elf/dl-lookup.c

   1 /* Look up a symbol in the loaded objects.
   2    Copyright (C) 1995, 1996, 1997, 1998 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #include <alloca.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <elf/ldsodefs.h>
  24 #include "dl-hash.h"
  25 #include <dl-machine.h>
  26
  27 #include <assert.h>
  28
  29 #define VERSTAG(tag)    (DT_NUM + DT_PROCNUM + DT_VERSIONTAGIDX (tag))
  30
  31 /* We need this string more than once.  */
  32 static const char undefined_msg[] = "undefined symbol: ";
  33
  34
  35 struct sym_val
  36   {
  37     const ElfW(Sym) *s;
  38     struct link_map *m;
  39   };
  40
  41
  42 #define make_string(string, rest...) \
  43   ({                                                                          \
  44     const char *all[] = { string, ## rest };                                  \
  45     size_t len, cnt;                                                          \
  46     char *result, *cp;                                                        \
  47                                                                               \
  48     len = 1;                                                                  \
  49     for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)                \
  50       len += strlen (all[cnt]);                                               \
  51                                                                               \
  52     cp = result = alloca (len);                                               \
  53     for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)                \
  54       cp = __stpcpy (cp, all[cnt]);                                           \
  55                                                                               \
  56     result;                                                                   \
  57   })
  58
  59
  60 /* Inner part of the lookup functions.  We return a value > 0 if we
  61    found the symbol, the value 0 if nothing is found and < 0 if
  62    something bad happened.  */
  63 static inline int
  64 do_lookup (const char *undef_name, unsigned long int hash,
  65            const ElfW(Sym) *ref, struct sym_val *result,
  66            struct r_scope_elem *scope, size_t i, const char *reference_name,
  67            const struct r_found_version *version, struct link_map *skip,
  68            int reloc_type)
  69 {
  70   struct link_map **list = scope->r_list;
  71   size_t n = scope->r_nlist;
  72   struct link_map *map;
  73
  74   for (; i < n; ++i)
  75     {
  76       const ElfW(Sym) *symtab;
  77       const char *strtab;
  78       const ElfW(Half) *verstab;
  79       ElfW(Symndx) symidx;
  80
  81       map = list[i];
  82
  83       /* Here come the extra test needed for `_dl_lookup_symbol_skip'.  */
  84       if (skip != NULL && map == skip)
  85         continue;
  86
  87       /* Skip objects that could not be opened, which can occur in trace
  88          mode.  */
  89       if (map->l_opencount == 0)
  90         continue;
  91
  92       /* Don't search the executable when resolving a copy reloc.  */
  93       if (elf_machine_lookup_noexec_p (reloc_type)
  94           && map->l_type == lt_executable)
  95         continue;
  96
  97       /* Skip objects without symbol tables.  */
  98       if (map->l_info[DT_SYMTAB] == NULL)
  99         continue;
 100
 101       /* Print some debugging info if wanted.  */
 102       if (_dl_debug_symbols)
 103         _dl_debug_message (1, "symbol=", undef_name, ";  lookup in file=",
 104                            map->l_name[0] ? map->l_name : _dl_argv[0],
 105                            "\n", NULL);
 106
 107       symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
 108       strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
 109       verstab = map->l_versyms;
 110
 111       /* Search the appropriate hash bucket in this object's symbol table
 112          for a definition for the same symbol name.  */
 113       for (symidx = map->l_buckets[hash % map->l_nbuckets];
 114            symidx != STN_UNDEF;
 115            symidx = map->l_chain[symidx])
 116         {
 117           const ElfW(Sym) *sym = &symtab[symidx];
 118
 119           if (sym->st_value == 0 || /* No value.  */
 120               (elf_machine_lookup_noplt_p (reloc_type) /* Reject PLT entry.  */
 121                && sym->st_shndx == SHN_UNDEF))
 122             continue;
 123
 124           if (ELFW(ST_TYPE) (sym->st_info) > STT_FUNC)
 125             /* Ignore all but STT_NOTYPE, STT_OBJECT and STT_FUNC entries
 126                since these are no code/data definitions.  */
 127             continue;
 128
 129           if (sym != ref && strcmp (strtab + sym->st_name, undef_name))
 130             /* Not the symbol we are looking for.  */
 131             continue;
 132
 133           if (version == NULL)
 134             {
 135               /* No specific version is selected.  When the object
 136                  file also does not define a version we have a match.
 137                  Otherwise we only accept the default version, i.e.,
 138                  the version which name is "".  */
 139               if (verstab != NULL)
 140                 {
 141                   ElfW(Half) ndx = verstab[symidx] & 0x7fff;
 142                   if (ndx > 2) /* map->l_versions[ndx].hash != 0) */
 143                     continue;
 144                 }
 145             }
 146           else
 147             {
 148               if (verstab == NULL)
 149                 {
 150                   /* We need a versioned system but haven't found any.
 151                      If this is the object which is referenced in the
 152                      verneed entry it is a bug in the library since a
 153                      symbol must not simply disappear.  */
 154                   if (version->filename != NULL
 155                       && _dl_name_match_p (version->filename, map))
 156                     return -2;
 157                   /* Otherwise we accept the symbol.  */
 158                 }
 159               else
 160                 {
 161                   /* We can match the version information or use the
 162                      default one if it is not hidden.  */
 163                   ElfW(Half) ndx = verstab[symidx] & 0x7fff;
 164                   if ((map->l_versions[ndx].hash != version->hash
 165                        || strcmp (map->l_versions[ndx].name, version->name))
 166                       && (version->hidden || map->l_versions[ndx].hash
 167                           || (verstab[symidx] & 0x8000)))
 168                     /* It's not the version we want.  */
 169                     continue;
 170                 }
 171             }
 172
 173           switch (ELFW(ST_BIND) (sym->st_info))
 174             {
 175             case STB_GLOBAL:
 176               /* Global definition.  Just what we need.  */
 177               result->s = sym;
 178               result->m = map;
 179               return 1;
 180             case STB_WEAK:
 181               /* Weak definition.  Use this value if we don't find
 182                  another.  */
 183               if (! result->s)
 184                 {
 185                   result->s = sym;
 186                   result->m = map;
 187                 }
 188               break;
 189             default:
 190               /* Local symbols are ignored.  */
 191               break;
 192             }
 193
 194           /* There cannot be another entry for this symbol so stop here.  */
 195           break;
 196         }
 197
 198       /* If this current map is the one mentioned in the verneed entry
 199          and we have not found a weak entry, it is a bug.  */
 200       if (symidx == STN_UNDEF && version != NULL && version->filename != NULL
 201           && _dl_name_match_p (version->filename, map))
 202         return -1;
 203     }
 204
 205   /* We have not found anything until now.  */
 206   return 0;
 207 }
 208
 209 /* Search loaded objects' symbol tables for a definition of the symbol
 210    UNDEF_NAME.  */
 211
 212 ElfW(Addr)
 213 internal_function
 214 _dl_lookup_symbol (const char *undef_name, const ElfW(Sym) **ref,
 215                    struct r_scope_elem *symbol_scope[],
 216                    const char *reference_name,
 217                    int reloc_type)
 218 {
 219   const unsigned long int hash = _dl_elf_hash (undef_name);
 220   struct sym_val current_value = { NULL, NULL };
 221   struct r_scope_elem **scope;
 222
 223   /* Search the relevant loaded objects for a definition.  */
 224   for (scope = symbol_scope; *scope; ++scope)
 225     if (do_lookup (undef_name, hash, *ref, &current_value,
 226                    *scope, 0, reference_name, NULL, NULL, reloc_type))
 227       break;
 228
 229   if (current_value.s == NULL)
 230     {
 231       if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
 232         /* We could find no value for a strong reference.  */
 233         _dl_signal_error (0, (reference_name  && reference_name[0]
 234                               ? reference_name
 235                               : (_dl_argv[0] ?: "<main program>")),
 236                           make_string (undefined_msg, undef_name));
 237       *ref = NULL;
 238       return 0;
 239     }
 240
 241   if (_dl_debug_bindings)
 242     _dl_debug_message (1, "binding file ",
 243                        (reference_name && reference_name[0]
 244                         ? reference_name
 245                         : (_dl_argv[0] ?: "<main program>")),
 246                        " to ", current_value.m->l_name[0]
 247                        ? current_value.m->l_name : _dl_argv[0],
 248                        ": symbol `", undef_name, "'\n", NULL);
 249
 250   *ref = current_value.s;
 251   return current_value.m->l_addr;
 252 }
 253
 254
 255 /* This function is nearly the same as `_dl_lookup_symbol' but it
 256    skips in the first list all objects until SKIP_MAP is found.  I.e.,
 257    it only considers objects which were loaded after the described
 258    object.  If there are more search lists the object described by
 259    SKIP_MAP is only skipped.  */
 260 ElfW(Addr)
 261 internal_function
 262 _dl_lookup_symbol_skip (const char *undef_name, const ElfW(Sym) **ref,
 263                         struct r_scope_elem *symbol_scope[],
 264                         const char *reference_name,
 265                         struct link_map *skip_map)
 266 {
 267   const unsigned long int hash = _dl_elf_hash (undef_name);
 268   struct sym_val current_value = { NULL, NULL };
 269   struct r_scope_elem **scope;
 270   size_t i;
 271
 272   /* Search the relevant loaded objects for a definition.  */
 273   scope = symbol_scope;
 274   for (i = 0; (*scope)->r_duplist[i] != skip_map; ++i)
 275     assert (i < (*scope)->r_nduplist);
 276
 277   if (! do_lookup (undef_name, hash, *ref, &current_value,
 278                    *scope, i, reference_name, NULL, skip_map, 0))
 279     while (*++scope)
 280       if (do_lookup (undef_name, hash, *ref, &current_value,
 281                      *scope, 0, reference_name, NULL, skip_map, 0))
 282         break;
 283
 284   if (current_value.s == NULL)
 285     {
 286       *ref = NULL;
 287       return 0;
 288     }
 289
 290   if (_dl_debug_bindings)
 291     _dl_debug_message (1, "binding file ",
 292                        (reference_name && reference_name[0]
 293                         ? reference_name
 294                         : (_dl_argv[0] ?: "<main program>")),
 295                        " to ", current_value.m->l_name[0]
 296                        ? current_value.m->l_name : _dl_argv[0],
 297                        ": symbol `", undef_name, "' (skip)\n", NULL);
 298
 299   *ref = current_value.s;
 300   return current_value.m->l_addr;
 301 }
 302
 303
 304 /* This function works like _dl_lookup_symbol but it takes an
 305    additional arguement with the version number of the requested
 306    symbol.
 307
 308    XXX We'll see whether we need this separate function.  */
 309 ElfW(Addr)
 310 internal_function
 311 _dl_lookup_versioned_symbol (const char *undef_name, const ElfW(Sym) **ref,
 312                              struct r_scope_elem *symbol_scope[],
 313                              const char *reference_name,
 314                              const struct r_found_version *version,
 315                              int reloc_type)
 316 {
 317   const unsigned long int hash = _dl_elf_hash (undef_name);
 318   struct sym_val current_value = { NULL, NULL };
 319   struct r_scope_elem **scope;
 320
 321   /* Search the relevant loaded objects for a definition.  */
 322   for (scope = symbol_scope; *scope; ++scope)
 323     {
 324       int res = do_lookup (undef_name, hash, *ref, &current_value,
 325                            *scope, 0, reference_name, version, NULL, reloc_type);
 326       if (res > 0)
 327         break;
 328
 329       if (res < 0)
 330         /* Oh, oh.  The file named in the relocation entry does not
 331            contain the needed symbol.  */
 332         _dl_signal_error (0, (reference_name && reference_name[0]
 333                               ? reference_name
 334                               : (_dl_argv[0] ?: "<main program>")),
 335                           make_string ("symbol ", undef_name, ", version ",
 336                                        version->name,
 337                                        " not defined in file ",
 338                                        version->filename,
 339                                        " with link time reference",
 340                                        res == -2
 341                                        ? " (no version symbols)" : ""));
 342     }
 343
 344   if (current_value.s == NULL)
 345     {
 346       if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
 347         /* We could find no value for a strong reference.  */
 348         _dl_signal_error (0, (reference_name && reference_name[0]
 349                               ? reference_name
 350                               : (_dl_argv[0] ?: "<main program>")),
 351                           make_string (undefined_msg, undef_name,
 352                                        ", version ", version->name ?: NULL));
 353       *ref = NULL;
 354       return 0;
 355     }
 356
 357   if (_dl_debug_bindings)
 358     _dl_debug_message (1, "binding file ",
 359                        (reference_name && reference_name[0]
 360                         ? reference_name
 361                         : (_dl_argv[0] ?: "<main program>")),
 362                        " to ", current_value.m->l_name[0]
 363                        ? current_value.m->l_name : _dl_argv[0],
 364                        ": symbol `", undef_name, "' [", version->name,
 365                        "]\n", NULL);
 366
 367   *ref = current_value.s;
 368   return current_value.m->l_addr;
 369 }
 370
 371
 372 /* Similar to _dl_lookup_symbol_skip but takes an additional argument
 373    with the version we are looking for.  */
 374 ElfW(Addr)
 375 internal_function
 376 _dl_lookup_versioned_symbol_skip (const char *undef_name,
 377                                   const ElfW(Sym) **ref,
 378                                   struct r_scope_elem *symbol_scope[],
 379                                   const char *reference_name,
 380                                   const struct r_found_version *version,
 381                                   struct link_map *skip_map)
 382 {
 383   const unsigned long int hash = _dl_elf_hash (undef_name);
 384   struct sym_val current_value = { NULL, NULL };
 385   struct r_scope_elem **scope;
 386   size_t i;
 387
 388   /* Search the relevant loaded objects for a definition.  */
 389   scope = symbol_scope;
 390   for (i = 0; (*scope)->r_duplist[i] != skip_map; ++i)
 391     assert (i < (*scope)->r_nduplist);
 392
 393   if (! do_lookup (undef_name, hash, *ref, &current_value,
 394                    *scope, i, reference_name, version, skip_map, 0))
 395     while (*++scope)
 396       if (do_lookup (undef_name, hash, *ref, &current_value,
 397                      *scope, 0, reference_name, version, skip_map, 0))
 398         break;
 399
 400   if (current_value.s == NULL)
 401     {
 402       if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
 403         {
 404           /* We could find no value for a strong reference.  */
 405           const size_t len = strlen (undef_name);
 406           char buf[sizeof undefined_msg + len];
 407           __mempcpy (__mempcpy (buf, undefined_msg, sizeof undefined_msg - 1),
 408                      undef_name, len + 1);
 409           _dl_signal_error (0, (reference_name && reference_name[0]
 410                                 ? reference_name
 411                                 : (_dl_argv[0] ?: "<main program>")), buf);
 412         }
 413       *ref = NULL;
 414       return 0;
 415     }
 416
 417   if (_dl_debug_bindings)
 418     _dl_debug_message (1, "binding file ",
 419                        (reference_name && reference_name[0]
 420                         ? reference_name
 421                         : (_dl_argv[0] ?: "<main program>")),
 422                        " to ",
 423                        current_value.m->l_name[0]
 424                        ? current_value.m->l_name : _dl_argv[0],
 425                        ": symbol `", undef_name, "' [", version->name,
 426                        "] (skip)\n", NULL);
 427
 428   *ref = current_value.s;
 429   return current_value.m->l_addr;
 430 }
 431
 432
 433 /* Cache the location of MAP's hash table.  */
 434
 435 void
 436 internal_function
 437 _dl_setup_hash (struct link_map *map)
 438 {
 439   ElfW(Symndx) *hash;
 440   ElfW(Symndx) nchain;
 441
 442   if (!map->l_info[DT_HASH])
 443     return;
 444   hash = (void *)(map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr);
 445
 446   map->l_nbuckets = *hash++;
 447   nchain = *hash++;
 448   map->l_buckets = hash;
 449   hash += map->l_nbuckets;
 450   map->l_chain = hash;
 451 }