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@c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1998, 2002

@c Free Software Foundation, Inc.

@c This is part of the GAS manual.

@c For copying conditions, see the file as.texinfo.

@c VAX/VMS description enhanced and corrected by Klaus K"aempf, kkaempf@progis.de

@ifset GENERIC

@node Vax-Dependent

@chapter VAX Dependent Features

@cindex VAX support

@end ifset

@ifclear GENERIC

@node Machine Dependencies

@chapter VAX Dependent Features

@cindex VAX support

@end ifclear

@menu

* VAX-Opts::                    VAX Command-Line Options

* VAX-float::                   VAX Floating Point

* VAX-directives::              Vax Machine Directives

* VAX-opcodes::                 VAX Opcodes

* VAX-branch::                  VAX Branch Improvement

* VAX-operands::                VAX Operands

* VAX-no::                      Not Supported on VAX

@end menu

@node VAX-Opts

@section VAX Command-Line Options

@cindex command-line options ignored, VAX

@cindex VAX command-line options ignored

The Vax version of @code{@value{AS}} accepts any of the following options,

gives a warning message that the option was ignored and proceeds.

These options are for compatibility with scripts designed for other

people's assemblers.

@table @code

@cindex @code{-D}, ignored on VAX

@cindex @code{-S}, ignored on VAX

@cindex @code{-T}, ignored on VAX

@item @code{-D} (Debug)

@itemx @code{-S} (Symbol Table)

@itemx @code{-T} (Token Trace)

These are obsolete options used to debug old assemblers.

@cindex @code{-d}, VAX option

@item @code{-d} (Displacement size for JUMPs)

This option expects a number following the @samp{-d}.  Like options

that expect filenames, the number may immediately follow the

@samp{-d} (old standard) or constitute the whole of the command line

argument that follows @samp{-d} (@sc{gnu} standard).

@cindex @code{-V}, redundant on VAX

@item @code{-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{@value{AS}} always does this, so this

option is redundant.

@cindex @code{-J}, ignored on VAX

@item @code{-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.

@cindex @code{-t}, ignored on VAX

@item @code{-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.  Since @code{@value{AS}} does not use a temporary disk file, this

option makes no difference.  @samp{-t} needs exactly one

filename.

@end table

@cindex VMS (VAX) options

@cindex options for VAX/VMS

@cindex VAX/VMS options

@cindex Vax-11 C compatibility

@cindex symbols with uppercase, VAX/VMS

The Vax version of the assembler accepts additional options when

compiled for VMS:

@table @samp

@cindex @samp{-h} option, VAX/VMS

@item -h @var{n}

External symbol or section (used for global variables) names are not

case sensitive on VAX/VMS and always mapped to upper case.  This is

contrary to the C language definition which explicitly distinguishes

upper and lower case.  To implement a standard conforming C compiler,

names must be changed (mapped) to preserve the case information.  The

default mapping is to convert all lower case characters to uppercase and

adding an underscore followed by a 6 digit hex value, representing a 24

digit binary value.  The one digits in the binary value represent which

characters are uppercase in the original symbol name.

The @samp{-h @var{n}} option determines how we map names.  This takes

several values.  No @samp{-h} switch at all allows case hacking as

described above.  A value of zero (@samp{-h0}) implies names should be

upper case, and inhibits the case hack.  A value of 2 (@samp{-h2})

implies names should be all lower case, with no case hack.  A value of 3

(@samp{-h3}) implies that case should be preserved.  The value 1 is

unused.  The @code{-H} option directs @code{@value{AS}} to display

every mapped symbol during assembly.

Symbols whose names include a dollar sign @samp{$} are exceptions to the

general name mapping.  These symbols are normally only used to reference

VMS library names.  Such symbols are always mapped to upper case.

@cindex @samp{-+} option, VAX/VMS

@item -+

The @samp{-+} option causes @code{@value{AS}} to truncate any symbol

name larger than 31 characters.  The @samp{-+} option also prevents some

code following the @samp{_main} symbol normally added to make the object

file compatible with Vax-11 "C".

@cindex @samp{-1} option, VAX/VMS

@item -1

This option is ignored for backward compatibility with @code{@value{AS}}

version 1.x.

@cindex @samp{-H} option, VAX/VMS

@item -H

The @samp{-H} option causes @code{@value{AS}} to print every symbol

which was changed by case mapping.

@end table

@node VAX-float

@section VAX Floating Point

@cindex VAX floating point

@cindex floating point, VAX

Conversion of flonums to floating point is correct, and

compatible with previous assemblers.  Rounding is

towards zero if the remainder is exactly half the least significant bit.

@code{D}, @code{F}, @code{G} and @code{H} floating point formats

are understood.

Immediate floating literals (@emph{e.g.} @samp{S`$6.9})

are rendered correctly.  Again, rounding is towards zero in the

boundary case.

@cindex @code{float} directive, VAX

@cindex @code{double} directive, VAX

The @code{.float} directive produces @code{f} format numbers.

The @code{.double} directive produces @code{d} format numbers.

@node VAX-directives

@section Vax Machine Directives

@cindex machine directives, VAX

@cindex VAX machine directives

The Vax version of the assembler supports four directives for

generating Vax floating point constants.  They are described in the

table below.

@cindex wide floating point directives, VAX

@table @code

@cindex @code{dfloat} directive, VAX

@item .dfloat

This expects zero or more flonums, separated by commas, and

assembles Vax @code{d} format 64-bit floating point constants.

@cindex @code{ffloat} directive, VAX

@item .ffloat

This expects zero or more flonums, separated by commas, and

assembles Vax @code{f} format 32-bit floating point constants.

@cindex @code{gfloat} directive, VAX

@item .gfloat

This expects zero or more flonums, separated by commas, and

assembles Vax @code{g} format 64-bit floating point constants.

@cindex @code{hfloat} directive, VAX

@item .hfloat

This expects zero or more flonums, separated by commas, and

assembles Vax @code{h} format 128-bit floating point constants.

@end table

@node VAX-opcodes

@section VAX Opcodes

@cindex VAX opcode mnemonics

@cindex opcode mnemonics, VAX

@cindex mnemonics for opcodes, VAX

All DEC mnemonics are supported.  Beware that @code{case@dots{}}

instructions have exactly 3 operands.  The dispatch table that

follows the @code{case@dots{}} instruction should be made with

@code{.word} statements.  This is compatible with all unix

assemblers we know of.

@node VAX-branch

@section VAX Branch Improvement

@cindex VAX branch improvement

@cindex branch improvement, VAX

@cindex pseudo-ops for branch, VAX

Certain pseudo opcodes are permitted.  They are for branch

instructions.  They expand to the shortest branch instruction that

reaches 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 do not need this feature, avoid these

opcodes.  Here are the mnemonics, and the code they can expand into.

@table @code

@item jbsb

@samp{Jsb} is already an instruction mnemonic, so we chose @samp{jbsb}.

@table @asis

@item (byte displacement)

@kbd{bsbb @dots{}}

@item (word displacement)

@kbd{bsbw @dots{}}

@item (long displacement)

@kbd{jsb @dots{}}

@end table

@item jbr

@itemx jr

Unconditional branch.

@table @asis

@item (byte displacement)

@kbd{brb @dots{}}

@item (word displacement)

@kbd{brw @dots{}}

@item (long displacement)

@kbd{jmp @dots{}}

@end table

@item j@var{COND}

@var{COND} may be any one of the conditional branches

@code{neq}, @code{nequ}, @code{eql}, @code{eqlu}, @code{gtr},

@code{geq}, @code{lss}, @code{gtru}, @code{lequ}, @code{vc}, @code{vs},

@code{gequ}, @code{cc}, @code{lssu}, @code{cs}.

@var{COND} may also be one of the bit tests

@code{bs}, @code{bc}, @code{bss}, @code{bcs}, @code{bsc}, @code{bcc},

@code{bssi}, @code{bcci}, @code{lbs}, @code{lbc}.

@var{NOTCOND} is the opposite condition to @var{COND}.

@table @asis

@item (byte displacement)

@kbd{b@var{COND} @dots{}}

@item (word displacement)

@kbd{b@var{NOTCOND} foo ; brw @dots{} ; foo:}

@item (long displacement)

@kbd{b@var{NOTCOND} foo ; jmp @dots{} ; foo:}

@end table

@item jacb@var{X}

@var{X} may be one of @code{b d f g h l w}.

@table @asis

@item (word displacement)

@kbd{@var{OPCODE} @dots{}}

@item (long displacement)

@example

@var{OPCODE} @dots{}, foo ;

brb bar ;

foo: jmp @dots{} ;

bar:

@end example

@end table

@item jaob@var{YYY}

@var{YYY} may be one of @code{lss leq}.

@item jsob@var{ZZZ}

@var{ZZZ} may be one of @code{geq gtr}.

@table @asis

@item (byte displacement)

@kbd{@var{OPCODE} @dots{}}

@item (word displacement)

@example

@var{OPCODE} @dots{}, foo ;

brb bar ;

foo: brw @var{destination} ;

bar:

@end example

@item (long displacement)

@example

@var{OPCODE} @dots{}, foo ;

brb bar ;

foo: jmp @var{destination} ;

bar:

@end example

@end table

@item aobleq

@itemx aoblss

@itemx sobgeq

@itemx sobgtr

@table @asis

@item (byte displacement)

@kbd{@var{OPCODE} @dots{}}

@item (word displacement)

@example

@var{OPCODE} @dots{}, foo ;

brb bar ;

foo: brw @var{destination} ;

bar:

@end example

@item (long displacement)

@example

@var{OPCODE} @dots{}, foo ;

brb bar ;

foo: jmp @var{destination} ;

bar:

@end example

@end table

@end table

@node VAX-operands

@section VAX Operands

@cindex VAX operand notation

@cindex operand notation, VAX

@cindex immediate character, VAX

@cindex VAX immediate character

The immediate character is @samp{$} for Unix compatibility, not

@samp{#} as DEC writes it.

@cindex indirect character, VAX

@cindex VAX indirect character

The indirect character is @samp{*} for Unix compatibility, not

@samp{@@} as DEC writes it.

@cindex displacement sizing character, VAX

@cindex VAX displacement sizing character

The displacement sizing character is @samp{`} (an accent grave) for

Unix compatibility, not @samp{^} as DEC writes it.  The letter

preceding @samp{`} may have either case.  @samp{G} is not

understood, but all other letters (@code{b i l s w}) are understood.

@cindex register names, VAX

@cindex VAX register names

Register names understood are @code{r0 r1 r2 @dots{} r15 ap fp sp

pc}.  Upper and lower case letters are equivalent.

For instance

@smallexample

tstb *w`$4(r5)

@end smallexample

Any expression is permitted in an operand.  Operands are comma

separated.

@c There is some bug to do with recognizing expressions

@c in operands, but I forget what it is.  It is

@c a syntax clash because () is used as an address mode

@c and to encapsulate sub-expressions.

@node VAX-no

@section Not Supported on VAX

@cindex VAX bitfields not supported

@cindex bitfields, not supported on VAX

Vax bit fields can not be assembled with @code{@value{AS}}.  Someone

can add the required code if they really need it.