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