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