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

/*	$NetBSD: rtld.c,v 1.2 1996/12/18 22:27:29 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 <ctype.h>

#include <dlfcn.h>
#include "debug.h"
#include "rtld.h"

#ifndef RTLD_NOW
#define	RTLD_NOW	(RTLD_LAZY + 1)
#endif

/*
 * Debugging support.
 */

typedef void (*funcptr)(void);

/*
 * Function declarations.
 */
static void _rtld_init(caddr_t);
static void _rtld_exit(void);

/*
 * Data declarations.
 */
static char *error_message;	/* Message for dlopen(), or NULL */

struct r_debug _rtld_debug;	/* for GDB; */
bool _rtld_trust;		/* False for setuid and setgid programs */
Obj_Entry *_rtld_objlist;	/* Head of linked list of shared objects */
Obj_Entry **_rtld_objtail;	/* Link field of last object in list */
Obj_Entry *_rtld_objmain;	/* The main program shared object */
Obj_Entry _rtld_objself;	/* The dynamic linker shared object */

Search_Path *_rtld_paths;
/*
 * Global declarations normally provided by crt0.
 */
char *__progname;
char **environ;

#ifdef OLD_GOT
extern Elf_Addr _GLOBAL_OFFSET_TABLE_[];
#else
extern Elf_Addr _GLOBAL_OFFSET_TABLE_[];
extern Elf_Dyn _DYNAMIC;
#endif

static void
_rtld_call_fini_functions(
    Obj_Entry *first)
{
    Obj_Entry *obj;

    for (obj = first;  obj != NULL;  obj = obj->next)
	if (obj->fini != NULL)
	    (*obj->fini)();
}

static void
_rtld_call_init_functions(
    Obj_Entry *first)
{
    if (first != NULL) {
	_rtld_call_init_functions(first->next);
	if (first->init != NULL)
	    (*first->init)();
    }
}

/*
 * Initialize the dynamic linker.  The argument is the address at which
 * the dynamic linker has been mapped into memory.  The primary task of
 * this function is to relocate the dynamic linker.
 */
static void
_rtld_init(
    caddr_t mapbase)
{
    _rtld_add_paths(&_rtld_paths, RTLD_DEFAULT_LIBRARY_PATH);

    /* Conjure up an Obj_Entry structure for the dynamic linker. */

    _rtld_objself.path = _PATH_RTLD;
    _rtld_objself.rtld = true;
    _rtld_objself.mapbase = mapbase;
    _rtld_objself.relocbase = mapbase;
    _rtld_objself.pltgot = NULL;
#ifdef OLD_GOT
    _rtld_objself.dynamic = (Elf_Dyn *) _GLOBAL_OFFSET_TABLE_[0];
#else
    _rtld_objself.dynamic = &_DYNAMIC;
#endif

    _rtld_digest_dynamic(&_rtld_objself);
#ifdef __alpha__
/* XXX XXX XXX */
_rtld_objself.pltgot = NULL;
#endif
    assert(_rtld_objself.needed == NULL);
    assert(!_rtld_objself.textrel);

    /* Set up the _rtld_objlist pointer, so that rtld symbols can be found. */
    _rtld_objlist = &_rtld_objself;

    _rtld_relocate_objects(&_rtld_objself, true);

    /* Make the object list empty again. */
    _rtld_objlist = NULL;
    _rtld_objtail = &_rtld_objlist;

    _rtld_debug.r_brk = _rtld_debug_state;
    _rtld_debug.r_state = RT_CONSISTENT;
}

/*
 * Cleanup procedure.  It will be called (by the atexit() mechanism) just
 * before the process exits.
 */
static void
_rtld_exit(void)
{
    dbg("rtld_exit()");

    _rtld_call_fini_functions(_rtld_objlist->next);
}

/*
 * Main entry point for dynamic linking.  The argument is the stack
 * pointer.  The stack is expected to be laid out as described in the
 * SVR4 ABI specification, Intel 386 Processor Supplement.  Specifically,
 * the stack pointer points to a word containing ARGC.  Following that
 * in the stack is a null-terminated sequence of pointers to argument
 * strings.  Then comes a null-terminated sequence of pointers to
 * environment strings.  Finally, there is a sequence of "auxiliary
 * vector" entries.
 *
 * This function returns the entry point for the main program in %eax,
 * and the dynamic linker's exit procedure in %edx.  We accomplish this
 * by declaring the return value to have the 64-bit type "long long".
 * Such values are returned with their most-significant 32 bits in %edx,
 * and their least-significant 32 bits in %eax.
 */
Elf_Addr
_rtld(
    Elf_Word *sp)
{
    const AuxInfo *aux_info[AUX_count];
    int i = 0;
    char **env;
    const AuxInfo *aux;
    const AuxInfo *auxp;
    Elf_Word * const osp = sp;
    bool bind_now = 0;
    const char *ld_bind_now;
    const char **argv;

    /*
     * On entry, the dynamic linker itself has not been relocated yet.
     * Be very careful not to reference any global data until after
     * _rtld_init has returned.  It is OK to reference file-scope statics
     * and string constants, and to call static and global functions.
     */
    /* Find the auxiliary vector on the stack. */
    /* first Elf_Word reserved to address of exit routine */
#ifdef RTLD_DEBUG
    xprintf("sp = %p, argc = %d, argv = %p <%s>\n", sp, sp[2], &sp[3], sp[3]);
    xprintf("got is at %p, dynamic is at %p\n", _GLOBAL_OFFSET_TABLE_, &_DYNAMIC);
    debug = 1;
    xprintf("_ctype_ is %p\n", _ctype_);
#endif

    sp += 2;		/* skip over return argument space */
    argv = (const char **) &sp[1];
    sp += sp[0] + 2;	/* Skip over argc, arguments, and NULL terminator */
    env = (char **) sp;
    while (*sp++ != 0) {	/* Skip over environment, and NULL terminator */
#ifdef RTLD_DEBUG
	xprintf("env[%d] = %p\n", i++, sp[-1]);
#endif
    }
    aux = (const AuxInfo *) sp;

    /* Digest the auxiliary vector. */
    for (i = 0;  i < AUX_count;  ++i)
	aux_info[i] = NULL;
    for (auxp = aux;  auxp->au_id != AUX_null;  ++auxp) {
	if (auxp->au_id < AUX_count)
	    aux_info[auxp->au_id] = auxp;
    }

    /* Initialize and relocate ourselves. */
    assert(aux_info[AUX_base] != NULL);
    _rtld_init((caddr_t) aux_info[AUX_base]->au_v);

#ifdef RTLD_DEBUG
    xprintf("_ctype_ is %p\n", _ctype_);
#endif
    if (aux_info[AUX_debug] != NULL)	/* Set debugging level */
	debug = aux_info[AUX_debug]->au_v;

    __progname = _rtld_objself.path;
    environ = env;

    _rtld_trust = geteuid() == getuid() && getegid() == getgid();

    ld_bind_now = getenv("LD_BIND_NOW");
    if (ld_bind_now != NULL && *ld_bind_now != '\0')
	bind_now = true;
    if (_rtld_trust) {
	const char *ld_debug = getenv("LD_DEBUG");
	if (ld_debug != NULL && *ld_debug != '\0')
	    debug = 1;
	_rtld_add_paths(&_rtld_paths, getenv("LD_LIBRARY_PATH"));
    }

    dbg("%s is initialized, base address = %p", __progname,
	(caddr_t) aux_info[AUX_base]->au_v);

    /*
     * Load the main program, or process its program header if it is
     * already loaded.
     */
    if (aux_info[AUX_execfd] != NULL) {	/* Load the main program. */
	int fd = aux_info[AUX_execfd]->au_v;
	dbg("loading main program");
	_rtld_objmain = _rtld_map_object(argv[0], fd);
	close(fd);
	if (_rtld_objmain == NULL)
	    _rtld_die();
    } else {				/* Main program already loaded. */
	const Elf_Phdr *phdr;
	int phnum;
	caddr_t entry;

	dbg("processing main program's program header");
	assert(aux_info[AUX_phdr] != NULL);
	phdr = (const Elf_Phdr *) aux_info[AUX_phdr]->au_v;
	assert(aux_info[AUX_phnum] != NULL);
	phnum = aux_info[AUX_phnum]->au_v;
	assert(aux_info[AUX_phent] != NULL);
	assert(aux_info[AUX_phent]->au_v == sizeof(Elf_Phdr));
	assert(aux_info[AUX_entry] != NULL);
	entry = (caddr_t) aux_info[AUX_entry]->au_v;
	_rtld_objmain = _rtld_digest_phdr(phdr, phnum, entry);
    }

    _rtld_objmain->path = xstrdup("main program");
    _rtld_objmain->mainprog = true;
    _rtld_digest_dynamic(_rtld_objmain);

    _rtld_linkmap_add(_rtld_objmain);
    _rtld_linkmap_add(&_rtld_objself);

    /* Link the main program into the list of objects. */
    *_rtld_objtail = _rtld_objmain;
    _rtld_objtail = &_rtld_objmain->next;
    ++_rtld_objmain->refcount;

    dbg("loading needed objects");
    if (_rtld_load_needed_objects(_rtld_objmain) == -1)
	_rtld_die();

    dbg("relocating objects");
    if (_rtld_relocate_objects(_rtld_objmain, bind_now) == -1)
	_rtld_die();

    dbg("doing copy relocations");
    if (_rtld_do_copy_relocations(_rtld_objmain) == -1)
	_rtld_die();

    dbg("calling _init functions");
    _rtld_call_init_functions(_rtld_objmain->next);

    dbg("transferring control to program entry point = %p",
	_rtld_objmain->entry);

    /* Return with the entry point and the exit procedure in at the top of
     * stack.
     */

    _rtld_debug_state();	/* say hello to gdb! */

    ((void **) osp)[0] = _rtld_exit;
    ((void **) osp)[1] = _rtld_objmain;
    return (Elf_Addr) _rtld_objmain->entry;
}

void
_rtld_die(
    void)
{
    const char *msg = _rtld_dlerror();

    if (msg == NULL)
	msg = "Fatal error";
    xerrx(1, "%s\n", msg);
}

static Obj_Entry *
_rtld_dlcheck(
    void *handle)
{
    Obj_Entry *obj;

    for (obj = _rtld_objlist;  obj != NULL;  obj = obj->next)
	if (obj == (Obj_Entry *) handle)
	    break;

    if (obj == NULL || obj->dl_refcount == 0) {
	xwarnx("Invalid shared object handle %p", handle);
	return NULL;
    }
    return obj;
}

static void
_rtld_unref_object_dag(
    Obj_Entry *root)
{
    assert(root->refcount != 0);
    --root->refcount;
    if (root->refcount == 0) {
	const Needed_Entry *needed;

	for (needed = root->needed;  needed != NULL;  needed = needed->next)
	    _rtld_unref_object_dag(needed->obj);
    }
}

int
_rtld_dlclose(
    void *handle)
{
    Obj_Entry *root = _rtld_dlcheck(handle);

    if (root == NULL)
	return -1;

    _rtld_debug.r_state = RT_DELETE;
    _rtld_debug_state();

    --root->dl_refcount;
    _rtld_unref_object_dag(root);
    if (root->refcount == 0) {	/* We are finished with some objects. */
	Obj_Entry *obj;
	Obj_Entry **linkp;

	/* Finalize objects that are about to be unmapped. */
	for (obj = _rtld_objlist->next;  obj != NULL;  obj = obj->next)
	    if (obj->refcount == 0 && obj->fini != NULL)
		(*obj->fini)();

	/* Unmap all objects that are no longer referenced. */
	linkp = &_rtld_objlist->next;
	while((obj = *linkp) != NULL) {
	    if (obj->refcount == 0) {
		munmap(obj->mapbase, obj->mapsize);
		free(obj->path);
		while(obj->needed != NULL) {
		    Needed_Entry *needed = obj->needed;
		    obj->needed = needed->next;
		    free(needed);
		}
		_rtld_linkmap_delete(obj);
		*linkp = obj->next;
		free(obj);
	    } else
		linkp = &obj->next;
	}
    }

    _rtld_debug.r_state = RT_CONSISTENT;
    _rtld_debug_state();

    return 0;
}

char *
_rtld_dlerror(
    void)
{
    char *msg = error_message;
    error_message = NULL;
    return msg;
}

void *
_rtld_dlopen(
    const char *name,
    int mode)
{
    Obj_Entry **old_obj_tail = _rtld_objtail;
    Obj_Entry *obj = NULL;

    _rtld_debug.r_state = RT_ADD;
    _rtld_debug_state();

    if (name == NULL) {
	obj = _rtld_objmain;
    } else {
	char *path = _rtld_find_library(name, NULL);
	if (path != NULL)
	    obj = _rtld_load_object(path);
    }

    if (obj != NULL) {
	++obj->dl_refcount;
	if (*old_obj_tail != NULL) {		/* We loaded something new. */
	    assert(*old_obj_tail == obj);

	    /* FIXME - Clean up properly after an error. */
	    if (_rtld_load_needed_objects(obj) == -1) {
		--obj->dl_refcount;
		obj = NULL;
	    } else if (_rtld_relocate_objects(obj, mode == RTLD_NOW) == -1) {
		--obj->dl_refcount;
		obj = NULL;
	    } else {
		_rtld_call_init_functions(obj);
	    }
	}
    }

    _rtld_debug.r_state = RT_CONSISTENT;
    _rtld_debug_state();

    return obj;
}

void *
_rtld_dlsym(
    void *handle,
    const char *name)
{
    const Obj_Entry *obj = _rtld_dlcheck(handle);
    const Elf_Sym *def;
    const Obj_Entry *defobj;

    if (obj == NULL)
	return NULL;

    /*
     * FIXME - This isn't correct.  The search should include the whole
     * DAG rooted at the given object.
     */
    def = _rtld_find_symdef(_rtld_objlist, 0, name, obj, &defobj, false);
    if (def != NULL)
	return defobj->relocbase + def->st_value;

    _rtld_error("Undefined symbol \"%s\"", name);
    return NULL;
}

/*
 * Error reporting function.  Use it like printf.  If formats the message
 * into a buffer, and sets things up so that the next call to dlerror()
 * will return the message.
 */
void
_rtld_error(
    const char *fmt, ...)
{
    static char buf[512];
    va_list ap;

    va_start(ap, fmt);
    xvsnprintf(buf, sizeof buf, fmt, ap);
    error_message = buf;
    va_end(ap);
}

void
_rtld_debug_state(
    void)
{
    /* do nothing */
}

void
_rtld_linkmap_add(
    Obj_Entry *obj)
{
    struct link_map *l = &obj->linkmap;
    struct link_map *prev;

    obj->linkmap.l_name = obj->path;
    obj->linkmap.l_addr = obj->mapbase;
    obj->linkmap.l_ld = obj->dynamic;

    if (_rtld_debug.r_map == NULL) {
	_rtld_debug.r_map = l;
	return;
    }

    for (prev = _rtld_debug.r_map; prev->l_next != NULL; prev = prev->l_next)
	;
    l->l_prev = prev;
    prev->l_next = l;
    l->l_next = NULL;
}

void
_rtld_linkmap_delete(
    Obj_Entry *obj)
{
    struct link_map *l = &obj->linkmap;

    if (l->l_prev == NULL) {
	if ((_rtld_debug.r_map = l->l_next) != NULL)
	    l->l_next->l_prev = NULL;
	return;
    }

    if ((l->l_prev->l_next = l->l_next) != NULL)
	l->l_next->l_prev = l->l_prev;
}