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/* On-demand PLT fixup for shared objects.
Copyright (C) 1995-1999, 2000 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., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
#include <alloca.h>
#include <stdlib.h>
#include <unistd.h>
#include <ldsodefs.h>
#include "dynamic-link.h"
#if !defined ELF_MACHINE_NO_RELA || ELF_MACHINE_NO_REL
# define PLTREL ElfW(Rela)
#else
# define PLTREL ElfW(Rel)
#endif
#ifndef VERSYMIDX
# define VERSYMIDX(sym) (DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (sym))
#endif
/* This function is called through a special trampoline from the PLT the
first time each PLT entry is called. We must perform the relocation
specified in the PLT of the given shared object, and return the resolved
function address to the trampoline, which will restart the original call
to that address. Future calls will bounce directly from the PLT to the
function. */
#ifndef ELF_MACHINE_NO_PLT
static ElfW(Addr) __attribute__ ((unused))
fixup (
# ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
ELF_MACHINE_RUNTIME_FIXUP_ARGS,
# endif
struct link_map *l, ElfW(Word) reloc_offset)
{
const ElfW(Sym) *const symtab
= (const void *) D_PTR (l, l_info[DT_SYMTAB]);
const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
const PLTREL *const reloc
= (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
lookup_t result;
ElfW(Addr) value;
/* The use of `alloca' here looks ridiculous but it helps. The goal is
to prevent the function from being inlined and thus optimized out.
There is no official way to do this so we use this trick. gcc never
inlines functions which use `alloca'. */
alloca (sizeof (int));
/* Sanity check that we're really looking at a PLT relocation. */
assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
/* Look up the target symbol. If the normal lookup rules are not
used don't look in the global scope. */
if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
{
switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
{
default:
{
const ElfW(Half) *vernum =
(const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
const struct r_found_version *version = &l->l_versions[ndx];
if (version->hash != 0)
{
result = _dl_lookup_versioned_symbol (strtab + sym->st_name,
l, &sym, l->l_scope,
version,
ELF_MACHINE_JMP_SLOT);
break;
}
}
case 0:
result = _dl_lookup_symbol (strtab + sym->st_name, l, &sym,
l->l_scope, ELF_MACHINE_JMP_SLOT);
}
/* Currently result contains the base load address (or link map)
of the object that defines sym. Now add in the symbol
offset. */
value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0);
}
else
{
/* We already found the symbol. The module (and therefore its load
address) is also known. */
value = l->l_addr + sym->st_value;
#ifdef DL_LOOKUP_RETURNS_MAP
result = l;
#endif
}
/* And now perhaps the relocation addend. */
value = elf_machine_plt_value (l, reloc, value);
/* Finally, fix up the plt itself. */
return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
}
#endif
#if !defined PROF && !defined ELF_MACHINE_NO_PLT
static ElfW(Addr) __attribute__ ((unused))
profile_fixup (
#ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
ELF_MACHINE_RUNTIME_FIXUP_ARGS,
#endif
struct link_map *l, ElfW(Word) reloc_offset, ElfW(Addr) retaddr)
{
void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount;
ElfW(Addr) *resultp;
lookup_t result;
ElfW(Addr) value;
/* The use of `alloca' here looks ridiculous but it helps. The goal is
to prevent the function from being inlined, and thus optimized out.
There is no official way to do this so we use this trick. gcc never
inlines functions which use `alloca'. */
alloca (sizeof (int));
/* This is the address in the array where we store the result of previous
relocations. */
resultp = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
value = *resultp;
if (value == 0)
{
/* This is the first time we have to relocate this object. */
const ElfW(Sym) *const symtab
= (const void *) D_PTR (l, l_info[DT_SYMTAB]);
const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
const PLTREL *const reloc
= (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
/* Sanity check that we're really looking at a PLT relocation. */
assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
/* Look up the target symbol. If the symbol is marked STV_PROTECTED
don't look in the global scope. */
if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
{
switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
{
default:
{
const ElfW(Half) *vernum =
(const void *) D_PTR (l,l_info[VERSYMIDX (DT_VERSYM)]);
ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
const struct r_found_version *version = &l->l_versions[ndx];
if (version->hash != 0)
{
result = _dl_lookup_versioned_symbol(strtab + sym->st_name,
l, &sym, l->l_scope,
version,
ELF_MACHINE_JMP_SLOT);
break;
}
}
case 0:
result = _dl_lookup_symbol (strtab + sym->st_name, l, &sym,
l->l_scope, ELF_MACHINE_JMP_SLOT);
}
/* Currently result contains the base load address (or link map)
of the object that defines sym. Now add in the symbol
offset. */
value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0);
}
else
{
/* We already found the symbol. The module (and therefore its load
address) is also known. */
value = l->l_addr + sym->st_value;
#ifdef DL_LOOKUP_RETURNS_MAP
result = l;
#endif
}
/* And now perhaps the relocation addend. */
value = elf_machine_plt_value (l, reloc, value);
/* Store the result for later runs. */
*resultp = value;
}
(*mcount_fct) (retaddr, value);
return value;
}
#endif /* PROF && ELF_MACHINE_NO_PLT */
/* This macro is defined in dl-machine.h to define the entry point called
by the PLT. The `fixup' function above does the real work, but a little
more twiddling is needed to get the stack right and jump to the address
finally resolved. */
ELF_MACHINE_RUNTIME_TRAMPOLINE
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