| 1 | \input texinfo |
| 2 | @c Copyright (C) 1991-2016 Free Software Foundation, Inc. |
| 3 | @setfilename internals.info |
| 4 | @node Top |
| 5 | @top Assembler Internals |
| 6 | @raisesections |
| 7 | @cindex internals |
| 8 | |
| 9 | This chapter describes the internals of the assembler. It is incomplete, but |
| 10 | it may help a bit. |
| 11 | |
| 12 | This chapter is not updated regularly, and it may be out of date. |
| 13 | |
| 14 | @menu |
| 15 | * Data types:: Data types |
| 16 | * GAS processing:: What GAS does when it runs |
| 17 | * Porting GAS:: Porting GAS |
| 18 | * Relaxation:: Relaxation |
| 19 | * Broken words:: Broken words |
| 20 | * Internal functions:: Internal functions |
| 21 | * Test suite:: Test suite |
| 22 | @end menu |
| 23 | |
| 24 | @node Data types |
| 25 | @section Data types |
| 26 | @cindex internals, data types |
| 27 | |
| 28 | This section describes some fundamental GAS data types. |
| 29 | |
| 30 | @menu |
| 31 | * Symbols:: The symbolS structure |
| 32 | * Expressions:: The expressionS structure |
| 33 | * Fixups:: The fixS structure |
| 34 | * Frags:: The fragS structure |
| 35 | @end menu |
| 36 | |
| 37 | @node Symbols |
| 38 | @subsection Symbols |
| 39 | @cindex internals, symbols |
| 40 | @cindex symbols, internal |
| 41 | @cindex symbolS structure |
| 42 | |
| 43 | The definition for the symbol structure, @code{symbolS}, is located in |
| 44 | @file{struc-symbol.h}. |
| 45 | |
| 46 | In general, the fields of this structure may not be referred to directly. |
| 47 | Instead, you must use one of the accessor functions defined in @file{symbol.h}. |
| 48 | These accessor functions should work for any GAS version. |
| 49 | |
| 50 | Symbol structures contain the following fields: |
| 51 | |
| 52 | @table @code |
| 53 | @item sy_value |
| 54 | This is an @code{expressionS} that describes the value of the symbol. It might |
| 55 | refer to one or more other symbols; if so, its true value may not be known |
| 56 | until @code{resolve_symbol_value} is called with @var{finalize_syms} non-zero |
| 57 | in @code{write_object_file}. |
| 58 | |
| 59 | The expression is often simply a constant. Before @code{resolve_symbol_value} |
| 60 | is called with @var{finalize_syms} set, the value is the offset from the frag |
| 61 | (@pxref{Frags}). Afterward, the frag address has been added in. |
| 62 | |
| 63 | @item sy_resolved |
| 64 | This field is non-zero if the symbol's value has been completely resolved. It |
| 65 | is used during the final pass over the symbol table. |
| 66 | |
| 67 | @item sy_resolving |
| 68 | This field is used to detect loops while resolving the symbol's value. |
| 69 | |
| 70 | @item sy_used_in_reloc |
| 71 | This field is non-zero if the symbol is used by a relocation entry. If a local |
| 72 | symbol is used in a relocation entry, it must be possible to redirect those |
| 73 | relocations to other symbols, or this symbol cannot be removed from the final |
| 74 | symbol list. |
| 75 | |
| 76 | @item sy_next |
| 77 | @itemx sy_previous |
| 78 | These pointers to other @code{symbolS} structures describe a doubly |
| 79 | linked list. These fields should be accessed with |
| 80 | the @code{symbol_next} and @code{symbol_previous} macros. |
| 81 | |
| 82 | @item sy_frag |
| 83 | This points to the frag (@pxref{Frags}) that this symbol is attached to. |
| 84 | |
| 85 | @item sy_used |
| 86 | Whether the symbol is used as an operand or in an expression. Note: Not all of |
| 87 | the backends keep this information accurate; backends which use this bit are |
| 88 | responsible for setting it when a symbol is used in backend routines. |
| 89 | |
| 90 | @item sy_mri_common |
| 91 | Whether the symbol is an MRI common symbol created by the @code{COMMON} |
| 92 | pseudo-op when assembling in MRI mode. |
| 93 | |
| 94 | @item sy_volatile |
| 95 | Whether the symbol can be re-defined. |
| 96 | |
| 97 | @item sy_forward_ref |
| 98 | Whether the symbol's value must only be evaluated upon use. |
| 99 | |
| 100 | @item sy_weakrefr |
| 101 | Whether the symbol is a @code{weakref} alias to another symbol. |
| 102 | |
| 103 | @item sy_weakrefd |
| 104 | Whether the symbol is or was referenced by one or more @code{weakref} aliases, |
| 105 | and has not had any direct references. |
| 106 | |
| 107 | @item bsym |
| 108 | This points to the BFD @code{asymbol} that |
| 109 | will be used in writing the object file. |
| 110 | |
| 111 | @item sy_obj |
| 112 | This format-specific data is of type @code{OBJ_SYMFIELD_TYPE}. If no macro by |
| 113 | that name is defined in @file{obj-format.h}, this field is not defined. |
| 114 | |
| 115 | @item sy_tc |
| 116 | This processor-specific data is of type @code{TC_SYMFIELD_TYPE}. If no macro |
| 117 | by that name is defined in @file{targ-cpu.h}, this field is not defined. |
| 118 | |
| 119 | @end table |
| 120 | |
| 121 | Here is a description of the accessor functions. These should be used rather |
| 122 | than referring to the fields of @code{symbolS} directly. |
| 123 | |
| 124 | @table @code |
| 125 | @item S_SET_VALUE |
| 126 | @cindex S_SET_VALUE |
| 127 | Set the symbol's value. |
| 128 | |
| 129 | @item S_GET_VALUE |
| 130 | @cindex S_GET_VALUE |
| 131 | Get the symbol's value. This will cause @code{resolve_symbol_value} to be |
| 132 | called if necessary. |
| 133 | |
| 134 | @item S_SET_SEGMENT |
| 135 | @cindex S_SET_SEGMENT |
| 136 | Set the section of the symbol. |
| 137 | |
| 138 | @item S_GET_SEGMENT |
| 139 | @cindex S_GET_SEGMENT |
| 140 | Get the symbol's section. |
| 141 | |
| 142 | @item S_GET_NAME |
| 143 | @cindex S_GET_NAME |
| 144 | Get the name of the symbol. |
| 145 | |
| 146 | @item S_SET_NAME |
| 147 | @cindex S_SET_NAME |
| 148 | Set the name of the symbol. |
| 149 | |
| 150 | @item S_IS_EXTERNAL |
| 151 | @cindex S_IS_EXTERNAL |
| 152 | Return non-zero if the symbol is externally visible. |
| 153 | |
| 154 | @item S_IS_WEAK |
| 155 | @cindex S_IS_WEAK |
| 156 | Return non-zero if the symbol is weak, or if it is a @code{weakref} alias or |
| 157 | symbol that has not been strongly referenced. |
| 158 | |
| 159 | @item S_IS_WEAKREFR |
| 160 | @cindex S_IS_WEAKREFR |
| 161 | Return non-zero if the symbol is a @code{weakref} alias. |
| 162 | |
| 163 | @item S_IS_WEAKREFD |
| 164 | @cindex S_IS_WEAKREFD |
| 165 | Return non-zero if the symbol was aliased by a @code{weakref} alias and has not |
| 166 | had any strong references. |
| 167 | |
| 168 | @item S_IS_VOLATILE |
| 169 | @cindex S_IS_VOLATILE |
| 170 | Return non-zero if the symbol may be re-defined. Such symbols get created by |
| 171 | the @code{=} operator, @code{equ}, or @code{set}. |
| 172 | |
| 173 | @item S_IS_FORWARD_REF |
| 174 | @cindex S_IS_FORWARD_REF |
| 175 | Return non-zero if the symbol is a forward reference, that is its value must |
| 176 | only be determined upon use. |
| 177 | |
| 178 | @item S_IS_COMMON |
| 179 | @cindex S_IS_COMMON |
| 180 | Return non-zero if this is a common symbol. Common symbols are sometimes |
| 181 | represented as undefined symbols with a value, in which case this function will |
| 182 | not be reliable. |
| 183 | |
| 184 | @item S_IS_DEFINED |
| 185 | @cindex S_IS_DEFINED |
| 186 | Return non-zero if this symbol is defined. This function is not reliable when |
| 187 | called on a common symbol. |
| 188 | |
| 189 | @item S_IS_DEBUG |
| 190 | @cindex S_IS_DEBUG |
| 191 | Return non-zero if this is a debugging symbol. |
| 192 | |
| 193 | @item S_IS_LOCAL |
| 194 | @cindex S_IS_LOCAL |
| 195 | Return non-zero if this is a local assembler symbol which should not be |
| 196 | included in the final symbol table. Note that this is not the opposite of |
| 197 | @code{S_IS_EXTERNAL}. The @samp{-L} assembler option affects the return value |
| 198 | of this function. |
| 199 | |
| 200 | @item S_SET_EXTERNAL |
| 201 | @cindex S_SET_EXTERNAL |
| 202 | Mark the symbol as externally visible. |
| 203 | |
| 204 | @item S_CLEAR_EXTERNAL |
| 205 | @cindex S_CLEAR_EXTERNAL |
| 206 | Mark the symbol as not externally visible. |
| 207 | |
| 208 | @item S_SET_WEAK |
| 209 | @cindex S_SET_WEAK |
| 210 | Mark the symbol as weak. |
| 211 | |
| 212 | @item S_SET_WEAKREFR |
| 213 | @cindex S_SET_WEAKREFR |
| 214 | Mark the symbol as the referrer in a @code{weakref} directive. The symbol it |
| 215 | aliases must have been set to the value expression before this point. If the |
| 216 | alias has already been used, the symbol is marked as used too. |
| 217 | |
| 218 | @item S_CLEAR_WEAKREFR |
| 219 | @cindex S_CLEAR_WEAKREFR |
| 220 | Clear the @code{weakref} alias status of a symbol. This is implicitly called |
| 221 | whenever a symbol is defined or set to a new expression. |
| 222 | |
| 223 | @item S_SET_WEAKREFD |
| 224 | @cindex S_SET_WEAKREFD |
| 225 | Mark the symbol as the referred symbol in a @code{weakref} directive. |
| 226 | Implicitly marks the symbol as weak, but see below. It should only be called |
| 227 | if the referenced symbol has just been added to the symbol table. |
| 228 | |
| 229 | @item S_SET_WEAKREFD |
| 230 | @cindex S_SET_WEAKREFD |
| 231 | Clear the @code{weakref} aliased status of a symbol. This is implicitly called |
| 232 | whenever the symbol is looked up, as part of a direct reference or a |
| 233 | definition, but not as part of a @code{weakref} directive. |
| 234 | |
| 235 | @item S_SET_VOLATILE |
| 236 | @cindex S_SET_VOLATILE |
| 237 | Indicate that the symbol may be re-defined. |
| 238 | |
| 239 | @item S_CLEAR_VOLATILE |
| 240 | @cindex S_CLEAR_VOLATILE |
| 241 | Indicate that the symbol may no longer be re-defined. |
| 242 | |
| 243 | @item S_SET_FORWARD_REF |
| 244 | @cindex S_SET_FORWARD_REF |
| 245 | Indicate that the symbol is a forward reference, that is its value must only |
| 246 | be determined upon use. |
| 247 | |
| 248 | @item S_GET_TYPE |
| 249 | @itemx S_GET_DESC |
| 250 | @itemx S_GET_OTHER |
| 251 | @cindex S_GET_TYPE |
| 252 | @cindex S_GET_DESC |
| 253 | @cindex S_GET_OTHER |
| 254 | Get the @code{type}, @code{desc}, and @code{other} fields of the symbol. These |
| 255 | are only defined for object file formats for which they make sense (primarily |
| 256 | a.out). |
| 257 | |
| 258 | @item S_SET_TYPE |
| 259 | @itemx S_SET_DESC |
| 260 | @itemx S_SET_OTHER |
| 261 | @cindex S_SET_TYPE |
| 262 | @cindex S_SET_DESC |
| 263 | @cindex S_SET_OTHER |
| 264 | Set the @code{type}, @code{desc}, and @code{other} fields of the symbol. These |
| 265 | are only defined for object file formats for which they make sense (primarily |
| 266 | a.out). |
| 267 | |
| 268 | @item S_GET_SIZE |
| 269 | @cindex S_GET_SIZE |
| 270 | Get the size of a symbol. This is only defined for object file formats for |
| 271 | which it makes sense (primarily ELF). |
| 272 | |
| 273 | @item S_SET_SIZE |
| 274 | @cindex S_SET_SIZE |
| 275 | Set the size of a symbol. This is only defined for object file formats for |
| 276 | which it makes sense (primarily ELF). |
| 277 | |
| 278 | @item symbol_get_value_expression |
| 279 | @cindex symbol_get_value_expression |
| 280 | Get a pointer to an @code{expressionS} structure which represents the value of |
| 281 | the symbol as an expression. |
| 282 | |
| 283 | @item symbol_set_value_expression |
| 284 | @cindex symbol_set_value_expression |
| 285 | Set the value of a symbol to an expression. |
| 286 | |
| 287 | @item symbol_set_frag |
| 288 | @cindex symbol_set_frag |
| 289 | Set the frag where a symbol is defined. |
| 290 | |
| 291 | @item symbol_get_frag |
| 292 | @cindex symbol_get_frag |
| 293 | Get the frag where a symbol is defined. |
| 294 | |
| 295 | @item symbol_mark_used |
| 296 | @cindex symbol_mark_used |
| 297 | Mark a symbol as having been used in an expression. |
| 298 | |
| 299 | @item symbol_clear_used |
| 300 | @cindex symbol_clear_used |
| 301 | Clear the mark indicating that a symbol was used in an expression. |
| 302 | |
| 303 | @item symbol_used_p |
| 304 | @cindex symbol_used_p |
| 305 | Return whether a symbol was used in an expression. |
| 306 | |
| 307 | @item symbol_mark_used_in_reloc |
| 308 | @cindex symbol_mark_used_in_reloc |
| 309 | Mark a symbol as having been used by a relocation. |
| 310 | |
| 311 | @item symbol_clear_used_in_reloc |
| 312 | @cindex symbol_clear_used_in_reloc |
| 313 | Clear the mark indicating that a symbol was used in a relocation. |
| 314 | |
| 315 | @item symbol_used_in_reloc_p |
| 316 | @cindex symbol_used_in_reloc_p |
| 317 | Return whether a symbol was used in a relocation. |
| 318 | |
| 319 | @item symbol_mark_mri_common |
| 320 | @cindex symbol_mark_mri_common |
| 321 | Mark a symbol as an MRI common symbol. |
| 322 | |
| 323 | @item symbol_clear_mri_common |
| 324 | @cindex symbol_clear_mri_common |
| 325 | Clear the mark indicating that a symbol is an MRI common symbol. |
| 326 | |
| 327 | @item symbol_mri_common_p |
| 328 | @cindex symbol_mri_common_p |
| 329 | Return whether a symbol is an MRI common symbol. |
| 330 | |
| 331 | @item symbol_mark_written |
| 332 | @cindex symbol_mark_written |
| 333 | Mark a symbol as having been written. |
| 334 | |
| 335 | @item symbol_clear_written |
| 336 | @cindex symbol_clear_written |
| 337 | Clear the mark indicating that a symbol was written. |
| 338 | |
| 339 | @item symbol_written_p |
| 340 | @cindex symbol_written_p |
| 341 | Return whether a symbol was written. |
| 342 | |
| 343 | @item symbol_mark_resolved |
| 344 | @cindex symbol_mark_resolved |
| 345 | Mark a symbol as having been resolved. |
| 346 | |
| 347 | @item symbol_resolved_p |
| 348 | @cindex symbol_resolved_p |
| 349 | Return whether a symbol has been resolved. |
| 350 | |
| 351 | @item symbol_section_p |
| 352 | @cindex symbol_section_p |
| 353 | Return whether a symbol is a section symbol. |
| 354 | |
| 355 | @item symbol_equated_p |
| 356 | @cindex symbol_equated_p |
| 357 | Return whether a symbol is equated to another symbol. |
| 358 | |
| 359 | @item symbol_constant_p |
| 360 | @cindex symbol_constant_p |
| 361 | Return whether a symbol has a constant value, including being an offset within |
| 362 | some frag. |
| 363 | |
| 364 | @item symbol_get_bfdsym |
| 365 | @cindex symbol_get_bfdsym |
| 366 | Return the BFD symbol associated with a symbol. |
| 367 | |
| 368 | @item symbol_set_bfdsym |
| 369 | @cindex symbol_set_bfdsym |
| 370 | Set the BFD symbol associated with a symbol. |
| 371 | |
| 372 | @item symbol_get_obj |
| 373 | @cindex symbol_get_obj |
| 374 | Return a pointer to the @code{OBJ_SYMFIELD_TYPE} field of a symbol. |
| 375 | |
| 376 | @item symbol_set_obj |
| 377 | @cindex symbol_set_obj |
| 378 | Set the @code{OBJ_SYMFIELD_TYPE} field of a symbol. |
| 379 | |
| 380 | @item symbol_get_tc |
| 381 | @cindex symbol_get_tc |
| 382 | Return a pointer to the @code{TC_SYMFIELD_TYPE} field of a symbol. |
| 383 | |
| 384 | @item symbol_set_tc |
| 385 | @cindex symbol_set_tc |
| 386 | Set the @code{TC_SYMFIELD_TYPE} field of a symbol. |
| 387 | |
| 388 | @end table |
| 389 | |
| 390 | GAS attempts to store local |
| 391 | symbols--symbols which will not be written to the output file--using a |
| 392 | different structure, @code{struct local_symbol}. This structure can only |
| 393 | represent symbols whose value is an offset within a frag. |
| 394 | |
| 395 | Code outside of the symbol handler will always deal with @code{symbolS} |
| 396 | structures and use the accessor functions. The accessor functions correctly |
| 397 | deal with local symbols. @code{struct local_symbol} is much smaller than |
| 398 | @code{symbolS} (which also automatically creates a bfd @code{asymbol} |
| 399 | structure), so this saves space when assembling large files. |
| 400 | |
| 401 | The first field of @code{symbolS} is @code{bsym}, the pointer to the BFD |
| 402 | symbol. The first field of @code{struct local_symbol} is a pointer which is |
| 403 | always set to NULL. This is how the symbol accessor functions can distinguish |
| 404 | local symbols from ordinary symbols. The symbol accessor functions |
| 405 | automatically convert a local symbol into an ordinary symbol when necessary. |
| 406 | |
| 407 | @node Expressions |
| 408 | @subsection Expressions |
| 409 | @cindex internals, expressions |
| 410 | @cindex expressions, internal |
| 411 | @cindex expressionS structure |
| 412 | |
| 413 | Expressions are stored in an @code{expressionS} structure. The structure is |
| 414 | defined in @file{expr.h}. |
| 415 | |
| 416 | @cindex expression |
| 417 | The macro @code{expression} will create an @code{expressionS} structure based |
| 418 | on the text found at the global variable @code{input_line_pointer}. |
| 419 | |
| 420 | @cindex make_expr_symbol |
| 421 | @cindex expr_symbol_where |
| 422 | A single @code{expressionS} structure can represent a single operation. |
| 423 | Complex expressions are formed by creating @dfn{expression symbols} and |
| 424 | combining them in @code{expressionS} structures. An expression symbol is |
| 425 | created by calling @code{make_expr_symbol}. An expression symbol should |
| 426 | naturally never appear in a symbol table, and the implementation of |
| 427 | @code{S_IS_LOCAL} (@pxref{Symbols}) reflects that. The function |
| 428 | @code{expr_symbol_where} returns non-zero if a symbol is an expression symbol, |
| 429 | and also returns the file and line for the expression which caused it to be |
| 430 | created. |
| 431 | |
| 432 | The @code{expressionS} structure has two symbol fields, a number field, an |
| 433 | operator field, and a field indicating whether the number is unsigned. |
| 434 | |
| 435 | The operator field is of type @code{operatorT}, and describes how to interpret |
| 436 | the other fields; see the definition in @file{expr.h} for the possibilities. |
| 437 | |
| 438 | An @code{operatorT} value of @code{O_big} indicates either a floating point |
| 439 | number, stored in the global variable @code{generic_floating_point_number}, or |
| 440 | an integer too large to store in an @code{offsetT} type, stored in the global |
| 441 | array @code{generic_bignum}. This rather inflexible approach makes it |
| 442 | impossible to use floating point numbers or large expressions in complex |
| 443 | expressions. |
| 444 | |
| 445 | @node Fixups |
| 446 | @subsection Fixups |
| 447 | @cindex internals, fixups |
| 448 | @cindex fixups |
| 449 | @cindex fixS structure |
| 450 | |
| 451 | A @dfn{fixup} is basically anything which can not be resolved in the first |
| 452 | pass. Sometimes a fixup can be resolved by the end of the assembly; if not, |
| 453 | the fixup becomes a relocation entry in the object file. |
| 454 | |
| 455 | @cindex fix_new |
| 456 | @cindex fix_new_exp |
| 457 | A fixup is created by a call to @code{fix_new} or @code{fix_new_exp}. Both |
| 458 | take a frag (@pxref{Frags}), a position within the frag, a size, an indication |
| 459 | of whether the fixup is PC relative, and a type. |
| 460 | The type is nominally a @code{bfd_reloc_code_real_type}, but several |
| 461 | targets use other type codes to represent fixups that can not be described as |
| 462 | relocations. |
| 463 | |
| 464 | The @code{fixS} structure has a number of fields, several of which are obsolete |
| 465 | or are only used by a particular target. The important fields are: |
| 466 | |
| 467 | @table @code |
| 468 | @item fx_frag |
| 469 | The frag (@pxref{Frags}) this fixup is in. |
| 470 | |
| 471 | @item fx_where |
| 472 | The location within the frag where the fixup occurs. |
| 473 | |
| 474 | @item fx_addsy |
| 475 | The symbol this fixup is against. Typically, the value of this symbol is added |
| 476 | into the object contents. This may be NULL. |
| 477 | |
| 478 | @item fx_subsy |
| 479 | The value of this symbol is subtracted from the object contents. This is |
| 480 | normally NULL. |
| 481 | |
| 482 | @item fx_offset |
| 483 | A number which is added into the fixup. |
| 484 | |
| 485 | @item fx_addnumber |
| 486 | Some CPU backends use this field to convey information between |
| 487 | @code{md_apply_fix} and @code{tc_gen_reloc}. The machine independent code does |
| 488 | not use it. |
| 489 | |
| 490 | @item fx_next |
| 491 | The next fixup in the section. |
| 492 | |
| 493 | @item fx_r_type |
| 494 | The type of the fixup. |
| 495 | |
| 496 | @item fx_size |
| 497 | The size of the fixup. This is mostly used for error checking. |
| 498 | |
| 499 | @item fx_pcrel |
| 500 | Whether the fixup is PC relative. |
| 501 | |
| 502 | @item fx_done |
| 503 | Non-zero if the fixup has been applied, and no relocation entry needs to be |
| 504 | generated. |
| 505 | |
| 506 | @item fx_file |
| 507 | @itemx fx_line |
| 508 | The file and line where the fixup was created. |
| 509 | |
| 510 | @item tc_fix_data |
| 511 | This has the type @code{TC_FIX_TYPE}, and is only defined if the target defines |
| 512 | that macro. |
| 513 | @end table |
| 514 | |
| 515 | @node Frags |
| 516 | @subsection Frags |
| 517 | @cindex internals, frags |
| 518 | @cindex frags |
| 519 | @cindex fragS structure. |
| 520 | |
| 521 | The @code{fragS} structure is defined in @file{as.h}. Each frag represents a |
| 522 | portion of the final object file. As GAS reads the source file, it creates |
| 523 | frags to hold the data that it reads. At the end of the assembly the frags and |
| 524 | fixups are processed to produce the final contents. |
| 525 | |
| 526 | @table @code |
| 527 | @item fr_address |
| 528 | The address of the frag. This is not set until the assembler rescans the list |
| 529 | of all frags after the entire input file is parsed. The function |
| 530 | @code{relax_segment} fills in this field. |
| 531 | |
| 532 | @item fr_next |
| 533 | Pointer to the next frag in this (sub)section. |
| 534 | |
| 535 | @item fr_fix |
| 536 | Fixed number of characters we know we're going to emit to the output file. May |
| 537 | be zero. |
| 538 | |
| 539 | @item fr_var |
| 540 | Variable number of characters we may output, after the initial @code{fr_fix} |
| 541 | characters. May be zero. |
| 542 | |
| 543 | @item fr_offset |
| 544 | The interpretation of this field is controlled by @code{fr_type}. Generally, |
| 545 | if @code{fr_var} is non-zero, this is a repeat count: the @code{fr_var} |
| 546 | characters are output @code{fr_offset} times. |
| 547 | |
| 548 | @item line |
| 549 | Holds line number info when an assembler listing was requested. |
| 550 | |
| 551 | @item fr_type |
| 552 | Relaxation state. This field indicates the interpretation of @code{fr_offset}, |
| 553 | @code{fr_symbol} and the variable-length tail of the frag, as well as the |
| 554 | treatment it gets in various phases of processing. It does not affect the |
| 555 | initial @code{fr_fix} characters; they are always supposed to be output |
| 556 | verbatim (fixups aside). See below for specific values this field can have. |
| 557 | |
| 558 | @item fr_subtype |
| 559 | Relaxation substate. If the macro @code{md_relax_frag} isn't defined, this is |
| 560 | assumed to be an index into @code{TC_GENERIC_RELAX_TABLE} for the generic |
| 561 | relaxation code to process (@pxref{Relaxation}). If @code{md_relax_frag} is |
| 562 | defined, this field is available for any use by the CPU-specific code. |
| 563 | |
| 564 | @item fr_symbol |
| 565 | This normally indicates the symbol to use when relaxing the frag according to |
| 566 | @code{fr_type}. |
| 567 | |
| 568 | @item fr_opcode |
| 569 | Points to the lowest-addressed byte of the opcode, for use in relaxation. |
| 570 | |
| 571 | @item tc_frag_data |
| 572 | Target specific fragment data of type TC_FRAG_TYPE. |
| 573 | Only present if @code{TC_FRAG_TYPE} is defined. |
| 574 | |
| 575 | @item fr_file |
| 576 | @itemx fr_line |
| 577 | The file and line where this frag was last modified. |
| 578 | |
| 579 | @item fr_literal |
| 580 | Declared as a one-character array, this last field grows arbitrarily large to |
| 581 | hold the actual contents of the frag. |
| 582 | @end table |
| 583 | |
| 584 | These are the possible relaxation states, provided in the enumeration type |
| 585 | @code{relax_stateT}, and the interpretations they represent for the other |
| 586 | fields: |
| 587 | |
| 588 | @table @code |
| 589 | @item rs_align |
| 590 | @itemx rs_align_code |
| 591 | The start of the following frag should be aligned on some boundary. In this |
| 592 | frag, @code{fr_offset} is the logarithm (base 2) of the alignment in bytes. |
| 593 | (For example, if alignment on an 8-byte boundary were desired, @code{fr_offset} |
| 594 | would have a value of 3.) The variable characters indicate the fill pattern to |
| 595 | be used. The @code{fr_subtype} field holds the maximum number of bytes to skip |
| 596 | when doing this alignment. If more bytes are needed, the alignment is not |
| 597 | done. An @code{fr_subtype} value of 0 means no maximum, which is the normal |
| 598 | case. Target backends can use @code{rs_align_code} to handle certain types of |
| 599 | alignment differently. |
| 600 | |
| 601 | @item rs_broken_word |
| 602 | This indicates that ``broken word'' processing should be done (@pxref{Broken |
| 603 | words}). If broken word processing is not necessary on the target machine, |
| 604 | this enumerator value will not be defined. |
| 605 | |
| 606 | @item rs_cfa |
| 607 | This state is used to implement exception frame optimizations. The |
| 608 | @code{fr_symbol} is an expression symbol for the subtraction which may be |
| 609 | relaxed. The @code{fr_opcode} field holds the frag for the preceding command |
| 610 | byte. The @code{fr_offset} field holds the offset within that frag. The |
| 611 | @code{fr_subtype} field is used during relaxation to hold the current size of |
| 612 | the frag. |
| 613 | |
| 614 | @item rs_fill |
| 615 | The variable characters are to be repeated @code{fr_offset} times. If |
| 616 | @code{fr_offset} is 0, this frag has a length of @code{fr_fix}. Most frags |
| 617 | have this type. |
| 618 | |
| 619 | @item rs_leb128 |
| 620 | This state is used to implement the DWARF ``little endian base 128'' |
| 621 | variable length number format. The @code{fr_symbol} is always an expression |
| 622 | symbol, as constant expressions are emitted directly. The @code{fr_offset} |
| 623 | field is used during relaxation to hold the previous size of the number so |
| 624 | that we can determine if the fragment changed size. |
| 625 | |
| 626 | @item rs_machine_dependent |
| 627 | Displacement relaxation is to be done on this frag. The target is indicated by |
| 628 | @code{fr_symbol} and @code{fr_offset}, and @code{fr_subtype} indicates the |
| 629 | particular machine-specific addressing mode desired. @xref{Relaxation}. |
| 630 | |
| 631 | @item rs_org |
| 632 | The start of the following frag should be pushed back to some specific offset |
| 633 | within the section. (Some assemblers use the value as an absolute address; GAS |
| 634 | does not handle final absolute addresses, but rather requires that the linker |
| 635 | set them.) The offset is given by @code{fr_symbol} and @code{fr_offset}; one |
| 636 | character from the variable-length tail is used as the fill character. |
| 637 | @end table |
| 638 | |
| 639 | @cindex frchainS structure |
| 640 | A chain of frags is built up for each subsection. The data structure |
| 641 | describing a chain is called a @code{frchainS}, and contains the following |
| 642 | fields: |
| 643 | |
| 644 | @table @code |
| 645 | @item frch_root |
| 646 | Points to the first frag in the chain. May be NULL if there are no frags in |
| 647 | this chain. |
| 648 | @item frch_last |
| 649 | Points to the last frag in the chain, or NULL if there are none. |
| 650 | @item frch_next |
| 651 | Next in the list of @code{frchainS} structures. |
| 652 | @item frch_seg |
| 653 | Indicates the section this frag chain belongs to. |
| 654 | @item frch_subseg |
| 655 | Subsection (subsegment) number of this frag chain. |
| 656 | @item fix_root, fix_tail |
| 657 | Point to first and last @code{fixS} structures associated with this subsection. |
| 658 | @item frch_obstack |
| 659 | Not currently used. Intended to be used for frag allocation for this |
| 660 | subsection. This should reduce frag generation caused by switching sections. |
| 661 | @item frch_frag_now |
| 662 | The current frag for this subsegment. |
| 663 | @end table |
| 664 | |
| 665 | A @code{frchainS} corresponds to a subsection; each section has a list of |
| 666 | @code{frchainS} records associated with it. In most cases, only one subsection |
| 667 | of each section is used, so the list will only be one element long, but any |
| 668 | processing of frag chains should be prepared to deal with multiple chains per |
| 669 | section. |
| 670 | |
| 671 | After the input files have been completely processed, and no more frags are to |
| 672 | be generated, the frag chains are joined into one per section for further |
| 673 | processing. After this point, it is safe to operate on one chain per section. |
| 674 | |
| 675 | The assembler always has a current frag, named @code{frag_now}. More space is |
| 676 | allocated for the current frag using the @code{frag_more} function; this |
| 677 | returns a pointer to the amount of requested space. The function |
| 678 | @code{frag_room} says by how much the current frag can be extended. |
| 679 | Relaxing is done using variant frags allocated by @code{frag_var} |
| 680 | or @code{frag_variant} (@pxref{Relaxation}). |
| 681 | |
| 682 | @node GAS processing |
| 683 | @section What GAS does when it runs |
| 684 | @cindex internals, overview |
| 685 | |
| 686 | This is a quick look at what an assembler run looks like. |
| 687 | |
| 688 | @itemize @bullet |
| 689 | @item |
| 690 | The assembler initializes itself by calling various init routines. |
| 691 | |
| 692 | @item |
| 693 | For each source file, the @code{read_a_source_file} function reads in the file |
| 694 | and parses it. The global variable @code{input_line_pointer} points to the |
| 695 | current text; it is guaranteed to be correct up to the end of the line, but not |
| 696 | farther. |
| 697 | |
| 698 | @item |
| 699 | For each line, the assembler passes labels to the @code{colon} function, and |
| 700 | isolates the first word. If it looks like a pseudo-op, the word is looked up |
| 701 | in the pseudo-op hash table @code{po_hash} and dispatched to a pseudo-op |
| 702 | routine. Otherwise, the target dependent @code{md_assemble} routine is called |
| 703 | to parse the instruction. |
| 704 | |
| 705 | @item |
| 706 | When pseudo-ops or instructions output data, they add it to a frag, calling |
| 707 | @code{frag_more} to get space to store it in. |
| 708 | |
| 709 | @item |
| 710 | Pseudo-ops and instructions can also output fixups created by @code{fix_new} or |
| 711 | @code{fix_new_exp}. |
| 712 | |
| 713 | @item |
| 714 | For certain targets, instructions can create variant frags which are used to |
| 715 | store relaxation information (@pxref{Relaxation}). |
| 716 | |
| 717 | @item |
| 718 | When the input file is finished, the @code{write_object_file} routine is |
| 719 | called. It assigns addresses to all the frags (@code{relax_segment}), resolves |
| 720 | all the fixups (@code{fixup_segment}), resolves all the symbol values (using |
| 721 | @code{resolve_symbol_value}), and finally writes out the file. |
| 722 | @end itemize |
| 723 | |
| 724 | @node Porting GAS |
| 725 | @section Porting GAS |
| 726 | @cindex porting |
| 727 | |
| 728 | Each GAS target specifies two main things: the CPU file and the object format |
| 729 | file. Two main switches in the @file{configure.ac} file handle this. The |
| 730 | first switches on CPU type to set the shell variable @code{cpu_type}. The |
| 731 | second switches on the entire target to set the shell variable @code{fmt}. |
| 732 | |
| 733 | The configure script uses the value of @code{cpu_type} to select two files in |
| 734 | the @file{config} directory: @file{tc-@var{CPU}.c} and @file{tc-@var{CPU}.h}. |
| 735 | The configuration process will create a file named @file{targ-cpu.h} in the |
| 736 | build directory which includes @file{tc-@var{CPU}.h}. |
| 737 | |
| 738 | The configure script also uses the value of @code{fmt} to select two files: |
| 739 | @file{obj-@var{fmt}.c} and @file{obj-@var{fmt}.h}. The configuration process |
| 740 | will create a file named @file{obj-format.h} in the build directory which |
| 741 | includes @file{obj-@var{fmt}.h}. |
| 742 | |
| 743 | You can also set the emulation in the configure script by setting the @code{em} |
| 744 | variable. Normally the default value of @samp{generic} is fine. The |
| 745 | configuration process will create a file named @file{targ-env.h} in the build |
| 746 | directory which includes @file{te-@var{em}.h}. |
| 747 | |
| 748 | There is a special case for COFF. For historical reason, the GNU COFF |
| 749 | assembler doesn't follow the documented behavior on certain debug symbols for |
| 750 | the compatibility with other COFF assemblers. A port can define |
| 751 | @code{STRICTCOFF} in the configure script to make the GNU COFF assembler |
| 752 | to follow the documented behavior. |
| 753 | |
| 754 | Porting GAS to a new CPU requires writing the @file{tc-@var{CPU}} files. |
| 755 | Porting GAS to a new object file format requires writing the |
| 756 | @file{obj-@var{fmt}} files. There is sometimes some interaction between these |
| 757 | two files, but it is normally minimal. |
| 758 | |
| 759 | The best approach is, of course, to copy existing files. The documentation |
| 760 | below assumes that you are looking at existing files to see usage details. |
| 761 | |
| 762 | These interfaces have grown over time, and have never been carefully thought |
| 763 | out or designed. Nothing about the interfaces described here is cast in stone. |
| 764 | It is possible that they will change from one version of the assembler to the |
| 765 | next. Also, new macros are added all the time as they are needed. |
| 766 | |
| 767 | @menu |
| 768 | * CPU backend:: Writing a CPU backend |
| 769 | * Object format backend:: Writing an object format backend |
| 770 | * Emulations:: Writing emulation files |
| 771 | @end menu |
| 772 | |
| 773 | @node CPU backend |
| 774 | @subsection Writing a CPU backend |
| 775 | @cindex CPU backend |
| 776 | @cindex @file{tc-@var{CPU}} |
| 777 | |
| 778 | The CPU backend files are the heart of the assembler. They are the only parts |
| 779 | of the assembler which actually know anything about the instruction set of the |
| 780 | processor. |
| 781 | |
| 782 | You must define a reasonably small list of macros and functions in the CPU |
| 783 | backend files. You may define a large number of additional macros in the CPU |
| 784 | backend files, not all of which are documented here. You must, of course, |
| 785 | define macros in the @file{.h} file, which is included by every assembler |
| 786 | source file. You may define the functions as macros in the @file{.h} file, or |
| 787 | as functions in the @file{.c} file. |
| 788 | |
| 789 | @table @code |
| 790 | @item TC_@var{CPU} |
| 791 | @cindex TC_@var{CPU} |
| 792 | By convention, you should define this macro in the @file{.h} file. For |
| 793 | example, @file{tc-m68k.h} defines @code{TC_M68K}. You might have to use this |
| 794 | if it is necessary to add CPU specific code to the object format file. |
| 795 | |
| 796 | @item TARGET_FORMAT |
| 797 | This macro is the BFD target name to use when creating the output file. This |
| 798 | will normally depend upon the @code{OBJ_@var{FMT}} macro. |
| 799 | |
| 800 | @item TARGET_ARCH |
| 801 | This macro is the BFD architecture to pass to @code{bfd_set_arch_mach}. |
| 802 | |
| 803 | @item TARGET_MACH |
| 804 | This macro is the BFD machine number to pass to @code{bfd_set_arch_mach}. If |
| 805 | it is not defined, GAS will use 0. |
| 806 | |
| 807 | @item TARGET_BYTES_BIG_ENDIAN |
| 808 | You should define this macro to be non-zero if the target is big endian, and |
| 809 | zero if the target is little endian. |
| 810 | |
| 811 | @item md_shortopts |
| 812 | @itemx md_longopts |
| 813 | @itemx md_longopts_size |
| 814 | @itemx md_parse_option |
| 815 | @itemx md_show_usage |
| 816 | @itemx md_after_parse_args |
| 817 | @cindex md_shortopts |
| 818 | @cindex md_longopts |
| 819 | @cindex md_longopts_size |
| 820 | @cindex md_parse_option |
| 821 | @cindex md_show_usage |
| 822 | @cindex md_after_parse_args |
| 823 | GAS uses these variables and functions during option processing. |
| 824 | @code{md_shortopts} is a @code{const char *} which GAS adds to the machine |
| 825 | independent string passed to @code{getopt}. @code{md_longopts} is a |
| 826 | @code{struct option []} which GAS adds to the machine independent long options |
| 827 | passed to @code{getopt}; you may use @code{OPTION_MD_BASE}, defined in |
| 828 | @file{as.h}, as the start of a set of long option indices, if necessary. |
| 829 | @code{md_longopts_size} is a @code{size_t} holding the size @code{md_longopts}. |
| 830 | |
| 831 | GAS will call @code{md_parse_option} whenever @code{getopt} returns an |
| 832 | unrecognized code, presumably indicating a special code value which appears in |
| 833 | @code{md_longopts}. This function should return non-zero if it handled the |
| 834 | option and zero otherwise. There is no need to print a message about an option |
| 835 | not being recognized. This will be handled by the generic code. |
| 836 | |
| 837 | GAS will call @code{md_show_usage} when a usage message is printed; it should |
| 838 | print a description of the machine specific options. @code{md_after_pase_args}, |
| 839 | if defined, is called after all options are processed, to let the backend |
| 840 | override settings done by the generic option parsing. |
| 841 | |
| 842 | @item md_begin |
| 843 | @cindex md_begin |
| 844 | GAS will call this function at the start of the assembly, after the command |
| 845 | line arguments have been parsed and all the machine independent initializations |
| 846 | have been completed. |
| 847 | |
| 848 | @item md_cleanup |
| 849 | @cindex md_cleanup |
| 850 | If you define this macro, GAS will call it at the end of each input file. |
| 851 | |
| 852 | @item md_assemble |
| 853 | @cindex md_assemble |
| 854 | GAS will call this function for each input line which does not contain a |
| 855 | pseudo-op. The argument is a null terminated string. The function should |
| 856 | assemble the string as an instruction with operands. Normally |
| 857 | @code{md_assemble} will do this by calling @code{frag_more} and writing out |
| 858 | some bytes (@pxref{Frags}). @code{md_assemble} will call @code{fix_new} to |
| 859 | create fixups as needed (@pxref{Fixups}). Targets which need to do special |
| 860 | purpose relaxation will call @code{frag_var}. |
| 861 | |
| 862 | @item md_pseudo_table |
| 863 | @cindex md_pseudo_table |
| 864 | This is a const array of type @code{pseudo_typeS}. It is a mapping from |
| 865 | pseudo-op names to functions. You should use this table to implement |
| 866 | pseudo-ops which are specific to the CPU. |
| 867 | |
| 868 | @item tc_conditional_pseudoop |
| 869 | @cindex tc_conditional_pseudoop |
| 870 | If this macro is defined, GAS will call it with a @code{pseudo_typeS} argument. |
| 871 | It should return non-zero if the pseudo-op is a conditional which controls |
| 872 | whether code is assembled, such as @samp{.if}. GAS knows about the normal |
| 873 | conditional pseudo-ops, and you should normally not have to define this macro. |
| 874 | |
| 875 | @item comment_chars |
| 876 | @cindex comment_chars |
| 877 | This is a null terminated @code{const char} array of characters which start a |
| 878 | comment. |
| 879 | |
| 880 | @item tc_comment_chars |
| 881 | @cindex tc_comment_chars |
| 882 | If this macro is defined, GAS will use it instead of @code{comment_chars}. |
| 883 | This has the advantage that this macro does not have to refer to a constant |
| 884 | array. |
| 885 | |
| 886 | @item tc_symbol_chars |
| 887 | @cindex tc_symbol_chars |
| 888 | If this macro is defined, it is a pointer to a null terminated list of |
| 889 | characters which may appear in an operand. GAS already assumes that all |
| 890 | alphanumeric characters, and @samp{$}, @samp{.}, and @samp{_} may appear in an |
| 891 | operand (see @samp{symbol_chars} in @file{app.c}). This macro may be defined |
| 892 | to treat additional characters as appearing in an operand. This affects the |
| 893 | way in which GAS removes whitespace before passing the string to |
| 894 | @samp{md_assemble}. |
| 895 | |
| 896 | @item line_comment_chars |
| 897 | @cindex line_comment_chars |
| 898 | This is a null terminated @code{const char} array of characters which start a |
| 899 | comment when they appear at the start of a line. |
| 900 | |
| 901 | @item line_separator_chars |
| 902 | @cindex line_separator_chars |
| 903 | This is a null terminated @code{const char} array of characters which separate |
| 904 | lines (null and newline are such characters by default, and need not be |
| 905 | listed in this array). Note that line_separator_chars do not separate lines |
| 906 | if found in a comment, such as after a character in line_comment_chars or |
| 907 | comment_chars. |
| 908 | |
| 909 | @item tc_line_separator_chars |
| 910 | @cindex tc_line_separator_chars |
| 911 | If this macro is defined, GAS will use it instead of |
| 912 | @code{line_separator_chars}. This has the advantage that this macro does not |
| 913 | have to refer to a constant array. |
| 914 | |
| 915 | |
| 916 | @item EXP_CHARS |
| 917 | @cindex EXP_CHARS |
| 918 | This is a null terminated @code{const char} array of characters which may be |
| 919 | used as the exponent character in a floating point number. This is normally |
| 920 | @code{"eE"}. |
| 921 | |
| 922 | @item FLT_CHARS |
| 923 | @cindex FLT_CHARS |
| 924 | This is a null terminated @code{const char} array of characters which may be |
| 925 | used to indicate a floating point constant. A zero followed by one of these |
| 926 | characters is assumed to be followed by a floating point number; thus they |
| 927 | operate the way that @code{0x} is used to indicate a hexadecimal constant. |
| 928 | Usually this includes @samp{r} and @samp{f}. |
| 929 | |
| 930 | @item LEX_AT |
| 931 | @cindex LEX_AT |
| 932 | You may define this macro to the lexical type of the @kbd{@@} character. The |
| 933 | default is zero. |
| 934 | |
| 935 | Lexical types are a combination of @code{LEX_NAME} and @code{LEX_BEGIN_NAME}, |
| 936 | both defined in @file{read.h}. @code{LEX_NAME} indicates that the character |
| 937 | may appear in a name. @code{LEX_BEGIN_NAME} indicates that the character may |
| 938 | appear at the beginning of a name. |
| 939 | |
| 940 | @item LEX_BR |
| 941 | @cindex LEX_BR |
| 942 | You may define this macro to the lexical type of the brace characters @kbd{@{}, |
| 943 | @kbd{@}}, @kbd{[}, and @kbd{]}. The default value is zero. |
| 944 | |
| 945 | @item LEX_PCT |
| 946 | @cindex LEX_PCT |
| 947 | You may define this macro to the lexical type of the @kbd{%} character. The |
| 948 | default value is zero. |
| 949 | |
| 950 | @item LEX_QM |
| 951 | @cindex LEX_QM |
| 952 | You may define this macro to the lexical type of the @kbd{?} character. The |
| 953 | default value it zero. |
| 954 | |
| 955 | @item LEX_DOLLAR |
| 956 | @cindex LEX_DOLLAR |
| 957 | You may define this macro to the lexical type of the @kbd{$} character. The |
| 958 | default value is @code{LEX_NAME | LEX_BEGIN_NAME}. |
| 959 | |
| 960 | @item NUMBERS_WITH_SUFFIX |
| 961 | @cindex NUMBERS_WITH_SUFFIX |
| 962 | When this macro is defined to be non-zero, the parser allows the radix of a |
| 963 | constant to be indicated with a suffix. Valid suffixes are binary (B), |
| 964 | octal (Q), and hexadecimal (H). Case is not significant. |
| 965 | |
| 966 | @item SINGLE_QUOTE_STRINGS |
| 967 | @cindex SINGLE_QUOTE_STRINGS |
| 968 | If you define this macro, GAS will treat single quotes as string delimiters. |
| 969 | Normally only double quotes are accepted as string delimiters. |
| 970 | |
| 971 | @item NO_STRING_ESCAPES |
| 972 | @cindex NO_STRING_ESCAPES |
| 973 | If you define this macro, GAS will not permit escape sequences in a string. |
| 974 | |
| 975 | @item ONLY_STANDARD_ESCAPES |
| 976 | @cindex ONLY_STANDARD_ESCAPES |
| 977 | If you define this macro, GAS will warn about the use of nonstandard escape |
| 978 | sequences in a string. |
| 979 | |
| 980 | @item md_start_line_hook |
| 981 | @cindex md_start_line_hook |
| 982 | If you define this macro, GAS will call it at the start of each line. |
| 983 | |
| 984 | @item LABELS_WITHOUT_COLONS |
| 985 | @cindex LABELS_WITHOUT_COLONS |
| 986 | If you define this macro, GAS will assume that any text at the start of a line |
| 987 | is a label, even if it does not have a colon. |
| 988 | |
| 989 | @item TC_START_LABEL |
| 990 | @itemx TC_START_LABEL_WITHOUT_COLON |
| 991 | @cindex TC_START_LABEL |
| 992 | You may define this macro to control what GAS considers to be a label. The |
| 993 | default definition is to accept any name followed by a colon character. |
| 994 | |
| 995 | @item TC_START_LABEL_WITHOUT_COLON |
| 996 | @cindex TC_START_LABEL_WITHOUT_COLON |
| 997 | Same as TC_START_LABEL, but should be used instead of TC_START_LABEL when |
| 998 | LABELS_WITHOUT_COLONS is defined. |
| 999 | |
| 1000 | @item TC_FAKE_LABEL |
| 1001 | @cindex TC_FAKE_LABEL |
| 1002 | You may define this macro to control what GAS considers to be a fake |
| 1003 | label. The default fake label is FAKE_LABEL_NAME. |
| 1004 | |
| 1005 | @item NO_PSEUDO_DOT |
| 1006 | @cindex NO_PSEUDO_DOT |
| 1007 | If you define this macro, GAS will not require pseudo-ops to start with a |
| 1008 | @kbd{.} character. |
| 1009 | |
| 1010 | @item TC_EQUAL_IN_INSN |
| 1011 | @cindex TC_EQUAL_IN_INSN |
| 1012 | If you define this macro, it should return nonzero if the instruction is |
| 1013 | permitted to contain an @kbd{=} character. GAS will call it with two |
| 1014 | arguments, the character before the @kbd{=} character, and the value of |
| 1015 | the string preceding the equal sign. GAS uses this macro to decide if a |
| 1016 | @kbd{=} is an assignment or an instruction. |
| 1017 | |
| 1018 | @item TC_EOL_IN_INSN |
| 1019 | @cindex TC_EOL_IN_INSN |
| 1020 | If you define this macro, it should return nonzero if the current input line |
| 1021 | pointer should be treated as the end of a line. |
| 1022 | |
| 1023 | @item TC_CASE_SENSITIVE |
| 1024 | @cindex TC_CASE_SENSITIVE |
| 1025 | Define this macro if instruction mnemonics and pseudos are case sensitive. |
| 1026 | The default is to have it undefined giving case insensitive names. |
| 1027 | |
| 1028 | @item md_parse_name |
| 1029 | @cindex md_parse_name |
| 1030 | If this macro is defined, GAS will call it for any symbol found in an |
| 1031 | expression. You can define this to handle special symbols in a special way. |
| 1032 | If a symbol always has a certain value, you should normally enter it in the |
| 1033 | symbol table, perhaps using @code{reg_section}. |
| 1034 | |
| 1035 | @item md_undefined_symbol |
| 1036 | @cindex md_undefined_symbol |
| 1037 | GAS will call this function when a symbol table lookup fails, before it |
| 1038 | creates a new symbol. Typically this would be used to supply symbols whose |
| 1039 | name or value changes dynamically, possibly in a context sensitive way. |
| 1040 | Predefined symbols with fixed values, such as register names or condition |
| 1041 | codes, are typically entered directly into the symbol table when @code{md_begin} |
| 1042 | is called. One argument is passed, a @code{char *} for the symbol. |
| 1043 | |
| 1044 | @item md_operand |
| 1045 | @cindex md_operand |
| 1046 | GAS will call this function with one argument, an @code{expressionS} |
| 1047 | pointer, for any expression that can not be recognized. When the function |
| 1048 | is called, @code{input_line_pointer} will point to the start of the |
| 1049 | expression. |
| 1050 | |
| 1051 | @item md_register_arithmetic |
| 1052 | @cindex md_register_arithmetic |
| 1053 | If this macro is defined and evaluates to zero then GAS will not fold |
| 1054 | expressions that add or subtract a constant to/from a register to give |
| 1055 | another register. For example GAS's default behaviour is to fold the |
| 1056 | expression "r8 + 1" into "r9", which is probably not the result |
| 1057 | intended by the programmer. The default is to allow such folding, |
| 1058 | since this maintains backwards compatibility with earlier releases of |
| 1059 | GAS. |
| 1060 | |
| 1061 | @item tc_unrecognized_line |
| 1062 | @cindex tc_unrecognized_line |
| 1063 | If you define this macro, GAS will call it when it finds a line that it can not |
| 1064 | parse. |
| 1065 | |
| 1066 | @item md_do_align |
| 1067 | @cindex md_do_align |
| 1068 | You may define this macro to handle an alignment directive. GAS will call it |
| 1069 | when the directive is seen in the input file. For example, the i386 backend |
| 1070 | uses this to generate efficient nop instructions of varying lengths, depending |
| 1071 | upon the number of bytes that the alignment will skip. |
| 1072 | |
| 1073 | @item HANDLE_ALIGN |
| 1074 | @cindex HANDLE_ALIGN |
| 1075 | You may define this macro to do special handling for an alignment directive. |
| 1076 | GAS will call it at the end of the assembly. |
| 1077 | |
| 1078 | @item TC_IMPLICIT_LCOMM_ALIGNMENT (@var{size}, @var{p2var}) |
| 1079 | @cindex TC_IMPLICIT_LCOMM_ALIGNMENT |
| 1080 | An @code{.lcomm} directive with no explicit alignment parameter will use this |
| 1081 | macro to set @var{p2var} to the alignment that a request for @var{size} bytes |
| 1082 | will have. The alignment is expressed as a power of two. If no alignment |
| 1083 | should take place, the macro definition should do nothing. Some targets define |
| 1084 | a @code{.bss} directive that is also affected by this macro. The default |
| 1085 | definition will set @var{p2var} to the truncated power of two of sizes up to |
| 1086 | eight bytes. |
| 1087 | |
| 1088 | @item md_flush_pending_output |
| 1089 | @cindex md_flush_pending_output |
| 1090 | If you define this macro, GAS will call it each time it skips any space because of a |
| 1091 | space filling or alignment or data allocation pseudo-op. |
| 1092 | |
| 1093 | @item TC_PARSE_CONS_EXPRESSION |
| 1094 | @cindex TC_PARSE_CONS_EXPRESSION |
| 1095 | You may define this macro to parse an expression used in a data allocation |
| 1096 | pseudo-op such as @code{.word}. You can use this to recognize relocation |
| 1097 | directives that may appear in such directives. |
| 1098 | |
| 1099 | @item BITFIELD_CONS_EXPRESSION |
| 1100 | @cindex BITFIELD_CONS_EXPRESSION |
| 1101 | If you define this macro, GAS will recognize bitfield instructions in data |
| 1102 | allocation pseudo-ops, as used on the i960. |
| 1103 | |
| 1104 | @item REPEAT_CONS_EXPRESSION |
| 1105 | @cindex REPEAT_CONS_EXPRESSION |
| 1106 | If you define this macro, GAS will recognize repeat counts in data allocation |
| 1107 | pseudo-ops, as used on the MIPS. |
| 1108 | |
| 1109 | @item md_cons_align |
| 1110 | @cindex md_cons_align |
| 1111 | You may define this macro to do any special alignment before a data allocation |
| 1112 | pseudo-op. |
| 1113 | |
| 1114 | @item TC_CONS_FIX_NEW |
| 1115 | @cindex TC_CONS_FIX_NEW |
| 1116 | You may define this macro to generate a fixup for a data allocation pseudo-op. |
| 1117 | |
| 1118 | @item TC_ADDRESS_BYTES |
| 1119 | @cindex TC_ADDRESS_BYTES |
| 1120 | Define this macro to specify the number of bytes used to store an address. |
| 1121 | Used to implement @code{dc.a}. The target must have a reloc for this size. |
| 1122 | |
| 1123 | @item TC_INIT_FIX_DATA (@var{fixp}) |
| 1124 | @cindex TC_INIT_FIX_DATA |
| 1125 | A C statement to initialize the target specific fields of fixup @var{fixp}. |
| 1126 | These fields are defined with the @code{TC_FIX_TYPE} macro. |
| 1127 | |
| 1128 | @item TC_FIX_DATA_PRINT (@var{stream}, @var{fixp}) |
| 1129 | @cindex TC_FIX_DATA_PRINT |
| 1130 | A C statement to output target specific debugging information for |
| 1131 | fixup @var{fixp} to @var{stream}. This macro is called by @code{print_fixup}. |
| 1132 | |
| 1133 | @item TC_FRAG_INIT (@var{fragp}) |
| 1134 | @cindex TC_FRAG_INIT |
| 1135 | A C statement to initialize the target specific fields of frag @var{fragp}. |
| 1136 | These fields are defined with the @code{TC_FRAG_TYPE} macro. |
| 1137 | |
| 1138 | @item md_number_to_chars |
| 1139 | @cindex md_number_to_chars |
| 1140 | This should just call either @code{number_to_chars_bigendian} or |
| 1141 | @code{number_to_chars_littleendian}, whichever is appropriate. On targets like |
| 1142 | the MIPS which support options to change the endianness, which function to call |
| 1143 | is a runtime decision. On other targets, @code{md_number_to_chars} can be a |
| 1144 | simple macro. |
| 1145 | |
| 1146 | @item md_atof (@var{type},@var{litP},@var{sizeP}) |
| 1147 | @cindex md_atof |
| 1148 | This function is called to convert an ASCII string into a floating point value |
| 1149 | in format used by the CPU. It takes three arguments. The first is @var{type} |
| 1150 | which is a byte describing the type of floating point number to be created. It |
| 1151 | is one of the characters defined in the @code{FLT_CHARS} macro. Possible |
| 1152 | values are @var{'f'} or @var{'s'} for single precision, @var{'d'} or @var{'r'} |
| 1153 | for double precision and @var{'x'} or @var{'p'} for extended precision. Either |
| 1154 | lower or upper case versions of these letters can be used. Note: some targets |
| 1155 | do not support all of these types, and some targets may also support other |
| 1156 | types not mentioned here. |
| 1157 | |
| 1158 | The second parameter is @var{litP} which is a pointer to a byte array where the |
| 1159 | converted value should be stored. The value is converted into LITTLENUMs and |
| 1160 | is stored in the target's endian-ness order. (@var{LITTLENUM} is defined in |
| 1161 | gas/bignum.h). Single precision values occupy 2 littlenums. Double precision |
| 1162 | values occupy 4 littlenums and extended precision values occupy either 5 or 6 |
| 1163 | littlenums, depending upon the target. |
| 1164 | |
| 1165 | The third argument is @var{sizeP}, which is a pointer to a integer that should |
| 1166 | be filled in with the number of chars emitted into the byte array. |
| 1167 | |
| 1168 | The function should return NULL upon success or an error string upon failure. |
| 1169 | |
| 1170 | @item TC_LARGEST_EXPONENT_IS_NORMAL |
| 1171 | @cindex TC_LARGEST_EXPONENT_IS_NORMAL (@var{precision}) |
| 1172 | This macro is used only by @file{atof-ieee.c}. It should evaluate to true |
| 1173 | if floats of the given precision use the largest exponent for normal numbers |
| 1174 | instead of NaNs and infinities. @var{precision} is @samp{F_PRECISION} for |
| 1175 | single precision, @samp{D_PRECISION} for double precision, or |
| 1176 | @samp{X_PRECISION} for extended double precision. |
| 1177 | |
| 1178 | The macro has a default definition which returns 0 for all cases. |
| 1179 | |
| 1180 | @item WORKING_DOT_WORD |
| 1181 | @itemx md_short_jump_size |
| 1182 | @itemx md_long_jump_size |
| 1183 | @itemx md_create_short_jump |
| 1184 | @itemx md_create_long_jump |
| 1185 | @itemx TC_CHECK_ADJUSTED_BROKEN_DOT_WORD |
| 1186 | @cindex WORKING_DOT_WORD |
| 1187 | @cindex md_short_jump_size |
| 1188 | @cindex md_long_jump_size |
| 1189 | @cindex md_create_short_jump |
| 1190 | @cindex md_create_long_jump |
| 1191 | @cindex TC_CHECK_ADJUSTED_BROKEN_DOT_WORD |
| 1192 | If @code{WORKING_DOT_WORD} is defined, GAS will not do broken word processing |
| 1193 | (@pxref{Broken words}). Otherwise, you should set @code{md_short_jump_size} to |
| 1194 | the size of a short jump (a jump that is just long enough to jump around a |
| 1195 | number of long jumps) and @code{md_long_jump_size} to the size of a long jump |
| 1196 | (a jump that can go anywhere in the function). You should define |
| 1197 | @code{md_create_short_jump} to create a short jump around a number of long |
| 1198 | jumps, and define @code{md_create_long_jump} to create a long jump. |
| 1199 | If defined, the macro TC_CHECK_ADJUSTED_BROKEN_DOT_WORD will be called for each |
| 1200 | adjusted word just before the word is output. The macro takes two arguments, |
| 1201 | an @code{addressT} with the adjusted word and a pointer to the current |
| 1202 | @code{struct broken_word}. |
| 1203 | |
| 1204 | @item md_estimate_size_before_relax |
| 1205 | @cindex md_estimate_size_before_relax |
| 1206 | This function returns an estimate of the size of a @code{rs_machine_dependent} |
| 1207 | frag before any relaxing is done. It may also create any necessary |
| 1208 | relocations. |
| 1209 | |
| 1210 | @item md_relax_frag |
| 1211 | @cindex md_relax_frag |
| 1212 | This macro may be defined to relax a frag. GAS will call this with the |
| 1213 | segment, the frag, and the change in size of all previous frags; |
| 1214 | @code{md_relax_frag} should return the change in size of the frag. |
| 1215 | @xref{Relaxation}. |
| 1216 | |
| 1217 | @item TC_GENERIC_RELAX_TABLE |
| 1218 | @cindex TC_GENERIC_RELAX_TABLE |
| 1219 | If you do not define @code{md_relax_frag}, you may define |
| 1220 | @code{TC_GENERIC_RELAX_TABLE} as a table of @code{relax_typeS} structures. The |
| 1221 | machine independent code knows how to use such a table to relax PC relative |
| 1222 | references. See @file{tc-m68k.c} for an example. @xref{Relaxation}. |
| 1223 | |
| 1224 | @item md_prepare_relax_scan |
| 1225 | @cindex md_prepare_relax_scan |
| 1226 | If defined, it is a C statement that is invoked prior to scanning |
| 1227 | the relax table. |
| 1228 | |
| 1229 | @item LINKER_RELAXING_SHRINKS_ONLY |
| 1230 | @cindex LINKER_RELAXING_SHRINKS_ONLY |
| 1231 | If you define this macro, and the global variable @samp{linkrelax} is set |
| 1232 | (because of a command line option, or unconditionally in @code{md_begin}), a |
| 1233 | @samp{.align} directive will cause extra space to be allocated. The linker can |
| 1234 | then discard this space when relaxing the section. |
| 1235 | |
| 1236 | @item TC_LINKRELAX_FIXUP (@var{segT}) |
| 1237 | @cindex TC_LINKRELAX_FIXUP |
| 1238 | If defined, this macro allows control over whether fixups for a |
| 1239 | given section will be processed when the @var{linkrelax} variable is |
| 1240 | set. The macro is given the N_TYPE bits for the section in its |
| 1241 | @var{segT} argument. If the macro evaluates to a non-zero value |
| 1242 | then the fixups will be converted into relocs, otherwise they will |
| 1243 | be passed to @var{md_apply_fix} as normal. |
| 1244 | |
| 1245 | @item md_convert_frag |
| 1246 | @cindex md_convert_frag |
| 1247 | GAS will call this for each rs_machine_dependent fragment. |
| 1248 | The instruction is completed using the data from the relaxation pass. |
| 1249 | It may also create any necessary relocations. |
| 1250 | @xref{Relaxation}. |
| 1251 | |
| 1252 | @item TC_FINALIZE_SYMS_BEFORE_SIZE_SEG |
| 1253 | @cindex TC_FINALIZE_SYMS_BEFORE_SIZE_SEG |
| 1254 | Specifies the value to be assigned to @code{finalize_syms} before the function |
| 1255 | @code{size_segs} is called. Since @code{size_segs} calls @code{cvt_frag_to_fill} |
| 1256 | which can call @code{md_convert_frag}, this constant governs whether the symbols |
| 1257 | accessed in @code{md_convert_frag} will be fully resolved. In particular it |
| 1258 | governs whether local symbols will have been resolved, and had their frag |
| 1259 | information removed. Depending upon the processing performed by |
| 1260 | @code{md_convert_frag} the frag information may or may not be necessary, as may |
| 1261 | the resolved values of the symbols. The default value is 1. |
| 1262 | |
| 1263 | @item TC_VALIDATE_FIX (@var{fixP}, @var{seg}, @var{skip}) |
| 1264 | @cindex TC_VALIDATE_FIX |
| 1265 | This macro is evaluated for each fixup (when @var{linkrelax} is not set). |
| 1266 | It may be used to change the fixup in @code{struct fix *@var{fixP}} before |
| 1267 | the generic code sees it, or to fully process the fixup. In the latter case, |
| 1268 | a @code{goto @var{skip}} will bypass the generic code. |
| 1269 | |
| 1270 | @item md_apply_fix (@var{fixP}, @var{valP}, @var{seg}) |
| 1271 | @cindex md_apply_fix |
| 1272 | GAS will call this for each fixup that passes the @code{TC_VALIDATE_FIX} test |
| 1273 | when @var{linkrelax} is not set. It should store the correct value in the |
| 1274 | object file. @code{struct fix *@var{fixP}} is the fixup @code{md_apply_fix} |
| 1275 | is operating on. @code{valueT *@var{valP}} is the value to store into the |
| 1276 | object files, or at least is the generic code's best guess. Specifically, |
| 1277 | *@var{valP} is the value of the fixup symbol, perhaps modified by |
| 1278 | @code{MD_APPLY_SYM_VALUE}, plus @code{@var{fixP}->fx_offset} (symbol addend), |
| 1279 | less @code{MD_PCREL_FROM_SECTION} for pc-relative fixups. |
| 1280 | @code{segT @var{seg}} is the section the fix is in. |
| 1281 | @code{fixup_segment} performs a generic overflow check on *@var{valP} after |
| 1282 | @code{md_apply_fix} returns. If the overflow check is relevant for the target |
| 1283 | machine, then @code{md_apply_fix} should modify *@var{valP}, typically to the |
| 1284 | value stored in the object file. |
| 1285 | |
| 1286 | @item TC_FORCE_RELOCATION (@var{fix}) |
| 1287 | @cindex TC_FORCE_RELOCATION |
| 1288 | If this macro returns non-zero, it guarantees that a relocation will be emitted |
| 1289 | even when the value can be resolved locally, as @code{fixup_segment} tries to |
| 1290 | reduce the number of relocations emitted. For example, a fixup expression |
| 1291 | against an absolute symbol will normally not require a reloc. If undefined, |
| 1292 | a default of @w{@code{(S_FORCE_RELOC ((@var{fix})->fx_addsy))}} is used. |
| 1293 | |
| 1294 | @item TC_FORCE_RELOCATION_ABS (@var{fix}) |
| 1295 | @cindex TC_FORCE_RELOCATION_ABS |
| 1296 | Like @code{TC_FORCE_RELOCATION}, but used only for fixup expressions against an |
| 1297 | absolute symbol. If undefined, @code{TC_FORCE_RELOCATION} will be used. |
| 1298 | |
| 1299 | @item TC_FORCE_RELOCATION_LOCAL (@var{fix}) |
| 1300 | @cindex TC_FORCE_RELOCATION_LOCAL |
| 1301 | Like @code{TC_FORCE_RELOCATION}, but used only for fixup expressions against a |
| 1302 | symbol in the current section. If undefined, fixups that are not |
| 1303 | @code{fx_pcrel} or for which @code{TC_FORCE_RELOCATION} |
| 1304 | returns non-zero, will emit relocs. |
| 1305 | |
| 1306 | @item TC_FORCE_RELOCATION_SUB_SAME (@var{fix}, @var{seg}) |
| 1307 | @cindex TC_FORCE_RELOCATION_SUB_SAME |
| 1308 | This macro controls resolution of fixup expressions involving the |
| 1309 | difference of two symbols in the same section. If this macro returns zero, |
| 1310 | the subtrahend will be resolved and @code{fx_subsy} set to @code{NULL} for |
| 1311 | @code{md_apply_fix}. If undefined, the default of |
| 1312 | @w{@code{! SEG_NORMAL (@var{seg})}} will be used. |
| 1313 | |
| 1314 | @item TC_FORCE_RELOCATION_SUB_ABS (@var{fix}, @var{seg}) |
| 1315 | @cindex TC_FORCE_RELOCATION_SUB_ABS |
| 1316 | Like @code{TC_FORCE_RELOCATION_SUB_SAME}, but used when the subtrahend is an |
| 1317 | absolute symbol. If the macro is undefined a default of @code{0} is used. |
| 1318 | |
| 1319 | @item TC_FORCE_RELOCATION_SUB_LOCAL (@var{fix}, @var{seg}) |
| 1320 | @cindex TC_FORCE_RELOCATION_SUB_LOCAL |
| 1321 | Like @code{TC_FORCE_RELOCATION_SUB_ABS}, but the subtrahend is a symbol in the |
| 1322 | same section as the fixup. |
| 1323 | |
| 1324 | @item TC_VALIDATE_FIX_SUB (@var{fix}, @var{seg}) |
| 1325 | @cindex TC_VALIDATE_FIX_SUB |
| 1326 | This macro is evaluated for any fixup with a @code{fx_subsy} that |
| 1327 | @code{fixup_segment} cannot reduce to a number. If the macro returns |
| 1328 | @code{false} an error will be reported. |
| 1329 | |
| 1330 | @item TC_GLOBAL_REGISTER_SYMBOL_OK |
| 1331 | @cindex TC_GLOBAL_REGISTER_SYMBOL_OK |
| 1332 | Define this macro if global register symbols are supported. The default |
| 1333 | is to disallow global register symbols. |
| 1334 | |
| 1335 | @item MD_APPLY_SYM_VALUE (@var{fix}) |
| 1336 | @cindex MD_APPLY_SYM_VALUE |
| 1337 | This macro controls whether the symbol value becomes part of the value passed |
| 1338 | to @code{md_apply_fix}. If the macro is undefined, or returns non-zero, the |
| 1339 | symbol value will be included. For ELF, a suitable definition might simply be |
| 1340 | @code{0}, because ELF relocations don't include the symbol value in the addend. |
| 1341 | |
| 1342 | @item S_FORCE_RELOC (@var{sym}, @var{strict}) |
| 1343 | @cindex S_FORCE_RELOC |
| 1344 | This function returns true for symbols |
| 1345 | that should not be reduced to section symbols or eliminated from expressions, |
| 1346 | because they may be overridden by the linker. ie. for symbols that are |
| 1347 | undefined or common, and when @var{strict} is set, weak, or global (for ELF |
| 1348 | assemblers that support ELF shared library linking semantics). |
| 1349 | |
| 1350 | @item EXTERN_FORCE_RELOC |
| 1351 | @cindex EXTERN_FORCE_RELOC |
| 1352 | This macro controls whether @code{S_FORCE_RELOC} returns true for global |
| 1353 | symbols. If undefined, the default is @code{true} for ELF assemblers, and |
| 1354 | @code{false} for non-ELF. |
| 1355 | |
| 1356 | @item tc_gen_reloc |
| 1357 | @cindex tc_gen_reloc |
| 1358 | GAS will call this to generate a reloc. GAS will pass |
| 1359 | the resulting reloc to @code{bfd_install_relocation}. This currently works |
| 1360 | poorly, as @code{bfd_install_relocation} often does the wrong thing, and |
| 1361 | instances of @code{tc_gen_reloc} have been written to work around the problems, |
| 1362 | which in turns makes it difficult to fix @code{bfd_install_relocation}. |
| 1363 | |
| 1364 | @item RELOC_EXPANSION_POSSIBLE |
| 1365 | @cindex RELOC_EXPANSION_POSSIBLE |
| 1366 | If you define this macro, it means that @code{tc_gen_reloc} may return multiple |
| 1367 | relocation entries for a single fixup. In this case, the return value of |
| 1368 | @code{tc_gen_reloc} is a pointer to a null terminated array. |
| 1369 | |
| 1370 | @item MAX_RELOC_EXPANSION |
| 1371 | @cindex MAX_RELOC_EXPANSION |
| 1372 | You must define this if @code{RELOC_EXPANSION_POSSIBLE} is defined; it |
| 1373 | indicates the largest number of relocs which @code{tc_gen_reloc} may return for |
| 1374 | a single fixup. |
| 1375 | |
| 1376 | @item tc_fix_adjustable |
| 1377 | @cindex tc_fix_adjustable |
| 1378 | You may define this macro to indicate whether a fixup against a locally defined |
| 1379 | symbol should be adjusted to be against the section symbol. It should return a |
| 1380 | non-zero value if the adjustment is acceptable. |
| 1381 | |
| 1382 | @item MD_PCREL_FROM_SECTION (@var{fixp}, @var{section}) |
| 1383 | @cindex MD_PCREL_FROM_SECTION |
| 1384 | If you define this macro, it should return the position from which the PC |
| 1385 | relative adjustment for a PC relative fixup should be made. On many |
| 1386 | processors, the base of a PC relative instruction is the next instruction, |
| 1387 | so this macro would return the length of an instruction, plus the address of |
| 1388 | the PC relative fixup. The latter can be calculated as |
| 1389 | @var{fixp}->fx_where + @var{fixp}->fx_frag->fr_address . |
| 1390 | |
| 1391 | @item md_pcrel_from |
| 1392 | @cindex md_pcrel_from |
| 1393 | This is the default value of @code{MD_PCREL_FROM_SECTION}. The difference is |
| 1394 | that @code{md_pcrel_from} does not take a section argument. |
| 1395 | |
| 1396 | @item tc_frob_label |
| 1397 | @cindex tc_frob_label |
| 1398 | If you define this macro, GAS will call it each time a label is defined. |
| 1399 | |
| 1400 | @item tc_new_dot_label |
| 1401 | @cindex tc_new_dot_label |
| 1402 | If you define this macro, GAS will call it each time a fake label is created |
| 1403 | off the special dot symbol. |
| 1404 | |
| 1405 | @item md_section_align |
| 1406 | @cindex md_section_align |
| 1407 | GAS will call this function for each section at the end of the assembly, to |
| 1408 | permit the CPU backend to adjust the alignment of a section. The function |
| 1409 | must take two arguments, a @code{segT} for the section and a @code{valueT} |
| 1410 | for the size of the section, and return a @code{valueT} for the rounded |
| 1411 | size. |
| 1412 | |
| 1413 | @item md_macro_start |
| 1414 | @cindex md_macro_start |
| 1415 | If defined, GAS will call this macro when it starts to include a macro |
| 1416 | expansion. @code{macro_nest} indicates the current macro nesting level, which |
| 1417 | includes the one being expanded. |
| 1418 | |
| 1419 | @item md_macro_info |
| 1420 | @cindex md_macro_info |
| 1421 | If defined, GAS will call this macro after the macro expansion has been |
| 1422 | included in the input and after parsing the macro arguments. The single |
| 1423 | argument is a pointer to the macro processing's internal representation of the |
| 1424 | macro (macro_entry *), which includes expansion of the formal arguments. |
| 1425 | |
| 1426 | @item md_macro_end |
| 1427 | @cindex md_macro_end |
| 1428 | Complement to md_macro_start. If defined, it is called when finished |
| 1429 | processing an inserted macro expansion, just before decrementing macro_nest. |
| 1430 | |
| 1431 | @item DOUBLEBAR_PARALLEL |
| 1432 | @cindex DOUBLEBAR_PARALLEL |
| 1433 | Affects the preprocessor so that lines containing '||' don't have their |
| 1434 | whitespace stripped following the double bar. This is useful for targets that |
| 1435 | implement parallel instructions. |
| 1436 | |
| 1437 | @item KEEP_WHITE_AROUND_COLON |
| 1438 | @cindex KEEP_WHITE_AROUND_COLON |
| 1439 | Normally, whitespace is compressed and removed when, in the presence of the |
| 1440 | colon, the adjoining tokens can be distinguished. This option affects the |
| 1441 | preprocessor so that whitespace around colons is preserved. This is useful |
| 1442 | when colons might be removed from the input after preprocessing but before |
| 1443 | assembling, so that adjoining tokens can still be distinguished if there is |
| 1444 | whitespace, or concatenated if there is not. |
| 1445 | |
| 1446 | @item tc_frob_section |
| 1447 | @cindex tc_frob_section |
| 1448 | If you define this macro, GAS will call it for each |
| 1449 | section at the end of the assembly. |
| 1450 | |
| 1451 | @item tc_frob_file_before_adjust |
| 1452 | @cindex tc_frob_file_before_adjust |
| 1453 | If you define this macro, GAS will call it after the symbol values are |
| 1454 | resolved, but before the fixups have been changed from local symbols to section |
| 1455 | symbols. |
| 1456 | |
| 1457 | @item tc_frob_symbol |
| 1458 | @cindex tc_frob_symbol |
| 1459 | If you define this macro, GAS will call it for each symbol. You can indicate |
| 1460 | that the symbol should not be included in the object file by defining this |
| 1461 | macro to set its second argument to a non-zero value. |
| 1462 | |
| 1463 | @item tc_frob_file |
| 1464 | @cindex tc_frob_file |
| 1465 | If you define this macro, GAS will call it after the symbol table has been |
| 1466 | completed, but before the relocations have been generated. |
| 1467 | |
| 1468 | @item tc_frob_file_after_relocs |
| 1469 | If you define this macro, GAS will call it after the relocs have been |
| 1470 | generated. |
| 1471 | |
| 1472 | @item tc_cfi_reloc_for_encoding |
| 1473 | @cindex tc_cfi_reloc_for_encoding |
| 1474 | This macro is used to indicate whether a cfi encoding requires a relocation. |
| 1475 | It should return the required relocation type. Defining this macro implies |
| 1476 | that Compact EH is supported. |
| 1477 | |
| 1478 | @item md_post_relax_hook |
| 1479 | If you define this macro, GAS will call it after relaxing and sizing the |
| 1480 | segments. |
| 1481 | |
| 1482 | @item LISTING_HEADER |
| 1483 | A string to use on the header line of a listing. The default value is simply |
| 1484 | @code{"GAS LISTING"}. |
| 1485 | |
| 1486 | @item LISTING_WORD_SIZE |
| 1487 | The number of bytes to put into a word in a listing. This affects the way the |
| 1488 | bytes are clumped together in the listing. For example, a value of 2 might |
| 1489 | print @samp{1234 5678} where a value of 1 would print @samp{12 34 56 78}. The |
| 1490 | default value is 4. |
| 1491 | |
| 1492 | @item LISTING_LHS_WIDTH |
| 1493 | The number of words of data to print on the first line of a listing for a |
| 1494 | particular source line, where each word is @code{LISTING_WORD_SIZE} bytes. The |
| 1495 | default value is 1. |
| 1496 | |
| 1497 | @item LISTING_LHS_WIDTH_SECOND |
| 1498 | Like @code{LISTING_LHS_WIDTH}, but applying to the second and subsequent line |
| 1499 | of the data printed for a particular source line. The default value is 1. |
| 1500 | |
| 1501 | @item LISTING_LHS_CONT_LINES |
| 1502 | The maximum number of continuation lines to print in a listing for a particular |
| 1503 | source line. The default value is 4. |
| 1504 | |
| 1505 | @item LISTING_RHS_WIDTH |
| 1506 | The maximum number of characters to print from one line of the input file. The |
| 1507 | default value is 100. |
| 1508 | |
| 1509 | @item TC_COFF_SECTION_DEFAULT_ATTRIBUTES |
| 1510 | @cindex TC_COFF_SECTION_DEFAULT_ATTRIBUTES |
| 1511 | The COFF @code{.section} directive will use the value of this macro to set |
| 1512 | a new section's attributes when a directive has no valid flags or when the |
| 1513 | flag is @code{w}. The default value of the macro is @code{SEC_LOAD | SEC_DATA}. |
| 1514 | |
| 1515 | @item DWARF2_FORMAT (@var{sec}) |
| 1516 | @cindex DWARF2_FORMAT |
| 1517 | If you define this, it should return one of @code{dwarf2_format_32bit}, |
| 1518 | @code{dwarf2_format_64bit}, or @code{dwarf2_format_64bit_irix} to indicate |
| 1519 | the size of internal DWARF section offsets and the format of the DWARF initial |
| 1520 | length fields. When @code{dwarf2_format_32bit} is returned, the initial |
| 1521 | length field will be 4 bytes long and section offsets are 32 bits in size. |
| 1522 | For @code{dwarf2_format_64bit} and @code{dwarf2_format_64bit_irix}, section |
| 1523 | offsets are 64 bits in size, but the initial length field differs. An 8 byte |
| 1524 | initial length is indicated by @code{dwarf2_format_64bit_irix} and |
| 1525 | @code{dwarf2_format_64bit} indicates a 12 byte initial length field in |
| 1526 | which the first four bytes are 0xffffffff and the next 8 bytes are |
| 1527 | the section's length. |
| 1528 | |
| 1529 | If you don't define this, @code{dwarf2_format_32bit} will be used as |
| 1530 | the default. |
| 1531 | |
| 1532 | This define only affects debug |
| 1533 | sections generated by the assembler. DWARF 2 sections generated by |
| 1534 | other tools will be unaffected by this setting. |
| 1535 | |
| 1536 | @item DWARF2_ADDR_SIZE (@var{bfd}) |
| 1537 | @cindex DWARF2_ADDR_SIZE |
| 1538 | It should return the size of an address, as it should be represented in |
| 1539 | debugging info. If you don't define this macro, the default definition uses |
| 1540 | the number of bits per address, as defined in @var{bfd}, divided by 8. |
| 1541 | |
| 1542 | @item MD_DEBUG_FORMAT_SELECTOR |
| 1543 | @cindex MD_DEBUG_FORMAT_SELECTOR |
| 1544 | If defined this macro is the name of a function to be called when the |
| 1545 | @samp{--gen-debug} switch is detected on the assembler's command line. The |
| 1546 | prototype for the function looks like this: |
| 1547 | |
| 1548 | @smallexample |
| 1549 | enum debug_info_type MD_DEBUG_FORMAT_SELECTOR (int * use_gnu_extensions) |
| 1550 | @end smallexample |
| 1551 | |
| 1552 | The function should return the debug format that is preferred by the CPU |
| 1553 | backend. This format will be used when generating assembler specific debug |
| 1554 | information. |
| 1555 | |
| 1556 | @item md_allow_local_subtract (@var{left}, @var{right}, @var{section}) |
| 1557 | If defined, GAS will call this macro when evaluating an expression which is the |
| 1558 | difference of two symbols defined in the same section. It takes three |
| 1559 | arguments: @code{expressioS * @var{left}} which is the symbolic expression on |
| 1560 | the left hand side of the subtraction operation, @code{expressionS * |
| 1561 | @var{right}} which is the symbolic expression on the right hand side of the |
| 1562 | subtraction, and @code{segT @var{section}} which is the section containing the two |
| 1563 | symbols. The macro should return a non-zero value if the expression should be |
| 1564 | evaluated. Targets which implement link time relaxation which may change the |
| 1565 | position of the two symbols relative to each other should ensure that this |
| 1566 | macro returns zero in situations where this can occur. |
| 1567 | |
| 1568 | @item md_allow_eh_opt |
| 1569 | If defined, GAS will check this macro before performing any optimizations on |
| 1570 | the DWARF call frame debug information that is emitted. Targets which |
| 1571 | implement link time relaxation may need to define this macro and set it to zero |
| 1572 | if it is possible to change the size of a function's prologue. |
| 1573 | @end table |
| 1574 | |
| 1575 | @node Object format backend |
| 1576 | @subsection Writing an object format backend |
| 1577 | @cindex object format backend |
| 1578 | @cindex @file{obj-@var{fmt}} |
| 1579 | |
| 1580 | As with the CPU backend, the object format backend must define a few things, |
| 1581 | and may define some other things. The interface to the object format backend |
| 1582 | is generally simpler; most of the support for an object file format consists of |
| 1583 | defining a number of pseudo-ops. |
| 1584 | |
| 1585 | The object format @file{.h} file must include @file{targ-cpu.h}. |
| 1586 | |
| 1587 | @table @code |
| 1588 | @item OBJ_@var{format} |
| 1589 | @cindex OBJ_@var{format} |
| 1590 | By convention, you should define this macro in the @file{.h} file. For |
| 1591 | example, @file{obj-elf.h} defines @code{OBJ_ELF}. You might have to use this |
| 1592 | if it is necessary to add object file format specific code to the CPU file. |
| 1593 | |
| 1594 | @item obj_begin |
| 1595 | If you define this macro, GAS will call it at the start of the assembly, after |
| 1596 | the command line arguments have been parsed and all the machine independent |
| 1597 | initializations have been completed. |
| 1598 | |
| 1599 | @item obj_app_file |
| 1600 | @cindex obj_app_file |
| 1601 | If you define this macro, GAS will invoke it when it sees a @code{.file} |
| 1602 | pseudo-op or a @samp{#} line as used by the C preprocessor. |
| 1603 | |
| 1604 | @item OBJ_COPY_SYMBOL_ATTRIBUTES |
| 1605 | @cindex OBJ_COPY_SYMBOL_ATTRIBUTES |
| 1606 | You should define this macro to copy object format specific information from |
| 1607 | one symbol to another. GAS will call it when one symbol is equated to |
| 1608 | another. |
| 1609 | |
| 1610 | @item obj_sec_sym_ok_for_reloc |
| 1611 | @cindex obj_sec_sym_ok_for_reloc |
| 1612 | You may define this macro to indicate that it is OK to use a section symbol in |
| 1613 | a relocation entry. If it is not, GAS will define a new symbol at the start |
| 1614 | of a section. |
| 1615 | |
| 1616 | @item EMIT_SECTION_SYMBOLS |
| 1617 | @cindex EMIT_SECTION_SYMBOLS |
| 1618 | You should define this macro with a zero value if you do not want to include |
| 1619 | section symbols in the output symbol table. The default value for this macro |
| 1620 | is one. |
| 1621 | |
| 1622 | @item obj_adjust_symtab |
| 1623 | @cindex obj_adjust_symtab |
| 1624 | If you define this macro, GAS will invoke it just before setting the symbol |
| 1625 | table of the output BFD. For example, the COFF support uses this macro to |
| 1626 | generate a @code{.file} symbol if none was generated previously. |
| 1627 | |
| 1628 | @item SEPARATE_STAB_SECTIONS |
| 1629 | @cindex SEPARATE_STAB_SECTIONS |
| 1630 | You may define this macro to a nonzero value to indicate that stabs should be |
| 1631 | placed in separate sections, as in ELF. |
| 1632 | |
| 1633 | @item INIT_STAB_SECTION |
| 1634 | @cindex INIT_STAB_SECTION |
| 1635 | You may define this macro to initialize the stabs section in the output file. |
| 1636 | |
| 1637 | @item OBJ_PROCESS_STAB |
| 1638 | @cindex OBJ_PROCESS_STAB |
| 1639 | You may define this macro to do specific processing on a stabs entry. |
| 1640 | |
| 1641 | @item obj_frob_section |
| 1642 | @cindex obj_frob_section |
| 1643 | If you define this macro, GAS will call it for each section at the end of the |
| 1644 | assembly. |
| 1645 | |
| 1646 | @item obj_frob_file_before_adjust |
| 1647 | @cindex obj_frob_file_before_adjust |
| 1648 | If you define this macro, GAS will call it after the symbol values are |
| 1649 | resolved, but before the fixups have been changed from local symbols to section |
| 1650 | symbols. |
| 1651 | |
| 1652 | @item obj_frob_symbol |
| 1653 | @cindex obj_frob_symbol |
| 1654 | If you define this macro, GAS will call it for each symbol. You can indicate |
| 1655 | that the symbol should not be included in the object file by defining this |
| 1656 | macro to set its second argument to a non-zero value. |
| 1657 | |
| 1658 | @item obj_set_weak_hook |
| 1659 | @cindex obj_set_weak_hook |
| 1660 | If you define this macro, @code{S_SET_WEAK} will call it before modifying the |
| 1661 | symbol's flags. |
| 1662 | |
| 1663 | @item obj_clear_weak_hook |
| 1664 | @cindex obj_clear_weak_hook |
| 1665 | If you define this macro, @code{S_CLEAR_WEAKREFD} will call it after cleaning |
| 1666 | the @code{weakrefd} flag, but before modifying any other flags. |
| 1667 | |
| 1668 | @item obj_frob_file |
| 1669 | @cindex obj_frob_file |
| 1670 | If you define this macro, GAS will call it after the symbol table has been |
| 1671 | completed, but before the relocations have been generated. |
| 1672 | |
| 1673 | @item obj_frob_file_after_relocs |
| 1674 | If you define this macro, GAS will call it after the relocs have been |
| 1675 | generated. |
| 1676 | |
| 1677 | @item SET_SECTION_RELOCS (@var{sec}, @var{relocs}, @var{n}) |
| 1678 | @cindex SET_SECTION_RELOCS |
| 1679 | If you define this, it will be called after the relocations have been set for |
| 1680 | the section @var{sec}. The list of relocations is in @var{relocs}, and the |
| 1681 | number of relocations is in @var{n}. |
| 1682 | @end table |
| 1683 | |
| 1684 | @node Emulations |
| 1685 | @subsection Writing emulation files |
| 1686 | |
| 1687 | Normally you do not have to write an emulation file. You can just use |
| 1688 | @file{te-generic.h}. |
| 1689 | |
| 1690 | If you do write your own emulation file, it must include @file{obj-format.h}. |
| 1691 | |
| 1692 | An emulation file will often define @code{TE_@var{EM}}; this may then be used |
| 1693 | in other files to change the output. |
| 1694 | |
| 1695 | @node Relaxation |
| 1696 | @section Relaxation |
| 1697 | @cindex relaxation |
| 1698 | |
| 1699 | @dfn{Relaxation} is a generic term used when the size of some instruction or |
| 1700 | data depends upon the value of some symbol or other data. |
| 1701 | |
| 1702 | GAS knows to relax a particular type of PC relative relocation using a table. |
| 1703 | You can also define arbitrarily complex forms of relaxation yourself. |
| 1704 | |
| 1705 | @menu |
| 1706 | * Relaxing with a table:: Relaxing with a table |
| 1707 | * General relaxing:: General relaxing |
| 1708 | @end menu |
| 1709 | |
| 1710 | @node Relaxing with a table |
| 1711 | @subsection Relaxing with a table |
| 1712 | |
| 1713 | If you do not define @code{md_relax_frag}, and you do define |
| 1714 | @code{TC_GENERIC_RELAX_TABLE}, GAS will relax @code{rs_machine_dependent} frags |
| 1715 | based on the frag subtype and the displacement to some specified target |
| 1716 | address. The basic idea is that several machines have different addressing |
| 1717 | modes for instructions that can specify different ranges of values, with |
| 1718 | successive modes able to access wider ranges, including the entirety of the |
| 1719 | previous range. Smaller ranges are assumed to be more desirable (perhaps the |
| 1720 | instruction requires one word instead of two or three); if this is not the |
| 1721 | case, don't describe the smaller-range, inferior mode. |
| 1722 | |
| 1723 | The @code{fr_subtype} field of a frag is an index into a CPU-specific |
| 1724 | relaxation table. That table entry indicates the range of values that can be |
| 1725 | stored, the number of bytes that will have to be added to the frag to |
| 1726 | accommodate the addressing mode, and the index of the next entry to examine if |
| 1727 | the value to be stored is outside the range accessible by the current |
| 1728 | addressing mode. The @code{fr_symbol} field of the frag indicates what symbol |
| 1729 | is to be accessed; the @code{fr_offset} field is added in. |
| 1730 | |
| 1731 | If the @code{TC_PCREL_ADJUST} macro is defined, which currently should only happen |
| 1732 | for the NS32k family, the @code{TC_PCREL_ADJUST} macro is called on the frag to |
| 1733 | compute an adjustment to be made to the displacement. |
| 1734 | |
| 1735 | The value fitted by the relaxation code is always assumed to be a displacement |
| 1736 | from the current frag. (More specifically, from @code{fr_fix} bytes into the |
| 1737 | frag.) |
| 1738 | @ignore |
| 1739 | This seems kinda silly. What about fitting small absolute values? I suppose |
| 1740 | @code{md_assemble} is supposed to take care of that, but if the operand is a |
| 1741 | difference between symbols, it might not be able to, if the difference was not |
| 1742 | computable yet. |
| 1743 | @end ignore |
| 1744 | |
| 1745 | The end of the relaxation sequence is indicated by a ``next'' value of 0. This |
| 1746 | means that the first entry in the table can't be used. |
| 1747 | |
| 1748 | For some configurations, the linker can do relaxing within a section of an |
| 1749 | object file. If call instructions of various sizes exist, the linker can |
| 1750 | determine which should be used in each instance, when a symbol's value is |
| 1751 | resolved. In order for the linker to avoid wasting space and having to insert |
| 1752 | no-op instructions, it must be able to expand or shrink the section contents |
| 1753 | while still preserving intra-section references and meeting alignment |
| 1754 | requirements. |
| 1755 | |
| 1756 | For the i960 using b.out format, no expansion is done; instead, each |
| 1757 | @samp{.align} directive causes extra space to be allocated, enough that when |
| 1758 | the linker is relaxing a section and removing unneeded space, it can discard |
| 1759 | some or all of this extra padding and cause the following data to be correctly |
| 1760 | aligned. |
| 1761 | |
| 1762 | For the H8/300, I think the linker expands calls that can't reach, and doesn't |
| 1763 | worry about alignment issues; the cpu probably never needs any significant |
| 1764 | alignment beyond the instruction size. |
| 1765 | |
| 1766 | The relaxation table type contains these fields: |
| 1767 | |
| 1768 | @table @code |
| 1769 | @item long rlx_forward |
| 1770 | Forward reach, must be non-negative. |
| 1771 | @item long rlx_backward |
| 1772 | Backward reach, must be zero or negative. |
| 1773 | @item rlx_length |
| 1774 | Length in bytes of this addressing mode. |
| 1775 | @item rlx_more |
| 1776 | Index of the next-longer relax state, or zero if there is no next relax state. |
| 1777 | @end table |
| 1778 | |
| 1779 | The relaxation is done in @code{relax_segment} in @file{write.c}. The |
| 1780 | difference in the length fields between the original mode and the one finally |
| 1781 | chosen by the relaxing code is taken as the size by which the current frag will |
| 1782 | be increased in size. For example, if the initial relaxing mode has a length |
| 1783 | of 2 bytes, and because of the size of the displacement, it gets upgraded to a |
| 1784 | mode with a size of 6 bytes, it is assumed that the frag will grow by 4 bytes. |
| 1785 | (The initial two bytes should have been part of the fixed portion of the frag, |
| 1786 | since it is already known that they will be output.) This growth must be |
| 1787 | effected by @code{md_convert_frag}; it should increase the @code{fr_fix} field |
| 1788 | by the appropriate size, and fill in the appropriate bytes of the frag. |
| 1789 | (Enough space for the maximum growth should have been allocated in the call to |
| 1790 | frag_var as the second argument.) |
| 1791 | |
| 1792 | If relocation records are needed, they should be emitted by |
| 1793 | @code{md_estimate_size_before_relax}. This function should examine the target |
| 1794 | symbol of the supplied frag and correct the @code{fr_subtype} of the frag if |
| 1795 | needed. When this function is called, if the symbol has not yet been defined, |
| 1796 | it will not become defined later; however, its value may still change if the |
| 1797 | section it is in gets relaxed. |
| 1798 | |
| 1799 | Usually, if the symbol is in the same section as the frag (given by the |
| 1800 | @var{sec} argument), the narrowest likely relaxation mode is stored in |
| 1801 | @code{fr_subtype}, and that's that. |
| 1802 | |
| 1803 | If the symbol is undefined, or in a different section (and therefore movable |
| 1804 | to an arbitrarily large distance), the largest available relaxation mode is |
| 1805 | specified, @code{fix_new} is called to produce the relocation record, |
| 1806 | @code{fr_fix} is increased to include the relocated field (remember, this |
| 1807 | storage was allocated when @code{frag_var} was called), and @code{frag_wane} is |
| 1808 | called to convert the frag to an @code{rs_fill} frag with no variant part. |
| 1809 | Sometimes changing addressing modes may also require rewriting the instruction. |
| 1810 | It can be accessed via @code{fr_opcode} or @code{fr_fix}. |
| 1811 | |
| 1812 | If you generate frags separately for the basic insn opcode and any relaxable |
| 1813 | operands, do not call @code{fix_new} thinking you can emit fixups for the |
| 1814 | opcode field from the relaxable frag. It is not guaranteed to be the same frag. |
| 1815 | If you need to emit fixups for the opcode field from inspection of the |
| 1816 | relaxable frag, then you need to generate a common frag for both the basic |
| 1817 | opcode and relaxable fields, or you need to provide the frag for the opcode to |
| 1818 | pass to @code{fix_new}. The latter can be done for example by defining |
| 1819 | @code{TC_FRAG_TYPE} to include a pointer to it and defining @code{TC_FRAG_INIT} |
| 1820 | to set the pointer. |
| 1821 | |
| 1822 | Sometimes @code{fr_var} is increased instead, and @code{frag_wane} is not |
| 1823 | called. I'm not sure, but I think this is to keep @code{fr_fix} referring to |
| 1824 | an earlier byte, and @code{fr_subtype} set to @code{rs_machine_dependent} so |
| 1825 | that @code{md_convert_frag} will get called. |
| 1826 | |
| 1827 | @node General relaxing |
| 1828 | @subsection General relaxing |
| 1829 | |
| 1830 | If using a simple table is not suitable, you may implement arbitrarily complex |
| 1831 | relaxation semantics yourself. For example, the MIPS backend uses this to emit |
| 1832 | different instruction sequences depending upon the size of the symbol being |
| 1833 | accessed. |
| 1834 | |
| 1835 | When you assemble an instruction that may need relaxation, you should allocate |
| 1836 | a frag using @code{frag_var} or @code{frag_variant} with a type of |
| 1837 | @code{rs_machine_dependent}. You should store some sort of information in the |
| 1838 | @code{fr_subtype} field so that you can figure out what to do with the frag |
| 1839 | later. |
| 1840 | |
| 1841 | When GAS reaches the end of the input file, it will look through the frags and |
| 1842 | work out their final sizes. |
| 1843 | |
| 1844 | GAS will first call @code{md_estimate_size_before_relax} on each |
| 1845 | @code{rs_machine_dependent} frag. This function must return an estimated size |
| 1846 | for the frag. |
| 1847 | |
| 1848 | GAS will then loop over the frags, calling @code{md_relax_frag} on each |
| 1849 | @code{rs_machine_dependent} frag. This function should return the change in |
| 1850 | size of the frag. GAS will keep looping over the frags until none of the frags |
| 1851 | changes size. |
| 1852 | |
| 1853 | @node Broken words |
| 1854 | @section Broken words |
| 1855 | @cindex internals, broken words |
| 1856 | @cindex broken words |
| 1857 | |
| 1858 | Some compilers, including GCC, will sometimes emit switch tables specifying |
| 1859 | 16-bit @code{.word} displacements to branch targets, and branch instructions |
| 1860 | that load entries from that table to compute the target address. If this is |
| 1861 | done on a 32-bit machine, there is a chance (at least with really large |
| 1862 | functions) that the displacement will not fit in 16 bits. The assembler |
| 1863 | handles this using a concept called @dfn{broken words}. This idea is well |
| 1864 | named, since there is an implied promise that the 16-bit field will in fact |
| 1865 | hold the specified displacement. |
| 1866 | |
| 1867 | If broken word processing is enabled, and a situation like this is encountered, |
| 1868 | the assembler will insert a jump instruction into the instruction stream, close |
| 1869 | enough to be reached with the 16-bit displacement. This jump instruction will |
| 1870 | transfer to the real desired target address. Thus, as long as the @code{.word} |
| 1871 | value really is used as a displacement to compute an address to jump to, the |
| 1872 | net effect will be correct (minus a very small efficiency cost). If |
| 1873 | @code{.word} directives with label differences for values are used for other |
| 1874 | purposes, however, things may not work properly. For targets which use broken |
| 1875 | words, the @samp{-K} option will warn when a broken word is discovered. |
| 1876 | |
| 1877 | The broken word code is turned off by the @code{WORKING_DOT_WORD} macro. It |
| 1878 | isn't needed if @code{.word} emits a value large enough to contain an address |
| 1879 | (or, more correctly, any possible difference between two addresses). |
| 1880 | |
| 1881 | @node Internal functions |
| 1882 | @section Internal functions |
| 1883 | |
| 1884 | This section describes basic internal functions used by GAS. |
| 1885 | |
| 1886 | @menu |
| 1887 | * Warning and error messages:: Warning and error messages |
| 1888 | * Hash tables:: Hash tables |
| 1889 | @end menu |
| 1890 | |
| 1891 | @node Warning and error messages |
| 1892 | @subsection Warning and error messages |
| 1893 | |
| 1894 | @deftypefun @{@} int had_warnings (void) |
| 1895 | @deftypefunx @{@} int had_errors (void) |
| 1896 | Returns non-zero if any warnings or errors, respectively, have been printed |
| 1897 | during this invocation. |
| 1898 | @end deftypefun |
| 1899 | |
| 1900 | @deftypefun @{@} void as_tsktsk (const char *@var{format}, ...) |
| 1901 | @deftypefunx @{@} void as_warn (const char *@var{format}, ...) |
| 1902 | @deftypefunx @{@} void as_bad (const char *@var{format}, ...) |
| 1903 | @deftypefunx @{@} void as_fatal (const char *@var{format}, ...) |
| 1904 | These functions display messages about something amiss with the input file, or |
| 1905 | internal problems in the assembler itself. The current file name and line |
| 1906 | number are printed, followed by the supplied message, formatted using |
| 1907 | @code{vfprintf}, and a final newline. |
| 1908 | |
| 1909 | An error indicated by @code{as_bad} will result in a non-zero exit status when |
| 1910 | the assembler has finished. Calling @code{as_fatal} will result in immediate |
| 1911 | termination of the assembler process. |
| 1912 | @end deftypefun |
| 1913 | |
| 1914 | @deftypefun @{@} void as_warn_where (char *@var{file}, unsigned int @var{line}, const char *@var{format}, ...) |
| 1915 | @deftypefunx @{@} void as_bad_where (char *@var{file}, unsigned int @var{line}, const char *@var{format}, ...) |
| 1916 | These variants permit specification of the file name and line number, and are |
| 1917 | used when problems are detected when reprocessing information saved away when |
| 1918 | processing some earlier part of the file. For example, fixups are processed |
| 1919 | after all input has been read, but messages about fixups should refer to the |
| 1920 | original filename and line number that they are applicable to. |
| 1921 | @end deftypefun |
| 1922 | |
| 1923 | @deftypefun @{@} void sprint_value (char *@var{buf}, valueT @var{val}) |
| 1924 | This function is helpful for converting a @code{valueT} value into printable |
| 1925 | format, in case it's wider than modes that @code{*printf} can handle. If the |
| 1926 | type is narrow enough, a decimal number will be produced; otherwise, it will be |
| 1927 | in hexadecimal. The value itself is not examined to make this determination. |
| 1928 | @end deftypefun |
| 1929 | |
| 1930 | @node Hash tables |
| 1931 | @subsection Hash tables |
| 1932 | @cindex hash tables |
| 1933 | |
| 1934 | @deftypefun @{@} @{struct hash_control *@} hash_new (void) |
| 1935 | Creates the hash table control structure. |
| 1936 | @end deftypefun |
| 1937 | |
| 1938 | @deftypefun @{@} void hash_die (struct hash_control *) |
| 1939 | Destroy a hash table. |
| 1940 | @end deftypefun |
| 1941 | |
| 1942 | @deftypefun @{@} void *hash_delete (struct hash_control *, const char *, int) |
| 1943 | Deletes entry from the hash table, returns the value it had. If the last |
| 1944 | arg is non-zero, free memory allocated for this entry and all entries |
| 1945 | allocated more recently than this entry. |
| 1946 | @end deftypefun |
| 1947 | |
| 1948 | @deftypefun @{@} void *hash_replace (struct hash_control *, const char *, void *) |
| 1949 | Updates the value for an entry already in the table, returning the old value. |
| 1950 | If no entry was found, just returns NULL. |
| 1951 | @end deftypefun |
| 1952 | |
| 1953 | @deftypefun @{@} @{const char *@} hash_insert (struct hash_control *, const char *, void *) |
| 1954 | Inserting a value already in the table is an error. |
| 1955 | Returns an error message or NULL. |
| 1956 | @end deftypefun |
| 1957 | |
| 1958 | @deftypefun @{@} @{const char *@} hash_jam (struct hash_control *, const char *, void *) |
| 1959 | Inserts if the value isn't already present, updates it if it is. |
| 1960 | @end deftypefun |
| 1961 | |
| 1962 | @node Test suite |
| 1963 | @section Test suite |
| 1964 | @cindex test suite |
| 1965 | |
| 1966 | The test suite is kind of lame for most processors. Often it only checks to |
| 1967 | see if a couple of files can be assembled without the assembler reporting any |
| 1968 | errors. For more complete testing, write a test which either examines the |
| 1969 | assembler listing, or runs @code{objdump} and examines its output. For the |
| 1970 | latter, the TCL procedure @code{run_dump_test} may come in handy. It takes the |
| 1971 | base name of a file, and looks for @file{@var{file}.d}. This file should |
| 1972 | contain as its initial lines a set of variable settings in @samp{#} comments, |
| 1973 | in the form: |
| 1974 | |
| 1975 | @example |
| 1976 | #@var{varname}: @var{value} |
| 1977 | @end example |
| 1978 | |
| 1979 | The @var{varname} may be @code{objdump}, @code{nm}, or @code{as}, in which case |
| 1980 | it specifies the options to be passed to the specified programs. Exactly one |
| 1981 | of @code{objdump} or @code{nm} must be specified, as that also specifies which |
| 1982 | program to run after the assembler has finished. If @var{varname} is |
| 1983 | @code{source}, it specifies the name of the source file; otherwise, |
| 1984 | @file{@var{file}.s} is used. If @var{varname} is @code{name}, it specifies the |
| 1985 | name of the test to be used in the @code{pass} or @code{fail} messages. |
| 1986 | |
| 1987 | The non-commented parts of the file are interpreted as regular expressions, one |
| 1988 | per line. Blank lines in the @code{objdump} or @code{nm} output are skipped, |
| 1989 | as are blank lines in the @code{.d} file; the other lines are tested to see if |
| 1990 | the regular expression matches the program output. If it does not, the test |
| 1991 | fails. |
| 1992 | |
| 1993 | Note that this means the tests must be modified if the @code{objdump} output |
| 1994 | style is changed. |
| 1995 | |
| 1996 | @bye |
| 1997 | @c Local Variables: |
| 1998 | @c fill-column: 79 |
| 1999 | @c End: |