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.  Don't use a PLT defn in UNDEF_MAP, since
  27    that is the object making the reference.  */
  28
  29 Elf32_Addr
  30 _dl_lookup_symbol (const char *undef_name, const Elf32_Sym **ref,
  31                    struct link_map *symbol_scope,
  32                    const char *reference_name)
  33 {
  34   unsigned long int hash = elf_hash (undef_name);
  35   struct link_map *map;
  36   struct
  37     {
  38       Elf32_Addr a;
  39       const Elf32_Sym *s;
  40     } weak_value = { 0, NULL };
  41
  42   /* Search the relevant loaded objects for a definition.  */
  43   for (map = symbol_scope; map; map = map->l_next)
  44     {
  45       const Elf32_Sym *symtab;
  46       const char *strtab;
  47       Elf32_Word symidx;
  48
  49       symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
  50       strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
  51
  52       /* Search the appropriate hash bucket in this object's symbol table
  53          for a definition for the same symbol name.  */
  54       for (symidx = map->l_buckets[hash % map->l_nbuckets];
  55            symidx != STN_UNDEF;
  56            symidx = map->l_chain[symidx])
  57         {
  58           const Elf32_Sym *sym = &symtab[symidx];
  59
  60           if (sym->st_value == 0)
  61             continue;
  62
  63           switch (ELF32_ST_TYPE (sym->st_info))
  64             {
  65             case STT_NOTYPE:
  66             case STT_FUNC:
  67             case STT_OBJECT:
  68               break;
  69             default:
  70               /* Not a code/data definition.  */
  71               continue;
  72             }
  73
  74           if (sym->st_shndx == SHN_UNDEF)
  75             /* This is the same symbol we are looking for the value for.
  76                If it is a PLT entry, it will have a value of its own;
  77                but that is not what we are looking for.  */
  78               continue;
  79
  80           if (sym != *ref && strcmp (strtab + sym->st_name, undef_name))
  81             /* Not the symbol we are looking for.  */
  82             continue;
  83
  84           switch (ELF32_ST_BIND (sym->st_info))
  85             {
  86             case STB_GLOBAL:
  87               /* Global definition.  Just what we need.  */
  88               *ref = sym;
  89               return map->l_addr;
  90             case STB_WEAK:
  91               /* Weak definition.  Use this value if we don't find another.  */
  92               if (weak_value.a == 0)
  93                 {
  94                   weak_value.s = sym;
  95                   weak_value.a = map->l_addr;
  96                 }
  97               break;
  98             default:
  99               /* Local symbols are ignored.  */
 100               break;
 101             }
 102         }
 103     }
 104
 105   if (weak_value.s == NULL)
 106     {
 107       const char msg[] = "undefined symbol: ";
 108       char buf[sizeof msg + strlen (undef_name)];
 109       memcpy (buf, msg, sizeof msg - 1);
 110       memcpy (&buf[sizeof msg - 1], undef_name, sizeof buf - sizeof msg + 1);
 111       _dl_signal_error (0, reference_name, buf);
 112     }
 113
 114   *ref = weak_value.s;
 115   return weak_value.a;
 116 }
 117
 118
 119 /* Cache the location of MAP's hash table.  */
 120
 121 void
 122 _dl_setup_hash (struct link_map *map)
 123 {
 124   Elf32_Word *hash = (void *) map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr;
 125   Elf32_Word nchain;
 126   map->l_nbuckets = *hash++;
 127   nchain = *hash++;
 128   map->l_buckets = hash;
 129   hash += map->l_nbuckets;
 130   map->l_chain = hash;
 131 }