tools/objtool/elf.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * elf.c - ELF access library
   4  *
   5  * Adapted from kpatch (https://github.com/dynup/kpatch):
   6  * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
   7  * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
   8  */
   9
  10 #include <sys/types.h>
  11 #include <sys/stat.h>
  12 #include <fcntl.h>
  13 #include <stdio.h>
  14 #include <stdlib.h>
  15 #include <string.h>
  16 #include <unistd.h>
  17 #include <errno.h>
  18 #include <objtool/builtin.h>
  19
  20 #include <objtool/elf.h>
  21 #include <objtool/warn.h>
  22
  23 #define MAX_NAME_LEN 128
  24
  25 static inline u32 str_hash(const char *str)
  26 {
  27         return jhash(str, strlen(str), 0);
  28 }
  29
  30 static inline int elf_hash_bits(void)
  31 {
  32         return vmlinux ? ELF_HASH_BITS : 16;
  33 }
  34
  35 #define elf_hash_add(hashtable, node, key) \
  36         hlist_add_head(node, &hashtable[hash_min(key, elf_hash_bits())])
  37
  38 static void elf_hash_init(struct hlist_head *table)
  39 {
  40         __hash_init(table, 1U << elf_hash_bits());
  41 }
  42
  43 #define elf_hash_for_each_possible(name, obj, member, key)                      \
  44         hlist_for_each_entry(obj, &name[hash_min(key, elf_hash_bits())], member)
  45
  46 static bool symbol_to_offset(struct rb_node *a, const struct rb_node *b)
  47 {
  48         struct symbol *sa = rb_entry(a, struct symbol, node);
  49         struct symbol *sb = rb_entry(b, struct symbol, node);
  50
  51         if (sa->offset < sb->offset)
  52                 return true;
  53         if (sa->offset > sb->offset)
  54                 return false;
  55
  56         if (sa->len < sb->len)
  57                 return true;
  58         if (sa->len > sb->len)
  59                 return false;
  60
  61         sa->alias = sb;
  62
  63         return false;
  64 }
  65
  66 static int symbol_by_offset(const void *key, const struct rb_node *node)
  67 {
  68         const struct symbol *s = rb_entry(node, struct symbol, node);
  69         const unsigned long *o = key;
  70
  71         if (*o < s->offset)
  72                 return -1;
  73         if (*o >= s->offset + s->len)
  74                 return 1;
  75
  76         return 0;
  77 }
  78
  79 struct section *find_section_by_name(const struct elf *elf, const char *name)
  80 {
  81         struct section *sec;
  82
  83         elf_hash_for_each_possible(elf->section_name_hash, sec, name_hash, str_hash(name))
  84                 if (!strcmp(sec->name, name))
  85                         return sec;
  86
  87         return NULL;
  88 }
  89
  90 static struct section *find_section_by_index(struct elf *elf,
  91                                              unsigned int idx)
  92 {
  93         struct section *sec;
  94
  95         elf_hash_for_each_possible(elf->section_hash, sec, hash, idx)
  96                 if (sec->idx == idx)
  97                         return sec;
  98
  99         return NULL;
 100 }
 101
 102 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
 103 {
 104         struct symbol *sym;
 105
 106         elf_hash_for_each_possible(elf->symbol_hash, sym, hash, idx)
 107                 if (sym->idx == idx)
 108                         return sym;
 109
 110         return NULL;
 111 }
 112
 113 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
 114 {
 115         struct rb_node *node;
 116
 117         rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
 118                 struct symbol *s = rb_entry(node, struct symbol, node);
 119
 120                 if (s->offset == offset && s->type != STT_SECTION)
 121                         return s;
 122         }
 123
 124         return NULL;
 125 }
 126
 127 struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
 128 {
 129         struct rb_node *node;
 130
 131         rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
 132                 struct symbol *s = rb_entry(node, struct symbol, node);
 133
 134                 if (s->offset == offset && s->type == STT_FUNC)
 135                         return s;
 136         }
 137
 138         return NULL;
 139 }
 140
 141 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
 142 {
 143         struct rb_node *node;
 144
 145         rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
 146                 struct symbol *s = rb_entry(node, struct symbol, node);
 147
 148                 if (s->type != STT_SECTION)
 149                         return s;
 150         }
 151
 152         return NULL;
 153 }
 154
 155 struct symbol *find_func_containing(struct section *sec, unsigned long offset)
 156 {
 157         struct rb_node *node;
 158
 159         rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
 160                 struct symbol *s = rb_entry(node, struct symbol, node);
 161
 162                 if (s->type == STT_FUNC)
 163                         return s;
 164         }
 165
 166         return NULL;
 167 }
 168
 169 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
 170 {
 171         struct symbol *sym;
 172
 173         elf_hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name))
 174                 if (!strcmp(sym->name, name))
 175                         return sym;
 176
 177         return NULL;
 178 }
 179
 180 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
 181                                      unsigned long offset, unsigned int len)
 182 {
 183         struct reloc *reloc, *r = NULL;
 184         unsigned long o;
 185
 186         if (!sec->reloc)
 187                 return NULL;
 188
 189         sec = sec->reloc;
 190
 191         for_offset_range(o, offset, offset + len) {
 192                 elf_hash_for_each_possible(elf->reloc_hash, reloc, hash,
 193                                        sec_offset_hash(sec, o)) {
 194                         if (reloc->sec != sec)
 195                                 continue;
 196
 197                         if (reloc->offset >= offset && reloc->offset < offset + len) {
 198                                 if (!r || reloc->offset < r->offset)
 199                                         r = reloc;
 200                         }
 201                 }
 202                 if (r)
 203                         return r;
 204         }
 205
 206         return NULL;
 207 }
 208
 209 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
 210 {
 211         return find_reloc_by_dest_range(elf, sec, offset, 1);
 212 }
 213
 214 static int read_sections(struct elf *elf)
 215 {
 216         Elf_Scn *s = NULL;
 217         struct section *sec;
 218         size_t shstrndx, sections_nr;
 219         int i;
 220
 221         if (elf_getshdrnum(elf->elf, &sections_nr)) {
 222                 WARN_ELF("elf_getshdrnum");
 223                 return -1;
 224         }
 225
 226         if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
 227                 WARN_ELF("elf_getshdrstrndx");
 228                 return -1;
 229         }
 230
 231         for (i = 0; i < sections_nr; i++) {
 232                 sec = malloc(sizeof(*sec));
 233                 if (!sec) {
 234                         perror("malloc");
 235                         return -1;
 236                 }
 237                 memset(sec, 0, sizeof(*sec));
 238
 239                 INIT_LIST_HEAD(&sec->symbol_list);
 240                 INIT_LIST_HEAD(&sec->reloc_list);
 241
 242                 s = elf_getscn(elf->elf, i);
 243                 if (!s) {
 244                         WARN_ELF("elf_getscn");
 245                         return -1;
 246                 }
 247
 248                 sec->idx = elf_ndxscn(s);
 249
 250                 if (!gelf_getshdr(s, &sec->sh)) {
 251                         WARN_ELF("gelf_getshdr");
 252                         return -1;
 253                 }
 254
 255                 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
 256                 if (!sec->name) {
 257                         WARN_ELF("elf_strptr");
 258                         return -1;
 259                 }
 260
 261                 if (sec->sh.sh_size != 0) {
 262                         sec->data = elf_getdata(s, NULL);
 263                         if (!sec->data) {
 264                                 WARN_ELF("elf_getdata");
 265                                 return -1;
 266                         }
 267                         if (sec->data->d_off != 0 ||
 268                             sec->data->d_size != sec->sh.sh_size) {
 269                                 WARN("unexpected data attributes for %s",
 270                                      sec->name);
 271                                 return -1;
 272                         }
 273                 }
 274                 sec->len = sec->sh.sh_size;
 275
 276                 list_add_tail(&sec->list, &elf->sections);
 277                 elf_hash_add(elf->section_hash, &sec->hash, sec->idx);
 278                 elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
 279         }
 280
 281         if (stats)
 282                 printf("nr_sections: %lu\n", (unsigned long)sections_nr);
 283
 284         /* sanity check, one more call to elf_nextscn() should return NULL */
 285         if (elf_nextscn(elf->elf, s)) {
 286                 WARN("section entry mismatch");
 287                 return -1;
 288         }
 289
 290         return 0;
 291 }
 292
 293 static void elf_add_symbol(struct elf *elf, struct symbol *sym)
 294 {
 295         struct list_head *entry;
 296         struct rb_node *pnode;
 297
 298         sym->type = GELF_ST_TYPE(sym->sym.st_info);
 299         sym->bind = GELF_ST_BIND(sym->sym.st_info);
 300
 301         sym->offset = sym->sym.st_value;
 302         sym->len = sym->sym.st_size;
 303
 304         rb_add(&sym->node, &sym->sec->symbol_tree, symbol_to_offset);
 305         pnode = rb_prev(&sym->node);
 306         if (pnode)
 307                 entry = &rb_entry(pnode, struct symbol, node)->list;
 308         else
 309                 entry = &sym->sec->symbol_list;
 310         list_add(&sym->list, entry);
 311         elf_hash_add(elf->symbol_hash, &sym->hash, sym->idx);
 312         elf_hash_add(elf->symbol_name_hash, &sym->name_hash, str_hash(sym->name));
 313
 314         /*
 315          * Don't store empty STT_NOTYPE symbols in the rbtree.  They
 316          * can exist within a function, confusing the sorting.
 317          */
 318         if (!sym->len)
 319                 rb_erase(&sym->node, &sym->sec->symbol_tree);
 320 }
 321
 322 static int read_symbols(struct elf *elf)
 323 {
 324         struct section *symtab, *symtab_shndx, *sec;
 325         struct symbol *sym, *pfunc;
 326         int symbols_nr, i;
 327         char *coldstr;
 328         Elf_Data *shndx_data = NULL;
 329         Elf32_Word shndx;
 330
 331         symtab = find_section_by_name(elf, ".symtab");
 332         if (!symtab) {
 333                 /*
 334                  * A missing symbol table is actually possible if it's an empty
 335                  * .o file.  This can happen for thunk_64.o.
 336                  */
 337                 return 0;
 338         }
 339
 340         symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
 341         if (symtab_shndx)
 342                 shndx_data = symtab_shndx->data;
 343
 344         symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 345
 346         for (i = 0; i < symbols_nr; i++) {
 347                 sym = malloc(sizeof(*sym));
 348                 if (!sym) {
 349                         perror("malloc");
 350                         return -1;
 351                 }
 352                 memset(sym, 0, sizeof(*sym));
 353                 sym->alias = sym;
 354
 355                 sym->idx = i;
 356
 357                 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
 358                                       &shndx)) {
 359                         WARN_ELF("gelf_getsymshndx");
 360                         goto err;
 361                 }
 362
 363                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 364                                        sym->sym.st_name);
 365                 if (!sym->name) {
 366                         WARN_ELF("elf_strptr");
 367                         goto err;
 368                 }
 369
 370                 if ((sym->sym.st_shndx > SHN_UNDEF &&
 371                      sym->sym.st_shndx < SHN_LORESERVE) ||
 372                     (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
 373                         if (sym->sym.st_shndx != SHN_XINDEX)
 374                                 shndx = sym->sym.st_shndx;
 375
 376                         sym->sec = find_section_by_index(elf, shndx);
 377                         if (!sym->sec) {
 378                                 WARN("couldn't find section for symbol %s",
 379                                      sym->name);
 380                                 goto err;
 381                         }
 382                         if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
 383                                 sym->name = sym->sec->name;
 384                                 sym->sec->sym = sym;
 385                         }
 386                 } else
 387                         sym->sec = find_section_by_index(elf, 0);
 388
 389                 elf_add_symbol(elf, sym);
 390         }
 391
 392         if (stats)
 393                 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
 394
 395         /* Create parent/child links for any cold subfunctions */
 396         list_for_each_entry(sec, &elf->sections, list) {
 397                 list_for_each_entry(sym, &sec->symbol_list, list) {
 398                         char pname[MAX_NAME_LEN + 1];
 399                         size_t pnamelen;
 400                         if (sym->type != STT_FUNC)
 401                                 continue;
 402
 403                         if (sym->pfunc == NULL)
 404                                 sym->pfunc = sym;
 405
 406                         if (sym->cfunc == NULL)
 407                                 sym->cfunc = sym;
 408
 409                         coldstr = strstr(sym->name, ".cold");
 410                         if (!coldstr)
 411                                 continue;
 412
 413                         pnamelen = coldstr - sym->name;
 414                         if (pnamelen > MAX_NAME_LEN) {
 415                                 WARN("%s(): parent function name exceeds maximum length of %d characters",
 416                                      sym->name, MAX_NAME_LEN);
 417                                 return -1;
 418                         }
 419
 420                         strncpy(pname, sym->name, pnamelen);
 421                         pname[pnamelen] = '\0';
 422                         pfunc = find_symbol_by_name(elf, pname);
 423
 424                         if (!pfunc) {
 425                                 WARN("%s(): can't find parent function",
 426                                      sym->name);
 427                                 return -1;
 428                         }
 429
 430                         sym->pfunc = pfunc;
 431                         pfunc->cfunc = sym;
 432
 433                         /*
 434                          * Unfortunately, -fnoreorder-functions puts the child
 435                          * inside the parent.  Remove the overlap so we can
 436                          * have sane assumptions.
 437                          *
 438                          * Note that pfunc->len now no longer matches
 439                          * pfunc->sym.st_size.
 440                          */
 441                         if (sym->sec == pfunc->sec &&
 442                             sym->offset >= pfunc->offset &&
 443                             sym->offset + sym->len == pfunc->offset + pfunc->len) {
 444                                 pfunc->len -= sym->len;
 445                         }
 446                 }
 447         }
 448
 449         return 0;
 450
 451 err:
 452         free(sym);
 453         return -1;
 454 }
 455
 456 static struct section *elf_create_reloc_section(struct elf *elf,
 457                                                 struct section *base,
 458                                                 int reltype);
 459
 460 int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
 461                   unsigned int type, struct symbol *sym, int addend)
 462 {
 463         struct reloc *reloc;
 464
 465         if (!sec->reloc && !elf_create_reloc_section(elf, sec, SHT_RELA))
 466                 return -1;
 467
 468         reloc = malloc(sizeof(*reloc));
 469         if (!reloc) {
 470                 perror("malloc");
 471                 return -1;
 472         }
 473         memset(reloc, 0, sizeof(*reloc));
 474
 475         reloc->sec = sec->reloc;
 476         reloc->offset = offset;
 477         reloc->type = type;
 478         reloc->sym = sym;
 479         reloc->addend = addend;
 480
 481         list_add_tail(&reloc->list, &sec->reloc->reloc_list);
 482         elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
 483
 484         sec->reloc->changed = true;
 485
 486         return 0;
 487 }
 488
 489 int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
 490                           unsigned long offset, unsigned int type,
 491                           struct section *insn_sec, unsigned long insn_off)
 492 {
 493         struct symbol *sym;
 494         int addend;
 495
 496         if (insn_sec->sym) {
 497                 sym = insn_sec->sym;
 498                 addend = insn_off;
 499
 500         } else {
 501                 /*
 502                  * The Clang assembler strips section symbols, so we have to
 503                  * reference the function symbol instead:
 504                  */
 505                 sym = find_symbol_containing(insn_sec, insn_off);
 506                 if (!sym) {
 507                         /*
 508                          * Hack alert.  This happens when we need to reference
 509                          * the NOP pad insn immediately after the function.
 510                          */
 511                         sym = find_symbol_containing(insn_sec, insn_off - 1);
 512                 }
 513
 514                 if (!sym) {
 515                         WARN("can't find symbol containing %s+0x%lx", insn_sec->name, insn_off);
 516                         return -1;
 517                 }
 518
 519                 addend = insn_off - sym->offset;
 520         }
 521
 522         return elf_add_reloc(elf, sec, offset, type, sym, addend);
 523 }
 524
 525 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 526 {
 527         if (!gelf_getrel(sec->data, i, &reloc->rel)) {
 528                 WARN_ELF("gelf_getrel");
 529                 return -1;
 530         }
 531         reloc->type = GELF_R_TYPE(reloc->rel.r_info);
 532         reloc->addend = 0;
 533         reloc->offset = reloc->rel.r_offset;
 534         *symndx = GELF_R_SYM(reloc->rel.r_info);
 535         return 0;
 536 }
 537
 538 static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 539 {
 540         if (!gelf_getrela(sec->data, i, &reloc->rela)) {
 541                 WARN_ELF("gelf_getrela");
 542                 return -1;
 543         }
 544         reloc->type = GELF_R_TYPE(reloc->rela.r_info);
 545         reloc->addend = reloc->rela.r_addend;
 546         reloc->offset = reloc->rela.r_offset;
 547         *symndx = GELF_R_SYM(reloc->rela.r_info);
 548         return 0;
 549 }
 550
 551 static int read_relocs(struct elf *elf)
 552 {
 553         struct section *sec;
 554         struct reloc *reloc;
 555         int i;
 556         unsigned int symndx;
 557         unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
 558
 559         list_for_each_entry(sec, &elf->sections, list) {
 560                 if ((sec->sh.sh_type != SHT_RELA) &&
 561                     (sec->sh.sh_type != SHT_REL))
 562                         continue;
 563
 564                 sec->base = find_section_by_index(elf, sec->sh.sh_info);
 565                 if (!sec->base) {
 566                         WARN("can't find base section for reloc section %s",
 567                              sec->name);
 568                         return -1;
 569                 }
 570
 571                 sec->base->reloc = sec;
 572
 573                 nr_reloc = 0;
 574                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 575                         reloc = malloc(sizeof(*reloc));
 576                         if (!reloc) {
 577                                 perror("malloc");
 578                                 return -1;
 579                         }
 580                         memset(reloc, 0, sizeof(*reloc));
 581                         switch (sec->sh.sh_type) {
 582                         case SHT_REL:
 583                                 if (read_rel_reloc(sec, i, reloc, &symndx))
 584                                         return -1;
 585                                 break;
 586                         case SHT_RELA:
 587                                 if (read_rela_reloc(sec, i, reloc, &symndx))
 588                                         return -1;
 589                                 break;
 590                         default: return -1;
 591                         }
 592
 593                         reloc->sec = sec;
 594                         reloc->idx = i;
 595                         reloc->sym = find_symbol_by_index(elf, symndx);
 596                         if (!reloc->sym) {
 597                                 WARN("can't find reloc entry symbol %d for %s",
 598                                      symndx, sec->name);
 599                                 return -1;
 600                         }
 601
 602                         list_add_tail(&reloc->list, &sec->reloc_list);
 603                         elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
 604
 605                         nr_reloc++;
 606                 }
 607                 max_reloc = max(max_reloc, nr_reloc);
 608                 tot_reloc += nr_reloc;
 609         }
 610
 611         if (stats) {
 612                 printf("max_reloc: %lu\n", max_reloc);
 613                 printf("tot_reloc: %lu\n", tot_reloc);
 614         }
 615
 616         return 0;
 617 }
 618
 619 struct elf *elf_open_read(const char *name, int flags)
 620 {
 621         struct elf *elf;
 622         Elf_Cmd cmd;
 623
 624         elf_version(EV_CURRENT);
 625
 626         elf = malloc(sizeof(*elf));
 627         if (!elf) {
 628                 perror("malloc");
 629                 return NULL;
 630         }
 631         memset(elf, 0, offsetof(struct elf, sections));
 632
 633         INIT_LIST_HEAD(&elf->sections);
 634
 635         elf_hash_init(elf->symbol_hash);
 636         elf_hash_init(elf->symbol_name_hash);
 637         elf_hash_init(elf->section_hash);
 638         elf_hash_init(elf->section_name_hash);
 639         elf_hash_init(elf->reloc_hash);
 640
 641         elf->fd = open(name, flags);
 642         if (elf->fd == -1) {
 643                 fprintf(stderr, "objtool: Can't open '%s': %s\n",
 644                         name, strerror(errno));
 645                 goto err;
 646         }
 647
 648         if ((flags & O_ACCMODE) == O_RDONLY)
 649                 cmd = ELF_C_READ_MMAP;
 650         else if ((flags & O_ACCMODE) == O_RDWR)
 651                 cmd = ELF_C_RDWR;
 652         else /* O_WRONLY */
 653                 cmd = ELF_C_WRITE;
 654
 655         elf->elf = elf_begin(elf->fd, cmd, NULL);
 656         if (!elf->elf) {
 657                 WARN_ELF("elf_begin");
 658                 goto err;
 659         }
 660
 661         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 662                 WARN_ELF("gelf_getehdr");
 663                 goto err;
 664         }
 665
 666         if (read_sections(elf))
 667                 goto err;
 668
 669         if (read_symbols(elf))
 670                 goto err;
 671
 672         if (read_relocs(elf))
 673                 goto err;
 674
 675         return elf;
 676
 677 err:
 678         elf_close(elf);
 679         return NULL;
 680 }
 681
 682 static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
 683 {
 684         Elf_Data *data;
 685         Elf_Scn *s;
 686         int len;
 687
 688         if (!strtab)
 689                 strtab = find_section_by_name(elf, ".strtab");
 690         if (!strtab) {
 691                 WARN("can't find .strtab section");
 692                 return -1;
 693         }
 694
 695         s = elf_getscn(elf->elf, strtab->idx);
 696         if (!s) {
 697                 WARN_ELF("elf_getscn");
 698                 return -1;
 699         }
 700
 701         data = elf_newdata(s);
 702         if (!data) {
 703                 WARN_ELF("elf_newdata");
 704                 return -1;
 705         }
 706
 707         data->d_buf = str;
 708         data->d_size = strlen(str) + 1;
 709         data->d_align = 1;
 710
 711         len = strtab->len;
 712         strtab->len += data->d_size;
 713         strtab->changed = true;
 714
 715         return len;
 716 }
 717
 718 struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name)
 719 {
 720         struct section *symtab, *symtab_shndx;
 721         struct symbol *sym;
 722         Elf_Data *data;
 723         Elf_Scn *s;
 724
 725         sym = malloc(sizeof(*sym));
 726         if (!sym) {
 727                 perror("malloc");
 728                 return NULL;
 729         }
 730         memset(sym, 0, sizeof(*sym));
 731
 732         sym->name = strdup(name);
 733
 734         sym->sym.st_name = elf_add_string(elf, NULL, sym->name);
 735         if (sym->sym.st_name == -1)
 736                 return NULL;
 737
 738         sym->sym.st_info = GELF_ST_INFO(STB_GLOBAL, STT_NOTYPE);
 739         // st_other 0
 740         // st_shndx 0
 741         // st_value 0
 742         // st_size 0
 743
 744         symtab = find_section_by_name(elf, ".symtab");
 745         if (!symtab) {
 746                 WARN("can't find .symtab");
 747                 return NULL;
 748         }
 749
 750         s = elf_getscn(elf->elf, symtab->idx);
 751         if (!s) {
 752                 WARN_ELF("elf_getscn");
 753                 return NULL;
 754         }
 755
 756         data = elf_newdata(s);
 757         if (!data) {
 758                 WARN_ELF("elf_newdata");
 759                 return NULL;
 760         }
 761
 762         data->d_buf = &sym->sym;
 763         data->d_size = sizeof(sym->sym);
 764         data->d_align = 1;
 765         data->d_type = ELF_T_SYM;
 766
 767         sym->idx = symtab->len / sizeof(sym->sym);
 768
 769         symtab->len += data->d_size;
 770         symtab->changed = true;
 771
 772         symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
 773         if (symtab_shndx) {
 774                 s = elf_getscn(elf->elf, symtab_shndx->idx);
 775                 if (!s) {
 776                         WARN_ELF("elf_getscn");
 777                         return NULL;
 778                 }
 779
 780                 data = elf_newdata(s);
 781                 if (!data) {
 782                         WARN_ELF("elf_newdata");
 783                         return NULL;
 784                 }
 785
 786                 data->d_buf = &sym->sym.st_size; /* conveniently 0 */
 787                 data->d_size = sizeof(Elf32_Word);
 788                 data->d_align = 4;
 789                 data->d_type = ELF_T_WORD;
 790
 791                 symtab_shndx->len += 4;
 792                 symtab_shndx->changed = true;
 793         }
 794
 795         sym->sec = find_section_by_index(elf, 0);
 796
 797         elf_add_symbol(elf, sym);
 798
 799         return sym;
 800 }
 801
 802 struct section *elf_create_section(struct elf *elf, const char *name,
 803                                    unsigned int sh_flags, size_t entsize, int nr)
 804 {
 805         struct section *sec, *shstrtab;
 806         size_t size = entsize * nr;
 807         Elf_Scn *s;
 808
 809         sec = malloc(sizeof(*sec));
 810         if (!sec) {
 811                 perror("malloc");
 812                 return NULL;
 813         }
 814         memset(sec, 0, sizeof(*sec));
 815
 816         INIT_LIST_HEAD(&sec->symbol_list);
 817         INIT_LIST_HEAD(&sec->reloc_list);
 818
 819         s = elf_newscn(elf->elf);
 820         if (!s) {
 821                 WARN_ELF("elf_newscn");
 822                 return NULL;
 823         }
 824
 825         sec->name = strdup(name);
 826         if (!sec->name) {
 827                 perror("strdup");
 828                 return NULL;
 829         }
 830
 831         sec->idx = elf_ndxscn(s);
 832         sec->len = size;
 833         sec->changed = true;
 834
 835         sec->data = elf_newdata(s);
 836         if (!sec->data) {
 837                 WARN_ELF("elf_newdata");
 838                 return NULL;
 839         }
 840
 841         sec->data->d_size = size;
 842         sec->data->d_align = 1;
 843
 844         if (size) {
 845                 sec->data->d_buf = malloc(size);
 846                 if (!sec->data->d_buf) {
 847                         perror("malloc");
 848                         return NULL;
 849                 }
 850                 memset(sec->data->d_buf, 0, size);
 851         }
 852
 853         if (!gelf_getshdr(s, &sec->sh)) {
 854                 WARN_ELF("gelf_getshdr");
 855                 return NULL;
 856         }
 857
 858         sec->sh.sh_size = size;
 859         sec->sh.sh_entsize = entsize;
 860         sec->sh.sh_type = SHT_PROGBITS;
 861         sec->sh.sh_addralign = 1;
 862         sec->sh.sh_flags = SHF_ALLOC | sh_flags;
 863
 864         /* Add section name to .shstrtab (or .strtab for Clang) */
 865         shstrtab = find_section_by_name(elf, ".shstrtab");
 866         if (!shstrtab)
 867                 shstrtab = find_section_by_name(elf, ".strtab");
 868         if (!shstrtab) {
 869                 WARN("can't find .shstrtab or .strtab section");
 870                 return NULL;
 871         }
 872         sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
 873         if (sec->sh.sh_name == -1)
 874                 return NULL;
 875
 876         list_add_tail(&sec->list, &elf->sections);
 877         elf_hash_add(elf->section_hash, &sec->hash, sec->idx);
 878         elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
 879
 880         elf->changed = true;
 881
 882         return sec;
 883 }
 884
 885 static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
 886 {
 887         char *relocname;
 888         struct section *sec;
 889
 890         relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
 891         if (!relocname) {
 892                 perror("malloc");
 893                 return NULL;
 894         }
 895         strcpy(relocname, ".rel");
 896         strcat(relocname, base->name);
 897
 898         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rel), 0);
 899         free(relocname);
 900         if (!sec)
 901                 return NULL;
 902
 903         base->reloc = sec;
 904         sec->base = base;
 905
 906         sec->sh.sh_type = SHT_REL;
 907         sec->sh.sh_addralign = 8;
 908         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 909         sec->sh.sh_info = base->idx;
 910         sec->sh.sh_flags = SHF_INFO_LINK;
 911
 912         return sec;
 913 }
 914
 915 static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
 916 {
 917         char *relocname;
 918         struct section *sec;
 919
 920         relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
 921         if (!relocname) {
 922                 perror("malloc");
 923                 return NULL;
 924         }
 925         strcpy(relocname, ".rela");
 926         strcat(relocname, base->name);
 927
 928         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
 929         free(relocname);
 930         if (!sec)
 931                 return NULL;
 932
 933         base->reloc = sec;
 934         sec->base = base;
 935
 936         sec->sh.sh_type = SHT_RELA;
 937         sec->sh.sh_addralign = 8;
 938         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 939         sec->sh.sh_info = base->idx;
 940         sec->sh.sh_flags = SHF_INFO_LINK;
 941
 942         return sec;
 943 }
 944
 945 static struct section *elf_create_reloc_section(struct elf *elf,
 946                                          struct section *base,
 947                                          int reltype)
 948 {
 949         switch (reltype) {
 950         case SHT_REL:  return elf_create_rel_reloc_section(elf, base);
 951         case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
 952         default:       return NULL;
 953         }
 954 }
 955
 956 static int elf_rebuild_rel_reloc_section(struct section *sec, int nr)
 957 {
 958         struct reloc *reloc;
 959         int idx = 0, size;
 960         void *buf;
 961
 962         /* Allocate a buffer for relocations */
 963         size = nr * sizeof(GElf_Rel);
 964         buf = malloc(size);
 965         if (!buf) {
 966                 perror("malloc");
 967                 return -1;
 968         }
 969
 970         sec->data->d_buf = buf;
 971         sec->data->d_size = size;
 972         sec->data->d_type = ELF_T_REL;
 973
 974         sec->sh.sh_size = size;
 975
 976         idx = 0;
 977         list_for_each_entry(reloc, &sec->reloc_list, list) {
 978                 reloc->rel.r_offset = reloc->offset;
 979                 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
 980                 gelf_update_rel(sec->data, idx, &reloc->rel);
 981                 idx++;
 982         }
 983
 984         return 0;
 985 }
 986
 987 static int elf_rebuild_rela_reloc_section(struct section *sec, int nr)
 988 {
 989         struct reloc *reloc;
 990         int idx = 0, size;
 991         void *buf;
 992
 993         /* Allocate a buffer for relocations with addends */
 994         size = nr * sizeof(GElf_Rela);
 995         buf = malloc(size);
 996         if (!buf) {
 997                 perror("malloc");
 998                 return -1;
 999         }
1000
1001         sec->data->d_buf = buf;
1002         sec->data->d_size = size;
1003         sec->data->d_type = ELF_T_RELA;
1004
1005         sec->sh.sh_size = size;
1006
1007         idx = 0;
1008         list_for_each_entry(reloc, &sec->reloc_list, list) {
1009                 reloc->rela.r_offset = reloc->offset;
1010                 reloc->rela.r_addend = reloc->addend;
1011                 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1012                 gelf_update_rela(sec->data, idx, &reloc->rela);
1013                 idx++;
1014         }
1015
1016         return 0;
1017 }
1018
1019 static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
1020 {
1021         struct reloc *reloc;
1022         int nr;
1023
1024         nr = 0;
1025         list_for_each_entry(reloc, &sec->reloc_list, list)
1026                 nr++;
1027
1028         switch (sec->sh.sh_type) {
1029         case SHT_REL:  return elf_rebuild_rel_reloc_section(sec, nr);
1030         case SHT_RELA: return elf_rebuild_rela_reloc_section(sec, nr);
1031         default:       return -1;
1032         }
1033 }
1034
1035 int elf_write_insn(struct elf *elf, struct section *sec,
1036                    unsigned long offset, unsigned int len,
1037                    const char *insn)
1038 {
1039         Elf_Data *data = sec->data;
1040
1041         if (data->d_type != ELF_T_BYTE || data->d_off) {
1042                 WARN("write to unexpected data for section: %s", sec->name);
1043                 return -1;
1044         }
1045
1046         memcpy(data->d_buf + offset, insn, len);
1047         elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
1048
1049         elf->changed = true;
1050
1051         return 0;
1052 }
1053
1054 int elf_write_reloc(struct elf *elf, struct reloc *reloc)
1055 {
1056         struct section *sec = reloc->sec;
1057
1058         if (sec->sh.sh_type == SHT_REL) {
1059                 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1060                 reloc->rel.r_offset = reloc->offset;
1061
1062                 if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) {
1063                         WARN_ELF("gelf_update_rel");
1064                         return -1;
1065                 }
1066         } else {
1067                 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1068                 reloc->rela.r_addend = reloc->addend;
1069                 reloc->rela.r_offset = reloc->offset;
1070
1071                 if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) {
1072                         WARN_ELF("gelf_update_rela");
1073                         return -1;
1074                 }
1075         }
1076
1077         elf->changed = true;
1078
1079         return 0;
1080 }
1081
1082 int elf_write(struct elf *elf)
1083 {
1084         struct section *sec;
1085         Elf_Scn *s;
1086
1087         /* Update changed relocation sections and section headers: */
1088         list_for_each_entry(sec, &elf->sections, list) {
1089                 if (sec->changed) {
1090                         if (sec->base &&
1091                             elf_rebuild_reloc_section(elf, sec)) {
1092                                 WARN("elf_rebuild_reloc_section");
1093                                 return -1;
1094                         }
1095
1096                         s = elf_getscn(elf->elf, sec->idx);
1097                         if (!s) {
1098                                 WARN_ELF("elf_getscn");
1099                                 return -1;
1100                         }
1101                         if (!gelf_update_shdr(s, &sec->sh)) {
1102                                 WARN_ELF("gelf_update_shdr");
1103                                 return -1;
1104                         }
1105
1106                         sec->changed = false;
1107                         elf->changed = true;
1108                 }
1109         }
1110
1111         /* Make sure the new section header entries get updated properly. */
1112         elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
1113
1114         /* Write all changes to the file. */
1115         if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
1116                 WARN_ELF("elf_update");
1117                 return -1;
1118         }
1119
1120         elf->changed = false;
1121
1122         return 0;
1123 }
1124
1125 void elf_close(struct elf *elf)
1126 {
1127         struct section *sec, *tmpsec;
1128         struct symbol *sym, *tmpsym;
1129         struct reloc *reloc, *tmpreloc;
1130
1131         if (elf->elf)
1132                 elf_end(elf->elf);
1133
1134         if (elf->fd > 0)
1135                 close(elf->fd);
1136
1137         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
1138                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
1139                         list_del(&sym->list);
1140                         hash_del(&sym->hash);
1141                         free(sym);
1142                 }
1143                 list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) {
1144                         list_del(&reloc->list);
1145                         hash_del(&reloc->hash);
1146                         free(reloc);
1147                 }
1148                 list_del(&sec->list);
1149                 free(sec);
1150         }
1151
1152         free(elf);
1153 }