linker.cpp revision c620059479c47a78d57086d73726c9adc2f337ad
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 75static 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)) 81struct soinfo_pool_t { 82 soinfo_pool_t* next; 83 soinfo info[SOINFO_PER_POOL]; 84}; 85static struct soinfo_pool_t* gSoInfoPools = NULL; 86static soinfo* gSoInfoFreeList = NULL; 87 88static soinfo* solist = &libdl_info; 89static soinfo* sonext = &libdl_info; 90static soinfo* somain; /* main process, always the one after libdl_info */ 91 92static const char* const gSoPaths[] = { 93 "/vendor/lib", 94 "/system/lib", 95 NULL 96}; 97 98static char gLdPathsBuffer[LDPATH_BUFSIZE]; 99static const char* gLdPaths[LDPATH_MAX + 1]; 100 101static char gLdPreloadsBuffer[LDPRELOAD_BUFSIZE]; 102static const char* gLdPreloadNames[LDPRELOAD_MAX + 1]; 103 104static soinfo* gLdPreloads[LDPRELOAD_MAX + 1]; 105 106__LIBC_HIDDEN__ int gLdDebugVerbosity; 107 108__LIBC_HIDDEN__ abort_msg_t* gAbortMessage = NULL; // For debuggerd. 109 110enum RelocationKind { 111 kRelocAbsolute = 0, 112 kRelocRelative, 113 kRelocCopy, 114 kRelocSymbol, 115 kRelocMax 116}; 117 118#if STATS 119struct linker_stats_t { 120 int count[kRelocMax]; 121}; 122 123static linker_stats_t linker_stats; 124 125static void count_relocation(RelocationKind kind) { 126 ++linker_stats.count[kind]; 127} 128#else 129static void count_relocation(RelocationKind) { 130} 131#endif 132 133#if COUNT_PAGES 134static 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)) 154DISALLOW_ALLOCATION(void*, malloc, (size_t u UNUSED)); 155DISALLOW_ALLOCATION(void, free, (void* u UNUSED)); 156DISALLOW_ALLOCATION(void*, realloc, (void* u1 UNUSED, size_t u2 UNUSED)); 157DISALLOW_ALLOCATION(void*, calloc, (size_t u1 UNUSED, size_t u2 UNUSED)); 158 159static char tmp_err_buf[768]; 160static char __linker_dl_err_buf[768]; 161 162char* linker_get_error_buffer() { 163 return &__linker_dl_err_buf[0]; 164} 165 166size_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 */ 174extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(); 175 176static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, 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#endif 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 440static Elf_Sym* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name) { 441 Elf_Sym* symtab = si->symtab; 442 const char* strtab = si->strtab; 443 444 TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %zd", 445 name, si->name, si->base, hash, hash % si->nbucket); 446 447 for (unsigned n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]) { 448 Elf_Sym* s = symtab + n; 449 if (strcmp(strtab + s->st_name, name)) continue; 450 451 /* only concern ourselves with global and weak symbol definitions */ 452 switch(ELF32_ST_BIND(s->st_info)){ 453 case STB_GLOBAL: 454 case STB_WEAK: 455 if (s->st_shndx == SHN_UNDEF) { 456 continue; 457 } 458 459 TRACE_TYPE(LOOKUP, "FOUND %s in %s (%08x) %d", 460 name, si->name, s->st_value, s->st_size); 461 return s; 462 } 463 } 464 465 return NULL; 466} 467 468static unsigned elfhash(const char* _name) { 469 const unsigned char* name = (const unsigned char*) _name; 470 unsigned h = 0, g; 471 472 while(*name) { 473 h = (h << 4) + *name++; 474 g = h & 0xf0000000; 475 h ^= g; 476 h ^= g >> 24; 477 } 478 return h; 479} 480 481static Elf_Sym* soinfo_do_lookup(soinfo* si, const char* name, soinfo** lsi, soinfo* needed[]) { 482 unsigned elf_hash = elfhash(name); 483 Elf_Sym* s = NULL; 484 485 if (si != NULL && somain != NULL) { 486 487 /* 488 * Local scope is executable scope. Just start looking into it right away 489 * for the shortcut. 490 */ 491 492 if (si == somain) { 493 s = soinfo_elf_lookup(si, elf_hash, name); 494 if (s != NULL) { 495 *lsi = si; 496 goto done; 497 } 498 } else { 499 /* Order of symbol lookup is controlled by DT_SYMBOLIC flag */ 500 501 /* 502 * If this object was built with symbolic relocations disabled, the 503 * first place to look to resolve external references is the main 504 * executable. 505 */ 506 507 if (!si->has_DT_SYMBOLIC) { 508 DEBUG("%s: looking up %s in executable %s", 509 si->name, name, somain->name); 510 s = soinfo_elf_lookup(somain, elf_hash, name); 511 if (s != NULL) { 512 *lsi = somain; 513 goto done; 514 } 515 } 516 517 /* Look for symbols in the local scope (the object who is 518 * searching). This happens with C++ templates on i386 for some 519 * reason. 520 * 521 * Notes on weak symbols: 522 * The ELF specs are ambiguous about treatment of weak definitions in 523 * dynamic linking. Some systems return the first definition found 524 * and some the first non-weak definition. This is system dependent. 525 * Here we return the first definition found for simplicity. */ 526 527 s = soinfo_elf_lookup(si, elf_hash, name); 528 if (s != NULL) { 529 *lsi = si; 530 goto done; 531 } 532 533 /* 534 * If this object was built with -Bsymbolic and symbol is not found 535 * in the local scope, try to find the symbol in the main executable. 536 */ 537 538 if (si->has_DT_SYMBOLIC) { 539 DEBUG("%s: looking up %s in executable %s after local scope", 540 si->name, name, somain->name); 541 s = soinfo_elf_lookup(somain, elf_hash, name); 542 if (s != NULL) { 543 *lsi = somain; 544 goto done; 545 } 546 } 547 } 548 } 549 550 /* Next, look for it in the preloads list */ 551 for (int i = 0; gLdPreloads[i] != NULL; i++) { 552 s = soinfo_elf_lookup(gLdPreloads[i], elf_hash, name); 553 if (s != NULL) { 554 *lsi = gLdPreloads[i]; 555 goto done; 556 } 557 } 558 559 for (int i = 0; needed[i] != NULL; i++) { 560 DEBUG("%s: looking up %s in %s", 561 si->name, name, needed[i]->name); 562 s = soinfo_elf_lookup(needed[i], elf_hash, name); 563 if (s != NULL) { 564 *lsi = needed[i]; 565 goto done; 566 } 567 } 568 569done: 570 if (s != NULL) { 571 TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = 0x%08x, " 572 "found in %s, base = 0x%08x, load bias = 0x%08x", 573 si->name, name, s->st_value, 574 (*lsi)->name, (*lsi)->base, (*lsi)->load_bias); 575 return s; 576 } 577 578 return NULL; 579} 580 581/* This is used by dlsym(3). It performs symbol lookup only within the 582 specified soinfo object and not in any of its dependencies. 583 584 TODO: Only looking in the specified soinfo seems wrong. dlsym(3) says 585 that it should do a breadth first search through the dependency 586 tree. This agrees with the ELF spec (aka System V Application 587 Binary Interface) where in Chapter 5 it discuss resolving "Shared 588 Object Dependencies" in breadth first search order. 589 */ 590Elf_Sym* dlsym_handle_lookup(soinfo* si, const char* name) { 591 return soinfo_elf_lookup(si, elfhash(name), name); 592} 593 594/* This is used by dlsym(3) to performs a global symbol lookup. If the 595 start value is null (for RTLD_DEFAULT), the search starts at the 596 beginning of the global solist. Otherwise the search starts at the 597 specified soinfo (for RTLD_NEXT). 598 */ 599Elf_Sym* dlsym_linear_lookup(const char* name, soinfo** found, soinfo* start) { 600 unsigned elf_hash = elfhash(name); 601 602 if (start == NULL) { 603 start = solist; 604 } 605 606 Elf_Sym* s = NULL; 607 for (soinfo* si = start; (s == NULL) && (si != NULL); si = si->next) { 608 s = soinfo_elf_lookup(si, elf_hash, name); 609 if (s != NULL) { 610 *found = si; 611 break; 612 } 613 } 614 615 if (s != NULL) { 616 TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, found->base = 0x%08x", 617 name, s->st_value, (*found)->base); 618 } 619 620 return s; 621} 622 623soinfo* find_containing_library(const void* p) { 624 Elf_Addr address = reinterpret_cast<Elf_Addr>(p); 625 for (soinfo* si = solist; si != NULL; si = si->next) { 626 if (address >= si->base && address - si->base < si->size) { 627 return si; 628 } 629 } 630 return NULL; 631} 632 633Elf_Sym* dladdr_find_symbol(soinfo* si, const void* addr) { 634 Elf_Addr soaddr = reinterpret_cast<Elf_Addr>(addr) - si->base; 635 636 // Search the library's symbol table for any defined symbol which 637 // contains this address. 638 for (size_t i = 0; i < si->nchain; ++i) { 639 Elf_Sym* sym = &si->symtab[i]; 640 if (sym->st_shndx != SHN_UNDEF && 641 soaddr >= sym->st_value && 642 soaddr < sym->st_value + sym->st_size) { 643 return sym; 644 } 645 } 646 647 return NULL; 648} 649 650#if 0 651static void dump(soinfo* si) 652{ 653 Elf_Sym* s = si->symtab; 654 for (unsigned n = 0; n < si->nchain; n++) { 655 TRACE("%04d> %08x: %02x %04x %08x %08x %s", n, s, 656 s->st_info, s->st_shndx, s->st_value, s->st_size, 657 si->strtab + s->st_name); 658 s++; 659 } 660} 661#endif 662 663static int open_library_on_path(const char* name, const char* const paths[]) { 664 char buf[512]; 665 for (size_t i = 0; paths[i] != NULL; ++i) { 666 int n = __libc_format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name); 667 if (n < 0 || n >= static_cast<int>(sizeof(buf))) { 668 PRINT("Warning: ignoring very long library path: %s/%s", paths[i], name); 669 continue; 670 } 671 int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC)); 672 if (fd != -1) { 673 return fd; 674 } 675 } 676 return -1; 677} 678 679static int open_library(const char* name) { 680 TRACE("[ opening %s ]", name); 681 682 // If the name contains a slash, we should attempt to open it directly and not search the paths. 683 if (strchr(name, '/') != NULL) { 684 int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC)); 685 if (fd != -1) { 686 return fd; 687 } 688 // ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now. 689 } 690 691 // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths. 692 int fd = open_library_on_path(name, gLdPaths); 693 if (fd == -1) { 694 fd = open_library_on_path(name, gSoPaths); 695 } 696 return fd; 697} 698 699static soinfo* load_library(const char* name) { 700 // Open the file. 701 int fd = open_library(name); 702 if (fd == -1) { 703 DL_ERR("library \"%s\" not found", name); 704 return NULL; 705 } 706 707 // Read the ELF header and load the segments. 708 ElfReader elf_reader(name, fd); 709 if (!elf_reader.Load()) { 710 return NULL; 711 } 712 713 const char* bname = strrchr(name, '/'); 714 soinfo* si = soinfo_alloc(bname ? bname + 1 : name); 715 if (si == NULL) { 716 return NULL; 717 } 718 si->base = elf_reader.load_start(); 719 si->size = elf_reader.load_size(); 720 si->load_bias = elf_reader.load_bias(); 721 si->flags = 0; 722 si->entry = 0; 723 si->dynamic = NULL; 724 si->phnum = elf_reader.phdr_count(); 725 si->phdr = elf_reader.loaded_phdr(); 726 return si; 727} 728 729static soinfo *find_loaded_library(const char *name) 730{ 731 soinfo *si; 732 const char *bname; 733 734 // TODO: don't use basename only for determining libraries 735 // http://code.google.com/p/android/issues/detail?id=6670 736 737 bname = strrchr(name, '/'); 738 bname = bname ? bname + 1 : name; 739 740 for (si = solist; si != NULL; si = si->next) { 741 if (!strcmp(bname, si->name)) { 742 return si; 743 } 744 } 745 return NULL; 746} 747 748static soinfo* find_library_internal(const char* name) { 749 if (name == NULL) { 750 return somain; 751 } 752 753 soinfo* si = find_loaded_library(name); 754 if (si != NULL) { 755 if (si->flags & FLAG_LINKED) { 756 return si; 757 } 758 DL_ERR("OOPS: recursive link to \"%s\"", si->name); 759 return NULL; 760 } 761 762 TRACE("[ '%s' has not been loaded yet. Locating...]", name); 763 si = load_library(name); 764 if (si == NULL) { 765 return NULL; 766 } 767 768 // At this point we know that whatever is loaded @ base is a valid ELF 769 // shared library whose segments are properly mapped in. 770 TRACE("[ init_library base=0x%08x sz=0x%08x name='%s' ]", 771 si->base, si->size, si->name); 772 773 if (!soinfo_link_image(si)) { 774 munmap(reinterpret_cast<void*>(si->base), si->size); 775 soinfo_free(si); 776 return NULL; 777 } 778 779 return si; 780} 781 782static soinfo* find_library(const char* name) { 783 soinfo* si = find_library_internal(name); 784 if (si != NULL) { 785 si->ref_count++; 786 } 787 return si; 788} 789 790static int soinfo_unload(soinfo* si) { 791 if (si->ref_count == 1) { 792 TRACE("unloading '%s'", si->name); 793 si->CallDestructors(); 794 795 for (Elf_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 796 if (d->d_tag == DT_NEEDED) { 797 const char* library_name = si->strtab + d->d_un.d_val; 798 TRACE("%s needs to unload %s", si->name, library_name); 799 soinfo_unload(find_loaded_library(library_name)); 800 } 801 } 802 803 munmap(reinterpret_cast<void*>(si->base), si->size); 804 notify_gdb_of_unload(si); 805 soinfo_free(si); 806 si->ref_count = 0; 807 } else { 808 si->ref_count--; 809 TRACE("not unloading '%s', decrementing ref_count to %zd", si->name, si->ref_count); 810 } 811 return 0; 812} 813 814void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) { 815 if (!get_AT_SECURE()) { 816 parse_LD_LIBRARY_PATH(ld_library_path); 817 } 818} 819 820soinfo* do_dlopen(const char* name, int flags) { 821 if ((flags & ~(RTLD_NOW|RTLD_LAZY|RTLD_LOCAL|RTLD_GLOBAL)) != 0) { 822 DL_ERR("invalid flags to dlopen: %x", flags); 823 return NULL; 824 } 825 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 826 soinfo* si = find_library(name); 827 if (si != NULL) { 828 si->CallConstructors(); 829 } 830 set_soinfo_pool_protection(PROT_READ); 831 return si; 832} 833 834int do_dlclose(soinfo* si) { 835 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 836 int result = soinfo_unload(si); 837 set_soinfo_pool_protection(PROT_READ); 838 return result; 839} 840 841/* TODO: don't use unsigned for addrs below. It works, but is not 842 * ideal. They should probably be either uint32_t, Elf_Addr, or unsigned 843 * long. 844 */ 845static int soinfo_relocate(soinfo* si, Elf_Rel* rel, unsigned count, 846 soinfo* needed[]) 847{ 848 Elf_Sym* symtab = si->symtab; 849 const char* strtab = si->strtab; 850 Elf_Sym* s; 851 Elf_Rel* start = rel; 852 soinfo* lsi; 853 854 for (size_t idx = 0; idx < count; ++idx, ++rel) { 855 unsigned type = ELF32_R_TYPE(rel->r_info); 856 unsigned sym = ELF32_R_SYM(rel->r_info); 857 Elf_Addr reloc = static_cast<Elf_Addr>(rel->r_offset + si->load_bias); 858 Elf_Addr sym_addr = 0; 859 char* sym_name = NULL; 860 861 DEBUG("Processing '%s' relocation at index %zd", si->name, idx); 862 if (type == 0) { // R_*_NONE 863 continue; 864 } 865 if (sym != 0) { 866 sym_name = (char *)(strtab + symtab[sym].st_name); 867 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 868 if (s == NULL) { 869 /* We only allow an undefined symbol if this is a weak 870 reference.. */ 871 s = &symtab[sym]; 872 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 873 DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); 874 return -1; 875 } 876 877 /* IHI0044C AAELF 4.5.1.1: 878 879 Libraries are not searched to resolve weak references. 880 It is not an error for a weak reference to remain 881 unsatisfied. 882 883 During linking, the value of an undefined weak reference is: 884 - Zero if the relocation type is absolute 885 - The address of the place if the relocation is pc-relative 886 - The address of nominal base address if the relocation 887 type is base-relative. 888 */ 889 890 switch (type) { 891#if defined(ANDROID_ARM_LINKER) 892 case R_ARM_JUMP_SLOT: 893 case R_ARM_GLOB_DAT: 894 case R_ARM_ABS32: 895 case R_ARM_RELATIVE: /* Don't care. */ 896#elif defined(ANDROID_X86_LINKER) 897 case R_386_JMP_SLOT: 898 case R_386_GLOB_DAT: 899 case R_386_32: 900 case R_386_RELATIVE: /* Dont' care. */ 901#endif /* ANDROID_*_LINKER */ 902 /* sym_addr was initialized to be zero above or relocation 903 code below does not care about value of sym_addr. 904 No need to do anything. */ 905 break; 906 907#if defined(ANDROID_X86_LINKER) 908 case R_386_PC32: 909 sym_addr = reloc; 910 break; 911#endif /* ANDROID_X86_LINKER */ 912 913#if defined(ANDROID_ARM_LINKER) 914 case R_ARM_COPY: 915 /* Fall through. Can't really copy if weak symbol is 916 not found in run-time. */ 917#endif /* ANDROID_ARM_LINKER */ 918 default: 919 DL_ERR("unknown weak reloc type %d @ %p (%d)", 920 type, rel, (int) (rel - start)); 921 return -1; 922 } 923 } else { 924 /* We got a definition. */ 925#if 0 926 if ((base == 0) && (si->base != 0)) { 927 /* linking from libraries to main image is bad */ 928 DL_ERR("cannot locate \"%s\"...", 929 strtab + symtab[sym].st_name); 930 return -1; 931 } 932#endif 933 sym_addr = static_cast<Elf_Addr>(s->st_value + lsi->load_bias); 934 } 935 count_relocation(kRelocSymbol); 936 } else { 937 s = NULL; 938 } 939 940/* TODO: This is ugly. Split up the relocations by arch into 941 * different files. 942 */ 943 switch(type){ 944#if defined(ANDROID_ARM_LINKER) 945 case R_ARM_JUMP_SLOT: 946 count_relocation(kRelocAbsolute); 947 MARK(rel->r_offset); 948 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 949 *reinterpret_cast<Elf_Addr*>(reloc) = sym_addr; 950 break; 951 case R_ARM_GLOB_DAT: 952 count_relocation(kRelocAbsolute); 953 MARK(rel->r_offset); 954 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 955 *reinterpret_cast<Elf_Addr*>(reloc) = sym_addr; 956 break; 957 case R_ARM_ABS32: 958 count_relocation(kRelocAbsolute); 959 MARK(rel->r_offset); 960 TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s", reloc, sym_addr, sym_name); 961 *reinterpret_cast<Elf_Addr*>(reloc) += sym_addr; 962 break; 963 case R_ARM_REL32: 964 count_relocation(kRelocRelative); 965 MARK(rel->r_offset); 966 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s", 967 reloc, sym_addr, rel->r_offset, sym_name); 968 *reinterpret_cast<Elf_Addr*>(reloc) += sym_addr - rel->r_offset; 969 break; 970#elif defined(ANDROID_X86_LINKER) 971 case R_386_JMP_SLOT: 972 count_relocation(kRelocAbsolute); 973 MARK(rel->r_offset); 974 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 975 *reinterpret_cast<Elf_Addr*>(reloc) = sym_addr; 976 break; 977 case R_386_GLOB_DAT: 978 count_relocation(kRelocAbsolute); 979 MARK(rel->r_offset); 980 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 981 *reinterpret_cast<Elf_Addr*>(reloc) = sym_addr; 982 break; 983#elif defined(ANDROID_MIPS_LINKER) 984 case R_MIPS_REL32: 985 count_relocation(kRelocAbsolute); 986 MARK(rel->r_offset); 987 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s", 988 reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); 989 if (s) { 990 *reinterpret_cast<Elf_Addr*>(reloc) += sym_addr; 991 } else { 992 *reinterpret_cast<Elf_Addr*>(reloc) += si->base; 993 } 994 break; 995#endif /* ANDROID_*_LINKER */ 996 997#if defined(ANDROID_ARM_LINKER) 998 case R_ARM_RELATIVE: 999#elif defined(ANDROID_X86_LINKER) 1000 case R_386_RELATIVE: 1001#endif /* ANDROID_*_LINKER */ 1002 count_relocation(kRelocRelative); 1003 MARK(rel->r_offset); 1004 if (sym) { 1005 DL_ERR("odd RELATIVE form..."); 1006 return -1; 1007 } 1008 TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x", reloc, si->base); 1009 *reinterpret_cast<Elf_Addr*>(reloc) += si->base; 1010 break; 1011 1012#if defined(ANDROID_X86_LINKER) 1013 case R_386_32: 1014 count_relocation(kRelocRelative); 1015 MARK(rel->r_offset); 1016 1017 TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s", reloc, sym_addr, sym_name); 1018 *reinterpret_cast<Elf_Addr*>(reloc) += sym_addr; 1019 break; 1020 1021 case R_386_PC32: 1022 count_relocation(kRelocRelative); 1023 MARK(rel->r_offset); 1024 TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s", 1025 reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); 1026 *reinterpret_cast<Elf_Addr*>(reloc) += (sym_addr - reloc); 1027 break; 1028#endif /* ANDROID_X86_LINKER */ 1029 1030#ifdef ANDROID_ARM_LINKER 1031 case R_ARM_COPY: 1032 if ((si->flags & FLAG_EXE) == 0) { 1033 /* 1034 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf 1035 * 1036 * Section 4.7.1.10 "Dynamic relocations" 1037 * R_ARM_COPY may only appear in executable objects where e_type is 1038 * set to ET_EXEC. 1039 * 1040 * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. 1041 * We should explicitly disallow ET_DYN executables from having 1042 * R_ARM_COPY relocations. 1043 */ 1044 DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); 1045 return -1; 1046 } 1047 count_relocation(kRelocCopy); 1048 MARK(rel->r_offset); 1049 TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s", reloc, s->st_size, sym_addr, sym_name); 1050 if (reloc == sym_addr) { 1051 Elf_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed); 1052 1053 if (src == NULL) { 1054 DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name); 1055 return -1; 1056 } 1057 if (lsi->has_DT_SYMBOLIC) { 1058 DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared " 1059 "library %s (built with -Bsymbolic?)", si->name, lsi->name); 1060 return -1; 1061 } 1062 if (s->st_size < src->st_size) { 1063 DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)", 1064 si->name, s->st_size, src->st_size); 1065 return -1; 1066 } 1067 memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size); 1068 } else { 1069 DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name); 1070 return -1; 1071 } 1072 break; 1073#endif /* ANDROID_ARM_LINKER */ 1074 1075 default: 1076 DL_ERR("unknown reloc type %d @ %p (%d)", 1077 type, rel, (int) (rel - start)); 1078 return -1; 1079 } 1080 } 1081 return 0; 1082} 1083 1084#ifdef ANDROID_MIPS_LINKER 1085static bool mips_relocate_got(soinfo* si, soinfo* needed[]) { 1086 unsigned* got = si->plt_got; 1087 if (got == NULL) { 1088 return true; 1089 } 1090 unsigned local_gotno = si->mips_local_gotno; 1091 unsigned gotsym = si->mips_gotsym; 1092 unsigned symtabno = si->mips_symtabno; 1093 Elf_Sym* symtab = si->symtab; 1094 1095 /* 1096 * got[0] is address of lazy resolver function 1097 * got[1] may be used for a GNU extension 1098 * set it to a recognizable address in case someone calls it 1099 * (should be _rtld_bind_start) 1100 * FIXME: maybe this should be in a separate routine 1101 */ 1102 1103 if ((si->flags & FLAG_LINKER) == 0) { 1104 size_t g = 0; 1105 got[g++] = 0xdeadbeef; 1106 if (got[g] & 0x80000000) { 1107 got[g++] = 0xdeadfeed; 1108 } 1109 /* 1110 * Relocate the local GOT entries need to be relocated 1111 */ 1112 for (; g < local_gotno; g++) { 1113 got[g] += si->load_bias; 1114 } 1115 } 1116 1117 /* Now for the global GOT entries */ 1118 Elf_Sym* sym = symtab + gotsym; 1119 got = si->plt_got + local_gotno; 1120 for (size_t g = gotsym; g < symtabno; g++, sym++, got++) { 1121 const char* sym_name; 1122 Elf_Sym* s; 1123 soinfo* lsi; 1124 1125 /* This is an undefined reference... try to locate it */ 1126 sym_name = si->strtab + sym->st_name; 1127 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1128 if (s == NULL) { 1129 /* We only allow an undefined symbol if this is a weak 1130 reference.. */ 1131 s = &symtab[g]; 1132 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1133 DL_ERR("cannot locate \"%s\"...", sym_name); 1134 return false; 1135 } 1136 *got = 0; 1137 } 1138 else { 1139 /* FIXME: is this sufficient? 1140 * For reference see NetBSD link loader 1141 * 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 1142 */ 1143 *got = lsi->load_bias + s->st_value; 1144 } 1145 } 1146 return true; 1147} 1148#endif 1149 1150void soinfo::CallArray(const char* array_name UNUSED, linker_function_t* functions, size_t count, bool reverse) { 1151 if (functions == NULL) { 1152 return; 1153 } 1154 1155 TRACE("[ Calling %s (size %zd) @ %p for '%s' ]", array_name, count, functions, name); 1156 1157 int begin = reverse ? (count - 1) : 0; 1158 int end = reverse ? -1 : count; 1159 int step = reverse ? -1 : 1; 1160 1161 for (int i = begin; i != end; i += step) { 1162 TRACE("[ %s[%d] == %p ]", array_name, i, functions[i]); 1163 CallFunction("function", functions[i]); 1164 } 1165 1166 TRACE("[ Done calling %s for '%s' ]", array_name, name); 1167} 1168 1169void soinfo::CallFunction(const char* function_name UNUSED, linker_function_t function) { 1170 if (function == NULL || reinterpret_cast<uintptr_t>(function) == static_cast<uintptr_t>(-1)) { 1171 return; 1172 } 1173 1174 TRACE("[ Calling %s @ %p for '%s' ]", function_name, function, name); 1175 function(); 1176 TRACE("[ Done calling %s @ %p for '%s' ]", function_name, function, name); 1177 1178 // The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures 1179 // are still writable. This happens with our debug malloc (see http://b/7941716). 1180 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 1181} 1182 1183void soinfo::CallPreInitConstructors() { 1184 // DT_PREINIT_ARRAY functions are called before any other constructors for executables, 1185 // but ignored in a shared library. 1186 CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false); 1187} 1188 1189void soinfo::CallConstructors() { 1190 if (constructors_called) { 1191 return; 1192 } 1193 1194 // We set constructors_called before actually calling the constructors, otherwise it doesn't 1195 // protect against recursive constructor calls. One simple example of constructor recursion 1196 // is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so: 1197 // 1. The program depends on libc, so libc's constructor is called here. 1198 // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. 1199 // 3. dlopen() calls the constructors on the newly created 1200 // soinfo for libc_malloc_debug_leak.so. 1201 // 4. The debug .so depends on libc, so CallConstructors is 1202 // called again with the libc soinfo. If it doesn't trigger the early- 1203 // out above, the libc constructor will be called again (recursively!). 1204 constructors_called = true; 1205 1206 if ((flags & FLAG_EXE) == 0 && preinit_array != NULL) { 1207 // The GNU dynamic linker silently ignores these, but we warn the developer. 1208 PRINT("\"%s\": ignoring %zd-entry DT_PREINIT_ARRAY in shared library!", 1209 name, preinit_array_count); 1210 } 1211 1212 if (dynamic != NULL) { 1213 for (Elf_Dyn* d = dynamic; d->d_tag != DT_NULL; ++d) { 1214 if (d->d_tag == DT_NEEDED) { 1215 const char* library_name = strtab + d->d_un.d_val; 1216 TRACE("\"%s\": calling constructors in DT_NEEDED \"%s\"", name, library_name); 1217 find_loaded_library(library_name)->CallConstructors(); 1218 } 1219 } 1220 } 1221 1222 TRACE("\"%s\": calling constructors", name); 1223 1224 // DT_INIT should be called before DT_INIT_ARRAY if both are present. 1225 CallFunction("DT_INIT", init_func); 1226 CallArray("DT_INIT_ARRAY", init_array, init_array_count, false); 1227} 1228 1229void soinfo::CallDestructors() { 1230 TRACE("\"%s\": calling destructors", name); 1231 1232 // DT_FINI_ARRAY must be parsed in reverse order. 1233 CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true); 1234 1235 // DT_FINI should be called after DT_FINI_ARRAY if both are present. 1236 CallFunction("DT_FINI", fini_func); 1237} 1238 1239/* Force any of the closed stdin, stdout and stderr to be associated with 1240 /dev/null. */ 1241static int nullify_closed_stdio() { 1242 int dev_null, i, status; 1243 int return_value = 0; 1244 1245 dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 1246 if (dev_null < 0) { 1247 DL_ERR("cannot open /dev/null: %s", strerror(errno)); 1248 return -1; 1249 } 1250 TRACE("[ Opened /dev/null file-descriptor=%d]", dev_null); 1251 1252 /* If any of the stdio file descriptors is valid and not associated 1253 with /dev/null, dup /dev/null to it. */ 1254 for (i = 0; i < 3; i++) { 1255 /* If it is /dev/null already, we are done. */ 1256 if (i == dev_null) { 1257 continue; 1258 } 1259 1260 TRACE("[ Nullifying stdio file descriptor %d]", i); 1261 status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 1262 1263 /* If file is opened, we are good. */ 1264 if (status != -1) { 1265 continue; 1266 } 1267 1268 /* The only error we allow is that the file descriptor does not 1269 exist, in which case we dup /dev/null to it. */ 1270 if (errno != EBADF) { 1271 DL_ERR("fcntl failed: %s", strerror(errno)); 1272 return_value = -1; 1273 continue; 1274 } 1275 1276 /* Try dupping /dev/null to this stdio file descriptor and 1277 repeat if there is a signal. Note that any errors in closing 1278 the stdio descriptor are lost. */ 1279 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 1280 if (status < 0) { 1281 DL_ERR("dup2 failed: %s", strerror(errno)); 1282 return_value = -1; 1283 continue; 1284 } 1285 } 1286 1287 /* If /dev/null is not one of the stdio file descriptors, close it. */ 1288 if (dev_null > 2) { 1289 TRACE("[ Closing /dev/null file-descriptor=%d]", dev_null); 1290 status = TEMP_FAILURE_RETRY(close(dev_null)); 1291 if (status == -1) { 1292 DL_ERR("close failed: %s", strerror(errno)); 1293 return_value = -1; 1294 } 1295 } 1296 1297 return return_value; 1298} 1299 1300static bool soinfo_link_image(soinfo* si) { 1301 /* "base" might wrap around UINT32_MAX. */ 1302 Elf_Addr base = si->load_bias; 1303 const Elf_Phdr *phdr = si->phdr; 1304 int phnum = si->phnum; 1305 bool relocating_linker = (si->flags & FLAG_LINKER) != 0; 1306 1307 /* We can't debug anything until the linker is relocated */ 1308 if (!relocating_linker) { 1309 INFO("[ linking %s ]", si->name); 1310 DEBUG("si->base = 0x%08x si->flags = 0x%08x", si->base, si->flags); 1311 } 1312 1313 /* Extract dynamic section */ 1314 size_t dynamic_count; 1315 Elf_Word dynamic_flags; 1316 phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, 1317 &dynamic_count, &dynamic_flags); 1318 if (si->dynamic == NULL) { 1319 if (!relocating_linker) { 1320 DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name); 1321 } 1322 return false; 1323 } else { 1324 if (!relocating_linker) { 1325 DEBUG("dynamic = %p", si->dynamic); 1326 } 1327 } 1328 1329#ifdef ANDROID_ARM_LINKER 1330 (void) phdr_table_get_arm_exidx(phdr, phnum, base, 1331 &si->ARM_exidx, &si->ARM_exidx_count); 1332#endif 1333 1334 // Extract useful information from dynamic section. 1335 uint32_t needed_count = 0; 1336 for (Elf_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1337 DEBUG("d = %p, d[0](tag) = 0x%08x d[1](val) = 0x%08x", d, d->d_tag, d->d_un.d_val); 1338 switch(d->d_tag){ 1339 case DT_HASH: 1340 si->nbucket = ((unsigned *) (base + d->d_un.d_ptr))[0]; 1341 si->nchain = ((unsigned *) (base + d->d_un.d_ptr))[1]; 1342 si->bucket = (unsigned *) (base + d->d_un.d_ptr + 8); 1343 si->chain = (unsigned *) (base + d->d_un.d_ptr + 8 + si->nbucket * 4); 1344 break; 1345 case DT_STRTAB: 1346 si->strtab = (const char *) (base + d->d_un.d_ptr); 1347 break; 1348 case DT_SYMTAB: 1349 si->symtab = (Elf_Sym *) (base + d->d_un.d_ptr); 1350 break; 1351 case DT_PLTREL: 1352 if (d->d_un.d_val != DT_REL) { 1353 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1354 return false; 1355 } 1356 break; 1357 case DT_JMPREL: 1358 si->plt_rel = (Elf_Rel*) (base + d->d_un.d_ptr); 1359 break; 1360 case DT_PLTRELSZ: 1361 si->plt_rel_count = d->d_un.d_val / sizeof(Elf_Rel); 1362 break; 1363 case DT_REL: 1364 si->rel = (Elf_Rel*) (base + d->d_un.d_ptr); 1365 break; 1366 case DT_RELSZ: 1367 si->rel_count = d->d_un.d_val / sizeof(Elf_Rel); 1368 break; 1369 case DT_PLTGOT: 1370 /* Save this in case we decide to do lazy binding. We don't yet. */ 1371 si->plt_got = (unsigned *)(base + d->d_un.d_ptr); 1372 break; 1373 case DT_DEBUG: 1374 // Set the DT_DEBUG entry to the address of _r_debug for GDB 1375 // if the dynamic table is writable 1376 if ((dynamic_flags & PF_W) != 0) { 1377 d->d_un.d_val = reinterpret_cast<uintptr_t>(&_r_debug); 1378 } 1379 break; 1380 case DT_RELA: 1381 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1382 return false; 1383 case DT_INIT: 1384 si->init_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1385 DEBUG("%s constructors (DT_INIT) found at %p", si->name, si->init_func); 1386 break; 1387 case DT_FINI: 1388 si->fini_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1389 DEBUG("%s destructors (DT_FINI) found at %p", si->name, si->fini_func); 1390 break; 1391 case DT_INIT_ARRAY: 1392 si->init_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1393 DEBUG("%s constructors (DT_INIT_ARRAY) found at %p", si->name, si->init_array); 1394 break; 1395 case DT_INIT_ARRAYSZ: 1396 si->init_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf_Addr); 1397 break; 1398 case DT_FINI_ARRAY: 1399 si->fini_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1400 DEBUG("%s destructors (DT_FINI_ARRAY) found at %p", si->name, si->fini_array); 1401 break; 1402 case DT_FINI_ARRAYSZ: 1403 si->fini_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf_Addr); 1404 break; 1405 case DT_PREINIT_ARRAY: 1406 si->preinit_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1407 DEBUG("%s constructors (DT_PREINIT_ARRAY) found at %p", si->name, si->preinit_array); 1408 break; 1409 case DT_PREINIT_ARRAYSZ: 1410 si->preinit_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf_Addr); 1411 break; 1412 case DT_TEXTREL: 1413 si->has_text_relocations = true; 1414 break; 1415 case DT_SYMBOLIC: 1416 si->has_DT_SYMBOLIC = true; 1417 break; 1418 case DT_NEEDED: 1419 ++needed_count; 1420 break; 1421#if defined DT_FLAGS 1422 // TODO: why is DT_FLAGS not defined? 1423 case DT_FLAGS: 1424 if (d->d_un.d_val & DF_TEXTREL) { 1425 si->has_text_relocations = true; 1426 } 1427 if (d->d_un.d_val & DF_SYMBOLIC) { 1428 si->has_DT_SYMBOLIC = true; 1429 } 1430 break; 1431#endif 1432#if defined(ANDROID_MIPS_LINKER) 1433 case DT_STRSZ: 1434 case DT_SYMENT: 1435 case DT_RELENT: 1436 break; 1437 case DT_MIPS_RLD_MAP: 1438 // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. 1439 { 1440 r_debug** dp = (r_debug**) d->d_un.d_ptr; 1441 *dp = &_r_debug; 1442 } 1443 break; 1444 case DT_MIPS_RLD_VERSION: 1445 case DT_MIPS_FLAGS: 1446 case DT_MIPS_BASE_ADDRESS: 1447 case DT_MIPS_UNREFEXTNO: 1448 break; 1449 1450 case DT_MIPS_SYMTABNO: 1451 si->mips_symtabno = d->d_un.d_val; 1452 break; 1453 1454 case DT_MIPS_LOCAL_GOTNO: 1455 si->mips_local_gotno = d->d_un.d_val; 1456 break; 1457 1458 case DT_MIPS_GOTSYM: 1459 si->mips_gotsym = d->d_un.d_val; 1460 break; 1461 1462 default: 1463 DEBUG("Unused DT entry: type 0x%08x arg 0x%08x", d->d_tag, d->d_un.d_val); 1464 break; 1465#endif 1466 } 1467 } 1468 1469 DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p", 1470 si->base, si->strtab, si->symtab); 1471 1472 // Sanity checks. 1473 if (relocating_linker && needed_count != 0) { 1474 DL_ERR("linker cannot have DT_NEEDED dependencies on other libraries"); 1475 return false; 1476 } 1477 if (si->nbucket == 0) { 1478 DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name); 1479 return false; 1480 } 1481 if (si->strtab == 0) { 1482 DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name); 1483 return false; 1484 } 1485 if (si->symtab == 0) { 1486 DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name); 1487 return false; 1488 } 1489 1490 // If this is the main executable, then load all of the libraries from LD_PRELOAD now. 1491 if (si->flags & FLAG_EXE) { 1492 memset(gLdPreloads, 0, sizeof(gLdPreloads)); 1493 size_t preload_count = 0; 1494 for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) { 1495 soinfo* lsi = find_library(gLdPreloadNames[i]); 1496 if (lsi != NULL) { 1497 gLdPreloads[preload_count++] = lsi; 1498 } else { 1499 // As with glibc, failure to load an LD_PRELOAD library is just a warning. 1500 DL_WARN("could not load library \"%s\" from LD_PRELOAD for \"%s\"; caused by %s", 1501 gLdPreloadNames[i], si->name, linker_get_error_buffer()); 1502 } 1503 } 1504 } 1505 1506 soinfo** needed = (soinfo**) alloca((1 + needed_count) * sizeof(soinfo*)); 1507 soinfo** pneeded = needed; 1508 1509 for (Elf_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1510 if (d->d_tag == DT_NEEDED) { 1511 const char* library_name = si->strtab + d->d_un.d_val; 1512 DEBUG("%s needs %s", si->name, library_name); 1513 soinfo* lsi = find_library(library_name); 1514 if (lsi == NULL) { 1515 strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf)); 1516 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1517 library_name, si->name, tmp_err_buf); 1518 return false; 1519 } 1520 *pneeded++ = lsi; 1521 } 1522 } 1523 *pneeded = NULL; 1524 1525 if (si->has_text_relocations) { 1526 /* Unprotect the segments, i.e. make them writable, to allow 1527 * text relocations to work properly. We will later call 1528 * phdr_table_protect_segments() after all of them are applied 1529 * and all constructors are run. 1530 */ 1531 DL_WARN("%s has text relocations. This is wasting memory and is " 1532 "a security risk. Please fix.", si->name); 1533 if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1534 DL_ERR("can't unprotect loadable segments for \"%s\": %s", 1535 si->name, strerror(errno)); 1536 return false; 1537 } 1538 } 1539 1540 if (si->plt_rel != NULL) { 1541 DEBUG("[ relocating %s plt ]", si->name ); 1542 if (soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) { 1543 return false; 1544 } 1545 } 1546 if (si->rel != NULL) { 1547 DEBUG("[ relocating %s ]", si->name ); 1548 if (soinfo_relocate(si, si->rel, si->rel_count, needed)) { 1549 return false; 1550 } 1551 } 1552 1553#ifdef ANDROID_MIPS_LINKER 1554 if (!mips_relocate_got(si, needed)) { 1555 return false; 1556 } 1557#endif 1558 1559 si->flags |= FLAG_LINKED; 1560 DEBUG("[ finished linking %s ]", si->name); 1561 1562 if (si->has_text_relocations) { 1563 /* All relocations are done, we can protect our segments back to 1564 * read-only. */ 1565 if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1566 DL_ERR("can't protect segments for \"%s\": %s", 1567 si->name, strerror(errno)); 1568 return false; 1569 } 1570 } 1571 1572 /* We can also turn on GNU RELRO protection */ 1573 if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { 1574 DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", 1575 si->name, strerror(errno)); 1576 return false; 1577 } 1578 1579 notify_gdb_of_load(si); 1580 return true; 1581} 1582 1583/* 1584 * This function add vdso to internal dso list. 1585 * It helps to stack unwinding through signal handlers. 1586 * Also, it makes bionic more like glibc. 1587 */ 1588static void add_vdso(KernelArgumentBlock& args UNUSED) { 1589#ifdef AT_SYSINFO_EHDR 1590 Elf_Ehdr* ehdr_vdso = reinterpret_cast<Elf_Ehdr*>(args.getauxval(AT_SYSINFO_EHDR)); 1591 1592 soinfo* si = soinfo_alloc("[vdso]"); 1593 si->phdr = reinterpret_cast<Elf_Phdr*>(reinterpret_cast<char*>(ehdr_vdso) + ehdr_vdso->e_phoff); 1594 si->phnum = ehdr_vdso->e_phnum; 1595 si->link_map.l_name = si->name; 1596 for (size_t i = 0; i < si->phnum; ++i) { 1597 if (si->phdr[i].p_type == PT_LOAD) { 1598 si->link_map.l_addr = reinterpret_cast<Elf_Addr>(ehdr_vdso) - si->phdr[i].p_vaddr; 1599 break; 1600 } 1601 } 1602#endif 1603} 1604 1605/* 1606 * This code is called after the linker has linked itself and 1607 * fixed it's own GOT. It is safe to make references to externs 1608 * and other non-local data at this point. 1609 */ 1610static Elf_Addr __linker_init_post_relocation(KernelArgumentBlock& args, Elf_Addr linker_base) { 1611 /* NOTE: we store the args pointer on a special location 1612 * of the temporary TLS area in order to pass it to 1613 * the C Library's runtime initializer. 1614 * 1615 * The initializer must clear the slot and reset the TLS 1616 * to point to a different location to ensure that no other 1617 * shared library constructor can access it. 1618 */ 1619 __libc_init_tls(args); 1620 1621#if TIMING 1622 struct timeval t0, t1; 1623 gettimeofday(&t0, 0); 1624#endif 1625 1626 // Initialize environment functions, and get to the ELF aux vectors table. 1627 linker_env_init(args); 1628 1629 // If this is a setuid/setgid program, close the security hole described in 1630 // ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc 1631 if (get_AT_SECURE()) { 1632 nullify_closed_stdio(); 1633 } 1634 1635 debuggerd_init(); 1636 1637 // Get a few environment variables. 1638 const char* LD_DEBUG = linker_env_get("LD_DEBUG"); 1639 if (LD_DEBUG != NULL) { 1640 gLdDebugVerbosity = atoi(LD_DEBUG); 1641 } 1642 1643 // Normally, these are cleaned by linker_env_init, but the test 1644 // doesn't cost us anything. 1645 const char* ldpath_env = NULL; 1646 const char* ldpreload_env = NULL; 1647 if (!get_AT_SECURE()) { 1648 ldpath_env = linker_env_get("LD_LIBRARY_PATH"); 1649 ldpreload_env = linker_env_get("LD_PRELOAD"); 1650 } 1651 1652 INFO("[ android linker & debugger ]"); 1653 1654 soinfo* si = soinfo_alloc(args.argv[0]); 1655 if (si == NULL) { 1656 exit(EXIT_FAILURE); 1657 } 1658 1659 /* bootstrap the link map, the main exe always needs to be first */ 1660 si->flags |= FLAG_EXE; 1661 link_map_t* map = &(si->link_map); 1662 1663 map->l_addr = 0; 1664 map->l_name = args.argv[0]; 1665 map->l_prev = NULL; 1666 map->l_next = NULL; 1667 1668 _r_debug.r_map = map; 1669 r_debug_tail = map; 1670 1671 /* gdb expects the linker to be in the debug shared object list. 1672 * Without this, gdb has trouble locating the linker's ".text" 1673 * and ".plt" sections. Gdb could also potentially use this to 1674 * relocate the offset of our exported 'rtld_db_dlactivity' symbol. 1675 * Don't use soinfo_alloc(), because the linker shouldn't 1676 * be on the soinfo list. 1677 */ 1678 { 1679 static soinfo linker_soinfo; 1680 strlcpy(linker_soinfo.name, "/system/bin/linker", sizeof(linker_soinfo.name)); 1681 linker_soinfo.flags = 0; 1682 linker_soinfo.base = linker_base; 1683 1684 /* 1685 * Set the dynamic field in the link map otherwise gdb will complain with 1686 * the following: 1687 * warning: .dynamic section for "/system/bin/linker" is not at the 1688 * expected address (wrong library or version mismatch?) 1689 */ 1690 Elf_Ehdr *elf_hdr = (Elf_Ehdr *) linker_base; 1691 Elf_Phdr *phdr = (Elf_Phdr*)((unsigned char*) linker_base + elf_hdr->e_phoff); 1692 phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, 1693 &linker_soinfo.dynamic, NULL, NULL); 1694 insert_soinfo_into_debug_map(&linker_soinfo); 1695 } 1696 1697 // Extract information passed from the kernel. 1698 si->phdr = reinterpret_cast<Elf_Phdr*>(args.getauxval(AT_PHDR)); 1699 si->phnum = args.getauxval(AT_PHNUM); 1700 si->entry = args.getauxval(AT_ENTRY); 1701 1702 /* Compute the value of si->base. We can't rely on the fact that 1703 * the first entry is the PHDR because this will not be true 1704 * for certain executables (e.g. some in the NDK unit test suite) 1705 */ 1706 si->base = 0; 1707 si->size = phdr_table_get_load_size(si->phdr, si->phnum); 1708 si->load_bias = 0; 1709 for (size_t i = 0; i < si->phnum; ++i) { 1710 if (si->phdr[i].p_type == PT_PHDR) { 1711 si->load_bias = reinterpret_cast<Elf_Addr>(si->phdr) - si->phdr[i].p_vaddr; 1712 si->base = reinterpret_cast<Elf_Addr>(si->phdr) - si->phdr[i].p_offset; 1713 break; 1714 } 1715 } 1716 si->dynamic = NULL; 1717 si->ref_count = 1; 1718 1719 // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). 1720 parse_LD_LIBRARY_PATH(ldpath_env); 1721 parse_LD_PRELOAD(ldpreload_env); 1722 1723 somain = si; 1724 1725 if (!soinfo_link_image(si)) { 1726 __libc_format_fd(2, "CANNOT LINK EXECUTABLE: %s\n", linker_get_error_buffer()); 1727 exit(EXIT_FAILURE); 1728 } 1729 1730 add_vdso(args); 1731 1732 si->CallPreInitConstructors(); 1733 1734 for (size_t i = 0; gLdPreloads[i] != NULL; ++i) { 1735 gLdPreloads[i]->CallConstructors(); 1736 } 1737 1738 /* After the link_image, the si->load_bias is initialized. 1739 * For so lib, the map->l_addr will be updated in notify_gdb_of_load. 1740 * We need to update this value for so exe here. So Unwind_Backtrace 1741 * for some arch like x86 could work correctly within so exe. 1742 */ 1743 map->l_addr = si->load_bias; 1744 si->CallConstructors(); 1745 1746#if TIMING 1747 gettimeofday(&t1,NULL); 1748 PRINT("LINKER TIME: %s: %d microseconds", args.argv[0], (int) ( 1749 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - 1750 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) 1751 )); 1752#endif 1753#if STATS 1754 PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", args.argv[0], 1755 linker_stats.count[kRelocAbsolute], 1756 linker_stats.count[kRelocRelative], 1757 linker_stats.count[kRelocCopy], 1758 linker_stats.count[kRelocSymbol]); 1759#endif 1760#if COUNT_PAGES 1761 { 1762 unsigned n; 1763 unsigned i; 1764 unsigned count = 0; 1765 for (n = 0; n < 4096; n++) { 1766 if (bitmask[n]) { 1767 unsigned x = bitmask[n]; 1768 for (i = 0; i < 8; i++) { 1769 if (x & 1) { 1770 count++; 1771 } 1772 x >>= 1; 1773 } 1774 } 1775 } 1776 PRINT("PAGES MODIFIED: %s: %d (%dKB)", args.argv[0], count, count * 4); 1777 } 1778#endif 1779 1780#if TIMING || STATS || COUNT_PAGES 1781 fflush(stdout); 1782#endif 1783 1784 TRACE("[ Ready to execute '%s' @ 0x%08x ]", si->name, si->entry); 1785 return si->entry; 1786} 1787 1788/* Compute the load-bias of an existing executable. This shall only 1789 * be used to compute the load bias of an executable or shared library 1790 * that was loaded by the kernel itself. 1791 * 1792 * Input: 1793 * elf -> address of ELF header, assumed to be at the start of the file. 1794 * Return: 1795 * load bias, i.e. add the value of any p_vaddr in the file to get 1796 * the corresponding address in memory. 1797 */ 1798static Elf_Addr get_elf_exec_load_bias(const Elf_Ehdr* elf) { 1799 Elf_Addr offset = elf->e_phoff; 1800 const Elf_Phdr* phdr_table = (const Elf_Phdr*)((char*)elf + offset); 1801 const Elf_Phdr* phdr_end = phdr_table + elf->e_phnum; 1802 1803 for (const Elf_Phdr* phdr = phdr_table; phdr < phdr_end; phdr++) { 1804 if (phdr->p_type == PT_LOAD) { 1805 return reinterpret_cast<Elf_Addr>(elf) + phdr->p_offset - phdr->p_vaddr; 1806 } 1807 } 1808 return 0; 1809} 1810 1811/* 1812 * This is the entry point for the linker, called from begin.S. This 1813 * method is responsible for fixing the linker's own relocations, and 1814 * then calling __linker_init_post_relocation(). 1815 * 1816 * Because this method is called before the linker has fixed it's own 1817 * relocations, any attempt to reference an extern variable, extern 1818 * function, or other GOT reference will generate a segfault. 1819 */ 1820extern "C" Elf_Addr __linker_init(void* raw_args) { 1821 KernelArgumentBlock args(raw_args); 1822 1823 Elf_Addr linker_addr = args.getauxval(AT_BASE); 1824 1825 Elf_Ehdr* elf_hdr = reinterpret_cast<Elf_Ehdr*>(linker_addr); 1826 Elf_Phdr* phdr = (Elf_Phdr*)((unsigned char*) linker_addr + elf_hdr->e_phoff); 1827 1828 soinfo linker_so; 1829 memset(&linker_so, 0, sizeof(soinfo)); 1830 1831 linker_so.base = linker_addr; 1832 linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); 1833 linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); 1834 linker_so.dynamic = NULL; 1835 linker_so.phdr = phdr; 1836 linker_so.phnum = elf_hdr->e_phnum; 1837 linker_so.flags |= FLAG_LINKER; 1838 1839 if (!soinfo_link_image(&linker_so)) { 1840 // It would be nice to print an error message, but if the linker 1841 // can't link itself, there's no guarantee that we'll be able to 1842 // call write() (because it involves a GOT reference). 1843 // 1844 // This situation should never occur unless the linker itself 1845 // is corrupt. 1846 exit(EXIT_FAILURE); 1847 } 1848 1849 // We have successfully fixed our own relocations. It's safe to run 1850 // the main part of the linker now. 1851 args.abort_message_ptr = &gAbortMessage; 1852 Elf_Addr start_address = __linker_init_post_relocation(args, linker_addr); 1853 1854 set_soinfo_pool_protection(PROT_READ); 1855 1856 // Return the address that the calling assembly stub should jump to. 1857 return start_address; 1858} 1859