1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * elf.c - ELF access library 4 * 5 * Adapted from kpatch (https://github.com/dynup/kpatch): 6 * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com> 7 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> 8 */ 9 10 #include <sys/types.h> 11 #include <sys/stat.h> 12 #include <sys/mman.h> 13 #include <fcntl.h> 14 #include <stdio.h> 15 #include <stdlib.h> 16 #include <string.h> 17 #include <unistd.h> 18 #include <errno.h> 19 #include <linux/interval_tree_generic.h> 20 #include <objtool/builtin.h> 21 22 #include <objtool/elf.h> 23 #include <objtool/warn.h> 24 25 static inline u32 str_hash(const char *str) 26 { 27 return jhash(str, strlen(str), 0); 28 } 29 30 #define __elf_table(name) (elf->name##_hash) 31 #define __elf_bits(name) (elf->name##_bits) 32 33 #define __elf_table_entry(name, key) \ 34 __elf_table(name)[hash_min(key, __elf_bits(name))] 35 36 #define elf_hash_add(name, node, key) \ 37 ({ \ 38 struct elf_hash_node *__node = node; \ 39 __node->next = __elf_table_entry(name, key); \ 40 __elf_table_entry(name, key) = __node; \ 41 }) 42 43 static inline void __elf_hash_del(struct elf_hash_node *node, 44 struct elf_hash_node **head) 45 { 46 struct elf_hash_node *cur, *prev; 47 48 if (node == *head) { 49 *head = node->next; 50 return; 51 } 52 53 for (prev = NULL, cur = *head; cur; prev = cur, cur = cur->next) { 54 if (cur == node) { 55 prev->next = cur->next; 56 break; 57 } 58 } 59 } 60 61 #define elf_hash_del(name, node, key) \ 62 __elf_hash_del(node, &__elf_table_entry(name, key)) 63 64 #define elf_list_entry(ptr, type, member) \ 65 ({ \ 66 typeof(ptr) __ptr = (ptr); \ 67 __ptr ? container_of(__ptr, type, member) : NULL; \ 68 }) 69 70 #define elf_hash_for_each_possible(name, obj, member, key) \ 71 for (obj = elf_list_entry(__elf_table_entry(name, key), typeof(*obj), member); \ 72 obj; \ 73 obj = elf_list_entry(obj->member.next, typeof(*(obj)), member)) 74 75 #define elf_alloc_hash(name, size) \ 76 ({ \ 77 __elf_bits(name) = max(10, ilog2(size)); \ 78 __elf_table(name) = mmap(NULL, sizeof(struct elf_hash_node *) << __elf_bits(name), \ 79 PROT_READ|PROT_WRITE, \ 80 MAP_PRIVATE|MAP_ANON, -1, 0); \ 81 if (__elf_table(name) == (void *)-1L) { \ 82 WARN("mmap fail " #name); \ 83 __elf_table(name) = NULL; \ 84 } \ 85 __elf_table(name); \ 86 }) 87 88 static inline unsigned long __sym_start(struct symbol *s) 89 { 90 return s->offset; 91 } 92 93 static inline unsigned long __sym_last(struct symbol *s) 94 { 95 return s->offset + s->len - 1; 96 } 97 98 INTERVAL_TREE_DEFINE(struct symbol, node, unsigned long, __subtree_last, 99 __sym_start, __sym_last, static, __sym) 100 101 #define __sym_for_each(_iter, _tree, _start, _end) \ 102 for (_iter = __sym_iter_first((_tree), (_start), (_end)); \ 103 _iter; _iter = __sym_iter_next(_iter, (_start), (_end))) 104 105 struct symbol_hole { 106 unsigned long key; 107 const struct symbol *sym; 108 }; 109 110 /* 111 * Find !section symbol where @offset is after it. 112 */ 113 static int symbol_hole_by_offset(const void *key, const struct rb_node *node) 114 { 115 const struct symbol *s = rb_entry(node, struct symbol, node); 116 struct symbol_hole *sh = (void *)key; 117 118 if (sh->key < s->offset) 119 return -1; 120 121 if (sh->key >= s->offset + s->len) { 122 if (s->type != STT_SECTION) 123 sh->sym = s; 124 return 1; 125 } 126 127 return 0; 128 } 129 130 struct section *find_section_by_name(const struct elf *elf, const char *name) 131 { 132 struct section *sec; 133 134 elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) { 135 if (!strcmp(sec->name, name)) 136 return sec; 137 } 138 139 return NULL; 140 } 141 142 static struct section *find_section_by_index(struct elf *elf, 143 unsigned int idx) 144 { 145 struct section *sec; 146 147 elf_hash_for_each_possible(section, sec, hash, idx) { 148 if (sec->idx == idx) 149 return sec; 150 } 151 152 return NULL; 153 } 154 155 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx) 156 { 157 struct symbol *sym; 158 159 elf_hash_for_each_possible(symbol, sym, hash, idx) { 160 if (sym->idx == idx) 161 return sym; 162 } 163 164 return NULL; 165 } 166 167 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset) 168 { 169 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree; 170 struct symbol *iter; 171 172 __sym_for_each(iter, tree, offset, offset) { 173 if (iter->offset == offset && iter->type != STT_SECTION) 174 return iter; 175 } 176 177 return NULL; 178 } 179 180 struct symbol *find_func_by_offset(struct section *sec, unsigned long offset) 181 { 182 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree; 183 struct symbol *iter; 184 185 __sym_for_each(iter, tree, offset, offset) { 186 if (iter->offset == offset && iter->type == STT_FUNC) 187 return iter; 188 } 189 190 return NULL; 191 } 192 193 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset) 194 { 195 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree; 196 struct symbol *iter; 197 198 __sym_for_each(iter, tree, offset, offset) { 199 if (iter->type != STT_SECTION) 200 return iter; 201 } 202 203 return NULL; 204 } 205 206 /* 207 * Returns size of hole starting at @offset. 208 */ 209 int find_symbol_hole_containing(const struct section *sec, unsigned long offset) 210 { 211 struct symbol_hole hole = { 212 .key = offset, 213 .sym = NULL, 214 }; 215 struct rb_node *n; 216 struct symbol *s; 217 218 /* 219 * Find the rightmost symbol for which @offset is after it. 220 */ 221 n = rb_find(&hole, &sec->symbol_tree.rb_root, symbol_hole_by_offset); 222 223 /* found a symbol that contains @offset */ 224 if (n) 225 return 0; /* not a hole */ 226 227 /* 228 * @offset >= sym->offset + sym->len, find symbol after it. 229 * When hole.sym is empty, use the first node to compute the hole. 230 * If there is no symbol in the section, the first node will be NULL, 231 * in which case, -1 is returned to skip the whole section. 232 */ 233 if (hole.sym) 234 n = rb_next(&hole.sym->node); 235 else 236 n = rb_first_cached(&sec->symbol_tree); 237 238 if (!n) 239 return -1; /* until end of address space */ 240 241 /* hole until start of next symbol */ 242 s = rb_entry(n, struct symbol, node); 243 return s->offset - offset; 244 } 245 246 struct symbol *find_func_containing(struct section *sec, unsigned long offset) 247 { 248 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree; 249 struct symbol *iter; 250 251 __sym_for_each(iter, tree, offset, offset) { 252 if (iter->type == STT_FUNC) 253 return iter; 254 } 255 256 return NULL; 257 } 258 259 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name) 260 { 261 struct symbol *sym; 262 263 elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) { 264 if (!strcmp(sym->name, name)) 265 return sym; 266 } 267 268 return NULL; 269 } 270 271 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec, 272 unsigned long offset, unsigned int len) 273 { 274 struct reloc *reloc, *r = NULL; 275 struct section *rsec; 276 unsigned long o; 277 278 rsec = sec->rsec; 279 if (!rsec) 280 return NULL; 281 282 for_offset_range(o, offset, offset + len) { 283 elf_hash_for_each_possible(reloc, reloc, hash, 284 sec_offset_hash(rsec, o)) { 285 if (reloc->sec != rsec) 286 continue; 287 288 if (reloc_offset(reloc) >= offset && 289 reloc_offset(reloc) < offset + len) { 290 if (!r || reloc_offset(reloc) < reloc_offset(r)) 291 r = reloc; 292 } 293 } 294 if (r) 295 return r; 296 } 297 298 return NULL; 299 } 300 301 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset) 302 { 303 return find_reloc_by_dest_range(elf, sec, offset, 1); 304 } 305 306 static bool is_dwarf_section(struct section *sec) 307 { 308 return !strncmp(sec->name, ".debug_", 7); 309 } 310 311 static int read_sections(struct elf *elf) 312 { 313 Elf_Scn *s = NULL; 314 struct section *sec; 315 size_t shstrndx, sections_nr; 316 int i; 317 318 if (elf_getshdrnum(elf->elf, §ions_nr)) { 319 WARN_ELF("elf_getshdrnum"); 320 return -1; 321 } 322 323 if (elf_getshdrstrndx(elf->elf, &shstrndx)) { 324 WARN_ELF("elf_getshdrstrndx"); 325 return -1; 326 } 327 328 if (!elf_alloc_hash(section, sections_nr) || 329 !elf_alloc_hash(section_name, sections_nr)) 330 return -1; 331 332 elf->section_data = calloc(sections_nr, sizeof(*sec)); 333 if (!elf->section_data) { 334 perror("calloc"); 335 return -1; 336 } 337 for (i = 0; i < sections_nr; i++) { 338 sec = &elf->section_data[i]; 339 340 INIT_LIST_HEAD(&sec->symbol_list); 341 342 s = elf_getscn(elf->elf, i); 343 if (!s) { 344 WARN_ELF("elf_getscn"); 345 return -1; 346 } 347 348 sec->idx = elf_ndxscn(s); 349 350 if (!gelf_getshdr(s, &sec->sh)) { 351 WARN_ELF("gelf_getshdr"); 352 return -1; 353 } 354 355 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name); 356 if (!sec->name) { 357 WARN_ELF("elf_strptr"); 358 return -1; 359 } 360 361 if (sec->sh.sh_size != 0 && !is_dwarf_section(sec)) { 362 sec->data = elf_getdata(s, NULL); 363 if (!sec->data) { 364 WARN_ELF("elf_getdata"); 365 return -1; 366 } 367 if (sec->data->d_off != 0 || 368 sec->data->d_size != sec->sh.sh_size) { 369 WARN("unexpected data attributes for %s", 370 sec->name); 371 return -1; 372 } 373 } 374 375 list_add_tail(&sec->list, &elf->sections); 376 elf_hash_add(section, &sec->hash, sec->idx); 377 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name)); 378 379 if (is_reloc_sec(sec)) 380 elf->num_relocs += sec_num_entries(sec); 381 } 382 383 if (opts.stats) { 384 printf("nr_sections: %lu\n", (unsigned long)sections_nr); 385 printf("section_bits: %d\n", elf->section_bits); 386 } 387 388 /* sanity check, one more call to elf_nextscn() should return NULL */ 389 if (elf_nextscn(elf->elf, s)) { 390 WARN("section entry mismatch"); 391 return -1; 392 } 393 394 return 0; 395 } 396 397 static void elf_add_symbol(struct elf *elf, struct symbol *sym) 398 { 399 struct list_head *entry; 400 struct rb_node *pnode; 401 struct symbol *iter; 402 403 INIT_LIST_HEAD(&sym->pv_target); 404 sym->alias = sym; 405 406 sym->type = GELF_ST_TYPE(sym->sym.st_info); 407 sym->bind = GELF_ST_BIND(sym->sym.st_info); 408 409 if (sym->type == STT_FILE) 410 elf->num_files++; 411 412 sym->offset = sym->sym.st_value; 413 sym->len = sym->sym.st_size; 414 415 __sym_for_each(iter, &sym->sec->symbol_tree, sym->offset, sym->offset) { 416 if (iter->offset == sym->offset && iter->type == sym->type) 417 iter->alias = sym; 418 } 419 420 __sym_insert(sym, &sym->sec->symbol_tree); 421 pnode = rb_prev(&sym->node); 422 if (pnode) 423 entry = &rb_entry(pnode, struct symbol, node)->list; 424 else 425 entry = &sym->sec->symbol_list; 426 list_add(&sym->list, entry); 427 elf_hash_add(symbol, &sym->hash, sym->idx); 428 elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name)); 429 430 /* 431 * Don't store empty STT_NOTYPE symbols in the rbtree. They 432 * can exist within a function, confusing the sorting. 433 */ 434 if (!sym->len) 435 __sym_remove(sym, &sym->sec->symbol_tree); 436 } 437 438 static int read_symbols(struct elf *elf) 439 { 440 struct section *symtab, *symtab_shndx, *sec; 441 struct symbol *sym, *pfunc; 442 int symbols_nr, i; 443 char *coldstr; 444 Elf_Data *shndx_data = NULL; 445 Elf32_Word shndx; 446 447 symtab = find_section_by_name(elf, ".symtab"); 448 if (symtab) { 449 symtab_shndx = find_section_by_name(elf, ".symtab_shndx"); 450 if (symtab_shndx) 451 shndx_data = symtab_shndx->data; 452 453 symbols_nr = sec_num_entries(symtab); 454 } else { 455 /* 456 * A missing symbol table is actually possible if it's an empty 457 * .o file. This can happen for thunk_64.o. Make sure to at 458 * least allocate the symbol hash tables so we can do symbol 459 * lookups without crashing. 460 */ 461 symbols_nr = 0; 462 } 463 464 if (!elf_alloc_hash(symbol, symbols_nr) || 465 !elf_alloc_hash(symbol_name, symbols_nr)) 466 return -1; 467 468 elf->symbol_data = calloc(symbols_nr, sizeof(*sym)); 469 if (!elf->symbol_data) { 470 perror("calloc"); 471 return -1; 472 } 473 for (i = 0; i < symbols_nr; i++) { 474 sym = &elf->symbol_data[i]; 475 476 sym->idx = i; 477 478 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym, 479 &shndx)) { 480 WARN_ELF("gelf_getsymshndx"); 481 goto err; 482 } 483 484 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link, 485 sym->sym.st_name); 486 if (!sym->name) { 487 WARN_ELF("elf_strptr"); 488 goto err; 489 } 490 491 if ((sym->sym.st_shndx > SHN_UNDEF && 492 sym->sym.st_shndx < SHN_LORESERVE) || 493 (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) { 494 if (sym->sym.st_shndx != SHN_XINDEX) 495 shndx = sym->sym.st_shndx; 496 497 sym->sec = find_section_by_index(elf, shndx); 498 if (!sym->sec) { 499 WARN("couldn't find section for symbol %s", 500 sym->name); 501 goto err; 502 } 503 if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) { 504 sym->name = sym->sec->name; 505 sym->sec->sym = sym; 506 } 507 } else 508 sym->sec = find_section_by_index(elf, 0); 509 510 elf_add_symbol(elf, sym); 511 } 512 513 if (opts.stats) { 514 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr); 515 printf("symbol_bits: %d\n", elf->symbol_bits); 516 } 517 518 /* Create parent/child links for any cold subfunctions */ 519 list_for_each_entry(sec, &elf->sections, list) { 520 sec_for_each_sym(sec, sym) { 521 char *pname; 522 size_t pnamelen; 523 if (sym->type != STT_FUNC) 524 continue; 525 526 if (sym->pfunc == NULL) 527 sym->pfunc = sym; 528 529 if (sym->cfunc == NULL) 530 sym->cfunc = sym; 531 532 coldstr = strstr(sym->name, ".cold"); 533 if (!coldstr) 534 continue; 535 536 pnamelen = coldstr - sym->name; 537 pname = strndup(sym->name, pnamelen); 538 if (!pname) { 539 WARN("%s(): failed to allocate memory", 540 sym->name); 541 return -1; 542 } 543 544 pfunc = find_symbol_by_name(elf, pname); 545 free(pname); 546 547 if (!pfunc) { 548 WARN("%s(): can't find parent function", 549 sym->name); 550 return -1; 551 } 552 553 sym->pfunc = pfunc; 554 pfunc->cfunc = sym; 555 556 /* 557 * Unfortunately, -fnoreorder-functions puts the child 558 * inside the parent. Remove the overlap so we can 559 * have sane assumptions. 560 * 561 * Note that pfunc->len now no longer matches 562 * pfunc->sym.st_size. 563 */ 564 if (sym->sec == pfunc->sec && 565 sym->offset >= pfunc->offset && 566 sym->offset + sym->len == pfunc->offset + pfunc->len) { 567 pfunc->len -= sym->len; 568 } 569 } 570 } 571 572 return 0; 573 574 err: 575 free(sym); 576 return -1; 577 } 578 579 /* 580 * @sym's idx has changed. Update the relocs which reference it. 581 */ 582 static int elf_update_sym_relocs(struct elf *elf, struct symbol *sym) 583 { 584 struct reloc *reloc; 585 586 for (reloc = sym->relocs; reloc; reloc = reloc->sym_next_reloc) 587 set_reloc_sym(elf, reloc, reloc->sym->idx); 588 589 return 0; 590 } 591 592 /* 593 * The libelf API is terrible; gelf_update_sym*() takes a data block relative 594 * index value, *NOT* the symbol index. As such, iterate the data blocks and 595 * adjust index until it fits. 596 * 597 * If no data block is found, allow adding a new data block provided the index 598 * is only one past the end. 599 */ 600 static int elf_update_symbol(struct elf *elf, struct section *symtab, 601 struct section *symtab_shndx, struct symbol *sym) 602 { 603 Elf32_Word shndx = sym->sec ? sym->sec->idx : SHN_UNDEF; 604 Elf_Data *symtab_data = NULL, *shndx_data = NULL; 605 Elf64_Xword entsize = symtab->sh.sh_entsize; 606 int max_idx, idx = sym->idx; 607 Elf_Scn *s, *t = NULL; 608 bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE && 609 sym->sym.st_shndx != SHN_XINDEX; 610 611 if (is_special_shndx) 612 shndx = sym->sym.st_shndx; 613 614 s = elf_getscn(elf->elf, symtab->idx); 615 if (!s) { 616 WARN_ELF("elf_getscn"); 617 return -1; 618 } 619 620 if (symtab_shndx) { 621 t = elf_getscn(elf->elf, symtab_shndx->idx); 622 if (!t) { 623 WARN_ELF("elf_getscn"); 624 return -1; 625 } 626 } 627 628 for (;;) { 629 /* get next data descriptor for the relevant sections */ 630 symtab_data = elf_getdata(s, symtab_data); 631 if (t) 632 shndx_data = elf_getdata(t, shndx_data); 633 634 /* end-of-list */ 635 if (!symtab_data) { 636 /* 637 * Over-allocate to avoid O(n^2) symbol creation 638 * behaviour. The down side is that libelf doesn't 639 * like this; see elf_truncate_section() for the fixup. 640 */ 641 int num = max(1U, sym->idx/3); 642 void *buf; 643 644 if (idx) { 645 /* we don't do holes in symbol tables */ 646 WARN("index out of range"); 647 return -1; 648 } 649 650 /* if @idx == 0, it's the next contiguous entry, create it */ 651 symtab_data = elf_newdata(s); 652 if (t) 653 shndx_data = elf_newdata(t); 654 655 buf = calloc(num, entsize); 656 if (!buf) { 657 WARN("malloc"); 658 return -1; 659 } 660 661 symtab_data->d_buf = buf; 662 symtab_data->d_size = num * entsize; 663 symtab_data->d_align = 1; 664 symtab_data->d_type = ELF_T_SYM; 665 666 mark_sec_changed(elf, symtab, true); 667 symtab->truncate = true; 668 669 if (t) { 670 buf = calloc(num, sizeof(Elf32_Word)); 671 if (!buf) { 672 WARN("malloc"); 673 return -1; 674 } 675 676 shndx_data->d_buf = buf; 677 shndx_data->d_size = num * sizeof(Elf32_Word); 678 shndx_data->d_align = sizeof(Elf32_Word); 679 shndx_data->d_type = ELF_T_WORD; 680 681 mark_sec_changed(elf, symtab_shndx, true); 682 symtab_shndx->truncate = true; 683 } 684 685 break; 686 } 687 688 /* empty blocks should not happen */ 689 if (!symtab_data->d_size) { 690 WARN("zero size data"); 691 return -1; 692 } 693 694 /* is this the right block? */ 695 max_idx = symtab_data->d_size / entsize; 696 if (idx < max_idx) 697 break; 698 699 /* adjust index and try again */ 700 idx -= max_idx; 701 } 702 703 /* something went side-ways */ 704 if (idx < 0) { 705 WARN("negative index"); 706 return -1; 707 } 708 709 /* setup extended section index magic and write the symbol */ 710 if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) { 711 sym->sym.st_shndx = shndx; 712 if (!shndx_data) 713 shndx = 0; 714 } else { 715 sym->sym.st_shndx = SHN_XINDEX; 716 if (!shndx_data) { 717 WARN("no .symtab_shndx"); 718 return -1; 719 } 720 } 721 722 if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) { 723 WARN_ELF("gelf_update_symshndx"); 724 return -1; 725 } 726 727 return 0; 728 } 729 730 static struct symbol * 731 __elf_create_symbol(struct elf *elf, struct symbol *sym) 732 { 733 struct section *symtab, *symtab_shndx; 734 Elf32_Word first_non_local, new_idx; 735 struct symbol *old; 736 737 symtab = find_section_by_name(elf, ".symtab"); 738 if (symtab) { 739 symtab_shndx = find_section_by_name(elf, ".symtab_shndx"); 740 } else { 741 WARN("no .symtab"); 742 return NULL; 743 } 744 745 new_idx = sec_num_entries(symtab); 746 747 if (GELF_ST_BIND(sym->sym.st_info) != STB_LOCAL) 748 goto non_local; 749 750 /* 751 * Move the first global symbol, as per sh_info, into a new, higher 752 * symbol index. This fees up a spot for a new local symbol. 753 */ 754 first_non_local = symtab->sh.sh_info; 755 old = find_symbol_by_index(elf, first_non_local); 756 if (old) { 757 758 elf_hash_del(symbol, &old->hash, old->idx); 759 elf_hash_add(symbol, &old->hash, new_idx); 760 old->idx = new_idx; 761 762 if (elf_update_symbol(elf, symtab, symtab_shndx, old)) { 763 WARN("elf_update_symbol move"); 764 return NULL; 765 } 766 767 if (elf_update_sym_relocs(elf, old)) 768 return NULL; 769 770 new_idx = first_non_local; 771 } 772 773 /* 774 * Either way, we will add a LOCAL symbol. 775 */ 776 symtab->sh.sh_info += 1; 777 778 non_local: 779 sym->idx = new_idx; 780 if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) { 781 WARN("elf_update_symbol"); 782 return NULL; 783 } 784 785 symtab->sh.sh_size += symtab->sh.sh_entsize; 786 mark_sec_changed(elf, symtab, true); 787 788 if (symtab_shndx) { 789 symtab_shndx->sh.sh_size += sizeof(Elf32_Word); 790 mark_sec_changed(elf, symtab_shndx, true); 791 } 792 793 return sym; 794 } 795 796 static struct symbol * 797 elf_create_section_symbol(struct elf *elf, struct section *sec) 798 { 799 struct symbol *sym = calloc(1, sizeof(*sym)); 800 801 if (!sym) { 802 perror("malloc"); 803 return NULL; 804 } 805 806 sym->name = sec->name; 807 sym->sec = sec; 808 809 // st_name 0 810 sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION); 811 // st_other 0 812 // st_value 0 813 // st_size 0 814 815 sym = __elf_create_symbol(elf, sym); 816 if (sym) 817 elf_add_symbol(elf, sym); 818 819 return sym; 820 } 821 822 static int elf_add_string(struct elf *elf, struct section *strtab, char *str); 823 824 struct symbol * 825 elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long size) 826 { 827 struct symbol *sym = calloc(1, sizeof(*sym)); 828 size_t namelen = strlen(orig->name) + sizeof("__pfx_"); 829 char *name = malloc(namelen); 830 831 if (!sym || !name) { 832 perror("malloc"); 833 return NULL; 834 } 835 836 snprintf(name, namelen, "__pfx_%s", orig->name); 837 838 sym->name = name; 839 sym->sec = orig->sec; 840 841 sym->sym.st_name = elf_add_string(elf, NULL, name); 842 sym->sym.st_info = orig->sym.st_info; 843 sym->sym.st_value = orig->sym.st_value - size; 844 sym->sym.st_size = size; 845 846 sym = __elf_create_symbol(elf, sym); 847 if (sym) 848 elf_add_symbol(elf, sym); 849 850 return sym; 851 } 852 853 static struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec, 854 unsigned int reloc_idx, 855 unsigned long offset, struct symbol *sym, 856 s64 addend, unsigned int type) 857 { 858 struct reloc *reloc, empty = { 0 }; 859 860 if (reloc_idx >= sec_num_entries(rsec)) { 861 WARN("%s: bad reloc_idx %u for %s with %d relocs", 862 __func__, reloc_idx, rsec->name, sec_num_entries(rsec)); 863 return NULL; 864 } 865 866 reloc = &rsec->relocs[reloc_idx]; 867 868 if (memcmp(reloc, &empty, sizeof(empty))) { 869 WARN("%s: %s: reloc %d already initialized!", 870 __func__, rsec->name, reloc_idx); 871 return NULL; 872 } 873 874 reloc->sec = rsec; 875 reloc->sym = sym; 876 877 set_reloc_offset(elf, reloc, offset); 878 set_reloc_sym(elf, reloc, sym->idx); 879 set_reloc_type(elf, reloc, type); 880 set_reloc_addend(elf, reloc, addend); 881 882 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc)); 883 reloc->sym_next_reloc = sym->relocs; 884 sym->relocs = reloc; 885 886 return reloc; 887 } 888 889 struct reloc *elf_init_reloc_text_sym(struct elf *elf, struct section *sec, 890 unsigned long offset, 891 unsigned int reloc_idx, 892 struct section *insn_sec, 893 unsigned long insn_off) 894 { 895 struct symbol *sym = insn_sec->sym; 896 int addend = insn_off; 897 898 if (!(insn_sec->sh.sh_flags & SHF_EXECINSTR)) { 899 WARN("bad call to %s() for data symbol %s", 900 __func__, sym->name); 901 return NULL; 902 } 903 904 if (!sym) { 905 /* 906 * Due to how weak functions work, we must use section based 907 * relocations. Symbol based relocations would result in the 908 * weak and non-weak function annotations being overlaid on the 909 * non-weak function after linking. 910 */ 911 sym = elf_create_section_symbol(elf, insn_sec); 912 if (!sym) 913 return NULL; 914 915 insn_sec->sym = sym; 916 } 917 918 return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend, 919 elf_text_rela_type(elf)); 920 } 921 922 struct reloc *elf_init_reloc_data_sym(struct elf *elf, struct section *sec, 923 unsigned long offset, 924 unsigned int reloc_idx, 925 struct symbol *sym, 926 s64 addend) 927 { 928 if (sym->sec && (sec->sh.sh_flags & SHF_EXECINSTR)) { 929 WARN("bad call to %s() for text symbol %s", 930 __func__, sym->name); 931 return NULL; 932 } 933 934 return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend, 935 elf_data_rela_type(elf)); 936 } 937 938 static int read_relocs(struct elf *elf) 939 { 940 unsigned long nr_reloc, max_reloc = 0; 941 struct section *rsec; 942 struct reloc *reloc; 943 unsigned int symndx; 944 struct symbol *sym; 945 int i; 946 947 if (!elf_alloc_hash(reloc, elf->num_relocs)) 948 return -1; 949 950 list_for_each_entry(rsec, &elf->sections, list) { 951 if (!is_reloc_sec(rsec)) 952 continue; 953 954 rsec->base = find_section_by_index(elf, rsec->sh.sh_info); 955 if (!rsec->base) { 956 WARN("can't find base section for reloc section %s", 957 rsec->name); 958 return -1; 959 } 960 961 rsec->base->rsec = rsec; 962 963 nr_reloc = 0; 964 rsec->relocs = calloc(sec_num_entries(rsec), sizeof(*reloc)); 965 if (!rsec->relocs) { 966 perror("calloc"); 967 return -1; 968 } 969 for (i = 0; i < sec_num_entries(rsec); i++) { 970 reloc = &rsec->relocs[i]; 971 972 reloc->sec = rsec; 973 symndx = reloc_sym(reloc); 974 reloc->sym = sym = find_symbol_by_index(elf, symndx); 975 if (!reloc->sym) { 976 WARN("can't find reloc entry symbol %d for %s", 977 symndx, rsec->name); 978 return -1; 979 } 980 981 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc)); 982 reloc->sym_next_reloc = sym->relocs; 983 sym->relocs = reloc; 984 985 nr_reloc++; 986 } 987 max_reloc = max(max_reloc, nr_reloc); 988 } 989 990 if (opts.stats) { 991 printf("max_reloc: %lu\n", max_reloc); 992 printf("num_relocs: %lu\n", elf->num_relocs); 993 printf("reloc_bits: %d\n", elf->reloc_bits); 994 } 995 996 return 0; 997 } 998 999 struct elf *elf_open_read(const char *name, int flags) 1000 { 1001 struct elf *elf; 1002 Elf_Cmd cmd; 1003 1004 elf_version(EV_CURRENT); 1005 1006 elf = malloc(sizeof(*elf)); 1007 if (!elf) { 1008 perror("malloc"); 1009 return NULL; 1010 } 1011 memset(elf, 0, sizeof(*elf)); 1012 1013 INIT_LIST_HEAD(&elf->sections); 1014 1015 elf->fd = open(name, flags); 1016 if (elf->fd == -1) { 1017 fprintf(stderr, "objtool: Can't open '%s': %s\n", 1018 name, strerror(errno)); 1019 goto err; 1020 } 1021 1022 if ((flags & O_ACCMODE) == O_RDONLY) 1023 cmd = ELF_C_READ_MMAP; 1024 else if ((flags & O_ACCMODE) == O_RDWR) 1025 cmd = ELF_C_RDWR; 1026 else /* O_WRONLY */ 1027 cmd = ELF_C_WRITE; 1028 1029 elf->elf = elf_begin(elf->fd, cmd, NULL); 1030 if (!elf->elf) { 1031 WARN_ELF("elf_begin"); 1032 goto err; 1033 } 1034 1035 if (!gelf_getehdr(elf->elf, &elf->ehdr)) { 1036 WARN_ELF("gelf_getehdr"); 1037 goto err; 1038 } 1039 1040 if (read_sections(elf)) 1041 goto err; 1042 1043 if (read_symbols(elf)) 1044 goto err; 1045 1046 if (read_relocs(elf)) 1047 goto err; 1048 1049 return elf; 1050 1051 err: 1052 elf_close(elf); 1053 return NULL; 1054 } 1055 1056 static int elf_add_string(struct elf *elf, struct section *strtab, char *str) 1057 { 1058 Elf_Data *data; 1059 Elf_Scn *s; 1060 int len; 1061 1062 if (!strtab) 1063 strtab = find_section_by_name(elf, ".strtab"); 1064 if (!strtab) { 1065 WARN("can't find .strtab section"); 1066 return -1; 1067 } 1068 1069 s = elf_getscn(elf->elf, strtab->idx); 1070 if (!s) { 1071 WARN_ELF("elf_getscn"); 1072 return -1; 1073 } 1074 1075 data = elf_newdata(s); 1076 if (!data) { 1077 WARN_ELF("elf_newdata"); 1078 return -1; 1079 } 1080 1081 data->d_buf = str; 1082 data->d_size = strlen(str) + 1; 1083 data->d_align = 1; 1084 1085 len = strtab->sh.sh_size; 1086 strtab->sh.sh_size += data->d_size; 1087 1088 mark_sec_changed(elf, strtab, true); 1089 1090 return len; 1091 } 1092 1093 struct section *elf_create_section(struct elf *elf, const char *name, 1094 size_t entsize, unsigned int nr) 1095 { 1096 struct section *sec, *shstrtab; 1097 size_t size = entsize * nr; 1098 Elf_Scn *s; 1099 1100 sec = malloc(sizeof(*sec)); 1101 if (!sec) { 1102 perror("malloc"); 1103 return NULL; 1104 } 1105 memset(sec, 0, sizeof(*sec)); 1106 1107 INIT_LIST_HEAD(&sec->symbol_list); 1108 1109 s = elf_newscn(elf->elf); 1110 if (!s) { 1111 WARN_ELF("elf_newscn"); 1112 return NULL; 1113 } 1114 1115 sec->name = strdup(name); 1116 if (!sec->name) { 1117 perror("strdup"); 1118 return NULL; 1119 } 1120 1121 sec->idx = elf_ndxscn(s); 1122 1123 sec->data = elf_newdata(s); 1124 if (!sec->data) { 1125 WARN_ELF("elf_newdata"); 1126 return NULL; 1127 } 1128 1129 sec->data->d_size = size; 1130 sec->data->d_align = 1; 1131 1132 if (size) { 1133 sec->data->d_buf = malloc(size); 1134 if (!sec->data->d_buf) { 1135 perror("malloc"); 1136 return NULL; 1137 } 1138 memset(sec->data->d_buf, 0, size); 1139 } 1140 1141 if (!gelf_getshdr(s, &sec->sh)) { 1142 WARN_ELF("gelf_getshdr"); 1143 return NULL; 1144 } 1145 1146 sec->sh.sh_size = size; 1147 sec->sh.sh_entsize = entsize; 1148 sec->sh.sh_type = SHT_PROGBITS; 1149 sec->sh.sh_addralign = 1; 1150 sec->sh.sh_flags = SHF_ALLOC; 1151 1152 /* Add section name to .shstrtab (or .strtab for Clang) */ 1153 shstrtab = find_section_by_name(elf, ".shstrtab"); 1154 if (!shstrtab) 1155 shstrtab = find_section_by_name(elf, ".strtab"); 1156 if (!shstrtab) { 1157 WARN("can't find .shstrtab or .strtab section"); 1158 return NULL; 1159 } 1160 sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name); 1161 if (sec->sh.sh_name == -1) 1162 return NULL; 1163 1164 list_add_tail(&sec->list, &elf->sections); 1165 elf_hash_add(section, &sec->hash, sec->idx); 1166 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name)); 1167 1168 mark_sec_changed(elf, sec, true); 1169 1170 return sec; 1171 } 1172 1173 static struct section *elf_create_rela_section(struct elf *elf, 1174 struct section *sec, 1175 unsigned int reloc_nr) 1176 { 1177 struct section *rsec; 1178 char *rsec_name; 1179 1180 rsec_name = malloc(strlen(sec->name) + strlen(".rela") + 1); 1181 if (!rsec_name) { 1182 perror("malloc"); 1183 return NULL; 1184 } 1185 strcpy(rsec_name, ".rela"); 1186 strcat(rsec_name, sec->name); 1187 1188 rsec = elf_create_section(elf, rsec_name, elf_rela_size(elf), reloc_nr); 1189 free(rsec_name); 1190 if (!rsec) 1191 return NULL; 1192 1193 rsec->data->d_type = ELF_T_RELA; 1194 rsec->sh.sh_type = SHT_RELA; 1195 rsec->sh.sh_addralign = elf_addr_size(elf); 1196 rsec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx; 1197 rsec->sh.sh_info = sec->idx; 1198 rsec->sh.sh_flags = SHF_INFO_LINK; 1199 1200 rsec->relocs = calloc(sec_num_entries(rsec), sizeof(struct reloc)); 1201 if (!rsec->relocs) { 1202 perror("calloc"); 1203 return NULL; 1204 } 1205 1206 sec->rsec = rsec; 1207 rsec->base = sec; 1208 1209 return rsec; 1210 } 1211 1212 struct section *elf_create_section_pair(struct elf *elf, const char *name, 1213 size_t entsize, unsigned int nr, 1214 unsigned int reloc_nr) 1215 { 1216 struct section *sec; 1217 1218 sec = elf_create_section(elf, name, entsize, nr); 1219 if (!sec) 1220 return NULL; 1221 1222 if (!elf_create_rela_section(elf, sec, reloc_nr)) 1223 return NULL; 1224 1225 return sec; 1226 } 1227 1228 int elf_write_insn(struct elf *elf, struct section *sec, 1229 unsigned long offset, unsigned int len, 1230 const char *insn) 1231 { 1232 Elf_Data *data = sec->data; 1233 1234 if (data->d_type != ELF_T_BYTE || data->d_off) { 1235 WARN("write to unexpected data for section: %s", sec->name); 1236 return -1; 1237 } 1238 1239 memcpy(data->d_buf + offset, insn, len); 1240 1241 mark_sec_changed(elf, sec, true); 1242 1243 return 0; 1244 } 1245 1246 /* 1247 * When Elf_Scn::sh_size is smaller than the combined Elf_Data::d_size 1248 * do you: 1249 * 1250 * A) adhere to the section header and truncate the data, or 1251 * B) ignore the section header and write out all the data you've got? 1252 * 1253 * Yes, libelf sucks and we need to manually truncate if we over-allocate data. 1254 */ 1255 static int elf_truncate_section(struct elf *elf, struct section *sec) 1256 { 1257 u64 size = sec->sh.sh_size; 1258 bool truncated = false; 1259 Elf_Data *data = NULL; 1260 Elf_Scn *s; 1261 1262 s = elf_getscn(elf->elf, sec->idx); 1263 if (!s) { 1264 WARN_ELF("elf_getscn"); 1265 return -1; 1266 } 1267 1268 for (;;) { 1269 /* get next data descriptor for the relevant section */ 1270 data = elf_getdata(s, data); 1271 1272 if (!data) { 1273 if (size) { 1274 WARN("end of section data but non-zero size left\n"); 1275 return -1; 1276 } 1277 return 0; 1278 } 1279 1280 if (truncated) { 1281 /* when we remove symbols */ 1282 WARN("truncated; but more data\n"); 1283 return -1; 1284 } 1285 1286 if (!data->d_size) { 1287 WARN("zero size data"); 1288 return -1; 1289 } 1290 1291 if (data->d_size > size) { 1292 truncated = true; 1293 data->d_size = size; 1294 } 1295 1296 size -= data->d_size; 1297 } 1298 } 1299 1300 int elf_write(struct elf *elf) 1301 { 1302 struct section *sec; 1303 Elf_Scn *s; 1304 1305 if (opts.dryrun) 1306 return 0; 1307 1308 /* Update changed relocation sections and section headers: */ 1309 list_for_each_entry(sec, &elf->sections, list) { 1310 if (sec->truncate) 1311 elf_truncate_section(elf, sec); 1312 1313 if (sec_changed(sec)) { 1314 s = elf_getscn(elf->elf, sec->idx); 1315 if (!s) { 1316 WARN_ELF("elf_getscn"); 1317 return -1; 1318 } 1319 1320 /* Note this also flags the section dirty */ 1321 if (!gelf_update_shdr(s, &sec->sh)) { 1322 WARN_ELF("gelf_update_shdr"); 1323 return -1; 1324 } 1325 1326 mark_sec_changed(elf, sec, false); 1327 } 1328 } 1329 1330 /* Make sure the new section header entries get updated properly. */ 1331 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY); 1332 1333 /* Write all changes to the file. */ 1334 if (elf_update(elf->elf, ELF_C_WRITE) < 0) { 1335 WARN_ELF("elf_update"); 1336 return -1; 1337 } 1338 1339 elf->changed = false; 1340 1341 return 0; 1342 } 1343 1344 void elf_close(struct elf *elf) 1345 { 1346 if (elf->elf) 1347 elf_end(elf->elf); 1348 1349 if (elf->fd > 0) 1350 close(elf->fd); 1351 1352 /* 1353 * NOTE: All remaining allocations are leaked on purpose. Objtool is 1354 * about to exit anyway. 1355 */ 1356 } 1357