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/* Look up a symbol in a single specified object.
Copyright (C) 1995-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <ldsodefs.h>
#include <string.h>
#include <elf_machine_sym_no_match.h>
#include <dl-hash.h>
/* This function corresponds to do_lookup_x in elf/dl-lookup.c. The
variant here is simplified because it requires symbol
versioning. */
static const ElfW(Sym) *
check_match (const struct link_map *const map, const char *const undef_name,
const char *version, uint32_t version_hash,
const Elf_Symndx symidx)
{
const ElfW(Sym) *symtab = (const void *) D_PTR (map, l_info[DT_SYMTAB]);
const ElfW(Sym) *sym = &symtab[symidx];
unsigned int stt = ELFW(ST_TYPE) (sym->st_info);
if (__glibc_unlikely ((sym->st_value == 0 /* No value. */
&& sym->st_shndx != SHN_ABS
&& stt != STT_TLS)
|| elf_machine_sym_no_match (sym)))
return NULL;
/* Ignore all but STT_NOTYPE, STT_OBJECT, STT_FUNC,
STT_COMMON, STT_TLS, and STT_GNU_IFUNC since these are no
code/data definitions. */
#define ALLOWED_STT \
((1 << STT_NOTYPE) | (1 << STT_OBJECT) | (1 << STT_FUNC) \
| (1 << STT_COMMON) | (1 << STT_TLS) | (1 << STT_GNU_IFUNC))
if (__glibc_unlikely (((1 << stt) & ALLOWED_STT) == 0))
return NULL;
const char *strtab = (const void *) D_PTR (map, l_info[DT_STRTAB]);
if (strcmp (strtab + sym->st_name, undef_name) != 0)
/* Not the symbol we are looking for. */
return NULL;
ElfW(Half) ndx = map->l_versyms[symidx] & 0x7fff;
if (map->l_versions[ndx].hash != version_hash
|| strcmp (map->l_versions[ndx].name, version) != 0)
/* It's not the version we want. */
return NULL;
return sym;
}
/* This function corresponds to do_lookup_x in elf/dl-lookup.c. The
variant here is simplified because it does not search object
dependencies. It is optimized for a successful lookup. */
const ElfW(Sym) *
_dl_lookup_direct (struct link_map *map,
const char *undef_name, uint32_t new_hash,
const char *version, uint32_t version_hash)
{
const ElfW(Addr) *bitmask = map->l_gnu_bitmask;
if (__glibc_likely (bitmask != NULL))
{
Elf32_Word bucket = map->l_gnu_buckets[new_hash % map->l_nbuckets];
if (bucket != 0)
{
const Elf32_Word *hasharr = &map->l_gnu_chain_zero[bucket];
do
if (((*hasharr ^ new_hash) >> 1) == 0)
{
Elf_Symndx symidx = ELF_MACHINE_HASH_SYMIDX (map, hasharr);
const ElfW(Sym) *sym = check_match (map, undef_name,
version, version_hash,
symidx);
if (sym != NULL)
return sym;
}
while ((*hasharr++ & 1u) == 0);
}
}
else
{
/* Fallback code for lack of GNU_HASH support. */
uint32_t old_hash = _dl_elf_hash (undef_name);
/* Use the old SysV-style hash table. Search the appropriate
hash bucket in this object's symbol table for a definition
for the same symbol name. */
for (Elf_Symndx symidx = map->l_buckets[old_hash % map->l_nbuckets];
symidx != STN_UNDEF;
symidx = map->l_chain[symidx])
{
const ElfW(Sym) *sym = check_match (map, undef_name,
version, version_hash, symidx);
if (sym != NULL)
return sym;
}
}
return NULL;
}
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