143 lines
4.8 KiB
C
143 lines
4.8 KiB
C
/* On-demand PLT fixup for shared 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 <link.h>
|
||
#include "dynamic-link.h"
|
||
|
||
|
||
/* The global scope we will use for symbol lookups.
|
||
This will be modified by _dl_open if RTLD_GLOBAL is used. */
|
||
struct link_map **_dl_global_scope = _dl_default_scope;
|
||
struct link_map **_dl_global_scope_end = &_dl_default_scope[3];
|
||
|
||
|
||
/* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
|
||
_dl_global_scope that should be passed to _dl_lookup_symbol for symbol
|
||
references made in the object L's relocations. */
|
||
inline struct link_map **
|
||
_dl_object_relocation_scope (struct link_map *l)
|
||
{
|
||
if (l->l_info[DT_SYMBOLIC])
|
||
{
|
||
/* This object's global references are to be resolved first
|
||
in the object itself, and only secondarily in more global
|
||
scopes. */
|
||
|
||
if (! l->l_searchlist)
|
||
/* We must construct the searchlist for this object. */
|
||
_dl_map_object_deps (l);
|
||
|
||
/* The primary scope is this object itself and its
|
||
dependencies. */
|
||
_dl_global_scope[0] = l;
|
||
|
||
/* Secondary is the dependency tree that reached L; the object
|
||
requested directly by the user is at the root of that tree. */
|
||
while (l->l_loader)
|
||
l = l->l_loader;
|
||
_dl_global_scope[1] = l;
|
||
|
||
/* Finally, the global scope follows. */
|
||
|
||
return _dl_global_scope;
|
||
}
|
||
else
|
||
{
|
||
/* Use first the global scope, and then the scope of the root of the
|
||
dependency tree that first caused this object to be loaded. */
|
||
while (l->l_loader)
|
||
l = l->l_loader;
|
||
*_dl_global_scope_end = l;
|
||
return &_dl_global_scope[2];
|
||
}
|
||
}
|
||
|
||
/* Figure out the right type, Rel or Rela. */
|
||
#define elf_machine_rel 1
|
||
#define elf_machine_rela 2
|
||
#if elf_machine_relplt == elf_machine_rel
|
||
#define PLTREL ElfW(Rel)
|
||
#elif elf_machine_relplt == elf_machine_rela
|
||
#define PLTREL ElfW(Rela)
|
||
#else
|
||
#error "dl-machine.h bug: elf_machine_relplt not rel or rela"
|
||
#endif
|
||
#undef elf_machine_rel
|
||
#undef elf_machine_rela
|
||
|
||
/* We need to define the function as a local symbol so that the reference
|
||
in the trampoline code will be a local PC-relative call. Tell the
|
||
compiler not to worry that the function appears not to be called. */
|
||
|
||
static ElfW(Addr) fixup (
|
||
#ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
|
||
ELF_MACHINE_RUNTIME_FIXUP_ARGS,
|
||
#endif
|
||
struct link_map *l, ElfW(Word) reloc_offset)
|
||
__attribute__ ((unused));
|
||
|
||
/* 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. */
|
||
|
||
static ElfW(Addr)
|
||
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 ElfW(Sym) *) (l->l_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);
|
||
const char *strtab =
|
||
(const char *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
|
||
|
||
const PLTREL *const reloc
|
||
= (const void *) (l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr +
|
||
reloc_offset);
|
||
|
||
/* Set up the scope to find symbols referenced by this object. */
|
||
struct link_map **scope = _dl_object_relocation_scope (l);
|
||
|
||
/* Perform the specified relocation. */
|
||
ElfW(Addr) resolve (const ElfW(Sym) **ref,
|
||
ElfW(Addr) reloc_addr, int noplt)
|
||
{
|
||
return _dl_lookup_symbol (strtab + (*ref)->st_name, ref,
|
||
scope, l->l_name, reloc_addr, noplt);
|
||
}
|
||
elf_machine_relplt (l, reloc, &symtab[ELFW(R_SYM) (reloc->r_info)], resolve);
|
||
|
||
*_dl_global_scope_end = NULL;
|
||
|
||
/* Return the address that was written by the relocation. */
|
||
return *(ElfW(Addr) *) (l->l_addr + reloc->r_offset);
|
||
}
|
||
|
||
|
||
/* 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
|