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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 <libelf.h>
#include <link.h>
#include <assert.h>
/* Search loaded objects' symbol tables for a definition of the symbol
UNDEF_NAME. The chosen value can't be RELOC_ADDR. If NOPLT is nonzero,
then a PLT entry cannot satisfy the reference; some different binding
must be found. */
Elf32_Addr
_dl_lookup_symbol (const char *undef_name, const Elf32_Sym **ref,
struct link_map *symbol_scope[2],
const char *reference_name,
Elf32_Addr reloc_addr,
int noplt)
{
unsigned long int hash = elf_hash (undef_name);
struct
{
Elf32_Addr a;
const Elf32_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 < &symbol_scope[2]; ++scope)
if (*scope)
for (i = 0; i < (*scope)->l_nsearchlist; ++i)
{
const Elf32_Sym *symtab;
const char *strtab;
Elf32_Word symidx;
map = (*scope)->l_searchlist[i];
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 Elf32_Sym *sym = &symtab[symidx];
if (sym->st_value == 0 || /* No value. */
/* Cannot resolve to the location being filled in. */
reloc_addr == map->l_addr + sym->st_value ||
(noplt && sym->st_shndx == SHN_UNDEF)) /* Reject PLT. */
continue;
switch (ELF32_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 (ELF32_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 && ELF32_ST_BIND ((*ref)->st_info) != STB_WEAK)
{
/* The symbol was not defined by any object in scope. To allow
access to dynamic linker functionality without using -ldl and
thereby brining the dynamic linker's symbols into scope, we
recognize a few magical symbol names and resolve them to the
addresses of functions inside the dynamic linker. */
struct magic
{
unsigned long int hash;
const char *name;
Elf32_Addr value;
};
static struct magic magic[] =
{
{ 0xd6a2a5e, "_GNU_libc_dl_open", (Elf32_Addr) &_dl_open },
{ 0x69ef845, "_GNU_libc_dl_close", (Elf32_Addr) &_dl_close },
{ 0xae4d63c, "_GNU_libc_dl_symbol", (Elf32_Addr) &_dl_symbol_value },
{ 0, NULL, 0 }
};
struct magic *m;
for (m = magic; m->hash; ++m)
if (hash == m->hash && !strcmp (name, m->name))
return m->value;
{
const char msg[] = "undefined symbol: ";
char buf[sizeof msg + strlen (undef_name)];
memcpy (buf, msg, sizeof msg - 1);
memcpy (&buf[sizeof msg - 1], undef_name,
sizeof buf - sizeof msg + 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)
{
Elf32_Word *hash = (void *) map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr;
Elf32_Word nchain;
map->l_nbuckets = *hash++;
nchain = *hash++;
map->l_buckets = hash;
hash += map->l_nbuckets;
map->l_chain = hash;
}
/* Look up symbol NAME in MAP's scope and return its run-time address. */
Elf32_Addr
_dl_symbol_value (struct link_map *map, const char *name)
{
Elf32_Addr loadbase;
const Elf32_Sym *ref = NULL;
struct link_map *scope[2] = { map, NULL };
loadbase = _dl_lookup_symbol (name, &ref, scope, map->l_name, 0, 0);
return loadbase + ref->st_value;
}
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