linker.cpp revision ca0c11bd823f37f03cc8067cb182876827d5275a
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/logd.h> 46#include <private/ScopedPthreadMutexLocker.h> 47 48#include "linker.h" 49#include "linker_debug.h" 50#include "linker_environ.h" 51#include "linker_phdr.h" 52 53/* Assume average path length of 64 and max 8 paths */ 54#define LDPATH_BUFSIZE 512 55#define LDPATH_MAX 8 56 57#define LDPRELOAD_BUFSIZE 512 58#define LDPRELOAD_MAX 8 59 60/* >>> IMPORTANT NOTE - READ ME BEFORE MODIFYING <<< 61 * 62 * Do NOT use malloc() and friends or pthread_*() code here. 63 * Don't use printf() either; it's caused mysterious memory 64 * corruption in the past. 65 * The linker runs before we bring up libc and it's easiest 66 * to make sure it does not depend on any complex libc features 67 * 68 * open issues / todo: 69 * 70 * - are we doing everything we should for ARM_COPY relocations? 71 * - cleaner error reporting 72 * - after linking, set as much stuff as possible to READONLY 73 * and NOEXEC 74 */ 75 76static bool soinfo_link_image(soinfo* si); 77 78// We can't use malloc(3) in the dynamic linker. We use a linked list of anonymous 79// maps, each a single page in size. The pages are broken up into as many struct soinfo 80// objects as will fit, and they're all threaded together on a free list. 81#define SOINFO_PER_POOL ((PAGE_SIZE - sizeof(soinfo_pool_t*)) / sizeof(soinfo)) 82struct soinfo_pool_t { 83 soinfo_pool_t* next; 84 soinfo info[SOINFO_PER_POOL]; 85}; 86static struct soinfo_pool_t* gSoInfoPools = NULL; 87static soinfo* gSoInfoFreeList = NULL; 88 89static soinfo* solist = &libdl_info; 90static soinfo* sonext = &libdl_info; 91static soinfo* somain; /* main process, always the one after libdl_info */ 92 93static const char* const gSoPaths[] = { 94 "/vendor/lib", 95 "/system/lib", 96 NULL 97}; 98 99static char gLdPathsBuffer[LDPATH_BUFSIZE]; 100static const char* gLdPaths[LDPATH_MAX + 1]; 101 102static char gLdPreloadsBuffer[LDPRELOAD_BUFSIZE]; 103static const char* gLdPreloadNames[LDPRELOAD_MAX + 1]; 104 105static soinfo* gLdPreloads[LDPRELOAD_MAX + 1]; 106 107__LIBC_HIDDEN__ int gLdDebugVerbosity; 108 109enum RelocationKind { 110 kRelocAbsolute = 0, 111 kRelocRelative, 112 kRelocCopy, 113 kRelocSymbol, 114 kRelocMax 115}; 116 117#if STATS 118struct linker_stats_t { 119 int count[kRelocMax]; 120}; 121 122static linker_stats_t linker_stats; 123 124static void count_relocation(RelocationKind kind) { 125 ++linker_stats.count[kind]; 126} 127#else 128static void count_relocation(RelocationKind) { 129} 130#endif 131 132#if COUNT_PAGES 133static unsigned bitmask[4096]; 134#define MARK(offset) \ 135 do { \ 136 bitmask[((offset) >> 12) >> 3] |= (1 << (((offset) >> 12) & 7)); \ 137 } while(0) 138#else 139#define MARK(x) do {} while (0) 140#endif 141 142// You shouldn't try to call memory-allocating functions in the dynamic linker. 143// Guard against the most obvious ones. 144#define DISALLOW_ALLOCATION(return_type, name, ...) \ 145 return_type name __VA_ARGS__ \ 146 { \ 147 const char* msg = "ERROR: " #name " called from the dynamic linker!\n"; \ 148 __libc_android_log_write(ANDROID_LOG_FATAL, "linker", msg); \ 149 write(2, msg, strlen(msg)); \ 150 abort(); \ 151 } 152#define UNUSED __attribute__((unused)) 153DISALLOW_ALLOCATION(void*, malloc, (size_t u UNUSED)); 154DISALLOW_ALLOCATION(void, free, (void* u UNUSED)); 155DISALLOW_ALLOCATION(void*, realloc, (void* u1 UNUSED, size_t u2 UNUSED)); 156DISALLOW_ALLOCATION(void*, calloc, (size_t u1 UNUSED, size_t u2 UNUSED)); 157 158static char tmp_err_buf[768]; 159static char __linker_dl_err_buf[768]; 160 161char* linker_get_error_buffer() { 162 return &__linker_dl_err_buf[0]; 163} 164 165size_t linker_get_error_buffer_size() { 166 return sizeof(__linker_dl_err_buf); 167} 168 169/* 170 * This function is an empty stub where GDB locates a breakpoint to get notified 171 * about linker activity. 172 */ 173extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(); 174 175static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, 176 RT_CONSISTENT, 0}; 177static link_map_t* r_debug_tail = 0; 178 179static pthread_mutex_t gDebugMutex = PTHREAD_MUTEX_INITIALIZER; 180 181static 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 205static 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 220static 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 237static 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 254void 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 261static 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 289static 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 297static 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 322static 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 355static 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 380static void parse_LD_LIBRARY_PATH(const char* path) { 381 parse_path(path, ":", gLdPaths, 382 gLdPathsBuffer, sizeof(gLdPathsBuffer), LDPATH_MAX); 383} 384 385static 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. */ 421int 422dl_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 442static Elf32_Sym* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name) { 443 Elf32_Sym* s; 444 Elf32_Sym* symtab = si->symtab; 445 const char* strtab = si->strtab; 446 unsigned n; 447 448 TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %d", 449 name, si->name, si->base, hash, hash % si->nbucket); 450 n = hash % si->nbucket; 451 452 for (n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]) { 453 s = symtab + n; 454 if (strcmp(strtab + s->st_name, name)) continue; 455 456 /* only concern ourselves with global and weak symbol definitions */ 457 switch(ELF32_ST_BIND(s->st_info)){ 458 case STB_GLOBAL: 459 case STB_WEAK: 460 if (s->st_shndx == SHN_UNDEF) { 461 continue; 462 } 463 464 TRACE_TYPE(LOOKUP, "FOUND %s in %s (%08x) %d", 465 name, si->name, s->st_value, s->st_size); 466 return s; 467 } 468 } 469 470 return NULL; 471} 472 473static unsigned elfhash(const char* _name) { 474 const unsigned char* name = (const unsigned char*) _name; 475 unsigned h = 0, g; 476 477 while(*name) { 478 h = (h << 4) + *name++; 479 g = h & 0xf0000000; 480 h ^= g; 481 h ^= g >> 24; 482 } 483 return h; 484} 485 486static Elf32_Sym* soinfo_do_lookup(soinfo* si, const char* name, soinfo** lsi, soinfo* needed[]) { 487 unsigned elf_hash = elfhash(name); 488 Elf32_Sym* s = NULL; 489 490 if (si != NULL && somain != NULL) { 491 492 /* 493 * Local scope is executable scope. Just start looking into it right away 494 * for the shortcut. 495 */ 496 497 if (si == somain) { 498 s = soinfo_elf_lookup(si, elf_hash, name); 499 if (s != NULL) { 500 *lsi = si; 501 goto done; 502 } 503 } else { 504 /* Order of symbol lookup is controlled by DT_SYMBOLIC flag */ 505 506 /* 507 * If this object was built with symbolic relocations disabled, the 508 * first place to look to resolve external references is the main 509 * executable. 510 */ 511 512 if (!si->has_DT_SYMBOLIC) { 513 DEBUG("%s: looking up %s in executable %s", 514 si->name, name, somain->name); 515 s = soinfo_elf_lookup(somain, elf_hash, name); 516 if (s != NULL) { 517 *lsi = somain; 518 goto done; 519 } 520 } 521 522 /* Look for symbols in the local scope (the object who is 523 * searching). This happens with C++ templates on i386 for some 524 * reason. 525 * 526 * Notes on weak symbols: 527 * The ELF specs are ambiguous about treatment of weak definitions in 528 * dynamic linking. Some systems return the first definition found 529 * and some the first non-weak definition. This is system dependent. 530 * Here we return the first definition found for simplicity. */ 531 532 s = soinfo_elf_lookup(si, elf_hash, name); 533 if (s != NULL) { 534 *lsi = si; 535 goto done; 536 } 537 538 /* 539 * If this object was built with -Bsymbolic and symbol is not found 540 * in the local scope, try to find the symbol in the main executable. 541 */ 542 543 if (si->has_DT_SYMBOLIC) { 544 DEBUG("%s: looking up %s in executable %s after local scope", 545 si->name, name, somain->name); 546 s = soinfo_elf_lookup(somain, elf_hash, name); 547 if (s != NULL) { 548 *lsi = somain; 549 goto done; 550 } 551 } 552 } 553 } 554 555 /* Next, look for it in the preloads list */ 556 for (int i = 0; gLdPreloads[i] != NULL; i++) { 557 s = soinfo_elf_lookup(gLdPreloads[i], elf_hash, name); 558 if (s != NULL) { 559 *lsi = gLdPreloads[i]; 560 goto done; 561 } 562 } 563 564 for (int i = 0; needed[i] != NULL; i++) { 565 DEBUG("%s: looking up %s in %s", 566 si->name, name, needed[i]->name); 567 s = soinfo_elf_lookup(needed[i], elf_hash, name); 568 if (s != NULL) { 569 *lsi = needed[i]; 570 goto done; 571 } 572 } 573 574done: 575 if (s != NULL) { 576 TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = 0x%08x, " 577 "found in %s, base = 0x%08x, load bias = 0x%08x", 578 si->name, name, s->st_value, 579 (*lsi)->name, (*lsi)->base, (*lsi)->load_bias); 580 return s; 581 } 582 583 return NULL; 584} 585 586/* This is used by dlsym(3). It performs symbol lookup only within the 587 specified soinfo object and not in any of its dependencies. 588 589 TODO: Only looking in the specified soinfo seems wrong. dlsym(3) says 590 that it should do a breadth first search through the dependency 591 tree. This agrees with the ELF spec (aka System V Application 592 Binary Interface) where in Chapter 5 it discuss resolving "Shared 593 Object Dependencies" in breadth first search order. 594 */ 595Elf32_Sym* dlsym_handle_lookup(soinfo* si, const char* name) 596{ 597 return soinfo_elf_lookup(si, elfhash(name), name); 598} 599 600/* This is used by dlsym(3) to performs a global symbol lookup. If the 601 start value is null (for RTLD_DEFAULT), the search starts at the 602 beginning of the global solist. Otherwise the search starts at the 603 specified soinfo (for RTLD_NEXT). 604 */ 605Elf32_Sym* dlsym_linear_lookup(const char* name, soinfo** found, soinfo* start) { 606 unsigned elf_hash = elfhash(name); 607 608 if (start == NULL) { 609 start = solist; 610 } 611 612 Elf32_Sym* s = NULL; 613 for (soinfo* si = start; (s == NULL) && (si != NULL); si = si->next) { 614 s = soinfo_elf_lookup(si, elf_hash, name); 615 if (s != NULL) { 616 *found = si; 617 break; 618 } 619 } 620 621 if (s != NULL) { 622 TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, found->base = 0x%08x", 623 name, s->st_value, (*found)->base); 624 } 625 626 return s; 627} 628 629soinfo* find_containing_library(const void* p) { 630 Elf32_Addr address = reinterpret_cast<Elf32_Addr>(p); 631 for (soinfo* si = solist; si != NULL; si = si->next) { 632 if (address >= si->base && address - si->base < si->size) { 633 return si; 634 } 635 } 636 return NULL; 637} 638 639Elf32_Sym* dladdr_find_symbol(soinfo* si, const void* addr) { 640 Elf32_Addr soaddr = reinterpret_cast<Elf32_Addr>(addr) - si->base; 641 642 // Search the library's symbol table for any defined symbol which 643 // contains this address. 644 for (size_t i = 0; i < si->nchain; ++i) { 645 Elf32_Sym* sym = &si->symtab[i]; 646 if (sym->st_shndx != SHN_UNDEF && 647 soaddr >= sym->st_value && 648 soaddr < sym->st_value + sym->st_size) { 649 return sym; 650 } 651 } 652 653 return NULL; 654} 655 656#if 0 657static void dump(soinfo* si) 658{ 659 Elf32_Sym* s = si->symtab; 660 for (unsigned n = 0; n < si->nchain; n++) { 661 TRACE("%04d> %08x: %02x %04x %08x %08x %s", n, s, 662 s->st_info, s->st_shndx, s->st_value, s->st_size, 663 si->strtab + s->st_name); 664 s++; 665 } 666} 667#endif 668 669static int open_library_on_path(const char* name, const char* const paths[]) { 670 char buf[512]; 671 for (size_t i = 0; paths[i] != NULL; ++i) { 672 int n = __libc_format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name); 673 if (n < 0 || n >= static_cast<int>(sizeof(buf))) { 674 PRINT("Warning: ignoring very long library path: %s/%s", paths[i], name); 675 continue; 676 } 677 int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC)); 678 if (fd != -1) { 679 return fd; 680 } 681 } 682 return -1; 683} 684 685static int open_library(const char* name) { 686 TRACE("[ opening %s ]", name); 687 688 // If the name contains a slash, we should attempt to open it directly and not search the paths. 689 if (strchr(name, '/') != NULL) { 690 int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC)); 691 if (fd != -1) { 692 return fd; 693 } 694 // ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now. 695 } 696 697 // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths. 698 int fd = open_library_on_path(name, gLdPaths); 699 if (fd == -1) { 700 fd = open_library_on_path(name, gSoPaths); 701 } 702 return fd; 703} 704 705static soinfo* load_library(const char* name) { 706 // Open the file. 707 int fd = open_library(name); 708 if (fd == -1) { 709 DL_ERR("library \"%s\" not found", name); 710 return NULL; 711 } 712 713 // Read the ELF header and load the segments. 714 ElfReader elf_reader(name, fd); 715 if (!elf_reader.Load()) { 716 return NULL; 717 } 718 719 const char* bname = strrchr(name, '/'); 720 soinfo* si = soinfo_alloc(bname ? bname + 1 : name); 721 if (si == NULL) { 722 return NULL; 723 } 724 si->base = elf_reader.load_start(); 725 si->size = elf_reader.load_size(); 726 si->load_bias = elf_reader.load_bias(); 727 si->flags = 0; 728 si->entry = 0; 729 si->dynamic = NULL; 730 si->phnum = elf_reader.phdr_count(); 731 si->phdr = elf_reader.loaded_phdr(); 732 return si; 733} 734 735static soinfo *find_loaded_library(const char *name) 736{ 737 soinfo *si; 738 const char *bname; 739 740 // TODO: don't use basename only for determining libraries 741 // http://code.google.com/p/android/issues/detail?id=6670 742 743 bname = strrchr(name, '/'); 744 bname = bname ? bname + 1 : name; 745 746 for (si = solist; si != NULL; si = si->next) { 747 if (!strcmp(bname, si->name)) { 748 return si; 749 } 750 } 751 return NULL; 752} 753 754static soinfo* find_library_internal(const char* name) { 755 if (name == NULL) { 756 return somain; 757 } 758 759 soinfo* si = find_loaded_library(name); 760 if (si != NULL) { 761 if (si->flags & FLAG_LINKED) { 762 return si; 763 } 764 DL_ERR("OOPS: recursive link to \"%s\"", si->name); 765 return NULL; 766 } 767 768 TRACE("[ '%s' has not been loaded yet. Locating...]", name); 769 si = load_library(name); 770 if (si == NULL) { 771 return NULL; 772 } 773 774 // At this point we know that whatever is loaded @ base is a valid ELF 775 // shared library whose segments are properly mapped in. 776 TRACE("[ init_library base=0x%08x sz=0x%08x name='%s' ]", 777 si->base, si->size, si->name); 778 779 if (!soinfo_link_image(si)) { 780 munmap(reinterpret_cast<void*>(si->base), si->size); 781 soinfo_free(si); 782 return NULL; 783 } 784 785 return si; 786} 787 788static soinfo* find_library(const char* name) { 789 soinfo* si = find_library_internal(name); 790 if (si != NULL) { 791 si->ref_count++; 792 } 793 return si; 794} 795 796static int soinfo_unload(soinfo* si) { 797 if (si->ref_count == 1) { 798 TRACE("unloading '%s'", si->name); 799 si->CallDestructors(); 800 801 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 802 if (d->d_tag == DT_NEEDED) { 803 const char* library_name = si->strtab + d->d_un.d_val; 804 soinfo* lsi = find_loaded_library(library_name); 805 if (lsi != NULL) { 806 TRACE("%s needs to unload %s", si->name, lsi->name); 807 soinfo_unload(lsi); 808 } else { 809 // TODO: should we return -1 in this case? 810 DL_ERR("\"%s\": could not unload dependent library", si->name); 811 } 812 } 813 } 814 815 munmap(reinterpret_cast<void*>(si->base), si->size); 816 notify_gdb_of_unload(si); 817 soinfo_free(si); 818 si->ref_count = 0; 819 } else { 820 si->ref_count--; 821 TRACE("not unloading '%s', decrementing ref_count to %d", si->name, si->ref_count); 822 } 823 return 0; 824} 825 826void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) { 827 if (!get_AT_SECURE()) { 828 parse_LD_LIBRARY_PATH(ld_library_path); 829 } 830} 831 832soinfo* do_dlopen(const char* name, int flags) { 833 if ((flags & ~(RTLD_NOW|RTLD_LAZY|RTLD_LOCAL|RTLD_GLOBAL)) != 0) { 834 DL_ERR("invalid flags to dlopen: %x", flags); 835 return NULL; 836 } 837 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 838 soinfo* si = find_library(name); 839 if (si != NULL) { 840 si->CallConstructors(); 841 } 842 set_soinfo_pool_protection(PROT_READ); 843 return si; 844} 845 846int do_dlclose(soinfo* si) { 847 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 848 int result = soinfo_unload(si); 849 set_soinfo_pool_protection(PROT_READ); 850 return result; 851} 852 853/* TODO: don't use unsigned for addrs below. It works, but is not 854 * ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned 855 * long. 856 */ 857static int soinfo_relocate(soinfo* si, Elf32_Rel* rel, unsigned count, 858 soinfo* needed[]) 859{ 860 Elf32_Sym* symtab = si->symtab; 861 const char* strtab = si->strtab; 862 Elf32_Sym* s; 863 Elf32_Rel* start = rel; 864 soinfo* lsi; 865 866 for (size_t idx = 0; idx < count; ++idx, ++rel) { 867 unsigned type = ELF32_R_TYPE(rel->r_info); 868 unsigned sym = ELF32_R_SYM(rel->r_info); 869 Elf32_Addr reloc = static_cast<Elf32_Addr>(rel->r_offset + si->load_bias); 870 Elf32_Addr sym_addr = 0; 871 char* sym_name = NULL; 872 873 DEBUG("Processing '%s' relocation at index %d", si->name, idx); 874 if (type == 0) { // R_*_NONE 875 continue; 876 } 877 if (sym != 0) { 878 sym_name = (char *)(strtab + symtab[sym].st_name); 879 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 880 if (s == NULL) { 881 /* We only allow an undefined symbol if this is a weak 882 reference.. */ 883 s = &symtab[sym]; 884 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 885 DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); 886 return -1; 887 } 888 889 /* IHI0044C AAELF 4.5.1.1: 890 891 Libraries are not searched to resolve weak references. 892 It is not an error for a weak reference to remain 893 unsatisfied. 894 895 During linking, the value of an undefined weak reference is: 896 - Zero if the relocation type is absolute 897 - The address of the place if the relocation is pc-relative 898 - The address of nominal base address if the relocation 899 type is base-relative. 900 */ 901 902 switch (type) { 903#if defined(ANDROID_ARM_LINKER) 904 case R_ARM_JUMP_SLOT: 905 case R_ARM_GLOB_DAT: 906 case R_ARM_ABS32: 907 case R_ARM_RELATIVE: /* Don't care. */ 908#elif defined(ANDROID_X86_LINKER) 909 case R_386_JMP_SLOT: 910 case R_386_GLOB_DAT: 911 case R_386_32: 912 case R_386_RELATIVE: /* Dont' care. */ 913#endif /* ANDROID_*_LINKER */ 914 /* sym_addr was initialized to be zero above or relocation 915 code below does not care about value of sym_addr. 916 No need to do anything. */ 917 break; 918 919#if defined(ANDROID_X86_LINKER) 920 case R_386_PC32: 921 sym_addr = reloc; 922 break; 923#endif /* ANDROID_X86_LINKER */ 924 925#if defined(ANDROID_ARM_LINKER) 926 case R_ARM_COPY: 927 /* Fall through. Can't really copy if weak symbol is 928 not found in run-time. */ 929#endif /* ANDROID_ARM_LINKER */ 930 default: 931 DL_ERR("unknown weak reloc type %d @ %p (%d)", 932 type, rel, (int) (rel - start)); 933 return -1; 934 } 935 } else { 936 /* We got a definition. */ 937#if 0 938 if ((base == 0) && (si->base != 0)) { 939 /* linking from libraries to main image is bad */ 940 DL_ERR("cannot locate \"%s\"...", 941 strtab + symtab[sym].st_name); 942 return -1; 943 } 944#endif 945 sym_addr = static_cast<Elf32_Addr>(s->st_value + lsi->load_bias); 946 } 947 count_relocation(kRelocSymbol); 948 } else { 949 s = NULL; 950 } 951 952/* TODO: This is ugly. Split up the relocations by arch into 953 * different files. 954 */ 955 switch(type){ 956#if defined(ANDROID_ARM_LINKER) 957 case R_ARM_JUMP_SLOT: 958 count_relocation(kRelocAbsolute); 959 MARK(rel->r_offset); 960 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 961 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 962 break; 963 case R_ARM_GLOB_DAT: 964 count_relocation(kRelocAbsolute); 965 MARK(rel->r_offset); 966 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 967 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 968 break; 969 case R_ARM_ABS32: 970 count_relocation(kRelocAbsolute); 971 MARK(rel->r_offset); 972 TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s", reloc, sym_addr, sym_name); 973 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 974 break; 975 case R_ARM_REL32: 976 count_relocation(kRelocRelative); 977 MARK(rel->r_offset); 978 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s", 979 reloc, sym_addr, rel->r_offset, sym_name); 980 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr - rel->r_offset; 981 break; 982#elif defined(ANDROID_X86_LINKER) 983 case R_386_JMP_SLOT: 984 count_relocation(kRelocAbsolute); 985 MARK(rel->r_offset); 986 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 987 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 988 break; 989 case R_386_GLOB_DAT: 990 count_relocation(kRelocAbsolute); 991 MARK(rel->r_offset); 992 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 993 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 994 break; 995#elif defined(ANDROID_MIPS_LINKER) 996 case R_MIPS_REL32: 997 count_relocation(kRelocAbsolute); 998 MARK(rel->r_offset); 999 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s", 1000 reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); 1001 if (s) { 1002 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 1003 } else { 1004 *reinterpret_cast<Elf32_Addr*>(reloc) += si->base; 1005 } 1006 break; 1007#endif /* ANDROID_*_LINKER */ 1008 1009#if defined(ANDROID_ARM_LINKER) 1010 case R_ARM_RELATIVE: 1011#elif defined(ANDROID_X86_LINKER) 1012 case R_386_RELATIVE: 1013#endif /* ANDROID_*_LINKER */ 1014 count_relocation(kRelocRelative); 1015 MARK(rel->r_offset); 1016 if (sym) { 1017 DL_ERR("odd RELATIVE form..."); 1018 return -1; 1019 } 1020 TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x", reloc, si->base); 1021 *reinterpret_cast<Elf32_Addr*>(reloc) += si->base; 1022 break; 1023 1024#if defined(ANDROID_X86_LINKER) 1025 case R_386_32: 1026 count_relocation(kRelocRelative); 1027 MARK(rel->r_offset); 1028 1029 TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s", reloc, sym_addr, sym_name); 1030 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 1031 break; 1032 1033 case R_386_PC32: 1034 count_relocation(kRelocRelative); 1035 MARK(rel->r_offset); 1036 TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s", 1037 reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); 1038 *reinterpret_cast<Elf32_Addr*>(reloc) += (sym_addr - reloc); 1039 break; 1040#endif /* ANDROID_X86_LINKER */ 1041 1042#ifdef ANDROID_ARM_LINKER 1043 case R_ARM_COPY: 1044 if ((si->flags & FLAG_EXE) == 0) { 1045 /* 1046 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf 1047 * 1048 * Section 4.7.1.10 "Dynamic relocations" 1049 * R_ARM_COPY may only appear in executable objects where e_type is 1050 * set to ET_EXEC. 1051 * 1052 * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. 1053 * We should explicitly disallow ET_DYN executables from having 1054 * R_ARM_COPY relocations. 1055 */ 1056 DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); 1057 return -1; 1058 } 1059 count_relocation(kRelocCopy); 1060 MARK(rel->r_offset); 1061 TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s", reloc, s->st_size, sym_addr, sym_name); 1062 if (reloc == sym_addr) { 1063 Elf32_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed); 1064 1065 if (src == NULL) { 1066 DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name); 1067 return -1; 1068 } 1069 if (lsi->has_DT_SYMBOLIC) { 1070 DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared " 1071 "library %s (built with -Bsymbolic?)", si->name, lsi->name); 1072 return -1; 1073 } 1074 if (s->st_size < src->st_size) { 1075 DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)", 1076 si->name, s->st_size, src->st_size); 1077 return -1; 1078 } 1079 memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size); 1080 } else { 1081 DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name); 1082 return -1; 1083 } 1084 break; 1085#endif /* ANDROID_ARM_LINKER */ 1086 1087 default: 1088 DL_ERR("unknown reloc type %d @ %p (%d)", 1089 type, rel, (int) (rel - start)); 1090 return -1; 1091 } 1092 } 1093 return 0; 1094} 1095 1096#ifdef ANDROID_MIPS_LINKER 1097static int mips_relocate_got(soinfo* si, soinfo* needed[]) { 1098 unsigned *got; 1099 unsigned local_gotno, gotsym, symtabno; 1100 Elf32_Sym *symtab, *sym; 1101 unsigned g; 1102 1103 got = si->plt_got; 1104 local_gotno = si->mips_local_gotno; 1105 gotsym = si->mips_gotsym; 1106 symtabno = si->mips_symtabno; 1107 symtab = si->symtab; 1108 1109 /* 1110 * got[0] is address of lazy resolver function 1111 * got[1] may be used for a GNU extension 1112 * set it to a recognizable address in case someone calls it 1113 * (should be _rtld_bind_start) 1114 * FIXME: maybe this should be in a separate routine 1115 */ 1116 1117 if ((si->flags & FLAG_LINKER) == 0) { 1118 g = 0; 1119 got[g++] = 0xdeadbeef; 1120 if (got[g] & 0x80000000) { 1121 got[g++] = 0xdeadfeed; 1122 } 1123 /* 1124 * Relocate the local GOT entries need to be relocated 1125 */ 1126 for (; g < local_gotno; g++) { 1127 got[g] += si->load_bias; 1128 } 1129 } 1130 1131 /* Now for the global GOT entries */ 1132 sym = symtab + gotsym; 1133 got = si->plt_got + local_gotno; 1134 for (g = gotsym; g < symtabno; g++, sym++, got++) { 1135 const char* sym_name; 1136 Elf32_Sym* s; 1137 soinfo* lsi; 1138 1139 /* This is an undefined reference... try to locate it */ 1140 sym_name = si->strtab + sym->st_name; 1141 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1142 if (s == NULL) { 1143 /* We only allow an undefined symbol if this is a weak 1144 reference.. */ 1145 s = &symtab[g]; 1146 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1147 DL_ERR("cannot locate \"%s\"...", sym_name); 1148 return -1; 1149 } 1150 *got = 0; 1151 } 1152 else { 1153 /* FIXME: is this sufficient? 1154 * For reference see NetBSD link loader 1155 * 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 1156 */ 1157 *got = lsi->load_bias + s->st_value; 1158 } 1159 } 1160 return 0; 1161} 1162#endif 1163 1164/* Please read the "Initialization and Termination functions" functions. 1165 * of the linker design note in bionic/linker/README.TXT to understand 1166 * what the following code is doing. 1167 * 1168 * The important things to remember are: 1169 * 1170 * DT_PREINIT_ARRAY must be called first for executables, and should 1171 * not appear in shared libraries. 1172 * 1173 * DT_INIT should be called before DT_INIT_ARRAY if both are present 1174 * 1175 * DT_FINI should be called after DT_FINI_ARRAY if both are present 1176 * 1177 * DT_FINI_ARRAY must be parsed in reverse order. 1178 */ 1179void soinfo::CallArray(const char* array_name UNUSED, linker_function_t* functions, size_t count, bool reverse) { 1180 if (functions == NULL) { 1181 return; 1182 } 1183 1184 TRACE("[ Calling %s (size %d) @ %p for '%s' ]", array_name, count, functions, name); 1185 1186 int begin = reverse ? (count - 1) : 0; 1187 int end = reverse ? -1 : count; 1188 int step = reverse ? -1 : 1; 1189 1190 for (int i = begin; i != end; i += step) { 1191 TRACE("[ %s[%d] == %p ]", array_name, i, functions[i]); 1192 CallFunction("function", functions[i]); 1193 } 1194 1195 TRACE("[ Done calling %s for '%s' ]", array_name, name); 1196} 1197 1198void soinfo::CallFunction(const char* function_name UNUSED, linker_function_t function) { 1199 if (function == NULL || reinterpret_cast<uintptr_t>(function) == static_cast<uintptr_t>(-1)) { 1200 return; 1201 } 1202 1203 TRACE("[ Calling %s @ %p for '%s' ]", function_name, function, name); 1204 function(); 1205 TRACE("[ Done calling %s @ %p for '%s' ]", function_name, function, name); 1206 1207 // The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures 1208 // are still writable. This happens with our debug malloc (see http://b/7941716). 1209 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 1210} 1211 1212void soinfo::CallPreInitConstructors() { 1213 CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false); 1214} 1215 1216void soinfo::CallConstructors() { 1217 if (constructors_called) { 1218 return; 1219 } 1220 1221 // We set constructors_called before actually calling the constructors, otherwise it doesn't 1222 // protect against recursive constructor calls. One simple example of constructor recursion 1223 // is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so: 1224 // 1. The program depends on libc, so libc's constructor is called here. 1225 // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. 1226 // 3. dlopen() calls the constructors on the newly created 1227 // soinfo for libc_malloc_debug_leak.so. 1228 // 4. The debug .so depends on libc, so CallConstructors is 1229 // called again with the libc soinfo. If it doesn't trigger the early- 1230 // out above, the libc constructor will be called again (recursively!). 1231 constructors_called = true; 1232 1233 if (!(flags & FLAG_EXE) && preinit_array) { 1234 DL_ERR("shared library \"%s\" has a preinit_array table @ %p", name, preinit_array); 1235 return; 1236 } 1237 1238 if (dynamic != NULL) { 1239 for (Elf32_Dyn* d = dynamic; d->d_tag != DT_NULL; ++d) { 1240 if (d->d_tag == DT_NEEDED) { 1241 const char* library_name = strtab + d->d_un.d_val; 1242 soinfo* lsi = find_loaded_library(library_name); 1243 if (lsi == NULL) { 1244 DL_ERR("\"%s\": could not initialize dependent library", name); 1245 } else { 1246 lsi->CallConstructors(); 1247 } 1248 } 1249 } 1250 } 1251 1252 CallFunction("DT_INIT", init_func); 1253 CallArray("DT_INIT_ARRAY", init_array, init_array_count, false); 1254} 1255 1256void soinfo::CallDestructors() { 1257 CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true); 1258 CallFunction("DT_FINI", fini_func); 1259} 1260 1261/* Force any of the closed stdin, stdout and stderr to be associated with 1262 /dev/null. */ 1263static int nullify_closed_stdio() { 1264 int dev_null, i, status; 1265 int return_value = 0; 1266 1267 dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 1268 if (dev_null < 0) { 1269 DL_ERR("cannot open /dev/null: %s", strerror(errno)); 1270 return -1; 1271 } 1272 TRACE("[ Opened /dev/null file-descriptor=%d]", dev_null); 1273 1274 /* If any of the stdio file descriptors is valid and not associated 1275 with /dev/null, dup /dev/null to it. */ 1276 for (i = 0; i < 3; i++) { 1277 /* If it is /dev/null already, we are done. */ 1278 if (i == dev_null) { 1279 continue; 1280 } 1281 1282 TRACE("[ Nullifying stdio file descriptor %d]", i); 1283 status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 1284 1285 /* If file is opened, we are good. */ 1286 if (status != -1) { 1287 continue; 1288 } 1289 1290 /* The only error we allow is that the file descriptor does not 1291 exist, in which case we dup /dev/null to it. */ 1292 if (errno != EBADF) { 1293 DL_ERR("fcntl failed: %s", strerror(errno)); 1294 return_value = -1; 1295 continue; 1296 } 1297 1298 /* Try dupping /dev/null to this stdio file descriptor and 1299 repeat if there is a signal. Note that any errors in closing 1300 the stdio descriptor are lost. */ 1301 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 1302 if (status < 0) { 1303 DL_ERR("dup2 failed: %s", strerror(errno)); 1304 return_value = -1; 1305 continue; 1306 } 1307 } 1308 1309 /* If /dev/null is not one of the stdio file descriptors, close it. */ 1310 if (dev_null > 2) { 1311 TRACE("[ Closing /dev/null file-descriptor=%d]", dev_null); 1312 status = TEMP_FAILURE_RETRY(close(dev_null)); 1313 if (status == -1) { 1314 DL_ERR("close failed: %s", strerror(errno)); 1315 return_value = -1; 1316 } 1317 } 1318 1319 return return_value; 1320} 1321 1322static bool soinfo_link_image(soinfo* si) { 1323 /* "base" might wrap around UINT32_MAX. */ 1324 Elf32_Addr base = si->load_bias; 1325 const Elf32_Phdr *phdr = si->phdr; 1326 int phnum = si->phnum; 1327 bool relocating_linker = (si->flags & FLAG_LINKER) != 0; 1328 1329 /* We can't debug anything until the linker is relocated */ 1330 if (!relocating_linker) { 1331 INFO("[ linking %s ]", si->name); 1332 DEBUG("si->base = 0x%08x si->flags = 0x%08x", si->base, si->flags); 1333 } 1334 1335 /* Extract dynamic section */ 1336 size_t dynamic_count; 1337 Elf32_Word dynamic_flags; 1338 phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, 1339 &dynamic_count, &dynamic_flags); 1340 if (si->dynamic == NULL) { 1341 if (!relocating_linker) { 1342 DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name); 1343 } 1344 return false; 1345 } else { 1346 if (!relocating_linker) { 1347 DEBUG("dynamic = %p", si->dynamic); 1348 } 1349 } 1350 1351#ifdef ANDROID_ARM_LINKER 1352 (void) phdr_table_get_arm_exidx(phdr, phnum, base, 1353 &si->ARM_exidx, &si->ARM_exidx_count); 1354#endif 1355 1356 /* extract useful information from dynamic section */ 1357 uint32_t needed_count = 0; 1358 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1359 DEBUG("d = %p, d[0](tag) = 0x%08x d[1](val) = 0x%08x", d, d->d_tag, d->d_un.d_val); 1360 switch(d->d_tag){ 1361 case DT_HASH: 1362 si->nbucket = ((unsigned *) (base + d->d_un.d_ptr))[0]; 1363 si->nchain = ((unsigned *) (base + d->d_un.d_ptr))[1]; 1364 si->bucket = (unsigned *) (base + d->d_un.d_ptr + 8); 1365 si->chain = (unsigned *) (base + d->d_un.d_ptr + 8 + si->nbucket * 4); 1366 break; 1367 case DT_STRTAB: 1368 si->strtab = (const char *) (base + d->d_un.d_ptr); 1369 break; 1370 case DT_SYMTAB: 1371 si->symtab = (Elf32_Sym *) (base + d->d_un.d_ptr); 1372 break; 1373 case DT_PLTREL: 1374 if (d->d_un.d_val != DT_REL) { 1375 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1376 return false; 1377 } 1378 break; 1379 case DT_JMPREL: 1380 si->plt_rel = (Elf32_Rel*) (base + d->d_un.d_ptr); 1381 break; 1382 case DT_PLTRELSZ: 1383 si->plt_rel_count = d->d_un.d_val / sizeof(Elf32_Rel); 1384 break; 1385 case DT_REL: 1386 si->rel = (Elf32_Rel*) (base + d->d_un.d_ptr); 1387 break; 1388 case DT_RELSZ: 1389 si->rel_count = d->d_un.d_val / sizeof(Elf32_Rel); 1390 break; 1391 case DT_PLTGOT: 1392 /* Save this in case we decide to do lazy binding. We don't yet. */ 1393 si->plt_got = (unsigned *)(base + d->d_un.d_ptr); 1394 break; 1395 case DT_DEBUG: 1396 // Set the DT_DEBUG entry to the address of _r_debug for GDB 1397 // if the dynamic table is writable 1398 if ((dynamic_flags & PF_W) != 0) { 1399 d->d_un.d_val = (int) &_r_debug; 1400 } 1401 break; 1402 case DT_RELA: 1403 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1404 return false; 1405 case DT_INIT: 1406 si->init_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1407 DEBUG("%s constructors (init func) found at %p", si->name, si->init_func); 1408 break; 1409 case DT_FINI: 1410 si->fini_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1411 DEBUG("%s destructors (fini func) found at %p", si->name, si->fini_func); 1412 break; 1413 case DT_INIT_ARRAY: 1414 si->init_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1415 DEBUG("%s constructors (init_array) found at %p", si->name, si->init_array); 1416 break; 1417 case DT_INIT_ARRAYSZ: 1418 si->init_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1419 break; 1420 case DT_FINI_ARRAY: 1421 si->fini_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1422 DEBUG("%s destructors (fini_array) found at %p", si->name, si->fini_array); 1423 break; 1424 case DT_FINI_ARRAYSZ: 1425 si->fini_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1426 break; 1427 case DT_PREINIT_ARRAY: 1428 si->preinit_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1429 DEBUG("%s constructors (preinit_array) found at %p", si->name, si->preinit_array); 1430 break; 1431 case DT_PREINIT_ARRAYSZ: 1432 si->preinit_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1433 break; 1434 case DT_TEXTREL: 1435 si->has_text_relocations = true; 1436 break; 1437 case DT_SYMBOLIC: 1438 si->has_DT_SYMBOLIC = true; 1439 break; 1440 case DT_NEEDED: 1441 ++needed_count; 1442 break; 1443#if defined DT_FLAGS 1444 // TODO: why is DT_FLAGS not defined? 1445 case DT_FLAGS: 1446 if (d->d_un.d_val & DF_TEXTREL) { 1447 si->has_text_relocations = true; 1448 } 1449 if (d->d_un.d_val & DF_SYMBOLIC) { 1450 si->has_DT_SYMBOLIC = true; 1451 } 1452 break; 1453#endif 1454#if defined(ANDROID_MIPS_LINKER) 1455 case DT_STRSZ: 1456 case DT_SYMENT: 1457 case DT_RELENT: 1458 break; 1459 case DT_MIPS_RLD_MAP: 1460 // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. 1461 { 1462 r_debug** dp = (r_debug**) d->d_un.d_ptr; 1463 *dp = &_r_debug; 1464 } 1465 break; 1466 case DT_MIPS_RLD_VERSION: 1467 case DT_MIPS_FLAGS: 1468 case DT_MIPS_BASE_ADDRESS: 1469 case DT_MIPS_UNREFEXTNO: 1470 break; 1471 1472 case DT_MIPS_SYMTABNO: 1473 si->mips_symtabno = d->d_un.d_val; 1474 break; 1475 1476 case DT_MIPS_LOCAL_GOTNO: 1477 si->mips_local_gotno = d->d_un.d_val; 1478 break; 1479 1480 case DT_MIPS_GOTSYM: 1481 si->mips_gotsym = d->d_un.d_val; 1482 break; 1483 1484 default: 1485 DEBUG("Unused DT entry: type 0x%08x arg 0x%08x", d->d_tag, d->d_un.d_val); 1486 break; 1487#endif 1488 } 1489 } 1490 1491 DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p", 1492 si->base, si->strtab, si->symtab); 1493 1494 // Sanity checks. 1495 if (relocating_linker && needed_count != 0) { 1496 DL_ERR("linker cannot have DT_NEEDED dependencies on other libraries"); 1497 return false; 1498 } 1499 if (si->nbucket == 0) { 1500 DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name); 1501 return false; 1502 } 1503 if (si->strtab == 0) { 1504 DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name); 1505 return false; 1506 } 1507 if (si->symtab == 0) { 1508 DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name); 1509 return false; 1510 } 1511 1512 /* if this is the main executable, then load all of the preloads now */ 1513 if (si->flags & FLAG_EXE) { 1514 memset(gLdPreloads, 0, sizeof(gLdPreloads)); 1515 for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) { 1516 soinfo* lsi = find_library(gLdPreloadNames[i]); 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 gLdPreloadNames[i], si->name, tmp_err_buf); 1521 return false; 1522 } 1523 gLdPreloads[i] = lsi; 1524 } 1525 } 1526 1527 soinfo** needed = (soinfo**) alloca((1 + needed_count) * sizeof(soinfo*)); 1528 soinfo** pneeded = needed; 1529 1530 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1531 if (d->d_tag == DT_NEEDED) { 1532 const char* library_name = si->strtab + d->d_un.d_val; 1533 DEBUG("%s needs %s", si->name, library_name); 1534 soinfo* lsi = find_library(library_name); 1535 if (lsi == NULL) { 1536 strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf)); 1537 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1538 library_name, si->name, tmp_err_buf); 1539 return false; 1540 } 1541 *pneeded++ = lsi; 1542 } 1543 } 1544 *pneeded = NULL; 1545 1546 if (si->has_text_relocations) { 1547 /* Unprotect the segments, i.e. make them writable, to allow 1548 * text relocations to work properly. We will later call 1549 * phdr_table_protect_segments() after all of them are applied 1550 * and all constructors are run. 1551 */ 1552 if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1553 DL_ERR("can't unprotect loadable segments for \"%s\": %s", 1554 si->name, strerror(errno)); 1555 return false; 1556 } 1557 } 1558 1559 if (si->plt_rel != NULL) { 1560 DEBUG("[ relocating %s plt ]", si->name ); 1561 if (soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) { 1562 return false; 1563 } 1564 } 1565 if (si->rel != NULL) { 1566 DEBUG("[ relocating %s ]", si->name ); 1567 if (soinfo_relocate(si, si->rel, si->rel_count, needed)) { 1568 return false; 1569 } 1570 } 1571 1572#ifdef ANDROID_MIPS_LINKER 1573 if (mips_relocate_got(si, needed)) { 1574 return false; 1575 } 1576#endif 1577 1578 si->flags |= FLAG_LINKED; 1579 DEBUG("[ finished linking %s ]", si->name); 1580 1581 if (si->has_text_relocations) { 1582 /* All relocations are done, we can protect our segments back to 1583 * read-only. */ 1584 if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1585 DL_ERR("can't protect segments for \"%s\": %s", 1586 si->name, strerror(errno)); 1587 return false; 1588 } 1589 } 1590 1591 /* We can also turn on GNU RELRO protection */ 1592 if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { 1593 DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", 1594 si->name, strerror(errno)); 1595 return false; 1596 } 1597 1598 // If this is a setuid/setgid program, close the security hole described in 1599 // ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc 1600 if (get_AT_SECURE()) { 1601 nullify_closed_stdio(); 1602 } 1603 notify_gdb_of_load(si); 1604 return true; 1605} 1606 1607/* 1608 * This code is called after the linker has linked itself and 1609 * fixed it's own GOT. It is safe to make references to externs 1610 * and other non-local data at this point. 1611 */ 1612static Elf32_Addr __linker_init_post_relocation(KernelArgumentBlock& args, Elf32_Addr linker_base) { 1613 /* NOTE: we store the args pointer on a special location 1614 * of the temporary TLS area in order to pass it to 1615 * the C Library's runtime initializer. 1616 * 1617 * The initializer must clear the slot and reset the TLS 1618 * to point to a different location to ensure that no other 1619 * shared library constructor can access it. 1620 */ 1621 __libc_init_tls(args); 1622 1623#if TIMING 1624 struct timeval t0, t1; 1625 gettimeofday(&t0, 0); 1626#endif 1627 1628 // Initialize environment functions, and get to the ELF aux vectors table. 1629 linker_env_init(args); 1630 1631 debuggerd_init(); 1632 1633 // Get a few environment variables. 1634 const char* LD_DEBUG = linker_env_get("LD_DEBUG"); 1635 if (LD_DEBUG != NULL) { 1636 gLdDebugVerbosity = atoi(LD_DEBUG); 1637 } 1638 1639 // Normally, these are cleaned by linker_env_init, but the test 1640 // doesn't cost us anything. 1641 const char* ldpath_env = NULL; 1642 const char* ldpreload_env = NULL; 1643 if (!get_AT_SECURE()) { 1644 ldpath_env = linker_env_get("LD_LIBRARY_PATH"); 1645 ldpreload_env = linker_env_get("LD_PRELOAD"); 1646 } 1647 1648 INFO("[ android linker & debugger ]"); 1649 1650 soinfo* si = soinfo_alloc(args.argv[0]); 1651 if (si == NULL) { 1652 exit(EXIT_FAILURE); 1653 } 1654 1655 /* bootstrap the link map, the main exe always needs to be first */ 1656 si->flags |= FLAG_EXE; 1657 link_map_t* map = &(si->link_map); 1658 1659 map->l_addr = 0; 1660 map->l_name = args.argv[0]; 1661 map->l_prev = NULL; 1662 map->l_next = NULL; 1663 1664 _r_debug.r_map = map; 1665 r_debug_tail = map; 1666 1667 /* gdb expects the linker to be in the debug shared object list. 1668 * Without this, gdb has trouble locating the linker's ".text" 1669 * and ".plt" sections. Gdb could also potentially use this to 1670 * relocate the offset of our exported 'rtld_db_dlactivity' symbol. 1671 * Don't use soinfo_alloc(), because the linker shouldn't 1672 * be on the soinfo list. 1673 */ 1674 { 1675 static soinfo linker_soinfo; 1676 strlcpy(linker_soinfo.name, "/system/bin/linker", sizeof(linker_soinfo.name)); 1677 linker_soinfo.flags = 0; 1678 linker_soinfo.base = linker_base; 1679 1680 /* 1681 * Set the dynamic field in the link map otherwise gdb will complain with 1682 * the following: 1683 * warning: .dynamic section for "/system/bin/linker" is not at the 1684 * expected address (wrong library or version mismatch?) 1685 */ 1686 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base; 1687 Elf32_Phdr *phdr = (Elf32_Phdr*)((unsigned char*) linker_base + elf_hdr->e_phoff); 1688 phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, 1689 &linker_soinfo.dynamic, NULL, NULL); 1690 insert_soinfo_into_debug_map(&linker_soinfo); 1691 } 1692 1693 // Extract information passed from the kernel. 1694 si->phdr = reinterpret_cast<Elf32_Phdr*>(args.getauxval(AT_PHDR)); 1695 si->phnum = args.getauxval(AT_PHNUM); 1696 si->entry = args.getauxval(AT_ENTRY); 1697 1698 /* Compute the value of si->base. We can't rely on the fact that 1699 * the first entry is the PHDR because this will not be true 1700 * for certain executables (e.g. some in the NDK unit test suite) 1701 */ 1702 si->base = 0; 1703 si->size = phdr_table_get_load_size(si->phdr, si->phnum); 1704 si->load_bias = 0; 1705 for (size_t i = 0; i < si->phnum; ++i) { 1706 if (si->phdr[i].p_type == PT_PHDR) { 1707 si->load_bias = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_vaddr; 1708 si->base = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_offset; 1709 break; 1710 } 1711 } 1712 si->dynamic = NULL; 1713 si->ref_count = 1; 1714 1715 // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). 1716 parse_LD_LIBRARY_PATH(ldpath_env); 1717 parse_LD_PRELOAD(ldpreload_env); 1718 1719 somain = si; 1720 1721 if (!soinfo_link_image(si)) { 1722 __libc_format_fd(2, "CANNOT LINK EXECUTABLE: %s\n", linker_get_error_buffer()); 1723 exit(EXIT_FAILURE); 1724 } 1725 1726 si->CallPreInitConstructors(); 1727 1728 for (size_t i = 0; gLdPreloads[i] != NULL; ++i) { 1729 gLdPreloads[i]->CallConstructors(); 1730 } 1731 1732 /* After the link_image, the si->load_bias is initialized. 1733 * For so lib, the map->l_addr will be updated in notify_gdb_of_load. 1734 * We need to update this value for so exe here. So Unwind_Backtrace 1735 * for some arch like x86 could work correctly within so exe. 1736 */ 1737 map->l_addr = si->load_bias; 1738 si->CallConstructors(); 1739 1740#if TIMING 1741 gettimeofday(&t1,NULL); 1742 PRINT("LINKER TIME: %s: %d microseconds", args.argv[0], (int) ( 1743 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - 1744 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) 1745 )); 1746#endif 1747#if STATS 1748 PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", args.argv[0], 1749 linker_stats.count[kRelocAbsolute], 1750 linker_stats.count[kRelocRelative], 1751 linker_stats.count[kRelocCopy], 1752 linker_stats.count[kRelocSymbol]); 1753#endif 1754#if COUNT_PAGES 1755 { 1756 unsigned n; 1757 unsigned i; 1758 unsigned count = 0; 1759 for (n = 0; n < 4096; n++) { 1760 if (bitmask[n]) { 1761 unsigned x = bitmask[n]; 1762 for (i = 0; i < 8; i++) { 1763 if (x & 1) { 1764 count++; 1765 } 1766 x >>= 1; 1767 } 1768 } 1769 } 1770 PRINT("PAGES MODIFIED: %s: %d (%dKB)", args.argv[0], count, count * 4); 1771 } 1772#endif 1773 1774#if TIMING || STATS || COUNT_PAGES 1775 fflush(stdout); 1776#endif 1777 1778 TRACE("[ Ready to execute '%s' @ 0x%08x ]", si->name, si->entry); 1779 return si->entry; 1780} 1781 1782/* Compute the load-bias of an existing executable. This shall only 1783 * be used to compute the load bias of an executable or shared library 1784 * that was loaded by the kernel itself. 1785 * 1786 * Input: 1787 * elf -> address of ELF header, assumed to be at the start of the file. 1788 * Return: 1789 * load bias, i.e. add the value of any p_vaddr in the file to get 1790 * the corresponding address in memory. 1791 */ 1792static Elf32_Addr get_elf_exec_load_bias(const Elf32_Ehdr* elf) { 1793 Elf32_Addr offset = elf->e_phoff; 1794 const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset); 1795 const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum; 1796 1797 for (const Elf32_Phdr* phdr = phdr_table; phdr < phdr_end; phdr++) { 1798 if (phdr->p_type == PT_LOAD) { 1799 return reinterpret_cast<Elf32_Addr>(elf) + phdr->p_offset - phdr->p_vaddr; 1800 } 1801 } 1802 return 0; 1803} 1804 1805/* 1806 * This is the entry point for the linker, called from begin.S. This 1807 * method is responsible for fixing the linker's own relocations, and 1808 * then calling __linker_init_post_relocation(). 1809 * 1810 * Because this method is called before the linker has fixed it's own 1811 * relocations, any attempt to reference an extern variable, extern 1812 * function, or other GOT reference will generate a segfault. 1813 */ 1814extern "C" Elf32_Addr __linker_init(void* raw_args) { 1815 KernelArgumentBlock args(raw_args); 1816 1817 Elf32_Addr linker_addr = args.getauxval(AT_BASE); 1818 1819 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr*) linker_addr; 1820 Elf32_Phdr *phdr = (Elf32_Phdr*)((unsigned char*) linker_addr + elf_hdr->e_phoff); 1821 1822 soinfo linker_so; 1823 memset(&linker_so, 0, sizeof(soinfo)); 1824 1825 linker_so.base = linker_addr; 1826 linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); 1827 linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); 1828 linker_so.dynamic = NULL; 1829 linker_so.phdr = phdr; 1830 linker_so.phnum = elf_hdr->e_phnum; 1831 linker_so.flags |= FLAG_LINKER; 1832 1833 if (!soinfo_link_image(&linker_so)) { 1834 // It would be nice to print an error message, but if the linker 1835 // can't link itself, there's no guarantee that we'll be able to 1836 // call write() (because it involves a GOT reference). 1837 // 1838 // This situation should never occur unless the linker itself 1839 // is corrupt. 1840 exit(EXIT_FAILURE); 1841 } 1842 1843 // We have successfully fixed our own relocations. It's safe to run 1844 // the main part of the linker now. 1845 Elf32_Addr start_address = __linker_init_post_relocation(args, linker_addr); 1846 1847 set_soinfo_pool_protection(PROT_READ); 1848 1849 // Return the address that the calling assembly stub should jump to. 1850 return start_address; 1851} 1852