elf/dl-lookup.c

   1 /* Look up a symbol in the loaded objects.
   2 Copyright (C) 1995 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
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, USA.  */
  19
  20 #include <stddef.h>
  21 #include <libelf.h>
  22 #include <link.h>
  23 #include <assert.h>
  24
  25 /* Search loaded objects' symbol tables for a definition of
  26    the symbol UNDEF_NAME.  If NOSELF is nonzero, then *REF
  27    cannot satisfy the reference itself; some different binding
  28    must be found.  */
  29
  30 Elf32_Addr
  31 _dl_lookup_symbol (const char *undef_name, const Elf32_Sym **ref,
  32                    struct link_map *symbol_scope,
  33                    const char *reference_name,
  34                    int noself)
  35 {
  36   unsigned long int hash = elf_hash (undef_name);
  37   struct link_map *map;
  38   struct
  39     {
  40       Elf32_Addr a;
  41       const Elf32_Sym *s;
  42     } weak_value = { 0, NULL };
  43
  44   /* Search the relevant loaded objects for a definition.  */
  45   for (map = symbol_scope; map; map = map->l_next)
  46     {
  47       const Elf32_Sym *symtab;
  48       const char *strtab;
  49       Elf32_Word symidx;
  50
  51       symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
  52       strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
  53
  54       /* Search the appropriate hash bucket in this object's symbol table
  55          for a definition for the same symbol name.  */
  56       for (symidx = map->l_buckets[hash % map->l_nbuckets];
  57            symidx != STN_UNDEF;
  58            symidx = map->l_chain[symidx])
  59         {
  60           const Elf32_Sym *sym = &symtab[symidx];
  61
  62           if (sym->st_value == 0 || /* No value.  */
  63               sym->st_shndx == SHN_UNDEF || /* PLT entry.  */
  64               (noself && sym == *ref))  /* The reference can't define it.  */
  65             continue;
  66
  67           switch (ELF32_ST_TYPE (sym->st_info))
  68             {
  69             case STT_NOTYPE:
  70             case STT_FUNC:
  71             case STT_OBJECT:
  72               break;
  73             default:
  74               /* Not a code/data definition.  */
  75               continue;
  76             }
  77
  78           if (sym != *ref && strcmp (strtab + sym->st_name, undef_name))
  79             /* Not the symbol we are looking for.  */
  80             continue;
  81
  82           switch (ELF32_ST_BIND (sym->st_info))
  83             {
  84             case STB_GLOBAL:
  85               /* Global definition.  Just what we need.  */
  86               *ref = sym;
  87               return map->l_addr;
  88             case STB_WEAK:
  89               /* Weak definition.  Use this value if we don't find another.  */
  90               if (! weak_value.s)
  91                 {
  92                   weak_value.s = sym;
  93                   weak_value.a = map->l_addr;
  94                 }
  95               break;
  96             default:
  97               /* Local symbols are ignored.  */
  98               break;
  99             }
 100         }
 101     }
 102
 103   if (weak_value.s == NULL && ELF32_ST_BIND ((*ref)->st_info) != STB_WEAK)
 104     {
 105       const char msg[] = "undefined symbol: ";
 106       char buf[sizeof msg + strlen (undef_name)];
 107       memcpy (buf, msg, sizeof msg - 1);
 108       memcpy (&buf[sizeof msg - 1], undef_name, sizeof buf - sizeof msg + 1);
 109       _dl_signal_error (0, reference_name, buf);
 110     }
 111
 112   *ref = weak_value.s;
 113   return weak_value.a;
 114 }
 115
 116
 117 /* Cache the location of MAP's hash table.  */
 118
 119 void
 120 _dl_setup_hash (struct link_map *map)
 121 {
 122   Elf32_Word *hash = (void *) map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr;
 123   Elf32_Word nchain;
 124   map->l_nbuckets = *hash++;
 125   nchain = *hash++;
 126   map->l_buckets = hash;
 127   hash += map->l_nbuckets;
 128   map->l_chain = hash;
 129 }