elf.c

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	hash = elf_hash(name);
	def = symlook_default(name, hash, refobj, &defobj, in_plt);
    } else {
	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) {
	def = &sym_zero;
	defobj = obj_main;
    }

    if (def != NULL) {
	*defobj_out = defobj;
	/* Record the information in the cache to avoid subsequent lookups. */
	if (cache != NULL) {
	    cache[symnum].sym = def;
	    cache[symnum].obj = defobj;
	}
    } else {
	if (refobj != &obj_rtld)
	    _rtld_error("%s: Undefined symbol \"%s\"", refobj->path, name);
    }
    return def;
}

#if 0

/*
 * Return the search path from the ldconfig hints file, reading it if
 * necessary.  Returns NULL if there are problems with the hints file,
 * or if the search path there is empty.
 */
static const char *
gethints(void)
{
    static char *hints;

    if (hints == NULL) {
	int fd;
	struct elfhints_hdr hdr;
	char *p;

	/* Keep from trying again in case the hints file is bad. */
	hints = "";

	if ((fd = open(_PATH_ELF_HINTS, O_RDONLY)) == -1)
	    return NULL;
	if (read(fd, &hdr, sizeof hdr) != sizeof hdr ||
	  hdr.magic != ELFHINTS_MAGIC ||
	  hdr.version != 1) {
	    close(fd);
	    return NULL;
	}
	p = xmalloc(hdr.dirlistlen + 1);
	if (lseek(fd, hdr.strtab + hdr.dirlist, SEEK_SET) == -1 ||
	  read(fd, p, hdr.dirlistlen + 1) != (ssize_t)hdr.dirlistlen + 1) {
	    free(p);
	    close(fd);
	    return NULL;
	}
	hints = p;
	close(fd);
    }
    return hints[0] != '\0' ? hints : NULL;
}

static void
init_dag(Obj_Entry *root)
{
    DoneList donelist;

    donelist_init(&donelist);
    init_dag1(root, root, &donelist);
}

static void
init_dag1(Obj_Entry *root, Obj_Entry *obj, DoneList *dlp)
{
    const Needed_Entry *needed;

    if (donelist_check(dlp, obj))
	return;

    obj->refcount++;
    objlist_push_tail(&obj->dldags, root);
    objlist_push_tail(&root->dagmembers, obj);
    for (needed = obj->needed;  needed != NULL;  needed = needed->next)
	if (needed->obj != NULL)
	    init_dag1(root, needed->obj, dlp);
}

/*
 * 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
init_rtld(caddr_t mapbase)
{
    Obj_Entry objtmp;	/* Temporary rtld object */

    /*
     * Conjure up an Obj_Entry structure for the dynamic linker.
     *
     * The "path" member can't be initialized yet because string constatns
     * cannot yet be acessed. Below we will set it correctly.
     */
    memset(&objtmp, 0, sizeof(objtmp));
    objtmp.path = NULL;
    objtmp.rtld = true;
    objtmp.mapbase = mapbase;
#ifdef PIC
    objtmp.relocbase = mapbase;
#endif
    if (RTLD_IS_DYNAMIC()) {
	objtmp.dynamic = rtld_dynamic(&objtmp);
	digest_dynamic(&objtmp, 1);
	assert(objtmp.needed == NULL);
	assert(!objtmp.textrel);

	/*
	 * Temporarily put the dynamic linker entry into the object list, so
	 * that symbols can be found.
	 */

	relocate_objects(&objtmp, true, &objtmp);
    }

    /* Initialize the object list. */
    obj_tail = &obj_list;

    /* Now that non-local variables can be accesses, copy out obj_rtld. */
    memcpy(&obj_rtld, &objtmp, sizeof(obj_rtld));

    /* Replace the path with a dynamically allocated copy. */
    obj_rtld.path = xstrdup(PATH_RTLD);

    r_debug.r_brk = r_debug_state;
    r_debug.r_state = RT_CONSISTENT;
}

/*
 * Add the init functions from a needed object list (and its recursive
 * needed objects) to "list".  This is not used directly; it is a helper
 * function for initlist_add_objects().  The write lock must be held
 * when this function is called.
 */
static void
initlist_add_neededs(Needed_Entry *needed, Objlist *list)
{
    /* Recursively process the successor needed objects. */
    if (needed->next != NULL)
	initlist_add_neededs(needed->next, list);

    /* Process the current needed object. */
    if (needed->obj != NULL)
	initlist_add_objects(needed->obj, &needed->obj->next, list);
}

/*
 * Scan all of the DAGs rooted in the range of objects from "obj" to
 * "tail" and add their init functions to "list".  This recurses over
 * the DAGs and ensure the proper init ordering such that each object's
 * needed libraries are initialized before the object itself.  At the
 * same time, this function adds the objects to the global finalization
 * list "list_fini" in the opposite order.  The write lock must be
 * held when this function is called.
 */
static void
initlist_add_objects(Obj_Entry *obj, Obj_Entry **tail, Objlist *list)
{
    if (obj->init_done)
	return;
    obj->init_done = true;

    /* Recursively process the successor objects. */
    if (&obj->next != tail)
	initlist_add_objects(obj->next, tail, list);

    /* Recursively process the needed objects. */
    if (obj->needed != NULL)
	initlist_add_neededs(obj->needed, list);

    /* Add the object to the init list. */
    if (obj->init != (Elf_Addr)NULL)
	objlist_push_tail(list, obj);

    /* Add the object to the global fini list in the reverse order. */
    if (obj->fini != (Elf_Addr)NULL)
	objlist_push_head(&list_fini, obj);
}

#ifndef FPTR_TARGET
#define FPTR_TARGET(f)	((Elf_Addr) (f))
#endif

static bool
is_exported(const Elf_Sym *def)
{
    Elf_Addr value;
    const func_ptr_type *p;

    value = (Elf_Addr)(obj_rtld.relocbase + def->st_value);
    for (p = exports;  *p != NULL;  p++)
	if (FPTR_TARGET(*p) == value)
	    return true;
    return false;
}

/*
 * Given a shared object, traverse its list of needed objects, and load
 * each of them.  Returns 0 on success.  Generates an error message and
 * returns -1 on failure.
 */
static int
load_needed_objects(Obj_Entry *first)
{
    Obj_Entry *obj;

    for (obj = first;  obj != NULL;  obj = obj->next) {
	Needed_Entry *needed;

	for (needed = obj->needed;  needed != NULL;  needed = needed->next) {
	    const char *name = obj->strtab + needed->name;
	    char *path = find_library(name, obj);

	    needed->obj = NULL;
	    if (path == NULL && !ld_tracing)
		return -1;

	    if (path) {
		needed->obj = load_object(path);
		if (needed->obj == NULL && !ld_tracing)
		    return -1;		/* XXX - cleanup */
	    }
	}
    }

    return 0;
}

static int
load_preload_objects(void)
{
    char *p = ld_preload;
    static const char delim[] = " \t:;";

    if (p == NULL)
	return 0;

    p += strspn(p, delim);
    while (*p != '\0') {
	size_t len = strcspn(p, delim);
	char *path;
	char savech;

	savech = p[len];
	p[len] = '\0';
	if ((path = find_library(p, NULL)) == NULL)
	    return -1;
	if (load_object(path) == NULL)
	    return -1;	/* XXX - cleanup */
	p[len] = savech;
	p += len;
	p += strspn(p, delim);
    }
    return 0;
}

/*
 * Load a shared object into memory, if it is not already loaded.  The
 * argument must be a string allocated on the heap.  This function assumes
 * responsibility for freeing it when necessary.
 *
 * Returns a pointer to the Obj_Entry for the object.  Returns NULL
 * on failure.
 */
static Obj_Entry *
load_object(char *path)
{
    Obj_Entry *obj;
    int fd = -1;
    struct stat sb;

    for (obj = obj_list->next;  obj != NULL;  obj = obj->next)
	if (strcmp(obj->path, path) == 0)
	    break;

    /*
     * If we didn't find a match by pathname, open the file and check
     * again by device and inode.  This avoids false mismatches caused
     * by multiple links or ".." in pathnames.
     *
     * To avoid a race, we open the file and use fstat() rather than
     * using stat().
     */
    if (obj == NULL) {
	if ((fd = open(path, O_RDONLY)) == -1) {
	    _rtld_error("Cannot open \"%s\"", path);
	    return NULL;
	}
	if (fstat(fd, &sb) == -1) {
	    _rtld_error("Cannot fstat \"%s\"", path);
	    close(fd);
	    return NULL;
	}
	for (obj = obj_list->next;  obj != NULL;  obj = obj->next) {
	    if (obj->ino == sb.st_ino && obj->dev == sb.st_dev) {
		close(fd);
		break;
	    }
	}
    }

    if (obj == NULL) {	/* First use of this object, so we must map it in */
	dbg("loading \"%s\"", path);
	obj = map_object(fd, path, &sb);
	close(fd);
	if (obj == NULL) {
	    free(path);
	    return NULL;
	}

	obj->path = path;
	digest_dynamic(obj, 0);

	*obj_tail = obj;
	obj_tail = &obj->next;
	obj_count++;
	linkmap_add(obj);	/* for GDB & dlinfo() */

	dbg("  %p .. %p: %s", obj->mapbase,
	  obj->mapbase + obj->mapsize - 1, obj->path);
	if (obj->textrel)
	    dbg("  WARNING: %s has impure text", obj->path);
    } else
	free(path);

    return obj;
}

static Obj_Entry *
obj_from_addr(const void *addr)
{
    Obj_Entry *obj;

    for (obj = obj_list;  obj != NULL;  obj = obj->next) {
	if (addr < (void *) obj->mapbase)
	    continue;
	if (addr < (void *) (obj->mapbase + obj->mapsize))
	    return obj;
    }
    return NULL;
}

/*
 * Call the finalization functions for each of the objects in "list"
 * which are unreferenced.  All of the objects are expected to have
 * non-NULL fini functions.
 */
static void
objlist_call_fini(Objlist *list)
{
    Objlist_Entry *elm;
    char *saved_msg;

    /*
     * Preserve the current error message since a fini function might
     * call into the dynamic linker and overwrite it.
     */
    saved_msg = errmsg_save();
    STAILQ_FOREACH(elm, list, link) {
	if (elm->obj->refcount == 0) {
	    dbg("calling fini function for %s at %p", elm->obj->path,
	        (void *)elm->obj->fini);
	    call_initfini_pointer(elm->obj, elm->obj->fini);
	}
    }
    errmsg_restore(saved_msg);
}

/*
 * Call the initialization functions for each of the objects in
 * "list".  All of the objects are expected to have non-NULL init
 * functions.
 */
static void
objlist_call_init(Objlist *list)
{
    Objlist_Entry *elm;
    char *saved_msg;

    /*
     * Preserve the current error message since an init function might
     * call into the dynamic linker and overwrite it.
     */
    saved_msg = errmsg_save();
    STAILQ_FOREACH(elm, list, link) {
	dbg("calling init function for %s at %p", elm->obj->path,
	    (void *)elm->obj->init);
	call_initfini_pointer(elm->obj, elm->obj->init);
    }
    errmsg_restore(saved_msg);
}

static void
objlist_clear(Objlist *list)
{
    Objlist_Entry *elm;

    while (!STAILQ_EMPTY(list)) {
	elm = STAILQ_FIRST(list);
	STAILQ_REMOVE_HEAD(list, link);
	free(elm);
    }
}

static Objlist_Entry *
objlist_find(Objlist *list, const Obj_Entry *obj)
{
    Objlist_Entry *elm;

    STAILQ_FOREACH(elm, list, link)
	if (elm->obj == obj)
	    return elm;
    return NULL;
}

static void
objlist_init(Objlist *list)
{
    STAILQ_INIT(list);
}

static void
objlist_push_head(Objlist *list, Obj_Entry *obj)
{
    Objlist_Entry *elm;

    elm = NEW(Objlist_Entry);
    elm->obj = obj;
    STAILQ_INSERT_HEAD(list, elm, link);
}

static void
objlist_push_tail(Objlist *list, Obj_Entry *obj)
{
    Objlist_Entry *elm;

    elm = NEW(Objlist_Entry);
    elm->obj = obj;
    STAILQ_INSERT_TAIL(list, elm, link);
}

static void
objlist_remove(Objlist *list, Obj_Entry *obj)
{
    Objlist_Entry *elm;

    if ((elm = objlist_find(list, obj)) != NULL) {
	STAILQ_REMOVE(list, elm, Struct_Objlist_Entry, link);
	free(elm);
    }
}

/*
 * Remove all of the unreferenced objects from "list".
 */
static void
objlist_remove_unref(Objlist *list)
{
    Objlist newlist;
    Objlist_Entry *elm;

    STAILQ_INIT(&newlist);
    while (!STAILQ_EMPTY(list)) {