xref: /src/libexec/ld.elf_so/symbol.c

/*	$NetBSD: symbol.c,v 1.1 1996/12/16 20:38:06 cgd Exp $	*/

/*
 * Copyright 1996 John D. Polstra.
 * Copyright 1996 Matt Thomas <matt (at) 3am-software.com>
 * 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 (at) polstra.com>.
 */

#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"

/*
 * 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;

    while(*p != '\0') {
	h = (h << 4) + *p++;
	if ((g = h & 0xf0000000) != 0)
	    h ^= g >> 24;
	h &= ~g;
    }
    return h;
}

/*
 * 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 = obj->buckets[hash % obj->nbuckets];

    while (symnum != ELF_SYM_UNDEFINED) {
	const Elf_Sym *symp;
	const char *strp;

	assert(symnum < obj->nchains);
	symp = obj->symtab + symnum;
	strp = obj->strtab + symp->st_name;
#if 0
	assert(symp->st_name != 0);
#endif
	if (strcmp(name, strp) == 0) {
	    if (symp->st_shndx != Elf_eshn_undefined
		|| (!in_plt && symp->st_value != 0 &&
		    ELF_SYM_TYPE(symp->st_info) == Elf_estt_func)) {
		return symp;
	    }
	}

	symnum = obj->chains[symnum];
    }

    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(
    const Obj_Entry *obj_list,
    Elf_Word r_info,
    const char *name,
    const Obj_Entry *refobj,
    const Obj_Entry **defobj_out,
    bool in_plt)
{
    Elf_Word symnum = ELF_R_SYM(r_info);
    const Elf_Sym *ref;
    const Obj_Entry *obj;
    unsigned long hash;

    if (name == NULL) {
	ref = refobj->symtab + symnum;
	name = refobj->strtab + ref->st_name;
    }
    hash = _rtld_elf_hash(name);

    if (refobj->symbolic) {	/* Look first in the referencing object */
	const Elf_Sym *def = _rtld_symlook_obj(name, hash, refobj, in_plt);
	if (def != NULL) {
	    *defobj_out = refobj;
	    return def;
	}
    }

    /*
     * Look in all loaded objects.  Skip the referencing object, if
     * we have already searched it.
     */
    for (obj = obj_list;  obj != NULL;  obj = obj->next) {
	if (obj != refobj || !refobj->symbolic) {
	    const Elf_Sym *def = _rtld_symlook_obj(name, hash, obj, in_plt);
	    if (def != NULL) {
		*defobj_out = obj;
		return def;
	    }
	}
    }

    if (ELF_R_TYPE(r_info) != R_TYPE(NONE)) {
	_rtld_error("%s: Undefined %ssymbol \"%s\" (reloc type = %d, symnum = %d)",
	      refobj->path, in_plt ? "PLT " : "", name,
	      ELF_R_TYPE(r_info), symnum);
    }
    return NULL;
}