gas/doc/c-vax.texi

   1 @c Copyright (C) 1991, 92, 93, 94, 95, 96, 1998 Free Software Foundation, Inc.
   2 @c This is part of the GAS manual.
   3 @c For copying conditions, see the file as.texinfo.
   4 @c VAX/VMS description exhanced and corrected by Klaus K"aempf, kkaempf@progis.de
   5 @ifset GENERIC
   6 @node Vax-Dependent
   7 @chapter VAX Dependent Features
   8 @cindex VAX support
   9
  10 @end ifset
  11 @ifclear GENERIC
  12 @node Machine Dependencies
  13 @chapter VAX Dependent Features
  14 @cindex VAX support
  15
  16 @end ifclear
  17
  18 @menu
  19 * VAX-Opts::                    VAX Command-Line Options
  20 * VAX-float::                   VAX Floating Point
  21 * VAX-directives::              Vax Machine Directives
  22 * VAX-opcodes::                 VAX Opcodes
  23 * VAX-branch::                  VAX Branch Improvement
  24 * VAX-operands::                VAX Operands
  25 * VAX-no::                      Not Supported on VAX
  26 @end menu
  27
  28
  29 @node VAX-Opts
  30 @section VAX Command-Line Options
  31
  32 @cindex command-line options ignored, VAX
  33 @cindex VAX command-line options ignored
  34 The Vax version of @code{@value{AS}} accepts any of the following options,
  35 gives a warning message that the option was ignored and proceeds.
  36 These options are for compatibility with scripts designed for other
  37 people's assemblers.
  38
  39 @table @code
  40 @cindex @code{-D}, ignored on VAX
  41 @cindex @code{-S}, ignored on VAX
  42 @cindex @code{-T}, ignored on VAX
  43 @item @code{-D} (Debug)
  44 @itemx @code{-S} (Symbol Table)
  45 @itemx @code{-T} (Token Trace)
  46 These are obsolete options used to debug old assemblers.
  47
  48 @cindex @code{-d}, VAX option
  49 @item @code{-d} (Displacement size for JUMPs)
  50 This option expects a number following the @samp{-d}.  Like options
  51 that expect filenames, the number may immediately follow the
  52 @samp{-d} (old standard) or constitute the whole of the command line
  53 argument that follows @samp{-d} (@sc{gnu} standard).
  54
  55 @cindex @code{-V}, redundant on VAX
  56 @item @code{-V} (Virtualize Interpass Temporary File)
  57 Some other assemblers use a temporary file.  This option
  58 commanded them to keep the information in active memory rather
  59 than in a disk file.  @code{@value{AS}} always does this, so this
  60 option is redundant.
  61
  62 @cindex @code{-J}, ignored on VAX
  63 @item @code{-J} (JUMPify Longer Branches)
  64 Many 32-bit computers permit a variety of branch instructions
  65 to do the same job.  Some of these instructions are short (and
  66 fast) but have a limited range; others are long (and slow) but
  67 can branch anywhere in virtual memory.  Often there are 3
  68 flavors of branch: short, medium and long.  Some other
  69 assemblers would emit short and medium branches, unless told by
  70 this option to emit short and long branches.
  71
  72 @cindex @code{-t}, ignored on VAX
  73 @item @code{-t} (Temporary File Directory)
  74 Some other assemblers may use a temporary file, and this option
  75 takes a filename being the directory to site the temporary
  76 file.  Since @code{@value{AS}} does not use a temporary disk file, this
  77 option makes no difference.  @samp{-t} needs exactly one
  78 filename.
  79 @end table
  80
  81 @cindex VMS (VAX) options
  82 @cindex options for VAX/VMS
  83 @cindex VAX/VMS options
  84 @cindex Vax-11 C compatibility
  85 @cindex symbols with uppercase, VAX/VMS
  86 The Vax version of the assembler accepts additional options when
  87 compiled for VMS:
  88
  89 @table @samp
  90 @cindex @samp{-h} option, VAX/VMS
  91 @item -h @var{n}
  92 External symbol or section (used for global variables) names are not
  93 case sensitive on VAX/VMS and always mapped to upper case.  This is
  94 contrary to the C language definition which explicitly distinguishes
  95 upper and lower case.  To implement a standard conforming C compiler,
  96 names must be changed (mapped) to preserve the case information.  The
  97 default mapping is to convert all lower case characters to uppercase and
  98 adding an underscore followed by a 6 digit hex value, representing a 24
  99 digit binary value.  The one digits in the binary value represent which
 100 characters are uppercase in the original symbol name.
 101
 102 The @samp{-h @var{n}} option determines how we map names.  This takes
 103 several values.  No @samp{-h} switch at all allows case hacking as
 104 described above.  A value of zero (@samp{-h0}) implies names should be
 105 upper case, and inhibits the case hack.  A value of 2 (@samp{-h2})
 106 implies names should be all lower case, with no case hack.  A value of 3
 107 (@samp{-h3}) implies that case should be preserved.  The value 1 is
 108 unused.  The @code{-H} option directs @code{@value{AS}} to display
 109 every mapped symbol during assembly.
 110
 111 Symbols whose names include a dollar sign @samp{$} are exceptions to the
 112 general name mapping.  These symbols are normally only used to reference
 113 VMS library names.  Such symbols are always mapped to upper case.
 114
 115 @cindex @samp{-+} option, VAX/VMS
 116 @item -+
 117 The @samp{-+} option causes @code{@value{AS}} to truncate any symbol
 118 name larger than 31 characters.  The @samp{-+} option also prevents some
 119 code following the @samp{_main} symbol normally added to make the object
 120 file compatible with Vax-11 "C".
 121
 122 @cindex @samp{-1} option, VAX/VMS
 123 @item -1
 124 This option is ignored for backward compatibility with @code{@value{AS}}
 125 version 1.x.
 126
 127 @cindex @samp{-H} option, VAX/VMS
 128 @item -H
 129 The @samp{-H} option causes @code{@value{AS}} to print every symbol
 130 which was changed by case mapping.
 131 @end table
 132
 133 @node VAX-float
 134 @section VAX Floating Point
 135
 136 @cindex VAX floating point
 137 @cindex floating point, VAX
 138 Conversion of flonums to floating point is correct, and
 139 compatible with previous assemblers.  Rounding is
 140 towards zero if the remainder is exactly half the least significant bit.
 141
 142 @code{D}, @code{F}, @code{G} and @code{H} floating point formats
 143 are understood.
 144
 145 Immediate floating literals (@emph{e.g.} @samp{S`$6.9})
 146 are rendered correctly.  Again, rounding is towards zero in the
 147 boundary case.
 148
 149 @cindex @code{float} directive, VAX
 150 @cindex @code{double} directive, VAX
 151 The @code{.float} directive produces @code{f} format numbers.
 152 The @code{.double} directive produces @code{d} format numbers.
 153
 154 @node VAX-directives
 155 @section Vax Machine Directives
 156
 157 @cindex machine directives, VAX
 158 @cindex VAX machine directives
 159 The Vax version of the assembler supports four directives for
 160 generating Vax floating point constants.  They are described in the
 161 table below.
 162
 163 @cindex wide floating point directives, VAX
 164 @table @code
 165 @cindex @code{dfloat} directive, VAX
 166 @item .dfloat
 167 This expects zero or more flonums, separated by commas, and
 168 assembles Vax @code{d} format 64-bit floating point constants.
 169
 170 @cindex @code{ffloat} directive, VAX
 171 @item .ffloat
 172 This expects zero or more flonums, separated by commas, and
 173 assembles Vax @code{f} format 32-bit floating point constants.
 174
 175 @cindex @code{gfloat} directive, VAX
 176 @item .gfloat
 177 This expects zero or more flonums, separated by commas, and
 178 assembles Vax @code{g} format 64-bit floating point constants.
 179
 180 @cindex @code{hfloat} directive, VAX
 181 @item .hfloat
 182 This expects zero or more flonums, separated by commas, and
 183 assembles Vax @code{h} format 128-bit floating point constants.
 184
 185 @end table
 186
 187 @node VAX-opcodes
 188 @section VAX Opcodes
 189
 190 @cindex VAX opcode mnemonics
 191 @cindex opcode mnemonics, VAX
 192 @cindex mnemonics for opcodes, VAX
 193 All DEC mnemonics are supported.  Beware that @code{case@dots{}}
 194 instructions have exactly 3 operands.  The dispatch table that
 195 follows the @code{case@dots{}} instruction should be made with
 196 @code{.word} statements.  This is compatible with all unix
 197 assemblers we know of.
 198
 199 @node VAX-branch
 200 @section VAX Branch Improvement
 201
 202 @cindex VAX branch improvement
 203 @cindex branch improvement, VAX
 204 @cindex pseudo-ops for branch, VAX
 205 Certain pseudo opcodes are permitted.  They are for branch
 206 instructions.  They expand to the shortest branch instruction that
 207 reaches the target.  Generally these mnemonics are made by
 208 substituting @samp{j} for @samp{b} at the start of a DEC mnemonic.
 209 This feature is included both for compatibility and to help
 210 compilers.  If you do not need this feature, avoid these
 211 opcodes.  Here are the mnemonics, and the code they can expand into.
 212
 213 @table @code
 214 @item jbsb
 215 @samp{Jsb} is already an instruction mnemonic, so we chose @samp{jbsb}.
 216 @table @asis
 217 @item (byte displacement)
 218 @kbd{bsbb @dots{}}
 219 @item (word displacement)
 220 @kbd{bsbw @dots{}}
 221 @item (long displacement)
 222 @kbd{jsb @dots{}}
 223 @end table
 224 @item jbr
 225 @itemx jr
 226 Unconditional branch.
 227 @table @asis
 228 @item (byte displacement)
 229 @kbd{brb @dots{}}
 230 @item (word displacement)
 231 @kbd{brw @dots{}}
 232 @item (long displacement)
 233 @kbd{jmp @dots{}}
 234 @end table
 235 @item j@var{COND}
 236 @var{COND} may be any one of the conditional branches
 237 @code{neq}, @code{nequ}, @code{eql}, @code{eqlu}, @code{gtr},
 238 @code{geq}, @code{lss}, @code{gtru}, @code{lequ}, @code{vc}, @code{vs},
 239 @code{gequ}, @code{cc}, @code{lssu}, @code{cs}.
 240 @var{COND} may also be one of the bit tests
 241 @code{bs}, @code{bc}, @code{bss}, @code{bcs}, @code{bsc}, @code{bcc},
 242 @code{bssi}, @code{bcci}, @code{lbs}, @code{lbc}.
 243 @var{NOTCOND} is the opposite condition to @var{COND}.
 244 @table @asis
 245 @item (byte displacement)
 246 @kbd{b@var{COND} @dots{}}
 247 @item (word displacement)
 248 @kbd{b@var{NOTCOND} foo ; brw @dots{} ; foo:}
 249 @item (long displacement)
 250 @kbd{b@var{NOTCOND} foo ; jmp @dots{} ; foo:}
 251 @end table
 252 @item jacb@var{X}
 253 @var{X} may be one of @code{b d f g h l w}.
 254 @table @asis
 255 @item (word displacement)
 256 @kbd{@var{OPCODE} @dots{}}
 257 @item (long displacement)
 258 @example
 259 @var{OPCODE} @dots{}, foo ;
 260 brb bar ;
 261 foo: jmp @dots{} ;
 262 bar:
 263 @end example
 264 @end table
 265 @item jaob@var{YYY}
 266 @var{YYY} may be one of @code{lss leq}.
 267 @item jsob@var{ZZZ}
 268 @var{ZZZ} may be one of @code{geq gtr}.
 269 @table @asis
 270 @item (byte displacement)
 271 @kbd{@var{OPCODE} @dots{}}
 272 @item (word displacement)
 273 @example
 274 @var{OPCODE} @dots{}, foo ;
 275 brb bar ;
 276 foo: brw @var{destination} ;
 277 bar:
 278 @end example
 279 @item (long displacement)
 280 @example
 281 @var{OPCODE} @dots{}, foo ;
 282 brb bar ;
 283 foo: jmp @var{destination} ;
 284 bar:
 285 @end example
 286 @end table
 287 @item aobleq
 288 @itemx aoblss
 289 @itemx sobgeq
 290 @itemx sobgtr
 291 @table @asis
 292 @item (byte displacement)
 293 @kbd{@var{OPCODE} @dots{}}
 294 @item (word displacement)
 295 @example
 296 @var{OPCODE} @dots{}, foo ;
 297 brb bar ;
 298 foo: brw @var{destination} ;
 299 bar:
 300 @end example
 301 @item (long displacement)
 302 @example
 303 @var{OPCODE} @dots{}, foo ;
 304 brb bar ;
 305 foo: jmp @var{destination} ;
 306 bar:
 307 @end example
 308 @end table
 309 @end table
 310
 311 @node VAX-operands
 312 @section VAX Operands
 313
 314 @cindex VAX operand notation
 315 @cindex operand notation, VAX
 316 @cindex immediate character, VAX
 317 @cindex VAX immediate character
 318 The immediate character is @samp{$} for Unix compatibility, not
 319 @samp{#} as DEC writes it.
 320
 321 @cindex indirect character, VAX
 322 @cindex VAX indirect character
 323 The indirect character is @samp{*} for Unix compatibility, not
 324 @samp{@@} as DEC writes it.
 325
 326 @cindex displacement sizing character, VAX
 327 @cindex VAX displacement sizing character
 328 The displacement sizing character is @samp{`} (an accent grave) for
 329 Unix compatibility, not @samp{^} as DEC writes it.  The letter
 330 preceding @samp{`} may have either case.  @samp{G} is not
 331 understood, but all other letters (@code{b i l s w}) are understood.
 332
 333 @cindex register names, VAX
 334 @cindex VAX register names
 335 Register names understood are @code{r0 r1 r2 @dots{} r15 ap fp sp
 336 pc}.  Upper and lower case letters are equivalent.
 337
 338 For instance
 339 @smallexample
 340 tstb *w`$4(r5)
 341 @end smallexample
 342
 343 Any expression is permitted in an operand.  Operands are comma
 344 separated.
 345
 346 @c There is some bug to do with recognizing expressions
 347 @c in operands, but I forget what it is.  It is
 348 @c a syntax clash because () is used as an address mode
 349 @c and to encapsulate sub-expressions.
 350
 351 @node VAX-no
 352 @section Not Supported on VAX
 353
 354 @cindex VAX bitfields not supported
 355 @cindex bitfields, not supported on VAX
 356 Vax bit fields can not be assembled with @code{@value{AS}}.  Someone
 357 can add the required code if they really need it.