linker.cpp revision c5db969aa4a24a76fc0964f2ff89533e832b47a6
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 /* 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#ifdef ANDROID_ARM_LINKER 355 356/* For a given PC, find the .so that it belongs to. 357 * Returns the base address of the .ARM.exidx section 358 * for that .so, and the number of 8-byte entries 359 * in that section (via *pcount). 360 * 361 * Intended to be called by libc's __gnu_Unwind_Find_exidx(). 362 * 363 * This function is exposed via dlfcn.cpp and libdl.so. 364 */ 365_Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount) 366{ 367 soinfo *si; 368 unsigned addr = (unsigned)pc; 369 370 for (si = solist; si != 0; si = si->next){ 371 if ((addr >= si->base) && (addr < (si->base + si->size))) { 372 *pcount = si->ARM_exidx_count; 373 return (_Unwind_Ptr)si->ARM_exidx; 374 } 375 } 376 *pcount = 0; 377 return NULL; 378} 379 380#elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) 381 382/* Here, we only have to provide a callback to iterate across all the 383 * loaded libraries. gcc_eh does the rest. */ 384int 385dl_iterate_phdr(int (*cb)(dl_phdr_info *info, size_t size, void *data), 386 void *data) 387{ 388 int rv = 0; 389 for (soinfo* si = solist; si != NULL; si = si->next) { 390 dl_phdr_info dl_info; 391 dl_info.dlpi_addr = si->linkmap.l_addr; 392 dl_info.dlpi_name = si->linkmap.l_name; 393 dl_info.dlpi_phdr = si->phdr; 394 dl_info.dlpi_phnum = si->phnum; 395 rv = cb(&dl_info, sizeof(dl_phdr_info), data); 396 if (rv != 0) { 397 break; 398 } 399 } 400 return rv; 401} 402 403#endif 404 405static Elf32_Sym *soinfo_elf_lookup(soinfo *si, unsigned hash, const char *name) 406{ 407 Elf32_Sym *s; 408 Elf32_Sym *symtab = si->symtab; 409 const char *strtab = si->strtab; 410 unsigned n; 411 412 TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %d\n", 413 name, si->name, si->base, hash, hash % si->nbucket); 414 n = hash % si->nbucket; 415 416 for(n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]){ 417 s = symtab + n; 418 if(strcmp(strtab + s->st_name, name)) continue; 419 420 /* only concern ourselves with global and weak symbol definitions */ 421 switch(ELF32_ST_BIND(s->st_info)){ 422 case STB_GLOBAL: 423 case STB_WEAK: 424 if(s->st_shndx == SHN_UNDEF) 425 continue; 426 427 TRACE_TYPE(LOOKUP, "FOUND %s in %s (%08x) %d\n", 428 name, si->name, s->st_value, s->st_size); 429 return s; 430 } 431 } 432 433 return NULL; 434} 435 436static unsigned elfhash(const char *_name) 437{ 438 const unsigned char *name = (const unsigned char *) _name; 439 unsigned h = 0, g; 440 441 while(*name) { 442 h = (h << 4) + *name++; 443 g = h & 0xf0000000; 444 h ^= g; 445 h ^= g >> 24; 446 } 447 return h; 448} 449 450static Elf32_Sym * 451soinfo_do_lookup(soinfo *si, const char *name, soinfo **lsi, 452 soinfo *needed[]) 453{ 454 unsigned elf_hash = elfhash(name); 455 Elf32_Sym *s = NULL; 456 int i; 457 458 if (si != NULL && somain != NULL) { 459 460 /* 461 * Local scope is executable scope. Just start looking into it right away 462 * for the shortcut. 463 */ 464 465 if (si == somain) { 466 s = soinfo_elf_lookup(si, elf_hash, name); 467 if (s != NULL) { 468 *lsi = si; 469 goto done; 470 } 471 } else { 472 /* Order of symbol lookup is controlled by DT_SYMBOLIC flag */ 473 474 /* 475 * If this object was built with symbolic relocations disabled, the 476 * first place to look to resolve external references is the main 477 * executable. 478 */ 479 480 if (!si->has_DT_SYMBOLIC) { 481 DEBUG("%s: looking up %s in executable %s\n", 482 si->name, name, somain->name); 483 s = soinfo_elf_lookup(somain, elf_hash, name); 484 if (s != NULL) { 485 *lsi = somain; 486 goto done; 487 } 488 } 489 490 /* Look for symbols in the local scope (the object who is 491 * searching). This happens with C++ templates on i386 for some 492 * reason. 493 * 494 * Notes on weak symbols: 495 * The ELF specs are ambiguous about treatment of weak definitions in 496 * dynamic linking. Some systems return the first definition found 497 * and some the first non-weak definition. This is system dependent. 498 * Here we return the first definition found for simplicity. */ 499 500 s = soinfo_elf_lookup(si, elf_hash, name); 501 if (s != NULL) { 502 *lsi = si; 503 goto done; 504 } 505 506 /* 507 * If this object was built with -Bsymbolic and symbol is not found 508 * in the local scope, try to find the symbol in the main executable. 509 */ 510 511 if (si->has_DT_SYMBOLIC) { 512 DEBUG("%s: looking up %s in executable %s after local scope\n", 513 si->name, name, somain->name); 514 s = soinfo_elf_lookup(somain, elf_hash, name); 515 if (s != NULL) { 516 *lsi = somain; 517 goto done; 518 } 519 } 520 } 521 } 522 523 /* Next, look for it in the preloads list */ 524 for(i = 0; preloads[i] != NULL; i++) { 525 s = soinfo_elf_lookup(preloads[i], elf_hash, name); 526 if(s != NULL) { 527 *lsi = preloads[i]; 528 goto done; 529 } 530 } 531 532 for(i = 0; needed[i] != NULL; i++) { 533 DEBUG("%s: looking up %s in %s\n", 534 si->name, name, needed[i]->name); 535 s = soinfo_elf_lookup(needed[i], elf_hash, name); 536 if (s != NULL) { 537 *lsi = needed[i]; 538 goto done; 539 } 540 } 541 542done: 543 if(s != NULL) { 544 TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = 0x%08x, " 545 "found in %s, base = 0x%08x, load bias = 0x%08x\n", 546 si->name, name, s->st_value, 547 (*lsi)->name, (*lsi)->base, (*lsi)->load_bias); 548 return s; 549 } 550 551 return NULL; 552} 553 554/* This is used by dl_sym(). It performs symbol lookup only within the 555 specified soinfo object and not in any of its dependencies. 556 */ 557Elf32_Sym *soinfo_lookup(soinfo *si, const char *name) 558{ 559 return soinfo_elf_lookup(si, elfhash(name), name); 560} 561 562/* This is used by dl_sym(). It performs a global symbol lookup. 563 */ 564Elf32_Sym *lookup(const char *name, soinfo **found, soinfo *start) 565{ 566 unsigned elf_hash = elfhash(name); 567 Elf32_Sym *s = NULL; 568 soinfo *si; 569 570 if(start == NULL) { 571 start = solist; 572 } 573 574 for(si = start; (s == NULL) && (si != NULL); si = si->next) 575 { 576 if(si->flags & FLAG_ERROR) 577 continue; 578 s = soinfo_elf_lookup(si, elf_hash, name); 579 if (s != NULL) { 580 *found = si; 581 break; 582 } 583 } 584 585 if(s != NULL) { 586 TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, si->base = 0x%08x\n", 587 name, s->st_value, si->base); 588 return s; 589 } 590 591 return NULL; 592} 593 594soinfo *find_containing_library(const void *addr) 595{ 596 soinfo *si; 597 598 for(si = solist; si != NULL; si = si->next) 599 { 600 if((unsigned)addr >= si->base && (unsigned)addr - si->base < si->size) { 601 return si; 602 } 603 } 604 605 return NULL; 606} 607 608Elf32_Sym *soinfo_find_symbol(soinfo* si, const void *addr) 609{ 610 unsigned int i; 611 unsigned soaddr = (unsigned)addr - si->base; 612 613 /* Search the library's symbol table for any defined symbol which 614 * contains this address */ 615 for(i=0; i<si->nchain; i++) { 616 Elf32_Sym *sym = &si->symtab[i]; 617 618 if(sym->st_shndx != SHN_UNDEF && 619 soaddr >= sym->st_value && 620 soaddr < sym->st_value + sym->st_size) { 621 return sym; 622 } 623 } 624 625 return NULL; 626} 627 628#if 0 629static void dump(soinfo *si) 630{ 631 Elf32_Sym *s = si->symtab; 632 unsigned n; 633 634 for(n = 0; n < si->nchain; n++) { 635 TRACE("%04d> %08x: %02x %04x %08x %08x %s\n", n, s, 636 s->st_info, s->st_shndx, s->st_value, s->st_size, 637 si->strtab + s->st_name); 638 s++; 639 } 640} 641#endif 642 643static int open_library_on_path(const char* name, const char* const paths[]) { 644 char buf[512]; 645 for (size_t i = 0; paths[i] != NULL; ++i) { 646 int n = format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name); 647 if (n < 0 || n >= static_cast<int>(sizeof(buf))) { 648 PRINT("Warning: ignoring very long library path: %s/%s\n", paths[i], name); 649 continue; 650 } 651 int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC)); 652 if (fd != -1) { 653 return fd; 654 } 655 } 656 return -1; 657} 658 659static int open_library(const char* name) { 660 TRACE("[ opening %s ]\n", name); 661 662 // If the name contains a slash, we should attempt to open it directly and not search the paths. 663 if (strchr(name, '/') != NULL) { 664 int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC)); 665 if (fd != -1) { 666 return fd; 667 } 668 // ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now. 669 } 670 671 // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths. 672 int fd = open_library_on_path(name, gLdPaths); 673 if (fd == -1) { 674 fd = open_library_on_path(name, gSoPaths); 675 } 676 return fd; 677} 678 679// Returns 'true' if the library is prelinked or on failure so we error out 680// either way. We no longer support prelinking. 681static bool is_prelinked(int fd, const char* name) 682{ 683 struct prelink_info_t { 684 long mmap_addr; 685 char tag[4]; // "PRE ". 686 }; 687 688 off_t sz = lseek(fd, -sizeof(prelink_info_t), SEEK_END); 689 if (sz < 0) { 690 DL_ERR("lseek failed: %s", strerror(errno)); 691 return true; 692 } 693 694 prelink_info_t info; 695 int rc = TEMP_FAILURE_RETRY(read(fd, &info, sizeof(info))); 696 if (rc != sizeof(info)) { 697 DL_ERR("could not read prelink_info_t structure for \"%s\": %s", name, strerror(errno)); 698 return true; 699 } 700 701 if (memcmp(info.tag, "PRE ", 4) == 0) { 702 DL_ERR("prelinked libraries no longer supported: %s", name); 703 return true; 704 } 705 return false; 706} 707 708/* verify_elf_header 709 * Verifies the content of an ELF header. 710 * 711 * Args: 712 * 713 * Returns: 714 * 0 on success 715 * -1 if no valid ELF object is found @ base. 716 */ 717static int 718verify_elf_header(const Elf32_Ehdr* hdr) 719{ 720 if (hdr->e_ident[EI_MAG0] != ELFMAG0) return -1; 721 if (hdr->e_ident[EI_MAG1] != ELFMAG1) return -1; 722 if (hdr->e_ident[EI_MAG2] != ELFMAG2) return -1; 723 if (hdr->e_ident[EI_MAG3] != ELFMAG3) return -1; 724 if (hdr->e_type != ET_DYN) return -1; 725 726 /* TODO: Should we verify anything else in the header? */ 727#ifdef ANDROID_ARM_LINKER 728 if (hdr->e_machine != EM_ARM) return -1; 729#elif defined(ANDROID_X86_LINKER) 730 if (hdr->e_machine != EM_386) return -1; 731#elif defined(ANDROID_MIPS_LINKER) 732 if (hdr->e_machine != EM_MIPS) return -1; 733#endif 734 return 0; 735} 736 737struct scoped_fd { 738 ~scoped_fd() { 739 if (fd != -1) { 740 close(fd); 741 } 742 } 743 int fd; 744}; 745 746struct soinfo_ptr { 747 soinfo_ptr(const char* name) { 748 const char* bname = strrchr(name, '/'); 749 ptr = soinfo_alloc(bname ? bname + 1 : name); 750 } 751 ~soinfo_ptr() { 752 soinfo_free(ptr); 753 } 754 soinfo* release() { 755 soinfo* result = ptr; 756 ptr = NULL; 757 return result; 758 } 759 soinfo* ptr; 760}; 761 762// TODO: rewrite linker_phdr.h to use a class, then lose this. 763struct phdr_ptr { 764 phdr_ptr() : phdr_mmap(NULL) {} 765 ~phdr_ptr() { 766 if (phdr_mmap != NULL) { 767 phdr_table_unload(phdr_mmap, phdr_size); 768 } 769 } 770 void* phdr_mmap; 771 Elf32_Addr phdr_size; 772}; 773 774static soinfo* load_library(const char* name) { 775 // Open the file. 776 scoped_fd fd; 777 fd.fd = open_library(name); 778 if (fd.fd == -1) { 779 DL_ERR("library \"%s\" not found", name); 780 return NULL; 781 } 782 783 // Read the ELF header. 784 Elf32_Ehdr header[1]; 785 int ret = TEMP_FAILURE_RETRY(read(fd.fd, (void*)header, sizeof(header))); 786 if (ret < 0) { 787 DL_ERR("can't read file \"%s\": %s", name, strerror(errno)); 788 return NULL; 789 } 790 if (ret != (int)sizeof(header)) { 791 DL_ERR("too small to be an ELF executable: %s", name); 792 return NULL; 793 } 794 if (verify_elf_header(header) < 0) { 795 DL_ERR("not a valid ELF executable: %s", name); 796 return NULL; 797 } 798 799 // Read the program header table. 800 const Elf32_Phdr* phdr_table; 801 phdr_ptr phdr_holder; 802 ret = phdr_table_load(fd.fd, header->e_phoff, header->e_phnum, 803 &phdr_holder.phdr_mmap, &phdr_holder.phdr_size, &phdr_table); 804 if (ret < 0) { 805 DL_ERR("can't load program header table: %s: %s", name, strerror(errno)); 806 return NULL; 807 } 808 size_t phdr_count = header->e_phnum; 809 810 // Get the load extents. 811 Elf32_Addr ext_sz = phdr_table_get_load_size(phdr_table, phdr_count); 812 TRACE("[ '%s' wants sz=0x%08x ]\n", name, ext_sz); 813 if (ext_sz == 0) { 814 DL_ERR("no loadable segments in file: %s", name); 815 return NULL; 816 } 817 818 // We no longer support pre-linked libraries. 819 if (is_prelinked(fd.fd, name)) { 820 return NULL; 821 } 822 823 // Reserve address space for all loadable segments. 824 void* load_start = NULL; 825 Elf32_Addr load_size = 0; 826 Elf32_Addr load_bias = 0; 827 ret = phdr_table_reserve_memory(phdr_table, 828 phdr_count, 829 &load_start, 830 &load_size, 831 &load_bias); 832 if (ret < 0) { 833 DL_ERR("can't reserve %d bytes in address space for \"%s\": %s", 834 ext_sz, name, strerror(errno)); 835 return NULL; 836 } 837 838 TRACE("[ allocated memory for %s @ %p (0x%08x) ]\n", name, load_start, load_size); 839 840 /* Map all the segments in our address space with default protections */ 841 ret = phdr_table_load_segments(phdr_table, 842 phdr_count, 843 load_bias, 844 fd.fd); 845 if (ret < 0) { 846 DL_ERR("can't map loadable segments for \"%s\": %s", 847 name, strerror(errno)); 848 return NULL; 849 } 850 851 soinfo_ptr si(name); 852 if (si.ptr == NULL) { 853 return NULL; 854 } 855 856 si.ptr->base = (Elf32_Addr) load_start; 857 si.ptr->size = load_size; 858 si.ptr->load_bias = load_bias; 859 si.ptr->flags = 0; 860 si.ptr->entry = 0; 861 si.ptr->dynamic = (unsigned *)-1; 862 si.ptr->phnum = phdr_count; 863 si.ptr->phdr = phdr_table_get_loaded_phdr(phdr_table, phdr_count, load_bias); 864 if (si.ptr->phdr == NULL) { 865 DL_ERR("can't find loaded PHDR for \"%s\"", name); 866 return NULL; 867 } 868 869 return si.release(); 870} 871 872static soinfo* init_library(soinfo* si) { 873 // At this point we know that whatever is loaded @ base is a valid ELF 874 // shared library whose segments are properly mapped in. 875 TRACE("[ init_library base=0x%08x sz=0x%08x name='%s') ]\n", 876 si->base, si->size, si->name); 877 878 if (!soinfo_link_image(si)) { 879 munmap((void *)si->base, si->size); 880 return NULL; 881 } 882 883 return si; 884} 885 886static soinfo *find_loaded_library(const char *name) 887{ 888 soinfo *si; 889 const char *bname; 890 891 // TODO: don't use basename only for determining libraries 892 // http://code.google.com/p/android/issues/detail?id=6670 893 894 bname = strrchr(name, '/'); 895 bname = bname ? bname + 1 : name; 896 897 for(si = solist; si != NULL; si = si->next){ 898 if(!strcmp(bname, si->name)) { 899 return si; 900 } 901 } 902 return NULL; 903} 904 905static soinfo* find_library_internal(const char* name) { 906 if (name == NULL) { 907 return somain; 908 } 909 910 soinfo* si = find_loaded_library(name); 911 if (si != NULL) { 912 if (si->flags & FLAG_ERROR) { 913 DL_ERR("\"%s\" failed to load previously", name); 914 return NULL; 915 } 916 if (si->flags & FLAG_LINKED) { 917 return si; 918 } 919 DL_ERR("OOPS: recursive link to \"%s\"", si->name); 920 return NULL; 921 } 922 923 TRACE("[ '%s' has not been loaded yet. Locating...]\n", name); 924 si = load_library(name); 925 if (si != NULL) { 926 si = init_library(si); 927 } 928 929 return si; 930} 931 932static soinfo* find_library(const char* name) { 933 soinfo* si = find_library_internal(name); 934 if (si != NULL) { 935 si->refcount++; 936 } 937 return si; 938} 939 940static int soinfo_unload(soinfo* si) { 941 if (si->refcount == 1) { 942 TRACE("unloading '%s'\n", si->name); 943 si->CallDestructors(); 944 945 for (unsigned* d = si->dynamic; *d; d += 2) { 946 if (d[0] == DT_NEEDED) { 947 soinfo* lsi = find_loaded_library(si->strtab + d[1]); 948 if (lsi != NULL) { 949 TRACE("%s needs to unload %s\n", si->name, lsi->name); 950 soinfo_unload(lsi); 951 } else { 952 // TODO: should we return -1 in this case? 953 DL_ERR("\"%s\": could not unload dependent library", si->name); 954 } 955 } 956 } 957 958 munmap(reinterpret_cast<void*>(si->base), si->size); 959 notify_gdb_of_unload(si); 960 soinfo_free(si); 961 si->refcount = 0; 962 } else { 963 si->refcount--; 964 TRACE("not unloading '%s', decrementing refcount to %d\n", si->name, si->refcount); 965 } 966 return 0; 967} 968 969soinfo* do_dlopen(const char* name) { 970 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 971 soinfo* si = find_library(name); 972 if (si != NULL) { 973 si->CallConstructors(); 974 } 975 set_soinfo_pool_protection(PROT_READ); 976 return si; 977} 978 979int do_dlclose(soinfo* si) { 980 set_soinfo_pool_protection(PROT_READ | PROT_WRITE); 981 int result = soinfo_unload(si); 982 set_soinfo_pool_protection(PROT_READ); 983 return result; 984} 985 986/* TODO: don't use unsigned for addrs below. It works, but is not 987 * ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned 988 * long. 989 */ 990static int soinfo_relocate(soinfo *si, Elf32_Rel *rel, unsigned count, 991 soinfo *needed[]) 992{ 993 Elf32_Sym *symtab = si->symtab; 994 const char *strtab = si->strtab; 995 Elf32_Sym *s; 996 Elf32_Rel *start = rel; 997 soinfo *lsi; 998 999 for (size_t idx = 0; idx < count; ++idx, ++rel) { 1000 unsigned type = ELF32_R_TYPE(rel->r_info); 1001 unsigned sym = ELF32_R_SYM(rel->r_info); 1002 unsigned reloc = (unsigned)(rel->r_offset + si->load_bias); 1003 unsigned sym_addr = 0; 1004 char *sym_name = NULL; 1005 1006 DEBUG("Processing '%s' relocation at index %d\n", si->name, idx); 1007 if (type == 0) { // R_*_NONE 1008 continue; 1009 } 1010 if(sym != 0) { 1011 sym_name = (char *)(strtab + symtab[sym].st_name); 1012 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1013 if(s == NULL) { 1014 /* We only allow an undefined symbol if this is a weak 1015 reference.. */ 1016 s = &symtab[sym]; 1017 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1018 DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); 1019 return -1; 1020 } 1021 1022 /* IHI0044C AAELF 4.5.1.1: 1023 1024 Libraries are not searched to resolve weak references. 1025 It is not an error for a weak reference to remain 1026 unsatisfied. 1027 1028 During linking, the value of an undefined weak reference is: 1029 - Zero if the relocation type is absolute 1030 - The address of the place if the relocation is pc-relative 1031 - The address of nominal base address if the relocation 1032 type is base-relative. 1033 */ 1034 1035 switch (type) { 1036#if defined(ANDROID_ARM_LINKER) 1037 case R_ARM_JUMP_SLOT: 1038 case R_ARM_GLOB_DAT: 1039 case R_ARM_ABS32: 1040 case R_ARM_RELATIVE: /* Don't care. */ 1041#elif defined(ANDROID_X86_LINKER) 1042 case R_386_JMP_SLOT: 1043 case R_386_GLOB_DAT: 1044 case R_386_32: 1045 case R_386_RELATIVE: /* Dont' care. */ 1046#endif /* ANDROID_*_LINKER */ 1047 /* sym_addr was initialized to be zero above or relocation 1048 code below does not care about value of sym_addr. 1049 No need to do anything. */ 1050 break; 1051 1052#if defined(ANDROID_X86_LINKER) 1053 case R_386_PC32: 1054 sym_addr = reloc; 1055 break; 1056#endif /* ANDROID_X86_LINKER */ 1057 1058#if defined(ANDROID_ARM_LINKER) 1059 case R_ARM_COPY: 1060 /* Fall through. Can't really copy if weak symbol is 1061 not found in run-time. */ 1062#endif /* ANDROID_ARM_LINKER */ 1063 default: 1064 DL_ERR("unknown weak reloc type %d @ %p (%d)", 1065 type, rel, (int) (rel - start)); 1066 return -1; 1067 } 1068 } else { 1069 /* We got a definition. */ 1070#if 0 1071 if((base == 0) && (si->base != 0)){ 1072 /* linking from libraries to main image is bad */ 1073 DL_ERR("cannot locate \"%s\"...", 1074 strtab + symtab[sym].st_name); 1075 return -1; 1076 } 1077#endif 1078 sym_addr = (unsigned)(s->st_value + lsi->load_bias); 1079 } 1080 count_relocation(kRelocSymbol); 1081 } else { 1082 s = NULL; 1083 } 1084 1085/* TODO: This is ugly. Split up the relocations by arch into 1086 * different files. 1087 */ 1088 switch(type){ 1089#if defined(ANDROID_ARM_LINKER) 1090 case R_ARM_JUMP_SLOT: 1091 count_relocation(kRelocAbsolute); 1092 MARK(rel->r_offset); 1093 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1094 *((unsigned*)reloc) = sym_addr; 1095 break; 1096 case R_ARM_GLOB_DAT: 1097 count_relocation(kRelocAbsolute); 1098 MARK(rel->r_offset); 1099 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1100 *((unsigned*)reloc) = sym_addr; 1101 break; 1102 case R_ARM_ABS32: 1103 count_relocation(kRelocAbsolute); 1104 MARK(rel->r_offset); 1105 TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1106 *((unsigned*)reloc) += sym_addr; 1107 break; 1108 case R_ARM_REL32: 1109 count_relocation(kRelocRelative); 1110 MARK(rel->r_offset); 1111 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s\n", 1112 reloc, sym_addr, rel->r_offset, sym_name); 1113 *((unsigned*)reloc) += sym_addr - rel->r_offset; 1114 break; 1115#elif defined(ANDROID_X86_LINKER) 1116 case R_386_JMP_SLOT: 1117 count_relocation(kRelocAbsolute); 1118 MARK(rel->r_offset); 1119 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1120 *((unsigned*)reloc) = sym_addr; 1121 break; 1122 case R_386_GLOB_DAT: 1123 count_relocation(kRelocAbsolute); 1124 MARK(rel->r_offset); 1125 TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1126 *((unsigned*)reloc) = sym_addr; 1127 break; 1128#elif defined(ANDROID_MIPS_LINKER) 1129 case R_MIPS_JUMP_SLOT: 1130 count_relocation(kRelocAbsolute); 1131 MARK(rel->r_offset); 1132 TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s\n", reloc, sym_addr, sym_name); 1133 *((unsigned*)reloc) = sym_addr; 1134 break; 1135 case R_MIPS_REL32: 1136 count_relocation(kRelocAbsolute); 1137 MARK(rel->r_offset); 1138 TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s\n", 1139 reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); 1140 if (s) { 1141 *((unsigned*)reloc) += sym_addr; 1142 } else { 1143 *((unsigned*)reloc) += si->base; 1144 } 1145 break; 1146#endif /* ANDROID_*_LINKER */ 1147 1148#if defined(ANDROID_ARM_LINKER) 1149 case R_ARM_RELATIVE: 1150#elif defined(ANDROID_X86_LINKER) 1151 case R_386_RELATIVE: 1152#endif /* ANDROID_*_LINKER */ 1153 count_relocation(kRelocRelative); 1154 MARK(rel->r_offset); 1155 if (sym) { 1156 DL_ERR("odd RELATIVE form..."); 1157 return -1; 1158 } 1159 TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x\n", reloc, si->base); 1160 *((unsigned*)reloc) += si->base; 1161 break; 1162 1163#if defined(ANDROID_X86_LINKER) 1164 case R_386_32: 1165 count_relocation(kRelocRelative); 1166 MARK(rel->r_offset); 1167 1168 TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s\n", reloc, sym_addr, sym_name); 1169 *((unsigned *)reloc) += (unsigned)sym_addr; 1170 break; 1171 1172 case R_386_PC32: 1173 count_relocation(kRelocRelative); 1174 MARK(rel->r_offset); 1175 TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s\n", 1176 reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); 1177 *((unsigned *)reloc) += (unsigned)(sym_addr - reloc); 1178 break; 1179#endif /* ANDROID_X86_LINKER */ 1180 1181#ifdef ANDROID_ARM_LINKER 1182 case R_ARM_COPY: 1183 if ((si->flags & FLAG_EXE) == 0) { 1184 /* 1185 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf 1186 * 1187 * Section 4.7.1.10 "Dynamic relocations" 1188 * R_ARM_COPY may only appear in executable objects where e_type is 1189 * set to ET_EXEC. 1190 * 1191 * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. 1192 * We should explicitly disallow ET_DYN executables from having 1193 * R_ARM_COPY relocations. 1194 */ 1195 DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); 1196 return -1; 1197 } 1198 count_relocation(kRelocCopy); 1199 MARK(rel->r_offset); 1200 TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s\n", reloc, s->st_size, sym_addr, sym_name); 1201 if (reloc == sym_addr) { 1202 Elf32_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed); 1203 1204 if (src == NULL) { 1205 DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name); 1206 return -1; 1207 } 1208 if (lsi->has_DT_SYMBOLIC) { 1209 DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared " 1210 "library %s (built with -Bsymbolic?)", si->name, lsi->name); 1211 return -1; 1212 } 1213 if (s->st_size < src->st_size) { 1214 DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)", 1215 si->name, s->st_size, src->st_size); 1216 return -1; 1217 } 1218 memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size); 1219 } else { 1220 DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name); 1221 return -1; 1222 } 1223 break; 1224#endif /* ANDROID_ARM_LINKER */ 1225 1226 default: 1227 DL_ERR("unknown reloc type %d @ %p (%d)", 1228 type, rel, (int) (rel - start)); 1229 return -1; 1230 } 1231 } 1232 return 0; 1233} 1234 1235#ifdef ANDROID_MIPS_LINKER 1236static int mips_relocate_got(soinfo* si, soinfo* needed[]) { 1237 unsigned *got; 1238 unsigned local_gotno, gotsym, symtabno; 1239 Elf32_Sym *symtab, *sym; 1240 unsigned g; 1241 1242 got = si->plt_got; 1243 local_gotno = si->mips_local_gotno; 1244 gotsym = si->mips_gotsym; 1245 symtabno = si->mips_symtabno; 1246 symtab = si->symtab; 1247 1248 /* 1249 * got[0] is address of lazy resolver function 1250 * got[1] may be used for a GNU extension 1251 * set it to a recognizable address in case someone calls it 1252 * (should be _rtld_bind_start) 1253 * FIXME: maybe this should be in a separate routine 1254 */ 1255 1256 if ((si->flags & FLAG_LINKER) == 0) { 1257 g = 0; 1258 got[g++] = 0xdeadbeef; 1259 if (got[g] & 0x80000000) { 1260 got[g++] = 0xdeadfeed; 1261 } 1262 /* 1263 * Relocate the local GOT entries need to be relocated 1264 */ 1265 for (; g < local_gotno; g++) { 1266 got[g] += si->load_bias; 1267 } 1268 } 1269 1270 /* Now for the global GOT entries */ 1271 sym = symtab + gotsym; 1272 got = si->plt_got + local_gotno; 1273 for (g = gotsym; g < symtabno; g++, sym++, got++) { 1274 const char *sym_name; 1275 Elf32_Sym *s; 1276 soinfo *lsi; 1277 1278 /* This is an undefined reference... try to locate it */ 1279 sym_name = si->strtab + sym->st_name; 1280 s = soinfo_do_lookup(si, sym_name, &lsi, needed); 1281 if (s == NULL) { 1282 /* We only allow an undefined symbol if this is a weak 1283 reference.. */ 1284 s = &symtab[g]; 1285 if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { 1286 DL_ERR("cannot locate \"%s\"...", sym_name); 1287 return -1; 1288 } 1289 *got = 0; 1290 } 1291 else { 1292 /* FIXME: is this sufficient? 1293 * For reference see NetBSD link loader 1294 * 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 1295 */ 1296 *got = lsi->load_bias + s->st_value; 1297 } 1298 } 1299 return 0; 1300} 1301#endif 1302 1303/* Please read the "Initialization and Termination functions" functions. 1304 * of the linker design note in bionic/linker/README.TXT to understand 1305 * what the following code is doing. 1306 * 1307 * The important things to remember are: 1308 * 1309 * DT_PREINIT_ARRAY must be called first for executables, and should 1310 * not appear in shared libraries. 1311 * 1312 * DT_INIT should be called before DT_INIT_ARRAY if both are present 1313 * 1314 * DT_FINI should be called after DT_FINI_ARRAY if both are present 1315 * 1316 * DT_FINI_ARRAY must be parsed in reverse order. 1317 */ 1318void soinfo::CallArray(const char* array_name UNUSED, unsigned* array, int count, bool reverse) { 1319 if (array == NULL) { 1320 return; 1321 } 1322 1323 int step = 1; 1324 if (reverse) { 1325 array += (count-1); 1326 step = -1; 1327 } 1328 1329 TRACE("[ Calling %s @ %p [%d] for '%s' ]\n", array_name, array, count, name); 1330 1331 for (int n = count; n > 0; n--) { 1332 TRACE("[ Looking at %s[%d] *%p == 0x%08x ]\n", array_name, n, array, *array); 1333 void (*func)() = (void (*)()) *array; 1334 array += step; 1335 if (((int) func == 0) || ((int) func == -1)) { 1336 continue; 1337 } 1338 TRACE("[ Calling func @ %p ]\n", func); 1339 func(); 1340 } 1341 1342 TRACE("[ Done calling %s for '%s' ]\n", array_name, name); 1343} 1344 1345void soinfo::CallFunction(const char* function_name UNUSED, void (*function)()) { 1346 if (function == NULL) { 1347 return; 1348 } 1349 1350 TRACE("[ Calling %s @ %p for '%s' ]\n", function_name, function, name); 1351 function(); 1352 TRACE("[ Done calling %s for '%s' ]\n", function_name, name); 1353} 1354 1355void soinfo::CallPreInitConstructors() { 1356 CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false); 1357} 1358 1359void soinfo::CallConstructors() { 1360 if (constructors_called) { 1361 return; 1362 } 1363 1364 // We set constructors_called before actually calling the constructors, otherwise it doesn't 1365 // protect against recursive constructor calls. One simple example of constructor recursion 1366 // is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so: 1367 // 1. The program depends on libc, so libc's constructor is called here. 1368 // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. 1369 // 3. dlopen() calls the constructors on the newly created 1370 // soinfo for libc_malloc_debug_leak.so. 1371 // 4. The debug .so depends on libc, so CallConstructors is 1372 // called again with the libc soinfo. If it doesn't trigger the early- 1373 // out above, the libc constructor will be called again (recursively!). 1374 constructors_called = true; 1375 1376 if (!(flags & FLAG_EXE) && preinit_array) { 1377 DL_ERR("shared library \"%s\" has a preinit_array table @ %p", name, preinit_array); 1378 return; 1379 } 1380 1381 if (dynamic) { 1382 for (unsigned* d = dynamic; *d; d += 2) { 1383 if (d[0] == DT_NEEDED) { 1384 soinfo* lsi = find_loaded_library(strtab + d[1]); 1385 if (lsi == NULL) { 1386 DL_ERR("\"%s\": could not initialize dependent library", name); 1387 } else { 1388 lsi->CallConstructors(); 1389 } 1390 } 1391 } 1392 } 1393 1394 CallFunction("DT_INIT", init_func); 1395 CallArray("DT_INIT_ARRAY", init_array, init_array_count, false); 1396} 1397 1398void soinfo::CallDestructors() { 1399 CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true); 1400 CallFunction("DT_FINI", fini_func); 1401} 1402 1403/* Force any of the closed stdin, stdout and stderr to be associated with 1404 /dev/null. */ 1405static int nullify_closed_stdio() { 1406 int dev_null, i, status; 1407 int return_value = 0; 1408 1409 dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 1410 if (dev_null < 0) { 1411 DL_ERR("cannot open /dev/null: %s", strerror(errno)); 1412 return -1; 1413 } 1414 TRACE("[ Opened /dev/null file-descriptor=%d]\n", dev_null); 1415 1416 /* If any of the stdio file descriptors is valid and not associated 1417 with /dev/null, dup /dev/null to it. */ 1418 for (i = 0; i < 3; i++) { 1419 /* If it is /dev/null already, we are done. */ 1420 if (i == dev_null) { 1421 continue; 1422 } 1423 1424 TRACE("[ Nullifying stdio file descriptor %d]\n", i); 1425 status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 1426 1427 /* If file is opened, we are good. */ 1428 if (status != -1) { 1429 continue; 1430 } 1431 1432 /* The only error we allow is that the file descriptor does not 1433 exist, in which case we dup /dev/null to it. */ 1434 if (errno != EBADF) { 1435 DL_ERR("fcntl failed: %s", strerror(errno)); 1436 return_value = -1; 1437 continue; 1438 } 1439 1440 /* Try dupping /dev/null to this stdio file descriptor and 1441 repeat if there is a signal. Note that any errors in closing 1442 the stdio descriptor are lost. */ 1443 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 1444 if (status < 0) { 1445 DL_ERR("dup2 failed: %s", strerror(errno)); 1446 return_value = -1; 1447 continue; 1448 } 1449 } 1450 1451 /* If /dev/null is not one of the stdio file descriptors, close it. */ 1452 if (dev_null > 2) { 1453 TRACE("[ Closing /dev/null file-descriptor=%d]\n", dev_null); 1454 status = TEMP_FAILURE_RETRY(close(dev_null)); 1455 if (status == -1) { 1456 DL_ERR("close failed: %s", strerror(errno)); 1457 return_value = -1; 1458 } 1459 } 1460 1461 return return_value; 1462} 1463 1464static bool soinfo_link_image(soinfo* si) { 1465 si->flags |= FLAG_ERROR; 1466 1467 /* "base" might wrap around UINT32_MAX. */ 1468 Elf32_Addr base = si->load_bias; 1469 const Elf32_Phdr *phdr = si->phdr; 1470 int phnum = si->phnum; 1471 int relocating_linker = (si->flags & FLAG_LINKER) != 0; 1472 soinfo **needed, **pneeded; 1473 1474 /* We can't debug anything until the linker is relocated */ 1475 if (!relocating_linker) { 1476 INFO("[ linking %s ]\n", si->name); 1477 DEBUG("si->base = 0x%08x si->flags = 0x%08x\n", si->base, si->flags); 1478 } 1479 1480 /* Extract dynamic section */ 1481 size_t dynamic_count; 1482 phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, 1483 &dynamic_count); 1484 if (si->dynamic == NULL) { 1485 if (!relocating_linker) { 1486 DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name); 1487 } 1488 return false; 1489 } else { 1490 if (!relocating_linker) { 1491 DEBUG("dynamic = %p\n", si->dynamic); 1492 } 1493 } 1494 1495#ifdef ANDROID_ARM_LINKER 1496 (void) phdr_table_get_arm_exidx(phdr, phnum, base, 1497 &si->ARM_exidx, &si->ARM_exidx_count); 1498#endif 1499 1500 /* extract useful information from dynamic section */ 1501 for (unsigned* d = si->dynamic; *d; ++d) { 1502 DEBUG("d = %p, d[0] = 0x%08x d[1] = 0x%08x\n", d, d[0], d[1]); 1503 switch(*d++){ 1504 case DT_HASH: 1505 si->nbucket = ((unsigned *) (base + *d))[0]; 1506 si->nchain = ((unsigned *) (base + *d))[1]; 1507 si->bucket = (unsigned *) (base + *d + 8); 1508 si->chain = (unsigned *) (base + *d + 8 + si->nbucket * 4); 1509 break; 1510 case DT_STRTAB: 1511 si->strtab = (const char *) (base + *d); 1512 break; 1513 case DT_SYMTAB: 1514 si->symtab = (Elf32_Sym *) (base + *d); 1515 break; 1516 case DT_PLTREL: 1517 if(*d != DT_REL) { 1518 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1519 return false; 1520 } 1521 break; 1522 case DT_JMPREL: 1523 si->plt_rel = (Elf32_Rel*) (base + *d); 1524 break; 1525 case DT_PLTRELSZ: 1526 si->plt_rel_count = *d / 8; 1527 break; 1528 case DT_REL: 1529 si->rel = (Elf32_Rel*) (base + *d); 1530 break; 1531 case DT_RELSZ: 1532 si->rel_count = *d / 8; 1533 break; 1534 case DT_PLTGOT: 1535 /* Save this in case we decide to do lazy binding. We don't yet. */ 1536 si->plt_got = (unsigned *)(base + *d); 1537 break; 1538 case DT_DEBUG: 1539#if !defined(ANDROID_MIPS_LINKER) 1540 // Set the DT_DEBUG entry to the address of _r_debug for GDB 1541 *d = (int) &_r_debug; 1542#endif 1543 break; 1544 case DT_RELA: 1545 DL_ERR("unsupported DT_RELA in \"%s\"", si->name); 1546 return false; 1547 case DT_INIT: 1548 si->init_func = (void (*)(void))(base + *d); 1549 DEBUG("%s constructors (init func) found at %p\n", si->name, si->init_func); 1550 break; 1551 case DT_FINI: 1552 si->fini_func = (void (*)(void))(base + *d); 1553 DEBUG("%s destructors (fini func) found at %p\n", si->name, si->fini_func); 1554 break; 1555 case DT_INIT_ARRAY: 1556 si->init_array = (unsigned *)(base + *d); 1557 DEBUG("%s constructors (init_array) found at %p\n", si->name, si->init_array); 1558 break; 1559 case DT_INIT_ARRAYSZ: 1560 si->init_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); 1561 break; 1562 case DT_FINI_ARRAY: 1563 si->fini_array = (unsigned *)(base + *d); 1564 DEBUG("%s destructors (fini_array) found at %p\n", si->name, si->fini_array); 1565 break; 1566 case DT_FINI_ARRAYSZ: 1567 si->fini_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); 1568 break; 1569 case DT_PREINIT_ARRAY: 1570 si->preinit_array = (unsigned *)(base + *d); 1571 DEBUG("%s constructors (preinit_array) found at %p\n", si->name, si->preinit_array); 1572 break; 1573 case DT_PREINIT_ARRAYSZ: 1574 si->preinit_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); 1575 break; 1576 case DT_TEXTREL: 1577 si->has_text_relocations = true; 1578 break; 1579 case DT_SYMBOLIC: 1580 si->has_DT_SYMBOLIC = true; 1581 break; 1582#if defined(DT_FLAGS) 1583 case DT_FLAGS: 1584 if (*d & DF_TEXTREL) { 1585 si->has_text_relocations = true; 1586 } 1587 if (*d & DF_SYMBOLIC) { 1588 si->has_DT_SYMBOLIC = true; 1589 } 1590 break; 1591#endif 1592#if defined(ANDROID_MIPS_LINKER) 1593 case DT_NEEDED: 1594 case DT_STRSZ: 1595 case DT_SYMENT: 1596 case DT_RELENT: 1597 break; 1598 case DT_MIPS_RLD_MAP: 1599 // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. 1600 { 1601 r_debug** dp = (r_debug**) *d; 1602 *dp = &_r_debug; 1603 } 1604 break; 1605 case DT_MIPS_RLD_VERSION: 1606 case DT_MIPS_FLAGS: 1607 case DT_MIPS_BASE_ADDRESS: 1608 case DT_MIPS_UNREFEXTNO: 1609 case DT_MIPS_RWPLT: 1610 break; 1611 1612 case DT_MIPS_PLTGOT: 1613#if 0 1614 /* not yet... */ 1615 si->mips_pltgot = (unsigned *)(si->base + *d); 1616#endif 1617 break; 1618 1619 case DT_MIPS_SYMTABNO: 1620 si->mips_symtabno = *d; 1621 break; 1622 1623 case DT_MIPS_LOCAL_GOTNO: 1624 si->mips_local_gotno = *d; 1625 break; 1626 1627 case DT_MIPS_GOTSYM: 1628 si->mips_gotsym = *d; 1629 break; 1630 1631 default: 1632 DEBUG("Unused DT entry: type 0x%08x arg 0x%08x\n", d[-1], d[0]); 1633 break; 1634#endif 1635 } 1636 } 1637 1638 DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p\n", 1639 si->base, si->strtab, si->symtab); 1640 1641 // Sanity checks. 1642 if (si->nbucket == 0) { 1643 DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name); 1644 return false; 1645 } 1646 if (si->strtab == 0) { 1647 DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name); 1648 return false; 1649 } 1650 if (si->symtab == 0) { 1651 DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name); 1652 return false; 1653 } 1654 1655 /* if this is the main executable, then load all of the preloads now */ 1656 if (si->flags & FLAG_EXE) { 1657 memset(preloads, 0, sizeof(preloads)); 1658 for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) { 1659 soinfo* lsi = find_library(gLdPreloadNames[i]); 1660 if (lsi == NULL) { 1661 strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf)); 1662 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1663 gLdPreloadNames[i], si->name, tmp_err_buf); 1664 return false; 1665 } 1666 preloads[i] = lsi; 1667 } 1668 } 1669 1670 /* dynamic_count is an upper bound for the number of needed libs */ 1671 pneeded = needed = (soinfo**) alloca((1 + dynamic_count) * sizeof(soinfo*)); 1672 1673 for (unsigned* d = si->dynamic; *d; d += 2) { 1674 if (d[0] == DT_NEEDED) { 1675 DEBUG("%s needs %s\n", si->name, si->strtab + d[1]); 1676 soinfo* lsi = find_library(si->strtab + d[1]); 1677 if (lsi == NULL) { 1678 strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf)); 1679 DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", 1680 si->strtab + d[1], si->name, tmp_err_buf); 1681 return false; 1682 } 1683 *pneeded++ = lsi; 1684 } 1685 } 1686 *pneeded = NULL; 1687 1688 if (si->has_text_relocations) { 1689 /* Unprotect the segments, i.e. make them writable, to allow 1690 * text relocations to work properly. We will later call 1691 * phdr_table_protect_segments() after all of them are applied 1692 * and all constructors are run. 1693 */ 1694 if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1695 DL_ERR("can't unprotect loadable segments for \"%s\": %s", 1696 si->name, strerror(errno)); 1697 return false; 1698 } 1699 } 1700 1701 if (si->plt_rel) { 1702 DEBUG("[ relocating %s plt ]\n", si->name ); 1703 if(soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) { 1704 return false; 1705 } 1706 } 1707 if (si->rel) { 1708 DEBUG("[ relocating %s ]\n", si->name ); 1709 if(soinfo_relocate(si, si->rel, si->rel_count, needed)) { 1710 return false; 1711 } 1712 } 1713 1714#ifdef ANDROID_MIPS_LINKER 1715 if (mips_relocate_got(si, needed)) { 1716 return false; 1717 } 1718#endif 1719 1720 si->flags |= FLAG_LINKED; 1721 DEBUG("[ finished linking %s ]\n", si->name); 1722 1723 if (si->has_text_relocations) { 1724 /* All relocations are done, we can protect our segments back to 1725 * read-only. */ 1726 if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { 1727 DL_ERR("can't protect segments for \"%s\": %s", 1728 si->name, strerror(errno)); 1729 return false; 1730 } 1731 } 1732 1733 /* We can also turn on GNU RELRO protection */ 1734 if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { 1735 DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", 1736 si->name, strerror(errno)); 1737 return false; 1738 } 1739 1740 // If this is a setuid/setgid program, close the security hole described in 1741 // ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc 1742 if (get_AT_SECURE()) { 1743 nullify_closed_stdio(); 1744 } 1745 notify_gdb_of_load(si); 1746 si->flags &= ~FLAG_ERROR; 1747 return true; 1748} 1749 1750static void parse_path(const char* path, const char* delimiters, 1751 const char** array, char* buf, size_t buf_size, size_t max_count) 1752{ 1753 if (path == NULL) { 1754 return; 1755 } 1756 1757 size_t len = strlcpy(buf, path, buf_size); 1758 1759 size_t i = 0; 1760 char* buf_p = buf; 1761 while (i < max_count && (array[i] = strsep(&buf_p, delimiters))) { 1762 if (*array[i] != '\0') { 1763 ++i; 1764 } 1765 } 1766 1767 // Forget the last path if we had to truncate; this occurs if the 2nd to 1768 // last char isn't '\0' (i.e. wasn't originally a delimiter). 1769 if (i > 0 && len >= buf_size && buf[buf_size - 2] != '\0') { 1770 array[i - 1] = NULL; 1771 } else { 1772 array[i] = NULL; 1773 } 1774} 1775 1776static void parse_LD_LIBRARY_PATH(const char* path) { 1777 parse_path(path, ":", gLdPaths, 1778 gLdPathsBuffer, sizeof(gLdPathsBuffer), LDPATH_MAX); 1779} 1780 1781static void parse_LD_PRELOAD(const char* path) { 1782 // We have historically supported ':' as well as ' ' in LD_PRELOAD. 1783 parse_path(path, " :", gLdPreloadNames, 1784 gLdPreloadsBuffer, sizeof(gLdPreloadsBuffer), LDPRELOAD_MAX); 1785} 1786 1787/* 1788 * This code is called after the linker has linked itself and 1789 * fixed it's own GOT. It is safe to make references to externs 1790 * and other non-local data at this point. 1791 */ 1792static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linker_base) 1793{ 1794 static soinfo linker_soinfo; 1795 1796 int argc = (int) *elfdata; 1797 char **argv = (char**) (elfdata + 1); 1798 unsigned *vecs = (unsigned*) (argv + argc + 1); 1799 1800 /* NOTE: we store the elfdata pointer on a special location 1801 * of the temporary TLS area in order to pass it to 1802 * the C Library's runtime initializer. 1803 * 1804 * The initializer must clear the slot and reset the TLS 1805 * to point to a different location to ensure that no other 1806 * shared library constructor can access it. 1807 */ 1808 __libc_init_tls(elfdata); 1809 1810#if TIMING 1811 struct timeval t0, t1; 1812 gettimeofday(&t0, 0); 1813#endif 1814 1815 // Initialize environment functions, and get to the ELF aux vectors table. 1816 vecs = linker_env_init(vecs); 1817 1818 debugger_init(); 1819 1820 // Get a few environment variables. 1821 const char* LD_DEBUG = linker_env_get("LD_DEBUG"); 1822 if (LD_DEBUG != NULL) { 1823 debug_verbosity = atoi(LD_DEBUG); 1824 } 1825 1826 // Normally, these are cleaned by linker_env_init, but the test 1827 // doesn't cost us anything. 1828 const char* ldpath_env = NULL; 1829 const char* ldpreload_env = NULL; 1830 if (!get_AT_SECURE()) { 1831 ldpath_env = linker_env_get("LD_LIBRARY_PATH"); 1832 ldpreload_env = linker_env_get("LD_PRELOAD"); 1833 } 1834 1835 INFO("[ android linker & debugger ]\n"); 1836 DEBUG("elfdata @ 0x%08x\n", (unsigned)elfdata); 1837 1838 soinfo* si = soinfo_alloc(argv[0]); 1839 if (si == NULL) { 1840 exit(EXIT_FAILURE); 1841 } 1842 1843 /* bootstrap the link map, the main exe always needs to be first */ 1844 si->flags |= FLAG_EXE; 1845 link_map* map = &(si->linkmap); 1846 1847 map->l_addr = 0; 1848 map->l_name = argv[0]; 1849 map->l_prev = NULL; 1850 map->l_next = NULL; 1851 1852 _r_debug.r_map = map; 1853 r_debug_tail = map; 1854 1855 /* gdb expects the linker to be in the debug shared object list. 1856 * Without this, gdb has trouble locating the linker's ".text" 1857 * and ".plt" sections. Gdb could also potentially use this to 1858 * relocate the offset of our exported 'rtld_db_dlactivity' symbol. 1859 * Don't use soinfo_alloc(), because the linker shouldn't 1860 * be on the soinfo list. 1861 */ 1862 strlcpy((char*) linker_soinfo.name, "/system/bin/linker", sizeof linker_soinfo.name); 1863 linker_soinfo.flags = 0; 1864 linker_soinfo.base = linker_base; 1865 /* 1866 * Set the dynamic field in the link map otherwise gdb will complain with 1867 * the following: 1868 * warning: .dynamic section for "/system/bin/linker" is not at the 1869 * expected address (wrong library or version mismatch?) 1870 */ 1871 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base; 1872 Elf32_Phdr *phdr = 1873 (Elf32_Phdr *)((unsigned char *) linker_base + elf_hdr->e_phoff); 1874 phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, 1875 &linker_soinfo.dynamic, NULL); 1876 insert_soinfo_into_debug_map(&linker_soinfo); 1877 1878 /* extract information passed from the kernel */ 1879 while (vecs[0] != 0){ 1880 switch(vecs[0]){ 1881 case AT_PHDR: 1882 si->phdr = (Elf32_Phdr*) vecs[1]; 1883 break; 1884 case AT_PHNUM: 1885 si->phnum = (int) vecs[1]; 1886 break; 1887 case AT_ENTRY: 1888 si->entry = vecs[1]; 1889 break; 1890 } 1891 vecs += 2; 1892 } 1893 1894 /* Compute the value of si->base. We can't rely on the fact that 1895 * the first entry is the PHDR because this will not be true 1896 * for certain executables (e.g. some in the NDK unit test suite) 1897 */ 1898 int nn; 1899 si->base = 0; 1900 si->size = phdr_table_get_load_size(si->phdr, si->phnum); 1901 si->load_bias = 0; 1902 for ( nn = 0; nn < si->phnum; nn++ ) { 1903 if (si->phdr[nn].p_type == PT_PHDR) { 1904 si->load_bias = (Elf32_Addr)si->phdr - si->phdr[nn].p_vaddr; 1905 si->base = (Elf32_Addr) si->phdr - si->phdr[nn].p_offset; 1906 break; 1907 } 1908 } 1909 si->dynamic = (unsigned *)-1; 1910 si->refcount = 1; 1911 1912 // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). 1913 parse_LD_LIBRARY_PATH(ldpath_env); 1914 parse_LD_PRELOAD(ldpreload_env); 1915 1916 somain = si; 1917 1918 if (!soinfo_link_image(si)) { 1919 char errmsg[] = "CANNOT LINK EXECUTABLE\n"; 1920 write(2, __linker_dl_err_buf, strlen(__linker_dl_err_buf)); 1921 write(2, errmsg, sizeof(errmsg)); 1922 exit(EXIT_FAILURE); 1923 } 1924 1925 si->CallPreInitConstructors(); 1926 1927 for (size_t i = 0; preloads[i] != NULL; ++i) { 1928 preloads[i]->CallConstructors(); 1929 } 1930 1931 /*After the link_image, the si->load_bias is initialized. 1932 *For so lib, the map->l_addr will be updated in notify_gdb_of_load. 1933 *We need to update this value for so exe here. So Unwind_Backtrace 1934 *for some arch like x86 could work correctly within so exe. 1935 */ 1936 map->l_addr = si->load_bias; 1937 si->CallConstructors(); 1938 1939#if TIMING 1940 gettimeofday(&t1,NULL); 1941 PRINT("LINKER TIME: %s: %d microseconds\n", argv[0], (int) ( 1942 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - 1943 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) 1944 )); 1945#endif 1946#if STATS 1947 PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol\n", argv[0], 1948 linker_stats.count[kRelocAbsolute], 1949 linker_stats.count[kRelocRelative], 1950 linker_stats.count[kRelocCopy], 1951 linker_stats.count[kRelocSymbol]); 1952#endif 1953#if COUNT_PAGES 1954 { 1955 unsigned n; 1956 unsigned i; 1957 unsigned count = 0; 1958 for(n = 0; n < 4096; n++){ 1959 if(bitmask[n]){ 1960 unsigned x = bitmask[n]; 1961 for(i = 0; i < 8; i++){ 1962 if(x & 1) count++; 1963 x >>= 1; 1964 } 1965 } 1966 } 1967 PRINT("PAGES MODIFIED: %s: %d (%dKB)\n", argv[0], count, count * 4); 1968 } 1969#endif 1970 1971#if TIMING || STATS || COUNT_PAGES 1972 fflush(stdout); 1973#endif 1974 1975 TRACE("[ Ready to execute '%s' @ 0x%08x ]\n", si->name, si->entry); 1976 return si->entry; 1977} 1978 1979/* 1980 * Find the value of AT_BASE passed to us by the kernel. This is the load 1981 * location of the linker. 1982 */ 1983static unsigned find_linker_base(unsigned **elfdata) { 1984 int argc = (int) *elfdata; 1985 char **argv = (char**) (elfdata + 1); 1986 unsigned *vecs = (unsigned*) (argv + argc + 1); 1987 while (vecs[0] != 0) { 1988 vecs++; 1989 } 1990 1991 /* The end of the environment block is marked by two NULL pointers */ 1992 vecs++; 1993 1994 while(vecs[0]) { 1995 if (vecs[0] == AT_BASE) { 1996 return vecs[1]; 1997 } 1998 vecs += 2; 1999 } 2000 2001 return 0; // should never happen 2002} 2003 2004/* Compute the load-bias of an existing executable. This shall only 2005 * be used to compute the load bias of an executable or shared library 2006 * that was loaded by the kernel itself. 2007 * 2008 * Input: 2009 * elf -> address of ELF header, assumed to be at the start of the file. 2010 * Return: 2011 * load bias, i.e. add the value of any p_vaddr in the file to get 2012 * the corresponding address in memory. 2013 */ 2014static Elf32_Addr 2015get_elf_exec_load_bias(const Elf32_Ehdr* elf) 2016{ 2017 Elf32_Addr offset = elf->e_phoff; 2018 const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset); 2019 const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum; 2020 const Elf32_Phdr* phdr; 2021 2022 for (phdr = phdr_table; phdr < phdr_end; phdr++) { 2023 if (phdr->p_type == PT_LOAD) { 2024 return (Elf32_Addr)elf + phdr->p_offset - phdr->p_vaddr; 2025 } 2026 } 2027 return 0; 2028} 2029 2030/* 2031 * This is the entry point for the linker, called from begin.S. This 2032 * method is responsible for fixing the linker's own relocations, and 2033 * then calling __linker_init_post_relocation(). 2034 * 2035 * Because this method is called before the linker has fixed it's own 2036 * relocations, any attempt to reference an extern variable, extern 2037 * function, or other GOT reference will generate a segfault. 2038 */ 2039extern "C" unsigned __linker_init(unsigned **elfdata) { 2040 unsigned linker_addr = find_linker_base(elfdata); 2041 Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_addr; 2042 Elf32_Phdr *phdr = 2043 (Elf32_Phdr *)((unsigned char *) linker_addr + elf_hdr->e_phoff); 2044 2045 soinfo linker_so; 2046 memset(&linker_so, 0, sizeof(soinfo)); 2047 2048 linker_so.base = linker_addr; 2049 linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); 2050 linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); 2051 linker_so.dynamic = (unsigned *) -1; 2052 linker_so.phdr = phdr; 2053 linker_so.phnum = elf_hdr->e_phnum; 2054 linker_so.flags |= FLAG_LINKER; 2055 2056 if (!soinfo_link_image(&linker_so)) { 2057 // It would be nice to print an error message, but if the linker 2058 // can't link itself, there's no guarantee that we'll be able to 2059 // call write() (because it involves a GOT reference). 2060 // 2061 // This situation should never occur unless the linker itself 2062 // is corrupt. 2063 exit(EXIT_FAILURE); 2064 } 2065 2066 // We have successfully fixed our own relocations. It's safe to run 2067 // the main part of the linker now. 2068 unsigned start_address = __linker_init_post_relocation(elfdata, linker_addr); 2069 2070 set_soinfo_pool_protection(PROT_READ); 2071 2072 // Return the address that the calling assembly stub should jump to. 2073 return start_address; 2074} 2075