178 lines
5.1 KiB
C
178 lines
5.1 KiB
C
/* Look up a symbol in the loaded objects.
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Copyright (C) 1995, 1996 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, write to the Free Software Foundation, Inc., 675 Mass Ave,
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Cambridge, MA 02139, USA. */
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#include <stddef.h>
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#include <libelf.h>
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#include <link.h>
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#include <assert.h>
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/* Search loaded objects' symbol tables for a definition of the symbol
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UNDEF_NAME. The chosen value can't be RELOC_ADDR. If NOPLT is nonzero,
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then a PLT entry cannot satisfy the reference; some different binding
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must be found. */
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Elf32_Addr
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_dl_lookup_symbol (const char *undef_name, const Elf32_Sym **ref,
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struct link_map *symbol_scope[2],
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const char *reference_name,
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Elf32_Addr reloc_addr,
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int noplt)
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{
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unsigned long int hash = elf_hash (undef_name);
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struct
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{
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Elf32_Addr a;
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const Elf32_Sym *s;
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} weak_value = { 0, NULL };
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size_t i;
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struct link_map **scope, *map;
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/* Search the relevant loaded objects for a definition. */
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for (scope = symbol_scope; scope < &symbol_scope[2]; ++scope)
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if (*scope)
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for (i = 0; i < (*scope)->l_nsearchlist; ++i)
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{
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const Elf32_Sym *symtab;
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const char *strtab;
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Elf32_Word symidx;
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map = (*scope)->l_searchlist[i];
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symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
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strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
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/* Search the appropriate hash bucket in this object's symbol table
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for a definition for the same symbol name. */
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for (symidx = map->l_buckets[hash % map->l_nbuckets];
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symidx != STN_UNDEF;
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symidx = map->l_chain[symidx])
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{
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const Elf32_Sym *sym = &symtab[symidx];
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if (sym->st_value == 0 || /* No value. */
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/* Cannot resolve to the location being filled in. */
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reloc_addr == map->l_addr + sym->st_value ||
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(noplt && sym->st_shndx == SHN_UNDEF)) /* Reject PLT. */
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continue;
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switch (ELF32_ST_TYPE (sym->st_info))
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{
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case STT_NOTYPE:
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case STT_FUNC:
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case STT_OBJECT:
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break;
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default:
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/* Not a code/data definition. */
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continue;
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}
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if (sym != *ref && strcmp (strtab + sym->st_name, undef_name))
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/* Not the symbol we are looking for. */
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continue;
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switch (ELF32_ST_BIND (sym->st_info))
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{
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case STB_GLOBAL:
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/* Global definition. Just what we need. */
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*ref = sym;
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return map->l_addr;
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case STB_WEAK:
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/* Weak definition. Use this value if we don't find
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another. */
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if (! weak_value.s)
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{
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weak_value.s = sym;
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weak_value.a = map->l_addr;
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}
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break;
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default:
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/* Local symbols are ignored. */
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break;
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}
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}
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}
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if (weak_value.s == NULL && ELF32_ST_BIND ((*ref)->st_info) != STB_WEAK)
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{
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/* The symbol was not defined by any object in scope. To allow
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access to dynamic linker functionality without using -ldl and
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thereby brining the dynamic linker's symbols into scope, we
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recognize a few magical symbol names and resolve them to the
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addresses of functions inside the dynamic linker. */
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struct magic
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{
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unsigned long int hash;
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const char *name;
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Elf32_Addr value;
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};
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static struct magic magic[] =
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{
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{ 0xd6a2a5e, "_GNU_libc_dl_open", (Elf32_Addr) &_dl_open },
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/* { 0x69ef845, "_GNU_libc_dl_close", (Elf32_Addr) &_dl_close },*/
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{ 0xae4d63c, "_GNU_libc_dl_symbol", (Elf32_Addr) &_dl_symbol_value },
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{ 0, NULL, 0 }
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};
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struct magic *m;
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for (m = magic; m->hash; ++m)
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if (hash == m->hash && !strcmp (undef_name, m->name))
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return m->value;
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{
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const char msg[] = "undefined symbol: ";
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char buf[sizeof msg + strlen (undef_name)];
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memcpy (buf, msg, sizeof msg - 1);
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memcpy (&buf[sizeof msg - 1], undef_name,
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sizeof buf - sizeof msg + 1);
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_dl_signal_error (0, reference_name, buf);
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}
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}
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*ref = weak_value.s;
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return weak_value.a;
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}
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/* Cache the location of MAP's hash table. */
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void
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_dl_setup_hash (struct link_map *map)
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{
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Elf32_Word *hash = (void *) map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr;
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Elf32_Word nchain;
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map->l_nbuckets = *hash++;
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nchain = *hash++;
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map->l_buckets = hash;
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hash += map->l_nbuckets;
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map->l_chain = hash;
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}
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/* Look up symbol NAME in MAP's scope and return its run-time address. */
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Elf32_Addr
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_dl_symbol_value (struct link_map *map, const char *name)
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{
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Elf32_Addr loadbase;
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const Elf32_Sym *ref = NULL;
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struct link_map *scope[2] = { map, NULL };
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loadbase = _dl_lookup_symbol (name, &ref, scope, map->l_name, 0, 0);
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return loadbase + ref->st_value;
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}
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