359 lines
11 KiB
Plaintext
359 lines
11 KiB
Plaintext
@c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1998
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@c Free Software Foundation, Inc.
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@c This is part of the GAS manual.
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@c For copying conditions, see the file as.texinfo.
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@c VAX/VMS description exhanced and corrected by Klaus K"aempf, kkaempf@progis.de
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@ifset GENERIC
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@node Vax-Dependent
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@chapter VAX Dependent Features
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@cindex VAX support
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@end ifset
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@ifclear GENERIC
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@node Machine Dependencies
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@chapter VAX Dependent Features
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@cindex VAX support
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@end ifclear
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@menu
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* VAX-Opts:: VAX Command-Line Options
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* VAX-float:: VAX Floating Point
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* VAX-directives:: Vax Machine Directives
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* VAX-opcodes:: VAX Opcodes
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* VAX-branch:: VAX Branch Improvement
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* VAX-operands:: VAX Operands
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* VAX-no:: Not Supported on VAX
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@end menu
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@node VAX-Opts
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@section VAX Command-Line Options
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@cindex command-line options ignored, VAX
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@cindex VAX command-line options ignored
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The Vax version of @code{@value{AS}} accepts any of the following options,
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gives a warning message that the option was ignored and proceeds.
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These options are for compatibility with scripts designed for other
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people's assemblers.
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@table @code
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@cindex @code{-D}, ignored on VAX
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@cindex @code{-S}, ignored on VAX
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@cindex @code{-T}, ignored on VAX
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@item @code{-D} (Debug)
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@itemx @code{-S} (Symbol Table)
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@itemx @code{-T} (Token Trace)
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These are obsolete options used to debug old assemblers.
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@cindex @code{-d}, VAX option
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@item @code{-d} (Displacement size for JUMPs)
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This option expects a number following the @samp{-d}. Like options
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that expect filenames, the number may immediately follow the
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@samp{-d} (old standard) or constitute the whole of the command line
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argument that follows @samp{-d} (@sc{gnu} standard).
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@cindex @code{-V}, redundant on VAX
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@item @code{-V} (Virtualize Interpass Temporary File)
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Some other assemblers use a temporary file. This option
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commanded them to keep the information in active memory rather
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than in a disk file. @code{@value{AS}} always does this, so this
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option is redundant.
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@cindex @code{-J}, ignored on VAX
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@item @code{-J} (JUMPify Longer Branches)
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Many 32-bit computers permit a variety of branch instructions
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to do the same job. Some of these instructions are short (and
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fast) but have a limited range; others are long (and slow) but
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can branch anywhere in virtual memory. Often there are 3
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flavors of branch: short, medium and long. Some other
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assemblers would emit short and medium branches, unless told by
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this option to emit short and long branches.
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@cindex @code{-t}, ignored on VAX
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@item @code{-t} (Temporary File Directory)
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Some other assemblers may use a temporary file, and this option
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takes a filename being the directory to site the temporary
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file. Since @code{@value{AS}} does not use a temporary disk file, this
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option makes no difference. @samp{-t} needs exactly one
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filename.
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@end table
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@cindex VMS (VAX) options
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@cindex options for VAX/VMS
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@cindex VAX/VMS options
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@cindex Vax-11 C compatibility
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@cindex symbols with uppercase, VAX/VMS
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The Vax version of the assembler accepts additional options when
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compiled for VMS:
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@table @samp
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@cindex @samp{-h} option, VAX/VMS
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@item -h @var{n}
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External symbol or section (used for global variables) names are not
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case sensitive on VAX/VMS and always mapped to upper case. This is
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contrary to the C language definition which explicitly distinguishes
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upper and lower case. To implement a standard conforming C compiler,
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names must be changed (mapped) to preserve the case information. The
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default mapping is to convert all lower case characters to uppercase and
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adding an underscore followed by a 6 digit hex value, representing a 24
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digit binary value. The one digits in the binary value represent which
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characters are uppercase in the original symbol name.
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The @samp{-h @var{n}} option determines how we map names. This takes
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several values. No @samp{-h} switch at all allows case hacking as
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described above. A value of zero (@samp{-h0}) implies names should be
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upper case, and inhibits the case hack. A value of 2 (@samp{-h2})
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implies names should be all lower case, with no case hack. A value of 3
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(@samp{-h3}) implies that case should be preserved. The value 1 is
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unused. The @code{-H} option directs @code{@value{AS}} to display
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every mapped symbol during assembly.
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Symbols whose names include a dollar sign @samp{$} are exceptions to the
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general name mapping. These symbols are normally only used to reference
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VMS library names. Such symbols are always mapped to upper case.
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@cindex @samp{-+} option, VAX/VMS
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@item -+
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The @samp{-+} option causes @code{@value{AS}} to truncate any symbol
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name larger than 31 characters. The @samp{-+} option also prevents some
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code following the @samp{_main} symbol normally added to make the object
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file compatible with Vax-11 "C".
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@cindex @samp{-1} option, VAX/VMS
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@item -1
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This option is ignored for backward compatibility with @code{@value{AS}}
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version 1.x.
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@cindex @samp{-H} option, VAX/VMS
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@item -H
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The @samp{-H} option causes @code{@value{AS}} to print every symbol
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which was changed by case mapping.
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@end table
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@node VAX-float
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@section VAX Floating Point
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@cindex VAX floating point
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@cindex floating point, VAX
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Conversion of flonums to floating point is correct, and
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compatible with previous assemblers. Rounding is
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towards zero if the remainder is exactly half the least significant bit.
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@code{D}, @code{F}, @code{G} and @code{H} floating point formats
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are understood.
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Immediate floating literals (@emph{e.g.} @samp{S`$6.9})
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are rendered correctly. Again, rounding is towards zero in the
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boundary case.
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@cindex @code{float} directive, VAX
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@cindex @code{double} directive, VAX
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The @code{.float} directive produces @code{f} format numbers.
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The @code{.double} directive produces @code{d} format numbers.
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@node VAX-directives
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@section Vax Machine Directives
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@cindex machine directives, VAX
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@cindex VAX machine directives
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The Vax version of the assembler supports four directives for
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generating Vax floating point constants. They are described in the
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table below.
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@cindex wide floating point directives, VAX
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@table @code
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@cindex @code{dfloat} directive, VAX
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@item .dfloat
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This expects zero or more flonums, separated by commas, and
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assembles Vax @code{d} format 64-bit floating point constants.
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@cindex @code{ffloat} directive, VAX
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@item .ffloat
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This expects zero or more flonums, separated by commas, and
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assembles Vax @code{f} format 32-bit floating point constants.
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@cindex @code{gfloat} directive, VAX
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@item .gfloat
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This expects zero or more flonums, separated by commas, and
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assembles Vax @code{g} format 64-bit floating point constants.
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@cindex @code{hfloat} directive, VAX
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@item .hfloat
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This expects zero or more flonums, separated by commas, and
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assembles Vax @code{h} format 128-bit floating point constants.
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@end table
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@node VAX-opcodes
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@section VAX Opcodes
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@cindex VAX opcode mnemonics
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@cindex opcode mnemonics, VAX
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@cindex mnemonics for opcodes, VAX
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All DEC mnemonics are supported. Beware that @code{case@dots{}}
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instructions have exactly 3 operands. The dispatch table that
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follows the @code{case@dots{}} instruction should be made with
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@code{.word} statements. This is compatible with all unix
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assemblers we know of.
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@node VAX-branch
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@section VAX Branch Improvement
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@cindex VAX branch improvement
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@cindex branch improvement, VAX
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@cindex pseudo-ops for branch, VAX
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Certain pseudo opcodes are permitted. They are for branch
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instructions. They expand to the shortest branch instruction that
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reaches the target. Generally these mnemonics are made by
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substituting @samp{j} for @samp{b} at the start of a DEC mnemonic.
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This feature is included both for compatibility and to help
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compilers. If you do not need this feature, avoid these
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opcodes. Here are the mnemonics, and the code they can expand into.
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@table @code
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@item jbsb
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@samp{Jsb} is already an instruction mnemonic, so we chose @samp{jbsb}.
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@table @asis
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@item (byte displacement)
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@kbd{bsbb @dots{}}
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@item (word displacement)
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@kbd{bsbw @dots{}}
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@item (long displacement)
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@kbd{jsb @dots{}}
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@end table
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@item jbr
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@itemx jr
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Unconditional branch.
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@table @asis
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@item (byte displacement)
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@kbd{brb @dots{}}
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@item (word displacement)
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@kbd{brw @dots{}}
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@item (long displacement)
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@kbd{jmp @dots{}}
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@end table
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@item j@var{COND}
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@var{COND} may be any one of the conditional branches
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@code{neq}, @code{nequ}, @code{eql}, @code{eqlu}, @code{gtr},
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@code{geq}, @code{lss}, @code{gtru}, @code{lequ}, @code{vc}, @code{vs},
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@code{gequ}, @code{cc}, @code{lssu}, @code{cs}.
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@var{COND} may also be one of the bit tests
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@code{bs}, @code{bc}, @code{bss}, @code{bcs}, @code{bsc}, @code{bcc},
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@code{bssi}, @code{bcci}, @code{lbs}, @code{lbc}.
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@var{NOTCOND} is the opposite condition to @var{COND}.
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@table @asis
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@item (byte displacement)
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@kbd{b@var{COND} @dots{}}
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@item (word displacement)
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@kbd{b@var{NOTCOND} foo ; brw @dots{} ; foo:}
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@item (long displacement)
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@kbd{b@var{NOTCOND} foo ; jmp @dots{} ; foo:}
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@end table
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@item jacb@var{X}
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@var{X} may be one of @code{b d f g h l w}.
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@table @asis
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@item (word displacement)
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@kbd{@var{OPCODE} @dots{}}
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@item (long displacement)
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@example
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@var{OPCODE} @dots{}, foo ;
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brb bar ;
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foo: jmp @dots{} ;
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bar:
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@end example
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@end table
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@item jaob@var{YYY}
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@var{YYY} may be one of @code{lss leq}.
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@item jsob@var{ZZZ}
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@var{ZZZ} may be one of @code{geq gtr}.
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@table @asis
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@item (byte displacement)
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@kbd{@var{OPCODE} @dots{}}
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@item (word displacement)
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@example
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@var{OPCODE} @dots{}, foo ;
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brb bar ;
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foo: brw @var{destination} ;
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bar:
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@end example
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@item (long displacement)
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@example
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@var{OPCODE} @dots{}, foo ;
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brb bar ;
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foo: jmp @var{destination} ;
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bar:
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@end example
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@end table
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@item aobleq
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@itemx aoblss
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@itemx sobgeq
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@itemx sobgtr
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@table @asis
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@item (byte displacement)
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@kbd{@var{OPCODE} @dots{}}
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@item (word displacement)
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@example
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@var{OPCODE} @dots{}, foo ;
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brb bar ;
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foo: brw @var{destination} ;
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bar:
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@end example
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@item (long displacement)
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@example
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@var{OPCODE} @dots{}, foo ;
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brb bar ;
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foo: jmp @var{destination} ;
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bar:
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@end example
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@end table
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@end table
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@node VAX-operands
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@section VAX Operands
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@cindex VAX operand notation
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@cindex operand notation, VAX
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@cindex immediate character, VAX
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@cindex VAX immediate character
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The immediate character is @samp{$} for Unix compatibility, not
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@samp{#} as DEC writes it.
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@cindex indirect character, VAX
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@cindex VAX indirect character
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The indirect character is @samp{*} for Unix compatibility, not
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@samp{@@} as DEC writes it.
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@cindex displacement sizing character, VAX
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@cindex VAX displacement sizing character
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The displacement sizing character is @samp{`} (an accent grave) for
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Unix compatibility, not @samp{^} as DEC writes it. The letter
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preceding @samp{`} may have either case. @samp{G} is not
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understood, but all other letters (@code{b i l s w}) are understood.
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@cindex register names, VAX
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@cindex VAX register names
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Register names understood are @code{r0 r1 r2 @dots{} r15 ap fp sp
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pc}. Upper and lower case letters are equivalent.
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For instance
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@smallexample
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tstb *w`$4(r5)
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@end smallexample
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Any expression is permitted in an operand. Operands are comma
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separated.
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@c There is some bug to do with recognizing expressions
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@c in operands, but I forget what it is. It is
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@c a syntax clash because () is used as an address mode
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@c and to encapsulate sub-expressions.
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@node VAX-no
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@section Not Supported on VAX
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@cindex VAX bitfields not supported
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@cindex bitfields, not supported on VAX
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Vax bit fields can not be assembled with @code{@value{AS}}. Someone
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can add the required code if they really need it.
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