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