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
  30 #include "elf.h"
  31 #include "warn.h"
  32
  33 /*
  34  * Fallback for systems without this "read, mmaping if possible" cmd.
  35  */
  36 #ifndef ELF_C_READ_MMAP
  37 #define ELF_C_READ_MMAP ELF_C_READ
  38 #endif
  39
  40 #define WARN_ELF(format, ...)                                   \
  41         WARN(format ": %s", ##__VA_ARGS__, elf_errmsg(-1))
  42
  43 struct section *find_section_by_name(struct elf *elf, const char *name)
  44 {
  45         struct section *sec;
  46
  47         list_for_each_entry(sec, &elf->sections, list)
  48                 if (!strcmp(sec->name, name))
  49                         return sec;
  50
  51         return NULL;
  52 }
  53
  54 static struct section *find_section_by_index(struct elf *elf,
  55                                              unsigned int idx)
  56 {
  57         struct section *sec;
  58
  59         list_for_each_entry(sec, &elf->sections, list)
  60                 if (sec->idx == idx)
  61                         return sec;
  62
  63         return NULL;
  64 }
  65
  66 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
  67 {
  68         struct section *sec;
  69         struct symbol *sym;
  70
  71         list_for_each_entry(sec, &elf->sections, list)
  72                 hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
  73                         if (sym->idx == idx)
  74                                 return sym;
  75
  76         return NULL;
  77 }
  78
  79 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
  80 {
  81         struct symbol *sym;
  82
  83         list_for_each_entry(sym, &sec->symbol_list, list)
  84                 if (sym->type != STT_SECTION &&
  85                     sym->offset == offset)
  86                         return sym;
  87
  88         return NULL;
  89 }
  90
  91 struct symbol *find_symbol_containing(struct section *sec, unsigned long offset)
  92 {
  93         struct symbol *sym;
  94
  95         list_for_each_entry(sym, &sec->symbol_list, list)
  96                 if (sym->type != STT_SECTION &&
  97                     offset >= sym->offset && offset < sym->offset + sym->len)
  98                         return sym;
  99
 100         return NULL;
 101 }
 102
 103 struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
 104                                      unsigned int len)
 105 {
 106         struct rela *rela;
 107         unsigned long o;
 108
 109         if (!sec->rela)
 110                 return NULL;
 111
 112         for (o = offset; o < offset + len; o++)
 113                 hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
 114                         if (rela->offset == o)
 115                                 return rela;
 116
 117         return NULL;
 118 }
 119
 120 struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
 121 {
 122         return find_rela_by_dest_range(sec, offset, 1);
 123 }
 124
 125 struct symbol *find_containing_func(struct section *sec, unsigned long offset)
 126 {
 127         struct symbol *func;
 128
 129         list_for_each_entry(func, &sec->symbol_list, list)
 130                 if (func->type == STT_FUNC && offset >= func->offset &&
 131                     offset < func->offset + func->len)
 132                         return func;
 133
 134         return NULL;
 135 }
 136
 137 static int read_sections(struct elf *elf)
 138 {
 139         Elf_Scn *s = NULL;
 140         struct section *sec;
 141         size_t shstrndx, sections_nr;
 142         int i;
 143
 144         if (elf_getshdrnum(elf->elf, &sections_nr)) {
 145                 WARN_ELF("elf_getshdrnum");
 146                 return -1;
 147         }
 148
 149         if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
 150                 WARN_ELF("elf_getshdrstrndx");
 151                 return -1;
 152         }
 153
 154         for (i = 0; i < sections_nr; i++) {
 155                 sec = malloc(sizeof(*sec));
 156                 if (!sec) {
 157                         perror("malloc");
 158                         return -1;
 159                 }
 160                 memset(sec, 0, sizeof(*sec));
 161
 162                 INIT_LIST_HEAD(&sec->symbol_list);
 163                 INIT_LIST_HEAD(&sec->rela_list);
 164                 hash_init(sec->rela_hash);
 165                 hash_init(sec->symbol_hash);
 166
 167                 list_add_tail(&sec->list, &elf->sections);
 168
 169                 s = elf_getscn(elf->elf, i);
 170                 if (!s) {
 171                         WARN_ELF("elf_getscn");
 172                         return -1;
 173                 }
 174
 175                 sec->idx = elf_ndxscn(s);
 176
 177                 if (!gelf_getshdr(s, &sec->sh)) {
 178                         WARN_ELF("gelf_getshdr");
 179                         return -1;
 180                 }
 181
 182                 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
 183                 if (!sec->name) {
 184                         WARN_ELF("elf_strptr");
 185                         return -1;
 186                 }
 187
 188                 sec->data = elf_getdata(s, NULL);
 189                 if (!sec->data) {
 190                         WARN_ELF("elf_getdata");
 191                         return -1;
 192                 }
 193
 194                 if (sec->data->d_off != 0 ||
 195                     sec->data->d_size != sec->sh.sh_size) {
 196                         WARN("unexpected data attributes for %s", sec->name);
 197                         return -1;
 198                 }
 199
 200                 sec->len = sec->data->d_size;
 201         }
 202
 203         /* sanity check, one more call to elf_nextscn() should return NULL */
 204         if (elf_nextscn(elf->elf, s)) {
 205                 WARN("section entry mismatch");
 206                 return -1;
 207         }
 208
 209         return 0;
 210 }
 211
 212 static int read_symbols(struct elf *elf)
 213 {
 214         struct section *symtab;
 215         struct symbol *sym;
 216         struct list_head *entry, *tmp;
 217         int symbols_nr, i;
 218
 219         symtab = find_section_by_name(elf, ".symtab");
 220         if (!symtab) {
 221                 WARN("missing symbol table");
 222                 return -1;
 223         }
 224
 225         symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 226
 227         for (i = 0; i < symbols_nr; i++) {
 228                 sym = malloc(sizeof(*sym));
 229                 if (!sym) {
 230                         perror("malloc");
 231                         return -1;
 232                 }
 233                 memset(sym, 0, sizeof(*sym));
 234
 235                 sym->idx = i;
 236
 237                 if (!gelf_getsym(symtab->data, i, &sym->sym)) {
 238                         WARN_ELF("gelf_getsym");
 239                         goto err;
 240                 }
 241
 242                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 243                                        sym->sym.st_name);
 244                 if (!sym->name) {
 245                         WARN_ELF("elf_strptr");
 246                         goto err;
 247                 }
 248
 249                 sym->type = GELF_ST_TYPE(sym->sym.st_info);
 250                 sym->bind = GELF_ST_BIND(sym->sym.st_info);
 251
 252                 if (sym->sym.st_shndx > SHN_UNDEF &&
 253                     sym->sym.st_shndx < SHN_LORESERVE) {
 254                         sym->sec = find_section_by_index(elf,
 255                                                          sym->sym.st_shndx);
 256                         if (!sym->sec) {
 257                                 WARN("couldn't find section for symbol %s",
 258                                      sym->name);
 259                                 goto err;
 260                         }
 261                         if (sym->type == STT_SECTION) {
 262                                 sym->name = sym->sec->name;
 263                                 sym->sec->sym = sym;
 264                         }
 265                 } else
 266                         sym->sec = find_section_by_index(elf, 0);
 267
 268                 sym->offset = sym->sym.st_value;
 269                 sym->len = sym->sym.st_size;
 270
 271                 /* sorted insert into a per-section list */
 272                 entry = &sym->sec->symbol_list;
 273                 list_for_each_prev(tmp, &sym->sec->symbol_list) {
 274                         struct symbol *s;
 275
 276                         s = list_entry(tmp, struct symbol, list);
 277
 278                         if (sym->offset > s->offset) {
 279                                 entry = tmp;
 280                                 break;
 281                         }
 282
 283                         if (sym->offset == s->offset && sym->len >= s->len) {
 284                                 entry = tmp;
 285                                 break;
 286                         }
 287                 }
 288                 list_add(&sym->list, entry);
 289                 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
 290         }
 291
 292         return 0;
 293
 294 err:
 295         free(sym);
 296         return -1;
 297 }
 298
 299 static int read_relas(struct elf *elf)
 300 {
 301         struct section *sec;
 302         struct rela *rela;
 303         int i;
 304         unsigned int symndx;
 305
 306         list_for_each_entry(sec, &elf->sections, list) {
 307                 if (sec->sh.sh_type != SHT_RELA)
 308                         continue;
 309
 310                 sec->base = find_section_by_name(elf, sec->name + 5);
 311                 if (!sec->base) {
 312                         WARN("can't find base section for rela section %s",
 313                              sec->name);
 314                         return -1;
 315                 }
 316
 317                 sec->base->rela = sec;
 318
 319                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 320                         rela = malloc(sizeof(*rela));
 321                         if (!rela) {
 322                                 perror("malloc");
 323                                 return -1;
 324                         }
 325                         memset(rela, 0, sizeof(*rela));
 326
 327                         if (!gelf_getrela(sec->data, i, &rela->rela)) {
 328                                 WARN_ELF("gelf_getrela");
 329                                 return -1;
 330                         }
 331
 332                         rela->type = GELF_R_TYPE(rela->rela.r_info);
 333                         rela->addend = rela->rela.r_addend;
 334                         rela->offset = rela->rela.r_offset;
 335                         symndx = GELF_R_SYM(rela->rela.r_info);
 336                         rela->sym = find_symbol_by_index(elf, symndx);
 337                         if (!rela->sym) {
 338                                 WARN("can't find rela entry symbol %d for %s",
 339                                      symndx, sec->name);
 340                                 return -1;
 341                         }
 342
 343                         list_add_tail(&rela->list, &sec->rela_list);
 344                         hash_add(sec->rela_hash, &rela->hash, rela->offset);
 345
 346                 }
 347         }
 348
 349         return 0;
 350 }
 351
 352 struct elf *elf_open(const char *name)
 353 {
 354         struct elf *elf;
 355
 356         elf_version(EV_CURRENT);
 357
 358         elf = malloc(sizeof(*elf));
 359         if (!elf) {
 360                 perror("malloc");
 361                 return NULL;
 362         }
 363         memset(elf, 0, sizeof(*elf));
 364
 365         INIT_LIST_HEAD(&elf->sections);
 366
 367         elf->fd = open(name, O_RDONLY);
 368         if (elf->fd == -1) {
 369                 perror("open");
 370                 goto err;
 371         }
 372
 373         elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL);
 374         if (!elf->elf) {
 375                 WARN_ELF("elf_begin");
 376                 goto err;
 377         }
 378
 379         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 380                 WARN_ELF("gelf_getehdr");
 381                 goto err;
 382         }
 383
 384         if (read_sections(elf))
 385                 goto err;
 386
 387         if (read_symbols(elf))
 388                 goto err;
 389
 390         if (read_relas(elf))
 391                 goto err;
 392
 393         return elf;
 394
 395 err:
 396         elf_close(elf);
 397         return NULL;
 398 }
 399
 400 void elf_close(struct elf *elf)
 401 {
 402         struct section *sec, *tmpsec;
 403         struct symbol *sym, *tmpsym;
 404         struct rela *rela, *tmprela;
 405
 406         if (elf->elf)
 407                 elf_end(elf->elf);
 408
 409         if (elf->fd > 0)
 410                 close(elf->fd);
 411
 412         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
 413                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
 414                         list_del(&sym->list);
 415                         hash_del(&sym->hash);
 416                         free(sym);
 417                 }
 418                 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
 419                         list_del(&rela->list);
 420                         hash_del(&rela->hash);
 421                         free(rela);
 422                 }
 423                 list_del(&sec->list);
 424                 free(sec);
 425         }
 426
 427         free(elf);
 428 }