linker.cpp revision d2b1a7311f023a1c532b5b418fc4bc7bd835be34
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/debug_format.h> 45#include <private/logd.h> 46#include <private/ScopedPthreadMutexLocker.h> 47 48#include "linker.h" 49#include "linker_debug.h" 50#include "linker_environ.h" 51#include "linker_phdr.h" 52 53/* Assume average path length of 64 and max 8 paths */ 54#define LDPATH_BUFSIZE 512 55#define LDPATH_MAX 8 56 57#define LDPRELOAD_BUFSIZE 512 58#define LDPRELOAD_MAX 8 59 60/* >>> IMPORTANT NOTE - READ ME BEFORE MODIFYING <<< 61 * 62 * Do NOT use malloc() and friends or pthread_*() code here. 63 * Don't use printf() either; it's caused mysterious memory 64 * corruption in the past. 65 * The linker runs before we bring up libc and it's easiest 66 * to make sure it does not depend on any complex libc features 67 * 68 * open issues / todo: 69 * 70 * - are we doing everything we should for ARM_COPY relocations? 71 * - cleaner error reporting 72 * - after linking, set as much stuff as possible to READONLY 73 * and NOEXEC 74 */ 75 76static bool soinfo_link_image(soinfo* si); 77 78// We can't use malloc(3) in the dynamic linker. We use a linked list of anonymous 79// maps, each a single page in size. The pages are broken up into as many struct soinfo 80// objects as will fit, and they're all threaded together on a free list. 81#define SOINFO_PER_POOL ((PAGE_SIZE - sizeof(soinfo_pool_t*)) / sizeof(soinfo)) 82struct soinfo_pool_t { 83 soinfo_pool_t* next; 84 soinfo info[SOINFO_PER_POOL]; 85}; 86static struct soinfo_pool_t* gSoInfoPools = NULL; 87static soinfo* gSoInfoFreeList = NULL; 88 89static soinfo *solist = &libdl_info; 90static soinfo *sonext = &libdl_info; 91static soinfo *somain; /* main process, always the one after libdl_info */ 92 93static const char* const gSoPaths[] = { 94 "/vendor/lib", 95 "/system/lib", 96 NULL 97}; 98 99static char gLdPathsBuffer[LDPATH_BUFSIZE]; 100static const char* gLdPaths[LDPATH_MAX + 1]; 101 102static char gLdPreloadsBuffer[LDPRELOAD_BUFSIZE]; 103static const char* gLdPreloadNames[LDPRELOAD_MAX + 1]; 104 105static soinfo *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, strlen(msg)); \ 150 abort(); \ 151 } 152#define UNUSED __attribute__((unused)) 153DISALLOW_ALLOCATION(void*, malloc, (size_t u UNUSED)); 154DISALLOW_ALLOCATION(void, free, (void* u UNUSED)); 155DISALLOW_ALLOCATION(void*, realloc, (void* u1 UNUSED, size_t u2 UNUSED)); 156DISALLOW_ALLOCATION(void*, calloc, (size_t u1 UNUSED, size_t u2 UNUSED)); 157 158static char tmp_err_buf[768]; 159static char __linker_dl_err_buf[768]; 160#define DL_ERR(fmt, x...) \ 161 do { \ 162 __libc_format_buffer(__linker_dl_err_buf, sizeof(__linker_dl_err_buf), fmt, ##x); \ 163 /* If LD_DEBUG is set high enough, send every dlerror(3) message to the log. */ \ 164 DEBUG(fmt "\n", ##x); \ 165 } while(0) 166 167const char* linker_get_error() { 168 return &__linker_dl_err_buf[0]; 169} 170 171/* 172 * This function is an empty stub where GDB locates a breakpoint to get notified 173 * about linker activity. 174 */ 175extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(); 176 177static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, 178 RT_CONSISTENT, 0}; 179static link_map* r_debug_tail = 0; 180 181static pthread_mutex_t gDebugMutex = PTHREAD_MUTEX_INITIALIZER; 182 183static void insert_soinfo_into_debug_map(soinfo * info) { 184 // Copy the necessary fields into the debug structure. 185 link_map* map = &(info->linkmap); 186 map->l_addr = info->base; 187 map->l_name = (char*) info->name; 188 map->l_ld = (uintptr_t)info->dynamic; 189 190 /* Stick the new library at the end of the list. 191 * gdb tends to care more about libc than it does 192 * about leaf libraries, and ordering it this way 193 * reduces the back-and-forth over the wire. 194 */ 195 if (r_debug_tail) { 196 r_debug_tail->l_next = map; 197 map->l_prev = r_debug_tail; 198 map->l_next = 0; 199 } else { 200 _r_debug.r_map = map; 201 map->l_prev = 0; 202 map->l_next = 0; 203 } 204 r_debug_tail = map; 205} 206 207static void remove_soinfo_from_debug_map(soinfo* info) { 208 link_map* map = &(info->linkmap); 209 210 if (r_debug_tail == map) { 211 r_debug_tail = map->l_prev; 212 } 213 214 if (map->l_prev) { 215 map->l_prev->l_next = map->l_next; 216 } 217 if (map->l_next) { 218 map->l_next->l_prev = map->l_prev; 219 } 220} 221 222static void notify_gdb_of_load(soinfo* info) { 223 if (info->flags & FLAG_EXE) { 224 // GDB already knows about the main executable 225 return; 226 } 227 228 ScopedPthreadMutexLocker locker(&gDebugMutex); 229 230 _r_debug.r_state = RT_ADD; 231 rtld_db_dlactivity(); 232 233 insert_soinfo_into_debug_map(info); 234 235 _r_debug.r_state = RT_CONSISTENT; 236 rtld_db_dlactivity(); 237} 238 239static void notify_gdb_of_unload(soinfo* info) { 240 if (info->flags & FLAG_EXE) { 241 // GDB already knows about the main executable 242 return; 243 } 244 245 ScopedPthreadMutexLocker locker(&gDebugMutex); 246 247 _r_debug.r_state = RT_DELETE; 248 rtld_db_dlactivity(); 249 250 remove_soinfo_from_debug_map(info); 251 252 _r_debug.r_state = RT_CONSISTENT; 253 rtld_db_dlactivity(); 254} 255 256void notify_gdb_of_libraries() { 257 _r_debug.r_state = RT_ADD; 258 rtld_db_dlactivity(); 259 _r_debug.r_state = RT_CONSISTENT; 260 rtld_db_dlactivity(); 261} 262 263static bool ensure_free_list_non_empty() { 264 if (gSoInfoFreeList != NULL) { 265 return true; 266 } 267 268 // Allocate a new pool. 269 soinfo_pool_t* pool = reinterpret_cast<soinfo_pool_t*>(mmap(NULL, sizeof(*pool), 270 PROT_READ|PROT_WRITE, 271 MAP_PRIVATE|MAP_ANONYMOUS, 0, 0)); 272 if (pool == MAP_FAILED) { 273 return false; 274 } 275 276 // Add the pool to our list of pools. 277 pool->next = gSoInfoPools; 278 gSoInfoPools = pool; 279 280 // Chain the entries in the new pool onto the free list. 281 gSoInfoFreeList = &pool->info[0]; 282 soinfo* next = NULL; 283 for (int i = SOINFO_PER_POOL - 1; i >= 0; --i) { 284 pool->info[i].next = next; 285 next = &pool->info[i]; 286 } 287 288 return true; 289} 290 291static void set_soinfo_pool_protection(int protection) { 292 for (soinfo_pool_t* p = gSoInfoPools; p != NULL; p = p->next) { 293 if (mprotect(p, sizeof(*p), protection) == -1) { 294 abort(); // Can't happen. 295 } 296 } 297} 298 299static soinfo* soinfo_alloc(const char* name) { 300 if (strlen(name) >= SOINFO_NAME_LEN) { 301 DL_ERR("library name \"%s\" too long", name); 302 return NULL; 303 } 304 305 if (!ensure_free_list_non_empty()) { 306 DL_ERR("out of memory when loading \"%s\"", name); 307 return NULL; 308 } 309 310 // Take the head element off the free list. 311 soinfo* si = gSoInfoFreeList; 312 gSoInfoFreeList = gSoInfoFreeList->next; 313 314 // Initialize the new element. 315 memset(si, 0, sizeof(soinfo)); 316 strlcpy(si->name, name, sizeof(si->name)); 317 sonext->next = si; 318 sonext = si; 319 320 TRACE("name %s: allocated soinfo @ %p\n", name, si); 321 return si; 322} 323 324static void soinfo_free(soinfo* si) 325{ 326 if (si == NULL) { 327 return; 328 } 329 330 soinfo *prev = NULL, *trav; 331 332 TRACE("name %s: freeing soinfo @ %p\n", si->name, si); 333 334 for(trav = solist; trav != NULL; trav = trav->next){ 335 if (trav == si) 336 break; 337 prev = trav; 338 } 339 if (trav == NULL) { 340 /* si was not ni solist */ 341 DL_ERR("name \"%s\" is not in solist!", si->name); 342 return; 343 } 344 345 /* prev will never be NULL, because the first entry in solist is 346 always the static libdl_info. 347 */ 348 prev->next = si->next; 349 if (si == sonext) sonext = prev; 350 si->next = gSoInfoFreeList; 351 gSoInfoFreeList = si; 352} 353 354 355static void parse_path(const char* path, const char* delimiters, 356 const char** array, char* buf, size_t buf_size, size_t max_count) { 357 if (path == NULL) { 358 return; 359 } 360 361 size_t len = strlcpy(buf, path, buf_size); 362 363 size_t i = 0; 364 char* buf_p = buf; 365 while (i < max_count && (array[i] = strsep(&buf_p, delimiters))) { 366 if (*array[i] != '\0') { 367 ++i; 368 } 369 } 370 371 // Forget the last path if we had to truncate; this occurs if the 2nd to 372 // last char isn't '\0' (i.e. wasn't originally a delimiter). 373 if (i > 0 && len >= buf_size && buf[buf_size - 2] != '\0') { 374 array[i - 1] = NULL; 375 } else { 376 array[i] = NULL; 377 } 378} 379 380static void parse_LD_LIBRARY_PATH(const char* path) { 381 parse_path(path, ":", gLdPaths, 382 gLdPathsBuffer, sizeof(gLdPathsBuffer), LDPATH_MAX); 383} 384 385static void parse_LD_PRELOAD(const char* path) { 386 // We have historically supported ':' as well as ' ' in LD_PRELOAD. 387 parse_path(path, " :", gLdPreloadNames, 388 gLdPreloadsBuffer, sizeof(gLdPreloadsBuffer), LDPRELOAD_MAX); 389} 390 391#ifdef ANDROID_ARM_LINKER 392 393/* For a given PC, find the .so that it belongs to. 394 * Returns the base address of the .ARM.exidx section 395 * for that .so, and the number of 8-byte entries 396 * in that section (via *pcount). 397 * 398 * Intended to be called by libc's __gnu_Unwind_Find_exidx(). 399 * 400 * This function is exposed via dlfcn.cpp and libdl.so. 401 */ 402_Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount) 403{ 404 soinfo *si; 405 unsigned addr = (unsigned)pc; 406 407 for (si = solist; si != 0; si = si->next){ 408 if ((addr >= si->base) && (addr < (si->base + si->size))) { 409 *pcount = si->ARM_exidx_count; 410 return (_Unwind_Ptr)si->ARM_exidx; 411 } 412 } 413 *pcount = 0; 414 return NULL; 415} 416 417#elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) 418 419/* Here, we only have to provide a callback to iterate across all the 420 * loaded libraries. gcc_eh does the rest. */ 421int 422dl_iterate_phdr(int (*cb)(dl_phdr_info *info, size_t size, void *data), 423 void *data) 424{ 425 int rv = 0; 426 for (soinfo* si = solist; si != NULL; si = si->next) { 427 dl_phdr_info dl_info; 428 dl_info.dlpi_addr = si->linkmap.l_addr; 429 dl_info.dlpi_name = si->linkmap.l_name; 430 dl_info.dlpi_phdr = si->phdr; 431 dl_info.dlpi_phnum = si->phnum; 432 rv = cb(&dl_info, sizeof(dl_phdr_info), data); 433 if (rv != 0) { 434 break; 435 } 436 } 437 return rv; 438} 439 440#endif 441 442static Elf32_Sym *soinfo_elf_lookup(soinfo *si, unsigned hash, const char *name) 443{ 444 Elf32_Sym *s; 445 Elf32_Sym *symtab = si->symtab; 446 const char *strtab = si->strtab; 447 unsigned n; 448 449 TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %d\n", 450 name, si->name, si->base, hash, hash % si->nbucket); 451 n = hash % si->nbucket; 452 453 for(n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]){ 454 s = symtab + n; 455 if(strcmp(strtab + s->st_name, name)) continue; 456 457 /* only concern ourselves with global and weak symbol definitions */ 458 switch(ELF32_ST_BIND(s->st_info)){ 459 case STB_GLOBAL: 460 case STB_WEAK: 461 if(s->st_shndx == SHN_UNDEF) 462 continue; 463 464 TRACE_TYPE(LOOKUP, "FOUND %s in %s (%08x) %d\n", 465 name, si->name, s->st_value, s->st_size); 466 return s; 467 } 468 } 469 470 return NULL; 471} 472 473static unsigned elfhash(const char *_name) 474{ 475 const unsigned char *name = (const unsigned char *) _name; 476 unsigned h = 0, g; 477 478 while(*name) { 479 h = (h << 4) + *name++; 480 g = h & 0xf0000000; 481 h ^= g; 482 h ^= g >> 24; 483 } 484 return h; 485} 486 487static Elf32_Sym * 488soinfo_do_lookup(soinfo *si, const char *name, soinfo **lsi, 489 soinfo *needed[]) 490{ 491 unsigned elf_hash = elfhash(name); 492 Elf32_Sym *s = NULL; 493 int i; 494 495 if (si != NULL && somain != NULL) { 496 497 /* 498 * Local scope is executable scope. Just start looking into it right away 499 * for the shortcut. 500 */ 501 502 if (si == somain) { 503 s = soinfo_elf_lookup(si, elf_hash, name); 504 if (s != NULL) { 505 *lsi = si; 506 goto done; 507 } 508 } else { 509 /* Order of symbol lookup is controlled by DT_SYMBOLIC flag */ 510 511 /* 512 * If this object was built with symbolic relocations disabled, the 513 * first place to look to resolve external references is the main 514 * executable. 515 */ 516 517 if (!si->has_DT_SYMBOLIC) { 518 DEBUG("%s: looking up %s in executable %s\n", 519 si->name, name, somain->name); 520 s = soinfo_elf_lookup(somain, elf_hash, name); 521 if (s != NULL) { 522 *lsi = somain; 523 goto done; 524 } 525 } 526 527 /* Look for symbols in the local scope (the object who is 528 * searching). This happens with C++ templates on i386 for some 529 * reason. 530 * 531 * Notes on weak symbols: 532 * The ELF specs are ambiguous about treatment of weak definitions in 533 * dynamic linking. Some systems return the first definition found 534 * and some the first non-weak definition. This is system dependent. 535 * Here we return the first definition found for simplicity. */ 536 537 s = soinfo_elf_lookup(si, elf_hash, name); 538 if (s != NULL) { 539 *lsi = si; 540 goto done; 541 } 542 543 /* 544 * If this object was built with -Bsymbolic and symbol is not found 545 * in the local scope, try to find the symbol in the main executable. 546 */ 547 548 if (si->has_DT_SYMBOLIC) { 549 DEBUG("%s: looking up %s in executable %s after local scope\n", 550 si->name, name, somain->name); 551 s = soinfo_elf_lookup(somain, elf_hash, name); 552 if (s != NULL) { 553 *lsi = somain; 554 goto done; 555 } 556 } 557 } 558 } 559 560 /* Next, look for it in the preloads list */ 561 for(i = 0; preloads[i] != NULL; i++) { 562 s = soinfo_elf_lookup(preloads[i], elf_hash, name); 563 if(s != NULL) { 564 *lsi = preloads[i]; 565 goto done; 566 } 567 } 568 569 for(i = 0; needed[i] != NULL; i++) { 570 DEBUG("%s: looking up %s in %s\n", 571 si->name, name, needed[i]->name); 572 s = soinfo_elf_lookup(needed[i], elf_hash, name); 573 if (s != NULL) { 574 *lsi = needed[i]; 575 goto done; 576 } 577 } 578 579done: 580 if(s != NULL) { 581 TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = 0x%08x, " 582 "found in %s, base = 0x%08x, load bias = 0x%08x\n", 583 si->name, name, s->st_value, 584 (*lsi)->name, (*lsi)->base, (*lsi)->load_bias); 585 return s; 586 } 587 588 return NULL; 589} 590 591/* This is used by dl_sym(). It performs symbol lookup only within the 592 specified soinfo object and not in any of its dependencies. 593 */ 594Elf32_Sym *soinfo_lookup(soinfo *si, const char *name) 595{ 596 return soinfo_elf_lookup(si, elfhash(name), name); 597} 598 599/* This is used by dl_sym(). It performs a global symbol lookup. 600 */ 601Elf32_Sym* lookup(const char* name, soinfo** found, soinfo* start) { 602 unsigned elf_hash = elfhash(name); 603 604 if (start == NULL) { 605 start = solist; 606 } 607 608 Elf32_Sym* s = NULL; 609 for (soinfo* si = start; (s == NULL) && (si != NULL); si = si->next) { 610 s = soinfo_elf_lookup(si, elf_hash, name); 611 if (s != NULL) { 612 *found = si; 613 break; 614 } 615 } 616 617 if (s != NULL) { 618 TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, found->base = 0x%08x\n", 619 name, s->st_value, (*found)->base); 620 } 621 622 return s; 623} 624 625soinfo *find_containing_library(const void *addr) 626{ 627 soinfo *si; 628 629 for(si = solist; si != NULL; si = si->next) 630 { 631 if((unsigned)addr >= si->base && (unsigned)addr - si->base < si->size) { 632 return si; 633 } 634 } 635 636 return NULL; 637} 638 639Elf32_Sym *soinfo_find_symbol(soinfo* si, const void *addr) 640{ 641 unsigned int i; 642 unsigned soaddr = (unsigned)addr - si->base; 643 644 /* Search the library's symbol table for any defined symbol which 645 * contains this address */ 646 for(i=0; i<si->nchain; i++) { 647 Elf32_Sym *sym = &si->symtab[i]; 648 649 if(sym->st_shndx != SHN_UNDEF && 650 soaddr >= sym->st_value && 651 soaddr < sym->st_value + sym->st_size) { 652 return sym; 653 } 654 } 655 656 return NULL; 657} 658 659#if 0 660static void dump(soinfo *si) 661{ 662 Elf32_Sym *s = si->symtab; 663 unsigned n; 664 665 for(n = 0; n < si->nchain; n++) { 666 TRACE("%04d> %08x: %02x %04x %08x %08x %s\n", n, s, 667 s->st_info, s->st_shndx, s->st_value, s->st_size, 668 si->strtab + s->st_name); 669 s++; 670 } 671} 672#endif 673 674static int open_library_on_path(const char* name, const char* const paths[]) { 675 char buf[512]; 676 for (size_t i = 0; paths[i] != NULL; ++i) { 677 int n = __libc_format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name); 678 if (n < 0 || n >= static_cast<int>(sizeof(buf))) { 679 PRINT("Warning: ignoring very long library path: %s/%s\n", paths[i], name); 680 continue; 681 } 682 int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC)); 683 if (fd != -1) { 684 return fd; 685 } 686 } 687 return -1; 688} 689 690static int open_library(const char* name) { 691 TRACE("[ opening %s ]\n", name); 692 693 // If the name contains a slash, we should attempt to open it directly and not search the paths. 694 if (strchr(name, '/') != NULL) { 695 int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC)); 696 if (fd != -1) { 697 return fd; 698 } 699 // ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now. 700 } 701 702 // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths. 703 int fd = open_library_on_path(name, gLdPaths); 704 if (fd == -1) { 705 fd = open_library_on_path(name, gSoPaths); 706 } 707 return fd; 708} 709 710// Returns 'true' if the library is prelinked or on failure so we error out 711// either way. We no longer support prelinking. 712static bool is_prelinked(int fd, const char* name) 713{ 714 struct prelink_info_t { 715 long mmap_addr; 716 char tag[4]; // "PRE ". 717 }; 718 719 off_t sz = lseek(fd, -sizeof(prelink_info_t), SEEK_END); 720 if (sz < 0) { 721 DL_ERR("lseek failed: %s", strerror(errno)); 722 return true; 723 } 724 725 prelink_info_t info; 726 int rc = TEMP_FAILURE_RETRY(read(fd, &info, sizeof(info))); 727 if (rc != sizeof(info)) { 728 DL_ERR("could not read prelink_info_t structure for \"%s\": %s", name, strerror(errno)); 729 return true; 730 } 731 732 if (memcmp(info.tag, "PRE ", 4) == 0) { 733 DL_ERR("prelinked libraries no longer supported: %s", name); 734 return true; 735 } 736 return false; 737} 738 739/* verify_elf_header 740 * Verifies the content of an ELF header. 741 * 742 * Args: 743 * 744 * Returns: 745 * 0 on success 746 * -1 if no valid ELF object is found @ base. 747 */ 748static int 749verify_elf_header(const Elf32_Ehdr* hdr) 750{ 751 if (hdr->e_ident[EI_MAG0] != ELFMAG0) return -1; 752 if (hdr->e_ident[EI_MAG1] != ELFMAG1) return -1; 753 if (hdr->e_ident[EI_MAG2] != ELFMAG2) return -1; 754 if (hdr->e_ident[EI_MAG3] != ELFMAG3) return -1; 755 if (hdr->e_type != ET_DYN) return -1; 756 757 /* TODO: Should we verify anything else in the header? */ 758#ifdef ANDROID_ARM_LINKER 759 if (hdr->e_machine != EM_ARM) return -1; 760#elif defined(ANDROID_X86_LINKER) 761 if (hdr->e_machine != EM_386) return -1; 762#elif defined(ANDROID_MIPS_LINKER) 763 if (hdr->e_machine != EM_MIPS) return -1; 764#endif 765 return 0; 766} 767 768struct scoped_fd { 769 ~scoped_fd() { 770 if (fd != -1) { 771 close(fd); 772 } 773 } 774 int fd; 775}; 776 777struct soinfo_ptr { 778 soinfo_ptr(const char* name) { 779 const char* bname = strrchr(name, '/'); 780 ptr = soinfo_alloc(bname ? bname + 1 : name); 781 } 782 ~soinfo_ptr() { 783 soinfo_free(ptr); 784 } 785 soinfo* release() { 786 soinfo* result = ptr; 787 ptr = NULL; 788 return result; 789 } 790 soinfo* ptr; 791}; 792 793// TODO: rewrite linker_phdr.h to use a class, then lose this. 794struct phdr_ptr { 795 phdr_ptr() : phdr_mmap(NULL) {} 796 ~phdr_ptr() { 797 if (phdr_mmap != NULL) { 798 phdr_table_unload(phdr_mmap, phdr_size); 799 } 800 } 801 void* phdr_mmap; 802 Elf32_Addr phdr_size; 803}; 804 805static soinfo* load_library(const char* name) { 806 // Open the file. 807 scoped_fd fd; 808 fd.fd = open_library(name); 809 if (fd.fd == -1) { 810 DL_ERR("library \"%s\" not found", name); 811 return NULL; 812 } 813 814 // Read the ELF header. 815 Elf32_Ehdr header[1]; 816 int ret = TEMP_FAILURE_RETRY(read(fd.fd, (void*)header, sizeof(header))); 817 if (ret < 0) { 818 DL_ERR("can't read file \"%s\": %s", name, strerror(errno)); 819 return NULL; 820 } 821 if (ret != (int)sizeof(header)) { 822 DL_ERR("too small to be an ELF executable: %s", name); 823 return NULL; 824 } 825 if (verify_elf_header(header) < 0) { 826 DL_ERR("not a valid ELF executable: %s", name); 827 return NULL; 828 } 829 830 // Read the program header table. 831 const Elf32_Phdr* phdr_table; 832 phdr_ptr phdr_holder; 833 ret = phdr_table_load(fd.fd, header->e_phoff, header->e_phnum, 834 &phdr_holder.phdr_mmap, &phdr_holder.phdr_size, &phdr_table); 835 if (ret < 0) { 836 DL_ERR("can't load program header table: %s: %s", name, strerror(errno)); 837 return NULL; 838 } 839 size_t phdr_count = header->e_phnum; 840 841 // Get the load extents. 842 Elf32_Addr ext_sz = phdr_table_get_load_size(phdr_table, phdr_count); 843 TRACE("[ '%s' wants sz=0x%08x ]\n", name, ext_sz); 844 if (ext_sz == 0) { 845 DL_ERR("no loadable segments in file: %s", name); 846 return NULL; 847 } 848 849 // We no longer support pre-linked libraries. 850 if (is_prelinked(fd.fd, name)) { 851 return NULL; 852 } 853 854 // Reserve address space for all loadable segments. 855 void* load_start = NULL; 856 Elf32_Addr load_size = 0; 857 Elf32_Addr load_bias = 0; 858 ret = phdr_table_reserve_memory(phdr_table, 859 phdr_count, 860 &load_start, 861 &load_size, 862 &load_bias); 863 if (ret < 0) { 864 DL_ERR("can't reserve %d bytes in address space for \"%s\": %s", 865 ext_sz, name, strerror(errno)); 866 return NULL; 867 } 868 869 TRACE("[ allocated memory for %s @ %p (0x%08x) ]\n", name, load_start, load_size); 870 871 /* Map all the segments in our address space with default protections */ 872 ret = phdr_table_load_segments(phdr_table, 873 phdr_count, 874 load_bias, 875 fd.fd); 876 if (ret < 0) { 877 DL_ERR("can't map loadable segments for \"%s\": %s", 878 name, strerror(errno)); 879 return NULL; 880 } 881 882 soinfo_ptr si(name); 883 if (si.ptr == NULL) { 884 return NULL; 885 } 886 887 si.ptr->base = (Elf32_Addr) load_start; 888 si.ptr->size = load_size; 889 si.ptr->load_bias = load_bias; 890 si.ptr->flags = 0; 891 si.ptr->entry = 0; 892 si.ptr->dynamic = (unsigned *)-1; 893 si.ptr->phnum = phdr_count; 894 si.ptr->phdr = phdr_table_get_loaded_phdr(phdr_table, phdr_count, load_bias); 895 if (si.ptr->phdr == NULL) { 896 DL_ERR("can't find loaded PHDR for \"%s\"", name); 897 return NULL; 898 } 899 900 return si.release(); 901} 902 903static soinfo *find_loaded_library(const char *name) 904{ 905 soinfo *si; 906 const char *bname; 907 908 // TODO: don't use basename only for determining libraries 909 // http://code.google.com/p/android/issues/detail?id=6670 910 911 bname = strrchr(name, '/'); 912 bname = bname ? bname + 1 : name; 913 914 for(si = solist; si != NULL; si = si->next){ 915 if(!strcmp(bname, si->name)) { 916 return si; 917 } 918 } 919 return NULL; 920} 921 922static soinfo* find_library_internal(const char* name) { 923 if (name == NULL) { 924 return somain; 925 } 926 927 soinfo* si = find_loaded_library(name); 928 if (si != NULL) { 929 if (si->flags & FLAG_LINKED) { 930 return si; 931 } 932 DL_ERR("OOPS: recursive link to \"%s\"", si->name); 933 return NULL; 934 } 935 936 TRACE("[ '%s' has not been loaded yet. Locating...]\n", name); 937 si = load_library(name); 938 if (si == NULL) { 939 return NULL; 940 } 941 942 // At this point we know that whatever is loaded @ base is a valid ELF 943 // shared library whose segments are properly mapped in. 944 TRACE("[ init_library base=0x%08x sz=0x%08x name='%s') ]\n", 945 si->base, si->size, si->name); 946 947 if (!soinfo_link_image(si)) { 948 munmap(reinterpret_cast<void*>(si->base), si->size); 949 soinfo_free(si); 950 return NULL; 951 } 952 953 return si; 954} 955 956static soinfo* find_library(const char* name) { 957 soinfo* si = find_library_internal(name); 958 if (si != NULL) { 959 si->refcount++; 960 } 961 return si; 962} 963 964static int soinfo_unload(soinfo* si) { 965 if (si->refcount == 1) { 966 TRACE("unloading '%s'\n", si->name); 967 si->CallDestructors(); 968 969 for (unsigned* d = si->dynamic; *d; d += 2) { 970 if (d[0] == DT_NEEDED) { 971 soinfo* lsi = find_loaded_library(si->strtab + d[1]); 972 if (lsi != NULL) { 973 TRACE("%s needs to unload %s\n", si->name, lsi->name); 974 soinfo_unload(lsi); 975 } else { 976 // TODO: should we return -1 in this case? 977 DL_ERR("\"%s\": could not unload dependent library", si->name); 978 } 979 } 980 } 981 982 munmap(reinterpret_cast<void*>(si->base), si->size); 983 notify_gdb_of_unload(si); 984 soinfo_free(si); 985 si->refcount = 0; 986 } else { 987 si->refcount--; 988 TRACE("not unloading '%s', decrementing refcount to %d\n", si->name, si->refcount); 989 } 990 return 0; 991} 992 993void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) { 994 if (!get_AT_SECURE()) { 995 parse_LD_LIBRARY_PATH(ld_library_path); 996 } 997} 998 999soinfo* do_dlopen(const char* name, int flags) { 1000 if ((flags & ~(RTLD_NOW|RTLD_LAZY|RTLD_LOCAL|RTLD_GLOBAL)) != 0) { 1001 DL_ERR("invalid flags to dlopen: %x", flags); 1002 return NULL; 1003 } 1004 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 1005 soinfo* si = find_library(name); 1006 if (si != NULL) { 1007 si->CallConstructors(); 1008 } 1009 set_soinfo_pool_protection(PROT_READ); 1010 return si; 1011} 1012 1013int do_dlclose(soinfo* si) { 1014 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 1015 int result = soinfo_unload(si); 1016 set_soinfo_pool_protection(PROT_READ); 1017 return result; 1018} 1019 1020/* TODO: don't use unsigned for addrs below. It works, but is not 1021 * ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned 1022 * long. 1023 */ 1024static int soinfo_relocate(soinfo *si, Elf32_Rel *rel, unsigned count, 1025 soinfo *needed[]) 1026{ 1027 Elf32_Sym *symtab = si->symtab; 1028 const char *strtab = si->strtab; 1029 Elf32_Sym *s; 1030 Elf32_Rel *start = rel; 1031 soinfo *lsi; 1032 1033 for (size_t idx = 0; idx < count; ++idx, ++rel) { 1034 unsigned type = ELF32_R_TYPE(rel->r_info); 1035 unsigned sym = ELF32_R_SYM(rel->r_info); 1036 unsigned reloc = (unsigned)(rel->r_offset + si->load_bias); 1037 unsigned sym_addr = 0; 1038 char *sym_name = NULL; 1039 1040 DEBUG("Processing '%s' relocation at index %d\n", si->name, idx); 1041 if (type == 0) { // R_*_NONE 1042 continue; 1043 } 1044 if(sym != 0) { 1045 sym_name = (char *)(strtab + symtab[sym].st_name); 1046 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1047 if(s == NULL) { 1048 /* We only allow an undefined symbol if this is a weak 1049 reference.. */ 1050 s = &symtab[sym]; 1051 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1052 DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); 1053 return -1; 1054 } 1055 1056 /* IHI0044C AAELF 4.5.1.1: 1057 1058 Libraries are not searched to resolve weak references. 1059 It is not an error for a weak reference to remain 1060 unsatisfied. 1061 1062 During linking, the value of an undefined weak reference is: 1063 - Zero if the relocation type is absolute 1064 - The address of the place if the relocation is pc-relative 1065 - The address of nominal base address if the relocation 1066 type is base-relative. 1067 */ 1068 1069 switch (type) { 1070#if defined(ANDROID_ARM_LINKER) 1071 case R_ARM_JUMP_SLOT: 1072 case R_ARM_GLOB_DAT: 1073 case R_ARM_ABS32: 1074 case R_ARM_RELATIVE: /* Don't care. */ 1075#elif defined(ANDROID_X86_LINKER) 1076 case R_386_JMP_SLOT: 1077 case R_386_GLOB_DAT: 1078 case R_386_32: 1079 case R_386_RELATIVE: /* Dont' care. */ 1080#endif /* ANDROID_*_LINKER */ 1081 /* sym_addr was initialized to be zero above or relocation 1082 code below does not care about value of sym_addr. 1083 No need to do anything. */ 1084 break; 1085 1086#if defined(ANDROID_X86_LINKER) 1087 case R_386_PC32: 1088 sym_addr = reloc; 1089 break; 1090#endif /* ANDROID_X86_LINKER */ 1091 1092#if defined(ANDROID_ARM_LINKER) 1093 case R_ARM_COPY: 1094 /* Fall through. Can't really copy if weak symbol is 1095 not found in run-time. */ 1096#endif /* ANDROID_ARM_LINKER */ 1097 default: 1098 DL_ERR("unknown weak reloc type %d @ %p (%d)", 1099 type, rel, (int) (rel - start)); 1100 return -1; 1101 } 1102 } else { 1103 /* We got a definition. */ 1104#if 0 1105 if((base == 0) && (si->base != 0)){ 1106 /* linking from libraries to main image is bad */ 1107 DL_ERR("cannot locate \"%s\"...", 1108 strtab + symtab[sym].st_name); 1109 return -1; 1110 } 1111#endif 1112 sym_addr = (unsigned)(s->st_value + lsi->load_bias); 1113 } 1114 count_relocation(kRelocSymbol); 1115 } else { 1116 s = NULL; 1117 } 1118 1119/* TODO: This is ugly. Split up the relocations by arch into 1120 * different files. 1121 */ 1122 switch(type){ 1123#if defined(ANDROID_ARM_LINKER) 1124 case R_ARM_JUMP_SLOT: 1125 count_relocation(kRelocAbsolute); 1126 MARK(rel->r_offset); 1127 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1128 *((unsigned*)reloc) = sym_addr; 1129 break; 1130 case R_ARM_GLOB_DAT: 1131 count_relocation(kRelocAbsolute); 1132 MARK(rel->r_offset); 1133 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1134 *((unsigned*)reloc) = sym_addr; 1135 break; 1136 case R_ARM_ABS32: 1137 count_relocation(kRelocAbsolute); 1138 MARK(rel->r_offset); 1139 TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1140 *((unsigned*)reloc) += sym_addr; 1141 break; 1142 case R_ARM_REL32: 1143 count_relocation(kRelocRelative); 1144 MARK(rel->r_offset); 1145 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s\n", 1146 reloc, sym_addr, rel->r_offset, sym_name); 1147 *((unsigned*)reloc) += sym_addr - rel->r_offset; 1148 break; 1149#elif defined(ANDROID_X86_LINKER) 1150 case R_386_JMP_SLOT: 1151 count_relocation(kRelocAbsolute); 1152 MARK(rel->r_offset); 1153 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1154 *((unsigned*)reloc) = sym_addr; 1155 break; 1156 case R_386_GLOB_DAT: 1157 count_relocation(kRelocAbsolute); 1158 MARK(rel->r_offset); 1159 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1160 *((unsigned*)reloc) = sym_addr; 1161 break; 1162#elif defined(ANDROID_MIPS_LINKER) 1163 case R_MIPS_REL32: 1164 count_relocation(kRelocAbsolute); 1165 MARK(rel->r_offset); 1166 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s\n", 1167 reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); 1168 if (s) { 1169 *((unsigned*)reloc) += sym_addr; 1170 } else { 1171 *((unsigned*)reloc) += si->base; 1172 } 1173 break; 1174#endif /* ANDROID_*_LINKER */ 1175 1176#if defined(ANDROID_ARM_LINKER) 1177 case R_ARM_RELATIVE: 1178#elif defined(ANDROID_X86_LINKER) 1179 case R_386_RELATIVE: 1180#endif /* ANDROID_*_LINKER */ 1181 count_relocation(kRelocRelative); 1182 MARK(rel->r_offset); 1183 if (sym) { 1184 DL_ERR("odd RELATIVE form..."); 1185 return -1; 1186 } 1187 TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x\n", reloc, si->base); 1188 *((unsigned*)reloc) += si->base; 1189 break; 1190 1191#if defined(ANDROID_X86_LINKER) 1192 case R_386_32: 1193 count_relocation(kRelocRelative); 1194 MARK(rel->r_offset); 1195 1196 TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s\n", reloc, sym_addr, sym_name); 1197 *((unsigned *)reloc) += (unsigned)sym_addr; 1198 break; 1199 1200 case R_386_PC32: 1201 count_relocation(kRelocRelative); 1202 MARK(rel->r_offset); 1203 TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s\n", 1204 reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); 1205 *((unsigned *)reloc) += (unsigned)(sym_addr - reloc); 1206 break; 1207#endif /* ANDROID_X86_LINKER */ 1208 1209#ifdef ANDROID_ARM_LINKER 1210 case R_ARM_COPY: 1211 if ((si->flags & FLAG_EXE) == 0) { 1212 /* 1213 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf 1214 * 1215 * Section 4.7.1.10 "Dynamic relocations" 1216 * R_ARM_COPY may only appear in executable objects where e_type is 1217 * set to ET_EXEC. 1218 * 1219 * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. 1220 * We should explicitly disallow ET_DYN executables from having 1221 * R_ARM_COPY relocations. 1222 */ 1223 DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); 1224 return -1; 1225 } 1226 count_relocation(kRelocCopy); 1227 MARK(rel->r_offset); 1228 TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s\n", reloc, s->st_size, sym_addr, sym_name); 1229 if (reloc == sym_addr) { 1230 Elf32_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed); 1231 1232 if (src == NULL) { 1233 DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name); 1234 return -1; 1235 } 1236 if (lsi->has_DT_SYMBOLIC) { 1237 DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared " 1238 "library %s (built with -Bsymbolic?)", si->name, lsi->name); 1239 return -1; 1240 } 1241 if (s->st_size < src->st_size) { 1242 DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)", 1243 si->name, s->st_size, src->st_size); 1244 return -1; 1245 } 1246 memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size); 1247 } else { 1248 DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name); 1249 return -1; 1250 } 1251 break; 1252#endif /* ANDROID_ARM_LINKER */ 1253 1254 default: 1255 DL_ERR("unknown reloc type %d @ %p (%d)", 1256 type, rel, (int) (rel - start)); 1257 return -1; 1258 } 1259 } 1260 return 0; 1261} 1262 1263#ifdef ANDROID_MIPS_LINKER 1264static int mips_relocate_got(soinfo* si, soinfo* needed[]) { 1265 unsigned *got; 1266 unsigned local_gotno, gotsym, symtabno; 1267 Elf32_Sym *symtab, *sym; 1268 unsigned g; 1269 1270 got = si->plt_got; 1271 local_gotno = si->mips_local_gotno; 1272 gotsym = si->mips_gotsym; 1273 symtabno = si->mips_symtabno; 1274 symtab = si->symtab; 1275 1276 /* 1277 * got[0] is address of lazy resolver function 1278 * got[1] may be used for a GNU extension 1279 * set it to a recognizable address in case someone calls it 1280 * (should be _rtld_bind_start) 1281 * FIXME: maybe this should be in a separate routine 1282 */ 1283 1284 if ((si->flags & FLAG_LINKER) == 0) { 1285 g = 0; 1286 got[g++] = 0xdeadbeef; 1287 if (got[g] & 0x80000000) { 1288 got[g++] = 0xdeadfeed; 1289 } 1290 /* 1291 * Relocate the local GOT entries need to be relocated 1292 */ 1293 for (; g < local_gotno; g++) { 1294 got[g] += si->load_bias; 1295 } 1296 } 1297 1298 /* Now for the global GOT entries */ 1299 sym = symtab + gotsym; 1300 got = si->plt_got + local_gotno; 1301 for (g = gotsym; g < symtabno; g++, sym++, got++) { 1302 const char *sym_name; 1303 Elf32_Sym *s; 1304 soinfo *lsi; 1305 1306 /* This is an undefined reference... try to locate it */ 1307 sym_name = si->strtab + sym->st_name; 1308 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1309 if (s == NULL) { 1310 /* We only allow an undefined symbol if this is a weak 1311 reference.. */ 1312 s = &symtab[g]; 1313 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1314 DL_ERR("cannot locate \"%s\"...", sym_name); 1315 return -1; 1316 } 1317 *got = 0; 1318 } 1319 else { 1320 /* FIXME: is this sufficient? 1321 * For reference see NetBSD link loader 1322 * 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 1323 */ 1324 *got = lsi->load_bias + s->st_value; 1325 } 1326 } 1327 return 0; 1328} 1329#endif 1330 1331/* Please read the "Initialization and Termination functions" functions. 1332 * of the linker design note in bionic/linker/README.TXT to understand 1333 * what the following code is doing. 1334 * 1335 * The important things to remember are: 1336 * 1337 * DT_PREINIT_ARRAY must be called first for executables, and should 1338 * not appear in shared libraries. 1339 * 1340 * DT_INIT should be called before DT_INIT_ARRAY if both are present 1341 * 1342 * DT_FINI should be called after DT_FINI_ARRAY if both are present 1343 * 1344 * DT_FINI_ARRAY must be parsed in reverse order. 1345 */ 1346void soinfo::CallArray(const char* array_name UNUSED, unsigned* array, int count, bool reverse) { 1347 if (array == NULL) { 1348 return; 1349 } 1350 1351 int step = 1; 1352 if (reverse) { 1353 array += (count-1); 1354 step = -1; 1355 } 1356 1357 TRACE("[ Calling %s @ %p [%d] for '%s' ]\n", array_name, array, count, name); 1358 1359 for (int n = count; n > 0; n--) { 1360 TRACE("[ Looking at %s[%d] *%p == 0x%08x ]\n", array_name, n, array, *array); 1361 void (*func)() = (void (*)()) *array; 1362 array += step; 1363 CallFunction("function", func); 1364 } 1365 1366 TRACE("[ Done calling %s for '%s' ]\n", array_name, name); 1367} 1368 1369void soinfo::CallFunction(const char* function_name UNUSED, void (*function)()) { 1370 if (function == NULL || reinterpret_cast<uintptr_t>(function) == static_cast<uintptr_t>(-1)) { 1371 return; 1372 } 1373 1374 TRACE("[ Calling %s @ %p for '%s' ]\n", function_name, function, name); 1375 function(); 1376 TRACE("[ Done calling %s for '%s' ]\n", function_name, name); 1377 1378 // The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures 1379 // are still writable. This happens with our debug malloc (see http://b/7941716). 1380 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 1381} 1382 1383void soinfo::CallPreInitConstructors() { 1384 CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false); 1385} 1386 1387void soinfo::CallConstructors() { 1388 if (constructors_called) { 1389 return; 1390 } 1391 1392 // We set constructors_called before actually calling the constructors, otherwise it doesn't 1393 // protect against recursive constructor calls. One simple example of constructor recursion 1394 // is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so: 1395 // 1. The program depends on libc, so libc's constructor is called here. 1396 // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. 1397 // 3. dlopen() calls the constructors on the newly created 1398 // soinfo for libc_malloc_debug_leak.so. 1399 // 4. The debug .so depends on libc, so CallConstructors is 1400 // called again with the libc soinfo. If it doesn't trigger the early- 1401 // out above, the libc constructor will be called again (recursively!). 1402 constructors_called = true; 1403 1404 if (!(flags & FLAG_EXE) && preinit_array) { 1405 DL_ERR("shared library \"%s\" has a preinit_array table @ %p", name, preinit_array); 1406 return; 1407 } 1408 1409 if (dynamic) { 1410 for (unsigned* d = dynamic; *d; d += 2) { 1411 if (d[0] == DT_NEEDED) { 1412 soinfo* lsi = find_loaded_library(strtab + d[1]); 1413 if (lsi == NULL) { 1414 DL_ERR("\"%s\": could not initialize dependent library", name); 1415 } else { 1416 lsi->CallConstructors(); 1417 } 1418 } 1419 } 1420 } 1421 1422 CallFunction("DT_INIT", init_func); 1423 CallArray("DT_INIT_ARRAY", init_array, init_array_count, false); 1424} 1425 1426void soinfo::CallDestructors() { 1427 CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true); 1428 CallFunction("DT_FINI", fini_func); 1429} 1430 1431/* Force any of the closed stdin, stdout and stderr to be associated with 1432 /dev/null. */ 1433static int nullify_closed_stdio() { 1434 int dev_null, i, status; 1435 int return_value = 0; 1436 1437 dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 1438 if (dev_null < 0) { 1439 DL_ERR("cannot open /dev/null: %s", strerror(errno)); 1440 return -1; 1441 } 1442 TRACE("[ Opened /dev/null file-descriptor=%d]\n", dev_null); 1443 1444 /* If any of the stdio file descriptors is valid and not associated 1445 with /dev/null, dup /dev/null to it. */ 1446 for (i = 0; i < 3; i++) { 1447 /* If it is /dev/null already, we are done. */ 1448 if (i == dev_null) { 1449 continue; 1450 } 1451 1452 TRACE("[ Nullifying stdio file descriptor %d]\n", i); 1453 status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 1454 1455 /* If file is opened, we are good. */ 1456 if (status != -1) { 1457 continue; 1458 } 1459 1460 /* The only error we allow is that the file descriptor does not 1461 exist, in which case we dup /dev/null to it. */ 1462 if (errno != EBADF) { 1463 DL_ERR("fcntl failed: %s", strerror(errno)); 1464 return_value = -1; 1465 continue; 1466 } 1467 1468 /* Try dupping /dev/null to this stdio file descriptor and 1469 repeat if there is a signal. Note that any errors in closing 1470 the stdio descriptor are lost. */ 1471 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 1472 if (status < 0) { 1473 DL_ERR("dup2 failed: %s", strerror(errno)); 1474 return_value = -1; 1475 continue; 1476 } 1477 } 1478 1479 /* If /dev/null is not one of the stdio file descriptors, close it. */ 1480 if (dev_null > 2) { 1481 TRACE("[ Closing /dev/null file-descriptor=%d]\n", dev_null); 1482 status = TEMP_FAILURE_RETRY(close(dev_null)); 1483 if (status == -1) { 1484 DL_ERR("close failed: %s", strerror(errno)); 1485 return_value = -1; 1486 } 1487 } 1488 1489 return return_value; 1490} 1491 1492static bool soinfo_link_image(soinfo* si) { 1493 /* "base" might wrap around UINT32_MAX. */ 1494 Elf32_Addr base = si->load_bias; 1495 const Elf32_Phdr *phdr = si->phdr; 1496 int phnum = si->phnum; 1497 int relocating_linker = (si->flags & FLAG_LINKER) != 0; 1498 soinfo **needed, **pneeded; 1499 1500 /* We can't debug anything until the linker is relocated */ 1501 if (!relocating_linker) { 1502 INFO("[ linking %s ]\n", si->name); 1503 DEBUG("si->base = 0x%08x si->flags = 0x%08x\n", si->base, si->flags); 1504 } 1505 1506 /* Extract dynamic section */ 1507 size_t dynamic_count; 1508 Elf32_Word dynamic_flags; 1509 phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, 1510 &dynamic_count, &dynamic_flags); 1511 if (si->dynamic == NULL) { 1512 if (!relocating_linker) { 1513 DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name); 1514 } 1515 return false; 1516 } else { 1517 if (!relocating_linker) { 1518 DEBUG("dynamic = %p\n", si->dynamic); 1519 } 1520 } 1521 1522#ifdef ANDROID_ARM_LINKER 1523 (void) phdr_table_get_arm_exidx(phdr, phnum, base, 1524 &si->ARM_exidx, &si->ARM_exidx_count); 1525#endif 1526 1527 /* extract useful information from dynamic section */ 1528 for (unsigned* d = si->dynamic; *d; ++d) { 1529 DEBUG("d = %p, d[0] = 0x%08x d[1] = 0x%08x\n", d, d[0], d[1]); 1530 switch(*d++){ 1531 case DT_HASH: 1532 si->nbucket = ((unsigned *) (base + *d))[0]; 1533 si->nchain = ((unsigned *) (base + *d))[1]; 1534 si->bucket = (unsigned *) (base + *d + 8); 1535 si->chain = (unsigned *) (base + *d + 8 + si->nbucket * 4); 1536 break; 1537 case DT_STRTAB: 1538 si->strtab = (const char *) (base + *d); 1539 break; 1540 case DT_SYMTAB: 1541 si->symtab = (Elf32_Sym *) (base + *d); 1542 break; 1543 case DT_PLTREL: 1544 if(*d != DT_REL) { 1545 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1546 return false; 1547 } 1548 break; 1549 case DT_JMPREL: 1550 si->plt_rel = (Elf32_Rel*) (base + *d); 1551 break; 1552 case DT_PLTRELSZ: 1553 si->plt_rel_count = *d / 8; 1554 break; 1555 case DT_REL: 1556 si->rel = (Elf32_Rel*) (base + *d); 1557 break; 1558 case DT_RELSZ: 1559 si->rel_count = *d / 8; 1560 break; 1561 case DT_PLTGOT: 1562 /* Save this in case we decide to do lazy binding. We don't yet. */ 1563 si->plt_got = (unsigned *)(base + *d); 1564 break; 1565 case DT_DEBUG: 1566 // Set the DT_DEBUG entry to the address of _r_debug for GDB 1567 // if the dynamic table is writable 1568 if ((dynamic_flags & PF_W) != 0) { 1569 *d = (int) &_r_debug; 1570 } 1571 break; 1572 case DT_RELA: 1573 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1574 return false; 1575 case DT_INIT: 1576 si->init_func = (void (*)(void))(base + *d); 1577 DEBUG("%s constructors (init func) found at %p\n", si->name, si->init_func); 1578 break; 1579 case DT_FINI: 1580 si->fini_func = (void (*)(void))(base + *d); 1581 DEBUG("%s destructors (fini func) found at %p\n", si->name, si->fini_func); 1582 break; 1583 case DT_INIT_ARRAY: 1584 si->init_array = (unsigned *)(base + *d); 1585 DEBUG("%s constructors (init_array) found at %p\n", si->name, si->init_array); 1586 break; 1587 case DT_INIT_ARRAYSZ: 1588 si->init_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); 1589 break; 1590 case DT_FINI_ARRAY: 1591 si->fini_array = (unsigned *)(base + *d); 1592 DEBUG("%s destructors (fini_array) found at %p\n", si->name, si->fini_array); 1593 break; 1594 case DT_FINI_ARRAYSZ: 1595 si->fini_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); 1596 break; 1597 case DT_PREINIT_ARRAY: 1598 si->preinit_array = (unsigned *)(base + *d); 1599 DEBUG("%s constructors (preinit_array) found at %p\n", si->name, si->preinit_array); 1600 break; 1601 case DT_PREINIT_ARRAYSZ: 1602 si->preinit_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); 1603 break; 1604 case DT_TEXTREL: 1605 si->has_text_relocations = true; 1606 break; 1607 case DT_SYMBOLIC: 1608 si->has_DT_SYMBOLIC = true; 1609 break; 1610#if defined(DT_FLAGS) 1611 case DT_FLAGS: 1612 if (*d & DF_TEXTREL) { 1613 si->has_text_relocations = true; 1614 } 1615 if (*d & DF_SYMBOLIC) { 1616 si->has_DT_SYMBOLIC = true; 1617 } 1618 break; 1619#endif 1620#if defined(ANDROID_MIPS_LINKER) 1621 case DT_NEEDED: 1622 case DT_STRSZ: 1623 case DT_SYMENT: 1624 case DT_RELENT: 1625 break; 1626 case DT_MIPS_RLD_MAP: 1627 // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. 1628 { 1629 r_debug** dp = (r_debug**) *d; 1630 *dp = &_r_debug; 1631 } 1632 break; 1633 case DT_MIPS_RLD_VERSION: 1634 case DT_MIPS_FLAGS: 1635 case DT_MIPS_BASE_ADDRESS: 1636 case DT_MIPS_UNREFEXTNO: 1637 break; 1638 1639 case DT_MIPS_SYMTABNO: 1640 si->mips_symtabno = *d; 1641 break; 1642 1643 case DT_MIPS_LOCAL_GOTNO: 1644 si->mips_local_gotno = *d; 1645 break; 1646 1647 case DT_MIPS_GOTSYM: 1648 si->mips_gotsym = *d; 1649 break; 1650 1651 default: 1652 DEBUG("Unused DT entry: type 0x%08x arg 0x%08x\n", d[-1], d[0]); 1653 break; 1654#endif 1655 } 1656 } 1657 1658 DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p\n", 1659 si->base, si->strtab, si->symtab); 1660 1661 // Sanity checks. 1662 if (si->nbucket == 0) { 1663 DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name); 1664 return false; 1665 } 1666 if (si->strtab == 0) { 1667 DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name); 1668 return false; 1669 } 1670 if (si->symtab == 0) { 1671 DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name); 1672 return false; 1673 } 1674 1675 /* if this is the main executable, then load all of the preloads now */ 1676 if (si->flags & FLAG_EXE) { 1677 memset(preloads, 0, sizeof(preloads)); 1678 for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) { 1679 soinfo* lsi = find_library(gLdPreloadNames[i]); 1680 if (lsi == NULL) { 1681 strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf)); 1682 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1683 gLdPreloadNames[i], si->name, tmp_err_buf); 1684 return false; 1685 } 1686 preloads[i] = lsi; 1687 } 1688 } 1689 1690 /* dynamic_count is an upper bound for the number of needed libs */ 1691 pneeded = needed = (soinfo**) alloca((1 + dynamic_count) * sizeof(soinfo*)); 1692 1693 for (unsigned* d = si->dynamic; *d; d += 2) { 1694 if (d[0] == DT_NEEDED) { 1695 DEBUG("%s needs %s\n", si->name, si->strtab + d[1]); 1696 soinfo* lsi = find_library(si->strtab + d[1]); 1697 if (lsi == NULL) { 1698 strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf)); 1699 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1700 si->strtab + d[1], si->name, tmp_err_buf); 1701 return false; 1702 } 1703 *pneeded++ = lsi; 1704 } 1705 } 1706 *pneeded = NULL; 1707 1708 if (si->has_text_relocations) { 1709 /* Unprotect the segments, i.e. make them writable, to allow 1710 * text relocations to work properly. We will later call 1711 * phdr_table_protect_segments() after all of them are applied 1712 * and all constructors are run. 1713 */ 1714 if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1715 DL_ERR("can't unprotect loadable segments for \"%s\": %s", 1716 si->name, strerror(errno)); 1717 return false; 1718 } 1719 } 1720 1721 if (si->plt_rel) { 1722 DEBUG("[ relocating %s plt ]\n", si->name ); 1723 if(soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) { 1724 return false; 1725 } 1726 } 1727 if (si->rel) { 1728 DEBUG("[ relocating %s ]\n", si->name ); 1729 if(soinfo_relocate(si, si->rel, si->rel_count, needed)) { 1730 return false; 1731 } 1732 } 1733 1734#ifdef ANDROID_MIPS_LINKER 1735 if (mips_relocate_got(si, needed)) { 1736 return false; 1737 } 1738#endif 1739 1740 si->flags |= FLAG_LINKED; 1741 DEBUG("[ finished linking %s ]\n", si->name); 1742 1743 if (si->has_text_relocations) { 1744 /* All relocations are done, we can protect our segments back to 1745 * read-only. */ 1746 if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1747 DL_ERR("can't protect segments for \"%s\": %s", 1748 si->name, strerror(errno)); 1749 return false; 1750 } 1751 } 1752 1753 /* We can also turn on GNU RELRO protection */ 1754 if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { 1755 DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", 1756 si->name, strerror(errno)); 1757 return false; 1758 } 1759 1760 // If this is a setuid/setgid program, close the security hole described in 1761 // ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc 1762 if (get_AT_SECURE()) { 1763 nullify_closed_stdio(); 1764 } 1765 notify_gdb_of_load(si); 1766 return true; 1767} 1768 1769/* 1770 * This code is called after the linker has linked itself and 1771 * fixed it's own GOT. It is safe to make references to externs 1772 * and other non-local data at this point. 1773 */ 1774static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linker_base) 1775{ 1776 static soinfo linker_soinfo; 1777 1778 int argc = (int) *elfdata; 1779 char **argv = (char**) (elfdata + 1); 1780 unsigned *vecs = (unsigned*) (argv + argc + 1); 1781 1782 /* NOTE: we store the elfdata pointer on a special location 1783 * of the temporary TLS area in order to pass it to 1784 * the C Library's runtime initializer. 1785 * 1786 * The initializer must clear the slot and reset the TLS 1787 * to point to a different location to ensure that no other 1788 * shared library constructor can access it. 1789 */ 1790 __libc_init_tls(elfdata); 1791 1792#if TIMING 1793 struct timeval t0, t1; 1794 gettimeofday(&t0, 0); 1795#endif 1796 1797 // Initialize environment functions, and get to the ELF aux vectors table. 1798 vecs = linker_env_init(vecs); 1799 1800 debugger_init(); 1801 1802 // Get a few environment variables. 1803 const char* LD_DEBUG = linker_env_get("LD_DEBUG"); 1804 if (LD_DEBUG != NULL) { 1805 debug_verbosity = atoi(LD_DEBUG); 1806 } 1807 1808 // Normally, these are cleaned by linker_env_init, but the test 1809 // doesn't cost us anything. 1810 const char* ldpath_env = NULL; 1811 const char* ldpreload_env = NULL; 1812 if (!get_AT_SECURE()) { 1813 ldpath_env = linker_env_get("LD_LIBRARY_PATH"); 1814 ldpreload_env = linker_env_get("LD_PRELOAD"); 1815 } 1816 1817 INFO("[ android linker & debugger ]\n"); 1818 DEBUG("elfdata @ 0x%08x\n", (unsigned)elfdata); 1819 1820 soinfo* si = soinfo_alloc(argv[0]); 1821 if (si == NULL) { 1822 exit(EXIT_FAILURE); 1823 } 1824 1825 /* bootstrap the link map, the main exe always needs to be first */ 1826 si->flags |= FLAG_EXE; 1827 link_map* map = &(si->linkmap); 1828 1829 map->l_addr = 0; 1830 map->l_name = argv[0]; 1831 map->l_prev = NULL; 1832 map->l_next = NULL; 1833 1834 _r_debug.r_map = map; 1835 r_debug_tail = map; 1836 1837 /* gdb expects the linker to be in the debug shared object list. 1838 * Without this, gdb has trouble locating the linker's ".text" 1839 * and ".plt" sections. Gdb could also potentially use this to 1840 * relocate the offset of our exported 'rtld_db_dlactivity' symbol. 1841 * Don't use soinfo_alloc(), because the linker shouldn't 1842 * be on the soinfo list. 1843 */ 1844 strlcpy((char*) linker_soinfo.name, "/system/bin/linker", sizeof linker_soinfo.name); 1845 linker_soinfo.flags = 0; 1846 linker_soinfo.base = linker_base; 1847 /* 1848 * Set the dynamic field in the link map otherwise gdb will complain with 1849 * the following: 1850 * warning: .dynamic section for "/system/bin/linker" is not at the 1851 * expected address (wrong library or version mismatch?) 1852 */ 1853 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base; 1854 Elf32_Phdr *phdr = 1855 (Elf32_Phdr *)((unsigned char *) linker_base + elf_hdr->e_phoff); 1856 phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, 1857 &linker_soinfo.dynamic, NULL, NULL); 1858 insert_soinfo_into_debug_map(&linker_soinfo); 1859 1860 /* extract information passed from the kernel */ 1861 while (vecs[0] != 0){ 1862 switch(vecs[0]){ 1863 case AT_PHDR: 1864 si->phdr = (Elf32_Phdr*) vecs[1]; 1865 break; 1866 case AT_PHNUM: 1867 si->phnum = (int) vecs[1]; 1868 break; 1869 case AT_ENTRY: 1870 si->entry = vecs[1]; 1871 break; 1872 } 1873 vecs += 2; 1874 } 1875 1876 /* Compute the value of si->base. We can't rely on the fact that 1877 * the first entry is the PHDR because this will not be true 1878 * for certain executables (e.g. some in the NDK unit test suite) 1879 */ 1880 int nn; 1881 si->base = 0; 1882 si->size = phdr_table_get_load_size(si->phdr, si->phnum); 1883 si->load_bias = 0; 1884 for ( nn = 0; nn < si->phnum; nn++ ) { 1885 if (si->phdr[nn].p_type == PT_PHDR) { 1886 si->load_bias = (Elf32_Addr)si->phdr - si->phdr[nn].p_vaddr; 1887 si->base = (Elf32_Addr) si->phdr - si->phdr[nn].p_offset; 1888 break; 1889 } 1890 } 1891 si->dynamic = (unsigned *)-1; 1892 si->refcount = 1; 1893 1894 // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). 1895 parse_LD_LIBRARY_PATH(ldpath_env); 1896 parse_LD_PRELOAD(ldpreload_env); 1897 1898 somain = si; 1899 1900 if (!soinfo_link_image(si)) { 1901 const char* msg = "CANNOT LINK EXECUTABLE\n"; 1902 write(2, __linker_dl_err_buf, strlen(__linker_dl_err_buf)); 1903 write(2, msg, strlen(msg)); 1904 exit(EXIT_FAILURE); 1905 } 1906 1907 si->CallPreInitConstructors(); 1908 1909 for (size_t i = 0; preloads[i] != NULL; ++i) { 1910 preloads[i]->CallConstructors(); 1911 } 1912 1913 /*After the link_image, the si->load_bias is initialized. 1914 *For so lib, the map->l_addr will be updated in notify_gdb_of_load. 1915 *We need to update this value for so exe here. So Unwind_Backtrace 1916 *for some arch like x86 could work correctly within so exe. 1917 */ 1918 map->l_addr = si->load_bias; 1919 si->CallConstructors(); 1920 1921#if TIMING 1922 gettimeofday(&t1,NULL); 1923 PRINT("LINKER TIME: %s: %d microseconds\n", argv[0], (int) ( 1924 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - 1925 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) 1926 )); 1927#endif 1928#if STATS 1929 PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol\n", argv[0], 1930 linker_stats.count[kRelocAbsolute], 1931 linker_stats.count[kRelocRelative], 1932 linker_stats.count[kRelocCopy], 1933 linker_stats.count[kRelocSymbol]); 1934#endif 1935#if COUNT_PAGES 1936 { 1937 unsigned n; 1938 unsigned i; 1939 unsigned count = 0; 1940 for(n = 0; n < 4096; n++){ 1941 if(bitmask[n]){ 1942 unsigned x = bitmask[n]; 1943 for(i = 0; i < 8; i++){ 1944 if(x & 1) count++; 1945 x >>= 1; 1946 } 1947 } 1948 } 1949 PRINT("PAGES MODIFIED: %s: %d (%dKB)\n", argv[0], count, count * 4); 1950 } 1951#endif 1952 1953#if TIMING || STATS || COUNT_PAGES 1954 fflush(stdout); 1955#endif 1956 1957 TRACE("[ Ready to execute '%s' @ 0x%08x ]\n", si->name, si->entry); 1958 return si->entry; 1959} 1960 1961/* 1962 * Find the value of AT_BASE passed to us by the kernel. This is the load 1963 * location of the linker. 1964 */ 1965static unsigned find_linker_base(unsigned **elfdata) { 1966 int argc = (int) *elfdata; 1967 char **argv = (char**) (elfdata + 1); 1968 unsigned *vecs = (unsigned*) (argv + argc + 1); 1969 while (vecs[0] != 0) { 1970 vecs++; 1971 } 1972 1973 /* The end of the environment block is marked by two NULL pointers */ 1974 vecs++; 1975 1976 while(vecs[0]) { 1977 if (vecs[0] == AT_BASE) { 1978 return vecs[1]; 1979 } 1980 vecs += 2; 1981 } 1982 1983 return 0; // should never happen 1984} 1985 1986/* Compute the load-bias of an existing executable. This shall only 1987 * be used to compute the load bias of an executable or shared library 1988 * that was loaded by the kernel itself. 1989 * 1990 * Input: 1991 * elf -> address of ELF header, assumed to be at the start of the file. 1992 * Return: 1993 * load bias, i.e. add the value of any p_vaddr in the file to get 1994 * the corresponding address in memory. 1995 */ 1996static Elf32_Addr 1997get_elf_exec_load_bias(const Elf32_Ehdr* elf) 1998{ 1999 Elf32_Addr offset = elf->e_phoff; 2000 const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset); 2001 const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum; 2002 const Elf32_Phdr* phdr; 2003 2004 for (phdr = phdr_table; phdr < phdr_end; phdr++) { 2005 if (phdr->p_type == PT_LOAD) { 2006 return (Elf32_Addr)elf + phdr->p_offset - phdr->p_vaddr; 2007 } 2008 } 2009 return 0; 2010} 2011 2012/* 2013 * This is the entry point for the linker, called from begin.S. This 2014 * method is responsible for fixing the linker's own relocations, and 2015 * then calling __linker_init_post_relocation(). 2016 * 2017 * Because this method is called before the linker has fixed it's own 2018 * relocations, any attempt to reference an extern variable, extern 2019 * function, or other GOT reference will generate a segfault. 2020 */ 2021extern "C" unsigned __linker_init(unsigned **elfdata) { 2022 unsigned linker_addr = find_linker_base(elfdata); 2023 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_addr; 2024 Elf32_Phdr *phdr = 2025 (Elf32_Phdr *)((unsigned char *) linker_addr + elf_hdr->e_phoff); 2026 2027 soinfo linker_so; 2028 memset(&linker_so, 0, sizeof(soinfo)); 2029 2030 linker_so.base = linker_addr; 2031 linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); 2032 linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); 2033 linker_so.dynamic = (unsigned *) -1; 2034 linker_so.phdr = phdr; 2035 linker_so.phnum = elf_hdr->e_phnum; 2036 linker_so.flags |= FLAG_LINKER; 2037 2038 if (!soinfo_link_image(&linker_so)) { 2039 // It would be nice to print an error message, but if the linker 2040 // can't link itself, there's no guarantee that we'll be able to 2041 // call write() (because it involves a GOT reference). 2042 // 2043 // This situation should never occur unless the linker itself 2044 // is corrupt. 2045 exit(EXIT_FAILURE); 2046 } 2047 2048 // We have successfully fixed our own relocations. It's safe to run 2049 // the main part of the linker now. 2050 unsigned start_address = __linker_init_post_relocation(elfdata, linker_addr); 2051 2052 set_soinfo_pool_protection(PROT_READ); 2053 2054 // Return the address that the calling assembly stub should jump to. 2055 return start_address; 2056} 2057