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 #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, &sections_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, *alias;
 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                 alias = sym;
 243
 244                 sym->idx = i;
 245
 246                 if (!gelf_getsym(symtab->data, i, &sym->sym)) {
 247                         WARN_ELF("gelf_getsym");
 248                         goto err;
 249                 }
 250
 251                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 252                                        sym->sym.st_name);
 253                 if (!sym->name) {
 254                         WARN_ELF("elf_strptr");
 255                         goto err;
 256                 }
 257
 258                 sym->type = GELF_ST_TYPE(sym->sym.st_info);
 259                 sym->bind = GELF_ST_BIND(sym->sym.st_info);
 260
 261                 if (sym->sym.st_shndx > SHN_UNDEF &&
 262                     sym->sym.st_shndx < SHN_LORESERVE) {
 263                         sym->sec = find_section_by_index(elf,
 264                                                          sym->sym.st_shndx);
 265                         if (!sym->sec) {
 266                                 WARN("couldn't find section for symbol %s",
 267                                      sym->name);
 268                                 goto err;
 269                         }
 270                         if (sym->type == STT_SECTION) {
 271                                 sym->name = sym->sec->name;
 272                                 sym->sec->sym = sym;
 273                         }
 274                 } else
 275                         sym->sec = find_section_by_index(elf, 0);
 276
 277                 sym->offset = sym->sym.st_value;
 278                 sym->len = sym->sym.st_size;
 279
 280                 /* sorted insert into a per-section list */
 281                 entry = &sym->sec->symbol_list;
 282                 list_for_each_prev(tmp, &sym->sec->symbol_list) {
 283                         struct symbol *s;
 284
 285                         s = list_entry(tmp, struct symbol, list);
 286
 287                         if (sym->offset > s->offset) {
 288                                 entry = tmp;
 289                                 break;
 290                         }
 291
 292                         if (sym->offset == s->offset) {
 293                                 if (sym->len == s->len && alias == sym)
 294                                         alias = s;
 295
 296                                 if (sym->len >= s->len) {
 297                                         entry = tmp;
 298                                         break;
 299                                 }
 300                         }
 301                 }
 302                 sym->alias = alias;
 303                 list_add(&sym->list, entry);
 304                 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
 305         }
 306
 307         /* Create parent/child links for any cold subfunctions */
 308         list_for_each_entry(sec, &elf->sections, list) {
 309                 list_for_each_entry(sym, &sec->symbol_list, list) {
 310                         char pname[MAX_NAME_LEN + 1];
 311                         size_t pnamelen;
 312                         if (sym->type != STT_FUNC)
 313                                 continue;
 314                         sym->pfunc = sym->cfunc = sym;
 315                         coldstr = strstr(sym->name, ".cold");
 316                         if (!coldstr)
 317                                 continue;
 318
 319                         pnamelen = coldstr - sym->name;
 320                         if (pnamelen > MAX_NAME_LEN) {
 321                                 WARN("%s(): parent function name exceeds maximum length of %d characters",
 322                                      sym->name, MAX_NAME_LEN);
 323                                 return -1;
 324                         }
 325
 326                         strncpy(pname, sym->name, pnamelen);
 327                         pname[pnamelen] = '\0';
 328                         pfunc = find_symbol_by_name(elf, pname);
 329
 330                         if (!pfunc) {
 331                                 WARN("%s(): can't find parent function",
 332                                      sym->name);
 333                                 return -1;
 334                         }
 335
 336                         sym->pfunc = pfunc;
 337                         pfunc->cfunc = sym;
 338
 339                         /*
 340                          * Unfortunately, -fnoreorder-functions puts the child
 341                          * inside the parent.  Remove the overlap so we can
 342                          * have sane assumptions.
 343                          *
 344                          * Note that pfunc->len now no longer matches
 345                          * pfunc->sym.st_size.
 346                          */
 347                         if (sym->sec == pfunc->sec &&
 348                             sym->offset >= pfunc->offset &&
 349                             sym->offset + sym->len == pfunc->offset + pfunc->len) {
 350                                 pfunc->len -= sym->len;
 351                         }
 352                 }
 353         }
 354
 355         return 0;
 356
 357 err:
 358         free(sym);
 359         return -1;
 360 }
 361
 362 static int read_relas(struct elf *elf)
 363 {
 364         struct section *sec;
 365         struct rela *rela;
 366         int i;
 367         unsigned int symndx;
 368
 369         list_for_each_entry(sec, &elf->sections, list) {
 370                 if (sec->sh.sh_type != SHT_RELA)
 371                         continue;
 372
 373                 sec->base = find_section_by_name(elf, sec->name + 5);
 374                 if (!sec->base) {
 375                         WARN("can't find base section for rela section %s",
 376                              sec->name);
 377                         return -1;
 378                 }
 379
 380                 sec->base->rela = sec;
 381
 382                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 383                         rela = malloc(sizeof(*rela));
 384                         if (!rela) {
 385                                 perror("malloc");
 386                                 return -1;
 387                         }
 388                         memset(rela, 0, sizeof(*rela));
 389
 390                         if (!gelf_getrela(sec->data, i, &rela->rela)) {
 391                                 WARN_ELF("gelf_getrela");
 392                                 return -1;
 393                         }
 394
 395                         rela->type = GELF_R_TYPE(rela->rela.r_info);
 396                         rela->addend = rela->rela.r_addend;
 397                         rela->offset = rela->rela.r_offset;
 398                         symndx = GELF_R_SYM(rela->rela.r_info);
 399                         rela->sym = find_symbol_by_index(elf, symndx);
 400                         rela->rela_sec = sec;
 401                         if (!rela->sym) {
 402                                 WARN("can't find rela entry symbol %d for %s",
 403                                      symndx, sec->name);
 404                                 return -1;
 405                         }
 406
 407                         list_add_tail(&rela->list, &sec->rela_list);
 408                         hash_add(sec->rela_hash, &rela->hash, rela->offset);
 409
 410                 }
 411         }
 412
 413         return 0;
 414 }
 415
 416 struct elf *elf_open(const char *name, int flags)
 417 {
 418         struct elf *elf;
 419         Elf_Cmd cmd;
 420
 421         elf_version(EV_CURRENT);
 422
 423         elf = malloc(sizeof(*elf));
 424         if (!elf) {
 425                 perror("malloc");
 426                 return NULL;
 427         }
 428         memset(elf, 0, sizeof(*elf));
 429
 430         INIT_LIST_HEAD(&elf->sections);
 431
 432         elf->fd = open(name, flags);
 433         if (elf->fd == -1) {
 434                 fprintf(stderr, "objtool: Can't open '%s': %s\n",
 435                         name, strerror(errno));
 436                 goto err;
 437         }
 438
 439         if ((flags & O_ACCMODE) == O_RDONLY)
 440                 cmd = ELF_C_READ_MMAP;
 441         else if ((flags & O_ACCMODE) == O_RDWR)
 442                 cmd = ELF_C_RDWR;
 443         else /* O_WRONLY */
 444                 cmd = ELF_C_WRITE;
 445
 446         elf->elf = elf_begin(elf->fd, cmd, NULL);
 447         if (!elf->elf) {
 448                 WARN_ELF("elf_begin");
 449                 goto err;
 450         }
 451
 452         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 453                 WARN_ELF("gelf_getehdr");
 454                 goto err;
 455         }
 456
 457         if (read_sections(elf))
 458                 goto err;
 459
 460         if (read_symbols(elf))
 461                 goto err;
 462
 463         if (read_relas(elf))
 464                 goto err;
 465
 466         return elf;
 467
 468 err:
 469         elf_close(elf);
 470         return NULL;
 471 }
 472
 473 struct section *elf_create_section(struct elf *elf, const char *name,
 474                                    size_t entsize, int nr)
 475 {
 476         struct section *sec, *shstrtab;
 477         size_t size = entsize * nr;
 478         struct Elf_Scn *s;
 479         Elf_Data *data;
 480
 481         sec = malloc(sizeof(*sec));
 482         if (!sec) {
 483                 perror("malloc");
 484                 return NULL;
 485         }
 486         memset(sec, 0, sizeof(*sec));
 487
 488         INIT_LIST_HEAD(&sec->symbol_list);
 489         INIT_LIST_HEAD(&sec->rela_list);
 490         hash_init(sec->rela_hash);
 491         hash_init(sec->symbol_hash);
 492
 493         list_add_tail(&sec->list, &elf->sections);
 494
 495         s = elf_newscn(elf->elf);
 496         if (!s) {
 497                 WARN_ELF("elf_newscn");
 498                 return NULL;
 499         }
 500
 501         sec->name = strdup(name);
 502         if (!sec->name) {
 503                 perror("strdup");
 504                 return NULL;
 505         }
 506
 507         sec->idx = elf_ndxscn(s);
 508         sec->len = size;
 509         sec->changed = true;
 510
 511         sec->data = elf_newdata(s);
 512         if (!sec->data) {
 513                 WARN_ELF("elf_newdata");
 514                 return NULL;
 515         }
 516
 517         sec->data->d_size = size;
 518         sec->data->d_align = 1;
 519
 520         if (size) {
 521                 sec->data->d_buf = malloc(size);
 522                 if (!sec->data->d_buf) {
 523                         perror("malloc");
 524                         return NULL;
 525                 }
 526                 memset(sec->data->d_buf, 0, size);
 527         }
 528
 529         if (!gelf_getshdr(s, &sec->sh)) {
 530                 WARN_ELF("gelf_getshdr");
 531                 return NULL;
 532         }
 533
 534         sec->sh.sh_size = size;
 535         sec->sh.sh_entsize = entsize;
 536         sec->sh.sh_type = SHT_PROGBITS;
 537         sec->sh.sh_addralign = 1;
 538         sec->sh.sh_flags = SHF_ALLOC;
 539
 540
 541         /* Add section name to .shstrtab (or .strtab for Clang) */
 542         shstrtab = find_section_by_name(elf, ".shstrtab");
 543         if (!shstrtab)
 544                 shstrtab = find_section_by_name(elf, ".strtab");
 545         if (!shstrtab) {
 546                 WARN("can't find .shstrtab or .strtab section");
 547                 return NULL;
 548         }
 549
 550         s = elf_getscn(elf->elf, shstrtab->idx);
 551         if (!s) {
 552                 WARN_ELF("elf_getscn");
 553                 return NULL;
 554         }
 555
 556         data = elf_newdata(s);
 557         if (!data) {
 558                 WARN_ELF("elf_newdata");
 559                 return NULL;
 560         }
 561
 562         data->d_buf = sec->name;
 563         data->d_size = strlen(name) + 1;
 564         data->d_align = 1;
 565
 566         sec->sh.sh_name = shstrtab->len;
 567
 568         shstrtab->len += strlen(name) + 1;
 569         shstrtab->changed = true;
 570
 571         return sec;
 572 }
 573
 574 struct section *elf_create_rela_section(struct elf *elf, struct section *base)
 575 {
 576         char *relaname;
 577         struct section *sec;
 578
 579         relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
 580         if (!relaname) {
 581                 perror("malloc");
 582                 return NULL;
 583         }
 584         strcpy(relaname, ".rela");
 585         strcat(relaname, base->name);
 586
 587         sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
 588         free(relaname);
 589         if (!sec)
 590                 return NULL;
 591
 592         base->rela = sec;
 593         sec->base = base;
 594
 595         sec->sh.sh_type = SHT_RELA;
 596         sec->sh.sh_addralign = 8;
 597         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 598         sec->sh.sh_info = base->idx;
 599         sec->sh.sh_flags = SHF_INFO_LINK;
 600
 601         return sec;
 602 }
 603
 604 int elf_rebuild_rela_section(struct section *sec)
 605 {
 606         struct rela *rela;
 607         int nr, idx = 0, size;
 608         GElf_Rela *relas;
 609
 610         nr = 0;
 611         list_for_each_entry(rela, &sec->rela_list, list)
 612                 nr++;
 613
 614         size = nr * sizeof(*relas);
 615         relas = malloc(size);
 616         if (!relas) {
 617                 perror("malloc");
 618                 return -1;
 619         }
 620
 621         sec->data->d_buf = relas;
 622         sec->data->d_size = size;
 623
 624         sec->sh.sh_size = size;
 625
 626         idx = 0;
 627         list_for_each_entry(rela, &sec->rela_list, list) {
 628                 relas[idx].r_offset = rela->offset;
 629                 relas[idx].r_addend = rela->addend;
 630                 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
 631                 idx++;
 632         }
 633
 634         return 0;
 635 }
 636
 637 int elf_write(struct elf *elf)
 638 {
 639         struct section *sec;
 640         Elf_Scn *s;
 641
 642         /* Update section headers for changed sections: */
 643         list_for_each_entry(sec, &elf->sections, list) {
 644                 if (sec->changed) {
 645                         s = elf_getscn(elf->elf, sec->idx);
 646                         if (!s) {
 647                                 WARN_ELF("elf_getscn");
 648                                 return -1;
 649                         }
 650                         if (!gelf_update_shdr(s, &sec->sh)) {
 651                                 WARN_ELF("gelf_update_shdr");
 652                                 return -1;
 653                         }
 654                 }
 655         }
 656
 657         /* Make sure the new section header entries get updated properly. */
 658         elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
 659
 660         /* Write all changes to the file. */
 661         if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
 662                 WARN_ELF("elf_update");
 663                 return -1;
 664         }
 665
 666         return 0;
 667 }
 668
 669 void elf_close(struct elf *elf)
 670 {
 671         struct section *sec, *tmpsec;
 672         struct symbol *sym, *tmpsym;
 673         struct rela *rela, *tmprela;
 674
 675         if (elf->elf)
 676                 elf_end(elf->elf);
 677
 678         if (elf->fd > 0)
 679                 close(elf->fd);
 680
 681         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
 682                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
 683                         list_del(&sym->list);
 684                         hash_del(&sym->hash);
 685                         free(sym);
 686                 }
 687                 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
 688                         list_del(&rela->list);
 689                         hash_del(&rela->hash);
 690                         free(rela);
 691                 }
 692                 list_del(&sec->list);
 693                 free(sec);
 694         }
 695
 696         free(elf);
 697 }