bfd/syms.c

   1 /* Generic symbol-table support for the BFD library.
   2    Copyright (C) 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
   3    Written by Cygnus Support.
   4
   5 This file is part of BFD, the Binary File Descriptor library.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 /*
  22 SECTION
  23         Symbols
  24
  25         BFD tries to maintain as much symbol information as it can when
  26         it moves information from file to file. BFD passes information
  27         to applications though the <<asymbol>> structure. When the
  28         application requests the symbol table, BFD reads the table in
  29         the native form and translates parts of it into the internal
  30         format. To maintain more than the information passed to
  31         applications, some targets keep some information ``behind the
  32         scenes'' in a structure only the particular back end knows
  33         about. For example, the coff back end keeps the original
  34         symbol table structure as well as the canonical structure when
  35         a BFD is read in. On output, the coff back end can reconstruct
  36         the output symbol table so that no information is lost, even
  37         information unique to coff which BFD doesn't know or
  38         understand. If a coff symbol table were read, but were written
  39         through an a.out back end, all the coff specific information
  40         would be lost. The symbol table of a BFD
  41         is not necessarily read in until a canonicalize request is
  42         made. Then the BFD back end fills in a table provided by the
  43         application with pointers to the canonical information.  To
  44         output symbols, the application provides BFD with a table of
  45         pointers to pointers to <<asymbol>>s. This allows applications
  46         like the linker to output a symbol as it was read, since the ``behind
  47         the scenes'' information will be still available.
  48 @menu
  49 @* Reading Symbols::
  50 @* Writing Symbols::
  51 @* typedef asymbol::
  52 @* symbol handling functions::
  53 @end menu
  54
  55 INODE
  56 Reading Symbols, Writing Symbols, Symbols, Symbols
  57 SUBSECTION
  58         Reading symbols
  59
  60         There are two stages to reading a symbol table from a BFD:
  61         allocating storage, and the actual reading process. This is an
  62         excerpt from an application which reads the symbol table:
  63
  64 |         long storage_needed;
  65 |         asymbol **symbol_table;
  66 |         long number_of_symbols;
  67 |         long i;
  68 |
  69 |         storage_needed = bfd_get_symtab_upper_bound (abfd);
  70 |
  71 |         if (storage_needed < 0)
  72 |           FAIL
  73 |
  74 |         if (storage_needed == 0) {
  75 |            return ;
  76 |         }
  77 |         symbol_table = (asymbol **) xmalloc (storage_needed);
  78 |           ...
  79 |         number_of_symbols =
  80 |            bfd_canonicalize_symtab (abfd, symbol_table);
  81 |
  82 |         if (number_of_symbols < 0)
  83 |           FAIL
  84 |
  85 |         for (i = 0; i < number_of_symbols; i++) {
  86 |            process_symbol (symbol_table[i]);
  87 |         }
  88
  89         All storage for the symbols themselves is in an obstack
  90         connected to the BFD; it is freed when the BFD is closed.
  91
  92
  93 INODE
  94 Writing Symbols, typedef asymbol, Reading Symbols, Symbols
  95 SUBSECTION
  96         Writing symbols
  97
  98         Writing of a symbol table is automatic when a BFD open for
  99         writing is closed. The application attaches a vector of
 100         pointers to pointers to symbols to the BFD being written, and
 101         fills in the symbol count. The close and cleanup code reads
 102         through the table provided and performs all the necessary
 103         operations. The BFD output code must always be provided with an
 104         ``owned'' symbol: one which has come from another BFD, or one
 105         which has been created using <<bfd_make_empty_symbol>>.  Here is an
 106         example showing the creation of a symbol table with only one element:
 107
 108 |       #include "bfd.h"
 109 |       main()
 110 |       {
 111 |         bfd *abfd;
 112 |         asymbol *ptrs[2];
 113 |         asymbol *new;
 114 |
 115 |         abfd = bfd_openw("foo","a.out-sunos-big");
 116 |         bfd_set_format(abfd, bfd_object);
 117 |         new = bfd_make_empty_symbol(abfd);
 118 |         new->name = "dummy_symbol";
 119 |         new->section = bfd_make_section_old_way(abfd, ".text");
 120 |         new->flags = BSF_GLOBAL;
 121 |         new->value = 0x12345;
 122 |
 123 |         ptrs[0] = new;
 124 |         ptrs[1] = (asymbol *)0;
 125 |
 126 |         bfd_set_symtab(abfd, ptrs, 1);
 127 |         bfd_close(abfd);
 128 |       }
 129 |
 130 |       ./makesym
 131 |       nm foo
 132 |       00012345 A dummy_symbol
 133
 134         Many formats cannot represent arbitary symbol information; for
 135         instance, the <<a.out>> object format does not allow an
 136         arbitary number of sections. A symbol pointing to a section
 137         which is not one  of <<.text>>, <<.data>> or <<.bss>> cannot
 138         be described.
 139
 140 */
 141
 142
 143
 144 /*
 145 DOCDD
 146 INODE
 147 typedef asymbol, symbol handling functions, Writing Symbols, Symbols
 148
 149 */
 150 /*
 151 SUBSECTION
 152         typedef asymbol
 153
 154         An <<asymbol>> has the form:
 155
 156 */
 157
 158 /*
 159 CODE_FRAGMENT
 160
 161 .
 162 .typedef struct symbol_cache_entry
 163 .{
 164 .       {* A pointer to the BFD which owns the symbol. This information
 165 .          is necessary so that a back end can work out what additional
 166 .          information (invisible to the application writer) is carried
 167 .          with the symbol.
 168 .
 169 .          This field is *almost* redundant, since you can use section->owner
 170 .          instead, except that some symbols point to the global sections
 171 .          bfd_{abs,com,und}_section.  This could be fixed by making
 172 .          these globals be per-bfd (or per-target-flavor).  FIXME. *}
 173 .
 174 .  struct _bfd *the_bfd; {* Use bfd_asymbol_bfd(sym) to access this field. *}
 175 .
 176 .       {* The text of the symbol. The name is left alone, and not copied; the
 177 .          application may not alter it. *}
 178 .  CONST char *name;
 179 .
 180 .       {* The value of the symbol.  This really should be a union of a
 181 .          numeric value with a pointer, since some flags indicate that
 182 .          a pointer to another symbol is stored here.  *}
 183 .  symvalue value;
 184 .
 185 .       {* Attributes of a symbol: *}
 186 .
 187 .#define BSF_NO_FLAGS    0x00
 188 .
 189 .       {* The symbol has local scope; <<static>> in <<C>>. The value
 190 .          is the offset into the section of the data. *}
 191 .#define BSF_LOCAL      0x01
 192 .
 193 .       {* The symbol has global scope; initialized data in <<C>>. The
 194 .          value is the offset into the section of the data. *}
 195 .#define BSF_GLOBAL     0x02
 196 .
 197 .       {* The symbol has global scope and is exported. The value is
 198 .          the offset into the section of the data. *}
 199 .#define BSF_EXPORT     BSF_GLOBAL {* no real difference *}
 200 .
 201 .       {* A normal C symbol would be one of:
 202 .          <<BSF_LOCAL>>, <<BSF_FORT_COMM>>,  <<BSF_UNDEFINED>> or
 203 .          <<BSF_GLOBAL>> *}
 204 .
 205 .       {* The symbol is a debugging record. The value has an arbitary
 206 .          meaning. *}
 207 .#define BSF_DEBUGGING  0x08
 208 .
 209 .       {* The symbol denotes a function entry point.  Used in ELF,
 210 .          perhaps others someday.  *}
 211 .#define BSF_FUNCTION    0x10
 212 .
 213 .       {* Used by the linker. *}
 214 .#define BSF_KEEP        0x20
 215 .#define BSF_KEEP_G      0x40
 216 .
 217 .       {* A weak global symbol, overridable without warnings by
 218 .          a regular global symbol of the same name.  *}
 219 .#define BSF_WEAK        0x80
 220 .
 221 .       {* This symbol was created to point to a section, e.g. ELF's
 222 .          STT_SECTION symbols.  *}
 223 .#define BSF_SECTION_SYM 0x100
 224 .
 225 .       {* The symbol used to be a common symbol, but now it is
 226 .          allocated. *}
 227 .#define BSF_OLD_COMMON  0x200
 228 .
 229 .       {* The default value for common data. *}
 230 .#define BFD_FORT_COMM_DEFAULT_VALUE 0
 231 .
 232 .       {* In some files the type of a symbol sometimes alters its
 233 .          location in an output file - ie in coff a <<ISFCN>> symbol
 234 .          which is also <<C_EXT>> symbol appears where it was
 235 .          declared and not at the end of a section.  This bit is set
 236 .          by the target BFD part to convey this information. *}
 237 .
 238 .#define BSF_NOT_AT_END    0x400
 239 .
 240 .       {* Signal that the symbol is the label of constructor section. *}
 241 .#define BSF_CONSTRUCTOR   0x800
 242 .
 243 .       {* Signal that the symbol is a warning symbol. If the symbol
 244 .          is a warning symbol, then the value field (I know this is
 245 .          tacky) will point to the asymbol which when referenced will
 246 .          cause the warning. *}
 247 .#define BSF_WARNING       0x1000
 248 .
 249 .       {* Signal that the symbol is indirect. The value of the symbol
 250 .          is a pointer to an undefined asymbol which contains the
 251 .          name to use instead. *}
 252 .#define BSF_INDIRECT      0x2000
 253 .
 254 .       {* BSF_FILE marks symbols that contain a file name.  This is used
 255 .          for ELF STT_FILE symbols.  *}
 256 .#define BSF_FILE          0x4000
 257 .
 258 .       {* Symbol is from dynamic linking information.  *}
 259 .#define BSF_DYNAMIC       0x8000
 260 .
 261 .  flagword flags;
 262 .
 263 .       {* A pointer to the section to which this symbol is
 264 .          relative.  This will always be non NULL, there are special
 265 .          sections for undefined and absolute symbols *}
 266 .  struct sec *section;
 267 .
 268 .       {* Back end special data. This is being phased out in favour
 269 .          of making this a union. *}
 270 .  PTR udata;
 271 .
 272 .} asymbol;
 273 */
 274
 275 #include "bfd.h"
 276 #include "sysdep.h"
 277
 278 #include "libbfd.h"
 279 #include "aout/stab_gnu.h"
 280
 281 /*
 282 DOCDD
 283 INODE
 284 symbol handling functions,  , typedef asymbol, Symbols
 285 SUBSECTION
 286         Symbol handling functions
 287 */
 288
 289 /*
 290 FUNCTION
 291         bfd_get_symtab_upper_bound
 292
 293 DESCRIPTION
 294         Return the number of bytes required to store a vector of pointers
 295         to <<asymbols>> for all the symbols in the BFD @var{abfd},
 296         including a terminal NULL pointer. If there are no symbols in
 297         the BFD, then return 0.  If an error occurs, return -1.
 298
 299 .#define bfd_get_symtab_upper_bound(abfd) \
 300 .     BFD_SEND (abfd, _bfd_get_symtab_upper_bound, (abfd))
 301
 302 */
 303
 304 /*
 305 FUNCTION
 306         bfd_is_local_label
 307
 308 SYNOPSIS
 309         boolean bfd_is_local_label(bfd *abfd, asymbol *sym);
 310
 311 DESCRIPTION
 312         Return true if the given symbol @var{sym} in the BFD @var{abfd} is
 313         a compiler generated local label, else return false.
 314 .#define bfd_is_local_label(abfd, sym) \
 315 .     BFD_SEND (abfd, _bfd_is_local_label,(abfd, sym))
 316 */
 317
 318 /*
 319 FUNCTION
 320         bfd_canonicalize_symtab
 321
 322 DESCRIPTION
 323         Read the symbols from the BFD @var{abfd}, and fills in
 324         the vector @var{location} with pointers to the symbols and
 325         a trailing NULL.
 326         Return the actual number of symbol pointers, not
 327         including the NULL.
 328
 329
 330 .#define bfd_canonicalize_symtab(abfd, location) \
 331 .     BFD_SEND (abfd, _bfd_canonicalize_symtab,\
 332 .                  (abfd, location))
 333
 334 */
 335
 336
 337 /*
 338 FUNCTION
 339         bfd_set_symtab
 340
 341 SYNOPSIS
 342         boolean bfd_set_symtab (bfd *abfd, asymbol **location, unsigned int count);
 343
 344 DESCRIPTION
 345         Arrange that when the output BFD @var{abfd} is closed,
 346         the table @var{location} of @var{count} pointers to symbols
 347         will be written.
 348 */
 349
 350 boolean
 351 bfd_set_symtab (abfd, location, symcount)
 352      bfd *abfd;
 353      asymbol **location;
 354      unsigned int symcount;
 355 {
 356   if ((abfd->format != bfd_object) || (bfd_read_p (abfd)))
 357     {
 358       bfd_set_error (bfd_error_invalid_operation);
 359       return false;
 360     }
 361
 362   bfd_get_outsymbols (abfd) = location;
 363   bfd_get_symcount (abfd) = symcount;
 364   return true;
 365 }
 366
 367 /*
 368 FUNCTION
 369         bfd_print_symbol_vandf
 370
 371 SYNOPSIS
 372         void bfd_print_symbol_vandf(PTR file, asymbol *symbol);
 373
 374 DESCRIPTION
 375         Print the value and flags of the @var{symbol} supplied to the
 376         stream @var{file}.
 377 */
 378 void
 379 bfd_print_symbol_vandf (arg, symbol)
 380      PTR arg;
 381      asymbol *symbol;
 382 {
 383   FILE *file = (FILE *) arg;
 384   flagword type = symbol->flags;
 385   if (symbol->section != (asection *) NULL)
 386     {
 387       fprintf_vma (file, symbol->value + symbol->section->vma);
 388     }
 389   else
 390     {
 391       fprintf_vma (file, symbol->value);
 392     }
 393
 394   /* This presumes that a symbol can not be both BSF_DEBUGGING and
 395      BSF_DYNAMIC.  */
 396   fprintf (file, " %c%c%c%c%c%c%c",
 397            (type & BSF_LOCAL) ? 'l' : ' ',
 398            (type & BSF_GLOBAL) ? 'g' : ' ',
 399            (type & BSF_WEAK) ? 'w' : ' ',
 400            (type & BSF_CONSTRUCTOR) ? 'C' : ' ',
 401            (type & BSF_WARNING) ? 'W' : ' ',
 402            (type & BSF_INDIRECT) ? 'I' : ' ',
 403            (type & BSF_DEBUGGING) ? 'd'
 404            : (type & BSF_DYNAMIC) ? 'D' : ' ');
 405 }
 406
 407
 408 /*
 409 FUNCTION
 410         bfd_make_empty_symbol
 411
 412 DESCRIPTION
 413         Create a new <<asymbol>> structure for the BFD @var{abfd}
 414         and return a pointer to it.
 415
 416         This routine is necessary because each back end has private
 417         information surrounding the <<asymbol>>. Building your own
 418         <<asymbol>> and pointing to it will not create the private
 419         information, and will cause problems later on.
 420
 421 .#define bfd_make_empty_symbol(abfd) \
 422 .     BFD_SEND (abfd, _bfd_make_empty_symbol, (abfd))
 423 */
 424
 425 /*
 426 FUNCTION
 427         bfd_make_debug_symbol
 428
 429 DESCRIPTION
 430         Create a new <<asymbol>> structure for the BFD @var{abfd},
 431         to be used as a debugging symbol.  Further details of its use have
 432         yet to be worked out.
 433
 434 .#define bfd_make_debug_symbol(abfd,ptr,size) \
 435 .        BFD_SEND (abfd, _bfd_make_debug_symbol, (abfd, ptr, size))
 436 */
 437
 438 struct section_to_type
 439 {
 440   CONST char *section;
 441   char type;
 442 };
 443
 444 /* Map section names to POSIX/BSD single-character symbol types.
 445    This table is probably incomplete.  It is sorted for convenience of
 446    adding entries.  Since it is so short, a linear search is used.  */
 447 static CONST struct section_to_type stt[] =
 448 {
 449   {"*DEBUG*", 'N'},
 450   {".bss", 'b'},
 451   {".data", 'd'},
 452   {".rdata", 'r'},              /* Read only data.  */
 453   {".rodata", 'r'},             /* Read only data.  */
 454   {".sbss", 's'},               /* Small BSS (uninitialized data).  */
 455   {".scommon", 'c'},            /* Small common.  */
 456   {".sdata", 'g'},              /* Small initialized data.  */
 457   {".text", 't'},
 458   {0, 0}
 459 };
 460
 461 /* Return the single-character symbol type corresponding to
 462    section S, or '?' for an unknown COFF section.  */
 463
 464 static char
 465 coff_section_type (s)
 466      char *s;
 467 {
 468   CONST struct section_to_type *t;
 469
 470   for (t = &stt[0]; t->section; t++)
 471     if (!strcmp (s, t->section))
 472       return t->type;
 473   return '?';
 474 }
 475
 476 #ifndef islower
 477 #define islower(c) ((c) >= 'a' && (c) <= 'z')
 478 #endif
 479 #ifndef toupper
 480 #define toupper(c) (islower(c) ? ((c) & ~0x20) : (c))
 481 #endif
 482
 483 /*
 484 FUNCTION
 485         bfd_decode_symclass
 486
 487 DESCRIPTION
 488         Return a character corresponding to the symbol
 489         class of @var{symbol}, or '?' for an unknown class.
 490
 491 SYNOPSIS
 492         int bfd_decode_symclass(asymbol *symbol);
 493 */
 494 int
 495 bfd_decode_symclass (symbol)
 496      asymbol *symbol;
 497 {
 498   char c;
 499
 500   if (bfd_is_com_section (symbol->section))
 501     return 'C';
 502   if (bfd_is_und_section (symbol->section))
 503     return 'U';
 504   if (bfd_is_ind_section (symbol->section))
 505     return 'I';
 506   if (!(symbol->flags & (BSF_GLOBAL | BSF_LOCAL)))
 507     return '?';
 508
 509   if (bfd_is_abs_section (symbol->section))
 510     c = 'a';
 511   else if (symbol->section)
 512     c = coff_section_type (symbol->section->name);
 513   else
 514     return '?';
 515   if (symbol->flags & BSF_GLOBAL)
 516     c = toupper (c);
 517   return c;
 518
 519   /* We don't have to handle these cases just yet, but we will soon:
 520      N_SETV: 'v';
 521      N_SETA: 'l';
 522      N_SETT: 'x';
 523      N_SETD: 'z';
 524      N_SETB: 's';
 525      N_INDR: 'i';
 526      */
 527 }
 528
 529 /*
 530 FUNCTION
 531         bfd_symbol_info
 532
 533 DESCRIPTION
 534         Fill in the basic info about symbol that nm needs.
 535         Additional info may be added by the back-ends after
 536         calling this function.
 537
 538 SYNOPSIS
 539         void bfd_symbol_info(asymbol *symbol, symbol_info *ret);
 540 */
 541
 542 void
 543 bfd_symbol_info (symbol, ret)
 544      asymbol *symbol;
 545      symbol_info *ret;
 546 {
 547   ret->type = bfd_decode_symclass (symbol);
 548   if (ret->type != 'U')
 549     ret->value = symbol->value + symbol->section->vma;
 550   else
 551     ret->value = 0;
 552   ret->name = symbol->name;
 553 }
 554
 555 void
 556 bfd_symbol_is_absolute ()
 557 {
 558   abort ();
 559 }