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A manual for the GNU assembler preprocessor.
This commit is contained in:
Roland Pesch
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\input texinfo @c -*- Texinfo -*-
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@finalout
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@setfilename gasp.info
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@c
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@c This file documents the assembly preprocessor "GASP"
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@c
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@c Copyright (c) 1994 Free Software Foundation, Inc.
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@c
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@c This text may be freely distributed under the terms of the GNU
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@c General Public License.
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@ifinfo
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@format
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START-INFO-DIR-ENTRY
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* gasp:(gasp). The GNU Assembler Preprocessor
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END-INFO-DIR-ENTRY
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@end format
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@end ifinfo
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@syncodeindex ky cp
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@syncodeindex fn cp
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@setchapternewpage odd
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@settitle GASP
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@titlepage
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@c FIXME boring title
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@title GASP, an assembly preprocessor
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@c FIXME! Get a version number, global-replace '??'
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@subtitle for GASP version ??
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@sp 1
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@subtitle January 1994
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@author Roland Pesch
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@page
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@tex
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{\parskip=0pt \hfill Cygnus Support\par
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}
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@end tex
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@vskip 0pt plus 1filll
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Copyright @copyright{} 1994 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
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are preserved on all copies.
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided also that
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the entire resulting derived work is distributed under the terms of a
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|
permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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into another language, under the above conditions for modified versions.
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@end titlepage
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@ifinfo
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Copyright @copyright{} 1994 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
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are preserved on all copies.
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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 a 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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@end ignore
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided also that
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the entire resulting derived work is distributed under the terms of a
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|
permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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into another language, under the above conditions for modified versions.
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@node Top
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@top GASP
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GASP is a preprocessor for assembly programs.
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This file describes version ?? of GASP.
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Steve Chamberlain wrote GASP; Roland Pesch wrote this manual.
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@menu
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* Overview:: What is GASP?
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* Invoking GASP:: Command line options.
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* Commands:: Preprocessor commands.
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* Index:: Index.
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@end menu
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@end ifinfo
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@node Overview
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@chapter What is GASP?
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The primary purpose of the @sc{gnu} assembler is to assemble the output of
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other programs---notably compilers. When you have to hand-code
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specialized routines in assembly, that means the @sc{gnu} assembler is
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an unfriendly processor: it has no directives for macros, conditionals,
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or many other conveniences that you might expect.
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In some cases you can simply use the C preprocessor, or a generalized
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preprocessor like @sc{m4}; but this can be awkward, since none of these
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things are designed with assembly in mind.
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@sc{gasp} fills this need. It is expressly designed to provide the
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facilities you need with hand-coded assembly code. Implementing it as a
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preprocessor, rather than part of the assembler, allows the maximum
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flexibility: you can use it with hand-coded assembly, without paying a
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penalty of added complexity in the assembler you use for compiler
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output.
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Here is a small example to give the flavor of @sc{gasp}. This input to
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@sc{gasp}
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@cartouche
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@example
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.MACRO saveregs from=8 to=14
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count .ASSIGNA \from
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; save r\from..r\to
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.AWHILE \&count LE \to
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mov r\&count,@@-sp
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count .ASSIGNA \&count + 1
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.AENDW
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.ENDM
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saveregs from=9
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saveregs 1,5
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.RADIX Q
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bar: mov #H'dead+12,r0
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foo .SDATAC "hello"<12>
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.END
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@end example
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@end cartouche
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@noindent
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generates this assembly program:
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@cartouche
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@example
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; save r9..r14
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mov r9,@@-sp
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mov r10,@@-sp
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mov r11,@@-sp
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mov r12,@@-sp
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mov r13,@@-sp
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mov r14,@@-sp
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; save r1..r5
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mov r1,@@-sp
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mov r2,@@-sp
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mov r3,@@-sp
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mov r4,@@-sp
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mov r5,@@-sp
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bar: mov #57005+10,r0
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foo: .byte 6,104,101,108,108,111,10
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@end example
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@end cartouche
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@node Invoking GASP
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@chapter Command Line Options
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@c FIXME! Or is there a simpler way, calling from GAS option?
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The simplest way to use @sc{gasp} is to run it as a filter and assemble
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its output. In Unix and its ilk, you can do this, for example:
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@c FIXME! GASP filename suffix convention?
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@example
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$ gasp prog.sp | as -o prog.o
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@end example
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Naturally, there are also a few command-line options to allow you to
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request variations on this basic theme. Here is the full set of
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possibilities for the @sc{gasp} command line.
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@example
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gasp [ -c ] [ -o @var{outfile} ] [ -p ] [ -s ] [ -u ] @var{infile} @dots{}
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@end example
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@c FIXME!! Aren't all GNU programs supposed to have a -V or --version
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@c option, that reports version info and exits?
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@ftable @code
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@item @var{infile} @dots{}
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@c FIXME! Why not stdin as default infile?
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The input file names. You must specify at least one input file; if you
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specify more, @sc{gasp} preprocesses them all, concatenating the output
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in the order you list the @var{infile} arguments.
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Mark the end of each input file with the preprocessor command
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@code{.END}. @xref{Other Commands,, Miscellaneous commands}.
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@item -c
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@c FIXME! Shouldn't there be an option to set the prefix char so it can
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@c always be the comment char for whatever assembly version we have?
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Copy the source lines to the output file. Use this option
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to see the effect of each preprocessor line on the @sc{gasp} output.
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@sc{gasp} marks the lines copied from the source file with @samp{!} at
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the beginning, to help you distinguish them from the rest of the output.
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@item -o @var{outfile}
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Write the output in a file called @var{outfile}. If you do not use the
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@samp{-o} option, @sc{gasp} writes its output on the standard output
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stream.
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@item -p
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Print line numbers. @sc{gasp} obeys this option @emph{only} if you also
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specify @samp{-c} to copy source lines to its output. With @samp{-c
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-p}, @sc{gasp} displays the line number of each source line copied
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(immediately after the @samp{!} that marks source lines in the output).
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@item -s
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Show statistics. In this version of @sc{gasp}, this option produces
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statistics about the string buffers that @sc{gasp} allocates internally.
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For each defined buffersize @var{s}, @sc{gasp} shows the number of
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strings @var{n} that it allocated, with a line like this:
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@example
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strings size @var{s} : @var{n}
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@end example
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@noindent
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@sc{gasp} displays these statistics on the standard error stream, when
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done preprocessing.
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@item -u
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Bypass ``unreasonable expansion'' limit. Since you can define @sc{gasp}
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macros inside other macro definitions, the preprocessor normally
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includes a sanity check. If your program requires more than 1,000
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nested expansions, @sc{gasp} normally exits with an error message. Use
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this option to turn off this check, allowing unlimited nested
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expansions.
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@end ftable
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@node Commands
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@chapter Preprocessor Commands
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@sc{gasp} commands have a straightforward syntax that fits in well with
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assembly conventions. In general, a command extends for a line, and may
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have up to three fields: an optional label, the command itself, and
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optional arguments to the command. You can write commands in upper or
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lower case, though this manual shows them in upper case. @xref{Syntax
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Details,, Details of the GASP syntax}, for more information.
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@menu
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* Conditionals::
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* Loops::
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* Variables::
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* Macros::
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* Data::
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* Listings::
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* Other Commands::
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* Syntax Details::
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@end menu
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@node Conditionals
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@section Conditional assembly
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The conditional-assembly directives allow you to include or exclude
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portions of an assembly depending on how a pair of expressions, or a
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pair of strings, compare.
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The overall structure of conditionals is familiar from many other
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contexts. @code{.AIF} marks the start of a conditional, and precedes
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assembly for the case when the condition is true. An optional
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@code{.AELSE} precedes assembly for the converse case, and an
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@code{.AENDI} marks the end of the condition.
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@c FIXME! Why doesn't -u turn off this check?
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You may nest conditionals up to a depth of 100; @sc{gasp} rejects
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nesting beyond that, because it may indicate a bug in your macro
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structure.
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@c FIXME! Why isn't there something like cpp's -D option? Conditionals
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@c would be much more useful if there were.
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Conditionals are primarily useful inside macro definitions, where you
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often need different effects depending on argument values.
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@xref{Macros,, Defining your own directives}, for details about defining
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macros.
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@ftable @code
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@item .AIF @var{expra} @var{cmp} @var{exprb}
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@itemx .AIF "@var{stra}" @var{cmp} "@var{strb}"
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The governing condition goes on the same line as the @code{.AIF}
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preprocessor command. You may compare either two strings, or two
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|
expressions.
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When you compare strings, only two conditional @var{cmp} comparison
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|
operators are available: @samp{EQ} (true if @var{stra} and @var{strb}
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are identical), and @samp{NE} (the converse).
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When you compare two expressions, @emph{both expressions must be
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absolute} (@pxref{Expressions,, Arithmetic expressions in GASP}). You
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can use these @var{cmp} comparison operators with expressions:
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@ftable @code
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@item EQ
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Are @var{expra} and @var{exprb} equal? (For strings, are @var{stra} and
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@var{strb} identical?)
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@item NE
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Are @var{expra} and @var{exprb} different? (For strings, are @var{stra}
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and @var{strb} different?
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@item LT
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Is @var{expra} less than @var{exprb}? (Not allowed for strings.)
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@item LE
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|
Is @var{expra} less than or equal to @var{exprb}? (Not allowed for strings.)
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|
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@item GT
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|
Is @var{expra} greater than @var{exprb}? (Not allowed for strings.)
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|
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@item GE
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|
Is @var{expra} greater than or equal to @var{exprb}? (Not allowed for
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|
strings.)
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@end ftable
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@item .AELSE
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Marks the start of assembly code to be included if the condition fails.
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|
Optional, and only allowed within a conditional (between @code{.AIF} and
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|
@code{.AENDI}).
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|
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|
@item .AENDI
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|
Marks the end of a conditional assembly.
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|
@end ftable
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|
@node Loops
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|
@section Repetitive sections of assembly
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|
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|
Two preprocessor directives allow you to repeatedly issue copies of the
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|
same block of assembly code.
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|
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|
@ftable @code
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|
@item .AREPEAT @var{aexp}
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|
@itemx .AENDR
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|
If you simply need to repeat the same block of assembly over and over a
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|
fixed number of times, sandwich one instance of the repeated block
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|
between these @code{.AREPEAT} and @code{.AENDR}. Specify the number of
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|
copies as @var{aexp} (which must be an absolute expression). For
|
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|
example, this repeats two assembly statements three times in succession:
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|
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|
@cartouche
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|
@example
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|
.AREPEAT 3
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|
rotcl r2
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|
div1 r0,r1
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|
.AENDR
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|
@end example
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|
@end cartouche
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|
@item .AWHILE @var{expra} @var{cmp} @var{exprb}
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|
@itemx .AENDW
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|
@itemx .AWHILE @var{stra} @var{cmp} @var{strb}
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|
@itemx .AENDW
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|
To repeat a block of assembly depending on a conditional test, rather
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|
than repeating it for a specific number of times, use @code{.AWHILE}.
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|
@code{.AENDW} marks the end of the repeated block. The conditional
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|
comparison works exactly the same way as for @code{.AIF}, with the same
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|
comparison operators (@pxref{Conditionals,, Conditional assembly}).
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||||||
|
|
||||||
|
Since the terms of the comparison must be absolute expression,
|
||||||
|
@code{.AWHILE} is primarily useful within macros. @xref{Macros,,
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||||||
|
Defining your own directives}.
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||||||
|
@end ftable
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|
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||||||
|
@cindex loops, breaking out of
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||||||
|
@cindex breaking out of loops
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||||||
|
You can use the @code{.EXITM} preprocessor directive to break out of
|
||||||
|
loops early (as well as to break out of macros). @xref{Macros,,
|
||||||
|
Defining your own directives}.
|
||||||
|
|
||||||
|
@node Variables
|
||||||
|
@section Preprocessor variables
|
||||||
|
|
||||||
|
You can use variables in @sc{gasp} to represent the results of
|
||||||
|
expressions, strings, or registers.
|
||||||
|
|
||||||
|
There are two kinds of preprocessor variable:
|
||||||
|
|
||||||
|
@c FIXME! Is this crud true about conditional comparisons vs variables?
|
||||||
|
@enumerate
|
||||||
|
@item
|
||||||
|
Variables defined with @code{.EQU} or @code{.ASSIGN}. To evaluate this
|
||||||
|
kind of variable in your assembly output, simply mention its name. For
|
||||||
|
example, these two lines define and use a variable @samp{eg}:
|
||||||
|
|
||||||
|
@cartouche
|
||||||
|
@example
|
||||||
|
eg .EQU FLIP-64
|
||||||
|
@dots{}
|
||||||
|
mov.l eg,r0
|
||||||
|
@end example
|
||||||
|
@end cartouche
|
||||||
|
|
||||||
|
@emph{Do not use} this kind of variable in conditional expressions or
|
||||||
|
while loops; @sc{gasp} only evaluates these variables when writing
|
||||||
|
assembly output.
|
||||||
|
|
||||||
|
@item
|
||||||
|
Variables defined as macro arguments, or with @code{.ASSIGNC} or
|
||||||
|
@code{.ASSIGNA}. To evaluate this kind of variable, write @samp{\&} before
|
||||||
|
the variable name; for example,
|
||||||
|
|
||||||
|
@cartouche
|
||||||
|
@example
|
||||||
|
opcit .ASSIGNA 47
|
||||||
|
@dots{}
|
||||||
|
.AWHILE \&opcit GT 0
|
||||||
|
@dots{}
|
||||||
|
.AENDW
|
||||||
|
@end example
|
||||||
|
@end cartouche
|
||||||
|
@end enumerate
|
||||||
|
|
||||||
|
@ftable @code
|
||||||
|
@item @var{pvar} .EQU @var{expr}
|
||||||
|
@c FIXME! Anything to beware of re GAS directive of same name?
|
||||||
|
Assign preprocessor variable @var{pvar} the value of the expression
|
||||||
|
@var{expr}. There are no restrictions on redefinition; use @samp{.EQU}
|
||||||
|
with the same @var{pvar} as often as you find it convenient.
|
||||||
|
|
||||||
|
@item @var{pvar} .ASSIGN @var{expr}
|
||||||
|
Almost the same as @code{.EQU}, save that you may not redefine
|
||||||
|
@var{pvar} using @code{.ASSIGN} once it has a value.
|
||||||
|
@c FIXME!! Supposed to work this way, apparently, but on 9feb94 works
|
||||||
|
@c just like .EQU
|
||||||
|
|
||||||
|
@item @var{pvar} .ASSIGNA @var{aexpr}
|
||||||
|
Define a variable with a numeric value, for use during preprocessing.
|
||||||
|
@var{aexpr} must be an absolute expression. You can redefine variables
|
||||||
|
with @code{.ASSIGNA} at any time.
|
||||||
|
|
||||||
|
@item @var{pvar} .ASSIGNC "@var{str}"
|
||||||
|
Define a variable with a string value, for use during preprocessing.
|
||||||
|
You can redefine variables with @code{.ASSIGNC} at any time.
|
||||||
|
|
||||||
|
@item @var{pvar} .REG (@var{register})
|
||||||
|
Use @code{.REG} to define a variable that represents a register. In
|
||||||
|
particular, @var{register} is @emph{not evaluated} as an expression.
|
||||||
|
You may use @code{.REG} at will to redefine register variables.
|
||||||
|
@end ftable
|
||||||
|
|
||||||
|
All these directives accept the variable name in the ``label'' position,
|
||||||
|
that is at the left margin. You may specify a colon after the variable
|
||||||
|
name if you wish; the first example above could have started @samp{eg:}
|
||||||
|
with the same effect.
|
||||||
|
|
||||||
|
@node Macros
|
||||||
|
@section Defining your own directives
|
||||||
|
|
||||||
|
The commands @code{.MACRO} and @code{.ENDM} allow you to define macros
|
||||||
|
that generate assembly output, and that you can use with a syntax
|
||||||
|
similar to built-in @sc{gasp} or assembler directives. For example,
|
||||||
|
this definition specifies a macro @code{SUM} that adds together a range of
|
||||||
|
consecutive registers:
|
||||||
|
|
||||||
|
@cartouche
|
||||||
|
@example
|
||||||
|
.MACRO SUM FROM=0, TO=9
|
||||||
|
; \FROM \TO
|
||||||
|
mov r\FROM,r10
|
||||||
|
COUNT .ASSIGNA \FROM+1
|
||||||
|
.AWHILE \&COUNT LE \TO
|
||||||
|
add r\&COUNT,r10
|
||||||
|
COUNT .ASSIGNA \&COUNT+1
|
||||||
|
.AENDW
|
||||||
|
.ENDM
|
||||||
|
@end example
|
||||||
|
@end cartouche
|
||||||
|
|
||||||
|
@noindent
|
||||||
|
With that definition, @samp{SUM 0,5} generates this assembly output:
|
||||||
|
|
||||||
|
@cartouche
|
||||||
|
@example
|
||||||
|
; 0 5
|
||||||
|
mov r0,r10
|
||||||
|
add r1,r10
|
||||||
|
add r2,r10
|
||||||
|
add r3,r10
|
||||||
|
add r4,r10
|
||||||
|
add r5,r10
|
||||||
|
@end example
|
||||||
|
@end cartouche
|
||||||
|
|
||||||
|
@ftable @code
|
||||||
|
@item .MACRO @var{macname}
|
||||||
|
@itemx .MACRO @var{macname} @var{macargs} @dots{}
|
||||||
|
Begin the definition of a macro called @var{macname}. If your macro
|
||||||
|
definition requires arguments, specify their names after the macro name,
|
||||||
|
separated by commas or spaces. You can supply a default value for any
|
||||||
|
macro argument by following the name with @samp{=@var{deflt}}. For
|
||||||
|
example, these are all valid @code{.MACRO} statements:
|
||||||
|
|
||||||
|
@table @code
|
||||||
|
@item .MACRO COMM
|
||||||
|
Begin the definition of a macro called @code{COMM}, which takes no
|
||||||
|
arguments.
|
||||||
|
|
||||||
|
@item .MACRO PLUS1 P, P1
|
||||||
|
@itemx .MACRO PLUS1 P P1
|
||||||
|
Either statement begins the definition of a macro called @code{PLUS1},
|
||||||
|
which takes two arguments; within the macro definition, these arguments
|
||||||
|
are evaluated as @samp{\&P} and @samp{\&P1}.
|
||||||
|
|
||||||
|
@item .MACRO RESERVE_STR P1=0 P2
|
||||||
|
Begin the definition of a macro called @code{RESERVE_STR}, with two
|
||||||
|
arguments. The first argument has a default value, but not the second.
|
||||||
|
After the definition is complete, you can call the macro either as
|
||||||
|
@samp{RESERVE_STR @var{a},@var{b}} (with @samp{\&P1} evaluating to
|
||||||
|
@var{a} and @samp{\&P2} evaluating to @var{b}), or as @samp{RESERVE_STR
|
||||||
|
,@var{b}} (with @samp{\&P1} evaluating as the default, in this case
|
||||||
|
@samp{0}, and @samp{\&P2} evaluating to @var{b}).
|
||||||
|
@end table
|
||||||
|
|
||||||
|
When you call a macro, the values are assigned by position to each
|
||||||
|
argument name. Macro arguments are preprocessor variables in the same
|
||||||
|
way as variables you define with @samp{.ASSIGNA} or @samp{.ASSIGNC}, and
|
||||||
|
you can therefore use them in conditionals or for loop control.
|
||||||
|
|
||||||
|
@item @var{name} .MACRO
|
||||||
|
@itemx @var{name} .MACRO ( @var{macargs} @dots{} )
|
||||||
|
@c FIXME check: I think no error _and_ no args recognized if I use form
|
||||||
|
@c NAME .MACRO ARG ARG
|
||||||
|
An alternative form of introducing a macro definition: specify the macro
|
||||||
|
name in the label position, and the arguments (if any) between
|
||||||
|
parentheses after the name. Defaulting rules and usage work the same
|
||||||
|
way as for the alternate macro definition syntax.
|
||||||
|
|
||||||
|
@item .ENDM
|
||||||
|
Mark the end of a macro definition.
|
||||||
|
|
||||||
|
@item .EXITM
|
||||||
|
Exit early from the current macro definition, @code{.AREPEAT} loop, or
|
||||||
|
@code{.AWHILE} loop.
|
||||||
|
|
||||||
|
@cindex number of macros executed
|
||||||
|
@cindex macros, count executed
|
||||||
|
@item \@@
|
||||||
|
@sc{gasp} maintains a counter of how many macros it has
|
||||||
|
executed in this pseudo-variable; you can copy that number to your
|
||||||
|
output with @samp{\@@}, but @emph{only within a macro definition}.
|
||||||
|
@end ftable
|
||||||
|
|
||||||
|
@node Data
|
||||||
|
@section Data output
|
||||||
|
|
||||||
|
In assembly code, you often need to specify working areas of memory;
|
||||||
|
depending on the application, you may want to initialize such memory or
|
||||||
|
not. @sc{gasp} provides preprocessor directives to help you avoid
|
||||||
|
repetitive coding for both purposes.
|
||||||
|
|
||||||
|
You can use labels as usual to mark the data areas.
|
||||||
|
|
||||||
|
@menu
|
||||||
|
* Initialized::
|
||||||
|
* Uninitialized::
|
||||||
|
@end menu
|
||||||
|
|
||||||
|
@node Initialized
|
||||||
|
@subsection Initialized data
|
||||||
|
|
||||||
|
These are the @sc{gasp} directives for initialized data, and the standard
|
||||||
|
@sc{gnu} assembler directives they expand to:
|
||||||
|
|
||||||
|
@ftable @code
|
||||||
|
@item .DATA @var{expr}, @var{expr}, @dots{}
|
||||||
|
@itemx .DATA.B @var{expr}, @var{expr}, @dots{}
|
||||||
|
@itemx .DATA.W @var{expr}, @var{expr}, @dots{}
|
||||||
|
@itemx .DATA.L @var{expr}, @var{expr}, @dots{}
|
||||||
|
Evaluate arithmetic expressions @var{expr}, and emit the corresponding
|
||||||
|
@code{as} directive (labelled with @var{lab}). The unqualified
|
||||||
|
@code{.DATA} emits @samp{.long}; @code{.DATA.B} emits @samp{.byte};
|
||||||
|
@code{.DATA.W} emits @samp{.short}; and @code{.DATA.L} emits
|
||||||
|
@samp{.long}.
|
||||||
|
|
||||||
|
For example, @samp{foo .DATA 1,2,3} emits @samp{foo: .long 1,2,3}.
|
||||||
|
|
||||||
|
@item .DATAB @var{repeat}, @var{expr}
|
||||||
|
@itemx .DATAB.B @var{repeat}, @var{expr}
|
||||||
|
@itemx .DATAB.W @var{repeat}, @var{expr}
|
||||||
|
@itemx .DATAB.L @var{repeat}, @var{expr}
|
||||||
|
@c FIXME! Looks like gasp accepts and ignores args after 2nd.
|
||||||
|
Make @code{as} emit @var{repeat} copies of the value of the expression
|
||||||
|
@var{expr} (using the @code{as} directive @code{.fill}).
|
||||||
|
@samp{.DATAB.B} repeats one-byte values; @samp{.DATAB.W} repeats
|
||||||
|
two-byte values; and @samp{.DATAB.L} repeats four-byte values.
|
||||||
|
@samp{.DATAB} without a suffix repeats four-byte values, just like
|
||||||
|
@samp{.DATAB.L}.
|
||||||
|
|
||||||
|
@c FIXME! Allowing zero might be useful for edge conditions in macros.
|
||||||
|
@var{repeat} must be an absolute expression with a positive value.
|
||||||
|
|
||||||
|
@item .SDATA "@var{str}" @dots{}
|
||||||
|
String data. Emits a concatenation of bytes, precisely as you specify
|
||||||
|
them (in particular, @emph{nothing is added to mark the end} of the
|
||||||
|
string). @xref{Constants,, String and numeric constants}, for details
|
||||||
|
about how to write strings. @code{.SDATA} concatenates multiple
|
||||||
|
arguments, making it easy to switch between string representations. You
|
||||||
|
can use commas to separate the individual arguments for clarity, if you
|
||||||
|
choose.
|
||||||
|
|
||||||
|
@item .SDATAB @var{repeat}, "@var{str}" @dots{}
|
||||||
|
Repeated string data. The first argument specifies how many copies of
|
||||||
|
the string to emit; the remaining arguments specify the string, in the
|
||||||
|
same way as the arguments to @code{.SDATA}.
|
||||||
|
|
||||||
|
@item .SDATAZ "@var{str}" @dots{}
|
||||||
|
Zero-terminated string data. Just like @code{.SDATA}, except that
|
||||||
|
@code{.SDATAZ} writes a zero byte at the end of the string.
|
||||||
|
|
||||||
|
@item .SDATAC "@var{str}" @dots{}
|
||||||
|
Count-prefixed string data. Just like @code{.SDATA}, except that
|
||||||
|
@sc{gasp} precedes the string with a leading one-byte count. For
|
||||||
|
example, @samp{.SDATAC "HI"} generates @samp{.byte 2,72,73}. Since the
|
||||||
|
count field is only one byte, you can only use @code{.SDATAC} for
|
||||||
|
strings less than 256 bytes in length.
|
||||||
|
@end ftable
|
||||||
|
|
||||||
|
@node Uninitialized
|
||||||
|
@subsection Uninitialized data
|
||||||
|
|
||||||
|
@c FIXME! .space different on some platforms, notably HPPA. Config?
|
||||||
|
Use the @code{.RES}, @code{.SRES}, @code{.SRESC}, and @code{.SRESZ}
|
||||||
|
directives to reserve memory and leave it uninitialized. @sc{gasp}
|
||||||
|
resolves these directives to appropriate calls of the @sc{gnu}
|
||||||
|
@code{as} @code{.space} directive.
|
||||||
|
|
||||||
|
@ftable @code
|
||||||
|
@item .RES @var{count}
|
||||||
|
@itemx .RES.B @var{count}
|
||||||
|
@itemx .RES.W @var{count}
|
||||||
|
@itemx .RES.L @var{count}
|
||||||
|
Reserve room for @var{count} uninitialized elements of data. The
|
||||||
|
suffix specifies the size of each element: @code{.RES.B} reserves
|
||||||
|
@var{count} bytes, @code{.RES.W} reserves @var{count} pairs of bytes,
|
||||||
|
and @code{.RES.L} reserves @var{count} quartets. @code{.RES} without a
|
||||||
|
suffix is equivalent to @code{.RES.L}.
|
||||||
|
|
||||||
|
@item .SRES @var{count}
|
||||||
|
@itemx .SRES.B @var{count}
|
||||||
|
@itemx .SRES.W @var{count}
|
||||||
|
@itemx .SRES.L @var{count}
|
||||||
|
@c FIXME! This is boring. Shouldn't it at least have a different
|
||||||
|
@c default size? (e.g. the "S" suggests "string", for which .B
|
||||||
|
@c would be more appropriate)
|
||||||
|
@code{.SRES} is a synonym for @samp{.RES}.
|
||||||
|
|
||||||
|
@item .SRESC @var{count}
|
||||||
|
@itemx .SRESC.B @var{count}
|
||||||
|
@itemx .SRESC.W @var{count}
|
||||||
|
@itemx .SRESC.L @var{count}
|
||||||
|
Like @code{.SRES}, but reserves space for @code{@var{count}+1} elements.
|
||||||
|
|
||||||
|
@item .SRESZ @var{count}
|
||||||
|
@itemx .SRESZ.B @var{count}
|
||||||
|
@itemx .SRESZ.W @var{count}
|
||||||
|
@itemx .SRESZ.L @var{count}
|
||||||
|
Like @code{.SRES}, but reserves space for @code{@var{count}+1} elements.
|
||||||
|
@end ftable
|
||||||
|
|
||||||
|
@node Listings
|
||||||
|
@section Assembly listing control
|
||||||
|
|
||||||
|
The @sc{gasp} listing-control directives map straightforwardly to
|
||||||
|
related @sc{gnu} @code{as} directives.
|
||||||
|
|
||||||
|
@ftable @code
|
||||||
|
@item .PRINT LIST
|
||||||
|
@itemx .PRINT NOLIST
|
||||||
|
Print control. This directive emits the @sc{gnu} @code{as} directive
|
||||||
|
@code{.list} or @code{.nolist}, according to its argument. @xref{List,,
|
||||||
|
@code{.list}, as.info, Using as}, for details on how these directives
|
||||||
|
interact.
|
||||||
|
|
||||||
|
@item .FORM LIN=@var{ln}
|
||||||
|
@itemx .FORM COL=@var{cols}
|
||||||
|
@itemx .FORM LIN=@var{ln} COL=@var{cols}
|
||||||
|
Specify the page size for assembly listings: @var{ln} represents the
|
||||||
|
number of lines, and @var{cols} the number of columns. You may specify
|
||||||
|
either page dimension independently, or both together. If you do not
|
||||||
|
specify the number of lines, @sc{gasp} assumes 60 lines; if you do not
|
||||||
|
specify the number of columns, @sc{gasp} assumes 132 columns.
|
||||||
|
(Any values you may have specified in previous instances of @code{.FORM}
|
||||||
|
do @emph{not} carry over as defaults.) Emits the @code{.psize}
|
||||||
|
assembler directive.
|
||||||
|
|
||||||
|
@item .HEADING @var{string}
|
||||||
|
Specify @var{string} as the title of your assembly listings. Emits
|
||||||
|
@samp{.title "@var{string}"}.
|
||||||
|
|
||||||
|
@item .PAGE
|
||||||
|
Force a new page in assembly listings. Emits @samp{.eject}.
|
||||||
|
@end ftable
|
||||||
|
|
||||||
|
@node Other Commands
|
||||||
|
@section Miscellaneous commands
|
||||||
|
|
||||||
|
@ftable @code
|
||||||
|
@item .ORG
|
||||||
|
@c FIXME! This is very strange, since _GAS_ understands .org
|
||||||
|
This command is recognized, but not yet implemented. @sc{gasp}
|
||||||
|
generates an error message for programs that use @code{.ORG}.
|
||||||
|
|
||||||
|
@item .RADIX @var{s}
|
||||||
|
@c FIXME no test cases in testsuite/gasp
|
||||||
|
@sc{gasp} understands numbers in any of base two, eight, ten, or
|
||||||
|
sixteen. You can encode the base explicitly in any numeric constant
|
||||||
|
(@pxref{Constants,, String and numeric constants}). If you write
|
||||||
|
numbers without an explicit indication of the base, the most recent
|
||||||
|
@samp{.RADIX @var{s}} command determines how they are interpreted.
|
||||||
|
@var{s} is a single letter, one of the following:
|
||||||
|
|
||||||
|
@table @code
|
||||||
|
@item .RADIX B
|
||||||
|
Base 2.
|
||||||
|
|
||||||
|
@item .RADIX Q
|
||||||
|
Base 8.
|
||||||
|
|
||||||
|
@item .RADIX D
|
||||||
|
Base 10. This is the original default radix.
|
||||||
|
|
||||||
|
@item .RADIX H
|
||||||
|
Base 16.
|
||||||
|
@end table
|
||||||
|
|
||||||
|
You may specify the argument @var{s} in lower case (any of @samp{bqdh})
|
||||||
|
with the same effects.
|
||||||
|
|
||||||
|
@item .EXPORT @var{name}
|
||||||
|
@itemx .GLOBAL @var{name}
|
||||||
|
@c FIXME! No test cases in testsuite/gasp
|
||||||
|
Declare @var{name} global (emits @samp{.global @var{name}}). The two
|
||||||
|
directives are synonymous.
|
||||||
|
|
||||||
|
@item .PROGRAM
|
||||||
|
No effect: @sc{gasp} accepts this directive, and silently ignores it.
|
||||||
|
|
||||||
|
@item .END
|
||||||
|
Mark end of each preprocessor file. @sc{gasp} issues a warning if it
|
||||||
|
reaches end of file without seeing this command.
|
||||||
|
|
||||||
|
@item .INCLUDE "@var{str}"
|
||||||
|
Preprocess the file named by @var{str}, as if its contents appeared
|
||||||
|
where the @code{.INCLUDE} directive does. @sc{gasp} imposes a maximum
|
||||||
|
limit of 30 stacked include files, as a sanity check.
|
||||||
|
@c FIXME! Why is include depth not affected by -u?
|
||||||
|
|
||||||
|
@item .ALIGN @var{size}
|
||||||
|
@c FIXME! Why is this not utterly pointless?
|
||||||
|
Evaluate the absolute expression @var{size}, and emit the assembly
|
||||||
|
instruction @samp{.align @var{size}} using the result.
|
||||||
|
@end ftable
|
||||||
|
|
||||||
|
@node Syntax Details
|
||||||
|
@section Details of the GASP syntax
|
||||||
|
|
||||||
|
Since @sc{gasp} is meant to work with assembly code, its statement
|
||||||
|
syntax has no surprises for the assembly programmer.
|
||||||
|
|
||||||
|
@cindex whitespace
|
||||||
|
@emph{Whitespace} (blanks or tabs; @emph{not} newline) is partially
|
||||||
|
significant, in that it delimits up to three fields in a line. The
|
||||||
|
amount of whitespace does not matter; you may line up fields in separate
|
||||||
|
lines if you wish, but @sc{gasp} does not require that.
|
||||||
|
|
||||||
|
@cindex fields of @sc{gasp} source line
|
||||||
|
@cindex label field
|
||||||
|
The @emph{first field}, an optional @dfn{label}, must be flush left in a
|
||||||
|
line (with no leading whitespace) if it appears at all. You may use a
|
||||||
|
colon after the label if you wish; @sc{gasp} neither requires the colon
|
||||||
|
nor objects to it (but will not include it as part of the label name).
|
||||||
|
|
||||||
|
@cindex directive field
|
||||||
|
The @emph{second field}, which must appear after some whitespace,
|
||||||
|
contains a @sc{gasp} or assembly @dfn{directive}.
|
||||||
|
|
||||||
|
@cindex argument fields
|
||||||
|
Any @emph{further fields} on a line are @dfn{arguments} to the
|
||||||
|
directive; you can separate them from one another using either commas or
|
||||||
|
whitespace.
|
||||||
|
|
||||||
|
@menu
|
||||||
|
* Markers::
|
||||||
|
* Constants::
|
||||||
|
* Symbols::
|
||||||
|
* Expressions::
|
||||||
|
* String Builtins::
|
||||||
|
@end menu
|
||||||
|
|
||||||
|
@node Markers
|
||||||
|
@subsection Special syntactic markers
|
||||||
|
|
||||||
|
@sc{gasp} recognizes a few special markers: to delimit comments, to
|
||||||
|
continue a statement on the next line, to separate symbols from other
|
||||||
|
characters, and to copy text to the output literally. (One other
|
||||||
|
special marker, @samp{\@@}, works only within macro definitions;
|
||||||
|
@pxref{Macros,, Defining your own directives}.)
|
||||||
|
|
||||||
|
@cindex comments
|
||||||
|
The trailing part of any @sc{gasp} source line may be a @dfn{comment}.
|
||||||
|
A comment begins with the first unquoted @samp{;} or @samp{\;}, and
|
||||||
|
extends to the end of a line. The two kinds of comment markers lead to
|
||||||
|
slightly different treatment:
|
||||||
|
|
||||||
|
@table @code
|
||||||
|
@item ;
|
||||||
|
Generate an assembly comment in the @sc{gasp} output. @sc{gasp} evaluates any
|
||||||
|
preprocessor variables (macro arguments, or variables defined with
|
||||||
|
@code{.ASSIGNA} or @code{.ASSIGNC}) present. For example, a macro that
|
||||||
|
begins like this
|
||||||
|
|
||||||
|
@example
|
||||||
|
.MACRO SUM FROM=0, TO=9
|
||||||
|
; \FROM \TO
|
||||||
|
@end example
|
||||||
|
|
||||||
|
@noindent
|
||||||
|
issues as the first line of output a comment that records the
|
||||||
|
values you used to call the macro.
|
||||||
|
|
||||||
|
@item \;
|
||||||
|
This marks a @sc{gasp} source comment. @sc{gasp} does not copy such
|
||||||
|
comments to the assembly output.
|
||||||
|
@end table
|
||||||
|
|
||||||
|
@cindex continuation character
|
||||||
|
@kindex +
|
||||||
|
To @emph{continue a statement} on the next line of the file, begin the
|
||||||
|
second line with the character @samp{+}.
|
||||||
|
|
||||||
|
@cindex literal copy to output
|
||||||
|
@cindex copying literally to output
|
||||||
|
@cindex preprocessing, avoiding
|
||||||
|
@cindex avoiding preprocessing
|
||||||
|
Occasionally you may want to prevent @sc{gasp} from preprocessing some
|
||||||
|
particular bit of text. To @emph{copy literally} from the @sc{gasp}
|
||||||
|
source to its output, place @samp{\(} before the string to copy, and
|
||||||
|
@samp{)} at the end. For example, write @samp{\(\;)} if you need the
|
||||||
|
characters @samp{\;} in your assembly output.
|
||||||
|
|
||||||
|
@cindex symbol separator
|
||||||
|
@cindex text, separating from symbols
|
||||||
|
@cindex symbols, separating from text
|
||||||
|
To @emph{separate a preprocessor variable} from text to appear
|
||||||
|
immediately after its value, write a single quote (@code{'}). For
|
||||||
|
example, @samp{.SDATA "\P'1"} writes a string built by concatenating the
|
||||||
|
value of @code{P} and the digit @samp{1}. (You cannot achieve this by
|
||||||
|
writing just @samp{\P1}, since @samp{P1} is itself a valid name for a
|
||||||
|
preprocessor variable.)
|
||||||
|
|
||||||
|
@node Constants
|
||||||
|
@subsection String and numeric constants
|
||||||
|
|
||||||
|
There are two ways of writing @dfn{string constants} in @sc{gasp}: as
|
||||||
|
literal text, and by numeric byte value. Specify a string literal
|
||||||
|
between double quotes (@code{"@var{str}"}). Specify an individual
|
||||||
|
numeric byte value as an absolute expression between angle brackets
|
||||||
|
(@code{<@var{expr}>}. Directives that output strings allow you to
|
||||||
|
specify any number of either kind of value, in whatever order is
|
||||||
|
convenient, and concatenate the result.
|
||||||
|
|
||||||
|
@c Details of numeric notation, e.g. base prefixes
|
||||||
|
You can write @dfn{numeric constants} either in a specific base, or in
|
||||||
|
whatever base is currently selected (either 10, or selected by the most
|
||||||
|
recent @code{.RADIX}).
|
||||||
|
|
||||||
|
To write a number in a @emph{specific base}, use the pattern
|
||||||
|
@code{'@var{s}@var{ddd}}: a single quote, followed by a base specifier
|
||||||
|
character @var{s}, followed by digits @var{ddd}. The base specifier
|
||||||
|
character matches those you can specify with @code{.RADIX}: @samp{B} for
|
||||||
|
base 2, @samp{Q} for base 8, @samp{D} for base 10, and @samp{H} for base
|
||||||
|
16. (You can write this character in lower case if you prefer.)
|
||||||
|
|
||||||
|
@c FIXME! What are rules for recognizing number in deflt base? Whatever
|
||||||
|
@c is left over after parsing other things??
|
||||||
|
|
||||||
|
@node Symbols
|
||||||
|
@subsection Symbols
|
||||||
|
|
||||||
|
@sc{gasp} recognizes symbol names that start with any alphabetic character,
|
||||||
|
@samp{_}, or @samp{$}, and continue with any of the same characters or
|
||||||
|
with digits. Label names follow the same rules.
|
||||||
|
|
||||||
|
@node Expressions
|
||||||
|
@subsection Arithmetic expressions in GASP
|
||||||
|
|
||||||
|
@cindex absolute expressions
|
||||||
|
@cindex relocatable expressions
|
||||||
|
There are two kinds of expressions, depending on their result:
|
||||||
|
@dfn{absolute} expressions, which resolve to a constant (that is, they
|
||||||
|
do not involve any values unknown to @sc{gasp}), and @dfn{relocatable}
|
||||||
|
expressions, which must reduce to the form
|
||||||
|
|
||||||
|
@example
|
||||||
|
@var{addsym}+@var{const}-@var{subsym}
|
||||||
|
@end example
|
||||||
|
|
||||||
|
@noindent
|
||||||
|
where @var{addsym} and @var{subsym} are assembly symbols of unknown
|
||||||
|
value, and @var{const} is a constant.
|
||||||
|
|
||||||
|
Arithmetic for @sc{gasp} expressions follows very similar rules to C.
|
||||||
|
You can use parentheses to change precedence; otherwise, arithmetic
|
||||||
|
primitives have decreasing precedence in the order of the following
|
||||||
|
list.
|
||||||
|
|
||||||
|
@enumerate
|
||||||
|
@item
|
||||||
|
Single-argument @code{+} (identity), @code{-} (arithmetic opposite), or
|
||||||
|
@code{~} (bitwise negation). @emph{The argument must be an absolute
|
||||||
|
expression.}
|
||||||
|
|
||||||
|
@item
|
||||||
|
@code{*} (multiplication) and @code{/} (division). @emph{Both arguments
|
||||||
|
must be absolute expressions.}
|
||||||
|
|
||||||
|
@item
|
||||||
|
@code{+} (addition) and @code{-} (subtraction). @emph{At least one argument
|
||||||
|
must be absolute.}
|
||||||
|
@c FIXME! Actually, subtraction doesn't check for this.
|
||||||
|
|
||||||
|
@item
|
||||||
|
@code{&} (bitwise and). @emph{Both arguments must be absolute.}
|
||||||
|
|
||||||
|
@item
|
||||||
|
@c FIXME! I agree ~ is a better notation than ^ for xor, but is the
|
||||||
|
@c improvement worth differing from C?
|
||||||
|
@code{|} (bitwise or) and @code{~} (bitwise exclusive or; @code{^} in
|
||||||
|
C). @emph{Both arguments must be absolute.}
|
||||||
|
@end enumerate
|
||||||
|
|
||||||
|
@node String Builtins
|
||||||
|
@subsection String primitives
|
||||||
|
|
||||||
|
You can use these primitives to manipulate strings (in the argument
|
||||||
|
field of @sc{gasp} statements):
|
||||||
|
|
||||||
|
@ftable @code
|
||||||
|
@item .LEN("@var{str}")
|
||||||
|
The length of string @code{"@var{str}"}, as an absolute expression. For
|
||||||
|
example, @samp{.RES.B .LEN("sample")} reserves six bytes of memory.
|
||||||
|
|
||||||
|
@item .INSTR("@var{string}", "@var{seg}", @var{ix})
|
||||||
|
Search for the first occurrence of @var{seg} after position @var{ix} of
|
||||||
|
@var{string}. For example, @samp{.INSTR("ABCDEFG", "CDE", 0)} evaluates
|
||||||
|
to the absolute result @code{2}.
|
||||||
|
|
||||||
|
The result is @code{-1} if @var{seg} does not occur in @var{string}
|
||||||
|
after position @var{ix}.
|
||||||
|
|
||||||
|
@item .SUBSTR("@var{string}",@var{start},@var{len})
|
||||||
|
The substring of @var{string} beginning at byte number @var{start} and
|
||||||
|
extending for @var{len} bytes.
|
||||||
|
@end ftable
|
||||||
|
|
||||||
|
@node Index
|
||||||
|
@unnumbered Index
|
||||||
|
|
||||||
|
@printindex cp
|
||||||
|
@bye
|
||||||
Loading…
Reference in New Issue
Block a user