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)
43 struct dso *next, *prev;
62 static struct dso *head, *tail, *libc;
63 static char *env_path, *sys_path, *r_path;
66 static jmp_buf rtld_fail;
67 static pthread_rwlock_t lock;
72 static void decode_vec(size_t *v, size_t *a, size_t cnt)
74 memset(a, 0, cnt*sizeof(size_t));
75 for (; v[0]; v+=2) if (v[0]<cnt) {
81 static uint32_t hash(const char *s0)
83 const unsigned char *s = (void *)s0;
92 static Sym *lookup(const char *s, uint32_t h, Sym *syms, uint32_t *hashtab, char *strings)
95 for (i=hashtab[2+h%hashtab[0]]; i; i=hashtab[2+hashtab[0]+i]) {
96 if (!strcmp(s, strings+syms[i].st_name))
102 #define OK_TYPES (1<<STT_NOTYPE | 1<<STT_OBJECT | 1<<STT_FUNC | 1<<STT_COMMON)
103 #define OK_BINDS (1<<STB_GLOBAL | 1<<STB_WEAK)
105 static void *find_sym(struct dso *dso, const char *s, int need_def)
107 uint32_t h = hash(s);
109 if (h==0x6b366be && !strcmp(s, "dlopen")) rtld_used = 1;
110 if (h==0x6b3afd && !strcmp(s, "dlsym")) rtld_used = 1;
111 for (; dso; dso=dso->next) {
113 if (!dso->global) continue;
114 sym = lookup(s, h, dso->syms, dso->hashtab, dso->strings);
115 if (sym && (!need_def || sym->st_shndx) && sym->st_value
116 && (1<<(sym->st_info&0xf) & OK_TYPES)
117 && (1<<(sym->st_info>>4) & OK_BINDS)) {
118 if (def && sym->st_info>>4 == STB_WEAK) continue;
119 def = dso->base + sym->st_value;
120 if (sym->st_info>>4 == STB_GLOBAL) break;
126 static void do_relocs(unsigned char *base, size_t *rel, size_t rel_size, size_t stride, Sym *syms, char *strings, struct dso *dso)
130 size_t sym_val, sym_size;
136 for (; rel_size; rel+=stride, rel_size-=stride*sizeof(size_t)) {
137 reloc_addr = (void *)(base + rel[0]);
138 type = R_TYPE(rel[1]);
139 sym_index = R_SYM(rel[1]);
141 sym = syms + sym_index;
142 name = strings + sym->st_name;
143 ctx = IS_COPY(type) ? dso->next : dso;
144 sym_val = (size_t)find_sym(ctx, name, IS_PLT(type));
145 if (!sym_val && sym->st_info>>4 != STB_WEAK) {
146 snprintf(errbuf, sizeof errbuf,
147 "Error relocating %s: %s: symbol not found",
149 if (runtime) longjmp(rtld_fail, 1);
150 dprintf(2, "%s\n", errbuf);
153 sym_size = sym->st_size;
155 do_single_reloc(reloc_addr, type, sym_val, sym_size, base, rel[2]);
159 /* A huge hack: to make up for the wastefulness of shared libraries
160 * needing at least a page of dirty memory even if they have no global
161 * data, we reclaim the gaps at the beginning and end of writable maps
162 * and "donate" them to the heap by setting up minimal malloc
163 * structures and then freeing them. */
165 static void reclaim(unsigned char *base, size_t start, size_t end)
168 start = start + 6*sizeof(size_t)-1 & -4*sizeof(size_t);
169 end = (end & -4*sizeof(size_t)) - 2*sizeof(size_t);
170 if (start>end || end-start < 4*sizeof(size_t)) return;
171 a = (size_t *)(base + start);
172 z = (size_t *)(base + end);
174 a[-1] = z[0] = end-start + 2*sizeof(size_t) | 1;
179 static void reclaim_gaps(unsigned char *base, Phdr *ph, size_t phent, size_t phcnt)
181 for (; phcnt--; ph=(void *)((char *)ph+phent)) {
182 if (ph->p_type!=PT_LOAD) continue;
183 if ((ph->p_flags&(PF_R|PF_W))!=(PF_R|PF_W)) continue;
184 reclaim(base, ph->p_vaddr & -PAGE_SIZE, ph->p_vaddr);
185 reclaim(base, ph->p_vaddr+ph->p_memsz,
186 ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE);
190 static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dynp)
192 Ehdr buf[(896+sizeof(Ehdr))/sizeof(Ehdr)];
194 size_t addr_min=SIZE_MAX, addr_max=0, map_len;
195 size_t this_min, this_max;
200 unsigned char *map, *base;
204 ssize_t l = read(fd, buf, sizeof buf);
205 if (l<sizeof *eh) return 0;
207 phsize = eh->e_phentsize * eh->e_phnum;
208 if (phsize + sizeof *eh > l) return 0;
209 if (eh->e_phoff + phsize > l) {
210 l = pread(fd, buf+1, phsize, eh->e_phoff);
211 if (l != phsize) return 0;
212 eh->e_phoff = sizeof *eh;
214 ph = (void *)((char *)buf + eh->e_phoff);
215 for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
216 if (ph->p_type == PT_DYNAMIC)
218 if (ph->p_type != PT_LOAD) continue;
219 if (ph->p_vaddr < addr_min) {
220 addr_min = ph->p_vaddr;
221 off_start = ph->p_offset;
222 prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) |
223 ((ph->p_flags&PF_W) ? PROT_WRITE: 0) |
224 ((ph->p_flags&PF_X) ? PROT_EXEC : 0));
226 if (ph->p_vaddr+ph->p_memsz > addr_max) {
227 addr_max = ph->p_vaddr+ph->p_memsz;
231 addr_max += PAGE_SIZE-1;
232 addr_max &= -PAGE_SIZE;
233 addr_min &= -PAGE_SIZE;
234 off_start &= -PAGE_SIZE;
235 map_len = addr_max - addr_min + off_start;
236 /* The first time, we map too much, possibly even more than
237 * the length of the file. This is okay because we will not
238 * use the invalid part; we just need to reserve the right
239 * amount of virtual address space to map over later. */
240 map = mmap((void *)addr_min, map_len, prot, MAP_PRIVATE, fd, off_start);
241 if (map==MAP_FAILED) return 0;
242 base = map - addr_min;
243 ph = (void *)((char *)buf + eh->e_phoff);
244 for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
245 if (ph->p_type != PT_LOAD) continue;
246 /* Reuse the existing mapping for the lowest-address LOAD */
247 if ((ph->p_vaddr & -PAGE_SIZE) == addr_min) continue;
248 this_min = ph->p_vaddr & -PAGE_SIZE;
249 this_max = ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE;
250 off_start = ph->p_offset & -PAGE_SIZE;
251 prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) |
252 ((ph->p_flags&PF_W) ? PROT_WRITE: 0) |
253 ((ph->p_flags&PF_X) ? PROT_EXEC : 0));
254 if (mmap(base+this_min, this_max-this_min, prot, MAP_PRIVATE|MAP_FIXED, fd, off_start) == MAP_FAILED) {
255 munmap(map, map_len);
258 if (ph->p_memsz > ph->p_filesz) {
259 size_t brk = (size_t)base+ph->p_vaddr+ph->p_filesz;
260 size_t pgbrk = brk+PAGE_SIZE-1 & -PAGE_SIZE;
261 memset((void *)brk, 0, pgbrk-brk & PAGE_SIZE-1);
262 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) {
263 munmap(map, map_len);
268 for (i=0; ((size_t *)(base+dyn))[i]; i+=2)
269 if (((size_t *)(base+dyn))[i]==DT_TEXTREL) {
270 mprotect(map, map_len, PROT_READ|PROT_WRITE|PROT_EXEC);
273 if (!runtime) reclaim_gaps(base, (void *)((char *)buf + eh->e_phoff),
274 eh->e_phentsize, eh->e_phnum);
281 static int path_open(const char *name, const char *search)
283 char buf[2*NAME_MAX+2];
284 const char *s=search, *z;
290 l = z ? z-s : strlen(s);
291 snprintf(buf, sizeof buf, "%.*s/%s", l, s, name);
292 if ((fd = open(buf, O_RDONLY))>=0) return fd;
297 static void decode_dyn(struct dso *p)
299 size_t dyn[DYN_CNT] = {0};
300 decode_vec(p->dynv, dyn, DYN_CNT);
301 p->syms = (void *)(p->base + dyn[DT_SYMTAB]);
302 p->hashtab = (void *)(p->base + dyn[DT_HASH]);
303 p->strings = (void *)(p->base + dyn[DT_STRTAB]);
306 static struct dso *load_library(const char *name)
308 unsigned char *base, *map;
309 size_t dyno, map_len;
314 /* Catch and block attempts to reload the implementation itself */
315 if (name[0]=='l' && name[1]=='i' && name[2]=='b') {
316 static const char *rp, reserved[] =
317 "c\0pthread\0rt\0m\0dl\0util\0xnet\0";
318 char *z = strchr(name, '.');
321 for (rp=reserved; *rp && memcmp(name+3, rp, l-3); rp+=strlen(rp)+1);
326 tail = libc->next ? libc->next : libc;
332 /* Search for the name to see if it's already loaded */
333 for (p=head->next; p; p=p->next) {
334 if (!strcmp(p->name, name)) {
339 if (strchr(name, '/')) {
340 fd = open(name, O_RDONLY);
342 if (strlen(name) > NAME_MAX) return 0;
344 if (r_path) fd = path_open(name, r_path);
345 if (fd < 0 && env_path) fd = path_open(name, env_path);
348 FILE *f = fopen(ETC_LDSO_PATH, "r");
350 if (getline(&sys_path, (size_t[1]){0}, f) > 0)
351 sys_path[strlen(sys_path)-1]=0;
355 if (sys_path) fd = path_open(name, sys_path);
356 else fd = path_open(name, "/lib:/usr/local/lib:/usr/lib");
359 if (fd < 0) return 0;
360 if (fstat(fd, &st) < 0) {
364 for (p=head->next; p; p=p->next) {
365 if (p->dev == st.st_dev && p->ino == st.st_ino) {
371 map = map_library(fd, &map_len, &base, &dyno);
374 p = calloc(1, sizeof *p + strlen(name) + 1);
376 munmap(map, map_len);
381 p->map_len = map_len;
383 p->dynv = (void *)(base + dyno);
390 strcpy(p->name, name);
399 static void load_deps(struct dso *p)
402 struct dso ***deps = &p->deps, **tmp, *dep;
403 for (; p; p=p->next) {
404 for (i=0; p->dynv[i]; i+=2) {
405 if (p->dynv[i] != DT_RPATH) continue;
406 r_path = (void *)(p->strings + p->dynv[i+1]);
408 for (i=0; p->dynv[i]; i+=2) {
409 if (p->dynv[i] != DT_NEEDED) continue;
410 dep = load_library(p->strings + p->dynv[i+1]);
412 snprintf(errbuf, sizeof errbuf,
413 "Error loading shared library %s: %m (needed by %s)",
414 p->strings + p->dynv[i+1], p->name);
415 if (runtime) longjmp(rtld_fail, 1);
416 dprintf(2, "%s\n", errbuf);
420 tmp = realloc(*deps, sizeof(*tmp)*(ndeps+2));
421 if (!tmp) longjmp(rtld_fail, 1);
431 static void load_preload(char *s)
436 for ( ; *s && isspace(*s); s++);
437 for (z=s; *z && !isspace(*z); z++);
445 static void make_global(struct dso *p)
447 for (; p; p=p->next) p->global = 1;
450 static void reloc_all(struct dso *p)
452 size_t dyn[DYN_CNT] = {0};
453 for (; p; p=p->next) {
454 if (p->relocated) continue;
455 decode_vec(p->dynv, dyn, DYN_CNT);
456 do_relocs(p->base, (void *)(p->base+dyn[DT_JMPREL]), dyn[DT_PLTRELSZ],
457 2+(dyn[DT_PLTREL]==DT_RELA), p->syms, p->strings, head);
458 do_relocs(p->base, (void *)(p->base+dyn[DT_REL]), dyn[DT_RELSZ],
459 2, p->syms, p->strings, head);
460 do_relocs(p->base, (void *)(p->base+dyn[DT_RELA]), dyn[DT_RELASZ],
461 3, p->syms, p->strings, head);
466 static void free_all(struct dso *p)
476 static size_t find_dyn(Phdr *ph, size_t cnt, size_t stride)
478 for (; cnt--; ph = (void *)((char *)ph + stride))
479 if (ph->p_type == PT_DYNAMIC)
484 static void do_init_fini(struct dso *p)
486 size_t dyn[DYN_CNT] = {0};
487 for (; p; p=p->prev) {
488 if (p->constructed) return;
489 decode_vec(p->dynv, dyn, DYN_CNT);
490 if (dyn[0] & (1<<DT_FINI))
491 atexit((void (*)(void))(p->base + dyn[DT_FINI]));
492 if (dyn[0] & (1<<DT_INIT))
493 ((void (*)(void))(p->base + dyn[DT_INIT]))();
498 void *__dynlink(int argc, char **argv)
500 size_t *auxv, aux[AUX_CNT] = {0};
504 static struct dso builtin_dsos[3];
505 struct dso *const app = builtin_dsos+0;
506 struct dso *const lib = builtin_dsos+1;
507 struct dso *const vdso = builtin_dsos+2;
510 /* Find aux vector just past environ[] */
511 for (i=argc+1; argv[i]; i++)
512 if (!memcmp(argv[i], "LD_LIBRARY_PATH=", 16))
513 env_path = argv[i]+16;
514 else if (!memcmp(argv[i], "LD_PRELOAD=", 11))
515 env_preload = argv[i]+11;
516 auxv = (void *)(argv+i+1);
518 decode_vec(auxv, aux, AUX_CNT);
520 /* Only trust user/env if kernel says we're not suid/sgid */
521 if ((aux[0]&0x7800)!=0x7800 || aux[AT_UID]!=aux[AT_EUID]
522 || aux[AT_GID]!=aux[AT_EGID] || aux[AT_SECURE]) {
527 /* The dynamic linker load address is passed by the kernel
528 * in the AUX vector, so this is easy. */
529 lib->base = (void *)aux[AT_BASE];
530 lib->name = "libc.so";
532 ehdr = (void *)lib->base;
533 lib->dynv = (void *)(lib->base + find_dyn(
534 (void *)(aux[AT_BASE]+ehdr->e_phoff),
535 ehdr->e_phnum, ehdr->e_phentsize));
538 /* Find load address of the main program, via AT_PHDR vs PT_PHDR. */
540 phdr = (void *)aux[AT_PHDR];
541 for (i=aux[AT_PHNUM]; i; i--, phdr=(void *)((char *)phdr + aux[AT_PHENT])) {
542 if (phdr->p_type == PT_PHDR)
543 app->base = (void *)(aux[AT_PHDR] - phdr->p_vaddr);
547 app->constructed = 1;
548 app->dynv = (void *)(app->base + find_dyn(
549 (void *)aux[AT_PHDR], aux[AT_PHNUM], aux[AT_PHENT]));
552 /* Attach to vdso, if provided by the kernel */
553 for (i=0; auxv[i]; i+=2) {
554 size_t vdso_base = auxv[i+1];
555 if (auxv[i] != AT_SYSINFO_EHDR) continue;
556 ehdr = (void *)vdso_base;
557 phdr = (void *)(vdso_base + ehdr->e_phoff);
558 for (i=ehdr->e_phnum; i; i--, phdr=(void *)((char *)phdr + ehdr->e_phentsize)) {
559 if (phdr->p_type == PT_DYNAMIC)
560 vdso->dynv = (void *)(vdso_base + phdr->p_offset);
561 if (phdr->p_type == PT_LOAD)
562 vdso->base = (void *)(vdso_base - phdr->p_vaddr + phdr->p_offset);
564 vdso->name = "linux-gate.so.1";
572 /* Initial dso chain consists only of the app. We temporarily
573 * append the dynamic linker/libc so we can relocate it, then
574 * restore the initial chain in preparation for loading third
575 * party libraries (preload/needed). */
582 /* PAST THIS POINT, ALL LIBC INTERFACES ARE FULLY USABLE. */
584 /* Donate unused parts of app and library mapping to malloc */
585 reclaim_gaps(app->base, (void *)aux[AT_PHDR], aux[AT_PHENT], aux[AT_PHNUM]);
586 ehdr = (void *)lib->base;
587 reclaim_gaps(lib->base, (void *)(lib->base+ehdr->e_phoff),
588 ehdr->e_phentsize, ehdr->e_phnum);
590 /* Load preload/needed libraries, add their symbols to the global
591 * namespace, and perform all remaining relocations. The main
592 * program must be relocated LAST since it may contain copy
593 * relocations which depend on libraries' relocations. */
594 if (env_preload) load_preload(env_preload);
597 reloc_all(app->next);
600 /* Switch to runtime mode: any further failures in the dynamic
601 * linker are a reportable failure rather than a fatal startup
602 * error. If the dynamic loader (dlopen) will not be used, free
603 * all memory used by the dynamic linker. */
611 reclaim((void *)builtin_dsos, 0, sizeof builtin_dsos);
615 return (void *)aux[AT_ENTRY];
618 void *dlopen(const char *file, int mode)
620 struct dso *volatile p, *orig_tail = tail, *next;
624 if (!file) return head;
626 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
627 pthread_rwlock_wrlock(&lock);
629 if (setjmp(rtld_fail)) {
630 /* Clean up anything new that was (partially) loaded */
631 if (p->deps) for (i=0; p->deps[i]; i++)
632 if (p->deps[i]->global < 0)
633 p->deps[i]->global = 0;
634 for (p=orig_tail->next; p; p=next) {
636 munmap(p->map, p->map_len);
645 } else p = load_library(file);
648 snprintf(errbuf, sizeof errbuf,
649 "Error loading shared library %s: %m", file);
654 /* First load handling */
657 if (p->deps) for (i=0; p->deps[i]; i++)
658 if (!p->deps[i]->global)
659 p->deps[i]->global = -1;
660 if (!p->global) p->global = -1;
662 if (p->deps) for (i=0; p->deps[i]; i++)
663 if (p->deps[i]->global < 0)
664 p->deps[i]->global = 0;
665 if (p->global < 0) p->global = 0;
668 if (mode & RTLD_GLOBAL) {
669 if (p->deps) for (i=0; p->deps[i]; i++)
670 p->deps[i]->global = 1;
676 pthread_rwlock_unlock(&lock);
677 pthread_setcancelstate(cs, 0);
681 static void *do_dlsym(struct dso *p, const char *s, void *ra)
686 if (p == RTLD_NEXT) {
687 for (p=head; p && (unsigned char *)ra-p->map>p->map_len; p=p->next);
691 if (p == head || p == RTLD_DEFAULT) {
692 void *res = find_sym(head, s, 0);
693 if (!res) errflag = 1;
697 sym = lookup(s, h, p->syms, p->hashtab, p->strings);
698 if (sym && sym->st_value && (1<<(sym->st_info&0xf) & OK_TYPES))
699 return p->base + sym->st_value;
700 if (p->deps) for (i=0; p->deps[i]; i++) {
701 sym = lookup(s, h, p->deps[i]->syms,
702 p->deps[i]->hashtab, p->deps[i]->strings);
703 if (sym && sym->st_value && (1<<(sym->st_info&0xf) & OK_TYPES))
704 return p->deps[i]->base + sym->st_value;
707 snprintf(errbuf, sizeof errbuf, "Symbol not found: %s", s);
711 void *__dlsym(void *p, const char *s, void *ra)
714 pthread_rwlock_rdlock(&lock);
715 res = do_dlsym(p, s, ra);
716 pthread_rwlock_unlock(&lock);
720 void *dlopen(const char *file, int mode)
724 void *__dlsym(void *p, const char *s, void *ra)
732 if (!errflag) return 0;