2 * Copyright 1996, 1997, 1998, 1999, 2000 John D. Polstra.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 * Dynamic linker for ELF.
31 * John Polstra <jdp@polstra.com>.
35 #error "GCC is needed to compile this file"
38 #include <sys/param.h>
55 #define END_SYM "_end"
56 #define PATH_RTLD "/usr/libexec/ld-elf.so.1"
59 typedef void (*func_ptr_type)();
62 * This structure provides a reentrant way to keep a list of objects and
63 * check which ones have already been processed in some way.
65 typedef struct Struct_DoneList {
66 Obj_Entry **objs; /* Array of object pointers */
67 unsigned int num_alloc; /* Allocated size of the array */
68 unsigned int num_used; /* Number of array slots used */
72 * Function declarations.
74 static const char *basename(const char *);
75 static void die(void);
76 static void digest_dynamic(Obj_Entry *);
77 static Obj_Entry *digest_phdr(const Elf_Phdr *, int, caddr_t, const char *);
78 static Obj_Entry *dlcheck(void *);
79 static bool donelist_check(DoneList *, Obj_Entry *);
80 static char *find_library(const char *, const Obj_Entry *);
81 static const char *gethints(void);
82 static void init_dag(Obj_Entry *);
83 static void init_dag1(Obj_Entry *root, Obj_Entry *obj, DoneList *);
84 static void init_rtld(caddr_t);
85 static void initlist_add_neededs(Needed_Entry *needed, Objlist *list);
86 static void initlist_add_objects(Obj_Entry *obj, Obj_Entry **tail,
88 static bool is_exported(const Elf_Sym *);
89 static void linkmap_add(Obj_Entry *);
90 static void linkmap_delete(Obj_Entry *);
91 static int load_needed_objects(Obj_Entry *);
92 static int load_preload_objects(void);
93 static Obj_Entry *load_object(char *);
94 static void lock_check(void);
95 static Obj_Entry *obj_from_addr(const void *);
96 static void objlist_call_fini(Objlist *);
97 static void objlist_call_init(Objlist *);
98 static void objlist_clear(Objlist *);
99 static Objlist_Entry *objlist_find(Objlist *, const Obj_Entry *);
100 static void objlist_init(Objlist *);
101 static void objlist_push_head(Objlist *, Obj_Entry *);
102 static void objlist_push_tail(Objlist *, Obj_Entry *);
103 static void objlist_remove(Objlist *, Obj_Entry *);
104 static void objlist_remove_unref(Objlist *);
105 static int relocate_objects(Obj_Entry *, bool);
106 static void rtld_exit(void);
107 static char *search_library_path(const char *, const char *);
108 static void set_program_var(const char *, const void *);
109 static const Elf_Sym *symlook_list(const char *, unsigned long,
110 Objlist *, const Obj_Entry **, bool in_plt, DoneList *);
111 static void trace_loaded_objects(Obj_Entry *obj);
112 static void unload_object(Obj_Entry *);
113 static void unref_dag(Obj_Entry *);
115 void r_debug_state(void);
116 void xprintf(const char *, ...);
121 static char *error_message; /* Message for dlerror(), or NULL */
122 struct r_debug r_debug; /* for GDB; */
123 static bool trust; /* False for setuid and setgid programs */
124 static char *ld_bind_now; /* Environment variable for immediate binding */
125 static char *ld_debug; /* Environment variable for debugging */
126 static char *ld_library_path; /* Environment variable for search path */
127 static char *ld_preload; /* Environment variable for libraries to
129 static char *ld_tracing; /* Called from ldd to print libs */
130 static Obj_Entry *obj_list; /* Head of linked list of shared objects */
131 static Obj_Entry **obj_tail; /* Link field of last object in list */
132 static Obj_Entry *obj_main; /* The main program shared object */
133 static Obj_Entry obj_rtld; /* The dynamic linker shared object */
134 static unsigned int obj_count; /* Number of objects in obj_list */
136 static Objlist list_global = /* Objects dlopened with RTLD_GLOBAL */
137 STAILQ_HEAD_INITIALIZER(list_global);
138 static Objlist list_main = /* Objects loaded at program startup */
139 STAILQ_HEAD_INITIALIZER(list_main);
140 static Objlist list_fini = /* Objects needing fini() calls */
141 STAILQ_HEAD_INITIALIZER(list_fini);
143 static LockInfo lockinfo;
145 static Elf_Sym sym_zero; /* For resolving undefined weak refs. */
147 #define GDB_STATE(s) r_debug.r_state = s; r_debug_state();
149 extern Elf_Dyn _DYNAMIC;
150 #pragma weak _DYNAMIC
153 * These are the functions the dynamic linker exports to application
154 * programs. They are the only symbols the dynamic linker is willing
155 * to export from itself.
157 static func_ptr_type exports[] = {
158 (func_ptr_type) &_rtld_error,
159 (func_ptr_type) &dlclose,
160 (func_ptr_type) &dlerror,
161 (func_ptr_type) &dlopen,
162 (func_ptr_type) &dlsym,
163 (func_ptr_type) &dladdr,
164 (func_ptr_type) &dllockinit,
169 * Global declarations normally provided by crt1. The dynamic linker is
170 * not built with crt1, so we have to provide them ourselves.
176 * Fill in a DoneList with an allocation large enough to hold all of
177 * the currently-loaded objects. Keep this as a macro since it calls
178 * alloca and we want that to occur within the scope of the caller.
180 #define donelist_init(dlp) \
181 ((dlp)->objs = alloca(obj_count * sizeof (dlp)->objs[0]), \
182 assert((dlp)->objs != NULL), \
183 (dlp)->num_alloc = obj_count, \
189 lockinfo.rlock_acquire(lockinfo.thelock);
190 atomic_incr_int(&lockinfo.rcount);
197 lockinfo.wlock_acquire(lockinfo.thelock);
198 atomic_incr_int(&lockinfo.wcount);
205 atomic_decr_int(&lockinfo.rcount);
206 lockinfo.rlock_release(lockinfo.thelock);
212 atomic_decr_int(&lockinfo.wcount);
213 lockinfo.wlock_release(lockinfo.thelock);
217 * Main entry point for dynamic linking. The first argument is the
218 * stack pointer. The stack is expected to be laid out as described
219 * in the SVR4 ABI specification, Intel 386 Processor Supplement.
220 * Specifically, the stack pointer points to a word containing
221 * ARGC. Following that in the stack is a null-terminated sequence
222 * of pointers to argument strings. Then comes a null-terminated
223 * sequence of pointers to environment strings. Finally, there is a
224 * sequence of "auxiliary vector" entries.
226 * The second argument points to a place to store the dynamic linker's
227 * exit procedure pointer and the third to a place to store the main
230 * The return value is the main program's entry point.
233 _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
235 Elf_Auxinfo *aux_info[AT_COUNT];
244 Obj_Entry **preload_tail;
248 * On entry, the dynamic linker itself has not been relocated yet.
249 * Be very careful not to reference any global data until after
250 * init_rtld has returned. It is OK to reference file-scope statics
251 * and string constants, and to call static and global functions.
254 /* Find the auxiliary vector on the stack. */
257 sp += argc + 1; /* Skip over arguments and NULL terminator */
259 while (*sp++ != 0) /* Skip over environment, and NULL terminator */
261 aux = (Elf_Auxinfo *) sp;
263 /* Digest the auxiliary vector. */
264 for (i = 0; i < AT_COUNT; i++)
266 for (auxp = aux; auxp->a_type != AT_NULL; auxp++) {
267 if (auxp->a_type < AT_COUNT)
268 aux_info[auxp->a_type] = auxp;
271 /* Initialize and relocate ourselves. */
272 assert(aux_info[AT_BASE] != NULL);
273 init_rtld((caddr_t) aux_info[AT_BASE]->a_un.a_ptr);
275 __progname = obj_rtld.path;
276 argv0 = argv[0] != NULL ? argv[0] : "(null)";
279 trust = geteuid() == getuid() && getegid() == getgid();
281 ld_bind_now = getenv("LD_BIND_NOW");
283 ld_debug = getenv("LD_DEBUG");
284 ld_library_path = getenv("LD_LIBRARY_PATH");
285 ld_preload = getenv("LD_PRELOAD");
287 ld_tracing = getenv("LD_TRACE_LOADED_OBJECTS");
289 if (ld_debug != NULL && *ld_debug != '\0')
291 dbg("%s is initialized, base address = %p", __progname,
292 (caddr_t) aux_info[AT_BASE]->a_un.a_ptr);
293 dbg("RTLD dynamic = %p", obj_rtld.dynamic);
294 dbg("RTLD pltgot = %p", obj_rtld.pltgot);
297 * Load the main program, or process its program header if it is
300 if (aux_info[AT_EXECFD] != NULL) { /* Load the main program. */
301 int fd = aux_info[AT_EXECFD]->a_un.a_val;
302 dbg("loading main program");
303 obj_main = map_object(fd, argv0, NULL);
305 if (obj_main == NULL)
307 } else { /* Main program already loaded. */
308 const Elf_Phdr *phdr;
312 dbg("processing main program's program header");
313 assert(aux_info[AT_PHDR] != NULL);
314 phdr = (const Elf_Phdr *) aux_info[AT_PHDR]->a_un.a_ptr;
315 assert(aux_info[AT_PHNUM] != NULL);
316 phnum = aux_info[AT_PHNUM]->a_un.a_val;
317 assert(aux_info[AT_PHENT] != NULL);
318 assert(aux_info[AT_PHENT]->a_un.a_val == sizeof(Elf_Phdr));
319 assert(aux_info[AT_ENTRY] != NULL);
320 entry = (caddr_t) aux_info[AT_ENTRY]->a_un.a_ptr;
321 if ((obj_main = digest_phdr(phdr, phnum, entry, argv0)) == NULL)
325 obj_main->path = xstrdup(argv0);
326 obj_main->mainprog = true;
329 * Get the actual dynamic linker pathname from the executable if
330 * possible. (It should always be possible.) That ensures that
331 * gdb will find the right dynamic linker even if a non-standard
334 if (obj_main->interp != NULL &&
335 strcmp(obj_main->interp, obj_rtld.path) != 0) {
337 obj_rtld.path = xstrdup(obj_main->interp);
340 digest_dynamic(obj_main);
342 linkmap_add(obj_main);
343 linkmap_add(&obj_rtld);
345 /* Link the main program into the list of objects. */
346 *obj_tail = obj_main;
347 obj_tail = &obj_main->next;
349 obj_main->refcount++;
350 /* Make sure we don't call the main program's init and fini functions. */
351 obj_main->init = obj_main->fini = NULL;
353 /* Initialize a fake symbol for resolving undefined weak references. */
354 sym_zero.st_info = ELF_ST_INFO(STB_GLOBAL, STT_NOTYPE);
355 sym_zero.st_shndx = SHN_ABS;
357 dbg("loading LD_PRELOAD libraries");
358 if (load_preload_objects() == -1)
360 preload_tail = obj_tail;
362 dbg("loading needed objects");
363 if (load_needed_objects(obj_main) == -1)
366 /* Make a list of all objects loaded at startup. */
367 for (obj = obj_list; obj != NULL; obj = obj->next)
368 objlist_push_tail(&list_main, obj);
370 if (ld_tracing) { /* We're done */
371 trace_loaded_objects(obj_main);
375 if (relocate_objects(obj_main,
376 ld_bind_now != NULL && *ld_bind_now != '\0') == -1)
379 dbg("doing copy relocations");
380 if (do_copy_relocations(obj_main) == -1)
383 dbg("initializing key program variables");
384 set_program_var("__progname", argv[0] != NULL ? basename(argv[0]) : "");
385 set_program_var("environ", env);
387 dbg("initializing thread locks");
388 lockdflt_init(&lockinfo);
389 lockinfo.thelock = lockinfo.lock_create(lockinfo.context);
391 /* Make a list of init functions to call. */
392 objlist_init(&initlist);
393 initlist_add_objects(obj_list, preload_tail, &initlist);
395 r_debug_state(); /* say hello to gdb! */
397 objlist_call_init(&initlist);
399 objlist_clear(&initlist);
402 dbg("transferring control to program entry point = %p", obj_main->entry);
404 /* Return the exit procedure and the program entry point. */
405 *exit_proc = rtld_exit;
407 return (func_ptr_type) obj_main->entry;
411 _rtld_bind(Obj_Entry *obj, Elf_Word reloff)
415 const Obj_Entry *defobj;
421 rel = (const Elf_Rel *) ((caddr_t) obj->pltrel + reloff);
423 rel = (const Elf_Rel *) ((caddr_t) obj->pltrela + reloff);
425 where = (Elf_Addr *) (obj->relocbase + rel->r_offset);
426 def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true);
430 target = (Elf_Addr)(defobj->relocbase + def->st_value);
432 dbg("\"%s\" in \"%s\" ==> %p in \"%s\"",
433 defobj->strtab + def->st_name, basename(obj->path),
434 (void *)target, basename(defobj->path));
436 reloc_jmpslot(where, target);
442 * Error reporting function. Use it like printf. If formats the message
443 * into a buffer, and sets things up so that the next call to dlerror()
444 * will return the message.
447 _rtld_error(const char *fmt, ...)
449 static char buf[512];
453 vsnprintf(buf, sizeof buf, fmt, ap);
459 basename(const char *name)
461 const char *p = strrchr(name, '/');
462 return p != NULL ? p + 1 : name;
468 const char *msg = dlerror();
476 * Process a shared object's DYNAMIC section, and save the important
477 * information in its Obj_Entry structure.
480 digest_dynamic(Obj_Entry *obj)
483 Needed_Entry **needed_tail = &obj->needed;
484 const Elf_Dyn *dyn_rpath = NULL;
485 int plttype = DT_REL;
487 for (dynp = obj->dynamic; dynp->d_tag != DT_NULL; dynp++) {
488 switch (dynp->d_tag) {
491 obj->rel = (const Elf_Rel *) (obj->relocbase + dynp->d_un.d_ptr);
495 obj->relsize = dynp->d_un.d_val;
499 assert(dynp->d_un.d_val == sizeof(Elf_Rel));
503 obj->pltrel = (const Elf_Rel *)
504 (obj->relocbase + dynp->d_un.d_ptr);
508 obj->pltrelsize = dynp->d_un.d_val;
512 obj->rela = (const Elf_Rela *) (obj->relocbase + dynp->d_un.d_ptr);
516 obj->relasize = dynp->d_un.d_val;
520 assert(dynp->d_un.d_val == sizeof(Elf_Rela));
524 plttype = dynp->d_un.d_val;
525 assert(dynp->d_un.d_val == DT_REL || plttype == DT_RELA);
529 obj->symtab = (const Elf_Sym *)
530 (obj->relocbase + dynp->d_un.d_ptr);
534 assert(dynp->d_un.d_val == sizeof(Elf_Sym));
538 obj->strtab = (const char *) (obj->relocbase + dynp->d_un.d_ptr);
542 obj->strsize = dynp->d_un.d_val;
547 const Elf_Addr *hashtab = (const Elf_Addr *)
548 (obj->relocbase + dynp->d_un.d_ptr);
549 obj->nbuckets = hashtab[0];
550 obj->nchains = hashtab[1];
551 obj->buckets = hashtab + 2;
552 obj->chains = obj->buckets + obj->nbuckets;
558 Needed_Entry *nep = NEW(Needed_Entry);
559 nep->name = dynp->d_un.d_val;
564 needed_tail = &nep->next;
569 obj->pltgot = (Elf_Addr *) (obj->relocbase + dynp->d_un.d_ptr);
577 obj->symbolic = true;
582 * We have to wait until later to process this, because we
583 * might not have gotten the address of the string table yet.
589 /* Not used by the dynamic linker. */
593 obj->init = (InitFunc) (obj->relocbase + dynp->d_un.d_ptr);
597 obj->fini = (InitFunc) (obj->relocbase + dynp->d_un.d_ptr);
601 /* XXX - not implemented yet */
602 dbg("Filling in DT_DEBUG entry");
603 ((Elf_Dyn*)dynp)->d_un.d_ptr = (Elf_Addr) &r_debug;
607 dbg("Ignoring d_tag %d = %#x", dynp->d_tag, dynp->d_tag);
614 if (plttype == DT_RELA) {
615 obj->pltrela = (const Elf_Rela *) obj->pltrel;
617 obj->pltrelasize = obj->pltrelsize;
621 if (dyn_rpath != NULL)
622 obj->rpath = obj->strtab + dyn_rpath->d_un.d_val;
626 * Process a shared object's program header. This is used only for the
627 * main program, when the kernel has already loaded the main program
628 * into memory before calling the dynamic linker. It creates and
629 * returns an Obj_Entry structure.
632 digest_phdr(const Elf_Phdr *phdr, int phnum, caddr_t entry, const char *path)
635 const Elf_Phdr *phlimit = phdr + phnum;
640 for (ph = phdr; ph < phlimit; ph++) {
641 switch (ph->p_type) {
644 if ((const Elf_Phdr *)ph->p_vaddr != phdr) {
645 _rtld_error("%s: invalid PT_PHDR", path);
648 obj->phdr = (const Elf_Phdr *) ph->p_vaddr;
649 obj->phsize = ph->p_memsz;
653 obj->interp = (const char *) ph->p_vaddr;
658 _rtld_error("%s: too many PT_LOAD segments", path);
661 if (nsegs == 0) { /* First load segment */
662 obj->vaddrbase = trunc_page(ph->p_vaddr);
663 obj->mapbase = (caddr_t) obj->vaddrbase;
664 obj->relocbase = obj->mapbase - obj->vaddrbase;
665 obj->textsize = round_page(ph->p_vaddr + ph->p_memsz) -
667 } else { /* Last load segment */
668 obj->mapsize = round_page(ph->p_vaddr + ph->p_memsz) -
675 obj->dynamic = (const Elf_Dyn *) ph->p_vaddr;
680 _rtld_error("%s: too few PT_LOAD segments", path);
689 dlcheck(void *handle)
693 for (obj = obj_list; obj != NULL; obj = obj->next)
694 if (obj == (Obj_Entry *) handle)
697 if (obj == NULL || obj->dl_refcount == 0) {
698 _rtld_error("Invalid shared object handle %p", handle);
705 * If the given object is already in the donelist, return true. Otherwise
706 * add the object to the list and return false.
709 donelist_check(DoneList *dlp, Obj_Entry *obj)
713 for (i = 0; i < dlp->num_used; i++)
714 if (dlp->objs[i] == obj)
717 * Our donelist allocation should always be sufficient. But if
718 * our threads locking isn't working properly, more shared objects
719 * could have been loaded since we allocated the list. That should
720 * never happen, but we'll handle it properly just in case it does.
722 if (dlp->num_used < dlp->num_alloc)
723 dlp->objs[dlp->num_used++] = obj;
728 * Hash function for symbol table lookup. Don't even think about changing
729 * this. It is specified by the System V ABI.
732 elf_hash(const char *name)
734 const unsigned char *p = (const unsigned char *) name;
740 if ((g = h & 0xf0000000) != 0)
748 * Find the library with the given name, and return its full pathname.
749 * The returned string is dynamically allocated. Generates an error
750 * message and returns NULL if the library cannot be found.
752 * If the second argument is non-NULL, then it refers to an already-
753 * loaded shared object, whose library search path will be searched.
755 * The search order is:
756 * rpath in the referencing file
762 find_library(const char *name, const Obj_Entry *refobj)
766 if (strchr(name, '/') != NULL) { /* Hard coded pathname */
767 if (name[0] != '/' && !trust) {
768 _rtld_error("Absolute pathname required for shared object \"%s\"",
772 return xstrdup(name);
775 dbg(" Searching for \"%s\"", name);
777 if ((refobj != NULL &&
778 (pathname = search_library_path(name, refobj->rpath)) != NULL) ||
779 (pathname = search_library_path(name, ld_library_path)) != NULL ||
780 (pathname = search_library_path(name, gethints())) != NULL ||
781 (pathname = search_library_path(name, STANDARD_LIBRARY_PATH)) != NULL)
784 _rtld_error("Shared object \"%s\" not found", name);
789 * Given a symbol number in a referencing object, find the corresponding
790 * definition of the symbol. Returns a pointer to the symbol, or NULL if
791 * no definition was found. Returns a pointer to the Obj_Entry of the
792 * defining object via the reference parameter DEFOBJ_OUT.
795 find_symdef(unsigned long symnum, Obj_Entry *refobj,
796 const Obj_Entry **defobj_out, bool in_plt)
802 const Obj_Entry *obj;
803 const Obj_Entry *defobj;
804 const Objlist_Entry *elm;
808 ref = refobj->symtab + symnum;
809 name = refobj->strtab + ref->st_name;
810 hash = elf_hash(name);
813 donelist_init(&donelist);
815 /* Look first in the referencing object if linked symbolically. */
816 if (refobj->symbolic && !donelist_check(&donelist, refobj)) {
817 symp = symlook_obj(name, hash, refobj, in_plt);
824 /* Search all objects loaded at program start up. */
825 if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
826 symp = symlook_list(name, hash, &list_main, &obj, in_plt, &donelist);
828 (def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
834 /* Search all dlopened DAGs containing the referencing object. */
835 STAILQ_FOREACH(elm, &refobj->dldags, link) {
836 if (def != NULL && ELF_ST_BIND(def->st_info) != STB_WEAK)
838 symp = symlook_list(name, hash, &elm->obj->dagmembers, &obj, in_plt,
841 (def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
847 /* Search all RTLD_GLOBAL objects. */
848 if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
849 symp = symlook_list(name, hash, &list_global, &obj, in_plt, &donelist);
851 (def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
858 * Search the dynamic linker itself, and possibly resolve the
859 * symbol from there. This is how the application links to
860 * dynamic linker services such as dlopen. Only the values listed
861 * in the "exports" array can be resolved from the dynamic linker.
863 if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
864 symp = symlook_obj(name, hash, &obj_rtld, in_plt);
865 if (symp != NULL && is_exported(symp)) {
872 * If we found no definition and the reference is weak, treat the
873 * symbol as having the value zero.
875 if (def == NULL && ELF_ST_BIND(ref->st_info) == STB_WEAK) {
881 *defobj_out = defobj;
883 _rtld_error("%s: Undefined symbol \"%s\"", refobj->path, name);
888 * Return the search path from the ldconfig hints file, reading it if
889 * necessary. Returns NULL if there are problems with the hints file,
890 * or if the search path there is empty.
899 struct elfhints_hdr hdr;
902 /* Keep from trying again in case the hints file is bad. */
905 if ((fd = open(_PATH_ELF_HINTS, O_RDONLY)) == -1)
907 if (read(fd, &hdr, sizeof hdr) != sizeof hdr ||
908 hdr.magic != ELFHINTS_MAGIC ||
913 p = xmalloc(hdr.dirlistlen + 1);
914 if (lseek(fd, hdr.strtab + hdr.dirlist, SEEK_SET) == -1 ||
915 read(fd, p, hdr.dirlistlen + 1) != hdr.dirlistlen + 1) {
923 return hints[0] != '\0' ? hints : NULL;
927 init_dag(Obj_Entry *root)
931 donelist_init(&donelist);
932 init_dag1(root, root, &donelist);
936 init_dag1(Obj_Entry *root, Obj_Entry *obj, DoneList *dlp)
938 const Needed_Entry *needed;
940 if (donelist_check(dlp, obj))
942 objlist_push_tail(&obj->dldags, root);
943 objlist_push_tail(&root->dagmembers, obj);
944 for (needed = obj->needed; needed != NULL; needed = needed->next)
945 if (needed->obj != NULL)
946 init_dag1(root, needed->obj, dlp);
950 * Initialize the dynamic linker. The argument is the address at which
951 * the dynamic linker has been mapped into memory. The primary task of
952 * this function is to relocate the dynamic linker.
955 init_rtld(caddr_t mapbase)
958 * Conjure up an Obj_Entry structure for the dynamic linker.
960 * The "path" member is supposed to be dynamically-allocated, but we
961 * aren't yet initialized sufficiently to do that. Below we will
962 * replace the static version with a dynamically-allocated copy.
964 obj_rtld.path = PATH_RTLD;
965 obj_rtld.rtld = true;
966 obj_rtld.mapbase = mapbase;
968 obj_rtld.relocbase = mapbase;
970 if (&_DYNAMIC != 0) {
971 obj_rtld.dynamic = rtld_dynamic(&obj_rtld);
972 digest_dynamic(&obj_rtld);
973 assert(obj_rtld.needed == NULL);
974 assert(!obj_rtld.textrel);
977 * Temporarily put the dynamic linker entry into the object list, so
978 * that symbols can be found.
980 obj_list = &obj_rtld;
981 obj_tail = &obj_rtld.next;
984 relocate_objects(&obj_rtld, true);
987 /* Make the object list empty again. */
989 obj_tail = &obj_list;
992 /* Replace the path with a dynamically allocated copy. */
993 obj_rtld.path = xstrdup(obj_rtld.path);
995 r_debug.r_brk = r_debug_state;
996 r_debug.r_state = RT_CONSISTENT;
1000 * Add the init functions from a needed object list (and its recursive
1001 * needed objects) to "list". This is not used directly; it is a helper
1002 * function for initlist_add_objects(). The write lock must be held
1003 * when this function is called.
1006 initlist_add_neededs(Needed_Entry *needed, Objlist *list)
1008 /* Recursively process the successor needed objects. */
1009 if (needed->next != NULL)
1010 initlist_add_neededs(needed->next, list);
1012 /* Process the current needed object. */
1013 if (needed->obj != NULL)
1014 initlist_add_objects(needed->obj, &needed->obj->next, list);
1018 * Scan all of the DAGs rooted in the range of objects from "obj" to
1019 * "tail" and add their init functions to "list". This recurses over
1020 * the DAGs and ensure the proper init ordering such that each object's
1021 * needed libraries are initialized before the object itself. At the
1022 * same time, this function adds the objects to the global finalization
1023 * list "list_fini" in the opposite order. The write lock must be
1024 * held when this function is called.
1027 initlist_add_objects(Obj_Entry *obj, Obj_Entry **tail, Objlist *list)
1031 obj->init_done = true;
1033 /* Recursively process the successor objects. */
1034 if (&obj->next != tail)
1035 initlist_add_objects(obj->next, tail, list);
1037 /* Recursively process the needed objects. */
1038 if (obj->needed != NULL)
1039 initlist_add_neededs(obj->needed, list);
1041 /* Add the object to the init list. */
1042 if (obj->init != NULL)
1043 objlist_push_tail(list, obj);
1045 /* Add the object to the global fini list in the reverse order. */
1046 if (obj->fini != NULL)
1047 objlist_push_head(&list_fini, obj);
1051 is_exported(const Elf_Sym *def)
1053 func_ptr_type value;
1054 const func_ptr_type *p;
1056 value = (func_ptr_type)(obj_rtld.relocbase + def->st_value);
1057 for (p = exports; *p != NULL; p++)
1064 * Given a shared object, traverse its list of needed objects, and load
1065 * each of them. Returns 0 on success. Generates an error message and
1066 * returns -1 on failure.
1069 load_needed_objects(Obj_Entry *first)
1073 for (obj = first; obj != NULL; obj = obj->next) {
1074 Needed_Entry *needed;
1076 for (needed = obj->needed; needed != NULL; needed = needed->next) {
1077 const char *name = obj->strtab + needed->name;
1078 char *path = find_library(name, obj);
1081 if (path == NULL && !ld_tracing)
1085 needed->obj = load_object(path);
1086 if (needed->obj == NULL && !ld_tracing)
1087 return -1; /* XXX - cleanup */
1096 load_preload_objects(void)
1098 char *p = ld_preload;
1099 static const char delim[] = " \t:;";
1104 p += strspn(p, delim);
1105 while (*p != '\0') {
1106 size_t len = strcspn(p, delim);
1112 if ((path = find_library(p, NULL)) == NULL)
1114 if (load_object(path) == NULL)
1115 return -1; /* XXX - cleanup */
1118 p += strspn(p, delim);
1124 * Load a shared object into memory, if it is not already loaded. The
1125 * argument must be a string allocated on the heap. This function assumes
1126 * responsibility for freeing it when necessary.
1128 * Returns a pointer to the Obj_Entry for the object. Returns NULL
1132 load_object(char *path)
1138 for (obj = obj_list->next; obj != NULL; obj = obj->next)
1139 if (strcmp(obj->path, path) == 0)
1143 * If we didn't find a match by pathname, open the file and check
1144 * again by device and inode. This avoids false mismatches caused
1145 * by multiple links or ".." in pathnames.
1147 * To avoid a race, we open the file and use fstat() rather than
1151 if ((fd = open(path, O_RDONLY)) == -1) {
1152 _rtld_error("Cannot open \"%s\"", path);
1155 if (fstat(fd, &sb) == -1) {
1156 _rtld_error("Cannot fstat \"%s\"", path);
1160 for (obj = obj_list->next; obj != NULL; obj = obj->next) {
1161 if (obj->ino == sb.st_ino && obj->dev == sb.st_dev) {
1168 if (obj == NULL) { /* First use of this object, so we must map it in */
1169 dbg("loading \"%s\"", path);
1170 obj = map_object(fd, path, &sb);
1178 digest_dynamic(obj);
1181 obj_tail = &obj->next;
1183 linkmap_add(obj); /* for GDB */
1185 dbg(" %p .. %p: %s", obj->mapbase,
1186 obj->mapbase + obj->mapsize - 1, obj->path);
1188 dbg(" WARNING: %s has impure text", obj->path);
1197 * Check for locking violations and die if one is found.
1204 rcount = lockinfo.rcount;
1205 wcount = lockinfo.wcount;
1206 assert(rcount >= 0);
1207 assert(wcount >= 0);
1208 if (wcount > 1 || (wcount != 0 && rcount != 0)) {
1209 _rtld_error("Application locking error: %d readers and %d writers"
1210 " in dynamic linker. See DLLOCKINIT(3) in manual pages.",
1217 obj_from_addr(const void *addr)
1219 unsigned long endhash;
1222 endhash = elf_hash(END_SYM);
1223 for (obj = obj_list; obj != NULL; obj = obj->next) {
1224 const Elf_Sym *endsym;
1226 if (addr < (void *) obj->mapbase)
1228 if ((endsym = symlook_obj(END_SYM, endhash, obj, true)) == NULL)
1229 continue; /* No "end" symbol?! */
1230 if (addr < (void *) (obj->relocbase + endsym->st_value))
1237 * Call the finalization functions for each of the objects in "list"
1238 * which are unreferenced. All of the objects are expected to have
1239 * non-NULL fini functions.
1242 objlist_call_fini(Objlist *list)
1246 STAILQ_FOREACH(elm, list, link) {
1247 if (elm->obj->refcount == 0) {
1248 dbg("calling fini function for %s", elm->obj->path);
1249 (*elm->obj->fini)();
1255 * Call the initialization functions for each of the objects in
1256 * "list". All of the objects are expected to have non-NULL init
1260 objlist_call_init(Objlist *list)
1264 STAILQ_FOREACH(elm, list, link) {
1265 dbg("calling init function for %s", elm->obj->path);
1266 (*elm->obj->init)();
1271 objlist_clear(Objlist *list)
1275 while (!STAILQ_EMPTY(list)) {
1276 elm = STAILQ_FIRST(list);
1277 STAILQ_REMOVE_HEAD(list, link);
1282 static Objlist_Entry *
1283 objlist_find(Objlist *list, const Obj_Entry *obj)
1287 STAILQ_FOREACH(elm, list, link)
1288 if (elm->obj == obj)
1294 objlist_init(Objlist *list)
1300 objlist_push_head(Objlist *list, Obj_Entry *obj)
1304 elm = NEW(Objlist_Entry);
1306 STAILQ_INSERT_HEAD(list, elm, link);
1310 objlist_push_tail(Objlist *list, Obj_Entry *obj)
1314 elm = NEW(Objlist_Entry);
1316 STAILQ_INSERT_TAIL(list, elm, link);
1320 objlist_remove(Objlist *list, Obj_Entry *obj)
1324 if ((elm = objlist_find(list, obj)) != NULL) {
1325 STAILQ_REMOVE(list, elm, Struct_Objlist_Entry, link);
1331 * Remove all of the unreferenced objects from "list".
1334 objlist_remove_unref(Objlist *list)
1339 STAILQ_INIT(&newlist);
1340 while (!STAILQ_EMPTY(list)) {
1341 elm = STAILQ_FIRST(list);
1342 STAILQ_REMOVE_HEAD(list, link);
1343 if (elm->obj->refcount == 0)
1346 STAILQ_INSERT_TAIL(&newlist, elm, link);
1352 * Relocate newly-loaded shared objects. The argument is a pointer to
1353 * the Obj_Entry for the first such object. All objects from the first
1354 * to the end of the list of objects are relocated. Returns 0 on success,
1358 relocate_objects(Obj_Entry *first, bool bind_now)
1362 for (obj = first; obj != NULL; obj = obj->next) {
1363 if (obj != &obj_rtld)
1364 dbg("relocating \"%s\"", obj->path);
1365 if (obj->nbuckets == 0 || obj->nchains == 0 || obj->buckets == NULL ||
1366 obj->symtab == NULL || obj->strtab == NULL) {
1367 _rtld_error("%s: Shared object has no run-time symbol table",
1373 /* There are relocations to the write-protected text segment. */
1374 if (mprotect(obj->mapbase, obj->textsize,
1375 PROT_READ|PROT_WRITE|PROT_EXEC) == -1) {
1376 _rtld_error("%s: Cannot write-enable text segment: %s",
1377 obj->path, strerror(errno));
1382 /* Process the non-PLT relocations. */
1383 if (reloc_non_plt(obj, &obj_rtld))
1386 if (obj->textrel) { /* Re-protected the text segment. */
1387 if (mprotect(obj->mapbase, obj->textsize,
1388 PROT_READ|PROT_EXEC) == -1) {
1389 _rtld_error("%s: Cannot write-protect text segment: %s",
1390 obj->path, strerror(errno));
1395 /* Process the PLT relocations. */
1396 if (reloc_plt(obj) == -1)
1398 /* Relocate the jump slots if we are doing immediate binding. */
1400 if (reloc_jmpslots(obj) == -1)
1405 * Set up the magic number and version in the Obj_Entry. These
1406 * were checked in the crt1.o from the original ElfKit, so we
1407 * set them for backward compatibility.
1409 obj->magic = RTLD_MAGIC;
1410 obj->version = RTLD_VERSION;
1412 /* Set the special PLT or GOT entries. */
1420 * Cleanup procedure. It will be called (by the atexit mechanism) just
1421 * before the process exits.
1430 /* Clear all the reference counts so the fini functions will be called. */
1431 for (obj = obj_list; obj != NULL; obj = obj->next)
1434 objlist_call_fini(&list_fini);
1435 /* No need to remove the items from the list, since we are exiting. */
1439 search_library_path(const char *name, const char *path)
1441 size_t namelen = strlen(name);
1442 const char *p = path;
1447 p += strspn(p, ":;");
1448 while (*p != '\0') {
1449 size_t len = strcspn(p, ":;");
1451 if (*p == '/' || trust) {
1453 const char *dir = p;
1454 size_t dirlen = len;
1456 pathname = xmalloc(dirlen + 1 + namelen + 1);
1457 strncpy(pathname, dir, dirlen);
1458 pathname[dirlen] = '/';
1459 strcpy(pathname + dirlen + 1, name);
1461 dbg(" Trying \"%s\"", pathname);
1462 if (access(pathname, F_OK) == 0) /* We found it */
1468 p += strspn(p, ":;");
1475 dlclose(void *handle)
1480 root = dlcheck(handle);
1486 /* Unreference the object and its dependencies. */
1487 root->dl_refcount--;
1490 if (root->refcount == 0) {
1492 * The object is no longer referenced, so we must unload it.
1493 * First, call the fini functions with no locks held.
1496 objlist_call_fini(&list_fini);
1498 objlist_remove_unref(&list_fini);
1500 /* Finish cleaning up the newly-unreferenced objects. */
1501 GDB_STATE(RT_DELETE);
1502 unload_object(root);
1503 GDB_STATE(RT_CONSISTENT);
1512 char *msg = error_message;
1513 error_message = NULL;
1518 * This function is deprecated and has no effect.
1521 dllockinit(void *context,
1522 void *(*lock_create)(void *context),
1523 void (*rlock_acquire)(void *lock),
1524 void (*wlock_acquire)(void *lock),
1525 void (*lock_release)(void *lock),
1526 void (*lock_destroy)(void *lock),
1527 void (*context_destroy)(void *context))
1529 static void *cur_context;
1530 static void (*cur_context_destroy)(void *);
1532 /* Just destroy the context from the previous call, if necessary. */
1533 if (cur_context_destroy != NULL)
1534 cur_context_destroy(cur_context);
1535 cur_context = context;
1536 cur_context_destroy = context_destroy;
1540 dlopen(const char *name, int mode)
1542 Obj_Entry **old_obj_tail;
1546 objlist_init(&initlist);
1551 old_obj_tail = obj_tail;
1557 char *path = find_library(name, obj_main);
1559 obj = load_object(path);
1564 if (mode & RTLD_GLOBAL && objlist_find(&list_global, obj) == NULL)
1565 objlist_push_tail(&list_global, obj);
1566 mode &= RTLD_MODEMASK;
1567 if (*old_obj_tail != NULL) { /* We loaded something new. */
1568 assert(*old_obj_tail == obj);
1570 if (load_needed_objects(obj) == -1 ||
1571 (init_dag(obj), relocate_objects(obj, mode == RTLD_NOW)) == -1) {
1574 if (obj->refcount == 0)
1578 /* Make list of init functions to call. */
1579 initlist_add_objects(obj, &obj->next, &initlist);
1584 GDB_STATE(RT_CONSISTENT);
1586 /* Call the init functions with no locks held. */
1588 objlist_call_init(&initlist);
1590 objlist_clear(&initlist);
1596 dlsym(void *handle, const char *name)
1598 const Obj_Entry *obj;
1601 const Obj_Entry *defobj;
1603 hash = elf_hash(name);
1608 if (handle == NULL || handle == RTLD_NEXT) {
1611 retaddr = __builtin_return_address(0); /* __GNUC__ only */
1612 if ((obj = obj_from_addr(retaddr)) == NULL) {
1613 _rtld_error("Cannot determine caller's shared object");
1617 if (handle == NULL) { /* Just the caller's shared object. */
1618 def = symlook_obj(name, hash, obj, true);
1620 } else { /* All the shared objects after the caller's */
1621 while ((obj = obj->next) != NULL) {
1622 if ((def = symlook_obj(name, hash, obj, true)) != NULL) {
1629 if ((obj = dlcheck(handle)) == NULL) {
1634 if (obj->mainprog) {
1637 /* Search main program and all libraries loaded by it. */
1638 donelist_init(&donelist);
1639 def = symlook_list(name, hash, &list_main, &defobj, true,
1643 * XXX - This isn't correct. The search should include the whole
1644 * DAG rooted at the given object.
1646 def = symlook_obj(name, hash, obj, true);
1653 return defobj->relocbase + def->st_value;
1656 _rtld_error("Undefined symbol \"%s\"", name);
1662 dladdr(const void *addr, Dl_info *info)
1664 const Obj_Entry *obj;
1667 unsigned long symoffset;
1670 obj = obj_from_addr(addr);
1672 _rtld_error("No shared object contains address");
1676 info->dli_fname = obj->path;
1677 info->dli_fbase = obj->mapbase;
1678 info->dli_saddr = (void *)0;
1679 info->dli_sname = NULL;
1682 * Walk the symbol list looking for the symbol whose address is
1683 * closest to the address sent in.
1685 for (symoffset = 0; symoffset < obj->nchains; symoffset++) {
1686 def = obj->symtab + symoffset;
1689 * For skip the symbol if st_shndx is either SHN_UNDEF or
1692 if (def->st_shndx == SHN_UNDEF || def->st_shndx == SHN_COMMON)
1696 * If the symbol is greater than the specified address, or if it
1697 * is further away from addr than the current nearest symbol,
1700 symbol_addr = obj->relocbase + def->st_value;
1701 if (symbol_addr > addr || symbol_addr < info->dli_saddr)
1704 /* Update our idea of the nearest symbol. */
1705 info->dli_sname = obj->strtab + def->st_name;
1706 info->dli_saddr = symbol_addr;
1709 if (info->dli_saddr == addr)
1717 linkmap_add(Obj_Entry *obj)
1719 struct link_map *l = &obj->linkmap;
1720 struct link_map *prev;
1722 obj->linkmap.l_name = obj->path;
1723 obj->linkmap.l_addr = obj->mapbase;
1724 obj->linkmap.l_ld = obj->dynamic;
1726 /* GDB needs load offset on MIPS to use the symbols */
1727 obj->linkmap.l_offs = obj->relocbase;
1730 if (r_debug.r_map == NULL) {
1736 * Scan to the end of the list, but not past the entry for the
1737 * dynamic linker, which we want to keep at the very end.
1739 for (prev = r_debug.r_map;
1740 prev->l_next != NULL && prev->l_next != &obj_rtld.linkmap;
1741 prev = prev->l_next)
1744 /* Link in the new entry. */
1746 l->l_next = prev->l_next;
1747 if (l->l_next != NULL)
1748 l->l_next->l_prev = l;
1753 linkmap_delete(Obj_Entry *obj)
1755 struct link_map *l = &obj->linkmap;
1757 if (l->l_prev == NULL) {
1758 if ((r_debug.r_map = l->l_next) != NULL)
1759 l->l_next->l_prev = NULL;
1763 if ((l->l_prev->l_next = l->l_next) != NULL)
1764 l->l_next->l_prev = l->l_prev;
1768 * Function for the debugger to set a breakpoint on to gain control.
1776 * Set a pointer variable in the main program to the given value. This
1777 * is used to set key variables such as "environ" before any of the
1778 * init functions are called.
1781 set_program_var(const char *name, const void *value)
1783 const Obj_Entry *obj;
1786 hash = elf_hash(name);
1787 for (obj = obj_main; obj != NULL; obj = obj->next) {
1790 if ((def = symlook_obj(name, hash, obj, false)) != NULL) {
1793 addr = (const void **)(obj->relocbase + def->st_value);
1794 dbg("\"%s\": *%p <-- %p", name, addr, value);
1801 static const Elf_Sym *
1802 symlook_list(const char *name, unsigned long hash, Objlist *objlist,
1803 const Obj_Entry **defobj_out, bool in_plt, DoneList *dlp)
1805 const Elf_Sym *symp;
1807 const Obj_Entry *defobj;
1808 const Objlist_Entry *elm;
1812 STAILQ_FOREACH(elm, objlist, link) {
1813 if (donelist_check(dlp, elm->obj))
1815 if ((symp = symlook_obj(name, hash, elm->obj, in_plt)) != NULL) {
1816 if (def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK) {
1819 if (ELF_ST_BIND(def->st_info) != STB_WEAK)
1825 *defobj_out = defobj;
1830 * Search the symbol table of a single shared object for a symbol of
1831 * the given name. Returns a pointer to the symbol, or NULL if no
1832 * definition was found.
1834 * The symbol's hash value is passed in for efficiency reasons; that
1835 * eliminates many recomputations of the hash value.
1838 symlook_obj(const char *name, unsigned long hash, const Obj_Entry *obj,
1841 if (obj->buckets != NULL) {
1842 unsigned long symnum = obj->buckets[hash % obj->nbuckets];
1844 while (symnum != STN_UNDEF) {
1845 const Elf_Sym *symp;
1848 if (symnum >= obj->nchains)
1849 return NULL; /* Bad object */
1850 symp = obj->symtab + symnum;
1851 strp = obj->strtab + symp->st_name;
1853 if (strcmp(name, strp) == 0)
1854 return symp->st_shndx != SHN_UNDEF ||
1855 (!in_plt && symp->st_value != 0 &&
1856 ELF_ST_TYPE(symp->st_info) == STT_FUNC) ? symp : NULL;
1858 symnum = obj->chains[symnum];
1865 trace_loaded_objects(Obj_Entry *obj)
1867 char *fmt1, *fmt2, *fmt, *main_local;
1870 if ((main_local = getenv("LD_TRACE_LOADED_OBJECTS_PROGNAME")) == NULL)
1873 if ((fmt1 = getenv("LD_TRACE_LOADED_OBJECTS_FMT1")) == NULL)
1874 fmt1 = "\t%o => %p (%x)\n";
1876 if ((fmt2 = getenv("LD_TRACE_LOADED_OBJECTS_FMT2")) == NULL)
1877 fmt2 = "\t%o (%x)\n";
1879 for (; obj; obj = obj->next) {
1880 Needed_Entry *needed;
1884 for (needed = obj->needed; needed; needed = needed->next) {
1885 if (needed->obj != NULL) {
1886 if (needed->obj->traced)
1888 needed->obj->traced = true;
1889 path = needed->obj->path;
1893 name = (char *)obj->strtab + needed->name;
1894 is_lib = strncmp(name, "lib", 3) == 0; /* XXX - bogus */
1896 fmt = is_lib ? fmt1 : fmt2;
1897 while ((c = *fmt++) != '\0') {
1923 printf("%s", main_local);
1926 printf("%s", obj_main->path);
1933 printf("%d", sodp->sod_major);
1936 printf("%d", sodp->sod_minor);
1943 printf("%p", needed->obj ? needed->obj->mapbase : 0);
1955 * Unload a dlopened object and its dependencies from memory and from
1956 * our data structures. It is assumed that the DAG rooted in the
1957 * object has already been unreferenced, and that the object has a
1958 * reference count of 0.
1961 unload_object(Obj_Entry *root)
1967 assert(root->refcount == 0);
1969 /* Remove the DAG from all objects' DAG lists. */
1970 STAILQ_FOREACH(elm, &root->dagmembers , link)
1971 objlist_remove(&elm->obj->dldags, root);
1973 /* Remove the DAG from the RTLD_GLOBAL list. */
1974 objlist_remove(&list_global, root);
1976 /* Unmap all objects that are no longer referenced. */
1977 linkp = &obj_list->next;
1978 while ((obj = *linkp) != NULL) {
1979 if (obj->refcount == 0) {
1980 dbg("unloading \"%s\"", obj->path);
1981 munmap(obj->mapbase, obj->mapsize);
1982 linkmap_delete(obj);
1993 unref_dag(Obj_Entry *root)
1995 const Needed_Entry *needed;
1997 assert(root->refcount != 0);
1999 if (root->refcount == 0)
2000 for (needed = root->needed; needed != NULL; needed = needed->next)
2001 if (needed->obj != NULL)
2002 unref_dag(needed->obj);
2006 * Non-mallocing printf, for use by malloc itself.
2007 * XXX - This doesn't belong in this module.
2010 xprintf(const char *fmt, ...)
2016 vsprintf(buf, fmt, ap);
2017 (void)write(1, buf, strlen(buf));