gas/doc/c-vax.texi

   1 @c Copyright (C) 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc.
   2 @c This is part of the GAS manual.
   3 @c For copying conditions, see the file as.texinfo.
   4 @ifset GENERIC
   5 @node Vax-Dependent
   6 @chapter VAX Dependent Features
   7 @cindex VAX support
   8
   9 @end ifset
  10 @ifclear GENERIC
  11 @node Machine Dependencies
  12 @chapter VAX Dependent Features
  13 @cindex VAX support
  14
  15 @end ifclear
  16
  17 @menu
  18 * Vax-Opts::                    VAX Command-Line Options
  19 * VAX-float::                   VAX Floating Point
  20 * VAX-directives::              Vax Machine Directives
  21 * VAX-opcodes::                 VAX Opcodes
  22 * VAX-branch::                  VAX Branch Improvement
  23 * VAX-operands::                VAX Operands
  24 * VAX-no::                      Not Supported on VAX
  25 @end menu
  26
  27
  28 @node Vax-Opts
  29 @section VAX Command-Line Options
  30
  31 @cindex command-line options ignored, VAX
  32 @cindex VAX command-line options ignored
  33 The Vax version of @code{@value{AS}} accepts any of the following options,
  34 gives a warning message that the option was ignored and proceeds.
  35 These options are for compatibility with scripts designed for other
  36 people's assemblers.
  37
  38 @table @code
  39 @cindex @code{-D}, ignored on VAX
  40 @cindex @code{-S}, ignored on VAX
  41 @cindex @code{-T}, ignored on VAX
  42 @item @code{-D} (Debug)
  43 @itemx @code{-S} (Symbol Table)
  44 @itemx @code{-T} (Token Trace)
  45 These are obsolete options used to debug old assemblers.
  46
  47 @cindex @code{-d}, VAX option
  48 @item @code{-d} (Displacement size for JUMPs)
  49 This option expects a number following the @samp{-d}.  Like options
  50 that expect filenames, the number may immediately follow the
  51 @samp{-d} (old standard) or constitute the whole of the command line
  52 argument that follows @samp{-d} (@sc{gnu} standard).
  53
  54 @cindex @code{-V}, redundant on VAX
  55 @item @code{-V} (Virtualize Interpass Temporary File)
  56 Some other assemblers use a temporary file.  This option
  57 commanded them to keep the information in active memory rather
  58 than in a disk file.  @code{@value{AS}} always does this, so this
  59 option is redundant.
  60
  61 @cindex @code{-J}, ignored on VAX
  62 @item @code{-J} (JUMPify Longer Branches)
  63 Many 32-bit computers permit a variety of branch instructions
  64 to do the same job.  Some of these instructions are short (and
  65 fast) but have a limited range; others are long (and slow) but
  66 can branch anywhere in virtual memory.  Often there are 3
  67 flavors of branch: short, medium and long.  Some other
  68 assemblers would emit short and medium branches, unless told by
  69 this option to emit short and long branches.
  70
  71 @cindex @code{-t}, ignored on VAX
  72 @item @code{-t} (Temporary File Directory)
  73 Some other assemblers may use a temporary file, and this option
  74 takes a filename being the directory to site the temporary
  75 file.  Since @code{@value{AS}} does not use a temporary disk file, this
  76 option makes no difference.  @samp{-t} needs exactly one
  77 filename.
  78 @end table
  79
  80 @cindex VMS (VAX) options
  81 @cindex options for VAX/VMS
  82 @cindex VAX/VMS options
  83 @cindex @code{-h} option, VAX/VMS
  84 @cindex @code{-+} option, VAX/VMS
  85 @cindex Vax-11 C compatibility
  86 @cindex symbols with lowercase, VAX/VMS
  87 @c FIXME!  look into "I think" below, correct if needed, delete.
  88 The Vax version of the assembler accepts two options when
  89 compiled for VMS.  They are @samp{-h}, and @samp{-+}.  The
  90 @samp{-h} option prevents @code{@value{AS}} from modifying the
  91 symbol-table entries for symbols that contain lowercase
  92 characters (I think).  The @samp{-+} option causes @code{@value{AS}} to
  93 print warning messages if the FILENAME part of the object file,
  94 or any symbol name is larger than 31 characters.  The @samp{-+}
  95 option also inserts some code following the @samp{_main}
  96 symbol so that the object file is compatible with Vax-11
  97 "C".
  98
  99 @node VAX-float
 100 @section VAX Floating Point
 101
 102 @cindex VAX floating point
 103 @cindex floating point, VAX
 104 Conversion of flonums to floating point is correct, and
 105 compatible with previous assemblers.  Rounding is
 106 towards zero if the remainder is exactly half the least significant bit.
 107
 108 @code{D}, @code{F}, @code{G} and @code{H} floating point formats
 109 are understood.
 110
 111 Immediate floating literals (@emph{e.g.} @samp{S`$6.9})
 112 are rendered correctly.  Again, rounding is towards zero in the
 113 boundary case.
 114
 115 @cindex @code{float} directive, VAX
 116 @cindex @code{double} directive, VAX
 117 The @code{.float} directive produces @code{f} format numbers.
 118 The @code{.double} directive produces @code{d} format numbers.
 119
 120 @node VAX-directives
 121 @section Vax Machine Directives
 122
 123 @cindex machine directives, VAX
 124 @cindex VAX machine directives
 125 The Vax version of the assembler supports four directives for
 126 generating Vax floating point constants.  They are described in the
 127 table below.
 128
 129 @cindex wide floating point directives, VAX
 130 @table @code
 131 @cindex @code{dfloat} directive, VAX
 132 @item .dfloat
 133 This expects zero or more flonums, separated by commas, and
 134 assembles Vax @code{d} format 64-bit floating point constants.
 135
 136 @cindex @code{ffloat} directive, VAX
 137 @item .ffloat
 138 This expects zero or more flonums, separated by commas, and
 139 assembles Vax @code{f} format 32-bit floating point constants.
 140
 141 @cindex @code{gfloat} directive, VAX
 142 @item .gfloat
 143 This expects zero or more flonums, separated by commas, and
 144 assembles Vax @code{g} format 64-bit floating point constants.
 145
 146 @cindex @code{hfloat} directive, VAX
 147 @item .hfloat
 148 This expects zero or more flonums, separated by commas, and
 149 assembles Vax @code{h} format 128-bit floating point constants.
 150
 151 @end table
 152
 153 @node VAX-opcodes
 154 @section VAX Opcodes
 155
 156 @cindex VAX opcode mnemonics
 157 @cindex opcode mnemonics, VAX
 158 @cindex mnemonics for opcodes, VAX
 159 All DEC mnemonics are supported.  Beware that @code{case@dots{}}
 160 instructions have exactly 3 operands.  The dispatch table that
 161 follows the @code{case@dots{}} instruction should be made with
 162 @code{.word} statements.  This is compatible with all unix
 163 assemblers we know of.
 164
 165 @node VAX-branch
 166 @section VAX Branch Improvement
 167
 168 @cindex VAX branch improvement
 169 @cindex branch improvement, VAX
 170 @cindex pseudo-ops for branch, VAX
 171 Certain pseudo opcodes are permitted.  They are for branch
 172 instructions.  They expand to the shortest branch instruction that
 173 reaches the target.  Generally these mnemonics are made by
 174 substituting @samp{j} for @samp{b} at the start of a DEC mnemonic.
 175 This feature is included both for compatibility and to help
 176 compilers.  If you do not need this feature, avoid these
 177 opcodes.  Here are the mnemonics, and the code they can expand into.
 178
 179 @table @code
 180 @item jbsb
 181 @samp{Jsb} is already an instruction mnemonic, so we chose @samp{jbsb}.
 182 @table @asis
 183 @item (byte displacement)
 184 @kbd{bsbb @dots{}}
 185 @item (word displacement)
 186 @kbd{bsbw @dots{}}
 187 @item (long displacement)
 188 @kbd{jsb @dots{}}
 189 @end table
 190 @item jbr
 191 @itemx jr
 192 Unconditional branch.
 193 @table @asis
 194 @item (byte displacement)
 195 @kbd{brb @dots{}}
 196 @item (word displacement)
 197 @kbd{brw @dots{}}
 198 @item (long displacement)
 199 @kbd{jmp @dots{}}
 200 @end table
 201 @item j@var{COND}
 202 @var{COND} may be any one of the conditional branches
 203 @code{neq}, @code{nequ}, @code{eql}, @code{eqlu}, @code{gtr},
 204 @code{geq}, @code{lss}, @code{gtru}, @code{lequ}, @code{vc}, @code{vs},
 205 @code{gequ}, @code{cc}, @code{lssu}, @code{cs}.
 206 @var{COND} may also be one of the bit tests
 207 @code{bs}, @code{bc}, @code{bss}, @code{bcs}, @code{bsc}, @code{bcc},
 208 @code{bssi}, @code{bcci}, @code{lbs}, @code{lbc}.
 209 @var{NOTCOND} is the opposite condition to @var{COND}.
 210 @table @asis
 211 @item (byte displacement)
 212 @kbd{b@var{COND} @dots{}}
 213 @item (word displacement)
 214 @kbd{b@var{NOTCOND} foo ; brw @dots{} ; foo:}
 215 @item (long displacement)
 216 @kbd{b@var{NOTCOND} foo ; jmp @dots{} ; foo:}
 217 @end table
 218 @item jacb@var{X}
 219 @var{X} may be one of @code{b d f g h l w}.
 220 @table @asis
 221 @item (word displacement)
 222 @kbd{@var{OPCODE} @dots{}}
 223 @item (long displacement)
 224 @example
 225 @var{OPCODE} @dots{}, foo ;
 226 brb bar ;
 227 foo: jmp @dots{} ;
 228 bar:
 229 @end example
 230 @end table
 231 @item jaob@var{YYY}
 232 @var{YYY} may be one of @code{lss leq}.
 233 @item jsob@var{ZZZ}
 234 @var{ZZZ} may be one of @code{geq gtr}.
 235 @table @asis
 236 @item (byte displacement)
 237 @kbd{@var{OPCODE} @dots{}}
 238 @item (word displacement)
 239 @example
 240 @var{OPCODE} @dots{}, foo ;
 241 brb bar ;
 242 foo: brw @var{destination} ;
 243 bar:
 244 @end example
 245 @item (long displacement)
 246 @example
 247 @var{OPCODE} @dots{}, foo ;
 248 brb bar ;
 249 foo: jmp @var{destination} ;
 250 bar:
 251 @end example
 252 @end table
 253 @item aobleq
 254 @itemx aoblss
 255 @itemx sobgeq
 256 @itemx sobgtr
 257 @table @asis
 258 @item (byte displacement)
 259 @kbd{@var{OPCODE} @dots{}}
 260 @item (word displacement)
 261 @example
 262 @var{OPCODE} @dots{}, foo ;
 263 brb bar ;
 264 foo: brw @var{destination} ;
 265 bar:
 266 @end example
 267 @item (long displacement)
 268 @example
 269 @var{OPCODE} @dots{}, foo ;
 270 brb bar ;
 271 foo: jmp @var{destination} ;
 272 bar:
 273 @end example
 274 @end table
 275 @end table
 276
 277 @node VAX-operands
 278 @section VAX Operands
 279
 280 @cindex VAX operand notation
 281 @cindex operand notation, VAX
 282 @cindex immediate character, VAX
 283 @cindex VAX immediate character
 284 The immediate character is @samp{$} for Unix compatibility, not
 285 @samp{#} as DEC writes it.
 286
 287 @cindex indirect character, VAX
 288 @cindex VAX indirect character
 289 The indirect character is @samp{*} for Unix compatibility, not
 290 @samp{@@} as DEC writes it.
 291
 292 @cindex displacement sizing character, VAX
 293 @cindex VAX displacement sizing character
 294 The displacement sizing character is @samp{`} (an accent grave) for
 295 Unix compatibility, not @samp{^} as DEC writes it.  The letter
 296 preceding @samp{`} may have either case.  @samp{G} is not
 297 understood, but all other letters (@code{b i l s w}) are understood.
 298
 299 @cindex register names, VAX
 300 @cindex VAX register names
 301 Register names understood are @code{r0 r1 r2 @dots{} r15 ap fp sp
 302 pc}.  Upper and lower case letters are equivalent.
 303
 304 For instance
 305 @smallexample
 306 tstb *w`$4(r5)
 307 @end smallexample
 308
 309 Any expression is permitted in an operand.  Operands are comma
 310 separated.
 311
 312 @c There is some bug to do with recognizing expressions
 313 @c in operands, but I forget what it is.  It is
 314 @c a syntax clash because () is used as an address mode
 315 @c and to encapsulate sub-expressions.
 316
 317 @node VAX-no
 318 @section Not Supported on VAX
 319
 320 @cindex VAX bitfields not supported
 321 @cindex bitfields, not supported on VAX
 322 Vax bit fields can not be assembled with @code{@value{AS}}.  Someone
 323 can add the required code if they really need it.