|
|
|
|
@item read.c
|
|
This implements all the directives of @code{_AS__}. This also deals
|
|
with passing input lines to the machine dependent part of the
|
|
assembler.
|
|
|
|
@item strstr.c
|
|
This is a C library function that isn't in most C libraries yet.
|
|
See @file{append.c} above.
|
|
|
|
@item subsegs.c
|
|
This implements subsegments.
|
|
|
|
@item symbols.c
|
|
This implements symbols.
|
|
|
|
@item write.c
|
|
This contains the code to perform relaxation, and to write out
|
|
the object file. It is mostly operating system independent, but
|
|
different OSes have different object file formats in any case.
|
|
|
|
@item xmalloc.c
|
|
This implements @code{malloc()} or bust. See @file{append.c} above.
|
|
|
|
@item xrealloc.c
|
|
This implements @code{realloc()} or bust. See @file{append.c} above.
|
|
|
|
@item atof-generic.c
|
|
The following files were taken from a machine-independent subroutine
|
|
library for manipulating floating point numbers and very large
|
|
integers.
|
|
|
|
@file{atof-generic.c} turns a string into a flonum internal format
|
|
floating-point number.
|
|
|
|
@item flonum-const.c
|
|
This contains some potentially useful floating point numbers in
|
|
flonum format.
|
|
|
|
@item flonum-copy.c
|
|
This copies a flonum.
|
|
|
|
@item flonum-multip.c
|
|
This multiplies two flonums together.
|
|
|
|
@item bignum-copy.c
|
|
This copies a bignum.
|
|
|
|
@end table
|
|
|
|
Here is a table of all the machine-specific files (this includes
|
|
both source and header files). Typically, there is a
|
|
@var{machine}.c file, a @var{machine}-opcode.h file, and an
|
|
atof-@var{machine}.c file. The @var{machine}-opcode.h file should
|
|
be identical to the one used by GDB (which uses it for disassembly.)
|
|
|
|
@table @file
|
|
|
|
@item atof-ieee.c
|
|
This contains code to turn a flonum into a ieee literal constant.
|
|
This is used by tye 680x0, 32x32, sparc, and i386 versions of @code{_AS__}.
|
|
|
|
@item i386-opcode.h
|
|
This is the opcode-table for the i386 version of the assembler.
|
|
|
|
@item i386.c
|
|
This contains all the code for the i386 version of the assembler.
|
|
|
|
@item i386.h
|
|
This defines constants and macros used by the i386 version of the assembler.
|
|
|
|
@item m-generic.h
|
|
generic 68020 header file. To be linked to m68k.h on a
|
|
non-sun3, non-hpux system.
|
|
|
|
@item m-sun2.h
|
|
68010 header file for Sun2 workstations. Not well tested. To be linked
|
|
to m68k.h on a sun2. (See also @samp{-DSUN_ASM_SYNTAX} in the
|
|
@file{Makefile}.)
|
|
|
|
@item m-sun3.h
|
|
68020 header file for Sun3 workstations. To be linked to m68k.h before
|
|
compiling on a Sun3 system. (See also @samp{-DSUN_ASM_SYNTAX} in the
|
|
@file{Makefile}.)
|
|
|
|
@item m-hpux.h
|
|
68020 header file for a HPUX (system 5?) box. Which box, which
|
|
version of HPUX, etc? I don't know.
|
|
|
|
@item m68k.h
|
|
A hard- or symbolic- link to one of @file{m-generic.h},
|
|
@file{m-hpux.h} or @file{m-sun3.h} depending on which kind of
|
|
680x0 you are assembling for. (See also @samp{-DSUN_ASM_SYNTAX} in the
|
|
@file{Makefile}.)
|
|
|
|
@item m68k-opcode.h
|
|
Opcode table for 68020. This is now a link to the opcode table
|
|
in the @code{GDB} source directory.
|
|
|
|
@item m68k.c
|
|
All the mc680x0 code, in one huge, slow-to-compile file.
|
|
|
|
@item ns32k.c
|
|
This contains the code for the ns32032/ns32532 version of the
|
|
assembler.
|
|
|
|
@item ns32k-opcode.h
|
|
This contains the opcode table for the ns32032/ns32532 version
|
|
of the assembler.
|
|
|
|
@item vax-inst.h
|
|
Vax specific file for describing Vax operands and other Vax-ish things.
|
|
|
|
@item vax-opcode.h
|
|
Vax opcode table.
|
|
|
|
@item vax.c
|
|
Vax specific parts of @code{_AS__}. Also includes the former files
|
|
@file{vax-ins-parse.c}, @file{vax-reg-parse.c} and @file{vip-op.c}.
|
|
|
|
@item atof-vax.c
|
|
Turns a flonum into a Vax constant.
|
|
|
|
@item vms.c
|
|
This file contains the special code needed to put out a VMS
|
|
style object file for the Vax.
|
|
|
|
@end table
|
|
|
|
Here is a list of the header files in the source directory.
|
|
(Warning: This section may not be very accurate. I didn't
|
|
write the header files; I just report them.) Also note that I
|
|
think many of these header files could be cleaned up or
|
|
eliminated.
|
|
|
|
@table @file
|
|
|
|
@item a.out.h
|
|
This describes the structures used to create the binary header data
|
|
inside the object file. Perhaps we should use the one in
|
|
@file{/usr/include}?
|
|
|
|
@item as.h
|
|
This defines all the globally useful things, and pulls in _0__<stdio.h>_1__
|
|
and _0__<assert.h>_1__.
|
|
|
|
@item bignum.h
|
|
This defines macros useful for dealing with bignums.
|
|
|
|
@item expr.h
|
|
Structure and macros for dealing with expression()
|
|
|
|
@item flonum.h
|
|
This defines the structure for dealing with floating point
|
|
numbers. It #includes @file{bignum.h}.
|
|
|
|
@item frags.h
|
|
This contains macro for appending a byte to the current frag.
|
|
|
|
@item hash.h
|
|
Structures and function definitions for the hashing functions.
|
|
|
|
@item input-file.h
|
|
Function headers for the input-file.c functions.
|
|
|
|
@item md.h
|
|
structures and function headers for things defined in the
|
|
machine dependent part of the assembler.
|
|
|
|
@item obstack.h
|
|
This is the GNU systemwide include file for manipulating obstacks.
|
|
Since nobody is running under real GNU yet, we include this file.
|
|
|
|
@item read.h
|
|
Macros and function headers for reading in source files.
|
|
|
|
@item struct-symbol.h
|
|
Structure definition and macros for dealing with the _AS__
|
|
internal form of a symbol.
|
|
|
|
@item subsegs.h
|
|
structure definition for dealing with the numbered subsegments
|
|
of the text and data segments.
|
|
|
|
@item symbols.h
|
|
Macros and function headers for dealing with symbols.
|
|
|
|
@item write.h
|
|
Structure for doing segment fixups.
|
|
@end table
|
|
|
|
@comment ~subsection Test Directory
|
|
@comment (Note: The test directory seems to have disappeared somewhere
|
|
@comment along the line. If you want it, you'll probably have to find a
|
|
@comment REALLY OLD dump tape~dots{})
|
|
@comment
|
|
@comment The ~file{test/} directory is used for regression testing.
|
|
@comment After you modify ~@code{_AS__}, you can get a quick go/nogo
|
|
@comment confidence test by running the new ~@code{_AS__} over the source
|
|
@comment files in this directory. You use a shell script ~file{test/do}.
|
|
@comment
|
|
@comment The tests in this suite are evolving. They are not comprehensive.
|
|
@comment They have, however, caught hundreds of bugs early in the debugging
|
|
@comment cycle of ~@code{_AS__}. Most test statements in this suite were naturally
|
|
@comment selected: they were used to demonstrate actual ~@code{_AS__} bugs rather
|
|
@comment than being written ~i{a prioi}.
|
|
@comment
|
|
@comment Another testing suggestion: over 30 bugs have been found simply by
|
|
@comment running examples from this manual through ~@code{_AS__}.
|
|
@comment Some examples in this manual are selected
|
|
@comment to distinguish boundary conditions; they are good for testing ~@code{_AS__}.
|
|
@comment
|
|
@comment ~subsubsection Regression Testing
|
|
@comment Each regression test involves assembling a file and comparing the
|
|
@comment actual output of ~@code{_AS__} to ``known good'' output files. Both
|
|
@comment the object file and the error/warning message file (stderr) are
|
|
@comment inspected. Optionally the ~@code{_AS__} exit status may be checked.
|
|
@comment Discrepencies are reported. Each discrepency means either that
|
|
@comment you broke some part of ~@code{_AS__} or that the ``known good'' files
|
|
@comment are now out of date and should be changed to reflect the new
|
|
@comment definition of ``good''.
|
|
@comment
|
|
@comment Each regression test lives in its own directory, in a tree
|
|
@comment rooted in the directory ~file{test/}. Each such directory
|
|
@comment has a name ending in ~file{.ret}, where `ret' stands for
|
|
@comment REgression Test. The ~file{.ret} ending allows ~code{find
|
|
@comment (1)} to find all regression tests in the tree, without
|
|
@comment needing to list them explicitly.
|
|
@comment
|
|
@comment Any ~file{.ret} directory must contain a file called
|
|
@comment ~file{input} which is the source file to assemble. During
|
|
@comment testing an object file ~file{output} is created, as well as
|
|
@comment a file ~file{stdouterr} which contains the output to both
|
|
@comment stderr and stderr. If there is a file ~file{output.good} in
|
|
@comment the directory, and if ~file{output} contains exactly the
|
|
@comment same data as ~file{output.good}, the file ~file{output} is
|
|
@comment deleted. Likewise ~file{stdouterr} is removed if it exactly
|
|
@comment matches a file ~file{stdouterr.good}. If file
|
|
@comment ~file{status.good} is present, containing a decimal number
|
|
@comment before a newline, the exit status of ~@code{_AS__} is compared
|
|
@comment to this number. If the status numbers are not equal, a file
|
|
@comment ~file{status} is written to the directory, containing the
|
|
@comment actual status as a decimal number followed by newline.
|
|
@comment
|
|
@comment Should any of the ~file{*.good} files fail to match their corresponding
|
|
@comment actual files, this is noted by a 1-line message on the screen during
|
|
@comment the regression test, and you can use ~@code{find (1)} to find any
|
|
@comment files named ~file{status}, ~file {output} or ~file{stdouterr}.
|
|
@comment
|
|
@node Retargeting, License, Maintenance, Top
|
|
@chapter Teaching the Assembler about a New Machine
|
|
|
|
This chapter describes the steps required in order to make the
|
|
assembler work with another machine's assembly language. This
|
|
chapter is not complete, and only describes the steps in the
|
|
broadest terms. You should look at the source for the
|
|
currently supported machine in order to discover some of the
|
|
details that aren't mentioned here.
|
|
|
|
You should create a new file called @file{@var{machine}.c}, and
|
|
add the appropriate lines to the file @file{Makefile} so that
|
|
you can compile your new version of the assembler. This should
|
|
be straighforward; simply add lines similar to the ones there
|
|
for the four current versions of the assembler.
|
|
|
|
If you want to be compatible with GDB, (and the current
|
|
machine-dependent versions of the assembler), you should create
|
|
a file called @file{@var{machine}-opcode.h} which should
|
|
contain all the information about the names of the machine
|
|
instructions, their opcodes, and what addressing modes they
|
|
support. If you do this right, the assembler and GDB can share
|
|
this file, and you'll only have to write it once. Note that
|
|
while you're writing @code{_AS__}, you may want to use an
|
|
independent program (if you have access to one), to make sure
|
|
that @code{_AS__} is emitting the correct bytes. Since @code{_AS__}
|
|
and @code{GDB} share the opcode table, an incorrect opcode
|
|
table entry may make invalid bytes look OK when you disassemble
|
|
them with @code{GDB}.
|
|
|
|
@section Functions You will Have to Write
|
|
|
|
Your file @file{@var{machine}.c} should contain definitions for
|
|
the following functions and variables. It will need to include
|
|
some header files in order to use some of the structures
|
|
defined in the machine-independent part of the assembler. The
|
|
needed header files are mentioned in the descriptions of the
|
|
functions that will need them.
|
|
|
|
@table @code
|
|
|
|
@item long omagic;
|
|
This long integer holds the value to place at the beginning of
|
|
the @file{a.out} file. It is usually @samp{OMAGIC}, except on
|
|
machines that store additional information in the magic-number.
|
|
|
|
@item char comment_chars[];
|
|
This character array holds the values of the characters that
|
|
start a comment anywhere in a line. Comments are stripped off
|
|
automatically by the machine independent part of the
|
|
assembler. Note that the @samp{/*} will always start a
|
|
comment, and that only @samp{*/} will end a comment started by
|
|
@samp{*/}.
|
|
|
|
@item char line_comment_chars[];
|
|
This character array holds the values of the chars that start a
|
|
comment only if they are the first (non-whitespace) character
|
|
on a line. If the character @samp{#} does not appear in this
|
|
list, you may get unexpected results. (Various
|
|
machine-independent parts of the assembler treat the comments
|
|
@samp{#APP} and @samp{#NO_APP} specially, and assume that lines
|
|
that start with @samp{#} are comments.)
|
|
|
|
@item char EXP_CHARS[];
|
|
This character array holds the letters that can separate the
|
|
mantissa and the exponent of a floating point number. Typical
|
|
values are @samp{e} and @samp{E}.
|
|
|
|
@item char FLT_CHARS[];
|
|
This character array holds the letters that--when they appear
|
|
immediately after a leading zero--indicate that a number is a
|
|
floating-point number. (Sort of how 0x indicates that a
|
|
hexadecimal number follows.)
|
|
|
|
@item pseudo_typeS md_pseudo_table[];
|
|
(@var{pseudo_typeS} is defined in @file{md.h})
|
|
This array contains a list of the machine_dependent directives
|
|
the assembler must support. It contains the name of each
|
|
pseudo op (Without the leading @samp{.}), a pointer to a
|
|
function to be called when that directive is encountered, and
|
|
an integer argument to be passed to that function.
|
|
|
|
@item void md_begin(void)
|
|
This function is called as part of the assembler's
|
|
initialization. It should do any initialization required by
|
|
any of your other routines.
|
|
|
|
@item int md_parse_option(char **optionPTR, int *argcPTR, char ***argvPTR)
|
|
This routine is called once for each option on the command line
|
|
that the machine-independent part of @code{_AS__} does not
|
|
understand. This function should return non-zero if the option
|
|
pointed to by @var{optionPTR} is a valid option. If it is not
|
|
a valid option, this routine should return zero. The variables
|
|
@var{argcPTR} and @var{argvPTR} are provided in case the option
|
|
requires a filename or something similar as an argument. If
|
|
the option is multi-character, @var{optionPTR} should be
|
|
advanced past the end of the option, otherwise every letter in
|
|
the option will be treated as a separate single-character
|
|
option.
|
|
|
|
@item void md_assemble(char *string)
|
|
This routine is called for every machine-dependent
|
|
non-directive line in the source file. It does all the real
|
|
work involved in reading the opcode, parsing the operands,
|
|
etc. @var{string} is a pointer to a null-terminated string,
|
|
that comprises the input line, with all excess whitespace and
|
|
comments removed.
|
|
|
|
@item void md_number_to_chars(char *outputPTR,long value,int nbytes)
|
|
This routine is called to turn a C long int, short int, or char
|
|
into the series of bytes that represents that number on the
|
|
target machine. @var{outputPTR} points to an array where the
|
|
result should be stored; @var{value} is the value to store; and
|
|
@var{nbytes} is the number of bytes in 'value' that should be
|
|
stored.
|
|
|
|
@item void md_number_to_imm(char *outputPTR,long value,int nbytes)
|
|
This routine is called to turn a C long int, short int, or char
|
|
into the series of bytes that represent an immediate value on
|
|
the target machine. It is identical to the function @code{md_number_to_chars},
|
|
except on NS32K machines.@refill
|
|
|
|
@item void md_number_to_disp(char *outputPTR,long value,int nbytes)
|
|
This routine is called to turn a C long int, short int, or char
|
|
into the series of bytes that represent an displacement value on
|
|
the target machine. It is identical to the function @code{md_number_to_chars},
|
|
except on NS32K machines.@refill
|
|
|
|
@item void md_number_to_field(char *outputPTR,long value,int nbytes)
|
|
This routine is identical to @code{md_number_to_chars},
|
|
except on NS32K machines.
|
|
|
|
@item void md_ri_to_chars(struct relocation_info *riPTR,ri)
|
|
(@code{struct relocation_info} is defined in @file{a.out.h})
|
|
This routine emits the relocation info in @var{ri}
|
|
in the appropriate bit-pattern for the target machine.
|
|
The result should be stored in the location pointed
|
|
to by @var{riPTR}. This routine may be a no-op unless you are
|
|
attempting to do cross-assembly.
|
|
|
|
@item char *md_atof(char type,char *outputPTR,int *sizePTR)
|
|
This routine turns a series of digits into the appropriate
|
|
internal representation for a floating-point number.
|
|
@var{type} is a character from @var{FLT_CHARS[]} that describes
|
|
what kind of floating point number is wanted; @var{outputPTR}
|
|
is a pointer to an array that the result should be stored in;
|
|
and @var{sizePTR} is a pointer to an integer where the size (in
|
|
bytes) of the result should be stored. This routine should
|
|
return an error message, or an empty string (not (char *)0) for
|
|
success.
|
|
|
|
@item int md_short_jump_size;
|
|
This variable holds the (maximum) size in bytes of a short (16
|
|
bit or so) jump created by @code{md_create_short_jump()}. This
|
|
variable is used as part of the broken-word feature, and isn't
|
|
needed if the assembler is compiled with
|
|
@samp{-DWORKING_DOT_WORD}.
|
|
|
|
@item int md_long_jump_size;
|
|
This variable holds the (maximum) size in bytes of a long (32
|
|
bit or so) jump created by @code{md_create_long_jump()}. This
|
|
variable is used as part of the broken-word feature, and isn't
|
|
needed if the assembler is compiled with
|
|
@samp{-DWORKING_DOT_WORD}.
|
|
|
|
@item void md_create_short_jump(char *resultPTR,long from_addr,
|
|
@code{long to_addr,fragS *frag,symbolS *to_symbol)}
|
|
This function emits a jump from @var{from_addr} to @var{to_addr} in
|
|
the array of bytes pointed to by @var{resultPTR}. If this creates a
|
|
type of jump that must be relocated, this function should call
|
|
@code{fix_new()} with @var{frag} and @var{to_symbol}. The jump
|
|
emitted by this function may be smaller than @var{md_short_jump_size},
|
|
but it must never create a larger one.
|
|
(If it creates a smaller jump, the extra bytes of memory will not be
|
|
used.) This function is used as part of the broken-word feature,
|
|
and isn't needed if the assembler is compiled with
|
|
@samp{-DWORKING_DOT_WORD}.@refill
|
|
|
|
@item void md_create_long_jump(char *ptr,long from_addr,
|
|
@code{long to_addr,fragS *frag,symbolS *to_symbol)}
|
|
This function is similar to the previous function,
|
|
@code{md_create_short_jump()}, except that it creates a long
|
|
jump instead of a short one. This function is used as part of
|
|
the broken-word feature, and isn't needed if the assembler is
|
|
compiled with @samp{-DWORKING_DOT_WORD}.
|
|
|
|
@item int md_estimate_size_before_relax(fragS *fragPTR,int segment_type)
|
|
This function does the initial setting up for relaxation. This
|
|
includes forcing references to still-undefined symbols to the
|
|
appropriate addressing modes.
|
|
|
|
@item relax_typeS md_relax_table[];
|
|
(relax_typeS is defined in md.h)
|
|
This array describes the various machine dependent states a
|
|
frag may be in before relaxation. You will need one group of
|
|
entries for each type of addressing mode you intend to relax.
|
|
|
|
@item void md_convert_frag(fragS *fragPTR)
|
|
(@var{fragS} is defined in @file{as.h})
|
|
This routine does the required cleanup after relaxation.
|
|
Relaxation has changed the type of the frag to a type that can
|
|
reach its destination. This function should adjust the opcode
|
|
of the frag to use the appropriate addressing mode.
|
|
@var{fragPTR} points to the frag to clean up.
|
|
|
|
@item void md_end(void)
|
|
This function is called just before the assembler exits. It
|
|
need not free up memory unless the operating system doesn't do
|
|
it automatically on exit. (In which case you'll also have to
|
|
track down all the other places where the assembler allocates
|
|
space but never frees it.)
|
|
|
|
@end table
|
|
|
|
@section External Variables You will Need to Use
|
|
|
|
You will need to refer to or change the following external variables
|
|
from within the machine-dependent part of the assembler.
|
|
|
|
@table @code
|
|
@item extern char flagseen[];
|
|
This array holds non-zero values in locations corresponding to
|
|
the options that were on the command line. Thus, if the
|
|
assembler was called with @samp{-W}, @var{flagseen['W']} would
|
|
be non-zero.
|
|
|
|
@item extern fragS *frag_now;
|
|
This pointer points to the current frag--the frag that bytes
|
|
are currently being added to. If nothing else, you will need
|
|
to pass it as an argument to various machine-independent
|
|
functions. It is maintained automatically by the
|
|
frag-manipulating functions; you should never have to change it
|
|
yourself.
|
|
|
|
@item extern LITTLENUM_TYPE generic_bignum[];
|
|
(@var{LITTLENUM_TYPE} is defined in @file{bignum.h}.
|
|
This is where @dfn{bignums}--numbers larger than 32 bits--are
|
|
returned when they are encountered in an expression. You will
|
|
need to use this if you need to implement directives (or
|
|
anything else) that must deal with these large numbers.
|
|
@code{Bignums} are of @code{segT} @code{SEG_BIG} (defined in
|
|
@file{as.h}, and have a positive @code{X_add_number}. The
|
|
@code{X_add_number} of a @code{bignum} is the number of
|
|
@code{LITTLENUMS} in @var{generic_bignum} that the number takes
|
|
up.
|
|
|
|
@item extern FLONUM_TYPE generic_floating_point_number;
|
|
(@var{FLONUM_TYPE} is defined in @file{flonum.h}.
|
|
The is where @dfn{flonums}--floating-point numbers within
|
|
expressions--are returned. @code{Flonums} are of @code{segT}
|
|
@code{SEG_BIG}, and have a negative @code{X_add_number}.
|
|
@code{Flonums} are returned in a generic format. You will have
|
|
to write a routine to turn this generic format into the
|
|
appropriate floating-point format for your machine.
|
|
|
|
@item extern int need_pass_2;
|
|
If this variable is non-zero, the assembler has encountered an
|
|
expression that cannot be assembled in a single pass. Since
|
|
the second pass isn't implemented, this flag means that the
|
|
assembler is punting, and is only looking for additional syntax
|
|
errors. (Or something like that.)
|
|
|
|
@item extern segT now_seg;
|
|
This variable holds the value of the segment the assembler is
|
|
currently assembling into.
|
|
|
|
@end table
|
|
|
|
@section External functions will you need
|
|
|
|
You will find the following external functions useful (or
|
|
indispensable) when you're writing the machine-dependent part
|
|
of the assembler.
|
|
|
|
@table @code
|
|
|
|
@item char *frag_more(int bytes)
|
|
This function allocates @var{bytes} more bytes in the current
|
|
frag (or starts a new frag, if it can't expand the current frag
|
|
any more.) for you to store some object-file bytes in. It
|
|
returns a pointer to the bytes, ready for you to store data in.
|
|
|
|
@item void fix_new(fragS *frag, int where, short size, symbolS *add_symbol, symbolS *sub_symbol, long offset, int pcrel)
|
|
This function stores a relocation fixup to be acted on later.
|
|
@var{frag} points to the frag the relocation belongs in;
|
|
@var{where} is the location within the frag where the relocation begins;
|
|
@var{size} is the size of the relocation, and is usually 1 (a single byte),
|
|
2 (sixteen bits), or 4 (a longword).
|
|
The value @var{add_symbol} @minus{} @var{sub_symbol} + @var{offset}, is added to the byte(s)
|
|
at _0__@var{frag->literal[where]}_1__. If @var{pcrel} is non-zero, the address of the
|
|
location is subtracted from the result. A relocation entry is also added
|
|
to the @file{a.out} file. @var{add_symbol}, @var{sub_symbol}, and/or
|
|
@var{offset} may be NULL.@refill
|
|
|
|
@item char *frag_var(relax_stateT type, int max_chars, int var,
|
|
@code{relax_substateT subtype, symbolS *symbol, char *opcode)}
|
|
This function creates a machine-dependent frag of type @var{type}
|
|
(usually @code{rs_machine_dependent}).
|
|
@var{max_chars} is the maximum size in bytes that the frag may grow by;
|
|
@var{var} is the current size of the variable end of the frag;
|
|
@var{subtype} is the sub-type of the frag. The sub-type is used to index into
|
|
@var{md_relax_table[]} during @code{relaxation}.
|
|
@var{symbol} is the symbol whose value should be used to when relax-ing this frag.
|
|
@var{opcode} points into a byte whose value may have to be modified if the
|
|
addressing mode used by this frag changes. It typically points into the
|
|
@var{fr_literal[]} of the previous frag, and is used to point to a location
|
|
that @code{md_convert_frag()}, may have to change.@refill
|
|
|
|
@item void frag_wane(fragS *fragPTR)
|
|
This function is useful from within @code{md_convert_frag}. It
|
|
changes a frag to type rs_fill, and sets the variable-sized
|
|
piece of the frag to zero. The frag will never change in size
|
|
again.
|
|
|
|
@item segT expression(expressionS *retval)
|
|
(@var{segT} is defined in @file{as.h}; @var{expressionS} is defined in @file{expr.h})
|
|
This function parses the string pointed to by the external char
|
|
pointer @var{input_line_pointer}, and returns the segment-type
|
|
of the expression. It also stores the results in the
|
|
@var{expressionS} pointed to by @var{retval}.
|
|
@var{input_line_pointer} is advanced to point past the end of
|
|
the expression. (@var{input_line_pointer} is used by other
|
|
parts of the assembler. If you modify it, be sure to restore
|
|
it to its original value.)
|
|
|
|
@item as_warn(char *message,@dots{})
|
|
If warning messages are disabled, this function does nothing.
|
|
Otherwise, it prints out the current file name, and the current
|
|
line number, then uses @code{fprintf} to print the
|
|
@var{message} and any arguments it was passed.
|
|
|
|
@item as_bad(char *message,@dots{})
|
|
This function should be called when @code{_AS__} encounters
|
|
conditions that are bad enough that @code{_AS__} should not
|
|
produce an object file, but should continue reading input and
|
|
printing warning and bad error messages.
|
|
|
|
@item as_fatal(char *message,@dots{})
|
|
This function prints out the current file name and line number,
|
|
prints the word @samp{FATAL:}, then uses @code{fprintf} to
|
|
print the @var{message} and any arguments it was passed. Then
|
|
the assembler exits. This function should only be used for
|
|
serious, unrecoverable errors.
|
|
|
|
@item void float_const(int float_type)
|
|
This function reads floating-point constants from the current
|
|
input line, and calls @code{md_atof} to assemble them. It is
|
|
useful as the function to call for the directives
|
|
@samp{.single}, @samp{.double}, @samp{.float}, etc.
|
|
@var{float_type} must be a character from @var{FLT_CHARS}.
|
|
|
|
@item void demand_empty_rest_of_line(void);
|
|
This function can be used by machine-dependent directives to
|
|
make sure the rest of the input line is empty. It prints a
|
|
warning message if there are additional characters on the line.
|
|
|
|
@item long int get_absolute_expression(void)
|
|
This function can be used by machine-dependent directives to
|
|
read an absolute number from the current input line. It
|
|
returns the result. If it isn't given an absolute expression,
|
|
it prints a warning message and returns zero.
|
|
|
|
@end table
|
|
|
|
|
|
@section The concept of Frags
|
|
|
|
This assembler works to optimize the size of certain addressing
|
|
modes. (e.g. branch instructions) This means the size of many
|
|
pieces of object code cannot be determined until after assembly
|
|
is finished. (This means that the addresses of symbols cannot be
|
|
determined until assembly is finished.) In order to do this,
|
|
@code{_AS__} stores the output bytes as @dfn{frags}.
|
|
|
|
Here is the definition of a frag (from @file{as.h})
|
|
@smallexample
|
|
struct frag
|
|
@{
|
|
long int fr_fix;
|
|
long int fr_var;
|
|
relax_stateT fr_type;
|
|
relax_substateT fr_substate;
|
|
unsigned long fr_address;
|
|
long int fr_offset;
|
|
struct symbol *fr_symbol;
|
|
char *fr_opcode;
|
|
struct frag *fr_next;
|
|
char fr_literal[];
|
|
@}
|
|
@end smallexample
|
|
|
|
@table @var
|
|
@item fr_fix
|
|
is the size of the fixed-size piece of the frag.
|
|
|
|
@item fr_var
|
|
is the maximum (?) size of the variable-sized piece of the frag.
|
|
|
|
@item fr_type
|
|
is the type of the frag.
|
|
Current types are:
|
|
rs_fill
|
|
rs_align
|
|
rs_org
|
|
rs_machine_dependent
|
|
|
|
@item fr_substate
|
|
This stores the type of machine-dependent frag this is. (what
|
|
kind of addressing mode is being used, and what size is being
|
|
tried/will fit/etc.
|
|
|
|
@item fr_address
|
|
@var{fr_address} is only valid after relaxation is finished.
|
|
Before relaxation, the only way to store an address is (pointer
|
|
to frag containing the address) plus (offset into the frag).
|
|
|
|
@item fr_offset
|
|
This contains a number, whose meaning depends on the type of
|
|
the frag.
|
|
for machine_dependent frags, this contains the offset from
|
|
fr_symbol that the frag wants to go to. Thus, for branch
|
|
instructions it is usually zero. (unless the instruction was
|
|
@samp{jba foo+12} or something like that.)
|
|
|
|
@item fr_symbol
|
|
for machine_dependent frags, this points to the symbol the frag
|
|
needs to reach.
|
|
|
|
@item fr_opcode
|
|
This points to the location in the frag (or in a previous frag)
|
|
of the opcode for the instruction that caused this to be a frag.
|
|
@var{fr_opcode} is needed if the actual opcode must be changed
|
|
in order to use a different form of the addressing mode.
|
|
(For example, if a conditional branch only comes in size tiny,
|
|
a large-size branch could be implemented by reversing the sense
|
|
of the test, and turning it into a tiny branch over a large jump.
|
|
This would require changing the opcode.)
|
|
|
|
@var{fr_literal} is a variable-size array that contains the
|
|
actual object bytes. A frag consists of a fixed size piece of
|
|
object data, (which may be zero bytes long), followed by a
|
|
piece of object data whose size may not have been determined
|
|
yet. Other information includes the type of the frag (which
|
|
controls how it is relaxed),
|
|
|
|
@item fr_next
|
|
This is the next frag in the singly-linked list. This is
|
|
usually only needed by the machine-independent part of
|
|
@code{_AS__}.
|
|
|
|
@end table
|
|
_fi__(0)
|
|
|
|
@node License, , Retargeting, Top
|
|
@unnumbered GNU GENERAL PUBLIC LICENSE
|
|
@center Version 1, February 1989
|
|
|
|
@display
|
|
Copyright @copyright{} 1989 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 license agreements of most software companies try to keep users
|
|
at the mercy of those companies. By contrast, our 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. The
|
|
General Public License applies to the Free Software Foundation's
|
|
software and to any other program whose authors commit to using it.
|
|
You can use it for your programs, too.
|
|
|
|
When we speak of free software, we are referring to freedom, not
|
|
price. Specifically, the General Public License is designed to make
|
|
sure that you have the freedom to give away or sell copies of free
|
|
software, 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 a 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 tell them 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.
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The precise terms and conditions for copying, distribution and
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|
modification follow.
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|
@iftex
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@unnumberedsec TERMS AND CONDITIONS
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@end iftex
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@ifinfo
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|
@center TERMS AND CONDITIONS
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|
@end ifinfo
|
|
|
|
@enumerate
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@item
|
|
This License Agreement 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 work containing the
|
|
Program or a portion of it, either verbatim or with modifications. Each
|
|
licensee is addressed as ``you''.
|
|
|
|
@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
|
|
General Public License and to the absence of any warranty; and give any
|
|
other recipients of the Program a copy of this General Public License
|
|
along with the Program. You may charge a fee for the physical act of
|
|
transferring a copy.
|
|
|
|
@item
|
|
You may modify your copy or copies of the Program or any portion of
|
|
it, and copy and distribute such modifications under the terms of Paragraph
|
|
1 above, provided that you also do the following:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
cause the modified files to carry prominent notices stating that
|
|
you changed the files and the date of any change; and
|
|
|
|
@item
|
|
cause the whole of any work that you distribute or publish, that
|
|
in whole or in part contains the Program or any part thereof, either
|
|
with or without modifications, to be licensed at no charge to all
|
|
third parties under the terms of this General Public License (except
|
|
that you may choose to grant warranty protection to some or all
|
|
third parties, at your option).
|
|
|
|
@item
|
|
If the modified program normally reads commands interactively when
|
|
run, you must cause it, when started running for such interactive use
|
|
in the simplest and most usual 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 General
|
|
Public License.
|
|
|
|
@item
|
|
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.
|
|
@end itemize
|
|
|
|
Mere aggregation of another independent work with the Program (or its
|
|
derivative) on a volume of a storage or distribution medium does not bring
|
|
the other work under the scope of these terms.
|
|
|
|
@item
|
|
You may copy and distribute the Program (or a portion or derivative of
|
|
it, under Paragraph 2) in object code or executable form under the terms of
|
|
Paragraphs 1 and 2 above provided that you also do one of the following:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
accompany it with the complete corresponding machine-readable
|
|
source code, which must be distributed under the terms of
|
|
Paragraphs 1 and 2 above; or,
|
|
|
|
@item
|
|
accompany it with a written offer, valid for at least three
|
|
years, to give any third party free (except for a nominal charge
|
|
for the cost of distribution) a complete machine-readable copy of the
|
|
corresponding source code, to be distributed under the terms of
|
|
Paragraphs 1 and 2 above; or,
|
|
|
|
@item
|
|
accompany it with the information you received as to where the
|
|
corresponding source code may be obtained. (This alternative is
|
|
allowed only for noncommercial distribution and only if you
|
|
received the program in object code or executable form alone.)
|
|
@end itemize
|
|
|
|
Source code for a work means the preferred form of the work for making
|
|
modifications to it. For an executable file, complete source code means
|
|
all the source code for all modules it contains; but, as a special
|
|
exception, it need not include source code for modules which are standard
|
|
libraries that accompany the operating system on which the executable
|
|
file runs, or for standard header files or definitions files that
|
|
accompany that operating system.
|
|
|
|
@item
|
|
You may not copy, modify, sublicense, distribute or transfer the
|
|
Program except as expressly provided under this General Public License.
|
|
Any attempt otherwise to copy, modify, sublicense, distribute or transfer
|
|
the Program is void, and will automatically terminate your rights to use
|
|
the Program under this License. However, parties who have received
|
|
copies, or rights to use copies, from you under this General Public
|
|
License will not have their licenses terminated so long as such parties
|
|
remain in full compliance.
|
|
|
|
@item
|
|
By copying, distributing or modifying 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.
|
|
|
|
@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.
|
|
|
|
@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 the 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
|
|
the 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 humanity, 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 a brief 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 1, 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 `show w' and `show c' should show the
|
|
appropriate parts of the General Public License. Of course, the
|
|
commands you use may be called something other than `show w' and `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' (a program to direct compilers to make passes
|
|
at assemblers) written by James Hacker.
|
|
|
|
@var{signature of Ty Coon}, 1 April 1989
|
|
Ty Coon, President of Vice
|
|
@end smallexample
|
|
|
|
That's all there is to it!
|
|
|
|
|
|
@summarycontents
|
|
@contents
|
|
@bye
|