365 lines
10 KiB
C
365 lines
10 KiB
C
/* $NetBSD: symbol.c,v 1.42 2007/02/23 01:16:32 matt Exp $ */
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/*
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* Copyright 1996 John D. Polstra.
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* Copyright 1996 Matt Thomas <matt@3am-software.com>
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* Copyright 2002 Charles M. Hannum <root@ihack.net>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by John Polstra.
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* 4. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* Dynamic linker for ELF.
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*
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* John Polstra <jdp@polstra.com>.
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*/
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#include <sys/cdefs.h>
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#ifndef lint
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__RCSID("$NetBSD: symbol.c,v 1.42 2007/02/23 01:16:32 matt Exp $");
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#endif /* not lint */
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#include <err.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <stdarg.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/mman.h>
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#include <dirent.h>
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#include "debug.h"
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#include "rtld.h"
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typedef void (*fptr_t)(void);
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static bool
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_rtld_is_exported(const Elf_Sym *def)
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{
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static fptr_t _rtld_exports[] = {
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(fptr_t)dlopen,
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(fptr_t)dlclose,
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(fptr_t)dlsym,
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(fptr_t)dlerror,
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(fptr_t)dladdr,
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NULL
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};
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int i;
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fptr_t value;
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value = (fptr_t)(_rtld_objself.relocbase + def->st_value);
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for (i = 0; _rtld_exports[i] != NULL; i++) {
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if (value == _rtld_exports[i])
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return true;
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}
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return false;
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}
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/*
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* Hash function for symbol table lookup. Don't even think about changing
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* this. It is specified by the System V ABI.
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*/
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unsigned long
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_rtld_elf_hash(const char *name)
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{
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const unsigned char *p = (const unsigned char *) name;
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unsigned long h = 0;
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unsigned long g;
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unsigned long c;
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for (; __predict_true((c = *p) != '\0'); p++) {
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h <<= 4;
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h += c;
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if ((g = h & 0xf0000000) != 0) {
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h ^= g;
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h ^= g >> 24;
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}
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}
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return (h);
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}
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const Elf_Sym *
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_rtld_symlook_list(const char *name, unsigned long hash, const Objlist *objlist,
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const Obj_Entry **defobj_out, bool in_plt)
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{
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const Elf_Sym *symp;
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const Elf_Sym *def;
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const Obj_Entry *defobj;
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const Objlist_Entry *elm;
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def = NULL;
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defobj = NULL;
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SIMPLEQ_FOREACH(elm, objlist, link) {
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rdbg(("search object %p (%s)", elm->obj, elm->obj->path));
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if ((symp = _rtld_symlook_obj(name, hash, elm->obj, in_plt))
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!= NULL) {
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if ((def == NULL) ||
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(ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
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def = symp;
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defobj = elm->obj;
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if (ELF_ST_BIND(def->st_info) != STB_WEAK)
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break;
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}
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}
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}
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if (def != NULL)
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*defobj_out = defobj;
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return def;
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}
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/*
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* Search the symbol table of a single shared object for a symbol of
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* the given name. Returns a pointer to the symbol, or NULL if no
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* definition was found.
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*
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* The symbol's hash value is passed in for efficiency reasons; that
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* eliminates many recomputations of the hash value.
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*/
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const Elf_Sym *
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_rtld_symlook_obj(const char *name, unsigned long hash,
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const Obj_Entry *obj, bool in_plt)
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{
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unsigned long symnum;
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for (symnum = obj->buckets[hash % obj->nbuckets];
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symnum != ELF_SYM_UNDEFINED;
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symnum = obj->chains[symnum]) {
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const Elf_Sym *symp;
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const char *strp;
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assert(symnum < obj->nchains);
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symp = obj->symtab + symnum;
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strp = obj->strtab + symp->st_name;
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rdbg(("check \"%s\" vs \"%s\" in %p", name, strp, obj));
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if (name[1] == strp[1] && !strcmp(name, strp)) {
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if (symp->st_shndx != SHN_UNDEF)
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return symp;
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#ifndef __mips__
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/*
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* XXX DANGER WILL ROBINSON!
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* If we have a function pointer in the executable's
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* data section, it points to the executable's PLT
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* slot, and there is NO relocation emitted. To make
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* the function pointer comparable to function pointers
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* in shared libraries, we must resolve data references
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* in the libraries to point to PLT slots in the
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* executable, if they exist.
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*/
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else if (!in_plt && symp->st_value != 0 &&
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ELF_ST_TYPE(symp->st_info) == STT_FUNC)
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return symp;
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#endif
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else
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return NULL;
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}
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}
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return NULL;
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}
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/*
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* Given a symbol number in a referencing object, find the corresponding
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* definition of the symbol. Returns a pointer to the symbol, or NULL if
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* no definition was found. Returns a pointer to the Obj_Entry of the
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* defining object via the reference parameter DEFOBJ_OUT.
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*/
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const Elf_Sym *
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_rtld_find_symdef(unsigned long symnum, const Obj_Entry *refobj,
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const Obj_Entry **defobj_out, bool in_plt)
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{
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const Elf_Sym *ref;
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const Elf_Sym *def;
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const Obj_Entry *defobj;
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const char *name;
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unsigned long hash;
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#ifdef COMBRELOC
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/*
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* COMBRELOC combines multiple reloc sections and sorts them to make
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* dynamic symbol lookup caching possible.
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*
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* So if the lookup we are doing is the same as the previous lookup
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* return the cached results.
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*/
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static unsigned long last_symnum;
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static const Elf_Sym *last_def;
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static const Obj_Entry *last_refobj;
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static const Obj_Entry *last_defobj;
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if (symnum == last_symnum && refobj == last_refobj
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&& in_plt == false) {
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*defobj_out = last_defobj;
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return last_def;
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}
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#endif
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ref = refobj->symtab + symnum;
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name = refobj->strtab + ref->st_name;
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/*
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* We don't have to do a full scale lookup if the symbol is local.
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* We know it will bind to the instance in this load module; to
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* which we already have a pointer (ie ref).
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*/
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if (ELF_ST_BIND(ref->st_info) != STB_LOCAL) {
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if (ELF_ST_TYPE(ref->st_info) == STT_SECTION) {
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_rtld_error("%s: Bogus symbol table entry %lu",
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refobj->path, symnum);
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}
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hash = _rtld_elf_hash(name);
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defobj = NULL;
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def = _rtld_symlook_default(name, hash, refobj, &defobj, in_plt);
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} else {
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rdbg(("STB_LOCAL symbol %s in %s", name, refobj->path));
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def = ref;
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defobj = refobj;
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}
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/*
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* If we found no definition and the reference is weak, treat the
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* symbol as having the value zero.
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*/
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if (def == NULL && ELF_ST_BIND(ref->st_info) == STB_WEAK) {
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rdbg((" returning _rtld_sym_zero@_rtld_objmain"));
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def = &_rtld_sym_zero;
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defobj = _rtld_objmain;
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}
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if (def != NULL) {
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*defobj_out = defobj;
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#ifdef COMBRELOC
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if (in_plt == false) {
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/*
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* Cache the lookup arguments and results if this was
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* non-PLT lookup.
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*/
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last_symnum = symnum;
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last_refobj = refobj;
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last_def = def;
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last_defobj = defobj;
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}
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#endif
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} else {
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rdbg(("lookup failed"));
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_rtld_error("%s: Undefined %ssymbol \"%s\" (symnum = %ld)",
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refobj->path, in_plt ? "PLT " : "", name, symnum);
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}
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return def;
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}
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/*
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* Given a symbol name in a referencing object, find the corresponding
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* definition of the symbol. Returns a pointer to the symbol, or NULL if
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* no definition was found. Returns a pointer to the Obj_Entry of the
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* defining object via the reference parameter DEFOBJ_OUT.
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*/
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const Elf_Sym *
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_rtld_symlook_default(const char *name, unsigned long hash,
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const Obj_Entry *refobj, const Obj_Entry **defobj_out, bool in_plt)
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{
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const Elf_Sym *def;
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const Elf_Sym *symp;
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const Obj_Entry *obj;
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const Obj_Entry *defobj;
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const Objlist_Entry *elm;
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def = NULL;
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defobj = NULL;
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/* Look first in the referencing object if linked symbolically. */
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if (refobj->symbolic) {
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rdbg(("search referencing object"));
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symp = _rtld_symlook_obj(name, hash, refobj, in_plt);
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if (symp != NULL) {
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def = symp;
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defobj = refobj;
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}
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}
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/* Search all objects loaded at program start up. */
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if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
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rdbg(("search _rtld_list_main"));
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symp = _rtld_symlook_list(name, hash, &_rtld_list_main, &obj,
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in_plt);
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if (symp != NULL &&
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(def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
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def = symp;
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defobj = obj;
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}
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}
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/* Search all RTLD_GLOBAL objects. */
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if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
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rdbg(("search _rtld_list_global"));
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symp = _rtld_symlook_list(name, hash, &_rtld_list_global,
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&obj, in_plt);
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if (symp != NULL &&
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(def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
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def = symp;
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defobj = obj;
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}
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}
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/* Search all dlopened DAGs containing the referencing object. */
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SIMPLEQ_FOREACH(elm, &refobj->dldags, link) {
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if (def != NULL && ELF_ST_BIND(def->st_info) != STB_WEAK)
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break;
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rdbg(("search DAG with root %p (%s)", elm->obj,
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elm->obj->path));
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symp = _rtld_symlook_list(name, hash, &elm->obj->dagmembers,
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&obj, in_plt);
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if (symp != NULL &&
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(def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
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def = symp;
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defobj = obj;
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}
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}
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/*
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* Search the dynamic linker itself, and possibly resolve the
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* symbol from there. This is how the application links to
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* dynamic linker services such as dlopen. Only the values listed
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* in the "_rtld_exports" array can be resolved from the dynamic
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* linker.
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*/
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if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
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rdbg(("Search the dynamic linker itself."));
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symp = _rtld_symlook_obj(name, hash, &_rtld_objself, in_plt);
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if (symp != NULL && _rtld_is_exported(symp)) {
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def = symp;
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defobj = &_rtld_objself;
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}
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}
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if (def != NULL)
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*defobj_out = defobj;
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return def;
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}
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