elf/dl-lookup-direct.c

   1 /* Look up a symbol in a single specified object.
   2    Copyright (C) 1995-2022 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <ldsodefs.h>
  20 #include <string.h>
  21 #include <elf_machine_sym_no_match.h>
  22 #include <dl-hash.h>
  23
  24 /* This function corresponds to do_lookup_x in elf/dl-lookup.c.  The
  25    variant here is simplified because it requires symbol
  26    versioning.  */
  27 static const ElfW(Sym) *
  28 check_match (const struct link_map *const map, const char *const undef_name,
  29              const char *version, uint32_t version_hash,
  30              const Elf_Symndx symidx)
  31 {
  32   const ElfW(Sym) *symtab = (const void *) D_PTR (map, l_info[DT_SYMTAB]);
  33   const ElfW(Sym) *sym = &symtab[symidx];
  34
  35   unsigned int stt = ELFW(ST_TYPE) (sym->st_info);
  36   if (__glibc_unlikely ((sym->st_value == 0 /* No value.  */
  37                          && sym->st_shndx != SHN_ABS
  38                          && stt != STT_TLS)
  39                         || elf_machine_sym_no_match (sym)))
  40     return NULL;
  41
  42   /* Ignore all but STT_NOTYPE, STT_OBJECT, STT_FUNC,
  43      STT_COMMON, STT_TLS, and STT_GNU_IFUNC since these are no
  44      code/data definitions.  */
  45 #define ALLOWED_STT \
  46   ((1 << STT_NOTYPE) | (1 << STT_OBJECT) | (1 << STT_FUNC) \
  47    | (1 << STT_COMMON) | (1 << STT_TLS) | (1 << STT_GNU_IFUNC))
  48   if (__glibc_unlikely (((1 << stt) & ALLOWED_STT) == 0))
  49     return NULL;
  50
  51   const char *strtab = (const void *) D_PTR (map, l_info[DT_STRTAB]);
  52
  53   if (strcmp (strtab + sym->st_name, undef_name) != 0)
  54     /* Not the symbol we are looking for.  */
  55     return NULL;
  56
  57   ElfW(Half) ndx = map->l_versyms[symidx] & 0x7fff;
  58   if (map->l_versions[ndx].hash != version_hash
  59       || strcmp (map->l_versions[ndx].name, version) != 0)
  60     /* It's not the version we want.  */
  61     return NULL;
  62
  63   return sym;
  64 }
  65
  66
  67 /* This function corresponds to do_lookup_x in elf/dl-lookup.c.  The
  68    variant here is simplified because it does not search object
  69    dependencies.  It is optimized for a successful lookup.  */
  70 const ElfW(Sym) *
  71 _dl_lookup_direct (struct link_map *map,
  72                    const char *undef_name, uint32_t new_hash,
  73                    const char *version, uint32_t version_hash)
  74 {
  75   const ElfW(Addr) *bitmask = map->l_gnu_bitmask;
  76   if (__glibc_likely (bitmask != NULL))
  77     {
  78       Elf32_Word bucket = map->l_gnu_buckets[new_hash % map->l_nbuckets];
  79       if (bucket != 0)
  80         {
  81           const Elf32_Word *hasharr = &map->l_gnu_chain_zero[bucket];
  82
  83           do
  84             if (((*hasharr ^ new_hash) >> 1) == 0)
  85               {
  86                 Elf_Symndx symidx = ELF_MACHINE_HASH_SYMIDX (map, hasharr);
  87                 const ElfW(Sym) *sym = check_match (map, undef_name,
  88                                                     version, version_hash,
  89                                                     symidx);
  90                 if (sym != NULL)
  91                   return sym;
  92               }
  93           while ((*hasharr++ & 1u) == 0);
  94         }
  95     }
  96   else
  97     {
  98       /* Fallback code for lack of GNU_HASH support.  */
  99       uint32_t old_hash = _dl_elf_hash (undef_name);
 100
 101       /* Use the old SysV-style hash table.  Search the appropriate
 102          hash bucket in this object's symbol table for a definition
 103          for the same symbol name.  */
 104       for (Elf_Symndx symidx = map->l_buckets[old_hash % map->l_nbuckets];
 105            symidx != STN_UNDEF;
 106            symidx = map->l_chain[symidx])
 107         {
 108           const ElfW(Sym) *sym = check_match (map, undef_name,
 109                                               version, version_hash, symidx);
 110           if (sym != NULL)
 111             return sym;
 112         }
 113     }
 114
 115   return NULL;
 116 }