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                                 continue;
 307
 308                         coldstr[0] = '\0';
 309                         pfunc = find_symbol_by_name(elf, sym->name);
 310                         coldstr[0] = '.';
 311
 312                         if (!pfunc) {
 313                                 WARN("%s(): can't find parent function",
 314                                      sym->name);
 315                                 goto err;
 316                         }
 317
 318                         sym->pfunc = pfunc;
 319                         pfunc->cfunc = sym;
 320
 321                         /*
 322                          * Unfortunately, -fnoreorder-functions puts the child
 323                          * inside the parent.  Remove the overlap so we can
 324                          * have sane assumptions.
 325                          *
 326                          * Note that pfunc->len now no longer matches
 327                          * pfunc->sym.st_size.
 328                          */
 329                         if (sym->sec == pfunc->sec &&
 330                             sym->offset >= pfunc->offset &&
 331                             sym->offset + sym->len == pfunc->offset + pfunc->len) {
 332                                 pfunc->len -= sym->len;
 333                         }
 334                 }
 335         }
 336
 337         return 0;
 338
 339 err:
 340         free(sym);
 341         return -1;
 342 }
 343
 344 static int read_relas(struct elf *elf)
 345 {
 346         struct section *sec;
 347         struct rela *rela;
 348         int i;
 349         unsigned int symndx;
 350
 351         list_for_each_entry(sec, &elf->sections, list) {
 352                 if (sec->sh.sh_type != SHT_RELA)
 353                         continue;
 354
 355                 sec->base = find_section_by_name(elf, sec->name + 5);
 356                 if (!sec->base) {
 357                         WARN("can't find base section for rela section %s",
 358                              sec->name);
 359                         return -1;
 360                 }
 361
 362                 sec->base->rela = sec;
 363
 364                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 365                         rela = malloc(sizeof(*rela));
 366                         if (!rela) {
 367                                 perror("malloc");
 368                                 return -1;
 369                         }
 370                         memset(rela, 0, sizeof(*rela));
 371
 372                         if (!gelf_getrela(sec->data, i, &rela->rela)) {
 373                                 WARN_ELF("gelf_getrela");
 374                                 return -1;
 375                         }
 376
 377                         rela->type = GELF_R_TYPE(rela->rela.r_info);
 378                         rela->addend = rela->rela.r_addend;
 379                         rela->offset = rela->rela.r_offset;
 380                         symndx = GELF_R_SYM(rela->rela.r_info);
 381                         rela->sym = find_symbol_by_index(elf, symndx);
 382                         if (!rela->sym) {
 383                                 WARN("can't find rela entry symbol %d for %s",
 384                                      symndx, sec->name);
 385                                 return -1;
 386                         }
 387
 388                         list_add_tail(&rela->list, &sec->rela_list);
 389                         hash_add(sec->rela_hash, &rela->hash, rela->offset);
 390
 391                 }
 392         }
 393
 394         return 0;
 395 }
 396
 397 struct elf *elf_open(const char *name, int flags)
 398 {
 399         struct elf *elf;
 400         Elf_Cmd cmd;
 401
 402         elf_version(EV_CURRENT);
 403
 404         elf = malloc(sizeof(*elf));
 405         if (!elf) {
 406                 perror("malloc");
 407                 return NULL;
 408         }
 409         memset(elf, 0, sizeof(*elf));
 410
 411         INIT_LIST_HEAD(&elf->sections);
 412
 413         elf->fd = open(name, flags);
 414         if (elf->fd == -1) {
 415                 fprintf(stderr, "objtool: Can't open '%s': %s\n",
 416                         name, strerror(errno));
 417                 goto err;
 418         }
 419
 420         if ((flags & O_ACCMODE) == O_RDONLY)
 421                 cmd = ELF_C_READ_MMAP;
 422         else if ((flags & O_ACCMODE) == O_RDWR)
 423                 cmd = ELF_C_RDWR;
 424         else /* O_WRONLY */
 425                 cmd = ELF_C_WRITE;
 426
 427         elf->elf = elf_begin(elf->fd, cmd, NULL);
 428         if (!elf->elf) {
 429                 WARN_ELF("elf_begin");
 430                 goto err;
 431         }
 432
 433         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 434                 WARN_ELF("gelf_getehdr");
 435                 goto err;
 436         }
 437
 438         if (read_sections(elf))
 439                 goto err;
 440
 441         if (read_symbols(elf))
 442                 goto err;
 443
 444         if (read_relas(elf))
 445                 goto err;
 446
 447         return elf;
 448
 449 err:
 450         elf_close(elf);
 451         return NULL;
 452 }
 453
 454 struct section *elf_create_section(struct elf *elf, const char *name,
 455                                    size_t entsize, int nr)
 456 {
 457         struct section *sec, *shstrtab;
 458         size_t size = entsize * nr;
 459         struct Elf_Scn *s;
 460         Elf_Data *data;
 461
 462         sec = malloc(sizeof(*sec));
 463         if (!sec) {
 464                 perror("malloc");
 465                 return NULL;
 466         }
 467         memset(sec, 0, sizeof(*sec));
 468
 469         INIT_LIST_HEAD(&sec->symbol_list);
 470         INIT_LIST_HEAD(&sec->rela_list);
 471         hash_init(sec->rela_hash);
 472         hash_init(sec->symbol_hash);
 473
 474         list_add_tail(&sec->list, &elf->sections);
 475
 476         s = elf_newscn(elf->elf);
 477         if (!s) {
 478                 WARN_ELF("elf_newscn");
 479                 return NULL;
 480         }
 481
 482         sec->name = strdup(name);
 483         if (!sec->name) {
 484                 perror("strdup");
 485                 return NULL;
 486         }
 487
 488         sec->idx = elf_ndxscn(s);
 489         sec->len = size;
 490         sec->changed = true;
 491
 492         sec->data = elf_newdata(s);
 493         if (!sec->data) {
 494                 WARN_ELF("elf_newdata");
 495                 return NULL;
 496         }
 497
 498         sec->data->d_size = size;
 499         sec->data->d_align = 1;
 500
 501         if (size) {
 502                 sec->data->d_buf = malloc(size);
 503                 if (!sec->data->d_buf) {
 504                         perror("malloc");
 505                         return NULL;
 506                 }
 507                 memset(sec->data->d_buf, 0, size);
 508         }
 509
 510         if (!gelf_getshdr(s, &sec->sh)) {
 511                 WARN_ELF("gelf_getshdr");
 512                 return NULL;
 513         }
 514
 515         sec->sh.sh_size = size;
 516         sec->sh.sh_entsize = entsize;
 517         sec->sh.sh_type = SHT_PROGBITS;
 518         sec->sh.sh_addralign = 1;
 519         sec->sh.sh_flags = SHF_ALLOC;
 520
 521
 522         /* Add section name to .shstrtab (or .strtab for Clang) */
 523         shstrtab = find_section_by_name(elf, ".shstrtab");
 524         if (!shstrtab)
 525                 shstrtab = find_section_by_name(elf, ".strtab");
 526         if (!shstrtab) {
 527                 WARN("can't find .shstrtab or .strtab section");
 528                 return NULL;
 529         }
 530
 531         s = elf_getscn(elf->elf, shstrtab->idx);
 532         if (!s) {
 533                 WARN_ELF("elf_getscn");
 534                 return NULL;
 535         }
 536
 537         data = elf_newdata(s);
 538         if (!data) {
 539                 WARN_ELF("elf_newdata");
 540                 return NULL;
 541         }
 542
 543         data->d_buf = sec->name;
 544         data->d_size = strlen(name) + 1;
 545         data->d_align = 1;
 546
 547         sec->sh.sh_name = shstrtab->len;
 548
 549         shstrtab->len += strlen(name) + 1;
 550         shstrtab->changed = true;
 551
 552         return sec;
 553 }
 554
 555 struct section *elf_create_rela_section(struct elf *elf, struct section *base)
 556 {
 557         char *relaname;
 558         struct section *sec;
 559
 560         relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
 561         if (!relaname) {
 562                 perror("malloc");
 563                 return NULL;
 564         }
 565         strcpy(relaname, ".rela");
 566         strcat(relaname, base->name);
 567
 568         sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
 569         free(relaname);
 570         if (!sec)
 571                 return NULL;
 572
 573         base->rela = sec;
 574         sec->base = base;
 575
 576         sec->sh.sh_type = SHT_RELA;
 577         sec->sh.sh_addralign = 8;
 578         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 579         sec->sh.sh_info = base->idx;
 580         sec->sh.sh_flags = SHF_INFO_LINK;
 581
 582         return sec;
 583 }
 584
 585 int elf_rebuild_rela_section(struct section *sec)
 586 {
 587         struct rela *rela;
 588         int nr, idx = 0, size;
 589         GElf_Rela *relas;
 590
 591         nr = 0;
 592         list_for_each_entry(rela, &sec->rela_list, list)
 593                 nr++;
 594
 595         size = nr * sizeof(*relas);
 596         relas = malloc(size);
 597         if (!relas) {
 598                 perror("malloc");
 599                 return -1;
 600         }
 601
 602         sec->data->d_buf = relas;
 603         sec->data->d_size = size;
 604
 605         sec->sh.sh_size = size;
 606
 607         idx = 0;
 608         list_for_each_entry(rela, &sec->rela_list, list) {
 609                 relas[idx].r_offset = rela->offset;
 610                 relas[idx].r_addend = rela->addend;
 611                 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
 612                 idx++;
 613         }
 614
 615         return 0;
 616 }
 617
 618 int elf_write(struct elf *elf)
 619 {
 620         struct section *sec;
 621         Elf_Scn *s;
 622
 623         /* Update section headers for changed sections: */
 624         list_for_each_entry(sec, &elf->sections, list) {
 625                 if (sec->changed) {
 626                         s = elf_getscn(elf->elf, sec->idx);
 627                         if (!s) {
 628                                 WARN_ELF("elf_getscn");
 629                                 return -1;
 630                         }
 631                         if (!gelf_update_shdr(s, &sec->sh)) {
 632                                 WARN_ELF("gelf_update_shdr");
 633                                 return -1;
 634                         }
 635                 }
 636         }
 637
 638         /* Make sure the new section header entries get updated properly. */
 639         elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
 640
 641         /* Write all changes to the file. */
 642         if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
 643                 WARN_ELF("elf_update");
 644                 return -1;
 645         }
 646
 647         return 0;
 648 }
 649
 650 void elf_close(struct elf *elf)
 651 {
 652         struct section *sec, *tmpsec;
 653         struct symbol *sym, *tmpsym;
 654         struct rela *rela, *tmprela;
 655
 656         if (elf->elf)
 657                 elf_end(elf->elf);
 658
 659         if (elf->fd > 0)
 660                 close(elf->fd);
 661
 662         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
 663                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
 664                         list_del(&sym->list);
 665                         hash_del(&sym->hash);
 666                         free(sym);
 667                 }
 668                 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
 669                         list_del(&rela->list);
 670                         hash_del(&rela->hash);
 671                         free(rela);
 672                 }
 673                 list_del(&sec->list);
 674                 free(sec);
 675         }
 676
 677         free(elf);
 678 }