linker.cpp revision 61a9ccb41eba8c35cae6e21318aca7160a402c5b
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/logd.h> 45#include <private/ScopedPthreadMutexLocker.h> 46 47#include "linker.h" 48#include "linker_debug.h" 49#include "linker_environ.h" 50#include "linker_format.h" 51#include "linker_phdr.h" 52 53/* Assume average path length of 64 and max 8 paths */ 54#define LDPATH_BUFSIZE 512 55#define LDPATH_MAX 8 56 57#define LDPRELOAD_BUFSIZE 512 58#define LDPRELOAD_MAX 8 59 60/* >>> IMPORTANT NOTE - READ ME BEFORE MODIFYING <<< 61 * 62 * Do NOT use malloc() and friends or pthread_*() code here. 63 * Don't use printf() either; it's caused mysterious memory 64 * corruption in the past. 65 * The linker runs before we bring up libc and it's easiest 66 * to make sure it does not depend on any complex libc features 67 * 68 * open issues / todo: 69 * 70 * - are we doing everything we should for ARM_COPY relocations? 71 * - cleaner error reporting 72 * - after linking, set as much stuff as possible to READONLY 73 * and NOEXEC 74 */ 75 76static bool soinfo_link_image(soinfo* si); 77 78// We can't use malloc(3) in the dynamic linker. We use a linked list of anonymous 79// maps, each a single page in size. The pages are broken up into as many struct soinfo 80// objects as will fit, and they're all threaded together on a free list. 81#define SOINFO_PER_POOL ((PAGE_SIZE - sizeof(soinfo_pool_t*)) / sizeof(soinfo)) 82struct soinfo_pool_t { 83 soinfo_pool_t* next; 84 soinfo info[SOINFO_PER_POOL]; 85}; 86static struct soinfo_pool_t* gSoInfoPools = NULL; 87static soinfo* gSoInfoFreeList = NULL; 88 89static soinfo *solist = &libdl_info; 90static soinfo *sonext = &libdl_info; 91static soinfo *somain; /* main process, always the one after libdl_info */ 92 93static const char* const gSoPaths[] = { 94 "/vendor/lib", 95 "/system/lib", 96 NULL 97}; 98 99static char gLdPathsBuffer[LDPATH_BUFSIZE]; 100static const char* gLdPaths[LDPATH_MAX + 1]; 101 102static char gLdPreloadsBuffer[LDPRELOAD_BUFSIZE]; 103static const char* gLdPreloadNames[LDPRELOAD_MAX + 1]; 104 105static soinfo *preloads[LDPRELOAD_MAX + 1]; 106 107static int debug_verbosity; 108 109enum RelocationKind { 110 kRelocAbsolute = 0, 111 kRelocRelative, 112 kRelocCopy, 113 kRelocSymbol, 114 kRelocMax 115}; 116 117#if STATS 118struct linker_stats_t { 119 int count[kRelocMax]; 120}; 121 122static linker_stats_t linker_stats; 123 124static void count_relocation(RelocationKind kind) { 125 ++linker_stats.count[kind]; 126} 127#else 128static void count_relocation(RelocationKind) { 129} 130#endif 131 132#if COUNT_PAGES 133static unsigned bitmask[4096]; 134#define MARK(offset) \ 135 do { \ 136 bitmask[((offset) >> 12) >> 3] |= (1 << (((offset) >> 12) & 7)); \ 137 } while(0) 138#else 139#define MARK(x) do {} while (0) 140#endif 141 142// You shouldn't try to call memory-allocating functions in the dynamic linker. 143// Guard against the most obvious ones. 144#define DISALLOW_ALLOCATION(return_type, name, ...) \ 145 return_type name __VA_ARGS__ \ 146 { \ 147 const char* msg = "ERROR: " #name " called from the dynamic linker!\n"; \ 148 __libc_android_log_write(ANDROID_LOG_FATAL, "linker", msg); \ 149 write(2, msg, sizeof(msg)); \ 150 abort(); \ 151 } 152#define UNUSED __attribute__((unused)) 153DISALLOW_ALLOCATION(void*, malloc, (size_t u UNUSED)); 154DISALLOW_ALLOCATION(void, free, (void* u UNUSED)); 155DISALLOW_ALLOCATION(void*, realloc, (void* u1 UNUSED, size_t u2 UNUSED)); 156DISALLOW_ALLOCATION(void*, calloc, (size_t u1 UNUSED, size_t u2 UNUSED)); 157 158static char tmp_err_buf[768]; 159static char __linker_dl_err_buf[768]; 160#define DL_ERR(fmt, x...) \ 161 do { \ 162 format_buffer(__linker_dl_err_buf, sizeof(__linker_dl_err_buf), fmt, ##x); \ 163 ERROR(fmt "\n", ##x); \ 164 } while(0) 165 166const char* linker_get_error() { 167 return &__linker_dl_err_buf[0]; 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, 177 RT_CONSISTENT, 0}; 178static link_map* r_debug_tail = 0; 179 180static pthread_mutex_t gDebugMutex = PTHREAD_MUTEX_INITIALIZER; 181 182static void insert_soinfo_into_debug_map(soinfo * info) { 183 // Copy the necessary fields into the debug structure. 184 link_map* map = &(info->linkmap); 185 map->l_addr = info->base; 186 map->l_name = (char*) info->name; 187 map->l_ld = (uintptr_t)info->dynamic; 188 189 /* Stick the new library at the end of the list. 190 * gdb tends to care more about libc than it does 191 * about leaf libraries, and ordering it this way 192 * reduces the back-and-forth over the wire. 193 */ 194 if (r_debug_tail) { 195 r_debug_tail->l_next = map; 196 map->l_prev = r_debug_tail; 197 map->l_next = 0; 198 } else { 199 _r_debug.r_map = map; 200 map->l_prev = 0; 201 map->l_next = 0; 202 } 203 r_debug_tail = map; 204} 205 206static void remove_soinfo_from_debug_map(soinfo* info) { 207 link_map* map = &(info->linkmap); 208 209 if (r_debug_tail == map) { 210 r_debug_tail = map->l_prev; 211 } 212 213 if (map->l_prev) { 214 map->l_prev->l_next = map->l_next; 215 } 216 if (map->l_next) { 217 map->l_next->l_prev = map->l_prev; 218 } 219} 220 221static void notify_gdb_of_load(soinfo* info) { 222 if (info->flags & FLAG_EXE) { 223 // GDB already knows about the main executable 224 return; 225 } 226 227 ScopedPthreadMutexLocker locker(&gDebugMutex); 228 229 _r_debug.r_state = RT_ADD; 230 rtld_db_dlactivity(); 231 232 insert_soinfo_into_debug_map(info); 233 234 _r_debug.r_state = RT_CONSISTENT; 235 rtld_db_dlactivity(); 236} 237 238static void notify_gdb_of_unload(soinfo* info) { 239 if (info->flags & FLAG_EXE) { 240 // GDB already knows about the main executable 241 return; 242 } 243 244 ScopedPthreadMutexLocker locker(&gDebugMutex); 245 246 _r_debug.r_state = RT_DELETE; 247 rtld_db_dlactivity(); 248 249 remove_soinfo_from_debug_map(info); 250 251 _r_debug.r_state = RT_CONSISTENT; 252 rtld_db_dlactivity(); 253} 254 255void notify_gdb_of_libraries() { 256 _r_debug.r_state = RT_ADD; 257 rtld_db_dlactivity(); 258 _r_debug.r_state = RT_CONSISTENT; 259 rtld_db_dlactivity(); 260} 261 262static bool ensure_free_list_non_empty() { 263 if (gSoInfoFreeList != NULL) { 264 return true; 265 } 266 267 // Allocate a new pool. 268 soinfo_pool_t* pool = reinterpret_cast<soinfo_pool_t*>(mmap(NULL, sizeof(*pool), 269 PROT_READ|PROT_WRITE, 270 MAP_PRIVATE|MAP_ANONYMOUS, 0, 0)); 271 if (pool == MAP_FAILED) { 272 return false; 273 } 274 275 // Add the pool to our list of pools. 276 pool->next = gSoInfoPools; 277 gSoInfoPools = pool; 278 279 // Chain the entries in the new pool onto the free list. 280 gSoInfoFreeList = &pool->info[0]; 281 soinfo* next = NULL; 282 for (int i = SOINFO_PER_POOL - 1; i >= 0; --i) { 283 pool->info[i].next = next; 284 next = &pool->info[i]; 285 } 286 287 return true; 288} 289 290static void set_soinfo_pool_protection(int protection) { 291 for (soinfo_pool_t* p = gSoInfoPools; p != NULL; p = p->next) { 292 if (mprotect(p, sizeof(*p), protection) == -1) { 293 abort(); // Can't happen. 294 } 295 } 296} 297 298static soinfo* soinfo_alloc(const char* name) { 299 if (strlen(name) >= SOINFO_NAME_LEN) { 300 DL_ERR("library name \"%s\" too long", name); 301 return NULL; 302 } 303 304 if (!ensure_free_list_non_empty()) { 305 DL_ERR("out of memory when loading \"%s\"", name); 306 return NULL; 307 } 308 309 // Take the head element off the free list. 310 soinfo* si = gSoInfoFreeList; 311 gSoInfoFreeList = gSoInfoFreeList->next; 312 313 // Initialize the new element. 314 memset(si, 0, sizeof(soinfo)); 315 strlcpy(si->name, name, sizeof(si->name)); 316 sonext->next = si; 317 sonext = si; 318 319 TRACE("name %s: allocated soinfo @ %p\n", name, si); 320 return si; 321} 322 323static void soinfo_free(soinfo* si) 324{ 325 if (si == NULL) { 326 return; 327 } 328 329 soinfo *prev = NULL, *trav; 330 331 TRACE("name %s: freeing soinfo @ %p\n", si->name, si); 332 333 for(trav = solist; trav != NULL; trav = trav->next){ 334 if (trav == si) 335 break; 336 prev = trav; 337 } 338 if (trav == NULL) { 339 /* si was not ni solist */ 340 DL_ERR("name \"%s\" is not in solist!", si->name); 341 return; 342 } 343 344 /* prev will never be NULL, because the first entry in solist is 345 always the static libdl_info. 346 */ 347 prev->next = si->next; 348 if (si == sonext) sonext = prev; 349 si->next = gSoInfoFreeList; 350 gSoInfoFreeList = si; 351} 352 353#ifdef ANDROID_ARM_LINKER 354 355/* For a given PC, find the .so that it belongs to. 356 * Returns the base address of the .ARM.exidx section 357 * for that .so, and the number of 8-byte entries 358 * in that section (via *pcount). 359 * 360 * Intended to be called by libc's __gnu_Unwind_Find_exidx(). 361 * 362 * This function is exposed via dlfcn.cpp and libdl.so. 363 */ 364_Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount) 365{ 366 soinfo *si; 367 unsigned addr = (unsigned)pc; 368 369 for (si = solist; si != 0; si = si->next){ 370 if ((addr >= si->base) && (addr < (si->base + si->size))) { 371 *pcount = si->ARM_exidx_count; 372 return (_Unwind_Ptr)si->ARM_exidx; 373 } 374 } 375 *pcount = 0; 376 return NULL; 377} 378 379#elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) 380 381/* Here, we only have to provide a callback to iterate across all the 382 * loaded libraries. gcc_eh does the rest. */ 383int 384dl_iterate_phdr(int (*cb)(dl_phdr_info *info, size_t size, void *data), 385 void *data) 386{ 387 int rv = 0; 388 for (soinfo* si = solist; si != NULL; si = si->next) { 389 dl_phdr_info dl_info; 390 dl_info.dlpi_addr = si->linkmap.l_addr; 391 dl_info.dlpi_name = si->linkmap.l_name; 392 dl_info.dlpi_phdr = si->phdr; 393 dl_info.dlpi_phnum = si->phnum; 394 rv = cb(&dl_info, sizeof(dl_phdr_info), data); 395 if (rv != 0) { 396 break; 397 } 398 } 399 return rv; 400} 401 402#endif 403 404static Elf32_Sym *soinfo_elf_lookup(soinfo *si, unsigned hash, const char *name) 405{ 406 Elf32_Sym *s; 407 Elf32_Sym *symtab = si->symtab; 408 const char *strtab = si->strtab; 409 unsigned n; 410 411 TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %d\n", 412 name, si->name, si->base, hash, hash % si->nbucket); 413 n = hash % si->nbucket; 414 415 for(n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]){ 416 s = symtab + n; 417 if(strcmp(strtab + s->st_name, name)) continue; 418 419 /* only concern ourselves with global and weak symbol definitions */ 420 switch(ELF32_ST_BIND(s->st_info)){ 421 case STB_GLOBAL: 422 case STB_WEAK: 423 if(s->st_shndx == SHN_UNDEF) 424 continue; 425 426 TRACE_TYPE(LOOKUP, "FOUND %s in %s (%08x) %d\n", 427 name, si->name, s->st_value, s->st_size); 428 return s; 429 } 430 } 431 432 return NULL; 433} 434 435static unsigned elfhash(const char *_name) 436{ 437 const unsigned char *name = (const unsigned char *) _name; 438 unsigned h = 0, g; 439 440 while(*name) { 441 h = (h << 4) + *name++; 442 g = h & 0xf0000000; 443 h ^= g; 444 h ^= g >> 24; 445 } 446 return h; 447} 448 449static Elf32_Sym * 450soinfo_do_lookup(soinfo *si, const char *name, soinfo **lsi, 451 soinfo *needed[]) 452{ 453 unsigned elf_hash = elfhash(name); 454 Elf32_Sym *s = NULL; 455 int i; 456 457 if (si != NULL && somain != NULL) { 458 459 /* 460 * Local scope is executable scope. Just start looking into it right away 461 * for the shortcut. 462 */ 463 464 if (si == somain) { 465 s = soinfo_elf_lookup(si, elf_hash, name); 466 if (s != NULL) { 467 *lsi = si; 468 goto done; 469 } 470 } else { 471 /* Order of symbol lookup is controlled by DT_SYMBOLIC flag */ 472 473 /* 474 * If this object was built with symbolic relocations disabled, the 475 * first place to look to resolve external references is the main 476 * executable. 477 */ 478 479 if (!si->has_DT_SYMBOLIC) { 480 DEBUG("%s: looking up %s in executable %s\n", 481 si->name, name, somain->name); 482 s = soinfo_elf_lookup(somain, elf_hash, name); 483 if (s != NULL) { 484 *lsi = somain; 485 goto done; 486 } 487 } 488 489 /* Look for symbols in the local scope (the object who is 490 * searching). This happens with C++ templates on i386 for some 491 * reason. 492 * 493 * Notes on weak symbols: 494 * The ELF specs are ambiguous about treatment of weak definitions in 495 * dynamic linking. Some systems return the first definition found 496 * and some the first non-weak definition. This is system dependent. 497 * Here we return the first definition found for simplicity. */ 498 499 s = soinfo_elf_lookup(si, elf_hash, name); 500 if (s != NULL) { 501 *lsi = si; 502 goto done; 503 } 504 505 /* 506 * If this object was built with -Bsymbolic and symbol is not found 507 * in the local scope, try to find the symbol in the main executable. 508 */ 509 510 if (si->has_DT_SYMBOLIC) { 511 DEBUG("%s: looking up %s in executable %s after local scope\n", 512 si->name, name, somain->name); 513 s = soinfo_elf_lookup(somain, elf_hash, name); 514 if (s != NULL) { 515 *lsi = somain; 516 goto done; 517 } 518 } 519 } 520 } 521 522 /* Next, look for it in the preloads list */ 523 for(i = 0; preloads[i] != NULL; i++) { 524 s = soinfo_elf_lookup(preloads[i], elf_hash, name); 525 if(s != NULL) { 526 *lsi = preloads[i]; 527 goto done; 528 } 529 } 530 531 for(i = 0; needed[i] != NULL; i++) { 532 DEBUG("%s: looking up %s in %s\n", 533 si->name, name, needed[i]->name); 534 s = soinfo_elf_lookup(needed[i], elf_hash, name); 535 if (s != NULL) { 536 *lsi = needed[i]; 537 goto done; 538 } 539 } 540 541done: 542 if(s != NULL) { 543 TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = 0x%08x, " 544 "found in %s, base = 0x%08x, load bias = 0x%08x\n", 545 si->name, name, s->st_value, 546 (*lsi)->name, (*lsi)->base, (*lsi)->load_bias); 547 return s; 548 } 549 550 return NULL; 551} 552 553/* This is used by dl_sym(). It performs symbol lookup only within the 554 specified soinfo object and not in any of its dependencies. 555 */ 556Elf32_Sym *soinfo_lookup(soinfo *si, const char *name) 557{ 558 return soinfo_elf_lookup(si, elfhash(name), name); 559} 560 561/* This is used by dl_sym(). It performs a global symbol lookup. 562 */ 563Elf32_Sym *lookup(const char *name, soinfo **found, soinfo *start) 564{ 565 unsigned elf_hash = elfhash(name); 566 Elf32_Sym *s = NULL; 567 soinfo *si; 568 569 if(start == NULL) { 570 start = solist; 571 } 572 573 for(si = start; (s == NULL) && (si != NULL); si = si->next) 574 { 575 if(si->flags & FLAG_ERROR) 576 continue; 577 s = soinfo_elf_lookup(si, elf_hash, name); 578 if (s != NULL) { 579 *found = si; 580 break; 581 } 582 } 583 584 if(s != NULL) { 585 TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, si->base = 0x%08x\n", 586 name, s->st_value, si->base); 587 return s; 588 } 589 590 return NULL; 591} 592 593soinfo *find_containing_library(const void *addr) 594{ 595 soinfo *si; 596 597 for(si = solist; si != NULL; si = si->next) 598 { 599 if((unsigned)addr >= si->base && (unsigned)addr - si->base < si->size) { 600 return si; 601 } 602 } 603 604 return NULL; 605} 606 607Elf32_Sym *soinfo_find_symbol(soinfo* si, const void *addr) 608{ 609 unsigned int i; 610 unsigned soaddr = (unsigned)addr - si->base; 611 612 /* Search the library's symbol table for any defined symbol which 613 * contains this address */ 614 for(i=0; i<si->nchain; i++) { 615 Elf32_Sym *sym = &si->symtab[i]; 616 617 if(sym->st_shndx != SHN_UNDEF && 618 soaddr >= sym->st_value && 619 soaddr < sym->st_value + sym->st_size) { 620 return sym; 621 } 622 } 623 624 return NULL; 625} 626 627#if 0 628static void dump(soinfo *si) 629{ 630 Elf32_Sym *s = si->symtab; 631 unsigned n; 632 633 for(n = 0; n < si->nchain; n++) { 634 TRACE("%04d> %08x: %02x %04x %08x %08x %s\n", n, s, 635 s->st_info, s->st_shndx, s->st_value, s->st_size, 636 si->strtab + s->st_name); 637 s++; 638 } 639} 640#endif 641 642static int open_library_on_path(const char* name, const char* const paths[]) { 643 char buf[512]; 644 for (size_t i = 0; paths[i] != NULL; ++i) { 645 int n = format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name); 646 if (n < 0 || n >= static_cast<int>(sizeof(buf))) { 647 WARN("Ignoring very long library path: %s/%s\n", paths[i], name); 648 continue; 649 } 650 int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC)); 651 if (fd != -1) { 652 return fd; 653 } 654 } 655 return -1; 656} 657 658static int open_library(const char* name) { 659 TRACE("[ opening %s ]\n", name); 660 661 // If the name contains a slash, we should attempt to open it directly and not search the paths. 662 if (strchr(name, '/') != NULL) { 663 int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC)); 664 if (fd != -1) { 665 return fd; 666 } 667 // ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now. 668 } 669 670 // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths. 671 int fd = open_library_on_path(name, gLdPaths); 672 if (fd == -1) { 673 fd = open_library_on_path(name, gSoPaths); 674 } 675 return fd; 676} 677 678// Returns 'true' if the library is prelinked or on failure so we error out 679// either way. We no longer support prelinking. 680static bool is_prelinked(int fd, const char* name) 681{ 682 struct prelink_info_t { 683 long mmap_addr; 684 char tag[4]; // "PRE ". 685 }; 686 687 off_t sz = lseek(fd, -sizeof(prelink_info_t), SEEK_END); 688 if (sz < 0) { 689 DL_ERR("lseek failed: %s", strerror(errno)); 690 return true; 691 } 692 693 prelink_info_t info; 694 int rc = TEMP_FAILURE_RETRY(read(fd, &info, sizeof(info))); 695 if (rc != sizeof(info)) { 696 DL_ERR("could not read prelink_info_t structure for \"%s\": %s", name, strerror(errno)); 697 return true; 698 } 699 700 if (memcmp(info.tag, "PRE ", 4) == 0) { 701 DL_ERR("prelinked libraries no longer supported: %s", name); 702 return true; 703 } 704 return false; 705} 706 707/* verify_elf_header 708 * Verifies the content of an ELF header. 709 * 710 * Args: 711 * 712 * Returns: 713 * 0 on success 714 * -1 if no valid ELF object is found @ base. 715 */ 716static int 717verify_elf_header(const Elf32_Ehdr* hdr) 718{ 719 if (hdr->e_ident[EI_MAG0] != ELFMAG0) return -1; 720 if (hdr->e_ident[EI_MAG1] != ELFMAG1) return -1; 721 if (hdr->e_ident[EI_MAG2] != ELFMAG2) return -1; 722 if (hdr->e_ident[EI_MAG3] != ELFMAG3) return -1; 723 if (hdr->e_type != ET_DYN) return -1; 724 725 /* TODO: Should we verify anything else in the header? */ 726#ifdef ANDROID_ARM_LINKER 727 if (hdr->e_machine != EM_ARM) return -1; 728#elif defined(ANDROID_X86_LINKER) 729 if (hdr->e_machine != EM_386) return -1; 730#elif defined(ANDROID_MIPS_LINKER) 731 if (hdr->e_machine != EM_MIPS) return -1; 732#endif 733 return 0; 734} 735 736struct scoped_fd { 737 ~scoped_fd() { 738 if (fd != -1) { 739 close(fd); 740 } 741 } 742 int fd; 743}; 744 745struct soinfo_ptr { 746 soinfo_ptr(const char* name) { 747 const char* bname = strrchr(name, '/'); 748 ptr = soinfo_alloc(bname ? bname + 1 : name); 749 } 750 ~soinfo_ptr() { 751 soinfo_free(ptr); 752 } 753 soinfo* release() { 754 soinfo* result = ptr; 755 ptr = NULL; 756 return result; 757 } 758 soinfo* ptr; 759}; 760 761// TODO: rewrite linker_phdr.h to use a class, then lose this. 762struct phdr_ptr { 763 phdr_ptr() : phdr_mmap(NULL) {} 764 ~phdr_ptr() { 765 if (phdr_mmap != NULL) { 766 phdr_table_unload(phdr_mmap, phdr_size); 767 } 768 } 769 void* phdr_mmap; 770 Elf32_Addr phdr_size; 771}; 772 773static soinfo* load_library(const char* name) { 774 // Open the file. 775 scoped_fd fd; 776 fd.fd = open_library(name); 777 if (fd.fd == -1) { 778 DL_ERR("library \"%s\" not found", name); 779 return NULL; 780 } 781 782 // Read the ELF header. 783 Elf32_Ehdr header[1]; 784 int ret = TEMP_FAILURE_RETRY(read(fd.fd, (void*)header, sizeof(header))); 785 if (ret < 0) { 786 DL_ERR("can't read file \"%s\": %s", name, strerror(errno)); 787 return NULL; 788 } 789 if (ret != (int)sizeof(header)) { 790 DL_ERR("too small to be an ELF executable: %s", name); 791 return NULL; 792 } 793 if (verify_elf_header(header) < 0) { 794 DL_ERR("not a valid ELF executable: %s", name); 795 return NULL; 796 } 797 798 // Read the program header table. 799 const Elf32_Phdr* phdr_table; 800 phdr_ptr phdr_holder; 801 ret = phdr_table_load(fd.fd, header->e_phoff, header->e_phnum, 802 &phdr_holder.phdr_mmap, &phdr_holder.phdr_size, &phdr_table); 803 if (ret < 0) { 804 DL_ERR("can't load program header table: %s: %s", name, strerror(errno)); 805 return NULL; 806 } 807 size_t phdr_count = header->e_phnum; 808 809 // Get the load extents. 810 Elf32_Addr ext_sz = phdr_table_get_load_size(phdr_table, phdr_count); 811 TRACE("[ '%s' wants sz=0x%08x ]\n", name, ext_sz); 812 if (ext_sz == 0) { 813 DL_ERR("no loadable segments in file: %s", name); 814 return NULL; 815 } 816 817 // We no longer support pre-linked libraries. 818 if (is_prelinked(fd.fd, name)) { 819 return NULL; 820 } 821 822 // Reserve address space for all loadable segments. 823 void* load_start = NULL; 824 Elf32_Addr load_size = 0; 825 Elf32_Addr load_bias = 0; 826 ret = phdr_table_reserve_memory(phdr_table, 827 phdr_count, 828 &load_start, 829 &load_size, 830 &load_bias); 831 if (ret < 0) { 832 DL_ERR("can't reserve %d bytes in address space for \"%s\": %s", 833 ext_sz, name, strerror(errno)); 834 return NULL; 835 } 836 837 TRACE("[ allocated memory for %s @ %p (0x%08x) ]\n", name, load_start, load_size); 838 839 /* Map all the segments in our address space with default protections */ 840 ret = phdr_table_load_segments(phdr_table, 841 phdr_count, 842 load_bias, 843 fd.fd); 844 if (ret < 0) { 845 DL_ERR("can't map loadable segments for \"%s\": %s", 846 name, strerror(errno)); 847 return NULL; 848 } 849 850 soinfo_ptr si(name); 851 if (si.ptr == NULL) { 852 return NULL; 853 } 854 855 si.ptr->base = (Elf32_Addr) load_start; 856 si.ptr->size = load_size; 857 si.ptr->load_bias = load_bias; 858 si.ptr->flags = 0; 859 si.ptr->entry = 0; 860 si.ptr->dynamic = (unsigned *)-1; 861 si.ptr->phnum = phdr_count; 862 si.ptr->phdr = phdr_table_get_loaded_phdr(phdr_table, phdr_count, load_bias); 863 if (si.ptr->phdr == NULL) { 864 DL_ERR("can't find loaded PHDR for \"%s\"", name); 865 return NULL; 866 } 867 868 return si.release(); 869} 870 871static soinfo* init_library(soinfo* si) { 872 // At this point we know that whatever is loaded @ base is a valid ELF 873 // shared library whose segments are properly mapped in. 874 TRACE("[ init_library base=0x%08x sz=0x%08x name='%s') ]\n", 875 si->base, si->size, si->name); 876 877 if (!soinfo_link_image(si)) { 878 munmap((void *)si->base, si->size); 879 return NULL; 880 } 881 882 return si; 883} 884 885static soinfo *find_loaded_library(const char *name) 886{ 887 soinfo *si; 888 const char *bname; 889 890 // TODO: don't use basename only for determining libraries 891 // http://code.google.com/p/android/issues/detail?id=6670 892 893 bname = strrchr(name, '/'); 894 bname = bname ? bname + 1 : name; 895 896 for(si = solist; si != NULL; si = si->next){ 897 if(!strcmp(bname, si->name)) { 898 return si; 899 } 900 } 901 return NULL; 902} 903 904static soinfo* find_library_internal(const char* name) { 905 if (name == NULL) { 906 return somain; 907 } 908 909 soinfo* si = find_loaded_library(name); 910 if (si != NULL) { 911 if (si->flags & FLAG_ERROR) { 912 DL_ERR("\"%s\" failed to load previously", name); 913 return NULL; 914 } 915 if (si->flags & FLAG_LINKED) { 916 return si; 917 } 918 DL_ERR("OOPS: recursive link to \"%s\"", si->name); 919 return NULL; 920 } 921 922 TRACE("[ '%s' has not been loaded yet. Locating...]\n", name); 923 si = load_library(name); 924 if (si != NULL) { 925 si = init_library(si); 926 } 927 928 return si; 929} 930 931static soinfo* find_library(const char* name) { 932 soinfo* si = find_library_internal(name); 933 if (si != NULL) { 934 si->refcount++; 935 } 936 return si; 937} 938 939static int soinfo_unload(soinfo* si) { 940 if (si->refcount == 1) { 941 TRACE("unloading '%s'\n", si->name); 942 si->CallDestructors(); 943 944 for (unsigned* d = si->dynamic; *d; d += 2) { 945 if (d[0] == DT_NEEDED) { 946 soinfo* lsi = find_loaded_library(si->strtab + d[1]); 947 if (lsi != NULL) { 948 TRACE("%s needs to unload %s\n", si->name, lsi->name); 949 soinfo_unload(lsi); 950 } else { 951 // TODO: should we return -1 in this case? 952 DL_ERR("\"%s\": could not unload dependent library", si->name); 953 } 954 } 955 } 956 957 munmap(reinterpret_cast<void*>(si->base), si->size); 958 notify_gdb_of_unload(si); 959 soinfo_free(si); 960 si->refcount = 0; 961 } else { 962 si->refcount--; 963 PRINT("not unloading '%s', decrementing refcount to %d\n", si->name, si->refcount); 964 } 965 return 0; 966} 967 968soinfo* do_dlopen(const char* name) { 969 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 970 soinfo* si = find_library(name); 971 if (si != NULL) { 972 si->CallConstructors(); 973 } 974 set_soinfo_pool_protection(PROT_READ); 975 return si; 976} 977 978int do_dlclose(soinfo* si) { 979 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 980 int result = soinfo_unload(si); 981 set_soinfo_pool_protection(PROT_READ); 982 return result; 983} 984 985/* TODO: don't use unsigned for addrs below. It works, but is not 986 * ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned 987 * long. 988 */ 989static int soinfo_relocate(soinfo *si, Elf32_Rel *rel, unsigned count, 990 soinfo *needed[]) 991{ 992 Elf32_Sym *symtab = si->symtab; 993 const char *strtab = si->strtab; 994 Elf32_Sym *s; 995 Elf32_Rel *start = rel; 996 soinfo *lsi; 997 998 for (size_t idx = 0; idx < count; ++idx, ++rel) { 999 unsigned type = ELF32_R_TYPE(rel->r_info); 1000 unsigned sym = ELF32_R_SYM(rel->r_info); 1001 unsigned reloc = (unsigned)(rel->r_offset + si->load_bias); 1002 unsigned sym_addr = 0; 1003 char *sym_name = NULL; 1004 1005 DEBUG("Processing '%s' relocation at index %d\n", si->name, idx); 1006 if (type == 0) { // R_*_NONE 1007 continue; 1008 } 1009 if(sym != 0) { 1010 sym_name = (char *)(strtab + symtab[sym].st_name); 1011 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1012 if(s == NULL) { 1013 /* We only allow an undefined symbol if this is a weak 1014 reference.. */ 1015 s = &symtab[sym]; 1016 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1017 DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); 1018 return -1; 1019 } 1020 1021 /* IHI0044C AAELF 4.5.1.1: 1022 1023 Libraries are not searched to resolve weak references. 1024 It is not an error for a weak reference to remain 1025 unsatisfied. 1026 1027 During linking, the value of an undefined weak reference is: 1028 - Zero if the relocation type is absolute 1029 - The address of the place if the relocation is pc-relative 1030 - The address of nominal base address if the relocation 1031 type is base-relative. 1032 */ 1033 1034 switch (type) { 1035#if defined(ANDROID_ARM_LINKER) 1036 case R_ARM_JUMP_SLOT: 1037 case R_ARM_GLOB_DAT: 1038 case R_ARM_ABS32: 1039 case R_ARM_RELATIVE: /* Don't care. */ 1040#elif defined(ANDROID_X86_LINKER) 1041 case R_386_JMP_SLOT: 1042 case R_386_GLOB_DAT: 1043 case R_386_32: 1044 case R_386_RELATIVE: /* Dont' care. */ 1045#endif /* ANDROID_*_LINKER */ 1046 /* sym_addr was initialized to be zero above or relocation 1047 code below does not care about value of sym_addr. 1048 No need to do anything. */ 1049 break; 1050 1051#if defined(ANDROID_X86_LINKER) 1052 case R_386_PC32: 1053 sym_addr = reloc; 1054 break; 1055#endif /* ANDROID_X86_LINKER */ 1056 1057#if defined(ANDROID_ARM_LINKER) 1058 case R_ARM_COPY: 1059 /* Fall through. Can't really copy if weak symbol is 1060 not found in run-time. */ 1061#endif /* ANDROID_ARM_LINKER */ 1062 default: 1063 DL_ERR("unknown weak reloc type %d @ %p (%d)", 1064 type, rel, (int) (rel - start)); 1065 return -1; 1066 } 1067 } else { 1068 /* We got a definition. */ 1069#if 0 1070 if((base == 0) && (si->base != 0)){ 1071 /* linking from libraries to main image is bad */ 1072 DL_ERR("cannot locate \"%s\"...", 1073 strtab + symtab[sym].st_name); 1074 return -1; 1075 } 1076#endif 1077 sym_addr = (unsigned)(s->st_value + lsi->load_bias); 1078 } 1079 count_relocation(kRelocSymbol); 1080 } else { 1081 s = NULL; 1082 } 1083 1084/* TODO: This is ugly. Split up the relocations by arch into 1085 * different files. 1086 */ 1087 switch(type){ 1088#if defined(ANDROID_ARM_LINKER) 1089 case R_ARM_JUMP_SLOT: 1090 count_relocation(kRelocAbsolute); 1091 MARK(rel->r_offset); 1092 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1093 *((unsigned*)reloc) = sym_addr; 1094 break; 1095 case R_ARM_GLOB_DAT: 1096 count_relocation(kRelocAbsolute); 1097 MARK(rel->r_offset); 1098 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1099 *((unsigned*)reloc) = sym_addr; 1100 break; 1101 case R_ARM_ABS32: 1102 count_relocation(kRelocAbsolute); 1103 MARK(rel->r_offset); 1104 TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1105 *((unsigned*)reloc) += sym_addr; 1106 break; 1107 case R_ARM_REL32: 1108 count_relocation(kRelocRelative); 1109 MARK(rel->r_offset); 1110 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s\n", 1111 reloc, sym_addr, rel->r_offset, sym_name); 1112 *((unsigned*)reloc) += sym_addr - rel->r_offset; 1113 break; 1114#elif defined(ANDROID_X86_LINKER) 1115 case R_386_JMP_SLOT: 1116 count_relocation(kRelocAbsolute); 1117 MARK(rel->r_offset); 1118 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1119 *((unsigned*)reloc) = sym_addr; 1120 break; 1121 case R_386_GLOB_DAT: 1122 count_relocation(kRelocAbsolute); 1123 MARK(rel->r_offset); 1124 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1125 *((unsigned*)reloc) = sym_addr; 1126 break; 1127#elif defined(ANDROID_MIPS_LINKER) 1128 case R_MIPS_JUMP_SLOT: 1129 count_relocation(kRelocAbsolute); 1130 MARK(rel->r_offset); 1131 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1132 *((unsigned*)reloc) = sym_addr; 1133 break; 1134 case R_MIPS_REL32: 1135 count_relocation(kRelocAbsolute); 1136 MARK(rel->r_offset); 1137 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s\n", 1138 reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); 1139 if (s) { 1140 *((unsigned*)reloc) += sym_addr; 1141 } else { 1142 *((unsigned*)reloc) += si->base; 1143 } 1144 break; 1145#endif /* ANDROID_*_LINKER */ 1146 1147#if defined(ANDROID_ARM_LINKER) 1148 case R_ARM_RELATIVE: 1149#elif defined(ANDROID_X86_LINKER) 1150 case R_386_RELATIVE: 1151#endif /* ANDROID_*_LINKER */ 1152 count_relocation(kRelocRelative); 1153 MARK(rel->r_offset); 1154 if (sym) { 1155 DL_ERR("odd RELATIVE form..."); 1156 return -1; 1157 } 1158 TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x\n", reloc, si->base); 1159 *((unsigned*)reloc) += si->base; 1160 break; 1161 1162#if defined(ANDROID_X86_LINKER) 1163 case R_386_32: 1164 count_relocation(kRelocRelative); 1165 MARK(rel->r_offset); 1166 1167 TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s\n", reloc, sym_addr, sym_name); 1168 *((unsigned *)reloc) += (unsigned)sym_addr; 1169 break; 1170 1171 case R_386_PC32: 1172 count_relocation(kRelocRelative); 1173 MARK(rel->r_offset); 1174 TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s\n", 1175 reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); 1176 *((unsigned *)reloc) += (unsigned)(sym_addr - reloc); 1177 break; 1178#endif /* ANDROID_X86_LINKER */ 1179 1180#ifdef ANDROID_ARM_LINKER 1181 case R_ARM_COPY: 1182 if ((si->flags & FLAG_EXE) == 0) { 1183 /* 1184 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf 1185 * 1186 * Section 4.7.1.10 "Dynamic relocations" 1187 * R_ARM_COPY may only appear in executable objects where e_type is 1188 * set to ET_EXEC. 1189 * 1190 * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. 1191 * We should explicitly disallow ET_DYN executables from having 1192 * R_ARM_COPY relocations. 1193 */ 1194 DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); 1195 return -1; 1196 } 1197 count_relocation(kRelocCopy); 1198 MARK(rel->r_offset); 1199 TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s\n", reloc, s->st_size, sym_addr, sym_name); 1200 if (reloc == sym_addr) { 1201 Elf32_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed); 1202 1203 if (src == NULL) { 1204 DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name); 1205 return -1; 1206 } 1207 if (lsi->has_DT_SYMBOLIC) { 1208 DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared " 1209 "library %s (built with -Bsymbolic?)", si->name, lsi->name); 1210 return -1; 1211 } 1212 if (s->st_size < src->st_size) { 1213 DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)", 1214 si->name, s->st_size, src->st_size); 1215 return -1; 1216 } 1217 memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size); 1218 } else { 1219 DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name); 1220 return -1; 1221 } 1222 break; 1223#endif /* ANDROID_ARM_LINKER */ 1224 1225 default: 1226 DL_ERR("unknown reloc type %d @ %p (%d)", 1227 type, rel, (int) (rel - start)); 1228 return -1; 1229 } 1230 } 1231 return 0; 1232} 1233 1234#ifdef ANDROID_MIPS_LINKER 1235static int mips_relocate_got(soinfo* si, soinfo* needed[]) { 1236 unsigned *got; 1237 unsigned local_gotno, gotsym, symtabno; 1238 Elf32_Sym *symtab, *sym; 1239 unsigned g; 1240 1241 got = si->plt_got; 1242 local_gotno = si->mips_local_gotno; 1243 gotsym = si->mips_gotsym; 1244 symtabno = si->mips_symtabno; 1245 symtab = si->symtab; 1246 1247 /* 1248 * got[0] is address of lazy resolver function 1249 * got[1] may be used for a GNU extension 1250 * set it to a recognizable address in case someone calls it 1251 * (should be _rtld_bind_start) 1252 * FIXME: maybe this should be in a separate routine 1253 */ 1254 1255 if ((si->flags & FLAG_LINKER) == 0) { 1256 g = 0; 1257 got[g++] = 0xdeadbeef; 1258 if (got[g] & 0x80000000) { 1259 got[g++] = 0xdeadfeed; 1260 } 1261 /* 1262 * Relocate the local GOT entries need to be relocated 1263 */ 1264 for (; g < local_gotno; g++) { 1265 got[g] += si->load_bias; 1266 } 1267 } 1268 1269 /* Now for the global GOT entries */ 1270 sym = symtab + gotsym; 1271 got = si->plt_got + local_gotno; 1272 for (g = gotsym; g < symtabno; g++, sym++, got++) { 1273 const char *sym_name; 1274 Elf32_Sym *s; 1275 soinfo *lsi; 1276 1277 /* This is an undefined reference... try to locate it */ 1278 sym_name = si->strtab + sym->st_name; 1279 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1280 if (s == NULL) { 1281 /* We only allow an undefined symbol if this is a weak 1282 reference.. */ 1283 s = &symtab[g]; 1284 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1285 DL_ERR("cannot locate \"%s\"...", sym_name); 1286 return -1; 1287 } 1288 *got = 0; 1289 } 1290 else { 1291 /* FIXME: is this sufficient? 1292 * For reference see NetBSD link loader 1293 * 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 1294 */ 1295 *got = lsi->load_bias + s->st_value; 1296 } 1297 } 1298 return 0; 1299} 1300#endif 1301 1302/* Please read the "Initialization and Termination functions" functions. 1303 * of the linker design note in bionic/linker/README.TXT to understand 1304 * what the following code is doing. 1305 * 1306 * The important things to remember are: 1307 * 1308 * DT_PREINIT_ARRAY must be called first for executables, and should 1309 * not appear in shared libraries. 1310 * 1311 * DT_INIT should be called before DT_INIT_ARRAY if both are present 1312 * 1313 * DT_FINI should be called after DT_FINI_ARRAY if both are present 1314 * 1315 * DT_FINI_ARRAY must be parsed in reverse order. 1316 */ 1317void soinfo::CallArray(const char* array_name UNUSED, unsigned* array, int count, bool reverse) { 1318 if (array == NULL) { 1319 return; 1320 } 1321 1322 int step = 1; 1323 if (reverse) { 1324 array += (count-1); 1325 step = -1; 1326 } 1327 1328 TRACE("[ Calling %s @ %p [%d] for '%s' ]\n", array_name, array, count, name); 1329 1330 for (int n = count; n > 0; n--) { 1331 TRACE("[ Looking at %s[%d] *%p == 0x%08x ]\n", array_name, n, array, *array); 1332 void (*func)() = (void (*)()) *array; 1333 array += step; 1334 if (((int) func == 0) || ((int) func == -1)) { 1335 continue; 1336 } 1337 TRACE("[ Calling func @ %p ]\n", func); 1338 func(); 1339 } 1340 1341 TRACE("[ Done calling %s for '%s' ]\n", array_name, name); 1342} 1343 1344void soinfo::CallFunction(const char* function_name UNUSED, void (*function)()) { 1345 if (function == NULL) { 1346 return; 1347 } 1348 1349 TRACE("[ Calling %s @ %p for '%s' ]\n", function_name, function, name); 1350 function(); 1351 TRACE("[ Done calling %s for '%s' ]\n", function_name, name); 1352} 1353 1354void soinfo::CallPreInitConstructors() { 1355 CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false); 1356} 1357 1358void soinfo::CallConstructors() { 1359 if (constructors_called) { 1360 return; 1361 } 1362 1363 // We set constructors_called before actually calling the constructors, otherwise it doesn't 1364 // protect against recursive constructor calls. One simple example of constructor recursion 1365 // is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so: 1366 // 1. The program depends on libc, so libc's constructor is called here. 1367 // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. 1368 // 3. dlopen() calls the constructors on the newly created 1369 // soinfo for libc_malloc_debug_leak.so. 1370 // 4. The debug .so depends on libc, so CallConstructors is 1371 // called again with the libc soinfo. If it doesn't trigger the early- 1372 // out above, the libc constructor will be called again (recursively!). 1373 constructors_called = true; 1374 1375 if (!(flags & FLAG_EXE) && preinit_array) { 1376 DL_ERR("shared library \"%s\" has a preinit_array table @ %p", name, preinit_array); 1377 return; 1378 } 1379 1380 if (dynamic) { 1381 for (unsigned* d = dynamic; *d; d += 2) { 1382 if (d[0] == DT_NEEDED) { 1383 soinfo* lsi = find_loaded_library(strtab + d[1]); 1384 if (lsi == NULL) { 1385 DL_ERR("\"%s\": could not initialize dependent library", name); 1386 } else { 1387 lsi->CallConstructors(); 1388 } 1389 } 1390 } 1391 } 1392 1393 CallFunction("DT_INIT", init_func); 1394 CallArray("DT_INIT_ARRAY", init_array, init_array_count, false); 1395} 1396 1397void soinfo::CallDestructors() { 1398 CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true); 1399 CallFunction("DT_FINI", fini_func); 1400} 1401 1402/* Force any of the closed stdin, stdout and stderr to be associated with 1403 /dev/null. */ 1404static int nullify_closed_stdio() { 1405 int dev_null, i, status; 1406 int return_value = 0; 1407 1408 dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 1409 if (dev_null < 0) { 1410 DL_ERR("cannot open /dev/null: %s", strerror(errno)); 1411 return -1; 1412 } 1413 TRACE("[ Opened /dev/null file-descriptor=%d]\n", dev_null); 1414 1415 /* If any of the stdio file descriptors is valid and not associated 1416 with /dev/null, dup /dev/null to it. */ 1417 for (i = 0; i < 3; i++) { 1418 /* If it is /dev/null already, we are done. */ 1419 if (i == dev_null) { 1420 continue; 1421 } 1422 1423 TRACE("[ Nullifying stdio file descriptor %d]\n", i); 1424 status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 1425 1426 /* If file is opened, we are good. */ 1427 if (status != -1) { 1428 continue; 1429 } 1430 1431 /* The only error we allow is that the file descriptor does not 1432 exist, in which case we dup /dev/null to it. */ 1433 if (errno != EBADF) { 1434 DL_ERR("fcntl failed: %s", strerror(errno)); 1435 return_value = -1; 1436 continue; 1437 } 1438 1439 /* Try dupping /dev/null to this stdio file descriptor and 1440 repeat if there is a signal. Note that any errors in closing 1441 the stdio descriptor are lost. */ 1442 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 1443 if (status < 0) { 1444 DL_ERR("dup2 failed: %s", strerror(errno)); 1445 return_value = -1; 1446 continue; 1447 } 1448 } 1449 1450 /* If /dev/null is not one of the stdio file descriptors, close it. */ 1451 if (dev_null > 2) { 1452 TRACE("[ Closing /dev/null file-descriptor=%d]\n", dev_null); 1453 status = TEMP_FAILURE_RETRY(close(dev_null)); 1454 if (status == -1) { 1455 DL_ERR("close failed: %s", strerror(errno)); 1456 return_value = -1; 1457 } 1458 } 1459 1460 return return_value; 1461} 1462 1463static bool soinfo_link_image(soinfo* si) { 1464 si->flags |= FLAG_ERROR; 1465 1466 /* "base" might wrap around UINT32_MAX. */ 1467 Elf32_Addr base = si->load_bias; 1468 const Elf32_Phdr *phdr = si->phdr; 1469 int phnum = si->phnum; 1470 int relocating_linker = (si->flags & FLAG_LINKER) != 0; 1471 soinfo **needed, **pneeded; 1472 1473 /* We can't debug anything until the linker is relocated */ 1474 if (!relocating_linker) { 1475 INFO("[ linking %s ]\n", si->name); 1476 DEBUG("si->base = 0x%08x si->flags = 0x%08x\n", si->base, si->flags); 1477 } 1478 1479 /* Extract dynamic section */ 1480 size_t dynamic_count; 1481 phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, 1482 &dynamic_count); 1483 if (si->dynamic == NULL) { 1484 if (!relocating_linker) { 1485 DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name); 1486 } 1487 return false; 1488 } else { 1489 if (!relocating_linker) { 1490 DEBUG("dynamic = %p\n", si->dynamic); 1491 } 1492 } 1493 1494#ifdef ANDROID_ARM_LINKER 1495 (void) phdr_table_get_arm_exidx(phdr, phnum, base, 1496 &si->ARM_exidx, &si->ARM_exidx_count); 1497#endif 1498 1499 /* extract useful information from dynamic section */ 1500 for (unsigned* d = si->dynamic; *d; ++d) { 1501 DEBUG("d = %p, d[0] = 0x%08x d[1] = 0x%08x\n", d, d[0], d[1]); 1502 switch(*d++){ 1503 case DT_HASH: 1504 si->nbucket = ((unsigned *) (base + *d))[0]; 1505 si->nchain = ((unsigned *) (base + *d))[1]; 1506 si->bucket = (unsigned *) (base + *d + 8); 1507 si->chain = (unsigned *) (base + *d + 8 + si->nbucket * 4); 1508 break; 1509 case DT_STRTAB: 1510 si->strtab = (const char *) (base + *d); 1511 break; 1512 case DT_SYMTAB: 1513 si->symtab = (Elf32_Sym *) (base + *d); 1514 break; 1515 case DT_PLTREL: 1516 if(*d != DT_REL) { 1517 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1518 return false; 1519 } 1520 break; 1521 case DT_JMPREL: 1522 si->plt_rel = (Elf32_Rel*) (base + *d); 1523 break; 1524 case DT_PLTRELSZ: 1525 si->plt_rel_count = *d / 8; 1526 break; 1527 case DT_REL: 1528 si->rel = (Elf32_Rel*) (base + *d); 1529 break; 1530 case DT_RELSZ: 1531 si->rel_count = *d / 8; 1532 break; 1533 case DT_PLTGOT: 1534 /* Save this in case we decide to do lazy binding. We don't yet. */ 1535 si->plt_got = (unsigned *)(base + *d); 1536 break; 1537 case DT_DEBUG: 1538#if !defined(ANDROID_MIPS_LINKER) 1539 // Set the DT_DEBUG entry to the address of _r_debug for GDB 1540 *d = (int) &_r_debug; 1541#endif 1542 break; 1543 case DT_RELA: 1544 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1545 return false; 1546 case DT_INIT: 1547 si->init_func = (void (*)(void))(base + *d); 1548 DEBUG("%s constructors (init func) found at %p\n", si->name, si->init_func); 1549 break; 1550 case DT_FINI: 1551 si->fini_func = (void (*)(void))(base + *d); 1552 DEBUG("%s destructors (fini func) found at %p\n", si->name, si->fini_func); 1553 break; 1554 case DT_INIT_ARRAY: 1555 si->init_array = (unsigned *)(base + *d); 1556 DEBUG("%s constructors (init_array) found at %p\n", si->name, si->init_array); 1557 break; 1558 case DT_INIT_ARRAYSZ: 1559 si->init_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); 1560 break; 1561 case DT_FINI_ARRAY: 1562 si->fini_array = (unsigned *)(base + *d); 1563 DEBUG("%s destructors (fini_array) found at %p\n", si->name, si->fini_array); 1564 break; 1565 case DT_FINI_ARRAYSZ: 1566 si->fini_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); 1567 break; 1568 case DT_PREINIT_ARRAY: 1569 si->preinit_array = (unsigned *)(base + *d); 1570 DEBUG("%s constructors (preinit_array) found at %p\n", si->name, si->preinit_array); 1571 break; 1572 case DT_PREINIT_ARRAYSZ: 1573 si->preinit_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); 1574 break; 1575 case DT_TEXTREL: 1576 si->has_text_relocations = true; 1577 break; 1578 case DT_SYMBOLIC: 1579 si->has_DT_SYMBOLIC = true; 1580 break; 1581#if defined(DT_FLAGS) 1582 case DT_FLAGS: 1583 if (*d & DF_TEXTREL) { 1584 si->has_text_relocations = true; 1585 } 1586 if (*d & DF_SYMBOLIC) { 1587 si->has_DT_SYMBOLIC = true; 1588 } 1589 break; 1590#endif 1591#if defined(ANDROID_MIPS_LINKER) 1592 case DT_NEEDED: 1593 case DT_STRSZ: 1594 case DT_SYMENT: 1595 case DT_RELENT: 1596 break; 1597 case DT_MIPS_RLD_MAP: 1598 // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. 1599 { 1600 r_debug** dp = (r_debug**) *d; 1601 *dp = &_r_debug; 1602 } 1603 break; 1604 case DT_MIPS_RLD_VERSION: 1605 case DT_MIPS_FLAGS: 1606 case DT_MIPS_BASE_ADDRESS: 1607 case DT_MIPS_UNREFEXTNO: 1608 case DT_MIPS_RWPLT: 1609 break; 1610 1611 case DT_MIPS_PLTGOT: 1612#if 0 1613 /* not yet... */ 1614 si->mips_pltgot = (unsigned *)(si->base + *d); 1615#endif 1616 break; 1617 1618 case DT_MIPS_SYMTABNO: 1619 si->mips_symtabno = *d; 1620 break; 1621 1622 case DT_MIPS_LOCAL_GOTNO: 1623 si->mips_local_gotno = *d; 1624 break; 1625 1626 case DT_MIPS_GOTSYM: 1627 si->mips_gotsym = *d; 1628 break; 1629 1630 default: 1631 DEBUG("Unused DT entry: type 0x%08x arg 0x%08x\n", d[-1], d[0]); 1632 break; 1633#endif 1634 } 1635 } 1636 1637 DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p\n", 1638 si->base, si->strtab, si->symtab); 1639 1640 // Sanity checks. 1641 if (si->nbucket == 0) { 1642 DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name); 1643 return false; 1644 } 1645 if (si->strtab == 0) { 1646 DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name); 1647 return false; 1648 } 1649 if (si->symtab == 0) { 1650 DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name); 1651 return false; 1652 } 1653 1654 /* if this is the main executable, then load all of the preloads now */ 1655 if (si->flags & FLAG_EXE) { 1656 memset(preloads, 0, sizeof(preloads)); 1657 for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) { 1658 soinfo* lsi = find_library(gLdPreloadNames[i]); 1659 if (lsi == NULL) { 1660 strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf)); 1661 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1662 gLdPreloadNames[i], si->name, tmp_err_buf); 1663 return false; 1664 } 1665 preloads[i] = lsi; 1666 } 1667 } 1668 1669 /* dynamic_count is an upper bound for the number of needed libs */ 1670 pneeded = needed = (soinfo**) alloca((1 + dynamic_count) * sizeof(soinfo*)); 1671 1672 for (unsigned* d = si->dynamic; *d; d += 2) { 1673 if (d[0] == DT_NEEDED) { 1674 DEBUG("%s needs %s\n", si->name, si->strtab + d[1]); 1675 soinfo* lsi = find_library(si->strtab + d[1]); 1676 if (lsi == NULL) { 1677 strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf)); 1678 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1679 si->strtab + d[1], si->name, tmp_err_buf); 1680 return false; 1681 } 1682 *pneeded++ = lsi; 1683 } 1684 } 1685 *pneeded = NULL; 1686 1687 if (si->has_text_relocations) { 1688 /* Unprotect the segments, i.e. make them writable, to allow 1689 * text relocations to work properly. We will later call 1690 * phdr_table_protect_segments() after all of them are applied 1691 * and all constructors are run. 1692 */ 1693 if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1694 DL_ERR("can't unprotect loadable segments for \"%s\": %s", 1695 si->name, strerror(errno)); 1696 return false; 1697 } 1698 } 1699 1700 if (si->plt_rel) { 1701 DEBUG("[ relocating %s plt ]\n", si->name ); 1702 if(soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) { 1703 return false; 1704 } 1705 } 1706 if (si->rel) { 1707 DEBUG("[ relocating %s ]\n", si->name ); 1708 if(soinfo_relocate(si, si->rel, si->rel_count, needed)) { 1709 return false; 1710 } 1711 } 1712 1713#ifdef ANDROID_MIPS_LINKER 1714 if (mips_relocate_got(si, needed)) { 1715 return false; 1716 } 1717#endif 1718 1719 si->flags |= FLAG_LINKED; 1720 DEBUG("[ finished linking %s ]\n", si->name); 1721 1722 if (si->has_text_relocations) { 1723 /* All relocations are done, we can protect our segments back to 1724 * read-only. */ 1725 if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1726 DL_ERR("can't protect segments for \"%s\": %s", 1727 si->name, strerror(errno)); 1728 return false; 1729 } 1730 } 1731 1732 /* We can also turn on GNU RELRO protection */ 1733 if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { 1734 DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", 1735 si->name, strerror(errno)); 1736 return false; 1737 } 1738 1739 // If this is a setuid/setgid program, close the security hole described in 1740 // ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc 1741 if (get_AT_SECURE()) { 1742 nullify_closed_stdio(); 1743 } 1744 notify_gdb_of_load(si); 1745 si->flags &= ~FLAG_ERROR; 1746 return true; 1747} 1748 1749static void parse_path(const char* path, const char* delimiters, 1750 const char** array, char* buf, size_t buf_size, size_t max_count) 1751{ 1752 if (path == NULL) { 1753 return; 1754 } 1755 1756 size_t len = strlcpy(buf, path, buf_size); 1757 1758 size_t i = 0; 1759 char* buf_p = buf; 1760 while (i < max_count && (array[i] = strsep(&buf_p, delimiters))) { 1761 if (*array[i] != '\0') { 1762 ++i; 1763 } 1764 } 1765 1766 // Forget the last path if we had to truncate; this occurs if the 2nd to 1767 // last char isn't '\0' (i.e. wasn't originally a delimiter). 1768 if (i > 0 && len >= buf_size && buf[buf_size - 2] != '\0') { 1769 array[i - 1] = NULL; 1770 } else { 1771 array[i] = NULL; 1772 } 1773} 1774 1775static void parse_LD_LIBRARY_PATH(const char* path) { 1776 parse_path(path, ":", gLdPaths, 1777 gLdPathsBuffer, sizeof(gLdPathsBuffer), LDPATH_MAX); 1778} 1779 1780static void parse_LD_PRELOAD(const char* path) { 1781 // We have historically supported ':' as well as ' ' in LD_PRELOAD. 1782 parse_path(path, " :", gLdPreloadNames, 1783 gLdPreloadsBuffer, sizeof(gLdPreloadsBuffer), LDPRELOAD_MAX); 1784} 1785 1786/* 1787 * This code is called after the linker has linked itself and 1788 * fixed it's own GOT. It is safe to make references to externs 1789 * and other non-local data at this point. 1790 */ 1791static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linker_base) 1792{ 1793 static soinfo linker_soinfo; 1794 1795 int argc = (int) *elfdata; 1796 char **argv = (char**) (elfdata + 1); 1797 unsigned *vecs = (unsigned*) (argv + argc + 1); 1798 1799 /* NOTE: we store the elfdata pointer on a special location 1800 * of the temporary TLS area in order to pass it to 1801 * the C Library's runtime initializer. 1802 * 1803 * The initializer must clear the slot and reset the TLS 1804 * to point to a different location to ensure that no other 1805 * shared library constructor can access it. 1806 */ 1807 __libc_init_tls(elfdata); 1808 1809#if TIMING 1810 struct timeval t0, t1; 1811 gettimeofday(&t0, 0); 1812#endif 1813 1814 // Initialize environment functions, and get to the ELF aux vectors table. 1815 vecs = linker_env_init(vecs); 1816 1817 debugger_init(); 1818 1819 // Get a few environment variables. 1820 const char* LD_DEBUG = linker_env_get("LD_DEBUG"); 1821 if (LD_DEBUG != NULL) { 1822 debug_verbosity = atoi(LD_DEBUG); 1823 } 1824 1825 // Normally, these are cleaned by linker_env_init, but the test 1826 // doesn't cost us anything. 1827 const char* ldpath_env = NULL; 1828 const char* ldpreload_env = NULL; 1829 if (!get_AT_SECURE()) { 1830 ldpath_env = linker_env_get("LD_LIBRARY_PATH"); 1831 ldpreload_env = linker_env_get("LD_PRELOAD"); 1832 } 1833 1834 INFO("[ android linker & debugger ]\n"); 1835 DEBUG("elfdata @ 0x%08x\n", (unsigned)elfdata); 1836 1837 soinfo* si = soinfo_alloc(argv[0]); 1838 if (si == NULL) { 1839 exit(EXIT_FAILURE); 1840 } 1841 1842 /* bootstrap the link map, the main exe always needs to be first */ 1843 si->flags |= FLAG_EXE; 1844 link_map* map = &(si->linkmap); 1845 1846 map->l_addr = 0; 1847 map->l_name = argv[0]; 1848 map->l_prev = NULL; 1849 map->l_next = NULL; 1850 1851 _r_debug.r_map = map; 1852 r_debug_tail = map; 1853 1854 /* gdb expects the linker to be in the debug shared object list. 1855 * Without this, gdb has trouble locating the linker's ".text" 1856 * and ".plt" sections. Gdb could also potentially use this to 1857 * relocate the offset of our exported 'rtld_db_dlactivity' symbol. 1858 * Don't use soinfo_alloc(), because the linker shouldn't 1859 * be on the soinfo list. 1860 */ 1861 strlcpy((char*) linker_soinfo.name, "/system/bin/linker", sizeof linker_soinfo.name); 1862 linker_soinfo.flags = 0; 1863 linker_soinfo.base = linker_base; 1864 /* 1865 * Set the dynamic field in the link map otherwise gdb will complain with 1866 * the following: 1867 * warning: .dynamic section for "/system/bin/linker" is not at the 1868 * expected address (wrong library or version mismatch?) 1869 */ 1870 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base; 1871 Elf32_Phdr *phdr = 1872 (Elf32_Phdr *)((unsigned char *) linker_base + elf_hdr->e_phoff); 1873 phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, 1874 &linker_soinfo.dynamic, NULL); 1875 insert_soinfo_into_debug_map(&linker_soinfo); 1876 1877 /* extract information passed from the kernel */ 1878 while (vecs[0] != 0){ 1879 switch(vecs[0]){ 1880 case AT_PHDR: 1881 si->phdr = (Elf32_Phdr*) vecs[1]; 1882 break; 1883 case AT_PHNUM: 1884 si->phnum = (int) vecs[1]; 1885 break; 1886 case AT_ENTRY: 1887 si->entry = vecs[1]; 1888 break; 1889 } 1890 vecs += 2; 1891 } 1892 1893 /* Compute the value of si->base. We can't rely on the fact that 1894 * the first entry is the PHDR because this will not be true 1895 * for certain executables (e.g. some in the NDK unit test suite) 1896 */ 1897 int nn; 1898 si->base = 0; 1899 si->size = phdr_table_get_load_size(si->phdr, si->phnum); 1900 si->load_bias = 0; 1901 for ( nn = 0; nn < si->phnum; nn++ ) { 1902 if (si->phdr[nn].p_type == PT_PHDR) { 1903 si->load_bias = (Elf32_Addr)si->phdr - si->phdr[nn].p_vaddr; 1904 si->base = (Elf32_Addr) si->phdr - si->phdr[nn].p_offset; 1905 break; 1906 } 1907 } 1908 si->dynamic = (unsigned *)-1; 1909 si->refcount = 1; 1910 1911 // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). 1912 parse_LD_LIBRARY_PATH(ldpath_env); 1913 parse_LD_PRELOAD(ldpreload_env); 1914 1915 somain = si; 1916 1917 if (!soinfo_link_image(si)) { 1918 char errmsg[] = "CANNOT LINK EXECUTABLE\n"; 1919 write(2, __linker_dl_err_buf, strlen(__linker_dl_err_buf)); 1920 write(2, errmsg, sizeof(errmsg)); 1921 exit(EXIT_FAILURE); 1922 } 1923 1924 si->CallPreInitConstructors(); 1925 1926 for (size_t i = 0; preloads[i] != NULL; ++i) { 1927 preloads[i]->CallConstructors(); 1928 } 1929 1930 /*After the link_image, the si->base is initialized. 1931 *For so lib, the map->l_addr will be updated in notify_gdb_of_load. 1932 *We need to update this value for so exe here. So Unwind_Backtrace 1933 *for some arch like x86 could work correctly within so exe. 1934 */ 1935 map->l_addr = si->base; 1936 si->CallConstructors(); 1937 1938#if TIMING 1939 gettimeofday(&t1,NULL); 1940 PRINT("LINKER TIME: %s: %d microseconds\n", argv[0], (int) ( 1941 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - 1942 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) 1943 )); 1944#endif 1945#if STATS 1946 PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol\n", argv[0], 1947 linker_stats.count[kRelocAbsolute], 1948 linker_stats.count[kRelocRelative], 1949 linker_stats.count[kRelocCopy], 1950 linker_stats.count[kRelocSymbol]); 1951#endif 1952#if COUNT_PAGES 1953 { 1954 unsigned n; 1955 unsigned i; 1956 unsigned count = 0; 1957 for(n = 0; n < 4096; n++){ 1958 if(bitmask[n]){ 1959 unsigned x = bitmask[n]; 1960 for(i = 0; i < 8; i++){ 1961 if(x & 1) count++; 1962 x >>= 1; 1963 } 1964 } 1965 } 1966 PRINT("PAGES MODIFIED: %s: %d (%dKB)\n", argv[0], count, count * 4); 1967 } 1968#endif 1969 1970#if TIMING || STATS || COUNT_PAGES 1971 fflush(stdout); 1972#endif 1973 1974 TRACE("[ Ready to execute '%s' @ 0x%08x ]\n", si->name, si->entry); 1975 return si->entry; 1976} 1977 1978/* 1979 * Find the value of AT_BASE passed to us by the kernel. This is the load 1980 * location of the linker. 1981 */ 1982static unsigned find_linker_base(unsigned **elfdata) { 1983 int argc = (int) *elfdata; 1984 char **argv = (char**) (elfdata + 1); 1985 unsigned *vecs = (unsigned*) (argv + argc + 1); 1986 while (vecs[0] != 0) { 1987 vecs++; 1988 } 1989 1990 /* The end of the environment block is marked by two NULL pointers */ 1991 vecs++; 1992 1993 while(vecs[0]) { 1994 if (vecs[0] == AT_BASE) { 1995 return vecs[1]; 1996 } 1997 vecs += 2; 1998 } 1999 2000 return 0; // should never happen 2001} 2002 2003/* Compute the load-bias of an existing executable. This shall only 2004 * be used to compute the load bias of an executable or shared library 2005 * that was loaded by the kernel itself. 2006 * 2007 * Input: 2008 * elf -> address of ELF header, assumed to be at the start of the file. 2009 * Return: 2010 * load bias, i.e. add the value of any p_vaddr in the file to get 2011 * the corresponding address in memory. 2012 */ 2013static Elf32_Addr 2014get_elf_exec_load_bias(const Elf32_Ehdr* elf) 2015{ 2016 Elf32_Addr offset = elf->e_phoff; 2017 const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset); 2018 const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum; 2019 const Elf32_Phdr* phdr; 2020 2021 for (phdr = phdr_table; phdr < phdr_end; phdr++) { 2022 if (phdr->p_type == PT_LOAD) { 2023 return (Elf32_Addr)elf + phdr->p_offset - phdr->p_vaddr; 2024 } 2025 } 2026 return 0; 2027} 2028 2029/* 2030 * This is the entry point for the linker, called from begin.S. This 2031 * method is responsible for fixing the linker's own relocations, and 2032 * then calling __linker_init_post_relocation(). 2033 * 2034 * Because this method is called before the linker has fixed it's own 2035 * relocations, any attempt to reference an extern variable, extern 2036 * function, or other GOT reference will generate a segfault. 2037 */ 2038extern "C" unsigned __linker_init(unsigned **elfdata) { 2039 unsigned linker_addr = find_linker_base(elfdata); 2040 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_addr; 2041 Elf32_Phdr *phdr = 2042 (Elf32_Phdr *)((unsigned char *) linker_addr + elf_hdr->e_phoff); 2043 2044 soinfo linker_so; 2045 memset(&linker_so, 0, sizeof(soinfo)); 2046 2047 linker_so.base = linker_addr; 2048 linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); 2049 linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); 2050 linker_so.dynamic = (unsigned *) -1; 2051 linker_so.phdr = phdr; 2052 linker_so.phnum = elf_hdr->e_phnum; 2053 linker_so.flags |= FLAG_LINKER; 2054 2055 if (!soinfo_link_image(&linker_so)) { 2056 // It would be nice to print an error message, but if the linker 2057 // can't link itself, there's no guarantee that we'll be able to 2058 // call write() (because it involves a GOT reference). 2059 // 2060 // This situation should never occur unless the linker itself 2061 // is corrupt. 2062 exit(EXIT_FAILURE); 2063 } 2064 2065 // We have successfully fixed our own relocations. It's safe to run 2066 // the main part of the linker now. 2067 unsigned start_address = __linker_init_post_relocation(elfdata, linker_addr); 2068 2069 set_soinfo_pool_protection(PROT_READ); 2070 2071 // Return the address that the calling assembly stub should jump to. 2072 return start_address; 2073} 2074