bfd/syms.c

   1 /* Generic symbol-table support for the BFD library.
   2    Copyright (C) 1990-1991 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 trys 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 infomation passed to
  31         applications some targets keep some information 'behind the
  32         sceans', 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 was read, but was 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 read, since the 'behind
  47         the sceens' 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 @node Reading Symbols, Writing Symbols, Symbols, Symbols
  56 SUBSECTION
  57         Reading Symbols
  58
  59         There are two stages to reading a symbol table from a BFD;
  60         allocating storage, and the actual reading process. This is an
  61         excerpt from an appliction which reads the symbol table:
  62
  63 |         unsigned int storage_needed;
  64 |         asymbol **symbol_table;
  65 |         unsigned int number_of_symbols;
  66 |         unsigned int i;
  67 |
  68 |         storage_needed = get_symtab_upper_bound (abfd);
  69 |
  70 |         if (storage_needed == 0) {
  71 |            return ;
  72 |         }
  73 |         symbol_table = (asymbol **) bfd_xmalloc (storage_needed);
  74 |           ...
  75 |         number_of_symbols =
  76 |            bfd_canonicalize_symtab (abfd, symbol_table);
  77 |
  78 |         for (i = 0; i < number_of_symbols; i++) {
  79 |            process_symbol (symbol_table[i]);
  80 |         }
  81
  82         All storage for the symbols themselves is in an obstack
  83         connected to the BFD, and is freed when the BFD is closed.
  84
  85
  86 @node Writing Symbols, typedef asymbol, Reading Symbols, Symbols
  87 SUBSECTION
  88         Writing Symbols
  89
  90         Writing of a symbol table is automatic when a BFD open for
  91         writing is closed. The application attaches a vector of
  92         pointers to pointers to symbols to the BFD being written, and
  93         fills in the symbol count. The close and cleanup code reads
  94         through the table provided and performs all the necessary
  95         operations. The outputing code must always be provided with an
  96         'owned' symbol; one which has come from another BFD, or one
  97         which has been created using <<bfd_make_empty_symbol>>.   An
  98         example showing the creation of a symbol table with only one element:
  99
 100 |       #include "bfd.h"
 101 |       main()
 102 |       {
 103 |         bfd *abfd;
 104 |         asymbol *ptrs[2];
 105 |         asymbol *new;
 106 |
 107 |         abfd = bfd_openw("foo","a.out-sunos-big");
 108 |         bfd_set_format(abfd, bfd_object);
 109 |         new = bfd_make_empty_symbol(abfd);
 110 |         new->name = "dummy_symbol";
 111 |         new->section = bfd_make_section_old_way(abfd, ".text");
 112 |         new->flags = BSF_GLOBAL;
 113 |         new->value = 0x12345;
 114 |
 115 |         ptrs[0] = new;
 116 |         ptrs[1] = (asymbol *)0;
 117 |
 118 |         bfd_set_symtab(abfd, ptrs, 1);
 119 |         bfd_close(abfd);
 120 |       }
 121 |
 122 |       ./makesym
 123 |       nm foo
 124 |       00012345 A dummy_symbol
 125
 126         Many formats cannot represent arbitary symbol information; for
 127         instance the <<a.out>> object format does not allow an
 128         arbitary number of sections. A symbol pointing to a section
 129         which is not one  of <<.text>>, <<.data>> or <<.bss>> cannot
 130         be described.
 131
 132 */
 133
 134
 135 /*
 136 @node typedef asymbol, symbol handling functions, Writing Symbols, Symbols
 137
 138 */
 139 /*
 140 SUBSECTION
 141         typedef asymbol
 142
 143         An <<asymbol>> has the form:
 144
 145 */
 146
 147 /*
 148 CODE_FRAGMENT
 149
 150 .typedef struct symbol_cache_entry
 151 .{
 152 .       {* A pointer to the BFD which owns the symbol. This information
 153 .          is necessary so that a back end can work out what additional
 154 .          (invisible to the application writer) information is carried
 155 .          with the symbol.  *}
 156 .
 157 .  struct _bfd *the_bfd;
 158 .
 159 .       {* The text of the symbol. The name is left alone, and not copied - the
 160 .          application may not alter it. *}
 161 .  CONST char *name;
 162 .
 163 .       {* The value of the symbol.*}
 164 .  symvalue value;
 165 .
 166 .       {* Attributes of a symbol: *}
 167 .
 168 .#define BSF_NO_FLAGS    0x00
 169 .
 170 .       {* The symbol has local scope; <<static>> in <<C>>. The value
 171 .          is the offset into the section of the data. *}
 172 .#define BSF_LOCAL      0x01
 173 .
 174 .       {* The symbol has global scope; initialized data in <<C>>. The
 175 .          value is the offset into the section of the data. *}
 176 .#define BSF_GLOBAL     0x02
 177 .
 178 .       {* Obsolete *}
 179 .#define BSF_IMPORT     0x04
 180 .
 181 .       {* The symbol has global scope, and is exported. The value is
 182 .          the offset into the section of the data. *}
 183 .#define BSF_EXPORT     0x08
 184 .
 185 .       {* The symbol is undefined. <<extern>> in <<C>>. The value has
 186 .          no meaning. *}
 187 .#define BSF_UNDEFINED_OBS 0x10
 188 .
 189 .       {* The symbol is common, initialized to zero; default in
 190 .          <<C>>. The value is the size of the object in bytes. *}
 191 .#define BSF_FORT_COMM_OBS      0x20
 192 .
 193 .       {* A normal C symbol would be one of:
 194 .          <<BSF_LOCAL>>, <<BSF_FORT_COMM>>,  <<BSF_UNDEFINED>> or
 195 .          <<BSF_EXPORT|BSD_GLOBAL>> *}
 196 .
 197 .       {* The symbol is a debugging record. The value has an arbitary
 198 .          meaning. *}
 199 .#define BSF_DEBUGGING  0x40
 200 .
 201 .       {* Used by the linker *}
 202 .#define BSF_KEEP        0x10000
 203 .#define BSF_KEEP_G      0x80000
 204 .
 205 .       {* Unused *}
 206 .#define BSF_WEAK        0x100000
 207 .#define BSF_CTOR        0x200000
 208 .
 209 .       {* This symbol was created to point to a section *}
 210 .#define BSF_SECTION_SYM 0x400000
 211 .
 212 .       {* The symbol used to be a common symbol, but now it is
 213 .          allocated. *}
 214 .#define BSF_OLD_COMMON  0x800000
 215 .
 216 .       {* The default value for common data. *}
 217 .#define BFD_FORT_COMM_DEFAULT_VALUE 0
 218 .
 219 .       {* In some files the type of a symbol sometimes alters its
 220 .          location in an output file - ie in coff a <<ISFCN>> symbol
 221 .          which is also <<C_EXT>> symbol appears where it was
 222 .          declared and not at the end of a section.  This bit is set
 223 .          by the target BFD part to convey this information. *}
 224 .
 225 .#define BSF_NOT_AT_END    0x40000
 226 .
 227 .       {* Signal that the symbol is the label of constructor section. *}
 228 .#define BSF_CONSTRUCTOR   0x1000000
 229 .
 230 .       {* Signal that the symbol is a warning symbol. If the symbol
 231 .          is a warning symbol, then the value field (I know this is
 232 .          tacky) will point to the asymbol which when referenced will
 233 .          cause the warning. *}
 234 .#define BSF_WARNING       0x2000000
 235 .
 236 .       {* Signal that the symbol is indirect. The value of the symbol
 237 .          is a pointer to an undefined asymbol which contains the
 238 .          name to use instead. *}
 239 .#define BSF_INDIRECT     0x4000000
 240 .
 241 .  flagword flags;
 242 .
 243 .       {* A pointer to the section to which this symbol is
 244 .          relative.  This will always be non NULL, there are special
 245 .          sections for undefined and absolute symbols *}
 246 .  struct sec *section;
 247 .
 248 .       {* Back end special data. This is being phased out in favour
 249 .          of making this a union. *}
 250 .  PTR udata;
 251 .
 252 .} asymbol;
 253 */
 254
 255 #include "bfd.h"
 256 #include "sysdep.h"
 257 #include "libbfd.h"
 258 #include "aout/stab_gnu.h"
 259
 260 /*
 261 @node symbol handling functions,  , typedef asymbol, Symbols
 262 SUBSECTION
 263         Symbol Handling Functions
 264 */
 265
 266 /*
 267 FUNCTION
 268         get_symtab_upper_bound
 269
 270 DESCRIPTION
 271         Returns the number of bytes required in a vector of pointers
 272         to <<asymbols>> for all the symbols in the supplied BFD,
 273         including a terminal NULL pointer. If there are no symbols in
 274         the BFD, then 0 is returned.
 275
 276 .#define get_symtab_upper_bound(abfd) \
 277 .     BFD_SEND (abfd, _get_symtab_upper_bound, (abfd))
 278
 279 */
 280
 281 /*
 282 FUNCTION
 283         bfd_canonicalize_symtab
 284
 285 DESCRIPTION
 286         Supplied a BFD and a pointer to an uninitialized vector of
 287         pointers. This reads in the symbols from the BFD, and fills in
 288         the table with pointers to the symbols, and a trailing NULL.
 289         The routine returns the actual number of symbol pointers not
 290         including the NULL.
 291
 292
 293 .#define bfd_canonicalize_symtab(abfd, location) \
 294 .     BFD_SEND (abfd, _bfd_canonicalize_symtab,\
 295 .                  (abfd, location))
 296
 297 */
 298
 299
 300 /*
 301 FUNCTION
 302         bfd_set_symtab
 303
 304 DESCRIPTION
 305         Provided a table of pointers to symbols and a count, writes to
 306         the output BFD the symbols when closed.
 307
 308 SYNOPSIS
 309         boolean bfd_set_symtab (bfd *, asymbol **, unsigned int );
 310 */
 311
 312 boolean
 313 bfd_set_symtab (abfd, location, symcount)
 314      bfd *abfd;
 315      asymbol **location;
 316      unsigned int symcount;
 317 {
 318   if ((abfd->format != bfd_object) || (bfd_read_p (abfd))) {
 319     bfd_error = invalid_operation;
 320     return false;
 321   }
 322
 323   bfd_get_outsymbols (abfd) = location;
 324   bfd_get_symcount (abfd) = symcount;
 325   return true;
 326 }
 327
 328 /*
 329 FUNCTION
 330         bfd_print_symbol_vandf
 331
 332 DESCRIPTION
 333         Prints the value and flags of the symbol supplied to the stream file.
 334
 335 SYNOPSIS
 336         void bfd_print_symbol_vandf(PTR file, asymbol *symbol);
 337 */
 338 void
 339 DEFUN(bfd_print_symbol_vandf,(file, symbol),
 340 PTR file AND
 341 asymbol *symbol)
 342 {
 343   flagword type = symbol->flags;
 344   if (symbol->section != (asection *)NULL)
 345       {
 346         fprintf_vma(file, symbol->value+symbol->section->vma);
 347       }
 348   else
 349       {
 350         fprintf_vma(file, symbol->value);
 351       }
 352   fprintf(file," %c%c%c%c%c%c%c%c",
 353           (type & BSF_LOCAL)  ? 'l':' ',
 354           (type & BSF_GLOBAL) ? 'g' : ' ',
 355           (type & BSF_IMPORT) ? 'i' : ' ',
 356           (type & BSF_EXPORT) ? 'e' : ' ',
 357           (type & BSF_CONSTRUCTOR) ? 'C' : ' ',
 358           (type & BSF_WARNING) ? 'W' : ' ',
 359           (type & BSF_INDIRECT) ? 'I' : ' ',
 360           (type & BSF_DEBUGGING) ? 'd' :' ');
 361
 362 }
 363
 364
 365 /*
 366 FUNCTION
 367         bfd_make_empty_symbol
 368
 369 DESCRIPTION
 370         This function creates a new <<asymbol>> structure for the BFD,
 371         and returns a pointer to it.
 372
 373         This routine is necessary, since each back end has private
 374         information surrounding the <<asymbol>>. Building your own
 375         <<asymbol>> and pointing to it will not create the private
 376         information, and will cause problems later on.
 377
 378 .#define bfd_make_empty_symbol(abfd) \
 379 .     BFD_SEND (abfd, _bfd_make_empty_symbol, (abfd))
 380 */
 381
 382 /*
 383 FUNCTION
 384         bfd_decode_symclass
 385
 386 DESCRIPTION
 387         Return a lower-case character corresponding to the symbol
 388         class of symbol.
 389
 390 SYNOPSIS
 391         int bfd_decode_symclass(asymbol *symbol);
 392 */
 393 int
 394 DEFUN(bfd_decode_symclass,(symbol),
 395 asymbol *symbol)
 396 {
 397   flagword flags = symbol->flags;
 398
 399   if (symbol->section == &bfd_com_section) return 'C';
 400   if (symbol->section == &bfd_und_section) return 'U';
 401
 402    if ( flags & (BSF_GLOBAL|BSF_LOCAL) ) {
 403      if ( symbol->section == &bfd_abs_section)
 404       return (flags & BSF_GLOBAL) ? 'A' : 'a';
 405      else if ( !strcmp(symbol->section->name, ".text") )
 406        return (flags & BSF_GLOBAL) ? 'T' : 't';
 407      else if ( !strcmp(symbol->section->name, ".data") )
 408        return (flags & BSF_GLOBAL) ? 'D' : 'd';
 409      else if ( !strcmp(symbol->section->name, ".bss") )
 410        return (flags & BSF_GLOBAL) ? 'B' : 'b';
 411      else
 412        return (flags & BSF_GLOBAL) ? 'O' : 'o';
 413     }
 414
 415   /* We don't have to handle these cases just yet, but we will soon:
 416      N_SETV: 'v';
 417      N_SETA: 'l';
 418      N_SETT: 'x';
 419      N_SETD: 'z';
 420      N_SETB: 's';
 421      N_INDR: 'i';
 422      */
 423
 424   return '?';
 425 }
 426
 427
 428 bfd_symbol_is_absolute()
 429 {
 430
 431   abort();
 432 }
 433