tools/objtool/elf.c

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