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 <stddef.h>
  22 #include <link.h>
  23 #include <assert.h>
  24 #include <string.h>
  25
  26 #include "dl-hash.h"
  27 #include <dl-machine.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     ElfW(Addr) a;
  38     const ElfW(Sym) *s;
  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 link_map *list[], size_t i, size_t n,
  67            const char *reference_name, const struct r_found_version *version,
  68            struct link_map *skip, int reloc_type)
  69 {
  70   struct link_map *map;
  71
  72   for (; i < n; ++i)
  73     {
  74       const ElfW(Sym) *symtab;
  75       const char *strtab;
  76       const ElfW(Half) *verstab;
  77       ElfW(Symndx) symidx;
  78
  79       map = list[i];
  80
  81       /* Here come the extra test needed for `_dl_lookup_symbol_skip'.  */
  82       if (skip != NULL && map == skip)
  83         continue;
  84
  85       /* Skip objects that could not be opened, which can occur in trace
  86          mode.  */
  87       if (map->l_opencount == 0)
  88         continue;
  89
  90       /* Don't search the executable when resolving a copy reloc.  */
  91       if (elf_machine_lookup_noexec_p (reloc_type) &&
  92           map->l_type == lt_executable)
  93         continue;
  94
  95       /* Skip objects without symbol tables.  */
  96       if (map->l_info[DT_SYMTAB] == NULL)
  97         continue;
  98
  99       symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
 100       strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
 101       if (map->l_nversions > 0 && map->l_info[VERSTAG (DT_VERSYM)] != NULL)
 102         verstab = ((void *) map->l_addr
 103                    + map->l_info[VERSTAG (DT_VERSYM)]->d_un.d_ptr);
 104       else
 105         verstab = NULL;
 106
 107       /* Search the appropriate hash bucket in this object's symbol table
 108          for a definition for the same symbol name.  */
 109       for (symidx = map->l_buckets[hash % map->l_nbuckets];
 110            symidx != STN_UNDEF;
 111            symidx = map->l_chain[symidx])
 112         {
 113           const ElfW(Sym) *sym = &symtab[symidx];
 114
 115           if (sym->st_value == 0 || /* No value.  */
 116               (elf_machine_lookup_noplt_p (reloc_type) /* Reject PLT entry.  */
 117                && sym->st_shndx == SHN_UNDEF))
 118             continue;
 119
 120           if (ELFW(ST_TYPE) (sym->st_info) > STT_FUNC)
 121             /* Ignore all but STT_NOTYPE, STT_OBJECT and STT_FUNC entries
 122                since these are no code/data definitions.  */
 123             continue;
 124
 125           if (sym != ref && strcmp (strtab + sym->st_name, undef_name))
 126             /* Not the symbol we are looking for.  */
 127             continue;
 128
 129           if (version == NULL)
 130             {
 131               /* No specific version is selected.  When the object
 132                  file also does not define a version we have a match.
 133                  Otherwise we only accept the default version, i.e.,
 134                  the version which name is "".  */
 135               if (verstab != NULL)
 136                 {
 137                   ElfW(Half) ndx = verstab[symidx] & 0x7fff;
 138                   if (ndx > 2) /* map->l_versions[ndx].hash != 0) */
 139                     continue;
 140                 }
 141             }
 142           else
 143             {
 144               if (verstab == NULL)
 145                 {
 146                   /* We need a versioned system but haven't found any.
 147                      If this is the object which is referenced in the
 148                      verneed entry it is a bug in the library since a
 149                      symbol must not simply disappear.  */
 150                   if (version->filename != NULL
 151                       && _dl_name_match_p (version->filename, map))
 152                     return -2;
 153                   /* Otherwise we accept the symbol.  */
 154                 }
 155               else
 156                 {
 157                   /* We can match the version information or use the
 158                      default one if it is not hidden.  */
 159                   ElfW(Half) ndx = verstab[symidx] & 0x7fff;
 160                   if ((map->l_versions[ndx].hash != version->hash
 161                        || strcmp (map->l_versions[ndx].name, version->name))
 162                       && (version->hidden || map->l_versions[ndx].hash
 163                           || (verstab[symidx] & 0x8000)))
 164                     /* It's not the version we want.  */
 165                     continue;
 166                 }
 167             }
 168
 169           switch (ELFW(ST_BIND) (sym->st_info))
 170             {
 171             case STB_GLOBAL:
 172               /* Global definition.  Just what we need.  */
 173               result->s = sym;
 174               result->a = map->l_addr;
 175               return 1;
 176             case STB_WEAK:
 177               /* Weak definition.  Use this value if we don't find
 178                  another.  */
 179               if (! result->s)
 180                 {
 181                   result->s = sym;
 182                   result->a = map->l_addr;
 183                 }
 184               break;
 185             default:
 186               /* Local symbols are ignored.  */
 187               break;
 188             }
 189
 190           /* There cannot be another entry for this symbol so stop here.  */
 191           break;
 192         }
 193
 194       /* If this current map is the one mentioned in the verneed entry
 195          and we have not found a weak entry, it is a bug.  */
 196       if (symidx == STN_UNDEF && version != NULL && version->filename != NULL
 197           && _dl_name_match_p (version->filename, map))
 198         return -1;
 199     }
 200
 201   /* We have not found anything until now.  */
 202   return 0;
 203 }
 204
 205 /* Search loaded objects' symbol tables for a definition of the symbol
 206    UNDEF_NAME.  */
 207
 208 ElfW(Addr)
 209 _dl_lookup_symbol (const char *undef_name, const ElfW(Sym) **ref,
 210                    struct link_map *symbol_scope[],
 211                    const char *reference_name,
 212                    int reloc_type)
 213 {
 214   const unsigned long int hash = _dl_elf_hash (undef_name);
 215   struct sym_val current_value = { 0, NULL };
 216   struct link_map **scope;
 217
 218   /* Search the relevant loaded objects for a definition.  */
 219   for (scope = symbol_scope; *scope; ++scope)
 220     if (do_lookup (undef_name, hash, *ref, &current_value,
 221                    (*scope)->l_searchlist, 0, (*scope)->l_nsearchlist,
 222                    reference_name, NULL, NULL, reloc_type))
 223       break;
 224
 225   if (current_value.s == NULL &&
 226       (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK))
 227     /* We could find no value for a strong reference.  */
 228     _dl_signal_error (0, reference_name,
 229                       make_string (undefined_msg, undef_name));
 230
 231   *ref = current_value.s;
 232   return current_value.a;
 233 }
 234
 235
 236 /* This function is nearly the same as `_dl_lookup_symbol' but it
 237    skips in the first list all objects until SKIP_MAP is found.  I.e.,
 238    it only considers objects which were loaded after the described
 239    object.  If there are more search lists the object described by
 240    SKIP_MAP is only skipped.  */
 241 ElfW(Addr)
 242 _dl_lookup_symbol_skip (const char *undef_name, const ElfW(Sym) **ref,
 243                         struct link_map *symbol_scope[],
 244                         const char *reference_name,
 245                         struct link_map *skip_map)
 246 {
 247   const unsigned long int hash = _dl_elf_hash (undef_name);
 248   struct sym_val current_value = { 0, NULL };
 249   struct link_map **scope;
 250   size_t i;
 251
 252   /* Search the relevant loaded objects for a definition.  */
 253   scope = symbol_scope;
 254   for (i = 0; (*scope)->l_dupsearchlist[i] != skip_map; ++i)
 255     assert (i < (*scope)->l_ndupsearchlist);
 256
 257   if (! do_lookup (undef_name, hash, *ref, &current_value,
 258                    (*scope)->l_dupsearchlist, i, (*scope)->l_ndupsearchlist,
 259                    reference_name, NULL, skip_map, 0))
 260     while (*++scope)
 261       if (do_lookup (undef_name, hash, *ref, &current_value,
 262                      (*scope)->l_dupsearchlist, 0, (*scope)->l_ndupsearchlist,
 263                      reference_name, NULL, skip_map, 0))
 264         break;
 265
 266   *ref = current_value.s;
 267   return current_value.a;
 268 }
 269
 270
 271 /* This function works like _dl_lookup_symbol but it takes an
 272    additional arguement with the version number of the requested
 273    symbol.
 274
 275    XXX We'll see whether we need this separate function.  */
 276 ElfW(Addr)
 277 _dl_lookup_versioned_symbol (const char *undef_name, const ElfW(Sym) **ref,
 278                              struct link_map *symbol_scope[],
 279                              const char *reference_name,
 280                              const struct r_found_version *version,
 281                              int reloc_type)
 282 {
 283   extern char **_dl_argv;
 284   const unsigned long int hash = _dl_elf_hash (undef_name);
 285   struct sym_val current_value = { 0, NULL };
 286   struct link_map **scope;
 287
 288   /* Search the relevant loaded objects for a definition.  */
 289   for (scope = symbol_scope; *scope; ++scope)
 290     {
 291       int res = do_lookup (undef_name, hash, *ref, &current_value,
 292                            (*scope)->l_searchlist, 0, (*scope)->l_nsearchlist,
 293                            reference_name, version, NULL, reloc_type);
 294       if (res > 0)
 295         break;
 296
 297       if (res < 0)
 298         /* Oh, oh.  The file named in the relocation entry does not
 299            contain the needed symbol.  */
 300         _dl_signal_error (0, (*reference_name
 301                               ? reference_name
 302                               : (_dl_argv[0] ?: "<main program>")),
 303                           make_string ("symbol ", undef_name, ", version ",
 304                                        version->name,
 305                                        " not defined in file ",
 306                                        version->filename,
 307                                        " with link time reference",
 308                                        res == -2
 309                                        ? " (no version symbols)" : ""));
 310     }
 311
 312   if (current_value.s == NULL &&
 313       (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK))
 314     /* We could find no value for a strong reference.  */
 315     _dl_signal_error (0, reference_name,
 316                       make_string (undefined_msg, undef_name,
 317                                    ", version ", version->name ?: NULL));
 318
 319   *ref = current_value.s;
 320   return current_value.a;
 321 }
 322
 323
 324 /* Similar to _dl_lookup_symbol_skip but takes an additional argument
 325    with the version we are looking for.  */
 326 ElfW(Addr)
 327 _dl_lookup_versioned_symbol_skip (const char *undef_name,
 328                                   const ElfW(Sym) **ref,
 329                                   struct link_map *symbol_scope[],
 330                                   const char *reference_name,
 331                                   const struct r_found_version *version,
 332                                   struct link_map *skip_map)
 333 {
 334   const unsigned long int hash = _dl_elf_hash (undef_name);
 335   struct sym_val current_value = { 0, NULL };
 336   struct link_map **scope;
 337   size_t i;
 338
 339   /* Search the relevant loaded objects for a definition.  */
 340   scope = symbol_scope;
 341   for (i = 0; (*scope)->l_dupsearchlist[i] != skip_map; ++i)
 342     assert (i < (*scope)->l_ndupsearchlist);
 343
 344   if (! do_lookup (undef_name, hash, *ref, &current_value,
 345                    (*scope)->l_dupsearchlist, i, (*scope)->l_ndupsearchlist,
 346                    reference_name, version, skip_map, 0))
 347     while (*++scope)
 348       if (do_lookup (undef_name, hash, *ref, &current_value,
 349                      (*scope)->l_dupsearchlist, 0, (*scope)->l_ndupsearchlist,
 350                      reference_name, version, skip_map, 0))
 351         break;
 352
 353   if (current_value.s == NULL &&
 354       (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK))
 355     {
 356       /* We could find no value for a strong reference.  */
 357       const size_t len = strlen (undef_name);
 358       char buf[sizeof undefined_msg + len];
 359       __mempcpy (__mempcpy (buf, undefined_msg, sizeof undefined_msg - 1),
 360                  undef_name, len + 1);
 361       _dl_signal_error (0, reference_name, buf);
 362     }
 363
 364   *ref = current_value.s;
 365   return current_value.a;
 366 }
 367
 368
 369 /* Cache the location of MAP's hash table.  */
 370
 371 void
 372 _dl_setup_hash (struct link_map *map)
 373 {
 374   ElfW(Symndx) *hash;
 375   ElfW(Symndx) nchain;
 376
 377   if (!map->l_info[DT_HASH])
 378     return;
 379   hash = (void *)(map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr);
 380
 381   map->l_nbuckets = *hash++;
 382   nchain = *hash++;
 383   map->l_buckets = hash;
 384   hash += map->l_nbuckets;
 385   map->l_chain = hash;
 386 }