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;
 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                 /*
 230                  * A missing symbol table is actually possible if it's an empty
 231                  * .o file.  This can happen for thunk_64.o.
 232                  */
 233                 return 0;
 234         }
 235
 236         symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 237
 238         for (i = 0; i < symbols_nr; i++) {
 239                 sym = malloc(sizeof(*sym));
 240                 if (!sym) {
 241                         perror("malloc");
 242                         return -1;
 243                 }
 244                 memset(sym, 0, sizeof(*sym));
 245
 246                 sym->idx = i;
 247
 248                 if (!gelf_getsym(symtab->data, i, &sym->sym)) {
 249                         WARN_ELF("gelf_getsym");
 250                         goto err;
 251                 }
 252
 253                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 254                                        sym->sym.st_name);
 255                 if (!sym->name) {
 256                         WARN_ELF("elf_strptr");
 257                         goto err;
 258                 }
 259
 260                 sym->type = GELF_ST_TYPE(sym->sym.st_info);
 261                 sym->bind = GELF_ST_BIND(sym->sym.st_info);
 262
 263                 if (sym->sym.st_shndx > SHN_UNDEF &&
 264                     sym->sym.st_shndx < SHN_LORESERVE) {
 265                         sym->sec = find_section_by_index(elf,
 266                                                          sym->sym.st_shndx);
 267                         if (!sym->sec) {
 268                                 WARN("couldn't find section for symbol %s",
 269                                      sym->name);
 270                                 goto err;
 271                         }
 272                         if (sym->type == STT_SECTION) {
 273                                 sym->name = sym->sec->name;
 274                                 sym->sec->sym = sym;
 275                         }
 276                 } else
 277                         sym->sec = find_section_by_index(elf, 0);
 278
 279                 sym->offset = sym->sym.st_value;
 280                 sym->len = sym->sym.st_size;
 281
 282                 /* sorted insert into a per-section list */
 283                 entry = &sym->sec->symbol_list;
 284                 list_for_each_prev(tmp, &sym->sec->symbol_list) {
 285                         struct symbol *s;
 286
 287                         s = list_entry(tmp, struct symbol, list);
 288
 289                         if (sym->offset > s->offset) {
 290                                 entry = tmp;
 291                                 break;
 292                         }
 293
 294                         if (sym->offset == s->offset && sym->len >= s->len) {
 295                                 entry = tmp;
 296                                 break;
 297                         }
 298                 }
 299                 list_add(&sym->list, entry);
 300                 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
 301         }
 302
 303         /* Create parent/child links for any cold subfunctions */
 304         list_for_each_entry(sec, &elf->sections, list) {
 305                 list_for_each_entry(sym, &sec->symbol_list, list) {
 306                         char pname[MAX_NAME_LEN + 1];
 307                         size_t pnamelen;
 308                         if (sym->type != STT_FUNC)
 309                                 continue;
 310                         sym->pfunc = sym->cfunc = sym;
 311                         coldstr = strstr(sym->name, ".cold");
 312                         if (!coldstr)
 313                                 continue;
 314
 315                         pnamelen = coldstr - sym->name;
 316                         if (pnamelen > MAX_NAME_LEN) {
 317                                 WARN("%s(): parent function name exceeds maximum length of %d characters",
 318                                      sym->name, MAX_NAME_LEN);
 319                                 return -1;
 320                         }
 321
 322                         strncpy(pname, sym->name, pnamelen);
 323                         pname[pnamelen] = '\0';
 324                         pfunc = find_symbol_by_name(elf, pname);
 325
 326                         if (!pfunc) {
 327                                 WARN("%s(): can't find parent function",
 328                                      sym->name);
 329                                 return -1;
 330                         }
 331
 332                         sym->pfunc = pfunc;
 333                         pfunc->cfunc = sym;
 334
 335                         /*
 336                          * Unfortunately, -fnoreorder-functions puts the child
 337                          * inside the parent.  Remove the overlap so we can
 338                          * have sane assumptions.
 339                          *
 340                          * Note that pfunc->len now no longer matches
 341                          * pfunc->sym.st_size.
 342                          */
 343                         if (sym->sec == pfunc->sec &&
 344                             sym->offset >= pfunc->offset &&
 345                             sym->offset + sym->len == pfunc->offset + pfunc->len) {
 346                                 pfunc->len -= sym->len;
 347                         }
 348                 }
 349         }
 350
 351         return 0;
 352
 353 err:
 354         free(sym);
 355         return -1;
 356 }
 357
 358 static int read_relas(struct elf *elf)
 359 {
 360         struct section *sec;
 361         struct rela *rela;
 362         int i;
 363         unsigned int symndx;
 364
 365         list_for_each_entry(sec, &elf->sections, list) {
 366                 if (sec->sh.sh_type != SHT_RELA)
 367                         continue;
 368
 369                 sec->base = find_section_by_name(elf, sec->name + 5);
 370                 if (!sec->base) {
 371                         WARN("can't find base section for rela section %s",
 372                              sec->name);
 373                         return -1;
 374                 }
 375
 376                 sec->base->rela = sec;
 377
 378                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 379                         rela = malloc(sizeof(*rela));
 380                         if (!rela) {
 381                                 perror("malloc");
 382                                 return -1;
 383                         }
 384                         memset(rela, 0, sizeof(*rela));
 385
 386                         if (!gelf_getrela(sec->data, i, &rela->rela)) {
 387                                 WARN_ELF("gelf_getrela");
 388                                 return -1;
 389                         }
 390
 391                         rela->type = GELF_R_TYPE(rela->rela.r_info);
 392                         rela->addend = rela->rela.r_addend;
 393                         rela->offset = rela->rela.r_offset;
 394                         symndx = GELF_R_SYM(rela->rela.r_info);
 395                         rela->sym = find_symbol_by_index(elf, symndx);
 396                         if (!rela->sym) {
 397                                 WARN("can't find rela entry symbol %d for %s",
 398                                      symndx, sec->name);
 399                                 return -1;
 400                         }
 401
 402                         list_add_tail(&rela->list, &sec->rela_list);
 403                         hash_add(sec->rela_hash, &rela->hash, rela->offset);
 404
 405                 }
 406         }
 407
 408         return 0;
 409 }
 410
 411 struct elf *elf_open(const char *name, int flags)
 412 {
 413         struct elf *elf;
 414         Elf_Cmd cmd;
 415
 416         elf_version(EV_CURRENT);
 417
 418         elf = malloc(sizeof(*elf));
 419         if (!elf) {
 420                 perror("malloc");
 421                 return NULL;
 422         }
 423         memset(elf, 0, sizeof(*elf));
 424
 425         INIT_LIST_HEAD(&elf->sections);
 426
 427         elf->fd = open(name, flags);
 428         if (elf->fd == -1) {
 429                 fprintf(stderr, "objtool: Can't open '%s': %s\n",
 430                         name, strerror(errno));
 431                 goto err;
 432         }
 433
 434         if ((flags & O_ACCMODE) == O_RDONLY)
 435                 cmd = ELF_C_READ_MMAP;
 436         else if ((flags & O_ACCMODE) == O_RDWR)
 437                 cmd = ELF_C_RDWR;
 438         else /* O_WRONLY */
 439                 cmd = ELF_C_WRITE;
 440
 441         elf->elf = elf_begin(elf->fd, cmd, NULL);
 442         if (!elf->elf) {
 443                 WARN_ELF("elf_begin");
 444                 goto err;
 445         }
 446
 447         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 448                 WARN_ELF("gelf_getehdr");
 449                 goto err;
 450         }
 451
 452         if (read_sections(elf))
 453                 goto err;
 454
 455         if (read_symbols(elf))
 456                 goto err;
 457
 458         if (read_relas(elf))
 459                 goto err;
 460
 461         return elf;
 462
 463 err:
 464         elf_close(elf);
 465         return NULL;
 466 }
 467
 468 struct section *elf_create_section(struct elf *elf, const char *name,
 469                                    size_t entsize, int nr)
 470 {
 471         struct section *sec, *shstrtab;
 472         size_t size = entsize * nr;
 473         struct Elf_Scn *s;
 474         Elf_Data *data;
 475
 476         sec = malloc(sizeof(*sec));
 477         if (!sec) {
 478                 perror("malloc");
 479                 return NULL;
 480         }
 481         memset(sec, 0, sizeof(*sec));
 482
 483         INIT_LIST_HEAD(&sec->symbol_list);
 484         INIT_LIST_HEAD(&sec->rela_list);
 485         hash_init(sec->rela_hash);
 486         hash_init(sec->symbol_hash);
 487
 488         list_add_tail(&sec->list, &elf->sections);
 489
 490         s = elf_newscn(elf->elf);
 491         if (!s) {
 492                 WARN_ELF("elf_newscn");
 493                 return NULL;
 494         }
 495
 496         sec->name = strdup(name);
 497         if (!sec->name) {
 498                 perror("strdup");
 499                 return NULL;
 500         }
 501
 502         sec->idx = elf_ndxscn(s);
 503         sec->len = size;
 504         sec->changed = true;
 505
 506         sec->data = elf_newdata(s);
 507         if (!sec->data) {
 508                 WARN_ELF("elf_newdata");
 509                 return NULL;
 510         }
 511
 512         sec->data->d_size = size;
 513         sec->data->d_align = 1;
 514
 515         if (size) {
 516                 sec->data->d_buf = malloc(size);
 517                 if (!sec->data->d_buf) {
 518                         perror("malloc");
 519                         return NULL;
 520                 }
 521                 memset(sec->data->d_buf, 0, size);
 522         }
 523
 524         if (!gelf_getshdr(s, &sec->sh)) {
 525                 WARN_ELF("gelf_getshdr");
 526                 return NULL;
 527         }
 528
 529         sec->sh.sh_size = size;
 530         sec->sh.sh_entsize = entsize;
 531         sec->sh.sh_type = SHT_PROGBITS;
 532         sec->sh.sh_addralign = 1;
 533         sec->sh.sh_flags = SHF_ALLOC;
 534
 535
 536         /* Add section name to .shstrtab */
 537         shstrtab = find_section_by_name(elf, ".shstrtab");
 538         if (!shstrtab) {
 539                 WARN("can't find .shstrtab section");
 540                 return NULL;
 541         }
 542
 543         s = elf_getscn(elf->elf, shstrtab->idx);
 544         if (!s) {
 545                 WARN_ELF("elf_getscn");
 546                 return NULL;
 547         }
 548
 549         data = elf_newdata(s);
 550         if (!data) {
 551                 WARN_ELF("elf_newdata");
 552                 return NULL;
 553         }
 554
 555         data->d_buf = sec->name;
 556         data->d_size = strlen(name) + 1;
 557         data->d_align = 1;
 558
 559         sec->sh.sh_name = shstrtab->len;
 560
 561         shstrtab->len += strlen(name) + 1;
 562         shstrtab->changed = true;
 563
 564         return sec;
 565 }
 566
 567 struct section *elf_create_rela_section(struct elf *elf, struct section *base)
 568 {
 569         char *relaname;
 570         struct section *sec;
 571
 572         relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
 573         if (!relaname) {
 574                 perror("malloc");
 575                 return NULL;
 576         }
 577         strcpy(relaname, ".rela");
 578         strcat(relaname, base->name);
 579
 580         sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
 581         free(relaname);
 582         if (!sec)
 583                 return NULL;
 584
 585         base->rela = sec;
 586         sec->base = base;
 587
 588         sec->sh.sh_type = SHT_RELA;
 589         sec->sh.sh_addralign = 8;
 590         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 591         sec->sh.sh_info = base->idx;
 592         sec->sh.sh_flags = SHF_INFO_LINK;
 593
 594         return sec;
 595 }
 596
 597 int elf_rebuild_rela_section(struct section *sec)
 598 {
 599         struct rela *rela;
 600         int nr, idx = 0, size;
 601         GElf_Rela *relas;
 602
 603         nr = 0;
 604         list_for_each_entry(rela, &sec->rela_list, list)
 605                 nr++;
 606
 607         size = nr * sizeof(*relas);
 608         relas = malloc(size);
 609         if (!relas) {
 610                 perror("malloc");
 611                 return -1;
 612         }
 613
 614         sec->data->d_buf = relas;
 615         sec->data->d_size = size;
 616
 617         sec->sh.sh_size = size;
 618
 619         idx = 0;
 620         list_for_each_entry(rela, &sec->rela_list, list) {
 621                 relas[idx].r_offset = rela->offset;
 622                 relas[idx].r_addend = rela->addend;
 623                 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
 624                 idx++;
 625         }
 626
 627         return 0;
 628 }
 629
 630 int elf_write(struct elf *elf)
 631 {
 632         struct section *sec;
 633         Elf_Scn *s;
 634
 635         /* Update section headers for changed sections: */
 636         list_for_each_entry(sec, &elf->sections, list) {
 637                 if (sec->changed) {
 638                         s = elf_getscn(elf->elf, sec->idx);
 639                         if (!s) {
 640                                 WARN_ELF("elf_getscn");
 641                                 return -1;
 642                         }
 643                         if (!gelf_update_shdr(s, &sec->sh)) {
 644                                 WARN_ELF("gelf_update_shdr");
 645                                 return -1;
 646                         }
 647                 }
 648         }
 649
 650         /* Make sure the new section header entries get updated properly. */
 651         elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
 652
 653         /* Write all changes to the file. */
 654         if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
 655                 WARN_ELF("elf_update");
 656                 return -1;
 657         }
 658
 659         return 0;
 660 }
 661
 662 void elf_close(struct elf *elf)
 663 {
 664         struct section *sec, *tmpsec;
 665         struct symbol *sym, *tmpsym;
 666         struct rela *rela, *tmprela;
 667
 668         if (elf->elf)
 669                 elf_end(elf->elf);
 670
 671         if (elf->fd > 0)
 672                 close(elf->fd);
 673
 674         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
 675                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
 676                         list_del(&sym->list);
 677                         hash_del(&sym->hash);
 678                         free(sym);
 679                 }
 680                 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
 681                         list_del(&rela->list);
 682                         hash_del(&rela->hash);
 683                         free(rela);
 684                 }
 685                 list_del(&sec->list);
 686                 free(sec);
 687         }
 688
 689         free(elf);
 690 }