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 symbol *find_symbol_containing(struct section *sec, unsigned long offset)
  89 {
  90         struct symbol *sym;
  91
  92         list_for_each_entry(sym, &sec->symbol_list, list)
  93                 if (sym->type != STT_SECTION &&
  94                     offset >= sym->offset && offset < sym->offset + sym->len)
  95                         return sym;
  96
  97         return NULL;
  98 }
  99
 100 struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
 101                                      unsigned int len)
 102 {
 103         struct rela *rela;
 104         unsigned long o;
 105
 106         if (!sec->rela)
 107                 return NULL;
 108
 109         for (o = offset; o < offset + len; o++)
 110                 hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
 111                         if (rela->offset == o)
 112                                 return rela;
 113
 114         return NULL;
 115 }
 116
 117 struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
 118 {
 119         return find_rela_by_dest_range(sec, offset, 1);
 120 }
 121
 122 struct symbol *find_containing_func(struct section *sec, unsigned long offset)
 123 {
 124         struct symbol *func;
 125
 126         list_for_each_entry(func, &sec->symbol_list, list)
 127                 if (func->type == STT_FUNC && offset >= func->offset &&
 128                     offset < func->offset + func->len)
 129                         return func;
 130
 131         return NULL;
 132 }
 133
 134 static int read_sections(struct elf *elf)
 135 {
 136         Elf_Scn *s = NULL;
 137         struct section *sec;
 138         size_t shstrndx, sections_nr;
 139         int i;
 140
 141         if (elf_getshdrnum(elf->elf, &sections_nr)) {
 142                 perror("elf_getshdrnum");
 143                 return -1;
 144         }
 145
 146         if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
 147                 perror("elf_getshdrstrndx");
 148                 return -1;
 149         }
 150
 151         for (i = 0; i < sections_nr; i++) {
 152                 sec = malloc(sizeof(*sec));
 153                 if (!sec) {
 154                         perror("malloc");
 155                         return -1;
 156                 }
 157                 memset(sec, 0, sizeof(*sec));
 158
 159                 INIT_LIST_HEAD(&sec->symbol_list);
 160                 INIT_LIST_HEAD(&sec->rela_list);
 161                 hash_init(sec->rela_hash);
 162                 hash_init(sec->symbol_hash);
 163
 164                 list_add_tail(&sec->list, &elf->sections);
 165
 166                 s = elf_getscn(elf->elf, i);
 167                 if (!s) {
 168                         perror("elf_getscn");
 169                         return -1;
 170                 }
 171
 172                 sec->idx = elf_ndxscn(s);
 173
 174                 if (!gelf_getshdr(s, &sec->sh)) {
 175                         perror("gelf_getshdr");
 176                         return -1;
 177                 }
 178
 179                 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
 180                 if (!sec->name) {
 181                         perror("elf_strptr");
 182                         return -1;
 183                 }
 184
 185                 sec->elf_data = elf_getdata(s, NULL);
 186                 if (!sec->elf_data) {
 187                         perror("elf_getdata");
 188                         return -1;
 189                 }
 190
 191                 if (sec->elf_data->d_off != 0 ||
 192                     sec->elf_data->d_size != sec->sh.sh_size) {
 193                         WARN("unexpected data attributes for %s", sec->name);
 194                         return -1;
 195                 }
 196
 197                 sec->data = (unsigned long)sec->elf_data->d_buf;
 198                 sec->len = sec->elf_data->d_size;
 199         }
 200
 201         /* sanity check, one more call to elf_nextscn() should return NULL */
 202         if (elf_nextscn(elf->elf, s)) {
 203                 WARN("section entry mismatch");
 204                 return -1;
 205         }
 206
 207         return 0;
 208 }
 209
 210 static int read_symbols(struct elf *elf)
 211 {
 212         struct section *symtab;
 213         struct symbol *sym;
 214         struct list_head *entry, *tmp;
 215         int symbols_nr, i;
 216
 217         symtab = find_section_by_name(elf, ".symtab");
 218         if (!symtab) {
 219                 WARN("missing symbol table");
 220                 return -1;
 221         }
 222
 223         symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 224
 225         for (i = 0; i < symbols_nr; i++) {
 226                 sym = malloc(sizeof(*sym));
 227                 if (!sym) {
 228                         perror("malloc");
 229                         return -1;
 230                 }
 231                 memset(sym, 0, sizeof(*sym));
 232
 233                 sym->idx = i;
 234
 235                 if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) {
 236                         perror("gelf_getsym");
 237                         goto err;
 238                 }
 239
 240                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 241                                        sym->sym.st_name);
 242                 if (!sym->name) {
 243                         perror("elf_strptr");
 244                         goto err;
 245                 }
 246
 247                 sym->type = GELF_ST_TYPE(sym->sym.st_info);
 248                 sym->bind = GELF_ST_BIND(sym->sym.st_info);
 249
 250                 if (sym->sym.st_shndx > SHN_UNDEF &&
 251                     sym->sym.st_shndx < SHN_LORESERVE) {
 252                         sym->sec = find_section_by_index(elf,
 253                                                          sym->sym.st_shndx);
 254                         if (!sym->sec) {
 255                                 WARN("couldn't find section for symbol %s",
 256                                      sym->name);
 257                                 goto err;
 258                         }
 259                         if (sym->type == STT_SECTION) {
 260                                 sym->name = sym->sec->name;
 261                                 sym->sec->sym = sym;
 262                         }
 263                 } else
 264                         sym->sec = find_section_by_index(elf, 0);
 265
 266                 sym->offset = sym->sym.st_value;
 267                 sym->len = sym->sym.st_size;
 268
 269                 /* sorted insert into a per-section list */
 270                 entry = &sym->sec->symbol_list;
 271                 list_for_each_prev(tmp, &sym->sec->symbol_list) {
 272                         struct symbol *s;
 273
 274                         s = list_entry(tmp, struct symbol, list);
 275
 276                         if (sym->offset > s->offset) {
 277                                 entry = tmp;
 278                                 break;
 279                         }
 280
 281                         if (sym->offset == s->offset && sym->len >= s->len) {
 282                                 entry = tmp;
 283                                 break;
 284                         }
 285                 }
 286                 list_add(&sym->list, entry);
 287                 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
 288         }
 289
 290         return 0;
 291
 292 err:
 293         free(sym);
 294         return -1;
 295 }
 296
 297 static int read_relas(struct elf *elf)
 298 {
 299         struct section *sec;
 300         struct rela *rela;
 301         int i;
 302         unsigned int symndx;
 303
 304         list_for_each_entry(sec, &elf->sections, list) {
 305                 if (sec->sh.sh_type != SHT_RELA)
 306                         continue;
 307
 308                 sec->base = find_section_by_name(elf, sec->name + 5);
 309                 if (!sec->base) {
 310                         WARN("can't find base section for rela section %s",
 311                              sec->name);
 312                         return -1;
 313                 }
 314
 315                 sec->base->rela = sec;
 316
 317                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 318                         rela = malloc(sizeof(*rela));
 319                         if (!rela) {
 320                                 perror("malloc");
 321                                 return -1;
 322                         }
 323                         memset(rela, 0, sizeof(*rela));
 324
 325                         if (!gelf_getrela(sec->elf_data, i, &rela->rela)) {
 326                                 perror("gelf_getrela");
 327                                 return -1;
 328                         }
 329
 330                         rela->type = GELF_R_TYPE(rela->rela.r_info);
 331                         rela->addend = rela->rela.r_addend;
 332                         rela->offset = rela->rela.r_offset;
 333                         symndx = GELF_R_SYM(rela->rela.r_info);
 334                         rela->sym = find_symbol_by_index(elf, symndx);
 335                         if (!rela->sym) {
 336                                 WARN("can't find rela entry symbol %d for %s",
 337                                      symndx, sec->name);
 338                                 return -1;
 339                         }
 340
 341                         list_add_tail(&rela->list, &sec->rela_list);
 342                         hash_add(sec->rela_hash, &rela->hash, rela->offset);
 343
 344                 }
 345         }
 346
 347         return 0;
 348 }
 349
 350 struct elf *elf_open(const char *name)
 351 {
 352         struct elf *elf;
 353
 354         elf_version(EV_CURRENT);
 355
 356         elf = malloc(sizeof(*elf));
 357         if (!elf) {
 358                 perror("malloc");
 359                 return NULL;
 360         }
 361         memset(elf, 0, sizeof(*elf));
 362
 363         INIT_LIST_HEAD(&elf->sections);
 364
 365         elf->name = strdup(name);
 366         if (!elf->name) {
 367                 perror("strdup");
 368                 goto err;
 369         }
 370
 371         elf->fd = open(name, O_RDONLY);
 372         if (elf->fd == -1) {
 373                 perror("open");
 374                 goto err;
 375         }
 376
 377         elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL);
 378         if (!elf->elf) {
 379                 perror("elf_begin");
 380                 goto err;
 381         }
 382
 383         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 384                 perror("gelf_getehdr");
 385                 goto err;
 386         }
 387
 388         if (read_sections(elf))
 389                 goto err;
 390
 391         if (read_symbols(elf))
 392                 goto err;
 393
 394         if (read_relas(elf))
 395                 goto err;
 396
 397         return elf;
 398
 399 err:
 400         elf_close(elf);
 401         return NULL;
 402 }
 403
 404 void elf_close(struct elf *elf)
 405 {
 406         struct section *sec, *tmpsec;
 407         struct symbol *sym, *tmpsym;
 408         struct rela *rela, *tmprela;
 409
 410         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
 411                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
 412                         list_del(&sym->list);
 413                         hash_del(&sym->hash);
 414                         free(sym);
 415                 }
 416                 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
 417                         list_del(&rela->list);
 418                         hash_del(&rela->hash);
 419                         free(rela);
 420                 }
 421                 list_del(&sec->list);
 422                 free(sec);
 423         }
 424         if (elf->name)
 425                 free(elf->name);
 426         if (elf->fd > 0)
 427                 close(elf->fd);
 428         if (elf->elf)
 429                 elf_end(elf->elf);
 430         free(elf);
 431 }