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 <fcntl.h> 13 #include <stdio.h> 14 #include <stdlib.h> 15 #include <string.h> 16 #include <unistd.h> 17 #include <errno.h> 18 #include <objtool/builtin.h> 19 20 #include <objtool/elf.h> 21 #include <objtool/warn.h> 22 23 #define MAX_NAME_LEN 128 24 25 static inline u32 str_hash(const char *str) 26 { 27 return jhash(str, strlen(str), 0); 28 } 29 30 static inline int elf_hash_bits(void) 31 { 32 return vmlinux ? ELF_HASH_BITS : 16; 33 } 34 35 #define elf_hash_add(hashtable, node, key) \ 36 hlist_add_head(node, &hashtable[hash_min(key, elf_hash_bits())]) 37 38 static void elf_hash_init(struct hlist_head *table) 39 { 40 __hash_init(table, 1U << elf_hash_bits()); 41 } 42 43 #define elf_hash_for_each_possible(name, obj, member, key) \ 44 hlist_for_each_entry(obj, &name[hash_min(key, elf_hash_bits())], member) 45 46 static bool symbol_to_offset(struct rb_node *a, const struct rb_node *b) 47 { 48 struct symbol *sa = rb_entry(a, struct symbol, node); 49 struct symbol *sb = rb_entry(b, struct symbol, node); 50 51 if (sa->offset < sb->offset) 52 return true; 53 if (sa->offset > sb->offset) 54 return false; 55 56 if (sa->len < sb->len) 57 return true; 58 if (sa->len > sb->len) 59 return false; 60 61 sa->alias = sb; 62 63 return false; 64 } 65 66 static int symbol_by_offset(const void *key, const struct rb_node *node) 67 { 68 const struct symbol *s = rb_entry(node, struct symbol, node); 69 const unsigned long *o = key; 70 71 if (*o < s->offset) 72 return -1; 73 if (*o >= s->offset + s->len) 74 return 1; 75 76 return 0; 77 } 78 79 struct section *find_section_by_name(const struct elf *elf, const char *name) 80 { 81 struct section *sec; 82 83 elf_hash_for_each_possible(elf->section_name_hash, sec, name_hash, str_hash(name)) 84 if (!strcmp(sec->name, name)) 85 return sec; 86 87 return NULL; 88 } 89 90 static struct section *find_section_by_index(struct elf *elf, 91 unsigned int idx) 92 { 93 struct section *sec; 94 95 elf_hash_for_each_possible(elf->section_hash, sec, hash, idx) 96 if (sec->idx == idx) 97 return sec; 98 99 return NULL; 100 } 101 102 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx) 103 { 104 struct symbol *sym; 105 106 elf_hash_for_each_possible(elf->symbol_hash, sym, hash, idx) 107 if (sym->idx == idx) 108 return sym; 109 110 return NULL; 111 } 112 113 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset) 114 { 115 struct rb_node *node; 116 117 rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) { 118 struct symbol *s = rb_entry(node, struct symbol, node); 119 120 if (s->offset == offset && s->type != STT_SECTION) 121 return s; 122 } 123 124 return NULL; 125 } 126 127 struct symbol *find_func_by_offset(struct section *sec, unsigned long offset) 128 { 129 struct rb_node *node; 130 131 rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) { 132 struct symbol *s = rb_entry(node, struct symbol, node); 133 134 if (s->offset == offset && s->type == STT_FUNC) 135 return s; 136 } 137 138 return NULL; 139 } 140 141 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset) 142 { 143 struct rb_node *node; 144 145 rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) { 146 struct symbol *s = rb_entry(node, struct symbol, node); 147 148 if (s->type != STT_SECTION) 149 return s; 150 } 151 152 return NULL; 153 } 154 155 struct symbol *find_func_containing(struct section *sec, unsigned long offset) 156 { 157 struct rb_node *node; 158 159 rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) { 160 struct symbol *s = rb_entry(node, struct symbol, node); 161 162 if (s->type == STT_FUNC) 163 return s; 164 } 165 166 return NULL; 167 } 168 169 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name) 170 { 171 struct symbol *sym; 172 173 elf_hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name)) 174 if (!strcmp(sym->name, name)) 175 return sym; 176 177 return NULL; 178 } 179 180 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec, 181 unsigned long offset, unsigned int len) 182 { 183 struct reloc *reloc, *r = NULL; 184 unsigned long o; 185 186 if (!sec->reloc) 187 return NULL; 188 189 sec = sec->reloc; 190 191 for_offset_range(o, offset, offset + len) { 192 elf_hash_for_each_possible(elf->reloc_hash, reloc, hash, 193 sec_offset_hash(sec, o)) { 194 if (reloc->sec != sec) 195 continue; 196 197 if (reloc->offset >= offset && reloc->offset < offset + len) { 198 if (!r || reloc->offset < r->offset) 199 r = reloc; 200 } 201 } 202 if (r) 203 return r; 204 } 205 206 return NULL; 207 } 208 209 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset) 210 { 211 return find_reloc_by_dest_range(elf, sec, offset, 1); 212 } 213 214 static int read_sections(struct elf *elf) 215 { 216 Elf_Scn *s = NULL; 217 struct section *sec; 218 size_t shstrndx, sections_nr; 219 int i; 220 221 if (elf_getshdrnum(elf->elf, §ions_nr)) { 222 WARN_ELF("elf_getshdrnum"); 223 return -1; 224 } 225 226 if (elf_getshdrstrndx(elf->elf, &shstrndx)) { 227 WARN_ELF("elf_getshdrstrndx"); 228 return -1; 229 } 230 231 for (i = 0; i < sections_nr; i++) { 232 sec = malloc(sizeof(*sec)); 233 if (!sec) { 234 perror("malloc"); 235 return -1; 236 } 237 memset(sec, 0, sizeof(*sec)); 238 239 INIT_LIST_HEAD(&sec->symbol_list); 240 INIT_LIST_HEAD(&sec->reloc_list); 241 242 s = elf_getscn(elf->elf, i); 243 if (!s) { 244 WARN_ELF("elf_getscn"); 245 return -1; 246 } 247 248 sec->idx = elf_ndxscn(s); 249 250 if (!gelf_getshdr(s, &sec->sh)) { 251 WARN_ELF("gelf_getshdr"); 252 return -1; 253 } 254 255 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name); 256 if (!sec->name) { 257 WARN_ELF("elf_strptr"); 258 return -1; 259 } 260 261 if (sec->sh.sh_size != 0) { 262 sec->data = elf_getdata(s, NULL); 263 if (!sec->data) { 264 WARN_ELF("elf_getdata"); 265 return -1; 266 } 267 if (sec->data->d_off != 0 || 268 sec->data->d_size != sec->sh.sh_size) { 269 WARN("unexpected data attributes for %s", 270 sec->name); 271 return -1; 272 } 273 } 274 sec->len = sec->sh.sh_size; 275 276 list_add_tail(&sec->list, &elf->sections); 277 elf_hash_add(elf->section_hash, &sec->hash, sec->idx); 278 elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name)); 279 } 280 281 if (stats) 282 printf("nr_sections: %lu\n", (unsigned long)sections_nr); 283 284 /* sanity check, one more call to elf_nextscn() should return NULL */ 285 if (elf_nextscn(elf->elf, s)) { 286 WARN("section entry mismatch"); 287 return -1; 288 } 289 290 return 0; 291 } 292 293 static void elf_add_symbol(struct elf *elf, struct symbol *sym) 294 { 295 struct list_head *entry; 296 struct rb_node *pnode; 297 298 sym->type = GELF_ST_TYPE(sym->sym.st_info); 299 sym->bind = GELF_ST_BIND(sym->sym.st_info); 300 301 sym->offset = sym->sym.st_value; 302 sym->len = sym->sym.st_size; 303 304 rb_add(&sym->node, &sym->sec->symbol_tree, symbol_to_offset); 305 pnode = rb_prev(&sym->node); 306 if (pnode) 307 entry = &rb_entry(pnode, struct symbol, node)->list; 308 else 309 entry = &sym->sec->symbol_list; 310 list_add(&sym->list, entry); 311 elf_hash_add(elf->symbol_hash, &sym->hash, sym->idx); 312 elf_hash_add(elf->symbol_name_hash, &sym->name_hash, str_hash(sym->name)); 313 314 /* 315 * Don't store empty STT_NOTYPE symbols in the rbtree. They 316 * can exist within a function, confusing the sorting. 317 */ 318 if (!sym->len) 319 rb_erase(&sym->node, &sym->sec->symbol_tree); 320 } 321 322 static int read_symbols(struct elf *elf) 323 { 324 struct section *symtab, *symtab_shndx, *sec; 325 struct symbol *sym, *pfunc; 326 int symbols_nr, i; 327 char *coldstr; 328 Elf_Data *shndx_data = NULL; 329 Elf32_Word shndx; 330 331 symtab = find_section_by_name(elf, ".symtab"); 332 if (!symtab) { 333 /* 334 * A missing symbol table is actually possible if it's an empty 335 * .o file. This can happen for thunk_64.o. 336 */ 337 return 0; 338 } 339 340 symtab_shndx = find_section_by_name(elf, ".symtab_shndx"); 341 if (symtab_shndx) 342 shndx_data = symtab_shndx->data; 343 344 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize; 345 346 for (i = 0; i < symbols_nr; i++) { 347 sym = malloc(sizeof(*sym)); 348 if (!sym) { 349 perror("malloc"); 350 return -1; 351 } 352 memset(sym, 0, sizeof(*sym)); 353 sym->alias = sym; 354 355 sym->idx = i; 356 357 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym, 358 &shndx)) { 359 WARN_ELF("gelf_getsymshndx"); 360 goto err; 361 } 362 363 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link, 364 sym->sym.st_name); 365 if (!sym->name) { 366 WARN_ELF("elf_strptr"); 367 goto err; 368 } 369 370 if ((sym->sym.st_shndx > SHN_UNDEF && 371 sym->sym.st_shndx < SHN_LORESERVE) || 372 (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) { 373 if (sym->sym.st_shndx != SHN_XINDEX) 374 shndx = sym->sym.st_shndx; 375 376 sym->sec = find_section_by_index(elf, shndx); 377 if (!sym->sec) { 378 WARN("couldn't find section for symbol %s", 379 sym->name); 380 goto err; 381 } 382 if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) { 383 sym->name = sym->sec->name; 384 sym->sec->sym = sym; 385 } 386 } else 387 sym->sec = find_section_by_index(elf, 0); 388 389 elf_add_symbol(elf, sym); 390 } 391 392 if (stats) 393 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr); 394 395 /* Create parent/child links for any cold subfunctions */ 396 list_for_each_entry(sec, &elf->sections, list) { 397 list_for_each_entry(sym, &sec->symbol_list, list) { 398 char pname[MAX_NAME_LEN + 1]; 399 size_t pnamelen; 400 if (sym->type != STT_FUNC) 401 continue; 402 403 if (sym->pfunc == NULL) 404 sym->pfunc = sym; 405 406 if (sym->cfunc == NULL) 407 sym->cfunc = sym; 408 409 coldstr = strstr(sym->name, ".cold"); 410 if (!coldstr) 411 continue; 412 413 pnamelen = coldstr - sym->name; 414 if (pnamelen > MAX_NAME_LEN) { 415 WARN("%s(): parent function name exceeds maximum length of %d characters", 416 sym->name, MAX_NAME_LEN); 417 return -1; 418 } 419 420 strncpy(pname, sym->name, pnamelen); 421 pname[pnamelen] = '\0'; 422 pfunc = find_symbol_by_name(elf, pname); 423 424 if (!pfunc) { 425 WARN("%s(): can't find parent function", 426 sym->name); 427 return -1; 428 } 429 430 sym->pfunc = pfunc; 431 pfunc->cfunc = sym; 432 433 /* 434 * Unfortunately, -fnoreorder-functions puts the child 435 * inside the parent. Remove the overlap so we can 436 * have sane assumptions. 437 * 438 * Note that pfunc->len now no longer matches 439 * pfunc->sym.st_size. 440 */ 441 if (sym->sec == pfunc->sec && 442 sym->offset >= pfunc->offset && 443 sym->offset + sym->len == pfunc->offset + pfunc->len) { 444 pfunc->len -= sym->len; 445 } 446 } 447 } 448 449 return 0; 450 451 err: 452 free(sym); 453 return -1; 454 } 455 456 static struct section *elf_create_reloc_section(struct elf *elf, 457 struct section *base, 458 int reltype); 459 460 int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset, 461 unsigned int type, struct symbol *sym, int addend) 462 { 463 struct reloc *reloc; 464 465 if (!sec->reloc && !elf_create_reloc_section(elf, sec, SHT_RELA)) 466 return -1; 467 468 reloc = malloc(sizeof(*reloc)); 469 if (!reloc) { 470 perror("malloc"); 471 return -1; 472 } 473 memset(reloc, 0, sizeof(*reloc)); 474 475 reloc->sec = sec->reloc; 476 reloc->offset = offset; 477 reloc->type = type; 478 reloc->sym = sym; 479 reloc->addend = addend; 480 481 list_add_tail(&reloc->list, &sec->reloc->reloc_list); 482 elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc)); 483 484 sec->reloc->changed = true; 485 486 return 0; 487 } 488 489 int elf_add_reloc_to_insn(struct elf *elf, struct section *sec, 490 unsigned long offset, unsigned int type, 491 struct section *insn_sec, unsigned long insn_off) 492 { 493 struct symbol *sym; 494 int addend; 495 496 if (insn_sec->sym) { 497 sym = insn_sec->sym; 498 addend = insn_off; 499 500 } else { 501 /* 502 * The Clang assembler strips section symbols, so we have to 503 * reference the function symbol instead: 504 */ 505 sym = find_symbol_containing(insn_sec, insn_off); 506 if (!sym) { 507 /* 508 * Hack alert. This happens when we need to reference 509 * the NOP pad insn immediately after the function. 510 */ 511 sym = find_symbol_containing(insn_sec, insn_off - 1); 512 } 513 514 if (!sym) { 515 WARN("can't find symbol containing %s+0x%lx", insn_sec->name, insn_off); 516 return -1; 517 } 518 519 addend = insn_off - sym->offset; 520 } 521 522 return elf_add_reloc(elf, sec, offset, type, sym, addend); 523 } 524 525 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx) 526 { 527 if (!gelf_getrel(sec->data, i, &reloc->rel)) { 528 WARN_ELF("gelf_getrel"); 529 return -1; 530 } 531 reloc->type = GELF_R_TYPE(reloc->rel.r_info); 532 reloc->addend = 0; 533 reloc->offset = reloc->rel.r_offset; 534 *symndx = GELF_R_SYM(reloc->rel.r_info); 535 return 0; 536 } 537 538 static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx) 539 { 540 if (!gelf_getrela(sec->data, i, &reloc->rela)) { 541 WARN_ELF("gelf_getrela"); 542 return -1; 543 } 544 reloc->type = GELF_R_TYPE(reloc->rela.r_info); 545 reloc->addend = reloc->rela.r_addend; 546 reloc->offset = reloc->rela.r_offset; 547 *symndx = GELF_R_SYM(reloc->rela.r_info); 548 return 0; 549 } 550 551 static int read_relocs(struct elf *elf) 552 { 553 struct section *sec; 554 struct reloc *reloc; 555 int i; 556 unsigned int symndx; 557 unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0; 558 559 list_for_each_entry(sec, &elf->sections, list) { 560 if ((sec->sh.sh_type != SHT_RELA) && 561 (sec->sh.sh_type != SHT_REL)) 562 continue; 563 564 sec->base = find_section_by_index(elf, sec->sh.sh_info); 565 if (!sec->base) { 566 WARN("can't find base section for reloc section %s", 567 sec->name); 568 return -1; 569 } 570 571 sec->base->reloc = sec; 572 573 nr_reloc = 0; 574 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) { 575 reloc = malloc(sizeof(*reloc)); 576 if (!reloc) { 577 perror("malloc"); 578 return -1; 579 } 580 memset(reloc, 0, sizeof(*reloc)); 581 switch (sec->sh.sh_type) { 582 case SHT_REL: 583 if (read_rel_reloc(sec, i, reloc, &symndx)) 584 return -1; 585 break; 586 case SHT_RELA: 587 if (read_rela_reloc(sec, i, reloc, &symndx)) 588 return -1; 589 break; 590 default: return -1; 591 } 592 593 reloc->sec = sec; 594 reloc->idx = i; 595 reloc->sym = find_symbol_by_index(elf, symndx); 596 if (!reloc->sym) { 597 WARN("can't find reloc entry symbol %d for %s", 598 symndx, sec->name); 599 return -1; 600 } 601 602 list_add_tail(&reloc->list, &sec->reloc_list); 603 elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc)); 604 605 nr_reloc++; 606 } 607 max_reloc = max(max_reloc, nr_reloc); 608 tot_reloc += nr_reloc; 609 } 610 611 if (stats) { 612 printf("max_reloc: %lu\n", max_reloc); 613 printf("tot_reloc: %lu\n", tot_reloc); 614 } 615 616 return 0; 617 } 618 619 struct elf *elf_open_read(const char *name, int flags) 620 { 621 struct elf *elf; 622 Elf_Cmd cmd; 623 624 elf_version(EV_CURRENT); 625 626 elf = malloc(sizeof(*elf)); 627 if (!elf) { 628 perror("malloc"); 629 return NULL; 630 } 631 memset(elf, 0, offsetof(struct elf, sections)); 632 633 INIT_LIST_HEAD(&elf->sections); 634 635 elf_hash_init(elf->symbol_hash); 636 elf_hash_init(elf->symbol_name_hash); 637 elf_hash_init(elf->section_hash); 638 elf_hash_init(elf->section_name_hash); 639 elf_hash_init(elf->reloc_hash); 640 641 elf->fd = open(name, flags); 642 if (elf->fd == -1) { 643 fprintf(stderr, "objtool: Can't open '%s': %s\n", 644 name, strerror(errno)); 645 goto err; 646 } 647 648 if ((flags & O_ACCMODE) == O_RDONLY) 649 cmd = ELF_C_READ_MMAP; 650 else if ((flags & O_ACCMODE) == O_RDWR) 651 cmd = ELF_C_RDWR; 652 else /* O_WRONLY */ 653 cmd = ELF_C_WRITE; 654 655 elf->elf = elf_begin(elf->fd, cmd, NULL); 656 if (!elf->elf) { 657 WARN_ELF("elf_begin"); 658 goto err; 659 } 660 661 if (!gelf_getehdr(elf->elf, &elf->ehdr)) { 662 WARN_ELF("gelf_getehdr"); 663 goto err; 664 } 665 666 if (read_sections(elf)) 667 goto err; 668 669 if (read_symbols(elf)) 670 goto err; 671 672 if (read_relocs(elf)) 673 goto err; 674 675 return elf; 676 677 err: 678 elf_close(elf); 679 return NULL; 680 } 681 682 static int elf_add_string(struct elf *elf, struct section *strtab, char *str) 683 { 684 Elf_Data *data; 685 Elf_Scn *s; 686 int len; 687 688 if (!strtab) 689 strtab = find_section_by_name(elf, ".strtab"); 690 if (!strtab) { 691 WARN("can't find .strtab section"); 692 return -1; 693 } 694 695 s = elf_getscn(elf->elf, strtab->idx); 696 if (!s) { 697 WARN_ELF("elf_getscn"); 698 return -1; 699 } 700 701 data = elf_newdata(s); 702 if (!data) { 703 WARN_ELF("elf_newdata"); 704 return -1; 705 } 706 707 data->d_buf = str; 708 data->d_size = strlen(str) + 1; 709 data->d_align = 1; 710 711 len = strtab->len; 712 strtab->len += data->d_size; 713 strtab->changed = true; 714 715 return len; 716 } 717 718 struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name) 719 { 720 struct section *symtab; 721 struct symbol *sym; 722 Elf_Data *data; 723 Elf_Scn *s; 724 725 sym = malloc(sizeof(*sym)); 726 if (!sym) { 727 perror("malloc"); 728 return NULL; 729 } 730 memset(sym, 0, sizeof(*sym)); 731 732 sym->name = strdup(name); 733 734 sym->sym.st_name = elf_add_string(elf, NULL, sym->name); 735 if (sym->sym.st_name == -1) 736 return NULL; 737 738 sym->sym.st_info = GELF_ST_INFO(STB_GLOBAL, STT_NOTYPE); 739 // st_other 0 740 // st_shndx 0 741 // st_value 0 742 // st_size 0 743 744 symtab = find_section_by_name(elf, ".symtab"); 745 if (!symtab) { 746 WARN("can't find .symtab"); 747 return NULL; 748 } 749 750 s = elf_getscn(elf->elf, symtab->idx); 751 if (!s) { 752 WARN_ELF("elf_getscn"); 753 return NULL; 754 } 755 756 data = elf_newdata(s); 757 if (!data) { 758 WARN_ELF("elf_newdata"); 759 return NULL; 760 } 761 762 data->d_buf = &sym->sym; 763 data->d_size = sizeof(sym->sym); 764 data->d_align = 1; 765 766 sym->idx = symtab->len / sizeof(sym->sym); 767 768 symtab->len += data->d_size; 769 symtab->changed = true; 770 771 sym->sec = find_section_by_index(elf, 0); 772 773 elf_add_symbol(elf, sym); 774 775 return sym; 776 } 777 778 struct section *elf_create_section(struct elf *elf, const char *name, 779 unsigned int sh_flags, size_t entsize, int nr) 780 { 781 struct section *sec, *shstrtab; 782 size_t size = entsize * nr; 783 Elf_Scn *s; 784 785 sec = malloc(sizeof(*sec)); 786 if (!sec) { 787 perror("malloc"); 788 return NULL; 789 } 790 memset(sec, 0, sizeof(*sec)); 791 792 INIT_LIST_HEAD(&sec->symbol_list); 793 INIT_LIST_HEAD(&sec->reloc_list); 794 795 s = elf_newscn(elf->elf); 796 if (!s) { 797 WARN_ELF("elf_newscn"); 798 return NULL; 799 } 800 801 sec->name = strdup(name); 802 if (!sec->name) { 803 perror("strdup"); 804 return NULL; 805 } 806 807 sec->idx = elf_ndxscn(s); 808 sec->len = size; 809 sec->changed = true; 810 811 sec->data = elf_newdata(s); 812 if (!sec->data) { 813 WARN_ELF("elf_newdata"); 814 return NULL; 815 } 816 817 sec->data->d_size = size; 818 sec->data->d_align = 1; 819 820 if (size) { 821 sec->data->d_buf = malloc(size); 822 if (!sec->data->d_buf) { 823 perror("malloc"); 824 return NULL; 825 } 826 memset(sec->data->d_buf, 0, size); 827 } 828 829 if (!gelf_getshdr(s, &sec->sh)) { 830 WARN_ELF("gelf_getshdr"); 831 return NULL; 832 } 833 834 sec->sh.sh_size = size; 835 sec->sh.sh_entsize = entsize; 836 sec->sh.sh_type = SHT_PROGBITS; 837 sec->sh.sh_addralign = 1; 838 sec->sh.sh_flags = SHF_ALLOC | sh_flags; 839 840 /* Add section name to .shstrtab (or .strtab for Clang) */ 841 shstrtab = find_section_by_name(elf, ".shstrtab"); 842 if (!shstrtab) 843 shstrtab = find_section_by_name(elf, ".strtab"); 844 if (!shstrtab) { 845 WARN("can't find .shstrtab or .strtab section"); 846 return NULL; 847 } 848 sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name); 849 if (sec->sh.sh_name == -1) 850 return NULL; 851 852 list_add_tail(&sec->list, &elf->sections); 853 elf_hash_add(elf->section_hash, &sec->hash, sec->idx); 854 elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name)); 855 856 elf->changed = true; 857 858 return sec; 859 } 860 861 static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base) 862 { 863 char *relocname; 864 struct section *sec; 865 866 relocname = malloc(strlen(base->name) + strlen(".rel") + 1); 867 if (!relocname) { 868 perror("malloc"); 869 return NULL; 870 } 871 strcpy(relocname, ".rel"); 872 strcat(relocname, base->name); 873 874 sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rel), 0); 875 free(relocname); 876 if (!sec) 877 return NULL; 878 879 base->reloc = sec; 880 sec->base = base; 881 882 sec->sh.sh_type = SHT_REL; 883 sec->sh.sh_addralign = 8; 884 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx; 885 sec->sh.sh_info = base->idx; 886 sec->sh.sh_flags = SHF_INFO_LINK; 887 888 return sec; 889 } 890 891 static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base) 892 { 893 char *relocname; 894 struct section *sec; 895 896 relocname = malloc(strlen(base->name) + strlen(".rela") + 1); 897 if (!relocname) { 898 perror("malloc"); 899 return NULL; 900 } 901 strcpy(relocname, ".rela"); 902 strcat(relocname, base->name); 903 904 sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0); 905 free(relocname); 906 if (!sec) 907 return NULL; 908 909 base->reloc = sec; 910 sec->base = base; 911 912 sec->sh.sh_type = SHT_RELA; 913 sec->sh.sh_addralign = 8; 914 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx; 915 sec->sh.sh_info = base->idx; 916 sec->sh.sh_flags = SHF_INFO_LINK; 917 918 return sec; 919 } 920 921 static struct section *elf_create_reloc_section(struct elf *elf, 922 struct section *base, 923 int reltype) 924 { 925 switch (reltype) { 926 case SHT_REL: return elf_create_rel_reloc_section(elf, base); 927 case SHT_RELA: return elf_create_rela_reloc_section(elf, base); 928 default: return NULL; 929 } 930 } 931 932 static int elf_rebuild_rel_reloc_section(struct section *sec, int nr) 933 { 934 struct reloc *reloc; 935 int idx = 0, size; 936 void *buf; 937 938 /* Allocate a buffer for relocations */ 939 size = nr * sizeof(GElf_Rel); 940 buf = malloc(size); 941 if (!buf) { 942 perror("malloc"); 943 return -1; 944 } 945 946 sec->data->d_buf = buf; 947 sec->data->d_size = size; 948 sec->data->d_type = ELF_T_REL; 949 950 sec->sh.sh_size = size; 951 952 idx = 0; 953 list_for_each_entry(reloc, &sec->reloc_list, list) { 954 reloc->rel.r_offset = reloc->offset; 955 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type); 956 gelf_update_rel(sec->data, idx, &reloc->rel); 957 idx++; 958 } 959 960 return 0; 961 } 962 963 static int elf_rebuild_rela_reloc_section(struct section *sec, int nr) 964 { 965 struct reloc *reloc; 966 int idx = 0, size; 967 void *buf; 968 969 /* Allocate a buffer for relocations with addends */ 970 size = nr * sizeof(GElf_Rela); 971 buf = malloc(size); 972 if (!buf) { 973 perror("malloc"); 974 return -1; 975 } 976 977 sec->data->d_buf = buf; 978 sec->data->d_size = size; 979 sec->data->d_type = ELF_T_RELA; 980 981 sec->sh.sh_size = size; 982 983 idx = 0; 984 list_for_each_entry(reloc, &sec->reloc_list, list) { 985 reloc->rela.r_offset = reloc->offset; 986 reloc->rela.r_addend = reloc->addend; 987 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type); 988 gelf_update_rela(sec->data, idx, &reloc->rela); 989 idx++; 990 } 991 992 return 0; 993 } 994 995 static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec) 996 { 997 struct reloc *reloc; 998 int nr; 999 1000 nr = 0; 1001 list_for_each_entry(reloc, &sec->reloc_list, list) 1002 nr++; 1003 1004 switch (sec->sh.sh_type) { 1005 case SHT_REL: return elf_rebuild_rel_reloc_section(sec, nr); 1006 case SHT_RELA: return elf_rebuild_rela_reloc_section(sec, nr); 1007 default: return -1; 1008 } 1009 } 1010 1011 int elf_write_insn(struct elf *elf, struct section *sec, 1012 unsigned long offset, unsigned int len, 1013 const char *insn) 1014 { 1015 Elf_Data *data = sec->data; 1016 1017 if (data->d_type != ELF_T_BYTE || data->d_off) { 1018 WARN("write to unexpected data for section: %s", sec->name); 1019 return -1; 1020 } 1021 1022 memcpy(data->d_buf + offset, insn, len); 1023 elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY); 1024 1025 elf->changed = true; 1026 1027 return 0; 1028 } 1029 1030 int elf_write_reloc(struct elf *elf, struct reloc *reloc) 1031 { 1032 struct section *sec = reloc->sec; 1033 1034 if (sec->sh.sh_type == SHT_REL) { 1035 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type); 1036 reloc->rel.r_offset = reloc->offset; 1037 1038 if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) { 1039 WARN_ELF("gelf_update_rel"); 1040 return -1; 1041 } 1042 } else { 1043 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type); 1044 reloc->rela.r_addend = reloc->addend; 1045 reloc->rela.r_offset = reloc->offset; 1046 1047 if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) { 1048 WARN_ELF("gelf_update_rela"); 1049 return -1; 1050 } 1051 } 1052 1053 elf->changed = true; 1054 1055 return 0; 1056 } 1057 1058 int elf_write(struct elf *elf) 1059 { 1060 struct section *sec; 1061 Elf_Scn *s; 1062 1063 /* Update changed relocation sections and section headers: */ 1064 list_for_each_entry(sec, &elf->sections, list) { 1065 if (sec->changed) { 1066 if (sec->base && 1067 elf_rebuild_reloc_section(elf, sec)) { 1068 WARN("elf_rebuild_reloc_section"); 1069 return -1; 1070 } 1071 1072 s = elf_getscn(elf->elf, sec->idx); 1073 if (!s) { 1074 WARN_ELF("elf_getscn"); 1075 return -1; 1076 } 1077 if (!gelf_update_shdr(s, &sec->sh)) { 1078 WARN_ELF("gelf_update_shdr"); 1079 return -1; 1080 } 1081 1082 sec->changed = false; 1083 elf->changed = true; 1084 } 1085 } 1086 1087 /* Make sure the new section header entries get updated properly. */ 1088 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY); 1089 1090 /* Write all changes to the file. */ 1091 if (elf_update(elf->elf, ELF_C_WRITE) < 0) { 1092 WARN_ELF("elf_update"); 1093 return -1; 1094 } 1095 1096 elf->changed = false; 1097 1098 return 0; 1099 } 1100 1101 void elf_close(struct elf *elf) 1102 { 1103 struct section *sec, *tmpsec; 1104 struct symbol *sym, *tmpsym; 1105 struct reloc *reloc, *tmpreloc; 1106 1107 if (elf->elf) 1108 elf_end(elf->elf); 1109 1110 if (elf->fd > 0) 1111 close(elf->fd); 1112 1113 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) { 1114 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) { 1115 list_del(&sym->list); 1116 hash_del(&sym->hash); 1117 free(sym); 1118 } 1119 list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) { 1120 list_del(&reloc->list); 1121 hash_del(&reloc->hash); 1122 free(reloc); 1123 } 1124 list_del(&sec->list); 1125 free(sec); 1126 } 1127 1128 free(elf); 1129 } 1130