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