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 <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 #include <stdio-common/_itoa.h>
  29
  30 #define VERSTAG(tag)    (DT_NUM + DT_PROCNUM + DT_VERSIONTAGIDX (tag))
  31
  32 /* We need this string more than once.  */
  33 static const char undefined_msg[] = "undefined symbol: ";
  34
  35
  36 struct sym_val
  37   {
  38     ElfW(Addr) a;
  39     const ElfW(Sym) *s;
  40   };
  41
  42
  43 #define make_string(string, rest...) \
  44   ({                                                                          \
  45     const char *all[] = { string, ## rest };                                  \
  46     size_t len, cnt;                                                          \
  47     char *result, *cp;                                                        \
  48                                                                               \
  49     len = 1;                                                                  \
  50     for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)                \
  51       len += strlen (all[cnt]);                                               \
  52                                                                               \
  53     cp = result = alloca (len);                                               \
  54     for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)                \
  55       cp = stpcpy (cp, all[cnt]);                                             \
  56                                                                               \
  57     result;                                                                   \
  58   })
  59
  60
  61 /* Inner part of the lookup functions.  We return a value > 0 if we
  62    found the symbol, the value 0 if nothing is found and < 0 if
  63    something bad happened.  */
  64 static inline int
  65 do_lookup (const char *undef_name, unsigned long int hash,
  66            const ElfW(Sym) *ref, struct sym_val *result,
  67            struct link_map *list[], size_t i, size_t n,
  68            const char *reference_name, const struct r_found_version *version,
  69            struct link_map *skip, int reloc_type)
  70 {
  71   struct link_map *map;
  72
  73   for (; i < n; ++i)
  74     {
  75       const ElfW(Sym) *symtab;
  76       const char *strtab;
  77       const ElfW(Half) *verstab;
  78       ElfW(Symndx) symidx;
  79
  80       map = list[i];
  81
  82       /* Here come the extra test needed for `_dl_lookup_symbol_skip'.  */
  83       if (skip != NULL && map == skip)
  84         continue;
  85
  86       /* Don't search the executable when resolving a copy reloc.  */
  87       if (elf_machine_lookup_noexec_p (reloc_type) &&
  88           map->l_type == lt_executable)
  89         continue;
  90
  91       symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
  92       strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
  93       if (map->l_nversions > 0 && map->l_info[VERSTAG (DT_VERSYM)] != NULL)
  94         verstab = ((void *) map->l_addr
  95                    + map->l_info[VERSTAG (DT_VERSYM)]->d_un.d_ptr);
  96       else
  97         verstab = NULL;
  98
  99       /* Search the appropriate hash bucket in this object's symbol table
 100          for a definition for the same symbol name.  */
 101       for (symidx = map->l_buckets[hash % map->l_nbuckets];
 102            symidx != STN_UNDEF;
 103            symidx = map->l_chain[symidx])
 104         {
 105           const ElfW(Sym) *sym = &symtab[symidx];
 106
 107           if (sym->st_value == 0 || /* No value.  */
 108               (elf_machine_lookup_noplt_p (reloc_type) /* Reject PLT entry.  */
 109                && sym->st_shndx == SHN_UNDEF))
 110             continue;
 111
 112           if (ELFW(ST_TYPE) (sym->st_info) > STT_FUNC)
 113             /* Ignore all but STT_NOTYPE, STT_OBJECT and STT_FUNC entries
 114                since these are no code/data definitions.  */
 115             continue;
 116
 117           if (sym != ref && strcmp (strtab + sym->st_name, undef_name))
 118             /* Not the symbol we are looking for.  */
 119             continue;
 120
 121           if (version == NULL)
 122             {
 123               /* No specific version is selected.  When the object
 124                  file also does not define a version we have a match.
 125                  Otherwise we only accept the default version, i.e.,
 126                  the version which name is "".  */
 127               if (verstab != NULL)
 128                 {
 129                   ElfW(Half) ndx = verstab[symidx] & 0x7fff;
 130                   if (ndx > 2) /* map->l_versions[ndx].hash != 0) */
 131                     continue;
 132                 }
 133             }
 134           else
 135             {
 136               if (verstab == NULL)
 137                 {
 138                   /* We need a versioned system but haven't found any.
 139                      If this is the object which is referenced in the
 140                      verneed entry it is a bug in the library since a
 141                      symbol must not simply disappear.  */
 142                   if (version->filename != NULL
 143                       && _dl_name_match_p (version->filename, map))
 144                     return -2;
 145                   /* Otherwise we accept the symbol.  */
 146                 }
 147               else
 148                 {
 149                   /* We can match the version information.  */
 150                   ElfW(Half) ndx = verstab[symidx] & 0x7fff;
 151                   if (map->l_versions[ndx].hash != version->hash
 152                       || strcmp (map->l_versions[ndx].name, version->name))
 153                     /* It's not the version we want.  */
 154                     continue;
 155                 }
 156             }
 157
 158           switch (ELFW(ST_BIND) (sym->st_info))
 159             {
 160             case STB_GLOBAL:
 161               /* Global definition.  Just what we need.  */
 162               result->s = sym;
 163               result->a = map->l_addr;
 164               return 1;
 165             case STB_WEAK:
 166               /* Weak definition.  Use this value if we don't find
 167                  another.  */
 168               if (! result->s)
 169                 {
 170                   result->s = sym;
 171                   result->a = map->l_addr;
 172                 }
 173               break;
 174             default:
 175               /* Local symbols are ignored.  */
 176               break;
 177             }
 178
 179           /* There cannot be another entry for this symbol so stop here.  */
 180           break;
 181         }
 182
 183       /* If this current map is the one mentioned in the verneed entry
 184          and we have not found a weak entry, it is a bug.  */
 185       if (symidx == STN_UNDEF && version != NULL && version->filename != NULL
 186           && _dl_name_match_p (version->filename, map))
 187         return -1;
 188     }
 189
 190   /* We have not found anything until now.  */
 191   return 0;
 192 }
 193
 194 /* Search loaded objects' symbol tables for a definition of the symbol
 195    UNDEF_NAME.  */
 196
 197 ElfW(Addr)
 198 _dl_lookup_symbol (const char *undef_name, const ElfW(Sym) **ref,
 199                    struct link_map *symbol_scope[],
 200                    const char *reference_name,
 201                    int reloc_type)
 202 {
 203   const unsigned long int hash = _dl_elf_hash (undef_name);
 204   struct sym_val current_value = { 0, NULL };
 205   struct link_map **scope;
 206
 207   /* Search the relevant loaded objects for a definition.  */
 208   for (scope = symbol_scope; *scope; ++scope)
 209     if (do_lookup (undef_name, hash, *ref, &current_value,
 210                    (*scope)->l_searchlist, 0, (*scope)->l_nsearchlist,
 211                    reference_name, NULL, NULL, reloc_type))
 212       break;
 213
 214   if (current_value.s == NULL &&
 215       (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK))
 216     /* We could find no value for a strong reference.  */
 217     _dl_signal_error (0, reference_name,
 218                       make_string (undefined_msg, undef_name));
 219
 220   *ref = current_value.s;
 221   return current_value.a;
 222 }
 223
 224
 225 /* This function is nearly the same as `_dl_lookup_symbol' but it
 226    skips in the first list all objects until SKIP_MAP is found.  I.e.,
 227    it only considers objects which were loaded after the described
 228    object.  If there are more search lists the object described by
 229    SKIP_MAP is only skipped.  */
 230 ElfW(Addr)
 231 _dl_lookup_symbol_skip (const char *undef_name, const ElfW(Sym) **ref,
 232                         struct link_map *symbol_scope[],
 233                         const char *reference_name,
 234                         struct link_map *skip_map)
 235 {
 236   const unsigned long int hash = _dl_elf_hash (undef_name);
 237   struct sym_val current_value = { 0, NULL };
 238   struct link_map **scope;
 239   size_t i;
 240
 241   /* Search the relevant loaded objects for a definition.  */
 242   scope = symbol_scope;
 243   for (i = 0; (*scope)->l_dupsearchlist[i] != skip_map; ++i)
 244     assert (i < (*scope)->l_ndupsearchlist);
 245
 246   if (! do_lookup (undef_name, hash, *ref, &current_value,
 247                    (*scope)->l_dupsearchlist, i, (*scope)->l_ndupsearchlist,
 248                    reference_name, NULL, skip_map, 0))
 249     while (*++scope)
 250       if (do_lookup (undef_name, hash, *ref, &current_value,
 251                      (*scope)->l_dupsearchlist, 0, (*scope)->l_ndupsearchlist,
 252                      reference_name, NULL, skip_map, 0))
 253         break;
 254
 255   *ref = current_value.s;
 256   return current_value.a;
 257 }
 258
 259
 260 /* This function works like _dl_lookup_symbol but it takes an
 261    additional arguement with the version number of the requested
 262    symbol.
 263
 264    XXX We'll see whether we need this separate function.  */
 265 ElfW(Addr)
 266 _dl_lookup_versioned_symbol (const char *undef_name, const ElfW(Sym) **ref,
 267                              struct link_map *symbol_scope[],
 268                              const char *reference_name,
 269                              const struct r_found_version *version,
 270                              int reloc_type)
 271 {
 272   const unsigned long int hash = _dl_elf_hash (undef_name);
 273   struct sym_val current_value = { 0, NULL };
 274   struct link_map **scope;
 275
 276   /* Search the relevant loaded objects for a definition.  */
 277   for (scope = symbol_scope; *scope; ++scope)
 278     {
 279       int res = do_lookup (undef_name, hash, *ref, &current_value,
 280                            (*scope)->l_searchlist, 0, (*scope)->l_nsearchlist,
 281                            reference_name, version, NULL, reloc_type);
 282       if (res > 0)
 283         break;
 284
 285       if (res < 0)
 286         /* Oh, oh.  The file named in the relocation entry does not
 287            contain the needed symbol.  */
 288         _dl_signal_error (0, *reference_name ? reference_name : NULL,
 289                           make_string ("symbol ", undef_name, ", version ",
 290                                        version->name,
 291                                        " not defined in file ",
 292                                        version->filename,
 293                                        " with link time reference",
 294                                        res == -2
 295                                        ? " (no version symbols)" : ""));
 296     }
 297
 298   if (current_value.s == NULL &&
 299       (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK))
 300     /* We could find no value for a strong reference.  */
 301     _dl_signal_error (0, reference_name,
 302                       make_string (undefined_msg, undef_name,
 303                                    ", version ", version->name ?: NULL));
 304
 305   *ref = current_value.s;
 306   return current_value.a;
 307 }
 308
 309
 310 /* Similar to _dl_lookup_symbol_skip but takes an additional argument
 311    with the version we are looking for.  */
 312 ElfW(Addr)
 313 _dl_lookup_versioned_symbol_skip (const char *undef_name,
 314                                   const ElfW(Sym) **ref,
 315                                   struct link_map *symbol_scope[],
 316                                   const char *reference_name,
 317                                   const struct r_found_version *version,
 318                                   struct link_map *skip_map)
 319 {
 320   const unsigned long int hash = _dl_elf_hash (undef_name);
 321   struct sym_val current_value = { 0, NULL };
 322   struct link_map **scope;
 323   size_t i;
 324
 325   /* Search the relevant loaded objects for a definition.  */
 326   scope = symbol_scope;
 327   for (i = 0; (*scope)->l_dupsearchlist[i] != skip_map; ++i)
 328     assert (i < (*scope)->l_ndupsearchlist);
 329
 330   if (! do_lookup (undef_name, hash, *ref, &current_value,
 331                    (*scope)->l_dupsearchlist, i, (*scope)->l_ndupsearchlist,
 332                    reference_name, version, skip_map, 0))
 333     while (*++scope)
 334       if (do_lookup (undef_name, hash, *ref, &current_value,
 335                      (*scope)->l_dupsearchlist, 0, (*scope)->l_ndupsearchlist,
 336                      reference_name, version, skip_map, 0))
 337         break;
 338
 339   if (current_value.s == NULL &&
 340       (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK))
 341     {
 342       /* We could find no value for a strong reference.  */
 343       const size_t len = strlen (undef_name);
 344       char buf[sizeof undefined_msg + len];
 345       memcpy (buf, undefined_msg, sizeof undefined_msg - 1);
 346       memcpy (&buf[sizeof undefined_msg - 1], undef_name, len + 1);
 347       _dl_signal_error (0, reference_name, buf);
 348     }
 349
 350   *ref = current_value.s;
 351   return current_value.a;
 352 }
 353
 354
 355 /* Cache the location of MAP's hash table.  */
 356
 357 void
 358 _dl_setup_hash (struct link_map *map)
 359 {
 360   ElfW(Symndx) *hash = (void *)(map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr);
 361   ElfW(Symndx) nchain;
 362   map->l_nbuckets = *hash++;
 363   nchain = *hash++;
 364   map->l_buckets = hash;
 365   hash += map->l_nbuckets;
 366   map->l_chain = hash;
 367 }