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

/*	$NetBSD: reloc.c,v 1.77 2002/11/25 19:49:25 mycroft 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"

#ifndef RTLD_INHIBIT_COPY_RELOCS
static int _rtld_do_copy_relocation __P((const Obj_Entry *, const Elf_Rela *));

/*
 * XXX: These don't work for the alpha and i386; don't know about powerpc
 *	The alpha and the i386 avoid the problem by compiling everything PIC.
 *	These relocation are supposed to be writing the address of the
 *	function to be called on the bss.rel or bss.rela segment, but:
 *		- st_size == 0
 *		- on the i386 at least the call instruction is a direct call
 *		  not an indirect call.
 */
static int
_rtld_do_copy_relocation(dstobj, rela)
	const Obj_Entry *dstobj;
	const Elf_Rela *rela;
{
	void           *dstaddr = (void *)(dstobj->relocbase + rela->r_offset);
	const Elf_Sym  *dstsym = dstobj->symtab + ELF_R_SYM(rela->r_info);
	const char     *name = dstobj->strtab + dstsym->st_name;
	unsigned long   hash = _rtld_elf_hash(name);
	size_t          size = dstsym->st_size;
	const void     *srcaddr;
	const Elf_Sym  *srcsym = NULL;
	Obj_Entry      *srcobj;

	for (srcobj = dstobj->next; srcobj != NULL; srcobj = srcobj->next)
		if ((srcsym = _rtld_symlook_obj(name, hash, srcobj, false)) != NULL)
			break;

	if (srcobj == NULL) {
		_rtld_error("Undefined symbol \"%s\" referenced from COPY"
		    " relocation in %s", name, dstobj->path);
		return (-1);
	}
	srcaddr = (const void *)(srcobj->relocbase + srcsym->st_value);
	(void)memcpy(dstaddr, srcaddr, size);
	rdbg(("COPY %s %s %s --> src=%p dst=%p *dst= %p size %ld",
	    dstobj->path, srcobj->path, name, (void *)srcaddr,
	    (void *)dstaddr, (void *)*(long *)dstaddr, (long)size));
	return (0);
}
#endif /* RTLD_INHIBIT_COPY_RELOCS */


/*
 * Process the special R_xxx_COPY relocations in the main program.  These
 * copy data from a shared object into a region in the main program's BSS
 * segment.
 *
 * Returns 0 on success, -1 on failure.
 */
int
_rtld_do_copy_relocations(dstobj)
	const Obj_Entry *dstobj;
{
#ifndef RTLD_INHIBIT_COPY_RELOCS

	/* COPY relocations are invalid elsewhere */
	assert(!dstobj->isdynamic);

	if (dstobj->rel != NULL) {
		const Elf_Rel  *rel;
		for (rel = dstobj->rel; rel < dstobj->rellim; ++rel) {
			if (ELF_R_TYPE(rel->r_info) == R_TYPE(COPY)) {
				Elf_Rela        ourrela;
				ourrela.r_info = rel->r_info;
				ourrela.r_offset = rel->r_offset;
				ourrela.r_addend = 0;
				if (_rtld_do_copy_relocation(dstobj,
				    &ourrela) < 0)
					return (-1);
			}
		}
	}
	if (dstobj->rela != NULL) {
		const Elf_Rela *rela;
		for (rela = dstobj->rela; rela < dstobj->relalim; ++rela) {
			if (ELF_R_TYPE(rela->r_info) == R_TYPE(COPY)) {
				if (_rtld_do_copy_relocation(dstobj, rela) < 0)
					return (-1);
			}
		}
	}
#endif /* RTLD_INHIBIT_COPY_RELOCS */

	return (0);
}

/*
 * Relocate newly-loaded shared objects.  The argument is a pointer to
 * the Obj_Entry for the first such object.  All objects from the first
 * to the end of the list of objects are relocated.  Returns 0 on success,
 * or -1 on failure.
 */
int
_rtld_relocate_objects(first, bind_now)
	Obj_Entry *first;
	bool bind_now;
{
	Obj_Entry *obj;
	int ok = 1;

	for (obj = first; obj != NULL; obj = obj->next) {
		if (obj->nbuckets == 0 || obj->nchains == 0 ||
		    obj->buckets == NULL || obj->symtab == NULL ||
		    obj->strtab == NULL) {
			_rtld_error("%s: Shared object has no run-time"
			    " symbol table", obj->path);
			return -1;
		}
		rdbg((" relocating %s (%ld/%ld rel/rela, %ld/%ld plt rel/rela)",
		    obj->path,
		    (long)(obj->rellim - obj->rel),
		    (long)(obj->relalim - obj->rela),
		    (long)(obj->pltrellim - obj->pltrel),
		    (long)(obj->pltrelalim - obj->pltrela)));

		if (obj->textrel) {
			/*
			 * There are relocations to the write-protected text
			 * segment.
			 */
			if (mprotect(obj->mapbase, obj->textsize,
				PROT_READ | PROT_WRITE | PROT_EXEC) == -1) {
				_rtld_error("%s: Cannot write-enable text "
				    "segment: %s", obj->path, xstrerror(errno));
				return -1;
			}
		}
		dbg(("doing non-PLT relocations"));
		if (_rtld_relocate_nonplt_objects(obj) < 0)
			ok = 0;
		if (obj->textrel) {	/* Re-protected the text segment. */
			if (mprotect(obj->mapbase, obj->textsize,
				     PROT_READ | PROT_EXEC) == -1) {
				_rtld_error("%s: Cannot write-protect text "
				    "segment: %s", obj->path, xstrerror(errno));
				return -1;
			}
		}
		dbg(("doing lazy PLT binding"));
		if (_rtld_relocate_plt_lazy(obj) < 0)
			ok = 0;
#if defined(__i386__)
		if (bind_now)
			if (_rtld_relocate_plt_objects(obj) < 0)
				ok = 0;
#endif
		if (!ok)
			return -1;


		/* Set some sanity-checking numbers in the Obj_Entry. */
		obj->magic = RTLD_MAGIC;
		obj->version = RTLD_VERSION;

		/* Fill in the dynamic linker entry points. */
		obj->dlopen = _rtld_dlopen;
		obj->dlsym = _rtld_dlsym;
		obj->dlerror = _rtld_dlerror;
		obj->dlclose = _rtld_dlclose;
		obj->dladdr = _rtld_dladdr;

		dbg(("fixing up PLTGOT"));
		/* Set the special PLTGOT entries. */
		if (obj->pltgot != NULL)
			_rtld_setup_pltgot(obj);
	}

	return 0;
}