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 <[email protected]>
   6  * Copyright (C) 2014 Seth Jennings <[email protected]>
   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 struct section *find_section_by_name(struct elf *elf, const char *name)
  41 {
  42         struct section *sec;
  43
  44         list_for_each_entry(sec, &elf->sections, list)
  45                 if (!strcmp(sec->name, name))
  46                         return sec;
  47
  48         return NULL;
  49 }
  50
  51 static struct section *find_section_by_index(struct elf *elf,
  52                                              unsigned int idx)
  53 {
  54         struct section *sec;
  55
  56         list_for_each_entry(sec, &elf->sections, list)
  57                 if (sec->idx == idx)
  58                         return sec;
  59
  60         return NULL;
  61 }
  62
  63 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
  64 {
  65         struct section *sec;
  66         struct symbol *sym;
  67
  68         list_for_each_entry(sec, &elf->sections, list)
  69                 hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
  70                         if (sym->idx == idx)
  71                                 return sym;
  72
  73         return NULL;
  74 }
  75
  76 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
  77 {
  78         struct symbol *sym;
  79
  80         list_for_each_entry(sym, &sec->symbol_list, list)
  81                 if (sym->type != STT_SECTION &&
  82                     sym->offset == offset)
  83                         return sym;
  84
  85         return NULL;
  86 }
  87
  88 struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
  89                                      unsigned int len)
  90 {
  91         struct rela *rela;
  92         unsigned long o;
  93
  94         if (!sec->rela)
  95                 return NULL;
  96
  97         for (o = offset; o < offset + len; o++)
  98                 hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
  99                         if (rela->offset == o)
 100                                 return rela;
 101
 102         return NULL;
 103 }
 104
 105 struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
 106 {
 107         return find_rela_by_dest_range(sec, offset, 1);
 108 }
 109
 110 struct symbol *find_containing_func(struct section *sec, unsigned long offset)
 111 {
 112         struct symbol *func;
 113
 114         list_for_each_entry(func, &sec->symbol_list, list)
 115                 if (func->type == STT_FUNC && offset >= func->offset &&
 116                     offset < func->offset + func->len)
 117                         return func;
 118
 119         return NULL;
 120 }
 121
 122 static int read_sections(struct elf *elf)
 123 {
 124         Elf_Scn *s = NULL;
 125         struct section *sec;
 126         size_t shstrndx, sections_nr;
 127         int i;
 128
 129         if (elf_getshdrnum(elf->elf, &sections_nr)) {
 130                 perror("elf_getshdrnum");
 131                 return -1;
 132         }
 133
 134         if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
 135                 perror("elf_getshdrstrndx");
 136                 return -1;
 137         }
 138
 139         for (i = 0; i < sections_nr; i++) {
 140                 sec = malloc(sizeof(*sec));
 141                 if (!sec) {
 142                         perror("malloc");
 143                         return -1;
 144                 }
 145                 memset(sec, 0, sizeof(*sec));
 146
 147                 INIT_LIST_HEAD(&sec->symbol_list);
 148                 INIT_LIST_HEAD(&sec->rela_list);
 149                 hash_init(sec->rela_hash);
 150                 hash_init(sec->symbol_hash);
 151
 152                 list_add_tail(&sec->list, &elf->sections);
 153
 154                 s = elf_getscn(elf->elf, i);
 155                 if (!s) {
 156                         perror("elf_getscn");
 157                         return -1;
 158                 }
 159
 160                 sec->idx = elf_ndxscn(s);
 161
 162                 if (!gelf_getshdr(s, &sec->sh)) {
 163                         perror("gelf_getshdr");
 164                         return -1;
 165                 }
 166
 167                 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
 168                 if (!sec->name) {
 169                         perror("elf_strptr");
 170                         return -1;
 171                 }
 172
 173                 sec->elf_data = elf_getdata(s, NULL);
 174                 if (!sec->elf_data) {
 175                         perror("elf_getdata");
 176                         return -1;
 177                 }
 178
 179                 if (sec->elf_data->d_off != 0 ||
 180                     sec->elf_data->d_size != sec->sh.sh_size) {
 181                         WARN("unexpected data attributes for %s", sec->name);
 182                         return -1;
 183                 }
 184
 185                 sec->data = (unsigned long)sec->elf_data->d_buf;
 186                 sec->len = sec->elf_data->d_size;
 187         }
 188
 189         /* sanity check, one more call to elf_nextscn() should return NULL */
 190         if (elf_nextscn(elf->elf, s)) {
 191                 WARN("section entry mismatch");
 192                 return -1;
 193         }
 194
 195         return 0;
 196 }
 197
 198 static int read_symbols(struct elf *elf)
 199 {
 200         struct section *symtab;
 201         struct symbol *sym;
 202         struct list_head *entry, *tmp;
 203         int symbols_nr, i;
 204
 205         symtab = find_section_by_name(elf, ".symtab");
 206         if (!symtab) {
 207                 WARN("missing symbol table");
 208                 return -1;
 209         }
 210
 211         symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 212
 213         for (i = 0; i < symbols_nr; i++) {
 214                 sym = malloc(sizeof(*sym));
 215                 if (!sym) {
 216                         perror("malloc");
 217                         return -1;
 218                 }
 219                 memset(sym, 0, sizeof(*sym));
 220
 221                 sym->idx = i;
 222
 223                 if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) {
 224                         perror("gelf_getsym");
 225                         goto err;
 226                 }
 227
 228                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 229                                        sym->sym.st_name);
 230                 if (!sym->name) {
 231                         perror("elf_strptr");
 232                         goto err;
 233                 }
 234
 235                 sym->type = GELF_ST_TYPE(sym->sym.st_info);
 236                 sym->bind = GELF_ST_BIND(sym->sym.st_info);
 237
 238                 if (sym->sym.st_shndx > SHN_UNDEF &&
 239                     sym->sym.st_shndx < SHN_LORESERVE) {
 240                         sym->sec = find_section_by_index(elf,
 241                                                          sym->sym.st_shndx);
 242                         if (!sym->sec) {
 243                                 WARN("couldn't find section for symbol %s",
 244                                      sym->name);
 245                                 goto err;
 246                         }
 247                         if (sym->type == STT_SECTION) {
 248                                 sym->name = sym->sec->name;
 249                                 sym->sec->sym = sym;
 250                         }
 251                 } else
 252                         sym->sec = find_section_by_index(elf, 0);
 253
 254                 sym->offset = sym->sym.st_value;
 255                 sym->len = sym->sym.st_size;
 256
 257                 /* sorted insert into a per-section list */
 258                 entry = &sym->sec->symbol_list;
 259                 list_for_each_prev(tmp, &sym->sec->symbol_list) {
 260                         struct symbol *s;
 261
 262                         s = list_entry(tmp, struct symbol, list);
 263
 264                         if (sym->offset > s->offset) {
 265                                 entry = tmp;
 266                                 break;
 267                         }
 268
 269                         if (sym->offset == s->offset && sym->len >= s->len) {
 270                                 entry = tmp;
 271                                 break;
 272                         }
 273                 }
 274                 list_add(&sym->list, entry);
 275                 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
 276         }
 277
 278         return 0;
 279
 280 err:
 281         free(sym);
 282         return -1;
 283 }
 284
 285 static int read_relas(struct elf *elf)
 286 {
 287         struct section *sec;
 288         struct rela *rela;
 289         int i;
 290         unsigned int symndx;
 291
 292         list_for_each_entry(sec, &elf->sections, list) {
 293                 if (sec->sh.sh_type != SHT_RELA)
 294                         continue;
 295
 296                 sec->base = find_section_by_name(elf, sec->name + 5);
 297                 if (!sec->base) {
 298                         WARN("can't find base section for rela section %s",
 299                              sec->name);
 300                         return -1;
 301                 }
 302
 303                 sec->base->rela = sec;
 304
 305                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 306                         rela = malloc(sizeof(*rela));
 307                         if (!rela) {
 308                                 perror("malloc");
 309                                 return -1;
 310                         }
 311                         memset(rela, 0, sizeof(*rela));
 312
 313                         if (!gelf_getrela(sec->elf_data, i, &rela->rela)) {
 314                                 perror("gelf_getrela");
 315                                 return -1;
 316                         }
 317
 318                         rela->type = GELF_R_TYPE(rela->rela.r_info);
 319                         rela->addend = rela->rela.r_addend;
 320                         rela->offset = rela->rela.r_offset;
 321                         symndx = GELF_R_SYM(rela->rela.r_info);
 322                         rela->sym = find_symbol_by_index(elf, symndx);
 323                         if (!rela->sym) {
 324                                 WARN("can't find rela entry symbol %d for %s",
 325                                      symndx, sec->name);
 326                                 return -1;
 327                         }
 328
 329                         list_add_tail(&rela->list, &sec->rela_list);
 330                         hash_add(sec->rela_hash, &rela->hash, rela->offset);
 331
 332                 }
 333         }
 334
 335         return 0;
 336 }
 337
 338 struct elf *elf_open(const char *name)
 339 {
 340         struct elf *elf;
 341
 342         elf_version(EV_CURRENT);
 343
 344         elf = malloc(sizeof(*elf));
 345         if (!elf) {
 346                 perror("malloc");
 347                 return NULL;
 348         }
 349         memset(elf, 0, sizeof(*elf));
 350
 351         INIT_LIST_HEAD(&elf->sections);
 352
 353         elf->name = strdup(name);
 354         if (!elf->name) {
 355                 perror("strdup");
 356                 goto err;
 357         }
 358
 359         elf->fd = open(name, O_RDONLY);
 360         if (elf->fd == -1) {
 361                 perror("open");
 362                 goto err;
 363         }
 364
 365         elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL);
 366         if (!elf->elf) {
 367                 perror("elf_begin");
 368                 goto err;
 369         }
 370
 371         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 372                 perror("gelf_getehdr");
 373                 goto err;
 374         }
 375
 376         if (read_sections(elf))
 377                 goto err;
 378
 379         if (read_symbols(elf))
 380                 goto err;
 381
 382         if (read_relas(elf))
 383                 goto err;
 384
 385         return elf;
 386
 387 err:
 388         elf_close(elf);
 389         return NULL;
 390 }
 391
 392 void elf_close(struct elf *elf)
 393 {
 394         struct section *sec, *tmpsec;
 395         struct symbol *sym, *tmpsym;
 396         struct rela *rela, *tmprela;
 397
 398         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
 399                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
 400                         list_del(&sym->list);
 401                         hash_del(&sym->hash);
 402                         free(sym);
 403                 }
 404                 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
 405                         list_del(&rela->list);
 406                         hash_del(&rela->hash);
 407                         free(rela);
 408                 }
 409                 list_del(&sec->list);
 410                 free(sec);
 411         }
 412         if (elf->name)
 413                 free(elf->name);
 414         if (elf->fd > 0)
 415                 close(elf->fd);
 416         if (elf->elf)
 417                 elf_end(elf->elf);
 418         free(elf);
 419 }