1 /* 2 * elf.c - ELF access library 3 * 4 * Adapted from kpatch (https://github.com/dynup/kpatch): 5 * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com> 6 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> 7 * 8 * This program is free software; you can redistribute it and/or 9 * modify it under the terms of the GNU General Public License 10 * as published by the Free Software Foundation; either version 2 11 * of the License, or (at your option) any later version. 12 * 13 * This program is distributed in the hope that it will be useful, 14 * but WITHOUT ANY WARRANTY; without even the implied warranty of 15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 16 * GNU General Public License for more details. 17 * 18 * You should have received a copy of the GNU General Public License 19 * along with this program; if not, see <http://www.gnu.org/licenses/>. 20 */ 21 22 #include <sys/types.h> 23 #include <sys/stat.h> 24 #include <fcntl.h> 25 #include <stdio.h> 26 #include <stdlib.h> 27 #include <string.h> 28 #include <unistd.h> 29 #include <errno.h> 30 31 #include "elf.h" 32 #include "warn.h" 33 34 #define MAX_NAME_LEN 128 35 36 struct section *find_section_by_name(struct elf *elf, const char *name) 37 { 38 struct section *sec; 39 40 list_for_each_entry(sec, &elf->sections, list) 41 if (!strcmp(sec->name, name)) 42 return sec; 43 44 return NULL; 45 } 46 47 static struct section *find_section_by_index(struct elf *elf, 48 unsigned int idx) 49 { 50 struct section *sec; 51 52 list_for_each_entry(sec, &elf->sections, list) 53 if (sec->idx == idx) 54 return sec; 55 56 return NULL; 57 } 58 59 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx) 60 { 61 struct section *sec; 62 struct symbol *sym; 63 64 list_for_each_entry(sec, &elf->sections, list) 65 hash_for_each_possible(sec->symbol_hash, sym, hash, idx) 66 if (sym->idx == idx) 67 return sym; 68 69 return NULL; 70 } 71 72 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset) 73 { 74 struct symbol *sym; 75 76 list_for_each_entry(sym, &sec->symbol_list, list) 77 if (sym->type != STT_SECTION && 78 sym->offset == offset) 79 return sym; 80 81 return NULL; 82 } 83 84 struct symbol *find_symbol_by_name(struct elf *elf, const char *name) 85 { 86 struct section *sec; 87 struct symbol *sym; 88 89 list_for_each_entry(sec, &elf->sections, list) 90 list_for_each_entry(sym, &sec->symbol_list, list) 91 if (!strcmp(sym->name, name)) 92 return sym; 93 94 return NULL; 95 } 96 97 struct symbol *find_symbol_containing(struct section *sec, unsigned long offset) 98 { 99 struct symbol *sym; 100 101 list_for_each_entry(sym, &sec->symbol_list, list) 102 if (sym->type != STT_SECTION && 103 offset >= sym->offset && offset < sym->offset + sym->len) 104 return sym; 105 106 return NULL; 107 } 108 109 struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset, 110 unsigned int len) 111 { 112 struct rela *rela; 113 unsigned long o; 114 115 if (!sec->rela) 116 return NULL; 117 118 for (o = offset; o < offset + len; o++) 119 hash_for_each_possible(sec->rela->rela_hash, rela, hash, o) 120 if (rela->offset == o) 121 return rela; 122 123 return NULL; 124 } 125 126 struct rela *find_rela_by_dest(struct section *sec, unsigned long offset) 127 { 128 return find_rela_by_dest_range(sec, offset, 1); 129 } 130 131 struct symbol *find_containing_func(struct section *sec, unsigned long offset) 132 { 133 struct symbol *func; 134 135 list_for_each_entry(func, &sec->symbol_list, list) 136 if (func->type == STT_FUNC && offset >= func->offset && 137 offset < func->offset + func->len) 138 return func; 139 140 return NULL; 141 } 142 143 static int read_sections(struct elf *elf) 144 { 145 Elf_Scn *s = NULL; 146 struct section *sec; 147 size_t shstrndx, sections_nr; 148 int i; 149 150 if (elf_getshdrnum(elf->elf, §ions_nr)) { 151 WARN_ELF("elf_getshdrnum"); 152 return -1; 153 } 154 155 if (elf_getshdrstrndx(elf->elf, &shstrndx)) { 156 WARN_ELF("elf_getshdrstrndx"); 157 return -1; 158 } 159 160 for (i = 0; i < sections_nr; i++) { 161 sec = malloc(sizeof(*sec)); 162 if (!sec) { 163 perror("malloc"); 164 return -1; 165 } 166 memset(sec, 0, sizeof(*sec)); 167 168 INIT_LIST_HEAD(&sec->symbol_list); 169 INIT_LIST_HEAD(&sec->rela_list); 170 hash_init(sec->rela_hash); 171 hash_init(sec->symbol_hash); 172 173 list_add_tail(&sec->list, &elf->sections); 174 175 s = elf_getscn(elf->elf, i); 176 if (!s) { 177 WARN_ELF("elf_getscn"); 178 return -1; 179 } 180 181 sec->idx = elf_ndxscn(s); 182 183 if (!gelf_getshdr(s, &sec->sh)) { 184 WARN_ELF("gelf_getshdr"); 185 return -1; 186 } 187 188 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name); 189 if (!sec->name) { 190 WARN_ELF("elf_strptr"); 191 return -1; 192 } 193 194 if (sec->sh.sh_size != 0) { 195 sec->data = elf_getdata(s, NULL); 196 if (!sec->data) { 197 WARN_ELF("elf_getdata"); 198 return -1; 199 } 200 if (sec->data->d_off != 0 || 201 sec->data->d_size != sec->sh.sh_size) { 202 WARN("unexpected data attributes for %s", 203 sec->name); 204 return -1; 205 } 206 } 207 sec->len = sec->sh.sh_size; 208 } 209 210 /* sanity check, one more call to elf_nextscn() should return NULL */ 211 if (elf_nextscn(elf->elf, s)) { 212 WARN("section entry mismatch"); 213 return -1; 214 } 215 216 return 0; 217 } 218 219 static int read_symbols(struct elf *elf) 220 { 221 struct section *symtab, *sec; 222 struct symbol *sym, *pfunc; 223 struct list_head *entry, *tmp; 224 int symbols_nr, i; 225 char *coldstr; 226 227 symtab = find_section_by_name(elf, ".symtab"); 228 if (!symtab) { 229 WARN("missing symbol table"); 230 return -1; 231 } 232 233 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize; 234 235 for (i = 0; i < symbols_nr; i++) { 236 sym = malloc(sizeof(*sym)); 237 if (!sym) { 238 perror("malloc"); 239 return -1; 240 } 241 memset(sym, 0, sizeof(*sym)); 242 243 sym->idx = i; 244 245 if (!gelf_getsym(symtab->data, i, &sym->sym)) { 246 WARN_ELF("gelf_getsym"); 247 goto err; 248 } 249 250 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link, 251 sym->sym.st_name); 252 if (!sym->name) { 253 WARN_ELF("elf_strptr"); 254 goto err; 255 } 256 257 sym->type = GELF_ST_TYPE(sym->sym.st_info); 258 sym->bind = GELF_ST_BIND(sym->sym.st_info); 259 260 if (sym->sym.st_shndx > SHN_UNDEF && 261 sym->sym.st_shndx < SHN_LORESERVE) { 262 sym->sec = find_section_by_index(elf, 263 sym->sym.st_shndx); 264 if (!sym->sec) { 265 WARN("couldn't find section for symbol %s", 266 sym->name); 267 goto err; 268 } 269 if (sym->type == STT_SECTION) { 270 sym->name = sym->sec->name; 271 sym->sec->sym = sym; 272 } 273 } else 274 sym->sec = find_section_by_index(elf, 0); 275 276 sym->offset = sym->sym.st_value; 277 sym->len = sym->sym.st_size; 278 279 /* sorted insert into a per-section list */ 280 entry = &sym->sec->symbol_list; 281 list_for_each_prev(tmp, &sym->sec->symbol_list) { 282 struct symbol *s; 283 284 s = list_entry(tmp, struct symbol, list); 285 286 if (sym->offset > s->offset) { 287 entry = tmp; 288 break; 289 } 290 291 if (sym->offset == s->offset && sym->len >= s->len) { 292 entry = tmp; 293 break; 294 } 295 } 296 list_add(&sym->list, entry); 297 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx); 298 } 299 300 /* Create parent/child links for any cold subfunctions */ 301 list_for_each_entry(sec, &elf->sections, list) { 302 list_for_each_entry(sym, &sec->symbol_list, list) { 303 char pname[MAX_NAME_LEN + 1]; 304 size_t pnamelen; 305 if (sym->type != STT_FUNC) 306 continue; 307 sym->pfunc = sym->cfunc = sym; 308 coldstr = strstr(sym->name, ".cold"); 309 if (!coldstr) 310 continue; 311 312 pnamelen = coldstr - sym->name; 313 if (pnamelen > MAX_NAME_LEN) { 314 WARN("%s(): parent function name exceeds maximum length of %d characters", 315 sym->name, MAX_NAME_LEN); 316 return -1; 317 } 318 319 strncpy(pname, sym->name, pnamelen); 320 pname[pnamelen] = '\0'; 321 pfunc = find_symbol_by_name(elf, pname); 322 323 if (!pfunc) { 324 WARN("%s(): can't find parent function", 325 sym->name); 326 return -1; 327 } 328 329 sym->pfunc = pfunc; 330 pfunc->cfunc = sym; 331 332 /* 333 * Unfortunately, -fnoreorder-functions puts the child 334 * inside the parent. Remove the overlap so we can 335 * have sane assumptions. 336 * 337 * Note that pfunc->len now no longer matches 338 * pfunc->sym.st_size. 339 */ 340 if (sym->sec == pfunc->sec && 341 sym->offset >= pfunc->offset && 342 sym->offset + sym->len == pfunc->offset + pfunc->len) { 343 pfunc->len -= sym->len; 344 } 345 } 346 } 347 348 return 0; 349 350 err: 351 free(sym); 352 return -1; 353 } 354 355 static int read_relas(struct elf *elf) 356 { 357 struct section *sec; 358 struct rela *rela; 359 int i; 360 unsigned int symndx; 361 362 list_for_each_entry(sec, &elf->sections, list) { 363 if (sec->sh.sh_type != SHT_RELA) 364 continue; 365 366 sec->base = find_section_by_name(elf, sec->name + 5); 367 if (!sec->base) { 368 WARN("can't find base section for rela section %s", 369 sec->name); 370 return -1; 371 } 372 373 sec->base->rela = sec; 374 375 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) { 376 rela = malloc(sizeof(*rela)); 377 if (!rela) { 378 perror("malloc"); 379 return -1; 380 } 381 memset(rela, 0, sizeof(*rela)); 382 383 if (!gelf_getrela(sec->data, i, &rela->rela)) { 384 WARN_ELF("gelf_getrela"); 385 return -1; 386 } 387 388 rela->type = GELF_R_TYPE(rela->rela.r_info); 389 rela->addend = rela->rela.r_addend; 390 rela->offset = rela->rela.r_offset; 391 symndx = GELF_R_SYM(rela->rela.r_info); 392 rela->sym = find_symbol_by_index(elf, symndx); 393 rela->rela_sec = sec; 394 if (!rela->sym) { 395 WARN("can't find rela entry symbol %d for %s", 396 symndx, sec->name); 397 return -1; 398 } 399 400 list_add_tail(&rela->list, &sec->rela_list); 401 hash_add(sec->rela_hash, &rela->hash, rela->offset); 402 403 } 404 } 405 406 return 0; 407 } 408 409 struct elf *elf_open(const char *name, int flags) 410 { 411 struct elf *elf; 412 Elf_Cmd cmd; 413 414 elf_version(EV_CURRENT); 415 416 elf = malloc(sizeof(*elf)); 417 if (!elf) { 418 perror("malloc"); 419 return NULL; 420 } 421 memset(elf, 0, sizeof(*elf)); 422 423 INIT_LIST_HEAD(&elf->sections); 424 425 elf->fd = open(name, flags); 426 if (elf->fd == -1) { 427 fprintf(stderr, "objtool: Can't open '%s': %s\n", 428 name, strerror(errno)); 429 goto err; 430 } 431 432 if ((flags & O_ACCMODE) == O_RDONLY) 433 cmd = ELF_C_READ_MMAP; 434 else if ((flags & O_ACCMODE) == O_RDWR) 435 cmd = ELF_C_RDWR; 436 else /* O_WRONLY */ 437 cmd = ELF_C_WRITE; 438 439 elf->elf = elf_begin(elf->fd, cmd, NULL); 440 if (!elf->elf) { 441 WARN_ELF("elf_begin"); 442 goto err; 443 } 444 445 if (!gelf_getehdr(elf->elf, &elf->ehdr)) { 446 WARN_ELF("gelf_getehdr"); 447 goto err; 448 } 449 450 if (read_sections(elf)) 451 goto err; 452 453 if (read_symbols(elf)) 454 goto err; 455 456 if (read_relas(elf)) 457 goto err; 458 459 return elf; 460 461 err: 462 elf_close(elf); 463 return NULL; 464 } 465 466 struct section *elf_create_section(struct elf *elf, const char *name, 467 size_t entsize, int nr) 468 { 469 struct section *sec, *shstrtab; 470 size_t size = entsize * nr; 471 struct Elf_Scn *s; 472 Elf_Data *data; 473 474 sec = malloc(sizeof(*sec)); 475 if (!sec) { 476 perror("malloc"); 477 return NULL; 478 } 479 memset(sec, 0, sizeof(*sec)); 480 481 INIT_LIST_HEAD(&sec->symbol_list); 482 INIT_LIST_HEAD(&sec->rela_list); 483 hash_init(sec->rela_hash); 484 hash_init(sec->symbol_hash); 485 486 list_add_tail(&sec->list, &elf->sections); 487 488 s = elf_newscn(elf->elf); 489 if (!s) { 490 WARN_ELF("elf_newscn"); 491 return NULL; 492 } 493 494 sec->name = strdup(name); 495 if (!sec->name) { 496 perror("strdup"); 497 return NULL; 498 } 499 500 sec->idx = elf_ndxscn(s); 501 sec->len = size; 502 sec->changed = true; 503 504 sec->data = elf_newdata(s); 505 if (!sec->data) { 506 WARN_ELF("elf_newdata"); 507 return NULL; 508 } 509 510 sec->data->d_size = size; 511 sec->data->d_align = 1; 512 513 if (size) { 514 sec->data->d_buf = malloc(size); 515 if (!sec->data->d_buf) { 516 perror("malloc"); 517 return NULL; 518 } 519 memset(sec->data->d_buf, 0, size); 520 } 521 522 if (!gelf_getshdr(s, &sec->sh)) { 523 WARN_ELF("gelf_getshdr"); 524 return NULL; 525 } 526 527 sec->sh.sh_size = size; 528 sec->sh.sh_entsize = entsize; 529 sec->sh.sh_type = SHT_PROGBITS; 530 sec->sh.sh_addralign = 1; 531 sec->sh.sh_flags = SHF_ALLOC; 532 533 534 /* Add section name to .shstrtab (or .strtab for Clang) */ 535 shstrtab = find_section_by_name(elf, ".shstrtab"); 536 if (!shstrtab) 537 shstrtab = find_section_by_name(elf, ".strtab"); 538 if (!shstrtab) { 539 WARN("can't find .shstrtab or .strtab section"); 540 return NULL; 541 } 542 543 s = elf_getscn(elf->elf, shstrtab->idx); 544 if (!s) { 545 WARN_ELF("elf_getscn"); 546 return NULL; 547 } 548 549 data = elf_newdata(s); 550 if (!data) { 551 WARN_ELF("elf_newdata"); 552 return NULL; 553 } 554 555 data->d_buf = sec->name; 556 data->d_size = strlen(name) + 1; 557 data->d_align = 1; 558 559 sec->sh.sh_name = shstrtab->len; 560 561 shstrtab->len += strlen(name) + 1; 562 shstrtab->changed = true; 563 564 return sec; 565 } 566 567 struct section *elf_create_rela_section(struct elf *elf, struct section *base) 568 { 569 char *relaname; 570 struct section *sec; 571 572 relaname = malloc(strlen(base->name) + strlen(".rela") + 1); 573 if (!relaname) { 574 perror("malloc"); 575 return NULL; 576 } 577 strcpy(relaname, ".rela"); 578 strcat(relaname, base->name); 579 580 sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0); 581 free(relaname); 582 if (!sec) 583 return NULL; 584 585 base->rela = sec; 586 sec->base = base; 587 588 sec->sh.sh_type = SHT_RELA; 589 sec->sh.sh_addralign = 8; 590 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx; 591 sec->sh.sh_info = base->idx; 592 sec->sh.sh_flags = SHF_INFO_LINK; 593 594 return sec; 595 } 596 597 int elf_rebuild_rela_section(struct section *sec) 598 { 599 struct rela *rela; 600 int nr, idx = 0, size; 601 GElf_Rela *relas; 602 603 nr = 0; 604 list_for_each_entry(rela, &sec->rela_list, list) 605 nr++; 606 607 size = nr * sizeof(*relas); 608 relas = malloc(size); 609 if (!relas) { 610 perror("malloc"); 611 return -1; 612 } 613 614 sec->data->d_buf = relas; 615 sec->data->d_size = size; 616 617 sec->sh.sh_size = size; 618 619 idx = 0; 620 list_for_each_entry(rela, &sec->rela_list, list) { 621 relas[idx].r_offset = rela->offset; 622 relas[idx].r_addend = rela->addend; 623 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type); 624 idx++; 625 } 626 627 return 0; 628 } 629 630 int elf_write(struct elf *elf) 631 { 632 struct section *sec; 633 Elf_Scn *s; 634 635 /* Update section headers for changed sections: */ 636 list_for_each_entry(sec, &elf->sections, list) { 637 if (sec->changed) { 638 s = elf_getscn(elf->elf, sec->idx); 639 if (!s) { 640 WARN_ELF("elf_getscn"); 641 return -1; 642 } 643 if (!gelf_update_shdr(s, &sec->sh)) { 644 WARN_ELF("gelf_update_shdr"); 645 return -1; 646 } 647 } 648 } 649 650 /* Make sure the new section header entries get updated properly. */ 651 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY); 652 653 /* Write all changes to the file. */ 654 if (elf_update(elf->elf, ELF_C_WRITE) < 0) { 655 WARN_ELF("elf_update"); 656 return -1; 657 } 658 659 return 0; 660 } 661 662 void elf_close(struct elf *elf) 663 { 664 struct section *sec, *tmpsec; 665 struct symbol *sym, *tmpsym; 666 struct rela *rela, *tmprela; 667 668 if (elf->elf) 669 elf_end(elf->elf); 670 671 if (elf->fd > 0) 672 close(elf->fd); 673 674 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) { 675 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) { 676 list_del(&sym->list); 677 hash_del(&sym->hash); 678 free(sym); 679 } 680 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) { 681 list_del(&rela->list); 682 hash_del(&rela->hash); 683 free(rela); 684 } 685 list_del(&sec->list); 686 free(sec); 687 } 688 689 free(elf); 690 } 691