NetBSD-5.0.2/libexec/ld.elf_so/symbol.c
/* $NetBSD: symbol.c,v 1.47 2008/10/04 09:37:12 skrll Exp $ */
/*
* Copyright 1996 John D. Polstra.
* Copyright 1996 Matt Thomas <matt@3am-software.com>
* Copyright 2002 Charles M. Hannum <root@ihack.net>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by John Polstra.
* 4. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* Dynamic linker for ELF.
*
* John Polstra <jdp@polstra.com>.
*/
#include <sys/cdefs.h>
#ifndef lint
__RCSID("$NetBSD: symbol.c,v 1.47 2008/10/04 09:37:12 skrll Exp $");
#endif /* not lint */
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <dirent.h>
#include "debug.h"
#include "rtld.h"
typedef void (*fptr_t)(void);
static bool
_rtld_is_exported(const Elf_Sym *def)
{
static const fptr_t _rtld_exports[] = {
(fptr_t)dlopen,
(fptr_t)dlclose,
(fptr_t)dlsym,
(fptr_t)dlerror,
(fptr_t)dladdr,
NULL
};
int i;
fptr_t value;
value = (fptr_t)(_rtld_objself.relocbase + def->st_value);
for (i = 0; _rtld_exports[i] != NULL; i++) {
if (value == _rtld_exports[i])
return true;
}
return false;
}
/*
* Hash function for symbol table lookup. Don't even think about changing
* this. It is specified by the System V ABI.
*/
unsigned long
_rtld_elf_hash(const char *name)
{
const unsigned char *p = (const unsigned char *) name;
unsigned long h = 0;
unsigned long g;
unsigned long c;
for (; __predict_true((c = *p) != '\0'); p++) {
h <<= 4;
h += c;
if ((g = h & 0xf0000000) != 0) {
h ^= g;
h ^= g >> 24;
}
}
return (h);
}
const Elf_Sym *
_rtld_symlook_list(const char *name, unsigned long hash, const Objlist *objlist,
const Obj_Entry **defobj_out, bool in_plt)
{
const Elf_Sym *symp;
const Elf_Sym *def;
const Obj_Entry *defobj;
const Objlist_Entry *elm;
def = NULL;
defobj = NULL;
SIMPLEQ_FOREACH(elm, objlist, link) {
rdbg(("search object %p (%s) for %s", elm->obj, elm->obj->path,
name));
if ((symp = _rtld_symlook_obj(name, hash, elm->obj, in_plt))
!= NULL) {
if ((def == NULL) ||
(ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
def = symp;
defobj = elm->obj;
if (ELF_ST_BIND(def->st_info) != STB_WEAK)
break;
}
}
}
if (def != NULL)
*defobj_out = defobj;
return def;
}
/*
* Search the symbol table of a shared object and all objects needed by it for
* a symbol of the given name. Search order is breadth-first. Returns a pointer
* to the symbol, or NULL if no definition was found.
*/
const Elf_Sym *
_rtld_symlook_needed(const char *name, unsigned long hash,
const Needed_Entry *needed, const Obj_Entry **defobj_out, bool inplt)
{
const Elf_Sym *def, *def_w;
const Needed_Entry *n;
const Obj_Entry *obj, *defobj, *defobj1;
def = def_w = NULL;
defobj = NULL;
for (n = needed; n != NULL; n = n->next) {
if ((obj = n->obj) == NULL ||
(def = _rtld_symlook_obj(name, hash, obj, inplt)) == NULL)
continue;
defobj = obj;
if (ELF_ST_BIND(def->st_info) != STB_WEAK) {
*defobj_out = defobj;
return (def);
}
}
/*
* Either the symbol definition has not been found in directly needed
* objects, or the found symbol is weak.
*/
for (n = needed; n != NULL; n = n->next) {
if ((obj = n->obj) == NULL)
continue;
def_w = _rtld_symlook_needed(name, hash, obj->needed, &defobj1,
inplt);
if (def_w == NULL)
continue;
if (def == NULL || ELF_ST_BIND(def_w->st_info) != STB_WEAK) {
def = def_w;
defobj = defobj1;
if (ELF_ST_BIND(def_w->st_info) != STB_WEAK)
break;
}
}
if (def != NULL)
*defobj_out = defobj;
return def;
}
/*
* Search the symbol table of a single shared object for a symbol of
* the given name. Returns a pointer to the symbol, or NULL if no
* definition was found.
*
* The symbol's hash value is passed in for efficiency reasons; that
* eliminates many recomputations of the hash value.
*/
const Elf_Sym *
_rtld_symlook_obj(const char *name, unsigned long hash,
const Obj_Entry *obj, bool in_plt)
{
unsigned long symnum;
for (symnum = obj->buckets[hash % obj->nbuckets];
symnum != ELF_SYM_UNDEFINED;
symnum = obj->chains[symnum]) {
const Elf_Sym *symp;
const char *strp;
assert(symnum < obj->nchains);
symp = obj->symtab + symnum;
strp = obj->strtab + symp->st_name;
rdbg(("check \"%s\" vs \"%s\" in %p", name, strp, obj));
if (name[1] == strp[1] && !strcmp(name, strp)) {
if (symp->st_shndx != SHN_UNDEF)
return symp;
#ifndef __mips__
/*
* XXX DANGER WILL ROBINSON!
* If we have a function pointer in the executable's
* data section, it points to the executable's PLT
* slot, and there is NO relocation emitted. To make
* the function pointer comparable to function pointers
* in shared libraries, we must resolve data references
* in the libraries to point to PLT slots in the
* executable, if they exist.
*/
else if (!in_plt && symp->st_value != 0 &&
ELF_ST_TYPE(symp->st_info) == STT_FUNC)
return symp;
#endif
else
return NULL;
}
}
return NULL;
}
/*
* Given a symbol number in a referencing object, find the corresponding
* definition of the symbol. Returns a pointer to the symbol, or NULL if
* no definition was found. Returns a pointer to the Obj_Entry of the
* defining object via the reference parameter DEFOBJ_OUT.
*/
const Elf_Sym *
_rtld_find_symdef(unsigned long symnum, const Obj_Entry *refobj,
const Obj_Entry **defobj_out, bool in_plt)
{
const Elf_Sym *ref;
const Elf_Sym *def;
const Obj_Entry *defobj;
const char *name;
unsigned long hash;
#ifdef COMBRELOC
/*
* COMBRELOC combines multiple reloc sections and sorts them to make
* dynamic symbol lookup caching possible.
*
* So if the lookup we are doing is the same as the previous lookup
* return the cached results.
*/
static unsigned long last_symnum;
static const Elf_Sym *last_def;
static const Obj_Entry *last_refobj;
static const Obj_Entry *last_defobj;
if (symnum == last_symnum && refobj == last_refobj
&& in_plt == false) {
*defobj_out = last_defobj;
return last_def;
}
#endif
ref = refobj->symtab + symnum;
name = refobj->strtab + ref->st_name;
/*
* We don't have to do a full scale lookup if the symbol is local.
* We know it will bind to the instance in this load module; to
* which we already have a pointer (ie ref).
*/
if (ELF_ST_BIND(ref->st_info) != STB_LOCAL) {
if (ELF_ST_TYPE(ref->st_info) == STT_SECTION) {
_rtld_error("%s: Bogus symbol table entry %lu",
refobj->path, symnum);
}
hash = _rtld_elf_hash(name);
defobj = NULL;
def = _rtld_symlook_default(name, hash, refobj, &defobj, in_plt);
} else {
rdbg(("STB_LOCAL symbol %s in %s", name, refobj->path));
def = ref;
defobj = refobj;
}
/*
* If we found no definition and the reference is weak, treat the
* symbol as having the value zero.
*/
if (def == NULL && ELF_ST_BIND(ref->st_info) == STB_WEAK) {
if (in_plt) {
_rtld_error(
"%s: Trying to call undefined weak symbol `%s'",
refobj->path, name);
}
rdbg((" returning _rtld_sym_zero@_rtld_objself"));
def = &_rtld_sym_zero;
defobj = &_rtld_objself;
}
if (def != NULL) {
*defobj_out = defobj;
#ifdef COMBRELOC
if (in_plt == false) {
/*
* Cache the lookup arguments and results if this was
* non-PLT lookup.
*/
last_symnum = symnum;
last_refobj = refobj;
last_def = def;
last_defobj = defobj;
}
#endif
} else {
rdbg(("lookup failed"));
_rtld_error("%s: Undefined %ssymbol \"%s\" (symnum = %ld)",
refobj->path, in_plt ? "PLT " : "", name, symnum);
}
return def;
}
/*
* Given a symbol name in a referencing object, find the corresponding
* definition of the symbol. Returns a pointer to the symbol, or NULL if
* no definition was found. Returns a pointer to the Obj_Entry of the
* defining object via the reference parameter DEFOBJ_OUT.
*/
const Elf_Sym *
_rtld_symlook_default(const char *name, unsigned long hash,
const Obj_Entry *refobj, const Obj_Entry **defobj_out, bool in_plt)
{
const Elf_Sym *def;
const Elf_Sym *symp;
const Obj_Entry *obj;
const Obj_Entry *defobj;
const Objlist_Entry *elm;
def = NULL;
defobj = NULL;
/* Look first in the referencing object if linked symbolically. */
if (refobj->symbolic) {
rdbg(("search referencing object for %s", name));
symp = _rtld_symlook_obj(name, hash, refobj, in_plt);
if (symp != NULL) {
def = symp;
defobj = refobj;
}
}
/* Search all objects loaded at program start up. */
if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
rdbg(("search _rtld_list_main for %s", name));
symp = _rtld_symlook_list(name, hash, &_rtld_list_main, &obj,
in_plt);
if (symp != NULL &&
(def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
def = symp;
defobj = obj;
}
}
/* Search all RTLD_GLOBAL objects. */
if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
rdbg(("search _rtld_list_global for %s", name));
symp = _rtld_symlook_list(name, hash, &_rtld_list_global,
&obj, in_plt);
if (symp != NULL &&
(def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
def = symp;
defobj = obj;
}
}
/* Search all dlopened DAGs containing the referencing object. */
SIMPLEQ_FOREACH(elm, &refobj->dldags, link) {
if (def != NULL && ELF_ST_BIND(def->st_info) != STB_WEAK)
break;
rdbg(("search DAG with root %p (%s) for %s", elm->obj,
elm->obj->path, name));
symp = _rtld_symlook_list(name, hash, &elm->obj->dagmembers,
&obj, in_plt);
if (symp != NULL &&
(def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
def = symp;
defobj = obj;
}
}
/*
* Search the dynamic linker itself, and possibly resolve the
* symbol from there. This is how the application links to
* dynamic linker services such as dlopen. Only the values listed
* in the "_rtld_exports" array can be resolved from the dynamic
* linker.
*/
if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
rdbg(("Search the dynamic linker itself."));
symp = _rtld_symlook_obj(name, hash, &_rtld_objself, in_plt);
if (symp != NULL && _rtld_is_exported(symp)) {
def = symp;
defobj = &_rtld_objself;
}
}
if (def != NULL)
*defobj_out = defobj;
return def;
}