elf/dl-lookup.c

   1 /* Look up a symbol in the loaded objects.
   2    Copyright (C) 1995, 1996, 1997 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 <stddef.h>
  21 #include <link.h>
  22 #include <assert.h>
  23 #include <string.h>
  24
  25 #include "dl-hash.h"
  26 #include <dl-machine.h>
  27 #include "../stdio-common/_itoa.h"
  28
  29 #define VERSTAG(tag)    (DT_NUM + DT_PROCNUM + DT_VERSIONTAGIDX (tag))
  30
  31 struct sym_val
  32   {
  33     ElfW(Addr) a;
  34     const ElfW(Sym) *s;
  35   };
  36
  37
  38 #define make_string(string, rest...) \
  39   ({                                                                          \
  40     const char *all[] = { string, ## rest };                                  \
  41     size_t len, cnt;                                                          \
  42     char *result, *cp;                                                        \
  43                                                                               \
  44     len = 1;                                                                  \
  45     for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)                \
  46       len += strlen (all[cnt]);                                               \
  47                                                                               \
  48     cp = result = alloca (len);                                               \
  49     for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)                \
  50       cp = stpcpy (cp, all[cnt]);                                             \
  51                                                                               \
  52     result;                                                                   \
  53   })
  54
  55
  56 /* Inner part of the lookup functions.  We return a value > 0 if we
  57    found the symbol, the value 0 if nothing is found and < 0 if
  58    something bad happened.  */
  59 static inline int
  60 do_lookup (const char *undef_name, unsigned long int hash,
  61            const ElfW(Sym) *ref, struct sym_val *result,
  62            struct link_map *list[], size_t i, size_t n,
  63            const char *reference_name, const struct r_found_version *version,
  64            struct link_map *skip, int reloc_type)
  65 {
  66   struct link_map *map;
  67
  68   for (; i < n; ++i)
  69     {
  70       const ElfW(Sym) *symtab;
  71       const char *strtab;
  72       const ElfW(Half) *verstab;
  73       ElfW(Symndx) symidx;
  74
  75       map = list[i];
  76
  77       /* Here come the extra test needed for `_dl_lookup_symbol_skip'.  */
  78       if (skip != NULL && map == skip)
  79         continue;
  80
  81       /* Don't search the executable when resolving a copy reloc.  */
  82       if (elf_machine_lookup_noexec_p (reloc_type) &&
  83           map->l_type == lt_executable)
  84         continue;
  85
  86       symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
  87       strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
  88       if (map->l_nversions > 0 && map->l_info[VERSTAG (DT_VERSYM)] != NULL)
  89         verstab = ((void *) map->l_addr
  90                    + map->l_info[VERSTAG (DT_VERSYM)]->d_un.d_ptr);
  91       else
  92         verstab = NULL;
  93
  94       /* Search the appropriate hash bucket in this object's symbol table
  95          for a definition for the same symbol name.  */
  96       for (symidx = map->l_buckets[hash % map->l_nbuckets];
  97            symidx != STN_UNDEF;
  98            symidx = map->l_chain[symidx])
  99         {
 100           const ElfW(Sym) *sym = &symtab[symidx];
 101
 102           if (sym->st_value == 0 || /* No value.  */
 103               (elf_machine_lookup_noplt_p (reloc_type) /* Reject PLT entry.  */
 104                && sym->st_shndx == SHN_UNDEF))
 105             continue;
 106
 107           switch (ELFW(ST_TYPE) (sym->st_info))
 108             {
 109             case STT_NOTYPE:
 110             case STT_FUNC:
 111             case STT_OBJECT:
 112               break;
 113             default:
 114               /* Not a code/data definition.  */
 115               continue;
 116             }
 117
 118           if (sym != ref && strcmp (strtab + sym->st_name, undef_name))
 119             /* Not the symbol we are looking for.  */
 120             continue;
 121
 122           if (version == NULL)
 123             {
 124               /* No specific version is selected.  When the object
 125                  file also does not define a version we have a match.
 126                  Otherwise we only accept the default version, i.e.,
 127                  the version which name is "".  */
 128               if (verstab != NULL)
 129                 {
 130                   ElfW(Half) ndx = verstab[symidx] & 0x7fff;
 131                   if (map->l_versions[ndx].hash != 0)
 132                     continue;
 133                 }
 134             }
 135           else
 136             {
 137               if (verstab == NULL)
 138                 {
 139                   /* We need a versioned system but haven't found any.
 140                      If this is the object which is referenced in the
 141                      verneed entry it is a bug in the library since a
 142                      symbol must not simply disappear.  */
 143                   if (version->filename != NULL
 144                       && _dl_name_match_p (version->filename, map))
 145                     return -1;
 146                   /* Otherwise we accept the symbol.  */
 147                 }
 148               else
 149                 {
 150                   /* We can match the version information.  */
 151                   ElfW(Half) ndx = verstab[symidx] & 0x7fff;
 152                   if (map->l_versions[ndx].hash != version->hash
 153                       || strcmp (map->l_versions[ndx].name, version->name))
 154                     /* It's not the version we want.  */
 155                     continue;
 156                 }
 157             }
 158
 159           switch (ELFW(ST_BIND) (sym->st_info))
 160             {
 161             case STB_GLOBAL:
 162               /* Global definition.  Just what we need.  */
 163               result->s = sym;
 164               result->a = map->l_addr;
 165               return 1;
 166             case STB_WEAK:
 167               /* Weak definition.  Use this value if we don't find
 168                  another.  */
 169               if (! result->s)
 170                 {
 171                   result->s = sym;
 172                   result->a = map->l_addr;
 173                 }
 174               break;
 175             default:
 176               /* Local symbols are ignored.  */
 177               break;
 178             }
 179         }
 180
 181       /* If this current is the one mentioned in the verneed entry it
 182          is a bug.  */
 183       if (version != NULL && version->filename != NULL
 184           && _dl_name_match_p (version->filename, map))
 185         return -1;
 186     }
 187
 188   /* We have not found anything until now.  */
 189   return 0;
 190 }
 191
 192 /* Search loaded objects' symbol tables for a definition of the symbol
 193    UNDEF_NAME.  */
 194
 195 ElfW(Addr)
 196 _dl_lookup_symbol (const char *undef_name, const ElfW(Sym) **ref,
 197                    struct link_map *symbol_scope[],
 198                    const char *reference_name,
 199                    int reloc_type)
 200 {
 201   const unsigned long int hash = _dl_elf_hash (undef_name);
 202   struct sym_val current_value = { 0, NULL };
 203   struct link_map **scope;
 204
 205   /* Search the relevant loaded objects for a definition.  */
 206   for (scope = symbol_scope; *scope; ++scope)
 207     if (do_lookup (undef_name, hash, *ref, &current_value,
 208                    (*scope)->l_searchlist, 0, (*scope)->l_nsearchlist,
 209                    reference_name, NULL, NULL, reloc_type))
 210       break;
 211
 212   if (current_value.s == NULL &&
 213       (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK))
 214     /* We could find no value for a strong reference.  */
 215     _dl_signal_error (0, reference_name,
 216                       make_string ("undefined symbol: ", undef_name));
 217
 218   *ref = current_value.s;
 219   return current_value.a;
 220 }
 221
 222
 223 /* This function is nearly the same as `_dl_lookup_symbol' but it
 224    skips in the first list all objects until SKIP_MAP is found.  I.e.,
 225    it only considers objects which were loaded after the described
 226    object.  If there are more search lists the object described by
 227    SKIP_MAP is only skipped.  */
 228 ElfW(Addr)
 229 _dl_lookup_symbol_skip (const char *undef_name, const ElfW(Sym) **ref,
 230                         struct link_map *symbol_scope[],
 231                         const char *reference_name,
 232                         struct link_map *skip_map)
 233 {
 234   const unsigned long int hash = _dl_elf_hash (undef_name);
 235   struct sym_val current_value = { 0, NULL };
 236   struct link_map **scope;
 237   size_t i;
 238
 239   /* Search the relevant loaded objects for a definition.  */
 240   scope = symbol_scope;
 241   for (i = 0; (*scope)->l_dupsearchlist[i] != skip_map; ++i)
 242     assert (i < (*scope)->l_ndupsearchlist);
 243
 244   if (! do_lookup (undef_name, hash, *ref, &current_value,
 245                    (*scope)->l_dupsearchlist, i, (*scope)->l_ndupsearchlist,
 246                    reference_name, NULL, skip_map, 0))
 247     while (*++scope)
 248       if (do_lookup (undef_name, hash, *ref, &current_value,
 249                      (*scope)->l_dupsearchlist, 0, (*scope)->l_ndupsearchlist,
 250                      reference_name, NULL, skip_map, 0))
 251         break;
 252
 253   *ref = current_value.s;
 254   return current_value.a;
 255 }
 256
 257
 258 /* This function works like _dl_lookup_symbol but it takes an
 259    additional arguement with the version number of the requested
 260    symbol.
 261
 262    XXX We'll see whether we need this separate function.  */
 263 ElfW(Addr)
 264 _dl_lookup_versioned_symbol (const char *undef_name, const ElfW(Sym) **ref,
 265                              struct link_map *symbol_scope[],
 266                              const char *reference_name,
 267                              const struct r_found_version *version,
 268                              int reloc_type)
 269 {
 270   const unsigned long int hash = _dl_elf_hash (undef_name);
 271   struct sym_val current_value = { 0, NULL };
 272   struct link_map **scope;
 273
 274   /* Search the relevant loaded objects for a definition.  */
 275   for (scope = symbol_scope; *scope; ++scope)
 276     {
 277       int res = do_lookup (undef_name, hash, *ref, &current_value,
 278                            (*scope)->l_searchlist, 0, (*scope)->l_nsearchlist,
 279                            reference_name, version, NULL, reloc_type);
 280       if (res > 0)
 281         break;
 282
 283       if (res < 0)
 284         /* Oh, oh.  The file named in the relocation entry does not
 285            contain the needed symbol.  */
 286         _dl_signal_error (0, *reference_name ? reference_name : NULL,
 287                           make_string ("symbol ", undef_name, ", version ",
 288                                        version->name,
 289                                        " not defined in file ",
 290                                        version->filename,
 291                                        " with link time reference"));
 292     }
 293
 294   if (current_value.s == NULL &&
 295       (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK))
 296     /* We could find no value for a strong reference.  */
 297     _dl_signal_error (0, reference_name,
 298                       make_string ("undefined symbol: ", undef_name,
 299                                    ", version ", version->name ?: NULL));
 300
 301   *ref = current_value.s;
 302   return current_value.a;
 303 }
 304
 305
 306 /* Similar to _dl_lookup_symbol_skip but takes an additional argument
 307    with the version we are looking for.  */
 308 ElfW(Addr)
 309 _dl_lookup_versioned_symbol_skip (const char *undef_name,
 310                                   const ElfW(Sym) **ref,
 311                                   struct link_map *symbol_scope[],
 312                                   const char *reference_name,
 313                                   const struct r_found_version *version,
 314                                   struct link_map *skip_map)
 315 {
 316   const unsigned long int hash = _dl_elf_hash (undef_name);
 317   struct sym_val current_value = { 0, NULL };
 318   struct link_map **scope;
 319   size_t i;
 320
 321   /* Search the relevant loaded objects for a definition.  */
 322   scope = symbol_scope;
 323   for (i = 0; (*scope)->l_dupsearchlist[i] != skip_map; ++i)
 324     assert (i < (*scope)->l_ndupsearchlist);
 325
 326   if (! do_lookup (undef_name, hash, *ref, &current_value,
 327                    (*scope)->l_dupsearchlist, i, (*scope)->l_ndupsearchlist,
 328                    reference_name, version, skip_map, 0))
 329     while (*++scope)
 330       if (do_lookup (undef_name, hash, *ref, &current_value,
 331                      (*scope)->l_dupsearchlist, 0, (*scope)->l_ndupsearchlist,
 332                      reference_name, version, skip_map, 0))
 333         break;
 334
 335   *ref = current_value.s;
 336   return current_value.a;
 337 }
 338
 339
 340 /* Cache the location of MAP's hash table.  */
 341
 342 void
 343 _dl_setup_hash (struct link_map *map)
 344 {
 345   ElfW(Symndx) *hash = (void *)(map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr);
 346   ElfW(Symndx) nchain;
 347   map->l_nbuckets = *hash++;
 348   nchain = *hash++;
 349   map->l_buckets = hash;
 350   hash += map->l_nbuckets;
 351   map->l_chain = hash;
 352 }