linker.cpp revision 24053a461e7a20f34002262c1bb122023134989d
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 Elf32_Sym* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name) { 441 Elf32_Sym* symtab = si->symtab; 442 const char* strtab = si->strtab; 443 444 TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %d", 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 Elf32_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 Elf32_Sym* soinfo_do_lookup(soinfo* si, const char* name, soinfo** lsi, soinfo* needed[]) { 482 unsigned elf_hash = elfhash(name); 483 Elf32_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 */ 590Elf32_Sym* dlsym_handle_lookup(soinfo* si, const char* name) 591{ 592 return soinfo_elf_lookup(si, elfhash(name), name); 593} 594 595/* This is used by dlsym(3) to performs a global symbol lookup. If the 596 start value is null (for RTLD_DEFAULT), the search starts at the 597 beginning of the global solist. Otherwise the search starts at the 598 specified soinfo (for RTLD_NEXT). 599 */ 600Elf32_Sym* dlsym_linear_lookup(const char* name, soinfo** found, soinfo* start) { 601 unsigned elf_hash = elfhash(name); 602 603 if (start == NULL) { 604 start = solist; 605 } 606 607 Elf32_Sym* s = NULL; 608 for (soinfo* si = start; (s == NULL) && (si != NULL); si = si->next) { 609 s = soinfo_elf_lookup(si, elf_hash, name); 610 if (s != NULL) { 611 *found = si; 612 break; 613 } 614 } 615 616 if (s != NULL) { 617 TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, found->base = 0x%08x", 618 name, s->st_value, (*found)->base); 619 } 620 621 return s; 622} 623 624soinfo* find_containing_library(const void* p) { 625 Elf32_Addr address = reinterpret_cast<Elf32_Addr>(p); 626 for (soinfo* si = solist; si != NULL; si = si->next) { 627 if (address >= si->base && address - si->base < si->size) { 628 return si; 629 } 630 } 631 return NULL; 632} 633 634Elf32_Sym* dladdr_find_symbol(soinfo* si, const void* addr) { 635 Elf32_Addr soaddr = reinterpret_cast<Elf32_Addr>(addr) - si->base; 636 637 // Search the library's symbol table for any defined symbol which 638 // contains this address. 639 for (size_t i = 0; i < si->nchain; ++i) { 640 Elf32_Sym* sym = &si->symtab[i]; 641 if (sym->st_shndx != SHN_UNDEF && 642 soaddr >= sym->st_value && 643 soaddr < sym->st_value + sym->st_size) { 644 return sym; 645 } 646 } 647 648 return NULL; 649} 650 651#if 0 652static void dump(soinfo* si) 653{ 654 Elf32_Sym* s = si->symtab; 655 for (unsigned n = 0; n < si->nchain; n++) { 656 TRACE("%04d> %08x: %02x %04x %08x %08x %s", n, s, 657 s->st_info, s->st_shndx, s->st_value, s->st_size, 658 si->strtab + s->st_name); 659 s++; 660 } 661} 662#endif 663 664static int open_library_on_path(const char* name, const char* const paths[]) { 665 char buf[512]; 666 for (size_t i = 0; paths[i] != NULL; ++i) { 667 int n = __libc_format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name); 668 if (n < 0 || n >= static_cast<int>(sizeof(buf))) { 669 PRINT("Warning: ignoring very long library path: %s/%s", paths[i], name); 670 continue; 671 } 672 int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC)); 673 if (fd != -1) { 674 return fd; 675 } 676 } 677 return -1; 678} 679 680static int open_library(const char* name) { 681 TRACE("[ opening %s ]", name); 682 683 // If the name contains a slash, we should attempt to open it directly and not search the paths. 684 if (strchr(name, '/') != NULL) { 685 int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC)); 686 if (fd != -1) { 687 return fd; 688 } 689 // ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now. 690 } 691 692 // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths. 693 int fd = open_library_on_path(name, gLdPaths); 694 if (fd == -1) { 695 fd = open_library_on_path(name, gSoPaths); 696 } 697 return fd; 698} 699 700static soinfo* load_library(const char* name) { 701 // Open the file. 702 int fd = open_library(name); 703 if (fd == -1) { 704 DL_ERR("library \"%s\" not found", name); 705 return NULL; 706 } 707 708 // Read the ELF header and load the segments. 709 ElfReader elf_reader(name, fd); 710 if (!elf_reader.Load()) { 711 return NULL; 712 } 713 714 const char* bname = strrchr(name, '/'); 715 soinfo* si = soinfo_alloc(bname ? bname + 1 : name); 716 if (si == NULL) { 717 return NULL; 718 } 719 si->base = elf_reader.load_start(); 720 si->size = elf_reader.load_size(); 721 si->load_bias = elf_reader.load_bias(); 722 si->flags = 0; 723 si->entry = 0; 724 si->dynamic = NULL; 725 si->phnum = elf_reader.phdr_count(); 726 si->phdr = elf_reader.loaded_phdr(); 727 return si; 728} 729 730static soinfo *find_loaded_library(const char *name) 731{ 732 soinfo *si; 733 const char *bname; 734 735 // TODO: don't use basename only for determining libraries 736 // http://code.google.com/p/android/issues/detail?id=6670 737 738 bname = strrchr(name, '/'); 739 bname = bname ? bname + 1 : name; 740 741 for (si = solist; si != NULL; si = si->next) { 742 if (!strcmp(bname, si->name)) { 743 return si; 744 } 745 } 746 return NULL; 747} 748 749static soinfo* find_library_internal(const char* name) { 750 if (name == NULL) { 751 return somain; 752 } 753 754 soinfo* si = find_loaded_library(name); 755 if (si != NULL) { 756 if (si->flags & FLAG_LINKED) { 757 return si; 758 } 759 DL_ERR("OOPS: recursive link to \"%s\"", si->name); 760 return NULL; 761 } 762 763 TRACE("[ '%s' has not been loaded yet. Locating...]", name); 764 si = load_library(name); 765 if (si == NULL) { 766 return NULL; 767 } 768 769 // At this point we know that whatever is loaded @ base is a valid ELF 770 // shared library whose segments are properly mapped in. 771 TRACE("[ init_library base=0x%08x sz=0x%08x name='%s' ]", 772 si->base, si->size, si->name); 773 774 if (!soinfo_link_image(si)) { 775 munmap(reinterpret_cast<void*>(si->base), si->size); 776 soinfo_free(si); 777 return NULL; 778 } 779 780 return si; 781} 782 783static soinfo* find_library(const char* name) { 784 soinfo* si = find_library_internal(name); 785 if (si != NULL) { 786 si->ref_count++; 787 } 788 return si; 789} 790 791static int soinfo_unload(soinfo* si) { 792 if (si->ref_count == 1) { 793 TRACE("unloading '%s'", si->name); 794 si->CallDestructors(); 795 796 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 797 if (d->d_tag == DT_NEEDED) { 798 const char* library_name = si->strtab + d->d_un.d_val; 799 TRACE("%s needs to unload %s", si->name, library_name); 800 soinfo_unload(find_loaded_library(library_name)); 801 } 802 } 803 804 munmap(reinterpret_cast<void*>(si->base), si->size); 805 notify_gdb_of_unload(si); 806 soinfo_free(si); 807 si->ref_count = 0; 808 } else { 809 si->ref_count--; 810 TRACE("not unloading '%s', decrementing ref_count to %d", si->name, si->ref_count); 811 } 812 return 0; 813} 814 815void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) { 816 if (!get_AT_SECURE()) { 817 parse_LD_LIBRARY_PATH(ld_library_path); 818 } 819} 820 821soinfo* do_dlopen(const char* name, int flags) { 822 if ((flags & ~(RTLD_NOW|RTLD_LAZY|RTLD_LOCAL|RTLD_GLOBAL)) != 0) { 823 DL_ERR("invalid flags to dlopen: %x", flags); 824 return NULL; 825 } 826 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 827 soinfo* si = find_library(name); 828 if (si != NULL) { 829 si->CallConstructors(); 830 } 831 set_soinfo_pool_protection(PROT_READ); 832 return si; 833} 834 835int do_dlclose(soinfo* si) { 836 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 837 int result = soinfo_unload(si); 838 set_soinfo_pool_protection(PROT_READ); 839 return result; 840} 841 842/* TODO: don't use unsigned for addrs below. It works, but is not 843 * ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned 844 * long. 845 */ 846static int soinfo_relocate(soinfo* si, Elf32_Rel* rel, unsigned count, 847 soinfo* needed[]) 848{ 849 Elf32_Sym* symtab = si->symtab; 850 const char* strtab = si->strtab; 851 Elf32_Sym* s; 852 Elf32_Rel* start = rel; 853 soinfo* lsi; 854 855 for (size_t idx = 0; idx < count; ++idx, ++rel) { 856 unsigned type = ELF32_R_TYPE(rel->r_info); 857 unsigned sym = ELF32_R_SYM(rel->r_info); 858 Elf32_Addr reloc = static_cast<Elf32_Addr>(rel->r_offset + si->load_bias); 859 Elf32_Addr sym_addr = 0; 860 char* sym_name = NULL; 861 862 DEBUG("Processing '%s' relocation at index %d", si->name, idx); 863 if (type == 0) { // R_*_NONE 864 continue; 865 } 866 if (sym != 0) { 867 sym_name = (char *)(strtab + symtab[sym].st_name); 868 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 869 if (s == NULL) { 870 /* We only allow an undefined symbol if this is a weak 871 reference.. */ 872 s = &symtab[sym]; 873 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 874 DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); 875 return -1; 876 } 877 878 /* IHI0044C AAELF 4.5.1.1: 879 880 Libraries are not searched to resolve weak references. 881 It is not an error for a weak reference to remain 882 unsatisfied. 883 884 During linking, the value of an undefined weak reference is: 885 - Zero if the relocation type is absolute 886 - The address of the place if the relocation is pc-relative 887 - The address of nominal base address if the relocation 888 type is base-relative. 889 */ 890 891 switch (type) { 892#if defined(ANDROID_ARM_LINKER) 893 case R_ARM_JUMP_SLOT: 894 case R_ARM_GLOB_DAT: 895 case R_ARM_ABS32: 896 case R_ARM_RELATIVE: /* Don't care. */ 897#elif defined(ANDROID_X86_LINKER) 898 case R_386_JMP_SLOT: 899 case R_386_GLOB_DAT: 900 case R_386_32: 901 case R_386_RELATIVE: /* Dont' care. */ 902#endif /* ANDROID_*_LINKER */ 903 /* sym_addr was initialized to be zero above or relocation 904 code below does not care about value of sym_addr. 905 No need to do anything. */ 906 break; 907 908#if defined(ANDROID_X86_LINKER) 909 case R_386_PC32: 910 sym_addr = reloc; 911 break; 912#endif /* ANDROID_X86_LINKER */ 913 914#if defined(ANDROID_ARM_LINKER) 915 case R_ARM_COPY: 916 /* Fall through. Can't really copy if weak symbol is 917 not found in run-time. */ 918#endif /* ANDROID_ARM_LINKER */ 919 default: 920 DL_ERR("unknown weak reloc type %d @ %p (%d)", 921 type, rel, (int) (rel - start)); 922 return -1; 923 } 924 } else { 925 /* We got a definition. */ 926#if 0 927 if ((base == 0) && (si->base != 0)) { 928 /* linking from libraries to main image is bad */ 929 DL_ERR("cannot locate \"%s\"...", 930 strtab + symtab[sym].st_name); 931 return -1; 932 } 933#endif 934 sym_addr = static_cast<Elf32_Addr>(s->st_value + lsi->load_bias); 935 } 936 count_relocation(kRelocSymbol); 937 } else { 938 s = NULL; 939 } 940 941/* TODO: This is ugly. Split up the relocations by arch into 942 * different files. 943 */ 944 switch(type){ 945#if defined(ANDROID_ARM_LINKER) 946 case R_ARM_JUMP_SLOT: 947 count_relocation(kRelocAbsolute); 948 MARK(rel->r_offset); 949 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 950 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 951 break; 952 case R_ARM_GLOB_DAT: 953 count_relocation(kRelocAbsolute); 954 MARK(rel->r_offset); 955 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 956 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 957 break; 958 case R_ARM_ABS32: 959 count_relocation(kRelocAbsolute); 960 MARK(rel->r_offset); 961 TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s", reloc, sym_addr, sym_name); 962 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 963 break; 964 case R_ARM_REL32: 965 count_relocation(kRelocRelative); 966 MARK(rel->r_offset); 967 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s", 968 reloc, sym_addr, rel->r_offset, sym_name); 969 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr - rel->r_offset; 970 break; 971#elif defined(ANDROID_X86_LINKER) 972 case R_386_JMP_SLOT: 973 count_relocation(kRelocAbsolute); 974 MARK(rel->r_offset); 975 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 976 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 977 break; 978 case R_386_GLOB_DAT: 979 count_relocation(kRelocAbsolute); 980 MARK(rel->r_offset); 981 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 982 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 983 break; 984#elif defined(ANDROID_MIPS_LINKER) 985 case R_MIPS_REL32: 986 count_relocation(kRelocAbsolute); 987 MARK(rel->r_offset); 988 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s", 989 reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); 990 if (s) { 991 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 992 } else { 993 *reinterpret_cast<Elf32_Addr*>(reloc) += si->base; 994 } 995 break; 996#endif /* ANDROID_*_LINKER */ 997 998#if defined(ANDROID_ARM_LINKER) 999 case R_ARM_RELATIVE: 1000#elif defined(ANDROID_X86_LINKER) 1001 case R_386_RELATIVE: 1002#endif /* ANDROID_*_LINKER */ 1003 count_relocation(kRelocRelative); 1004 MARK(rel->r_offset); 1005 if (sym) { 1006 DL_ERR("odd RELATIVE form..."); 1007 return -1; 1008 } 1009 TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x", reloc, si->base); 1010 *reinterpret_cast<Elf32_Addr*>(reloc) += si->base; 1011 break; 1012 1013#if defined(ANDROID_X86_LINKER) 1014 case R_386_32: 1015 count_relocation(kRelocRelative); 1016 MARK(rel->r_offset); 1017 1018 TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s", reloc, sym_addr, sym_name); 1019 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 1020 break; 1021 1022 case R_386_PC32: 1023 count_relocation(kRelocRelative); 1024 MARK(rel->r_offset); 1025 TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s", 1026 reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); 1027 *reinterpret_cast<Elf32_Addr*>(reloc) += (sym_addr - reloc); 1028 break; 1029#endif /* ANDROID_X86_LINKER */ 1030 1031#ifdef ANDROID_ARM_LINKER 1032 case R_ARM_COPY: 1033 if ((si->flags & FLAG_EXE) == 0) { 1034 /* 1035 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf 1036 * 1037 * Section 4.7.1.10 "Dynamic relocations" 1038 * R_ARM_COPY may only appear in executable objects where e_type is 1039 * set to ET_EXEC. 1040 * 1041 * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. 1042 * We should explicitly disallow ET_DYN executables from having 1043 * R_ARM_COPY relocations. 1044 */ 1045 DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); 1046 return -1; 1047 } 1048 count_relocation(kRelocCopy); 1049 MARK(rel->r_offset); 1050 TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s", reloc, s->st_size, sym_addr, sym_name); 1051 if (reloc == sym_addr) { 1052 Elf32_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed); 1053 1054 if (src == NULL) { 1055 DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name); 1056 return -1; 1057 } 1058 if (lsi->has_DT_SYMBOLIC) { 1059 DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared " 1060 "library %s (built with -Bsymbolic?)", si->name, lsi->name); 1061 return -1; 1062 } 1063 if (s->st_size < src->st_size) { 1064 DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)", 1065 si->name, s->st_size, src->st_size); 1066 return -1; 1067 } 1068 memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size); 1069 } else { 1070 DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name); 1071 return -1; 1072 } 1073 break; 1074#endif /* ANDROID_ARM_LINKER */ 1075 1076 default: 1077 DL_ERR("unknown reloc type %d @ %p (%d)", 1078 type, rel, (int) (rel - start)); 1079 return -1; 1080 } 1081 } 1082 return 0; 1083} 1084 1085#ifdef ANDROID_MIPS_LINKER 1086static bool mips_relocate_got(soinfo* si, soinfo* needed[]) { 1087 unsigned* got = si->plt_got; 1088 if (got == NULL) { 1089 return true; 1090 } 1091 unsigned local_gotno = si->mips_local_gotno; 1092 unsigned gotsym = si->mips_gotsym; 1093 unsigned symtabno = si->mips_symtabno; 1094 Elf32_Sym* symtab = si->symtab; 1095 1096 /* 1097 * got[0] is address of lazy resolver function 1098 * got[1] may be used for a GNU extension 1099 * set it to a recognizable address in case someone calls it 1100 * (should be _rtld_bind_start) 1101 * FIXME: maybe this should be in a separate routine 1102 */ 1103 1104 if ((si->flags & FLAG_LINKER) == 0) { 1105 size_t g = 0; 1106 got[g++] = 0xdeadbeef; 1107 if (got[g] & 0x80000000) { 1108 got[g++] = 0xdeadfeed; 1109 } 1110 /* 1111 * Relocate the local GOT entries need to be relocated 1112 */ 1113 for (; g < local_gotno; g++) { 1114 got[g] += si->load_bias; 1115 } 1116 } 1117 1118 /* Now for the global GOT entries */ 1119 Elf32_Sym* sym = symtab + gotsym; 1120 got = si->plt_got + local_gotno; 1121 for (size_t g = gotsym; g < symtabno; g++, sym++, got++) { 1122 const char* sym_name; 1123 Elf32_Sym* s; 1124 soinfo* lsi; 1125 1126 /* This is an undefined reference... try to locate it */ 1127 sym_name = si->strtab + sym->st_name; 1128 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1129 if (s == NULL) { 1130 /* We only allow an undefined symbol if this is a weak 1131 reference.. */ 1132 s = &symtab[g]; 1133 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1134 DL_ERR("cannot locate \"%s\"...", sym_name); 1135 return false; 1136 } 1137 *got = 0; 1138 } 1139 else { 1140 /* FIXME: is this sufficient? 1141 * For reference see NetBSD link loader 1142 * 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 1143 */ 1144 *got = lsi->load_bias + s->st_value; 1145 } 1146 } 1147 return true; 1148} 1149#endif 1150 1151void soinfo::CallArray(const char* array_name UNUSED, linker_function_t* functions, size_t count, bool reverse) { 1152 if (functions == NULL) { 1153 return; 1154 } 1155 1156 TRACE("[ Calling %s (size %d) @ %p for '%s' ]", array_name, count, functions, name); 1157 1158 int begin = reverse ? (count - 1) : 0; 1159 int end = reverse ? -1 : count; 1160 int step = reverse ? -1 : 1; 1161 1162 for (int i = begin; i != end; i += step) { 1163 TRACE("[ %s[%d] == %p ]", array_name, i, functions[i]); 1164 CallFunction("function", functions[i]); 1165 } 1166 1167 TRACE("[ Done calling %s for '%s' ]", array_name, name); 1168} 1169 1170void soinfo::CallFunction(const char* function_name UNUSED, linker_function_t function) { 1171 if (function == NULL || reinterpret_cast<uintptr_t>(function) == static_cast<uintptr_t>(-1)) { 1172 return; 1173 } 1174 1175 TRACE("[ Calling %s @ %p for '%s' ]", function_name, function, name); 1176 function(); 1177 TRACE("[ Done calling %s @ %p for '%s' ]", function_name, function, name); 1178 1179 // The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures 1180 // are still writable. This happens with our debug malloc (see http://b/7941716). 1181 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 1182} 1183 1184void soinfo::CallPreInitConstructors() { 1185 // DT_PREINIT_ARRAY functions are called before any other constructors for executables, 1186 // but ignored in a shared library. 1187 CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false); 1188} 1189 1190void soinfo::CallConstructors() { 1191 if (constructors_called) { 1192 return; 1193 } 1194 1195 // We set constructors_called before actually calling the constructors, otherwise it doesn't 1196 // protect against recursive constructor calls. One simple example of constructor recursion 1197 // is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so: 1198 // 1. The program depends on libc, so libc's constructor is called here. 1199 // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. 1200 // 3. dlopen() calls the constructors on the newly created 1201 // soinfo for libc_malloc_debug_leak.so. 1202 // 4. The debug .so depends on libc, so CallConstructors is 1203 // called again with the libc soinfo. If it doesn't trigger the early- 1204 // out above, the libc constructor will be called again (recursively!). 1205 constructors_called = true; 1206 1207 if ((flags & FLAG_EXE) == 0 && preinit_array != NULL) { 1208 // The GNU dynamic linker silently ignores these, but we warn the developer. 1209 PRINT("\"%s\": ignoring %d-entry DT_PREINIT_ARRAY in shared library!", 1210 name, preinit_array_count); 1211 } 1212 1213 if (dynamic != NULL) { 1214 for (Elf32_Dyn* d = dynamic; d->d_tag != DT_NULL; ++d) { 1215 if (d->d_tag == DT_NEEDED) { 1216 const char* library_name = strtab + d->d_un.d_val; 1217 TRACE("\"%s\": calling constructors in DT_NEEDED \"%s\"", name, library_name); 1218 find_loaded_library(library_name)->CallConstructors(); 1219 } 1220 } 1221 } 1222 1223 TRACE("\"%s\": calling constructors", name); 1224 1225 // DT_INIT should be called before DT_INIT_ARRAY if both are present. 1226 CallFunction("DT_INIT", init_func); 1227 CallArray("DT_INIT_ARRAY", init_array, init_array_count, false); 1228} 1229 1230void soinfo::CallDestructors() { 1231 TRACE("\"%s\": calling destructors", name); 1232 1233 // DT_FINI_ARRAY must be parsed in reverse order. 1234 CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true); 1235 1236 // DT_FINI should be called after DT_FINI_ARRAY if both are present. 1237 CallFunction("DT_FINI", fini_func); 1238} 1239 1240/* Force any of the closed stdin, stdout and stderr to be associated with 1241 /dev/null. */ 1242static int nullify_closed_stdio() { 1243 int dev_null, i, status; 1244 int return_value = 0; 1245 1246 dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 1247 if (dev_null < 0) { 1248 DL_ERR("cannot open /dev/null: %s", strerror(errno)); 1249 return -1; 1250 } 1251 TRACE("[ Opened /dev/null file-descriptor=%d]", dev_null); 1252 1253 /* If any of the stdio file descriptors is valid and not associated 1254 with /dev/null, dup /dev/null to it. */ 1255 for (i = 0; i < 3; i++) { 1256 /* If it is /dev/null already, we are done. */ 1257 if (i == dev_null) { 1258 continue; 1259 } 1260 1261 TRACE("[ Nullifying stdio file descriptor %d]", i); 1262 status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 1263 1264 /* If file is opened, we are good. */ 1265 if (status != -1) { 1266 continue; 1267 } 1268 1269 /* The only error we allow is that the file descriptor does not 1270 exist, in which case we dup /dev/null to it. */ 1271 if (errno != EBADF) { 1272 DL_ERR("fcntl failed: %s", strerror(errno)); 1273 return_value = -1; 1274 continue; 1275 } 1276 1277 /* Try dupping /dev/null to this stdio file descriptor and 1278 repeat if there is a signal. Note that any errors in closing 1279 the stdio descriptor are lost. */ 1280 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 1281 if (status < 0) { 1282 DL_ERR("dup2 failed: %s", strerror(errno)); 1283 return_value = -1; 1284 continue; 1285 } 1286 } 1287 1288 /* If /dev/null is not one of the stdio file descriptors, close it. */ 1289 if (dev_null > 2) { 1290 TRACE("[ Closing /dev/null file-descriptor=%d]", dev_null); 1291 status = TEMP_FAILURE_RETRY(close(dev_null)); 1292 if (status == -1) { 1293 DL_ERR("close failed: %s", strerror(errno)); 1294 return_value = -1; 1295 } 1296 } 1297 1298 return return_value; 1299} 1300 1301static bool soinfo_link_image(soinfo* si) { 1302 /* "base" might wrap around UINT32_MAX. */ 1303 Elf32_Addr base = si->load_bias; 1304 const Elf32_Phdr *phdr = si->phdr; 1305 int phnum = si->phnum; 1306 bool relocating_linker = (si->flags & FLAG_LINKER) != 0; 1307 1308 /* We can't debug anything until the linker is relocated */ 1309 if (!relocating_linker) { 1310 INFO("[ linking %s ]", si->name); 1311 DEBUG("si->base = 0x%08x si->flags = 0x%08x", si->base, si->flags); 1312 } 1313 1314 /* Extract dynamic section */ 1315 size_t dynamic_count; 1316 Elf32_Word dynamic_flags; 1317 phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, 1318 &dynamic_count, &dynamic_flags); 1319 if (si->dynamic == NULL) { 1320 if (!relocating_linker) { 1321 DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name); 1322 } 1323 return false; 1324 } else { 1325 if (!relocating_linker) { 1326 DEBUG("dynamic = %p", si->dynamic); 1327 } 1328 } 1329 1330#ifdef ANDROID_ARM_LINKER 1331 (void) phdr_table_get_arm_exidx(phdr, phnum, base, 1332 &si->ARM_exidx, &si->ARM_exidx_count); 1333#endif 1334 1335 // Extract useful information from dynamic section. 1336 uint32_t needed_count = 0; 1337 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1338 DEBUG("d = %p, d[0](tag) = 0x%08x d[1](val) = 0x%08x", d, d->d_tag, d->d_un.d_val); 1339 switch(d->d_tag){ 1340 case DT_HASH: 1341 si->nbucket = ((unsigned *) (base + d->d_un.d_ptr))[0]; 1342 si->nchain = ((unsigned *) (base + d->d_un.d_ptr))[1]; 1343 si->bucket = (unsigned *) (base + d->d_un.d_ptr + 8); 1344 si->chain = (unsigned *) (base + d->d_un.d_ptr + 8 + si->nbucket * 4); 1345 break; 1346 case DT_STRTAB: 1347 si->strtab = (const char *) (base + d->d_un.d_ptr); 1348 break; 1349 case DT_SYMTAB: 1350 si->symtab = (Elf32_Sym *) (base + d->d_un.d_ptr); 1351 break; 1352 case DT_PLTREL: 1353 if (d->d_un.d_val != DT_REL) { 1354 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1355 return false; 1356 } 1357 break; 1358 case DT_JMPREL: 1359 si->plt_rel = (Elf32_Rel*) (base + d->d_un.d_ptr); 1360 break; 1361 case DT_PLTRELSZ: 1362 si->plt_rel_count = d->d_un.d_val / sizeof(Elf32_Rel); 1363 break; 1364 case DT_REL: 1365 si->rel = (Elf32_Rel*) (base + d->d_un.d_ptr); 1366 break; 1367 case DT_RELSZ: 1368 si->rel_count = d->d_un.d_val / sizeof(Elf32_Rel); 1369 break; 1370 case DT_PLTGOT: 1371 /* Save this in case we decide to do lazy binding. We don't yet. */ 1372 si->plt_got = (unsigned *)(base + d->d_un.d_ptr); 1373 break; 1374 case DT_DEBUG: 1375 // Set the DT_DEBUG entry to the address of _r_debug for GDB 1376 // if the dynamic table is writable 1377 if ((dynamic_flags & PF_W) != 0) { 1378 d->d_un.d_val = (int) &_r_debug; 1379 } 1380 break; 1381 case DT_RELA: 1382 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1383 return false; 1384 case DT_INIT: 1385 si->init_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1386 DEBUG("%s constructors (DT_INIT) found at %p", si->name, si->init_func); 1387 break; 1388 case DT_FINI: 1389 si->fini_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1390 DEBUG("%s destructors (DT_FINI) found at %p", si->name, si->fini_func); 1391 break; 1392 case DT_INIT_ARRAY: 1393 si->init_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1394 DEBUG("%s constructors (DT_INIT_ARRAY) found at %p", si->name, si->init_array); 1395 break; 1396 case DT_INIT_ARRAYSZ: 1397 si->init_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1398 break; 1399 case DT_FINI_ARRAY: 1400 si->fini_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1401 DEBUG("%s destructors (DT_FINI_ARRAY) found at %p", si->name, si->fini_array); 1402 break; 1403 case DT_FINI_ARRAYSZ: 1404 si->fini_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1405 break; 1406 case DT_PREINIT_ARRAY: 1407 si->preinit_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1408 DEBUG("%s constructors (DT_PREINIT_ARRAY) found at %p", si->name, si->preinit_array); 1409 break; 1410 case DT_PREINIT_ARRAYSZ: 1411 si->preinit_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1412 break; 1413 case DT_TEXTREL: 1414 si->has_text_relocations = true; 1415 break; 1416 case DT_SYMBOLIC: 1417 si->has_DT_SYMBOLIC = true; 1418 break; 1419 case DT_NEEDED: 1420 ++needed_count; 1421 break; 1422#if defined DT_FLAGS 1423 // TODO: why is DT_FLAGS not defined? 1424 case DT_FLAGS: 1425 if (d->d_un.d_val & DF_TEXTREL) { 1426 si->has_text_relocations = true; 1427 } 1428 if (d->d_un.d_val & DF_SYMBOLIC) { 1429 si->has_DT_SYMBOLIC = true; 1430 } 1431 break; 1432#endif 1433#if defined(ANDROID_MIPS_LINKER) 1434 case DT_STRSZ: 1435 case DT_SYMENT: 1436 case DT_RELENT: 1437 break; 1438 case DT_MIPS_RLD_MAP: 1439 // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. 1440 { 1441 r_debug** dp = (r_debug**) d->d_un.d_ptr; 1442 *dp = &_r_debug; 1443 } 1444 break; 1445 case DT_MIPS_RLD_VERSION: 1446 case DT_MIPS_FLAGS: 1447 case DT_MIPS_BASE_ADDRESS: 1448 case DT_MIPS_UNREFEXTNO: 1449 break; 1450 1451 case DT_MIPS_SYMTABNO: 1452 si->mips_symtabno = d->d_un.d_val; 1453 break; 1454 1455 case DT_MIPS_LOCAL_GOTNO: 1456 si->mips_local_gotno = d->d_un.d_val; 1457 break; 1458 1459 case DT_MIPS_GOTSYM: 1460 si->mips_gotsym = d->d_un.d_val; 1461 break; 1462 1463 default: 1464 DEBUG("Unused DT entry: type 0x%08x arg 0x%08x", d->d_tag, d->d_un.d_val); 1465 break; 1466#endif 1467 } 1468 } 1469 1470 DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p", 1471 si->base, si->strtab, si->symtab); 1472 1473 // Sanity checks. 1474 if (relocating_linker && needed_count != 0) { 1475 DL_ERR("linker cannot have DT_NEEDED dependencies on other libraries"); 1476 return false; 1477 } 1478 if (si->nbucket == 0) { 1479 DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name); 1480 return false; 1481 } 1482 if (si->strtab == 0) { 1483 DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name); 1484 return false; 1485 } 1486 if (si->symtab == 0) { 1487 DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name); 1488 return false; 1489 } 1490 1491 // If this is the main executable, then load all of the libraries from LD_PRELOAD now. 1492 if (si->flags & FLAG_EXE) { 1493 memset(gLdPreloads, 0, sizeof(gLdPreloads)); 1494 size_t preload_count = 0; 1495 for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) { 1496 soinfo* lsi = find_library(gLdPreloadNames[i]); 1497 if (lsi != NULL) { 1498 gLdPreloads[preload_count++] = lsi; 1499 } else { 1500 // As with glibc, failure to load an LD_PRELOAD library is just a warning. 1501 DL_WARN("could not load library \"%s\" from LD_PRELOAD for \"%s\"; caused by %s", 1502 gLdPreloadNames[i], si->name, linker_get_error_buffer()); 1503 } 1504 } 1505 } 1506 1507 soinfo** needed = (soinfo**) alloca((1 + needed_count) * sizeof(soinfo*)); 1508 soinfo** pneeded = needed; 1509 1510 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1511 if (d->d_tag == DT_NEEDED) { 1512 const char* library_name = si->strtab + d->d_un.d_val; 1513 DEBUG("%s needs %s", si->name, library_name); 1514 soinfo* lsi = find_library(library_name); 1515 if (lsi == NULL) { 1516 strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf)); 1517 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1518 library_name, si->name, tmp_err_buf); 1519 return false; 1520 } 1521 *pneeded++ = lsi; 1522 } 1523 } 1524 *pneeded = NULL; 1525 1526 if (si->has_text_relocations) { 1527 /* Unprotect the segments, i.e. make them writable, to allow 1528 * text relocations to work properly. We will later call 1529 * phdr_table_protect_segments() after all of them are applied 1530 * and all constructors are run. 1531 */ 1532 DL_WARN("%s has text relocations. This is wasting memory and is " 1533 "a security risk. Please fix.", si->name); 1534 if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1535 DL_ERR("can't unprotect loadable segments for \"%s\": %s", 1536 si->name, strerror(errno)); 1537 return false; 1538 } 1539 } 1540 1541 if (si->plt_rel != NULL) { 1542 DEBUG("[ relocating %s plt ]", si->name ); 1543 if (soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) { 1544 return false; 1545 } 1546 } 1547 if (si->rel != NULL) { 1548 DEBUG("[ relocating %s ]", si->name ); 1549 if (soinfo_relocate(si, si->rel, si->rel_count, needed)) { 1550 return false; 1551 } 1552 } 1553 1554#ifdef ANDROID_MIPS_LINKER 1555 if (!mips_relocate_got(si, needed)) { 1556 return false; 1557 } 1558#endif 1559 1560 si->flags |= FLAG_LINKED; 1561 DEBUG("[ finished linking %s ]", si->name); 1562 1563 if (si->has_text_relocations) { 1564 /* All relocations are done, we can protect our segments back to 1565 * read-only. */ 1566 if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1567 DL_ERR("can't protect segments for \"%s\": %s", 1568 si->name, strerror(errno)); 1569 return false; 1570 } 1571 } 1572 1573 /* We can also turn on GNU RELRO protection */ 1574 if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { 1575 DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", 1576 si->name, strerror(errno)); 1577 return false; 1578 } 1579 1580 notify_gdb_of_load(si); 1581 return true; 1582} 1583 1584/* 1585 * This function add vdso to internal dso list. 1586 * It helps to stack unwinding through signal handlers. 1587 * Also, it makes bionic more like glibc. 1588 */ 1589static void add_vdso(KernelArgumentBlock& args UNUSED) { 1590#ifdef AT_SYSINFO_EHDR 1591 Elf32_Ehdr* ehdr_vdso = reinterpret_cast<Elf32_Ehdr*>(args.getauxval(AT_SYSINFO_EHDR)); 1592 1593 soinfo* si = soinfo_alloc("[vdso]"); 1594 si->phdr = reinterpret_cast<Elf32_Phdr*>(reinterpret_cast<char*>(ehdr_vdso) + ehdr_vdso->e_phoff); 1595 si->phnum = ehdr_vdso->e_phnum; 1596 si->link_map.l_name = si->name; 1597 for (size_t i = 0; i < si->phnum; ++i) { 1598 if (si->phdr[i].p_type == PT_LOAD) { 1599 si->link_map.l_addr = reinterpret_cast<Elf32_Addr>(ehdr_vdso) - si->phdr[i].p_vaddr; 1600 break; 1601 } 1602 } 1603#endif 1604} 1605 1606/* 1607 * This code is called after the linker has linked itself and 1608 * fixed it's own GOT. It is safe to make references to externs 1609 * and other non-local data at this point. 1610 */ 1611static Elf32_Addr __linker_init_post_relocation(KernelArgumentBlock& args, Elf32_Addr linker_base) { 1612 /* NOTE: we store the args pointer on a special location 1613 * of the temporary TLS area in order to pass it to 1614 * the C Library's runtime initializer. 1615 * 1616 * The initializer must clear the slot and reset the TLS 1617 * to point to a different location to ensure that no other 1618 * shared library constructor can access it. 1619 */ 1620 __libc_init_tls(args); 1621 1622#if TIMING 1623 struct timeval t0, t1; 1624 gettimeofday(&t0, 0); 1625#endif 1626 1627 // Initialize environment functions, and get to the ELF aux vectors table. 1628 linker_env_init(args); 1629 1630 // If this is a setuid/setgid program, close the security hole described in 1631 // ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc 1632 if (get_AT_SECURE()) { 1633 nullify_closed_stdio(); 1634 } 1635 1636 debuggerd_init(); 1637 1638 // Get a few environment variables. 1639 const char* LD_DEBUG = linker_env_get("LD_DEBUG"); 1640 if (LD_DEBUG != NULL) { 1641 gLdDebugVerbosity = atoi(LD_DEBUG); 1642 } 1643 1644 // Normally, these are cleaned by linker_env_init, but the test 1645 // doesn't cost us anything. 1646 const char* ldpath_env = NULL; 1647 const char* ldpreload_env = NULL; 1648 if (!get_AT_SECURE()) { 1649 ldpath_env = linker_env_get("LD_LIBRARY_PATH"); 1650 ldpreload_env = linker_env_get("LD_PRELOAD"); 1651 } 1652 1653 INFO("[ android linker & debugger ]"); 1654 1655 soinfo* si = soinfo_alloc(args.argv[0]); 1656 if (si == NULL) { 1657 exit(EXIT_FAILURE); 1658 } 1659 1660 /* bootstrap the link map, the main exe always needs to be first */ 1661 si->flags |= FLAG_EXE; 1662 link_map_t* map = &(si->link_map); 1663 1664 map->l_addr = 0; 1665 map->l_name = args.argv[0]; 1666 map->l_prev = NULL; 1667 map->l_next = NULL; 1668 1669 _r_debug.r_map = map; 1670 r_debug_tail = map; 1671 1672 /* gdb expects the linker to be in the debug shared object list. 1673 * Without this, gdb has trouble locating the linker's ".text" 1674 * and ".plt" sections. Gdb could also potentially use this to 1675 * relocate the offset of our exported 'rtld_db_dlactivity' symbol. 1676 * Don't use soinfo_alloc(), because the linker shouldn't 1677 * be on the soinfo list. 1678 */ 1679 { 1680 static soinfo linker_soinfo; 1681 strlcpy(linker_soinfo.name, "/system/bin/linker", sizeof(linker_soinfo.name)); 1682 linker_soinfo.flags = 0; 1683 linker_soinfo.base = linker_base; 1684 1685 /* 1686 * Set the dynamic field in the link map otherwise gdb will complain with 1687 * the following: 1688 * warning: .dynamic section for "/system/bin/linker" is not at the 1689 * expected address (wrong library or version mismatch?) 1690 */ 1691 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base; 1692 Elf32_Phdr *phdr = (Elf32_Phdr*)((unsigned char*) linker_base + elf_hdr->e_phoff); 1693 phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, 1694 &linker_soinfo.dynamic, NULL, NULL); 1695 insert_soinfo_into_debug_map(&linker_soinfo); 1696 } 1697 1698 // Extract information passed from the kernel. 1699 si->phdr = reinterpret_cast<Elf32_Phdr*>(args.getauxval(AT_PHDR)); 1700 si->phnum = args.getauxval(AT_PHNUM); 1701 si->entry = args.getauxval(AT_ENTRY); 1702 1703 /* Compute the value of si->base. We can't rely on the fact that 1704 * the first entry is the PHDR because this will not be true 1705 * for certain executables (e.g. some in the NDK unit test suite) 1706 */ 1707 si->base = 0; 1708 si->size = phdr_table_get_load_size(si->phdr, si->phnum); 1709 si->load_bias = 0; 1710 for (size_t i = 0; i < si->phnum; ++i) { 1711 if (si->phdr[i].p_type == PT_PHDR) { 1712 si->load_bias = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_vaddr; 1713 si->base = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_offset; 1714 break; 1715 } 1716 } 1717 si->dynamic = NULL; 1718 si->ref_count = 1; 1719 1720 // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). 1721 parse_LD_LIBRARY_PATH(ldpath_env); 1722 parse_LD_PRELOAD(ldpreload_env); 1723 1724 somain = si; 1725 1726 if (!soinfo_link_image(si)) { 1727 __libc_format_fd(2, "CANNOT LINK EXECUTABLE: %s\n", linker_get_error_buffer()); 1728 exit(EXIT_FAILURE); 1729 } 1730 1731 add_vdso(args); 1732 1733 si->CallPreInitConstructors(); 1734 1735 for (size_t i = 0; gLdPreloads[i] != NULL; ++i) { 1736 gLdPreloads[i]->CallConstructors(); 1737 } 1738 1739 /* After the link_image, the si->load_bias is initialized. 1740 * For so lib, the map->l_addr will be updated in notify_gdb_of_load. 1741 * We need to update this value for so exe here. So Unwind_Backtrace 1742 * for some arch like x86 could work correctly within so exe. 1743 */ 1744 map->l_addr = si->load_bias; 1745 si->CallConstructors(); 1746 1747#if TIMING 1748 gettimeofday(&t1,NULL); 1749 PRINT("LINKER TIME: %s: %d microseconds", args.argv[0], (int) ( 1750 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - 1751 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) 1752 )); 1753#endif 1754#if STATS 1755 PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", args.argv[0], 1756 linker_stats.count[kRelocAbsolute], 1757 linker_stats.count[kRelocRelative], 1758 linker_stats.count[kRelocCopy], 1759 linker_stats.count[kRelocSymbol]); 1760#endif 1761#if COUNT_PAGES 1762 { 1763 unsigned n; 1764 unsigned i; 1765 unsigned count = 0; 1766 for (n = 0; n < 4096; n++) { 1767 if (bitmask[n]) { 1768 unsigned x = bitmask[n]; 1769 for (i = 0; i < 8; i++) { 1770 if (x & 1) { 1771 count++; 1772 } 1773 x >>= 1; 1774 } 1775 } 1776 } 1777 PRINT("PAGES MODIFIED: %s: %d (%dKB)", args.argv[0], count, count * 4); 1778 } 1779#endif 1780 1781#if TIMING || STATS || COUNT_PAGES 1782 fflush(stdout); 1783#endif 1784 1785 TRACE("[ Ready to execute '%s' @ 0x%08x ]", si->name, si->entry); 1786 return si->entry; 1787} 1788 1789/* Compute the load-bias of an existing executable. This shall only 1790 * be used to compute the load bias of an executable or shared library 1791 * that was loaded by the kernel itself. 1792 * 1793 * Input: 1794 * elf -> address of ELF header, assumed to be at the start of the file. 1795 * Return: 1796 * load bias, i.e. add the value of any p_vaddr in the file to get 1797 * the corresponding address in memory. 1798 */ 1799static Elf32_Addr get_elf_exec_load_bias(const Elf32_Ehdr* elf) { 1800 Elf32_Addr offset = elf->e_phoff; 1801 const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset); 1802 const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum; 1803 1804 for (const Elf32_Phdr* phdr = phdr_table; phdr < phdr_end; phdr++) { 1805 if (phdr->p_type == PT_LOAD) { 1806 return reinterpret_cast<Elf32_Addr>(elf) + phdr->p_offset - phdr->p_vaddr; 1807 } 1808 } 1809 return 0; 1810} 1811 1812/* 1813 * This is the entry point for the linker, called from begin.S. This 1814 * method is responsible for fixing the linker's own relocations, and 1815 * then calling __linker_init_post_relocation(). 1816 * 1817 * Because this method is called before the linker has fixed it's own 1818 * relocations, any attempt to reference an extern variable, extern 1819 * function, or other GOT reference will generate a segfault. 1820 */ 1821extern "C" Elf32_Addr __linker_init(void* raw_args) { 1822 KernelArgumentBlock args(raw_args); 1823 1824 Elf32_Addr linker_addr = args.getauxval(AT_BASE); 1825 1826 Elf32_Ehdr* elf_hdr = (Elf32_Ehdr*) linker_addr; 1827 Elf32_Phdr* phdr = (Elf32_Phdr*)((unsigned char*) linker_addr + elf_hdr->e_phoff); 1828 1829 soinfo linker_so; 1830 memset(&linker_so, 0, sizeof(soinfo)); 1831 1832 linker_so.base = linker_addr; 1833 linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); 1834 linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); 1835 linker_so.dynamic = NULL; 1836 linker_so.phdr = phdr; 1837 linker_so.phnum = elf_hdr->e_phnum; 1838 linker_so.flags |= FLAG_LINKER; 1839 1840 if (!soinfo_link_image(&linker_so)) { 1841 // It would be nice to print an error message, but if the linker 1842 // can't link itself, there's no guarantee that we'll be able to 1843 // call write() (because it involves a GOT reference). 1844 // 1845 // This situation should never occur unless the linker itself 1846 // is corrupt. 1847 exit(EXIT_FAILURE); 1848 } 1849 1850 // We have successfully fixed our own relocations. It's safe to run 1851 // the main part of the linker now. 1852 args.abort_message_ptr = &gAbortMessage; 1853 Elf32_Addr start_address = __linker_init_post_relocation(args, linker_addr); 1854 1855 set_soinfo_pool_protection(PROT_READ); 1856 1857 // Return the address that the calling assembly stub should jump to. 1858 return start_address; 1859} 1860