21 static char errbuf[128];
27 #if ULONG_MAX == 0xffffffff
28 typedef Elf32_Ehdr Ehdr;
29 typedef Elf32_Phdr Phdr;
30 typedef Elf32_Sym Sym;
31 #define R_TYPE(x) ((x)&255)
32 #define R_SYM(x) ((x)>>8)
34 typedef Elf64_Ehdr Ehdr;
35 typedef Elf64_Phdr Phdr;
36 typedef Elf64_Sym Sym;
37 #define R_TYPE(x) ((x)&0xffffffff)
38 #define R_SYM(x) ((x)>>32)
53 struct dso *next, *prev;
71 void __init_ssp(size_t *);
73 static struct dso *head, *tail, *libc;
74 static char *env_path, *sys_path, *r_path;
79 static jmp_buf rtld_fail;
80 static pthread_rwlock_t lock;
81 static struct debug debug;
83 struct debug *_dl_debug_addr = &debug;
88 static void decode_vec(size_t *v, size_t *a, size_t cnt)
90 memset(a, 0, cnt*sizeof(size_t));
91 for (; v[0]; v+=2) if (v[0]<cnt) {
97 static uint32_t hash(const char *s0)
99 const unsigned char *s = (void *)s0;
105 return h & 0xfffffff;
108 static Sym *lookup(const char *s, uint32_t h, Sym *syms, uint32_t *hashtab, char *strings)
111 for (i=hashtab[2+h%hashtab[0]]; i; i=hashtab[2+hashtab[0]+i]) {
112 if (!strcmp(s, strings+syms[i].st_name))
118 #define OK_TYPES (1<<STT_NOTYPE | 1<<STT_OBJECT | 1<<STT_FUNC | 1<<STT_COMMON)
119 #define OK_BINDS (1<<STB_GLOBAL | 1<<STB_WEAK)
121 static void *find_sym(struct dso *dso, const char *s, int need_def)
123 uint32_t h = hash(s);
125 if (h==0x6b366be && !strcmp(s, "dlopen")) rtld_used = 1;
126 if (h==0x6b3afd && !strcmp(s, "dlsym")) rtld_used = 1;
127 if (h==0x595a4cc && !strcmp(s, "__stack_chk_fail")) ssp_used = 1;
128 for (; dso; dso=dso->next) {
130 if (!dso->global) continue;
131 sym = lookup(s, h, dso->syms, dso->hashtab, dso->strings);
132 if (sym && (!need_def || sym->st_shndx) && sym->st_value
133 && (1<<(sym->st_info&0xf) & OK_TYPES)
134 && (1<<(sym->st_info>>4) & OK_BINDS)) {
135 if (def && sym->st_info>>4 == STB_WEAK) continue;
136 def = dso->base + sym->st_value;
137 if (sym->st_info>>4 == STB_GLOBAL) break;
143 static void do_relocs(unsigned char *base, size_t *rel, size_t rel_size, size_t stride, Sym *syms, char *strings, struct dso *dso)
147 size_t sym_val, sym_size;
153 for (; rel_size; rel+=stride, rel_size-=stride*sizeof(size_t)) {
154 reloc_addr = (void *)(base + rel[0]);
155 type = R_TYPE(rel[1]);
156 sym_index = R_SYM(rel[1]);
158 sym = syms + sym_index;
159 name = strings + sym->st_name;
160 ctx = IS_COPY(type) ? dso->next : dso;
161 sym_val = (size_t)find_sym(ctx, name, IS_PLT(type));
162 if (!sym_val && sym->st_info>>4 != STB_WEAK) {
163 snprintf(errbuf, sizeof errbuf,
164 "Error relocating %s: %s: symbol not found",
166 if (runtime) longjmp(rtld_fail, 1);
167 dprintf(2, "%s\n", errbuf);
170 sym_size = sym->st_size;
172 do_single_reloc(reloc_addr, type, sym_val, sym_size, base, rel[2]);
176 /* A huge hack: to make up for the wastefulness of shared libraries
177 * needing at least a page of dirty memory even if they have no global
178 * data, we reclaim the gaps at the beginning and end of writable maps
179 * and "donate" them to the heap by setting up minimal malloc
180 * structures and then freeing them. */
182 static void reclaim(unsigned char *base, size_t start, size_t end)
185 start = start + 6*sizeof(size_t)-1 & -4*sizeof(size_t);
186 end = (end & -4*sizeof(size_t)) - 2*sizeof(size_t);
187 if (start>end || end-start < 4*sizeof(size_t)) return;
188 a = (size_t *)(base + start);
189 z = (size_t *)(base + end);
191 a[-1] = z[0] = end-start + 2*sizeof(size_t) | 1;
196 static void reclaim_gaps(unsigned char *base, Phdr *ph, size_t phent, size_t phcnt)
198 for (; phcnt--; ph=(void *)((char *)ph+phent)) {
199 if (ph->p_type!=PT_LOAD) continue;
200 if ((ph->p_flags&(PF_R|PF_W))!=(PF_R|PF_W)) continue;
201 reclaim(base, ph->p_vaddr & -PAGE_SIZE, ph->p_vaddr);
202 reclaim(base, ph->p_vaddr+ph->p_memsz,
203 ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE);
207 static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dynp)
209 Ehdr buf[(896+sizeof(Ehdr))/sizeof(Ehdr)];
211 size_t addr_min=SIZE_MAX, addr_max=0, map_len;
212 size_t this_min, this_max;
217 unsigned char *map, *base;
221 ssize_t l = read(fd, buf, sizeof buf);
222 if (l<sizeof *eh) return 0;
224 phsize = eh->e_phentsize * eh->e_phnum;
225 if (phsize + sizeof *eh > l) return 0;
226 if (eh->e_phoff + phsize > l) {
227 l = pread(fd, buf+1, phsize, eh->e_phoff);
228 if (l != phsize) return 0;
229 eh->e_phoff = sizeof *eh;
231 ph = (void *)((char *)buf + eh->e_phoff);
232 for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
233 if (ph->p_type == PT_DYNAMIC)
235 if (ph->p_type != PT_LOAD) continue;
236 if (ph->p_vaddr < addr_min) {
237 addr_min = ph->p_vaddr;
238 off_start = ph->p_offset;
239 prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) |
240 ((ph->p_flags&PF_W) ? PROT_WRITE: 0) |
241 ((ph->p_flags&PF_X) ? PROT_EXEC : 0));
243 if (ph->p_vaddr+ph->p_memsz > addr_max) {
244 addr_max = ph->p_vaddr+ph->p_memsz;
248 addr_max += PAGE_SIZE-1;
249 addr_max &= -PAGE_SIZE;
250 addr_min &= -PAGE_SIZE;
251 off_start &= -PAGE_SIZE;
252 map_len = addr_max - addr_min + off_start;
253 /* The first time, we map too much, possibly even more than
254 * the length of the file. This is okay because we will not
255 * use the invalid part; we just need to reserve the right
256 * amount of virtual address space to map over later. */
257 map = mmap((void *)addr_min, map_len, prot, MAP_PRIVATE, fd, off_start);
258 if (map==MAP_FAILED) return 0;
259 base = map - addr_min;
260 ph = (void *)((char *)buf + eh->e_phoff);
261 for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
262 if (ph->p_type != PT_LOAD) continue;
263 /* Reuse the existing mapping for the lowest-address LOAD */
264 if ((ph->p_vaddr & -PAGE_SIZE) == addr_min) continue;
265 this_min = ph->p_vaddr & -PAGE_SIZE;
266 this_max = ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE;
267 off_start = ph->p_offset & -PAGE_SIZE;
268 prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) |
269 ((ph->p_flags&PF_W) ? PROT_WRITE: 0) |
270 ((ph->p_flags&PF_X) ? PROT_EXEC : 0));
271 if (mmap(base+this_min, this_max-this_min, prot, MAP_PRIVATE|MAP_FIXED, fd, off_start) == MAP_FAILED)
273 if (ph->p_memsz > ph->p_filesz) {
274 size_t brk = (size_t)base+ph->p_vaddr+ph->p_filesz;
275 size_t pgbrk = brk+PAGE_SIZE-1 & -PAGE_SIZE;
276 memset((void *)brk, 0, pgbrk-brk & PAGE_SIZE-1);
277 if (pgbrk-(size_t)base < this_max && mmap((void *)pgbrk, (size_t)base+this_max-pgbrk, prot, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) == MAP_FAILED)
281 for (i=0; ((size_t *)(base+dyn))[i]; i+=2)
282 if (((size_t *)(base+dyn))[i]==DT_TEXTREL) {
283 if (mprotect(map, map_len, PROT_READ|PROT_WRITE|PROT_EXEC) < 0)
287 if (!runtime) reclaim_gaps(base, (void *)((char *)buf + eh->e_phoff),
288 eh->e_phentsize, eh->e_phnum);
294 munmap(map, map_len);
298 static int path_open(const char *name, const char *search, char *buf, size_t buf_size)
300 const char *s=search, *z;
306 l = z ? z-s : strlen(s);
307 snprintf(buf, buf_size, "%.*s/%s", l, s, name);
308 if ((fd = open(buf, O_RDONLY))>=0) return fd;
313 static void decode_dyn(struct dso *p)
315 size_t dyn[DYN_CNT] = {0};
316 decode_vec(p->dynv, dyn, DYN_CNT);
317 p->syms = (void *)(p->base + dyn[DT_SYMTAB]);
318 p->hashtab = (void *)(p->base + dyn[DT_HASH]);
319 p->strings = (void *)(p->base + dyn[DT_STRTAB]);
322 static struct dso *load_library(const char *name)
324 char buf[2*NAME_MAX+2];
325 const char *pathname;
326 unsigned char *base, *map;
327 size_t dyno, map_len;
332 /* Catch and block attempts to reload the implementation itself */
333 if (name[0]=='l' && name[1]=='i' && name[2]=='b') {
334 static const char *rp, reserved[] =
335 "c\0pthread\0rt\0m\0dl\0util\0xnet\0";
336 char *z = strchr(name, '.');
339 for (rp=reserved; *rp && memcmp(name+3, rp, l-3); rp+=strlen(rp)+1);
344 tail = libc->next ? libc->next : libc;
350 if (strchr(name, '/')) {
352 fd = open(name, O_RDONLY);
354 /* Search for the name to see if it's already loaded */
355 for (p=head->next; p; p=p->next) {
356 if (p->shortname && !strcmp(p->shortname, name)) {
361 if (strlen(name) > NAME_MAX) return 0;
363 if (r_path) fd = path_open(name, r_path, buf, sizeof buf);
364 if (fd < 0 && env_path) fd = path_open(name, env_path, buf, sizeof buf);
367 FILE *f = fopen(ETC_LDSO_PATH, "r");
369 if (getline(&sys_path, (size_t[1]){0}, f) > 0)
370 sys_path[strlen(sys_path)-1]=0;
374 if (sys_path) fd = path_open(name, sys_path, buf, sizeof buf);
375 else fd = path_open(name, "/lib:/usr/local/lib:/usr/lib", buf, sizeof buf);
379 if (fd < 0) return 0;
380 if (fstat(fd, &st) < 0) {
384 for (p=head->next; p; p=p->next) {
385 if (p->dev == st.st_dev && p->ino == st.st_ino) {
386 /* If this library was previously loaded with a
387 * pathname but a search found the same inode,
388 * setup its shortname so it can be found by name. */
389 if (!p->shortname) p->shortname = strrchr(p->name, '/')+1;
395 map = map_library(fd, &map_len, &base, &dyno);
398 p = calloc(1, sizeof *p + strlen(pathname) + 1);
400 munmap(map, map_len);
405 p->map_len = map_len;
407 p->dynv = (void *)(base + dyno);
414 strcpy(p->name, pathname);
415 /* Add a shortname only if name arg was not an explicit pathname. */
416 if (pathname != name) p->shortname = strrchr(p->name, '/')+1;
422 if (ldd_mode) dprintf(1, "\t%s => %s (%p)\n", name, pathname, base);
427 static void load_deps(struct dso *p)
430 struct dso ***deps = &p->deps, **tmp, *dep;
431 for (; p; p=p->next) {
432 for (i=0; p->dynv[i]; i+=2) {
433 if (p->dynv[i] != DT_RPATH) continue;
434 r_path = (void *)(p->strings + p->dynv[i+1]);
436 for (i=0; p->dynv[i]; i+=2) {
437 if (p->dynv[i] != DT_NEEDED) continue;
438 dep = load_library(p->strings + p->dynv[i+1]);
440 snprintf(errbuf, sizeof errbuf,
441 "Error loading shared library %s: %m (needed by %s)",
442 p->strings + p->dynv[i+1], p->name);
443 if (runtime) longjmp(rtld_fail, 1);
444 dprintf(2, "%s\n", errbuf);
448 tmp = realloc(*deps, sizeof(*tmp)*(ndeps+2));
449 if (!tmp) longjmp(rtld_fail, 1);
459 static void load_preload(char *s)
464 for ( ; *s && isspace(*s); s++);
465 for (z=s; *z && !isspace(*z); z++);
473 static void make_global(struct dso *p)
475 for (; p; p=p->next) p->global = 1;
478 static void reloc_all(struct dso *p)
480 size_t dyn[DYN_CNT] = {0};
481 for (; p; p=p->next) {
482 if (p->relocated) continue;
483 decode_vec(p->dynv, dyn, DYN_CNT);
484 do_relocs(p->base, (void *)(p->base+dyn[DT_JMPREL]), dyn[DT_PLTRELSZ],
485 2+(dyn[DT_PLTREL]==DT_RELA), p->syms, p->strings, head);
486 do_relocs(p->base, (void *)(p->base+dyn[DT_REL]), dyn[DT_RELSZ],
487 2, p->syms, p->strings, head);
488 do_relocs(p->base, (void *)(p->base+dyn[DT_RELA]), dyn[DT_RELASZ],
489 3, p->syms, p->strings, head);
494 static void free_all(struct dso *p)
504 static size_t find_dyn(Phdr *ph, size_t cnt, size_t stride)
506 for (; cnt--; ph = (void *)((char *)ph + stride))
507 if (ph->p_type == PT_DYNAMIC)
512 static void do_init_fini(struct dso *p)
514 size_t dyn[DYN_CNT] = {0};
515 for (; p; p=p->prev) {
516 if (p->constructed) return;
517 decode_vec(p->dynv, dyn, DYN_CNT);
518 if (dyn[0] & (1<<DT_FINI))
519 atexit((void (*)(void))(p->base + dyn[DT_FINI]));
520 if (dyn[0] & (1<<DT_INIT))
521 ((void (*)(void))(p->base + dyn[DT_INIT]))();
526 void _dl_debug_state(void)
530 void *__dynlink(int argc, char **argv)
532 size_t *auxv, aux[AUX_CNT] = {0};
536 static struct dso builtin_dsos[3];
537 struct dso *const app = builtin_dsos+0;
538 struct dso *const lib = builtin_dsos+1;
539 struct dso *const vdso = builtin_dsos+2;
542 /* Find aux vector just past environ[] */
543 for (i=argc+1; argv[i]; i++)
544 if (!memcmp(argv[i], "LD_LIBRARY_PATH=", 16))
545 env_path = argv[i]+16;
546 else if (!memcmp(argv[i], "LD_PRELOAD=", 11))
547 env_preload = argv[i]+11;
548 auxv = (void *)(argv+i+1);
550 decode_vec(auxv, aux, AUX_CNT);
552 /* Only trust user/env if kernel says we're not suid/sgid */
553 if ((aux[0]&0x7800)!=0x7800 || aux[AT_UID]!=aux[AT_EUID]
554 || aux[AT_GID]!=aux[AT_EGID] || aux[AT_SECURE]) {
559 /* If the dynamic linker was invoked as a program itself, AT_BASE
560 * will not be set. In that case, we assume the base address is
561 * the start of the page containing the PHDRs; I don't know any
562 * better approach... */
564 aux[AT_BASE] = aux[AT_PHDR] & -PAGE_SIZE;
565 aux[AT_PHDR] = aux[AT_PHENT] = aux[AT_PHNUM] = 0;
568 /* The dynamic linker load address is passed by the kernel
569 * in the AUX vector, so this is easy. */
570 lib->base = (void *)aux[AT_BASE];
571 lib->name = lib->shortname = "libc.so";
573 ehdr = (void *)lib->base;
574 lib->dynv = (void *)(lib->base + find_dyn(
575 (void *)(aux[AT_BASE]+ehdr->e_phoff),
576 ehdr->e_phnum, ehdr->e_phentsize));
580 /* Find load address of the main program, via AT_PHDR vs PT_PHDR. */
581 phdr = (void *)aux[AT_PHDR];
582 for (i=aux[AT_PHNUM]; i; i--, phdr=(void *)((char *)phdr + aux[AT_PHENT])) {
583 if (phdr->p_type == PT_PHDR)
584 app->base = (void *)(aux[AT_PHDR] - phdr->p_vaddr);
587 app->dynv = (void *)(app->base + find_dyn(
588 (void *)aux[AT_PHDR], aux[AT_PHNUM], aux[AT_PHENT]));
591 char *ldname = argv[0];
592 size_t dyno, l = strlen(ldname);
593 if (l >= 3 && !strcmp(ldname+l-3, "ldd")) ldd_mode = 1;
594 *argv++ = (void *)-1;
595 if (argv[0] && !strcmp(argv[0], "--")) *argv++ = (void *)-1;
597 dprintf(2, "musl libc/dynamic program loader\n");
598 dprintf(2, "usage: %s pathname%s\n", ldname,
599 ldd_mode ? "" : " [args]");
602 fd = open(argv[0], O_RDONLY);
604 dprintf(2, "%s: cannot load %s: %s\n", ldname, argv[0], strerror(errno));
608 ehdr = (void *)map_library(fd, &app->map_len, &app->base, &dyno);
610 dprintf(2, "%s: %s: Not a valid dynamic program\n", ldname, argv[0]);
616 app->dynv = (void *)(app->base + dyno);
617 aux[AT_ENTRY] = ehdr->e_entry;
620 app->constructed = 1;
623 /* Attach to vdso, if provided by the kernel */
624 for (i=0; auxv[i]; i+=2) {
625 size_t vdso_base = auxv[i+1];
626 if (auxv[i] != AT_SYSINFO_EHDR) continue;
627 ehdr = (void *)vdso_base;
628 phdr = (void *)(vdso_base + ehdr->e_phoff);
629 for (i=ehdr->e_phnum; i; i--, phdr=(void *)((char *)phdr + ehdr->e_phentsize)) {
630 if (phdr->p_type == PT_DYNAMIC)
631 vdso->dynv = (void *)(vdso_base + phdr->p_offset);
632 if (phdr->p_type == PT_LOAD)
633 vdso->base = (void *)(vdso_base - phdr->p_vaddr + phdr->p_offset);
635 vdso->name = vdso->shortname = "linux-gate.so.1";
643 /* Initial dso chain consists only of the app. We temporarily
644 * append the dynamic linker/libc so we can relocate it, then
645 * restore the initial chain in preparation for loading third
646 * party libraries (preload/needed). */
653 /* PAST THIS POINT, ALL LIBC INTERFACES ARE FULLY USABLE. */
655 /* Donate unused parts of app and library mapping to malloc */
656 reclaim_gaps(app->base, (void *)aux[AT_PHDR], aux[AT_PHENT], aux[AT_PHNUM]);
657 ehdr = (void *)lib->base;
658 reclaim_gaps(lib->base, (void *)(lib->base+ehdr->e_phoff),
659 ehdr->e_phentsize, ehdr->e_phnum);
661 /* Load preload/needed libraries, add their symbols to the global
662 * namespace, and perform all remaining relocations. The main
663 * program must be relocated LAST since it may contain copy
664 * relocations which depend on libraries' relocations. */
665 if (env_preload) load_preload(env_preload);
668 reloc_all(app->next);
671 if (ldd_mode) _exit(0);
673 /* Switch to runtime mode: any further failures in the dynamic
674 * linker are a reportable failure rather than a fatal startup
675 * error. If the dynamic loader (dlopen) will not be used, free
676 * all memory used by the dynamic linker. */
679 for (i=0; app->dynv[i]; i+=2)
680 if (app->dynv[i]==DT_DEBUG)
681 app->dynv[i+1] = (size_t)&debug;
683 debug.bp = _dl_debug_state;
685 debug.base = lib->base;
689 if (ssp_used) __init_ssp(auxv);
696 reclaim((void *)builtin_dsos, 0, sizeof builtin_dsos);
700 return (void *)aux[AT_ENTRY];
703 void *dlopen(const char *file, int mode)
705 struct dso *volatile p, *orig_tail = tail, *next;
709 if (!file) return head;
711 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
712 pthread_rwlock_wrlock(&lock);
714 if (setjmp(rtld_fail)) {
715 /* Clean up anything new that was (partially) loaded */
716 if (p->deps) for (i=0; p->deps[i]; i++)
717 if (p->deps[i]->global < 0)
718 p->deps[i]->global = 0;
719 for (p=orig_tail->next; p; p=next) {
721 munmap(p->map, p->map_len);
730 } else p = load_library(file);
733 snprintf(errbuf, sizeof errbuf,
734 "Error loading shared library %s: %m", file);
739 /* First load handling */
742 if (p->deps) for (i=0; p->deps[i]; i++)
743 if (!p->deps[i]->global)
744 p->deps[i]->global = -1;
745 if (!p->global) p->global = -1;
747 if (p->deps) for (i=0; p->deps[i]; i++)
748 if (p->deps[i]->global < 0)
749 p->deps[i]->global = 0;
750 if (p->global < 0) p->global = 0;
753 if (mode & RTLD_GLOBAL) {
754 if (p->deps) for (i=0; p->deps[i]; i++)
755 p->deps[i]->global = 1;
763 pthread_rwlock_unlock(&lock);
764 pthread_setcancelstate(cs, 0);
768 static void *do_dlsym(struct dso *p, const char *s, void *ra)
773 if (p == RTLD_NEXT) {
774 for (p=head; p && (unsigned char *)ra-p->map>p->map_len; p=p->next);
776 void *res = find_sym(p->next, s, 0);
777 if (!res) goto failed;
780 if (p == head || p == RTLD_DEFAULT) {
781 void *res = find_sym(head, s, 0);
782 if (!res) goto failed;
786 sym = lookup(s, h, p->syms, p->hashtab, p->strings);
787 if (sym && sym->st_value && (1<<(sym->st_info&0xf) & OK_TYPES))
788 return p->base + sym->st_value;
789 if (p->deps) for (i=0; p->deps[i]; i++) {
790 sym = lookup(s, h, p->deps[i]->syms,
791 p->deps[i]->hashtab, p->deps[i]->strings);
792 if (sym && sym->st_value && (1<<(sym->st_info&0xf) & OK_TYPES))
793 return p->deps[i]->base + sym->st_value;
797 snprintf(errbuf, sizeof errbuf, "Symbol not found: %s", s);
801 void *__dlsym(void *p, const char *s, void *ra)
804 pthread_rwlock_rdlock(&lock);
805 res = do_dlsym(p, s, ra);
806 pthread_rwlock_unlock(&lock);
810 void *dlopen(const char *file, int mode)
814 void *__dlsym(void *p, const char *s, void *ra)
822 if (!errflag) return 0;