1 /* 2 * Copyright (C) 2008, 2009 The Android Open Source Project 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in 12 * the documentation and/or other materials provided with the 13 * distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS 22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #include <dlfcn.h> 30 #include <errno.h> 31 #include <fcntl.h> 32 #include <linux/auxvec.h> 33 #include <pthread.h> 34 #include <stdio.h> 35 #include <stdlib.h> 36 #include <string.h> 37 #include <sys/atomics.h> 38 #include <sys/mman.h> 39 #include <sys/stat.h> 40 #include <unistd.h> 41 42 // Private C library headers. 43 #include <private/bionic_tls.h> 44 #include <private/KernelArgumentBlock.h> 45 #include <private/ScopedPthreadMutexLocker.h> 46 47 #include "linker.h" 48 #include "linker_debug.h" 49 #include "linker_environ.h" 50 #include "linker_phdr.h" 51 52 /* Assume average path length of 64 and max 8 paths */ 53 #define LDPATH_BUFSIZE 512 54 #define LDPATH_MAX 8 55 56 #define LDPRELOAD_BUFSIZE 512 57 #define LDPRELOAD_MAX 8 58 59 /* >>> IMPORTANT NOTE - READ ME BEFORE MODIFYING <<< 60 * 61 * Do NOT use malloc() and friends or pthread_*() code here. 62 * Don't use printf() either; it's caused mysterious memory 63 * corruption in the past. 64 * The linker runs before we bring up libc and it's easiest 65 * to make sure it does not depend on any complex libc features 66 * 67 * open issues / todo: 68 * 69 * - are we doing everything we should for ARM_COPY relocations? 70 * - cleaner error reporting 71 * - after linking, set as much stuff as possible to READONLY 72 * and NOEXEC 73 */ 74 75 static bool soinfo_link_image(soinfo* si); 76 77 // We can't use malloc(3) in the dynamic linker. We use a linked list of anonymous 78 // maps, each a single page in size. The pages are broken up into as many struct soinfo 79 // objects as will fit, and they're all threaded together on a free list. 80 #define SOINFO_PER_POOL ((PAGE_SIZE - sizeof(soinfo_pool_t*)) / sizeof(soinfo)) 81 struct soinfo_pool_t { 82 soinfo_pool_t* next; 83 soinfo info[SOINFO_PER_POOL]; 84 }; 85 static struct soinfo_pool_t* gSoInfoPools = NULL; 86 static soinfo* gSoInfoFreeList = NULL; 87 88 static soinfo* solist = &libdl_info; 89 static soinfo* sonext = &libdl_info; 90 static soinfo* somain; /* main process, always the one after libdl_info */ 91 92 static const char* const gSoPaths[] = { 93 "/vendor/lib", 94 "/system/lib", 95 NULL 96 }; 97 98 static char gLdPathsBuffer[LDPATH_BUFSIZE]; 99 static const char* gLdPaths[LDPATH_MAX + 1]; 100 101 static char gLdPreloadsBuffer[LDPRELOAD_BUFSIZE]; 102 static const char* gLdPreloadNames[LDPRELOAD_MAX + 1]; 103 104 static soinfo* gLdPreloads[LDPRELOAD_MAX + 1]; 105 106 __LIBC_HIDDEN__ int gLdDebugVerbosity; 107 108 __LIBC_HIDDEN__ abort_msg_t* gAbortMessage = NULL; // For debuggerd. 109 110 enum RelocationKind { 111 kRelocAbsolute = 0, 112 kRelocRelative, 113 kRelocCopy, 114 kRelocSymbol, 115 kRelocMax 116 }; 117 118 #if STATS 119 struct linker_stats_t { 120 int count[kRelocMax]; 121 }; 122 123 static linker_stats_t linker_stats; 124 125 static void count_relocation(RelocationKind kind) { 126 ++linker_stats.count[kind]; 127 } 128 #else 129 static void count_relocation(RelocationKind) { 130 } 131 #endif 132 133 #if COUNT_PAGES 134 static unsigned bitmask[4096]; 135 #define MARK(offset) \ 136 do { \ 137 bitmask[((offset) >> 12) >> 3] |= (1 << (((offset) >> 12) & 7)); \ 138 } while(0) 139 #else 140 #define MARK(x) do {} while (0) 141 #endif 142 143 // You shouldn't try to call memory-allocating functions in the dynamic linker. 144 // Guard against the most obvious ones. 145 #define DISALLOW_ALLOCATION(return_type, name, ...) \ 146 return_type name __VA_ARGS__ \ 147 { \ 148 const char* msg = "ERROR: " #name " called from the dynamic linker!\n"; \ 149 __libc_format_log(ANDROID_LOG_FATAL, "linker", "%s", msg); \ 150 write(2, msg, strlen(msg)); \ 151 abort(); \ 152 } 153 #define UNUSED __attribute__((unused)) 154 DISALLOW_ALLOCATION(void*, malloc, (size_t u UNUSED)); 155 DISALLOW_ALLOCATION(void, free, (void* u UNUSED)); 156 DISALLOW_ALLOCATION(void*, realloc, (void* u1 UNUSED, size_t u2 UNUSED)); 157 DISALLOW_ALLOCATION(void*, calloc, (size_t u1 UNUSED, size_t u2 UNUSED)); 158 159 static char tmp_err_buf[768]; 160 static char __linker_dl_err_buf[768]; 161 162 char* linker_get_error_buffer() { 163 return &__linker_dl_err_buf[0]; 164 } 165 166 size_t linker_get_error_buffer_size() { 167 return sizeof(__linker_dl_err_buf); 168 } 169 170 /* 171 * This function is an empty stub where GDB locates a breakpoint to get notified 172 * about linker activity. 173 */ 174 extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(); 175 176 static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, RT_CONSISTENT, 0}; 177 static link_map_t* r_debug_tail = 0; 178 179 static pthread_mutex_t gDebugMutex = PTHREAD_MUTEX_INITIALIZER; 180 181 static void insert_soinfo_into_debug_map(soinfo * info) { 182 // Copy the necessary fields into the debug structure. 183 link_map_t* map = &(info->link_map); 184 map->l_addr = info->base; 185 map->l_name = (char*) info->name; 186 map->l_ld = (uintptr_t)info->dynamic; 187 188 /* Stick the new library at the end of the list. 189 * gdb tends to care more about libc than it does 190 * about leaf libraries, and ordering it this way 191 * reduces the back-and-forth over the wire. 192 */ 193 if (r_debug_tail) { 194 r_debug_tail->l_next = map; 195 map->l_prev = r_debug_tail; 196 map->l_next = 0; 197 } else { 198 _r_debug.r_map = map; 199 map->l_prev = 0; 200 map->l_next = 0; 201 } 202 r_debug_tail = map; 203 } 204 205 static void remove_soinfo_from_debug_map(soinfo* info) { 206 link_map_t* map = &(info->link_map); 207 208 if (r_debug_tail == map) { 209 r_debug_tail = map->l_prev; 210 } 211 212 if (map->l_prev) { 213 map->l_prev->l_next = map->l_next; 214 } 215 if (map->l_next) { 216 map->l_next->l_prev = map->l_prev; 217 } 218 } 219 220 static void notify_gdb_of_load(soinfo* info) { 221 if (info->flags & FLAG_EXE) { 222 // GDB already knows about the main executable 223 return; 224 } 225 226 ScopedPthreadMutexLocker locker(&gDebugMutex); 227 228 _r_debug.r_state = RT_ADD; 229 rtld_db_dlactivity(); 230 231 insert_soinfo_into_debug_map(info); 232 233 _r_debug.r_state = RT_CONSISTENT; 234 rtld_db_dlactivity(); 235 } 236 237 static void notify_gdb_of_unload(soinfo* info) { 238 if (info->flags & FLAG_EXE) { 239 // GDB already knows about the main executable 240 return; 241 } 242 243 ScopedPthreadMutexLocker locker(&gDebugMutex); 244 245 _r_debug.r_state = RT_DELETE; 246 rtld_db_dlactivity(); 247 248 remove_soinfo_from_debug_map(info); 249 250 _r_debug.r_state = RT_CONSISTENT; 251 rtld_db_dlactivity(); 252 } 253 254 void notify_gdb_of_libraries() { 255 _r_debug.r_state = RT_ADD; 256 rtld_db_dlactivity(); 257 _r_debug.r_state = RT_CONSISTENT; 258 rtld_db_dlactivity(); 259 } 260 261 static bool ensure_free_list_non_empty() { 262 if (gSoInfoFreeList != NULL) { 263 return true; 264 } 265 266 // Allocate a new pool. 267 soinfo_pool_t* pool = reinterpret_cast<soinfo_pool_t*>(mmap(NULL, sizeof(*pool), 268 PROT_READ|PROT_WRITE, 269 MAP_PRIVATE|MAP_ANONYMOUS, 0, 0)); 270 if (pool == MAP_FAILED) { 271 return false; 272 } 273 274 // Add the pool to our list of pools. 275 pool->next = gSoInfoPools; 276 gSoInfoPools = pool; 277 278 // Chain the entries in the new pool onto the free list. 279 gSoInfoFreeList = &pool->info[0]; 280 soinfo* next = NULL; 281 for (int i = SOINFO_PER_POOL - 1; i >= 0; --i) { 282 pool->info[i].next = next; 283 next = &pool->info[i]; 284 } 285 286 return true; 287 } 288 289 static void set_soinfo_pool_protection(int protection) { 290 for (soinfo_pool_t* p = gSoInfoPools; p != NULL; p = p->next) { 291 if (mprotect(p, sizeof(*p), protection) == -1) { 292 abort(); // Can't happen. 293 } 294 } 295 } 296 297 static soinfo* soinfo_alloc(const char* name) { 298 if (strlen(name) >= SOINFO_NAME_LEN) { 299 DL_ERR("library name \"%s\" too long", name); 300 return NULL; 301 } 302 303 if (!ensure_free_list_non_empty()) { 304 DL_ERR("out of memory when loading \"%s\"", name); 305 return NULL; 306 } 307 308 // Take the head element off the free list. 309 soinfo* si = gSoInfoFreeList; 310 gSoInfoFreeList = gSoInfoFreeList->next; 311 312 // Initialize the new element. 313 memset(si, 0, sizeof(soinfo)); 314 strlcpy(si->name, name, sizeof(si->name)); 315 sonext->next = si; 316 sonext = si; 317 318 TRACE("name %s: allocated soinfo @ %p", name, si); 319 return si; 320 } 321 322 static void soinfo_free(soinfo* si) 323 { 324 if (si == NULL) { 325 return; 326 } 327 328 soinfo *prev = NULL, *trav; 329 330 TRACE("name %s: freeing soinfo @ %p", si->name, si); 331 332 for (trav = solist; trav != NULL; trav = trav->next) { 333 if (trav == si) 334 break; 335 prev = trav; 336 } 337 if (trav == NULL) { 338 /* si was not in solist */ 339 DL_ERR("name \"%s\" is not in solist!", si->name); 340 return; 341 } 342 343 /* prev will never be NULL, because the first entry in solist is 344 always the static libdl_info. 345 */ 346 prev->next = si->next; 347 if (si == sonext) { 348 sonext = prev; 349 } 350 si->next = gSoInfoFreeList; 351 gSoInfoFreeList = si; 352 } 353 354 355 static void parse_path(const char* path, const char* delimiters, 356 const char** array, char* buf, size_t buf_size, size_t max_count) { 357 if (path == NULL) { 358 return; 359 } 360 361 size_t len = strlcpy(buf, path, buf_size); 362 363 size_t i = 0; 364 char* buf_p = buf; 365 while (i < max_count && (array[i] = strsep(&buf_p, delimiters))) { 366 if (*array[i] != '\0') { 367 ++i; 368 } 369 } 370 371 // Forget the last path if we had to truncate; this occurs if the 2nd to 372 // last char isn't '\0' (i.e. wasn't originally a delimiter). 373 if (i > 0 && len >= buf_size && buf[buf_size - 2] != '\0') { 374 array[i - 1] = NULL; 375 } else { 376 array[i] = NULL; 377 } 378 } 379 380 static void parse_LD_LIBRARY_PATH(const char* path) { 381 parse_path(path, ":", gLdPaths, 382 gLdPathsBuffer, sizeof(gLdPathsBuffer), LDPATH_MAX); 383 } 384 385 static void parse_LD_PRELOAD(const char* path) { 386 // We have historically supported ':' as well as ' ' in LD_PRELOAD. 387 parse_path(path, " :", gLdPreloadNames, 388 gLdPreloadsBuffer, sizeof(gLdPreloadsBuffer), LDPRELOAD_MAX); 389 } 390 391 #ifdef ANDROID_ARM_LINKER 392 393 /* For a given PC, find the .so that it belongs to. 394 * Returns the base address of the .ARM.exidx section 395 * for that .so, and the number of 8-byte entries 396 * in that section (via *pcount). 397 * 398 * Intended to be called by libc's __gnu_Unwind_Find_exidx(). 399 * 400 * This function is exposed via dlfcn.cpp and libdl.so. 401 */ 402 _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount) 403 { 404 soinfo *si; 405 unsigned addr = (unsigned)pc; 406 407 for (si = solist; si != 0; si = si->next){ 408 if ((addr >= si->base) && (addr < (si->base + si->size))) { 409 *pcount = si->ARM_exidx_count; 410 return (_Unwind_Ptr)si->ARM_exidx; 411 } 412 } 413 *pcount = 0; 414 return NULL; 415 } 416 417 #elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) 418 419 /* Here, we only have to provide a callback to iterate across all the 420 * loaded libraries. gcc_eh does the rest. */ 421 int 422 dl_iterate_phdr(int (*cb)(dl_phdr_info *info, size_t size, void *data), 423 void *data) 424 { 425 int rv = 0; 426 for (soinfo* si = solist; si != NULL; si = si->next) { 427 dl_phdr_info dl_info; 428 dl_info.dlpi_addr = si->link_map.l_addr; 429 dl_info.dlpi_name = si->link_map.l_name; 430 dl_info.dlpi_phdr = si->phdr; 431 dl_info.dlpi_phnum = si->phnum; 432 rv = cb(&dl_info, sizeof(dl_phdr_info), data); 433 if (rv != 0) { 434 break; 435 } 436 } 437 return rv; 438 } 439 440 #endif 441 442 static Elf32_Sym* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name) { 443 Elf32_Sym* symtab = si->symtab; 444 const char* strtab = si->strtab; 445 446 TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %d", 447 name, si->name, si->base, hash, hash % si->nbucket); 448 449 for (unsigned n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]) { 450 Elf32_Sym* s = symtab + n; 451 if (strcmp(strtab + s->st_name, name)) continue; 452 453 /* only concern ourselves with global and weak symbol definitions */ 454 switch(ELF32_ST_BIND(s->st_info)){ 455 case STB_GLOBAL: 456 case STB_WEAK: 457 if (s->st_shndx == SHN_UNDEF) { 458 continue; 459 } 460 461 TRACE_TYPE(LOOKUP, "FOUND %s in %s (%08x) %d", 462 name, si->name, s->st_value, s->st_size); 463 return s; 464 } 465 } 466 467 return NULL; 468 } 469 470 static unsigned elfhash(const char* _name) { 471 const unsigned char* name = (const unsigned char*) _name; 472 unsigned h = 0, g; 473 474 while(*name) { 475 h = (h << 4) + *name++; 476 g = h & 0xf0000000; 477 h ^= g; 478 h ^= g >> 24; 479 } 480 return h; 481 } 482 483 static Elf32_Sym* soinfo_do_lookup(soinfo* si, const char* name, soinfo** lsi, soinfo* needed[]) { 484 unsigned elf_hash = elfhash(name); 485 Elf32_Sym* s = NULL; 486 487 if (si != NULL && somain != NULL) { 488 489 /* 490 * Local scope is executable scope. Just start looking into it right away 491 * for the shortcut. 492 */ 493 494 if (si == somain) { 495 s = soinfo_elf_lookup(si, elf_hash, name); 496 if (s != NULL) { 497 *lsi = si; 498 goto done; 499 } 500 } else { 501 /* Order of symbol lookup is controlled by DT_SYMBOLIC flag */ 502 503 /* 504 * If this object was built with symbolic relocations disabled, the 505 * first place to look to resolve external references is the main 506 * executable. 507 */ 508 509 if (!si->has_DT_SYMBOLIC) { 510 DEBUG("%s: looking up %s in executable %s", 511 si->name, name, somain->name); 512 s = soinfo_elf_lookup(somain, elf_hash, name); 513 if (s != NULL) { 514 *lsi = somain; 515 goto done; 516 } 517 } 518 519 /* Look for symbols in the local scope (the object who is 520 * searching). This happens with C++ templates on i386 for some 521 * reason. 522 * 523 * Notes on weak symbols: 524 * The ELF specs are ambiguous about treatment of weak definitions in 525 * dynamic linking. Some systems return the first definition found 526 * and some the first non-weak definition. This is system dependent. 527 * Here we return the first definition found for simplicity. */ 528 529 s = soinfo_elf_lookup(si, elf_hash, name); 530 if (s != NULL) { 531 *lsi = si; 532 goto done; 533 } 534 535 /* 536 * If this object was built with -Bsymbolic and symbol is not found 537 * in the local scope, try to find the symbol in the main executable. 538 */ 539 540 if (si->has_DT_SYMBOLIC) { 541 DEBUG("%s: looking up %s in executable %s after local scope", 542 si->name, name, somain->name); 543 s = soinfo_elf_lookup(somain, elf_hash, name); 544 if (s != NULL) { 545 *lsi = somain; 546 goto done; 547 } 548 } 549 } 550 } 551 552 /* Next, look for it in the preloads list */ 553 for (int i = 0; gLdPreloads[i] != NULL; i++) { 554 s = soinfo_elf_lookup(gLdPreloads[i], elf_hash, name); 555 if (s != NULL) { 556 *lsi = gLdPreloads[i]; 557 goto done; 558 } 559 } 560 561 for (int i = 0; needed[i] != NULL; i++) { 562 DEBUG("%s: looking up %s in %s", 563 si->name, name, needed[i]->name); 564 s = soinfo_elf_lookup(needed[i], elf_hash, name); 565 if (s != NULL) { 566 *lsi = needed[i]; 567 goto done; 568 } 569 } 570 571 done: 572 if (s != NULL) { 573 TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = 0x%08x, " 574 "found in %s, base = 0x%08x, load bias = 0x%08x", 575 si->name, name, s->st_value, 576 (*lsi)->name, (*lsi)->base, (*lsi)->load_bias); 577 return s; 578 } 579 580 return NULL; 581 } 582 583 /* This is used by dlsym(3). It performs symbol lookup only within the 584 specified soinfo object and not in any of its dependencies. 585 586 TODO: Only looking in the specified soinfo seems wrong. dlsym(3) says 587 that it should do a breadth first search through the dependency 588 tree. This agrees with the ELF spec (aka System V Application 589 Binary Interface) where in Chapter 5 it discuss resolving "Shared 590 Object Dependencies" in breadth first search order. 591 */ 592 Elf32_Sym* dlsym_handle_lookup(soinfo* si, const char* name) 593 { 594 return soinfo_elf_lookup(si, elfhash(name), name); 595 } 596 597 /* This is used by dlsym(3) to performs a global symbol lookup. If the 598 start value is null (for RTLD_DEFAULT), the search starts at the 599 beginning of the global solist. Otherwise the search starts at the 600 specified soinfo (for RTLD_NEXT). 601 */ 602 Elf32_Sym* dlsym_linear_lookup(const char* name, soinfo** found, soinfo* start) { 603 unsigned elf_hash = elfhash(name); 604 605 if (start == NULL) { 606 start = solist; 607 } 608 609 Elf32_Sym* s = NULL; 610 for (soinfo* si = start; (s == NULL) && (si != NULL); si = si->next) { 611 s = soinfo_elf_lookup(si, elf_hash, name); 612 if (s != NULL) { 613 *found = si; 614 break; 615 } 616 } 617 618 if (s != NULL) { 619 TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, found->base = 0x%08x", 620 name, s->st_value, (*found)->base); 621 } 622 623 return s; 624 } 625 626 soinfo* find_containing_library(const void* p) { 627 Elf32_Addr address = reinterpret_cast<Elf32_Addr>(p); 628 for (soinfo* si = solist; si != NULL; si = si->next) { 629 if (address >= si->base && address - si->base < si->size) { 630 return si; 631 } 632 } 633 return NULL; 634 } 635 636 Elf32_Sym* dladdr_find_symbol(soinfo* si, const void* addr) { 637 Elf32_Addr soaddr = reinterpret_cast<Elf32_Addr>(addr) - si->base; 638 639 // Search the library's symbol table for any defined symbol which 640 // contains this address. 641 for (size_t i = 0; i < si->nchain; ++i) { 642 Elf32_Sym* sym = &si->symtab[i]; 643 if (sym->st_shndx != SHN_UNDEF && 644 soaddr >= sym->st_value && 645 soaddr < sym->st_value + sym->st_size) { 646 return sym; 647 } 648 } 649 650 return NULL; 651 } 652 653 #if 0 654 static void dump(soinfo* si) 655 { 656 Elf32_Sym* s = si->symtab; 657 for (unsigned n = 0; n < si->nchain; n++) { 658 TRACE("%04d> %08x: %02x %04x %08x %08x %s", n, s, 659 s->st_info, s->st_shndx, s->st_value, s->st_size, 660 si->strtab + s->st_name); 661 s++; 662 } 663 } 664 #endif 665 666 static int open_library_on_path(const char* name, const char* const paths[]) { 667 char buf[512]; 668 for (size_t i = 0; paths[i] != NULL; ++i) { 669 int n = __libc_format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name); 670 if (n < 0 || n >= static_cast<int>(sizeof(buf))) { 671 PRINT("Warning: ignoring very long library path: %s/%s", paths[i], name); 672 continue; 673 } 674 int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC)); 675 if (fd != -1) { 676 return fd; 677 } 678 } 679 return -1; 680 } 681 682 static int open_library(const char* name) { 683 TRACE("[ opening %s ]", name); 684 685 // If the name contains a slash, we should attempt to open it directly and not search the paths. 686 if (strchr(name, '/') != NULL) { 687 int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC)); 688 if (fd != -1) { 689 return fd; 690 } 691 // ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now. 692 } 693 694 // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths. 695 int fd = open_library_on_path(name, gLdPaths); 696 if (fd == -1) { 697 fd = open_library_on_path(name, gSoPaths); 698 } 699 return fd; 700 } 701 702 static soinfo* load_library(const char* name) { 703 // Open the file. 704 int fd = open_library(name); 705 if (fd == -1) { 706 DL_ERR("library \"%s\" not found", name); 707 return NULL; 708 } 709 710 // Read the ELF header and load the segments. 711 ElfReader elf_reader(name, fd); 712 if (!elf_reader.Load()) { 713 return NULL; 714 } 715 716 const char* bname = strrchr(name, '/'); 717 soinfo* si = soinfo_alloc(bname ? bname + 1 : name); 718 if (si == NULL) { 719 return NULL; 720 } 721 si->base = elf_reader.load_start(); 722 si->size = elf_reader.load_size(); 723 si->load_bias = elf_reader.load_bias(); 724 si->flags = 0; 725 si->entry = 0; 726 si->dynamic = NULL; 727 si->phnum = elf_reader.phdr_count(); 728 si->phdr = elf_reader.loaded_phdr(); 729 return si; 730 } 731 732 static soinfo *find_loaded_library(const char *name) 733 { 734 soinfo *si; 735 const char *bname; 736 737 // TODO: don't use basename only for determining libraries 738 // http://code.google.com/p/android/issues/detail?id=6670 739 740 bname = strrchr(name, '/'); 741 bname = bname ? bname + 1 : name; 742 743 for (si = solist; si != NULL; si = si->next) { 744 if (!strcmp(bname, si->name)) { 745 return si; 746 } 747 } 748 return NULL; 749 } 750 751 static soinfo* find_library_internal(const char* name) { 752 if (name == NULL) { 753 return somain; 754 } 755 756 soinfo* si = find_loaded_library(name); 757 if (si != NULL) { 758 if (si->flags & FLAG_LINKED) { 759 return si; 760 } 761 DL_ERR("OOPS: recursive link to \"%s\"", si->name); 762 return NULL; 763 } 764 765 TRACE("[ '%s' has not been loaded yet. Locating...]", name); 766 si = load_library(name); 767 if (si == NULL) { 768 return NULL; 769 } 770 771 // At this point we know that whatever is loaded @ base is a valid ELF 772 // shared library whose segments are properly mapped in. 773 TRACE("[ init_library base=0x%08x sz=0x%08x name='%s' ]", 774 si->base, si->size, si->name); 775 776 if (!soinfo_link_image(si)) { 777 munmap(reinterpret_cast<void*>(si->base), si->size); 778 soinfo_free(si); 779 return NULL; 780 } 781 782 return si; 783 } 784 785 static soinfo* find_library(const char* name) { 786 soinfo* si = find_library_internal(name); 787 if (si != NULL) { 788 si->ref_count++; 789 } 790 return si; 791 } 792 793 static int soinfo_unload(soinfo* si) { 794 if (si->ref_count == 1) { 795 TRACE("unloading '%s'", si->name); 796 si->CallDestructors(); 797 798 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 799 if (d->d_tag == DT_NEEDED) { 800 const char* library_name = si->strtab + d->d_un.d_val; 801 TRACE("%s needs to unload %s", si->name, library_name); 802 soinfo_unload(find_loaded_library(library_name)); 803 } 804 } 805 806 munmap(reinterpret_cast<void*>(si->base), si->size); 807 notify_gdb_of_unload(si); 808 soinfo_free(si); 809 si->ref_count = 0; 810 } else { 811 si->ref_count--; 812 TRACE("not unloading '%s', decrementing ref_count to %d", si->name, si->ref_count); 813 } 814 return 0; 815 } 816 817 void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) { 818 if (!get_AT_SECURE()) { 819 parse_LD_LIBRARY_PATH(ld_library_path); 820 } 821 } 822 823 soinfo* do_dlopen(const char* name, int flags) { 824 if ((flags & ~(RTLD_NOW|RTLD_LAZY|RTLD_LOCAL|RTLD_GLOBAL)) != 0) { 825 DL_ERR("invalid flags to dlopen: %x", flags); 826 return NULL; 827 } 828 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 829 soinfo* si = find_library(name); 830 if (si != NULL) { 831 si->CallConstructors(); 832 } 833 set_soinfo_pool_protection(PROT_READ); 834 return si; 835 } 836 837 int do_dlclose(soinfo* si) { 838 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 839 int result = soinfo_unload(si); 840 set_soinfo_pool_protection(PROT_READ); 841 return result; 842 } 843 844 /* TODO: don't use unsigned for addrs below. It works, but is not 845 * ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned 846 * long. 847 */ 848 static int soinfo_relocate(soinfo* si, Elf32_Rel* rel, unsigned count, 849 soinfo* needed[]) 850 { 851 Elf32_Sym* symtab = si->symtab; 852 const char* strtab = si->strtab; 853 Elf32_Sym* s; 854 Elf32_Rel* start = rel; 855 soinfo* lsi; 856 857 for (size_t idx = 0; idx < count; ++idx, ++rel) { 858 unsigned type = ELF32_R_TYPE(rel->r_info); 859 unsigned sym = ELF32_R_SYM(rel->r_info); 860 Elf32_Addr reloc = static_cast<Elf32_Addr>(rel->r_offset + si->load_bias); 861 Elf32_Addr sym_addr = 0; 862 char* sym_name = NULL; 863 864 DEBUG("Processing '%s' relocation at index %d", si->name, idx); 865 if (type == 0) { // R_*_NONE 866 continue; 867 } 868 if (sym != 0) { 869 sym_name = (char *)(strtab + symtab[sym].st_name); 870 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 871 if (s == NULL) { 872 /* We only allow an undefined symbol if this is a weak 873 reference.. */ 874 s = &symtab[sym]; 875 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 876 DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); 877 return -1; 878 } 879 880 /* IHI0044C AAELF 4.5.1.1: 881 882 Libraries are not searched to resolve weak references. 883 It is not an error for a weak reference to remain 884 unsatisfied. 885 886 During linking, the value of an undefined weak reference is: 887 - Zero if the relocation type is absolute 888 - The address of the place if the relocation is pc-relative 889 - The address of nominal base address if the relocation 890 type is base-relative. 891 */ 892 893 switch (type) { 894 #if defined(ANDROID_ARM_LINKER) 895 case R_ARM_JUMP_SLOT: 896 case R_ARM_GLOB_DAT: 897 case R_ARM_ABS32: 898 case R_ARM_RELATIVE: /* Don't care. */ 899 #elif defined(ANDROID_X86_LINKER) 900 case R_386_JMP_SLOT: 901 case R_386_GLOB_DAT: 902 case R_386_32: 903 case R_386_RELATIVE: /* Dont' care. */ 904 #endif /* ANDROID_*_LINKER */ 905 /* sym_addr was initialized to be zero above or relocation 906 code below does not care about value of sym_addr. 907 No need to do anything. */ 908 break; 909 910 #if defined(ANDROID_X86_LINKER) 911 case R_386_PC32: 912 sym_addr = reloc; 913 break; 914 #endif /* ANDROID_X86_LINKER */ 915 916 #if defined(ANDROID_ARM_LINKER) 917 case R_ARM_COPY: 918 /* Fall through. Can't really copy if weak symbol is 919 not found in run-time. */ 920 #endif /* ANDROID_ARM_LINKER */ 921 default: 922 DL_ERR("unknown weak reloc type %d @ %p (%d)", 923 type, rel, (int) (rel - start)); 924 return -1; 925 } 926 } else { 927 /* We got a definition. */ 928 #if 0 929 if ((base == 0) && (si->base != 0)) { 930 /* linking from libraries to main image is bad */ 931 DL_ERR("cannot locate \"%s\"...", 932 strtab + symtab[sym].st_name); 933 return -1; 934 } 935 #endif 936 sym_addr = static_cast<Elf32_Addr>(s->st_value + lsi->load_bias); 937 } 938 count_relocation(kRelocSymbol); 939 } else { 940 s = NULL; 941 } 942 943 /* TODO: This is ugly. Split up the relocations by arch into 944 * different files. 945 */ 946 switch(type){ 947 #if defined(ANDROID_ARM_LINKER) 948 case R_ARM_JUMP_SLOT: 949 count_relocation(kRelocAbsolute); 950 MARK(rel->r_offset); 951 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 952 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 953 break; 954 case R_ARM_GLOB_DAT: 955 count_relocation(kRelocAbsolute); 956 MARK(rel->r_offset); 957 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 958 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 959 break; 960 case R_ARM_ABS32: 961 count_relocation(kRelocAbsolute); 962 MARK(rel->r_offset); 963 TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s", reloc, sym_addr, sym_name); 964 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 965 break; 966 case R_ARM_REL32: 967 count_relocation(kRelocRelative); 968 MARK(rel->r_offset); 969 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s", 970 reloc, sym_addr, rel->r_offset, sym_name); 971 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr - rel->r_offset; 972 break; 973 #elif defined(ANDROID_X86_LINKER) 974 case R_386_JMP_SLOT: 975 count_relocation(kRelocAbsolute); 976 MARK(rel->r_offset); 977 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 978 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 979 break; 980 case R_386_GLOB_DAT: 981 count_relocation(kRelocAbsolute); 982 MARK(rel->r_offset); 983 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 984 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 985 break; 986 #elif defined(ANDROID_MIPS_LINKER) 987 case R_MIPS_REL32: 988 count_relocation(kRelocAbsolute); 989 MARK(rel->r_offset); 990 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s", 991 reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); 992 if (s) { 993 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 994 } else { 995 *reinterpret_cast<Elf32_Addr*>(reloc) += si->base; 996 } 997 break; 998 #endif /* ANDROID_*_LINKER */ 999 1000 #if defined(ANDROID_ARM_LINKER) 1001 case R_ARM_RELATIVE: 1002 #elif defined(ANDROID_X86_LINKER) 1003 case R_386_RELATIVE: 1004 #endif /* ANDROID_*_LINKER */ 1005 count_relocation(kRelocRelative); 1006 MARK(rel->r_offset); 1007 if (sym) { 1008 DL_ERR("odd RELATIVE form..."); 1009 return -1; 1010 } 1011 TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x", reloc, si->base); 1012 *reinterpret_cast<Elf32_Addr*>(reloc) += si->base; 1013 break; 1014 1015 #if defined(ANDROID_X86_LINKER) 1016 case R_386_32: 1017 count_relocation(kRelocRelative); 1018 MARK(rel->r_offset); 1019 1020 TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s", reloc, sym_addr, sym_name); 1021 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 1022 break; 1023 1024 case R_386_PC32: 1025 count_relocation(kRelocRelative); 1026 MARK(rel->r_offset); 1027 TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s", 1028 reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); 1029 *reinterpret_cast<Elf32_Addr*>(reloc) += (sym_addr - reloc); 1030 break; 1031 #endif /* ANDROID_X86_LINKER */ 1032 1033 #ifdef ANDROID_ARM_LINKER 1034 case R_ARM_COPY: 1035 if ((si->flags & FLAG_EXE) == 0) { 1036 /* 1037 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf 1038 * 1039 * Section 4.7.1.10 "Dynamic relocations" 1040 * R_ARM_COPY may only appear in executable objects where e_type is 1041 * set to ET_EXEC. 1042 * 1043 * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. 1044 * We should explicitly disallow ET_DYN executables from having 1045 * R_ARM_COPY relocations. 1046 */ 1047 DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); 1048 return -1; 1049 } 1050 count_relocation(kRelocCopy); 1051 MARK(rel->r_offset); 1052 TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s", reloc, s->st_size, sym_addr, sym_name); 1053 if (reloc == sym_addr) { 1054 Elf32_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed); 1055 1056 if (src == NULL) { 1057 DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name); 1058 return -1; 1059 } 1060 if (lsi->has_DT_SYMBOLIC) { 1061 DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared " 1062 "library %s (built with -Bsymbolic?)", si->name, lsi->name); 1063 return -1; 1064 } 1065 if (s->st_size < src->st_size) { 1066 DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)", 1067 si->name, s->st_size, src->st_size); 1068 return -1; 1069 } 1070 memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size); 1071 } else { 1072 DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name); 1073 return -1; 1074 } 1075 break; 1076 #endif /* ANDROID_ARM_LINKER */ 1077 1078 default: 1079 DL_ERR("unknown reloc type %d @ %p (%d)", 1080 type, rel, (int) (rel - start)); 1081 return -1; 1082 } 1083 } 1084 return 0; 1085 } 1086 1087 #ifdef ANDROID_MIPS_LINKER 1088 static bool mips_relocate_got(soinfo* si, soinfo* needed[]) { 1089 unsigned* got = si->plt_got; 1090 if (got == NULL) { 1091 return true; 1092 } 1093 unsigned local_gotno = si->mips_local_gotno; 1094 unsigned gotsym = si->mips_gotsym; 1095 unsigned symtabno = si->mips_symtabno; 1096 Elf32_Sym* symtab = si->symtab; 1097 1098 /* 1099 * got[0] is address of lazy resolver function 1100 * got[1] may be used for a GNU extension 1101 * set it to a recognizable address in case someone calls it 1102 * (should be _rtld_bind_start) 1103 * FIXME: maybe this should be in a separate routine 1104 */ 1105 1106 if ((si->flags & FLAG_LINKER) == 0) { 1107 size_t g = 0; 1108 got[g++] = 0xdeadbeef; 1109 if (got[g] & 0x80000000) { 1110 got[g++] = 0xdeadfeed; 1111 } 1112 /* 1113 * Relocate the local GOT entries need to be relocated 1114 */ 1115 for (; g < local_gotno; g++) { 1116 got[g] += si->load_bias; 1117 } 1118 } 1119 1120 /* Now for the global GOT entries */ 1121 Elf32_Sym* sym = symtab + gotsym; 1122 got = si->plt_got + local_gotno; 1123 for (size_t g = gotsym; g < symtabno; g++, sym++, got++) { 1124 const char* sym_name; 1125 Elf32_Sym* s; 1126 soinfo* lsi; 1127 1128 /* This is an undefined reference... try to locate it */ 1129 sym_name = si->strtab + sym->st_name; 1130 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1131 if (s == NULL) { 1132 /* We only allow an undefined symbol if this is a weak 1133 reference.. */ 1134 s = &symtab[g]; 1135 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1136 DL_ERR("cannot locate \"%s\"...", sym_name); 1137 return false; 1138 } 1139 *got = 0; 1140 } 1141 else { 1142 /* FIXME: is this sufficient? 1143 * For reference see NetBSD link loader 1144 * http://cvsweb.netbsd.org/bsdweb.cgi/src/libexec/ld.elf_so/arch/mips/mips_reloc.c?rev=1.53&content-type=text/x-cvsweb-markup 1145 */ 1146 *got = lsi->load_bias + s->st_value; 1147 } 1148 } 1149 return true; 1150 } 1151 #endif 1152 1153 void soinfo::CallArray(const char* array_name UNUSED, linker_function_t* functions, size_t count, bool reverse) { 1154 if (functions == NULL) { 1155 return; 1156 } 1157 1158 TRACE("[ Calling %s (size %d) @ %p for '%s' ]", array_name, count, functions, name); 1159 1160 int begin = reverse ? (count - 1) : 0; 1161 int end = reverse ? -1 : count; 1162 int step = reverse ? -1 : 1; 1163 1164 for (int i = begin; i != end; i += step) { 1165 TRACE("[ %s[%d] == %p ]", array_name, i, functions[i]); 1166 CallFunction("function", functions[i]); 1167 } 1168 1169 TRACE("[ Done calling %s for '%s' ]", array_name, name); 1170 } 1171 1172 void soinfo::CallFunction(const char* function_name UNUSED, linker_function_t function) { 1173 if (function == NULL || reinterpret_cast<uintptr_t>(function) == static_cast<uintptr_t>(-1)) { 1174 return; 1175 } 1176 1177 TRACE("[ Calling %s @ %p for '%s' ]", function_name, function, name); 1178 function(); 1179 TRACE("[ Done calling %s @ %p for '%s' ]", function_name, function, name); 1180 1181 // The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures 1182 // are still writable. This happens with our debug malloc (see http://b/7941716). 1183 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 1184 } 1185 1186 void soinfo::CallPreInitConstructors() { 1187 // DT_PREINIT_ARRAY functions are called before any other constructors for executables, 1188 // but ignored in a shared library. 1189 CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false); 1190 } 1191 1192 void soinfo::CallConstructors() { 1193 if (constructors_called) { 1194 return; 1195 } 1196 1197 // We set constructors_called before actually calling the constructors, otherwise it doesn't 1198 // protect against recursive constructor calls. One simple example of constructor recursion 1199 // is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so: 1200 // 1. The program depends on libc, so libc's constructor is called here. 1201 // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. 1202 // 3. dlopen() calls the constructors on the newly created 1203 // soinfo for libc_malloc_debug_leak.so. 1204 // 4. The debug .so depends on libc, so CallConstructors is 1205 // called again with the libc soinfo. If it doesn't trigger the early- 1206 // out above, the libc constructor will be called again (recursively!). 1207 constructors_called = true; 1208 1209 if ((flags & FLAG_EXE) == 0 && preinit_array != NULL) { 1210 // The GNU dynamic linker silently ignores these, but we warn the developer. 1211 PRINT("\"%s\": ignoring %d-entry DT_PREINIT_ARRAY in shared library!", 1212 name, preinit_array_count); 1213 } 1214 1215 if (dynamic != NULL) { 1216 for (Elf32_Dyn* d = dynamic; d->d_tag != DT_NULL; ++d) { 1217 if (d->d_tag == DT_NEEDED) { 1218 const char* library_name = strtab + d->d_un.d_val; 1219 TRACE("\"%s\": calling constructors in DT_NEEDED \"%s\"", name, library_name); 1220 find_loaded_library(library_name)->CallConstructors(); 1221 } 1222 } 1223 } 1224 1225 TRACE("\"%s\": calling constructors", name); 1226 1227 // DT_INIT should be called before DT_INIT_ARRAY if both are present. 1228 CallFunction("DT_INIT", init_func); 1229 CallArray("DT_INIT_ARRAY", init_array, init_array_count, false); 1230 } 1231 1232 void soinfo::CallDestructors() { 1233 TRACE("\"%s\": calling destructors", name); 1234 1235 // DT_FINI_ARRAY must be parsed in reverse order. 1236 CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true); 1237 1238 // DT_FINI should be called after DT_FINI_ARRAY if both are present. 1239 CallFunction("DT_FINI", fini_func); 1240 } 1241 1242 /* Force any of the closed stdin, stdout and stderr to be associated with 1243 /dev/null. */ 1244 static int nullify_closed_stdio() { 1245 int dev_null, i, status; 1246 int return_value = 0; 1247 1248 dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 1249 if (dev_null < 0) { 1250 DL_ERR("cannot open /dev/null: %s", strerror(errno)); 1251 return -1; 1252 } 1253 TRACE("[ Opened /dev/null file-descriptor=%d]", dev_null); 1254 1255 /* If any of the stdio file descriptors is valid and not associated 1256 with /dev/null, dup /dev/null to it. */ 1257 for (i = 0; i < 3; i++) { 1258 /* If it is /dev/null already, we are done. */ 1259 if (i == dev_null) { 1260 continue; 1261 } 1262 1263 TRACE("[ Nullifying stdio file descriptor %d]", i); 1264 status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 1265 1266 /* If file is opened, we are good. */ 1267 if (status != -1) { 1268 continue; 1269 } 1270 1271 /* The only error we allow is that the file descriptor does not 1272 exist, in which case we dup /dev/null to it. */ 1273 if (errno != EBADF) { 1274 DL_ERR("fcntl failed: %s", strerror(errno)); 1275 return_value = -1; 1276 continue; 1277 } 1278 1279 /* Try dupping /dev/null to this stdio file descriptor and 1280 repeat if there is a signal. Note that any errors in closing 1281 the stdio descriptor are lost. */ 1282 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 1283 if (status < 0) { 1284 DL_ERR("dup2 failed: %s", strerror(errno)); 1285 return_value = -1; 1286 continue; 1287 } 1288 } 1289 1290 /* If /dev/null is not one of the stdio file descriptors, close it. */ 1291 if (dev_null > 2) { 1292 TRACE("[ Closing /dev/null file-descriptor=%d]", dev_null); 1293 status = TEMP_FAILURE_RETRY(close(dev_null)); 1294 if (status == -1) { 1295 DL_ERR("close failed: %s", strerror(errno)); 1296 return_value = -1; 1297 } 1298 } 1299 1300 return return_value; 1301 } 1302 1303 static bool soinfo_link_image(soinfo* si) { 1304 /* "base" might wrap around UINT32_MAX. */ 1305 Elf32_Addr base = si->load_bias; 1306 const Elf32_Phdr *phdr = si->phdr; 1307 int phnum = si->phnum; 1308 bool relocating_linker = (si->flags & FLAG_LINKER) != 0; 1309 1310 /* We can't debug anything until the linker is relocated */ 1311 if (!relocating_linker) { 1312 INFO("[ linking %s ]", si->name); 1313 DEBUG("si->base = 0x%08x si->flags = 0x%08x", si->base, si->flags); 1314 } 1315 1316 /* Extract dynamic section */ 1317 size_t dynamic_count; 1318 Elf32_Word dynamic_flags; 1319 phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, 1320 &dynamic_count, &dynamic_flags); 1321 if (si->dynamic == NULL) { 1322 if (!relocating_linker) { 1323 DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name); 1324 } 1325 return false; 1326 } else { 1327 if (!relocating_linker) { 1328 DEBUG("dynamic = %p", si->dynamic); 1329 } 1330 } 1331 1332 #ifdef ANDROID_ARM_LINKER 1333 (void) phdr_table_get_arm_exidx(phdr, phnum, base, 1334 &si->ARM_exidx, &si->ARM_exidx_count); 1335 #endif 1336 1337 // Extract useful information from dynamic section. 1338 uint32_t needed_count = 0; 1339 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1340 DEBUG("d = %p, d[0](tag) = 0x%08x d[1](val) = 0x%08x", d, d->d_tag, d->d_un.d_val); 1341 switch(d->d_tag){ 1342 case DT_HASH: 1343 si->nbucket = ((unsigned *) (base + d->d_un.d_ptr))[0]; 1344 si->nchain = ((unsigned *) (base + d->d_un.d_ptr))[1]; 1345 si->bucket = (unsigned *) (base + d->d_un.d_ptr + 8); 1346 si->chain = (unsigned *) (base + d->d_un.d_ptr + 8 + si->nbucket * 4); 1347 break; 1348 case DT_STRTAB: 1349 si->strtab = (const char *) (base + d->d_un.d_ptr); 1350 break; 1351 case DT_SYMTAB: 1352 si->symtab = (Elf32_Sym *) (base + d->d_un.d_ptr); 1353 break; 1354 case DT_PLTREL: 1355 if (d->d_un.d_val != DT_REL) { 1356 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1357 return false; 1358 } 1359 break; 1360 case DT_JMPREL: 1361 si->plt_rel = (Elf32_Rel*) (base + d->d_un.d_ptr); 1362 break; 1363 case DT_PLTRELSZ: 1364 si->plt_rel_count = d->d_un.d_val / sizeof(Elf32_Rel); 1365 break; 1366 case DT_REL: 1367 si->rel = (Elf32_Rel*) (base + d->d_un.d_ptr); 1368 break; 1369 case DT_RELSZ: 1370 si->rel_count = d->d_un.d_val / sizeof(Elf32_Rel); 1371 break; 1372 case DT_PLTGOT: 1373 /* Save this in case we decide to do lazy binding. We don't yet. */ 1374 si->plt_got = (unsigned *)(base + d->d_un.d_ptr); 1375 break; 1376 case DT_DEBUG: 1377 // Set the DT_DEBUG entry to the address of _r_debug for GDB 1378 // if the dynamic table is writable 1379 if ((dynamic_flags & PF_W) != 0) { 1380 d->d_un.d_val = (int) &_r_debug; 1381 } 1382 break; 1383 case DT_RELA: 1384 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1385 return false; 1386 case DT_INIT: 1387 si->init_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1388 DEBUG("%s constructors (DT_INIT) found at %p", si->name, si->init_func); 1389 break; 1390 case DT_FINI: 1391 si->fini_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1392 DEBUG("%s destructors (DT_FINI) found at %p", si->name, si->fini_func); 1393 break; 1394 case DT_INIT_ARRAY: 1395 si->init_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1396 DEBUG("%s constructors (DT_INIT_ARRAY) found at %p", si->name, si->init_array); 1397 break; 1398 case DT_INIT_ARRAYSZ: 1399 si->init_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1400 break; 1401 case DT_FINI_ARRAY: 1402 si->fini_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1403 DEBUG("%s destructors (DT_FINI_ARRAY) found at %p", si->name, si->fini_array); 1404 break; 1405 case DT_FINI_ARRAYSZ: 1406 si->fini_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1407 break; 1408 case DT_PREINIT_ARRAY: 1409 si->preinit_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1410 DEBUG("%s constructors (DT_PREINIT_ARRAY) found at %p", si->name, si->preinit_array); 1411 break; 1412 case DT_PREINIT_ARRAYSZ: 1413 si->preinit_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1414 break; 1415 case DT_TEXTREL: 1416 si->has_text_relocations = true; 1417 break; 1418 case DT_SYMBOLIC: 1419 si->has_DT_SYMBOLIC = true; 1420 break; 1421 case DT_NEEDED: 1422 ++needed_count; 1423 break; 1424 #if defined DT_FLAGS 1425 // TODO: why is DT_FLAGS not defined? 1426 case DT_FLAGS: 1427 if (d->d_un.d_val & DF_TEXTREL) { 1428 si->has_text_relocations = true; 1429 } 1430 if (d->d_un.d_val & DF_SYMBOLIC) { 1431 si->has_DT_SYMBOLIC = true; 1432 } 1433 break; 1434 #endif 1435 #if defined(ANDROID_MIPS_LINKER) 1436 case DT_STRSZ: 1437 case DT_SYMENT: 1438 case DT_RELENT: 1439 break; 1440 case DT_MIPS_RLD_MAP: 1441 // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. 1442 { 1443 r_debug** dp = (r_debug**) d->d_un.d_ptr; 1444 *dp = &_r_debug; 1445 } 1446 break; 1447 case DT_MIPS_RLD_VERSION: 1448 case DT_MIPS_FLAGS: 1449 case DT_MIPS_BASE_ADDRESS: 1450 case DT_MIPS_UNREFEXTNO: 1451 break; 1452 1453 case DT_MIPS_SYMTABNO: 1454 si->mips_symtabno = d->d_un.d_val; 1455 break; 1456 1457 case DT_MIPS_LOCAL_GOTNO: 1458 si->mips_local_gotno = d->d_un.d_val; 1459 break; 1460 1461 case DT_MIPS_GOTSYM: 1462 si->mips_gotsym = d->d_un.d_val; 1463 break; 1464 1465 default: 1466 DEBUG("Unused DT entry: type 0x%08x arg 0x%08x", d->d_tag, d->d_un.d_val); 1467 break; 1468 #endif 1469 } 1470 } 1471 1472 DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p", 1473 si->base, si->strtab, si->symtab); 1474 1475 // Sanity checks. 1476 if (relocating_linker && needed_count != 0) { 1477 DL_ERR("linker cannot have DT_NEEDED dependencies on other libraries"); 1478 return false; 1479 } 1480 if (si->nbucket == 0) { 1481 DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name); 1482 return false; 1483 } 1484 if (si->strtab == 0) { 1485 DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name); 1486 return false; 1487 } 1488 if (si->symtab == 0) { 1489 DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name); 1490 return false; 1491 } 1492 1493 // If this is the main executable, then load all of the libraries from LD_PRELOAD now. 1494 if (si->flags & FLAG_EXE) { 1495 memset(gLdPreloads, 0, sizeof(gLdPreloads)); 1496 size_t preload_count = 0; 1497 for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) { 1498 soinfo* lsi = find_library(gLdPreloadNames[i]); 1499 if (lsi != NULL) { 1500 gLdPreloads[preload_count++] = lsi; 1501 } else { 1502 // As with glibc, failure to load an LD_PRELOAD library is just a warning. 1503 DL_WARN("could not load library \"%s\" from LD_PRELOAD for \"%s\"; caused by %s", 1504 gLdPreloadNames[i], si->name, linker_get_error_buffer()); 1505 } 1506 } 1507 } 1508 1509 soinfo** needed = (soinfo**) alloca((1 + needed_count) * sizeof(soinfo*)); 1510 soinfo** pneeded = needed; 1511 1512 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1513 if (d->d_tag == DT_NEEDED) { 1514 const char* library_name = si->strtab + d->d_un.d_val; 1515 DEBUG("%s needs %s", si->name, library_name); 1516 soinfo* lsi = find_library(library_name); 1517 if (lsi == NULL) { 1518 strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf)); 1519 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1520 library_name, si->name, tmp_err_buf); 1521 return false; 1522 } 1523 *pneeded++ = lsi; 1524 } 1525 } 1526 *pneeded = NULL; 1527 1528 if (si->has_text_relocations) { 1529 /* Unprotect the segments, i.e. make them writable, to allow 1530 * text relocations to work properly. We will later call 1531 * phdr_table_protect_segments() after all of them are applied 1532 * and all constructors are run. 1533 */ 1534 DL_WARN("%s has text relocations. This is wasting memory and is " 1535 "a security risk. Please fix.", si->name); 1536 if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1537 DL_ERR("can't unprotect loadable segments for \"%s\": %s", 1538 si->name, strerror(errno)); 1539 return false; 1540 } 1541 } 1542 1543 if (si->plt_rel != NULL) { 1544 DEBUG("[ relocating %s plt ]", si->name ); 1545 if (soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) { 1546 return false; 1547 } 1548 } 1549 if (si->rel != NULL) { 1550 DEBUG("[ relocating %s ]", si->name ); 1551 if (soinfo_relocate(si, si->rel, si->rel_count, needed)) { 1552 return false; 1553 } 1554 } 1555 1556 #ifdef ANDROID_MIPS_LINKER 1557 if (!mips_relocate_got(si, needed)) { 1558 return false; 1559 } 1560 #endif 1561 1562 si->flags |= FLAG_LINKED; 1563 DEBUG("[ finished linking %s ]", si->name); 1564 1565 if (si->has_text_relocations) { 1566 /* All relocations are done, we can protect our segments back to 1567 * read-only. */ 1568 if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1569 DL_ERR("can't protect segments for \"%s\": %s", 1570 si->name, strerror(errno)); 1571 return false; 1572 } 1573 } 1574 1575 /* We can also turn on GNU RELRO protection */ 1576 if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { 1577 DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", 1578 si->name, strerror(errno)); 1579 return false; 1580 } 1581 1582 notify_gdb_of_load(si); 1583 return true; 1584 } 1585 1586 /* 1587 * This function add vdso to internal dso list. 1588 * It helps to stack unwinding through signal handlers. 1589 * Also, it makes bionic more like glibc. 1590 */ 1591 static void add_vdso(KernelArgumentBlock& args UNUSED) { 1592 #ifdef AT_SYSINFO_EHDR 1593 Elf32_Ehdr* ehdr_vdso = reinterpret_cast<Elf32_Ehdr*>(args.getauxval(AT_SYSINFO_EHDR)); 1594 1595 soinfo* si = soinfo_alloc("[vdso]"); 1596 si->phdr = reinterpret_cast<Elf32_Phdr*>(reinterpret_cast<char*>(ehdr_vdso) + ehdr_vdso->e_phoff); 1597 si->phnum = ehdr_vdso->e_phnum; 1598 si->link_map.l_name = si->name; 1599 for (size_t i = 0; i < si->phnum; ++i) { 1600 if (si->phdr[i].p_type == PT_LOAD) { 1601 si->link_map.l_addr = reinterpret_cast<Elf32_Addr>(ehdr_vdso) - si->phdr[i].p_vaddr; 1602 break; 1603 } 1604 } 1605 #endif 1606 } 1607 1608 /* 1609 * This code is called after the linker has linked itself and 1610 * fixed it's own GOT. It is safe to make references to externs 1611 * and other non-local data at this point. 1612 */ 1613 static Elf32_Addr __linker_init_post_relocation(KernelArgumentBlock& args, Elf32_Addr linker_base) { 1614 /* NOTE: we store the args pointer on a special location 1615 * of the temporary TLS area in order to pass it to 1616 * the C Library's runtime initializer. 1617 * 1618 * The initializer must clear the slot and reset the TLS 1619 * to point to a different location to ensure that no other 1620 * shared library constructor can access it. 1621 */ 1622 __libc_init_tls(args); 1623 1624 #if TIMING 1625 struct timeval t0, t1; 1626 gettimeofday(&t0, 0); 1627 #endif 1628 1629 // Initialize environment functions, and get to the ELF aux vectors table. 1630 linker_env_init(args); 1631 1632 // If this is a setuid/setgid program, close the security hole described in 1633 // ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc 1634 if (get_AT_SECURE()) { 1635 nullify_closed_stdio(); 1636 } 1637 1638 debuggerd_init(); 1639 1640 // Get a few environment variables. 1641 const char* LD_DEBUG = linker_env_get("LD_DEBUG"); 1642 if (LD_DEBUG != NULL) { 1643 gLdDebugVerbosity = atoi(LD_DEBUG); 1644 } 1645 1646 // Normally, these are cleaned by linker_env_init, but the test 1647 // doesn't cost us anything. 1648 const char* ldpath_env = NULL; 1649 const char* ldpreload_env = NULL; 1650 if (!get_AT_SECURE()) { 1651 ldpath_env = linker_env_get("LD_LIBRARY_PATH"); 1652 ldpreload_env = linker_env_get("LD_PRELOAD"); 1653 } 1654 1655 INFO("[ android linker & debugger ]"); 1656 1657 soinfo* si = soinfo_alloc(args.argv[0]); 1658 if (si == NULL) { 1659 exit(EXIT_FAILURE); 1660 } 1661 1662 /* bootstrap the link map, the main exe always needs to be first */ 1663 si->flags |= FLAG_EXE; 1664 link_map_t* map = &(si->link_map); 1665 1666 map->l_addr = 0; 1667 map->l_name = args.argv[0]; 1668 map->l_prev = NULL; 1669 map->l_next = NULL; 1670 1671 _r_debug.r_map = map; 1672 r_debug_tail = map; 1673 1674 /* gdb expects the linker to be in the debug shared object list. 1675 * Without this, gdb has trouble locating the linker's ".text" 1676 * and ".plt" sections. Gdb could also potentially use this to 1677 * relocate the offset of our exported 'rtld_db_dlactivity' symbol. 1678 * Don't use soinfo_alloc(), because the linker shouldn't 1679 * be on the soinfo list. 1680 */ 1681 { 1682 static soinfo linker_soinfo; 1683 strlcpy(linker_soinfo.name, "/system/bin/linker", sizeof(linker_soinfo.name)); 1684 linker_soinfo.flags = 0; 1685 linker_soinfo.base = linker_base; 1686 1687 /* 1688 * Set the dynamic field in the link map otherwise gdb will complain with 1689 * the following: 1690 * warning: .dynamic section for "/system/bin/linker" is not at the 1691 * expected address (wrong library or version mismatch?) 1692 */ 1693 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base; 1694 Elf32_Phdr *phdr = (Elf32_Phdr*)((unsigned char*) linker_base + elf_hdr->e_phoff); 1695 phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, 1696 &linker_soinfo.dynamic, NULL, NULL); 1697 insert_soinfo_into_debug_map(&linker_soinfo); 1698 } 1699 1700 // Extract information passed from the kernel. 1701 si->phdr = reinterpret_cast<Elf32_Phdr*>(args.getauxval(AT_PHDR)); 1702 si->phnum = args.getauxval(AT_PHNUM); 1703 si->entry = args.getauxval(AT_ENTRY); 1704 1705 /* Compute the value of si->base. We can't rely on the fact that 1706 * the first entry is the PHDR because this will not be true 1707 * for certain executables (e.g. some in the NDK unit test suite) 1708 */ 1709 si->base = 0; 1710 si->size = phdr_table_get_load_size(si->phdr, si->phnum); 1711 si->load_bias = 0; 1712 for (size_t i = 0; i < si->phnum; ++i) { 1713 if (si->phdr[i].p_type == PT_PHDR) { 1714 si->load_bias = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_vaddr; 1715 si->base = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_offset; 1716 break; 1717 } 1718 } 1719 si->dynamic = NULL; 1720 si->ref_count = 1; 1721 1722 // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). 1723 parse_LD_LIBRARY_PATH(ldpath_env); 1724 parse_LD_PRELOAD(ldpreload_env); 1725 1726 somain = si; 1727 1728 if (!soinfo_link_image(si)) { 1729 __libc_format_fd(2, "CANNOT LINK EXECUTABLE: %s\n", linker_get_error_buffer()); 1730 exit(EXIT_FAILURE); 1731 } 1732 1733 add_vdso(args); 1734 1735 si->CallPreInitConstructors(); 1736 1737 for (size_t i = 0; gLdPreloads[i] != NULL; ++i) { 1738 gLdPreloads[i]->CallConstructors(); 1739 } 1740 1741 /* After the link_image, the si->load_bias is initialized. 1742 * For so lib, the map->l_addr will be updated in notify_gdb_of_load. 1743 * We need to update this value for so exe here. So Unwind_Backtrace 1744 * for some arch like x86 could work correctly within so exe. 1745 */ 1746 map->l_addr = si->load_bias; 1747 si->CallConstructors(); 1748 1749 #if TIMING 1750 gettimeofday(&t1,NULL); 1751 PRINT("LINKER TIME: %s: %d microseconds", args.argv[0], (int) ( 1752 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - 1753 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) 1754 )); 1755 #endif 1756 #if STATS 1757 PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", args.argv[0], 1758 linker_stats.count[kRelocAbsolute], 1759 linker_stats.count[kRelocRelative], 1760 linker_stats.count[kRelocCopy], 1761 linker_stats.count[kRelocSymbol]); 1762 #endif 1763 #if COUNT_PAGES 1764 { 1765 unsigned n; 1766 unsigned i; 1767 unsigned count = 0; 1768 for (n = 0; n < 4096; n++) { 1769 if (bitmask[n]) { 1770 unsigned x = bitmask[n]; 1771 for (i = 0; i < 8; i++) { 1772 if (x & 1) { 1773 count++; 1774 } 1775 x >>= 1; 1776 } 1777 } 1778 } 1779 PRINT("PAGES MODIFIED: %s: %d (%dKB)", args.argv[0], count, count * 4); 1780 } 1781 #endif 1782 1783 #if TIMING || STATS || COUNT_PAGES 1784 fflush(stdout); 1785 #endif 1786 1787 TRACE("[ Ready to execute '%s' @ 0x%08x ]", si->name, si->entry); 1788 return si->entry; 1789 } 1790 1791 /* Compute the load-bias of an existing executable. This shall only 1792 * be used to compute the load bias of an executable or shared library 1793 * that was loaded by the kernel itself. 1794 * 1795 * Input: 1796 * elf -> address of ELF header, assumed to be at the start of the file. 1797 * Return: 1798 * load bias, i.e. add the value of any p_vaddr in the file to get 1799 * the corresponding address in memory. 1800 */ 1801 static Elf32_Addr get_elf_exec_load_bias(const Elf32_Ehdr* elf) { 1802 Elf32_Addr offset = elf->e_phoff; 1803 const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset); 1804 const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum; 1805 1806 for (const Elf32_Phdr* phdr = phdr_table; phdr < phdr_end; phdr++) { 1807 if (phdr->p_type == PT_LOAD) { 1808 return reinterpret_cast<Elf32_Addr>(elf) + phdr->p_offset - phdr->p_vaddr; 1809 } 1810 } 1811 return 0; 1812 } 1813 1814 /* 1815 * This is the entry point for the linker, called from begin.S. This 1816 * method is responsible for fixing the linker's own relocations, and 1817 * then calling __linker_init_post_relocation(). 1818 * 1819 * Because this method is called before the linker has fixed it's own 1820 * relocations, any attempt to reference an extern variable, extern 1821 * function, or other GOT reference will generate a segfault. 1822 */ 1823 extern "C" Elf32_Addr __linker_init(void* raw_args) { 1824 KernelArgumentBlock args(raw_args); 1825 1826 Elf32_Addr linker_addr = args.getauxval(AT_BASE); 1827 1828 Elf32_Ehdr* elf_hdr = (Elf32_Ehdr*) linker_addr; 1829 Elf32_Phdr* phdr = (Elf32_Phdr*)((unsigned char*) linker_addr + elf_hdr->e_phoff); 1830 1831 soinfo linker_so; 1832 memset(&linker_so, 0, sizeof(soinfo)); 1833 1834 linker_so.base = linker_addr; 1835 linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); 1836 linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); 1837 linker_so.dynamic = NULL; 1838 linker_so.phdr = phdr; 1839 linker_so.phnum = elf_hdr->e_phnum; 1840 linker_so.flags |= FLAG_LINKER; 1841 1842 if (!soinfo_link_image(&linker_so)) { 1843 // It would be nice to print an error message, but if the linker 1844 // can't link itself, there's no guarantee that we'll be able to 1845 // call write() (because it involves a GOT reference). 1846 // 1847 // This situation should never occur unless the linker itself 1848 // is corrupt. 1849 exit(EXIT_FAILURE); 1850 } 1851 1852 // We have successfully fixed our own relocations. It's safe to run 1853 // the main part of the linker now. 1854 args.abort_message_ptr = &gAbortMessage; 1855 Elf32_Addr start_address = __linker_init_post_relocation(args, linker_addr); 1856 1857 set_soinfo_pool_protection(PROT_READ); 1858 1859 // Return the address that the calling assembly stub should jump to. 1860 return start_address; 1861 } 1862
