elf/dl-lookup.c

   1 /* Look up a symbol in the loaded objects.
   2 Copyright (C) 1995, 1996 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 the symbol
  26    UNDEF_NAME.  If NOPLT is nonzero, then a PLT entry cannot satisfy the
  27    reference; some different binding must be found.  */
  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                    int noplt)
  34 {
  35   unsigned long int hash = elf_hash (undef_name);
  36   struct link_map *map;
  37   struct
  38     {
  39       Elf32_Addr a;
  40       const Elf32_Sym *s;
  41     } weak_value = { 0, NULL };
  42
  43   /* Search the relevant loaded objects for a definition.  */
  44   for (map = symbol_scope; map; map = map->l_next)
  45     {
  46       const Elf32_Sym *symtab;
  47       const char *strtab;
  48       Elf32_Word symidx;
  49
  50       symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
  51       strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
  52
  53       /* Search the appropriate hash bucket in this object's symbol table
  54          for a definition for the same symbol name.  */
  55       for (symidx = map->l_buckets[hash % map->l_nbuckets];
  56            symidx != STN_UNDEF;
  57            symidx = map->l_chain[symidx])
  58         {
  59           const Elf32_Sym *sym = &symtab[symidx];
  60
  61           if (sym->st_value == 0 || /* No value.  */
  62               (noplt && sym->st_shndx == SHN_UNDEF)) /* Unwanted PLT entry.  */
  63             continue;
  64
  65           switch (ELF32_ST_TYPE (sym->st_info))
  66             {
  67             case STT_NOTYPE:
  68             case STT_FUNC:
  69             case STT_OBJECT:
  70               break;
  71             default:
  72               /* Not a code/data definition.  */
  73               continue;
  74             }
  75
  76           if (sym != *ref && strcmp (strtab + sym->st_name, undef_name))
  77             /* Not the symbol we are looking for.  */
  78             continue;
  79
  80           switch (ELF32_ST_BIND (sym->st_info))
  81             {
  82             case STB_GLOBAL:
  83               /* Global definition.  Just what we need.  */
  84               *ref = sym;
  85               return map->l_addr;
  86             case STB_WEAK:
  87               /* Weak definition.  Use this value if we don't find another.  */
  88               if (! weak_value.s)
  89                 {
  90                   weak_value.s = sym;
  91                   weak_value.a = map->l_addr;
  92                 }
  93               break;
  94             default:
  95               /* Local symbols are ignored.  */
  96               break;
  97             }
  98         }
  99     }
 100
 101   if (weak_value.s == NULL && ELF32_ST_BIND ((*ref)->st_info) != STB_WEAK)
 102     {
 103       const char msg[] = "undefined symbol: ";
 104       char buf[sizeof msg + strlen (undef_name)];
 105       memcpy (buf, msg, sizeof msg - 1);
 106       memcpy (&buf[sizeof msg - 1], undef_name, sizeof buf - sizeof msg + 1);
 107       _dl_signal_error (0, reference_name, buf);
 108     }
 109
 110   *ref = weak_value.s;
 111   return weak_value.a;
 112 }
 113
 114
 115 /* Cache the location of MAP's hash table.  */
 116
 117 void
 118 _dl_setup_hash (struct link_map *map)
 119 {
 120   Elf32_Word *hash = (void *) map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr;
 121   Elf32_Word nchain;
 122   map->l_nbuckets = *hash++;
 123   nchain = *hash++;
 124   map->l_buckets = hash;
 125   hash += map->l_nbuckets;
 126   map->l_chain = hash;
 127 }