linker.cpp revision 8f7120bbacb0bb7a8aca1102f76f64a462f40231
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 108enum RelocationKind { 109 kRelocAbsolute = 0, 110 kRelocRelative, 111 kRelocCopy, 112 kRelocSymbol, 113 kRelocMax 114}; 115 116#if STATS 117struct linker_stats_t { 118 int count[kRelocMax]; 119}; 120 121static linker_stats_t linker_stats; 122 123static void count_relocation(RelocationKind kind) { 124 ++linker_stats.count[kind]; 125} 126#else 127static void count_relocation(RelocationKind) { 128} 129#endif 130 131#if COUNT_PAGES 132static unsigned bitmask[4096]; 133#define MARK(offset) \ 134 do { \ 135 bitmask[((offset) >> 12) >> 3] |= (1 << (((offset) >> 12) & 7)); \ 136 } while(0) 137#else 138#define MARK(x) do {} while (0) 139#endif 140 141// You shouldn't try to call memory-allocating functions in the dynamic linker. 142// Guard against the most obvious ones. 143#define DISALLOW_ALLOCATION(return_type, name, ...) \ 144 return_type name __VA_ARGS__ \ 145 { \ 146 const char* msg = "ERROR: " #name " called from the dynamic linker!\n"; \ 147 __libc_format_log(ANDROID_LOG_FATAL, "linker", "%s", msg); \ 148 write(2, msg, strlen(msg)); \ 149 abort(); \ 150 } 151#define UNUSED __attribute__((unused)) 152DISALLOW_ALLOCATION(void*, malloc, (size_t u UNUSED)); 153DISALLOW_ALLOCATION(void, free, (void* u UNUSED)); 154DISALLOW_ALLOCATION(void*, realloc, (void* u1 UNUSED, size_t u2 UNUSED)); 155DISALLOW_ALLOCATION(void*, calloc, (size_t u1 UNUSED, size_t u2 UNUSED)); 156 157static char tmp_err_buf[768]; 158static char __linker_dl_err_buf[768]; 159 160char* linker_get_error_buffer() { 161 return &__linker_dl_err_buf[0]; 162} 163 164size_t linker_get_error_buffer_size() { 165 return sizeof(__linker_dl_err_buf); 166} 167 168/* 169 * This function is an empty stub where GDB locates a breakpoint to get notified 170 * about linker activity. 171 */ 172extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(); 173 174static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, 175 RT_CONSISTENT, 0}; 176static link_map_t* r_debug_tail = 0; 177 178static pthread_mutex_t gDebugMutex = PTHREAD_MUTEX_INITIALIZER; 179 180static void insert_soinfo_into_debug_map(soinfo * info) { 181 // Copy the necessary fields into the debug structure. 182 link_map_t* map = &(info->link_map); 183 map->l_addr = info->base; 184 map->l_name = (char*) info->name; 185 map->l_ld = (uintptr_t)info->dynamic; 186 187 /* Stick the new library at the end of the list. 188 * gdb tends to care more about libc than it does 189 * about leaf libraries, and ordering it this way 190 * reduces the back-and-forth over the wire. 191 */ 192 if (r_debug_tail) { 193 r_debug_tail->l_next = map; 194 map->l_prev = r_debug_tail; 195 map->l_next = 0; 196 } else { 197 _r_debug.r_map = map; 198 map->l_prev = 0; 199 map->l_next = 0; 200 } 201 r_debug_tail = map; 202} 203 204static void remove_soinfo_from_debug_map(soinfo* info) { 205 link_map_t* map = &(info->link_map); 206 207 if (r_debug_tail == map) { 208 r_debug_tail = map->l_prev; 209 } 210 211 if (map->l_prev) { 212 map->l_prev->l_next = map->l_next; 213 } 214 if (map->l_next) { 215 map->l_next->l_prev = map->l_prev; 216 } 217} 218 219static void notify_gdb_of_load(soinfo* info) { 220 if (info->flags & FLAG_EXE) { 221 // GDB already knows about the main executable 222 return; 223 } 224 225 ScopedPthreadMutexLocker locker(&gDebugMutex); 226 227 _r_debug.r_state = RT_ADD; 228 rtld_db_dlactivity(); 229 230 insert_soinfo_into_debug_map(info); 231 232 _r_debug.r_state = RT_CONSISTENT; 233 rtld_db_dlactivity(); 234} 235 236static void notify_gdb_of_unload(soinfo* info) { 237 if (info->flags & FLAG_EXE) { 238 // GDB already knows about the main executable 239 return; 240 } 241 242 ScopedPthreadMutexLocker locker(&gDebugMutex); 243 244 _r_debug.r_state = RT_DELETE; 245 rtld_db_dlactivity(); 246 247 remove_soinfo_from_debug_map(info); 248 249 _r_debug.r_state = RT_CONSISTENT; 250 rtld_db_dlactivity(); 251} 252 253void notify_gdb_of_libraries() { 254 _r_debug.r_state = RT_ADD; 255 rtld_db_dlactivity(); 256 _r_debug.r_state = RT_CONSISTENT; 257 rtld_db_dlactivity(); 258} 259 260static bool ensure_free_list_non_empty() { 261 if (gSoInfoFreeList != NULL) { 262 return true; 263 } 264 265 // Allocate a new pool. 266 soinfo_pool_t* pool = reinterpret_cast<soinfo_pool_t*>(mmap(NULL, sizeof(*pool), 267 PROT_READ|PROT_WRITE, 268 MAP_PRIVATE|MAP_ANONYMOUS, 0, 0)); 269 if (pool == MAP_FAILED) { 270 return false; 271 } 272 273 // Add the pool to our list of pools. 274 pool->next = gSoInfoPools; 275 gSoInfoPools = pool; 276 277 // Chain the entries in the new pool onto the free list. 278 gSoInfoFreeList = &pool->info[0]; 279 soinfo* next = NULL; 280 for (int i = SOINFO_PER_POOL - 1; i >= 0; --i) { 281 pool->info[i].next = next; 282 next = &pool->info[i]; 283 } 284 285 return true; 286} 287 288static void set_soinfo_pool_protection(int protection) { 289 for (soinfo_pool_t* p = gSoInfoPools; p != NULL; p = p->next) { 290 if (mprotect(p, sizeof(*p), protection) == -1) { 291 abort(); // Can't happen. 292 } 293 } 294} 295 296static soinfo* soinfo_alloc(const char* name) { 297 if (strlen(name) >= SOINFO_NAME_LEN) { 298 DL_ERR("library name \"%s\" too long", name); 299 return NULL; 300 } 301 302 if (!ensure_free_list_non_empty()) { 303 DL_ERR("out of memory when loading \"%s\"", name); 304 return NULL; 305 } 306 307 // Take the head element off the free list. 308 soinfo* si = gSoInfoFreeList; 309 gSoInfoFreeList = gSoInfoFreeList->next; 310 311 // Initialize the new element. 312 memset(si, 0, sizeof(soinfo)); 313 strlcpy(si->name, name, sizeof(si->name)); 314 sonext->next = si; 315 sonext = si; 316 317 TRACE("name %s: allocated soinfo @ %p", name, si); 318 return si; 319} 320 321static void soinfo_free(soinfo* si) 322{ 323 if (si == NULL) { 324 return; 325 } 326 327 soinfo *prev = NULL, *trav; 328 329 TRACE("name %s: freeing soinfo @ %p", si->name, si); 330 331 for (trav = solist; trav != NULL; trav = trav->next) { 332 if (trav == si) 333 break; 334 prev = trav; 335 } 336 if (trav == NULL) { 337 /* si was not in solist */ 338 DL_ERR("name \"%s\" is not in solist!", si->name); 339 return; 340 } 341 342 /* prev will never be NULL, because the first entry in solist is 343 always the static libdl_info. 344 */ 345 prev->next = si->next; 346 if (si == sonext) { 347 sonext = prev; 348 } 349 si->next = gSoInfoFreeList; 350 gSoInfoFreeList = si; 351} 352 353 354static void parse_path(const char* path, const char* delimiters, 355 const char** array, char* buf, size_t buf_size, size_t max_count) { 356 if (path == NULL) { 357 return; 358 } 359 360 size_t len = strlcpy(buf, path, buf_size); 361 362 size_t i = 0; 363 char* buf_p = buf; 364 while (i < max_count && (array[i] = strsep(&buf_p, delimiters))) { 365 if (*array[i] != '\0') { 366 ++i; 367 } 368 } 369 370 // Forget the last path if we had to truncate; this occurs if the 2nd to 371 // last char isn't '\0' (i.e. wasn't originally a delimiter). 372 if (i > 0 && len >= buf_size && buf[buf_size - 2] != '\0') { 373 array[i - 1] = NULL; 374 } else { 375 array[i] = NULL; 376 } 377} 378 379static void parse_LD_LIBRARY_PATH(const char* path) { 380 parse_path(path, ":", gLdPaths, 381 gLdPathsBuffer, sizeof(gLdPathsBuffer), LDPATH_MAX); 382} 383 384static void parse_LD_PRELOAD(const char* path) { 385 // We have historically supported ':' as well as ' ' in LD_PRELOAD. 386 parse_path(path, " :", gLdPreloadNames, 387 gLdPreloadsBuffer, sizeof(gLdPreloadsBuffer), LDPRELOAD_MAX); 388} 389 390#ifdef ANDROID_ARM_LINKER 391 392/* For a given PC, find the .so that it belongs to. 393 * Returns the base address of the .ARM.exidx section 394 * for that .so, and the number of 8-byte entries 395 * in that section (via *pcount). 396 * 397 * Intended to be called by libc's __gnu_Unwind_Find_exidx(). 398 * 399 * This function is exposed via dlfcn.cpp and libdl.so. 400 */ 401_Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount) 402{ 403 soinfo *si; 404 unsigned addr = (unsigned)pc; 405 406 for (si = solist; si != 0; si = si->next){ 407 if ((addr >= si->base) && (addr < (si->base + si->size))) { 408 *pcount = si->ARM_exidx_count; 409 return (_Unwind_Ptr)si->ARM_exidx; 410 } 411 } 412 *pcount = 0; 413 return NULL; 414} 415 416#elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) 417 418/* Here, we only have to provide a callback to iterate across all the 419 * loaded libraries. gcc_eh does the rest. */ 420int 421dl_iterate_phdr(int (*cb)(dl_phdr_info *info, size_t size, void *data), 422 void *data) 423{ 424 int rv = 0; 425 for (soinfo* si = solist; si != NULL; si = si->next) { 426 dl_phdr_info dl_info; 427 dl_info.dlpi_addr = si->link_map.l_addr; 428 dl_info.dlpi_name = si->link_map.l_name; 429 dl_info.dlpi_phdr = si->phdr; 430 dl_info.dlpi_phnum = si->phnum; 431 rv = cb(&dl_info, sizeof(dl_phdr_info), data); 432 if (rv != 0) { 433 break; 434 } 435 } 436 return rv; 437} 438 439#endif 440 441static Elf32_Sym* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name) { 442 Elf32_Sym* s; 443 Elf32_Sym* symtab = si->symtab; 444 const char* strtab = si->strtab; 445 unsigned n; 446 447 TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %d", 448 name, si->name, si->base, hash, hash % si->nbucket); 449 n = hash % si->nbucket; 450 451 for (n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]) { 452 s = symtab + n; 453 if (strcmp(strtab + s->st_name, name)) continue; 454 455 /* only concern ourselves with global and weak symbol definitions */ 456 switch(ELF32_ST_BIND(s->st_info)){ 457 case STB_GLOBAL: 458 case STB_WEAK: 459 if (s->st_shndx == SHN_UNDEF) { 460 continue; 461 } 462 463 TRACE_TYPE(LOOKUP, "FOUND %s in %s (%08x) %d", 464 name, si->name, s->st_value, s->st_size); 465 return s; 466 } 467 } 468 469 return NULL; 470} 471 472static unsigned elfhash(const char* _name) { 473 const unsigned char* name = (const unsigned char*) _name; 474 unsigned h = 0, g; 475 476 while(*name) { 477 h = (h << 4) + *name++; 478 g = h & 0xf0000000; 479 h ^= g; 480 h ^= g >> 24; 481 } 482 return h; 483} 484 485static Elf32_Sym* soinfo_do_lookup(soinfo* si, const char* name, soinfo** lsi, soinfo* needed[]) { 486 unsigned elf_hash = elfhash(name); 487 Elf32_Sym* s = NULL; 488 489 if (si != NULL && somain != NULL) { 490 491 /* 492 * Local scope is executable scope. Just start looking into it right away 493 * for the shortcut. 494 */ 495 496 if (si == somain) { 497 s = soinfo_elf_lookup(si, elf_hash, name); 498 if (s != NULL) { 499 *lsi = si; 500 goto done; 501 } 502 } else { 503 /* Order of symbol lookup is controlled by DT_SYMBOLIC flag */ 504 505 /* 506 * If this object was built with symbolic relocations disabled, the 507 * first place to look to resolve external references is the main 508 * executable. 509 */ 510 511 if (!si->has_DT_SYMBOLIC) { 512 DEBUG("%s: looking up %s in executable %s", 513 si->name, name, somain->name); 514 s = soinfo_elf_lookup(somain, elf_hash, name); 515 if (s != NULL) { 516 *lsi = somain; 517 goto done; 518 } 519 } 520 521 /* Look for symbols in the local scope (the object who is 522 * searching). This happens with C++ templates on i386 for some 523 * reason. 524 * 525 * Notes on weak symbols: 526 * The ELF specs are ambiguous about treatment of weak definitions in 527 * dynamic linking. Some systems return the first definition found 528 * and some the first non-weak definition. This is system dependent. 529 * Here we return the first definition found for simplicity. */ 530 531 s = soinfo_elf_lookup(si, elf_hash, name); 532 if (s != NULL) { 533 *lsi = si; 534 goto done; 535 } 536 537 /* 538 * If this object was built with -Bsymbolic and symbol is not found 539 * in the local scope, try to find the symbol in the main executable. 540 */ 541 542 if (si->has_DT_SYMBOLIC) { 543 DEBUG("%s: looking up %s in executable %s after local scope", 544 si->name, name, somain->name); 545 s = soinfo_elf_lookup(somain, elf_hash, name); 546 if (s != NULL) { 547 *lsi = somain; 548 goto done; 549 } 550 } 551 } 552 } 553 554 /* Next, look for it in the preloads list */ 555 for (int i = 0; gLdPreloads[i] != NULL; i++) { 556 s = soinfo_elf_lookup(gLdPreloads[i], elf_hash, name); 557 if (s != NULL) { 558 *lsi = gLdPreloads[i]; 559 goto done; 560 } 561 } 562 563 for (int i = 0; needed[i] != NULL; i++) { 564 DEBUG("%s: looking up %s in %s", 565 si->name, name, needed[i]->name); 566 s = soinfo_elf_lookup(needed[i], elf_hash, name); 567 if (s != NULL) { 568 *lsi = needed[i]; 569 goto done; 570 } 571 } 572 573done: 574 if (s != NULL) { 575 TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = 0x%08x, " 576 "found in %s, base = 0x%08x, load bias = 0x%08x", 577 si->name, name, s->st_value, 578 (*lsi)->name, (*lsi)->base, (*lsi)->load_bias); 579 return s; 580 } 581 582 return NULL; 583} 584 585/* This is used by dlsym(3). It performs symbol lookup only within the 586 specified soinfo object and not in any of its dependencies. 587 588 TODO: Only looking in the specified soinfo seems wrong. dlsym(3) says 589 that it should do a breadth first search through the dependency 590 tree. This agrees with the ELF spec (aka System V Application 591 Binary Interface) where in Chapter 5 it discuss resolving "Shared 592 Object Dependencies" in breadth first search order. 593 */ 594Elf32_Sym* dlsym_handle_lookup(soinfo* si, const char* name) 595{ 596 return soinfo_elf_lookup(si, elfhash(name), name); 597} 598 599/* This is used by dlsym(3) to performs a global symbol lookup. If the 600 start value is null (for RTLD_DEFAULT), the search starts at the 601 beginning of the global solist. Otherwise the search starts at the 602 specified soinfo (for RTLD_NEXT). 603 */ 604Elf32_Sym* dlsym_linear_lookup(const char* name, soinfo** found, soinfo* start) { 605 unsigned elf_hash = elfhash(name); 606 607 if (start == NULL) { 608 start = solist; 609 } 610 611 Elf32_Sym* s = NULL; 612 for (soinfo* si = start; (s == NULL) && (si != NULL); si = si->next) { 613 s = soinfo_elf_lookup(si, elf_hash, name); 614 if (s != NULL) { 615 *found = si; 616 break; 617 } 618 } 619 620 if (s != NULL) { 621 TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, found->base = 0x%08x", 622 name, s->st_value, (*found)->base); 623 } 624 625 return s; 626} 627 628soinfo* find_containing_library(const void* p) { 629 Elf32_Addr address = reinterpret_cast<Elf32_Addr>(p); 630 for (soinfo* si = solist; si != NULL; si = si->next) { 631 if (address >= si->base && address - si->base < si->size) { 632 return si; 633 } 634 } 635 return NULL; 636} 637 638Elf32_Sym* dladdr_find_symbol(soinfo* si, const void* addr) { 639 Elf32_Addr soaddr = reinterpret_cast<Elf32_Addr>(addr) - si->base; 640 641 // Search the library's symbol table for any defined symbol which 642 // contains this address. 643 for (size_t i = 0; i < si->nchain; ++i) { 644 Elf32_Sym* sym = &si->symtab[i]; 645 if (sym->st_shndx != SHN_UNDEF && 646 soaddr >= sym->st_value && 647 soaddr < sym->st_value + sym->st_size) { 648 return sym; 649 } 650 } 651 652 return NULL; 653} 654 655#if 0 656static void dump(soinfo* si) 657{ 658 Elf32_Sym* s = si->symtab; 659 for (unsigned n = 0; n < si->nchain; n++) { 660 TRACE("%04d> %08x: %02x %04x %08x %08x %s", n, s, 661 s->st_info, s->st_shndx, s->st_value, s->st_size, 662 si->strtab + s->st_name); 663 s++; 664 } 665} 666#endif 667 668static int open_library_on_path(const char* name, const char* const paths[]) { 669 char buf[512]; 670 for (size_t i = 0; paths[i] != NULL; ++i) { 671 int n = __libc_format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name); 672 if (n < 0 || n >= static_cast<int>(sizeof(buf))) { 673 PRINT("Warning: ignoring very long library path: %s/%s", paths[i], name); 674 continue; 675 } 676 int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC)); 677 if (fd != -1) { 678 return fd; 679 } 680 } 681 return -1; 682} 683 684static int open_library(const char* name) { 685 TRACE("[ opening %s ]", name); 686 687 // If the name contains a slash, we should attempt to open it directly and not search the paths. 688 if (strchr(name, '/') != NULL) { 689 int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC)); 690 if (fd != -1) { 691 return fd; 692 } 693 // ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now. 694 } 695 696 // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths. 697 int fd = open_library_on_path(name, gLdPaths); 698 if (fd == -1) { 699 fd = open_library_on_path(name, gSoPaths); 700 } 701 return fd; 702} 703 704static soinfo* load_library(const char* name) { 705 // Open the file. 706 int fd = open_library(name); 707 if (fd == -1) { 708 DL_ERR("library \"%s\" not found", name); 709 return NULL; 710 } 711 712 // Read the ELF header and load the segments. 713 ElfReader elf_reader(name, fd); 714 if (!elf_reader.Load()) { 715 return NULL; 716 } 717 718 const char* bname = strrchr(name, '/'); 719 soinfo* si = soinfo_alloc(bname ? bname + 1 : name); 720 if (si == NULL) { 721 return NULL; 722 } 723 si->base = elf_reader.load_start(); 724 si->size = elf_reader.load_size(); 725 si->load_bias = elf_reader.load_bias(); 726 si->flags = 0; 727 si->entry = 0; 728 si->dynamic = NULL; 729 si->phnum = elf_reader.phdr_count(); 730 si->phdr = elf_reader.loaded_phdr(); 731 return si; 732} 733 734static soinfo *find_loaded_library(const char *name) 735{ 736 soinfo *si; 737 const char *bname; 738 739 // TODO: don't use basename only for determining libraries 740 // http://code.google.com/p/android/issues/detail?id=6670 741 742 bname = strrchr(name, '/'); 743 bname = bname ? bname + 1 : name; 744 745 for (si = solist; si != NULL; si = si->next) { 746 if (!strcmp(bname, si->name)) { 747 return si; 748 } 749 } 750 return NULL; 751} 752 753static soinfo* find_library_internal(const char* name) { 754 if (name == NULL) { 755 return somain; 756 } 757 758 soinfo* si = find_loaded_library(name); 759 if (si != NULL) { 760 if (si->flags & FLAG_LINKED) { 761 return si; 762 } 763 DL_ERR("OOPS: recursive link to \"%s\"", si->name); 764 return NULL; 765 } 766 767 TRACE("[ '%s' has not been loaded yet. Locating...]", name); 768 si = load_library(name); 769 if (si == NULL) { 770 return NULL; 771 } 772 773 // At this point we know that whatever is loaded @ base is a valid ELF 774 // shared library whose segments are properly mapped in. 775 TRACE("[ init_library base=0x%08x sz=0x%08x name='%s' ]", 776 si->base, si->size, si->name); 777 778 if (!soinfo_link_image(si)) { 779 munmap(reinterpret_cast<void*>(si->base), si->size); 780 soinfo_free(si); 781 return NULL; 782 } 783 784 return si; 785} 786 787static soinfo* find_library(const char* name) { 788 soinfo* si = find_library_internal(name); 789 if (si != NULL) { 790 si->ref_count++; 791 } 792 return si; 793} 794 795static int soinfo_unload(soinfo* si) { 796 if (si->ref_count == 1) { 797 TRACE("unloading '%s'", si->name); 798 si->CallDestructors(); 799 800 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 801 if (d->d_tag == DT_NEEDED) { 802 const char* library_name = si->strtab + d->d_un.d_val; 803 soinfo* lsi = find_loaded_library(library_name); 804 if (lsi != NULL) { 805 TRACE("%s needs to unload %s", si->name, lsi->name); 806 soinfo_unload(lsi); 807 } else { 808 // TODO: should we return -1 in this case? 809 DL_ERR("\"%s\": could not unload dependent library", si->name); 810 } 811 } 812 } 813 814 munmap(reinterpret_cast<void*>(si->base), si->size); 815 notify_gdb_of_unload(si); 816 soinfo_free(si); 817 si->ref_count = 0; 818 } else { 819 si->ref_count--; 820 TRACE("not unloading '%s', decrementing ref_count to %d", si->name, si->ref_count); 821 } 822 return 0; 823} 824 825void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) { 826 if (!get_AT_SECURE()) { 827 parse_LD_LIBRARY_PATH(ld_library_path); 828 } 829} 830 831soinfo* do_dlopen(const char* name, int flags) { 832 if ((flags & ~(RTLD_NOW|RTLD_LAZY|RTLD_LOCAL|RTLD_GLOBAL)) != 0) { 833 DL_ERR("invalid flags to dlopen: %x", flags); 834 return NULL; 835 } 836 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 837 soinfo* si = find_library(name); 838 if (si != NULL) { 839 si->CallConstructors(); 840 } 841 set_soinfo_pool_protection(PROT_READ); 842 return si; 843} 844 845int do_dlclose(soinfo* si) { 846 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 847 int result = soinfo_unload(si); 848 set_soinfo_pool_protection(PROT_READ); 849 return result; 850} 851 852/* TODO: don't use unsigned for addrs below. It works, but is not 853 * ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned 854 * long. 855 */ 856static int soinfo_relocate(soinfo* si, Elf32_Rel* rel, unsigned count, 857 soinfo* needed[]) 858{ 859 Elf32_Sym* symtab = si->symtab; 860 const char* strtab = si->strtab; 861 Elf32_Sym* s; 862 Elf32_Rel* start = rel; 863 soinfo* lsi; 864 865 for (size_t idx = 0; idx < count; ++idx, ++rel) { 866 unsigned type = ELF32_R_TYPE(rel->r_info); 867 unsigned sym = ELF32_R_SYM(rel->r_info); 868 Elf32_Addr reloc = static_cast<Elf32_Addr>(rel->r_offset + si->load_bias); 869 Elf32_Addr sym_addr = 0; 870 char* sym_name = NULL; 871 872 DEBUG("Processing '%s' relocation at index %d", si->name, idx); 873 if (type == 0) { // R_*_NONE 874 continue; 875 } 876 if (sym != 0) { 877 sym_name = (char *)(strtab + symtab[sym].st_name); 878 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 879 if (s == NULL) { 880 /* We only allow an undefined symbol if this is a weak 881 reference.. */ 882 s = &symtab[sym]; 883 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 884 DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); 885 return -1; 886 } 887 888 /* IHI0044C AAELF 4.5.1.1: 889 890 Libraries are not searched to resolve weak references. 891 It is not an error for a weak reference to remain 892 unsatisfied. 893 894 During linking, the value of an undefined weak reference is: 895 - Zero if the relocation type is absolute 896 - The address of the place if the relocation is pc-relative 897 - The address of nominal base address if the relocation 898 type is base-relative. 899 */ 900 901 switch (type) { 902#if defined(ANDROID_ARM_LINKER) 903 case R_ARM_JUMP_SLOT: 904 case R_ARM_GLOB_DAT: 905 case R_ARM_ABS32: 906 case R_ARM_RELATIVE: /* Don't care. */ 907#elif defined(ANDROID_X86_LINKER) 908 case R_386_JMP_SLOT: 909 case R_386_GLOB_DAT: 910 case R_386_32: 911 case R_386_RELATIVE: /* Dont' care. */ 912#endif /* ANDROID_*_LINKER */ 913 /* sym_addr was initialized to be zero above or relocation 914 code below does not care about value of sym_addr. 915 No need to do anything. */ 916 break; 917 918#if defined(ANDROID_X86_LINKER) 919 case R_386_PC32: 920 sym_addr = reloc; 921 break; 922#endif /* ANDROID_X86_LINKER */ 923 924#if defined(ANDROID_ARM_LINKER) 925 case R_ARM_COPY: 926 /* Fall through. Can't really copy if weak symbol is 927 not found in run-time. */ 928#endif /* ANDROID_ARM_LINKER */ 929 default: 930 DL_ERR("unknown weak reloc type %d @ %p (%d)", 931 type, rel, (int) (rel - start)); 932 return -1; 933 } 934 } else { 935 /* We got a definition. */ 936#if 0 937 if ((base == 0) && (si->base != 0)) { 938 /* linking from libraries to main image is bad */ 939 DL_ERR("cannot locate \"%s\"...", 940 strtab + symtab[sym].st_name); 941 return -1; 942 } 943#endif 944 sym_addr = static_cast<Elf32_Addr>(s->st_value + lsi->load_bias); 945 } 946 count_relocation(kRelocSymbol); 947 } else { 948 s = NULL; 949 } 950 951/* TODO: This is ugly. Split up the relocations by arch into 952 * different files. 953 */ 954 switch(type){ 955#if defined(ANDROID_ARM_LINKER) 956 case R_ARM_JUMP_SLOT: 957 count_relocation(kRelocAbsolute); 958 MARK(rel->r_offset); 959 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 960 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 961 break; 962 case R_ARM_GLOB_DAT: 963 count_relocation(kRelocAbsolute); 964 MARK(rel->r_offset); 965 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 966 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 967 break; 968 case R_ARM_ABS32: 969 count_relocation(kRelocAbsolute); 970 MARK(rel->r_offset); 971 TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s", reloc, sym_addr, sym_name); 972 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 973 break; 974 case R_ARM_REL32: 975 count_relocation(kRelocRelative); 976 MARK(rel->r_offset); 977 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s", 978 reloc, sym_addr, rel->r_offset, sym_name); 979 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr - rel->r_offset; 980 break; 981#elif defined(ANDROID_X86_LINKER) 982 case R_386_JMP_SLOT: 983 count_relocation(kRelocAbsolute); 984 MARK(rel->r_offset); 985 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); 986 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 987 break; 988 case R_386_GLOB_DAT: 989 count_relocation(kRelocAbsolute); 990 MARK(rel->r_offset); 991 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); 992 *reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr; 993 break; 994#elif defined(ANDROID_MIPS_LINKER) 995 case R_MIPS_REL32: 996 count_relocation(kRelocAbsolute); 997 MARK(rel->r_offset); 998 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s", 999 reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); 1000 if (s) { 1001 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 1002 } else { 1003 *reinterpret_cast<Elf32_Addr*>(reloc) += si->base; 1004 } 1005 break; 1006#endif /* ANDROID_*_LINKER */ 1007 1008#if defined(ANDROID_ARM_LINKER) 1009 case R_ARM_RELATIVE: 1010#elif defined(ANDROID_X86_LINKER) 1011 case R_386_RELATIVE: 1012#endif /* ANDROID_*_LINKER */ 1013 count_relocation(kRelocRelative); 1014 MARK(rel->r_offset); 1015 if (sym) { 1016 DL_ERR("odd RELATIVE form..."); 1017 return -1; 1018 } 1019 TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x", reloc, si->base); 1020 *reinterpret_cast<Elf32_Addr*>(reloc) += si->base; 1021 break; 1022 1023#if defined(ANDROID_X86_LINKER) 1024 case R_386_32: 1025 count_relocation(kRelocRelative); 1026 MARK(rel->r_offset); 1027 1028 TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s", reloc, sym_addr, sym_name); 1029 *reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr; 1030 break; 1031 1032 case R_386_PC32: 1033 count_relocation(kRelocRelative); 1034 MARK(rel->r_offset); 1035 TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s", 1036 reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); 1037 *reinterpret_cast<Elf32_Addr*>(reloc) += (sym_addr - reloc); 1038 break; 1039#endif /* ANDROID_X86_LINKER */ 1040 1041#ifdef ANDROID_ARM_LINKER 1042 case R_ARM_COPY: 1043 if ((si->flags & FLAG_EXE) == 0) { 1044 /* 1045 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf 1046 * 1047 * Section 4.7.1.10 "Dynamic relocations" 1048 * R_ARM_COPY may only appear in executable objects where e_type is 1049 * set to ET_EXEC. 1050 * 1051 * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. 1052 * We should explicitly disallow ET_DYN executables from having 1053 * R_ARM_COPY relocations. 1054 */ 1055 DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); 1056 return -1; 1057 } 1058 count_relocation(kRelocCopy); 1059 MARK(rel->r_offset); 1060 TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s", reloc, s->st_size, sym_addr, sym_name); 1061 if (reloc == sym_addr) { 1062 Elf32_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed); 1063 1064 if (src == NULL) { 1065 DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name); 1066 return -1; 1067 } 1068 if (lsi->has_DT_SYMBOLIC) { 1069 DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared " 1070 "library %s (built with -Bsymbolic?)", si->name, lsi->name); 1071 return -1; 1072 } 1073 if (s->st_size < src->st_size) { 1074 DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)", 1075 si->name, s->st_size, src->st_size); 1076 return -1; 1077 } 1078 memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size); 1079 } else { 1080 DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name); 1081 return -1; 1082 } 1083 break; 1084#endif /* ANDROID_ARM_LINKER */ 1085 1086 default: 1087 DL_ERR("unknown reloc type %d @ %p (%d)", 1088 type, rel, (int) (rel - start)); 1089 return -1; 1090 } 1091 } 1092 return 0; 1093} 1094 1095#ifdef ANDROID_MIPS_LINKER 1096static int mips_relocate_got(soinfo* si, soinfo* needed[]) { 1097 unsigned *got; 1098 unsigned local_gotno, gotsym, symtabno; 1099 Elf32_Sym *symtab, *sym; 1100 unsigned g; 1101 1102 got = si->plt_got; 1103 local_gotno = si->mips_local_gotno; 1104 gotsym = si->mips_gotsym; 1105 symtabno = si->mips_symtabno; 1106 symtab = si->symtab; 1107 1108 /* 1109 * got[0] is address of lazy resolver function 1110 * got[1] may be used for a GNU extension 1111 * set it to a recognizable address in case someone calls it 1112 * (should be _rtld_bind_start) 1113 * FIXME: maybe this should be in a separate routine 1114 */ 1115 1116 if ((si->flags & FLAG_LINKER) == 0) { 1117 g = 0; 1118 got[g++] = 0xdeadbeef; 1119 if (got[g] & 0x80000000) { 1120 got[g++] = 0xdeadfeed; 1121 } 1122 /* 1123 * Relocate the local GOT entries need to be relocated 1124 */ 1125 for (; g < local_gotno; g++) { 1126 got[g] += si->load_bias; 1127 } 1128 } 1129 1130 /* Now for the global GOT entries */ 1131 sym = symtab + gotsym; 1132 got = si->plt_got + local_gotno; 1133 for (g = gotsym; g < symtabno; g++, sym++, got++) { 1134 const char* sym_name; 1135 Elf32_Sym* s; 1136 soinfo* lsi; 1137 1138 /* This is an undefined reference... try to locate it */ 1139 sym_name = si->strtab + sym->st_name; 1140 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1141 if (s == NULL) { 1142 /* We only allow an undefined symbol if this is a weak 1143 reference.. */ 1144 s = &symtab[g]; 1145 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1146 DL_ERR("cannot locate \"%s\"...", sym_name); 1147 return -1; 1148 } 1149 *got = 0; 1150 } 1151 else { 1152 /* FIXME: is this sufficient? 1153 * For reference see NetBSD link loader 1154 * 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 1155 */ 1156 *got = lsi->load_bias + s->st_value; 1157 } 1158 } 1159 return 0; 1160} 1161#endif 1162 1163/* Please read the "Initialization and Termination functions" functions. 1164 * of the linker design note in bionic/linker/README.TXT to understand 1165 * what the following code is doing. 1166 * 1167 * The important things to remember are: 1168 * 1169 * DT_PREINIT_ARRAY must be called first for executables, and should 1170 * not appear in shared libraries. 1171 * 1172 * DT_INIT should be called before DT_INIT_ARRAY if both are present 1173 * 1174 * DT_FINI should be called after DT_FINI_ARRAY if both are present 1175 * 1176 * DT_FINI_ARRAY must be parsed in reverse order. 1177 */ 1178void soinfo::CallArray(const char* array_name UNUSED, linker_function_t* functions, size_t count, bool reverse) { 1179 if (functions == NULL) { 1180 return; 1181 } 1182 1183 TRACE("[ Calling %s (size %d) @ %p for '%s' ]", array_name, count, functions, name); 1184 1185 int begin = reverse ? (count - 1) : 0; 1186 int end = reverse ? -1 : count; 1187 int step = reverse ? -1 : 1; 1188 1189 for (int i = begin; i != end; i += step) { 1190 TRACE("[ %s[%d] == %p ]", array_name, i, functions[i]); 1191 CallFunction("function", functions[i]); 1192 } 1193 1194 TRACE("[ Done calling %s for '%s' ]", array_name, name); 1195} 1196 1197void soinfo::CallFunction(const char* function_name UNUSED, linker_function_t function) { 1198 if (function == NULL || reinterpret_cast<uintptr_t>(function) == static_cast<uintptr_t>(-1)) { 1199 return; 1200 } 1201 1202 TRACE("[ Calling %s @ %p for '%s' ]", function_name, function, name); 1203 function(); 1204 TRACE("[ Done calling %s @ %p for '%s' ]", function_name, function, name); 1205 1206 // The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures 1207 // are still writable. This happens with our debug malloc (see http://b/7941716). 1208 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 1209} 1210 1211void soinfo::CallPreInitConstructors() { 1212 CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false); 1213} 1214 1215void soinfo::CallConstructors() { 1216 if (constructors_called) { 1217 return; 1218 } 1219 1220 // We set constructors_called before actually calling the constructors, otherwise it doesn't 1221 // protect against recursive constructor calls. One simple example of constructor recursion 1222 // is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so: 1223 // 1. The program depends on libc, so libc's constructor is called here. 1224 // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. 1225 // 3. dlopen() calls the constructors on the newly created 1226 // soinfo for libc_malloc_debug_leak.so. 1227 // 4. The debug .so depends on libc, so CallConstructors is 1228 // called again with the libc soinfo. If it doesn't trigger the early- 1229 // out above, the libc constructor will be called again (recursively!). 1230 constructors_called = true; 1231 1232 if (!(flags & FLAG_EXE) && preinit_array) { 1233 DL_ERR("shared library \"%s\" has a preinit_array table @ %p", name, preinit_array); 1234 return; 1235 } 1236 1237 if (dynamic != NULL) { 1238 for (Elf32_Dyn* d = dynamic; d->d_tag != DT_NULL; ++d) { 1239 if (d->d_tag == DT_NEEDED) { 1240 const char* library_name = strtab + d->d_un.d_val; 1241 soinfo* lsi = find_loaded_library(library_name); 1242 if (lsi == NULL) { 1243 DL_ERR("\"%s\": could not initialize dependent library", name); 1244 } else { 1245 lsi->CallConstructors(); 1246 } 1247 } 1248 } 1249 } 1250 1251 CallFunction("DT_INIT", init_func); 1252 CallArray("DT_INIT_ARRAY", init_array, init_array_count, false); 1253} 1254 1255void soinfo::CallDestructors() { 1256 CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true); 1257 CallFunction("DT_FINI", fini_func); 1258} 1259 1260/* Force any of the closed stdin, stdout and stderr to be associated with 1261 /dev/null. */ 1262static int nullify_closed_stdio() { 1263 int dev_null, i, status; 1264 int return_value = 0; 1265 1266 dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 1267 if (dev_null < 0) { 1268 DL_ERR("cannot open /dev/null: %s", strerror(errno)); 1269 return -1; 1270 } 1271 TRACE("[ Opened /dev/null file-descriptor=%d]", dev_null); 1272 1273 /* If any of the stdio file descriptors is valid and not associated 1274 with /dev/null, dup /dev/null to it. */ 1275 for (i = 0; i < 3; i++) { 1276 /* If it is /dev/null already, we are done. */ 1277 if (i == dev_null) { 1278 continue; 1279 } 1280 1281 TRACE("[ Nullifying stdio file descriptor %d]", i); 1282 status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 1283 1284 /* If file is opened, we are good. */ 1285 if (status != -1) { 1286 continue; 1287 } 1288 1289 /* The only error we allow is that the file descriptor does not 1290 exist, in which case we dup /dev/null to it. */ 1291 if (errno != EBADF) { 1292 DL_ERR("fcntl failed: %s", strerror(errno)); 1293 return_value = -1; 1294 continue; 1295 } 1296 1297 /* Try dupping /dev/null to this stdio file descriptor and 1298 repeat if there is a signal. Note that any errors in closing 1299 the stdio descriptor are lost. */ 1300 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 1301 if (status < 0) { 1302 DL_ERR("dup2 failed: %s", strerror(errno)); 1303 return_value = -1; 1304 continue; 1305 } 1306 } 1307 1308 /* If /dev/null is not one of the stdio file descriptors, close it. */ 1309 if (dev_null > 2) { 1310 TRACE("[ Closing /dev/null file-descriptor=%d]", dev_null); 1311 status = TEMP_FAILURE_RETRY(close(dev_null)); 1312 if (status == -1) { 1313 DL_ERR("close failed: %s", strerror(errno)); 1314 return_value = -1; 1315 } 1316 } 1317 1318 return return_value; 1319} 1320 1321static bool soinfo_link_image(soinfo* si) { 1322 /* "base" might wrap around UINT32_MAX. */ 1323 Elf32_Addr base = si->load_bias; 1324 const Elf32_Phdr *phdr = si->phdr; 1325 int phnum = si->phnum; 1326 bool relocating_linker = (si->flags & FLAG_LINKER) != 0; 1327 1328 /* We can't debug anything until the linker is relocated */ 1329 if (!relocating_linker) { 1330 INFO("[ linking %s ]", si->name); 1331 DEBUG("si->base = 0x%08x si->flags = 0x%08x", si->base, si->flags); 1332 } 1333 1334 /* Extract dynamic section */ 1335 size_t dynamic_count; 1336 Elf32_Word dynamic_flags; 1337 phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, 1338 &dynamic_count, &dynamic_flags); 1339 if (si->dynamic == NULL) { 1340 if (!relocating_linker) { 1341 DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name); 1342 } 1343 return false; 1344 } else { 1345 if (!relocating_linker) { 1346 DEBUG("dynamic = %p", si->dynamic); 1347 } 1348 } 1349 1350#ifdef ANDROID_ARM_LINKER 1351 (void) phdr_table_get_arm_exidx(phdr, phnum, base, 1352 &si->ARM_exidx, &si->ARM_exidx_count); 1353#endif 1354 1355 /* extract useful information from dynamic section */ 1356 uint32_t needed_count = 0; 1357 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1358 DEBUG("d = %p, d[0](tag) = 0x%08x d[1](val) = 0x%08x", d, d->d_tag, d->d_un.d_val); 1359 switch(d->d_tag){ 1360 case DT_HASH: 1361 si->nbucket = ((unsigned *) (base + d->d_un.d_ptr))[0]; 1362 si->nchain = ((unsigned *) (base + d->d_un.d_ptr))[1]; 1363 si->bucket = (unsigned *) (base + d->d_un.d_ptr + 8); 1364 si->chain = (unsigned *) (base + d->d_un.d_ptr + 8 + si->nbucket * 4); 1365 break; 1366 case DT_STRTAB: 1367 si->strtab = (const char *) (base + d->d_un.d_ptr); 1368 break; 1369 case DT_SYMTAB: 1370 si->symtab = (Elf32_Sym *) (base + d->d_un.d_ptr); 1371 break; 1372 case DT_PLTREL: 1373 if (d->d_un.d_val != DT_REL) { 1374 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1375 return false; 1376 } 1377 break; 1378 case DT_JMPREL: 1379 si->plt_rel = (Elf32_Rel*) (base + d->d_un.d_ptr); 1380 break; 1381 case DT_PLTRELSZ: 1382 si->plt_rel_count = d->d_un.d_val / sizeof(Elf32_Rel); 1383 break; 1384 case DT_REL: 1385 si->rel = (Elf32_Rel*) (base + d->d_un.d_ptr); 1386 break; 1387 case DT_RELSZ: 1388 si->rel_count = d->d_un.d_val / sizeof(Elf32_Rel); 1389 break; 1390 case DT_PLTGOT: 1391 /* Save this in case we decide to do lazy binding. We don't yet. */ 1392 si->plt_got = (unsigned *)(base + d->d_un.d_ptr); 1393 break; 1394 case DT_DEBUG: 1395 // Set the DT_DEBUG entry to the address of _r_debug for GDB 1396 // if the dynamic table is writable 1397 if ((dynamic_flags & PF_W) != 0) { 1398 d->d_un.d_val = (int) &_r_debug; 1399 } 1400 break; 1401 case DT_RELA: 1402 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1403 return false; 1404 case DT_INIT: 1405 si->init_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1406 DEBUG("%s constructors (init func) found at %p", si->name, si->init_func); 1407 break; 1408 case DT_FINI: 1409 si->fini_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr); 1410 DEBUG("%s destructors (fini func) found at %p", si->name, si->fini_func); 1411 break; 1412 case DT_INIT_ARRAY: 1413 si->init_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1414 DEBUG("%s constructors (init_array) found at %p", si->name, si->init_array); 1415 break; 1416 case DT_INIT_ARRAYSZ: 1417 si->init_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1418 break; 1419 case DT_FINI_ARRAY: 1420 si->fini_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1421 DEBUG("%s destructors (fini_array) found at %p", si->name, si->fini_array); 1422 break; 1423 case DT_FINI_ARRAYSZ: 1424 si->fini_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1425 break; 1426 case DT_PREINIT_ARRAY: 1427 si->preinit_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr); 1428 DEBUG("%s constructors (preinit_array) found at %p", si->name, si->preinit_array); 1429 break; 1430 case DT_PREINIT_ARRAYSZ: 1431 si->preinit_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); 1432 break; 1433 case DT_TEXTREL: 1434 si->has_text_relocations = true; 1435 break; 1436 case DT_SYMBOLIC: 1437 si->has_DT_SYMBOLIC = true; 1438 break; 1439 case DT_NEEDED: 1440 ++needed_count; 1441 break; 1442#if defined DT_FLAGS 1443 // TODO: why is DT_FLAGS not defined? 1444 case DT_FLAGS: 1445 if (d->d_un.d_val & DF_TEXTREL) { 1446 si->has_text_relocations = true; 1447 } 1448 if (d->d_un.d_val & DF_SYMBOLIC) { 1449 si->has_DT_SYMBOLIC = true; 1450 } 1451 break; 1452#endif 1453#if defined(ANDROID_MIPS_LINKER) 1454 case DT_STRSZ: 1455 case DT_SYMENT: 1456 case DT_RELENT: 1457 break; 1458 case DT_MIPS_RLD_MAP: 1459 // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. 1460 { 1461 r_debug** dp = (r_debug**) d->d_un.d_ptr; 1462 *dp = &_r_debug; 1463 } 1464 break; 1465 case DT_MIPS_RLD_VERSION: 1466 case DT_MIPS_FLAGS: 1467 case DT_MIPS_BASE_ADDRESS: 1468 case DT_MIPS_UNREFEXTNO: 1469 break; 1470 1471 case DT_MIPS_SYMTABNO: 1472 si->mips_symtabno = d->d_un.d_val; 1473 break; 1474 1475 case DT_MIPS_LOCAL_GOTNO: 1476 si->mips_local_gotno = d->d_un.d_val; 1477 break; 1478 1479 case DT_MIPS_GOTSYM: 1480 si->mips_gotsym = d->d_un.d_val; 1481 break; 1482 1483 default: 1484 DEBUG("Unused DT entry: type 0x%08x arg 0x%08x", d->d_tag, d->d_un.d_val); 1485 break; 1486#endif 1487 } 1488 } 1489 1490 DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p", 1491 si->base, si->strtab, si->symtab); 1492 1493 // Sanity checks. 1494 if (relocating_linker && needed_count != 0) { 1495 DL_ERR("linker cannot have DT_NEEDED dependencies on other libraries"); 1496 return false; 1497 } 1498 if (si->nbucket == 0) { 1499 DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name); 1500 return false; 1501 } 1502 if (si->strtab == 0) { 1503 DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name); 1504 return false; 1505 } 1506 if (si->symtab == 0) { 1507 DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name); 1508 return false; 1509 } 1510 1511 /* if this is the main executable, then load all of the preloads now */ 1512 if (si->flags & FLAG_EXE) { 1513 memset(gLdPreloads, 0, sizeof(gLdPreloads)); 1514 for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) { 1515 soinfo* lsi = find_library(gLdPreloadNames[i]); 1516 if (lsi == NULL) { 1517 strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf)); 1518 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1519 gLdPreloadNames[i], si->name, tmp_err_buf); 1520 return false; 1521 } 1522 gLdPreloads[i] = lsi; 1523 } 1524 } 1525 1526 soinfo** needed = (soinfo**) alloca((1 + needed_count) * sizeof(soinfo*)); 1527 soinfo** pneeded = needed; 1528 1529 for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { 1530 if (d->d_tag == DT_NEEDED) { 1531 const char* library_name = si->strtab + d->d_un.d_val; 1532 DEBUG("%s needs %s", si->name, library_name); 1533 soinfo* lsi = find_library(library_name); 1534 if (lsi == NULL) { 1535 strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf)); 1536 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1537 library_name, si->name, tmp_err_buf); 1538 return false; 1539 } 1540 *pneeded++ = lsi; 1541 } 1542 } 1543 *pneeded = NULL; 1544 1545 if (si->has_text_relocations) { 1546 /* Unprotect the segments, i.e. make them writable, to allow 1547 * text relocations to work properly. We will later call 1548 * phdr_table_protect_segments() after all of them are applied 1549 * and all constructors are run. 1550 */ 1551 if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1552 DL_ERR("can't unprotect loadable segments for \"%s\": %s", 1553 si->name, strerror(errno)); 1554 return false; 1555 } 1556 } 1557 1558 if (si->plt_rel != NULL) { 1559 DEBUG("[ relocating %s plt ]", si->name ); 1560 if (soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) { 1561 return false; 1562 } 1563 } 1564 if (si->rel != NULL) { 1565 DEBUG("[ relocating %s ]", si->name ); 1566 if (soinfo_relocate(si, si->rel, si->rel_count, needed)) { 1567 return false; 1568 } 1569 } 1570 1571#ifdef ANDROID_MIPS_LINKER 1572 if (mips_relocate_got(si, needed)) { 1573 return false; 1574 } 1575#endif 1576 1577 si->flags |= FLAG_LINKED; 1578 DEBUG("[ finished linking %s ]", si->name); 1579 1580 if (si->has_text_relocations) { 1581 /* All relocations are done, we can protect our segments back to 1582 * read-only. */ 1583 if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1584 DL_ERR("can't protect segments for \"%s\": %s", 1585 si->name, strerror(errno)); 1586 return false; 1587 } 1588 } 1589 1590 /* We can also turn on GNU RELRO protection */ 1591 if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { 1592 DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", 1593 si->name, strerror(errno)); 1594 return false; 1595 } 1596 1597 // If this is a setuid/setgid program, close the security hole described in 1598 // ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc 1599 if (get_AT_SECURE()) { 1600 nullify_closed_stdio(); 1601 } 1602 notify_gdb_of_load(si); 1603 return true; 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 debuggerd_init(); 1631 1632 // Get a few environment variables. 1633 const char* LD_DEBUG = linker_env_get("LD_DEBUG"); 1634 if (LD_DEBUG != NULL) { 1635 gLdDebugVerbosity = atoi(LD_DEBUG); 1636 } 1637 1638 // Normally, these are cleaned by linker_env_init, but the test 1639 // doesn't cost us anything. 1640 const char* ldpath_env = NULL; 1641 const char* ldpreload_env = NULL; 1642 if (!get_AT_SECURE()) { 1643 ldpath_env = linker_env_get("LD_LIBRARY_PATH"); 1644 ldpreload_env = linker_env_get("LD_PRELOAD"); 1645 } 1646 1647 INFO("[ android linker & debugger ]"); 1648 1649 soinfo* si = soinfo_alloc(args.argv[0]); 1650 if (si == NULL) { 1651 exit(EXIT_FAILURE); 1652 } 1653 1654 /* bootstrap the link map, the main exe always needs to be first */ 1655 si->flags |= FLAG_EXE; 1656 link_map_t* map = &(si->link_map); 1657 1658 map->l_addr = 0; 1659 map->l_name = args.argv[0]; 1660 map->l_prev = NULL; 1661 map->l_next = NULL; 1662 1663 _r_debug.r_map = map; 1664 r_debug_tail = map; 1665 1666 /* gdb expects the linker to be in the debug shared object list. 1667 * Without this, gdb has trouble locating the linker's ".text" 1668 * and ".plt" sections. Gdb could also potentially use this to 1669 * relocate the offset of our exported 'rtld_db_dlactivity' symbol. 1670 * Don't use soinfo_alloc(), because the linker shouldn't 1671 * be on the soinfo list. 1672 */ 1673 { 1674 static soinfo linker_soinfo; 1675 strlcpy(linker_soinfo.name, "/system/bin/linker", sizeof(linker_soinfo.name)); 1676 linker_soinfo.flags = 0; 1677 linker_soinfo.base = linker_base; 1678 1679 /* 1680 * Set the dynamic field in the link map otherwise gdb will complain with 1681 * the following: 1682 * warning: .dynamic section for "/system/bin/linker" is not at the 1683 * expected address (wrong library or version mismatch?) 1684 */ 1685 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base; 1686 Elf32_Phdr *phdr = (Elf32_Phdr*)((unsigned char*) linker_base + elf_hdr->e_phoff); 1687 phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, 1688 &linker_soinfo.dynamic, NULL, NULL); 1689 insert_soinfo_into_debug_map(&linker_soinfo); 1690 } 1691 1692 // Extract information passed from the kernel. 1693 si->phdr = reinterpret_cast<Elf32_Phdr*>(args.getauxval(AT_PHDR)); 1694 si->phnum = args.getauxval(AT_PHNUM); 1695 si->entry = args.getauxval(AT_ENTRY); 1696 1697 /* Compute the value of si->base. We can't rely on the fact that 1698 * the first entry is the PHDR because this will not be true 1699 * for certain executables (e.g. some in the NDK unit test suite) 1700 */ 1701 si->base = 0; 1702 si->size = phdr_table_get_load_size(si->phdr, si->phnum); 1703 si->load_bias = 0; 1704 for (size_t i = 0; i < si->phnum; ++i) { 1705 if (si->phdr[i].p_type == PT_PHDR) { 1706 si->load_bias = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_vaddr; 1707 si->base = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_offset; 1708 break; 1709 } 1710 } 1711 si->dynamic = NULL; 1712 si->ref_count = 1; 1713 1714 // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). 1715 parse_LD_LIBRARY_PATH(ldpath_env); 1716 parse_LD_PRELOAD(ldpreload_env); 1717 1718 somain = si; 1719 1720 if (!soinfo_link_image(si)) { 1721 __libc_format_fd(2, "CANNOT LINK EXECUTABLE: %s\n", linker_get_error_buffer()); 1722 exit(EXIT_FAILURE); 1723 } 1724 1725 si->CallPreInitConstructors(); 1726 1727 for (size_t i = 0; gLdPreloads[i] != NULL; ++i) { 1728 gLdPreloads[i]->CallConstructors(); 1729 } 1730 1731 /* After the link_image, the si->load_bias is initialized. 1732 * For so lib, the map->l_addr will be updated in notify_gdb_of_load. 1733 * We need to update this value for so exe here. So Unwind_Backtrace 1734 * for some arch like x86 could work correctly within so exe. 1735 */ 1736 map->l_addr = si->load_bias; 1737 si->CallConstructors(); 1738 1739#if TIMING 1740 gettimeofday(&t1,NULL); 1741 PRINT("LINKER TIME: %s: %d microseconds", args.argv[0], (int) ( 1742 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - 1743 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) 1744 )); 1745#endif 1746#if STATS 1747 PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", args.argv[0], 1748 linker_stats.count[kRelocAbsolute], 1749 linker_stats.count[kRelocRelative], 1750 linker_stats.count[kRelocCopy], 1751 linker_stats.count[kRelocSymbol]); 1752#endif 1753#if COUNT_PAGES 1754 { 1755 unsigned n; 1756 unsigned i; 1757 unsigned count = 0; 1758 for (n = 0; n < 4096; n++) { 1759 if (bitmask[n]) { 1760 unsigned x = bitmask[n]; 1761 for (i = 0; i < 8; i++) { 1762 if (x & 1) { 1763 count++; 1764 } 1765 x >>= 1; 1766 } 1767 } 1768 } 1769 PRINT("PAGES MODIFIED: %s: %d (%dKB)", args.argv[0], count, count * 4); 1770 } 1771#endif 1772 1773#if TIMING || STATS || COUNT_PAGES 1774 fflush(stdout); 1775#endif 1776 1777 TRACE("[ Ready to execute '%s' @ 0x%08x ]", si->name, si->entry); 1778 return si->entry; 1779} 1780 1781/* Compute the load-bias of an existing executable. This shall only 1782 * be used to compute the load bias of an executable or shared library 1783 * that was loaded by the kernel itself. 1784 * 1785 * Input: 1786 * elf -> address of ELF header, assumed to be at the start of the file. 1787 * Return: 1788 * load bias, i.e. add the value of any p_vaddr in the file to get 1789 * the corresponding address in memory. 1790 */ 1791static Elf32_Addr get_elf_exec_load_bias(const Elf32_Ehdr* elf) { 1792 Elf32_Addr offset = elf->e_phoff; 1793 const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset); 1794 const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum; 1795 1796 for (const Elf32_Phdr* phdr = phdr_table; phdr < phdr_end; phdr++) { 1797 if (phdr->p_type == PT_LOAD) { 1798 return reinterpret_cast<Elf32_Addr>(elf) + phdr->p_offset - phdr->p_vaddr; 1799 } 1800 } 1801 return 0; 1802} 1803 1804/* 1805 * This is the entry point for the linker, called from begin.S. This 1806 * method is responsible for fixing the linker's own relocations, and 1807 * then calling __linker_init_post_relocation(). 1808 * 1809 * Because this method is called before the linker has fixed it's own 1810 * relocations, any attempt to reference an extern variable, extern 1811 * function, or other GOT reference will generate a segfault. 1812 */ 1813extern "C" Elf32_Addr __linker_init(void* raw_args) { 1814 KernelArgumentBlock args(raw_args); 1815 1816 Elf32_Addr linker_addr = args.getauxval(AT_BASE); 1817 1818 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr*) linker_addr; 1819 Elf32_Phdr *phdr = (Elf32_Phdr*)((unsigned char*) linker_addr + elf_hdr->e_phoff); 1820 1821 soinfo linker_so; 1822 memset(&linker_so, 0, sizeof(soinfo)); 1823 1824 linker_so.base = linker_addr; 1825 linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); 1826 linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); 1827 linker_so.dynamic = NULL; 1828 linker_so.phdr = phdr; 1829 linker_so.phnum = elf_hdr->e_phnum; 1830 linker_so.flags |= FLAG_LINKER; 1831 1832 if (!soinfo_link_image(&linker_so)) { 1833 // It would be nice to print an error message, but if the linker 1834 // can't link itself, there's no guarantee that we'll be able to 1835 // call write() (because it involves a GOT reference). 1836 // 1837 // This situation should never occur unless the linker itself 1838 // is corrupt. 1839 exit(EXIT_FAILURE); 1840 } 1841 1842 // We have successfully fixed our own relocations. It's safe to run 1843 // the main part of the linker now. 1844 Elf32_Addr start_address = __linker_init_post_relocation(args, linker_addr); 1845 1846 set_soinfo_pool_protection(PROT_READ); 1847 1848 // Return the address that the calling assembly stub should jump to. 1849 return start_address; 1850} 1851