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/* Look up a symbol in the loaded objects.
Copyright (C) 1995, 1996 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 Library General Public License as
published by the Free Software Foundation; either version 2 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
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA. */
#include <stddef.h>
#include <link.h>
#include <assert.h>
#include <string.h>
/* This is the hashing function specified by the ELF ABI. */
static inline unsigned
_dl_elf_hash (const char *name)
{
unsigned long int hash = 0;
while (*name != '\0')
{
unsigned long int hi;
hash = (hash << 4) + *name++;
hi = hash & 0xf0000000;
if (hi != 0)
{
hash ^= hi >> 24;
/* The ELF ABI says `hash &= ~hi', but this is equivalent
in this case and on some machines one insn instead of two. */
hash ^= hi;
}
}
return hash;
}
/* Search loaded objects' symbol tables for a definition of the symbol
UNDEF_NAME. FLAGS is a set of flags. If DL_LOOKUP_NOEXEC is set,
then don't search the executable for a definition; this used for
copy relocs. If DL_LOOKUP_NOPLT is set, then a PLT entry cannot
satisfy the reference; some different binding must be found. */
ElfW(Addr)
_dl_lookup_symbol (const char *undef_name, const ElfW(Sym) **ref,
struct link_map *symbol_scope[],
const char *reference_name,
int flags)
{
const unsigned long int hash = _dl_elf_hash (undef_name);
struct
{
ElfW(Addr) a;
const ElfW(Sym) *s;
} weak_value = { 0, NULL };
size_t i;
struct link_map **scope, *map;
/* Search the relevant loaded objects for a definition. */
for (scope = symbol_scope; *scope; ++scope)
for (i = 0; i < (*scope)->l_nsearchlist; ++i)
{
const ElfW(Sym) *symtab;
const char *strtab;
ElfW(Symndx) symidx;
map = (*scope)->l_searchlist[i];
/* Don't search the executable when resolving a copy reloc. */
if (flags & DL_LOOKUP_NOEXEC && map->l_type == lt_executable)
continue;
symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
/* Search the appropriate hash bucket in this object's symbol table
for a definition for the same symbol name. */
for (symidx = map->l_buckets[hash % map->l_nbuckets];
symidx != STN_UNDEF;
symidx = map->l_chain[symidx])
{
const ElfW(Sym) *sym = &symtab[symidx];
if (sym->st_value == 0 || /* No value. */
((flags & DL_LOOKUP_NOPLT) != 0 /* Reject PLT entry. */
&& sym->st_shndx == SHN_UNDEF))
continue;
switch (ELFW(ST_TYPE) (sym->st_info))
{
case STT_NOTYPE:
case STT_FUNC:
case STT_OBJECT:
break;
default:
/* Not a code/data definition. */
continue;
}
if (sym != *ref && strcmp (strtab + sym->st_name, undef_name))
/* Not the symbol we are looking for. */
continue;
switch (ELFW(ST_BIND) (sym->st_info))
{
case STB_GLOBAL:
/* Global definition. Just what we need. */
*ref = sym;
return map->l_addr;
case STB_WEAK:
/* Weak definition. Use this value if we don't find
another. */
if (! weak_value.s)
{
weak_value.s = sym;
weak_value.a = map->l_addr;
}
break;
default:
/* Local symbols are ignored. */
break;
}
}
}
if (weak_value.s == NULL &&
(*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK))
{
/* We could find no value for a strong reference. */
const char msg[] = "undefined symbol: ";
const size_t len = strlen (undef_name);
char buf[sizeof msg + len];
memcpy (buf, msg, sizeof msg - 1);
memcpy (&buf[sizeof msg - 1], undef_name, len + 1);
_dl_signal_error (0, reference_name, buf);
}
*ref = weak_value.s;
return weak_value.a;
}
/* Cache the location of MAP's hash table. */
void
_dl_setup_hash (struct link_map *map)
{
ElfW(Symndx) *hash = (void *)(map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr);
ElfW(Symndx) nchain;
map->l_nbuckets = *hash++;
nchain = *hash++;
map->l_buckets = hash;
hash += map->l_nbuckets;
map->l_chain = hash;
}
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